Material HandlingModule7Definitions

Material Handling Equipment & Classifications

Analysis and Design of Material Handling Conveyor SystemsAGV systemsAS/RS

Material Handling in Production Systems

IntroductionPurpose of Material handling (MH) is the movement, storage, tracking (or control) of all materials during manufacturing; and; also during distribution, consumption, and disposal.

Materials include raw materials, finished parts, tools, and supplies

Cost of MH could be a significant portion (10 to 70%) of total production cost

MH equipment is the conduit for materials flow and physical integration within a factory (95% of time).

Automated MH is a key element in any flexible manufacturing system (primary and secondary systems)

Because of movements, MH equipment are associated with many accidental injuries on the job.

RequirementsSafety (humans and products including fragile items)Efficient (low cost)Effective (Timely, Accurately)

Equipment: Classification by Types Hand Trucks: dollies, wheeled trucks for manual transport of all material. Powered Trucks: forklifts (powered by propane, battery or gasoline), tractor-trailer trains, and other vehicles.Cranes and Hoists: specialized overhead equipment for lifting and manipulating heavy objects usually powered.Conveyors: move large quantities of materials over a fixed path. Can be continuously moving or use gravity. Automated Guided Vehicle Systems (AGVS): powered vehicles that automatically follow a fixed path.Automated Storage/Retrieval Systems (ASRS): mechanized systems that automatically store and retrieve items.Others indexing table, pipelines

Non-Powered Trucks

Powered Trucks

Cranes and Hoist

Conveyor Systems:Types of Conveyors Roller: a series of short tubes roll under the action of gravity or powered ( belts or chains). Very common.( Skate wheel conveyors)Belt: a continuous belt loop driven by pulleys for moving pallets, parts or bulk materials (troughed).Overhead trolley: an endless moving cable or chain carries trolleys on overhead rails. Hooks or baskets suspended from the trolleys to carried loads.In-floor tow line: a moving cable or chain buried in the floor moves wheeled trailer carts along a fixed path.Cart-on-track: individual carts ride on tracks driven by rotating tube. (high positioning)

Types of Conveyors-1

Types of Conveyors-2

Conveyor AccessoriesAngle PushersDivertersTurntableSwitchesFlow Control traffic copGatesSorting

Automated Guided Vehicle Systems (AGVS):Vehicle TypesDriverless train: a guided vehicle tows several trailers carrying heavy loads (up to 50,000 lbs) over long distances.Unit-load carrier: a lighter duty (500-1000 lbs) version of the pallet truck with its own automatic load/unload mechanisms.Pallet truck: a manually loaded guided vehicle for dispatching medium-duty (

Automated Guided Vehicles -AGVs

Automated Guided Vehicle Systems (AGVS): Factory ApplicationsWarehousing, shipping and receiving: moving large quantities over large distances in large factories and warehouses typically require drivereless trains.Storage and distribution: unit load carriers and pallet trucks typically move materials randomly and in varied quantities to and from automated storage systems.Assembly-Lines: extra light duty (

Vehicle Guidance TechnologiesFixed PathwayImpeded Guide Wires (magnetic (coil) sensors)Paint Strip (UV sensors)

Vehicle Guidance TechnologiesFlexible PathwaySelf-Guided Vehicle (SGV) Has on board navigation computerTerm Dead Reckoning

Vehicle Management and SafetyObjectives

Minimize waiting time at loading/unloading stationsEquipment utilization and service time management issuesMinimize traffic congestionsOperate safely

AGVS: Vehicle Management and SafetyTraffic Control (on-board sensing)

Zone Control (control units on pathway)

Vehicle Dispatching On-board control panelRemote call stationsCentral computerSafety (speed, safety bumper, obstacle detection, etc)Additional technologies that can improve above issues are ?????

