Add Emergency Stop Feature; Exclusive Transitions - Automation Direct DL05 User Manual

Chapter 7: RLL
PLUS

Add Emergency Stop Feature

Some garage door openers today will detect an object under
1
the door. This halts further lowering of the door. Usually
implemented with a photocell ("electric-eye"), a door in the
2
process of being lowered will halt and begin raising. We will
define our safety feature to work in this way, adding the
input from the photocell to the block diagram as shown to
3
the right. X3 will be on if an object is in the path of the
door.
4
Next, we make a simple addition to the state transition
diagram, shown in shaded areas in the figure below. Note
5
the new transition path at the top of the LOWER state. If
we are lowering the door and detect an obstruction (X3),
we then jump to the Push-UP State. We do this instead of
6
jumping directly to the RAISE state, to give the Lower
output Y2 one scan to turn off, before the Raise output Y1
7
energizes.
8
9
10
11
12

Exclusive Transitions

It is theoretically possible that the down limit (X2) and the obstruction input (X3) could
13
energize at the same moment. In that case, we would "jump" to the Push-UP and DOWN
states simultaneously, which does not make sense.
14
Instead, we give priority to the obstruction by
changing the transition condition to the DOWN
A
state to [X2 AND NOT X3]. This ensures the
obstruction event has the priority. The
modifications we must make to the LOWER Stage
B
(S5) logic are shown to the right. The first rung
remains unchanged. The second and third rungs
C
implement the transitions we need. Note the
opposite relay contact usage for X3, which ensures
D the stage will execute only one of the JMP
instructions.
7–14
DL05 Micro PLC User Manual, 6th Edition, Rev. A
Stage Programming
X0
DOWN
X2 X3
X0
RAISE
Push–UP
X0
LIGHT
X3
X0
LOWER
Push–DOWN
X0
SG
S5
Inputs Outputs
Toggle
X0 Y1
Up limit
X1 Y2
Ladder
Program
Down limit
X2 Y3
Obstruction
X3
X1
UP
T0
X0
LOWER State
SP1
to DOWN
X2 X3
to Push-UP
X3
Raise
Lower
Light
Y2
OUT
S0
JMP
S2
JMP