Conical Shank Anti-Ligature Door Lever Design
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Solution Overview
Problem
Suicide attempts by patients in psychiatric institutions using cords or ligatures draped over door handles pose a significant risk, as these attempts can occur undetected and result in high numbers of successful suicides, particularly in private rooms with unlocked doors.
Innovation Solution
The development of an Anti-Ligature Lever Latch Lock (A4L) system that operates in Passage Mode and Classroom Mode, featuring a conical escutcheon and lever design that allows ligatures to slide off easily, combined with a keyed mechanism to prevent unauthorized entry, ensuring the ligature cannot be used for hanging, and is ADA-compliant for widespread use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a traditional door lever or knob is used, then the door can be easily operated for entry and exit, but it can be used as an anchor point for ligatures in suicide attempts
Solution Approach 1:
The door lever is designed with an asymmetric conical shape where the diameter decreases from the base toward the tip. This asymmetric geometry prevents ligatures from being securely anchored while maintaining ease of door operation, as the conical surface allows the lever to be pushed or pulled effectively without providing a secure grip point for ligatures
Solution Approach 2:
The lever incorporates a conical (curved) surface instead of a flat or angular design. This curvature ensures that ligatures cannot be securely positioned on the lever surface, as the sloping conical shape causes any wrapped material to slide off rather than remain anchored, thereby reducing suicide risk while preserving operational functionality
2Reliability
If the door lever is designed with anti-ligature features, then suicide attempts are prevented, but the lever may become more complex in structure
Solution Approach 1:
Only the exterior surface of the lever that contacts the user's hand is given the anti-ligature conical shape. The internal mechanical structure remains traditional and simple, maintaining the original door operation mechanism. This localized application of the conical shape provides suicide prevention without requiring complex structural changes throughout the entire lever assembly
Solution Approach 2:
The lever's exterior surface parameter is changed from a traditional flat or cylindrical shape to a conical shape with a specific angle range (30-60 degrees). This parameter change alone provides the anti-ligature function without altering the fundamental structure or adding complex components, achieving reliability improvement through simple geometric modification
3Reliability
If a conical lever design is implemented, then ligatures slide off easily, but the lever shape must be precisely controlled during manufacturing
Solution Approach 1:
The conical shape is applied to only the critical exterior surface area of the lever that contacts ligatures, rather than requiring the entire lever to be perfectly conical. This partial application reduces manufacturing precision requirements, as only the surface geometry in the ligature contact zone needs to meet specific angular tolerances, while other portions of the lever can be manufactured with standard tolerances
Data Source
AI summary
A lever latch lock assembly including:a. a lock housing mounted in the door including a lock bolt movable along a first axis, a spindle extending along a second axis generally perpendicular to the first axis, the spindle extending outward at each of the interior and exterior sides of the housing and terminating in opposite ends, and a transmission which converts rotation of the spindle to axial motion the lock bolt,b. a lever assembly attached to each of the spindle's ends and adapted to rotate the spindle, the lever assembly, including:(1) an escutcheon formed as a truncated generally conical cylinder having(i) a base of first diameter adapted to be situated closely adjacent one of the interior and exterior sides of the door and coaxial with the second axis,(ii) a top end having a top edge opposite the base, the top end having a smaller diameter than the first diameter, and(iii) a bore through which extends the spindle, and(2) a lever including(i) a hub part and(ii) an elongated handle part extending from one side of the escutcheon in a direction transverse of the second axis, the handle having a top part that extends as a smooth contiguous uninterrupted surface from the top of the hub.