Hi All.....

One of our engineer did an application with a vertical axis,servo motor connected with a ball screw. When the machine is running at lower speed (2 M/Min) with out any load it is taking high current(5 Amps) and for higher speed(6 M/Min) with out load it is taking less current (3 Amps). What could be the possible reason for this. One of my friend said If I reduce the gains may be current taken by the servo will be come down.

Is that possible? Or what all are the chances for high current...

 

To ask this question as a function of speed only is not enough information.

If I were to guess I would say that the motion were occurring in the same amount of time the acceleration would have to be greater on the first move versus the other. Current doesn't change tremendously on speed change as you are still overcoming similar friction, and perhaps a bit more current (i.e. torque) due to viscous friction at higher speeds.

In general when you want to learn about current draw, look at the acceleration. When you have high accels you should see your current drive up (or down depending on direction). Once you have hit max speed (assuming you do hit max speed, its not always the case) the current will drop substantially. Your motion controller or amplifier should have a plot or oscilloscope tool to analyze these things. You want to keep the acceleration in the range allowable by the manufacturer of the ballscrew, which the calculations should be on the datasheet. Usually the biggest factor is the moment torques imparted by your tooling mounted off of the ballscrew. The life of the screw will be shortened if you run it very long at very high accelerations.

KEJR

 

If the vertical axis is not counterbalanced, it will require current to develop enough force to just hold it in place. If the axis is moved down, that current and force will lessen. If moved up, the current will increase.

If it is counterbalanced, is it the motor current that you are monitoring or the line current to the drive. I don't think the gain would affect the current unless the system was in oscillation.

Tom Bullock
[email protected]

 

It could be unstable at low speeds which could cause an oscillation. Or maybe it is an issue of breakaway friction.

Bill Sturm