Robotics

What is Robotics: 

What is Robotics Robotics is the study of the design, construction and use of robots. Czech word robota, meaning forced work or compulsory service

Definition of a Robot: 

Definition of a Robot A reprogrammable, multifunctional manipulator designed to move material, parts, tools, or specialized devices through various programmed motions for the performance of a variety of tasks“ or A machine in the form of human being that performs the mechanical functions of a human being but lacks sensitivity

Asimov’s Laws of Robotics: 

Asimov’s Laws of Robotics A robot may not injure a human being, or, through inaction, allow a human being to come to harm A robot must obey orders given it by human beings, except where such orders would conflict with the First Law A robot must protect its own existence as long as such protection does not conflict with the First or Second Law

Robotic Motion: 

Robotic Motion As per LERT classification system says four basic motions are L inear, E xtensional, R otational and T wisting Linear motion – Rack and pinion Extension motion – Telescoping motion Rotational motion – move/rotate about other than its centre axis Twisting motion – move/rotate about its own centre axis

Degrees of freedom, DOF: 

Degrees of freedom, DOF Each joint, moveable axis, on the arm is considered a degree of freedom. (DOF) the number of different ways in which a robot arm can move. How many DOF are needed in order too achieve an arbitrary position? Roll, Pitch, Yaw Pose: position and orientation taken together A body has at most 6 degrees of freedoms: 3 space coordinates (translation) and 3 rotary angles (orientation)

Redundancy: 

Redundancy Robots with more than 6 DOF or with parallel joints are redundant, which means that they can achieve the same pose in more than one way Singularity- pose that can be reached in different ways sometimes creates problems

Singularities: 

Singularities At a singularity the end-effector loses one or more degrees of twist freedom (instantaneously, the end-effector cannot move in these directions) Serial robots with less than six independent joints are always singular in the sense that they can never span a six-dimensional twist space This is often called an architectural singularity. A singularity is usually not an isolated point in the workspace of the robot, but a sub-manifold

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 Robot Anatomy Base End Effector Arm Wrist

Robot Anatomy: 

Robot Anatomy Manipulator constructed of a serious of joints and links Joints provide relative motion between the input link and the output link Links are rigid members between joints Each joint provides a “degree-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 Base Link0 Joint1 Link2 Link3 Joint3 End of Arm Link1 Joint2

Wrist Configurations: 

Wrist Configurations Wrist assembly is attached to end-of-arm End effector is attached to wrist assembly Function of wrist assembly is to orient end effector It may exhibit compliance, overload protection & strength Two or three degrees of freedom: Roll Pitch Yaw Notation :RRT

The Robot System: 

The Robot System A robot system has six major components Robot arm (or) Manipulator End Effector Power source Controller Sensor Actuator

Manipulator Joints: 

Manipulator Joints Translational motion Linear joint (type L) - Prismatic Orthogonal joint (type O) Rotary motion Rotational joint (type R) Twisting joint (type T) Revolving joint (type V)

Joint Notation Scheme: 

Joint Notation Scheme Uses the joint symbols (L, O, R, T, V) to designate joint types used to construct robot manipulator Separates body-and-arm assembly from wrist assembly using a colon (:) Example: TLR : TR Common body-and-arm configurations …

Work envelope: 

Work envelope The region of space a robot can reach

Working Envelope : 

Working Envelope

Work cell: 

Work cell Programming of Robots/Manipulators are typically only a minor part of an automated process Work cell describes a local collection of equipments which includes one (or) more manipulators, conveyor system, Part feeders, & fixtures, etc.., Sometimes workcell may be interconnected with factory network. So computers can control the overall flow.

