Lens Drive Position Sensing for Faster, Stable Autofocus
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Solution Overview
Problem
Conventional camera modules suffer from long auto-focusing times, inaccurate lens positioning, and instability due to electromagnetic force fluctuations and lens barrel eccentricity, limiting the performance of lens driving devices in miniature digital cameras.
Innovation Solution
A lens driving device with a bobbin mounted sensing magnet and a position sensor on a circuit board, where the sensing magnet is positioned to avoid interference with the coil unit, and an even number of driving magnets maintain electromagnetic balance, allowing precise detection and control of lens position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall sensor and sensing magnet are arranged to face each other perpendicular to the optical axis to detect lens focal position, then the lens position can be detected, but the Hall sensor is incapable of accurately sensing the movement of the lens in the optical axis direction, resulting in poor measurement precision
Solution Approach 1:
The patent replaces the conventional Hall sensor arrangement (which relies on magnetic field sensing perpendicular to the optical axis) with a position sensor that directly detects the position of the sensing magnet along the optical axis direction. This substitution enables accurate sensing of lens movement in the optical axis direction, resolving the measurement precision issue while maintaining reliable detection capability.
2Loss of time
If efforts are made to shorten auto-focusing time, then the auto-focusing speed improves, but the performance of the lens driving device deteriorates due to unstable electromagnetic force and lens barrel eccentricity
Solution Approach 1:
The patent employs a position sensor to detect the position of the sensing magnet mounted on the bobbin, providing real-time feedback on the lens barrel position. This feedback mechanism enables precise control of the lens driving device, allowing rapid auto-focusing while maintaining stable electromagnetic force and preventing lens barrel eccentricity, thus resolving the contradiction between speed and stability.
3Device complexity
If the sensing magnet is mounted on the outer peripheral surface of the bobbin, then space efficiency is improved and assembly is simplified, but the sensing magnet may interfere with the coil unit
Solution Approach 1:
The patent applies local quality by positioning the sensing magnet at a specific location on the outer peripheral surface of the bobbin where it does not interfere with the coil unit. This selective placement allows the sensing magnet to be mounted in a region that maintains both space efficiency and proper electromagnetic interaction, resolving the contradiction between simplified assembly and interference prevention.
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 enables rapid and accurate auto-focusing, improves space efficiency, and enhances durability by simplifying assembly and maintaining linear movement characteristics, thus shortening focal alignment time and improving lens positioning accuracy.
Implementation Method 1
a voice coil unit motor is commonly used. The voice coil unit motor is operated by the electromagnetic interaction between a magnet secured to a housing and a coil unit wound around an outer peripheral surface of a bobbin
Implementation Method 2
The Hall sensor senses a magnetic field of the sensing magnet and outputs a voltage corresponding thereto
Data Source
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AI summary
A lens driving device according to an embodiment comprises: a movable unit on which at least one lens is mounted; a first coil and a driving magnet which face and interact with each other such that the movable unit is moved in the optical axis direction of the lens; a position sensor for sensing the position of the movable unit in the optical axis direction or a driver comprising the position sensor; and a positively magnetized magnet arranged to face the position sensor or the driver, wherein the positively magnetized magnet comprises a first side surface, which faces the position sensor and has a first polarity, and a second side surface, which faces the position sensor, which is arranged to be spaced from the first side surface in a direction parallel with the optical axis direction or arranged to abut the first side surface, and which has a second polarity that is the opposite of the first polarity of the first side surface, and the length of the first side surface in the optical axis direction may be equal to or larger than the length of the second side surface in the optical axis direction.