best system for control of oscillating motion...

[stampyoldani]

hello,
I am researching for a design of a test rig that I would like to build, and could use some expert help regarding servo systems.

in my test rig I would like to drive the test motor first clockwise/then counterclockwise repeatedly and very fast.
Here is a link to the product I am wanting to drive:

http://blog.wired.com/wiredscience/2008/03/video-the-lates.html

I want to spec a servo system that will directly drive an inertial load of about: 0.000959in lb s^2

At a torque range of about 5-25 in-lbs

It would be cool if I could control torque and speed profiles.

I want to be able to vary speeds of about 2000-4000 RPM clockwise, then counterclockwise, at a frequency between 1 and 5hz. continuous duty cycle

I was hoping that I could get away with a system like the sureservo ones sold by automation direct, but I am having a hard time finding a motor that won't have a significant inertial mismatch. Right now their SVL-202 motor looks best with a rotor inertia of 1.59E-4 in lbs s^2

Is this a feasible request to ask of such a system?
Am I missing any critical specifications?

Your assistance is greatly appreciated!
-Luigi

 

[bklauba]

A modest sized, brushless DC motor could do this. Emoteq or IIS-Servo come to mind. I know that the IIS folks recently put together a machine with a 5 HP motor, running start / stop cycles of 2000+ RPM, with 450 stops / minute.

BK

 

[stampyoldani]

Thanks for the response! I will look into those systems..

I guess my fear was controlling the acceleration of the load from 0-4000-0 rpm clockwise then 0-4000-0 counterclockwise repeatedly, at a rate of 5 times per second.

This seems pretty amazing to me! but I am inexperienced...

 

[stampyoldani]

I am also concerned about the inertia mismatch with a system like this, it seems like at these rates of acceleration it will be highly sensitive to inertial mismatches?

 

[itsmoked]

You are paying a whole lot of money for adjust-ability. If you are really just going to test a device like this you may want to reconsider.

Something like a bell crank may be far less expensive and still achieve what you need without the energy waste and inertial aspects of doing this with a reversing motor.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[stampyoldani]

yeah,
there is some on-board pcba and software, and it's very valuable to be able to put it through its paces, the adjustability also helps me study thermal effects at different rates.

I do have a parallel path for a fixed drive mechanical tester, and we have a pneumatic rig right now. But the automation direct servo package at right around $1,500 would be a really great way to test the system.

Any feedback into if the system could handle that kind of life?

thanks!
-Luigi

 

[sreid]

A 10 to one inertia mismatch is not a problem if the load is hard coupled to the motor shaft. However, you will be right at the motor maximum ratings for your worst case limits, 0 to 4000 RPM in 0.1 sec. That's an acceleration of 4180 radians/sec. Your total inertia (motor plus load) is about 0.00116 lb-in-sec^2 so the torque required is

T = I a = 0.00116 x 4180 = 4.85 lb-in.

That's roughly the motor continuous duty rating. Also (somewhere in the fine print), servo motors are usually rated "Attached to a 1/2 inch thick, 12 inch x 12 inch aluminum plate." And the motor temperature will be 100 degrees C (if the room temperature is 20 C).

 

[stampyoldani]

Cool!
That formula (basic as it may seem) is what I needed to understand the acceleration effects on the system!

Way cool! I think I can now better control my selection process.

 

[Warpspeed]

I am with Keith on this. Reversing a high rpm motor is probably not the best solution here.

How about something pneumatic or hydraulic? This type of thing is routine for many types of industrial machines that push, pull, or lift things repeatedly.

Another commonly used technique for fast repeated reversal, is to use a pair of clutches driven from constantly rotating shafts. Reversal can be almost instantaneous.

If it absolutely has to be electrical, perhaps a linear motor may be a much better approach to the problem?

 

[stampyoldani]

how much control over the velocity profile would I have with the servo?

I like the idea of using clutches and a continuous rotating shaft! although It would be beneficial to have more control over the velocity profile. and I would wonder about clutch lifetime for something operating at those speeds on a continuous duty cycle.

We currently have a pneumatic system that works OK. the motion is very jerky and difficult to smooth. using a 5port two way solenoid with meter out speed valves.

Thanks for the advice! I'm looking forward to any more feedback thats out there!

 

[waross]

You could use electro magnetic clutches and get a little control over the acceleration time by forcing or reducing the control current.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Warpspeed]

I was once involved with a coil winding machine that had to accurately lay constant pitch windings, then suddenly reverse at the end of each layer, and place another layer on top, over many successive layers.

This was accomplished with a ball screw that had an electromagnetic clutch at each end. Both these clutches were driven off the same motor, in opposite directions via right angle worm gearboxes, and a simple belt drive.

The drive motor was powered from a variable frequency drive to adjust the winding pitch. The electromagnetic clutches activated from optical sensors that defined each end of the stroke.

It was easy to build using off the shelf parts, and it worked wonderfully well.

If you want constant velocity, and very fast and accurately positioned reversals, I can recommend this.

 

[sreid]

What you need is a larger servo motor. Look for one that has about the same inertia as your load. A servo will let you run any profile you can program in the controller.

Automation Direct has very good pricing. For really good motors and servo amplifiers look at Danaher-Kollmorgen and Yaskawa.