Abstract:
The present invention relates to an apparatus that controllably allows the relative rotation between structures, such as a gimbal and a structure to which it is mounted. According to one aspect, the apparatus includes a twist capsule assembly with internal stop mechanisms that controllably prevents the amount of clockwise and counterclockwise rotation with respect to a rotation axis. According to another aspect of the invention, by limiting the amount of relative rotation, other means of communicating power and signals between the structures can be used, thus avoiding or reducing the limitations imposed by conventional slip ring assemblies. According to yet another aspect, the invention includes techniques and structures for allowing conventionally shielded cables and wires to be used in place of slip rings, while allowing for rotation between structures, thus even further improving the communication of power and signals between structures.

Description:
FIELD OF THE INVENTION 
     The present invention relates to assemblies for supporting relative rotation between two structures such as gimbals attached to vehicles, and more particularly to assemblies for providing a limited amount of relative rotation, while supporting the provision of power and signals between components in the separate structures. 
     BACKGROUND OF THE INVENTION 
     As is known, some types of gimbals can include sensors for collecting image and other data, as well as gyroscopes for maintaining an orientation of such sensors. Such gimbals are sometimes mounted to structures such as vehicles (e.g. airplanes, motor vehicles and marine vessels) in a rotatable fashion such that they can rotate about a gimbal axis (e.g. azimuth). In such circumstances, a rotatable gimbal support or mount structure can include slip ring assemblies for providing power and signal information to and from inertial components such as sensors and motors within the gimbal (e.g. through brush-ring coupling). Typically, these slip ring assemblies also provide for unlimited rotation of the gimbal (e.g. 360 degrees) about the gimbal axis with respect to the fixed structure or vehicle. 
     In many applications, such as where sensor information is in the form of high frequency and/or digital signals, the noise produced by conventional slip ring assemblies becomes unacceptable. However, given the need to allow for relative rotation between a gimbal and a structure to which it is mounted, one cannot simply replace the power and signaling provided through such slip ring assemblies with conventional shielded wires and cabling, especially within similar volumes used by slip ring assemblies. Accordingly, there remains a need in the art for a solution that allows for relative rotation between structures such as gimbals while also allowing for the communication of power and signals to the gimbal. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus that controllably allows the relative rotation between structures, such as a gimbal and a structure to which it is mounted. According to one aspect, the apparatus includes a twist capsule assembly with internal stop mechanisms that controllably prevents the amount of clockwise and counterclockwise rotation with respect to a rotation axis. According to another aspect of the invention, by limiting the amount of relative rotation, other means of communicating power and signals between the structures can be used, thus avoiding or reducing the limitations imposed by conventional slip ring assemblies. According to yet another aspect, the invention includes techniques and structures for allowing conventionally shielded cables and wires to be used in place of slip rings, while allowing for rotation between structures, thus even further improving the communication of power and signals between structures. According to yet another aspect, the invention includes techniques for minimizing stress on conventionally shielded cables and wires used in place of slip rings, while allowing for rotation between structures, thus enhancing the reliable lifetime of the system. 
     In furtherance of these and other objects, an apparatus according to the invention, coupled between first and second structures, comprises a first portion that rotates in accordance with the first structure, a second portion that rotates in accordance with the second structure, and a rotation prevention mechanism coupled to the first and second portions to control relative rotation between the first and second structures within a predetermined range. In additional furtherance of these and other objects, in certain embodiments the rotation prevention mechanism comprises a pin formed on the first portion that travels in a radial groove formed in the second portion during relative rotation between the first and second structures, and a stop formed in the radial groove that limits travel of the pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, wherein: 
         FIG. 1  illustrates an example implementation of an apparatus for providing relative rotation between two structures according to the principles of the invention; 
         FIG. 2  illustrates an example of a twist capsule assembly that can be included in the apparatus of  FIG. 1 ; 
         FIG. 3  illustrates further aspects of communicating power and/or signals between structures using an apparatus such as that illustrated in  FIG. 1 ; 
         FIGS. 4A and 4B  illustrate one example of how wires can be bundled within an enclosure such as that shown in  FIG. 3 ; 
         FIG. 5  illustrates an alternative embodiment of an enclosure to that shown in  FIG. 3 ; and 
         FIGS. 6A and 6B  illustrate apparatuses and techniques for determining and monitoring an absolute relative rotation between two structures in accordance with aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration. 
     Generally, the present invention recognizes that complete freedom of relative rotation between two structures is not necessary in all applications. However, at least one complete rotation is generally needed. By limiting the amount of relative rotation, while allowing for at least approximately one complete rotation, more conventional means of providing power and signals, such as through shielded wires, can be used, thus eliminating or reducing the noise problem afflicting conventional slip ring assemblies. 
