Materials Handling. To review modern technologies for material handling: - Part handling - AGV’s -...

Materials Handling

•To review modern technologies for material handling: - Part handling- AGV’s- AS/RS- conveyors

•To consider application conditions (student presentations)

•To introduce assessment criteria

•To test understanding of the material presented

Objectives

Material handling principles

Principle 1 - PLANNING PRINCIPLE: All material handling should be the result of a deliberate plan where the needs, performance objectives, and functional specification of the proposed methods are completely defined at the outset.

• The plan should be developed in consultation between the planner(s) and all who will use and benefit from the equipment to be employed.

• Success in planning large-scale material handling projects generally requires a team approach involving suppliers, consultants when appropriate, and end user specialists from management, engineering, computer and information systems, finance, and operations.

• The plan should promote concurrent engineering of product, process design, process layout, and material handling methods as opposed to independent and sequential design practices.

• The plan should reflect the strategic objectives of the organization as well as the more immediate needs.

( from Groover )

Principle 2 - STANDARDIZATlON PRINCIPLE: Material handling methods, equipment, controls, and software should be standardized within the limits of achieving overall performance objectives and without sacrificing needed flexibility modularity, and throughput.

• Standardization means less variety and customization in the methods and equipment employed.

• Standardization applies to sizes of containers and other load forming components as well as operating procedures and equipment.

• The planner should select methods and equipment that can perform a variety of tasks under a variety of operating conditions and in anticipation of changing future requirements.

• Standardization, flexibility, and modularity must not be incompatible.

Material handling principles ( from Groover )

Principle 3 - WORK PRINCIPLE: Material handling work should be minimized without sacrificing productivity or the level of service required of the operation.

• The measure of material handling work is flow rate (volume, weight, or count per unit of time) multiplied by distance moved.

• Consider each pickup and set-down, or placing material in and out of storage, as distinct moves and components of the distance moved.

• Simplifying processes by reducing, combining, shortening, or eliminating unnecessary moves will reduce work.

• Where possible, gravity should be used to move materials or to assist in their movement while respecting consideration of safety and the potential for product damage.


Principle 3 - WORK PRINCIPLE: Material handling work should be minimized without sacrificing productivity or the level of service required of the operation.

• The Work Principle applies universally, from mechanized material handling in a factory to over-the-road trucking.

• The Work Principle is implemented best by appropriate layout planning: locating the production equipment into a physical arrangement corresponding to the flow of work. This arrangement tends to minimize the distances that must be traveled by the materials being processed.


Principle 4 - ERGONOMIC PRINCIPLE: Human capabilities and limitations must be recognized and respected in the design of material handling tasks and equipment to ensure safe and effective operations.

• Ergonomics is the science that seeks to adapt work or working conditions to suit the abilities of the worker.

• The material handling workplace and the equipment must be designed so they are safe for people.

• The ergonomic principle embraces both physical and mental tasks.

• Equipment should be selected that eliminates repetitive and strenuous manual labor and that effectively interacts with human operators and users.


Principle 5 - UNIT LOAD PRINCIPLE: Unit loads shall be appropriately sized and configured in a way which achieves the material flow and inventory objectives at each stage in the supply chain.

• A unit load is one that can be stored or moved as a single entity at one time, such as a pallet, container, or tote, regardless of the number of individual items that make up the load.

• Less effort and work are required to collect and move many individual items as a single load than to move many items one at a time.

• Large unit loads are common in both pre- and post-manufacturing in the form of raw materials and finished goods.

• Smaller unit loads are consistent with manufacturing strategies that embrace operating objectives such as flexibility, continuous flow and just-in-time delivery. Smaller unit loads (as few as one item) yield less in-process inventory and shorter item throughput times.


Principle 6 - SPACE UTILIZATION PRINCIPLE: Effective and efficient use must be made of all available space.

• Space in material handling is three-dimensional and therefore is counted as cubic space.

• In storage areas, the objective of maximizing storage density must be balanced against accessibility and selectivity.

