Torque control for brush DC motors

[solaremperor]

Hello everyone - first time poster here!

In the lab I work in, we run brush DC motors to drive wire-driven humanoid robotic hands. So, the motors need to run in torque mode and in stall. But, they should also be capable of fast wind-up speeds (but speed need not be regulated).

Currently, we use linear servo amplifiers (Western Servo Design LDU-S1: wsdi.com/ldu-s1.htm) to drive brush DC motors in torque mode. These things are very old and have reached their EOL, so I have been tasked with finding a suitable replacement. So, I am trying to learn how they work and find suitable replacements. I would much appreciate it if the community could help me demystify the operation of linear servo amplifiers and/or help me find answers to the following questions.

• How are these servo amplifiers different from PWM servo drives?
• Also, how is it that the LDU-S1 is able to claim that it has numerous advantages over PWM type amplifiers including minimum motor heating, increased brush life and the ability to drive zero inductance loads?
• Finally, the LDU-S1 uses the PCU-S1 (wsdi.com/pcu-sx.htm) which claims to use shunt regulators to prevent back EMF generated by the motors from damaging components in the Bus Supply and amplifiers when using PWM amplifiers. What circuits enable this?

I am willing to roll out custom PCB designs too, so circuit design ideas are welcome! If I've accidentally broken posting rules or you need more information, please let me know and I will try to edit the post and fix the issues.

Thanks,
Solaremperor

[fourtytwo42]

There is someone on this forum who is a servo expert BUT I can tell you these are linear constant current drives very different from PWM that is a chopped signal only suitable for some motors.

I don't quite understand what you mean by EOL, if the units have failed they are easely repairable so why re-invent the wheel ?

[LaserSteve]

You might want t start with some Apex MicroTechnology Application notes on Brushed Motor Drive.

Steve

[solaremperor]

Thanks Fourtytwo42 and LaserSteve!