Abstract:
The objective is to improve durability while making it possible to maintain an excellent cutting plane and feeling of use with a simpler configuration. Disclosed is a tabletop circular saw for which a main body equipped with a saw blade that is rotated by the driving of a motor is provided to be capable of vertical movement on a base on which a material to be cut is placed; the output shaft of the motor is provided parallel to a spindle of the saw blade; and an automatic torque adjustment mechanism, which is equipped with a drive pulley, a follower pulley, and a belt, and which automatically adjusts the torque transmitted from the output shaft to the spindle according to the load when the saw blade rotates, is provided between the output shaft and the spindle.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a cutter such as a bench circular saw, a slide type circular saw. 
       BACKGROUND ART 
       [0002]    A conventional bench circular saw, for example, includes a body having a saw blade (cutting blade) on a base on which a workpiece is placed, which is rotated by a motor. The body moves vertically and is energized to the top dead center. Under a state the saw blade is rotated, the body is lowered resisting energization, and thereby the workpiece on the base can be cut. 
         [0003]    In such a bench circular saw, when the condition of pressing the body downward during cutting is uneven, the saw blade vibrates, thereby finishing of the cut surface and a feeling of usage are deteriorated. Therefore, a motor control means and a brake means are provided to relatedly control the rotational speed and torque of the motor. The motor control means detects the rotational speed of the motor or the saw blade and the load current of the motor, and then controls the rotational speed and the torque of the motor so that the rotational speed and the torque of the endless belt do not exceed the allowable rotational speed and allowable torque of the endless belt while the motor is driven. The brake means stops the motor by deceleration torque not exceeding the allowable transmission torque of the endless belt when the motor is braked (refer to Patent Document 1). 
       Citation List 
     Patent Literature 
       [0004]    [Patent Document 1] Japanese Patent Publication No. 3079937 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    However, even if such means are adopted, a problem of insufficient torque in cutting a large-sized workpiece cannot be addressed. On the other hand, when a gear ratio with a large speed reduction ratio is adopted, the rotational speed is insufficient, and cutting cannot be performed well at the beginning of cutting. 
         [0006]    Under such circumstance, the object of the present invention is to provide a cutter capable of responding a variety of cutting situations in order to maintain excellent cut surface and feeling of usage. 
       Solution to Problem 
       [0007]    In order to achieve the object, the invention described in claim  1  is a cutter including a body provided with a cutting blade rotating by a motor arranged so as to move vertically on a base on which a workpiece is placed, and an automatic torque adjusting mechanism arranged between an output shaft of the motor and a rotary shaft of the cutting blade, automatically adjusting torque transmitted from the output shaft to the rotary shaft according to a load in rotating of the cutting blade. 
         [0008]    “Rotary shaft” includes an intermediate shaft disposed in a preceding stage of the rotary shaft (spindle) to which the cutting blade is directly fixed, reducing the rotational speed of the output shaft of the motor, and transmitting the rotation to the rotary shaft. 
         [0009]    The invention described in claim  2  is the cutter according to claim  1  in which the automatic torque adjusting mechanism adjusts the torque steplessly. 
         [0010]    The invention described in claim  3  is the cutter according to claim  1  or  2  in which the automatic torque adjusting mechanism includes a driving pulley, a driven pulley, and an endless belt. The driving pulley is arranged in the output shaft and has a pair of pulley plates with the distance therebetween being adjustable. The driven pulley is arranged in the rotary shaft and has a pair of pulley plates with the distance therebetween being adjustable according to the load. The endless belt is stretched between the driving pulley and the driven pulley. Torque is adjusted by that the driven pulley changes the distance between the pulley plates according to the load to change a winding position of the belt steplessly, and thereby the driving pulley changes the distance between the pulley plates through the belt to change a winding position of the belt steplessly. 
         [0011]    The invention described in claim  4  is the cutter according to claim  3  in which the output shaft and the rotary shaft are protruded to either right or left same side of the body and are arranged parallel with each other. 
