GB2224872A - Signalling system - Google Patents

Abstract

A system for providing a signal indicative of a location in a predetermined area (e.g. a picking face in a warehouse) comprises a plurality of resistors 12, 18, 24 in series with a supply voltage and a plurality of switch means 14, 20, 26 for making contact between a signal line 30 and respective points between adjacent pairs of resistors 12, 18, 24 so as to thereby form a potential divider and supply an identification signal voltage to a receiving station 28 by way of the signal line 30. <IMAGE>

Description

SIGNALLING SYSTEM DESCRIPTION The invention relates to a signalling system and more specifically to a signalling system for use for example in warehouses and stores in which various products have to be collected together from bulk stores of the individual products, for subsequent delivery or dispatch.

In installations of this kind, bulk packages of the various goods are stored typically on pallets in a main store, from which the bulk packages are moved to what are known as "picking faces". At the picking faces, pickers collect together, from a variety of different bulk packages, the products they need to fulfill a specific order. These picking operations have of course to be interrupted whenever a bulk package of a particular product becomes exhausted.

Randomly located bulk stock in the main store can conveniently be managed by a control system including a computer communicating by radio with terminals on the fork-lift trucks handling the pallets supporting the bulk packages. It would not be feasible to extend this system to all the pickers working at the picking faces because a large number of expensive terminals would be required, which would be used relatively infrequently.

There is consequently a need for a simple and effective signalling system which will enable the pickers to indicate that a particular picking face needs to be replenished from the main store, by the movement from the store of a bulk package typically by a fork lift truck. A signalling system for this purpose needs to include switch units of a suitable form, for which the most convenient locations will usually be the picking faces, and means responsive to operation of a switch unit to provide an output signal that uniquely identifies the picking face with which the switch unit is associated. The system should avoid the expense of complex digital hardware in the switch units, which would allow multiplexing of signals on a simple cable, and also the expense of a multi-way cable, which would permit a simple switch unit but which would incur high cable and installation costs.

The invention accordingly provides a signalling system comprising an array of series-connected resistors connected to a voltage course, and a plurality of signalling stations each having a switch operable to tap into the resistor array at a respective position as a potential divider, so as to take from the array an output signal which is uniquely associated with the signalling station at which the switch is located.

In one use, in a warehouse combining picking faces with a main store operated by a computerised control system, the signalling system of the invention provides a switch, conveniently a simple push button operated switch, associated with each picking face, and typically located at the face, together with necessary resistors and wiring. An output signal is obtained on operation of a switch which identifies the associated picking face, because it is dependent on the particular number of the resistors through which the potential of the voltage source has dropped.

The output signal or a signal derived from it can be supplied to the control system so as to cause this to indicate to a fork lift truck driver that a particular picking face requires immediate replenishment. The system must of course be sufficiently sensitive to distinguish outputs due to operation of a switch from those that would arise were two switches to be operated together.

The signalling system of the invention readily lends itself to use with the usual linear configuration of picking faces, along which the series-connected resistors can extend. Where a large number of picking faces is involved plural arrays of series-connected resistors can be used, so that each picking face lies in effect on two potential dividers.

The signalling system preferably also includes means for indicating to a picker who has operated one of the switches of the signalling system of the invention that his request for replenishment of a picking face has been registered by the control system.

For this purpose, the switch can be ganged with a further switch connecting an L.E.D. to a supply circuit energised by the control system in response to the reception of an output signal, preferably for no longer than is needed to indicate such reception to the picker.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a circuit diagram of one embodiment of a signalling system according to the present invention; Figure 2 is a circuit diagram of another embodiment of a signalling system according to the present invention; Figure 3 is a circuit diagram of a further development of a signalling unit according to Figure 2; Figure 4 illustrates yet a further development to the circuit of Figure 2; Figure 5 is a diagrammatic representation of an operating condition of a further embodiment of the present invention; Figure 6 is a diagrammatic representation of another operating condition of the further embodiment of the present invention; and Figure 7 is a diagrammatic representation of yet another embodiment of a signalling system according to the present invention: The signalling system in Figure 1 comprises signalling units, of which three units 10, 16, 22 only are shown, each unit being located at a particular picking face in a warehouse, so that when the stock at any of those faces has been depleted, a signal can be sent from the appropriate unit to indicate that the particular face needs replenishing.

The units 10, 16, 22 include resistors 12, 18, 24 respectively, which are connected in series and form a potential divider chain. A potential is applied between the ends A, B of the divider chain, and is divided between the three resistors 12, 18, 24 which are of nominally equal resistance.

A signal line 30 is connected through each of the units 10, 16, 22 and also to a voltage measuring device 28 which can supply an output at C, indicative of the voltage measured.

