PLAT: An Automated Fault and Behavioural Anomaly Detection Tool for PLC Controlled Manufacturing Systems

Table 4

Fault and behavioural anomaly detection result.

PLAT tool	Fault or behavioural anomaly description	Faulty or erroneous transition	Expected transition/s	Affected device
1	The sensor signal PRT_CHK of the Part Loader (PrtLDR) is turned ON while the Part Loader (PrtLDR) is returning back to its home position	PrtLDR-ADV_OFF → PrtLDR-PRT_CHK_ON	PrtLDR-ADV_OFF → PrtLDR-RET_ON	Part Loader (PrtLDR)
2	The sensor signal OpSen1 of the Daecha Clamp (DCLAMP) is permanently turned ON while Robot 1 (RBT1) is picking up the part from the Part Loader (PrtLDR); the sensor input will always be 1 even if the left clamp is not opened	DCLAMP-CLOSE_ON → DCLAMP-OpSen2_OFF	DCLAMP-CLOSE_ON → DCLAMP-OpSen1_OFF	Daecha Clamp (DCLAMP)
3	The actuator related to the signal OPEN of the Daecha Clamp (DCLAMP) is decelerated while the clamps are being opened	DCLAMP-OPEN_ON → DCLAMP-ClsSenl_OFF	Not applicable [transition time error has occurred]; Expected (maximum) transition time: 0.03 and observed transition time: 2.11 (in seconds)	Daecha Clamp (DCLAMP)
4	The sensor signal 1ST_WORK_COMP of Robot 1 (RBT1) is turned OFF while Robot 1 (RBT1) is transferring the part to the Daecha (DCHA)	RBT1-PRT_MOVE_ON → RBT1-1ST_WORK_COMP_OFF	RBT 1-PRT_MOVE_ON → RBT1-2ND_WORK_COMP_ON	Robot 1 (RBT1)
5	The actuator related to the signal FORWARD of the Part Loader (PrtLDR) is deactivated while the part is being loaded to the Part Loader (PrtLDR); if an actuator is deactivated then the corresponding mechanical operation cannot be carried out	The subsystem has stopped working [PLAT has already waited for 180 seconds]	Last observed signal state: PrtLDR-FORWARD_ON	Part Loader (PrtLDR)
6	Seven parts are presented to the system with interval of (approximately) thirty seconds and twenty-three parts are presented to the system with interval of (approximately) sixty seconds [the periodic checking of the probability values is done after every thirty group cycles]	PrtLDR-BACKWARD_OFF → PrtLDR-PRT_CHK_ON	Not applicable [transition time probability error has occurred]; Expected probabilities: 0.47 and 0.52 and observed probabilities: 0.20 and 0.79	Part Loader (PrtLDR)
7	The sensor signal RET of the Part Loader (PrtLDR) is turned OFF while the Part Loader (PrtLDR) is in its home position [during the first group cycle]	PrtLDR-RET_ON → PrtLDR-RET_OFF	PrtLDR-RET_ON → PrtLDR-BACKWARD_OFF; OR; PrtLDR-RET_ON → PrtLDR-PRT_CHK_ON	Part Loader (PrtLDR)
8	The sensor signal HOME_POS of Robot 1 (RBT1) is turned ON while Robot 1 (RBT1) is placing the part to the Daecha (DCHA)	RBT1-2ND_WORK_COMP_ON → RBT1-HOME_POS_ON	RBT1-2ND_WORK_COMP_ON → RBT1-PRT_MOVE_OFF	Robot 1 (RBT1)
9	The actuator related to the signal BACKWARD of the Part Loader (PrtLDR) is decelerated while the Part Loader (PrtLDR) is returning back to its home position	PrtLDR-BACKWARD_ON → PrtLDR-ADV_OFF	Not applicable [transition time error has occurred]; Expected (maximum) transition time: 0.04; and observed transition time: 2.57 (in seconds)	Part Loader (PrtLDR)
10	The sensor signal ClsSenl of the Daecha Clamp (DCLAMP) is deactivated while the Part Loader (PrtLDR) is proceeding towards its advanced position if a sensor is deactivated then it is not able to send any further input value to the PLC controller	DCLAMP-OpSen2_OFF → DCLAMP-ClsSen2_ON	DCLAMP-OpSen2_OFF → DCLAMP-ClsSenl_ON	Daecha Clamp (DCLAMP)
11	The actuator related to the signal PRT_PICK of Robot 1 (RBT1) is deactivated while Daecha (DCHA) is returning back to its home position	The subsystem has stopped working [PLAT has waited for 180 seconds]	Last observed signal state: RBT1-PRT_PICK_ON	Robot 1 (RBT1)
12	The actuator related to the signal PRT_MOVE of Robot 1 (RBT1) is decelerated while Robot 1 (RBT1) is loading the part to the Daecha (DCHA)	RBT 1-PRT_MOVE_ON → RBT1-2ND_WORK_COMP_ON	Not applicable [transition time error has occurred]; Expected (maximum) transition time: 16.01; and observed transition time: 24.56 (in seconds)	Robot 1 (RBT1)

In this table, the arrow symbol (→) represents the signal-state transition; and rows numbers 3, 6, 9, and 12 are the examples of behavioural anomalies others are the examples of faults.
A transition time error occurs if any transition takes longer time than the following: (its corresponding maximum transition time + user-defined threshold value Δ).
Δ = 1.5 if Max_Time ≤ 15; Δ = 3 if Max_Time > 15 and ≤ 30; Δ = 4 if Max_Time > 30 Max Time: maximum transition time; all the times are given in seconds.
A transition time probability error occurs if significant changes (i.e., the changes greater than 0.15) in the transition time probabilities associated with a transition take place.
The name of the “Affected Device” can easily be determined from the name of signal-states associated with the faulty/erroneous transition (this column is continually updated based on the propagation of the fault/behavioural anomaly).