Patent Publication Number: US-2021178560-A1

Title: Air duster structure and driving tool

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. patent application Ser. No. 15/848,326, filed on Dec. 20, 2017, which is based upon and claims the benefit of priority from prior Japanese patent application No. 2016-256590, filed on Dec. 28, 2016, the entire contents of which are incorporated herein by reference and priority is claimed to each of the foregoing. 
    
    
     BACKGROUND 
     The present disclosure relates to an air duster structure that jets air from a nozzle by using externally supplied compressed air and to a driving tool provided with the air duster structure. 
     An air duster gun or an air duster included with a driving tool has been used in order to blow off fine wood debris and the like before performing nail driving. For example, JP-A-H10-109280 discloses a driving tool including an air duster. The related-art technique disclosed in JP-A-H10-109280 is structured so that air is jetted out of a nozzle by pushing in an operation button that opens and closes a release valve. 
     To adjust the amount of air jetted out of the nozzle according to the operation amount of the operation button in an air duster as described above, it is considered to form the release valve or a pipe line in a tapered shape to increase the area of the flow channel of the air according to the pushing amount of the operation button . At this time, if the flow amount gradually increases while the pushing amount of the operation button and the flow amount of the air maintain a proportional relationship therebetween, and the flow amount of the air is largest when the operation amount is highest, operability is excellent. 
     However, in actuality, as the flow amount of the air being jetted out increases, the pressure in the accumulator provided on the upstream side of the release valve decreases and the difference in the pressure between in front of and behind the throttle of the release valve becomes small, so that the change in the flow amount with respect to the change in the operation amount becomes small. This produces an inconvenience in that after the operation button is operated to a certain extent, even if the operation button is operated any further, the amount of air jetted out of the nozzle does not largely change and this deteriorates operability. 
     SUMMARY 
     Accordingly, an object of the present disclosure is to provide an air duster structure and a driving tool where the adjustment of the flow amount of the air being jetted out is easy. 
     According to an aspect of the disclosure, there is provided an air duster structure that is configured to jet compressed air out of a nozzle, the air duster structure comprising: a flow amount adjustment mechanism which is configured to adjust an amount of air jetted out of the nozzle, wherein the flow amount adjustment mechanism includes: a pipe line for circulating air; a valve member disposed inside the pipe line and being movable; and a throttle portion configured to gradually change an area of a flow channel in which air circulates, with a movement of the valve member, to control a flow amount of the air in the pipe line, and the throttle portion is structured so as to increase the area of the flow channel at an accelerated rate when the valve member moves in a direction that opens the pipe line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a right side view of a driving tool provided with an air duster structure. 
         FIG. 2  is a left side view of the driving tool provided with the air duster structure. 
         FIG. 3  is an A-A cross-sectional view of the driving tool. 
         FIG. 4  is a left side view of the driving tool from which a tip cover member and a side cover member are detached. 
         FIG. 5A  is a perspective view of the tip cover member viewed from the reverse side, and  FIG. 5B  is a perspective view of the tip cover member viewed from the obverse side. 
         FIG. 6  is a perspective view of the driving tool viewed from below. 
         FIG. 7  is a cross-sectional view of a flow amount adjustment mechanism according to a first embodiment, and a view of a condition where an operation portion is not operated. 
         FIG. 8  is a cross-sectional view of the flow amount adjustment mechanism according to the first embodiment, and a view of a condition where the operation portion is depressed all the way in. 
         FIGS. 9A to 9D  are views explaining the operation of the flow amount adjustment mechanism according to the first embodiment,  FIG. 9A  is a view of the condition where the operation portion is not operated,  FIG. 9B  is a view of a condition where the operation portion is operated approximately ⅓ the way,  FIG. 9C  is a view of a condition where the operation portion is operated approximately ⅔ the way, and  FIG. 9D  is a view of a condition where the operation portion is fully operated. 
         FIG. 10  is a graph showing a relationship between the operation amount, and the flow amount and the flow channel area according to the first embodiment. 
         FIG. 11  is a cross-sectional view of a flow amount adjustment mechanism according to a second embodiment, and a view of a condition where the operation portion is not operated. 
         FIG. 12  is a cross-sectional view of the flow amount adjustment mechanism according to the second embodiment, and a view of a condition where the operation portion is depressed all the way in. 
         FIGS. 13A to 13E  are views explaining the operation of the flow amount adjustment mechanism according to the second embodiment,  FIG. 13A  is a view of the condition where the operation portion is not operated,  FIG. 13B  is a view of a condition where the operation portion is operated approximately ¼ the way,  FIG. 13C  is a view of a condition where the operation portion is operated approximately 2/4 the way,  FIG. 13D  is a view of a condition where the operation portion is operated approximately ¾ the way, and  FIG. 13E  is a view of a condition where the operation portion is fully operated. 
