module 2 part 2robotics and control applications

robotics

1. Module -2 Control Systems and Components: Basic control systems concepts and models, controllers, robot actuation and feedback components. Robot end effectors: T ypes of end effecters, mechanical grippers, other types of grippers, tools as end effectors, robot/end effector interface, consideration in gripper selection and design, problems. Sensors in Robotics : Transducers and sensors, sensors in robotics, tactile sensors, proximity and range sensors [Textbook-1]

2. Module -2 C o nt ro l Sy st ems and C o mpon e n t s: Ba s ic c on t ro l sy s t ems c o n c ep t s a n d mode l s, c o nt roll er s , robo t a ct u ati o n a n d f ee d b a c k co mpon e nt s . Ro b o t e n d ef f ec t or s: T y pes of end e f fe c t er s , m e c ha ni c al g r i p p e r s , o t h e r t y pes of g r i p p e r s , t o ols a s end eff e c to r s , ro b ot / end e ff ec t or inte r fa c e, c on s i de r at i on i n g r i p p er s e l e c t i on and d e s i gn , p r obl e ms . Se n s or s in Ro b o t ics : T r a n s d u c e r s and s en s o r s , s e n s ors i n r obot i c s , t a c t i l e s ens o r s , p r o xi mi ty a n d ra ng e s en s ors [T e x t b o o k - 1]

3. C o nt ro l Sy st ems and C o mpon e n t s: Ba s ic c on t ro l sy s t ems c o n c ep t s a n d mode l s, c o nt roll er s , robo t a ct u ati o n a n d f ee d b a c k co mpon e nt s .

4. The task involves the movement of the manipulator arm, so the primary function of the robot control system is to position and orient the wrist (and end effector) with a specified speed and precision .

5. We can divide a system into five major components:  The input (or inputs) to the system  The controller and actuating devices  The plant (the mechanism or process being controlled)  The output (the controlled variable)  Feedback elements (sensors)

6. Mathematical Models are simply mathematical representations of real world systems. They are developed by applying the known rules of behavior for the elements in a system. Hook's law for the operation of a spring is an example: F = Ks x ……………………..(3-1) where F is the force applied to the spring x is the displacement due to the application of the force , K is the "spring constant." Using physical relationships of this sort we can develop models of more complex systems than just a spring. As an example, let us formulate the model for a familiar mechanical system: the spring-mass-damper system.

7. The operation of the system can be described as a sum of the forces on the mass. The force due to acceleration of the mass is y - the displacement of the mass M - the mass of the block Ks - the spring constant Kd - the damping coefficient of the dashpot x - the displacement of the end of the spring

8. y - the displacement of the mass M - the mass of the block Ks - the spring constant Kd - the damping coefficient of the dashpot x - the displacement of the end of the spring

9. In this system the input is x, representing the displacement of the end of the spring, the system output is y, representing the displacement of the block. The system has been described by a second-order linear differential equation which relates the input and the output. This mathematical description of the system allows us to analyze its behavior.

10. Transfer Functions Linear differential equations can be rewritten using the differential operator, s. The variable, s, is used to represent the mathematical operation of taking the derivative of a time-dependent variable with respect to time. functions which are variables of time [e.g., x(t) and y(t )] become functions of the variables [e.g., X(s) and Y(s)]. By using s with Laplace transforms, linear differential equations can be converted to equivalent expressions which are functions of s .

11. Block Diagrams A common means of graphically representing the relationships among the components of the system is the block diagram. Block diagrams are constructed from four basic elements:  Function blocks  Signal arrows  Summing junctions  Takeoff points

12. ROBOT ACTUATION AND FEEDBACK COMPONENTS Control of the robot manipulator requires the application of the preceding control theory to a mechanical system. We classify these devices into four categories:  Position sensors  Velocity sensors  Actuators  Power transmission devices

13. Position and velocity sensors are used in robotics as feedback devices . While actuators and power transmission devices are used to accomplish the control actions indicated by the controller. Position sensors provide the necessary means for determining whether the joints have moved to linear or rotational locations in order to achieve the orientation of the end effector.

