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ROBOTICS (VII Semester, B. Tech. Mechatronics) Prepared By: Nehul J. Thakkar Asst. Professor U. V. Patel College of Engineering Ganpat University
Chapter 2: Fundamentals of Robot Technology q q q Robot Anatomy Robot Motions Work Volume Degree of Freedom (DOF) Robot Drive Systems Speed of Motions Load-carrying Capacity Control Systems Dynamic Performance Compliance End Effectors Sensors 3/16/2018 2 Cont.
Robot Anatomy Ø Ø Ø The physical construction of the body, arm and wrist of the machine The wrist is oriented in a variety of positions Relative movements between various components of body, arm and wrist are provided by a series of joints Joints provide either sliding or rotating motions The assembly of body, arm and wrist is called “Manipulator” 3/16/2018 3 Cont.
Robot Anatomy. . Ø Ø Attached to the robot’s wrist is a hand which is called “end effector” The body and arm joints position the end effector and wrist joints orient the end effector 3/16/2018 4 Cont.
Robot Anatomy. . Robot Configurations Ø Variety of sizes, shapes and physical configuration 1. 2. 3. 4. 5. 3/16/2018 Cartesian Coordinates Configuration Cylindrical Configuration Polar or Spherical Configuration Articulated or Jointed-arm Configuration Selective Compliance Assembly Robot Arm (SCARA) Configuration 5 Cont.
Robot Anatomy. . 1. Ø Ø Ø Cartesian Coordinate Configuration Uses three perpendicular slides to construct x , y and z axes X-axis represents right and left motions, Yaxis represents forward-backward motions and Z-axis represents up-down motions Kinematic designation is PPP/LLL Other names are xyz robot or Rectilinear robot or Gantry robot Operate within a rectangular work volume 3/16/2018 6 Cont.
Robot Anatomy. . 1. Cartesian Coordinate Configuration. . 3/16/2018 7 Cont.
Robot Anatomy. . 1. Ø Cartesian Coordinate Configuration. . Advantages § § § § 3/16/2018 Linear motion in three dimension Simple kinematic model Rigid structure Higher repeatability and accuracy High lift-carrying capacity as it doesn’t vary at different locations in work volume Easily visualize Can increase work volume easily Inexpensive pneumatic drive can be used for P&P operation 8 Cont.
Robot Anatomy. . 1. Ø Cartesian Coordinate Configuration. . Disadvantages § § Ø requires a large volume to operate in work space is smaller than robot volume unable to reach areas under objects must be covered from dust Applications § § 3/16/2018 Assembly Palletizing and loading-unloading machine tools, Handling Welding 9 Cont.
Robot Anatomy. . 2. Ø Ø Ø Cylindrical Configuration Use vertical column which rotates and a slide that can be moved up or down along the column Arm is attached to slide which can be moved in and out Kinematic designation is RPP Operate within a cylinder work volume Work volume may be restricted at the back side 3/16/2018 10 Cont.
Robot Anatomy. . 2. Cylindrical Configuration. . 3/16/2018 11 Cont.
Robot Anatomy. . 2. Ø Cylindrical Configuration. . Advantages § § Ø Disadvantages § § § Ø Simple kinematic model Rigid structure & high lift-carrying capacity Easily visualize Very powerful when hydraulic drives used Restricted work space Lower repeatability and accuracy Require more sophisticated control Applications 3/16/2018 § § Palletizing, Loading and unloading 12 Material transfer, foundry and forging Cont.
Robot Anatomy. . 3. Ø Ø Ø Polar or Spherical Configuration Earliest machine configuration Has one linear motion and two rotary motions First motion is a base rotation, Second motion correspond to an elbow rotation and Third motion is radial or in-out motion Kinematic designation is RRP Capability to move its arm within a spherical space, hence known as ‘Spherical’ robot Elbow rotation and arm reach limit the design of full spherical motion 3/16/2018 13 Cont.
Robot Anatomy. . 3. Polar or Spherical Configuration. . 3/16/2018 14 Cont.
