Temp Cnt

INTRODUCTION Temperature control is widely used in various processes. These processes, no matter if it is in a large industrial plant, or in a home appliance, share several unfavorable features. These include non-linearity, interference, dead time, and external disturbances, among others. Conventional approaches usually do not result in satisfactory temperature control. In this Application Note we provide examples of fuzzy logic used to control temperature in several different situations. These examples are developed using FIDE, an integrated fuzzy inference development environment. FUZZY CONTROL IN A GLASS MELTING FURNACE A glass melting furnace has two rooms, a melter and a refiner. Raw materials are melted into glass at high temperature in the melter. The temperature of the melted glass is adjusted to a suitable temperature for the glass forming process to follow. It takes a long time to change the temperature in the furnace, which is an example of dead-time in this process. The flow of melted glass is not uniform, especially at the bottom of the furnace. In addition to temperature, other factors also contribute to the thermal characteristics of melted glass. Raw material mixing procedure, glass color, and the amount of the glass are some of the factors. Because there are many variables and the procedure complex, it is very difficult to design an effective temperature controller for this application using conventional control approaches. Control Objective Control temperature in a dead time process such as in a glass melting furnace. Fuzzy Control System The control block diagram for a glass melting furnace is shown in Figure 1. Control value u is applied to the process to adjust the temperature. This value is changed by two compensators. The variation of u can be written as u = ud + ue where ud is the output of the dead time compensator, and ue is the output of the error compensator. The dead time compensator is used to reduce the effect dead time has on the process. Its output (ud), an incremental change in control value, is derived from the change in the current and previous control value (u) and the time differential of output temperature (y). The error compensator is used to reduce the difference between the desired temperature and the actual temperture of hte furnace. Its outpu (ue), also an incremental change in control value, is inferred from the difference(error) e and its time differential �. ud and ue are combined to change the control value u.

Input/Output Variables of the Dead Time Compensator Labels and membership functions of input/output variables of the dead time compensator are shown in Figure 2a, 2b, 2c. The membership functions can be created by using the MF editor in FIDE. FIU Source Code for the Dead Time Compensator The following is the source code for the dead time compensator written in FIL, the fuzzy inference language provided in FIDE. $ FILENAME: $ DATE: $ UPDATE: $ $ $ $

temp/temp1_dt.fil 08/31/1992 09/02/1992

Temperature Controller : Part 1 : dead time compensator Two inputs, one output INPUT(S): Prev(ious)_Var(iationOf)_Ctrl, TimeDiff(erentialOf)_Output OUTPUT(S): Var(iationOf)_Ctrl

$ FIU HEADER fiu tvfi (min max) *8; $ DEFINITION OF INPUT VARIABLE(S) invar Prev_Var_Ctrl " " : -1 () 1 [ P_Large (@0.45, 0, @0.75, P_Medium (@0.15, 0, @0.45, P_Small (@-0.15, 0, @0.15, N_Small (@-0.45, 0, @-0.15, N_Medium (@-0.75, 0, @-0.45, N_Large (@-1.00, 1, @-0.75, ]; invar TimeDiff_Output P_Large (@20, P_Small (@-20, N_Small (@-60, N_Large (@-90, ];

" " 0, 0, 0, 1,

: -90 @60, @20, @-20, @-60,

$ RULES

" = = = = = = =

@1.00, @0.75, @0.45, @0.15, @-0.15, @-0.45,

() 90 [ 1, @90, 1, @60, 1, @20, 1, @-20,

$ DEFINITION OF OUTPUT VARIABLE(S) outvar Var_Ctrl P_Large P_Medium P_Small Zero N_Small N_Medium N_Large );

1, 1, 1, 1, 1, 1,

" : -1 () 1 * ( 0.80, 0.40, 0.20, 0.00, -0.20, -0.40, -0.80

1), 0), 0), 0)

