Equivalent servo system of step motor

[bunalmis]

I want to do equivalent servo system of 200 step/rev step motor.
(Stepper motor will work full step mode)

I will use DC brush type servo motor and PID controller.

I want same step responce by step motor.

How i can choise encoder. (I will use x4 mode)

50 ppr encoder enough if we think simple . But i think i need minimum 500 ppr.

May I learn your ideas?

[kreutz]

50 ppr at 4x is just OK for 200 steps/rev stepper in Full step mode. What will happen when you try to do half stepping or micro-stepping? You wont get any feedback until a full step position is reached. If your design can work with +/- 1 full step error, then 50 ppr is OK.

If you want to minimize the error you will need a lot more pprs. If you want to get a smooth movement you will need the equivalent to 8 to 10 micro-steps/step minimum. 10 micro-steps => 2000 ppr(at 4x) => 500 ppr encoder.

[bunalmis]

I will give one full step puls to step motor and i will measure the position change by time. (I will use too sensitive position sensor for this examination)
(Normaly i expect dumped vibration)

After i will do same test by servo motor.

Step motor and servo motor must give me same response.

I think PID controller notting do with 50ppr encoder at this condition.

50 ppr give very bad results. (my idea)

[kreutz]

Using the 50 ppr encoder you can expect a +/- 1.8 degrees error in positioning (+/- 1 step) due to the limited resolution of your sensor. Using PID will do nothing to improve that error (garbage in => garbage out). As I wrote before, you will need at least a 500 ppr encoder in order to see better results.

[unterhaus]

It doesn't hurt to have some multiple of 50 for your encoder. Should make the control easier. You preferably would like to know when you are approaching the end of your move so you can slow down.