GB 1320002 relates to a detector system to detect the presence of a person or vehicle on a railway crossing. A transmitter is arranged to transmit a beam across the crossing onto a retro-reflective marker which reflects the beam to a detector. The presence of aperson or vehicle is inferred by detecting the absence of a reflected signal.

An analogous method is used in WO83/01855 to detect an intruder in a room.

EP2120216 relates to a personal security system having a light source that directs polarised light into a detection zone and a detector arranged to detect light from a retro-reflector. In one embodiment, detection of reflected light causes a controller to release a locking mechanism of a door to allow entry of a worker into a site. In an alternative embodiment illustrated in Fig 5, detection of reflected light, in conjunction to detection of the presence of person by a separate detector, prevents the operation of an alarm bell and light.

The current invention was conceived from efforts to provide a portable safety alarm system to detect and warn of the presence of a worker within a hazardous zone.

According to a first aspect of the invention there is provided apparatus for detecting and warning of the presence of a person or object carrying a retro-reflector; the apparatus comprising: i) an electromagnetic transmitter arranged to transmit electro magnetic radiation; ii) a detector arranged to detect electro-magnetic radiation transmitted in i) above that has been reflected by a retro-reflector; and iii) an alarm means arranged to be activated in response to the detector detecting said reflected electro-magnetic radiation.

In an application of the invention, the apparatus maybe mounted to machinery and arranged to warn an operator of said machinery of the presence of a worker wearing aretro-reflector (e.g. as part of a hi-vis garment) in a zone proximate the machinery such as a blind spot of the operator. Thus according to a second aspect of the invention there is provided a method to warn an operator of a machine of the presence of a person or object carrying a retro-reflector in a zone proximate the machinery; the method comprising: i) providing an electromagnetic transmitter arranged to transmit electro magnetic radiation into the zone proximate the machinery; ii) providing a detector arranged to detect electro-magnetic radiation transmitted in i) above that has been reflected by a retro-reflector within the zone proximate the machinery; and iii) providing an alarm means arranged to be activated, to alert the operator, in response to the detector detecting said reflected electro-magnetic radiation.

One particular use is to mount the apparatus, or at least that fall in parts i) and ii) above to vehicles which are operated around workers on the ground, e.g. construction vehicles on worksites or fork lift trucks in factories or depots.

In a variation, the apparatus maybe configured to detect and warn that a worker has left a safety zone. For example, the apparatus may be mounted to a road marker such as a traffic cone located on a highway, and used to warn a worker carrying out works on said highway that he has strayed too far away from the cone and consequently in danger of passing traffic. Thus according to a variation of the invention there is provided apparatus for detecting and warning that a person or object carrying a retro- reflector has left an inclusion zone, the apparatus comprising: i) an electromagnetic transmitter arranged to transmit electro magnetic radiation across the inclusion zone; ii) a detector arranged to detect electro-magnetic radiation transmitted in i) above that has been reflected by a retro-reflector within the inclusion zone; and iii) an alarm means arranged to be activated in response to the detector no longer detecting said reflected electro-magnetic radiation.

In another example the apparatus could be used as a security feature to detect the removal of an object carrying a retro-reflector from an area, e.g. a worksite.

The alarm means may be arranged to provide one or more of an audio, visual or haptic warning signal. In addition, the alarm means may be arranged to cause shutdown of machinery so to reduce the likelihood of an accident.

In one preferred embodiment the transmitter transmits a beam of electromagnetic radiation and the apparatus comprises means to adjust the direction of the beam to trace a pattern to define a detection zone. The pattern may, for example, be based on a set of Lissajous curves. It is further preferred that the apparatus is configured to selectively alter the shape of the detection zone by changing the pattern.

In another preferred embodiment the apparatus comprises means to alter the shape of the beam to alter the shape of the detection zone.

Where the transmitter is arranged to emit a wider angle beam, the shape of the detection zone may be selected using a mask placed in front of the transmitter. The mask has at least one aperture shaped to provide the desired shape of detection zone. The mask may be arranged to be removable or adjustable to vary the shape of the detection zone.

Both this and the pattern method allows the shape/ size of the detection zone to be varied to best suit the application in which it will be used.

In a preferred embodiment the apparatus comprises compensation means to compensate for a change in the orientation of the transmitter and/or detector. This feature is expected to be particularly beneficial when the apparatus is supported on a moving object such as portable machinery, e.g. a digger or forklift, to compensate for a change in the orientation of the transmitter and/or detector as a result of a change in orientation of the moving object; an example being . because the object is operating on uneven ground leading, without compensation, to all or a portion of the beam or pattern to be projected at too great an angle upwards into the air over the top of the person/object, or downwards into the ground.

One way to provide compensation is to change the shape of the beam, or pattern as described before. An alternative is to provide means to re-orientate the transmitter and/or detector in response to a detected change in orientation caused by movement of a moving object about which the transmitter is supported.

