Capacitive Force Sensor Mechanical Change Compensation

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Solution Overview

Problem

Capacitive sensing devices face challenges in accurately determining force information on an input surface due to mechanical changes and variations in the air gap distance between sensor electrodes and force electrodes, leading to inaccurate force measurements.

Innovation Solution

A method is introduced that involves storing a baseline capacitance and determining a mechanical change compensation factor through calibration, allowing for accurate force information determination by accounting for changes in capacitance and mechanical changes, independent of the air gap distance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If capacitive sensing is used to detect force on an input surface, then force information can be obtained, but mechanical changes and air gap distance variations cause measurement inaccuracies

Engineering Contradiction:

Improveforce measurement accuracyVSAvoidmeasurement consistency

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The system measures the actual air gap distance between the sensor electrode and force electrode using capacitive sensing, then uses this feedback information to dynamically compensate for mechanical changes. The controller adjusts the force measurement based on the measured air gap distance, ensuring accurate force detection despite variations in the mechanical structure or air gap distance.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system changes the parameter being measured from direct force detection to indirect detection via air gap distance measurement. By measuring the capacitance change that corresponds to air gap distance variations, the system can infer and compensate for mechanical changes, thereby improving force measurement accuracy without being directly affected by mechanical instability.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If the air gap distance between sensor electrode and force electrode varies, then device assembly tolerances are accommodated, but force measurement accuracy deteriorates

Engineering Contradiction:

Improveassembly tolerance accommodationVSAvoidforce information accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The system continuously monitors the air gap distance between the sensor electrode and force electrode using capacitive measurements. This feedback allows the controller to compensate for variations in air gap distance caused by assembly tolerances, ensuring that force measurements remain accurate across different devices and assembly conditions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system replaces direct mechanical force measurement with an electrical capacitive sensing approach. By measuring the capacitance between the sensor electrode and force electrode, the system can indirectly detect both air gap distance variations and force applied to the input surface, eliminating the need for precise mechanical alignment while maintaining measurement accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Duration of action of stationary object

If mechanical changes occur in the capacitive sensing device, then device durability and flexibility are improved, but capacitance measurements become inaccurate

Engineering Contradiction:

Improvedevice operational lifespanVSAvoidcapacitance measurement accuracy

Core Design Contradiction:

Duration of action of stationary objectVSMeasurement precision

Solution Approach 1:

The system performs preliminary measurement of the air gap distance and mechanical state during normal operation, before force measurements are taken. This allows the system to establish baseline values and compensation factors that account for mechanical changes, ensuring that subsequent force measurements remain accurate throughout the device's operational lifespan.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system dynamically adjusts measurement parameters based on detected mechanical changes. By monitoring capacitance variations that indicate mechanical state changes, the system can adapt its measurement approach to compensate for these changes, maintaining measurement precision over time and across different operational conditions.

Inventive Principle:

Principle #35Parameter changes

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 approach enhances the accuracy of force information measurement by compensating for mechanical changes, reducing dependency on air gap distance variations and ensuring consistent force detection across different devices and over time.

Implementation Method 1

a sensor electrode configured to deflect toward the force electrode in response to a force applied to the input surface

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

at least a portion of the plurality of sensor electrode are configured to deflect towards the at least one force electrode

Methodology Applied

Scientific EffectElectrostatic force: Electrostatics

Data Source

PatentUS10048801B2Adaptive mechanical change compensation for force detector

Publication Date: 2018.08.14 SYNAPTICS INC

AI summary

A capacitive sensing device is configured to detect force being applied to an input surface of the device by an input object, in addition to the position of the input object using touch sensing methods. Embodiments generate a compensation factor that is used to determine the force information in order to compensate for physical changes to the capacitive sensing device over time, air-gap non-uniform distribution, and other mechanical variations and changes.