       FIG. 1  illustrates one example implementation of the present invention. 
     As shown in  FIG. 1 , a twist capsule  100  according to the invention is disposed on a shaft  130  between a mount structure  110  and a rotatable payload  120 . Shaft  130  is fixedly attached to payload  120  and payload  120  rotates about an axis (e.g. azimuth) through the center of shaft  130  under control of one or more motors (not shown). In one preferred example, payload  120  is a gimbal that may further provide additional mechanisms for rotating or displacing payload components (not shown) along other axes (e.g. elevation, etc.). In this example, mount structure  110  can be part of a top hat upper mount for a gimbal. 
     It should be apparent that other support structures can be used in addition to those shown in  FIG. 1 , such as pivots and harnesses, and so twist capsule  100  need not by itself attach or support payload  120  from structure  110 . However, details and illustrations of such other support structures will be omitted so as not to obscure the invention. 
     In the example of  FIG. 1 , twist capsule  100  includes three rings  102 ,  104  and  106 . Top ring  102  is fixedly attached to the mount structure  110 , and bottom ring  106  is fixedly attached to shaft  130 . Accordingly, the relative rotation between mount structure  110  and payload  120  is determined by the amount of rotation allowed between ring  102  and  106 , as will be explained in more detail below. Center ring  104  provides a predetermined additional amount of rotation between rings  102  and  106  in a manner that will also be described in more detail below. It should be noted that center ring  104  can be omitted, or additional center rings  104  may be provided in other alternative embodiments which will become readily apparent to those skilled in the art after being taught by this example. 
       FIG. 2  illustrates example implementations of rings  102 ,  104  and  106  in more detail. As shown in  FIG. 2 , rings  104  and  106  include radial grooves  202  and  204 , respectively, which accept pins  206  and  208  or rings  102  and  204 , respectively. Rings  104  and  106  further include stops  210  and  212 , respectively. When assembled together (e.g., they are held in place through other support structures not shown), pins  206  and  208  travel in grooves  202  and  204  respectively as payload  120  rotates with respect to mount structure  110  until both simultaneously encounter the clockwise limit edge ( 210 - a  and  212 - a ) or counterclockwise limit edge ( 210 - b  and  212 - b ) of stops  210  and  212  respectively. At that point, further rotation in the same direction is prevented. In this example, ring  104  is a “floater” ring that can continue to rotate in tandem with either ring  102  or  106  depending on which of pins  206  or  208  encounters stops  210  or  212  first, and rotation between structure  110  and payload  120  in the same direction continues. In this manner, ring  104  makes possible an additional range of possible rotation, including ranges in excess of one full rotation between structure  110  and payload  120 . 
     As should be apparent from the foregoing descriptions, the size of the pins and stops, as well as the presence and/or number of “floater” rings in assembly  100 , thus define the amount of maximum rotation permitted between mount structure  110  and payload  120 . In one example, rings  102 ,  104  and  106  are comprised of top, center and bottom hardened steel and are about 1.125 inches in diameter, and shaft  130  is hardened steel, with a 0.375 in. diameter hexagonal cross-section. In this example implementation, the total range of possible rotation is approximately ±315 degrees, or approximately 630 degrees total rotation (i.e. about 1-¾ full rotations) between stops. 
     It should be noted that, in certain embodiments such as the one described above, the shaft  130  can function as a torsion bar to soften the impact in case the payload  120  is inadvertently driven into the hard stops built into the twist cap  100  or the system, either under software or manual control or force. Another benefit of the small shaft diameter is that it helps control the wire harness during wind and unwind sequences as will become more apparent from the descriptions below. In general, the small shaft means more rotation can be allowed with less space. 
     In certain embodiments, the amount of rotation is monitored and controlled in real-time, for example to provide soft stops. In one example implementation, the rotation is driven by a motor, which is controlled by software. Such motors and control software for rotatable payloads such as gimbals are well-known in the art, and so details thereof will be omitted here for sake of clarity. However, an aspect of the invention is that such control software can utilize positional feedback from sensors to monitor rotation in real time and prevent occurrences of the motor driving the payload into potentially damaging hard stops as fixed by twist capsule  100 . For example, the software can allow quick rotation (e.g. 100 degrees/s) in areas outside of a few degrees of the hard stops, while forcing slow rotation (e.g. 10 degrees/s) within these extreme rotation edges. 
