Offset cardan gimbal

Details Offset cardan gimbal Offset cardan gimbal

2001-04-18

2002-09-24

Ramirez, Ramon O. (Department: 3632)

Supports

Stand

To hold a particular article

Reexamination Certificate

active

06454229

ABSTRACT:

RELATED APPLICATION
This application is related to another utility patent application by the same applicants, being filed concurrently, entitled “Cardan Support”.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention, in general relates to gimbals and, more particularly, to gimbals that provide accurate alignment of sensors and instrumentation that they support and which include a cardan that is offset.
Gimbals are commonly used to hold sensors stable when mounted on a moving vehicle, be it a land based vehicle, a sea (i.e., a water based) vehicle such as a boat or ship, or an air based vehicle such as an airplane.
The ability to hold a sensor stable while the vehicle moves is useful for a great variety of purposes. These purposes include obtaining information useful for navigation. Another purpose relates in general to an ability to align and then to hold the sensors where desired. Whatever information is being provided by the sensors is more reliable if the sensors themselves are held steady.
In general, gimbals have a plurality of outer axes and a plurality of inner axes. Coarse adjustments are commonly accomplished by movements made along the outer axes. Finer adjustments are commonly made with the inner axes.
There are a number of discreet functions a gimbal must achieve. It must both properly orient, maintain position, and support the size and weight of the sensors. This can vary from application to application.
The sensors are placed inside of a gimbal ball along with numerous other component parts that are used to orient the gimbal ball as required. In general, for any given size of the gimbal ball, the space (i.e., volume) that is available for the sensors is limited and a greater volume is desirable.
Another problem with prior art designs is supporting the weight of the sensors, also referred to as the “payload”. It is desirable to increase the effective payload of a gimbal.
Gimbals include a cardan assembly that is disposed within a ball. The cardan assembly supports the weight of the payload that is carried by the gimbal as well as allowing small angular rotation in the positioning of the payload within the ball.
These changes in position are accomplished by rotating the payload (within the gimbal ball) about three axes (typical), namely elevation, roll, and azimuth. Coarser adjustments are accomplished by moving the gimbal ball itself typically in two axes, elevation and azimuth.
The cardan assembly includes a cardan shaft that traverses the inside diameter of the ball. The center of the cardan shaft is used, in certain designs, to define the internal elevation axis. Obviously, any type of a sensor that is contained within the ball cannot look through the cardan shaft.
Prior art designs place the cardan shaft so that it aligns with the external axis. In particular, the internal elevation axis is set to align with the external elevation axis. Prior art has taught away from the cardan shaft having any offset in this regard and instead certain of the prior art gimbal designs have labored to design gimbals where the internal and external axes are as nearly coincident as possible.
Any type of an offset between the internal and external elevation axes of the cardan assembly was believed to introduce instability into the design. An offset payload (i.e., mass) swinging inside the ball was also believed to severely limit the range of motion that is possible and was, accordingly, avoided in prior art gimbal design.
Increasing the size of the payload means more than merely increasing the weight carrying ability. The weight of the payload that is being suspended off of the cardan assembly is less of an issue now than it was in the past due, in part, to other innovations by the applicants, which are the subject of a related patent application being concurrently filed.
A current pressing problem of payload size relates to the simple fact that sensors cannot “see” through the cardan assembly. These sensors may be optical or other types of instruments. As is well known in the optical and other sensing arts, the size of the viewing lens largely determines its light gathering ability. In particular, a larger viewing area allows more light to enter. In the camera arts this is often referred to as the aperture. A larger aperture is desired. Often that part of an optical system that is the final interface to the outside is called an “objective” lens. A larger diameter objective lens means a smaller aperture number (in the camera arts) which means more light gathering ability.
Optical sensors of the type used in gimbals, like other optical types of instruments, are typically either reflective or refractive (or a combination of both). Reflective devices rely upon mirrors to direct and focus the collected image whereas refractive devices rely upon lenses to direct and focus the image.
In either case, an “optical path” is required and this optical path requires distance to accomplish. This distance must be accomplished entirely within the ball. The cardan assembly interferes with not only the size of the aperture by limiting its maximum size, but it also limits the space that is available for the optical path.
The efficacy of any type of a sensor depends upon providing both a maximum aperture size (for any given ball diameter size) as well as a maximum amount of clear, open space for the design of the optical path.
Offsetting the cardan assembly (with respect to the elevation axis) allows for a larger aperture and it provides more space (i.e., volume) within the ball for the optical path. It also allows for physically larger payloads to be carried.
It is also possible to offset the cardan assembly (that portion that controls the roll and azimuth axes) off to the side. This, while also contrary to prior gimbal design, provides for an even larger open area for maximizing both aperture size and for optical path considerations for any given ball diameter size. In those instances where such an offset is provided, counterweights are employed to balance the payload while other limits are provided to ensure that the payload does not swing excessively and “bump” into the ball.
It is important to understand that the internal axes provide finer corrections than do the external axes and accordingly, a smaller range of motion is therefore acceptable for the payload in the gimbal ball. Larger corrections are made by moving the entire gimbal ball relative to the vehicle upon which the gimbal itself is mounted.
Therefore, it is desirable to be able to increase the aperture size of a sensor for any given size of a gimbal ball. Certain physical parameters inherent in a gimbal (such as the need to maintain close alignment between and outer elevation axis and an inner elevation axis) have, in the past, served to limit the maximum size for the aperture possible. Ideally, for any given size of a gimbal as large an aperture as can be had is preferred as is providing the maximum area possible for the design of the optical path.
It is also noted that other types of sensors which may employ direct viewing of the subject may be supported by the cardan assembly as the payload. These direct viewing types of sensors include any and all known modalities of data collection (and are adapted for use with emergent technologies). Examples of different modalities that may incorporated direct viewing types of sensors include infrared, ultraviolet, and radio-frequency. Direct viewing types of sensor also benefit from a larger viewing area (i.e., aperture size) as well as from providing a maximum area to accommodate their physical size.
It is also important to note that the cardan assembly may be used to support multiple types of sensors simultaneously. For example, a zoom television camera can be used for general spotting purposes and to locate an object of interest as well as for general pointing (i.e., aiming) of the gimbal. Upon locating the object of interest, a larger focal length camera can be used to more carefully study it. Accordingly, both types of cameras can be simultaneously mounted as part

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