# Patent

## Title
Orbit attitude control device, and method of controlling orbit attitude

## Abstract

An orbit attitude control device includes a plurality of nozzles and a control section. The nozzles inject a combustion gas supplied from a combustion chamber, opening degrees being controlled in accordance with opening degree command values. The control section calculates nozzle opening degree correction values for the opening degree command values in response to a detection value of a pressure of the combustion chamber and a command value for the pressure, and correct the opening degree command values by the nozzle opening degree correction values. Each nozzle opening degree correction value is determined based on each opening degree command value.

## Background
INCORPORATION BY REFERENCE
This application is based upon and claims the benefit of priority from Japanese patent application No. 2012-259005, filed on Nov. 27, 2012, the disclosure of which is incorporated herein in its entirety by reference.
TECHNICAL FIELD
The present invention rerates to a technique for controlling an orbit of a flying object.
BACKGROUND ART
Technologies for controlling an attitude or orbit of a flying object flying through space or the atmosphere have been developed. In a system typically called DACS (Divert and Attitude Control System), an attitude control thruster for controlling an attitude of the flying object and an orbit control thruster for changing an orbit are used for controlling the attitude and orbit.
Patent Literature 1 discloses one example of a thruster control method. The method includes: detecting a pressure of a combustion chamber, comparing the detected pressure with a predetermined pressure value, and changing discharge areas of a plurality of nozzles for substantially same amount so that the pressure of the combustion chamber becomes the predetermined pressure, based on a difference between the detected pressure and the predetermined pressure.
CITATION LIST
[Patent literature 1] U.S. Pat. No. 5,456,425
SUMMARY OF THE INVENTION
A combustion gas is supplied to a plurality of nozzles included in a thruster from a common combustion chamber. The each nozzle includes a valve which is controlled based on a designated opening degree command value. Each nozzle injects the combustion gas with an amount corresponding to the opening degree, and thereby an orbit attitude of the flying object is controlled.
A pressure of the combustion chamber for supplying the combustion gas of the thruster is desirably kept constant. Accordingly, the opening degree of the valve of the nozzle is controlled so that the pressure of the combustion chamber is kept constant. However, in fact, when the opening degree command value is inputted so as to keep the pressure of the combustion chamber constant, there is a case that the pressure of the combustion chamber unpredictably changes because of various disrupting factors. As such disrupting factors, a mechanical accidental error, thermal expansion of the valve or the like, and ununiformity of a fuel or the like are considered. It is expected that the pressure of the combustion chamber is controlled to be kept constant in order to maintain stable combustion.
An orbit attitude control device according to the present invention includes: a plurality of nozzles configured to inject a combustion gas supplied from a combustion chamber, wherein opening degrees of the plurality of nozzles are configured to be controlled in accordance with opening degree command values; and a control section configured to calculate nozzle opening degree correction values which are correction values for the opening degree command values of the nozzles, in response to a detection value of the pressure of the combustion chamber and a command value for a pressure, and correct the opening degree command values by the nozzle opening degree correction values. Each of the nozzle opening degree correction values for the plurality of nozzles is determined based on the opening degree command values.
A method of controlling an orbit attitude according to the present invention includes: inputting opening degree command values for opening degrees of a plurality of nozzles which inject combustion gas supplied from a combustion chamber; calculating nozzle opening degree correction values which are correction values for the opening degree command values of the nozzles, in response to a detection value of the pressure of the combustion chamber and a command value for the pressure; and calculating nozzle opening degree correction values for the plurality of nozzles based on the opening degree command values to correct the opening degree command values by the calculated nozzle opening degree correction values.
According to the present invention, an orbit attitude control device and a method of controlling an orbit attitude are provided, which are able to keep the pressure of the combustion chamber constant.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1A is a sectional view showing an attitude control device;
FIG. 1B is a graph indicating a relationship between an angle of a valving element and a throat area;
FIG. 2A is a sectional view showing a divert thruster;
FIG. 2B is a graph indicating a relationship between a location of a valving element and a throat area;
FIG. 3 is a diagram for explaining a distribution of opening degrees in the divert thruster;
FIG. 4A is a diagram showing a distribution of opening degrees of pintle valves when a total of opening degree command values is changed in the divert thruster;
FIG. 4B is a diagram showing a distribution of opening degrees of pintle valves when a total of opening degree command values is changed in the divert thruster;
FIG. 5A is a diagram showing a distribution of opening degrees of pintle valves when a total of opening degree command values is changed in the divert thruster;
FIG. 5B is a diagram showing a distribution of opening degrees of pintle valves when a total of opening degree command values is changed in the divert thruster;
FIG. 6 is a diagram for explaining an operation of a control section; and
FIG. 7 is a diagram for explaining an operation of a control section.



