Patent Description:
Electric driven motors are used in a wide variety of applications including both commercial and military applications. In many applications, the individual actuators are part of a multi-actuator system in which the actuators are controlled externally in a cooperative scheme to achieve one or more combined effects. Some typical applications include fins and control surfaces on aircraft, missiles or guided projectiles, in which at least two or more control surfaces are used collectively or differentially to control roll, pitch and yaw motions of the air vehicle. Typical multi-actuator system applications use individual actuators to drive individiual control fins in a <NUM>:<NUM> relationship. Each actuator subsystem is independently controlled and receives individual fin position commands from an external system computer, such as an autopilot, and reports back estimates of the fin position and angular rate.

While conventional methods and systems have generally been considered satisfactory for their intended purpose, there is still a need in the art for a system and method that can control the response bandwidth of each of effect (such as roll, pitch and yaw) independently. <CIT>, over which claim <NUM> is characterised, discloses a method of operating a flight control system wherein specific actuator commands may have their bandwidths modified.

The purpose and advantages of the below described illustrated embodiments will be set forth in and apparent from the description that follows. Additional advantages of the illustrated embodiments will be realized and attained by the devices, systems and methods particularly pointed out in the written description and claims hereof, as well as from the appended drawings. According to an aspect of the present invention, there is provided a method as claimed in claim <NUM>.

The illustrated embodiments are now described more fully with reference to the accompanying drawings wherein like reference numerals identify similar structural/functional features.

It is to be appreciated the illustrated embodiments discussed below are preferably a software algorithm, program or code residing on computer useable medium having control logic for enabling execution on a machine having a computer processor. The machine typically includes memory storage configured to provide output from execution of the computer algorithm or program.

As used herein, the term "software" is meant to be synonymous with any code or program that can be in a processor of a host computer, regardless of whether the implementation is in hardware, firmware or as a software computer product available on a disc, a memory storage device, or for download from a remote machine. The embodiments described herein include such software to implement the equations, relationships and algorithms described above. One skilled in the art will appreciate further features and advantages of the illustrated embodiments based on the above-described embodiments. Accordingly, the illustrated embodiments are not to be limited by what has been particularly shown and described, except as indicated by the appended claims.

Turning now descriptively to the drawings, in which similar reference characters denote similar elements throughout the several views, <FIG> depicts an exemplary actuator system <NUM> in which below illustrated embodiments may be implemented. Actuator system <NUM> includes an actuator controller <NUM> that is configured to allow user or automated selection of bandwidth or response time of the actuator system <NUM> during operation. The selected bandwidth can be provided, for example by an external system controller (not shown). Bandwidth is related to the reciprocal of response time, and each reference to bandwidth encompasses reference to response time.

The purpose and advantages of the below described illustrated embodiments will be set forth in and apparent from the description that follows. Additional advantages of the illustrated embodiments will be realized and attained by the devices, systems and methods particularly pointed out in the written description and claims hereof, as well as from the appended drawings.

<FIG> shows a cooperative multi-actuator variable bandwidth controller architecture system <NUM>. This system differs from the typical actuator controller architecture in three important ways: <NUM>) A single controller <NUM> receives a first amount (m) of system commands and computes a second amount (n) of actuator motor controller commands for all of the individual actuators in the system, <NUM>) The single controller <NUM> incorporates knowledge of allocation matrix that apportions m effects into n actuators <NUM> as well as the desired bandwidths of the m effect responses, <NUM>) an embedded computation of the cooperative multi-actuator controller gains based on the externally commanded bandwidths and allocation matrix.

Externally supplied bandwidths may be either be fixed in software settings or may be modified during operation by an external system controller <NUM> to allow the system <NUM> to assume a different bandwidth responses at different times or phases of system operation. The system <NUM> has the ability to control the response bandwidth of each of the m effects (such as roll, pitch and yaw) independently. Modifying the bandwidth in real time is beneficial in applications where the response requirements change significantly during its operation, such as for a missile system during mid-course glide versus terminal maneuver. The ability to use lower bandwidths when appropriate can lead to significant power savings, which can reduce battery size and/or electric generation requirements.

<FIG> shows the architecture of the Cooperative Multi-Actuator Variable Bandwidth Controller <NUM>. The architecture consists of a Multi-Actuator Effects Controller module <NUM> and Actuator Controller modules <NUM><NUM>. The Multi-Actuator Effects Controller <NUM> communicates with the external user supplied System Controller <NUM> (shown in <FIG>) and receives the Bandwidth and Allocation Matrix information for the m number of effects (such as roll, pitch, yaw), and the m number of effects commands. The Multi-Actuator Effects Controller <NUM> also provides feedbacks to the external System Controller <NUM> such as positions and rates of the m effects.

