Priority Documents

[0001] The present application claims priority from Australian Provisional Application No. 2020901906 titled “EXCLUSION ZONE MONITORING” and filed on 10 June 2020, the content of which is hereby incorporated by reference in its entirety.

Background of the Invention

[0002] The present invention relates to a method and apparatus for monitoring an exclusion zone, and in one particular example, to a method and apparatus using a light curtain arrangement to selectively provide access to an exclusion zone.

Description of the Prior Art

[0003] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0004] Exclusion zones are used in a wide variety of circumstances to prevent ingress of people, equipment or other objects into a defined area. This may be performed for the purpose of safety and/or to prevent damage to equipment or the like. For example in the construction industry, exclusion zones are commonly used to prohibit the entry of personnel into dangerous areas, established through the risk assessment process for a construction activity. Thus, where equipment such as an excavator, crane, brick laying machine or similar is used, an exclusion zone might be defined to prevent individuals entering a region where they could inadvertently come into contact with the equipment.

[0005] It is known to monitor exclusion zones using light curtains, which are opto-electronic devices that are used to safeguard personnel in the vicinity of moving machinery with the potential to cause harm such as presses, winders and palletisers. Light curtains can be used as an alternative to mechanical barriers and other forms of traditional machine guarding. By reducing the need for physical guards and barriers, light curtains can increase the maintainability of the equipment they are guarding. The operability and efficiency of machinery can also be improved by the use of light curtains by, for example, allowing easier access for semi-automatic procedures.

[0006] Whilst light curtains are useful for this purpose, they suffer from the disadvantage that they are indiscriminate, and prevent any access to the exclusion zone, when there may be situations when it is desirable to allow authorised individuals into the zone to perform specific tasks. In this situation, it is typical to simply disable the light curtain, which renders the exclusion zone unprotected, meaning any operations within the exclusion zone must be ceased to prevent inadvertent injury. This in turn prevents individuals entering the zone for example to interact with operative equipment or the like.

Summary of the Present Invention

[0007] In one broad form, as aspect of the present invention seeks to provide a system for monitoring an exclusion zone, the system including: a) a light curtain including a plurality of segments each including an emitter and a receiver separated by an opening, wherein the emitter is configured to emit beams of electromagnetic radiation across the opening to the receiver, and the receiver is configured to detect received beams, wherein the light curtain is configured to include: i) a plurality of perimeter segments defining a perimeter extending at least part way around the exclusion zone; and, ii) at least one zone access segment positioned proximate a perimeter access segment to define an access zone adjacent the perimeter; and, b) a control system configured to: i) monitor one or more segments by:

(1) acquiring signals from one or more receivers of the perimeter segments, the signals being indicative of detection of the beams; and,

(2) using the signals to detect intrusion into the exclusion zone in response to obstruction of one of the beams; and, ii) permit access to the exclusion zone by selectively enabling or disabling the zone access segment and perimeter access segment.

[0008] In one embodiment: a) enabling a segment includes at least one of: i) enabling the emitter; and, ii) monitoring the segment; and, b) disabling a segment includes at least one of: i) disabling the emitter; and, ii) not monitoring the segment.

[0009] In one embodiment, the control system is configured to permit ingress into the exclusion zone by: a) enabling the zone access segment and disabling the perimeter access segment to allow entry into the access zone; and, b) disabling the zone access segment and enabling the perimeter access segment to allow entry into the exclusion zone.

[0010] In one embodiment, the control system is configured to permit egress from the exclusion zone by: a) enabling the zone access segment and disabling the perimeter access segment after entry into the access zone; and, b) disabling the zone access segment and enabling the perimeter access segment after exit from the access zone.

[0011] In one embodiment, the control system includes first and second inputs that control the perimeter access segment and the zone access segment.

[0012] In one embodiment, the first input is located external to the perimeter and the second input is located within the access zone.

[0013] In one embodiment, the inputs are switches.

