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Ultrasonic distance meter
Document
Type
and
Number:United
States
Patent
5442592
Abstract:An
ultrasonic
distance
meter
cancels
out
the
effects
of
temperature
and
humidity
variations by
including a measuring unit and a reference unit.
In each of the units, a
repetitive
series of pulses is generated, each having a
repetition rate directly related to
the
respective distance between an electroacoustic
transmitter and an electroacoustic
receiver.
The
pulse
trains
are
provided
to
respective
counters,
and
the
ratio
of
the
counter
outputs is utilized to determine the distance
being measured.
Publication Date:08/15/1995
Primary Examiner:Lobo, Ian
J.
OUND OF THE INVENTION
This
invention
relates
to
apparatus
for
the
measurement
of
distance
and,
more
particularly, to such
apparatus which transmits ultrasonic waves between
two points.
Precision machine tools must be
calibrated. In the past, this has been
accomplished
utilizing mechanical
devices such as calipers, micrometers, and the
like. However, the
use of such devices
does not readily lend itself to automation
techniques. It is known
that the
distance between two points can be determined by
measuring the propagation
time
of
a
wave
travelling
between
those
two
points.
One
such
type
of
wave
is
an
ultrasonic, or acoustic,
wave. When an ultrasonic wave travels
between two points,
the
distance between the two points can be measured by
multiplying the transit time
of
the
wave
by
the
wave
velocity
in
the
medium
separating
the
two
points.
It
is
therefore an object of
the present invention to provide apparatus
utilizing ultrasonic
waves to
accurately measure the distance between two
points.
When the medium between the two points
whose spacing is being measured is air,
the
sound
velocity
is
dependent
upon
the
temperature
and
humidity
of
the
air.
It
is
therefore
a
further
object
of
the,present
invention
to
provide
apparatus
of
the
type
described which is
independent of temperature and humidity
variations.
Y
OF THE INVENTION
The foregoing and additional objects
are attained in accordance with the principles
of
this
invention
by
providing
distance
measuring
apparatus
which
includes
a
reference unit and a measuring unit.
The reference and measuring units are the same
and each includes an electroacoustic
transmitter and an electroacoustic receiver. The
spacing
between
the
transmitter
and
the
receiver
of
the
reference
unit
is
a
fixed
reference
distance,
whereas
the
spacing
between
the
transmitter
and
receiver
of
the
measuring unit is the distance to be
measured. In each of the units, the transmitter
and
receiver are coupled by a feedback
loop which causes the transmitter to generate an
acoustic pulse which is received by the
receiver and converted into an electrical pulse
which is then fed back to the
transmitter, so that a repetitive series of pulses
results.
The
repetition
rate
of
the
pulses
is
inversely
related
to
the
distance
between
the
transmitter and the receiver. In each
of the units, the pulses are provided to a
counter.
Since the reference distance
is known, the ratio of the counter outputs is
utilized to
determine
the
desired
distance
to
be
measured.
Since
both
counts
are
identically
influenced by temperature and humidity
variations, by taking the ratio of the counts,
the resultant measurement becomes
insensitive to such variations.
ED
DESCRIPTION
ple of
ultrasonic distance measurement
1, the principle of piezoelectric
ultrasonic generator
Piezoelectric
ultrasonic
generator
is
the
use
of
piezoelectric
crystal
resonators
to
work.
Ultrasonic
generator,
the
internal
structure
as
shown
in
Figure
1,
it
has
two
piezoelectric
chip
and
a
resonance
plate.
When
it's
two
plus
pulse
signal,
the
frequency equal to the intrinsic
piezoelectric oscillation frequency chip, the chip
will
happen
piezoelectric
resonance,
and
promote
the
development
of
plate
vibration
resonance,
ultrasound
is
generated.
Conversely,
if
the
two
are
not
inter-electrode
voltage,
when
the
board
received
ultrasonic
resonance,
it
will
be
for
vibration
suppression
of
piezoelectric
chip,
the
mechanical
energy
is
converted
to
electrical
signals, then it
becomes the ultrasonic receiver.
