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Lecture 02: Experiment 01: Teaching of Serial Manipulator
NPTEL IIT Kharagpur
Overview
This lecture introduces the concept of teaching a serial manipulator, specifically the UR-5 robot. It covers the robot's components, including the teach pendant and controller, and explains the fundamental types of robotic joints (linear and rotary) and their variations. The lecture details the Denavit-Hartenberg parameters for kinematic analysis, distinguishing between forward and inverse kinematics. It then delves into teaching methodologies, contrasting online (manual, lead-through) and offline (programming, simulation) approaches. Finally, it outlines three practical tasks: basic control via teach pendant, programming for pick-and-place operations, and programming for continuous path tasks, all to be demonstrated on the UR-5 robot.
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Chapters
- Serial manipulators are robots with a fixed base and a series of links connected by joints.
- The UR-5 is a specific model of a serial manipulator used in this experiment.
- Teaching a robot involves providing instructions on how to perform tasks.
- The experiment will cover robot description, specifications, tasks, precautions, applications, and references.
Understanding the basic structure and purpose of teaching is crucial for operating and programming robotic systems effectively.
The UR-5 robot, featuring a teach pendant and a controller, is introduced as the subject of the experiment.
- Robotic joints connect rigid links and can be either linear or rotary.
- Linear joints include prismatic (sliding with rectangular/square cross-section) and sliding joints.
- Rotary joints include revolute joints (axis of output link perpendicular to rotation axis) and twisting joints (axes coincide).
- The UR-5 has six rotary joints: three revolute and three twisting, each providing one degree of freedom.
Knowing the different types of joints and their properties is fundamental to understanding how robots move and achieve their degrees of freedom.
A prismatic joint allows one component to slide linearly within another, like a drawer, while a revolute joint allows rotation around a specific axis, like a hinge.
- Kinematic analysis, often using Denavit-Hartenberg parameters, determines the robot's position and orientation.
- Forward kinematics calculates the end-effector's pose from joint angles.
- Inverse kinematics determines the required joint angles for a desired end-effector pose.
- Teaching methods are categorized as online (robot is used during instruction) or offline (robot is not used).
- Online methods include manual teaching and lead-through teaching; offline methods involve programming or simulation.
Understanding kinematic analysis and different teaching methods allows for efficient and accurate robot programming for various tasks.
In manual teaching (online), a user physically moves the robot arm to desired positions using a teach pendant, while offline programming might involve using simulation software like UR-SIM.
- Point-to-point tasks involve moving the robot from one discrete location to another, often with pauses in between (e.g., drilling holes).
- Continuous path tasks require the robot to follow a specific trajectory while maintaining contact with a surface or object (e.g., cutting a profile, drawing).
- Point-to-point tasks are typically programmed using manual teaching.
- Continuous path tasks often utilize lead-through teaching or simulation to define the path.
Differentiating between task types is essential for selecting the appropriate teaching method and programming commands.
Drilling holes at specific locations on a steel plate is a point-to-point task, whereas cutting a complex shape with a milling cutter is a continuous path task.
- The UR-5 is a 6-DOF serial manipulator with a payload of 5 kg and a reach of 850 mm.
- It features rotary joints, a brushless DC motor, gearbox, encoder, and braking mechanism.
- The teach pendant is a sophisticated remote controller with a touchscreen, power, emergency stop, and controls for joint and TCP movement.
- Operating modes on the teach pendant include Run Program, Program Robot, Setup Robot, and Shutdown Robot.
Understanding the robot's specifications and the teach pendant's interface is necessary for its operation, programming, and safe use.
The teach pendant's display shows joint angles and TCP position/orientation, and its buttons allow for manual control of individual joints or programmed movements.
- Programming involves using commands like 'move', 'waypoint', 'wait', 'set', 'pop-up', and 'halt'.
- Move commands include 'move j' (fastest, non-linear path), 'move l' (linear motion), 'move p' (fixed TCP speed), and 'move c' (circular motion).
- A waypoint defines a specific location and orientation (pose) in space.
- Task 1: Basic control of UR-5 using the teach pendant.
- Task 2: Programming pick-and-place operations.
- Task 3: Programming continuous path tasks like drawing geometric shapes.
Familiarity with programming commands and the defined tasks enables the learner to instruct the robot to perform specific industrial or research operations.
To move the robot linearly from point A to point B, the 'move l' command would be used, specifying the coordinates of both points.
Key takeaways
- Serial manipulators are constructed with links and joints arranged in series, enabling complex movements.
- Understanding the difference between linear (prismatic, sliding) and rotary (revolute, twisting) joints is key to robot mechanics.
- Kinematic analysis (forward and inverse) is essential for calculating robot motion and planning tasks.
- Teaching methods (online vs. offline) offer different approaches to programming robots based on task complexity and available resources.
- Point-to-point tasks are for discrete movements, while continuous path tasks require smooth, unbroken trajectories.
- The teach pendant is the primary interface for controlling, programming, and setting up the UR-5 robot.
- Specific programming commands (e.g., move j, move l, waypoint) are used to define robot actions.
- The UR-5 robot has specific technical specifications (payload, reach, speed, repeatability) that dictate its capabilities.
Key terms
Serial ManipulatorTeach PendantController/DirectorLinear JointRotary JointPrismatic JointRevolute JointTwisting JointDegree of Freedom (DOF)Forward KinematicsInverse KinematicsOnline TeachingOffline TeachingPoint-to-Point TaskContinuous Path TaskTool Center Point (TCP)WaypointUR-5
Test your understanding
- What are the two main categories of robotic joints, and what are their sub-types?
- How does forward kinematics differ from inverse kinematics in the context of a serial manipulator?
- Explain the fundamental difference between online and offline teaching methods for robots.
- What is the distinction between a point-to-point task and a continuous path task, and what type of programming is typically used for each?
- Describe the primary functions and components of a robot's teach pendant.