Lens Drive Coil Switching for Long-Travel Precision Positioning
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Solution Overview
Problem
Conventional voice coil motors (VCMs) face limitations in providing a long travel range while maintaining accuracy, as enlarging the magnet to increase the travel range reduces resolution due to fixed analog-to-digital converter resolution in closed loop circuits.
Innovation Solution
The lens driving device incorporates a magnetic group with multiple pairs of magnetic elements, a driving element group with coils and position sensors, and a control device that alternates between open and closed loop power supply to the coils, allowing precise movement across multiple magnetic pairs without exceeding their range, thereby maintaining high resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the magnet is enlarged to increase the travel range from 1 mm to 10 mm, then the travel range is improved, but the resolution is reduced to one tenth of the original value
Solution Approach 1:
The patent divides the magnetic pole into multiple magnetic elements (first magnetic element, second magnetic element, third magnetic element, fourth magnetic element) arranged in sequence. The coils are also divided into multiple coil groups (first coil group, second coil group, third coil group, fourth coil group). This segmentation allows the system to achieve both long travel range (by having multiple elements to move through) and high resolution (by having fine-grained control over each segment), resolving the contradiction between travel range and resolution.
2Measurement precision
If a closed loop circuit is used for position feedback with fixed 12 bits A/D converter resolution, then positioning control accuracy is improved, but the travel range is limited to within 1 mm
Solution Approach 1:
The patent dynamically switches between open loop control and closed loop control based on the required operation. Open loop control is used for coarse positioning over long distances (traveling between magnetic elements), while closed loop control is used for fine positioning within each magnetic element's range. This dynamic control strategy allows the system to achieve both long travel range and high positioning accuracy without being constrained by the fixed resolution of the A/D converter in closed loop mode alone.
3Measurement precision
If the coils are moved in accordance with voltage magnitude for positioning control, then high frequency response and high accuracy are achieved, but the travel range is limited to the magnetic pole range
Solution Approach 1:
The patent employs periodic action by sequentially activating different coil groups as the lens frame moves through different magnetic elements. Each coil group is activated in sequence to propel the lens frame to the next magnetic element, creating a periodic drive pattern that enables long travel range. Within each magnetic element's range, the system uses continuous voltage control for fine positioning, thus achieving both long travel range and high positioning accuracy.
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 enables a long travel range with maintained accuracy, doubling the angular resolution and allowing for precise positioning of the lens frame, addressing the resolution reduction issue in conventional VCMs.
Implementation Method 1
A voice coil motor (VCM) is a motor in which coils are disposed in a permanent magnetic field and the stretch of a spring piece is controlled by changing a direct electric current passing through the coils, thereby providing an upwards/downwards movement
Implementation Method 2
The at least one driving element group further includes at least one position sensor, the control device in a closed loop way
Data Source
AI summary
A lens driving device and a driving method thereof are provided. The lens driving device includes a lens frame, a magnetic group, a driving element group and a control device. The lens frame carries at least one optical element. The magnetic group includes a plurality of pairs of magnetic elements. The driving element group includes at least two coils. The control device supplies power to the driving element group so that the lens frame is driven by the driving element group to move. The driving element group is disposed on the lens frame, and the amount of the lens frame is equal to that of the driving element group. The control device in a first driving state supplies the power to the coils in sequence so that the driving element group is moved from a pair of magnetic elements to another pair of magnetic elements.