Abstract:
A vibration isolator which may be constructed in the form of a cube for use in retrofitting a device which is subjected to unwanted vibration present in an attached member which utilizes an active vibration isolator and a passive isolator in series between the members and which may include an overload protection device in the form of a deformable member in parallel with the isolators.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to vibration isolators and more particularly to small easily installed retrofittable modular vibration isolators for active and passive use in a variety of applications such as may be found in satellite payloads for laser cross-link systems, precision pointing systems, submarine decking, launch isolation for precision equipment, E-beam lithography, micro lithography and other optical payloads. 
     2. Description of the Prior Art 
     Many passive and active vibration isolation devices exist in the art. Active systems using magneto restrictive or piezoelectric actuators work well for low frequency response, precision pointing and active force cancellation, but are usually more complicated than passive systems. Passive systems work well for solving many high frequency problems but have some material limits. Examples of passive systems include a bellows with fluid in it such as shown in L. P. Davis U.S. Pat. No. 4,760,996 entitled “Damper and Isolation,” issued on Aug. 2, 1988, in L. P. Davis U.S. Pat. No. 5,332,070 entitled “Three Parameter Viscous Damper and Isolator,” issued on Jul. 26, 1994, and in L. P. Davis U.S. Pat. No. 5,219,051 entitled “Folded Viscous Damper,” issued Jun. 15, 1993 (sometimes referred to herein as a “Folded D Strut”) all of which are assigned to the assignee of the present invention. These devices perform vibration isolation remarkably well in a variety of applications including those in space. Other isolators such as large rubber materials or shape memory alloys, SMAs, such as nickel titanium based materials, are sometimes used in situations where large shock vibrations are expected such as during satellite launchings. Most of the prior art vibration isolators are designed to be part of the members to be isolated or are installed at least at the time of assembly of the two members. As such, they are specifically designed for the particular parameters to be encountered. The size of the isolator and ease of mounting it are seldom problems, so great latitude has been permitted in the designs. 
     When dealing with some situations, however, vibration isolation is an afterthought since the desirability of using vibration isolators is not discovered until after the equipment is constructed and assembled and undesirable vibrations are discovered in use. Likewise, particularly in space applications, the space allotted for vibration isolation is extremely limited, and the retrofitting of vibration isolators into an already existing assembly becomes quite difficult. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention combines several types of vibration isolators into a single unitary structure to handle a wide variety of conditions and is of small overall dimensions for use in crowded environments and is further capable of being easily mounted in a large number of already existing environments. More particularly, a small, preferably cubic, structure of as little as one inch in each dimension is employed constructed of 1) a passive isolator, preferably a Folded D Strut such as shown in the above mentioned U.S. Pat. No. 5,219,051 of Lawrence P. Davis, 2) an active isolator preferably one employing a piezoelectric actuator with closed loop control, and, if needed, 3) a shock vibration isolator preferably one using a deformable material, or SMA. One end of the active system is connected to the member which may vibrate, and one end of the passive system is connected to the payload to be isolated. The other ends of the active and passive systems are connected to an interstage mass. One corner of the cube contains a threaded mounting hole for attachment to a first of the two members to be isolated and the opposite corner of the cube is mounted on the second of the two members to be isolated. The third shock-type vibration isolator, if used, may be a removable bumper, or preferably, a “shape memory alloy” material, SMA, may also be included in parallel with the other two isolators in the event that a shock, such as by satellite launching, is to be encountered. The advantages of such a system include being sized for retrofitting light to heavy payloads and the ability to be placed directly in the load path of an existing or new payload and tuned to meet the isolation requirements of the system. It may be used in the purely passive mode, in the passive/active mode or in the active mode. When used in the active or passive/active modes, each individual isolator local controller can be linked to another isolator local controller or to a central control system so as to perform global control by receiving feedback signals from each of the local controllers and providing an augmentation signal to adjust the individual responses. In addition, the isolator can provide shock load protection so that it can be used during launch and in orbit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a showing of the use of the invention between two members to be isolated; 
     FIG. 2 is a schematic force representation of an active, a passive and shock isolation scheme; 
     FIG. 3 is a cross-sectional view of a preferred embodiment of an active and passive isolation scheme; 
     FIG. 4 is a showing of the cubical form of the vibration isolator of the present invention; 
     FIG. 5 is a showing of the alterations used on the cubical form of FIG. 4; 
     FIG. 6 is a perspective view of the preferred embodiment of the present invention; and 
     FIG. 7 is a cross-sectional view of an alternate embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a base  10  which may be a satellite or an arm of a satellite is shown to carry a payload  12  which may be any of a variety of devices such as a camera. Of course, the invention is not limited to space applications and base  10  and payload  12  may be any two members between which there is a desire to reduce or eliminate vibration. 
