Abstract:
A main spindle of an air saw is reciprocated by sliding a piston in a cylinder chamber with the pressure of air supplied to the cylinder chamber via an air supply path so as to alternately apply the air pressure to pressure-receiving surfaces of a back plate and a front plate, wherein a rear air-cushion chamber is formed in a portion for fixing a return spring for urging the back plate toward the center of a cylinder while a front air-cushion chamber is formed in a portion for fixing a return spring for urging the front plate toward the center of the cylinder, so that the front and rear balance is maintained.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an improvement in an air saw used for plate cutting work and deburring of metallic products as a kind of air tool. 
   2. Description of the Related Art 
   As shown in  FIGS. 9 and 10 , a general structure of an air saw  101  includes: a piston  113  slidably accommodated in a cylindrical cylinder chamber  112  arranged in a saw casing  102 ; a main spindle  129  passing through the piston  113  and having a back plate  130  arranged toward the rear end and a front plate  131  arranged toward the front end; and a blade-applied part  103  arranged at the front end of the main spindle  129  for attaching a saw blade  109  thereto. 
   Return springs  132  and  144  are respectively arranged in return-spring chambers  150  and  151 , which are provided at the rear of the back plate  130  and the front of the front plate  131 , respectively. Due to the return springs  132  and  144 , the back plate  130  and the front plate  131  are urged toward the center of a cylinder  111 , respectively. The front return-spring chamber  151  is open to the atmospheric air while the rear return-spring chamber  150  is formed to be an air-cushion chamber  149  communicating with an exhaust path  115  via a ventilation port  117 . The exhaust path  115  is provided with two front and rear exhaust ports  152  and  153  controlled to open and close by the sliding of the piston  113 . 
   Due to the pressure of air supplied from a charging path  104  via a charging port  114 , the piston  113  in the cylinder chamber  112  is slid, so that the main spindle  129  reciprocates (moves back-and-forth) by alternately applying the pressure to pressure-receiving surfaces  130   a  and  131   a  of the back plate  130  and the front plate  131 , so as to reciprocate the saw blade  109  attached to the blade-applied part  103 . 
   However, in the conventional air saw  101  formed as described above, although the return-spring chamber  151  accommodating the return spring  144  urging the front plate  131  toward the center of the cylinder  111  is open to the atmospheric air, the rear return-spring chamber  150  accommodating the return spring  132  urging the back plate  130  toward the center of the cylinder  111  is formed to be the air-cushion chamber  149  communicating with the exhaust path  115  via the ventilation port  117 , as described above. Therefore, the air in the cylinder chamber  112 , for example, enters the air-cushion chamber  149  from the exhaust path  115  via the ventilation port  117  so as to increase the internal pressure of the air-cushion chamber  149 . 
   Furthermore, the air entering the air-cushion chamber  149  through the clearance between the back plate  130  and the internal peripheral surface of the cylinder  111  also increases the internal pressure of the air-cushion chamber  149 . 
   When the internal pressure of the air-cushion chamber  149  is increased in such a manner, the forces urging the main spindle  129  toward the center by the front and rear return springs  144  and  132  are off-balance because the internal pressure of the air-cushion chamber  149  is applied in addition to the elastic force of the return spring  132  from rear to the front relative to the elastic force of the return spring  144  from front to the rear. 
   As a result, as shown in  FIG. 11 , the back plate  130  extends beyond the normal advanced position to the front (to the left in the drawing), so that the pressure-receiving surface (front surface)  130   a  of the back plate  130  abuts the rear surface  113   a  of the retracting piston  113  so as to generate so-called chattering (which is a clink-clanking sound). The chattering is further liable to be generated when the supplied air pressure is increased. 
   Also, the chattering is generated when the saw blade is caught on an object to be cut, as shown in the phantom line in  FIG. 11 . That is, when the saw blade is caught on an object to be cut  154 , in order to break this up, the air saw is instinctively pulled toward the operator (the right in the drawing, i.e., rear side). Thus, the back plate  130  extends beyond the normal advanced position of the reciprocating to the front, so that the pressure-receiving surface (front surface)  130   a  of the back plate  130  abuts the rear surface  113   a  of the retracting piston  113  so as to generate the chattering. 