Work Space: 

Work Space The work space in which the endpoint of robot arm is capable of operating (or) searchability of robot arm The shape and size of the workspace depends on the arm configuration, structure, DOF, size of links and design of joints

Work Volume: 

Work Volume The Volume of the space swept by the Robot arm is called work volume This may be more or less than the arm end point work space

Dexterous and Reachable workspace: 

Dexterous and Reachable workspace Dexterous workspace is the volume of space which the robot can reach with all orientations. That is, at each point in the dexterous workspace, the end-effector can be arbitrarily oriented The Reachable workspace is the volume of space which the robot can reach in at least one orientation In the dexterous workspace the robot has complete manipulative capability. However, in the Reachable workspace, the manipulator's operational capacity is limited because the terminal device can only be placed in a restricted range of orientations In other words, the dexterous workspace is a subset of the Reachable workspace

Polar Coordinate Body-and-Arm Assembly: 

Polar Coordinate Body-and-Arm Assembly 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) Spherical Work envelop

Cylindrical Body-and-Arm Assembly: 

Cylindrical Body-and-Arm Assembly Notation TLO: Consists of a vertical column, relative to which an arm assembly is moved up or down The arm can be moved in or out relative to the column

Cartesian Coordinate Body-and-Arm Assembly: 

Cartesian Coordinate Body-and-Arm Assembly Notation LOO: Consists of three sliding joints, two of which are orthogonal Other names include rectilinear robot and x-y-z robot

Jointed-Arm Robot: 

Jointed-Arm Robot Notation TRR:

SCARA Robot: 

SCARA Robot 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

Example: 

Example Sketch following manipulator configurations (a) TRT:R, (b) TVR:TR, (c) RR:T. Solution :

Robot Control Systems: 

Robot Control Systems Limited sequence control – pick-and-place operations using mechanical stops to set positions Playback with point-to-point control – records work cycle as a sequence of points, then plays back the sequence during program execution Playback with continuous path control – greater memory capacity and/or interpolation capability to execute paths (in addition to points) Intelligent control – exhibits behavior that makes it seem intelligent, e.g., responds to sensor inputs, makes decisions, communicates with humans

Robot Control System: 

Robot Control System Joint 1 Joint 2 Joint 3 Joint 4 Joint 5 Joint 6 Controller & Program Cell Supervisor Sensors Level 0 Level 1 Level 2

Slide 28: 

Consider typical robots… What could a robot do without “end effectors”?

End Effectors: 

End Effectors The special tooling attached to the end of the wrist arm for a robot that enables it to perform a specific task

Consideration of End Effector Design: 

Consideration of End Effector Design 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..,

Classification of End effector: 

Classification of End effector Two types: Grippers – to grasp and manipulate objects (e.g., parts) during work cycle Tools – to perform a process, e.g., spot welding, spray painting

Grippers and Tools: 

Grippers and Tools

Grippers: 

Grippers Used to grasp, hold, and release the objects that to be transported, like loading, unloading, picking parts from moving conveyor, etc.., Grippers

Mechanical Grippers: 

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 Dual Gripper Multi Gripper Internal Gripper External Gripper, etc..,

Single Gripper: 

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: 

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 Grips the external surface of the object with closed finger Finger pads pressed against the parts Grips/fits the internal surface of the object Finger pads mounted on outside of the fingers

Interchangeable finger: 

Interchangeable finger Function of the gripper mechanism - Power input into the grasping action of the fingers against the part Power Input – Pneumatic, Electric, Mechanical, or Hydraulic Two ways of constraining the part in the gripper The first method is designing the contacting surfaces of the fingers to be in the approximate shape of the part geometry The second way of holding the part is by friction between the fingers and the work part

Common Fingers of end effector: 

Common Fingers of end effector Parallel Finger Angular Finger

Types of Gripper Mechanisms: 

Types of Gripper Mechanisms 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 fixed pivot points of the gripper to open and close

Linkage actuation: 

Linkage actuation The fingers open and close by moving in parallel to each other

Gear-and-rack actuation: 

Gear-and-rack actuation Rack Finger

Cam-actuated Gripper: 

Cam-actuated Gripper The movement of the cam in one direction would force the gripper to open, while movement of the cam in the opposite direction would force the gripper to open, while movement of the cam in the opposite direction would cause the spring to force the gripper to close The advantage of this arrangement is that the spring action would accommodate different sized parts – Raw material & Finished Part

