Abstract:
A compactor machine of the kind controlled by a pedestrian operator. The machine includes a base plate, an operative unit mounted on the base plate, a support plate, and a main frame. The operative unit causes the base plate to vibrate during use of the machine. The machine also includes a handle by which the operator controls the machine during use. A plurality of damping mounts attach a secondary frame to the main frame at a point distant from the base plate and the handle is mounted on the secondary frame to reduce the transmission of vibrations to an operator holding the handle.

Description:
BACKGROUND TO THE INVENTION 
     The invention relates to a compactor machine and in particular to one of the kind operated by a pedestrian for fairly light compacting of the ground. 
     Compactor machines of this kind are generally known as forward vibrating plate compactors, and many slightly different forms are known. In general they comprise an engine which transmits power via a pulley belt to an eccentric mass unit attached to a base plate. The mass is rotated generating a centrifugal force, and simultaneously applying a downward force with motion in a forward direction. The machine is guided by a pedestrian operator via a steering handle. 
     A major problem with many of the prior art compactors of this type is the level of vibration transmitted to the hands of the operator, and generally known as Hand-Arm Vibration (H.A.V.). Various approaches to the problem have been tried without much success, as significant vibration is still transmitted. This can lead to a medical condition, commonly known as Vibration White Finger, in operators who use these machines for extended periods of time, and which is clearly undesirable. The European Union has issued guidelines for safe levels of H.A.V., which can be experienced over an eight hour duration, of 2.5 ms −2 . If manufacturers produce machines with levels of H.A.V. higher than this level they are required to state this in their product literature. 
     Clearly, if the level of H.A.V. can be reduced the operators&#39; health and comfort are considerably enhanced, and longer working periods can also be contemplated. 
     It is an object of the present invention to mitigate the above described problem. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided compactor machine of the kind controlled by a pedestrian operator and including a base plate, an operative unit, mounted on the base plate, and having a support plate and a main frame, and means to cause the base plate to vibrate when in use, and a handle by which the operator controls the machine in use, wherein the compactor machine further comprises a secondary frame mounted on the main frame by means of a plurality of first damping mounts and wherein the handle is mounted on the secondary frame. 
     Preferably the secondary frame is mounted on the main frame distant from the base plate. 
     The handle may be pivotally mounted on the secondary frame. 
     Preferably the plurality of first damping mounts comprises four arranged substantially in a rectangle in a plane substantially parallel to the base plate. Each first damping mount may be inclined upwardly and outwardly. 
     The main frame may substantially define the outer dimensions of the operative unit. 
     The plurality of first damping mounts may have a stiffness in the range 10 to 20 Nmm −1 , or it may be in the range 12.5 to 17.5 Nmm −1 . 
     Preferably the operative unit is mounted on the base plate by means of a plurality of second damping mounts. 
     The plurality of second damping mounts generally comprises four arranged substantially in a rectangle. 
     Conveniently the plurality of second damping mounts have a stiffness in the range 30 to 70 Nmm −1 , or it may be in the range 40 to 60 Nmm −1 . 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of a compactor machine according to the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
     FIG. 1 is a simplified side view of the compactor machine according to the invention; 
     FIG. 2 is a simplified plan view of the compactor machine of FIG. 1; 
     FIG. 3 is a simplified front view of the compactor machine of FIGS. 1 and 2; 
     FIG. 4 is a partially exploded perspective view of the compactor machine of FIGS. 1 and 2; and 
     FIG. 5 is an enlarged exploded view of the area referenced C on FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the Figures, a compactor machine  10  is of the kind generally known as a forward vibrating plate compactor. It includes a base plate  12  on which is supported an operative unit  14  by means of primary damping mounts  16 . There are four primary damping mounts  16  arranged in a rectangle, two on each side of the machine  10  with their outer edges separated by 295 mm. The pairs on each side of the machine  10  are themselves separated forwardly and rearwardly, with their centers 220 mm apart. The primary damping mounts  16  take the form of relatively stiff rubber having a stiffness in the range 30 to 70 Nmm −1 , with the value of 50 Nmm −1  being preferred in many instances. 
     The operative unit  14  includes a support plate  18 , with mounted thereon conventional means to cause the base plate  12  to vibrate in use. Such means comprise an engine  20 , an eccentric mass  22  mounted on the base plate  12  and driveable by the engine  20  by means of a drive belt  24 . A fuel tank  26  supplies fuel for the engine  20 . 
     The frequency of operation of the machine  10  is 98 Hz, but could generally be any where in the range 90-105 Hz. The machine  10  has a weight of 75 kg, but that generally could lie in the range 65-85 kg. Clearly machines of this kind could also be manufactured with operating frequencies or weights outside these ranges. 
