Impact tool

According to an aspect of the present invention, there is provided an impact tool including: a motor drivable in an intermittent driving mode; a hammer connected to the motor; an anvil to be struck by the hammer to thereby rotate/strike a tip tool; and a control unit that controls a rotation of the motor by switching a driving pulse supplied to the motor in accordance with a load applied onto the tip tool.

TECHNICAL FIELD

An aspect of the present invention relates to an impact tool which is driven by a motor and realizes a new striking mechanism.

Another aspect of the present invention relates to a power tool, and particularly, to an electronic pulse driver which outputs a rotational driving force.

Still another aspect of the present invention relates to a power tool, and particularly, to an electronic pulse driver which outputs a rotational driving force.

Still another aspect of the present invention relates to a power tool, and particularly, to an electronic pulse driver which outputs a rotational driving force.

Still another aspect of the present invention relates to a power tool, and particularly, to an electronic pulse driver which outputs a rotational driving force.

Still another aspect of the present invention relates to a power tool, and particularly, to an electronic pulse driver which outputs a rotational driving force.

Still another aspect of the present invention relates to a power tool, and particularly, to an electronic pulse driver which outputs a rotational driving force.

Still another aspect of the present invention relates to a power tool, and particularly, to an electronic pulse driver which outputs a driving force.

Still another aspect of the present invention relates to a power tool, and particularly, to an electronic pulse driver which outputs a rotational driving force.

Still another aspect of the present invention relates to a power tool, and particularly, to an electronic pulse driver which outputs a rotational driving force.

BACKGROUND ART

In an impact tool, a rotation striking mechanism is driven by a motor as a driving source to provide rotation and striking to an anvil, thereby intermittently transmitting rotation striking power to a tip tool for performing operation, such as screwing. As a motor, a brushless DC motor is widely used. The brushless DC motor is, for example, a DC (direct current) motor with no brush (brush for commutation). Coils (windings) are used on the stator side, magnets (permanent magnets) are used on the rotor side, and a rotor is rotated as the electric power driven by an inverter circuit is sequentially applied to predetermined coils. The inverter circuit is constructed using an FET (field effect transistor), and a high-capacity output transistor such as an IGBT (insulated gate bipolar transistor), and is driven by a large current. The brushless DC motor has excellent torque characteristics as compared with a DC motor with a brush, and is able to fasten a screw, a bolt, etc. to a base member with a stronger force.

JP-2009-072888-A discloses an impact tool using the brushless DC motor. In JP-2009-072888-A, the impact tool has a continuous rotation type impact mechanism. When torque is given to a spindle via a power transmission mechanism (speed-reduction mechanism), a hammer which movably engages in the direction of a rotary shaft of the spindle rotates, and an anvil which abuts on the hammer is rotated. The hammer and the anvil have two hammer convex portions (striking portions) which are respectively arranged symmetrically to each other at two places on a rotation plane, these convex portions are at positions where the gears mesh with each other in a rotation direction, and rotation striking power is transmitted by meshing between the convex portions. The hammer is made axially slidable with respect to the spindle in a ring region surrounding the spindle, and an inner peripheral surface of the hammer includes an inverted V-shaped (substantially triangular) cam groove. A V-shaped cam groove is axially provided in an outer peripheral surface of the spindle, and the hammer rotates via balls (steel balls) inserted between the cam groove and the inner peripheral cam groove of the hammer.

In the conventional power transmission mechanism, the spindle and the hammer are held via the balls arranged in the cam groove, and the hammer is constructed so as to be able to retreat axially rearward with respect to the spindle by the spring arranged at the rear end thereof. As a result, the number of parts of the spindle and the hammer increases, high attaching accuracy between the spindle and the hammer is required, thereby increasing the manufacturing cost.

Meanwhile, in the impact tool of the conventional technique, in order to perform a control so as not to operate the impact mechanism (that is, in order that striking does not occur), for example, a mechanism for controlling a retreat operation of the hammer is required. The impact tool of JP-2009-072888-A cannot be used in a so-called drill mode. Further, even if a drill mode is realized (even if a retreat operation of the hammer is controlled), in order to realize even the clutch operation of interrupting power transmission when a given fastening torque is achieved, it is necessary to provide a clutch mechanism separately, and realizing the drill mode and the drill mode with a clutch in the impact tool leads to cost increase.

Further, in JP-2009-072888-A, the driving electric power to be supplied to the motor is constant irrespective of the load state of a tip tool during the striking by the hammer. Accordingly, striking is performed with a high fastening torque even in the state of light load. As a result, excessive electric power is supplied to the motor, and useless power consumption occurs. And, a so-called coming-out phenomenon occurs where a screw advances excessively during screwing as striking is performed with a high fastening torque, and the tip tool is separated from a screw head.

A conventional power tool mainly has a motor, a hammer rotationally driven by the motor, and an anvil to which torque is imparted through collision with the hammer (for example, refer to JP-2008-307664-A). As the torque transmitted to the anvil is imparted to a tip tool, the fastening work of a screw or the like is performed. In the power tool, as an engaging projection provided on the hammer and an engaged projection provided on the anvil collide with each other, torque is imparted to the anvil, and the torque is transmitted to the tip tool.

However, in a conventional power tool, the engaging projection collides in a state where the speed has been increased by the motor. For this reason, a problem occurs in that the impact of the collision between the engaging projection and the engaged projection becomes large, and fastening torque increases. Particularly when the increased fastening of fastening a screw or the like which has been fastened again is performed, since the fastening torque is already imparted to the screw, the torque may become excessively large due to the impact of the collision between the engaging projection and the engaged projection. Thus, the object of the invention is to provide a power tool capable of preventing torque exceeding a target torque from being supplied to a fastener.

In conventional power tools, there is a power tool in which it is determined that a predetermined torque has been obtained when a predetermined current value is reached, and supply of electric power to a motor is automatically stopped. Although such products have been sold, the stopping of the supply of electric power to the motor occurs, for example, when a power cord has been pulled in a case where the power cord is used, or when the remaining battery level of the charging battery has been reduced in a case where the charging battery is used, other than when the predetermined torques are reached. For this reason, when a predetermined torque is reached, it is necessary to make the event easily understood by a worker.

However, in the conventional power tool, the operation continues unless the worker takes his/her finger off the trigger. Therefore, useless power consumption occurs, and the temperature of the motor also rises. Especially when compared with normal operation (the motor rotates continuously in one direction), the normal rotation and stop of the motor are repeated in a ratcheting operation mode. Therefore, the power consumption and the temperature rise of the battery are conspicuous. Thus, an object of the invention is to provide a power tool capable of, when a predetermined torque is reached, making the event easily understood. Another object of the invention is to provide a power tool capable of making it hard to uselessly consume electric power and obtaining high-precision torque, when making the event easily understood.

A worker is able to make a screw or the like and a tip tool of a power tool fit each other, and to depress a trigger, thereby performing fastening work of a fastener. When a worker fastens a bolt to a member to be worked in which a lead is formed, since resistance is small, a current value shifts to a low value, and at a moment when a bolt is seated, the current value abruptly rises and exceeds a threshold value at once.

In such a case, even if the motor is stopped by turning OFF the trigger, a stop operation is delayed due to the inertia of the motor, and the bolt is fastened with a value which is equal to or more than a desired torque value. Thus, the object of the invention is to provide a power tool capable of supplying a precise target torque.

In a conventional power tool, a structure in which an anvil is struck in a given direction by a hammer which rotates in the given direction is known (for example, refer to JP-2008-307664-A).

However, in the conventional power tool, when a trigger is depressed in a state where the fitting between a screw and a tip tool is in an imperfect state at the time of start-up, the fitting between the screw and the tip tool may be released (coming-out), and the head of the screw may be damaged. Thus, the object of the invention is to provide a power tool capable of preventing the coming-out of a tip tool from a fastener.

In a conventional power tool, a motor is controlled regardless of the temperature of a built-in object of the housing (for example, refer to JP-2010-058186-A).

In the conventional power tool, the motor is driven without taking generation of heat of the built-in object of the housing into consideration. For this reason, for example, if the ambient temperature is low, there is a case where the viscosity of grease of a gear mechanism changes, the grease hardens, and the current value of the motor rises. For this reason, it is necessary to alter the electric power to be supplied to the motor depending on whether the ambient temperature is low, or the ambient temperature is high.

Additionally, if the ambient temperature is high, switching elements for supplying electric power to coils of the motor may be damaged as the switching elements generate heat. For this reason, it is necessary to prevent the temperature of the switching elements from becoming too high. The object of the invention is to provide a power tool adapted to change the control method of a motor according to the temperature of a built-in object of the housing.

In a conventional power tool, a structure in which an anvil is struck in a given direction by a hammer which rotates in the given direction is known (for example, refer to JP-2008-307664-A).

Meanwhile, the applicant of the invention has newly developed an electronic pulse driver constructed to normally rotate and reversely rotate the hammer, thereby striking the anvil. However, in the newly developed electronic pulse driver, the fitting between a screw or the like and a tip tool may be released (come-out), and the head of the screw may be damaged. Moreover, a force in the direction reverse to the rotational direction is generated in the power tool by the reaction caused by the operation after seating, and the worker experiences discomport. Thus, the object of the invention is to provide a power tool capable of reducing the reaction force from a member to be worked.

A conventional power tool is adapted to rotate a fastener by an output shaft. The control of a motor is the same even when a plurality of fasteners is used (for example, refer to JP-2008-307664-A).

However, in the conventional power tool, it is difficult to perform fastening according to the fasteners used. Particularly when the fastening work of a wood screw is performed, the wood screw needs to perform fastening even after seating, and a control which gives a high torque to a tip tool is required. Moreover, when the fastening work of a bolt is performed, further fastening cannot be performed after seating. Therefore, when the normal rotation time of pulses is long, a force reverse to a rotational direction is generated in an impact driver by the reaction of the bolt, and the worker experiences discomfort. Then, the object of the invention is to provide a power tool capable of discriminating a fastener. By such a power tool, the control of a motor can be varied in a case where fasteners are different.

In an electric impact driver which is an example of a conventional power tool, a motor is rotated in a given rotational direction to rotate a hammer in the given direction and to rotate an anvil in a given direction (for example, refer to JP-2008-307664-A).

In the conventional power tool, the motor is controlled regardless of the temperature of a built-in object of the housing. Additionally, as an embodiment of the invention, in a power tool which normally rotates or reversely rotates the motor, generation of heat by the motor increases. As such, in the power tool in which generation of heat of the motor becomes large, the temperature of the motor may rise excessively in a case where the motor is controlled regardless of the temperature of the motor. The object of the invention is to provide a power tool capable of controlling a motor according to the temperature of a built-in object of the housing. By such a power tool, the temperature of the built-in object of the housing rarely rises excessively.

In a conventional power tool, a structure in which an anvil is struck in a given direction by a hammer which rotates in the given direction is known (for example, refer to JP-2008-307664-A).

Meanwhile, the applicant of the invention has newly developed an electronic pulse driver constructed to normally rotate and reversely rotate the hammer, thereby striking the anvil. However, in the newly developed electronic pulse driver, if the normal rotation time is long during high-load work, the reaction of the impact driver also increases, and the worker experiences increasing discomfort. Thus, the object of the invention is to provide a power tool which is comfortable to use.

SUMMARY OF INVENTION

One object of the invention is to provide an impact tool in which an impact mechanism is realized by a hammer and an anvil with a simple mechanism.

Another object of the invention is to provide an impact tool which can drive a hammer and an anvil between which the relative rotation angle is less than 360 degrees, thereby performing a fastening operation, by devising a driving method of a motor.

According to Point 1 of the present invention, there is provided an impact tool including: a motor drivable in an intermittent driving mode; a hammer connected to the motor; an anvil to be struck by the hammer to thereby rotate/strike a tip tool; and a control unit that controls a rotation of the motor by switching a driving pulse supplied to the motor in accordance with a load applied onto the tip tool.

According to Point 2 of the present invention, there may be provided the impact tool, wherein the control unit switches the driving pulse based on a rotation number of the motor.

According to Point 3 of the present invention, there may be provided the impact tool, wherein the control unit switches the driving pulse based on a change in a driving current flowing into the motor.

According to Point 4 of the present invention, there may be provided the impact tool, wherein the control unit changes an output time of the driving pulse in accordance with the load on the tip tool.

According to Point 5 of the present invention, there may be provided the impact tool, wherein the control unit changes an effective value of the driving pulse in accordance with the load on the tip tool.

According to Point 6 of the present invention, there may be provided the impact tool, wherein the control unit changes a maximum value of the driving pulse in accordance with the load on the tip tool.

According to Point 7 of the present invention, there may be provided the impact tool, wherein the intermittent driving mode includes: a first intermittent driving mode in which the motor is driven only in a normal rotation; and a second intermittent driving mode in which the motor is driven in the normal rotation and in a reverse rotation.

According to Point 8 of the present invention, there may be provided the impact tool, wherein the control unit supplies a driving pulse to the motor so that a section where a driving current is supplied to the motor and a section where the driving current is not supplied to the motor appear alternately.

According to Point 1, since the motor is driven in an intermittent driving mode, and the control unit switches a driving pulse supplied to the motor according to the load state applied to the tip tool, it is possible to prevent useless electric power from being consumed when the load applied to the tip tool is light. Further, it is possible to prevent a so-called coming-out phenomenon where the tip tool is separated from the head of a screw or the like, by being driven with large electric power during light load.

According to Point 2, since the control unit switches the driving pulse based on the rotation number of the motor, switching control of the driving pulse can be performed by using a rotation number detection sensor which has conventionally been loaded. And, it is possible to realize the simplification and/or cost reduction for configuring the control unit.

According to Point 3, since the control unit switches the driving pulse based on a change in a driving current which flows into the motor, switching control of the driving pulse can be performed by using a current sensor which has conventionally been loaded. And, it is possible to realize the simplification and/or cost reduction for configuring the control unit.

According to Point 4, since the control unit changes the output time of the driving pulse according to the load state of the tip tool, striking torque can be adjusted while suppressing a peak current to be supplied to the motor. Therefore, there is no need for enlarging the switching element used for the inverter circuit.

According to Point 5, since the control unit changes the output time of the driving pulse according to the load state of the tip tool, the switching element in the inverter circuit can be protected from an excess current.

According to Point 6, since the control unit changes the maximum value of the driving pulse according to the load state of the tip tool, consumption of the useless electric power when the load applied to the tip tool is light can be prevented.

According to Point 7, since two different intermittent driving modes include an intermittent driving mode of only the normal rotation and an intermittent driving mode of the normal rotation and the reverse rotation, fastening can be performed at high speed with a lower fastening torque in the intermittent driving mode of only normal rotation, and fastening can be reliably performed with a higher fastening torque in the intermittent driving mode of normal rotation and reverse rotation.

According to Point 8, since the control unit supplies a driving pulse to the motor so that a section where a driving current is supplied to the motor, and a section where a driving current is not supplied to the motor appear alternately, the conventional inverter circuit can be used to realize the intermittent driving mode.

In order to achieve the above object, the invention provides an electronic pulse driver including a rotatable motor; a hammer rotated by a driving force being supplied thereto from the motor; an anvil provided separately from the hammer and rotated by the hammer integrally therewith; a tip tool holding portion capable of holding a tip tool and transmitting the rotation of the anvil to the tip tool; an electric power supply unit which supplies the driving electric power to the motor; and a control unit which controls the electric power supply unit so as to stop the supply of the driving electric power to the motor in a case where an electric current which flows into the motor in a state where the driving electric power is supplied has increased to a predetermined value. The control unit controls the electric power supply unit so as to supply electric power for soft starting which is smaller than the driving electric power to the motor before the driving electric power is supplied, in order to make the electric power supply unit supply the driving electric power in a state where the hammer and the anvil are brought into contact with each other.

According to such a construction, the hammer and the anvil are brought into contact with each other by supplying electric power for soft starting to the motor before the driving electric power is supplied. Thus, it is possible to prevent torque exceeding a target torque from being supplied to a fastener by striking.

Additionally, the invention provides a power tool including a motor serving as a power source; a hammer connected to and rotated by the motor; and an anvil rotatable with respect to the hammer, and capable of supplying first power which integrally rotates the hammer and the anvil, and second power smaller than the first power, to the hammer from the motor. The second power is supplied to the hammer at the beginning of the starting of the motor, and the first power is supplied to the hammer after the supply of the second power.

According to such a construction, as power for pre-start is applied to the hammer, the hammer and the anvil are prevented from colliding with each other to generate a large impact. For this reason, a large torque is prevented from being generated due to the impact between the hammer and the anvil. For this reason, the tip tool rarely fastens a fastener with a greater torque than a targeted torque.

Additionally, the invention provides a power tool including an electric motor; a hammer connected to the electric motor; and an anvil rotatable with respect to the hammer, and capable of supplying first electric power, and second electric power smaller than the first electric power, to the electric motor. The second electric power is supplied to the electric motor at the beginning of the starting of the motor, and the first electric power is supplied to the electric motor after the supply of the second electric power.

