Abstract:
A vibration table includes a base, a plurality of springs, and a platform supported by the springs on the base. The platform includes spaced-apart first and second sides and at least one reinforcing member extending transversely across the second side. The first side of the platform defines a mounting or support surface for mounting articles on the vibration table. The second side includes a plurality of reinforcing members. The platform is vibrated by a plurality of vibration assemblies which are mounted to the reinforcing members whereby the reinforcing member distributes vibration from the vibration assemblies uniformly across the platform. At least one of the reinforcing members includes a mounting surface which extends generally orthogonal to the second side of the platform.

Description:
TECHNICAL FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to a vibration table and, more particularly, to a vibration table that provides substantially uniform vibration across the table to test a plurality of devices mounted on the table for device reliability. 
     Shaker or vibration tables are often used in an assembly line to screen devices for any possible defects which may result or may have resulted from the manufacturing process. In this manner, products which have defects identified by the vibration table may be screened out of the production line process before being shipped to a customer. Often vibration tables are used in conjunction with a heating and cooling temperature cycling or burn in chamber so that the devices can be further screened for defects that may arise from exposure to elevated and lowered temperatures or from the combined synergism of both temperature and vibration. 
     Typical vibration tables include a base and a floating platform on which devices are secured or mounted for testing. The vibration table includes a plurality of vibration assemblies or “hammers”, which are secured to the lower surface of the platform to induce vibration in the platform. The vibration assemblies are typically secured to the platform at angles between thirty five degrees (35°) to forty-five degrees (45°) with respect to the vertical axis to induce vibration pulses in three axes of the platform. FIGS. 21 and 22 illustrate a standard vibrator to table mounting configuration for pneumatic vibrator vibration systems, i.e., a horizontal table with vibrators attached to the horizontal plane. There are varying modifications made to this arrangement by different table manufactures in an effort to produce more desirable table acceleration characteristics, i.e. consistent acceleration levels from point to point and in all three axes (x, y, and z). For example, the vibration tables described in U.S. Pat. Nos. 4,181,026; 4,181,027; 4,181,208; and 4,181,029 each use multiple layers of honeycomb and elastomers to spread and dampen the localized vibration energy of each vibrator. U.S. Pat. Nos. 5,412,991; 5,589,637; 5,675,098; 5,744,724; and 5,836,202 disclose vibration tables which incorporate a very thick aluminum plate for rigidity with cored-out sections to reduce the weight. In U.S. Pat. No. 5,594,177, a table is disclosed which uses two thin aluminum plates separated by spaces to achieve rigidity while still reducing the table weight. 
     Vibration tables available from THERMOTRON include spacers mounted on top of the table for product mounting to try and isolate the product from acceleration hot spots. As illustrated in FIGS. 21 and 22 with these standard mounting techniques, there are only three primary force vectors, i.e. a, b, and c. Depending on the rotational position of the mounted vibrator, forces a and b may be imparting acceleration forces in an x direction, a y direction or any angle between the two. Although the plate is solid in most cases, and vibration energy will be distributed over the entire plate, the energy imparted by the vibrator will be greater directly over the vibrator than any other place on the plate. 
     Notwithstanding these various improvements, heretofore, known vibration tables do not achieve uniform vibration across the platform. As a result, one part on the platform is subjected to one set of vibration levels and another part in another section of the platform is subjected to another set of vibration levels. Consequently, multiple parts tested by a presently known vibration table may not be tested or screened at the same stress levels. 
     Accordingly, there is a need for a vibration table that can generate substantially uniform vibration energy across the full spectrum of the platform support surface along each of the axes in order to provide a reliable testing procedure. 
     SUMMARY OF THE INVENTION 
     According to the present invention, the vibration table includes a base and a floating platform. The floating platform is movable with respect to the base and may be supported via any method that allows the platform freedom of movement in any of the x, y, and z axes, including any rotational directions derived from the three axes. The vibration table translates the pulses generated by the attached vibrators into a multi-axially acceleration spectrum. The vibrators are attached to the table via reinforcing members that act as load spreaders and aid in force vectoring of the vibrator energy pulses. 