[0014] In one embodiment, the switches are configured so that: a) with the first switch in a first position and the second switch in a second position the zone access segment is disabled and the perimeter access segment is enabled; b) with the first switch in a second position and the second switch in the second position the zone access segment is enabled and the perimeter access segment is disabled; and, c) with the first switch in the second position and the second switch in a first position the zone access segment is disabled and the perimeter access segment is enabled.

[0015] In one embodiment, the first and second switches are rotary binary switches.

[0016] In one embodiment, the first and second switches are configured to be locked in the first position using a lock.

[0017] In one embodiment, the inputs include biometric sensors.

[0018] In one embodiment, the control system includes a biometric sensor and the control system is configured to use sensed biometric information to determine if a person is authorised to enter the exclusion zone.

[0019] In one embodiment, the zone access segment is positioned within the perimeter and spaced from the perimeter access segment.

[0020] In one embodiment, the zone access segment and the perimeter access segment are joined by at least one of: a) one or more physical barriers; and, b) one or more light curtain segments.

[0021] In one embodiment, in response to detection of intrusion into the exclusion zone the control system is configured to at least one of: a) generate an audible alert; b) generate a visual notification; and, c) cause equipment within the exclusion zone to deactivate. [0022] In one embodiment, the control system is configured to transmit signals indicative of a state of the light curtain to equipment, the equipment being responsive to intrusion to deactivate.

[0023] In one embodiment, the control system is configured to operate in different operating modes, including at least one of: a) an operative mode in which the perimeter segments are enabled and monitored; b) an inactive mode in which the perimeter segments are disabled; and, c) a mute mode in which the perimeter segments are enabled but not monitored.

[0024] In one embodiment, one or more emitters and receivers are independently powered by a battery that is charged by a solar panel.

[0025] In one embodiment, a signal indicative of a break in an upstream segment of the light curtain is transmitted to a master controller of the control system via a wireless optical transmission path.

[0026] In one embodiment, the signal indicative of a break in an upstream segment of the light curtain causes a sequential break in each downstream segment of the light curtain until the master controller receives the break signal.

[0027] In one embodiment, each downstream segment of the light curtain is broken by a signal transmitted from a local controller that disables an associated emitter.

[0028] In one embodiment, the local controller sends the signal to disable an associated emitter in response to another signal indicative of an adjacent receiver detecting a break in the beam.

[0029] In another broad form, an aspect of the present invention seeks to provide a method for monitoring an exclusion zone, the method including: a) providing a light curtain including a plurality of segments each including an emitter and a receiver separated by an opening, wherein the emitter is configured to emit beams of electromagnetic radiation across the opening to the receiver, and the receiver is configured to detect received beams, wherein the light curtain is configured to include: i) a plurality of perimeter segments defining a perimeter extending at least part way around the exclusion zone; and, ii) at least one zone access segment positioned proximate a perimeter access segment to define an access zone adjacent the perimeter; and, b) using a control system to: i) monitor one or more segments by:

(1) acquiring signals from one or more receivers of the perimeter segments, the signals being indicative of detection of the beams; and,

(2) using the signals to detect intrusion into the exclusion zone in response to obstruction of one of the beams; and, i i ) permit access to the exclusion zone by selectively enabling or disabling the zone access segment and perimeter access segment.

[0030] It will be appreciated that the broad forms of the invention and their respective features can be used in conjunction and/or independently, and reference to separate broad forms is not intended to be limiting. Furthermore, it will be appreciated that features of the method can be performed using the system or apparatus and that features of the system or apparatus can be implemented using the method.

