Abstract:
A vibration control system having at least one pneumatic vibrator for vibrating a vibration apparatus is provided. The vibration control system comprises an air manifold having a plurality of varying sized orifices, each pneumatic vibrator fluidly connected to one of the orifices. A method for oscillating pneumatic vibrators at different repetition rates with each pneumatic vibrator secured to a vibration apparatus is also provided.

Description:
[0001]     The present application is a continuation of pending provisional patent application Ser. No. 60/524,985, filed on Nov. 25, 2003, entitled “Means for Adjusting the Repetition Rates of Individual Vibrators in a Pneumatic Vibrations System”. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to shake tables or random vibration apparatus that use pneumatic hammers for stressing other devices. The present invention is intended to smear the frequencies generated by the random vibration apparatus.  
         [0004]     2. Description of the Prior Art  
         [0005]     In the past, vibration screening of equipments, e.g., electronic and mechanical assemblies, was accomplished by single-axis mechanical vibration apparatus or by electro-dynamic shakers. Multiple axis systems were constructed of multiple single axis systems. These systems were very expensive and required technically skilled personnel to operate. Starting in the late 1980&#39;s, pneumatic vibrations systems, such as described in U.S. Pat. No. 4,735,089, were coming into use. These systems were fairly inexpensive to purchase and maintain, and required much less skilled personnel to operate. Another advantage of the pneumatic vibration tables is that they produce six degree&#39;s of freedom vibration accelerations, i.e., X-axis, Y-axis, Z axis, roll, pitch and Yaw movements.  
         [0006]     One of the problems when using multiple pneumatic vibrators supplied from a single air source, is that they will all run (vibrate) at the same frequency (repetition rate). This will produce a line spectrum, i.e., the fundamental frequency of the vibrator, followed by all of the related harmonics. In screening test products, it is desirable to excite the product under test with a continuous spectrum, thus ensuring that the product is subjected to all frequencies within the selected range. The result of not having a continuous spectrum may result in excessive excitation occurring at the fundamental or harmonic frequencies which may destroy the product, or in not finding or precipitating flaws in the device under test due to lack of energy being supplied at the activation frequency needed to produce a resonance.  
         [0007]     Various means have been used to produce continuous spectrums. U.S. Pat. No. 4,181,025 utilizes adjustable valves, which control individual orifices in the airlines to each vibrator. U.S. Pat. No. 5,493,944 utilizes a dual piston within each vibrator, with one piston being controlled and the other left to randomly oscillate between first piston and the end of the cylinder. U.S. Pat. No. 5,365,788 utilizes a vibrator housing that creates an angular path for the input airflow that changes the piston stroke length as the piston rotates. U.S. Pat. No. 4,164,151 utilizes a plurality of loose projectiles (balls) within cavities of a chamber (vibration table), that when excited by external vibration energy, causes the balls to bounce around their individual chambers in a random fashion.  
         [0008]     Each of these methods produces a somewhat random spectrum, but each also has its drawbacks. The first listed is expensive to implement, requiring an excessive amount of hardware. The third method has problems with the individual vibrators syncing up in frequency, and creating wild vibration level changes. The fourth requires projectiles of vary large mass to create any useful vibration levels. The second is inexpensive, but due to internal characteristics, produces less energy than standard vibrators and looses effectiveness if used with other standard pneumatic vibrators.  
         [0009]     Other methods that have been used include; using multiple vibrators of different sizes, that run at different repetition rates, using manually adjustable valves inline with each vibrator and amplitude modulation of the electrical current-to-pressure valve used to control the overall vibration level. Using multiple dissimilar vibrators does create multiple frequencies that will tend to fill in the spectrum, but using different size vibrators will also create different energy levels at each attachment point, making the levels vary across the table.  
         [0010]     Using manually adjustable valves to adjust the frequency of each vibrator, is almost impossible to do accurately, as the changes in orifice sizes needed to produce acceptable results is in the order of 5-10 thousandths for each vibrator. In the last case, modulating the control to all of the vibrators simultaneously will also change the overall vibration level, making control at the desired level difficult.  
