if you havn't seen it already you may want to look at schilling robotics (now fmc), or just google "ROV manipulator". you can control a rate arm spatially with pwm to some degree. for the scale you are at it may work for a prototype.

When I was a little kid watching the Six Million Dollar Man I always wondered why his normal arm moved as fast as his super bionic arm when he ran instead of flapping like a noodle at 60 mph and why his super bionic arm didnt just rip out of his normal human shoulder when he lifted a car. Perhaps this project will answer some of those questions.

I love anything that makes my life easier. If this exoskeleton will make lifting my car easier, I'm all for it! Thanks for entering the Hackaday Prize! Please try to upload some more information on your project - How will it be powered? How do you ensure the users safety (The arm is great, but how do you make sure the wearer won't overload their un-aided shoulder joint?)

In regards to that, I have a suggestion:

Perhaps add secondary tactile sensors that will interrupt the flow to the actuator if they sense an increasing pressure. An example being extending the arm, a sensor that would detect the edge of the forearm being pressed against it would override the EMG sensor. Parameters would have to limit when and how the controller accepts input from these sensors. I would imagine they would have to sense an invalid motion in more than one area, and the motion would have to be normally valid but outside of the safe range of operation.

I suppose if the arm was used in an industrial capacity this could be taken a step further. Instead of merely saying, "hey, stop moving!" the sensors could also trigger the opposite actuator and say, "hey, reverse motion!" if the arm was forced beyond into an invalid position. There would have to be a limited range that would trigger this effect, immediately prior to the invalid range.

Also, as for the shoulder joint issue, the arm would have to be supported by a some type of harness, probably one that mimics a heavy hiking pack. (one with a back frame) Something to evenly distribute the load on the shoulders, hips, and against the back, especially in an industrial model. Assuming this arm is used for medical assistance, perhaps some limited support against the rib cage or using other parts of the torso could also be included.