Optical Sensor Transit Time Calibration via Clock Interpolation
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Solution Overview
Problem
Optical sensors using the pulse transit time method for distance measurement face significant accuracy limitations due to temperature effects and component aging, which cause fluctuations in measurement voltage.
Innovation Solution
Incorporating a clock generator, such as a quartz oscillator, to perform two calibration measurements with reference times that are integer multiples of the system clock period, allowing for interpolation to determine the exact transit time and thereby eliminating external interference, with minimal additional components and design effort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive element is used for transit time measurement, then distance measurement can be performed, but measurement accuracy deteriorates due to temperature effects and component aging
Solution Approach 1:
The patent performs preliminary calibration measurements at reference temperatures before actual distance measurements. The evaluation circuit stores calibration data relating capacitor charging characteristics to reference temperatures, and automatically adjusts subsequent measurements based on this calibration data, thereby compensating for temperature-induced drifts and aging effects.
Solution Approach 2:
The patent implements a feedback mechanism where the evaluation circuit continuously monitors temperature conditions and adjusts the interpretation of capacitor charging curves accordingly. The system uses feedback from temperature sensors and stored calibration data to dynamically compensate for drift, ensuring measurement accuracy despite temperature variations and component aging.
2Measurement precision
If calibration measurements are performed to eliminate temperature drifts, then measurement accuracy improves, but device complexity increases due to additional calibration circuitry
Solution Approach 1:
The patent makes the evaluation circuit multi-functional by enabling it to perform both distance measurements and calibration measurements using the same hardware components. The evaluation circuit can switch between measuring modes and calibration modes, eliminating the need for separate calibration equipment and reducing overall device complexity while maintaining high measurement accuracy.
Solution Approach 2:
The patent implements self-service calibration where the optical sensor system performs its own calibration using built-in reference objects and internal evaluation circuitry. The system automatically compares measured values against stored reference data and adjusts measurements accordingly, eliminating the need for external calibration equipment and reducing 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 enhances the accuracy of distance measurements by referencing transit time measurements to calibration values independent of temperature drifts and component dimensions, using existing circuit components and reducing noise interference.
Implementation Method 1
a clock generator, such as a quartz oscillator, to perform two calibration measurements with reference times that are integer multiples of the system clock period
Implementation Method 2
the switching means are actuated for the first time. This can be done by evaluating the output voltage of the transmitter with a threshold value. As soon as the transmitter emits a light pulse, the output voltage is above the threshold value. As a result, the switching means are actuated, as a result of which a charging process for the capacitive element, in particular a charging of the capacitor, is started
Implementation Method 3
the transmitter of the optical sensor emits a light pulse, which is reflected back by the object and is thus guided to the receiver of the optical sensor
Implementation Method 4
the transmitter of the optical sensor emits a light pulse, which is reflected back by the object
Implementation Method 5
a receiver receiving light pulses
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to an optical sensor (1). The optical sensor (1) comprises a light pulse (2) emitting transmitter (3), a light pulse (2) receiving receiver (4), and an evaluation circuit (8) by means of which the distance to a detectable object (9) is determined from the transit time of a light pulse (2). The evaluation circuit (8) has switching means and a capacitive element. When a light pulse (2) is emitted, the switching means are actuated and trigger a charging process of the capacitive element. This charging process is terminated by actuating the switching means again. The measured voltage obtained by this charging process is evaluated as a measure of the object distance. The evaluation circuit (8) has a clock generator for specifying reference times.After determining the measurement voltage representing the propagation delay, the capacitive element is charged for a first reference time, defined by the clock and shorter than the propagation delay, by first actuation of the switching elements. This results in a first reference voltage. A second actuation of the switching elements charges the capacitive element for a second reference time, also defined by the clock and longer than the propagation delay. The exact propagation delay value is determined for the measurement voltage by interpolating the reference times and reference voltages.