DESCRIPTION OF EMBODIMENTS
Configuration of a Thruster
With reference to the drawings, embodiments will be described. FIG. 1A is a sectional view showing an attitude control device according to the present embodiment. A flying object including this attitude control device has an outer shape which is almost symmetrical to the x-axis illustrated in the drawing, and is propelled roughly along the x-axis direction. FIG. 2A is a sectional view showing A-A cross-section of a divert thruster 8 of FIG. 1A.
A solid fuel 4 is arranged inside a main body 2 of the attitude control device. When the flying object flies, the solid fuel 4 combusts and a combustion chamber 6 of the main body 2 is filled with combustion gas. An internal pressure of the combustion chamber 6 is detected by a combustion pressure sensor 7. A relatively small part of the combustion gas is supplied to an attitude control thruster 10. The attitude control thruster 10 includes a plurality of nozzles which face to a radial direction of a cylindrical coordinate system whose center is the x-axis (a direction in YZ-plane whose start point is arranged on the x-axis in FIG. 1A). Each of the plurality of nozzle includes a rotary valve 12. An opening degree of the rotary valve 12 is controlled by an electrical signal. The combustion gas supplied to the attitude control thruster 10 is injected from the each nozzle for an amount corresponding to the opening degree of the rotary valve 12, and thereby the attitude of the flying object is controlled. A shape 14 of an opening portion of the rotary valve 12 is indicated in a lower right part of FIG. 1A. FIG. 1B shows a graph indicating a relationship between an angle of a valving element and a throat area of the rotary valve 12.
A relatively large part of the combustion gas of the combustion chamber 6 is supplied to the divert thruster 8. The divert thruster 8 includes a plurality of nozzles 15-1 to 15-4 which face to a radial direction of the cylindrical coordinate system whose center is the x-axis (a direction in YZ-plane whose start point is arranged on the x-axis in FIG. 1A). The plurality of nozzle 15-1 to 15-4 includes pintle valves 16-1 to 16-4, respectively.
Opening degree command values concerning the pintle valves 16-1 to 16-4 are provided, based on a wireless communication with an outside of the flying object or data stored in a storage device included in the flying object. A control section 17 controls actuators 18, based on the opening degree command values and a detection value of a pressure in the combustion chamber 6 which is detected by the combustion pressure sensor 7. The actuators 18 control opening degrees of the pintle valves 16-1 to 16-4. The combustion gas supplied to the divert thruster 8 is injected from the each of the nozzles 15-1 to 15-4 for an amount corresponding to each of opening degrees of the pintle valves 16-1 to 16-4, and thereby the attitude of the flying object is controlled. A shape of an opening portion of the each of pintle valves 16-1 to 16-4 is indicated in a lower right part of FIG. 2A. FIG. 2B shows a graph indicating a relationship between a location of a valving element and a throat area of the each of pintle valves 16-1 to 16-4.
With reference to FIG. 3, a method of distributing opening degrees of the divert thruster 8 will be explained, which is a basis of the present embodiment. When the solid fuel 4 stably combusts, an amount of the generated combustion gas in a unit of time is substantially constant. Accordingly, a flow rate of the combustion gas supplied to the outside from the combustion chamber 6 is desirably kept constant. In particular, it is desired that a flow rate of the combustion gas injected from the divert thruster 8 whose injection amount is large is kept constant. Therefore, the opening degree of the each pintle valve is controlled so that a total of throat areas of the pintle valves 16-1 to 16-4 included in the divert thruster 8 is a constant (this constant value is assumed to be 100%). The combustion pressure of the combustion chamber 6 is kept constant by such control, and a transitive fluctuation of the combustion pressure is suppressed.
FIG. 3 (a) to (d) shows four pintle valves 16-1 to 16-4, respective percentages of throat areas, and a resultant force by injections from the pintle valves 16-1 to 16-4. As shown in FIG. 3(a), when the opening degree of the pintle valve 16-1 is 100% and the pintle valves 16-2 to 16-4 are fully closed, the resultant force acts along an upper direction of the drawing (the negative direction along the z-axis) and the orbit of the flying object is changed to be a direction that is opposite to the resultant force. As shown in FIG. 3(b), when the opening degree of the each of pintle valves 16-1 and 16-2 is 50% and the pintle valves 16-3 and 16-4 are fully closed, the resultant force acts along an upper right direction and the orbit of the flying object is changed to be a direction that is opposite to the resultant force. When the resultant force by the injection of the divert thruster is required to be reduced, as shown FIG. 3(c), a pintle valve facing to one direction and a pintle valve facing to the opposite direction are simultaneously opened. For example, in FIG. 3(c), the pintle valve 16-3 facing to the positive direction along the z-axis is opened with opening degree of 10%, and the pintle valve 16-1 facing to the negative direction along the z-axis is opened with opening degree of 60%. As a result, a force is obtained, which is equal to a resultant force that is obtained when the pintle valve facing to the negative direction along the z-axis is opened with opening degree of 50%. If the orbit is not to be changed by the divert thruster 8, as shown in FIG. 3(d), in the pintle valves 16-1 to 16-4, the pintle valves facing to each other are set to be same opening degrees.
