Hall Sensor Temperature Compensation in Camera VCM Actuators

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Solution Overview

Problem

Small form factor cameras face challenges in maintaining positional accuracy due to temperature-induced changes in Hall sensor output voltage, primarily caused by reversible demagnetization effects, which affect the magnetic field and subsequently the sensitivity of Voice Coil Motor (VCM) actuators used for autofocus and optical image stabilization.

Innovation Solution

A method is implemented to determine expected drive current values for Hall sensor outputs, measure actual values, and adjust the drive current to compensate for differences, thereby stabilizing the actuator position across varying temperatures without requiring factory calibration at multiple temperatures. This involves characterizing the open-loop sensitivity of VCM actuators and Hall sensors during factory calibration to account for temperature changes in the magnetic field.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If factory calibration is performed at multiple temperatures, then measurement precision is improved, but manufacturing complexity and time increase

Engineering Contradiction:

ImproveHall sensor output accuracyVSAvoidcalibration process

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent performs preliminary characterization of the VCM actuator and Hall sensor during factory calibration to establish a model that predicts temperature-induced changes. This preliminary action enables runtime compensation without requiring actual multi-temperature calibration, thus improving measurement precision while avoiding the complexity of multi-temperature calibration procedures

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the operational parameters by adjusting the drive current based on temperature compensation calculations. By modifying the drive current parameter dynamically, the system compensates for temperature effects on Hall sensor output, achieving high measurement precision without complex calibration procedures

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If temperature compensation is implemented, then positional accuracy is improved, but device complexity increases

Engineering Contradiction:

Improvepositional accuracyVSAvoidcontrol algorithm

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent implements a feedback mechanism where the actual Hall sensor output is compared against the expected output based on the characterization model. The difference (error) is used to adjust the drive current, creating a closed-loop control system that maintains positional accuracy without requiring complex hardware modifications

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces complex mechanical calibration procedures with a computational approach. By using characterization data and mathematical models to calculate compensation values, the system achieves high positional accuracy through software-based solutions rather than complex mechanical adjustment mechanisms

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If drive current is adjusted for temperature compensation, then reliability is improved, but energy consumption increases

Engineering Contradiction:

Improvepositional stabilityVSAvoiddrive current

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent applies partial compensation by adjusting the drive current only to the extent necessary to counteract temperature effects. Rather than over-compensating or using excessive current, the system calculates the precise compensation needed based on the characterization model and error signal, achieving reliable positional stability with minimal additional energy consumption

Inventive Principle:

Principle #16Partial or excessive action

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 effectively maintains positional accuracy over a wide temperature range by adjusting the drive current to counteract temperature-induced changes, ensuring accurate autofocus and optical image stabilization without the need for individual actuator calibration at multiple temperatures.

Implementation Method 1

temperature-induced changes in Hall sensor output voltage, primarily caused by reversible demagnetization effects, which affect the magnetic field

Methodology Applied

Scientific EffectHall effect: Hall Effect

Implementation Method 2

Voice Coil Motor (VCM) actuators used for autofocus and optical image stabilization

Methodology Applied

Scientific EffectElectromagnetic force: Lorentz Force

Data Source

PatentUS9179066B1Temperature compensation for sensors

Publication Date: 2015.11.03 APPLE INC

AI summary

In some embodiments, a plurality of expected values of a drive current corresponding to respective ones of a plurality of potential values of a Hall sensor output is determined. An actual value of the Hall sensor output is measured. An actual value of the drive current is measured. A potential value of the Hall sensor output corresponding to the actual value of the Hall sensor output is selected. The expected value of the drive current associated with the selected potential value of the Hall sensor output is compared to the actual value of the drive current. A value of the drive current is adjusted to reduce a difference between the expected value of the drive current associated with the selected potential value of the Hall sensor output to the actual value of the drive current.