Automation and robotics

Chapter – 01 Automation 1.1 Automation 1.2 Industrial Automation 1.3 Building Blocks of Automation 1.3.1 Building Block Systems 1.3.1.1 Processing Systems 1.3.1.2 Multi-Microprocessor Systems 1.3.1.3 Local Area Networks 1.3.1.4 Analog and Digital I/O Modules 1.3.1.5 Supervisory Control and Data Acquisition Systems (SCADA) 1.3.1.6 Remote Terminal Unit 1.3.1.7 PID Controllers 1.3.2 Building Block Components 1.3.2.1 Sensors 1.3.2.2 Analyzers 1.3.2.3 Actuators 1.3.2.4 Drives Chapter – 01 1.1 Automation “The control of an industrial process (manufacturing, production etc) by automatic rather than manual means is often called automation” Automation is prevalent in the chemical, electric power, paper, automobile and steel industries, among others The concept of automation is central to our industrial society In its modern usage, automation can be defined as a technology that uses programmed commands to operate a given process, combined with feedback of information to determine that the commands have been properly executed Automation is often used for processes that were previously operated by humans When automated, the process can operate without human assistance or interference A semi automated process is one that incorporates both humans and robots For instance, many automobile assembly line operations require cooperation between a human operator and an intelligent robot Examples of manufacturing automation include: 1.2 Automatic machine tools to process parts Industrial robots Automatic material handling Automated storage and retrieval, and inspection systems Feedback control systems Computer systems for designing, automatically transforming designs into products, planning and decision making to support manufacturing Industrial Automation From the moment people started doing work, they began trying to find methods of automating the work Progress in such methods can be seen in the use of automated machines, computer-aided designs, computer-aided manufacturing, computer-aided robotics, and industrial robots Programmable controllers and robots are key components for industrial automation These systems have enabled our factories to increase productivity, decrease costs and increase the quality of manufactured goods Automation or Industrial Automation is the use of computers to control industrial machinery and processes, replacing human operators It is a step beyond mechanization, where human operators are provided with machinery to help them in their jobs The most visible part of automation can be said to be industrial robotics Some advantages are repeatability, tighter quality control, waste reduction, integration with business systems, increased productivity and Automation reduction of labour Some disadvantages are high initial costs and increased dependence on maintenance By the middle of the 20th century, automation had existed for many years on a small scale, using mechanical devices to automate the production of simply shaped items However the concept only became truly practical with the addition of the computer, whose flexibility allowed it to drive almost any sort of task Computers with the required combination of power, price, and size first started to appear in the 1960s, and since then have taken over the vast majority of assembly line tasks (some food production/inspection being a notable exception) In most cases specialised hardened computers refered to as PLCs (Programmable Logic Controllers) are used to synchronize the flow of inputs from sensors and events with the flow of outputs to actuators and events This leads to precisely controlled actions that permit a tight control of the process or machine HMIs (Human-Machine Interfaces) are usually employed to communicate to PLCs e.g.: To enter and monitor temperatures or pressures to be maintained Social issues of automation Automation raises several important social issues Among them is automation's impact on employment/unemployment Some argue automation leads to fuller employment One author made that case here: When automation was first introduced, it caused widespread fear It was thought that the displacement of human workers by computerized systems would lead to unemployment (this also happened with mechanization, centuries earlier) In fact the opposite was true, the freeing up of the labor force allowed more people to enter information jobs, which are typically higher paying One odd side effect of this shift is that "unskilled labor" now is paid very well in most industrialized nations, because fewer people are available to fill such jobs leading to supply and demand issues Some argue the reverse, at least in the long term First, automation has only just begun and short-term conditions might partially obscure its long-term impact For instance many manufacturing jobs left the United States during the early 1990s, but a massive upscaling of IT jobs at the same time offset this as a whole It appears that automation does devalue unskilled labor through its replacement with less-expensive machines, however the overall effect of this on the workforce as a whole remains unclear Today automation of the workforce in the "western world" is quite advanced, yet during the same period the general wellbeing of its Chapter – 01 citizens has increased dramatically What role automation played in these chanes has not been well studied 1.3 Building Blocks of Automation One by one, better methods are being found to sense, move, position, orient, fabricate, and assemble products using a wide variety of ingenious basic components – the building blocks of