RMC75E-QA2 and Mitsubishi MR-J3 servo amp


I am using a RMC75E-QA2 controller to drive a Mitsubishi MR-J3-350A4 servo amplifier in speed control mode. I have the rotary axis set up in the RMC and can read the servo position, but I can’t move it, using either closed loop or open-loop commands.

If I use the direct command on the RMC to run the control output to soem small voltage, say +3 VDC, I can see the input on teh servo amp using Mitsubishi’s MR Configurator2 software. I suspect that part of the problem lies in the servo amp’s need for a forward/reverse motion command input.

Has anybody else tried this particular combination? If so, how did you get it all to work? This is my first project using an RMC controller and Mitsubishi servo amp, but have to believe that I’m not the first to tie the two together.


I have not used the MR-J3, but according to section 3.6.2 of the MR-J3 manual, the Forward Rotation Start (STR1) and Reverse Direction Start (ST2) inputs define the speed polarity based on the +/-10V input signal. At least one of the ST1 and ST2 inputs must be high, or the servo will be locked.

Yes, I discovered that yesterday, and got the motion commands to work. I also ran the servo on (SON) input through the Enable + and Enable - and that works now too.

Did you used both Motor and Amplifier from Mitsubishi?

I am interested to know the same as the OP as I may be implementing a similar setup with a future machine build, if it can be done without too much trouble. That is, can the RMC motion controller be incorporated to control servo motors (>20 HP) using the RMC software only, such as give all motion commands, programming, etc, straight from the RMC software? We would most likely be using Rexroth motors for this project. What other hardware would be required if this can be done. Is this a common implementation with RMC controllers? The motors would be used for velocity/speed commands only, not position. Ramping to X-speed @ X-acceleration rate…hold for X-amount of time, ramp down…stop, etc, etc… Being able to use the RMC software for this would be ideal since the programming would frequently change depending on test criteria. We have an RMC150 being used for servo valve control on a hydraulic system and that works really well, and the programming is easy for our technicians. Wondering if we can implement the same for this velocity servo motor machine.