Reciprocating electric tool

The invention provides a reciprocating electric tool (1) having a brushless motor (3), a plunger (52), and control means (6). The plunger (52) is driven by the brushless motor and reciprocating between two dead centers. A end bit (7) is mounted to one end of the plunger in a reciprocating direction. The control means (6) controls a rotational speed of the brushless motor based on a position of the plunger.

This application is a U.S. National Stage of International Application No. PCT/JP2010/050997 filed Jan. 20, 2010, and which claims the benefit of Japanese Patent Application No. 2009-020276, filed Jan. 30, 2009, the entireties of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a reciprocating electric tool, and more particularly relates to a portable reciprocating electric tool provided with an end bit, such as a blade, for cutting a workpiece by reciprocating movements of the end bit.

BACKGROUND ART

A conventional reciprocating electric tool, such as a jigsaw, includes a blade and a base that directly contacts a workpiece. The blade is designed to protrude from the base so as to be capable of moving in a vertical direction with respect to the base, thereby allowing the workpiece to be cut.

PATENT LITERATURE

SUMMARY OF INVENTION

Technical Problem

In such a conventional reciprocating electric tool, when performing reciprocal movements (vertical movements in case of a jigsaw), an end bit (the blade) and a plunger on which the blade is mounted are required to reverse a motion direction thereof at both dead centers (top dead center and bottom dead center). At these dead centers, the motion direction of the blade (the plunger) is forced to be turned around drastically, causing vibrations and noises to occur.

Further, when carrying the reciprocating electric tool, since the blade is a bother, a user has to grasp the blade for pushing the same into the base, or to manipulate an operation switch in order for the blade (plunger) to stop at one of the dead centers where the blade is retracted most (at the top dead center in case of the jigsaw). To the contrary, when replacing the blade, the user needs to grasp the blade for pulling the same out of the base, or to manipulate the operation switch so that the blade can be located at the other dead center where the blade protrudes most (at the bottom dead center in case of the jigsaw) in order to facilitate replacement of the blade. Either case results in low workability.

Solution to Problem

In view of the forgoing, it is an object of the present invention to provide a reciprocating electric tool, with enhanced workability, capable of realizing low vibration and low noise.

In order to achieve the above and other objects, the present invention features a reciprocating electric tool having a brushless motor, a plunger, and control means. The plunger is driven by the brushless motor and reciprocating between two dead centers. An end bit is mounted to one end of the plunger in a reciprocating direction. The control means controls a rotational speed of the brushless motor based on a position of the plunger.

With this configuration, the position of the plunger can be easily controlled by the brushless motor.

In the reciprocating electric tool having the above configuration, preferably, detection means for detecting the position of the plunger be provided.

With this configuration, since detection of the position of the plunger can become easier, the position and speed of the plunger can be controlled more easily. Preferably, the detection means be a sensor that detects that the plunger reaches a predetermined position.

With this configuration, the position of the plunger can be detected more precisely with a simple configuration. Therefore, controlling the position and speed of the plunger can be done with high accuracy.

Preferably, the control means decelerates the rotational speed of the brushless motor in accordance with the position of the plunger.

With this configuration, the brushless motor can be decelerated in accordance with the position of the plunger, thereby reducing noises and vibrations.

Preferably, the control means decelerates the rotational speed of the brushless motor, while the plunger moves from one of the dead centers to an other of the dead centers.

With this configuration, the brushless motor can be decelerated before the moving direction of the plunger is turned around, thereby enabling noises and vibrations to be reduced at the time of turning the moving direction of the plunger.

Preferably, the control means decelerates the rotational speed of the brushless motor when the plunger reaches a position in proximity to and just before either one of the dead centers.

With this configuration, the brushless motor can be slowed down before the moving direction of the plunger is switched, thereby reducing noises an vibrations at the time of switching the direction in which the plunger moves.

Preferably, the control means decelerates the rotational speed of the brushless motor when the plunger reaches a position in proximity to and just before either one of the dead centers, and after the plunger passes through the either one of the dead centers, the control means accelerates the rotational speed of the brushless motor.

With this configuration, the brushless motor can be slowed down before the moving direction of the plunger is switched, thereby reducing noises an vibrations at the time of switching the direction in which the plunger moves. At the same time, the motor can be subsequently speeded up, thereby maintaining the ability to cut the workpiece.

Preferably, speed decelerating position setting means is provided for setting a speed decelerating position of the rotational speed for the brushless motor according to the position of the plunger. The control means decelerates the rotational speed of the brushless motor in accordance with the speed decelerating position set by the speed decelerating position setting means.

With this configuration, the deceleration position of the brushless motor can be arbitrarily set. Hence, the deceleration position can be set to such a position at which vibrations and noises are generated most.

Preferably, the control means maintains the brushless motor at the reduced rotational speed until the plunger passes through either one of the dead centers.

This configuration contributes to reduction of vibrations and noises generated at the time of the plunger's turning around the moving direction thereof.

Preferably, the control means maintains the rotation of the brushless motor in a reduced speed state for a predetermined time period since the rotational speed of the brushless motor is reduced.

With this configuration, the brushless motor is kept decelerated for a prescribed period of time, thereby leading to reduction in vibrations and noises.

Preferably, storage means is provided for storing a plurality of speed decelerating position information which the speed decelerating position setting means sets. the control means calculates a first time period to maintain the brushless motor in a reduced speed state, based on the speed decelerating position set by the speed decelerating position setting means, and stores the calculated first time period as a reduced speed maintaining period in the storage means, and the control means maintains the brushless motor in the reduced speed state until the speed reduction maintaining period stored in the storage means elapses.

With this configuration, the deceleration position can be set to a position at which noises and vibrations are assumed to be generated most. Further, the brushless motor is maintained to be decelerated while the vibrations and noises continue. Hence, reduction in noises and vibrations can be further realized.

Preferably, the control means calculates a second time period to reach the dead point at a first since the rotational speed of the brushless motor is decelerated based on the speed decelerating position information, and stores the calculated second time period in the storage means, and the rotation of the brushless motor is accelerated after the plunger passes through the dead point.

With this configuration, the brushless motor is slowed down in the vicinity of the dead centers where noises and vibrations are assumed to occur most intensively.

Preferably, speed setting means is provided for setting the rotational speed of the brushless motor. Further, storage means is provided for storing a plurality of speed decelerating position which the speed decelerating position setting means sets. The control means calculates a reduced speed maintaining time period to maintain the brushless motor in the reduced speed state based on the speed decelerating position set by the speed decelerating position setting means and the rotational speed of the brushless motor set by the speed setting means, and stores the calculated reduced speed maintaining time period in the storage means.

With this configuration, the deceleration position can be set in accordance with the setting speed of the brushless motor. Hence, vibrations and noises can be reduced regardless of the setting speed of the brushless motor.

Preferably, speed setting means is provided for setting the rotational speed of the brushless motor. Further, storage means is provided for previously storing a reduced speed maintaining time period to maintain the brushless motor in the speed reduced state, based on a setting signal from the speed setting means and the speed decelerating position setting means. The control means decelerates the rotation of the brushless motor according to the reduced speed maintaining time period stored in the storage means.

