Hybrid Laser Sensor for Speed and Length Measurement
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Solution Overview
Problem
Existing optical length measurement methods for products, such as those in extrusion devices, face challenges in providing reliable measurements at slow speeds, standstills, and large accelerations, and are often costly and complex due to limitations in bandwidth, spatial resolution, and directional sensitivity.
Innovation Solution
A device combining a spatial filter method with an imaging measurement using the optical flow tracking method, employing a first sensor with a transmission grating and an image sensor, along with a beam splitter to detect speckle patterns and evaluate intensity modulation for accurate speed and length measurement, allowing for directional sensitivity and operation at low speeds, including standstill conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If optical spatial filter measuring devices are used for length measurement, then structural and metrological simplicity is achieved, but reliable measurement at low speeds, standstills, or large accelerations is not delivered
Solution Approach 1:
The patent combines two different measurement methods: optical spatial filter measurement (for simplicity and high-speed measurement) and laser Doppler measurement (for reliable measurement at low speeds and standstills). The system uses both a first sensor with transmission grating and a second sensor with image element array to detect speckle patterns, allowing each method to complement the other and achieve reliable measurement across the entire speed range including low speeds and standstills.
2Reliability
If laser Doppler measuring devices are used for speed measurement, then popular and reliable measurement is achieved, but expensive Bragg cells are required to detect direction of movement or standstill
Solution Approach 1:
The patent uses a second sensor with image element array to create an optical copy of the speckle pattern instead of requiring expensive Bragg cells for directional detection. The image sensor captures the speckle pattern, and by evaluating the displacement of this pattern, the system can determine the direction of movement and detect standstill without needing additional expensive components like Bragg cells.
Solution Approach 2:
The patent divides the detection function into two separate sensors: the first sensor with transmission grating for intensity modulation detection and the second sensor with image element array for speckle pattern displacement detection. This segmentation allows each sensor to be optimized for its specific function, with the image sensor providing directional information and standstill detection without requiring expensive Bragg cells.
3Adaptability or versatility
If imaging sensors are used for optical length measurement, then multiple signals can be generated simultaneously, but limited bandwidth and spatial resolution result in limitations in measurement accuracy and measurable speed range
Solution Approach 1:
The patent merges the advantages of both imaging sensors and spatial filter sensors by using a hybrid detection system. The first sensor with transmission grating provides high-bandwidth intensity modulation detection, while the second sensor with image element array provides speckle pattern displacement detection. This combination allows the system to achieve both high-speed measurement capability and high measurement accuracy across the entire speed range.
4Adaptability or versatility
If product surface structure is used as optical pattern, then directional sensitivity is enabled, but problems arise with very smooth product surfaces
Solution Approach 1:
The patent introduces a laser beam as an intermediary to create speckle patterns on the product surface. Instead of relying on the product's own surface structure as the optical pattern, the laser creates a synthetic speckle pattern that can be detected by the image sensor. This intermediary approach enables directional sensitivity while working reliably on very smooth surfaces that would otherwise lack sufficient optical contrast.
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
Enables reliable, structurally simple, and cost-effective measurement of speed and length over a wide range, including slow speeds and standstill conditions, with improved signal quality and reduced complexity in calibration and alignment, suitable for smooth surfaces and varying distances.
Implementation Method 1
a laser for irradiating a surface of the product and comprising a detector device for detecting laser radiation scattered back from the surface of the product
Implementation Method 2
an optical pattern generated by irradiating the product surface is detected by a sensor via a transmission grating. Movement of the product and the associated movement of the optical pattern are detected by the sensor, in the simplest case as a simple intensity modulation
Implementation Method 3
the illuminated surface is projected onto an imaging sensor, such as a CCD sensor, using a lens. In this case, the surface structure of the product itself serves as the optical pattern
Implementation Method 4
a first beam splitter which splits laser radiation scattered back by the product into laser radiation directed to the first sensor on the one hand and to the image sensor on the other hand
Data Source
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Figure 3
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AI summary
The invention relates to a device for determining the speed and/or the length of a product, in particular a strand, which is moving along a conveyor device, comprising a laser for irradiating a surface of the product and comprising a detector device for detecting laser radiation scattered back from the surface of the product, wherein the detector device comprises a first sensor, in particular a photodiode, with a first transmission grating arranged in front of the sensor and a second sensor which is made of an image sensor, and additionally a first beam splitter is provided which splits laser radiation scattered back from the product into laser radiation which is conducted to the first sensor and to the image sensor. An analysis device is designed to determine the speed and/or the length of the product using an intensity modulation detected by the first sensor during a movement of the product and/or using a speckle pattern shift detected by the image sensor during a movement of the product, said speckle pattern being formed on the image sensor.