ROBOTS AND ROBOTICS

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ROBOTS AND ROBOTICS

  1. 1. BEE4393 Automation and Robotics ROBOTS AND ROBOTICS WHO INTRODUCED THE WORD ROBOT? o The terms robot and robotics are only recently used. The term robot was first introduced by a Czech dramatist, Karel Capek in his 1921 play "Rossum's Universal Robots". He was referring to a perfect and tireless worker performing manual labour jobs for human beings. o Isaac Asimov, coined the word robotics as the science of the study of robots, in his science fiction stories about robots in 1940s. o Webster's New World Dictionary, 1988, defines robotics as 'the science or technology of robots, their design, manufacture, application, use etc'. o In Europe robotics is defined as 'the science of robotology' and robotology is defined as 'the means by which robot machines are put together and made to work'. o Many people think of robotics as a single area of technology, but in fact robotics encompasses such diverse areas of technology as mechanical, electrical, electronics, systems, computer hardware and software and a host of other advanced technology. WHAT CAN ROBOTS DO? o In the past industrial robots were best suited for repetitive, unskilled or semiskilled, monotonous and burdensome tasks. o There is however, a new move to apply intelligence to robots that will allow them to "think smart" and make decisions. These are what can be termed as autonomous and intelligent robots. o Today the human analogy of an industrial robot is very limited. Robots do not look like humans, and they do not behave like humans. Instead, they are one-armed machines which almost always operate from a fixed location on the factory floor. o Future robots are likely to have a greater number of attributes similar to humans, such as having greater sensor capabilities, more intelligence, a higher level of manual dexterity, and a limited degree of mobility. There is no denying that the technology of robotics is moving in a direction to provide these machines with more and more capabilities like those of humans. 1
  2. 2. BEE4393 Automation and Robotics AUTOMATION AND ROBOTICS What is the distinction between 'Automation' and 'Robotics'? 'Robots' is only a small sub-set of the technologies covered by the much broader term Automation'. 'Automation' refers to a mode of operation in which any machine or piece of equipment is capable of working without human intervention. Originally, automation was limited in its potential, as automatic machines could only replace physical effort and not mental effort. Automation is generally regarded as being able to be divided into 2 types: 1. Fixed automation 2. Flexible automation In fixed automation the task is fixed and the equipment is dedicated to the performance of that task. If the equipment is controlled by mechanisms, it is generally referred to as 'mechanisation'. Some quite sophisticated automatic control can be achieved by mechanisation if a number of linked mechanisms are used. Some authors insist that mechanisation does not allow the use of feedback to control a machine, but a mechanical governor on a steam engine can provide effective closed loop control over the engine speed. Fixed automation can also be achieved by electronic means. Complex logic can be constructed with appropriate components and circuits and the hard-wired nature of the system can make it very fast in operation. In flexible automation the task is variable and the equipment has to be reconfigurable so that it is capable of performing a range of tasks. The equipment has to be controlled by some 'programmable' device. Technically the 'programmable' device could be anything capable of effecting a change in the equipment behaviour, but in practice nowadays it is invariably a digital computer. Benefits of flexible automation Can respond quickly to changes in demand - the equipment can be reprogrammed to perform different functions depending on the current requirements eg: numerically controlled machine tools. May use 'off the shelf' equipment rather than design and build a specialised 'one off'. This usually leads to quicker implementation and is cheaper in the long run eg using a robot as a durability test rig to open and close car doors. Less de-bugging and more reliable than a one off piece of equipment. Any new piece of purpose built equipment is by definition a prototype and there will be some unknown quantities in the way it performs. A commercially available machine like a robot will already have been through various stages of development and should be reliable with good documentation on fault finding if this should be necessary. Disadvantages of flexible automation 2
