Home Search Program Example - Automation Direct DL05 User Manual

Home Search Program Example

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.
Positioning System
Limit Switches
Motion
Numbering 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.
• 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).
• 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!
Direct SOFT
Direct SOFT
SP0
Mode 30
Locate
Parameter
Table (optional*)
Select Pulse /
Direction
* If the Locate Parameter Table is not used you must remove both the LDA function and the OUT function below it.
Appendix E: High-speed Input and Pulse Output Features
CCW limit (X1) Home limit (X2)
-3000 -2000 -1000
Selects Mode 30 as
LD
the HSIO mode.
K30
OUT
V7633
Configure the address
LDA
of the parameter table.
O2320
OUT
V7630
Configure the Y0 and Y1
LD
pulse outputs for pulse
K103
and direction, respectively
OUT
V7637
DL05 Micro PLC User Manual, 6th Edition, Rev. A
Load
CW limit (X3)
0 1000 2000 3000
Filtered Inputs
LD
K2006
OUT
V7635
LD
K1006
OUT
.
V7636
Motor
10
11
14
The constant K2006
selects a 20 ms filter
time constant.
Output this constant to
V7635, configuring X1.
The constant K1006
selects a 10 ms filter
time constant.
Output this constant to
V7636, configuring X2, the
registration interrupt input.
E–37
1
2
3
D
E
6
7
8
9
1
1
A
B
C
D