With this configuration, the deceleration position can be stored in advance based on the rotational speed of the brushless motor and the deceleration position information. Hence, in addition to the reduction in noises and vibrations regardless of the setting speed of the brushless motor, the control means does not have to perform calculation each time the speed of the brushless motor is set.

Preferably, storage means is provided for storing a predetermined rotational speed of the brushless motor. The control means maintains the rotation of the brushless motor at a fixed rotational speed regardless of an output from the speed decelerating position setting means when the rotational speed of the brushless motor set by the speed setting means is lower than the predetermined rotational speed stored in the storage means.

With this configuration, when the rotational speed of the brushless motor is slow, specially when the rotational speed is the slowest, the brushless motor is not controlled to be decelerated. Hence, the ability of the reciprocating electric tool to cut a workpiece can be maintained.

Preferably, reset means is provided for resetting a decelerating position of the brushless motor which has been set by the deceleration position setting means.

With this configuration, the deceleration position can be easily set to such a position that greater noises and vibrations are assumed to be generated.

Preferably, the control means controls the brushless motor in order to stop the plunger in proximity to one of the dead centers.

With this configuration, the plunger is allowed to stop at a position where the plunger protrudes most from the base of the reciprocating electric tool so that the blade can be replaced easily. The plunger is further allowed to stop at a position where the plunger is retracted most. Hence, when the user carries the reciprocating electric tool, the plunger and the end bit do not bother the user.

Preferably, stop position switching means is provided for switching the stop position of the plunger to an other of the dead centers.

With this configuration, the stop position of the plunger can be selected depending on the intended purposes of the user, leading to an improved workability.

Preferably, stop position setting means is provided for setting a stop position of the plunger. the control means controls the plunger in order to stop the plunger at a predetermined position set by the stop position setting means.

This configuration enables the user to stop the plunger at a prescribed position in accordance with the usages intended by the user, for example, for the purpose of carrying the reciprocating electric tool or replacing the end bit. The workability is therefore enhanced.

Preferably, the stop position setting means outputs a signal to the control means the signal being for stopping the plunger in proximity to either one of the dead centers. The control means controls the brushless motor in order to stop the plunger according to the output signal from the stop position setting means.

With this configuration, when the plunger stops at the most protruding position, replacement of the end bit can be facilitated. When the plunger stops at the most retracting position, the portability of the reciprocating electric tool is not damaged.

Further, conventionally, the stop position of the plunger cannot be specified by the user. Hence, the portion on which the end bit is mounted is required to have a large dimension so that the end bit can be replaced regardless of the position of the plunger. To the contrary, since the reciprocating electric tool according to the present invention enables the stop position to be specified by the user, the portion on which the end bit is mounted can be made compact, thereby realizing reduction in size and weight of the reciprocating electric tool.

Preferably, the stop position setting means outputs a switching signal to the control means, the signal being for switching the stop position of the plunger to a position in proximity to an other of the dead centers. The control means controls the brushless motor according to the switching signal.

This configuration allows the user to select positions at which the plunger stops based on the purposes intended by the user, leading to enhanced workability.

Preferably, rotational position detecting means is provided for detecting a rotational position of the brushless motor. Further, storage means is provided for prestore positional data associated with a rotational position of the brushless motor and a position of the plunger, on the basis of the position of the plunger corresponding to the rotational position of the brushless motor. The control means calculates the position of the plunger on the basis of the rotational position of the brushless motor detected by the rotational position detecting means and positional data stored in the storage means.

With this configuration, the position of the plunger can be detected based upon the rotating position information of the brushless motor. Hence, there is no need to employ means for detecting the position of the plunger.

Preferably, storage reset means is provided for resetting the positional data associated with the rotational position of the brushless motor and the position of the plunger stored in the storage means.

With this configuration, the user can reset the relationship between the rotating positions of the brushless motor and the position of the plunger stored in the storage means whenever there arises an error in the relationship therebetween.

Preferably, storage reconfiguring means for reconfiguring positional data associated with the rotational position of the brushless motor and the position of the plunger stored in the storage means.

With this configuration, since the relationship between the rotating position of the blushless motor and the position of the plunger can be stored precisely, the brushless motor can be controlled with accuracy depending on the position of the plunger.

Further, a battery may be provided for supplying power to the brushless motor.

This configuration increases portability of the reciprocating electric tool, thereby enhancing the workability thereof.

Further, an AC power source may be provided for supplying power to the brushless motor.

With this configuration, the user can operate the reciprocating electric tool for a longer period of time, thereby increasing the workability thereof.

The present invention further provides a reciprocating electric tool having a brushless motor, a plunger, and control means. The plunger is driven by the brushless motor and reciprocating between two dead centers. An end bit is mounted to one end of the plunger in a reciprocating direction. The control means controls a rotational speed of the brushless motor based on a position of the plunger during a cycle of reciprocation movement of the plunger.

With the above structure, the position of the plunger can be easily controlled by the brushless motor during the cycle of the reciprocation movement of the plunger.

The present invention further provides a reciprocating electric tool having a brushless motor, a plunger, and control means. The plunger is driven by the brushless motor and reciprocating between two dead centers. An end bit is mounted to one end of the plunger in a reciprocating direction. The control means controls the brushless motor to stop the plunger in a predetermined stop area.

With the above structure, the position of the plunger can be easily controlled by the brushless motor. Generally, the stop position of the plunger is a predetermined position such as each dead center. Additionally, any position such as an adjacent area to the predetermined position and a predetermined area including the predetermined position can be selected as the stop position of the plunger.

Advantageous Effects of Invention

According to the present invention, workability can be enhanced while vibrations and noises are suppressed at a low level.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a reciprocating electric tool (jigsaw)1according to an embodiment of the present invention will be described with reference toFIGS. 1 through 7.

As shown inFIG. 1, the jigsaw1includes a housing2, a motor3, a base4, a drive section5, a control unit6and a blade7serving as an end bit. The jigsaw1moves in a designated direction while cutting a workpiece (not shown) with the blade7. In the following description, a direction in which the jigsaw1moves while cutting the workpiece will be referred to as a ‘cutting direction.’ In the cutting direction, a side toward which the jigsaw1heads will be referred to as ‘forward’. Also, a vertical (top-to-bottom) direction is defined as follows: a direction from the housing2toward the base4will be referred to as the ‘lower’ direction, while a direction toward the housing2from the base4will be referred to as the ‘upper’ direction. Further, a horizontal (left-to-right) direction will be defined as a direction perpendicular to the vertical direction as well as the cutting direction.

The housing2is configured of a frame which is made of a material such as aluminum. The housing2is formed with a handle21at an upper rear end portion thereof for enabling a user to grip the jigsaw1. A trigger switch22including a trigger22A is provided on a base end portion of the handle21so that the user can operate the trigger22A to control electric power supply to the motor3.