         [0011]     Accordingly, there exists a need for a vibration control system wherein the repetition rate of the enclosed piston in pneumatic vibrators is directly proportional to its supplied air pressure. Additionally, a need exists for a vibration control system wherein all pneumatic vibrators utilized in a pneumatic vibration system oscillate at different repetition rates. Furthermore, there exists a need for a vibration control system wherein the air pressures to each vibrator used in a pneumatic vibration system are altered via an air manifold that uses multiple orifice sizes, calculated to make each vibrator run at a slightly different rate.  
       SUMMARY  
       [0012]     The present invention is a vibration control system having at least one pneumatic vibrator for vibrating a vibration apparatus is provided. The vibration control system comprises an air manifold having a plurality of varying sized orifices, each pneumatic vibrator fluidly connected to one of the orifices.  
         [0013]     Additionally, the present invention is a method for oscillating pneumatic vibrators at different repetition rates. Each pneumatic vibrator is secured to a vibration apparatus. The method comprises providing an air manifold having a plurality of varying sized orifices and fluidly connecting each pneumatic vibrator to one of the orifices.  
         [0014]     The present invention further includes a vibration control device system having at least one pneumatic vibrator for vibrating a vibration apparatus. The vibration control device comprises means for oscillating each pneumatic vibrator at different repetition rates.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is an exploded top view illustrating the assembly of the vibration control unit, constructed in accordance with the present invention;  
         [0016]      FIG. 2  is an exploded perspective view illustrating the assembly of the vibration control unit, constructed in accordance with the present invention;  
         [0017]      FIG. 3  is an elevational side view illustrating the assembly of the vibration control unit, constructed in accordance with the present invention;  
         [0018]      FIG. 4  is a top plan view illustrating the assembly of the vibration control unit, constructed in accordance with the present invention;  
         [0019]      FIG. 5  is an end view illustrating the assembly of the vibration control unit, constructed in accordance with the present invention;  
         [0020]      FIG. 6  is a perspective view of the variable port manifold, constructed in accordance with the present invention;  
         [0021]      FIG. 7  is an exploded perspective view illustrating the vibration table, constructed in accordance with the present invention;  
         [0022]      FIG. 8  is an exploded perspective view illustrating the pneumatic hammer, constructed in accordance with the present invention;  
         [0023]      FIG. 9  is a graph illustrating the spectrum with a standard manifold; and  
         [0024]      FIG. 10  is a graph illustrating the spectrum with the modified manifold. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]     There is general concern in the industry concerning generating a continuous spectrum. As illustrated in  FIGS. 1-10 , the present invention is a vibration control system, indicated generally at  10 , and method of generating a continuous spectrum that is both predictable and controlled.  
         [0026]     The vibration control system  10  includes the following parts connected to a pneumatic vibrator  12  ( FIG. 8 ) for use with a vibrator apparatus  14  ( FIG. 7 ):  
                                       Item               No.   Quantity   Description                   16   1   Panel, Pneumatics Mounting, OVS - 1.5/2.5       18   1   Manifold, Pneumatics, OVS 2.5 Manifold 12       20   1   Valve, Ball Type, M-FM, ⅛″ NPT       22   9   Fitting, Male Elbow, {fraction (5/16)}″ Tube, ⅛″ NPT       24   4   Plug, Countersink, Hex, ⅛″ NPT       26   1   Fitting, Male Conn., ¼″ Tube, ⅛″ NPT       28   1   Fitting, Plug, CS SKT Head, ¾″ NPT       30   1   Fitting, Hex Nipple, ½″ NPT       32   1   Valve, Solenoid, ½″ NPT       34   1   Fitting, M Con, ½″ Tube, ½″ NPT       36   2   Fitting, Space with T Bracket, ½″       38   1   Regulator, E-P, 30 Series, 24 V, {fraction (1/2 )}″ NPT, with STR               Cable       40   1   Fitting, Male Elbow, ½″ Tube, ½″ NPT       42   1   Cross Spacer, ½″, ¼″ NPT, with 2 Plugs       44   2   Fitting, Male Conn., ¼″ Tube, ¼″ NPT       46   1   Fitting, Spacer, ½″       48   1   Mist Separator, 4000 Series, ½″ NPT       50   1   Filter/Regulator, 4000 Series, ½″ NPT, with Gauge       52   1   Nylon Tubing, ¼″ OD, 9″ long       54   1   Nylon Tubing, ½″ OD, 4″ long       56   4   Washer, ¼″, Flat, SS       58   8   Washer, ¼″, Split Lock, SS       60   4   Screw, ¼-20 × ¾″, SHCS, SS       62   4   Screw, ¼-20 × 2.5″, PPMS, SS                  
 
 It will be understood by those persons skilled in the art that the parts of the vibration control system  10  listed above are representative only and that other equivalent parts are within the scope of the present invention. 
