US4042809A — System for controlling two variables

Claim 1

Independent Claim 339 words

In a system for controlling first and second variables (S and P) by variably exciting first and second control elements (V 1 and V 2 ), said first element (V 1 ) directly affecting both variables as its excitation is increased or decreased, and said second element (V 2 ) directly affecting one variable but oppositely affecting the other variable, said system including: a. means for creating a first error function signal (E s ) which varies according to the error between set point and actual values of one controlled variable, b. means for creating a second error function signal (E p ) which varies according to the error between set point and actual values of the other controlled variable, c. means for combining said first and second error function signals to create a first command signal (C 1 ) which varies with a cumulative effect of changes in such function signals, d. means for combining said first and second error function signals to create a second command signal (C 2 ) which varies with a differential or opposite effect of changes in the respective function signals, e. means for exciting the first control element (V 1 ) with said first command signal to increase or decrease said two variables, and f. means for exciting the second control element (V 2 ) with said second command signal, thereby to increase or decrease one of said variables while respectively decreasing or increasing the other variable, the improvement which comprises g. means responsive to one of said error function signals (E s or E p ) for creating a threshold signal (T) which varies as a predetermined function of such one signal, and h. means for supplying to one of said means (c) or said means (d) either (i) the other of the function signals (E p or E s ) or, in lieu thereof, (ii) said threshold signal, --whenever said other function signal lies respectively (i) within or (ii) without a boundary represented by the magnitude of the threshold signal.

Claim 2

Dependent Claim 339 words

In a system for controlling first and second variables (S and P) by variably exciting first and second control elements (V 1 and V 2 ), said first element (V 1 ) directly affecting both variables as its excitation is increased or decreased, and said second element (V 2 ) directly affecting one variable but oppositely affecting the other variable, said system including: a. means for creating a first error function signal (E s ) which varies according to the error between set point and actual values of one controlled variable, b. means for creating a second error function signal (E p ) which varies according to the error between set point and actual values of the other controlled variable, c. means for combining said first and second error function signals to create a first command signal (C 1 ) which varies with a cumulative effect of changes in such function signals, d. means for combining said first and second error function signals to create a second command signal (C 2 ) which varies with a differential or opposite effect of changes in the respective function signals, e. means for exciting the first control element (V 1 ) with said first command signal to increase or decrease said two variables, and f. means for exciting the second control element (V 2 ) with said second command signal, thereby to increase or decrease one of said variables while respectively decreasing or increasing the other variable, the improvement which comprises g. means responsive to one of said error function signals (E s or E p ) for creating a threshold signal (T) which varies as a predetermined function of such one signal, and h. means for supplying to one of said means (c) or said means (d) either (i) the other of the function signals (E p or E s ) or, in lieu thereof, (ii) said threshold signal, --whenever said other function signal lies respectively (i) within or (ii) without a boundary represented by the magnitude of the threshold signal.

Claim 3

Dependent Claim 110 words

The improved system set forth in claim 1 wherein one of said control elements (V 1 or V 2 ) has a physical limit of response and produces no effect upon the controlled variables even though the corresponding one command signal (C 1 or C 2 ) applied thereto varies beyond a predetermined saturation point (C s ) and further characterized in that said means (g) includes: 81. means for creating said threshold signal with a value which, when combined in the means (c) or (d) to create said one command signal (C 1 or C 2 ) makes the said one command signal take on said predetermined saturation point.

Claim 4

Dependent Claim 62 words

The improved system set forth in claim 2 wherein said physical limit of response of said one control element is the maximum extent of the influence which the control element can exert to increase the variable or variables directly affected thereby, and said predetermined saturation point is the maximum value of said one command signal to which said one control element responds.

Claim 5

Dependent Claim 65 words

The improved system set forth in claim 2 wherein said physical limit of response of said one control element is the minimum extent of the influence which the control element can exert in an increasing sense on the variable or variables directly affected thereby, and said predetermined saturation point is the minimum value of said one command signal to which said one control element responds.

Claim 6

Dependent Claim 129 words

The improved system set forth in claim 1 further characterized in that said means (g) includes: g1. means responsive to one of said error function signals for creating upper and lower threshold signals which vary as respective predetermined functions of such one signal, and said means (h) includes h1. means for supplying to said one of means (c) or said means (d) either: i. the other of said error function signals, ii. said upper threshold signal, or iii. said lower threshold signal respectively when said other function signal: i. is in value intermediate the values of the upper and lower threshold signal, ii. is in value greater than the value of the upper threshold signal, or iii. is in value less than the value of the lower threshold signal.