         FIG. 14  is a graph showing a relationship between the operation amount, and the flow amount and the flow channel area according to the second embodiment. 
         FIG. 15  is a cross-sectional view of a flow amount adjustment mechanism according to a third embodiment, and a view of a condition where the operation portion is not operated. 
         FIG. 16  is a cross-sectional view of the flow amount adjustment mechanism according to the third embodiment, and a view of a condition where the operation portion is depressed all the way in. 
         FIGS. 17A to 17D  are views explaining the operation of the flow amount adjustment mechanism according to the third embodiment,  FIG. 17A  is a view of the condition where the operation portion is not operated,  FIG. 17B  is a view of a condition where the operation portion is operated approximately ⅓ the way,  FIG. 17C  is a view of a condition where the operation portion is operated approximately ⅔ the way, and  FIG. 17D  is a view of a condition where the operation portion is fully operated. 
         FIGS. 18A and 18B  are views explaining a stepwise adjustment of the flow channel area according to the third embodiment,  FIG. 18A  is a view of a condition where the flow amount of the air is controlled by the change of the clearance amount at a throttle portion, and  FIG. 18B  is a view of the condition where the flow amount of the air is controlled by the change of the opening amount of the opening portion. 
         FIG. 19  is a graph showing a relationship between the operation amount, and the flow amount and the flow channel area according to the third embodiment. 
         FIG. 20  is a graph showing the relationship between the operation amount, and the flow amount and the flow channel area when a release valve or a pipe line is formed in a simple tapered shape. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. While in the following embodiments, as a usage example of the air duster structure, a driving tool  10  provided with an air duster structure is cited as an example, the present disclosure is not limited thereto; the air duster structure according to the present disclosure may be applied to different tools. For example, the air duster structure according to the present embodiments may be applied to an air duster gun. 
     First Embodiment 
     A first embodiment of the present disclosure will be described with reference to  FIGS. 1 to 10 . 
     The driving tool  10  according to the present embodiment ejects a fastener by using externally supplied compressed air, and is provided with an air duster structure that jets air out of a nozzle  17   b  by using this externally supplied compressed air. By thus providing the driving tool  10  with the air duster structure, driving by the fastener and cleaning by the air duster can be performed without exchanging tools. 
     As shown in  FIG. 1 , this driving tool  10  is provided with a tool body  11  having a striking mechanism inside, a grip  12  provided so as to protrude from the tool body  11  in an orthogonal direction, a trigger  13  provided on the grip  12  so as to be operable, a nose portion  14  provided so as to protrude on the tip of the tool body  11 , a magazine  15  connected in the rear of the nose portion  14 , and an operation portion  30  provided so as to be depressable in order to actuate the air duster structure. 
     The striking mechanism incorporated in the tool body  11  actuates a driver (which is a fastener driving member) by using the force of the compressed air. The driver is movable in the direction toward the nose portion  14  in order to eject a fastener. The driver having moved in the driving direction ejects a fastener that is set inside the nose portion  14 . The fastener ejected by the driver is ejected from an ejection hole  14   a  that is open at the tip of the nose portion  14 . 
     When this driving tool  10  is used, the grip  12  is gripped and grasped, and the trigger  13  is pulled. By this operation, the above-described striking mechanism is actuated to eject a fastener. 
     In the magazine  15 , a connection fastener is accommodated, and the foremost fasteners of this connection fastener are successively supplied in the direction toward the nose portion  14  (immediately below the driver before the driving operation). 
     The compressed air for actuating the above-described striking mechanism and air duster structure is supplied from an air supply source such as an air compressor. Specifically, an air hose for supplying air connected to a compressor or the like is connected to an end cap portion  16  provided on the rear end of the grip  12 , and the compressed air is supplied through this air hose. The compressed air supplied from the end cap portion  16  passes through an air supply channel formed inside the grip  12 , and is supplied to the striking mechanism or to the air duster structure. 
     In the striking mechanism, when the trigger  13  is operated, the compressed air is supplied into a striking cylinder, this compressed air acts on a striking piston to drive the striking piston, and the driver coupled to the striking piston drives a nail. 
     In the air duster structure, when the operation portion  30  is operated, the compressed air is jetted out of the nozzle  17   b  that is open in the neighborhood of the nose portion  14 . As shown in  FIG. 1 , the operation portion  30  according to the present embodiment is disposed in a position where it can be operated with the hand grasping the grip  12  when the worker grasps the grip  12 . Specifically, it is disposed in a position where it can be operated with the thumb of the right hand when the grip  12  is gripped with the right hand. 
