User guide

98 6000 Series Programmer's Guide
Servo Setup (servo products only)
EXAMPLES
Pages 103 and 104
show examples of
servo setup
commands as used
in a setup program.
Servo products are closed loop systems (see diagram below). As such, they require
configuration so that the control algorithm can effectively calculate the value of the control
signal output based on the feedback data from a feedback device, such as an encoder, resolver,
ANI input, or LDT:
• Tuning:
- Select gains to achieve optimal servo performance.
- Select the participating axes (as on page 79) and the trajectory/servo ratio. These
two parameters determine the performance for the servo sampling update, the
motion trajectory update, and the system update.
- Define the maximum position error, which is the maximum allowable error between
the commanded position and the position as measured by the feedback device.
- Select and configure the feedback device(s) you are using with your controller.
• Feedback Device Polarity (optional): Servo stability requires a direct correlation between
the commanded direction and the direction of the feedback device counts (i.e., a positive
commanded direction from the controller must result in positive counts from the feedback
device). If the feedback device is counting in the wrong direction, you may reverse the
polarity without having to change the actual wiring to the feedback device.
• Commanded Direction Polarity (optional): may be required to reverse the direction that
the controller considers to be the “positive” direction; this also reverses the polarity of
the counts from the feedback devices.
• Dither (optional): Add a square wave signal to the analog output to overcome stiction.
• DAC Output Limits (optional): Define the region of the controller's -10V to +10V
output range to be used for your application.
• Servo Control Signal Offset (optional): During setup and troubleshooting, you may
need to disable the servo control algorithm and directly control the analog output to the
drive.
Servo System:
Closed Loop
Load
Command
Digital
Control
Algorithm
Control
Signal
Offset
Drive Command =
Control Signal + Offset
Servo
Drive
Feedback Data
Motor
Feedback Device
(Encoder, Resolver,
ANI Input, or LDT)