Optical Hand Position Detection for Magnetic Interference
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Solution Overview
Problem
Conventional hand position detecting devices for timepieces fail to accurately detect rotational positions of seconds, center, and hour hands due to external magnetic fields interfering with the operation of drive motors, leading to incorrect positioning.
Innovation Solution
A hand position detecting device that uses a first and second driving system with stepping motors and light-passing apertures, combined with a detection unit including a light emission and photo detection element, to accurately determine the rotational positions of seconds, center, and hour hands by detecting light through specific apertures at precise angles, ensuring correct alignment and operation even in the presence of external magnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photosensor and light emission element are used to detect hand positions, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines the light emission element and photosensor into an integrated detection system that shares common structural support and alignment mechanisms. The light emission element, photosensor, and reflecting surface are positioned to form a compact triangular arrangement, reducing the overall footprint and simplifying the detection system structure while maintaining high measurement precision for hand position detection.
2Adaptability or versatility
If multiple drive motors are used for different hands, then functionality is improved, but reliability deteriorates due to magnetic field interference
Solution Approach 1:
The patent introduces a light-based detection system as an intermediary mechanism to monitor the positions of hands driven by multiple drive motors. This optical intermediary provides a reliable reference framework that is independent of the magnetic field interference affecting the motors, enabling accurate position detection and compensation for any drift or errors in the motor-driven hands.
3Productivity
If detection is performed at every two steps of drive motors, then productivity is improved, but measurement precision deteriorates when motors operate abnormally
Solution Approach 1:
The patent implements a feedback mechanism where the photosensor continuously monitors the positions of the light-passing apertures on the hands. When abnormal motor operation is detected through position deviations from expected values, the system can trigger corrective actions such as recalibration or error notification, maintaining measurement precision even when productivity is reduced due to abnormal conditions.
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
The device ensures accurate detection of hand positions with high reliability, reducing errors caused by external magnetic fields and maintaining correct timekeeping, while also optimizing power consumption and structural simplicity.
Implementation Method 1
a photosensor including a light emission element and a photo detection element
Implementation Method 2
the photosensor optically detects a first, a second and a third light-passing apertures provided respectively in the seconds, center and hour wheels with the aid of the light emission element and the photo detection element
Data Source
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AI summary
When detecting a rotational position of a seconds hand, it is determined whether data stored in a register in correspondence with a supply state of a drive current previously supplied to a coil (17a) of a stepping motor (17) is "0". When the data is "0", the rotational position of the seconds hand is optically detected. When the data is "1", the seconds hand is rotated one step, and then, the rotational position of the seconds hand is optically detected. Even though the seconds hand is shifted one second, the position detection is executed every two steps.