Patent Description:
Patent Literature <NUM> discloses an electric rotary tool (electric tool). The electric tool includes a motor unit (motor) and a control circuit section for controlling the motor unit. The control circuit section calculates fastening torque based on either a drive current for the motor unit as detected by a current detection means or the number of revolutions of the motor unit as detected by a number of revolutions detection means. When the fastening torque thus calculated becomes equal to or greater than preset fastening torque, the control circuit section stops running the motor unit.

In the electric tool of Patent Literature <NUM>, it takes some time for the motor to stop running due to the inertial force of the motor. Thus, chances are that the electric tool fastens a fastening member such as a screw, a bolt, or a nut with fastening torque greater than preset fastening torque.

Patent Literature <NUM>: <CIT>
Document <CIT> describes a mode change mechanism for a power tool including an actuator with a permanent magnet. The actuator is moveable between a first position for a first mode of operation, and a second position for a second mode of operation. A first positioning member is adjacent the first position composed of a ferromagnetic material to attract the permanent magnet. A second positioning member is adjacent the second position and composed of a ferromagnetic material to attract the permanent magnet. An electromagnet may be energized to move the actuator between the first position and the second position. When the electromagnet is not energized, and the actuator is in the first position. the actuator is retained in the first position. When the electromagnet is not energized and the actuator is in the second position, the actuator is retained in the second position. When the electromagnet is energized, the actuator moves between the first and second positions.

Document <CIT> describes a torque control system comprising an operation shaft for revolving a screw fixture combined with the output shaft at one end of an electromagnetic clutch mechanism, wherein the other end of the electromagnetic clutch mechanism is fixed inside a holding part casing through a supporting body extended coaxially with the mechanism. A strain gauge is attached to one side surface of the supporting body and the electromagnetic clutch mechanism is configured to be engaged/disengaged based on the output signal of the strain gauge.

Document <CIT> describes a rotary power tool comprising a motor, an output shaft that receives torque from the motor, a clutch positioned between the motor and the output shaft for selectively engaging the output shaft to the motor, and a transducer for detecting an amount of torque transferred through the clutch to the output shaft. The clutch is capable of being actuated from a first mode in which the output shaft is engaged to the motor, to a second mode in which the output shaft is disengaged from the motor, in response to feedback from the transducer of the detected amount of torque transferred through the clutch.

Document <CIT> describes a hand-held power tool having a tool body, a motor housed in the tool body and a grip part designed to be held by a user and performs a predetermined operation on a workpiece by a tool bit rotationally driven by the motor. The power tool includes a clutch that transmits torque and interrupts torque transmission between the motor and the tool bit, a non-contact torque sensor that detects torque acting on the tool bit in non-contact with a rotation axis rotating together with the tool bit, and a clutch control system that controls coupling and decoupling of the clutch according to a torque value detected by the non-contact torque sensor.

An object of the present disclosure is to control an electric tool more accurately according to torque (fastening torque).

An electric tool according to an exemplary embodiment will now be described with reference to the accompanying drawings. Note that the embodiment to be described below is only an exemplary one of various embodiments of the present disclosure and should not be construed as limiting.

The drawings to be referred to in the following description of embodiments are all schematic representations. Thus, the ratio of the dimensions (including thicknesses) of respective constituent elements illustrated on the drawings does not always reflect their actual dimensional ratio.

As shown in <FIG> and <FIG>, an electric tool <NUM> according to this embodiment includes a holder <NUM>, a motor <NUM>, a transmission mechanism <NUM>, a torque detection unit <NUM>, a clutch mechanism C1, and a controller <NUM>. The holder <NUM> is configured to hold a tip tool <NUM> thereon. The transmission mechanism <NUM> transmits torque of the motor <NUM> to the holder <NUM>. The torque detection unit <NUM> detects the torque transmitted from the motor <NUM> to the holder <NUM>. The clutch mechanism C1 is switchable from a transmitting state where the torque of the motor <NUM> is transmitted to the holder <NUM> to an interrupted state where no torque of the motor <NUM> is transmitted to the holder <NUM>, and vice versa. The controller <NUM> switches, when a predetermined condition about the torque detected by the torque detection unit <NUM> is satisfied, the clutch mechanism C1 from the transmitting state to the interrupted state. In this embodiment, the predetermined condition includes a condition that the torque detected by the torque detection unit <NUM> be greater than a threshold value.

According to this embodiment, the controller <NUM> switches the clutch mechanism C1 from the transmitting state to the interrupted state according to the torque detected by the torque detection unit <NUM>. That is to say, the clutch mechanism C1 is switched from the transmitting state to the interrupted state by an electronic control performed by the controller <NUM>.

In parallel with the control of switching the clutch mechanism C1 from the transmitting state to the interrupted state, the motor <NUM> is controlled to stop running. Nevertheless, the motor <NUM> continues to run for a while due to inertial energy. In the interrupted state, the motor <NUM> is cut off from both the holder <NUM> and the tip tool <NUM> held by the holder <NUM>, thus reducing the chances of the holder <NUM> and the tip tool <NUM> continuing to turn due to the inertial energy of the motor <NUM>.

A clutch mechanism for making a switch from the transmitting state to the interrupted state by mechanical action using torque, not by electronic control, is called a "mechanical clutch. " According to the mechanical clutch, a switch is made from the transmitting state to the interrupted state if the torque is greater than a threshold value. Nevertheless, according to the mechanical clutch, the switch is made to the interrupted state with reliability if the torque is sufficiently greater than the threshold value, but the switch to the interrupted state may fail to be made the instant the torque reaches the threshold value.

In contrast, the electric tool <NUM> according to this embodiment switches the clutch mechanism C1 to the interrupted state by electronic control based on the torque detected by the torque detection unit <NUM>, thus allowing the clutch mechanism C1 to be switched quickly to the interrupted state. Switching the clutch mechanism C1 to the interrupted state reduces the rotation of the holder <NUM> and the tip tool <NUM>. As can be seen, the electric tool <NUM> according to this embodiment improves the accuracy of rotational control of the holder <NUM> and the tip tool <NUM> based on the torque. This reduces the chances of a fastening member such as a screw, a bolt, or a nut being fastened with excessive torque.

