Four-Scanning Unit Position Measuring Device Thermal Compensation
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Solution Overview
Problem
Existing position-measuring devices, such as 1Dplus encoders, are sensitive to thermal expansions due to the lack of a thermally neutral point, leading to relative movements and positional deviations in degrees of freedom X, Y, and RZ under temperature changes.
Innovation Solution
A position-measuring device with a scale having two measuring graduations inclined relative to the main measurement direction, utilizing four scanning units to ensure thermally invariant position measurement and signal compensation, allowing for accurate determination of the scanning unit carrier's position in all degrees of freedom, including thermal expansion compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a 1Dplus encoder with three scanning locations is used to measure degrees of freedom X, Y, RZ, then the position of the tool center point can be determined, but the device becomes sensitive to thermal expansions of the scale and scanning unit carrier, leading to positional deviations
Solution Approach 1:
The patent introduces a fourth scanning location in addition to the traditional three scanning locations. This additional dimension in the scanning arrangement enables the system to distinguish between actual positional changes and thermal expansion effects, thereby maintaining measurement accuracy while compensating for thermal instability
Solution Approach 2:
The patent changes the thermal parameter behavior by introducing a thermally neutral point through the specific geometric arrangement of four scanning locations. This configuration allows the system to identify and compensate for thermal expansion parameters, transforming the system from thermally sensitive to thermally stable
2Measurement precision
If scanning locations are arranged to satisfy the Abbe condition with projection outside the part, then simple 1Dplus encoders can accurately determine TCP position, but relative movements occur between scanning locations under temperature changes
Solution Approach 1:
By adding a fourth scanning location to the traditional three-point arrangement, the system creates an overdetermined system that can detect and compensate for relative movements between scanning locations caused by thermal expansion, while maintaining Abbe condition compliance for accurate TCP determination
3Device complexity
If three scanning locations are used in a 1Dplus encoder, then the device structure remains relatively simple, but it is not possible to implement a thermally neutral point, causing undesired positional deviations
Solution Approach 1:
The patent adds one scanning location to the traditional three-point configuration, increasing the scanning unit complexity minimally while enabling thermally neutral point implementation. This single additional point provides the necessary geometric constraint to eliminate thermal expansion effects from position measurements
Data Source
AI summary
A position-measuring device includes a scale having first and second measuring graduations, which each include graduation structures that respectively extend parallel to first and second directions. A first scanning unit is associated with the first measuring graduation, and second and third scanning units are associated with the second measuring graduation. A fourth scanning unit is associated with the first or second measuring graduation. In the former case, a first straight connecting line running through scanning locations of the first and fourth scanning units and a second straight connecting line running through scanning locations of the second and third scanning units are parallel or form a predetermined angle therebetween that is not equal to a sum of the angles of the first and second directions. In the latter case, the scanning locations of the second, third and fourth scanning units do not lie on a common straight connecting line.