Patent Description:
<CIT>]) discloses a control method suitable for an inceptor, comprising subtracting a force feedback signal from a force applied to the inceptor and deriving a velocity signal from said difference.

<CIT>]) discloses a haptic accelerator for force feedback computer peripherals.

<CIT>]) discloses calibration of haptic feedback systems for input devices.

<CIT>]) discloses adaptive control of aircraft using structural health monitoring.

<CIT>) discloses systems and methods to prevent an aircraft from tail contact with the ground.

Active inceptor systems may be used to provide force feedback to a user input device. An active inceptor system may be used in control of flight surfaces of aircraft, such as helicopters or aeroplanes. However, they may also have applications in other vehicles or any other application where force feedback is useful.

An active inceptor system <NUM> is illustrated in <FIG>. Active inceptor system <NUM> comprises a user input device <NUM>, a pivot <NUM>, a force sensor <NUM>, and a grip portion <NUM>. The active input device also comprises mechanism <NUM> and force feedback circuitry <NUM>. The active inceptor system <NUM> may also comprise other sensors, not indicated in <FIG>, for example position, velocity and/or acceleration sensors. The active inceptor system <NUM> may also comprise more than one force sensor and/or other type of sensor.

The user input device <NUM> may move about the pivot <NUM> in at least one axis. The user may grip the user input device <NUM> using grip portion <NUM>, although they are not limited to gripping the user input device <NUM> at grip portion <NUM>.

The user input device <NUM> may be a stick, an inceptor, or throttle. The user input device <NUM> may have any shape. The grip portion <NUM> may be the part of the user input device <NUM> that is designed for the user to hold. Grip portion <NUM> may also be merely a portion of user input device <NUM> that has a different mass or profile than the rest of the user input device <NUM>.

Force sensor <NUM> is illustrated as being coupled to the user input device <NUM>, however it may be positioned in any location that still enables the user input force to be determined. For example, it may be located on the grip portion <NUM>, the user input device <NUM>, pivot <NUM> or mechanism <NUM>.

Force feedback may be provided to the user input device <NUM> with a force feedback control loop using force feedback circuitry <NUM>. Force feedback system <NUM> may internally simulate a feel model, such as a second order mass-spring-damper (MSD) model, although other models may be used. The force feedback circuitry <NUM> may cause mechanism <NUM> to apply a force to the user input device <NUM>, the force dependent upon predetermined settings and chosen feel model.

A user may also input an operator force on the user input device <NUM> to move the user input device <NUM>. The user may feel a feedback force from mechanism <NUM> dependent upon the predetermined settings and chosen feel model.

Due in part to the inertia of the mass of the grip portion <NUM>, when movement of the user input device <NUM> is initiated, either by user input force or the mechanism <NUM>, a force is felt on the force sensor <NUM>. The magnitude and direction of the force is dependent upon at least the location of the force sensor <NUM>, the direction of the applied force, and whether the movement is initiated by the mechanism <NUM> or by the user (i.e. the relationship between the location of the force sensor <NUM> and the position of the user or mechanism applied force).

Two examples of the force felt on the force sensor <NUM> are illustrated in <FIG> and <FIG>.

In <FIG>, the movement is initiated by the mechanism <NUM>, moving the user input device <NUM> in direction 190a about the pivot <NUM>. Inertial effects, since the grip portion <NUM> has a mass that resists movement, cause a tension force 101a to be felt on the right hand side of force sensor <NUM>. Similarly the inertial effects would cause a compression on the other side of the force sensor <NUM>.

In <FIG> the movement is initiated by a user applying a force causing the user input device <NUM> to move in the direction 190b about the pivot <NUM>. The force may be applied at the grip portion <NUM> (i.e. above the force sensor). The force applied by the user, may be felt as a tension 101b on the left hand side of the force sensor <NUM>. Similarly the inertial effects would cause a compression on the other side of the force sensor <NUM>.

The force induced due to the inertial effects is a physical property of the active inceptor system <NUM>. However to improve the system bandwidth the forces induced due to the inertial effects should be mitigated. If the inertial forces are not mitigated, then they may limit the maximum bandwidth of the active input device system <NUM>, deteriorating the tactile feel of the active input device, in some examples making it feel sluggish. This in turn may limit performance of the user and/or vehicle the active inceptor system <NUM> controls.

The user input device <NUM> may comprise a stick or an inceptor, or any other appropriate input device. The active inceptor system <NUM> may be used to control the flight surfaces of an aircraft. The active inceptor system <NUM> may be used to control vehicles, such as trains. The active inceptor system <NUM> may also be used for other applications, and is not limited to being applied to vehicles.

The force sensor <NUM> may comprise a strain gauge, such as a wheatstone bridge type arrangement, although it is not limited to this type of sensor.

<FIG> is an exemplary Bode plot of sensed force plotted against inceptor position. The response is very similar to an inverted 2nd order mass-spring-damper model, and the reason this looks so similar is because that is substantially what is happening within the active inceptor system <NUM>. To counteract the reduction in bandwidth due to the inertial forces, an estimate of the transfer function illustrated in <FIG> may be determined.

The transfer function may be estimated by determining a total compensation force, which may be removed from the sensed force sensed by force sensor <NUM>. The total compensation force is determined by determining a damping force and an inertial force. The damping force is dependent upon the velocity of the grip portion <NUM>, and the inertial force is dependent upon the acceleration of the grip portion <NUM>.

