Introduction to Robotics

1. Introduction to Robotics Instructed by: Iksan Bukhori

2. Outline • Course Information • Course Overview & Objectives • Course Materials • Course Requirement/Evaluation/Grading (REG)

3. I. Course Information • Instructor + Name : Arthur Silitonga + Address : Jl. Ki Hadjar Dewantara, President University, Cikarang, Bekasi + Email Address : arthur@president.ac.id + Office Hours : Tuesday, 17.00 – 18.00 • Course‘s Meeting Time & Location + Meeting Time : Tuesday -> 10.30 – 13.00 (Lec) : Friday -> 07.30 – 10.00 (Lab) + Location : Room B, President University, Cikarang Baru, Bekasi

4. II. Course Overview & Objectives • Lecture sessions are tightly focused on introducing basic concepts of robotics from perspectives of mainly mechanics, control theory, and computer science. • Experiments at the lab occupying LEGO Mindstrom Kit, Wheeled Robot, and Robotic Atm. • Students are expected to design and implementing a real wheeled robot “from the scratch“. Course Overview

5. Course Objectives The objectives of this course are students should be able to : • describe positions and orientations in 3-space mathematically, and explain the geometry of mechanical manipulators generally • acquire concept of kinematics to velocities and static forces, general thought of forces & moments required to cause a motion of a manipulator, and sub-topics related to motions & mechanical designs of a manipulator • recognize methods of controlling a manipulator, and simulate the methods during lab works concerning to concepts of Wheeled Robot and Robotic Arm • design a wheeled robot “from the scratch“ based on knowledge of mechatronics To accomplish the objectives students will : • have homework assignments and participate in quizzes • implement calculations of 3-space positions & orientations using LEGO Mindstrom kit • design a wheeled robot considerating to theoretical and practical aspects • implement software aspects of a robotic arm • should take the mid-term exam, and the final exam

6. III. Course Materials

7. Final Exam : All Chapters/Activities

8. IV. Course Requirement/Evaluation/Grading • Requirements : - physics 1(mechanics) - linear algebra (matrix and vector) • Evaluation for the final grade will be based on : - Mid-Term Exam : 30 % - Final Exam : 30 % - Lab Experiments or Assignments : 20 % - Course Project : 20% Every two weeks, a quiz will be given as a preparation of several lab experiments

9. Mid-Term Exam consists of Lectures given in between the Week 1 and the Week 6. • Final Exam covers whole subjects or materials given duringthe classes. • Grading Policy Final grades may be adjusted; however, you are guaranteed the following: If your final score is 85 - 100, your grade will be A. If your final score is 70 - 84, your grade will be B. If your final score is 60 - 69, your grade will be C. If your final score is 55 - 59, your grade will beD. If your final score is < 55, your grade will be E.

10. REFERENCES • [Cra05]Craig, John., Introduction to Robotics : Mechanics and Control(Third Edition). Pearson Education, Inc.: New Jersey, USA. 2012. • [Sie04] Siegwart, Roland. & Nourbakhsh, Illah., Introduction to Autonomous Mobile Robots. The MIT Press : Cambridge, USA. 2004. • [Sic08]Siciliano, Bruno. & Khatib, Oussama., Handbook of Robotics. Springer-Verlag: Wuerzburg, Germany. 2008. • [Do08]Dorf, Richard. & Bishop, Robert., Modern Control Systems (Eleventh Edition). Pearson Education, Inc: Singapore, Singapore. 2008.

11. Robotic Arm

12. i.1 Assembly A more challenging domain, assembly by industrial robot, accounted for 10% of installations. i.2 Mechanical Manipulator Exactly what constitutes an industrial robot is sometimes debated. Mechanical manipulator is the main form of mechanics and control of industrial robots. Devices such as that shown in Fig. 8.1 are always included, while numerically controlled (NC) milling machines are usually not. The distinction lies somewhere in the sophistication of the programmability of the device —if a mechanical device can be programmed to perform a wide variety of applications, it is probably an industrial robot.

13. Fig. 8.1. The Adept 6 Manipulator hassixrotationaljoints. Courtesyof Adept Technology, Inc.

14. i.3 Fixed Automation • Machines which are for the most part limited to one class of task are considered fixed automation. • For the purposes of this text, the distinctions need not be debated; most material is of a basic nature that applies to a wide variety of programmable machines.

15. ii. The Mechanics and Controlof Mechanical Manipulator

16. ii.1 Description of Position and Orientation In the study of robotics, we are constantly concerned with the location of objects in three-dimensional space. These objects are the links of the manipulator, the parts and tools with which it deals, and other objects in the manipulator's environment. These objects are described by just two attributes: position and orientation. Naturally, one topic of immediate interest is the manner in which we represent these quantities and manipulate them mathematically.

