Can I Run Two Servo Motors On a Single Axis In a Non-Synchronous Manner?

[Miengineer313]

Successfully retrofiited a Koike Aronson CNC Plasma Cutter to Centroid Acorn & Clearpath Servo Motors last year. Still on a learning curve but overall working pretty well! On to the next project......

We're a fab shop and I'd like to retrofit a machine to use as a CNC beam drill line. It's basically a three axis mill, but I'd need the table to also move over the X axis to get the required 20FT of travel (or more) along that path. The machine I'm considering currently has 10FT of travel for the head only.

Is it possible to set up Acorn & CNC12 so both the head and the table move along the X axis to get the required 20Ft of travel seamlessly? As an example, if 0,0,0 is at one end of a 20Ft beam on the table and I need to drill holes at 17Ft along the X axis, then the head would move 10Ft to one end of the table and the table would move another two feet to the correct position. Can Acorn/CNC12 be configured so all I do is program hole location and from a home position on the X axis the system adds & subtracts from the two servo motors to get to the correct positon.

Feedback is much appreciated. Thx.

[cncsnw]

Usually that would be done with two independent axes.

A second linear axis that moves parallel with X is typically called 'U'.

The CNC program would need to call out U movement, wherever needed, separate from X movement (e.g. "G0 X120 U24").


If you want both axes to move automatically in response to just an "X" command, then you would have to set them up to be synchronous using any of the several existing axis-pairing features. That would be an unusual configuration, but it could be made to work.

Using axis pairing, any given X movement command would require that both your servos move the same number of pulses. If the available travel of the two axes is different, then you would need to configure your servos and drive trains so that the same number of pulses caused more movement of the longer axis than of the shorter axis.

You would adjust the drive ratios and servo resolution so that, for example, a move from "X0" to "X100" moves each servo 50 inches; or moves the longer axis 60 inches and the shorter axis 40 inches; or whatever ratio is needed.

If I were doing it, I would go with independent X and U axes.

[jhnmdahl]

I like the second solution CNCSNW proposed due in part to its relative simplicity. If he currently has 10 feet of travel on the X axis and wants 20 including moving the bed, he may be able to simply double the number of steps per revolution for X and U axes and supply the same signal to both, making it a virtual 20 ft X axis without significant further modification of the control system. I suppose there's a chance that they could come out of sync somehow during operation, so there may be some benefit to being able to address them separately for homing (could be done via a relay rather than tying up an additional output axis of the Acorn controller).

[tblough]

I also think the second will be easier from a user point of view. with separate X and U axis, the CAM system or programmer will have to decide which axis to move, X or U. For a hole at 17', does it move X 7' and U 10', or X10' and U7', or X9' and Y8'... With the second implementation, you just program the hole at X17' and the control takes care of the movement.