     One example embodiment of providing such feedback and control is illustrated further in connection with  FIGS. 6A and 6B . As shown in  FIG. 6A , in a preferred embodiment of a payload whose rotation is driven by a motor tinder the control of software, there is a Hall sensor  602  mounted in the payload  120  and positioned to detect certain degrees of rotation for providing software control. For example, the Hall sensor  602  is configured to rotate past three magnets  604  mounted in the structure  110  adjacent to the payload  120 . In one example where there is a range of rotation of approximately ±180 degrees or more, the magnets are positioned to coincide with relative rotations of slightly less than 180 degrees in a first, e.g. counter-clockwise direction (i.e. magnet  604 - ccw ), “zero” degrees or “home” position (i.e. magnet  604 - z ), and slightly less than 180 degrees in a second, e.g. clockwise direction (i.e. magnet  604 - cw ). 
     In this example where relative rotation between structure  110  and payload  120  is controlled by a motor, the motor preferably further provides encoder feedback which determines the degrees of movement away from the zero point. The control code reads the encoder feedback and fixes a “soft stop” point relative to the zero point where it reduces the velocity of the motor to not drive it at full speed into the hard stop. For example, the encoder provides multiple pulses (e.g.  4096 ) through the course of a single rotation. The encoder also incorporates an “index” position that occurs only once on each rotation, and is aligned to occur within the zero position Hall region and not within the two end stop Hall regions. 
     In order for the control code to know the absolute degree of rotation at all times during operation, an initialization sequence is performed to fix the zero point and determine the hard stops. For example, when the system powers up or when a built-in test sequence is triggered, the degree of relative rotation between payload  120  and structure  110  is unknown. The control code causes the motor to slowly drive the system in one direction until a hard stop is reached, which is detected, for example, by determining that no encoder pulses are received for a predetermined time while actively commanding the motor to turn. Once this stall condition is detected, the motor is commanded to rotate in the opposite direction while monitoring for the simultaneous occurrence of the Hall sense signal and an encoder index assertion. The control system then uses this “point” as an absolute zero reference, and uses all encoder pulses as indicating rotation relative to point. For example, the control code can calculate the range of possible rotation by counting the number of encoder pulses from the home sensor to the previously detected hard stop, and all future angular position determination can be referenced from this point. The software then causes the motor to drive the payload in the same direction of rotation quickly again to the other Hall sense signal (i.e. when the Hall sensor detects one of magnets  604 - cw  or  604 - ccw , depending on the direction), then slows the motor again to find the end of movement as performed above. By counting the number of encoder pulses that occur in this opposite direction, the entire range of rotation from the home sensor to either hard stop can now be determined and used for future rotation control. The “soft” stops can then be programmed as a certain percentage of the full possible rotation in each direction from the home position. 
       FIG. 3  illustrates further aspects of the invention. Generally, instead of or in addition to using conventional slip ring mechanisms for conveying power and signals, this embodiment of the invention allows for conventional wiring and cabling to be used. 
     In a first embodiment shown in  FIG. 3 , an enclosure  300  is fixedly attached to either the mount structure  110  or the rotatable payload  120 . In a manner that will be described in more detail below, signal wires and/or power cabling  330  extend from conduits  302  to feedthroughs  304 , and from thence may be further routed to components in payload  120 . Although only one wire/bundle/cable  330  is shown for clarity, it should be apparent that there may be two or more, including additional wires or cables between the shown or additional conduits  302  and feedthroughs  304 . In one example implementation, there are two signal and two power bundles, for a total of four, although some designs have coax cables also routed through. 
     In one example, one or more conduits  302  include jacks such as MIL-DTL-38999 connectors from Amphenol. In this example, wires and/or cables that are routed in enclosure  300  from conduits  302  to feedthroughs  304  are soldered or otherwise electrically connected to the connectors at conduits  302  so that coupling of signal and power to/from payload  120  can be achieved by plugging mating connectors into conduits  302  from the opposite side. It should be further apparent that other conventional wire or cabling mechanisms (not shown) can be used, such as tie-downs and strain reliefs, either adjacent to conduits  302  or in other positions inside enclosure  300 . 
     Returning to  FIG. 3 , enclosure  300  includes a tray portion  310  and a shroud portion  320 , both with substantially cylindrical shapes centered around shaft  130 , wherein the tray portion has larger outer radius from shaft  130  than the shroud portion  320 . In one example, tray portion  310  has a diameter of about 6.25 in., whereas shroud portion  320  has a diameter of about 2 in. In a preferred implementation that will be described in more detail below, during rotation between structure  110  and payload  120 , cables and wires are allowed to wind and unwind within tray portion  310 , whereas they maintain a relatively constant amount of winding within shroud portion  320 . 
     Wire/bundle/cable  330  can include various types and numbers of wires including shielded wires and/or bundles of same, coaxial cables, fiber optic cables, etc. However,  FIGS. 4A and 4B  illustrate one preferred embodiment of how wires can be bundled to even further accommodate rotation of the twist capsule according to the invention. 
