Rotary Encoder Disc Spring Mount for Repeatable Shaft Centering
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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 the edge of a planar disc, which engage with a cylindrical shaft to self-center and locate the disc, ensuring consistent radial positioning and balanced spring forces, even with varying shaft diameters and 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 the segmentation allows the system to achieve both high repeatability through multiple load paths and controlled complexity through modular arrangement.
Solution Approach 2:
The cantilevered spring members provide dynamic compliance, allowing the disc to self-adjust its radial position in response to manufacturing tolerances, shaft variations, and thermal expansion. The springs absorb dimensional variations while maintaining consistent contact, enabling the system to adapt to changing conditions without requiring precise pre-adjustment.
2Length of moving object
If the disc thickness is reduced to achieve a compact encoder, then the encoder profile is lower, but the structural strength and stability decrease
Solution Approach 1:
The disc is constructed using composite material structures, combining rigid outer layers for dimensional stability with flexible intermediate layers for shock absorption and stress distribution. This composite approach enables thin disc profiles while maintaining adequate structural strength through material property optimization rather than increased thickness.
Solution Approach 2:
Instead of increasing disc thickness to improve strength, the solution transfers structural reinforcement to the radial direction through cantilevered spring members that provide support from the rim toward the center. This dimensional redistribution allows the disc to maintain thin profile in the axial direction while achieving adequate strength through radial support structures.
3Measurement precision
If conventional self-locating solutions are used, then the encoder can be manufactured, but the metrological accuracy and setup ease are compromised
Solution Approach 1:
The cantilevered spring members enable the disc to self-center and self-locate on the shaft without requiring external adjustment mechanisms or complex alignment procedures. The springs automatically compensate for minor shaft diameter variations and disc manufacturing tolerances, allowing the encoder to achieve high metrological accuracy through self-adjustment rather than manual calibration.
Solution Approach 2:
The spring support system allows the disc to dynamically adjust its radial position parameters in response to shaft diameter variations and thermal conditions. The springs maintain optimal contact force and disc centering across a range of operating conditions, ensuring consistent metrological accuracy without requiring re-adjustment when environmental parameters change.
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 metrological accuracy and repeatability, ensuring the disc sits consistently on customer-site shafts as it did on manufacturer-site shafts, despite variations in shaft diameters and temperature fluctuations.
Implementation Method 1
radially locating (e.g. centring) the planar disc on, a cylindrical shaft inserted therethrough
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.