Method and apparatus for stabilizing payloads, including airborne cameras

ES 2 393 322 T3

DESCRIPTION

Procedure and apparatus for stabilizing payloads, including aerial cameras.

TECHNICAL FIELD

The present invention relates generally to methods and apparatus for stabilizing aerial cameras.

BACKGROUND

Airplanes or unmanned aerial vehicles (UAVs) provide better and cheaper access to areas where manned flight operations are unacceptably expensive and / or dangerous. For example, drones equipped with remote control cameras can perform a wide variety of surveillance missions, including locating schools of fish for the fishing industry, monitoring weather conditions, setting up border patrols for national governments, and the provision of military surveillance before, during and / or after military operations.

To carry out a surveillance mission, a drone typically carries a remotely operated mobile camera. If it does not stabilize, the orientation direction of the aerial camera oscillates as the aircraft maneuvers. Common practice is to mount a camera within a gimbal system and drive the gimbal so that the orientation axis is stabilized. This approach can provide a high quality stabilized orientation, but typically involves large and heavy mechanical systems to support the aerial camera. Such systems are the subject of US patent 5,897,223, US patent 3,638,502, US patent 4,989,466, US patent 4,643,539 and US patent 5,184,521.

To fully stabilize an aerial camera, typically at least three axes of roll freedom are required. Each of the above-mentioned patents describes a 3-axis system, while US Patent 5,897,223 also describes a 2-axis system. Even with three axes of roll freedom, stabilization degrades in some orientation directions. This occurs when two of the mechanical axes become collinear, and is known as gimbal lock ”. Stabilization performance can noticeably degrade when working near this gimbal lock setting. " In Figure 1A of US Patent 5,897,223, for example, gimbal lock can occur when the "horizon axis" is rotated ± 90 degrees from the drawn configuration. Figure 1B of the same US patent 5,897,223 shows a 2-axis gimbal system in which the stabilization of the outer axes can degrade as long as the orientation direction is towards the nadir of the flight vehicle.

To avoid this stabilization degradation, existing systems have included additional stabilization shafts within the wide-motion gimbal shafts. A drawback associated with this proposal is that the additional inner shafts can increase the weight, size, complexity and energy consumption of the entire stabilization system.

US-A-3 085 354 describes a multiple gimbal simulator which is carried out to simulate movements of a flight and which can provide flight equipment for airplanes with rapid simulation of a flight attitude. The described gimbal system uses three actuators to produce rotary movements around three axes.

US-A-3 464 116 describes a satellite tracking carrier that uses a gimbal system having four axes for satellite tracking. The support for the tracking of satellites has a base element, a fork adjustably positioned on said base element, an outer gimbal mounted to rotate on said fork element, an inner gimbal rotatably mounted within said outer gimbal, and a main transmission or detection instrument arranged to rotate within said inner gimbal and with respect thereto towards a displaced position.

The object of the present invention is to provide an improved apparatus and method for stabilizing aerial cameras using three axes.

The object is solved by the content of the independent claims.

Preferred embodiments are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates an aircraft having a camera configured and installed in accordance with one embodiment of the invention.

Figures 2A-2C illustrate a camera mounted on a scrolling gimbal system in accordance with one embodiment of the invention.

ES 2 393 322 T3

Figures 3A-3C illustrate the camera and gimbal system shown in Figures 2A-2C tilted to three different positions in accordance with one embodiment of the invention.

Figures 4A-4C illustrate the camera and gimbal system shown in Figures 2A-2C scanned to three different positions in accordance with one embodiment of the invention.

Figure 4D is a partially schematic illustration of a camera image aligned with respect to two perpendicular axes in accordance with one embodiment of the invention.

Figures 5A-5C are block diagrams illustrating procedures for controlling camera movement in accordance with various embodiments of the invention.

Figure 6 illustrates a camera mounted on a gimbal system carrying a displacement actuated protective housing in accordance with one embodiment of the invention.

