Patent Publication Number: US-7896101-B2

Title: Pneumatically operated power tool having mechanism for changing compressed air pressure

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a pneumatically operated power tool, such as a pneumatically operated screw driver driven by compressed air to perform a prescribed operation. 
     Pneumatically operated screw drivers are well known in the art as a type of pneumatically operated power tool. In the examples of Japanese Patent Application Publications Nos. H11-300639 and 2005-118895, the screw driver includes a rotating body driven to rotate by a pneumatic motor, a rotation slide member accommodated in the rotating body so as to be capable of sliding up and down therein, a driver bit mounted on the lower end of the rotation slide member, and a piston formed circumferentially around the lower end of the rotation slide member and fitted into a cylinder so as to be capable of moving vertically therein. 
     With this type of screw driver, the rotation of the pneumatic motor is transmitted to the driver bit through the rotation slide member, and air compression applied to the piston moves the rotation slide member within the cylinder, thereby applying rotational and axial movement to the driver bit mounted on the rotation slide member in order to drive a screw into a workpiece. After the screw driving operation is completed, compressed air accumulated in a return chamber returns the rotation slide member and the driver bit to their initial states. 
     Although this screw driver is applied to applications for fastening a gypsum plaster board, for example, to a base member formed of wood, a steel plate, or the like, the amount of energy required for driving the screw in the case of the steel plate varies considerably depending on the thickness and hardness of the steel plate. If the steel plate is considerably thick or hard, the screw driver cannot drive the screw into the plate, as the tip of the screw does not penetrate the plate in some cases. Hence, the pressure of the supplied compressed air is set sufficiently high to produce a large driving force for penetrating the steel plate. However, since this driving force is too large when driving a screw into a thinner steel plate, the screw will penetrate the steel plate too far so that the gypsum plaster board or the like is not securely fastened. Hence, this conventional screw driver requires means for adjusting the force of the compressed air to suit the type of base member. 
     Conventionally, a pressure reduction valve has been used to change the force of compressed air. Normally, the pressure reduction valve is mounted on or disposed near the compressor at a position separated from the working position. Therefore, the operator of the screw driver must walk to the location, in which the compressor is positioned, to change the pressure reduction valve when the type of base member requires a different driving force, resulting in cumbersome work for the operator. 
     Hence, some screw drivers that are now available commercially incorporate a pressure changing mechanism having a pressure reduction valve in the body of the screw driver. 
     SUMMARY OF THE INVENTION 
     However, normally the pressure changing mechanism provided in these conventional screw drivers cannot be changed in steps, but are configured of an adjustment knob that the operator rotates to change the pressure. Consequently, the operator cannot instantaneously switch the pressure changing mechanism to a desired pressure, resulting in poor operability and user-friendliness for situations in which work conditions change frequently. 
     Therefore, it is an object of the present invention to provide a pneumatically operated power tool having improved operability by allowing the operator to switch between desired pressures easily and instantaneously. 
     In order to attain the above and other objects, the present invention provides a pneumatically operated power tool including an outer frame, driving components, a pressure reduction valve, and a switching valve. The outer frame has a compressed air intake portion and defines therein a compressed air chamber. The driving components are disposed in the outer frame and are driven by a compressed air in the compressed air chamber. The pressure reduction valve defines a pressure receiving space and allows a compressed air to flow from the air intake portion to the compressed air chamber and to the pressure receiving space. The switching valve is movable between a first position where the compressed air flows from the compressed air intake portion to the pressure receiving space, and a second position where a communication between the compressed air intake portion and the pressure receiving space is blocked. The pressure reduction valve is configured to set a compressed air pressure in the compressed air chamber to a first pressure level if the switching valve is located at the first position and to set the compressed air pressure to a second pressure level lower than the first pressure level if the switching valve is located at the second position. 
