RockB (Customer) asked a question.
Dynamic current and torque measurement for a stepper motor?
Hello,
I wanted to know if it is possible to measure dynamic current consumption and torque of a stepper motor. I currently have an integrated stepper motor (Part #: STP-MTRD-17038E) driven by a DoMore PLC (Part #: BX-DM1E-18ED13)
I need these measurements to monitor and control a deposition process.
It's difficult to do with a stepper. Doing it with a servo is no problem. You may want to look at either using a servo or using a torque transducer.
@Adisharr (Customer) Thank you for the suggestion. Can you explain how it can be done using a servo? and if the current and torque measurements can be logged by DoMore PLC?
Many servo's you can simply read the current or torque from a parameter over modbus or other protocol. The drive needs to know these things for controlling the motor so they are readily available. For example on the SureServo line you can set P0-04 to tell you the current load and read that value out via modbus. P0-03 is an analog output that can be set to the motor torque value. So you can take that analog signal and read it in the PLC to get the most up to date torque load on the motor.
Steppers are open loop, so much less data is available and many things are unknown. You could use an external torque transducer to read the torque and convert it to analog which you then read in the PLC. Perhaps you could also use an amp meter around the motor wires to read the current being drawn and convert that to a single to be read by the PLC. In the end with the cost of all those parts, it may be roughly the same as just using a servo in the first place though.
Thanks for the detailed info! I will look into sureServo line
Hi Rock, you would need a drive that allows access to the live motor current. I don't know much about the AD models they have but many other drives allows access either over Ethernet/IP or Modbus TCP. Once you know the motor current, you can use that along with the motors listed torque constant to give you an actual torque constant. The DoMore line supports both protocols.
How fast would you need to sample the current value?
Thanks for the info. I am not looking for ultra fast data logging rates. Sampling every 100 ms or 500 ms should be fine.
Automation Direct's Sure Servo system uses serial (rs 485/232) coms instead of Ethernet/IP or Modbus TCP, but it does allow monitoring torque, and allows you to set it up or change to torque mode to only apply a specified torque.
Thanks. I will take a look at it. I currently use a Nema 17 size stepper. Does servo come in same Nema 17 size? looking if it's easier to swap out or need some new mounting hardware.
The smallest they have is a 40mm flange (Nema 17 is 1.7") so you'll probably need an adapter. The servo shaft is also larger.
https://www.automationdirect.com/adc/shopping/catalog/motion_control/servo_systems/drives_-a-_motors_components/svl-201
I haven't seen a stepper driver that gives you a current output reading. The average DC current can be measured on the stepper controller DC power side but since there is little change in the amount of current required to turn the stepper under load or no load conditions I have to use the encoder feedback to make sure the stepper is turning and not in a stalled condition. Don't need to have the encoder doing anything other than send me pulses on the single output line since I don't care about it's position but just the fact that it's turning.