     In a preferred embodiment, the vibration table includes a top plate with a grid of multiple threaded holes for product retention, multiple reinforcing members secured to the underside of the plate with mounting holes for vibrators, and a plurality of support springs to float the platform on a base. The top plate may be of any material that can withstand the high energy impacts of the vibrators without incurring damage. The top plate may be of any physical size or configuration. Furthermore, the number of mounting holes in the mounting hole grid may be increased or decreased as desired and may assume a number of different configurations. 
     In the preferred configuration, the reinforcing members comprise cross-beams and perimeter beams. Additionally, the reinforcing members may include mounting brackets which are used between the cross-beams and perimeter beams. It should be understood, that other configurations of beams and mounting brackets may also be used. The reinforcing members spread the energy from the vibrators into larger areas on the top plate at lower energy levels. In addition, the reinforcing members vector the energy pulses from the vibrators into a desired horizontal axis brackets x or y. In one preferred configuration, the cross-beams cross the platform lower surface at an angle of 45°. Furthermore, the vibrators are preferably mounted in a range of 35° to 45° with respect to the mounting surfaces of the respective reinforcing members. When the vibrators mounting angles combined with the angular orientation of the cross-beams, the vibrators produce a maximum thrust to the tables x and y axes. 
     In further aspects, the vibrators are mounted to vertical mounting surfaces of the reinforcing members. By mounting the vibrators to the vertical mounting surfaces of the reinforcing members, the vibration assemblies may now have an adjustable vertical angle in combination with a fixed horizontal angle. This dual mounting angle imparts in effect four energy thrust vectors into the vibration table instead of the three thrust vectors associated with conventional vibration tables. This fourth force vector combined with the load spreading function of the reinforcing members, which also aid in producing more x and y axes motion, create a more even point to point energy distribution across the platform which exhibits less differences between the energy levels of each individual axes x, y, or z than previous vibration table design. 
     According to one form of the invention, a vibration table includes a base and a floating platform. The floating platform is movable with respect to the base and includes first and second spaced sides, with the first side for supporting articles to be vibrated by the vibration table. The platform further includes at least one projecting mounting surface which extends outwardly from the second side of the platform. The platform is vibrated by a plurality of vibration assemblies, with at least one of the vibration assemblies coupled the projecting mounting surface of the platform. 
     In one aspect, the platform includes at least one transverse member which extends over and is mounted to the second side of the platform in order to increase the stiffness of the platform. The transverse member includes the projecting mounting surface and may comprise, for example, a beam. 
     In other aspects, a first group of the vibration assemblies is mounted on the transverse member on the second side of the platform and are angled with respect to the transverse member mounting surface in a range of approximately 40° to 50° and, more preferably, at an angle of approximately 45. In further aspects, the platform further includes a plurality of projecting mounting surfaces with a second group of vibration assemblies being mounted to respective projecting mounting surfaces. The second group of vibration assemblies is preferably mounted to the projecting mounting surfaces equidistant from a center of the platform. 
     In yet further aspects, the vibration table includes a third group of vibration assemblies mounted to the respective projecting mounting surfaces, which are spaced, radially inward of the second group of vibration assemblies. Preferably, the third group of vibration assemblies are mounted to their respective projecting mounting surfaces approximately equidistant from the center of the platform. 
     In preferred form, the platform includes a plurality of reinforcing members, with each defining a projecting mounting surface. The reinforcing members may, for example, comprise perimeter members and cross-members, with the perimeter members being secured to the second side of the platform along the perimeter portion of the platform. The cross-members extend diagonally across the second side of the platform and may be interconnected with the perimeter members to thereby form a reinforcing member to stiffen the platform. In this manner, the platform has an increased stiffness and effectively transfers vibration from the various vibration assemblies across the full width and length of the platform such that the vibration levels in the platform are within a standard deviation of less than 2. 
