29-12-2012, 06:59 PM
Intelligent Control and Integration Software for Flexible Manufacturing Cells
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Abstract
Flexible manufacturing cells (FMC) are capable
of producing a broad variety of products and changing their
characteristics quickly and frequently. This flexibility provides
for more efficient use of resources but makes the control of these
systems more difficult. This paper presents several software applications
developed for industrial robots and computer numerical
control (CNC) machines. The objective of this software is to allow
these equipments to be integrated, in an easy and efficient way,
in modern FMC. For the industrial robots, we developed the
“winRS232ROBOTcontrol” and “winEthernetROBOTcontrol”
software. For the CNC machines, the software that was developed
was “winMILLcontrol” for the mill and “winTURNcontrol” for
the lathe.With this software, industrial robots and CNC machines
can be integrated in modern FMC, in an easy and efficient way.
An FMC was developed, with industrial characteristics, with the
objective of showing the potentialities of the developed software.
Thus, the proposed software in this paper was tested and validated
in the developed FMC, and the experimental results show the
viability and success of this software in the coordination of the
different sectors in the FMC and in the improvement of their
performance.
INTRODUCTION
ONE of the most recent developments in the area of industrial
automation is the concept of the flexible manufacturing
cell (FMC). These are highly computerized systems composed
by several types of equipment, usually connected through
a local area network (LAN) under some hierarchical computer
integrated manufacturing (CIM) structure [1], [2], [16], [17].
Developing an FMC is not an easy task. Usually, an FMC
uses equipment—robots, computer numerical control (CNC)
machines, ASRS, etc.—from different manufacturers, having
their own programming language and environments. CNC
machines and industrial robots are still machines that are difficult
to program, because it is necessary to be knowledgeable
in several programming languages and environments.
STATE OF THE ART IN FMS AND FMC CONTROL
An FMS or FMC consists of two major components: hardware
and controlling software. The hardware, which includes
CNC machines, robots, storage and material handling systems,
etc., has been around for decades and problems associated with
the hardware have been well studied and are reasonably well
understood [14]. However, to write FMS and FMC control software
is not a trivial task [14], [15], [21], [23]. Nowadays, the
software is typically custom written, very expensive, difficult to
modify, and often the main source of inflexibility in FMC. Most
FMS and FMC are sold to manufacturing companies as turnkey
systems by integration vendors. As a result, the software expertise
does not reside at the companies and logic/software changes
can only be made by the FMS and FMC vendor.
winRS232ROBOTcontrol
The “winRS232ROBOTcontrol” was developed to be used
in robots manipulators where the communication with the
controller is only possible through the RS232 serial port. With
the “winRS232ROBOTcontrol,” it is possible to develop robot
programs in C++, executed at the PC level, not at the robot’s
controller level. Nevertheless, the “winRS232ROBOTcontrol”
also allows the development of programs to be executed at
a robot’s controller level. Furthermore, it is also possible to
have programs running in the PC and in the robot’s controller
(mix solution), individually or simultaneously. The
“winRS232ROBOTcontrol” was developed for industrial robot
manipulators and was implemented for the special case of
Scorbot ER VII robot. Nevertheless, “winRS232ROBOTcontrol”
was designed to work with all robots that support RS232.
However, of course, whenever we use a different robot, it is
necessary to make some upgrades in the RobotControlAPI
library, according to the used robot.
winEthernetROBOTcontrol
The “winEthernetROBOTcontrol” was developed to be used
in robots manipulators where the communication with the controller
is possible through an Ethernet network. The “winEthernetROBOTcontrol”
is a Dynamic Link Library (DLL) and allows
development of simple and fast applications for robots. The
developed software uses the original capabilities of the robot’s
controllers, in a distributed client/server environment. Fig. 2(a)
shows the PC1 and PC4 communicating with the robots through
“winEthernetROBOTcontrol.”
Table II presents same procedures, functions, and events developed
for the “winEthernetROBOTcontrol.” The procedure
“Robot” allows makes a connection between one PC (with
winEthernetROBOTcontrol) and one or more robots. For that,
it is necessary to create and configure one connection between
the PC and the robot controller (Add New Alias), as shown in
Fig. 2(b). After that, it is possible to communicate and control
the robot remotely through the connection (Alias).
Description of the DNC Interface for CNC Machines
The DNC interface creates a connection between a client
computer (PC client, production master computer, FMS computer,
DNC host computer, etc.) and the control computer of a
CNC machine (PC server) [2]. After activation of the DNC operation,
the DNC computer (PC client) takes over the control of
the CNC machine (PC server). All data such as NC programs,
tool data, and zero point shifts can be transmitted between DNC
computer and CNC machine. The entire production control is
completely taken over by the DNC computer. The automation
devices such as doors, clamping chuck (collet), sleeve, coolant,
etc. can be controlled by the DNC computer. The present status
of the CNC machine is displayed on the DNC computer.
Communication—the connection between PC server and the
PC client can be carried out via block-oriented (e.g., Ethernet/
TCP/IP). In case the TCP/IP connection is interrupted in operation,
the control remains inDNCoperation and can be controlled
again with commands after a new connection reset-up. The protocol
for the communication between CNC machine and the PC
server is designed in such a way that a connection can be carried
out via character-oriented (e.g., RS232).
USB SOFTWARE AND USB KIT
We have developed hardware (USB Kit) and software (USB
software) for control and integration of several equipments in
FMS and FMC (e.g., conveyors, motors, sensors, actuators, and
so on). The USB Kit has various inputs and outputs where we
can connect various sensors and actuators from different manufacturers.
The communication between the PC1 and USB Kit is
done by USB port, as shown in Fig. 4. The PC1 communicates
with others PCs through Ethernet.
CONCLUSION
Robust control software is a necessity for an automated FMS
and FMC and plays an important role in the attainable flexibility.
Often, FMS and FMC are built with very flexible machines
(robots, CNC machines, ASRS, etc.), but the available
control software is unable to exploit the flexibility of adding new
machines, parts, changing control algorithms, etc. The present
robot control and CNC machines control systems are closed and
with deficient software interfaces. Manufacturers should provide
powerful APIs to enable user access to system resources,
from a remote computer. Writing FMS and FMC control software
is not a trivial task. Nowadays, the software is typically
custom written, very expensive, difficult to modify, and often
the main source of inflexibility in FMS.