Rotary Encoder Cantilevered Spring Self-Locating Disc
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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, which self-locate and center on a cylindrical shaft, ensuring balanced and predictable radial engagement through identical spring forces and opposing forces to stabilize the disc, even with temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-cantilevered spring arrangements are used for self-locating the disc, then the structure may be simpler, but the self-locating performance and repeatability are insufficient
Solution Approach 1:
The spring support system is segmented into multiple independent cantilevered spring members (typically three or more) distributed around the disc perimeter. Each spring member independently provides radial locating force, and their combined action achieves stable self-centering. This segmentation allows each spring to be simple in structure while the overall system achieves high repeatability.
Solution Approach 2:
The cantilevered spring members are pre-loaded to provide continuous radial contact force between the disc and shaft. This beforehand cushioning ensures that the disc is constantly pushed toward the shaft center, compensating for manufacturing tolerances and thermal expansion, thereby maintaining repeatable self-locating performance without complex adjustment mechanisms.
2Length of moving object
If the disc thickness is reduced for compactness, then the encoder profile is lower, but the self-locating performance and structural stability deteriorate
Solution Approach 1:
The spring members extend in the radial dimension (perpendicular to the disc thickness) to provide self-locating function. This allows the disc to remain thin in the axial dimension while the springs provide the necessary radial support and locating forces, effectively transferring the structural function to another dimension.
Solution Approach 2:
The cantilevered spring members are designed as flexible elastic elements that can deform within their elastic limit. These thin flexible structures provide the necessary radial locating force while occupying minimal space, enabling compact disc design without sacrificing self-locating performance.
3Ease of manufacture
If manufacturing tolerances cause spring width variations, then production is easier, but the self-locating predictability and accuracy decrease
Solution Approach 1:
The cantilevered spring members are designed to automatically compensate for manufacturing tolerances through their elastic deformation characteristics. The spring force is primarily determined by the spring's length and material properties rather than width, allowing the system to self-adjust and maintain predictable self-locating performance despite variations in spring dimensions.
Solution Approach 2:
The design shifts the critical parameters for spring force from dimensional parameters (width) to material parameters (elastic modulus) and geometric parameters (length, thickness). This parameter change makes the spring force less sensitive to manufacturing tolerances in width while maintaining ease of manufacture.
4Measurement precision
If the encoder is designed for high resolution with tight eccentricity requirements, then measurement precision improves, but the complexity of achieving consistent self-centering increases
Solution Approach 1:
The cantilevered spring members combine multiple functions into a single structural element: radial support, axial location, and self-centering. This merging eliminates the need for separate complex adjustment mechanisms while achieving the tight eccentricity control required for high-resolution encoding.
Solution Approach 2:
The spring system provides automatic self-centering through elastic deformation, eliminating the need for manual adjustment or complex control systems. The springs continuously adapt to maintain optimal disc-shaft alignment, enabling high measurement precision through a relatively simple passive mechanism.
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 provides a compact, high-performance encoder with improved repeatability and stability, achieving less than 10µm eccentricity and maintaining accurate radial location across varying shaft diameters.
Implementation Method 1
The spring members are elastically deformable and, when mounted on a shaft, are each radially displaced within their elastic limit, whereupon they each provide a spring force
Data Source
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AI summary
A rotary scale apparatus for an encoder apparatus comprising a planar disc on which at least one track comprising scale features is provided, in which the planar disc comprises a hole through its centre for receiving a cylindrical shaft, and in which the rotary scale member comprises 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.