Optoelectronic Position Sensor for Electromagnetic Force Compensation Weighing Cell
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Solution Overview
Problem
Existing electromagnetic force compensation balances face challenges in achieving high accuracy and reproducibility of zero position and linearity of sensor signals, particularly in compact designs and under temperature fluctuations, shocks, or vibrations, due to limitations in the geometry of optoelectronic position sensors.
Innovation Solution
The position sensor arrangement places the shutter vane closer to the light receiver than the light source, with a subsection of the space interval adjacent to the light receiver, optimizing sensitivity and linearity by maintaining a steep slope angle and invariance with shifts, and using a differential photodiode with equal rectangular photosensitive surface areas for improved signal generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the shutter vane is positioned in the middle of the space interval between light source and light receiver, then the device structure is simplified, but the zero position accuracy and sensor signal linearity deteriorate
Solution Approach 1:
The patent positions the shutter vane in a specific subsection of the space interval adjacent to the light receiver rather than in the middle, creating an asymmetric optical path. This dimensional repositioning along the optical axis enables steeper characteristic curves and improved zero position accuracy while maintaining manufacturing feasibility through defined geometric relationships.
2Volume of moving object
If the space interval between light source and light receiver is reduced for compact design, then the device size is reduced, but the sensor signal sensitivity and linearity deteriorate
Solution Approach 1:
The patent defines specific geometric parameters including the shutter distance being 0.05 to 0.2 times the space interval, and the light receiver distance being 0.8 to 0.95 times the space interval. These parameter relationships maintain optimal sensitivity and linearity even when the overall space interval is reduced for compact device design.
3Adaptability or versatility
If the photosensitive surface areas of the light receiver are made unequal to accommodate misalignments, then the tolerance to positional shifts is improved, but the zero position accuracy and signal linearity deteriorate
Solution Approach 1:
The patent specifies that the shutter vane should have a width of 0.4 to 0.6 times the distance between the centers of the two photosensitive surface areas. This preliminary dimensional relationship ensures that the shutter fully blocks light to both areas at the zero position while maintaining equal area symmetry, thereby preserving zero position accuracy even with production tolerances.
4Adaptability or versatility
If the shutter vane width is increased to cover larger misalignments, then the tolerance to positional shifts is improved, but the sensor signal sensitivity deteriorates
Solution Approach 1:
The patent establishes optimal parameter relationships where the shutter width is 0.4 to 0.6 times the distance between photoarea centers, and the photoarea height is 0.2 to 0.4 times the space interval. These parameter changes simultaneously achieve adequate misalignment tolerance and maintain steep characteristic curves for high sensitivity.
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 configuration enhances the accuracy and reproducibility of the zero position and linearity of the sensor signal, ensuring a stable and proportional response to deflections, even under varying conditions, while accommodating production tolerances without increasing production costs.
Implementation Method 1
A photodiode is a semiconductor element which, when exposed to light, generates a current which, within a certain range, is proportionate to the amount of incident light
Implementation Method 2
the electromagnetic force between the coil and the permanent magnet, the shutter vane and movable parts of the balance that are connected to the shutter vane are brought back to the zero position
Data Source
AI summary
A weighing cell based on the principle of electromagnetic force compensation and having an optoelectronic position sensor that includes a light source, a light receiver, and a shutter vane. The light receiver functions to generate a position sensor signal corresponding to a deflection of the shutter vane from a zero position which occurs as a result of placing a load onto a load receiver of the weighing cell. A controller functions to regulate compensation current in response to the position sensor signal in such a way that the shutter vane and the movable parts of the weighing cell connected to the shutter vane are returned to the zero position by the electromagnetic force between a coil and permanent magnet system of the weighing cell.