Offset Receiver Encoder for Absolute Position Determination
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Solution Overview
Problem
Conventional encoder systems face challenges in accurately determining absolute positions due to misalignment and electronic influences, leading to ambiguous decoding and potential large errors, especially in motor feedback systems where precise mechanical and electronic tolerances are critical.
Innovation Solution
A transmitter device with two receivers offset by a fraction of a code element, where a control and evaluation unit selects the better-aligned receiver to reconstruct the code word without switching between channels, using a phase offset to distinguish between favorable and unfavorable alignments, and employing a synchronization marking for initial phase alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodiodes are arranged in a row to detect code elements, then absolute position can be determined, but misalignment between photodiodes and code elements causes partial detection and ambiguous decoding
Solution Approach 1:
The code track is segmented into multiple code elements (e.g., 16 code elements for 16-bit absolute position), and photodiodes are arranged in multiple rows (e.g., 4 rows) with different offsets. Each row detects a subset of code elements with a specific phase relationship, allowing the system to segment the detection task across multiple channels to avoid partial detection ambiguity.
Solution Approach 2:
The patent introduces asymmetric offset relationships between photodiode rows and code elements. The first and second rows are offset by different fractions of the code element length (e.g., first row offset by 1/16, second row offset by 3/16). This asymmetric arrangement ensures that at any given position, at least one row has optimal alignment with the code elements, eliminating the ambiguity caused by symmetric misalignment.
2Reliability
If two channels A and B are used with photodiodes offset by half the length of a code element, then unique bits can be captured, but synchronization between channels becomes complex and error-prone
Solution Approach 1:
Instead of using temporal switching between two channels (time dimension), the patent uses spatial arrangement with multiple photodiode rows detecting code elements simultaneously (space dimension). The different row offsets create inherent spatial encoding that eliminates the need for temporal synchronization switching, reducing complexity while maintaining reliability.
3Reliability
If additional photodiodes are used for oversampling to recognize codeword reliably, then phase relationship independence is achieved, but device complexity increases
Solution Approach 1:
The patent uses a minimal set of photodiode rows (e.g., 4 rows) with specific offset relationships that provide just enough oversampling capability to reliably recognize codewords across all phase positions. This partial action approach achieves sufficient reliability without the excessive number of photodiodes that would be required for complete phase independence, optimizing the trade-off between reliability and complexity.
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 approach enables precise, self-sufficient absolute position determination without relying on additional incremental tracks or synchronization, maximizing mechanical and electronic tolerance reserves and reducing errors, while maintaining functional safety through redundant channel evaluation.
Implementation Method 1
In the case of transmitted light in a transmission arrangement of a light source and a scanning sensor, optically transparent and opaque areas are provided; for reflected light in a reflection arrangement of a light source and scanning sensor, reflective and absorbing areas are provided.
Data Source
Figure 1~2
Figure 3~5b
AI summary
A transmitter device (10) for determining the absolute position of a first object relative to a second object is specified, comprising a measuring instrument (14) connected to the first object with an absolute code track (16) consisting of a plurality of code elements, a scanning device (18) connected to the second object with at least one first receiver (20a) and a second receiver (20b) for scanning the absolute code track (16) at least twice, wherein the receivers (20a-b) are arranged offset from each other along the absolute code track (16) by a fraction of the extent of a code element and each comprises a plurality of individual receiving elements in a series arrangement along the absolute code track (16) for generating scanning signals of the code elements, and a control and evaluation unit (24) configured forFor each determination of an absolute position, the receiver (20a-b) most favorably aligned with the absolute code track (16) is selected, and a codeword is reconstructed from the sampling signals of the individual receiving elements of the selected receiver (20a-b) to determine the absolute position. The control and evaluation unit (24) is further configured to determine in which receiver (20a-b) an individual receiving element is sampling a different code element than in a previous determination of the absolute position, and to select the other receiver (20b-a) for determining the current absolute position.