DETAILED DESCRIPTION

The present description describes support systems for payloads, including cameras, that can be incorporated into an aircraft, including a drone. Many specific details of certain embodiments of the invention are set forth in the following description and in Figures 1-6 to provide a complete understanding of these embodiments. Those skilled in the art, however, will understand that the present invention may have additional embodiments, and that the invention may be practiced without various of the details described below.

Aspects of the present invention include apparatus for stabilizing the orientation direction of an aerial camera. The apparatus may include a gimbal system on which the camera is mounted, together with appropriate motors to orient the camera by actuating the gimbal system, and sensors suitable for producing a signal to drive the gimbal motors. Other aspects of the invention may include a sequence of actions on the gimbal axes that achieve stabilization of the camera. This sequence of actions can reduce system complexity, avoid gimbal lockup, and provide better redundancy and performance.

Still other aspects of the present invention may include a camera mounted on a gimbal system that includes two long travel gimbal shafts, augmented by a single shorter travel inner shaft. The axes can be arranged as offset (outside) over tilt (intermediate) over scan (inside). The scan axis can be arranged so that it is parallel to the axis of travel when the payload is oriented horizontally (for example, when the camera is pointing straight ahead). When the payload is pointing toward the aircraft's nadir (for example, when the camera is pointing down), the scan axis may allow stabilization, which is not otherwise possible with a two-axis system due to gimbal lock .

A feature of the above arrangement is that it can result in a very compact setup of a stabilized gimbal system for an aerial camera. Advantages of this arrangement may include reduced size, weight, complexity, and power requirements.

As described above, a gimbal arrangement in accordance with one embodiment of the invention can provide redundant performance when the tilt axis points to the camera's line of sight horizontally. In this configuration, the travel and scan axes are parallel or collinear. This redundancy gradually decreases towards zero as the tilt axis points to the nadir line of sight. In one aspect of this embodiment, movement along the axis of travel may be synchronized with movement along the scan axis, such that the travel actuator moves with a (relatively) slower frequency response to keep the angle of the scanning gimbal almost at zero. This approach allows for a less agile and less precise roll actuator, which can flip 180 degrees around the roll axis as long as the target passes through or near nadir. In another embodiment, the use of a (relatively) less agile, and less accurate travel actuator may allow the gimbal system to carry a rolling drive weather housing without additional cost, weight and complexity penalties typically associated with an additional actuator. for this case.

Figure 1 is a partially schematic isometric view of a drone 100 configured to support an aerial apparatus 110 in accordance with one embodiment of the invention. In one aspect of this embodiment, the drone 100 may include a fuselage 101, a pair of wings 102 extending outward from the fuselage 101, and a propeller 104 disposed at the aft end of the fuselage 101 to propel the aircraft. during flight 100. Each wing 102 may include an upwardly extending fin 103 for stability and lateral control.

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The apparatus 110 may include a camera 111 or other payload supported by a gimbal apparatus 120. The apparatus

110 can be placed behind a surveillance dome 140 in a portion of the tip 105 of the aircraft 100. The camera

111 it can move relative to aircraft 100 to capture and / or track a target located on the ground, at sea, or in the air. Further details of the ways in which the gimbal apparatus 120 controls the movement of the camera 111 are described below with reference to Figures 2A-6.

Figure 2A is a partially schematic isometric illustration of apparatus 110 substantially similar to that shown schematically above in Figure 1. As described above, apparatus 110 may include camera 111 supported by gimbal apparatus 120. In one embodiment , the gimbal apparatus 120 may include a first bracket or carriage 121 carrying a second bracket or base 122. The camera 111 can be disposed on the base 122. As described in greater detail below, gimbal apparatus 120 can be configured to move camera 111 about three axes relative to plane 100 (FIG. 1).

