DDE 3443 DDE 3443 CHAPTER 1CHAPTER 1

INTRODUCTION TO INTRODUCTION TO AUTOMATIONAUTOMATION1

1.11.1 INTRODUCTIONINTRODUCTION

• The technology by which a process or procedure The technology by which a process or procedure is accomplished without human assistance.is accomplished without human assistance.

• A technique that can be used to reduce costs A technique that can be used to reduce costs and/or to improve quality.and/or to improve quality.

• Can increase manufacturing speed, while Can increase manufacturing speed, while reducing cost.reducing cost.

• Can lead to products having consistent quality, Can lead to products having consistent quality, perhaps even consistently good qualityperhaps even consistently good quality

• It is implemented using a program of instructions It is implemented using a program of instructions combined with a control system that executes the combined with a control system that executes the instructions.instructions.

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• To automate a process, power is required, both To automate a process, power is required, both to drive the process itself and to operate the to drive the process itself and to operate the program and control system.program and control system.

• Automated processes can be controlled by Automated processes can be controlled by human operators, by computers, or by a human operators, by computers, or by a combination of the two.combination of the two.

• If a human operator is available to monitor and If a human operator is available to monitor and control a manufacturing process, control a manufacturing process, open loop open loop controlcontrol may be acceptable. may be acceptable.

• If a manufacturing process is automated, then If a manufacturing process is automated, then it requires it requires closed loop controlclosed loop control, also known as , also known as feedback controlfeedback control..

• Figure 1.1 shows example of open loop control Figure 1.1 shows example of open loop control and closed loop control.and closed loop control.

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BASIC ELEMENT OF AN BASIC ELEMENT OF AN AUTOMATED SYSTEMAUTOMATED SYSTEM

• Consists of 3 basic elements: Consists of 3 basic elements:

1)1) The actuator (which does the work)The actuator (which does the work)• Controlled by the controller.Controlled by the controller.

• The actuator in an automated process may in fact be The actuator in an automated process may in fact be several actuators, each of which provides an output several actuators, each of which provides an output that drives another in the series of actuator.that drives another in the series of actuator.

• Some actuators can only be on and off. Other Some actuators can only be on and off. Other actuators respond proportionally with the signal they actuators respond proportionally with the signal they receive from a controllerreceive from a controller

• Actuators can be selected for the types of inputs they Actuators can be selected for the types of inputs they require, either DC or AC.require, either DC or AC.

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2)2) The controller (which ‘tells’ the actuator to The controller (which ‘tells’ the actuator to do work)do work)

• A controlled system either may be a simple digital A controlled system either may be a simple digital system or an analog system.system or an analog system.

• Digital and analog controllers are available ‘off the Digital and analog controllers are available ‘off the shelf’ so that systems can be constructed shelf’ so that systems can be constructed inexpensive and with little specialized knowledge inexpensive and with little specialized knowledge required.required.

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3)3) The sensor (which provides feedback to The sensor (which provides feedback to the controller so that it knows the actuator the controller so that it knows the actuator is doing work) is doing work)

• Obviously, controlled automation requires devices to Obviously, controlled automation requires devices to sense system output.sense system output.

• Sensors also can be used so that a controller can Sensors also can be used so that a controller can detect and respond to changing conditions in its detect and respond to changing conditions in its working environment.working environment.

• Switches and transducers are another name for Switches and transducers are another name for sensors.sensors.

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• Switches can detect when a measured condition Switches can detect when a measured condition exceeds a pre-set level. Examples, closes when a exceeds a pre-set level. Examples, closes when a workpiece is close enough to work on.workpiece is close enough to work on.

• Transducers can describe a measured condition. Transducers can describe a measured condition. Examples, output increased voltage as a workpiece Examples, output increased voltage as a workpiece approaches the working zone.approaches the working zone.