Brief Description of the Drawings

[0031] Various examples and embodiments of the present invention will now be described with reference to the accompanying drawings, in which: -

[0032] Figure 1A is a schematic plan view of an example of an exclusion zone and a system for monitoring the exclusion zone;

[0033] Figure IB is a schematic side view of an example of a light curtain segment;

[0034] Figure 2A is a flow chart of an example of an intrusion detection process;

[0035] Figure 2B is a flow chart of an access process;

[0036] Figures 3 A to 3 C are schematic plan views illustrating an example of an ingress process; [0037] Figures 4A to 4C are schematic front views of example switch configurations of an ingress process;

[0038] Figure 5 is a schematic diagram of an example of the control system;

[0039] Figure 6 is a flow chart of a specific example of an ingress process;

[0040] Figure 7 is a flow chart of a specific example of an egress process;

[0041] Figure 8 is a schematic plan view of a further example of an exclusion zone and a system for monitoring the exclusion zone; and;

[0042] Figure 9 is a schematic plan view of yet a further example of an exclusion zone and a system for monitoring the exclusion zone.

Detailed Description of the Preferred Embodiments

[0043] An example of a system for monitoring an exclusion zone will now be described with reference to Figures 1A and IB.

[0044] In this example, an exclusion zone EZ is defined by a combination of a physical barrier B and a light curtain, which together extend around the exclusion zone EZ, so that the exclusion zone EZ can only be entered by passing through the light curtain. It will be appreciated that this particular configuration is for the purpose of example only and a physical barrier may not be required if the light curtain extends around an entire perimeter of the exclusion zone EZ.

[0045] The light curtain is formed from a number of perimeter segments SP, each of which includes an emitter 121 and a receiver 122 separated by an opening O. The emitter 121 is configured to emit beams of electromagnetic radiation 125 across the opening O to the receiver 122, with the receiver 122 being configured to detect received beams. In one particular example, a module 120 can be provided which includes a base 126 that supports the emitter 121 and receiver 122 in back-to-back abutment, so that the emitter 121 forms a part of one perimeter segment SP and the receiver 122 forms part of another adjacent perimeter segment SP. It will be noted that ends of the light curtain do not require both an emitter 121 and receiver 122, and hence a module 120 may include an emitter 121 only, or receiver 122 only, as required. [0046] In the above described example, each emitter 121 can include a number of radiation sources 123, with the receiver 122 including corresponding detectors 124. The nature of the radiation sources 123 and the detectors 124 will vary depending upon the preferred implementation. For example, the emitters could include laser diodes that generate low power laser beams, whilst the detectors 124 could include optical detectors. In one specific example, the light curtain uses Detem4 Core transmitter and/or receiver light curtains from SICK.

[0047] In addition to the exclusion zone EZ, an access zone AZ is defined by at least one zone access segment SZA . which is positioned proximate a perimeter access segment SPA, which is one of the perimeter light curtain segments that is selected to be a suitable access point into the exclusion zone EZ. The zone access segment SZA is a light curtain segment, and hence includes an emitter 121 and corresponding receiver 122, similar to those described above. In this example, the zone access segment SZA is positioned inwardly of the exclusion zone perimeter, spaced from the perimeter access segment SPA and with physical barriers 131, 132 interconnecting the zone access segment SZA and the perimeter access segment SPA, so that the access zone AZ is enclosed. It will be appreciated however that this configuration is not essential and a number of variations are possible. For example, the zone access segment SZA could be connected to the perimeter access segment SPA using light curtain segments. Additionally and/or alternatively the zone access segment SZA could be positioned outwardly of the perimeter, so the access zone AZ is outside the perimeter.

[0048] The system further includes a control system 110. The control system 110 is typically adapted to acquire signals from one or more of the receivers 122, and use these to determine whether intrusion into the exclusion zone has occurred, and optionally trigger an appropriate response. Additionally, the control system 110 can be configured to permit access to the exclusion zone by selectively enabling or disabling the zone access segment SZA and the perimeter access segment SPA .

[0049] Examples of the control processes implemented by the control system will be described with reference to Figures 2A and 2B.

[0050] In this example, Figure 2A represents an intrusion detection process, whereas Figure 2B represents an exclusion zone EZ access process. Typically, these processes run in parallel substantially independently, however this is not essential and it will be appreciated that alternatively these two processes could be run as a part of a single overall control process.