     According to another aspect, the invention also provides a pressure changing mechanism for use in a pneumatically operated power tool including an outer frame having a compressed air intake portion and defining therein a compressed air chamber, and driving components disposed in the outer frame and driven by a compressed air in the compressed air chamber. The pressure changing mechanism includes a pressure reduction valve and a switching valve. The pressure reduction valve defines a pressure receiving space and allows a compressed air to flow from the air intake portion to the compressed air chamber and to the pressure receiving space. The switching valve is movable between a first position where the compressed air flows from the compressed air intake portion to the pressure receiving space, and a second position where a communication between the compressed air intake portion and the pressure receiving space is blocked. The pressure reduction valve is configured to set a compressed air pressure in the compressed air chamber to a first pressure level if the switching valve is located at the first position and to set the compressed air pressure to a second pressure level lower than the first pressure level if the switching valve is located at the second position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a cross-sectional view of a pneumatically operated screw driver according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of a pressure changing mechanism provided in the screw driver according to the first embodiment when a switching valve is in a first position; 
         FIG. 3  is a cross-sectional view of a pressure changing mechanism provided in the compressed air screwdriver according to the first embodiment when the switching valve is in a second position; 
         FIG. 4  is a cross-sectional view of a pressure changing mechanism provided in the screw driver according to a second embodiment of the present invention when the switching valve is in the first position; 
         FIG. 5  is a cross-sectional view of a pressure changing mechanism provided in the screw driver according to the second embodiment when the switching valve is in the second position; 
         FIG. 6  is a cross-sectional view of a nail gun according to a variation of the present invention; and 
         FIG. 7  is a side cross-sectional view of an impact driver according to another variation of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A pneumatically operated power tool according to a first embodiment of the present invention will be described with reference to  FIGS. 1 through 3 . The first embodiment pertains to a screw driver. 
       FIG. 1  is a cross-sectional view of the pneumatically operated screw driver  1  according to the first embodiment. The screw driver  1  includes a having a T-shape in a side view. Inside the outer frame  2 , a compressed air chamber S 1  is defined in which a compressed air supplied from an external compressor (not shown) is accumulated. The outer frame  2  also has a handle  2   a . A pressure changing mechanism  3  is connected to a rear end of the handle  2   a . An air plug  4  is provided on the rear end of the pressure changing mechanism  3  for connecting an air hose (not shown) leading from the external compressor (not shown). The handle  2   a  is formed with a discharge path  42  for discharging compressed air from the outer frame  2 . 
     A magazine  5  capable of accommodating a plurality of screws (not shown) linked to one another is mounted on the lower end of the outer frame  2 . The screw driver  1  also includes an operation valve  8  and a trigger  6 . The operation valve is provided in the region where the handle  2   a  connects to the outer frame  2  and has a plunger  7 . The trigger  6  moves the plunger  7  up and down. 
     A pneumatic motor  9  having a rotor  9   a  is accommodated in a top section of the outer frame  2 . A planetary gear mechanism  10  is disposed beneath the pneumatic motor  9 . A cylindrical rotary member  11  having a closed bottom is rotatably supported in the outer frame  2  by a bearing  12 . The rotary member  11  is connected to the rotor  9   a  of the pneumatic motor  9  via the planetary gear mechanism  10 . A rotation of the rotor  9   a  is decelerated by the planetary gear mechanism  10  and transmitted to the rotary member  11 . A damper plate  41  is provided below the rotary member  11  to close the bottom of the rotary member  11 . 
     A plurality of air holes  13  is formed in a side wall of the rotary member  11  near a axial center of the rotary member  11 . A main valve  15  having a cylindrical shape and being capable of moving in a axial direction of the rotary member  11  is disposed in a groove formed in the outer frame  2  at a position corresponding to the air holes  13 . The main valve  15  is formed with an air hole  17 . A spring  16  urges the main valve  15  upward. 
     An air hole  18  in communication with the operation valve  8  is formed below the groove in the outer frame  2 . 
