Optical Positioning Device Wavefront Correction
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Solution Overview
Problem
High-resolution optical position-measuring devices face significant signal degradation due to wavefront deformations when used with curved measuring directions, such as radial or drum graduations, leading to reduced mounting tolerances and compromised signal quality.
Innovation Solution
An optical position-measuring device with a reflector unit comprising a first and second wavefront corrector and a beam direction inverter, which corrects wavefront deformations by converting them into plane wavefronts, ensuring maximum interference contrast and improved signal quality even with misalignment of the scale and scanning unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If radial or drum graduations are used for curved measuring directions, then the device can measure curved paths, but wavefront deformations occur causing signal degradation
Solution Approach 1:
A wavefront corrector is introduced as an intermediary optical element between the graduated disk and the detector. This wavefront corrector compensates for the deformations caused by the radial/drum graduations, acting as a mediator that restores the wavefront quality without eliminating the curved measuring capability. The wavefront corrector includes optical elements positioned to correct the specific deformation patterns introduced by the curved scale geometry.
2Ease of operation
If small radial, tangential or longitudinal position deviations occur, then mounting flexibility is improved, but strong signal drop results due to wave front deformations
Solution Approach 1:
The wavefront corrector is designed beforehand to compensate for expected positioning deviations and wavefront deformations. By pre-configuring the optical correction elements to address the specific deformation patterns caused by radial/drum graduations, the system maintains signal strength even when mounting deviations occur within the tolerance range.
3Reliability
If the beam focus lies on the roof edge of the roof prism, then retroreflection is achieved, but production requirements become extremely high due to defect sensitivity
Solution Approach 1:
The critical function of retroreflection is extracted from the roof prism configuration and implemented using alternative optical elements with more relaxed manufacturing tolerances. The wavefront corrector design achieves the necessary beam redirection and retroreflection effect without requiring the beam focus to lie on the sensitive roof edge, thereby eliminating the extreme production requirements while maintaining optical performance.
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 significantly enhances signal quality and allows for larger mounting tolerances by compensating for both nominal and tolerance-related wavefront deformations, enabling the use of smaller graduation periods and higher resolution.
Implementation Method 1
The first wavefront corrector converts the from the first combination of material measure and the first wavefront corrector into collimated partial beams of rays with plane wavefronts. The second wavefront corrector converts the wavefronts emerging from the second combination of material measure and second wavefront corrector into collimated partial beams of rays with flat wavefronts
Implementation Method 2
partial beams of rays are reflected back in the direction of the material measure via the beam direction inverter
Implementation Method 3
a collimated beam of rays from a laser light source is divided into partial beams of rays +1 on the linear grating of the scale and -1 diffraction order diffracted
Implementation Method 4
the two partial beams of rays are brought to interference at a superimposition location. There is then no wavefront tilting of the interfering partial beams of rays. This results in a maximum interference contrast in the overlapping area of the interfering partial beams of rays
Data Source
Figure 1a~1c
Figure 1d~1e
Figure 2
AI summary
The optical position measuring device has a reflector unit and a detector unit, where the reflector unit has a shaft front corrector, a radiation direction inverter and another shaft front corrector. The reflector unit is arranged or formed in a scanning unit (20).