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FEATURE CLUTCHES, BRAKES & COUPLINGS


improving tHe safety of quarry equipment


To improve reliability and safety on site, WEG and its premier


partner Technidrive have developed a skip drive with a brake control solution for TH Moore’s (Contracts) quarry equipment


I


n hazardous industries like quarrying, motion control is paramount – if a skip laden with a ton and a half of product were to go hurtling


off its rails at 80mph, the consequences could be devastating. At one quarry, a skip drive system on a set of rails, powered by a motor, was used to move products on site. The system saw a skip drive up the rails to sit below a mixer or above three different bin positions – one used for loading straight into a lorry and two for storage bins. However, electrical problems and equipment


breakdowns resulted in multiple safety concerns, and with the issues getting increasingly difficult to diagnose, the contractor decided an entire system upgrade was necessary. So, to overcome the problems, a skip drive with a brake control solution was developed for TH Moore’s (Contracts) quarry equipment.


tHe solution


Technidrive (www.technidrive.co.uk) was brought on board to design and commission a new skip drive solution and control system with a programmable logic controller (PLC) and full touch screen integration; and the company turned to WEG to supply a motor and a variable speed drive (VSD) for the skip upgrade project. One of the main problems associated with the


old system was the excessive brake wear on the skip motor, as it wasn’t used with a VSD. If an operator selected bin one and pressed start, the skip would firstly drive down to the mixer. As soon as it would hit the limit switch it would slam the brake on and disengage the motor, resulting in a harsh stopping time. Once the system had sent the message that the deposit was complete, it would then engage the motor and run harsh acceleration to drive up to bin one’s position. WEG provided a 22kW 4 pole B5 cast iron


brake motor with an integrated 1024 pulse encoder, and for the skip drive it recommended the CFW700 VSD with integrated high torque brake control. This brake control, along with some intelligent programming of the on board soft PLC, means that Technidrive has been able to virtually eliminate brake wear and significantly reduce motor maintenance. The skip system features an auto slow down


function, which allows the motor to stop on the VSD before the brake is applied. Now the brake is only used as a holding mechanism and the system is no longer driving against an engaged brake. Furthermore, virtual positions programmed for each location allow for a slow ramp up using the VSD. Before the skip arrives into its final position, the new system leaves space for slow down. This allows the skip to


stop from a slower speed in the same position every time. This has further reduced wear and tear on the mechanical system.


reducing downtime


The old system also had an outdated, unreliable and obsolete PLC system. This meant that if there was a digital input or card that went faulty, replacements were not readily available. The PLC system worked off a series of limit switches used as part of the control system as a safety interlock, so Technidrive designed a new PLC system that was able to read the encoder. This has a 10in Hitachi human machine interface (HMI) instead of a series of push buttons and controls. Due to the encoder feedback and the live skip


position function, the operator knows exactly where the skip is at any point, meaning easier and safer control between the four positions, visible on the touch screen display. Monitoring can also be conducted from a tablet or mobile. If the encoder fails, the operator also has


full manual control. For example, if the encoder slips on the shaft of the motor and the skip is moving up, the encoder will not recognise it, and a belt and braces system is in place to prevent the skip driving over the end. To further increase safety, anti-free wheel protection was built into the system to stop the skip motor if freewheeling. Commenting on the


solution, Mark Poots, quarry manager at GibsonBros, said: “We used to be marred with electrical problems, but Technidrive and WEG provided a cost-effective way of upgrading the obsolete control system to an industry leading alternative. This has not only reduced downtime but, if component failure does occur, replacements are more readily available. No one wants to see a skip rocket across the quarry and our new system is the safest way of operating this system.”


WEG www.weg.net


5 DESIGN SOLUTIONS OCTOBER 2022 0


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