GRAFCET — Lift Car Door Interlock
The safety sequence a lift door cannot be certified without: dwell, close, and the alternative divergence on the closing step that sends a photo-eye or door-edge trip to a re-open step and back to the dwell timer, so the interlock is only made when the closed limit and the lock both prove.
Make it your own.
title "Lift car door — open, dwell, close interlock"
step 10 "Doors closed, car parked" initial
N "Door zone lamp"
step 11 "Open doors"
N "Door motor open"
S "Car call inhibit"
step 12 "Dwell at landing"
L 5s "Dwell timer"
N "Landing gong"
step 13 "Close doors"
N "Door motor close"
step 14 "Re-open on obstruction"
R "Door motor close"
N "Door motor open"
P "Nudging buzzer"
step 15 "Doors locked, motion permitted"
R "Car call inhibit"
S "Motion permit"
transition t1 : "landing_call + car_call"
transition t2 : "door_open_limit"
transition t3 : "dwell_elapsed . /photo_eye"
transition t4 : "door_closed_limit . lock_made"
transition t5 : "photo_eye + door_edge"
transition t6 : "door_open_limit"
transition t7 : "start_move"
10 -> t1 -> 11 -> t2 -> 12 -> t3 -> 13
# Closed and locked, or obstructed: the two receptivities are exclusive
# by construction, which is what an alternative divergence asserts.
alternative 13 -> t4, t5
t4 -> 15
t5 -> 14
14 -> t6 -> 12
15 -> t7 -> 10