Abstract:
An aerial videocamera system for installation on an airplane comprises a videocamera/recorder which has an internal stabilization system, a camera mounting enclosure that provides a weather-proof enclosure with vibration isolation for the videocamera, and a pan/tilt head that bolts to a spar attachment plate and provides variable control to the camera in both the pan and tilt axis. The spar attachment plate is secured to the airplane and provides an access point for cabling carrying power, position control signals, and camera video and control to connect the externally mounted systems to components housed in the cabin. In the cabin, a pan/tilt controller processes input control signals from a joystick mounted on a control wand and outputs control and power signals to control the position of the videocamera. The control wand precisely positions the remote camera and controls the camera functions. A power package draws DC power from the airplane battery and converts it to AC power for the active components.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Applicant claims priority under 35 U.S.C. Section 119(e) to U.S. Provisional Application Serial No. 60/137,686 filed Jun. 4, 1999, entitled: “High Performance Aerial Videocamera SYSTEM”. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT N/A 
     BACKGROUND OF THE INVENTION 
     Aerial Photography has application both in art and in business. All high performance aerial videocamera systems require effective vibration compensation of high frequency, airplane and wind vibration components for smooth, jitter-free operation. The current state of the art for effective compensation is only achieved using some form of gyro-stabilized platform, usually for the camera mount. While gyro-stabilization is effective, this method of compensation is complex and expensive, with complete systems often costing more than the airplane itself. 
     BRIEF SUMMARY OF THE INVENTION 
     A modular and portable high performance aerial videocamera system is provided in accordance with the invention to be quickly attached to the underside of an airplane such as a Cessna 150 or 172. This videocamera system achieves a level of performance comparable to a gyro-stabilized system at a much lower cost. 
     The modular system includes a videocamera/recorder which has an internal stabilization system, a camera mounting enclosure that provides a weather-proof enclosure with vibration isolation for the videocamera, and a pan/tilt head that bolts to a spar attachment plate and provides variable control to the camera in both the pan and tilt axis. The spar attachment plate is secured to the airplane and provides an access point for cabling carrying power, position control signals, and camera video and control to connect the externally mounted systems to components housed in the cabin. In the cabin, a pan/tilt controller processes input control signals from a joystick mounted on a control wand and outputs control and power signals to control the position of the videocamera. The control wand precisely positions the remote camera and controls the camera functions. A power package draws DC power from the airplane battery and converts it to AC power for the active components. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The invention will be understood from the following detailed description in conjunction with the drawings, of which: 
     FIG. 1 a  is a side view of and airplane with wing-mounted aerial camera subsystem in place; 
     FIG. 1 b  is a front view of the airplane with wing-mounted aerial camera subsystem in place; 
     FIG. 2 a  is a front view of the wing-mounted subsystem; 
     FIG. 2 b  is a side view of the wing-mounted subsystem; 
     FIG. 2 c  is a back view of the wing-mounted subsystem; 
     FIG. 3 is a side view of the inboard system mounted in the airplane cabin; 
     FIG. 4 is a front view of an airplane instrument panel; 
     FIG. 5 is a schematic diagram of the interconnected components of the system; 
     FIG. 6 a  is a front view of the control wand; 
     FIG. 6 b  is a side view of the control wand; 
     FIGS. 7 a,    7   b  and  7   c  are the top, side and bottom views respectively of one implementation of a power pack of the inboard subsystem; 
     FIG. 8 is a pictorial view of a foam sleeve and camera enclosure for a video camera; 
     FIG. 9 is a pictorial view of a foam sleeve fitted in a camera enclosure for a video camera; 
     FIGS. 10 a  and  10   b  are the side and rear view of a video camera cradled by the foam sleeve in the camera enclosure; 
     FIG. 11 is a two dimensional schematic model of the suspended camera. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Aerial videocameras and the use of video photography have been limited by the prior art that requires gyroscopically stabilized cameras to produce video recordings that adequately filter out the vibration of the airplane and the environmental conditions around the airplane. These prior art systems are very costly and usually are integrally mounted with the airplane. Therefore, any aerial photography assignment requires that a specially configured airplane travel to the location with a crew. 
