Servovalves, Servomotors and Servodrives

I'll give you the general outlines. Someone else may want to fill in more details if you need.

Sometimes people use servodrive as an overly broad term to describe a servosystem. I think that's sloppy language, but it's done and you might see it.

But, basically, a servomotor is a motor where the position (rotation) of the armature is controlled and monitored. This can also be done at the velocity level by using derivatives. You would use a servomotor for something like turning a welding fixture 17^o between welds on a robotic welder.

A servodrive is properly the electronic control (OK, you can do this hydraulically or pneumatically, but either will drive most people utterly mad) which monitors the servomotor and compares it's present state to an input signal and then provides an output to the servomotor to change to match the desired position.

A servovalve is a valve that can be deliberately partially open at a monitored position. Most valves are either open or closed. Proportional valves can be partly open, but you have no way of knowing exactly how much. A servovalve has a feedback element that tells you how open.

So, the differences are almost infinite. These are three completely different things, except they get used in the same kinds of systems.

I would probably Google Kollmorgen and Moog to get more information.