Re: Motion Controllers

HoPpeR© trading at 1492¥ wrote: 
On Tue, 08 Nov 2005 22:30:17 -0800, Tim Wescott <tim@xxxxxxxxxxxxxxxx>
proclaimed to the world:


My technical needs are pretty basic -- an analog command input and an analog feedback need to be subtracted, with PID applied to the error signal and an output of either a PWM or analog drive to an amplifier (an on-board amplifier would be nice, but not necessary). Because the command and feedback are both velocities, the ability to monitor a position signal for limiting the drive would be nice but probably not necessary.


Tim I did some work recently that involved an indexer by YASKAWA.
While the company was not to great with tech help the rep was and the
product was good. I don't have the reps name and address here but need
to retrieve it at the job site anyway. 

The servo and controller works in both velocity and position with all
the feedback and amp built in. Pretty universal package. The only
problem I see is the analog. My setup involved sending a command to go
to a programmed position. The position was selected by BCD input not
analog.

I feel the rep could answer your questions quick and dirty but I
suspect he works regionally and you may be outside his territory.
Someone else may have a better suggestion but I will get his name in
the next day or so and post it to you if you want it.

What is the analog set point signals form and function. Is it a
velocity or position signal? What type of motor do you want to control
or are you looking for the servo too? You just didn't give enough info
for me to nail it.

It's angular velocity for both feedback and setpoint (command input, really, from a joystick attached to a user). It's to add gyro feedback to a pan-tilt table which has DC motors but no other closed-loop control. It doesn't need to engage in any autonomous motion. It just needs to turn as fast as the joystick tells it to, maintain a gyro-aligned pointing angle when its base moves, and not burn up the motors when it runs into a stop.

Since you work mainly in custom board level
controls you may not be familiar with some of the standard universal
motion packages available today.

No kidding. About all I know is that they're out there, they're well accepted, and there's a gazillion of them. In fact, when I originally started talking prices with the poor guy I had assumed a custom solution so implicitly that I just quoted a development price without thinking that this could be done with an OEM board. I could almost hear the "thud" of him hitting the floor in his return email, and I'm glad that he didn't just drop the conversation right there.

It is this lack of familiarity that leads to the post -- I want to get something that will do what the manufacturer says it will and won't disappear tomorrow.

I'm thinking I also lack some terminology as well -- would the thingie that implements the PID loop and possibly an amplifier be called a "motion controller" or a "servo"? In custom systems the thingie that issues commands is either called the "executive controller" or the "#$%@!"; the thingie that implements the PID is called the "compensator", and it's usually followed either by an amplifier or a string of curses from a more experienced engineer. Nowadays the usual way to implement all this is in software, with an appropriate DAC and ADC and an amplifier tacked on out there in the real world. 

If you are looking for a simple PWM DC controller, Mineric makes a
whole line of good OEM boards that take 1-5/10 vdc inputs that I have
used a lot of with good results. If memory serves they go up to 3 hp
on 90/180 volt motors. They are inexpensive and designed for the OEM.
After thinking on what you wrote (and left out) I suspect that this is
what you are looking for. They have armature feedback built in or tach
for tighter control.

Want to give me a little better description of the app?

Be well,

I've described most if it above. The only tidbit that I've left out (that I know of) is that it'll be a small production run OEM thing; having a board that could be easily configured in a repeatable manner would be ideal. I don't really care whether the configuration involves setting switches or downloading parameters on RS-232 or dancing around the thing widdershins just as long as it is easy to do in a light industrial setting by someone who isn't an electronics expert.

I think a simple PWM DC controller (servo?) will be just the ticket -- I'm going to look at your link as soon as I hit the "send" button.

Knowing what I know about his market I suspect that as soon as the customer implements this he's going to get requirements from _his_ customers that make him wish he had a custom solution, and I'm going to (gently) tell him so. None the less starting out with an off-the-shelf solution may be a good choice for him at this time -- he can prove out all of the other system additions, gain street cred, then move to a custom or semi-custom controller at a later date.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
.

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