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1. w open motor rews w changing direction motor rews 100 2 2 2 24 2 6 2 8 3 time s Figure 4 Measurement of the motor velocity by 1 Short circuit motor motor voltage is changed to OV 2 Open circuit motor motor set point is changed from 1A to 0A 3 Changing motor direction motor set point is changed from 1 A to 1 A Control Engineering 6 End stops for the Mechatronic Demonstrator Motor velocity 80 T 60 w shortcut motor revs w open motor revs T w changing direction motor rev s 2 4 1 Tt 20 0 T MI 2 201 202 203 204 205 206 207 208 2 09 time s Figure 5 Close up of the measurement of the motor velocity without slider by 1 Short circuit motor terminals 2 Open circuit motor terminals 3 Changing motor direction In the first test the motor velocity decreases exponentially This exponential behavior can be explained because the motor voltage is regulated by the short circuit The average deceleration of the motor is approximately 2000 rev s The measurement was done without slider but when this data is converted to translation the slider should be decelerating 100 m s average In test 2 and 3 the motor deceleration is constant Deceleration of test 2 is approximately 88 rev s The slider decelerates theoretically 4 m s In test 3 the deceleration is 1350 rev s and the slider deceleration is theoretical
2. The emergency stop should be fast enough so the demonstrator will not damage or the safety layer has to prevent such situations Noneed to move the slider manually in case of errors and for the homing operation When this is realized there is no need to remove the plastic cover anymore The end stops are suitable to support the homing operation The power amplifier Maxon Servo amplifier DES 50 5 should be kept because it is a special linear current amplifier together with the digital analog converter Sensoray 526 1 5 Outline of the report In this chapter the mechatronic demonstrator is introduced Some imperfections of the safety layer are seen And so the functionality of the end stops of the demonstrator has to improve Chapter 2 describes the analysis of the demonstrator This analysis is necessary to get an overview of the different parts of the demonstrator A good knowledge of the hardware functionality is necessary to identify the problems and limitations of the safety layer After this analysis several alternatives are given and discussed In chapter 3 the methods to improve the functionality of the end stops will be discussed A new hardware design is introduced and the used components are explained The implementation and measurements of the safety layer are discussed in chapter 4 And last the conclusions and recommendations are discussed in chapter 5 Control Engineering 2 Analysis of the funct
3. e The solid state relay SSR is a fast electronic switch which is based on transistor technology The lifetime of the ssr is higher then a relay because that there are no moving parts and thus no mechanical wear e A mosfet is a cheap and fast switching device But the implementation is more difficult compared to using a relay e The TRIAC or triode for alternating current is a bidirectional electronic switch The low power type is used in many domestic appliances Triacs are obtainable in different versions and different power versions It is also based on transistor technology and therefore fast switching Triacs are available for very high currents and voltages Here the possible solutions in a table are Alternatives Advantage Disadvantage Conclusion Relays Straightforward circuit Slow switching Switch bouncing Solid State Straightforward circuit High current SSR is Relays East ewitchine not so cheap Mosfet Fast switching Difficult circuit and Cheap implementation TRIAC Fast switching ae Cheap High current and voltage Straightforward circuit Table 2 Alternatives for the motor short circuit The best and cheapest method to short circuit the motor is the TRIAC The TRIAC can switch high currents and there is no difficult development 2 2 3 Direction sensor alternatives A sub problem is that the motor amplifier becomes disabled independent of the movement direction of th
4. Status LEDS sese nnne nne rre 2 F 8 Connector J9 Power supply eene entren nnne ine entente nns 2 F 9 Connector SW1 Start or Set switch nennen enneenvenvennvenvennvenvennvenvenreenvenvennennverne 2 F 10 Connector SW2 Emergency switch aans saneronnennersneersensvenseersnvenseensenensvenseensvenseeens 2 Appendix G 20SIM sub models naan onenenreeneneereenneeereennnnerenenenerenennnnenvennenenenenen 2 Appendix H Characterization of the demonstrator nnen neen eenneneneeeneneerveneneeneennen 2 H 1 Required Force for maximal acceleration sess eene 2 H2 Maximu m Lorque uice rae Ree tig e n REDI ee eU 2 L3 Maximum CULTeDILs tr te P e eR ERE RE a RR UE AR dk ernendakad baden 2 H 4 Maximum velocity esessessssseseeeeeeee eene nere nnnennn rennen entente trennen enne nn sienne enne 2 Hic Measured velocity attend tee ee eve eire Dr WDR ern 2 H6 Required stop distance giuste onte ete Beute ist ut 2 EHO ATG zitiert EE PEE ete ete ee EE eee 2 University of Twente 1 Introduction The aim of this Individual Design Assignment is to improve the functionality of the end stops of the Mechatronic Demonstrator This chapter gives a short introduction on the mechatronic demonstrator The function of the demonstrator and the current safety layer will be explained shortly And last the problems with the requirements are mentioned 1 1 Mechatronic Demonstrat
5. Different velocities are measured when the end stop is pushed at t 1s the slider brakes and the velocity decreases to zero Braking distance at different velocities 0 135 0 13 r rd 0 125 0 12 fi fi P J Distance m v 1 7 m s 0 115 d m Distance m v 1 6 m s if Distance m v 1 5 m s Distance m v 1 3 m s 7 Distance m v 1 1 m s 11 l Distance m v 0 9 m s 0 Distance m v 0 7 m s 1 Distance m vy 0 4 m s 0 105 1 1 02 1 08 1 1 1 04 06 Mino tsi Figure 17 Braking distances x t meter The position of the slider is measured with different velocities and the end stop is located at position x 0 105m The matching velocities are shown in Figure 16 University of Twente Realization and testing 23 In Figure 16 the stop distance of the slider is shown The stop distance is longer when the velocity is higher When the slider moves more than 3cm the switch is passed because the size of the slider is 3cm So the velocity of the slider has to be limited at maximal 1 5m s The force of the motor is passed on the slider by the belt In Figure 17 the different braking distances are shown for the specific test velocities The end stop is pushed at t 1s The velocities do not decrease linear because the brake force is not constant because the matching current is not constant but dependent on the decreasing voltage of the motor Test Start
6. Z d3avaH er z 1QdS A2M MS 1 dv Yoon pud uogas ongAes Z u3avaH ooyeageua uono81 ooN 48 E ooon 3 z anjenos ienos amp t 101 u0 DOJO uonoeuq zr S d3Qv3H 0 ET a ameo ordo y z z d3avaH 6r v d3Qv3H or vy d3Qv3H sr Figure 24 Main schematic University of Twente 33 Motor control schematic C2 Appendices voronergeua any HOLON HOLON HOLOW dV HOLOW foueGieua Eod 0 wet leu O0LOHvZ aen le ho LENZ AN PLIOHPL m zosi AN PLLOHPL asn L aen T ge IT rg OOLOHPL ordn or TE van ozy PLLOHbL 99 osn x N33H9 O31 Ak ason amp za ta vws Hnoze WIS AUOOL oo SL AL ia ely v 8 99 u3AMG OVIEL 10 z wark lo Hu AH E ane Stu PLLOHPL ven OOH vig zn OL ely O2 o OL dE 99 99 1uBhudoispu3 _yerdomspug vonoengsoron dois Kouetiieu3 ves Figure 25 Schematic of the logic and the short circuit of the motor Control Engineering 34 End stops for the Mechatronic Demonstrator C 3 Direction schematic SetValue gt SetValue gt V Figure 26 Motor direction detector The voltage comparator c
7. cHominpg3oethodz tkn eaten ost esie tte 2 3 2 Block diagram mete n eee eie re eI ek PEE RE ede 2 3 3 EIeCETIC CIC S och Sd ett SN eue Tele De NN PE ea 2 3 3 1 Electric circuit of the motor brake eren 2 3 3 2 Electric circuit of the direction dependency sssssssssseeeeeeeees 2 3 3 3 Electric circuit of the end stops sssssssssssssesseeseeee eene eene enne enne nnns 2 3 3 4 Electric circuit of the initialization unne onee onsernnvennerenersnsersnerssersneerseersnenveesneensnn 2 34 CONGCIUSION M htt 2 4 Realization and testing uae iana Pees be os dees Poet Peo Pe ete acs oe tes Pees Does Pha ees Pree Rma 2 4 1 Preparation oen eee e e ETE Pe REESE ER TE Peek E Re HERR E ERR ed 2 4 2 R alization s sn a lenen Banennet eenen ies 2 423 Powertsupply eec e ean Cen ABIDE paie 2 4 2 2 Printed circuit board details esses ener 2 4 3 Test procedure sided ie ieia leer deti eget decies dete aaea en ene dee 2 43 3Motorbrake test im oen rr EET Ue D nere RU te IR RIOT 2 432 Shderdirecton test si eee aee oi ae neat ee al ete ue iae denn 2 4 3 3 Slider homing iest ine eed t RHET Ue t ed 2 434 Other tests cce sedet ed ee re ee eee e eee een 2 4 4 Results cec ant aa elsi ann Eet Renden 2 4 4 1 Increasing deceleration eorne roine apotee tenente eaat esep eaea ente ea eaa iE 2 4 4 2 Direction dependency ners anne eene eenseernvensevenseess
8. if Position lt 0 then 0 else 1 end EndStop2 if Position gt side then 0 else end Figure 36 20SIM code of the EndStopSimulator sub model Switch1 stop go left go right go home home gt output Control Engineering 44 End stops for the Mechatronic Demonstrator Appendix H Characterization of the demonstrator In this appendix some calculations have been done to stipulate the theoretical value of the follow parameters maximal acceleration maximum torque maximum current maximum velocity maximum stop distance Belt The belt that is used for the demonstrator has the following specifications datasheet of the belt Width 3 mm and a pitch 2 032 mm Maximum Operating Tension 7 N Maximum Speed up to 20 000 rpm Pulley Type TP7A6M W2 24 Number of teeth 24 Diameter 15 52 mm Rail and slider Under normal operation conditions the permissible speed is 3 m s and the accelerations up to 80 m s2 datasheet of the rail Slider mass 0 119 kg Kleijn 2003 Motor Type RE 35 35 mm Graphite Brushes 90 Watt DC motor Datasheet of the motor Torque constant 38 9 mN m A Motor supply Type Maxon motor control 4 Qudrant DC ADS 50 5 Datasheet of the amplifier Table 7 Some characteristics of the demonstrator H 1 Required Force for maximal acceleration The maximum allowed acceleration of the r
