Page 460 - Sensors and Control Systems in Manufacturing

Sensors in Flexible Manufacturing Systems
by sensors or in an active way by mechanical means such as contain- 413
erization, feeding, fixturing, or gripping.
The part mating function imposes successive modifications of the
positions of the parts in such a way as to mate them finally in the
required assembly pattern. The modification of the position of the parts
is carried out by manipulating them by transport systems and robot
arms. The part mating function requires a priori information about the
parts to be manipulated and the present state of the assembly. During
this manipulation, the part entropy may increase because of errors in
the robot position or by accidental changes in the manipulated parts.
An example of a multisensor system is a test bed for research on
sensor control of robotic assembly and inspection, particularly com-
parisons of passive entropy reduction to active mechanical means.
Programs for the system must be easy to develop and must perform
in real time. Commercially available systems and sensors had to be
used as much as possible. The system had to be very flexible in inter-
facing with different subsystems and their protocols. The flexible
assembly system (Fig. 8.32) consists of three main parts:

• Robot equipped with a transport system
• Vision sensors, force-torque sensors, and ultrasound sensors
• Control system

The system was built with a variable transport system (VTS)
(Fig. 8.33). It is a modular system in which product carriers are trans-
ported to the system. Two docking stations that can clamp the product
carriers are included in the system. Some of the product carriers have
translucent windows to allow backlighting of the vision system. The VTS
system has its own controller operated by parallel input/output lines.
The robot is equipped with six degrees of freedom and a payload
capacity of 4 kg. The absolute accuracy is 0.2 mm. The robot control-
ler consists of two 68000 microprocessors. The standard way of pro-
gramming the robot is through a teach pendant.
Three different interfaces can connect the robot and control sys-
tem: (1) computer link at 9600 baud (RS-232), (2) adaptive control,
and (3) parallel interrupt lines.
The computer link lets the control computer give commands to
the robot such as:

• Load programs from disk
• Start programs
• Set position registers
• Read out robot positions
• Take direct control of robot movement
• Up- and download robot programs