MFGE 404 Computer Integrated Manufacturing CIM A T I L I M U N I V E R S I T Y Manufacturing Engineering Department Lecture 8– Industrial Robots Fall 2005/2006 Dr. Saleh AMAITIK
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 for the performance of a variety of tasks. • The robot, therefore, represents flexible automation and so it fits well in the frame of CIM
Robot Construction • The manipulator of an industrial robot consists of a number of rigid links connected by joints of different types, controlled and monitored by a computer. • The link assembly is connected to the body, which is usually mounted on a base. • To a large extend, the physical construction of a robot resembles a human arm. • A wrist is attached to the arm. • To facilitate gripping or handling, a hand is attached at the end of the wrist, this hand is called an end-effector. • The complete motion of the end-effector is accomplished through a series of motions and positions of the links, joints, and wrist. • Robot construction is concerned with the types and sizes of joints, links and other aspects of the manipulator.
Joints and Links or Robots • A joint of an industrial robot is similar to a joint in the human body: It provides relative motion between two parts of the body. • Each joint, or axis as it is sometimes called, provides the robot with a so-called degree-of-freedom (D.O.F) of motion. • In nearly all cases, only one degree-of-freedom is associated with a joint. • Connected to each joint are two links, an input link and output link. • Links are the rigid components of the robot manipulator. • The purpose of the joint is to provide controlled relative movement between the input link and the output link.
Joints and Links or Robots • Most of robots are mounted on a stationary base on the floor. • The base and its connection to the first joint is Link 0. • Link 0 is the input link of joint 1, the first joint of a series of joints used in the construction of the robot. • The output link of joint 1 is the link 1. • Link 1 is the input lint to joint 2, whose output link is link 2, and so forth.
Classification of Robot Joints • Nearly all industrial robots have mechanical joints that can be classified into one of the five types: • Two types that provide translational motion. • Three types that provide rotary motion • Linear Joint (type L joint) • The relative movement between the input link and the output link is a translational sliding motion, with the axes of the two links being parallel.
Classification of Robot Joints • Orthogonal joint (type O joint) • This is also a translational sliding motion, but the input link and output links are perpendicular to each other during the move.
Classification of Robot Joints • Rotational Joint (type R joint) • This type provides rotational relative motion, with the axis of rotation perpendicular to the axes of the input and output links.
Classification of Robot Joints • Twisting Joint (type T joint) • This joint also involves rotary motion, but the axis of rotation is parallel to the axes of the two links.
Classification of Robot Joints • Revolving Joint (type V joint, V from the “v” in revolving) • In this joint 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
Common Robot Configurations • A robot manipulator can be divided into two sections: • A Body-and-arm assembly. • Wrist assembly. • There are usually three degree-of-freedom associated with the body-and-arm , and either two or three degrees-of-freedom with the wrist. • At the end of the manipulator’s wrist is a device related to the task that must be accomplished by the robot. The device, called an end effector, is usually either: • A gripper for holding a workpart, or • A tool for performing some process. • The body-and-arm of the robot is used to position the end effector, and the robot’s wrist is used to orient the end effector.
Body-and-Arm Configurations • There are five basic configurations commonly available in commercial industrial robots: • Spherical (Polar) Configuration • This configuration consists of a sliding arm (L joint) actuated relative to the body, that can rotate about a vertical axis (T joint) and a horizontal axis (R joint)
Body-and-Arm Configurations • Cylindrical Configuration • This robot configuration consists of a vertical column, relative to which an arm assembly is moved up and down. The arm can be moved in and out relative to the axis of the column. • A T joint to rotate the column about its axis. An L joint is used to move the arm assembly vertically along the column. An O joint is used to achieve radial movement of the arm.
Body-and-Arm Configurations Body-and-Arm Configurations • Cartesian (Rectangular) Configuration • It is composed of three sliding joints, two of which are orthogonal.
Body-and-Arm Configurations Body-and-Arm Configurations Body-and-Arm Configurations • Jointed-arm robot (articulated) Configuration • This robot manipulator has the general configuration of a human arm. The joined arm consists of a vertical column that swivels about the base using a T joint. • At the top of the column is a shoulder joint (R joint), whose about link connects to an elbow joint (R joint)
Body-and-Arm Configurations • SCARA (Selective Complains Assembly Robot Arm) • This configuration is similar to the jointed robot except that the shoulder and elbow rotational axes are vertical, which means that the arm is very rigid in the vertical direction, but complaint in the horizontal direction.
