Storage / Retrieval System


Large quantities are put into storage in a
high-bay warehouse. There are many aisles but the material flow
rate is low. In this case, the storage and retrieval system has
to have cornering capability because it must travel along many aisles.
Cornering capability means that there is a differential between
the front and rear drives, and that high transverse force during
cornering can be avoided by means of active cornering control. When the
front wheel enters the corner, the rear wheel is still running on
the straight and is decelerated. Then, when the rear wheel enters
the corner, the front one is running on the straight again. This
results in a significant acceleration of the rear wheel, which may be
as much as a factor of 2 or more depending on the radius and the
distance between the axes.

Storage / Retrieval System

This puts the following requirements on the
drive system:

  • Load distribution, both wheels
    are driven
  • Slip control
  • Cornering capability, electronic differential

Intelligent inverters are needed particularly
for cornering capability. The machine control cannot manage this
Storage / Retrieval System

The basis for this is that the speed of both
wheels is known. Both wheels of the storage/retrieval system are
driven; the load is shared by both drives. The driving motors are
equipped with an incremental encoder and each one is supplied by
its own inverter.

Both wheels are driven and each one is supplied
by its own MOVIDRIVE® inverter.
The inverters are connected via the system bus (SBus) and via the
RS-485 interface. Both are standard.
  • Electronic differential with system
    bus (SBus)
  • Load distribution with the RS-485 interface

A significant feature of MOVIDRIVE® drive inverters, the IPOSplus® positioning and sequence control
system, now comes into play. An IPOSplus® program
in MOVIDRIVE® calculates the
setpoint speed of the master drive based on the speed specification
for cornering and the actual speed of both drive wheels. The slave
drive operates with torque control.

  • The MOVIDRIVE® units
    exchange the data for speed control and load distribution via the
    system bus and the RS-485 interface.
  • All movement control is carried out by the IPOSplus® program in MOVIDRIVE®.
  • High overhung loads are avoided through the electronic
    differential, which ensures safer operation of the storage/retrieval
  • Safe traction of the storage/retrieval system through
    slip control
  • With active cornering control it is possible to negotiate
    corners 2.5 to 3 times as quickly
  • Safe operation of asynchronous AC motors even in the
    field weakening range
  • Simple integration into higher-level machine control
    systems is possible via fieldbus.

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