WO2013081191A2 - Electric tool - Google Patents

Electric tool

Info

Publication number
WO2013081191A2
WO2013081191A2 PCT/JP2012/081726 JP2012081726W WO2013081191A2 WO 2013081191 A2 WO2013081191 A2 WO 2013081191A2 JP 2012081726 W JP2012081726 W JP 2012081726W WO 2013081191 A2 WO2013081191 A2 WO 2013081191A2
Authority
WO
WIPO (PCT)
Prior art keywords
coils
phase
motor
winding
switching
Prior art date
Application number
PCT/JP2012/081726
Other languages
French (fr)
Other versions
WO2013081191A3 (en
Inventor
Tetsuya Monzen
Takeshi Takeda
Yuji Kishima
Original Assignee
Hitachi Koki Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hitachi Koki Co., Ltd. filed Critical Hitachi Koki Co., Ltd.
Publication of WO2013081191A2 publication Critical patent/WO2013081191A2/en
Publication of WO2013081191A3 publication Critical patent/WO2013081191A3/en

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
    • H02P25/16—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring
    • H02P25/18—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring with arrangements for switching the windings, e.g. with mechanical switches or relays
    • H02P25/188—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring with arrangements for switching the windings, e.g. with mechanical switches or relays wherein the motor windings are switched from series to parallel or vice versa to control speed or torque
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25F—COMBINATION OR MULTI-PURPOSE TOOLS NOT OTHERWISE PROVIDED FOR; DETAILS OR COMPONENTS OF PORTABLE POWER-DRIVEN TOOLS NOT PARTICULARLY RELATED TO THE OPERATIONS PERFORMED AND NOT OTHERWISE PROVIDED FOR
    • B25F5/00—Details or components of portable power-driven tools not particularly related to the operations performed and not otherwise provided for
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K3/00—Details of windings
    • H02K3/04—Windings characterised by the conductor shape, form or construction, e.g. with bar conductors
    • H02K3/28—Layout of windings or of connections between windings
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
    • H02K7/14—Structural association with mechanical loads, e.g. with hand-held machine tools or fans
    • H02K7/145—Hand-held machine tool
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
    • H02P25/16—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring
    • H02P25/18—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring with arrangements for switching the windings, e.g. with mechanical switches or relays
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
    • H02P6/08—Arrangements for controlling the speed or torque of a single motor

Definitions

  • the present invention relates to an electric tool using a brushless motor and, more particularly, to an electric tool in which motor characteristics can be changed in accordance with working conditions in the drive control of a motor having a winding including a plurality of coils (a plurality of winding specifications).
  • the brushless motor refers to a DC (Direct Current) motor which has no brush (brush for rectification).
  • the brushless motor uses a coil (winding) at a stator side and a permanent magnet at a rotor side and has a configuration that power driven by an inverter is sequentially energized to a predetermined coil to rotate the rotor.
  • a switching element for turning on/off the energization of coils wound around the stator is arranged on a circuit board which is provided near the motor.
  • the switching element is arranged on a substantially circular circuit board which is attached to a rear side (a side opposite to the end tool) of the motor.
  • FIG. 11 shows a configuration of a stator part of a brushless motor which is used in an electric tool according to a related art.
  • a stator 204 includes a stator core 241 and coils 261-1 to 261-6 wound around a plurality of teeth 244-1 to 244-6 which are formed at the stator core 241.
  • the stator core 241 is manufactured by stacking a plurality of thin metal plates such as a steel plate in an axial direction and has a substantially cylindrical outer shape.
  • a plurality of teeth 244-1 to 244-6 is formed to extend inward in a radial direction from a cylindrical part of the stator core at predetermined intervals in a circumferential direction.
  • Innermost peripheral sides of these teeth 244-1 to 244-6 respectively have an arc shape so as to be slightly spaced apart from a cylindrical rotor (not shown). Copper wire is wound around each of the teeth 244-1 to 244-6 by a predetermined number of times to form the coils 261-1 to 261 -6. Although connection wires between the coils 261-1 to 261-6 are not shown in Fig. 11, opposing coils are connected to each other.
  • the coil 261-1 and the coil 261-2 form U phase
  • the coil 261-3 and the coil 261-4 form V phase
  • the coil 261-5 and the coil 261-6 form W phase.
  • One sides of U phase, V phase and W phase are respectively connected to a predetermined switching element of an inverter circuit as a drive circuit and the other sides thereof are connected to each other.
  • Fig. 12 is a block diagram showing a circuit configuration of a drive control system of the brushless motor according to the related art.
  • the brushless motor includes the stator 204 which has the star-connected coils 261-1 to 261-6 (U phase, V phase and W phase) and a rotor (not shown).
  • An inverter circuit 269 and a control part 270 are provided to drive and control the brushless motor.
  • the control part 270 controls the rotation number of the brushless motor, etc., and includes an operation part 71 , a rotor position detection circuit 73, a rotation number detection circuit 74, a current detection circuit 75, an applied voltage setting circuit 76, a rotational direction setting circuit 78 and a control signal output circuit 279.
  • a trigger 8a which has a switch function for starting operation of the motor and setting rotation speed of the motor, or the like.
  • the applied voltage setting circuit 76 is activated by the trigger and a voltage signal corresponding to a trigger operation amount (stroke) is outputted to the operation part 71.
  • a forward/reverse switching lever 10 is provided for switching between a forward rotation and a reverse rotation of the motor and a setting signal for the rotational direction is outputted to the operation part 71 via the rotational direction setting circuit 78.
  • the rotor is rotated by the stator 204 having the star-connected coils 261-1 to 261-6 (U phase, V phase and W phase).
  • three position detection elements 33 are arranged at a predetermined interval (for example, an angle of 60°) in a circumferential direction to detect the rotation position of the rotor.
  • the rotor position detection circuit 73 Based on the rotation position detection signal from the position detection elements 33, the rotor position detection circuit 73 outputs a rotor position detection signal to the operation part 71, the rotation number detection circuit 74 outputs a rotor rotation number detection signal to the operation part 71 and the inverter circuit 269 is controlled by an output signal of the control signal output circuit 279 which is controlled by the operation part 71. In this way, the current flowing direction and time to each of the coils 261-1 to 261-6 configuring the stator windings (U phase, V phase and W phase) are controlled and thus the motor can be rotated.
  • Each gate of the six switching elements Ql to Q6 which can be connected in the bridge form is connected to the control signal output circuit 279 and each drain or each source of the switching elements Ql to Q6 is connected to the star-connected stator windings U phase, V phase and W phase.
  • the switching elements Ql to Q6 perform a switching operation in accordance with switching element driving signals (driving signals HI to H6) inputted from the control signal output circuit 279.
  • a direct current voltage of a battery 11 applied to the inverter circuit 269 is supplied to the stator windings U phase, V phase and W phase as three-phase (U phase, V phase and W phase) voltages Vu, Vv and Vw.
  • the operation part 71 supplies three negative power supply side switching elements Q4, Q5 and Q6 with pulse width modulation signals (PWM signals) as H4, H5 and H6, out of the switching element driving signals (three-phase signals) for driving each gate of the six switching elements Ql to Q6, in accordance with the trigger operation amount (stroke) of the trigger 8a. Further, the operation part 71 changes the pulse widths (duty ratios) of the PWM signals based on the detection signal of the trigger operation amount (stroke) of the trigger 8a. In this way, it is possible to adjust an amount of power supplied to the motor 3.
  • PWM signals pulse width modulation signals
  • a motor has been known in which two motor characteristics can be obtained for the rotation control of the motor by arranging a winding having two coils in each of the teeth and switching these coils as necessary.
  • a switching method there is an example where a pulling amount of the trigger has a threshold value or an example (see, JP-A-S59-59062) where a semiconductor element has been used although a specific embodiment is not disclosed.
  • the motor in which two motor characteristics can be obtained is difficult to handle since rotation number or torque of the motor rapidly changes at the moment of switching the windings. For example, in a case of a driver drill, the torque is rapidly increased and thus an operator cannot respond to the change. This can be a cause of a so-called "come out” that the tool is swung and separated from the screw, etc.
  • Aspect of the present invention has been made to solve the above-described problems and an object thereof is to provide an electric tool which is easy to handle and in which the motor characteristics can be gradually switched, in a case of including a motor in which two or more motor characteristics can be obtained by providing a winding having a plurality of coils in each of the teeth of the stator and changing the winding specifications as necessary.
  • the electric tool of the present invention has a configuration that winding specifications are changed via an intermediate motor characteristic between the motor characteristics for each winding specification and thus the rapid changes in the torque or rotation number at the moment of switching the winding specifications can be prevented.
  • another object of the present invention is to provide an electric tool which can be operated at an intermediate motor characteristic between the motor characteristics for each winding specification and which can respond to various situations, in a case of including a motor in which two or more motor characteristics can be obtained by providing a winding having a plurality of coils in each of the teeth of the stator and changing the winding specifications as necessary.
  • an electric tool comprising: a motor including a plurality of coils; an end tool configured to be driven by the motor; a drive circuit configured to supply a drive current to the plurality of coils; a control part configured to control the drive circuit; and a switch configured to control activation and rotation of the motor, characterized in that: the control part is configured to repeat switching of connection relationships between the plurality of coils.
