Lens Driving Apparatus Backlash Compensation via Motor Current Feedback
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Solution Overview
Problem
Existing lens driving apparatuses face inaccuracies in rotational position and speed control due to backlash in the gear train, leading to uncomfortable image movements and unintended control signals, especially when reversing direction.
Innovation Solution
A driving apparatus with a feedback signal switching mechanism that differentiates between lens position and motor position signals, using a scissors gear to reduce backlash and employing a motor electric current detector to derive accurate rotational positions and speeds, allowing for precise control without separate position detectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a position detector is used to detect lens position for feedback control, then position feedback control can be implemented, but the detection accuracy is reduced due to backlash in the gear train
Solution Approach 1:
The patent replaces mechanical position detection (which is affected by gear backlash) with electrical measurement of motor current. By detecting the counter electromotive force (back EMF) generated by the motor during rotation, the system calculates rotational speed and position electrically, bypassing the mechanical gear train entirely. This substitution eliminates the impact of mechanical backlash on measurement accuracy.
Solution Approach 2:
The patent introduces motor current and counter electromotive force as intermediary parameters between the motor and lens position control. Instead of directly measuring lens position through the gear train, the system uses motor electrical characteristics (current, back EMF) as intermediaries to infer position and speed, thereby avoiding the backlash problem in the mechanical transmission path.
2Speed
If speed feedback control is implemented using position detector signals, then constant speed control can be achieved, but the control accuracy deteriorates when the lens reverses direction due to backlash
Solution Approach 1:
The patent replaces mechanical speed detection (through position detector signals affected by backlash) with electrical measurement of motor counter electromotive force. The counter EMF is directly proportional to motor rotational speed and is not affected by gear train backlash. This allows accurate speed feedback control during direction reversals without the delays and inaccuracies caused by mechanical backlash.
Solution Approach 2:
The patent performs preliminary calculation of rotational speed based on motor current and counter electromotive force before using it for feedback control. By pre-calculating speed from electrical parameters (which are not affected by backlash), the system ensures accurate speed feedback is available immediately during direction reversals, eliminating the delay that occurs with mechanical position detectors.
3Measurement precision
If separate position detectors are used for both lens position and motor position detection, then accurate detection can be achieved, but the device complexity and cost increase
Solution Approach 1:
The patent makes the motor current detector serve multiple functions: it detects motor current for power control, calculates motor rotational speed via counter electromotive force, and provides feedback for both position and speed control. This multi-functionality eliminates the need for separate position detectors for the motor, reducing device complexity while maintaining detection accuracy.
Solution Approach 2:
The patent merges the functions of motor current detection, speed detection, and position detection into a single integrated approach using motor electrical characteristics. By combining these detection functions and calculating derived parameters from motor current and counter EMF, the system eliminates redundant detectors and reduces overall device complexity.
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 solution enables accurate lens drive control by distinguishing between backlash periods and non-backlash periods, reducing unwanted drive signals and improving operational comfort, while minimizing hardware components and costs.
Implementation Method 1
a rotational speed of the motor is determined based on a motor electric current detected by the motor electric current detector
Data Source
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AI summary
A driving apparatus (200) connected to a lens barrel (100) including a movable optical member (102) to drive the movable optical member, includes: a drive unit (201) driving the movable optical member; a controller (208) controlling the drive unit; a first deriving unit (206) deriving a first information indicating at least one of position or speed of the movable optical member; and a second information indicating at least one of position or speed of the drive unit based on a counter-electromotive voltage generated through the drive of the drive unit; and a selection unit (207) to select the first information or the second information as a selected information according to a state of a backlash of the drive unit, the controller controlling the drive unit based on : the first information or the second information selected by the selection unit; and the command information to direct driving of the movable optical member.