The gyro sensor in Apple's iPad is a miniature, solid-state device that accurately tracks changes in the iPad's orientation. In addition to its tiny size, the component senses motion using a principle different from the one that makes traditional spinning gyroscopes work. The gyroscope complements the iPad's accelerometers and other sensors, providing a comprehensive and accurate set of location, motion and orientation data.
The iPad uses gyro sensors made by STMicroelectronics, a company that produces micro electro mechanical systems components. MEMS devices have the same silicon fabrication technology originally developed for integrated circuits combined with electronics and tiny gears, springs, levers and other mechanical parts. To the casual observer, traditional computer chips and MEMS chips appear the same. MEMS mechanical devices are rugged, compact and available at low cost.
Vibrating Structure Gyroscope
Technicians call the iPad's gyro a "vibrating structure gyroscope," as it employs a vibrating mass instead of a spinning one to sense orientation. In the gyro, a mass oscillates on silicon springs. When the plane in which the mass vibrates tilts, it experiences a stress produced by the Coriolis Force, the same type of force that produces cyclones from the Earth's rotation. This changes the electrical capacitance of an attached sensor, which an electronic circuit measures.
Solid-state gyroscopes for mobile devices measure tilt in three dimensions, corresponding to roll, pitch and yaw. Although some MEMS gyros employ three pairs of vibrating masses, each perpendicular to the others, the STMicroelectronics device uses a consolidated design with a single driving mass. According to the company, the single-mass gyro reduces erratic data problems caused by normal bumps and shocks.
Electronics and iOS
The MEMS gyro chip produces three pairs of electronic signals, one pair for each of the three dimensions needed. The chip delivers its data in a "raw" format; other components in the iPad convert the data into useful angular velocity information, such as degrees of rotation per second. The iPad's iOS software makes the information available for games and other apps. When a program needs gyro data, it invokes an iOS function that retrieves the current information from the chip.
The information provided here is accurate as of the fourth-generation iPad running iOS 6 software. Mobile device hardware and software technology changes rapidly; future iPad models may rely on other types of gyro sensors.
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