Abstract:
In a conventional impact generator, a great shock is generated when a weight collides with a rotary member, and a rotary shaft of the rotary member and a bearing supporting the rotary shaft receive the great shock. Therefore, it is necessary to employ a bearing having a great load capacity. Furthermore, great vibrations and noises are also generated in the impact generator. A rotary member ( 10 ) is rotatably supported by rotary shafts ( 11 ) and ( 12 ). A weight ( 30 ) is movably held by the rotary member ( 10 ). A shock absorber ( 40 ) for absorbing, by elastic force, a shock generated between the weight ( 30 ) and the rotary member ( 10 ) is provided between the weight ( 30 ) and the rotary member ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an impact generator for rotating a weight by means of a rotary member and striking a struck member with the weight, thereby continuously generating impact force for working. 
     2. Description of the Related Art 
     An impact generator is a device for continuously generating impact force (shock force). Such impact generator may be applied to a crusher for crushing concrete or hardened asphalt in a road construction, a building site and the like, a reaper for cutting off fruit and branches of plants, and a root cutter for cutting off roots of plants, for example. 
     By way of example, Japanese Laid-Open Patent Publication No. Hei 7-164351 has disclosed an impact generator according to the prior art. FIG. 5A is a transverse sectional view showing the impact generator D 100  according to the prior art and FIG. 5B is a longitudinal sectional view showing the impact generator D 100  according to the prior art. The impact generator D 100  is applied to a reaper and serves to give continuous impact force to a cutting blade  191 . The impact generator D 100  converts rotating force transmitted from a power unit such as an engine into reciprocating impact force and transmits the reciprocating impact force to the cutting blade  191 . 
     As shown in FIGS. 5A and 5B, the impact generator D 100  comprises a rotary member  110  and a weight  130 . The rotary member  110  is rotatably supported in a casing  150  by means of rotary shafts  111  and  112 . The rotary member  110  has plate-shaped holding portions  113  and  114 . The plate-shaped holding portions  113  and  114  are connected to each other through a connecting shaft portion  115 . The connecting shaft portion  115  is positioned eccentrically from a center C 100  of rotation of the rotary member  110 . Elliptical holes  113   a  and  114   a  are formed on the plate-shaped holding portions  113  and  114 , respectively. A cylindrical weight  130  is held in the holes  113   a  and  114   a . The holes  113   a  and  114   a  have diameters which are larger than the diameter of the weight  130 . Therefore, the weight  130  can freely move to some extent in the holes  113   a  and  114   a . More specifically, the weight  130  is movably held by the rotary member  110 . 
     When the weight  130  performs a circular motion around the rotary shafts  111  and  112  of the rotary member  110  by the rotation of the rotary member  110 , the top of a tappet  192  positioned to interfere with the locus of the circular motion is struck with the weight  130 . The tappet  192  is supported movably in an axial direction thereof (in a right and left direction in FIGS.  5 A and  5 B). Therefore, the tappet  192  is struck, thereby giving an impact to the cutting blade  191  positioned on the left of the tappet  192  in FIGS. 5A and 5B. Thus, when the rotary member  110  is rotated, continuous impact force is given to the cutting blade  191 . 
     In the above-mentioned impact generator D 100 , the tappet  192  is struck with the weight  130 , thereby generating the impact force. However, when the tappet  192  is struck with the weight  130 , the weight  130  receives a reaction in a direction toward the center C 100  of rotation of the rotary member  110  from the tappet  192 . Then, the weight  130  collides with points P 101  and P 102  on internal walls defining the holes  113   a  and  114   a  which are the closest to the center C 100  of rotation. By the collision, the rotary shafts  111  and  112  supporting the rotary member  110  and bearings  151  and  152  supporting the rotary shafts  111  and  112  receive a shock. Accordingly, the load capacities of the bearings  151  and  152  should be increased. 
     By the collision, moreover, great vibrations are also given to a machine (a reaper or the like) to which the impact generator is applied. Further for this reason, great noises are made in some cases. 
     SUMMARY OF THE INVENTION 
     In consideration of above-mentioned circumstances, it is an object of the invention to relieve a shock to be given to a rotary shaft of a rotary member and a bearing supporting the rotary shaft. 
     In order to solve the above-mentioned problems, the invention provides an impact generator comprising a rotary member rotatably supported by a rotary shaft for being rotated upon receipt of rotating force, a weight movably held by the rotary member for striking a struck member, and a shock absorber provided between the weight and the rotary member for absorbing, by elastic force, a shock generated between the weight and the rotary member. 
