Patent Publication Number: US-2023158657-A1

Title: Electric work machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2021-189994, filed on Nov. 24, 2021, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an electric work machine. 
     2. Description of the Background 
     In the technical field of electric work machines, power tools with a spindle locking assembly are known, as one example is described in Japanese Unexamined Patent Application Publication No. 2014-168840. 
     BRIEF SUMMARY 
     In an electric work machine, a rotational force from a motor may be transmitted to a spindle through a planetary gear assembly. For example, as greater torque is applied to the spindle in a screwing operation, a greater load is applied onto the planetary gear assembly or onto a spindle locking assembly. This may at least partially damage the planetary gear assembly or the spindle locking assembly. 
     One or more aspects of the present disclosure are directed to reducing damage to components of an electric work machine under a greater load on a spindle. 
     A first aspect of the present disclosure provides an electric work machine, including: a motor; 
     a planetary gear assembly at least partially located frontward from the motor, rotatable with a rotational force from the motor, and including a carrier, the carrier having a hole having an inner surface including two carrier flat surfaces; 
     a spindle at least partially located frontward from the planetary gear assembly and including a rear portion received in the hole, the rear portion having an outer surface including two spindle flat surfaces, each of the two spindle flat surfaces being configured to come in contact with a corresponding carrier flat surface of the two carrier flat surfaces; and 
     a spindle locking assembly configured to transmit a rotational force in one direction from the carrier to the spindle, the spindle locking assembly including
         a lock cam surrounding the spindle frontward from a front surface of the carrier and rotatable together with the spindle,   a lock ring surrounding the lock cam, and   a plurality of cylindrical members between the lock cam and the lock ring.       

     A second aspect of the present disclosure provides an electric work machine, including: 
     a motor; 
     a planetary gear assembly at least partially located frontward from the motor, rotatable with a rotational force from the motor, and including a carrier, the carrier having a hole having an inner surface including a plurality of carrier flat surfaces; 
     a spindle at least partially located frontward from the planetary gear assembly and including a rear portion received in the hole, the rear portion having an outer surface including a plurality of spindle flat surfaces, each of the plurality of spindle flat surfaces being configured to come in contact with a corresponding carrier flat surface of the plurality of carrier flat surfaces; and 
     a spindle locking assembly configured to transmit a rotational force in one direction from the carrier to the spindle, the spindle locking assembly including
         a lock cam surrounding the spindle frontward from a front surface of the carrier and rotatable together with the spindle,   a lock ring surrounding the lock cam, and   two cylindrical members between the lock cam and the lock ring.       

     The electric work machine according to the above aspects of the present disclosure reduces damage to its components under a greater load on the spindle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a front perspective view of a driver drill according to an embodiment. 
         FIG.  2    is a rear perspective view of the driver drill according to the embodiment. 
         FIG.  3    is a side view of the driver drill according to the embodiment. 
         FIG.  4    is a sectional view of the driver drill according to the embodiment. 
         FIG.  5    is a partial sectional view of the driver drill according to the embodiment. 
         FIG.  6    is a front perspective view of a spindle locking assembly in the embodiment. 
         FIG.  7    is an exploded perspective view of the spindle locking assembly in the embodiment as viewed from the front. 
         FIG.  8    is a rear perspective view of the spindle locking assembly in the embodiment. 
         FIG.  9    is an exploded perspective view of the spindle locking assembly in the embodiment as viewed from the rear. 
         FIG.  10    is a sectional view of the spindle locking assembly in the embodiment. 
         FIG.  11    is a sectional view of the spindle locking assembly in the embodiment. 
         FIG.  12    is a front perspective view of the spindle in the embodiment. 
         FIG.  13    is a front perspective view of a third carrier in the embodiment. 
         FIG.  14    is a front view of the third carrier in the embodiment. 
         FIG.  15    is a front perspective view of a lock cam and pins in the embodiment. 
         FIG.  16    is a rear perspective view of the lock cam and the pins in the embodiment. 
         FIG.  17    is a front view of the third carrier, the lock cam, and the pins in the embodiment, describing the positional relationship between them. 
