Stepper encoder issues?

[dcwood]

I have got my CNC bench top mill put back together. When I energize the servos the Y axis just takes off until it limits. I am thinking it is not reading the encoder and I need a new dc stepper? Help Please

[Zappautomation]

If a servo runs away like this it is normally a feedback issue, so check the encoder cable, connector and encoder.
If they look ok, and you have the same motor on the X axis swap them over to see if the problem stays on the axis of follows the motor.
Also if your control software reads out the encoder position, manually move the Y axis and see if the position changes.

Originally Posted by dcwood I have got my CNC bench top mill put back together. When I energize the servos the Y axis just takes off until it limits. I am thinking it is not reading the encoder and I need a new dc stepper? Help Please

[der_fisherman]

I hope that this is not off topic, I just thought that I would mention it for the servo Guys.....
I used to be in the robotics industry and we had several ways of checking things out to make sure that servo runaway did not happen in the first place.
The simplest form is a timer (hardware) that is triggered when power/movement is applied to a motor and needs to be reset from the signals from the encoder within a short time.
No signals within the timer period, remove power. The timer only needs to be coarse, just so that at any speed required, some encoder signals SHOULD be seen.....or a variable timer, depending upon speed required.
Also, we did not use limit switches believe it or not. At power on, we ran at a slow speed into hard mechanical endstops at both ends of each axis and we simultaneously checked the motor current. The rise in current told us when the motor was stalled at the endstop. This way the machine knew exactly how many encoder steps lay between the stops and exactly where each one is......
We used this system for many, many years without any problems at all.....the limited reliabilty of limit switches over long periods was the original reason for doing this....do not forget, being able to remove something electromechanical, is always good for reliability. I do not remember what chips we used for monitoring the motor current, sorry.
It is not really usable for a stepper system I feel, unless you fit an encoder to the stepper in some way...........generally it has to be servo......
I have personally never seen such a system on any other manufacturers equipment, not that I have seen many!!