[0051] In any event in this example, at step 200 the control system 110 receives signals from one or more of the receivers 122. At step 210 the control system 110 uses the signals to ascertain if any intrusion has occurred, and if not the process returns to step 200. In the event that intrusion into the exclusion zone EZ is detected at step 210, action can then be taken such as generating an alert and/or disabling machines or equipment at step 220. These processes will be described in more detail below, and in any event it will be appreciated that these largely correspond to a standard light curtain exclusion zone control process.

[0052] In one example, a signal indicative of a break in an upstream segment of the light curtain is transmitted to a master controller of the control system via a wireless optical transmission path. In this regard, the signal indicative of a break in an upstream segment of the light curtain causes a sequential break in each downstream segment of the light curtain until the master controller receives the break signal. In one implementation, each downstream segment of the light curtain is broken by a signal transmitted from a local controller that disables an associated emitter. The local controller sends the signal to disable an associated emitter in response to another signal indicative of an adjacent receiver detecting a break in the beam. In this way, the control system 110 does not necessarily monitor signals from each receiver and may only monitor the signal from a terminal receiver located proximate the master controller (i.e. the most downstream node in the light curtain chain). In an implementation such as this, break signals in segment of the light curtain may be transmitted via an optical path instead of an electrical path which minimises the amount of cabling required onsite.

[0053] When intentional access to the exclusion zone is required, the exclusion zone control process shown in Figure 2B is utilised.

[0054] In this example control system 110 operates to determine if access is required at step 250. The manner in which the control system 110 determines that access is required varies depending upon the preferred implementation, and this can, for example, involve the use of inputs, such as control at switches, sensors, or the like. Further examples will be described in more detail below. If access is not required, no action is taken and the control system 110 waits.

[0055] Assuming access is required, at step 260 the control system 110 selectively controls the zone access segment SZA and perimeter access segment SPA, in particular enabling or disabling the segments in order to permit access.

[0056] In a preferred example, the access zone is used in a manner similar to an airlock, in that the zone access segment SZA and perimeter access segment SPA are enabled and disabled in a sequence so that at least one segment is always functioning so that after entering the access zone AZ, the person can only exit once the entrance has closed. An example ingress sequence will now be described with reference to Figures 3A to 3C.

[0057] In the configuration shown in Figure 3A, the perimeter access segment SPA is initially enabled and the zone access segment SZA is disabled, although it will be appreciated the zone access segment SZA could alternatively be enabled.

[0058] When access is initially requested, the control system 110 will enable the zone access segment SZA and disable the perimeter access segment SPA, as shown in Figure 3B, allowing the person to enter the access zone AZ. It will be appreciated that the zone access segment SZA and perimeter access segment SPA could be enabled and disabled at the same time, or alternatively the zone access segment SZA could be enabled first, as long as both access segments are not disabled at the same time.

[0059] Once the individual enters the access zone AZ and is ready to enter the exclusion zone EZ, the control system 110 will operate to enable the perimeter access segment SPA and disable the zone access segment SZA, as shown in Figure 3C, allowing the individual to exit the access zone and enter the exclusion zone. Again, this enabling and disabling process is performed so that the perimeter access segment SPA and the zone access segment SZA are not disabled at the same time.

[0060] It will be appreciated that the egress from the exclusion zone EZ can be performed utilising the same steps in reverse, so that the person initially enters the access zone AZ with the access segments SZA, SPA in the configuration shown in Figure 3C, before the control system 110 enables the zone access segment SZA and then disables the perimeter access segment SPA, as shown in Figure 3B, allowing the person to leave the access zone AZ. Following this, the perimeter access segment SPA is enabled and the zone access segment SZA optionally disabled, returning to the configuration shown in Figure 3A.

[0061] A number of further features will now be described.

[0062] In one example, enabling a segment is achieved by enabling the emitter 121 or monitoring segment, and in particular acquiring and interpreting signals from the receivers 122. Similarly, disabling a segment can be achieved by disabling the emitter 121, or not monitoring signals received by the receiver 122.

