Patent Publication Number: US-2020284316-A1

Title: Passive motion isolation system

Description:
CROSS-REFERENCE 
     This application claims the benefit of U.S. Provisional Application No. 62/815,743, filed Mar. 8, 2019, entitled Passive Motion Isolation System which application is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND 
     Field 
     This disclosure relates to motion isolation systems for motion-sensitive electronic equipment. 
     Description of the Related Art 
     Motion-sensitive electronic equipment may include, and/or be mounted on, elastic vibration isolators. A particular combination of a piece of equipment and a vibration isolator will have a natural resonant frequency. The vibration isolator may be effective to minimize or prevent coupling of vibrations from the ambient to the equipment for vibration frequencies significantly higher than the resonant frequency. However, the frequency spectrum of ground motion due to earthquakes may be concentrated at frequencies below 3 Hertz and may include significant motion at frequencies of 0.5 Hz or lower. It is generally impractical to lower the resonant frequency of vibration-isolated equipment to less than 0.5 Hz. Thus conventional vibration isolation systems may be ineffective at isolating the equipment from low-frequency motions such as those caused by earthquakes. 
     SUMMARY 
     An aspect of the disclosure is directed to motion isolation systems for motion-sensitive equipment. Suitable motion isolation systems comprise: a base subject to ambient motions; a three-axis free motion platform mounted on the base; and a vibration isolation subsystem coupled between the motion-sensitive equipment and the three-axis free motion platform. 
     Additionally, the three-axis free motion platforms are configurable to comprise: an x-axis free motion stage and a y-axis free motion stage, the x-axis and the y-axis orthogonal to each other and essentially horizontal, and a z-axis free motion stage, the z-axis being orthogonal to both the x-axis and the y-axis and essentially vertical. For example, the x-axis free motion stage can comprise an x-axis carriage free to move along an x-axis rail, the y-axis free motion stage comprises a y-axis carriage free to move along a y-axis rail, and the z-axis free motion stage comprises a z-axis carriage free to move along a z-axis rail. Additionally, in some configurations the y-axis rail is attached to, and moves with, the x-axis carriage, the z-axis rail is attached to, and moves with, the y-axis carriage, and the vibration isolation subsystem is coupled between the z-axis carriage and the motion-sensitive equipment. In some configurations it might be desirable for the z-axis free motion stage to comprise a counterbalance mechanism to offset a total weight of the z-axis carriage, the vibration isolation subsystem, and the motion-sensitive equipment. The counterbalance mechanism can additionally comprise at least one constant force spring. Each of the x-axis rail, the y-axis rail, and the z-axis rail can be configurable to have a finite length between respective ends, in which case the system can further comprise: a plurality of resilient firm stops, a firm stop from the plurality of firm stops located proximate each end of each of the x-axis rail, the y-axis rail, and the z-axis rail to limit a range of motion of the respective carriage in both directions along the rail. Motion isolation systems can also have a plurality of resilient soft stops, a soft stop from the plurality of soft stops located proximate each end of each of the x-axis rail, the y-axis rail, and the z-axis rail, wherein each soft stop is configured such that a carriage nearing an end of the respective rail contacts the soft stop located proximate the end of the rail before contacting the corresponding firm stop. Each soft stop can also be configured to extend further along the respective rail and has a smaller cross-sectional area than the corresponding firm stop. At least some configurations of the vibration isolation subsystem can further comprise: a support attached to the z-axis carriage; four elongate resilient pillars, each pillar having a first end affixed to the support, a length extending from the support parallel to the z-axis, and a second end; and a mounting structure to couple the motion-sensitive equipment to the second ends of the four pillars. The mounting structure can also be configured such that all or a portion of the motion-sensitive equipment is disposed between the four pillars. 
