automation pg i chapter

8/3/2019 Automation PG I Chapter

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I Semester M. Tech. I Chapter Industrial Automation 11IAE11

DEVADATTADEVADATTADEVADATTADEVADATTA V R Asst. Professor P E S C E Mandya 1

INDUSTRIAL AUTOMATION

Manufacturing can be defined as the application of physical and chemical processes to alter

the geometry, properties and /or appearance of a given raw material to make parts /products.

Manufacturing also includes the joining of multiple parts to make assembled products.

Manufacturing is always carried out as a sequence of operations and each successive operation

brings the material closer to the desired final state. A manufacturing company attempts to organize

its facilities like machines & tools, material handling system, inspection equipment and computer

systems that assist manufacturing operations in the most efficient way to serve the particular

mission of the plant i.e. good quality product at high production rate. The product variety and

quantity of product produced by a factory has a very significant influence on its facilities and the

way manufacturing is organized.

Production activity can be divided into four main categories.

1.Continuous Process (Continuous flow process)In this type of industry, the production process generally follows a specific sequence. It is the

dedicated continuous production of large amounts of bulk product. These industries can be

easily automated and computers are widely used for process monitoring, control and

optimization. Oil refineries, chemical plants, food processing industries, etc are examples of

continuous process industries.

2.Mass Production (High volume of discrete parts):Dedicated production of large quantities of one product (with little variation) is termed as mass

production. Production lines are specially designed and optimized to ensure automatic and cost

effective operation. Automation can be either fixed type or flexible. Industries manufacturing

fasteners (nuts, bolts etc.), integrated chips, automobiles, entertainment electronic products,

bicycles, bearings etc. which are all mass produced can be classified as mass production

industries.

3.Batch Production (Discrete Manufacturing)The largest percentage of manufacturing industries can be classified as batch production

industries. The distinguishing features of this type of manufacture are the small to medium size

of the batch, and varieties of such products to be taken up in a single shop. The lots may be

produced once or repeated periodically. Due to the variety of components handled, work

centres should have broader specifications. Another important fact is that small batch size

involves loss of production time associated with product changeover. Example: Books,

Clothing & appliances, etc.

Job Shop production:

The type of production facility usually associated with the quantity range of 1 to 100 units /

year is called Job Shop production, which makes low quantities of specialized and customized

products. The products are typically complex, such as space capsules, aircraft, and special

machinery. A job shop must be designed for maximum flexibility to deal with the wide part

and product variations encountered. Equipment in a job shop is general purpose and the labor


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force is highly skilled. Examples of such products include Ships, aircraft, Railway

locomotives, and heavy machinery.

Automation

Automation involves machines, tools, devices, installations, and systems that are allplatforms developed by humans to perform a given set of activities without human involvement

during those activities. The following six imperatives have been proven about automation:

Automation has always been developed by people Automation has been developed for the sake of people The benefits of automation are tremendous Often automation performs tasks that are impossible or impractical for humans As with other technologies, care should be taken to prevent abuse of automation, and to

eliminate the possibilities of unsafe automation

Automation is usually inspiring further creativity of the human mind.Automation can be defined as a technology that is concerned with the use of mechanical,

electronic, and computer based systems in the operation and control of production. Above

mentioned production activities can be automated to get high quality products.

Examples of automated manufacturing systems include:

Automated machine tools that process parts Transfer lines that perform a series of machining operations Automated assembly systems Manufacturing systems that use industrial robots to perform processing or assembly

operations

Automatic material handling and storage systems to integrate manufacturing operations Automatic inspection systems for quality control

Industrial robots for processing or assembly operation.Example: - Transfer lines, mechanized assembly lines, feedback control systems, NC m/c

tools and robots.

The three broad classification of industrial automation

1. Fixed Automation. 2. Programmable automation. 3. Flexible automation.

Fixed automation: - In this sequence of processing or assembly operations are fixed by the

equipment configuration. It has integrated transfer lines consisting of several workstations where

processing or assembly operations are done sequentially to manufacture the product. Each of the

operations in the sequence is usually simple and many such operations into one piece of equipment

make the system complex. Fixed automation is used when the volume of production is very high


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and hence it requires specialized equipment to process the product very efficiently and at high

production rates. The features of fixed automation are: High initial investment, High production

rates, relatively inflexible in accommodating product variety.

