Construction Of Industrial Automation

PART ONE – Automated System For Production

Section 1.1

Automated System

The purpose of this introductory chapter is to update the reader on:

·         The objectives, structures and behaviour of automated system

·         Comparisons between hard-wired and programmable technology

·         Understanding electronic components and devices

·         Changing requirements in industrial automation.

These are areas where changing needs and technological developments create problems which need to be carefully considered.

Using this knowledge, the problems of selecting both technology and equipment can be considered in the next section.

Automating for production

1. Gobal approach to a production system

The purpose of a production system is to provide added value. Starting from materials, parts and sub- assemblies higher value products are manufactured. The may be either :

·         Finished product, which can be directly marketed

·         Or intermediate product, used for manufacturing finished products.

The diagram below illustrates a production system. Working materials are received and finished products are produced. This system also uses energy such as electric power, compressed air and auxiliary consumables, cooling water and lubricants the production system also generates various types of waste, such as chips from cutting operations and slurries.

Operating a production system calls for different kinds of human intervention:

·         Operating personnel, who intervene according to the degree of automation in order to:

Ø  Supervise automatic machines

Ø  Load, inspect and unload semiautomatic machines

Ø  Control the production process, if workstations are used

·         Technicians,  responsible for making the necessary adjustment to obtain the desired quality, or to start a production run on a variant of the initial product

·         Maintenance personnel, who intervene when the production system fails and who carry out regular preventive maintenance.

Objectives for automated production

Industrial production is increasingly automated. Progress has been made in the following areas:

·         Automation of previously entirely manual operations, for example, assembly and inspection.

·         Increased automation of operations already partially automated, for example :

-       upgrading from semi-automatic to automatic machines

-       replacement of dedicated machines, manufacturing only one type of product, by flexible machines capable of working on several product variants.

Objectives for automation can vary widely:

·         cutting production costs, by reducing labour cost and saving materials and energy

·         eliminating dangerous or arduous task and improving working conditions, thereby increasing job satisfaction

·         improving product quality by limiting the human factor and increasing automated monitoring and inspection

·         performing operations that cannot be done manually, for example miniature assembly and operation requiring high speed or complex coordination

Competitive product through automation

In a market economy, automation is intended to assist in improving the overall competitiveness of a product, either directly, by reducing cost and improving quality, or indirectly, by improving working conditions.

A competitive final product is one which sells well in the targeted market. As you can see from the figure below, competitiveness stems essentially from the following factor : cost, quality, innovation and availability.

We have seen that automation of production equipment can improve cost, quality and even availability of product, for example, by using flexible automation.

It is important to ensure that the product itself is optimized to the fullest extent, and always responds to changing market requirements.

Experience shows that invest in automation often leads to questioning the manufacturing process, and therefore the product itself. By simultaneously considering the manufacturing facilities and the design of the product itself, the most competitive results are obtained. Also, as illustrated below, automation of production equipment must be carried out in cooperation with the product and process manager.

     

Calculating the profitability of an automation project  

As with any investment, an automation project is jugged by its profitability. This can be expressed in terms of investment playback time.

Investment              

                   = number of years for investment

Annual profit   payback

Generally, the project will be considered worthwhile if the investment payback time is less than 3 years, provided that the expected lifetime of the production facility is greater than 3 years.

Note: indirect profit or gain resulting from increased productivity due to improvement in working conditions, are not included in the calculation as they cannot easily be assessed.

Structure of automated application

Separating the control system and the

Application

All automated system consists of two parts:

·         the application. (formally called the operative unit but which, for clarity we will refer to in this book as the “application”) where actuator act upon the automated process;

·         The control system which coordinates action of the “application”.

Application

The application operates on the worked material and the product. It generally consists of:

·         tooling and various facilities performing the production process ,for example moulds, punches, cutting tools, welding heads and marking heads.

·         Actuator intended to drive or operate these facilities, such as :

  -     Electric motor to active pumps

  -     Hydraulic cylinder to close moulds

  -     Pneumatic cylinder to drive marking heads.

