DESCRIPTION

POWER TOOL Technical Field The present invention relates to a power tool for driving a fastener, such as a nail, rivet, or staple, with a driver blade. More particularly, the invention relates to a power tool having a controller with a control circuit for controlling a drive circuit of a combustion-type or an electric-type power generating mechanism, for example, based on the operation of a ^' push switch and a trigger switch. Background Art

One common type of power tool for driving such fasteners is a portable tool having a nickel cadmium battery, lithium ion battery, or other secondary battery as the power source.

For example, a portable combustion-type power tool, such as those disclosed in Japanese examined patent application publications Nos. SHO-64-9149, HEI-1-34753, and HEI-4-48589; Japanese unexamined patent application publications Nos. HEI-8-216052 and 2005-28568; and U.S. Patents 4,483,474 and 5,133,329, injects a combustible gas contained in a small gas cylinder into a combustion chamber provided in a cylinder above a piston. When both a push switch and a trigger switch are operated, an ignition circuit powered by the battery generates a spark for igniting a mixture of the combustible gas and air in the combustion chamber, driving the piston, which is slidably movably supported in the cylinder, so that a driver blade mounted on the piston strikes the nail or other fastener.

With this combustion-type power tool, the combustion chamber is formed when the user presses the push lever

against a workpiece. In this state, a liquefied gas is injected from the gas cylinder into the combustion chamber. Further, a fan is driven by the activation of the push switch functioning in association with the push lever. The fan agitates and mixes the combustible gas with air in the combustion chamber. When the user turns on the power tool by pressing the trigger switch at this time, a sparkplug produces a spark for igniting the air-fuel mixture and driving the piston. The driver blade mounted on the piston drives the fastener into the workpiece, such as a piece of wood. The frame of the combustion chamber is maintained in contact with a head cap for a prescribed time after combustion while the combusted gas is exhausted from the chamber. After the gas is exhausted, a check valve closes in order to hermetically seal the combustion chamber. The decrease in pressure in the combustion chamber from the resulting drop in temperature (referred to as a thermal vacuum) produces a pressure differential between the top and bottom of the piston, causing the piston to rise. Another type of portable power tool is an electric power tool, such as that disclosed in Japanese unexamined patent application publication No. HEI-8-205573. This electric power tool has a motor for driving a flywheel to rotate and converts the kinetic energy of the flywheel into a linear kinetic energy for driving a fastener. The electric power tool has a power transmission mechanism, such as a clutch, for transmitting the rotational energy of the flywheel to a striking mechanism, including the driver blade in which the nail or other fastener is set, in order to execute a fastener driving operation.

This type of fastener-driving power tool typically includes a push switch for detecting when the power tool is

pressed against a workpiece, and a trigger switch for initiating an operation to strike the fastener with the driver blade. The power tool also includes a controller for controlling operations of the power tool based on signals received from these switches. Disclosure of Invention Technical Problem

However, the push switch and trigger switch in the conventional power tools described above typically have mechanical contacts. Impacts occurring when the power tool strikes or drives a fastener can produce chattering in the mechanical contacts. Chattering can accelerate contact failure by increasing wear in the contacts or depositing abrasive particles on the contacts, making the tool inoperable. While it is conceivable to use a contactless switch or photoelectric switch configured of an optical switch for preventing wear in contacts caused by chattering, such switches themselves are complex and expensive. Technical Solution Therefore, it is an object of the present invention to provide a power tool capable of extending the life of mechanical switches, such as the push switch or trigger switch.

It is another object of the present invention to provide a power tool having an inexpensive controller with a relatively simple input circuit structure for the push switch or trigger switch.

In order to attain the above and other objects, according to one aspect of the present invention, there is provided a power tool that includes: a power generating mechanism that generates power to strike the fastener;

a drive unit that drives the power generating mechanism; a first switch activated when an operation to strike the fastener is ready to be performed; and a second switch activated by a user when the operation to strike the fastener is triggered, wherein at least one of the first switch and the second switch is configured of a normally closed switch.

It is preferable that the power tool further includes : a first detection unit that is connected to the first switch and detects that the first switch is activated, the first detection unit outputting a first detection signal indicative of activation of the first switch; a second detection unit that is connected to the second switch and detects that the second switch is activated, the second detection unit outputting a second detection signal indicative of activation of the second switch; and a control unit that is connected to the first detection unit and the second detection unit and instructs the drive unit to drive the power generating mechanism in response to the first detection signal and the second detection signal.

When the first switch is configured of the normally closed switch, the first detection circuit may include an inverter circuit to invert a signal from the first switch and apply an inverted signal to the control unit as the first detection signal.

Similarly, when the second switch is configured of the normally closed switch, the second detection circuit may include an inverter circuit to invert a signal from the second switch and apply an inverted signal to the control

unit as the second detection signal.

It is preferable that the first switch and the second switch be connected in series.

One of the first switch and the second switch can be configured of a normally open switch, while remaining one of the first switch and the second switch can be configured of a normally closed switch, and it is also preferable in this case that the first switch and the second switch be connected in series. In such a case, it is further preferable to set a current flowing through the normally closed switch when the normally open switch is ON to be greater than a current flowing in the normally closed switch when the normally open switch is OFF.

According to another aspect of the present invention, the power tool includes: a housing; a cylinder disposed inside the housing; a head cap provided on one end of the housing; a piston disposed in and capable of reciprocating in the cylinder; a driver blade fixed to the piston for driving a fastener into a workpiece; a push lever extending from another end of the housing and capable of moving when pushed against the workpiece; a combustion chamber frame disposed in the housing and capable of moving in association with movement of the push lever, the combustion chamber frame defining a combustion chamber together with the cylinder, the piston, and the head cap; a push switch activated in association with the push lever; a sparkplug disposed facing an interior of the

combustion chamber; and a trigger switch activated by a user for triggering an operation to ignite the sparkplug, wherein at least one of the push switch and the trigger switch is configured of a normally closed switch.

It is preferable that the power tool may further include : a first detection unit that is connected to the push switch and detects that the push switch is activated, the first detection unit outputting a first detection signal indicative of activation of the push switch; a second detection unit that is connected to the trigger switch and detects that the trigger switch is activated, the second detection unit outputting a second detection signal indicative of activation of the trigger switch; and a control unit that is connected to the first detection unit and the second detection unit, and instructs the sparkplug to ignite in response to the first detection signal and the second detection signal.

When the push switch is configured of the normally closed switch, it is preferable that the first detection circuit include an inverter circuit to invert a signal from the push switch and apply an inverted signal to the control unit as the first detection signal.