Claim 7

Dependent Claim 128 words

The improved system set forth in claim 1, further characterized in that: f1. said means (f) constitutes means for exciting said second control element with said second command signal to cause said first variable to increase when the first error function signal increases, and to cause said second variable to increase when the second error function signal increases, g1. said means (g) constitutes means responsive to said first error function signal (E s ) to make said threshold signal vary as a predetermined function of such function signal, and h1. said means (h) constitutes means for supplying to said means (c) the second function signal (E p ) while preventing the signal so supplied from going beyond a boundary which is the then-existing value of said threshold signal.

Claim 8

Dependent Claim 81 words

The improved system set forth in claim 1 further characterized in that: g1. said means (g) constitutes means responsive to said second error function signal (E p ) to make said threshold signal vary as a predetermined function of such signal, and h1. said means (h) constitutes means for supplying to means (d) the first error function signal (E s ) while preventing the signal so supplied from going beyond a boundary which is the then-existing value of said threshold signal.

Claim 9

Dependent Claim 214 words

The improved system defined by claim 6, further characterized in that: c1. said means (c) constitutes a means for creating said first command signal C 1 substantially according to the relationship C.sub.1 = K.sub.1 E.sub.s + K.sub.2 E.sub.p + K.sub.3 where the K's are preselected constants and E s and E p represent the values of said first and second error function signals, d1. said means (d) constitutes a means for creating said second command signal C 2 according substantially to the relationship C.sub.2 = K.sub.4 E.sub.5 - K.sub.5 E.sub.p + K.sub.6 where the K's are preselected constants and E s and E p represent the values of said first and second error function signals, g2. said means (g1) constitutes a means responsive to said first error function signal (E s ) to create said threshold signal T 2 substantially according to the relationship ##EQU15## where C 2s represents the maximum or the minimum saturation value of the command signal C 2 to which said second control element effectively responds, and h2. said means (h1) constitutes means for supplying as an input to said means (c) either (i) said second function signal E p or, when the latter signal exceeds the boundary represented by the threshold signal T 2 , the threshold signal value.

Claim 10

Dependent Claim 192 words

The improved system defined by claim 7, further characterized in that: c1. said means (c) constitutes a means for creating said first command signal C 1 substantially according to the relationship C.sub.1 = K.sub.1 E.sub.s + K.sub.2 E.sub.p + K.sub.3 where the K's are preselected constants and E s and E p represent the values of said first and second error function signals, C.sub.2 = K.sub.4 E.sub.s - K.sub.5 E.sub.p + K.sub.6 where the K's are preselected constants and E s and E p represent the values of said first and second error function signals, g2. said means (g1) constitutes a means responsive to said second error function signal (E p ) to create said threshold signal T 1 substantially according to the relationship ##EQU16## where C 1s represents the maximum or minimum saturation value of the command signal C 1 to which said first control element effectively responds, and h2. said means (h1) constitutes means for supplying as an input to said means (d) either (i) said first function signal E s or, when the latter exceeds the boundary represented by the threshold signal T 1 , the threshold signal value.

Claim 11

Dependent Claim 170 words

The improved system defined by claim 8 further characterized in that: g3. said means (g2) constitutes a means for producing said threshold signal T 2 as a lower threshold T 2L according to the recited relationship, where C 2s represents the maximum saturation value C 2u of the command signal C 2 to which said second control element effectively responds, g4. said system includes a means responsive to said first function error signal (E s ) to create an upper threshold signal T 2u substantially according to the relationship ##EQU17## where C 2L represents the minimum saturation value of the command signal C 2 to which said second control element effectively responds, and h3. said means (h2) constitutes a means for supplying as an input to said means (c) either: i. the signal E p when T 2L < E p < T 2u , or ii. the signal T 2L when E p < T 2L , iii. the signal T 2u when E p < T 2u .

