Automation and Robotics - Industrial Robotics Notes: GO

INDUSTRIAL ROBOTICS

UNIT I INTRODUCTION

  • Definition of a Robot:

    • A machine that looks and acts like a human being.

    • An efficient but insensitive person

    • An automatic apparatus.

    • Something guided by automatic controls (e.g., remote control).

    • A computer whose main function is to produce motion.

  • Law’s of Robotics (Asimov):

    • Law 1: A robot may not injure a human being or, through inaction, allow a human being to come to harm.

    • Law 2: A robot must obey orders given to it by human beings, except where such orders would conflict with a higher order law.

    • Law 3: A robot must protect its own existence as long as such protection does not conflict with a higher order law.

  • Robot Anatomy:

    • Robot manipulator consists of two sections:

      • Body-and-arm – for positioning of objects in the robot's work volume

      • Wrist assembly – for orientation of objects

  • Wrist Assembly:

    • Attached to end-of-arm.

    • End effector is attached to wrist assembly.

    • Function of wrist assembly is to orient end effector.

    • Body-and-arm determines global position of end effector

    • Two or three degrees of freedom:

      • Roll

      • Pitch

      • Yaw

  • Robot Configurations:

    • Rectangular (or) Cartesian

    • Cylindrical (or) Post-type

    • Spherical (or) Polar

    • SCARA (Selective Compliance Assembly Robot Arm)

  • Cartesian/Rectangular Manipulator:

    • Straight, or linear motion along three axes:

      • In and out (x)

      • Back and forth (y)

      • Up and down (z)

  • Cylindrical Manipulator:

    • Rotation about the base or shoulder (θ\theta).

    • Up and down (z)

    • In and out (R)

  • Polar or Spherical Manipulator:

    • Rotation about the base.

    • Rotation about an axis in the vertical plane to raise and lower it.

    • Reaches in and out.

  • SCARA Robot:

    • Selective Compliance Assembly Robot Arm.

    • The same work area as a cylindrical-coordinates robot.

    • The reach axis includes a rotational joint in a plane parallel to the floor.

  • Types of Robot Drives:

    • Electric:

      • All robots use electricity as the primary source of energy.

      • Electricity turns the pumps that provide hydraulic and pneumatic pressure.

      • It also powers the robot controller and all the electronic components and peripheral devices.

      • In all electric robots, the drive actuators, as well as the controller, are electrically powered.

      • Because electric robots do not require a hydraulic power unit, they conserve floor space and decrease factory noise.

      • No energy conversion is required.

    • Pneumatic:

      • These are generally found in relatively low-cost manipulators with low load carrying capacity.

      • Pneumatic drives have been used for many years for powering simple stop-to-stop motions.

      • It is inherently light weight, particularly when operating pressures are moderate.

    • Hydraulic:

      • Are either linear position actuators or a rotary vane configuration.

      • Hydraulic actuators provide a large amount of power for a given actuator.

      • The high power-to-weight ratio makes the hydraulic actuator an attractive choice for moving moderate to high loads at reasonable speeds and moderate noise level.

      • Hydraulic motors usually provide a more efficient way of energy to achieve a better performance, but they are expensive and generally less accurate.

  • Basic Robot Motions:

    • A robot manipulator can make four types of motion in travelling from one point to another in the workplace:

      • Slew motion: simplest type of motion. Robot is commanded to travel from one point to another at default speed.

      • Joint-interpolated motion: requires the robot controller to calculate the time it will take each joint to reach its destination at the commanded speed.

      • Straight-line interpolation motion: requires the end of the end effector to travel along a straight path determine in rectangular coordinates.

        • Useful in applications such as arc welding, inserting pins into holes, or laying material along a straight path.

      • Circular interpolation motion: requires the robot controller to define the points of a circle in the workplace based on a minimum of three specified positions.

        • Circular interpolation produces a linear approximation of the circle and is more readily available using a programming language rather than manual or teach pendant techniques.

  • Point to Point Control:

    • These robots are most common and can move from one specified point to another but cannot stop at arbitrary points not previously designated.

