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12 Commercial Robot Manipulators

communications ports (e.g. RS-232), or in some through direct connections
to the robot controller data bus. Recent integration efforts are making it
possible to interface robotic workcells to the internet to allow remote site
monitoring and control. There are many techniques for this, the most
convenient of which is Lab VIEW 6.1, which doe not require programming
in Java.

1.4 Sensors

Much of the information in this section was prepared by Kok-Meng Lee
[Lewis 1998]. Sensors and actuators [Tzou and Fukuda 1992] function as
transducers, devices through which high-level workcell Planning,
Coordination, and Control systems interface with the hardware components
that make up the workcell. Sensors are a vital element as they convert states
of physical devices into signals appropriate for input to the workcell PC&C
control system; inappropriate sensors can introduce errors that make proper
operation impossible no matter how sophisticated or expensive the PC&C
system, while innovative selection of sensors can make the control and co-
ordination problem much easier.
Sensors are of many different types and have many distinct uses. Having
in mind an analogy with biological systems, proprioceptors are sensors
internal to a device that yield information about the internal state of that
device (e.g. robot arm joint-angle sensors). Exteroceptors yield information
about other hardware external to a device. Sensors yield outputs that are
either analog or digital; digital sensors often provide information about the
status of a machine or resource (gripper open or closed, machine loaded, job
complete). Sensors produce outputs that are required at all levels of the PC&C
hierarchy, including uses for:

• servo-level feedback control (usually analog proprioceptors)
• process monitoring and coordination (often digital exteroceptors or part
inspection sensors such as vision)
• failure and safety monitoring (often digital—e.g. contact sensor,
pneumatic pressure-loss sensor)
• quality control inspection (often vision or scanning laser).

Sensor output data must often be processed to convert it into a form
meaningful for PC&C purposes. The sensor plus required signal processing
is shown as a Virtual Sensor. It functions as a data abstraction—a set of data
plus operations on that data (e.g. camera, plus framegrabber, plus signal
processing algorithms such as image enhancement, edge detection,

Copyright © 2004 by Marcel Dekker, Inc.