Pulse Width Modulation & Servo Motors Explained

[LabGuy330]

Hi everyone,

I am really trying to get the concept of Servo Motors and am sort of stuck on something, particularly how the motor gets its Pulse Width Modulation.

I understand the 0 to 5V with a period of about 20ms and different pulse widths generate different angular positions. What I am unfamiliar with is how the motor's controller knows the desired position? Is it as simple as a certain voltage input into the controller generates a corresponding PWM for that voltage and thus varies linearly?

Any help is greatly appreciated!

 

[MRFMengineer]

Different pulse widths (duty cycles), generate different torque (0-100%), not angular position. The desired position/torque/speed is commanded by something or someone, the actual position/torque/speed is measured with a feedback device: angular encoder/load cell/tach/etc.

 

[LabGuy330]

Thanks for the reply!

I basically get that the duty cycles dictate the position/torque, what I am unfamiliar with is how I command the driver to do so. I can't just stand next to the motor and say "turn 90 degrees please." what electronically does the driver receive to generate the PWM?

 

[MRFMengineer]

It depends on the controller, some are a 0-5V analog input, others are digital command ("clockwise, 50%" ) e.g. over USB, ethernet, RS232 etc...