Patent Publication Number: US-8994576-B2

Title: Work area monitor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. National Phase patent application Ser. No. 13/810,608, filed Jan. 16, 2013, which claims priority to PCT/AU2011/001042, filed Aug. 16, 2011, which claims priority to Australian Patent Application No. 2010-903669, filed Aug. 16, 2010 and Australian Patent Application No. 2010-905280, filed Nov. 24, 2010, the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a work area monitor that employs radar to detect movement of a slope and raise an alarm if dangerous movement is detected. The invention is particularly useful for open cut mine sites and civil excavation sites, and potentially useful for underground mines. 
     BACKGROUND TO THE INVENTION 
     The use of radar to produce interferometry maps for identifying movement in a slope is known. U.S. Pat. No. 6,850,183 describes a slope monitoring system that consists of a radar module that records radar images of a selected slope and a video module that records visual images of the same slope. A data processor performs coordinate registration to align the radar images and the visual images. Slope movement is detected by interferometry. The invention is embodied in a product produced by GroundProbe Pty Ltd that is referred to as the SSR. 
     The SSR product has been used very successfully to monitor the stability of large slopes in open-cut mines. The SSR has detected and provided an alarm prior to many hundreds of large slope failures and is widely recognised as an essential mine safety tool. Nonetheless, the SSR is not ideal for all situations. 
     Mine workers are exposed to a number of major hazards including sudden or unexpected movement of ground in their immediate work area. Mine workers are not equipped with the knowledge or tools to understand whether a wall that they are planning to work under is and remains safe. SSR is used by mine geotechnical engineers to assess overall slope stability over an extended period, typically days or weeks, and to critically monitor slopes that are actively moving and may become unsafe. The complexity of SSR allows for geotechnical engineers to assess movement types and movement rates across multiple work areas of a mine from long ranges, with alarm capability to a central location. However there are specific work areas in a mine that are not adequately covered or alarmed by SSR. What is required is a simple short-range, fast-scanning tool that can be operated directly by a work crew and can provide a local alarm with sufficient warning when a movement occurs within the work area. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide a Work Area Monitor (referred to as WAM). 
     It is another object of the invention to overcome or at least alleviate one or more of the above limitations. 
     Further objects will be evident from the following description. 
     SUMMARY OF INVENTION 
     In one form, although it need not be the only or indeed the broadest form, the invention resides in a Work Area Monitor comprising; 
     a radar module that scans a selected field of view and collects radar images; 
     a display that shows an image of the field of view; 
     a processor that processes the radar images interferometrically to extract movement data and analyse the movement data; 
     an alarm that provides an audible, visible or tactile warning if the movement data exceeds a threshold; and 
     a motorised vehicle mounting the radar module and the processor. 
     The image of the field of view may be overlaid with the movement data on the display. Suitably this will only be if the movement data exceeds the threshold, although movement data below the threshold could be displayed if desired. 
     The Work Area Monitor may also include a camera. The camera is suitably a digital camera capable of recording sequential still images or video images. The camera is preferably mounted on the vehicle separate from the radar module. Alignment between the radar field of view and the camera field of view is preferably set up during manufacture. The camera preferably takes a new image during every radar scan so any movement of the slope measured by the radar and the location of the movement is visually captured at the time of detection. The camera may have low light capability to work effectively at night. 
     The radar module is preferably mounted on a scanning gimbal with a scan increment of 2° horizontally×2° vertically. This is a larger scan increment than an SSR but the work area monitor is located much closer to the wall and the scan increment of 2.0 m×2.0 m at 60 meters range is sufficient to detect rock falls, sub-bench and multi-bench failures in the work area. The scan area may be rectangular and is selectable by the operator to focus on the immediate work area. A typical scan time for an immediate work area is one minute or less, which is much shorter than an SSR and can provide earlier warning of rapid slope failure to the work crew. Typical scan duration for the immediate work area is one shift, or up to 12 hours, which is much shorter than many days or weeks of scan duration for an SSR. 