Material Handling System Design Consideration

Material Handling System DesignObjectives Safety (humans and products fragile)Efficient (low cost)Effective (Timely, Accurately)

Factors that influence designMaterial CharacteristicsFlow rate, Routing, and SchedulingPlant Layout

Material Characteristics

Flow rate, Routing, and Scheduling

Flow rate (dedicated and shared?) Routing (distances? conditions?)Scheduling (MH system response?)

Plant Layout Information required for system design are:Path of materials flow and potential obstaclesLoad and unload locationsMaterials flow pattern and potential congestion pointsDistances traveled Arrangement of equipment within each departmentStorage requirements and location for WIPTotal area of the facility

Plant layout strongly influences the type and the configuration of equipment in a MH system (new ?)- Fixed-position, Process (or Cellular) Type, Product-Flow

Plant Layout

The 10 Principles of MH (Table 9.3)Planning PrincipleStandardization PrincipleWork PrincipleErgonomics Principle human capabilities and limitationsUnit Load PrincipleSpace utilization principleSystem principleAutomation principleEnvironmental principleLife Cycle Cost principle

Analysis of Materials Handling Systems

Flow diagram From-to chart

Conveyor Systems: Common Characteristics Are generally mechanized and sometimes automatedFollow fixed path (single direction, continuous loop, recirculating)Mounted on the floor or overheadMove materials mostly in one-directionMove discrete parts or bulk (continuous load)Used for transport and dynamic storage (Later?)Non-powered individual carriers or pallets ride on the powered or gravity-driven conveyor

Conveyor Analysis:Single Direction Conveyorswhere:Td = delivery time (min/carrier)Ld = conveying distance between load and unload stations (m,ft)vc = conveyor speed (m/min, ft/min)Rf = material flow rate (parts/min)Assumptions:1. Belt moves in one direction2. One load station at the input end3. One unload station at the output endRL= loading rate (parts/min)np= number of parts per carriersc = carriers spacing on conveyor (m/carrier, ft/carrier)TL= loading time (min/carrier)TU= unloading time (min/carrier) LoadStationUnloadStationTLTUTU < TL

Conveyor Analysis:Example 1It takes 20 sec to load 18 parts into each tote pan and 4 sec to load the tote pan onto the single direction belt conveyor. Find: (a) delivery time, Td (min)(b) minimum tote pan spacing, sc (ft)(b) maximum possible parts flow rate, Rf (parts/min); (c) maximum unload time TU

TLTU= 4.0 min (for a specific tote)sc = vc TL = (50 ft/min) (20 s + 4 s) (1 min/60 s) = 20 ft = 45 parts/minTU < TL < 24 s/pan 0.40 min/pan

Conveyor Analysis:Continuous Closed-Loop ConveyorsConsider a continuous closed-loop conveyor, such as an overhead trolley system with one load and one unload station. Assume that all carriers are emptied at the unload station. nc = number of carriers in the systemLd = length of the delivery leg (ft or m)Le = length of the return leg (ft or m)sc = carriers spacing (ft or m/carrier)Np = total number of parts in the systemnp = number of parts in each carrierRf = part feed rate (parts/min)vc = conveyor speed (ft/min or m/min)

Conveyor Analysis:Recirculating ConveyorsContinuous loop conveyors can be used for storage, if loaded carries are allowed to flow back on the return leg raising the following possibilities:Empty carriers are not available when needed for loading

Full carriers are not immediately available for unloading (airport conveyor)

Conveyor Analysis:Recirculating ConveyorsKwos recirculating conveyor design requirements with ONE load station and ONE unload station. Three rules

Speed rule: Operating speed within a certain limit determined by #carriers/min (vc/ sc ). The lower limit should be greater than or equal the required loading or unloading rate whichever is the greater.

The upper limit should be less or equal to the capabilities of the material handlers.

parts/minmin/carrier

Conveyor Analysis:Recirculating Conveyors

Capacity constraint: The flow rate capacity of the conveyor must be at least equal to the flow rate requirement to accommodate reserve stock and allow for the time elapsed between loading and unloading due to delivery distance.

