A POSITION INDICATING SYSTEM

Abstract: A position indicating system suitable for use at container terminals for indicating the correct positioning of container transporters during loading and unloading. The system includes a transmitter (7) which transmits two differently modulated beams (C) (D) of electromagnetic radiation which have a region of overlapping modulation (E) at the correct location. Detection means (8) carried on the transporter (2) are responsive to the overlapping modulation and provide an output to the transport driver indicating the position of the transporter (2).

Description: "A POSITION INDICATING SYSTEM" The present invention relates to a position indicating system using modulated electromagnetic radiation. BACKGROUND ART The present invention rises out of the need to position large trucks to an accuracy of the order of 2-3 cm. Such accuracy is required in the loading and unloading of cargo containers onto and from trucks from and onto ships by means of gantries or cranes. Previously the positioning of the truck was judged by eye by the truck driver, or by another person who then signalled the driver. Such methods were inefficient, and particularly awkward for the driver. DISCLOSURE OF THE INVENTION In one broad form the invention provides apparatus for indicating the positioning of a body at a desired location, said apparatus comprising transmitter means for transmitting at least two differently modulated beams of electromagnetic radiation which have a region of overlapping modulation at the desired location, and detector means adapted to be carried on said body into said beams, said detector means comprising demodulating means for demodulating the received radiation and responsive to said overlapping modulation to provide an output indicating that the body is at the desired location. Preferably the radiation is infrared radiation and the beams are each pulse width modulated with a unique binary code. Thus the overlapping modulation consists of the presence of pulse codes from both beams. BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the present invention will now be described with reference to the drawings in which: Fig. 1 is a schematic end elevational view of a mobile gantry adapted to unload containers from trucks and load same onto ships; Fig. 2 is a schematic side elevational view of the transmitter and truck of Fig. 1; Fig. 3 is a block diagram of the transmitter ____ OMPI electronics; and Fig. 4 is a block diagram of the receiver electronics. = BEST MODE OF CARRYING OUT THE INVENTION As indicated schematically in Fig. 1, a problem arises when wishing to transfer a container 1 from the back of a truck 2 at a wharf 3 to a waiting ship 4. It is known to use a mobile gantry 5 for this purpose, the gantry 5 having wheels 6 which permit the gantry to be moved parallel to the edge of the wharf 3. The gantry 5 includes lifting apparatus (not illustrated) which grasps the container 1 and lifts it from the truck 2 and onto the ship 4. However, for the lifting apparatus to suitably grip the container 1, it is necessary that the truck 2 be positioned longitudinally with some degree of accuracy. Typically, the lifting apparatus on the gantry 5 is approximately 10 metres above the level of the wharf 3 and the truck 2 must be longitudinally positioned with an accuracy of the order of 2-3 cm. Similar considerations apply when loading the truck 2 with a container 1 from the ship 4. Although it is possible to so position the truck 2 by means of trial and error, this is a relatively lengthy procedure and therefore does not lead to rapid turn around times for the loading, and also unloading, of the ship 4. In order to overcome this problem, an infrared transmitter 7 is positioned on the gantry 5 and a single detector 8 is located on the upper surface of the cabin of the truck 2. As seen in Fig. 2a, the transmitter 7 includes two infrared emitting diodes 9 and 10 which are located as shown with respect to a mirror assembly containing two parallel front-silvered mirrors 11 and 12. Infrared radiation from 10 reflects from both mirrors, producing a ' beam C with a sharp spatial edge. Infrared radiation from 9 passes by the top rear edge of mirror 11, producing a second beam D with a sharp spatial edge. These edges overlap slightly to define the desired position of the detector 8 when the truck 2 is located in the desired position below the gantry 5 (or relative to the crane) . Two further infrared emitting diodes 13 and 14 produce approach beams A and B which warn the; truck driver of the proximity of the stopping point. Any suitable method of modulating the four beams which will discriminate amongst them can be used. In one embodiment, a pulse width modulated subcarrier, using four bits to differentiate between the diodes, is used. The diodes 9, 10, 13, 14 radiate the binary codes 1000, 0100, 0010 and 0001, respectively. This allows ready detection of each region and each overlap. The transmitter's electronic circuit is shown in Fig. 3, and operates as follows. An oscillator 30 provides a subcarrier frequency of 35kHz. This is divided by 8 to give the fundamental pulse rate, and further by 64 to give the frame rate (the rate at which the entire signal repeats) . A pulse width modulator 35 produces for each diode the required driving current, which comprises four bursts of 35 kHz, three short and one long. (The long burst corresponds to 1, the short to 0) . Each diode is driven by a different pattern of bursts, thus providing the unique individual binary codes. Fig. 4 shows the operation of the detector 8 when it enters any of the beams A, B, C or D. The 35 kHz modulated infrared beam is detected by a PIN photodiode 40 and then amplified by a low noise tuned amplifier 42. The signal is then demodulated by a pulse width demodulator circuit 44, and the resulting signal passed to a pulse sorting circuit 46 where the four channels are separated back. Each channel represents a signal from a single diode on the transmitter. A display decoder 48 accepts this input and produces driving signals for an appropriate display device 50, which may be a linear array of LED indicators, for example. The operation of the system of the preferred embodiment of the present invention is as follows. As seen in Figs. 1 and 2, the truck 2 is positioned by the driver a desired distance from the edge of the wharf 3 by driving the truck 2 along a line (not illustrated) painted along the surface of the wharf 3. That is to say, the truck 2 OMPI moves from left to right as seen in Fig. 2. As the truck enters the first beam 1 the detector receives the modulated pulses produced by diode 13, the display device indicating region A. As the truck continues to move, the display device indicates sequentially as follows: Region A, A & B overlap, region B, B & C overlap, region C, C & D overlap, region D. The desired position is of course given by C & D overlap, which is sharply defined because of the mirrors 11 and 12 in Fig. 2a. Furthermore, with the present embodiment, use may be made of the pulse amplitude differences which occur in the C & D overlap region. By including analog circuitry to detect and display these differences a much more accurate crossover position may be defined. In addition, extra infrared emitting diodes may be placed in the near vicinity of diodes 9 and 10 which, when fed in parallel with these diodes, allow control of the width of the overlap region so that the truck can be accurately positioned in two dimensions. The foregoing describes only one embodiment of the present invention and modifications, obvious to those skilled in the art, may be made to the present invention without departing from the scope thereof as defined in the following claims. For example, different frequencies such as microwaves and millimetric waves can also be used as can different methods of modulating the radiation sources. Furthermore, more than two sources can be used in conjunction with the mirrors in order to arrive at different patterns of beams and thereby indicate one of a plurality of positions. Where it is desired to specify a location in two dimensions (rather than the single dimension as described above) another set of diodes with mirrors set orthogonally to the existing two mirrors can be used.