     As shown in  FIGS. 3 and 4 , the above-described air duster structure is provided with a flow amount adjustment mechanism provided inside the housing of the tool body  11 . On the downstream side of this flow amount adjustment mechanism, an air outlet  40  for taking out air to the outside of the housing is provided. To this air outlet  40 , a duster pipe arrangement  42  extending in a direction toward the tip of the tool body  11  (that is, a direction toward the nose portion  14 ) is connected. More specifically, the duster pipe arrangement  42  is connected through a joint part  41  rotatably provided between it and the air outlet  40 . 
     The air outlet  40  is disposed on a side surface of the tool body  11  on the side opposite to the operation portion  30 . While the duster pipe arrangement  42  and the joint part  41  connected to the air outlet  40  are disposed outside the housing of the tool body  11 , as shown in  FIG. 2 , they are covered with a tip cover member  17  covering the tip of the tool body  11  and a side cover member  18  disposed in a position covering the air outlet  40 . 
     On the reverse side of the tip cover member  17 , as shown in  FIG. 5A , a pipe arrangement holding portion  17   a  holding a tip portion  42   a  of the duster pipe arrangement  42  is provided, and by this, the tip portion  42   a  of the duster pipe arrangement  42  is fixed by the tip cover member  17 . The duster pipe arrangement  42  is easily assembled to the pipe arrangement holding portion  17   a  since it is a flexible tube made of a resin or the like and elastically deformable. 
     On the obverse side of the tip cover member  17 , as shown in  FIGS. 5B and 6 , the air nozzle  17   b  is open. This air nozzle  17   b  communicates with the above-described pipe arrangement holding portion  17   a . By this provision, on the tip cover member  17 , of the air nozzle  17   b  communicating with the duster pipe arrangement  42 , air is jetted out of this nozzle  17   b  when the operation portion  30  is operated. 
     The flow amount adjustment mechanism is for adjusting the amount of air jetted out of the nozzle  17   b,  and as shown in  FIG. 7 , is provided with a pipe line formation portion  20  forming a pipe line  23  for circulating air, a valve member  31  disposed within the pipe line  23  and movable, the operation portion  30  disposed on the tip of the valve member  31  so as to be operable, and a valve member pushing member  36  that pushes the valve member in the protruding direction. Into this flow amount adjustment mechanism, the compressed air can be introduced from the upstream side, and when the air supply source such as an air compressor and the tool body  11  are connected together, the compressed air is supplied to the upstream side at all times. On the downstream side of this flow amount adjustment mechanism, the air outlet  40  to which the duster pipe arrangement  42  (the joint part  41 ) is connectable is open. 
     The pipe line formation portion  20  has a hollow portion forming the pipe line  23 , and as shown in  FIG. 8 , is structured so as to take the compressed air into the pipe line  23  through an upstream opening portion  21  that is open toward the upstream side. On the downstream side of the upstream opening portion  21 , a throttle portion  23   a  is provided that controls the flow amount of the air in the pipe line  23  by gradually changing the amount of clearance between the pipe line  23  and the valve member  31  when the valve member  31  moves. This throttle portion  23   a  is formed, as shown in  FIGS. 7 and 8 , in a tapered shape (a trumpet shape) such that the width of the opening (the diameter of the cross section) increases at an accelerated rate toward the movement direction of the valve member  31 , and is structured so that when the valve member  31  moves in a direction that opens the pipe line  23 , the amount of clearance is increased at an accelerated rate. 
     To “increase at an accelerated rate” referred to here means not that the flow channel area increases proportionally to the movement amount of the valve member  31  when the valve member  31  moves in the opening direction but that the flow channel area increases more rapidly than proportionally. 
     The “amount of clearance” referred to here means the length of the gap between the pipe line  23  and the valve member  31 . 
     The valve member  31  is structured so as to slide along with the depression of the operation portion  30 . While the valve member  31  is pushed in the protruding direction by the valve member pushing member  36  under natural conditions, when the operation portion  30  is depressed against the pushing force of the valve member pushing member  36 , the valve member  31  moves in the direction that opens the pipe line  23 . In the present embodiment, a tip sealing member  32  formed of an O ring or the like is attached to the tip of the valve member  31 , and under natural conditions, the pipe line  23  is closed by this tip sealing member  32  abutting on the throttle portion  23   a . When the valve member  31  moves in the direction that opens the pipe line  23 , a clearance occurs between the tip sealing member  32  and the throttle portion  23   a,  and by this clearance, the flow amount of the air in the pipe line  23  is controlled. Then, when the valve member  31  opens the pipe line  23 , air is released from the air outlet  40 , and air is jetted out of the nozzle  17   b . In the present embodiment, it is unnecessary to dispose the duster pipe arrangement  42  inside the housing since the valve member  31  and the air outlet  40  are disposed in the pushing direction of the operation portion  30  and the air outlet  40  is formed on the side opposite to the operation portion  30 . 