         [0012]    The invention described in claim  5  is the cutter according to any one of claims  1  to  3  in which the motor is arranged so that the output shaft is oriented in the front and rear direction. 
         [0013]    The invention described in claim  6  is the cutter according to any one of claims  1  to  5  in which the rotary shaft is made an intermediate shaft disposed in a preceding stage of a spindle to which the cutting blade is fixed, an idle gear is interposed between the intermediate shaft and the spindle, and torque of the intermediate shaft is transmitted to the spindle through the idle gear. 
       Advantageous Effects of Invention 
       [0014]    According to the invention described in claim  1 , due to adoption of the automatic torque adjusting mechanism, the cutting blade rotates by appropriate torque matching the load in response to a variety of cutting situations. Therefore, even when the belt is stretched between the output shaft and the rotary shaft, slippage of the belt can be prevented and vibration during cutting can be suppressed. Accordingly, durability is improved with a simple constitution, and an excellent cut surface and a feeling of usage are maintained. 
         [0015]    According to the invention described in claim  2 , in addition to the effects of claim  1 , torque adjustment more properly responding to the cutting situations becomes possible by adjusting torque steplessly. 
         [0016]    According to the invention described in claim  3 , in addition to the effects of claim  1  or  2 , the automatic torque adjusting mechanism utilizing the belt can be obtained easily. 
         [0017]    According to the invention described in claim  4 , in addition to the effects of claim  3 , the body can be made compact. 
         [0018]    According to the invention described in claim  5 , in addition to the effects of any of claims  1  to  3 , interference of the motor and the guide fence with each other in tilted cutting can be effectively prevented, and cutting performance can be secured. 
         [0019]    According to the invention described in claim  6 , in addition to the effects of any of claims  1  to  5 , a shift amount of the motor to the upper side can be gained which is effective in preventing interference of the motor and the guide fence with each other in tilted cutting. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is an overall elevation view of a bench circular saw. 
           [0021]      FIG. 2  is an explanatory drawing of a body. 
           [0022]      FIG. 3  is an explanatory elevation view of a bench circular saw of a modification. 
           [0023]      FIG. 4  is a cross-sectional view taken from line A-A of  FIG. 3 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0024]    Embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. 
         [0025]      FIG. 1  is an overall elevation view of a bench circular saw which is an example of a cutter. In a bench circular saw  1 ,  2  is a base, and a turntable  3  is mounted in the center thereof so as to turn horizontally. A guide fence  5  is stretched between right and left ends  4 ,  4  of the base  2  positioned on both sides of the turntable  3  so as to position a workpiece set on the turntable  3 . 
         [0026]    Further, an arm  6  is erected behind the turntable  3  so as to tilt to the right and left to the maximum of 45° respectively. A body  7  is provided with a motor  8  and a saw blade  10  that is a cutting blade, and is arranged at the upper end of the arm  6  under a state in which the body  7  is turnable in the vertical direction by a support shaft not shown and is energized to the top dead center by a torsion spring arranged in the support shaft portion. 
         [0027]    As shown in  FIG. 2 , in the body  7 , a motor housing  12  accommodating the motor  8  is laterally connected to the upper part of a blade case  11  accommodating the saw blade  10  vertically, and a spindle  13  to which the saw blade  10  is tightly fixed is pivoted inside the blade case  11 . Here, the motor  8  greatly shifts to the upper side from the spindle  13  that becomes the rotational center of the saw blade  10  so as not to interfere with the guide fence  5  when the arm  6  is tilted. 
         [0028]    Further, between an output shaft  9  of the motor  8  and the spindle  13  protruding to the right side of the body  7  to become parallel with each other,  2  pieces of first and second intermediate shafts  14 ,  15  are pivotally supported in parallel respectively. The output shaft  9  and the first intermediate shaft  14  are transmittingly rotated by a belt  23  of an automatic torque adjusting mechanism  20  that will be described below, and the first intermediate shaft  14  and the spindle  13  are transmittingly rotated so as to reduce the speed by mutual meshing of gears  16 - 18  tightly fixed to respective intermediate shafts  14 ,  15  and the spindle  13 . 
