SERVOSTAR S- and CD-series Sine Encoder Feedback
Contents
1. 8 SV Supply Return DC Com 5V Supply Return DC Com 5V Supply Return DC Com Hall A Colector C Channel Low e Ee a E 15 MarkerHigh i MarkerHigh i 16 MarkerLow l MarkerLow t S Data a5 A Crawiainigh 6 eos U eC e e e a Table 2 Drive Connections Several Power Supply Connections are Available Document Number P SS 001 13 Rev 4 Old Numbers ASS00120101 ASU009H Revised 11 20 2003 www DanaherMotion com Page 7 Specifications CB or SB Designator Parameter Units Value Comments Maximum Input Hz 125 k Maximum Sinusoidal Input Frequency representing a Frequency maximum data rate of 128 MHZ Nominal Single ended volt peak 0 5 per 1 Volt Differential Signal Amplitude to peak signal Nominal DC Offset per VDC 2 5 Channel Minimum Differential V 0 5 An A B Out Of Range Fault occurs when the input falls Input Voltage below this value Maximum Differential V 1 15 Analog amplifiers begin to clip causing read inaccuracies Input Voltage Absolute Maximum V 1 2 A voltage at any input channel with respect to DC Differential Input Common causes the drive to detect a broken wire Voltage Maximum Input Count 256x 4x The internal counts of the drive is 1024 Sine periods per Interpolation Factor Sinus period revolution Maximum Encoder Lines 128x Encoder Equivalent Output Signal is Incremental Pulses Equivalent Output Interpolation Factor Maximum Encoder MHz 2 5 Designe2. When these signals are presented to a differential receiver the resulting waveform is 1 V peak to peak riding on 0 VDC These signals are sampled with analog to digital converters every 1 6 us The resultant digital words are handled with digital electronics FPGA providing arithmetic processing to decode the interpolated position The resulting position word is fed to internal capture registers for use in the control algorithms and to an accumulator that outputs the Encoder Equivalent output signal for the user There is a limit to the amount of position change that is allowed in each 1 6 us that establishes the 125 kHz input frequency limit 2 5 VDC at 500 mVp p A Sine Encoder 5120 Input A f 0 VDCat 1 Vp p gt control circuit uadratur go es Quadrature Lp Decode x4 Quadrature Encoder Equivalent x SININOUT ag ER Output to SERVOSTAR Figure 1 Equivalent Circuit and Diagram The x256 box shown in the diagram can actually be made to a lesser multiply if required by the user by adjusting the MSININT variable See EnDat below The encoder equivalent output is scaled according to the SININTOUT variable to allow reduction in the output resolution to keep the output frequency within limits after considering maximum system speed The encoder equivalent output circuit immediately begins to reduce the accumulator value by outputting pulses while limiting the max
3. IR loss of the power supply which should be no smaller than 18 AWG Power supply tolerance must be considered in the voltage loss calculations Maximum Cable Lengths for IR Loss 250 200 450 Maximum Cable Length w Single 18AWG 5 100 Pair T Maimm Cable Length w Dual 18AWG 50 Pair 0 3 g 8 8 Current mA Encoder Equivalent Output The Encoder Equivalent Output supplied by the SERVOSTAR drive is converted from sinus signals to incremental pulses The SININTOUT and ENCOUT variables can adjust the resolution of the encoder equivalent output The value is determined by the read only variable ENCOUT ENCOUT is determined by ENCOUT MENCRES SININTOUT ENCOUTO Recognizing that users will attach the encoder output port to equipment incapable of receiving such high data rates an error detection system is provided The MSINFRQ variable can be set to fault the system should the drive be required to send out pulses higher than the limit set by this variable This variable can also be set to ignore overflows but be careful as pulses may be lost Document Number P SS 001 13 Rev 4 Old Numbers ASS00120101 ASU009H Revised 11 20 2003 www DanaherMotion com Page 5 Frequency Limitations The sinus inputs to the SERVOSTAR must not exceed 125 kHz The encoder equivalent output to the user is limited to 2 5 MHz quadrature encoded or 10 MHz data rate but the user should
