Patent Publication Number: US-2021162572-A1

Title: Driving tool

Description:
TECHNICAL FIELD 
     The present invention relates to a driving tool including a striking unit capable of being actuated to strike a fastener. 
     BACKGROUND ART 
     A driving tool including a striking unit and a driver unit is described in Patent Document 1. The driving tool described in Patent Document 1 has a housing, a pressure accumulation chamber, a pressure chamber, a striking unit, a push lever, a cylinder, a trigger, a trigger valve, and a delay valve as an actuator. The pressure accumulation chamber is provided in the housing, and compressed air is supplied to the pressure accumulation chamber. 
     In the case where a worker uses the driving tool described in Patent Document 1, if an elapsed time from the time when the worker applies an operation force to the trigger is within a predetermined time, the delay valve connects a passage to supply the compressed gas in the pressure accumulation chamber to the pressure chamber. Therefore, when the push lever is pressed to a workpiece within the predetermined time from the time when the operation force is applied to the trigger, compressed air is supplied to the pressure chamber, and the striking unit is actuated in the direction of striking the fastener. 
     On the other hand, when the predetermined time has passed from the time when the operation force is applied to the trigger, the delay valve disconnects the passage to supply the compressed gas in the pressure accumulation chamber to the pressure chamber. Therefore, the compressed air is not supplied to the pressure chamber even if the push lever comes into contact with an object other than the workpiece after the predetermined time has passed from the time when the operation force is applied to the trigger. Namely, the striking unit is not actuated in the direction of striking the fastener. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: International Patent Application Publication No. 2017-115593 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     The inventor of this application has recognized that there is a possibility that the power consumption of an actuator increases when the actuator is actuated by electric power. 
     An object of the present invention is to provide a driving tool capable of suppressing the power consumed for actuating an actuator. 
     Means for Solving the Problems 
     A driving tool according to an embodiment includes a striking unit configured to strike a fastener, a housing in which the striking unit is provided, an operation member provided on the housing, and a contact member actuated by being pressed to a workpiece into which the fastener is driven, and the driving tool comprises: a stopper having a first position where the actuation of the contact member is blocked and a second position where the actuation of the contact member is enabled; and an actuator configured to drive the stopper, wherein the actuator holds the stopper at the second position by being supplied with electric power when the stopper is at the second position. 
     Effects of the Invention 
     In the driving tool according to an embodiment, it is possible to suppress the power consumed for actuating the actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front cross-sectional view showing an overall structure of a driving tool according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view showing the principal part of the driving tool; 
         FIG. 3(A)  is a cross-sectional view showing a mounting structure of a trigger provided in the driving tool and  FIG. 3(B)  is a schematic diagram showing a state where an operation force is applied to the trigger; 
         FIG. 4(A)  is a schematic diagram showing a state where an operation force is applied to the trigger and a transmission member is actuated and  FIG. 4(B)  is a schematic diagram showing a state where an operation force is applied to the trigger and the actuation of the transmission member is blocked; 
         FIG. 5  is a block diagram showing a control system of the driving tool; 
         FIG. 6  is a flowchart showing a first control example executed in the driving tool; 
         FIG. 7(A)  and  FIG. 7(B)  are partial cross-sectional views showing another example of a solenoid provided in the driving tool; 
         FIG. 8  is a flowchart showing a second control example executed in the driving tool; 
         FIG. 9  is a flowchart showing a third control example executed in the driving tool; and 
         FIG. 10  is a diagram showing a relationship between a stroke of a plunger and a magnetic attraction force. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Next, some driving tools according to embodiments of the present invention will be described with reference to drawings. 
     A driving tool  10  shown in  FIG. 1  includes a housing  11 , a cylinder  12 , a striking unit  13 , a trigger  14 , an ejection unit  15 , and a push lever  16 . Also, a magazine  17  is attached to the driving tool  10 . The housing  11  has a tubular main body  18 , a head cover  21  fixed to the main body  18 , and a handle  19  connected to the main body  18 . 
     A pressure accumulation chamber  20  is formed across an inside of the handle  19 , an inside of the main body  18 , and an inside of the head cover  21 . A plug is attached to the handle  19 . An air hose is connected to the plug. Compressible gas is supplied to the pressure accumulation chamber  20  through the air hose. Air or inert gas can be used as the compressible gas. Examples of the inert gas include nitrogen gas, rare gas, and others. The cylinder  12  is provided in the main body  18 . The head cover  21  has an exhaust passage  24 . The exhaust passage  24  is connected to an outside B 1  of the housing  11 . 
     A head valve  31  is provided in the head cover  21 . The head valve  31  can be actuated in the direction of a center line A 1  of the cylinder  12 . A control chamber  27  is formed in the head cover  21 . A biasing member  28  is provided in the control chamber  27 . The biasing member  28  is, for example, a metal spring. A stopper  29  is provided in the head cover  21 . A valve seat  32  is attached to an end portion of the cylinder  12  that is closest to the head valve  31  in the direction of the center line A 1 . 