     In some configurations the mounting structure is configured such that the motion-sensitive equipment does not contact the four pillars and the support. Each of the four pillars can further comprise first and second segments, the vibration isolation subsystem can also further comprise a first frame, the first segments of each of the four pillars can be configured to couple the mounting structure to the first frame, and the second segments of each of the four pillars couple the first frame to the support. Each of the four pillars can further comprise first, second, and third segments, the vibration isolation subsystem can further comprise first and second frames, and the first segments of the four pillars can couple the mounting structure to the first frame, the second segments of the four pillars couple the first frame to the second frame, and the third segments of the four pillars couple the second frame to the support. In other configurations at least one motion limiter can be provided to limit a range of motion of the mounting structure with respect to the support. One or more motion limiter can further comprise one or more of a resilient grommet attached to the support, and a post extending from the mounting structure through a center hole in the resilient grommet. 
     Another aspect of the disclosure is directed to methods of using the disclosed motion isolation systems for motion-sensitive equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
         FIG. 1  is a schematic depiction of a passive motion isolation system; 
         FIG. 2  is a perspective view of a motion isolation system; 
         FIG. 3  is a front view of the motion isolation system of  FIG. 2 ; 
         FIG. 4  is an end view of the motion isolation system of  FIG. 2 ; 
         FIG. 5  is a back view of the motion isolation system of  FIG. 2 ; 
         FIG. 6  is a perspective view of a multi-axis motion platform used in the motion isolation system of  FIG. 2 ; 
         FIG. 7  is another perspective view of the multi-axis motion platform of  FIG. 6 ; and 
         FIG. 8  is a perspective view of a portion of a vibration isolation subsystem showing details of a motion limiter. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic depiction of a motion isolation system  10  that employs a tiered or stacked structure to isolate motion-sensitive equipment  15  from vibration and movement introduced through a base  40 . The equipment  15  is coupled to the base  40  through a two-tiered structure including a vibration isolator  20  and a low-frequency motion isolator  30 . The base  40  is subject to ambient movement including, but not limited to, vibrations caused by machinery or traffic; and building motions due to earth quakes. The combination of the equipment  15  and the vibration isolator  20  may have a natural resonant frequency. The vibration isolator  20  may be effective to minimize or prevent coupling of vibrations from the base  40  to the equipment  15  for vibration frequencies significantly higher than the resonant frequency. The low-frequency motion isolator  30  isolates the motion-sensitive equipment  15  from small-amplitude motions of the base  40  for frequencies comparable to, or less than, the resonant frequency. The low-frequency motion isolator  30  isolates larger amplitude low-frequency motions, such as motions caused by earthquakes, so that they are coupled to the motion-sensitive equipment  15  with limited acceleration that may not substantially degrade the performance of the motion-sensitive equipment 
       FIG. 2  is a perspective view of a motion isolation system  100  which is an embodiment of the motion isolation system  10  of  FIG. 1 .  FIG. 3 ,  FIG. 4 , and  FIG. 5  are front, end, and back views, respectively of the motion isolation system  100 . The relative position of various parts of the motion isolation system  100  will be described based upon these views. Throughout this description, terms indicating direction, relative position, or size (e.g. “up”, “down”, “left”, “right”, “over”, “under”, “height”, “width”, etc.) may be used when referring to the drawing figure 
     As shown in  FIG. 2 , the motion isolation system  100  includes a vibration isolation subsystem  200  and a multi-axis motion platform  300 . Equipment module  110  is supported by the vibration isolation subsystem  200  which is an embodiment of the vibration isolator  20 . The vibration isolation subsystem  200  is mounted on the multi-axis motion platform  300 , which is an embodiment of the low-frequency motion isolator  30 . In  FIGS. 2-7 , x, y, and z axes are defined for ease of description of the elements of the motion isolation system. In  FIGS. 3-8 , components of the vibration isolation subsystem  200  are identified by reference designators between  210  and  270 . Components of the multi-axis motion platform  300  are identified by reference designators between  310  and  375 . 