  3. 3. BEE4393 Automation and Robotics Generally slower operating rate than purpose built (dedicated) automation. A dedicated piece of equipment can be designed so that it is optimised to perform the one task. There need not be any compromises in its design or its operation eg a light bulb testing machine. Robots Robots are just one example of flexible automation. Other examples in the industrial sector are NC machine tools, automated assembly machines (including automated component insertion machines), automated guided vehicles (AGV's) automated storage and retrieval systems (ASRS's), co-ordinate measuring machines (CMM's) laser / plasma / water jet cutting machines etc etc. There are many examples of flexible automation that pre-date the term 'robot'. These include Vaucanson's flute playing doll, c 1750; Jacquard's loom, 1801; Maillardet drawing doll, 1805; and there are many others. In all of these cases programs were stored on cams, drums or punched cards which controlled the sequence of movements and the type of movements made. The programs could be changed relatively quickly (a few minutes) but it could take a very long time (weeks / months) to make a new rotating drum for example. The word 'robot' first appeared in 1921 but was not a technical term. It was used by a Czech playwright called Karel Capek in a satirical play called 'Rossums Universal Robots' to describe slave labourers who had their souls removed to make them work harder. In, 1942 Isaac Asimov wrote a short science fiction story in which the word 'robotics' was first used and lit) presented 3 laws of robotics. 1. Robots must not injure humans 2. Robots must obey orders 3. Robots must protect their own existence Asimov was exploring the possibilities and potential problems of artificial intelligence associated with human-like machine but at the same time engineers were developing mechanical arms which could be controlled remotely by a human operator to carry out hazardous operations at a safe distance. These mechanical arms were referred to as 'teleoperators' but the next major development was to eliminate the human operator and replace them with some form of controller with a memory to allow movements to be repeated without the operator present. This was first done successfully by George Devol who went on to form a company which became the Unimation Corporation whose most famous product was the Unimate robot. The terms 'robot' and robotics' both therefore originated in science fiction and the original perception was one of human-like machines or androids. In popular culture, and particularly in films, robots are often considered to have all the human attributes with some capabilities considerably enhanced over that normally found in humans, but in reality current technology is not yet able to match this vision. There are a variety of definitions of an industrial robot, two of which are as follows: 'A robot is a re-programmable multi-function manipulator designed to move material parts, tools or specialised devices, through variable programmed motions for the performance of a variety of tasks'. (Robotic Institute of America) 3
  4. 4. BEE4393 Automation and Robotics 'An industrial robot is a re-programmable device designed to both manipulate and transport parts, tools or specialised manufacturing implements through variable programmed motions for the performance of specific manufacturing tasks' (British Robots Association) The vast majority of industrial robots are mechanical arms attached to a fixed base, with some form of programmable control for automatic execution of motion. This is simply because a market exists for such products and current technology is able to provide a product with acceptable performance at an affordable price. A feature which is currently possible but not yet widely used is mobility. Mobility can be provided by the use of wheels, tracks, or legs and a mobile robot may be concerned more with transportation than with manipulation and so may not carry an arm (or manipulator). Mobility requires an ability to navigate and to plan paths around obstacles in an environment where the position of obstacles is unknown. The level of performance of mobile robots is currently poor and the cost is prohibitive for all but highly specialised applications, eg decommissioning or maintaining nuclear power plant. BRIEF HISTORY OF ROBOTICS Chronology of developments related to robotics technology, including significant robot applications Date Development mid- 1 J. de Vaucanson built several human-sized mechanical dolls that played music. 700s 1801 J. Jacquard invented the Jacquard loom, a programmable machine for weaving threads or yarn 4
