Web-based Hardware-Neutral Sequential Controller Chiaming Yen, Wujeng Li and Jui Cheng Lin Department of Mechanical Design Engineering National Hu-wei Institute of Technology Yu-lin, Taiwan 632 E-mail:
[email protected],
[email protected],
[email protected]
Abstract built electronically [1]. This trend results in the This research creates a web-based hardware
integration
of
mechanical
actuators
and
neutral sequential controller system to assist user on
micro-controlled devices. In these systems, flexibilities
design of the general-purpose sequential controller. The
can be further achieved using the powerful and
functions of the system include control circuit setup
configurable control units. In view of the quick advance on the new
and simulation, physical system control and Web-based remote control. The main objective of these systems is to provide
technology, control system product inevitably has to apply
new
devices
and
components
to
gain
a hardware neutral environment for integration of
considerably competitiveness.
Therefore, legacy
different types of data acquisition units from different
systems surrounded by state-of-the-art components are
manufacturing companies. This controller environment
usually the case to challenge engineers on almost every
allows one to add or remove corresponding modules
industrial application. Under these circumstances, for
without further modification of the original control
industrial on-line field monitor and control system
software.
design, to integrate various new, old, closed, and open
This system is written in Java, thus can be either
products to work together has become a very important
executed as a unique program or embedded in an html
task. In this study, a hardware neutral controller system
page. The hardware neutral capability is achieved
design methodology has been implemented to solve
through the applications of Java dynamic linkage and
these problems.
object reflection. Due to the nature of being a Java
The development of the sequential controller
program, this system can be used in a Microsoft
today is not only reaching a PC-based controller era,
Windows or Linux system.
but also entering into a networked age. Sequential
(Keywords: Object-Oriented Programming, Pneumatic
controllers
may include
Circuit Design, Sequential Controller, Programmable
hand-held
PC and
Logic Controller)
electronic. To integrate all these devices of different
mobile
others
phones,
embedded
PDA,
consumer
brand, a hardware neutral controller scheme with 1. Introduction
real-time simulation and monitor functions becomes an important issue to address.
In recent years, due to the fast development of the microprocessors, most sequential controllers are
2. Motivation and Literature Review
To communicate hardware controller of different
As a sequential controller deployed on a network,
brand with network functions, DCOM from Microsoft
it may involve a lot of devices and personnel. To take
[2], RMI from SUN [3] and CORBA [4] are some
this situation into consideration, the WebLadderCAD
major techniques to follow. Among these, OPC (OLE
has collaborative functions to allow multi-user to work
for Process Control) [5] is proposed to solve the
on a set of design simultaneously. In order to connect
industrial process control problem under DCOM
the web browser and server, data communication is
methodology from Microsoft.
established through Java applet and servlet techniques
Recently, the network connecting speed has
[9]. Technically, the Java servlet works like the
improved to allow high volume data storage to separate
application layer of multi-tier model to incorporate
from the computing unit. Therefore, in the future,
with the Apache web server [10] through the Tomcat
PC-based control system design also treat network as a
servlet engine [11]. All the data acquire/retrieve
major component to allow more legacy hardware to
functions were implemented by Java servlets. One of the data acquisition components used in
work with new devices. In this study, Java technology [6] [7] is used to
this paper is called NAP7000 [12]. This device has a
develop a hardware neutral sequential controller to
RS232 interface to connect with a computer. On the
allow different control hardware to work together. This
ethernet side, an Adam6000 [13] is used. These two
software
data
remote data acquisition hardware with different data
acquisition modules, allows a designer to efficiently
transfer functions were used to test the feasibility of the
integrate different sequential control devices to achieve
system proposed in this paper.
package
combined
with
remote
designated job.
The procedures to use the sequential controller system developed in this paper were listed as follows:
3. Controller Architecture 1. Define controlled system: The architecture of the implemented sequential controller is shown as Figure 1. This includes the main controller software called WebLadderCAD that is a
Select controlled device icons and place it on the virtual pneumatic lab area. 2. Design control circuit:
web-based sequential controller package written in
Select electrical device icons and fulfill the
Java. This WebLadderCAD can also embed into a web
corresponding circuit design.
page to become part of a remote control courseware
3. Simulate controlled system: Upon the designed electrical circuit, the
[8].
computer software can be asked to simulate the corresponding results. 4. Perform PC-based control: To execute the local site PC-based sequential control, one should select server mode and let the system automatically scanning available data acquisition modules. After the input and output signals of the hardware connection were set, the control privilege can be claimed Figure 1. Sequential Controller Architecture
to activate the associated control sequence.
