Material Handling and Storage Systems PDF

LECTURE 07: MATERIAL HANDLING AND STORAGE SYSTEMS MATERIAL HANDLING Defined “The movement, storage, protection and control of materials throughout the manufacturing and distribution process including their consumption (a) Wooden Pallet (b) Pallet Box (c) Tote Box and disposal” (Th...

LECTURE 07: MATERIAL HANDLING AND STORAGE SYSTEMS MATERIAL HANDLING Defined “The movement, storage, protection and control of materials throughout the manufacturing and distribution process including their consumption (a) Wooden Pallet (b) Pallet Box (c) Tote Box and disposal” (The Material Handling Industry of America) Design Considerations in Material Handling Material Handling 1. Material characteristics 2. Flow rate, routing, and scheduling Handling of materials must be performed: 3. Plant layout 4. Unit load principle Safely Efficiently Material characteristics At low cost Material characteristics affect type of transport and storage equipment required: In a timely manner Solid, liquid or gas Accurately Size And without damage to the materials Weight Shape - long, flat, bulky Condition - hot, cold, wet, dirty Categories of Material Handling Equipment Risk of damage - fragile, brittle, sturdy 1. Material transport equipment – to move materials Safety risk - explosive, flammable, toxic, inside a factory, warehouse, or other facility corrosive 2. Positioning Equipment - category consists of equipment used to handle parts and other Flow rate, routing, and scheduling materials at a single location. a) Flow Rate - amount of material moved per unit 3. Unitizing equipment - refers to: time. a) Containers to hold materials, and o Examples: pieces/hr, pallet loads/hr, tons/hr b) equipment used to load and package the o Whether the material must be moved in containers. individual units, as batches, or continuously 4. Identification and tracking systems – to identify (pipeline) and keep track of the materials being moved and b) Routing - pick-up and drop-off locations, move stored. distances, routing variations, conditions along the route (surface, traffic, elevation) Unit Load Principle (unitizing) c) Scheduling - timing of each delivery In general, the unit load should be as large as Prompt delivery when required. practical for the material handling system that will Use of buffer stocks to mitigate against late move and store it. deliveries. A Unit Load is the mass that is to be moved or Plant layout otherwise handled at one time. a) Material handling equipment considerations - self-propelled, guided or driven by must be included in the plant layout design human. problem. - common example: forklift truck b) Correlation between layout type and material Walkie Truck handling equipment: Material Handling Plant Layout Type Equipment Cranes, hoists, Fixed - position industrial trucks Hand Trucks, forklift Process Wheeled forks insert into pallet openings. trucks, AGVs No provision for riding; truck is steered by worker using control handle at front of vehicle. Conveyors for product Product flow Forklift Truck Trucks to deliver parts to stations. Material Transport Equipment Five categories: 1. Industrial trucks 2. Automated guided vehicles 3. Monorails and other rail guided vehicles. 4. Conveyors Widely used in factories and warehouses because 5. Cranes and hoists pallet loads are so common. Capacities from 450 kg (1000 lb) up to 4500 kg (10,000 lb) Industrial Trucks Power sources include on-board batteries and internal combustion motors. Two basic categories: Towing Tractor a) Non-powered - human workers push or pull loads. Hand Trucks Designed to pull one or more trailing carts in factories and warehouses, as well as for airport baggage handling. Powered by on-board batteries or IC engines. b) Powered Automated Guided Vehicles Unit Load Carrier An Automated Guided Vehicle System (AGVS) is a material handling system that uses independently operated, self-propelled vehicles guided along defined pathways in the facility floor. Types of AGV: Driverless trains Used to move unit loads from station to station. Pallet trucks Often equipped for automatic loading/unloading Unit load AGVs of pallets and tote pans using roller conveyors, moving belts, or mechanized lift platforms. Driverless Automated Guided Train Vehicle Safety Travel velocity of AGV is slower than typical walking speed of human worker. Automatic stopping of vehicle if it strays from guide path. o Acquisition distance Obstacle detection system in forward direction o Use of ultrasonic sensors common Emergency bumper - brakes vehicle when First type of AGVS to be introduced around contact is made with forward object. 