By such a construction, as a normal rotation voltage for pre-start is applied to the motor, the hammer and the anvil are prevented from colliding with each other to generate a large impact. For this reason, a large torque is prevented from being generated due to the impact between the hammer and the anvil. For this reason, the tip tool rarely fastens a fastener with a greater torque than a targeted torque.

Preferably, the hammer is capable of striking the anvil.

Preferably, the supply of the electric power to the motor is stopped by detecting that predetermined electric power has been supplied to the motor.

Since the supply of the electric power to the motor is automatically stopped by such a construction, the fastening torque of a fastener can be made highly precise. For this reason, the fastening high-precision torque can be obtained by an effect which is synergetic with pre-start.

Preferably, the time during which the second electric power is supplied is longer than the time until the anvil and the hammer come into contact with each other.

By using such a construction to make the pre-start time longer than the time until the hammer and the anvil come into contact with each other, the hammer and the anvil come into contact with each other within the pre-start time. For this reason, the hammer is prevented from striking the anvil to generate a large impact. For this reason, generation of a large impact when the collision between the anvil and the hammer occurs can be reduced. If the pre-start time is shorter than the time until the hammer and the anvil come into contact with each other, the hammer accelerates, and strikes the anvil, and a large impact is transmitted to the anvil from the hammer.

Preferably, the power tool further includes a trigger capable of energizing the motor, and capable of changing the amount of electric power to be supplied to the motor, and the second electric power is smaller than a predetermined value irrespective of the pulling amount of the trigger.

Preferably, the amount of electric power to be supplied to the motor is capable of being changed by changing the duty ratio of a PWM signal.

Preferably, the second electric power is smaller than a predetermined value during a predetermined time.

According to the power tool of the invention, it is possible to provide a power tool capable of preventing torque exceeding a target torque from being supplied to a fastener.

In order to achieve the above object, the invention provides an electronic pulse driver including a motor capable of normally rotating and reversely rotating; a hammer rotated in a normal rotation direction or a reverse rotation direction by a driving force being supplied thereto from the motor; an anvil provided separately from the hammer and rotated by the hammer integrally therewith in the normal rotation direction; a tip tool holding portion capable of holding a tip tool and transmitting the rotation of the anvil to the tip tool; an electric power supply unit which supplies the motor with normal rotation electric power for rotation, normal rotation electric power for a clutch smaller than the normal rotation electric power for rotation, or reverse rotation electric power for a clutch having a smaller absolute value than the normal rotation electric power for rotation; and a control unit which controls the electric power supply unit so as to alternately switch the normal rotation electric power for a clutch and the reverse rotation electric power for a clutch to generate a pseudo-clutch in a case where an electric current which flows into the motor in a state where the normal rotation electric power for rotation is supplied has increased to a predetermined value, and stop the pseudo-clutch after the elapse of a predetermined time from the generation of the pseudo-clutch.

According to such a construction, since the pseudo-clutch is stopped after the elapse of a predetermined time from the generation thereof, it is possible to suppress power consumption and a temperature rise.

Additionally, the invention provides a power tool including a motor; and an output shaft rotated by the motor. If the electric power to be supplied to the motor for rotating the output shaft in the normal rotation direction has become a first electric power value, a second electric power value smaller than the first electric power value is capable of being intermittently supplied to the motor.

By such a construction, the second electric power is smaller than the first electric power. Thus, fastening/loosening of a fastener hardly occurs while the second electric power is added. For this reason, high-precision torque can be obtained.

Preferably, the supply of the second electric power value to the motor is automatically stopped after a predetermined time.

By such a construction, since the motor automatically stops, electric power can be prevented from being excessively used.

Preferably, the motor is rotatable in the normal rotation direction and the reverse rotation direction by the supply of the second electric power value to the motor.

By such a construction, as the motor rotates in the normal rotation direction and the reverse rotation direction, a fastener hardly fastens or loosens. For this reason, high-precision torque can be obtained. If the second electric power value is only in the normal rotation, fastening is apt to occur.

According to the power tool of the invention, it is possible to provide a power tool capable of, when a predetermined torque is reached, making the event easily understood. Additionally, it is possible to provide a power tool capable of making it hard to consume electric power uselessly and obtaining high-precision torque, when making the event easily understood.

In order to achieve the above object, the invention provides an electronic pulse driver including a motor capable of normally rotating and reversely rotating; a hammer rotated in a normal rotation direction or a reverse rotation direction by a driving force being supplied thereto from the motor; an anvil provided separately from the hammer and rotated by the hammer integrally therewith in the normal rotation direction; a tip tool holding portion capable of holding a tip tool and transmitting the rotation of the anvil to the tip tool; an electric power supply unit which supplies the motor with normal rotation electric power or reverse rotation electric power; and a control unit which controls the electric power supply unit so as to supply the reverse rotation electric power to the motor if the increasing rate of an electric current when the electric current which flows into the motor in a state where the normal rotation electric power has increased to a predetermined value is supplied is equal to or more than a predetermined value.

According to such a construction, the reverse rotation electric power is supplied to the motor when the electric current which flows into the motor has increased to a predetermined value. Thus, even if a fastener such as a bolt in which torque abruptly increases just before a target torque is fastened, it is possible to prevent the torque caused by an inertial force from being supplied, and it is possible to supply an accurate target torque.

Additionally, the invention provides a power tool including a motor; and an output shaft rotated by the motor. If a normal rotation current to the motor for rotating the output shaft in one direction is equal to or more than a predetermined value, a reverse rotation current for rotating the output shaft in a direction reverse to the one direction is supplied to the motor.

According to such a construction, since the reverse rotation current is supplied if the normal rotation current has a predetermined value, a fastener can be kept from being excessively fastened due to the inertia of the normal rotation current. For this reason, an accurate screw fastening torque can be obtained.

Additionally, the invention provides a power tool including a motor; and an output shaft rotated by the motor. If the increasing rate of a normal rotation current per unit time to the motor for rotating the output shaft in one direction is equal to or more than a predetermined value, a reverse rotation current for rotating the output shaft in a direction reverse to the one direction is supplied to the motor.

By such a construction, since the reverse rotation current is supplied if the increasing rate of the normal rotation current has a predetermined value, a fastener can be kept from being excessively fastened due to the inertia of the normal rotation current. For this reason, an accurate screw fastening torque can be obtained.

According to the power tool of the invention, it is possible to provide a power tool capable of supplying a precise target torque.

In order to achieve the above object, the invention provides an electronic pulse driver including a motor capable of normally rotating and reversely rotating; a hammer rotated in a normal rotation direction or a reverse rotation direction by a driving force being supplied thereto from the motor; an anvil provided separately from the hammer and rotated by torque being supplied thereto by the rotation of the hammer in the normal rotation direction; a tip tool holding portion capable of holding a tip tool and transmitting the rotation of the anvil to the tip tool; an electric power supply unit which supplies the motor with normal rotation electric power for rotation or reverse rotation electric power for fitting; and a control unit which controls the electric power supply unit so as to supply the reverse rotation electric power for fitting to the motor so that the hammer rotates in the reverse rotation direction to strike the anvil before the normal rotation electric power for rotation is supplied.

According to such a construction, the hammer is reversely rotated and struck on the anvil by supplying the reverse rotation electric power for fitting to the motor before the supply of the normal rotation electric power for rotation. Thus, even if the fitting between a fastener and a tip tool is insufficient, the fastener and the tip tool can be made to fit to each other firmly, and it is possible to prevent the tip tool from coming out of the fastener during operation.

Additionally, the invention provides a power tool including a motor, a hammer rotated by the motor, and an anvil struck by the hammer. The anvil is rotated in the reverse rotation direction before the hammer strikes the anvil in the normal rotation direction.

By such a construction, since the anvil rotates in the reverse rotation direction, the fitting between the anvil and a fastener can be made firm. For this reason, the fastener is rarely damaged by the anvil. For this reason, the durability of the fastener can be enhanced.

Additionally, the invention provides a power tool including a motor, a hammer rotated by the motor, and an anvil struck by the hammer. The hammer and the anvil come into contact with each other in the reverse rotation direction before the hammer strikes the anvil in the normal rotation direction.

By such a construction, since the anvil is struck and rotates in the reverse rotation direction, the fitting between the anvil and a fastener can be made firm. For this reason, the fastener is rarely damaged by the anvil. For this reason, the durability of the fastener can be enhanced.

Preferably, in the invention, the tip tool is held by the anvil.

Additionally, the invention provides a power tool including a motor, and a tip tool holding portion rotated by the motor. The tip tool holding portion is constructed so as to reversely rotate before the tip tool holding portion rotates in the normal rotation direction.

According to the power tool of the invention, it is possible to provide a power tool capable of preventing the coming-out of a tip tool from a fastener.

In order to achieve the above object, the invention provides an electronic pulse driver including a rotatable motor; switching elements for powering the motor; a gear mechanism connected to the motor to change the rotational speed of the motor; a hammer rotated by a driving force being supplied thereto via the gear mechanism from the motor; an anvil provided separately from the hammer and rotated by torque being supplied thereto by the rotation of the hammer; a tip tool holding portion capable of holding a tip tool and transmitting the rotation of the anvil to the tip tool; an electric power supply unit which supplies the driving electric power to the motor; a control unit which controls the electric power supply unit so as to change the magnitude of the driving electric power in a case where the electric current which flows into the motor in a state where the driving electric power is supplied has increased to a predetermined threshold value; a temperature detection unit which detects the temperature of the switching elements; and a threshold value changing portion which changes the threshold value based on the temperature of the switching elements.

According to such a construction, by changing the threshold value in consideration of a change in temperature, it is possible to change the mode of striking in a suitable situation.

Additionally, the invention provides a power tool including a motor, an output unit driven by the motor, and a housing which houses the motor. A temperature detection unit capable of detecting the temperature of a built-in object of the housing is provided, and a control method of the motor is capable of being changed according to the output value of the temperature detection unit.

By such a construction, it is possible to keep the built-in object of the housing from excessively generating heat. For this reason, the built-in object is rarely damaged by heat.

Additionally, the invention provides a power tool including a motor unit, an output unit driven by the motor, and a housing which houses the motor. A temperature detection unit capable of detecting the temperature of the motor unit is provided, and a control method of the motor unit is capable of being changed according to the output value of the temperature detection unit.

By such a construction, it is possible to keep the motor unit from excessively generating heat. For this reason, the motor unit can be rarely damaged by heat.

Preferably, the motor unit has a circuit board, and switching elements and temperature detecting elements are provided on the circuit board.

By such a construction, by detecting the temperature of the switching elements, which are apt to be especially influenced by the generation of heat, via the circuit board, it is possible to perform a control so as to prevent the generation of heat of the switching elements. For this reason, the switching elements are hardly damaged.

According to the invention, it is possible to provide a power tool adapted to change the control method of the motor according to the temperature of a built-in object of the housing.

In order to achieve the above object, the invention provides an electronic pulse driver including a motor capable of normally rotating and reversely rotating; a hammer rotated in a normal rotation direction or a reverse rotation direction by a driving force being supplied thereto from the motor; an anvil provided separately from the hammer and struck and rotated by the rotation of the hammer, which has gained acceleration distance due to the rotation in the reverse rotation direction, in the normal rotation direction; a tip tool holding portion capable of holding a tip tool and transmitting the rotation of the anvil to the tip tool; an electric power supply unit which switches between normal rotation electric power or reverse rotation electric power in a first cycle so as to be supplied to the motor; and a control unit which controls the electric power supply unit so as to switches between the normal rotation electric power and the reverse rotation electric power in a second cycle shorter than the first cycle if the increasing rate of an electric current when the electric current which flows into the motor in a state where the normal rotation electric power and the reverse rotation electric power are supplied has increased to a predetermined value is equal to or greater than a predetermined value.

According to such a construction, if the increasing rate of an electric current when the electric current which flows into the motor has increased to a predetermined value is equal to or greater than a predetermined value, a wood screw is regarded as seated, and the switching cycle of the normal rotation electric power and the reverse rotation electric power is switched to a short cycle. Thus it is possible to reduce a subsequent reaction force from a member to be worked.

Additionally, the invention provides a power tool including a motor, a hammer rotated by the motor, and an anvil struck by the hammer. If an electric current which flows into the motor is equal to or less than a predetermined value, the hammer strikes the anvil at a first interval, and if the electric current to be supplied to the motor is equal to or greater than a predetermined value, the hammer strikes the anvil at a second interval shorter than the first interval.

By such a construction, if the electric current is equal to or greater than a predetermined value, the torque is also made to be equal to or greater than a predetermined value, and if the torque is equal to or greater than a predetermined value, the striking interval is shortened. For this reason, since striking increases in a shorter time when the torque increases, worker's productivity increases. If the anvil is not struck at the second interval, the reaction force is large. Thus, the rotation of a fastener decreases and the rotating speed of the fastener becomes low. For this reason, worker's productivity will worsen.

Additionally, the invention provides a power tool including a motor, a hammer rotated by the motor, and an anvil struck by the hammer. If the electric current which flows into the motor is equal to or less than a predetermined value, the hammer strikes the anvil at a first interval, and if the electric current to be supplied to the motor is equal to or greater than a predetermined value, the hammer strikes the anvil at a second interval shorter than the first interval.

Additionally, in another aspect of the invention, the invention provides a power tool including a motor, and an output shaft rotationally driven ed by the motor. Seating is detected according to electric current caused in the motor.

According to the power tool of the invention, it is possible to provide a power tool capable of reducing the reaction force from a member to be worked.

In order to achieve the above object, the invention provides, as Point 10 thereof, an electronic pulse driver including a motor capable of normally rotating and reversely rotating; a hammer rotated in a normal rotation direction or a reverse rotation direction by a driving force being supplied thereto from the motor; an anvil provided separately from the hammer and rotated by torque being supplied by the rotation of the hammer in the normal rotation direction; a tip tool holding portion capable of holding a tip tool and transmitting the rotation of the anvil to the tip tool; an electric power supply unit which supplies the motor with normal rotation electric power or reverse rotation electric power; and a control unit which controls the electric power supply unit so as to supply the normal rotation electric power to the motor in order to rotate the anvil integrally with the hammer during a predetermined period, and supply the reverse rotation electric power to the motor when the predetermined period has elapsed, and which controls the electric power supply unit so as to switch between the normal rotation electric power and the reverse rotation electric power in a first switching cycle if the electric current which flows into the motor by the reverse rotation electric power is equal to or greater than a first predetermined value, and switch between the normal rotation electric power and the reverse rotation electric power in a second cycle if the electric current is less than the first predetermined value.

According to such a construction, the switching cycle of the normal rotation electric power and the reverse rotation electric power is changed according to an electric current which flows into the motor by the reverse rotation electric power. For example, if the electric current which flows into the motor is large, the fastener can be determined to be a wood screw, and if the electric current is small, the fastener can be determined to be a bolt. Thereby, the normal rotation electric power and the reverse rotation electric power can be switched between in a cycle suitable for each fastener, and it is possible to perform suitable fastening according to the kind of fasteners.

Additionally, the invention provides, as Point 9 thereof, a power tool including a motor, and an output shaft rotated in a normal rotation direction by the motor. A control method of the motor is automatically changed according to a current value occurring when a signal is imparted so as to reversely rotate the motor.

According to such a construction, since a fastener which is rotated by the output shaft can be determined according to a current value when the output shaft is reversely rotated, only the output of a current has to be detected. For this reason, since other separate detections or the like are not necessary, an inexpensive electric power tool can be obtained.

According to the power tool of the invention, it is possible to provide a power tool capable of discriminating a fastener.

In order to achieve the above object, the invention provides, as Point 11 thereof, an electronic pulse driver including a motor capable of normally rotating and reversely rotating; a hammer rotated in a normal rotation direction or a reverse rotation direction by a driving force being supplied thereto from the motor; an anvil provided separately from the hammer and struck and rotated by the rotation of the hammer, which has gained acceleration distance due to rotation in the reverse rotation direction, in the normal rotation direction; a tip tool holding portion capable of holding a tip tool and transmitting the rotation of the anvil to the tip tool; an electric power supply unit which alternately switches normal rotation electric power or reverse rotation electric power in a first cycle so as to be supplied to the motor; a temperature detection unit which detects the temperature of the motor; and a control unit which controls the electric power supply unit so as to switch between the normal rotation electric power and the reverse rotation electric power in a second cycle longer than the first cycle if the temperature of the motor has risen to a predetermined value.

According to such a construction, the normal rotation electric power and the reverse rotation electric power is switched in a second cycle longer than the first cycle if the temperature of the motor has risen to a predetermined value. Thus, generation of heat caused at the time of the switching can be suppressed, and it is possible to enhance the durability of the whole impact driver.

Additionally, the invention provides a power tool including a motor, an output unit driven by the motor, a housing which houses the motor, and a temperature detection unit capable of detecting the temperature of a built-in object of the housing. A control method of the motor is changed according to the output value from the temperature detection unit.