4. have fallen out of the specified range of a minimum 0 5 volts minimum peak to peak and 1 15 volts maximum peak to peak This can be the result of a loss of a single channel loss of a single differential line signal degradation excessive DC Offset or excessive phase shift in one channel Theoretically a scope plot with the A channel on the x axis and the B channel on the y axis produces a circle with a radius of 0 5 volts 1 2 the peak to peak voltage Any portion of this circle collapsing less than 0 25 volts causes this error r9 Burst Overflow Error 4 9 This code means the Encoder Equivalent Output accumulator has overflowed and pulses are lost It is possible to change the action of this fault using the MSINFRQ variable Document Number P SS 001 13 Rev 4 Old Numbers ASS00120101 ASU009H Revised 11 20 2003 www DanaherMotion com Page 6 r10 Endat Communication Fault This code means serial communication to the Endat Encoder has failed The drive makes several attempts before aborting to this error Drive Connections SERVOSTAR Sine Encoders with Sine Encoder with C2 Connection Marker and Open Marker and C D EnDat Encoders rn nes Sannes oo 1 Sine High A Sine High A Sine High A 2 SineLow A Sine Low 1A Sine Low is 4 Cosinehign B Cosine High B Cosine High B 5 CosineLow B Cosine Low B CosineLow B 7 5V Supply Return DC Com 5V Supply Return DC Com 5V Supply Return DC Com
5. MENCTYPE 7 and systems not using a marker channel MENCTYPE 8 The information in the SERVOSTAR S and CD User Manual provides data on use with a marker channel and the MENCOFF variable The actual hardware read position of these signals is returned by the HWPOS command used while the drive is in ZERO mode see ZERO The variable MPHASE is available as a software offset for these channels Document Number P SS 001 13 Rev 4 Old Numbers ASS00120101 ASU009H Revised 11 20 2003 www DanaherMotion com Page 3 Incremental with EnDat EnDat is a trademark of Heidenhain Corporation and refers to a method of serial communication to several of their encoder product offerings associated with absolute position encoders These devices remember where they are through power cycle The SERVOSTAR uses the EnDat MENCTYPE 9 communication channel to automatically query power up position from the encoder These encoders have internal non volatile memory used by the drive to store offset values The HSAVE command causes the MPHASE ZPOS and PFBOFF variables to be saved in the encoder The memory is read back at power up or during a LOAD command execution The command HWPOS is provided to allow querying of the encoder s absolute position not interpolated directly from the encoder as defined by Heidenhain s EnDAT specification PFBOFF allows the user to conveniently offset a machine home or zero The multi turn versions of EnDat encoders are capabl
6. ammable ZPOS variable When the two are equal an index pulse is output The user can adjust the actual physical location of the index pulse by varying the ZPOS parameter Range checking of the ZPOS parameter is not done so the user must enter a reasonable value negative numbers are allowed The ZPOS variable can be changed on the fly The actual functional range is 0 to MENCRES MSININTOUT units are Encoder Output Lines and the default value is 0 The pulse width of the marker is 90 of the Encoder Equivalent Output pulse signal The ENCOUT value has no effect on this function While ENCOUT may be changed the marker pulse width is unaffected Document Number P SS 001 13 Rev 4 Old Numbers ASS00120101 ASU009H Revised 11 20 2003 www DanaherMotion com Page 4 Cable Limitations The Sine Encoder transmits analog signals of 1 volt peak to peak to the SERVOSTAR drive These signals are subject to noise induction if not carefully installed Cables must have twisted pairs with an overall shield The shields should be tied to earth at both ends of the cable The cable should be routed in a clean conduit free of motor armature cables and other noise sources As with any feedback device cable capacitance should be kept low no more than 47 pF per foot IR loss total capacitance and noise susceptibility largely limit cable lengths It is best to keep these cables short less than 50 ft Actual wire gage requirements are driven by the
7. d to 1 25 MHz to allow sufficient room for overshoot Equivalent Output MSINFRQ can be set to trigger a Burst Overflow fault if Frequency this value is exceeded Maximum Encoder Equivalent Output Data Rate Minimum Edge ns 100 200 Selectable with MSINFRQ 10 Separation of Encoder 400 800 Equivalent Output Channel Relative Accuracy Electrical 3 5 Interpolation Accuracy of one Sine Wave Cycle or 1 Degrees percent Encoder Supply Voltage V 5 2 SERVOSTAR Supply to Encoder 250 mA Max Differential Input Ohms 120 Impedance gt is aregistered trade name of Heidenhain Corporation Quadrature Encoded Pulses equate to 4x data rate at receiver electronics Some encoder manufactures output C and D channels with 1 V peak to peak Signals referenced to a 2 5 VDC offset instead of 2 500 mV differential channels These signals are acceptable to the SERVOSTAR as the receiver electronics still decode this differential signal as a 1V peak to peak waveform References Please refer to the SERVOSTAR S and CD Setup and Reference Guide for current syntax and related information on the variables and commands VER MSININT SININTOUT MENCTYPE MENCRES MSINFRQ MENCOFF MPHASE ENCOUT ENCOUTO PFBOFF HWPOS ZPOS HSAVE ZERO Document Number P SS 001 13 Rev 4 Old Numbers ASS00120101 ASU009H Revised 11 20 2003 www DanaherMotion com Page 8