     In contrast to the prior art, the present invention is a modular high performance aerial videocamera system that can be installed in any small airplane, especially with a high wing configuration. The system is low cost compared to prior art systems because it utilizes high performance commercial components where possible, operates from the power available through the power outlet on the aircraft instrument panel and stabilizes the videocamera using passive cushioning to dynamically isolate the videocamera from the airplane. This dynamic isolation effectively augments the active, electrical motion compensation provided by the video camera itself. 
     FIG. 1 a  illustrates a side view of an airplane  10 , in this case a Cessna 150. The airplane incorporates a high wing  12 , which provides space under the wing with an unobstructed view, while an operator in the cockpit  22  can see the underside of the wing  12 . In this embodiment, the wing is supported by a strut  14  that braces the outer region of the wing against the body  24  of the airplane. Video pod  19  is suspended from the wing  12 /strut  14  junction. Although the system is illustrated using the Cessna 150, it can be adapted to any airplane designed to perform within the system&#39;s maximum speed of 100 knots. Mounting arrangements in other aircraft (or other parts of this type of airplane) are possible provided there is sufficient clearance. It is not a requirement that the pilot be able to see the video pod  19 . FIG. 1 b  is a front view of the area highlighted by the box  24  of FIG. 1 a.  This figure illustrates the main cockpit  22 , wing  12  and strut  14 . Video pod  19  is suspended from the wing at the juncture of the wing  12  and strut  14 . The video pod includes a mounting assembly  18 , supporting a pan/tilt assembly  15 , that moves a video camera  16  environmentally protected by a mounting enclosure  17 . The video pod active components are connected to an onboard electronics package, mounted in the cockpit  22 , via cables  20 . The pilot or another operator in the cockpit  22  controls the operation of the video pod  19 . 
     Details of the Cessna 150 type of mounting of the camera are shown in FIG. 2, where FIG. 2 a  is the front view of the video pod assembly  19 . A tie down ring  52  is already present near the junction of the strut  14  and the wing  12  in many of these airplanes. Strut  14  provides support for the sparred attachment assembly  18  that is composed of the clamping mechanism  30 , the spar  32  and the mounting plate  34 . The pan/tilt motor head  15  is attached to the mounting plate  34 . The mounting for the camera assembly  13  is connected to the pointing attachment  38  of the pan/tilt motor head  15 . 
     All parts of the mounting assembly  19  are made of stainless steel. The clamping mechanism  30  and mounting plate  34  are welded to the stainless steel spar  32 . The clamping mechanism  30  clamps around the strut  14 , and may use the tie down ring  52  as an additional clamp and positive connection to the strut. The clamping mechanism provides a quickly secured assembly that can be easily removed, but is also sturdy enough to be permanently mounted to the airplane. The tie down ring may optionally be used as a lead for cabling  44  between the onboard electronics and the camera  16  and pan/tilt head electronics  36 . The mounting plate  34  is connected to the end of the spar  32  away from the mounting clamp. The entire sparred attachment assembly is a rigid, high tensile strength assembly that resists deflection by the wind forces striking it. The sparred attachment assembly does not damp airplane vibrations but transmits any wing/strut vibrations caused by the airplane engine to the mounting plate  34 . 
     The pan/tilt assembly  15  bolts directly to the mounting plate  34  and is composed of a pan/tilt motor head  36  and a pointing mount  38 . The pan/tilt motor head  36  is a commercial unit that in a preferred embodiment covers up to 360 degrees in the pan axis and 180 degrees in the tilt axis. The pan/tilt head supports a camera assembly weighing up to 20 Kg. The preferred pan/tilt head is able to move the maximum load against the force generated by airspeeds of up to 100 knots at speeds of 0 to 10° per sec in each and/or both axes. The pointing mount  38  is the portion of the pan/tilt assembly  15  that is moved and provides support for the camera assembly  13 . The pan/tilt motor head  36  receives control signals from the onboard control pack via the cables  44  and moves pointing mount  38  in response to commands transmitted over the cables. 