By such a construction, since the value of electric power supplied to the motor can be changed according to the temperature of the built-in object of the housing. Thus, it is possible to keep the temperature of the built-in object of the housing from becoming too high. For this reason, it is possible to keep the built-in object of the housing from being damaged due to a high temperature.

Additionally, the invention provides a power tool including a motor unit, an output unit driven by the motor, a housing which houses the motor unit, and a temperature detection unit capable of detecting the temperature of the motor unit. The value of electric power supplied to the motor unit is changed according to the output value from the temperature detection unit.

By such a construction, since the value of electric power supplied to the motor can be changed according to the temperature of the motor unit. Thus, it is possible to keep the temperature of the motor unit from becoming too high. For this reason, it is possible to keep the motor unit from being damaged due to a high temperature.

Preferably, a hammer is connected to the motor unit, the anvil is enabled to be struck by the hammer, if the output value from the temperature detection unit is a first value, the hammer strikes the anvil at a first interval, and if the output value from the temperature detection unit is a second value greater than the first value, the hammer strikes the anvil at a second interval longer than the first interval.

By such a construction, if the temperature is high, the load decreases. Thus, if the temperature of the motor unit is high, the temperature of the motor unit can be prevented from rising. For this reason, it is rare that the motor unit is damaged as the temperature of the motor unit rises excessively.

Additionally, in another aspect of the invention, the invention provides a power tool including an intermittently driven motor, an output unit driven by the motor, a housing which houses the motor, and a temperature detection unit capable of detecting the temperature of a built-in object of the housing. A cycle in which the motor is intermittently driven is changed according to the output value from the temperature detection unit.

According to the power tool of the invention, it is possible to provide a power tool capable of controlling a motor according to the temperature of a built-in object of the housing.

In order to achieve the above object, the invention provides, as Point 12 thereof, an electronic pulse driver including a motor capable of normally rotating and reversely rotating; a hammer rotated in a normal rotation direction or a reverse rotation direction by a driving force being supplied thereto from the motor; an anvil struck and rotated by the rotation of the hammer, which has gained acceleration distance due to rotation in the reverse rotation direction, in the normal rotation direction; a tip tool holding portion capable of holding a tip tool and transmitting the rotation of the anvil to the tip tool; an electric power supply unit which alternately switches between normal rotation electric power or reverse rotation electric power so as to be supplied to the motor; and a control unit which controls the electric power supply unit so as to increase the ratio of a period during which the reverse rotation electric power is supplied with respect to a period during which the normal rotation electric power is supplied, with an increase in the electric current which flows into the motor.

According to such a construction, the ratio of the reverse rotation period to the normal rotation period is increased with an increase in the electric current which flows into the motor. Thus, the reaction force from a member to be worked can be suppressed, and it is possible to provide an impact tool which is comfortable to use.

According to Point 13 of the present invention, preferably, the control unit controls the electric power supply unit in a first mode in which the normal rotation period during which the normal rotation electric power is supplied is reduced, in a first step where the electric current which flows into the motor increases to a predetermined value, and controls the electric power supply unit in a second mode in which the reverse rotation period during which the reverse rotation electric power is supplied is increased, in a second step where the electric current which flows into the motor has exceeded the predetermined value.

According to such a construction, if the electric current which flows into the motor is equal to or less than a predetermined value, fastening is performed in the first mode centered on a pressing force, and if the electric current is greater than the predetermined value, fastening is performed in the second mode centered on a striking force. Thus, it is possible to perform fastening in a mode which is most suitable for the fastener.

According to Point 14 of the present invention, preferably, the control unit is capable of selecting one mode from a plurality of second modes with different ratios, in the second step.

According to such a construction, even if the electric current which flows into the motor has abruptly increased, it is possible to perform fastening in a suitable striking mode.

According to Point 15 of the present invention, preferably, the control unit permits only shifting to a second mode with a long reverse rotation period from a second mode with a short reverse rotation period, among a plurality of second modes with different ratios, in the second step.

According to such a construction, it is possible to prevent an abrupt change in feeling.

According to Point 16 of the present invention, preferably, the control unit permits only shifting to a second mode which is adjacent in its length of the reverse rotation period, among a plurality of second modes with different ratios, in the second step.

According to such a construction, it is possible to prevent an abrupt change in feeling.

Additionally, the invention provides, as Point 17 thereof, a power tool including an intermittently driven motor, a hammer driven by the motor, and an anvil struck by the hammer. The time during which the hammer is normally rotated is gradually decreased.

By such a construction, since the time during which the hammer is normally rotated is gradually decreased, the striking interval of the hammer can be decreased in correspondence with the load which gradually increases. For this reason, the reaction force to a worker decreases, and a power tool which hardly slips off the fastener and good productivity can be obtained.

Additionally, the invention provides, as Point 18 thereof, a power tool including an intermittently driven motor, a hammer driven by the motor, and an anvil struck by the hammer. The time during which the hammer is reversely rotated is gradually increased.

By such a construction, since the time during which the hammer is reversely rotated is gradually increased, the amount of reverse rotation of the hammer can be increased in correspondence with the rotational amount of the anvil having decreased in correspondence to the load which gradually increases. For this reason, an acceleration interval of the hammer can be enlarged. For this reason, the anvil can be struck by accelerating the hammer reliably, and the anvil can be efficiently struck. For this reason, a power tool with good productivity can be obtained.

Additionally, the invention provides, as Point 19 thereof, a power tool including an intermittently driven motor; a hammer driven by the motor; an anvil struck by the hammer; and a detecting means capable of detecting the value of the electric current which flows into the motor. A first current value, a second current value greater than the first current value, and a third current value greater than the second current value are capable of flowing to the motor. A control is capable of being performed by a first mode according to the first current value, a second mode according to the second current value, and a third mode according to the third current value. A control is performed in the second mode after the control in the first mode if the detecting means of the motor has detected the first current value, and has detected the third current value immediately after the detection of the first current value.

By such a construction, even if the current value has abruptly changed (for example, even if a change to the third current value from the first current value), a mode is not abruptly changed (a change to the second mode from the first mode is made (an abrupt change to the third mode is not made)). Thus, a worker rarely feels a sense of discomfort by a change in mode. For this reason, a power tool with good workability can be obtained.

Additionally, the invention provides, as Point 20 thereof, a power tool including an intermittently driven motor; a hammer driven by the motor; an anvil struck by the hammer; and a detecting means capable of detecting the value of the electric current which flows into the motor. A first current value, and a second current value greater than the first current value are capable of flowing to the motor. A control is capable of being performed by a first mode according to the first current value, and a second mode according to the second current value. A control is not performed in the first mode after a control is performed in the first mode, and a control is performed in the second mode.

By such a construction, even if the load becomes light during screw fastening, the pattern of the voltage is not changed to a mode for light load. Thus, the mode is gradually changed to a mode for heavy load. For this reason, modes for light load and heavy load are not repeated. For this reason, a power tool with a good feeling of use for a worker can be obtained.

According to Point 21 of the present invention, preferably, a third current value greater than the second current value is capable of flowing into the motor, a control is capable of being performed by the third mode according to the third current value, and a control is performed in the second mode or the third mode after the control in the second mode.

Additionally, the invention provides, as Point 22 thereof, a power tool including an intermittently driven motor; a hammer driven by the motor; an anvil struck by the hammer; and a detecting means capable of detecting the value of the electric current which flows into the motor. A first current value, a second current value greater than the first current value, and a third current value greater than the second current value are capable of flowing to the motor. A control is capable of being performed by a first mode according to the first current value, a second mode according to the second current value, and a third mode according to the third current value. A control is performed in the third mode after the first mode if the first current value has been detected, and the third current value has been detected.

By such a construction, if it has been detected that the current value becomes large and the load become large, work can be performed in a mode according to a load by changing to the mode according to the load. For this reason, a power tool with good working efficiency can be obtained.

Additionally, in another aspect of the invention, the invention, as Point 23 thereof, provides a power tool including an intermittently driven motor, a hammer driven by the motor, and an anvil struck by the hammer. The control method of the motor is capable of being automatically changed.

According to Point 24 of the present invention, preferably, the control method of the motor is automatically changed according to the load to the motor.

According to Point 25 of the present invention, preferably, the load of the motor is an electric current generated in the motor.

According to Point 26 of the present invention, preferably, the control method of the motor is automatically changed according to the amount of time.

According to the power tool of the invention, it is possible to provide a power tool with good feeling in use.

The above and other objects and new features of the invention will be apparent from the following description of the specification and the drawings.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described with reference to the drawings. In the following description, the directions of up and down, front and rear, and right and left correspond to the directions shown inFIGS. 1 and 2.

FIG. 1illustrates an impact tool1according to one embodiment. The impact tool1drives the striking mechanism40with a chargeable battery pack30as a power source and a motor3as a driving source, and gives rotation and striking to the anvil46as an output shaft to transmit continuous torque or intermittent striking power to a tip tool (not shown), such as a driver bit, thereby performing an operation, such as screwing or bolting.

The motor3is a brushless DC motor, and is accommodated in a tubular trunk portion6aof a housing6which has a substantial T-shape as seen from the side. The housing6is splittable into two substantially-symmetrical right and left members, and the right and left members are fixed by plural screws. For example, one (the left member in the embodiment) of the right and left members of the housing6is formed with plural screw bosses20, and the other (the right member in the embodiment) is formed with plural screw holes (not shown). In the trunk portion6a, the rotary shaft19of the motor3is rotatably held by bearings17bat the rear end, and bearings17aprovided around the central portion. A board on which six switching elements10are loaded is provided at the rear of the motor3, and the motor3is rotated by inverter-controlling these switching elements10. A rotational position detecting element58, such as a Hall element or a Hall IC, are loaded at the front of the board7to detect the position of the rotor3a.

In the housing6, a grip portion6bextends almost perpendicularly and integrally from the trunk portion6a. A trigger switch8and a normal/reverse switching lever14are provided at an upper portion in the grip portion6b. A trigger operating portion8aof the trigger switch8is urged by a spring (not shown) to protrude from the grip portion6b. A control circuit board9for controlling the speed of the motor3through the trigger operating portion8ais accommodated in a lower portion in the grip portion6b. A battery holding portion6cis formed in the lower portion of the grip portion6b, and a battery pack30including plural nickel hydrogen or lithium ion battery cells is detachably mounted on the battery holding portion6c.

A cooling fan18is attached to the rotary shaft19at the front of the motor3to synchronizedly rotate therewith. The cooling fan18sucks air through air inlets26aand26bprovided at the rear of the trunk portion6a. The sucked air is discharged outside the housing6from plural slits26c(refer toFIG. 2) formed around the radial outer peripheral side of the cooling fan18in the trunk portion6a.

The striking mechanism40includes the anvil46and the hammer41. The hammer41is fixed so as to connect rotary shafts of plural planetary gears of the planetary gear speed-reduction mechanism21. Unlike a conventional impact mechanism which is now widely used, the hammer41does not have a cam mechanism which has a spindle, a spring, a cam groove, balls, etc. The anvil46and the hammer41are connected with each other by a fitting shaft41aand a fitting groove46fformed around rotation centers thereof so that only less than one relative rotation can be performed therebetween. At a front end of the anvil46, an output shaft portion to mount a tip tool (not shown) and a mounting hole46ahaving a hexagonal cross-sectional shape in an axial direction are integrally formed. The rear side of the anvil46is connected to the fitting shaft41aof the hammer41, and is held around the axial center by a metal bearing16aso as to be rotatable with respect to a case5. The detailed shape of the anvil46and the hammer41will be described later.

The case5is integrally formed from metal for accommodating the striking mechanism40and the planetary gear speed-reduction mechanism21, and is mounted on the front side of the housing6. The outer peripheral side of the case5is covered with a cover11made of resin in order to prevent a heat transfer, and an impact absorption, etc. The tip of the anvil46includes a sleeve15and balls24for detachably attaching the tip tool. The sleeve15includes a spring15a, a washer15band a retaining ring15c.

When the trigger operating portion8ais pulled and the motor3is started, the rotational speed of the motor3is reduced by the planetary gear speed-reduction mechanism21, and the hammer41rotates at a rotation number with a given reduction ratio with respect to the rotation number of the motor3. When the hammer41rotates, the torque thereof is transmitted to the anvil46, and the anvil46starts rotation at the same speed as the hammer41. When the force applied to the anvil46becomes large by a reaction force received from the tip tool side, a control unit detects an increase in fastening reaction force, and drives the hammer41continuously or intermittently while changing the driving mode of the hammer41before the rotation of the motor3is stopped (the motor3is locked).

FIG. 2illustrates the appearance of the impact tool1ofFIG. 1. The housing6includes three portions6a,6b, and6c, and slits26cfor discharge of cooling air is formed around the radial outer peripheral side of the cooling fan18in the trunk portion6a. A control panel31is provided on the upper face of the battery holding portion6c. Various operation buttons, indicating lamps, etc. are arranged at the control panel31, for example, a switch for turning on/off an LED light12, and a button for confirming the residual amount of the battery pack are arranged on the control panel31. A toggle switch32for switching the driving mode (the drill mode and the impact mode) of the motor3is provided on a side face of the battery holding portion6c, for example. Whenever the toggle switch32is depressed, the drill mode and the impact mode are alternately switched.

The battery pack30includes release buttons30A located on both right and left sides thereof, and the battery pack30can be detached from the battery holding portion6cby moving the battery pack30forward while pushing the release buttons30A. A metallic belt hook33is detachably attached to one of the right and left sides of the battery holding portion6c. Although the belt hook33is attached at the left side of the impact tool1inFIG. 2, the belt hook33can be detached therefrom and attached to the right side. A strap34is attached around a rear end of the battery holding portion6c.

FIG. 3enlargedly illustrates around a striking mechanism40ofFIG. 1. The planetary gear speed-reduction mechanism21is a planetary type. A sun gear21aconnected to the tip of the rotary shaft19of the motor3functions as a driving shaft (input shaft), and plural planetary gears21brotate within an outer gear21dfixed to the trunk portion6a. Plural rotary shafts21cof the planetary gears21bis held by the hammer41as a planetary carrier. The hammer41rotates at a given reduction ratio in the same direction as the motor3, as a driven shaft (output shaft) of the planetary gear speed-reduction mechanism21. This reduction ratio is set based on factors, such as a fastening subject (a screw or a bolt) and the output of the motor3and the required fastening torque. In the present embodiment, the reduction ratio is set so that the rotation number of the hammer41becomes about ⅛ to 1/15 of the rotation number of the motor3.

An inner cover22is provided on the inner peripheral side of two screw bosses20inside the trunk portion6a. The inner cover22is manufactured by integral molding of synthetic resin, such as plastic. A cylindrical portion is formed on the rear side of the inner cover, and bearings17awhich rotatably fixes the rotary shaft19of the motor3are held by a cylindrical portion of the inner cover. A cylindrical stepped portion which has two different diameters is provided on the front side of the inner cover22. Ball-type bearings16bare provided at the stepped portion with a smaller diameter, and a portion of an outer gear21dis inserted from the front side at the cylindrical stepped portion with a larger diameter. Since the outer gear21dis non-rotatably attached to the inner cover22, and the inner cover22is non-rotatably attached to the trunk portion6aof the housing6, the outer gear21dis fixed in a non-rotating state. An outer peripheral portion of the outer gear21dincludes a flange portion with a largely formed external diameter, and an O ring23is provided between the flange portion and the inner cover22. Grease (not shown) is applied to rotating portions of the hammer41and the anvil46, and the O ring23performs sealing so that the grease does not leak into the inner cover22side.

In the present embodiment, a hammer41functions as a planetary carrier which holds the plural rotary shafts21cof the planetary gear21b. Therefore, the rear end of the hammer41extends to the inner peripheral side of the bearings16b. The rear inner peripheral portion of the hammer41is arranged in a cylindrical inner space which accommodates the sun gear21aattached to the rotary shaft19of the motor3. A fitting shaft41awhich protrudes axially forward is formed around the front central axis of the hammer41, and the fitting shaft41afits to a cylindrical fitting groove46fformed around the rear central axis of the anvil46. The fitting shaft41aand the fitting groove46fare journalled so that both are rotatable relative to each other.

FIG. 4illustrates the cooling fan18. The cooling fan18is manufactured by integral molding of synthetic resin, such as plastic. The rotation center of the cooling fan is formed with a through hole18awhich the rotary shaft19passes through, a cylindrical portion18bwhich secures a given distance from a rotor3awhich covers the rotary shaft19by a given distance in the axial direction is formed, and plural fins18cis formed on an outer peripheral side from the cylindrical portion18b. An annular portion is provided on the front and rear sides of each fin18c, and the air sucked from the axial rear side (not only the rotation direction of the cooling fan18) is discharged outward in the circumferential direction from plural openings18dformed around the outer periphery of the cooling fan. Since the cooling fan18exhibits the function of a so-called centrifugal fan, and is directly connected to the rotary shaft19of the motor3without going through the planetary gear speed-reduction mechanism21, and rotates with a sufficiently larger rotation number than the hammer41, sufficient air volume can be secured.

