74
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Chapter 6 Programming Motion
DMC-1000
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 X axis is
CE
6
Additional Commands for the Auxiliary Encoder
The command, DE x,y,z,w, 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 X and Z auxiliary encoders.
The auxiliary encoder position may be assigned to variables with the instructions
V1=
_DEX
The command, TD XYZW, returns the current position of the auxiliary encoder.
The command, DV XYZW, configures the auxiliary encoder to be used for backlash compensation.
Backlash Compensation
There are two methods for backlash compensation using the auxiliary encoders:
Continuous dual loop
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
Note: In order to have a stable continuous dual loop system, the encoder on the motor must be of
equal or higher resolution than the encoder on the load.
Connect the load encoder to the main encoder port and connect the motor encoder to the dual encoder
port. The dual loop method splits the filter function between the two encoders. It applies the KP
(proportional) and KI (integral) terms to the position error, based on the load encoder, and applies the
KD (derivative) term to the motor encoder. This method results in a stable system.
The dual loop method is activated with the instruction DV (Dual Velocity), where
DV 1,1,1,1
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