     Pointing mount  38  receives the clamping collar  40  of the camera assembly  13 . The clamping collar  40  surrounds and is securely attached to the camera enclosure  42 . Clamping collar  40  is secured to the pointing mount  38  by bolts that are welded to the clamping collar  40 . The camera enclosure  42  incorporates a clear window  50  through which the camera  16  can capture images. The camera enclosure  42  can be any weatherproof enclosure made to hold the chosen videocamera  16  and be adapted to the clamping collar  40 . In one embodiment, the camera enclosure  42  is made of Lexan™. The camera enclosure  42  is adapted to accept power, control and video signals connections for the videocamera  16 . 
     Side view FIG. 2 b  and back view FIG. 2 c  illustrate that the cables  44  coming from the onboard control pack are composed of two distinct cables  46  and  48 . The pan/tilt cable set  46  plugs into the pan/tilt motor assembly  36  while the video cables  48  plug into the videocamera  16  through the camera enclosure  42 . The entire pan/tilt assembly  15  has no damping characteristics so any vibration transmitted through the mounting plate  34  is transmitted to the camera enclosure  42  via the pointing mount  38 . 
     FIG. 3 is a side view of the airplane cockpit  22  illustrating the placement and interconnection of the onboard control pack  62  relative to the cockpit components. The onboard control pack  62  encloses all of the electronics needed for the high performance aerial camera system, draws power from the airplane through the instrument panel  60  and is mounted internal to the cabin. On the instrument panel  60 , a DC outlet  62  makes airplane power available. A power cable  64  takes the DC power from the outlet  62  to the onboard control pack  66  where it is converted to AC voltage for use by the other electronics. While Airplane DC voltages of 12 VDC and 24 VDC are currently known, other DC voltages can be accommodated by changing the conversion range of the power inverter incorporated in the onboard control pack  62 . In the Cessna 150, Cables  44  exit the onboard control pack  66  and are dressed around the edge of the cockpit  22  and exit through an access port  68  to travel through the wing  12  to the strut mount location. Similar routings may be configured for alternate mounting locations. A signal cable  67  remains in the cockpit  22  and connects the onboard control pack  66  to the control wand  80  that is placed to be controlled by a person sitting in one of the front seats. The onboard control pack  66  is configured so that it may be secured to a rear location by tie-down straps  69  or other similar mechanism. FIG. 4 illustrates the airplane instrumentation panel  60  with the 12-volt connector  62  and a power cable going toward the onboard control pack  66 . 
     FIG. 5 illustrates the interconnection of the components within the system. Cable  64  brings DC power from the instrument panel  60  to a power inverter  70  mounted in the onboard control pack  66 . The power inverter  70  converts the DC power into 115 Volt AC and supplies that AC power to an AC power strip  72  also contained in the onboard control pack  66 . The power adapter for the video camera  78 , for a viewfinder display  76  and for the pan/tilt controller  74  all plug into the power strip  72 . The onboard control pack  66  is accommodates mounting the pan/tilt controller  74  in addition to the power-related components. 
     The control wand  80 , physically illustrated in FIGS. 6 a  and  6   b,  incorporates a joystick  84 , a camera view screen  82 , and start/stop and zoom control  86  for the videocamera  16 . The control wand is stabilized by an attachment means such as a Velcro™ strap around the leg or a foot to be placed beneath the operator&#39;s leg. The joystick  84  generates very smooth pan/tilt rate control signals that are sent via the signal cable  67  to the pan/tilt controller  74 . The joystick  84  preferably will return to the neutral position when not actively deflected. The direction of the camera motion will reflect the direction indicated by the joystick  84  while the rate of motion will be proportional to the extent of displacement from neutral. The camera view screen  82 , preferably a LCD view screen, is fed directly from the video signal from the videocamera  16 . The start/stop and zoom control  86  signals meet the videocamera specifications, using the LANC control signal protocol, for remote signals and cause the videocamera to begin recording, stop recording and adjust the focal length. 