1954. Warning lights (blinking or rotating red lights) Common application is moving heavy payloads Warning sounds of approaching vehicles over long distances in warehouses and factories without intermediate stops along the route. Rail-Guided Vehicles AGV Pallet Truck Self-propelled vehicles that ride on a fixed rail system Vehicles operate independently and are driven by electric motors that pick-up power from an electrified rail. Fixed rail system o Overhead monorail - suspended overhead from the ceiling o On-floor - parallel fixed rails, tracks generally protrude up from the floor. Used to move palletized loads along predetermined routes. Vehicle is backed into loaded pallet by worker; pallet is then elevated from floor. Worker drives pallet truck to AGV guide path and programs destination.  Overhead Monorail Pathway consists of a series of rollers that are perpendicular to direction of travel. Loads must possess a flat bottom to span several rollers. Powered rollers rotate to drive the loads forward. Un-powered roller conveyors also available Skate-Wheel Conveyor Conveyor Systems Large family of material transport equipment designed to move materials over fixed path, usually in large quantities or volumes. 1. Non-powered Similar in operation to roller conveyor but use - Materials moved by human workers or by skate wheels instead of rollers. trolly Lighter weight and unpowered 2. Powered - Power mechanism for transporting materials is contained in the fixed path, Belt Conveyor using chains, belts, rollers, or other mechanical devices. Conveyor Types Roller Skate-wheel Belt In-floor towline Overhead trolley conveyor Continuous loop with forward path to move Roller Conveyor loads. Belt is made of reinforced elastomer. Support slider or rollers used to support forward loop.  In-floor Tow-line Conveyor A trolley is a wheeled carriage running on an overhead track from which loads can be suspended. Trolleys are connected and moved by a chain or cable that forms a complete loop. Often used to move parts and assemblies between major production areas. Powered Conveyor Operations and Features Types of motions 1. Continuous - conveyor moves at constant velocity 2. Asynchronous - conveyor moves with stop- and-go motion Four-wheel carts powered by moving chains or - They stop at stations, move between stations cables in trenches in the floor. Carts use steel pins (or grippers) to project below Another classification of conveyors: floor level and engage the chain (or pulley) for 1. Single direction towing. This allows the carts to be disengaged from 2. Continuous loop towline for loading and unloading. Overhead Trolley Conveyor Cranes and Hoists Handling devices for lifting, lowering and transporting materials, often as heavy loads. Cranes - used for horizontal movement of materials. Hoists - used for vertical lifting of materials. Cranes usually include hoists so that the crane- and-hoist combination provides. Horizontal transport Vertical lifting and lowering STORAGE SYSTEM Shelves and Bins Storage System Performance Performance measures for storage systems: Storage capacity Storage density Accessibility System throughput Utilization and availability (reliability) Drawer Storage Storage Location Strategies 1. Randomized storage 2. Dedicated storage Conventional Storage Methods Bulk Storage Rack Systems Shelving and Bins Drawer Storage Contents easily visible Good accessibility Relatively high cost Bulk Storage Small items (tools, repair parts, etc.) Automated Storage Systems Mechanized and automated storage equipment to reduce the human resources required to operate a storage facility. Bulk storage arrangements: Significant investment Level of automation varies: (a) high-density bulk storage provides low In mechanized systems, an operator accessibility, participates in each storage/retrieval (b) bulk storage with loads forming rows and transaction. blocks for improved accessibility. In highly automated systems, loads are Pallet Rack System entered or retrieved under computer control. Pallet loads placed on racks in multi- rack Types of Automated Storage System structure. 1. Automated Storage/Retrieval System (a) Low cost (AS/AR) (b) Good storage density 2. Carousel Storage System (c) Good accessibility AS/AR LECTURE 09: AUTOMATIC IDENTIFICATION AND DATA CAPTURE Unit load on pallet AS/RS with one aisle. Sections: 1. Overview of Automatic Identification Methods 2. Bar Code Technology 3. Radio Frequency Identification Automatic Identification and Data Capture A family of technologies that provide direct entry of data into a computer or other microprocessor-controlled system without using a keyboard. AIDC Applications Retail sales and inventory control Material handling Factory operations Other Components of AIDC AS/AR Types Nearly all AIDC technologies consist of three Unit load AS/RS – large automated system for principal components, which are the sequential steps pallet loads in AIDC: Deep-lane AS/RS - uses flow-through racks and fewer access aisles. 1. Encoded Data - alphanumeric characters are Miniload AS/RS - handles small loads contained translated to machine-readable form. in bins or drawers to perform order picking. 