     A rotation slide member  20  is fitted into the rotary member  11  so as to be axially movable relative to the rotary member  11  in the axial direction. A raised portion provided on the periphery of the rotation slide member  20  is fitted into a recessed portion formed in the inner peripheral surface of the rotary member  11 . Thus, the rotation slide member  20  is rotatable together with the rotary member  11 . A piston  20   a  is provided around the lower end of the rotation slide member  20 . The rotation slide member  20  defines a blocking surface  20   b  for sealing a fluid communication between the inside of the rotary member  11  and the inside of the pneumatic motor  9 . A driver bit  21  is provided on the bottom end of the rotation slide member  20  and extends downward therefrom. 
     A cylinder  22  formed with an opening in the top surface thereof extends along the axial direction in the lower section of the outer frame  2 . The piston  20   a  fits into the cylinder  22  so as to be capable of sliding in the axial direction along the inner peripheral surface of the cylinder  22 . A return chamber S 2  is defined by the cylinder  22  and a lower outer frame part  2 B. A piston damper  23  is provided in the bottom of the cylinder  22 . 
     A screw feeder  24  is provided on the bottom of the outer frame  2  for automatically supplying the screws accommodated in the magazine  5 . A push lever  25  is provided below the screw feeder  24 , with one end extending near the trigger  6 . 
     Next, the operations of the screw driver  1  having the above structure will be described. 
     Compressed air is introduced into the groove below the main valve  15  through the compressed air chamber S 1 , operation valve  8 , and air hole  18 . At this time, the air pressure and the biasing force of the spring  16  push the main valve  15  upward, closing off the air holes  13  that provide the fluid communication between the compressed air chamber S 1  and the rotary member  11  and sealing the supply of compressed air into the rotary member  11  and toward the pneumatic motor  9 . 
     With the screw driver  1  in this state, the operator pushes the push lever  25  against a workpiece such as a wood or a gypsum plaster board, and pulls the trigger  6  to actuate the operation valve  8 . At this time, the compressed air beneath the main valve  15  is discharged from the screw driver  1  through the air hole  18  and operation valve  8 . Since air pressure is being applied to the top surface of the main valve  15  near the outer periphery thereof, the main valve  15  is pressed downward against the biasing force of the spring  16 . Hence, compressed air flows into the rotary member  11 , applying air pressure to the top surface of the piston  20   a . Consequently, the rotation slide member  20  is pressed downward together with the driver bit  21 , allowing compressed air to be supplied to the pneumatic motor  9  for driving the same. 
     As described above, upon driving the pneumatic motor  9 , the planetary gear mechanism  10  transmits the rotation of the rotor  9   a  to the rotary member  11  at a reduced ratio, thereby rotating the rotary member  11  and rotation slide member  20 . Therefore, the driver bit  21  mounted on the rotation slide member  20  rotates while being pushed downward in order to drive a screw into the workpiece (not shown). 
     When the driver bit  21  reaches the end of its downward drop at which the screw driving operation is complete, the piston  20   a  of the rotation slide member  20  collides with the piston damper  23 , halting the drop of the rotation slide member  20  and driver bit  21 . At the same time, the air blocking surface  20   b  of the rotation slide member  20  contacts the damper plate  41 , thereby sealing the supply of compressed air to the pneumatic motor  9 . Since the pneumatic motor  9  halts operations at this time, the rotary member  11 , rotation slide member  20 , and driver bit  21  cease to rotate. At this time, compressed air is collected in the return chamber S 2 . 
     After the operator subsequently releases the push lever  25  and the trigger  6  so that the operation valve  8  returns to its initial position, compressed air and the biasing force of the spring  16  push the main valve  15  upward. The compressed air flows into the groove beneath the main valve  15  from the compressed air chamber S 1  via the operation valve  8  and air hole  18 . At this time, the fluid communication between the compressed air chamber S 1  and rotary member  11  is sealed, while the air hole  17  formed in the main valve  15  is in communication with the discharge path  42  through an air passage (not shown). Accordingly, compressed air in the rotary member  11  is discharged from the outer frame  2 . Since the compressed air accumulated in the return chamber S 2  is supplied into the cylinder  22 , the bottom surface of the piston  20   a  receives the force of this compressed air so that the rotation slide member  20  rises together with the driver bit  21  and returns to its initial position. At the same time, the screw feeder  24  feeds the next screw from the magazine  5  to a position aligned with the axis of the driver bit  21  and subsequently returns to its initial state. 
