Capacitive Motion Enable Switch for Single-Digit Safety 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 unexpected 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, allowing operation with a single digit and ensuring both switches are active for safe operation, thus reducing ergonomic strain and preventing unintended 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 operator ergonomic strain increases leading to repetitive stress injuries
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 the operator's presence and intent before the mechanical switch is fully depressed. This merging allows the device to meet functional safety requirements through dual-sensor verification while improving ergonomics by reducing the physical effort and awkward positioning needed compared to two separate mechanical buttons.
Solution Approach 2:
The capacitive sensor acts as an intermediary between the operator and the mechanical switch. It detects the operator's approach and intent before the mechanical button is fully pressed, providing an intermediate detection layer that verifies operator presence and intent. This intermediary sensor enables the system to confirm dual activation requirements are met while allowing more natural operator positioning, thereby reducing ergonomic strain.
2Reliability
If two mechanical buttons are used in motion enable devices, then safety redundancy is provided, but undetected button failure can lead to unexpected hazardous motion
Solution Approach 1:
The capacitive sensor provides continuous feedback about the operator's presence and interaction with the device. Because capacitive sensors detect changes in electrical field caused by the operator's body, they provide real-time feedback that can indicate whether proper activation is occurring. This feedback mechanism helps detect anomalies in the activation process that might indicate mechanical button failure, making it easier to identify safety issues before they lead to hazardous motion.
Solution Approach 2:
The patent replaces one of the two mechanical buttons with a capacitive sensor, eliminating the need for two mechanical components that could both fail in the closed position. The capacitive sensor has no moving parts and cannot mechanically fail in the closed position like mechanical buttons can. This substitution maintains safety redundancy through dual-sensor verification while eliminating the specific failure mode where both mechanical buttons could be stuck closed, and improves the ability to detect activation issues.
3Reliability
If two separate mechanical switches are used, then functional safety standards are met, but device complexity increases
Solution Approach 1:
The patent substitutes a capacitive sensor for one of the two mechanical switches required by functional safety standards. The capacitive sensor is a solid-state device with no moving parts, reducing mechanical complexity. The system still meets functional safety requirements by requiring activation of both the mechanical switch and the capacitive sensor, providing dual-verification of operator intent. This substitution reduces the number of mechanical components from two to one, simplifying the device while maintaining safety compliance.
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 addresses the ergonomic issues and ensures safe operation by enabling motion only when both the mechanical switch and capacitive sensor are actively engaged, reducing the risk of repetitive stress injuries and adhering to safety standards.
Implementation Method 1
the capacitive sensor is configured to enable the second signal when a conductive object (such as a digit) is disposed in the 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.