• When transporting loads within a facility, the use of overhead space should be considered as an option. Use of overhead material handling systems saves valuable floor space for productive purposes.


Principle 7 - SYSTEM PRINCIPLE: Material movement and storage activities should be fully integrated to form a coordinated, operational system that spans receiving, inspection, storage, production, assembly, packaging, unitizing, order selection, shipping, transportation, and the handling of returns.

• Systems integration should encompass the entire supply chain, including reverse logistics. It should include suppliers, manufacturers, distributors, and customers.

• Inventory levels should be minimized at all stages of production and distribution while respecting considerations of process variability and customer service.

• Information flow and physical material flow should be integrated and treated as concurrent activities.

• Methods should be provided for easily identifying materials and products, for determining their location and status within facilities and within the supply chain, and for controlling their movement.


Principle 8 - AUTOMATION PRINCIPLE: Material handling operations should be mechanized and/or automated where feasible to improve operational efficiency, increase responsiveness, improve consistency and predictability, decrease operating costs, and eliminate repetitive or potentially unsafe manual labor.

• In any project in which automation is being considered, pre-existing processes and methods should be simplified and/or re-engineered before any efforts to install mechanized or automated systems. Such analysis may lead to elimination of unnecessary steps in the method. If the method can be sufficiently simplified, it may not be necessary to automate the process.

• Items that are expected to be handled automatically must have standard shapes and/or features that permit mechanized and/or automated handling.

• Interface issues are critical to successful automation, including equipment-to-equipment, equipment-to-load, equipment-to-operator, and in-control communications.

• Computerized material handling systems should be considered where appropriate for effective integration of material flow and information management.


Principle 9 - ENVIRONMENTAL PRINCIPLE: Environmental impact and energy consumption should be considered as criteria when designing or selecting alternative equipment and material handling systems.

• Environmental consciousness stems from a desire not to waste natural resources and to predict and eliminate the possible negative effects of our daily actions on the environment.

• Containers, pallets, and other products used to form and protect unit loads should be designed for reusability when possible and/or biodegradability after disposal.

• Materials specified as hazardous have special needs with regard to spill protection, combustibility, and other risks.


Principle 10 - LIFE CYCLE COST PRINCIPLE: A thorough economic analysis should account for the entire life cycle of all material handling equipment and resulting systems.

• Life cycle costs include all cash flows that occur between the time the first dollar is spent to plan a new material handling method or piece of equipment until that method and/or equipment is totally replaced.

• Life cycle costs include capital investment, installation, setup and equipment programming, training, system testing and acceptance, operating (labor, utilities, etc.), maintenance and repair, reuse value, and ultimate disposal.

• A plan for preventive and predictive maintenance should be prepared for the equipment, and the estimated cost of maintenance and spare parts should be included in the economic analysis.


Principle 10 - LIFE CYCLE COST PRINCIPLE: A thorough economic analysis should account for the entire life cycle of all material handling equipment and resulting systems.

• A long-range plan for replacement of the equipment when it becomes obsolete should be prepared.

• Although measurable cost is a primary factor, it is certainly not the only factor in selecting among alternatives. Other factors of a strategic nature to the organization and that form the basis for competition in the market place should be considered and quantified whenever possible.


Automated Guided Vehicle (AGV)

Definition - An AGV is an independently operated vehicle that moves material along defined paths between defined delivery points or stations. Typically the paths are defined by either using wires embedded in the floor or reflecting paint strips on the floor.

Some of the more advanced technologies use laser triangulation or inertial guidance systems on-board the vehicles, with distributed calibration stations for position updating.

AGV classification

Driverless trains - AGV is a towing vehicle used to tow one or more trailers forming a train between stations.

Pallet trucks - Used to move palletized loads along predetermined routes. Typically, personnel will steer the AGV to the pallet, acquire the pallet, then steer it to the guide-path where the automated guidance system will then move it to its destination. In a sense, it can be thought of as an automated forklift.

