We will discuss some important non-technical aspects of robotics. What are the problems facing our society that robots might help to address? There are lots of tasks that robots could do, but should they? What are the ethical considerations around robots? Why are people scared of robots?
This video gives summary of rigid-body dynamics.
So far we have worked out the torques on a robot’s joints based on joint position, velocity and acceleration. For simulation we want the opposite, to know its motion given the torques applied to the joints. This is called the forward dynamics problem.
A number of strategies exist to reduce the effect of these coupling torques between the joints, from introducing a gearbox between the motor and the joint, to advanced feed forward strategies.
We describe the velocity coupling terms of the robot as a matrix which represents how the torque on one joint depends on the velocity of other joints.
We describe inertia of the robot as a matrix which represents how inertia of a joint depends on the position of all the joints, and how the torque on one joint depends on the acceleration of other joints.
We examine the gravity term and explore the effect of changing robot payload.
We can factorise the joint torque expression into an elegant matrix equation with terms that describe the effects of inertia, Coriolis and centripetal and gravity effects.
In a serial-link manipulator arm each joint has to support all the links between itself and the end of the robot. We introduce the recursive Newton-Euler algorithm which allows us to compute the joint torques given the robot joint positions, velocities and accelerations and the link inertial parameters.
We start by considering the effect of gravity acting on a robot arm, and how the torque exerted will disturb the position of the robot controller leading to a steady state error. Then we discuss a number of strategies to reduce this error.
We will learn about the forces that are exerted on a robot’s joint by gravity acting on links, friction, and the coupling forces where the motion of one joint imparts a force on other joints.
This video gives Summary of Robot Actuators and Control.
In this video we will study the limits of electric motor performance.
We will use Simulink to create a dynamic model of a single robot joint and simulate its operation.
A robot joint controller is a type of feedback control system which is an old and well understood technique. We will learn how to assemble the various mechatronic components such as motors, gearboxes, sensors, electronics and embedded computing in a feedback configuration to implement a robot joint controller.
All mechanical systems exhibit friction and we learn about two broad classes of friction: linear and non-linear.
Electric motors are typically quite weak, they produce a low torque, so it’s very common to add a reduction gearbox.
We can model a DC motor as a resistor and a voltage source, and then understand the implications of controlling either the voltage or current supplied to the motor. We also learn about common methods for motor control such as the H-bridge driver and pulse width modulation.
If your knowledge of dynamics is a bit rusty then let’s quickly revise the basics of second-order systems and the Laplace operator. Not rusty? Then go straight to the next section.
The most common type of actuator is a rotary electric motor so let’s look at the basic principles.