Photography – Aerial camera – Support or holder
Reexamination Certificate
1999-06-11
2001-07-17
Gray, David M. (Department: 2851)
Photography
Aerial camera
Support or holder
C396S419000, C396S428000, C248S550000
Reexamination Certificate
active
06263160
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to stabilized platform systems for isolating a payload from angular motions of a supporting structure.
BACKGROUND OF THE INVENTION
As imaging devices such as motion picture and video cameras are more frequently being mounted on unstable structures to achieve a desired point of view, image stabilizing devices are becoming more necessary. With the long focal length video lenses in use today, even a tripod on a concrete stadium floor can impart enough undesirable motion to spoil the shot. Scaffolds, cranes and moving vehicles all impart significant levels of motion which can limit the use of long focal length imaging devices. This problem can be overcome by using a stabilized platform system such as described in U.S. Pat. No. 3,638,502 (Leavitt et al) issued Feb. 1, 1972 and U.S. Pat. No. 4,989,466 (Goodman) issued Feb. 5, 1991. However, the platform systems described in these patents have many disadvantages, for example complexity, size and weight.
U.S. Pat. No. 5,897,223 (Tritchew et al) issued Apr. 27, 1999 (the contents of which are hereby incorporated herein by reference) describes an improved stabilized platform system for isolating a payload from angular motion and translational vibration of a supporting structure. The platform system has an inner gimbal for carrying the payload, a sprung shell containing and carrying the inner gimbal in a manner permitting the inner gimbal a limited amount of angular movement relative thereto amount pitch, roll and yaw axes, an outer gimbal containing the sprung shell and inner gimbal, and a passive vibration isolator connected between the sprung shell and the outer gimbal and having two symmetrical arrays of dampened coil springs located on opposite sides of the sprung shell. The angular position measured between the inner and outer gimbals is used as an error signal to drive the outer gimbal to follow the inner gimbal, thereby allowing large ranges of steering motion.
While the platform system described by Tritchew et al has many advantages and improvements over the previously mentioned systems of Leavitt et al and Goodman, the universal joint and supporting structure still occupies the central area of the inner gimbal. For use with single sensors such as large video and film cameras, the Tritchew et al platform system would require the use of large counterweights to balance the sensor about the central pivot. The size and weight of such a platform system, relative to such a sensor, would therefore be significant.
Conventional gimballing methods for freeing up the central area require the use of large gimbal rings around the payload connected together through bearing axes orthogonally. Such large rings can limit system performance due to structural resonances and inertial effects. Such gimbal rings also add weight and restrict payload volume.
Another problem with such prior art platform systems is that it is difficult to adapt them to standard film or video camera packages currently used by the motion picture and broadcast industry. Instead, specific custom camera packages are normally engineered to operate with known Gimbal systems. While a certain degree of interchangeability can be designed into these systems, the camera packages still have custom designed features or characteristics.
Many non-stabilized camera steering heads have been developed to utilize standard camera packages. Such steering heads tend to have large open structures which are prone to low frequency structural resonances which contribute to undesirable motion of the camera. Some attempts have been made to stabilize such steering heads. However, torquing through these large open structures severely limits the attainable system bandwidth.
It is therefore an object of the present invention to provide a stabilized platform system which at least substantially overcomes the problems described above.
SUMMARY OF THE INVENTION
According to the present invention, a stabilized platform system for isolating a payload from angular motions of a supporting structure has a base assembly securable to the supporting structure, and a payload stabilizing assembly carried by the base assembly and mounted for angular movement relative thereto about two or more separate axes. At least one of the axes is non-orthogonal with respect to another of the axes and is mounted for limited angular movement relative to the base assembly. The axes have extensions which meet at a common point, which is preferably within the periphery of the payload.
The payload stabilizing assembly may include a first angular adjustment arm with one end pivotally mounted on the base assembly for limited angular movement relative thereto about a first of said three axes, a second angular adjustment arm having one end pivotally mounted on another end of the first angular adjustment arm for limited angular movement relative thereto about a second of said three axes, and a payload carrier pivotally mounted on another arm of the second angular adjustment arm for limited angular movement relative thereto about the third of said three axes.
The platform system may also include an array of at least three magnetic torque motors, each motor having an electrically energizable coil portion carried by the base assembly and a magnetic structure portion carried by the payload stabilizing assembly, each magnetic torque motor having an active axis along which a payload stabilizing assembly positioning force can be applied but having freedom of movement about the other two axes, and a controller for controlling energization of the motors to apply controlled moments to the payload stabilizing assembly about any axis of rotation.
The stabilized platform system may have at least one capacitive angle sensor having a first portion carried by the base assembly and the second portion carried by the payload stabilizing assembly with an air gap between said first and second portions, said capacitive angle sensor being responsive to relative movement between the first and second portions to provide a signal indicative of the angular position of the payload stabilizing assembly relative to the base assembly.
The payload stabilizing assembly may carry at least one angular rate sensor operable to provide the signal of angular movement of the payload stabilizing assembly about a pre-determined axis.
The angular rate sensor may be a fibre optic gyro.
REFERENCES:
patent: 4197548 (1980-04-01), Smith et al.
patent: 4919382 (1990-04-01), Forman
patent: 5638303 (1997-06-01), Edberg et al.
Delbridge Robert F.
Gray David M.
Wescam Inc.
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