A battery23is detachably mounted in the jigsaw1at a position rearward of the handle21in the cutting direction. The battery23supplies, as a power source, electric power to the motor3, the control unit6and the like, thereby contributing to improved portability and workability of the jigsaw1. As an alternative power source, an external commercial power supply (an AC power source90) may be used as shownFIG. 8instead of the battery23. In this case, a converter80is required for converting an alternating current to a direct current (seeFIG. 8). Employing the AC power source90is advantageous in that the user can use the jigsaw1for a longer period of time, leading to an improved workability.

Within the housing2a position sensor24(proximity sensor, for example) is provided at a position above the drive section5. The position sensor24detects movements of a plunger52between both dead centers (as will be described later) and outputs signals to the control unit6. Hence, the position sensor24should preferably be located at a position vertically above the longitudinal direction of the plunger52.

The motor3is a DC brushless motor for allowing the control unit6to precisely control rotational speeds and rotational angles of the motor3. The motor3is accommodated within the housing2approximately in the middle thereof. An output shaft31protrudes from the motor3in a direction substantially parallel to the horizontal direction, and a pinion gear31A is provided on an end of the output shaft31. A cooling fan32is also provided on the output shaft31at a base end portion thereof. The cooling fan32introduces air into the housing2from an inlet port (not shown) formed on the housing2so that the motor3and the control unit6can be cooled down with the air.

The base4is mainly made of aluminum, and formed in a substantially rectangular shape. The base4has an opposing surface41A which is in opposition to and in contact with the workpiece (a wooden plate). The longitudinal direction of the substantially rectangular opposing surface41A is configured to be coincident with the cutting direction of the jigsaw1. In this way, the base4supports the housing2. Assume an imaginary axis extending in the horizontal direction on the opposing surface41A and intersecting the blade7. The housing2is configured to be pivotally movable about this imaginary axis (a pivot axis) relative to the base4.

The blade7has a cutting teeth section and a back section. As shown inFIG. 1, the blade7is mounted on the plunger52(described later) such that the cutting teeth section faces upward and forward in the cutting direction and the back section faces rearward in the cutting direction.

The drive section5is mainly configured of a crank section51, the plunger52, a power transmission section53and a roller holder54.

The crank section51includes a spur gear51A, a pin51B and a spindle51C. The spur gear51A meshingly engages the pinion gear31A. The spur gear51A is provided with a cam51D at a base end portion thereof. The cam51D engages the power transmission section53. The pin51B protrudes forward from the spur gear51A such that an axis of the pin51B extends in a direction parallel to a rotational axis of the spur gear51A. The axis of the pin51B and the rotational axis of the spur gear51A are different from each other. The spindle51C is fixed to the housing2for rotatably supporting the spur gear51A.

The plunger52is formed in a substantially rod like shape. The plunger5is slidingly movably supported within the housing2such that the longitudinal direction of the plunger52is in parallel with the vertical direction. As shown inFIG. 2, the plunger52includes a holding section52A and a receiving section52B. The holding section52A holds the blade7and is provided on the plunger52at the lower end thereof. The receiving section52B is formed at a center of the plunger52. The receiving section52B is formed with a groove52bextending in the horizontal direction (left-to-right direction) within which the pin51B is inserted. The pin51B is allowed to move in the horizontal direction but restricted to move vertically within the groove52b. Hence, the receiving section52B is only allowed to make vertical movements in conjunction with the movements of the pin51B. In other words, the pivotal movements of the pin51B about the spindle51C can be converted into the vertical movements of the plunger52. The plunger52moves in the vertical direction within a predetermined range of stroke S (SeeFIG. 4).

As shown inFIG. 1, the power transmission section53is supported to the housing2and engages the cam51D such that the power transmission section53is capable of moving in the vertical direction within the housing2. The power transmission section53has a bottom portion that contacts the roller holder54.

The roller holder54is configured of a holder54A, a roller54B and a shaft54C extending in the left-to-right direction. The holder54A is disposed rearward of the blade7and is pivotably movable about the shaft54C in a direction perpendicular to the left-to-right direction. The holder54A has an upper portion that contacts the bottom portion of the power transmission section53. Hence, in accordance with the vertical movements of the power transmission section53, the holder54A pivotably moves in counterclockwise and clockwise directions inFIG. 1. The roller54B is rotatably supported to a bottom portion of the holder54A, while in contact with the back section of the blade7.

The control unit6is disposed rearward of the motor3as shown inFIG. 1so that the control unit6can be situated in a path of the air generated by the rotation of the cooling fan32. The control unit6includes a control circuit61and an FET drive circuit (inverter circuit)62, as will be described later.

Next, the control unit6will be described in more detail with reference toFIG. 7. The motor3(DC brushless motor) includes a rotor3A, a stator3B, and stator windings (armature windings)3C. The rotor3A has permanent magnets having south and north poles that are embedded therein and extend toward the output shaft31. The stator3B has a substantially hollow cylindrical outline and the rotor3A is disposed within the stator3B. The stator winding3C are concentrically disposed within the stator3B. The stator windings3C are configured of three-phase windings U, V and W of the stator3B. Each stator winding3C is star-connected and wound within a slot of the stator3B via an insulation layer (not shown: made of a resin material) such that the stator windings3C surround the stator3B.

Three hole ICs65,66and67are disposed in the vicinity of the rotor3A for detecting rotating positions of the rotor3A. Each of the hole ICs65,66and67is arranged at every 60 degrees along the rotating direction of the rotor3A. The FET drive circuit62controls the current flowing into the stator windings3C based on position detection signals outputted from the hole ICs65,66and67. At this time, the current flowing into the stator winding3C is controlled to fall within a conducting range of an electric angle of 120°.

As shown inFIG. 7, the FET drive circuit62includes six three-phase bridge connected semiconductor switching elements62A. The semiconductor switching elements62A are configured of insulated gate bipolar transistors (IGBT) Q1-Q6. Six bridge-connected FETs may also be employed instead of the semiconductor switching elements62A. Each gate of the semiconductor switching elements62A (Q1-Q6) is connected to a control signal output circuit63of the control circuit61. On the other hand, either collector or emitter of each of the semiconductor switching elements62A is connected to the star-connected stator windings3C (U, V and W) of the motor3. With this configuration, the six semiconductor switching elements62A perform a switching operation in accordance with PWM drive signals (switching signals) H1-H6inputted from the control signal output circuit63, convert the direct current of the battery23applied to the FET drive circuit62into voltages of three phases (U-phase, V-phase and W-phase) Vu, Vv and Vw, and supply the three-phase alternating current to the stator windings3C.

The control circuit61controls the motor3and others by outputting the switching signals H1-H6to the FET drive circuit62via the control signal output circuit63. The control circuit61includes a control/calculation unit61A, a rotor position detection circuit68, a rotational speed detection circuit69, a current detection circuit70, an applied voltage setting circuit71, a speed instructing circuit61E and a plunger position detection circuit74.