automated systems Unless and until a manufacturing workstation has been analyzed thoroughly and fitted out with the basic components of automation, it usually is not ready for more exotic hardware such as industrial robots Indeed, the industrial robots themselves are constructed of some of these same basic components of automation To make sense out of the diversity of automation components, some sort of crude classification is needed The classification is rough because some of the most useful components find their way into several of the categories, depending upon how they are used Generally, automation is distributed into two main categories; namely,  o o o o o o o  o o o o Building Block Systems Processing systems Multi-microprocessor systems Local area networks Analog and Digital I/O modules Supervisory Control and Data Acquisition Systems (SCADA) Remote Terminal Unit PID Controllers Building Block components Sensors Analyzers Actuators Drives It should be noted that, the operator of an automated system is again a human himself; the industrial robot is the part of the automated system The industrial robot is actually an integrated system made up of all four of the basic automation component categories – sensors, analyzers, actuators and drives 1.3.1 Building Block Systems The development in the field of automation and in the field of intelligent machines, (i.e., starting from computers, microprocessors to present day expert Automation systems and neural networks) which constitutes the basic building block systems, were almost simultaneous It is a known fact that growth in computer and microprocessor technology was one single big cause for the growth in automation techniques like Direct Digital Control (DDC), Distributed Control, and Adaptive Control etc 1.3.1.1 Processing system Computers and microprocessors: The computers are predecessors to microprocessors The basic concepts of computers were evolved before the dawn of the microprocessor By the early 1970’s, small integrated circuits (TTL logic) were well established while MOS integrated circuits, such as calculator components had started to appear The use of a microcomputer or control processor (as against the use of general purpose computers) was also well known It was clear to some semiconductor engineers that if the calculator chip could become more general, it would have wider application Figure 1-1: Von Neumann organization of computer Also, the mini-computer users were confident that if it could be made more compact and cheaper its application areas will become further wide These were the two mainstreams that led to the microprocessor development Undoubtedly, what made the processor possible was MOS technology and the remarkable properties of silicon, providing that, the microprocessor was inevitable Figure 1-1 shows the block diagram of computer showing different units and is known as Von Neumann Organization of Computers The computer organization proposed by Von Neumann envisages that binary number systems are used for Chapter – 01 both data as well as instructions There is a direct correlation between the microprocessor organization and the organization proposed by Von Neumann for computers Due to advancements in micro-miniaturization, the arithmetic logic unit and control unit have been put on a single chip known as microprocessors Microcomputers and microcontrollers: Microcomputers are microprocessors with on-chip memory Some microcomputer chips contain timer/counter, interrupt handling, also along with processor and memory Timer/counter and interrupts are useful for control application and these microcomputers are called microcontrollers To be compatible with analog and digital world in some cases analog to digital converter and digital to analog converter have also been integrated on the chip There is a variety of microcomputers/microcontrollers from different manufacturers like 8048, 8051 and 8086 series of Intel, Z8 from Zilog, M6801 and 68HC11 from Motorola,1650 series from General Instruments, IM61000 from Internal Inc etc In general, these chips come in three versions namely “on-chip ROM version”, “on-chip EPROM version” and “ROM-less version” The later two versions are used for development purposes After the development is complete, the large number of ‘on-chip ROM’ version chips can be obtained by getting the program fused at source, at low cost The Transputer: The principle behind the design of the transputer is to provide the system designer with a building block component which can be used in large numbers to construct very high performance systems The transputers have been specifically developed for concurrent processing The on-chip local memory assists in eliminating processor to memory bottlenecks and each transputer supports a number of asynchronous high speed serial links to other transputer units The efficient utilization of processors time slices is carried out by a micro coded scheduler The transputer to transputer links provide a combined data communications capacity of Mega bytes per sec, and operate concurrently with internal process This is a radical difference from the shared bus concept employed in the majority of multi-microprocessor architectures It allows parallel connection without overhead because of the complex communication between conventional parallel processors The advantages over multiprocessor are as follows:    No contention for communication No capacitive load penalties as transputers are added The bandwidth does not become saturated as system increases in size The system supports high level concurrent programming language