2. Machine reader or scanner - scanner reads the Man-on-board AS/RS - human operator rides encoded data and converts it to alternative form, on the carriage to pick individual items from usually an electrical signal. storage. 3. Decoder - electrical signal is transformed into Automated item retrieval System - picks digital data and finally back into original individual items alphanumeric characters. Vertical lift storage modules (VLSM) - uses a vertical aisle rather than a horizontal aisle as in AIDC Technologies other AS/RS types. 1. Optical Carousel Storage Systems 2. Electromagnetic Horizontal 3. Magnetic 4. Smart card Vertical 5. Touch techniques 6. Biometric Measure of AIDC Reading Accuracy Bar Code Scanner 1) First read rate (FRR) 2) Substitution error rate (SER) Barcode Technology Bar codes are of two basic types: Stationary moving beam bar code scanner located 1) Linear (a) along a moving conveyor. 2) Two-dimensional (b) Two-Dimensional Bar Codes First 2-D bar code introduced in 1987. Linear (One-Dimensional) Bar Codes Two basic types of 2-D bar code symbols Two forms of linear bar codes: 1. Stacked Bar Codes 1. Width-modulated Consists of multiple rows of conventional bar Symbol consists of bars and spaces of codes stacked on top of each other. varying width. Most widely used (e.g., Universal Product 2. Matrix Symbologies Code) Consists of 2-D patterns of data cells that are usually square and are colored dark or white. 2. Height-modulated Advantage over stacked bar codes is Symbol consists of bars and spaces of capability to contain more data. varying height. Used only by U.S. Postal Service for ZIP code identification. 2-D Stacked Bar Code (PDF417) Two forms of Bar Codes a) Width-modulated bar code 2-D Matrix Bar Code (Data Matrix) b) height-modulated bar code Linear Bar Code Readers Usually classifies as: 1. Contact 2. Noncontact  Bar Codes vs RFID Comparison Bar Codes RFID Radio Technology Optical Frequency Read-write Read-write Read only capability available Memory 14 to 16 digits 96 to 256 digits Capacity (linear) Line-of-sight Required Not required reading Radio Frequency Identification Reusability One-time use Reusable RFID uses an identification tag containing Very low cost Approx 10x Cost electronically coded data that is attached to the subject per label cost of bar code Susceptible to Mode durable in item. Durability dirt and plant The tag consists of a memory microchip and an scratches environment antenna, usually encased in a plastic container. o The tag is a transponder. LECTURE 10: INTRODUCTION TO MANUFACTURING SYSTEMS Types of RFID Tags Sections: 1. Passive tags 1. Components of a Manufacturing System 2. Active tags 2. A Classification Scheme for Manufacturing Systems 3. Overview of the Classification System Industrial Applications of RFID Inventory management Manufacturing Systems Defined Supply chain management Tracking systems “A collection of integrated equipment and human Warehouse control resources, whose function is to perform one or more Location identification processing and/or assembly operations on a starting raw material, part, or set of parts.” Work-in-progress Equipment includes: RFID Advantages and Disadvantages Production machines and tools Advantages Material handling and work positioning devices Identification does not depend on physical Computer systems contact or direct line of sight. Much more data can be contained in the Human resources are required either full-time or identification. periodically to keep the system running. tag than with most AIDC technologies Examples of Manufacturing Systems Data in read/write tags can be altered for historical usage purposes or to reuse the tag. Single-station cells Machine clusters Disadvantages Manual assembly lines More expensive than most other AIDC Automated transfer lines technologies Automated assembly systems Machine cells (cellular manufacturing) Flexible manufacturing systems Components of a Manufacturing Systems Material Handling System 1. Production machines In most manufacturing systems that process or 2. Material handling system assemble discrete parts and products, the following 3. Computer system to coordinate and/or control the material handling functions must be provided: preceding components. 4. Human workers to operate and manage the system. 