   

Control system

The control system sends order to the application which then feeds signal back to the control system. In the way, actions are coordinated. Increasingly, control system are based on programmable controller which are the main subject of this book.

The control system coordinates three types of dialogue:

1)     dialogue with the machine

control of the actuator such as, motor and cylinder via preactuators, contactor, control valves and variable speed drive :

Acquisition of feed back signals from sensor reporting the progress of the

              Machine.

2)     Man-machine dialogue

Order to operate, adjust and repair the machine, operations personnel enter instructions and receive data in return.

3)     Communication with other machines

Several machines can operate within the same production system. these machines coordinate through dialogue between their respective control system.

The diagram below illustrates the organization of the control system and application.

  

Methods of describing the behaviour of an automated system

To design, construct and operate an automated system, it is essential to describe its behavior. The tools or languages to do this may be literal, symbolic or graphic, as described. it is important to understand these methods in order to define the problem clearly and concisely. The section on “specification and programming tools for automation” in the appendix develops this initial discussion.

Written description of the behavior of

An automated system

We can define what the automated system is supposed to do in plain language, describing each step, and stating the conditions to be met at each moment.

This method of description becomes increasingly complex for developing automated production and often leads to weight specification. It has been necessary, therefore, to develop symbolic and graphic tools to provide a concise and clear description.

Graphic representation of automated system behavior

Graphic representation is well accepted as an addition to symbolic expressions:

1)Because it directly represents certain types of automation technology such as relays or logic modules,

2)And because it can provide a functional description of sequential problems without having to define the technology to be.

The ladder diagram

This graphic method for describing automated system was created at a period when relays were the only control technology available.

The illustrations on the right show how it is possible to produce each of the basic logic functions, AND, OR, NOT and MEMORY, simply by connecting normally closed contacts in series or parallel.

in this way it is easy to describe combinational expressions. Sequential problems, however, require a sequence of MEM circuit to represent them and this complicates matters.

Ladder diagram are used universally. Because of their familiarity to electrical engineers and electrician, they are used to represent program by nearly all programmable controller.

 

Function block diagram

This graphic representation is used to represent logic relationships with AND, OR, NOT and MEMORY logic functions.

This method is standardized internationally, and it provides clear, concise representation by graphically combining basic logic functions as shown on the right. Sequential production processes cannot be clearly described by a ladder diagram or a function block diagram. For this reason several graphic languages have been developed with the specific objective of representing sequential problems.

Function block diagram describe the combinational relationships

S= a.b.e (c+d)

Function chart (grafcet)

In the evolution of automated system representation

Timing diagram, phrase diagrams, Petri networks and flow charts are graphic languages that have been used to represent automated system. Each languages has contributed in building the basic for the development of function charts.

Now a standard, function chart is recognized as the graphic languages best suited to representing the sequential part of automated production system.

Function chart represents the sequence of steps in the cycle. Step-by-step progression of the cycle is controlled by “transitions” located between each step. Each step may consist of one or more action. A “transition condition “ is associated with each transition. This condition must be satisfied to allow the transition to be cleared and allow progress to the next step.

The cycle advances step by step. The initial step (step 0 in the figure on the right), is activated at the beginning of operation and enables the transition which follows. It is cleared when transition condition x is true. Step 1 is then activated and step 0 deactivated. Actions associated with step 1 will then take place until the transition conditions of the next transition are satisfied.

Hard – wired and programmable control technology

After learning about methods for describing the operations of automated system, it is important to learn about the technology for implementing the control. This falls into two major categories:

·         Hard – wired technology;

·         Programmable technology

1. Comparing the principles

With hard- wired technology, the control system consists of interconnected modules. The resulting operation is a function of the types of module selected and of the wiring. Thus the system is totally customized by the hardware.

With programmable technology, however, the control system is implemented by programming equipment designed for this purpose.

The resulting operation depends on the program that has been entered.

