Winch Safety Switch Actuator for Hoist Cable Direction
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Solution Overview
Problem
Hoists with motorized winches often face issues when the hoist cable becomes unweighted or when the winch continues to wind the cable in reverse direction after being fully unwound, leading to potential damage and safety hazards due to ineffective safety cutoff switches.
Innovation Solution
A safety switch is integrated with the up-down switch to disable the winch motor when the hoist cable becomes unweighted or when it starts winding in reverse, using a modified 'whisker switch' with an actuating member that moves into actuated positions upon contact with the hoist cable, preventing further operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a safety cutoff switch is designed to operate only when the winch is in the raising mode, then the switch structure is simple, but the switch becomes ineffective when the winch turns in the unwinding direction causing the cable to be improperly wound
Solution Approach 1:
The safety cutoff switch is modified to detect cable movement in both winding and unwwinding directions. The switch actuator engages with the cable regardless of winding direction, allowing the single switch to perform the safety function for both raising and lowering operations, thereby achieving multi-functionality without significantly increasing structural complexity
Solution Approach 2:
Instead of detecting winch rotation direction to control safety cutoff, the invention inverts the approach by directly detecting cable movement and using that to trigger the safety cutoff switch. This bypasses the need to differentiate between winding and unwinding directions of the winch itself
2Ease of operation
If the winch is operated without weight on the cable, then the operator has flexibility in positioning, but the cable becomes tangled and may come off the spool
Solution Approach 1:
The safety cutoff switch is positioned and configured to preemptively detect when the cable becomes detached or tangled during unwinding operations. By placing the actuator in a location where it will engage with the cable under abnormal conditions, the system prevents catastrophic failures before they occur
Solution Approach 2:
The safety cutoff switch provides immediate feedback to the control system when cable abnormalities are detected. This feedback mechanism allows the system to respond automatically by stopping the winch motor, preventing further damage from tangling or cable detachment
3Productivity
If the winch continues operating after the cable is fully unwound, then the motor runs efficiently, but the cable is wound in reverse direction causing safety hazards
Solution Approach 1:
The safety cutoff switch is pre-positioned to detect cable movement in the unwinding direction before reverse winding can occur. This preliminary detection allows the system to stop the motor before the harmful reverse winding action begins, preventing damage while allowing efficient operation up to the safety limit
Data Source
AI summary
An improved hoist for raising and lowering a weighted object secured to a hoist cable, wherein the improvement comprises a safety switch in series with an up-down switch of the hoist. The safety switch has an actuating member with spaced-apart first and second portions on either side of the hoist cable and proximate the take-up shaft of the winch, and, when the hoist cable becomes unweighted or becomes wound upon the take-up shaft in an improper direction, the hoist cable moves the actuating member and prevents the up-down switch from applying power to the winch motor, thereby disabling the winch motor.