The control/calculation unit61A includes a microcomputer for generating output signals to be outputted to the control signal output circuit63based on processing programs, control data and input signals such as motor position signals. The rotor position detection circuit68detects positional relationships between the rotor3A and the stator windings3C of the stator3B based on the output signals from the hole ICs65,66and67, and outputs information on positions of the rotor3A to the control/calculation unit61A. The rotational speed detection circuit69detects rpm of the motor3from intervals of the signals outputted from the hole ICs65,66and67.

The current detection circuit70continuously detects drive current flowing through the motor3and outputs detection signals to the control/calculation unit61A. The applied voltage setting circuit71sets PWM duty ratio of the switching signals corresponding to output control signals which are generated by the trigger switch22in response to the amounts of depression of the trigger22A. The speed instructing circuit61E outputs indicated speed signals to the control/calculation unit61A in accordance with signals from speed setting means72(volume VR) that sets rotational speeds of the motor3. The plunger position detection circuit74detects the position of the plunger52from detection signals of the position sensor24.

The control/calculation unit61A controls voltages applied to the stator windings3C of the motor3(Vu, Vv and Vw) by controlling the PWM duty ratio of the PWM drive signals of the semiconductor switching elements62A in accordance with the output signals from the current detection circuit70, the applied voltage setting circuit71, the speed instructing circuit61E and the like. The control/calculation unit61A also controls the voltages (Vu, Vv and Vw) applied to the stator windings3C in a prescribed order by switching the semiconductor switching elements62A in the prescribed order, thereby controlling rotation of the motor3.

The control/calculation unit61A also calculates the position of the plunger52based on the output signals of the plunger position detection circuit74, thereby controlling the rotational speed of the motor3(to speed up, speed down or stop) in accordance with the position of the plunger52.

The control/calculation unit61A is further connected to deceleration position setting means76and stop position setting means75. The deceleration position setting means76designates a position at which the plunger52needs to decelerate during the reciprocal movements thereof (See a1and a2inFIG. 4). The stop position setting means75sets a position at which the plunger52stops when the trigger switch22is turned off. The control/calculation unit61A controls rotational speeds and rotational angles of the motor3based on the position of the plunger52detected by the position sensor24and the output signals of the stop position setting means75and the deceleration position setting means76.

The control circuit61changes the PWM duty ratios of the switching signals of the semiconductor switching elements62A in accordance with the output signals of the applied voltage setting circuit71that corresponds to the amounts of depression of the trigger22A and the motor speed signals that is set by the speed setting means72and is outputted from the speed instructing circuit61E. In this way, the control circuit61regulates electric power supply to the motor3, thereby controlling rotational speed of the motor3. When the trigger22A is depressed fully to the maximum amount thereof, the control circuit61controls the rotational speed (rpm) of the motor3to be equal to the rpm set by the speed setting means72.

The control/calculation unit61A is configured of a microcomputer. The microcomputer includes a CPU (not shown), a ROM (storage means64), a RAM (storage means64) and a timer78(seeFIG. 7). The CPU outputs drive signals based on processing programs and each processed data. The ROM stores processing programs for executing control routines described later and control data. The RAM temporality stores data, such as positional relationship between the plunger52and the motor3(the rotor3A) and time periods during which the plunger52makes reciprocal movements and moves from a deceleration position to either dead center at a prescribed speed. The timer78counts time during which the plunger52moves from a prescribed position to a dead center.

The control/calculation unit61A further includes a position detection section61B, a speed control section61C and a voltage control section61D, as shown inFIG. 3.

The position detection section61B is connected to the rotor position detection circuit68(the rotational speed detection circuit69) and the plunger position detection circuit74. In accordance with the signals outputted from these circuits, the position detection section61B calculates rotating positions and rotational speeds of the motor3and the position of the plunger52. Alternatively, terminal voltage detection means77may be connected to the position detection section61B instead of the rotor position detection circuit68, as will be described later.

The speed control section61C determines whether the rotational speed of the motor3becomes the designated motor speed by referring to the designated motor speed signal outputted from the speed instructing circuit61E based on the signals from the speed setting means72, the motor rotational speed signals from the position detection section61B, the motor rotating position signals, and the plunger position signals.

The voltage control section61D outputs drive signals regarding the motor3, via the control signal output circuit63, to the FET drive circuit62based on the output signals from the speed control section61C.

In the jigsaw1having the above-described configuration, when the battery23is mounted on (therefore connected to) the housing2and the user of the jigsaw1operates the trigger switch22, the motor starts to rotate. In response to the rotation to the motor3, driving force of the motor3is transmitted, from the output shaft31of the motor3, to the plunger52via the power transmission section53, thereby enabling the plunger52to make reciprocating movements. Following the reciprocal movements of the plunger52, the blade7mounted on the tip of the plunger52can cut the workpiece.

More precisely, when the trigger switch22is operated, the applied voltage setting circuit71outputs a signal corresponding to the amount of depression of the trigger22A to the control circuit61. Based on this signal, the control/calculation unit61A generates switching signals for the semiconductor switching elements62A and outputs the same to the FET drive circuit62via the control signal output circuit63. The control/calculation unit61A thus controls the motor3to rotate at a speed corresponding to the amount of depression of the trigger22A, allowing the jigsaw1to cut the workpiece. The maximum speed of the motor3is set to be the speed specified by the speed setting means72.

Subsequently, the control circuit61detects rotating positions and rotational speed of the rotor3A with the signals from the hole ICs65,66and67via the rotor position detection circuit68and the rotational speed detection circuit69. In this way, the control circuit61controls the rotational speed of the motor3. At the same time, the control circuit61calculates the position of the plunger52based on the outputs from the position sensor24and the plunger position detection circuit74. Upon finding that the plunger52has reached the deceleration position, the control circuit61decelerates the plunger52. When the trigger switch22is turned off, the control circuit61stops the plunger52at the stop position set by the stop position setting means75and terminates the operation of the jigsaw1.

As an alternative method of detecting rotating positions of the rotor3A, the terminal voltage detection means77may be provided, instead of the hole ICs65,66and67, for detecting terminal voltages (induced voltages) between the stator windings3C of the motor3, as shown inFIG. 3. In this case, the control circuit61detects rotating positions and rotational speed of the rotor3A from the terminal voltages of the motor3(sensor-less method). The terminal voltage detection means77may be so configured as to retrieve terminal voltages between the stator windings3C as logic signals through a filter.

Next, how the plunger52(the motor3) is controlled and decelerated in the present embodiment will be described with reference toFIG. 4.

In the present embodiment, the control circuit61calculates the position of the plunger52based on either one of or both of the positional information of the plunger52from the position sensor24and the positional information of the rotor3A of the motor3.

In accordance with the positional information of the plunger52, the control circuit61controls the rotational speed or rotating angle of the motor3when the plunger52comes to a prescribed position. In this way, in the jigsaw, vibrations and noises are reduced, while the workability is improved.

In the present embodiment, the motor3is set, with the deceleration position setting means76, such that the motor3starts decelerating at positions close to both dead centers (before reaching both dead centers).