Robot Anatomy. . 3. Ø Polar or Spherical Configuration. . Advantages § § § Ø Disadvantages § § Ø Covers a large volume Can bend down to pick objects up off the floor Higher reach ability Complex kinematic model Difficult to visualize Applications § § 3/16/2018 Palletizing Handling of heavy loads e. g. casting, forging 15 Cont.
Robot Anatomy. . 4. Ø Ø Ø Jointed Arm Configuration Similar to human arm Consists of two straight components like human forearm and upper arm, mounted o a vertical pedestal Components are connected by two rotary joints corresponding to the shoulder and elbow Kinematic designation is RRR Work volume is spherical 3/16/2018 16 Cont.
Robot Anatomy. . 4. Jointed Arm Configuration. . 3/16/2018 17 Cont.
Robot Anatomy. . 4. Jointed Arm Configuration. . 3/16/2018 18 Cont.
Robot Anatomy. . 4. Ø Jointed Arm Configuration. . Advantages § § Ø Disadvantages § § § Ø Maximum flexibility Cover large space relative to work volume objects up off the floor Suits electric motors Higher reach ability Complex kinematic model Difficult to visualize Structure not rigid at full reach Applications 3/16/2018 § Spot welding, Arc 19 welding Cont.
Robot Anatomy. . 5. Ø Ø Ø SCARA Configuration Most common in assembly robot Arm consists of two horizontal revolute joints at the waist and elbow and a final prismatic joint Can reach at any point within horizontal planar defined by two concentric circles Kinematic designation is RRP Work volume is cylindrical in nature Most assembly operations involve building up assembly by placing parts on top of a partially complete assembly 3/16/2018 20 Cont.
Robot Anatomy. . 5. SCARA Configuration. . 3/16/2018 21 Cont.
Robot Anatomy. . 5. SCARA Configuration. . 3/16/2018 22 Cont.
Robot Anatomy. . 5. Ø SCARA Configuration. . Advantages § § Ø Disadvantages § Ø Floor area is small compare to work area Compliance Rectilinear motion requires complex control of the revolute joints Applications § § § 3/16/2018 Assembly operations Inspection and measurements Transfer or components 23 Cont.
Robot Motions Ø Ø Industrial robots perform productive work To move body, arm and wrist through a series of motions and positions End effector is used to perform a specific task Robot’s movements divided into two categories: 1. 2. Ø Ø Arm and body motions Wrist motions Individual joint motions referred as ‘ DOF ’ Motions are accomplished by powered joints 3/16/2018 24 Cont.
Robot Motions. . Ø Ø Ø Three joints are associated with the action of arm and body Two or three used to actuate the wrist Rigid members are used to connect manipulator joints are called links Input link is closest to the base Output link moves with respect to the input link 3/16/2018 25 Cont.
Robot Motions. . Ø Ø Ø Joints involve relative motions of the adjoining links that may be linear or rotational Linear joints involve a sliding or translational motion which can be achieved by piston, telescopic mechanism May be called ‘Prismatic’ joint Represented as L or P joint Three types of rotating motion: 1. 2. 3. 3/16/2018 Rotational (R) Twisting (T) Revolving (V) 26 Cont.
Robot Motions. . 3/16/2018 27 Cont.
Robot Motions. . Ø Ø Ø Ø Ø Physical configuration of the robot can be described by a joint notation scheme Considering the arm and body first Starting with the joint closest to the base till the joint connected to the wrist Examples are LLL, TRL, TRR, VVR Wrist joints can be included for notation From joint closest to the arm to the mounting plate for the end effector have either T or R type Examples are TRL : TRT, TRR : RT The scheme also provide that robot move on a track or fixed to a platform Example TRL : TRT, L-TRL : TRT 3/16/2018 28 Cont.
Robot Motions. . 3/16/2018 29 Cont.
Robot Motions. . 3/16/2018 30 Cont.
Robot Motions. . 3/16/2018 31 Cont.
Robot Work Volume Ø Ø Ø The space within which the robot can manipulate its wrist end different end effector might be attached to wrist but not counted as part of the robot’s work space Long end effector add to the extension of the robot compared to smaller end effector End effector may not be capable of reaching certain points within the robot’s normal work volume Larger volume costs more but can increase capabilities of robot 3/16/2018 32 Cont.