14. The speed with which the manipulator s moved is another performance feature which must be regulated Many robots utilize feedback system to ensure proper speed control. This is especially important as sophisticated control systems are being developed to tine dynamic performance of the manipulator during acceleration and deceleration as it moves between points in the workspace. Actuators and power transmission devices provide the muscle to move robot arm. Actuators include hydraulic, electric, and pneumatic devices corresponding to the three basic robot drive systems .

15. TYPES OF END EFFECTORS There are wide assortments of end effectors required to perform the variety of different work functions. The various types can be divided into two major categories: Grippers Tools MECHANICAL GRIPPERS

16. Types of Gripper Mechanisms There are various ways of classifying mechanical grippers and their actuating mechanisms. One method is according to the type of finger movement used by the gripper. In this classification, the grippers can actuate the opening and closing of the fingers by one of the following motions: Pivoting movement Linear or translational movement In this classification we have the following types: 1. Linkage actuation 2. Gear-and-rack actuation 3. Cam actuation 4. Screw actuation 5. Rope-and-pulley actuation 6. Miscellaneous

17. OTHER TYPES OF GRIPPERS In addition to mechanical grippers there are a variety of other devices that can be designed to lift and hold objects. Included among these other types of grippers are the following: Vacuum cups Magnetic grippers Adhesive grippers Hooks, scoops, and other miscellaneous devices

18. Vacuum Cups Vacuum cups, also called suction cups, can be used as gripper devices for handling certain types of objects. The usual requirements on the objects to be handled are that they be flat, smooth, and clean, conditions necessary to form a satisfactory vacuum between the object and the suction cup. Ar. example of a vacuum cup used to lift flat glass is pictured in Fig. 5-13. The lift capacity of the suction cup depends on the effective area of the cup and the negative air pressure between the cup and the object. The relationship can be summarized in the following equation

19. Some of the features and advantages that characterize the operation of suction cup grippers used in robotics applications are: Requires only one surface of the part for grasping Applies a uniform pressure distribution on the surface of the part Relatively light-weight gripper Applicable to a variety of different material

20. Magnetic Grippers Magnetic grippers can be a very feasible means of handling ferrous materials. The stainless steel plate in Example 5-3 would not be an appropriate application for a magnetic gripper because 18-8 stainless steel is not attracted by a magnet. Other steels, however, including certain types of stainless steel, would be suitable candidates for this means of handling, especially when the materials are handled in sheet or plate form. In general, magnetic grippers offer the following advantages in robotic handling applications: Pickup times are very fast. Variations in part size can be tolerated. The gripper does not have to be designed for one particular workpart. They have the ability to handle metal parts with holes (not possible with vacuum grippers). They require only one surface for gripping.

21. TOOLS AS END EFFECTORS In many applications, the robot is required to manipulate a tool rather than a workpart. In a limited number of these applications, the end effector is a gripper that is designed to grasp and handle the tool. The reason for using a gripper in these applications is that there may be more than one tool to be used by the robot in the work cycle. The use of a gripper permits the tools to be exchanged during the cycle, and thus facilitates this multitool handling function. References 8 and 9 examine the design problems involved in a tool exchange mechanism. In most of the robot applications in which a tool is manipulated, the tool is attached directly to the robot wrist. In these cases the tool is the end effector. Some examples of tools used as end effectors in robot applications include: Spot-welding tools Arc-welding torch Spray-painting nozzle Rotating spindles for operations such as: drilling routing wire brushing grinding Liquid cement applicators for assembly Heating torches Water jet cutting tool

22. THE ROBOT/END EFFECTOR INTERFACE An important aspect of the end effector applications engineering involves the interfacing of the end effector with the robot. This interface must accomplish at least some of the following functions: Physical support of the end effector during the work cycle must be provided. Power to actuate the end effector must be supplied through the interface. Control signals to actuate the end effector must be provided. This is often accomplished by controlling the actuating power. Feedback signals must sometimes be transmitted back through the interface to the robot controller.

23. CONSIDERATIONS IN GRIPPER SELECTION AND DESIGN

24. The important factors that determine the required grasping force are: The weight of the object. Consideration of whether the part can be grasped consistently about its center of mass. If not, an analysis of the possible moments from off-center grasping should be considered. The speed and acceleration with which the robot arm moves (acceleration and deceleration forces), and the orientational relationship between the direction of movement and the position of the fingers on the object (whether the movement is parallel or perpendicular to the finger surface contacting the part). Whether physical constriction or friction is used to hold the part. Coefficient of friction between the object and the gripper fingers.

