Optical Rotation and Push Detection of Knob-On-Display

Touch displays are becoming more common in car cockpits, and they are replacing mechanical rotary knobs and switches that were used previously. Flat display is hard to use without looking at it, which causes safety issues when driver cannot look at road. The solution is to add mechanical controllers for touch display. Increasing size of touch displays results in locating mechanical controllers far from the driver’s field of view. Knobs-On-Display make it possible to place knobs closer to the driver’s field of view, which increases safety. Knobs-On-Display are usually based on capacitive detection, which often utilizes touch sensors already in displays for detecting rotation and push of the knob. The knobs are electrically passive, so they do not need to be connected to power. Capacitive detection is tied to the refresh rate of the display. Fast rotation of a knob can exceed this rate, and the movements of the knob cannot be measured fast enough, which causes incorrect operation. Capacitive detection also limits the reduction of deadband of the knob and the outer surface of the knob must be electrically conductive, which limits design options. A new method for the detection of knob movements is investigated in this thesis. Infrared LED and light sensor are placed behind LCD to detect the movements of the knob from changing light intensity. The knob has reflectors in it and infrared light from the LED passes through the LCD and is reflected back to the sensor. Rotating or pushing the knob moves reflectors and reflectivity changes which affect light intensity. Optical detection is separate from the display so measurement rate can be faster than capacitive detection. The knob also does not need to be electrically conductive, so materials can be chosen freely. The objective of the thesis is to verify if optical detection is possible method to detect the movements of the knob. The ratio of adjacent signal levels must be at least 3. The optical detection system and the rotary knob are designed to measure it. The rotary knob is designed to be realistic, so the size of the reflectors that can be fitted to the final product can be known. The objective of the thesis is also to investigate how the reflectivity of the reflectors in the knob can be changed when it is rotated or pushed, and where the sensor and LED should be placed in the system. First, optical detection system operation with the different setups was measured. The best options were used in push and rotation measurements, which were made using the prototype knob fixed on the display surface. The signal values from the sensor were measured when the knob was rotated or pushed. Three setups had the ratio of maximum and minimum signal values over 3. These ratios ranged from 4.6 to 6.4. The same setups had ratios between 3.3 and 5.9 when the rotary reflectors were measured. Push and rotation graphs were also measured. The signal values changed fast when the reflectors moved, which makes the system more robust, and the derivative of the signal can also be used for detection. The optical detection using infrared through LCD was found to be a possible method for detection of the push and rotation of the knob. The next step would be to design a complete display device and develop software designed for optical detection. Then the optical detection and the rotary knob could be measured in the real environment.