The clutch mechanism C1 according to this embodiment includes an electromagnet <NUM> and switches between the transmitting state and the interrupted state by changing the energization state of the electromagnet <NUM>. Nevertheless, not covered by the invention the clutch mechanism C1 does not have to have such a configuration including the electromagnet <NUM>. Alternatively, the clutch mechanism C1 may also be a mechanical clutch for use with an actuator. In that case, the actuator may drive the mechanical clutch under the electronic control by the controller <NUM> to switch the mechanical clutch from the transmitting state to the interrupted state. The electric tool <NUM> may further include such an actuator. The actuator may include, for example, a cylinder which stretches and shrinks under the control of the controller <NUM>.

A configuration for the electric tool <NUM> will now be described in further detail. In the following description of embodiments, the direction in which the motor <NUM> and the transmission mechanism <NUM> are arranged side by side will be defined as a "rightward/leftward direction," the transmission mechanism <NUM> is regarded as being located on the right of the motor <NUM>, and the motor <NUM> is regarded as being located on the left of the transmission mechanism <NUM>. Note that these definitions should not be construed as specifying the direction in which the electric tool <NUM> should be used.

The electric tool <NUM> may be used as, for example, an electric screwdriver, drill, drill-screwdriver, or wrench. Alternatively, the electric tool <NUM> may also be used as an electric saw, plane, nibbler, hole saw, or grinder, for example. In the following description of exemplary embodiments, a situation where the electric tool <NUM> is used as a screwdriver for tightening a fastening member such as a screw, a bolt or a nut will be described as a typical example.

As shown in <FIG>, the electric tool <NUM> includes a housing <NUM>, a motor <NUM>, a power supply unit B1, an operating member <NUM>, a power control block <NUM>, a driver circuit section <NUM>, the clutch mechanism C1, the transmission mechanism <NUM>, a chuck <NUM>, and a tip tool <NUM>.

The housing <NUM> includes a barrel <NUM>, a grip <NUM>, and an attachment <NUM>. The barrel <NUM> has a cylindrical shape. The grip <NUM> protrudes from a side surface of the barrel <NUM>. The grip <NUM> also has a cylindrical shape. The attachment <NUM> is provided at the tip of the grip <NUM>. In other words, the barrel <NUM> and the attachment <NUM> are coupled to each other via the grip <NUM>. The power supply unit B1 is attached removably to the attachment <NUM>.

In the barrel <NUM>, housed are the driver circuit section <NUM>, the motor <NUM>, the clutch mechanism C1, and the transmission mechanism <NUM>. The grip <NUM> holds the operating member <NUM>. The power control block <NUM> is housed in the attachment <NUM>.

As shown in <FIG>, the chuck <NUM> includes an outer shell <NUM> and the holder <NUM>.

The outer shell <NUM> has a circular columnar shape. The outer shell <NUM> is attached to the tip of the barrel <NUM>. Inside the outer shell <NUM>, the holder <NUM> is disposed. The outer shell <NUM> holds the holder <NUM> rotatably.

The holder <NUM> has a circular cylindrical shape. The holder <NUM> is mounted on the output shaft of the transmission mechanism <NUM>. The holder <NUM> rotates with the torque transmitted from the motor <NUM> via the transmission mechanism <NUM>. The tip tool <NUM> is attached removably to the holder <NUM>. The tip tool <NUM> rotates along with the holder <NUM>. The electric tool <NUM> rotates the tip tool <NUM> by turning the holder <NUM> with the torque of the motor <NUM>.

The tip tool <NUM> (also called a "bit") may be a screwdriver bit or a drill bit, for example. One of various types of tip tools <NUM> is selected depending on the intended use and attached to the holder <NUM> for the intended use.

In this embodiment, the tip tool <NUM> is replaceable depending on the intended use. However, the tip tool <NUM> does not have to be replaceable. Alternatively, the electric tool <NUM> may also be an electric tool system designed to allow the use of only a particular type of tip tool <NUM>, for example.

As shown in <FIG>, the transmission mechanism <NUM> is interposed between the holder <NUM> and the motor <NUM>. The transmission mechanism <NUM> includes a plurality of gears. The transmission mechanism <NUM> transmits the torque of the motor <NUM> to the holder <NUM>. More specifically, the transmission mechanism <NUM> receives the torque of the motor <NUM> via the clutch mechanism C1 and transmits the torque to the holder <NUM>. The transmission mechanism <NUM> reduces the rotational velocity of the motor <NUM>. More specifically, the transmission mechanism <NUM> reduces the rotational velocity of the motor <NUM> at a predetermined speed reduction ratio and outputs rotational force with the rotational velocity thus reduced. That is to say, the rotational velocity of the output shaft of the transmission mechanism <NUM> is lower than the rotational velocity of the input shaft.

The plurality of gears of the transmission mechanism <NUM> includes a gear <NUM>. The gear <NUM> meshes with a gear <NUM> (to be described later) provided for the clutch mechanism C1. In this manner, the transmission mechanism <NUM> receives the torque from the clutch mechanism C1.

The motor <NUM> may be a brushless motor, for example. In particular, the motor <NUM> according to this embodiment is a synchronous motor. More specifically, the motor <NUM> may be a permanent magnet synchronous motor (PMSM). As shown in <FIG>, the motor <NUM> includes a rotor <NUM> having a permanent magnet <NUM> and a stator <NUM> having a motor coil <NUM>. The rotor <NUM> further includes a rotary shaft <NUM> (refer to <FIG>) that outputs torque. The rotor <NUM> rotates with respect to the stator <NUM> due to electromagnetic interaction between the motor coil <NUM> and the permanent magnet <NUM>.

As shown in <FIG>, the clutch mechanism C1 is interposed between the holder <NUM> and the motor <NUM>. More specifically, the clutch mechanism C1 is interposed between the motor <NUM> and the transmission mechanism <NUM>. While the clutch mechanism C1 is in the transmitting state, the clutch mechanism C1 transmits the torque of the motor <NUM> to the transmission mechanism <NUM>. As a result, the torque of the motor <NUM> is transmitted to the holder <NUM> via the clutch mechanism C1 and the transmission mechanism <NUM>. On the other hand, while the clutch mechanism C1 is in the interrupted state, the clutch mechanism C1 does not transmit the torque of the motor <NUM> to the transmission mechanism <NUM>. As a result, the torque of the motor <NUM> is not transmitted to the holder <NUM>.

The clutch mechanism C1 includes a first rotating part <NUM>, a second rotating part <NUM>, and at least one (e.g., two in the example illustrated in <FIG>) coupling portion <NUM>. The first rotating part <NUM> rotates as the motor <NUM> runs. The holder <NUM> is coupled either directly or indirectly to the second rotating part <NUM>. In this embodiment, the holder <NUM> is coupled indirectly to the second rotating part <NUM> via the transmission mechanism <NUM>.

