Week 1_2 UME805 RE Introduction PDF

Introduction to Robotics: Standard Terminologies, Joint Configurations, and Classifications Dr. Jyotindra Narayan Assistant Professor Department of Mechanical Engineering Thapar Institute of Engineering and Techno...

Introduction to Robotics: Standard Terminologies, Joint Configurations, and Classifications Dr. Jyotindra Narayan Assistant Professor Department of Mechanical Engineering Thapar Institute of Engineering and Technology, Patiala, India UME805 Robotics Engineering July-November 2024 August 7, 2024 August 7, 2024 1 / 42 Outline 1 Standard Terminologies Components 2 Design Specifications of Robot Performance Characteristics Reach and Stroke Tool Orientation 3 Configurations of Robot August 7, 2024 2 / 42  Standard Terminologies Outline 1 Standard Terminologies Components 2 Design Specifications of Robot Performance Characteristics Reach and Stroke Tool Orientation 3 Configurations of Robot August 7, 2024 3 / 42  Standard Terminologies Components Components August 7, 2024 4 / 42  Standard Terminologies Components Robot Manipulator Manipulator A mechanism, usually consisting of a series of segments, or links, jointed or sliding relative to one another, for grasping and moving objects, usually in several degrees of freedom. It is remotely controlled by a human (manual manipulator) or a computer (programmable manipulator). The term refers mainly to the mechanical aspect of a robot. Arm An interconnected set of of links and powered joints comprising a manipulator which supports or move a wrist, hand, or end-effector. Anthropomorphic Robot Also known as a jointed-arm robot. A robot with all rotary joints and motions similar to a person’s arm. August 7, 2024 5 / 42  Standard Terminologies Components Robot Manipulator Articulated Robot A robot arm that contains at least two consecutive revolute joints acting around parallel axes resembling human arm motion. Partial cylinders or spheres form the work envelope. The two basic types of articulated robots, vertical and horizontal, are sometimes called anthropomorphic because of their resemblance to the motions of the human arm. Axis A traveled path in space, usually referred to as a linear direction of travel in any three dimensions. In Cartesian coordinate systems, labels of X, Y, and Z are commonly used to depict axis directions relative to Earth. X refers to a directional plane or line parallel to Earth. Y refers to a directional plane or line that is parallel to Earth and perpendicular to X. Z refers to a directional plane or line that is vertical to and perpendicular to the Earth’s surface. August 7, 2024 6 / 42  Standard Terminologies Components Robot Manipulator Flexible Arm A robot arm with mechanical flexibility, such as inflatable links or links made of mechanically flexible materials. Chain Robot Arm A robot arm designed especially for use as a monoarticulate chain manipulator, featuring a cross-sectional profile no larger than the chain links. Parallel Manipulator Robotic mechanisms containing two or more serial kinematic chains connecting the end-effector to the base. They generally offer more accuracy in positioning and orienting objects than open-chain manipulators. August 7, 2024 7 / 42  Standard Terminologies Components Robot Manipulator Kinematic Chain The combination of rotary and/or translational joints or axes of motion that constitute a manipulator. Joint Space The space defined by a vector whose components are the angular or translational displacement of each joint of a multi-degree-of-freedom linkage relative to a reference displacement for each such joint. Mobile Robot A freely moving programmable industrial robot which can be automatically moved in one, two, or three axes along a fixed or programmed path by means of a conveying unit, in addition to its usual five or six axes. August 7, 2024 8 / 42  Standard Terminologies Components Robot Manipulator Proximal The area on a robot close to the base but away from the end-effector of the arm. Joint A rotary or linear articulation or axis of rotational or translational motion in a manipulator system. Cobot A robot that is designed specifically to collaborate with humans. It is typically a safe, mechanically passive robotic device intended for direct physical contact with a human operator. August 7, 2024 9 / 42  Standard Terminologies Components Actuators Actuator A motor or transducer that converts electrical, hydraulic, or pneumatic energy into power for motion or reaction. Servo Mechanism An automatic control mechanism consisting of a motor or actuator driven by a signal which is a function of the difference between commanded position and/or rate, and measured actual position and/or rate. Servo Valve A transducer whose input is a low-energy signal and whose output is a higher-energy fluid flow which is proportional to the low-energy signal. August 7, 2024 10 / 42  Standard Terminologies Components Actuators Hydraulic Motor An actuator consisting of interconnected valves and pistons or vanes that convert high-pressure hydraulic or pneumatic fluid into mechanical motion. Pneumatic Motor A device that converts pneumatic pressure and flow into continuous rotary or reciprocating motion. DC Servo Drives Electric motors controlled using a feedback mechanism. A transducer feedback and a speed control form a servo loop. DC servo drives are controlled through a voltage change; the motor runs