Displacement Detecting Device With Polynomial Scale Marks
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Solution Overview
Problem
Conventional displacement detecting devices have limited measurement ranges due to reliance on origin marks and signals, and their accuracy decreases when the scale tilts or expands due to temperature changes, restricting their application in machine tools and industrial machines.
Innovation Solution
A displacement detecting device with a scale featuring marks whose pitch interval can be approximated by a quadratic or higher-order polynomial, using multiple displacement detecting units to calculate absolute position without relying on origin marks, allowing for extended measurement ranges and improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the measurement range is extended by increasing the intervals in the first and second regions, then the measurement range is extended, but detection accuracy reduces considerably when the scale tilts or when the scale expands or shrinks due to temperature changes
Solution Approach 1:
The scale is divided into multiple regions with different mark interval characteristics. The first region has marks at predetermined intervals suitable for high-accuracy detection, while the second region has marks at larger intervals to extend the measurement range. The detection head can switch between or combine information from both regions to achieve both extended range and maintained accuracy.
2Measurement precision
If the displacement detecting device relies on origin marks and origin signals, then the absolute position can be detected, but the measurement range is limited to lengths of the first region and the second region in the measurement direction
Solution Approach 1:
The invention extracts and eliminates the dependency on origin marks and origin signals from the displacement detection system. By using multiple regions with different mark intervals and processing the phase differences between these regions, the system can determine absolute position without requiring traditional origin marks, thereby extending the measurement range beyond the limitations imposed by origin signal requirements.
3Length of stationary object
If the second region is arranged in a direction parallel to the measurement surface of the scale and orthogonal to the measurement direction, then the measurement range may be extended, but the measurement range when the first reading unit or the second reading unit moves in the orthogonal direction is limited
Solution Approach 1:
The invention arranges the second region in a direction parallel to the measurement surface and orthogonal to the measurement direction, creating a two-dimensional mark distribution pattern. This dimensional arrangement allows the system to extend measurement range in the primary measurement direction while maintaining adaptability for movements in orthogonal directions through the spatial distribution of marks across multiple regions.
Data Source
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AI summary
A scale 2 has marks S1 whose pitch interval changes along a measurement direction X1 in a manner that can be approximated to a quadratic or higher-order polynomial. A comparing unit 6 calculates a difference between first relative position information and second relative position information per unit displacement in a position where a first displacement detecting unit 9 is arranged. Then, an absolute position computing unit 7 computes an absolute position in the measurement direction X1 with respect to the scale 2 based on absolute position information and the relative position information of at least one of the first relative position information and the second relative position information, and outputs the absolute position.