     The processor compares successive radar images on a pixel by pixel basis to identify pixels that indicate slope movement of greater than a selected threshold. Suitably the threshold is chosen to be above the error stack of the work area monitor. For the embodied invention, a suitable threshold of 5 mm has been chosen. The threshold may be different in other embodiments but in general the inventors envisage that the threshold will be 5 mm or less. A higher error stack over the SSR can be accommodated by the work area monitor because its scan rate is much quicker and the alarm is localised to the work area only. The operational range of the radar module and processor is about 30 m to about 200 m. This range is short compared to the typical range of an SSR which may be 1000 m or more. 
     The display may display a synthetic image of the field of view generated from the radar images. The synthetic image may be generated by the processor, or another processor specific to the application. A suitable synthetic image is a digital terrain map. Alternatively the display displays the images recorded by the camera. 
     The alarm is preferably an audible and visible alarm on the Work Area Monitor platform and may further comprise a personal alarm that is remote from the Work Area Monitor but in communication with the local work area. The personal alarm suitably receives alarms from the processor and generates a local alarm. The personal alarm may be carried by a worker and suitably generates tactile and audible alarms. 
     The vehicle is typically a utility automobile having a cabin and tray back. The vehicle provides a motorised platform for deployment of the Work Area Monitor and the engine may provide a source of power. The cabin may suitably be climate controlled in which case the processor, other electronics and display may be mounted in the cabin. 
     The vehicle may be mechanically stabilised using legs or jacks. 
     The work area monitor may further comprise a movement detector mounted on the vehicle that detects any movement of the vehicle that could be misinterpreted as a slope movement. Before an alarm is raised by the processor the movement detector is checked to ensure the vehicle has not moved at a time that could have caused the alarm. 
     The work area monitor may further comprise an anomaly detector module that detects any foreground activity in the field of view that could cause a false alarm. 
     Suitably the work area monitor further comprises a touch screen interface for set up and operation. Using the touch screen interface a user can select the field of view of the work area monitor and can select a spotlight mode that selectively monitors a subset of the field of view. 
     Further features and advantages of the present invention will become apparent from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, preferred embodiments of the invention will be described by way of example only with reference to the accompanying drawings, in which: 
         FIG. 1  shows an image of a Work Area Monitor; 
         FIG. 2  shows a touch screen interface of the Work Area Monitor; 
         FIG. 3  shows an initial set up screen; 
         FIG. 4  shows the screen of  FIG. 3  with a work selection area; 
         FIG. 5  indicates how the selected radar scan and pixels are overlayed on the camera&#39;s field of view of a slope; 
         FIG. 6  is a diagram showing the Work Area Monitor output derived from interferometrically-measured displacement; 
         FIG. 7  demonstrates the pixels in the selected radar scan area that have alarmed; 
         FIG. 8  shows one form of vehicle stabilisation; 
         FIG. 9  shows a user screen observing a slope without movement; 
         FIG. 10  shows the screen of  FIG. 9  but now with initial movement; 
         FIG. 11  shows the screen of  FIG. 9  with more slope movement; 
         FIG. 12  shows an alert triggered by the slope movement shown; 
         FIG. 13  shows an alert set up and adjustment screen; 
         FIG. 14  shows an area masking screen; 
         FIG. 15  shows a playback screen; 
         FIG. 16  shows an example digital terrain map; and 
         FIG. 17  shows an alternate form of vehicle stabilisation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention reside primarily in a Work Area Monitor providing a visual image of a slope near a work area overlaid with a movement map obtained from interferometrically analysed radar data. The Work Area Monitor is mounted on a motor vehicle for easy mobility, comfortable user setup and reliable power source. The elements of the Work Area Monitor have been illustrated in concise schematic form in the attached drawings, showing only those specific details that are necessary for understanding the embodiments of the present invention, but so as not to obscure the disclosure with excessive detail that will be readily apparent to those of ordinary skill in the art having the benefit of the present description. 
     In this specification, adjectives such as first and second, left and right, and the like may be used solely to distinguish one element or action from another element or action without necessarily requiring or implying any actual such relationship or order. Words such as “comprises” or “includes” are intended to define a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed, including elements that are inherent to such a process, method, article, or apparatus. 
     Referring to  FIG. 1  there is shown a first embodiment of a Work Area Monitor  10 . The Work Area Monitor  10  comprises a radar module  11  and (optionally) a camera  12  mounted on the tray of a utility motor vehicle  13  or otherwise associated with the radar module  11 . A processor (not visible) is located in the cabin  14  together with the display screen  23 . 