faster if a higher voltage is applied. August 7, 2024 11 / 42  Standard Terminologies Components Actuators Drive Power The source or means of supplying energy to the robot actuators to produce motion. Degree of Freedom The number of independent ways the end-effector can move. It is defined by the number of rotational or translational axes through which motion can be obtained. Every variable representing a degree of freedom must be specified if the physical state of the manipulator is to be completely defined. Servo-System A control system for the robot in which the control computer issues motion commands to the actuators and internal measurement devices measure the motion and signal the results back to the computer. This process continues until the arm reaches the desired position. August 7, 2024 12 / 42  Standard Terminologies Components Control Closed-Loop Control A feedback loop is used to measure and compare actual system performance with desired performance. This strategy allows the robot control to make any necessary adjustments. Continuous Path Control A type of robot control in which the robot moves according to a replay of closely spaced points programmed on a constant time base during teaching. The points are first recorded as the robot is guided along a desired path, and the position of each axis is recorded by the control unit on a constant time basis by scanning axis encoders during the robot motion. The replay algorithm attempts to duplicate that motion. Alternatively, a continuous path control can be accomplished by interpolation of a desired path curve between a few taught points. August 7, 2024 13 / 42  Standard Terminologies Components Control Control Hierarchy A system in which higher-level control elements are used to control lower-level ones and the results of lower-level elements are utilized as inputs by higherlevel elements. Embodied in the phrase “distributed intelligence,” in which processing units (usually microprocessors) are dispersed to control individual axes of a robot. Controller A hardware/ software device that continuously measures the value of a variable quantity or condition and then automatically acts on the controlled equipment to correct any deviation from a desired preset value. Force Control A method of error detection in which the force exerted on the endeffector is sensed and fed back to the controller, usually by mechanical, hydraulic, or electric transducers. August 7, 2024 14 / 42  Standard Terminologies Components Control Joint Level Control A level of robot control which requires the programming of each individual joint of the robot structure to achieve the required overall positions. Master–Slave Control Control strategy for teleoperated systems which allows the operator to specify the end position of the slave (remote) end-effector by specifying the position of a master unit. Commands are resolved into the separate joint actuators either by the kinematic similarity of the master and slave units or mathematically by a control unit performing a transformation of coordinates. Open-Loop Control Control of a manipulator in which preprogrammed signals are delivered to the actuators without the actual response at the actuators being measured. This control is the opposite of closed-loop control. August 7, 2024 15 / 42  Standard Terminologies Components Control Optimal Control A control scheme whereby the system response to a commanded input, given the dynamics of the process to be controlled and the constraints on measuring, is optimal according to a specified objective function or criterion of performance. Point-to-Point Control A robot motion control in which the robot can be programmed by a user to move from one position to the next. The intermediate paths between these points cannot be specified. Position Control A control by a system in which the input command is the desired position of a body. August 7, 2024 16 / 42  Standard Terminologies Components Sensor Contact Sensor A grouping of sensors consisting of tactile, touch, and force/torque sensors. A contact sensor is used to detect contact of the robot hand with external objects Force–Torque Sensors The sensors that measure the amount of force and torque exerted by the mechanical hand along three hand-referenced orthogonal directions and applied around a point ahead and away from the sensors. Position Sensor Device detecting the position of the rotor relative to the stator of the actuator. The rotor speed is derived from the position information by differentiation with respect to time. The servo-system uses this sensor data to control the position as well as the speed of the motor. August 7, 2024 17 / 42  Standard Terminologies Components Sensor Proximity Sensor A device which senses that an object is only a short distance (e.g., a few inches or feet) away and/ or measures how far away it is. Proximity sensors typically work on the principles of triangulation of reflected light, elapsed time for reflected sound, intensity-induced eddy currents, magnetic fields, back pressure from air jets, and others. Sensor Fusion Also known as sensor integration. The coordination and integration of data from diverse sources to produce a usable perspective for a robotics system. A large number of sensors can be applied, and the information they gather from the work environment or workpiece is analyzed and integrated in a unique meaningful stream of