Motion control and data acquistion system

I am looking for a motion control solution. I want to advance a carriage on a ball (or Acme) screw or screw jack with a resistance up to 3,000 lbs force. The ball screw diameter will probably be about =BE" to 1" in diameter.

I have not yet decided on what method to use. I am considering:

1=2E DC motor with pot to adjust the speed (least desirable method) 2=2E Gear Motor with encoder 3=2E Stepper Motor or Servo Motor with Driver and Controller using: =B7 Computer Interface or =B7 LCD and basic pushbutton interface on the machine itself.

I need to do the following:

1=2E Set linear speed rate from 0.001 in/min (or slower) to max speed for return to home position 2=2E Set a home position 3=2E cycle the carriage back and forth X inches about the home position Y amount of times. 4=2E go to X inches and return to home 5=2E have safety limit switches.

I will also be collecting data from 2 LVDT's or Digital indicators and Force from an S-type load cell. One of these LVTD's would be to record the carriage position. This could be eliminated if I could calculate the position to 0.001 inches. These would be in a separate Data Acquisition system but if I could group it all together with the controls that would be great.

I don't have much experience in this field and was looking for as close to a canned package as possible with the flexibility to design my own interface.

I am not an Electrical or Mechanical Engineer. I need this for an inhouse project but may consider selling the system if things work out. What kind of costs am I looking at and can anyone recomend a consultant or company that can help.


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I'm surprised you haven't gotten an answer yet.

There is an almost infinite number of directions that you can go on this with actuator, feedback & controller selections. Much of what you want to do will depend on how quickly you want it to go together and how well integrated you want it to be when you're done.

I'm mostly an expert in building full-custom systems, but here's my guess at how to do this with off-the-shelf hardware:

You've got three or four parts of the system to select: the actuator (motor), the sensor(s), the controller (which may be more than one piece) and the operator interface (which may be part of one of the controller pieces).

I would use a servo motor with an encoder as the actuator, with an amplifier that supported encoder feedback. For a reasonably sized motor you'd probably want to gear this down to your screw. Direct drive would require a huge motor, and for most applications you'd go insanely fast (figure that a motor really wants to go 3000 to 6000RPM; if you use a

10TPI screw that's ten inches a second, once it gets to speed).

You'll have some backlash in your gear train and your lead screw, so unless you can always go at your target position from the same direction you'll want some feedback straight from the thing you're moving. Even if you _are_ always going from the same direction the feedback will be nice. You could use an LVDT here, but that has a limited stroke. I'd consider an optical encoder strip of the sort that is used for direct read outs for machine tools -- dunno where you'd get one, but I'll bet that it's out there. If you have to go at the target position from two directions the backlash will _still_ give you fits, but it won't be as bad.

I would consider using a net-enabled controller, and putting the supervisory control, the data acquisition, and the user interface on a PC. This has some down sides with closing loops in real time, but it has the strong advantage of giving you a flexible programming environment that is (relatively) easy to work with and that folks have a lot of familiarity with. I would strongly consider using National Instrument's software to make this work, particularly as a one-off. Even if you were going to make multiple copies to sell, I'd still advocate using N-I for the prototype, then moving the application to stand-alone thing for production, to avoid Labview's limitations and royalties.

If you call National Instruments and tell them you think they can do it they'll assure you that they can (it doesn't matter whether they can or not: they'll sell hardware either way) and they'll recommend a local consultant (who may or may not be able to make it work), who will certainly use National Instruments software and hardware to do it.

I'm being pretty cynical about N-I, but if you keep your BS filter turned on you'll do OK.

Reply to
Tim Wescott

On 14 Feb 2007 13:04:56 -0800, "RG" proclaimed to the world:

It sounds like you are making a test gig for QA of some product. I have lots of experience building these kind of rigs for factories.

As Tim said, there are lots of ways to go about this. Which way you go depends on consideration of price, flexibility, application, production scale, etc. When I build something like this for a customer, I usually spend many hours going over their needs. Many times the customer does not even consider things that affect design until I bring this up, so several meetings happen before I do any firm designing.

Are you really wanting to use LVDTs or are you using that term as generic for any linear position sensor?

