The ability to control the speed, acceleration and deceleration of conveyors is crucial to maximise material handling efficiency. In particular, it is extremely important to avoid abrupt start-ups, prevent conveyors from running backwards when travelling uphill or from rushing downhill under the influence of their load. Braking control is also necessary when mine operators need to halt conveyors or to avoid issues during power failures.
In these situations, the conveyor should not immediately come to a halt. The brakes should rather stop it in a gradual and controlled way to protect the powertrain from shock loads – a practice commonly referred to as ‘soft braking’. In this way, it is possible to avoid excessive tension on the conveyor belt and eliminate considerable stress to multiple pieces of equipment, such as rollers.
The Problem With Conventional Braking Systems
Conventional braking systems, while facilitating controlled stopping and holding, have seldom been able to effectively modulate speed in operation or operate autonomously. Therefore, it is important for mine operators to explore new technologies that can deliver more responsive and reliable solutions to allow them to maximise productivity and increase equipment service life.
In addition to the traditional considerations of brake specification, a modern system should be specified based on its ability to automatically modulate the braking force: regulating the conveyor’s speed, acceleration and deceleration. The most effective way to introduce soft braking is to equip the system with a control system based on a closed-loop feedback mechanism.
How To Choose A Braking Control System
Closed-loop braking system controllers receive one or more reference signal from sensors associated with the conveyor, such as the conveyor’s torque, speed and/or pressure. The controllers compare the data received to pre-defined setpoints, the results of which trigger a proportional corrective change to adjust the motion of the conveyor accordingly.
The best way to manage the data and modulate the braking force involves the use of controllers based on proportional integral (PI) algorithms, such as the SOBO (Soft Braking Option) iQ solution from Svendborg Brakes. By combining proportional and integral responses, these controllers are able to handle the fast dynamics of the braking process in a highly efficient and reliable way.
Firstly, the proportional response offers immediate action to address a major difference between sensor data and setpoint. For example, if the conveyor’s speed starts to rise significantly, exceeding the setpoint, PI controllers will need to promptly slow the conveyor by applying an elevated braking force.
The proportional action responds quickly, addressing big fluctuations, but cannot get the setpoint and sensor data to precisely match. In fact, the proportional term alone would likely excessively reduce the speed as well as consume more energy.
This is why the secondary, integral response is needed. This conducts an averaging operation that filters out small oscillations by taking into account past and present deviations over time. As a result, the controller is able to stabilise the braking force and ensure a gentle stop.
Having chosen to use PI braking controllers, it is essential for mines to fine-tune the proportional and integral terms, both individually and in relation to one another, to get the most suitable output and response: maximising performance, productivity and efficiency. This task requires extensive knowledge on how mining conveyors should move in different situations. This insight can be gained by leveraging the power of Big Data.
In systems such as SOBO iQ, all the sensor data points obtained by the braking controllers are accessible and can be used by mine operators. In this way, they can identify key patterns as well as having real-time, remote monitoring capabilities to make on-the-fly adjustments when needed. As a result, the system helps operators to implement the IIoT within their mining facilities.
Controlling The World’s Highest Downhill Mine Conveyor
A coal mine in Colorado, USA, needed a braking control system for its two downhill longwall panel conveyors. The challenge arose in maintaining a consistent stopping time of 35 seconds, even as the length of the conveyor changed as the longwall machine retreated.
Svendborg Brakes’ SOBO iQ offered the ideal system. Its dual-loop PI control, coupled with advanced functions, such as independent overspeed monitoring, rollback, gearbox and out-of-band monitoring, allowed the operators to ensure consistent stopping times in any situation.
Minimising The Effects Of Power Failures
A mine in Chile wanted a solution that would minimise the effects of power failures on its conveying operations. The most important aspect consisted in providing parking and tension control during a power failure. By ensuring that tension in the conveyor’s belt is maintained, equipment stress would be minimised.
To address this issue, Svendborg Brakes decided to apply a torque feedback sensor on its SOBO iQ. In this way, the system would monitor the line pull of the take-up winch cable, rather than conveyor’s speed, thus gathering actionable insight into the actual tension. Thanks to this smart brake modulating set-up, the Chilean mine could maximise reliability and equipment service life.
Tilman Speer is with Svendborg Brakes