Rotary Encoder Disc Springs for Repeatable Self-Centering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing rotary encoders, particularly those with glass or metal discs, face challenges in providing a compact, high-resolution, and highly repeatable self-locating solution, especially when dealing with varying shaft diameters and temperature changes, which affect the disc's radial location and encoder performance.
Innovation Solution
A rotary scale apparatus with cantilevered spring members arranged around a planar disc, providing self-locating capabilities by engaging with a cylindrical shaft, ensuring balanced and predictable radial positioning through identical spring forces and opposing forces to stabilize the disc, even with temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If non-cantilevered spring arrangements are used for self-locating the disc, then the structure may be simpler, but the self-locating performance is poor and manufacturing tolerances cause unpredictable positioning
Solution Approach 1:
The patent changes the spring configuration from non-cantilevered to cantilevered, and specifies that at least three cantilevered spring members should be provided. This parameter change in the spring arrangement provides predictable self-locating performance with manufacturing tolerances, achieving less than 10 μm eccentricity as required.
2Length of moving object
If the disc thickness is reduced for compact design, then the encoder profile is lower, but maintaining self-locating accuracy becomes more difficult
Solution Approach 1:
The patent specifies that the disc should be made of metal or glass material. These materials provide the necessary rigidity and dimensional stability to maintain self-locating accuracy even when the disc thickness is reduced for compact encoder design.
3Ease of manufacture
If manufacturing tolerances are relaxed to reduce cost, then production becomes easier, but shaft diameter variations cause poor self-locating repeatability
Solution Approach 1:
The patent employs cantilevered spring members that can elastically deform to accommodate variations in shaft diameter. This dynamic capability allows the spring members to adapt to manufacturing tolerances in both the disc and shaft, maintaining repeatable self-locating performance across different production batches.
4Stability of the object's composition
If traditional spring arrangements are used, then the design may be simpler, but temperature changes and manufacturing variations cause unstable positioning
Solution Approach 1:
The patent specifies that the spring members should be provided in plane with the disc and spaced around the edge of the hole, with at least three spring members required. This localized configuration provides temperature compensation and stabilizes positioning by distributing mechanical stresses uniformly around the shaft interface.
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 enhances the encoder's metrological performance by ensuring repeatable and accurate radial self-location, maintaining stability and accuracy even with varying shaft diameters and temperature fluctuations, thus meeting high precision demands.
Implementation Method 1
The spring members are elastically deformable and, when mounted on a shaft, are each radially displaced within their elastic limit, and they each provide a force which together work to radially locate the disc on the shaft
Data Source
AI summary
A rotary scale apparatus for an encoder apparatus including a planar disc on which at least one track including scale features is provided, in which the planar disc includes a hole through its centre for receiving a cylindrical shaft, and in which the rotary scale member includes at least three cantilevered spring members which are provided substantially in plane with the planar disc and spaced around the edge of the hole, for engaging with, and radially locating the disc on, a cylindrical shaft inserted therethrough.