Optical Positioning Device with Variable Focal Length
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Solution Overview
Problem
High-resolution optical position-measuring devices operating in incident light face challenges in generating reference signals when the scanning unit and reflection scale are tilted, leading to position errors, especially with large fluctuations in scanning distance.
Innovation Solution
The optical position measuring device incorporates imaging optics with a changing object-side focal length and a diaphragm structure with partial areas for beam deflection, ensuring the neutral pivot points of incremental and reference signal scans coincide, thus minimizing tilting effects and maintaining accurate position measurements across varying scanning distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the scanning unit and reflection scale are tilted relative to each other, then the position measurement can still be performed, but position errors occur in the generated reference signals and incremental signals
Solution Approach 1:
The imaging optics employ a variable object-side focal length that changes along the transverse direction. This parameter change allows the focal length to be adapted for each scanning distance, ensuring that the neutral pivot point of reference signal generation coincides with the neutral pivot point of incremental signal generation, thereby eliminating position errors caused by tilting.
2Adaptability or versatility
If the scanning distance fluctuates significantly, then the measurement range is improved, but it becomes difficult to ensure that the neutral pivot points of incremental and reference signal scans coincide
Solution Approach 1:
The imaging optics feature a dynamic, variable focal length that can be adjusted according to the scanning distance. This dynamic adaptation ensures that regardless of the scanning distance fluctuations, the neutral pivot points of both incremental and reference signal scans remain coincident, maintaining measurement precision across the full measurement range.
3Device complexity
If a fixed focal length is used in the imaging optics, then the device complexity is reduced, but position errors occur due to tilting and scanning distance variations
Solution Approach 1:
Instead of using a fixed focal length, the imaging optics employ a variable object-side focal length that changes along the transverse direction. This parameter change enables the system to compensate for tilting and scanning distance variations, eliminating position errors while maintaining a relatively simple optical design.
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 ensures minimal disturbance to reference signal generation due to tilting and large scanning distance fluctuations, preventing incorrect position measurements and ensuring correct absolute position determination even after system restarts.
Implementation Method 1
imaging optics with a changing, object-side focal length along a transverse direction
Implementation Method 2
imaging optics have a changing, object-side focal length
Implementation Method 3
diffractive reference marking structures
Data Source
Figure 1a
Figure 1b
Figure 2
AI summary
The present invention relates to an optical position measuring device with a reflective scale and a scanning unit movable in at least one measuring direction. The reflective scale has an incremental measuring scale and a reference mark at at least one reference position. In addition to scanning means for incremental signal generation, the scanning unit for reference signal generation comprises at least one light source, an imaging optic, an aperture structure arranged in an aperture plane, and several detector elements; the reference mark is imaged onto the aperture structure by the imaging optic. The reference mark is integrated into the incremental measuring scale on the reflective scale. Furthermore, the imaging optic has a changing, object-side focal length along a transverse direction oriented perpendicular to the measuring direction (Fig. 5).