Motion Enable Switch With Capacitive Sensing for Safer Single-Finger Actuation
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Solution Overview
Problem
The use of two mechanical buttons in motion enable devices for applications like radiation therapy and medical imaging leads to repetitive stress injuries in operators due to awkward positioning and can result in unsafe unintended motion if one button fails, violating functional safety standards.
Innovation Solution
A motion enable system that combines a mechanical switch with a capacitive sensor, where the capacitive sensor is activated before or simultaneously with the mechanical switch, enabling operation only when both are actively engaged, thus reducing the risk of injury and ensuring safe operation by requiring both signals for apparatus motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two mechanical buttons are used in motion enable devices, then functional safety requirements are met, but operators suffer repetitive stress injuries due to awkward positioning and significant pressure required
Solution Approach 1:
The patent combines a mechanical button with a capacitive sensor into a single integrated motion enable device. The mechanical button provides tactile feedback and reliable actuation, while the capacitive sensor detects finger proximity or contact without requiring significant physical pressure. This merging allows the device to meet functional safety requirements through dual-sensor verification while eliminating repetitive stress injuries by reducing the physical force needed for operation.
Solution Approach 2:
The capacitive sensor acts as an intermediary between the operator's finger and the mechanical button. It detects the operator's intent through capacitance changes caused by finger proximity or contact, triggering the motion enable function before full mechanical actuation occurs. This intermediary detection mechanism reduces the physical pressure required while maintaining safety through coordinated verification of both sensor states.
2Reliability
If two mechanical buttons are used in motion enable devices, then functional safety is addressed, but undetected button failure can lead to unexpected hazardous motion
Solution Approach 1:
The capacitive sensor provides continuous feedback about the operator's interaction with the device, detecting finger proximity or contact independently of the mechanical button's state. This feedback mechanism enables the system to monitor for abnormal conditions, such as a mechanical button stuck in the closed position, because the capacitive sensor will not be activated unless the operator's finger is actually present. This dual-feedback system makes button failures detectable and prevents unexpected hazardous motion.
Solution Approach 2:
The capacitive sensor detects finger proximity or contact before the mechanical button is fully actuated. This preliminary detection allows the system to verify operator presence and intent prior to enabling motion, creating an additional safety checkpoint. If a mechanical button has failed in the closed position, the capacitive sensor will not activate because no finger contact occurs, preventing false motion enablement and allowing the system to detect the discrepancy.
3Area of stationary object
If mechanical buttons are positioned on vertical surfaces for side panel control, then space is optimized, but operators must cock wrist at awkward angles increasing injury risk
Solution Approach 1:
The capacitive sensor replaces the need for full mechanical button actuation with an electrical field-based detection system. It senses finger proximity or contact through capacitance changes, eliminating the requirement for operators to apply significant physical pressure or maintain awkward wrist positions. The mechanical button remains for tactile feedback but requires minimal actuation force, allowing operators to interact with vertically positioned controls in a more natural, ergonomic manner while preserving space-efficient panel design.
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
This configuration reduces the risk of repetitive stress injuries and ensures safe operation by requiring both signals for apparatus motion, adhering to functional safety standards and preventing unintended hazardous motion.
Implementation Method 1
the capacitive sensor is configured to enable the second signal when a conductive object (such as a digit) is within a sensing region of the capacitive sensor
Data Source
AI summary
A motion-enable device includes a mechanical switch and a capacitive sensor with a sensing region that is located adjacent to the mechanical switch. The mechanical switch enables a first signal when closed or actuated that indicates that the mechanical switch is in an active state. The capacitive sensor enables a second signal when a conductive object is disposed in the sensing region, where the second signal indicates that the capacitive sensor is in an active state. Enablement of operation of an apparatus depends on receipt of both the first signal and the second signal. The mechanical switch and the capacitive sensor act as the two separate switches required by functional safety requirements for a motion enable device. Because the sensing region of the capacitive sensor is adjacent to the mechanical switch, the first and second signals are generated when an operator actuates the mechanical switch with a single digit.