Similarly, when the trigger switch is configured of the normally closed switch, it is preferable that the second detection circuit include an inverter circuit to invert a signal from the trigger switch and apply an inverted signal to the control unit as the second detection signal.

One of the push switch and the trigger switch can be configured of a normally open switch, while remaining one of

the push switch and the trigger switch can be configured of a normally closed switch, and the push switch and the trigger switch may be connected in series. In this case, it is preferable that a current flowing through the normally closed switch when the normally open switch is ON be greater than a current flowing in the normally closed switch when the normally open switch is OFF.

According to still another aspect of the invention, there is provided a power tool including: a motor for rotating a flywheel; a driver blade for driving a fastener into a workpiece, the driver blade moving in a predetermined direction; a blade feeding mechanism that converts a rotational force of the flywheel into a force for moving the driver blade in a predetermined direction; a power transmitter that transmits or interrupts the rotational force of the flywheel to the blade feeding mechanism; a push switch activated when an operation to strike the fastener is ready to be performed; a trigger switch activated by a user when the operation to strike the fastener is triggered; and a control unit that controls the motor and the power transmitter based on activations of the push switch and the trigger switch, wherein at least one of the push switch and the trigger switch is configured of a normally closed switch.

It is preferable that one of the push switch and the trigger switch be configured of a normally open switch, while remaining one of the push switch and the trigger switch be configured of a normally closed switch. In this case, the push switch and the trigger switch may be

connected in series. In this case, it is preferable to set a current flowing through the normally closed switch when the normally open switch is ON be greater than a current flowing in the normally closed switch when the normally open switch is OFF.

The term "normally closed switch" used in this specification denotes a type of switch that is normally ON (i.e. the switch terminals are electrically connected) when not operated; and that is turned OFF (i.e. the switch terminals are electrically open) when the switch is operated. The opposite of a normally closed switch is a "normally open switch." A normally open switch denotes the type of switch that is normally OFF (i.e. the switch terminals are electrically open) when the switch is not operated; and is turned ON (i.e. the terminals are electrically connected) when the switch is operated. Advantageous Effects

With the power tool of the present invention, the trigger switch signals the control circuit to drive the fastener after the push switch is operated, and at least one of the push switch and the trigger switch is configured of a normally closed switch. Hence, this configuration avoids the chattering that occurs in the conventional power tool when the normally open switch is switched from an OFF state to an ON state, thereby preventing wear caused by chattering and extending the life of the switch. Further, since the desired objects can be attained with mechanical switches, the controller can be configured of a relatively inexpensive circuit structure, similar to the conventional devices. Brief Description of Drawings

Fig. 1 is a block diagram of a controller employed in a power tool according to one embodiment of the present

invention;

Fig. 2 is a cross-sectional view of a combustion-type power tool according to a preferred embodiment of the present invention; Fig. 3 is a block diagram of a controller used in the combustion-type power tool shown in Fig. 2;

Fig. 4 is a cross-sectional view of an electric-type power tool according to another embodiment of the present invention; and Fig. 5 is a block diagram of a controller used in the electric-type power tool shown in Fig. 4. Explanation of Reference

1 Nose

2 Bumper 3 Exhaust port

4 Cylinder

5 Temperature sensor

6 Fan

7 Gas cylinder 7a Measuring valve

8 Fan motor

9 Sparkplug

10 Piston

10a Driver blade 11 Handle

12 Trigger switch (normally closed switch)

13 Magazine

14 Housing

15 Combustion chamber frame 15a Combustion chamber

16 Fins 17, 18 Gap

_

19 Gas injection port

20 Head cover 20a Head cap

21 Push lever 22 Sealing member

23 Push switch (normally open switch)

24 Nail

25 Battery 26 Spring 28 Air intake 29 Workpiece

60 Power tool

61 Drive circuit

62 Control circuit (microcomputer) 63 Low-voltage power supply circuit

64 Self-holding circuit

65 Push switch

65a First detection circuit

66 Trigger switch 66a Second detection Circuit

67 Main power supply switch

68 Display circuit

69 Battery

70 Electric-type power tool (cordless nail driver) 71a Main housing

71b Handle housing 71c Nail-striking part 71d Discharge outlet

72 Magazine 72a Nail

73 Driver

73a Driver blade

73b Rack

73c Driver feeding mechanism

74 Driver feeding spring

75 Trigger switch (normally closed switch) 77 Battery pack

78 Motor gear

79 Flywheel

80 Pinion

81 Controller 82 Push switch (normally closed switch) 84 Low-voltage supply circuit

86 Microcomputer

86a Central processing unit (CPU)

86b Read-only memory (ROM) 86c Random access memory (RAM)

86d Timer (TIM)

87 Self-holding circuit

89 Motor detection circuit

90 Combustion-type power tool (nail driver) 91 Solenoid driving circuit

92 Solenoid driving transistor

93 Solenoid

94 Motor driving circuit

95 Motor driving transistor 96 Motor

100 Controller

101 Microcomputer (arithmetic control circuit)

102 Low-voltage power supply circuit (regulator)

103 Self-holding circuit 104 Trigger switch circuit

105 Push switch circuit

106 Battery voltage detection circuit

107 Charging circuit

108 Ignition circuit

109 Motor driving circuit

110 Display circuit 111 Crystal oscillator

Best Mode for Carrying Out the Invention

Next, a power tool according to the present invention will be described while referring to the accompanying drawings . Fig. 1 is a block diagram of a controller 60a provided in a power tool 60 of the present invention. The controller

60a includes a drive circuit 61, a control circuit

(arithmetic control circuit) 62 configured of a microcomputer and the like, a low-voltage power supply circuit 63, a self-holding circuit 64, a push switch 65, a trigger switch 66, a display circuit 68, a battery (battery pack) including nickel cadmium cells, lithium ion cells, or other secondary batteries, and a main power supply switch 67. A first detection circuit 65a is provided for detecting whether the push switch 65 was operated and for inputting a signal in response to an operation of the push switch 65 into the control circuit 62. Similarly, a second detection circuit 66a is provided for detecting whether the trigger switch 66 was operated and for inputting a signal in response to an operation of the trigger switch 66 into the control circuit 62. If the control circuit 62 responds to a low-level input signal, for example, the first detection circuit 65a or second detection circuit 66a inputs a low signal (ground level) into the control circuit 62 when the respective push switch 65 or trigger switch 66 is operated.

The battery 69 supplies a voltage of 7.2 V with lithium ion cells, for example, to the drive circuit 61,

such as a motor driving circuit or a spark ignition circuit. The voltage of the battery 69 is regulated to a low voltage of 3.3 V, for example, by the low-voltage power supply circuit 63 and supplied to the control circuit 62 as an operating voltage.