The
traditional
way
to
determine
the
moment
of
the
echo's
arrival
is
based
on
thresholding the received
signal with a fixed reference. The threshold is
chosen well
above the noise level,
whereas the moment of arrival of an echo is
defined as the first
moment
the echo signal surpasses that threshold. The
intensity of an echo reflecting
from
an
object
strongly
depends
on
the
object's
nature,
size
and
distance
from
the
sensor. Further, the time interval from
the echo's starting point to the moment when it
surpasses the threshold changes with
the intensity of the echo. As a consequence, a
considerable
error
may
occur
Even
two
echoes
with
different
intensities
arriving
exactly at the same
time will surpass the threshold at different
moments. The stronger
one
will
surpass
the
threshold
earlier
than
the
weaker,
so
it
will
be
considered
as
belonging to a nearer object.
2, the principle of ultrasonic distance
measurement
Ultrasonic transmitter in a direction
to launch ultrasound, in the moment to launch
the beginning of time at the same time,
the spread of ultrasound in the air, obstacles
on
his
way
to
return
immediately,
the
ultrasonic
reflected
wave
received
by
the
receiver immediately
stop the clock. Ultrasound in the air as the
propagation velocity
of 340m / s,
according to the timer records the time t, we can
calculate the distance
between the
launch distance barrier (s), that is: s = 340t / 2
onic Ranging System for the
Second Circuit Design
System
is
characterized
by
single-chip
microcomputer
to
control
the
use
of
ultrasonic
transmitter
and
ultrasonic
receiver
since
the
launch
from
time
to
time,
single-chip
selection
of
8751,
economic-to-use,
and
the
chip
has
4K
of
ROM,
to
facilitate programming. Circuit
schematic diagram shown in Figure 2. Draw only the
front range of the circuit wiring
diagram, left and right in front of Ranging
Ranging
circuits and the same circuit,
it is omitted.
1,40 kHz
ultrasonic pulse generated with the launch
Ranging
system
using
the
ultrasonic
sensor
of
piezoelectric
ceramic
sensors
UCM40, its operating voltage of the
pulse signal is 40kHz, which by the single-chip
implementation of the following
procedures to generate.
puzel: mov 14h, # 12h; ultrasonic
firing continued 200ms
here: cpl p1.0; output 40kHz square
wave
nop;
nop;
nop;
djnz 14h, here;
ret
Ranging
in
front
of
single-chip
termination
circuit
P1.0
input
port,
single
chip
implementation of the above procedure,
the P1.0 port in a 40kHz pulse output signal,
after
amplification
transistor
T,
the
drive
to
launch
the
first
ultrasonic
UCM40T,
issued 40kHz ultrasonic pulse, and the
continued launch of 200ms. Ranging the right
and the left side of the circuit,
respectively, then input port P1.1 and P1.2, the
working
principle and circuit in front
of the same location.
2,
reception and processing of ultrasonic
Used
to
receive
the
first
launch
of
the
first
pair
UCM40R,
the
ultrasonic
pulse
modulation
signal
into
an
alternating
voltage,
the
op-amp
amplification
IC1A
and
after polarization IC1B
to IC2. IC2 is locked loop with audio decoder chip
LM567,
internal
voltage-
controlled
oscillator
center
frequency
of
f0
=
1/1.1R8C3,
capacitor
C4
determine
their
target
bandwidth.
R8-conditioning
in
the
launch
of
the
carrier
frequency on the LM567 input signal is
greater than 25mV
, the output from the
high
jump 8 feet into a low-level, as
interrupt request signals to the single-chip
processing.
