BACKGROUND OF THE INVENTION

This invention relates to tracking systems. The invention has particular, although not exclusive, relevance to tracking systems for tracking merchandise in, for example, warehouses so as to prevent theft of the merchandise.

It is well known that there is a problem of theft in the transportation of merchandise between locations, for example, factories and warehouses. Generally, the merchandise is loaded on to trolleys which are then loaded on to the lorries which transport the merchandise. It is found that a large number of trolleys, together with the merchandise carried on them, tend to disappear every year.

It is an object of the present invention to provide a tracking system which is suitable for monitoring the movement of such trolleys.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention

there is provided a tracking system including a central control system incorporating a transmitter means and a receiver means; a plurality of transport devices each carried on a number of wheel members wherein at least one of the wheel members for each transport device carries at least one transceiver, and an electrically conductive pattern arranged on the support surface for the transport devices effective to constitute an aerial for the transmitter means and receiver means incorporated in the central control system; the central control system being effective to send signals to the transceivers and receive and process signals from the transceivers, thereby monitoring the presence of the transport devices.

It will be seen that by positioning the transceivers in the wheel members, it is possible to distance the transceivers from other metallic portions of the transport device which otherwise may cause electrical interference. Furthermore, by positioning the antennae for the transceivers in the wheel members, and the antenna for the central control system on the support surface for the transport devices, the distance between the antennae for the transceivers, and the antenna for the central control system is minimised, thus minimising the transmission power requirements of the system.

An electrically conductive track may be arranged around said one wheel member so as to constitute an antenna for the transceiver. Such an arrangement will allow the distance between the antennae for the transceivers, and the antenna for the central control system to be reduced even further.

Each transport device is suitably a trolley.

Each wheel member is suitably a caster.

The electrically conductive pattern may take the form of an electrically conductive loop around the edge of the floor of an enclosed area. Such an enclosed area may, for example, be in a vehicle in which the transport devices are located. Alternatively, the electrically conductive pattern is formed on a mat on which the transport devices sit. The conductive pattern may be formed into a number of zones such that the central control system is able to differentiate between the zones.

Preferably, the central control system includes means for transmitting a series of interrogating signals to each transceiver, the first interrogating signal in each series being effective to elicit a response signal from

the transceiver which is used by the central control system to determine whether the transceiver is within a first range of transceivers, and the subsequent signals within the series being effective to elicit a further response signal from the transceiver to determine whether the transceiver lies in a second, narrower, range of transceivers within the first range.

According to a second aspect of the present invention, there is provided a wheel member for use on a transport device, the wheel member incorporating a transceiver; and an electrically conductive track formed around the wheel member so as to form an antenna for the transceiver.

The wheel member is suitably in the form of a caster.

DESCRIPTION OF THE DRAWINGS

One tracking system, in accordance with an embodiment of the invention, will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 is a schematic diagram of the system;

Figure 2 is a schematic diagram of a caster incorporated in the system of Figure 1 on an enlarged scale;

Figure 3 is a schematic flow diagram of the operation of the base station;

Figure 4 shows (on an enlarged scale) a threadguard device for incorporation on a caster, a transceiver being mounted on the device; and

Figure 5 is a side view of the threadguard of Figure 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly to Figure 1, the tracking system includes a central control station 1, including a central radio transmitter and receiver, whose circuitry may be combined if required, so as to constitute a central radio transceiver. Positioned within the area which it is required to monitor, this typically being a warehouse, are a number of trolleys 3, each designed to carry goods. Each trolley is supported by four casters 5. Only three such trolleys are shown in the figure, for the sake of clarity, but it will be appreciated that generally there may be several hundred such trolleys.

Referring now also to Figure 2, within one of the casters 5 of each trolley 3 there is provided a small radio transceiver 7, of the form commonly referred to as a "tag". Each transceiver 7 is programmed with an identity code uniquely identifying the transceiver. Around the perimeter of each caster 5 containing a radio transceiver 7, there is provided a metallic track 9 which constitutes an antenna for the transceiver.

The floor of the area being monitored is provided with an electrically insulating mat 11 on which is formed a network of metallic strips 13. These strips 13 are designed so as to form an antenna for the central radio transmitter and receiver incorporated in the control station 1.

In use of the system, the transmitter of the central control station 1 produces RF signals which are transmitted by the network of strips 13 formed on the mat 11. When a trolley 3 is positioned such that the caster of the trolley which contains a transceiver lies within the range of the signals transmitted by the conductive strips 13 formed on the mat 11, the metallic track 9 formed round the perimeter of the caster 5 will pick up signals transmitted by the strip 13 on the mat 11. Each transceiver 7 will generally be positioned

within the casters 5 such that the antenna 9 will have the maximum possible range.