In one aspect of an embodiment shown in Figure 2A, carriage 121 can be coupled to a displacement actuator 123 to rotate about a displacement rotary axis 124, as indicated by arrow P. Base 122 can be coupled to a tilt actuator 127 to rotate about a tilt rotation axis 128, as indicated by the arrow T. The carriage 121 can support the tilt actuator 127 and therefore the latter can move with the carriage 121 as the carriage 121 travels. The gimbal apparatus 120 may further include a scan actuator 130 that is operatively coupled to the camera 111 with a crank 131 or other linkage. The scan actuator 130 can rotate the camera 111 relative to the base 122 about a scan rotation axis 132, as indicated by the arrow S. In one embodiment, actuators 123, 127, 130 may include AM1524-A motors, available from MicroMo Electronics, Inc. of Clearwater, FL. In other embodiments, actuators 123, 127, 130 may include other devices.

Camera 111 may include a camera aperture 113 having a line of sight L. In one embodiment, camera 111 may include a video camera configured to capture images formed by radiation in the visible spectrum. For example, camera 111 may include a model FCB 780, available from Sony Corp. of Tokyo, Japan. In other embodiments, the camera 111 may be configured to capture images formed by radiation having other wavelengths, eg, infrared images. For example, camera 111 may include an infrared unit available from Indigo Systems Corp. of Santa Barbara, Ca or a CamNoii® unit available from Irvine Sensors Corp. of Costa Mesa, CA. In still other embodiments, camera 111 may include a photographic camera and / or may be configured to capture still images. The image captured by camera 111 can be stored on board aircraft 100 and / or transmitted to a remote location, eg, a monitor based on land or at sea.

In any of the above embodiments, the movement of the camera 111 relative to the aircraft 100 can have at least two aspects. In one aspect, the camera 111 can move to capture a target or track the target once the target is captured. This movement tends to be relatively intentional, since the aircraft 100 does not normally experience extreme maneuvers while capturing or tracking a target.

Another aspect of camera movement is aimed at keeping the image recorded by camera 111 relatively stable, despite the relatively high frequency disturbances that camera 111 may experience. vibration of the aircraft 100 produced by its propulsion system, and / or other sources. To correct jitters and / or other image noise resulting from such disturbances, the camera 111 can be stabilized about two perpendicular axes by the movements of at least two of the actuators. For example, in one embodiment, the tilt actuator 127 and the scan actuator 130 can be moved at relatively high frequencies to control relatively high frequency disturbances experienced by the camera 111. Scroll actuator 123 can be configured to apply relatively low frequency motion to the camera

111. For example, in one embodiment, scan actuator 130 and tilt actuator 127 may have a closed-loop bandwidth frequency of approximately 5 Hz, and scroll actuator 123 may have a loop bandwidth frequency. closed about 1 Hz. In other embodiments, these actuators may have different response frequencies. In any of these embodiments, shift actuator 123 may have a first frequency response (for example, for target capture and / or tracking), and tilt actuator 127 and scan actuator 130 may have a second. response frequency (eg for image stabilization), with the second response frequency being greater than the first response frequency. The maximum range for actuators 123, 127, 130 can be the same (eg 90 degrees / second) or different.

In any of the above embodiments, the scan axis of rotation 132 may initially be parallel to the axis of travel rotation 124, as shown in FIG. 2A. As the camera 111 is tilted about the tilt pan axis 128, the scan pan axis 132 may deviate from its alignment parallel to the roll pan axis 124. As described in greater detail below with reference to Figures 3A-4D, this arrangement can allow camera 111 to capture and track targets while monitoring high-frequency disturbances over a wide range of pan and tilt angles, all with a relatively simple mechanism.

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Gimbal apparatus 120 may further include gyros or other devices for tracking the speed at which camera 111 rotates about axes of rotation 124, 128, and / or 132. For example, in one embodiment, gimbal apparatus 120 may include a tilt gyro 129 configured to track the angular velocity about the tilt pan axis 128 and a scanning gyro 133 configured to track the speed at which the camera 111 rotates about scan rotation axis 132. An optional offset gyroscope (not visible in Figure 2A) can track the speed at which camera 111 rotates about offset spin axis 124. In one embodiment, the gyros can include model CRS03-02 units, available from Silicon Sensing Systems of Plymouth, UK. In other embodiments, the gyros can include other devices.