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1.21.2 TYPE OF TYPE OF AUTOMATIONAUTOMATION

• Hard AutomationHard Automation• Controllers were built for specific purposes and Controllers were built for specific purposes and

could not be altered easily.could not be altered easily.• Early analog process controllers had to be Early analog process controllers had to be

rewired to be reprogrammed.rewired to be reprogrammed.• This controllers do what they are designed and This controllers do what they are designed and

built to do, quickly and precisely perhaps, but built to do, quickly and precisely perhaps, but with little adaptability for change (beyond minor with little adaptability for change (beyond minor adjustments).adjustments).

• Modification of hard automation is time-Modification of hard automation is time-consuming and expensive, since modifications consuming and expensive, since modifications can only be performed while the equipment sits can only be performed while the equipment sits idle.idle. 8

• Soft AutomationSoft Automation

• Modern digital computers are re-Modern digital computers are re-programmable.programmable.

• It is even possible to reprogram them and It is even possible to reprogram them and test the changes while they work.test the changes while they work.

• Even if hardware changes are required to a Even if hardware changes are required to a soft automation system, the lost time during soft automation system, the lost time during changeover is less than for hard automationchangeover is less than for hard automation

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• In other books/references, automation can be In other books/references, automation can be classified into three basic types:classified into three basic types:

• Fixed AutomationFixed Automation

• A system which the sequence of processing A system which the sequence of processing (or assembly) operations is fixed by the (or assembly) operations is fixed by the equipment configurations.equipment configurations.

• Each operations in the sequence is usually Each operations in the sequence is usually simple.simple.

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• The features of fixed automation;The features of fixed automation;• High initial investment for custom-engineered High initial investment for custom-engineered

equipmentequipment

• High production ratesHigh production rates

• Relatively inflexible in accommodating product variety.Relatively inflexible in accommodating product variety.

• Examples, machining transfer lines and automated Examples, machining transfer lines and automated assembly machines.assembly machines.

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• Programmable AutomationProgrammable Automation

• The production equipment is designed with The production equipment is designed with the capability to change the sequence of the capability to change the sequence of operations to accommodate different product operations to accommodate different product configurations.configurations.

• The operation sequence is controlled by a The operation sequence is controlled by a program, which is a set of instruction coded program, which is a set of instruction coded so that they can be read and interpreted by so that they can be read and interpreted by the system.the system.

• New programs can be prepared and entered New programs can be prepared and entered into the equipment to produce new products.into the equipment to produce new products.

• The physical setup of the machine must be The physical setup of the machine must be changed for each new products.changed for each new products.

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• This changeover procedures takes time.This changeover procedures takes time.

• Examples: numerical control (NC) machine Examples: numerical control (NC) machine tools, industrial robots and PLC.tools, industrial robots and PLC.

• The features of programmable automation;The features of programmable automation;• High investment in general purpose equipment.High investment in general purpose equipment.

• Lower production rates than fixed automation.Lower production rates than fixed automation.

• Flexibility to deal with variations and changes in Flexibility to deal with variations and changes in product configuration.product configuration.

• Most suitable for batch production.Most suitable for batch production.

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• Flexible AutomationFlexible Automation

• An extension of programmable automation.An extension of programmable automation.

• Capable of producing a variety of Capable of producing a variety of parts/products with virtually no time lost for parts/products with virtually no time lost for changeovers from one part style to the next.changeovers from one part style to the next.

• The features of flexible automation;The features of flexible automation;• High investment for custom-engineered system.High investment for custom-engineered system.

• Continuous production of variable mixtures of products.Continuous production of variable mixtures of products.

• Medium production rates.Medium production rates.

• Flexibility to deal with product design variations.Flexibility to deal with product design variations.

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• Examples, flexible manufacturing systems Examples, flexible manufacturing systems for performing machining operations. for performing machining operations.

The relative positions of the three types of The relative positions of the three types of automation for different production volume automation for different production volume and product varieties are shown in Figure and product varieties are shown in Figure 1.2.1.2.