17. In order to describe the position and orientation of a body in space, we will always attach a coordinate system, or frame, rigidly to the object. • We then proceed to describe the position and orientation of this frame with respect to some reference coordinate system. • Any frame can serve as a reference system within which to express the position and orientation of a body, so we often think of transforming or changing the description of these attributes of a body from one frame to another.

18. Developing good skills concerning the description of position and rotation of rigid bodies is highly useful even in fields outside of robotics. !!!

19. ii.2 Forward Kinematics of Manipulator Kinematics is the science of motion that treats motion without regard to the forces which cause it. Fig. 8.2 Coordinate systems or "frames" are attached to the manipulator and to objects in the environment.

20. the study of the kinematics of manipulators refers to all the geometrical and time-based properties of the motion. position, velocity, acceleration, and all higher order derivatives of the position variables (with respect to time or any other variable(s))

21. Manipulators consist of nearly rigid links, which are connected by joints that allow relative motion of neighboring links. • These joints are usually instrumented with position sensors, which allow the relative position of neighboring links to be measured. • In the case of rotary or revolute joints, these displacements are called joint angles. • Some manipulators contain sliding (or prismatic) joints, in which the relative displacement between links is a translation, sometimes called the joint offset.

22. The number of degrees of freedom that a manipulator possesses is the number of independent position variables that would have to be specified in order to locate all parts of the mechanism. • In the case of typical industrial robots, because a manipulator is usually an open kinematic chain, and because each joint position is usually defined with a single variable, the number of joints equals the number of degrees of freedom.

23. At the free end of the chain of links that make up the manipulator is the end effector. • We generally describe the position of the manipulator by giving a description of the tool frame, which is attached to the end-effector, relative to the base frame, which is attached to the nonmoving base of the manipulator.

24. A very basic problem in the study of mechanical manipulation is called forward kinematics. • This is the static geometrical problem of computing the position and orientation of the end-effector of the manipulator.

25. Fig. 8.3 Kinematic equations describe the tool frame relative to the base frame as a function of the joint variables.

26. Sometimes, we think of this as changing the representation of manipulator position • from a joint space description into a Cartesian space description.

27. ii.3 Inverse Kinematics of Manipulator Concept : Given the position and orientation of the end-effector of the manipulator, calculate all possible sets of joint angles that could be used to attain this given position and orientation.

28. We can think of this problem as a mapping of "locations" in 3-D Cartesian space to "locations" in the robot's internal joint space. • This need naturally arises anytime a goal is specified in external 3-D space coordinates. • Some early robots lacked this algorithm—they were simply moved (sometimes by hand) to desired locations, which were then recorded as a set of joint values (i.e., as a location in joint space) for later playback.

29. Fig. 8.4 For a given position and orientation of the tool frame, values for the joint variables can be calculated via the inverse kinematics.

30. The inverse kinematics problem is not as simple as the forward kinematics one. Because the kinematic equations are nonlinear, their solution is not always easy (or even possible) in a closed form. • The existence or nonexistence of a kinematic solution defines the workspace of a given manipulator. • The lack of a solution means that the manipulator cannot attain the desired position and orientation because it lies outside of the manipulator‘s workspace. !!!

31. ii.4 Velocities, Static Forces, and Singularities • In performing velocity analysis of a mechanism, it is • convenient to define a matrix quantity called the • Jacobianof the manipulator. • The Jacobianspecifies a mapping from velocities in • joint space to velocities in Cartesian space. • At certain points, called singularities, this mapping is not • invertible. An understanding of the phenomenon is • important to designers and users of manipulators.

32. Fig. 8.5 The geometrical relationship between joint rates and velocity of the end-effector can be described in a matrix called the Jacobian

33. Fig. 8.6 A World War I biplane with a pilot and a rear gunner The rear gunner mechanism is subject to the problem of singular positions.

36. ii.5 Dynamics Dynamics is a huge field of study devoted to studying the forces required to cause motion. In order to accelerate a manipulator from rest, glide at a constant end off v ector velocity, and finally decelerate to a stop, a complex set of torque functions must be applied by the joint actuators. Many of us have experienced lifting an object that is actually much lighter thanweexpected. Such asmisjudgmentofpayloadcancause an unusualliftingmotoion. This kindofobservationindicatesthatthe human controlsystemismoresophisticatedthan a purelykinematicscheme,. Ourmanipulationcontrolsystemmakesuseofknowledgeofmassandotherdynamiceffects. Likewise, algorithmsthatweconstructtocontrolthemotionsof a robotmanipulatorshouldtakedynamicsintoaccount.

37. Figure 8.10 The relationshipbetweenthetorquesappliedbytheactuators andtheresultingmotionofthemanipulatorisembodied in thedynamic equationsofmotion

38. A second use of the dynamic equations of motion is in simulation. • By reformulating the dynamic equations so that acceleration is computed as a function of actuator torque, it is possible to simulate how a manipulator would move under application of a set of actuator torques.

