Re: Low cost Servo Controller

Dave,

Sounds like what you're looking for is right at the state of the art in control. Two pieces of information to consider:

1) S-curves. This is the reduction of jerk in start and stop by dividing the motion curve into several parts: zero to maximum accelleration, maximum accelleration to maximum speed, maintaining top speed, maximum speed to maximum deccelleration, and maximum decelleration to zero motion. These stages of each motion can be controlled without complex math by giving a time in milliseconds to spend in each of the first two stages. Chips to do this aren't as cheap as your own custom circuit but here's a supplier: http://www.pmdcorp.com/

2) Adding a spring after the actuator. The idea here is to use a fairly stiff spring and a strain gauge to measure the distortion as the tool is engaging the work. The values of strain can be tuned by software control to a specific combination of tool and stock. Another advantage is safety as you can detect when the strain exceeds expected levels at any point and thus if something (like a human) gets in the way or a tool breaks it can shut down. A thesis describing this technology is at: http://www.ai.mit.edu/projects/cog/publications.html near the bottom of the page -- Williamson, Matthew. Series Elastic Actuators.

Combining these two technologies should help provide the best performance possible. The S-curve technology alone is supposed to double performance of CNC sewing machines. The spring technology can be used to tune it even better.