Principles of Motion Sensing

Principlesof Motion Sensing

Various sensors capable of detecting motionin free space have been commercially available for several decades and havebeen used in automobiles, aircraft and ships. Initial size, power consumptionand price, however, prevented their mass adoption in consumer electronics untilthe past few years.

While there are other motion sensortechnologies available, the following four fundamental motion sensors are themost relevant for tracking motion for consumer electronics:

Accelerometers (G-sensors)

Accelerometers measure linear accelerationand tilt angle. Single and multi-axis accelerometers detect the combinedmagnitude and direction of linear and gravitational acceleration. They can beused to provide limited motion sensing functionality. For example, a devicewith an accelerometer can detect movement from a vertical to horizontal statein a fixed location. As a result, accelerometers are primarily used for sensingdevice orientation with respect to gravity, and delivering simple functions,such as changing the screen on a mobile device from portrait to landscape mode.

Gyroscopes (Gyros)

Gyroscopes measure the angular rate ofrotation about one or more axes. Gyroscopes can measure complex motionsaccurately in free space, hence, making it a required motion sensor fortracking the position and rotation of a moving object. Unlike accelerometersand compasses, gyroscopes are not dependent on any external forces such asgravity or magnetic fields, and can therefore function fairly autonomously.

Magnetic Sensors (E-Compasses)

Compasses are used to detect heading basedon the Earth’s magnetic field. Consumer electronics applications for eCompassesinclude correctly orienting a down-loaded map on a mobile screen or providingbasic heading information for navigation applications. As the earth’s magneticfield is relatively weak compared to magnetic interference from electronicequipment and building materials, the compass sensor output can easily beimpacted by varying environmental conditions particularly indoor. As such,eCompasses require frequent calibration in order to maintain their headingaccuracy.

Pressure Sensors (Barometers)

Pressure sensors measure relative and absolute altitude through theanalysis of changes in the atmospheric pressure. Pressure sensors are beingused in consumer devices for sports and fitness, and for location-basedapplications where map information can be adjusted as a consumer moves todifferent floors in a building.

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