   During the chattering that is the collision between the pressure-receiving surface  130   a  of the back plate  130  and the rear surface  113   a  of the retracting piston  113 , since the front plate  131  integrated with the main spindle  129  advances further than normal, the return spring  144  is compressed further than a predetermined degree so as to reduce the strength of the spring because of dimensional changes. Thus, the force returning the main spindle  129  rearwardly (the right in the drawing) is reduced, so that the chattering is further more liable to be generated. There has also been a problem that part of the main spindle  129  attaching the back plate  130  is liable to break, reducing durability. 
   Moreover, the part fixing the saw blade  109  may be loosened or the saw blade  109  may come off because of the vibration due to the chattering, so that the work efficiency may be reduced. Furthermore, the chattering not only causes increased noise, but also increases the vibration, thereby deteriorating the work environment and the worker&#39;s health. 
   Additionally, when a member to be cut has a double structure with two plates, the rear plate may be cut even if it is not required to be cut. In order to avoid this, air supply is reduced, and even the stroke is reduced. However, the force driving the main spindle is extremely reduced because of reduced energy supply, which is not fit for practical use. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above described problems, and it is an object thereof to provide an air saw capable of reducing noise, deterioration in work efficiency and work environment, and adverse effects on worker&#39;s health by preventing chattering. 
   In order to achieve the above-described object, an air saw according to the present invention comprises a casing, a cylinder chamber formed in the casing, a cylinder, a piston movably arranged in the cylinder chamber, a main spindle passing through the piston and having a back plate disposed toward the rear end and a front plate disposed toward the front end, and each of the back and front plates has a return spring. The air saw further comprises a saw blade, a blade-applied part arranged at the front end of the main spindle for attaching the saw blade thereto, and an air supply path, wherein the back plate and the front plate are urged toward the center of the cylinder by the respective return springs while the main spindle is reciprocated by sliding the piston in the cylinder chamber with the pressure of air supplied to the cylinder chamber via the air supply path so as to alternately apply the air pressure to pressure-receiving surfaces of the back plate and the front plate. A rear air-cushion chamber is formed in a portion for fixing the return spring for urging the back plate toward the center of the while a front air-cushion chamber is formed in a portion for fixing the return spring for cylinder, urging the front plate toward the center of the cylinder. 
   Preferably, the air saw further comprises at least one exhaust path with one end atmospherically opened, wherein the front air-cushion chamber communicates with the exhaust path via at least one exhaust port, and the exhaust port is formed to have a position at which the exhaust port is closed when the front plate advances beyond a normal advanced position. The air saw further comprises a flow-regulating valve arranged in the exhaust path, wherein the stroke of the saw blade can be adjusted by the flow regulation with the flow-regulating valve. 
   In the air saw according to the present invention, as described above, the rear air-cushion chamber is formed in a portion for fixing the return spring for urging the back plate toward the center of the cylinder while the front air-cushion chamber is formed in a portion for fixing the return spring for urging the front plate toward the center of the cylinder, so that the main spindle is located at a normal position by forces urging both ends thereof toward the center of the cylinder due to the elastic forces of the return springs and the air pressures of the air-cushion chambers. 
   During the operation of the air saw, when the saw blade is caught on an object to be worked and the operator pulls the air saw so as to break this up, if the main spindle further advances across the normal advanced position, the front air-cushion chamber is sealed. Thus, due to the air pressure in the sealed front air-cushion chamber and the elastic force of the front return-spring, the front plate is pushed rearward, so that the abnormal advancement of the main spindle is blocked, preventing the chattering. 
   Therefore, the breakdown of part of the main spindle due to the chattering is prevented, improving the durability while the part fixing the saw blade is prevented from loosening or allowing the saw blade to come off because of the vibration due to the chattering. Thus, the work efficiency can be greatly improved. 