The Multi-Actuator Effects Controller <NUM> computes the applicable controller gain and product matrices and uses them to compute the actuator current loop inputs for the n physical actuators <NUM> in the system. The Actuator Controller modules <NUM>. n each receive the specific current input command i<NUM>ref. inref and compute individual voltage commands to control the <NUM>. n actuators <NUM>. The Actuator Controller modules <NUM> each contain a Current Loop Controller <NUM>, a Motor Interface module <NUM> and the High Gain Observer Module <NUM> specific to each of the <NUM>. n physical actuators <NUM>. The current loop controller <NUM> receives the actuator motor current reference commands iqref, idref, and uses a standard PID electric-motor controller design in the d-q reference frame to compute the required voltage reference commands vqref, vdref, to the motor interface module <NUM>. The motor interface module <NUM> receives the <NUM> phase current measurements from the motor current monitor device and the estimated motor rotor position from the High Gain Observer module <NUM>. The motor controller interface module <NUM> converts the voltage reference commands from the d-q reference frame to the <NUM> phase voltages required to control the actuator electric motor. The current monitor interface module <NUM> converts the <NUM> phase current measurement received from the current monitor device into the d-q reference frame, and provides the motor current feedbacks to the current loop controller module. The design of the Current Loop Controller <NUM> and the Motor Interface modules <NUM> may be tailored to meet different types and grades of motors used in actuation systems, including but not limited to inductive motors, permanent magnetic synchronous motors, and with additional interface calculations, motors requiring pulse width modulation (PWM) control.

<FIG> shows The High Gain Observer <NUM> configured to measure motor positions received from the motor position encoder device to provide real time estimates of the motor rotor position, angular rate and reaction torque. The High Gain Observer <NUM> is designed for each of the <NUM>. n actuators <NUM> and embedded in the Actuator Controller module <NUM> with Current Loop Controller module <NUM> and Motor Interface Module <NUM>. The High Gain Observer module <NUM> contains parameters and gains that are specific to individual actuators and may be tailored to accommodate actuators <NUM> of different types and with different characteristics within the multi-actuator group. Because the reaction torque of each actuator <NUM> is estimated quickly by the High Gain Observer <NUM> and directly compensated for in the Effects Multi-Actuator eController <NUM>, the bandwidth requirements of the individual actuators are decoupled from the max load torque requirements. This allows the multi-actuator system <NUM> bandwidths to be lowered even when the multi-actuator system is subjected to relatively high external load torques. Another advantage of this architecture is that the multi-actuator system <NUM> displays a consistent response for the specified effects bandwidths independent of the external loading. For example, this could prevent or reduce asymmetric responses of missile or aircraft roll control surfaces, which are experiencing different aerodynamic loading due to angle of attack or aerodynamic shading. Although the example application described is for controlling an airframe using four actuated fins for roll, pitch and yaw control, this example is for illustrative purposes and in no way is intended to limit the scope of applicability of the invention. The invention applies to any application where two or more actuators are used in a cooperative system to control one or more effects.

Multi-actuator systems are often used to achieve control effects through the combined effects of their independent dynamics. The system designer must apportion each of the m desired effects to the n individual actuators by establishing an allocation, or mixing, transformation defined by: Δn = MΔm where n ≥ m , that is the number of actuators must greater or equal to the number of effects to be controlled. As an example, consider the design of a fin controlled missile system in which <NUM> fin actuators are used to control the <NUM> body motions of roll, pitch and yaw.

One example of such a <NUM> fin allocation matrix is <MAT> where the fins are used in the "X" aerodynamic configuration, with combinations of all four fins are used to control all three axes of roll, pitch and yaw motion. Another example is given by: <MAT> where the fins are used in the "+" aerodynamic configuration, with all four fins used for roll, but two fins used exclusively for pitch and two fins used exclusively for yaw. Many different variations and examples are found in the control of aerospace vehicles from aircraft, rotor vehicles, missiles, launch rockets and spacecraft. However, the applicability and scope of this invention is not limited to aerospace vehicles, but extends to any application where multiple actuators are used to achieve cooperative or collaborative effects.

In each case a reverse transformation, MI, can be found: <MAT> by taking the pseudo inverse ofM: <MAT>.

It is well established that for the Penrose-Moore pseudo inverse given above every real n x m matrix M of rank r, there is a unique m x n pseudo inverse M# of rank r.

Referencing the examples above: <MAT> <MAT>.

In some cases it may be desirable or necessary to change the allocation transformation matrix during operation. This ability could be used to accommodate actuators which "deploy" or begin operation at different times, such as deployable canards or deployable wings with actuated ailerons. This ability could also be used to accommodate robust reconfigurable control systems after the loss or failure of an actuator or actuated surface.

Claim 1:
A method for operating a system comprising a group of an n number of actuators (<NUM>), a system
controller (<NUM>) and an actuator controller (<NUM>), the method comprising the steps of:
transmitting by the system controller (<NUM>) an m number of effect commands in order to produce an m number of effect responses by the group of n actuators (<NUM>) acting in combination;
commanding the actuator controller (<NUM>) to initiate at least one actuation combined effect based on the m effect commands, wherein the n number of actuators is greater than or equal to the m number of effect commands;
controlling by the actuator controller (<NUM>) the n number of actuators in order to achieve the at least one combined effect on a vehicle based on the m effect commands;
and the method characterised by:
computing by the actuator controller independent bandwidths for each of the effect responses of the m number of effect responses, wherein each of the effect responses of the m number of effect responses includes a different bandwidth, the bandwidths being modified in real time to achieve the different bandwidths at different times or phases of system operation;
apportioning by the actuator controller the m number of effect responses of each of the actuators and the bandwidths for each effect response of the m number of effect responses;
controlling the actuators according to the bandwidths; and
the actuator controller using an estimated reaction torque and rotational speed of each actuator to maintain the bandwidths of each of the m number of effect responses in the presence of external loads;
wherein the m number of effect responses includes one or more of roll, pitch or yaw.