Reference Example
A reference example for explaining the embodiment will be described. When the pintle valves 16-1 to 16-4 are controlled by a fixed total opening degree command value, the combustion pressure of the combustion chamber 6 does not necessarily become constant, because of disturbing factors such as mechanical errors, thermal expansions of valves or the like, and ununiformity of the fuel and so on. Accordingly, feed back control for total opening degree of the divert thruster 8 is carried out by using the detection value of the combustion pressure sensor 7, so that the pressure of the combustion chamber 6 becomes constant.
FIGS. 4A and 4B show a reference example of control in a case where the detection value of the pressure of the combustion chamber 6 is smaller than a set value and the total opening degree of the divert thruster 8 is controlled to be reduced. By reducing the total opening degree, an amount of the injected combustion gas is reduced, and the pressure of the combustion chamber 6 increases.
FIG. 4A indicates a case where the total opening degree command value of the divert thruster 8 is 100%, 70% of it is distributed to the pintle valve 16-1, and 10% of it is distributed to each of the pintle valves 16-2 to 16-4. At this state, it is assumed that the detection value of the pressure of the combustion chamber 6 becomes smaller than the set value and the total opening degree command value is changed to be 90% by addition of a total correction value of −10%. In this example, the total correction value is evenly distributed to all pintle values 16-1 to 16-4. As shown in FIG. 4B, by evenly distributing the total correction value of −10% to the all pintle valves 16-1 to 16-4, the pressure of the combustion chamber 6 can be increased, keeping the direction of the resultant force the same.
On the contrary, when the detection value of the pressure of the combustion chamber 6 is larger than the set value and the total opening degree of the divert thruster 8 is controlled to be increased, the amount of the injected combustion gas is increased and the pressure of the combustion chamber 6 is decreased, by addition of a positive total correction value (by increasing the total opening degree). In this case, by changing a symbol of the correction value for the opening degree of the pintle valve (−2.5% in FIG. 4B) to be opposite, the pressure of the combustion chamber can be controlled to be kept constant.
Embodiment
Next, control according to the present embodiment will be explained. FIGS. 5A and 5B show one example of control in a case where the detection value of the pressure of the combustion chamber 6 is smaller than the set value and the total opening degree of the divert thruster 8 is controlled to be reduced. FIG. 5A shows a case where the total opening degree command value of the divert thruster 8 is 100%, 70% of it is distributed to the pintle valve 16-1, and 10% of it is distributed to each of the pintle valves 16-2 to 16-4. At this state, a case is shown in FIG. 5B where the detection value of the pressure of the combustion chamber 6 becomes smaller than the set value and the total opening degree command value is changed to be 90%.
In this example, the total correction value for the opening degree command values is distributed in proportion to the each of the opening degree command values of the pintle valves 16-1 to 16-4 which are prior to correction. In an example shown in FIG. 5A, the opening degree command values of the pintle valves 16-1 to 16-4 are 70:10:10:10. Accordingly, if the total correction value is −10%, as shown in FIG. 5B, the correction values are distributed to the each of pintle valves 16-1 to 16-4 with a ratio of −7%:−1%:−1%:−1%.
Such control provides following advantages. As disturbing factors of the control, fluctuation of an injection amount of the divert thruster 8 due to a thermal expansion is considered. It is assumed that influences by the thermal expansion are approximately same as uniform expansions of parts that are arranged near the pintle valve 16. In this case, when the opening degree of the pintle valve 16 is large, an increased amount of the throat area by the thermal expansion becomes large, and accordingly, an increased amount of the injection by the thermal expansion becomes large.
In order to adequately suppress the increase in the injection amount, it is considered to be appropriate that the total correction value for the opening degree command values is largely distributed to the pintle valve having a large opening degree. In an example shown in FIG. 5B, the total correction value is distributed in proportion to the each opening degree command value of the each pintle valve, and thereby desirable control can be realized, that is, the opening degree of the largely thermally-expanded valve is largely corrected.
FIG. 6 shows a configuration of a control section 17 for realizing the above mentioned control. Opening degree commands A1c to A4c for the pintle valves 16-1 to 16-4 are inputted into the control section 17, based on a wireless communication or data stored in a storage section. These values are corrected by correction values ΔA1 to ΔA4 for the opening degree commands of the pintle valves 16-1 to 16-4, respectively. The control section 17 outputs the corrected opening degree commands to respective actuators 18-1 to 18-4 of the pintle valves 16-1 to 16-4. The actuators 18-1 to 18-4 drive, opening areas of the pintle valves 16-1 to 16-4 are respectively set to be A1 to A4, and a total opening area At is determined. Following thrust forces are obtained by injection from each of the nozzles 15-1 to 15-4.