     According to another form of the invention, a vibration table includes a base, a plurality of springs, and a platform which is supported by the springs on the base. The platform includes a plurality of reinforcing members which are secured to one side of the platform, with the opposed side of the platform defining a mounting surface for mounting articles to the vibration table. The vibration table further includes a plurality of vibration assemblies mounted to the reinforcing member for vibrating the platform, whereby the reinforcing members distribute vibration from the vibration assemblies uniformly across the platform. 
     In one aspect, the platform includes a plate and a sheet of insulation. The plate includes a plurality of mounting openings extending into a first side of the plate, which are configured to receive fasteners for securing articles to the plate. The reinforcing members are mounted to a second side of the plate through the sheet of insulation. 
     In another aspect, the reinforcing members comprise a plurality of beams. A first group of the beams is secured to the platform along a perimeter portion of the platform, and a second group of the beams extends diagonally across the second side of the platform. In further aspects, the beams of the first group are interconnected with the beams of the second group to form a reinforcing frame. 
     Other purposes and advantages of the present invention will become apparent from a study of the following portion of the specification claims and attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the vibration table of the present invention; 
     FIG. 2 is a perspective view of the base frame of the vibration table of FIG. 1; 
     FIG. 3 is an exploded perspective view of the platform of the vibration table of FIG. 1; 
     FIG. 3A is a top plan view of a mounting plate of the platform of FIG. 3; 
     FIG. 3B is a bottom plan view of the mounting plate of FIG. 3A; 
     FIG. 4 is a bottom plan view of the platform of FIG. 3; 
     FIG. 5 is a cross-section view taken along line V—V of FIG. 4; 
     FIG. 6 is a cross-section view taken along line VI—VI of FIG. 4; 
     FIG. 6A is cross-section view taken along line VIA—VIA of FIG. 6; 
     FIG. 6B is a similar view to FIG. 6A of another embodiment of the cross-member; 
     FIG. 6C is a partial cross-section view taken along line VIC—VIC of FIG. 4; 
     FIG. 6D is a partial cross-section view taken along line VID—VID of FIG. 4; 
     FIG. 7 is a partial cross-section elevation taken along line VII—VII of FIG. 4; 
     FIG. 8 is an exploded view of a vibration assembly of the vibration table of FIG. 1; 
     FIG. 9 is a top plan view of the vibration assembly of FIG. 8; 
     FIG. 10 is a bottom plan view of the vibration assembly of FIG. 8; 
     FIG. 11A is a plan view of the mounting bracket for the vibration assembly of FIG. 8; 
     FIG. 11B is a side view of the mounting bracket of FIG. 11A; 
     FIG. 12 is a flow diagram for the control system of the vibration table of FIG. 1; 
     FIGS. 13-16 illustrate vibration levels across the platform of the vibration table of the present invention; 
     FIG. 17 illustrates vibration levels across the platform of a prior art vibration table; 
     FIGS. 18-20 are schematic representations of the force vectors generated by the vibration assemblies of the present invention; and 
     FIGS. 21 and 22 illustrate prior art vibration table arrangements. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the numeral  10  generally designates a vibration table of the present invention which can be used for testing devices, for example, mechanical or electronic devices or the like. Vibration table  10  includes a base  12  and a floating table or platform  14 . In the illustrated embodiment, platform  14  is mounted to base  12  on a plurality of springs  16  (FIG.  2 ), which permit platform  14  to move independently of base  12 . It should be understood that platform  14  may be supported on base  12  by any method that permits the platform to have freedom of movement in any of the three axes, x, y, or z. 