Occam (high level concurrent programming language) specifically designed to run efficiently on transputer systems The Occam allows access to machine features and removes the need for a low level assembly language Automation 1.3.1.2 Multi-microprocessor Systems The architecture proposed by Von Neumann was a Single Instruction Single Data (SISD) stream A number of computers have been designed around this structure The single instruction and single data stream computers are easy to conceptualize and design since the computer is executing only one instruction at a time The data flow is from/to only from one input/output unit at an instant Multitasking concept was used for increasing the speed of program execution This allows a number of programs resident in the computer’s memory at one time The computer switches from current task to other task as and when an I/O instruction is encountered Since I/O units are comparatively slower than CPU, the computer on encountering the I/O instruction initiates its execution and then starts executing another program On completion of I/O, the computer gets signal to switch back to the original program This optimizes the CPU time However, the branch and return addresses as well as the status of various programs are to be maintained by CPU A number of new concepts have been introduced both in computers and microprocessors with the aim of increasing the speed, by incorporating parallelism in memory and processing These concepts are: Parallelism in memory a Interleaving b Cache Memory c Multiple Memory Access Parallelism in processing a Pipelining b Pipeline Vector Processing c Parallel Processing Most of the above concepts have found their way to microprocessors The pipelining, cache memory, vector processing etc are widely used in today’s highperformance microprocessors It was however clear that parallelism is necessary for increased speed which is measured by millions instructions per seconds (MIPS) executed by the CPU It was thought that instead of SISD architecture, data and instruction stream can be increased The classification of computer architecture with respect to data stream and instruction stream is shown in Figure 1-2 Other equally important reasons for introducing parallelism were reliability through redundancy in control systems and geographically or functionally distributed control systems Chapter – 01 Figure 1-2: Classification of computer architecture 1.3.1.3 Local Area Networks Local area networks generally called LANs are basically loosely coupled systems having autonomous microprocessors with local memories interconnected via I/O circuits The transfer of information requires Input-Output operations (Figure 1-3) Both serial and parallel interconnections are possible Local area networks are privately-owned networks, and not subjected to Federal Communication Commission (FCC), within a single building or campus of up to a few kilometers in size They are widely used to connect personal computers and work stations in such a way that every device is potentially able to communicate with every other device in company offices and factories to share resources (e.g., printers) and exchange information Traditional LANs run at speeds of 10 to 100 Mbps, have low delay (tens of microseconds), and make very few errors Newer LANs may operate at higher speeds, up to hundreds of megabit/sec LANs are distinguished from other kind of networks by three characteristics: (1) their size, (2) their transmission technology, and (3) their topology Automation Figure 1-3: Local area network interconnection The LAN puzzle      Workstation: personal computer or a processor that is able to run PC software Individual workstations on the LAN are usually microcomputers or PCs with some degree of intelligence A LAN workstation may run application software on its own processor using its own ROM, but may also store and retrieve programs and data files elsewhere in the network Server: a station in the network that handles special functions, such as disc storage or programs, documents or data files, for the purpose of printing The server station provides a shared resource device for programs, documents, and data files available to other users To be suitable for use as a server, the PC must have a hard disc for storage of information and the ability to load the appropriate server control software Networking software: the file server runs a series of programs known as the network software Topology: the arrangement of the workstations in relation to each other Network interface card (NIC): the circuit board or hardware device which connects or permits the attachment of each workstation to the transmission media The most common type of interface between a PC and the transmission media is through an interface card This is a printed circuit board designed to fit inside the PC cabinet The cable will attach directly to the card Besides serving as the physical connections, the interface controls the signaling method incorporated by the workstations as they attempt to transmit messages throughout the network Chapter – 01 Another type of interface (transceiver) is called a T-connector This is a hardware device in the shape of a “T” which permits the connections of the workstation directly to the coaxial cabling    Patch Cord - (Also called a Patch Cable) This is the cable that usually connects computers to computers (NIC to NIC), computers to Hubs, or computers to Transceivers Protocol: the access method (protocol) is the technique under whose control the network determines the order of message transmission among the