Anti-tamper Safety Switch with Cam Locking Mechanism
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Solution Overview
Problem
Existing safety switches with cam operating mechanisms are vulnerable to tampering, allowing users to bypass the safety feature by permanently biasing the cam towards a position that keeps power supplied to machines even when the guard door is open, posing a risk to personnel safety.
Innovation Solution
A safety switch system with a cam mechanism, solenoid plunger, and a locking mechanism that includes a moveable safety arm and sliding lock, which prevents the actuator from being removed until certain conditions are met, ensuring the cam returns to its datum position and power is disabled when the guard door is opened.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the cam plunger is directly biased onto the cam without a locking mechanism, then the structure is simple and ease of operation is improved, but the reliability deteriorates as the actuator can be easily removed and the cam permanently biased towards the power-supplied position
Solution Approach 1:
The locking mechanism performs preliminary locking of the actuator to the cam plunger before the cam can be rotated to the power-supplied position. The locking means engages the actuator in the engagement means, preventing removal until the cam returns to its datum position, thus preventing tampering before it can occur.
Solution Approach 2:
The locking mechanism acts as an intermediary between the actuator and the cam plunger. It mediates the interaction by controlling when the actuator can be removed, requiring the cam to return to the datum position first, thus preventing direct manipulation of the cam plunger bias.
2Ease of operation
If the cam can be freely rotated to enable power supply, then the ease of operation is improved for legitimate use, but the reliability deteriorates as it allows unauthorized bypassing of the safety switch
Solution Approach 1:
The locking mechanism applies preliminary anti-action by preventing actuator removal until the cam is in the correct position (datum position with power disabled). This counteracts any attempt to bypass the safety switch by ensuring the actuator remains locked until the safe state is achieved.
Solution Approach 2:
The locking mechanism dynamically changes its state based on cam position. When the cam is rotated to the power-supplied position, the locking means releases the actuator. When the cam returns to the datum position, the locking means re-engages, dynamically adapting to the system state to maintain safety.
3Ease of repair
If the actuator can be removed at any time, then the ease of repair and maintenance is improved, but the reliability deteriorates as it allows bypassing of the safety mechanism
Solution Approach 1:
Before allowing actuator removal for maintenance, the system requires the cam to be in the datum position (power disabled state). This preliminary condition ensures that maintenance can only be performed when the machine is in a safe state, preventing accidental activation during repair.
Solution Approach 2:
The locking mechanism provides feedback about the cam position to control actuator removal. The locking means only releases the actuator when the cam is in the correct position, providing continuous feedback to ensure safety conditions are met before maintenance operations can proceed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively prevents unauthorized bypassing of the safety switch, ensuring power is cut to the machine only when the guard door is properly closed, thereby enhancing personnel safety by requiring the cam to return to its power-off position.
Implementation Method 1
a cam mechanism, a cam operated solenoid switch
Implementation Method 2
a cam operated solenoid switch
Implementation Method 3
the locking mechanism has means to lock the actuator in the engagement means to prevent its removal
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A solenoid plunger 14 of the switch 4 is moved by cam plunger 34 and is biased towards the cam plunger 34, a locking plate 40b is positioned between the plungers 14 and 34. Cam 34 is biased for movement towards a cam 22 and is moved towards the solenoid plunger by rotation of the cam 22 by removal of actuator 8 which causes retraction of the solenoid plunger into the switch 4. The locking plate 40b is lockable when the cam plunger 34 is biased into a detent 36 in the cam 22 when the actuator is inserted, to lock the cam plunger 34 and cam 22 and prevent removal of the actuator 8.