Force-Sensing Track Pad for Noise-Robust Click and Haptic Control

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Solution Overview

Problem

Existing track pads face issues with electromechanical switches that wear out and allow fluid ingress, and haptic feedback is often expensive and limited, while capacitive sensing is prone to noise interference.

Innovation Solution

Implement inductive force sensing on track pads to determine pressure and position, using inductive coils and brackets to measure inductance changes, and integrate this with capacitive sensing for redundancy and haptic feedback adjustment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If electromechanical switches are used for track pad sensing, then click detection is achieved, but reliability deteriorates due to wear and fluid ingress

Engineering Contradiction:

Improveswitch reliabilityVSAvoidswitch lifespan

Core Design Contradiction:

ReliabilityVSDuration of action of moving object

Solution Approach 1:

The patent replaces electromechanical switches with a capacitive sensing system that detects finger proximity and touch events through electrical field changes rather than mechanical contact. This eliminates moving parts, wear, and fluid ingress issues while maintaining click detection functionality through adjustable capacitive thresholds.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an intermediary capacitive sensing layer between the user's finger and the underlying electronics. This capacitive interface detects touch events through changes in electrical capacitance caused by finger proximity, eliminating the need for direct mechanical contact with switches while preserving tactile feedback capabilities.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If multiple haptic engines are used for haptic feedback, then haptic quality improves, but cost increases

Engineering Contradiction:

Improvehaptic qualityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent makes the capacitive sensing system serve multiple functions: it detects both light touch events for scrolling and heavier press events for clicks, while also enabling haptic feedback control. This multi-functionality eliminates the need for separate haptic engines, reducing cost while maintaining haptic quality through software-controlled feedback based on capacitive event classification.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent changes the operational parameters of the capacitive sensing system by implementing adjustable sensitivity thresholds that differentiate between various touch intensities. This allows the same sensing mechanism to provide both tactile feedback for scrolling and click detection without requiring additional haptic hardware, thereby reducing manufacturing cost while maintaining haptic quality.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If capacitive sensing is used for touch detection, then touch sensitivity improves, but measurement precision deteriorates due to noise interference

Engineering Contradiction:

Improvetouch sensitivityVSAvoidtouch detection accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent implements dynamic threshold adjustment in the capacitive sensing system, where sensitivity thresholds are not fixed but adapt based on environmental conditions, touch patterns, and contextual information. This dynamic approach maintains high touch sensitivity while filtering out noise and spurious events, thereby improving measurement precision without sacrificing ease of operation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent incorporates feedback mechanisms where the system continuously monitors capacitive sensing data, compares it against learned patterns and thresholds, and adjusts its response accordingly. This feedback loop enables the system to distinguish between genuine touch events and noise interference, maintaining high sensitivity while improving detection accuracy through adaptive filtering and pattern recognition.

Inventive Principle:

Principle #23Feedback

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

Provides reliable, cost-effective force sensing with adjustable haptic feedback, reducing false events and enhancing capacitive sensing accuracy through redundancy checks and adaptive calibration.

Implementation Method 1

the force sensing is performed on a track pad comprising a bracket that bends under pressure and is constructed in a way that changes proximity between an inductive coil(s) and a metal or ferrite object(s). The resulting change in distance between the inductor and an interfering member is reflected in a change in inductance which in turn is directly related to the pressure applied on the track pad.

Methodology Applied

Scientific EffectInductance: Inductor

Data Source

PatentUS12591320B2Track pad with force sensing and haptic features

Publication Date: 2026.03.31 AZOTEQ HLDG LTD

AI summary

A capacitive track pad using force sensing to determine the approximate position of touch on the track pad and to use this position as a check against a capacitive touch determined position in order to disqualify potential noise generated signals. The position resolved from the inductive force sensing measurements can also be used to assist in generating a uniform haptic experience for the user. The force sensing measurements are also used to determine if the threshold for a “click” has been met.