     The head valve  31  constantly receives the pressure of the pressure accumulation chamber  20 , and the head valve  31  is biased in a direction away from the valve seat  32  by the pressure of the pressure accumulation chamber  20 . The biasing member  28  biases the head valve  31  toward the valve seat  32  in the direction of the center line A 1 . A passage  91  is formed between the head valve  31  and the stopper  29 . The passage  91  is opened and closed by the actuation of the head valve  31  in the direction of the center line A 1 . When the passage  91  is closed, a piston upper chamber  36  and the outside B 1  are disconnected. When the passage  91  is opened, the piston upper chamber  36  and the outside B 1  are connected. 
     The striking unit  13  includes a piston  34  and a driver blade  35  fixed to the piston  34 . The piston  34  is arranged in the cylinder  12 . The striking unit  13  can be actuated in the direction of the center line A 1  and stopped. A sealing member  30  is attached to an outer peripheral surface of the piston  34 . The piston upper chamber  36  is formed between the stopper  29  and the piston  34 . A passage  110  is formed between the head valve  31  and the valve seat  32 . 
     When the head valve  31  is separated from the valve seat  32 , the passage  110  is opened and the pressure accumulation chamber  20  is connected to the piston upper chamber  36 . When the head valve  31  is pressed to the valve seat  32 , the passage  110  is closed and the pressure accumulation chamber  20  is disconnected from the piston upper chamber  36 . Also, the piston upper chamber  36  is connected to the outside B 1  of the housing  11  via the exhaust passage  24 . 
     The ejection unit  15  is fixed to an end portion of the main body  18  on a side opposite to the head cover  21  in the direction of the center line A 1 . The ejection unit  15  has an ejection path  72 . The center line A 1  is located in the ejection path  72 , and the driver blade  35  is movable in the ejection path  72  in the direction of the center line A 1 . 
     A bumper  37  is provided in the cylinder  12 . The bumper  37  is arranged at a position closest to the ejection unit  15  in the direction of the center line A 1  in the cylinder  12 . The bumper  37  has a shaft hole  38 , and the driver blade  35  can be actuated in the shaft hole  38  in the direction of the center line A 1 . In the cylinder  12 , a piston lower chamber  39  is formed between the piston  34  and the bumper  37 . 
     A trigger valve  51  is provided at a connection portion between the main body  18  and the handle  19 . As shown in  FIG. 2 , the trigger valve  51  has a tubular holder  53 , a plunger  52 , a tubular valve body  55 , passages  56  and  90 , and a biasing member  69 . The holder  53  is fixed to the housing  11 . The valve body  55  is arranged in the holder  53 . Sealing members  58  and  59  are attached to an outer peripheral surface of the valve body  55 . The valve body  55  can be actuated with respect to the holder  53  in the direction of a center line A 2 . 
     The passage  56  is connected to the control chamber  27  via a passage  57 . The passage  90  is connected to the outside B 1  of the housing  11 . The plunger  52  is arranged in the valve body  55 . The plunger  52  can be actuated with respect to the valve body  55  in the direction of the center line A 2 . The center line A 1  and the center line A 2  are parallel to each other. The biasing member  69  is, for example, a compression spring, and the biasing member  69  biases the plunger  52  in the direction away from the pressure accumulation chamber  20  in the direction of the center line A 2 . 
     When the valve body  55  is actuated and the sealing member  58  is separated from the holder  53  as shown in  FIG. 2 , the pressure accumulation chamber  20  and the passage  56  are connected. Also, when the sealing member  58  is pressed to the holder  53 , the passage  56  and the passage  90  are disconnected. 
     When the valve body  55  is actuated and the sealing member  58  is pressed to the holder  53 , the pressure accumulation chamber  20  and the passage  56  are disconnected. Also, the sealing member  58  is separated from the holder  53 , and the passage  56  and the passage  90  are connected. 
     The magazine  17  is supported by the ejection unit  15  and the handle  19 . The magazine  17  stores fasteners  73 . The magazine  17  has a feeder  74 , and the feeder  74  sends the fasteners  73  in the magazine  17  to the ejection path  72 . 
     As shown in  FIG. 1 , the push lever  16  is attached to the ejection unit  15 . The push lever  16  can be actuated with respect to the ejection unit  15  and the housing  11  in the direction of the center line A 1 . A transmission member  75  is connected to the push lever  16 . The transmission member  75  can be actuated together with the push lever  16  within a predetermined range in the direction of the center line A 2 . 
     As shown in  FIG. 2 ,  FIG. 3(A) ,  FIG. 3(B) ,  FIG. 4(A) , and  FIG. 4(B) , the trigger  14  is attached to a mounting portion  22  via a support shaft  40 . The mounting portion  22  is provided so as to protrude from an outer surface of the main body  18 . The trigger  14  can be actuated about the support shaft  40  within a predetermined angle range. A biasing member  41  is provided, and the biasing member  41  biases the trigger  14  clockwise in  FIG. 2 . The biasing member  41  is, for example, a metal spring. 