The control circuit61controls the rotation of the motor3by controlling switching operations of the semiconductor switching elements62A of the FET drive circuit62, thereby enabling the plunger52to make vertical movements. Assume that the motor3currently rotates at a rotational speed (first speed) that is set by the speed setting means72. The control/calculation unit61A always monitors the positional information of the plunger52coming from the position sensor24. When the position sensor24and the plunger position detection circuit74detect that the plunger52is approaching to the positions close to, but before reaching, the both dead centers for each cycle of the vertical movements, the control/calculation unit61A controls the semiconductor switching elements62A so that the motor3can be slowed down to a second speed, which is slower than the first speed.

Specifically, as shown inFIG. 4, when the plunger52is moving from the top dead center (at t=0) toward the bottom dead center, the motor3rotates at the first speed. Upon detecting that the plunger52has come to (or passed) a deceleration position designated by the deceleration position setting means76, i.e., a positional before the bottom dead center, the control/calculation unit61A (position detection section61B) outputs, to the semiconductor switching elements62A of the FET drive circuit62, signals to slow down the rotational speed of the motor3from the first speed to the second speed. In this way, the rotational speed of the motor3is decelerated to the second speed from the first speed at the position α1.

There inevitably generated are noises and vibrations at both dead centers at which the plunger52changes the motion direction thereof. Hence, preferably, the rotational speed of the motor3is slowed down in the vicinity of both dead centers, especially at positions before reaching each dead center. With this configuration, inertial energy (motion energy) of the motor3can be reduced at positions where the direction of the movement of the plunger52is switched, thereby allowing the noises and vibrations to be suppressed most efficiently.

Referring toFIG. 4, L1represents a case where the rotational speed of the motor3is maintained constantly at the first speed. L2represents a case where the rotational speed of the motor3is slowed down from the first speed to the second speed at the position α1. In case of L1, moving the plunger52from the top dead center to the bottom dead center requires a time period of T. On the other hand in case of L2, the movement of the plunger52from the top dead center to the bottom dead center requires a time period of T+ΔT.

Here, the amount of movement of the plunger52is determined as ΔX per a marginal period of time Δt. The second speed is assumed to be set to a speed that is equal to 40 percent of the first speed. In this case, specifically, ΔX at the second speed is 40 percent of ΔX at the first speed. Provided that a mass M is identical, motion energy from the positional to the bottom dead center can be defined as being proportional to the square of the speed. i.e., 0.5×M×(ΔX/Δt)2for L1. Hence, inFIG. 4, motion energy from the positional to the bottom dead center for L2is 0.5×M×(0.4×ΔX/Δt)2, resulting in 16 percent of the motion energy of L1. At the bottom dead center, the speed vector of the plunger52becomes opposite, thereby inevitably generating an impact. Since the motion energy in case of L2is only 16 percent of the motion energy of L1, the motion energy at the time of the impact in case of L2is also reduced to be 16 percent of the motion energy in case of L1. In this way, with the reduced speed, the impact generated at the time of the change in the speed vector of the plunger52can be efficiently suppressed.

Upon detecting that the plunger52has reached (passed) the bottom dead center, the control/calculation unit61A (the speed control section61C) outputs switching signals H1-H6indicative of the first speed to the semiconductor switching elements62A of the FET drive circuit62. The rotational speed of the motor3is thus speeded up to the first speed when the plunger52passes the bottom dead center.

The control/calculation unit61A detects that the plunger52has reached the bottom dead center from the plunger position signals outputted from the position sensor24. Alternatively, the storage means64may prestore time periods necessary for the plunger52to move from each deceleration position to either dead center. The control/calculation unit61A may detect that the plunger52has reached the bottom end by measuring time period required for the plunger52to move from one deceleration position (α1) to the bottom dead center with the timer78and then by comparing the measured time period with the prestored time data. Still alternatively, the storage means64may store time ranges (a predetermined range within the amount of stroke S) at which vibrations and noises have been known to occur. As a further alternative, the storage means64may count and store a time period each time for the plunger52to move from one deceleration position to one dead center using the timer78in accordance with the signals from the position sensor24. The control/calculation unit61A may use this time period stored by the storage means64for detecting the position of the plunger52.

In the present embodiment, the rotational speed (first speed) of the motor3can be configured to be set at a plurality of stages. Hence, the control/calculation unit61A can calculate a time period during which the plunger52needs to be decelerated based on the setting speed and the deceleration position and store the same in the storage means64. In this way, the control/calculation unit61A can control the rotational speed of the motor3in accordance with the stored period of time. This configuration allows the jigsaw1to reliably control the motor3regardless of the setting speed of the motor3, thereby suppressing occurrence of vibrations and noises. The workability of the jigsaw1can also be improved.

In the present embodiment, the rotational speed of the motor3is configured to be decelerated from the first speed to the second speed when the plunger52has approached areas where vibrations and noises would become large (i.e., in the vicinity of the bottom dead center), and subsequently to be accelerated from the second speed to the first speed after the plunger52has passed the bottom dead center. In this way, since the rotation of the motor3is not configured to be maintained at the reduced second speed even after the motor3has been once slowed down, the improved workability can be maintained while vibrations and noises can be held down.

Similarly, when the plunger52moves from the bottom dead center to the top dead center, the rotational speed of the motor3is decelerated to the second speed from the first speed at a position α2, as shown inFIG. 4. This position α2has a phase different from the phase of the positional by 180 degree. In other words, the position α2is a position in the vicinity of, but before the top dead center.

When the plunger52has passed the top dead center, the control/calculation unit61A controls the semiconductor switching elements62A such that the rotational speed of the motor3is speeded up again to the first speed from the second speed. Note that, a distance between the deceleration positional to the bottom dead center may not be identical to a distance between the deceleration position α2to the top dead center. The deceleration position setting means76may set each deceleration position (α1and α2) to be different from each other.

If the rotational speed (first speed) of the motor3is set to such a speed that the jigsaw1would not generate vibrations nor noises, or to such a speed that vibrations and noises are relatively low even when generated, the motor3does not need to be slowed down regardless of the settings of the deceleration position setting means76. For example, the storage means64may prestore a rotational speed at which vibrations nor noises would not be generated. If the deceleration position setting means76sets a rotational speed that is equal to or smaller than the prestored speed, the control/calculation unit61A controls the motor3not to slow down regardless of the rotational speed designated by the deceleration position setting means76, thereby leading to improvement in the workability of the jigsaw1.

Alternatively, a reset switch may be provided for resetting deceleration positions, deceleration time and positional information of the plunger52and the motor3stored in the storage means64. In this case, each time the user uses the jigsaw1, each of the above information may be configured to be reset by the reset switch. Therefore, the motor3is always controlled with the latest information.

As described above, the jigsaw1is controlled such that, while the plunger52makes the reciprocating movements (starting from the top dead center, to the deceleration position α1before the bottom dead center, then to the bottom dead center, then to the deceleration position α2before the top dead center, and back to the top dead center again), the rotational speed of the motor3is decelerated when the plunger52reaches prescribed positions α1and α2. When cutting the workpiece by repeating such vertical movements, the jigsaw1can suppress impacts from being generated at the both dead centers, leading to improved workability. Note that, when the first speed and the second speed are alternately employed for the sake of suppressing generation of noises and vibrations as in the present embodiment, the time cycle of the plunger52(for L2) becomes longer by 2ΔT, compared to the case of L1, as shown inFIG. 4. However, this period is small enough to have little effect on the workability of the jigsaw1. If there is some effect on the workability, the first speed may be set to be faster in advance.