     According to this structure, since the flow channel area of the throttle portion  23   a  rapidly increases as the operation amount of the operation portion  30  increases, even if the difference in pressure between in front of and behind the throttle portion  23   a  becomes small by operating the operation portion  30  to a certain extent, the decrease in the flow amount because of the decrease in the pressure difference can be compensated by the increase in the flow channel area, so that the relationship between the operation amount of the operation portion  30  and the amount of air jetted out of the nozzle  17   b  can be made close to a proportional relationship. 
     That is, when the throttle portion  23   a  is formed not in the trumpet shape but in a simple tapered shape (conical surface), as shown in  FIG. 20 , as the flow amount of the air increases, the pressure in the accumulator provided on the upstream side of the release valve decreases and the pressure difference between in front of and behind the throttle of the release valve becomes small, so that the change in the flow amount with respect to the change in the operation amount becomes small. For this reason, after the operation portion  30  is operated to a certain extent, the amount of air jetted out of the nozzle  17   b  does not largely change even if the operation portion  30  is operated any further and this deteriorates operability. 
     In this regard, according to the present embodiment, as shown in  FIGS. 9A to 9D , since operation amounts M 1  to M 3  of the operation portion  30  are not proportional to the clearance amounts G 1  to G 3 , it is possible to make the flow channel area very small at the start of the operation of the operation portion  30  and make the flow channel area very large at the end of the operation of the operation portion  30 . Specifically, when the operation portion  30  is operated by the predetermined operation amount M 1  from an initial position BL of the valve member  31  where the flow channel is closed (see  FIG. 9A ), the clearance amount is G 1  (see  FIG. 9B ). When the operation portion  30  is operated by twice the predetermined operation amount M 1  (M 2 ) from the initial position BL of the valve member  31 , the clearance amount is G 2  (see  FIG. 9C ). When the operation portion  30  is operated by three times the predetermined operation amount M 1  (M 3 ) from the initial position BL of the valve member  31 , the clearance amount is G 3  (see  FIG. 9C ). In the case of a simple tapered shape (a conical surface), G 2  should be twice G 1 , and G 3  should be three times G 1 ; however, in the present embodiment, since the clearance amount increases at an accelerated rate with respect to the operation amount of the operation portion  30 , G 2  is not less than twice G 1 , and G 3  is not less than three times G 1 . As described above, the present embodiment is purposefully structured so that the flow channel area largely increases extremely toward the rear. Therefore, even when the pressure difference between in front of and behind the throttle portion  23   a  becomes small by operating the operation portion  30  to a certain extent and the pressure to jet out the air decreases, the decrease in the pressure can be compensated by the increase in the flow channel area, so that as shown in  FIG. 10 , the relationship between the operation amount of the operation portion  30  and the amount of air jetted out of the nozzle  17   b  can be made close to a proportional relationship. 
     Second Embodiment 
     A second embodiment of the present disclosure will be described with reference to  FIGS. 11 to 14 . Since the second embodiment is different from the first embodiment only in the structure of the flow amount adjustment mechanism, overlapping descriptions are avoided and only the flow amount adjustment mechanism will be described. 
     The flow amount adjustment mechanism according to the present embodiment is for adjusting the amount of air jetted out of the nozzle  17   b,  and as shown in  FIG. 11 , is provided with the pipe line formation portion  20  forming the pipe line  23  for circulating air, the valve member  31  disposed within the pipe line  23  and movable, the operation portion  30  disposed on the tip of the valve member  31  so as to be operable, and the valve member pushing member  36  that pushes the valve member  31  in the protruding direction. Into this flow amount adjustment mechanism, the compressed air can be introduced from the upstream side, and when the air supply source such as an air compressor is connected to the tool body  11 , the compressed air is supplied to the upstream side at all times. On the downstream side of this flow amount adjustment mechanism, the air outlet  40  to which the duster pipe arrangement  42  (the joint part  41 ) is connectable is open. 
     The pipe line formation portion  20  has a hollow portion forming the pipe line  23 , and as shown in  FIG. 12 , is structured so as to take the compressed air into the pipe line  23  through the upstream opening portion  21  that is open toward the upstream side. On the downstream side of the upstream opening portion  21 , the throttle portion  23   a  is provided that controls the flow amount of the air in the pipe line  23  by gradually changing the amount of clearance between the pipe line  23  and the valve member  31  when the valve member  31  moves. This throttle portion  23   a  is formed, as shown in  FIGS. 11 and 12 , in a stepped shape where tapered portions and cylindrical portions are alternately arranged. Specifically, the following are provided: a first tapered portion  23   c  expanding toward the downstream side; a first parallel portion  23   f  formed in substantially the same diameter as the maximum diameter of the first tapered portion  23   c  so as to be continuous with the first tapered portion  23   c ; a second tapered portion  23   d  expanding toward the downstream side so as to be continuous with the first parallel portion  23   f ; a second parallel portion  23   g  formed in substantially the same diameter as the maximum diameter of the second tapered portion  23   d  so as to be continuous with the second tapered portion  23   d ; a third tapered portion  23   e  expanding toward the downstream side so as to be continuous with the second parallel portion  23   g ; and a third parallel portion  23   h  formed in substantially the same diameter as the maximum diameter of the third tapered portion  23   e  so as to be continuous with the third tapered portion  23   e . This embodiment is merely an example and the number of steps of the stepped shape may be changed as appropriate. 
