Guard Locking Device
A guard locking device is an interlocking safety device that locks a movable guard in the closed position and integrates with the machine control system. It prevents hazardous machine functions until the guard is closed and locked, and maintains the guard locked until hazardous motion has ceased, ensuring safe access only after risks are eliminated.
On the shop floor, guard locking devices are used on movable guards like doors, gates, and covers for high-inertia equipment such as robot cells, CNC machines, presses, and tumblers. They physically lock the guard closed during operation, preventing access until hazardous motion stops. The control system monitors stopping time and speed, unlocking only after hazards cease. A separate start command is required after closure, preventing auto-restart. These devices provide higher protection than simple interlocks by integrating timing and speed conditions, and they complement lockout procedures for maintenance tasks.
How is a guard locking device different from a standard interlock switch?
A standard interlock monitors guard position and issues a stop command when opened. A guard locking device locks the guard closed, integrates with the control system, and ensures hazardous functions cannot operate unless the guard is closed and locked, physically inhibiting opening until hazards cease, as per ISO 14119.
What are the two safety functions of an interlocking device with guard locking?
The two safety functions are: 1) Prevention of guard release while motion exists, where the guard remains locked until motor speed is zero or hazards are absent. 2) Prevention of unexpected start-up when the guard is not closed or locked, ensuring hazardous motion cannot occur unless both conditions are confirmed.
When should guard locking be used instead of simple interlocking on WorkSafeBC-regulated equipment?
Guard locking should be used when the machine has high inertia or slow stopping times, such as rotating drums or robot arms, where opening the guard before motion ceases exposes workers to hazards. It is also needed for routine access during production, like loading robot cells, to physically prevent access until all motion stops.