feedback data to the robotic manipulator(s). August 7, 2024 18 / 42  Standard Terminologies Components Sensor Ultrasonic Sensor A range-measuring device which transmits a narrow-band pulse of sound towards an object. A receiver senses the reflected sound when it returns. The time it takes for the pulse to travel to the object and back is proportional to the range. Wrist Force Sensor A structure with some compliant sections and transducers that serve as force sensors by measuring the deflections of the compliant sections. The types of transducers used are strain-gauge, piezoelectric, magnetostrictive, and magnetic. Touch Sensors Sensors that measure the distribution and amount of contact area pressure between hand and objects perpendicular to the hand. Touch sensors may be singlepoint, multiple-point (array), simple binary (yes–no), or proportional sensors, or may appear in the form of artificial skin. August 7, 2024 19 / 42  Design Specifications of Robot Outline 1 Standard Terminologies Components 2 Design Specifications of Robot Performance Characteristics Reach and Stroke Tool Orientation 3 Configurations of Robot August 7, 2024 20 / 42  Design Specifications of Robot Design Specifications of Robot 1 Degrees of freedom 2 Number of axes 3 Performance characteristics (mm) 4 Load carrying capacity ( kg ) 5 Maximum speed ( mm/sec ) 6 Reach and stroke (mm) 7 Tool orientation (deg) 8 Operating environment August 7, 2024 21 / 42  Design Specifications of Robot Performance Characteristics Performance Characteristics 1 Spatial resolution 2 Accuracy 3 Repeatability Assumptions 1 The definitions will apply at the robot’s wrist end with no hand attached to the wrist. 2 The terms apply to the worst case conditions, the conditions under which the robot’s precision will be at its wont. This generally means that the robot’s arm is fully extended in the case of a jointed arm or polar configurable. 3 Third, our definitions will he developed in the context of a point-topoint robot. August 7, 2024 22 / 42  Design Specifications of Robot Performance Characteristics Performance Characteristics The spatial resolution of a robot is the smallest increment of movement into which the robot can divide its work volume. Spatial resolution depends on two factors: the system’s control resolution and the robot’s mechanical inaccuracies. It is easiest to conceptualize these factors in terms of a robot with 1 degree of freedom. Mathematically The no. of increments = 2n Where n = the number of bits in the control memory. The control resolution = Total movements range/ The number of increments. August 7, 2024 23 / 42  Design Specifications of Robot Performance Characteristics Performance Characteristics Problem: Using our robot with 1 degree of freedom as an illustration, we will assume it has one sliding joint with a full range of 1.0 m ( 39.37 in.). The robot’s control memory has a 12 -bit storage capacity. The problem is determining the control resolution for this axis of motion. Answer: The number of control increments can be determined as follows: Number of increments = 212 = 4096 The total range of 1 m is divided into 4096 increments. Each position will be separated by 1 m/4096 = 0.000244 m or 0.244 mm The control resolution is 0.244 mm ( 0.0096 in.). August 7, 2024 24 / 42  Design Specifications of Robot Performance Characteristics Performance Characteristics Accuracy refers to a robot’s ability to position its wrist end at a desired target point within the work volume. The accuracy of a robot can be determined in terms of spatial resolution because the ability to achieve a given target point depends on how closely the robot can define the control increments for each of its joint motions. August 7, 2024 25 / 42  Design Specifications of Robot Performance Characteristics Performance Characteristics Repeatability is concerned with the robot’s ability to position its wrist or an end effector attached to its wrist at a point in space is known as repeatability. Repeatability and accuracy refer to two different aspects of the robot’s precision. Accuracy relates to the robot’s capacity to be programmed to achieve a given target point. The actual programmed point will probably be different from the target point due to limitations of control resolution. Repeatability refers to the robot’s ability to return to the programmed point when commanded. August 7, 2024 26 / 42  Design Specifications of Robot Reach and Stroke Reach and Stroke Reach and stroke of the robot are the measure of the work volume of the robot. Horizontal reach: It is the maximum radial distance at which the robotic wrist can be positioned away from the vertical axis about which the robot rotates or the base of the robot. Horizontal stroke: It is the total radial distance the wrist can move. There is always a certain minimum distance the robot’s wrist will remain away from the base axis. Thus, the horizontal stroke is always less than equal to the horizontal reach. Vertical reach: It is the maximum vertical distance above the working surface that can be reached by the robot’s wrist. Vertical stroke: It is the total vertical distance that the wrist can move. The vertical stroke is also always less than equal to the vertical reach. Articulated robots have full work envelopes, which means the stroke is equal to reach. However, it is necessary to program to avoid collision with itself or the work surface. August 