MOVE TO POSITION ACCURACY

[STEVE]

I’m new to the TMC457. The application I have is a linear stage with a 25 lines/mm linear quadrature encoder. If I use the TMC457 to control the stepper motor (using a TMC262 based driver) and I want to go to a target position will there be an error reaching the exact target position? Plus or minus one or more encoder counts perhaps?

[Dr.LarsLarsson (TRINAMIC)]

Do you go via PID of the TMC457 to a target position?

[STEVE]

I suppose yes. I am not familiar with the TMC547 details yet – just trying to determine if its capable of what I’m looking for before I dig in deeper and spend time understanding the finer details. I do not have a preference at the moment. If the TMC 457 can accomplish to stop exactly at the target position more then one way I’ll take anyone of the possible solutions and use the TMC457 instead of developing microcontroller firmware.
In our old system I had the microcontroller do this work. The requirement was to stop exactly on the target position and we were doing it. This took up quite a bit of microcontroller time and I would like to offload this work to the TMC457 if possible.

As I have mentioned, I do have a linear encoder - optical quadrature, no index pulse just the A and B signals. The motor is driving an acme screw. The encoder is mounted on the linear stage and not on the motor. From what I understood from the datasheet so far is:

1) If there is an encoder feedback the system should operate in the PID mode.
2) If sufficient ramp down time (distance) is given the motor will stop at the target position. Is this exactly on the target encoder position or there is an uncertainty of a few encoder counts?

Regards,


Steve

[Dr.LarsLarsson (TRINAMIC)]

Concerning your questions:

1) Using an encoder and PID control allows regulation to a position. The Resolution of the encoder determines the resolution of the position. When using an encoder w/o zero (N) you need to take care that the encoder resolution and the stepper motor system resolution fit together.

2) In positioning mode the TMC457 stops exactly at the electrical target position.