     
    
    
     DETAILED DESCRIPTION 
     Although one or more embodiments of the present disclosure will now be described with reference to the drawings, the present disclosure is not limited to the present embodiments. The components in the embodiments described below may be combined as appropriate. One or more components may be eliminated. 
     In the embodiments, the positional relationships between the components will be described using the directional terms such as right and left (or lateral), front and rear (or forward and backward), and up and down (or vertical). The terms indicate relative positions or directions with respect to the center of an electric work machine. 
     The electric work machine includes a motor. In the embodiments, a direction parallel to a rotation axis AX of the motor is referred to as an axial direction for convenience. A direction about the rotation axis AX is referred to as a circumferential direction or circumferentially, or a rotation direction for convenience. A direction radial from the rotation axis AX is referred to as a radial direction or radially for convenience. 
     In the embodiments, the rotation axis AX extends in the front-rear direction. The axial direction corresponds to the front-rear direction. The axial direction is from the front to the rear or from the rear to the front. A position nearer the rotation axis AX in the radial direction, or a radial direction toward the rotation axis AX, is referred to as radially inward for convenience. A position farther from the rotation axis AX in the radial direction, or a radial direction away from the rotation axis AX, is referred to as radially outward for convenience. 
     Overview of Driver Drill 
     The electric work machine according to the embodiment is a driver drill, which is an example of a screwing work machine. 
       FIG.  1    is a front perspective view of a driver drill  1  according to the embodiment.  FIG.  2    is a rear perspective view of the driver drill  1  according to the embodiment.  FIG.  3    is a side view of the driver drill  1  according to the embodiment.  FIG.  4    is a sectional view of the driver drill  1  according to the embodiment. The driver drill  1  according to the embodiment is a vibration driver drill. 
     As shown in  FIGS.  1  to  4   , the driver drill  1  includes a housing  2 , a rear cover  3 , a casing  4 , a battery mount  5 , a motor  6 , a power transmission  7 , an output unit  8 , a fan  9 , a trigger lever  10 , a forward-reverse switch lever  11 , a speed switch lever  12 , a mode switch ring  13 , a lamp  14 , an interface panel  15 , a dial  16 , and a controller  17 . 
     The housing  2  is formed from a synthetic resin. The housing  2  in the embodiment is formed from nylon. The housing  2  includes a left housing  2 L and a right housing  2 R. The left housing  2 L and the right housing  2 R are fastened together with screws  2 S, thus forming the housing  2 . 
     The housing  2  includes a motor compartment  21 , a grip  22 , and a battery holder  23 . 
     The motor compartment  21  accommodates the motor  6 . The motor compartment  21  is cylindrical. 
     The grip  22  is grippable by an operator. The grip  22  is located below the motor compartment  21 . The grip  22  extends downward from the motor compartment  21 . The trigger lever  10  is located in a front portion of the grip  22 . 
     The battery holder  23  accommodates the controller  17 . The battery holder  23  is located under the grip  22 . The battery holder  23  is connected to a lower end of the grip  22 . The battery holder  23  has larger outer dimensions than the grip  22  in the front-rear and lateral directions. 
     The rear cover  3  is formed from a synthetic resin. The rear cover  3  is located behind the motor compartment  21 . The rear cover  3  accommodates the fan  9 . The rear cover  3  covers a rear opening of the motor compartment  21 . The rear cover  3  is fastened to the motor compartment  21  with screws  3 S. 
     The motor compartment  21  has inlets  18 . The rear cover  3  has outlets  19 . Air outside the housing  2  flows into an internal space of the housing  2  through the inlets  18 . Air in the internal space of the housing  2  flows out of the housing  2  through the outlets  19 . 
     The casing  4  accommodates the power transmission  7 . The casing  4  includes a first casing  4 A, a second casing  4 B, a bracket plate  4 C, and a stop plate  4 D. The second casing  4 B is located in front of the first casing  4 A. The mode switch ring  13  is located in front of the second casing  4 B. The first casing  4 A is formed from a synthetic resin. The second casing  4 B is formed from a metal. The second casing  4 B in the embodiment is formed from aluminum. The casing  4  is located in front of the motor compartment  21 . The first casing  4 A and the second casing  4 B are cylindrical. 
