An Effective Way of Displaying Situation Awareness ...

An Effective Way of Displaying Situation Awareness Information in Mining Vehicles 1

1

D Orchansky , S Worrall and E Nebot

1

ABSTRACT Accidents caused by vehicles are a major concern when evaluating safety in the mining industry (DME, 2003, 2007), (DCEP, 2008). Every year hundreds of accidents occur, with consequences varying from simple injuries and minor property damage, to multiple deaths. Collision avoidance systems provide great potential for reducing the amount of accidents caused by vehicles in the mining sites. A major challenge for these types of systems is how to design an efficient user interface that improves safety. This paper describes the design concepts of a human-machine interface currently being developed for a collision avoidance system for vehicles in open cast mines developed at the Australian Centre for Field Robotics (ACFR) in conjunction with CRCMining.

INTRODUCTION Every year hundreds of vehicle accidents occur in mining sites. Vehicle collision has been reported as the primary cause of serious accidents in several mines (DME, 2003, 2007). The impact of these accidents varies from vehicle damage, property damage, minor injuries, up to multiple casualties. Inappropriate speed is one of the primary factors in vehicle accidents (OECD, 2003). Collision avoidance systems offer a great potential for the mining industry by providing an important aid in the prevention of injuries, vehicle collisions and property damage. They also have the added benefit of increasing situational awareness in an environment where there are many different types of vehicles operating at different speeds in often adverse conditions such as dust and fog. Collision avoidance systems have successfully proven their achievement in reducing accidents (OECD, 2003). The ACFR, in conjunction with CRCMining, has developed a situation awareness system for improving safety in vehicles that operate in open cut mines (Worrall, 2007). The objective of the system is to provide information to vehicle drivers in order to avoid collisions with other vehicles, personnel and infrastructure. This system is based on the exchange of GPS information between vehicles, people, and infrastructure in the mine by using mesh network technology. A redundant mechanism based on close proximity and RSSI calculations adds extra robustness and reliability on the process of nodes detection. The key benefits of this system are scalability, ease of deployment and adaptation for the mining site. The strategy for communicating situational awareness information with the user (in this case, the driver of the vehicle) plays a crucial role in the overall success of the system. The two main issues to resolve are what information should be provided to the driver under different circumstances, and how to provide this information in order to facilitate the making of decisions and aid in accident prevention. A description on how these issues were accomplished in the situation awareness system is provided in the following sections. 1.

Australian Centre for Field Robotics, The University of Sydney, Sydney NSW 2006.

Australian Mining Technology Conference

16 - 18 September 2008

51

D ORCHANSKY, S WORRALL and E NEBOT

THE DATA ACQUISITION SYSTEM For the purposes of this paper we assume that every vehicle in the mine sends and receives GPS data broadcasted by themselves and by other vehicles in the surroundings. This is done through the data acquisition system, composed of a long distance transmission module (based on mesh network technology) and a close proximity subsystem (based on RSSI calculations). The principal content of these packets of data are the current location of the vehicle, its speed and heading. The accuracy of the information, which is based on satellite count, is also included in this information package. This raw information is then used for identification of dangers and for making the driver aware of the situation in an audio-visual representation. The process of identifying warnings and threats is explained in the following section.

DANGERS AND THREATS In order for collisions to occur (or any accident in general) vehicles have to be close to each other. If the vehicle is slowly approaching the other vehicle, ie their relative speeds are low, then the driver might have enough time to react and avoid an accident. On the other hand, if the relative speeds of the vehicles are high, the reaction time is much shorter, and the occurrence of an accident may be inevitable. Therefore two variables are taken into account to prevent accidents: distance to other objects, and relative speed. Our system uses these two variables to enhance driver awareness of the situation by informing of possible threats. Based on the average speed of the vehicles in the different areas of the mine, two categories or contexts have been identified: a slow manoeuvring context (or slow speed context), and a high speed context. Areas in each context share similar characteristics of what to consider dangers and threats. The first type of context includes all the areas such as the parking lot, crusher area, loader area, washing bay area, and others. In this context the driver has to be aware of unexpected potential high risk situations such as vehicles reversing, moving vehicles not visible from the driver’s cab and personnel in the vicinity of the vehicle. The high speed context involves all the transition areas of the mining site, such as roads and intersections. The issues that the driver must be aware of, in this context, are vehicles that approach at a high speed, environmental conditions such as rain, dust and fog, and vehicles approaching intersections. Based on these contexts we consider two methods for identifying threats and dangers: one based on the distance between objects, and a second one based on the time to collision. A third methodology, based on map-matching techniques, can extend the accuracy of threat detection. Currently only the first method presented has been included as part of the system, although the following two methods are planned to be included as well.

