Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reexamination Certificate
1999-08-17
2001-06-12
Camby, Richard M. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C244S178000, C701S005000, C701S006000
Reexamination Certificate
active
06246929
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an autopilot controller, and to a method, for controlling a vehicle, and more particularly, an autopilot controller for controlling a vehicle traveling in a fluid medium, in any one of pre-stall, stall and post stall regions.
BACKGROUND OF THE INVENTION
Vehicles such as aircraft, missiles, drones, etc. (hereafter referred to as “aircraft” or “vehicles”) are generally provided with a flight control system so that the orientation of the vehicle during flight can be controlled along the three principle axes, namely, yaw, pitch, and roll. The pitch axis, which in an aircraft extends along the wingspan, defines a degree to which the nose of the vehicle is pointed above or below the horizon. The roll axis extends along the length of the aircraft and defines the degree to which the wings of the aircraft are banked. The yaw axis is perpendicular to both the pitch axis and the roil axis.
The control system provides a means for varying the orientation of the aircraft during flight so that, for instance, the wings can be banked to change a direction of flight, or the nose can be raised or lowered to change the altitude. In one type of conventionally configured aircraft, the control system can include: ailerons for controlling the roll angle (bank) of the aircraft in response to a rotation of a control wheel; an elevator for controlling the pitch angle of the aircraft in response to a pushing or pulling on the control yoke; and a rudder for controlling the yaw angle of the aircraft in response to an input to the control pedals.
Other aircraft and other types of vehicles can employ different control devices such as canards, rotatable fins or wings, spoilers, moveable tail surfaces, etc., to affect the orientation of the vehicle.
While aircraft can be controlled via the control system by a human pilot (often referred to as “man-in-the-loop”), aircraft can also be controlled for a portion of a flight, or for an entire flight, by an autopilot system. In the autopilot situation, the autopilot—as opposed to a human pilot—manipulates the control surfaces in order to control the orientation of the vehicle in response to an established or inputted command. Examples of an inputted signal include, but are not limited to: a course guidance signal inputted to an autopilot, so that the autopilot can control the direction of flight so as to follow the heading or course set; an altitude hold/altitude capture input, so that the autopilot can control the altitude and/or the rate of change of the altitude of the vehicle; and a turn rate command, so that the autopilot will initiate a turn at a requested rate or acceleration amount.
Aircraft can also be controlled in a manner which is not purely manual or purely automatic but where a flight director is used. Where a flight director is used, the flight director receives a command signal from the autopilot which would normally be used to control the flight control elements. However, instead of controlling the flight control elements, the command signal controls the position of a flight director indicator on the pilot's attitude indicator or multi function display, which tells the pilot how to manipulate the flight control elements so that the aircraft flies according to a desired flight profile.
In the cases where an autopilot is used, the autopilot must interpret an inputted guidance or altitude command and, based on that inputted command, output a command for manipulating the flight control elements which is suitable for achieving the desired result. For instance, in response to a guidance command which requests a left turn at a 2 g rate, the autopilot must output a command for a particular control surface—or combination of control surfaces—instructing a direction and amount of control surface movement which is appropriate for achieving the requested 2 g left turn.
The autopilot will generally be implemented with some type of feedback which provides information pertaining to the operating status of the vehicle relative to the guidance command, so that the autopilot can determine when the desired result has been achieved or whether additional flight control manipulation is required to achieve or maintain the desired result.
FIG. 1
is a conceptual block diagram of an autopilot which is implemented as a control system with feedback. As shown, a guidance command is inputted to the autopilot controller
10
, which interprets the command and outputs a control surface actuation or deflection command &dgr;. The control surface actuation or deflection command &dgr; is received by a device
12
such as a control surface servo or actuator, which in turn moves the control surface
14
. Generally, the control surface
14
or the control surface actuator
12
will be equipped with a device, such as an encoder (not shown) which outputs the current position of the control surface. The output from the encoder is fed back to the autopilot controller
10
so that the autopilot controller
10
can determine the control surface/actuator deflection output &dgr; based on the current position of the control surface
14
.
The autopilot controller
10
determines the control surface response which is needed to accomplish the inputted command based, in part, on vehicle condition information which is fed back from, for insance, a sensor
16
on the vehicle. A difference, generally referred to as an error signal, between the feedback signal and the guidance command, is evaluated in order to determine the control surface response which is needed to accomplish the inputted command. Because both the actuation of the control surface as well as the response of the vehicle to the control surface actuation occur over a period of time, the error signal is continually monitored as the control surface is moved so that the autopilot controller can determine when the guidance command has been successfully performed. The autopilot controller determines that a guidance command has been successfully performed when the error signal goes to zero. So long as a non-zero error signal is received, that indicates a situation where the guidance commandei request has not yet been accomplished and/or where further control surface actuation may be required.
As an example, this general autopilot system can be described in the context of an autopilot for controlling the altitude of a vehicle where information from an altimeter (sensor
16
) would be fed back to the autopilot controller
10
. Thus, if a guidance command is inputted which requires a change in the altitude, a non-zero error signal will be generated so long as the current altitude is different from the requested altitude, and the autopilot controller
10
will output control surface commands to change the altitude of the vehicle. When the current altitude of the vehicle matches the commanded altitude, i.e., when the error signal becomes zero, the autopilot controller
10
will cease to output control surface commands or will output control surface commands appropriate to maintain the commanded altitude.
While the example above addresses only one aspect of the vehicle (altitude), it should also be appreciated that the autopilot can control pitch, roll, yaw, or other aspects. Additionally, a multi-axis autopilot can be employed where several of the aspects of the vehicle are simultaneously controlled.
Because, for a given command, the autopilot must output flight control commands which are appropriate for the vehicle on which it operates, each autopilot must, to some degree, be designed for, or tailored to, the specific vehicle for which it is intended.
In designing or tailoring the autopilot, not only must the types of control surfaces which are provided on the vehicle (and the aspect of the vehicle orientation which they effect) be comprehended, but also the vehicle response to varying degrees of control surface deflection need to be addressed so that the autopilot can respond to more or less aggressive maneuvers and so that the autopilot can limit the control outputs to those which will no
Camby Richard M.
Lockheed Martin Corporation
Sadacca Stephen S.
Sidley & Austin
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