Claims: CLAIMS 1. Apparatus for indicating the positioning of a body at a desired location, said apparatus comprising transmitter means for transmitting at least two differently modulated beams of electromagnetic radiation which have a region of overlapping modulation at the desired location, and detector means adapted to be carried on said body into said beams, said detector means comprising demodulating means for demodulating the received radiation and responsive to said overlapping modulation to provide an output indicating that the body is at the desired location. 2. Apparatus as claimed in claim 1, wherein the beams are each pulse width modulated with a unique binary code whereby the presence of the body at the desired location is indicated by the binary code derived from demodulating the overlapping modulation. 3. Apparatus as claimed in claim 1 or 2, wherein said transmitter transmits two beams overlapping at the desired location, and two successive approach beams before the desired location, said transmitter means comprising a modulator for pulse width modulating each said beam with a unique binary code, whereby the binary code output of said demodulating means uniquely determines the position of said body with respect to said beams. 4. Apparatus as claimed in claim 3, wherein the binary code for each beam is a four bit binary code having only one bit of a particular status in a unique respective position within said code, whereby the position of the detector is indicated by the position(s) of said one bit(s) in the demodulated code. 5. Apparatus as claimed in any one of claims 1 to 4, wherein said transmitting means comprises an arrangement of mirrors for directing at least two beams into a sharply defined overlapping region covering said desired location. 6. Apparatus as claimed in any one of claims 1 to 5, further comprising a display for displaying the location of said body with respect to said beams, said display having a plurality of light emitting diodes, each corresponding to a particular beam, whereby the positioning of said body within a beam or beams lights up the corresponding diode(s). 7. Apparatus έis claimed in any preceding claim, wherein said radiation is infrared radiation. 8. Apparatus as claimed in any preceding claim, further comprising an additional pair of overlapping differently modulated beams directed orthogonally to said at least two differently modulated beams, whereby said body can be positioned in two dimensions. 9. A system for loading ships from trucks, said system comprising apparatus as claimed in any preceding claim. 10. Apparatus for indicating the positioning of a body at a desired location, said apparatus being substantially as described herein with reference to the accompanying drawings.

Inventors: CRAGGS JOHN STANLEY, KACHWALLA ZAIN, POULTON GEOFFREY THOMAS, CRAGGS, JOHN, STANLEY, KACHWALLA, ZAIN, POULTON, GEOFFREY, THOMAS
Applicants: COMMW SCIENT IND RES ORG, COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH OR
Application year: 1982
Main classification: G01S1
IPC codes: B66C13, G01S1, G08G1, G08G3