  • a plurality of winding specifications may be realized by the switching of the connection relationships between the plurality of coils, and an intermediate motor characteristic between motor characteristics corresponding to each of the plurality of winding specifications may be obtained by repeating the switching of the connection relationships between the plurality of coils.
  • the plurality of coils may be connected in parallel.
  • the plurality of coils may be connected in series. Additionally, a plurality of winding specifications may be realized by the switching of the connection relationships between the plurality of coils, and the motor characteristic may be gradually changed from a first motor characteristic corresponding to a first winding specification among the plurality of winding specifications to a second motor characteristic corresponding to a second winding specification among the plurality of winding specifications by stepwisely changing an energization time of current respectively flowing through the plurality of coils and gradually changing ratio of the current flowing through each of the plurality of coils.
  • the electric tool may further include a switching element configured to switch on and off of the current respectively flowing through the plurality of coils, and a duty ratio of the switching element may be changed.
  • a plurality of winding specifications may be realized by the switching of the connection relationships between the plurality of coils, and the control part may be configured to change the winding specification via an intermediate motor characteristic between motor characteristics corresponding to each of the plurality of winding specifications, the intermediate motor characteristic obtained by repeating the switching of the connection relationships between the plurality of coils.
  • any combinations of the above components and a modification of the present invention to a method or a system are also effective as an embodiment of the present invention.
  • the motor characteristics can be gradually changed by changing the winding specifications via an intermediate motor characteristic between the motor characteristics corresponding to each winding specification and thus preventing the rapid changes in the torque or rotation number at the timing of changing the winding specifications, in a case of including a motor in which two or more motor characteristics can be obtained by providing a winding having a plurality of coils in each of the teeth of the stator and switching the winding specifications as necessary. Accordingly, it is possible to realize the electric tool which is capable of preventing "come out” due to the rapid changes in the torque or rotation number and which is easy to handle. Further, in addition to operating the electric tool at the motor characteristics corresponding to each winding specification, it is also possible to continuously operate the electric tool at the intermediate motor characteristic.
  • Fig. 1 is a side cross-sectional view showing an inner configuration of an impact driver as an electric tool according to an illustrative embodiment of the present invention
  • Fig. 2 is a side view showing an external appearance of the impact driver shown in Fig. 1 ;
  • Fig. 3 is a front view showing a stator of a motor shown in Fig. 1 ;
  • Fig. 4 is a flowchart showing a control procedure of the impact driver
  • Fig. 5-1 is a graph showing a variation of a current and a rotation number over time according to the illustrative embodiment
  • Fig. 5-2 is a graph showing an enlarged view of the variation of the current over time according to the illustrative embodiment
  • Fig. 6 is a block diagram showing a circuit configuration of a drive control system of a brushless motor according to the illustrative embodiment
  • Fig. 7 is a schematic block diagram showing a coil switching control procedure of the brushless motor according to the illustrative embodiment
  • Fig. 8 is a front view showing a first supply path of a drive voltage to a coil according to the illustrative embodiment
  • Fig. 9 is a front view showing a second supply path of the drive voltage to the coil according to the illustrative embodiment
  • Fig. 10 is a block diagram showing a circuit configuration of a drive control system of a brushless motor according to another illustrative embodiment of the present invention.
  • Fig. 11 is a front view showing a stator of a brushless motor in an electric tool according to a related art.
  • Fig. 12 is a block diagram showing a circuit configuration of a drive control system in the electric tool according to the related art.
  • Fig. 1 is a side cross-sectional view showing an inner configuration of an impact driver as an example of an electric tool according to the present invention
  • Fig. 2 is a side view showing an external appearance of the impact driver shown in Fig. 1.
  • a front-rear direction and an upper-lower direction are referred to the directions shown Fig. 1.
  • the impact driver 1 is powered by a rechargeable battery 11 and uses a motor 3 as a driving source to drive a rotary striking mechanism 21.
  • the impact driver 1 applies a rotating force and a striking force to an anvil 30 which is an output shaft.
  • the impact driver 1 intermittently transmits a rotational striking force to an end tool (not-illustrated) such as a driver bit to fasten a screw or a bolt.
  • the end tool is held on an mounting hole 30a which is covered by a sleeve 31.
  • the motor 3 is a brushless DC motor and is configured so that a rotor 5 is provided at an inner peripheral side and a stator 4 is provided at an outer peripheral side.
  • the rotor 5 is formed by integrating two sets of permanent magnets.
  • the stator 4 includes six slots. That is, the motor is a so called "four-pole six slots motor.”
  • the rotor 5 is provided at its outer peripheral surface with two N poles and two S poles, which are alternately arranged.
  • the stator 4 is provided with a stator winding 6 (to be described later). Further, the present invention is not limited to the four-pole six-slot motor but may be a motor having other number of poles and other number of slots.
  • the motor 3 is accommodated in a cylindrical trunk part 2a of a housing 2 which is substantially T-shaped, as seen from the side.
  • a rotation shaft 7 (which is integral with the rotor 5) of the motor 3 is rotatably held by a bearing 19a and a bearing 19b.
  • the bearing 19a is provided near the center of the trunk part 2a of the housing 2 and the bearing 19b is provided on a rear end side thereof.
  • a rotor fan 13 is provided in front of the motor 3.
  • the rotor fan 13 is mounted coaxial with the rotation shaft 7 and rotates in synchronous with the motor 3.
  • An inverter circuit board 12 for driving the motor 3 is arranged in the rear of the motor 3.
  • the rotor 5 forms a magnetic path of magnetic flux which is generated by a permanent magnet 5a.
  • the sleeve 36 can be formed by plastic or metal, for example. If the sleeve is formed by metal, it is desired that the metal is a non-magnetic material so as not to affect the magnetic path of the rotor 5. As necessary, a balance correcting groove is formed at an outer periphery of the sleeve 36.
  • the rotor fan 13 is integrally formed by plastic molding, for example. The rotor fan 13 is a so-called centrifugal fan which sucks air from an inner peripheral side at the rear side and discharges the air radially outwardly at the front side.
  • Airflow generated by the rotor fan 13 is introduced into the trunk part 2a through an air intake 17a and a slit 17b (Fig. 2) formed on a portion of the housing around the inverter circuit board 12. And then, the airflow mainly flows to pass through between the rotor 5 and the stator 4. In addition, the airflow is sucked form the rear side of the rotor fan 13 and flows in the radial direction of the rotor fan 13. The airflow is discharged to the outside of the housing 2 through a slit 18 (Fig. 2) formed on a portion of the housing around the rotor fan 13.
  • the inverter circuit board 12 is a double-sided board having an approximately circular shape substantially equal to an outer shape of the motor 3.
  • a plurality of switching elements 14 such as FETs and position detection elements 33 such as hall ICs are mounted on the inverter circuit board.
  • a plastic spacer 35 is provided between the rotor 5 and the bearing 19b.
  • the spacer 35 has an approximately cylindrical shape and defines a gap between the bearing 19b and the rotor 5. This gap is necessary for arranging the inverter circuit board 12 coaxially and forming a space which is necessary as a flow path of airflow to cool the switching elements 14.
  • a handle part 2b extends substantially at a right angle from and integrally with the trunk part 2a of the housing 2.
  • the trigger 8a is provided on an upper side region of the handle part 2b.
  • a switch circuit 8 is provided below the trigger 8a.
  • a control circuit board 9 is accommodated in a lower side region of the handle part 2b.
  • the control circuit board 9 has a function to control the speed of the motor 3 by an operation of pulling the trigger 8a.
  • the control circuit board 9 is electrically connected to the battery 11 and the trigger 8a.
  • the control circuit board 9 is connected to the inverter circuit board 12 via a signal line.
  • the battery 11 such as a nickel-cadmium battery, a lithium-ion battery is detachably mounted.
  • an illumination light 16 is provided at a front side of the trunk part 2a.
  • the rotary striking mechanism 21 includes a hammer case 15 which is integral with the front side of the trunk part 2a, a planetary gear reduction mechanism 22 which is connected to the rotation shaft 7, a spindle 27 and a hammer 24.
  • a rear end of the rotary striking mechanism is held by a bearing 20 and a front end thereof is held by a metal bearing 29 which is fixed to the hammer case 15.
  • the motor 3 starts to rotate in a direction set by a forward/reverse switching lever 10.
  • the rotating force of the motor 3 is decelerated by the planetary gear reduction mechanism 22 and transmitted to the spindle 27. Accordingly, the spindle 27 is rotationally driven in a predetermined speed.
  • the cam mechanism includes a V-shaped spindle cam groove 25 formed on an outer peripheral surface of the spindle 27, a hammer cam groove 28 formed on an inner peripheral surface of the hammer 24 and balls 26 engaged with these cam grooves 25, 28.
  • the hammer 24 is normally urged forward by a spring 23. In a still state, the hammer 24 is located at a position spaced away from an end surface of the anvil 30 by engagement of the balls 26 and the cam grooves 25, 28. And, convex portions (not shown) are symmetrically formed respectively in two locations on the rotation planes of the hammer 24 and the anvil 30 which are opposed to each other.
  • the rotation of the spindle is transmitted to the hammer 24 via the cam mechanism.
  • the convex portion of the hammer 24 is engaged with the convex portion of the anvil 30 before the hammer 24 makes a half turn, the anvil 30 is rotated.
  • the hammer 24 starts to retreat toward the motor 3 while compressing the spring 23 along the spindle cam groove 25 of the cam mechanism.
