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Fundamental of robotic manipulator


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Fundamental of robotic manipulator

  1. 1. Mrs. S. N. Kale Asst. Professor PVPIT, Budhgaon Fundamental of Robotic Manipulator
  2. 2. In the first part of this unit we would be studying the basics associated with the industrial robots, like basic types, Classifications: the methods to specify the robots, types of drive technologies used in robotic applications, Motion control methods the various applications of the robots. specifications: Example: RHINO XR-3 2 Fundamental of Robotic Manipulator
  3. 3. •Mankind has always strived to give life like qualities to its artifacts. •He tries to find substitute for himself to carry out his orders and also work in hostile environment. •Broadly robot is a machine that looks and work like a human being. •The industry is moving from automation to robotization , to increase productivity and to deliver uniform quality.Robots are employed in hostile environment: 1. Atomic plant to handle radioactive material. 2. Construct and repair space station and satellites. 3. Nursing and aiding patient in medical field. 4. Heavy earth moving equipments. 3 Fundamental of Robotic Manipulator
  4. 4. reasons for using a robot but the central reason is to eliminate a human operator. The most obvious reason : •To save labor and reduce cost. Other classes of applications concern the product: •Human is bad for the product: e.g. semiconductor handling, food handling, pharmaceuticals, etc. •Product is bad for the human : e.g. radioactive product. robots can be used to replace human operators where the dangers are: 1.Repetitive strain syndrome. 2.Working with machinery that is dangerous for example presses, winders. 3.Working with materials which might be harmful in the short or long term(toxic chemicals, radioactive material. 4 Fundamental of Robotic Manipulator
  5. 5. Here robot is considered as industrial robot called as robotic manipulator or robotic arm. This arm is roughly similar to human arm. It is modeled as chain of rigid links interconnected by flexible joints. Links corresponds to :chest, upper arm, fore arm Joints: shoulder, elbow, and wrist. At end of arm is an end effector ( tool, gripper or hand). Tool has two or more fingers that open and closes. 5 Fundamental of Robotic Manipulator
  6. 6. 6 Fundamental of Robotic Manipulator
  7. 7. Wrists connects end effector to forearm. End effector may be a tool and its fixture or gripper or any other device 1. Grippers: are generally used to grasp and hold an object and place it at a desired location. Grippers classified as mechanical grippers, vacuum or suction cups, magnetic grippers, adhesive grippers, hooks, scoops, and so forth. 2. Tools: a robot is required to manipulate a tool to perform an operation on a work part. Here the tool acts as end- effector. Spot-welding tools, arc-welding tools, spray-painting nozzles, and rotating spindles for drilling and grinding are typical examples of tools used as end-effectors.7 Fundamental of Robotic Manipulator
  8. 8. Automation and robot: Automation is technology which is concerned with the use of mechanical ,electrical and computer based system in operation and control of production. e.g. Transfer lines,mechanized asembly machines,feedback control system,numerically controlled machine tools and robot Two types: Hardware automation and software automation 8 Fundamental of Robotic Manipulator
  9. 9. Hard automation, also called fixed automation, is built with a specific production purpose. This automation approach is best suited for mass production of the same product with few alterations or change-overs. When volume of production is very high, special equipment are designed to process product efficiently and at high production rate. When production cycle ends or new product is introduced ,that m/c have to be shut down and h/w retooled for next generation of models. CNC machines are examples of hard automation 9 Fundamental of Robotic Manipulator
  10. 10. Soft automation, often referred to as flexible automation, is reprogrammable and reconfigurable. Now auto industry and other industries have introduced more flexible forms of automation in manufacturing cycle. Programmable mechanical manipulator are now being used to perform task as spot welding ,spray painting, material handling etc. Since computer controlled mechanical manipulators can be converted through s/w to do variety of task they are referred as soft automation. Robots fall into this soft automation category. This method is ideal for handling small batches of product and 10 Fundamental of Robotic Manipulator
  11. 11. Manual labor Soft automation hard automation v1 v2 Product volume Unit cost Qualitative comparison of cost effectiveness of manual labor ,hard automation and soft automation Upto v1-manual labor is cost effective. After v2 –hard automation is cost effective V1 to v2-soft automation is cost effective 11 Fundamental of Robotic Manipulator