Uniformity Principle: empty and full carriers should be uniformly distributed along the line to avoid excessive waiting for carriers.

Conveyor Analysis: Example 2A recirculation conveyor has a total length of 300m. Its speed is 60m/min, and the spacing of part carriers along its length is 12m. Each carrier can hold 2 parts. The time required to load 2 parts into each carrier is 0.20min and the unload time is the same. The required loading and unloading rates are both defined by the specified flow rate, which is 4parts/min. Evaluate the conveyor system design with respect to Kwos three principle.

Find: Specified flow rate , Rf = 4 parts/minConveyor speed, vc = 60m/minSpacing of carriers, Sc =12m Number of parts per carrier, np = 2 parts Loading TL = Unloading TU = 0.2 min/carrier

Solution: 1) Speed Rule

Example 2 (continue)2) Capacity Constraint

Actual flow rate capacity = 10 parts/min (> 4 parts/min) 3) Uniformity Principle -Loading rate = unloading rate -Other Flow rate capacity (10 parts/min) is substantially greater than required loading / unloading rate (4parts /min)

AGVS: Common Characteristics

An AGVS is a automated material handling system consisting of independently operated, self-propelled vehicles that are automatically guided along defined paths.

AGVS: Common CharacteristicsOn-board batteries usually power AGVS vehicles for 10 to 16 hrs of operation.

On-board control system uses sensors to detect the position of wires buried in the floor or strips of reflective paint and guide the vehicle along the desired path within a certain margin of error (pp387-393).

Vehicles automatically (sensors) detect obstacles and avoid collisions with other objects

AGVS: Factors to Consider in System DesignGuide path type (?) and vehicle typePath routing and layoutFlow direction along each path segmentNumber and location of docking points for loading and unloadingNumber and locations of vehicle parking sitesRequired number of vehiclesDispatching rules and frequency of pickups and deliveries

AGVS Analysis: Delivery Cycle Time Analysis begins with estimating the total time Tc in a delivery cycle of a vehicle on the average, ignoring effects of traffic congestion:

Tc = delivery cycle time for one vehicle (min/del) TL = loading time (min)Ld = average distance traveled while loaded per delivery (ft or m)vc = AGV speed which is assumed to be constant (ft/min, m/min)TU = unloading time (min)Le = average distance traveled while empty per delivery (ft or m) Other Assumptions?

AGVS: Factors affect Delivery Cycle TimeAvailability (A)

Traffic congestion (Tf )

Efficiency of manual elements (E)

AGVS: Rate of deliveries

AGVS: Number of Vehicles

AGV: ExampleIt is desired to design a particular AGVS system that iscapable of making 40 deliveries/hr. The performance characteristics of the system are: Vehicle velocity = 150 ft/min Average distance traveled per delivery = 450 ft Average distance traveled empty = 450 ftPick up time = 45 sec Drop-off time = 45 sec Traffic factor = 0.90Determine the required number of vehicles.

Storage Systems

Storage System- Types of Materials

Storage System- Location StrategiesSKU?Most Common:Randomized StorageDesigned based on the average inventory level

Dedicated Storage Designed based on max inventory level

Class-based dedicated storageDesigned based on activity level

Which uses less Space?Which is Faster?

Storage Capacity : Example 4 Determine the number of storage locations required in the system based on the randomized storage and dedicated storage strategiesNote : a different SKU arrives each day Total 50 SKU

Storage System- PerformanceStorage cycle (pick, travel, place, travel)Retrieval cycle?Traditional SystemsStorage CapacityDensityAccessibilityThroughput

Mechanized and Automated Systems:UtilizationAvailability (Uptime Reliability)

Storage Capacity/ Density/AccessibilityStorage Capacity is defined by the number of total unit loads stored in the systemPhysical capacity should be greater than the MAX number of unit loads anticipated to be stored (Why?)