  • the hammer 24 As the convex portion of the hammer 24 gets beyond the convex portion of the anvil 30 by the retreating movement of the hammer 24 and thus engagement between these convex portions is released, the hammer 24 is rapidly accelerated in a rotation direction and also in a forward direction by the action of the cam mechanism and the elastic energy accumulated in the spring 23, in addition to the rotation force of the spindle 27. Further, the hammer 24 is moved in the forward direction by an urging force of the spring 23 and the convex portion of the hammer 24 is again engaged with the convex portion of the anvil 30. Thereby, the hammer starts to rotate integrally with the anvil.
  • the stator 4 includes a substantially cylindrical stator core 41 which is provided at its inner peripheral side with six teeth 44-1 to 44-6. Copper wire is wound around each of the teeth to form the stator winding 6 (Fig. 1).
  • the stator winding 6 includes coils 61-1 to 61-6 which are wound around inner peripheral sides of the teeth 44-1 to 44-6 and coils 62-1 to 62-6 which are wound around outer peripheral sides of the teeth.
  • a plurality of coils 61-1 , 62-1 is wound around the teeth 44-1
  • a plurality of coils 61-2, 62-2 is wound around the teeth 44-2
  • a plurality of coils 61-3, 62-3 is wound around the teeth 44-3
  • a plurality of coils 61-4, 62-4 is wound around the teeth 44-4
  • a plurality of coils 61-5, 62-5 is wound around the teeth 44-5
  • a plurality of coils 61-6, 62-6 is wound around the teeth 44-6.
  • the coils 61-1 to 61-6 are connected in a star-connection to form U phase, V phase and W phase.
  • the coils 62-1 to 62-6 are respectively connected in series with the star-connected coils 61-1 to 61-6 to form U2 phase, V2 phase and W2 phase.
  • Current is controlled at current energization interval of 120° electrical angle on the basis of position detection signals from the position detection elements 33 and supplied to the coils 61-1 to 61-6 (U phase, V phase and W phase) and the coils 62-1 to 62-6 (U2 phase, V2 phase and W2 phase) via the switching elements 14 (Fig. 1).
  • the rotor 5 which is integrated with the rotating shaft 7 is rotatably held at an inner peripheral side of the stator 4.
  • An inner peripheral side of the teeth 44-1 to 44-6 is located at a position slightly spaced apart from an outer peripheral surface of the cylindrical rotor 5.
  • an inner peripheral surface of the teeth is formed in a curved shape corresponding to an outer peripheral surface of the rotor 5.
  • the stator core 41 is a laminated iron core which is configured by punching plate materials such as high-silicon steel plate to form six teeth 44-1 to 44-6 as shown in Fig. 3 and laminating a plurality of the punched plate materials in an axial direction. Further, the stator core 41 is disposed at an inner side of a motor housing 42 having screw holes 43. Four screw holes 43 are intended to fix the inverter circuit board 12 to the motor housing 42.
  • a coil to be energized is selected from first coils (the coils 61-1 to 61-6) or a set of the first coils and second coils (the coils 62-1 to 62-6) which are connected in series.
  • Step 81 in Fig. 4 In a state where the battery 11 is mounted to the impact driver 1 and the trigger 8a is not pulled, energization to the coils of the motor 3 is stopped and thus rotation of the motor 3 is stopped (Step 81 in Fig. 4). In this state, an operator puts an end tool into contact with a fastening member such as a screw. And then, a control part 170 detects whether the trigger 8a is pulled by an operator or not, that is, whether the trigger switch is turned on or not (Step 82). When it is detected that the trigger switch is turned on, energization is performed in "winding specification 1" (high-rotation mode) in which the coils 61-1 to 61-6 are selected (Step 83). At this time, the switching elements (such as FET) Q7 to Q9 are in an ON-state. When it is detected at Step 82 that the trigger switch is not turned on, the control procedure returns to Step 81.
  • a control part 170 detects whether the trigger 8a is pulled
  • the control part 170 always monitors the change in motor current (stator winding current) due to load and determines whether the winding current is not less than a threshold current value 1 or not (Step 84). Specifically, such a monitoring is carried out in such a way that the current detection circuit 75 detects a current value in a current path returning to the battery 11 from an inverter circuit 169 (Fig. 6) and outputs the detected current value to the operation part 71.
  • the winding current is subjected to PWM control as described below, the winding current is varied in a pulsed form. Accordingly, an averaged winding current value is used when compared with the threshold current value.
  • energization is performed by switching between the "winding specification 1", in which only the first coils are energized, and "winding specification 2", in which the first coils and the second coils are connected in series and energized, by a set number of times (for example, ten times) for each predetermined time (for example, 0.1 second) using the switching elements Q7 to Q9.
  • this state refers to a "winding specification 3" (Step 85).
  • Step 85 the switching elements Q7 to Q9 are turned off and thus the control procedure is switched to an operation in the "winding specification 2" (high-torque mode) (Step 86).
  • Step 87 it is monitored whether the winding current is less than the threshold current value 2 or not.
  • the switching elements Q7 to Q9 are used to return the control procedure to Step 82 via the winding specification 3 (Step 88).
  • Fig. 5-1 is a graph schematically showing a variation of a current and a rotation number over time when a division number N of a switching operation period T in Fig. 4 is 1 and 10. As the division number N of the switching operation period T increases, more gradual characteristic change can be obtained.
  • Fig. 5-2 is an enlarged view of portion A in the graph showing the variation of the current over time when the division number N is 10. Control is performed in such a way that when the winding current reaches the threshold current value 1 during the operation in the "winding specification 1 ", the switching of the switching elements Q7 to Q9 is started but a conduction period (duty ratio D) is gradually reduced every time when the switching elements are turned on and off. For example, in a case where the switching operation period T is one second, the duty ratio of the switching elements Q7 to Q9 is 91% in the first interval of 0 to 0.1 second and the duty ratio is 82% in the next interval of 0.1 to 0.2 second. And then, the duty ratio is similarly reduced and thus the duty ratio is 9% in the final interval of 0.9 to 1.0 second.
  • Fig. 6 is a block diagram showing the configuration of the drive control system of the motor.
  • the motor 3 is configured by a three-phase brushless DC motor.
  • the brushless DC motor is a so-called inner rotor type and includes the rotor 5 (Fig. 1), the stator 4 and three position detection elements 33.
  • the rotor 5 includes the permanent magnet 5a (Fig. 1) which has plural sets (two sets in the present embodiment) of N-pole and S-pole.
  • the stator 4 includes the star-connected three-phase stator windings ⁇ U phase (coils 61-1, 61-2), V phase (coils 61-3, 61-4) and W phase (coils 61-5, 61 -6), and U2 phase (coils 62-1, 62-2), V2 phase (coils 62-3, 62-4) and W2 phase (coils 62-5, 62-6) which are connected in series with U phase, V phase and W phase ⁇ .
  • the position detection elements 33 are arranged at a predetermined interval (for example, an angle of 60°) in the circumferential direction to detect the rotation position of the rotor 5.
  • the current-carrying direction and time to the stator windings (U phase, V phase and W phase, and U2 Phase, V2 phase and W2 phase) are controlled based on the rotation position detection signal from the position detection elements 33.
  • Electronic elements included in the inverter circuit 169 as a drive circuit include six switching elements Ql to Q6 such as FETs which are connected to form a three-phase bridge. Furthermore, both ends of each coil of U2 Phase, V2 phase and W2 phase which are connected in series with each coil of U phase, V phase and W phase are short-circuited. Three switching elements Q7 to Q9 for stopping the excitation of these coils are provided. Switching element driving signals (driving signals HI 3 to HI 5) from a control signal output circuit 179 are inputted to each gate of the switching elements Q7 to Q9.
  • stator 4 When three switching elements Q7 to Q9 are turned on and thus conducted, the stator 4 is driven (excited) by the stator windings only composed of U phase (coils 61-1 , 61-2), V phase (coils 61-3, 61-4) and W phase (coils 61-5, 61-6).
  • the stator 4 is driven by the stator windings composed of U phase (coils 61-1, 61-2), V phase (coils 61-3, 61-4) and W phase (coils 61-5, 61-6), and U2 phase (coils 62-1, 62-2), V2 phase (coils 62-3, 62-4) and W2 phase (coils 62-5, 62-6) which are connected in series with U phase, V phase and W phase.
  • Each gate of the six switching elements Ql to Q6 which can be connected to form a bridge is connected to the control signal output circuit 179 mounted on the control circuit board 9 of Fig. 1. Further, each drain or each source of the switching elements Ql to Q6 is connected to the coils of U2 phase, V2 phase and W2 phase. Thereby, the switching elements Ql to Q6 perform a switching operation in accordance with switching element driving signals (driving signals HI to H6) inputted from the control signal output circuit 179.
  • a direct current voltage of the battery 11 applied to the inverter circuit 169 is supplied to the stator windings U phase, V phase and W phase as a three-phase (U phase, V phase and W phase) voltage Vu, Vv and Vw or supplied to the stator windings (U phase+U2 phase, V phase +V2 phase, W phase+W2 phase) as a three phase voltage.
  • the switching elements Q7 to Q9 are turned on and the stator 4 is excited only by the stator windings composed of the coils of (U phase, V phase and W phase).
