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自动化立体仓库(英文)[1]

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2021-01-25 03:00
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2021年1月25日发(作者:查尔斯)
关于自动化立体仓库使用双货叉问题的探讨
-An
Analysis
Of
Dual
Shuttle
Automated
Storage/Retrieval Systems




An Analysis Of Dual Shuttle
Automated Storage/Retrieval Systems

Adhinarayan Keserla
Brett A. Peters

August 1, 1994

This
working paper
is not
to
be
copied, quoted,
or
cited
without
the
permission
of
the
authors.
Address
correspondence
to
Brett
A.
Peters,
Dept.
of
Industrial
Engineering,
Texas
A&M
University, College Station, TX 77843-3131 or email to bpeters@



Abstract
This
paper
addresses
the
throughput
improvement
possible
with
the
use
of
a
dual
shuttle
automated storage and retrieval system. With the use of such a system, travel between time in a
dual command cycle is virtually eliminated resulting in a large throughput improvement. The dual
shuttle system is then extended to perform an equivalent of two dual commands in one cycle in a
quadruple command mode (QC). A heuristic that sequences retrievals to minimize travel time in
QC mode is developed. Monte Carlo simulation results are provided for evaluating the heuristic's
performance and show that it performs well, achieving large throughput improvements compared
with
that
of
the
dual
command
cycle
operating
under
the
nearest
neighbor
retrieval
sequencing
heuristic.

Keywords:
Automated
Storage/Retrieval
Systems
Design;
Automated
Storage/Retrieval
Systems
Operation;
Material Handling Systems; Performance Modeling and Analysis



Introduction
Automated storage/retrieval systems (AS/RS) are widely used in warehousing and manufacturing
applications. A typical unit load AS/RS consists of storage racks, S/R machines, link conveyors,
and
input/output
(I/O)
stations.
An
important
system
performance
measure
is
the
throughput
capacity
of
the
system.
The
throughput
capacity
for
a
single
aisle
is
the
inverse
of
the
mean
transaction
time,
which
is
the
expected
amount
of
time
required
for
the
S/R
machine
to
store
and/or retrieve a unit load.
The service time for a transaction includes both S/R machine travel
time and pickup/deposit time. This time typically depends on the configuration of the storage rack
and the S/R machine specifications.

Han
et
al.
[2]
improved
the
throughput
capacity
of
the
AS/RS
through
sequencing
retrievals.
Intelligently sequencing the retrievals can reduce unproductive travel between time when the S/R
machine is traveling empty and thereby increase the throughput. They develop an expression for
the maximum possible improvement in throughput if travel between is eliminated for an AS/RS
that is throughput bound and operates in dual command mode. In essence, this means that if the
S/R
machine
travels
in
a
single
command
path
but
performs
both
a
storage
and
a
retrieval
operation, the above throughput improvement could be obtained.
In this paper, we analyze an alternative design of the S/R machine that has two shuttles instead of
one as in a regular AS/RS. The new design eliminates the travel between the storage and retrieval
points and performs both a storage and a retrieval at the point of retrieval, thereby achieving the
maximum throughput increase calculated by Han et al. [3].

The
dual
shuttle
AS/RS
is
a
new
design
aimed
at
improving
S/R
machine
performance.
most
studies on AS/RS systems have been based on a single shuttle design. In our analysis of the dual
shuttle AS/RS performance, we build upon these previous research results.

Alternative S/R Machine Design
A
typical
unit-load
AS/RS
has
an
S/R
machine
operating
in
each
aisle
of
the
system.
The
S/R
machine has a mast which is supported at the floor and the ceiling and travels horizontally within
the
aisle.
Connected
to
this
mast
is
a
shuttle
mechanism
that
carries
the
unit
load
and
moves
vertically up and down the mast. The shuttle mechanism also transfers loads in and out of storage
locations in the rack. Figure 1 provides an illustration of the single shuttle S/R machine.

Figure 1. Single Shuttle S/R Machine Design

A typical single shuttle AS/RS can perform a single command cycle or a dual command cycle. A
single command cycle consists of either a storage or a retrieval. For a storage, the time consists of
the time to pickup the load
at the
I/O point, travel to
the storage point, deposit the load at that
point, and return to the I/O point. The time for a retrieval is developed similarly.

A dual command cycle involves both a storage and a retrieval in the same cycle. The cycle time
involves the time to pickup the load at the I/O point, travel to the storage location, place the load
in
the
rack,
travel
empty
to
the
retrieval
location,
retrieve
a
load,
return
to
the
I/O
point,
and
deposit the load at the I/O point.

If we critically analyze the dual command cycle of the S/R machine (shown by the solid line in
Figure 2), a potential open location for a future storage is created when a retrieval is performed.
Furthermore, if both a retrieval and a storage are performed at the same point, the travel between
time (TB) is eliminated, and the travel time will be equal to the single command travel time. With
the existing AS/RS design, this mode of operation is not possible; therefore, an alternative to the
S/R machine, a dual shuttle R/S machine, is proposed.

Figure 2. Dual Command Travel Paths of S/R and R/S Machines

R/S Machine Operation
Consider
an
S/R
machine
with
two
shuttle
mechanisms
instead
of
one.
This
new
S/R
machine
could now carry two loads simultaneously. Each shuttle mechanism could operate independently
of the other, so that individual loads can still be stored and retrieved. An illustration of the dual
shuttle
S/R
machine
is
shown
in
Figure
3.
This
new
S/R
machine
would
operate
as
described
below.

Figure 3. Dual Shuttle S/R Machine Design

The S/R machine picks up the item to be stored from the I/O point, loads it into the first shuttle,
and
moves
to
the
retrieval
location.
After
reaching
the
retrieval
location,
the
second
shuttle
is
positioned to pickup the item to be retrieved. After retrieval, the S/R machine positions the first
shuttle and deposits the load. The S/R machine then returns to the I/O point. The operation can
easily be seen as a single command operation plus a small travel time for repositioning the S/R
machine
between
the
retrieval
and
storage
(as
well
as
the
additional
pickup
and
deposit
time
associated
with
the
second
load).
Therefore,
the
S/R
machine
now
operates
as
an
R/S
machine
performing a retrieval first then a storage in a dual command cycle.

Since the R/S machine has two shuttles, the position of the shuttles has a role in the operation of

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