Considerations to design actuators, and loop feedback systems, for a robotic arm [closed]

Question

Let's say I have an industrial sized 6DOF robotic arm. I want to control each one of the six joints despite the non-linearity produced by the chain structure, the gravity and the weight of the loads it could lift.

I don't focus here on the speed nor the power limitations, I just want the arm to respond well. Moreover, I would like to avoid the use of any prior knowledge such as inertial computation. Then I had these considerations, considering that I can play with both the actuator design, and the loop feedback control system:

1. Limit the maximum speed of each actuator to smooth their error variation.
2. Increase the damping of the actuators to avoid high frequency instability.
3. Find a good control system, such as a PID, to make sure the targets are reached without oscillations.

Do you have any other considerations in mind? Do you know what process(es) industrial designers follow?

EDIT: As it is said in the comments, my question concern the design of an adaptive controller for a robot arm, which is, how to design a joint control system (actuator + loop control) that don't need inertia and masses to be computed (the controller could adapt to its own structure, or to the loads it lifts). I'll be very much interested if you know some paper about adaptive control in the field of robotic arms.

Answer 1

As I commented on your question, I'm not really sure what you're looking for or what your list is for.

I'll try to answer your last question, "What is the process the engineer takes?"

In short, the engineer uses everything you said you wanted to ignore.

Specifications are the heart of engineering. I, and I think most engineers too, detest "feelings" kind of terms, by which I mean qualitative statements.

"I want an actuator that works good" is the kind of statement I mean. What is good? What does that mean to you? Is good low cost, or high reliability, or high power, or high speed, or something else? What is "high" or "low" to you?

In general, design is based on worst case scenarios.

1. What is the maximum payload mass (and shape!) you want to move?
2. What is the top speed you want it to move?
3. How fast do you want it to get from zero speed to top speed?

These three questions go a long way to "ballparking" the actuator(s). Next, you need to pick a design for the arm. Is it SCARA, Cartesian, or something else? This is important because each actuator has to be capable of moving the load and all the actuators after itself.

Now, for each degree of freedom, you have to evaluate the worst case load on the actuator to spec the actuator.

Once you have all the actuators specified, which generally takes several iterations, because heavier actuators require even bigger ones "upstream", then you can begin to design the controller.

Control design has to happen last because you need to have some idea of what kind of output you're going to get for a particular input. You can't define that without a model of the plant (actuator).

You could, of course, "turn off" gravity, mass, moment of inertia, etc. in your simulation, use ideal motors and tune speed regulators on them to perfect responses, but you're just wasting your time. If that's all you want then why not just put a low pass filter on your position request?

So, tl;dr - if you're going to design, you need specifications. If you don't care about specifications, don't waste your time designing, just cheat an answer.