Aux Encoder/ Dual Loop (Dmc-1415 And Dmc-1416 Only); Backlash Compensation - Galil Motion Control DMC-14 5 Series Manual

Aux Encoder/ Dual Loop (DMC-1415 and DMC-1416 only)

The DMC-141X provides an interface for a second encoder except when the controller is configured
for stepper motor operation. When used, the second encoder is typically mounted on the motor or the
load, but may be mounted in any position. The most common use for the second encoder is backlash
compensation, described below.
The second encoder may be of the standard quadrature type, or it may be of the pulse and direction
type. The controller also offers the provision for inverting the direction of the encoder rotation. The
main and auxiliary encoders are configured with the CE command. The command form is CE x where
x equals the sum of n and m below.
m= Main Encoder
0 Normal quadrature
1 Pulse & direction
2 Reverse quadrature
3 Reverse 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 is
CE 6
Additional Commands for the Auxiliary Encoder
The DE command can be used to define the position of the auxiliary encoders. For example,
DEO
sets the initial value.
The positions of the auxiliary encoders may be interrogated with DE?. For example
DE ?
returns the value of the auxiliary encoder.
The auxiliary encoder position may be assigned to variables with the instructions
V1=_DE
The current position of the auxiliary encoder may also be interrogated with the TD command.

Backlash Compensation

The dual loop methods can be used for backlash compensation. This can be done by two approaches:
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.
DMC-14x5/6
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n= Second Encoder
0 Normal quadrature
4 Pulse & direction
8 Reversed quadrature
12 Reversed pulse & direction
Chapter 6 Programming Motion 83
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