Retro-reflectors commonly used on safety clothing reflect transmitted light back with a plane of polarisation rotated by around 90° compared with the incident light. This can be used to improve the effectiveness of the apparatus by arranging the alarm to only be activated if the detected light has the same frequency as the transmitted light and has a plane of polarisation which is 90 degrees to that of the transmitted light. This can be achieved using a first polarisation filter to ensure that transmitted light is orientated in one plane, and a second polarisation filter to only allow light polarised in a plane rotated by an angle of 90 degrees from that of the transmitted light to reach the receiver. The invention will now be described by way of embodiment with reference to the following figures in which:

Figure 1 illustrates, schematically, portable apparatus for detecting a person/object carrying a retro-reflector R within an exclusion zone Z. The apparatus comprises a transmitter 1 arranged to transmit electromagnetic radiation. A first polarising filter 2 positioned in front of the transmitter 1, a receiver 4 arranged to receive the transmitted light that has been reflected from the retro-reflector R and a second polarising filter 3 positioned in front of the receiver 4. The first filter 2 allows through passage of light in a first plane of polarisation, the second filter 3 allows through passage of light in a second plane of polarisation which is rotated 90 degrees from the first.

The apparatus further comprises a processor 5 arranged to receive a signal from the receiver 4, a siren 6, light 7 and a shut down mechanism, e.g. kill switch, 8.

In operation the transmitter 1 is arranged to transmit electromagnetic radiation of a particular frequency in the visible spectrum across a zone Z. The transmitted light passes through filter 2 so that it is polarised in a single plane.

Light reflected by the retro reflector R has a polarisation in a plane approximately 90 degrees out from the incident radiation. The reflected light passes through the second filter 3 and is detected by receiver 4.

Upon detection of reflected light, the receiver 4 sends a signal to controller 5 which in response activates one or more of the siren 6,and light source 7 to provide a warning. The controller 5 may also optionally activate shut off mechanism 8.

In an alternative embodiment, the apparatus may be used to activate an alarm in the instance that it is detects that a person/object carrying a retro reflector has moved out of an inclusion zone. To provide this function the processor 5 is programmed to activate the siren 6 or light source 7 in the event that the receiver 4 does not detect light reflected from a retro-reflector R. Preferably the processor 5 will activate the alarm in the instance that the receiver 4 does not detect a retro-reflector R following a period in which it does detect a retro-reflector R. To reduce the likelihood of false alarm, it is preferred that the processor 5 is arranged to activate the alarm when the receiver stops detecting a retro-reflector for a specific length of time, e.g. 3 seconds.

Figure 2 illustrates the aforementioned apparatus housed in a unit 100 residing on a traffic cone C. The unit 100 comprises multiple transmitters and detectors so as to form an inclusion zone Y which extends substantially 360 degrees around the cone C. An alarm in the form of a light 6 and horn (not shown) is arranged to be activated in the instance that a retro-reflector is not detected for a specific period of time.

Figure 3 illustrates schematically an alternative embodiment similar to Fig 1 but with the addition of a mask 9 in front of the transmitter 1, and optionally in front of filter 2. The mask 9 comprises an opaque member having at least one aperture through which the transmitted light passes to form a pattern defining the detection zone. The pattern can be changed by using a mask with a different shape or pattern of apertures.

Figure 4 illustrates a further alternative embodiment that uses a number of moveable mirrors 10 to direct a beam of light 11 from the transmitter 1 in order to trace out a pattern to define the detection zone. The movement of the mirrors 10 is effected by a motor(s)not shown controlled by processor 5. Typically the pattern will be traced out repeatedly. A suitable pattern may be defined using Lissajous curves. Details of this are found in EP2120216 which is incorporated here by reference.

Figures 5A and 5B illustrate a detection and warning apparatus as described above mounted to a fork lift truck and earth mover respectively. They illustrate two difference shaped zones which may be selected. Figure 6 illustrates a further embodiment in which the transmitter 1, filters 2, 3, receiver 4 and control 5 are housed in a housing 20. Also housed within housing 20 is an accelerometer 21 and transmitter 26. The housing is supported to a vehicle 22 by first and second supporting members 23, 24. The first supporting member 23 is hinged to the vehicle (or alternatively the housing 20 is hinged to supporting member 23) to allow the housing's 20 orientation to vary with respect to the vehicle 22. The second supporting member 24 is telescopic, and with the aid of a motor 25, its length can be varied so as to cause the housing 20 to rotate relative to the vehicle 21.

Signals from the accelerometer 21 indicative of the housing's 20 orientation are received by the controller 5. In response to an indication that the housing's orientation has changed, the controller 5 causes operation of the motor 25 to extend or retract the telescopic member 24 to re-orientate the housing 20 towards a 'home' orientation relative to the horizontal. It will be evident that means other than a telescopic member, e.g. a toothed gear mech., could be used to re-orientate the housing to equal effect.

Upon receipt of a signal from the receiver 4 that a retro-reflector has been detected, the control 5 causes a wireless signal to be broadcast by transmitter 26 for receipt by a remove alarm means, e.g. a light or siren which may be mounted in the cabin of the vehicle.

Any of the earlier embodiments may incorporate a transmitter arranged to transmit are number of different wavelengths, preferably simultaneously, within the visible spectrum. The apparatus also comprises a RGB colour receiver 4A to detect light that has been reflected from the retro-reflector R. By determining which of the transmitted wavelengths are reflected, it is possible to identify retro-reflectors of different colours. This may be of use where, for example, it is wished only to cause an alarm to be activated in the instance that one colour of retro-reflector is detected (or not detected) whilst ignoring another colour of retro-reflector. The apparatus may also be used to activate different alarms depending on the colour of the retro-reflector detected (or not detected).