Next, a description will be given on how the plunger52(the blade7) is controlled when the jigsaw1stops operating.

If the blade7still protrudes from the base4when the user ends using the jigsaw1, the blade7may become an obstacle in accommodating or transporting the jigsaw1. Therefore, the control circuit61according to the present embodiment is configured to control the plunger52to stop either at the top dead center or at a position close to the top dead center, as shown inFIG. 5.

When the control circuit61detects that the trigger switch22outputs no more drive signals of the motor3, i.e., when cutting the workpiece has ended, the control circuit61outputs switching signals of the semiconductor switching elements62A to the FET drive circuit62while observing the position of the plunger52based on position signals from the position sensor24. Upon detecting that the plunger52has reached the prescribed position (either at the top dead center or at the position near the top dead center), for example at the top dead center or at the position α2inFIG. 4, the control/calculation unit61A stops supplying the switching signals to the FET drive circuit62or compulsorily terminates driving the motor3. In this way, the plunger52can stop at the position shown inFIG. 5. Alternatively, the control/calculation unit61A may stop driving the motor3before the plunger52reaches the prescribed position.

To the contrary, when the plunger52stops at the top dead center or the position in the vicinity of the top dead center at the time of replacement of the blade7, such a replacement operation will result in low workability because the base4covers the blade7. Hence, the jigsaw1according to the present embodiment is provided with the stop position setting means75for allowing the plunger52to switch stop positions thereof. With the stop position setting means75, the control/calculation unit61A can control the motor3so that the plunger52can be moved to either the bottom dead center (as shown inFIGS. 1 and 4) or a position close to the bottom dead center (positional inFIG. 4) after the plunger52has once stopped at the top dead center or the position close to the top dead center.

Alternatively, the storage means64may store information indicative of positions at which the stop position setting means75sets the plunger52to stop (for example, time period required until the stop position of the plunger52). In this case, the control/calculation unit61A detects the position of the plunger52from the position sensor24when the trigger switch22is switched off. The control/calculation unit61A then calculates a period of time required from the detected position of the plunger52to the stored stop position using the timer78, and controls the plunger52to stop at the prescribed position.

Still alternatively, instead of providing the stop position setting means75, the control/calculation unit61A may control the plunger52to stop either at the bottom dead center or at the position close to the bottom dead center based on the signals outputted from the trigger switch22. Specifically, when the user softly depresses the trigger22A of the trigger switch22once, i.e., the control/calculation unit61A detects the signal from the trigger22A once, the control/calculation unit61A detects the position of the plunger52from the position detection section61B (the position sensor24and the plunger position detection circuit74), thereby controlling the position of the plunger52to come to the prescribed position.

Still alternatively, the stop position setting means75may not only switch the position of the plunger52between the top dead center and the bottom dead center, but may also serve as means to set the stop position of the plunger52(a dial or a switch, for example).

As above described, when the stop position setting means75is a dial, the user may adjust the dial to the desired stop position. When the stop position setting means75is a switch, and especially is provided with a plurality of switches, the user may depress a switch corresponding to the prescribed stop position. When the stop position setting means75is provided with only one switch, the user may set the stop position of the plunger52by depressing the switch for a predetermined number of times. Based on the stop position signal and the position signals of the plunger52(signals from the position sensor24, signals from the hole ICs65,66and67), the control/calculation unit61A may control the motor3so that the plunger52can stop at the prescribed position.

If the stop position of the plunger52is not necessary to be set, the control/calculation unit61A may control the motor3such that the plunger52can stop at a prescribed position when the trigger switch22is turned off. In this case, the control/calculation unit61A receives a signal to cancel the settings of position of the plunger52when the user presses a reset switch (not shown) or adjusts the stop position setting means75(to a position indicative of setting being unnecessary if the plunger52is a dial).

The stop position setting means75does not necessarily set the stop position of the plunger52before the trigger switch22is turned on, i.e., before the user starts operating the jigsaw1. Instead, the stop position of the plunger52may be set by the stop position setting means75during and after the cutting operations. In this way, the user can determine where to stop the plunger52whenever necessary, thereby improving the workability of the jigsaw1.

Next, a description will be given on how the jigsaw1is controlled during the operation thereof with reference to a flowchart inFIG. 6. Note that, in this example shown in this flowchart ofFIG. 6, the position sensor24is assumed to be used for detecting the position of the plunger52.

First of all, in S01the volume VR (the speed setting means72) sets a speed for the motor3. In S02the control circuit61determines whether the trigger switch22is activated by the user. If the trigger switch22is determined not to have been activated since the user does not operate the trigger22A (S02:NO), the flow returns to S01.

Upon determining in SO2that the user has operated the trigger22A to activate the trigger switch22(S02:YES), in S03the control circuit61(the control/calculation unit61A including the speed control section61C, as shown inFIG. 4) outputs signals to drive the motor3(the switching signals H1-H16) to the to the FET drive circuit62(to the semiconductor switching elements62A) in S03. The control circuit61then controls the battery23to supply electric power to the motor3, thereby rotating the motor3at the speed designated by the volume VR.

In S04the control circuit61determines whether the position sensor24has detected the plunger52. In other words, the control circuit61detects whether the plunger52is located at a position at which the position sensor24can detect, i.e., a position in proximity to either the top dead center or the bottom dead center. As described earlier, the position sensor24may instead be configured to always detect the position of the plunger52.

If the position sensor24does not detect the plunger52(S04:NO), the flow returns to S03. If the position sensor24detects the plunger52(S04:YES), in S05the control/calculation unit61A (the position detection section61B) identifies the position of the plunger52and specifies the rotating positions of the motor3based on the terminal voltages among the stator windings3C or the hole ICs65,66and67.

Subsequently in S06, the control/calculation unit61A (the position detection section61B) determines whether the plunger52has reached the deceleration position set by the deceleration position setting means76based on the output signals from the position sensor24. In the present embodiment, the control/calculation unit61A determines whether or not the plunger52has passed the positional before the bottom dead center or the position α2before the top dead center. The storage means64prestores information on the current position of the plunger52relative to each of the positions α1, α2, the top dead center and the bottom dead center (such as time periods set in accordance with the rotational speeds, position signals of the plunger52, and position signals of the motor3and the like). The control/calculation unit61A determines that the plunger52has reached the prescribed position by comparing the actual detected values with the prestored values.

When the control/calculation unit61A does not detect that the plunger52has passed either position α1or the position α2(S06:NO), the flow returns to S03. On the other hand, when the control/calculation unit61A detects that the plunger52has passed either one of the position α1and the position α2(S06:YES), in S07the control/calculation unit61A outputs switching signals H1-H6to the FET drive circuit62so that the rotational speed of the motor3can be slowed down to a speed lower than the rotational speed set by the volume VR in S01. Here, the storage means64stores decelerated rotational speeds in association with the plurality of setting speeds that the volume VR can designate.