     The radar module  11  is a scanning dish device that consists of a dish  20  mounted on a scanning gimbal  21  that has a vertical scan of −10 to +40 degrees and a horizontal scan of −55 to +55 degrees. The gimbal houses a 600 mm parabolic dish with an offset feed. The antenna transmits and receives radio frequency signals in X-band with T/R gating to separate the direct path from the wall reflection and sufficient range resolution to separate foreground anomalies (such as mining vehicles) from the wall reflections. The mean transmitter RF power supplied to the dish is 30 mW and peak is 60 mW. A phase stable cable connects the dish to the radar module  11 . The control for scanning the gimbal is contained in the cabin  14 . A computer interface connects the processor to the radar module  11 , camera  12  and display screen  23 . 
     The camera  12  has a lens that is optically optimised for a wide field of view without distortion in the vertical plane. The camera field of view is 120 degrees by 104 degrees. The image from the camera is displayed on a screen  23  located in the cabin  14  (as seen in  FIG. 2 ). 
     It is not always practical for the vehicle to be reversed into position so that the camera and radar point at the monitored wall over the back of the vehicle. Therefore, in one alternate embodiment, the camera is configured to be rotatable within a 180 degree field of view centred over the rear of the vehicle. The centre of the radar field of view is aligned with the centre of the camera field of view so that the image viewed on the screen  23  represents what will be monitored by the radar. 
     In the absence of the camera the radar images are used to generate a synthetic image of the field of view. The synthetic image is able to display salient features in the field of view which a user is able to use for directing the Work Area Monitor. The synthetic image may be a digital terrain map, which is a 3D image comprising azimuth, elevation and range of each pixel measured by the radar. An example of a digital terrain map is shown in the lower part of  FIG. 16 . The corresponding visual image formed from a composite of photographs is shown in the top part of  FIG. 16 . 
     The utility motor vehicle  13  may be a conventional vehicle with a diesel or petrol internal combustion engine. The engine may be left running during operation of the Work Area Monitor so as to provide power to the Work Area Monitor. In the preferred embodiment the Work Area Monitor is operated from batteries that are bulk-charged by the engine of the utility motor vehicle  13 . The Work Area Monitor is distinctly different from other slope stability radars in the ability to operate from the tray back of a vehicle while the engine is running. This is due to the unique operating parameters of the Work Area Monitor as described below. It is also convenient to provide a mains power interface for battery trickle-charging as is conventionally known. 
     The Work Area Monitor  10  is a comparatively short range device that provides movement monitoring of slopes at a range of about 30 meters to about 200 meters. In operation the utility motor vehicle  13  is located so that the radar  11  and camera  12  point at a section of slope or wall to be monitored. An image of the slope as seen by the camera  12  is displayed on the screen  23 . The radar dish  20  is aligned with the field of view of the camera  12  during manufacture so that it is known, to within an acceptable degree of accuracy, that the centre of the field of view of the radar corresponds with the centre of the field of view of the camera. 
     The Work Area Monitor  10  is set up by driving the vehicle  13  to a location from which the area to be monitored can be viewed. The vehicle  13  is positioned so that the radar and (optionally) the camera point at the monitored area. The system is turned on using a single switch in the cabin  14 . After a short pause an initial screen is displayed, for example as shown in  FIG. 3 . 
     An operator selects a region of wall to monitor. In the preferred embodiment the screen  23  is a touch screen and the operator selects the region by tracing the region on the touch screen. A grid of pixels is overlayed on the scene to display the area that will be monitored. The area can be adjusted by moving the corners of the area, as shown in  FIG. 4 . The user clicks ‘OK’ on the work area selection screen to commence monitoring. 
     The grid of pixels are also used to display which pixels have moved to sound the alarm, as seen in  FIG. 5  and described in greater detail below. 
     The gimbal mount  21  scans the radar dish  20  to collect reflected radar signals at a rate to build an interferometric map of the scene in a scan time of between about 20 seconds and 2 minutes, with scan rates of one minute or less being preferable to provide sufficient warning. The interferometric map is constructed in the same manner as described in U.S. Pat. No. 6,850,183. The interferometric map that is generated has a deformation precision that allows movements above the error stack of the system to be easily detected.  FIG. 6  shows the displacement versus time output of a single pixel in the interferometric map for a wall progressing towards failure. The threshold is selected above the error stack of the system. 
