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					Introduction
Categories of materials stored by manufacturing firms:
    - product-related:
           o raw material
           o purchased parts
           o WIP
           o Finished products
           o Rework and scrap
    - process-related:
           o refuse
           o tooling
           o spare parts
    - overall support of factory operations:
           o office supplies
           o plant records
These require different storage methods and controls.
Manual storage: inefficient (HR, floor space, material control, etc)
Automated: higher efficiency

11-1 Storage System Performance:
1- Storage Capacity
   a- total Space Available
   b- Total number of storage compartments (pallets, boxes, containers, etc.)

2- Storage Density
   - Volumetric space available for actual storage relative to total storage volume.
       The larger the density, the better the storage system.
   - Sometimes floor area is used to calculate the density because it is easier to visualize and draw
       using top views, but volume is more accurate
3- Accessibility
   - capability to access the desired item
   - inversely proportional to storage density
4- Throughput
   - The hourly rate at which the system receives loads and/or retrieves and delivers them.
   - It is related to the time to perform a S/R transaction which includes:
           o Storage: (pick up load – travel to storage location – place load into location – travel back)
           o Retrieval: (travel to storage location – pick item – travel to output location – unload at
               output location)
   - There are two main types of cycles:
   - Single command cycle: either retrieval or storage transaction
   - Dual command cycle: combined storage and retrieval transaction
For automated storage systems:
5- Utilization
   - proportion of time the system is being used
   - For automated systems, 80-90% is the optimum utilization range.
   - Less than that it would be very low for its cost
   - Higher than that, there wouldn’t be any place for rush times
6- Availability
   - Proportion of time the system is capable of operating (not down or on maintenance).
   - Stoppages occur due to computer failure, human errors, maintenance, load jams, mechanical
       breakdowns, etc.

11-2 Storage Location Strategies:
Each item type is stored in warehouse in a “stock-keeping-unit” (SKU).
1- Randomized Storage:
   - SKU’s are stored at any location
   - Retrieval on a first-come-first-go basis
   - Minimal space required
2- Dedicated Storage:
   - SKU’s are assigned to specific locations according to:
          a- P/N
          b- Activity level
          c- Activity-to-space ratio
   - Highest throughput, but needs larger space
3- Class-Based Dedicated Storage:
   - Storage according to class division according to activity level
   - Within each class, randomized strategy is used in storage to minimize space within each class

11-3 Conventional Storage Methods and Equipment
1- Bulk Storage: see fig.

2- Rack Systems:
   - Pallet Rack: see fig.
   - Cantilever rack:
   - Portable racks: box frame with single pallet load on top of each other like bulk
   - Drive-through racks (drive-in)
   - Flow-through racks
3- Shelving and Bins
4- Drawer Storage: see fig.

11-4     Automated Storage Systems
11-4-1   ASRS:
   -     custom designed for each application
   -     degree of automation varies
   -     One or more storage aisles
   -     Each has a S/R machine (crane)
   -     The aisles have storage racks
   -     The S/R machine has an input-output station called pickup-and-deposit (P&D) station

ASRS Types:
1- Unit load AS/RS: see fig 11.5 - This is the generic AS/RS
2- Deep-lane AS/RS: for large quantity (higher density) unit load systems but low number of SKU’s
3- Mini-load
4- Man-on-board
5- Automated item retrieval system
6- Vertical Lift Storage Modules (VLSM)

WIP Storage:
  - In job shop and batch production, AS/RS are efficient in storing material between processing
      steps.
  - In high production rates, conveyors are used for storage (buffers) and transport

Reasons justifying the use of AS/RS for WIP:
   - Buffer storage in production (between two different processes where the first one has a higher
      production rate
   - Supporting Just In Time delivery (to buffering reduce some of JIT Risks
   - Kitting of parts for assembly
   - Compatible with Automatic Identification Systems (see CH12)
   - Computer control and tracking of materials
   - Support of factory-wide automation
AS/RS components and features:
See fig. 11-5
              1- Storage structure (frame)
              2- S/R machine [horizontal movement of the mast, vertical movement of the carriage,
                  and shuttle transfers between the carriage and storage compartments
              3- Storage modules (compartments, pallets)
              4- Pickup-and-deposit stations
              5- Control systems

11-4-2 Carousel Storage System:
- chain conveyor revolving around a long oval rail system
- human worker at the load/unload station
- if carousel is very big, higher capacity but higher cycle time

Types of Carousels:
      1- Horizontal Carousel: more common
      2- Vertical Carousel: less floor space, but also less capacity because of height limitation (ceiling)

Carousel Applications:
- high throughput
- alternative to mini-load AS/RS
- relatively low cost
- Versatility
- High reliability

Carousel Applications:
      1- Storage / retrieval
      2- Transport and accumulation (sorting)
      3- WIP [especially in Electronics Industry]

11-5 Engineering Analysis of Storage Systems:
AS/RS:
- Sizing the structure
- Throughput

Carousel:
- Storage Capacity
- Throughput

				
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