The transmitting state of the clutch mechanism C1 is a state where the first rotating part <NUM> and the second rotating part <NUM> are coupled to each other via the at least one coupling portion <NUM> so that the torque of the first rotating part <NUM> is transmitted to the second rotating part <NUM>. The interrupted state of the clutch mechanism C1 is a state where the first rotating part <NUM> and the second rotating part <NUM> are decoupled from each other so that the torque of the first rotating part <NUM> is not transmitted to the second rotating part <NUM>.

As shown in <FIG> and <FIG>, the clutch mechanism C1 further includes a stator part <NUM>, a first bearing <NUM>, and a second bearing <NUM>.

The stator part <NUM> is fixed to the housing <NUM>. The stator part <NUM> has a cylindrical shape. The first bearing <NUM> is fixed onto an inner surface of the stator part <NUM>.

The first rotating part <NUM> is held by the first bearing <NUM>. This allows the first rotating part <NUM> to rotate freely with respect to the stator part <NUM>. The first rotating part <NUM> is coupled to the rotary shaft <NUM> of the motor <NUM>. This causes the first rotating part <NUM> to rotate as the motor <NUM> turns. The rotary shaft <NUM> is arranged to be aligned with the center axis of the first rotating part <NUM>.

The first rotating part <NUM> includes a cylindrical member <NUM> and a facing member <NUM>. The cylindrical member <NUM> has a circular cylindrical shape. The facing member <NUM> is connected to the tip of the cylindrical member <NUM>. The facing member <NUM> has a disklike shape. The facing member <NUM> faces the second rotating part <NUM>. The facing member <NUM> has a plurality of (e.g., two in the example illustrated in <FIG>) first recesses <NUM> on a surface thereof facing the second rotating part <NUM>.

The second rotating part <NUM> is disposed on the right of the first rotating part <NUM>. The second rotating part <NUM> is interposed between the first rotating part <NUM> and the transmission mechanism <NUM>. The first rotating part <NUM> is interposed between the motor <NUM> and the second rotating part <NUM>.

The second rotating part <NUM> has a disklike shape. The second rotating part <NUM> has a plurality of (e.g., two in the example illustrated in <FIG>) second recesses <NUM> on a surface thereof facing the first rotating part <NUM>.

The second bearing <NUM> is fixed to the second rotating part <NUM>. The second bearing <NUM> holds the rotary shaft <NUM> of the motor <NUM>. While the clutch mechanism C1 is in the interrupted state, the rotary shaft <NUM> rotates with respect to the second rotating part <NUM>. On the other hand, while the clutch mechanism C1 is in the transmitting state, the second rotating part <NUM> rotates at the same number of revolutions as the rotary shaft <NUM>.

The clutch mechanism C1 further includes a gear <NUM>. The gear <NUM> is formed integrally with the second rotating part <NUM>. The gear <NUM> is provided for the other surface, opposite from the first rotating part <NUM>, of the second rotating part <NUM>. The gear <NUM> meshes with a gear <NUM> (refer to <FIG>) of the transmission mechanism <NUM>, thus transmitting the torque of the second rotating part <NUM> to the transmission mechanism <NUM>.

The first rotating part <NUM> and the second rotating part <NUM> face each other. Specifically, the first rotating part <NUM> and the second rotating part <NUM> face each other with a narrow gap left between themselves. Alternatively, the first rotating part <NUM> and the second rotating part <NUM> may be in contact with each other at least in some region. Optionally, the electric tool <NUM> may further include a spacer. In that case, the spacer may be fixed to either the first rotating part <NUM> or the second rotating part <NUM> and sandwiched between the first rotating part <NUM> and the second rotating part <NUM>.

The rotary shaft <NUM> of the motor <NUM> may be used as an input shaft of the clutch mechanism C1. That is to say, the rotary shaft <NUM> serves as not only a constituent element of the motor <NUM> but also a constituent element of the clutch mechanism C1. The rotary shaft <NUM> transmits the torque of the motor <NUM> to the first rotating part <NUM>.

The gear <NUM> is used as an output shaft of the clutch mechanism C1. The gear <NUM> transmits the rotational force of the second rotating part <NUM> to the holder <NUM>. More specifically, the gear <NUM> transmits the rotational force of the second rotating part <NUM> to the holder <NUM> via the transmission mechanism <NUM>.

The gear <NUM> (output shaft) is arranged coaxially with the rotary shaft <NUM> (input shaft). This reduces the axial runout of the input shaft and the output shaft.

The plurality of first recesses <NUM> provided for the first rotating part <NUM> correspond one to one to the plurality of second recesses <NUM> provided for the second rotating part <NUM>. While the clutch mechanism C1 is in the transmitting state, a pair of first and second recesses <NUM>, <NUM> corresponding to each other face each other.

Each of the plurality of coupling portions <NUM> includes the electromagnet <NUM> and a permanent magnet block <NUM>. The electromagnet <NUM> includes a magnetic pole <NUM> and a coil <NUM>. The permanent magnet block <NUM> includes a permanent magnet <NUM> and an elastic member <NUM>.

That is to say, the coupling portion <NUM> includes the electromagnet <NUM> and the permanent magnet <NUM>, and the electromagnet <NUM> includes the magnetic pole <NUM>. The magnetic pole <NUM> is made of a magnetic material such as iron (e.g., electromagnetic soft iron). The permanent magnet <NUM> faces the magnetic pole <NUM>.

The magnetic pole <NUM> is held by the first rotating part <NUM>. The permanent magnet <NUM> is held by the second rotating part <NUM>. The controller <NUM> (refer to <FIG>) switches the clutch mechanism C1 from the transmitting state to the interrupted state, or vice versa, by changing the energization state of the electromagnet <NUM>. That is to say, electromagnetic force acting between the magnetic pole <NUM> and the permanent magnet <NUM> changes according to the energization state of the coil <NUM> of the electromagnet <NUM>, and the clutch mechanism C1 switches between the transmitting state and the interrupted state accordingly.

More specifically, while the controller <NUM> is performing control such that the magnitude of a current supplied to the coil <NUM> becomes equal to or greater than a predetermined magnitude, electromagnetic repulsive force is generated between the magnetic pole <NUM> and the permanent magnet <NUM>, thus producing the interrupted state where the first rotating part <NUM> and the second rotating part <NUM> are decoupled from each other. That is to say, the controller <NUM> switches the clutch mechanism C1 from the transmitting state to the interrupted state by generating the electromagnetic repulsive force between the magnetic pole <NUM> and the permanent magnet <NUM>.

