29:43
Lecture 03: Experimentation I
NPTEL IIT Kharagpur
Overview
This lecture introduces the fundamental concepts and practical applications of robotic experimentation, focusing on the UR5 serial manipulator. It covers the robot's hardware components, coordinate frames, and trajectory planning methods (joint space vs. task space). The lecture then demonstrates how to program the UR5 using its teach pendant for two primary tasks: pick-and-place operations using point-to-point motion, and continuous path tracing for tasks like drawing a rectangle. It highlights different command types like 'move j', 'move l', and 'move p', along with auxiliary commands for program control and execution.
How was this?
Save this permanently with flashcards, quizzes, and AI chat
Chapters
- The UR5 is a 6-degree-of-freedom serial manipulator with a 5 kg payload capacity.
- Key hardware components include the manipulator arm, control unit, and teach pendant for user interaction.
- The teach pendant allows users to provide instructions and control the robot's movements.
- The robot's structure consists of a base joint, shoulder, elbow, and three wrist joints, all rotary.
Understanding the physical components and capabilities of the robot is crucial for setting up experiments and comprehending its operational limits.
The UR5's 6 joints (base, shoulder, elbow, wrist 1, wrist 2, wrist 3) allow for complex movements in 3D space.
- Defining a robot's position and orientation requires understanding different coordinate frames.
- The World Frame is a fixed, permanent reference frame.
- The Base Frame is attached to the manipulator's base and serves as its primary reference.
- The Tool Center Point (TCP) Frame is located at the end-effector where a tool or gripper is mounted.
Accurate definition and understanding of coordinate frames are essential for precise robot motion planning and execution, ensuring the robot interacts with its environment as intended.
The position and orientation of the TCP frame must be known relative to the base frame for the robot to perform tasks like grasping an object.
- Trajectory planning defines how a robot moves between points in its workspace.
- Joint Space Trajectory Planning: The robot moves directly between specified joint angle configurations, potentially resulting in non-linear end-effector paths.
- Cartesian (Task) Space Trajectory Planning: The desired path of the end-effector in 3D space is defined, and the robot's joint movements are calculated to follow this path linearly.
Choosing the correct trajectory planning method impacts the robot's movement smoothness, efficiency, and the predictability of its end-effector's path.
In joint space, moving from point A to B might result in the end-effector taking a curved path, whereas in task space, the end-effector would move in a straight line between A and B.
- The teach pendant is the primary interface for controlling and programming the UR5.
- Upon startup, brakes are disengaged, allowing robot movement.
- Four main modes of operation: Run Program (execute existing programs), Programmer (create/edit programs), Setup (configure robot, external control), and Shutdown (power off).
- The 'Run' mode within 'Run Program' allows manual control of individual joints and Cartesian movements.
Familiarity with the teach pendant's interface and operational modes is fundamental for interacting with and controlling the robot for various tasks.
Using the 'Move' screen in 'Run Program' mode, users can directly manipulate each of the 6 joints or control linear/rotational movements of the tool center point.
- Pick-and-place tasks involve programming point-to-point motions.
- Key commands include 'Move J' (joint space), 'Move L' (linear task space), and 'Move P' (constant speed task space).
- 'Move J' is independent of the path, while 'Move L' follows a linear path.
- 'Move P' ensures constant speed and can provide smoother transitions between waypoints using a blend radius.
- Auxiliary commands like 'Wait', 'Pop Up', and 'Halt' control program flow and provide feedback.
Understanding these programming commands allows for the creation of automated sequences for tasks like picking up and placing objects, forming the basis of many industrial robotic applications.
To pick up an object, a 'Move L' command might be used to linearly approach the object, followed by a 'Wait' command to allow a gripper to close, and then another 'Move L' to lift it.
- Programming involves defining waypoints for the robot to move to.
- Waypoints can be set manually using joint/Cartesian controls or by enabling 'Free Drive' to move the robot by hand.
- The 'Move J' command is used to transition between waypoints in joint space for a pick-and-place sequence.
- A 'Halt' command can be used to stop the program after a sequence, or it can be omitted for continuous looping.
This practical demonstration shows how to translate abstract programming concepts into a functional robotic task, reinforcing the learning of commands and waypoint definition.
The process involves moving the robot to a starting position, then using 'Free Drive' to position the end-effector over an object, saving this as Waypoint 1, and repeating for other necessary locations.
- Continuous path tasks, like drawing, require precise linear movements.
- The 'Move L' command is essential for tracing defined paths accurately.
- Multiple waypoints are defined to form the desired shape (e.g., a rectangle).
- The program can be set to run once or in a loop by including or omitting a 'Halt' command.
Executing continuous path tasks demonstrates the robot's ability to perform more complex, coordinated movements beyond simple point-to-point actions, applicable to tasks like welding or painting.
To draw a rectangle, the robot is programmed to move linearly between four corner waypoints using 'Move L' commands, tracing the shape on a surface.
Key takeaways
- Robotic systems like the UR5 require understanding of their physical structure, coordinate frames, and control interfaces.
- Trajectory planning in joint space and task space offers different approaches to robot motion, each with distinct characteristics.
- The teach pendant provides a user-friendly interface for manual control, programming, and configuration of the robot.
- Programming commands ('Move J', 'Move L', 'Move P') are the building blocks for creating automated robotic tasks.
- Defining and saving waypoints is a critical step in programming both pick-and-place and continuous path movements.
- Auxiliary commands are vital for managing program execution, flow control, and user feedback.
- Practical experimentation with the teach pendant is essential for solidifying understanding of robotic programming concepts.
Key terms
Serial ManipulatorUR5Degree of Freedom (DOF)Payload CapacityTeach PendantControl UnitWorld FrameBase FrameTool Center Point (TCP) FrameWorkspaceJoint Space Trajectory PlanningCartesian/Task Space Trajectory PlanningRun Program ModeProgrammer ModeSetup ModeMove J CommandMove L CommandMove P CommandWaypointFree DriveBlend RadiusHalt Command
Test your understanding
- What are the three primary coordinate frames used when defining a robot's position, and what is the purpose of each?
- How does joint space trajectory planning differ from Cartesian (task) space trajectory planning, and what are the implications for the robot's end-effector path?
- Describe the function of the 'Move J', 'Move L', and 'Move P' commands in robot programming.
- What is 'Free Drive' mode, and how is it used during the process of programming waypoints?
- Why is understanding the different modes of operation on the teach pendant (Run, Programmer, Setup) important for a user?