     In a preferred embodiment, the pan/tilt controller  74  and joystick  84  combination are critical to providing acceptable video quality when the operator is adjusting the camera position. When the pan/tilt controller  74  provides true proportional rate movement, based on the extent of displacement of the joystick  84 , the operator has minimal problems operating the videocamera in a jitter-free and jerk-free manner. The pan/tilt controller and assembly preferred is a commercially available product that allows true proportional rate movement. Alternate pan/tilt controllers and assembly can be used provided the range of motion and discernable motion of the camera produce an acceptable recording. 
     The signals between the camera assembly  13  and the onboard control pack  62  are dressed from the access port  68  for the pod assembly  19 , around the interior edges of the cockpit  22 , to the region near the onboard control pack  66 . The power connections and pan/tilt motor control signals terminate at connectors on the onboard control pack  66  to facilitate the modular and easy installation of the system. The video control signals break out of the full length spiral sheath that has held all the cables together to this point and terminate at a connector in the vicinity of the control wand  80 . The cable that traverses the airplane  10  conforms to Mil. Spec. standards and is encased in a full length durable, heat-resistant polymer spiral sheath. 
     When operating the control wand  80 , an operator views what the camera is seeing on the LCD viewscreen  82  and changes where the camera is pointing by sending controls to the pan/tilt motor  36  using the joy stick  84 . Cables to the pan/tilt head motor control exit from the proportional rate controller  74  via cables  46 . The operator starts and stops recording using the start/stop switch  86  and adjusts the focal length using the zoom control switch  86 . The camera control switches are mounted on the stock  98  of the control wand  80 . Signals between the control wand  80  and the video subsystem are carried on cable  48 . 
     FIGS. 6 a  and  6   b  further illustrate the control wand  80 . A side view, FIG. 6 a,  shows the LCD display enclosure  92  and the electronic and signal connections to the LCD display  90 . Joy stick  84  is positioned directly beneath the LCD display  82  and provided with a connector  94  to facilitate modularity while enabling connection to the pan/tilt controller  74 . Video camera start/stop and zoom control  86  similarly has a connector  96  on its controller cables to provide for easy installation. 
     In FIGS. 7 a,    7   b  and  7   c  one configuration of the packing of components in the onboard control pack  66  is illustrated. Looking at the bottom view, the pan/tilt controller  74  is against the bottom with sufficient space next to it to allow the control wand  80  to be placed in the space  104 . Atop the controller  74  is the power equipment including the power inverter  100 , the power strip  72  and room for the power adapters  102  for all three of the pan/tilt motor assembly  74 , the videocamera  16  and the LCD display  82 . The components are most conveniently mounted in an enclosure  103  with a handle  105  to facilitate connection, installation and transport of the system. 
     The camera enclosure system  42 , as shown in FIG. 8, is an industry available component typically consisting of two pieces, a camera mounting piece  112  and an end securing piece  114 . The camera enclosure system  42  keeps the environmental elements away from the camera  16 . In addition to these two pieces, the camera enclosure system  42  includes a foam sleeve  110  to dampen the vibrations of the airplane so that the vibrations will not be evident on the video. In FIG. 9 the foam  110  is shown placed inside the camera mounting piece  112 . Note that in this embodiment there is a thicker side  120  of the foam  110  to accommodate the orientation of the camera while the remainder of the camera is surrounded by uniform thickness  122 . Alternate configurations of foam  110  can accommodate the physical parameters of other enclosures. The foam  110  must at all times be thick enough to prevent contact between the camera  16  and the camera enclosure  42  even under maximum compression from camera weight and the vibration of the airplane. 