Ex: - In Automobile industry, highly integrated transfer lines consisting of several workstations and

robots are used to perform machining operations on engine & transmission components, welding &

painting of automobile body etc.

Programmable Automation: - The production equipment is designed to be adaptable to variations

in the sequence of operations to accommodate different product configurations. The production

equipment operates under the control of a program of instructions, which has been prepared

especially for the given product. With the help of this feature many different and unique products

can be made economically in small batches. When one batch is completed, the equipment is

reprogrammed and physical setup is altered to process the next batch. Hence the production timeincludes reprogramming time, setup time and actual process time. It is used when the volume of

production is relatively low and there are a variety of products to be made. The features of

programmable automation are: High investment in general purpose machines, Flexibility to deal

with variations in the product configuration, production rate is less than fixed automation, most

suitable for batch production.

Ex: - CNC and robots which can be programmed are used for processing of parts.

Flexible automation: - It is also known as flexible manufacturing system or computer integrated

manufacturing systems. In this, different products can be made at the same time on the same

manufacturing system, i.e. the products can be produced on a flexible system in batches or several

different product styles can be mixed on the system. It is capable of producing a variety of parts

with virtually no time lost for changeovers from one part style to another. A flexible automated

system consists of a series of workstations interconnected by a material handling and storage

system. A central computer controls the various activities that occur in the system, like routing the

various parts to the appropriate workstations and controlling the programmed operations at thedifferent stations. The features of flexible automation are: High investment for a custom engineered

system, Continuous production of variable mixtures of products, Medium production rates,

Flexibility to deal with product design variations.

Ex: - Flexible manufacturing systems for performing machining operations on engine cylinder.

Table: Automation achievements to the four types of production

Category Automation achievements

Continuous flow process Flow process from beginning to end, Sophisticated control and

optimization strategies using sensors, Fully automated plants

Mass Production Automated transfer lines, Dial indexing machines, Robots for painting,

welding, etc. Automated material handling, automated assembly

machine.

Batch Production NC machines, Robots for painting, welding, etc. CIM

Job Shop production NC machines, Robots for painting, welding, etc


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Reasons for Automating:

1 To increase labor productivity: Automating a manufacturing operation usually increases the

production rate and labor productivity. This means greater output per hour

2. To reduce labor cost: Ever-increasing labor cost has been and continues to be the trend in the

world's industrialized societies. Consequently, higher investment in automation has becomeeconomically justifiable to replace manual operations. Machines are increasingly being substituted

for human labor to reduce unit product cost.

3. To mitigate the effects of labor shortages: There is a general shortage of labor in many advanced

nations and this has stimulated the development of automated operations as a substitute tor labor

4. To reduce or eliminate routine manual and clerical tasks: An argument can be put forth that

there is social value in automating operations that are routine boring, fatiguing and possibly

irksome. Automating such tasks serves a purpose of improving the general level of working

conditions.

5. To improve worker safety: By automating a given operation and transferring the worker from

active participation in the process to a supervisory role, the work is made safer. Safety and well

being of the worker has become a national objective with the enactment of the Occupational Safety

and Health Act (OSHA) in 1970.This has provided an impetus for automation.

6. To improve product quality: Automation not only results in higher production rates than manual

operations; it also performs the manufacturing process with greater uniformity and conformity to

quality specifications. Reduction fraction defect rate is one of the chief benefits of automation

7. To reduce manufacturing lead time: Automation helps to reduce the elapsed time between

customer order and product delivery, providing a competitive advantage to the manufacturer for

future orders. By reducing manufacturing lead time, the manufacturer also reduces work-in-process

inventory

8. To accomplish processes that cannot be done manually: Certain operations cannot be

accomplished without the aid of a machine. These processes have requirements for precision,

miniaturization or complexity of geometry that cannot be achieved manually. Examples include

certain integrated circuit fabrication operations, rapid prototyping processes based on computer

graphics (CAD) models, and the machining of complex, mathematically defined surfaces using

computer numerical control. These processes can only be realized by computer controlled systems.