     In one embodiment the output of the work area monitor is a binary alarm based on whether wall movement has been detected (‘1’) or not detected (‘0’). The Work Area Monitor operates over a short time scale of minutes and hours and alarms when there is movement in the local work area rather than providing displacement measurements of the slope over days to weeks as is the case with the SSR. The Work Area Monitor is a short term monitor that can afford a higher error stack to achieve ease of use. 
     It has been found from many measurements of slope failure using the SSR that initial movements of a few to many millimeters are apparently always present as a precursor to a larger movement. Thus, as a safety device, the Work Area Monitor is very useful as a short term, short range safety device that detects movements of a few millimeters or more and provides a warning to workers in the immediate area. This compliments the operation of the SSR described in U.S. Pat. No. 6,850,183, which provides longer term, high precision displacement measurements over a much larger wall area. 
     An alarm is generated by setting a threshold for detected movement. If the radar processing results in a detected movement of greater than the set threshold the Work Area Monitor generates an audible and visible alarm that warns workers that they should vacate the area. In addition, the moving area may be highlighted on the screen  23  using a colour code.  FIG. 7  shows the output of the screen  23  where a wall region with red overlay has moved. Another preferred option is to flash the pixels that show movement above the threshold. 
     The Work Area Monitor triggers an alarm based on the following parameters: 
     Threshold: The movement in ‘mm’ of the work area to be considered as dangerous; 
     Alarming Cells: Determines the minimum size of the area to have moved before considering the movement as dangerous; 
     Looks: The number of looks over which the movement is to be measured; 
     Direction: The direction of the movement of the work area being monitored. 
     If the work area contains vegetation or machinery a false alarm may be generated. Areas that may generate a false alarm can be masked. An ‘Edit Mask’ mode is selected and a green mask is drawn over the problem areas as described in more detail below. 
     In another embodiment dimensionless alarms are calculated as described in our earlier published international application number WO2007012112 titled METHOD AND SYSTEM OF DETERMINING ALARM CONDITIONS. 
     In many work sites the audible and visible alarm may not be immediately noticed. Therefore, in one embodiment, the Work Area Monitor includes a personal alarm that is carried by each worker. The Work Area Monitor generates a short range radio signal (or other suitable communication carrier) that triggers the personal alarm to provide a tactile and audible alarm, typically this would be a vibration and a buzzing, to warn the carrier to leave the area. 
     The worker may also be provided with a display device that shows an image of the monitored wall indicating the region of movement. Modern communication devices, such as smart phones; are compact with relatively large screens. They also incorporate modems for short range and long range wireless communication. 
     If an alarm has sounded or if there is a suspect rock hanging on the wall, the Work Area Monitor may be operated in a spotlight mode. In spotlight mode a user is able to select a single pixel from the display shown in  FIG. 5 . The radar then ceases scanning and focuses on the selected pixel with much faster measurement time, typically many times per second. This allows a suspect region of the monitored slope to be monitored more intensely. 
     It is possible in a mining environment that disturbances could occur that generate a false movement alarm. Generally these disturbances fall into two categories: non-slope movements within the field of view of the radar; movement of the Work Area Monitor. The first category of disturbances can be detected and ignored by detecting differential range changes or by comparing the short-term and long-term coherence of the radar. A movement within the radar field of view, for instance the tip of the drill rig mast  30  in the foreground of  FIG. 5  and  FIG. 7 , will have highly differential ranges from the slope, or will have low short-term coherence compared to the long-term coherence whereas a movement of the slope will have both high short-term and high long-term coherence. 
     The second category of disturbances can be eliminated by using a vehicle stabilising apparatus on the front and/or rear of the vehicle, such as those used for stabilising large recreational vehicles. One example of a rear stabilisation device is shown in  FIG. 8  and another example is shown in  FIG. 17 . The stabilisation device shown in  FIG. 8  comprises a pair of legs, such as  80 , that are lowered to take a portion of the weight of the vehicle. A similar device is used at the front of the vehicle. The inventors have found that the stabilisation works most effectively if the legs take about 10% to about 20% of the weight of the vehicle. 