On the other hand, while the controller <NUM> keeps the coil <NUM> not energized or if the magnitude of the current supplied to the coil <NUM> is less than the predetermined magnitude, the electromagnetic repulsive force is relatively small. Thus, the transmitting state where the torque of the first rotating part <NUM> is transmitted to the second rotating part <NUM> is maintained.

As can be seen, the clutch mechanism C1 turns into the interrupted state while the electromagnet <NUM> (coil <NUM>) is energized with a current, of which the magnitude is equal to or greater than the predetermined magnitude. The clutch mechanism C1 turns into the transmitting state while the electromagnet <NUM> (coil <NUM>) is not energized or if the electromagnet <NUM> (coil <NUM>) is energized with a current, of which the magnitude is less than the predetermined magnitude.

The plurality of magnetic poles <NUM> of the plurality of electromagnets <NUM> correspond one to one to the plurality of first recesses <NUM> of the first rotating part <NUM>. Each magnetic pole <NUM> is inserted into a corresponding one of the first recesses <NUM>. The plurality of coils <NUM> of the plurality of electromagnets <NUM> are fixed to the stator part <NUM>. The plurality of coils <NUM> are arranged on the left of a region where the plurality of magnetic poles <NUM> are arranged.

The plurality of permanent magnet blocks <NUM> correspond one to one to the plurality of second recesses <NUM> of the second rotating part <NUM>. The permanent magnet <NUM> and elastic member <NUM> of each permanent magnet block <NUM> are inserted into a corresponding one of the second recesses <NUM>. The permanent magnet <NUM> has a cylindrical shape. The second rotating part <NUM> has shaft portions <NUM>, each of which protrudes from the bottom surface of a corresponding one of the second recesses <NUM> and is inserted into a corresponding one of the permanent magnets <NUM>. The permanent magnet <NUM> is movable along the shaft portion <NUM>.

The elastic member <NUM> is disposed on the right of the permanent magnet <NUM>. The elastic member <NUM> is interposed between the bottom of the second recess <NUM> and the permanent magnet <NUM>. The elastic member <NUM> is a compressed spring. More specifically, the elastic member <NUM> may be a compressed coil spring. The elastic member <NUM> is arranged to surround the shaft portion <NUM>. The elastic member <NUM> applies leftward force to the permanent magnet <NUM>. That is to say, the elastic member <NUM> applies force that biases the permanent magnet <NUM> toward the first rotating part <NUM>.

The plurality of coupling portions <NUM> are arranged to surround at least one of the rotary shaft <NUM> (input shaft) or the gear <NUM> (output shaft). <FIG> illustrates the first rotating part <NUM> as viewed from the right. The plurality of magnetic poles <NUM> of the plurality of coupling portions <NUM> are arranged in a circle to surround the rotary shaft <NUM>. In the same way, the plurality of coils <NUM> (refer to <FIG>) are also arranged in a circle to surround the rotary shaft <NUM>. Note that if the plurality of coupling portions <NUM> surrounds at least one of the rotary shaft <NUM> (input shaft) or the gear <NUM> (output shaft), then the number of the coupling portions <NUM> provided may be equal to or greater than three.

The plurality of permanent magnet blocks <NUM> are also arranged in a circle to surround the rotary shaft <NUM>. In addition, when viewed in the rightward/leftward direction, the plurality of permanent magnet blocks <NUM> are arranged in a circle to surround the gear <NUM>.

Next, it will be described how the clutch mechanism C1 operates.

While the coil <NUM> is not energized or energized with a current, of which the magnitude is smaller than a predetermined magnitude, the clutch mechanism C1 maintains the transmitting state. While the clutch mechanism C1 is in the transmitting state, the permanent magnets <NUM> are inserted into the first recesses <NUM> of the first rotating part <NUM> as shown in <FIG>. At this time, each permanent magnet <NUM> is in contact with a corresponding one of the magnetic poles <NUM>. More specifically, the permanent magnet <NUM> is sandwiched between the magnetic pole <NUM> and a corresponding one of the elastic members <NUM>. The elastic energy applied by the elastic member <NUM> holds the permanent magnet <NUM> at the same position. Inserting the permanent magnet <NUM> into the first recess <NUM> in each of the plurality of coupling portions <NUM> couples the first rotating part <NUM> and the second rotating part <NUM> to each other. Thus, while the clutch mechanism C1 is in the transmitting state, the first rotating part <NUM> and the second rotating part <NUM> rotate at the same number of revolutions.

In this manner, the permanent magnets <NUM> are fitted into the first recesses <NUM>. That is to say, the clutch mechanism C1 has a fitting structure, which is formed by the first recesses <NUM> and the permanent magnets <NUM>. While the clutch mechanism C1 is in the transmitting state, the fitting structure couples the first rotating part <NUM> and the second rotating part <NUM> to each other by fitting.

If the coils <NUM> are energized with a current, of which the magnitude is equal to or greater than a predetermined magnitude, while the clutch mechanism C1 is in the transmitting state, electromagnetic repulsive force is generated between the magnetic poles <NUM> and the permanent magnets <NUM>, thus causing the permanent magnets <NUM> to move to the right. That is to say, the permanent magnets <NUM> come out of contact with the magnetic poles <NUM> while compressing the elastic members <NUM> to move out of the first recesses <NUM> of the first rotating part <NUM> as shown in <FIG>. More specifically, the permanent magnets <NUM> are retracted into the second recesses <NUM> of the second rotating part <NUM>. Moving the permanent magnet <NUM> out of the first recess <NUM> in each of the coupling portions <NUM> decouples the first rotating part <NUM> and the second rotating part <NUM> from each other. That is to say, the clutch mechanism C1 turns into the interrupted state.

While the clutch mechanism C1 is in the interrupted state, as the rotary shaft <NUM> of the motor <NUM> turns, only the first rotating part <NUM> rotates with the second rotating part <NUM> not rotating. In addition, the holder <NUM> and the tip tool <NUM> that are coupled to the second rotating part <NUM> via the transmission mechanism <NUM> do not rotate, either. More specifically, as the clutch mechanism C1 switches from the transmitting state to the interrupted state, the second rotating part <NUM>, the plurality of gears of the transmission mechanism <NUM>, the holder <NUM>, and the tip tool <NUM> continue to rotate for a while due to the inertial energy but will soon stop rotating when the inertial energy is lost.