     A trigger arm  42  is attached to the trigger  14  via a support shaft  43 . The trigger arm  42  can be actuated with respect to the trigger  14  about the support shaft  43  within a predetermined angle range. A biasing member  44  is provided on the trigger  14 . The biasing member  44  biases the trigger arm  42  counterclockwise with respect to the trigger  14 . The biasing member  44  is, for example, a metal spring. A part of the trigger arm  42  is arranged between the trigger valve  51  and the transmission member  75  in the direction of the center line A 2 . 
     A stopper  76  shown in  FIG. 2  is attached to the support shaft  40 . The stopper  76  can be actuated, that is, is rotatable with respect to the trigger  14  about the support shaft  40  within a predetermined angle range. When the stopper  76  is actuated about the support shaft  40 , a part of the stopper  76  enters or exits the actuation range of the transmission member  75 . The stopper  76  is made of metal, for example. A contact  77  is provided in the stopper  76 . The contact  77  is, for example, a pin. 
     A biasing member  122  for biasing the stopper  76  is provided. The biasing member  122  biases the stopper  76  counterclockwise about the support shaft  40 . The biasing force of the biasing member  122  is less than the biasing force of the biasing member  41 . When the stopper  76  is actuated clockwise with respect to the trigger  14 , the contact  77  is separated from the trigger  14 . When the stopper  76  is actuated counterclockwise with respect to the trigger  14 , the contact  77  approaches the trigger  14  and comes into contact with the trigger  14 . 
     A solenoid  78  shown in  FIG. 2  is provided in the mounting portion  22  (the mounting portion  22  is shown in  FIG. 3(B) ). The solenoid  78  is an example of an actuator. The solenoid  78  has a coil  79  and a plunger  80 . The plunger  80  can be actuated in a direction parallel to the center line A 2 . The plunger  80  is made of a magnetic material, for example, iron. The plunger  80  is coupled to the stopper  76  via a link member  81 . When electric power is supplied to the solenoid  78 , the solenoid  78  generates a magnetic attraction force, so that the solenoid  78  stops the plunger  80 . When the power supply to the solenoid  78  is stopped, the solenoid  78  releases the magnetic attraction force. 
       FIG. 5  is a block diagram showing a control system of the driving tool  10 . A power source unit  82  is attached to the handle  19  or the magazine  17 . The power source unit  82  has a plurality of battery cells. The battery cell is a secondary battery that can be charged and discharged, and any of a lithium ion battery, a nickel hydrogen battery, a lithium ion polymer battery, and a nickel cadmium battery can be used as the battery cell. The battery cell may be a primary battery. 
     The control unit  83  is provided in the handle  19  or the magazine  17 . The control unit  83  is a microcomputer including an input interface, an output interface, an arithmetic processing unit, a memory, and a timer. 
     A mode changing switch  84  is provided on the handle  19 . The worker selects either the first mode or the second mode as the mode for actuating the striking unit  13 . The worker operates the mode changing switch  84  to select the first mode or the second mode. 
     The mode in which the striking unit  13  is actuated by pressing the push lever  16  to a workpiece  123  in the state where the worker is applying an operation force to the trigger  14  (is operating the trigger  14 ) is the first mode. The first mode can be defined as a continuous firing mode. The mode in which the striking unit  13  is actuated by applying an operation force to the trigger  14  in the state where the worker is pressing the push lever  16  to the workpiece  123  is the second mode. The second mode can be defined as a single firing mode. 
     When the worker selects the first mode, the mode changing switch  84  is turned on. When the mode changing switch  84  is turned on, the electric power of the power source unit  82  is supplied to the control unit  83 , and the control unit  83  is activated. When the worker selects the second mode, the mode changing switch  84  is turned off. When the mode changing switch  84  is turned off, the power supply to the control unit  83  is stopped, and the control unit  83  is stopped. 
     An actuator switch  85  is provided between the power source unit  82  and the solenoid  78 . The control unit  83  controls the on and off of the actuator switch  85 . When the control unit  83  turns on the actuator switch  85 , the electric power of the power source unit  82  is supplied to the solenoid  78 . When the control unit  83  turns off the actuator switch  85 , the power supply to the solenoid  78  is stopped. Note that, when the control unit  83  is stopped, the actuator switch  85  is turned off. 
     Further, a trigger switch  87  is provided in the handle  19  or the main body  18 . When the worker applies an operation force to the trigger  14 , the trigger switch  87  is turned on. When the worker releases the operation force on the trigger  14 , the trigger switch  87  is turned off. Further, a push lever switch  86  is provided in the ejection unit  15 . When the push lever  16  is actuated from the initial position with respect to the ejection unit  15 , the push lever switch  86  is turned on. When the push lever  16  is stopped at the initial position with respect to the ejection unit  15 , the push lever switch  86  is turned off. The signal of the trigger switch  87  and the signal of the push lever switch  86  are input to the control unit  83 . 
