Optical Encoder Curved Reflective Scale Compact Design
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Solution Overview
Problem
Conventional optical encoders for detecting lens positions and rotational displacements in cameras face challenges such as large size, poor workability, and insufficient resolution due to their design, which is not optimized for curved reflective scales and results in errors related to light beam deflection and curvature.
Innovation Solution
A small optical encoder with a curved reflective scale having a constant radius of curvature and a point light source emitting divergent beams, allowing for high-precision detection and a thin sensor design without lenses, capable of adapting to both curved and flat reflective scales.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transmissive type encoder with U-shaped holder is used, then the encoder can support light-emitting and light-receiving elements, but the size in direction perpendicular to optical axis becomes large and assembling workability deteriorates
Solution Approach 1:
The patent inverts the conventional transmissive encoder design by using a reflective type encoder where the light-receiving element detects reflected light from a scale instead of transmitting light through a U-shaped holder. This inversion eliminates the need for the bulky U-shaped holder structure while maintaining encoder functionality, thereby reducing the encoder size in the direction perpendicular to the optical axis.
2Volume of moving object
If a reflective scale on cylinder is used, then size reduction is easier, but sufficient resolution cannot be achieved and errors are generated by radius of curvature
Solution Approach 1:
The patent changes the critical parameter of the reflective scale from a large radius of curvature (cylindrical) to a small radius of curvature (arc-shaped). By optimizing the radius of curvature to be sufficiently small, the patent achieves two objectives: maintaining compact encoder size while eliminating the light beam deflection errors that occur with large radii, thereby achieving both size reduction and high detection resolution.
3Measurement precision
If detecting sensor is disposed outside cylinder for improved optical detection, then high-precision detection is achieved, but thickness of detecting sensor is increased
Solution Approach 1:
The patent repositions the light-receiving element from outside the cylindrical scale to inside the scale structure. By placing the light-receiving element within the scale assembly rather than outside, the patent achieves high-precision detection while minimizing the overall thickness of the detecting sensor assembly, effectively utilizing the internal space of the scale structure.
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 solution enables high-resolution, high-precision displacement detection suitable for modern camera lenses, achieving improved signal quality and reducing sensor thickness, thus addressing the limitations of existing technologies.
Implementation Method 1
a point light source for irradiating the reflective scale with divergent light beams
Implementation Method 2
a light-receiving element disposed inside the cylinder and facing the reflective surface of the scale
Data Source
AI summary
An optical encoder includes a cylindrical reflective scale, a point light source for irradiating the reflective scale, and light-receiving elements for receiving the light beams reflected by the reflective scale. The pitch of the reflective scale is set to an appropriate value such that the pitch of interference fringes formed by light beams that are reflected by the reflective scale is matched to the pitch of the light-receiving elements at a position with a desired gap.