chapter six

6 Robot geometry and manipulator kinematics: Building Snackbot

This chapter covers

Geometric and kinematic robot descriptions
Individual joint motor control
Point-to-point (PTP) motions

The previous two chapters provided us with the tools to begin building (virtual) robots: a robotics software framework (ROS) and a robotics simulator (Gazebo).

We will now build a simple robot, SnackBot, which ensures we are well energized throughout the book. SnackBot picks up snacks from a known location on a table, a stack of potato chips in a can, and delivers them to another known location, a plate next to our keyboard. It is a three-degree-of-freedom (DoF) manipulator fixed to the table, using electric motors as joint actuators, controlled individually, and moving in point-to-point (PTP) motions. We will look at each of these aspects in turn, starting with modeling the robot in software.

Figure 6.1 CAD model of the 3 DoF SCARA-style SnackBot manipulator, which uses three independently actuated joints to pick up snacks from a chip can and deliver them to a plate.

6.1 Robot Description

6.1.1 Shapes, Poses, and Dimensions

6 Robot geometry and manipulator kinematics: Building Snackbot

This chapter covers

Figure 6.1 CAD model of the 3 DoF SCARA-style SnackBot manipulator, which uses three independently actuated joints to pick up snacks from a chip can and deliver them to a plate.

6.1 Robot Description

6.1.1 Shapes, Poses, and Dimensions

6.1.2 Coordinate Systems (Frames)

6.1.3 Coordinate Transformations

6.1.4 ROS tf2

6.1.5 Shapes and surfaces

6.1.6 Common Kinematics Representations

6.2 Manipulator Kinematics

6.2.1 Forward Kinematics

6.2.2 Inverse Kinematics

6.3 Summary