     Payload  12  may have been designed to be mounted at three or more corners to base  10  by bolts (not shown) and then later found to need vibration isolation because of some unexpected motions in the base. Because of previous design and assembly of the members, vibration isolation cannot be built into the structure. Accordingly, three or more vibration isolators such as those shown as VI boxes  14  and  16  are placed between base  10  and payload  12  at the three or more mounting points. The number of mounting points is not of particular significance, and other stable mounting arrangements including different numbers of mounting points may be involved. It is understood that the payload may be the member causing the vibration and the base the member to be isolated in which case the vibration isolators need merely to be inverted (either through internal organization or physically). After so placing the vibration isolators, they are tuned to minimize the undesirable vibrations and the payload and base may thereafter perform their function. 
     In FIG. 2, the base  10  of FIG. 1, which will be considered as the vibrating member, is shown as a lower flat member  18  and the payload  12  of FIG. 1, which will be considered the quiet member to be isolated from vibrations of the base  18  is shown as an upper flat member  20 . A passive isolator which may be a “folded D strut” like that shown in the above mentioned L. P. Davis U.S. Pat. No. 5,219,051 is shown schematically as a spring  22  in parallel with a spring  24  and damper  25  to form a three-parameter passive isolation stage that connects the payload  20  and a floating member shown as a flat plate  26 . An active isolator shown as a spring  28  in parallel with an active force producing member  30  which may be a magneto restrictive device or preferably a piezoelectric stack is shown connected between base member  18  and the floating  26 . Finally, the shock or launch protection mechanism such as a SMA flexure is shown schematically as a spring  34  connected between the base  18  and the payload  20 . In operation, the arrangement of FIG. 2 allows for both high frequency and low frequency damping with launch shock protection. 
     Referring to FIG. 3, a cross-sectional view of an active and passive isolator is shown. In FIG. 3, the base member is shown as a flat plate  40  fastened to a piezoelectric stack  42  by a bolt  44 , a spacer  45  and a nut  46 . Other forms of attachment may, of course be used. A first bellows  48  mounted on an upper plate  49 , extends down around a casing  50  which surrounds the piezoelectric stack  42  and is connected to a floating member or plate which is movable, up and down, with the bellows  48 , casing  50  and the piezoelectric stack  42  in order to keep vibration from being transmitted from the base  40  to the upper plate  49 . Upper plate  49  has a fluid passage  56  therein which communicates with the interior of bellows  48 . A set screw  59  is shown for use in carrying the size of the passage  56  to alter the damping characteristics at the folded D strut. A secondary bellows  58  is shown connected to plate  49  and its interior is also connected by passage  56  to the interior of bellows  48 . The other end of bellows  58  is attached to a cup shaped member  60 . The interiors of bellows  48  and  58  are filled with fluid by way of a port  62  in plate  49 . 
     Base plate  40  is equipped with electronic circuitry shown as circuit boards  66  and  68  which are electrically connected to the piezoelectric stack  42  by conductors such as wires  70  and  72 . 
     A motion sensing device, Micro Electro-Mechanical System (MEMS), such as an accelerometer  74 , is shown mounted on the floating plate  52  and is electrically connected to circuit boards  66  and  68  by conductors such as wires  76  and  78 . 
     The arrangement including bellows  48  and  58  is the “folded D-strut” apparatus described in the above mentioned Davis U.S. Pat. No. 5,219,051. The launch protection mechanism  34  of FIG. 2 is not shown in FIG.  3 . 
     As mentioned, the active and passive isolators are preferably formed as a cube with opposite corners modified for use in mounting the cube to the members to be isolated. FIG. 4 shows a cube  80  with eight corners c 1 , c 2 , c 3 , c 4 , c 5 , c 6 , c 7  and c 8  (c 7  is not visible in FIG.  4 ). FIG. 5 shows the cube  80  of FIG. 4 with opposite corners, c 1  and c 8 , cut off to provide mounting surfaces  82  and  84  as will be described in connection with FIG.  6 . 