I normally use an AC or DC gear motor on applications like this with an inexpensive variable speed drive. As far as controls go, this depends on your needs. One customer I had wanted the test stand to be tied to a PC where the entire test sequence was controlled, monitored and recorded. They wanted that test data dumped to Excel Spreadsheets they supplied, with a single click of a mouse. They also wanted the ability to run the tests with the computer shut down and totally by hand. All these needs had to be considered.

If you are interested in hiring me to help in some manner beyond what I can do here, send me a note at

Reply to
Paul M

Whereabouts are you based?

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The most difficult part of this will be going at a speed of .001/min. The resolution of the feedback would need to be very fine to achieve this slow speed without bumping from one count to the next. I don't think a steady speed of 0.001 in/min is achievable over a period of time. Moving 0.001 every minute is. The rest is easy and the parts can be bought off the shelf. A good motion controller can not only do the motion control but can also control or monitor the force and buffer data so NI labview can retrieve it over Ethernet.

Peter Nachtwey

Reply to
Peter Nachtwey

Sorry for delay but just returned from a conference.

That is quite a large effort (1.3 tonne of force or about about 140N.

The effort you are putting in requires a torque intensive gear-motor for which a multi-phase AC drive system would probably be the best suited. This would utilise a full vector AC drive package that can apply torque at low speed. You will also need quite a high gear ratio.


How fast do you need the max speed to be. This should be known as we could not optimise the gear ratio required without this figure.

The last points are a matter of system architecture and selection of suitable components. All quite easily accomplished.

I would keep the position sensing but would need more details about such as maximum stroke length and whether or not you could consider zero-backlash gearing with such loads. If the drive back-lash were minimised position of the carriage could be evaluated from the rotation of the drive shaft with multiple geared synchro/resolvers. If the LVDT used for monitoring the position could give you a resolution over the whole length of less than

0.001 inches you may stand a chance. Achieving the positional accuracy at the slow speed you mention would not be too much of a problem if you could ramp down the motor for the positional landing. However, if you have a high-ish rate of movement required (like the unspecified max speed) then this may get to be more difficult (not necessarily impossible).

Your motion control system will need access to the position and force data to ensure maintaining proper control over the actuation. You will also want to monitor motor temperature and motor current.

Company's like Infranor do packages for AC and Brushless DC. They can handle single and multi-axis solutions and I have worked with them in the past (two high integrity projects). Also worth a look would be Emersons/Control Techniques who do similar packages. I have used some of their stuff but not the drives or servos.

If you can provide the other information I or others in this group may be able to get a bit more specific about a suitable, and most likely off the shelf, solution.

Reply to
Paul E. Bennett

to max speed

I once worked on a lead-screw device for ruling precision gratings. (My work consisted of design and installing the position-measuring system.) The first discovery when the instrumentation was in place was that the initial motion when the motor started up was retrograde. Small motions at high loads often harbor surprises.


Reply to
Jerry Avins

On Sat, 17 Feb 2007 23:46:30 +0000, "Paul E. Bennett" proclaimed to the world:

Not really. At the reduction ratio he is talking about a pretty small motor will do the job. Loss is high for many gearbox setups, but there are ones on the market to do this at these speeds. I did a 15 tonne press for a test lab with a 2 hp.

Reply to
Paul M

On Sat, 17 Feb 2007 20:56:31 -0500, Jerry Avins proclaimed to the world:

A 20 ton calendar I reworked used hydro assist to ease the load on the adjusting screws used to set the nip gage. I had .0001 in sensors on the bearing blocks to the frame and, under preload calibrated the nip indicators. Take the 2 ton preload off the bearings and the nip changed .0070 in. It is very hard to work at these tolerances and loads.

Reply to
Paul M

Peter Nachtwey wrote in news:2aydnc_om7mr1ErYnZ2dnUVZ

Heidenhain Linear scales for NC control such as the LC series offer resolutions of 0.005 micron.

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As the OP did not state what his maximum speed requirement is it is hard to tell. We know what he wants the slow speed to be. When I said "torque intensive" I was rather referring to the output torque of the gear-motor combination that would be needed to drive the ball-screw or ACME threaded shaft. If the speed requirement is not too high then a fractional hp motor might suit.

Reply to
Paul E. Bennett

On Sun, 18 Feb 2007 21:49:09 +0000, "Paul E. Bennett" proclaimed to the world:

True, but I don't know of any system out there that has a turn down ratio so high as to need this.

Reply to
Paul M

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