Comparision of fixed aisle vs. aisle changing s/r machine technology.

1. Solution Profile
An Unbiased Comparison of
Captive-Aisle & Aisle-
Changing AS/RS
Technologies

2. DAMBACH Lagersysteme manufactures Automatic Storage /
Retrieval Machines of all shapes, sizes, types, and performance
– including “aisle-changing” and “aisle-bound”.
Customer requirements will dictate the best technology and
material flow for the application.
Aisle-changing Automated Storage and Retrieval Systems
(AS/RS) involve the utilization of fewer Storage and Retrieval
Machines (SRMs) than there are aisles of storage.
The following factors are considered when planning any AS/RS,
including both aisle-bound and aisle-changing:
1. Throughput
2. Inventory management
3. Asset utilization
4. Reactivity
5. Investment
6. System sizing
7. Technical complexity
8. Vulnerability
9. Storage capacity
1. Throughput
Throughput is a function of system layout and machine
performance. Aisle-changing systems (when changing at the
rear) work best when machines can perform multiple
transactions before changing aisles (i.e. “wave based” systems).
Aisle-changing machines have equal performance to aisle-
bound machines in terms of speed, acceleration, and
positioning.
Example calculation (loads in/out per machine):
 System 80ft tall x 300ft long.
 Pick-up / drop-off at front-end of system. Aisle change at
rear (1) machine, (2) aisles.
 Single-deep. Both technologies capable of multiple-deep
storage.
 For the aisle change machine it changes aisles every 10
double cycles.
 If aisle-bound then 34.7 combined cycles / hour / machine.
 If aisle-changing then 32.7 combined cycles / hour /
machine.
 This means the aisle-changing machine sacrifices 5.7% in
performance to change aisles.

3. Aisle-bound systems generally tune machine performance to
minimize the number of aisles, with limited ability increase
performance in the future without expanding the complete
system.
Aisle-changing systems performance can be increased without
changing the complete system (adding rack and building) by
simply adding additional machines.
2. Inventory Management
Incoming loads are balanced across all aisles in both aisle-
changing and aisle-bound systems.
Warehouse control software will dictate frequency of aisle-
change to optimize material flow, shipping / receiving
requirements, and equipment utilization.
Contrary to aisle-bound systems, any aisle-changing machine
can access any aisle. This means that even if a machine is out
of service, 100% of storage locations are accessible by the
remaining machines.
3. Asset Utilization
Aisle-changing systems can be single-ended or double-ended.
It depends on the application.
In many scenarios, the aisle-changing occurs at the front of the
system. This has the advantage that only (1) set of input /
output points is required for each machine (as opposed to each
aisle, for an aisle-bound system).
For example, in a system with (2) machines in (6) aisles – the
aisle-changing system can be designed with (2) pairs of
inputs/outputs as opposed to (6) pairs. Of course, there are
many other design possibilities. It depends on the application.
As with aisle-bound systems, aisle-changing systems usually
“velocity zone” the rack.
4. Reactivity
Reactivity of the aisle-changing system depends on system
design. Particularly, whether the system uses front or rear
aisle-changing.

4. Using the previous application (80ft tall x 300ft long). In the
aisle-bound system, the “average” single-cycle (hot pick) is 62.3
seconds. In an aisle-changing system with rear-aisle change,
where the machine is in the “wrong aisle” a single-cycle will take
126.7 seconds.
On the other hand – the system design should not be configured
around a very small percentage of “hot picks”. If there are high-
percentages of “hot picks” throughout the day, other factors
should be considered in the design of your material handling
system.
Periodic “hot picks” will not significantly affect total system
performance.
5. Investment
Total cost of ownership (and original capital cost) should be
evaluated on a case-by-case basis for each customer. In many
cases, choice of technology is “operationally based” or “material
flow” based. Capital cost is only one part of the equation.
Each system is unique, but generally speaking an aisle-
changing system requires fewer SRMs, thereby minimizing
maintenance and spare-parts requirements. Track switches are
very reliable and only require 15 minutes of preventative
maintenance 3x per year each aisle.
Aisle-changing machines by DAMBACH Lagersysteme do not
require batteries to change aisles. The machines are in
constant contact with 480VAC buss-bar.
6. System Sizing
Both aisle-changing and aisle-bound systems are sized for the
application by adjusting design elements such as: machine
performance, rack length and height.
Both aisle-changing and aisle-bound machines are capable of
the same machine performance (speed / acceleration) in all
axis’. Both technologies are capable of single, double, triple-
deep and deep-lane storage.
Both technologies allow system heights in excess of 120ft. In
fact, DAMBACH Lagersysteme built an aisle-changing machine
in 1982 (27 years ago!) that was 117ft tall. We’ve been building
aisle-changing machines that height and taller ever since.