participating workstations Repeaters and amplifiers: to overcome distance limitations of the basic network, vendors may supply repeaters or analog amplifiers to boost the signal strength on the transmission media, and which can effectively allow for the connection of two segments of a LAN LAN Topologies There are a number of different LAN topologies, as shown in Figure 1-4, each suited to particular application environments Issues such as reliability, speed, cost, and distance influence the choice of LAN In many of these topologies, communicating devices share a common transmission medium instead of being connected by individual point-to-point links The major point becomes how you gain access to the medium that you share with others Figure 1-4: LAN Topologies Star Topology: A star network has a central or controlling workstation with branches to various slave devices The controlling workstation is often a computerized switch Each slave device is linked to the central workstation with a point-to-point serial connection 10 Chapter – 10  10.9 disadvantages First, it is the most costly drive system Second, the hydraulic fluid may leak onto the shop floor The torque delivered by the hydraulic system is the best of the three systems Electric: they use either AC or DC electric motors These motors are connected to the manipulator’s axes through the gear reduction process The gear reduction process allows the electric motor to develop the torque necessary for the robots to lift the heavy payloads The electric drive systems are very versatile in their operations Workspace In order to study the workspace of a robot, the structure of the robot can be considered as consisting of the arm and the hand The arm is the large regional structure for global positioning of the hand, which is the small orientation structure for orienting the tool The most important characteristic to any individual working near the robotic system is how far the robot can reach The reach of the robot is defined as the workspace or work envelope of the system All programmed points within the reach of the robot are part of the workspace The primary workspace of such a robot with a large regional structure and a small orientation structure is determined by the arm The hand generates the secondary workspace of a robot In performing tasks, a manipulator has to reach a number of workpieces or fixtures Workspace is a volume of space which the end-effector of the manipulator can reach Workspace is also called work volume or work envelope The size and shape of the workspace depends on the coordinate geometry of the robot arm, and also on the number of degrees of freedom Some workspaces are quite flat, confined almost entirely to one horizontal plane Others are cylindrical; still others are spherical Some workspaces have very complicated shapes When choosing a robot arm for a certain industrial purpose, it is important that the workspace be large enough to encompass all the points that the robot arm will need to reach But it's wasteful to use a robot arm with a workspace much bigger than necessary The Cartesian coordinate has a rectangular work envelope The envelope of a cylindrical coordinate robot is cylindrical The work envelope of the polar coordinate robot is spherical Moreover, the articulate coordinate robot has a tear-shaped work envelope 172 Manipulator For the description (drawing) of a work envelope, the measurements are taken from the wrist flange Thus if any end-of-arm tooling is attached to the robot, the work envelope size will increase by the length of the end-of-arm tooling 10.9.1 Dexterous and Accessible workspace The workspace of a robot is an important criterion in evaluating manipulator geometries Manipulator workspace may be described in terms of the dexterous workspace and the accessible workspace Dexterous workspace is the volume of space which the robot can reach with all orientations That is, at each point in the dexterous workspace, the end-effector can be arbitrarily oriented The accessible workspace is the volume of space which the robot can reach in at least one orientation In the dexterous workspace the robot has complete manipulative capability However, in the accessible workspace, the manipulator's operational capacity is limited because the terminal device can only be placed in a restricted range of orientations In other words, the dexterous workspace is a subset of the accessible workspace 10.9.2 Developing the workspace Figure 10-10 shows the work area of two- and three-link robots These plots can be obtained on a microcomputer programmed so that the numeric keypad could be used to move each link The procedure for obtaining these areas is to move each link through its angular range of motion in a manner similar to the physical motion of the robot arm Figure 10-10: Development of workspace 173 Chapter – 10 Review Questions Choose the Appropriate Answer Cartesian coordinate system identifies basic axe(s) a One b Two c Three The cylindrical coordinate system incorporates degrees of freedom a b c One Two Three The theta, or waist axis, provides the around the base a b c Rotation Bending movement Base For a manipulator, the joint angles and the different configurations of the manipulator are derived from the position and orientation of the endeffector, the scheme is called the problem a b c Forward kinematics Reverse kinematics None of above The Cartesian coordinate robot is restricted to _ robotic system a Low-technology b Medium-technology c High-technology The theta axis in cylindrical coordinate robots defines the rotation around the _ a b