52 Robotics: Force/Torque, Accelerometers, Tactile part1
Description
This article is from the Robotics FAQ, by Kevin Dowling nivek@cs.cmu.edu with numerous contributions by others.
52 Robotics: Force/Torque, Accelerometers, Tactile part1
Force measurement provides indications of magnitude and direction of
forces for use in manipulation or locomotion. A variety of control
schemes have been implemented in force controlled systems to allow
smooth and accurate control in situations that would otherwise be
precluded without such devices. A number of load cells and
acceleration measuring devices are described here:
Rich Voyles embarked on a force/torque sensor comparison many months
ago and compiled some of the results in a paper that is available via
the web or anonymous ftp.
[37]http://www.cs.cmu.edu:8001/afs/cs.cmu.edu/user/deadslug/ftp/home.h
tml [38]ftp://ftp.cs.cmu.edu/usr/anon/user/deadslug/ The
paper is woefully incomplete. The JR3 sensor we borrowed was broken so
we borrowed another and got limited data. The old Lord data collection
is incomplete and the Assurance Technologies data is not fully
included in the report. There is some data from California
Cybernetics. If there is sufficient interest, we can finish the
compilation. By the way, we only seek to provide the data we gathered
an make no claims as to its accuracy or completeness. Use at your own
risk. The opinions expressed do not represent those of Carnegie Mellon
University nor any of its sponsors. Send e-mail to robodude@cmu.edu
with the subject "More Force Data" if you read the report and would
like to see it expanded. Any other comments can be put in the body.
-Richard Voyles
"Analog Devices"
tel: 617.937.1426
Analog Devices have the ADXL50 accelerometer which comes in a 10-pin
TO-5 can. It is primarily used with air-bags and has a 1994 projected
price of $5 in quantities. In the Electronic Design August 8, 1991
issue it quoted the current price as $21.75 for 1000 off quantities.
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
"ATI Industrial Automation"
(formerly Assurance Technologies)
(formerly Lord Industrial Automation)
Peachtree Center
503D Highway 70 East
Garner, North Carolina 27529
tel: 919.772.0115
fax: 919.772.8259
net: [39]info@ati-ia.com
Largest supplier of multi-axis force sensors. Use silicon rather than
foil strain gages for lower strain levels and increased life. F/T
sensor ratings from +/- 15lbs to +/- 150lbs (+/- 15 in-lbs to +/- 600
in-lbs) weights are 0.4 and 2.2 lbs for the 4 available sensors.
Serial or parallel digital interface or analog interface. ATI also
makes robotic tool-changers and an RCC device for assembly operations.
An ATI sensor is also incorporated in the Hughes SMARTee end-effector.
"Bonneville Scientific "
1849 W. No. Temple, Bldg E.
Salt Lake City, UT 84116
tel: 801.359.0402
fax: 801.359.0416
Array sensor system that uses PVDF ultrasonic emmitter/detector
attached to an elastomer material. Time-of-flight of the pulse as it
bounces off of other side of the material is porportional to distance
through the elastomer. The distance is porportional the pressure on
the pad. Bonneville claims it can be made thin enough for a skin and
they have pictures of it being used on a robot finger picking up a
washer which can be recognized on their output graphics. Example
product:
Model 300 - 16x16 tactile sensor system - $5K
TOF resolution - 12.5 ns
Sheet thickness resolution - 6 microns
Pressure resolution - 0.5 psi (3.4 kPa)
Force resolution - 1g
Rubber linearity - 5-15% deviation
Overload - > 1000PSI (7000kPa)
Spatial resolution - 1.8mm
Scan rate on 16x16 pad - 240 Hz
An evaluation kit is available SE-1 Evaluation Kit - $99.00 includes
SE-1 sensor and electronics. SE-1 Sensor is $42 in single quantity.
"California Cybernetics "
10322 Sherman Grove
Sunland, CA 91040
tel: 818.353.5991
fax: 818.951.3889
Six DOF F-T devices. Up to 1000Hz sampling rate, reportedly easy to
interface.
"Cybernet "
1919 Green Road
Suite B-101
Ann Arbor, MI 48105
tel: 313.668.2567
fax: 313.668.8780
net: heidi_jocobus@um.cc.umich.edu
PER-force - A 6dof compact force-reflecting controller. Can be used
for teleoperationor interactive graphics applications.
"Ercon "
Need addresses
Somewhere in MA
Conductive rubber and conductive inks. You build a semi-rigid circuit
board with inter-digitated fingers to apply to one side of the rubber.
The rubber has a rough surface that under increasing load allows more
rubber to contact. They can make rubber with all sorts of conductive
properties.
"Force Imaging "
3424 Touhy Avenue
Chicago, IL 60645-2717
tel: 708.674.7665
tel: 800.348.3240
fax: 708.674.6355
Uniforce Force Sensors. They function similiar to a variable resistor
in an electrical circuit. As a force is exerted on the sensor, the two
layers of pressure sensitive material compress together and cause a
change in resistance which corresponds to a change in pressure. As
force increases, resistance decreases. A Uniforce experimenters kit is
available for $550 and includes PC-AT card, cables, software, manual
and nine Uniforce sensors in three force ranges. They have ISA boards,
PCMCIA version and a PPIO version as well. Sensors available in ranges
from 0-500g to 0-400kg. Uniforce sensors can be provided in a wide
variety of shapes, sizes and force ranges. Software is also available
to display force values in real-time.
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