Unit load carriers - Move unit loads from from one station to another station. A unit load is a collection of items that is delivered repetitively as a unit.

AGV applications

Driverless train operations - Movement of large material quantity over large distances (between buildings, warehouses).

Storage/distribution systems - Uses unit load carriers and pallet trucks to transfer material between stations, sometimes interfacing with other automated systems such as an AS/RS (Automated Storage and Retrieval System). Works well in assembly operations where the unit loads (or kits) can be transferred from a central storage area to assembly sites.

Assembly line operations - AGV’s become part of the assembly operation by transferring material along an assembly line (such as moving an engine block between operational stations)

Flexible manufacturing systems (FMS) - AGV’s are used to transfer parts, materials and tooling between the FMS process stations.

Miscellaneous applications - Non-manufacturing applications include the handling of sensitive waste, transportation of material at hospitals, mail transportation.

AGV guidance and control

Guidance and control functions:

Vehicle guidance - on-board control system to move the vehicle along pre-defined paths by a feedback loop between the control system and the guide wire (or paint). More modern systems use inertial guidance to move the AGV between calibration stations. In situations where the guide wire or paint is discontinuous, the control system uses dead reckoning to transition these points.

Traffic control - collision avoidance between multiple AGV’s. The control system is

designed with blocking algorithms that use a combination of on-board vehicle sensing and zone control.

Systems management - programming interfaces and algorithms for moving AGV’s between

stations, and for scheduling the movement of multiple AGV’s.

AGV material handling analysisTerms:

vc - AGV average speed

(c = conveyor, carrier, cart, etc.)

ve - AGV empty speed

Th - load handling time

Ld - destination distance

Le - empty move distance

Tf - traffic factor (<= 1)

Eh - handling system efficiency

A - proportion of time vehicle is operational

AT- available time in min/hr/veh

E - worker efficiency

Rdv - rate of deliveries per vehicle

nc - number of carriers required

Rf - specified flow rate of system (del/hr)

Tc - delivery cycle time (min/del)

TL - time to load at load station (min)

TU - time to unload at load station (min)

WL - workload (total work in min per hour)

AGV material handling analysis

Equations:

del cycle time Tc = TL + TU + Ld / vc + Le / ve (min)

available time AT = 60 A Tf E (min/hr/veh)

rate of del per vehicle Rdv = AT / Tc (num del/hr/veh)

work by handling system per hr WL = Rf Tc (min/hr)

num of vehicles for workload nc = WL/AT = Rf / Rdv (num of veh for work load)

AGV example (from text)

Given the AGV layout in the figure and the info listed, determine the number of vehicles required for a delivery (flow) rate of 40 del/hr.

Info:Loading time = 0.75 min Unloading time = 0.5 minVehicle speed = 50 m/min Availability = 0.95Traffic factor = 0.9 (from fig) =>Ld = 110 m ; Le = 80 m

E = 1

Solution:

Ideal cycle time/del/veh = Tc = 0.75 + 0.5 + 110/50 + 80/50 = 5.05 min

Compute workload = WL = (40) (5.05) = 202 min/hr

Available time = AT = (60) (0.95) (0.90) (1.0) = 51.3 min/hr/veh

Num of vehicles = nc = 202/51.3 = 3.94 veh => 4 vehicles!

AGV questions

• Who are major vendors of AGV’s?

• Describe their components (power source, transmission system,

communication system, etc.)?

• What are typical costs?

• What type of interfaces do they have? How are they programmed?

• How fast do they move?

• What are load to weight ratios?

• Unusual maintenance requirements?

• How do they avoid collisions?

• How are they scheduled?

Automated Storage and Retrieval System (AS/RS)

Definition - An AS/RS is a

combination of equipment and

controls which handles, stores,

and retrieves materials with

precision, accuracy, and speed

under a defined degree of

automation. (Materials Handling Institute)

AS/RS classification

Unit load AS/RS - Large automated system designed to use S/R machines

to move unit loads on pallets into and out of storage racks.