9. To avoid the high cast of not automating: There is a significant competitive advantage gained in

automating a manufacturing plant. The advantage cannot easily be demonstrated on a company's

project authorization form. The benefits of automation often show up in unexpected and intangible

ways, such as in improved quality, higher sales, better labor relations, and better company image.

Companies that do not automate are likely to find themselves at a competitive disadvantage with

their customers, their employees, and the general public.

Three approaches for dealing with automation projects:

(1) The USA Principle

(2) The Ten Strategies for Automation and Production Systems

(3) An Automation Migration Strategy


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1.USA PrincipleThe USA Principle is a common sense approach to automation projects. Similar procedures have

been suggested in the manufacturing and automation trade literature, but none has a more

captivating title than this one. The USA approach is so general that it is applicable to nearly any

automation project. Going through each step of the procedure for an automation project may in fact

reveal that simplifying the process is sufficient and automation is not necessary. USA stands for

a. Understandthe existing processb. Simplify the processc. Automate the process.

a. Understand the Existing Process: The first step in this approach is to understand existing

production process in detail. Like studying existing type of inputs, type of outputs, different


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processes, its function and its importance, production sequence, type of workstations etc. Some of

the basic charting tools used in methods analysis are useful in this regard, such as the operation

process chart and the flow process chart. Application of these tools to the existing process provides

a model of the process that can be analyzed and searched for weaknesses (and strengths). The

number of steps in the process, the number and placement of inspections, the number of moves and

delays experienced by the work unit, and the time spent in storage can be ascertained by these

charting techniquesMathematical models of the process may also be useful to indicate relationships between input

parameters and output variables. What are the important output variables? How are these output

variables affected by inputs to the process, such as raw material properties, process settings,

operating parameters, and environmental conditions? This information may be valuable in

identifying what output variables need to be measured for feedback purposes and in formulating

algorithms for automatic process control.

b. Simplify the Process: Once the existing process is understood, then the search can begin for ways

to simplify. This often involves a checklist of Questions about the existing process. What is the

purpose of this step or this transport? Is this step necessary? Can this step be eliminated? Is the

most appropriate technology being used in this step? How can this step be simplified? Are thereunnecessary steps in the process that might be eliminated without detracting from function? Some

of the ten strategies at automation and production systems are applicable to try to simplify the

process. Can steps be combined? Can steps be performed simultaneously? Can steps be integrated

into a manually operated production line?

c. Automate the Process: Once the process has been reduced to its simplest form, then automation

can be considered. The possible forms of automation include those listed in the ten strategies

discussed in the following section. An automation migration strategy might be implemented for a

new product that has not yet proven itself.

2. Ten Strategies for Automation and Production Systemsa. Specialization of operations: The first strategy involves the use of special-purpose equipment

designed to perform one operation with the greatest possible efficiency. This is analogous to the

concept of labor specialization, which is employed to improve labor productivity

b.Combined operations: Production occurs as a sequence of operations. Complex parts mayrequire dozens, or even hundreds, of processing steps. The strategy of combined operations

involves .reducing the number of distinct production machines or workstations through which

the part must be routed. This is accomplished by performing more than one operation at a given

machine, thereby reducing the number of separate machines needed. Since each machine

typically involves a setup, setup time can usually be saved as a consequence of this strategy.Material handling effort and non operation time are also reduced. Manufacturing lead time is

reduced for better customer service.

c. Simultaneous operations: A logical extension of the combined operations strategy is tosimultaneously perform the operations that are combined at one workstation. In effect, two or

more processing (or assembly) operations are being performed simultaneously on the same

work part thus reducing total processing time.

d.Integration of operations: Another strategy is to link several workstations together into a singleintegrated mechanism, using automated work handling devices to transfer parts between

stations. In effect, this reduces the number of separate machines through which the product

must be scheduled with more than one workstation. Several parts can be processed

simultaneously, thereby increasing the overall output of the system.