1), 0), 0), 0), 0), 0)

if Prev_Var_Ctrl is P_Large Var_Ctrl is N_Large; if Prev_Var_Ctrl is P_Large Var_Ctrl is N_Medium; if Prev_Var_Ctrl is P_Large Var_Ctrl is N_Small; if Prev_Var_Ctrl is P_Large Var_Ctrl is Zero; if Prev_Var_Ctrl is P_Medium Var_Ctrl is N_Medium; if Prev_Var_Ctrl is P_Medium Var_Ctrl is N_Small; if Prev_Var_Ctrl is P_Medium Var_Ctrl is Zero; if Prev_Var_Ctrl is P_Medium Var_Ctrl is Zero;

and TimeDiff_Output is P_Large then and TimeDiff_Output is P_Small then and TimeDiff_Output is N_Small then and TimeDiff_Output is N_Large then and TimeDiff_Output is P_Large then and TimeDiff_Output is P_Small then and TimeDiff_Output is N_Small then and TimeDiff_Output is N_Large then

if Prev_Var_Ctrl is P_Small Var_Ctrl is N_Small; if Prev_Var_Ctrl is P_Small Var_Ctrl is Zero; if Prev_Var_Ctrl is P_Small Var_Ctrl is Zero; if Prev_Var_Ctrl is P_Small Var_Ctrl is Zero;

and TimeDiff_Output is P_Large then

if Prev_Var_Ctrl is N_Small Var_Ctrl is Zero; if Prev_Var_Ctrl is N_Small Var_Ctrl is Zero; if Prev_Var_Ctrl is N_Small Var_Ctrl is Zero; if Prev_Var_Ctrl is N_Small Var_Ctrl is P_Small;

and TimeDiff_Output is P_Large then

if Prev_Var_Ctrl is N_Medium Var_Ctrl is Zero; if Prev_Var_Ctrl is N_Medium Var_Ctrl is Zero; if Prev_Var_Ctrl is N_Medium Var_Ctrl is P_Small; if Prev_Var_Ctrl is N_Medium Var_Ctrl is P_Medium; if Prev_Var_Ctrl is N_Large Var_Ctrl is Zero; if Prev_Var_Ctrl is N_Large Var_Ctrl is P_Small; if Prev_Var_Ctrl is N_Large Var_Ctrl is P_Medium; if Prev_Var_Ctrl is N_Large Var_Ctrl is P_Large end

and TimeDiff_Output is P_Small then and TimeDiff_Output is N_Small then and TimeDiff_Output is N_Large then

and TimeDiff_Output is P_Small then and TimeDiff_Output is N_Small then and TimeDiff_Output is N_Large then and TimeDiff_Output is P_Large then and TimeDiff_Output is P_Small then and TimeDiff_Output is N_Small then and TimeDiff_Output is N_Large then and TimeDiff_Output is P_Large then and TimeDiff_Output is P_Small then and TimeDiff_Output is N_Small then and TimeDiff_Output is N_Large then

Input/Output Response of the Dead Time Compensator Figure 3 shows the response surface of the dead time compensator. This surface can be obtained by using the Analyzer tool provided in FIDE. Input/Output Variables of the Error Compensator Labels and membership functions of input/output variables of the Error Compensator are shown in Figure 4a, 4b, 4c. FIU Source Code of Error Compensator $ FILENAME: $ DATE: $ UPDATE: $ $ $ $

temp/temp1_er.fil 09/02/1992 09/03/1992

Temperature Controller : Part 2 : error compensator Two inputs, one output INPUT(S): Error, TimeDiff(erentialOf)_Error OUTPUT(S): Var(iationOf)_Ctrl

$ FIU HEADER fiu tvfi (min max) *8; $ DEFINITION OF INPUT VARIABLE(S) invar Error " " : -100 () 100 [ P_Large (@50, 0, @80, P_Medium (@20, 0, @50, P_Small (@0, 0, @20, Zero (@-20, 0, @0, N_Small (@-50, 0, @-20, N_Medium (@-80, 0, @-50, N_Large (@-100,1, @-80, ];

1, 1, 1, 1, 1, 1, 1,

invar TimeDiff_Error " " : -90 () 90 [ P_Large (@50, 0, @70, 1, P_Medium (@30, 0, @50, 1, P_Small (@0, 0, @30, 1, Zero (@-30, 0, @0, 1, N_Small (@-50, 0, @-30, 1, N_Medium (@-70, 0, @-50, 1, N_Large (@-90, 1, @-70, 1, ]; $ DEFINITION OF OUTPUT VARIABLE(S) outvar Var_Ctrl " " : -1 () 1 * ( P_Large = 0.80, P_Medium = 0.40, P_Small = 0.20, Zero = 0.00,