     As best seen in FIG. 2, base  12  includes a plurality of interconnecting members which form middle and lower frames  12   a  and  12   b  and side frame  12   c  and  12   d . Frames  12   a  and  12   b  are supported by and between side frames  12   c  and  12   d . Middle frame  12   a  supports a drip pan  13 , which extends across frame  12   a  and under platform  14  to catch liquids such as condensate, or that may leak from devices undergoing testing. Springs  16  are supported by base  12  on drip pan  13  and are housed in spring standoffs  16   a  which permit height adjustment of platform  14 . Spring standoffs  16   a  are located at the respective corners of drip pan  13  and middle frame  12   a . Preferably, middle frame  12   a  is reinforced by plates  13   a , which are welded between the adjoining interconnecting frame members, which form middle frame  12   a , and to inner legs  13   b , which extend between middle frame  12   a  and lower frame  12   b . Inner legs  13   b  are similarly preferably welded to the respective interconnecting members that form frames  12   a  and  12   b . Optionally, base  12  may include perimeter frame members  17  (FIG. 1) supported on side frame  12   c  and  12   d , which extend around and are spaced from platform  14 . In this manner, frame members  17  provide a safety barrier when platform  14  is being vibrated and a thermal seal for use in a test chamber. 
     As best seen in FIG. 3, platform  14  includes an upper plate member  20  and an optional insulation sheet  24 . Plate member  20  preferably comprises a metal plate, such as aluminum, and includes a plurality of mounting openings  22  (FIGS. 1 and 3,  3 A) which are arranged in a grid pattern and extend into plate member  20  from an upper surface or side  20   a  of plate member  20 . Openings  22  are configured to receive fasteners so that devices or parts can be rigidly mounted to the upper side of platform  14  for vibration testing. In preferred form, openings  22  do not extend through plate  20 . It should be understood that plate  20  may be of any material that can withstand high-energy impact without incurring damage. In addition, plate  20  may be of practically any shape or size and, further, may have a wide variety of mounting opening patterns. 
     Plate member  20  further includes a second plurality of openings  23  (FIG. 3B) which extend through plate member  20  from a lower surface or side  20   b  of plate member  20 . Openings  23  provide mounting openings and are configured to receive fasteners which attach transverse reinforcing members to plate  20 , which will be more fully described below. Both sets of openings  22  and  23  are preferably threaded openings. In the illustrated embodiment, plate member  20  is square but it should be understood that plate members  20  may comprise other shapes. 
     Insulation sheet  24  preferably comprises a fiberglass sheet of insulation and includes a plurality of openings  24   a  which align with openings  23  of plate member  20  to permit transverse reinforcing members  26  to be directly mounted to plate  20 . If the vibration table is used in a heating and cooling chamber, insulation sheet  24  reduces the temperature gradient through plate  20  so that the devices mounted to plate  20  can be shielded from ambient temperatures and the vibrators can be thermally isolated from chamber temperature extremes. 
     Referring to FIG. 4, mounted to the reinforcing members  26  are a plurality of vibration assemblies  18 , which vibrate platform  14  and induce substantially uniform vibration across platform  14  in both x, y and z axes. As will be more fully described below, vibration table  10  translates the attached vibration assembly pulses into multi-axial acceleration spectrum from approximately 20 Hz to 3,000 Hz, for example. Vibration assemblies  18  are preferably pneumatic vibration assemblies and are actuated by a control system  15 , which may be located in a remote control housing or console  29 . Further description of control system  15  is provided in reference to the operation of the vibration table below. 
