GB2158911A

GB2158911A - Machinery security systems

Info

Publication number: GB2158911A
Application number: GB08511540A
Authority: GB
Inventors: Michael Ian Henville
Original assignee: Unimax Switch Ltd
Current assignee: Unimax Switch Ltd
Priority date: 1984-05-05
Filing date: 1985-05-07
Publication date: 1985-11-20
Also published as: GB8511540D0

Abstract

To restrict access to an area whilst a function in that area is operable a key 9 is provided on one of a guard 8 or a frame 6, and a sensing unit 1 on the other. The sensing unit 1 incorporates at least one emitter 2 and one receiver 3 of radiation, e.g. infra-red. The key 9 incorporates transmission means which when the guard 8 is in an enabling position provides a propagation path from the emitter 2 to at least one receiver 3. The system is so arranged that the receipt of a signal by a receiver 3, or a predetermined coding condition of receiving or not receiving by a series of receivers 3, results in an enabling signal which controls the function that is to be allowed to occur only when the guard 8 is in an enabling position. In one embodiment the propagation path is defined by at least two reflectors to be returned in the opposite direction to which it was emitted. <IMAGE>

Description

SPECIFICATION Security systems The invention relates to security systems, in particular, though not exclusively, to locking removable guards for machines. It is often desirable that a machine should be operable only when its guard is in position, and that the apparatus for detecting the presence of the guard is tamper-proof.

Some systems incorporate complementary halves of plug-and-socket arrangements, for example key cards having contact tags with coded interconnections. Some mechanisms require the insertion of a key card incorporating active circuitry which interacts with that of a sensing unit to establish the necessary condition for unlocking or enablement of operation of a machine. Such arrangements depend upon good electrical contact between the key and the reading components of the sensing unit, which in dirty or corrosive conditions may not be practicable. Other systems use key cards having optically-read bar codes or incorporating magnetically recorded strips.

These systems rely on mechanical movement of either the card or a reading head to generate a signal, with the attendant disadvantages of unreliability and wear. In addition, all of these previously known arrangements require close tolerances to be observed in their manufacture and use.

It is also known for a security device to use electromagnetic radiation incident upon a key as a means of ensuring that the key is correctly located with respect to a lock. In such a method characteristic physical properties of the radiation that are modified by the presence of the key, such as the polarisation of the radiation, are detected after the radiation has been incident upon the key. These properties are compared with those expected for the correct location of the appropriate key.

It is an aim of the invention at least partially to overcome the above mentioned disadvantages and to provide a tamper-proof security system which relies neither on good electrical contact nor relative mechanical movement between key and sensing unit, and furthermore does not require the observance of close tolerances.According to the invention, this is achieved by provision of a security system for machinery and other areas to which access is to be restricted comprising a movable guard member and a co-operating frame member, movement of the guard member away from the frame member giving access to the restricted area, and a sensing unit on one of the said members co-operating with a key on the other member, the sensing unit incorporating at least one emitter for the emitting of radiation and at least one receiver for the receiving of radiation, the key incorporating transmission means which provides a propagation path by way of which the radiation is transmitted from at least one said emitter to at least one said receiver only when the guard member is in an enabling position in relation to the frame member in which it prevents access to the restricted area, receipt of a signal from the emitter by the receiver via the transmission means in the key results in an enabling signal which controls a function which is to be allowed to occur only when the guard member is in the said enabling position.

In this way the only conditions required for efficient functioning of the sensing unit are good propagation of the radiation in the region of the sensing unit and key and efficient functioning of the transmission means associated with the key. In a preferred embodiment the transmission means comprises one or more reflective surfaces by means of which when the key is in the enabling position radiation from at least one emitter is directed to at least one receiver.

Either or both of the sensing unit and key may be shrouded to present a 'dead front' appearance so that the positions of the emitters, receivers and reflective surfaces cannot be readily discerned. Preferably the sensing unit, and more preferably also the key, has at least outer surfaces of material transparent to the radiation but opaque to visible light thereby to disguise the positions of the emitter or emitters and the receiver or receivers. This could be achieved by pigmentation of the materials of the sensing unit and key or by coating with a filter material opaque to visible light but transparent to the particular radiation used.

Preferably the propagation path is defined between at least two reflectors, and may be defined at least in part between two reflectors at substantially 90" to each other, and each inclined at substantially 45 to the direction of radiation incident upon the first reflector, the reflectors being arranged so that an incoming beam of radiation is returned substantially parallel, but travelling in the opposite direction, to the radiation incident upon the first reflector.

The propagation path is preferably substantially within the key.

In a preferred embodiment the radiation utilised is electromagnetic, in particular infrared radiation.

