Ron,
There are two primary facets to motion control...
1. Number Cruching (calculating).
2. Speed of the system being controlled.
Number crunching, or calculating, is nothing more than grinding your way through the various mathematical algorithms to obtain the required result (gee, that was easy to say!).
Any particular algorithm takes a certain number of steps (number crunching is not time-dependent per say, rather, it is step-dependent, which is then time-dependent... sort of) to obtain a result. Some algorithms have many steps, some have few. If a processor is available to do nothing but crunch through these algorithms then the speed of the result is dependent solely on the speed of the processor and the number of steps.
However, if the processor is loaded down with extra responsibilities and the processor can only do number crunching on a time-share basis then the speed of the result also depends on the extent of that extra load as well.
If a processor can only provide 10% of its' time to crunching numbers, then it will take ten times longer to crunch the numbers than a dedicated processor would take.
Ultimately, the result will be available.
However, the question becomes... "Are the results available in a timely manner?"
That is... Are the results available soon enough to provide adequate control over the driven device?
If a motion system is operating at speeds and times such that results must be available in such-n-such time, then the processor must ALWAYS be able to produce those results in no more than that time!
The results of the calculation must available soon enough to keep the motion on-track as expected.
In the final analysis, the ability of any particular controller to control any particular motion system depends on the ability of the processor to provide results as they are needed by that system.
For one particular application, one motion control system might not be good enough to handle the job because it is too slow. The driven device moves faster than expected and thus produces greater errors. In that case a faster control system is needed. It depends both on the application and the speed of the controller.
In another application, a particular motion control system might be so fast that the controller finds itself recalculating the same parameters, over and over, before it notices a detectable change in the process. In this case, the driven device moves much slower than the processor expects. This not to say that the processor can't handle it but the particular processor is simply much more than is required by the process.
Speed is expensive. The question becomes... "Is that speed worth the expense?"
To simply say "I feel the need for speed" is to say "I want to blow some bucks!" Do you really need that speed? Can you afford those bucks?
Depending on the particular situation, a small PLC dedicated to nothing but motion control can be quite effective.
Speed of the process, resolution required, and processor speed determines the final solution.
(427) Wow! Chevy!