1. Loading work units at each station 2. Positioning work units at each station 3. Unloading work units at each station Production Machines 4. Transporting work units between stations in multi- station systems In virtually all modern manufacturing systems, most 5. Temporary storage of work units of the actual processing or assembly work is accomplished by machines or with the aid of tools. Classification of production machines: Work Transport Between Stations 1. Manually Operated Machines Two general categories of work transport in multi- 2. Semi-automated station manufacturing systems: 3. Fully Automated Machines a) Fixed routing Manually Operated Machines b) Variable routing Semi-automated Machine Common Material Transport Equipment Used for Variable and Fixed Routing in Multiple Station Manufacturing Systems Material Handling Types of Part Routing Equipment Automated guided vehicle system Power-and-free overhead Variable Routing conveyor Monorail system Cart-on-track conveyor Fully Automated Machines Powered roller conveyor Belt conveyor Drag chain conveyor Overhead trolley Fixed Routing conveyor Rotary indexing mechanisms Walking beam transfer equipment Computer Control System System Layout Typical computer functions in a manufacturing Applies mainly to multi-station systems. system: Fixed routing vs. variable routing Communicate instructions to workers (receive In systems with fixed routing, workstations are processing or assembly instructions for the usually arranged linearly. specific work unit) In systems with variable routing, a variety of Download part programs to computer-controlled layouts are possible. machines. System layout is an important factor in determining Control material handling system the most appropriate type of material handling Schedule production system. Failure diagnosis when malfunctions occur and preventive maintenance. Automation and Manning Levels Safety monitoring (protect both the human worker and equipment) Level of workstation automation Quality control (detect and reject defective work Manually operated units produced by the system) Semi-automated Operations management (manage overall Fully automated operations) Manning level Mi = proportion of time worker is in attendance at station i Classification of Manufacturing Systems Mi = 1 means that one worker must be at the Factors that define and distinguish manufacturing station continuously systems: Mi >= 1 indicates manual operations Types of operations performed Mi < 1 usually denotes some form of automation Number of workstations System layout Part or Product Variety: Flexibility Automation and manning level Part or product variety “The degree to which the system is capable of dealing with variations in the parts or products it produces.” Types of Operations Performed Three cases of Product Variety in Manufacturing Systems: Processing operations on work units versus assembly operations to combine individual parts into assembled a) Single-model case entities. b) Batch-model case Type(s) of materials processed. c) Mixed-model case Size and weight of work units Part or product complexity Part geometry o For machined parts, rotational vs. non-rotational Number of Workstations Convenient measure of the size of the system Let n = number of workstations Individual workstations can be identified by subscript i, where i = 1, 2,...,n Affects performance factors such as workload capacity, production rate, and reliability. As n increases, this usually means greater workload capacity and higher production rate. Enablers of Flexibility LECTURE 11: FLEXIBLE MANUFACTURING SYSTEMS (FMS) Identification of the different work units Quick changeover of operating instructions A highly automated GT machine cell, consisting Quick changeover of the physical setup of a group of processing stations (usually CNC machine tools), interconnected by an automated material handling and storage system, and controlled by an integrated Overview of Classification Scheme computer system Single-station cells The FMS relies on the principles of GT n=1 No manufacturing system can produce an Manual or automated unlimited range of products Multi-station systems with fixed routing An FMS is capable of producing a single part n>1 family or a limited range of part families Typical example: production line Multi-station systems with variable routing n>1 WHERE TO APPLY FMS TECHNOLOGY? The plant presently either: Single-station Cells Produces parts in batches or Uses manned GT cells and management wants to Two categories: automate the cells 1. Manned workstations - manually operated or It must be possible to group a portion of the parts semi- automated production machine (M = 1) made in the plant into part families 2. Fully automated machine (M < 1) The part similarities allow them to be processed on the FMS workstations Most widely used manufacturing system - reasons: Parts and products are in the mid-volume, mid-variety Easiest and least expensive to implement. production range Most adaptable, adjustable, and flexible system Can be converted to automated station if demand for part or product justifies. Flexibility Tests in an Automated Manufacturing System Multi-Station Systems with Fixed Routing To qualify as being flexible, a manufacturing Common example = production line - a series of system should satisfy the following criteria (“yes” answer workstations laid out so that the part or product moves for each question): through each station, and a portion of the total work content is performed at each station 1. Can it process different part styles in a non-batch Conditions favoring the use of production lines: mode? 2. Can it accept changes in production schedule? Quantity of work units is high. 3. Can it respond gracefully to equipment malfunctions Work units are similar or identical, so similar and breakdowns? operations are required in the same sequence. 