  12. 12. Robots, the industrial robots are the specialized, highly automated mechanical manipulators which are controlled by sophisticated electronic control systems and computer systems The robots can be programmed to do a variety of operations by just changing the predetermined set of instructions called program , through some compatible software. This is also termed as soft automation. 12 Fundamental of Robotic Manipulator
  13. 13. What is an Industrial Robot?  An industrial robot is a programmable, multi- functional manipulator designed to move materials, parts, tools, or special devices through variable programmed motions to perform a variety of tasks. An industrial robot consists of a number of rigid links connected by joints of different types, controlled and monitored by a computer. 13 Fundamental of Robotic Manipulator
  14. 14. An industrial robot can be defined as : Robot can also be defined as a software controllable mechanical device that uses actuators and sensors to guide one or more end effectors through programmed motions in a workspace in order to manipulate physical objects. 14 Fundamental of Robotic Manipulator
  15. 15. What are the parts of a robot? • Manipulator • Pedestal • Controller • End Effectors • Power Source 15 Fundamental of Robotic Manipulator
  16. 16. Manipulator (Mimics the human arm) • Base • Appendage Shoulder Arm Grippers 16 Fundamental of Robotic Manipulator
  17. 17. Pedestal •Supports the manipulator. •Acts as a counterbalance. 17 Fundamental of Robotic Manipulator
  18. 18. Controller (The brain) • Issues instructions to the robot. • Controls peripheral devices. • Interfaces with robot. • Interfaces with humans.18 Fundamental of Robotic Manipulator
  19. 19. End Effectors(The hand) • Spray paint attachments • Welding attachments • Vacuum heads • Hands • Grippers19 Fundamental of Robotic Manipulator
  20. 20. Power Source (The food) • Electric • Pneumatic • Hydraulic 20 Fundamental of Robotic Manipulator
  21. 21. 21 Fundamental of Robotic Manipulator
  22. 22. Classification : based on drive technologies: An important element: The drive system ,it supplies the power for the actuation of various linkages and joints of a robot and enabling the robot to move. The dynamic performance depends on the type of power source. three types of power sources for robots: Electric drive: Most of the industrial robots use electric drive system, in the form of either DC stepper motor drive (open loop control), or, DC servo motor drive (closed loop control). Advantages: This drive system gives better positioning accuracy and repeatability, and is suitable to keep cleaner environment around.22 Fundamental of Robotic Manipulator
  23. 23. Hydraulic drive: at higher speeds and at substantial loads hydraulic drive robot are preferred. Disadvantage: it occupies large space area and there is a danger of oil leak to the shop floor. But it gives lower movement compare to the hydraulic robots and the electric drive system is good for small and medium size robots only. 23 Fundamental of Robotic Manipulator
  24. 24. Pneumatic drive: used for high speed and/or high-load-carrying capabilities. A pneumatic drive is clean and fast but it is difficult to control because air is a compressible fluid. For both electrical and hydraulic drive robots most of the time make use of the pneumatic tools or end effectors. Pneumatic drives used especially when the gripping action of the end effectors is simple open and close operation to pick light objects. the pneumatic drive system is preferred for smaller robots as these are less expensive than electric or hydraulic robots and suitable for relatively less degrees of freedom design for simple pick and place application. 24 Fundamental of Robotic Manipulator
  25. 25. The Robotic Motions: oThe industrial robots are designed to perform some desirable work o This can be performed by enabling the manipulator to move the body, arm and wrist through a series of motions. oIt helps the end effectors of the robot to achieve the desirable position and orientation in the three dimensional space surrounding the base of the robot. Work envelop geometries: 25 Fundamental of Robotic Manipulator
  26. 26. Robot Joints •A robot joint permits relative movement between parts of a robot arm. •The joints of a robot are designed to enable the robot to move its end-effector along a path from one position to another as desired. The end effector is mounted on a flange or some plate secured to the wrist. • It is the tool to perform some operation or some gripper for pick and place operations. 26 Fundamental of Robotic Manipulator
