GB1595071A

GB1595071A - Length measuring apparatus

Info

Publication number: GB1595071A
Application number: GB1690477A
Authority: GB
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1978-03-31
Filing date: 1978-03-31
Publication date: 1981-08-05

Description

(54) IMPROVEMENTS IN OR RELATING TO LENGTH MEASURING APPARATUS (71) We, THE PLESSEY COMPANY LIMITED, a British Company of 2/60 Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to apparatus and methods for assessing the length of a moving vehicle.

Apparatus for assessing the length of a moving vehicle is described in our G.B. Patent No. 1,348,786 and comprises two vehicle sensing means sited at spaced apart locations along a vehicle path. Such an arrangement is entirely satisfactory only if the vehicle travels between the sensing means at substantially constant speed.

It is an object of the present invention to provide an alternative apparatus wherein an entirely satisfactory assessment of vehicle length is facilitated not only when the vehicle is travelling at constant speed but also when the vehicle is subject to conditions of substantially constant acceleration or deceleration.

According to the present invention apparatus for assessing the length of a moving vehicle comprises two vehicle sensing means sited at positions located along a vehicle path, first measuring means responsive to one of the sensing means for providing a first signal proportional to the time elapsing during which a vehicle is sensed by the said one sensing means only as said vehicle travels along said path, second measuring means responsive to the other of the sensing means to provide a second signal proportional to the time elapsing during which the vehicle is sensed by the said other sensing means only, as the said vehicle travels along the said path, and third measuring means responsive to both sensing means for providing a third signal proportional to the time elapsing during which the vehicle is contemporaneously sensed by both sensing means as said vehicle travels along said path and output means responsive to said first, second and third signals for providing an output signal indicative of vehicle length.

The sensing means may comprise loops laid on or in a roadway traffic lane or the like a vehicle being sensed when it is over the loop or over part of the loop.

The loops may be spaced apart in the direction of travel of the vehicle.

Alternatively the loops may be arranged to overlap.

As a further alternative the front edge of one loop may be arranged positionally to coincide with at least a part of the back edge of the other loop.

The loops may be square or rectangular and may be as shown in our G.B. Patent No.

1,348,786.

The measuring means may comprise an arrangement of gating circuits, a clock pulse generator and counter means whereby the vehicle length is determined in dependence upon the number of clock pulses counted for the time elapsing during which the vehicle is sensed by the sensing means.

The output means may comprise microprocessor or computer means responsive to the said first, second and third signals for providing the output signal indicative of vehicle length.

Some exemplary embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a generally schematic diagram of an arrangement showing two detector loops and associated processing circuitry; Figure 2 is a generally schematic diagram of an alternative detector loop arrangement, and Figure 3 is a generally schematic diagram of a further alternative detector loop arrangement.

Referring now to Figure 1 apparatus for determining the length of vehicle such as car shown schematically at 1 comprises a pair of loops A and B which are buried in a roadway traffic lane or the like. The loop A feeds a detector 2 and the loop B feeds a detector 3. The detector 2 feeds measuring apparatus 4 which provides a signal proportional to a time t1 for which conditions AB obtain during which the car 1 is sensed by loop A alone. Detector 3 feeds measuring apparatus 5 which provides a signal proportional to a time t2 for which conditions AB obtain during which the car 1 is sensed by the loop B alone. Both detectors 2 and 3 feed further measuring apparatus 6 which provides a signal proportional to a time t3 for which the condition AB obtains during which both loops sense the presence of the car 1.

If the length of the car 1 is L, the width of the loop A is f l and the width of the loop B is ez and the distance between the loops A and B is t3 then the mean velocity of the car V, as it passes the loop A is V, = & +L t, and the mean velocity of the car as it passes the loop B is V t2 2 + L t2 and the mean velocity of the car Vm as it passes a point between the loops is Vm = L - t3 t3 There are three alternative loop arrangements as shown in Figures 1, 2 and 3 and if the loop configuration as shown in Figure 3 is utilised then the distance e, between the loops is zero.If the loops have identical dimensions i.e. e, = e2 = e and 63 = zero as shown in Figure 3, then it can be shown that

In order to solve this equation a microprocessor or similar computation arrangement 7 is provided fed from the measuring apparatus 4, 5, and an output signal from the microprocessor on line 8 is afforded indicative of the length of the vehicle.

The foregoing arrangement has the advantage that the mean vehicle speed Vm is determined effectively at a point between the loops A and B and therefore it will be appreciated that even if the vehicle is accelerating or decelerating over the loops the length of the vehicle will be accurately indicated provided the vehicle acceleration or deceleration is substantially constant. The arrangement just before described is therefore an improvement over the system described in our G.B. Patent No. 1,348,786.

It will be appreciated that the various integers of the circuit shown schematically in Figure 1 may be fabricated using conventional logic circuitry after the fashion described in our U.K. Patent No. 1,348,786. Thus a clock generator may be utilised and pulses counted from the clock generator when the detectors 2 and 3 are operated during the passage of a vehicle over their associated loops whereby signals proportional to the times tl, t2 and t3 are derived. The circuits required to solve the equation for L may take any conventional form and are well understood by those skilled in the art. Although the equation for L has been shown only for the case shown in Figure 3 where t3 = 0, it will be understood that alternative arrangements may simply be provided taking account of the length (; as necessary for application of the loop arrangements shown in Figures 1 and 2.

