A software solution for mechanical change measurement
Contents
1. Angular speed 1 RPM 1000 60 n msec Pulse counting N MA pulses sec pulses min left A2 B2 gt NS igh movement movement RPM RPM RPMpr RPM U Arp A Calculate movement parameters SaaS Se Direction false Direction true Signalisation of direction Signalisation of direction Direction Fig 16 Angular displacement and velocity measurement algorithm R millisecond timer value millisecond timer value ee Se ee L A S True Y Ey 4 Ex oi E z KY Es D A J False ao oOo True Fig 18 Main program algorithm gosesssss Based on this algorithm the virtual instrument is built and the block diagram is shown in Fig 19 Acquisition is executed in two sequences and the program begins with reset of the local variable CTR and timing setting that will be used to define the graphical representation of X signal for the Channel A respectively Channel B graphical indicators Fig 17 Algorithm implementation by virtual instrumentation ISSN 1109 2734 752 Issue 12 Volume 9 December 2010 WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS ka DAC Assistant Channel A error aut task out r error in stop iT t timeout is ls SELECT CI Cnt Edges iil Counter U32 15amp Nicolae Patrascoiu Aron Poanta Adrian Tomus Bogdan Sochirca Cr a ANGULAR DISPLACEMENT a gt PULSES NUMBER SEE Ib K message warnings C2. 5 Conclusion Using of this virtual instrument has a very high interest for data acquisition systems that do not accept at their counters signals provided by quadrature encoder and these systems are used to measure displacements or angular velocities Testing the functionality of the system was realized for direction displayed and also for measuring displacements and angular velocities Tests were performed using quadrature encoders with 4 200 E6A2 CWSC respectively 500 HEDS 5500 pulses per revolution for a wide range of speeds connected to digital inputs of the PCI 6024E data acquisition board from which were used the two counters ctrl and ctr0 The solution presented can be applied to any data acquisition boards which no accept to their input signals in quadrature but have a FPGAs chip embedded that make possible to implement the logic functions 1 and the algorithms shown in Fig 16 and Fig 18 Also the same software solution can be implemented in an 8 bit microcontroller even making it possible to connect directly a quadrature encoder for local control of processes where there are rotation or translation movements References 1 M Series User Manual National Instruments Corporation 371022F 01 april 2006 2 Reconfigurable I O Devices for PCI PXI CompactPCI Bus Computers National Instruments Corporation 370489B 01 april 2004 3 Quadrature Encoder Velocity and Acceleration Estimation wit
3. Variables derivate from this are position distance or proximity The measure of these quantities is represented by displacement against a reference In many applications the displacement is considered as a vector so it is necessary to calculate both size and direction for this variable Usual procedure for calculating the size of the displacement is to use an incremental sensor that generates a pulse train so by counting these pulses a number that represent the size of the displacement is generated Considering the physical relationship between displacement and velocity by determining the size of displacement using an incremental sensor methods for determining the size of velocity are obtained Most used methods are based on measurement of elapsed time between successive pulses or counting the number of pulses during the prescribed time Like in the displacement case the velocity also should be considered a vector so it is necessary to determine the value and the direction of movement Same incremental sensor can be used to detect the direction of movement if it provides two trains of pulses shifted by one quarter of the period in which case it is named quadrature encoder A quadrature encoder can have up to three channels channels A B and Z ISSN 1109 2734 746 2 Connecting quadrature encoders to data acquisition board There are data acquisition boards DAQ such as the NI 622x NI 625x NI 628x M series devices or