Storage Density is defined as the volumetric space available for actual storage relative to the total volumetric space in the storage facility (floor area?)

Accessibility refers to the the capability to access any desired unit load in the systemTrade-offs are made between storage density and accessibility

System Throughput Defined as the hourly rate at which the storage systemReceives and puts loads into storage (storage transaction) and/orRetrieves and delivers loads to the output station (retrieval transaction)

Single command cycle or Dual command cycle

System is designed to handle the MAX hourly rate required.

Utilization and Reliability Utilization is defined as the proportion of time that the system is actually being used for performing storage and retrieval operations compared with the time it is available (80-90%)Utilization varies throughout the day

Availability is a measure or reliability. It is defined as the proportion of time that the system is capable of operating (not broken down) compared with the normally scheduled shift hours. General approaches to improve reliability (preventive maintenance, redundancy)

Some Formulas

Scheduled time/shift = hrs in a shift (8 hrs)

Available time/shift = (Scheduled time/shift) (Downtime/shift)

Utilization = (Actual time used )/ (Available time)

Availability = (Uptime) / (Scheduled time)

Automated Storage and Retrieval Systems (AS/RSs) An AS/RS is an automated system of storage, control and actuating devices which handles, stores and retrieves materials with precision, accuracy and speed.

An AS/RS automatically:Stores an item at predetermined storage siteRemoves a specified item from a storage siteTransports the item to a processing or transfer point

Automating Storage Operations

AS/RS Common CharacteristicsCustom designedComputer Controlled (or manual)Storage locations serviced by S/R (storage/Retrieval) machines One or more P&D stations (Pick up and Deposit). Manually operated or interfaced to handling system Two basic types of AS/RS:Standard (unit load) or Conventional Carousel storage systems

Unit Load AS/RS

AS/RS : Standard SystemsSeveral types

Unit loadMiniloadMan-on-boardOthers

Carousel AS/RS

Unit Load vs Carousel Storage

Unit-Load LayoutTop viewFront view

Unit Load AS/RS (most common)A Unit load AS/RS is a massive structure for handling individual bulky items or groups of items on pallets or in containers

Unit load systems have the following physical features:Storage Structure. A series of storage racks arranged horizontally in rows and vertically in bays separated by aisles for accessA Storage/Retrieval (S/R) machine servicing each aisleOne or more Pickup/Deposit (P/D) stationsStorage modules (unit load containers-pallets)

Special featuresAile Transfer Cars (when S/R car services more than ONE aisle)Full-Empty DetectorsSizing StationLoad Identification Stations (tracking)

AS/RS Design:System Requirements SpecificationStorage capacity:load sizessize and number of storage compartmentsnumber of rows and number of bays in each rowSpace requirements:bay width, bay depth, rack length and rack height (30-90')aisle spacing, number of racks and system overall size System performance:required number of (store/retrieve) cycles per hour,capacity of each S/R machine in (cycles/hr)number of S/R machines required cycle time for retrieve, store or for both

AS/RS : Sizing and Space RequirementsThe dimensions Ls , Hs and Ws of an aisle unit are given in terms of the dimensions x, y and z of the basic unit load and clearance:The size of the overall system is determined by the number of aisle units Na needed to hold the inventory levelsLs = nh (x + a)Hs = nv(y + b)Ws = k (z + c)For a standard pallet:x = 42 inch and a = 8 inchy = 48 inch and b = 10 inchz = 36 inch and c = 6 inchK = 1-3x+ay+bz+cBasic storage compartment containing a unit loadnv is the number of rows and nh is the number of bays. Each aisle unit contains 2nv nh compartments.

