AutomationDirect DL105, User Manual

Page: 112 / 350

High
-S
peed
Input
and
Pulse
O
utput
Features
3--36
High-speed Input and Pulse Output Features
DL105 PLC User Manual, 3rd Edition
One of the more challenging aspects of motion control is the establishment of actual
position at powerup. This is especially true for open-loop systems which do not have
a position feedback device. However, a simple limit switch located at an exact
location on the positioning mechanism can provide “position feedback” at one point.
For most stepper control systems, this method is a good and economical solution.
Motion
Numbering System
Motor
Load
CCW limit (X1) CW limit (X3) Home limit (X2)
0 1000 2000 3000 --1000 --2000 --3000
Limit Switches
Positioning System
In the drawing above, the load moves left or right depending on the CCW/CW
direction of motor rotation. The PLC ladder program senses the CCW and CW limit
switches to stop the motor, before the load moves out-of-bounds and damages the
machine. The home limit switch is used at powerup to establish the actual position.
The numbering system is arbitrary, depending on a machine’s engineering units.
At powerup, we do not know whether the load is located to the left or to the right of the
home limit switch. Therefore, we will initiate a home search profile , using the
registration mode. The home limit switch is wired to X2, causing the interrupt. We
choose an arbitrary initial search direction, moving in the CW (left-to-right) direction.
S
If the home limit switch closes first, then we stop and initialize the
position (this value is typically “0”, but it may be different if preferred).
S
However, if the CW limit switch closes first, we must reverse the motor
and move until the home limit switch closes, stopping just past it.
In the latter case, we repeat the first move, because we always need to make the
final approach to the home limit switch from the same direction , so that the final
physical position is the same in either case!
SP0
LD
K30
Selects Mode 30 as
the HSIO mode.
OUT
V7633
LDA
O2320
OUT
V7630
Configure the address
of the parameter table.
Direct SOFT
Mode 30
LD
K103
Configure the Y0 and Y1
pulse outputs for pulse
and direction, respectively.
OUT
V7634
Select Pulse /
Direction
Locate
Parameter
Table (optional)
LD
K2006
The constant K2006
selects a 20 mS filter
time constant.
OUT
V7635
Output this constant to
V7635, configuring X1.
OUT
V7637
Output this constant to
V7637, configuring X3.
LD
K1006
The constant K1006
selects a 10 mS filter
time constant.
OUT
V7636
Output this constant to
V7636, configuring X2, the
registration interrupt input.
Filtered Inputs
Home Search
Program Example