4. inputs DIOO respectively DIO1 Thus the two components will ISSN 1109 2734 750 Nicolae Patrascoiu Aron Poanta Adrian Tomus Bogdan Sochirca Counting Selection Logical diagram of the Counting Selection function be the inputs Channel A and Channel B of the system developed used to determine the direction of displacement The system generates the output signal named Counting Selection In Fig 13 the structure of this system is shown built with logical functions based on the logical diagram presented in Fig 7 Compound Arithmetic Logic functions are used through which we can select basic arithmetic or logic operations with two or more input variables To observe two signals two waveform chart indicators are used For these charts Property Nodes were created through which it is achieved an offset scaling and history for time axis 12 In Fig 14 is shown the front panel for the two situations corresponding to two states of operation for the virtual instrument We can observe in Fig 14 two screen captures that the direction is determined by the order of movement succession of the two trains of pulses Channel A and Channel B which means the phase shifts between them 4 Angular displacement and velocity measurement Determination of displacement is achieved by counting the increments that corresponds to the slots of incremental encoder They are expressed in degrees and the value of an increments for angula
5. 786 805 14 H K Jafari Design and Implementation of DC Motor Speed Controller Using Fuzzy Adaptive Controllers WSEAS Transactions on Circuits and Systems Vol 7 April 2008 pp 203 212 15 Patrascoiu N Poanta A Tomus A Sochirca B Detection of motion direction implemented by virtual instrumentation Recent Advanced in Automation amp Information WSEAS Proceeding ICAP 10 72 75 16 Patrascoiu N Poanta A Tomus A Sochirca B A software solution for displacement and angular speed measurement through virtual instrumentation Applied Computing Conference WSEAS Proceeding ACC 10 11 15 17 A Valachi M Timis M Danubianu Some Contributions to Synthesis and Implementation of Multifunctional Registers 2nd WSEAS International Conference on Multivariate Analysis and its Application in Science and Engineering pp 146 149 8 Issue 12 Volume 9 December 2010
6. NI USB6211 that have direct support for quadrature encoder measurements so that these devices accept at their input counters signals provided by quadrature encoder Values counter increases or decreases depending on the relative time of occurrence of the two trains of pulses So when channel A Ch A leads channel B Ch B in a quadrature cycle the counter increments and when channel B leads channel A in the same quadrature cycle the counter decrements The amount of increments and decrements per cycle depends on the type of encoding X1 X2 or X4 Fig 1 shows a quadrature cycle and the resulting increments and decrements for X1 encoding When channel A leads channel B the increment occurs on the rising edge of channel A When channel B leads channel A the decrement occurs on the falling edge of channel A 1 Fig 1 The input signals for data acquisition board With an M Series board for these signals can be used any PFI line for any of the encoder output To select the desired PFI line it can be use a channel property node In order to connect signals it can use the configuration presented in Table 1 where ctrO and ctrl Issue 12 Volume 9 December 2010 WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS are the two counters and PFIxx are programmable function terminals configured as inputs by default 1 Table 1 Ch A Input ChB Input Z Input PFI8 PFI10 PFI9 Another way to connect and use quadrature encoders with a data
7. WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Nicolae Patrascoiu Aron Poanta Adrian Tomus Bogdan Sochirca A software solution for mechanical change measurement through virtual instrumentation NICOLAE PATRASCOIU ARON POANTA ADRIAN TOMUS BOGDAN SOCHIRCA Automatics Applied Informatics and Computers Engineering University of Petrosani Universitatii 20 332006 Petrosani ROMANIA patrascoiu upet ro http ime upet ro caiac index html Abstract This paper presents a software solution for implementing a method to measure a displacement and angular speed for a mobile that is moving in a linear or circular direction In order to achieve this we determine a function for sensing the direction of movement and also we propose the algorithm through which is made the measurement In order to implement this we use a instrument built in LabVIEW By this algorithm is possible to use a data acquisition boards for general use such as PCI 6024E which has no inputs for quadrature signals with a quadrature encoder such as E6A2 CW5C Omron or HEDS 5500 Avago Technologies that generates this type of signals Key Words quadrature encoder data acquisition board algorithm virtual instrument measurement 1 Introduction Movement is defined as a physical quantity of a mechanical change through which is possible to provide information about position of a material point or mobile that is moving on linear or circular trajectory against a reference system
