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Positioning drives at the heart of a carpet recycling machine

Positioning drives at the heart of a carpet recycling machine Sellers Engineers of Huddersfield manufacture carpet finishing machinery for markets across the world. Their new patent-protected Fibrebak machine, aimed at the North American market, processes waste and used carpet, recovering the reusable fibres. Seventeen axes of Lenze drives are used and ten of these have built-in positioning functionality capable of achieving precise machine settings. The end result is a simple automated system that reduces costs through a reduction in components and faster build times.

The Sellers company was formed 99 years ago to service the local cloth industry in West Yorkshire. They came to specialise in carpet finishing machinery such as coating, shearing, backing and drying. As well as their Huddersfield factory, new in 2011, they have an operation in Georgia, USA, which services North and South America. In recent years the rising cost of waste management has opened the market for recycling machinery. Carpets make high volume waste, costly to dispose of, and incineration is not a practical alternative due to toxic chemicals in the backing. The USA market was looking for machines to separate nylon based fibres from the carpet backing so that the fibres can be reused. The machines should suit both carpet manufacturers who have to dispose of edge trimmings, and waste recycling companies handing end-of-life carpet.

The new Fibrebak pile removal system separates the fibres from the backing and gives separate outputs suiting both carpet factories and post-consumer waste. An infeed conveyor is manually fed with carpets or carpet tiles. The carpet is brought to a horizontal saw blade that is finely adjustable to the heights of the pile and backing. Vertical motion is achieved through 10KN screw jacks and positional accuracy is achieved with the aid of motor-mounted 2048 pulse encoders. Separate outfeeds deliver fibres to the side of the machine and backing material to the rear. A touch screen operator panel is positioned to the front and side of the machine, easily accessible for the operators.

One of the big advantages offered by the Lenze system is the way 10 inverter variable speed drives have integrated positioning functionality. On the Fibrebak machine, positioning is required to set the height of the blade head, the tracking and the blade grinding wheels. The Lenze 8400 HighLine inverters feature point-to-point positioning with the associated travel profiles and 100 kHz evaluation of encoder signals, all without need for external control. Set-up is made simple with L-force engineer software, and a plug-in memory module allows drives to be exchanged without reprogramming.

The Lenze solution ranges from the motors right up to the screw jacks and the inverter drives. CAN is the chosen field bus as it is standard at no extra cost in the 8400 inverter drives. The CAN network covers the 10 HighLine and a further two 8400 StateLine inverters. The remaining five motors are fixed speed.

Further system simplification and cost reduction is achieved by the Safe Torque Off (STO) option on the Lenze inverters. This is certified to ISO 13849-1 Performance Level "e" meaning that after a safety stop signal the machine can be worked on without fear of uncontrolled movement. The STO option means that a safety contactor between the drive and the motor is not required. Furthermore there is no need to disconnect the power to the drives so restart can be instantaneous without waiting for the drives to boot up. Safe Torque off is a popular option on all 8400 drives that invariably reduces cost through system simplification.

A mix of motors and geared motors is supplied by Lenze. For intermittent duties such as adjustments, worm gearboxes are suitable as they are low cost and the energy losses through inefficiency are insignificant. The same applies to the screw jacks which have short running times. Where the duty approaches 100%, for example on the feeds, high efficiency geared motors are supplied such as the type GKR, a bevel helical design with wear-free efficiency at around 96%. Power ranges from 90W for the blade tracking up too 11KW for the blade drive.

For the Fibrebak machine Sellers engineers needed easy operation and simple low cost positioning which they get from the 8400 Highline inverter drives. The additional simplification and cost reduction from choosing the STO safety option was a bonus. The Fibrebak design is heavily based on the drive technology. The drive package from Lenze makes sense in terms of a single point of responsibility that led to easier engineering.

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