The illustration below compares the principles for “hard-wired” and “programmable” systems using the three methods of description presented in the previous pages:

·         Contact diagram, used for hard-wired relay technology and converted into ladder diagram for representation on a programming terminal;

·         Logic expressions (function block diagram and Boolean expression);

·         Function charts, implemented in hard-wired technology using modules, and displayed directly on the terminal with programmable technology

2. Hard wired systems

Three types of technology are used in hard-wired automation system:

* Electro-magnetic relays

*Pneumatic logic modules

*Printed circuit boards (electronic modules)

Electronic magnetic relays

The relay, consisting of contacts actuated by an electro-magnetic coil, is the basic component used for this hard wired technology.

Current is provided by wires which are screwed, soldered or crimped to the relay terminal. Relays can be connected to each other and combined in a circuit with sensor contact and preactuator coils.

 Pneumatic logic modules

Compressed air is used to actuate diaphragms, which in turn operate switching valves.

Logic AND, OR, NOT and memory modules are interconnected through flexible hoses. A sequencer connects to the modules to implement the function chart.

Printed circuit boards (electronic modules)

The basic modules are made from electronic components (diodes, transistor, and integrated circuit boards.

Connections between modules are made wiring.

3. Programmable technology

Only the availability of high integration technology has made it possible to attain the response time necessary for using programmable equipment. This equipment comes in various forms:

1) Standard and special electronic printed circuit boards ;

2) Micro and minicomputer

3) Programmable controller

The ease or difficulty of programming these devices depends on the type of equipment selected.

The choice between “hard-wired” and “programmable” options and between the various forms of programmable technologies are discussed in section 1.2.

From programmable electronic devices to functional automated systems

We have seen that only high integration electronic technology provides the concentration of function required to manufacture programmable automation systems.

To appreciate fully the guidelines for selecting equipment explained in the next section, it is important to be aware of the problems that are involved in implementing programmable control system using both programmable and non programmable electronic devices.

1. Programming languages

In order to operate, the assembled system must be programmed. The user can program the system by using “development tools” and special “programming terminals”.

The block diagram below classifies the various programming languages by level:

1) At the component level, binary (low level) execution language, consisting        of bits in the forms of “discrete” elementary signals.

2) At the opposite end of the scale, at the application level, specialized (high Level)language such as ladder diagram and function chart are used for automation system. The nearer the language to the application, the easier and faster the programming. It is therefore possible to classify in ascending order of ease:

-       Electronic printed circuit boards

-       Micro and minicomputer ;

-       Programmable controller

3. Manufacturing special purpose boards

Electronic boards may be:

*Standard off-the-shelf boards, providing desired sub-functions. These must be assembled in a rack and programmed to provide the final system required by the application

*Or special purpose boards combining all the function required for operating the application.

The illustration on the rights show the various steps required in industrial production of electronic boards. Board design and manufacture are now automated. The design stage, using specialized CAD equipment, provides all the elements needed by the automated manufacturing process including

*Numerically controlled drilling

*Production of printed circuits

*Robot insertion’ of components

*Wave flow-soldering

*Automatic testing.

The whole procedure should constitute and efficient CAD-CAM system.

There are several essential stages to obtaining the high degree of reliability required by industrial applications. This calls for highly specialized “know-how” and equipment:

*Component acceptances testing, to avoid accepting poor quality components which may already have been rejected by other users

*Final board testing, to avoid using unreliable boards.

Manufacturing special purpose boards for an automation project can lead to a compact solution. However, in order to remain competitive and to be able to debug each card efficiently and to implement quality control tests, manufacture of 500 identical boards are considered to be the minimum. Such quantities are commonly found in mass automation equipment such as in car parks and ticket issuing machines, but are rare in the manufacture of automated systems.

The various steps in the production of electronic boards

4. Combining standard boards

For automated production system, where the quantity of system is small and reliability requirements are high, combining standard off-the-shelf boards in racks and then programming the system is preferable to manufacturing special purpose boards.

The diagram on the right shows four types of boards or modules, each providing a sub- function:

*Power supply module

*Processor board

*Memory board

*Input-output board

These boards communicate with each other via the rack backplane which also supplies power.