Screw – Type Gripper Actuation: 

Screw – Type Gripper Actuation The screw is turned by a motor, usually accompanied by a speed reduction mechanism When the screw is rotated in one direction, this causes a threaded block to be translated in one direction When the screw rotates in opposite direction, the threaded block also moves in the opposite direction The threaded block is, in turn, connected to the gripper fingers is to cause the corresponding opening and closing action

Rope & Pulley Grippers: 

Rope & Pulley Grippers A motor attached to the pulley makes the winding and unwinding motion of rope in turn it set gripper action into motion via connecting link

Gripper with Rotary Actuator: 

Gripper with Rotary Actuator

Magnetic Gripper: 

Magnetic Gripper Grippers in which, magnetic substance performs the grasping action is called Magnetic Grippers – Ferrous material Advantages Pickup times are very fast. Variations in part size can be tolerated The gripper does not have to be designed for one particular work part They have the ability to handle metal parts with holes (not possible with vacuum grippers) They require only one surface for gripping

Electromagnetic Grippers: 

Electromagnetic Grippers Electromagnetic grippers are easier to control, but require a source of dc power and an appropriate controller unit As with any other robotic-gripping device, the part must be released at the end of the handling cycle This is easier to accomplish with an electromagnet than with a permanent magnet When the part is to be released, the controller unit reverses the polarity at a reduced power level before switching off the electromagnet This procedure acts to cancel the residual magnetism in the work piece and ensures a positive release of the part

Permanent magnetic Grippers: 

Permanent magnetic Grippers Permanent magnets have the advantage of not requiring an external power source to operate the magnet The device that accomplishes a stripper (or) stripping device to mechanically detach the part from the magnet This Grippers handling tasks in hazardous environments - explosion proof, danger of sparks, ignition environment

Vacuum Gripper: 

Vacuum Gripper Vacuum Gripper has two components Vacuum cups, also called suction cups Vacuum system Number of grippers depends the size and weight of the Object Vacuum Gripper is used for handling of fragile parts, too thin to be handled, etc..,

Vacuum Cups: 

Vacuum Cups Vacuum Cups made of a elastic material - Flexible rubber and hard rubber Round in shape The cup creates negative pressure, which in turn, create the vacuum, that creates the necessary lifting power Vacuum is created between the cup and object The Vacuum can be generated by a vacuum pump (or) Venturi system An example of a vacuum cup used to lift flat glass Object

Adhesive Gripper: 

Adhesive Gripper This Adhesive Gripper performs the grasping action to handle fabrics , lightweight materials, flexible material The requirements Adhesive Gripper to be handled are that they must be gripped on one side only(other forms of grasping such as a vacuum or magnet are not appropriate) Main limitations of an adhesive gripper is that the adhesive substance loses its tackiness on repeated usage The adhesive material is loaded in the form of a continuous ribbon into a feeding mechanism that is attached to the robot wrist – Typewriter ribbon mechanism

Laser Cutting Robots – Tools: 

Laser Cutting Robots – Tools

Robotic Arc-Welding Cell: 

Robotic Arc-Welding Cell Robot performs flux-cored arc welding (FCAW) operation at one workstation while fitter changes parts at the other workstation

Characteristics of End Effector: 

Characteristics of End Effector Less weight Ability to grasp and release the part as required by manufacturing process

Robot Specification – Physical: 

Robot Specification – Physical Mechanical Robot configuration Number of axes of movement Floor space required for mounting Weight Physical dimensions Physical details Power Power drive system Power/services requirements Control Programming method Type of control system External sensors supported Program backing storage device Memory size

Robot Specification – Performance: 