     In FIG. 6, elements common to FIGS. 3,  4  and  5  will carry the same reference numerals. In FIG. 6, the cutoff mounting surface  82  of corner c 1  in FIG. 5 is shown having a mounting hole  86  which is threaded for use in attaching the cube  80  to one of the members to be isolated. Surface  84  of corner c 8  in FIG. 5, is not visible in FIG. 6 but will be similarly attachable to the other of the two members to be isolated. The lower plate  40  of FIG. 3 is shown forming one of the housing walls around cube  80 . Two other housing walls  40 A and  40 B are also shown but the other three housing walls have been removed to expose the interior. As with the lower plate  40 , housing walls  40 A and  40 B are the lower plates for their respective vibration isolator units and comprise the vibrating member which produces vibration in 3 mutually perpendicular axes in the present example. Surface  82  passes through the housing walls (not shown) and is not attached thereto. The upper plate  49  of FIG. 3 is shown bering against the cutoff corner c 1  of cube  80 . A number of SMA members shown as squares  88 , which represent the same feature as the parallel spring  34  in FIG. 2, are mounted between the cube housing walls (not shown) and the cut corner c 1  during launch and will deform to absorb the shock of launch. After deformation they are removed or withdrawn so that corner c 1  is thereafter free to move with plate  49 . The folded D-strut comprising bellows  48  and  58  are shown connected to plate  49  and attached to floating plate  52 . Plate  52  carries the accelerometer  74 . The bottom plate  40  which is in contact with the vibrating member in the present example by way of the housing walls  40 A,  40 B and the surface  84  of cutoff corner c 8 , (not seen in FIG.  6 ), carries the electronic circuitry  68 . The circuitry  66  of FIG. 3 is not visible in FIG. 6 but lies under bottom plate  40 . In some cases, the bottom plate  40  (and the housing walls  40 A and  40 B) may have the electronic circuitry printed directly thereon. The piezoelectric stack  42  of FIG. 3 is inserted within the bellows  48  to save space and is not visible in FIG. 6, but the mounting spacer  45  and the nut  46  connecting it to the bottom plate  40  are seen. 
     Protection for other axes is provided by similar isolation devices including folded D-struts, shown partly by bellows  90  and  92  mounted between housing walls  40 A and  40 B and corner c 1  along axes perpendicular to the mounting of bellows  48 . As such, protection for vibration in all axes is provided by the structure of FIG.  6 . 
     FIG. 7 shows a cross-section of an alternate embodiment which can perform the same functions as the apparatus of FIG.  6 . In FIG. 7, a first or lower member  120 , adapted to be mounted to the base  10  of FIG. 1, is shown. A second or upper member,  122 , is removably fastened to lower member  120  such as by bolts (not shown). Mounted by launch protection devices or SMAs  124  and  126 , to protect the payload  12  during launch, is a movable member,  130 , having a threaded mounting hole  132  adapted to accept the mounting bolts (not shown) which previously fastened the payload  12  to the base  10  in FIG.  1 . Once in orbit, the SMAs  124  and  126  will be pulled out by a small electric current via the inherent phase transformation of the material to allow the vibration isolators to work. 
     Attached to lower member  120  is a box  134  containing microelectronics for use in programming and system checkout and is the equivalent of the PC boards  66  and  68  of FIG. 3. A bus  136 , built into the lower member  120 , is connected to the microelectronics  134  by conductors shown as lines  138  and  140 . The interior of the combination of lower member  120 , upper member  122  and movable member  130  is formed to provide a shaped cavity  146  which is dimensioned to house vibration isolating elements comprising a pair of folded D-Struts  148  and  150 , similar to those described above. A pair of piezoelectric stacks  152  and  154  is shown positioned within the primary bellows of D-struts  148  and  150 . Piezoelectric stacks  152  and  154  are connected to bus  136  by conductors  156  and  158 . Conductors  138 ,  140 ,  156  and  158  provide the access for the input and the output from the bus  36  to the microelectronics and the piezoelectric stacks for programming and system checkout. The accelerometers like MEMS  74  in FIGS. 3 and 4 are shown in FIG. 7 by blocks  160  and  162  connected to the D Struts  148  and  150  respectively. The structure of FIG. 7 is a two-axis structure (unlike the 3-axis structure of FIG. 6) but, if desired, 3 units in a tripod fashion may be used and the third unit (not shown) would be located behind the two shown. The structure of FIG. 7 provides the same protection as the structure of FIG. 6 but is somewhat less adaptable to be formed in a convenient cube shape. Three or more vibration isolators such as shown in FIG. 7 will be employed between the vibrating member and the member to be isolated and when two axis isolators are used, the mounting arrangements of the other isolators will be so as to provide vibration isolation in all three axes of vibration. The passive D-Strut stage can be tuned by a set screw (not shown) which varies the orifice size between the bellows  48  and  58  and hence the damping center frequency of the unit. 
     If the vibration isolator were to be used for a situation, such as submarine decking, where the vibration comes from the payload, the above described architecture would be changed so that the passive and active stages were reversed and the active stage would have to be increased in force capability to handle larger loads of a submarine deck. Also, the SMA launch protection devices  124  and  126  may not be removed during operation and instead may be used as an additional spring. The size of the vibration isolator might also have to increase to about a six inch, rather than a one-inch, cube. 
     It will be seen that the architectures of FIGS. 6 and 7 provide for easy mounting between a payload  12  and a base  10  in FIG. 1, or vice versa, and the structure is rugged and well adapted to provide retrofit vibration isolation. Many changes will occur to those having skill in the art and we do not wish to be limited by the specific embodiments used in connection with the description of the preferred embodiments.