[0063] In one example, the control system 110 includes first and second inputs that control the perimeter access segment SPA and zone access segment SZA. The nature of the inputs can vary depending upon the preferred implementation. In one example, inputs include switches, although alternatively sensors, such as presence sensors, biometric sensors, or the like, could be used.

[0064] In one example, the first input is located external to the perimeter, and can be used to enable or disable the perimeter access segment SPA, whilst the second input is located within the access zone AZ, allowing the zone access segment SZA to be controlled.

[0065] In one example, the first and second inputs are first and second switches. A variety of different types of first and second switches could be used, but in one example the switches are rotary binary switches. Such switches provide a number of advantages, in particular only allowing two different states to be controlled, whilst also allowing the current state of the switch to be easily verified by visual inspection.

[0066] In one particular example, the switches are configured so that when the first switch is in a first position and the second switch is in a second position, the zone access segment SZA is disabled and the perimeter access segment SPA is enabled. With the first switch in a second position and the second switch in the second position, the zone access segment SZA is enabled and the perimeter access segment SPA is disabled, whilst with the first switch in the second position and the second switch in the first position, the zone access segment SZA is disabled and the perimeter access segment SPA is enabled. It will be appreciated that this allows a person to enter the access zone AT. utilising the first switch and then traverse from the access zone AT. into the exclusion zone EZ using the second switch.

[0067] In one example, the first and second switches are configured to be locked in the first position using an isolation lock, such as a padlock or the like. This can be used to prevent access to the exclusion zone EZ by unauthorised personnel. For example, an isolation lock on the first switch can prevent unauthorised personnel entering the access zone AZ. whilst an isolation lock on the second switch also locks the perimeter access segment SPA into the enabled state preventing ingress when a person is already within the exclusion zone EZ.

[0068] In one example, the control system 110 includes a biometric sensor, in which case the control system can be configured to use sensed biometric information to determine if a person is authorised to enter the exclusion zone. For example, this could involve using the sensed biometric information to determine an identity of an individual attempting to enter the exclusion zone, with the identity being used to determine if the individual is permitted entry into the exclusion zone, for example by accessing a list of authorised personnel. Alternatively, sensed biometric information could be compared to pre-stored biometric data for authorised personnel. It will be appreciated that the nature of such biometric sensing could vary depending on the preferred implementation and this could include iris or retinal scans, facial recognition, fingerprint recognition, voice recognition, or the like. It will also be appreciated that other identifying information, could be used, such as using a passcode, such as a password, PIN, or similar.

[0069] Irrespective of the sensing performed, a single biometric sensor could be used in conjunction with alternative inputs, such as switches or the like, so that the individual is authorised using the biometric sensor and control of the perimeter access segment SPA and zone access segment SZA is performed utilising the switches. Alternatively however it will be appreciated that biometric sensors could be used as the first and second inputs, so that these provide a mechanism to both authorise the individual and control the access segments, for example by having sensors outside the perimeter and within the access zone AZ. [0070] As previously mentioned, the control system can be configured to respond to intrusion into the exclusion zone in a number of appropriate manners. This includes generating an audible alert, generating a visual notification, or causing equipment within the exclusion zone to deactivate, or enter a safe mode. Such actions could be triggered in any appropriate manner. For example, the control system may broadcast signals indicative of the state of the light curtain, with equipment being responsive to a change in state, such as breaching of the curtain to respond accordingly. In one example, such broadcast signals operate as a “dead man” switch, so that equipment can only function in the event that a signal is transmitted that confirms integrity of the light curtain. In this instance, if the light curtain and/or control system fails for any reason, the equipment will stop.

[0071] In one example the control system is configured to operate in different operating modes depending on the particular situation. For example, this can include an operative mode in which the perimeter segments are enabled and monitored, an inactive mode in which the perimeter segments are disabled, and a mute mode in which the perimeter segments are enabled but not monitored. This is particularly advantageous as the mute mode can be allowed to provide unrestricted access to the exclusion zone on a temporary basis. In particular, the light curtain segments remain active but are simply not monitored. In this mode, the control system will typically not transmit any signals and the equipment will remain inactive.