Next, the construction and operation of the motor driving control system will be described with reference toFIG. 5.FIG. 5illustrates the motor driving control system. In the present embodiment, the motor3includes a three-phase brushless DC motor. This brushless DC motor is a so-called inner rotor type, and has a rotor3aincluding permanent magnets (magnets) including plural (two, in the embodiment) N-S poles sets, a stator3bcomposed of three-phase stator windings U, V, and W which are wired as a stator, and three rotational position detecting elements (Hall elements)58arranged at given intervals, for example, at 60 degrees in the peripheral direction in order to detect the rotational position of the rotor3a. Based on position detection signals from the rotational position detecting elements58, the energizing direction and time to the stator windings U, V, and W are controlled, thereby rotating the motor3. The rotational position detecting elements58are provided at positions which face the permanent magnets3cof the rotor3aon the board7.

Electronic elements to be loaded on the board7include six switching elements Q1to Q6, such as FET, which are connected as a three-phase bridge. Respective gates of the bridge-connected six switching elements Q1to Q6are connected to a control signal output circuit53loaded on the control circuit board9, and respective drains/sources of the six switching elements Q1to Q6are connected to the stator windings U, V, and W which are wired as a stator. Thereby, the six switching elements Q1to Q6perform switching operations by switching element driving signals (driving signals, such as H4, H5, and H6) input from the control signal output circuit53, and supplies electric power to the stator windings U, V, and W with the direct current voltage of the battery pack30to be applied to the inverter circuit52as three-phase voltages (U phase, V phase, and W phase) Vu, Vv, and Vw.

Among switching elements driving signals (three-phase signals which drive the respective signals of the six switching elements Q1to Q6, driving signals for the three negative power supply side switching element Q4, Q5, and Q6are supplied as pulse width modulation signals (PWM signals) H4, H5, and H6, and the pulse width (duty ratio) of the PWM signals is changed by the computing unit51loaded on the control circuit board9based on a detection signal of the operation amount (stroke) of the trigger operating portion8aof the trigger switch8, whereby the power supply amount to the motor3is adjusted, and the start/stop and rotating speed of the motor3are controlled.

PWM signals are supplied to either the positive power supply side switching elements Q1to Q3or the negative power supply side switching elements Q4to Q6of the inverter circuit52, and the electric power to be supplied to stator windings U, V, and W from the direct current voltage of the battery pack30is controlled by switching the switching elements Q1to Q3or the switching elements Q4to Q6at high speed. In the present embodiment, PWM signals are supplied to the negative power supply side switching elements Q4to Q6. Therefore, the rotating speed of the motor3can be controlled by controlling the pulse width of the PWM signals, thereby adjusting the electric power to be supplied to each of the stator windings U, V, and W.

The impact tool1includes the normal/reverse switching lever14for switching the rotation direction of the motor3. Whenever a rotation direction setting circuit62detects the change of the normal/reverse switching lever14, the control signal to switch the rotation direction of the motor is transmitted to a computing unit51. The computing unit51includes a central processing unit (CPU) for outputting a driving signal based on a processing program and data, a ROM for storing a processing program or control data, and a RAM for temporarily storing data, a timer, etc., although not shown.

The control signal output circuit53forms a driving signal for alternately switching predetermined switching elements Q1to Q6based on output signals of the rotation direction setting circuit62and a rotor position detecting circuit54, and outputs the driving signal to the control signal output circuit53. This alternately energizes a predetermined winding wire of the stator windings U, V, and W, and rotates the rotor3ain a set rotation direction. In this case, driving signals to be applied to the negative power supply side switching elements Q4to Q6are output as PWM modulating signals based on an output control signal of an applied voltage setting circuit61. The value of a current to be supplied to the motor3is measured by the current detecting circuit59, and is adjusted into a set driving electric power as the value of the current is fed back to the computing unit51. The PWM signals may be applied to the positive power supply side switching elements Q1to Q3.

A striking impact sensor56which detects the magnitude of the impact generated in the anvil46is connected to the control unit50loaded on the control circuit board9, and the output thereof is input to the computing unit51via the striking impact detecting circuit57. The striking impact sensor56can be realized by a strain gauge, etc. attached to the anvil46, and when fastening is completed with normal torque by using the output of the striking impact sensor56, the motor3may be automatically stopped.

Next, before the striking operation of the hammer41and the anvil46related to the present embodiment is described, the basic construction of the hammer and the anvil and the striking operation principle thereof will be described with reference toFIGS. 6 and 7.FIG. 6illustrates the hammer151and the anvil156related to a basic construction (a second embodiment). The hammer151is formed with a set of protruding portions, i.e., a protruding portion152and a protruding portion153which protrude axially from the cylindrical main body portion151b. The front center of the main body portion151bis formed with a fitting shaft151awhich fits to a fitting groove (not shown) formed at the rear of the anvil156, and the hammer151and the anvil156are connected together so as to be rotatable relative to each other by a given angle of less than one rotation (less than 360 degrees). The protruding portion152acts as a striking pawl, and has planar striking-side surfaces152aand152bformed on both sides in a circumferential direction. The hammer151further includes a protruding portion153for maintaining rotation balance with the protruding portion152. Since the protruding portion153functions as a weight portion for taking rotation balance, no striking-side surface is formed.

A disc portion151cis formed on the rear side of the main body portion151bvia a connecting portion151d. The space between the main body portion151band the disc portion151dis provided to arrange the planetary gear21bof the planetary gear mechanism21, and the disc portion151dis formed with a through hole151ffor holding the rotary shafts21cof the planetary gear21b. Although not shown, a holding hole for holding the rotary shafts21cof the planetary gear21bis formed also on the side of the main body portion151bwhich faces disc portion151d.

The anvil156is formed with a mounting hole156afor mounting the tip tool on the front end side of the cylindrical main body portion156b, and two protruding portions157and158which protrude radially outward from the main body portion156bare formed on the rear side of the main body portion156b. The protruding portion157is a striking pawl which has struck-side surfaces157aand157b, and is a weight portion in which a protruding portion158does not have a struck-side surface. Since the protruding portion157is adapted to collide with the protruding portion152, the external diameter thereof is made equal to the external diameter of the protruding portion152. Both the protruding portions153and158only acting as a weight are formed to not interfere with each other and not to collide with any part. In order to take the rotation angle between the hammer151and the anvil156as much as possible (less than one rotation at the maximum), the radial thicknesses of the protruding portions153and158are made small to increase a circumferential length so that the rotation balance between the protruding portions152and157is maintained. By setting the relative rotation angle greatly, a large acceleration section (run-up section) of the hammer when the hammer is made to collide with the anvil can be taken, and striking can be performed with considerable energy.

FIG. 7illustrates one rotation movement in the usage state of the hammer151and the anvil156in six stages. The sectional plane ofFIG. 7is vertical to the axial direction, and includes a striking-side surface152a(FIG. 6). In the state ofFIG. 7(1), while fastening torque received from the tip tool is small, the anvil156rotates counterclockwise by being pushed from the hammer151. However, when the fastening torque becomes large, and rotation becomes impossible only by the pushing force from the hammer151, since the anvil156is struck by the hammer151, the reverse rotation of the motor3is started in order to reversely rotate the hammer151in the direction of arrow161. By starting the reverse rotation of the motor3in a state shown in (1), thereby rotating the protruding portion152of the hammer151in the direction of arrow161, and further reversely rotate the motor3, the protruding portion152rotates while being accelerated in the direction of arrow162through the outer peripheral side of the protruding portion158as shown in (2). Similarly, the external diameter Ra1of the protruding portion158is made smaller than the internal diameter Rh1of the protruding portion152, and thus both the protruding portions do not collide with each other. The external diameter Ra2of the protruding portion157is made smaller than the internal diameter Rh2of the protruding portion153, and thus both the protruding portions do not collide with each other. If the protruding portions are constructed in such positional relationship, the relative rotation angle of the hammer151and the anvil156can be made greater than 180 degrees, and the sufficient reverse rotation angle of the hammer151with respect to the anvil156can be secured.

When the hammer151further reversely rotates, and arrives at a position (stop position of the reverse rotation) ofFIG. 7(3) as shown by arrow163a, the rotation of the motor3is paused for a given time period, and then, the rotation of the motor3in the direction of arrow163b(the normal rotation direction) is started. When the hammer151is reversely rotated, it is important to stop the hammer151reliably at a stop position so as not to collide with the anvil156. Although the stop position of the hammer151before a position where the hammer collides with the anvil156is arbitrary set, it is desirable to make the stop position as large as possible according to the required fastening torque. It is not necessary to set the stop position to the same position each time, and the reverse rotation angle may be made small in an initial stage of fastening, and the reverse rotation angle may be set large as fastening proceeds. If the stop position is made variable in this way, since the time required for reverse rotation can be set to the minimum, striking operation can be rapidly performed in a short time.

Then, the hammer151is further accelerated while passing through the position ofFIG. 7(4) in the direction of arrow164, and the striking-side surface152aof the protruding portion152collides with the struck-side surface157aof the anvil156at a position shown inFIG. 7(5) in a state under acceleration. As a result of this collision, powerful rotation torque is transmitted to the anvil156, and the anvil156rotates in the direction shown by arrow166. The position ofFIG. 7(6) is a state where both the hammer151and the anvil156have rotated at a given angle from the state ofFIG. 7(1), and a fastening subject member is fastened to a proper torque by repeating the operation from the state shown inFIG. 7(1) toFIG. 7(5) again.

As described above, in the hammer151and the anvil156related to the second embodiment, an impact tool can be realized with a simple construction of the hammer151and the anvil156serving as a striking mechanism by using a driving mode where the motor3is reversely rotated. In the striking mechanism of this construction, the motor can also be rotated in the drill mode by the setting of the driving mode of the motor3. For example, in the drill mode, it is possible to rotate the hammer so as to follow the anvil156likeFIG. 7(6) simply by rotating the motor3from the state ofFIG. 7(5) to rotate the hammer151in a normal direction. Thus, by repeating this, members to be fastened, such as screws or bolts, capable of making fastening torque small, can be fastened at high speed.

In the impact tool1related to the present embodiment, a brushless DC motor is used as the motor3. Therefore, by calculating the value of a current which flows into the motor3from the current detecting circuit59(refer toFIG. 5), detecting a state where the value of the current has become larger than a given value, and making the computing unit51stop the motor3, a so-called clutch mechanism in which power transmission is interrupted after fastening to a given torque can be electronically realized. Accordingly, in the impact tool1related to the present embodiment, the clutch mechanism during the drill mode can also be realized, and the multi-use fastening tool which has a drill mode with no clutch, a drill mode with a clutch, and an impact mode can be realized by the striking mechanism with a simple construction.

Next, the detailed structure of the striking mechanism40shown inFIGS. 1 and 2will be described with reference toFIGS. 8 and 9.FIG. 8illustrates the hammer41and the anvil46related to a first embodiment, in which the hammer41is seen obliquely from the front, and the anvil46is seen obliquely from the rear.FIG. 9illustrates the hammer41and the anvil46, in which the hammer41is seen obliquely from the rear, and the anvil46is seen obliquely from the front. The hammer41is formed with two blade portions41cand41dwhich protrude radially from the cylindrical main body portion41b. Although the blade portions41dand41care respectively formed with the protruding portions which protrude axially, this construction is different from the basic construction (second embodiment) shown inFIG. 6in that a set of striking portions and a set of weight portions are formed in the blade portions41dand41c, respectively.

The outer peripheral portion of the blade portion41chas the shape of a fan, and the protruding portion42protrudes axially forward from the outer peripheral portion. The fan-shaped portion and the protruding portion42function as both a striking portion (striking pawl) and a weight portion. The striking-side surfaces42aand42bare formed on both sides of the protruding portion42in a circumferential direction. Both the striking-side surfaces42aand42bare formed into flat surfaces, and a moderate angle is given so as to come into surface contact with a struck-side surface (which will be described later), of the anvil46well. Meanwhile, the blade portion41dis formed to have a fan-shaped outer peripheral portion, and the mass of the fan-shaped portion increases due to the shape thereof. As a result, the blade portion acts well as a weight portion. Further, a protruding portion43which protrudes axially forward from around the radial center of the blade portion41dis formed. The protruding portion43acts as a striking portion (striking pawl), and striking-side surfaces43aand43bare formed on both sides of the protruding portion in the circumferential direction. Both the striking-side surfaces43aand43bare formed into flat surfaces, and a moderate angle is given in the circumferential direction so as to come into surface contact with a struck-side surface (which will be described later), of the anvil46well.

The fitting shaft41ato be fitted into the fitting groove46fof the anvil46is formed on the front side around the axial center of the main body portion41b. Connecting portions44cwhich connect two disc portions44aand44bat two places in the circumferential direction so as to function as a planetary carrier are formed on the rear side of the main body portion41b. Through holes44dare respectively formed at two places of the disc portions44aand44bin the circumferential direction, two planetary gears21b(refer toFIG. 3) are arranged between the disc portions44aand44b, and the rotary shafts21c(refer toFIG. 3) of the planetary gear21bare mounted on the through holes44d. A cylindrical portion44ewhich extends with a cylinder shape is formed on the rear side of the disc portion44b. The outer peripheral side of the cylindrical portion44eis held inside the bearings16b. The sun gear21a(refer toFIG. 3) is arranged in a space44finside the cylindrical portion44e. It is preferable not only in strength but also in weight to manufacture the hammer41and the anvil46which are shown inFIGS. 8 and 9as a metallic integral structure.

The anvil46is formed with two blade portions46cand46dwhich protrude radially from the cylindrical main body portion46b. A protruding portion47which protrudes axially rearward is formed around the outer periphery of the blade portion46c. Struck-side surfaces47aand47bare formed on both sides of the protruding portion47in the circumferential direction. Meanwhile, a protruding portion48which protrudes axially rearward is formed around the radial center of the blade portion46d. Struck-side surfaces48aand48bare formed on both sides of the protruding portion48in the circumferential direction. When the hammer41normally rotates (a rotation direction in which a screw, etc. is fastened), the striking-side surface42aabuts on the struck-side surface47a, and simultaneously, the striking-side surface43aabuts on the struck-side surface48a. When the hammer41reversely rotates (a rotation direction in which a screw, etc. is loosened), the striking-side surface42babuts on the struck-side surface47b, and simultaneously, the striking-side surface43babuts on the struck-side surface48b. The protruding portions42,43,47, and48are formed to simultaneously abut at two places.

As such, according to the hammer41and the anvil46which are shown inFIGS. 8 and 9, since striking is performed at two places which are symmetrical with respect to the rotating axial center, the balance during striking is good, and the impact tool1is hardly shaken during striking. Since striking-side surfaces are respectively provided on both sides of a protruding portion in the circumferential direction, impact operation becomes possible not only during normal rotation but also during reverse rotation, an impact tool which is easy to use can be realized. Since the hammer41strikes the anvil46only in the circumferential direction, and the hammer41does not strike the anvil46axially forward, the tip tool does not unnecessarily push a fastening subject member, and there is an advantage when a wood screw, etc. is fastened into timber.

Next, the striking operation of the hammer41and the anvil46which are shown inFIGS. 8 and 9will be described with reference toFIG. 10. The basic operation is the same as the operation described inFIG. 7, and the difference is that striking simultaneously performed in striking-side surfaces not at one place but at substantially-axisymmetric two places during striking.FIG. 10illustrates a cross-section of a portion A-A ofFIG. 3.FIG. 10illustrates the positional relationship between the protruding portions42and43which protrude axially from the hammer41, and the protruding portions47and48which protrude axially from the anvil46. The rotation direction of the anvil47during the fastening operation (during normal rotation) is counterclockwise.

FIG. 10(1) is in a state where the hammer41reversely rotates to the maximum reverse rotation position with respect to the anvil46(equivalent to the state ofFIG. 7(3)). From this state, the hammer41is accelerated in the direction of arrow91(in the normal direction) to strike the anvil46. Then, likeFIG. 10(2), the protruding portion42passes through the outer peripheral side of the protruding portion48, and simultaneously the protruding portion43passes through the inner peripheral side of the protruding portion47. In order to allow passage of both the protruding portions, the internal diameter RH2of the protruding portion42is made greater than the external diameter RA1of the protruding portion48, and thus the protruding portions do not collide with each other. Similarly, the external diameter RH1of the protruding portion43is made smaller than the internal diameter RA2of the protruding portion47, and thus both the protruding portions do not collide with each other. According to such positional relationship, the relative rotation angle of the hammer41and the anvil46can be made larger more than 180 degrees, the sufficient reverse rotation angle of the hammer41to the anvil46can be secured, and this reverse rotation angle can be located in the accelerating section before the hammer41strikes the anvil46.