     A voltage detection sensor  88  that detects the voltage of the power source unit  82  is provided. The signal of the voltage detection sensor  88  is input to the control unit  83 . Further, a display unit  89  is provided. The display unit  89  is provided on, for example, the housing  11  or the handle  19 . The display unit  89  is composed of a liquid crystal panel, a light emitting diode lamp, and the like. The control unit  83  controls the display unit  89 , and the display unit  89  displays the voltage of the power source unit  82  and the like. 
     Next, the first control example executed in the driving tool  10  will be described with reference to the flowchart of  FIG. 6 . 
     First, the initial state of the driving tool  10  shown in  FIG. 1  and step S 10  will be described. When the worker releases the operation force on the trigger  14  and separates the push lever  16  from the workpiece  123 , the driving tool  10  is in the initial state. The trigger  14  biased by the biasing member  41  is stopped at the initial position shown in  FIG. 2 , and the trigger arm  42  biased by the biasing member  44  is stopped at the initial position shown in  FIG. 2 . 
     When the trigger arm  42  is stopped at the initial position, the trigger valve  51  is stopped in the standby state. In the standby state of the trigger valve  51 , the pressure accumulation chamber  20  and the passage  56  are connected, and compressed air is supplied to the control chamber  27 . Therefore, the head valve  31  is pressed to the valve seat  32  by the biasing member  28 . The head valve  31  closes the passage  110  and opens the passage  91 . Therefore, the pressure accumulation chamber  20  and the piston upper chamber  36  are disconnected, and the piston upper chamber  36  and the outside B 1  are connected. Accordingly, the striking unit  13  is stopped at the initial position shown in  FIG. 1 , that is, at the top dead center. 
     Further, the contact  77  is pressed to the trigger  14  as shown in  FIG. 2 , and the stopper  76  is stopped at the second position. When the stopper  76  is stopped at the second position, all of the stopper  76  is located outside the actuation range of the transmission member  75 . Further, the power supply to the solenoid  78  is stopped, and the plunger  80  is stopped at the second position in  FIG. 2 . 
     (Example of Selecting the First Mode) 
     When the worker selects the first mode in step S 11  and the mode changing switch  84  is turned on, the control unit  83  is activated. In step S 12 , the control unit  83  determines whether or not the voltage of the power source unit  82  is equal to or higher than a predetermined value capable of supplying electric power to the solenoid  78 . When the control unit  83  determines Yes in step S 12 , the control unit  83  supplies the electric power of the power source unit  82  to the solenoid  78  in step S 13 . The solenoid  78  generates a magnetic attraction force to stop the plunger  80  at the second position shown in  FIG. 2 . 
     The control unit  83  determines whether or not the trigger switch  87  is turned on in step S 14 . When the control unit  83  determines No in step S 14 , the control unit  83  repeats the determination in step S 14 . When the control unit  83  determines Yes in step S 14 , the control unit  83  starts the timer in step S 15  and continues to supply electric power to the solenoid  78 . 
     In step S 16 , the control unit  83  determines whether or not the push lever switch  86  is turned on within a predetermined time from the time when the timer is started. The predetermined time is, for example, 3 seconds. When the control unit  83  determines Yes in step S 16 , the control unit  83  resets the timer in step S 17  and continues to supply electric power to the solenoid  78 . 
     When an operation force is applied to the trigger  14 , the trigger arm  42  is actuated clockwise as shown in  FIG. 3(B) . The biasing force of the biasing member  122  is applied to the stopper  76 , but the plunger  80  is stopped at the second position by the magnetic attraction force of the solenoid  78 , and the stopper  76  is also stopped at the second position. Therefore, when the worker presses the push lever  16  to the workpiece  123  and the push lever  16  is actuated with respect to the ejection unit  15  from the initial position, the transmission member  75  is actuated in the direction toward the trigger valve  51  as shown in  FIG. 4(A) . 
     The actuation force of the transmission member  75  is transmitted to the plunger  52  via the trigger arm  42 . Then, the valve body  55  is actuated, and the trigger valve  51  switches from the standby state to the actuated state. When the trigger valve  51  is in the actuated state, the pressure accumulation chamber  20  and the passage  56  are disconnected, and the passage  56  and the passage  90  are connected. Therefore, the compressible gas in the control chamber  27  is discharged to the outside B 1  through the passage  90 . 
     Then, the head valve  31  is actuated and separated from the valve seat  32  to open the passage  110 , so that the pressure accumulation chamber  20  and the piston upper chamber  36  are connected. Further, the head valve  31  closes the passage  91 , so that the piston upper chamber  36  and the external B 1  are disconnected. Then, the compressible gas in the pressure accumulation chamber  20  is supplied to the piston upper chamber  36 , the striking unit  13  is actuated from the top dead center to the bottom dead center in step S 17 , and the driver blade  35  strikes the fastener  73 . Further, when the control unit  83  detects that the push lever switch  86  is off in step S 18 , the flow proceeds to step S 14 . 
