A 1.743Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE
As the competition and the requirements for safe and reliable dry bulk operations have increased rapidly over the years, the use of advanced automation technologies has become a key success factor in order to establish an efficient, high-quality, stable and competitive supply chain. Among some of the daily challenges for the dry bulk operations are insufficient utilization of stockyard area, low machine performance, as well as complex planning and coordination of the stockyard operations. Beside this, many dry bulk operations are located in remote locations, where it is difficult to find skilled man-power, resulting in considerable "fly-in/fly-out" expenses for the man-power necessary to operate the machines.
By using LiDAR equipment in conjunction with advanced automation processing technologies it is now possible to minimise or completely eliminate the factors resulting in low infrastructure utilization. The right composition of LiDAR and automation allows one single remotely located person to operate an entire dry bulk stockyard, containing several large mobile machines, and at the same time increase the stockyard throughput by up to 15-20%, compared to a manually operated stockyard.
For a dry bulk export or import terminal this means that a bulk carrier will be loaded or unloaded faster, contributing to significant savings by allowing a smaller "slot" for the loading or unloading sequence or by avoiding demurrage fees when the carrier is not loaded/unloaded timely. The same is typically the case when mines are loading a train: The faster and more efficient this can be done, the higher operational cost savings.
FLSmidth has, as one of the global market leading EPC’s for material handling equipment, used more than 10 years of research and development in finding the optimum solution to ensure that the customer’s expectations of maximum utilization of their capex investments are fulfilled. This work has resulted in FLSmidth obtaining the intellectual property rights and patents on an advanced automation solution containing LiDAR 3D terrain mapping technologies, allowing for unmanned and optimized control of dry bulk reclaimers and stackers.
The basic principle
The basic automation principle is to supplement the conventional PLC control on a machine, with a separate industrial control PC. A LiDAR system, which is the eyes of the system, is providing the PC with stockpile profile information and a GPS system provides the exact machine position. Based on the data derived from the LiDAR and GPS systems, the PC will use advanced algorithms to control the machine movements.
Dry bulk machines are constructed as either standalone bucket wheel reclaimers or stackers–or as combined machines suitable for stacking and reclaiming. In both cases, the machine structure always consists of a boom and a pylon, which are also used for installing the necessary instrumentation for the advanced automation. The 3D laser scanner device will be installed on the machine apex, together with a real-time phase-differential GPS receiver (RTKGPS). A second RTK-GPS receiver will be mounted on the boom tip. The RTK-GPS system is providing information of the machine position in all three dimensions with an impressive accuracy of 2-4 cm.
Laser scanners and RTK-GPS receivers are synchronized via a real-time connection, so that even when the equipment is moving, an accurate stabilization of each image spot and a high precision of the terrain model will be ensured. The terrain database will be made available in the central control room as a 3D image including a real-time online repository of information on materials and their location in the stockyard.
The 3D view, based on data derived from the LiDAR system, is not only allowing the machine to operate without an operator placed onboard, but gives also the remotely placed operator the possibility to perform real-time "walk in the stockyard" and thereby archive an important inventory overview.
Choosing a 3D mapping technology
The market today offers a broad range of sensor technologies suitable for equipping the mobile machines with the necessary "eyes" to obtain data to build the real-time 3D stockyard terrain model. In particular, radar and laser technologies are competing to be considered as the bulk industries preferred solution.
During the development of the automated stockyard operation system, it quickly became clear that a key element to consider was the ability of the scanning equipment to work in a very harsh environment with high dust and dirt concentrations, heavy rain and fog. Another very important element was the accuracy of the 3D terrain model in order to optimize reclaiming efficiency and stabilize reclaiming feed. A typical reclaimer bucket cuts between 0.3 1.5 meter into the pile. A positioning error to the material of just +/- 10-20 cm, will reduce machine performance drastically when cutting too shallow, or the bucket wheel motor can be overloaded when cutting too deep.
Radar scanners-lacking in accuracy and range
Radars are without doubt good at handling tough conditions such as dust or rain. This is mainly due to the long wavelengths of typically around 4mm that allows the radar beams to "travel" around airborne particles. However, several tests performed have revealed that radar accuracy is insufficient and becomes progressively worse the farther the sensor is from the point it has to measure. Some of the best radar technologies on the market today are having limited distance accuracy of 200mm at a 30m distance and only with a 30 field of view.
This limited distance accuracy and field of view means that up to 6 radar devices would need to be placed near the bucket wheel on a reclaimer to provide a 3D model of the area the machine is working in. But having the "eyes" so close to the area to be measured is like giving a horse blinkers–the 3D terrain model overview becomes very limited and will not be suitable for giving the remote based operator a "true" and real-time overview of the stockyard inventory in order to plan his next actions in a timely manner. To get a full pile profile with a radar system will require additional scan-runs along the material surface, before executing the actual machine order–a procedure that will take unnecessary and costly time.
Example of what a radar system would look like. As illustrated, even 6 radar devices only give a limited "window" of view around the bucket wheel -requiring additional scan-runs.
Laser scanners and the rough mining environment
Concluding that radars were not suitable for providing an adequate real-time inventory overview and the accuracy needed for optimized machine control, attention was directed to a laser scanner solution. Laser scanners still deliver accuracy far better than any radar technology, which is mainly due to the short laser light wave length of around 2-4m (1/1000 less than the radars tested). However, this low wave length is problematic when attempting to bypass large dust or other air contamination particles, especially when the laser is placed a short distance from the area to be measured i.e. next to the bucket wheel.
The solution
The solution for retaining accuracy of a laser scanner without undesired disturbances from air contamination in the working area, is to place the laser scanner on the machine apex. The longer distance from the scanner to the material surface, results in a wide laser spot at the measuring point, allowing the laser light to pass air contamination particles and detect the real surfaces behind. The laser scanning principle used is including special features like last time of flight, multiple echoes with a large array of measuring points and intelligent image filter algorithms to pass through rain, fog, dust or other disturbances. The laser scanner has the advantage of still being very accurate even though it is placed further away from the pile surface and is at the same time providing scanning frequencies and measurement speeds far better than any radar can do.
The specific laser scanner FLSmidth has chosen for the systems offers a wide field of view of up to 95 vertically and 360 horizontally, with a scanning range of at least 150m, but often up to 400m–depending on the bulk material type. A coal or iron-ore stockyard will typically have between 3 -10 mobile machines operating. Each one of these machines will have a 3D laser scanner installed on the apex. Combined the installed scanners provide a nearly complete inventory overview of the stockyard. Any "gaps" in the image will be covered when a machine moves to a new position, as all data always will be updated with the latest scan. The laser scanner provides a resolution as high as 10 x 10 cm of the total stockyard terrain model, which can be in the size of around 500 x 1500 meters.
Conclusion
With more than 35 fully unmanned mobile machine systems in successful operation over the last 10 years, LiDAR has proven to be a reliable and trust worthy technology, suitable for even the harshest environments, as long as proper considerations are taken in the design of the full system. FLSmidth’s objective with the use of advanced automation technologies is to ensure customers are guaranteed the optimum performance of their installed infrastructure and thereby lower the cost per tonnes of material exported or imported–a task that only an accurate and reliable LiDAR system can solve.
Ole Knudsen is Global Manager for FLSmidth Automation, Copenhagen, Denmark, and is heading a global business unit focusing on advanced automation technologies in the mineral business.
A 1.743Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE