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6) (20%) A car wash automation system is shown in Figure 4

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6) (20%) A car wash automation system is shown in Figure 4. The system comprises:
Figure 4
a) One gantry supporting one horizontal roller and two vertical rollers. The gantry is driven by one
motor with two operating modes: gantry forward (G_F) and gantry reverse (G_R);
b) One single motor to rotate both the horizontal roller and vertical rollers (MR);
c) One motor to raise and lower the horizontal roller with two operating modes: raise (MH_R) and
lower (MH_L);
d) One TOF timer;
e) One CTU counter to monitor the number of vehicles washed weekly. This counter is reset
manually.
f) One buzzer (BUZZER);
g) One red flasher (FLASHER) operating at a rate of 0.5/0.5 second;
h) One pilot lamp (PL), push-buttons (PBs), and NC (normally closed) limit and proximity sensors.
Automation requirement:
A_1) Initial conditions: The gantry is at the rear position, the horizontal roller is in the raised
position, and a vehicle is present in the washing area. When the initial conditions are fulfilled,
pressing the normally open (NO) start PB starts the following cycle:
A_2) Cycle indicator lamp (PL) is lit, followed by a 10-second wait period;
A_3) The horizontal roller moves down for 5 seconds precisely;
A_4) The rollers start to rotate AND the gantry moves forward;

Note: It is presumed here that the water spray pumps are activated at the same time as the
motor which rotates the rollers. You are not required to take this action into account!

A_5) Forward movement of the gantry is stopped by the gantry forward limit switch. At this point,
the gantry reverse command is given. The rollers still rotate;
A_6) Gantry reverse operation AND rotation of the rollers are stopped by the gantry rear limit
switch. A command is given to raise the horizontal roller up. At this point, the washing
counter is updated;
A_7) If required, a latching emg push button must stop the cycle at any time (emergency stop of
all motors) and activate a buzzer and a 0.5/0.5 sec flasher. Throwing back the emg PB must
interrupt the buzzer and flasher immediately. Operation then resumes from where it had been
stopped. Use a single pole double throw (SPDT) mushroom PB for this purpose.
6.1) Establish a list of input and output field devices;
6.2) Develop a GRAFCET to solve the automation problem. Keep the original nomenclature when
specifying triggers and actions;
6.3) Write the equations for transitions, steps and actions (Use Eq_G4);
6.4) Transform the GRAFCET equations into a handwritten PLC ladder program in accordance
with the Allen Bradley standards.