     The first casing  4 A is fixed to the rear end of the second casing  4 B. The bracket plate  4 C covers the opening at the rear end of the first casing  4 A. The bracket plate  4 C is fastened to the rear end of the first casing  4 A with screws  4 E. The stop plate  4 D covers the opening at the front end of the second casing  4 B. The stop plate  4 D is fastened to the front end of the second casing  4 B with screws  4 F. 
     The casing  4  covers the front opening of the motor compartment  21 . The first casing  4 A is located inside the motor compartment  21 . The second casing  4 B is fastened to the motor compartment  21  with screws  4 S. 
     The battery mount  5  is located under the battery holder  23 . The battery mount  5  is connected to a battery pack  20 . The battery pack  20  is detachable from the battery mount  5 . The battery pack  20  includes a secondary battery. The battery pack  20  in the embodiment includes a rechargeable lithium-ion battery. The battery pack  20  is attached to the battery mount  5  to power the driver drill  1 . The motor  6  is driven by power supplied from the battery pack  20 . The interface panel  15  and the controller  17  operate on power supplied from the battery pack  20 . 
     The motor  6  powers the driver drill  1 . The motor  6  is a brushless inner-rotor motor. The motor  6  is accommodated in the motor compartment  21 . The motor  6  includes a cylindrical stator  61  and a rotor  62 . The rotor  62  is located inside the stator  61 . The rotor  62  includes a rotor shaft  63  extending in the axial direction. 
     The power transmission  7  is located in front of the motor  6 . The power transmission  7  is accommodated in the casing  4 . The power transmission  7  connects the rotor shaft  63  and the output unit  8  together. The power transmission  7  transmits power generated by the motor  6  to the output unit  8 . The power transmission  7  includes multiple gears. 
     The power transmission  7  includes a reducer  30  and a vibrator  40 . 
     The reducer  30  reduces rotation of the rotor shaft  63  and rotates the output unit  8  at a lower rotational speed than the rotor shaft  63 . The reducer  30  in the embodiment includes a first planetary gear assembly  31 , a second planetary gear assembly  32 , and a third planetary gear assembly  33 . The first planetary gear assembly  31  is at least partially located frontward from the motor  6 . The second planetary gear assembly  32  is located frontward from the first planetary gear assembly  31 . The third planetary gear assembly  33  is located frontward from the second planetary gear assembly  32 . Each of the first to third planetary gear assemblies  31  to  33  rotates with a rotational force from the motor  6 . 
     The vibrator  40  vibrates the output unit  8  in the axial direction. The vibrator  40  includes a first cam  41 , a second cam  42 , and a vibration switch ring  43 . 
     The output unit  8  is located frontward from the motor  6 . The output unit  8  rotates with a rotational force from the motor  6 . The output unit  8  holding a tip tool rotates with a rotational force transmitted from the motor  6  through the power transmission  7 . The output unit  8  includes a spindle  81  and a chuck  82 . The spindle  81  rotates about the rotation axis AX with a rotational force transmitted from the motor  6 . The tip tool is attached to the chuck  82 . The spindle  81  is located at least partially frontward from the third planetary gear assembly  33 . 
     The fan  9  is located behind the motor  6 . The fan  9  generates an airflow for cooling the motor  6 . The fan  9  is fixed to at least a part of the rotor  62 . The fan  9  is fixed to a rear portion of the rotor shaft  63 . As the rotor shaft  63  rotates, the fan  9  rotates together with the rotor shaft  63 . Thus, air outside the housing  2  flows into the internal space of the housing  2  through the inlets  18 . Air flowing into the internal space of the housing  2  flows through the internal space of the housing  2  and thus cools the motor  6 . The air then flows out of the housing  2  through the outlets  19 . 
     The trigger lever  10  activates the motor  6 . The trigger lever  10  is located in an upper portion of the grip  22 . The trigger lever  10  has a front end protruding frontward from the front portion of the grip  22 . The trigger lever  10  is movable in the front-rear direction. The trigger lever  10  is operable by the operator. The trigger lever  10  is operated to move backward to activate the motor  6 . When the trigger lever  10  is released from being operated, the motor  6  is stopped. 
