UNIT I FUNDAMENTALS OF ROBOT Part A 1. Define Robot. An industrial robot is a re-programmable, multifunctional manipulator designed to move materials, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks.(defined by Robotics Association of America(RIA) ). 2. What is Robot Anatomy? Study of skeleton of Robot (or) physical part. Mechanical structure of a robot=skeleton of human body Study of structure of a robot=physical structure of the manipulator structure The mechanical structure of manipulator that consists of rigid bodies(links) connected by means of joints, is segmented into an arm that ensures mobility and reachability, a wrist that confers orientation and an end effector performs the required task 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 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 3. Mention the different Types of Manipulator joints Translational motion Linear joint (type L) Orthogonal joint (type O) Rotary motion Rotational joint (type R) Twisting joint (type T) Revolving joint (type V) Linear joint (type L)
Orthogonal joint (type O) Rotational joint (type R) 4. Mention the Degree of freedom in Robot. Joint type Revolute (R) 1 Prismatic (P) 1 Screw (H) 1 Cylindrical (C) 2 Spherical (S) 3 5. What is Work Envelope? DOF Work Volume is define as the space within which the robot can manipulate its wrist end. The work volume determined by the following physical characteristics of the robot. 6. Discuss the Specifications of Robot. Joint Notations, Uses the joint symbols (P, R, T, V) to designate joint types used to construct robot manipulator. P Polar(Linear & Orthogonal) R - Rotational T - Transitional V - Vertical insertion Separates body-and-arm assembly from wrist assembly using a colon (:) Example: TLR : TR 6. What is End Effectors?
Device attached to the robot s wrist to perform a specific task. Last link on a robot Interact with objects 7. What is repeatability of robot? Repeatability refers to robot s ability to return to the programmed point when it is commanded to do so. 8. What is meant by pitch, yaw and roll? Pitch is rotation around the X axis, yaw is around the Y axis, and roll is around the Z axis. Yaw is side to side swinging around an axis. Pitch is up and down movement about an axis and roll is rotatory motion about an axis. 9. What are the four basic robot configurations available commercially? Cartesian coordinate system Cylindrical coordinate system Polar or spherical coordinate system Revolute coordinate system 10. Explain the types of rotary joint notations Rotational joint (type R) Twisting joint (type T) Revolving joint (type V) PART B 1. Explain the various Co-ordinate Systems or Configurations in detail Five common body-and-arm configurations for industrial robots: 1. Polar coordinate body-and-arm assembly 2. Cylindrical body-and-arm assembly 3. Cartesian coordinate body-and-arm assembly 4. Jointed-arm body-and-arm assembly 5. Selective Compliance Assembly Robot Arm (SCARA) Function of body-and-arm assembly is to position an end effector (e.g., gripper, tool) in space Polar coordinate Notation TRL:
Consists of a sliding arm (L joint) actuated relative to the body, which can rotate about both a vertical axis (T joint) and horizontal axis (R joint) Cartesian coordinate Notation LOO: Consists of three sliding joints, two of which are orthogonal Other names include rectilinear robot and x-y-z robot Jointed Arm Notation TRR: General configuration of a human arm SCARA Notation VRO SCARA stands for Selectively Compliant Assembly Robot Arm
Similar to jointed-arm robot except that vertical axes are used for shoulder and elbow joints to be compliant in horizontal direction for vertical insertion tasks 2.Describe the Types of Robots and Classification of Robot Pick and place Moves items between points. Continuous path control Moves along a programmed path. Sensory Employs sensors for feedback. Pick and place Moves items from one point to another Does not need to follow a specific path between points Uses include loading and unloading machines, placing components on circuit boards, and moving parts off conveyor belts. Continuous path control Moves along a specific path Uses include welding, cutting, machining parts. Uses sensors for feedback.
Closed-loop robots use sensors in conjunction with actuators to gain higher accuracy (servo motors). Uses include mobile robotics, telepresence, search and rescue, pick and place with machine vision. Classification of Robot The following is the classification of Robots according to the Robotics Institute of America Variable-Sequence Robot : A device that performs the successive stages of a task according to a predetermined method easy to modify Playback Robot :A human operator performs the task manually by leading the Robot Numerical Control Robot : The operator supplies the movement program rather than teaching it the task manually. Intelligent Robot : A robot with the means to understand its environment and the ability to successfully complete a task despite changes to the environment. 3. Explain Wrist assembly and parts of Robot Pitch, Yaw, Roll, Wrist assembly is 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 Parts and Functions A Robot is a system, consists of the following elements, which are integrated to form a whole: Manipulator : This is the main body of the Robot and consists of links, joints and structural elements of the Robot.