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e.Increased flexibility: This strategy attempts to achieve maximum utilization of equipment forjob shop and medium-volume situations by using the same equipment for a variety of parts or

products, It involves the use of the flexible automation concepts (Section 1.3.1). Prime

objectives are to reduce setup time and programming time for the production machine. This

normally translates into lower manufacturing lead time and less work-in-process.

f.Improved material handling and storage: A great opportunity for reducing nonproductive limeexists in the use of automated material handling and storage systems. Typical benefits includereduced work-in-process and shorter manufacturing lead times.

g.On-line inspection: Inspection for quality of work is traditionally performed after the process iscompleted. This means that any poor-quality product has already been produced by the time it

is inspected. Incorporating inspection into the manufacturing process permits corrections to the

process as the product is being made. This reduces scrap and brings the overall quality of the

product closer to the nominal specifications intended by the designer.

h.Process control and optimization: This includes a wide range of control schemes intended tooperate the individual processes and associated equipment more efficiently. By this strategy, the

individual process times can be reduced and product quality improved.

i. Plant operations control: Whereas the previous strategy was concerned with the control of theindividual manufacturing process, this strategy is concerned with control at the plant level. Itattempts to manage and coordinate the aggregate operations in the plant more efficiently. Its

implementation usually involves a high level of computer networking within the factory.

j. Computer-integrated manufacturing (CIM): Taking the previous strategy one level higher wehave the integration of factory operations with engineering design and the business functions of

the firm, CIM involves extensive use of computer applications, computer data bases, and

computer networking throughout the enterprise automation

3. Migration Strategy

Phase 1Manual production using single-station manned cells operating independently. Thisis used for introduction of the new product for reasons already mentioned quick and low-

cost tooling to get started

Phase 2 Automated production using single-station automated cells operatingindependently. As demand for the product grows, and it becomes clear that automation can

be justified, then the single stations are automated to reduce labor and increase production

rate. Work units are still moved between workstations manually.

Phase 3Automated integrated production using a multistation automated system with serialoperations and automated transfer of work units between stations. When the company is

certain that the product will be produced in mass quantities and for several years, thenintegration of the single-station automated cells is warranted to further reduce labor and

increase production rate.


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Fig: Migration Strategy

Opportunities of automation in a production system are plenty. Automation can be done in facility

level for manufacturing system ( machine tool, assembly work stations etc), material transport

system (Conveyor system, part feeding devices, AGV) and also in manufacturing support system

including quality control system( automatic gauging, CMM).

Automation and control technologies in the production system

Fig


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There are three basic Elements of an Automated System

(1)Power to accomplish the process and operate the system.(2)A Program of instructions to direct the process,(3)A Control system to actuate the instructions.

1. Power: An automated system is used to operate some process, and power is required to drive the

process as well as the controls. The principal source of power in automated systems is electricity.2. Process: The term process refers to the manufacturing operation that is performed on a work

unit.

o Power is required to drive the process as well as the controls.o Loading and unloading the work unito Material transport between operations.

Additional power is required for the following in automation.

o Controller unit: This requires electrical power to read the program of instructions, make thecontrol calculations, and execute the instructions by transmitting the proper commands to

the actuating devices.

o Power to actuate the control signals: The commands sent by the controller unit are carriedout by means of electromechanical devices, such as switches and motors. The commands

are generally transmitted by means of low-voltage and so the control signals must be

amplified to provide the proper power level for the actuating device control signals.

o For Data acquisition and information processing: The data must be collected from theprocess and used as input to the control algorithms. In addition, a requirement of the process

may include keeping records of process performance or product quality. These data

acquisition and record keeping functions require power, although in modest amounts.

3. Program of Instructions

The actions performed by an automated process are defined by a program of instructions Each

part or product style made in the operation requires one or more processing steps that are unique to

that style, These processing steps are performed during a work cycle. A new part is completed

during each work cycle. The particular processing steps for the work cycle are specified in a work

cycle program.Work cycleprograms are called part programs in numerical control. Other process

controlapplications use different names for this type of program.