     On the other hand, when the control unit  83  determines No in step S 16 , the control unit  83  resets the timer in step S 19  and stops the power supply to the solenoid  78 . Then, the stopper  76  shown in  FIG. 3(B)  is actuated counterclockwise by the biasing force of the biasing member  122 . Further, when the contact  77  comes into contact with the trigger  14 , the stopper  76  is stopped at the first position in  FIG. 4(B) . Note that the actuation force of the stopper  76  is transmitted to the plunger  80  via the link member  81 . The plunger  80  is actuated in the direction toward the trigger  14  from the second position, and the plunger  80  is stopped at the first position in  FIG. 4(B) . 
     When the stopper  76  is stopped at the first position, a part of the stopper  76  is located within the actuation range of the transmission member  75 . Therefore, in step S 20 , when the push lever  16  comes into contact with a foreign object other than the workpiece  123  to turn on the push lever switch  86  and the transmission member  75  is actuated in the state where the trigger switch  87  is turned on, the transmission member  75  is engaged with the stopper  76  as shown in  FIG. 4(B) . Namely, the stopper  76  blocks the increase in the actuation amount of the transmission member  75 . Therefore, the actuation force of the transmission member  75  is not transmitted to the trigger arm  42 , and the trigger valve  51  is held in the standby state. 
     As described above, when the push lever  16  comes into contact with a foreign object after a predetermined time has passed from the time when the operation force is applied to the trigger  14 , the trigger valve  51  is maintained in the standby state and the striking unit  13  is stopped at the top dead center in step S 21 , and the control example of  FIG. 6  ends. Therefore, it is possible to prevent the fastener  73  from being driven into a foreign object. 
     When the worker releases the operation force on the trigger  14  following step S 21 , the trigger  14  is actuated clockwise from the actuated position shown in  FIG. 4(B)  by the biasing force of the biasing member  41 , and the trigger  14  returns to the initial position of  FIG. 2  and is stopped. Further, the actuation force of the trigger  14  is transmitted to the stopper  76  via the contact  77 . Therefore, the stopper  76  is actuated clockwise from the first position shown in  FIG. 4(B) , and the stopper  76  returns to the second position shown in  FIG. 2  and is stopped. 
     When the control unit  83  determines No in step S 12 , the flow proceeds to step S 19  and the control unit  83  continues to stop the power supply to the solenoid  78 . 
     As described above, the plunger  80  of the solenoid  78  is actuated from the second position to the first position by the biasing force of the biasing member  122 , and is actuated from the first position to the second position by the biasing force of the biasing member  41 . Namely, it is sufficient if the electric power supplied from the power source unit  82  to the solenoid  78  has a value capable of holding each of the stopper  76  and the plunger  80  at the second position shown in  FIG. 3(B)  against the biasing force of the biasing member  122 . Therefore, it is possible to reduce the power consumed by the solenoid  78 . The electric power consumed by the solenoid  78  varies depending on the biasing force of the biasing member  122 . Accordingly, the more the biasing force of the biasing member  122  is reduced, the more the electric power consumed by the solenoid  78  can be reduced. 
     Also, in this embodiment, the stopper  76  is stopped at the second position in the state where the power supply to the solenoid  78  is stopped and the plunger  80  is stopped at the position farthest from the trigger valve  51 . Further, a magnetic attraction force is applied to the plunger  80  by supplying electric power to the solenoid  78 , and the stopper  76  is held at the second position. 
       FIG. 10  shows the relationship between the stroke of the plunger  80  and the magnetic attraction force applied to the plunger  80 . The stroke of the plunger  80  is the actuation amount of the plunger  80  from the position farthest from the trigger valve  51 . The stroke increases as the plunger  80  comes close to the trigger valve  51 . In this embodiment, electric power is supplied to the solenoid  78  so that the magnetic attraction force applied to the plunger  80  becomes the maximum value or a value close to the maximum value. Therefore, the solenoid  78  can be downsized and the power consumption of the solenoid  78  can be reduced. 
     Note that the control unit  83  can perform a process of proceeding from step S 18  to step S 12  instead of the process of proceeding from step S 18  to step S 14 . 
     (Example of Selecting the Second Mode) 
     When the worker selects the second mode and the mode changing switch  84  is turned off in the case where the driving tool  10  is in the initial state of  FIG. 1  and step S 10 , the control unit  83  is stopped, and the power supply to the solenoid  78  is stopped. 
     Then, when the worker presses the push lever  16  to the workpiece  123 , the transmission member  75  is actuated from the initial position. The stopper  76  is stopped at the second position, and all of the stopper  76  is located outside the actuation range of the transmission member  75 . Accordingly, the transmission member  75  is not engaged with the stopper  76 , and the transmission member  75  comes into contact with the trigger arm  42 . Further, when the worker applies an operation force to the trigger  14 , the trigger  14  is actuated from the initial position to the actuated position and is stopped. Therefore, the trigger valve  51  switches from the standby state to the actuated state, and the striking unit  13  is actuated from the top dead center to the bottom dead center. 