5. 7. Technical Complexity
Aisle-changing machines have been used in the industry for
over 30 years. They utilize time-proven designs, are reliable
and easy to maintain.
DAMBACH aisle-changing machines do not use batteries; no
controls or electronics on upper guide rail (all “intelligence” at
floor level); “firmware” changes are automatic across all
machines simultaneously through the “Master Controller” in the
event of changes to the rack or system layout.
Both aisle-changing and aisle-bound machines require similar
preventative maintenance and spare parts inventories.
Maintenance hours and cost depends on number of machines
and aisles.
8. Vulnerability
Both aisle-changing and aisle-bound SRMs by DAMBACH
Lagersysteme provide an availability rating of 99%. However,
with aisle-changing machines access to inventory is virtually
100%.
In an aisle-bound system, if the machine is out of service – the
inventory in that aisle is completely unavailable. With an aisle-
changing machine, the out of service machine can be moved to
a maintenance area and the remaining machines can service all
aisles.
9. Storage Capacity / Building Size
Aisle-changing machines require very compact run-out
dimensions. For example:
Aisle-bound machine with GMA pallet, 80ft tall:
 Front runout: 106”
 Rear runout: 204”
 Total runout (front + rear): 310”
Aisle-changing machine with GMA pallet, 80ft tall:
 Front runout: 106”
 Rear aisle change (cross-aisle): 193”
 Total runout (front + rear aisle change): 299”
The required building footprint with both technologies is very
similar. All else is equal in terms of clearances, storage depths,
heights, etc.

6. Example System Designs
Aisle Change at Back
CRANE
Aisle Change at Front
CRANE
 Aisle-change at back increases throughput when machines
stay in aisle for multiple cycles.
 Aisle changing at front minimizes front end conveyor
complexity.
 Aisle changing at front allows additional storage for “staged”
loads and “A” movers.
For more information regarding DAMBACH Lagersysteme,
call (616) 334-9969 or visit www.dambach-usa.com.

7. Example System Designs
Aisle Change at Back
CRANE
Aisle Change at Front
CRANE
 Aisle-change at back increases throughput when machines
stay in aisle for multiple cycles.
 Aisle changing at front minimizes front end conveyor
complexity.
 Aisle changing at front allows additional storage for “staged”
loads and “A” movers.
For more information regarding DAMBACH Lagersysteme,
call (616) 334-9969 or visit www.dambach-usa.com.

8. Example System Designs
Aisle Change at Back
CRANE
Aisle Change at Front
CRANE
 Aisle-change at back increases throughput when machines
stay in aisle for multiple cycles.
 Aisle changing at front minimizes front end conveyor
complexity.
 Aisle changing at front allows additional storage for “staged”
loads and “A” movers.
For more information regarding DAMBACH Lagersysteme,
call (616) 334-9969 or visit www.dambach-usa.com.

9. Example System Designs
Aisle Change at Back
CRANE
Aisle Change at Front
CRANE
 Aisle-change at back increases throughput when machines
stay in aisle for multiple cycles.
 Aisle changing at front minimizes front end conveyor
complexity.
 Aisle changing at front allows additional storage for “staged”
loads and “A” movers.
For more information regarding DAMBACH Lagersysteme,
call (616) 334-9969 or visit www.dambach-usa.com.