c Reach Base Range The yaw axis describes the wrist’s from the left to right a b c Rotational movement Angular movement Linear movement For a manipulator, if the position and orientation of the end-effector are derived from the given joint angles and link parameters, the scheme is called the _ problem a b c Forward kinematics Reverse kinematics None of above 174 Manipulator The pitch axis describes the wrist’s _ up and down a b c Rotational movement Angular movement Linear movement 10 The degrees of rotation that the wrist provides are a b c Fixed Variable None of above Fill in the blanks 11 The work envelope is the area in which the _ motions can operate without any obstruction 12 If the arm not only rotates about the base, but also rotates about an axis in the vertical plane, the robot is known as or coordinates robot 13 If the arm can rotate about all three axes, the robot is called a(n) coordinate robot 14 The addition of a _ at the end of the robot’s arm extends the mobility of the robotic system 15 The reach of the robot is defined as the of the system True False 16 The Cartesian coordinate system operates within a cylindrical pattern 17 Movement between two of the axes in the Cartesian system is impossible 18 Degrees of freedom determine the flexibility in the movement of robot 19 The addition of the wrist to the robot’s arm restricts the end effector to reach into areas that could not be reached by robots using only one of the four coordinate systems for the arm 20 The total environment in which a robot can perform its tasks is known as the base 175 Chapter – 11 End Effector 11.1 Introduction 11.2 Basic Considerations for End Effectors 11.3 Gripper Design 11.4 Mechanical Grippers 11.4.1 Gripping Force 11.4.2 Drive Systems 11.5 Vacuum Grippers 11.6 Magnetic Grippers 11.7 End of Arm Tooling End Effector 11.1 Introduction In robotics, an end effector is a device or tool connected to the end of a robot arm The structure of an end effector, and the nature of the programming and hardware that drives it, depends on the intended task If a robot is designed to set a table and serve a meal, then robotic hands, more commonly called grippers, are the most functional end effectors The same or similar gripper might be used, with greater force, as a pliers or wrench for tightening nuts or crimping wire In a robot designed to tighten screws, however, a driver-head end effector is more appropriate A gripper is a hindrance in that application; the driver can be attached directly to the robot arm The driver can be easily removed and replaced with a device that operates with similar motion, such as a bit for drilling or an emery disk for sanding A robot arm can accommodate only certain end-effector task modes without changes to the ancillary hardware and/or programming It is not possible to directly replace a gripper with a screwdriver head, for example, and expect a favorable result It is necessary to change the programming of the robot controller and use a different set of end-effector motors to facilitate torque rather than gripping force Then the gripper can be replaced with a driver head The purpose of the robot manipulator is to perform work The work performed by the manipulator must be accomplished by an end effector attached to the end of robot’s arm The end effector can be a gripper (hand) or end-of-arm tooling The manipulator is responsible for moving the end effector to programmed locations Once the robot has moved the end effector to its location, the particular task that is programmed for the end effector will be performed Many different designs can be used as an end effector, depending on the task to be performed by the robot The robot’s end effector can be designed to mechanically grip a part, to use a vacuum to lift and transfer a part, or to use an electromagnet to lift and move 11.2 Basic Considerations for End Effectors The end effector of the manipulator will cause certain problems that the programmer must be aware of These problems involve program control, the size of the work envelope, cycle times, and the safety of worker 178 Chapter – 11  Types: End effectors are classified into two classifications: grippers (hands) and end-of-arm tooling The gripper is used to lift parts or to transfer parts from one location to another A typical gripper is illustrated in Figure 11-1 In this figure, the gripper is responsible for picking up parts from an assembly line and placing the parts into chuck of a machine With the same gripper, the robot then picks the part from the chuck and palletizes the parts on the table The gripper in this application is doing nothing to part itself The end effector is generally mounted to the left of the manipulator’s arm This mounting is called end effector mounting flange In the majority of industrial robots, a bolt hole pattern is mounted on this flange The holes are arranged so that the end effector can be mounted in several different planes The end effector is then screwed into the flange for a secure fit Each manipulator is able to lift the certain number of pounds This lifting capacity of manipulator is called its payload The user of the robotic system must know the weight of the end effector in order to determine the robot’s actual payload Figure 11-1: Gripper used to transfer parts   Program control: The programmer of the robot can control the action and path of the end effector through the program Thus, the programmer is able to move the end effector to the same location repeatedly Work envelopes: The programmer must be aware that the addition of an end effector to the manipulator