     As noted above, platform  14  includes a stiffening system such as the plurality of transverse reinforcing members  26 . Reinforcing members  26  increase the stiffness of plate  20  and further provide horizontal and vertically oriented mounting surfaces for mounting vibration assemblies  18  at varied locations across platform  14 . In this manner, reinforcing members  26  act as load spreaders and aid in force vectoring of the vibration assemblies&#39; energy pulses. Reinforcing members  26  are respectively mounted directly to plate  20  through insulation sheet  24 , for example, by a plurality of mounting bolts  28 . In preferred form, reinforcing members  26  include a pair of cross-members or cross-beams  30  and  32 , perimeter rail members or beams  34 ,  35 ,  36 , and  37 , and mounting brackets  40 . Cross-members  30  and  32  extend diagonally across plate  20  from opposed corners of plate member  20  to stiffen plate member  20 . In the illustrated embodiment, cross-members  30  and  32  are orthogonal and mounted at approximately 45 degrees with respect to the x and y axes of platform  14 . In the illustrated embodiment, cross-members  30  and  32  have a rectangular cross-section (FIG. 6A) and include at their respective medial portions notched portions  30   a  and  32   a  (FIG. 6) to permit cross-members  30  and  32  to interlock by the aligning the two notched portions  30   a  and  32   a . It should be understood that cross-members  30  and  32 , as well as rail members  34 - 37 , may have different cross-sections, including for example a trapezoidal cross-section (shown in FIG. 6B for cross-member  32 ′) or tubular cross-sections, including other structural shapes, or the like. In addition, cross-members  30  and  32  may be interconnected at their respective distal ends  30   b  and  32   b  by rail members  34 ,  35 ,  36 , and  37 . In the illustrated embodiment, rail members  34 ,  35 ,  36 , and  37  are respectively secured at their distal ends  34   a ,  35   a ,  36   a , and  37   a  to the distal ends of the cross-members  30  and  32  by fasteners  31 . In this manner, cross-members and rail members  30 ,  32 ,  34 ,  35 ,  36 , and  37  form a reinforcing frame. As a result, when cross-members and rail members  30 ,  32 ,  34 ,  35 ,  36 , and  37  are secured to platform  14 , platform  14  has a substantially uniform stiffness across its width and length and, further, includes a plurality of generally vertically oriented mounting surfaces to which vibration assemblies  18  may be mounted. Similar to cross-members  30  and  32 , in the illustrated embodiment rail members  34 - 37  have a rectangular cross-section, but it should be understood that rail members  34 - 37  may also assume other shapes. In addition, it should be understood that reinforcing members  26  may include further members or beams and may be arranged in other configurations. 
     In the illustrated embodiment, each mounting brackets  40  comprises a triangular-shaped plate with mounting holes  42  located at each of the corners of bracket  40  for mounting bracket  40  to platform  14 . Mounting brackets  40  provide spaced horizontal mounting surfaces and are mounted to plate  20  between cross-members  30 ,  32  and rail members  34 - 37 . In addition, mounting brackets  40  may be arranged in a radial arrangement, which will be more fully described below in reference to the vibration assemblies. As best seen in FIG. 5, each mounting brackets  40  has a similar thickness to that of plate  20 . As a result, similar to beams  30 ,  32 , and  34 - 37 , mounting brackets  40  locally increase the stiffness of plate  20  and, further, act as load spreaders. 
     To further enhance the uniformity of the vibration across platform  14 , vibration assemblies  18  are mounted to reinforcing members  26  in a plurality of different orientations and mounted to a plurality of mounting surfaces, which are arranged in different planes of platform  14 . In the illustrated embodiment, a first group  38  of vibration assemblies  38   a ,  38   b ,  38   c , and  38   d  are mounted to mounting brackets  40  (FIGS.  11 A and  11 B). Each mounting bracket  40  includes a central mounting hole  44  through which each respective vibration assembly  38   a ,  38   b ,  38   c , and  38   d  is mounted to platform  14 . In this manner, the first group of vibration assemblies are mounted to a horizontal mounting surface of platform  14 , which is spaced from plate  20  and which lies in a first plane of platform  14 . Vibration assemblies  38   a ,  38   b ,  38   c , and  38   d  and mounting brackets  40  may be mounted in a radial formation or arrangement and generally aligned along the 0°, 90°, 180°, and 270° radial axes  15   a ,  15   b ,  15   c , and  15   d  which extend outwardly from the central portion of platform  14 . In preferred form, each of the vibration assemblies  38   a ,  38   b ,  38   c , and  38   d  is mounted at an angle A (FIG. 5) with respect to its respective mounting bracket  40  in a range of approximately 35° to 45°, and most preferably at an angle of approximately 45°. Consequently, all four vibration assemblies produce vibration vector forces in the x, y, and z axes. Furthermore, since vibrating assemblies are mounted to a surface spaced from plate  20 , vibration assemblies  38   a ,  38   b ,  38   c , and  39   d  produce a fourth vibration vector and bending force vector. 