Circuit boards 126 may include circuitry that provides electrical communication between chamber 111, gyroscopes 129, 133, and actuators 123, 127, and 130. Circuit boards 126 may also allow communication between these components and other components located within. of airplane 100 (figure 1). Processors (not visible in FIG. 2A) can be arranged mounted on or remote from circuit boards 126. In one embodiment, the processors can include a master processor connected to three individual processors, each of the three individual processors being connected to one of the actuators 123, 127, 130. In a further aspect of this embodiment, the above processors can include Model MSP430 units, available from Texas Instruments of Dallas, TX. In other embodiments, the processors can include different units and / or can be arranged in different configurations.

Figure 2B illustrates the camera 111 after it has been rotated about the rotational axis of displacement 124 (as indicated by the arrow P) such that the line of sight L is oriented in a direction other than that shown in Figure 2A. . From this angle a shift gyroscope 125 (which can track the speed at which camera 111 rotates about shift axis 124) is visible. Camera 111 may continue to rotate about axis of displacement rotation 124, for example, toward the orientation shown in Figure 2C. In this orientation, other aspects of gimbal apparatus 120 are visible, including flexible cable 134. Flexible cable 134 can provide electrical communication to, from, and between components of apparatus 110.

Figures 3A-3C illustrate chamber 111 as it rotates about tilt axis 128 in accordance with one embodiment of the invention. Starting with Figure 3A, the camera 111 can rotate about the tilt axis 128, as indicated by the arrow T, so that the line of sight L is oriented upward, for example, if the aircraft 100 (Figure 1 ) plummets or is following an aerial target. If the aircraft 100 pitches up, or if the target begins to pass under the aircraft, the camera 111 may tilt downward about the tilt pan axis 128, as shown in Figure 3B, so that the line view L faces downward. As the aircraft 100 passes over the target, the line of sight L can pass through the vertical (as indicated by the dotted line V in Figure 3C), so that it faces rearward, still toward the objective. As the line of sight L passes through the vertical, the camera 111 can rotate 180 ° about the axis of displacement rotation 124 (as indicated by the arrow P) from the orientation shown in Figure 3C so that the resulting image transmitted by camera 111 does not appear upside down to the viewer. The camera 111 can then continue to tilt away from the vertical axis V as the plane 100 moves away from the target, with the transmitted image in a vertical position. In another aspect of this embodiment, the camera 111 can automatically rotate 180 ° about the axis of displacement rotation 124. For example, a sensor on the axis of the tilt actuator 127 (Figure 1A) can detect when the line of sight L of the camera 111 passes through the vertical, and can transmit instructions (for example, through the processors described above) to travel actuator 123 to perform 180 ° rotation. An advantage of this arrangement is that the workload of the operator can be reduced by automatically performing an operation that would otherwise be performed manually.

Figures 4A-4C illustrate camera 111 as it rotates about scan axis 132 (perpendicular to the plane of Figures 4A-4C) in accordance with one embodiment of the invention. Beginning with Figure 4A, camera 111 is shown pointing at least approximately downward, with line of sight L approximately aligned with vertical V. The scan actuator 130 can rotate the camera 111 about the scan rotation axis 132 at a relatively high speed clockwise (as shown in Figure 4B) and counterclockwise (as shown in Figure 4C). . Therefore, the scan actuator 130 can provide relatively high frequency movement aligned with an image axis of the image provided by the camera 111. For example, as shown in Figure 4D, an image 150 provided by camera 111 may have a first image axis 151 and a second image axis 152. Scan actuator 130 may provide image stability 150 along the first axis of image 151. The tilt actuator 127 can rotate (also at a relatively high speed) to move the camera 111 in a direction perpendicular to the direction of motion applied by the scan actuator 130. Consequently, the tilt actuator 127 can provide stability to the camera. Image 150 along the second axis of Image 152. Accordingly, the scan actuator 130 and the tilt actuator 127 together can correct for high frequency disturbances that the camera 111 experiences as the aircraft 100 flies over its target. In one embodiment, the tilt gyro 129 may provide information on the

ES 2 393 322 T3 angular velocity that corrects the tilt actuator 127, and the scanning gyro 133 (Figure 1A) can provide the angular velocity information that the scanning actuator 130 corrects. In other embodiments, the inputs for the actuators may be provided by other sources. In any of these embodiments, the processor (s) described above can coordinate communication to and from the actuators.

