Binding

[kylecroft]

Hi

I just finished building a linear translation slide based around a 1/4" allthread rod. I am using this motor:
http://www.eminebea.com/content/html...pm42s096.shtml
Pictures of the setup can be found here:
http://www.flickr.com/photos/7261353...7600211462368/
I am using a Linistepper to drive the motor. When I run it with CSTEP or KCAM4, the motor attempts to turn, but often can't overcome the load and steps backwards. If a small amount of pressure is applied in the direction it is trying to turn, it will turn unassisted for a while. A colleague suggested that instead of having the guide rod above of the motor, I should put it parallel to the screw. Any other ideas of how to reduce binding or friction would be greatly appreciated.

Thanks,
Kyle

UPDATE: My guide rail is a hollow aluminum tube and my "linear bearings" and end supports are flanged nylon spaces. My coupler consists of a 5/16" to 1/4" reducing nut, which has a small O-ring placed inside of the 5/16's half. The motor is then force-fitted onto the coupler. It is near impossible to get it on straight, could this be a problem? Also, I noticed a few brownish spots on the threaded rod, could this be causing extra friction. However, I can drive the motor fine over one section or the threaded rod in one direction fine, then have it bind up going the opposite direction over the same spot. I noticed that the assembly binds up more the closer it is to the motor, too. I hope this makes sense!

[kylecroft]

UPDATE: When I run the motor at a faster speed, and without the guide rod, it moves much smoother, but sometimes misses direction changes. For example, when the it gets to the top of a triangle, and the diagonal line is supposed to go down, the motor sometimes switches directions, so it draws the same line again. Also, when I run it across it's whole range, I noticed a small nudge in the opposite direction causes it to change directions. I will be replacing the guide rod by the end of the week. Please tell me any advice or questions you have!

Thanks
Kyle

[hotponyshoes]

If the motor is changing direction without you asking it sounds like a feedback problem internally.
Try removing the motor and running it out the machine and try loading it up by hand.
While its out try running your rail along by hand to see if there are any sticky spots..

[kylecroft]

Thanks for the help, I'll try this out tonight

[kylecroft]

Okay, I unhooked the motor from the rail and ran it. When I gave it a little push in the opposite direction, it obediently switched directions. Spinning a separate coupling nut showed no noticeable sticky spots on the rail. One thing I forgot to add was the motor has trouble starting up. When I first turn on the system and run the motor, it gives off a humming noise but doesn't turn the shaft. With a small nudge it starts moving. If the motor is inactive for a while, it will refuse to start moving without a nudge. My coupler has been bothering me because I cannot get it straight. Would fixing the O-ring in place permanently help at all?

Thanks
Kyle

[kylecroft]

Does anyone have any information about internal motor feedback? I tried searching but couldn't find anything relevant.

Thanks
Kyle

[ahren]

What sort of drives are you using with your motor? Some drives will reduce the current to the motor if it is inactive for a while to reduce heating, but if there is a problem with your drive, it might not be ramping the current back up. Also, let us know what sort of voltage you are running at. You should be using several times the rated voltage of the motor. This shouldn't affect startup, but if we can get a clear picture of your electronics setup we might be able to help more.

As for the coupler, you should consider getting a flexible coupler -- this will make thing easier on the small bearings in your motor and should help prevent binding. A Lovejoy connector is a good and inexpensive way to go here. You can get these at enco, and specify the opening on each side:

http://www.use-enco.com/CGI/INPDFF?P...MITEM=990-4044

Good luck!

Ahren

[kylecroft]

Thanks for the reply Ahren. My driver is a Linistepper
configured for 0.266 Amps and running off of a 30V 0.5A power supply. The Enco website is down right now, so I can't look at that coupler, but I won't be home all weekend anyways. Also, I have reason to believe that my driver isn't working correctly at certain speeds -- I will post pictures of some 'scope traces next week.

Thanks again
Kyle

[kylecroft]

UPDATE: Enco is up again and I have a few questions. First of all, what is a keyway? Also, is there a set screw or sometting to secure the shaft with? My motor shaft is just under 5/16" but the closest size they have is 3/8". Thanks!

[kylecroft]

UPDATE: I think I figured out what a keyway is. Anyways, about the feedback thing. Since I have two Linisteppers, I first looked at one motor output on each motor. This is the signal the Linistepper sends to the motor. On the motor I'm having trouble with, the signal is in the 30V range with a few spikes. The good motor is getting a nice sine wave type thing. When I switch the motors, the signal stays the same with the motor. So, the drivers must both work. Does this mean I have a motor feedback problem? I noticed in the scanner I got the first motor out of, there was a toroid that the motor wires were wrapped around. Would this help at all?

Thanks again
Kyle

[aggie_67]

Just a newbie myself but it looks like to me the steppers are way to small to expect any good movement.

[kylecroft]

I agree. I think I'll replace it with this motor:
http://www.allelectronics.com/cgi-bi...ER_MOTOR_.html

Kyle