25. Module -1 Fundamentals of Robotics & Automation: Automation and robotics, history of robotics, robotics market and future prospects, robot anatomy, work volume, robot drive systems, control systems, precision of movement, end effectors, robotic sensors, robot programming and work cell control, robot applications, problems. Automation Concepts: SCADA, introduction and brief history of SCADA, SCADA systems software, distributed control system (DCS), introduction to the PLC, considerations and benefits of SCADA system. Module -2 Robot Motion Analysis, Sensors and Control: Introduction to manipulator kinematics, homogeneous transformations and robot kinematics, manipulator path control, robot dynamics, configuration of a robot controller, types of end effecters, mechanical grippers, other types of grippers, tools as end effectors, robot/end effector interface, consideration in gripper selection and design, problems. Sensors in Robotics : Transducers and sensors, sensors in robotics, tactile sensors, proximity and range sensors, uses of sensors in robotics, problems

26. TRANSDUCERS AND SENSORS A transducer is a device that converts one type of physical variable (e.g., force, pressure, temperature, velocity, flow rate, etc.) into another form. A common conversion is to electrical voltage, and the reason for making the conversion is that the converted signal is more convenient to use and evaluate. A sensor is a transducer that is used to make a measurement of a physical variable of interest. Some of the common sensors and transducers include strain gauges (used to measure force and pressure), thermocouples (temperatures), speedometers (velocity), and Pitot tubes (flow rates). Any sensor or transducer requires calibration in order to be useful as a measuring device. Calibration is the procedure by which the relationship between the measured variable and the converted output signal is established.

27. Transducers and sensors can be classified into two basic types depending on the form of the converted signal. The two types are: Analog transducers Digital transducers

28. Table 6-1 Desirable features of sensors l. Accuracy. The accuracy of the measurement should be as high as possible. Accuracy is interpreted to mean that the true value of the variable can be sensed with no systematic positive or negative errors in the measurement. Over many measurements of the variable, the average error between the actual value and the sensed value will tend to be zero. 2. Precision. The precision of the measurement should be as high as possible. Precision means that there is little or no random variability in the measured variable. The dispersion in the values of a series of measurements will be minimized. 3. Operating range. The sensor should possess a wide operating range and should be accurate and precise over the entire range. 4. Speed of response. The transducer should be capable of responding to changes in the sensed variable in minimum time. Ideally, the response would be instantaneous.

29. 5. Calibration. The sensor should be easy to calibrate. The time and trouble required to accomplish the calibration procedure should be minimum. Further, the sensor should not require frequent recalibration. The term "drift" is commonly applied to denote the gradual loss in accuracy of the sensor with time and use, and which would necessitate recalibration. 6. Reliability. The sensor should possess a high reliability. It should not be subject to frequent failures during operation. 7. Cost and ease of operation. The cost to purchase, install, and operate the sensor should be as low as possible. Further, the ideal circumstance would be that the installation and operation of the device would not require a specially trained, highly skilled operator.

30. Table 6-2 Sensor devices used in robot Workcell Ammeter—(miscellaneous). Electrical meter used to measure electrical current. Eddy current detectors-(proximity sensor). Device that emits an alternating magnetic field at the tip of a probe, which induces eddy currents in any conductive object in the range of the device. Can be used to indicate presence or absence of a conductive object. Electrical contact switch-(touch sensor). Device in which an electrical potential is established between two objects, and when the potential becomes zero, this indicates contact between the two objects. Not a commercial device. Can he used to indicate presence or absence of a conductive object. lnfrared sensor-(proximity sensor). Transducer which measures temperatures by the infrared light emitted from the surface of an object. Can be used to indicate presence or absence of a hot object. Limit switch-(touch sensor). Electrical on-off switch actuated by depressing a mechanical lever or button on the device. Can be used to measure presence or absence of an object. Linear variable differential transformer-(miscellaneous). Electromechanical transducer used to measure linear or angular displacement.

