Resistive Key Spacer Geometry for Stable Force Sensor Preload
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Solution Overview
Problem
Control panels in motor vehicles face issues with mechanical play and uneven pressure distribution due to spacers used between force sensors and covers, leading to loss of pre-load at varying temperatures, which affects the detection of tactile pressing forces.
Innovation Solution
A spacer made of elastically compressible material with a transversal top surface and a larger bottom surface is used to minimize reaction force on the cover and ensure even distribution of prestressing and tactile pressing forces over the force sensor, maintaining a consistent pre-stress despite manufacturing and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spacer is arranged to be axially compressed between the force sensor and the cover to eliminate mechanical play, then the direct transmission of tactile pressing force is ensured, but the greatest amount of pre-load occurs on the outer peripheral edge of the spacer causing uneven pressure distribution
Solution Approach 1:
The spacer features an asymmetric thickness profile where the central portion is thinner than the peripheral portion. This asymmetric geometry redistributes the compressive load away from the outer peripheral edge toward the central area, achieving more uniform pressure distribution across the spacer while maintaining direct force transmission between the cover and sensor.
2Measurement precision
If the thickness of the cover in the detection zone is made relatively small to permit elastic deformation during tactile pressing, then detection of tactile pressing is enabled, but the mounting of the spacer in compression causes outward deformation of the cover that detracts from external appearance
Solution Approach 1:
The spacer's thickness varies locally across its surface, with the central portion being thinner and the peripheral portion being thicker. This local variation in geometry allows the spacer to provide sufficient compression for force transmission while reducing the outward deformation effect on the cover's external appearance, as the thinner central portion exerts less expansive force on the cover surface.
3Ease of manufacture
If a conventional spacer in the form of a parallelepipedal slab of uniform axial thickness is used, then simple manufacturing is achieved, but the prestressing force is excessive leading to risks of creep at the sensor and cover
Solution Approach 1:
The spacer transitions from a uniform thickness design to a variable thickness design where the central portion is thinner than the peripheral portion. This parameter change in the spacer's geometric dimensions reduces the overall prestressing force applied to the sensor and cover, minimizing the risk of creep while maintaining sufficient force transmission capability.
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 solution reduces the risk of creep and enhances the detection of control button activation by minimizing the prestressing force, ensuring reliable operation across different conditions.
Implementation Method 1
a spacer made of elastically compressible material that is interposed between the sensor and the cover, the spacer being mounted axially compressed between the sensor and the cover
Data Source
AI summary
Control panel including a cover mounted on a support that is provided with a tactile pressing detection zone in which a force sensor that includes a pressure-sensitive zone is arranged behind a detection zone between the cover and the support so as to produce an electrical control signal when a user applies a determined tactile pressing force to the detection zone. The tactile pressing force is transmitted axially (X1) towards the sensitive zone via a spacer made of elastically compressible material interposed between the sensor and the cover. The spacer includes at least one compressible portion that defines a transversal top surface that bears against the cover and a transversal bottom surface that bears against the sensitive zone of the sensor. The top surface has an area smaller than the area of the bottom surface.