Signals from the receivers can be fed to a conventional electronic circuit which operates relay or other switching means. The circuit can be arranged to switch only when all the receivers are activated or when specific receivers are activated or non-activated. The latter case prevents tampering or accidental operation by flooding the receivers with radiation from another source. Preferably the key, when in an enabling position, prevents at lest one receiver from detecting radiation from the emitter. There may be a separate emitter associated with each receiver, or the radiation from at least one emitter may be directed by the key, when in an enabling position, to more than one receiver.

The emitter may be arranged to pulse at a particular rate and the circuit tuned to recognise only the same pulse rate at the receivers.

This arrangement has the advantage of providing a higher intensity emission as an increased current in the emitter can be employed, and the further advantage of increased security against unauthorised enablement or operation.

In a preferred embodiment radiation having a distinguishing characteristic is emitted from at least one emitter, at least one receiver being adapted to detect the characteristic and to distinguish radiation having that characteristic from radiation lacking that characteristic.

The characteristic may be the wavelength of the radiation or, as described earlier, radiation may be chopped or pulsed at a predtermined frequency, that frequency being the characteristic.

Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a diagrammatic cross-sectional view of a first security system in accordance with the invention; Figure 2 is an underneath plan view of the key of the system shown in Figure 1; Figure 3 is a diagrammatic cross-sectional view of a second security system in acordance with the invention; Figure 4 is an underneath plan view of the system shown in Figure 3; Figure 5 is a diagrammatic underneath plan view of a third security system in accordance with the invention; Figure 6 is a diagrammatic cross-sectional view of a fourth security system in accordance with the invention; Figure 7 is a diagrammatic cross-sectional view of a fifth security system in accordance with the invention;; Figure 8 is a perspective view of a sixth security system in accordance with the invention; Figure 9 is a diagrammatic cross-sectional view of the system shown in Figure 8; Figure 10 is an underneath plan view of the key of the system shown in Figure 8; Figure ii is a biock diagram of part of the circuit of a security system according to the invention; and Figure 12 is a schematic diagram of the circuit of the security system shown in part in Figure 11.

Figure 1 shows a sensing unit 1 comprising an infra-red emitter 2 and four infra-red receivers 3 (only three of which are shown) mounted on a PCB 4 and set in apertures of a plate 5, the plate and the PCB being mounted within a housing 6. Leads 7 from the PCB are connected to an external control circuit (not shown). The sensing unit 1 is mounted on a machine (not shown) having a removable guard 8 to which a key 9 is fixed. The key 9 is provided on its underside with transmission means in the form of polished reflective facets 10, which are arranged such that when the guard is in a closed position, as shown in Figure 1, the key is in an enabling position relative to the sensing unit and infra-red radiation from the emitter 2 is reflected by the facets 10 onto the receivers 3.The signals from the receivers 3 are then passed through leads 7 to the external control system to start the machine or enable it to be started, the guard now having been identified as the correct guard and in such a position as to render the machine safe to use. The underside 11 of the key and the top surface 1 2 of the sensing unit are coated with a material which is impervious to visible light thus giving a 'dead front' appearance but transparent to infra-red so that the position of the emitter and receivers, and the facets, cannot be discerned and the likelihood of tampering is reduced.

Figures 3 and 4 show a scheme of a similar security system to that shown in figures 1 and 2. They show a security device for a sliding protective guard of a machine, such as a lathe. The infra-red beam emitted by emitter 2 is reflected at four facets of reflector 1 0a of the key 9. The facets are inclined at 45" to the direction of the emitter beam and are so constructed and arranged as to split a beam incident from the emitter into four separate reflected beams in the same plane, the incident beam being normal to that plane. Each of the four reflected beams is at right angles to its respective adjacent reflected beam. Four second reflecting facets 1 Ob are also provided on the key 9. Each facet lOb corresponds to one of the four beams reflected from facets 1 Oa, and is positioned to intersect the plane of the reflected beam and to reflect it towards associated receiver 3.

Four receivers 3 are provided within the lock housing, one or more of which is located so as to detect infra-red radiation reflected from the second reflecting facets 1 Ob when the key 9 is in the enabling position. At least one of the receivers 3 is positioned so as to receive substantially no infra-red radiation when the key is in an enabling position. A predetermined combination of detecting, and not detecting, infra-red radiation by the receivers is required before logic circuitry will allow operation of the machine for which the system shown in Figures 3 and 4 is a security system. The necessity for at least one of the receivers 3 to receive no infra-red radiation enables the sensing unit 1 to distinguish between general radiation and the selective radiation received in the enabling position of the guard 8.

The security systems of figures 1, 2, 3 and 4 are all suitable for sensing the position of guards on machines. The sensing unit 1 is attached to the machine or stationary part of the guard and the reflecting key 3 is attached to the guard. The sensing unit 1 will disable the machine unless the guard is correctly located in the enabling position.