4. Can it accommodate introduction of new part Total work content can be divided into separate designs? tasks of approximately equal duration. Multi-Station Systems with Fixed Routing Types of FMS Defined as a group of workstations organized to Kinds of operations achieve some special purpose, such as: Processing vs. assembly Production of a family of parts requiring similar Type of processing (but not identical) processing operations o If machining, rotational vs. non-rotational Assembly of a family of products requiring Number of machines (workstations): similar (but not identical) assembly operations 1. Single machine cell (n = 1) Production of a complete set of components used 2. Flexible manufacturing cell (n = 2 or 3) to assemble one unit of a final product. 3. Flexible manufacturing system (n = 4 or more) Single-Machine Manufacturing Cell A two-machine flexible manufacturing cell for machining (photo courtesy of Cincinnati Milacron) A single-machine CNC machining cell (photo courtesy of Cincinnati Milacron) A five-machine flexible manufacturing system for machining Flexible Manufacturing Cell FMS Types Level of Flexibility 1. Dedicated FMS Designed to produce a limited variety of part styles The complete universe of parts to be made on the system is known in advance Part family likely based on product commonality rather than geometric similarity 2. Random-order FMS Appropriate for large part families New part designs will be introduced Production schedule is subject to daily changes FMS Components FMS In-Line Layout 1. Workstations 2. Material handling and storage system 3. Computer control system 4. Human labor Straight line flow, well-defined processing sequence Workstations similar for all work units Workflow is from left to right through the same Load and unload station(s) workstations Factory interface with FMS No secondary handling system Manual or automated Includes communication interface with worker to specify parts to load, fixtures needed, etc. Material Handling and Storage Functions: Random, independent movement of parts between stations Capability to handle a variety of part styles Linear transfer system with secondary parts handling system at each workstation to facilitate flow in two Standard pallet fixture base directions Work holding fixture can be adapted Temporary storage Convenient access for loading and unloading FMS Loop Layout Compatibility with computer control Material Handling Equipment Primary handling system establishes basic FMS layout Secondary handling system - functions: Transfers work from primary handling system to workstations One direction flow, but variations in processing Position and locate part with sufficient accuracy sequence possible for different part types and repeatability for the operation Secondary handling system at each workstation Reorient part to present correct surface for processing Buffer storage to maximize machine utilization FMS Rectangular Layout Five Types of FMS Layouts The layout of the FMS is established by the material handling system Five basic types of FMS layouts 1. In-line Rectangular layout allows recirculation of pallets 2. Loop back to the first station in the sequence after 3. Ladder unloading at the final station 4. Open field 5. Robot-centered cell FMS Ladder Layout Robot-Centered Cell Suited to the handling of rotational parts and turning operations Duties Performed by Human Labor Loop with rungs to allow greater variation in Loading and unloading parts from the system processing sequence Changing and setting cutting tools Maintenance and repair of equipment Programming and operating the computer system FMS Open Field Layout Overall management of the system FMS Benefits Increased machine utilization Reasons: o 24 hour operation likely to justify investment o Automatic tool changing o Automatic pallet changing at stations o Queues of parts at stations to maximize utilization o Dynamic scheduling of production to account for changes in demand Fewer machines required Reduction in factory floor space required Greater responsiveness to change Reduced inventory requirements Different parts produced continuously rather than in batches Lower manufacturing lead times Multiple loops and ladders, suitable for large part Reduced labor requirements families Higher productivity Opportunity for unattended production Machines run overnight ("lights out operation") LECTURE 12-13: MANUAL AND AUTOMATED Assembly Workstation Manual Assembly Line A designated location along the work flow path at which one or more work elements are performed by one A production line consisting of a sequence of or more workers workstations where