A method, <NUM>, to determine the total compensation force information is illustrated in <FIG>. The method comprises obtaining, <NUM>, velocity information of the user input device and/or grip portion. The damping force information is obtained, <NUM>, based on the velocity information.

At substantially the same time as the velocity information is obtained the acceleration information is obtained <NUM>. The inertial force information may be obtained, <NUM>, based on the acceleration information.

The damping force information and inertial force information are combined <NUM> by summing to produce total compensation force information <NUM>. The total compensation force information may then be provided to the force feedback circuitry <NUM> which may use it to update the sensed force supplied to the model to provide compensated force information.

The velocity information may be obtained without using a velocity sensor, or may be obtained using a velocity sensor close to or on the grip portion <NUM>.

In some examples obtaining, <NUM>, velocity information of the user input device and/or grip portion may comprise obtaining position information of the user input device <NUM> from a position sensor located close or on the grip portion <NUM> and differentiating the position information to obtain the velocity information.

In some examples obtaining, <NUM>, velocity information of the user input device and/or grip portion may comprise obtaining acceleration information of the user input device <NUM> from an acceleration sensor located close to or on the grip portion <NUM> and integrating the acceleration information.

In some examples the acceleration information may be obtained from an acceleration sensor close to or on the grip portion <NUM>. In some examples, obtaining, <NUM>, acceleration information may comprise double differentiating a sensed position of the user input device or differentiating a velocity.

In some examples obtaining, <NUM>, the damping force information may comprise multiplying the velocity information with a damping constant. The damping constant may depend on the physical properties of the active inceptor system <NUM>, and may be predetermined.

In some examples obtaining, <NUM>, the inertial force information may comprise multiplying the acceleration information with an inertia constant. The inertial constant may depend on the physical properties of the active inceptor system <NUM>, and may be predetermined.

The accuracy of the total compensation force information may be improved by locating the sensors as close as possible to the grip portion <NUM>, or on the grip portion <NUM>. This is because structural flexure between the actual grip position and the location of the sensor may cause inaccuracies to build up in the sensed output.

<FIG> illustrates a method, <NUM>, in accordance with some examples. The method <NUM> is substantially the same as the method described in relation to <FIG>, and any of the features described above may be applied to the method <NUM>. The method also comprises applying, <NUM>, a lag filter to the summed inertial compensation force information and damping compensation force information, and applying, <NUM>, a saturation limit to the filtered total compensation force information.

A lag filter may be applied, <NUM>, as the velocity and/or acceleration information may have high levels of noise, for example due to the use of differentiators. Using a lag filter reduces the noise of the signal. Although the lag filter is shown as occurring after the summation, is it to be understood that the lag filter could be used at any suitable positon in the method. Furthermore, other methods to reduce noise could be used instead or in addition to the application of the lag filter. There could also be more than one lag filter, for example a separate lag filters may be used at any point in the method.

Applying, <NUM>, the saturation limit, limits the magnitude of the compensation force information to be below a predetermined value. The predetermined value may be equal to the available maximum grip force which is the maximum force a pilot is expected to apply. Limiting the compensation force information to be below a predetermined value allows for unexpectedly large forces to be identified and not summed with the sensed force. Summing an unexpectedly large force with the sensed force may reduce the performance of the active inceptor system <NUM>. An unexpectedly large force might be result when double differentiating a position signal, which can lead to very large transient spikes in response.

<FIG> illustrates a method to obtain, <NUM>, the compensated sensed force information <NUM>. The sensed force <NUM> may be summed <NUM> with the compensation force information <NUM> to obtain the compensated sensed force <NUM>. The compensated force <NUM> may then be provided to the force feedback circuitry <NUM> in order to calculate the appropriate force to apply to the user input device <NUM> using the mechanism <NUM>.

<FIG> illustrates a computer readable medium <NUM> in accordance with some examples. Computer readable medium <NUM> comprises a damping force module <NUM> comprising instructions, that when executed, cause a processing means <NUM> to obtain damping force information. Computer readable medium <NUM> also comprises an inertial force module <NUM> comprising instructions, that when executed, cause a processing means <NUM> to obtain inertial force information. Computer readable medium <NUM> comprises a total compensation force module <NUM> comprising instructions, that when executed, cause a processing means <NUM> to obtain total compensation force information.

The description refers to position information, velocity information, acceleration information, inertial force information, damping force information, and total compensation force information. This is because the method and systems may not require an absolute value of the variables to be calculated. In some examples the position information, velocity information, acceleration information, inertial force information, damping force information, and total compensation force information may comprise absolute values, in some examples they may be proportionate to the actual absolute value.

Claim 1:
A method to obtain total compensation force information of a user input device (<NUM>), characterised in that forces induced by inertial effects of the user input device (<NUM>) can be mitigated, the method comprising:
obtaining velocity information (<NUM>) of a portion of the user input device (<NUM>);
obtaining acceleration information (<NUM>) of the portion of the user input device (<NUM>);
obtaining damping compensation force information (<NUM>) based on the velocity information (<NUM>);
obtaining inertial compensation force information (<NUM>) based on the acceleration information (<NUM>), the inertial compensation force information (<NUM>) representing physical inertial effects of the portion of the user input device (<NUM>); and
combining (<NUM>) the damping compensation force information (<NUM>) and inertial compensation force information (<NUM>) to provide a total compensation force information (<NUM>; <NUM>) of the user input device,
wherein the method further comprises compensating a sensed force (<NUM>) acting on the user input device (<NUM>) based on the total compensation force information (<NUM>; <NUM>).