     The vibration isolation subsystem  200  is supported by a support  240  which is attached to the multi-axis motion platform  300 . In this example, the support  240  is a rigid metal plate. The support  240  may be a plate, a frame, or some other rigid structure. Four elongated resilient pillars  250 A,  250 B,  250 C,  250 D, of which only  250 A and  250 B are visible in  FIG. 3 , extend upward from the support  240 . The other two elongated resilient pillars  250 C,  250 D are located behind the equipment module  110  as shown in  FIG. 5 . Each elongated resilient pillar  250 A-D has a first end affixed to the support  240 , a length extending parallel to the z-axis, and a second end remote from the support  240 . The equipment module  110  is coupled to the second ends of the four elongated resilient pillars  250 A-D by a mounting structure  210 . In this example, the mounting structure  210  consists of two support brackets  215 , only one of which is visible in  FIG. 3 . A second support bracket (which is a mirror image of the support bracket visible in  FIG. 3 ) is located behind the equipment module as shown in  FIG. 5 . The two support brackets  215  are attached to the second ends of the four elongated resilient pillars  250 A-D (each support bracket attaches to two of the elongated resilient pillars  250 A-D) and extend downward from a plane defined by the second ends of the four elongated resilient pillars  250 A-D. The overall height (i.e., dimension parallel to the z-axis) of the four elongated resilient pillars  250 A-D is greater than a height of the equipment module  110  such that the bottom of the equipment module  110  is suspended above the support  240 . Other mounting structures may be used to couple an equipment module to the four elongated resilient pillars  250 A-D such that all or a portion of the equipment module is disposed between the elongated resilient pillars  250 A-D and above the support  240 . 
     To prevent excess lateral or rotational motion of the equipment module  110 , each of the four elongated resilient pillars  250 A-D may be divided into two or more segments, with joints between the segments connected together by frames that connect the four elongated resilient pillars  250 A-D without contacting the mounting structure  210  or equipment module  110 . In this example, each elongated resilient pillar  250 A-D is divided into upper pillar segment  252 , middle pillar segment  254 , and lower pillar segments  256  as shown in  FIGS. 3, 5 and 8 . The mounting structure  210  is coupled to a first frame  220  by four upper pillar segments  252 , of which only two are visible in  FIG. 3 . The first frame  220  is coupled to a second frame  230  by four middle pillar segments  254 , of which only two are visible in  FIG. 3 . The second frame  230  is coupled to the support  240  by four lower pillar segments  256 , of which only two are visible in  FIG. 3 . The upper pillar segment  252 , middle pillar segment  254 , and lower pillar segment  256  may be made from a resilient or viscoelastic material such as a polyurethane foam. The upper pillar segment  252 , middle pillar segment  254 , and lower pillar segment  256  may be attached to the associated mounting structure  210 , first frame  220 , second frame  230 , and support  240  by adhesive. Two motion limiters  260  (of which only one is visible in  FIG. 2 ) limit the range of motion of the mounting structure  210  and equipment module  110  with respect to the support  240 . The motion limiters will be described in additional detail in conjunction figure  FIG. 8 . 
     The left and right ends of the first frame  220  are twice folded to form a vertical portion  222  and a horizontal portion  224  that passes under the equipment module  110 . The second frame  230  is similarly folded. Alternatively, the first frame  220  and the second frame  230  could be unfolded. In this case, the ends of the first and second frame will extend beyond the left and right ends of the equipment module  110  (not shown). The folded-frame configuration shown in  FIG. 3  is more compact. 
     The number of segments in each pillar and the number of frames in the vibration isolation subsystem  200  may be tailored to the size and mass of the equipment module. A vibration isolation subsystem may have more or fewer than three segments in each pillar and more or fewer than two frames. The number of segments in each pillar will be equal to the number of frames plus one. 
       FIG. 4  is an end view of the motion isolation system  100  showing the equipment module  110 , the two support brackets  215 , the two motion limiters  260 , two upper pillar segments  252  of elongated resilient pillars  250 B and  250 C. It also shows vertical portions  222  and horizontal portion  224  of the first frame  220 . The multi-axis motion platform  300  includes an x-axis/y-axis (e.g., x-axis and y-axis) motion stage  310  and a z-axis motion stage  350 . Although not visible in  FIG. 4 , the support  240  of the vibration isolation subsystem  200  is attached to a movable portion of the z-axis motion stage  350 . 