The low-voltage power supply circuit 63 includes a common DC power supply stabilization circuit (regulator) and is connected to the output of the self-holding circuit 64 described later with a control input terminal 63a for outputting or halting output of the low voltage to the control circuit 62.

During a normal standby mode or operating mode in which a trigger signal (control signal) is not received from the control circuit 62 described later, the self-holding circuit 64 supplies a control signal at a prescribed level to the control input terminal 63a of the low-voltage power supply circuit 63 for controlling the low-voltage power supply circuit 63 to output a low voltage to the control circuit 62 or part of the drive circuit 61 as a power supply voltage. When a trigger signal (control signal) is received from the control circuit 62 for entering a low power consumption mode, the self-holding circuit 64 has a function for inverting its stable state (from a first stable state, or OFF state, to a second stable state, or ON state, for example) , thereby inverting the prescribed level of the control signal supplied to the control input terminal 63a for halting the low voltage supplied from the low-voltage power supply circuit 63 to the control circuit 62 or part of the drive circuit 61. Hence, the self-holding circuit 64 enters the low power consumption mode in response to a trigger signal from the control circuit 62 and halts output of the low voltage from the low-voltage power supply circuit

63.

For example, as in the embodiment of the combustion- type power tool described below, the self-holding circuit 64 may be configured of a circuit having a PNP transistor and an NPN transistor whose respective bases are connected to the others' collectors, with one transistor applying a positive feedback effect to the other transistor.

As will be understood from the embodiment of the combustion-type power tool described below, when the push switch 65 or trigger switch 66 is operated and subsequently operated again within a prescribed time period (10 minutes, for example) , the self-holding circuit 64 maintains the OFF state (first stable state) and the low-voltage power supply circuit 63 preserves the operating mode (standby mode) for supplying the prescribed supply voltage (3.3 V, for example) . Hence, the power tool 60 continues operating normally. However, if the push switch 65 or trigger switch 66 is not operated within the prescribed time period, the self-holding circuit 64 shifts to the ON state (second stable state) and enters the low power consumption mode for dropping the control input terminal 63a of the low-voltage power supply circuit 63 to ground level and for setting the output voltage of the low-voltage power supply circuit 63 to a voltage less than the 3.3 V prescribed voltage (0 V, for example) . In this way, the self-holding circuit 64 can prevent unnecessary power consumption when the power tool 60 is not in use.

If the main power supply switch 67 is switched off and back on at this time, the self-holding circuit 64 shifts back to the OFF state (first stable state, i.e. returns to the normal operating mode) . If the push switch 65 or trigger switch 66 is subsequently operated, the control

circuit 62 can control the drive circuit 61 to execute a fastener-driving operation.

One feature of the present invention is that at least one of the push switch 65 and trigger switch 66 is configured of a normally closed mechanical switch. In the preferred embodiment, the push switch 65 is connected in series to the trigger switch 66, and the trigger switch 66 is a normally closed switch. In other words, the trigger switch 66 is configured of a switch that is ON in its normal state when not being operated. The push switch 65, on the other hand, is a normally open switch that is OFF in its normal state when not being operated. Since the trigger switch 66 is a normally closed switch, the second detection circuit 66a includes an inverter circuit for inputting a low signal into the control circuit 62 when the trigger switch 66 is switched off. The signal level inputted into the control circuit 62 based on an operation of the push switch 65 and trigger switch 66 is a low signal (ground level) .

However, since the push switch 65 is connected in series to the trigger switch 66, the first detection circuit 65a is not provided with an inverter circuit and can input a low signal into the control circuit 62 when the push switch 65 is switched on.

Since at least one of the push switch 65 and trigger switch 66 in the present invention is configured of a normally closed switch, the power tool of the present invention can prevent the occurrence of chattering inherent in the conventional power tools when the normally open switch is switched to an ON state, thereby eliminating wear caused by chattering and extending the life of the trigger switch 66. Further, since the desired objects are attained with mechanical switches, the controller 60a can be

configured of a relatively inexpensive circuit structure, as in the prior art.

In the present invention, normally closed switches may also be used for both the push switch 65 and the trigger switch 66. Further, the push switch 65 and trigger switch

66 need not be connected in series, but may input signals into the control circuit 62 via the first detection circuit

65a and second detection circuit 66a connected in parallel.

Next, a preferred embodiment will be described in which the present invention is applied to a combustion-type power tool .

Fig. 2 is a cross-sectional view showing the structure of a combustion-type power tool 90 according to a preferred embodiment of the present invention, when a piston in the combustion-type power tool 90 is in an initial position. Fig. 3 shows a controller 100 for the combustion-type power tool 90 in Fig. 2. In the following description, it is assumed that the power tool of the present invention is held in an orientation for driving nails or other fasteners in a downward direction, but the present invention is not limited to any particular embodiment or purpose.

As shown in Fig. 2, the combustion-type power tool (nail driver) 90 has a housing 14 forming an outer frame, and a head cover 20 mounted on top of the housing 14. Inside the housing 14, the combustion-type power tool 90 is provided with a cylinder 4, a bumper 2, a piston 10, a driver blade 10a formed integrally with the piston 10, a fan 6, a motor 8, a sparkplug 9, a gas injection port 19, a gas cylinder 7, a combustion chamber frame 15, and a head cap 20a. A handle 11, a nose 1, a push lever 21, a magazine 13, and a trigger switch 12 are mounted on the housing 14.

As will be described next, the controller 100 is

provided in the magazine 13 for controlling the generation of sparks in the sparkplug 9. As shown in Fig. 3., the controller 100 includes a circuit board on which are mounted a microcomputer (arithmetic control circuit) 101, a low- voltage power supply circuit (regulator) 102 for regulating the voltage supplied from a battery 25 to a low voltage, an ignition circuit 108 for producing a spark in the sparkplug 9, and a motor driving circuit 109 for driving the fan 6. The controller 100 is electrically connected to such components as a push switch 23, the trigger switch 12, and a temperature sensor 5 (see Fig. 2) and receives electric signals from these components for charging an ignition energy storage capacitor (ignition capacitor) C5 described later, producing a spark in the sparkplug 9 and starting or controlling rotation of the fan motor 8. The battery 25 is a secondary battery (battery pack) including lithium ion cells or the like and is provided in a holder of the handle 11. The controller 100 is connected to the battery 25 and supplies power from the battery 25 via a main power supply switch SWl.

