Position Detection Apparatus with Dual Grating Resolution Modes
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Solution Overview
Problem
Existing optical position detection apparatuses face decreased accuracy due to increased efficiency and junction capacitance issues when the ratio between resolutions is large, leading to degradation in position detection performance.
Innovation Solution
A position detection apparatus with a scale and detector using a first and second grating pattern, along with an optical grating, where the optical grating is offset from the interference image's spatial frequency, allowing for phase detection of different spatial frequencies in high and low resolution modes, optimizing the number of light receiving elements for efficient signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of light receiving elements is increased to achieve high resolution detection, then the position detection accuracy is improved, but the junction capacitance increases and detection efficiency decreases
Solution Approach 1:
The patent divides the detection task into two separate detection paths: one for high resolution (using first grating pattern with higher spatial frequency) and one for wide range (using second grating pattern with lower spatial frequency). Each path uses an optimized number of light receiving elements, avoiding the need to use a large number of elements for both resolutions simultaneously. This segmentation resolves the contradiction by allowing each detection path to be independently optimized.
Solution Approach 2:
The patent implements dynamic switching between high resolution mode and wide range mode based on detection requirements. The switching mechanism allows the system to use only the necessary number of light receiving elements for the current detection task, thereby maintaining low junction capacitance and high detection efficiency while still providing high resolution capability when needed.
2Adaptability or versatility
If the ratio between resolutions is large to cover both high precision and wide range detection, then the adaptability is improved, but the number of light receiving elements must be increased leading to increased junction capacitance
Solution Approach 1:
The patent segments the detection functionality into two independent detection paths with different spatial frequencies. The first grating pattern handles high resolution detection while the second grating pattern handles wide range detection. This segmentation allows the system to achieve large detection range coverage without increasing the number of light receiving elements beyond what is needed for each individual path.
Solution Approach 2:
The patent makes the same light receiving element array serve multiple functions by using it in two different detection paths with different spatial frequencies. The first light receiving element array detects both the first grating pattern (high resolution) and the second grating pattern (wide range), allowing one component to provide multiple detection capabilities without requiring separate arrays for each function.
3Measurement precision
If more light receiving elements are used to detect both high and low frequency components, then the measurement precision is improved, but the separation band structure degrades due to increased junction capacitance
Solution Approach 1:
The patent segments the signal detection into two separate frequency bands using two different grating patterns. The first grating pattern detects high frequency components for high resolution, while the second grating pattern detects low frequency components for wide range. This segmentation allows each detection path to use an optimized number of light receiving elements, preventing the accumulation of excessive junction capacitance that would degrade the separation band structure.
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 configuration enables high-accuracy position detection across varying resolutions while preventing increases in junction capacitance and maintaining light receiving efficiency, thereby enhancing detection responsiveness and efficiency.
Implementation Method 1
detect a position of the target object by detecting light from the scale by the detector
Implementation Method 2
a second grating pattern having a second spatial frequency lower than the first spatial frequency... a phase of a component of a fourth spatial frequency lower than a spatial frequency corresponding to the frequency offset amount is detected from light that has passed the first grating pattern and the optical grating
Data Source
AI summary
The present invention provides a position detection apparatus that is provided with a scale and a detector and includes a processing unit configured to perform processing for setting a number of light receiving elements that are consecutive in a direction of relative movement and whose outputs are to be added for the light receiving elements so that, in a first resolution mode, a phase of a component of a fourth spatial frequency lower than a spatial frequency corresponding to a frequency offset amount is detected and, in a second resolution mode for which a resolution is lower than the first resolution mode, a phase of a component of a spatial frequency of an interference image of a second grating pattern is detected.