will increase the size of the robot’s work envelope For instance, a typical articulate robot arm has a work envelope of about feet When end-of-arm tooling is added to the manipulator, the size of the work envelope increases by 1.5 feet This simple addition of 1.5 feet to the size of the robot’s work envelope might mean that the robot now will not fit in the area for which, it was planned Thus, the designer of the robotic 179 End Effector  work cell must take the size of the end effector into account when planning a robotic application Cycle times: The cycle times of the robot are very important in meeting the production deadlines In addition, the movement of the robot’s end effector should be articulated only in small movements to ensure that cycle times are met Several methods can be employed to ensure that a robot with an end effector will perform its task within the correct cycle times The parts presented to the robot should always be placed in front of the manipulator Placing the part in front of the manipulator means that the robot needs to make only short moves to grasp a part Thus, the orientation of the workpiece can shorten the cycle time  Safety: A safety joint is normally attached between the manipulator and the end effector to prevent any damage to the robot In many high- and mediumtechnology controllers, an electronic circuit is added to the end effector’s flange Figure 11-2 illustrates an electronic switch added to the end effector’s flange The switch is normally closed switch When the safety joint is broken, the switch is activated The switch then sends a signal to the robot controller, alerting the controller that the safety joint has broken This alarm condition causes the robot to cease operation and calls for an operator to come to the work cell Figure 11-2: Safety joint and an Alarm Switch for an end effector 11.3 Gripper Design The choice of grippers can determine whether a robot succeeds or fails in performing a task A very accurate and expensive robot equipped with the wrong gripper can be useless for a specific task 180 Chapter – 11 The gripper or hand of the robot attaches to the wrist end of the arm and serves to handle or process parts The human hand is one of the most versatile end effectors in existence Besides having pitch, yaw and roll control, the hand also has three joints in each finger and two in the thumb While these joints have only a simple rotational ability, the joints at the base of the fingers can also move sideways, thus allowing the hand to assume many shapes and grip objects of many different sizes and shapes The hand is also covered with positional feedback indicators, in the form of pressure and heat sensors These tell what is being touched, how hard it is, and how hot or cold it is relative to the hand’s temperature The gripper is composed of two sections: the fingers that grip the part and the actuating circuitry that causes the fingers to open and close A person who is designing grippers should consider several key factors The following list describes some of these concerns: The part the gripper is to grasp should be within reach The fingers of the gripper should be able to accommodate various size of parts and should be self-adjusting Finger pads should be used when the gripper will pick up and place delicate parts The gripper must be in correct position to grasp the part The gripper must grasp the part in the area where the part is largest 11.4 Mechanical Grippers Many of the grippers are used to transfer parts from one location to another or to assemble parts These grippers are called mechanical grippers Figure 11-3: Inside diameter gripper 181 End Effector  Inside diameter gripper: Figure 11-3 illustrates a typical inside diameter gripper Notice that the gripper’s finger pads are mounted on the outside of the finger This mounting allows the pads to fit into the inside diameter of the part that it must lift The pads are pressed against the inside walls of the part The frictional force developed allows the fingers to hold the part securely when the gripper lifts the part The two point grip is the best type of contact for the inside diameter gripper Another type of the inside diameter gripper is Captivation, or, flexible gripper; in this type of gripper, shown in Figure 11-4, the pads of the finger conforms to the inside diameter of the part These pads are usually made of polyurethane Figure 11-4: Contact for an inside diameter gripper  Outside diameter gripper: Figure 11-5 gives the schematic view of an outside diameter gripper The gripper is designed so that the finger pads press against the outside of the component The pads of the gripper are made from polyurethane bonded to steel An outside diameter gripper may be designed to pick up a family of parts, that is, a group of parts with the same shapes but with different sizes One type of the outside diameter gripper is four-point contact with V-block; shown in Figure 11-6, gives four points of contacts with the surface of the part This type of design ensures that a high coefficient of friction is developed between the fingerpoints and the parts outside diameter Compliance: the final consideration for the mechanical grippers is compliance That is, the gripper should be able to lift the part even if the part is off center 182 Chapter – 11 Figure 11-5: Outside diameter gripper Figure 11-6: Four-point contact with Vee blocks 11.4.1 Gripping Force The gripping force or the amount of lifting power that a gripper develops depends on the amount of contact surface between the gripper’s finger and the part The gripping force should