Threat identification based on distance A simple approach for identifying dangers and threats is to define a safety area that surrounds a vehicle and is composed by two regions: a danger region and a threat region. The warning region is used to identify nodes that require some attention from the operator as these nodes have the potential, if they intrude into the threat region, of becoming hazards and thereby needing operator attention. Nodes located within the threat region are considered to have a high potential of interaction with the vehicle, thereby possibly causing an accident. In this region, the operator is alerted to the presence of threats. By having these two regions, the transition of vehicles that become threats is smooth and can be anticipated with enough time to alert the operator to their presence.

52



AN EFFECTIVE WAY OF DISPLAYING SITUATION AWARENESS INFORMATION IN MINING VEHICLES

The regions are measures of distance that vary proportionally to the speed of the vehicle. At high speeds the regions increase in radius and, at lower speeds the regions become smaller. Figure 1 (left) shows the two regions (the threat region in red, and the danger region in yellow) and three vehicles located in the different ranges. The triangle in the middle represents the vehicle in question. The white square represents a vehicle that is not considered a danger or a threat. At the moment the values used for the ranges are experimental and they will be adjusted in future experiments. It is also important to keep in mind that these values can vary for different types of vehicle, and from one mine to another.

FIG 1 - Methods for threat and danger identification.

Threat identification based on time to collision Another approach for identifying dangers and threats is by using a time to collision (TTC) value. The TTC is calculated based on the distance of two objects and their relative speed. In this method the range used for detecting dangers and threats is a measure in time rather than distance. With this method it is possible to detect threats that are not necessarily a short distance away, but are approaching with a relative velocity that merits concern. This method provides better performance compared to the previous one in the sense that it can identify situations where the vehicles are very close to each other, but it is very unlikely for them to collide (ie they are moving in opposite directions). This method can be either used as a replacement or in conjunction with of the distance based methodology, Figure 1 (centre) illustrates a simple case of this method. The red square represents a threat and the yellow squares represent dangers. The arrows represent the measure of the vehicles speed. Notice that in this case the proximity is defined by the time to collide rather than their closeness.

Map-matching techniques A more sophisticated method based on the use of map-matching techniques can enhance the process of threat detection in the previous approaches by providing a more accurate identification of dangers and threats. This method requires the use of road map information for accurate position calculation and allows us to identify in which road a vehicle is located and in which direction it is moving. With this information it is possible to filter threats and dangers that, according to the previous methods where identified as such. This method is exemplified in Figure 1 (right) where the threats are calculated based on map information in addition to the time to collide. The white square represents a vehicle that is not considered a danger because it is located in a different road.



53


THE INTERFACE The interface developed for this system is an audio-visual interface that is composed of a Gumstix motherboard that controls a set of speakers and a 4.3” touchscreen LCD panel. It communicates with the data acquisition system through RS232. The key factors for achieving a highly effective interface are to provide reliable and sufficient information to the driver by causing minimal distraction, in an adequate manner, and by attracting the driver’s attention at the appropriate moment. A brief summary of each goal is described below:

• Reliable information: incorporate error estimates of the data provided from the acquisition system in order to measure the reliability of the data.

• Sufficient information: show the sufficient information for making good decisions and avoid making awkward manoeuvres. Proving insufficient information or an excessive amount of information to the driver may overwhelm or annoy the driver, and eventually cause an adverse reaction (Lunenfeld, 1989).

• Minimal distraction: avoid unnecessary distractions that could harm the normal operation of the vehicle. Unnecessary sounds or irrelevant visual information reduce the attention of the driver on the road (Lunenfeld, 1989).

• Attract attention: using the appropriate medium for providing information to the driver. Voice and sounds are better for high priority alarms, whether visual information, such as text and graphs should display low priority information.

• Timeliness of the information: provide the information to the operator allowing sufficient time for them to process the data, evaluate the situation and react accordingly.

