The Satellite Review Magazine The Satellite Review Magazine Vol 2 | Page 36

BATTERY POWERED AND BATTERY-FREE
AUTOMATED GUIDED VEHICLES (AGVS)
By Rod Griffith, Director of Marketing, Conductix-Wampfler
Automated Guided Vehicles (AGVs)
have long being used for delivery and
material handling in logistics and
warehouse applications. AGVs are also
playing an increasing role as primary
assembly line conveyances. While most
material handling AGVs are battery
powered, a key enabling technology permitting AGVs to perform in the heavy
duty world of production line manufacturing is “Inductive Power Transfer”, also
known as wireless power. Wireless power allows AGVs to abandon the battery
and operate continuously without need
for recharging or risk of down time due
to dead batteries.
The classic battery powered AGV is ideally suited to operate in the warehouse
environment. An overnight charge
using a Battery Charging Contact is
usually sufficient to permit operations
through an entire work day. There are
enough stopping points and stopping
times to permit opportunity charging.
However, the higher duty cycle required
in production and continuous assembly line operations do not easily permit
opportunity charging. Battery operated
AGVs have often failed to perform adequately, especially in two and three shift
operations. The main limiting factor is
the energy storage capability of the AGV
battery.
AGVs could use bigger batteries, but
this adds cost and weight to each AGV
and they still need to be charged. There
needs to be sufficient ‘dead time’ for
the AGVs to be parked for charging.
Additional AGVs can be added so that
some can be offline in a charging station. But that adds extra cost as well.
Assembly line AGVs tend to be larger
and more expensive than delivery AGVs,
with additional features such as tooling
plates, lifts, and fixtures. Getting battery

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operated AGVs to operate through a
two shift production cycle is a challenge.
Operating them continuously through
three shifts is not practical. An AGV
powered with a wireless power supply
eliminates the battery and permits the
AGVs to operate continuously, without
ever needing to stop for a charge, just as
if they were ‘plugged in’, but without the
plug.
Wireless data communication for machine control has proven to be robust
and stable in even the most demanding
manufacturing environments, including
automotive. Wireless data is not only
being used for monitoring and data
acquisition, but also for machine control
and safety monitoring. Multiple devices
that are rated to transmit safety signals
via wireless can meet safety and security standards. Wireless power supply
enables the ‘cord’ to be cut completely so
the AGV can operate automatically and
indefinitely.
Logistics battery powered AGVs are
free to roam over large distances in a
warehouse or on a factory floor. Their
travel paths are flexible. A small number of AGVs, covering relatively large
distances, can deliver material from one
location to another. On-board energy storage in the form of a battery is
ideal for this application. Production or
assembly line AGVs, on the other hand,
tend to have much more clearly defined
paths since they need to interface with
tooling or defined workstations and also
frequently engage with other conveyors
such as overhead electrified monorail
systems. There are also typically a larger
number of AGVs on assembly lines, and
the routes tend to be shorter. So, there is
a higher density of AGVs on the assembly line, and they are always on the go.
These distinct characteristics of assembly

line AGVs place unique demands on the
power supply system for the conveyance,
which wireless power is able to fulfill.
Battery-free AGVs offer a number of
advantages over other assembly line
conveyance solutions.
Battery-free AGVs are:
1. Cleaner and quieter, while providing
a safer work environment and better
operator access.
2. Easier to install and can be thoroughly
tested before installation.
3. Can operate in a number of different
modes, either as an indexing line, or a
continuously moving line.
4. Provide an investment that is portable,
scalable, and flexible.
5. Need significantly less maintenance
and cause less downtime.
6. Are more sustainability, since they
don’t require batteries.
“Inductive Power Transfer” technology,
capable of transferring power in the kW
range, has been commercially available
since the 1990’s. It uses the same basic
electromagnetic induction principles as
conventional transformers. However,
instead of tightly wound and closely coupled coils on a shared magnetic core, the
IPT primary and secondary windings are
separate and move with respect to one
another. Alternating current in the primary conductor induces an alternating
current in the secondary, with which it is
loosely coupled by the magnetic field. In
order to make this process practical, the
operating frequency is increased to 20
kHz. Since energy density is increases
in proportion to the frequency, this high
frequency reduces the size and weight of
the electrical components. In addition,
IPT uses tuned resonant coils in order
to improve the coupling. The end result
is that loosely coupled inductive power
systems are about 96% efficient, whereas
batteries are typically only able to return
80% of the charging energy applied.

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