Page 471 - Sensors and Control Systems in Manufacturing

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Cha p te r
Ei g h t

The common features of such units are the ability to manu-
ally send the robot to a desired position, or “inch” or “jog” to
adjust a position. They also have a means to change the speed
since a low speed is usually required for careful positioning
or while test-running through a new or modified routine. A
large emergency stop button is usually included as well. Typ-
ically, once the robot has been programmed there is no more
use for the teach pendant.
• Lead-by-the-nose. Lead-by-the-nose is a technique offered by
most robot manufacturers. While the user holds the robot end
effector, another person enters a command that de-energizes the
robot and it goes limp. The user then moves the robot by hand
to the required positions or along a required path, while the
software logs these positions into memory. The program can
later run the robot to these positions or along the taught path.
This technique is popular for tasks such as paint spraying.
In addition, machine operators often use user interface devices,
typically touch screen units, which serve as the operator control panel.
The operator can switch from program to program, make adjust-
ments within a program and also operate a host of peripheral devices
that may be integrated within the same robotic system. These include
end effectors, feeders that supply components to the robot, conveyer
belts, emergency stop controls, machine vision systems, safety inter-
lock systems, bar code printers, and an almost infinite array of other
industrial devices that are accessed and controlled via the operator
control panel.
The teach pendant or PC is usually disconnected after program-
ming and the robot then runs on the program that has been installed
in its controller. However, a computer is often used to “supervise” the
robot and any peripherals, or to provide additional storage for access
to numerous complex paths and routines.
A robot and a collection of machines or peripherals is referred to
as a work cell, or cell. A typical cell might contain a parts feeder, a
molding machine and a robot. The various machines are “integrated”
and controlled by a single computer or PLC.

8.14.3 End Effectors
The most essential robot peripheral is the end effector, or end-of-arm-
tooling. Common examples of end effectors include welding devices,
such as MIG-welding guns, spot-welders, and others; spray guns,
grinding and deburring devices (such as pneumatic disk or belt
grinders, burrs, etc.); and grippers, devices that can grasp an object,
and that are electromechanical or pneumatic. Another common
means of picking up an object is by vacuum. End effectors are fre-
quently highly complex, made to match the handled product, and are