Embedded Systems Design Europe - March 2008 - (Page 21)

cover feature FUZZY LOGIC DEFINITIONS Centroid calculation function: used for producing an exact output value by calculating the center of gravity of the union of areas bound by membership functions and the input variable axes. Defuzziﬁcation: a general method for determining the best exact or “crisp” output of a given fuzzy set, defuzziﬁcation uses the centroid calculation function or a similar function to generate a crisp output. Fuzziﬁcation: a method for converting a “crisp” input value to a fuzzy membership function. The resulting fuzzy value is a member of a multivalued set. Fuzzy control system: a control system based on fuzzy IF-THEN rules that use fuzzy sets for input and output. Fuzzy inference system: a collection of fuzzy IF-THEN rules. Fuzzy logic: logic that uses linguistic variables to describe a system. Examples include: “fast,” “slow,” and “medium.” Fuzzy set: any set that allows its members to have different “grades” of membership. Each member may be expressed by a continuous number between zero and one: [0,1]. This contrasts to Boolean logic that limits set members to a value of either zero or one. Fuzzy system: a system whose variables range over states that are fuzzy sets. Membership function: the mapping of a fuzzy set that associates each set member with its grade of membership. bounds, and appropriate action is taken if it is not. Finally the fuzzy controller returns the updated PWM duty cycle count to the calling routine. Figure 8 shows a debug session of the demo application. Channels 1 &2 (the display window in the upper-right hand corner) displays the PWM counter, and the capture of the hall-effect sensors respectively. Channels 3 & 4 (the display window beneath channels 1 & 2) show the edge-triggered versions of the PWM counter and the hall-effect sensors. The watch window displays important variables. Most important are SetSpeed, and CurrentSpeed. These values are close enough so that the output of the fuzzy controller has a zero value. Also note the other values used in the controller process. This session shows the motor under no-load conditions. The behavior may be slightly different with a load. Moreover, if a ﬁner granularity is desired it may be necessary to tune the controller. Byron Miller is an independent ﬁrmware engineer specializing in the design of microprocessors, DSPs, hardware debug, porting, as well as the development of ﬁrmware for control, data acquisition, fuzzy logic, and Internet appliances. He has a BA in computer science and a masters in software engineering. You can reach him at bmiller2@isd.net. FURTHER READING: Von Altrock, Constantin. Fuzzy Logic and NeuroFuzzy Applications Explained. Englewood Cliffs, NJ: Prentice Hall, 1995. Miller, Byron. The Design and Development of Fuzzy Logic Controllers. Minneapolis, MN: Impatiens Publications, 1997 G. Klir, D. Schwartz, “Fuzzy logic flowers in Japan, IEEE Spectrum JULY 1992, p. 32. Brubaker, David. “Fuzzy-logic basics: intuitive rules replace complex math,” EDN June 18, 1992, p. 111. Brubaker, David. “Fuzzy-logic system solves control problem,” EDN June 18, 1992, p. 121. Brubaker, David. “Design and simulate your own fuzzy setpoint controller,” EDN January 5, 1995, p. 167. V. Donescu, D.O. Ncacsu, G. Griva, “Design of a Fuzzy Logic Speed Controller for Brushless DC Motor Drives,” IEEE Spectrum September 1996, p. 404. M. Chow, Y. Tipsuwan, “Fuzzy Logic Microcontroller Implementation for DC Motor Speed Control,” IEEE Spectrum March 1999, p. 1271. J. Lee, T. Im, H. Sung, Y. Kim, “A Low Cost Speed Control System of Brushless DC Motor Using Fuzzy Logic,” IEEE Spectrum April 1999, p. 433. Miller, Byron. “A Top-Down Approach to Fuzzy Logic Design,” Embedded Systems Programming, July 1998, p. 52. Simon, Dan. “Fuzzy Control,” ESP July, 2003, p. 55. Miller, Byron. “Fuzzy Logic Does Real Time on the DSP,” Dr. Dobbs Journal, July 2004, p. 25. Fuzzy Logic: An Overview of the Latest Control Methodology. (TI doc – SPRA028). Fuzzy Logic Motor Control with MSP430x14x. (TI docSLAA235). TMS320F/C28xx Data Manual. (TI doc – SPRS174M). 21 www.embedded.com/europe | embedded systems design europe | MARCH 2008 014-015-016-018-020-021_EETE.ind21 21 5/03/08 12:50:14 http://www.embedded.com/europe

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Embedded Systems Design Europe - March 2008 Distributors to Increase Embedded Focus Kontron and Quanta to Join Forces Coverity Raises $22m as European Business Booms Help is at Hand for Europe's Industrial Control Developers Milestones in Embedded Systems Microsoft is Recruiting for Embedded Center in Aachen European Designers to Win Cash for Green Designs Duo Work on Smaller Form Factor Europe Invests in Real-Time Java for Multicore Systems Curtiss-Wright Buys Pentland Systems Designing DSP-Based Motor Control Using Fuzzy Logic Lower the Cost of Intelligent Power Control with FPGAs Virtualizing Embedded Linux Back to the Future: Manchester Encoding Is Multicore Hype or Reality New Products Advertising Contacts

Embedded Systems Design Europe - March 2008

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