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1.31.3 REASON FOR REASON FOR AUTOMATINGAUTOMATING

• To increase labor productivityTo increase labor productivity

• To reduce labor costTo reduce labor cost

• To improve worker safetyTo improve worker safety

• To improve product qualityTo improve product quality

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AUTOMATION CONTROLAUTOMATION CONTROL

• Usually implies a sequence of mechanical steps.Usually implies a sequence of mechanical steps.

• A camshaft is an automation controller because A camshaft is an automation controller because it mechanically sequences the steps in the it mechanically sequences the steps in the operation of an internal combustion engine.operation of an internal combustion engine.

• Manufacturing processes are often sequenced Manufacturing processes are often sequenced by special digital computers, known as by special digital computers, known as programmable logic controller (PLC).programmable logic controller (PLC).

• PLC can detect and can switch electrical signals PLC can detect and can switch electrical signals on and off. on and off.

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PROCESS CONTROLPROCESS CONTROL• Usually implies that the product is produced in a Usually implies that the product is produced in a

continuous stream. continuous stream. • Often, it is a liquid that is being processed.Often, it is a liquid that is being processed.• Early process control system consisted of Early process control system consisted of

specially-designed analog circuitry that measured specially-designed analog circuitry that measured a system’s output ( e.g., the temperature of liquid a system’s output ( e.g., the temperature of liquid leaving a tank), and changed that input ( e.g., leaving a tank), and changed that input ( e.g., changing the amount of cool liquid mixed in) to changing the amount of cool liquid mixed in) to force the output to stay at a preset value.force the output to stay at a preset value.

• Now, process control is accomplished using digital Now, process control is accomplished using digital computers.computers.

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Production Quantity and Production Quantity and Product VarietyProduct Variety

• First, let First, let • Q= production quantity Q= production quantity

• P=product varietyP=product variety

• Q refers to the number of units of a given Q refers to the number of units of a given part or product that are produced annually part or product that are produced annually by a plant.by a plant.

• Let us identify each part or product style by Let us identify each part or product style by using the subscript j, so that Qusing the subscript j, so that Q jj =annual =annual quantity of product style j (products/yr).quantity of product style j (products/yr).

• Then let QThen let Qff =total quantity of all parts or =total quantity of all parts or products made in the factory.products made in the factory.

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where P = total number of different part or product where P = total number of different part or product styles, and j is a subscript to identify products, j=1,2,…,Pstyles, and j is a subscript to identify products, j=1,2,…,P

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P

jjf QQ

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QQjj and Q and Qff are related as follows : are related as follows :

• P refers to the different product designs or types P refers to the different product designs or types that are produced in a plant. It is a parameter that are produced in a plant. It is a parameter that can be counted, and yet we recognize that that can be counted, and yet we recognize that the difference between products can be great or the difference between products can be great or small.small.

• Hard product variety is when the products differ Hard product variety is when the products differ substantially. Refers to the number of distinct substantially. Refers to the number of distinct product lines produced by the factory.product lines produced by the factory.

• Soft product variety is when there are only small Soft product variety is when there are only small differences between products. Refers to the differences between products. Refers to the number of models in a product line.number of models in a product line.

• Let us divide P into two levels, P1 represents Let us divide P into two levels, P1 represents hard product variety and P2 is for soft varietyhard product variety and P2 is for soft variety

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Product and Part Product and Part ComplexityComplexity• Let nLet npp = the number of parts per product. = the number of parts per product.

• Let nLet n00 = the number of operations or processing = the number of operations or processing steps to make a partsteps to make a part

• Assuming that the number of product designs P Assuming that the number of product designs P are produced in equal quantities Q, all products are produced in equal quantities Q, all products have the same number of component nhave the same number of component npp, and all , and all components require an equal number of components require an equal number of processing step nprocessing step n00. In this case, the total number . In this case, the total number of product units produced by the factory given by :of product units produced by the factory given by :

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PQQ f

• The total number of parts produced by the The total number of parts produced by the factory is given by :factory is given by :

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ppf PQnn

And the total number of manufacturing operation cycles And the total number of manufacturing operation cycles performed by the factory is given by :performed by the factory is given by :

opof nPQnn