HEALTH & SAFETY
COMPLETE SKIP DRIVE SOLUTION OFFERS SUPERIOR CONTROL
Increasing the safety and reliability of quarrying operations Motion control is paramount in hazardous industries like quarrying. 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. Here’s how motor and drive manufacturer WEG and the company’s premier partner Technidrive, developed a new skip drive with a brake control solution to upgrade TH Moore (Contracts) Ltd’s quarry equipment to improve reliability and safety on site.
H Moore, a GibsonBros Ltd associated company, is a supplier of quarry materials, high grade aggregates and CE marked bituminous products. Before the project, the quarry in question used an outdated skip drive system on a set of rails powered by a motor to move product on site.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. The system’s usage was dependent on the product, operational intermittently with no set running hours. Plagued with a wide range of electrical problems, and equipment breakdowns leading to multiple safety concerns, these faults were made harder to identify and rectify as the system was only operational for two to three months each year. The electrical contractor was the first point of contact for these breakdowns, but as the issues were getting increasingly difficult to diagnose, the contractor decided an entire system upgrade was necessary. Technidrive was brought on board to design and
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commission a new skip drive solution and control system with a programmable logic controller (PLC) and full touch screen integration. The company turned to its long-term partner WEG to supply a
motor and a variable speed drive (VSD) for the skip upgrade project.
REDUCED MECHANICAL WEAR 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. For the upgrade, Technidrive turned to WEG
who provided a 22kW 4 pole B5 cast iron brake motor with an integrated 1024 pulse encoder. With superior efficiency levels, this motor was selected as it offers excellent cost effectiveness, greater productivity and the durability required for quarrying applications. For the skip drive, WEG recommended the CFW700 VSD with integrated high torque brake control. This integrated brake control, along with some intelligent programming
28 FEBRUARY 2023 | FACTORY&HANDLINGSOLUTIONS
of the on board soft PLC, means that Technidrive have been able to virtually eliminate brake wear and significantly reduce motor maintenance. The new 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.
REPLACING AN OBSOLETE SYSTEM: CONTROL, VISIBILITY AND RELIABILITY Another glaring issue with the old system was that it used 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 original PLC system worked off a series of limit switches used as part of the control system as
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