Two-Part Capacitive Force Sensor for Stable Actuation Input Detection
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Solution Overview
Problem
Force sensors with a film layer structure are sensitive to temperature fluctuations and moisture ingress, and they can be distorted due to insufficient mechanical fixation, making them unreliable for force detection, especially in adverse conditions.
Innovation Solution
An input device with a two-part structure comprising a first component with an actuating layer and a second component with a carrier, both having electrodes facing each other through an air gap, connected by a fastener, and a detection and evaluation unit that applies measuring capacitance to detect changes in displacement caused by actuating forces, enhancing reliability and avoiding the drawbacks of film layer structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a film layer structure is used for force detection, then the sensor can be integrated between components, but the sensor becomes highly sensitive to temperature fluctuations and moisture ingress
Solution Approach 1:
The sensor is divided into two separate components: a first component with the actuating layer and first electrode, and a second component with the carrier and second electrode. This segmentation allows each component to be optimized independently, with the sensor elements protected within their respective housings, reducing sensitivity to environmental factors while maintaining integration capability.
Solution Approach 2:
An air gap is introduced as an intermediary between the first electrode and second electrode. This air gap acts as a protective barrier that prevents direct contact and potential damage to the electrodes, while still allowing capacitive coupling for force detection. The air gap also provides thermal and moisture isolation, reducing sensitivity to environmental fluctuations.
2Strength
If the film layer structure is embedded or clamped between components, then mechanical fixation is achieved, but the structure can be distorted considerably
Solution Approach 1:
By separating the sensor into two distinct components with the air gap between them, the film layer structure is no longer clamped or embedded under stress. Each component maintains its structural integrity independently, eliminating the distortion that would occur from clamping while still providing secure mechanical fixation through separate mounting points.
Solution Approach 2:
The air gap serves as an intermediary that eliminates direct mechanical contact between the electrodes and their mounting structures. This allows the film layer to remain unstressed and undistorted, as it is not clamped between components but rather suspended with controlled spacing maintained by the air gap and supporting elements.
3Ease of operation
If insufficient mechanical fixation is applied to allow mobility for force detection, then the sensor can detect forces, but the layer structure is difficult to mount in a bubble-free manner
Solution Approach 1:
Dividing the sensor into two separate components allows each to be pre-assembled and tested independently before final assembly. The first component can be mounted with its actuating layer and first electrode, and the second component with its carrier and second electrode, reducing the complexity of achieving bubble-free mounting of a single large assembly while maintaining the mobility needed for force detection.
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 solution provides reliable force detection across varying temperatures and humidity levels by minimizing distortion and improving mechanical fixation, ensuring accurate actuation detection and tactile feedback.
Implementation Method 1
The detection and evaluation device is configured to apply a measuring capacitance to the first electrode and to the second electrode, and to detect a change in the measuring capacitance dependent on the displacement moving the first electrode and the second electrode closer to each other
Implementation Method 2
The first electrode, under an influence of an actuating force acting on the actuating surface undergoes, upon an actuation, a displacement so as to move the first electrode closer to the second electrode against an elastic restoring force
Data Source
AI summary
An input device includes a first component with an actuating layer and a first electrode arranged adjacent thereto, a second component with a carrier and a second electrode, and a device which electrically contacts the first and second electrodes. The first and second electrodes face each other with an air gap therebetween. The first electrode, under an influence of an actuating force acting on the actuating surface undergoes, upon an actuation, a displacement so as to move the first electrode closer to the second electrode against an elastic restoring force. A detection and evaluation device applies a measuring capacitance to the first and second electrodes and detects a change in the measuring capacitance dependent on the displacement moving the first and second electrodes closer to each other in order to associate the actuation with a switching or controlling function after detecting a predetermined change in the measuring capacitance.