Reference point

[Derik 0]

Hi, I’m a university student and I’m doing a project on the Trajexia controller. I’m building a robotic arm with three axis controlled by servo’s to move chess pieces on a chess board. I want the controller to move to a reference point at start-up so that I can use a MOVEABS function to move the pieces to different positions. This is still a learning process for me so I was wondering if someone could give me some guidance or advice on this.

[Michael Walsh 268]

Derik, With incremental encoders: what you are trying to do is establish a home or an origin position. Usually this is acheived by providing an input signal into the Trajexia controller. You will then use the DATUM_IN command to define which input is being used for which axis. Next, you will need to do a DATUM command (there are several options for DATUM) for each axis. This process involves the servo moving to the assigned input (usually a proximity switch) and then the servo will slow down and travel off of the switch until it finds a Z-Phase pulse. This signal, also known as the marker pulse provides an exact location in the revolution of the motor (only one pulse per revolution). When it sees the Z-Phase pulse, the servo will stop and establish the origin position. From here you can perform your MOVEABS command. If you do not want to use inputs, it is also possible to jog your servo's to a known position (or manually move them to a known position with the power off) and upon power up use the DEFPOS(0) to force the present position to 0. With an absolute encoder, this origin search routine is not required as the encoder can "remember" its location when the power turns off. If you have an absolute encoder, you will need to establish its position only 1 time (initializing the encoder) and the process for this usually dependent upon which servo drive and motor you are using. I hope this helps.

[Derik 0]

[Michael Walsh 268]

Yes, the DEFPOS command will establish that position as the origin for all three axis. Just be sure to issue a BASE(x) command (where x is the first of the 3 axes) before you issue the DEFPOS(0,0,0) command. Of course you will then need to enable each axis before attempting to perform the MOVEABS command. Good luck. Edited 23 Jul 2008 by Michael Walsh