  • the driving of the switching elements Q 1 to Q6 is controlled in such a way that the switching element driving signals for three negative power supply side switching elements Q4, Q5 and Q6 are supplied as pulse width modulation signals (PWM signals) H4, H5 and H6 and the operation part 71 mounted on the control circuit board 9 changes the pulse widths (duty ratios) of the PWM signals based on the detection signal of the current detection circuit 75.
  • PWM signals pulse width modulation signals
  • the driving of the switching elements Ql to Q6 is controlled in such a way that the switching element driving signals for three negative power supply side switching elements Q4, Q5 and Q6 are supplied as pulse width modulation signals (PWM signals) H4, H5 and H6 and the operation part 71 mounted on the control circuit board 9 changes the pulse widths (duty ratios) of the PWM signals based on the detection signal of the current detection circuit 75. In this way, a power supply amount to the motor 3 is adjusted.
  • PWM signals pulse width modulation signals
  • a control switching procedure of the motor 3 is described with reference to Figs. 6 and 7.
  • the winding current detected by the current detection circuit 75 is compared with the threshold current value set at a winding switching setting circuit 77 and then inputted to the operation part 71.
  • a control is performed in such a way that "any one of the switching elements Ql to Q3 and any one of the switching elements Q4 to Q6 are turned on", as indicated in Box 88 of Fig. 7. That is, this control is intended to excite the stator 4 by the stator windings in which each coil of U phase, V phase and W phase and each coil of U2 phase, V2 phase and W2 phase are connected in series with each other, as indicated in Box 89. As an example, this is effective in a case where a large torque is necessary, as in the second half of the wood screw tightening work (winding specification 2).
  • Fig. 8 shows the path of the power feeding to the coil in a case (Winding specification 2) where the current value of the stator winding is greater than the threshold value in the present embodiment.
  • the drive current at a certain rotational position of the rotor 5 flows to U2 phase (62-1, 62-2) as in a direction from (1) to (2), then flows to the serial connected U phase (61-1, 61-2) as in a direction from (3) to (4), then flows toward V phase (61-3, 61-4) connected to (4) as in a direction from (5) to (6), and then flows to the serial connected V2 phase (62-3, 62-4) as in a direction from (7) to (8).
  • the present invention is characterized by that the drive current flows in series to both the outer peripheral side coils 62-1 to 62-4 (U2 phase, V2 phase) and the inner peripheral side coils 61-1 to 61-4 (U phase, V phase) which are wound around the teeth 44-1 to 44-4. Accordingly, in a state where the current value of the stator winding is greater than the threshold value, each of the teeth 44-1 to 44-6 is excited by both the inner peripheral side coils 61-1 to 61-6 and the outer peripheral side coils 62-1 to 62-6.
  • the motor characteristic can be changed via an intermediate motor characteristic between the winding specification 1 and the winding specification 2 by repeatedly turning on/off the switching elements Q7 to Q9 for every set time (for example, 0.1 second) when changing between the winding specification 1 and the winding specification 2 is performed, the rapid changes in the torque or the rotation number can be prevented.
  • the stator winding 6 has a plurality of winding specifications (for example, winding specification 1 and winding specification 2) by providing a plurality of coils to each of the teeth of the stator core 41. Further, the operation part 71 changes the energization to the plurality of coils in accordance with the current flowing through the motor 3, so that the winding specifications can be changed via an intermediate motor characteristic (winding specification 3) between the motor characteristics for each winding specification. Accordingly, the rapid changes in the torque or rotation number at the moment of changing the winding specifications can be suppressed and thus it is possible to prevent the come out due to the sharp changes in the torque or rotation number.
  • winding specification 1 and winding specification 2 by providing a plurality of coils to each of the teeth of the stator core 41.
  • the operation part 71 changes the energization to the plurality of coils in accordance with the current flowing through the motor 3, so that the winding specifications can be changed via an intermediate motor characteristic (winding specification 3) between the motor characteristics for each winding specification. According
  • Fig. 10 is a block diagram showing a circuit configuration of a drive control system of the brushless motor according to another embodiment of the present invention.
  • the start-connected three-phase stator windings of the stator 4 are connected so that a plurality of coils ⁇ (a set of coils 61-1, 61-2 and coils 62-1 , 62-2) (a set of coils 61-3, 61-4 and coils 62-3, 62-4) (a set of coils 61-5, 61-6 and coils 62-5, 62-6) ⁇ of each phase can be connected in parallel.
  • an inverter circuit 69 is further provided with switching elements Q7 to Q12, in addition to the switching elements Ql to Q6.
  • a control part 70 is controlled to cause a control signal output circuit 79 to generate switching element driving signals (driving signals HI to HI 2) and respectively outputs the switching element driving signals to the gates of the switching elements Ql to Q12.
  • the motor is driven by the stator winding which is only composed of U phase (coils 61-1, 61-2), V phase (coils 61-3, 61-4) and W phase (coils 61-5, 61-6). That is, the motor 3 is driven in high-speed rotation by the switching operation of the switching elements Ql to Q6.
  • the switching elements Q7 to 12 are maintained in an off-state.
  • the motor is energized in a state where U phase (coils 61-1, 61-2), V phase (coils 61-3,
  • a set of the switching elements Ql and Q7, a set of the switching elements Q2 and Q8, a set of the switching elements Q3 and Q9, a set of the switching elements Q4 and Q10, a set of the switching elements Q5 and Ql l and a set of the switching elements Q6 and Q12 perform an operation to turn on/off.
  • the duty ratio of the switching elements Q7 to Q12 is gradually increased in the transition period from the winding specification 1 to the winding specification 2 and thus becomes 100% at the end of the transition period.
  • the switching elements Q7 to Q12 are turned on/off in pair with the switching elements Ql to Q6.
  • the drive control system of the brushless motor in Fig. 10 has the same effects as the case of Fig. 6 described above.
  • the motor characteristics of the winding specification 1 and the winding specification 2 may be realized in such a way that the number of turns of the coils of U phase, V phase and W phase is set different from that of the coils of Ul phase, VI phase and Wl phase, any one group of the switching elements Ql to Q6 or the switching elements Q7 to Q12 is selected and any one of the coils of U phase, V phase and W phase or the coils of Ul phase, VI phase and Wl phase is used in a switching manner.
  • the brushless motor may be continuously operated by the intermediate motor characteristic.
  • stator winding in Fig. 3 has a winding configuration in which two coils are provided to each of the teeth
  • the present invention may have a winding configuration where three or more coils are provided to each of the teeth.
  • three or more motor characteristics can be realized by switching the connection of each coil in series or in parallel, and the motor characteristics can be gradually switched.
  • the present invention is not limited to the impact driver, but may be applicable to various electric tools (for example, drill, etc.) which require two or more motor characteristics.
  • an electric tool which is easy to handle and in which the motor characteristics can be gradually switched, in a case of including a motor in which two or more motor characteristics can be obtained by providing a winding having a plurality of coils in each of the teeth of the stator and changing the winding specifications as necessary.

Abstract

An electric tool including: a motor including a plurality of coils; an end tool configured to be driven by the motor; a drive circuit configured to supply a drive current to the plurality of coils; a control part configured to control the drive circuit; and a switch configured to control activation and rotation of the motor, characterized in that: the control part is configured to repeat switching of connection relationships between the plurality of coils.

Description

DESCRIPTION
Title of Invention
ELECTRIC TOOL
Technical Field
The present invention relates to an electric tool using a brushless motor and, more particularly, to an electric tool in which motor characteristics can be changed in accordance with working conditions in the drive control of a motor having a winding including a plurality of coils (a plurality of winding specifications).
Background Art
Recently, in an electric tool where an end tool such as a drill or a driver is rotationally driven by a motor to perform a desired work, a brushless motor has been used. For example, the brushless motor refers to a DC (Direct Current) motor which has no brush (brush for rectification). The brushless motor uses a coil (winding) at a stator side and a permanent magnet at a rotor side and has a configuration that power driven by an inverter is sequentially energized to a predetermined coil to rotate the rotor. In the brushless motor, a switching element for turning on/off the energization of coils wound around the stator is arranged on a circuit board which is provided near the motor. For example, the switching element is arranged on a substantially circular circuit board which is attached to a rear side (a side opposite to the end tool) of the motor.
Fig. 11 shows a configuration of a stator part of a brushless motor which is used in an electric tool according to a related art. A stator 204 includes a stator core 241 and coils 261-1 to 261-6 wound around a plurality of teeth 244-1 to 244-6 which are formed at the stator core 241. The stator core 241 is manufactured by stacking a plurality of thin metal plates such as a steel plate in an axial direction and has a substantially cylindrical outer shape. In the stator core, a plurality of teeth 244-1 to 244-6 is formed to extend inward in a radial direction from a cylindrical part of the stator core at predetermined intervals in a circumferential direction. Innermost peripheral sides of these teeth 244-1 to 244-6 respectively have an arc shape so as to be slightly spaced apart from a cylindrical rotor (not shown). Copper wire is wound around each of the teeth 244-1 to 244-6 by a predetermined number of times to form the coils 261-1 to 261 -6. Although connection wires between the coils 261-1 to 261-6 are not shown in Fig. 11, opposing coils are connected to each other. The coil 261-1 and the coil 261-2 form U phase, the coil 261-3 and the coil 261-4 form V phase and the coil 261-5 and the coil 261-6 form W phase. One sides of U phase, V phase and W phase are respectively connected to a predetermined switching element of an inverter circuit as a drive circuit and the other sides thereof are connected to each other.
