“The objective was to develop a specialised continuous system for monitoring the mining shovels to enable a predictive maintenance strategy for these crucial machines.”
Electromechanical shovels for open-pit mining are huge, non-stationary machines used to load haul trucks which transport ore to processing plants. Usually, the shovel-to-trucks ratio is about 1-to-12, so unexpected shovel downtime has a direct effect on production. Hence, electromechanical shovels are considered critical machines.
Traditionally, it has been difficult to apply condition monitoring and predictive techniques to these shovels due to inadequate analysis algorithms and equipment as well as the harsh environment. Traditional vibration analysis, the main tool for predictive maintenance on rotating machines, is based on the Fourier transform which assumes constant rotational speed. This is not adequate for the shovel; therefore a different approach is needed.
The solution
A tailor-made vibration and continuous stress monitoring system created using the NI CompactRIO platform and NI LabVIEW software. The monitoring application on the CompactRIO platform can search for the best measurement periods for analysis and optimise the signal-to-noise ratio.
The urgent need to move from a reactive and preventive maintenance strategy to a predictive and proactive strategy led to the creation of SiAMFlex, the Advanced System for Flexible Monitoring. SiAMFlex was initially an initiative of Professor Pedro Saavedra at the University of Concepción, Chile, and beginning with research to develop a vibration analysis algorithm suitable for the vibration signals of electromechanical shovels. Once the algorithm was ready, the second stage was to implement this technique as the core of a continuous monitoring system. Now, SiAMFlex is supported and continually updated by CADETECH to maintain a complete mechanical and structural asset integrity management and analysis tool.
The monitoring system consists of on-board equipment, an off-board server, computers, and wireless network equipment. The on-board equipment includes:
* The CompactRIO system with the NI cRIO-9014 8-slot embedded chassis.
* The NI 9233 module for vibration measurement.
* The NI 9237 module for dynamic strain measurement.
* The NI 9422 module for precise, high resolution tachometric data.
* The NI 9205 module for complementary signals from the shovel control system.
* Piezoelectric accelerometers mounted on shovel’s main rotary components (motors and gearbox transmissions).
* Strain gauges mounted on the shovel’s main structural components.
* Incremental encoders on the main motors.
* Wireless networking equipment.
* Power filtering equipment.
Principle of operation
The on-board CompactRIO system acquires simultaneous signals from accelerometers, encoders, and strain gauges. Vibration and strain signals are continually monitored and compared to alert and alarm set points as a first indicator of trouble. Signals are periodically stored at user-defined intervals in case of an alert or alarm. In this case, the monitoring application on the CompactRIO system searches for the best measurement periods to analyse and optimise the signal-to-noise ratio. With this approach, data is stored at regular, predefined intervals to control eventual mechanical changes in the machine, and data is recorded when a sudden event occurs. In both cases, complementary signals from the shovel control system are stored for reference and to enhance the possibilities of proactive corrections.
Acquired data is temporarily stored on the CompactRIO internal flash disk, and is later automatically downloaded via a wireless link to a master server, where the data is processed, compared against more complex alert and alarm parameters, and stored in a database. Once the data is processed and stored, it is available for user visualisation, analysis, manual processing, and trends management on the server or on any computer with network access to the database. All configurations, data transfer, processing, visualisation, and analysis software was built using LabVIEW.
As of April 2008, nine shovels are continuously monitored with SiAMFlex at four different open-pit mining locations in Chile, two of which are among the biggest copper mines in the world. In addition to continuous monitoring systems, CADETECH developed several portable instruments for shovels that do not use the SiAMFlex system. One of which is based on the NI CompactDAQ system and the other uses the CompactRIO and the NI TPC-2006 touch-panel computer to configure a fully autonomous, rugged 16-channel instrument in a suitcase form factor that performs vibration analysis.
These developments are evidence of the flexibility, ease of use, and determinism of the hardware and software development platform by National Instruments.
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version