As can be seen from the foregoing description, each of the plurality of coupling portions <NUM> further includes the elastic member <NUM> that stores elastic energy while the electromagnet <NUM> is being energized. That is to say, letting the permanent magnet <NUM> compress the elastic member <NUM> causes the elastic member <NUM> to store elastic energy. The clutch mechanism C1 is caused to switch to either the transmitting state or the interrupted state by the elastic energy of the elastic member <NUM>. In this embodiment, the clutch mechanism C1 is caused to switch from the interrupted state to the transmitting state by the elastic energy of the elastic member <NUM>. That is to say, adjusting the respective rotational angles of the first rotating part <NUM> and the second rotating part <NUM> such that the respective permanent magnets <NUM> face the magnetic poles <NUM> causes the permanent magnets <NUM> to be moved by the elastic energy of the elastic members <NUM> to be inserted into the first recesses <NUM>. This means that the clutch mechanism C1 has switched from the interrupted state to the transmitting state.

Optionally, the respective rotational angles of the first rotating part <NUM> and the second rotating part <NUM> may also be adjusted by, for example, letting the user operate an operating part coupled to either the first rotating part <NUM> or the second rotating part <NUM>. Alternatively, the rotational angles may also be adjusted by letting the user activate a driving mechanism for rotating either the first rotating part <NUM> or the second rotating part <NUM> using a power source such as electrical energy. In that case, the rotational velocity of either the first rotating part <NUM> or the second rotating part <NUM> driven by the driving mechanism is lower than the rotational velocity of the motor <NUM>.

The power supply unit B1 shown in <FIG> supplies a current to the motor <NUM>, the electromagnets <NUM>, and the power control block <NUM>, for example. The power supply unit B1 may be a battery pack, for example. The power supply unit B1 may include, for example, either a single secondary battery or a plurality of secondary batteries.

The operating member <NUM> accepts the operation of controlling the rotation of the motor <NUM>. The motor <NUM> may be selectively activated (turned ON or OFF) by the operation of pulling the operating member <NUM>. In addition, the rotational velocity of the motor <NUM> is adjustable depending on the manipulative variable of the operation of pulling the operating member <NUM> (i.e., depending on how deep the operating member <NUM> is pulled). As a result, the rotational velocity of the holder <NUM> is adjustable depending on the manipulative variable of the operation of pulling the operating member <NUM>. The greater the manipulative variable is, the higher the rotational velocity of the motor <NUM> becomes. The power control block <NUM> either starts or stops rotating the motor <NUM>, and controls the rotational velocity of the motor <NUM>, depending on the manipulative variable of the operation of pulling the operating member <NUM>.

As shown in <FIG>, the driver circuit section <NUM> is disposed adjacent to the motor <NUM>. The driver circuit section <NUM> supplies power to the motor <NUM> under the control of the power control block <NUM>. The driver circuit section <NUM> includes an inverter circuit section <NUM> (refer to <FIG>). The inverter circuit section <NUM> converts the power supplied from the power supply unit B1 into power with a desired voltage and supplies the power thus converted to the motor <NUM>.

The electric tool <NUM> further includes a motor rotation measuring unit <NUM> (refer to <FIG>). The motor rotation measuring unit <NUM> measures the rotational angle of (the rotor <NUM> of) the motor <NUM>. As the motor rotation measuring unit <NUM>, a photoelectric encoder or a magnetic encoder may be adopted, for example.

As shown in <FIG>, the power control block <NUM> is used along with the inverter circuit section <NUM> and controls the operation of the motor <NUM> by feedback control.

The power control block <NUM> includes a computer system including one or more processors and a memory. At least some of the functions of the power control block <NUM> are performed by making the processor(s) of the computer system execute a program stored in the memory of the computer system. The program may be stored in the memory. The program may also be downloaded via a telecommunications line such as the Internet or distributed after having been stored in a non-transitory storage medium such as a memory card.

The power control block <NUM> includes a command value generator <NUM>, a velocity controller <NUM>, a current controller <NUM>, a first coordinate transformer <NUM>, a second coordinate transformer <NUM>, a flux controller <NUM>, an estimator <NUM>, a controller <NUM>, and a calculator <NUM>. Note that these constituent elements of the power control block <NUM> just represent functions to be performed by the power control block <NUM> and do not always have a substantive configuration.

The electric tool <NUM> further includes a plurality of (e.g., two in the example illustrated in <FIG>) current sensors <NUM>, <NUM>. Each of the plurality of current sensors <NUM>, <NUM> includes, for example, a hall element current sensor or a shunt resistor element. The plurality of current sensors <NUM>, <NUM> measure an electric current supplied from the power supply unit B1 (refer to <FIG>) to the motor <NUM> via the inverter circuit section <NUM>. In this embodiment, three-phase currents (namely, a U-phase current, a V-phase current, and a W-phase current) are supplied to the motor <NUM>. The plurality of current sensors <NUM>, <NUM> measure currents in at least two phases. In <FIG>, the current sensor <NUM> measures the U-phase current to output a current measured value iu<NUM> and the current sensor <NUM> measures the V-phase current to output a current measured value iv<NUM>.

The estimator <NUM> obtains a time derivative of the rotational angle θ1, measured by the motor rotation measuring unit <NUM>, of the motor <NUM> to calculate an angular velocity ω1 of the motor <NUM>.

The torque detection unit <NUM> includes a current measuring unit <NUM> and the calculator <NUM>. The current measuring unit <NUM> is made up of the two current sensors <NUM>, <NUM> and the second coordinate transformer <NUM>. The current measuring unit <NUM> acquires a d-axis current (excitation current) and a q-axis current (torque current), both of which are to be supplied to the motor <NUM>. That is to say, the current measured value id1 of the d-axis current and the current measured value iq1 of the q-axis current are calculated by having two-phase currents measured by the two current sensors <NUM>, <NUM> transformed by the second coordinate transformer <NUM>.

The second coordinate transformer <NUM> performs, based on the rotational angle θ1, measured by the motor rotation measuring unit <NUM>, of the motor <NUM>, coordinate transformation on the current measured values iu<NUM>, iv<NUM> measured by the plurality of current sensors <NUM>, <NUM>, thereby calculating current measured values id1, iq1. That is to say, the second coordinate transformer <NUM> transforms the current measured values iu<NUM>, iv<NUM>, corresponding to currents in two phases, into a current measured value id1 corresponding to a magnetic field component (d-axis current) and a current measured value iq1 corresponding to a torque component (q-axis current).