     Next, the pressure changing mechanism  3  provided in the screw driver  1  according to the first embodiment will be described in greater detail with reference to  FIGS. 2 and 3 . 
       FIGS. 2 and 3  are cross-sectional views of the pressure changing mechanism  3 . The pressure changing mechanism  3  has a pressure reduction valve  26  disposed between the air plug  4  and the compressed air chamber S 1 . The pressure reduction valve  26  mainly includes a main body  26 A, a piston  27 , a first spring  28 , a valve head  29 , a second spring  30 , an end cap  32 , and a holder  32 A. The main body  26 A further includes a first section  26 A 1 , a second section  26 A 2 , and a third section  26 A 3 . The first section  26 A 1  is cylindrical in shape with a closed bottom and defines a valve chamber S 6  extending in the front-to-rear direction therein. The second section  26 A 2  is formed with a first through-hole  34 , a second through-hole  35 , and an air hole  44 . The third section  26 A 3  is also cylindrical in shape with a closed bottom and is formed with a communication hole  26   d  communicating with the compressed air chamber S 1 . 
     The piston  27  is disposed inside the third section  26 A 3  and, together with the third section  26 A 3 , defines a spring chamber S 3 . The piston  27  also has a first seal member  27   a  and a second seal member  27   b . The first seal  27   a  has an outer diameter larger than that of the second seal  27   b . Both the first and second seal members  27   a  and  27   b  are configured of an O-ring. The third section  26 A 3  also includes a first wall  26 B, and a second wall  26 C. The first wall  26 B has an inner diameter, which is substantially equal to the outer diameter of the first seal member  27   a , while the second wall  26 C has an inner diameter, which is substantially equal to the outer diameter of the second seal member  27   b . Thus, the first seal member  27   a  slidingly moves along the first wall  26 B, while the second seal member  27   b  slidingly moves along the second wall  26 C. Accordingly, the piston  7  is slidingly movable relative to the third section  26 A 3 . The first seal member  27   a , second seal member  27   b , first wall  26 B, second wall  26 C and piston  27  define a seal space S 5 . 
     The piston  27  also has a first pressure receiving surface  27 A, formed on the rear side, in confrontation with the holder  32 A, and a second pressure receiving surface  27 B formed as a step part between the first seal member  27   a  and second seal member  27   b  and facing the seal space S 5 . A valve stem  27 C extends from the first pressure receiving surface  27 A. The first spring  28  is interposed between a bottom of the main body  26 A and the piston  27  for urging the piston  27  toward the air plug  4 . 
     The holder  32 A is disposed on the rear side of the piston  27  for sealing fluid communication between the compressed air chamber S 1  and a compressed air injection chamber S 7  defined by the end cap  32  and the holder  32 A. A through-hole  31  is formed in the holder  32 A for allowing penetration of the valve stem  27 C. Accordingly, an annular space is formed between the valve stem  27 C and the through-hole  31 . The valve head  29  is fixed to a distal end of the valve stem  27 C and moves together with the piston  27 . The valve head  29  can contact the holder  32 A to close the through-hole  31  when the piston  27  moves forward. 
     The second spring  30  is interposed between the valve head  29  and end cap  32  for urging the valve head  29  toward the piston  27 . Hence, the valve head  29  is supported by the spring  30  while being allowed to move. The end cap  32  is disposed at the open edge of the third section  26 A 3 . The holder  32 A and the end cap  32  define a compressed air injection chamber S 7  in communication with the air plug  4 . Further, the first pressure receiving surface  27 A is formed with diametrically extending cruciform grooves  43  communicating with the compressed air chamber S 1  via the communication hole  26   d . The spring chamber S 3  is constantly in fluid communication with external air through the air hole  44 . 