     The valve member  31  is structured so as to slide along with the depression of the operation portion  30 . While the valve member  31  is pushed in the protruding direction by the valve member pushing member  36  under natural conditions, when the operation portion  30  is depressed against the pushing force of the valve member pushing member  36 , the valve member  31  moves in the direction that opens the pipe line  23 . In the present embodiment, the tip sealing member  32  formed of an O ring or the like is attached to the tip of the valve member  31 , and under natural conditions, the pipe line  23  is closed by this tip sealing member  32  abutting on the throttle portion  23   a . When the valve member  31  moves in the direction that opens the pipe line  23 , a clearance occurs between the tip sealing member  32  and the throttle portion  23   a,  and by this clearance, the flow amount of the air in the pipe line  23  is controlled. Then, when the valve member  31  opens the pipe line  23 , air is released from the air outlet  40 , and air is jetted out of the nozzle  17   b . In the present embodiment, it is unnecessary to dispose the duster pipe arrangement  42  inside the housing since the valve member  31  and the air outlet  40  are disposed in the pushing direction of the operation portion  30 . 
     According to this structure, since the flow channel area can be stepwisely adjusted by the stepped shape, even when the pressure difference between in front of and behind the throttle portion  23   a  becomes small by operating the operation portion  30  to a certain extent and the pressure to jet out the air decreases, the decrease in the pressure can be compensated by the increase in the flow channel area, so that the relationship between the operation amount of the operation portion  30  and the amount of air jetted out of the nozzle  17   b  can be made close to a proportional relationship. 
     That is, according to the present embodiment, as shown in  FIG. 13B , when the tip sealing member  32  is moving in a position facing a tapered portion, the amount of clearance between the tip sealing member  32  and the throttle portion  23   a  increases little by little, whereas as shown in  FIGS. 13C, 13D and 13E , when the tip sealing member  32  faces a parallel portion, the amount of clearance between the tip sealing member  32  and the throttle portion  23   a  does not change. For this reason, by adjusting the intervals and the diameters of the tapered portions and the parallel portions, the relationship between the operation amount of the operation portion  30  and the flow channel area can be easily set and changed. For this reason, even when the pressure difference between in front of and behind the throttle portion  23   a  becomes small by operating the operation portion  30  to a certain extent and the pressure to jet out the air decreases, the decrease in the pressure can be compensated by the increase in the flow channel area, so that as shown in  FIG. 14 , the relationship between the operation amount of the operation portion  30  and the amount of air jetted out of the nozzle  17   b  can be made close to a proportional relationship. 
     Moreover, by stepwisely adjusting the flow channel area, it is made easy to keep constant the amount of air jetted out of the nozzle  17   b . For example, as shown in  FIG. 13C , in a range where the tip sealing member  32  faces the first parallel portion  23   f , as shown at S 1  in  FIG. 14 , even if the operation amount of the operation portion  30  changes in some degree, the amount of air jetted out of the nozzle  17   b  is kept substantially constant. Likewise, as shown in  FIG. 13D , in a range where the tip sealing member  32  faces the second parallel portion  23   g , as shown at S 2  in  FIG. 14 , even if the operation amount of the operation portion  30  changes in some degree, the amount of air jetted out of the nozzle  17   b  is kept substantially constant. Moreover, as shown in  FIG. 13E , when the tip sealing member  32  is operated to a position where the tip sealing member  32  faces the third parallel portion  23   h  (to the bottom dead point), as shown at S 3  in  FIG. 14 , the amount of air jetted out of the nozzle  17   b  is stabilized. 
     As described above, by making it possible to keep substantially constant the amount of air jetted out of the nozzle  17   b  even if the operation amount of the operation portion  30  changes in some degree, the amount of air jetted out of the nozzle  17   b  can be kept constant without the user continuing to apply a constant force to the operation portion  30 . For example, even in a situation where it is difficult to continue applying a constant force to the operation portion  30  such as a situation where the user uses the machine while shaking the nozzle  17   b  under a condition where he/she is holding the machine, the amount of air jetted out of the nozzle  17   b  can be kept constant. 
