Electro Cam PL-1746 Series - Manual (Page 54)

4-9 PLS Functions
Group Offset (cont’d)
Description In many machines with rotary motion, it is often necessary to provide some means to
adjust the phase or angular position of one shaft with respect to another. This adjustability
is usually obtained through the use of timing chains or belts, or possibly clutches, differ-
entials, or couplings. All of these devices allow the position of a driven shaft to be offset
from the position of the driving shaft. The PL-1746 has the ability to add offsets to the
resolver position. This feature of the PL-1746 allows the user to change the timing of
machine functions without incurring the time consuming task of mechanically altering
the machine.
The group functions in the PL-1746 work off of machine position (see Positions & Off-
sets in Chapter 1 for more information). The PL-1746 always has at least one group
and may have up to six groups. Each group can be individually offset from the machine
position to allow individual functions to be properly timed with respect to the rest of the
machine.
When a group is operating in modes 0, 3, 4, or 5, machine offset is entered by the user
and remains fixed. The value is also stored in non-volatile memory and so is in effect
during subsequent power cycles.
When a group is operating in modes 1 or 2, the user supplies a preset position or offset.
When the group enable becomes active, the PL-1746 calculates an offset from the
current machine position, such that the group position becomes the preset position.
This allows the timing of outputs in groups operating in these modes to be synchronized to
machine operations that do not occur at the same time during each machine revolution.
Group Position
Jog the machine to a position that corresponds to the desired group position and enter
the group position.
• For standard PL-1746 controllers using Electro Cam resolvers, the ABS value will
directly show the relationship between the group position and machine position in
scale factor increments. For example, suppose that machine position is at 0 and
SCALE FACTOR is set to 360. If the ABS of a group is 20, its position will be 20
degrees.
• If groups have been programmed with their own offsets, changing machine offset will
change all of the group positions at once. It is usually best to set machine offset to
the desired zero position in the machine cycle before programming individual
group offsets.
• If groups have been programmed with their own offsets, changing GRP POS DISP to
“ONE” will immediately change ABS for all groups to value programmed for Group 0.
Programming Preset
Preset is programmed in scale factor units.
• The preset value is stored in the controller on power down. However, the last group
position is not. On power up, the group position will be the same as machine posi-
tion. When the group’s input terminal is energized, then the group position will reset
to the preset value.
Also see MACHINE OFFSET, GRP POS DISP, OUTPUT GROUPS, and Section 6 for
details on Output Grouping & Modes.