The calculator <NUM> calculates, based on the torque current (current measured value iq1) measured by the current measuring unit <NUM>, the torque to be transmitted from the motor <NUM> to the holder <NUM>. The calculator <NUM> calculates the torque to be transmitted from the motor <NUM> to the holder <NUM> by, for example, multiplying the current measured value iq1 representing the torque current by a predetermined constant.

As used herein, the torque to be transmitted from the motor <NUM> to the holder <NUM> may be the torque of the motor <NUM>, the torque of the holder <NUM>, or the torque of a constituent element (which may be the clutch mechanism C1 or the transmission mechanism <NUM>) for transmitting the torque of the motor <NUM> to the holder <NUM>.

The controller <NUM> switches the energization state of the coil <NUM> (refer to <FIG>) of the electromagnet <NUM>. This allows the controller <NUM> to switch the clutch mechanism C1 from the transmitting state to the interrupted state.

The controller <NUM> switches the clutch mechanism C1 from the transmitting state to the interrupted state when a predetermined condition about the torque detected by the torque detection unit <NUM> (hereinafter referred to as "detected torque") is satisfied. In addition, the controller <NUM> causes the motor <NUM> to stop running when the predetermined condition is satisfied. The predetermined condition may include a condition that the detected torque be greater than a threshold value.

The predetermined condition may be, for example, a condition that the detected torque be greater than the threshold value. Alternatively, the predetermined condition may also be, for example, a condition that the detected torque remain greater than the threshold value for at least a predetermined time. Still alternatively, the torque detection unit <NUM> may detect the torque at predetermined time intervals and the predetermined condition may also be, for example, a condition that the detected torque be greater than the threshold value at least a predetermined number of times.

The controller <NUM> does not perform the control of switching the clutch mechanism C1 from the interrupted state to the transmitting state while the clutch mechanism C1 is in the interrupted state and the motor <NUM> is running. That is to say, while the motor <NUM> is running after the clutch mechanism C1 has turned into the interrupted state, the controller <NUM> maintains a state where the coil <NUM> is energized with a current, of which the magnitude is equal to or greater than a predetermined magnitude. This enables maintaining the interrupted state and preventing the tip tool <NUM> from rotating until the motor <NUM> stops running.

The command value generator <NUM> generates a command value cω1 for the angular velocity of the motor <NUM>. The command value generator <NUM> receives, from the operating member <NUM>, for example, a command value cω0 corresponding to the manipulative variable of the operation of pulling the operating member <NUM>. The command value generator <NUM> generate a command value cω1 corresponding to the command value cω0 That is to say, as the manipulative variable increases, the command value generator <NUM> increases the command value cω1 of the angular velocity accordingly.

The velocity controller <NUM> generates a command value ciq1 based on the difference between the command value cω1 generated by the command value generator <NUM> and the angular velocity ω1 calculated by the estimator <NUM>. The command value ciq1 is a command value specifying the magnitude of a torque current (q-axis current) of the motor <NUM>. The power control block <NUM> performs control to bring the torque current (q-axis current) to be supplied to the motor coil <NUM> closer toward the command value ciq1. The velocity controller <NUM> determines the command value ciq1 such that the difference between the command value cω1 and the angular velocity ω1 becomes less than a predetermined value.

The flux controller <NUM> generates a command value cid1 based on the angular velocity ω1 calculated by the estimator <NUM> and the current measured value iq1. The command value cid1 is a command value that specifies the magnitude of the excitation current (d-axis current) of the motor <NUM>. That is to say, the power control block <NUM> controls the operation of the motor <NUM> to bring the excitation current (d-axis current) to be supplied to the motor coil <NUM> closer toward the command value cid1.

In this embodiment, the command value cid1 generated by the flux controller <NUM> may be, for example, a command value to set the magnitude of the excitation current at zero. The flux controller <NUM> may generate the command value cid1 to set the magnitude of the excitation current at zero constantly or may generate the command value cid1 to set the magnitude of the excitation current at a value greater or smaller than zero only as needed. When the command value cid1 of the excitation current becomes smaller than zero, a negative excitation current (i.e., a flux-weakening current) flows through the motor <NUM>, thus weakening the magnetic flux that drives the rotor <NUM>.

The current controller <NUM> generates a command value cvd1 based on the difference between the command value cid1 generated by the flux controller <NUM> and the current measured value id1 calculated by the second coordinate transformer <NUM>. The command value cvd1 is a command value that specifies the magnitude of d-axis voltage of the motor <NUM>. The current controller <NUM> determines the command value cvd1 to make the difference between the command value cid1 and the current measured value id1 less than a predetermined value.

In addition, the current controller <NUM> also generates a command value cvq1 based on the difference between the command value ciq1 generated by the velocity controller <NUM> and the current measured value iq1 calculated by the second coordinate transformer <NUM>. The command value cvq1 is a command value that specifies the magnitude of q-axis voltage of the motor <NUM>. The current controller <NUM> generates the command value cvq1 to make the difference between the command value ciq1 and the current measured value iq1 less than a predetermined value.

The first coordinate transformer <NUM> performs coordinate transformation on the command values cvd1, cvq1 based on the rotational angle θ1, measured by the motor rotation measuring unit <NUM>, of the motor <NUM> to calculate command values cvu<NUM>, cvv<NUM>, cvw<NUM>. Specifically, the first coordinate transformer <NUM> transforms the command value cvd1 for a magnetic field component (d-axis voltage) and the command value cvq1 for a torque component (q-axis voltage) into command values cvu<NUM>, cvv<NUM>, cvw<NUM> corresponding to voltages in three phases. The command value cvu<NUM> corresponds to a U-phase voltage, the command value cvv<NUM> corresponds to a V-phase voltage, and the command value cvw<NUM> corresponds to a W-phase voltage.

The inverter circuit section <NUM> supplies voltages in three phases, corresponding to the command values cvu<NUM>, cvv<NUM>, cvw<NUM>, respectively, to the motor <NUM>. The inverter circuit section <NUM> controls the power to be supplied to the motor <NUM> by performing pulse width modulation (PWM) control, for example.

The motor <NUM> is driven with the power (voltages in three phases) supplied from the inverter circuit section <NUM>, thereby generating torque.

As a result, the power control block <NUM> controls the excitation current flowing through the motor coil <NUM> such that the excitation current comes to have a magnitude corresponding to the command value cid1 generated by the flux controller <NUM>. In addition, the power control block <NUM> also controls the angular velocity of the motor <NUM> such that the angular velocity of the motor <NUM> becomes an angular velocity corresponding to the command value cω1 generated by the command value generator <NUM>.