  5. 5. BEE4393 Automation and Robotics into cloth. 1805 H. Maillarcict constructed a mechanical doll capable of drawing pictures. 1946 American inventor G. C. Devol developed a controller device that could record electrical signals magnetically and play them back to operate a mechanical machine. U.S. patent issued in 1952. 1951 Development work on tclcoperators (remote-control manipulators) for handling radioactive materials. Related US. patents issued to Goertz (1954) and Bergsland (1958). 1952 Prototype Numerical Control machine demonstrated at the Massachusetts Institute of Technology after several years of development. Part programming language called APT (Automatically Programmed Tooling)subsequently developed and released in 1961. 1954 British inventor C. W. Kenward applied for patent for robot design. British patent issued in 1957. 1954 G. C. Devol develops designs for "programmed article transfer"U.S. patent issued for design in 1961. 1959 First commercial robot introduced by Planet Corporation. It was controlled by limit switches and cams. 1960 First "Unimate" robot introduced, based on Devol's -programmed article transfer." It used numerical control principles for manipulator control and was a hydraulic drive robot. 1961 Unimate robot installed at Ford Motor Company for tending a die casting machine. 1966 Trallfa, a Norwegian firm, built and installed a spray painting robot. 1968 A mobile robot named "Shakey" developed at SRI (Stanford Research Institute). It was equipped with a variety of sensors, including a vision camera and touch sensors, and it can move about the floor. 1971 The -Stanford Arm," a small electrically powered robot arm, developed at Stanford University. 1973 First computer-type robot programming language developed at SRI for research called WAVE. Followed by the language AL in 1974. The two languages were subsequently developed into the commercial VAL language for Unimation by Victor Scheinman and Bruce Simano. 1974 ASEA introduced the all-electric drive IRb6 robot. 1974 Kawasaki, under Unimation license, installed arc-welding operation for motorcycle frames. 1974 Cincinnati Milacron introduced the V robot with computer control 1975 Olivetti "Sigma" robot used in assembly operation-one of the very first assembly applications of robotics. 1976 Remote Center Compliance (RCC) device for part insertion in assembly developed at Charles Stark Draper Labs in United States. 1978 PUMA (Programmable Universal Machine for Assembly) robot introduced for assembly by Unimation, based on designs from a General Motors study 1978 Cincinnati Milacron T3 robot adapted and programmed to perform drilling and routing operations on aircraft components, under Air Force ICAM(Integrated Computcr-Aidcd Manufacturing) sponsorship. 1979 Development of S.CARA type robot (Selective Compliance Arm for Robotic Assembly) at Yamanashi University in Japan for assembly. Several commercial SCARA robots introduced around 1981 1980 Bin-picking robotic system demonstrated at University of Rhode Island. Using machine vision, the system was capable of picking parts in random orientations and positions out of a bin 1981 A "dircct-drivc robot" developed at Carnegic-Mellon University. It used electric motors located at the manipulator joints without the usual mechanical transmission linkages used on most robots 1982 IBM introduces the RS- 1 robot for assembly, based on several years of in-house development. It is a box-frame robot, using an arm consisting of three orthogonal slides. The robot language AML, developed by IBM, also introduced to program the RS-1 1983 Report issued on research at Wcstinghouse Corp. under National Science Foundation sponsorship on “adaptable-programmable assembly system"(APAS), a pilot project for a flexible automated assembly line using robots 1984 Several off-line programming systems demonstrated at the Robots 8 show.Typical operation of these systems allowed the robot program to be developed using interactive graphics on a personal computer and then downloaded to the robot 5
  6. 6. BEE4393 Automation and Robotics SOCIAL AND ECONOMIC ISSUES o In the social area, what are the main issues related to robotics? How will the labour and manpower market be affected by robotics? How many workers are likely to be displaced? o What are the impacts on the professional and semiprofessional work force who are employed in manufacturing? Also, will robotics affect productivity and international economic competition? o What kind of retraining and education is needed to upgrade the present work force? o Will foreign investors still choose Malaysia (as cheap labour will not be needed when factories are run by robots)? o Some 90 percent of Malaysian industry is in the SMI (Small and Medium Industry) catagory. Can SMIs afford installation of robotics in the near future? Or will robotics benefit only MNCs (Multinational Corporations)? ANATOMY OF A ROBOT BASIC COMPONENTS OF INDUSTRIAL ROBOTS o An industrial robot has three types of components : 1. Physical parts or anatomy 2. Built-in instructions or instinct (placed there by the manufacturer) 3. Learned behaviour or task programs (on-the-job training). WHAT IS A JOINT? o A joint of an industrial robot is similar to a joint in the human body. o Each joint gives the robot with a degree-of-freedom (d.o.f) of motion. o In nearly all cases, only 1 d.o.f is allowed to a joint. o However, future robots may be designed with joints having more than 1 d.o.f each. o Robots are often identified according to the total number of d.o.f they possess, such as a 6 degree-of-freedom robot. WHAT IS A ROBOT LINK ? o Links are rigid components that form a chain connected together by joints, o Each joint has two links, known as an input link and an output link. TYPES OF ROBOT JOINTS 6