Subsequently in S08the control/calculation unit61A determines whether the plunger52has passed either one of the top dead center and the bottom dead center based on the signals outputted from the position sensor24. Alternatively, the control/calculation unit61A may calculate the current position of the plunger52from the information stored in the storage means64.

When the plunger52is determined not to have passed the top dead center nor the bottom dead center (S08:NO), the flow returns to S09and the motor3is maintained at the decelerated speed. Upon detecting that the plunger52has passed either the top dead center or the bottom dead center (S08:YES), in S09the control/calculation unit61A (the speed control section61C) controls the outputs of the switching signals H1-H6to the FET drive circuit62so that the rotational speed of the motor3can be accelerated up to the speed set by the volume VR in S01.

Subsequently in S10the control circuit61determines whether or not the user has operated the trigger22A. When the user is operating the trigger22A and therefore the trigger switch22is active (S10:YES), the flow returns to S03and repeats the steps from S03to S10.

When the control circuit61determines in S10that the trigger switch22has not been activated by the user (S10:NO), in S11the control/calculation unit61A (the speed control section61C) controls the outputs of the switching signals H1-H6to the FET drive circuit62, reduces the power supply from the battery23to the motor3, and decelerates the rotational speed of the motor3.

In S12the control circuit61detects the position of the plunger52from the signals of the position sensor24. When the position of the plunger52cannot be detected (S12:NO), the flow returns to S11. The position sensor24may be configured to always monitor the position of the plunger52.

Upon detecting the position of the plunger52(S12:YES), in S13the control/calculation unit61A (the position detection section61B) determines whether the plunger52has reached the stop position of the motor3set by the stop position setting means75. In the present embodiment, the control/calculation unit61A determines whether the plunger52has reached either the top dead center or the position near the top dead center.

When the plunger52has reached neither the top dead center nor the position close to the top dead center (S13:NO), the flow returns to S11. On the other hand, when the plunger52has determined to have come to the top dead center or the position near the top dead center (S13:YES), in S14the control/calculation unit61A (the speed control section61C) controls the switching signals H1-H6outputted to the FET drive circuit62so that the motor3can stop rotating, thereby completely stopping the rotation of the output shaft31of the motor3. The control circuit61then terminates controlling the operation of the jigsaw1. In this way, when the user can end using the jigsaw1, the plunger52can be positioned at the top dead center or at the position near the top dead center.

When replacing the blade7, the control/calculation unit61A controls the blade7(the plunger52) to come to the bottom dead center in S13and S14. The user may switch the stop position of the plunger52from the top dead center to the bottom dead center by manipulating the stop position setting means75, or by softly pulling the trigger22A once. With this configuration, since the blade7is located at the bottom dead center, the user can easily replace the blade7that is mounted on the holding section52A of the plunger52.

Next, a variation of the present embodiment will be described with reference toFIG. 8. In the variation, the motor3is driven by the AC power source90and, instead of employing the position sensor24, the position of the plunger52is detected from the rotating positions and the rotational speeds of the motor3.

In this variation, the rotating positions and the rotational speeds of the motor3are controlled based on the hole ICs65,66and67that detect positions of the rotor3A, and the terminal voltage detection means77(SeeFIG. 3) that detects terminal voltages between the stator windings3C. In case of employing the brushless motor (the motor3), detection of the rotating positions and rotational speeds of the motor3(the rotor3A) is inevitably required. Hence, detecting the position of the plunger52only from the motor rotation signals, without employing the position sensor24, can contribute to reduction of the parts, thereby suppressing costs of the parts necessary for the jigsaw1.

As shown inFIG. 8, the variation of the present invention is different from the preferred embodiment shown inFIG. 7in that the position sensor24and the plunger position detection circuit74are deleted and the AC power source90is used for supplying electric power to the motor3instead of the battery23. Since the AC power source90is employed, a converter80, a pair of resistances81and82, and a voltage detection circuit83are added in the variation. Further, display means91and reference position setting means92are also added in the present variation.

The converter80converts an AC current coming from the AC power source90to a DC current. The resistances81and82detect the DC current converted by the converter80. The voltage detection circuit83detects the DC current and outputs a detection signal to the control/calculation unit61A. The display means91displays information on the settings of the jigsaw1. The reference position setting means92sets a reference position of the plunger52. The reference position setting means92includes a switch.

When calculating the position of the plunger52only from the positional information of the motor3, one reciprocating movement of the plunger52(from the time0to the time2T inFIG. 4) does not necessarily correspond to one revolution of the motor3(the rotor3A). Hence, the position of the plunger52and the position of the motor3are required to be associated with each other. Hereinafter, how the position of the plunger52and the motor3are set will be described.

At the time of shipment (or assembly) of the jigsaw1, an external apparatus rotates the motor3for detecting the rotating position of the rotor3A and the position of the plunger52. Such an external apparatus may detect the position of the plunger52based on a distance between the plunger52and a position sensor provided in the external apparatus. Alternatively, a spring may be connected to the plunger52so that the external apparatus can detect the position of the plunger52based on the tension power of the spring. Other detecting methods may also be applied.

Still alternatively, instead of using such an external apparatus, the positional relationships between the plunger52and the motor3may be initially determined at the jigsaw1itself.

First of all, the plunger52is positioned to a reference position, for example, to the top dead center. At this time, the user operates the reference position setting means92in order to let the control/calculation unit61A (the storage means64) memorize the reference position of the plunger52(i.e., the top dead center). Instead of the user, an external device may be used for setting the reference position by monitoring the position of the plunger52. The control/calculation unit61A (the storage means64) has prestored the rpm of the motor3required for the plunger52to make one reciprocating movement. Here, as an example, the motor3is assumed to revolve for ten times during one vertical movement of the plunger52.

When the motor3rotates, the hole ICs65,66and67detect the rotating positions and rotational speeds of the rotor3A. The hole ICs65,66and67output pulse signals associated with the polarities of the rotor3A (the north pole and the south pole). The rotor position detection circuit68and the rotational speed detection circuit69convert the pulse signals outputted from the hole ICs65,66and67into pulse signals in a format that the control/calculation unit61A can recognize, and then input the same to the control/calculation unit61A. In case ofFIG. 8, since the rotor3A is provided with a pair of north pole and south pole, the hole ICs65,66and67output signals in accordance with changes in each polarity. Specifically, each hole IC outputs two pulses for each revolution of the rotor3A, and therefore, as a total, six pulses are to be outputted. Hence, when the motor3revolves for ten times, each hole IC outputs twenty pulses. That is, the hole ICs65,66and67output sixty pulses as a whole. The control/calculation unit61A prestores this number of pulses outputted from the hole ICs65,66and67. The control/calculation unit61A also prestores that the number of pulses is equal to zero when the plunger52is located at the reference position set by the reference position setting means92. In this way, the control/calculation unit61A can control the plunger52based on the rotation information of the motor3during one vertical movement of the plunger52(i.e., the number of pulses). If the number of pulses inputted to the control/calculation unit61A needs to be increased for a more accurate control of the plunger52, additional frequency divider may be provided for the number of pulses outputted from the hole ICs65,66and67.

