Position Measuring Device with Constant Fringe Pattern
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Solution Overview
Problem
Existing position measuring devices with ring-like circumferential reflection measuring graduations face challenges in maintaining a constant fringe pattern period in the detection plane when the scanning distance changes, leading to instability in scanning signals and mounting difficulties due to varying periodicity of the stripe pattern.
Innovation Solution
A position measuring device with a cylindrical object featuring a ring-like circumferential reflection measuring graduation, a stationary scanning unit, and a transmission grating, where the normal distance between the transmission grating and detector is set to 2*u^2/R plus a tolerance of +/-20%, ensuring the fringe pattern period remains constant regardless of scanning distance fluctuations, using the equations d_D = d_M * (1 + v/u) and ε = 2*u^2/R to maintain stable scanning signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the scanning distance changes in a position measuring device with a ring-like circumferential reflection measuring graduation, then the device can accommodate different mounting positions, but the fringe pattern period in the detection plane changes, leading to instability in scanning signals
Solution Approach 1:
The patent applies parameter changes by establishing a specific mathematical relationship between the scanning distance (u) and the detector position (v), where v = 2*u^2/R. This parameter relationship ensures that as the scanning distance changes, the detector position is adjusted accordingly to maintain a constant fringe pattern period in the detection plane, thereby preserving scanning signal stability while accommodating different mounting positions
2Adaptability or versatility
If the scanning distance varies, then the device can be mounted at different distances from the graduation, but the periodicity of the stripe pattern changes, causing mounting difficulties
Solution Approach 1:
The patent resolves the manufacturing precision issue by deriving and implementing the specific parameter relationship v = 2*u^2/R. This formula allows the detector position to be calculated based on the scanning distance, ensuring that the fringe pattern periodicity remains constant across different mounting distances. This eliminates the need for precise manual adjustment during manufacturing and installation
3Device complexity
If the normal distance between transmission grating and detector is not optimized, then the device structure is simpler, but the fringe pattern period depends on scanning distance, reducing signal stability
Solution Approach 1:
The patent introduces a specific parameter relationship v = 2*u^2/R between the detector position (v) and scanning distance (u), which adds a degree of complexity to the optical path configuration. However, this complexity is justified by the significant improvement in scanning signal stability, as the relationship ensures constant fringe pattern periodicity regardless of scanning distance variations
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
The solution ensures the stripe pattern period in the detection plane is independent of the scanning distance, providing stable scanning signals and easy mounting with large tolerances, as the periodicity of the fringe pattern matches the detector's periodicity, maintaining signal stability even with fluctuations in scanning distance.
Implementation Method 1
Each illuminated transmission grating line sends a cylindrical wave to the scale, which is at a distance u behind the transmission grating. In the beam path, enlarged self-images of the material measure are created at distances v through each of these cylindrical shafts.
Implementation Method 2
a back-reflection takes place in the direction of the detector, via which rotation-dependent position signals can be generated
Implementation Method 3
The periodicity d D of the self-images results in a detection plane... the self-images of the scale moves in the detection plane
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
The device has a cylindrical object (2) rotatable about a longitudinal axis (A) and comprising circumferential annular reflection measuring graduation (2.1). A stationary scanning unit (1) has a light source i.e. LED, a transmission grating and a detector. The scanning unit optically scans the graduation by beams of light from the light source. Optically effective perpendicular distance between the detector and the measuring graduation is greater or smaller than optically effective perpendicular distance between the grating and the graduation based on radius of the object.