8. e of knowing where they are out to 4096 revolutions 12 bit Some versions have 2048 sine wave when decoded providing 21 bit resolution The total result is 33 bits of data The SERVOSTAR position loop operates on 32 bit signed data For systems using full turns data from the encoder system resolution must be reduced using the MSININT variable set to 128 or 64 depending on the use of the sign bit of the 32 bit position word MSININT 256 32 Word Justification for Maximum Resolution MSININT 128 32 aa caescescesees 1 0 Justification for Max Turns Bi directional MSININT 64 EJZ ssinivesene sess 2 1 0 Justification for Max Turns Unidirectional EnDat Encoders do not have an index pulse integral to the encoder but systems often require an index pulse for an accurate homing process especially when applying a single turn EnDat encoder to a multi turn system An index pulse is created by the SERVOSTAR drive for the encoder equivalent output port by doing a position compare modulo Encoder Equivalent Output counts per revolution The compare value is programmable via the ZPOS variable stored in encoder memory This feature is available only with MENCTYPE 9 EnDat Encoders The system reads the EnDat absolute position adds the sine interpolated value adjusted by MSININT and adjusts to SININTOUT units and uses this value as the initial value for the encoder equivalent output as the reference compared to the user s progr
9. ifferent encoder types In its crudest form a power up poling sequence can be used This requires motor motion and is subject to commutation errors and limits on stiction and inertia While the SERVOSTAR does support this method it is not recommended More information is contained in the VarCom document The SERVOSTAR is able to receive many types of auxiliary signals from many different types of encoders for this power up position information These auxiliary signals give the SERVOSTAR information to begin commutation at power up Incremental with Hall Effect Sensors Hall channels provide coarse information about the motor position and are used only at power up to determine enough information to begin motor commutation More information can be found about this type of operation in the SERVOSTAR S and CD User Manual A description of use with and without marker channels is described MENCTYPES 0 and 6 There are no anomalies to this operation when using a sine encoder Incremental with C amp D lines C amp D channels reference sine encoders that provide an auxiliary commutation track They are typically two channels equivalent to the A and B channels but have only one sine wave per mechanical revolution The SERVOSTAR uses the same interpolation method on these channels to provide commutation information at power up to part in 1024 The SERVOSTAR performs this operation automatically Support is provided for systems using a marker channel
10. imum frequency to 2 5 MHz or less depending on the value MSINFRQ Systems like this inherently distort the encoder output quadrate encoding If the accumulator gets more than 1 count per 1 6 us it outputs the signals at 2 5 MHz which can distort the 90 edge separation This is normally not a problem but is worth noting and another reason to keep the design limit to 1 25 MHz Document Number P SS 001 13 Rev 4 Old Numbers ASS00120101 ASU009H Revised 11 20 2003 www DanaherMotion com Page 2 Some receiver circuits in user controllers have digital filtering that attempt to discriminate the small edge separation as noise resulting in pulse loss The FPGA has a small accumulator to allow for pulse storage beyond the 2 5 MHz If this buffer overflows an error is generated and encoder equivalent pulses from the output port are lost Accuracy The system accuracy is a direct function of the accuracy of the sine encoder Typical values range are 20 and 60 arc seconds The on board electronic decoder adds another 1 of one sine wave period to the total system error For example using a 2048 line encoder rated for 20 arc seconds accuracy the electronics adds another 6 5 arc seconds of inaccuracy for a total of 26 5 arc seconds Types of Sine Encoders Since all encoder signals are incremental some method of providing information about the motor s position at power up time is required Different methods for accomplishing this exist in d
