1. Field of the Invention
The present invention, in general, relates to gimbals and, more particularly, to permanent magnet wide-gap motors that are used to move the gimbal payload about its inner axes.
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. All manner of sensors may be used, for example, television cameras as well as other sensors that use any preferred technology. 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. Course 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 shell along with numerous other component parts that are used to orient the gimbal ball as required. The gimbal shell is often in the general shape of a ball and is therefore sometimes also referred to as a gimbal ball or simply a ball. In general, for any given size of the gimbal shell, the space (i.e., volume) that is available for the sensors is limited and a more usable volume is desirable. Accordingly, it is desirable to locate the motors that move the payload within the ball (i.e., the inner axes) as far away from the center payload area as possible. Another way of stating this objective is to locate the motors in a space that is not well used by sensors.
Gimbals often 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 rotational movements (inner axis motion) that affect 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. Courser adjustments are accomplished by moving the gimbal ball itself typically about the two outer axes, elevation and azimuth.
The cardan assembly includes a cardan shaft that spans the inside diameter of the ball. The center of the cardan shaft is used, in certain designs, to define the internal elevation axis.
Prior art designs place the cardan shaft so that it also aligns with the external axis. In particular, the internal elevation axis is set to align with the external elevation axis.
The instant invention is applicable for use with prior art designs and also with a newer offset cardan type of gimbal, as is described in an application filed for an Offset Cardan in the section, “Related Applications”.
The sensor(s) is used to look at any given object(s) of interest, which is sometimes called a target(s). For example, the gimbal may be disposed in an airplane and it may be used for mapping terrain or for some other purpose. There may be a reference location that the gimbal must periodically slew to, perhaps to periodically coincide the area that is being mapped with a reference location or perhaps to periodically look for changes that might be occurring at the reference location. Then the gimbal must slew back to its original orientation to continue the mapping process. Ideally, this slewing action is preferably accomplished as quickly as possible.
This type of slewing typically occurs primarily along the azimuth axis. Smaller angular changes typically occur on the pitch and roll axes. Another common name applied to motion about the azimuth axis is “yaw”. This is when an airplane, for example, moves left or right as controlled by its rudder. Such motion in an airplane is referred to as yaw and it occurs about the azimuth axis.
Because the payload has mass, the ability to slew quickly, especially about the azimuth axis, is related to the torque that is applied. A greater torque for any given configuration results in faster slew times, which is desirable.
There is another problem that limits the slew rate along the inner azimuth axis for a gimbal. The outer azimuth axis serves to keep a viewing window disposed in front of the sensor (i.e., camera) within its range of travel, which includes a greater range of travel than the inner axis. However, the inner axis must also slew as fast as the outer axis in order to prevent the limited rotation inner axis from exceeding its travel, that is to keep the sensor (camera) pointing at its intended target.
If the inner axis cannot accelerate as fast as the outer axis, the rate of slew for the inner axis will slow down and therefore limit the slew rate for the outer axis. This makes it especially important to be able to accelerate the inner axes as fast as possible.
Therefore it is desirable to speed up the inner rate of slew, primarily along the azimuth axis because that axis is where the greatest angular degree of motion and also where periodic changes in orientation often occur.
Another problem relates to the shaking of the payload during use of the gimbal. Isolators (i.e., any means to isolate the payload from the gimbal ball and the vehicle upon which the gimbal is itself mounted) are provided in virtually all high performance gimbals to isolate vibration and other changes in position of the vehicle, for example the airplane, apart from that of the payload (i.e., the sensors). The object is to minimize the sensor's vibration as it is pointed at the intended object of interest while the airplane vibrates, for example.
The isolators allow the payload to translate (i.e., move) within a given range of motion inside of the ball. Wide-gap motors provide a relatively wide space intermediate the magnets thereof with uniform magnetic flux. This allows space for the payload to move without impacting the magnet or any other part of the motor as the isolators translate.
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.
It is useful to note that the cardan assembly may be used to support multiple types of sensors simultaneously as the payload. 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 of the payload that is supported by the cardan assembly.
The payload may also be active instead of passive. A passive payload merely observes the object of interest whereas an active payload is adapted to affect it. The payload may be used to support an active component that can, for example, illuminate the object. For example, a gimbal can contain a source of illumination, such as a spotlight or a laser, and be mounted on, for example, a helicopter. Accordingly, as the helicopter hovers and fluctuates in its position relative to the object, the gimbal can be used to compensate for any movement by the helicopter in order to hold the source of illumination constantly upon the object.
If the source of illumination is a spotlight, then a larger physical payload capacity allows for a larger and brighter spotlight to be used. A larger payload typically increases the mass that is being carried which tends to slow down the rate of slewing. It is desirable to optimally locate as high a torque motor as possible which, all other factors being equal, allows for a greater payload mass and therefore increased utility for the gimbal.
Accordingly, there exists today a need for a cross plane wide-gap motor system for a gimbal that improves the aforementioned prior art limitations. In particular there is a need to step with high torque and allow good stability with the same motor arrangement simultaneously.
Clearly, such an apparatus would be useful and desirable.
2. Description of Prior Art
Gimbals are, in general, known. While the structural arrangements of the known types of devices, at first appearance, may have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.