Wrist Configurations • The robot’s wrist is used to establish the orientation of the end effector. Robot wrists usually consists of two or three degrees-of-freedom. The three joints are defined as: • Roll, using a T joint to accomplish rotation about the robot’s arm axis. • Pitch, which involves up-and-down rotation, typically a R joint. • Yaw, which involves right-and-left rotation, also accomplished by means of an R-Joint. • A two D-O-F wrist typically includes only roll and pitch joints (T and R joints)
Joint Notation System • The letter symbols for the five joint types (L, O, R, T, and V) can be used to define a joint notation system for the robot manipulator. • In this notation system, the manipulator is described by the joints that make up the body-and-arm assembly, followed by the joint symbols that make up the wrist. • For example, the notation TLR:TR represents a five degree-of-freedom manipulator whose body-and-arm is made up of : • A twisting joint (Joint 1 = T) • A linear joint (joint 2 = L) • A rotational joint (joint 3 = R) • The wrist consists of two joints: • A twisting joint (joint 4 = T) • A rotational joint (joint 5 = R) • A colon separates the bod-and-arm notation from the wrist notation.
Joint Notation System - Example • Designate the robot configurations shown below, using the joint notation scheme. • Solution • This configuration has two linear joints, Hence, it is designated LL. • This configuration has three rotational joints, Hence, it is designated RRR. • This configuration has one twsiting joint and one linear joint. This is indicated by TL
Joint Notation System - Example • The robots shown below are equipped with a wrist that has twisting, rotary, and twisting joints in sequence from the arm to the end-effector. Give the designation for the complete configuration of each robot • For the robots shown above, the complete designation is as follows: • LRL:TRT (b) RRL:TRT (c) TRL:TRT (d) LVL:TRT
Work Volume • The work volume (work envelope) of the manipulator is defined as the envelope or space within which the robot can manipulate the end of its wrist. • Work volume is determined by: • the number and types of joints in the manipulator (body-and-arm and wrist), • the ranges of the various joints, and • the physical sizes of the links • The shape of the work volume depends largely on the robot’s configuration
Work Volume • A Cartesian robot has a rectangular work volume
Work Volume • A cylindrical robot has a cylindrical work volume
Work Volume • A spherical robot tends to have a sphere as its work volume
Joint Drive System • A robot joints are actuated using any of three possible types of drive systems: • Electric drive. • Hydraulic drive. • Pneumatic drive • Electric drive systems use electric motors as joint actuators. • Hydraulic and pneumatic drive systems use devices such as linear pistons and rotary vane actuators to accomplish the motion of the joint. • Pneumatic drive is typically limited to smaller robots used in simple material transfer applications. • Electric drive and hydraulic drive are used on more-sophisticated industrial robots. • Electric drive robots are relatively accurate compared with hydraulically powered robots. By contrast, the advantages of hydraulic drive include greater speed and strength.
Robot Control Systems • The actuations of the individual joints must be controlled in a coordinated fashion for the manipulator to perform a desired motion cycle. • Robot controllers can be classified into four categories: • Limited sequence control. • Point-to-point control. • Continuous path control. • Intelligent control. • Limited sequence control uses mechanical stops to provide the extreme ranges of motion and when motion command is used, the joint is driven until the mechanical stop is reached. This technique is no longer used.
Robot Control Systems • Point-to-point involves the specification of the starting point and end point (and often intermediate points) of the robot motion requiring a control system which renders some feedback at those points. • This technique is used for spot welding, pick-and-place operations and so on. • Continuous Path Control requires the robot end effector to follow a stated path from the starting point to the end point. • This technique is required in many applications that require the actual tracing of a contour, for instance, in arc welding or spray painting. • The continuous path robots usually follow a series of closely spaced points on a path and these points are defined by the control unit rather than the programmer. In many cases, the paths between points are straight lines
Robot Control Systems • Intelligent Control An intelligent robot is one that exhibits behavior that makes it seem intelligent. Some of the characteristics that make a robot appear intelligent include the capacity to : • Interact with its environment. • Make decisions when things go wrong during the work cycle. • Make computations during the motion cycle. • Respond to advanced sensor inputs such as machine vision.
End Effectors • The end effector enables the robot to accomplish a specific task. Because of the wide variety of tasks performed by industrial robots, the end effector must usually be custom-engineered and fabricated for each different application. • Two categories of end effectors are • Grippers. • Tools. • Tools are used in applications where the robot must perform some processing operation on the part. Examples of the tools are: • Spot welding gun. • Arc welding tool. • Spray painting gun. • Rotating spindle for drilling, grinding, and so forth. • Assembly tool (e.g. automatic screw driver) • Heating torch.
End Effectors • Grippers are end effectors used to grasp and manipulate objects during the work cycle
Industrial Robot Applications • The general characteristics of industrial work situations that tend to promote the substitution of robots for human labor are the following: • Hazardous work environment for human. • Repetitive work cycle. • Difficult handling for human. • Multishift operation. • Infrequent changeover • Part position and orientation are established in the work cell
Industrial Robot Applications • Robots are being used in a wide field of applications in industry. Most of the current applications of industrial robots are in manufacturing. • The applications can usually classified into one of the following categories: • Material handling applications • Material transfer. • Machine loading and/or unloading. • Processing operations • Spot welding • Continuous arc welding • Spray coating • Other processing applications • Assembly