     A motion stage is a mechanical device including a carriage that is movable in a linear direction along an axis defined by a guide. A free-motion stage is a motion stage where the carriage is free to move with respect to the guide, rather than driven by a motor or other positioning device. A motion isolation system that uses only free-motion stages may be considered passive. The guide may be a single rail having a rectangular, triangular, trapezoidal, or x-shaped cross-section, a channel having a u-shaped cross-section, a pair of parallel ways (commonly having circular cross-sections), or some other elongate structure that defines a direction of motion of the carriage. The carriage may be configured to move freely along the guide in the defined direction and may be constrained to not move in directions orthogonal to the defined direction. Typically, a carriage is in contact with two or more surfaces of the guide to prevent motion in directions orthogonal to the defined direction. Friction at the points of contact between a carriage and a guide may be minimized through the use of ball bearings, roller bearings, bushings, lubricants, and/or other devices. Since the length of a guide must be finite, a motion stage typically includes stops to prevent a carriage from moving past the ends of the guide. 
     Motion stages may be stacked to allow motions along multiple axis. For example, a first motion stage may include a first rail and a first carriage that moves along the first rail in a first direction. A second rail may be attached to the first carriage such that the second rail is not parallel to the first rail. Typically, the second rail may be perpendicular to the first rail. The second carriage moves along the second rail in a second direction, and the second carriage, second rail, and first carriage are free to move, as a unit, along the first rail in the first direction. Similarly, a third rail may be attached to the second carriage, with the third rail typically extending in a direction perpendicular to both the first and second rails. 
     In the motion isolation system  100 , the x and y axes are defined as two orthogonal axes, each of which is essentially horizontal. The z axis is defined to be orthogonal to both the x and y axes and thus essentially vertical. The directions of each of the x and y axes are considered essentially horizontal if a component of gravity along both of the x and y axes is insufficient to cause motion of the corresponding carriage along the respective axis of the x-y motion stage  310 . 
       FIG. 5  is a back view of the motion isolation system  100 . The equipment module  110 , one of the support brackets  215 , the first frame  220  and second frame  230 , the support  240 , upper pillar segment  250 , middle pillar segment  254 , lower pillar segment  256  of elongated resilient pillars  250 C and  250 D, and one of the two motion limiters  260  are visible. 
     The z-axis motion stage  350  includes a z-axis carriage  360  that slides along a z-axis rail  355 . The support  240  is attached to the z-axis carriage  360  such that the z-axis carriage supports the vibration isolation subsystem  200 , and the equipment module  110 . Since the z-axis is essentially vertical, gravity will attempt to pull the z-axis carriage  360  to its lowest position. To allow the z-axis carriage to float along the z-axis rail without being pulled to its lowest position by gravity, the total weight of the z-axis carriage  360 , the vibration isolation subsystem  200 , and the equipment module  110  is offset or counterbalanced in the upward direction with a force equal to the total weight. In an exemplary motion isolation system  100 , two constant force springs  365  are used to counterbalance the weight of the z-axis carriage  360 , the vibration isolation subsystem  200 , and the equipment module  110 . Other techniques to counterbalance this weight may be used. 
       FIG. 6  and  FIG. 7  are perspective views of the multi-axis motion platform  300 , including the x-y motion stage  310  and the z-axis motion stage  350 . Note that the constant force springs  365  are not shown in  FIG. 6  to allow visibility of other portions of the z-axis stage  350 . The x-y motion stage  310  includes a base  305  that supports an x-axis rail  315 . The base  305  is subject to ambient movement including, but not limited to, vibrations caused by machinery or traffic, and building motions due to earth quakes. An x-axis carriage  320  slides along the x-axis rail  315 . The x-axis carriage  320  supports a y-axis rail  325 . A y-axis carriage  330  slides along the y-axis rail  325 . The z-axis rail  355  is supported by the y-axis carriage  330 . 
