You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
     The present invention pertains to vibratory plates of the type used in various construction activities to tamp and compact soil and other loose base materials. A typical vibratory plate construction includes a flat, ground-engaging plate made of steel or other strong and rigid material. The plate is attached to an overlying frame and separated therefrom by elastomer shock mounts, typically two shock mounts near the front edge of the plate and two mounts near the rear edge of the plate. The prior art teaches a variety of orientations for the shock mounts depending on the properties of the elastomer material that are used to optimize vibratory compaction. 
     The frame carries an engine and the plate carries a rotary vibratory exciter connected to the engine by a drive belt. Vibratory plates may be uni-directional or bi-directional (reversible), but the present invention relates particularly to single direction vibratory plates. The driven exciter imparts vibratory forces to the plate and the underlying surface material being compacted. In a single direction vibratory plate, the exciter is typically mounted toward the front of the plate to maximize the amplitude of the vibratory forces and to facilitate forward movement of the plate. The prior art shows many different arrangements in the positioning of elastomeric shock mounts on vibratory plates, but often with no discussion as to how operation of the shock mounts in shear or compression can be utilized to optimize performance. 
     SUMMARY 
     In accordance with the present invention, conventional prior art shock mounts are attached to and positioned between the plate and the frame utilizing a simple construction that permits adjustment or fine tuning of the plate to optimize performance. 
     In accordance with one embodiment, the plate has an upwardly angled front edge that defines a lower front attachment face for a pair of front shock mounts. The plate also has an upwardly angled rear edge that defines a lower rear attachment face for a pair of rear shock mounts. The frame has a generally flat front edge that is spaced from and parallel to the lower front attachment face of the plate and defines an upper front attachment face for the front shock mounts. The frame also has an upwardly angled rear edge face that is spaced from and parallel to the lower rear attachment face of the plate and defines an upper rear attachment face for a pair of rear shock mounts. The front shock mounts are positioned between the lower front attachment face and the upper front attachment face and attached to extend between those faces. The central axis of each front shock mount extends perpendicular to the lower front attachment face and the upper front attachment face at an angle from the plane of the bottom surface of the plate in the range of about 20° to 40°, and a pair of rear shock mounts that are positioned between the lower rear attachment face and the upper rear attachment face and attached therebetween. A central axis of each rear shock mount extends perpendicular to the lower rear attachment face and the upper rear attachment face at an angle from the plane of the bottom surface of the plate in the range of about 50° to 90°. 
     In accordance with a presently preferred embodiment of the invention, the lower front edge of the plate is an integral extension of the plate and is joined to the plate along a laterally extending lower front bend line set to selectively position the central axes of the front shock mounts at an angle from the plane of the plate surface in the range of about 20° to 40°, and the upper front edge of the frame is an integral extension of the frame and is joined thereto along an upper front bend line set to position the front edge face of the frame parallel to the lower front face of the plate. 
     In a similar manner, the lower rear edge of the plate comprises an integral extension of the plate and is connected thereto along a lower rear bend line that is set to selectively position the central axes of the rear shock mounts at an angle in the range of 50° to 90°, and the upper rear face of the frame comprises an integral extension of the frame and is connected thereto along an upper rear bend line that is set to position the rear edge face of the frame parallel to the lower rear face of the plate. Thus, the front and rear bend lines of the plate and the respective front and rear bend lines of the frame permit adjustment of the axes of the shock mounts over a range of angles as indicated. 
     The elastomer material, preferably natural rubber, of the front shock mounts and the rear shock mounts has a preferred durometer in the range of about 25-45 Shore A on the Shore Hardness Scale. The front shock mounts are positioned to operate primarily in shear and the rear shock mounts are positioned to operate primarily in compression. 
     The engine is mounted atop the frame near the rear end thereof, and the exciter is mounted near the front end of the plate. The drive belt extends downwardly and forwardly from the engine to the exciter at an angle of about 30° from the horizontal. 
