Lens Driver Circuit Ringing Compensation

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Solution Overview

Problem

Spring-based voice coil motors (VCMs) used in compact camera applications experience significant oscillation or 'ringing' when moving a lens through focal positions, increasing the time required to find an in-focus position, especially when stepping through positions quickly.

Innovation Solution

A lens driver circuit that employs a voice coil motor with a coil, lens, and body structure, including a spring, uses a current driver to apply a first amount of current to move the structure to a new position and a second amount of current after a delay time, calculated as half of the resonant frequency period, to minimize oscillation around the new position.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a spring-based VCM is used to move the lens through focal positions, then the lens can be positioned at different focal points, but the momentum of the moving structure causes the spring and connected components to oscillate around the desired position, increasing the time required to stabilize

Engineering Contradiction:
Improvelens positioning speedVSAvoidtime to stabilize at position
Core Design Contradiction:
SpeedVSLoss of time

Solution Approach 1:

The patent applies preliminary action by calculating and applying a compensation current before the lens structure naturally comes to rest. The compensation current is applied after a delay time (half of the resonant frequency period) to counteract the oscillation that would otherwise occur, allowing the lens to stabilize faster at the desired focal position

Inventive Principle:
Principle #10Preliminary action

2Productivity

If the lens steps through multiple focal positions quickly, then focusing efficiency is improved, but the oscillation or ringing around each position increases, significantly increasing the time required to find an in-focus position

Engineering Contradiction:
Improvefocusing efficiencyVSAvoidtime to find in-focus position
Core Design Contradiction:
ProductivityVSLoss of time

Solution Approach 1:

The patent implements feedback by monitoring the position of the lens structure and applying a compensation current based on the detected position. The current driver applies a second amount of current after a delay time to counteract oscillation, creating a feedback mechanism that actively reduces ringing and enables faster, more efficient focusing through multiple positions

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

This approach substantially reduces oscillation, allowing the lens to stabilize quickly at new positions, thereby reducing the time needed to find an in-focus position and improving focusing efficiency.

Implementation Method 1

A current can be passed through the coil so that the reacting magnetic fields move the coil and the body

Methodology Applied
Scientific EffectElectromagnetic interaction: Lorentz Force

Implementation Method 2

The energy stored in the compressed spring can then be used to return the coil and the body to a previous position

Methodology Applied
Scientific EffectElastic energy storage: Elasticity

Implementation Method 3

the momentum of the moving structure causes the spring, and thereby the coil, lens, and body structure connected to the spring, to oscillate around the desired position

Methodology Applied
Scientific EffectResonance: Resonance

Data Source

PatentUS9513456B2Lens driver circuit with ringing compensation
Publication Date: 2016.12.06 TEXAS INSTRUMENTS INC
  • US9513456B2 patent drawing
  • US9513456B2 patent drawing
  • US9513456B2 patent drawing

AI summary

A lens driver circuit determines the resonant frequency at a number of positions that a lens can move to so that the lens can move from an old position to a new position in two steps where the second step occurs a delay time after the first step. The delay time can be one-half of the period of the resonant frequency at the new position.