[0072] A specific example of control inputs will now be described with reference to Figures 4A to 4C.

[0073] In this example, the control inputs include first and second switch modules 440.1, 440.2, which are located outside the perimeter and within the access zone AZ, respectively. Each switch module is substantially identical and so the following describes both switch modules collectively, with the .1, .2 suffixes used to distinguish between switches omitted for ease of description. The switches 440 includes a body 441, a binary rotary switch 442, switch markings 443 indicating the current switch status, an indicator light 444 and an information panel 445, which shows instructions for use.

[0074] In the configuration shown in Figure 4A, the first switch 442.1 is in a first position and the second switch 442.2 is in a second position. An isolation lock 451 is attached to the first switch 442.1, so that the first switch 442.1 cannot be moved. The first and second indicator lights 444.1, 444.2 are illuminated red and un-illuminated respectively, showing that the perimeter access segment SPA is active and that the zone access segment SZA is inactive.

[0075] In the configuration shown in Figure 4B, the isolation lock has been removed and the first switch 442.1 moved to the second position, whilst the second switch 442.2 remains in the second position. In this configuration the first and second indicator lights 444.1, 444.2 are green and amber respectively, showing that the perimeter access segment SPA is inactive and the zone access segment SZA is active.

[0076] In the configuration shown in Figure 4C, the first switch 442.1 is in the second position and the second switch 442.2 is in the first position, with the second switch 442.2 being locked using an isolation lock 452. In this instance the first and second indicator lights 444.1, 444.2 are amber and green respectively, indicating that the perimeter access segment SPA is active and the zone access segment SZA is a disabled.

[0077] An example of the control system will be described in more detail with reference to Figure 5.

[0078] In this example control system 510 includes a processing device 511, such as a microprocessor or similar, a memory 512, a control input/output system 513, and an interface 514, interconnected via a bus 515. The control input/output system includes a status indicator light 513.1, a rotary binary switch 513.2, a key lock 513.3 andaresetbutton 513.4. The external interface 514 is connected to the first and second switch modules 440.1, 440.2. The control system 510 also includes external indicator lights 516, which typically act as traffic light notifications to show a status of the light curtain.

[0079] In use, the microprocessor 511 executes instructions in the form of applications software stored in the memory 512 to allow the required processes to be performed. The applications software may include one or more software modules, and may be executed in a suitable execution environment, such as an operating system environment, or the like.

[0080] Accordingly, it will be appreciated that the control system may be formed from any suitable processing system, such as a suitably programmed computer system, custom hardware, or the like. In one example, the control system 510 includes any electronic processing device such as a microprocessor, microchip processor, logic gate configuration, firmware optionally associated with implementing logic such as an FPGA (Field Programmable Gate Array), or any other electronic device, system or arrangement.

[0081] In use, and as previously mentioned, the light curtain can operate in three modes, including operative, inactive and mute modes. In general, the active and inactive modes are selected utilising the rotary switch 513.2, with the active mode being indicated by a green indicator light 516 and the inactive mode by a red indicator light 516. In the event that the light curtain is obstructed, the control system 510 generates a stop signal, which is transferred to necessary equipment, and switches the indicator light 516 to red. The control system 510 will then remain in this state until the reset button 513.4 is used to reset the system. The mute mode is selected using the key lock 513.3 so that the light curtain can only be muted by authorised personnel, with this being indicated by having the indicator light 516 turn orange. Finally, illumination of the light 513.1 is used to indicate the control system is active, independent of the particular operating mode.

[0082] A specific example process for entering the exclusion zone EZ will be described with reference to Figure 6.

[0083] For the purpose of this example, it is assumed that the switch modules are initially configured as shown in Figure 4A, with the access segments SPA, SZA configured as shown in Figure 3A.