     According to the impact generator described above, the shock force generated between the weight and the rotary member is absorbed by the shock absorber. Consequently, the shock to be given to the rotary member can be relieved. Accordingly, it is also possible to relieve the shocks to be given to the rotary shaft supporting the rotary member and a bearing supporting the rotary shaft. 
     The shock absorber can be provided in any configuration if it is provided between the weight and the rotary member to absorb the shock therebetween. For example, the rotary member may have two plate-shaped holding portions provided in almost parallel with each other for holding the weight, and a connecting shaft portion for connecting the two plate-shaped holding portions in a position which is eccentric from the center of rotation of the rotary member, and the shock absorber may be provided between the weight and the connecting shaft portion. 
     Moreover, any shock absorber capable of absorbing a shock by elastic force can be employed. For example, the shock absorber may be constituted by a coil spring, and a supporting hole may be formed in the connecting shaft portion of the rotary member, fitting one of ends of the coil spring therein to support the coil spring. 
     These objects as well as other objects, features and advantages of the invention will become more apparent to those skilled in the art from the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing a reaper employing an impact generator according to a preferred embodiment of the invention; 
     FIG. 2A is a view showing a state in which fruit and branches of an oil palm are cut off by the reaper of FIG. 1; 
     FIG. 2B is a view showing a state in which roots of plants are cut off by the root cutter whose basic structure is the same as the reaper of FIG. 1; 
     FIG. 3A is a transverse sectional view showing the impact generator; 
     FIG. 3B is a longitudinal sectional view showing the impact generator; 
     FIG. 4 is a perspective view showing main members of the impact generator, a part of which is cut away; and 
     FIG. 5A is a transverse sectional view showing an impact generator according to the prior art; 
     FIG. 5B is a longitudinal sectional view showing the impact generator according to the prior art; 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the invention will be described below with reference to the drawings. 
     An impact generator according to the invention can be applied to a reaper, a root cutter, a crusher and the like, for example. FIG. 1 is a perspective view showing a reaper A 1 . An impact generator D according to an embodiment of the invention is applied to the reaper A 1 . 
     First of all, the basic structure of the reaper A 1  will be described with reference to FIG.  1 . The reaper A 1  comprises an engine  70  acting as a power unit, a rod member  80 , the impact generator D, a cutting blade  91 , and the like. 
     The engine  70  generates rotating force. 
     The rod member  80  connects the engine  70  to the impact generator D. The rod member  80  is constituted by a hollow pipe in which a drive shaft  81  penetrates. The rotating force generated by the engine  70  is transmitted to the impact generator D by the drive shaft  81  penetrating the rod member  80 . 
     The impact generator D converts the rotating force generated by the engine  70  into continuous striking force (impact force) of reciprocating. 
     The cutting blade  91  is formed by welding a plate-shaped blade portion  91   c  to a shank portion  91   a . The shank portion  91   a  is inserted into a blade attaching portion  16  of the impact generator D. The shank portion  91   a  is attached to the blade attaching portion  16  such that it can be displaced in the longitudinal direction of the reaper A 1  by a predetermined length. The shank portion  91   a  receives a periodic impact by the striking force generated by the impact generator D through a tappet  92  (refer FIGS.  3 A and  3 B). The impact is directed from the shank portion  91   a  toward the edge of the plate-shaped blade portion  91   c.    
     A first grip portion  82  and a second grip portion  83  are formed in the rod member  80  of the reaper A 1 , and an operation lever  84  is attached adjacently to the first grip portion  82 . The operation lever  84  serves to control the speed of the engine  70 . The engine  70  and the drive shaft  81  penetrating the rod member  80  are connected to each other through a centrifugal clutch. When the operation lever  84  is released to bring the engine  70  into an idling state, the centrifugal clutch is brought into a disconnecting state so that the rotating force of the engine  70  is not transmitted to the impact generator D. When the operation lever  84  is gripped more tightly, the engine speed of the engine  70  is gradually increased so that the centrifugal clutch is connected. Consequently, the impact generator D starts to give a periodic impact to the shank portion  91   a  of the cutting blade  91 . When the operation amount of the operation lever  84  is further increased, the engine speed of the engine  70  is increased so that an impact cycle (striking cycle) is shortened. 
     Also in the case where the impact generator according to the invention is applied to a root cutter, a basic structure thereof is the same as in the reaper A 1 . 
     FIG. 2A shows a state in which fruit and branches of an oil palm B 1  are cut off by the reaper A 1  and FIG. 2B shows a state in which roots of a plant B 2  are cut off by the root cutter A 2 . 