     A second group  42  of vibration assemblies  42   a ,  42   b ,  42   c , and  42   d  are mounted to perimeter rails  34 ,  35 ,  36 , and  37 , respectively. In preferred form, each vibration assembly  42   a ,  42   b ,  42   c , and  42   d  is mounted to a respective vertical side surface  34   a ,  35   a ,  36   a , and  37   a  of perimeter rails  34 ,  35 ,  36 , and  37  at an angle B with respect to the x-axis and at an angle B′ with respect to the z-axis. Angles B and B′ are preferably in a range of about 35° to 45°, and most preferably approximately 45°. In this manner, vibration assemblies  42   a ,  42   b ,  42   c , and  42   d  mount to four different mounting surfaces in four different planes of platform  14  and produce x , y, and z vectors forces in each of the planes and, further, produce a bending force vector. In addition, each vibration assembly  42   a ,  42   b ,  42   c , and  42   d  is mounted to a medial portion of each respective perimeter rail  34 ,  35 ,  36 , and  37  and, more preferably, mounted such their respective fasteners are mounted to perimeter rails along radial axes  15   a ,  15   b ,  15   c , and  15   d . In this manner, the vibration which is induced by the second group of vibration assemblies is generally uniformly distributed across plate  20  by perimeter rail members  34 ,  35 ,  36  and  37  and, further, by cross-members  30  and  32 . 
     A third group  48  of vibration assemblies  48   a ,  48   b ,  48   c , and  48   d  are mounted to cross-members  30  and  32 , and preferably to a respective vertical side surface  30   c  and  32   c  of cross-members  30  and  32  such that vibration assemblies  48   a ,  48   b ,  48   c , and  48   d  lie in a common plane and apply forces to a third set of mounting surfaces which lie in a third set of planes of platform  14 . Vibration assemblies  48   a ,  48   b ,  48   c , and  48   d  are similarly mounted to vertical side surfaces  30   c  and  32   c  at an angle C with respect to the longitudinal axis of cross-members  30  and  32  in a range of approximately 35° to 45°, and, most preferably, at an angle of approximately 45°. In addition, vibration assemblies  48   a ,  48   b ,  48   c , and  48   d  are mounted to vertical mounting surfaces  30   c  and  32   c  at an angle C′ with respect to the z axis preferably in a range of 35° to 45° and, more preferably at approximately 45°. As a result, vibration assemblies  48   a ,  48   b ,  48   c , and  48   d  produce x, y, and z vector forces in each of the third set of mounting surfaces and planes. Furthermore, vibration assemblies  48   a ,  48   b ,  48   c , and  48   d  are preferably mounted to cross-members  30  and  32  at medial portions of the respective cross-members but spaced radially outward from the center of platform  14 . 
     A fourth group  50  of vibration assemblies  50   a ,  50   b ,  50   c , and  50   d  are mounted to cross-members  30  and  32  radially outward from vibration assemblies  48   a ,  48   b ,  48   c , and  48   d  and are similarly mounted to vertical side surfaces  30   c  and  32   c  of cross-members  30  and  32 . Similar to vibration assemblies  48   a ,  48   b ,  48   c , and  48   d , vibration assemblies  50   a ,  50   b ,  50   c , and  50   d  are mounted directly to vertical side surfaces  30   c  and  32   c  at an angle with respect to the longitudinal axes of cross-members  30  and  32  in a range of 35° to 45°, and most preferably at an angle of approximately 45° and at an angle with respect to the z-axis in a range of 35° to 45° and, most preferably, at approximately 45°. Consequently, vibration assemblies  50   a ,  50   b ,  50   c , and  50   d  may produce x, y, and z vector forces in the same planes as vibration assemblies  48   a ,  48   b ,  48   c , and  48   d.    