  27. 27. The robot movements are broadly classified into two main categories, namely (i)arm and body motions (ii) wrist motions. The individual joint motions associated with these two categories are also referred to as the degrees of freedom . The first three axes of the robot are referred to as the major axes. The position of the end-effector of the robot is determined by the position of the major axes. Similarly three more axes associated with the wrist, are called minor axes and are used to establish the orientation of the tool or the gripper at wrist. 27 Fundamental of Robotic Manipulator
  28. 28. Degrees of Freedom Degrees of freedom (DOF) is a term used to describe a robot’s freedom of motion in three dimensional space —specifically, the ability to move forward and backward, up and down, and to the left and to the right. For each degree of freedom, a joint is required. A robot requires minimum six degrees of freedom to be completely versatile. Its movements are clumsier than those of a human hand, which has 22 degrees of freedom 28 Fundamental of Robotic Manipulator
  29. 29. 29 Fundamental of Robotic Manipulator
  30. 30. The number of degrees of freedom defines the robot’s configuration. For example, many simple applications require movement along three axes: X, Y, and Z. See Figure 2-10. These tasks require three joints, or three degrees of freedom 30 Fundamental of Robotic Manipulator
  31. 31. The locus of the points in the three dimensional space that can be reached by the wrist by the various combinations of the movements of the robot joints from base up to wrist, is called the gross work envelop of the robot. The robot motions are accomplished by means of powered joints. Thus a minimum of six axes are required to achieve any desirable position and orientation in the robot’s work volume or work envelop or workspace. 31 Fundamental of Robotic Manipulator
  32. 32. The rigid members connected at the joints of the robot are called links. In the link-joint-link chain, the link closest to the base is referred to as the input link . The output link is the one which moves with respect to the input link. There are basically two types of joints commonly used in industrial robots, which are: (i) prismatic or linear joints,(p) which have sliding or linear (translational) motion along an axis. 32 Fundamental of Robotic Manipulator
  33. 33. (ii)Revolute ,(R) : which exhibits the rotary motion about an axis. the links are aligned perpendicular to one another at this kind of joint. The rotation involves revolution of one link about another. 33 Fundamental of Robotic Manipulator
  34. 34. Based on the physical configuration or the combination of the revolute or prismatic joints for the three major axes, a particular geometry of the work envelop is achieved. The table shows the some of the most common robot work envelops based on the major axes: robot Axis 1 Axis 2 Axis 3 Total revolute cartesian P P P 0 Cylindrical R P P 1 Spherical R R P 2 SCARA R R P 2 Articulated R R R 3 34 Fundamental of Robotic Manipulator
  35. 35. Cartesian Gantry Robot Arm 35 Fundamental of Robotic Manipulator
  36. 36.  robots with Cartesian configuration consist of links connected by linear joints (p).  Thus the resulting configuration is (PPP). The three joints corresponds to the notation for the moving the wrist up and down, in and out, and back and forth. Thus the work envelop/ work volume generated by this robot is a rectangular box. example: the gantry robot Cartesian Gantry Robot Arm Uses 3 perpendicular slides to construct x , y , z axes. Hence called xyz/rectilinear robot. e.g. IBM RS-I robot 36 Fundamental of Robotic Manipulator
  37. 37. Cartesian Gantry Robot Arm commonly used : •for pick and place work for heavy loads • assembly operations • handling machine tools • arc welding operations 37 Fundamental of Robotic Manipulator
  38. 38. work envelop/ work volume 38 Fundamental of Robotic Manipulator
  39. 39. The major advantages : 1.Ability to do straight line insertions into furnaces. 2.Easy computation and programming. 3.Most rigid structure for given length. Disadvantages : 1.Requires large operating volume. 2.Exposed guiding surfaces require covering in corrosive or dusty environments 3.Can only manipulate the objects in front of it. 4.Axes of robot are hard to seal 39 Fundamental of Robotic Manipulator
  40. 40. Changing the first prismatic joint of the Cartesian coordinate robot by revolute joint, to have RPP configuration we get the cylindrical coordinate robot. The space in which this robot operates is cylindrical in shape, hence the name cylindrical configuration. Cylindrical Robot Arm The revolute joint swings the arm back and forth about vertical base axis. The prismatic joints then move the wrist up and down along vertical axis and in and out along a radial axis. R P P 40 Fundamental of Robotic Manipulator
  41. 41. Cylindrical Robot Arm 41 Fundamental of Robotic Manipulator
  42. 42. As there is always some minimum radial position, the work envelop is actually the volume between two concentric cylinders. 42 Fundamental of Robotic Manipulator