9. 100n C12 100n C13 100n Table 5 Capacitors overview of the PCB E 3 Remaining components Component Description Farnell part number Price euro D1 SMD LED red 1142617 0 32 D2 SMD LED green 1142615 0 24 ISO Opto isolator 1021184 0 33 ISO2 Opto isolator 1021184 0 33 Ll Inductor Choke 120uH 6A 1187672 4 08 QI K3010P Triac driver 4402900 0 52 Q2 Triac BTA08 600BRG 8A 600V 1057269 0 63 Ul LM311 Voltage comparator 2293183 0 189 U2 IA05128 DCDC converter 5V to 12V 8727503 5 81 U3 74HCT00 Quad NAND gate 1236257 0 196 U4 7474 D Type Flip flop 1013996 0 27 US 74HCT 14 Inverter Gate 1236216 0 23 U6 74HCT00 Quad NAND gate 1236257 0 196 Table 6 Part list of used components for the PCB The sum price of the components is 13 34 exclusive the resistors capacitors and the connectors Control Engineering 40 End stops for the Mechatronic Demonstrator Appendix F Connectors user manual In this appendix the connectors of the PCB will be explained for each connector the pin layout is given Fl Connector J1 Control signals to the motor amplifier The PCB is connected to the motor amplifier The set point and the enable signal were connected to the amplifier A separated ground is used with pin 2 The enable signal is separated optical with an optocoupler This optocoupler has a transistor outputs witch are connected to pi
10. Further calculate the deceleration of these velocities Control Engineering 20 End stops for the Mechatronic Demonstrator Action Expected result Move the slider with a velocity v to e The switch is activated and the slider stops the switch Vn 0 3 1 5 m s step 0 1 m s e Measurement results are available to plot graphs 4 3 2 Slider direction test Left end stop In this test the direction dependency of the slider is tested When the direction of the set point has changed from left to right or reverse while the slider is pressing an end stop the motor amplifier is not more disabled So the slider can leave the switch Check the functionality of the direction LEDs on the PCB Precondition The slider is pressing the left end stop Action Expected result Change the set point slowly from e The slider moves to the right side left to 0 to right e The direction LED left is turned off and the LED right is turned on Stop the test e Right end stop Repeat the previous test for the right end stop 4 3 3 Slider homing test In this test the following aspects are measured The status information of the right end stop is available on the controller The status information of the left end stop is available on the controller The PC 104 controls the movement of the slider Action Expected result Move the slider to the left e The slider move
11. altijd van de eindschakelaar verwijderen Ook zijn de eindschakelaars op de computer aangesloten Met behulp van deze data is een homing operatie gemaakt met 20SIM De andere eindschakelaar functies zijn gerealiseerd op een printplaat Dit onderzoek heeft uiteindelijk geleidt tot verbetering van de functionaliteit van de eindschakelaars van de mechatronic demonstrator Enkele aanbevelingen komen naar voren in dit verslag e Fen software veiligheidslaag wordt aanbevolen De software voorkomt dat de slider de eindschakelaars aanraakt Deze software verbetert de bestaande oplossing e Het implementeren van a snelheidsbegrenzer in software zodat de slidersnelheid begrensd wordt op ongeveer 1 5 m s e Toevoegen van de detectie van de marker in de homing Deze functie zit nog niet in de bestaande homing functie Verder kan de efficiency van homing snelheid onderzocht worden e Vervang de huidige tandriem voor een sterker exemplaar en vervang de pulley s voor gelagerde pulley s om de tandriem beter op spanning te kunnen brengen University of Twente iii Contents LEN ii aE jo De ie GEE 2 1 1 Mechatronic Demonstrator nanos anne vene eenseersvensevenseenseensvennvenseeenseensvennvenneeenteenseenseennn 2 1 2 Problem description essere eene nennen eene tnn enne desdensa 2 1 3 Objective exte etii RR eee eee Seeded te eorr 2 1 4 R qUitermentss arena Op Agnete i qe NEUE Ete iUe 2 1 5 QOutline of the epo PAE E A ME EL NI I M
12. differentiated motor position sensor to the motor brake 4 Feedback of a motor voltage to the motor brake First the effects of the voltage decreasing of the motor have to be discussed The motor velocity is dependent of the motor voltage in accordance with formula u Koo Further the motor amplifier is used as current source so the Torque is controlled T Ko0i Also the acceleration a is controlled because T I a Torque and acceleration are proportional with constant inertia So the motor torque and acceleration can be controlled by the current But the maximum velocity is depended of the motor voltage Al Different power supply Different power supplies can be used for the motor amplifier The Maxon motor amplifier has a width input power supply range of 12 50 VDC The voltage of the current power supply is 21 5 V and the maximum velocity of the motor is 88rev s But if the minimum voltage is used then the motor velocity is 47rev s by 12V But the slider is still moving to hard A2 Voltage reduction In this experiment the voltage over the motor is reduced The voltage must be reduced by a component that only reduced the voltage and not the current so the torque and acceleration are not changed Eq BATTERY a Wi EA BATTERY O S MOTOR SERVO Figure 21 Voltage of the motor is simply PE reduced by a diode Figure 22 Voltage of the motor is reduced by a power transistor which is simply
13. on the Model Started LED e The Model Started LED is on Switch off the Model Started LED Status amplifier enabled e The Model Started LED is off Action Expected result Press the start button Press the emergency button e The amplifier is enabled e This status information is available in 20Sim controller e The amplifier is disabled e This status information is available in 20Sim controller Start the demonstrator Action Expected result Switch on the power of the e The PCB set the amplifier in disable mode demonstrator Press the start button 4 4 Results This section discusses some measurements of the final print The different test cases in the previous e The amplifier is enabled section have to be executed and the measurements have to be shown 44 1 Increasing deceleration In the first test the stop distance of the slider was measured with different velocities This measurement data is shown in Figure 16 and Figure 17 Control Engineering 22 End stops for the Mechatronic Demonstrator Braking velocity Velocity Vi 1 7 m s Velocity v 1 6 m s Velocity vi 1 5 m s Velocity vi 1 3 m s Velocity v 1 1 m s Velocity vi 0 9 m s Velocity vi 0 7 m s Velocity vi 0 4 m s 1 6 0 2 eed n 1 102 104 106 108 14 Figure 16 Braking velocities v t m s
14. power supply which have to be higher than its input range The necessary voltages for this comparator are generated by a DCDC converter The chosen DCDC converter is the IA05128 it generates 12V and 12V from the 5V A DCDC converter is needed because only 5V is available on the print The V and V in the schematic are generated by the DCDC converter 1A0512S Figure 12 DCDC converter It creates a 12V and 12V for the voltage comparator University of Twente Method to improve the end stop functionality 17 In Figure 12 the electric schematic of the DCDC converter is shown Further logic components are needed to create a function of the inputs to get the desired output The inputs exist of two end stops the emergency stop and the motor direction signal The function can simply been written MotorBrake EndStopLeft Direction EndStopRight Direction EmergencyStop There are several solutions to implement this function in hardware One possibility is to use programmable logic but the function is small and fixed So another method is chosen using standard gates The function can be implemented with one Nand IC and one Not IC The components are Nand gate 7400 Not gate 7414 The function of the logic 1s to give a brake signal dependent on the inputs the end stops and the motor direction The logic is fast enough so the reaction time is not a bottleneck UBE U6A Motor direction o u 10 ad CNN E
15. so the slider can leave the end stop This part in the block diagram has the following inputs the two end stops and the direction information from the set point the output is the enable signal for the motor brake This block diagram contains a logic block a direction detector block and a motor brake block End stop 1 End stop 2 Emergency stop Logic function block Short circuit Figure 9 Block diagram of the hardware safety layer 3 3 Electric circuits This section explains the electric circuits that implement the functionality from Figure 9 See Appendix C for all schematics and see Appendix B for more information about the configuration of the hardware connectors 3 3 1 Electric circuit of the motor brake The TRIAC needs some other components to function properly This section explains the schematics R1 M amp XOR RE 35 118777 i Maxon Motor i Amplifier TRIAC DRIVER Motor wv P dh K3010P3 i Motor CHOKE Figure 10 Triac circuit Figure 10 shows the electric motor brake circuit with the TRIAC The TRIAC is controlled by a TRIAC driver The TRIAC driver provides an optic isolation between the digital electronics and the TRIAC The resistor R1 and the capacitor C1 build a snubber network A snubber network is a resistor Control Engineering 16 End stops for the Mechatronic Demonstrator and capacitor in series and is placed in parallel with the output of the TRIAC The snubber network
16. t 2 0 2 t a z 0 098s The required time to move 20cm at maximum acceleration 42 0m s v a t 42 0 098 4 1m s Theoretical and neglected friction The theoretical maximum velocity of the slider is 4 1m s In the next graph Figure 37 the real velocity is measured The slider moves approximately 20 cm over the rail Control Engineering 46 End stops for the Mechatronic Demonstrator H 5 Measured velocity model 0 1 Position m Velocity m s 0 12 0 14 0 16 0 18 0 2 0 22 0 24 0 26 time s Figure 37 Measurement results position and velocity of the slider The velocity of the slider is dependent on the friction of the rail and the tension of the belt and the current of the motor The maximum measured velocity is 2 6 m s The difference between the measured and the theoretical values can be explained because in the theoretical calculation some imperfection of the slider friction is neglected H 6 Required stop distance The stop distance of the slider is dependent to the velocity and the deceleration or the force The maximum velocity of the slider is 2 6m s and the maximum force is 7N The deceleration is a MTM NN 58 8m s m O 119kg The stop time is t v ou 0 044s a 58 8m s and the stop distance is s v t 1 3m s 0 044s 5 7cm The maximum available stop distance is 3cm because first the free space of the slider is too restricted to a longe