8. Data storage:
5. Remote monitoring and control: As the remote system performing PC-based
All the design results were saved on a remote
sequential control, any local computer can
database system.
either use the sequential control software in
9. Collaborative Design:
the applet mode or application mode to start
For multi-user design purpose, the software can be
and monitor the control.
activated on a collaborative mode. 10. User defined component extension: Users can extend the software functions by adding
3.1 Sequential Controller Design Software
custom-built control devices in specially formatted The WebLadderCAD [8] software is designed to
ASCII file.
perform web-based computer aided sequential control system design. This system has the following functions: 1. Visualized control system process: The system allows users to perform control system design by assembly of the visualized device icons. 2. Visualized pneumatic and electrical devices: System provides complete set of general pneumatic and electrical device icons. 3. Computer aided pneumatic and electrical circuit design: The software can assist users to complete required
Figure 2. Sequential Controller Design Software
sequential control system designs. An example of using the sequential control
4. Design automation of pneumatic and electrical circuit design:
design software was shown on Figure 2. The user
Users can ask software to automatically complete
combined valve controlled pneumatic devices with
sequential control system designs by giving the
limit switches and electrical devices to complete the
designated
definition of the system. Consequently, a motion
input
sequence
requirements
and
parameters.
sequence window is open to add the required motion sequences. Automatic design function can then be used
5. Diagnosis and analysis on pneumatic and electrical circuit:
to perform the corresponding design.
The software can automatically check the design errors, such as the incorrect wiring and overloading,
3.2 Remote Data Acquisition System
etc. 6. Dynamic simulation:
After the computer aided design and simulation
Design results can be simulated through the
processes , the simulated results can be transmitted
animation
through the digital I/O module to activate the physical
of
the
corresponding
actions
of
pneumatic and electrical devices. 7. PLC control commands:
control components. As shown in Figure 3., the NAP7000 is a set of
The software can transfer the design circuit into the
remote data acquisition system communicated with PC
specific brand PLC commands.
through a RS232 interface. There is unique address for
each module. The modules are treated as passive units
setup.
In
this
study,
the
controller
system
to response commands from the computer. On the other
communicates with the ADAM6000 module through a
hand, transmit baud rate can be set for each module,
simple ModBus protocol [15] Java class libraries.
checksum method was used to ensure the rightness of each set of transmitted data.
3.3 Controller Software Design
The software architecture was shown in Figure 5. The
processes
include
control
system
design,
simulation and physical system control. The control system
design
involves
control
circuit
design
interactively or automatically. The simulation can be used to check the rightness of the design. Before the simulation starts, the control circuit is translated into PLC codes. During the simulation process, a PLC code interpreter is used to execute the PLC codes repeatedly. Figure 3. NAP 7000 Remote Data Acquisition System
The final procedure is to activate the physical devices by sending the component status to the respective data
In this study, Java Communications API [14] was
acquisition modules.
used to support the serial port communication. Since the hardware related driver was packed inside a high level Java class, this API preserved Java’s cross platform advantage. As the codes ported into a different platform, no changes on the Java codes were necessary.
Figure 5. Controller Software Architecture
The hardware neutral function of the system is to allow the addition and removal of data acquisition Figure 4. ADAM6000 Remote Data Acquisition System
modules (hardware) without any modification of the controller core codes. Hardware neutral can be
The ADAM6000 is another set of remote data
achieved by defining these functions into abstract
acquisition system used in this paper. The module is
classes or interfaces. These will allow the system
shown as Figure 4. The system is connected with a PC
driver and module driver program to inherit these
through an Ethernet connection. There is one IP for
abstract classes and implement the required functions.
each module to embed associated web page server.
