Chapter 10 Interfacing and Vision Systems 247
Digital
system
controller
or
PC
GPIB data bus - 8 bit
GPIB control bus - 8 bit
Peripheral
equipment
1
Peripheral
equipment
2
Peripheral
equipment
3
Figure 10-7. The GPIB parallel interface bus is used here to connect external test equipment to a
digital system controller or PC.
number of connected devices, whichever is less. The cable between
any two devices must not exceed 4 meters. The bus carries data in both
directions, 8 bits at a time, and controls both the data and the direction.
The bus can connect various kinds of devices to the controller, such as
equipment that can only “talk,” equipment that can only “listen,” and
equipment that can both “talk” and “listen.” Many controllers can be
attached to the GPIB, but only one controller may have command at
any given time.
10.2 Machine Vision
Machine vision systems give a robot “eyes,” which allow it to perform
in a more intelligent manner. These systems may be used for such applica-
tions as guidance, part orientation, measuring and inspecting parts, and
image identification, Figure 10-8. Machine vision has become an essen-
tial requirement in automated work cells. Robotic work cells that are not
equipped with machine vision require all parts to be pre-oriented before a
robot can grasp them and perform its task.
Machine vision eliminates the need for many machine operators by
performing many of the complex tasks once done only by humans. Systems
used for assembly and inspection have had a major impact in the automotive
and electronics industries. For example, today’s printed circuit boards often
contain thousands of individual parts. If even a tiny fraction of these parts is
incorrectly placed on the board, the cost of finding and repairing the problem
is enormous. When human workers perform circuit board assembly, fatigue
can cause as much as a 20 percent error rate. Using robots with machine
vision for circuit board assembly significantly reduces the error rate.