Mini-load AS/RS - Smaller automated system designed to move smaller

loads into and out of storage bins or drawers.

Man-on-board AS/RS - Uses personnel to pick items from racks or bins,

reducing transaction time.

Automated item retrieval system - Items to be moved are stored in single

file lanes, rather than in bins or drawers.

AS/RS applications

Unit load storage and handling - Warehousing for finished

goods/products.

Order picking - Used to store and retrieve materials in less than full unit

load quantities, such as man-on-board or mini-load applications.

Work-in-process - Support just-in-time production activities, buffer

storage, and as integral part of assembly systems.

AS/RS control

The S/R is a large Cartesian type robot that integrates modern control technology, I/O, and sensors (compartment identification) to move between storage compartments. AS/RS control is integrated with modern material management software for real-time inventory control, storage transactions, and material delivery.

AS/RS material handling analysisTerms:

C – capacity per aisle

x - width of unit load

y - length of unit load (in horizontal direction)

z - height of unit load (in vertical direction)

nz - number of vertical compartments

ny - number of horizontal compartments

U - system utilization per hr

W - width of AS/RS rack

H - height of AS/RS rack

L - length of AS/RS rack

vz - vertical speed (m/min, ft/min)

vy - horizontal speed (m/min, ft/min)

tz - vertical travel time (min)

ty - horizontal travel time (min)

Tcs - single command cycle time

(min/cycle)

Tcd - dual command cycle time (min/cycle)

Tpd – pickup and deposit time (min)

Rcs - num of single commands per hr

Rcd - num of dual commands per hr

Rc - total cycle rate in cycles/hr

Rt - num transactions per/hr

AS/RS material handling analysis

Equations:

AS/RS dimensions W = 3 (x + a) a = 6 inL = ny (y + b) b = 8 inH = nz (z + c) c = 10 in

capacity per aisle C = 2 ny nz

single command cycle Tcs = Max {L/vy , H/vz } + 2 Tpd “uniform racks,

random storage”

dual command cycle Tcd = Max {1.5 L/vy , 1.5 H/vz } + 4 Tpd

utilization 60 U = Rcs Tcs + Rcd Tcd

hourly cycle rate Rc = Rcs + Rcd

num transactions per hr Rt = Rcs + 2 Rcd

AS/RS example (from text)

Given a 4 aisle AS/RS layout, each aisle contains 60 horizontal racks and 12 vertical racks. Unit load dimensions are x = 42 in, y = 48 in, and z = 36 in. The S/R machine has a horizontal speed of 200 ft/min and vertical speed of 75 ft/min. It takes 20 s for a P&D operation. Find

a) Num of unit loads that can be storedb) Total dimensions of AS/RSc) Single and dual command cycle timesd) Throughput per aisle assuming utilization = 90% and num of single command cycles equals the num of dual command cycles

Solution:

Total capacity = 4C = (4) 2 ny nz = (4)(2)(60) (12) = 5760 unit loads

Width = 3 (42 + 6) = 144 in => 12 ft/aisle

Length = 60 (48 + 8) = 3360 in = 280 ft

Height = 12 (36 + 10) = 552 in = 46 ft

AS/RS example (cont)

Solution:

Single command cycle time = Tcs = Max{280/200,46/75} + 2(20/60) = 2.066 min/cycle

Dual command cycle time = Tcd = Max{(1.5)(280/200), (1.5)(46/75)} + 4(20/60) = 3.432 min/cycle

Utilization = 0.9: 2.066 Rcs + 3.432 Rcd = 60 (0.9) = 54 min, but Rcs = Rcd

Thus, solve and get Rcs = Rcd = 9.822 command cycles/hr

System throughput is the total number of S/R transactions per hour = 4 Rt

Throughput = 4 Rt = 4(Rcs + 2 Rcd) = 4(29.46) = 117.84 transactions/hr

AS/RS questions

1. Who are major vendors of AS/RS?

2. Describe their components (power source, transmission system,

communication system, etc.)?