The cylinder 4 and the head cap 20a are fixed relative to the housing 14 inside the same. The combustion chamber frame 15 is joined with the push lever 21 disposed below the cylinder 4 and is capable of moving in the axial direction of the housing 14. The combustion chamber frame 15 is guided in movement by the housing 14 and cylinder 4. A spring 26 urges the combustion chamber frame 15 downward in Fig. 2, i.e. the direction for driving a nail 24 serving as the fastener. When the push lever 21 is pressed against a workpiece 29, such as a piece of wood, the push lever 21 is pushed upward relative to the housing 14, and the combustion

chamber frame 15 moves toward the top of the cylinder 4 together with the push lever 21 against the urging force of the spring 26, forming a combustion chamber 15a. More specifically, the combustion chamber 15a is formed of a space enclosed by the combustion chamber frame 15, head cap 20a, and piston 10 and is used for the combustion of a mixture of combustible gas and air. A sealing member 22 configured of an O-ring, for example, is provided between the top end of the cylinder 4 and the bottom end of the head cap 20a for hermetically sealing the combustion chamber 15a. When the push lever 21 rises, the push switch 23 configured of the normally open switch is turned on..

The piston 10 is provided inside the cylinder 4 and is capable of reciprocating vertically therein through a slidable sealing member 27, such as an O-ring. On the bottom of the cylinder 4 are provided an exhaust port 3, a check valve (not shown) for opening and closing the exhaust port 3, and the bumper 2 for receiving the impact of the piston 10. When the piston 10 moves abruptly downward to the bottom dead center for driving the nail 24 and collides with the bumper 2, the bumper 2 deforms to absorb excess energy in the piston 10.

Within the combustion chamber 15a are provided the fan 6, which can be rotated by the motor 8 disposed in the top of the head cap 20a; the sparkplug 9, which produces a spark when the trigger switch 12 configured of the normally closed switch according to the present invention is turned off; the gas injection port 19 for injecting combustible gas

(liquefied gas) supplied from the gas cylinder 7; and fins 16 protruding radially inward in the combustion chamber 15a like ribs.

The magazine 13 and the nose 1 are integrally mounted

on the cylinder 4 below the housing 14. The magazine 13 is loaded with nails 24, and the nose 1 guides nails 24 supplied from the magazine 13 to the workpiece 29.

In the rest state shown in Fig. 2, the push lever 21 protrudes below the lower end of the nose 1 by the urging force of the spring 26. At this time, a gap 17 is formed in the upper end of the cylinder 4 beneath the combustion chamber frame 15 joined with the push lever 21, and a gap 18 is formed in the upper end of the combustion chamber frame 15 below the head cap 20a. The piston 10 is halted in the cylinder 4 at the top dead center.

When the combustion-type power tool 90 is in this state, if the user grips the handle 11 and presses the tip of the push lever 21 against the workpiece 29, the push lever 21 rises against the spring 26 and the combustion chamber frame 15 rises together with the push lever 21. Consequently, the gaps 17 and 18 above and below the combustion chamber frame 15 are closed, forming the combustion chamber 15a, which is hermetically sealed from the outside by the sealing members 22.

In association with the operation of the push lever 21, the gas cylinder (fuel tank) 7 subsequently injects combustible gas into the combustion chamber 15a through the gas injection port 19. Further, when the push switch 23 (normally open switch) detects that the combustion chamber frame 15 is in the top dead center position and turns on, the drive circuit of the motor 8 is also turned on for rotating the fan 6. The rotation of the fan 6 in the hermetically sealed combustion chamber 15a together with the fins 16 protruding into the combustion chamber 15a function to agitate and mix the injected combustible gas with air in the combustion chamber 15a. The gas cylinder 7 stores a

liquefied combustible gas in a pressurized state. The liquefied gas is vaporized when injected into the combustion chamber 15a. A measuring valve 7a is provided in the top end of the gas cylinder 7 for regulating the amount of gas injected therefrom. Hence, a regulated amount of gas is supplied through the gas injection port 19.

When the user pulls the normally closed trigger switch 12 on the handle 11, turning the trigger switch 12 off, after pressing the push lever 21 against the workpiece 29, the operations of the controller 100 described below control the sparkplug 9 to generate a spark for igniting and combusting the air-fuel mixture. The expanded combusted gas forces the piston 10 downward to strike the nail 24 in the nose 1. After driving the nail 24, the piston 10 contacts the bumper 2, and the combusted gas escapes from the cylinder 4 through the exhaust port 3. As described above, a check valve (not shown) is provided with the exhaust port 3. The check valve is closed after the gas escapes from the cylinder 4 and the cylinder 4 and combustion chamber 15a return to atmospheric pressure. Since the combusted gas remaining in the cylinder 4 and combustion chamber 15a is hot immediately after combustion, the inner walls of the cylinder 4 and the combustion chamber frame 15, the fins 16, and the like absorb the combustion heat. Consequently, the combusted gas is cooled rapidly and decreases in volume, producing a thermal vacuum in which the pressure in the combustion chamber 15a drops below atmospheric pressure, allowing the piston 10 to be pulled back to its initial top dead center position.

When the user subsequently releases the trigger switch 12, returning the trigger switch 12 to the ON state

(normally closed state) , and lifts the body of the tool so that the push lever 21 separates from the workpiece 29, the urging force of the spring 26 moves the push lever 21 and the combustion chamber frame 15 downward to their original state shown in Fig. 2. At this time, under control of the controller 100, the fan 6 continues to rotate for a prescribed time, even if the push switch 23 is switched off.

In the state shown in Fig. 2, the gaps 17 and 18 are formed above and below the combustion chamber frame 15, releasing the combustion chamber 15a from its hermetically sealed state. In this state, the fan 6 generates airflow capable of drawing fresh air through an air intake 28 formed in the top surface of the housing 14 and blowing residual combusted gas out through an exhaust port 30 formed in the housing 14, thereby scavenging air in the combustion chamber 15a. Subsequently, the fan 6 is halted and returned to its initial rest state.

In the preferred embodiment, a normally open switch is used for the push switch 23 and a normally closed switch for the trigger switch 12. Next, the controller 100 using the push switch 23 and trigger switch 12 having this configuration will be described. <Structure of the Controller 100>

Fig. 3 shows the circuit structure of the controller 100. The controller 100 includes the low-voltage power supply circuit 102, a self-holding circuit 103, a battery voltage detection circuit 106, a push switch circuit 105, a trigger switch circuit 104, the microcomputer (arithmetic control circuit) 101, an oscillator 111, a charging circuit 107, the ignition circuit 108, the motor driving circuit 109, and a display circuit 110. As described above, the battery 25 is configured of a battery pack accommodating lithium ion

cells and has a power supply voltage of 7.2 V, for example. The battery 25 supplies the 7.2 V voltage to the output parts of the motor driving circuit 109 and charging circuit 107 (transistors Q7, QlO, and QIl) via the main power supply switch SWl, and also to the low-voltage power supply circuit 102 via a unidirectional diode D8.