         [0029]    Further, the automatic torque adjusting mechanism  20  includes a driving pulley  21  arranged in the output shaft  9 , a driven pulley  22  arranged in the first intermediate shaft  14 , and the endless belt  23  stretched between both pulleys  21 ,  22 . 
         [0030]    First, the driving pulley  21  includes a disk-shaped fixed pulley plate  25 , a disk-shaped movable pulley plate  26 , and a coil spring  28 . The disk-shaped fixed pulley plate  25  is arranged on the side of a ball bearing  24  pivotally supporting the end of the output shaft  9  and rotates integrally with the output shaft  9 . The disk-shaped movable pulley plate  26  is arranged so as to oppose the fixed pulley plate  25  and connected to the output shaft  9  by spline connection so as to integrally rotate and axially move. The coil spring  28  is provided between a flange  27  circumferentially arranged on the root side of the output shaft  9  and the movable pulley plate  26 , and energizes the movable pulley plate  26  to the fixed pulley plate  25  side. The belt  23  has a cross-section of a generally V-shape with the width becoming narrower as it goes toward the center, and the opposing faces against the fixed pulley plate  25  and the movable pulley plate  26  are of a conical shape matching the shape of the belt  23 . 
         [0031]    On the other hand, the driven pulley  22  also includes a disk-shaped fixed pulley plate  30 , a disk-shaped movable pulley plate  31 , a fixed cam  32 , and a coil spring  34 . The disk-shaped fixed pulley plate  30  is arranged on the side of a ball bearing  29  pivotally supporting the end of the first intermediate shaft  14  and rotates integrally with the first intermediate shaft  14 . The disk-shaped movable pulley plate  31  is arranged so as to oppose the fixed pulley plate  30  and externally mounted on the first intermediate shaft  14 . The movable pulley plate  31  rotates separately from the first intermediate shaft  14  and axially moves. The fixed cam  32  is arranged between the movable pulley plate  31  and the gear  16  so as to rotate integrally with the first intermediate shaft  14 , and is provided with cam claws  33 ,  33 , . . . of a triangle shape protruding toward the movable pulley plate in the periphery. The coil spring  34  is arranged between the movable pulley plate  31  and the fixed cam  32 , and energizes the movable pulley plate  31  toward the fixed pulley plate  30 . 
         [0032]    Further, the opposing faces against the fixed pulley plate  30  and the movable pulley plate  31  are also of a conical shape matching the cross-sectional shape of the belt  23 . Cam claws  35 ,  35 , . . . of a triangle shape meshing with the cam claw  33  of the fixed cam  32  are protrudingly arranged on the fixed cam  32  side in the periphery of the movable pulley plate  31 . Mutual engagement of the cam claws  33 ,  35  is maintained constantly regardless of axial movement of the movable pulley plate  31  described below. Furthermore, here, the diameter of respective pulley plates  25 ,  26  of the driving pulley  21  is set to be larger than the diameter of respective pulley plates  30 ,  31  of the driven pulley  22 , and the energizing force of the coil spring  28  on the driving pulley  21  side is set to be greater than that of the coil spring  34  on the driven pulley  22  side. 
         [0033]    In the bench circular saw  1  constituted as described above, when a switch not shown arranged in the body  7  is operated ON, the motor  8  is driven to rotate the output shaft  9 , and the rotation is transmitted to the driven pulley  22  from the driving pulley  21  through the belt  23  to rotate the first intermediate shaft  14 . Accordingly, rotation of the first intermediate shaft  14  is transmitted to the spindle  13  through the second intermediate shaft  15  while reducing the speed to rotate the saw blade  10  along with the spindle  13 . 
