User`s manual

C-2 Motion Mate™ DSM314 for Series 90™-30 PLCs User's Manual – January 2001 GFK-1742A
C
valid and the A
ctual Position
%AI status word as reported by the DSM314 will wrap from high to
low count or from low to high count values. This is an excellent mode for continuous applications
that will always operate via incremental moves, in the same direction.
Home Offset
and
Home
Position
configuration items allow simple referencing to the desired location
.
Absolute Encoder Mode Considerations
The GE Fanuc 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.
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.
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.