  7. 7. BEE4393 Automation and Robotics o The purpose of the joint is to provide controlled relative movement between the input link and the output link. o Nearly all industrial robots have mechanical joints that can be classified into one of five types. o They include two types that provide linear motion and three types that provide rotary motion. o Each of the joints have a range over which it can be moved. The five joint types illustrated in the figures below are: 1. Linear joint. The relative movement between the input link and the output link is a linear sliding motion, with the axes of the two links being parallel. 2. Orthogonal joint. This is also a linear sliding motion, but the input and output links are perpendicular to each other during the move. 3. Rotational joint. This type provides a rotational relative motion of the joints, with the axis of rotation perpendicular to the axes of the input and output links. 4. Twisting joint. This joint also involves a rotary motion, but the axis of rotation is parallel to the axes of the two links. 7
  8. 8. BEE4393 Automation and Robotics 5. Revolving joint. In this type, the axis of the input link is parallel to the axis of rotation of the joint, and the axis of the output link is perpendicular to the axis of rotation. o Most robots are mounted on a stationary base on the floor. We will call it as robot base and its connection to the first joint as link 0. o It is the input link to Joint 1, the first in the series of joints used in the construction of the robot. The output link of joint 1 is link 1. Link 1 is the input link to joint 2, whose output link is link 2, and so on. o This joint-link numbering, scheme is shown below. GENERAL CLASIFICATION OF ROBOTS Based on the level technology: o Low technology  Material handling, using simple assembly  2 to 4 axes of movement 8
  9. 9. BEE4393 Automation and Robotics  Stop at extreme o Medium technology  Pick-and-place  Material handling  4 to 6 axes o High technology  Material handling  Pick-and-place  Loading and unloading  Painting and welding  6 to 9 axes ROBOT CLASSIFICATION BASED ON KINEMATIC STRUCTURE Normally, robot manipulators are classified according, to their arm geometry or kinematic structure. The majority of these manipulators fall into one of these five configurations: Cartesian (PPP), Cylindrical (RPP), Spherical (RRP), SCARA (RRP) or Articulate/Revolute (RRR).The work envelope or work volume is defined as the space within which the robot cans manipulator the end of its wrist. The shape of work volume is determined by the type of robot configuration. o Cartesian Type Configuration (PPP) Manipulator whose first three joints are prismatic are known as a Cartesian manipulator. The joint variables are the Cartesian coordinates of the end-effector with respect to the base. The kinematic description of this type of manipulator is the simplest of all the configurations. Cartesian manipulator are useful for table-top assembly applications and, as gantry robots for transfer of material and cargo Advantages:  3 linear axes  Easy to visualize  Rigid structure  Easy to program off-line  Linear axes make for easy mechanical stops Disadvantage:  Can only reach in front of itself  Requires large floor space for size of work envelop  Axes hard to seal 9
  10. 10. BEE4393 Automation and Robotics Figure: (a) A Cartesian or rectangular coordinate arm. (b) The box shaped work envelope within which a Cartesian coordinate manipulator operates (c) An overhead crane. Its movement is similar to those of a Cartesian coordinate arm o Cylindrical Type Configuration (RPP) For cylindrical type manipulator, its first joint is revolute which produces a rotation about the based, while its second and third joints are prismatic. The joint variables are the cylindrical coordinates of the end effector with respect to the base. Advantages:  2 linear axes, 1 rotating axis  Can reach all around itself  Reach and height axes rigid  Rotational axis easy to seal. Disadvantages:  Cannot reach above itself  Base rotation axis is less rigid than a linear axis  Linear axes hard to seal  Will not reach around obstacles  Horizontal motion is circular Figure: (a) A cylinder coordinate arm. It rotates about the base, moves in and out, and moves up and down. (b) The space between the two cylinders shown is the work envelop occupied by a cylindrical coordinates manipulator (c) A construction crane on top of a tall building. Its movement are similar to those of a cylindrical coordinates manipulator. 10