     The example shown in  FIG. 17  comprises a jack (not visible) under the radar module  171 . The jack lifts the radar module  171  off the tray of the vehicle  170 . The legs  172  are extended and clamped in position so that the radar module is supported by the ground rather than the vehicle  170 . 
     Alternatively (or as well) the Work Area Monitor can employ a movement detection device such as tilt meters or accelerometers or other motion detection devices. Any movement of the Work Area Monitor, such as due to a person entering the vehicle or strong wind gusts will be detected by the movement detection device and the apparent corresponding movement of the slope will be ignored. 
     In the absence of any detected movement the screen  23  will display the work area, as shown in  FIG. 9 . In one embodiment, if the Work Area Monitor  10  detects movement within the selected work area the pixels that have movement are highlighted, for example by rendering the pixel boundaries in yellow as shown in  FIG. 10 . The pixel boundaries may also flash to highlight the movement. If the movement continues or expands the manner of highlighting may adjust accordingly.  FIG. 11  shows a central few pixels that have larger or prolonged movement and are therefore highlighted in red. Adjacent pixels with large movement that is above the threshold may be shown in orange or red with small movement shown in yellow. Other schemes for displaying movement would also be suitable. 
     If the movement exceeds a threshold an alarm is triggered, such as displayed in  FIG. 12 . The alarm may be triggered, for instance, due to the number of pixels moving, the amount of movement or the duration of movement. In  FIG. 12  the alarm indicates that 2 cells moved more than 4 mm between observations. 
     It will be noted that the alarm conditions can be reset or changed by selecting either option through clicking the appropriate button shown in  FIG. 12 . Selecting either option takes the user to an alert screen shown in  FIG. 13 . On the alert screen a user can adjust various alarm conditions such as the movement threshold (in millimeters), the number of moving cells required to trigger an alarm, the number of ‘looks’ that need to show the movement to trigger the alarm and the direction of movement. The alert screen also may display an alert history in the current location to assist the user to determine if the alert is significant or possibly a false alarm. The alert level can also be set. For instance,  FIG. 13  shows a configuration where a yellow alarm is notified to local crew but a red alarm is notified to a supervisor, as well as local crew. 
     The user can also elect to add a mask from the alert screen. This may be required, for instance, if movement is apparently due to a non-slope artefact such as the drill mast referred to earlier. Clicking the “edit mask” button takes the user to the “edit alarm mask” screen shown in  FIG. 14 . From this screen the user can mask out certain areas using common tools as shown across the top of the screen shot. Once selected the screen is exited by selecting “ok”. 
     The Work Area Monitor  10  may have facility for local recording of a limited amount of history of monitoring of an area. Operation of the WAM can be paused to allow a user to play back the monitoring data to assist with deciding whether detected movement presents a safety hazard. The pause and playback screen is shown in  FIG. 15 . From this screen a user can playback recent recorded slope movements. The user can also access the alerts screen to make changes to the alerts. 
     The Work Area Monitor operates in a similar manner to the SSR described in the aforementioned United States patent but is different in a number of significant respects. Counter-intuitively it is operated on a motorised vehicle platform that can be quickly and easily moved from place to place for short range monitoring. It is designed to provide much shorter timescale monitoring with less precision but much faster scan rates than an SSR. It provides a simple and local area alarm to warn workers of slope movement in their vicinity as opposed to the broader pit monitoring and long-term deformation measurements of the known SSR system. It is particularly simple to set up and operate. 
     Although described by reference to application in an open-cut or pit mining situation the Work Area Monitor is not limited to any specific application. The Work Area Monitor could also be useful for underground mining operations. 
     The above description of various embodiments of the present invention is provided for purposes of description to one of ordinary skill in the related art. It is not intended to be exhaustive or to limit the invention to a single disclosed embodiment. As mentioned above, numerous alternatives and variations to the present invention will be apparent to those skilled in the art of the above teaching. Accordingly, while some alternative embodiments have been discussed specifically, other embodiments will be apparent or relatively easily developed by those of ordinary skill in the art. Accordingly, this invention is intended to embrace all alternatives, modifications and variations of the present invention that have been discussed herein, and other embodiments that fall within the spirit and scope of the above described invention.