Servo Load Testing is a procedure that can be done before and after a Servo Drive has been repaired or replaced. Load testing allows for a Servo Drive to be tested at a point that it would see during a normal to non-normal operation conditions. In many applications, this is beneficial because it can let you know if the drive can handle the workload you are putting it through or it needs to be looked at because it cannot operate at the specified specs that it is rated for.
There are a couple of ways to load test Servo Drives. There is Dynomometer Load Testing which can be quite expensive to build or purchase. There is also the way we load test which involves two motors that are coupled together. Typically, the two motors include a DC Servo Motor and an AC Servo Motor that is rated for the Servo Drive you are looking to load test.
The two motors are coupled together either directly at the shafts, with a pulley or belt system. If they are coupled directly at the shaft you need to make sure that the two motor shafts line up so that it is not off-center and causing damage to the motors.
Along with the motors you have the AC Servo Drive that you are load testing and a DC Servo Drive. The DC Servo Drive needs to have the capability to run in Torque Mode. This means that as the motor shaft is spun it maintains the same amount of torque as it spins. The AC Servo Drive is operated in the Speed Mode. When running both together in opposite directions, it generates a load on the AC Servo Drive you are testing. This is done by the constant torque that the DC Servo Drive applies to the DC Servo Motor: as it spins in the opposite direction, it causes the AC Servo Drive to work harder to maintain the speed of the AC Servo Motor.
This load is a current rating on the AC Motor Power leads going from the drive to the motor. Typically, you would want the current on wires to be higher than the rating on the drive to show that the drive is good and can handle the load that your application requires.
To increase the load on the drive you would have to increase the torque on the DC Servo Motor. If you go too high on the load you can either cause the drive to alarm out or you can damage the drive so, make sure to monitor the amount of current on the motor power leads. If the drive generates an alarm before you even get to the rated current that the drive can handle, then you know that it has failed the load test and needs to be repaired or replaced.