Slightly OT: Simple motion control

I'm looking for an alternative to a master/follower control like Dart's ASP10. The ASP10 (in follower mode) is a simple PI controller: it counts pulses and adjusts the slave speed to match the ratio set by the operator. We currently are using two 1/2hp dc motors controlled by Dart 125DV-C-K drives (fixed accel ramp at 6 sec. =/ ).


One problem we're having is during starting/stopping. I have both drives powered through a small contactor, so they both are energized at the same time. When the master starts, there is a delay before the follower starts running. The delay is longest on initial powerup. Since the ASP10 is counting pulses and the follower is already behind, it starts running very fast to catch up, overshoots, slows down, and back up as the ASP compensates. When the drives are stopped, the master tends to coast a little longer than the slave. I have adjusted the PI settings to try and get the best performance, but I would like to find something better.


I think part of the problem is the fixed accel on the DC drives. At the very least I'd like to try fitting a VFD and 3 phase gearmotor on the follower for better control options/faster response. I think a servo setup for electronic gearing or camming would also work, but that seems a rather expensive fix. Dart also has an ASP20 that seems to have better control options but I would need two of them. Is there another option for a simple electronic gearing setup?

Ideally (in my mind, at least) I would like to get rid of the Dart controls, use a VFD with an encoder input (or two) to control the follower, and have a speed pot or other control to adjust the ratio. Neither the master speed nor the ratio are changed very often, but sometimes it is necessary.

Thanks for any suggestions

Tazikel,

Since you suggested an AC VFD and 3 phase motors. Let me suggest ABB ACS800 drives, with fiber optic comms between them, the optional encoder interfaces, and a couple of Marathon Black Max motors with encoders.

I have a setup like I described and I find the accuracy to be .1 in 240 including stops and starts.

I'm sure other responders will have their own "favorites"

Nothing wrong with the ABB. My prefered drive is SSD. The 690 has an optional board that will emulate the encoder ouput on the "master" drive and send it to the slave drive.

Never tried it but it should work slick.

Allscot:
I'm not sure I've ever come across an SSD drive in my travels. =/ I'm not saying they're bad though

Milldrone:
The ACS800 is one drive I was looking at. The only time I worked with them though was for a customer that had a custom firmware written for their application. It's also been over 2 years since I've even looked at one. They worked pretty well from my experiences save for one or two.

I thought about using two AC drives, but didn't think about linking the two together though. How were those programmed to stay in sync? And how easy (operator friendly) would it be to change the ratio? I would imagine that would just be changing the program configuration to look at an analog input? Would that be using Adaptive Programming?

Thanks