At the time of shipment of the jigsaw1, the reference position of the plunger52is set by the reference position setting means92, and the storage means64stores the number of pulses outputted from the hole ICs65,66and67for a period during which the plunger52makes one reciprocating movement from the reference position. During cutting the workpiece, when the user manipulates the reference position setting means92, the control/calculation unit61A can detect the position of the plunger52from the rotation information of the motor3, i.e., the pulse signals outputted from the hole ICs65,66and67. For example, if the total number of pulses outputted from the hole ICs65,66and67is thirty, the control/calculation unit61A compares the detected number of pulses (thirty pulses) with the pulse information stored in the storage means64, and determines that the plunger52has reached a position corresponding to a half of the number of pulses to be outputted during one reciprocating movement, that is, the plunger52has reached the dead center.

When the plunger52makes vertical movements for a plurality of times, the control/calculation unit61A recognizes that the plunger52has come to the reference position each time the number of pulses becomes an integral multiple of sixty. If the speed setting means72sets the rpm of the motor3to 3000 rpm, for example, the motor3revolves for fifty times per one second. Hence, in the meantime, the plunger52makes five vertical movements. During the five vertical movements, the hole ICs65,66and67output three-hundred pulse signals. The control/calculation unit61A compares the detected number of pulses with the stored number of pulses, and detects the position of the plunger52. The control/calculation unit61A can also compare the number of pulses outputted from the hole ICs65,66and67with the signals from the deceleration position setting means76and the stop position setting means75, i.e., signals associated with the number of pulses from the hole ICs65,66and67, thereby accurately detecting that the plunger52has reached the deceleration position and the stop position.

In this way, the control/calculation unit61A can control the motor3such that the motor3can decelerate and stop at prescribed positions. As above described, the control/calculation unit61A can detect the position of the plunger52only from the rotation position information of the motor3(the rotor3A), even without the position sensor24(and the plunger position detection circuit74shown inFIG. 7).

Hereinafter, a method for controlling the position of the plunger52based on the position information of the motor3will be described in detail.

The user operates the trigger switch22to start rotating the motor3. The control circuit61is inputted with signals indicative of the rotating position of the motor3(pulse signals) detected by the hole ICs65,66and67via the rotor position detection circuit68. The control/calculation unit61A calculates the position of the plunger52from the detected motor position signals (number of pulses) and the motor position information (number of pulses) stored in the storage means64. For example, if twenty pulses are detected, the control/calculation unit61A determines that the plunger52has not yet reached the bottom dead center (whose number of pulses is thirty).

Simultaneously, the control/calculation unit61A determines whether the plunger52has reached the prescribed deceleration position designated by the deceleration position setting means76, such as the position before the top dead center and the position before the bottom dead center. Upon determining that the deceleration position has been set to a position corresponding to the number of pulses twenty, the control/calculation unit61A outputs the (switching) signals H1-H6to the FET drive circuit62for decelerating the rotational speed of the motor3. Subsequently, upon detecting that the number of pulses coming from the hole ICs65,66and67is thirty, the control/calculation unit61A controls the motor3to accelerate.

When detecting that the trigger switch22has been turned off, the control/calculation unit61A determines whether the number of pulses from the hole ICs65,66and67indicates that the plunger52has reached the prescribed stop position (the top dead center, for example) designated by the stop position setting means75. Upon determining that the plunger52has reached the stop position, the control/calculation unit61A controls the motor3to stop so that the plunger52can stop at the stop position. In this way, even if the position sensor24is not provided, the position of the plunger52can be calculated from the position information of the motor3that has been prestored in association with the position of the plunger52in the storage means64.

Further, the jigsaw1may also be provided with memory reset means and memory reconfiguring means. The memory reset means resets information on the positional relationship between the plunger52and the motor3stored in the storage means64. The memory reconfiguring means re-establishes the positional relationship between the plunger52and the motor3. With the memory reset means and the memory reconfiguring means, old data stored in the storage means64can be deleted and the storage means64can store latest data therein, enabling a more accurate control of the motor3. Note that, the stop position setting means75and the deceleration position setting means76may also serve as the memory reset means and the memory reconfiguring means. If the stop position setting means75and the deceleration position setting means76are dials, these means75and76can be so configured as to be switched to either one of the memory reset means and the memory reconfiguring means by successively turning the dials for predetermined times. In case of the stop position setting means75and the deceleration position setting means76being switches, the means75and76may be so configured as to be switchable between the memory reset means and the memory reconfiguring means depending on periods of time during which each switch is depressed.

When the memory reconfiguring means is provided, re-configuration of the positional relationship between the motor3and the plunger52may be performed with the external device used at the time of shipment of the jigsaw1. However, the re-configuration may also be performed on the jigsaw1having the storage means64. In this case, the position sensor24and the plunger position detection circuit74are required.

Upon operation of the memory reconfiguring means, the control circuit61rotates the motor3regardless of the status of the trigger switch22. The control/calculation unit61A reads the positional information on the rotor3A for prescribed angles from the terminal voltages of hole ICs65,66and67or the stator windings3C and stores the same in the storage means64. At the same time, the control/calculation unit61A reads the positional information of the plunger52in association with the prescribed angles from the position sensor24, and stores the same in the storage means64. The control circuit61stops rotating the motor3and terminates this storing operation. In this way, as long as the positional relationship between the motor3and the plunger52has been stored, even if the position sensor24is broken for some reason, the control circuit61can control the motor3in accordance with the position of the plunger52, thereby improving the workability of the jigsaw1.

Further, since the display means91(such as a display or an LED) is provided in the present variation, the user can visually confirm various information on the jigsaw1. The display means91may display, for example, information indicating that the storing operation is in process, the designated rotational speed of the motor3, and the position of the plunger52. Hence, the workability will also be enhanced. Also, displaying information can facilitate confirming the storing method and status of the deceleration position and the stop position.

Although the present invention has been described with respect to specific embodiments thereof, it will be appreciated by one skilled in the art that a variety of changes may be made without departing from the scope of the invention.

For example, not only providing one position sensor (the position sensor24) on the top dead center side of the plunger52, another position sensor may also be provided on the bottom dead center side. In this case, the position of the plunger52can be detected with much high accuracy. Further, other types of sensors may also be employed as the position sensor24, instead of a proximity sensor.

Further, in addition to the jigsaw1as a cutting tool, the present invention can also be applicable to other reciprocating electric tools that have an end bit making vertical movements, such as a saber saw (reciprocating saw), a hammer, a hammer drill and a table jig saw.

Industrial Applicability

The present invention is applicable to reciprocating electric tool such as a jigsaw and any type of electric tool having an end bit which reciprocates.

EXPLANATION OF REFERENCE

1reciprocating electric tool