  11. 11. BEE4393 Automation and Robotics o Spherical Type Configuration (RRP) Spherical type manipulator is also known as the polar type manipulator.The first two joints of this type of manipulators are revolute, while its third Joint is prismatic. The joint variables are the spherical coordinates of the end-effector with respect to the base. Advantages:  1 linear axis, 2 rotating axes  Long horizontal reach Disadvantages:  Cannot reach around obstacles  Generally has short vertical reach Figure: (a) A polar or spherical coordinate manipulator. It rotates about the base and about the shoulder and moves linearly in and out (b) The work envelop for a polar-coordinates manipulator is the space between the two hemispheres (c) A ladder on a hook and ladder truck has movement similar to those of a polar coordinates manipulator o SCARA Type Configuration (RRP or PRR) The word SCARA stands for Selective Compliant Articulated Robot for Assembly. There are two type of SCARA robot configuration: either the first two joints are revolute with the third joint as prismatic, or the first joint is revolute with the second and third Joints as prismatic. Although some of the SCARA robots have the RRP structure, it is quite different from the polar type manipulator in both appearance and its range of applications. As its name suggests, SCARA robot is tailored for assembly operations. Advantages:  1 linear axis, 2 rotating axes  Height axis is rigid  Large work area floor space  Can reach around obstacles  Two ways to reach a point Disadvantages:  Difficult to program off-line  Highly complex arm 11
  12. 12. BEE4393 Automation and Robotics Figure: (a) A SCARA manipulator. It rotates in two axes in the horizontal plane and moves linearly up and down (b) The work envelope for the SCARA manipulator is the space between the two cylinders. The SCARA manipulator can reach around obstacles. (c) A folding lamp has movements similar to those of a SCARA manipulator o Revolute Type Configuration (RRR) Revolute manipulator is also called articulated or anthromorphic manipulator. These type of robot resembles human arm. Two common revolute designs are the elbow type manipulator such as the PUMA and the parallelogram linkage such as the Cincinnati Milacron T3 735. The elbow type configuration provides relatively large freedom of movement in a compact space. The parallelogram linkage configuration, although less dextrous typically than the elbow manipulator structure, nevertheless has several advantages that make it an attractive and popular design. Advantages:  3 rotating, axes  Can reach above or below obstacles  Largest work area for least work space  Two or four ways to reach a point Disadvantages:  Difficult to program off-line  The most complex manipulator 12
  13. 13. BEE4393 Automation and Robotics MOTORS AND ACTUATORS o Each joint of the manipulator is actuated by an actuator. o Actuators are devices that make robot move. o Robot drive systems determine  the capacity to move its body  the speed of operation  the strength  dynamic performance  and the kinds of applications that the robot can be used o For most industrial robots, the actuators are coupled to the respective robot link through a, gear train. The effect of the gear reduction is largely to decoupled the system by reducing the coupling among the joints. However, the present of gears introduces friction, backlash and drive train compliance. o For direct-drive robots, the problems of backlash, friction, and compliance due to gears are eliminated since no gears are used in such a robot. However, the nonlinear coupling among the links is significant, and the dynamics of the actuators themselves may be much more complex. o The commonly used actuators are : 1. Stepper motors 2. DC servomotors 3. AC servomotors 4. Hydraulic pistons 5. Pneumatic pistons o By far, hydraulic and electric drives are the most commonly used on more sophisticated robots. SOME COMPARISON ON THE DRIVE SYSTEMS 13