17. the acceleration is not constant between 0 25rev s The acceleration decreases dependently of the motor voltage and this is not desirable In general the motor acceleration is not constant in the last 20rev s so the last increase of 5V can not be used This method is not desirable to limit the velocity of the slider because the acceleration is not constant in the used range so the limiter does not work adequate Control Engineering 30 End stops for the Mechatronic Demonstrator A3 Feedback of the motor velocity Solution 3 contains a feedback of the motor velocity to the motor brake This is not easy to implement in hardware because the motor position sensor has to be differentiated because the velocity is not measured It is easier to implement this feedback in software A4 Feedback of the motor voltage Solution 4 contains a feedback of the motor voltage to the motor brake because the motor voltage is proportional to the motor velocity The PWM voltage of the motor has to be transformed to an effective voltage Another method is to use the monitor n output of the Maxon amplifier but the amplifier is configured as current control It is not so simple to implement a voltage feedback This report shall not discuss this development or implementation University of Twente Appendices 31 Appendix B Hardware connector configuration This appendix contains the configuration of the hardware connector for the mechatron
18. toe te passen in de praktijk De demonstrator is voorzien van een hardwarematige veiligheidslaag voor persoonlijke veiligheid en ter voorkoming van schade aan de opstelling De huidige beveiliging bestaat uit twee eindschakelaars die de motorversterker buiten werking stellen wanneer de slider een schakelaar aanraakt Op deze manier wordt voorkomen dat de motor schade aan de opstelling toebrengt De oude veiligheidslaag is niet voldoende en heeft te weinig functionaliteit In deze individuele onderzoeksopdracht is een analyse uitgevoerd naar problemen en verbeteringen met betrekking tot de veiligheidslaag van de mechatronic demonstrator en in het bijzonder de functionaliteit van de eindschakelaars Drie aspecten van de schakelaars moeten verbeterd worden Het eerste punt is het remmen van de motor wanneer een eindschakelaar is ingedrukt Het tweede punt is richtingsafhankelijkheid van de slider wanneer een eindschakelaar is geactiveerd Het laatste punt is dat de eindschakelaars geen initialisatie van de slider positie ondersteunen homing Bovenstaande punten zijn verbeterd en nieuwe functionaliteit is toegevoegd en gerealiseerd op een printplaat Het remmen van de motor is verbeterd met behulp van een TRIAC De TRIAC sluit de motor kort waardoor de deceleratie van de motor sneller wordt in tegenstelling tot de vorige uitschakeling van de motor versterker Verder is de richtingsafhankelijkheid van de slider ge mplementeerd Hierdoor kan de slider zich
19. velocity v m s Braking distance Average deceleration cm m s 1 y A Eu 1 1 7 3 1 47 2 1 6 3 0 43 3 1 5 2 8 40 4 1 3 2 7 31 5 1 1 2 5 24 6 0 9 2 2 18 7 0 7 1 8 14 8 0 4 1 7 5 Table 3 Measurement results of the braking test Table 3 shows a survey of the measurement results It is clear that the braking distance gets bigger when the velocity gets higher Also the average deceleration gets higher but the stop distance is not smaller or stays constant but de distance becomes longer The deceleration of test 8 5 m s is approximately equal to 4 m s which is the measured deceleration of section 2 1 1 with no braking functionality So with low slider velocities the short circuit does not increase the deceleration The short circuit method works but insufficient When an end stop is activated the motor is short circuit and it stops But the stop distance of the slider is dependently on the velocity When the velocity is too high the slider bangs to the side Therefore the velocity has to be limited So a velocity limiter is recommended 4 4 2 Direction dependency The motor amplifier is disabled only dependently on the slider direction in combination with an end stop When an end stop is activated the motor supply is disabled but when the set point is changed the motor direction becomes negative to the previous direction previous set point and then the motor supply is enabled and the slider can leave the en
20. Cac Motor controlschematic e er d eee aad ae bilan 2 C3 Direction schematic ccccccscescorssvccersevecsccevsevicevcevecencessevicsvesvecsccevtevs covcovedvedessebeced ona de eee dns 2 GAs JJEnd stop schematie so veis nere e tee prt intenet deste ep tree ettet 2 C3 Remaining CIrCuits sec 5 casts o Mb eta Bea eee eA tie ette eei mph ees 2 Appendix D Printed Circuit Board Configuration annen eneneenvennnenenenen 2 D l Connections overview nnn enveneeeneenerenvenveneeenveneeenvenveneeenveneeenvenvenveenvenvenveenvenveenvenvent 2 Appendix E Part list printed circuit board nnee ereenennenneereneeenennnnneeennnnn 2 E 1 ReSISLOISsG san vonni venete tete end e Hv x Pre a a Ee aTa a R 2 E 2 ETN EE AA Need AST 2 E 3 Remaining components annees inak pasiene aiani aa aaah poed oan aaa tha dariit 2 Appendix F Connectors user manual nnn onnnnenneennnnenvenennenereeennneereeneervennneenenenenen 2 F 1 Connector J1 Control signals to the motor amplifier eee 2 F2 Connector J2 Set point of the Controller essere 2 F 3 Connector J3 Motor power of the amplifier nnn snnv anne eensernsersnereneerseerenennseenseennnn 2 F4 Connector J4 Motor power to the motor essere enne nnns 2 F 5 Connector J5 and J6 End stops with LED sss 2 F 6 Connector J7 Digital Input Output ennemi enne nns 2 F 7 Connector J8 and J10
21. Control Engineering 2 End stops for the Mechatronic Demonstrator Digital Analog Motor amplifier Motor Belt Slider Converter Maxon ADS 50 5 RE 35 118777 L_pl L Sensoray 526 Computer PC 104 End stops Digital Position Input Output sensors Rotation sensor Figure 2 Simple model of the demonstrator 1 2 Problem description A hardware safety layer exists on the demonstrator The safety layer prevents damage to the slider and motor when someone makes a mistake or the controller becomes unstable The safety layer of the demonstrator consists of three switches one emergency stop and two end stops mounted on the left and right end of the rail The three switches disable the motor supply so the motor is switched off 12 V o O Left end stop Right end stop e ji Emergency 5 switch Motor Amplifier Enable Figure 3 Electric schematic of the end stops in the old situation In Figure 3 the schematic of the old electronic circuit is displayed This safety layer is simple and the functionality of the end stops is limited in this situation The problem can be divided in three sub problems University of Twente Introduction 3 1 The slider does not stop in time The slider moves to the end of the rail the switch is activated but the slider bangs against the side and therefore sometimes the belt tears off because the disabling of the motor
22. First a short preparation of the implementation is discussed Then the realization is discussed Furthermore the test cases of the test procedure are described and the results are shown Finally the validation of the results with the objective is done 4 1 Preparation Before the rest of this chapter a short preparation is described of the first trail run The printed circuit board is created and the connectors have to be connected The left and right end stop can be mistaken but this is depending to the connected and poles of the set point It is recommend to remove the slider in the first trail run and to check if the polarity of the set point is matching with the two connected end stops After the right installation the end stops appeared to work properly Take care of the timing belt because in the case of an extremely braking force of the motor the teeth of the belt are destroyed So it is recommended that a stronger timing belt is used and also replace the pulleys into bearing ones to pre tension of the timing belt 4 2 Realization For a stable and robust realization of the hardware safety layer the final circuit is made on a printed circuit board The different circuits described in chapter 3 are created on a single print The specific information about the printed circuit board is discussed in the appendixes 4 2 1 Power supply The required voltage of the print is 5 Volt The print uses approximately 100mA and so simply t
23. Fonchon Investment in the old motor supply is Simple solution wasted 20 sim models have to be changed Current Torque characteristic is less linear 2 Using voltage control instead of current control The motor brake is similar to short circuit the motor Advantage Disadvantage No extra hardware is required the current Difficult modeling because there is no motor supply can be used linearity between voltage and torque The current torque characteristic is approximately linear and therefore it is used in the current demonstrator An extra option by 2 is to change the current control into voltage control only then when an end stop is activated So no automation is possible because the change of the configuration is made by dipswitches 3 Change the set point In this option the set point is changed by extra hardware or software when an end stop is active The new set point value is negative to the old value and maximal so the motor stops fast Advantage Disadvantage The current motor supply can be used Feedback of the velocity of the motor is because this is a 4 quadrant motor control required because when the velocity of the slider reaches 0 m s the set point must be changed to 0A The maximum deceleration is proportional to the current but the current is limited by the amplifier 4 An extra circuit between the motor and the power supply The function of t
