Automatic storage and retrieval system

AUTOMATIC STORAGE AND RETRIEVAL SYSTEMPRESENTED AS PART OF COMPUTER INTEGRATED MANUFACTURING COURSE

FUNCTIONS OF STORAGE SYSTEMS AND DEFINITION OF AS/RS1. Definition- AS/RS by material handling Institute as“ A combination of equipment and controls which handles, stores, and retrieves materials with precision, accuracy and speed under a defined degree of automation.”2. AS/RS perform a basic set of operations without human intervention:

1. Automatic removal of an item from a storage location2. Transportation of this item to a specific processing or interface point3. Automatic storage of an item in a predetermined location, having received an

item from a processing or interface point.

AS/RS COMPONENTS AND TERMINOLOGY USED• An automated storage and retrieval system

comprises the following:• A series storage aisles having storage racks• Storage and retrieval machines, normally one machine per

aisle, to store and retrieve materials • One or more pickup and delivery stations where materials

are delivered for entry to the system and materials are picked up from the system.

AS/RS COMPONENTS AND TERMINOLOGY USED

1. Storage space- 3-D space in the storage racks that is normally required to store a single load unit of material.

2. Bay- Vertical stack of storage locations from floor to the ceiling.

3. Row- A series of bays placed side by side.

4. Aisle- The space between two rows for the AS/RS machine operations

5. Aisle unit- Aisle space and racks adjacent to an aisle constitute an aisle unit.

AS/RS COMPONENTS AND TERMINOLOGY USED6. Storage racks- A structure entity comprising storage locations, bays, and

rows.7. Storage structure- A storage structure comprises storage racks and is used

to store inventory items.8. Storage/retrieval machine- An S/R machine moves items in and out of

inventory. 9. Storage modules- Storage modules are used to hold the inventory items.

The modules may be pallets, bins, wire baskets, pans, or other containers.10.Pickup and deposit stations- To allow inventory into the system, it is

necessary to have pickup and deposit (P/D) stations. These are generally placed at the end of the aisles so that they can be accessed by the S/R machines from the external material handling system.

WHY AN AS/RS ?• Reasons for selecting AS/RS include:1. An AS/RS is highly space efficient. 2. Increased storage capacity to meet long range plans.3. Improved inventory management and control.4. Quick response time to locate, store, and retrieve items.5. Reduced shortage of inventory items due to real-time

information and control.6. Reduced labor cost due to automation.7. Improved stock rotation.

WHY AN AS/RS ?8. Improved security and reduced pilferage because of closed

storage area.9. Flexibility in design to accommodate a wide variety of loads.10. Flexibility in interfacing with other systems such as AGVS, FMS,

and inspection systems such as coordinate measuring machines.11.Reduced scrap and rework due to automatic handling of parts.12.Reduced operating expenses for light, power and heat.13. Helps in implementing JIT concepts by getting the right parts,

tools, pallets, and fixtures to the right place at the right time because of automatic control of storage and retrieval functions and accurate inventory management.

TYPE OF AS/RS• Several types of ASRS are

distinguished based on certain features and applications. Some of the important categories include:1. Unit Load ASRS2. Miniload ASRS3. Person-on-board ASRS4. Deep-lane ASRS5. Automated item retrieval

system

UNIT LOAD ASRS

• It is used to store and retrieve loads that are palletized or stored in standard-sized containers. • The system is computer controlled. • The S/R machines are automated and designed to handle the

unit load containers. • Usually, a mechanical clamp mechanism on the S/R machine

handles the load. • However, there are other mechanisms such as a vacuum or a

magnet-based mechanism for handling sheet metal. • The loads are generally over 200 Kgs per unit.

MINILOAD ASRS

• This system is designed to handle small loads such as individual parts, tools, and supplies that are contained in bins or drawers in the storage system.• This system is applicable where the availability of space is

limited. • Also useful where the volume is too low for a full-scale unit

load system and too high for a manual system. • A mini load AS/RS is generally smaller than a unit load

AS/RS and is often enclosed for security of items stored.

PERSON-ON-BOARD ASRS

• This system allows storage of items in less than unit load quantities. • Human operator rides on the carriage of the S/R machine to pick up

individual items from a bin or drawer. • The system permits individual items to be picked directly at their storage

locations. • This provides an opportunity to increase system throughput. • The operator can select the items and place them in a module. • It is then carried by the S/R machine to the end of the aisle or to a

conveyor to reach its destination.

DEEP-LANE ASRS

• This is a high-density unit load storage system that is appropriate for storing large quantities of stock.• The items are stored in multi deep storage with up to 10 items in a single rack,

one load behind the next. • Each rack is designed for flow-through, with input and output on the opposite

side. • Machine is used on the entry side of the rack for input load and loads are

retrieved from other side by an S/R- type machine. • The S/R machines are similar to unit load S/R machine except that it has

specialized functions such as controlling rack-entry vehicles.