     The ranges of motion of the carriages  320 ,  330  along the respective x-axis and y-axis rails  315 ,  325  are limited by resilient stops. For example, motion of the y-axis carriage  330  to the left (as seen in  FIG. 6 ) along the y-axis rail  325  limited by a soft stop  340  and a firm stop  335 . Although not clearly visible or identified in  FIG. 6 , similar soft and firm stops are positioned at the other end of the y-axis rail  325  and both ends of the x-axis rail  315 . The range of motion of the z-axis carriage  360  is limited by soft stops  370  and  375  and firm stops  380  and  385 . 
     The soft stops and firm stops may be made from a resilient or viscoelastic material. Each soft stop (such as the soft stop  340 ) can be configured to have a longer length and smaller cross-sectional area than each firm stop (such as the firm stop  335 ). As will be appreciated by those skilled in the art, the length of a stop can be measured along the respective motion axis and the cross-sectional area of a stop is measured in a plane orthogonal to the motion axis. A carriage nearing the end of its motion range first contacts a soft stop. The soft stop then compresses and/or deforms to gradually decelerate, but not necessarily stop, the motion of the carriage. The soft stops may be inclined and/or curved with respect to the respective motion axis to ensure both compression and deformation occur. The motion of the carriage is stopped when the carriage reaches a firm stop. 
     Within the limits of the soft stops and firm stops, the x-, y-, and z-axis carriages  320 ,  330 ,  360  are free to move along the respective rails. The range of free motion and the material, shape, and cross-sectional area of the soft and firm stops may be configured based on the weight to be mounted on the x-y motion platform and the environment in which the motion isolation system will be used. The range of free motion may be, for example, one inch or greater along each axis. In another configuration the range of free motion may be, for example, between 1 and 12 inches along each axis. 
     When the base  305  is subjected to low frequency ambient movements smaller than the free travel range of the carriages  320 ,  330 ,  360 , inertia may cause one or more of the carriages to slide along their respective rails  315 ,  325 ,  355  while the base  305  moves. In this case, the vibration isolation subsystem  200  and the equipment module  110  may remain substantially stationary. When the base  305  is subjected to larger low frequency movements, one or more of the rails  315 ,  325 ,  355  may move sufficiently to cause a soft stop to contact the respective carriage  320 ,  330 ,  360 . In this case, the soft stop will gradually compress and/or deform, coupling the movement of the base to the stage as a gentle acceleration. The length, cross-sectional shape, and material of the stops and the free travel range of the carriages with respect to the rails may be configured such that the worse-case anticipated motions of the base do not disrupt or damage the equipment module. Higher frequency vibrations of the base may be coupled through the multi-axis motion platform  300  to be attenuated by the vibration isolation subsystem  200  (see  FIG. 3 ). 
       FIG. 8  is a perspective view of a portion of the vibration isolation subsystem  200  showing one of the motion limiters  260 . The motion limiter  260  includes a post  262  which is anchored at one end to the mounting structure  210  that supports the equipment module  110 . The post  262  extends through a center hole in a grommet  264 . The grommet  264  extends through a ring  266  that is attached to the support  240 . Motion of the mounting structure  210  with respect to the support  240  in a plane normal to the axis of the post  262  is limited by the post  262  contacting an inner surface of the grommet  264 . A washer  270  may be attached to a lower surface (as shown in  FIG. 8 ) of the ring  266 . Motion of the mounting structure  210  with respect to the support  240  along the axis of the post  262  is limited by an enlarged head  268  of the post  262  contacting the washer  270 . The grommet  264  and the washer  270  may be formed from a resilient or viscoelastic material such as a polyurethane foam. The grommet  264  and the washer  270  may be two separate pieces or combined into a single physical piece. The grommet  264  and the washer  270  may be attached to the ring  266  by adhesive bonding or some other method. 
     While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.