31. Microswitch -(touch sensor). Small electrical limit switch (see limit switch). Can he used to indicate presence or absence of an object. Ohmmeter---{miscellaneous). Meter used to measure electrical resistance. Optical pyrometer-(proximity sensor. miscellaneous). Device used to measure high temperatures by sensing the brightness of an object's surface. Can be used to indicate presence ·or absence of a hot object. Photometric sensors-(proximity sensor, miscellaneous). Various transducers used lo sense light. Category includes photocells, photoelectric transducers. phototubes. photodiodes. phototransistors, and photoconductors. Can be used to indicate presence or absence of an object. Piezoelectric acceleromeler -(miscellaneous). Sensor used to indicate or measure vibration. Potentiometer-(miscellaneous). Electrical meter used to measure voltage. Pressure transducers-(miscellaneous). Various transducers used to indicate air pressure and other fluid pressures.

32. Radiation pyromeler -(proximity sensor, miscellaneous). Device used to measure high temperatures by sensing the thermal radiation emitting from the surface of an object. Can be used to indicate presence or absence of a hot object. Strain gauge--{force sensor). Common transducer used to measure force, torque. pressure, and other related variables. Can be used to indicate force applied to grasp an object. Thermistor-(miscellaneous). Device based on electrical resistance used to measure temperatures. Thermocouple-(miscellaneous). Commonly used device used to measure temperatures. Based on the physical principle that a junction of two dissimilar metals will emit an emf which can he related to temperature.

33. Vacuum switches-(proximity sensor. miscellaneous). Device used to indicate negative air pressures. Can be used with a vacuum gripper to indicate presence or absence of an object. Vision sensors-(vision system). Advanced sensor system used in conjunction with pattern recognition and other techniques to view and interpret events occurring in the robot workplace. Voice sensor- (voice und speech recognition). Advanced sensor system used to communicate commands or information orally to the robot.

34. SENSORS IN ROBOTICS The sensors used in robotics include a wide range of devices which can be divided into the following general categories: Tactile sensors Proximity and range sensors Miscellaneous sensors and sensor-based systems Machine vision systems

35. TACTILE SENSORS Tactile sensors are devices which indicate contact between themselves and some other solid object. Tactile sensing devices can be divided into two classes: touch sensors and force sensors . Touch sensors provide a binary output signal which indicates whether or not contact has been made with the object. Force sensors (also sometimes called stress sensors) indicate not only that contact has been made with the object but also the magnitude of the contact force between the two objects.

36. a) Touch Sensors Touch sensors are used to indicate that contact has been made between two objects without regard to the magnitude of the contacting force . Included within this category are simple devices such as limit switches, microswitches and the like. The simpler devices are frequently used in the design of interlock systems in robotics. For example, they can be used to indicate the presence or absence of parts in a fixture or at the pickup point along a conveyor. Another use for a touch-sensing device would be as part of an inspection probe which is manipulated by the robot to measure dimensions on a workpart.

37. b) Force Sensors The capacity to measure forces permits the robot to perform a number of tasks. These include the capability to grasp parts of different sizes in material handling, machine loading, and assembly work, applying the appropriate level of force for the given part. In assembly applications, force sensing could be used to determine if screws have become cross-threaded or if parts are jammed. Force sensing in robotics can be accomplished in several ways. A commonly used technique is a "force-sensing wrist." This consists of a special load-cell mounted between the gripper and the wrist. Another technique is to measure the torque being exerted by each joint. This is usually accomplished by sensing motor current for each of the joint motors. Finally, a third technique is to form an array of force-sensing elements so that the shape and other information about the contact surface can be determined.

38. PROXIMITY AND RANGE SENSORS Proximity sensors are devices that indicate when one object is close to another object. How close the object must be in order to activate the sensor is dependent on the particular device. The distances can be anywhere between several millimeters and several feet. Some of these sensors can also be used to measure the distance between the object and the sensor, and these devices are called range sensors. Proximity and range sensors would typically be located on the wrist or end effector since these are the moving parts of the robot. One practical use of a proximity sensor in robotics would be to detect the presence or absence of a workpart or other object. Another important application is for sensing human beings in the robot workcell. Range sensors would be useful for determining the location of an object (e.g., the workpart) in relation to the robot.