24. S 2 2 Analysis of the functionality of the end stops sssssssseeeeenne 2 2 1 Characterization of the demonstrator naaar rnnerenvennersneernverseeesersneervenvensversenn 2 2 1 1 Characterization of the motor brake senses eennn enne ersneerseensvensenensvenseennvensenenn 2 2 1 2 Characterization of the motor control nanne nens eene ener enne 2 2 1 3 Characterization of the homing nnnsennernvenseersnvennvenvenseerseeenseersvensevenseenseennvenneeenn 2 2 2 Alternatives sans nanne toten dtes Sa coerce ed elses 2 2 4 Motor brake alternatives u einen itm ti iret elsi tense tu uu te fee itd 2 2 2 2 Shortcircuit alternatives snan nrden nr esed tele ee eerie 2 2 23 Direction serisor alternatives eese te ee eere ee e Ee RES ST RUE EE EX ede 2 22 4 Hominp alterativesu s een oed tee te e ER t eed 2 2 3 Additional restrictions eiecit ee a eenn daat erkennen redii 2 2 37 Maximum deceleration ctae eee inta uu ettet etes 2 2 3 2 Maximum Current 2 scele ee thesis ree desig iet einden ganden 2 2 33 Maximurm VELOCITY 23 5 s redeo t PERDE CIN ee i orte tete ee 2 23 4 Maximum stop distance iss antur suce iie ascen fetus 2 24 GONClUSTON ee euer DE Dn e Am aV Alu io A ML ele inei e 2 3 Method to improve the end stop functionality 2 3 1 Chosen methods nani nee ee eee ee ipee ed iere ET ee eve rennen aas 2 JEH Brakegoethod An eruere et ten Die tp v EE 2 3 1 2 Direction dependency method nanne eene ener 2 3 1 3
25. University of Twente fa EEMCS Electrical Engineering Control Engineering Endstops for the Mechatronic Demonstrator Albert Post Individual Design Assignment Supervisors prof dr ir J van Amerongen dr ir J F Broenink ir M A Groothuis A P de Vries June 2008 Report nr 013CE2008 Control Engineering EE Math CS University of Twente P O Box 217 7500 AE Enschede The Netherlands NW T Summary The mechatronic demonstrator is developed for students to learn the theoretical aspects of control engineering and to apply this theory in practice The demonstrator is provided with a hardware safety layer for personal security and to prevent damage The safety layer exists of two end switches which disable the motor amplifier when the slider pushes a switch This layer prevents that the motor damages the demonstrator The old safety layer is not sufficient and the end stops have too little functionality In this individual design assignment an analysis has been done to solve the problems and improvements concerning the safety layer of the mechatronic demonstrator Especially the end stop functionality of the demonstrator needs to be analyzed Three items of the end stops have to be improved The first item is the motor brake when an end stop is pushed The second item is the direction dependency of the slider when an end stop is active And the last imperfection is that the end stops do not support the homing of
26. ail and slider is published by the supplier in the datasheet The maximum acceleration is 80 m s The slider has a mass of 0 119 kg The calculated force is F 0 119 80 9 52N But the maximum force of the belt is only 7 Newton in the datasheet University of Twente Appendices 45 H 2 Maximum Torque The maximum torque can be calculated by Torque F tpuiey The used force in this calculation is the lowest force of the belt 7 Newton The pulley has a radius of 7 76mm So the maximum torque is Torque F rguie 7N 0 00776m 0 05432 N m H 3 Maximum current The maximum current to deliver this torque can be calculated to divide by the motor constant The motor has a torque constant of 38 9mN m A So the maximum current is 0 05432 0 0389 1 4 A The current limiter is configured with a maximum current of 1A When the set point of the controller is at maximum 1 0 then the supplied current is 1A So the maximum delivered force is lower than the maximum force of the rail and belt And the motor is unable to damage the slider H 4 Maximum velocity The maximum velocity has to calculate The maximum torque by 1A is current times torque constant 1A 38 9mN m A 38 9mN m The Force can be calculated by T F r Een 5 0Newton r 0 00776 The maximum acceleration is E n 42 0m s amem m O 119kg When friction is neglected the maximum acceleration is 42 0m s and in 20cm the maximum velocity can be calculated v a
27. alized The connector has status information about the end switches and the status of the start emergency switch The outputs have information about the status LEDs of the front panel of the Mechatronic Demonstrator Connectors J8 and J10 Connector pin Function SENSORAY J5 Digital pin University of Twente Appendices 41 1 Not Connected 49 2 Not Connected 50 3 DIO6 Input Status of Start Emergency stop 47 4 DIO7 Not Connected 48 5 DIO4 Input End Stop 1 45 6 DIOS Input End Stop 2 46 7 DIO2 Not Connected 43 8 DIO3 Not Connected 44 9 DIOO Output LED Server Online 41 10 DIO1 Output LED Model Started 42 This connector is connected to the Sensoray board This Sensoray connector has to configure right in hardware and software The DIO has been manually configured as inputs respectively outputs in groups of 4 bits The DIO 0 3 are outputs and DIO 4 7 are inputs The outputs have an output current of 25mA drive sink The input pull up resistor is 10kOhm F 7 Connector J8 and J10 Status LEDs The two LEDs are red status LEDs The Server Online LED is connected with connector J8 and the Model started LED is connected with connector J10 Both LEDs are mounted on the front panel of the Mechatronic Demonstrator Connector pin Function Anode 2 Cathode Ground F 8 Connector J9 Power supply This is the pow
28. amplifier is not sufficiently to brake the motor 2 The end stop responds independently to the slider direction When the slider activates the end stop the motor power amplifier is disabled and so the controller cannot move the slider left or right So the slider must be moved to the middle of the rail by hand and the motor power amplifier must be reset 3 The computer does not know the start position of the slider at starting The cause of this is that the position sensor only measures the relative displacement and not an absolute position The computer needs to remember the place of the slider and have to calculate the position each time again Comparable to the second problem the slider must be moved to the middle of the rail by hand 1 3 Objective The objective of this individual design assignment is to solve the problems and to improve the functionality of the end stops Research has to be done to create an overview of the current and alternative brake systems Finally the homing operation has to renewed so the computer can initialize the position of the slider Summarized a demonstrator with improved safety layer has to be created where it is not needed to remove the plastic cover and to move the slider manually 1 4 Requirements The new safety layer has to satisfy several requirements This section presents the requirements The safety layer has to stop the motor in case of an end switch or the emergency switch is pressed
29. configured by the resistors University of Twente Appendices 29 The simplest method is to add a diode to the circuit In Figure 21 the voltage of the motor is 0 6V lower than the battery And in Figure 22 the voltage of the motor is reduced by 0 0 6V OR R R 2 Vmotor Vbattery Vo The circuit of Figure 22 is tested in practice The voltage of the PWM is reduced to 6 5V instead of 21 5V Some results are shown in Figure 23 100 600 500 400 300 200 100 Motor velocity Current set point 0 5A w revs V 21 5V w revs V 6 5V 2 gs sS so 4 s 5 time s a Motor acceleration Current set point 0 5A rews2 V 21 5V rews2 V 6 5V 2 Ps 8 85 ag ah MUS time s C Motor velocity Current set point 0 5A w revs V 21 5V w revs V 6 5V 18 19 2 21 22 23 24 25 time s b Figure 23 Measurement results of reducing of the motor voltage In figure a is shown the motor velocity with set point 0 5A The red one is created with the normal PWM voltage of 21 5V and the black one is created with a reduced voltage of 6 5V Figure b is a close up of a Figure c shows the motor acceleration The maximum of red is approximately 550rev s and the black one 500rev s The conclusion of this test is that it is possible to decrease the maximum motor velocity when the voltage is decreased But
30. cy method The chosen method for the direction problem is to use a voltage comparator to get the direction information from the set point The comparator converts the analog value of the set point into a digital value 1 or 0 This value corresponds to the direction of the slider left or right So the voltage comparator seems to be a Sign function The voltage comparator should have a high impedance input so the Sensoray 526 DAC is not overloaded The Sensoray has an analog output with a range of 10 10V and 2mA output The chosen voltage comparator is the LM311 3 1 3 Homing method The homing operation initializes the controller with the absolute position information of the slider It is a moving operation of the slider to a reference point The reference point consists of a marker on the linear encoder strip The detector detects the marker and gives feedback to the controller The marker has the same precision as the resolution of the linear strip and the position sensor 40 000 ticks m this means an accuracy of 25um The implementation of the homing is simple a move action to the left end stop and a move action to the right to detect the marker or to calculate the center Control Engineering 14 End stops for the Mechatronic Demonstrator L Detect Marker yes Detect Left End stop Detect Marker Positiong Marker Detect Left End stop Offset A right left lef