  14. 14. BEE4393 Automation and Robotics o Electric Drive  Small and medium size robots are usually powered by electric drives via gear trains using servomotors and stepper motors.  Most commonly used are dc motors, although for larger robots, ac motors may be utilised.  Advantages  Better accuracy & repeatability  Require less floor space  More towards precise work such as assembly applications  Disadvantages  Generally not as speedy and powerful as hydraulic robots  Expensive for large and powerful robots, can become fire hazard  There is now a trend towards designing, robot with all electric drives.  A new design based on direct drives (without gear trains) is being developed. o Hydraulic Drive  Larger robots make use of hydraulic drives.  Hydraulic drive system can provide  rotational motion (rotary vane actuators)  and linear motion (hydraulic pistons).  Advantages:  more strength-to-weight ratio  can also actuate at a higher speed  Disadvantages:  Requires more floor space  Tendency to oil leakage.  There is now a trend towards designing robot with all electric drives.  A new design based on direct drives (without gear trains) is being developed. o Pneumatic Drive  For smaller robots that possess fewer degrees of freedom (two- to fourjoint motions).  They are limited to pick-and-place tasks with fast cycles.  Pneumatic drive system can be applied to the actuation of piston devices to provide linear motions. Rotational motions can be achieved by rotary actuators. 14
  15. 15. BEE4393 Automation and Robotics o Direct Drive Robots  In 1981 a "direct- drive robot" was developed at Carnegle-Mellon University, USA. Is used electric motors located at the manipulator joints without the usual mechanical transmission linkages used on most robots.  The drive motor is located contiguous to the joint.  Benefits:  Eliminate backlash and mechanical defiencies  Eliminate the need of a power transmission (thus more efficient)  Joint backdrivable (allowing for joint-space force sensing) ROBOT GRIPPERS AND TOOLS DESIGN o The robot wrist refers to the joints in the kinematic chain between the robot arm and the hand or tool. In general, the wrist joints are revolute. Depending on its applications, the wrist can be of either one, two or three degree-of-freedom. o The arm and wrist assemblies of a robot are used primarily for positioning the end-effector and any tool it may carry. o It is the end-effector or tool that actually performs the work. It is the moving components which have to rasp, lift and manipulate workpieces without causing any damage, and without letting go. o Being less adaptable than human hands, the robot hands/end-effector have to be chosen or designed specially for a particular industrial application. o The robots have earned themselves the reputation of being general purpose automation, the hands/end-effector are not quite so flexible and may to be included along with the special tooling requirements of the job. o The simplest form of End-effector is the gripper. Grippers normally can perform two action, i.e., open and close. o For material transfer, or holding simple tool, or parts handling, gripper is enough to. do the job. It is not suitable for application such as welding,assembling, grinding, spray painting, etc.. Methods of Grisping o There are many ways of grasping or other-wise handling a job, depending to a large extent on the nature of the material being processed. o These includes 1. Mechanical grippers. 2. Hooking on to a part. 3. Lifting and transferring a part on a thin platform or spatula. 4. Scooping or ladling 15
  16. 16. BEE4393 Automation and Robotics 5. Electromagnets. 6. Vacuum cups. 7. Sticky fingers, using adhesives. 8. Quick disconnect bayonet sockets. o Some examples of appropriate handling methods 1. Forgings - normally handled by massive steel hands. 2. Thin metal sheets vacuum cups and magnets are preferable. 3. Powders, Granular solid, liquids and molten metals-ladles or scoops. 4. Fabrics and similar flimsy material - vacuum cups, adhesives, and electrostatic devices all offer possible solutions. 5. Spot welding - weld gun permanently bolted to the robot wrist or exchangeable by means of bayonet socket. Mechanical Grippers o Mechanical grippers are the simplest and usually used end-effectors. o How hard the robot must grasp 'the 'object depends on the weight of the object, the friction between the object and the fingers, how fast the robot is to move, and the relation between the direction of movement to the finger's Position on the object. o Grippers are one area of robotization where specialized design of tooling is often necessary. However it is seldom expensive. o There are a wide variety of mechanical grippers which have been designed to meet different robot applications in the market. Some of these grippers are shown in the following, Cam-operated hand It can easily handle heavy weights or bulky objects. It is designed to hold the object so that its center of gravity (CG) is kept very closed to the wrist of hand. The short distance between the wrist and the CG minimizes the twisting tendency of a heavy or bulky object. Wide-opening hand It is recommended for picking up object which is not always in a constant orientation or at the same size. The hand develops low force when opening and maximum force when closed. It is for objects of moderate weight. Cam-operated hand with inside and outside jaws Assume that a part is reoriented between the time when the part is placed in a machine and it is 16
