First let me say that I have used the ClearPath SK system for one retrofit and found it to work very well and easy to set up. I would use it again in a similar installation. This was to replace step & direction servos in an semi-open loop system where the loop was closed at the drives.

There are only two systems that I am familiar with that actually close all of the loops into a single CPU or at least on a single board, the Fanuc PulseCoder system, and the Galil 4000 series controllers when using the built in amps with Hall effect feedback. I'm sure there are others but I'm not familiar with them. In both of those cases, the motor commutation is done at the controller CPU level along with velocity, torque, and position control. So everything is done in one black box.

From a system designer standpoint, the Fanuc system is useless to me in that it is difficult to program at best, and generally not user friendly. Not to mention everything is proprietary and expensive.

The Galil system is flexible and very user friendly, almost like open source. But the built in amps that are available are limited in power to the point that for my applications are rarely practical.

So that leaves me with some type of motion controller and a servo motor/drive combination where the drive is responsible for commutating the motor. This of course divorces the controller CPU from the motor commutation CPU. I have to count on the drive/motor combination doing what it's told to do.

To throw another element into the mix, for most applications it is my preference to put the position feedback on the load rather than to rely on the mechanics of the system to position the load correctly through belts, screws, or gear systems. I am not talking about a dual loop system here, but rather the only position/velocity feedback to the controller comes from the load encoders. I couldn't care less what any installed motor encoders/tachs are doing, I'll let the drive handle that.

The above is where the ClearPath system is a problem for me since I normally use analog control. I am aware of the available Analog Send Unit, but it only handles 0-10 V, with digitally switched direction, where I need +/- 10V for full functionality.

But overall for the average user, the ClearPath systems are easy to install and a good value.