A control system is normally found inside a control cabinet, where it is protected from all types of environmental influences. Control systems can also be installed on mobile machinery, where they may be subjected to rigorous shaking. Shock and vibration must not be allowed to compromise the safe function of the control system in any way. Pilz Australia ’s programmable control systems used in mining on roadheaders, monitor the spray function.
Underground mining is risky. To ensure that man and machine are not exposed to risks, special safety concepts are in place to keep the ‘explosive hazards’ in check. In conjunction with Sandvik Mining and Construction, Pilz Australia have developed PSS control systems, designed in accordance with the principles for integrated explosion safety. In the mining sector, it provides security against explosive dust concentration.
Roadheaders made by Sandvik Mining and Construction are used in underground mining, to excavate coal and salt. Rotating cutter heads on the front of the machine excavate the material. A huge amount of dust is formed as a result, which can cause a dust explosion underground under certain circumstances. A water-based spray system on the machine is designed to prevent this by binding the dust particles and preventing excessive dust concentration in the air. It is important that the spray system operates reliably while the cutter heads are in operation, so it must be permanently monitored.
The spray system on the rotating cutter heads is generally monitored using digital flow and pressure sensors. With the new concept from Sandvik Mining and Construction, analogue sensors measure flow rate and pressure, while a PSS control system evaluates the results. The operating conditions of the machinery used in coal mining are a challenge in this case. Due to the hardness of the overburden material, the drilling device as well as the machine must be able to withstand strong vibrations. PSS control systems are exposed to this, offering a ‘vibration-free’ solution.
Pilz Australia modified an existing compact PSS control system with digital and analogue inputs to make it suitable for use in mining, in accordance with Sandvik Mining and Construction requirements. It is called the ‘rugged version’ of the PSS control system and is temperature-resistant as well as vibration-proof. Its components are not free-standing and the boards are bonded and therefore ‘vibration-free’. This helps to counteract wear. As a result, PSS control systems meet the high shock and vibration requirements. With three-dimensional, sinusoidal continuous duty with sliding frequency, the required vibration and shock resistance is achieved for up to 1000 half sine shocks. PSS control systems are installed on the roadheader in a flameproof enclosure, as the machine is located inside the potentially explosive area.
The spray system must operate reliably to guarantee safety underground while the roadheader is in use. Consequently, water flow rate and pressure must not exceed or fall below certain limit values. When the machines are operating properly, the conditions in terms of flow rate and pressure are constant. PSS control systems use a calculation formula to constantly establish and compare limit values and operating values. If there are any deviations, as a result of a faulty spray system or a change in pressure or flow rate, the control system stops the cutting motor that drives the excavation cutter heads. This stops any more dust from forming. Various types are available for monitoring the spray system and these are defined in advance in the user program. Each of these is evaluated in the control system program.
Sandvik Mining and Construction and Pilz Australia worked together in developing the new control system type. The safety concept and technical design were planned and implemented in the hardware at the customer's end. Pilz Australia generated the software including the user program for the PSS control system, in accordance with the customer's specifications.
The safety functions were verified during joint tests on the machine. The first prototype was able to go into testing after a few months.
PSS control systems can be used to meet high safety requirements in accordance with the international standards for machine safety EN 954-1, IEC 62061 and EN ISO 13849, and also in accordance with application-specific standards for press applications, railway applications, cable cars and drag lifts. PSS control systems are approved by BG, TÜV and international certification bodies. PSS control systems have a range of interfaces for connection to standard fieldbuses and, in addition to SafetyBUS p, can also exchange data through Ethernet-IP, PROFINET and SafetyNET p. PSS control systems are suitable for incorporating into existing control structures, while users are free to select how to network their plant.
PSS control systems are also designed with a modular structure. Pilz Australia offer a PSS control system for specific environmental conditions, as is the case with cablecars through to crane applications with a direct connection to external encoder systems.