     The forward-reverse switch lever  11  is operable to change the rotation direction of the motor  6 . The forward-reverse switch lever  11  is located in the upper portion of the grip  22 . The forward-reverse switch lever  11  has a left end protruding leftward from a left portion of the grip  22 . The forward-reverse switch lever  11  has a right end protruding rightward from a right portion of the grip  22 . The forward-reverse switch lever  11  is movable in the lateral direction. The forward-reverse switch lever  11  is operable by the operator. The forward-reverse switch lever  11  moves leftward to rotate the motor  6  forward. The forward-reverse switch lever  11  moves rightward to rotate the motor  6  reversely. Switching the rotation direction of the motor  6  switches the rotation direction of the spindle  81 . 
     The speed switch lever  12  is operable to change the speed mode of the reducer  30 . The speed switch lever  12  is located in an upper portion of the motor compartment  21 . The speed switch lever  12  is movable in the front-rear direction. The speed switch lever  12  is operable by the operator. The speed mode of the reducer  30  includes a low-speed mode, a medium-speed mode, and a high-speed mode. In the low-speed mode, the output unit  8  rotates at a low speed. In the medium-speed mode, the output unit  8  rotates at a medium speed. In the high-speed mode, the output unit  8  rotates at a high speed. The movable range of the speed switch lever  12  is defined in the front-rear direction. The speed switch lever  12  moves forward in its movable range to set the reducer  30  to the low-speed mode. The speed switch lever  12  moves to the middle in its movable range to set the reducer  30  to the medium-speed mode. The speed switch lever  12  moves backward in its movable range to set the reducer  30  to the high-speed mode. 
     The mode switch ring  13  is operable to change the operation mode of the vibrator  40 . The mode switch ring  13  is located in front of the casing  4 . The mode switch ring  13  is rotatable. The mode switch ring  13  is operable by the operator. The operation mode of the vibrator  40  includes a vibration mode and a non-vibration mode. In the vibration mode, the output unit  8  vibrates in the axial direction. In the non-vibration mode, the output unit  8  does not vibrate in the axial direction. The mode switch ring  13  at a vibration mode position in the rotation direction sets the vibrator  40  to the vibration mode. The mode switch ring  13  at a non-vibration mode position in the rotation direction sets the vibrator  40  to the non-vibration mode. 
     The lamp  14  emits illumination light to illuminate ahead of the driver drill  1 . The lamp  14  includes, for example, a light-emitting diode (LED). The lamp  14  is located under a front portion of the motor compartment  21 . The lamp  14  is located above the trigger lever  10 . 
     The interface panel  15  is located on the battery holder  23 . The interface panel  15  includes an operation unit  24  and a display  25 . The interface panel  15  is a plate. The operation unit  24  includes an operation button. The display  25  is, for example, a segment display including multiple segment light emitters, a flat display panel such as a liquid crystal display, or an indicator display including multiple LEDs. 
     The battery holder  23  has a panel opening  27 . The panel opening  27  is formed in an upper surface of the battery holder  23  and frontward from the grip  22 . The interface panel  15  is at least partially located in the panel opening  27 . 
     The operation unit  24  is operable to change the drive mode of the motor  6 . The operation unit  24  is operable by the operator. The motor  6  has a drill mode and a clutch mode as its drive mode. In the drill mode, the motor  6  is driven independently of the torque applied to the motor  6  in driving the motor  6 . In the clutch mode, the motor  6  is stopped in response to torque exceeding a torque threshold being applied to the motor  6  in driving the motor  6 . 
     The dial  16  is operable to change the drive conditions of the motor  6 . The dial  16  is located in a front portion of the battery holder  23 . The dial  16  is supported by the battery holder  23  in a rotatable manner. The dial  16  is rotatable by 360° or greater. The dial  16  is operable by the operator. The drive conditions of the motor  6  include the torque threshold. The dial  16  is operable to change the torque threshold in the clutch mode set by the operation unit  24 . 
     The battery holder  23  has a dial opening  28 . The dial opening  28  is formed in a front right portion of the battery holder  23 . The dial  16  is at least partially received in the dial opening  28 . 
