Note: Descriptions are shown in the official language in which they were submitted.
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l`his invention relates to measuring systems and has pa-rticular,
but not exclusive, application to the measurement o~ the lengtll of moving vehicles.
In the txansportation oE commercial road vehicles by sea ferries, the
tariEf charged is based, inter alia, on vehicle length. The tarife is normally
expressed as a charge per metre with a gradation down to 0.1 metre which is
charged proportianally. At the present time the declared lengths of vehicles are
checked on a random basis to discourage under-declarations of length. This
checking is carried out by inspectors using tape-measures or the like and has to
be carried out while the vehicles are stationary; it is thereEore time-~onsuming and
labour intensive.
The main object Oe the present invention is to provide a measuring system
which enables the length of a vehicle to be measured automatically while the
vehicle is moving.
Accordingly the present invention provides a measuring system comprising:-
(a) a pair of detector stations spaced a predetermined distance apart along a
path of movement for a vehicle, each detector station comprising a vertically
extending series of electromagnetic radiation emitters disposed on one side of
said path, each emitter producing a clirectional beam of radiation, and at least
one electromagnetic radiation detector ~hich is designed to produce an electrical
output signal related to the quantity or intensity ot radiation incident upon it, said
detector being disposed on the other side of said path and said emitters or a group
of said emitters being arranged to direct their l~eams at it, whereby the said
quantity or intensity of incident electromagnetic radiation re~istered by said detector
is dependent upon the number of said beams interceptecl by a passing ~ehicle, and
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(b) data processing mean.s for processing the output signals from said
detectors on a time basis and utilising the Icnown predetermined spacing of
said detector stations to provide a velocity related vehicle measurement.
Said electromagnetic radiation is advantageous,ly infra-red radiation.
Thus the measuring systèm of the invention can be used to measure
vehicle length and/or vehicle velocity.
As will be explained the measurement of vehicle length is a function of
vehicle velocity, which in turn is a function of the time taken for an identifiable
point on the vehicle to cover the known distance between the two detector stations.
With the above defined emitter and detector arrangements at the two detector stations,
a vehicle as it passes each detector station will produce on the d~tector a radiation
lntensity or quantity pattern determined by the number of said radiation beams which
are interrupted by each cross-section of the vehicle passsing through that station,
From these patterns certain characteristic points along the vehicle are readily
identiflable. Hence a measurement of the time taken for a number of identifiable
points to move between the two stations can be made and an average transit
time arrived at, which will compensate within limits for variation in vehicle velocity
as it i9 moving between the two stations.
One of the characteristic points which is iderltifiable by pattern recognition
are vehicle axles. The system can therefore additionally be used to count the number
of vehicle axles, and this in combination with a weight measurement can provide
information regarding axle loading.
'rhe measuring system of the present invention can readily be incorporated
into a comprehensive vehicle data system. Thus the measuxing system can be
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installed adjacent a dynamic weighbridge system and the infor~llation provided by
the two systems can be fed to a data base where it is combined with other relevant
~rehicle data, to provide a composite read-out of all this data.
One embodiment of the measuring system Oe the invention as applied to
vehicle length measurement will now be described by way of example with reference
to the accompanying diagrammatic drawings, in which:-
Figure 1 shows the measuring system in association with a dynamic weighbridge,
Figure 2 shows a view of one of the detector stations as seen by the vehiclemoving along its path of travel,
~ igure 3 shows a block circuit diagram of tlle data processing means for
processing the output signals from the detector stations,
Figure 4 shows radiation intensity or (luantity patterns on a time base as a
vehicle moves past the detector stations, and
Figure 5 shows a view similar to Figure 2 of a modified detector station.
Referring to the drawings, the measuring system comprises two detector
stations 1 and 2, which in effect form gateways at either end of a dynamic weighbridge
3 so that a vehicle ~ passing over the weighbridge 3 also passes through the two
detector stations 1 and 2. As will be described the two detector stations 1 and 2
pro~ide electrical outputs to data processing means 5 which provides as its output
a signal representative of overall ~ehicle length. This output together with an
output from the weighbridge data unit 6 representative of gross vehicle weight is
fed to a data base 7 in a freight office and from which a print-out of these items of
information together with other vehicle data can be obtained. The data base may
have provision for feeding its information to a central computer.
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The detector stations 1 and 2 are spaced a predetermined distance
apart (e. g. 2 metres). Each station comprises a pair of posts 8 and 9 disposed on
opposite sides of the patlh of vehicle travel. The posts 8 each carry a vertical
series of infra-red radiation emitting diodes 10 spaced for example 0. 2 metres apart
and each producing a constant radiation intensity output. Each of the diodes
10 incorporates a lens system so that it produces a conically diverging beam of
infra-red radiation, the cone angle being for example 10 . The posts 9 each carry a
sing.~e infra-red detector diode 11, whose vertical posi~ion on the post 9 is adjustable
for convenience in setting up the system. The diodes 10 are oriented so that
their optical axes are directed at the detector diode 11 of the associated detector
station. Thus a triangular curtain of infra-red radiation extends across the
path of vehicle travel at each station as shown in Figures 1 and 2.
