242 Unit Four Control Systems and Maintenance
10.1 Interfacing
An interface is the common point at which two or more systems
communicate with each other. External end effector sensors, work cell
limit switches, external relays, operator alarms, safety equipment, bar code
readers, conveyors, transfer lines, programmable logic controllers, and
machine vision systems all interface with robots.
A robot must be equipped with I/O ports (input/output) to communi-
cate with other systems. The digital signals used for communication travel
from system to system through these ports. Common I/O ports include
digital input ports, digital output ports, serial ports, and parallel ports.
Digital Input Ports
Robots receive a signal indicating the state of an external switch (on or
off) through a digital input port. Limit switches, Figure 10-2, communi-
cate information about such things as the presence or absence of a part at a
given location. This information is used by the robot’s computer program
Figure 10-1. In a robotic work cell, robots interface with other equipment. (Motoman)