Each unit 10, 16, 22 includes a switch 14, 20, 26 respectively, which when operated, connects the signal line 30 to a particular location along the potential divider. As can be seen from figure 1, each of these locations experiences a unique potential.

The values of the resistors 12, 18, 24 are chosen so as to maintain an appropriately small current represented by arrow I flowing along the divider network, and so that each resistor has a large value compared with the interconnecting wiring between units.

The voltage measuring device 28 is arranged to draw negligible current.

In operation, one of the switches 14, 20, 26 is manually closed when a particular picking face area needs replenishing and a unique voltage signal is measured by the device 28. The voltage measuring device 28 is associated with a central control unit (not shown) which initiates a suitable response to the signal sent from one of the units 10, 16, 22, for example, it instructs a fork lift truck operator to replenish that particular face.

The system of Figure 1 can be extended to include for example, at least five hundred units, provided that the resistance of the interconnecting wiring is small enough to be neglected and secular changes in the values of the resistors can be ignored.

Figure 2 illustrates a system which can be extended to include a larger number of units, for example, 1000 units. Although the system of Figure 2 is represented in two dimensions, as are the systems of later Figures, it will be understood that the units will normally be linearly arranged.

The system of Figure 2 comprises a series of potential divider chains which form a grid pattern including a first series of units 34, 36, 38, 40, a second series 42, 44, 46, 48, a third series 50, 52, 54, 56 and a fourth series 58, 60, 62, 64. The first series comprises a potential divider network 35, 37, 39, 41, the second series comprises a potential divider network 43, 45, 47, 49, the third series comprises a potential divider network 51, 53, 55, 57 and the fourth series comprises a potential divider network 59, 61, 63, 65. The first units 34, 42, 50, 58 in each series, each comprise a second resistor 66, 68, 70, 72. These second resistors are connected in series by a line 71 so as to form yet another potential divider.As before all of the resistors forming the potential dividers are of nominally equal resistance and a potential difference is applied across the resistance networks. Equal positive potentials are applied to points X and Y.

Each of the series of signal units has two signal lines passing therethrough, each of which is connected to a corresponding signal line in the other series so as to provide two output signal lines 73, 74.

Each unit includes a double switch 75 (see unit 36). When closed, this switch connects part of the potential divider network to the output signal line 74 and also part of the potential divider network, formed by the second resistors 66, 68, 70, 72, to the output signal line 73. In this manner, the output signal line 73 exhibits a voltage which is dependent on which of the four series of units is accessed, and the output signal line 74 exhibits a voltage which is dependent on which of the particular units in that series is accessed. Thus, each of the units in the grid pattern is identified by a unique voltage output at the output signal lines 73, 74. The voltages appearing at the output signal line are then applied to a voltage measuring device (not shown in Figure 2) which draws negligible current and is used to provide an output identifying the particular unit accessed.

Figure 3 illustrates a further development which can be incorporated into the system of Figure 1 or Figure 2 but is illustrated with reference to one of the units 36 of the system of Figure 2.

The unit includes an L.E.D. 77 in series with a switch 76 which is ganged to the double switch 75 so that the switches are operated in parallel. Thus, when the switch 75 is closed so as to indicate that the associated picking face needs replenishing, the switch 76 is also closed. The switch 76 then connects two lines O, P which lead back to the central control.

The central control unit on receiving a signal from the unit, applies a voltage to line P so that the L.E.D. 77 is illuminated. In this manner a visual indication is given at the particular picking face area that the signal has been received by the central control unit.

The systems illustrated in Figures 1 and 2 do however exhibit operational problems when more than one of the units is switched or accessed at the same time.

At least one of the signal lines 73 and 74 may exhibit a voltage differing from either of the voltages corresponding to the two switches which have been operated at thes am time. In a particularly large warehouse, this situation could lead to confusion.

Figure 4 is an adaptation which can be made to the system of the present invention and is illustrated with reference to the system of Figure 2. The adaptation allows for the identification of a situation in which at least two units have been accessed.

In Figure 4, all the resistors of the system of Figure 2 are represented as five parallel networks, each of which networks represents one of the potential dividers of the system of Figure 2. As before, a predetermined potential difference is applied between points X and Z so that a step in potential is exhibited at each resistor. Figure 4 thus represents the potential dividers of Figure 2 as connected to a power supply for operation.

A resistor RR is connected to point Z and so appears in series with the combined resistance of the resistors of the potential divider. A voltage VR appearing at point Z is measured and used as a reference voltage. The magnitude of the reference voltage VR is dependent on the potential divider formed by RR and the above mentioned combined resistance.

