Sunday, April 19, 2009

InfraRed Distance Sensor Project

Test Setup for the Sharp GP2D12
Distance Measurement Detector

I use the Sharp GP2D12 non-contact infrared distance sensor
for determining the level of salt on the Water Softener Monitor
project. To test the Sharp sensor and to determine the
voltages at particular distances, I created a test apparatus
out of a level and some machined plastic parts. This test
setup is compatible with the whole family of Sharp distance
sensors, which are capable of different measurement distances

and different types of outputs


Design and development of a new sensor
system for assistive powered wheelchairs

Abstract. Many disabled people experience considerable
difficulties when driving a powered wheelchair. Disabled people
who are not able to drive a powered wheelchair are seriously
limited in their mobility. Several robotic assistive wheelchairs
have been devised in the past. These wheelchairs are equipped
with range sensors, which detect obstacles and measure the
distance to the closest object. The authors are involved in this
kind of projects but, although many sensors exist commercially,
they never found satisfactory range sensors for wheelchair
applications. After identifying these sensor requirements, this
paper presents the design of an optical ranging system, more in
particular a lidar (Light Detection and Ranging) scanner for
wheelchair applications. Test results are reported to show that
this scanner meets the identified requirements.

Sensor design
An approach that is now feasible at a modest price
tag, is using a lidar scanner (Light Detection And
Ranging). Various systems already exist on the market
that use light instead of the microwaves of the well
known radar. A lot of research has been done on range
finders, anti-collision systems for the car industry and
pollution surveillance systems. Most of these systems
use large aperture optical telescopes, powerful lasers
and ultra fast electronic devices for the processing of
the data to determinate the time of flight of the emitted
and reflected light. They have a range of several hundred
metres up to a few kilometres. This performance
is much too high and most of these systems are rather
bulky and very expensive and are not always eye-safe.
All these factors exclude their use on a wheelchair.
The range of the obstacle detection system is from zero
up to 4 m. The determination of the time-of-flight in
this range, calls for ultra fast electronics (660 ps time
resolution for a spatial resolution of 10 cm) and puts
a high demand on the switching characteristics of the
opto-electronic components.
In order to keep the complexity of the system, the demand
on the opto-electronic components and the price
tag low, it is proposed to substitute the direct timeof-
flight measurement by the measurement of a phase
shift. The light from an infra-red laser diode is amplitude
modulated with a signal of 5–20 MHz, depending
on intended range or resolution. The difference in
phase between the signals from the transmitted and re-
flected light is directly proportional to the distance. The
advantages of this method are the much lower switch
frequency, the lower data processing speed and the use
of less exotic components. The disadvantages are the
longer time it takes to get the measurement (some microseconds),
compared to the time-of-flight measurement
(some nanoseconds). This is only important in
3D scanning systems where data throughput must be
very high. If the signal-to-noise ratio does not enable
a stable measurement, the bandwidth of the processing
circuit must be further reduced, increasing processing
time. This is not necessarily a drawback in wheelchair
applications because the sample rate can still be suffi-
cient high. Scanning in a horizontal plane can be performed
by a rotating mirror, reflecting transmitted and
received beams, or by rotating optics. The scanning
rate of the lidar amounts to 5 rev/s.
Different modules for the lidar scanner have been

– aspheric lens design for optical transmitter and
– laser diode output stage (transmitter),
– PIN diode preamplifier,
– limiter and phase measurement (distance measuring),
– microprocessor and interface,
– scanning system.

More pdf

Relate Posts