39. The formula for the distance between the object and the sensor is given as follows: x = 0.5 y tan(A) where x = the distance of the object from the sensor y = the lateral distance between the light source and the reflected light beam against the linear array. This distance corresponds to the number of elements contained within the reflected beam in the sensor array A = the angle between the object and the sensor array as illustrated in Fig. 6-7.

40. Acoustical devices can be used as proximity sensors. Ultrasonic frequencies (above 20,000 Hz) are often used in these devices because the sound is beyond the range of human hearing. One type of acoustical proximity sensor uses a cylindrical open-ended chamber with an acoustic emitter at the closed end of the chamber. The emitter sets up a pattern of standing waves in the cavity which is altered by the presence of an object near the open end. A microphone located in the wall of the chamber is used to sense the change in the sound pattern. This kind of device can also be used as a range sensor. .

41. Proximity and range sensors based on the use of electrical fields are commercially available. Two of the types in this category and eddy-current sensors and magnetic field sensors. Eddy-current devices create a primary alternating magnetic field in the small region near the probe. This field induces eddy currents in an object placed in the region so long as the object is made of a conductive material. These eddy currents produce their own magnetic field which interacts with the primary field to change its flux density. The probe detects the change in the flux density and this indicates the presence of the object. Magnetic field proximity sensors are relatively simple and can be made using a reed switch and a permanent magnet. The magnet can be made a part of the object being detected or it can be part of the sensor device. In either case, the device can be designated so that the presence of the object in the region of the sensor completes the magnetic circuit and activates the reed switch. This type of proximity sensor design is attractive because of its relative simplicity and because no external power supply is required for its operation

42. USES OF SENSORS IN ROBOTICS The major uses of sensors in industrial robotics and other automated manufacturing systems can be divided into four basic categories: 1. Safety monitoring 2. Interlocks in workcell control 3. Part inspection for quality control 4. Determining positions and related information about objects in the robot cell

43. One of the important applications of sensor technology in automated manufacturing operations is safety or hazard monitoring which concerns the protection of human workers who work in the vicinity of the robot or other equipment. The second major use of sensor technology in robotics is to implement interlocks in workcell control. Interlocks are used to coordinate the sequence of activities of the different pieces of equipment in the workcell. The third category is quality control. Sensors can be used to determine a variety of part quality characteristics. Traditionally, quality control has been performed using manual inspection techniques on a statistical sampling basis. The fourth major use of sensors in robotics is to determine the positions and other information about various objects in the workcell (e.g., workparts, fixtures, people, equipment, etc.). In addition to positional data about a particular object, other information required to properly execute the work cycle might include the object's orientation, color, size, and other characteristics. Reasons why this kind of data would need to be determined during the program execution include: Workpart identification. Random position and orientation of parts in the workcell. Accuracy requirements in a given application exceed the inherent capabilities of the robot. Feedback information is required to improve the accuracy of the robot's positioning.

44. Assignment 1 (Answer any 15 Full Questions) (Module 1 & 2) Module 1a: Fundamentals of Robotics With a neat graph, differentiate between three classes of industrial automation. With neat graph explain the Robotics market and the future prospects. With appropriate diagrams, explain the types of joints used in robots. List the common robot configurations based on size and shape. With neat sketches, explain the Four Common Robot Configurations. What do you mean by work volume? With neat diagrams, explain different work volumes with reference to robot anatomies. Briefly explain applications of Robots. Module 1b: SCADA With a block diagram explain SCADA Systems Software. With suitable examples, briefly explain operation of different sensors used in robotics Describe considerations and benefits of SCADA system .

45.   Module 2a: Control Systems and Components: Describe control systems Components Classify and explain robot actuation and feedback components. Module 2b: Robot end effectors Classify final Control elements With a neat sketches explain Mechanical grippers Briefly describe Adhesive grippers. Draw the neat diagram of Vacuum cups employed in grippers. Discuss applications of sensors in industrial robotics and automated manufacturing systems. Discuss the general considerations in design and selection of suitable gripper in robots. Module 2c: Sensors in Robotics: List out and explain desirable features of sensors Classify and briefly explain sensors used in Robotics. With a neat schematic, explain proximity Sensor using reflected light against a sensor array Discuss applications of sensors in industrial robotics and automated manufacturing systems .

46. THANK YOU