     The operative unit  14  also includes a main frame  28  which has two tubular parts  28   a  and  28   b  one on each side of the machine  10 , and which are each substantially “C” shaped, with one end secured to the support plate  18  at the rear and the other end secured to the support plate  18  at the front. The main frame  28  also has cross braces between the two parts  28   a  and  28   b , two straight cross-braces  28   c  and two with upturned ends  28   d  at the top. Thus in this embodiment the support plate  18  and main frame  28  between them substantially define the outer dimensions of the operative unit  14 . 
     The compactor machine  10  further comprises a secondary frame  30  which is substantially rectangular in shape and which is mounted upon the main frame  28  by means of damping mounts  32 . The secondary frame  30  is cast from aluminum alloy, but may be formed of other materials and by other techniques, e.g. from lengths of steel tube bent and welded. 
     In this embodiment there are four damping mounts  32  arranged in a rectangle, two on each side of the machine  10  with their outer edges separated by 340 mm. Each pair is separated forwardly and rearwardly, with their centers 340 mm apart. The forward damping mounts  32  are located 95.5 mm in front of the center of the engine  20 . 
     The damping mounts  32  are not arranged horizontally, but rather are located on the ends of cross-members  28   d  of the main frame  28  which are upturned at their outer edges. Thus the damping means  32  are inclined upwardly and outwardly at an angle of approximately 20 degrees to the horizontal. 
     The damping mounts  32  take the form of relatively softer rubber having a stiffness in the range 10 to 20 Nmm −1 , with the value of 15 Nmm −1  being preferred in many instances. 
     A steering handle  34 , with a grip portion  36 , is pivotally secured to the secondary frame  30 , such that it may be used at a comfortable angle of choice by an operator, and folded flat towards the machine  10  for storage. The handle  34  is pivoted 70 mm in front of the rearward damping mounts  32 . 
     The handle  34  is conveniently formed from bent steel tube and has a cross-member  35  towards its upper end. The cross-member  35  has been formed to reduce transmission of vibrations up the handle  34  best when formed of solid bar, rather than tube with a weight in excess of 1 kg. 
     The handle  34  is lockable at any desired position relative to the operative unit  14 , as this has been found to further reduce the transmission of vibrations to the grip portion  36  when compared with “floating” handles. The locking arrangement is shown in FIG.  5 . Two lugs  31  extend upwardly from the top of the secondary frame  30 , each of which has an inwardly facing square recess  31   a , and an opening  31   b  in the center thereof. The handle  34  has at each end a boss  33  with an outwardly facing square recess  33   a , and an opening  33   b  in the center thereof. Four serrated inserts  37  have square protuberances  37   a  on their rear faces and central openings  37   b . An insert  37  is received in each of the square recesses  31   a  and  33   a  such that pairs of inserts  37  are facing each other and the serrations can inter-engage. 
     To hold the components together bolts  38  are passed through the aligned openings  31   b ,  37   b ,  33   b  and nuts  39 , adapted for use by hand, are screwed onto their threads, various washers being used as desired. 
     To secure the handle  34  at the desired angle to the operative unit  14  the operator simply loosens off the two nuts  39  such that the serrations on the inserts  37  are no longer forced into engagement with each other, pivots the handle  34  to the desired angle and re-tightens the nuts  39 . 
     This arrangement for the locking and pivoting of the handle  34  has a number of advantages. One of these is that the serrated inserts  37 , which are the parts that will wear in use, are readily replaceable without the use of tools. 
     Also secured to the secondary frame  30 , towards the front, i.e. distant from the steering handle  34 , is a lifting handle  40  to assist in lifting the machine  10  when required. 
     The embodiment described above provides the advantage that the damping mounts  32  and the general arrangement of the main and secondary frames  28 ,  30  significantly reduces the vibrations passed from the operative unit  14  to the steering handle  34 , and thus reduces the vibration transmitted to the operator&#39;s hands. 
     Variations to the above described embodiment may be made whilst remaining within the scope of the invention. For example there may be more or fewer damping mounts  16  and/or  32 , and they may be arranged in other ways. Further, the damping mounts  32  and  16  themselves need not be made of rubber but may be formed of any appropriate material. The various dimensions given above may also be varied as appropriate for other weights of machine and individual components such as the engine  20 . Likewise the weight and frequency of operation may vary outside the ranges described if appropriate. 
     In the present specification “comprise” means “includes or consists of” and “comprising” means “including or consisting of”. 
     The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.