8. acquisition board is to use data acquisition systems using reconfigurable I O such as PCI 7831R and PXI 7831R or other systems in this class R series devices 2 These data acquisition boards are based on a reconfigurable FPGA core surrounded by fixed I O resources for analog and digital input and output It can configure the behavior of the reconfigurable core to match the requirements of the measurement and control system and it can implement this user defined behavior as an FPGA application to create an application specific I O device Thus it is possible to use only two digital inputs properly configured to take appropriate signals channel A and channel B from a quadrature encoder Fig 2 below shows digital input channels DIO and DII selected for quadrature encoder inputs A and B respectively and also an example of using FPGA functions in LabVIEW to retrieve information from displacement and velocity 3 gt Configure Digital Input Alias Defaut in Italics A Connector I DIOP w LIDIO H Connector 1 DIC react r 37 Connector Dic General Arbitration cRIO Configuration IO Synchronization Terminal Connector 1 DIO0 v gt Addinput Delete input Fig 2 Using quadrature encoder with FPGA functions There are also data acquisition boards which have no specific inputs for quadrature signals or reconfigurable digital inputs like the NI PCI 6024 E series devices In this case it is necessary to
9. bles 1 e x and x2 ee COI 0 Sy Ss Sy pt Sg Ss Si Fig 9 Encoding reduced states Counting Selection ISSN 1109 2734 749 Nicolae Patrascoiu Aron Poanta Adrian Tomus Bogdan Sochirca In order to eliminate the hazard which can occurs due to simultaneous change of more than one input variable during transition between two states the Gray code is used The matrix that represents the encoding of reduced states is shown in Fig 9 To construct the state functions x and x it is necessary to build matrices of transition for reduced states and matrix number must be equal to the number of state variables These matrices are shown in Fig 10 in which notation x means states impossible during operation E ofo fi J 10 Counting Selection Counting Selection Fig 10 State transition matrix for x and x2 Applying the method of synthesis of logical functions based on Karnaugh diagrams the logical functions of the state variables x x respectively it can identified for function of output signal Counting Selection as follows X B x A B x Bex x PAY XY Xo 1 X2 X Xo A x B x Counting Selection x From equations 1 it can be seen that the output signal is identical to the state x2 which simplifies implementation with logic gates for the scheme that generates the control signal for counting direction Based on logical functions 1 a logical diagram of the system
10. build a logical system that detects the direction of motion and also increments or decrements a counting value depending on the direction of movement Such a system can be achieved through hardware structure but also can be done by a ISSN 1109 2734 147 Nicolae Patrascoiu Aron Poanta Adrian Tomus Bogdan Sochirca software solution using digital inputs and counters on the data acquisition board The E series devices with diagram bloc shown in Fig 3 use the National Instruments DAQ STC system timing controller for time related functions The DAQ STC consists of three timing groups that control analog input analog output and general purpose counter timer functions These groups include a total of seven 24 bit and three 16 bit counters and a maximum timing resolution of 50 ns The DAQ STC makes possible such applications as buffered pulse generation equivalent time sampling and seamless changing of the sampling rate 4 Data 16 Son fpuration Momay onnmector WOC i i i Anaka pal miem k Ei i Timing Tomra Reguesi A FPCMCIA Connector a ee O Ma it ai aA Counter Bus a Timing o DA0 sTC interlace jaa Digital kO l Analog Output ATS Bus hee i Timingi Conrad interlace aa a ul aleg eppi i drah i Domina J DAG PCMCIA STE J anh p Albiar s g ts Fig 3 DAQ PCI 6024E Block Diagram If the hardware solution will be chosen specialized circuits
11. can be created shown in Fig 11 Through this system we can make a selection for direction of counting Checking the correctness of system operation was achieved by simulation using Multisim program from National Instruments 11 Based on simulation results presented in Fig 12 we can observe that selection signal changes logical levels according to the direction of rotation given by the Issue 12 Volume 9 December 2010 WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Fig 12 Simulation results sequence of pulse trains Channel A respectively Channel B 3 2 Counting Selection function implemented in LabVIEW A program developed in LabVIEW is called a virtual instrument VI and it has two components the block diagram that represents the program itself and the front panel that is the user interface Through such a virtual instrument we can control the operation of the data acquisition board PCI 6024 whose digital inputs DIOO and DIO1 are used for acquisition of Channel A and Channel B signals from quadrature encoder In order to implement a virtual instrument DAQ Assistant function is used for creating editing and running tasks NI DAQmx function represents a data acquisition driver Through this function is read an array with eight boolean components corresponding to the eight digital inputs of the data acquisition board Through Index Array function are selected components with index 0 and 1 that correspond to digital
