Optical Distance Sensor Tilt Error Correction
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Solution Overview
Problem
Conventional optical sensors fail to accurately measure free-form surfaces with the required precision and accuracy due to optical system deficiencies, such as aberrations and manufacturing errors, especially when the surface is tilted or inclined, leading to increased measurement uncertainty and limited measurement range.
Innovation Solution
The optical sensor employs a pupil-sensing system to determine the tilt-dependent shift of the reflected measuring beam radiation distribution, using a position-sensitive detector to measure the beam center and compensate for inclination-dependent errors through a calibration procedure, and incorporates a movable focusing unit with an interferometer system to extend the measurement range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical sensors are used for measuring free-form surfaces, then the device complexity is low, but the measurement precision deteriorates due to optical system deficiencies and increased measurement uncertainty on tilted surfaces
Solution Approach 1:
The optical sensor is divided into functionally independent modules: a radiation source unit, a focusing unit with movable lens, a detection system with radiation-sensitive detectors, and a signal processing circuit. This segmentation allows each module to be optimized independently for its specific function while maintaining overall measurement precision.
Solution Approach 2:
The focusing unit incorporates a movable lens that can be dynamically adjusted along the optical axis. This dynamic adjustment capability enables the sensor to maintain focus and measurement precision across varying distances and surface inclinations, resolving the contradiction between precision and system complexity.
2Adaptability or versatility
If the measurement range is extended to 5 mm, then the adaptability improves for measuring large optical elements, but the measurement precision deteriorates due to optical system deficiencies
Solution Approach 1:
The movable lens in the focusing unit enables dynamic adjustment of the focal point along the optical axis. This allows the sensor to maintain precise focus across an extended measurement range of 5 mm, accommodating both large optical elements and maintaining measurement precision simultaneously.
Solution Approach 2:
The system changes the positional parameter of the lens within the focusing unit to adapt to different measurement distances. By adjusting the lens position, the optical system maintains optimal focus and precision across the extended measurement range from close distances up to 5 mm.
3Measurement precision
If the measurement uncertainty is reduced to 10 nm for perpendicular surfaces and 35 nm for inclined surfaces, then the measurement precision improves, but the device complexity increases due to the need for sophisticated optical systems
Solution Approach 1:
The detection system incorporates radiation-sensitive detectors that provide feedback signals to the signal processing circuit. This feedback mechanism enables real-time compensation for measurement variations due to surface inclination, achieving reduced measurement uncertainty (10 nm for perpendicular, 35 nm for inclined surfaces) without requiring overly complex optical systems.
Solution Approach 2:
The system replaces complex mechanical adjustment mechanisms with an optical-mechanical hybrid approach using a movable lens controlled by precise positioning. This substitution achieves high measurement precision through optical field control rather than mechanical surface manipulation, reducing overall device complexity while maintaining 10-35 nm measurement uncertainty.
4Adaptability or versatility
If a movable focusing unit with interferometer system is incorporated, then the measurement range increases to 5 mm, but the device complexity increases
Solution Approach 1:
The interferometer system is merged with the existing optical path of the sensor. The movable lens and interferometer components share the same optical axis and structural support, allowing the measurement range to be extended to 5 mm while minimizing additional device complexity through integrated design.
Solution Approach 2:
The movable focusing unit serves multiple functions: it extends the measurement range to 5 mm, maintains focus across varying distances, and works in conjunction with the interferometer system for precise distance measurement. This multi-functionality reduces the need for separate systems, thereby limiting the increase in device complexity.
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 approach significantly improves measurement accuracy and resolution, reducing measurement uncertainty to 10 nm for perpendicular surfaces and 35 nm for surfaces with up to 5 degrees inclination, while increasing the measurement range to 5 mm, and enhances the sensor's stability and cost-effectiveness.
Implementation Method 1
focusing unit for focusing the measuring beam to a spot on the object surface
Implementation Method 2
radiation-sensitive detection means for converting measuring beam radiation reflected from the object surface into an electrical signal
Implementation Method 3
incorporates a movable focusing unit with an interferometer system to extend the measurement range
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
In a optical sensor (30) for measuring object surfaces (2) with high precision, measuring errors due to tilt of an object surface can be corrected by using a pupil monitor (72), which senses the intensity distribution of the reflected measuring beam (b') in combination with a correction/calibration table (76) and use the monitor signal to correct the primary measuring signal (FES) of the sensor. Especially for a differential confocal sensor, a further order of correction can be obtained by determining optimum position and diameter of the pinholes. The measurement beam is directed to an object via a beams splitter cube and an objective that focuses the beam on an object surface. Light is received back from the object surface through the objective and split off by the splitter, from where it is directed to a sensor. In order to increase the measurement range the objective is mounted on an actuator. An interferometer is used to measure the position of the objective. The interferometer involves a mirror on the objective and an interferometer beam path that also uses the splitter cube. Thus, errors affect the interferometer and distance measurement in the same way. Additionally errors due to tilt of an object surface can be corrected by using a pupil monitor (72), which senses the intensity distribution of the reflected measuring beam (b1) in combination with a correction/ calibration table (76) and use the monitor signal to correct the primary measuring signal (FES) of the sensor. Especially for a differential confocal sensor, a further order of correction can be obtained by determining optimum position and diameter of the pinholes.