In one embodiment, scan actuator 130 can move camera 111 relative to scan axis of rotation 132 over a relatively limited range of angles. In one aspect of this embodiment, the angle range can be ± 20 (relative to the zero position shown in Figure 4A). In other embodiments, this range may be about ± 10, or this range may have other values ​​less than, for example, ± 180 ° or ± 90 °. An advantage of this feature is that the scan actuator 130 and crank 131 (FIG. 1A) can be relatively simple and it is not necessary to drive the camera 111 at high speeds over large ranges of angles.

A possible drawback with the above angle range arrangement is that the narrow range of angular movements about the scan rotation axis 132 can be limiting. A feature of the gimbal apparatus 120 according to one embodiment of the invention can overcome this drawback. In one aspect of this embodiment, shift actuator 123 can be synchronized with scan actuator 130. Consequently, the shift actuator 123 can receive information about the position of the camera 111 relative to the scan axis of rotation 132 (for example, from a sensor on the axis of the scan actuator 130) and can be moved to position the camera 111 in the middle of its available range of motion about the axis of displacement rotation 132 (ie, at the zero position shown in FIG. 4A). For example, referring now to FIG. 2A, travel actuator 123 can provide low-precision movement about travel rotational axis 124, and scan actuator 130 can provide high-frequency, precision movement around axis. scan rotation axis (parallel) 132. When camera 111 is not tilted, as shown in Figures 2A-2C, shift actuator 123 can rotate camera 111 to the correct orientation for target capture and / or tracking, and scan actuator 130 and the tilt actuator 127 together can allow relatively high frequency movement of the camera 111 along the two image axes 151, 152 (FIG. 4D) to correct for vibrations and other disturbances. As the camera 111 is tilted towards the orientation shown in Figures 4A-4C, the redundancy between the scan rotation axis 132 and the displacement rotation axis 124 disappears. Consequently, the displacement actuator 123 becomes less and less capable of zeroing the position of the camera 111 relative to the scanning axis of rotation 132. However, scan actuator 130 and tilt actuator 127 can still function to stabilize the camera against high frequency disturbances in two perpendicular directions without encountering the problem of gimbal lock described above.

Figures 5A-5C illustrate methods for controlling the movement of camera 111 described above, in accordance with various embodiments of the invention. In one aspect of these embodiments, the processes or steps can be completed by a computer or other numerical processor such as the processors described above. Referring first to FIG. 5a, a method 500 in accordance with one embodiment of the invention may include receiving information regarding the angular position of the camera around the axis of scan rotation (process part 501). In process part 502, the shift actuator can be activated until the angular position of the camera relative to the scan axis is zero, based on the information received in process part 501. Process 500 can be repeated continuously to realign the camera relative to the scan axis (via the scan actuator) in a timed arrangement, as described above. The angular position of the camera around the scan pan axis can be sent to the pan actuator, with a gain that can depend on the current position of the camera relative to the tilt pan axis.

Referring now to FIG. 5B, a process 505 may include stabilizing the image created by the camera in accordance with one embodiment of the invention. A process part 503a may include receiving information about the inertial movement (eg, angular velocity) of the camera relative to the first axis of the image. This information can be received from the gyros, as described above. In a process part 504a, the scan actuator may be activated to control inertial motion. Consequently, the image transmitted by the camera can be stabilized with respect to the first image axis. A process part 503b may include receiving information about the inertial movement (e.g., angular velocity) of the camera relative to the second image axis, and a process part 504b may include activating the tilt actuator to correct for the inertial movement with respect to the second axis of the image. Consequently, the image transmitted by the camera can be stabilized on two perpendicular axes. One aspect of an embodiment of the process 505 shown in Figure 5B is that the image can be stabilized in two directions, either simultaneously or sequentially, without cross-coupling between instructions relating to movement with respect to the first axis of the image, and instructions relating to the second. movement of the image axis.