Robot Specification – Performance Accuracy – Ability of a robot to be in Position. Repeatability – Ability to do the same whenever it is commanded Reliability – Expected % of time to operate with out delay Resolution – Smallest increment of motion by the controller Spatial Resolution – Ability of Robot to breakdown its movements into increments Precision – Smallest increment can be controlled Quality – Precision Accuracy Reach – Horizontal distance from centre to end of wrist Payload – Weight can carry, & remain with its specifications

Joint Drive Systems: 

Joint Drive Systems Electric Uses electric motors to actuate individual joints Preferred drive system in today's robots Hydraulic Uses hydraulic pistons and rotary vane actuators Noted for their high power and lift capacity Pneumatic Typically limited to smaller robots and simple material transfer applications

Industrial Robot Applications: 

Industrial Robot Applications Material handling applications Material transfer – pick-and-place, palletizing Machine loading and/or unloading Processing operations Welding Spray coating Cutting and grinding Assembly and inspection

Robot Programming: 

Robot Programming Leadthrough programming Work cycle is taught to robot by moving the manipulator through the required motion cycle and simultaneously entering the program into controller memory for later playback Robot programming languages Textual programming language to enter commands into robot controller Simulation and off-line programming Program is prepared at a remote computer terminal and downloaded to robot controller for execution without need for leadthrough methods

Leadthrough Programming: 

Leadthrough Programming Powered leadthrough Common for point-to-point robots Uses teach pendant Manual leadthrough Convenient for continuous path control robots Human programmer physical moves manipulator

Leadthrough Programming Advantages: 

Leadthrough Programming Advantages Advantages: Easily learned by shop personnel Logical way to teach a robot No computer programming Disadvantages: Downtime during programming Limited programming logic capability Not compatible with supervisory control

Robot Programming: 

Robot Programming Textural programming languages Enhanced sensor capabilities Improved output capabilities to control external equipment Program logic Computations and data processing Communications with supervisory computers

Coordinate Systems: 

Coordinate Systems World coordinate system Tool coordinate system

Motion Commands: 

Motion Commands MOVE P1 HERE P1 - used during lead through of manipulator MOVES P1 DMOVE(4, 125) APPROACH P1, 40 MM DEPART 40 MM DEFINE PATH123 = PATH(P1, P2, P3) MOVE PATH123 SPEED 75

Interlock and Sensor Commands: 

Interlock and Sensor Commands Interlock Commands WAIT 20, ON SIGNAL 10, ON SIGNAL 10, 6.0 REACT 25, SAFESTOP Gripper Commands OPEN CLOSE CLOSE 25 MM CLOSE 2.0 N

Simulation and Off-Line Programming: 

Simulation and Off-Line Programming

Example: 

Example A robot performs a loading and unloading operation for a machine tool as follows: Robot pick up part from conveyor and loads into machine (Time=5.5 sec) Machining cycle (automatic). (Time=33.0 sec) Robot retrieves part from machine and deposits to outgoing conveyor. (Time=4.8 sec) Robot moves back to pickup position. (Time=1.7 sec) Every 30 work parts, the cutting tools in the machine are changed which takes 3.0 minutes. The uptime efficiency of the robot is 97%; and the uptime efficiency of the machine tool is 98% which rarely overlap. Determine the hourly production rate.

Solution: 

Solution T c = 5.5 + 33.0 + 4.8 + 1.7 = 45 sec/cycle Tool change time T tc = 180 sec/30 pc = 6 sec/pc Robot uptime E R = 0.97, lost time = 0.03. Machine tool uptime E M = 0.98, lost time = 0.02. Total time = T c + T tc /30 = 45 + 6 = 51 sec = 0.85 min/pc R c = 60/0.85 = 70.59 pc/hr Accounting for uptime efficiencies, R p = 70.59(1.0 - 0.03 - 0.02) = 67.06 pc/hr

http://www1bpt.bridgeport.edu/~risc/html/proj/sanjeev/project.html: 

http://www1bpt.bridgeport.edu/~risc/html/proj/sanjeev/project.html

Thanks M.Ganesh Murugan: 

Thanks M.Ganesh Murugan