In industrial practice, using these subassemblies requires some careful attention. The user must::

*Ensure that the selected boards are compatible and comply with the requirements of the application

*Undertake long and difficult assembly language programming

*Carry out exhaustive debugging of the prototype

These difficulties entail high costs and long project times. For this reason, combining standard boards to make a system is only competitive for manufacture of more than 50 identical systems.

Such large quantities of system are seldom found in production automation. For this type of automation, industrial programmable systems are preferable.

5. Using industrial programmable systems

The following two pages highlight new requirements in production automation. Only industrial equipment which can be easily programmed and reprogrammed can meet these requirements because of flexibility, ease of modification, extend edibility, hierarchical and distributed communication, and simple man-machine dialogue.

Industrial programmable systems include:

*Industrial micro and minicomputers

*Industrial programmable controllers

For production automation, these systems offer language closer to the application than those offered by printed circuit boards. Some programmable controller allows direct programming in function chart language which greatly simplifies the user’s task.

Section 1.2 deals with technological choices in automation and compares the capabilities of microcomputer and minicomputer with programmable controllers.

Changing requirements in automation

1. New requirements for automated systems

Until recently, machine automation was generally limited to :

*REACTIVE automation, providing control and monitoring so that elementary operation are performed within stated response times and according to a schedule.

*Relatively restricted operator dialogue, which was of limited use since machines themselves offered little mechanical flexibility.

Today, new requirements exist for PRODUCTIVITY, QUALITY, FLEXIBILITY and SAFETY, calling for increasing COMPLEXITY.

2. Evolving structure

The development of automation has led to changes in the structure of the control system.

 Inj, the automated machine is simple and independent. Conventional automation (hard-wired or programmable) is perfectly appropriate. k Other machines are added as required for form a production line. However, this type of association is not flexible, and is difficult to adapt to product changes.

To remedy this drawback, it is possible to install a single overall control systeml. This excessively centralized control system causes problems. Operation is difficult and localized problems may cause general shut down .

, a compromise is sought by decentralizing the control functions and coordinating them to optimize production system resources.

This structure is more flexible, adaptable and gradual.

3. The automated machine: _ an element in the automated workshop

The ability to organize and hierarchize control and decision function illustrates the fact that the automated machine is simply an element within the GLOBAL PROCESS forming the AUTOMATED WORKSHOP. Not only the local control function need to be optimized but attention must also be paid to this overall process. Working material must be supplied to the machines without interruptions, work must be monitored and measured and build-up of worked parts, causing costly blockages, must be avoided.

The machines must, therefore, he capable of COMMUNICATING, i.e. receiving and acknowledging instructions.

4. Communication with and between people

The automated machine is like a road junction where numerous “skills” meet. Providing communication between all parties and enabling them to express themselves is a major problem. A working methodology, based on common methods-tools, helps to establish the system specifications. Various document produced by the design departments will be used for implementing the system. These documents will be updated when the machine is started-up and as changes are made.

A dominant factor in successful automation is the ability of programmable equipment to edit and keep document up to date in a clear firm and at a lower cost than manually drawn up documents.

Part One – Automated systems serving production 

Choices in automation

Problems encountered in industrial automation come in a variety of forms. To ensure that an automated system is rational and competitive, it is essential to study the choices to be made for both the application and for the control system.

·      Hard-wired technology : electro- magnetic relays and pneumatic control

·      Programmable technology : standard and special purpose boards, micro and minicomputers and programmable controllers

Selection criteria are analyzed to achieve best total cost for the installation, taking into consideration the application of each technology.

Implementing automation projects

1.   stages in the life cycle of an automated system

the choice of control technology should facilitate all stages in the machine life. The diagram on the right shows how these stages are organized.

Preliminary discussions on the automated production system define production objectives (products involved, operations, processes, production rates, etc.) and the automation objectives (automation level, flexibility, dialogue, need for future changes, etc.).

A draft project of the system to be auto mated is drawn up, and is developed into a combined specification for the application and the control system.

The automation process then begins. The application and the control system are each designed by specialist teams. The application design should lead the control system design slightly. The two designs are coordinated at each stage of their development. The application and the control system are manufactured independently and the control system is then integrated into the application for start-up.

