Servo Position Reliability With Hsrv Motion Module

[Guest Bruce]

I have a number of units that use 50/3's and hsrv motion modules for the control. I have positional problem with the axis. They will drift off .020 to .060". Do this frequently for a number of weeks, then we will have no problems for two months. All mechanical points have been keyed so there should be no mechanical movement. I have heard that the 50/3 cannot really handle servo motion control and the hsrv motion module are just a jury rigged system. Can anyone enlighten me on? Our machine builder, who by his own statement knows more about everything then anyone else including Allen Bradley is of no help. Thanks for any info

[Chris Elston 78]

I got some questions: Is your application Open Loop or Closed Loop control? In other words, do you have encoder feedback? What is the HSRV module commanding? Some sort of a dumb drive?

[panic mode 246]

An HSRV module is SLC servo card (1746-HSRV). I didn't use one in a long time but I sure remember that it worked perfectly. If you need repeatability and accurate positioning, you definitelly need feedback (encoder or resolver would be perfect). If you have drifts despite feedback, problem is definitelly in the feedback. I would check wiring (always first thing to do). Make sure that terminations are clean and shield covers everything but some 1.5-2" of the end of the cable. Just few months ago I was troubleshooting "drifting system" and problem was that shield was removed for good 10" of the cable end wired to high speed counter card. Another thing to check is power for encoder. It better solid connections. Some systems are not monitoring feedback power and short interruptions will not create fault but the feedback reading (and positioning based on it) would drift. Example is 1394 servo drive from AB. So check the encoder power from power supply to encoder point by point and take scredriver in your own hand (don't rely on second person like electrician). If still doesn't work, try to use separate power supply for encoder and consider use of noise filter on the power line (even UPS, at least as a test measure). Besides wiring, check the mechanical connections and eventual play. Don't forget to check the motor cable (must be shielded as well) and grounding. I hope this helps panic mode