31. d The chosen method is to use a TRIAC to short circuit the motor Further to determine the direction of the slider a voltage comparator is chosen to convert the analog set point The methods of the chosen items are described in chapter 3 Control Engineering 3 Method to improve the end stop functionality This chapter discusses the methods to improve the end stop functionality and how these can be realized First the different methods are discussed Further a block diagram is introduced to make the different parts understandable At the end of this chapter a final electric schematic for every part is discussed 3 1 Chosen methods 3 1 1 Brake method This section describes the brake method The main component to brake the motor is the TRIAC This component is chosen in the previous chapter The TRIAC or TRIode for Alternating Current is an electronic component and exists of N and P material just like a transistor but with an different structure The TRIAC is a bidirectional electronic switch which can conduct current in either direction when it is enabled It is enabled by a voltage which is applied to its gate electrode The used TRIAC is displayed in Figure 7 _ eb N EN o Figure 7 TRIAC BTA08 600BRG TO 220AB The chosen type is the Triac BTA08 600BRG this is an 8A 600V TRIAC with a current peak of 80A It is chosen arbitrary however the current and voltage of this type are enough 3 1 2 Direction dependen
32. d stop So the software has to change the set point and is be able to drive the slider In the next section it is shown that the direction dependency works properly 4 4 3 End stop connection to the computer The end stops are connected to the computer So it is possible to check the state of the end stops and do a homing operation In 20SIM a simple homing operation with end stops is added to an existing 20SIM model Control Engineering 24 End stops for the Mechatronic Demonstrator Advanced Controller Advanced Controller Figure 18 20SIM model of the Mechatronic Demonstrator with homing functionality In Figure 18 the 20SIM model is shown The EndStopSimulator sub model and the AdvancedController are added EndStop2 StateMachine positiont position position3 I NormalOperation E gt output Ticks2meter SignalLiniter4 Figure 19 Advanced Controller sub model The advanced controller exists of a normal operation controller and a homing controller The state machine has five different states State 0 The initial state waits until the start button is pressed while the emergency button is not pressed Then go to state 1 State 1 The homing operation is started and the slider moves to left until the left end stop is activated This slider position is saved and then go to state 2 State 2 The slider
33. d stop functionality of the mechatronic demonstrator 5 2 Recommendation This section discusses some recommendations for further research e A software safety layer is recommended This software prevents that the slider does not touch the end stops and so it improves the solutions of the problems 1 and 2 of session 1 2 e Implement a slider velocity limiter is software The slider velocity has to limit to approximately 1 5 m s e Implement the detection of the marker in the homing operation because this detection is currently not implemented in the homing operation Furthermore examine the efficiency of the homing speed e Change the current timing belt for a stronger one and replace the pulleys for bearing pulleys to pre tension the belt Control Engineering 28 End stops for the Mechatronic Demonstrator Appendix A Limiting motor velocity In the safety layer for the demonstrator the motor velocity has to be limited The velocity of the slider has to be limited to a maximum because the deceleration and the stop distance are not infinity The velocity of the slider has to be limited to approximately 1 m s This limiting process can be done in hardware and software This appendix discusses some hardware trials The software solutions shall not be discussed in this report Four hardware solutions shall be explained 1 A different power supply for the motor amplifier 2 Voltage reduction of the motor 3 Feedback of the
34. e 32 Connections overview of the PCB Control Engineering 38 End stops for the Mechatronic Demonstrator Appendix E Part list printed circuit board This appendix contains tables with components which are used on the PCB El Resistors Resistor Value Description RI 50 Resistor for LED by end stop 1 R2 50 Resistor for LED by end stop 2 R3 550 Resistor for LED Server Online R4 550 Resistor for LED Model Started R5 2k2 LED of optocoupler R6 5k Transistor of Optocoupler R7 560k Input voltage comparator R8 10k Pull up resistor end stop 1 R9 10k Pull up resistor end stop 1 R10 10k Pull up resistor end stop 2 R11 10k Pull up resistor end stop 2 R12 10k Pull up resistor start button R13 10k Pull up resistor emergency button R14 Ik RC Delay for reset by start up R15 10 Snubber network R16 270 LED of TRIAC driver R17 10 Triac driver R18 200 LED red motor direction R19 200 LED green motor direction R20 1k LED Optocoupler Enabling amp R21 12k Transistor Optocoupler Enabling amp Table 4 Resistor overview of the PCB E Capacitors Capacitor Value F Description Cl 35u Vee 5V C2 100n C3 100p Input voltage comparator C4 25u Supply 12V C5 100n C6 25u Supply 12V C7 100n C8 100n University of Twente Appendices C9 220n RC delay for reset by start up C10 100n Snubber network Cll
35. e slider when it hits one of the end stops It is desirable that the motor amplifier is enabled when the set point changes in such way that the slider moves back Some alternatives for direction sensors will be described e One solution is that the software driver converts the analog signal to a digital signal which contains the direction information and sends this calculated value to a digital output port e The other solution is to use a voltage comparator The detecting of the motor direction can be measured by the set point The set point has an analog value between 10 10V generated by the digital to analog converter Sensoray 526 A voltage comparator can translate this analog voltage to a digital value The hardware solution is chosen because in the case of a software crash the hardware can stop the motor Control Engineering 10 End stops for the Mechatronic Demonstrator 2 2 4 Homing alternatives For the homing problem three alternatives are discussed e An alternative is to change the position sensor strip for another strip which contains absolute position indication For this solution it is necessary to adjust the sensors and decoders With this solution a homing operation is no longer needed because the controller always knows the absolute position of the slider e Connect the end stops to the PC 104 The current position strip contains a marker at a fixed position The controller can move the slider t
36. eensvenneeesneenseennvennevenseenseennvenseeens 2 4 4 3 End stop connection to the computer naan eenn vennvennvenseersneenseersvensevenseenvenneeenseenn 2 4 5 Conclusione sss etenengenieten eee 2 4 5 1 Motor brake functionality iei tette e SE ee e entre 2 4 5 2 Direction dependency functionality esses eene 2 4 5 3 Homung functionality esci cede cese ec ir et i Pe ERR dake ER Fe ERN ERE EE ER E ede 2 Control Engineering iv End stops for the Mechatronic Demonstrator 5 Conclusions and Recommendations nnen eenenenreennneereeennnereeeneeeervennnnenenenen 2 5 1 COMCIUSIONS assasin utere eder ut eer ta E oki deeds EE 2 52 Recommendation eee eere dedere douderderederdenddeddevsevederdend end devdevedendend inisee rinis 2 Appendix A Limiting motor velocity nneennenenenenneeeeereennnnennneereneeenennnnnneeennenn 2 Al Differentpower supply sere ana aa ra a ea tee MA AG 2 Adi lt Moltagereductonis smste enten TO QOO T edt 2 A 3 Feedback of the motor velocity sess enne ener enne nenne 2 A44 Eeedbackeof the motor voltage a s epe Ele NI e ett 2 Appendix B Hardware connector configuration nnnnnnnnenennnennneeneneeneennennneeeeneee venen 2 B 1 Input 5t etd ute od UE btt a tis io ele ses 2 B 2 idu E 2 Appendix C Printed circuit board schematics sssssssseeeeeenne 2 Cl Main scherdati s ns versorerre G oJ 2
37. er connector of the print The power is obtained of the 5V computer power supply Connector pin Function 1 Vee 5V 2 Ground F 9 Connector SW1 Start or Set switch This connector connects the green start button to the PCB The button enables the PCB after the emergency button is pushed and reset Connector pin Function 1 Switch Common Ground 2 NC 3 Switch Normally Open F 10 Connector SW2 Emergency switch This connector connects the red emergency button to the PCB Connector pin Function 1 Switch Common Ground 2 Switch Normally Closed 3 NC Control Engineering 42 End stops for the Mechatronic Demonstrator Appendix G 20SIM sub models parameters integer initial logic state 0 0 is initial state 1 is going left 2 is going right 3 is going home 4 is at home variables integer logic_state new_logic_state real position_left position_right real new_position initialequations new logic state 0 position left 0 position right 0 HomingOffset 0 State 0 code definition of logic state itself logic state previous new logic state initial logic state logic state transitions switch case Switch logic state end equations case 0 do case do case 2 do case 3 do case 4 do default do State logic state HomingOffset posi
38. eration Therefore the available position sensors on the demonstrator have to be analyzed There are three types of sensors a linear strip with detector end stops and a rotation encoder on the motor The strip with detector on the demonstrator measures relative displacement These sensors are transmissive optical encoder modules These are designed to detect linear relative displacement when used together with a linear strip The strip also has a marker which can be used as a reference The rotation encoder measures relatively angular displacement When the slider hits an end stop its position is known but the controller is currently unable to detect the slider position or the end stop status 2 2 Alternatives This section discusses some alternatives to solve the problems see section 1 2 2 2 1 Motor brake alternatives There are several possibilities to stop the motor The analysis shows clearly that for slowing down the slider the current must be changed of direction or the motor has to be short circuited First the options will be explained 1 A different motor amplifier for example an H bridge with brake functionality In the current configuration the motor amplifier is configured as a current source The current motor amplifier has no brake function Control Engineering 8 End stops for the Mechatronic Demonstrator Advantage Disadvantage The new amplifier supports a brake Purchase costs of the new supply