12. chosen by convention for the values of movement to the left and Issue 12 Volume 9 December 2010 WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS SIGNAL Channel 4 Channel 4 Nicolae Patrascoiu Aron Poanta Adrian Tomus Bogdan Sochirca MEASUREMENT DIRECTION ANGULAR SPEED ANGULAR DISPLACEMENT PULSES NUMBER 95 MEASUREMENT DIRECTION ANGULAR SPEED ANGULAR DISPLACEMENT PULSES NUMBER 86 Fig 20 User interface of the virtual instrument the sign is chosen for the values of movement to the right Experiments with this virtual instrument whose results are shown in Fig 20 were performed with an incremental encoder with 4 slots which means 4 pulses per revolution n 4 As we can see in the case of movement to the left by the N 95 pulses counting is obtained angular displacement a a degree LL ee ee 3 n 4 ISSN 1109 2734 754 1 99 The sign which appears before the displacement value is obtained by downward counting of pulses and corresponds to the convention mentioned above Also in the case of movement to the right by the N 86 pulses counting is obtained an angular displacement a 3600 3600 a degree N 86 7440 4 n The sign in this case is and is obtained by upwards counting of pulses and corresponds to movement in the right the same convention Issue 12 Volume 9 December 2010 WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS
13. constant 2 and the value of N representing the output of function DAQm x Read Counter U32 1CH 1Samp Based on ISSN 1109 2734 753 this pulses number is calculated the displacement and angular speed values 16 Clockwise motion is considered to be displayed with a positive sign and counterclockwise motion is considered to be displayed with a negative one This convention requires continuous tracking of the value of the two counters The continuous tracking is achieved by using local variable CTR whose value is loaded into each of the two counters selected according counting sense through the input parameter initial count of the DAQm x Create Virtual Channel function Displaying number of pulses and calculating the displacement and angular speed based on the relation between the direction of motion and sign of these dimensions is achieved through a Case structure Selection of the two cases is done through the comparison between the value N that represents the output of the function DAQmx Read and constant 10 considered to be cover for measurements made under the following conditions measurement time for one direction of displacement about 33 minutes n 200 slots and maximum speed 1500 revolutions per minute In Fig 20 we can observe screen captures of the front panel which is also the user interface corresponding to two states of operation for the virtual instrument for the two directions of movement The sign is
14. e the duration of speed pulse increases with decreasing measurement accuracy at low speed The algorithm used for the measure of the angular displacement and velocity is shown in Fig 16 The implementation of this algorithm by a virtual instrument called RPM that is a SubVI in the main program is shown in Fig 17 Value of angular velocity expressed in revolutions per minute RPM is calculated with relation 2 speed this method has poor Issue 12 Volume 9 December 2010 Nicolae Patrascoiu Aron Poanta WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Adrian Tomus Bogdan Sochirca Getting prescribed time necessary for calculating speed is achieved by using function Tick Count msec ee 1 N 4000 60 that returns the timer value in milliseconds between n 1 msec consecutive loops in the While Loop n 2 pulses sec pulses min 4 1 System Implementation with Virtual Instrument The main program algorithm is shown in Fig 18 and where n represents the number of pulses corresponding this includes SubVI s SELECT and RPM We use a to one complete revolution and N represents the While Loop structure that ensures the continuous counting pulses running of the program until the user stop it through the STOP button CTR 0 Real time read Number of pulses N 0 PTO an Left Right Angular displacement aered y Select Select n Counter ctrl Counter ctr0 Count Down Count Up B gt false B true CTR 2 N CTR N