The start-up process, essentially concerning the application, is often problematic. Every step should be taken to ensure that the control system provides facilities to simplify this.

Finally, we enter the system operation stage, which generates the investment payback. During this period, the control system must assist with:

·      adjustment to optimize  production,

·      Maintenance.

Selection guidelines for rational and profitable automated systems

Represent only a small part of the investment, yet a careful selection of control technology is essential to facilitate each stage of the machine life.

As a general rule, machine control equipment should:

·      simplify machine start-up  by enabling each action to be controlled separately under adequate safety conditions, and informing the start-up engineer of the machine status (by providing access) at any time

·      enable machine adjustment to be made by providing the production phase by providing the maintenance  engineer with the same facilities

·      Enable future updates and changes.

Often, it is necessary to ensure that the system provides:

·      automatic printout of machine documentation to aid maintenance and to simplify any future updates

·      production reports to the central computerized production management system

·      Machine-to-machine connection.

The SELECTION GUIDELINES presented in the following pages will help the reader to choose the control technology so as to best rationalize the machine and maximize its profitability. In particular, the notion of TOTAL COST is covered. In addition to the purchase cost of control equipment, the TOTAL COST (1) includes machine manufacture, start-up cost and shut-down cost during repairs. All cost can be considerably reduced by correct choice of control system.

  Methods for selecting automation equipment

1.  Choices to be made

We have seen that technology choices must be made for each of the two parts of the automated machine:

·      The application :

the main types of actuator are listed in the figure opposite.

·      The control system :

the previous chapter showed the major developments in control technology. These are also shown in the figure opposite. Throughout this book we will be focusing on the control system which is usually based on programmable equipment.

 

             Electrical motor ,                                        relay control,

             Pneumatic cylinder,                                   pneumatic controls

             Hydraulic cylinder,                                     programmable        controller,

             Heating elements,                                      micro and mini-computer

                Valves.                                                               Standard electronic

                                                                               Boards,

                                                                               Special purpose board

The type of equipment must be selected for both the application and for the control system.

2. Method for choosing control system technology

 

Part two – Automated systems based on controllers

Section 2.1

The programmable controllers at the heart of the automated system

·         An automated system consists of many components:

·      Actuator: motor, pneumatic cylinders, etc.

·      Preactuators : contactor, variables speed drives, directional valves

·      Sensor of all types : proximity detectors, position switches, digital sensor

·      Operator interfaces

·      Adjustment terminals.

At the heart of the system, the programmable controllers connect to all these devices.

This section reviews the various function of the automated system, describes and classifies the different units, and shows how the programmable controller is organized to connect and to communicate with each unit, and shows how the programmable controller is organized to connect and to communicate with each unit.

Programmable controller can be integrated easily into automated industrial system. This is their major advantage.

Automated system function communicating with the programmable controller

·         The illustration opposite classifies the various functions associated with the programmable controller and shows two communication methods used:

·      Direct “hard-wired” links via programmable controller input-output modules

·      “Serial or parallel” links via cables, connected to the programmable controller or its specialized modules.

The 5 main function associated with the programmable controller are :

1-    sensing, by various types of sensor located on the machine

2-    action by control of the actuator and Preactuators

3-    dialogue with the operator

4-    dialogue with the production supervision system

5-    dialogue for programming

Programming dialogue

Programming dialogue is needed for the initial installation and for subsequent alterations. Section 2.2 explains the use of programming terminals, designed for this purpose.

Modular organization of the programmable controller

The programmable controller consists of a set of functional blocks linked via a communication channel called the internal bus. Generally, each block is physically implemented as separate module. This modular organization offer excellent configuration flexibility to meet user requirements, and to facilitate diagnostics and maintenance.

