servo motor

want to control (Slave) rotational speed of servo motor based on linear distance it travels in horizontal axis (0-1") it should stop rotating when programmed distance is done. No controller or motor selected yet

gregi said:

want to control (Slave) rotational speed of servo motor based on linear distance it travels in horizontal axis (0-1") it should stop rotating when programmed distance is done. No controller or motor selected yet

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Not clear whether this motor performs the displacement itself or is being displaced by another motor and its speed is a function of the displacement distance.

Also, do you intend to use a PLC or want to implement this function by servodrive only?

actually the rotational servo will move along horizontal axis due to spring tension while driving the screw thru threaded hole. its position will be monitored by linear scale as a feeback position signal. Plc will just send a Start signal.

Sounds like you are inserting a screw into a part. Many times there is a torque specification for doing this and you can use that to control the servo motor.

What I have seen is the servo is set up with a torque limit that matches the specified torque (may need some slight adjusting but this is the idea). Then the motor is run at the speed desired to insert the screw and when the torque limit is reached the driver is stopped.

He could be doing just about anything with the vague description given.

It could be a flying shear, or a paint applicator for all we know.

We now know that one of the axes has a screw drive...and a spring...

I think you need to give a little more info on the application. However I think one of Peter's RMC motion controllers could do what you need. All you would need is a program to cal the speed based on position. This would run all the time and update the speed each scan of the controller.

Norm is right to a point. I am driving a screw thru sheetmetal to depth not torque, which will be more or less the same. The rotating screwdriver will be suspended above screw with just enough tensin on it so its bit engages with the slot in the screw.Once it starts rotating the screw will go down and the srewdriver will start descending based on pitch and rotation speed. Travel distance to required depth will decrease which in turn should slow the rotation until required depth is reached - then rotation should stop and screwdriver will be lifted up by a pneumatic cylinder.

gregi said:

Norm is right to a point. I am driving a screw thru sheetmetal to depth not torque, which will be more or less the same. The rotating screwdriver will be suspended above screw with just enough tensin on it so its bit engages with the slot in the screw

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So there is servo motor AND a pneumatic cylinder controlling the vertical motion of the screw driver?

Once it starts rotating the screw will go down and the srewdriver will start descending based on pitch and rotation speed. Travel distance to required depth will decrease which in turn should slow the rotation until required depth is reached - then rotation should stop and screwdriver will be lifted up by a pneumatic cylinder.

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Synchronizing the turn of the screw with the vertical motion is easy. A Synch Move Relative issued to the turning of the screw and the pushing of the screw will generate a motion profile so that the screw turning rate will be proportional to the vertical motion. This is all based on the screw pitch.

Now what is the pneumatic cylinder for? Why not simply retract the screw driver?

The trick will be the initial motion downward before the screw driver makes contact with the screw. The screw driver will need to turn slowly until the screw driver settles in the screw head slot. It may be as simple as simply forcing the screw driver down while turning hoping the screw driver falls into the slot without stripping anything. It make take turning the screw driver and forcing it down at low torque until the screw driver falls in the slot. The required torque to move should go up significantly then so the turning and downward motion will stall. Then the synchronized move happens at full torque.

Peter Nachtwey said:

So there is servo motor AND a pneumatic cylinder controlling the vertical motion of the screw driver?

Click to expand...

It sounds like the pneumatic cylinder is only used to return the screw driver but that begs the question about where gregi says:

The rotating screwdriver will be suspended above screw with just enough tensin on it so its bit engages with the slot in the screw.

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What is providing this tension?

gregi do you have a picture or drawing of this? It's hard to know how to help you without really knowing what you are doing. The "picture is worth 1000 words" phrase really applies here.

The pneumatic cylinder is used to lift (retract) the screwdriver. When it disangages the slide with screwdriver will drop drop down due to gravity and will be partially compensated by springs (providing enough tension so screwdriver can engage with screw). Slow rotation will allow the bit to engage and it will be monitored by a laser photoeye on the screwdriver slide. So what I need is a slow start and then upon a signal from PLC that s-driver is engaged - full speed decreasing inversly proportionally to distance traveled. Distance will be only monitored from the slide scale which will be going down under its weight minus spring counterbalance during driving the screw down. Hope this make it more clear.

Why are you not using the air cylinder retract to also drive the driver into the piece?

Sounds like your either on a tight budget or just re-inventing the wheel. There are many good companies that make these systems, ready to go. (example: http://www.deprag.com/ )

From an automation/production view, this seems like a nightmare to keep working correctly.

Putting in a screw seems simple....until you try to automate it! Then you see the hundreds of things that can go wrong.