         [0034]    Here, under a no-load state in which the saw blade  10  does not cut the workpiece, in the driving pulley  21 , the movable pulley plate  26  is pressed by the coil spring  28  to the side of and approaches the fixed pulley plate  25 , and the belt  23  dislocates to the upper side guided by the conical opposing faces of both pulley plates  25 ,  26 . Thus, the pulley diameter defined by the winding position of the belt  23  between both pulley plates  25 ,  26  increases. On the other hand, in the driven pulley  22 , due to dislocation of the belt  23  to the upper side, the movable pulley plate  31  moves to the fixed cam  32  side resisting energization of the coil spring  34  and departs from the fixed pulley plate  30 . Thus, the pulley diameter defined by the winding position of the belt  23  between both pulley plates  30 ,  31  decreases. Accordingly, the speed ratio (pulley diameter of driving pulley  21 /pulley diameter of driven pulley  22 ) increases. 
         [0035]    When the body  7  is lowered and the workpiece on the turntable  3  is cut by the saw blade  10 , rotational resistance (load) occurs in the saw blade  10  by cutting into the workpiece. Then, in the driven pulley  22 , speed difference is generated between the movable pulley plate  31  and the fixed cam  32 , and therefore the movable pulley plate  31  departs from the fixed cam  32  while the cam claws  33 ,  35  slidingly contact with each other. Therefore, the distance between the movable pulley plate  31  and the fixed pulley plate  30  narrows, the belt  23  dislocates to the lower side as shown in  FIG. 2 , and the pulley diameter increases. On the other hand, in the driving pulley  21 , by dislocation of the belt  23  to the lower side, the movable pulley plate  26  moves toward the direction departing from the fixed pulley plate  25  resisting energization of the coil spring  28 , and the pulley diameter decreases. Accordingly, the speed ratio decreases and the torque of the first intermediate shaft  14  increases. Because the dislocation amount increases  steplessly as the rotational resistance increases, the speed ratio also changes steplessly. 
         [0036]    Thus, since the speed ratio decreases according to the rotational resistance, the torque transmitted from the first intermediate shaft  14  to the spindle  13  through the second intermediate shaft  15  increases, and the saw blade  10  rotates by optimum torque. 
         [0037]    When cutting finishes and the rotational resistance disappears, in the driving pulley  21 , the movable pulley plate  26  moves toward the fixed pulley plate  25  by energization of the coil spring  28 , therefore the belt  23  dislocates to the upper side and the pulley diameter increases. On the other hand, in the driven pulley  22 , the movable pulley plate  31  moves toward the fixed cam  32  by dislocation of the belt  23  to the upper side, and the pulley diameter decreases. Accordingly, the speed ratio is restored to the initial value. 
         [0038]    As described above, according to the bench circular saw  1  of the embodiment, the body  7  provided with the cutting blade  10  rotating by the motor  8  is arranged on the base  2  on which a workpiece is placed so as to move vertically, and the automatic torque adjusting mechanism  20  automatically adjusting torque transmitted from the output shaft  9  to the spindle  13  according to the load in rotating of the cutting blade  10  is arranged between the output shaft  9  of the motor  8  and the spindle  13  of the saw blade  10 . Thus, the saw blade  10  rotates by appropriate torque matching the load in response to a variety of cutting situations such as cutting a large-sized workpiece, the beginning of cutting and the like, therefore slippage of the belt  23  can be prevented and vibration during cutting can be suppressed. Accordingly, shortening of the life of the belt  23  is prevented with a simple constitution so that durability is improved and an excellent cut surface and a feeling of usage are maintained. 
         [0039]    In particular, because the torque is adjusted steplessly in the automatic torque adjusting mechanism  20 , torque adjustment more properly responding to the cutting situations becomes possible. 
         [0040]    The automatic torque adjusting mechanism  20  is constituted to include the driving pulley  21  arranged in the output shaft  9  and having a pair of pulley plates  25 ,  26  with the distance therebetween being adjustable, the driven pulley  22  arranged in the spindle  13  and having a pair of pulley plates  30 ,  31  with the distance therebetween being adjustable according to the load, and the endless belt  23  stretched between the driving pulley  21  and the driven pulley  22 . Torque is adjusted by that the driven pulley  22  changes the distance between both pulley plates  30 ,  31  according to the load to change the winding around position of the belt  23  steplessly, thereby the driving pulley  21  changes the distance between both pulley plates  25 ,  26  through the belt  23  to change the winding position of the belt  23  steplessly, and therefore the automatic torque adjusting mechanism utilizing the belt  23  can be obtained easily. 