     FIGS. 10 a  and  10   b  show the configuration of the camera enclosure  42  as utilized with camera  16  installed. The camera  16  is placed with its lens  130  adjacent to the window  50  in the camera enclosure  42 . Foam  120  and  122  suspends the camera in the enclosure with no contact between the actual enclosure mechanics and the camera. The foam sleeve  110  presents a snug fit for the camera when installed in the camera enclosure  42 . The foam sleeve is configured with a lip near the window  50  so that it prevents contact between the window  50  and the lens  130 . 
     The camera selected for the application can be selected from commercially available videocameras. Presently, digital videocameras are preferred because they incorporate more functional motion compensation systems and offer a digital zoom feature that has utility. In the preferred embodiment, the camera is a commercially available digital videocamera supporting the LANC remote control protocol, remote video monitoring, superior electrical motion compensation and a shape conducive to easy insertion and removal. Optical characteristics such as zoom range, light sensitivity, and recording media can be selected to accommodate the task objective. 
     The vibration compensation system for the high performance videocamera system utilizes two main components—the entire mounting configuration including the foam sleeve and the motion compensation capability built into the camera. The camera mounting configuration is rigidly constructed so that any airplane vibration is transmitted to the camera enclosure  42  and any additional vibration induced in the mounting configuration by interaction with high frequency turbulence is minimized. Since the airplane vibrations exceed the limits of the videocamera motion compensation system, the foam sleeve  110  is designed to absorb most of the vibration so that the vibration the videocamera  16  experiences is within the specifications of the videocamera motion compensation system. 
     The foam used to create the foam sleeve  110  is precisely chosen to dampen the high frequency component of any vibration reaching the camera enclosure  42  to a value below the compensation level. The vibration reaching the camera enclosure  42  is the sum of the vibrations from the airplane motor and high frequency turbulence affecting the airplane. For the purpose of selecting the foam, high frequency is defined as any source at greater than approximately 25 Hz. The foam characteristics are determined by modeling the action of the suspended camera mathematically. 
     FIG. 11 illustrates a linear dynamic model for the camera system in its foam sleeve, perturbed by a sinusoidal forcing function Asin(wt). Such a model can readily be extended to cover the three-dimensional situation. The camera mass M is balanced in the four directions by forces that are represented by a spring K and a damper B. In particular, K is the spring constant of the foam whereas B represents the viscous damping co-efficient of the foam. In steady state, the system will oscillate at the frequency w. The amplitude of the oscillation will be determined by A, w, k 1  and B 1 , where the relationship among this parameters cane be found by solving differential equation 1. 
     
       
           F   ext   =m{umlaut over (x)}=A sin( wt )−2 k   1   x− 2 B   1   {dot over (x)}   (EQ. 1) 
       
     
     where 
     w=airframe vibration frequency 
     A=amplitude of vibration 
     x=displacement from center equilibrium of mass m. 
     Based on this model, the properties, k and B, needed to stabilize the camera can be calculated. 
     As detailed above, the foam is selected to dampen vibrations above approximately 25 Hz because the videocamera system alone does not provide sufficient compensation. The motion compensation system built into high performance video cameras is used to eliminate the remaining vibrations above approx. 25 Hz in the system. This motion compensation system typically is set up to cut off all frequencies above a threshold and only allow the frequencies below that threshold to affect the video. In particular, the cut off frequency is chosen to allow panning of the landscape or tilting of the camera to get a different perspective while removing the jitter of, for instance, a shaky arm, or in this case a vibrating airplane. However, the motion compensation in the videocamera can only compensate for a certain amount of high frequency vibration and camera alone in the airplane environment would exceed that amount. Suspending the camera in foam selected for the appropriate damping characteristics is vital to allowing the camera&#39;s motion compensating system to work. 
     The 25 Hz cutoff frequency is an optimum in the range of 23-28 Hz that will provide adequate performance. High quality digital videocameras generally incorporate vibration compensation with a cutoff frequency, but the cutoff frequency is generally not specified. Therefore, the videocameras used in the invention are selected to meet this criterion. 
     Having described preferred embodiments of the invention it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts may be used. Accordingly, it is submitted that the invention should not be limited by the described embodiments but rather should encompass the spirit and full scope of the appended claims.