be sufficient to overcome the gravity – that is, the weight – for the part that the gripper is to hold 11.4.2 Drive Systems Mechanical grippers are generally driven by pneumatic systems or gearing systems Figure 11-7 illustrates a pneumatic drive system for a gripper The air cylinder develops the action that closes or opens the fingers of the gripper For this system to operate, a constant pressure must be applied to the pneumatic cylinder 183 End Effector Figure 11-7: Pneumatic cylinder for a gripper The parts handled by the gripper can have various weights Two factors must be considered in the determination of the weight a gripper will lift: When a part is lifted, the weight of the part will be three times its normal weight The additional weight is due to the gravitational pull, g, of the earth: 1g is due to the weight of the part, and 2g is due to the acceleration of the part When a part is moved in a horizontal plane, the weight of the part is twice its normal weight, because of its gravity and acceleration 11.5 Vacuum Grippers The vacuum gripper uses a vacuum instead of fingers to lift a part There are two types of vacuum grippers, a dual vacuum gripper and a single vacuum cup The vacuum cup operates on the principle that a vacuum is created between the cup and the part This bond causes the friction The friction allows the cup to lift a part The vacuum gripper has two components: the cups and the vacuum system The vacuum cup consists of a flexible rubber-cup and a hard-rubber cup The cup creates negative pressure, which in turn, creates the vacuum and the necessary lifting part The vacuum system is a pump that generates the suction once the cup is placed on the part Two types of vacuum systems can be used to generate the vacuum: a vacuum pump or a venturi system The vacuum of a vacuum pump is generated by a piston driven by an electric motor The vacuum pump provides high vacuum pressure at a low cost The venture system provides high reliability and low cost for start-up The holding force of the cup depends on the difference of pressure between 184 Chapter – 11 the outside area of the cup and the inside area of the cup multiplied by the effective area of the cup For the best possible results from a vacuum system, the designer should use a large value of pressure difference rather than a large vacuum cup Once the manipulator has moved the part, it must deposit the part So, the vacuum system must also be able to release the vacuum This release is controlled by the robot’s program On command from the robot controller, the vacuum is released, and the part is deposited in the programmed location 11.6 Magnetic Grippers The magnetic gripper employs the effect of a magnetic field being exposed to a ferrous metal A dual magnetic gripper is made of an electromagnet A direct, constant current flows through the electromagnet, developing a magnetic field When the magnetic field of the gripper meets the part, which is made up of ferrous metal, it induces a magnetic field of opposite polarity into the part This field causes the molecules of the ferrous metal to align and develop smaller magnetic field in the part These smaller magnetic fields have a polarity that is opposite to the polarity of the electromagnetic field Therefore, the two poles of opposite polarity attract each other, allowing the gripper to lift the part The magnetic gripper has several special characteristics, like:    Lifting capability must be large enough The temperature that an electromagnet gripper can handle is about 140ºF The gripper should always make a parallel contact with the part The releasing procedure must also be designed for the magnetic gripper The release of the part is accomplished by simply reversing the magnetic field through the electromagnet The magnetic field is reversed by reversing the current flow through the magnet A switching circuit called the controlled drop circuit reverses the current The controlled drop circuit also removes any residual magnetism that has been developed in the ferrous metal part 11.7 End of Arm Tooling End-of-arm tooling connected to a manipulator performs work (welding, sealing, gluing, etc) on a part The end-of-arm tooling is mounted to the end effector flange It requires a safety joint between the tool and the robot manipulator One of the most common jobs for end-of-arm tooling is welding The paths followed by the tool are developed by the robot’s path control programming 185 End Effector Review Questions Choose the Appropriate Answer Addition of an end effector to the manipulator will _ the size of the robot’s work envelope a Not effect b Increase c Decrease The magnetic gripper employs the effect of a field being exposed to a ferrous metal a b c Electric Magnetic Electromagnetic When a part is lifted, the weight of the part will be time(s) its normal weight a b c One Two Three Mechanical grippers are generally driven by systems a b c Pneumatic Hydraulic Electric The V-block type design ensures that a _ coefficient of friction is developed between the finger-points The user of the robotic system must know the weight of the _ to determine the actual payload a Manipulator b End effector c None of above The vacuum system is a that generates the suction once the cup is place on the part a b c Motor Cylinder Pump When a part is moved in a horizontal plane, the weight of the part is twice its normal weight a b c Equal to Twice Thrice The human hand has joints in each finger and in the thumb a b c Two, three Three, two Three, three 10 A is normally attached between the manipulator and the end effector to prevent any