  43. 43. commonly used for: handling at die-casting machines, assembly operations, handling machine tools, and spot welding operations. major advantages : 1.can reach all around itself 2.rotational axis easy to seal 3.relatively easy programming 4.rigid enough to handle heavy loads through large working space. 5.good access into cavities and machine openings. Disadvantages : 1.can't reach above itself. 2.linear axes is hard to seal. 3.won’t reach around obstacles. drives are difficult to cover from dust and liquids. 43 Fundamental of Robotic Manipulator
  44. 44. Spherical Robot Arm 44 Fundamental of Robotic Manipulator
  45. 45. If second joint of cylindrical coordinate robot is replaced with revolute joint (RRP) this produces spherical coordinate robot. •Here the first revolute joint swings the arm back and forth about a vertical base axis, •the second revolute joint moves the arm up and down about the horizontal shoulder axis, • the prismatic joint moves the wrist radially in and out 45 Fundamental of Robotic Manipulator
  46. 46. The work envelope is the volume between two concentric spheres e.g. UNIMATE 2000 series, MAKER 110 46 Fundamental of Robotic Manipulator
  47. 47. commonly used for: material handling at die casting or fettling machines, handling machine tools and for arc/spot welding etc. the advantages: 1.Large working envelope. 2.Two rotary drives are easily sealed against liquids/dust. The disadvantages are: 1.Complex coordinates more difficult to visualize, control, and program. 2.Exposed linear drive. 3.Low accuracy Spherical: RRP 47 Fundamental of Robotic Manipulator
  48. 48. SCARA Robot Arm Adept's SCARA robots 48 Fundamental of Robotic Manipulator
  49. 49. Like a spherical coordinate robot, a SCARA robot (Selective Compliance Assembly Robot Arm) is a robot with at least two parallel revolute joints (R) and having one linear joint for the positioning of the wrist. But for a SCARA robot all three joint axes are vertical 49 Fundamental of Robotic Manipulator
  50. 50. The first revolute axis swings the arm back and forth about base axis i.e vertical shoulder axis. The second revolute joint swings the forearm back and forth about the vertical elbow axis. Thus two revolute joints control motion in a horizontal plane. The vertical component of motion is provided by third joint, a prismatic joint which slides the wrist up and down.50 Fundamental of Robotic Manipulator
  51. 51. It gives rigidity in vertical direction and complianc e in horizontal axis Work envelope 51 Fundamental of Robotic Manipulator
  52. 52. commonly used for: pick and place work, and assembly operation with high working speeds. main advantages : 1.High speed. 2.Height axis is rigid. 3.Large work area for floor space. 4.Moderately easy to program. The main disadvantages : 1.Limited applications. 2.Two ways to reach a point. 3.Difficult to program off-line. 4.Highly complex arm. 52 Fundamental of Robotic Manipulator
  53. 53. Articulated Robot Arm 53 Fundamental of Robotic Manipulator
  54. 54. In articulated coordinate robot all joints are revolute joint (RRR). It closely resembles the anatomy of human arm. First revolute joint swings robot back and forth about vertical base axis. Second joint pitches the arm up and down about horizontal shoulder axis. Third joint pitches the forearm up and down about horizontal elbow axis.54 Fundamental of Robotic Manipulator
  55. 55. Work envelope 55 Fundamental of Robotic Manipulator
  56. 56. commonly used for: assembly operations, welding, weld sealing, spray painting, and handling at die casting or fettling machines. main advantages : 1.All rotary joints allows for maximum flexibility 2.All joints can be sealed from the environment. The main disadvantages are: 1.Extremely difficult to visualize, control, and program these robots. 2.Restricted volume coverage. 3.Low accuracy.56 Fundamental of Robotic Manipulator
  57. 57. Manipulators 57  Robot Configuration: Cartesian: PPP Cylindrical: RPP Spherical: RRP SCARA: RRP (Selective Compliance Assembly Robot Arm) Articulated: RRR Hand coordinate: n: normal vector; s: sliding vector; a: approach vector, normal to the tool mounting plateFundamental of Robotic Manipulator
  58. 58. Classification based on motion control methods: It is based on method used to control the movement of end effec There are two types of motions: 1. Point to point motion: • Tool moves to sequence of discrete points in a workspac • The path between points is not explicitly controlled by user • It is useful for operation which is discrete in nature. e.g. Spot welding , pick and place , loading and unloading Continuous motion: •End effector follows a prescribed path in three dimensional space. •The speed of motion may vary along the path. e.g. arc welding , spray painting 58 Fundamental of Robotic Manipulator