     The frame preferably comprises a recessed rear planar engine mounting surface and a raised front surface joined to the engine mounting surface by a generally vertical connecting plate. The engine mounting surface extends downwardly and forwardly and terminates in the flat front edge. The flat front edge extends generally perpendicular to the raised surface along a front bend line. The engine mounting surface extends rearwardly from the connecting plate and terminates in said rear edge. The rear edge extends at an acute angle to the engine mounting surface along a rear bend line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the vibratory plate of the present invention. 
         FIG. 2  is vertical sectional view through the vibratory plate of  FIG. 1  taken on line  2 - 2  thereof. 
         FIG. 3  is a perspective view similar to  FIG. 1 . 
         FIG. 4  is a front view of the vibratory plate. 
         FIG. 5  is an exploded view of the vibratory plate. 
         FIG. 6  is an enlarged detail of the rear shock mount in  FIG. 2  taken on line  6 - 6  thereof. 
         FIG. 7  is an enlarged detail of the front shock mount in  FIG. 2  taken on line  7 - 7  thereof. 
     
    
    
     DETAILED DESCRIPTION 
     Referring initially to  FIGS. 1 and 2 , a vibratory plate  10  includes, as its main components, a plate  11  having a planar bottom working surface  12 , a frame  13  mounted above plate  11  and isolated therefrom by a pair of front shock mounts  14  and a pair of rear shock mounts  15 . The frame carries an engine  16  that is operative to drive a vibratory exciter  17  mounted to the forward portion of the frame  14  and driven by a drive belt  18  connecting the engine output shaft and the shaft of the exciter. The engine  16  is mounted toward the rear of the frame  13  where also are located a fuel tank  20 , a water tank  21  and related accessories. The conventional U-shaped operator handle  22  is attached by its lower ends to the rear of the frame  13 . Thus, the shock mounts  14  and  15  isolate the frame  13  and the handle  22  from the vibratory plate  10 . 
     The plate  11  is formed from a single steel sheet providing the planar bottom surface  12 , an upwardly angled front edge  23  and an upwardly angled rear edge  24 . The upwardly angled front edge defines a lower front attachment face  25  for the front shock mounts  14  and the rear edge  24  defines a lower rear attachment face  26  for the rear shock mounts  15 . 
     The frame  13  is formed from a single steel sheet having a number of laterally extending bends, the functions of which will be described below. The frame includes a generally flat front edge  27  that, in the mounted position, is parallel to the front edge  23  and lower front attachment face  25  of the plate  11  and defines an upper front attachment face  28  for the front shock mounts  14 . The frame  13  also includes an upwardly angled rear edge  29  that is spaced from and parallel to the lower rear attachment face  26  of the plate  11  and defines an upper rear attachment face for the rear shock mounts  15 . 
     The shock mounts  14  and  15  may be identical in construction and in the flexible elastomer material of which they are made. The elastomer material is preferably natural rubber having a durometer in the range of about 25-45 Shore A on the Shore Hardness Scale and, preferably, a durometer of about 30 Shore A on the Shore Hardness Scale. The front shock mounts  14  are mounted between the lower front attachment face  25  of the plate and the upper front attachment face  28  of the frame  13 . The rear shock mounts  15  are attached between the lower rear attachment face  26  of the plate and the upper front rear attachment face  30  of the frame  13 . Each shock mount  14  or  15  is preferably of a cylindrical shape. Each end of shock mount  14  or  15  includes a rigid frustoconical end plate  41  that is bonded to the elastomer material. Prior to bonding, a nut  32  is welded to the end plate  41  to provide attachment for the shock mount to one of the attachment faces  25 ,  26 ,  28  and  30  using a bolt  31  and washer  33 . The front shock mounts  14  are positioned between the lower front attachment face  25  and the upper front attachment face  28  at an angle from the plane of the bottom surface  12  of the plate in the range of about 20° to about 40°. The rear shock mounts  15  are positioned between the lower rear attachment face  26  of the plate  11  and the upper rear attachment face  30  of the frame at an angle from the plane of the bottom surface  12  of the plate in the range of about 50° to about 90°. Preferably, the mounting angle of the front shock mounts  14  is about 30° and the mounting angle of the rear shock mounts  15  is about 60°. 