     Referring to FIG. 2A, an operator grips the first and second grip portions  82  and  83  by both hands, thereby supporting the reaper A 1 . One of operator&#39;s hands operates the operation lever  84  while gripping the first grip portion  82 . Then, the operator presses the edge of the cutting blade  91  against the base portion of the branch and the stem portion of the fruit while adjusting an impact cycle by the operation of the operation lever  84 , thereby cutting off the branches and the fruits by impact force. 
     Referring to FIG. 2B, the operator operates the operation lever  84  while supporting the reaper A 2  by both hands. Then, the operator presses the edge of the cutting blade  91  against the root of the plant B 2  in the ground while adjusting the impact cycle by the operation of the operation lever  84 , thereby cutting off the root by the impact force. 
     FIG. 3A is a transverse sectional view showing the impact generator D and FIG. 3B is a longitudinal sectional view showing the impact generator D. FIG. 4 is a perspective view showing main members of the impact generator D, a part of which is cut away. 
     The impact generator D mainly comprises a rotary member  10 , a weight  30  and a coil spring  40  acting as a shock absorber. These members (the rotary member  10 , the weight  30  and the coil spring  40 ) are accommodated in a casing  50 . The cutting blade  91  is attached to the casing  50 . 
     The rotary member  10  is rotatably supported on the casing  50 . More specifically, the rotary member  10  has rotary shafts  11  and  12  protruded in a vertical direction (in FIG.  3 B). The rotary shafts  11  and  12  are supported on the casing  50  through bearings  51  and  52 . The bearing  51  supporting the upper rotary shaft  11  is a ball bearing, and the bearing  52  supporting the lower rotary shaft  12  is a needle bearing. 
     On the other hand, one of the ends of the drive shaft  81  penetrating the rod member  80  is supported by a ball bearing  53  fixed to the casing  50 . The drive shaft  81  transmits rotating force generated by the engine  70  to the impact generator D. The drive shaft  81  and the rotary shaft  11  are connected to each other through a pair of gears  54  and  55 . The gear  54  is a driving gear and the gear  55  is a driven gear. The rotating force of the drive shaft  81  is converted by about 90 degrees in a rotating direction through the gears  54  and  55 , and is transmitted to the rotary member  10 . 
     The rotary member  10  has upper and lower plate-shaped holding portions  13  and  14  provided in almost parallel with each other. The upper and lower plate-shaped holding portions  13  and  14  are connected to each other through a cylindrical connecting shaft portion  15 . A central axis  15   a  of the connecting shaft portion  15  is positioned eccentrically from a center C of rotation of the rotary member  10 . 
     Elliptical weight holding holes  13   a  and  14   a  are formed in the upper and lower plate-shaped holding portions  13  and  14 , respectively. The weight  30  is held in the weight holding holes  13   a  and  14   a . The weight  30  is almost cylindrical and has upper and lower end portions entering in the weight holding holes  13   a  and  14   a , respectively. The weight holding holes  13   a  and  14   a  have diameters which are larger than the diameter of the weight  30 . Therefore, the weight  30  can freely move to some extent in the weight holding holes  13   a  and  14   a . More specifically, the weight  30  is movably held by the rotary member  10 . The weight  30  performs a circular motion around the center C of rotation of the rotary member  10  by the rotation of the rotary member  10 . The connecting shaft portion  15  has the function of acting as a balance weight for the weight  30  to perform a circular motion as well as the function of connecting the upper and lower plate-shaped holding portions  13  and  14 . 
     The coil spring  40  acting as a shock absorber is provided between the weight  30  and the rotary member  10 . A supporting hole  15   b  is formed in the connecting shaft portion  15 , and one of ends of the coil spring  40  is fitted in the supporting hole  15   b . Thus, the coil spring  40  is fixed to the connecting shaft portion  15 . The other end of the coil spring  40  abuts against the side face of the weight  30 . 
     A grease is put in the casing  50 , in particular, around the gears  54  and  55  and the rotary member  10 . 
