Balance Act for Robotic Exoskeletons: Internship with MEMS ACCELEROMETERS

Balance Act for Robotic Exoskeletons: MEMS ACCELEROMETERS

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We first got three of the Accelerometer ‘Cubes’ a few years ago when they were new.  They were a bit like the telephone companies first line of phones and Fords first line of cars that you could have in any style and color as long as you took the model A in black.

Since that time they have come a long way.  One of the most appealing features in the various models is the upgrade that includes the Kalman filter.

from my facebook page “Pondering the new Analog Devices ‘Cube’ for robot balance that includes a Kalman filter: also known as linear quadratic estimation. is an algorithm which uses a series of measurements observed over time, containing noise (random variations) and other inaccuracies, and produces estimates of unknown variables that tend to be more precise than those that would be based on a single measurement alone. More formally, the Kalman filter operates recursively on streams of noisy input data to produce a statistically optimal estimate of the underlying system state. The filter is named for Rudolf (Rudy) E. Kálmán, one of the primary developers of its theory.”

The Internship opportunity will include electrical engineers and students working together to develop several balance platforms for developing a “balance pak”  The balance pak uses the accelerometer cube or other combination accelorometers and rate gyros to ‘tell’ the electronics and software ‘where’ a reference point or ‘test point cube’ is and how it travels through space.

The 2012-2013 project will include a rotary table and a ‘pick and place’ robot system that can move the test point (Test Point Cube: TPC) around.  The test point is where the accelerometer will be placed.

So imagine a robotic hand holding the ‘test point cube’ TPC in the palm and then a person or another robotic hand moving the TPC.  The balance pak will need to determine the movement and anticipate corrective action using algorithms, most likely probabilistic algorithms, to keep the TPC balanced.  In this example the TPC will be sitting in the palm of the robots hand and then the tests will be repeated with the TPC sitting on top of a one inch by one inch cube that will create an ‘inverted pendulum’ that acts much like a leg.

Remember balancing a pencil in your palm?  If it has been a while or if you have never done it go grab a pencil now and balance it upright in the palm of your hand.  Now imagine you are a robot and your electronics, mechanics and software are helping you balance the pencil.  Now blow on it.  Keep it balanced.  That is what we will be doing in the lab.

If you are in Seattle or will be over the next year consider joining this project.  Talented students have been working in the lab with very gifted mentors.  You can be one of them.   The goal is to develop a better balance package for the LIFESUIT robotic exoskeleton.  There will be a benefit to robotics as a whole because we publish 90% of the work we do.  Students are encouraged to write abstracts for the work they do in the lab and apply for publication at conferences.  You can be part of that.

Find MEMS accelerometers and iSensor MEMS accelerometer subsystems that reliably and accurately detect and measure acceleration, tilt, shock and vibration in performance-driven applications. ADI’s MEMS accelerometer portfolio leads the industry in power, noise, bandwidth, and temperature specifications, and offers a range of MEMS sensor and signal conditioning integration on chip.

http://www.analog.com/en/mems-sensors/mems-accelerometers/products/index.html

ADXL362 Micropower, 3-Axis, MEMS Accelerometer

The ADXL362 consumes 2 μA @ 100 Hz in full measurement mode, and only 300 nA in motion sensing wake-up mode. In addition to its native low-power operation, the ADXL362 has additional features that enable system-level power efficiency.

http://www.analog.com/en/mems-sensors/mems-accelerometers/adxl362/products/product.html?src=videos

Product Details

Product Status:Recommended for New Designs

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The ADXL362 is an ultralow power, 3-axis MEMS accelerometer that consumes less than 2 μA at a 100 Hz output data rate and 270 nA when in motion triggered wake-up mode. Unlike accelerometers that use power duty cycling to achieve low power consumption, the ADXL362 does not alias input signals by undersampling; it samples the full bandwidth of the sensor at all data rates.

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• ADXL362: Micropower, 3-Axis, ±2 g/±4 g/±8 g Digital Output MEMS Accelerometer

FEATURES AND BENEFITS

• Ultralow power
  — Power can be derived from coin cell battery
  — 1.8 μA @ 100 Hz ODR,
  2.0 V supply
  — 3.0 μA @ 400 Hz ODR,
  2.0 V supply
  — 270 nA motion activated wake-up mode
  — 10 nA standby current
• High resolution: 1 mg/LSB
• Built-in features for system-level power savings:
  — Adjustable threshold sleep/wake modes for motion activation
  — See data sheet for additional features

• Low noise down to
  175 μg/√Hz
• Wide supply and I/O voltage ranges:
  1.6 V to 3.5 V
  — Operates off 1.8 V to 3.3 V rails
• Acceleration sample synchronization via external trigger
• On-chip temperature sensor
• See ADXL362 product videos

SPECIFICATIONS

• # of Axes: 3
• Range: +/- 2/4/8g
• Sensitivity: 1 to 4 mg/LSB

• Output Type: Digital
• Typical Bandwidth (kHz): 0.2kHz

FUNCTIONAL BLOCK DIAGRAM FOR ADXL362

Typical Applications and Other Diagrams

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SIMILAR PRODUCTS

Other 3-axis, low-g, digital-output sensors include:

• ADXL346: 3-Axis, ±2 g/±4 g/±8 g/±16 g Ultralow Power Digital Accelerometer
  Pin-compatible to ADXL362; 23µA to 140 µA current consumption

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VIDEO: ADXL362 MICROPOWER, 3-AXIS, MEMS ACCELEROMETER

Additional ADXL362 Videos:

• ADXL362: Awake Status Output & Motion Activated Switch Function
• ADXL362: Demo Video: Power Levels vs. Competition
• ADXL362: Enhanced Activity Detection for System-Level Power Savings

POWER COMPARISON CHART

Product Recommendations & Reference Designs

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Tested.
Ready to Integrate.

• Learn about reference circuits.
• View all reference circuits.

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Ultralow Power Standalone Motion Switch

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Circuit Benefits and Features:

• Self contained motion switch
• Low power
• High-side power switch

Products Used in This Circuit

• ADP195: Logic Controlled, High-Side Power Switch with Reverse Current Blocking
• ADXL362: Micropower, 3-Axis, ±2 g/±4 g/±8 g Digital Output MEMS Accelerometer

Circuit Design Assistance:

• Design & Integration Files

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• ADXL345: 3-Axis, ±2 g/±4 g/±8 g/±16 g Digital Accelerometer
• ADXL335: Small, Low Power, 3-Axis ±3 g Accelerometer
• ADXL377: 3-Axis High g Analog MEMS Accelerometer
• ADXL330: Small, Low Power, 3-Axis ±3g iMEMS® Accelerometer
• ADXL203: Precision ±1.7 g, ±5 g, ±18 g Dual-Axis iMEMS® Accelerometer