  59. 59. What Can Robots Do? Industrial Robots Material Handling Manipulator Assembly Manipulator Spot Welding •Material handling •Material transfer •Machine loading and/or unloading •Spot welding •Continuous arc welding •Spray coating •Assembly •Inspection59 Fundamental of Robotic Manipulator
  60. 60. 1.12.1 Loading/unloading parts to/from the machines (i)Unloading parts from die-casting machines (ii)Loading a raw hot billet into a die, holding it during forging and unloading it from the forging die (iii)Loading sheet blanks into automatic presses (iv)Unloading molded parts formed in injection molding machines (v)Loading raw blanks into NC machine tools and unloading the finished parts from the machines 60 Fundamental of Robotic Manipulator
  61. 61. 61 Fundamental of Robotic Manipulator
  62. 62. Single machine robotic cell applications include: (i)The incoming conveyor delivers the parts to the fixed position (ii)The robot picks up a part from the conveyor and moves to the machine (iii)The robot loads the part onto the machine (iv)The part is processed on the machine (v)The robot unloads the part from the machine (vi)The robot puts the part on the outgoing conveyor (vii)The robot moves from the output conveyor to the input conveyor Multi-machine robotic cell application: Two or three CNC machines are served by a robot. The cell layout is normally circular. 62 Fundamental of Robotic Manipulator
  63. 63. Assembly Operations: Electronic component assemblies and machine assemblies are two areas of application. Inspection: Industrial robots are used for inspection applications, in which the robot end effector is special inspection probe. 63 Fundamental of Robotic Manipulator
  64. 64. Palletizing and Depalletizing: Many products are packaged in boxes of regular shape and stacked on standard pallets for shipping. Robots are commonly used to palletize and depalletize boxes because they can be programmed to move through the array of box positions layer after layer. 64 Fundamental of Robotic Manipulator
  65. 65. Drilling Hole drilling is a precision machining process. Drilling robots use special drilling end effectors which locate and dock onto the work piece or a fixture. 65 Fundamental of Robotic Manipulator
  66. 66. Spot Welding Spot welding is the most common welding application found in the manufacturing field. 66 Fundamental of Robotic Manipulator
  67. 67. Fastening Robots are commonly used for applying threaded fasteners in the automobile industry for fastening wheels, in the electronics industry for screwing components to circuit boards and circuit boards into chassis. 67 Fundamental of Robotic Manipulator
  68. 68. Paint and Compound Spraying Robots provide a consistency in paint quality and widely used in automobile industry for medium batch production. Painting booths are hazardous because the paint material is often toxic, and flammable. 68 Fundamental of Robotic Manipulator
  69. 69. Arc Welding Ship building, aerospace, construction industries are among the many areas of application 69 Fundamental of Robotic Manipulator
  70. 70. Robot specification But in addition to classification, there are several additional characteristics : (i)Number of axes (ii)Load carrying capacity (kg) (iii)Maximum speed (mm/sec) (iv)Reach and stroke (mm) (v)Tool orientation (deg) (vi)Precision, accuracy and Repeatability of movement (mm) (viii) Operating environment 70 Fundamental of Robotic Manipulator
  71. 71. Number of Axes The industrial robots have got a number of axes about which its various links rotate or translate. the first three axes of the robot called major axes are used to establish the position of the wrist. The remaining axes of the robot are used to establish the orientation of the robots wrist, called minor axes . Thus a six axes robot is a general manipulator which can move its end effector to both an arbitrary location and an arbitrary orientation with in its work volume. 71 Fundamental of Robotic Manipulator
  72. 72. Some industrial robots have more than six axes, termed as the redundant axes , which are generally used to avoid certain obstacle in the robots work volume. The mechanism to activate the robot tool (end effector), or the opening and closing of the robots gripper, is not considered as the independent robot axis, as this mechanism (axis) do not contribute to acquire either the position or the orientation of the end effector in robots working space. 72 Fundamental of Robotic Manipulator
  73. 73. Load Carrying Capacity: The load carrying capacity is mainly determined by various factors : robot’s size, configuration, type of drive system and the type of application for which it is designed. A very wide range: from few grams to several thousand of kilograms. The maximum load carrying capacity should be specified for the condition that it is in its weakest position. It is the position when the robots arm is at maximum horizontal extension. 73 Fundamental of Robotic Manipulator