The low-voltage power supply circuit 102 includes a regulator ICl for generating a supply voltage and reference voltage for the microcomputer 101; a transistor Q13, capacitors C2, C3, C9, and ClO; and a reset IC IC2.

The regulator ICl is configured of a low voltage power supply unit for receiving the 7.2 V supply voltage from the battery 25 via a diode D8 in an input terminal 2, regulating the voltage to an operating voltage (3.3 V in the preferred embodiment) required for drive control units of the microcomputer 101, motor driving circuit 109, and charging circuit 107, and for outputting the regulated voltage as a DC voltage from an output terminal 4. The regulator ICl also has a control terminal 1 for controlling whether the voltage 3.3 V is outputted from the output terminal 4 in response to an ON or OFF operation of the transistor Q13 connected to the control terminal 1. In the preferred embodiment, the voltage 3.3 V is outputted from the output terminal 4 when the transistor Q13 is ON, and is halted when the transistor Q13 is OFF. The transistor Q13 connected to the control terminal 1 of the regulator ICl is controlled by output from the self-holding circuit 103. In Fig. 3, the notation "3.3V DC" at the supply terminal of the battery voltage detection circuit 106 and the like indicates that the supply terminal is electrically connected to the output terminal 4 of the regulator ICl. Further, a notation of ^λx 7.2V DC" at a supply terminal indicates that the terminal

is electrically connected to a 7.2 V power supply line from the battery 25 that supplies power via the main power supply switch SWl.

The self-holding circuit 103 is configured of a positive feedback circuit that connects the collector and base of a PNP transistor Q3 to the base and collector of an NPN transistor Q4. Both transistors Q3 and Q4 connected to a circuit providing mutually positive feedback, well known in the art, possess an ability to operate in two stable states- with respect to the load (Rβ and R5 ) : an OFF state and ON state. Further, if a trigger signal is inputted for increasing the base current in the PNP transistor Q3 or NPN transistor Q4 while applying a prescribed supply voltage (operating voltage) , the transistors Q3 and Q4 change from the OFF state to the ON state through the positive feedback effect. Conversely, the transistors Q3 and Q4 are returned to the OFF state if the supply voltage to the transistors Q3 and Q4 is temporarily stepped down.

The self-holding circuit 103 also includes a field- effect transistor (hereinafter abbreviated as FET) Q5 for applying a trigger signal to the transistors Q3 and Q4 constituting the positive feedback circuit; resistors R4-R9 and R28; and a capacitor C8. The self-holding circuit 103 has a self-holding effect for switching the transistors Q3 and Q4 from an OFF state to an ON state when a halt output signal (high signal) outputted from an output terminal 14 of the microcomputer 101 is received in the FET Q5, effectively setting the transistor Q13 in an OFF state. Specifically, when output from the regulator ICl is halted, the microcomputer 101 temporarily outputs a high signal from the output terminal 14 as a trigger signal, turning the FET Q5 on and switching both the transistors Q3 and Q4 connected on

the positive feedback circuit from the OFF state to the ON state. The self-holding circuit 103 therefore switches the transistor Q13 from the ON state to the OFF state in order to halt output from the regulator ICl. In this way, this circuit structure can detect abnormal states, such as when the combustion-type power tool 90 is left for a long period of time with the main power supply switch SWl in the operating state (standby state) , when the push lever 21 is unintentionally pressed when the combustion-type power tool 90 is neglected, leaving the push switch 23 on, or when the push switch 23 is continuously on due to fused contacts, and can enter the low power consumption mode for maintaining output from the regulator ICl in a halted state to prevent unnecessary power consumption in the battery 25. In order to return to the operating mode (standby mode) , the transistors Q3 and Q4 connected in the positive feedback circuit can be returned to the ON state. To return the transistors Q3 and Q4 to the OFF state, the operator can remove and reconnect the battery 25 or switch the main power supply switch SWl off and back on, at which time the regulator ICl begins supplying the prescribed voltage of 3.3 V to the microcomputer 101 and the like. In this way, it is possible to return the low-voltage power supply circuit 102 to its operating mode (standby mode), i.e. to reset the low- voltage power supply circuit 102. The reset IC IC2 is an integrated circuit device for transmitting a reset signal to a reset terminal 6 of the microcomputer 101 when the battery 25 is inserted and the main power supply switch SWl turned on or when the output voltage from the regulator ICl is reset within a prescribed voltage range.

The battery voltage detection circuit 106 includes FETs Ql and Q2 ; resistors R1-R3, R14, and R15; and a

capacitor Cl. The voltage supplied from the battery 25 is divided by the resistors R14 and R15 and inputted into the microcomputer 101. The battery voltage detection circuit 106 is also provided with a voltage detection halting circuit 10 βc£ configured of the FETs Ql and Q2 and the resistors R1-R3. The FETs Ql and Q2 are turned off when the self-holding circuit 103 and low-voltage power supply circuit 102 enter the low power consumption mode, halting power output from the regulator ICl, thereby interrupting the circuit used to detect the battery voltage to prevent unnecessary power consumption by the dividing resistors R14 and R15.

The push switch circuit 105 includes the push switch 23 having normally open type mechanical contacts; resistors RlO and RlI; diodes Dl and D2; and a capacitor C7. When the combustion-type power tool 90 is pressed against the workpiece 29, such as a piece of wood, turning on the push switch 23, a low signal is transmitted to a terminal 20 of the microcomputer 101. Owing to the mechanical structure of the combustioή-type power tool 90, the push switch 23 and the trigger switch 12 are positioned separate from the circuit board of the controller 100 and are connected to the circuit board via cables (not shown) . However, in some cases the cable may pick up noise produced during ignition or the like, inducing a voltage that makes the ground side positive. Therefore, by providing the diodes Dl and D2 in the ground circuit, the induced voltage passes through the diodes Dl and D2, preventing an excessive voltage being applied to the microcomputer 101. In the preferred embodiment, the push switch 23 is configured of a normally open switch having mechanical contacts.

The trigger switch circuit 104 includes the trigger

switch 12 having mechanical contacts; a transistor Qlβ; resistors R161, R162, R12, R13, and R43; diodes D4 and D5; and a capacitor Cβ. According to the present invention, the trigger switch 12 is configured of a normally closed switch with mechanical contacts. In the preferred embodiment, the trigger switch 12 is electrically connected in series with the push switch 23. When operated, the normally closed type trigger switch 12 switches to the OFF state, and the transistor Qlβ constituting an inverter circuit switches to an ON state, inputting a low signal into an input terminal 19 of the microcomputer 101. Since the trigger switch 12 is normally operated and switched to an OFF state after operating the push switch 23, a low signal can easily be inputted into a terminal 20 of the microcomputer 101 by first pressing the push switch 23 to switch the push switch 23 to the ON state.