  17. 17. BEE4393 Automation and Robotics removed. This special hand is one of those which deal with this problem. When the part is orinted as shown, the hand can grasp it on the outside by employing the outer self-aligning pads. If '-he part is turned over, the inner pads will grasp the inside Special hand with one movable jaw A hand with single-acting should be considered when there is any access underneath a part, as when it is on a rack. Where this hand can be applied, it will scoop up a part quite quickly. Simplicity of the design makes this one of the most econimical hands. Special hind for cartons The dual-jaw hand will open wide to grasp inexactly located objects of light weight. Lifting and placement of cardboard cartoons is an application. Special hand with modular gripper This special hand, with pair of pneumatic actuators, is one of the many special hand designs for industrial robots. It is suitable for parts of light weight. Special hand for glass tubes This hand is specially designed for industrial robots to securely grasping of relatively short tubes. The fingers of the hand close in two stages -First, they travel through an arc until they are vertical; second, the actuator draws them together axially. Linear travel in this second stage of closure is selected to accommodate the range of tube lengths to be handled. 17
  18. 18. BEE4393 Automation and Robotics Special hand chuck type This special end-effector is designed to pick up drums and similar type large cylindrical parts of various diameters. It is relatively a simple mechanism consisting of three fingers and a single actuator. The actuator drives all three fingers simultaneously by means of a chain or sprockets. The fingers expand against the inside diameter of the drum. Vacuum Systems o The vacuum systems uses the suction force to pick up on object. The system uses the vacuum cups which are normally made of an elastic material that conforms and forms a seal to the surface of the object to be handled. o The holding, force of a vacuum cup is the effective are multiplied by the different of pressure between the outside and the inside of the cup. To get the best utilization of a cup, the largest possible vacuum or pressure differential should be used. o The number of cups to be used in a design depends on such factors as weight of the load, size of cups available, location of the center of gravity, and support needed to handle large flimsy objects. o To create vacuum, a choice exists between two devices : the vacuum pump or the venturi. o The vacuum pump is either a piston or vane-type pump driven by electric motor. The venturi is a device where vacuum is created by having. a secondary high energy stream of flow impinge on the primary flow, it is actually converting pressure into vacuum. The venturi system differs from the pump system in that It is not controlled by a valve in the vacuum line, but rather by control of the high pressure air into the venturi. o The advantages of the pump are : Able to create a high vacuum; Low cost of operation; and relatively silent. Its disadvantages are : High initial cost; Requires a more complex system ~ vacuum tank and blow off valve o The advantages of a venturi are : Low initial cost; Does not normally need 18
  19. 19. BEE4393 Automation and Robotics blow-off-valve or vacuum tank; and highly reliable. o Its disadvantages are: Very noisy. and high cost of operation. o Some typical vacuum pick-up systems are as shown in the following: Vacuum cup hand The vacuum pick-up has the virtues of the magnetic pickup and is much less susceptible to workpiece side slip. For light to moderate weight glass, plastic, ferrous, and non-ferrous parts, the vacuum pick-up Is often an excellent choice. Simple vacuum cup hand This simple vacuum cup hand is suitable for handling fragile parts such as cathode ray tube face plates (Illustrated). The vacuum pick-up has better reliability than the magnetic pick-up : there are welldesigned telescoping vacuum lines for long-reach arms. Expansion bladder hand Large cylindrical vessels with flexible walls are difficult for mechanical hand and fingers to grasp, but an expendable bladder in the form of a cuff will do the job. A rigid back up ring supports the bladder. Magnetic Pickups o Magnetic handling is most suitable for parts of ferrous contents. Magnets can be scientifically designed and made in numerous shapes and sizes to perform various tasks. 19