     The tappet  92  acting as a struck member is accommodated in the casing  50  such that it can move in the axial direction thereof (in a right and left direction of FIGS.  3 A and  3 B). The struck member serves to directly receive striking force (impact force) from the weight  30  by the collision with the weight  30 . The tappet  92  is supported on a bush  56  fixed into the casing  50 . A portion between the bush  56  and the tappet  92  is sealed by an O ring  57  in order to prevent the grease in the casing  50  from leaking out. The casing  50  has a blade attaching portion  16  for attaching the cutting blade  91  thereto. The blade attaching portion  16  has an attaching hole in which the shank portion  91   a  of the cutting blade  91  is inserted. A notch portion  91   b  is formed on the side face of the shank portion  91   a . The blade attaching portion  16  is provided with a clamp  17 . The clamp  17  is engaged with the notch portion  91   b  for fixation. The cutting blade  91  can reciprocate in the axial direction thereof (in the right and left direction of FIGS. 3A and 3B) within a range in which the clamp  17  can interfere with the notch portion  91   b . More specifically, the clamp  17  has the function of preventing the cutting blade  91  from coming off and the function of regulating the range of the reciprocation of the cutting blade  91 . The tappet  92  interferes with the locus of the circular motion of the weight  30  when it is set in a rightmost position of FIGS. 3A and 3B within the moving range. Moreover, the tappet  92  does not interfere with the locus of the circular motion of the weight  30  when it is set in a leftmost position of FIGS. 3A and 3B within the moving range. Thus, the tappet  92  can reciprocate between an interference position where it interferes with the locus of the circular motion of the weight  30  and a noninterference position where it does not interfere with the locus of the circular motion of the weight  30 . 
     In the impact generator D having the above-mentioned structure, when the rotary member  10  is rotated by the rotation of the drive shaft  81 , the weight  30  held by the rotary member  10  is forced to the offside (outer side) of the weight holding holes  13   a  and  14   a  (on the side distant from the center of rotation of the rotary member  10  and the left side in FIGS. 3A and 3B) by centrifugal force and the force of the coil spring  40 , and performs a circular motion around the axial core of the rotary member  10  in this state. When the weight  30  disposed at the offside of the weight holding holes  13   a  and  14   a  collides with the tappet  92  set in the interference position to strike the tappet  92  in the direction toward the noninterference position (to the left in FIGS.  3 A and  3 B), the tappet  92  gives an impact to the cutting blade  91 . The cutting blade  91  and the tappet  92  try to move integrally in the direction toward the noninterference position (to the left in FIGS.  3 A and  3 B). The weight  30  is repelled in the direction toward the center C of rotation in the weight holding holes  13   a  and  14   a  upon receipt of a reaction from the tappet  92 . Consequently, the coil spring  40  is contracted to absorb shock force generated between the weight  30  and the rotary member  10 . The weight  30  repelled by the reaction of the tappet  92  collides with the points P 1  and P 2  on the internal walls defining the weight holding holes  13   a  and  14   a  which are the closest to the center C of rotation. However, even if the collision is caused, the shock given to the rotary member  10  is relieved by the coil spring  40 . Accordingly, the shock given to the rotary shafts  11  and  12  is relieved and the shock given to the bearings  51  and  52  is also reduced. Consequently, bearings having small load capacities can be employed for the bearings  51  and  52 . Moreover, a vibration generated on the impact generator D is also reduced, resulting in a smaller noise. By regulating a vacancy of the weight holding holes  13   a  and  14   a  (a range in which the weight  30  can freely move) and the elastic force of the coil spring  40 , the weight  30  can also be prevented from colliding with the points P 1  and P 2  on the internal walls defining the weight holding holes  13   a  and  14   a.    
     When the tappet  92  is struck, the cutting blade  91  gives impact force to the branches of the plants and the like which are positioned on an edge. thereof and are objects for working. By the cutting blade  91  is pressed against the objects for working or receives a reaction from the objects for working, the cutting blade  91  is then pushed back to the right in FIGS. 3A and 3B. The tappet  92  moves to the interference position again and is then struck with the weight  30  which has taken a round. Thus, the striking force is continuously given to the tappet  92 . 
     In the above mentioned embodiment, one coil spring  40  acting as a shock absorber has been provided in the almost central position of the connecting shaft portion  15  in the height direction in FIG. 3B. A plurality of coil springs, however, may be provided in a plurality of places of the connecting shaft portion  15  in the height direction. Moreover, the elastic force of the shock absorber can be caused to act on any position of the rotary member  10  where the shock given from the weight  30  to the rotary shafts  11  and  12  of the rotary member  10  can be absorbed. Furthermore, the elastic force of the shock absorber can be caused to act on the rotary member  10  and the weight  30  through a mediate member, that is, indirectly. In addition, the shock absorber may be constituted by a spring other than the coil spring or be constituted by using, as a main member, other elastic materials such as rubber and the like. 
     Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and/or function may be varied substantially without departing from the spirit of the invention and all modifications which come within the scope of the appended claims are reserved.