[0084] In this example at step 600, typically a designated isolation officer removes the isolation lock 451 (e.g. a yellow lock belonging to the isolation officer) and toggles the first switch module 440.1 so the first switch 442.1 is moved to the second position at step 610, as shown in Figure 4B. In other words, the switch is toggled from NORMAL to PIZ (Person in Zone) to allow a person to enter the access zone AZ. This causes the control system 510 to disable the perimeter access segment SPA and enable the zone access segment SZA at step 620, as shown in Figure 3B.

[0085] At step 630 the person enters the access zone AZ and toggles the second switch at step 640 from NORMAL to PIZ. This causes the control system 510 to enable the perimeter access segment SPA and disable the zone access segment SZA as shown in Figure 3C. The person then attaches their personal danger lock (e.g. a red lock) 660, so that the second switch is retained in the first position (i.e. PIZ) as shown in Figure 4C, before entering the exclusion zone at step 670.

[0086] An example of a process for egress from the exclusion zone will now be described with reference to Figure 7.

[0087] For the purpose of this example, it is assumed that the switch modules are initially configured as shown in Figure 4C, with the access segments SPA, SZA configured as shown in Figure 3C.

[0088] At step 700 the person enters the access zone AZ and removes their personal dangerlock 452 at step 710, before toggling the second switch 442.2 into the second position at step 720, so that the switches are in the configuration shown in Figure 4B (i.e. toggling back from PIZ to NORMAL). This causes the control system 510 to disable the perimeter access segment SPA and enable the zone access segment SZA at step 730, so that the access segments SPA, SZA are configured as shown in Figure 3B.

[0089] At this stage the person can exit the access zone AZ at step 740, before toggling the first switch 750 into the first position at step 750 (i.e. toggling back from PIZ to NORMAL), which causes the control system 510 to enable the perimeter access segment SPA and disable the zone access segment SZA at step 760, as shown in Figure 3A. The isolation officer can then attach the isolation officer lock 451 at step 770, so the switches are configured as shown in Figure 4A.

[0090] It should be noted that in the above-described arrangements, if an access segment SPA, SZA to be enabled is obstructed, the segment will not be enabled and the other access segment will not be disabled, thereby effectively halting the access process.

[0091] Referring now to Figures 8 and 9, further specific examples of an exclusion zone and a system for monitoring the exclusion zone will now be described.

[0092] In Figure 8, there is shown a further example of an exclusion zone around a restricted access area (such as a building site) that comprises both a physical fence around part of the perimeter and a light curtain arrangement around the remaining part. In this arrangement, there are two light curtain segments, namely a first light curtain segment between sender (i.e. emitter) 801 and receiver 802 and a second light curtain segment between sender 803 and receiver 804. Each sender 801, 803 is independently powered by a solar panel and battery which obviates the need to run power cables from a source of site power (such as shore power supply, a generator or the work machine) to each sender. This significantly reduces the amount of cabling required on site and additionally would enable a light curtain chain to be easily extended for larger sites (e.g. construction sites, mine sites, roads etc). The arrangement in Figure 8 additionally includes an access zone AZ as previously described for selectively allowing a Person in Zone (PIZ) to access the exclusion zone to perform works without breaking the light curtain. In this example, the access zone AZ comprising light curtain access segments SPA, SZA is connected by electrical cable 805 to the work machine and would therefore be powered by the power source of the work machine.

[0093] Referring now to Figure 9, there is shown an example of an exclusion zone around a restricted access area (such as a building site) that comprises a light curtain arrangement only (i.e. there is no physical fence around the perimeter). In this arrangement, there are four light curtain segments comprising two chains in series, namely first light curtain chain including first light curtain segment between sender 901 and receiver 902 and second light curtain segment between sender 903 and receiver 904 and second light curtain chain including third light curtain segment between sender 905 and receiver 906 and fourth light curtain segment between sender 907 and receiver 908. In this example, senders 901, 903, 905, 907 and receivers 902, 906 are independently powered by a solar panel and battery.