WHAT WE CLAIM IS: 1. Apparatus for assessing the length of a moving vehicle comprising two vehicle sensing means sited at positions located along a vehicle path, first measuring means

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Figure 2 is a generally schematic diagram of an alternative detector loop arrangement, and Figure 3 is a generally schematic diagram of a further alternative detector loop arrangement. Referring now to Figure 1 apparatus for determining the length of vehicle such as car shown schematically at 1 comprises a pair of loops A and B which are buried in a roadway traffic lane or the like. The loop A feeds a detector 2 and the loop B feeds a detector 3. The detector 2 feeds measuring apparatus 4 which provides a signal proportional to a time t1 for which conditions AB obtain during which the car 1 is sensed by loop A alone. Detector 3 feeds measuring apparatus 5 which provides a signal proportional to a time t2 for which conditions AB obtain during which the car 1 is sensed by the loop B alone. Both detectors 2 and 3 feed further measuring apparatus 6 which provides a signal proportional to a time t3 for which the condition AB obtains during which both loops sense the presence of the car 1. If the length of the car 1 is L, the width of the loop A is f l and the width of the loop B is ez and the distance between the loops A and B is t3 then the mean velocity of the car V, as it passes the loop A is V, = & +L t, and the mean velocity of the car as it passes the loop B is V t2 2 + L t2 and the mean velocity of the car Vm as it passes a point between the loops is Vm = L - t3 t3 There are three alternative loop arrangements as shown in Figures 1, 2 and 3 and if the loop configuration as shown in Figure 3 is utilised then the distance e, between the loops is zero.If the loops have identical dimensions i.e. e, = e2 = e and 63 = zero as shown in Figure 3, then it can be shown that In order to solve this equation a microprocessor or similar computation arrangement 7 is provided fed from the measuring apparatus 4, 5, and an output signal from the microprocessor on line 8 is afforded indicative of the length of the vehicle. The foregoing arrangement has the advantage that the mean vehicle speed Vm is determined effectively at a point between the loops A and B and therefore it will be appreciated that even if the vehicle is accelerating or decelerating over the loops the length of the vehicle will be accurately indicated provided the vehicle acceleration or deceleration is substantially constant. The arrangement just before described is therefore an improvement over the system described in our G.B. Patent No. 1,348,786. It will be appreciated that the various integers of the circuit shown schematically in Figure 1 may be fabricated using conventional logic circuitry after the fashion described in our U.K. Patent No. 1,348,786. Thus a clock generator may be utilised and pulses counted from the clock generator when the detectors 2 and 3 are operated during the passage of a vehicle over their associated loops whereby signals proportional to the times tl, t2 and t3 are derived. The circuits required to solve the equation for L may take any conventional form and are well understood by those skilled in the art.Although the equation for L has been shown only for the case shown in Figure 3 where t3 = 0, it will be understood that alternative arrangements may simply be provided taking account of the length (; as necessary for application of the loop arrangements shown in Figures 1 and 2. WHAT WE CLAIM IS:

1. Apparatus for assessing the length of a moving vehicle comprising two vehicle sensing means sited at positions located along a vehicle path, first measuring means

responsive to one of the sensing means for providing a first signal proportional to the time elapsing during which a vehicle is sensed by the said one sensing means only as said vehicle travels along said path, second measuring means responsive to the other of the sensing means to provide a second signal proportional to the time elapsing during which the vehicle is sensed by the said other sensing means only as the said vehicle travels along the said path, and third measuring means responsive to both sensing means for providing a third signal proportional to the time elapsing during which the vehicle is contemporaneously sensed by both sensing means as said vehicle travels along said path and output means responsive to said first, second and third signals for providing an output signal indicative of vehicle length.

2. Apparatus as claimed in claim 1, wherein the sensing means comprises loops laid on or in a roadway traffic lane or the like a vehicle being sensed when it is over the loop or over a part of the loop.

3. Apparatus as claimed in claim 2 wherein the loops are spaced apart in the direction of travel of the vehicle.

4. Apparatus as claimed in claim 2, wherein the loops are arranged to overlap.

5. Apparatus as claimed in claim 2, wherein the front edge of one loop is arranged to positionally coincide with at least a part of the back edge of the other loop.

6. Apparatus as claimed in any preceeding claim wherein the measuring means comprises gating circuits, a clock pulse generator and counter means arranged so that the vehicle length is determined in dependence upon the number of clock pulses counted for the time elapsing during which the vehicle is sensed by the sensing means.

7. Apparatus as claimed in any preceeding claim wherein the output means comprises a micro processor or computer means responsive to the first, second and third signals for providing the output signal indicative of vehicle length.

8. Apparatus for measuring the length of a moving vehicle substantially as hereinbefore described with reference to the accompanying drawings.