Articulating Joint Optical Encoder for CMM Precision
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Solution Overview
Problem
Conventional coordinate measuring machines (CMMs) face challenges in achieving high accuracy due to limitations in the measurement of rotational degrees of freedom and the need for manual operation, which can lead to reduced precision and increased user effort.
Innovation Solution
The design incorporates an articulating joint assembly with an optical encoder system that includes a housing, shaft, and encoder hub, allowing for precise measurement of rotational positions and enabling six axes of movement, along with a user-friendly interface and modular probe configurations for versatile measurement techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional rotational transducers are used to measure each rotational degree of freedom, then the measurement capability is provided, but the measurement precision is reduced
Solution Approach 1:
The patent changes the measurement dimension from axial (parallel to rotation axis) to radial (transverse to rotation axis). The encoder hub is positioned radially outward from the rotation axis, and the read head measures positional changes in this radial dimension as the shaft rotates, thereby achieving high-precision measurement without complex axial transducers.
Solution Approach 2:
The patent introduces an encoder hub as an intermediary element between the rotating shaft and the read head. The encoder hub has features (such as eccentricity or radial markings) that convert rotational motion into measurable positional changes in the radial direction, enabling precise angle measurement through a simplified read head design.
2Measurement precision
If manual operation is used to move the probe, then the device is easy to operate, but the measurement accuracy is reduced
Solution Approach 1:
The system enables self-service measurement by automatically tracking the position of each joint through encoders and calculating probe coordinates through software. The computer automatically processes position signals from all encoders and computes three-dimensional probe position without requiring manual measurement input or user calculation, thereby maintaining ease of operation while achieving high measurement accuracy.
3Measurement precision
If dedicated rotational transducers are used for each joint, then the rotational position can be measured, but the device complexity increases
Solution Approach 1:
The patent segments the measurement function by placing individual encoders at each joint (first joint, second joint, third joint) rather than using a single complex transducer system. Each encoder independently measures its joint's rotational position, and the computer integrates these segmented measurements to determine overall probe position, thereby maintaining measurement capability while simplifying each individual component.
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
This solution enhances measurement accuracy and user convenience by allowing for precise positioning and easy switching of measurement tools, reducing user effort and improving the flexibility of the CMM in capturing three-dimensional geometry data.
Implementation Method 1
The encoder assembly comprises a read head coupled to one of said housing and said shaft; and an encoder hub attached to the other of said housing and said shaft, the encoder hub having a read surface
Data Source
AI summary
An articulating joint for a coordinate measurement machine can include an improved optical encoder. The optical encoder can have an encoder hub and a read head that are rotatable with respect to each other based on movement of the articulating joint about an axis of rotation of the joint. The encoder hub has a read surface. The read surface can be an outer surface of a generally cylindrical segment. The read head can be positioned such that a read direction defined by the read surface is generally perpendicular to the axis of rotation of the articulating joint.