Next, when the hammer41normally rotates to the state ofFIG. 10(3), the striking-side surface42aof the protruding portion42collides with the struck-side surface47aof the protruding portion47. Simultaneously, the striking-side surface43aof the protruding portion43collides with the striking-side surface48aof the protruding portion48. By causing collision at two places opposite to a rotation axis in this way, the striking which is well-balanced with respect to the anvil46can be performed. As a result of this striking, as shown inFIG. 10(4), the anvil46rotates in the direction of arrow94, and fastening of a fastening subject member is performed by this rotation. The hammer41has the protruding portion42which is a solitary protrusion at a radial concentric position (a position above RH2and below RH3), and has the protruding portion43which is a third solitary protrusion at a concentric position (position below RH1). The anvil46has the protruding portion47which is a solitary protrusion at a radial concentric position (a position above RA2and below RA3), and has the protruding portion48which is a solitary protrusion at a concentric position (position below RA1).

Next, the driving method of the impact tool1related to the present embodiment will be described. In the impact tool1related to the present embodiment, the anvil46and the hammer41are formed so as to be relatively rotatable at a rotation angle of less than 360 degrees. Since the hammer41cannot perform rotation of more than one rotation relative to the anvil46, the control of the rotation is also unique.FIG. 11illustrates a trigger signal during the operation of the impact tool1, a driving signal of an inverter circuit, the rotating speed of the motor3, and the striking state of the hammer41and the anvil46. The horizontal axis is time in the respective graphs (timings of the respective graphs are matched).

In the impact tool1related to the present embodiment, in the case of the fastening operation in the impact mode, fastening is first performed at high speed in the drill mode, fastening is performed by switching to the impact mode (1) if it is detected that the required fastening torque becomes large, and fastening is performed by switching to the impact mode (2) if the required fastening torque becomes still larger. In the drill mode from time T1to time T2ofFIG. 11, the control unit51controls the motor3based on a target rotation number. For this reason, the motor is accelerated until the motor3reaches the target rotation number shown by arrow85a. Thereafter, the rotating speed of the motor3with a large fastening reaction force from the tip tool attached to the anvil46decreases gradually as shown by arrow85b. Thus, decrease of the rotation speed is detected by the value of a current to be supplied to the motor3, and switching to the rotation driving mode by the pulse mode (1) is performed at time T2.

The pulse mode (1) is a mode in which the motor3is not continuously driven but intermittently driven, and is driven in pulses so that “pause→normal rotation driving” is repeated multiple times. The expression “driven in pulses” means controlling driving so as to pulsate a gate signal to be applied to the inverter circuit52, pulsate a driving current to be supplied to the motor3, and thereby pulsate the rotation number or output torque of the motor3. This pulsation is generated by repeating ON/OFF of a driving current with a large period (for example, about several tens of hertz to a hundred and several tens of hertz), such as ON (driving) of the driving current to be supplied to the motor from time T2to time T21(pause), ON (driving) of the driving current of the motor from time T21to time T3, OFF (pause) of the driving current from time T3to time T31, and ON of the driving current from time T31to time T4. Although PWM control is performed for the control of the rotation number of the motor3in the ON state of the driving current, the period to be pulsated is sufficiently small compared with the period (usually several kilohertz) of duty ratio control.

In the example ofFIG. 11, after supply of the driving current to the motor3for a given time period from T2is paused, and the rotating speed of the motor3decreases to arrow85b, the control unit51(refer toFIG. 5) sends a driving signal83ato the control signal output circuit53, thereby supplying a pulsating driving current (driving pulse) to the motor3to accelerate the motor3. This control during acceleration does not necessarily mean driving at a duty ratio of 100% but means control at a duty ratio of less than 100%. Next, striking power is given as shown by arrow88aas the hammer41collides with the anvil46strongly at arrow85c. When striking power is given, the supply of a driving current to the motor3for a given time period is paused, and the rotating speed of the motor decreases again as shown by arrow85b. Thereafter, the control unit51sends a driving signal83bto the control signal output circuit53, thereby accelerating the motor3. Then, striking power is given as shown by arrow88bas the hammer41collides with the anvil46strongly at arrow85e. In the pulse mode (1), the above-described intermittent driving of repeating “pause→normal rotation driving” of the motor3is repeated one time or multiple times. If it is detected that further higher fastening torque is required, switching to the rotation driving mode by the pulse mode (2) is performed. Whether or not further higher fastening torque is required can be determined using, for example, the rotation number (before or after arrow85e) of the motor3when the striking power shown by arrow88bis given.

Although the pulse mode (2) is a mode in which the motor3is intermittently driven, and is driven in pulses similarly to the pulse mode (1), the motor is driven so that “pause→reverse rotation driving→pause (stop)→normal rotation driving” is repeated plural times. That is, in the pulse mode (2), in order to add not only the normal rotation driving but also the reverse rotation driving of the motor3, the hammer41is accelerated in the normal rotation direction so as to strongly collide with the anvil46after the hammer41is reversely rotated by a sufficient angular relation with respect to the anvil46. By driving the hammer41in this way, strong fastening torque is generated in the anvil46.

In the example ofFIG. 11, when switching to the pulse mode (2) is performed at time T4, driving of the motor3is temporarily paused, and then, the motor3is reversely rotated by sending a driving signal84ain a negative direction to the control signal output circuit53. When normal rotation or reverse rotation is performed, this normal rotation or reverse rotation is realized by switching the signal pattern of each driving signal (ON/OFF signal) to be output to each of the switching elements Q1to Q6from the control signal output circuit53. If the motor3is reversely rotated by a given rotation angle, driving of the motor3is temporarily paused to start normal rotation driving. For this reason, a driving signal84bin a positive direction is sent to the control signal output circuit53. In the rotational driving using the inverter circuit52, a driving signal is not switched to the plus side or minus side. However, a driving signal is classified into the + direction and − direction and is schematically expressed inFIG. 11so that whether the motor is rotationally driven in any direction can be easily understood.

The hammer41collides with the anvil46at a time when the rotating speed of the motor3reaches a maximum speed (arrow86c). Due to this collision, significant large fastening torque89ais generated compared to fastening torques (88a,88b) to be generated in the pulse mode (1). When collision is performed in this way, the rotation number of the motor3decreases so as to reach arrow86dfrom arrow86c. In addition, the control of stopping a driving signal to the motor3at the moment when the collision shown by arrow89ais detected may be performed. In that case, if a fastening subject is a bolt, a nut, etc., the recoil transmitted to the user's hand after striking is little. By applying a driving current to the motor3as in the present embodiment even after collision, the reaction force to the user is small as compared to the drill mode, and is suitable for the operation in a middle load state. Thus, the fastening speed can be increased, and power consumption can be reduced as compared to a strong pulse mode. Thereafter, similarly, fastening with strong fastening torque is performed by repeating “pause→reverse rotation driving→pause (stop)→normal rotation driving” by a given number of times, and the motor3is stopped to complete the fastening operation as the user releases a trigger operation at time T7. In addition to the release of the trigger operation by the user, the motor3may be stopped when the computing unit51determines that fastening with set fastening torque is completed based on the output of the striking impact detecting sensor56(refer toFIG. 5).

As described above, in the present embodiment, rotational driving is performed in the drill mode in an initial stage of fastening where only small fastening torque is required, fastening is performed in the impact mode (1) by intermittent driving of only normal rotation as the fastening torque becomes large, and fastening is strongly performed in the impact mode (2) by intermittent driving by the normal rotation and reverse rotation of the motor3, in the final stage of fastening. In addition, driving may be performed using the impact mode (1) and the impact mode (2). The control of proceeding directly to the impact mode (2) from the drill mode without providing the impact mode (1) is also possible. Since the normal rotation and reverse rotation of the motor are alternately performed in the impact mode (2), fastening speed becomes significantly slower than that in the drill mode or impact mode (1). When the fastening speed becomes abruptly slow in this way, the sense of discomfort when transiting to the striking operation becomes large compared to an impact tool which has a conventional rotation striking mechanism. Thus, in the shifting to the impact mode (2) from the drill mode, an operation feeling becomes a natural feeling by interposing the impact mode (1) therebetween. For example, by performing fastening in the drill mode or impact mode (1) as much as possible, fastening operation time can be shortened.

Next, the control procedure of the impact tool1related to the embodiment will be described with reference toFIG. 12toFIG. 16.FIG. 12illustrates the control procedure of the impact tool1related to the embodiment. The impact tool1determines whether or not the impact mode is selected using the toggle switch32(refer toFIG. 2) prior to start of the operation by the user (Step101). If the impact mode is selected, the process proceeds to Step102, and if the impact mode is not selected, that is, in the case of a normal drill mode, the process proceeds to Step110.

In the impact mode, the computing unit51determines whether or not the trigger switch8is turned on. If the trigger switch is turned on (the trigger operating portion8ais pulled), as shown inFIG. 11, the motor3is started by the drill mode (Step103), and the PWM control of the inverter circuit52is started according to the pulling amount of the trigger operating portion8a(Step104). Then, the rotation of the motor3is accelerated while performing a control so that a peak current to be supplied to the motor3does not exceed an upper limit p. Next, the value I of a current to be supplied to the motor3after t milliseconds have elapsed after starting is detected using the output of the current detecting circuit59(refer toFIG. 5). If the detected current value I does not exceed p1 ampere, the process returns to Step104, and if the current value has exceeded p1 ampere, the process proceeds to Step108(Step107). Next, it is determined whether or not the detected current value I exceeds p2 ampere (Step108).

If the detected current value I does not exceed p2 [A] in Step108, that is, if the relationship of p1<I<p2 is satisfied, the process proceeds to Step109(Step120) after the procedure of the pulse mode (1) shown inFIG. 14is executed. Then, if the detected current value I exceeds p2 [A], the process proceeds directly to Step109, without executing the procedure of the pulse mode (1). In Step109, it is determined whether or not the trigger switch8is set to ON. If the trigger switch is turned off, the processing returns to Step101. If the ON state is continued, the processing returns to Step101after the procedure of the pulse mode (2) shown inFIG. 16is executed.

If the drill mode is selected in Step101, the drill mode110is executed, but the control of the drill mode is the same as the control of Steps102to107. Then, by detecting a control current in an electronic clutch or an overcurrent state immediately before the motor3is locked as p1 of Step107, thereby stopping the motor3(Step111), the drill mode is ended, and the processing returns to Step101.

The determination procedure of the mode shifting in Steps107and108will be described with reference toFIG. 13. An upper graph shows the relationship between elapsed time and the rotation number of the motor3, a lower graph shows the relationship between a current value to be supplied to the motor3, and time, and the time axes of the upper and lower graphs are made the same. In the left graph, when the trigger switch is pulled at time TA(equivalent to Step102ofFIG. 12), the motor3is started and accelerated as shown by arrow113a. During this acceleration, a constant current control in a state where the maximum current value p is limited as shown by arrow114ais performed. When the rotation number of the motor3reaches a given rotation number (arrow113b), a current during acceleration becomes a usual current as shown by arrow114b. Therefore, the current value decreases. Thereafter, when the reaction force received from a fastening member increases as fastening of a screw, a bolt, etc. proceeds, the rotation number of the motor3decreases gradually as shown by arrow113c, and the value of a current to be supplied to the motor3increases. Then, the current value is determined after t milliseconds have elapsed from the starting of the motor3. If the relationship of p1<I<p2 is satisfied as shown by arrow114c, the process shifts to the control of the pulse mode (1) which will be described later, as shown in Step120.

In the right graph, when the trigger switch is pulled at time TB(equivalent to Step102ofFIG. 12), the motor3is started and accelerated as shown by arrow115a. During this acceleration, a constant current control in a state where the maximum current value p is limited as shown by arrow116ais performed. When the rotation number of the motor3reaches a given rotation number (arrow115b), a current during acceleration becomes a usual current as shown by arrow116b. Therefore, the current value decreases. Thereafter, when the reaction force received from a fastening member increases as fastening of a screw, a bolt, etc. proceeds, the rotation number of the motor3decreases gradually as shown by arrow115c, and the value of a current to be supplied to the motor3increases. In this example, the reaction force received from a fastening member increased rapidly. Therefore, as shown by arrow116c, decrease of the rotation number of the motor3is large, and the rising degree of the current value is large. Then, since the current value after t milliseconds have elapsed from the starting of the motor3satisfies the relationship of p2<I as shown by arrow116c, the process shifts to the control of the pulse mode (2) shown inFIG. 16as shown in Step140.

Usually, in the fastening operation of a screw, a bolt, etc., required that fastening torque is not often constant due to variation in the machining accuracy of a screw or a bolt, the state of a fastening subject member, variation in materials, such as knots, grain, etc. of timber. Therefore, fastening may be performed at a stroke until immediately before completion of the fastening only by the drill mode. In such a case, when fastening in the impact mode (1) is skipped, and shifting to the fastening by the drill mode (2) with a higher fastening torque is made, the fastening operation can be efficiently completed in a short time.

Next, the control procedure of the impact tool in the pulse mode (1) will be described with reference toFIG. 14. If the process has shifted to the pulse mode (1), the peak current is first limited to equal to or less than p3 ampere (Step121) after a given pause period, and the motor3is rotated by supplying a normal rotation current to the motor3during a given time, i.e., T milliseconds (Step122). Next, the rotation number N1n[rpm] of the motor3after time T milliseconds have elapsed is detected (n=1, 2, . . . ) (Step123). Next, a driving current to be supplied to the motor3is turned off, and the time t1nwhich is required until the rotation number of the motor3is lowered to N2n(=N1n/2) from N1nis measured. Next, t2nis obtained from t2n=X−t1n, a normal rotation current is applied to the motor3during a period of this t2n(Step126), and the peak current is suppressed to equal to or less than p3 ampere, thereby accelerating the motor3. Next, it is determined whether or not the rotation number N1(n+1)of the motor3is equal to or less than a threshold rotation number Rthfor shifting to the pulse mode (2) after the elapse of the time t2n. If the rotation number of the motor is equal to or less than Rth, the processing of the pulse mode (1) is ended, the processing returns to Step120ofFIG. 12, and if the rotation number of the motor is equal to or more than Rth, the processing returns to Step124(Step128).

FIG. 15illustrates the relationship between the rotation number of the motor3and elapsed time and the relationship between a current to be supplied to the motor3and elapsed time while the control procedure illustrated inFIG. 14is executed. A driving current132is first supplied to the motor3by time T. Since the driving current limits the peak current to equal to or less than p3 ampere, the current during acceleration is limited as shown by arrow132a, and thereafter, the current value decreases as shown by arrow132bas the rotation number of the motor3increases. At time T1, when it is measured that the rotation number of the motor3has reached N11, the rotation number N21which starts the rotation of the motor3from N21=N11/2 is calculated by calculation. The rotation number N11is, for example, 10,000 rpm. When the rotation number of the motor3decreases to N21, a driving current133is supplied, and the motor3is accelerated again. Time t2nduring which the driving current133is applied is determined by t2n=X−t1n. Similarly, although the same control is performed at times 2× and 3×, the rising degree of the rotation number of the motor3decreases as the fastening reaction force becomes large, and the rotation number N14will become equal to or less than the threshold rotation value Rthat time 4×. At this time, the processing of the pulse mode (1) is ended, and the process shifts to the processing of the pulse mode (2).

Next, the control procedure of the impact tool in the pulse mode (2) will be described with reference toFIG. 16. First, a driving current to be supplied to the motor3is turned off, and standby is performed for 5 milliseconds (Step141). Next, a reverse rotation current is supplied to the motor3so as to rotate the motor at −3000 rpm (Step142). The ‘minus’ means that the motor3is rotated in a direction reverse to the rotation direction under operation at 3000 rpm. Next, if the rotation number of the motor3has reached −3000 rpm, a current to be supplied to the motor3is turned off, and standby is performed for 5 milliseconds (Step143). The reason why standby is performed for 5 milliseconds is because there is a possibility that the main body of the impact tool may be shaken when the motor3is reversely rotated suddenly in a reverse direction. Further, this is also because there is no consumption of electric power during this standby, and thus, energy saving can be achieved. Next, a normal rotation current is turned on in order to rotate the motor3in the normal rotation direction (Step144). A current to be supplied to the motor3is turned off 95 milliseconds after the normal rotation current is turned on. However, strong fastening torque is generated in the tip tool as the hammer41collides with (strikes) the anvil46before this current is turned off, (Step145). Thereafter, it is detected whether or not the ON state of the trigger switch is maintained. If the trigger switch is in an OFF state, the rotation of a motor3is stopped, the processing of the pulse mode (2) is ended, and the processing returns to Step140ofFIG. 12(Steps147and148). In Step147, if the trigger switch8is in an ON state, the processing returns to Step141(Step147).

As described above, according to the present embodiment, a fastening member can be efficiently fastened by performing continuous rotation, intermittent rotation only in the normal direction, and intermittent rotation in the normal direction and in the reverse direction for the motor using the hammer and the anvil between which the relative rotation angle is less than one rotation. Further, since the hammer and the anvil can be made into a simple structure, miniaturization and cost reduction of the impact tool can be realized.