damage to the 186 Chapter – 11 and the parts outside diameter robot a b c a b c Low High None of above Safety joint Wrist flange Cup Fill in the blanks 11 End effectors are _ classified into two classifications: _ and 12 The lifting capacity of manipulator is called its 13 The gripper is composed of two sections: the _ that grip the part and the _ that causes the fingers to open and close 14 The vacuum of a vacuum pump is generated by a(n) driven by a(n) _ 15 Two types of vacuum grippers are _ and a True False 16 The addition of an end effector to the manipulator will increase the size of the robot’s work envelope 17 Captivation or flexible gripper; is the type of outside diameter gripper 18 The end effector is responsible for moving the manipulator to programmed locations 19 The release of the part in magnetic grippers is accomplished by simply reversing the magnetic field through the electromagnet 20 The venture system pump provides high vacuum pressure at a low cost 187 [...]... Analog and Digital I/O Modules After having discussed the computers and microprocessors, we shall now be dealing with the modules which connect the process to the data processing unit Analog input signals are received from sensors and signal conditioner and represent the value of measured like flow, position, displacement, temperature etc The signal conditioner takes as input the output of sensor and. .. without intervention by the operator There are literally thousands of styles and models of limit switches, because they are designed to be exactly correct in size for the specific automation application Levers, toggles, pushbuttons, plungers, rollers, “cat whiskers” actuate limit switches and just about anything the inventor can devise to make an automation application feasible Robot switches employ limit... action upon the process at the command of a computer or other analyzer For purpose of classification, the distinction being made here between actuators and drives is that actuators are used to effect short, complete, discrete motion – usually linear – and drives execute more continuous movements typified by, but not limited to, rotation Actuators may turn drive on and off, and drives may provide the energy... drives may provide the energy for the movement of actuators Some automation devices, such as Geneva’s and walking beams, seem to belong to both categories Motors: An automation engineer must have a broad perspective of the term motor to include not only electric motors but hydraulic and pneumatic motors as 29 Chapter – 01 well Hydraulic and pneumatic motors are the converse of their corresponding pumps... Figure 1-6: Supervisory control and data acquisition system 14 Automation Interrupt Scanning: Another way of scanning the channels may be to provide some primitive facility after transducer to check for violation of limits It sends interrupt signal request to processor when the analog signal from transducer is not within High and Low limits boundary set by Analog High and Analog Low signals This is... particular engineering value based on the following parameters   Calibration of transmitters ADC mode and digital output lines Depending on the input range of measurand value for transmitter, a calibration factor is determined If a transmitter is capable of measuring parameter within the input range X1 and X2 and provides 0 – 5 V signal at output then calibration factor is 1 Volt  X2  X1 units 5 If we.. .Automation Any protocol or code conversions may be centralized in the controlling workstation, thus eliminating expensive and complex network interfaces However, in a star network, the controlling workstation is a critical node and if it fails, the associated terminals and other devices are rendered inoperative Ring Topology: The Ring... tiny objects that are capable of breaking the beam at large and varying distances Figure 1-14: Laser light source 1.3.2.2 Analyzers Once information is sensed up by an automated system, it must be registered and analyzed for content, and then a decision must be made by the systems to what action should be taken The function can be quite complex, and the system components that perform it are also generally... timers to robots and automation are even greater than that of counters Besides being available as separate units, industrial timers can be internal to programmable controllers and online process control computers Bar Code Readers: although it can be considered a sensor, a bar code reader is an analyzing system that incorporates conventional photoelectric or laser scanner along with timers and counters... and counters Successive bars of varying width are scanned and counted The scan is orthogonal to the bars, and thus voltage pulses from the photoelectric sensor can be compared to determine individual bar widths Optical encoders: the capability of rapidly scanning a series of bars makes possible additional automation opportunities when light and dark bars are placed in concentric rings on a disk The ... automobile and steel industries, among others The concept of automation is central to our industrial society In its modern usage, automation can be defined as a technology that uses programmed commands... material handling Automated storage and retrieval, and inspection systems Feedback control systems Computer systems for designing, automatically transforming designs into products, planning and decision... computer-aided manufacturing, computer-aided robotics, and industrial robots Programmable controllers and robots are key components for industrial automation These systems have enabled our factories