  74. 74. The specification provided by manipulator manufacturers is actually the gross weight capacity that can be put at the robotic wrist. Thus to use this specification the user must know weight of the end effector. E.g., if the gross load carrying capacity of a robot is 10.0 kg and it’s end effector weigh 3.0 kg, then the net load carrying capacity of the robot would be only 7.0 kg. 74 Fundamental of Robotic Manipulator
  75. 75. The maximum tool tip speed of the robots is from a few mm per second to several meters per second. The speed of the robot is measured at robot’s wrist. Thus the highest speeds can be achieved with maximum horizontal extension of arm away from the base of the robot. Also the type of the drive system affects the joint speeds, e.g. the hydraulic robots are having faster joint motions than the electrical drive robots. Maximum Speed of Motion 75 Fundamental of Robotic Manipulator
  76. 76. A meaningful measure of the robot speed is the cycle time, which is the time required to perform several periodic motions of robot. As it is desirable for any production operation to minimize the cycle time of task, most of robots have the provision to regulate or adjust the speed. 76 Fundamental of Robotic Manipulator
  77. 77. Reach and Stroke: Reach and stroke of the robot are the measure of the work volume of the robot. The horizontal reach: it is the maximum radial distance at which the robotic wrist can be positioned away from the vertical axis about which the robot rotates, or the base of the robot. The horizontal stroke: it is the total radial distance the wrist can move. There is always a certain minimum distance the robot’s wrist will remain away from the base axis. 77 Fundamental of Robotic Manipulator
  78. 78. Thus, the horizontal stroke is always less than equal to the horizontal reach. For a cylindrical coordinate robot the horizontal reach is the outer cylinder of the workspace, while the horizontal stroke is the difference between the radii of the concentric outer cylinder and the inner cylinder, as shown in figure 1.10 78 Fundamental of Robotic Manipulator
  79. 79. The vertical reach: is the maximum vertical distance above the working surface that can be reached by the robot’s wrist. The vertical stroke: is the total vertical distance that the wrist can move. the vertical stroke is also always less than equal to the vertical reach. articulated robot have full work envelope means stroke equal to reach But necessary to program to avoid collision with itself or work surface. 79 Fundamental of Robotic Manipulator
  80. 80. Tool Orientation The three major axes of the robot determine the work volume, while remaining additional axes of the robot determine the orientation of the robot’s end effector. If three independent minor axes are present then the end effector will able to achieve any arbitrary orientation in the three dimensional work volume of the robot. the three axes associated with the wrist are called as yaw- pitch and roll which are used to define the orientation of end effector of robot. 80 Fundamental of Robotic Manipulator
  81. 81. Degrees of Freedom Degrees of freedom (DOF) is a term used to describe a robot’s freedom of motion in three dimensional space —specifically, the ability to move forward and backward, up and down, and to the left and to the right. For each degree of freedom, a joint is required. A robot requires six degrees of freedom to be completely versatile. Its movements are clumsier than those of a human hand, which has 22 degrees of freedom 81 Fundamental of Robotic Manipulator
  82. 82. For applications that require more freedom, additional degrees can be obtained from the wrist, which gives the end effector its flexibility. The three degrees of freedom in the wrist have names: pitch, yaw,and roll. See Figure 2-11. The pitch, or bend, is the up-and- down movement of the wrist. The yaw is the side-to- side movement, and the roll, or swivel, involves rotation. 82 Fundamental of Robotic Manipulator
  83. 83. 83 Fundamental of Robotic Manipulator
  84. 84. 1.Wrist roll: it involves the rotation of the wrist mechanism about the arm axis. Wrist roll is also referred to as wrist swivel. 2. Wrist pitch: if the wrist roll is in its center position, the wrist pitch is the up or down rotation of the wrist. also called wrist bend. 3.Wrist yaw: if the wrist roll is in center position of its range, wrist yaw is the right or the left rotation of the wrist. The wrist yaw and pitch definitions are specified w.r.t.the central position of the wrist roll, the rotation of the wrist about the arm axis will change the orientation of the pitch and yaw movements. The robot would have a spherical wrist if the axes used to orient the tool intersect at a common point. 84 Fundamental of Robotic Manipulator
  85. 85. F3,m3 F2,m2 F1,m1 wrist Roll Pitch Yaw 85 Fundamental of Robotic Manipulator