7, 2024 27 / 42  Design Specifications of Robot Reach and Stroke Reach and Stroke For a cylindrical coordinate robot the horizontal reach is the outer cylinder of the workspace, while the horizontal stroke is the difference between the radii of the concentric outer cylinder and the inner cylinder. August 7, 2024 28 / 42  Design Specifications of Robot Tool Orientation Tool Orientation The three major axes of the robot determine the work volume, while the remaining additional axes of the robot determine the orientation of the robot’s end effector. If three independent minor axes are present, then the end effector will able to achieve any arbitrary orientation in the three-dimensional work volume of the robot. The three axes associated with the wrist are called yaw, pitch, and roll, which are used to define the orientation of the end effector of the robot. August 7, 2024 29 / 42  Design Specifications of Robot Tool Orientation Tool Orientation 1 Wrist roll: It involves the rotation of the wrist mechanism about the arm axis. A wrist roll is also referred to as a wrist swivel. 2 Wrist pitch: If the wrist roll is in its center position, the wrist pitch is the up or down rotation of the wrist. also called wrist bend. 3 Wrist yaw: If the wrist roll is in the center position of its range, the wrist yaw is the right or the left rotation of the wrist. Robot would have a spherical wrist if the axes to orient the tool intersect at a common point. August 7, 2024 30 / 42  Design Specifications of Robot Tool Orientation 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) August 7, 2024 31 / 42  Configurations of Robot Outline 1 Standard Terminologies Components 2 Design Specifications of Robot Performance Characteristics Reach and Stroke Tool Orientation 3 Configurations of Robot August 7, 2024 32 / 42  Configurations of Robot Configurations of Robot Based on the coordinate system of motion of the manipulator and end effector, there are four basic configurations of robots: 1 Cartesian Configuration Robots (LOO) 2 Cylindrical Configuration Robots (TLO) 3 Polar (Spherical) Configuration Robots (TRL) 4 Jointed-Arm (Articulated) Configuration Robots Revolute Robots (TRR) SCARA Robots (VRO) 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 August 7, 2024 33 / 42  Configurations of Robot Cartesian Configuration Robots (LOO) Provides three linear motions along three mutually perpendicular axes: X, Y, and Z. However, there is no rotary motion. Configuration provides rectangular work envelope. Used for assembly, palletizing and machine tool loading. August 7, 2024 34 / 42  Configurations of Robot Cartesian Configuration Robots (LOO) Advantages: Work envelope can be increased by travelling along the x axis. Linear movement and hence simpler control. High degree of accuracy and repeatability due to their structure. Can carry heavier loads since load carrying capacity does not differ at different position of the work envelope. Disadvantages: Movement is limited to only one direction at a time. Applications: Pick and place operation. Adhesive applications. Assembly and sub assembly. Nuclear material handling. Welding August 7, 2024 35 / 42  Configurations of Robot Cylindrical Configuration Robots (TLO) Provides two linear and one rotary motions Configuration provides a cylindrical work envelope and a good work area-to-floor area ratio. Used for loading and unloading on machine tools. August 7, 2024 36 / 42  Configurations of Robot Cylindrical Configuration Robots (TLO) Advantages: Results in larger work volume than a rectangular manipulator. Vertical structure conserves floor space. Capable of carrying large payloads. Disadvantages: Repeatability and accuracy are lower in the direction of rotary motion. Requires more sophisticated control system. Applications: Assembly. Coating application Die casting. Foundry and forging application Machine loading and unloading. August 7, 2024 37 / 42  Configurations of Robot Polar (Spherical) Configuration Robots (TRL) Provides one linear and two rotary motions Configuration provides spherical work envelope. Used for spot welding and manipulation (handling) of heavy loads. August 7, 2024 38 / 42  Configurations of Robot Polar (Spherical) Configuration Robots (TRL) Advantages: Larger work envelope than the rectilinear or cylindrical configuration. Vertical structure conserves less space. Disadvantages: Repeatability and accuracy are also lower in the direction of rotary motion. Requires more sophisticated control system. Applications: Die casting. Forging. Glass handling. Injection molding. Stacking and unstacking. August 7, 2024 39 / 42  Configurations of Robot Jointed Arm Configuration Robots (TRR) Provides three rotary motions about three mutually perpendicular axes Provides spherical work envelope, has excellent work areas to floor area ratio Configuration is similar to that of human arm. Consists of two straight links, corresponding to the human forearm and upper arm, connected by a rotary joint. Used to spray painting, seam welding, spot welding, assembly, heavy material handling, etc August 7, 2024 40 / 42  Configurations of Robot SCARA (Selective Compliance Assembly Arm) Robots Provides one linear and two rotary motions. Provides cylindrical work envelope with high speed drive motors Used for assembly operations. August 7, 2024 41 / 42  Configurations of Robot Configurations Overview August 7, 2024 42 / 42