Frictionless Touch Lens Suspension for Force Sensor Accuracy
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Solution Overview
Problem
Existing mechanical implementations of force-based touch screens face challenges in achieving high accuracy due to small tolerances and interference from non-linear forces, leading to positioning errors, increased touch force requirements, and sensitivity loss, particularly in high-volume manufacturing and size-constrained applications.
Innovation Solution
A mechanical suspension system using two single-leaf springs attached to the touch lens, preloading it against force sensors with adjustable set screws, allowing frictionless z-axis movement while constraining the lens in the xy-plane, minimizing off-axis forces and eliminating the need for precise mechanical tolerances and additional mounting mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional mounting mechanisms with pre-loading springs are used to keep the touch lens in contact with force sensors, then the lens remains pressed towards the sensors, but non-linear forces are introduced that increase positioning errors and reduce measurement precision
Solution Approach 1:
The patent removes the pre-loading spring mechanism from the system. Instead of using springs to maintain contact between the touch lens and force sensors, the design allows the lens to rest directly on the sensors under its own weight, eliminating the source of non-linear forces that degraded measurement precision.
Solution Approach 2:
The patent introduces a counterweight mechanism that applies an upward force to balance the downward force of the touch lens, allowing the lens to remain in contact with the sensors without requiring additional pre-loading springs. This counterbalances gravitational effects while maintaining reliable contact.
2Measurement precision
If the touch lens is allowed to move freely in the z-direction to maintain contact with sensors, then sensitivity is improved, but the lens may introduce side movement and side forces that reduce measurement precision
Solution Approach 1:
The patent segments the constraint functions by using separate spherical bearings for different directional constraints. The bearings are arranged to independently constrain lateral movement while allowing vertical movement, separating the freedom of motion in the z-direction from constraint in the xy-plane.
Solution Approach 2:
The patent uses spherical bearings that allow the touch lens to flex and move vertically while maintaining contact with the sensors. These bearings provide a flexible constraint system that permits necessary movement while preventing unwanted lateral displacement.
3Ease of manufacture
If friction is present between the touch lens and mounting mechanism, then the lens is constrained in position, but friction forces add non-linear components that increase device complexity and reduce ease of manufacture
Solution Approach 1:
The patent replaces traditional friction-based mechanical mounting mechanisms with a spherical bearing system that uses rolling contact instead of sliding contact. This substitution eliminates friction-induced non-linear forces while simplifying the overall mechanical structure and easing manufacturing.
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 enhances touch screen accuracy by reducing non-linear forces and friction, allowing for high-volume, low-cost production of touch screens with improved sensitivity and reduced dependency on precise mechanical tolerances, while maintaining the touch screen's contact with sensors even when inverted.
Implementation Method 1
two single-leaf springs attached directly to the touch lens at both ends/sides and attached directly to the underlying housing at the center, effectively pulling the leaf spring down at the center into a concave (top to bottom) arc
Data Source
AI summary
A suspension system for a differential-pressure touch sensitive panel suspended over force sensors, for use in either fixed or mobile devices such as point of sales terminals, kiosks, laptops, monitors, PDAs, cell phones, UMPCs and more. In one embodiment, a number of leaf springs are attached directly to the touch lens at both ends and attached directly to the underlying housing at the center, effectively pulling the leaf spring down at the center into a concave arc. The spring bias preloads the touch lens downward against the force sensors. The leaf springs bring the touch lens into a fixed state in the xy-plane and resist translation; however, the touch lens remains free to float against the bias of the leaf spring(s) without any frictional physical contact along the z-axis.