39. he 5V computer supply that is present on the demonstrator is used 4 2 2 Printed circuit board details All schematics of the electric circuits that are made are added in Appendix C Printed circuit board schematics The next appendix shows visually the connections between the PCB and the mechatronic demonstrator See Appendix D Printed Circuit Board Configuration For a detailed description of the used components and the used connectors the next two appendices are added Appendix E Part list printed circuit board this appendix presents the tables with the resistors capacitors and other used components And Appendix F Connectors user manual explains the connectors of the PCB The pin layout of each connector is described 4 3 Test procedure This section describes the functional tests cases of the PCB The results of these test cases are described in section 4 4 4 3 1 Motor brake test Simple motor brake test Action Expected result Start the slider with a constant e The slider moves with a velocity of 0 5 m s velocity of 0 5 m s The slider activates a switch e The motor amplifier is disabled e The slider brakes Deceleration of the slider In this test case the deceleration of the slider for different slider velocities will be measured 20SIM is used to steer the motor to move the slider with a defined velocity as far as the end stop and measure the velocity of the slider during this experiment
40. he amplifier are interesting The amplifier has no explicit braking function but when the amplifier is configured as a voltage source and the set point becomes 0 or negative the motor velocity will decrease fast This is possible because the motor amplifier is a four quadrant amplifier The current torque relation is approximately linear Maxon motor datasheet and therefore the power amplifier of the motor is configured as current source When the current source is disabled or similar the set point becomes zero the motor velocity will decrease linear and slowly depending on its friction If the set point of the current source is not zero the motor will decelerate or accelerate with respect to the current The maximum acceleration and deceleration are bounded by the current limiter Computer A Digital Analog Motor amplifier me Motor PC104 Converter Maxon ADS 50 5 RE 35 118777 Sensoray 526 Figure 6 Set point The motor amplifier is controlled by the PC 104 This is the controller of the demonstrator Because the set point input of the motor amplifier requires an analog signal therefore between the amplifier and the PC 104 an analog digital converter is present The set point has a value between 10V and 10V this corresponds to a current of between 1 A and 1A The current limiter of the motor amplifier has been set to 1A 2 1 3 Characterization of the homing The position of the slider is needed for a correct homing op
41. his circuit is to short circuit the motor when an end stop is active There are several solutions of this circuit to short circuit Advantage Disadvantage The analysis has shown that the Requires an extra circuit with development deceleration of the velocity is high costs and development time The current motor supply can be used 5 Mechanical brake There are several solutions to stop the motor or the slider For example fix some bumpers on the demonstrator to catch the slider Or mount a Maxon motor brake on the motor These options are extra it can be implemented parallel to the electrical solution And first the electrical solution is chosen When the solutions are compared a short circuit is the best option Because the deceleration of the motor is high and the current motor supply can be used in the same configuration current control And also the 20SIM models do not need to be changed University of Twente Analysis of the functionality of the end stops 2 2 2 Short circuit alternatives This section shows some alternatives to short circuit the motor First the alternatives are described and one of them is chosen The alternatives are Relay Solid State Relay SSR Mosfet and TRIAC e The relay is a simple method to short circuit the motor The circuit is simple too but there are a few disadvantages The switch time of a relay is not so fast and this mechanical switching creates switch bouncing
42. ic demonstrator B 1 Input O Device 0 Sensoray 526 O Type Encoder Channel 0 Motor angle 2000 ticks revolution Channel 1 Slider position 1 World 40 000 ticks m Channel 2 Slider position 2 Top 40 000 ticks m Channel 3 Slider position 3 Bottom 40 000 ticks m O Type Digital In Channel 0 End stop 1 Channel 1 End stop 2 Channel 2 Status of Start Emergency stop Channel 3 NC B 2 Output O Device 0 Sensoray 526 O Type DAC digital analog converter Channel 0 Set point motor Channel 1 NC Channel 2 NC Channel 3 NC O Type Digital Out Channel 0 LED Server Online Channel 1 LED Model Started Channel 2 NC Channel 3 NC Control Engineering End stops for the Mechatronic Demonstrator 32 ICS t board schemati ircul Appendix C Printed c Main schematic Cl dk u vu Z u3avaH orr ZXS 83QY3H uoot EN ar zo Se nge z E to t Z d3QvaH sr 6 oF Y es u S 9 xX z 99 dojspug 0a Loo oa z iedoigpu3 1 uendoispua E i 01300 1010 1o1u091019N AL zu 99 fouebieu3 Cod KoueDieur3 Od B ye 7do spuz 4 E 1dois pus Hn Z iu amp rudoigpu3 Y AuBrgdoispu3 B L 1u6rudoispua 44 E iosu a 99 doigpu3 doon Z u3avaH vr o 1QdS A34 MS EMS yg dois AoueBieu3 amp nv soon wis o
43. ifier when the set point is changed This implementation is discussed in the previous chapter With this implementation the problem is solved 4 5 3 Homing functionality The homing functionality of slider 1s the last problem The start position of the slider was not defined The position sensors of the slider detect only the relative position This problem is solved by a homing operation on start up of the controller The end stops are connected to the controller The controller uses the end stop status to do the homing operation With this solution the last problem is solved University of Twente 27 5 Conclusions and Recommendations 5 1 Conclusions This individual design assignment has resulted in an improved hardware safety layer The end stops have more functionality and improve the safety of the Mechatronic Demonstrator e The motor brake is improved with a TRIAC The TRIAC short circuits the motor to decelerate faster instead of the previous disabling of the motor amplifier Thus the motor stops faster The deceleration of the slider is now maximal 40 m s instead of 4 m s e The end switches are now direction dependent allowing the slider always to move away from the end switch e The end stops are connected to the computer PC 104 With this end stop information a homing operation is added These new functionality is implemented on a printed circuit board This bachelor assignment has resulted in an increased en
44. ionality of the end stops This chapter discusses the characteristics of the demonstrator and especially the end stop functionality This analysis is necessary to get an overview of the used hardware The characteristics will be analyzed to identify the problems and limitations Several alternatives are discussed to get a realistic solution 2 1 Characterization of the demonstrator 2 1 1 Characterization of the motor brake In the old situation there is only passive braking of the motor When an end stop is pushed the motor amplifier is switched off and that is all see Figure 3 So the slider decelerates only by the friction of the slider and motor Next the characteristics of the current motor without slider will follow Three tests have been done to measure the stop time with different brake methods to stop the motor In all three test cases the velocity of the motor is measured in revolutions per second as function of the time see Figure 4 and Figure 5 The motor has in these tests a constant velocity of 88rev s at t 0 The brake action starts each time at tis 2 s In the first test the motor poles are short circuit the motor voltage becomes OV In the other two tests the motor amplifier is configured as a current source The second test shows the motor velocity with a switched set point from 1 to 0 Ampere at t 2s And in the last test the set point is changed from 1 A to 1 A att 2s model w shortcut motor revs
45. is needed because the motor causes noise The resistor R2 regulates and limits the current into the gate The TRIAC can short circuit the motor fast and independently of the motor polarity A choke is added to the motor circuit according to the datasheet of the Maxon motor amplifier Maxon motor amplifier datasheet an extra choke is necessary if the DC motor has a terminal inductance lower than 0 35mH The currently used motor has a terminal inductance of 0 34mH A choke of 120uH is added A choke is added instead of an inductor because an inductor stores energy and the choke dissipates energy for higher frequencies 3 3 2 Electric circuit of the direction dependency This section discusses the electric circuits concerning the direction dependency Three schematics are shown the voltage comparator the power supply schematic and the logic schematic V VCC o R2 R3 MotorEnable SetValue SetValue Inputs Figure 11 Motor direction detector The voltage comparator converts the analog voltage to a digital signal In Figure 11 the voltage comparator is shown Dependent on the set point the output voltage is high or low The optocoupler is added for galvanic isolation between the output and the motor amplifier The right side of the optocoupler is connected to the motor amplifier together with its power and ground In the schematic different symbols are used The comparator needs a positive and a negative
46. ity limiting in hardware but no hardware solution serve the purpose Therefore in the final realizations of University of Twente Analysis of the functionality of the end stops 11 the PCB no velocity restriction is present A recommendation is to implement a velocity limiter in the controller software 2 3 4 Maximum stop distance The slider needs some distance to decelerate The faster the deceleration gets the shorter the needed stop distance The maximal available distance between the end stop and the end of the rail is approximately 3 cm The slider length is also approximately 3cm When the stop distance becomes bigger the free space of the slider is proportionally smaller Thus the slider has to stop within 3 cm without touching the side 2 4 Conclusion From the analysis of the demonstrator it has become clear that the end stops have to be improved When the slider activates an end stop the slider does not brake but only the motor power amplifier is disabled So the deceleration of the slider is insufficient Furthermore it is necessary that the maximum speed of the slider is not too high because the deceleration is limited A speed limitation will not be implemented in hardware Furthermore from the analysis it has become clear that the brake force of the motor is limited by the current limiter of the motor amplifier because of this the slider can not decelerate fast enough Necessarily a brake function has to be implemente