11. limit it to a design maximum of 1 25 MHz to allow for overshoot The following table shows the recommended speed output frequency limitations that should be used for design SININTOUT Setting EEO Resolution Lines per Rev Encoder Resolution 128 512 1140 rpm Max 2285 rpm 4575 rpm 9150 rpm Sine Wave per Rev 65 536 LPR 32 768 LPR 16 384 LPR 8 192 LPR 2048 280 rpm Max 570 rpm 1140 rpm 2 288 rpm Sine Wave per Rev 262 144 LPR 131 072 LPR 65 536 LPR 32 768 LPR Table 1 Maximum Design Speeds vs Maximum EEO Resolution for 1 25MHz Limit Encoder Alignment Danaher Motion motors with integral encoders are factory aligned and require no adjustments Systems using encoders mounted by the customer may have the encoder aligned electrically If so the drive contains no motor specific variables regarding encoder alignment This allows each drive from machine to machine to have the same parameter set Alignment may also be done through the software variables MPHASE and MENCOFF System Fault Codes The SERVOSTAR is capable of detecting errors within the system and displaying a fault status on its 7 segment display r3 Sine Encoder Init Fail Error 4 3 This code means a hardware problem internal to the drive has been detected The system requires factory repair r7 C D Line Break Error 4 7 This code means the C and D channel decode is invalid See r8 for further details r8 A B Out of Range Error 4 8 This code means the A and B channels
12. t B combine to create a 1 volt peak to peak signal to the control electronics with good noise immunity Because the signals are separated by 90 degrees quadrature encoded the receiving electronics quadrature decode is capable of multiplying the fundamental resolution by a factor of four Through a method called interpolation the SERVOSTAR breaks down the sine wave into an additional 256 parts For every sinus encoder cycle corresponding to one line count the SERVOSTAR sine encoder cycle provides up to 1024 extra internal counts For example if a sine encoder specifies a resolution of 2048 lines per revolution its actual controllable resolution per mechanical revolution becomes a maximum of 2 097 152 2048 x 4 x 256 counts The SERVOSTAR drive uses this increased feedback resolution in both the velocity loop and the position loop controls Increased resolution in the velocity loop helps to reduce truncation and quantitization errors for reduced noise resulting in the ability to achieve higher loop gains required for large inertial loads improved stiffness and command smother current reduced system noise The increased resolution in the position loop gives the user increased repeatability and the ability to use higher loop gains with less noise Theory of Operation The incoming sine signals from the encoder are complementary presenting a single ended signal waveform of 500 mVp p riding on a 2 5 VDC carrier for each signal see Figure 1
13. www DanaherMotion com SERVOSTAR S and CD series Sine Encoder Feedback The SERVOSTAR S and SERVOSTAR CD family of drives offers the ability to accept signals from various feedback devices Sine Encoders provide analog encoded motor position data to the drive amplifier The advantage of these analog signals is that they can be resolved to extremely small intervals providing a lot of data about the motor shaft position while maintaining reasonable data transmission rates The disadvantage is that analog signals are notably susceptible to noise pickup and require good wiring installation practices A multi turn absolute position option is available to eliminate the need for machine homing after power up Application Details Sine encoders offer advantages over standard Digital encoders Because the output signal is a continuous sinusoidal waveform the drive electronics is able to break down each cycle into many sub parts or counts This increases the system s ability to position within smaller increments More importantly but not as obvious is the increased data flowing into the velocity loop compensator allowing increased system gains to overcome large load inertia while controlling current hash noise Much greater system stiffness can be achieved Resolution Sine encoders provide two incremental sinusoidal signals A and B with a phase shift of 90 Because they are differential the complementary channels A and Not A B and No
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