Describe three different types of proximity sensors. In some applications, it may be required to sense only two-state positions (e.g., presence or absence, go or no-go). Proximity sensors can be used in such applications, and in that context they are termed proximity switches (or limit switches). For example, consider a parts-handling application in automated manufacturing in which a robot end effector grips a part and picks it up to move it from a conveyor to a machine tool. We can identify four separate steps in the gripping process. Explain how proximity switches can be used for sensing in each of these four tasks:
(a) Make sure that the part is at the expected location on the conveyor.
(b) Make sure that the gripper is open.
(c) Make sure that the end effector has moved to the correct location so that the part is in between the gripper fingers.
(d) Make sure that the part did not slip when the gripper was closed.