Position Measurement Initialization Using Dual-Track Evaluation
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Solution Overview
Problem
High-precision position measurement in multiple degrees of freedom is hindered by initial large alignment tolerances between scanning heads and scales, making it difficult to detect and assign absolute position information to incremental tracks, especially in sequential measurement setups.
Innovation Solution
A method involving an initialization step using a first evaluation method to align the movable object with the measuring frame, followed by a detection step with a second evaluation method to achieve precise alignment within a narrow connection tolerance, allowing for exact position measurement by clearly assigning absolute track signals to incremental track signal periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a sequential measurement arrangement is used to reduce device complexity, then the alignment tolerance between scanning heads and scales must be very small (connection tolerance), but initial alignment tolerance (initial tolerance) is large making initialization difficult
Solution Approach 1:
The patent applies preliminary action by performing an initialization step before the actual measurement process. During initialization, the system determines rough absolute positions of the object despite large initial misalignments, then uses this information to pre-align the scanning heads with the scales. This preliminary alignment brings the system within the narrow connection tolerance required for accurate measurement, solving the contradiction between simple sequential structure and difficult initialization.
2Length of stationary object
If the scanning distance is large to cover the measurement range, then the initial alignment tolerance must be very small to ensure accurate reading, but large scanning distance makes it impossible to evaluate absolute information with large initial tolerance
Solution Approach 1:
The patent uses preliminary action by performing initialization before measurement to determine rough absolute positions even with large initial misalignments and large scanning distances. This preliminary information is then used to adjust the system into the narrow connection tolerance range, enabling accurate absolute position reading across the full scanning distance without requiring precise initial alignment.
Solution Approach 2:
The patent resolves the contradiction by transitioning from a single-dimension problem (alignment tolerance) to a two-dimensional solution space. It separates the alignment problem into two stages: initialization with large tolerance for coarse positioning, and measurement with small tolerance for fine positioning. This dimensional separation allows large scanning distances to be compatible with accurate measurement by using the initialization phase to bridge the tolerance gap.
3Measurement precision
If the connection tolerance between absolute track and incremental track is small to ensure exact position values, then the initial alignment tolerance must be very small, but mechanical stops only provide large initial tolerance
Solution Approach 1:
The patent applies preliminary action by implementing an initialization step that determines rough absolute positions despite large initial alignment tolerances from mechanical stops. This preliminary measurement data is then used to pre-align the scanning heads with the scales within the narrow connection tolerance required for exact position values. This separates the commissioning ease (large initial tolerance) from the measurement precision (small connection tolerance) requirements.
Data Source
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AI summary
A method for initializing a position measuring system on an object (1) movable in at least two degrees of freedom (Rx, Ry, Z) relative to a measuring frame (6) is described. The position measuring system comprises a position measuring device (10, 11, 12) for each degree of freedom, with a scale (2) having an incremental track (3) for measuring relative positions and an absolute track (4) for measuring absolute positions, as well as scanning heads (5) associated with the scales for reading the incremental and absolute tracks. According to one embodiment, in an initialization step (100), the incremental tracks (3) are evaluated using a first evaluation method with a large tolerance regarding the orientation of the scanning head (5) and the associated scale (2), thereby determining approximate absolute positions for each degree of freedom (Rx, Ry, Z). In an alignment step (200) the movable object (1) is aligned based on its approximate position relative to the measuring frame (6).In a capture step (300), the absolute tracks (4) are evaluated with a second evaluation method with low tolerance regarding the alignment of the scanning head (5) and associated scale (2) and precise absolute positions for each degree of freedom (Rx, Ry, Z) are determined.