| DC Drive Gearmotors
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GSI has redesigned standard DC gearmotors required for
Mobile Service Robot locomotion systems to deliver long life,
high torque, efficiency, and compact size. Delivering over
148 inch-pounds of torque to each drive wheel, GSI's Mobile Service Robots
are capable of lifting over a 1.5 inch vertical lift
such as a doorway, carpet, tile or other flooring traverse.
Constant speed for each wheel is maintained utilizing advanced
Proportional-Integral-Derivative Control (PID) algorithms
which control the motors
such that they do not stall when transitioning
from tile to carpet or crossing a doorway traverse from one
room to another.
Even though the MSR weighs 80 to 120 pounds (the exact weight
depends on the 12V DC battery installed), the locomotion system
was designed to transport up to 100 pounds throughout homes and
offices. This provides great flexibility to augment the configuration
with additional components or peripherals such as a pan/tilt multiple
sensor head, 2 articulated arms capable of reaching the floor,
or security and medical equipment. |
GeckoPowerModule™
GSI has developed a motor driver board utilizing power field
effect transistors (FETs) to control current to the motor. These transistors
are rated at 50 amperes, over 40% greater than the stall current
rating of the DC motors. Configured as an H-Bridge to provide
forward and reverse, the driver is capable of switching at speeds
greater than 20 kHz. Peripheral circuitry develops a floating
power supply used to drive the high side FETs. Each motor has
its own driver board.
GeckoPowerDistribution™
| GSI has developed a 12V DC power distribution
architecture for power management, safety, and expandability.
This includes a 50 ampere auto-resetting circuit breaker between
the battery and master power, a "system kill" switch.
The master power switch is a 40 ampere, illuminated rocker
switch mounted on the front of the frame, at an easily accessable
height for adults and older children. |
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To minimize power loss due to heating a heavier gauge wiring
is used. The battery cabling is high count, fine strand for flexibility
and ease of use. Wingnut stud fasteners with ring tongue connectors
are used in conjunction with top post battery connectors for ready
attachment. Quick battery swapping can be accomplished readily
with the open battery tray and the wing nut terminal posts.
Power distribution expansion is provided by an eight circuit
fuse block using common automotive ATO style fuses. Only four
of the eight available are used at present. One is used for each of the
two motor driver boards. They are fused at 15 amperes each. The
third fused circuit is for the present on board electronics. This
leaves four fuseable circuits available for expansion utilizing
industry standard .25" male terminals. A total of 40 amperes
total load at 12V DC, or over 480 watts of electrical power, can
be safely managed and accessed (in comparison, PC's routinely
have 200 to 300 watt power supply capabilities).
CompoundedSensorArray™ 2.0
Our MSRs use a scanning, stepping positioning system capable
of +/- 90 degrees, from hard left to hard right. The sensor array
mounts vertically on the output shaft of a stepping motor. As the sensor array
sweeps from hard left to hard right back to hard left, it stops
25 times to send distance readings to GeckoNav. A full left/right
sweep occurs every 1 to 1.5 seconds. (Most high end, research autonomous
mobile robots have no more than 10 or 16 transducers in fixed positions,
covering the same 180 degrees from hard left to hard right. The new
CompounedeSensorArray™ 2.0 has 340 virtual sensors.)
Ultrasonic sensors measure the distance or presence of a target
object by sensing a reflected sound wave, above the range of hearing,
from an object in its field of view, and then measuring the time
for the sound echo to return. Knowing the speed of sound, the
sensor circuitry can determine the distance of the object from
the transducer element.
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The transducer transmits at a frequency much higher than that
of human hearing. Some people may hear a clicking as the transducer
is energized, but not even dogs can hear this ultrasonic sound
of 50,000 Hertz.
The range finding sensors are compounded (scanned) using a
high speed DC stepping motor to give the Mobile Service Robot "real-time"
vision for seeing the world about it.
Over 25 discrete stepper positions and fourteen uniquely
oriented digital rangefinders gives the CompoundedSensorArray™
2.0 340 virtual, stepped non-tactile,
distance measuring sensors.
The ability for the GeckoNav to chose the most relevant
scanning scenario depending on the dynamics of the environment
allows for faster and slower paces for the Mobile Service Robot as it follows
its path.
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