Ranging in
front
of single-chip
termination
circuit output port
INT0 interrupt the
highest
priority,
right
or
left
location
of
the
output
circuit
with
output
gate
IC3A
access INT1 port
single-chip, while single-chip P1.3 and P1. 4
received input IC3A,
interrupted
by
the
process
to
identify
the
source
of
inquiry
to
deal
with,
interrupt
priority level for
the first left right after. Part of the source
code is as follows:
receive1: push psw
push acc
clr
ex1; related external interrupt 1
jnb
p1.1,
right;
P1.1
pin
to
0,
ranging
from
right
to
interrupt
service routine
circuit
jnb p1.2, left; P1.2 pin to 0, to the
left ranging circuit interrupt
service
routine
return: SETB EX1;
open external interrupt 1
pop
acc
pop
psw
reti
right:
...?; right location entrance circuit interrupt
service routine
Ajmp
Return
left:
...; left Ranging entrance circuit interrupt
service routine
Ajmp
Return
3, the calculation of
ultrasonic propagation time
When
you
start
firing
at
the
same
time
start
the
single-chip
circuitry
within
the
timer
T0,
the
use
of
timer
counting
function
records
the
time
and
the
launch
of
ultrasonic
reflected
wave
received
time.
When
you
receive
the
ultrasonic
reflected
wave,
the
receiver
circuit
outputs
a
negative
jump
in
the
end
of
INT0
or
INT1
interrupt request generates a signal,
single-chip microcomputer in response to external
interrupt request, the implementation
of the external interrupt service subroutine, read
the time difference, calculating the
distance . Some of its source code is as follows:
RECEIVE0:
PUSH PSW
PUSH ACC
CLR EX0;
related external interrupt 0
MOV
R7, TH0; read the time value
MOV
R6, TL0
CLR C
MOV A, R6
SUBB A, # 0BBH;
calculate the time difference
MOV
31H, A; storage results
MOV A, R7
SUBB A, # 3CH
MOV 30H, A
SETB EX0; open external
interrupt 0
POP ACC
POP PSW
RETI
For
a
flat
target,
a
distance
measurement
consists
of
two
phases:
a
coarse
measurement and. a fine measurement:
Step 1: Transmission of one pulse train
to produce a simple ultrasonic wave.
Step 2:
Changing the
gain
of both
echo
amplifiers according to
equation , until
the
echo is detected.
Step 3:
Detection of the amplitudes and zero-crossing
times of both echoes.
Step 4: Setting
the gains of both echo amplifiers to normalize the
output at, say 3 volts.
Setting
the
period
of
the
next
pulses
according
to
the
:
period
of
echoes.
Setting the time
window according to the data of step 2.
Step
5:
Sending
two
pulse
trains
to
produce
an
interfered
wave.
Testing
the
zero-
crossing times and amplitudes of the echoes. If
phase inversion occurs
in
the
echo,
determine
to
otherwise
calculate
to
by
interpolation
using
the
amplitudes near the
trough. Derive t sub m1 and t sub m2 .
Step 6: Calculation of the distance y
using equation .
, the
ultrasonic ranging system software design
Software is divided into two parts, the
main program and interrupt service routine,
shown in Figure 3 (a) (b) (c) below.
Completion of the work of the main program is
initialized, each sequence of
ultrasonic transmitting and receiving control.
Interrupt
service
routines
from
time
to
time
to
complete
three
of
the
rotation
direction of ultrasonic launch, the
main external interrupt service subroutine to read
the value of completion time, distance
calculation, the results of the output and so on..
System initialization after the start
timer T1 starts counting from 0 to enter the
main program to wait for the T1
overflow into the T1 interrupt service routine
when
the
time
is
reached;
T1
interrupt
service
routine
will
start
a
new
ultrasonic
transmitting, the
square wave will be generated in the P1.0 pin at
the same time open
the timer T0 timing,
in order to avoid the diffraction of the direct
wave, the delay 1ms
and
then,
after
the
INT0
interrupt
Enable;
the
INT0
interrupt
to
allow
open,
if
thisoccurs
when
the
low
is
representative
of
the
received
echo
signal,
the
interrupt