Fig. 12 is a block diagram showing a circuit configuration of a drive control system of the brushless motor according to the related art. The brushless motor includes the stator 204 which has the star-connected coils 261-1 to 261-6 (U phase, V phase and W phase) and a rotor (not shown). An inverter circuit 269 and a control part 270 are provided to drive and control the brushless motor.
As electronic elements included in the inverter circuit 269 as a drive circuit, there are six switching elements Ql to Q6 such as FETs (Field Effect Transistor) which are connected in three-phase bridge form. The control part 270 controls the rotation number of the brushless motor, etc., and includes an operation part 71 , a rotor position detection circuit 73, a rotation number detection circuit 74, a current detection circuit 75, an applied voltage setting circuit 76, a rotational direction setting circuit 78 and a control signal output circuit 279.
Further, a trigger 8a is provided which has a switch function for starting operation of the motor and setting rotation speed of the motor, or the like. The applied voltage setting circuit 76 is activated by the trigger and a voltage signal corresponding to a trigger operation amount (stroke) is outputted to the operation part 71. A forward/reverse switching lever 10 is provided for switching between a forward rotation and a reverse rotation of the motor and a setting signal for the rotational direction is outputted to the operation part 71 via the rotational direction setting circuit 78.
The rotor is rotated by the stator 204 having the star-connected coils 261-1 to 261-6 (U phase, V phase and W phase). In the vicinity of the rotor, three position detection elements 33 are arranged at a predetermined interval (for example, an angle of 60°) in a circumferential direction to detect the rotation position of the rotor. Based on the rotation position detection signal from the position detection elements 33, the rotor position detection circuit 73 outputs a rotor position detection signal to the operation part 71, the rotation number detection circuit 74 outputs a rotor rotation number detection signal to the operation part 71 and the inverter circuit 269 is controlled by an output signal of the control signal output circuit 279 which is controlled by the operation part 71. In this way, the current flowing direction and time to each of the coils 261-1 to 261-6 configuring the stator windings (U phase, V phase and W phase) are controlled and thus the motor can be rotated.
Each gate of the six switching elements Ql to Q6 which can be connected in the bridge form is connected to the control signal output circuit 279 and each drain or each source of the switching elements Ql to Q6 is connected to the star-connected stator windings U phase, V phase and W phase. Thereby, the switching elements Ql to Q6 perform a switching operation in accordance with switching element driving signals (driving signals HI to H6) inputted from the control signal output circuit 279. In this way, a direct current voltage of a battery 11 applied to the inverter circuit 269 is supplied to the stator windings U phase, V phase and W phase as three-phase (U phase, V phase and W phase) voltages Vu, Vv and Vw.
The operation part 71 supplies three negative power supply side switching elements Q4, Q5 and Q6 with pulse width modulation signals (PWM signals) as H4, H5 and H6, out of the switching element driving signals (three-phase signals) for driving each gate of the six switching elements Ql to Q6, in accordance with the trigger operation amount (stroke) of the trigger 8a. Further, the operation part 71 changes the pulse widths (duty ratios) of the PWM signals based on the detection signal of the trigger operation amount (stroke) of the trigger 8a. In this way, it is possible to adjust an amount of power supplied to the motor 3.
Further, a motor has been known in which two motor characteristics can be obtained for the rotation control of the motor by arranging a winding having two coils in each of the teeth and switching these coils as necessary. As a switching method, there is an example where a pulling amount of the trigger has a threshold value or an example (see, JP-A-S59-59062) where a semiconductor element has been used although a specific embodiment is not disclosed.
Summary' of Invention
Technical Problem
The motor in which two motor characteristics can be obtained is difficult to handle since rotation number or torque of the motor rapidly changes at the moment of switching the windings. For example, in a case of a driver drill, the torque is rapidly increased and thus an operator cannot respond to the change. This can be a cause of a so-called "come out" that the tool is swung and separated from the screw, etc.
Aspect of the present invention has been made to solve the above-described problems and an object thereof is to provide an electric tool which is easy to handle and in which the motor characteristics can be gradually switched, in a case of including a motor in which two or more motor characteristics can be obtained by providing a winding having a plurality of coils in each of the teeth of the stator and changing the winding specifications as necessary. The electric tool of the present invention has a configuration that winding specifications are changed via an intermediate motor characteristic between the motor characteristics for each winding specification and thus the rapid changes in the torque or rotation number at the moment of switching the winding specifications can be prevented.
In addition, another object of the present invention is to provide an electric tool which can be operated at an intermediate motor characteristic between the motor characteristics for each winding specification and which can respond to various situations, in a case of including a motor in which two or more motor characteristics can be obtained by providing a winding having a plurality of coils in each of the teeth of the stator and changing the winding specifications as necessary.
Solution to Problem
According to an aspect of the invention, there is provided an electric tool comprising: a motor including a plurality of coils; an end tool configured to be driven by the motor; a drive circuit configured to supply a drive current to the plurality of coils; a control part configured to control the drive circuit; and a switch configured to control activation and rotation of the motor, characterized in that: the control part is configured to repeat switching of connection relationships between the plurality of coils.
Additionally, a plurality of winding specifications may be realized by the switching of the connection relationships between the plurality of coils, and an intermediate motor characteristic between motor characteristics corresponding to each of the plurality of winding specifications may be obtained by repeating the switching of the connection relationships between the plurality of coils.
Additionally, the plurality of coils may be connected in parallel.
Additionally, the plurality of coils may be connected in series. Additionally, a plurality of winding specifications may be realized by the switching of the connection relationships between the plurality of coils, and the motor characteristic may be gradually changed from a first motor characteristic corresponding to a first winding specification among the plurality of winding specifications to a second motor characteristic corresponding to a second winding specification among the plurality of winding specifications by stepwisely changing an energization time of current respectively flowing through the plurality of coils and gradually changing ratio of the current flowing through each of the plurality of coils.
Additionally, the electric tool may further include a switching element configured to switch on and off of the current respectively flowing through the plurality of coils, and a duty ratio of the switching element may be changed.
Additionally, a plurality of winding specifications may be realized by the switching of the connection relationships between the plurality of coils, and the control part may be configured to change the winding specification via an intermediate motor characteristic between motor characteristics corresponding to each of the plurality of winding specifications, the intermediate motor characteristic obtained by repeating the switching of the connection relationships between the plurality of coils.
Further, any combinations of the above components and a modification of the present invention to a method or a system are also effective as an embodiment of the present invention.
Advantageous Effects of Invention According to the electric tool of the aspects of the present invention, the motor characteristics can be gradually changed by changing the winding specifications via an intermediate motor characteristic between the motor characteristics corresponding to each winding specification and thus preventing the rapid changes in the torque or rotation number at the timing of changing the winding specifications, in a case of including a motor in which two or more motor characteristics can be obtained by providing a winding having a plurality of coils in each of the teeth of the stator and switching the winding specifications as necessary. Accordingly, it is possible to realize the electric tool which is capable of preventing "come out" due to the rapid changes in the torque or rotation number and which is easy to handle. Further, in addition to operating the electric tool at the motor characteristics corresponding to each winding specification, it is also possible to continuously operate the electric tool at the intermediate motor characteristic.
Brief Description of Drawings
Fig. 1 is a side cross-sectional view showing an inner configuration of an impact driver as an electric tool according to an illustrative embodiment of the present invention;
Fig. 2 is a side view showing an external appearance of the impact driver shown in Fig. 1 ;
Fig. 3 is a front view showing a stator of a motor shown in Fig. 1 ;
Fig. 4 is a flowchart showing a control procedure of the impact driver;
Fig. 5-1 is a graph showing a variation of a current and a rotation number over time according to the illustrative embodiment;
Fig. 5-2 is a graph showing an enlarged view of the variation of the current over time according to the illustrative embodiment;
Fig. 6 is a block diagram showing a circuit configuration of a drive control system of a brushless motor according to the illustrative embodiment;
Fig. 7 is a schematic block diagram showing a coil switching control procedure of the brushless motor according to the illustrative embodiment;
Fig. 8 is a front view showing a first supply path of a drive voltage to a coil according to the illustrative embodiment;
Fig. 9 is a front view showing a second supply path of the drive voltage to the coil according to the illustrative embodiment;
Fig. 10 is a block diagram showing a circuit configuration of a drive control system of a brushless motor according to another illustrative embodiment of the present invention;
Fig. 11 is a front view showing a stator of a brushless motor in an electric tool according to a related art; and
Fig. 12 is a block diagram showing a circuit configuration of a drive control system in the electric tool according to the related art.
Description of Embodiment
Hereinafter, a preferred embodiment of the present invention will be described by referring to the accompanying drawings. The same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the repetitive description thereof will be omitted. Further, the embodiment is illustrative and not intended to limit the present invention. It should be noted that all the features and their combinations described in the embodiment are not necessarily considered as an essential part of the present invention. Fig. 1 is a side cross-sectional view showing an inner configuration of an impact driver as an example of an electric tool according to the present invention and Fig. 2 is a side view showing an external appearance of the impact driver shown in Fig. 1. Further, as used herein, a front-rear direction and an upper-lower direction are referred to the directions shown Fig. 1.
