User guide

Chapter 3. Basic Operation Setup 95
Closed-Loop Stepper Setup (steppers only)
NOTE
Closed Loop operation
is not available for the
OEM-AT6400.
Closed-loop refers to operating with position feedback from an encoder. This section discusses
how you can use an incremental encoder to perform closed-loop functions with the controller.
When using an encoder in an application, you may configure the following (described below):
• Encoder Resolution
• Encoder vs. Motor Step Mode
• Position Maintenance Enable & Correction Parameters
• Position Maintenance Deadband
• Stall Detection & Kill-on-Stall
• Stall Deadband
• Counter
• Encoder Polarity
• Commanded Direction Polarity
Encoder Resolution
You must specify the encoder resolution with the ERES command. The power-up default
value for encoder resolution is 4,000 counts/rev respectively. Listed below are the resolution
values for Compumotor encoders.
Compumotor Encoder Resolution ERES Command
E Series 4000 counts/rev (1000 lines) ERES4ØØØ
OEM-83 Series 4000 counts/rev (1000 lines) ERES4ØØØ
OEM-57 Series 2048 counts/rev (512 lines) ERES2Ø48
IMPORTANT NOTE
To achieve accurate encoder step positioning, the drive resolution (DRES), see page 81,
should be at least four times greater than the encoder resolution (ERES). This allows the
motor to successfully find the commanded encoder step position.
Encoder Step Mode
The controller can perform moves in either motor steps or encoder steps. In Motor Step Mode
(ENCØ), the distance command (D) defines moves in motor steps. Motor Step Mode is the
controller's default setting. In Encoder Step mode (ENC1), the distance command defines
moves in encoder steps.
Position Maintenance
The EPM1 command enables the position maintenance function. To enable position
maintenance, you must first connect an encoder and enable the Encoder Step Mode (ENC1).
Enabling position maintenance causes the indexer to servo (adjust) the motor until the correct
encoder position is achieved. This occurs at the end of a move (if the final position is incorrect)
or any time the indexer senses a change in position while the motor is at zero velocity.
The EPMG and EPMV commands define the gain factor and the maximum velocity of a
position maintenance correction move. The gain factor is the velocity increment used per
encoder step of error. The EPMV command sets the maximum velocity a position maintenance
move can achieve. If either of these is too large, position instability may result. If either is
too small, position correction may be too slow. The values are determined by experiment.
Position Maintenance Deadband
The EPMDB command sets the number of encoder steps of error allowed before a position
maintenance correction move is initiated. This is useful for situations in which it is not
desirable to have the load position continuously corrected, but correction is required outside the
deadband. Positioning under a microscope is an example.