    • All Axes start and end simultaneously

    • All Geometry is computed for targets and relevant Joint changes which are then forced to be followed during program execution

    • Only the end points are programmed, the path used to connect the end points are computed by the controller

    • User can control velocity, and may permit linear or piece wise linear motion

    • Feedback control is used during motion to ascertain that individual joints have achieved desired location

    • Often used hydraulic drives, recent trend towards servomotors

    • Loads up to 500lb and large reach Applications

    • Pick and place type operations

    • Palletizing

    • Machine loading

  • Continuous Path Control:

    • It is an extension of the point-to-point method. This involves the utilization of more points and its path can be arc, a circle, or a straight line.

    • Because of the large number of points, the robot is capable of producing smooth movements that give the appearance of continuous or contour movement.

    • In addition to the control over the endpoints, the path taken by the end effector can be controlled

    • Path is controlled by manipulating the joints throughout the entire motion, via closed loop control.

    • Applications:

      • Spray painting

      • Polishing

      • Grinding

      • Arc welding

  • Controlled Path:

    • It is a specialized control method that is a part of general category of a point-to-point robot but with more precise control.

    • The controlled path robot ensures that the robot will describe the right segment between two taught points.

    • Controlled-path is a calculated method and is desired when the manipulator must move in the perfect path motion.

UNIT II COMPONENTS & OPERATIONS

  • Basic Control System Concepts:

    • Open-Loop Control Systems

    • Closed-Loop Control Systems

    • Multivariable Control Systems

  • Open-Loop Control Systems:

    • Open-Loop Control Systems utilize a controller or control actuator to obtain the desired response.

  • Closed-Loop Control Systems:

    • Closed-Loop Control Systems utilizes feedback to compare the actual output to the desired output response

  • Manipulators:

    • Manipulator consists of joints and links

      • Joints provide relative motion

      • Links are rigid members between joints

      • Various joint types: linear and rotary

      • Each joint provides a “degree-of-freedom”

      • Most robots possess five or six degrees-of- freedom

  • Degrees of Freedom:

    • Degree of Freedom is the number of independent relative motion in the form of translation and rotation

    • The body in space has got the maximum of 6 degrees of motion(3 translatory & 3 rotary motions)

    • Each Translatory has 1 DOF and each Rotary has 1 DOF

  • Kinematics:

    • It is the branch of dynamics which deals with the relative motion existing between members.

  • Forward Kinematics (Angles to Position):

    • What you are given:

      • The length of each link

      • The angle of each joint

    • What you can find:

      • The position of any point (i.e. it’s (x, y, z) coordinates

  • Inverse Kinematics (Position to Angles):

    • What you are given:

      • The length of each link

      • The angle of each joint

    • What you can find:

      • The angles of each joint needed to obtain that position

      • Inverse kinematics of 2 link manipulator Squaring on both sides and adding

  • Types of Robot End Effectors:

    • Inflatable bladder

    • Two-finger clamp

    • Vaccum cups

    • Three-fingers clamp

    • Magnet head

    • Tubing pickup device

  • End-Of-Arm-Tooling:

    • This general class of devices is also called end-of-arm tooling (EOAT).

    • Robot end-of-arm tooling is not limited to various kinds of gripping devices.

    • Grippers not available by default in general-purpose robots

    • In some situations, a robot must change its gripper during its task. If so, the robot's wrist must be fitted with a quick-disconnect device.

  • Grippers:

    • Grippers are end effectors used to grasp and manipulate objects.

    • Just like a hand, a gripper enables holding, tightening, handling and releasing of an object.

    • A gripper can be attached to a robot or it can be part of a fixed automation system

  • Gripper Actuation:

    • Manual: Actuated by hand crank, wheel, levers, or other manual or mechanical means.

    • Electric: Grippers fingers or jaws actuated by electric motor, solenoid, etc.

    • Pneumatic: Gripper is actuated by compressed air acting on a cylinder or vanes.

    • Hydraulic: Gripper is actuated by hydraulic fluid acting on a cylinder or vanes.

  • Requirements for an Effective Gripper:

    • Parts or items must be grasped and held without damage

    • Parts must be positioned firmly or rigidly while being operated on.

    • Hands or grippers must accommodate parts of differing sizes or even of varying sizes

    • Self-aligning jaws are required to ensure that the load stays centered in the jaws

    • Grippers or end effectors must not damage the part being handled.

    • Jaws or grippers must make contact at a minimum of three points to ensure that the part doesn’t rotate while being positioned.