     Third Embodiment 
     A third embodiment of the present disclosure will be described with reference to  FIGS. 15 to 19 . Since the third embodiment is different from the first embodiment only in the structure of the flow amount adjustment mechanism, overlapping descriptions are avoided and only the flow amount adjustment mechanism will be described. 
     The flow amount adjustment mechanism according to the present embodiment is for adjusting the amount of air jetted out of the nozzle  17   b,  and as shown in  FIG. 15 , is provided with the pipe line formation portion  20  forming the pipe line  23  for circulating air, the valve member  31  disposed within the pipe line  23  and movable, the operation portion  30  disposed on the tip of the valve member  31  so as to be operable, the valve member pushing member  36  that pushes the valve member  31  in the protruding direction, and a sealing member  37  that abuts the valve member  31  to seal the air. Into this flow amount adjustment mechanism, the compressed air can be introduced from the upstream side, and when the air supply source such as an air compressor is connected, the compressed air is supplied to the upstream side at all times. On the downstream side of this flow amount adjustment mechanism, the air outlet  40  to which the duster pipe arrangement  42  (the joint part  41 ) is connectable is open. 
     The pipe line formation portion  20  has a hollow portion forming the pipe line  23 , and in the present embodiment, part of the housing of the tool body  11  is made the pipe line formation portion  20 . That is, in the housing of the tool body  11 , a through hole that passes through in a direction orthogonal to the driving direction of the fastener is formed, and the pipe line  23  is formed of this through hole. This pipe line formation portion  20  is structured, as shown in  FIG. 16 , so as to take in the compressed air into the pipe line  23  from the upstream opening portion  21  that is open toward the upstream side. This pipe line formation portion  20  is provided with a blocking portion  23   i  capable of adjusting the opening amount of an opening portion  35  described later. The blocking portion  23   i  has a cylinder inner surface shape facing the outer peripheral surface of the valve member  31 . 
     The valve member  31  is structured so as to slide along with the depression of the operation portion  30 . While the valve member  31  is pushed in the protruding direction by the valve member pushing member  36  under natural conditions, when the operation portion  30  is depressed against the pushing force of the valve member pushing member  36 , the valve member  31  moves in the direction that opens the pipe line  23 . 
     This valve member  31  is hollow and provided with an inner pipe line  34  through which air can pass . On the upstream side of the inner pipe line  34 , an intake  33  for taking in the compressed air is provided, and on the downstream side of the inner pipe line  34 , the opening portion  35  for discharging the compressed air toward the air outlet  40  is provided. The compressed air supplied from the air supply source flows into the inner pipe line  34  from the intake  33 , and passes through the opening portion  35  to flow in a direction toward the air outlet  40 . The opening portion  35  is open in a direction orthogonal to the movement direction of the valve member  31 , and can face the blocking portion  23   i  of the pipe line formation portion  20 . Specifically, this opening portion  35  is provided, as shown in  FIGS. 17A to 17D , continuously with the throttle portion  23   a  described later, and after the valve member  31  moves and the throttle portion  23   a  passes the blocking portion  23   i , the opening portion  35  faces the blocking portion  23   i.    
     On the downstream side of this opening portion  35 , the throttle portion  23   a  is provided that controls the flow amount of the air in the pipe line  23  by gradually changing the amount of clearance between the pipe line  23  and the valve member  31  when the valve member  31  moves. While the throttle portion  23   a  is formed by tapering the outer peripheral surface of the valve member  31  in the present embodiment, the present disclosure is not limited thereto; the throttle portion  23   a  may be formed by tapering the inner peripheral surface of the pipe line  23  or a stepped shape may be used instead of the tapered shape. 
     In the present embodiment, the sealing member  37  formed of an O ring or the like is fixed to the housing side of the tool body  11 . Under natural conditions, as shown in  FIG. 15 , this sealing member  37  abuts on the outer peripheral surface (a sealing surface  38 ) of the valve member  31  to seal so that no air flows into the intake  33 . When the valve member  31  moves in the direction that opens the pipe line  23 , the sealing state of the sealing member  37  and the sealing surface  38  is released, so that air is supplied from the intake  33  to the inner pipe line  34 . The flow amount of the air supplied to the inner pipe line  34  is controlled by the change in the clearance amount at the throttle portion  23   a  and the change in the opening amount of the opening portion  35 . The air having its flow amount controlled is released from the air outlet  40  and jetted out of the nozzle  17   b . In the present embodiment, it is unnecessary to dispose the duster pipe arrangement  42  inside the housing since the valve member  31  and the air outlet  40  are disposed in the pushing direction of the operation portion  30  and the air outlet  40  is formed on the side opposite to the operation portion  30 . 
