9. A fuzzy feedback controlling method for operating a fuzzy inference control system to regulate a process value of an object with improved stability and accuracy, the steps of said method comprising operating a fuzzy inference control system as follows: determining a fuzzy control rule including the substeps of: representing a reference straight line in a phase plane with a deviation and a variation of said deviation as coordinates axes, a speed type control output variation of a proportional/integral control being zero; generating a deviation between an actual process value from the object and a set value; generating a variation of the deviation; dividing said phase plane into rectangles equal in size in such a manner that vertices of said rectangles are on said reference straight line and a line parallel with said reference straight line; and regulating a variation of a control output variation corresponding to a distance between said reference straight line and said parallel line which is so defined as to be proportional to absolute values of said deviation and said variation of said deviation; regulating antecedent membership functions concerning said deviation and said variation of said deviation as fuzzy variables, with centers of isosceles triangles of said antecedent membership functions being deviation components and deviation variation components of coordinates of centers of said rectangles; regulating consequent membership functions concerning a control output variation as fuzzy variables, with centers of isosceles triangles of said consequent membership functions being defined by a distance between said reference straight line and said parallel straight line; normalizing said deviation, and said variation of said deviation at least with respective reference variation widths; determining by fuzzy inference a variation of said control output using said fuzzy control rule, said antecedent membership functions, said consequent membership functions, said normalized deviation, and said normalized variation of said deviation; normalizing said variation of said control output at least with a reference variation width; and applying the control output, as varied by fuzzy inference, to control the object.
9. A fuzzy feedback controlling method for operating a fuzzy inference control system to regulate a process value of an object with improved stability and accuracy, the steps of said method comprising operating a fuzzy inference control system as follows: determining a fuzzy control rule including the substeps of: representing a reference straight line in a phase plane with a deviation and a variation of said deviation as coordinates axes, a speed type control output variation of a proportional/integral control being zero; generating a deviation between an actual process value from the object and a set value; generating a variation of the deviation; dividing said phase plane into rectangles equal in size in such a manner that vertices of said rectangles are on said reference straight line and a line parallel with said reference straight line; and regulating a variation of a control output variation corresponding to a distance between said reference straight line and said parallel line which is so defined as to be proportional to absolute values of said deviation and said variation of said deviation; regulating antecedent membership functions concerning said deviation and said variation of said deviation as fuzzy variables, with centers of isosceles triangles of said antecedent membership functions being deviation components and deviation variation components of coordinates of centers of said rectangles; regulating consequent membership functions concerning a control output variation as fuzzy variables, with centers of isosceles triangles of said consequent membership functions being defined by a distance between said reference straight line and said parallel straight line; normalizing said deviation, and said variation of said deviation at least with respective reference variation widths; determining by fuzzy inference a variation of said control output using said fuzzy control rule, said antecedent membership functions, said consequent membership functions, said normalized deviation, and said normalized variation of said deviation; normalizing said variation of said control output at least with a reference variation width; and applying the control output, as varied by fuzzy inference, to control the object. 13. A method as claimed in claim 9, or 10, or 11, or 12 in which the regulating consequent membership functions step regulates said consequent membership functions such that a parameter value for a fuzzy variable small in absolute value is decreased, and a parameter value for a fuzzy variable large in absolute value is increased.