Driving line upgrades
April 1st 2004

When increased demand meant Parcelines sorter lines could no longer cope, modern drive solutions from Lenze formed an essential element of the upgrade Parceline, part of GeoPost, handles over 250,000 parcels each night more than half of which pass through four sorter lines at its Birmingham Superhub. Increasing levels of business and more demand for next day delivery meant that the 20 year old lines had to be replaced, added to or upgraded. Each line consists of a 150m conveyor, along which are 41 diverters that push the parcels across the stainless steel belt into specific destination tubes. The diverters use a flipper arm driven through a crank system from a geared motor. In ten motor revolutions the arm is driven through its cycle, then stopped and held by an electromagnetic brake. The inertia of the diverter arm mechanism, combined with the capacity and response times of the brake, meant that the system was unable to complete the cycle any faster. It also needed regular brake maintenance as wear resulted in inaccuracies in the parking position of the flipper arm and parcels became stuck, potentially causing damage to the contents. Modern drive solutions Chosen to upgrade the line, systems integrators Automation Software Engineering (ASE), approached drives specialist Lenze for advice on modern drive solutions for the project. Since the lines were originally installed, technology has developed new options for drives faster cycles can be achieved using inverter control of the motor for smoother acceleration and deceleration, without high current peaks. Inverters can also eliminate the need for dynamic friction braking, dissipating the energy electrically as heat. In this case, no longer using the electronic brakes has contributed to reduced cycle times of below 600ms and an increase in belt speed up to 168m/min. Decentralised ASE and Lenze decided to fit each diverter with a new geared motor and integrated frequency inverter. This made a decentralised solution essential as the cost of panel-mounted inverters would have been unacceptable as well as panel space, each inverter would have required shielded cables between the motor and the inverter. Instead the Lenze motec terminal box mounted inverters allow the use of an energy bus, ie. a single mains cable with short spur connections to each motor. As only cables between the inverter and the motor have to meet EMC regulations, the energy bus cabling to the inverter does not need shielding, further reducing costs and installation time. In fact, as the connection between the terminal mounted inverters and the motor are integral, no further power connections were necessary. Rather than individually wiring all components back to the control panel, ASE used AS-i field bus. Low cost and easy to install, it has simple 2 core self-healing cabling, which allows fast connection directly into the cable using simple adaptors. With a maximum of 31 slaves each, two AS-i networks have been used on each line. Each diverter has a spur connection to the Lenze inverter. In operation the inverters are given a high signal to start the arm movement. An existing proximity sensor hard wired to the control cabinet detects the position at which braking should start. Through the master PLC, this signal switches the AS-I output to low and the inverter stops the arm followed by the holding torque. The PLC constantly monitors two AS-i outputs from each inverter quickly providing alarm information to the sorter SCADA system if any of the 164 units require attention. The motec inverter, with built-in intelligence handles all aspects of normal operation, controlling acceleration, speed and braking from the single high/low signal. Each of the 5000 parcels handled every hour is barcoded. By the time they reach the barcode readers at the start of the line conveyors, they are moving at 140m/min, with a separation of one metre. When the barcode is scanned, a signal is sent to one of the 41 diverters. If consecutive parcels have the same destination, the diverter has an operating frequency of 0.75 seconds. From the point at which each parcel is off-loaded on to the sorter system, it takes just 90 seconds for it to be sorted and loaded on to the destination truck. Further increases Carried out over an eight week period without any disruption to operation, the upgrade means that Parceline can now run with a belt speed of 168m/min and there is scope for further increases through drive optimisation. With the higher speed comes the ability to handle peak demands and get the parcels into the trailers and away on time. Improvements in the holding position of the diverter arms, which result from the inverter, can be seen in a reduction in parcel damage and consequent claims. There are also lower operating noise levels.

More articles from Lenze Ltd: