Automatic structurally induced line of sight jitter compensation for electro-optical/infrared turret system

A light sensor system including a reference light source that moves in unison with a primary mirror and/or an inertial measurement device, and/or the reference light source is directed toward an obscured region of the light sensor system. The reference light source may allow for improved jitter compensation based on feedback of the reference light. The feedback may be representative of the elastic deformation of the optics and telescope optical axis. The improved jitter compensation may allow for the light sensor system (e.g., the housing and/or mirrors) to be built with less stiff materials, which can reduce the cost of manufacturing the present light sensor system compared to previously known optical sensor systems. In cases of high vibration levels which would otherwise degrade the resulting image quality after material stiffness property selections have been exhausted, the light sensor system may provide jitter compensation to improve video or still image quality.

FIELD OF INVENTION

The present invention relates generally to jitter compensation, and more particularly to jitter compensation for electro-optical/infrared turret systems for aircraft.

BACKGROUND

Some aircraft have a gimbaled optical sensor system. The optical sensor system may be used to detect target objects that are located great distances from the aircraft. For example, the optical sensor systems detect target objects that are below the aircraft while the aircraft is in flight.

The optical sensor systems often include an optical sensor and a telescope optical assembly to magnify the light received by the optical sensor to allow the optical sensor to capture images of the target object at great distances. However, during flight of the aircraft the telescope optical assembly and the optical sensor are subjected to random vibration causing optical elements to move relative to one another, resulting in image jitter, which can reduce image quality of full motion video or still images.

Typically, very stiff materials (such as beryllium or silicon carbide) are utilized to build the telescope optical assemblies to increase image quality by limiting optics and telescope deformation which assists in mitigating the jitter. These materials tend to be expensive, which adds to the overall cost of the optical sensor system. Additionally under large enough vibration input levels material stiffness alone will not provide the required optical system stability and image quality will be impacted regardless of cost and complexity in telescope design.

SUMMARY OF INVENTION

The present invention provides a light sensor system including a reference light source that moves in unison with a primary mirror and/or an inertial measurement device, and/or the reference light source is directed toward an obscured region of the light sensor system. The reference light source may allow for improved jitter compensation based on feedback of the reference light. The feedback may be representative of the elastic deformation of the optics and telescope optical axis. The improved jitter compensation may allow for the light sensor system (e.g., the housing and/or mirrors) to be built with less stiff materials, which can reduce the cost of manufacturing the present light sensor system compared to previously known optical sensor systems. In cases of high vibration levels which would otherwise degrade the resulting image quality after material stiffness property selections have been exhausted, the light sensor system may provide jitter compensation to improve video or still image quality.

Directing the reference light source toward the obscured region allows the light sensor system to avoid or reduce any negative impact the reference light source or its associated components may have on the quality of the primary light detected. For example, the reference light source and/or a retroreflector may be arranged in the obscured region so that a minimal additional portion of the primary light, if any, is blocked from reaching the primary light sensor, compared to previously known optical sensor systems.

The light sensor system may include a primary mirror that directs the reference light from the primary mirror along a path of the primary light through the light sensor system to the reference light sensor. The reference light sensor may be able to detect structural movement of the primary mirror and/or other light reflectors that reflect the primary light and the reference light. At least part of the light sensor system may be adjusted based on the reference light directed to the reference light sensor. The adjustment allows correction of components of the light sensor system to compensate for jitter and increase the quality of the primary light received by the primary light sensor.

The adjustable light component (e.g., an adjustable light reflector, such as a fast steering mirror, or an adjustable light refractor, such as a Risley prism assembly) that receives the primary light may be adjusted based on the feedback of the reference light. For example, the adjustable light reflector may be adjusted based on the position and/or movement of the reference light to account for jitter in the light system.

The inertial sensor and the reference light source may be fixed relative to one another to accurately determine the non-inertial motion of the reference light source caused by relative deflections between optical components and the primary mirror. For example, the inertial sensor and/or the reference light source may be fixed in the obscured region to the same inertial sensor mount.

The term “light” is used herein to refer to visible light and invisible light. For example, the term light may be used herein to refer to radio waves, infrared waves, ultraviolet waves, electromagnetic waves having wavelengths anywhere from 400 nanometers (nm) to 700 nm, and/or X-rays.

The term “jitter” is used herein to refer to undesirable motion of the optical axis of the imaging system that occurs during a single frame integration time, which results in blurring the image.

According to one aspect of the invention, a light sensor system includes a housing, a primary mirror with a reflective side facing in a first direction to receive a primary light along a central axis of the primary mirror from a target object, wherein the primary mirror is disposed within the housing, a plurality of light reflectors, at least one of the plurality of light reflectors receiving the primary light directly from the primary mirror, wherein each of the plurality of light reflectors is arranged in a path of the primary light such that each of the plurality of light reflectors receives and reflects the primary light, an inertial sensor mount that is fixed to the primary mirror, a reference light source having an output directed along the first direction, the reference light source attached to the inertial sensor mount and movable with the inertial sensor mount such that, when the inertial sensor mount moves, the output of the reference light source moves with the inertial sensor mount.

According to another aspect of the invention, a light sensor system includes a housing, a primary mirror with a reflective side facing in a first direction to receive a primary light along a central axis of the primary mirror from a target object, wherein the primary mirror is disposed within the housing, a plurality of light reflectors, at least one of the plurality of light reflectors receives the primary light directly from the primary mirror, and wherein each of the plurality of light reflectors is arranged in a path of the primary light such that each of the plurality of light reflectors receives and reflects the primary light, one or more light obstructions between the primary mirror and the target object, wherein the one or more light obstructions form an obscured region where the primary light from the target object would not pass through to reach the reflective side of the primary mirror, and a reference light source that is movable with the primary mirror, wherein an output of the reference light source is directed toward a portion of the obscured region such that when the output provides the reference light the reference light would pass through the portion of the obscured region.

The features of the different aspects may be independently combined with one another or utilized separately. Thus, a light sensor system according to the present invention may include all of, any one of, or any combination of the reference light source that moves with the primary mirror, and the output of the reference light source that is directed toward the portion of the obscured region.

DETAILED DESCRIPTION

The principles of this present application have particular application to reducing the effects of jitter for aircraft light sensor systems, for example electro-optical/infrared turret systems that have a Three Mirror Anastigmat (TMA) form telescope to magnify the image of a target object, and thus will be described below chiefly in this context. It will be appreciated that principles of this invention may be applicable to other light sensor systems where it is desirable to reduce the effects of jitter, such as other telescope forms.

Referring now to the drawings and initially toFIG. 1, an exemplary aircraft is designated generally by reference numeral20. The aircraft20can be provided with an exemplary light sensor system22. The light sensor system22may capture images of primary light received from a target object, such as an infrared heat signature of a vehicle thousands of feet below the aircraft20. In an embodiment, the aircraft is another type of vehicle, such as a ground operated vehicle.

The light sensor system22may include any or all of the components of the sensor system disclosed in U.S. Pat. No. 9,170,106 entitled SHOCK-RESISTANT DEVICE AND METHOD issued on Oct. 27, 2015, the entirety of which is hereby incorporated by reference.

FIG. 2illustrates a front view of the light sensor system22that may include a housing (e.g., a coarse pointing structure30), a primary mirror32(e.g., a parabolic primary mirror of a TMA telescope) disposed within the coarse pointing structure30, multiple light obstructions, and a reference light reflector (e.g., retroreflectors34-40that are shown in dashed lines hidden beyond the light obstructions). Referring briefly toFIG. 3, an optical bench33(shown schematically) may fixedly attach the primary mirror32and the light obstructions to an inner gimbal assembly35(shown schematically) that movably attaches the optical bench33to the coarse pointing structure30.

Referring again toFIG. 2, the light obstructions may form an obscured region42of the light sensor system22between the primary mirror32and the target object where the primary light from the target object is not able to pass through to reach a reflective side44of the primary mirror32. The light obstructions may be formed by a secondary mirror46(e.g., a hyperbolic secondary mirror of a TMA telescope) and/or multiple support arms48that extend radially outwardly from the secondary mirror46to attach the secondary mirror46to the inner gimbal assembly35(shown schematically inFIG. 3) through the optical bench33. For example, the secondary mirror46may form a centrally-obscured region50of the obscured region42and/or the support arms48may form an obscured-spider-support region52of the obscured region42. A portion of the retroreflectors34-40may be in the obscured-spider-support region52(shown best inFIG. 5).

The optical bench33, the inner gimbal assembly35, the coarse pointing structure30, and/or the support arms48may be made of a material with a stiffness of 10,000,000 pounds per square inch (psi), such as aluminum. Aluminum and other materials with a similar stiffness may be easier and less expensive to machine compared to high stiffness materials often utilized in previously known optical sensor systems. In an embodiment, the optical bench, the inner gimbal assembly, the coarse pointing structure, and/or the support arms may be made of a material with a stiffness of 10,000,000 psi or less. In another embodiment, the optical bench, the inner gimbal assembly, the coarse pointing structure, and/or the support arms may be made of a material with a stiffness of 10,000,000 psi or greater.

Turning toFIG. 3, the light sensor system22may include a gimbal system60and may include a plurality of light reflectors that receive the primary light (e.g., the secondary mirror46and/or primary light reflectors70-80), a reference light source82, an inertial sensor84(e.g., a pair of fiber optic gyroscopes) attached to the primary mirror32, a reference light sensor86(e.g., a duo lateral photodiode or quad detector), and a primary light sensor88that receives the primary light.

The reflective side44of the primary mirror32faces in a first direction D1to receive the primary light along a central axis A of the primary mirror32from the target object. The reference light source82may be axially offset from the reflective side44along the central axis A in a second direction D2that is opposite the first direction D1. For example, the reference light source82may have an output110that is directed toward the retroreflector36, and that is offset from the reflective side44in the second direction D2. Offsetting the reference light source82behind the primary mirror32may minimize if not eliminate any reduction of primary light that is received by the reflective side44, compared to another embodiment where reference light source82is arranged between the reflective side44and the target object.

The output110may be arranged in the obscured-spider-support region52. Arranging the output110in the obscured-spider-support region52allows the retroreflector36to be arranged entirely in the obscured-spider-support region52, as shown inFIG. 2. In an embodiment, the retroreflector is arranged at least partially in the obscured-spider-support region.

The retroreflector36may face in the second direction D2toward the reflective side44of the primary mirror32. The retroreflector36may include a reflective portion112, which may be arranged in the obscured-spider-support region52and oriented to receive the reference light from the output110of the reference light source82. The reflective portion112may be oriented to output the reference light toward the reflective side44of the primary mirror32prior to the reference light reaching any of the secondary mirror46and the primary light reflectors70-78. The reflective portion112may be configured to output the reference light parallel and laterally offset to the path of the input of the reference light. In an embodiment, the entire reflective portion is in the obscured region. In another embodiment, only a portion of the reflective portion is in the obscured region.

Arranging the reflective portion112in the obscured region42allows the retroreflector36to minimize if not eliminate the amount of primary light blocked by the retroreflector36compared to another embodiment where the reflective portion112is arranged partially or entirely outside of the obscured region42. For example, most of the retroreflector36is in the obscured region42(shown best inFIG. 5) so that at most only part of the retroreflector36blocks primary light from reaching the reflective side44. In an embodiment, the retroreflector is entirely within the obscured region. In another embodiment, the retroreflector is mostly if not entirely outside of the obscured region.

Still referring toFIG. 3, the light reflectors70-80that receive the primary light may be each arranged in a path of the primary light such that each of the light reflectors70-80receives and reflects the primary light. Each of the light reflectors70-80may be at least partially attached to the optical bench33so that each light reflector70-80at least partially moves with the optical bench33.

The secondary mirror46may be arranged to receive the primary light directly from the primary mirror32. For example, the primary light reflected by the reflective side44of the primary mirror32does not need to reflect off of another reflector before reaching the secondary mirror46.

The support arms48hold the secondary mirror46offset from the primary mirror32along the central axis A. For example, the support arms48are able to hold the secondary mirror46coaxially with the central axis A.

The primary light sensor88may be arranged to receive the primary light from the light reflectors70-80. The plurality of light reflectors70-80and the primary mirror32may be oriented such that the primary light is directed from the primary mirror32to the plurality of light reflectors70-80, and from the plurality of light reflectors70-80to the primary light sensor88. For example, a light control system114may receive the primary light and adjust the primary light to compensate for jitter before outputting the primary light to the primary light sensor88.

The light control system114may include an adjustable light component (e.g., the adjustable light reflector78), a beam splitter122, the reference light sensor86, a reference light filter124(e.g., a lens with a 405 or 1940 nanometer (nm) notch filter) and control circuitry126(e.g., a processor and/or memory with programmed instructions). The beam splitter122, the reference light sensor86, and the reference light filter124may be fixedly attached to the optical bench33. In an embodiment, the adjustable light component is an adjustable light refractor, such as a Risley prism assembly.

Still referring toFIG. 3, the control circuitry126is connected via information lines (e.g., electrical communication lines, shown as dashed lines) to the primary light reflector76, the adjustable light reflector78, the inertial sensor84, and to the reference light sensor86. The adjustable light reflector78is able to compensate for jitter based on gimbal compensation, acceleration and/or movement detected by the inertial sensor84, and/or detection of the reference light by the reference light sensor86(as shown best in the control system diagram ofFIG. 10).

For example, the control circuity126may instruct the adjustable light reflector78to compensate for jitter based on the detection of the reference light by the reference light sensor86. The reference light sensor86may output a digital signal based on the position or positions of the sensed reference lights, as explained further below with reference toFIG. 8. In an embodiment, the reference light sensor outputs an analog voltage based on the position or positions of the sensed reference lights.

The control circuitry126may adjust the optical power of the reference light emitted by the reference light source82based on the optical power of the reference light sensed by the reference light sensor86. Adjusting the optical power allows the control circuity126to maintain a constant optical power of the reference light reaching the reference light sensor86. Maintaining constant optical power allows consistent noise performance. In an embodiment, the control circuitry adjusts the optical power of each reference light together or individually.

The beam splitter122may be arranged after the light reflector80to separate the reference light and the primary light. The beam splitter may have a relatively high reflective property for the reference light frequency to reflect the reference light toward the reference light sensor86. The beam splitter122may have a relatively low reflective property for the primary light frequency to allow the primary light to pass through to reach the primary light sensor88. For example, the beam splitter122may reflect light in the ultraviolet range and allow light in the visible range to pass through.

The light sensor system22may further include focus lenses150(e.g., electro-optical focus lenses), a primary light reflector154, and/or a primary light reflector156. The light control system114may direct the primary light to the primary light sensor88via the focus lenses150, the primary light reflector154, and/or the primary light reflector156.

The primary light sensor88may be any one of or multiple of a short wavelength infrared sensor, a jitter camera, a color digital television sensor, a wave front error sensor, and/or a monochrome low noise visible to near infrared sensor. In an embodiment, the light sensor system includes a light switch to select between the primary light sensor and another light sensor. For example, the light switch may be the five-position switch disclosed in U.S. patent Ser. No. 15/009,292 entitled OPTICAL SWITCHING DEVICE filed on Jan. 28, 2017, the entirety of which is hereby incorporated by reference.

The gimbal system60may allow movement in multiple directions while allowing primary light in through a window162that blocks light with a wavelength that is detectable by the reference light sensor86(e.g., solar radiation), and allows the primary light to pass through. For example, the reference light sensor86may detect wavelengths anywhere from 10 nm to 405 nm and the window162may have a coating that blocks 99% of 405 nm or shorter wavelengths.

The gimbal system60may include an azimuth base164attached to a housing of the vehicle20(shown inFIG. 1), an azimuth yoke166, a coarse elevation gimbal168, and the inner gimbal assembly35(e.g., a fine elevation gimbal170and a cross elevation gimbal172), each of which are configured to coordinate pointing of the primary mirror32at the target object to be imaged.

Referring now toFIG. 4, the reference light source82may be attached to the primary mirror32such that, when the primary mirror32moves, the output110moves with the primary mirror32. For example, the reference light source82may be attached to an inertial sensor mount180that is fixed to the primary mirror32. The reference light source82may be movable with the inertial sensor mount180such that, when the inertial sensor mount180moves, the output110of the reference light source82moves with the inertial sensor mount180.

Attaching the output110to move with the primary mirror32allows the reference light to move when the primary mirror32and/or the inertial sensor84moves.

The inertial sensor84may be fixed to the inertial sensor mount180such that, when the output110of the reference light source82moves, the inertial sensor84would be moved with the output110. For example, when the reference light source82moves due to vibration of the primary mirror32the inertial sensor84moves with the output110.

The light sensor system22may include at least a second reference light source182with a corresponding output184. For example, when the outputs110and184of the reference light sources82and182move the inertial sensor84would be moved with the outputs110and184.

The output110of the reference light source82may be arranged opposite the output184of the reference light source182relative to the central axis A. For example, the respective output110or184of the reference light source82and the reference light source182may be diametrically opposite one another relative to the central axis A (i.e., spaced circumferentially apart 180° from one another relative to the central axis A).

The reference light sources82and182may be collimated light sources. The reference light sources82and182may include a collimator186, a prism assembly188, and a fold prism190that are mounted to the inertial sensor mount180. The collimator186may be attached to the inertial sensor mount180such that, when the primary mirror32moves, an output192of the collimator186moves with the primary mirror32.

Still referring toFIG. 4, a reference light generator194(e.g., a light emitting diode (LED) such as a violet LED) may have an output that is optically connected to the corresponding collimator186. For example, a fiber optic cable directs light generated by one of the reference light generators194to the corresponding collimator186. The collimator186is able to collimate the light generated by the corresponding reference light generator194into parallel or substantially parallel rays to form the reference light that is output by the output of the fold prism190. For example, the output of the fold prism190may be aligned with a through hole196(shown best inFIG. 5) formed in the inertial sensor mount180. The fold prism190may be aligned with the corresponding retroreflector34(shown best inFIG. 7).

The prism assembly188may be attached to the inertial sensor mount180such that, when the primary mirror32moves, the prism assembly188moves with the primary mirror32. The prism assembly188may include a pair of Risley prism pairs198and spur gears200that are coupled to each prism of the Risley prism pairs198to adjust each prism198. The spur gears200may be configured to adjust the alignment of the prisms198.

In an embodiment, the two reference light sources include a single laser diode and a 1:2 fiber splitter. In another embodiment, more than two reference light sources are utilized. Each reference light source may be collimated. For example, each reference light source may be identical to one another. Each corresponding output may be equally spaced from the central axis and/or arranged equally spaced circumferentially apart from one another.

The inertial sensor mount180may be fixed to the primary mirror32such that the inertial sensor mount180moves with the primary mirror32. The inertial sensor mount180may be made of a material with a stiffness of 10,000,000 psi, such as aluminum, to keep the inertial sensor mount180fixed to the primary mirror32. In an embodiment, inertial sensor mount may be made of a material with a stiffness of 10,000,000 psi or less. In another embodiment, inertial sensor mount may be made of a material with a stiffness of 10,000,000 psi or greater.

FIG. 5illustrates a cross-section of the light sensor system22. Each reference light source82and182may be arranged in the obscured region42. For example, the output184of the reference light source182may be directed toward a portion of the obscured region42such that, when the output184provides the reference light, the reference light would pass through the portion of the obscured region42. The output110and184of each reference light source82and182may be directed along the first direction D1toward the corresponding retroreflector34or36.

The output of the fold prism190may form the output184of the reference light source182. In an embodiment, the output of the reference light source may be formed by another component of the reference light source, such as a Risley prism or an output of the collimator. For example, at least one Risley prism pair may be attached to the inertial sensor mount and configured to form the output of the reference light source that outputs the reference light to the corresponding retroreflector. It should be appreciated that the output110of the reference light source82may be similarly formed.

Referring still toFIG. 5and later toFIG. 6, the reference light from each reference light source82and182may be directed to the light reflectors46and70along the path of the primary light (shown best inFIG. 3). For example, each reference light travels through an opening210of the primary mirror32and the hole196prior to reaching the corresponding retroreflector34or36, or any of the primary light reflectors46or70-80(shown inFIG. 3). The reference lights travel from the corresponding reference light source110or182through the obscured region42to the correspondence retroreflector34or36. Each retroreflector34or36redirects the corresponding reference light along the path of the primary light.

Referring now toFIG. 6, for example, the retroreflector34redirects the corresponding reference light toward the primary mirror32parallel to the incoming primary light (e.g., parallel to the central axis A). The reference light may be laterally offset from the incoming primary light.

The reference light may impinge the primary mirror32and the primary mirror32may reflect the reference light toward the secondary mirror46. For example, the reference light impinges an obscured portion212(shown best inFIG. 5) of the primary mirror32and is reflected to the secondary mirror46.

The reference light may continue to follow the path of the primary light. For example, the reference light may reflect off the secondary mirror46to the primary light reflector70, from the primary light reflector70to the primary light reflector72, from the primary light reflector72to the primary light reflector74, from the primary light reflector74to the primary light reflector76, and from the primary light reflector76and the remaining primary light reflectors78and80(shown inFIG. 3) to the reference light sensor86of the light control system114.

Referring again toFIG. 3, as discussed above, the reference light may be directed to from the light reflectors70-80to the reference light sensor86. The reference light may reflect off the primary light reflector76toward the primary light reflector78, from the primary light reflector78to the primary light reflector80, from the primary light reflector80to the beam splitter122, and from the beam splitter122to the reference light sensor86through the reference light filter124.

The reference light sensor86may detect the reference lights after the reference lights reflect off each light reflector70-80. The reference light sensor86may be able to detect displacement of the reference lights that is due to structural dynamics of the primary mirror32and any of the light reflectors46and/or70-80.

For example, the reference sensor86may detect the position, movement, and/or angle of the reference light (e.g., azimuth and elevation motion of the primary light sensor88). The position, movement, and/or angle of the reference light may be based the structural movement information of the primary mirror32and/or the light reflectors70-80. Accordingly, the primary light reflector78can compensate for jitter based on the detected reference light.

The adjustable light reflector78may be adjusted in accordance with the control system described below. For example, the adjustable light reflector78and/or another adjustable light reflector (e.g., primary light reflector80) are adjusted based on the reference light to compensate for jitter of the light sensor system22. The adjustable light reflector78may be adjustable based on the structural movement information of each reference light relative to the other. In an embodiment, one or more of the adjustable light reflectors is adjustable based on the structural movement information of a reference light independent of any other reference light.

The reference light source82may provide the reference light at a frequency that is offset from the electromagnetic frequency range of the corresponding primary light sensor88. For example, the primary light sensor88may be able to detect light within the infrared range and the reference light source82may provide the reference light within the ultraviolet light range such that the primary light sensor is unable to detect the reference light.

Referring now toFIGS. 7 and 8, the reference light filter124of the light sensor system22may include a light mask240before the reference light sensor86to any light that is not near the position of the reference light (e.g., to block solar radiation) from reaching the reference light sensor86. As shown inFIG. 8, when there is no jitter, each reference light may be directed to the same position on the reference light sensor86. When jitter is present, both reference lights may both be directed to a second position on the reference light sensor86. If the primary mirror32(shown inFIG. 3) is elastically deformed due to the jitter, the primary mirror32may cause the reference lights to be directed to different positions on the reference light sensor86.

In an embodiment, the position of each sensed reference light is output separately. The reference lights may be turned on and off in an alternating fashion (i.e., time modulated) so that the output digital signal is specific to the reference light that is on when the digital signal is output. Detecting the position of each reference light individually allows the reference light sensor to detect the elastic deformation of the primary mirror based on relative movement of each reference light output by the corresponding reference light source. For example, more than two reference lights may be time modulated so that only one reference light is on at any given time to allow the reference light sensor to detect the deformation of the primary mirror.

The light mask240may include a fused silica lens. The light mask240is able to reduce solar radiation before the reference light reaches the reference light sensor86.

Referring now toFIG. 9, the light mask240may include a masking portion246that blocks solar radiation and a reference light through path248that allows the reference lights to pass through to reach the reference light sensor86(shown inFIG. 8). The reference light through path248may be aligned with the reference lights to allow the reference lights to pass through the light mask240to the reference light sensor86(shown inFIG. 8). For example, the nominal position of each reference light is illustrated as a corresponding circle within the reference light through path248.

FIG. 10illustrates a control system diagram of the light sensor system22(shown inFIG. 3). The control circuitry126(shown inFIG. 3) and/or other circuitry (e.g., a processor and/or memory with programmed instructions) may be configured to perform any portion of or all of the summation, subtraction, or integration functions of the control system diagram. For example, the control circuitry126may receive sensor data from each sensor described above and perform the summation, subtraction, and integration functions of the control system diagram.

As illustrated inFIG. 10, a subtractor260may receive a reference light sensor command (Reference Sensorcmd) (e.g., integrated rate error motion) and a reference light sensor feedback (Reference Sensorfb) that is based on the position detected by the reference light sensor86(e.g., based on a motion of the reference light). The subtractor260may subtract the reference light sensor feedback from the reference light sensor command and the result may be input into a reference light sensor compensator262to account for jitter detected by the reference light sensor86.

A subtractor264may receive an image motion compensator angle command (e.g., an Adjustable Reflector Anglecmd) that is output from the reference light sensor compensator262, and may receive an angle feedback of the adjustable reflector78(e.g., an Adjustable Reflectorfb) based on an amount of motion of the adjustable light reflector78(shown inFIG. 3). The subtractor264may subtract the Adjustable Reflectorfbfrom the Adjustable Reflector Anglecmd. The result may be input into an image motion compensator (e.g., an adjustable reflector compensator266), the output of which may be provided to the adjustable light reflector78.

The adjustable light reflector78may cause an image motion compensator output motion (e.g., an angle change of the reference light caused by the adjustable reflector θAR). The angle change of the reference light caused by the adjustable reflector θARmay be summed by an adder269with a jitter motion θJITTERthat is based on disturbance introduced to the light sensor system22(shown inFIG. 3) (e.g., disturbance based on the structural dynamics of the light sensor system22and vibration of the aircraft20(shown inFIG. 1)). The resulting output is the motion of the reference light (e.g., an angle of the reference light θRLrelative to the position of the inner gimbal assembly35(shown inFIG. 3)).

The angle of the reference light θRLmay be summed by an adder271with an optical bench motion (e.g., a position θIGof the inner gimbal assembly35with respect to a forward direction of the aircraft20). A system operator may adjust the position θIGof the inner gimbal assembly35to adjust the orientation of the optical bench33so that primary mirror32(shown inFIG. 3) is directed at the target object. The resulting output may be a line of sight motion θLOS(e.g., residual error remaining after corrections have been made based on the Reference Sensorfband a rate feedback (Ratefb)).

The control system may further include a subtractor268that subtracts the Ratefbthat is based on the output of the inertial sensor84from a rate command (Ratecmd) that is based on a target position of the line of sight (e.g., the target object) of the light sensor system22. The resulting output may be integrated by an integrator270and the resulting integration may be the Reference Sensorcmdthat may be input into an inner gimbal compensator272. The output of the inner gimbal compensator272may be summed by an adder267with a disturbance torque TDist. The disturbance torque TDistmay be the resulting total force or torque exerted on the imaging components of the light sensor system22(shown inFIG. 3), including the total external forces acting on the imaging components through the inner gimbal assembly35(shown inFIG. 3). For example, forces mainly due to vibration of the aircraft20(shown inFIG. 1).

The disturbance torque TDistmay present errors in the position θIGof the inner gimbal assembly35that direct the optical bench33away from the target object. These position errors may be fed forward in the Reference Sensorcmdso that the adjustable reflector78adjusts to compensate for the position errors and jitter, as discussed above.

The output of the adder267may be provided to an inertial load integrator274. The output of the inertial load integrator274may be an optical bench rate of motion (e.g., an inner gimbal rate of motion {dot over (θ)}IG), which may be integrated by an integrator276to provide the position of the inner gimbal assembly θIGthat is added to the position of the reference light θRL.

Turning now toFIG. 11, an exemplary embodiment of the light sensor system is shown at322. The light sensor system322is substantially the same as the above-referenced light sensor system22, and consequently the same reference numerals are used to denote structures corresponding to similar structures in the light sensor systems. In addition, the foregoing descriptions of the light sensor system22is equally applicable to the light sensor system322except as noted below. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the light sensor systems may be substituted for one another or used in conjunction with one another where applicable.

The light sensor system322allows the reference light to move with the primary light past the primary light reflectors154and156. In this embodiment, the beam splitter122does not reflect the reference light before the reference light reaches the primary light reflector154. The beam splitter122may be positioned to receive the primary light and the reference light from the primary light reflector156so that the beam splitter122may split the reference light and the primary light. For example, beam splitter122reflects the reference light to the reference light sensor86, and the primary light passes through the beam splitter122to reach the primary light sensor88.

The reference light sensor86may detect the structural dynamics of a focus lens150and the primary light reflectors154and156in addition to the structural dynamics of preceding optical components, as discussed above with reference toFIG. 3. For example, the reference light filter124and the reference light sensor86may be positioned to receive the reference light after the reference light moves past the primary light reflectors154and156.

Turning now toFIG. 12, an exemplary embodiment of the light sensor system is shown at422. The light sensor system422is substantially the same as the above-referenced light sensor systems22and322, and consequently the same reference numerals are used to denote structures corresponding to similar structures in the light sensor systems. In addition, the foregoing descriptions of the light sensor systems22and322are equally applicable to the light sensor system422except as noted below. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the light sensor systems may be substituted for one another or used in conjunction with one another where applicable.

The light sensor system422allows the reference light to move with the primary light past the first focus lens150. The light sensor system422includes a beam splitter424before the primary light reflector156.

In this embodiment, the beam splitter424does not reflect the reference light before the first focus lens150after the reference light is reflected by the primary light reflector80. The beam splitter424may be positioned to receive the primary light and the reference light from the primary light reflector80so that the beam splitter424may split the reference light and the primary light. For example, the reference light passes through the beam splitter424to reach the reference light sensor86, and the beam splitter424reflects the primary light to the primary light sensor88via the primary light reflector156.

The reference light sensor86may detect the structural dynamics of the first focus lens150. For example, the reference light filter124and the reference light sensor86may be positioned to receive the reference light after the reference light moves past the first focus lens150and the beam splitter424.