Sizing Servo Motor for Variable Torque Application

[knji]

What I've got is a regulation problem.

I need my motor to be able to reject disturbances by provide a variable torque onto one link of my robotic arm.

I can obtain a closed-loop time based torque profile of the load for any initial condition and can also obtain the torque profile at the motor shaft through my gearbox.

I need to size a motor capable of producing variable torques as required. So far, I am working with worst case scenarios. I've deduced the maximum instantenous torque, which coincides with the maximum permissible initial disturbance. For optimum performance, I'm thinking of using a motor whoes midrange torque matches the maximum instantenous torque required for my application.

Is this a proper way to select a servo motor? Besides current limitations of the servo-amp, are there any other constraints I should be considering when selecting the motor?

This is my first sizing exercise.

TIA.

 

[gcaudill]

Probably as important as correctly sizing the motor is finding a motor controller that has adequate torque control. Many manufacturers show you their torque accuracy in percent, but do not show you the torque linearity over the operating range. You could end up in a situation where the controller does not work well in a particular range.

 

[Barry1961]

As a rule of thumb I like to limit the reflected inertia to rotor inertia at 10:1 max. You might also want to note the conditions under which the servo motor's rated torque was tested. Some servos are rated with very high skin temperatures which may not be desirable in your application. In some cases they will give the torque rating at over 120 C(248 F).

Barry1961