47. ly 66m s So the bigger the deceleration the shorter the brake distances See Table 1 for a summary Test Description Measured Theoretical slider deceleration Motor a 2 z r a m s deceleration a rev s with r 2 7 7610 m l Short circuit 2000 100 2 Set point change 88 4 1A gt 0A 3 Set point change 1350 66 1A gt 1A Table 1 Measurement results of the motor velocity by different motor brakes The start velocity of the motor is 88 rev s in these measurements this corresponds to a theoretical slider velocity of 4 m s but the slider can not move with this velocity in practice This measurement is only been done to analyze the deceleration of the used motor with different voltage and current changes 2 1 2 Characterization of the motor control The currently used motor amplifier is the Maxon ADS 50 5 This motor power amplifier of the demonstrator can be configured in different ways voltage current tacho and encoder control The University of Twente Analysis of the functionality of the end stops 7 first two controllers use the internal voltage and current sensors to control the motor The last two configurations require an external tacho or encoder sensor The sensors of the demonstrator are only connected to the computer and not to the motor amplifier because the computer with sensors has to control the slider So only the voltage and current configurations of t
48. moves right until the right end stop is activated This slider position is also saved The next state is state 3 State 3 The slider moves to home The slider calculates the center with the left and right position values and the slider moves to this position State 4 The slider starts the normal operation University of Twente Realization and testing 25 Position ticks 4 EndStop1 EndStop2 0 5 10 15 20 time s Figure 20 Measurement results of the 20SIM model with homing functionality Figure 20 shows some measurement values The slider moves and activates the end stops The end stops change the active state of the state machine After the homing operation the slider moves according to a block wave pattern which is controlled by the normal operation controller In this simulation the slider does not start in the middle of the rail so the homing operation creates an offset value In Figure 19 the offset signal is subtracted of the slider position so the controller moves the slider with a block pattern round the middle 4 5 Conclusion This section evaluates the improved functionality and if the problems are been solved sufficiently and if there are still possible restrictions In section 1 2 the three imperfections of the end stops are discussed 4 5 1 Motor brake functionality The first problem is that the slider does not brake whe
49. n 3 4 5 Connector pin Function MAXON Motor amplifier 1 Set point analog 10 10V Signal pin 1 2 Set point analog ground Signal pin 2 3 Enable of the amplifier Signal pin 3 4 Ground of the amplifier Signal pin 4 5 12V of the amplifier Signal pin 10 F 2 Connector J2 Set point of the Controller The PCB gets the Set point with this connector from the ADC Sensoray The set point is an analog value between 10 and 10V Connector pin Function SENSORAY J3 Analog 1 Set point analog 10 10V Pin 23 2 Set point analog ground Pin 25 F 3 Connector J3 Motor power of the amplifier The output power of the amplifier is connected to the PCB with connector J3 Connector pin Function MAXON Motor amplifier 1 Motor Power pin 1 2 Motor Power pin 2 F4 Connector J4 Motor power to the motor The motor is connected to J4 Connector pin Function 1 Motor 2 Motor F 5 Connector J5 and J6 End stops with LED The pin configurations of both end stop connectors are the same The status LED is directly mounted on the switch The LED is on when the switch is pushed Connector pin Function 1 LED anode 2 Switch Normally Closed 3 Switch Normally Open LED cathode 4 Switch Common Ground F 6 Connector J7 Digital Input Output With this connector the digital IO with the controller is re
50. n an end stop is pushed Because of this damage can occur The old electric circuit with the end stops does not brake the motor active The solution is a new electric circuit that brakes the motor actively This is realised with a TRIAC which is short circuited the motor The deceleration of the slider is increased from 4 m s to 40 m s Because of this increased deceleration the stop distance gets shorter but the real stop distance is determined by the velocity of the slider When the slider velocity is below 1 5 m s the stop distance should be acceptable approximately 3cm So a slider velocity limiter is recommended Further it is recommend to replace the timing belt for a stronger one because this one has reached the boundaries of its specification when the motor brakes with maximum power 4 5 2 Direction dependency functionality The second problem is the direction dependency of the end stops This function is not implemented in the old end stop realization In the old situation the power amplifier is disabled independently to the slider direction When an end stop is activated the power amplifier is always disabled The controller cannot enable the amplifier and also it cannot be enabled with a slider direction change Control Engineering 26 End stops for the Mechatronic Demonstrator To solve this problem a slider direction dependency motor brake is implemented The electrical circuit contains logic to enable the motor ampl
51. nable Motor 7414 7414 Endstop Left U4A Oo 1 N Emergency stop _U4D UAC U6B 12 7400 9 U4B 7400 7414 4 7400 7414 Endstop Right 6 e 5 7400 Figure 13 Logic circuit Figure 13 shows the realized circuit with a NAND and NOT gate The end stops and the emergency switch are switches that are connected in normally closed mode This means that the functionality of a not connected switch equals a presses switch Some LEDs are added to the schematic for extra functionality Two LEDs show the status of the switch and two other LEDs red and green indicate the motor direction Furthermore these LEDs indicate 1f the print 1s active and the power 1s turned on 3 3 3 Electric circuit of the end stops A debounce circuit is added between the end switches and the computer The emergency stop and the two end stops are connected to the computer More precisely the switches are connected to the digital IO connector of the Sensoray IO board The debounce circuit is added to remove the contact bounce because contact bounce is a problem of mechanical switches VCC VCC o R8 R9 10K 10K EndStopLett 1 gt 4 il 3 EndStopLett 2 4 2 DIO4 U3B 74HCTOO lt EndStopLeft Figure 14 Debounce circuit for the end stops Control Engineering 18 End stops for the Mechatronic Demonstrator In Figure 14 the debounce circuit is shown The end stop is c
52. nal restrictions This section analyzes some additional restrictions The deceleration and velocity of the slider are related The faster the slider moves the bigger the deceleration to keep constant the stop distance of the slider This section discusses these parameters The used calculations are discussed in Appendix H 2 3 4 Maximum deceleration The deceleration and the force have a linear relation The force is limited by the weakest link For the timing belt a maximal tension of 7 Newton is specified by the manufacturer The manufacturer of the rail has specified a maximal acceleration of 80 m s This corresponds with a force of 9 52 N The mass of the slider is 119 gram So the maximal brake force 1s limited by the timing belt 7 Newton This corresponds to a maximal deceleration of 58m s 2 3 2 Maximum current The conversion of the voltage to the current of the power amplifier is established as 0 1 A V Dirne 2005 This establishment is configured by the current limiter of the amplifier Therefore the current of the motor amplifier is limited to 1 Ampere So the maximal acceleration or deceleration of the slider controlled by the amplifier is theoretical 42 m s Appendix H discusses this calculation 2 3 3 Maximum velocity The velocity has to be limited because the deceleration is limited Some alternatives to limit the velocity are discussed in Appendix A This appendix discusses four possibilities to realize the veloc
53. o the marker with the help of the end stops So the controller can calculate the position of the slider with the marker position or with the end stop positions e Itis not per se necessary to connect the end stops to the computer The computer can detect the end stops with the position detectors and without the end stop status signals With this relative position information the computer can calculate the velocity and the acceleration These data together with the output current give the end stop information For example when the slider is activating an end stop the velocity and the acceleration of the slider become zero The computer can detect an end stop when the set point of the current is not equal to 0 Ampere and simultaneously the velocity is 0 m s and the acceleration is 0 m s The last alternative is not so simple to implement in software because double differentiation of the position is required to calculate the acceleration And digital differentiation needs filtering to remove the noise Furthermore the end stop information is not immediately available because the deceleration of the slider needs to be calculated The connection of the end stops to the pc is in any case a good idea and the position strip with marker is already available on the demonstrator So the second solution 1s chosen Therefore the end stops have to be connected to the computer The status of the end stop can then be used for the homing operation 2 3 Additio