The impact driver 1 is powered by a rechargeable battery 11 and uses a motor 3 as a driving source to drive a rotary striking mechanism 21. The impact driver 1 applies a rotating force and a striking force to an anvil 30 which is an output shaft. The impact driver 1 intermittently transmits a rotational striking force to an end tool (not-illustrated) such as a driver bit to fasten a screw or a bolt. The end tool is held on an mounting hole 30a which is covered by a sleeve 31.
The motor 3 is a brushless DC motor and is configured so that a rotor 5 is provided at an inner peripheral side and a stator 4 is provided at an outer peripheral side. The rotor 5 is formed by integrating two sets of permanent magnets. The stator 4 includes six slots. That is, the motor is a so called "four-pole six slots motor." The rotor 5 is provided at its outer peripheral surface with two N poles and two S poles, which are alternately arranged. The stator 4 is provided with a stator winding 6 (to be described later). Further, the present invention is not limited to the four-pole six-slot motor but may be a motor having other number of poles and other number of slots.
The motor 3 is accommodated in a cylindrical trunk part 2a of a housing 2 which is substantially T-shaped, as seen from the side. A rotation shaft 7 (which is integral with the rotor 5) of the motor 3 is rotatably held by a bearing 19a and a bearing 19b. The bearing 19a is provided near the center of the trunk part 2a of the housing 2 and the bearing 19b is provided on a rear end side thereof. A rotor fan 13 is provided in front of the motor 3. The rotor fan 13 is mounted coaxial with the rotation shaft 7 and rotates in synchronous with the motor 3. An inverter circuit board 12 for driving the motor 3 is arranged in the rear of the motor 3.
Between the rotor 5 and the bearing 19a, a sleeve 36 and the rotor fan 13 are mounted coaxially with the rotation shaft 7. The rotor 5 forms a magnetic path of magnetic flux which is generated by a permanent magnet 5a. The sleeve 36 can be formed by plastic or metal, for example. If the sleeve is formed by metal, it is desired that the metal is a non-magnetic material so as not to affect the magnetic path of the rotor 5. As necessary, a balance correcting groove is formed at an outer periphery of the sleeve 36. The rotor fan 13 is integrally formed by plastic molding, for example. The rotor fan 13 is a so-called centrifugal fan which sucks air from an inner peripheral side at the rear side and discharges the air radially outwardly at the front side.
Airflow generated by the rotor fan 13 is introduced into the trunk part 2a through an air intake 17a and a slit 17b (Fig. 2) formed on a portion of the housing around the inverter circuit board 12. And then, the airflow mainly flows to pass through between the rotor 5 and the stator 4. In addition, the airflow is sucked form the rear side of the rotor fan 13 and flows in the radial direction of the rotor fan 13. The airflow is discharged to the outside of the housing 2 through a slit 18 (Fig. 2) formed on a portion of the housing around the rotor fan 13. The inverter circuit board 12 is a double-sided board having an approximately circular shape substantially equal to an outer shape of the motor 3. A plurality of switching elements 14 such as FETs and position detection elements 33 such as hall ICs are mounted on the inverter circuit board.
A plastic spacer 35 is provided between the rotor 5 and the bearing 19b. The spacer 35 has an approximately cylindrical shape and defines a gap between the bearing 19b and the rotor 5. This gap is necessary for arranging the inverter circuit board 12 coaxially and forming a space which is necessary as a flow path of airflow to cool the switching elements 14.
A handle part 2b extends substantially at a right angle from and integrally with the trunk part 2a of the housing 2. The trigger 8a is provided on an upper side region of the handle part 2b. A switch circuit 8 is provided below the trigger 8a. A control circuit board 9 is accommodated in a lower side region of the handle part 2b. The control circuit board 9 has a function to control the speed of the motor 3 by an operation of pulling the trigger 8a. The control circuit board 9 is electrically connected to the battery 11 and the trigger 8a. The control circuit board 9 is connected to the inverter circuit board 12 via a signal line. Below the handle part 2b, the battery 11 such as a nickel-cadmium battery, a lithium-ion battery is detachably mounted. Further, an illumination light 16 is provided at a front side of the trunk part 2a.
The rotary striking mechanism 21 includes a hammer case 15 which is integral with the front side of the trunk part 2a, a planetary gear reduction mechanism 22 which is connected to the rotation shaft 7, a spindle 27 and a hammer 24. A rear end of the rotary striking mechanism is held by a bearing 20 and a front end thereof is held by a metal bearing 29 which is fixed to the hammer case 15. As the trigger 8a is pulled and thus the motor 3 is started, the motor 3 starts to rotate in a direction set by a forward/reverse switching lever 10. The rotating force of the motor 3 is decelerated by the planetary gear reduction mechanism 22 and transmitted to the spindle 27. Accordingly, the spindle 27 is rotationally driven in a predetermined speed. Here, the spindle 27 and the hammer 24 are connected to each other by a cam mechanism. The cam mechanism includes a V-shaped spindle cam groove 25 formed on an outer peripheral surface of the spindle 27, a hammer cam groove 28 formed on an inner peripheral surface of the hammer 24 and balls 26 engaged with these cam grooves 25, 28.
The hammer 24 is normally urged forward by a spring 23. In a still state, the hammer 24 is located at a position spaced away from an end surface of the anvil 30 by engagement of the balls 26 and the cam grooves 25, 28. And, convex portions (not shown) are symmetrically formed respectively in two locations on the rotation planes of the hammer 24 and the anvil 30 which are opposed to each other.
As the spindle 27 is rotationally driven, the rotation of the spindle is transmitted to the hammer 24 via the cam mechanism. At this time, since the convex portion of the hammer 24 is engaged with the convex portion of the anvil 30 before the hammer 24 makes a half turn, the anvil 30 is rotated. However, in a case where the relative rotation occurs between the spindle 27 and the hammer 24 by an engagement reaction force at that time, the hammer 24 starts to retreat toward the motor 3 while compressing the spring 23 along the spindle cam groove 25 of the cam mechanism. As the convex portion of the hammer 24 gets beyond the convex portion of the anvil 30 by the retreating movement of the hammer 24 and thus engagement between these convex portions is released, the hammer 24 is rapidly accelerated in a rotation direction and also in a forward direction by the action of the cam mechanism and the elastic energy accumulated in the spring 23, in addition to the rotation force of the spindle 27. Further, the hammer 24 is moved in the forward direction by an urging force of the spring 23 and the convex portion of the hammer 24 is again engaged with the convex portion of the anvil 30. Thereby, the hammer starts to rotate integrally with the anvil. At this time, since a powerful rotational striking force is applied to the anvil 30, the rotational striking force is transmitted to a screw via an end tool (not shown) mounted on the mounting hole 30a of the anvil 30. Thereafter, the same operation is repeatedly performed and thus the rotational striking force is intermittently and repeatedly transmitted from the end tool to the screw. Thereby, the screw can be screwed into a member to be fastened (not shown) such as wood, for example.
Next, the arrangement of a winding for the stator 4 is described with reference to Fig. 3. The stator 4 includes a substantially cylindrical stator core 41 which is provided at its inner peripheral side with six teeth 44-1 to 44-6. Copper wire is wound around each of the teeth to form the stator winding 6 (Fig. 1). In the present embodiment, the stator winding 6 includes coils 61-1 to 61-6 which are wound around inner peripheral sides of the teeth 44-1 to 44-6 and coils 62-1 to 62-6 which are wound around outer peripheral sides of the teeth. Specifically, a plurality of coils 61-1 , 62-1 is wound around the teeth 44-1, a plurality of coils 61-2, 62-2 is wound around the teeth 44-2, a plurality of coils 61-3, 62-3 is wound around the teeth 44-3, a plurality of coils 61-4, 62-4 is wound around the teeth 44-4, a plurality of coils 61-5, 62-5 is wound around the teeth 44-5, a plurality of coils 61-6, 62-6 is wound around the teeth 44-6.
As will be described later in Fig. 6, the coils 61-1 to 61-6 are connected in a star-connection to form U phase, V phase and W phase. The coils 62-1 to 62-6 are respectively connected in series with the star-connected coils 61-1 to 61-6 to form U2 phase, V2 phase and W2 phase. Current is controlled at current energization interval of 120° electrical angle on the basis of position detection signals from the position detection elements 33 and supplied to the coils 61-1 to 61-6 (U phase, V phase and W phase) and the coils 62-1 to 62-6 (U2 phase, V2 phase and W2 phase) via the switching elements 14 (Fig. 1).
Although not shown in Fig. 3, the rotor 5 which is integrated with the rotating shaft 7 is rotatably held at an inner peripheral side of the stator 4. An inner peripheral side of the teeth 44-1 to 44-6 is located at a position slightly spaced apart from an outer peripheral surface of the cylindrical rotor 5. Also, an inner peripheral surface of the teeth is formed in a curved shape corresponding to an outer peripheral surface of the rotor 5.
Preferably, the stator core 41 is a laminated iron core which is configured by punching plate materials such as high-silicon steel plate to form six teeth 44-1 to 44-6 as shown in Fig. 3 and laminating a plurality of the punched plate materials in an axial direction. Further, the stator core 41 is disposed at an inner side of a motor housing 42 having screw holes 43. Four screw holes 43 are intended to fix the inverter circuit board 12 to the motor housing 42.