The embodiments of figures 1, 2, 3 and 4 are particularly suited for use in conjunction with sliding guards. Since the emitted and received beams are substantially parallel, these embodiments have the advantage of allowing the reflector to move along the direction of the beams while still operating correctly. This reduces the need for great precision in the sliding mechanism of the guard.

The sensing unit will, however, still detect any significant movement at right angles to the emitted beam.

The mechanisms of figures 1, 2, 3 and 4 can, however, be adapted for use with removable or hinged guards by angling the reflectors 1 Oa and lOb such that the emitted and returned beams are not parallel. In this way they will respond to a small movement of the key in the direction of the emitted beam, which is necessary to detect the opening of such guards.

Figure 5 shows another scheme of a security system similar to that shown in the previous figures except that there are separate emitters 3, not shown. Reflecting facets 1 0a reflect the infra-red radiation incident from each of emitters 3 onto one of four second reflecting facets lOb.

Each of the facets 1 Oa and 1 0b is at substantially 45t to its incoming beam, and together they return the reflected beam in the direction substantially opposite, and parallel to, that of the emitted beam. A separate receiver is provided for each reflected beam.

This system enables the emitted and returned beams to be maintained more accurately parallel to each other and is therefore suitable for situations where the key 9 is some distance from the sensing unit 1.

Figure 6 shows a scheme for a different security system having only one reflector in the propagation path of the infra-red.

Reflecting facets 1 0c which reflect the incident beam from the emitter 2 direct to the receivers 3 are provided on the key 9. The receivers 3 are masked by shrouds 3c so that they can receive radiation substantially from only one direction.

The emitted beam is split into two by the reflector 1 Oc, and each of the reflected beams so produced is aimed at a specific receiver when the guard 8 is in the enabling position.

As in the previous embodiments at least one additional receiver 3 is provided, and is located in such a position that in the enabling position of the guard 8 it receives no infra-red radiation.

The embodiment of figure 10 is particularly suited for hinged or removable guards due to its sensitivity to movement in any direction.

Figure 7 shows a similar security system to that of Figures 1 to 5, applied to a machine guard 8', but with the receivers 3' placed at right angles to any unauthorised infra-red flooding. In this embodiment the emitter 2' emits infra-red into the key 9' which is reflected by a reflector cone 1 3 and a chamfer reflector face 1 4 mounted in a boss 1 5 fixed to the guard 8'. Internal reflector faces 10' of the key reflect the infra-red through the sides of the key 9' onto the receivers 3'. The body 1 7 of the key is made up of pigmented material transparent to infra-red which conceals the position of the reflector faces 10', 13, 14, Figures 8 to 10 show a further security system of more general application in which the key 9" takes the form of a flat card or tag.A body portion 1 8 lies between top and bottom layers 19, and surrounds and locates bodies 10" which incorporate reflective surfaces. Infra-red from the emitter 2" is reflected by the reflective surfaces of the key 9" onto receivers 3" located remotely from the emitter 2". The emitter 2" and receivers 3" are set in apertures in the base 5" of a box-like sensing unit unit 1" having a slot 20 in which the key 9" is received. The PCB 4" upon which the emitter 2" and receivers 3" are mounted is housed beneath the sensing unit 1".

Figure 11 shows in diagrammatic form the emitter circuit 21 connected to the infra-red emitter 2a. The emitter is arranged to emit pulses of infra-red at a rate of 1 KHz. The key 9a, attached to a machine guard (not shown), is shown to have reflective faces 1 0d which, when the key 9a is in its enabling position, direct infra-red onto three of four receivers 3a, 3b.

Each receiver 3a, 3b is connected to a comparators 22 to 25 which has its other input connected to a rail 26 to which a pre-set voltage is applied. The outputs of comparators 22 to 24 are connected to the inputs of inverters 27 to 29 respectively, whose outputs are connected to three inputs of a fourinput AND gate 30. The fourth input of the AND gate 30 is taken from the output of the fourth comparator 25, and the TTL output of the AND gate is fed to the control circuitry governing the switching of the machine, which may comprise a relay or further control logic, for example.

When no infra-red is received, all the comparator outputs are high, so the inverted inputs to the AND gate are low and the noninverted input high, so the TTL output is low.

However, when the key is in the enabling position, receivers 3a are energised causing the outputs of comparators 22 to 24 to go low, and hence the respective inputs to the AND gate high. If the sensing unit is operated by the key, no infra-red is received by receiver 3b and the output of comparator 25 remains high, and the TTL output of the AND gate is switched to high. If, however, the sensing unit is flooded with infra-red in an attempt to unlock the mechanism without closing the guard, receiver 3b will cause the output of comparator 25 to go low and the output of the AND gate will remain low even though its inverted inputs are switched to high. In this way, this particular arrangement guards against unauthorised enablement by flooding the sensing unit with infra-red.

