William Edwards
L01/Dr. Keezer
Plasma Etchers
Compact Programmable Logic Controllers in Systems
Introduction
Programmable Logic Controllers (PLCs) were initially adopted by the automotive industry when
software revision replaced the re-wiring of hard-wired control panels each time the production models
changed. Small PLCs have a fixed number of connections for inputs and outputs, while modular PLCs
have a chassis into which modules are placed with different functions. This wide range of complexity
creates several opportunities for commercial applications. This paper focuses on the latest advances in
programmable logic controllers, discusses some of the technologies commercially available, and
identifies some of the techniques used to manage the control of autonomous and semi-autonomous
systems.
Commercial Applications
PLCs are used in technologies such as machine automation and automatic guided vehicles
(AGV). For controlling the navigation of the AGV, controllers integrate fuzzy logic with a programmable
logic controller [1]. The commercial demands for PLCs are met by multiple companies such as AllenBradley, GE, Siemens, and Schneider Electric. The important factor when choosing a PLC is
consideration of the number of necessary inputs and outputs. This customization keeps suppliers from
advertising cost since PLCs are designed specifically for their application. Allen-Bradley makes the
CompactLogix L35E, which can handle up to 30 I/O devices while being able to handle up to eight
processes simultaneously. This PLC cost $2700 base and can be customized with additional modules [2].
Similarly GE makes the QuickPanel Control PLC which allows for 100 I/O devices with an integrated
visualization screen and cost approximately $8000 [3].
Underlying Technology of PLCs
Unlike general-purpose computers, the PLC is designed for multiple input and output
arrangements, extended temperature ranges, protection from electrical noise, and resistance to vibration
and impact. Programs to control machine operation are typically stored in battery-backed memory. A
PLC is an example of a real-time system since output results must be produced in response to input
conditions within a bounded time. Current enhancement efforts are targeting speed and programming.
With compact PLC’s able to handle more that 30 I/O devices, communication speed is being enhanced
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with the use of 100Mb Ethernet connections [2]. Panasonic is attempting to revolutionize PLC
programming. They have designed an apparatus for and method of programming a logic device,
comprising a plurality of serially connected programmable logic regions. The method puts together the
steps of receiving initial programming data and receiving transformation data related to the presence and
location of at least one faulty serially connected programmable logic region. The program comprises the
steps of generating bypass data which, if any region fails, renders a serially connected programmable
logic region logically invisible [4].
Building Blocks for Implementation
Programs for microprocessor-based systems have to be in machine code; as a consequence,
ladder programming was developed. This is a means of writing programs with circuit blocks which can
then be converted into machine code by the PLC microprocessor [5]. This programming technique is
being enhanced by the direct conversion of ladder programming to circuit design language, which can
operate at faster speeds [6].The ladder diagram is sequentially executed inside this PLC microprocessor in
a cyclic scan period. PLC performance is limited by the cyclic scan period, which depends on the
program length and the microprocessor’s processing speed.
In order to overcome these drawbacks with the programmable hardware solution, many
researchers are focusing on field programmable gate array (FPGA)-based PLC with its reconfigurable
hardware structure and parallel execution advantage.
Choice of power for PLCs is determined by application. Compact PLCs require 24 Volts and can
be powered with RF or DC power supplies. RF recommended applications include etch, RIE, parallel
plate, ICP, RF sputtering, CVD and PVD, as well as induction and dielectric heating processes in
industrial systems, and solar photovoltaic applications [7].
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[1]
M. Yahyaei, J. Jam, and R. Hosnavi, (2010, March). Controlling the Navigation of Automatic
Guided Vehicle (AGV) Using Integrated Fuzzy Logic Controller with Programmable Logic
Controller (IFLPLC)-stage 1. International Journal of Advanced Manufacturing Technology,
[Online]. 47(5-8), pp. 795-807. Available:
http://www.springerlink.com.www.library.gatech.edu:2048/content/772n40662w137174/fulltext.
pdf
[2]
1769 CompactLogix Controllers User Manual, Allen-Bradley, Milwaukee, WI, 2009. pp 13,112.
[3]
Control Systems Solutions Catalog, General Electric, New York, NY, 2010. pp. 265.
[4]
S. Deeley, “System and method for local generation of programming data in a programmable
device,” U.S. Patent 7 679 400, March 16, 2010.
[5]
W. Bolton, “Ladder and functional block programming,” in Programmable Logic Controllers,
4th ed. London, England: 2006, ch. 5, sec. 1, pp. 322–323.
[6]
D. Du, X. Xu, and K. Yamazaki, (2010, July). A Study on the Generation of Silicon-based
Hardware Plc by Means of the Direct Conversion of the Ladder Diagram to Circuit Design
Language. International Journal of Advanced Manufacturing Technology, [Online]. 49(5-8), pp.
615-626.Available:
http://www.springerlink.com.www.library.gatech.edu:2048/content/u28870t03k13h321/fulltext.p
df
[7]
Comdel Inc,. (2010, Sept.). CB Series High Frequency RF Power Supplies. [Online]. Available:
http://www.comdel.com/pages/comdel_products/product_pdfs/cbseries3.pdf
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