Next, a control procedure of the impact driver 1 according to the present embodiment is described with reference to the flowchart of Fig. 4 and Figs. 5 and 6. In the below, a bolting is described as an example. In the impact driver 1 , a coil to be energized is selected from first coils (the coils 61-1 to 61-6) or a set of the first coils and second coils (the coils 62-1 to 62-6) which are connected in series.
In a state where the battery 11 is mounted to the impact driver 1 and the trigger 8a is not pulled, energization to the coils of the motor 3 is stopped and thus rotation of the motor 3 is stopped (Step 81 in Fig. 4). In this state, an operator puts an end tool into contact with a fastening member such as a screw. And then, a control part 170 detects whether the trigger 8a is pulled by an operator or not, that is, whether the trigger switch is turned on or not (Step 82). When it is detected that the trigger switch is turned on, energization is performed in "winding specification 1" (high-rotation mode) in which the coils 61-1 to 61-6 are selected (Step 83). At this time, the switching elements (such as FET) Q7 to Q9 are in an ON-state. When it is detected at Step 82 that the trigger switch is not turned on, the control procedure returns to Step 81.
The control part 170 always monitors the change in motor current (stator winding current) due to load and determines whether the winding current is not less than a threshold current value 1 or not (Step 84). Specifically, such a monitoring is carried out in such a way that the current detection circuit 75 detects a current value in a current path returning to the battery 11 from an inverter circuit 169 (Fig. 6) and outputs the detected current value to the operation part 71. When the winding current is subjected to PWM control as described below, the winding current is varied in a pulsed form. Accordingly, an averaged winding current value is used when compared with the threshold current value.
When the winding current reaches a value not less than the threshold current value 1 , energization is performed by switching between the "winding specification 1", in which only the first coils are energized, and "winding specification 2", in which the first coils and the second coils are connected in series and energized, by a set number of times (for example, ten times) for each predetermined time (for example, 0.1 second) using the switching elements Q7 to Q9. In the following description, this state refers to a "winding specification 3" (Step 85).
After Step 85, the switching elements Q7 to Q9 are turned off and thus the control procedure is switched to an operation in the "winding specification 2" (high-torque mode) (Step 86).
During the operation in the "winding specification 2", it is monitored whether the winding current is less than the threshold current value 2 or not (Step 87). When it is monitored that the winding current is less than the threshold current value 2, the switching elements Q7 to Q9 are used to return the control procedure to Step 82 via the winding specification 3 (Step 88).
As described above, since changing between the high-speed mode and the high-torque mode can be gradually performed in an automatic manner by using the switching elements Q7 to Q9 in the present embodiment, it is possible to prevent the come out which is liable to occur at the moment of switching the motor characteristics.
Fig. 5-1 is a graph schematically showing a variation of a current and a rotation number over time when a division number N of a switching operation period T in Fig. 4 is 1 and 10. As the division number N of the switching operation period T increases, more gradual characteristic change can be obtained.
Fig. 5-2 is an enlarged view of portion A in the graph showing the variation of the current over time when the division number N is 10. Control is performed in such a way that when the winding current reaches the threshold current value 1 during the operation in the "winding specification 1 ", the switching of the switching elements Q7 to Q9 is started but a conduction period (duty ratio D) is gradually reduced every time when the switching elements are turned on and off. For example, in a case where the switching operation period T is one second, the duty ratio of the switching elements Q7 to Q9 is 91% in the first interval of 0 to 0.1 second and the duty ratio is 82% in the next interval of 0.1 to 0.2 second. And then, the duty ratio is similarly reduced and thus the duty ratio is 9% in the final interval of 0.9 to 1.0 second.
Next, a configuration and operation of the drive control system of the motor 3 will be described with reference to Fig. 6. Fig. 6 is a block diagram showing the configuration of the drive control system of the motor. In the present embodiment, the motor 3 is configured by a three-phase brushless DC motor. The brushless DC motor is a so-called inner rotor type and includes the rotor 5 (Fig. 1), the stator 4 and three position detection elements 33. The rotor 5 includes the permanent magnet 5a (Fig. 1) which has plural sets (two sets in the present embodiment) of N-pole and S-pole. The stator 4 includes the star-connected three-phase stator windings {U phase (coils 61-1, 61-2), V phase (coils 61-3, 61-4) and W phase (coils 61-5, 61 -6), and U2 phase (coils 62-1, 62-2), V2 phase (coils 62-3, 62-4) and W2 phase (coils 62-5, 62-6) which are connected in series with U phase, V phase and W phase}. The position detection elements 33 are arranged at a predetermined interval (for example, an angle of 60°) in the circumferential direction to detect the rotation position of the rotor 5. The current-carrying direction and time to the stator windings (U phase, V phase and W phase, and U2 Phase, V2 phase and W2 phase) are controlled based on the rotation position detection signal from the position detection elements 33.
Electronic elements included in the inverter circuit 169 as a drive circuit include six switching elements Ql to Q6 such as FETs which are connected to form a three-phase bridge. Furthermore, both ends of each coil of U2 Phase, V2 phase and W2 phase which are connected in series with each coil of U phase, V phase and W phase are short-circuited. Three switching elements Q7 to Q9 for stopping the excitation of these coils are provided. Switching element driving signals (driving signals HI 3 to HI 5) from a control signal output circuit 179 are inputted to each gate of the switching elements Q7 to Q9. When three switching elements Q7 to Q9 are turned on and thus conducted, the stator 4 is driven (excited) by the stator windings only composed of U phase (coils 61-1 , 61-2), V phase (coils 61-3, 61-4) and W phase (coils 61-5, 61-6). Further, when three switching elements Q7 to Q9 are turned off and thus non-conducted, the stator 4 is driven by the stator windings composed of U phase (coils 61-1, 61-2), V phase (coils 61-3, 61-4) and W phase (coils 61-5, 61-6), and U2 phase (coils 62-1, 62-2), V2 phase (coils 62-3, 62-4) and W2 phase (coils 62-5, 62-6) which are connected in series with U phase, V phase and W phase.
Each gate of the six switching elements Ql to Q6 which can be connected to form a bridge is connected to the control signal output circuit 179 mounted on the control circuit board 9 of Fig. 1. Further, each drain or each source of the switching elements Ql to Q6 is connected to the coils of U2 phase, V2 phase and W2 phase. Thereby, the switching elements Ql to Q6 perform a switching operation in accordance with switching element driving signals (driving signals HI to H6) inputted from the control signal output circuit 179. In this way, a direct current voltage of the battery 11 applied to the inverter circuit 169 is supplied to the stator windings U phase, V phase and W phase as a three-phase (U phase, V phase and W phase) voltage Vu, Vv and Vw or supplied to the stator windings (U phase+U2 phase, V phase +V2 phase, W phase+W2 phase) as a three phase voltage.
If the current value of the stator windings (U phase, V phase and W phase) is less than the threshold value, as described in the flowchart of Fig. 4, the switching elements Q7 to Q9 are turned on and the stator 4 is excited only by the stator windings composed of the coils of (U phase, V phase and W phase). At this time, the driving of the switching elements Q 1 to Q6 is controlled in such a way that the switching element driving signals for three negative power supply side switching elements Q4, Q5 and Q6 are supplied as pulse width modulation signals (PWM signals) H4, H5 and H6 and the operation part 71 mounted on the control circuit board 9 changes the pulse widths (duty ratios) of the PWM signals based on the detection signal of the current detection circuit 75. In this way, a power supply amount to the motor 3 is adjusted. Similarly, if the current value of the stator windings (U phase, V phase and W phase) is not less than the threshold value, the switching elements Q7 to Q9 are turned off and the stator 4 is excited by the stator windings in which each coil of U phase, V phase and W phase and each coil of U2 phase, V2 phase and W2 phase are connected in series with each other. At this time, the driving of the switching elements Ql to Q6 is controlled in such a way that the switching element driving signals for three negative power supply side switching elements Q4, Q5 and Q6 are supplied as pulse width modulation signals (PWM signals) H4, H5 and H6 and the operation part 71 mounted on the control circuit board 9 changes the pulse widths (duty ratios) of the PWM signals based on the detection signal of the current detection circuit 75. In this way, a power supply amount to the motor 3 is adjusted.
Next, a control switching procedure of the motor 3 is described with reference to Figs. 6 and 7. First, when the trigger 8a (Fig. 1) is pulled, a current value (motor current=stator winding current) is inputted to the current detection circuit 75. The winding current detected by the current detection circuit 75 is compared with the threshold current value set at a winding switching setting circuit 77 and then inputted to the operation part 71.
When the current value of the stator winding is less than the threshold value, a control is performed in such a way that "any one of the switching elements Ql to Q3 and any one of the switching elements Q7 to Q9 are turned on", as indicated in Box 86 of Fig. 7. It is noted that the switching elements Q7 to Q9 may be continuously operated in an ON state. That is, this control is intended to rotate the motor 3 only using the stator windings U phase, V phase and W phase, as indicated in Box 87. In this control, the number of turns of the coil is reduced as compared to the serial connection state indicated in Box 88. Accordingly, it is possible to drive the motor 3 with high-rotation number, although the torque is reduced. As an example, this is effective in a case where a relatively large torque is not necessary but high-rotation speed is important, as in the first half of a wood screw tightening work, (winding specification 1)
When the current value of the stator winding is greater than the threshold value, a control is performed in such a way that "any one of the switching elements Ql to Q3 and any one of the switching elements Q4 to Q6 are turned on", as indicated in Box 88 of Fig. 7. That is, this control is intended to excite the stator 4 by the stator windings in which each coil of U phase, V phase and W phase and each coil of U2 phase, V2 phase and W2 phase are connected in series with each other, as indicated in Box 89. As an example, this is effective in a case where a large torque is necessary, as in the second half of the wood screw tightening work (winding specification 2).