 

The various modules of the programmable controller are mounted in a rack with a “black-plane” (common by and connectors). Each input/output module is provided with a terminal block equipped with a display system to show the logic condition of each channel (LED). Two types of connection to external devices are used:

- Direct “hard-wired” links

- “serial” or “parallel” links

Connecting sensors to the programmable controller

1. Sensor and the programmable controller

The diagram below shows the individual leads or terminals of a sensor wired directly to the programmable controller. When the sensor closes the circuit, the module input terminals are activated and the signal is accepted by the programmable controller. The sensors are connected directly to the programmable controller, without any intermediate interfacing, via input modules with suitable adapters and protective circuits.

Detecting physical phenomena with sensor

Many different kinds of physical values can be measured by sensor , such as position, speed, acceleration, pressure, level, flow rate, temperature, light, force, weight, stress, pH and magnetism. Since position sensors are the most widely used on production machines we will describe the principal ‘discrete’ and digital’ version.

Discrete position sensor

A – limit switch

Switches when the object to be sensed physically activates the sensor arm. Switching is made by the closing or opening of an electromechanical contact. Limit switches vary enormously and range from micros itches up to large limit switches.

 

                                                                                                                 

B – Proximity detector

There is no physical contact with the object to be sensed. An inductive electronic sensor changes state when the field it emits is disturbed by the proximity of a metal object. Capacitive detectors are used for non- metal objects.

C- Photocell

A light beam is broken by the object to be sensed. A photo-receiver converts this presence into an electrical signal.

 

Digital position sensor

In this case, the position of the object is converted into digital signals transmitted over one or several wires. As an example, the movements of an object might be monitored by detecting the rotation of a multi- grooved disk.

§  Other sensors

These cover a very wide range of uses and have many different forms. Generally they provide either dry contact (two-wire or more). The following pages explain how these different types of sensor are connected to the programmable controller.

Connecting “discrete” sensor to the programmable controller

Individual terminals or leads of “discrete” sensor are wired directly to  the terminals of the programmable controller input module. Discrete sensor may be either electro mechanical switching sensor (two wires) or electronic switching sensor (two or three-wire).

1. Electromechanical switching sensor

The input module circuit contains a current detecting element which detects when the sensor is closed. This type of input module also provides a signal time-delay of approximately 10 ms to remove any interference caused by contact bounce or noise.

Often, the input module provides a common terminal to reduce the connections to only one terminal per sensor.

Individual terminals are frequently labeled to identify the corresponding sensor, and light emitting diodes (LEDs) indicate sensor status.

The availability of a wide variety of electromechanical sensor enables many different kinds of sensing problems encountered on machines to be solved.

2. Electronic switching sensor

  3-wire sensor

These features:

·         2-wire power supply

Signal between the common pole and

Third wire

Connection to an input module is illustrated in the diagrams:

·         Either individually to 2 terminals

·         Or collectively with a single common to the input module.

The terminal on the programmable controller receiving the signal from the detector identifies the signal by a label and indicates its status by an LED displays.

It should be noted that the response time of electronic sensors is very short and standard input modules may not be appropriate, since they have a time delay of approximately 10 ms, designed to remove electro-mechanical contact bounce effects. For fast response it is necessary to use “fast” input modules which have only very short time-delays.

signal

Power supply

 

Connecting several 3- wire sensor

§  2 – wire sensors

With this type of sensor, the signal is sent over the supply wires. The programmable controller detects whether the circuit is conductive or not by examining the load on the circuit within the sensor. Direct connection of 2- wire sensors to the programmable controller is possible only with input modules which are not affected by leakage currents.

 

“Intelligent” sensor communicating with the programmable controller

To meet certain automation requirements, it is often necessary to use “intelligent” sensor in addition to “discrete” sensor.

The addition of intelligence to sensor means that more complete information has to be transmitted:

·         Either in the form of “parallel” coded transmissions, over several wires connected to “discrete” input-output modules of the programmable controller.

·         Or in the form of serially coded transmissions over a special cable connected to a corresponding module at the programmable controller.

Ranges of intelligent sensor are constantly developing. We will only review those most frequently encountered.

1. Position encoders

§  Linear encoders

These convert the position of a moving object along an axis, usually by using a fixed potentiometer.

§   Rotary encoders

A motion detecting disk contains several marked tracks. The position of the disk is read by photo-sensor.