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Robotics

Advanced Joint Control Strategies

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.  

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Velocity Coupling

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.  

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Inertia and Acceleration Coupling

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.  

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Rigid-Body Dynamics

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.  

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Forces Acting On Robot Links

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.  

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Joint Control with Disturbances

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.  

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Introduction to Rigid-Body Dynamics

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.  

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Robot Joint Control System

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.  

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Friction

All mechanical systems exhibit friction and we learn about two broad classes of friction: linear and non-linear.  

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Gearbox

Electric motors are typically quite weak, they produce a low torque, so it’s very common to add a reduction gearbox.  

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Modelling an Electric Motor

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.  

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Second Order Dynamic Systems

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.  

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Electric Motors

The most common type of actuator is a rotary electric motor so let’s look at the basic principles.  

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Actuators

Actuators are the components that actually move the robot’s joint. So let’s look at a few different actuation technologies that are used in robots.  

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Introduction to Robot Joint Control

We will learn about how we make the the robot joints move to the angles or positions that are required in order to achieve the desired end-effector motion. This is the job of the robot’s joint controller and in this lecture we will learn how this works. This journey will take us in to the realms of control theory.  

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