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PMAC PCI Lite Problem
#1
We are using PMAC PCI Lite (4 axes motion control card) for controlling 3 hydraulic servo valves [ out of 4 axes we are using only 3 axes, i.e axis 2,3 & 4) in position loop with encoder feedback. Encoder used is incremental encoders having A, A-, B, B- and C, C-(Marker) pulses. As we are using incremental encoder, we do a homing operation for each axis (by finding the marker pulse). System gets its actual positions after this referencing.
Sometime after this referencing (don’t know the exact instant), system is moving by its own to a new position, but PMAC is not detecting this movement. [After referencing we keep all axes at zero position, from this zero position system is moving to another position by itself (without any user command, and PMAC is not detecting this movement also]. This happened once in axis 2 and a second time in axis 3 (after two weeks of 1st incident, system was operating as expected between these two incidences).
We are using SCADA developed in LabVIEW as user interface for this system. PComm32W.dll drivers supplied by DELTA Tau are used in LabVIEW to access PMAC variables, loading motion programs etc.
What could be the reason for this unwanted movement? Any help is greatly appreciated.
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#2
One more doubt is 'Is there any way in PMAC to detect encoder signals getting open?' I think in our case as encoders are configured for differential, it will be easy for PMAC to detect encoder failure.
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#3
The problem occurs basically while the motors are being commanded to hold position, because no feedback and holding position look the same to PMAC, in both cases there are little or no encoder counts. Fatal following error should kick in during a move if feedback produces too few (or no) counts. The problem could be with the encoders, PMAC, or cabling. Not so likely for all the encoders to be failing. I would suspect the JMACH 60-pin ribbon cable which is common to all encoders. These cables are susceptible to connector contacts oxidation as they age. Sometimes you can tug on a flakey cable one way or the other to make it work or not work. One person told me his problem went away after spraying the connectors with contact cleaner. Ideally, change the cable.
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#4
It turns out that the PMAC Lite PCI is a new enough product to have encoder loss detection, which will detect if complementary encoder signals are open circuit, e.g. A and A/ both open. Resistor packs RP60, 62, 66, and 68 have to be reversed (see under "Resistor Pack Configuration: Differential or Single-Ended Encoder
Selection" in the hardware reference manual). Had to do some digging thru old app notes, but it looks like the following addresses could be mapped to M variables for indicating encoder loss on channels 1 thru 4, respectively:

Y:$E801,1
Y:$E801,2
Y:$E801,3
Y:$E801,4
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#5
Thanks Greg.. Are these variables listed in 'SUGGESTED M-VARIABLE DEFINITIONS' in PMAC datasheet? Can you send the particular application note where encoder loss detection is discussed?
One more help required is ' Is there any single command/tool in PewinPro to download/upload full configuration of a PMAC card (Including P, M, Q variables, M variable definitions, PLC programs etc. ). What I am looking for is any shortcut to take a backup of the full configuration?
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#6
I attached that document, and no, encoder loss bits are not in the suggested M Variables.

There is no other quick way to backup/restore other than thru the PEWIN menu tabs.


Attached Files
.pdf   Encoder Loss Detection2.pdf (Size: 173.86 KB / Downloads: 3)
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#7
Is it possible to use an absolute encoder (with output of 4-20mA or 0-10V) with this PMAC ( our PMAC card is 4-3657CF-1001-000000 with OPT-5CF( 80Mhz), OPT- 2V (DPRAM) ) ?
This card has resistor pack for encoder pullup option, right? ( not jumpers)
For encoder loss detection, i will reverse the resistor pack, and map Y:$E801,1,1 ( for axis -1), Y:$E801,2,1 ( for axis -2), Y:$E801,3,1 ( for axis -3) to some M variable, say M185 to M187 and use these bit to monitor loss of encoder. Is this the correct procedure to get encoder loss detection? Do i need to do any other settings?
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#8
There is no onboard 0-10V, but an ACC-28A would provide that capability. 0-5V absolute feedback is possible with option 12, but that option is not present based on your part number. (0-20mA is only available with an ACC-59E3 in a Power UMAC).

Correct, for encoder loss detection, reverse the resistor packs, same as on PMAC1 PCI, and map those register bits.
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