Robot Work Volume. . Ø It depends upon following physical characteristics: § § § 3/16/2018 Robot’s configuration Size of the body, arm and wrist components Limits of the robot’s joint movements 33 Cont.
Robot Work Volume. . 3/16/2018 34 Cont.
Robot Work Volume. . 3/16/2018 35 Cont.
Degree of Freedom (DOF) Rotate Base of Arm Pivot Base of Arm Bend Elbow Wrist Up and Down Wrist Left and Right Rotate Wrist 3/16/2018 36 Cont.
Degree of Freedom. . Ø Ø Ø It is a joint , a place where it can bend or rotate or translate Can identify by the number of actuators on the arm Few DOF allowed for an application because each degree requires motor, complicated algorithm and cost Each configurations discussed before utilizes three DOF in the arm and the body Three DOF located in the wrist give the end effector all the flexibility 3/16/2018 37 Cont.
Degree of Freedom. . Ø Ø Ø A total 6 DOF is needed to locate a robot’s hand at any point in its work space The arm and body joints move end effector to a desired position within the limits of robot’s size and joint movements Polar, cylindrical and jointed arm configuration consist 3 DOF with the arm and body motions are: 1. Rotational traverse: Rotation of the arm about vertical axis such as left-and-right swivel of the robot arm about a base 3/16/2018 38 Cont.
Degree of Freedom. . Ø 2. Radial traverse: Involve the extension and retraction (in or out movement) of the arm relative to the base 3. Vertical traverse: Provide up-and-down motion of the arm For a Cartesian coordinate robot, 3 DOF are vertical movement (z-axis motion), in-and-out movement (yaxis motion), and right-and-left movement (x-axis motion) which are achieved by slides of the robot arm 3/16/2018 39 Cont.
Degree of Freedom. . 3/16/2018 40 Cont.
Degree of Freedom. . Ø Ø Wrist movement enable the robot to orient the end effector properly to perform a task Provided with up to 3 DOF which are: 1. Wrist Pitch/Bend: Provide up-and-down rotation to the wrist 2. Wrist Yaw: Involve right-and-left rotation of the wrist 3. Wrist Roll/Swivel: Is the rotation of the wrist about the arm axis 3/16/2018 41 Cont.
Degree of Freedom. . 3/16/2018 42 Cont.
Degree of Freedom. . 3/16/2018 43 Cont.
Drive Systems Ø Ø Capacity to move robot’s body, arm and wrist Determine speed of the arm movements, strength of the robot & dynamic performance Type of applications that the robot can accomplish Powered by three types of drive systems: 1. 2. 3. 3/16/2018 Hydraulic Pneumatic Electric 44 Cont.
Drive Systems. . 3/16/2018 45 Cont.
Drive Systems. . Hydraulic Drive 1. Associated with large robot Provide greater speed & strength Add floor space Leakage of oil Provide either rotational or linear motions Applications such as: ü ü ü • • • 3/16/2018 Spray coating robot Heavy part loading robot Material handling robot Translatory motions in cartesian robot Gripper mechanism 46 Cont.
Drive Systems. . 1. Hydraulic Drive. . 3/16/2018 47 Cont.
Drive Systems. . 1. Hydraulic Drive. . 3/16/2018 48 Cont.
Drive Systems. . Pneumatic Drive 2. ü ü ü 3/16/2018 Reserved for smaller robot Limited to “pick-and-place” operations with fast cycles Drift under load as air is compressible Provide either rotational or linear motions Simple and low cost components Used to open and close gripper 49 Cont.
Drive Systems. . 3/16/2018 50 Cont.
Drive Systems. . Electric Drive 3. ü ü 3/16/2018 Rotor, stator, brush and commutator assembly Rotor has got windings of armature and stator has got magnets The brush and the commutator assembly switch the current in armature windings The most commonly used are DC servomotors, AC servomotors and stepper motors 51 Cont.
Drive Systems. . 3. Electric Drive. . Servomotor 3/16/2018 52 Cont.
Drive Systems. . 3. Electric Drive. . 3/16/2018 53 Cont.
Drive Systems. . 3. Electric Drive. . 3/16/2018 54 Cont.