     On the other hand, the stopper  76  is biased clockwise by the biasing force of the biasing member  122 . However, the stopper  76  comes into contact with the transmission member  75 , and this prevents the stopper  76  from being actuated counterclockwise. Also, the plunger  80  is held at the second position. 
     After the striking unit  13  is actuated from the top dead center to the bottom dead center, the worker releases the operation force on the trigger  14  and separates the push lever  16  from the workpiece  123 . Then, the trigger  14  returns from the actuated position to the initial position by the biasing force of the biasing member  41  and is stopped. Also, the trigger  14  comes into contact with the contact  77 , and the stopper  76  is held at the initial position by the biasing force of the biasing member  41 . When the worker selects the second mode, the striking unit  13  can be actuated from the top dead center to the bottom dead center regardless of the voltage of the power source unit  82 . 
     It is also possible to use an electromagnet  78 A instead of the solenoid  78 . The electromagnet  78 A is configured by winding a coil  79  around a cylinder made of a magnetic material and arranging a plunger  80  in the cylinder so as to be actuatable. When electric power is supplied to the electromagnet  78 A, the plunger  80  is stopped at the initial position shown in  FIG. 2  by the attraction force of the electromagnet  78 A. 
     (Other Examples of Actuator) 
     Other examples of the actuator will be described with reference to  FIG. 7(A)  and  FIG. 7(B) . A solenoid  111  is provided in the magazine  17 . The solenoid  111  has a casing  115 , a coil  112 , and a plunger  113 . A stopper  114  is fixed to the plunger  113 . The plunger  113  and the stopper  114  can be linearly actuated within a predetermined range in a direction intersecting the center line A 1 . Namely, the stopper  114  and the plunger  113  can be actuated in the directions toward and away from the ejection unit  15 . A lever  119  is provided on the stopper  114 . 
     A biasing member  116  is provided in the casing  115 . The biasing member  116  is, for example, a metal spring. The biasing member  116  biases the stopper  114  in the direction toward the ejection unit  15 . The worker can grasp the lever  119  with fingers and actuate the stopper  114  and the plunger  113  in the direction away from the ejection unit  15  against the force of the biasing member  116 . An arm  117  for transmitting the actuation force of the push lever  16  to the transmission member  75  is provided. The arm  117  has a concave portion  120  and an engagement portion  118 . The arm  117  is actuated in the direction of the center line A 1  together with the push lever  16 . An actuator switch  85  is provided in the magazine  17 . 
     When the worker grasps the lever  119  with fingers and the stopper  114  is actuated in the direction away from the ejection unit  15 , the actuator switch  85  is turned on. When the actuator switch  85  is turned on, electric power of the power source unit  82  is supplied to the solenoid  111 . 
     The control unit  83  has a function of turning off the actuator switch  85 . When the actuator switch  85  is turned off and the power supply to the solenoid  111  is stopped, the stopper  114  approaches the arm  117  by the biasing force of the biasing member  116  and is stopped. Note that the mode changing switch  84  shown in  FIG. 5  is not provided, and electric power of the power source unit  82  is always supplied to the control unit  83 . 
     Next, a usage example of the driving tool  10  shown in  FIG. 7(A)  and  FIG. 7(B)  will be described with reference to the flowchart of  FIG. 8 . 
     When the worker releases the operation force on the trigger  14  and separates the push lever  16  from the workpiece  123 , the driving tool  10  is in the initial state shown in step S 30  of  FIG. 8 . Also, the trigger  14  is stopped at the initial position, and the push lever  16  is stopped at the initial position. Further, the trigger valve  51  is stopped in the standby state. 
     No electric power is supplied to the solenoid  111 . The stopper  114  is biased toward the ejection unit  15  by the biasing force of the biasing member  116 , and the tip of the stopper  114  is located inside the concave portion  120 . When the worker applies an operation force to the lever  119  and actuates the stopper  114  and the plunger  113  in the direction away from the ejection unit  15  as shown in  FIG. 7(B) , the actuator switch  85  is turned on in step S 31 . 
     Electric power is supplied to the solenoid  111  in step S 32 , and the solenoid  111  stops the plunger  113  and the stopper  114  at the second position shown in  FIG. 7(B)  by a magnetic attraction force. When the stopper  114  is stopped at the second position, the actuator switch  85  is maintained in an on state. Therefore, even if the worker releases the operation force on the lever  119 , the plunger  113  and the stopper  114  are stopped at the second position. All of the stopper  114  stopped at the second position is located outside the concave portion  120 . 
     The control unit  83  determines whether or not the trigger switch  87  is turned on in step S 33 . When the control unit  83  determines Yes in step S 33 , the control unit  83  starts the timer in step S 34  and continues to supply electric power to the solenoid  111 . 