   Moreover, the chattering can be prevented, so that a conventional large amount of noise and vibration can be reduced, improving the work environment and the worker&#39;s health. 
   In addition to these, ends of the front and rear air-cushion chambers communicate with the atmospherically opened exhaust path while a flow-regulating valve is provided in the exhaust path so as to adjust the stroke of the saw blade by the flow regulation with the flow-regulating valve. Therefore, only the external side of the member to be cut having a double structure can be cut, for example, further improving the work efficiency. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an air saw according to the present invention; 
       FIG. 2  is a longitudinal sectional side-view of the air saw according to the present invention; 
       FIG. 3  is a longitudinal sectional plan-view of the air saw according to the present invention; 
       FIG. 4  is a cross-sectional view at the line A—A of  FIG. 2  of the air saw according to the present invention; 
       FIG. 5  is a schematic representation for illustrating an operation in the cross-sectional view at the line A—A of  FIG. 2  of the air saw according to the present invention; 
       FIG. 6  is a schematic representation for illustrating an operation in the cross-sectional view at the line A—A of  FIG. 2  of the air saw according to the present invention; 
       FIG. 7  is a longitudinal sectional side-view of the air saw according to the present invention; 
       FIG. 8  is a longitudinal sectional side-view of the air saw according to the present invention; 
       FIG. 9  is a longitudinal sectional side-view of a conventional air saw; 
       FIG. 10  is a longitudinal sectional side-view of the conventional air saw; 
       FIG. 11  is a longitudinal sectional side-view of the conventional air saw; 
       FIG. 12  is a drawing equivalent to  FIG. 4 , showing part of a modified flow-regulating valve of the air saw according to the present invention; 
       FIG. 13  is a drawing equivalent to  FIG. 5 , showing part of the modified flow-regulating valve of the air saw according to the present invention; and 
       FIG. 14  is a drawing equivalent to  FIG. 6 , showing part of the modified flow-regulating valve of the air saw according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An air saw according to an embodiment of the present invention will be described below with reference to the drawings. 
     FIG. 1  is a perspective view of the air saw and the entire air saw is indicated by numeral  1 . The air saw  1  comprises a substantially cylindrical casing  2 , a blade-connection part  3  arranged in the front of the casing  2 , and a hose-connection part  6  disposed at the rear end of the casing  2  to be connected to a hose  5  for supplying the air pressurized by a compressor (not shown) to an air-supply path  4 . On the rear bottom surface of the casing  2 , an operating lever  8  is provided for supplying the air supplied to the hose-connection part  6  to the air-supply path  4  by operating an on-off valve  7  interposed in the air-supply path  4  (see  FIG. 2 ). 
   The casing  2  is provided with a blade driver  10  assembled therein for reciprocating a saw blade  9  attached to the blade-connection part  3  by operation of the operating lever  8  with the air supplied from the hose-connection part  6 . The blade driver  10  is configured as follows. 
   As shown in  FIGS. 2 and 3 , the casing  2  is provided with a cylinder  11  inner-packed therein, and a piston  13  is accommodated within the cylinder  11  so as to be able to move back and forth for defining the front and rear of a cylinder chamber  12 . At the lower center of the cylinder  11 , an air-supply port  14  is formed for communicating with the air-supply path  4 . 
   In the vicinities of the upper front and rear ends of the cylinder  11 , as shown  FIG. 2 , first-side exhaust ports  16  and  17  each communicate with a first exhaust path  15  formed between the casing  2  and the cylinder  11 . On one side-wall of the cylinder  11 , as shown in  FIG. 3 , second-side exhaust ports  19 ,  20 ,  21 , and  22  are formed for communicating with a second exhaust path  18  formed between the casing  2  and the cylinder  11  in the same way as in the first exhaust path  15 . 
   The diameters of the first-side exhaust ports  16  and  17  and the second-side exhaust ports  19  and  22  are small, and the diameters of the second-side exhaust ports  20  and  21  are comparatively larger. 