assembly tasks are performed by human workers as the product moves along the line Typical Operations Performed at Manual Assembly Stations Organized to produce a single product or a limited range of products Adhesive Electrical Snap Fitting Each product consists of multiple components Application Connection joined together by various assembly work Sealant Component Soldering elements Application Insertion o Total work content - the sum of all work Arc Welding Press Fitting Stitching/Stapling elements required to assemble one product Threaded Spot Welding Riveting unit on the line Fasteners Factors favoring the use of assembly lines: Work Transport Systems High or medium demand for product Two basic categories: Identical or similar products 1. Manual Total work content can be divided into work 2. Mechanized elements It is technologically impossible or economically Manual Work Transport Systems infeasible to automate the assembly operations Work units are moved between stations by the Most consumer products are assembled on manual workers without the aid of a powered conveyor assembly lines Types: o Work units moved in batches o Work units moved one at a time Typical Products Made on Assembly Lines Problems: Automobiles Personal Computers o Starving of stations Cooking Ranges Power Tools o Blocking of stations Dishwashers Refrigerators Dryers Telephones Mechanized Work Transport Systems Furniture Toasters Work units are moved by powered conveyor or other Lamps Trucks mechanized apparatus Luggage Video DVD Players Categories: Microwave Ovens Washing Machines o Work units attached to conveyor o Work units are removable from conveyor Why Assembly Lines are so Productive? Problems o Starving of stations Specialization of labor o Incomplete units Interchangeable parts Workflow principle Types of Mechanized Work Transport Line pacing Continuous transport Conveyor moves at constant speed Manual Assembly Line Synchronous transport Work units are moved simultaneously with stop- and-go (intermittent) motion to next stations Asynchronous transport Work units are moved independently between workstations Configuration of a manual assembly line with n Queues of work units can form in front of each manually operated workstations station Line Pacing Coping with Product Variety A manual assembly line operates at a certain cycle Single model assembly line (SMAL) time - On average, each worker must complete his/her Batch model assembly line (BMAL) assigned task within this cycle time Mixed model assembly line (MMAL) Pacing provides a discipline for the assembly line workers that more or less guarantees a certain production rate for the line Automated Production Line Several levels of pacing: Fixed-routing manufacturing system that consists 1. Rigid pacing of multiple workstations linked together by a material 2. Pacing with margin handling system to transfer parts from one station to the 3. No pacing next Slowest workstation sets the pace of the line Rigid Pacing Workpart transfer: Each worker is allowed only a certain fixed time each Palletized transfer line cycle to complete the assigned task o Uses pallet fixtures to hold and move work Allowed time is set equal to the cycle time less parts between stations repositioning time Free transfer line Synchronous work transport system provides Part geometry allows transfer without pallet rigid pacing fixtures Undesirable aspects of rigid pacing: Incompatible with inherent human variability Automated Production Line Emotionally and physically stressful to worker Incomplete work units if task not completed Pacing with Margin Worker is allowed to complete the task within a General configuration of an automated production specified time range, the upper limit of which is line consisting of n automated workstations that greater than the cycle time perform processing operations On average, the worker’s average task time must balance with the cycle time of the line Where to Use Automated Production Lines How to achieve pacing with margin: High product demand Allow queues of work units between stations Requires large production quantities Provide for tolerance time to be longer than cycle Stable product design time Difficult to change the sequence and content of Allow worker to move beyond station boundaries processing operations once the line is built Multiple operations required on product No Pacing The different operations are assigned to different workstations in the line No time limit within which task must be completed Each assembly worker works at his/her own pace No pacing can occur when: Benefits of Automated Production Lines Manual transport of work units is used Low direct labor content Work units can be removed from the conveyor to Low product cost perform the task High production rates An asynchronous conveyor is used Production lead time and work-in-process are minimized Factory floor space is minimized System Configurations Control