Optical Position Sensor Contamination Resistance
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Solution Overview
Problem
Optical position measuring devices are prone to contamination, such as cooling lubricants or oil mist, which can impair their functionality and lead to failures, despite existing protective measures, as they are not entirely insensitive to scattering contamination.
Innovation Solution
The optical position measuring device incorporates a scanning unit with a light source, scanning grating, and detector device, where the incremental and absolute detectors are in a common detection plane, with a defined normal distance from the scanning grating, and the periodicity of the fringe pattern on the incremental detector is selected to ensure even amplitude drops in the presence of scattering contamination, minimizing its impact on signal generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If protective measures such as encapsulation or compressed air flushing are implemented, then the device is protected against contamination, but the complexity of the device increases and mechanical protective measures may still fail against scattering contamination
Solution Approach 1:
The patent replaces mechanical protective measures (encapsulation, compressed air flushing) with an optical solution by optimizing the detection plane position and fringe pattern periodicity. This substitution eliminates complex mechanical components while achieving contamination resistance through geometric optimization of the optical path, where the specific relationship between detection plane distance and fringe pattern period compensates for scattering effects without requiring additional protective mechanisms.
Solution Approach 2:
The patent changes critical optical parameters - specifically the normal distance of the detection plane from the scanning grating and the periodicity of the fringe pattern on the incremental detector. By optimizing these parameters according to specific mathematical relationships, the system achieves insensitivity to scattering contamination, transforming the approach from passive protection to active parameter-based compensation.
2Object-affected harmful factors
If the detection plane is positioned closer to the scanning grating, then the optical path is shorter and less prone to contamination, but the measurement precision and signal quality deteriorate
Solution Approach 1:
The patent identifies and optimizes two critical parameters: the normal distance of the detection plane from the scanning grating and the periodicity of the fringe pattern. By establishing specific mathematical relationships between these parameters and other system parameters (such as the distance between measuring standard and scanning grating, graduation period, and absolute coding structure width), the system achieves a balance where measurement precision is maintained while insensitivity to scattering contamination is achieved.
3Reliability
If complex mechanical protective measures are used to prevent contamination, then reliability improves, but the device complexity and cost increase
Solution Approach 1:
The patent replaces complex mechanical protective measures with an optimized optical configuration. By positioning the detection plane at a specific normal distance from the scanning grating and designing the fringe pattern with an optimized periodicity, the system achieves high availability and contamination resistance without requiring additional mechanical protective components, thereby reducing overall device complexity and cost.
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 design significantly increases the device's contamination resistance, ensuring reliable position signal generation even under critical conditions, potentially reducing the need for complex mechanical protective measures and enhancing availability.
Implementation Method 1
The scanning unit has a light source
Implementation Method 2
a scanning grating for the optical scanning of the incremental graduation
Implementation Method 3
a detector device. The detector device has an incremental detector for generating incremental signals from the optical scanning
Data Source
Figure 1
Figure 2a~2c
Figure 3~4b
AI summary
The present invention relates to an optical position measuring device. This device comprises, firstly, a scale extending along a measuring direction and featuring incremental graduations and absolute coding. Secondly, a scanning unit is provided, which is arranged to be movable relative to the scale along the measuring direction and comprises a light source, a scanning grating for optically scanning the incremental graduations, and a detector assembly. The detector assembly includes an incremental detector for generating incremental signals from the optical scanning of the incremental graduations and an absolute detector for generating absolute signals from the optical scanning of the absolute coding; the incremental detector and the absolute detector are arranged in a common detection plane.The detection plane has a defined normal distance from the scanning grid and/or the periodicity of a stripe pattern on the incremental detector is chosen such that, in the case of scattering contamination in the area of the scale and/or the scanning grid, the amplitudes of the incremental signals and the absolute signals drop uniformly (Fig. 1).