3. What are typical costs?

4. What type of interfaces do they have? How are they programmed?

5. How fast do they move?

6. What are load capabilities?

7. Unusual maintenance requirements?

8. What type of S/R control is used? PID?

9. Who are primary users?

Conveyors

Definition - A conveyor is a

mechanized device to move

materials in relatively large

quantities between specific

locations over a fixed path.

Conveyors

Roller conveyors - Series of tube rollers perpendicular to motion direction, which can be powered or use gravity for motion.

Skate-wheel conveyors - Similar to rollers but use skate wheels parallel to motion direction.

Belt conveyors - Drives move flat or belts shaped into a trough.

Skatewheel

Belt

Conveyors

Chain conveyors - Uses loops of chain that are typically moved by sprockets as driven by motors.

Overhead trolley conveyors - Items are moved in discrete loads by hooks or baskets suspended from overhead rails.

Trolley

Conveyors

In-floor towline conveyors - Similar to overhead trolley but carts are pulled by hook to in-floor conveyor.

Cart on track conveyors - Items are moved by a cart attached to a rail system, which uses a rotating tube to move the cart along the rail.

Towline

Conveyor material handling

Terms:

vc – carrier average speed

(c = conveyor, carrier, cart, etc.)

sc – material spacing on conveyor

TL – loading time (min)

TU – unloading time (min)

Rf – material flow rate (parts/min)

Ld – distance between load and unload

Le –distance of return loop (empty)

L – length of conveyor loop

Td – delivery time

np – number of parts per carrier

nc – number of carriers

RL – loading rate (parts/min)

RU – unloading rate (parts/min)

Tc – total cycle time (min)

Np – total number of parts in system

Note: If one part per carrier, then part flow rate is carrier flow rate.

Conveyor handling analysis

Equations – single direction:

time from load to unload Td = Ld /vc (min)

“delivery time = delivery distance divided by carrier speed”

material flow rate (np = 1) Rf = RL = vc /sc 1/ TL (num carriers/min)

“system flow rate = loading rate = flow rate of carriers on conveyor”

material flow rate (np > 1) Rf = np vc /sc 1/ TL (num parts per min)

“system flow rate = loading rate of parts = flow rate of parts on conveyor”

unloading constraint TU TL (min)

“unloading time must be less than loading time or else pile up carriers”


Equations – continuous loop:

time to complete loop Tc = L /vc (min)

“full loop carrier time = loop distance divided by carrier speed”

time in delivery Td = Ld/vc (min)

“delivery time = delivery distance divided by carrier speed”

number of carriers nc = L /sc

“num of carriers = loop distance divided by carrier spacing”

total parts in system Np = np nc Ld/ L

“parts in system = num of parts per carrier times num carriers with parts”

material flow rate Rf = np vc /sc (num carriers per min)

“material flow rate = num parts per carrier times carrier flow rate”


Equations – recirculating:

Speed rule – operating conveyor speed must fall within a certain range

from load/unload rates Rf = np vc /sc Max{RL , RU}

“flow rate of parts on conveyor must exceed the max load or unload part rate to maintain part spacing”

from time to load/unload carriers vc /sc Min{1/TL,1/TU}

“flow rate of carriers on conveyor must exceed the max load or unload carrier rate to maintain part spacing”

Capacity constraint –conveyor capability (np vc /sc ) must exceed desired/specified

flow rate Rf

conveyor speed and carrier parts np vc /sc Rf

Uniformity principle –loads should be distributed uniformly over the conveyor

Conveyor questions

1. Who are major vendors of conveyors?

2. Describe their components (power source, transmission system, I/O

subsystem, etc.)?

3. What are typical costs?

4. How are they programmed and controlled?

5. How fast do they move?

6. What are load capabilities?

7. Unusual maintenance requirements?

8. Who are primary users?

Material handling

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Materials Handling. To review modern technologies for material handling: - Part handling - AGV’s -...

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