Automatic Guided Vehicles for pallet handling in large warehouses generate many advantages, for example efficient running 24 hours per day and less damage to goods. JBT Corporation are a world leader in automated material handling. For a recent contract to automate the handling in a distribution warehouse, they approached Lenze for dc geared motors to lift loads of up to two pallets. The Lenze solution was a customised geared motor resulting in lower current demands and extended battery life for the AGV.
JBT Corporation, also known as John Bean Technologies, was established in 2008 as a spin-off from FMC Technologies. Their US headquarters is in Pennsylvania, and the European headquarters at Blaby, Leicestershire with satellite operations in Belgium and France. Their speciality is AGV’s that are battery powered and laser guided meaning that no floor tracks are needed so the system can be more flexible and future proof. Customers for these AGV systems are usually handling high volumes of products destined for the consumer market, for example food, beverage and pharmaceuticals. In this case 17 forked AGV’s were required to lift 1 or 2 pallets at a time, each pallet weighing up to 1100Kg. A traditional limit on AGV performance is the life of the on-board 48V batteries so battery consumption is an area which is important.
Lenze Ltd were asked to supply an equivalent to the lifting drive previously used – a 3kW dc worm geared motor of American manufacture. The motor is connected by shaft coupling to a vertical ballscrew, 50mm diameter and 10mm pitch. This lifts the pallet load with a maximum capacity of 2500kg plus the framework of 750kg at a speed of 25mm/s. The Lenze approach was to ‘Rightsize’ by going back to basics, re-calculating the requirements and optimising the drive. Two main factors reduced the size of the drive. Lenze chose an efficient gearbox, the type GKR helical bevel which has an efficiency at 96% compared to around 70% for the previous worm gearbox. Secondly advantage was taken of the intermittent duty for the lifting drive. An S3-50% rating allowed the motor speed to be increased to 3700 r/min by means of a special winding which in turn increased the power from 600 to 850W. Together these factors brought down the size and weight of the lifting drive, plus the running currents were sharply reduced.
The Rightsizing process also considered the lifetime. The safety factor for the ballscrew was known to be 2, so the gearbox was selected to be with a higher factor, actually 2.9, in order to be sure of a long service life. There was also attention to the brake fitted to the back of the motor which is required to stop and hold the load. A spring applied model from Lenze partner INTORQ was selected, rated at 4Nm. The brake disc is a wearing item so Lenze calculated the stopping time of 0.4s, the energy per stop and subsequently the lifetime which was above 50K operations, even under full load. With components proven to handle the loads and duties, Lenze combined the motor, brake and gearbox into a customised assembly. This included a special second output shaft for JBT to fit their standard encoder feedback. The geared motor has a rated output torque of 51Nm and an output speed of 148r/min.
In operation a master computer initiates demand on the AGV’s. A wireless network communicates the route to be followed to the on-board processor. Within the processor each AGV has a 3D graphical image of the plant. On the top of each vehicle a rotating laser sensor triangulates actual position from reflective strips positioned around the plant. At the same time the distance moved and position is being calculated by signals from an encoder on the wheel drive. Safety sensors mounted to the side of the AGV give 360° detection of obstructions.
JBT are proud to supply AGV systems that maximise safety, performance and value for the service life. As part of a process of continuous improvement, the incorporation of Lenze geared motors for the lifting drives has achieved more efficiency, a lower purchase cost and extended battery life. The case illustrates the benefits of the Lenze Rightsizing process which reduced the motor power from 3kW to 850W by the use of special motor windings and an efficient gearbox.
Lenze Ltd
Tel: 01234 321242
Email: sales@lenze.co.uk
www.lenze.co.uk
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