Brush DC Motor Lens Control via Back-EMF Integration
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Solution Overview
Problem
Existing lens position control devices for endoscopes face challenges in achieving simple configurations and high accuracy, particularly due to the complexity of three-phase brushless DC motors and the potential for decreased accuracy from fluctuations in rotation speed caused by load changes.
Innovation Solution
A lens position control device utilizing a DC motor with a brush, a drive circuit that repeats application and release states, and a processor that controls the lens position based on a time-integrated value of the counter-electromotive force generated during the release state, allowing for accurate and simple control of the variable magnification lens.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a three-phase brushless DC motor is used for lens position control, then the motor configuration is more advanced, but the overall device configuration becomes complicated
Solution Approach 1:
The patent replaces the expensive and complex brushless DC motor with a simpler, more cost-effective DC motor with brush. While the brush motor has shorter lifespan due to brush wear, it significantly reduces device complexity and cost, which is acceptable for the endoscope application where the motor is not a long-life critical component.
Solution Approach 2:
The patent substitutes the electrical feedback system (encoders, sensors, signal lines) with an electrical measurement approach by detecting counter-electromotive force. This replaces complex mechanical/electrical feedback mechanisms with a simpler electrical detection method that uses existing motor components.
2Ease of operation
If the amount of rotation is controlled by counting drive time, then the control method is simple, but accuracy decreases due to rotation speed fluctuations from load changes
Solution Approach 1:
The patent introduces feedback by detecting the counter-electromotive force generated during the release state and integrating it over time. This feedback mechanism compensates for rotation speed fluctuations caused by load changes, thereby maintaining accurate lens position control without requiring complex sensor systems.
Solution Approach 2:
The patent changes the control parameter from simple time counting to time-integrated counter-electromotive force measurement. By integrating the counter-electromotive force over the release period, the system obtains a parameter that reflects actual motor rotation despite load variations, thus improving measurement precision.
3Measurement precision
If a sensor is used for feedback control to detect motor rotation, then position control accuracy is improved, but the number of wiring lines increases
Solution Approach 1:
The patent extracts the position detection function from separate sensors and encoders and relocates it to the motor's inherent counter-electromotive force signal. By using the motor itself as the detection element during the release state, the system eliminates the need for additional sensors and their associated wiring lines.
Solution Approach 2:
The patent makes the DC motor multi-functional by using it both for driving the lens and for detecting position information through counter-electromotive force measurement during the release state. This eliminates the need for separate detection devices and reduces wiring 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 the control of lens positions with a simple configuration and high accuracy, even in the presence of load fluctuations, by leveraging the correlation between counter-electromotive force and rotation speed to accurately determine the lens position.
Implementation Method 1
a processor that controls the position of the variable magnification lens based on a time-integrated value of a counter-electromotive force generated at the DC motor with a brush in the release state
Data Source
AI summary
A lens position control device is a lens position control device that controls a position of a variable magnification lens of a zooming optical system provided at an endoscope and includes a DC motor with a brush that generates a drive force for changing the position of the variable magnification lens, a drive circuit that drives the DC motor with a brush by repeating an application state where a drive voltage is applied between a pair of terminals of the DC motor with a brush and a release state where the terminals are released from each other, and a processor that controls the position of the variable magnification lens based on a time-integrated value of a counter-electromotive force generated at the DC motor with a brush in the release state.