54. onnected to DIO 4 this is a digital input output pin number of the Sensoray board The complete configuration of the connectors is described in Appendix F 3 3 4 Electric circuit of the initialization In the circuit with the start and emergency stop a D flip flop is added to hold the enable signal The start and emergency are respectively the set and reset The resistor and capacitor create a reset on startup because when the main power to the demonstrator is turned on the amplifier and the motor have to be disabled to prevent unwanted movements R12 Enable Motor 10K D a Q Stat P CLK CLR R13 pis E vcco PRE 10K TT U4A Emergency C gt 1 7 7474 R1 U5A 74HCT14 Figure 15 Initialization circuit 3 4 Conclusion In this chapter the chosen methods to improve the mechatronic demonstrator are described These methods are used to realize the new functionality of the end stops First the method to create an active motor brake with a TRIAC is discussed Further the method to realize direction dependency of the slider is discussed and last the end stops connection to the IO board of the computer is discussed All method descriptions are equipped with the electric schematics The next chapter handles the implementation and realization of these methods University of Twente 19 4 Realization and testing This chapter discusses the realization and testing of the new functionality of the end stops
55. onverts the analog voltage to a digital voltage V 1A0512S j OV Figure 27 DCDC converter It creates a 12V and 12V for the voltage comparator University of Twente Appendices 35 C 4 End stop schematic vee vee O o R8 R9 10K 10K U3A 74HCTOO Left 1 EndStopLeft 1 gt Biss EndStopLeft 2 gt U3B 74HCTOO lt __ EndStopLeft R10 10K EndStopRight_1 EndStopRight_2 R11 10K U3C 74HCTOO 10 DIO5 13 U3D 74HCTOO ee JEndStopRight PC3 Emergency _ gt 7 AS a jpIo6e Figure 28 Debounce circuits for the end stops Control Engineering 36 End stops for the Mechatronic Demonstrator C5 Remaining circuits vee vee oon ca n t iid TAHCTIA Figure 29 Uncoupled capacitors Figure 30 The input Figure 31 The inputs of of the not used inverter the not used D flipflop are is grounded grounded University of Twente 37 Appendices Appendix D Printed Circuit Board Configuration Connections overview D 1 puepazyms u open SE vanos SOS SOV u vd 49901 0 0 J06 20 0 janu soou voreui 4O0jou uoxeus iW TENNVHI VIENNVHI 9 18 TANNVHI 8713NNVHO 8 ANO VWZIJAZL bb ANO VWZIJAZI OF Apoy 6 qpowow g UuJOWJON Z indup ouder 9 indu ouder S uueg Aeespung woni Z 2010 b SENSORAY Digital J5 202325220251 me cees GND Vee 5V Figur
56. or 20 Sim is a software application for creation and simulation of dynamic models and control systems One of the supported features is the ability to generate C code of the model for a real time computer These Mechatronic Demonstrator setup is supposed to be used at lectures in Control Engineering in the Electrical Engineering and Mechatronics curriculum of the University of Twente These Lectures contain theory of simulation of dynamic models and control systems The objective of the demonstrator is to support that theory by examples in practice on a mechatronic device Besides making the theory more insightful real limitations in practical setups can be shown easily Figure 1 The Mechatronic Demonstrator Dirne 2005 The mechatronic demonstrator contains electronics and mechanics a computer PC 104 with an external IO board with a digital to analog converter and a mechanical slider on a rail A belt is used for the connection between motor and slider The rail is connected via a special construction with two springs to the fixed world Due to this flexible frame the demonstrator is assumed to behave like a fourth order model which makes it interesting for educational purposes In 2003 the first mechatronic demonstrator was build by Controllab Products BV Kleijn 2003 Hans Dirne builds a second demonstrator More information about this mechatronic demonstrator is reported by Dirne 2005 Figure 1 shows this demonstrator
57. r stop distance Further with the current end stops the slider can pass the switch when the stop distance is to long So the end stop is switched on and off when the slider is passed The preferred stop distance is 3 cm or shorter Because a With a longer stop distance on both sides the free space of the slider is too restricted b With a longer stop distance the slider can pass the current used switch because the length of the slider is 3 cm too c With a shorter stop distance the velocity of the slider has to decrease or the braking force has to increase The maximal allowed force of the belt is 7 Newton University of Twente Appendices 47 Literature Dirne H Demonstrator of advanced controllers MSc Report 013CE2005 Control Laboratory University of Twente May 2005 Kleijn C Ontwerp Demo Opstelling internal rapport Controllab Products B V Enschede 2003 Maxon motor datasheet Maxon RE35 no 118777 http www maxonmotor com Maxon motor amplifier datasheet Maxon ADS50 5 no 145391 http www maxonmotor com Rail SKF Miniature Profile Rail Guides SKF Mini Profielrail pdf http www linearmotion skf com Timing Belts Berg Manufacturing Berg TB7EF2 400 pdf Control Engineering
58. s to left e The slider activates the left end stop e The status information of the left end stop has changed to active on the controller The left position of the slider 1s saved Move the slider to the right The slider moves right The slider activates the right end stop The status information of the right end stop 1s available on the controller e The controller calculates the distance between the end stops Move the slider to the center e Calculate the center of the rail e Move the slider to the center Optional The position detector detects the e The slider uses the fixed marker as reference marker in one of above sequences e The slider moves to the marker 4 3 4 Other tests Power consumption Action Expected result Connect the PCB to a 5 V power e The PCB is ready and one direction LED is on supply together with a current meter University of Twente Realization and testing 21 Measure the current consumption of the PCB e The current is 100 mA or less Status LED Server Online Test the Server Online LED Action Expected result Switch on the Server Online LED e The Server Online LED is on Switch off the Server Online LED e The Server Online LED is off Status LED Model Started Test the Model Started LED Action Expected result Switch
59. t Positiono position offset Move center The homing has finished The slider is at Positiong Figure 8 Homing operation The offset of the marker to the middle of the rail can be calculated to initialize the position at 0 when the slider is in the middle between the end stops 3 2 Block diagram Figure 9 shows a block diagram of the wanted end switch implementation Two parts of the block diagram are obviously the motor and the power amplifier The motor amplifier is the current source for the motor Further the block diagram contains a short circuit block This short circuit block 1s inserted to connect the two terminals of the motor together with a low resistant conductor when the motor amplifier is disabled So when an end stop is activated the amplifier has to be disabled and the motor has to be short circuit The brake function of the slider has to be direction dependent This means that the slider has to be brake if and only if the end stop is activated and the slider moves in the wrong direction in the direction of the end of the rail The enable signal has to be a function of the direction of the slider University of Twente Method to improve the end stop functionality 15 The objective is that the motor only brakes when an end stop is touched and the orientation of the set point is wrong When the set point orientation is good the slider has not to be brake even if the end stop is touched
60. the slider These imperfections are improved and new functionality is implemented on a printed circuit board The motor brake is improved with a TRIAC The TRIAC short circuits the motor to decelerate faster instead of the previous disabling of the motor amplifier Further the end switches are now direction dependent allowing the slider always to move away from the end switch Furthermore the end stops are connected to the computer With this end stop information a homing operation is added This bachelor assignment has resulted in an increased end stop functionality of the mechatronic demonstrator Some recommendations are presented in this report e A software safety layer is recommended This software prevents that the slider does not touch the end stops and so it improves the solutions of some problems e Implement a slider velocity limiter is software The slider velocity has to limit to approximately 1 5 m s e Implement the detection of the marker in the homing operation because this detection is currently not implemented in the homing operation Furthermore examine the efficiency of the homing speed e Change the current timing belt for a stronger one and replace the pulleys for bearing pulleys to pre tension the belt Control Engineering ii End stops for the Mechatronic Demonstrator Samenvatting De mechatronic demonstrator is een opstelling voor studenten om theoretische aspecten van de regeltechniek te leren en
61. tion right position left 2 position left new position Position HomingOffset stop if StartStop 1 then new logic state 1 end go left if EndStop1 0 then position_left Position new_logic_state 2 end go right if EndStop2 0 then position_right Position new_logic_state 3 end go home if new_position lt 0 then new logic state 4 end home if StartStop 0 then new logic state 0 end new logic state 0 Figure 33 20SIM code of the State Machine sub model University of Twente Appendices 43 State EnableHoming NG A HomingAction i didt SVF ef S a 1 o i h Cr s a z gt Constant2 Figure 34 20SIM sub model Homing parameters real homingVelocity 0 1 m s 2 cm seconds homing velocity 0 is not active 1 is going left 2 is going right 3 is going home 4 is at home initialequations output 0 code logic state equations switch case switch State case 0 do output 0 case 1 do output homingVelocity case 2 do output homingVelocity case 3 do output homingVelocity case 4 do output 0 default do output 0 end Figure 35 20SIM code of the sub model HomingOperation parameters real side 0 435 m initialequations EndStopl 1 EndStop2 1 equations EndStopl

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