Fig. 8 shows the path of the power feeding to the coil in a case (Winding specification 2) where the current value of the stator winding is greater than the threshold value in the present embodiment. When the current value of the stator winding is greater than the threshold value, the drive current at a certain rotational position of the rotor 5 flows to U2 phase (62-1, 62-2) as in a direction from (1) to (2), then flows to the serial connected U phase (61-1, 61-2) as in a direction from (3) to (4), then flows toward V phase (61-3, 61-4) connected to (4) as in a direction from (5) to (6), and then flows to the serial connected V2 phase (62-3, 62-4) as in a direction from (7) to (8). Here, the present invention is characterized by that the drive current flows in series to both the outer peripheral side coils 62-1 to 62-4 (U2 phase, V2 phase) and the inner peripheral side coils 61-1 to 61-4 (U phase, V phase) which are wound around the teeth 44-1 to 44-4. Accordingly, in a state where the current value of the stator winding is greater than the threshold value, each of the teeth 44-1 to 44-6 is excited by both the inner peripheral side coils 61-1 to 61-6 and the outer peripheral side coils 62-1 to 62-6.
Next, a control in a case (winding specification 1) where the current value of the stator winding is less than the threshold value is described with reference to Fig. 9. In a state where the current value of the stator winding is less than the threshold value, the drive current at a certain rotational position of the rotor 5 flows only to the serial connected U phase (61-1 , 61-2) as in a direction from (1) to (2) and then flows only to V phase (61-3, 61-4) connected to (2) as in a direction from (3) to (4). Here, the present invention is characterized by that the drive current does not flow to the outer peripheral side coils 62-1 to 62-4 (U2 phase, V2 phase) which are wound around the teeth 44-1 to 44-4. Accordingly, in a case where the current value of the stator winding is less than the threshold value, each of the teeth 44-1 to 44-6 is excited only by the inner peripheral side coils 61-1 to 61-6.
Since the motor characteristic can be changed via an intermediate motor characteristic between the winding specification 1 and the winding specification 2 by repeatedly turning on/off the switching elements Q7 to Q9 for every set time (for example, 0.1 second) when changing between the winding specification 1 and the winding specification 2 is performed, the rapid changes in the torque or the rotation number can be prevented.
According to the present embodiment, following effects can be obtained.
(1) The stator winding 6 has a plurality of winding specifications (for example, winding specification 1 and winding specification 2) by providing a plurality of coils to each of the teeth of the stator core 41. Further, the operation part 71 changes the energization to the plurality of coils in accordance with the current flowing through the motor 3, so that the winding specifications can be changed via an intermediate motor characteristic (winding specification 3) between the motor characteristics for each winding specification. Accordingly, the rapid changes in the torque or rotation number at the moment of changing the winding specifications can be suppressed and thus it is possible to prevent the come out due to the sharp changes in the torque or rotation number.
(2) It is possible to gradually change the current-carrying time of the each coil by gradually changing the duty ratio of the switching elements Q7 to Q9 when changing from the winding specification 1 to the winding specification 2 is performed. In this way, it is possible to change the winding specification more smoothly. Further, the smoothness of the switching can be arbitrarily set depending on the product of the electric tool equipped with the motor 3.
Fig. 10 is a block diagram showing a circuit configuration of a drive control system of the brushless motor according to another embodiment of the present invention. In this case, the start-connected three-phase stator windings of the stator 4 are connected so that a plurality of coils {(a set of coils 61-1, 61-2 and coils 62-1 , 62-2) (a set of coils 61-3, 61-4 and coils 62-3, 62-4) (a set of coils 61-5, 61-6 and coils 62-5, 62-6)} of each phase can be connected in parallel. In addition, an inverter circuit 69 is further provided with switching elements Q7 to Q12, in addition to the switching elements Ql to Q6. A control part 70 is controlled to cause a control signal output circuit 79 to generate switching element driving signals (driving signals HI to HI 2) and respectively outputs the switching element driving signals to the gates of the switching elements Ql to Q12.
In the winding specification 1 where the motor current (stator winding current) is less than the threshold value, the motor is driven by the stator winding which is only composed of U phase (coils 61-1, 61-2), V phase (coils 61-3, 61-4) and W phase (coils 61-5, 61-6). That is, the motor 3 is driven in high-speed rotation by the switching operation of the switching elements Ql to Q6. The switching elements Q7 to 12 are maintained in an off-state.
In the winding specification 2 for performing the high-torque operation, the motor is energized in a state where U phase (coils 61-1, 61-2), V phase (coils 61-3,
61- 4) and W phase (coils 61-5, 61-6) are connected in parallel with Ul phase (coils
62- 1, 62-2), VI phase (coils 62-3, 62-4) and Wl phase (coils 62-5, 62-6), respectively. That is, a set of the switching elements Ql and Q7, a set of the switching elements Q2 and Q8, a set of the switching elements Q3 and Q9, a set of the switching elements Q4 and Q10, a set of the switching elements Q5 and Ql l and a set of the switching elements Q6 and Q12 perform an operation to turn on/off. When the current value of the stator winding is greater than the threshold value (reaches the threshold value), the duty ratio of the switching elements Q7 to Q12 is gradually increased in the transition period from the winding specification 1 to the winding specification 2 and thus becomes 100% at the end of the transition period. The switching elements Q7 to Q12 are turned on/off in pair with the switching elements Ql to Q6.
The drive control system of the brushless motor in Fig. 10 has the same effects as the case of Fig. 6 described above.
In the drive control system in Fig. 10, the motor characteristics of the winding specification 1 and the winding specification 2 may be realized in such a way that the number of turns of the coils of U phase, V phase and W phase is set different from that of the coils of Ul phase, VI phase and Wl phase, any one group of the switching elements Ql to Q6 or the switching elements Q7 to Q12 is selected and any one of the coils of U phase, V phase and W phase or the coils of Ul phase, VI phase and Wl phase is used in a switching manner.
While description has been made in connection with particular embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modification may be made therein without departing from the scope of the claims.
Although various motor characteristics are realized by changing the winding specification of the stator winding and the motor characteristics is gradually changed via an intermediate motor characteristic in the above-described embodiments, the brushless motor may be continuously operated by the intermediate motor characteristic.
Further, although the stator winding in Fig. 3 has a winding configuration in which two coils are provided to each of the teeth, the present invention may have a winding configuration where three or more coils are provided to each of the teeth. In this case, three or more motor characteristics can be realized by switching the connection of each coil in series or in parallel, and the motor characteristics can be gradually switched.
The present invention is not limited to the impact driver, but may be applicable to various electric tools (for example, drill, etc.) which require two or more motor characteristics.
This application claims priority from Japanese Patent Application No. 2011-262681 filed on November 30, 2011, the entire contents of which are incorporated herein by reference.
Industrial Applicability
According to an aspect of the invention, there is provided an electric tool which is easy to handle and in which the motor characteristics can be gradually switched, in a case of including a motor in which two or more motor characteristics can be obtained by providing a winding having a plurality of coils in each of the teeth of the stator and changing the winding specifications as necessary.

Claims

Claims What is claimed is:
1. An electric tool comprising:
a motor including a plurality of coils;
an end tool configured to be driven by the motor;
a drive circuit configured to supply a drive current to the plurality of coils; a control part configured to control the drive circuit; and
a switch configured to control activation and rotation of the motor,
characterized in that:
the control part is configured to repeat switching of connection relationships between the plurality of coils.
2. The electric tool according to claim 1,
wherein a plurality of winding specifications are realized by the switching of the connection relationships between the plurality of coils, and
wherein an intermediate motor characteristic between motor characteristics corresponding to each of the plurality of winding specifications is obtained by repeating the switching of the connection relationships between the plurality of coils.
3. The electric tool according to claim 1,
wherein the plurality of coils are connected in parallel.
4. The electric tool according to claim 1,
wherein the plurality of coils are connected in series.
5. The electric tool according to claim 1,
wherein a plurality of winding specifications are realized by the switching of the connection relationships between the plurality of coils, and
wherein the motor characteristic is gradually changed from a first motor characteristic corresponding to a first winding specification among the plurality of winding specifications to a second motor characteristic corresponding to a second winding specification among the plurality of winding specifications by stepwisely changing an energization time of current respectively flowing through the plurality of coils and gradually changing ratio of the current flowing through each of the plurality of coils.
6. The electric tool according to claim 5, further comprising a switching element configured to switch on and off of the current respectively flowing through the plurality of coils,
wherein a duty ratio of the switching element is changed.
7. The electric tool according to claim 1,
wherein a plurality of winding specifications are realized by the switching of the connection relationships between the plurality of coils, and
wherein the control part is configured to change the winding specification via an intermediate motor characteristic between motor characteristics corresponding to each of the plurality of winding specifications, the intermediate motor characteristic obtained by repeating the switching of the connection relationships between the plurality of coils.
PCT/JP2012/081726 2011-11-30 2012-11-30 Electric tool WO2013081191A2 (en)

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