     A switching valve  33  is slidably movably fitted into the valve chamber S 6 . A space S 4  is defined by the first section  26 A 1  and the switching valve  33 . When the switching valve  33  is in a first position shown in  FIG. 2 , the space S 4  is in fluid communication with the cruciform grooves  43  through the first through-hole  34  and in fluid communication with the seal space S 5  through the second through-hole  35 . When the switching valve  33  is in a second position shown in  FIG. 3 , the space S 4  is only in fluid communication with the cruciform grooves  43  through the first through-hole  34 . 
     The switching valve  33  includes a first O-ring  36  for constantly sealing communication between the first through-hole  34  and external air, and a second O-ring  37  for sealing or opening communication between the space S 4  and the second through-hole  35  as the switching valve  33  is moved left and right in the drawings. A spring  38  is interposed between a bottom of the first section  26 A 1  and the switching valve  33  in the valve chamber S 6  for urging the switching valve  33  rearward in  FIG. 2 . 
     A through-hole  33   b  is formed in the switching valve  33 , and a knob  39  is inserted into the through-hole  33   b . The knob  39  is rotated to move the switching valve  33  in the front-to-rear direction. A tapered surface  33   a  is formed on the rear end of the switching valve  33  and engages with a pin  40  protruding at a position eccentric to the rotational axis of the knob  39 . Since a position at which the pin  40  engages the tapered surface  33   a  changes as the knob  39  is rotated, the switching valve  33  is moved in the front-to-rear direction (between the first position shown in  FIG. 2  and the second position shown in  FIG. 3 ) as the knob  39  is rotated. 
       FIG. 2  shows a first state of the pressure changing mechanism  3  when the knob  39  has moved the switching valve  33  forward. In the first state, the first and second through-holes  34  and  35  are in fluid communication with each other. Further, a force acting on the piston  27  for moving the piston  27  rearward includes both the biasing force of the first spring  28  and the force of compressed air introduced from the compressed air chamber S 1  into the seal space S 5  via the cruciform grooves  43  and the first and second through-holes  34  and  35 . Therefore, a first setting pressure of the pressure reduction valve  26  is set to a high pressure. Specifically, the valve head  29  closes the through-hole  31  when a force by the pressure P 1  of compressed air applied to the first pressure receiving surface  27 A of the piston  27  having a surface area SA is equivalent to a force by a pressure P 1  of compressed air applied to the second pressure receiving surface  27 B of the piston  27  having a surface area SB and the biasing force F of the first spring  28  (SA×P 1 =SB×P 1 +F). Thus, a pressure level in the compressed air chamber S 1  is maintained by the pressure reduction valve  26 . Since the pressure P 1  of compressed air is applied to both the first and second pressure receiving surfaces  27 A and  27 B of the piston  27 , this case can be considered equivalent to the case in which the pressure receiving surface area of the piston  27  is decreased. With this construction, it is possible to vary the pressure receiving surface area of the piston  27 . More specifically, it is possible to vary the effective pressure receiving surface area for moving the piston  27  forward in  FIG. 2  against the biasing force of the first spring  28 . At this time, the first setting pressure in the screw driver  1  (pressure level of the compressed air chamber S 1 ) is normally about 8 atm. 
     If the pressure in the compressed air chamber S 1  is lowered, the piston  27  is moved toward the air plug  4  by the biasing force of the first spring  28 . As a result, the valve head  29  opens the through-hole  31 . Thus, a new compressed air can be introduced into the compressed air chamber S 1  through the pressure reduction valve  26 . In this way, the pressure in the compressed air chamber S 1  can be maintained at the first setting pressure lower than the pressure level in the air plug  4 . 
       FIG. 3  shows a second state of the pressure changing mechanism  3  when the switching valve  33  has been moved rearward by rotating the knob  39  180° from the first state shown in  FIG. 2 . In the second state, the second O-ring  37  of the switching valve  33  seals communication between the first and second through-holes  34  and  35 , while simultaneously allowing communication between the seal space S 5  and the external air. Since only the biasing force of the first spring  28  is applied to the piston  27  for moving the piston  27  rearward at this time, a second setting pressure of the pressure reduction valve  26  is lower than the first setting pressure of the state shown in  FIG. 2 . Specifically, the valve head  29  closes the through-hole  31  when the force by the pressure P 1  of compressed air applied to the first pressure receiving surface  27 A of the piston  27  having a surface area SA is equivalent to the biasing force F of the first spring  28  (SA×P 1 =F). At this time, the second setting pressure in the screw driver  1  (pressure level of the compressed air chamber S 1 ) is normally about 5 atm. 