Work Cycle Programs:

In the simplest automated processes, the work cycle consists of essentially one step, whichis to maintain a single process parameter at a defined level,

In more complicated systems, the process involves a work cycle consisting of multiple stepsthat are repeated with no deviation from one cycle to the next. During each step, there are

one or more activities that involve changes in one or more process parameters.

Process parameters are inputs to the process such as temperature setting of a furnace,coordinate axis value in a positioning system, valve opened or closed in a fluid flow system,

and motor on or off.

Many production operations consist of multiple steps, Examples automatic screw machine cycles,

sheet metal stamping operations, plastic injection molding, and die casting. In earlier versions of


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these operations the work cycles were controlled by hardware components, such as limit switches,

timers, cams, and electromechanical relays. The hardware components and their arrangements

served as the program of instructions that directed the sequence of steps in the processing cycle

The disadvantages of the hardware system are:

They often required considerable time to design and fabricate, thus forcing the productionequipment to be used for batch production only;

Making even minor changes in the program was difficult and time consuming The program was in a physical form that is not readily compatible with computer data

processing and communication.

Decision-Making in the Programmed Work Cycle:

Many automated manufacturing operations require decisions to be made during the programmed

work cycle to cope with variations in the cycle. In many cases, the variations are routine elements

of the cycle, and the corresponding instructions for dealing with them are incorporated into the

regular part program.

Operator interaction: In a work cycle operator has to interact with the system for decision making.

Ex. In Engraving operation operator has to decide the alphabets and type of font to engrave

Different part or product styles processed by the system: In a single manufacturing line,different

models of the car has to be welded, the robot with the help of sensors and control programs decides

location and type of weld for each model and then performs welding different body styles

Variations in the starting work units: Sand casted parts do have some variations in their sizes due

to material properties, temperature etc. the machining part programs should be flexible enough to

machine such casted parts

The program can be designed to respond to sensor or operator inputs by executing the appropriate

subroutine corresponding to the input. In other cases, the variations in the work cycle are not

routine at all. They are infrequent and unexpected, such as the failure of an equipment component.

In these instances, the program must include contingency procedures or modifications in thesequence to cope with conditions that lie outside the normal routine.

4. Control System

The control element of the automated system executes the program of instructions. The control

system causes the process to carry out some manufacturing operation. The controls in an automated

system can be either closed loop or open loop.

Advanced automation functionsThese are made possible by special subroutines included in the program of instructions. In some

cases, the functions provide information only and do not involve any physical actions by the controlsystem,

Example: Reporting a list of preventive maintenance tasks that should be accomplished. Any

actions taken on the basis of this report are decided by the human operators and managers of the

system and not by the system itself.

In other cases, the program of instructions must be physically executed by means of the control

system using available actuators. Example: A safety monitoring system that sounds an alarm when

a human worker gets dangerously close to the automated system.

Three Advanced Automation Functions are

Safety Monitoring Maintenance and Repair Diagnostics Error Detection and Recovery


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Safety Monitoring :One of the significant reasons for automating a manufacturing operation is to remove workers from

a hazardous working environment.

(1)To protect human workers in the vicinity of the system(2)To protect the equipment associated with the system

Safety monitoring in an automated system involves the use or sensors to track the system's

operation and identify conditions and events that are unsafe or potentially unsafe.The safety monitoring system is programmed to respond to unsafe conditions in some appropriate

way. Possible responses to various hazards might include one or more of the following:

complete stoppage of the automated system

sounding an alarm

reducing the operating speed of the process

taking corrective actions to recover from the safety violation

Sensors and their applications for safety monitoring:

Limit switches Photoelectric sensors Temperature sensors Heat or smoke detectors. Pressure-sensitive floor pads Machine vision systems

Maintenance and Repair Diagnostics:Three modes of operation of a modern maintenance and repair diagnostics subsystem

Status Monitoring, Failure Diagnostics Recommendation of Repair Procedure.. Status Monitoring

In the status monitoring mode, the diagnostic subsystem monitors and records the status of key

sensors and parameters of the system during normal operation. On request, the diagnostics

subsystem can display any of these values and provide an interpretation of current system status,

perhaps warning of an imminent failure. Status monitoring serves two important functions of

machine diagnostics:

Providing information for diagnosing a current failure

Providing data to predict future malfunction or failure.

