master-slave servos

[js412000]

I want to build a horizontal spindle , heavy duty, metal cutting cnc mill. It will have a number 50 taper spindle. For the y axis (up and down) The linear guide rails will be relatively short, so I want to use 3 or 4 ball screws,each with it's own servo motor, using the master-slave feature.
Will this work? What happens during homing and zero return at power up,etc. The ball screws must remain in sync at all times or there will be tremendous racking forces created on the guides. I suppose I could put a swivel connection in there, but that would reduce stiffness.
Do the ball screws need to have the same pitch? I have read about a feature called electronic gearing, would this work to compensate?
I have thought about using one big servo motor with timing belts connecting to the four ball screws. The timing belt pulley center distances would be about 24 inches. I wonder if the strech and "flapping" with a belt that long would introduce too much error.

[Al_The_Man]

Is the ball screws operating four spindles? Like a Gang drill etc, is it the spindles you are moving or four tables,
Is there any reason you have to do four operations simultaneously and not four repeated operations?
Just trying to get a feel of what you are doing.
Al.

[mcpltd]

It will come down the the drivers you use.
What you are reffering to is what is called follower, most good quality digital drivers have this feature.
Have a look Elmo Motion Control, their digital drivers all have this feature and it works very well.
It is a good idea to use the same pitch screws.

I want to build a horizontal spindle , heavy duty, metal cutting cnc mill. It will have a number 50 taper spindle. For the y axis (up and down) The linear guide rails will be relatively short, so I want to use 3 or 4 ball screws,each with it's own servo motor, using the master-slave feature.
Will this work? What happens during homing and zero return at power up,etc. The ball screws must remain in sync at all times or there will be tremendous racking forces created on the guides. I suppose I could put a swivel connection in there, but that would reduce stiffness.
Do the ball screws need to have the same pitch? I have read about a feature called electronic gearing, would this work to compensate?
I have thought about using one big servo motor with timing belts connecting to the four ball screws. The timing belt pulley center distances would be about 24 inches. I wonder if the strech and "flapping" with a belt that long would introduce too much error.

[js412000]

My goal is to build a horizontal machining center ,to do large workpieces, that has all three axi self contained. The work piece would be bolted to a floor plate and would not move. The "machining center" would also be bolted to the floor plate, and could moved around as necessary. I am only going to have one spindle, mounted horizontally in a ram.(Z axis) The ram will be mounted on a way unit with 52 inches of travel (X axis) I would like to have the entire way unit, with ram and spindle,(X and Z axis) move up and down 24 inches to give me a Y axis. This will weigh several thousand pounds and need to be counterbalanced. With a conventional approach to machine tool building, a massive structure with very long vertical guideways would be required to keep the y axis level and square.
I want to use 4 ball screws, mounted vertically, at the 4 corners of the 52 inch X axis way unit. I would rely on the electronics to keep everything square. I would need some linear guides to keep side loads off the ball screws. It should be pretty accurate. with 4 screws being used, ball screw pitch errors would be averaged out.

[Al_The_Man]

I think I am getting the idea, If you are raising a verticle structure weighing many thousands of pounds by means of ballscrews, You may want to look at Nook Ballscrew Jacks. I used these once on a Avey Mill/drill to replace a Hydraulic driven Z axis.
If the load is being raised vertically on the ballscrews the weight will prevent any error that may be present in backlash due to the screws loaded in one direction.
They can be driven by motors with encoders, if you can find a control that will electronically gear 3 servo's off of one master encoder.
The ball screws do not turn in this application so the encoders would have to be on the motors.
Al.