 
         [0027]     The vibration control system  10  of the present invention entails use of compressed air that passes through the air filters, an air regulator, a current to pressure regulator, and a solenoid valve. The vibration control system  10  controls the air pressure that is fed into the variable port manifold  18  having a plurality of ports  22 . Each port  22  formed in the manifold  18  feeds the tubing that connects to each pneumatic vibrator  12 . The vibrators  12  are attached to the underside of the-vibration apparatus  14 , as known in the art.  
         [0028]     In the present invention, the pneumatic manifold  18  has multiple output ports  22  (as many as needed for the system being implemented). Each succeeding port  22  has a smaller orifice than the preceding port. Regardless of the overall air pressure, with the varying size multiple output ports  22 , each pneumatic vibrator  12  will continue to run at a different frequency. In actual implementation, it is desirable that the multiple orifices or ports  22  selected be such that the fundamental frequency of the highest frequency vibrator  12  be close to the first harmonic of the fundamental frequency of the lowest frequency vibrator  12 , thereby ensuring a substantially continuous spectrum.  
         [0029]     It follows that the repetition rate of the enclosed piston in the pneumatic vibrators  12  is directly proportional to its supplied air pressure. The vibration control system  10  of the present invention ensures that all the pneumatic vibrators  12  utilized in the pneumatic vibration control system  10  oscillate at different repetition rates. The air pressure to each vibrator  12  used in the vibration control system  10  is altered via the air manifold that uses multiple orifice  22  sizes, calculated to make each vibrator  12  run at a slightly different rate. As the repetition rate of the vibrator  12  is directly proportional to air pressure, the lower the air pressure, the lower the repetition rate.  
         [0030]     Augmenting the above spectrum is a condition know as “heterodyning”, i.e., two fundamental frequencies will produce an additional frequency that is the difference between the two original fundamental frequencies. For example, a frequency of fifteen (15) Hz and another of twenty (20) Hz will produce a difference frequency of five (5) Hz. With multiple separated vibration frequencies being generated at all times, multiple heterodyne frequencies are also generated, which also aids in filling in the spectrum. The vibration platform (table) has its own multi-modal structural vibrational modes, which also fill in and shape the spectrum.  
         [0031]     In sum, random vibration is used to precipitate defects from a product or assembly. It is desirable for the energy at each frequency to have substantially the same order of magnitude thereby increasing the likelihood of forcing latent defects to be captured by the screen. Holes in the frequency spectrum allow defects that would be excited in that frequency range to escape. With each vibrator  12  running at a different frequency, the frequency spectrum is less likely to have gaps and/or peaks, and be better able to capture defect in the product under test.  
         [0032]     The present invention utilizes a different size orifice  22  for each vibrator  12  or set of vibrators  12  thereby allowing each vibrator  12  to run at a different frequency. The orifice  22  can be machined in a single manifold  18  for cost effectiveness. The vibrator frequencies are stable and, therefore, easy to control. The orifice size can be optimized for each vibrator  12  and vibrator location on the table allowing for very tight control of the frequency range generated.  
         [0033]     The foregoing exemplary descriptions and the illustrative preferred embodiments of the present invention have been explained in the drawings and described in detail, with varying modifications and alternative embodiments being taught. While the invention has been so shown, described and illustrated, it should be understood by those skilled in the art that equivalent changes in form and detail may be made therein without departing from the true spirit and scope of the invention, and that the scope of the present invention is to be limited only to the claims except as precluded by the prior art. Moreover, the invention as disclosed herein, may be suitably practiced in the absence of the specific elements which are disclosed herein.