Speed of Motion Ø Ø Ø Speed determines how quickly the robot can accomplish a given work cycle Desirable in production to minimize cycle time Industrial robot speed range up to a maximum of 1. 7 m/s Speed would be measured at wrist Highest speed can be obtained by large robot with fully extended arm 3/16/2018 55 Cont.
Speed of Motion. . Ø Most desirable speed depends on factors: § § § Ø Ø Ø Accuracy Weight of the object Distance Inverse relation between the accuracy and the speed Heavier objects must be handled more slowly Capable of traveling one long distance in less time than a sequence short distances whose sum is equal to the long distance 3/16/2018 56 Cont.
Speed of Motion. . Ø Short distance may not permit for programmed operating speed 3/16/2018 57 Cont.
Load-Carrying Capacity Ø Ø Ø It depends upon size, configuration, construction and drive system Robot arm must be in its weakest position to calculate load-carrying capacity In polar, cylindrical and jointed-arm, the robot arm is at maximum extension Ranges from less than a pond to several thousand pounds Gross weight include the weight of the end effector 3/16/2018 58 Cont.
Control Systems Ø Ø Controlling drive system to properly regulate its motions Four categories according to control systems 1. 2. 3. 4. 3/16/2018 Limited-sequence robot Playback robots with PTP control Playback robots with continuous path control Intelligent robot 59 Cont.
Speed of Response & Stability Ø Ø The speed of response refers to the capability of the robot to move to the next position in a short amount of time Stability is defined as a measure of the oscillations which occur in the arm during movement from one position to the next Good stability exhibit little or no oscillation and poor stability indicated by a large amount of stability Damping control stability but reduces the speed of response 3/16/2018 60 Cont.
Speed of Response & Stability. . 3/16/2018 61 Cont.
Spatial Resolution 3/16/2018 62 Cont.
Spatial Resolution. . Ø Ø Defined as smallest increment of movement into which the robot can divide its work volume Depends on two factors: system’s control resolution and the robot’s mechanical inaccuracies Control resolution is determined by robot’s position control system and its feedback measurement system Ability to divide total range of movement for the particular joint into individual increments that can be addressed in the controller 3/16/2018 63 Cont.
Spatial Resolution. . Ø Ø Joint range depends on the bit storage capacity in the control memory Number of increments for a axis is given by Number of Increments = 2 n Ø Ø Ø Have a control resolution for each joint in case of several DOF Resolution for each joint to be summed vectorially Total control resolution depend on the wrist motions as well as the body and arm motions 3/16/2018 64 Cont.
Spatial Resolution. . Ø Ø Mechanical inaccuracies come from elastic deflection in the structure elements, gear backlash, stretching of pulley cords, leakage of hydraulic fluids and other imperfections in the mechanical system Also affected by load being handled, the speed of arm moving, condition of maintenance of robot 3/16/2018 65 Cont.
Accuracy Ø Ability to position its wrist end at a desired target point within the work volume 3/16/2018 66 Cont.
Accuracy. . Ø Ø Ø Depends on spatial resolution means how closely the robot can define the control increments Lie in the middle between two adjacent control increments One half of the control resolution 3/16/2018 67 Cont.
Accuracy. . Ø Ø Ø Depends on spatial resolution means how closely the robot can define the control increments Lie in the middle between two adjacent control increments One half of the control resolution Same anywhere in work volume It may be changed in work volume due to mechanical inaccuracies 3/16/2018 68 Cont.
Accuracy. . Ø Affected by many factors § § § 3/16/2018 Mechanical inaccuracies Work range Weight 69 Cont.
Repeatability Ø Ø Ability to position its wrist at a point in space that had been taught Accuracy relates to its capacity to be programmed to achieve a given target point Programmed point and target point may be different due to limitations of resolution Repeatability refers to ability to return to the programmed point when commanded to do so 3/16/2018 70 Cont.
Repeatability. . 3/16/2018 71 Cont.
Compliance Ø Ø Ø Displacement of the wrist end in response to a force or a torque exerted against it High compliance means that wrist is displaced a large amount by small force known as ‘Springy’ Reduce the robot precision of movement under load Directional feature Reaction force of the part may cause deflection to the manipulator 3/16/2018 72 Cont.
Thank You 3/16/2018 73