@100, @80, @50, @20, @0, @-20, @-50,

1), 0), 0), 0), 0), 0), 0)

@90, @70, @50, @30, @0, @-30, @-50,

1), 0), 0), 0), 0), 0), 0)

N_Small N_Medium N_Large );

= -0.20, = -0.40, = -0.80

$ RULES if Error is P_Large; if Error is P_Medium; if Error is Zero; if Error is Zero; if Error is Zero; if Error is N_Medium; if Error is N_Large;

Zero and TimeDiff_Error is P_Large then Var_Ctrl is

if Error is P_Large; if Error is P_Medium; if Error is Zero; if Error is Zero; if Error is N_Medium; if Error is N_Large;

P_Large

if Error is P_Large; if Error is Zero; if Error is Zero; if Error is N_Medium; if Error is P_Medium; if Error is Zero; if Error is Zero; if Error is N_Large

P_Medium and TimeDiff_Error is P_Medium then Var_Ctrl is

Zero and TimeDiff_Error is P_Medium then Var_Ctrl is Zero and TimeDiff_Error is P_Small then Var_Ctrl is Zero and TimeDiff_Error is Zero then Var_Ctrl is Zero and TimeDiff_Error is N_Small then Var_Ctrl is Zero and TimeDiff_Error is N_Medium then Var_Ctrl is Zero and TimeDiff_Error is N_Large then Var_Ctrl is and TimeDiff_Error is Zero then Var_Ctrl is

P_Medium and TimeDiff_Error is Zero then Var_Ctrl is P_Small

and TimeDiff_Error is Zero then Var_Ctrl is

N_Small

and TimeDiff_Error is Zero then Var_Ctrl is

N_Medium and TimeDiff_Error is Zero then Var_Ctrl is N_Large

P_Small

and TimeDiff_Error is Zero then Var_Ctrl is

and TimeDiff_Error is P_Small then Var_Ctrl is

P_Medium and TimeDiff_Error is N_Medium then Var_Ctrl is P_Small

and TimeDiff_Error is N_Large then Var_Ctrl is

N_Small

and TimeDiff_Error is P_Large then Var_Ctrl is

N_Medium and TimeDiff_Error is P_Medium then Var_Ctrl is N_Small

and TimeDiff_Error is N_Small then Var_Ctrl is

N_Medium and TimeDiff_Error is N_Medium then Var_Ctrl is

end Input/Output Response of Error Compensator

Figure 5 shows the response surface of the error compensator. COMMENTS Temperature above, have better than show robust process.

control systems, using fuzzy controllers as shown been put into operation and provide performance conventional control systems. Fuzzy controllers also response in the handling of dead time behavior in the

(Weijing Zhang, Applications Engineer, Aptronix Inc.)

For Further Information Please Contact: Aptronix Incorporated 2150 North First Street #300 San Jose, CA 95131 Tel (408) 428-1888 Fax (408) 428-1884 FuzzyNet (408) 428-1883 data 8/N/1

Aptronix Company Overview Headquartered in San Jose, California, Aptronix develops and markets fuzzy logic-based software, systems and development tools for a complete range of commercial applications. The company was founded in 1989 and has been responsible for a number of important innovations in fuzzy technology. Aptronix's product Fide (Fuzzy Inference Development Environment) -- is a complete environment for the development of fuzzy logic-based systems. Fide provides system engineers with the most effective fuzzy tools in the industry and runs in MS-Windows(TM) on 386/486 hardware. The price for Fide is $1495 and can be ordered from any authorized Motorola distributor. For a list of authorized distributors or more information, please call Aptronix. The software package comes with complete documentation on how to develop fuzzy logic based applications, free telephone support for 90 days and access to the Aptronix FuzzyNet information exchange.

Temperature Control FIDE Application Note 004-080992 Aptronix Inc., 1992