     According to this structure, since the flow channel area can be stepwisely adjusted by the flow amount adjustment at two places, even when the pressure difference between in front of and behind the throttle portion  23   a  becomes small by operating the operation portion  30  to a certain extent and the pressure to jet out the air decreases, the decrease in the pressure can be compensated by the increase in the flow channel area, so that the relationship between the operation amount of the operation portion  30  and the amount of air jetted out of the nozzle  17   b  can be made close to a proportional relationship. 
     That is, according to the present embodiment, as shown in  FIGS. 17A to 17C , since the opening portion  35  is blocked until the operation portion  30  is operated and moves to a predetermined position, the flow amount adjustment is performed only by the throttle portion  23   a . At this stage, as shown in  FIG. 18A , the flow amount of the air is controlled by the change in the amount of clearance between the throttle portion  23   a  and the blocking portion  23   i . Then, as shown in  FIG. 17D , when the operation portion  30  is further operated and moves to the predetermined position, part of the opening portion  35  moves to the downstream side of the blocking portion  23   i , so that the air flows directly to the downstream side from the opening portion  35 . At this stage, the flow amount adjustment by the throttle portion  23   a  is not performed, and as shown in  FIG. 18B , the flow amount of the air is controlled by the change in the opening amount of the opening portion  35 . 
     According to this structure, the flow amount of the air can be increased as a stretch when the operation portion  30  is operated to a certain extent. For this reason, even when the pressure difference between in front of and behind the throttle portion  23   a  becomes small by operating the operation portion  30  to a certain extent and the pressure to jet out the air decreases, the decrease in the pressure can be compensated by the increase in the flow channel area, so that as shown in  FIG. 19 , the relationship between the operation amount of the operation portion  30  and the amount of air jetted out of the nozzle  17   b  can be made close to a proportional relationship. 
     While in the above-described embodiment, the flow amount of the air in the pipe line  23  is controlled by the change in the clearance amount at the throttle portion  23   a  and the change in the opening amount of the opening portion  35 , the method of adjusting the flow channel area by the flow amount adjustment at two places is not limited thereto. That is, at least two throttle portions where the flow channel area change amounts with respect to the movement amount of the valve member  31  are different may be provided. For example, a throttle portion where the change in the flow channel area is small and a throttle portion where the change is large may be combined. Specifically, by providing two or more tapered throttle portions as described in the first embodiment and making the angles of the tapered surfaces of the throttle portions different from each other, the flow channel area change amounts with respect to the movement amount of the valve member  31  can be made different from each other. 
     In the above-described embodiment, the opening portion  35  is provided on the valve member  31 , and the blocking portion  23   i  is provided on the pipe line formation portion  20  (the pipe line  23 ). However, the opening portion  35  may be provided on the pipe line formation portion  20  (the pipe line  23 ), and the blocking portion  23   i  may be provided on the valve member  31 . 
     According to an aspect of the disclosure, there is provided an air duster structure that is configured to jet compressed air out of a nozzle, the air duster structure comprising: a flow amount adjustment mechanism which is configured to adjust an amount of air jetted out of the nozzle, wherein the flow amount adjustment mechanism includes: a pipe line for circulating air; a valve member disposed inside the pipe line and being movable; and a throttle portion configured to gradually change an area of a flow channel in which air circulates, with a movement of the valve member, to control a flow amount of the air in the pipe line, and the throttle portion is structured so as to increase the area of the flow channel at an accelerated rate when the valve member moves in a direction that opens the pipe line. 
     In the above described structure, the throttle portion is structured so as to increase the area of the flow channel at an accelerated rate when the valve member moves in the direction that opens the pipe line. According to the structure, as the operation amount increases, the flow channel area of the throttle portion increases at an accelerated rate. Therefore, even when the pressure difference between in front of and behind the throttle portion becomes small by operating the operation portion to a certain extent and the pressure in an accumulator decreases, the decrease in the pressure can be compensated by the increase in the flow channel area, so that the relationship between the operation amount of the operation portion and the amount of air jetted out of the nozzle can be made close to a proportional relationship. 
     According to an aspect of the disclosure, there is provided an air duster structure that is configured to jet compressed air out of a nozzle, the air duster structure comprising: a flow amount adjustment mechanism which is configured to adjust an amount of air jetted out of the nozzle, wherein the flow amount adjustment mechanism includes: a pipe line for circulating air; a valve member disposed inside the pipe line and being movable; and a throttle portion configured to gradually change an area of a flow channel in which air circulates, with a movement of the valve member, to control a flow amount of the air in the pipe line, and the throttle portion has a stepped shape where the area of the flow channel is stepwisely changed when the valve member moves. 