     In the present invention, the vibrators are mounted on the vertical mounting surfaces of the respective reinforcing members. This configuration has multiple advantages over the previous methods. Referring to FIGS. 18-20, vibration assemblies  18  generate the same three force vectors described previously, i.e. a, b, and c. However, these force vectors are generated in the reinforcing members which are attached to the lower horizontal surface of the vibration platform. The reinforcing members act like large load spreaders distributing the energy across the platform so that the high energy “spots” are diluted in amplitude and cover a much larger area. Since the vibration assemblies attachment point is preferably several inches below the platform, which will tend to create a small pivoting action, the force vectors are made less defined and include some rotational energy. As best seen in FIG. 20, an additional force vector d is created by mounting the vibration assembly at an angle on the vertical mounting surface of the reinforcing member. By applying the acceleration forces into four vectors instead of three, the benefits derived from the reinforcing members creates a vibration platform that has much improved vibration characteristics. As a result, the platform has more consistent acceleration levels from point to point on the table. In addition, with the arrangement of vibration assemblies  18 , the force vectors generated by the vibration assemblies can be more accurately balanced to achieve uniform vibration pulses in platform  14 . 
     The standard deviations of measured energy levels on all axes are significantly less than any other table currently available. Furthermore, the platform exhibits close average vibration levels between the three axes. In addition, the platform exhibits reduced harmonics as compared to other rigid table types. Moreover, by mounting the vibrators to the vertical mounting surfaces of the reinforcing members, the vibration assemblies may now have an adjustable vertical angle in combination with a fixed horizontal angle. This dual mounting angle imparts in effect four energy thrust vectors into the vibration table instead of the three thrust vectors associated with conventional vibration tables. This fourth force vector combined with the load spreading function of the reinforcing members, which also aid in producing more x and y axes motion, create a more even point to point energy distribution across the platform which exhibits less differences between the energy levels of each individual axes x, y, or z than previous vibration table design. 
     Referring to FIG. 8, each vibration assembly  18  includes a piston housing  70  and a piston assembly  71  which is slidable within housing  70 . Housing  70  preferably includes an angled end portion  72  which defines a skewed mounting surface  70   a  such that when fastener  18   a  extend through end portion  72  of housing  70 , vibration assembly  18  is mounted at an angle with respect to the respective mounting surface of platform  14 , as previously noted. Housing  70  further includes an open end  74 , which is closed by a cover or end cap  76  which is secured to housing by fasteners  78 . Piston assembly  71  includes a piston body  80  in which a resilient cylindrical body or “programmer”  82  is mounted. Cylindrical body  82  includes a transverse passage  84 , which permits air to move through piston assembly  71 , as will be more fully described below. Piston assembly  71  moves along the interior of housing  70  under the influence of pressurized air which is introduced into housing  70  through a pressure inlet port  86  which includes a fitting  88   a  for coupling to a hose or tubing  88   b . As viewed in FIGS. 8,  9  and  10 , piston assembly  71  moves to the left to impact or strike an inner surface  90  of housing  70  which imparts a force through mounting surface  70   a  to platform  14 . As air enters housing  70  through inlet  86 , air is directed into a thrust chamber  92  rearwardly of piston body  80  by a passageway  94  formed in piston body  80 . The term “rearwardly” is arbitrary and used just a naming convention with “forward” or “forwardly” indicating toward the angle portion  72 . As piston assembly  71  moves toward impact surface  90  of housing  70 , air exhausts from a forward or second chamber  91  formed between forward end of piston assembly  71  and impact surface  90  through an exhaust port  93  formed in housing  70 . When piston assembly  71  is fully extended through housing  70  and in the thrust position, air pressure inlet  86  is aligned with and directs air into a second passageway  95  formed in piston body  80 . Second passageway  95  is in fluid communication with a central chamber  96  of the piston body  80 , which in turn is in fluid communication with passageway  84  which extends transversely though cylindrical body  82 . Therefore, pressurized air moves from inlet port  86  to passageway  95  into central chamber  96 , through passageway  84  of cylindrical body  82  and into forward chamber  91 . Forward chamber  91  is therefore pressurized and moves piston assembly  71  from the thrust position to a rebound position as air exhausts from thrust chamber  92  through a second outlet passageway  98  provided in housing  70 . It can be understood that the movement of piston assembly  71  through housing  70  and resulting frequency of the impact force on platform  14  is increased with increasing air pressure. 