15. for signal conditioning may be used For example the LS7084 quadrature clock converter from LSI Computer Systems Inc converts the A and B signals from an encoder into a clock signal and up down signal that can connect directly to the data acquisition board The LS7084 includes lowpass filters to prevent miscounts due to noise and jitter In addition the LS7804 uses dual one shots to prevent the miscounting produced by vibration or dither In accordance with circuit operation the CLK output when in X4 mode will pulse once for every transition of either the A or B signals 5 The UP DOWN output indicates the direction of rotation It can connect the A and B signals from a quadrature encoder directly to the LS7084 and Quadrature encoder Fig 4 Encoder connection to DAQ STC using LS7084 clock converter circuit Issue 12 Volume 9 December 2010 WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS connect the CLK and UP DOWN outputs directly to the SOURCE and UP_DOWN inputs of the DAQ STC Fig 4 illustrates the connections of the encoder to the data acquisition board using a LS7084 quadrature clock converter 3 Direction of motion detection implemented by software As was mentioned above to determine either linear or angular motion is first necessary to find its direction After that we can control the counting direction of the counter The value of the displacement is determined by counting the train of pulses To measure the a
16. gdan Sochirca pulse trains according to the direction of rotation Following the signals chart presented in Fig 5 8 distinct states denoted by Si i 0 7 can be identified corresponding to 8 possible combinations of logic levels for both Channel A and Channel B signals and output signal Counting Selection Based on this signals chart it is built the states transition graph presented in Fig 6 The transition graph consists by nodes which Fig 6 Transition graph of states represent the 8 states previously identified and arcs which represent binary combinations of both Channel A and Channel B signals through which is made the transition between states Each node is characterized by the logical level of the signal Counting Selection and has an arc with logical combination of both Channel A and Channel B signals for which the status for state of respectively node does not change Based on the transition graph it is built the primitive matrix that contains on the columns the correlation between combination of the input signals Channel A and Channel B and at least one stable state The rows contain all possible transitions from one internal stable state This is accompanied by a full matrix of the output that contains the values of output variable during both states and Ghannel A So S1 S2 S354 S4 S2 S384 S5 Se S7So Ss Se S7So S4 S25354 S1S251 S4 S5 S657 So S5 S655 So Si Se S S Fig 5 Signals chart that identify
17. h CompactRIO and LabVIEW FPGA National Instruments Corporation http zone ni com devzone cda tut p id 3921 may 2010 4 6023E 6024E 6025E User Manual National Instruments Corporation Austin Texas 2000 5 LS7083 7084 Quadrature Clock Converter Datasheet LSI Computer Systems Inc October 2000 6 Webster G J The measurement Instrumentation and Sensors Handbook CRC Press LLC 2000 ISSN 1109 2734 Nicolae Patrascoiu Aron Poanta Adrian Tomus Bogdan Sochirca 7 D M Purcaru E Niculescu I Purcaru Measuring Method for Computerized Study of Rotary Incremental Encoders WSEAS Transactions on Electronics Vol 3 2006 pp 349 355 D M Purcaru E Niculescu I Purcaru Experimental Measuring System with Rotary Incremental Encoder in WSEAS Transactions On Advances In Engineering Education Volume 4 September 2007 pp 180 186 9 Carroll J Long D Theory of Finite Automata Prentice Hall New Jersey 1989 10 Poanta A Patrascoiu N Circuite si echipamenete electronice in industrie Ed Didactica si Pedagogica Bucuresti 1997 11 Multisim User Manual National Instruments Corporation Austin Texas 2008 12 Patrascoiu N Sisteme de achizitie si prelucrare a datelor Instrumentatie Virtuala Ed Didactica si Pedagogica Bucuresti 2004 13 Yuhua L Fengshou G and others The measurement of instantaneous angular speed Mechanical Systems and Signal Processing 19 2005
18. hannel B TF Waveform Chart sein inienn aaseista i DAC Assishant2 error out task out r error in stop iT F timeoutis Fig 19 Diagram bloc of the virtual instrument The input signals Channel A and Channel B are taken from the incremental sensor by line 1 and line 0 of the digital port O port of the data acquisition board PCI 6024E using DAQ Assistant function As we mentioned above the direction is selected through Counting Selection signal 15 Once direction is selected this it will be displayed on the front panel The selection signal is also used for selecting the direction of counting Count Up or Count Down by applying it to the selection terminal of the Case structure Through this structure we can also select one of the counters ctr or ctrO so that the counting upwards is performed by counter ctrO and counting downwards is performed by counter ctr For the two counters ctr and ctrO counting values may increase Count Up when their value increases with each pulse applied to the entry CtriSource i O or I in domain 0 2 16777216 or may decrease Count Down when its value decreases with each pulse applied to the entry CtriSource i O or 1 in domain 2 16777216 0 If it detects a number N higher than 10 counter ctrO is considered selected and counting is carried downwards since 2 which represent the maximum counter value Number of pulses is obtained by the difference between
