Pointer Devices Using Thermal Motion Sensors

Xiang Zheng Tu

 

Pointer devices are used for tracking movements of objects. They can be categorized as electromagnetic, acoustic, image-based, inertial systems, and optical types. The most common pointer device is the computer mouse detecting two-dimensional motion relative to a surface. Other applications include motion capture when producing animation in computer games, video production, movie production and virtual environments.

The present pointer is a new type of pointer devices. Its working principle is based on a thermal motion sensor. The thermal motion sensor comprises a suspended bridge created in a silicon substrate, a resistive heater, and two thermopiles both are formed on the surface of the bridge. It is easy to understand when the sensor moves the heat of the bridge generated by the heated resistor will transfer away by flowing air. The corresponding change of the output voltage of the thermopiles can be calibrated to the moving velocity of the sensor.

The laws of physics teaches that the temperature field generated by a moving heat source is asymmetry and able to be measured. In steady state, the vertical cross-sectional temperature field is a sequence of symmetry concentric circles each representing an isotherm on the lateral plane. When the heat source moves the vertical cross-sectional temperature field will be skewed towards down motion direction. The skewed lateral cross-sectional temperature field consists of a contracted half plane and an expended half plane both are divided by a line perpendicular to the motion direction. If a temperature sensor array is placed on the plane around the heat source, all isotherms can be reconstructed. A lot of useful information including the direction and velocity of the moving heat source can be extracted form the reconstructed plane isotherms.

Similarly, the pointers based on thermal motion sensors can be used to control movements of objects, people, or body parts. As an example, the above picture shows a hand-held pointer guiding an unmanned air vehicle. The hand-held pointer consists of three thermal motion sensor modules each locates on an axis of Cartesian coordinates and measures the velocity component of this axis, respectively. After conditioning and processing the measured signals send by wireless to a ground communication station for further processing. Then the processed signal transfers to the unmanned air vehicle so that the vehicle is able to coordinate its movement according to the hand-held pointer. 

The pointers using the thermal motion sensors can be explored wide range of applications for their small size, short response time, low power consumption, higher sensitivity to low velocity, and low cost. Among them is patient activity monitoring such as Parkinson’s disease assessment. The assessments often entail one to three silicon accelerometers, each designed to detect even slight motion in a single axis. Three of these devices can be mounted orthogonally to provide an accurate description of movement in three directions. Actually the thermal motion sensors are more suitable for such application because it directly measures velocity of the motion without integration of acceleration measured using the accelerometers.