User Manual
Appendix C
GFK-1742F
Jan 2020
Position Feedback Devices
415
C-3
Absolute Encoder Mode Considerations
The Digital serial encoder can be used as an absolute type encoder by adding a battery pack
to retain servo position while system power is off. A Find Home cycle or Set Position %AQ
command must be performed initially or whenever encoder battery power is lost with the
servo amplifier also in a powered down state. Feedback Mode set to ABSOLUTE must be
selected in the configuration software for proper operation with a battery pack.
C-3.1
Absolute Encoder - First Time Use or Use After Loss of
Encoder Battery Power
The absolute encoder temporarily provides incremental data during the first use or after
restoring encoder battery power. The incremental data is lost when motor shaft rotation
causes the encoder to pass a reference point (similar to a marker signal) within one
revolution of the motor shaft. The Digital Absolute serial encoder must be rotated up to one
full revolution after the absolute mode battery has been reattached to the amplifier. The
encoder will reference itself within one revolution and report a referenced status to the
DSM314.
C-3.2
Absolute Encoder Mode - Position Initialization
When a system is first powered up in Absolute Encoder mode, a position offset for the
encoder must be established. Using the %Q Find Home cycle or the Set Position % AQ
command can accomplish this.
Find Home Cycle - Absolute Encoder Mode
The Find Home Mode can be configured for Move (+), Move (
–
) or Home Switch operation.
Refer to Chapter 4 for additional details of Home Cycle operation. The Home Offset and
Home Position configuration items function the same as in Incremental Encoder mode. At
the completion of the Home Cycle, the Actual Position %AI status word is set to the
configured Home Position value. The DSM314 internally calculates the encoder Absolute
Feedback Offset needed to produce the configured Home Position at the completion of the
Home Cycle. This Absolute Feedback Offset is immediately saved in the DSM314 non-
volatile (capacitor backup) memory.
Once an absolute position is established by successful completion of a Find Home cycle, the
DSM314 will automatically initialize the Actual Position %AI status word after a power cycle
and set the Position Valid %I bit.
Note:
If the Position Valid %I bit is set before initiating a Home Cycle, the Home Cycle clears Position Valid
and then sets Position Valid again when the cycle completes. If the Home cycle is halted by an
Abort All Moves %Q bit command, Position Valid will remain off. However cycling power will cause
a valid Actual Position to be restored and Position Valid will be automatically set.