Although the invention has been described hitherto based on the shown embodiments, the invention is not limited to the above-described embodiments and can be variously changed without departing from the spirit or scope thereof. For example, a brushless DC motor is exemplified as the motor in the present embodiment, the invention is not limited thereto, and other kinds of motor which can be driven in the normal direction and in the reverse direction may be used.

Further, the shape of the anvil and the hammer is arbitrary. It is only necessary to provide a structure in which the anvil and the hammer cannot continuously rotate relative to each other (cannot rotate while riding over each other), secure a given relative rotation angle of less than 360 degrees, and form a striking-side surface and a struck-side surface. For example, the protruding portion of the hammer and the anvil may be constructed so as not to protrude axially but to protrude in the circumferential direction. Further, since the protruding portions of the hammer and the anvil are not necessarily only protruding portions which become convex to the outside, and have only to be able to form a striking-side surface and a struck-side surface in a given shape, the protruding portions may be protruding portions (that is, recesses) which protrude inside the hammer or the anvil. The striking-side surface and the struck-side surface are not necessarily limited to flat surfaces, and may be a curved shape or other shapes which form a striking-side surface or a struck-side surface well.

Hereinafter, an electronic pulse driver1001is exemplified as a power tool related to an embodiment will be described with reference toFIGS. 17 to 29. The electronic pulse driver1001shown inFIG. 17includes a housing1002, a motor1003, a hammer portion1004, an anvil portion1005, and a switch mechanism1006. The housing1002is made of resin, forms the outer shell of the electronic pulse driver1001, and includes a substantially tubular trunk portion1021, and a handle portion1022extending from a trunk portion.

As shown inFIG. 17, within the trunk portion1021, the motor1003is arranged so that the longitudinal direction thereof coincides with the axial direction of the motor1003, and the hammer portion1004and the anvil portion1005are aligned toward one axial end of the motor1003. In the following description, a direction parallel to the axial direction of the motor1003is defined as a front-back direction with a direction toward the hammer portion1004and the anvil portion1005from the motor1003as the front side. Additionally, an up-down direction is defined with a direction in which the handle portion1022extends from a trunk portion1021as the lower side, and a direction orthogonal to the front-back direction is defined as a right-left direction.

A hammer case1023in which the hammer portion1004and the anvil portion1005are built is arranged at a front-side position within the trunk portion1021. The hammer case1023is made of metal, is formed substantially in the shape of a funnel whose diameter becomes gradually smaller as it goes to the front, and is arranged so that a funnel-shaped tip faces the front side. A front end portion of the hammer case is formed with an opening1023athrough which a tip tool mounting portion1051which will be described later protrudes to the front side, and a metal1023A which supports the anvil portion1005rotatably is provided at the inner wall which defines the opening1023a.

In the trunk portion1021, a light1002A is held at a position near the opening1023aand at a lower position of the hammer case1023. The light1002A is constructed so as to be capable of irradiating around a front end of a bit which is a tip tool which is not shown when the bit is mounted on the tip tool mounting portion1051which will be described later. Additionally, in the trunk portion1021, a dial plate1002B which is a switching portion is arranged in a rotationally operable manner at the lower position of the light1002A. Because of the structure in which the light1002A is held by the trunk portion1021, there is no particular need to provide a member holding the light1002A separately, and the light1002A can be reliably held with a simple construction. Additionally, the light1002A and dial plate1002B are arranged substantially at the middle position of the trunk portion1021, respectively, in the right-left direction. Additionally, the trunk portion1021is formed with an intake port and an exhaust port (not shown) through which ambient air is sucked into or exhausted from the trunk portion1021by a fan1032which will be described later.

The handle portion1022extends toward the lower side from the middle position of the trunk portion1021in the front-back direction, and is formed integrally with the trunk portion1021. A switch mechanism1006is built inside the handle portion1022, and a battery1024which supplies electric power to the motor1003is detachably mounted on the tip position of the switch mechanism in the extension direction. In the handle portion1022, a trigger1025which is operated by a worker is provided at a front-side position in a root portion from the trunk portion1021. Additionally, the position where the trigger1025is provided is a position near the dial plate1002B below the aforementioned dial plate1002B. Hence, the trigger1025and the dial plate1002B can be operated with one finger, respectively. In addition, a drill mode, a clutch mode, and a pulse mode which will be described later can be switched by rotating the dial plate1002B.

A display unit1026is arranged at an upper portion of the trunk portion1021on the rear side thereof. The display unit1026displays which mode is selected among the drill mode, clutch mode, and pulse mode which will be described later.

As shown inFIG. 17, the motor1003is a brushless motor including a rotor1003A having an output shaft portion1031, and a stator1003B arranged at a position which faces the rotor1003A, and is arranged within the trunk portion1021so that the axial direction of the output shaft portion1031coincides with the front-back direction. The output shaft portion1031protrudes forward or backward from the rotor1003A, and is rotatably supported on the trunk portion1021by bearings in the protruding places thereof. In the output shaft portion1031, the fan1032which rotates coaxially and integrally with the output shaft portion1031rotates is provided in a place where the output shaft portion protrudes to the front side. A pinion gear1031A is provided so as to rotate coaxially and integrally with the output shaft portion1031at a foremost end position in the place where the output shaft portion protrudes to the front side.

The hammer portion1004includes a gear mechanism1041and a hammer1042, and is arranged so as to be built within the hammer case1023on the front side of the motor1003. The gear mechanism1041includes two planetary gear mechanisms1041B and1041C which share one outer gear1041A. The outer gear1041A is built within the hammer case1023, and is fixed to the trunk portion1021. One planetary gear mechanism1041B is arranged within the outer gear1041A so as to mesh with the outer gear1041A, and the pinion gear1031A is used as a sun gear. The other planetary gear mechanisms1041C is arranged on the front side of the one planetary gear mechanism1041B within the outer gear1041A so as to mesh with the outer gear1041A, and an output shaft of the one planetary gear mechanism1041B is used as a sun gear.

The hammer1042is defined on the front surface of a planetary carrier of the planetary gear mechanism1041C, and has a first engaging projection1042A which protrudes toward the front side and is arranged at a position which has deviated from the rotation center of the planetary carrier of the planetary gear mechanism1041C, and a second engaging projection1042B which is located opposite to the first engaging projection1042A across the rotation center of the planetary carrier of the planetary gear mechanism1041C (FIG. 19).

The anvil portion1005includes the tip tool mounting portion1051and the anvil1052, and is arranged in front of the hammer portion1004. The tip tool mounting portion1051is cylindrically constructed, and is rotatably supported via the metal1023A within the opening1023aof the hammer case1023. Additionally, the tip tool mounting portion1051has a drilled hole1051awhich is drilled toward the rear from the front end, and allows a bit (not shown) to be inserted thereinto, and has a chuck1051A which holds the bit (not shown) at a front end portion.

The anvil1052is formed integrally with the tip tool mounting portion1051so as to be located within the hammer case1023behind the tip tool mounting portion1051, and has a first engaged projection1052A which protrudes toward the rear side, and is arranged at a position which has deviated from the rotation center of the tip tool mounting portion1051, and a second engaged projection1052B which is located opposite to the first engaged projection across the rotation center of the tip tool mounting portion1051. When the hammer1042rotates, the first engaging projection1042A and the first engaged projection1052A collide with each other, and simultaneously, the torque of the hammer1042is transmitted to the anvil1052as the second engaging projection1042B and the second engaged projection1052B collide with each other. The detailed operation will be described later.

The switch mechanism1006includes a board1061, a trigger switch1062, a switching board1063, and wiring lines which connect these. The board1061is arranged at a position near the battery1024within the handle portion1022, is connected to the battery1024, and is connected to the light1002A, the dial plate1002B, the trigger switch1062, the switching board1063, and the display unit1026.

Next, the construction of a driving control system of a motor1003will be described with reference toFIG. 18. In the present embodiment, the motor1003includes a three-phase brushless DC motor. The rotor1003A of this brushless DC motor including permanent magnets including plural (two sets in the present embodiment) N-S poles sets, and the stator1003B includes three-phase stator wirings U, V, and W which are star-wired. In order to detect the rotational position of the rotor1003A, rotational position detecting elements (Hall elements)1064are arranged at predetermined intervals, for example, at every 60-degrees angle in the circumferential direction of the rotor1003A on the board1061. Based on position detection signals from the rotational position detecting elements1064, the energizing direction and time to the stator windings U, V, and W are controlled, and the motor1003rotates. The rotational position detecting elements1064are provided at positions which face the permanent magnets1003C of the rotor1003A on the switching board1063.

Electronic elements to be loaded on the switching board1063include six switching elements Q1001to Q1006, such as FET, which are connected in the form of a three-phase bridge. Respective gates of the six switching elements Q1001to Q1006which are bridge-connected are connected to a control signal output circuit1065loaded on the board1061, and respective drains or respective sources of the six switching elements Q1001to Q1006are connected to the stator windings U, V, and W which are star-wired. Thereby, the six switching elements Q1001to Q1006perform switching operations by switching element driving signals (driving signals, such as H4, H5, and H6) input from the control signal output circuit1065, and supply electric power to the stator windings U, V, and W with the direct current voltage of the battery1024to be applied to the inverter circuit1066being three-phase voltages (U phase, V phase, and W phase) Vu, Vv, and Vw.

Among switching elements driving signals (three-phase signals) which drive the respective gates of the six switching elements Q1001to Q1006, driving signals for the three negative power supply side switching elements Q1004, Q1005, and Q1006are supplied as pulse width modulation signals (PWM signals) H4, H5, and H6, and the pulse width (duty ratio) of the PWM signals is changed by the computing unit1067loaded on the board1061Based on a detection signal of the operation amount (stroke) of the trigger1025, whereby the amount of electric power supplied to the motor1003is adjusted, and the start/stop and rotating speed of the motor1003are controlled.

Here, PWM signals are supplied to either the positive power supply side switching elements Q1001to Q1003or the negative power supply side switching elements Q1004to Q1006of the inverter circuit1066, and the electric power to be supplied to the stator windings U, V, and W from the direct current voltage of the battery1024is controlled by switching the switching elements Q1001to Q1003or the switching elements Q1004to Q1006at high speed. In addition, PWM signals are supplied to the negative power supply side switching elements Q1004to Q1006. Therefore, the rotating speed of the motor1003can be controlled by controlling the pulse width of the PWM signals, thereby adjusting the electric power to be supplied to each of the stator windings U, V, and W.

The control unit1072is carried on the board1061, and has a control signal output circuit1065, a computing unit1067, a current detecting circuit1071, a switch operation detecting circuit1076, an applied voltage setting circuit1070, a rotational direction setting circuit1068, a rotor position detecting circuit1069, a rotation number detecting circuit1075, and a striking impact detecting circuit1074. The computing unit1067includes a central processing unit (CPU) for outputting a driving signal Based on a processing program and data, a ROM for storing a processing program or control data, and a RAM for temporarily storing data, a timer, etc., although not shown. The computing unit1067forms a driving signal for alternately switching predetermined switching elements Q1001to Q1006Based on output signals of the rotational direction setting circuit1068and the rotor position detecting circuit1069, and outputs the control signal to the control signal output circuit1065. This alternately energizes a predetermined winding wire of the stator windings U, V, and W, and rotates the rotor1003A in a set rotational direction. In this case, driving signals to be applied to the negative power supply side switching elements Q1004to Q1006are output as PWM modulating signals Based on an output control signal of the applied voltage setting circuit1070. The value of a current to be supplied to the motor1003is measured by the current detecting circuit1071, and is adjusted so as to become set driving electric power as the value of the current is fed back to the computing unit1067. In addition, the PWM signals may be applied to the positive power supply side switching elements Q1001to Q1003.

The electronic pulse driver1001is provided with a normal/reverse switching lever (not shown) for switching the rotational direction of the motor1003. Whenever the rotational direction setting circuit1068detects the change of the normal/reverse switching lever (not shown), the lever switches the rotational direction of the motor1003to transmit the control signal thereof to the computing unit1067. A striking impact detecting sensor1073which detects the magnitude of the impact generated in the anvil1052is connected to the control unit1072, and the output thereof is input to the computing unit1067via the striking impact detecting circuit1074.

FIG. 19is a sectional view seen from the direction III inFIG. 17, and illustrates the positional relationship between the hammer1042and the anvil1052during the operation of the electronic pulse driver1001.FIG. 19(1) shows a state where the first engaging projection1042A and the first engaged projection1052A come in contact with each other, and simultaneously the second engaging projection1042B and the second engaged projection1052B come in contact with each other. The external diameter RH3of the first engaging projection1042A and the external diameter RA3of the first engaged projection1052A are made equal to each other. From this state, the hammer1042rotates in a clockwise direction ofFIG. 19, and is brought into a state shown inFIG. 19(2). Since the internal diameter RH2of the first engaging projection1042A is made greater than the external diameter RA1of the second engaged projection1052B, the first engaging projection1042A and the second engaged projection1052B do not come into contact with each other. Similarly, since the external diameter RH1of the second engaging projection1042B is made smaller than the internal diameter RA2of the first engaged projection1052A, the second engaging projection1042B and the first engaged projection1052A do not come into contact with each other. Then, when the hammer1042rotates to a position shown inFIG. 19(3), the motor1003starts reverse rotation, and the hammer1042rotates in the counterclockwise direction. At the position shown inFIG. 19(3), the hammer1042is brought into a state where the hammer1042has reversely rotated to a maximum reversal position with respect to the anvil1052. Through the normal rotation of the motor1003, the hammer1042operates as shown inFIG. 19(5) via a state shown inFIG. 19(4) such that the first engaging projection1042A and the first engaged projection1052A collide with each other, and simultaneously the second engaging projection1042B and second engaged projection1052B collide with each other. Through the impact at the time of this collision, as shown inFIG. 19(6), the anvil1052rotates in the counterclockwise direction.

As described above, two engaging projections provided on the hammer1042collide with two engaging projections provided on the anvil1052at positions symmetrical with respect to the rotating axial center. By such a construction, the balance at the time of striking is stabilized, and a worker can be made to be hardly shaken by the electronic pulse driver1001at the time of striking.

Additionally, since the internal diameter RH2of the first engaging projection1042A is made greater than the external diameter RA1of the second engaged projection1052B, and the external diameter RH1of the second engaging projection1042B is made smaller than the internal diameter RA2of the first engaged projection1052A, the relative rotation angle between the hammer1042and the anvil1052can be made greater than 180 degrees. Thereby, a sufficient reversal angle and acceleration distance of the hammer1042with respect to the anvil1052can be secured.

Additionally, the first engaging projection1042A and the second engaging projection1042B are able to collide with the first engaged projection1052A and the second engaged projection1052B at both ends in the circumferential direction. Therefore, an impact operation is possible not only during normal rotation but also during reverse rotation. Thus, an easy-to-use impact tool can be provided. Additionally, when the anvil1052is struck by the hammer1042, the anvil1052is not struck in the axial direction (forward). Thus, the tip tool is prevented from being pressed against a member to be worked, which is an advantage when fastening a wood screw into timber.

Next, operation modes which can be used in the electronic pulse driver according to the present embodiment will be described with reference toFIGS. 20 to 25. The electronic pulse driver according to the present embodiment has three operation modes including a drill mode, a clutch mode, and a pulse mode.

The drill mode is a mode in which the hammer1042and the anvil1052are integrally rotated, and is used mainly in a case where a wood screw is fastened. An electric current which flows into the motor1003increases as fastening proceeds as shown inFIG. 20.

The clutch mode, as shown inFIGS. 21 and 22, is a mode in which driving of the motor1003is stopped in a case where an electric current which flows into the motor1003in a state where the hammer1042and the anvil1052have been integrally rotated has increased to a target value (target torque), and is mainly used in a case where importance is placed on fastening with an accurate torque, such as a case where a fastener which is outwardly visible after fastening is fastened. In addition, although described later, in the clutch mode, the motor1003is reversely rotated for generation of a pseudo-clutch, and when a wood screw is fastened, the motor1003is reversely rotated for prevention of screw slackening (refer toFIG. 22).

The pulse mode, as shown inFIGS. 23 to 25, is a mode in which the normal rotation and reverse rotation of the motor1003are alternately switched and a fastener is fastened by striking in a case where an electric current which flows into the motor1003in a state where the hammer1042and the anvil1052have been integrally rotated has increased to a predetermined value (predetermined torque), and is mainly used in, for example, a case where a long screw is fastened at a place where the screw is not outwardly visible. Thereby, a powerful fastening force can be supplied, and simultaneously, a repulsive force from a member to be worked can be reduced.

Next, the control by the control unit1072when the electronic pulse driver according to the present embodiment performs a fastening work will be described. In addition, since a special control is not performed regarding the drill mode, the description thereof is omitted. Additionally, in the following description, a starting current will not be taken into consideration in the determination based on an electric current. Additionally, an abrupt increase in the value of an electric current when an electric current for normal rotation has been imparted will also not be taken into consideration. This is because, for example, an abrupt increase in the value of an electric current when a normal rotation current as shown inFIGS. 22 to 25is imparted does not contribute to screw or bolt fastening. By providing a dead time of, for example, about 20 ms, it is possible to avoid taking into consideration this abrupt increase in the value of an electric current.

