I. Read and give a short summary of Text 9.

Industrial robots are classic examples of position control systems. In most cases, the robot has a single arm with shoulder, elbow, and wrist joints, as well as some kind of hand known as an end effector. The end effector is either a gripper or other tool such

as a paint spray gun. Robots are used to move parts from place to place, assemble parts, load and off-load NC machines, and perform such tasks as spray painting and welding. Pick-and-place robots, the simplest type, pick up parts and place them somewhere else nearby. Instead of using sophisticated feedback control, they are often run open-loop using mechanical stops or limit switches to determine how far in each direction to go (sometimes called a " bang-bang" system). An example is shown in Figure 1.13. This robot uses pneumatic cylinders to lift, rotate, and extend the arm. It can be programmed to repeat simple sequence of operations. Sophisticated robots use closed-loop position systems for all joints. An example is the indus­trial robot shown in Figure 1.14. It has six independently controlled axes (known as six degrees of freedom) allowing it to get to difficult-to-reach places. The robot comes with and is controlled by a dedicated computer-based controller. This unit is also capable of translating human instructions into the robot program during the " teaching" phase.

The arm can move from point to point at a specified velocity and arrive within a few thousandths of an inch.