Time-of-Flight Method for Automotive Interior Applications
Koivukangas, Eedit (2022)
2022
Teknis-luonnontieteellinen DI-ohjelma - Master's Programme in Science and Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2022-11-30
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202211288684
https://urn.fi/URN:NBN:fi:tuni-202211288684
Tiivistelmä
There is a growing desire to make driving safer, easier and more comfortable. This thesis explored how optical sensors can be applied to automotive equipment. Optical sensing can be used to detect both the interior and exterior of a car. In the interior, one application that has been much studied is gesture control for infotainment systems. Gesture control is less distracting to the driver than, for example, control via touch screen.
Time-of-Flight technology is most commonly used in optical distance sensors. As its name suggests, it measures the time it takes for light to travel from the transmitter to the target and back to the receiver. The principle of operation and the components involved are explained in the theoretical section of this thesis. Time-of-Flight can be used to measure distance alone or to measure a 3D depth image using multiple receivers. The Time-of-Flight sensor provides not only distance information but also the intensity of the light reaching the receiver. Intensity is one indicator of the reliability of the distance measurement.
In the experimental part of this work, two distance sensors based on the Time-of-Flight method were investigated. One was the TMF8805 manufactured by ams and the other was the S13021- 1CT manufactured by Hamamatsu. Most commonly, touch sensors are based on capacitive sensing. However, it is not suitable for metallic surfaces. The aim was to investigate whether Time-of Flight sensors could optically detect the position of a finger on a touch surface. The requirements were sufficient measurement accuracy at distances between 0 and 300 mm, eye safety of the light source and a measurement duration of less than 20 ms.
The TMF8805 met the requirements well in the range 0-200 mm. Thereafter, a clear dip in the measurement results was observed. When the manufacturer was consulted, it was explained that the problem was known and was due to a change in the algorithm when the measurement mode was changed at 200 mm. The S13021-1CT did not work as required. The thesis shows how the performance of the sensor was improved, for example by changing the light source. Ambient light caused problems for the operation of the sensor, and at distances below 50 mm the measurement results were anomalous. An attempt was made to minimize the effect of ambient light by using a bandpass filter, but when this was used the measured distance did not increase linearly with the actual distance. Another weakness of the sensor was that the measurement duration was too long.
Further research would be needed under changing conditions to bring the application into production. The measurements carried out in this work were made under very stable laboratory conditions. In reality, the conditions in the car are highly variable in terms of temperature, ambient light and vibration. In addition, the reflectivity of the finger is not always constant. The range of skin tones is quite wide and the driver may also be wearing gloves. The influence of reflectivity on the success of the measurement should be taken into account more carefully.
Time-of-Flight technology is most commonly used in optical distance sensors. As its name suggests, it measures the time it takes for light to travel from the transmitter to the target and back to the receiver. The principle of operation and the components involved are explained in the theoretical section of this thesis. Time-of-Flight can be used to measure distance alone or to measure a 3D depth image using multiple receivers. The Time-of-Flight sensor provides not only distance information but also the intensity of the light reaching the receiver. Intensity is one indicator of the reliability of the distance measurement.
In the experimental part of this work, two distance sensors based on the Time-of-Flight method were investigated. One was the TMF8805 manufactured by ams and the other was the S13021- 1CT manufactured by Hamamatsu. Most commonly, touch sensors are based on capacitive sensing. However, it is not suitable for metallic surfaces. The aim was to investigate whether Time-of Flight sensors could optically detect the position of a finger on a touch surface. The requirements were sufficient measurement accuracy at distances between 0 and 300 mm, eye safety of the light source and a measurement duration of less than 20 ms.
The TMF8805 met the requirements well in the range 0-200 mm. Thereafter, a clear dip in the measurement results was observed. When the manufacturer was consulted, it was explained that the problem was known and was due to a change in the algorithm when the measurement mode was changed at 200 mm. The S13021-1CT did not work as required. The thesis shows how the performance of the sensor was improved, for example by changing the light source. Ambient light caused problems for the operation of the sensor, and at distances below 50 mm the measurement results were anomalous. An attempt was made to minimize the effect of ambient light by using a bandpass filter, but when this was used the measured distance did not increase linearly with the actual distance. Another weakness of the sensor was that the measurement duration was too long.
Further research would be needed under changing conditions to bring the application into production. The measurements carried out in this work were made under very stable laboratory conditions. In reality, the conditions in the car are highly variable in terms of temperature, ambient light and vibration. In addition, the reflectivity of the finger is not always constant. The range of skin tones is quite wide and the driver may also be wearing gloves. The influence of reflectivity on the success of the measurement should be taken into account more carefully.