Optical Position Detection Light Restriction for Watch Precision
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Solution Overview
Problem
Conventional optical-type rotational body position detection apparatuses for wristwatches suffer from precision issues due to manufacturing tolerances and backlash errors, leading to inaccurate alignment of hands at standard positions.
Innovation Solution
Incorporating a light transmission restriction unit on the fixing support member that limits the light diameter to account for positional displacement errors, ensuring precise detection of the rotational body's standard position by restricting the light passage to a specific diameter that aligns with the peripheral edge of the standard position light transmission hole.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the standard position light transmission hole is made to coincide with the optical axis for detection, then the detection function is achieved, but manufacturing tolerances and backlash cause the center of the light transmission hole to not coincide with the optical axis, resulting in positional displacement
Solution Approach 1:
The patent applies beforehand cushioning by designing the light transmission hole with a predetermined radius that is larger than the maximum expected positional displacement caused by manufacturing tolerances and backlash. This ensures that even when the hole center is displaced within the tolerable range, the hole still overlaps with the optical axis, maintaining reliable detection without requiring ultra-precise manufacturing.
2Manufacturing precision
If the light transmission hole has a large radius to accommodate manufacturing errors, then the tolerable error range is increased, but the detection precision is reduced because the hole may overlap with the optical axis even when displaced
Solution Approach 1:
The patent applies parameter changes by optimizing the radius of the light transmission hole to a specific value that balances two requirements: (1) it must be large enough to accommodate the maximum positional displacement from manufacturing tolerances and backlash, and (2) it must be small enough to ensure that only when the hole center is within the tolerable range of the optical axis does the hole overlap with the optical axis. This optimal radius parameter resolves the contradiction between tolerable error range and detection precision.
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
Enhances the precision of rotational body position detection by compensating for manufacturing tolerances and backlash errors, ensuring accurate alignment of watch hands at standard positions, thereby improving the reliability of timekeeping.
Implementation Method 1
a light emitting unit which is configured to emit light
Implementation Method 2
a light detecting unit which is configured to detect light
Implementation Method 3
a light transmission restriction unit which is integrally provided on the fixing support member, which is disposed at a position crossing the optical axis, which permits passing of light, and which restricts a diameter of the passing light
Data Source
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AI summary
An optical-type rotational body position detection apparatus includes a body (20) rotational in a predetermined angle at each predetermined time interval to cross an optical axis (13a) between fixed light emitting and detecting units (31, 32), including a standard hole (21a) on a rotational locus crossing the axis, and configured such that after rotating the body at one interval from a standard position at which the hole coincides with the axis, a periphery of the hole is positioned outside the periphery at the standard position. The apparatus further includes a restriction unit (15a) on a support to cross the axis and to permit light passing and to restrict a diameter of the passing light. The restriction unit restricts the diameter of the passing light to be smaller than a minimum distance within a positional displacement tolerable error range (R1) of the hole after the predetermined angled rotation of the body.