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At some point since 2009 the GeoBrick Default I7m03 changed from 1234 to 2257. I understand that this was for reasons of limiting either the maximum ADC or DAC frequency. I have recently used a 1A geobrick variant and selected the recommended 40kHz PWM frequency , but at this rate the ADC values as read by Mxx05 are random and range from zero to full scale, even without motor power. If I reduce the ADC clock divider from 3 to 2 this reading becomes stable , but I want to be sure I don't exceed the new maximum allowable settings. Does anyone on here know what the maximum allowable settings are for the hardware clock settings of an 8 channel 1A/3A geobrick LV running at 210MHz. ( avoiding 240 just in case we have some older hardware that predates the wait states firmware fix) Thanks in advance

16-axis MACRO CPU is using Acc24E2S to provide the PFM output. No need to use the JHW port. We have tested the CPU and the ACC24 using a TPMAC VME Ultralight, so we are confident that these parts of the system still work.

Hi Wayne If you think it is unrelated to the servo IC then we found that newer versions of the GBLV amp firmware were more prone to nC faults than previously. Careful setting of Ixx69 ( as small as practical) mitigated against these faults on respective axes. This problem was not seen in early GBLV set up files when the ECT threw away everal significant bits of integrated torque demand, but is more apparent in the newer set up's where all the bits are read. We now normally use 10,000 step per rev ( Ix71=6400) so only need Ix69 of 5 or 10. We only need to increase Ixx69 when we need to go to the high resolution microstepping ( ix71=64000 giving 100000 step per rev from 1.8° motor). Having low Ixx30 and relatively high Ixx32 also helps.

Nearly a year later. Perhaps I should come here more often. We have many such systems working here at Diamond light source. ( 600 plus axes). Tuning is the same , but different. One of the challenges is that stepper motors respond 'slower' than the servo loop of the delta tau, so what might just be normal stepper motor response can be made much worse by the 'tuning'. Similarly vibrations ( many of the above motors are only operating at 1000 steps per rev) cannot be tuned out. So what we have done in the vast majority of these cases is to add an exponential filter to the feedback. This then 'masks ' the vibrations and we can get on with normal but stepper motor specific tuning. The high pitch whining you describe is a result of the motor stalling. The PMAC than responds to the unchanging encoder feedback by increasing the demand until eventually ( maybe only a few tens of milliseconds) this frequency is in the audible range. The current is still changing in the motor making the noise, but the rotor has long since given up. As long as the motor resolution ( including any micro stepping you are using) is less than the encoder resolution ( by 2 or 4 :1 say) then you should get quite good results, unless of course ( as Curt mentions) the mechanics are introducing imperfections) . If you have spare encoder channels you could do a dual loop thing. Put the linear encoder in one channel, and use this as the position feedback, and then use the pulses as the velocity feedback. Again, when the mechanics have been sloppy we have done as Curt describes and used the pulses to give the feedback on one channel, and the encoder to do position corrections via another. In this instance our supervisory control system compares values at the end of a move and makes corrective moves if necessary. In this way we have more than doubled achievable speeds on some of our more troublesome axes.

But if you are prepared to use a Geo MACRO amplifier, you could use an Acc24EM2A and configure that to use PFM output. This requires some internal jumpers to be changed. We have done it here at Diamond Light Source to connect to amplifiers that derive the DC link by rectifying the mains input, giving me a 6A 350VDC amplifier.

But if you are prepared to use a Geo MACRO amplifier, you could use an Acc24EM2A and configure that to use PFM output. This requires some internal jumpers to be changed. We have done it here at Diamond Light Source to connect to amplifiers that derive the DC link by rectifying the mains input, giving me a 6A 350VDC amplifier.

I am sorry for Ben's dossapointment. I have commented to Charles recently that the resolver information in the GEO BRICK USER MANUAL is not as comprehensive as say the endat or SSI, especially in regard to power on and ongoing phasing. Could this oversite be addressed as soon as possibly. By the way we are successfully using resolver feedback on stepper motors in UHV high radiation environments, but as ever system wiring is a key contributor to a stable system.

In our experience ( 200 + geobrick - Lv) the current loop tuning will have a significant affect upon smoothness. Alsoi that as stepper speed approaches the const current - const volts cross over some detunuing of the loop can reduce resonances, but we have yet to make an automatic detection and detune for thsi problem. Further we have been previously advised by SINA that it is possible to set I7m04 to 0 for stepper motors ONLY, but this will only apply to units shipped after a certain date. Is this still the case ( I note his post suggests a value of 4)?

As an aside we have a couple of geoMacro drives here which don't report 'fault conditions' on the front panel led which is confusing. As yet these drives don't generate random amp faults.

As a long time user of Geobrick-LV on stepping motors we inherited the Ixx71 value of 4096 from teh original as delivered .pmc files and have used it successfully. We are finding now that depending upon the differences between the encoder feedback ( often at the end of a long mechanical train) and the motor resolution ( Ixx71=4096 gives us 6400 counts per rev from a200 step motor) we get improved closed loop perfromance by varying Ixx71. In one extreme however a mechanical vendor told us his syetem would only work with half stepping motors so we successfully changed Ixx71 to 256. I don't think the performance was significantly different but at least it stopped the vendor balmig our geobrick-LV settings for shortfalls in his mechanical performance.

We have had some success reducing this phenomena on 'sloppy' mechanics by using an exponential filter in the ECT. This works very well with low resolution steppers ( say 1/10 stepping). Vibrations introduced by the motor which happen interstep, but at a rate which the servo loop will try and 'pull in' can cause this effect, and a filter in the ECT seems to fix this.

I have inherited a mechanical build which has a stepper motor driven linear stage and a load mounted renishaw linear encoder. When reversing, the large backlash inherent in the system quickly builds into either a huge servo demand that takes a relatively long time to run out, or else generates a fatal following error. This limits boith the speeds I can achieve and the gains I can apply for low following error at standstill. Does anyone have any methods to over come this. cheers