Failure Diagnostics.The failure diagnostics mode is invoked when a malfunction or failure occurs. Its purpose is to

interpret the current values of the monitored variables and to analyze the recorded values preceding

the failure so that the cause of the failure can be identified

Recommendation of Repair Procedure.The subsystem provides a recommended procedure to the repair crew as to the steps that should be

taken to effect repairs. Methods for developing the recommendations are sometimes based on the

use of expert systems in which the collective judgments of many repair experts arc pooled and

incorporated into a computer program that uses artificial intelligence techniques.

Error Detection and Recovery:The error detection and recovery consists of two steps:

(1) Error Detection

(2) Error Recovery.


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Error Detection:The error detection step uses the automated system's available sensor systems to determine when a

deviation or malfunction has occurred, correctly interpret the sensor signals and classify-the error.

The errors must be anticipated in advance in order to select sensors that will enable their detection

Three general categories of errors in production are, 1.Random Errors occur as a result of the

normal stochastic nature of the process. These errors occur when the process is in statistical control

Large variations in part dimensions, even when the production process is in statistical control, cancause problems in downstream operations. 2. Systematic Errors are those that result from some

assignable cause such as a change in raw material properties or a drift in an equipment setting.

3.Aberrations results from either an equipment failure or a human mistake.

The two main design problems in error detection are: (1) to anticipate all of the possible errors that

can occur in a given process and (2) to specify the appropriate sensor systems and associated

interpretive software so that the system is capable of recognizing each error.

Error Recovery:Error Recovery is concerned with applying the necessary corrective action to overcome the error

and bring the system back to normal operation. The problem of designing an error recovery system

focuses on devising appropriate strategies and procedures that will either correct or compensate for

the variety of errors that can occur in the process. Generally, a specific recovery strategy and

procedure must be designed for each different error

1. Make adjustments at the end of the current work cycle: When the current work cycle is

completed, the part program branches to a corrective action subroutine specifically designed for the

error detected, executes the subroutine, and then returns to the work cycle program. This action

reflects a low level of urgency and is most commonly associated with random errors in the process.

2. Make adjustments during the current cycle: This generally indicates a higher level of urgency

than the preceding type. In this case, the action to correct or compensate for the detected error is

initiated as soon as the error is detected. However, it must be possible to accomplish the designated

corrective action while the work cycle is still being executed3. Stop the process to invoke corrective action:In this case, the deviation or malfunction requires

that the execution of the work cycle be suspended during corrective action. It is assumed that the

system is capable of automatically recovering from the error without human assistance. At the end

of the corrective action, the regular work cycle Is continued.

4. Stop the process and call for help: In this case, the error requiring stoppage of the process cannot

be resolved through automated recovery procedures. This situation arises because:

i. The automated cell is not enabled to correct the problemii. The error cannot be classified into the predefined list of errors. In either case, human

assistance is required to correct the problem and restore the system to fully automated

operation.

Error detection and recovery requires an interrupt system. When an error in the process is sensedand identified, an interrupt in the current program execution is invoked to branch to the appropriate

recovery subroutine. This is done either at the end of the current cycle or immediately depending

upon type of error. At the completion of the recovery procedure, program execution reverts back to

normal operation.