     The angles at which the shock mounts  14  and  15  are mounted with respect to the horizontal has a significant effect on the manner in which vibrations from the plate-mounted exciter  17  are transmitted to the plate  11 . This results in a greater amplitude of vibration toward the front of the plate which beneficially affects both compaction efficiency and the uni-directional movement of the plate. To provide these benefits in the vibratory plate of the present invention, the angles of the shock mounts  14  and  15  are carefully controlled to optimize compaction and, at the same time, minimize the transmission of vibrations to the frame and the operator. As indicated, the front shock mounts  14  are positioned so their axes A preferably extend at a shallow angle of about 30° to the horizontal. Rear shock mounts  15 , on the other hand, are mounted with their axes B at a substantially greater angle, preferably 60° to the horizontal. 
     However, the simple construction of the plate  11  permits fine tuning of the positions of the shock mounts  14  and  15  to further optimize performance. Because the front shock mounts  14  must handle the high amplitude movement from the exciter and, in addition, the horizontal load created by drive belt tension, the front shock mounts are positioned at an angle closer to the horizontal than to the vertical, causing the shock mounts to work primarily in shear. This permits greater movement in the shock mounts to accommodate base plate movement, as well as compression of the mount to accommodate belt tension. 
     The rear shock mounts  15 , on the other hand, are positioned to support the vertical load from the engine and are thus positioned at an angle closer to the vertical than to the horizontal. This permits the shock mounts to work primarily in compression, allowing the mount to provide support without causing the shock mount material to be overstressed. 
     In order to further enhance performance of the vibratory plate, the angular positioning of the shock mounts may be adjusted slightly within the ranges set forth above. Changing these angles may be facilitated by positioning the integral front edge  23  of the plate  11  to selectively bend the front edge of the plate on a lateral lower front bend line  34  and, correspondingly, the integral front edge  27  of the frame  13  can be bent slightly along the upper front bend line  35  to reset the position of the upper front edge  27  of the frame parallel to the lower front edge  23  of the plate. In a similar manner, the integral lower rear edge  24  of the plate is joined to the plate along a lower rear bend line  36  to permit selective positioning of the rear edge  24 . An upper rear bend line  37  is set to selectively position the upper rear edge  29  of the frame parallel to the lower rear edge  24  of the plate. This type of angular adjustment of the plate and the frame is relatively easy with the construction of the plate of the present invention. 
     The engine  16  is mounted on the frame  13  near the rear end of the frame. As is previously mentioned, the exciter  17  is mounted near the front end of the plate such that the drive belt  18  extends downwardly and forwardly from the engine to the exciter at an angle preferably of about 30°, but could be adjusted anywhere in the range of about 20° to 40°. The frame  13  includes a recessed rear planar engine mounting surface  38  and a raised front surface  39  that is joined to the engine mounting surface by a generally vertical connecting surface  40 . The raised front surface  39  extends downwardly and forwardly to terminate in the flat front edge  27  of the frame  13 . The flat front edge  27  extends generally perpendicular to the raised front surface  39  along the front bend line  35 . The engine mounting surface  38  extends rearwardly from the connecting surface  40  and terminates in the rear edge  29 . The rear edge extends at the preferred acute angle of about 30° to the engine mounting surface  38  along the upper rear bend line  37 . 
     To summarize briefly, the front shock mounts  14  are angled to operate primarily in shear to accommodate the higher amplitude vibrations at the front of the plate. The rear shock mounts  15  are positioned to operate primarily in compression to provide stability to the frame and engine and to isolate the amplitude of the vibrations at the rear of the plate which are already lower as a result of the forward mounting of the exciter. Angular adjustment may be limited to only the front of the plate or only to the rear of the plate, or to both, as described above.

Summary:
A vibratory compaction plate utilizes pairs of front and rear shock absorbing mounts, each pair of which is set at a different angle with respect to the horizontal plate to optimize the respective shear and compression capabilities and optimize performance. A front mounted vibratory exciter and a rear mounted engine provide different performance capabilities that are optimized by the mounting angles. A flat sheet metal plate and sheet metal frame permit the angles at which the shock mounts are oriented to be adjusted along laterally extending end lines to fine tune performance.