Claim 12

Dependent Claim 364 words

In a system for controlling first and second variables S and P by variably exciting first and second control elements V 1 and V 2 , said first element V 1 directly affecting both variables as its excitation is increased or decreased, and said second element V 2 directly affecting the first variable S and oppositely affecting the second variable P as its excitation is increased or decreased, said system including: a. means for producing a first error function signal E s which varies according to the error between set point and actual values of the first variable S, b. means for producing a second error function signal E p which varies according to the error between set point and actual values of the second variable P, c. means receiving said first and second error function signals E s and E p for producing a first command signal C 1 which varies as an additive function C 1 = f(E s + E p ) of its inputs, d. means receiving said first and second signals E s and E p for producing a second command signal C 2 which varies as a substractive function C 2 = f(E s - E p ) of its inputs, e. means for exciting said first control element V 1 with said first command signal C 1 to cause increase or decrease of said variables S and P as such signal increases or decreases, and f. means for exciting said second control element V 2 with said second command signal C 2 to cause said first variable S to increase or decrease, and said second variable P to decrease or increase, as such signal respectively increases or decreases, the improvement which comprises g. means responsive to one of said error function signals (E s or E p ) for creating a threshold signal T which varies as a predetermined function of such one signal, and h. means for bounding the variations of the other error function signal (E p or E s ), before it is fed to said means (c) or (d), at a limit value equal to the then-existing value of the threshold signal T.

Claim 13

Dependent Claim 364 words

In a system for controlling first and second variables S and P by variably exciting first and second control elements V 1 and V 2 , said first element V 1 directly affecting both variables as its excitation is increased or decreased, and said second element V 2 directly affecting the first variable S and oppositely affecting the second variable P as its excitation is increased or decreased, said system including: a. means for producing a first error function signal E s which varies according to the error between set point and actual values of the first variable S, b. means for producing a second error function signal E p which varies according to the error between set point and actual values of the second variable P, c. means receiving said first and second error function signals E s and E p for producing a first command signal C 1 which varies as an additive function C 1 = f(E s + E p ) of its inputs, d. means receiving said first and second signals E s and E p for producing a second command signal C 2 which varies as a substractive function C 2 = f(E s - E p ) of its inputs, e. means for exciting said first control element V 1 with said first command signal C 1 to cause increase or decrease of said variables S and P as such signal increases or decreases, and f. means for exciting said second control element V 2 with said second command signal C 2 to cause said first variable S to increase or decrease, and said second variable P to decrease or increase, as such signal respectively increases or decreases, the improvement which comprises g. means responsive to one of said error function signals (E s or E p ) for creating a threshold signal T which varies as a predetermined function of such one signal, and h. means for bounding the variations of the other error function signal (E p or E s ), before it is fed to said means (c) or (d), at a limit value equal to the then-existing value of the threshold signal T.

Claim 14

Dependent Claim 183 words

The improved system set out in claim 11 further characterized in that one of said control elements (V 2 or V 1 ) is physically limited and lacks response to its excitation signal (C 2 or C 1 ) rising above or falling below saturation values (C 2u , C 2L , or C 1u , C 1L ), and wherein g1. said means (g) constitutes means for making said threshold signal T vary with said one error function signal (E s or E p ) to take on values which --when combined in one of said means (c) or (d) with the other error function signal (E p or E s )-- causes the resultant excitation signal (C 2 or C 1 ) to have one of its saturation values (C 2u or C 2L , OR C 1u or C 1L ), whereby the other of said control elements (V 1 or V 2 ) is prevented from producing major transient disturbances in consequence of said other error function signal (E p or E s ) passing through said limit value.

Claim 15

Dependent Claim 103 words

The improved system set out in claim 11 further characterized in that g1. said means (g) constitutes means responsive to one of said error function signals (E s or E p ) for creating lower and upper threshold signals T L and T u which vary as respective predetermined functions of such one signal, and h1. said means (h) constitutes means for bounding the variations of the other error function signal (E p or E s ), before it is fed to said means (c) or (d), between limit values equal to the then existing values of the lower and upper threshold signals.

Claim 16

Dependent Claim 154 words

The improved system set out in claim 11 further characterized in that: c1. said additive function is substantially of the form C.sub.1 = K.sub.1 E.sub.s + K.sub.2 E.sub.p + K.sub.3 where the K's are preselected constants d1. said subtractive function is substantially of the form C.sub.2 = K.sub.4 E.sub.s - K.sub.5 E.sub.p + K.sub.6 where the K's are preselected constants, g1. said means (g) constitutes means for creating said threshold signal T with a predetermined function substantially of the form ##EQU18## where C 2s is an upper or lower saturation value of the second command signal C 2 beyond which said second control element (V 2 ) will not respond, and h1. said means (h) constitutes means for bounding the variations of said other error function signal (E p ), before it is fed to said means (c), at a limit value equal to the then-existing value of the threshold signal T 2 .

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1980-08-15	1981-02-14	1981-08-16	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1984-08-15	1985-02-14	1985-08-16	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1988-08-15	1989-02-14	1989-08-16	$7700.00	Window Closed / Lapsed

System for controlling two variables

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