  86. 86. To specify tool orientation a mobile tool coordinate frame M={m1,m2,m3} is attached to tool and moves with tool. M3 is aligned with principal axis of tool and pts away from wrist M2 is parallel to line followed by fingertips of tool as it opens or closes. M1 completes right handed tool coordinate frame MBy convention, yaw pitch and roll motions are performed in specific order about set of fixed axis Initially mobile tool frame is coincide with wrist coordinate frame F= {f1,f2,f3} attached at fore arm 1) Yaw motion is performed by rotating tool about wrist axis f1 2) Pitch motion by rotating tool about wrist axis f2 3) Roll motion rotating tool about wrist axis f3 86 Fundamental of Robotic Manipulator
  87. 87. 87 Fundamental of Robotic Manipulator
  88. 88. 88 Fundamental of Robotic Manipulator
  89. 89. 89 Fundamental of Robotic Manipulator
  90. 90. Precision, Accuracy and Repeatability of movement The precision of movement is basically a function of three features: special resolution, accuracy, And repeatability These terms are defined for: • the robot's wrist end without any tool attached • for the conditions under which the robot's precision will be at its worst. the robot has least precision of movement with the robot's arm is fully extended 90 Fundamental of Robotic Manipulator
  91. 91. The control resolution for a robot is determined by the position control system and the feedback measurement system. It is the controller's ability to divide the total range of movement for the particular joint into individual increments that can be addressed in the controller. (i) Spatial Resolution It is defined as the smallest increment of movement into which the robot can divide its work volume. depends on the system’s control resolution and the robot's mechanical in accuracies. 91 Fundamental of Robotic Manipulator
  92. 92. Accuracy is an absolute concept, repeatability is relative. Accuracy relates to the robot's capacity to be programmed to achieve a given target point. The actual programmed point will probably be different from the target point due to limitations of control resolution.92 Fundamental of Robotic Manipulator
  93. 93. It is measure of ability of robot to place tool tip at arbitrarily prescribed location in work envelope. Error is half of spatial resolution. Error is worst in outer range of its work volume and better when arm is closer to base. 93 Fundamental of Robotic Manipulator
  94. 94. Repeatability: Repeatability is the measure of the ability of the robot to position the tool tip at same position repeatedly. There is always some repeatability error associated because of backlash in gears, flexibility of the mechanical linkages and drive systems. The repeatability errors are very small in magnitude for well designed robotic manipulators. Repeatability and accuracy refer to two different aspects. 94 Fundamental of Robotic Manipulator
  95. 95. Repeatability errors form a random variable and constitute a statistical distribution.95 Fundamental of Robotic Manipulator
  96. 96. A robot that is repeatable may not be very accurate, and visa versa. Let T be the desired target point to where the robot is commanded to move , but due to limitations on its accuracy, the programmed position becomes point P. The distance between points T and P is robot's accuracy. When, the robot wrist is commanded to the programmed point P again , it does not return to the exact same position. Instead, it returns to position R. The difference between P and R is limitations on the robot's repeatability. The robot will not always return to the same position R on subsequent repetitions of the motion cycle. Instead, it will form a cluster of points on both sides of the position P 96 Fundamental of Robotic Manipulator
  97. 97. Precision : It is closely related to repeatability. It is measure of spatial resolution with which tool can be positioned within work envelope. A B If tool tip is positioned at A then next closest position that it moves is B Then distance bet. A and B is precision. Tool tip might be positioned anywhere on 3 dimensional grid of pts within work space. Overall precision is max. distance between neighboring pts in grid97 Fundamental of Robotic Manipulator
  98. 98. Cartesian robot: interior grid pt have 8 neighbors in horizontal plane + 9 neighbors in plane above and below For Cartesian robot, Precision is uniform throughout work envelop 98 Fundamental of Robotic Manipulator
  99. 99. Robot type Horizontal precision Vertical precision Cartesian Uniform Uniform Cylindrical Decreases radially Uniform Spherical Decreases radially Decreases radially SCARA varies Uniform articulated varies varies 99 Fundamental of Robotic Manipulator
  100. 100. cartesian Cylindrical robot 100 Fundamental of Robotic Manipulator
  101. 101. a b c d ∆r r∆ф Grid elemen t ∆ф 101 Fundamental of Robotic Manipulator