F1=Pc·A1·Cf 

F2=Pc·A2·Cf 

F3=Pc·A3·Cf 

F4=Pc·A4·Cf 

The Pc indicates the pressure of the combustion chamber 6, and Cf indicates a thrust coefficient. A thrust force Fz along the z-axis direction is determined by a difference between F1 and F3. A thrust force Fy along the y-axis direction is determined by a difference between F2 and F4.
The Pressure Pc of the combustion chamber 6 is detected by the combustion pressure sensor 7. A calculator provided in the control section 17 calculates a total correction value ΔAt that is a correction value for the total opening area At, based on a deviation ΔPc between the detected pressure Pc and a combustion pressure target value Pcom which is provided by data stored in the storage section, in order to carry out feed back control that is typically PID control.
The calculator of the control section 17 distributes the total correction value ΔAt to the correction values ΔA1 to ΔA4 for the pintle valves 16-1 to 16-4. This distribution is carried out according to the following formulas.

ΔA1=ΔAt×f(A1c)/{f(A1c)+f(A2c)+f(A3c)+f(A4c)}

ΔA2=ΔAt×f(A2c)/{f(A1c)+f(A2c)+f(A3c)+f(A4c)}

ΔA3=ΔAt×f(A3c)/{f(A1c)+f(A2c)+f(A3c)+f(A4c)}

ΔA4=ΔAt×f(A4c)/{f(A1c)+f(A2c)+f(A3c)+f(A4c)}

f (opening degree command) is a monotonically increasing function of the opening degree command, as indicated at a lower part of FIG. 6. Especially, if f (opening degree command) is a proportional function, the control explained by FIGS. 5A and 5B is realized. Since these correction values are used for the opening degree commands A1c to A4c of the pintle valves 16-1 to 16-4, a larger correction amount is provided to a valve having a larger opening degree, and the pressure of the combustion chamber 6 can be controlled to be kept constant.
[Control of Correcting the Opening Degree by a Measurement Value of Acceleration]
As mentioned above, the example was explained in a case where the divert thruster is controlled in response to a change of the pressure in the combustion chamber. On the other hand, in order that the flying object accurately flies along an orbit according to a command, feed back control using a measurement value of an acceleration of the flying object is desired. FIG. 7 shows an example of such control.
The orbit attitude control device includes an acceleration sensor section. The acceleration sensor section includes a y-axis acceleration sensor for measuring an acceleration in the y-axis direction of the coordinate axes illustrated in FIG. 1A and FIG. 2A, and a z-axis acceleration sensor for measuring an acceleration in the z-axis direction.
Respective opening degree commands A1c to A4c for each of the pintle valves 16-1 to 16-4 are inputted into the control section 17, based on a wireless communication or data stored in a storage section. These values are corrected by correction values ΔA1 to ΔA4 for the opening degree commands of the respective pintle values 16-1 to 16-4. The control section 17 outputs the corrected opening degree commands to respective actuators 18-1 to 18-4 of the pintle valves 16-1 to 16-4. Actuators 18-1 to 18-4 drive, the opening areas of the pintle valves 16-1 to 16-4 are respectively set to be A1 to A4, and a total opening area At is determined. The following thrust forces are obtained by the injection from the each of nozzles 15-1 to 15-4.