End Effectors : This is the part that generally handles objects, makes connection to other machines, or performs the required tasks. It can vary in size and complexity from a endeffector on the space shuttle to a small gripper. Acutators : Actuators are the muscles of the manipulators. Common types of actuators are servomotors, stepper motors, pneumatic cylinders etc. Sensors : Sensors are used to collect information about the internal state of the robot or to communicate with the outside environment. Robots are often equipped with external sensory devices such as a vision system, touch and tactile sensors etc which help to communicate with the environment Controller : The controller receives data from the computer, controls the motions of the actuator and coordinates these motions with the sensory feedback information. 4. Explain the Applications of Robots in detail. 1. Material handling applications Material transfer pick-and-place, palletizing Machine loading and/or unloading 2. Processing operations Spot welding and continuous arc welding Spray coating Other water jet cutting, laser cutting, grinding 3. Assembly and inspection IDEAL TASKS Tasks which are: Dangerous Space exploration Chemical spill cleanup Disarming bombs Disaster cleanup Boring and/or repetitive Welding car frames Part pick and place Manufacturing parts. High precision or high speed Electronics testing Surgery Precision machining. 5.Explain the Broad Classification of End Effectors The two types of end effectors are Grippers to grasp and manipulate objects (e.g., parts) during work cycle
Tools to perform a process, e.g., spot welding, spray painting Used to grasp, hold, and release the objects that to be transported, like loading, unloading, picking parts from moving conveyor, etc. Types of End Effectors 1. Based on drive used for gripper 1.1 Mechanical Gripper 1.2 Pneumatic gripper 1.3 Hydraulic Gripper 1.4 Electric Gripper 2. Based on the magnetic force 2.1 Electromagnetic gripper 2.2 Permanent Magnetic Griper 3. Based on the vacuum force 3.1 Vacuum Cup Gripper 3.2 Venturi Jet gripper 1.1 Mechanical Grippers A Mechanical gripper is an end effector that uses mechanical finger actuated by some mechanism to grasp the part. There are Single Gripper One grasping device is mounted on the robot s wrist Like the Robot reach the production machine twice, once to unload the finished part from the machine, the second time to load the next part into the machine.
Dual Gripper A double gripper has two separate objects/fingers actuating together to perform the grasp Sometimes, these two gripping devices can also be actuated independently Internal Grippers Grips/fits the internal surface of the object Finger pads mounted on outside of the fingers External Grippers
Grips the external surface of the object with closed finger pads pressed against the parts. In this classification, the grippers can actuate the opening and closing of the fingers by one of the following motions Pivoting Mechanism -The fingers rotate about fixeid pivot points of the gripper to open and close Linkage actuation. The fingers open and close by moving in parallel to each other Selection and Design Considerations. Magnetic Grippers The magnetic grippers are suitable for ferrous materials. The magnetic grippers are of two types namely Electromagnetic gripper and Permanent gripper. Electromagnetic grippers Electromagnetic grippers are easier to control. It requires a source of dc power and an appropriate controller unit. Part must be released at the end of the handling cycle easier by means of electromagnetic gripper. When the part is to be released, the controller unit reverses the polarity at a reduced power level before switching off the electro magnet. This procedure cancels the residual magnetism in the work piece and ensures the positive release of the part. Permanent Magnetic gripper Permanent Magnets have the advantages of not requiring an external source of power to operate the magnet. When the part is to be removed at the end of the handling cycle, a stripper device is used to remove the part from the magnet.
Permanent magnets are often considered for handling hazardous environments requiring explosion proof apparatus. No electrical circuit needed to operate the magnet reduces the danger of sparks which might cause ignition in such environment. Advantages Suitable for h materials. Single surface gripping is possible. Invariant with respect totype of object. Ability to handle metal parts with hole. Disadvantages More than one sheet will be lifted by the magnet from the stack. Side slip Residual stress present in the work piece may cause problems
Vacuum Gripper Vacuum cup grippers Vacuum grippers are also called suction cups. The usual requirement of the object to be lifted are that they are flat,smooth and clean. It consists of a flexible and a hard rubber cup. The cups are round in shape and made up of elastic material. The cups creates a negative pressure and necessary lifting force. The vacuum is created between cup and object In this vacuum cup grippers, the vacuum can be created by vacuum pump. It creates relatively high vacuum. The lift capacity of the suction cups depends on the effective area of the cup and the negative pressure between the cup and the object. The relationship can be represented by the equation Where F P A F = P.A = Force or lift capacity =the Negative Pressure = the total effective area of suction cups used create the vacuum
Venturi jet vacuum grippers It is a simple device. It can be driven by means of shop air pressure. It initial cost is less than that of vacuum cup. It is relatively reliable because of simplicity Applications of Vacuum grippers Vacuum cup grippers used for handling fragile parts. Advantages The gripper is light in weight Pressure is distributed entirely in some area Disadvantages Create vacuum in the cup takes time
It is not suitable for component having holes as well as curved surface. Adhesive grippers Gripper in which an adhesive substance performs action is called Adhesive grippers the grasping It is used to handle fabrics and other light weight materials. One of important disadvantage of Vacuum grippers is that the adhesive substance loses its tackiness on repeated usage. To overcome the above disadvantage, the adhesive material is loaded in the form of continuous ribbon in the feeding mechanism that is attached to the robot wrist. The feeding mechanism is similar to type writer mechanism. Pneumatic grippers In a pneumatic gripper, power of piston cylinder arrangement is used to create a gripping force. Pneumatic grippers can be employed for handling flat faced objects like plates by creating vacuum in the cup shaped gripper.
Design Considerations Design can varies as several fingers, Joints, & Operations Change in size of part between operations Surface of part Inherent size Variation Grasp method Effect on the part Scratch, Distortion, compression, etc.., Grasping force Weight, Center of gravity, speed, acceleration, Friction, etc.., 6. Explain the control loop, Intelligence and Robot control. Control loop in robots Intelligence and Robot control Artificial Intelligence Robot control They usually operate in computer- They operate in real physical world
stimulated worlds. The input to an AI program is in symbols and rules. Inputs to robots is analog signal in the form of speech waveform or images They need general purpose computers to operate on. They need special hardware with sensors and effectors.