Example: Numerically controlled machine tools rely on sensors that detect positions of each

machine component and convert them into digital information. Digital position information is used

in control units to control actuators to position the cutting tool properly with respect to the work

piece being cut. The precision of such motion is determined by the resolution of the position sensor

(feedback device), the digital control algorithm, and the mechanical and thermal behavior of the

machine structural elements. Specifically, machine tools are composed of multiple slides, rotary


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tables, and rotary joints, which are usually assembled on top of each other, each designed to move

along a single axis of motion, providing either a translational or a rotational degree of freedom. In

reality, each moving element of a machine tool has error motions in six degrees of freedom, three

translations, and three rotations. Depending on the number of axes of motion, a machine tool can

therefore have as many as 30 individual error components. Furthermore, the construction of

moving slides and their assemblies with respect to each other introduce additional error

components such as squareness and parallelism between axes of motion

Automation of machine tool operation by computer numerical control and the modeling of machine

tool systematic errors led to the creation of new hardware and software error compensation

technologies enabling improvement of machine tool performance. Machine error compensation in

the form of lead screw pitch errors has been available since the early implementations of CNC.

Such lead screw error compensation is carried out using error tables in the machine controller.When executing motion commands, the controller accesses these tables to adjust target positions

used in motion servo algorithms (feed forward control). The lead screw error compensation tables

therefore provide one-dimensional error compensation. Modern machine controllers have more

sophisticated compensation tables enabling two or three-dimensional error compensation based on

preprocess measurement of error motions. For more general error compensation capabilities,

researchers have developed other means of interfacing with the controllers. One approach for such

an interface was through hardware modification of the communication between the controller and

the position feedback devices. In this case, the position feedback signals are diverted to an external

microcomputer, where they are counted to determine the instantaneous positions of the slides, and

corresponding corrections were introduced by modifying the feedback signals before they are read

by the machine controller. Similarly, the software approaches to error compensation were also

implemented by interfacing with the CNC through the controller executive software and regular

input/output (I/O) devices (such as parallel I/O) Generic functional diagrams depicting the two

approaches are shown in Fig.below.


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Error Detection in an Automated Machining Cell

Consider an automated cell consisting of a CNC machine tool, a parts storage unit, and a robot for

loading and unloading the parts between the machine and the storage unit. Possible errors that

might affect this system can be divided into the following categories: (1) machine and process, (2)

cutting tools, (3) work holding fixture, (4) part storage unit, and (5) load/unload robot


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Levels of Automation

The concept of automated systems can be applied to various levels of factory operations. One

normally associates automation with the individual production machines. For example.A modern

numerical control (NC) machine tool is an automated system. However, the NC machine itself is

composed of multiple control systems. AnyNCmachine has at least two axes of motion, and some

machines have up to five axes. Each of these axes operates as a positioning system and is, in effect,

itself an automated system. Similarly, a NC machine is often part of a larger manufacturing system,

and the larger system may itself be automated. For example, two or three machine tools may be

connected by an automated part handling system operating under computer control. The machine

tools also receive instructions (e.g., part programs) from the computer. Thus we have three levels of

automation and control included here (the positioning system level, the machine tool level, and the

manufacturing system level). There are five possible levels of automation in a production plant.


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Device level: This is the lowest level in our automation hierarchy. It includes the actuators, sensors,

and other hardware components that comprise the machine level. The devices are combined into

the individual control loops of the machine, for example: the feedback control loop for one axis of a

CNC machine or one joint of an industrial robot.

Machine level: Hardware at the device level is assembled into individual machines. Examples

include CNC machine tools and similar production equipment, industrial robots, poweredconveyors, and automated guided vehicles. Control functions at this level include performing the

sequence of steps in the program of instructions in the correct order and making sure that each step

is properly executed.

Cell or system level: This is the manufacturing cell or system level, which operates under

instructions from the plant level. A manufacturing cell or system is a group of machines or

workstations connected and supported by a material handling system, computer and other

equipment appropriate to the manufacturing process. Production lines are included in this level.

Functions include part dispatching and machine loading coordination among machines and material

handling system, and collecting and evaluating inspection data.

Plant level: This is the factory or production systems level. It receives instructions from the

corporate information system and translates them into operational plans for production. Likely

functions include order processing, process planning, inventory control, purchasing, material

requirements planning, shop floor control, and quality control.

Enterprise level: This is the highest level consisting of the corporate information system. It is

concerned with all of the functions necessary to manage the company: marketing and sales,

accounting, design, research, aggregate planning, and master production scheduling.

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automation pg i chapter

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