Tandem control method of two axes with different reduction ratios (Comparison of three methods to equalize the transmission torque for a load)

Abstract

Tandem control is the control to drive one load with multiple motors. We compare three tandem control methods to suppress the natural vibration of the system: 1) a common torque method, 2) an average rate feedback method, 3) an individual rate feedback method. The common torque method is to feedback the position signal and rate signal from the motor 1 to obtain the torque reference of the motor 1, and give the torque reference to the motor 2 with the correction calculation to equalize the torque. We found that the difference in reduction ratio affects the suppression effect of the natural vibration. The average rate feedback method feedbacks the average position, the average angular velocity, and the rate difference of the motors to execute the tandem control. In addition, it is a method to equalize the torque by calculating a torque correction signal of the same value with a different sign, from the average rate and average current of the motors. The rate difference signal feedbacks through a high-pass filter that passes the natural vibration of the system, so the natural vibration is suppressed in the transient state. The individual rate feedback method feedbacks the angular velocity individually. In addition, it is a method to equalize the torque by calculating its torque correction signal from the rate of the each motor. We could equalize the torque and suppress the natural vibration through this simulation and experiment, in all three methods. We result the individual feedback method is the best, because the common torque method is not able to tune the natural vibration with the control gain, and the average rate feedback method is complicated to tune the control gain.