First, a case where the operation mode is set to the clutch mode will be described with reference toFIGS. 21, 22, and26.

FIG. 21illustrates a control when a fastener (hereinafter, bolt), such as a bolt, is fastened in the clutch mode,FIG. 22illustrates a control when a fastener (hereinafter, a wood screw), such as a wood screw, is fastened in the clutch mode, andFIG. 26is a flow chart when a fastener is fastened in the clutch mode.

The flow chart ofFIG. 26is started by pulling a trigger, and the fastening work is completed by determining that a target torque has been reached in a case where an electric current which flows into the motor1003has increased to a target current value T (refer toFIGS. 21 and 22), in the clutch mode according to the present embodiment.

When the trigger is pulled, the control unit1072first applies a reverse rotation voltage for fitting to the motor1003, thereby reversing the hammer1042to make the hammer collide with the anvil1052lightly (t1ofFIGS. 21 and 22, and S1601ofFIG. 26). In the present embodiment, the reverse rotation voltage for fitting is set to 5.5 V, and the reverse rotation voltage application time for fitting is set to 200 ms. This makes it possible to make the fastener and the tip tool fit to each other reliably.

When the trigger has been pulled, there is a possibility that the hammer1042and the anvil1052are separated from each other. In that state, when an electric current flows into the motor1003, striking is applied to the anvil1052by the hammer1042. Meanwhile, the clutch mode is a mode in which driving of the motor1003is stopped in a case where an electric current which flows into the motor1003in a state where the hammer1042and the anvil1052have been integrally rotated has increased to a target value (target torque). In this case, when striking may be applied to the anvil1052, the torque which exceeds the target value may be supplied to the fastener simply by the striking. Particularly when the increased fastening of fastening a screw or the like which has been fastened again is performed, such a problem becomes conspicuous.

Accordingly, in the clutch mode, subsequently to S1601, a normal rotation voltage for pre-start is applied to the motor1003during a first period in order to bring the hammer1042into contact with the anvil1052without rotating the anvil1052(pre-start) (t2ofFIGS. 21 and 22, and S1602ofFIG. 26). In the present embodiment, the normal rotation voltage for pre-start is set to 1.5 V, and the normal rotation voltage application time for pre-start is set to 800 ms. Additionally, in the present embodiment, there is a possibility that the hammer1042and the anvil1052are separated from each other by about 315 degrees. Thus, the first period is set to a period which is taken in order for the hammer1042to be rotated 315 degrees by the motor1003to which the normal rotation voltage for pre-start has been applied.

Subsequently, a normal rotation voltage for fastening the fastener is applied to the motor1003(t3ofFIGS. 21and22, and S1603ofFIG. 26), and it is determined whether or not an electric current which flows into the motor1003became greater than a threshold value a (S1604). In the present embodiment, the normal rotation voltage for fastening is set to 14.4 V, and the threshold value a is a current value in the final stage of wood screw fastening within a range where screw slackening does not occur, and is set to 15 A in the present embodiment.

If an electric current which flows into the motor1003is greater than the threshold value a (t4ofFIG. 21andFIG. 22, and S1604: YES ofFIG. 26), it is determined whether or not the increasing rate of the electric current is greater than a threshold value b (S1605). The increasing rate of the electric current can be computed according to (A(Tr+t)−A(Tr))/A(Tr), for example, as in the case ofFIG. 21. t represents the elapsed time from a certain point of time Tr. Additionally, the increasing rate of the electric current can be computed according to (A(N+1)−A(N))/A(N), as in the case ofFIG. 22. N is a maximum value of an electric current in the load of a specific normal rotation current, and N+1 is a maximum value of an electric current in the load of the normal rotation current next to the specific normal rotation current. For example, in the case ofFIG. 22, the threshold value b of (A(N+1)−A(N))/A(N) is set to 20%.

Generally, if a bolt is fastened, as shown inFIG. 21, an electric current, which flows into the motor1003, abruptly increases in the final stage of fastening. In contrast, in a case where a wood screw is fastened, as shown inFIG. 22, the electric current gently increases.

Accordingly, the control unit1072determines that the fastener is a bolt if the increasing rate of the electric current when an electric current which flows into the motor1003becomes greater than the threshold value a is greater than the threshold value b, and determines that the fastener is a wood screw if the increasing rate is equal to or less than the threshold value b.

The fastener in a case where the increasing rate of the electric current is greater than the threshold value b is a bolt which does not need to take screw slackening into consideration. Therefore, when the value of the electric current has subsequently increased to the target current value T (t5ofFIG. 21, and S1606: YES ofFIG. 26), the supply of torque to the bolt is stopped. However, as described above, the electric current abruptly increases in the case of the bolt. Therefore, there is a possibility that torque is imparted to the bolt by an inertial force, simply by stopping the application of a normal rotation voltage. Therefore, in the present embodiment, a reverse rotation voltage for braking is applied to the motor1003in order to stop the supply of the torque to the bolt, (t5ofFIG. 21, and S1607ofFIG. 26). In the present embodiment, the reverse rotation voltage application time for braking is set to 5 ms.

Subsequently, a normal rotation voltage and a reverse rotation voltage for a pseudo-clutch are alternately applied to the motor1003(t7ofFIGS. 21 and 22, and S1608ofFIG. 26). In the present embodiment, the normal rotation voltage and reverse rotation voltage application time for a pseudo-clutch are set to 1000 ms (1 second). Here, the pseudo-clutch means that, when a desired torque has been obtained as a predetermined current value is reached, a function to notify the worker of the event is provided. Although the output from the motor is not practically lost, a notification means which provides notification that the output from the motor is lost in a pseudo manner is provided.

When the reverse rotation voltage for a pseudo-clutch is applied, the hammer1042is separated from the anvil1052, and when the normal rotation voltage for a pseudo-clutch is applied, the hammer1042strikes the anvil1052. However, since the normal rotation voltage and reverse rotation voltage for a pseudo-clutch are set to such a voltage (for example, 2 V) that a fastening force is not applied to the fastener, a pseudo-clutch is only generated as a striking sound. Through the generation of this pseudo-clutch, a user is able to recognize the end of fastening.

On the other hand, since the fastener in a case where the increasing rate of the electric current is equal to or less than the threshold value b is a wood screw which needs to take screw slackening into consideration, a reverse rotation voltage for screw slackening is subsequently applied to the motor1003at predetermined intervals with respect to a voltage for fastening (t5ofFIG. 22, and S1609aofFIG. 26). The screw slackening means that, as the fitting between a cross-shaped concave portion provided in a screw head of a wood screw and a cross-shaped convex portion of a tip tool (bit) is released, the cross-shaped convex portion of the tip tool will be unevenly caught by the cross-shaped concave portion, and the cross-shaped concave portion will collapse. The anvil is reversely rotated by the application of the reverse rotation voltage for screw slackening. Through the reverse rotation of this anvil, the cross-shaped convex portion of the tip tool attached to the anvil, and the cross-shaped concave portion of the wood screw are fitted to each other firmly. In addition, the reverse rotation voltage for screw slackening is not for increasing the acceleration distance for imparting striking to the anvil1052from the hammer1042, but for imparting reverse rotation to the anvil1052from the hammer1042to such a degree that the torque of reverse rotation is imparted to the screw from the anvil1052. In the present embodiment, the reverse rotation voltage for screw slackening is set to a voltage of 14.4 V.

Then, when the electric current has increased to the target current value T (t6ofFIG. 22, and S1610a: YES ofFIG. 26), the normal rotation voltage and reverse rotation voltage for a pseudo-clutch (hereinafter referred to as voltages for a pseudo-clutch) are alternately applied to the motor1003, a pseudo-clutch is generated (t7ofFIG. 22, and S1608ofFIG. 26), and the end of fastening is notified to a user.

Finally, the application of the voltage for a pseudo-clutch is stopped after the elapse of a predetermined time (S1609: YES) from the application of the voltage for a pseudo-clutch (S1610).

Next, a case where the operation mode is set to the pulse mode will be described with reference toFIGS. 23 to 25, andFIG. 27.

FIG. 23illustrates a control when a bolt is fastened in the pulse mode,FIG. 24illustrates a control in a case where shifting to a second pulse mode which will be described later is not carried out when a wood screw is fastened in the pulse mode,FIG. 25illustrates a control in a case where shifting to the second pulse mode which will be described later is carried out when a wood screw is fastened in the pulse mode, andFIG. 27is a flow chart when a fastener is fastened in the pulse mode.

Additionally, the flow chart ofFIG. 27is also started by pulling a trigger, similarly to the clutch mode.

When the trigger is pulled, the control unit1072first applies the reverse rotation voltage for fitting to the motor1003similarly to the clutch mode (t1ofFIGS. 23 to 25, and S1701ofFIG. 27). On the other hand, in the pulse mode, importance is not placed on fastening with accurate torque. Thus, a step equivalent to S1602(pre-start) in the clutch mode is omitted.

Next, the same normal rotation voltage for fastening as that in the clutch mode is applied (t2ofFIGS. 23 to 25, and S1702ofFIG. 27), and it is determined whether an electric current which flows into the motor1003has become greater than a threshold value c (S1703).

Here, in the case of a wood screw, the load (electric current) increases gradually from the beginning of fastening. In contrast, in the case of a bolt, the load increases only slightly at the beginning of fastening, and abruptly increases when the fastening has proceeded to some extent. When the load is applied in the case of a bolt, a reaction force received from fasteners which make a pair becomes greater than a reaction force received from a member to be worked in the case of a wood screw. Accordingly, in the case of a bolt, a force which is auxiliary for a reverse rotation voltage is received from the fasteners which make a pair. Therefore, when the reverse rotation voltage for a fastener is applied to the motor1003, a reverse rotation current which has a smaller absolute value than that in the case of a wood screw flows into the motor1003. In the present embodiment, an electric current near the start of an increase in the load in the case of a bolt (for example, 15 A) is set to the threshold value c.

If an electric current which flows into the motor1003has become greater than the threshold value c, a reverse rotation voltage for fastener discrimination is applied to the motor1003(t3ofFIGS. 23 to 25, and S1704ofFIG. 27). The reverse rotation voltage for fastener discrimination is set to such a value (for example, 14.4V) that striking is not imparted to the anvil1052from the hammer1042.

Then, the control unit1072determines whether or not the absolute value of an electric current which flows into the motor1003when the reverse rotation voltage for fastener discrimination is applied is greater than a threshold value d (S1705), discriminates that a wood screw is fastened if the absolute value is greater than the threshold value d (FIGS. 24 and 25), and that a bolt is fastened if the absolute value is equal to or less than the threshold value d (FIG. 23), and controls the motor1003so as to perform the striking fastening according to the fastener which has been discriminated. In the present embodiment, the threshold value d is set to 20 A.

In detail, striking fastening is performed by alternately applying a normal rotation voltage and a reverse rotation voltage to the motor1003. In the present embodiment, however, a normal rotation voltage and a reverse rotation voltage are alternately applied to the motor1003so that a period (hereinafter referred to as a reverse rotation period) during which a reverse rotation voltage is applied with respect to a period (hereinafter referred to as a normal rotation period) during which a normal rotation voltage is applied increases in proportion to the magnitude of the load.

Additionally, in a case where the fastening by pressing becomes difficult, shifting to the fastening by striking is usual. However, it is preferable from the viewpoint of user comfort to perform the shifting gradually. Accordingly, in the present embodiment, striking fastening centered on pressing is performed in a first pulse mode, and striking fastening centered on striking is performed in a second pulse mode.

Specifically, in the first pulse mode, a pressing force is supplied to the fastener during a long normal rotation period. On the other hand, in the second pulse mode, the reverse rotation period increases gradually as the load becomes large, while striking power is supplied with the normal rotation period being gradually decreased. In addition, in the present embodiment, in the first pulse mode, in order to reduce the reaction force from a member to be worked, the normal rotation period is gradually decreased while the reverse rotation period remains constant as the load becomes large.

Returning to the flow chart ofFIG. 27, shifting to the first pulse mode and the second pulse mode will be described.

First, shifting to the first pulse mode and second pulse mode if the absolute value of an electric current which flows into the motor1003is greater than the threshold value d (S1705: YES), i.e., if a wood screw is fastened will be described.

In this case, the control unit1072first applies a voltage for the first pulse mode to the motor1003in order to perform striking fastening centered on pressing (t5ofFIGS. 24 and 25, and S1706ato S1706cofFIG. 27). Specifically, pause (5 ms)→reverse rotation voltage (15 ms)→pause (5 ms)→normal rotation voltage (300 ms) which are equivalent to one set is applied to the motor1003(S1706a). After the elapse of a predetermined time, pause (5 ms)→reverse rotation voltage (15 ms)→pause (5 ms)→normal rotation voltage (200 ms) which are equivalent to one set is applied to the motor1003(S1706b). Further, after the elapse of a predetermined time, pause (5 ms)→reverse rotation voltage (15 ms)→pause (5 ms)→normal rotation voltage (100 ms) which are equivalent to one set is applied to the motor1003(S1706c).

Subsequently, the control unit1072determines whether or not an electric current which flows into the motor1003when the voltage for the first pulse mode is applied is greater than a threshold value e (S1707). The threshold value e is provided to discriminate whether or not shifting to the second pulse mode should be carried out, and is set to 75 A in the present embodiment.

If an electric current which flows into the motor1003when the voltage (normal rotation voltage) for the first pulse mode is applied is equal to or less than the threshold value e (S1707: NO), S1706ato S1707c, and S1707are repeated. In addition, whenever the number of times by which the voltage for the first pulse mode is applied increases, the load becomes large, and the reaction force from a member to be worked becomes large. Therefore, in order to reduce the reaction force from a member to be worked, the voltage for the first pulse mode such that the normal rotation period decreases gradually while the reverse rotation period remains constant is applied. In the present embodiment, the normal rotation period is set so as to decrease such as 300 ms→200 ms→100 ms.

On the other hand, if an electric current which flows into the motor1003when the voltage (normal rotation voltage) for the first pulse mode is applied is greater than the threshold value e (t6ofFIGS. 24 and 25, and S1707: YES ofFIG. 27), first, it is determined whether or not an increasing rate in an electric current caused by the voltage for the first pulse mode (normal rotation voltage) is greater than a threshold value f (S1708). The threshold value f is provided to discriminate whether or not a wood screw is seated on to a member to be worked, and is set to 4% in the present embodiment.

If the increasing rate in the electric current is greater than the threshold value f (S1708: YES ofFIGS. 24 and 27), a wood screw is regarded as seated on a member to be worked. Therefore, in order to reduce a subsequent reaction force, a voltage for seating is applied to the motor1003(t11ofFIG. 24, and S1709ofFIG. 27). In addition, the voltage for seating in the present embodiment is repeated with pause (5 ms)→reverse rotation voltage (15 ms)→pause (5 ms)→normal rotation voltage (40 ms) as one set.

On the other hand, if the increasing rate in the electric current is equal to or less than the threshold value f (S1708: NO), the load is high irrespective of the fact that a wood screw is not seated. Thus, the fastening force centered on the pressing force caused by the voltage for the first pulse mode is regarded to be insufficient. Accordingly, shifting to the second pulse mode will be carried out after that.

In the present embodiment, the second pulse mode is selected from voltages1to5for the second pulse mode. As for the voltages1to5for the second pulse mode, in this order, the reverse rotation period increases, while the normal rotation period decreases. Specifically, one set of pause (5 ms)→reverse rotation voltage (15 ms)→pause (5 ms)→normal rotation voltage (75 ms) is performed in the voltage1for the second pulse mode, one set of pause (7 ms)→reverse rotation voltage (18 ms)→pause (10 ms)→normal rotation voltage (65 ms) is performed in the voltage2for the second pulse mode, one set of pause (9 ms)→reverse rotation voltage (20 ms)→pause (12 ms)→normal rotation voltage (59 ms) is performed in the voltage3for the second pulse mode, one set of pause (11 ms)→reverse rotation voltage (23 ms)→pause (13 ms)→normal rotation voltage (53 ms) is performed in the voltage4for the second pulse mode, and one set of pause (15 ms)→reverse rotation voltage (25 ms)→pause (15 ms)→normal rotation voltage (45 ms) is performed in the voltage5for the second pulse mode.

First, if shifting to the second pulse mode has been determined in S1708(S1708: NO), it is determined whether or not an electric current which flows into the motor1003when the normal rotation voltage of the voltage for the first pulse mode is applied (during falling) is greater than a threshold value g1(S1710). The threshold value g1is provided to discriminate whether or not a voltage for the second pulse mode which is higher than the voltage1for the second pulse mode should be applied to the motor1003, and is set to 76 A in the present embodiment. In addition, in the following, an electric current which flows into the motor1003when the normal rotation voltage of each voltage for the pulse mode is applied is generically referred to as a reference current.