Functions in an Automated Production Line In-line - straight line arrangement of workstations Sequence control Segmented in-line – two or more straight line To coordinate the sequence of actions of the segments, usually perpendicular to each other transfer system and workstations Rotary indexing machine (e.g., dial indexing Safety monitoring machine) To avoid hazardous operation for workers and equipment Quality control Segmented In-Line Configurations To detect and possibly reject defective work units produced on the line Automated Assembly The use of mechanized and automated devices to perform the various assembly tasks in an assembly line or cell Fixed automation usually Most automated assembly systems are designed to perform a fixed sequence of assembly steps on a specific product that is produced in very large Rotary Indexing Machine quantities Application Characteristics Where is automated assembly appropriate: High product demand Stable product design The assembly consists of no more than a limited number of components Typical Products Alarm Clocks Light Bulbs Storage Buffers in Production Lines Ball Bearings Locks Ball Point Pens Mechanical Pencils A location in the sequence of workstations where Cigarette Lighters PCB Assemblies parts can be collected and temporarily stored before Door Mechanisms Small Electric Motors proceeding to subsequent downstream stations Gear Boxes Wrist Watches Reasons for using storage buffers: To reduce effect of station breakdowns Assembly Processes in Automated Assembly To provide a bank of parts to supply the line Adhesive Bonding Snap Fitting To provide a place to put the output of the line Insertion of Components Soldering To allow curing time or other required delay Placement of To store parts between stages with different Spot Welding Components production rates Riveting Stapling Screw Fastening Stitching System Configurations Single-Station Assembly Cell 1. In-line assembly machine Assembly operations are performed on a base part 2. Dial indexing machine at a single location 3. Carousel assembly system A robot is sometimes used as the assembly machine 4. Single-station assembly cell In-Line Assembly Machine A series of automatic workstations located along and in-line transfer system Either synchronous or asynchronous work transfer used Parts Delivery at Workstations Typical parts delivery system at a workstation consists of the following hardware components: 1. Hopper - container for parts 2. Parts feeder - removes parts from hopper 3. Selector and/or orientor - to assure part is in proper orientation for assembly at workhead Dial Indexing Machine 4. Feed track - moves parts to assembly workhead 5. Escapement and placement device - removes parts from feed track and places them at station Parts Delivery System at Station Base parts are loaded onto fixtures or nests attached to a circular dial table, and components are added at workstations located around the periphery of the dial as it indexes from station to station Carousel Assembly System Selector and/or Orientor Purpose - to establish the proper orientation of the components for the assembly workhead Selector Acts as a filter Only parts in proper orientation are allowed to pass through to feed track Orientor A hybrid between circular work flow of dial indexing machine and straight work flow of in-line system Allows properly oriented parts to pass Reorients parts that are not properly oriented Parts Selection and Orientation LECTURE 15: INSPECTION TECHNOLOGIES Inspection Metrology Measurement - a procedure in which an unknown quantity is compared to a known standard, using an accepted and consistent system of units The means by which inspection by variables is accomplished Metrology – the science of measurement Concerned with seven basic quantities: length, mass, electric current, temperature, luminous intensity, time, and matter Feed Track From these basic quantities, other physical quantities are derived Moves parts from hopper to assembly workhead Categories: Characteristics of Measuring Instruments 1. Gravity - hopper and feeder are located at higher Accuracy – how closely the measured value agrees elevation than workhead with the true value 2. Powered - uses air or vibration to move parts Precision – a measure of the repeatability of toward workhead the measurement process Resolution – the smallest variation of the variable that Escapement and Placement Device can be detected Speed of response – how long the instrument takes to Escapement device measure the variable Removes parts from feed track at time intervals Others: operating range, reliability, cost that are consistent with the cycle time of the assembly workhead Accuracy vs Precision Placement device Physically places the parts in the correct location at the assembly workstation Escapement and placement devices are sometimes the same device, sometimes different devices Analog vs Digital Instrument Analog