   As shown in  FIG. 4 , the cross-sectional area of the first exhaust path  15  is large while the cross-sectional area of the second exhaust path  18  is comparatively smaller. In the vicinity of the outlets of the first exhaust path  15  and the second exhaust path  18 , a flow-regulating valve  23  is provided so as to atmospherically discharge the exhausted air from both exhaust paths  15  and  18 . 
   The flow-regulating valve  23 , as shown in  FIGS. 4 to 6 , adjusts the opening area of the second exhaust path  18  while maintaining the opening area of the first exhaust path  15 , and has a valve body  26  provided on the opening area of the second exhaust path  18 . The rotational angle of the valve body  26  is limited by a knock-pin  24  and an elongated hole  25 , into which the knock-pin  24  passes through. 
   In addition, according to the embodiment, as shown in  FIGS. 4 to 6 , the first exhaust path  15  and the second exhaust path  18  converge at the part of the valve body  26 . Alternatively, they may of course converge in an exhaust-air chamber  27 , which is disposed in the rear of the valve body  26  and will be described later, while the first exhaust path  15  and the second exhaust path  18  are independent from each other at the part of the valve body  26 , as shown in  FIGS. 12 to 14 . 
   As for the cross-sectional areas of the first exhaust path  15  and the second exhaust path  18 , as indicated by dotted lines in  FIGS. 12 to 14 , the first exhaust path  15  may be small while the second exhaust path  18  may be formed larger. While the opening area of a hole  26   a  for the first exhaust path  15  formed in the valve body  26  is maintained, the opening area of the second exhaust path  18  may also be adjusted with a hole  26   b  for the second exhaust path  18 . 
   In the rear portion of the valve body  26 , the exhaust-air chamber  27  is formed for releasing the pressure of the air discharged from the first exhaust path  15  and the second exhaust path  18 , so that the exhaust note is reduced because the air is substantially uniformly discharged from a number of small holes  28  formed in the periphery of the hose-connection part  6 . 
   The cylinder  11  is provided with a main spindle  29  boring through the piston  13 . In the rear end (the right end in the drawing) portion of the main spindle  29 , there is a back plate  30  with its periphery internally touching the internal peripheral surface  11   a  of the cylinder  11 , while in the front end (the left end in the drawing) portion of the main spindle  29 , there is provided a front plate  31  with its periphery internally touching the internal peripheral surface  11   a  of the cylinder  11 . 
   It is preferable that the mass of the piston  13  and the mass of the main spindle  29  when the masses of the front plate  31  and the back plate  30  are added thereto be substantially the same. 
   In the rear of the back plate  30 , a rear air-cushion chamber  49  is formed, in which a rear return-spring  32  is accommodated. The first-side exhaust port  17  communicating with the first exhaust path  15  and the second-side exhaust port  22  communicating with the second exhaust path  18  shown in  FIG. 3  are formed in the part of the cylinder  11  within (surrounding) the rear air-cushion chamber  49 . 
   On the other hand, to the front of the front plate  31  at the end of the cylinder  11 , a sealing cap  33  is attached so as to form a front air-cushion chamber  34  at the front plate  31 . 
   While a front return-spring  44  is accommodated in the front air-cushion chamber  34 , the first-side exhaust port  16  communicating with the first exhaust path  15  and the second-side exhaust port  19  communicating with the second exhaust path  18  are formed in the part of the cylinder  11  within (surrounding) the front air-cushion chamber  34 . 
   The first-side exhaust port  16  and second-side exhaust port  19  are located at positions at which the ports are closed with the front plate  31  when the front plate  31  extends beyond the normal advanced position. 
   The piston  13  moving in the cylinder  11  with the main spindle  29  passing therethrough is provided with annular lands  35 ,  36 , and  37  formed in the central periphery, and the rear periphery for internally touching the internal peripheral surface  11   a  of the cylinder  11 . 