Referring now to FIG. 5C, a process 509 in accordance with another embodiment of the invention may include rotating camera 111 180 ° to reorient the camera image, for example, as the aircraft flies over its target. Process part 510 may include receiving information regarding the angular position of the camera relative to the tilt axis. Process part 511 may include determining whether the position

ES 2 393 322 T3 angular relative to the tilt axis is approximately at the nadir of the aircraft. If not, the process can return to process part 510. If positive, process part 512 can include activation of the displacement actuator to rotate the camera 180 ° about the axis of displacement rotation.

In one embodiment, aspects of the procedures described above with reference to Figures 5A-5C may be combined. For example, a process may include checking the angular position of the camera relative to the axis of scan rotation while simultaneously monitoring the position of the camera relative to the axis of tilt rotation. The shift actuator can be simultaneously activated to both zero the camera position relative to the scan rotation axis and to reverse the camera relative to the shift rotation axis to keep the camera image in a vertical position.

Figure 6 is a partially schematic isometric illustration of a portion of the aircraft 100 described above with reference to Figure 1, having a tip 605 configured in accordance with another embodiment of the invention. In one aspect of this embodiment, the aircraft tip 605 may include a conical section 606 having a forward-facing concave end 607. The concave end 607 may receive a surveillance dome 640 that has the general shape of a part of a sphere. The surveillance dome 640 may be operatively coupled to the carriage 121 of the gimbal apparatus 120 (or directly to the displacement actuator 123 shown in FIG. 2A), located within the surveillance dome 640. Consequently, the surveillance dome 640 can rotate together with the carriage 121 about the axis of displacement rotation 124, as indicated by the arrow P.

In one aspect of an embodiment shown in Figure 6, the surveillance dome 640 may include a strip-shaped window 641 aligned with the aperture 113 of the chamber 111. The window 641 may be transparent to radiation to which it is sensitive. camera 111, while the rest of surveillance dome 640 can be translucent and / or opaque to this radiation. For example, if camera 111 is sensitive to infrared radiation, window 641 may be transparent to infrared radiation. The shape of the window 641 can be configured to accommodate the movement of the line of sight L of the camera 111 as the camera 111 is tilted about the tilt rotation axis 128, as indicated by the arrow T.

A feature of one embodiment of the arrangement described above with reference to FIG. 6 is that the surveillance dome 640 can be configured to rotate about the rotational axis of displacement 124. An advantage of this feature is that the surveillance dome 640 only requires rotation about an axis, and consequently can have a relatively simple actuation system that "overlaps the existing actuation arrangement for the axis of travel 124. A further advantage of this feature is that the axis of travel 124 around which the guard dome 640 rotates need only provide a relatively slow rotation, as previously described with reference to Figures 2A-4C. Accordingly, the displacement actuator 123 (FIG. 2A) need not be significantly larger in size (and therefore weight) to accommodate the movement of the surveillance dome 640.

Another feature of an embodiment of the arrangement described above with reference to Figure 6 is that the surveillance dome 640 may include a window 641 that occupies less than the entire surface of the surveillance dome 640. In one embodiment, the window 641 may include a physical strip-shaped slot in surveillance dome 640. This embodiment may be suitable for an aircraft 100 (FIG. 1) that can overcome the substantial increase in drag resulting from such a configuration. In other embodiments, window 641 may include a solid material other than the material that forms the remainder of surveillance dome 640. An advantage of this arrangement is that the amount of transparent material (which can be expensive) required for the dome can be reduced. surveillance 640 compared to other provisions. An additional advantage is that the material that forms window 641 can be difficult to form into complex configurations. By forming the window from a single flat piece of strip-shaped material, the window 641 can be bent or curved in a single direction (eg, around the axis of tilt rotation 128) rather than curving in a compound manner. In any of these embodiments, window 641 can be formed from a single glass or multiple glasses.

From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for illustrative purposes, but that various modifications can be made.