The microcomputer 101 has input terminals 4, 8, 19, and 20; and output terminals 10, 11, 12, 14, 15, and 16. While not shown in the drawings, the microcomputer 101 is also configured of an arithmetic processor (CPU) , a random access memory (RAM) , a read-only memory (ROM) , an analog-to- digital (A/D) converter, a timer, and an input/output port. The crystal oscillator 111 configured of a built-in timer in the microcomputer 101 is connected to terminals 3 and 4. The microcomputer 101 drives the motor 8 and controls operations of the charging circuit 107, ignition circuit 108, and the like. While the microcomputer 101 is used as an arithmetic control unit in the preferred embodiment, a digital circuit other than a microcomputer may be used as an arithmetic control circuit.

The charging circuit 107 functions to charge the ignition capacitor C5 and is configured of a transformer Tl;

diodes Dβ, D5, and D9; transistors Qβ and Q12; an FET Q7; and resistors R18, Rl9, R20, R27, R121, and R122.

The charging circuit 107 begins charging the ignition capacitor C5 when the trigger switch 12 is operated. Specifically, when the normally closed type trigger switch 12 is operated and enters an OFF state, the inverting transistor Qlβ outputs an ON signal. The ON signal is transmitted to the charging circuit 107 along two paths. On the first path, the collector side A of the transistor Qlβ inputs the signal into the base of the transistor Q12 via the resistor R121, turning the transistor Q12 on. Hence, the signal is transmitted to the collector of the transistor Q6. When the trigger switch 12 is operated and turned off, the transistor Qlβ simultaneously inputs an ON signal into the terminal 19 of the microcomputer 101 as the second path. Consequently, the microcomputer 101 outputs a low signal from the terminal 11 intermittently. The signal is inputted into the base of the transistor Qβ in the charging circuit 107, thereby turning the transistor Qβ on and off. Owing to the signals on these two paths, the FET Q7 is repeatedly turned on and off, producing a high voltage on the secondary side of the transformer Tl for charging the ignition capacitor C5 via the diode D6.

The charging circuit 107 described above does not turn on the transistor Q12 and begin charging the ignition capacitor C5 while the trigger switch 12 has not been operated, i.e. when the trigger switch 12 is on, even when the microcomputer 101 outputs a signal for charging the ignition capacitor C5 due to an abnormal voltage generated by noise or the like being inputted into the terminal 19 of the microcomputer 101.

The ignition circuit 108 includes the sparkplug 9; a

thyristor SCRl; a transistor Q8; a diode D7; a capacitor C4; and resistors R81, R82, R21, and R22. The microcomputer 101 generates a low signal from a terminal 10 as an ignition timing signal, turning on the transistor Q8. Accordingly, the signal is transmitted to the gate of the thyristor SCRl, turning on the thyristor SCRl. When the thyristor SCRl is turned on, energy stored in the ignition capacitor C5 is discharged. The energy discharged from the ignition capacitor C5 is boosted to about 15 KV by a transformer T2 to produce a spark with the sparkplug 9. After starting the ignition circuit, the microcomputer 101 functions to input an ON signal into the gate of the thyristor SCRl for an interval of 10 msec, for example.

The motor driving circuit 109 is configured of NPN transistors Q9 and QlO; a PNP transistor QIl; resistors R23- R26; diodes D10-D13; and a capacitor ClI. When the push switch 23 is operated and changes from OFF to ON, the microcomputer 101 outputs a low signal from a terminal 12, turning off the NPN transistor Q9 and turning on the NPN transistor QlO and PNP transistor QIl to apply the battery voltage of 7.2 V to the drive circuit section of the motor 8. Hence, the fan 6 is rotated when the combustion-type power tool 90 is pressed against the workpiece 29, turning on the push switch 23. The display circuit 110 includes light-emitting diodes

(LEDs); and resistors Rlβ and R17. When the battery 25 is mounted in the combustion-type power tool 90 and the main power supply switch SWl is switched on, the microcomputer

101 generates a low signal in the terminal 16 intermittently, causing the LEDs to begin flashing a green light to signify that the combustion-type power tool 90 is ready to use. When the combustion-type power tool 90 is pressed against

the workpiece 29, the motor 8 is driven and the microcomputer 101 outputs a low signal from the terminal 16 to turn on the green light in the LED 11, signifying that a nail can be discharged. Further, while the controller 100 is not in the low power consumption mode, the controller 100 outputs a low signal from the terminal 15 when the voltage in the battery 25 has not reached the reference voltage (7.2 V, for example) . Consequently, the LEDs 11 are lit in red, signifying to the user of the combustion-type power tool 90 that the battery 25 must be charged.

When the combustion-type power tool 90 is pressed against the workpiece 29, moving the push lever 21 upward, the gas cylinder 7 injects combustible gas into the combustion chamber 15a, and the push switch 23 is in the ON state, as described above, applying a signal to the control terminal 20 of the microcomputer 101. The microcomputer 101 outputs a drive signal from the output terminal 12 to the motor driving circuit 109, driving the motor 8 to begin rotating the fan 6 for agitating and mixing the combustible gas and air in the combustion chamber 15a.

As described above, when the user subsequently operates the trigger switch 12, turning the trigger switch 12 from ON to OFF, the microcomputer 101 controls the charging circuit 107 and ignition circuit 108 to generate a spark in the sparkplug 9 for igniting the air-fuel mixture. As a result, the driver blade 10a drives the nail 24 into the workpiece 29.

If the combustion-type power tool 90 is idle for a prescribed time (10 minutes, for example) after the push switch 23 is turned on, during which time the trigger switch 12 is not operated, the self-holding circuit 103 enters the low power consumption mode described above. Since the

combustion-type power tool 90 cannot be operated at this time, it is necessary to return the combustion-type power tool 90 to the operating mode, as described above. Operations to rotate the fan 6, charge the ignition capacitor C5, ignite the sparkplug 9, and the like according to the push switch 23 and trigger switch 12 continue without regard for the ON/OFF state of the other switch. Hence, by pressing the combustion-type power tool 90 against the workpiece 29 so that combustible gas is injected into the combustion chamber 15a, if the combustible gas is not sufficiently vaporized or agitated due to the ambient temperature or pressure in the gas cylinder, the combustible gas can still be ignited by pulling the trigger switch 12 multiple times while keeping the combustion-type power tool 90 pressed against the workpiece 29.