measuring instrument – output signal varies continuously with the variable being measured Output signal can take on any of an infinite number of possible values over its operating range Digital measuring instrument – can assume any of a discrete number of incremental values corresponding to the variable being measured Number of possible output values is finite Advantages: o Ease of reading the instrument o Ease of interfacing to a computer Two Basic Types of Inspection Techniques Coordinate Metrology 1. Contact inspection Concerned with the measurement of the actual Makes contact with object being inspected shape and dimensions of an object and comparing these 2. Noncontact inspection with the desired shape and dimensions specified on a part Does not make contact with object being drawing inspected Coordinate measuring machine (CMM) – an electromechanical system designed to perform Contact Inspection Techniques coordinate metrology A CMM consists of a contact probe that can be Uses a mechanical probe that makes contact with positioned in 3-D space relative to workpart features, the object being measured or gaged and the x-y-z coordinates can be displayed and Principal techniques: recorded to obtain dimensional data about geometry Conventional measuring and gaging instruments, manual and automated Coordinate Measuring Machine Coordinate measuring machines Stylus type surface texture measuring machines Noncontact Inspection Techniques Uses a sensor or probe located a certain distance away from the object being measured or gaged Two categories: Optical – uses light to accomplish the inspection Nonoptical - uses energy form other than light Advantages of noncontact inspection: Avoids possible damage to surface of object Inherently faster than contact inspection CMM Components Can often be accomplished in production without additional part handling Probe head and probe to contact workpart surfaces Increased opportunity for 100% inspection Mechanical structure that provides motion of the probe in x-y-z axes, and displacement transducers to measure the coordinate values of each axis Conventional Measuring and Gaging Techniques Optional components (on many CMMs): Measuring instruments - provide a quantitative value Drive system and control unit to move each axis of the part feature of interest Digital computer system with application Examples: software o Steel rules, calipers, micrometer, dial indicator, protractor Contact Probe Configurations Gages - determines whether a part feature falls within a certain acceptable range Examples: o Snap gages for external dimensions, plug gages for hole diameters, thread gages CMM Mechanical Structure CMM Operation and Controls – Four Main Categories Six common types of CMM mechanical structures: 1. Cantilever 1. Manual drive CMM – human operator physically 2. Moving bridge moves the probe and records x-y-z- data 3. Fixed bridge 2. Manual drive and computer-assisted data processing 4. Horizontal arm – can perform calculations to assess part features 5. Gantry 3. Motor-driven CMM with computer-assisted data 6. Column processing – uses joystick to actuate electric motors to drive probe 4. Direct computer control (DCC) – operates like a CNC CMM Structures machine tool and requires part program DCC Programming Manual leadthrough Operator leads the CMM probe through the various motions in the inspection sequence, indicating points and surfaces to be measured and recording these into control memory Off-line programming Program includes motion commands, measurement commands, and report formatting commands and is prepared off-line Advantages of Using CMMs over Manual Inspection Reduced inspection cycle time – translates to higher throughput rate Especially with DCC, approximately 90% reduction in certain tasks Flexibility – CMMs are general-purpose machines Reduced operator errors in measurement and setup Greater inherent accuracy and precision Avoidance of multiple setups – in general all measurements of a given part can be made in one setup Surface Measurement Most surface measuring devices use a contacting stylus Therefore, classified as contact inspection As stylus is traversed across surface, tip also moves vertically to follow the surface topography Movement is converted to electronic signal that can be displayed as either 1. Profile of the surface 2. Average roughness value of the surface Machine Vision Acquisition of image data, followed by the processing and interpretation of these data by computer for some useful application Also called “computer vision” Machine Vision Applications 1. Inspection: Dimensional measurement Dimensional gaging Verify presence or absence of components in an assembly (e.g., PCB) Verify hole locations or number of holes Detection of flaws in printed labels 2. Identification – for parts sorting or counting 3. Visual guidance and control – for bin picking, seam tracking in continuous arc welding, part positioning