Hall Element Position Detection Ratio Method
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Solution Overview
Problem
Conventional position detecting devices using magnetic sensors face errors due to looseness in the vertical direction and temperature variations, hindering miniaturization and accurate detection of autofocus or zoom positions in cameras.
Innovation Solution
A position detecting device employing a plurality of Hall elements with a magnetic flux generating body that moves relative to them, utilizing a control section to maintain a constant output voltage from one Hall element and driving the other with the same current, and calculating the ratio of their output voltages to determine the original position, thereby canceling errors and enabling miniaturization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a magnetic sensor with magnet and Hall elements is used for position detection, then temperature characteristics are stable, but errors occur due to looseness in the vertical direction and the device size increases
Solution Approach 1:
The patent replaces the conventional magnetic sensor system (magnet + Hall elements) with a photo interrupter-based optical detection system. This substitution eliminates the mechanical looseness issues and size constraints while maintaining stable temperature characteristics, as the optical system is not affected by mechanical tolerances in the vertical direction.
Solution Approach 2:
The patent changes the detection parameter from magnetic field detection to optical detection. By using a photo interrupter to detect light interruption caused by the position of the lens unit, the system achieves higher measurement precision without the errors associated with mechanical looseness, while the photo interrupter's inherent stability provides consistent temperature characteristics.
2Reliability
If a magnetic sensor with magnet and Hall elements is used for position detection, then temperature characteristics are stable, but device size increases hindering miniaturization
Solution Approach 1:
The patent replaces the bulky magnetic sensor assembly (requiring space for magnet, Hall elements, and associated circuitry) with a compact photo interrupter system. The photo interrupter integrates the light source and detector in a small package, enabling miniaturization of the AF unit while the optical detection method maintains stable temperature characteristics independent of size.
Solution Approach 2:
The patent transitions from magnetic field-based detection to optical detection, changing the fundamental detection parameter. This allows the use of a photo interrupter with a much smaller form factor, reducing the AF unit size while the optical system's physical principles ensure stable temperature characteristics are maintained despite the size reduction.
3Reliability
If photo interrupter or photo reflector is used for position detection, then temperature characteristics are stable, but device size increases
Solution Approach 1:
The patent merges the light source and light detector into a single integrated photo interrupter component, rather than using separate elements. This integration simplifies the sensor structure, reducing the number of parts and assembly steps while maintaining the stable temperature characteristics inherent to photo interrupter technology.
Solution Approach 2:
The patent employs the photo interrupter to perform multiple functions: position detection, origin detection, and providing stable temperature characteristics all in a single component. This multi-functionality reduces overall device complexity compared to systems requiring separate components for each function.
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 effectively eliminates errors caused by looseness and temperature variations, allowing for precise detection of the autofocus or zoom position while enabling the miniaturization of the AF unit by using the ratio method, which provides a nonzero output at the origin and zero output when the magnet is removed.
Implementation Method 1
a first Hall element 22a and a second Hall element 22b which are placed separately from each other... the first Hall element 22a and the second Hall element 22b output Hall voltages in accordance with magnetic flux density
Data Source
AI summary
The present invention relates to a position detecting device capable of canceling an error due to looseness in a vertical direction and of eliminating variation in temperature characteristics by calculating a ratio between output voltages of a plurality of Hall elements. Assuming that the Hall voltage Vhe1 of a Hall element becomes A·K·Bhe1 (A is the amplification factor of a preamplifier, K is a constant, and Bhe1 is the magnetic flux density the Hall element receives), then a PI regulator automatically adjusts the bias point of the PI output by feedback control in such a manner that A·K·Bhe1+Vref=AGND (=0) holds. The Hall voltage Vhe2 of the Hall element after amplification becomes A·K·Bhe2. Since K=−Vref/A·Bhe1, the Hall voltage Vhe2 of the Hall element is given by −Vref·Bhe2/Bhe1.