   A space  38  between the front land  35  and central land  36  communicates with a retracting path  40  for supplying the air from the air-supply port  14  to a space  39  between the rear surface  13   a  of the piston  13  and the front surface (air-receiving surface) portion  30   a  of the back plate  30  so as to apply a force in the retracting direction of the main spindle  29  (the advancing direction of the piston  13 ). 
   A space  41  between the rear land  37  and central land  36  communicates with an advancing path  43  for supplying the air from the air-supply port  14  to a space  42  between the front surface  13   b  of the piston  13  and the rear surface (air-receiving surface) portion  31   a  of the front plate  31  so as to apply a force in the advancing direction of the main spindle  29  (the retracting direction of the piston  13 ). 
   In addition, a blade holder  45  disposed in the blade-connection part  3  is attached to the front end of the front plate  31  which is attached to the front end of the main spindle  29  with a bolt  47 . A blade guide  46  is adjustably attached (i.e., adjustable in a forward and rear direction) to a blade cap  48  attached to the end of the casing  2 . 
   The operation of the air saw  1  configured as above will be described below. 
   First, prior to starting the air saw  1 , the rearwardly pressing force of the front plate  31  with the front return-spring  44  and the forwardly pressing force of the back plate  30  with the rear return-spring  32  are balanced, so that the main spindle  29  is located at a neutral position in the normal reciprocating stroke while the piston  13  is located at an arbitrary position, the position shown in  FIG. 2 , for example. 
   Next, from the state shown in  FIG. 2 , when the on-off valve  7  is opened by the operation of the operating lever  8 , the air pressurized by a compressor from the hose  5  in the hose-connecting part  6  enters the space  41  between the rear land  37  and central land  36  via the air-supply port  14 . Then, the air from the space  41  enters the space  42  between the front surface  13   b  of the piston  13  and the rear surface (air-receiving surface) portion  31   a  of the front plate  31  via the advancing path  43 . 
   When the air enters the space  42  in such a manner, the front plate  31  is moved forwardly (toward the left in the drawing) by the pressure of the air against the elastic force of the front return-spring  44  and the air-cushioning force so as to advance the saw blade  9  to the position shown in  FIG. 7  while the piston  13  is moved rearwardly (toward the right in the drawing). 
   When the front plate  31  moves forwardly, the air in the front air-cushion chamber  34  flows into the first exhaust path  15  via the first-side exhaust port  16  while also flowing into the second exhaust path  18  via the second-side exhaust port  19 . On the other hand, the air enters the rear air-cushion chamber  49  in the rear of the forwardly moving back plate  30  from the first-side exhaust port  17  communicating with the first exhaust path  15  and from the second-side exhaust port  22  communicating with the second exhaust path  18 , so that the main spindle  29  is smoothly moved forwardly (toward the left in the drawing). 
   Simultaneously, when the piston  13  is moved rearwardly (toward the right in the drawing), together with the forward (left in the drawing) movement of the back plate  30 , the space  39  between the rear surface  13   a  of the piston  13  and the front surface (air-receiving surface) portion  30   a  of the back plate  30  is pressurized, so that the air in the space  39  is discharged to the second exhaust path  18  via the second-side exhaust port  21 . 
   Also, through the retracting path  40 , the air in the space  38  between the front land  35  and central land  36  is discharged to the second exhaust path  18  via the second-side exhaust port  20 . 
   Therefore, when the air amount discharging outside from the second exhaust path  18  is changed while running from the state shown in  FIG. 4  down to the state shown in  FIGS. 5 and 6 , the rearward (right in the drawing) moving speed of the piston  13  can be adjusted, so that the stroke can be adjusted substantially without changing the driving force of the main spindle  29  by adjusting the back pressure applied to the front plate  31 . 
   In addition, when the opening area of the second exhaust path  18  is entirely closed with the valve body  26  of the flow-regulating valve  23 , as shown in  FIG. 6 , the air discharged to the second exhaust path  18  via the second-side exhaust port  20  or  21  enters the front air-cushion chamber  34  from the second-side exhaust port  19  to be discharged from the first-side exhaust port  16 . 
