Let’s have a look at a few different kinds of robots. The first one we’re going to consider is what’s called a Gantry robot and sometimes called a Cartesian robot. It’s a robot that allows us to control the position of the tool-tip in three-dimensional space, so we can control the X, Y and Z coordinate of the tool-tip. The Gantry robot has got a boom which moves in the direction indicated by the blue arrow and the tool moves along the boom in the direction shown by the red arrow. And, finally, the tool itself moves up and down in the direction indicated by the green arrow. We have three motion axes, each orthogonal to the others.
This kind of robot is known as a SCARA robot and they are widely used in manufacturing and package handling applications.
The part of the robot that’s highlighted in red rotates around the axis shown here. And, the part of the robot that’s highlighted in blue rotates around this axis. And, finally, the tool moves up and down along the axis shown here by the green arrow. Some variants of the SCARA robots also rotate the tool around the axis shown by the green dashed line. The term SCARA is an acronym for Selective Compliance Articulating Robot and so why the complex and tortured acronym. But essentially, what it means is that the robot is quite free to move in the horizontal plane, but it’s very, very stiff in the vertical direction and that’s just a consequence of the way it has been designed and constructed.
A relatively new class of robot is the parallel link robot and this is an example of one shown here. A great advantage of the parallel link robot is all of the motors can be situated in the base of the robot and they are connected via mechanical linkages to the tool. So, there are a number of mechanical linkages in parallel connecting the tool to the motors. This is a very different architecture to the Gantry robot and the SCARA robot. Those robots are referred to as serial link robots because there is a chain of links from the base to the tool-tip. Here, the links are all in parallel.
Here are a couple of examples of educational robots. The one on the left is a hobby robot that has got four mechanical joints connecting the base to the tool-tip where there is a parallel jaw or a two-finger gripper.
The Aldebaran NAO robot shown here has got two arms and two legs. And, each of the arms and the legs is essentially a serial link manipulator. In the case of the arms, there are four joints, two at the shoulder, one at the elbow and one at the wrist, which control the position and orientation of the wrist which holds a number of fingers. And, those fingers themselves have got a number of joints within them.
A very common class of robots have got six axes, the six-axis serial link robot. On the left, we can see an example of a state of the art industrial robot which has got six links. And, on the right, we can see a very unusual example of a six-axis robot. This arm is used to load and unload satellites and other cargo from the shuttle’s payload bay. Here is a very famous robotic arm in the history of robot arm development. It was developed at Stanford University and it’s commonly known just as the Stanford Robotic Arm. It was developed in 1969. That’s the year that people first walked on the moon.
What differentiates this robot arm from robot arms that are very common today is that it has got a sliding joint. The third joint in this robot slides backwards and forwards and changes the distance between the robot’s tool, it’s wrist and the base of the robot.
The first company to produce an industrial robot was Unimation Inc, a Connecticut-based company and they were founded in 1956 and installed their first industrial robot in to a manufacturing plant a couple of years later. The technology is really quite old. This is an example of one of those Unimate robots from 1983. It’s the PUMA 560 robot, quite a famous robot really in the history of robotics research. There were many, many of these robots actively involved in manufacturing, but there are also a great number of them in university research labs such as learning how to hack these robots so that they could add their own control algorithms to the robot. So, many, many early robotics research papers are all based on these particular PUMA robots, the PUMA 560.
We start by looking at a number of different types of robot arm with particular focus on serial-link robot manipulators.