Optical Distance Sensor Sensitivity Control Across Temperature Shifts
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Solution Overview
Problem
Existing photoelectric sensors struggle with sensitivity issues when detecting workpieces with low reflectance and are unstable in varying environmental temperatures, particularly in factory automation settings, and require flexible sensitivity adjustment based on the detection object's properties.
Innovation Solution
An optical distance measuring sensor that includes a charge accumulation unit for generating pulse current, a pulse current controller to adjust intensity based on target sensitivity, a light-receiving element controller to adjust multiplication factor based on temperature and sensitivity, and a calculation unit to calculate distance using adjusted signals, allowing for high sensitivity and stability across temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the amplification factor of the light-receiving element is increased to improve sensitivity for low reflectance workpieces, then the sensitivity is improved, but the temperature characteristics deteriorate and the sensor becomes unstable across temperature ranges
Solution Approach 1:
The sensor performs preliminary actions by measuring the temperature beforehand and storing characteristic data (breakdown voltage, temperature coefficient) at different temperatures. Based on this preliminary temperature information, the sensor pre-adjusts the reverse bias voltage to the appropriate level, ensuring optimal sensitivity while maintaining temperature stability before actual measurement begins.
Solution Approach 2:
The sensor implements feedback by continuously monitoring the temperature through a temperature sensor, comparing it with stored characteristic data, and automatically adjusting the reverse bias voltage of the light-receiving element. This closed-loop feedback mechanism ensures the sensor maintains optimal performance across varying temperature conditions.
2Measurement precision
If the sensitivity is set too high to detect low reflectance workpieces, then the detection capability for dark objects is improved, but the ability to detect high reflectance workpieces deteriorates
Solution Approach 1:
The sensor applies dynamics by making the reverse bias voltage adjustable rather than fixed. The control unit dynamically changes the reverse bias voltage based on the detected object's reflectance properties - using higher voltages for low reflectance objects to enhance sensitivity, and lower voltages for high reflectance objects to prevent saturation, thereby achieving versatile detection across different object types.
3Measurement precision
If a light-receiving element with amplification function is used to improve sensitivity, then the detection sensitivity is enhanced, but the temperature characteristics worsen
Solution Approach 1:
The sensor applies parameter changes by dynamically adjusting the reverse bias voltage parameter based on temperature conditions. The control unit selects appropriate reverse bias voltage levels from stored characteristic data corresponding to different temperatures, thereby optimizing the amplification effect of the light-receiving element while compensating for temperature-induced performance degradation.
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 sensor achieves a wide dynamic range and stable operation by emitting high or low intensity light pulses and adjusting the light-receiving element's multiplication factor, ensuring consistent performance despite environmental temperature fluctuations.
Implementation Method 1
a light-receiving element configured to receive the reflected light
Implementation Method 2
detection light is repeatedly generated by a light-emitting element
Data Source
AI summary
An optical distance measuring sensor includes a charge accumulation unit for generating a pulse current to be supplied to a light-emitting element; a setting unit that sets a target sensitivity; a pulse current controller that generates the pulse current in synchronization with a repetitive signal, pulse-drives the light-emitting element, and adjusts the pulse current based on the target sensitivity; a light-receiving element that receives the reflected light; a nonvolatile memory having characteristic data of the individual light-receiving element stored therein; a light-receiving element controller that adjusts a multiplication factor of the light-receiving element based on a temperature measured by a temperature sensor, the characteristic data, and the target sensitivity; and a calculation unit that calculates a time from when light is emitted to an object to when reflected light is received based on an output signal repeatedly obtained from the light-receiving element in which the multiplication factor has been adjusted.