Posted to News on 16th Nov 2009, 15:08
Custom gearmotor cuts AGV cost and power consumption
Lenze has applied its Rightsizing process when specifying a geared motor for an AGV; the result is a customised geared motor that costs less, offers high reliability and extends the AGV's battery life.
Automatic guided vehicles for pallet handling in large warehouses offer many advantages, such as efficient running 24 hours per day and less damage to goods. JBT Corporation is a world leader in automated material handling and for a recent contract to automate the handling in a distribution warehouse, the company approached Lenze for DC geared motors to lift loads of up to two pallets. Lenze supplied a customised geared motor that resulted in lower current demands and extended battery life for the AGV.
JBT Corporation (John Bean Technologies) was established in 2008 as a spin-off from FMC Technologies, specialising in AGVs that are battery powered and laser guided, meaning that no floor tracks are needed and the system is 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 AGVs were required to lift one or two pallets at a time, with 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 important consideration.
Lenze was asked to supply an equivalent to the lifting drive previously used - a 3kW DC worm geared motor of American manufacture. The motor is connected via a shaft coupling to a vertical ball screw of 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 the geared motor by going back to basics, re-calculating the requirements and optimising the drive. Two main factors reduced the size of the drive: first, Lenze chose an efficient gearbox, the type GKR helical bevel, which has an efficiency at 96 per cent compared to around 70 per cent for the previous worm gearbox; second, advantage was taken of the intermittent duty for the lifting drive. An S3-50 per cent rating allowed the motor speed to be increased to 3700rpm by means of a special winding that, 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.
Operating life
The Rightsizing process also considered the lifetime. The safety factor for the ball screw was known to be 2, so a gearbox was selected with a higher factor (2.9) in order to be sure of a long service life. Attention was also paid to the brake fitted to the back of the motor, which is required to stop and hold the load. A spring-applied brake 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 50,000 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 its standard encoder. The geared motor has a rated output torque of 51Nm and an output speed of 148rpm.
In operation a master computer initiates demand on the AGVs. A wireless network communicates the route to be followed to the on-board processor. Within the processor each AGV has a 3D digitised model 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 calculated by signals from an encoder on the wheel drive. Safety sensors mounted to the side of the AGV give 360-degree detection of obstructions.
JBT is 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. This case study 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.
Contact Lenze for more information about Rightsizing and custom geared motors.