[0094] The arrangement in Figure 9 additionally includes an access zone AZ as previously described for selectively allowing a Person in Zone (PIZ) to access the exclusion zone to perform works without breaking the light curtain. In this example, the access zone AZ comprising light curtain access segments SPA, SZA is connected by electrical cable 909 to the work machine and would therefore be powered by the power source of the work machine.

[0095] The light curtain chains described above are configured such that if the first light curtain segment is broken, receiver 902 does not detect any beam and a signal is provided to a local controller of adjacent sender 903 that disables the sender 903 and thereby also breaks the second light curtain segment. Receiver 904 therefore does not detect any beam and provides a signal to a master controller that an intrusion has been detected which triggers the work machine to deactivate. In a similar fashion, if the third light curtain segment is broken, receiver 906 does not detect any beam and provides a signal to a local controller of adjacent sender 907 that disables the sender 907 and thereby also breaks the fourth light curtain segment. Receiver 908 therefore does not detect any beam and provides a signal to a master controller that an intrusion has been detected which triggers the work machine to deactivate. In the above- described manner, the status of a light curtain segment is transmitted wirelessly via an optical path in series from an upstream node to a downstream node and the master controller which is able to deactivate the work machine if a break in the optical transmission path is detected upstream as a result of an intrusion.

[0096] Accordingly, it will be appreciated that the above-described examples provide a system for allowing access to an exclusion zone. In one particular example this is achieved utilising a light curtain access zone, which is analogous to an airlock where inner and outer doors of the airlock are formed from light curtain segments. The light curtain segments are selectively enabled/disabled, so that a person is able to enter and exit the access zone either from the outside of the exclusion zone or inside the exclusion zone. It will be appreciated that this provides individuals with access to the exclusion zone, whilst maintaining the integrity of the perimeter and preventing third parties accessing the exclusion zone inadvertently. Additionally, in at least some examples, one or more sender or emitter units may be powered by a battery which is charged by a solar panel to thereby reduce the amount of cabling required to setup the light curtain safety system. Also in some examples, the status of a light curtain may be transmitted via a wireless optical transmission path from an upstream to a downstream node by sequentially disabling each light curtain in a series chain until a master controller receives the signal that there has been a break in the light curtain. In this way, electrical cabling can be further reduced as status signals are not required to be transmitted electrically via cable back to the master controller.

[0097] Whilst reference has been made to people in the above description, it will be appreciated that this is for ease of description only and that in practice, the above-described techniques could be used to allow access for any entity or object. For example, this could be used to allow access for autonomous vehicles or similar. [0098] Furthermore, the above described ingress and egress processes assume the access zone is inside the perimeter. However, it will be appreciated that alternatively the access zone could be located outside the perimeter, in which case the ingress and egress procedures will be modified as needed.

[0099] The above described exclusion zone can be used in a wide range of different situations. In one particular example, this is used in conjunction with construction equipment, in which case the exclusion zone could represent a construction zone, such as a build site for a house or other similar building. In this case, the equipment being used could be an automated brick laying machine, examples of which are described in patent publications and co-pending applications US8166727, PCT/AU2008/001274, PCT/AU2008/001275,

PCT/AU2017/050731, PCT/AU2017/050730, PCT/AU2017/050728, PCT/AU2017/050739, PCT/AU2017/050738, PCT/AU2018/050698, AU2017902625, AU2017903310,

AU2017903312, AU2017904002, AU2017904110, PCT/AU2018/050698, AU2018902566, AU2018902557, PCT/AU2018/050733, PCT/AU2018/050734, PCT/AU2018/050740, PCT/AU2018/050737 and PCT/AU2018/050739, among others, the contents of which are incorporated herein by cross reference.

[00100] Throughout this specification and claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers. As used herein and unless otherwise stated, the term "approximately" means ±20%.

[00101] Persons skilled in the art will appreciate that numerous variations and modifications will become apparent. All such variations and modifications which become apparent to persons skilled in the art, should be considered to fall within the spirit and scope that the invention broadly appearing before described.