     In the above described structure, the throttle portion has the stepped shape where the area of the flow channel is stepwisely changed when the valve member moves. According to the structure, the flow channel area can be stepwisely adjusted by the stepped shape. Therefore, even when the pressure difference between in front of and behind the throttle portion becomes small by operating the operation portion to a certain extent and the pressure to jet out the air decreases, the decrease in the pressure can be compensated by the increase in the flow channel area, so that the relationship between the operation amount of the operation portion and the amount of air jetted out of the nozzle can be made close to a proportional relationship. 
     By stepwisely adjusting the flow channel area, it is made easy to keep constant the amount of air jetted out of the nozzle. That is, if the release valve or the pipe line is formed in the tapered shape and the amount of air is adjusted, the operation amount of the operation portion directly affects the amount of air being jetted out, so that in order to keep constant the amount of air jetted out of the nozzle, it is necessary that the operation amount of the operation portion be also kept constant. For this reason, it is difficult to keep constant the amount of air jetted out of the nozzle in a situation where it is difficult for the user to continue applying a constant force to the operation portion (for example, in a situation where the user uses the machine while shaking the nozzle under a condition where he/she is holding the machine). In this regard, according to the present disclosure, since the amount of air jetted out of the nozzle can be kept substantially constant even if the operation amount of the operation portion changes in some degree, the amount of air jetted out of the nozzle can be kept constant without the user continuing to apply a constant force to the operation portion. 
     According to an aspect of the disclosure, there is provided an air duster structure that is configured to jet compressed air out of a nozzle, the air duster structure comprising: a flow amount adjustment mechanism which is configured to adjust an amount of air jetted out of the nozzle, wherein the flow amount adjustment mechanism includes: a pipe line for circulating air; a valve member disposed inside the pipe line and being movable; and at least two throttle portions configured to gradually change areas of flow channels in which air circulates, with a movement of the valve member, to control a flow amount of the air in the pipe line, and change amounts of the areas of the flow channels of the throttle portions with respect to a movement amount of the valve member are different from each other. 
     In the above described structure, at least two throttle portions are provided where the flow channel area change amounts with respect to the movement amount of the valve member can be made different from each other. According to the structure, the flow channel area can be stepwisely adjusted by the flow amount adjustment at two places. Therefore, even when the pressure difference between in front of and behind the throttle portion becomes small by operating the operation portion to a certain extent and the pressure to jet out the air decreases, the decrease in the pressure can be compensated by the increase in the flow channel area, so that the relationship between the operation amount of the operation portion and the amount of air jetted out of the nozzle can be made close to a proportional relationship. 
     The throttle portion may be configured to gradually change an amount of clearance between the pipe line and the valve member when the valve member moves, to control the flow amount of the air in the pipe line. In this case, the flow channel area can be changed by the change of the clearance amount. 
     According to an aspect of the disclosure, there is provided an air duster structure that is configured to jet compressed air out of a nozzle, the air duster structure comprising: a flow amount adjustment mechanism which is configured to adjust an amount of air jetted out of the nozzle, wherein the flow amount adjustment mechanism includes: a pipe line for circulating air; a valve member disposed inside the pipe line and being movable; and a throttle portion configured to gradually change an amount of clearance between the pipe line and the valve member when the valve member moves, an opening portion that is open in a direction orthogonal to a direction in which the valve member moves is provided on one of the pipe line or the valve member, a blocking portion capable of adjusting an opening amount of the opening portion is provided on the other of the pipe line or the valve member, and the flow amount adjustment mechanism is configured to control a flow amount of the air in the pipe line by a change of the clearance amount at the throttle portion and a change of the opening amount of the opening portion. 
     In the above described structure, the flow amount of the air in the pipe line is controlled by the change of the clearance amount at the throttle portion and the change of the opening amount of the opening portion. According to the structure, the flow channel area can be stepwisely adjusted by the flow amount adjustment at two places. Therefore, even when the pressure difference between in front of and behind the throttle portion becomes small by operating the operation portion to a certain extent and the pressure to jet out the air decreases, the decrease in the pressure can be compensated by the increase in the flow channel area, so that the relationship between the operation amount of the operation portion and the amount of air jetted out of the nozzle can be made close to a proportional relationship. 
     According to an aspect of the disclosure, there is also provided a driving tool comprising the air duster structure, the driving tool configured to eject a fastener by using the compressed air. 
     According to an aspect of the disclosure, there is also provided a driving tool which includes an air duster structure that is configured to jet compressed air out of a nozzle, and which is configured to eject a fastener by using the compressed air, the driving tool comprising: an operation portion; a pipe line for circulating air; and a valve member which is configured to move in the pipe line with an operation to the operation portion, wherein, when the operation portion is operated, the compressed air is jetted out of the nozzle, and, when the operation portion is operated, the valve member moves in the pipe line, and an area of a flow channel in which air circulates is changed with the movement of the valve member so that a flow amount of the air in the pipe line is adjusted.