     In this example, wires  330  comprise a bundle of seven 16-gauge silicone-jacketed wires. Silicone-jacketed wires are preferred over Teflon because these provide additional protection against friction. According to an aspect of the invention, these wires can be bundled in a fashion from standard looming practices found in wire and rope manufacturing. As shown in  FIGS. 4A and 4B , a single wire  402  has six wires  404  surrounding it in a bundle of seven total wires and then loomed together with a clockwise twist. In this example, the seven wires are soldered to a seven-conductor MIL-DTL-38999 jack at conduit  302  and then loomed together as shown in  FIGS. 4A and 4B  and routed through enclosure  300  toward feedthrough  304 . By having the bundles in the loomed fashion described, the cables naturally want to follow the clockwise twist. 
     Returning to the example shown in  FIG. 3 , bundle  330  is wound approximately one full 360 degree turn within shroud portion  320  of enclosure  300 . Meanwhile, the total length of the bundle  330  within enclosure  300  preferably allows for at least two full rotations of payload  120  with respect to mount structure  110 , to which conduit  302  is affixed. In one extreme position of rotation (e.g. at a full stop in one direction), the bundle  330  is not wound around shaft  130  at all within tray portion  310 . At the other extreme position (e.g. at a full stop in the opposite direction of rotation), bundle  330  is wound around shaft  130  in tray portion  310  in an amount corresponding to the full range of relative rotation provided between structure  110  and payload  120 . The limit of rotation provided by the hard stops in twist capsule  100  thus ensures that the winding and unwinding of the cable bundles will not exceed the fixed length. 
     The way this system can ensure reliability and long operating life will be appreciated from the above descriptions and foregoing remarks. Without simultaneously considering and addressing the amount of rotation, and the winding and bundling of wires during rotation, many problems can occur. For example, with too much rotation permitted or without bundling correctly, in one direction the wires limit the travel by wrapping too tightly around the shaft  130 . Additionally or alternatively, in the other, unwinding, direction the limits are when the wire is no longer wrapped around the shaft  130  and begin to “double back,” that is, wind in the opposite direction. Both conditions can stress the wires and in general are likely to cause an early failure of the system. By bundling and wrapping the wires with a view toward the rotation limits as described above, the objectives of high reliability long, reliable operating life can be achieved. This is especially critical in high vibration and shock environments such as those that occur during flight. 
     In certain embodiments, shaft  130  can further include a Teflon protector below twist capsule  100  to further protect against wear due to friction from the winding and unwinding of wires  330  around shaft  130  during rotation. 
     Moreover, those skilled in the art will recognize the number and arrangement of windings that are possible or desirable within enclosure  300  based on the number and size of wires, the size of the enclosure, the possible range of rotation and other factors, so details thereof will be omitted here for clarity of the invention. 
     Many alternative embodiments of enclosure  300  are possible, for example depending on the numbers and types of wires that need to be provided to payload  120 . One alternative embodiment is shown in  FIG. 5 . 
     As shown in  FIG. 5 , enclosure  500  further includes an inner tray  504  to separate two or more separate types of cables and/or wires. For example, cables/wires  530  can be routed from conduits  502  to feedthroughs  506 , with appropriate allowances for winding and unwinding, whereas other cables and/or wires (not shown) extending from conduits  302  may be confined within tray  504  before extending to shroud portion  320 . 
     In one example, cables/wires  530  can be a bundle of fiber optic cables, whereas wires housed in tray  504  (not shown) may be signal/power wires such as wires  330  that are bundled as described above and exit through holes  304 . In this example implementation, the twist capsule limits rotation to less than approximately ±80 degrees, or less than one full rotation. 
     In one example, the fiber optic cables in tray  504  are wound approximately five times around shaft  130  at one stop, and about four times at the other stop, and wind/unwind within tray portion  310  of enclosure  300  with a clock spring-like contraction and expansion. More particularly, bundle  530  will not travel down shroud portion  320 . Rather, bundle  530  will clock spring wrap in the tray area formed between  310  and  504 , and exit enclosure  500  through hole  506 . It does not exit through feedthroughs  304 , but is secured to the outside of  320 . Therefore, all the clock-spring motion of bundle  530  occurs in the area between  310  and  504 . Bundle  330  simultaneously coils up in tray  504  and then wraps around shaft  130 , through shroud portion  320  and exits at  304  as described above. Therefore, bundles  530  and  330  rotate at the same time with respect to each other and the fixed surfaces  110  and  120 , but do not come in contact with each other during the rotation. 
     Although the present invention has been particularly described with reference to the preferred embodiments thereof, it should be readily apparent to those of ordinary skill in the art that changes and modifications in the form and details may be made without departing from the spirit and scope of the invention. It is intended that the appended claims encompass such changes and modifications.