   When the central land  36  advances rearward beyond the air-supply port  14  because of the further movement of the piston  13 , the air pressurized by a compressor enters the space  38  between the front land  35  and central land  36  from the air-supply port  14  in contrast to the above description. From the space  38 , the air enters the space  39  between the rear surface  13   a  of the piston  13  and the front surface (air-receiving surface) portion  30   a  of the back plate  30  via the retracting path  40 . 
   When the air enters the space  39  in such a manner, the back plate  30  is moved rearwardly (toward the right in the drawing) by the pressure of the air against the elastic force of the rear return-spring  32  and the air-cushioning force so as to retract the saw blade  9  from the position shown in  FIG. 7  while the piston  13  is moved forwardly (toward the left in the drawing). 
   When the back plate  30  moves rearwardly, the air in the rear air-cushion chamber  49  flows to the first exhaust path  15  via the first-side exhaust port  17  while also flowing to the second exhaust path  18  via the second-side exhaust port  22 . The air enters the front air-cushion chamber  34  in the front of the rearwardly moving front plate  31  from the first-side exhaust port  16  communicating with the first exhaust path  15  and from the second-side exhaust port  19  communicating with the second exhaust path  18 , so that the main spindle  29  is smoothly moved rearwardly (toward the right in the drawing). 
   On the other hand, when the piston  13  is moved forwardly (toward the left in the drawing), together with the rearward (right in the drawing) movement of the front plate  31 , the space  42  between the front surface  13   b  of the piston  13  and the rear surface (air-receiving surface) portion  31   a  of the front plate  31  is pressurized, so that the air in the space  42  is discharged to the second exhaust path  18  via the second-side exhaust port  20 . 
   Also, through the advancing path  43 , the air in the space  41  between the rear land  37  and central land  36  is discharged to the second exhaust path  18  via the second-side exhaust port  21 . 
   Therefore, also during the rearward (right in the drawing) movement of the main spindle  29 , when the air amount discharging outside from the second exhaust path  18  is changed while running from the state shown in  FIG. 4  down to the state shown in  FIGS. 5 and 6 , the forward (left in the drawing) moving speed of the piston  13  can be adjusted. Therefore, the stroke can be adjusted substantially without changing the driving force of the main spindle  29  by adjusting the back pressure applied to the back plate  30 . Thus, the stroke of the main spindle  29  can be adjusted corresponding to an object to be worked. 
   By repeating such back-and-forth movement of the main spindle  29  so as to reciprocate the saw blade  9 , an object to be worked is cut. However, as shown in  FIG. 8 , the saw blade  9  may be caught on an object to be worked  50 . When the saw blade  9  is caught on an object to be cut  50 , the operator pulls the air saw  1  automatically so as to break this up. In such a manner, when the air saw  1  is pulled toward the operator (the right in the drawing), the main spindle  29  further extends beyond the normal advanced position. 
   When the main spindle  29  advances beyond the normal advanced position, the front plate  31  closes the first-side exhaust port  16  communicating with the first exhaust path  15  and the second-side exhaust port  19  communicating with the second exhaust path  18 , so as to seal up the front air-cushion chamber  34 . 
   Therefore, the front plate  31  is pushed rearward by the air pressure in the sealed front air-cushion chamber  34  and an elastic force of the front return-spring  44 , so as to prevent the main spindle  29  from moving further forward. Thus, a conventional chattering due to excessive forward movement of the main spindle  29  can be prevented. 
   In addition, according to the embodiment, the flow-regulating valve  23  is configured to have the valve body  26  provided on the opening area of the second exhaust path  18 . The rotational angle of the valve body  26  is limited by the knock-pin  24  and the elongated hole  25 , into which the knock-pin  24  passes through, so as to adjust the opening area of the second exhaust path  18  while maintaining the opening area of the first exhaust path  15 . However, not being limited to this arrangement, the flow-regulating valve  23  may also be configured as other type valves such as a choke valve. 
   According to the embodiment, the saw blade is provided. Alternatively, a file blade and so forth may of course be attached instead of the saw blade.