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Microelectromechanical Systems (MEMS) Gyroscopes
Angular rate-sensing tunes up motion control
By Design News Staff -- Design News, June 6, 2005
Many motion control advancements have resulted from products and technology developed initially for other markets, such as automotive or consumer. Among the newest products are angular rate sensors—gyroscopes. In vehicles, they are used for navigation systems or vehicle stabilization, but in motion control, they are finding applications in robotics as well as stabilization. Four products pose a strong case for greater use of gyros in future motion control systems.
QUARTZ ANGULAR RATE SENSOR
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BEI Technologies' LCG50 MEMS GyroChip is a single -axis angular rate sensor on a small pc board that targets embedded applications. The sensing element has its roots in automotive applications. The design uses a double-ended quartz tuning fork to react to the Coriolis force produced when the device is rotated. The separately housed micromachined inertial sensing element and all of the electronics to drive the piezoelectric structure are mounted on the pc board requiring only a dc power source to sense angular rotation. The dc output signal is directly proportional to the angular rate of rotation and reverses sign with reversed rotation. The units measure angular rate from ±100 to ±500 degrees/sec. The bandwidth is greater than 50 Hz and output noise is less than 0.005 degree/sec (in the ±100 degree/sec range). Measuring 29.4 mm × 29.4 mm × 10.7 mm, the unit weighs less than 12 gm (0.4 oz). For more info on BEI Technologies Systron Donner Inertial Division's LCG50 GyroChip, go to http://rbi.ims.ca/4392-514.
SINGLE CHIP YAW RATE SENSOR
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Analog Devices ADXRS401 angular rate-sensing gyroscope was designed for automotive navigation and other applications. Using a combination of surface-micromachining and BiMOS circuitry, the monolithic device integrates the sensing structure with all of the required electronics on one chip. Two polysilicon sensing structures are electrostatically driven to resonance producing the velocity element required to sense the Coriolis force during angular motion. Movable fingers at the outer extremes of each frame, orthogonal to the driven motion, provide a capacitive sensing structure for sensing the Coriolis motion. The dynamic range of the sensor is a minimum of ±75 degrees/sec. The unit is available in a 7 mm × 7 mm × 3 mm chip-scale ball grid array package (CSBGA). For more information on Analog Devices' ADXRS401, go to http://rbi.ims.ca/4392-511.
HIGH RATE ANGULAR SENSOR
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Segway's HT two-wheeled human transporter uses dynamic stabilization with five angular rate sensors to maintain balance. The Silicon Sensing gyros have a shell resonator ring structure with a 6 mm ring resonator that vibrates in one plane. A magnetic field provides the resonance. The high rate range (±573 degrees/sec) MEMS sensor uses deep dry trench etching to produce the mechanical structure and closed-loop excitation on a separate pc board. Drift over time is less than ±0.55 degree/sec in any 30-sec period after the ready time (&0.2 sec). Silicon Sensing recently introduced the CRS07 with similar specifications and a reduced packaging format. The pc board for the CRS07 is 22 mm square, with a maximum height of 12 mm. For more info on Silicon Sensing's CRS07 go to http://rbi.ims.ca/4392-512.
INTEGRATED DUAL-AXIS ANGULAR RATE SENSOR
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Targeting image stabilization for cameras, InvenSense IDG-1000 is an integrated dual-axis X, Y gyroscope with integrated digital electronics. The design uses a bulk micromachining process, vertically integrated electronics, and wafer-scale packaging. The gyro design includes an integrated dual-mass electrostatically driven actuating mechanism with capacitance sensing. An out-of-plane resonating proof mass system senses the rate of rotation in either the X or Y axis. The unit is packaged in a 6 mm × 6 mm × 1.4 mm QFN package. Limited samples have been provided to targeted customers for consumer electronics applications. InvenSense plans a formal introduction later this year. For more info on InvenSense IDG-1000, go to http://rbi.ims.ca/4392-513.
| Web Resources | ||
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For an informative technology review of MEMS gyroscope technology, go to:
http://rbi.ims.ca/4392-515 |
Another source on MEMS gyroscopes, Robert Bosch GmbH:
http://rbi.ims.ca/4392-516 |
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