Visual interface Two different screens have been designed to satisfy the driver with situation awareness information in each context. In the high-speed context (Figure 2, left) the system provides a summary of the top three threats or dangers, the distance relative to these vehicles, and the direction of the main threat (illustrated with the green arrow). The idea is to provide, at a quick glance, the major threat and where it is located. When driving at high speed it is recommended to minimise the distraction caused by the display. In situations where the visibility is very poor this screen becomes very necessary and can facilitate the driving tasks.

~ 40 [m] TRUCK ~ 70 [m] 4WD ~ 100 [m] Haul Road

Sat: 7

Loader

Sat: 7

FIG 2 - The visual interface screens.

54



AN EFFECTIVE WAY OF DISPLAYING SITUATION AWARENESS INFORMATION IN MINING VEHICLES

A second screen used in the slow speed context (Figure 2, right), includes a detailed overview of the position of threats and dangers. In this context the number of threats could be very high, and the threats might be coming from many directions. Therefore the complexity of the situation is resolved by displaying the complete scenario, reducing at the same time the understanding error. The red circle in this screen is to be used as a fixed reference of distance to nearby threats. Road diagrams are also displayed in the background. Notice that both screens show an indication of the current context, and the number of satellites. This information is only displayed for control purposes. The information in the screen is displayed continuously and is available for the driver at any moment. Some important design considerations are: the screen brightness (the information has to be easily readable during the day, and the contrast should not cause distraction during the night). A full description of other considerations can be found in (Lunenfeld, 1989).

Audio interface As it is stated in (Burnet, 2000), ‘The use of voice is widely believed to be critical for effective vehicle navigation systems’. Although this is not a navigation system, we take advantage of the properties of the audio interface by providing awareness information with very little distraction. The system generates voice alarms when a vehicle in the proximity of another vehicle becomes a threat. A succinct message indicates what type of threat it is, and where is it located. Due to the problem that voice messages can be easily missed (Verwey, 2001) the alarms are backed up by the visual information in the display. To avoid raising audio alarms frequently (and annoying the driver) the system emits alarms (and repeats them if it is necessary) only after a certain period of time. Figure 3 shows a screen from the current audio-visual interface indicating that a threat was detected in the proximity (a truck is five metres in front).

FIG 3 - The audio-visual interface.

OTHER CONSIDERATIONS Although the above discussion mainly refers to vehicles it also applies to personnel and infrastructure. The fact that vehicles can be present in all areas of the mine, and their speed can be increasingly high they are considered to be the biggest threat.



55


For correct and successful use of this situation awareness system it is very important that the user is instructed in all the capabilities and limitations of the system and how to correctly react according to the information provided. Although some benefits of using the system with the proposed methodology may appear soon after the system is tested, some others – such as the reduction of collisions, or the number of accidents avoided due to the presence of the system – will take a longer time to be perceived (OECD, 2003).

CONCLUSIONS This paper presents an overview of the methods utilised in an audio-visual interface for providing situation awareness information to the drivers of vehicle in the mine site. Several methods for threat identification were described, and in the near future will be included as part of the system. Upcoming experiments will help on the process of adjusting range variables.

REFERENCES Burnet, G E, 2000. Usable vehicle navigation systems: Are we there yet?, in Vehicle Electronic Systems 2000 – European Conference and Exhibition, ERA Technology Ltd, pp 3.1.1-3.1.11. Department of Consumer and Employment Protection, 2008. Safety performance in the Western Australian mineral industry – accident and injury statistics 2006-07; Resources Safety, Department of Consumer and Employment Protection, Western Australia, 41 pp. Department of Mines and Energy (DME), Queensland, 2003. Coal open cut – High potential incidents – Vehicles (1 July 1999 - 30 June 2003). [online] . Department of Mines and Energy (DME), Queensland, 2007. Queensland safety summary, 14 November, serious accidents report 4 September 2007. [online] . Lunenfeld, H, 1989. Human factor considerations of motorist navigation and information systems, in Vehicle Navigation and Information Systems Conference Proceedings, pp 35-42. Organisation for Economic Co-operation and Development (OECD), 2003. Road Safety – Impact of New Technologies. Verwey, W B, 2001. Evaluating safety effects of in-vehicle information systems, in Stress, Workload and Fatigue (eds: P A Hancock and P A Desmond) pp 409-425 (Lawrence Erlbaum: Mahwah). Worrall, S and Nebot, E, 2007. A comprehensive approach to improving safety in mining, in Proceedings 2007 Australian Mining Technology Conference, pp 293-301 (The Australasian Institute of Mining and Metallurgy: Melbourne).

56