     With the first embodiment described above, the effective pressure receiving surface area of the piston  27  can be varied through a simple operation of rotating the knob  39  180° (a half rotation). In this way, the setting pressure in the compressed air chamber S 1  can easily be changed in two stages (first and second setting pressure), thereby improving operability for instantaneously switching the setting pressure to a pressure suitable for different types of workpieces. 
     Next, a pneumatically operated power tool according to a second embodiment of the present invention will be described with reference to  FIGS. 4 and 5 . 
       FIGS. 4 and 5  are cross-sectional views of the pressure changing mechanism  103  provided in a screw driver according to the second embodiment, wherein like parts and components are designated with the same reference numerals to avoid duplicating description. 
     A feature of the second embodiment is that a first through-hole  134  is in communication with the compressed air injection chamber S 7  rather than the compressed air chamber S 1  (cruciform grooves  43 ). The remaining structure is identical to that of the first embodiment shown in  FIGS. 2 and 3 . 
       FIG. 4  shows a third state of the pressure changing mechanism  103  when the knob  39  has moved the switching valve  33  forward to allow communication between the first and second through-holes  134  and  35 . In the third state, a force acting on the piston  27  for moving the piston  27  rearward includes both the biasing force of the first spring  28  and the force of pressure compressed air introduced from the compressed air injection chamber S 7  into the seal space S 5  through the first and second through-holes  134  and  35 . Therefore, a third setting pressure of the pressure reduction valve  26  is set to a high pressure. Specifically, the valve head  29  closes the through-hole  31  when a force by a pressure P 2  of compressed air applied to the first pressure receiving surface  27 A of the piston  27  having the surface area SA is equivalent to the biasing force F of the first spring  28  and a force by the pressure P 2  of compressed air applied to the second pressure receiving surface  27 B of the piston  27  having the surface area SB (SA×P 2 =SB×P 2 +F). Accordingly, the pressure level in the compressed air chamber S 1  does not exceed the setting pressure (8 atm, for example). 
       FIG. 5  shows a fourth state of the pressure changing mechanism  103  when the switching valve  33  has been moved rearward by rotating the knob  39  180° from the third state shown in  FIG. 4 . In the fourth state, the second O-ring  37  of the switching valve  33  seals communication between the first and second through-holes  134  and  35 , while simultaneously allowing communication between the seal space S 5  and the external air. Since only the biasing force of the first spring  28  is applied to the piston  27  for moving the piston  27  rearward, a fourth setting pressure of the pressure reduction valve  26  is lower than the third setting pressure of the state shown in  FIG. 4 . Specifically, the valve head  29  closes the through-hole  31  when a force by the pressure P 2  of compressed air applied to the first pressure receiving surface  27 A of the piston  27  having the surface area SA is equivalent to the biasing force F of the first spring  28  (SA×P 2 =F). Hence, the pressure level in the compressed air chamber S 1  does not exceed the set pressure (5 atm, for example). 
     In the second embodiment described above, the setting pressure in the compressed air chamber S 1  can easily be changed in two stages (third and fourth setting pressure) through the simple operation of rotating the knob  39  180° (a half turn), thereby improving operability for instantaneously switching the setting pressure to a pressure suited to the type of workpiece. 
     While the invention has been described in detail with reference to specific embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims. For example, it should be apparent that the present invention can similarly be applied to another type of pneumatically operated power tool other than the screw driver, such as a nail gun  201  shown in  FIG. 6  and an impact driver  301  shown in  FIG. 7 . In either variation, the pressure changing mechanisms  203  and  303  are mounted on one ends of the handles  202   a  and  302   a  of the outer frames  202  and  302 , respectively.