Position Detection Grating Frequency Offset for Machine Tool Accuracy
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Solution Overview
Problem
Conventional position detection methods in machine tools require a fine light receiving element array for high accuracy, leading to increased costs and larger apparatus sizes due to the need for different grating areas to generate reversed-phase pulses.
Innovation Solution
A position detection apparatus with a scale and detector that use a divergent light beam and detection grating with a predetermined frequency offset, allowing for high-accuracy reference position detection using a light intensity distribution and a plurality of light receiving elements, reducing the need for fine grating areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fine light receiving element array is used to obtain high accuracy reference position signal, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The invention changes the spatial frequency parameter of the detection grating by introducing a frequency offset relative to the interference image from the reference position grating. This parameter change allows the system to detect reference positions with high accuracy using a coarser light receiving element array, thereby reducing device complexity and manufacturing cost while maintaining measurement precision.
Solution Approach 2:
The invention replaces the mechanical/optical constraint of requiring fine light receiving elements with an optical field manipulation approach. By using a detection grating with offset spatial frequency to modulate the light intensity distribution, the system achieves high-precision reference position detection without relying on fine physical spacing of light receiving elements.
2Measurement precision
If different grating areas are used to generate reversed-phase pulses, then measurement precision is improved, but apparatus size increases
Solution Approach 1:
Instead of using different grating areas to generate reversed-phase pulses, the invention changes the spatial frequency parameter of the detection grating. By offsetting the spatial frequency of the detection grating from the interference image frequency, the system generates the necessary phase information through frequency modulation rather than area variation, thereby maintaining measurement precision while reducing apparatus size.
3Device complexity
If a light receiving element with large area is used, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The invention substitutes the mechanical requirement for fine light receiving element spacing with an optical field manipulation mechanism. By using a detection grating with offset spatial frequency, the system encodes position information in the spatial frequency domain, allowing large-area light receiving elements to detect high-precision reference positions without the need for fine physical element spacing.
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
Enables small-size, cost-effective position detection with high accuracy by utilizing a divergent light beam and detection grating configuration, allowing for precise reference position detection without the need for extensive fine grating areas.
Implementation Method 1
a light source configured to emit a divergent light beam
Implementation Method 2
a reference position grating configured to change a pattern period along a first direction... a detection grating configured to change a pattern period in the first direction
Implementation Method 3
a light intensity distribution of the divergent light beam obtained via the reference position grating and the detection grating
Implementation Method 4
a light receiver including a plurality of light receiving elements arrayed along the first direction... the light receiver detects a component of a second spatial frequency
Data Source
AI summary
A position detection apparatus (100) includes a scale (20) including a reference position grating (22), a detector (10), a detection grating (19), and a signal processor (10), the signal processor acquires a relative reference position between the scale and the detector by using a light intensity distribution of a divergent light beam obtained via the reference position grating and the detection grating, the detection grating has a first spatial frequency that is offset by a predetermined frequency offset amount with respect to a local spatial frequency of an interference image from the reference position grating, the detection grating is provided in an optical path between the scale and a light receiver of the detector, and the light receiver detects a component of a second spatial frequency that is lower than the first spatial frequency in the light intensity distribution transmitting through the detection grating.