Each of the detector diodes 11 produces an electrical output representative
of the intensity or quamity of the infra-red radiation incident upon it so that as
long as any part of a vehicle is interrupting one of the radiation curtains the
output from the associated diode 11 will be a "less than maximum intensity or
quantity" signal. If therefore the data processing means fundamentally has the
facility for measuring the time taken for output signals from each of the detectors 11
to move from "maximum intensity or quantity" back to "maximum intensity or ,
quantity" through a continuous range of "less than maximum intensity or quantity",
the length of a vehicle can be measured using the following two equations:
L = (tlR ~ tl~')V (1)
D
( 2F lE~ ) (2)
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from which two equations:-
~t - t ) D
~ 2F lF ) ( )
where tlF i9 the time in absolute terms at which the front of the
vehicle interrupts the detector station 1,
t2F is the time at which the front of the vehicle interrupts
the detector station 2,
tlR is the time at which the rear of the vehicle clears the detector
~t~tion 1,
t2R is the time at which the rear o~ the vehicle clears the detector
station 2,
L is the length of the vehicle,
V is the velocity of the vehicle,
D is the distance between the detector stations.
It will be appreciated from equation ~3) that there is no need for an indication
of vehicle velocity to be given. However a constant vehicle velocity has been
assumed and this fact could introduce unacceptable errors into the length measurement
if in fact the vehicle velocity does vary as it passes between the two detector
stations 1 and 2. As will now be described the measuring system has an inbuilt
facility for deternnining, in eEfect an average vehicle velocity of transit so that,
within limits changes in vehicle velocity oL transit are compensated for in the
length measurement.
As a vehicle passes through each ot the radiation curtains each ~ross-section
of the vehicle will interrupt a certain number of infra-red~beafns so that on
a time base a radiation ~intensity or quantity pattern will be produced on the
associated detector diode 11 nnd this will be rellected in the Olltput from the
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detector diode. Such intensity or ~luantity patterns from the two detector
stations are shown superimposed in Figure 4. Using pattern recognition tecllnklues
therefore certain ~eatures of the vehicle can be recognised, for example as annotated
on Figure 4 where the front of the vehicle cab 100, the cab body 101, the wheels
103
102, 104 and 105 and the trailer bodyAare indicated. ~lence a number of velocitymeasurements can be made for different points along the vehicle length and an
average velocity derived for use in equation (3). Thus the general equation for
vehicle velocity corresponding to equation (2) is
V = D (4)
(t ~ t
Where tlX is the time in absolute terms at which a given point in the length of
the vehicle interrupts the detector station 1 and t2X is lhe time at which said
given point interrupts detector station 2.
Figure 3 shows a block diagram of the data processing means 5 in which
the outputs of the two detector diodes 11 are fed to an interface unit 12 which includes
an analogue-to-digital converter for converting the analogue output signals fro-m the
diodes 11 to equivalent digital values. Under the control of the micro-computer 13
either of these digital values can be fed into the micro-computer store. The
operator's console 14 has a keyboard and display which enable the operator to initiate
the measuring process, to select which measurements are re~luired (e. g. "length",
"num~er of axles"), and to supply data such as the vehicle registration, With this
information, the micro-computer receives and stores the sequence of radiation
intensity or quantity values from the detectors 11, computes the desired measurements
using the quoted equatior6 and causes these measurements to be printed by the printer
on the operator's console 14, and transmitted to the Freight Office data base 7.
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With the lengtll measurement system descril)ed above a narrow band
optical filter is advantageously placed in front of each Oe the detector diodes 11
to block radiation other than that in the infra-red zone of the spectrum. ~ny
problems with reflected light can be overcome by time modulating the output
of the radiation emitting diodes at a fixed frequency and tuning the detectors to this
frequency. Such modulation can conveniently be achie~red by switching a d. c,
supply to one station's light-emitting diodes for alternate half cycl~s of said
predetermined frequency and to the seconcl station's light-emitting diodes
for the other half cycles.
In the above described æystem a single detector 11 is used at each detector
station. In a modif i cation two or more detectors may be used, a respective
group of the infra-red emitting diodes 10 having their optical axes directed at
each of the detectors. ~igure 5 shows one such arrangement in which two detectoræ
referenced 11 and 11 are used, one at the same level as in Figure 2 and the
other at a relatively low level. The upper group of diodes referenced 10 have
their optical axes directed at the detector 11 and the lower group of diodes
referenced 10 have their optical axes directed at the detector 11 .
The quantity of radiation falling on the two detectors 11 and 11 is summed
and produces a pattern for the ~ehicle similar to that shown in Figure 4. 'rhe
advantage of having a plural detector arrangement as shown in Figure 5, is that
it enables recognition of the lower part of the vehicle more accurately and thus
for example provides a more reliable axle count arrangement. In fact the
detect 11 and its associated group of electrodes 10 could be used ~lone for
axle counting.
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