Figure 1 2 is a circuit diagram of the security system shown in Figure 11, with a power supply circuit shown at 40. The emitter circuit for the emitter 2a is shown at 21 and incorporates a pulse generator based on the integrated programmable timer circuit ICRS2240.

A read circuit 42 is fed by receivers 3a, 3b.

The emitter 2a and receivers 3a, 3b take the form of an infra-red light emitting diode and infra-red photodetector diodes respectively.

The read circuit 42 includes an it339 which is a integrated comparator circuit and to which the receiver diodes 3a, 3b are connected.

The outputs of the comparators are fed to IC40106B which is an integrated inverter circuit, except that comparator output associated with receiver 3b which is fed directly to IC4073B, a triple 3 input AND gate integrated circuit. The inverter outputs are also fed to IC4073B. The TTL output of the AND gate IC4073B is connected to the machine control system (not shown). In Figure 8, la denotes LED's which display the status of the inputs to the AND gate IC4073B, and Ib denotes an LED which displays the status of the output of the AND gate.

Although infra-red is a suitable form of radiation to use in security systems of the above type, other wavelengths could be used, for example, microwaves or visible light, or ultrasonic waves, by substituting appropriate emitters, receivers and transmission means.

Systems employing pulsed emitters could be arranged such that the sensing unit will respond only to pulses delivered in coded sequence, thereby increasing the security of the system against unauthorised enablement or operation.

Claims

1. A security system for machinery and other areas to which access is to be restricted comprising a movable guard member and a co-operating frame member, movement of the guard member away from the frame member giving access to the restricted area, and a sensing unit on one of the said members cooperating with a key on the other member, the sensing unit incorporating at least one emitter for the emitting of radiation, at least one receiver for the receiving of radiation, and the key incorporating transmission means which provides a propagation path by way of which the radiation is transmitted from at least one said emitter to at least one said receiver only when the guard member is in an enabling position in relation to the frame member in which it prevents access to the restricted area, receipt of a signal from the emitter by the receiver via the transmission means in the key results in an enabling signal which controls a function which is to be allowed to occur only when the guard member is in the said enabling position.

2. A security system according to claim 1 in which the transmission means comprises one or more reflective surfaces by means of which when the key is in the enabling position radiation from at least one emitter is directed to at least one receiver.

3. A security system according to claim 2 in which the propagation path is defined between at least two reflectors.

4. A security system according to claim 3 in which the propagation path is defined at least in part betwen two reflectors inclined at substantially 90" to each other, and each inclined at substantially 45 to the direction of radiation incident upon the first reflector, the reflectors being arranged so that an incoming beam of radiation is returned substantially parallel, but travelling in the opposite direction, to the radiation incident upon the first reflector.

5. A security system according to any preceding claim in which the propagation path is subtantially within the key.

6. A security system according to any preceding claim in which the sensing unit has at least outer surfaces of material transparent to .the radiation but opaque to visible light thereby to disguise the positions of the emitter or emitters and the receiver or receivers.

7. A security system according to any preceding claim in which the key has at least an outer surface of material transparent to the radiation but opaque to visible light thereby to disguise the positions of the transmission means.

8. A security system according to any preceding claim in which the radiation is infra-red radiation.

9. A security system according to any preceding claim in which radiation having a distinguishing characteristic is emitted from at least one emitter, at least one receiver being adapted to detect the characteristic and to distinguish radiation having that characteristic from radiation lacking that characteristic.

1 0. A security system according to claim 9 in which the characteristic is the wavelength of the radiation.

11. A security system according to claim 9 in which the characteristic is that the radiation is chopped or pulsed at a predetermined fre quency.

1 2. A security system according to any preceding claim in which there is a separate emitter associated with each receiver.

1 3. A security system according to any of claims 1 to 11 in which the radiation from at least one emitter is directed by the key, when in an enabling position, to more than one receiver.

14. A security system according to any preceding claim in which the key, when in an enabling position, prevents at least one receiver from detecting radiation.

1 5. A security system substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

1 6. A security system substantially as described with reference to Figures 3 and 4 of the accompanying drawings.

17. A security system substantially as described with reference to Figure 5 of the accompanying drawings.

18. A security system substantially as described with reference to Figure 6 of the accompanying drawings.

1 9. A security system substantially as described with reference to Figure 7 of the accompanying drawings.

20. A security system substantially as described with reference to Figures 8 to 10 of the accompanying drawings.

21. A security system substantially as described with reference to Figures 11 and 1 2 of the accompanying drawings.