  20. 20. BEE4393 Automation and Robotics o Magnets falls into two principle categories : Permanent and electro o Electro magnets are well suited for remote control as well as for moderately high speed pick-up and release of parts. A source of DC power is required. o Permanent magnets do not require a power source for operation which makes them well adapted for hazardous atmospheres that require explosion proof electrical equipment. They do, however, require a means of separating material from the magnet. To accomplish this, a slipper device may be employed, or if the part is positioned and clamped, welded or otherwise secured, the magnet can be pulled from the part. o Regardless of either the permanent magnet or electro magnet is used, there several matters that must be considered before a proper selection can be made : Shape of part; Weight. Temperature. Surface condition; and position to be handled. o An example of typical electro magnet pick-up Tools o There is a wide range of tools designed for robot applications available. These tools can be either permanently fastened to the robot hands, or if the robot has two or more tools to choose among, then quick disconnect selection of tool may be in order. o Some of the tools are as illustrated below : Stud-welding head Equipping an industrial robot with a stud-welding head is also practical. Studs are fed to the head from a tubular feeder suspended from overhead. Heating torch The industrial robot can also manipulate a heating torch to bake out foundry molds by playing the torch over the surface, letting the flame linger where more. heat input is needed. Fuel is saved because heat is applied directly, and the bakeout is faster than it would be if the molds were conveyed through a gas-fired oven. 20
  21. 21. BEE4393 Automation and Robotics Inert gas arc welding torch Arc welding with a robot held torch is another application in which an industrial robot is used. The welds can be single or multiple pass. The most effective use is for running simple-curved and compound-curved joints, as well as running multiple short welds at different angles and on various planes. Spotwelding gun A general purpose industrial robot can maneuver and operate a spotwelding gun to place a series of spot welds on flat, simple-curved, or compound-curved surfaces. Ladle Ladling hot materials such as molten metal is a hot and hazardous job for which industrial robots are well suited. In piston casting permanent mold die casting and related applications, the robot can be programmed to scoop up and transfer the molten metal from the pot to the mold, and then do the pouring. Routers, grinders A routine, head, grinder, belt sander, or disc sander can be mounted readily on the wrist of an industrial robot. Thus equipped, the robot can rout workpiece edges, remove flash from plastic parts, and do rough snagging of casting 21
  22. 22. BEE4393 Automation and Robotics Spray gun Ability of the industrial robot to do multipass spraying with controlled velocity fits it for automated application of primers, paints, and ceramic or glass frits, as well as application of masking agents used before plating. For short or medium-length production runs, the industrial robot would often be a better choice than a special purpose setup requiring a lengthy change-over procedure for each different part. Also the robot can spray parts with compound curvatures and multiple surfaces. Tool changing A single industrial robot can also handle several tools sequentially, with an automatic tool-changing operation programmed into the robot's memory. The tools can be of different types or sizes, permitting multiple operations an the same workpiece SAFETY CONSIDERATIONS WHEN? o Practise it as soon as starting robotics project o Must be built into robotics system at the outset 22
  23. 23. BEE4393 Automation and Robotics o Do not risk injuries by robots 3 R'S OF ROBOTIC SAFETY Robots Require Respect o Human safety first then Robot Safety then other equipment o then Robot Safety o then other equipment WHAT DANGERS ? Starting with the most dangerous: o Repairing a robot (has to be within work cell) - Faulty robots can suddenly move unexpectedly o Training/programming a robot - For PTP (Point-to-Point) motion, human nearby to check - Robot programming results in physical motion o Normal operation -If other equipment fails, it is a source of danger e.g. case of Kawasaki robot engineer (10 years experience), died when struck by a robot while repairing a malfunctioning machine o Power supply -Apart from normal dangers of electrical supply, high pressure hydraulic leakage can punch a hole through a person's hand. WHAT SORT OF INJURES? ? o Bodily impact o Pinching - caught in grippers or joints o Pinning human against a structure SAFETY AIDS o Use Sensors: Range & Proximity: Perimeter penetration detection Intruder detection inside work cell Intruder detection near a robot o Brakes and holding technology o Simulation packages (test the programs by simulation first) o Design of interlocks 23
  24. 24. BEE4393 Automation and Robotics o Work cell design layout 24

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