Framo Morat and Dunkermotoren Produce Drive Systems for AGVs
Driverless
transport systems have proven to be extremely economical and productive.
For example, they are used to distribute goods that are picked in large storage
and freight forwarding halls. The vehicles—often referred to as Automatic
Guided Vehicles (AGVs)—are also used to transport individual parts and
prefabricated components into processing stations in assembly and production
halls. They usually work autonomously, using sophisticated sensor technology to
orient themselves within their environment. Their routes and destinations are
programmed and stored in a built-in computer, and the electric power for the
driving motor is provided by rechargeable batteries carried in the vehicle.
Compact vehicles ensure a long useful life
AGVs are particularly productive and economical if
they can complete long distances and operating periods without repeated
recharging of their batteries. This places special demands on their design and
construction. In particular, the vehicles and components installed therein must
be lightweight and compact. Especially, the AGV manufacturers require high
power density and energy efficiency from the drive system. As a further
problem, the increasingly smaller shuttle vehicles used for distribution systems
in warehouses contain little available space for these drives. This means that
the standard drive units with axially arranged electric motors and multi-stage
spur gears and planetary gears cannot be installed due to their overall length.
With unattended operation around the clock, driverless
transport systems (AGVs) in warehouses, parcel distribution
centers and production halls ensure maximum profitability
and reliability when distributing goods, packaging materials
or components (photo courtesy of Framo Morat).
In accordance with the requirements of the AGV
manufacturers, the gear manufacturer Framo Morat from Eisenbach and the motor
manufacturer Dunkermotoren from Bonndorf have developed and implemented a
particularly compact DC drive system. The system’s hub gears, which were
designed by Framo Morat, are a particularly impressive feature.
As Wolfgang Sühling, who is responsible for the
development of custom drives explains at Framo Morat, this is the first time
that this gearbox design has been used in a drive system for an AGV.
“In addition to its compact dimensions, this gearbox
design has further decisive advantages, especially for the wheel and toothed
belt drives that are frequently installed in shuttle vehicles,” he says. In
conventional wheel or belt drives, in which a planetary gear unit or a spur
gear unit is used, large radial loads act on the bearings due to the load
distribution into the protruding shaft. The bearings installed in the gearbox
must be able to withstand this.”
However, standard shaft bearings with grooved ball
bearings or preloaded tapered roller bearings have some major disadvantages,
according to Sühling.
“When ball bearings are arranged closely behind one other,
radial loads acting on the protruding shaft end lead to high bearing loads. Due
to the bearing clearance in combination with the short bearing spacing, which
is dictated by the design limitations, this also results in an inclined
position of the output shaft and individual transmission components, for example
the planetary carrier. As a result, the gears wear very quickly and the
required service life and reliability cannot be guaranteed. In addition, the
inclination of the shaft causes increased noise emissions. Although pairs of
pre-tensioned tapered roller bearings can easily accommodate larger radial
loads, they suffer greater bearing losses than grooved ball bearings,
especially in the partial load range. Moreover, they are larger and heavier
than grooved ball bearings,” explains Sühling. For this reason, the gearbox
specialists from the Black Forest looked for an alternative to the usual spur
and planetary gearboxes that are flanged to the electric motor.
Thanks to their compact design and high efficiency,
drive systems consisting of DC motors as well as
bevel gears and hub gears are beneficial for mobile
applications (photo courtesy of Dunkermotoren).
Compact design easily handles
large radial forces
The newly developed hub gears use standard ball bearings
to absorb the high radial loads. “The designation of this gearbox design
provides an insight into its special design features. The entire gearbox can be
accommodated inside a narrow wheel hub,” reports Sühling. In this gearbox type,
the drive shaft and output shaft are arranged coaxially, one inside the other.
The radial forces are distributed almost centrally between the two ball
bearings via the hollow shaft. The small clearance between the ball bearings
has a positive effect on the bending stiffness of the hollow output shaft,
which scarcely bends at all.
A planetary gearbox transmits the torques between the
drive and the output shaft. It provides the required transmission ratios for
the speeds between the drive and the output side. For the attached
electronically controlled DC motors from Dunkermotoren, these are usually
between i=20 and i=30. And because the
planetary carrier is only inclined to an insignificant degree, the gearbox runs
extremely quietly.
Hub gears from Framo Morat prove their value
as wheel drives for AGVs due to the advantageous
arrangement of both the bearings and the drive and
output shafts (photo courtesy of Framo Morat).
In order to make the
entire drive package particularly compact, a bevel gearbox connects the DC
motor to the input shaft of the hub gears. “With this combination, we can
achieve the smallest installation space with the maximum energy density,” emphasizes
Stefan Tröndle, product manager at Dunkermotoren in Bonndorf. “The combination
of our brushless, electronically controlled DC motors with over 90 percent
efficiency and the very light, low-loss bevel and planetary gearboxes enable us
to achieve very high efficiency for the entire drive system and thus high
energy efficiency. This innovative drive system plays a decisive role in making
the shuttle vehicles particularly cost-effective,” adds Tröndle.
Custom modular configuration
The drive units are configured according to the
individual requirements of the AGV manufacturers. At the same time, by using
their existing modular system, the motor and gearbox manufacturers can ensure
short delivery times and economic investments. The two companies can thus
combine their standardized, modular components to create the required drive
system.
The electronics integrated into the DC motor enable
the drive systems to be networked via different fieldbus
systems (photo courtesy of Dunkermotoren).
For this purpose, Dunkermotoren provides electronically
commutated DC motors from its BG series. Depending on the model, they operate
with 10 V to 60 V DC. With a 24 V supply voltage, they can provide a permanent
drive power of 1100 W and can reach a maximum of 2600 W for short periods. In
addition to models with integrated commutation, versions with built-in speed
control or positioning electronics are also available. The integrated
electronics allow, for example, complete driving profiles to be stored and
retrieved. The CANopen, Profibus or EtherCAT bus systems provide data
communication with higher-level controllers. As a modular component,
Dunkermotoren offers suitable brakes for the respective motor size. As an option,
the motor manufacturer can implement Safe-Torque-Off (STO) via software and the
motor control. This ensures safe operation of the drives and helps to avoid
hazards for personnel and equipment in critical situations.
The hub gears designed by Framo Morat are based on gear
components from the standard gearbox series with nominal output torques of up
to 350 Nm. The gearbox manufacturer from Eisenbach customizes the outer contour
of the output shaft and the torque support in accordance with the customer’s requirements,
for example with standard toothing for toothed belts, customer-specific
shaft-hub toothing or as a smooth shaft with flange bores for a wheel rim.
For more information:
Framo Morat, Inc.
Phone: (505) 359-2949 www.framo-morat.com