Due to the dynamic linkage property of Java,
Users can use the web browser to connect to its web
Java codes are loaded only when they are about to be
page and execute specific applet to show the module’s
executed. This attribute allows us to expand a Java
program without recompilation on the source codes. This also let us add drivers to our controller without any change on original codes. In this study, the sequential controller comprises the local PC-based control and remote control modes. The remote controller function is achieved through client-server architecture, as shown in Figure 6. In the remote control mode, users connect to server program through a web browser to activate the program as an applet. The applet will download the mirror of data acquisition module from the hardware server program. Hence, the program will allow user to enter monitor mode. The user can also enter into the administration mode to claim the control privilege. In
Figure 7. Hardware Auto-Search
this case, the user can upload design data into server and start the control action to monitor the control
As shown in Figure 8., the NAP7000 and ADAM6000
results.
modules were used to control two sequential pneumatic pistons. Figure 9 shows the application of remote monitor and control for system developed in this paper. In this case, the lower computer executes the program in a client mode and connects to the upper server computer to claim for control token. Once it takes the control privilege, the client computer can control the hardware devices and monitor their control results.
Figure 6. Remote Controller and Monitor Design: Client/Server Based.
4. Results
Figure 7 shows two data acquisition systems linked with the sequential controller developed in this paper. As the program entering into the hardware mode, it scans in certain directories and subdirectories until all the hardware driver classes were found. Once the classes were found, the codes were loaded and instanced to show the graphic module images as shown in Figure 7.
Figure 8. PC-based Sequential Control
6. References
[1] W. Li and S. Jen, Pneumatics and Hydraulics. Taipei: Gou-Li Publishing Co., 1998. [2] Thuan L. Thai, Thuuan L. Thai, Andy Oram (Editor),”Learning DCOM”, O'Reilly & Associates; ISBN: 1565925815. [3] JavaTM Remote Method Invocation (RMI), Figure 9. Remote Sequential Control
http://java.sun.com/products/jdk/rmi/index.html. [4] Michi Henning, Steve Vinoski,” Advanced CORBA
5. Concluding Remarks
Programming with C++”, Addison-Wesley Pub Co; ISBN: 0201379279.
As the potential for linking many advanced
[5] OPC (OLE for Process Control),
network-ready hardware devices into a powerful
http://www.opcfoundation.org/.
controller increases, we need to create more software packages that can “grow” with the hardware setup. In this paper, a web-based hardware neutral sequential controller system was created to deal with these problems. This hardware neutral system can be used to
[6] The JavaTM 2 Platform, Standard Edition v1.3.1, http://java.sun.com/j2se/1.3/. [7] Bruce Eckel,”Thinking in Java”, 2nd edition,http://www.mindview.net/Books/TIJ/. [8] C.Yen, W. Li, and R. Lin,”A Web-based,
assist user on implementing the design of the
Collaborative, Computer-Aided Sequential Control
general-purpose pneumatic sequential controller. The
Design Tool, to appear in IEEE Control System
functions of the system include control circuit setup
Magazine, 2003.
and simulation, physical system control and web-based remote control. The main objective of these systems is to provide a hardware neutral environment for integration of different type of data acquisition units from different manufacturing companies. This controller environment allows one to add or remove corresponding modules without further modification of the original control software. This system is written in Java, thus can be either
[9] Jason Hunter and William Crawford,”Java Servlet Programming”, 2nd edition, 2001, http://www.amazon.com/. [10] The Apache Software Foundation,”Apache Server”, http://www.apache.org/. [11] The Apache Software Foundation,”Servlet Engine”
Tomcat, http://jakarta.apache.org/.
[12] NAP7000 Remote Data Acquisition Module, ICPDAS Co., Ltd. htp://www.icpdas.com.tw/. [13] Adam6000 Remote Data Acquisition
executed as a unique program or embedded in an html
Module,Advantech Co., Ltd.,
page. The hardware neutral capability is achieved
http://www.advantech.com.tw/
through the applications of Java dynamic linkage and
[14] Sun Microsystems, Inc” JavaTM Communications
object reflection. The system can be used in any
API”,
environment with Java virtual machine and therefore
http://java.sun.com/products/javacomm/index.html
can be used as a software component to develop cross-platform computer aided control system design coursewares.
[15] MODBUS Protocol, http://www.modbus.org/.