F1=Pc·A1·Cf 

F2=Pc·A2·Cf 

F3=Pc·A3·Cf 

F4=Pc·A4·Cf 

The Pc indicates the pressure of the combustion chamber 6, and Cf indicates the thrust coefficient. A thrust force Fz along the z-axis direction is determined by a difference between F1 and F3. A thrust force Fy along the y-axis direction is determined by a difference between F2 and F4. Accelerations along the y-axis and z-axis are generated in the flying object, by the thrust forces Fy and Fz.
The y-axis acceleration sensor and the z-axis acceleration sensor detect a y-axis acceleration Gy and a z-axis acceleration Gz, respectively. An observer 32 provided in the control section 17 corrects the opening degree command values of the divert thruster based on these accelerations. A storage device in the observer 32 stores an inertia model of the flying object. The observer 32 calculates estimated values of a thrust force Fye along the y-axis direction and a thrust force Fze along the z-axis direction, based on this inertia model, the inputted y-axis acceleration Gy and z-axis acceleration Gz.
The observer 32 transforms the opening degree commands A1c to A4c of the pintle valves into a command values for the thrust forces along the y-axis direction and the z-axis direction, based on a previously prepared formula or a table. Furthermore, the observer 32 calculates deviations ΔFy, ΔFz between these command values for the thrust forces and the estimated values Fye, Fze for the thrust forces. A correction value ΔAz for a relative difference between the opening degrees of pintle valves 16-1 and 16-3 of a first group is calculated so that the deviation ΔFz becomes smaller. A correction value ΔAy for a relative difference between the opening degrees of pintle valves 16-2 and 16-4 of a second group is calculated so that the deviation ΔFy becomes smaller.
When ΔAy and ΔAz are evenly distributed to the pintle valves facing each other, following correction amounts are distributed to the each pintle valve.

ΔA1:+ΔAz/2

ΔA2:+ΔAy/2

ΔA3:−ΔAz/2

ΔA4:−ΔAy/2

Furthermore, in the control method according to the present embodiment which is against the change of the detection value of the pressure of the combustion chamber 6, when the function f (opening degree command) is a proportional function, the opening degree correction values ΔA1 to ΔA4 for the each of pintle valves are determined as follows.

ΔA1=ΔAt×A1c/(A1c+A2c+A3c+A4c)+ΔAz/2

ΔA2=ΔAt×A2c/(A1c+A2c+A3c+A4c)+ΔAy/2

ΔA3=ΔAt×A3c/(A1c+A2c+A3c+A4c)−ΔAz/2

ΔA4=ΔAt×A4c/(A1c+A2c+A3c+A4c)−ΔAy/2

The orbit of the flying object can be accurately controlled, by the feed back control with the detection value of the acceleration about the injection direction of the divert thruster. Moreover, control for keeping the combustion pressure constant can be realized.
Although the present invention has described above in connection with several embodiments thereof, it would be apparent to those skilled in the art that those embodiments are provided solely for illustrating the present invention, and should not be relied upon to construe the appended claims in a limiting sense.

## Claims

1. An orbit attitude control device comprising:
a plurality of nozzles configured to inject a combustion gas supplied from a combustion chamber; and
a control section configured to receive opening degree command values for the plurality of nozzles, calculate a pressure difference between a detection value of a pressure inside the combustion chamber and a command value for the pressure, determine a total control value based on the pressure difference, calculate nozzle opening degree correction values by distributing the total control value to the opening degree command values to be proportional to the opening degree command values, correct the opening degree command values by the nozzle opening degree correction values, and control the plurality of nozzles based on the corrected opening degree command values such that the plurality of nozzles inject the combustion gas supplied from the combustion chamber based on the corrected opening degree command values.

2. The orbit attitude control device according to claim 1, wherein each of the nozzle opening degree correction values is determined based on a monotonically increasing function of a corresponding one of the opening degree command values.

3. The orbit attitude control device according to claim 2, wherein each of the nozzle opening degree correction values is determined to be proportional to the corresponding one of the opening degree command values.

4. A method of controlling an orbit attitude, the method comprising:
receiving opening degree command values for a plurality of nozzles;
calculating a pressure difference between a detection value of a pressure inside a combustion chamber and a command value for the pressure;
determining a total control value based on the pressure difference;
calculating nozzle opening degree correction values by distributing the total control value to the opening degree command values to be proportional to the opening degree command values;
correcting the opening degree command values by the nozzle opening degree correction values; and
controlling the plurality of nozzles based on the corrected opening degree command values such that the plurality of nozzles inject the combustion gas supplied from the combustion chamber based on the corrected opening degree command values.

5. The method according to claim 4, wherein each of the nozzle opening degree correction values is determined based on a monotonically increasing function of a corresponding one of the opening degree command values.

6. The method according to claim 5, wherein each of the nozzle opening degree correction values is determined to be proportional to the corresponding one of the opening degree command values.