In the initial phase of operation of the combustion- type power tool 90 when the battery 25 is inserted and the main power supply switch SWl is turned on, the microcomputer 101 is reset. While the push switch 23 is continuously off, the microcomputer 101 detects whether the combustion-type power tool 90 is being used, in order to prevent depletion in the battery 25 when the combustion-type power tool 90 is left in the operating mode for a long period of time. For example, if the push switch 23 is in the OFF state for more than 10 minutes, the microcomputer 101 transmits a trigger signal from the terminal 14 to the self-holding circuit 103 for putting the low-voltage power supply circuit 102 in the low power consumption mode.

As described above, the trigger switch 12, which receives a large impact during a driving operation of the combustion-type power tool 90, is configured of a normally closed type mechanical switch in the present invention.

Hence, the mechanical contacts in the trigger switch 12 are open (OFF) when operating the trigger switch 12 and are not in contact when the switch receives an impact during the nail-driving operation, thereby preventing mechanical wear of the switch.

However, since the push switch 23 and trigger switch 12 are connected in series in the present invention, the push switch 23 and trigger switch 12 are connected to a low- voltage power supply (3.3 V) via the resistor RlO. Further, a power supply voltage of 3.3 V is connected to the point of connection between the push switch 23 and trigger switch 12 via the resistor R43. This construction enables a current limited by the resistor R43 to flow to the trigger switch 12 when the push switch 23 and trigger switch 12 are not operated, thereby suppressing the consumption current during a non-operation period. However, when the push switch 23 is turned on, a current regulated by the resistor RlO flows to the push switch 23, and the current flowing to the trigger switch 12 is the sum of the current limited by the resistor R43 and the current limited by the resistor RlO.

According to the operations described above, when the normally open type push switch 23 is turned on, the microcomputer 101 receives a low signal at the terminal 20, controlling the motor driving circuit 109 to drive the motor 8. Subsequently, when the normally closed type trigger switch 12 is operated, turning the trigger switch 12 off, electrical conduction in the trigger switch 12 is interrupted. Hence, the current flowing through the resistor R43 can flow to the base of the transistor Qlβ, turning on the transistor Qlβ and enabling the microcomputer 101 to receive a low signal at the terminal 19 for controlling the ignition circuit 108 to produce a spark in

the sparkplug 9.

The construction of the preferred embodiment described above can restrict the electric current flowing to the trigger switch 12 when the push switch 23 is not operated to a minute current of a required minimum amount and can provide a current when the push switch 23 is operated that is sufficient for preventing the generation of an oxide film on the contact points of the switch, which can lead to contact failure. Further, rather than increasing power consumption unnecessarily, this construction can flow a portion of the current in the motor 8 (armature current) to the trigger switch 12 to provide a current sufficient for preventing oxidation. Specifically, the motor current is flowed from the negative terminal of the motor 8 to the contact point between the push switch 23 and trigger switch 12 through the diode D13. The diode D12 is inserted on the ground side of a bypass on which the motor current is supplied to the contact point of the trigger switch 12. By flowing the motor current to the contact point of the trigger switch 12, this construction can prevent oxidation. In the preferred embodiment described above, the push switch 23 is connected in series with the trigger switch 12, but the ground side of the push switch 23 may be separated from the trigger switch 12 and directly grounded. In this case, the push switch 23 should be configured of a normally closed switch having mechanical contacts, like the trigger switch 12, and an inverter circuit similar to the circuit for the trigger switch 12 comprising the transistor Qlβ and resistors R161 and R162 should be added to the push switch 23. <Embodiment of an Electric-type Power Tool 70>

Fig. 4 shows the structure of an electric-type power

tool (cordless nail driver) 70 having a push switch and a trigger switch according to another embodiment of the present invention. Fig. 5 is a block diagram of a controller 81 used in the electric-type power tool 70. In the preferred embodiment, the electric-type power tool 70 has a push switch 82 and a trigger switch 75, both of which are configured of normally closed switches with mechanical contacts and therefore change from the ON state to the OFF state when operated. As in the embodiment of the combustion-type power tool described above, the structure of this electric-type power tool can prevent friction in the mechanical contacts caused by chattering.

As shown in Fig. 4, the electric-type power tool 70 is configured of a main housing 71a having a nail-striking part 71c on the front end thereof; a magazine 72 disposed on the nail-striking part 71c of the main housing 71a for continuously supplying nails to the nail-striking part 71c; a handle housing 71b extending vertically downward from the main housing 71a; the trigger switch 75 provided on a branching part of the handle housing 71b for executing a nail-driving operation; and a battery pack 77 connected to the bottom end of the handle housing 71b and configured of lithium ion cells or other secondary batteries.

While not shown in the drawings, the magazine 72 is loaded with a plurality of linked nails (a block) . The block of nails is urged from the bottom of the magazine 72 by a spring (not shown) so that nails 72a are consecutively supplied to the nail-striking part 71c to be driven through a discharge outlet 71d or the nail-striking part 71c. A driver 73 .is provided in the main housing 71a for applying a striking force to the nail 72a in the nail- striking part 71c to drive the nail 72a. The driver 73

includes a driver blade 73a for transmitting the striking force to the head of the nail 72a, and a rack 73b engaged with a rotatable pinion 80. The rack 73b of the driver 73 and the pinion 80 engaged with the rack 73b constitute a driver feeding mechanism 73c for applying the rotational drive force of the pinion 80 to the driver 73 as a linear drive force.

The main housing 71a also accommodates a motor 96 (see Fig. 5) , such as a DC commutator motor, driven by a DC power supply from the battery pack 77 and serving as the drive source for driving nails; a motor gear 78 fixed to the rotational shaft of the motor 96; and a flywheel 79 having a gear engaged with the motor gear 78. The flywheel 79 and pinion 80 rotate coaxially to each other, but are provided with a clutch mechanism for switching between an engaged state in which the outer surface of the rotational shaft in the flywheel 79 contacts the inner surface of the rotational shaft in the pinion 80, and a separate state in which the outer surface of the rotational shaft in the flywheel 79 does not contact the inner surface of the rotational shaft in the pinion 80. While not shown in the drawings, the clutch mechanism is controlled by reciprocating movement of a solenoid 93 (see Fig. 5) .

The flywheel 79 is engaged with the motor gear 78 and stores kinetic energy from the rotational movement of the motor 96. The driver feeding mechanism 73c applies the rotational drive force of the flywheel 79 to the driver blade 73a as a linear drive force for driving the driver blade 73a into the nail 72a provided in the nail-striking part 71c.

