Neil Sandhu discusses collision avoidance in the outdoors
The mining sector faces increasing pressure to structure safe work procedures and processes in outdoor environments, without compromising on efficiency or productivity. Accident-free navigation of mobile machinery, as well as efficient and safe loading and unloading of materials, are major everyday challenges. Failure to make adequate provision for collision avoidance could lead to unplanned stoppages, expensive delays, reduced throughput or personal injury.
But, in surface mines, quarries and stockyards, static and mobile machinery can be lumbering giants that struggle to see around every corner and obstacle. Large machines frequently work together in confined areas. Driver-operated mobile vehicles such as bucket and shovel excavators, haul trucks and wheel loaders, have considerable blind spots that impair operator visibility. The harsh environment, weather conditions and difficult terrain all add to the risk of stoppages.
Sensing technologies provide the “eyes” to “see” around the corners and through the dust clouds. Increasingly, with Internet of Things (IoT) intelligence, they also feed their data back and integrate with automated software and maintenance systems. Technologies such as lidar and radar combine with gateway systems to help mine operators to reduce potential dangers and increase operational efficiency. But what kinds of “eyes” are best?
Lighting The Way
Laser distance sensors and lidar are common technologies used for collision avoidance in outdoor industrial environments. They use optical time of flight (ToF) technologies to send invisible, but safe, infrared light beams to an object and measure the time they take to be reflected back to the sensor.
Sick’s laser-based sensors overcome harsh environments using the company’s HDDM+ technology and send out multiple echoes – up to five – to overcome the limitations otherwise caused by bad weather, bright light, dust, smoke or mist. The sensor automatically filters out irrelevant reflections, such as from water droplets or dust particles, and reliably identifies the actual measurement signals. As a result, the risk of false trips is eliminated.
2D Lidar Sensors
2D lidar sensors scan in a fan-shape around the sensor, creating a plane that can be divided into several detection zones. Mounted on machinery or infrastructure, the best-performing can reach a wide angle of view to the side and behind a scanner, typically up to 275°, although some can scan up to a full 360° around their environment and measure up to ranges
2D lidars, such as Sick’s LMS1000, perform distance sensing and ranging duties to detect moving and stationary objects and output accurate data that can be processed to measure both lengths and widths. Access into zoned areas can be controlled by creating vertical monitoring areas, for example, to control safe access for people or vehicles. Protection against collisions with over height objects, or with stockpiles, can be achieved by establishing horizontal monitoring areas. Systems can be expanded using RFiD tags, GPS or other sensors to identify manned or unmanned mobile vehicles entering a pre-defined area.
3D Lidar Sensors
3D lidar sensors go further by scanning in several measurement levels to map a more detailed profile of the environment and its contours, as well as the shape of objects detected. Sick’s AOS lidar solution combines a 2D laser scanner with the firm’s Flexi Soft safety controller to provide a complete system that can help avoid collisions, with sensor self-monitoring to avoid system failures.
Radar sensors work on similar ToF principles to lidar but they emit electromagnetic radio waves instead of infrared light. Radio waves are not affected by environmental conditions in the same way as light-based technologies, so radar sensors can be the ultimate, super-tough choice for harsh environments and operation during the hours of darkness. Sick’s recently launched RMS1000 radar sensor can achieve 24-hour detection performance with long-range resolution and distance accuracy.
The key difference is that, while lidar scans in a 2D plane, radar emits its radio waves in a cone shape, which expands over distance. So, radar is less well suited to detecting small objects further away because of its longer wavelengths, especially at longer distances. The RMS1000 performs exceptionally well, for example, to identify a human at 50m, but not so well for smaller objects. However, radar technology may scan a wider environment at longer ranges than an equivalent lidar scanner, but with less accuracy.
For mobile machinery in mining environments, manoeuvring and reversing are the most frequent causes of accidents. Using sensing technologies to deliver data to a cab-based monitor gives the driver a view of areas that would not be otherwise visible. A good driver assistance system provides the driver with information without becoming distracting.
Guidance And Collision Awareness
Many mines and quarries worldwide trust in Sick’s Minesic100 driver guidance and awareness solutions to prevent collisions in dangerous areas. There are specially developed systems for excavator protection (EPS,) truck protection (TPS) and wheel loader protection (WPS), designed to gain the acceptance of operators and to avoid unnecessary distractions.
These systems adopt behaviour recognition, automatic warning zone adjustment and context switching according to different driving manoeuvres. For example, the Minesic100 EPS installations on large excavators monitor and detect their environment with an almost gap-free 2D lidar sensor, regardless of whether the objects are moving or not.
The EPS’s advanced application software uses the mounting position, excavator size, tail swing radius, safety margin, truck spotting radius and maximal loading area for detecting and processing object information, such as positions and size.
On the cab display, objects and infrastructure are displayed as outlines. The visualisation is simple and distances are visible without the need to interpret a camera picture.
System Monitoring And Feedback
Increasingly operators are harnessing sensor data through gateway systems to manage operations in real-time, analyse incidents and make maintenance decisions through cloud-based monitoring dashboards.
The Sick Monitoring Box uses a Sick telematic data collector (TDC) connected via Ethernet cable to the sensor. The data is sent securely via LAN, WLAN, or mobile communications, so that a system can be monitored in real time from a smartphone or desktop. By analysing and comparing data and studying the statistical frequency of near-misses or costly stoppages, hazardous situations can be identified and prevented. Driving routes or machine operations can be optimised to ensure the most efficient operations. Data can also be input into digital maintenance software systems.
Neil Sandhu is Sick UK's product manager for Imaging Measurement and Ranging