         [0041]    Further, as the output shaft  9  and the spindle  13  are protruded to the same side of the body  7  (here, right side) so as to be arranged parallel with each other, the body  7  can be made compact. 
         [0042]    Furthermore, although the intermediate shafts are arranged by 2 pieces in the above embodiment, the number of pieces can be increased or decreased as appropriate. Alternatively, the intermediate shaft can be eliminated and the driven pulley of the automatic torque adjusting mechanism can be mounted directly on the spindle. Further, arrangement of the fixed pulley plate and the movable pulley plate can be opposite between the driving pulley and the driven pulley, and the movable pulley plate of the driving pulley can be made axially movable by means of key connection. 
         [0043]    On the other hand, in the above embodiment, in order not to interfere with the guide fence  5  in tilting of the arm  6 , the motor  8  is shifted to the upper side of the spindle  13  and is connected laterally to the blade case  11 . A modification shown in  FIGS. 3 ,  4  is also possible to the same effect. That is, in a bench circular saw  1   a,  the motor housing  12  accommodating the motor  8  is connected to the upper part of the right side face of the blade case  11  in the front and rear direction so as to direct the output shaft  9  toward the near side. Even if the motor  8  is arranged so that the output shaft  9  is oriented in the front and rear direction, the protruding amount of the output shaft  9  to the right is further reduced, thereby interference between the motor housing  12  and the guide fence  5  in tilted cutting can be effectively prevented, and cutting performance can be secured. According to the direction of the output shaft  9 , the first intermediate shaft  14  is also pivotally supported in the front and rear direction therebeneath. In this case, the automatic torque adjusting mechanism  20  between the output shaft  9  and the first intermediate shaft  14  is the same with that of the above embodiment. 
         [0044]    Further, in the blade case  11 , the second intermediate shaft  15  orthogonal in a plan view to and with the same height with the first intermediate shaft  14  is pivotally supported in the right and left direction so that a first bevel gear  40  arranged in the end of the first intermediate shaft  14  meshes with a second bevel gear  41  arranged in the middle part of the second intermediate shaft  15 . 
         [0045]    Furthermore, below the second intermediate shaft  15 , a third intermediate shaft  43  is pivotally supported in parallel so that a third gear  42  arranged on the left of the second intermediate shaft  15  meshes with a fourth gear  44  arranged in the third intermediate shaft  43 . By meshing of the fourth gear  44  with a fifth gear  45  arranged in the spindle  13 , rotation of the first intermediate shaft  14  can be transmitted to the spindle  13  while reducing the speed. However, the fourth gear  44  is an idle gear having an equal number of teeth with that of the fifth gear  45  and does not reduce the speed. By adoption of the idle gear, the shift amount of the motor  8  to the upper side can be gained which is more effective in preventing interference with the guide fence  5 . 
         [0046]    The cutter is not limited to the bench circular saw of the embodiment and the modification, and the present invention can be applied even to a bench circular saw without a turntable and a slide type circular saw in which the body slides in the front and rear direction. 
       REFERENCE SIGNS LIST 
       [0047]      1 : bench circular saw,  2 : base,  3 : turntable,  5 : guide fence,  6 : arm,  7 : body,  8 : motor,  9 : output shaft,  10 : saw blade,  12 : motor housing,  13 : spindle,  14 : first intermediate shaft,  15 : second intermediate shaft,  20 : automatic torque adjusting mechanism,  21 : driving pulley,  22 : driven pulley,  23 : belt,  25 ,  30 : fixed pulley plate,  26 ,  31 : movable pulley plate,  28 ,  34 : coil spring,  32 : fixed cam,  33 ,  35 : cam claw,  43 : third intermediate shaft,  44 : fourth gear