re:Re: Re: stepper motor in servo loop question

Jon and ballendo wrote:

>ballendo wrote:

>>Elliot,
>
>>What do you gain over just replacing the servo motors/drives in
>>the "old...equipment"? Prices are lower. Reliability is higher.
>>Tuning is easier. Why do this?
>>
>>Price, maybe???
>>This method requires that the analog output section of the control be
>>working. You trade the cost of the servo drive for the cost of the
>>stepper drive(plus whatever VCO related circuitry you use). The
>>motors will similarly balance out,IMO.
>>
>>In the end, you have lower performance at possibly a HIGHER cost...
>>For reasons Mariss has eloquently explained, the stepper will never
>>reach the performance of the servo.

The system is rather peculiar, it has steppers connected to a precision
optical stage (ball screws and linear bearings). A high resolution linear
encoder is built into the stage. I want to use these stages (3 of them) for
their intended purpose: moving optical measuring equipment around to micron
accuracy with low speed. 1 mm/sec will be fine for rapids. There is no
reason to thrash these things.

Price matters. If I can just hook up the motors and encoders to a
controller I'm way ahead of the game.

>You may want to talk to Otto at MaxNC, as his CL "servo" system uses
>steppers with encoders....
>
>
>My universal stepper controller board also can command stepper drivers
>with step/direction
>inputs and take advantage of encoder feedback. See
>http://jelinux.pico-systems.com/univstep.html
>for more info. This board can be used with EMC.

>Jon

Thanks, guys. A mixed mode servo would probably be a nightmare, I'm glad
you knew of a simpler way. Will check these things out.
The way it could work is the Mach1 OCX will control the motors, and an ADC
card will handle data acquisition. Will use Visual Basic to glue the
various parts together.

Jon, how is a stepper/encoder system implemented with the universal stepper
controller? I see the encoder inputs and stepper outputs, but how exactly
is the loop closed? Is there another layer of software required to do this,
or can the board just be run with software on a PC that already exists?

The MaxNC CL system looks like it might work for me, I'll give them a call.

regards-
Elliot B.