48 Robotics: Inertial, Acceleration and Heading sensors part1
Description
This article is from the Robotics FAQ, by Kevin Dowling nivek@cs.cmu.edu with numerous contributions by others.
48 Robotics: Inertial, Acceleration and Heading sensors part1
An excellent summary technical report on this area can be found at:
[34]CMU-RI-TR-94-15 (compressed)
"Modern Inertial and Satellite Navigation" by Alonzo Kelly, May 1994.
Inertial measurement includes such devices as accelerometers, gyros,
and devices for measuring orientation or acceleration of moving
vehicles. Accelerometers are devices for measuring the rate of change
in velocity and can provide estimations of distance or be used to
detect high forces.
Much of the initial research, development and marketing in this area
were for military applications. However, markets and commercial units
are now found in mass market and even consumer applications these
days. This has brought the price of systems down significantly. There
are several inexpensive gyros used in radio controlled helicopters.
These are rate gyros, used to sense the rate of turn about a
particular axis (usually vertical, for tail rotor control), and are
designed to connect between an R/C receiver and a servo.
These gyros work by modifying the PWM signal that the rx produces,
before it gets to the servo. The sensing is usually done by a linear
hall effect device, which senses the position of a magnet on the
bottom of the flywheel assembly. The gyros have both sensitivity and
gain controls, and some can be switched on and off remotely. They have
been used for sensing rotation about an axis for a VR headset, with
some success. The big advantage is they are relatively cheap, the big
disadvantage is high drift rate.
"Analog Devices"
One Technology Way
P.O. Box 9106,
Norwood, MA 02062-9106
tel: 617.329.4700
fax: 617.326.8703
Analog Devices ADXL50 accelerometer.
Power Supply........................... +5V (+/- 5%)
Measurement Range...................... +/- 50g
Pre-Amp Zero-g output level............ +1.8V
Pre-Amp output span.................... +1.8V (+/-1.2V) at +/-50g
Uncommitted amp output range........... +0.25V to +4.75V
Overall Accuracy....................... 5% of Full Scale
Linearity.............................. 0.5% of Full Scale
Bandwidth.............................. DC to 1kHz
Voltage Noise (p-p)
at BW = 0.3kHz..................... +/-0.24% of Full Scale
at BW = 1.0kHz..................... +/-0.48% of Full Scale
Transverse Sensitivity................. 2%
Unpowered Shock Survival............... 2000g
Distributed by Newark, Hamilton-Hallmark and Active.
"Andrew Corporation"
10500 W. 153rd Street
Orland Park, IL 60462
tel: 708.349.5957
fax: 708.349.5294
fax: 800.349.5444
Fiber-optic gyro. 77mm diameter by 88mm high. Analog out porportional
to rotation rate. Also digital version available. Rate +/- 100
degrees/sec. Stable over -40C to +85C. Power 8-13.5VDC at 250mA. Bias
drift 0.005 deg/sec (18 deg/hr). 0.63kg $1100.00 for digital version,
$950 for analog.
"AMP"
P.O. Box 799
Valley Forge, PA 19482
tel: 610.666.3500
fax: 610.666.3509
Piezo Film Accelerometer Sensors
AHC-04-08 accelerometer/shock sensor contains three sensing elements
oriented to measure acceleration in two linear axes and one angular
axis. Each sensor has a dedicated channel with adjustable gain, an
adjustable comparator, and selectable output control to provide either
a digital or analog signal. It is a low profile surface mount chip
with 14 pins. It has internal eeprom for programming the adjustable
gains, and output modes.
Lower limit on the frequency response is typically about 7-13 Hz. This
means if it were subjected to a steady 10 G acceleration for example,
the output would rise to 10 G's then decay down to zero even though it
were still at 10 G's. This is good for measuring shocks but not steady
accelerations. About $30 for a single unit.
"BEI - Systron Donner"
2700 Systron Drive,
Concord, CA 94518-1399
tel: 510.682.6161
fax: 510.671.6590
GyroChip - a very small solid state angular rate sensor. Based a
quartz tuning fork device - all support electronics are included. Max
range available: +/-10 deg/sec to +/-1000 deg/sec. Input +/- 5VDC
Output scale +/- 2.5VDC. Systron Donner also makes a variety of linear
accelerometers and inertial measurement products. Solid state six axis
inertial sensor. It provides analog signals for 3 axis acceleration
and 3 axis rate. The package is 7.5cmx7.5cmx8cm, weighs ~600grams and
takes +-15V unreg in (7W). Bias drift is on the order of 0.005 deg/sec
short term (0.1deg/sec long term). Cost is $12,000 for one or $10,000
for 2-9 (a good single axis rate gyro usually costs $6K+). Various
acceleration and rate range combinations are available (up to +- 20g).
Delivery is about 6wks. A new Gyrochip two is available as well. Specs
aren't quite as good but it is cheaper.
"Endevco Corporation"
30700 Rancho Viejo Road
San Juan Capistrano, CA 92675
tel: 714.493.8181
fax: 714.661.7231
Variable Capacitance and Piezoresistive Accelerometers. Many models,
contact Endevco for literature.
"Gyration Inc."
Saratoga CA
tel: 408.255.3016
fax: 408.255.9075
Sells small vertical and directional gyros for ~$500. These are
standard gimballed gyros, but the drift specs probaly aren't as good
as aircraft-quality gyros. Now also sell innovative computer pointers
and devices termed 'Gyroengines' that provide quadrature outputs from
heading devices. Gyroengines are $3.5K
"Honeywell"
11601 Roosevelt Blvd
St. Petersburg, FL 33716
tel: 813.579.6604
fax: 813.579.6696
Honeywll manufactures the modular azimuth and postioning system (MAPS)
and utilizes ring-laser gyros. (RLG). The RLG uses two beams of laser
light rotating in opposite directions along a path within a sealed and
enclosed cavity. As the unit changes heading, the distances the beams
travel differ. This difference is can be measured and is directly
related to heading. When combined with linear accelerometers the unit
provides position and orientation. MAPS has an RS-422 interface, is
approx 22x27x38cm and is 20kg. 100W power draw. [Rad hard and rated
for howitzer gunfire!]
"Humphrey"
9212 Balboa Avenue
San Diego, CA 92123
tel: 619.565.6631
fax: 619.565.6873
Wide variety of gyros, north seekers, vertical indicators, position
transducers, pendulums, magnetometers, dynamic stabilization systems,
and accelerometer devices.
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