As with the combustion-type power tool described above, the electric-type power tool also enters an operating state

(standby state) when the push switch 82 is pressed against a workpiece, turning the push switch 82 off. When the user subsequently operates the trigger switch 75, turning the trigger switch 75 off, a transistor 92 (see Fig. 5) is turned on for supplying current to the solenoid 93. Consequently, the solenoid 93 constituting the clutch mechanism transmits the rotational energy accumulated in the flywheel 79 from the rotational force of the motor 96 to the pinion 80 constituting the driver feeding mechanism 73c. As the pinion 80 rotates, the rack 73b engaged with the pinion 80 converts the rotational motion of the pinion 80 to linear motion for driving the driver blade 73a fixed to the driver 73 into the head of the nail 72a. After the driver blade 73a impacts the nail 72a, the current flowing to the solenoid 93 is turned off, returning the clutch mechanism to the separated state. Further, a driver feeding spring 74 configured of a constant-force spring, for example, is connected to the end of the driver 73. The elastic force of the driver feeding spring 74 returns the driver feeding mechanism 73c (rack 73b and pinion 80) from its position following impact to its original position prior to impact.

The controller 81 provided in the main housing 71a controls the overall operations of the electric-type power tool 70 based on operations of the push switch 82 and trigger switch 75.

<Structure of the Controller 81>

Next, the controller 81 will be described with reference to Fig. 5.

As shown in Fig. 5, the controller 81 includes a microcomputer (control circuit) 86, a low-voltage supply circuit 84, a self-holding circuit 87, a motor driving circuit 94, a motor driving transistor 95, a solenoid

driving circuit 91, a solenoid driving transistor 92, the push switch 82, and the trigger switch 75. As in the first embodiment described above, the battery pack 77 is the power supply of the controller 81 and is configured of a 7.2 V lithium ion secondary battery (battery pack), for example. The battery pack 77 supplies power to the low-voltage supply circuit 84, motor driving transistor 95, and solenoid driving transistor 92 via a main power supply switch 88. The low-voltage supply circuit 84 has a function for stepping down the power supply to 3.3 V, for example, and a function for selecting whether to output a prescribed low voltage or to halt output of the low voltage in response to input signals from a control input terminal 84a.

A motor detection circuit 89 is provided for detecting the timing at which the motor 96 reaches the required rotational force for driving a nail and inputs detection signals into the microcomputer 86.

In the present invention, the push switch 82 and the trigger switch 75 are configured of normally closed switches having mechanical contacts, as described above, and switch from the ON state to the OFF state when operated. First and second detection circuits 82a and 75a having inverters for inverting phase are provided for the push switch 82 and trigger switch 75, respectively, and are configured to input an ON level (ground level) signal into the microcomputer 86 when the respective switch is operated.

The microcomputer 86 controls the motor driving circuit 94 and motor driving transistor 95 of the motor 96 and the solenoid driving circuit 91 and solenoid driving transistor 92 of the solenoid 93 based on the rotational state of the motor 96 and detection signals generated by the first detection circuit 82a and second detection circuit 75a

when the push switch 82 and trigger switch 75 are operated, i.e. turned off. The solenoid 93 constituting the clutch mechanism functions to place the outer surface of the rotational shaft in the flywheel 79 in contact with the inner surface of the rotational shaft in the pinion 80 to transmit the rotational energy of the flywheel 79 to the pinion 80 when the motor 96 reaches the required rotational force for driving a nail. The microcomputer 86 includes a read-only memory (ROM) 86b for storing control programs used to control driving of the motor 96 and solenoid 93, and a table for determining the rotational state of the motor 96, such as the rotating time; a central processing unit (CPU) 86a having an arithmetic unit for executing the control programs stored in the ROM 86b and the like; a random access memory (RAM) 86c serving as a work area for the CPU 86a and for temporarily storing data inputted from the motor 96; and a timer (TIM) 86d including a reference clock signal generator.

The microcomputer 86 supplies a motor drive signal to the motor driving circuit 94 for controlling the base current of the motor driving transistor 95 (a PNP transistor, for example) in order to apply the voltage of the battery pack 77 to the motor 96, and supplies a solenoid drive signal to the solenoid driving circuit 91 for controlling the driving time (ON time) of the solenoid 93. The motor driving circuit 94 drives the motor driving transistor 95 for switching the motor driving transistor 95 ON or OFF in order to control whether or not a drive current is supplied to the motor 96. The solenoid driving circuit 91 drives the solenoid driving transistor 92 (a PNP transistor, for example) in order to control whether a drive current is supplied to the solenoid 93.

As in the preferred embodiment of the combustion-type power tool described above, the self-holding circuit 87 can be attained with a positive feedback circuit in which the collectors of a PNP transistor and an NPN transistor are connected to the bases of the other. The self-holding circuit 87 has a function for switching the microcomputer 86, solenoid driving circuit 91, and motor driving circuit 94 into a low power consumption mode. Specifically, as in the first embodiment described above, if the electric-type power tool 70 has not been operated for a prescribed time after turning off the push switch 82, the microcomputer 86 transmits a halt output signal to the self-holding circuit 87 as a trigger signal so that the self-holding circuit 87 holds itself in the first stable state (ON state, for example) for halting output of the output voltage (3.3 V) from the low-voltage supply circuit 84. In other words, the self-holding circuit 87 holds itself in the low power consumption mode, thereby preventing unnecessary power consumption when the electric-type power tool 70 is not being used. If the user wishes to exit the low power consumption mode with the intention of using the electric- type power tool 70, the user can switch the main power supply switch 88 off and back on to return the electric-type power tool 70 to the operating mode (standby mode) . With this construction, the electric-type power tool 70 enters the operating state (standby state) when the user presses the push switch 82 against a workpiece, turning the push switch 82 off. If the user subsequently operates the trigger switch 75, the solenoid driving transistor 92 is turned on, supplying current to the solenoid 93. Accordingly, the solenoid 93 constituting the clutch mechanism transmits rotational energy accumulated in the

flywheel 79 by the rotational force of the motor 96 to the pinion 80 constituting the driver feeding mechanism 73c. As the pinion 80 rotates, the rack 73b engaged with the pinion 80 converts the rotational motion of the pinion 80 to linear motion for driving the driver blade 73a fixed to the driver 73 against the head of the nail 72a. Although the push switch 82 and trigger switch 75 receive vibrations when the driver blade 73a impacts the nail 72a, both the push switch 82 and the trigger switch 75 are in the OFF state, preventing wear of the mechanical contacts in these switches.

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 . Industrial Applicability

This invention can be applied to power tools such as for driving a fastener into a workpiece. The power tool to which the invention is applicable should include a push switch for detecting that the tool is pressed against the workpiece and a trigger switch for instructing to drive a fastener into the workpiece.