Lens Drive Unit with Differential Gear Reduction Ratios
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Solution Overview
Problem
Existing lens drive units in imaging apparatuses face challenges in size reduction and operability due to inappropriate reduction ratios in manual and automatic drive transmission mechanisms, leading to increased gear count and backlash, which degrades performance.
Innovation Solution
A lens drive unit configuration with a sun gear, internal gear, planetary gear, and planetary carrier, where the reduction ratio of the fourth gear to the first gear is greater than that of the fourth gear to the second gear, using a DC motor and spur gears to achieve efficient and compact gear transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the reduction ratio of the fourth gear to the first gear is set to be greater than the reduction ratio of the fourth gear to the second gear, then the number of gears is reduced and size reduction is achieved, but the operability may be affected due to different reduction ratios
Solution Approach 1:
The patent applies different reduction ratios to different drive paths (automatic drive via first gear and manual drive via second gear) to optimize each path's performance locally. The fourth gear has different engagement characteristics with the first gear versus the second gear, allowing tailored reduction ratios for autofocusing and manual focusing operations respectively.
Solution Approach 2:
The patent changes the reduction ratio parameter differently for automatic and manual drive paths. By setting the reduction ratio of the fourth gear to the first gear to be greater than the reduction ratio of the fourth gear to the second gear, the system optimizes motor torque transmission for autofocusing while maintaining appropriate speed control for manual focusing.
2Volume of moving object
If the number of gears is reduced, then size reduction is achieved, but the total amount of backlash increases resulting in degradation of fine adjustment capability
Solution Approach 1:
The third gear acts as an intermediary between the second gear (manual operation) and the fourth gear (output). This intermediate gear allows the manual operation path to achieve fine adjustment with fewer total gears in the transmission chain, reducing overall backlash while maintaining precision.
Solution Approach 2:
The patent replaces a traditional multi-gear train with a more efficient gear arrangement where the third gear directly engages both the first and second gears. This substitution reduces the total number of meshing interfaces, thereby reducing cumulative backlash while maintaining compact size.
3Power
If the reduction ratio of the fourth gear to the first gear is set to be greater than twice the reduction ratio of the fourth gear to the second gear, then the reduction ratio of the driven member to the drive motor is sufficiently large, but the mechanism complexity increases
Solution Approach 1:
The patent merges the automatic drive path and manual drive path into a unified gear system where the third gear serves both paths. By having the third gear engage with both the first gear (from drive motor) and the second gear (from manual operation), the system achieves the required reduction ratio without adding separate transmission chains, thus avoiding increased complexity.
Solution Approach 2:
The third gear performs multiple functions: it acts as a driven gear from the first gear during automatic focusing, as a driving gear from the second gear during manual focusing, and as an intermediary that enables both drive paths to converge to the fourth gear. This multi-functionality achieves the complex reduction ratio requirement without increasing overall mechanism complexity.
Data Source
AI summary
A lens drive unit includes: a driven member that moves a lens in an optical axis direction; a first gear rotated by a drive force of a drive motor; a second gear rotated by a drive force of a manual operation section; a third gear that engages with the first gear and the second gear and is rotated when the first gear is rotated but the second gear is not rotated whereas rotated when the second gear is rotated but the first gear is not rotated; and a fourth gear rotated when the third gear is rotated to transmit the drive force of the drive motor or the drive force of the manual operation section to the driven member, wherein the reduction ratio of the fourth gear to the first gear is set to be greater than the reduction ratio of the fourth gear to the second gear.