19. ngular displacement and velocity we use PCI 6024E a data acquisition board from National Instruments that has 8 digital I O DIOO DIO7 lines TTL CMOS and two 24 bit counter timers without having the dedicated inputs to connect a quadrature encoder Other main features of this data acquisition boards are 16 channels of analog input two channels of analog output a 68 pin connector and eight lines of digital I O Control of the operation of data acquisition boards is achieved through a program written in LabVIEW graphical programming language and called a virtual instrument To achieve the determination of displacement direction is necessary in these conditions to use two digital inputs to connect the A and B signals carried from the quadrature encoder Displacement value is obtained by counting the pulses A or B and its direction is necessary for counting sense determination otherwise said for increment or decrement the counter value 6 To realize the virtual instrument for angular displacement and velocity measurement based on two trains of pulses shifted by one quarter of period is necessary to synthesize a control command for counting direction 7 8 3 1 Generating the counting direction control signal For synthesizing the command control signal called Counting Selection is considered a signals chart Fig 5 that identifies all the possibilities of combining the two Nicolae Patrascoiu Aron Poanta Adrian Tomus Bo
20. r displacement correspond to the relation between the angle at the center of the circle and the number of slots Angular velocity measurement is based on counting pulses during the prescribed time 13 14 The basic measuring process of pulse during a prescribed time method is shown in Fig 15 Issue 12 Volume 9 December 2010 WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS Channel 4 SNO es 7 Scale Offset Pe Scale Minimum eScale Maximum DAQ Assistant i Kaini iia i ii A n a ai a i E Fig 13 Diagram bloc of the virtual instrument Start counting time Fig 14 Front panel corresponding to the displacement in right and left direction ISSN 1109 2734 751 Fe hts qe 3 E l Prescribed time Nicolae Patrascoiu Aron Poanta Adrian Tomus Bogdan Sochirca Channel B E Direction of displacement Stop counting Start Stop 1 counting counting Prescribed time Fig 15 Pulse counting during prescribed time The duration of a measurement cycle is fixed and set a priori The speed pulse counter and the timer are both started at a rising edge of the speed pulse The pulse counter is stopped when the timer runs to the end of the prescribed time The angular velocity is then derived from the content of the pulse counter and the prescribed This method can result in a loss of up to one speed pulse Becaus
21. the direction of displacement ISSN 1109 2734 748 Issue 12 Volume 9 December 2010 WSEAS TRANSACTIONS on CIRCUITS and SYSTEMS transitions Number of columns is M 2 where m is the number of input variables and in this case m 2 then M 4 columns Columns are cyclic coded so that from one column to another more than one input variable does not change and therefore Gray code is used Primitive matrix of states is presented in Fig 7 48 00 01 11 10 So So Ss Si pS Sa S Sr ee eee Counting Selection a ee ee oo Se Sg Ss Si Ss So Ss So p Se Ss So Sy LS So Sy Fig 7 Primitive matrix of states and output To identify a minimal configuration of the sequentially system a reduced matrix of states is built The technique used to reduce the number of states from primitive matrix 1s based only on the equivalence from the theory of sequential automatic and reduction of state is made through merger or annexation in compliance with specific rules 9 10 Applying these rules the reduced matrix of states will be obtain and the corresponding output shown in Fig 8 ere p Sa Sa Ss fT Si Fig 8 Reduced matrix of states and output To obtain the state functions of the sequentially system is required to encode the reduced matrix states We can observe the existence of 4 reduced states so that would be necessary to encrypt them by two state varia
Download Pdf Manuals
Related Search