AUTOMATED ITEM RETRIEVAL SYSTEM

• This system is designed for retrieval of individual items or small product cartoons. • The items are stored in lanes rather than bins or drawers. • When an item is retrieved from the front by use of a rear-mounted

pusher bar, it is delivered to the pickup station by pushing it from its lane and dropping onto a conveyor. • The supply of items in each lane is periodically replenished and thus

permitting first-in/first-out inventory rotation. • After moving itself to the correct lane, the picking head activates

DESIGN OF AS/RS• Bozer and White(1980) and the Material

Handling Institute provide a list of user and supplier related issues that must be considered while designing an automated storage and retrieval system. Here we will discuss following important issues related to the layout and design of AS/RS:

1. Determining load sizes2. Determining the dimension of an

individual storage space3. Determining the storage space

considering• Dedicated storage• Randomized storage

4. Determining the system throughput and number of S/R machines

5. Determining the size parameters of storage and retrieval system• Determining the number of rows

and number of bays in each row• Determining bay width , rack

length, system length, bay depth, aisle unit, and system width

6. Determining single and dual command cycle times

7. Determining utilization of S/R machines

DETERMINING LOAD SIZES

• The variety and volume of parts types and the type of production system used essentially determine the overall workflow, that is, the movement frequency of parts, tools, fixtures, pallets, and other supplies.• The work flow information is required to determine load size,

which is the most important element in the design AS/RS.• The load size refers to depth, width and height.• The dimensions of the unit loads with approximate

clearances provide the individual storage space dimensions.

DETERMINING THE DIMENSION OF AN INDIVIDUAL STORAGE SPACE

• Height of a storage space= h+c1.

• Length of a storage space= l+c2.

• Width of individual storage space= u(w+c3).• Normally, the storage space depth(width) is up to maximum of three

unit loads(u=3).Where h = Height of unit loadl = Length of unit loadw = Width of unit loadc1, c2, c3 = height, length and width clearances required for the unit load respectively.

u = storage depth in number of unit loads

DETERMINING THE STORAGE SPACE CONSIDERING1. Considering Dedicated Storage (fixed slot storage) Policy- In this policy, a particular set of storage slots or locations is assigned to a specific product. Therefore, the number of slots required to store the products equals the sum of the maximum inventory levels for all the products.2. Considering Randomized Storage (floating-slot storage) Policy-In this, each empty storage slot is equally likely to be selected for storage when a storage operation is performed. Likewise, each unit of a particular product is equally likely to be retrieved when a retrieval operation is performed.

DETERMINING THE SYSTEM THROUGHPUT AND NUMBER OF S/R MACHINES

• The system throughput refers to the number of loads to be stored and number of loads to be retrieved per hour. These numbers are of course, a function of production activity. Factors that influence the throughput include:1. Speed of S/R machine2. Mix of single- and dual-cycle transactions3. Percent utilization of the storage racks4. Arrangement of stored items5. AS/RS control system speed6. Speed and efficiency of the material- handling equipment such as AGVs,

conveyors, and forklifts used to move loads to the input and removal loads from the output

DETERMINING THE SYSTEM THROUGHPUT AND NUMBER OF S/R MACHINES

• To carry out the production activity efficiently, the calculation of the number of S/R machines should be based on the maximum number of loads out per hour.• The number of S/R machines are determined as follows:

Number of S/R machines=

DETERMINING THE SIZE PARAMETERS OF STORAGE AND RETRIEVAL SYSTEM

• l+C2+C4 ,where c4 is center to center rack support width• Rack length=bay width*number of bays• System length= rack length+ clearance for S/R machine run-out+ clearance for the P/D area• Bay depth= width of individual storage space+ bay side support allowance• Bay depth=u(w+c3)+c5 , where c5 is bay side support allowance• Aisle unit=aisle width+(2*bay depth)• System width= aisle unit*desired number of aisles

DETERMINING SINGLE AND DUAL COMMAND CYCLE TIMES

• In Single Command cycle either a storage or a retrieval operation is performed, but not both. To determine cycle time, a storage cycle is assumed to begin with the S/R machine at the P/D station. • Dual command cycle is assumed to begin with the S/R

machine at the P/D station. The machine picks up a load, travels empty to the retrieval location and retrieves a load from there, travels back to P/D station, and deposits the load.

DETERMINING SINGLE AND DUAL COMMAND CYCLE TIMES

• Single Command Cycle Time• Double Command Cycle TimeWhere T= max(th, tv)Q= min(th/T, tv/T)Tpd= time to perform either a pick up or depositth= time required to travel full horizontal aisle distancetv= time required to travel full vertical aisle distance

DETERMINING UTILIZATION OF S/R MACHINES• Suppose the system throughput (ST) for an AS/RS is known.

Remember, the system throughput is defined as the number of loads to be stored and number of loads to be retrieved per hour. Suppose each aisle is served by one S/R machine and there are N S/R machines. Then the number of transections per S/R machine per hour is

nt=

DETERMINING UTILIZATION OF S/R MACHINES• Assuming the number of storages and retrievals are equal in the long run, • Where and β are the percentages of operations done by single and dual command cycles, respectively and (β=1)

REFERENCES• Systems approach to computer-integrated design and

manufacturing Author Nanua Singh, Publisher Wiley, 1996 ISBN 9788126530410• Random sources has been used to acquire relevant images for the

presentation using Google image searches

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