Page 56 - Toucpad robotics C11

A Frame is a coordinate system (with an origin and a set of three perpendicular axes, typically labelled X, Y, and Z) that
provides a reference for defining the position and orientation of objects within that system. Every object in a robotic
system, from the robot’s base to its gripper, is described relative to some frame. By understanding these frames and how
they relate to each other, a robot can navigate its environment and perform tasks with extreme precision.
Frames: The Local Coordinate System

Every component in a robot has its own local frame. For instance, a robot’s forearm has a frame attached to it, an
accelerometer sensor has a frame attached to it, and a workpiece on a table has its own frame.
Position: The location of an object’s origin can be described by a position vector from the origin of a reference frame
u
to the object’s origin. The position of a point in space (e.g., the fingertip of a gripper) is defined by a set of coordinates
(x, y, z) relative to the origin of a frame. For instance, if a robot’s base frame is at the origin (0, 0, 0) of a room, the
position of a table could be a vector to its centre at (2, 5, 0) metres.
Orientation: The orientation of an object (e.g., which way the gripper is facing) is defined by the rotation of its local
u
frame’s axes relative to the axes of a reference frame. For example, if a gripper needs to be rotated 90 degrees to
pick up an object, this is described as a rotation of the gripper’s frame relative to the frame of the object.
Pose: The combination of an object’s position and orientation is called its pose. A robot’s entire movement can be
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described as a change in the pose of its various parts.
The beauty of using frames is that once you know the relationship between different frames, you can translate positions
and orientations from one frame to another. This is the core of how a robot’s ‘brain’ understands its body.

Reference Frames: Understanding Moving and Fixed Frames
In robotics, we primarily deal with two types of reference frames: fixed frames and moving frames.

Fixed Frames (Static Reference Frames)
Description: A fixed frame is a coordinate system that remains stationary and does not move. It serves as the main,
u
universal reference point for the entire system or environment.
Common Fixed Frames:
u
World Frame: This is the ultimate, global reference frame. It’s often placed at a convenient, fixed location in the
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robot’s workspace, such as a corner of the factory floor or the centre of a room. All other positions are ultimately
referenced back to this world frame.
Base Frame: This is a fixed frame attached to the robot’s base. It’s often coincident with the world frame but is a
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more direct reference for the robot’s own structure. All of the robot’s movements and joint angles are calculated
relative to this base frame.

Crucial Role: Fixed frames are the anchor points. They provide a stable, unchanging reference for everything. For
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a robot to know where to go, it needs to know the destination’s coordinates in a fixed frame. For example, in a car
factory, the location of a car’s chassis on the assembly line is defined by coordinates in the world frame.
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Touchpad Robotics - XI