     Referring to FIG. 12, vibration table  10  includes an air manifold  52 , which delivers air to the respective vibration assemblies  18  through tubing  88   b . Air is delivered to manifold  52  from a supply of air  54 . Control system  15  includes a closed loop process or PID controller  56  that receives input from accelerometers  58 , which are mounted to platform  14 . Accelerometers  58  measure the G-RMS values of the platform and generate signals that are proportional to the G-RMS values. The signals generated by accelerometers  58  are forwarded to an RMS converter which generates a voltage proportional to the G-RMS levels measured by accelerometers  58 . The air supplied by air supply  54  is regulated to manifold  52  by an air supply system  60  which is controlled by the closed loop controller  56 . Preferably, air supply system  60  includes an air filter  60   a , a regulator  60   b , a slave regulator  60   c  which regulates the flow of air to an air valve  60   d , which, in turn, delivers air to manifold  52 . The pressure in slave regulator  60   c  is controlled by closed loop controller  56  which adjusts the air flow through air valve  60   d  in response to increases or decreases in the vibration on vibration table  10  as measured by accelerometers  58 . As best seen in FIG. 13, closed loop controller  56  adjusts the pressure in slave regulator  60   c  through a voltage and pressure converter  60   e . Preferably, air valve or valves  60   d  are coupled to vibration controls  60   f , which may include, for example, on/off controls, vibration level selection controls, and vibration time controls. In this manner, control system  15  measures the vibration of vibration table  10  and includes a feedback of this measurement to compare it with the desired vibration of vibration table  10 . 
     In this manner, when vibration assemblies  18  are actuated by control system  15 , vibration assemblies  18  generate impact forces on platform  14  at frequencies that are a function of the air pressure delivered to the vibration assemblies. The impact forces are transmitted through and distributed by reinforcing members  26 , resulting in substantially uniform vibration in the x, y, and z axes in plate  20 . Consequently, vibration table  10  produces induce uniform vibration levels across the full width and length of platform  14  and induces uniform vibration in the respective parts which are mounted to plate  20 . 
     FIGS. 13-16 illustrate the vibration levels along each of the axes of one quadrant of vibration table  10  and the average vibration levels of all three axes in the same quadrant. Referring to FIG. 13, the vibration levels along the x axis of the quadrant of the table vary from approximately 6.0 G-RMS (root mean square) to approximately 3.5 G-RMS with a standard deviation of approximately 0.61. With reference to FIG. 14, the vibration along the y axis is similarly substantially uniform over the quadrant of the table and vary from approximately 6.5 G-RMS to approximately 4.5 G-RMS, with a standard deviation equal to approximately 0.62. Referring to FIG. 15, the z axis vibration levels are, likewise, substantially uniform over the same quadrant table and vary from approximately 12 G-RMS to approximately 7.5, G-RMS with a standard deviation of 1.2. The data shown in FIGS. 13-15 establish that the vibration levels across platform  14  along any one axis are within a standard deviation of less than 2. In addition, the average vibration levels of all three axes has a standard deviation of 0.44 as shown in FIG.  16 . Therefore, it can be seen from the vibration levels for each of the axes that the vibration across vibration table  10  is substantially uniform. Consequently, parts that are mounted to platform  14  are subjected to substantially uniform vibration levels regardless of where on platform  14  they are mounted. 
     Furthermore, while various forms of the invention have been shown and described, other forms are being apparent to those skilled in the art. Therefore, the embodiment of the invention shown in the drawings is not intended to limit the scope of the invention which is instead defined by the claims which follows. 
     Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the doctrine of equivalents.