39. ii.6 Trajectory Generation • Commonly, each joint starts and ends its motion at the same time, so that the manipulator motion appears coordinated. (See Figure 8.11.) • Often, a path is described not only by a desired destination but also by some intermediate locations, or via points, through which the manipulator must pass enroute to the destination. • In such instances the term splineis sometimes used to refer to a smooth function that passes through a set of via points.

40. In order to force the end-effector to follow a straight line (or other geometric shape) through space, the desired motion must be converted to an equivalent set of joint motions. • Manipulators are, in theory, universal devices applicable to many situations, economics generally dictates that the intended task domain influence the mechanical design of the manipulator. • Issues such as size, speed, and load capability, the designer ->consider the number of joints and their geometric arrangement.

41. Figure 8.11 In ordertomovethe end-effectorthroughspacefrompoint A topoint B, we must compute a trajectoryforeachjointto follow.

42. ii.7 Manipulator Design & Sensors Manipulators areapplicabletomanysituations. However, economics generallydictatesthattheintendedtaskdomaininfluencethe mechanical design ofthemanipulator.

43. In designing a usefulrobot, twoapproachescanbetaken: • Build a specializedrobot (forspecifictask) • Build a universtalrobotthatwouldbeabletoperform a wide • varietyoftasks. • A specializedrobotneedssomecarefulthinkingto design it • which will yield a solutionofhowmanyjointsareneeded. • In thecaseof a universitalrobot, itisinterestingthat fundamental • propertiesofthephysicalworldwelive in dictatetheminimum • numberofjoints – thatminimumnumberissix. • Integral tothe design ofthemanipulatorareissuesinvolvingthe • choiceandlocationofactuators, transmissionsystems, and • internal-position (andsometimesforce) sensors.

44. ii.8 Linear Position Control Vastmajorityofmanipulatorsaredrivenbyactuatorsathatsupply a force ortorquetocausemotionofthe links. The problemofdynamicsiscentralto design of such algorithms, but it does not in itselfconstitute a solution. A primaryconcernof a linear positioncontrolsystemistocompensate automaticallyforerrors in knowledgeoftheparametersof a systemand tosuppressdisturbancesthattendtoperturbthesustemfromthedesired trajectory. (See Figure 8.13). Position andvelocitysensorsaremonitoredbythecontrolalgorithm, and neededtoaccomplishthe linear positioncontrolsystem.

45. Figure 8.13 In ordertocausethemanipulatorto follow thedesiredtrajectory, a position-controlsystem must beimplemented. Such a systemusesfeedback fromjointsensorstokeepthemanipulator on course.

46. ii.9 Nonlinear Position Control Someindustrialrobotsarenowbeingintroducedwhich makeuseofnonlinearcontrolalgorithms in the theircontrollers. These nonlineartechniquesofcontrollingmanipulator promisebetterperformancecomparedto do simple linear schemes.

47. ii.10 Force Control The abilityof a manipulatortocontrolforcesofcontactwhenittouchesparts, tools, orworksurfacesseemstobe a greatimportance in applyingmanipulators tomanyworldtasks. Force control in complementarytopositioncontrol, in thatweusuallythinkof onlyortheotherasapplicable in a certainsituation. Manipulators arerarelyconstrainedbyreactionsurfaces in all directions simultaneously, so a mixed hybrid controlisrquired, withsomedirections controlledby a position-controllawandremainingdirectionscontrolledby a force-controllaw.

48. ii.11 Programming Robots A robotprogramminglanguageservesastheinterfacebetweenthe human user andindustrialrobot. Robot manipulatorsdifferentiatethemselvesfromfixedautomationbybeing “flexible“, whichmeansprogrammable. Not onlyarethemovementsofmanipulatorsareprogrammable, but, through theuseofsensorsandcommunicationswithotherfactoryautomation, mani- Pulatorscanadapttovariationsasthetaskproceeds. In typicaleobotsystems, thereis a shorthandwayfor a human usertoinstruct therobotwhichpathitisto follow. Motionsoftherobot will bedescribedbytheuser in termsofdesiredlocations Ofthe operational point relative to a user-specifiedcoordinatesystem. Generally, theuser will definethisdifferencecoordinatesystem relative tothe robot‘sbasecoodrinatesystem in some task-relevant location.

49. ii.12 Off-line Programming and Simulation An off-lineprogrammingsystemisrobotprogrammingenvironmentthathas beensufficientlyextended, generallybymeansofcomputergraphics, thatthe developmentofrobotprogramscantakeplacewithoutaccesstotherobotitself. A commonargumentraised in theirfavoristhat an off-lineprogrammingsystem will not causeproductionequipment (therobot) tobetiedupwhenitneedstobe Reprogrammed. Automatedfactoriescanstay in productionmode a greaterpercentageofthe time. Theay also serveasnaturalvehicletotie computer-aided design (CAD) database used in the design phaseof a producttotheactualmanufacturingoftheproduct. In somecases, thisdirectuseof CAD datacandrammaticallyreducethe programming time requiredforthemanufacturingprocess.

50. iii. Notation