over-current solutions

[tkb11]

We are working with a custom turning machine. The X drive uses the Electro-Craft E652 motor and a Electro-Craft MAX400 drive. The Z axis uses a E652 motor and a MAX430 drive. The machine has worked well for years. But we are now trying to machine a surface that demands better X-Z coordination that anything we've done before.

The Z axis is not responding as quickly as the X axis resulting in unacceptable deviations (stuff measured in optical wavelengths) in the finished part. This kinda makes sense, looking at the machine the Z motor is moving a lot more weight (at least 4X) than the X motor. So we tried to raise the Z servo gain a little and started getting over-current conditions.

So what is the cure? A stronger motor? What kind of torque is the 652 capable of? Is there some difference in the 2 drives that could account for this? Should I test the motors looking for significant deviations?

Thanks in advance for any comments and suggestions. I apologize if my vocabulary is goofy or my questions are phrased poorly. I'm an EE, not a master machinist.

TIA,
Keith

[Al_The_Man]

One of the problems faced in motor/machine design is what acceleration & deceleration demands are placed on the motor/drive.
This relates to something call motor/load inertia which may be too high, of which accel/decel is a major factor.
One resolution is to increase the gearing rather than increase the motor size,then the same motor and drive can be reused.
Fortunately you may not need alot, with gearing, the torque increase is directly relative to the ratio and the inertia ratio decreases by the square of the ratio.
Al.

[tkb11]

Thanks for the advice. The gear train inside this machine is rather exotic (ie crazy expensive) but maybe we can add something to the motor.