Obvious target applications are vehicle-mounted cameras and antennas, commercial aircraft guidance units, robotics, and prosthetics. Another important area is inertial backup when GPS signals are lost. That’s significant not only in aviation, but also in commercial-vehicle fleet operations and automated harvesting equipment on mega-farms.
Specs were impressive, with 14-bit precision. Output and control is via a simple serial peripheral interface (SPI) port. Each gyro has a ±300°/s dynamic measurement range, and each accelerometer has a ±10-g measurement range. And although their maximum dynamic range is ±300°/s, the IMUs provide ±75°/s and ±150°/s ranges as well.
Each sensor’s signal-conditioning circuit has an analog bandwidth of approximately 350 Hz. The IMU provides a Bartlett Window finite impulse response (FIR) filter with programmable step sizes for additional noise reduction on all of the output data registers.
In addition to the calibrated motion measurements, the IMU measures power supply and temperature, as well as provides an auxiliary 12-bit analog-to-digital converter (ADC) channel. This output data updates internally, regardless of user read rates. Output data can be either 12 bits or 14 bits long.
An auxiliary 12-bit successive-approximation ADC makes it possible to digitize other system-level analog signals. Furthermore, an auxiliary 0- to 2.5-V output digital-to-analog converter (DAC) provides a 12-bit level-adjustment function.
Late in 2008, we saw the four-degree-of-freedom ADIS16300 and six-degree-of-freedom ADIS16405 IMUs with 14-bit gyroscope featuring digital range scaling; ±75°/s, ±150°/s, and ±300°/s settings; a tri-axis, 14-bit, ±5-g digital accelerometer; and 180-ms response time (Fig. 3). In addition, they provided factory-calibrated sensitivity, bias and axial alignment, digitally controlled bias calibration, and a digitally controlled sampling rate up to 819.2 samples/s. (An external clock allows sampling up to 1200 samples/s.)
Also released in that timeframe was the ADIS16209 dual-mode inclinometer. It delivers either dual-axis horizontal operation of ±90° or single-axis vertical operation of ±180°. It operates from a 3.3-V power supply and communicates via an SPI bus.
When it was announced, ADI said its dimensions of 9.2 by 9.2 by 3.9 mm made it 100 times smaller than other available products and that it cost one-tenth the cost of functionally equivalent competitive units. As noted earlier, multiple applications are medical. Ultrasound, mammography, and X-ray equipment all need precision and accuracy in scanner alignment. The devices are being used in hip and knee surgical procedures as well.
Those kinds of medical applications are also one target of the six-degree-of-freedom 16405 IMU, with its tri-axis magnetometer sensor for heading sensing. ADI says that it, too, costs up to 10 times less than competitive products.
RECENT DEVELOPMENTS Last March, ADI announced the ADXL346 digital three-axis iMEMS smart motion sensor as part of its family of small, powersipping smart motion sensors for portable devices. It operates at primary supply voltages down to 1.8 V and comes in a 3- by 3- by 0.95-mm package. Furthermore, it measures both dynamic acceleration (resulting from motion or shock) and static acceleration (such as gravity, which allows it to be used as a tilt sensor).
To save power, it buffers up to 32 sample sets of X-, Y-, and Z-axis data in a first-in first-out (FIFO) arrangement, enabling the host processor and other power-hungry peripherals to go into a sleep mode until needed. Bandwidth is selectable from 0.1 to 1600 Hz, allowing tradeoffs between responsiveness and battery life. Power consumption ranges from less than 150 µA at 1600-Hz bandwidth down to 25 µA under 10 Hz.
The ADXL346 measures dynamic acceleration with ±2/4/8/16-g user-selectable ranges and includes built-in orientation sensing via simple register reads. Special sensing functions with userprogrammable thresholds include inactivity, tap/double-tap, and free-fall sensing. Pricing for the ADXL346 is $3.04 per unit in 1000-unit quantities.
Earlier in the year, ADI unveiled the ADXL345 three-axis accelerometer, claiming an 80% power savings compared to competing three-axis sensors. Power-saving design elements include the low single-cell operating voltage and FIFO arrangement like the one described before, which offloads the task of responding to a change in movement or acceleration from the host processor. Also, the output data range scales from 0.1 Hz to 3.2 kHz, allowing portable-system designers to precisely allocate power for specific system functions. Pricing is $3.04 in 1000-unit quantities.
ADI, of course, isn’t the only manufacturer of MEMS motion sensors. Freescale Semiconductor’s MMA745xL three-axis digital- output accelerometers for mobile devices support tilt scrolling in all directions, gaming control, gesture recognition, and tap to mute. They also support theft protection, freefall detection, and GPS backup applications.
STMicroelectronics’ LIS302DLH 16-bit three-axis accelerometer suits motion sensing, orientation awareness, freefall detection, and vibration monitoring (Fig. 4). At 0.75 mm tall, it is the market’s thinnest device, according to the company. (Otherwise, it shares the 3- by 5-mm footprint of other devices in ST’s Piccolo MEMS family.) It outputs acceleration data up to ±8 g via a serial peripheral interface (SPI) bus. Currently sampling, production pricing is $1.35 for orders over 10,000 pieces.
Sorry, the gyroscopic effect is not the same as the Corrolis effect. I suggest you look this up. (Try Wikipedia) The Rosby for such MEMS sytems would be huge (probably > million) and therefore the Corrolis effect completetly negligible. Gyroscopes typically operate due to torques created by the interaction of the suspension force and its angular momentum .
Jason Pressesky -July 09, 2009
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