     In step S 35 , the control unit  83  determines whether or not the push lever switch  86  is turned on within a predetermined time from the time when the timer is started. Note that the stopper  114  does not hinder the actuation of the push lever  16  and the arm  117 . Also, the predetermined time is, for example, 3 seconds. 
     When the control unit  83  determines Yes in step S 35 , the control unit  83  resets the timer in step S 36  and continues to supply electric power to the solenoid  111 . Also, in step S 36 , the trigger valve  51  switches from the standby state to the actuated state, and the striking unit  13  is actuated from the top dead center to the bottom dead center. Further, when the control unit  83  detects that the push lever switch  86  is off in step S 37 , the flow proceeds to step S 33 . Note that the usage mode in which Yes is determined in step S 33  and Yes is determined in step S 35  is the first mode. 
     On the other hand, when the control unit  83  determines No in step S 35 , the control unit  83  resets the timer in step S 38 , turns off the actuator switch  85 , and stops the power supply to the solenoid  111 . Then, the stopper  114  shown in  FIG. 7(B)  is actuated toward the arm  117  by the biasing force of the biasing member  116 , so that the tip of the stopper  114  enters the concave portion  120  and the stopper  114  comes into contact with the arm  117  and is stopped at the first position. 
     Therefore, in step S 39 , when the push lever  16  comes into contact with a foreign object other than the workpiece  123  in the state where the trigger switch  87  is turned on, the engagement portion  118  is engaged with the stopper  114 . Namely, the stopper  114  prevents the increase in the actuation amount of the arm  117 . Therefore, the actuation force of the arm  117  is not transmitted to the trigger arm  42 , and the trigger valve  51  is held in the standby state. Therefore, the striking unit  13  is stopped at the top dead center in step S 40 , and the control example of  FIG. 8  ends. 
     As described above, even if the push lever  16  comes into contact with a foreign object after a predetermined time has passed from the time when the operation force is applied to the trigger  14 , the trigger valve  51  is maintained in the standby state, and the striking unit  13  is stopped at the top dead center. Therefore, it is possible to prevent the fastener  73  from being driven into the foreign object. 
     When the control unit  83  determines No in step S 33 , the control unit  83  determines in step S 41  whether or not the push lever switch  86  is turned on. When the control unit  83  determines No in step S 41 , the control example of  FIG. 8  ends. 
     When the control unit  83  determines Yes in step S 41 , the control unit  83  determines in step S 42  whether or not the trigger switch  87  is turned on. When the control unit  83  determines No in step S 42 , the control unit  83  repeats the determination in step S 42 . When the control unit  83  determines Yes in step S 42 , the trigger valve  51  switches from the standby state to the actuated state in step S 43  and the striking unit  13  is actuated from the top dead center to the bottom dead center, and the control example of  FIG. 8  ends. 
     Note that the usage example in which Yes is determined in step S 41  and Yes is determined in step S 42  is the second mode. 
     As described above, the stopper  114  and the plunger  113  are each actuated from the first position to the second position by the operation force of the worker. Also, when the power supply to the solenoid  111  is stopped, the stopper  114  and the plunger  113  are each actuated from the second position to the first position by the biasing force of the biasing member  116 , and the stopper  114  and the plunger  113  are each stopped at the first position. Therefore, it is sufficient if the electric power supplied from the power source unit  82  to the solenoid  111  has a value capable of holding each of the stopper  114  and the plunger  113  at the second position shown in  FIG. 7(B)  against the biasing force of the biasing member  116 . 
     Therefore, it is possible to reduce the power consumed by the solenoid  111 . The electric power consumed by the solenoid  111  varies depending on the biasing force of the biasing member  116 . Accordingly, the more the biasing force of the biasing member  116  is reduced, the more the electric power consumed by the solenoid  111  can be reduced. 
     Another control example executed by the control unit  83  in parallel with the control example of  FIG. 8  will be described with reference to  FIG. 9 . 
     In step S 50 , the actuator switch  85  is turned on and electric power is supplied to the solenoid  111 . In step S 51 , the control unit  83  determines whether or not the voltage of the power source unit  82  is equal to or higher than a predetermined value. The predetermined value corresponds to the minimum value of the voltage that can be applied to the solenoid  111 . 
     When the control unit  83  determines Yes in step S 51 , the control unit  83  maintains the actuator switch  85  in an on state and continues to supply electric power to the solenoid  111  in step S 52 , and the control example of  FIG. 9  ends. 
     When the control unit  83  determines No in step S 51 , the control unit  83  turns off the actuator switch  85  and stops the power supply to the solenoid  111  in step S 53 , and the control example of  FIG. 9  ends. In step S 53 , the control unit  83  causes the display unit  89  to display that the voltage of the power source unit is less than the predetermined value. 