Sizing AS/RS system : Example A four aisle AS/RS is to contain 60 storage compartments in the length direction and 12 compartments vertically. All storage compartments will be the same size to accommodate standard size pallets. Determine Storage capacity and dimensions of the storage rack structure.Ls = nh (x + a) = 60 (48 + 8) = 3360 in = 280 ftHs = nv(y + b) = 12 (36+10) = 552 in = 46 ftWs = k (z + c) = 3 (42 + 6) = 144 in = 12 ftx+aStorage capacity per aisle = 2 nv nh = 2(12)(60) = 1440 unit loads

Total Storage Capacity = 4(1440) = 5760 unit loads

AS/RS : Throughput Transaction cycle time Tsc depends on average travel times of the S/R machine and pickup or deposit times:AssumptionsSingle-command cycle initiating a store or retrieve transaction (dual-)

Randomized storage of pallets

Storage compartments of equal size

P/D station located at base and end of aisle

Uniform horizontal and vertical speed of S/R machine

Simultaneous horizontal and vertical movement of S/R

Storage System Performance Criteria

There are several standard measuresStorage CapacityDensityAccessibilityThroughputUtilizationReliability (Uptime Reliability)

AS/RS Design: # S/R Machines and ThroughputThe number of single-command transactions nsc each S/R machine completes each hour isWhere: nsc= number of P/D cycles a machine can make per hour Tsc= single-command transaction cycle time per machine (min) A = fraction of time an S/R machine is availableThe minimum number of S/R machines required is:Where: Nm,min= minimum number of S/R machines requirednsc= number of P/D cycles a machine can make per hr ndt = total number of P/D cycles required per hourThe actual required number of S/R machines Nm should at least equals the number of aisles, Na.Nm = max (Nm,min, Na)

AS/RS Design: Example 6Determine the number of S/R machines required to achieve up to 240 pickup or deposit transactions per hour. The horizontal travel speed of the S/R machines is 320 ft/min and the vertical speed is 80 ft/min. Each P/D operation takes about 0.50 min. The horizontal travel is 280 ft and the vertical travel is 46 ft Solution:Need to determine cycle time Tsc: th = Ls/Vh = 280 ft/320 ft/min = 0.875 mintv = Hs/Vv = 46 ft/80 ft/min = 0.575 min T = max (th, tv) = max (0.875,0.575) = 0.875 minQ = min (th/T, tv/T) = min (0.875/0.875, 0.575/0.875) = min (1.0,0.657) = 0.657Tsc = T [(Q2/3) + 1] + 2 tpd = 0.875[(0.657)2/3 + 1] + 2(0.50) = 2.00 minMinimum number of S/R machines Nm,min nsc = 60A/Tsc = 60 (min/hr) (1)/2.00 min = 30 cycles/hr per machine Nm,min = ndt / nsc = 240/30 = 8 machines.

The number of ailes Na?

Combination of Single & Dual cycles?

AS/RS:Storage CarouselGroover, M., 1987, Automation, Production Systems, and Computer Integrated Manufacturing

Carousel Applications & AdvantagesLow cost versatile, and reliable

Storage and Retrieval applications (kitting, service room)Transport and Accumulation (assembly system?)Suited for Automated WIP applications (others?)

AS/RS: Advantages (Table 15.2)Efficient use of valuable space (up instead of out)Improved inventory management (find and account for any and all inventory items)Increased responsiveness to materials handling service requestsMinimized waste, theft and spoilageEase of interfacing with other automated systems such as FMS, CNC and AGVSEase of tracking products for quality and regulatory purposes.

Traditional WIP StorageBatch and Job shop

While the cell is processing one orderSeveral orders awaiting at the cellFinished orders awaiting to be transported

WIP placed in Close proximity to cell

DisadvantagesLost parts and /or ordersIdentificationPriority of processingLonger lead timeCost, etc

Automated WIP StorageJustification

Kitting of parts for assemblyIntegral part in an assembly system Support JIT (critical components)Buffer storage (un-equal operation time) Improved control and tracking of materialsSupport factory wide automation (including Automated Data Collection)