The reference voltage VR is continually monitored to ascertain whether more than one unit has been accessed. If, for example, two units are accessed then, as described later, either one or more of the resistors of one of the five potential divider networks will be shorted out, and/or part of the five potential divider network will be shorted. In either case the combined resistance of the five potential divider networks will alter, and thus so will the value of the reference voltage VR. A change in the reference voltage VR therefore indicates if two or more units are accessed at the same time. A similar but inherently more simple situation can arise in use of the system of Figure 1.

Figure 5 illustrates the situation in which two adjacent units in the same series of units are accessed at the same time. In this case, one of the resistors R is shorted out by a connection path 78 formed through the switches 75 of the two units.

When such a situation occurs, the combined network resistance decreases from a value R to a value S, where N is the number of units in each series: (1/S) = (N-1)/NR + /(N-1)R so that: S = (N(N-1)}R/{(N-1)2 + N} for the situation in which there are twenty units in each series, i.e. N = 20 S = 380R/381 = 0.9974R Figure 6 illustrates the situation in which two units, each of which is in an adjacent series of units, are accessed at the same time. In this case part of the potential divider network is shunted through a connection path 79 formed through the switches 75 of the two units.

The resistance of the two series illustrated in Figure 6 is: [(mn/(m+n)) + ((N-m)(N-n)/(2N-m-n))1R = aR say (1/S) = (N-2)/NR + 1/(aR) S = (aN)/ia(N-2) + N) As m 7! n, the highest value of S will occur, inter alia, as follows:

m n N odd 0.5(N-1) 0.5(N+1) N even 0.5 N+1 0.5N Thus when N = 20, then m = 11 and n = 10, so that: a = (110/21) + (90/19) = 9.975 and so s = 0.99975 R.

Thus when at least two units are accessed at the same time the combined network resistance is altered and the reference voltage VR is thereby altered.

Figure 7 illustrates another embodiment of a system according to the present invention having only two potential divider networks. A first network 80, and a second network 82 from the axes of a grid of signal units 87. A potential difference is applied across the two divider networks 80, 82, between points 84 and 83. Each of the signal units 87 comprises a double-throw switch for selectively connecting a particular location in the potential divider 80 to a signal output line 86, and for selectively connecting a particular location on the potential divider 82 to a signal output line 85. The connection 89, 91; 88, 90, to one of the signal units 87 only are illustrated in Figure 7, but it should be understood that all of the signal units 87 are connected to the appropriate locations on the potental dividers 80, 82 in a similar way.

Although the above description refers to systems with two potential divider arrays, the invention is not so limited and more than two such arrays can be employed. It will be evident that the invention can be embodied in a variety of ways other than those specifically described and illustrated.

Claims (10)

1. Signalling apparatus comprising a plurality of resistors for connection in series with a supply voltage, a signal line, and a plurality of switch means each operable to make electrical contact between the signal line and a respective point between adjacent pairs of resistors so as to form a potential divider and thereby supply a signal voltage to a receiving station when a switch means is closed, which signal voltage and switch means are associated with a particular location to be identified in a predetermined area.

2. Apparatus as claimed in claim 1 wherein the receiving station comprises a voltage measuring device for measuring the signal voltage and supplying an output indicative of the voltage measured.

3. Apparatus as claimed in claim 1 or 2 having at least one further plurality of resistors connected in series to a supply voltage and associated with a further signal line, wherein each switch means is operable to connect a respective point between adjacent pairs of resistors of each of the plurality of resistors to a respective signal line.

4. Apparatus as claimed in claim 1, 2 or 3, comprising means for indicating simultaneous closure of two or more switch means.

5. Apparatus as claimed in claim 4 wherein the means for indicating simultaneous closure of two or more switch means comprise a reference resistor in series with the resistors, and means for measuring the voltage at a point between the resistors and the reference resistor so as to monitor a change in the total value of resistance of the resistors.

6. Apparatus as claimed in any preceding comprising indicating means for indicating receipt at the receiving station of the signal voltage.

7. Apparatus as claimed in claim 6 wherein the indicating means comprises a secondary switch operable on closure of each switch means to permit energization from the receiving station of an indicator located in the region of the switch means.

8. Apparatus as claimed in claim 7, wherein each indicator comprises a LED.

9. An installation comprising a plurality of picking faces from which goods can be selected from bulk pavckages of the goods brought to the picking faces from a main-store and a signalling system as claimed in any preceding claim, the switch means each being located at a respective picking face for operation to signal exhaustion of the bulk package thereat, and the receiving station comprising a control station for supply of bulk packages to the picking faces.

10. Signalling apparatus substantially as hereinbefore described with reference to Fig. 1, Fig.

2, Fig. 3, Fig. 4, Figs. 5 and 6 and Fig. 7 of the accompanying drawings.