If the reference current is greater than the threshold value g1(S1710: YES), it is determined whether or not the electric current is greater than a threshold value g2(S1711). The threshold value g2is provided to discriminate whether or not a voltage for the second pulse mode which is higher than the voltage2for the second pulse mode should be applied to the motor1003, and is set to 77 A in the present embodiment.

If the electric current is greater than the threshold value g2(S1711: YES), it is determined whether or not the electric current is greater than a threshold value g3(S1712). The threshold value g3is provided to discriminate whether or not a voltage for the second pulse mode which is higher than the voltage3for the second pulse mode should be applied to the motor1003, and is set to 79 A in the present embodiment.

If the electric current is greater than the threshold value g3(S1712: YES), it is determined whether or not the electric current is greater than a threshold value g4(S1713). The threshold value g4is provided to discriminate whether or not a voltage for the second pulse mode which is higher than the voltage4for the second pulse mode should be applied to the motor1003, and is set to 80 A in the present embodiment.

In the manner as described above, it is first determined which voltage for the second pulse mode should be applied to the motor1003Based on an electric current which flows into the motor1003when the voltage (normal rotation voltage) for the first pulse mode is applied, and subsequently, the determined voltage for the second pulse is applied to the motor1003.

Specifically, if the electric current is equal to or less than the threshold value g1(S1710: NO), the voltage1for the second pulse mode is applied to the motor1003(S1714); if the electric current is greater than the threshold value g1, and is equal to or less than the threshold value g2(S1711: NO), the voltage2for the second pulse mode is applied to the motor1003(S1715); if the electric current is greater than threshold value g2, and is equal to or less than the threshold value g3(S1712: NO), the voltage3for the second pulse mode is applied to the motor1003(S1716); if the electric current is greater than the threshold value g3, and is equal to or less than the threshold value g4(S1713: NO), the voltage4for the second pulse mode is applied to the motor1003(S1717); and if the electric current is greater than the threshold value4(S1713: YES), the voltage5for the second pulse modes is applied to the motor1003(S1718).

After the application (S1714) of the voltage1for the second pulse mode, it is subsequently determined whether or not an electric current which flows into the motor1003when the voltage1(normal rotation voltage) for the second pulse mode is applied is greater than the threshold value g1(S1719).

If the electric current is equal to or less than the threshold value g1(S1719: NO), the processing returns to S1707where it is determined again which of the voltages for the first pulse mode and the voltage1for the second pulse mode should be applied to the motor1003. On the other hand, if the electric current is greater than the threshold value g1(S1719: YES), the voltage2for the second pulse mode is applied to the motor1003(S1715).

After the application (S1715) of the voltage2for the second pulse mode, it is subsequently determined whether or not an electric current which flows into the motor1003when the voltage2(normal rotation voltage) for the second pulse mode is applied is greater than the threshold value g2(S1720).

If the electric current is equal to or less than the threshold value g2(S1720: NO), the processing returns to S1710where it is determined again which of the voltage1for the second pulse mode and the voltage2for the second pulse mode should be applied to the motor1003. On the other hand, if the electric current is greater than the threshold value g2(S1720: YES), the voltage3for the second pulse mode is applied to the motor1003(S1716).

After the application (S1716) of the voltage3for the second pulse mode, it is subsequently determined whether or not an electric current which flows into the motor1003when the voltage3(normal rotation voltage) for the second pulse mode is applied is greater than the threshold value g3(S1721).

If the electric current is equal to or less than the threshold value g3(S1721: NO), the processing returns to S1711where it is determined again which of the voltage2for the second pulse mode and the voltage3for the second pulse mode should be applied to the motor1003. If the electric current is greater than the threshold value g3(S1721: YES), the voltage4for the second pulse mode is applied to the motor1003(S1717).

After the application (S1717) of the voltage4for the second pulse mode, it is subsequently determined whether or not an electric current which flows into the motor1003when the voltage4(normal rotation voltage) for the second pulse mode is applied is greater than the threshold value g4(S1722).

If the electric current is equal to or less than the threshold value g4(S1722: NO), the processing returns to S1712where it is determined again which of the voltage3for the second pulse mode and the voltage4for the second pulse mode should be applied to the motor1003. If the electric current is greater than the threshold value g4(S1722: YES), the voltage5for the second pulse mode is applied to the motor1003(S1718).

After the application (S1718) of the voltage5for the second pulse mode, it is subsequently determined whether or not an electric current which flows into the motor1003when the voltage5(normal rotation voltage) for the second pulse mode is applied is greater than the threshold value g5(S1723). The threshold value g5is provided to discriminate whether or not the voltage5for the second pulse mode should be applied to the motor1003, and is set to 82 A in the present embodiment.

If the electric current is equal to or less than the threshold value g5(S1723: NO), the processing returns to S1713where it is determined again which of the voltage4for the second pulse mode and the voltage5for the second pulse mode should be applied to the motor1003. If the electric current is greater than the threshold value g5(S1723: YES), the voltage5for the second pulse mode is applied to the motor1003(S1718).

On the other hand, if the absolute value of an electric current which flows into the motor1003is equal to or less than the threshold value d (S1705: NO), i.e., if a bolt is fastened, it is preferable that there is no necessity for the fastening by pressing, and striking is preferably carried out in a mode where the reaction force is most reduced. Accordingly, in this case, the voltage5for the second pulse mode is applied to the motor1003without via the first pulse mode and the voltages1to4for the second pulse mode (S1718).

As such, in the electronic pulse driver in the pulse mode according to the present embodiment, with an increase in an electric current (load) which flows into the motor1003, the ratio of the reverse rotation period to the normal rotation period is increased (a decrease in the normal rotation period of the first pulse mode (S1706ofFIG. 27), shifting to the second pulse mode from the first pulse mode (S1707ofFIG. 27), and the shifting between the second pulse modes1to5(S1719to S1722ofFIG. 27)). Thus, a reaction force from a member to be worked can be suppressed, and an impact tool which is comfortable when being used can be provided.

Additionally, in the electronic pulse driver1001in the pulse mode according to the present embodiment, the fastening is performed in the first pulse mode centered on a pressing force if an electric current which flows into the motor1003is equal to or less than the threshold value e when a wood screw is fastened. Thus, the fastening is performed in the second pulse mode centered on striking power if the electric current is greater than the threshold value e (S1707ofFIG. 27). Thus, it is possible to perform fastening in a mode which is more suitable for a wood screw.

Additionally, in the electronic pulse driver1001in the pulse mode according to the present embodiment, the reverse rotation voltage for fastener discrimination is applied to the motor1003(S1704ofFIG. 27). In that case, if an electric current which flows into the motor1003is greater than the threshold value d, the fastener is determined to be a wood screw, and if the electric current is less than the threshold value d, the fastener is determined to be a bolt. The processing proceeds to modes which are suitable for the respective cases (S1705ofFIG. 27). Thus, it is possible to perform suitable fastening according to the kind of fasteners.

Additionally, in the electronic pulse driver1001in the pulse mode according to the present embodiment, if the increasing rate of an electric current when an electric current which flows into the motor1003has increased to the threshold value e is equal to or more than the threshold value f (S1708: YES ofFIG. 27), a wood screw is regarded as seated, and the voltage for seating is applied to the motor1003with the switching cycle of normal rotation electric power and reverse rotation electric power being shortened. Thereby, the subsequent reaction force from a member to be worked can be reduced, and simultaneously, the same feeling as a conventional electronic pulse driver in which a striking interval becomes short as fastening proceeds is provided.

Additionally, in the electronic pulse driver1001in the pulse mode according to the present embodiment, shifting to the optimal second pulse mode according to an electric current which flows into the motor1003from the first pulse mode is carried out (S1710to S1713ofFIG. 27). Thus, even if the electric current which flows into the motor1003has abruptly increased, it is possible to perform fastening in a suitable striking mode.

Additionally, in the electronic pulse driver in the pulse mode according to the present embodiment, the shifting between the second pulse modes1to5is possible only between the second pulse modes where switching cycles of normal rotation and reverse rotation are adjacent to each other (S1719to S1723ofFIG. 27). Thus, it is possible to prevent an abrupt change in feeling.

Additionally, in the electronic pulse driver1001in the present embodiment, the hammer1042is reversely rotated and struck on the anvil1052by applying the reverse rotation voltage for fitting to the motor1003before application of the reverse rotation voltage for fastening (S1601ofFIG. 26). Thus, even if the fitting between a fastener and a tip tool is insufficient, the fastener and the tip tool can be made to fit to each other firmly, and it is possible to prevent the tip tool from coming out of the fastener during operation.

Additionally, in the electronic pulse driver1001in the clutch mode according to the present embodiment, the hammer1042and the anvil1052are brought into contact with each other by applying the normal rotation voltage for pre-start before the normal rotation voltage for fastening is applied (S1601ofFIG. 26, and S1701ofFIG. 27). Thus, it is possible to prevent a torque exceeding a target torque from being supplied to a fastener due to the striking.

Additionally, in the electronic pulse driver1001in the clutch mode according to the present embodiment, a pseudo-clutch is stopped after the elapse of a predetermined time from the generation thereof (S1609and S1610ofFIG. 26). Thus, it is possible to suppress power consumption and a temperature rise.

Additionally, in the electronic pulse driver1001in the clutch mode according to the present embodiment, the reverse rotation voltage for braking is applied to the motor1003when a bolt is fastened, and a target torque is reached (S1607ofFIG. 26). Thus, even if a fastener like the bolt in which torque abruptly increases just before a target torque is fastened, it is possible to prevent the torque caused by an inertial force from being supplied, and it is possible to supply an accurate target torque.

Next, an electronic pulse driver1201according to a fourth embodiment will be described with reference toFIGS. 28 and 29.

In the third embodiment, the aspect of striking has been changed when an electric current or the like has been increased to a certain threshold value, without taking a change in temperature into consideration. However, for example, since the viscosity of the grease within the gear mechanism1041is low in cold districts, an electric current which flows into the motor1003tends to become greater than usual. In that case, an electric current which flows into the motor1003is apt to exceed the threshold value, and irrespective of a situation where the aspect of striking is changed, there is a possibility of changing the striking aspect.

Accordingly, the present embodiment is characterized by changing a threshold value in consideration of a change in temperature. Specifically, a temperature detection unit is provided on the switching board1063, and the control unit1072changes each threshold value Based on a temperature detected by the temperature detection unit.

FIG. 28illustrates a threshold value change during fastening of a wood screw in the clutch mode, andFIG. 29illustrates a threshold value change during fastening of a wood screw in the pulse mode.

The control unit1072, for example, as shown inFIG. 28, sets a threshold value a′ and a target current value T′ which trigger the application of a reverse rotation voltage for screw slackening at a low temperature to values which are higher than the threshold value a and the target current value T which trigger the application of a reverse rotation voltage for screw slackening at room temperature, and as shown inFIG. 29, sets a threshold value c′ for shifting to the first pulse mode and a threshold value e′ for shifting to the second pulse mode at a low temperature to values which are higher than the threshold value c for shifting to the first pulse mode and the threshold value e for shifting to the second pulse mode at room temperature.

By changing the threshold value in consideration of a change in temperature in this way, it is possible to change the aspect of striking in a suitable situation. In addition, the threshold value to be changed is not limited to the aforementioned one, and any other threshold values may be changed. Additionally, the temperature detection unit may be provided at locations other than the motor1003.

Next, an electronic pulse driver1301according to a fifth embodiment will be described with reference toFIG. 14.

In the fourth embodiment, importance is given to workability, and the threshold value is changed. In the present embodiment, however, importance is given to the durability of the electronic pulse driver1201, and the switching cycle of normal rotation and reverse rotation is changed.

Specifically, even in the present embodiment, similarly to the fourth embodiment, the motor1003is equipped with a temperature detection unit, and the control unit1072changes the switching cycle of normal rotation and reverse rotation Based on a temperature detected by the temperature detection unit. In addition, even in this case, the temperature detection unit may be provided at locations other than the motor1003.

FIG. 30illustrates a change in the switching cycle of normal rotation and reverse rotation during fastening of a wood screw in the pulse mode.

The control unit1072, for example, as shown inFIG. 30, sets the switching cycle of the normal rotation period and reverse rotation period of the first pulse mode at a high temperature to be longer than the switching cycle of the normal rotation period and reverse rotation period of the first pulse mode at room temperature. This can suppress generation of heat caused at the time of switching, and can suppress any damage caused by the high temperature of FET of the electronic pulse driver1301. Additionally, the coating of a starter coil can be kept from being damaged by heat, and it is possible to enhance the durability of the whole electronic pulse driver1301.

Next, an electronic pulse driver1401according to a sixth embodiment will be described with reference toFIGS. 16 and 17. The same components as those of the electronic pulse driver1001according to the third embodiment are designated by the same reference numerals, and the description thereof is omitted.

As shown inFIG. 32, the electronic pulse driver1401includes a hammer1442and an anvil1452. In the electronic pulse driver1001according to the third embodiment, the gap in a rotational direction between the hammer1042and the anvil1052is set to about 315 degrees. In the electronic pulse driver1401according to the sixth embodiment, the gap in a rotational direction between the hammer1442and the anvil1452is set to about 135 degrees.

FIG. 33is a sectional view seen from the direction XVII ofFIG. 32, and illustrates the positional relationship between the hammer1442and the anvil1452during the operation of the electronic pulse driver1401. Reverse rotation is carried out to the maximum reversal position of the hammer1442with respect to the anvil1452inFIG. 33(3) via the state ofFIG. 33(2) from a state where the hammer1442and the anvil1452come into contact with each other likeFIG. 33(1). Then, the motor1003normally rotates, the hammer1442and the anvil1452collide with each other (FIG. 33(5)), and the anvil1452rotates in the counterclockwise direction ofFIG. 33by the impact (FIG. 33(6)).

In this case, the voltage value, current value, number-of-seconds, etc. of the third embodiment can be appropriately changed so as to suit the electronic pulse driver1401in the sixth embodiment.

In addition, the electronic pulse driver of the invention is not limited to the above-described embodiments, and various modifications and improvements can be made within the scope set forth in the claims.

For example, in the above-described embodiments, in the shifting between the second pulse modes1to5, even a case where the processing returns to a voltage for the second pulse mode one place before a voltage (S1719to S1722: NO ofFIG. 26) is considered. However, as shown inFIG. 31, a worker feels comfortable as a result of performing a control so as not to return to a previous voltage for the second pulse mode. Additionally, although the control when a wood screw or a bolt is fastened has been described in the above-described embodiments, the idea of the invention can be utilized even during loosening (removal). Specifically, as shown in the schematic diagram ofFIG. 34, when a wood screw or the like is loosened, application of a voltage is started from the voltage5for the second pulse mode with a longest reverse rotation period, and as an electric current becomes equal to or less than each threshold value, a gradual change to the voltage1for the second pulse mode is made. Thereby, even when a wood screw or the like is made, it is possible to provide a comfortable feeling.

Additionally, in the above-described embodiments, a fastener is discriminated Based on an electric current which flows into the motor1003after application of the reverse rotation voltage for fastener discrimination (S1705ofFIG. 27). However, the fastener may be discriminated Based on the rotation number or the like of the motor1003.

Additionally, in the above-described embodiments, the same threshold values g1to g4as S1710to S1713are used in S1719to S1722ofFIG. 27. However, separate values may be used.

Additionally, in the above-described embodiments, there is only one anvil1052provided in the electronic pulse driver. Thus, there is a possibility that the anvil1052and the hammer1042are separated from each other by the maximum 360 degrees. However, for example, another anvil may be provided between the anvil and the hammer. Thereby, it is possible to shorten the time required when the reverse rotation voltage for fitting is applied (S1601ofFIGS. 26, and S1701ofFIG. 27) or when the normal rotation voltage for pre-start is applied (S1602ofFIG. 26).

Additionally, in the above-described embodiments, the hammer1042and the anvil1052are brought into contact with each other by applying the normal rotation voltage for pre-start. However, other aspects are conceivable as long as the initial position relationship of the hammer1042with respect to the anvil1052can be kept constant even if the hammer and the anvil are not necessarily brought into contact with each other.

Additionally, although the power tool of the invention is constructed so that the hammer is normally rotated or reversely rotated, the electric power need not have such a construction. For example, a power tool which strikes the anvil by continuously driving the hammer so as to be normally rotated may be adopted. Although the power tool of the invention has a construction in which the hammer is driven by an electric motor driven by a charging battery, the hammer may be driven by power sources other than the electric motor. For example, as examples of the power sources, an engine may be used, or an electric motor may be driven by a fuel cell or a solar cell.

INDUSTRIAL APPLICABILITY

According to an aspect of the invention, there is provided an impact tool in which an impact mechanism is realized by a hammer and an anvil with a simple mechanism.

According to another aspect of the invention, there is provided an impact tool which can drive a hammer and an anvil between which the relative rotation angle is less than 360 degrees, thereby performing a fastening operation, by devising a driving method of a motor.