The power to be supplied to the motor <NUM> is controlled by the power control block <NUM> using vector control. The vector control is a type of motor control technique by which the current to be supplied to the motor coil <NUM> is broken down into a current component (excitation current) that generates a magnetic flux and a current component that generates torque (torque current) and these current components are controlled independently of each other.

The current measured value iq1 for the torque current is used to perform the vector control and to calculate the torque to be transmitted from the motor <NUM> to the holder <NUM>. This allows a part of a circuit for performing the vector control and a part of a circuit for calculating the torque to be shared. This contributes to reducing the areas and dimensions of the circuits provided for the electric tool <NUM> and cutting down the cost required for the circuits.

Next, variations of the exemplary embodiment will be enumerated one after another. Note that the variations to be described below may be adopted in combination as appropriate.

The tip tool <NUM> does not have to be one of the constituent elements of the electric tool <NUM>.

The power supply unit B1 does not have to be one of the constituent elements of the electric tool <NUM>.

The elastic member <NUM> may also be a tensile spring (such as a tensile coil spring). In that case, the controller <NUM> maintains the clutch mechanism C1 in the transmitting state by generating electromagnetic suction force between the magnetic poles <NUM> and the permanent magnets <NUM>. When the controller <NUM> either reduces or removes the electromagnetic suction force, the elastic energy of the tensile spring causes the permanent magnets <NUM> to move out of the first recesses <NUM>, thus switching the clutch mechanism C1 from the transmitting state to the interrupted state.

In the exemplary embodiment described above, the first rotating part <NUM> and the second rotating part <NUM> are coupled to each other to rotate at the same number of revolutions by inserting the permanent magnets <NUM> into the first recesses <NUM> of the first rotating part <NUM>. However, the permanent magnets <NUM> do not have to be inserted into the first recesses <NUM>. Alternatively, the first rotating part <NUM> and the second rotating part <NUM> may also be coupled to each other only with the magnetic suction force acting between the permanent magnets <NUM> and the magnetic poles <NUM>.

The holder <NUM> may be formed integrally with a part of the transmission mechanism <NUM>.

The first rotating part <NUM> may form an integral part of the rotor <NUM> of the motor <NUM>.

In the exemplary embodiment described above, the fitting structure for coupling the first rotating part <NUM> and the second rotating part <NUM> to each other by fitting is formed by the first recesses <NUM> and the permanent magnets <NUM>. However, this is only an example and should not be construed as limiting. According to a first alternative example, the fitting structure may also be formed by recesses (which are either the first recesses <NUM> or other recesses) provided for the first rotating part <NUM> and projections provided for the second rotating part <NUM>. According to a second alternative example, the fitting structure may also be formed by recesses (which are either the second recesses <NUM> or other recesses) provided for the second rotating part <NUM> and projections provided for the first rotating part <NUM>. According to the first or second alternative example, the recesses and the projections only need to be fitted into each other by changing the relative positions of the first rotating part <NUM> and the second rotating part <NUM> with the electromagnetic force acting between the electromagnets <NUM> and the permanent magnets <NUM>.

The clutch mechanism C1 does not have to be arranged as described for the exemplary embodiment. Alternatively, the clutch mechanism C1 may also be interposed, for example, between the transmission mechanism <NUM> and the holder <NUM>.

The torque detection unit <NUM> may be a torque sensor. As the torque sensor, a resistive strain sensor or a magnetostrictive strain sensor may be used, for example.

The exemplary embodiment and its variations described above are specific implementations of the following aspects of the present disclosure.

An electric tool (<NUM>) according to the claimed invention is defined by the features set forth in the appended independent claim.

According to this configuration, the controller (<NUM>) switches the clutch mechanism (C1) to the interrupted state according to the torque detected by the torque detection unit (<NUM>). This improves the accuracy of control according to the torque, compared to switching the clutch mechanism (C1) to the interrupted state by mechanical action according to the torque, not by electronic control by the controller (<NUM>).

In an electric tool (<NUM>) according to a second aspect, which may be implemented in conjunction with the claimed invention, the predetermined condition includes a condition that the torque detected by the torque detection unit (<NUM>) be greater than a threshold value.

This configuration may reduce the chances of a fastening member being fastened with excessive torque, of which the magnitude is greater than a threshold value.

In an electric tool (<NUM>) according to a third aspect, which may be implemented in conjunction with the claimed invention or second aspect, the torque detection unit (<NUM>) includes a current measuring unit (<NUM>) and a calculator (<NUM>). The current measuring unit (<NUM>) measures a torque current flowing through the motor (<NUM>). The calculator (<NUM>) calculates, based on the torque current measured by the current measuring unit (<NUM>), the torque transmitted from the motor (<NUM>) to the holder (<NUM>).

This configuration allows the torque to be calculated based on the torque current.

In an electric tool (<NUM>) according to a fourth aspect, which may be implemented in conjunction with the claimed invention or any one of the second to third aspects, the controller (<NUM>) suspends, while the clutch mechanism (C1) is in the interrupted state and the motor (<NUM>) is running, performing control of switching the clutch mechanism (C1) from the interrupted state to the transmitting state.

This configuration may prevent the tip tool (<NUM>) from rotating by maintaining the interrupted state until the motor (<NUM>) stops running.

In an electric tool (<NUM>) according to a fifth aspect, which may be implemented in conjunction with the claimed invention or any one of the second to fourth aspects, the transmission mechanism (<NUM>) reduces a rotational velocity of the motor (<NUM>). The clutch mechanism (C1) is interposed between the motor (<NUM>) and the transmission mechanism (<NUM>).

The transmission mechanism (<NUM>) reduces the rotational velocity of the motor (<NUM>), and therefore, the torque of the motor (<NUM>) is less than the torque of the transmission mechanism (<NUM>). Thus, this configuration may reduce the load on the clutch mechanism (C1) while the clutch mechanism (C1) is in the transmitting state, compared to a situation where the clutch mechanism (C1) is interposed between the transmission mechanism (<NUM>) and the holder (<NUM>).

