Galil DMC-2X00 user manual Additional Commands for the Auxiliary Encoder, Backlash Compensation

Using the CE Command

m= Main Encoder

n=

Second Encoder

0	Normal quadrature		0	Normal quadrature
1	Pulse & direction	4		Pulse & direction
2	Reverse quadrature	8		Reversed quadrature
3	Reverse pulse & direction	12		Reversed pulse & direction

For example, to configure the main encoder for reversed quadrature, m=2, and a second encoder of pulse and direction, n=4, the total is 6, and the command for the A axis is

CE 6

Additional Commands for the Auxiliary Encoder

The command, DE a,b,c,d can be used to define the position of the auxiliary encoders. For example, DE 0,500,-30,300

sets their initial values.

The positions of the auxiliary encoders may be interrogated with the command, DE?. For example DE ?,,?

returns the value of the A and C auxiliary encoders.

The auxiliary encoder position may be assigned to variables with the instructions V1= _DEA

The command, TD a,b,c,d, returns the current position of the auxiliary encoder.

The command, DV a,b,c,d, configures the auxiliary encoder to be used for backlash compensation.

Backlash Compensation

There are two methods for backlash compensation using the auxiliary encoders:

1.Continuous dual loop

2.Sampled dual loop

To illustrate the problem, consider a situation in which the coupling between the motor and the load has a backlash. To compensate for the backlash, position encoders are mounted on both the motor and the load.

The continuous dual loop combines the two feedback signals to achieve stability. This method requires careful system tuning, and depends on the magnitude of the backlash. However, once successful, this method compensates for the backlash continuously.

The second method, the sampled dual loop, reads the load encoder only at the end point and performs a correction. This method is independent of the size of the backlash. However, it is effective only in point-to-point motion systems which require position accuracy only at the endpoint.

Example

Continuous Dual Loop

The motor (aux) encoder needs a finer resolution than load (main) encoder. Connect the load encoder to the main encoder port and connect the motor encoder to the dual encoder port. The dual loop

68 • Chapter 6 Programming Motion DMC-2X00