Referring now also to the flow diagram shown in Figure

3, the transmitter of the base station 1 is arranged to send a series of interrogating signals which will be picked up by all those transceivers 7 whose antennae 9 are within the range of the signals transmitted by the conductive strips 13 on the mat 11. The initial signals within each set of signals transmitted by the central control station 1, is designed to interrogate a predetermined set of transceivers 7 determined by the identity codes of the transceivers 9, for example within the range 1-100, and within a specified zone determined by the conductive strips 13. The interrogating signals cause each transceiver 7 within the range of the signals, to transmit a response signal via the transceiver's antenna 9 containing the identity code of the transceiver 7, each activated transceiver 7 being powered by the incoming RF signals picked up by the antenna. This response signal is picked up by the antenna constituted by the conductive strips on the mat and thereby transmitted to the base station 1. If there is no response, then the transmitter for the base station 1 sends out a further interrogation signal effective to interrogate a different set of transceivers, for example within the range 101-200.

If, on the other hand, the central receiver in the base station 1, does receive a response signal, this is decoded to determine which transceiver 7 has sent that particular response signal. If, however, the received response signal can not be decoded due to more than one transceiver 7 in the range 1-100 responding, a second signal is transmitted by the base station 1. This second interrogation signal may be effective to poll a diminished range of transceivers 7, for example in the range 1-50, with further interrogation signals effective to poll subsequent diminished ranges, for example in the range 1-25 then being transmitted if necessary. Alternatively, the second interrogation signal may be effective to poll successively individual transceivers 7, for example transceiver no. 1,2 ... until a response is detected.

It will be appreciated that as the base station 1 is software controlled, the interrogation pattern of the base station 1 may readily be varied to fit the particular circumstances, for example how many trolleys must be monitored.

It will be seen that the conductive strips 13 on the mat 11 make it possible for the area being monitored to be divided into zones, thus enabling the base station to

determine the location of any particular trolley 3 within the area being monitored.

It will be appreciated, however, that the conductive pattern on the support surface for the trolleys may be arranged in various ways. Thus, the pattern may take the form of a loop around the edge of the floor of an enclosed area, for example in a truck. Alternatively, the conductive pattern may take the form of a continuous electrically conductive area.

It will be appreciated that it may be advantageous to mount the transceivers 7 in such a manner that they do not rotate with the rotation of the caster. This may be achieved by mounting the transceiver on a so-called "threadguard" as shown in Figures 4 and 5. Such a device is mounted on the axis of rotation of a caster and is commonly used to prevent build-up of dirt on the shaft of the caster. Such a device will of course, keep the transceivers hidden from view.

Alternatively, it may be useful in other circumstances to mount the transceivers so as to rotate with the casters.

Whilst in the above example, only one transceiver 7 is

carried by each caster 5, it may in some circumstances be advantageous to include more than one transceiver in each caster, for example three transceivers. These may then be used to derive information concerning the direction in which the trolley carrying the casters is heading.

It will be appreciated that by the combination of the conductive track antennae for the transceivers 7, and the closely positioned antenna for the transmitter and receiver of the central control station, the power requirements of the system will be minimised. Thus it may be possible to avoid the requirement of a broadcasting licence for the system from the U.K. Department of Trade and Industry. It is found, however that by use of a powerful transceiver, such as the TIR1S (Registered Trade Mark) transponder marketed by Texas Instruments, the metallic tract 9 around the perimeter of each caster 5 can be omitted. Such a transceiver has its own helically wound antenna, and has a range of up to 50 cm.

It will also be appreciated that it is particularly advantageous for the transceivers 7 not to contain their own power supply, but to be powered by incoming RF signals from the base station 1. Thus it is not

necessary to monitor the transceivers 7 to determine whether their power supply has failed. In some systems in accordance with the invention, however, it may be appropriate to incorporate an individual power source in each transceiver 7. This may take the form of a small battery, for example a long life lithium battery. Alternatively, a dynamo arrangement may be incorporated in each caster carrying a transceiver 7, rotation of the caster being operative to power the transceiver via the dynamo arrangement.

It will also be appreciated that by incorporating the transceivers within the casters, the transceivers will not generally be visible thus reducing the possibility of unauthorised persons removing the transceivers. Furthermore, the transceivers 7 are located as far away as possible from the rest of the trolleys which will generally be metallic or carry metallic goods, and which would thus otherewise cause electrical interference of the RF signals.

It will also be appreciated that whilst the particular tracking system described herebefore by way of example, is a system for tracking the movement of caster borne trolleys, a tracking system in accordance with the invention may also be used for monitoring the presence

of other forms of transport device within a predetermined area. Thus the transceivers may be incorporated in wheels rather than casters. Where the wheel is the wheel of, for example, a car, the antenna for the transceiver may be constituted by the metal band which is already usually incorporated in tyres for car wheels.

INDUSTRIAL APPLICABILITY

The invention has applicability to tracking systems, particularly, though not exclusively, tracking systems for tracking merchandise in, for example, warehouses so as to prevent theft of the merchandise.