In an electric tool (<NUM>) according to the claimed invention the clutch mechanism (C1) includes a first rotating part (<NUM>), a second rotating part (<NUM>), and at least one coupling portion (<NUM>). The first rotating part (<NUM>) rotates as the motor (<NUM>) runs. The holder (<NUM>) is coupled either directly or indirectly to the second rotating part (<NUM>). The transmitting state is a state where the first rotating part (<NUM>) and the second rotating part (<NUM>) are coupled to each other via the at least one coupling portion (<NUM>) so that torque of the first rotating part (<NUM>) is transmitted to the second rotating part (<NUM>). The interrupted state is a state where the first rotating part (<NUM>) and the second rotating part (<NUM>) are decoupled from each other so that no torque of the first rotating part (<NUM>) is transmitted to the second rotating part (<NUM>).

This configuration allows the clutch mechanism (C1) to selectively transmit or interrupt the torque.

In an electric tool (<NUM>) according to the invention, the at least one coupling portion (<NUM>) includes: an electromagnet (<NUM>) having a magnetic pole (<NUM>); and a permanent magnet (<NUM>) facing the magnetic pole (<NUM>). The magnetic pole (<NUM>) is held by the first rotating part (<NUM>). The permanent magnet (<NUM>) is held by the second rotating part (<NUM>). The controller (<NUM>) switches the clutch mechanism (C1) from the transmitting state to the interrupted state, or vice versa, by changing an energization state of the electromagnet (<NUM>).

This configuration enables switching the clutch mechanism (C1) from the transmitting state to the interrupted state, or vice versa, using electromagnetic force.

In an electric tool (<NUM>) according to the invention, the controller (<NUM>) switches the clutch mechanism (C1) from the transmitting state to the interrupted state by generating electromagnetic repulsive force between the magnetic pole (<NUM>) and the permanent magnet (<NUM>).

This configuration allows the clutch mechanism (C1) to be quickly switched from the transmitting state to the interrupted state.

In an electric tool (<NUM>) according to the invention, the the clutch mechanism (C1) turns into the interrupted state when the electromagnet (<NUM>) is energized with a current, of which magnitude is equal to or greater than predetermined magnitude, and turns into the transmitting state when the electromagnet (<NUM>) is either not energized or energized with a current, of which magnitude is less than the predetermined magnitude.

This configuration may cut down the power consumption in the transmitting state.

In an electric tool (<NUM>) according to the invention, the at least one coupling portion (<NUM>) further includes an elastic member (<NUM>). The elastic member (<NUM>) stores elastic energy while the electromagnet (<NUM>) is energized. The clutch mechanism (C1) is caused to switch from one state selected from the transmitting state and the interrupted state to the other state selected from the transmitting state and the interrupted state by the elastic energy of the elastic member (<NUM>).

This configuration enables switching the clutch mechanism (C1) from the transmitting state to the interrupted state, or vice versa, using the elastic energy stored in the elastic member (<NUM>).

In an electric tool (<NUM>) according to an eleventh aspect, which may be implemented in conjunction with any one of the sixth to tenth aspects, the clutch mechanism (C1) further includes an input shaft (rotary shaft <NUM>) and an output shaft (gear <NUM>). The input shaft transmits the torque of the motor (<NUM>) to the first rotating part (<NUM>). The output shaft is arranged coaxially with the input shaft. The output shaft transmits rotational force of the second rotating part (<NUM>) to the holder (<NUM>).

According to this configuration, the input shaft and the output shaft are arranged coaxially with each other, thus reducing the axial runout of the input shaft and the output shaft.

In an electric tool (<NUM>) according to a twelfth aspect, which may be implemented in conjunction with the eleventh aspect, the clutch mechanism (C1) includes a plurality of the coupling portions (<NUM>). The plurality of the coupling portions (<NUM>) are arranged to surround at least one of the input shaft or the output shaft.

According to this configuration, the plurality of coupling portions (<NUM>) are arranged in a circle, thus reducing the bias of the force while the clutch mechanism (C1) is operating. This reduces the chances of the clutch mechanism (C1) tilting. This also reduces the chances of tilt of the clutch mechanism (C1) making it difficult for the clutch mechanism (C1) to operate properly.

In an electric tool (<NUM>) according to a thirteenth aspect, which may be implemented in conjunction with any one of the sixth to twelfth aspects, the clutch mechanism (C1) has a fitting structure (including a first recess <NUM> and a permanent magnet <NUM>). The fitting structure couples, by fitting, the first rotating part (<NUM>) and the second rotating part (<NUM>) to each other in the transmitting state.

Claim 1:
An electric tool (<NUM>) comprising:
a holder (<NUM>) configured to hold a tip tool (<NUM>) thereon;
a motor (<NUM>);
a transmission mechanism (<NUM>) configured to transmit torque of the motor (<NUM>) to the holder (<NUM>);
a torque detection unit (<NUM>) configured to detect the torque transmitted from the motor (<NUM>) to the holder (<NUM>);
a clutch mechanism (C1) configured to be switchable from a transmitting state where the torque of the motor (<NUM>) is transmitted to the holder (<NUM>) to an interrupted state where no torque of the motor (<NUM>) is transmitted to the holder (<NUM>), and vice versa; and
a controller (<NUM>) configured to, when a predetermined condition about the torque detected by the torque detection unit (<NUM>) is satisfied, switch the clutch mechanism (C1) from the transmitting state to the interrupted state, wherein
the clutch mechanism (C1) comprising:
a plurality of first recesses (<NUM>) provided for a first rotating part (<NUM>) that rotates as the motor (<NUM>) runs;
a plurality of magnetic poles (<NUM>) corresponding one to one to the plurality of first recesses (<NUM>), each of the plurality of magnetic poles (<NUM>) being inserted into a corresponding one of the plurality of first recesses (<NUM>);
a plurality of second recesses (<NUM>) provided for a second rotating part (<NUM>) coupled either directly or indirectly to the holder (<NUM>), the plurality of second recesses (<NUM>) corresponding one to one to the plurality of first recesses (<NUM>), a pair of first and second recesses (<NUM>, <NUM>) corresponding to each other facing each other while the clutch mechanism (C1) is in the transmitting state; and
a plurality of permanent magnet blocks (<NUM>) corresponding one to one to the plurality of second recesses (<NUM>), each permanent magnet block (<NUM>) of the plurality of permanent magnet blocks (<NUM>) including a permanent magnet (<NUM>), the permanent magnet (<NUM>) of each permanent magnet block (<NUM>) being inserted into a corresponding one of the plurality of second recesses (<NUM>);
in each of the plurality of second recesses (<NUM>), an elastic member (<NUM>) being interposed between a bottom of a corresponding one second recess (<NUM>) of the plurality of second recesses (<NUM>) and a corresponding one permanent magnet (<NUM>) of the plurality of permanent magnet blocks (<NUM>).