     It is also possible to use an electromagnet  111 A instead of the solenoid  111 . The electromagnet  111 A is configured by winding the coil  112  around a cylinder  121  made of a magnetic material and arranging the plunger  113  in the cylinder  121  so as to be actuatable. When electric power is supplied to the electromagnet  111 A, the electromagnet  111 A generates an attraction force and the plunger  113  and the stopper  114  are each stopped at the second position shown in  FIG. 7(B) . 
     Examples of the technical meanings of the matters disclosed in the embodiments areas follows. The striking unit  13  is an example of a striking unit. The trigger valve  51  and the head valve  31  are examples of a driver unit. The state where the valve body  55  connects the passage  56  and the pressure accumulation chamber  20  and disconnects the passage  56  and the passage  90  is the standby state of the trigger valve  51 . The state where the head valve  31  closes the passage  110  is the standby state of the head valve  31 . 
     The state where the valve body  55  disconnects the passage  56  and the pressure accumulation chamber  20  and connects the passage  56  and the passage  90  is the actuated state of the trigger valve  51 . The state where the head valve  31  opens the passage  110  is the actuated state of the head valve  31 . 
     The housing  11  is an example of a housing. The trigger  14  is an example of an operation member. The push lever  16  is an example of a contact member. 
     The pressure accumulation chamber  20  is an example of a pressure accumulation chamber. The piston upper chamber  36  is an example of a pressure chamber. The pressure accumulation chamber and the pressure chamber are spaces that can store the compressible gas. The passage  110  is an example of a passage. The stoppers  76  and  114  are examples of a stopper. 
     The second position of the stopper  76  shown in  FIG. 2  is an example of a second position of the stopper. The first position of the stopper  76  shown in  FIG. 4(B)  is an example of a first position of the stopper. The first position of the stopper  114  shown in  FIG. 7(A)  is an example of a first position of the stopper. The second position of the stopper  114  shown in  FIG. 7(B)  is an example of a second position of the stopper. The biasing members  116  and  122  are examples of a biasing member. 
     The first position of the stopper is a position where the actuation of the contact member is blocked. Here, blocking the actuation of the contact member means that the actuation amount of the contact member is suppressed to a predetermined value or less. When the actuation amount of the contact member is equal to or less than the predetermined value, the driver unit does not switch from the standby state to the actuated state and is maintained in the standby state. When the actuation amount of the contact member exceeds the predetermined value, the driver unit switches from the standby state to the actuated state. 
     The solenoids  78  and  111  and the electromagnets  78 A and  111 A are examples of an actuator. The solenoids  78  and  111  are examples of a solenoid. The electromagnets  78 A and  111 A are examples of an electromagnet. The plungers  80  and  113  are examples of a plunger. The control unit  83  is an example of a control unit. 3 seconds is an example of a predetermined time, and the predetermined time may exceed 3 seconds. 
     Step S 15  in  FIG. 6  is an example of a first control. Step S 17  in  FIG. 6  is an example of a second control. Step S 19  in  FIG. 6  is an example of a third control. Step S 34  in  FIG. 8  is an example of the first control. Step S 36  in  FIG. 8  is an example of the second control. Step S 38  in  FIG. 8  is an example of the third control. 
     The driving tool is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention. For example, the control unit may be a single electric component or electronic component, or a unit having a plurality of electric components or a plurality of electronic components. Examples of the electric components and the electronic components include a processor, a control circuit, and a module. 
     The actuator includes a unit in which an electric motor and a rack and pinion mechanism are combined. The pinion is provided on a rotation shaft of the electric motor, and the rack is provided on the stopper. The stopper can be rotated within a predetermined angle range, or can be linearly actuated within a predetermined angle range. It is possible to stop the stopper at the first position by the biasing force of the biasing member without supplying electric power to the electric motor. On the other hand, it is possible to stop the stopper at the second position by supplying electric power to the electric motor to rotate the pinion and actuate the rack. Examples of the passage include a gap and a port. 
     The housing may be a frame, a body, and a casing. Examples of the operation member include a lever, a knob, and an arm that can be rotated within a predetermined angle range with respect to the housing. Examples of the operation member include a lever, a knob, and an arm that can reciprocate linearly within a predetermined range with respect to the housing. The contact member can reciprocate linearly within a predetermined range with respect to the housing. Examples of the contact member include a lever, an arm, a shaft and a plunger. 
     Examples of the stopper include a stopper that can be rotated within a predetermined angle range with respect to the housing and a stopper that can reciprocate linearly within a predetermined range with respect to the housing. Examples of the biasing member include a solid spring, a gas spring, and synthetic rubber. 
     REFERENCE SIGNS LIST 
       10  . . . driving tool,  11  . . . housing,  13  . . . striking unit,  14  . . . trigger,  16  . . . push lever,  20  . . . pressure accumulation chamber,  31  . . . head valve,  36  . . . piston upper chamber,  51  . . . trigger valve,  76 ,  114  . . . stopper,  78 ,  111  . . . solenoid,  78 A,  111 A . . . electromagnet,  80 ,  113  . . . plunger,  83  . . . control unit,  110  . . . passage,  116 ,  122  . . . biasing member