     The controller  17  includes a computer system. The controller  17  outputs a control command for controlling the motor  6 . The controller  17  is at least partially accommodated in a controller case  26 . The controller  17  is held by the controller case  26  and is accommodated in the battery holder  23 . The controller  17  includes a circuit board on which multiple electronic components are mounted. Examples of the electronic components mounted on the circuit board include a processor such as a central processing unit (CPU), a nonvolatile memory such as a read-only memory (ROM) or a storage device, a volatile memory such as a random-access memory (RAM), a transistor, a capacitor, and a resistor. 
     The controller  17  sets the drive conditions of the motor  6  based on an operation on the dial  16 . The drive conditions of the motor  6  include the torque threshold. In the clutch mode, the controller  17  sets a torque threshold based on the operation on the dial  16 . 
     In the clutch mode, the controller  17  stops the motor  6  in response to torque exceeding the set torque threshold being applied to the motor  6  in driving the motor  6 . 
     The controller  17  displays the set drive conditions of the motor  6  on the display  25 . The controller  17  displays the set torque threshold on the display  25 . 
     Motor and Power Transmission 
       FIG.  5    is a partial sectional view of the driver drill  1  according to the embodiment. The motor  6  includes the cylindrical stator  61  and the rotor  62  as shown in  FIG.  5   . The rotor  62  is located inside the stator  61 . The rotor  62  includes the rotor shaft  63  extending in the axial direction. 
     The stator  61  includes a stator core  61 A, a front insulator  61 B, a rear insulator  61 C, multiple coils  61 D, a sensor circuit board  61 E, and a short-circuiting member  61 F. The stator core  61 A includes multiple steel plates stacked on one another. The front insulator  61 B is located in front of the stator core  61 A. The rear insulator  61 C is located behind the stator core  61 A. The coils  61 D are wound around the stator core  61 A with the front insulator  61 B and the rear insulator  61 C between them. The sensor circuit board  61 E is attached to the front insulator  61 B. The short-circuiting member  61 F is supported by the front insulator  61 B. The sensor circuit board  61 E includes multiple rotation detectors to detect the rotation of the rotor  62 . The short-circuiting member  61 F connects multiple coils  61 D with fusing terminals. The short-circuiting member  61 F is connected to the controller  17  with lead wires. 
     The rotor  62  rotates about the rotation axis AX. The rotor  62  includes the rotor shaft  63 , a rotor core  62 A, and multiple permanent magnets  62 B. The rotor core  62 A surrounds the rotor shaft  63 . The multiple permanent magnets  62 B are held by the rotor core  62 A. The rotor core  62 A is cylindrical. The rotor core  62 A includes multiple steel plates stacked on one another. The rotor core  62 A has a through-hole extending in the axial direction. The rotor core  62 A has multiple through-holes located circumferentially. The permanent magnets  62 B are received in the respective through-holes in the rotor core  62 A. 
     The rotation detector in the sensor circuit board  61 E detects the magnetic fields of the permanent magnets  62 B to detect the rotation of the rotor  62 . The controller  17  provides a drive current to the coils  61 D based on the detection data from the rotation detector. 
     The rotor shaft  63  rotates about the rotation axis AX. The rotation axis AX of the rotor shaft  63  is aligned with the rotation axis of the output unit  8 . The rotor shaft  63  includes a front portion supported by a bearing  64  in a rotatable manner. The rotor shaft  63  includes a rear portion supported by a bearing  65  in a rotatable manner. The bearing  64  is held on the bracket plate  4 C. The bracket plate  4 C is located in front of the stator  61 . The bearing  65  is held by the rear cover  3 . The rotor shaft  63  has its front end located frontward from the bearing  64 . The rotor shaft  63  has its front end located in an internal space of the casing  4 . 
     A pinion gear  31 S is located at the front end of the rotor shaft  63 . The pinion gear  31 S includes a larger-diameter portion  311 S and a smaller-diameter portion  312 S. The smaller-diameter portion  312 S is located in front of the larger-diameter portion  311 S. The rotor shaft  63  is connected to the first planetary gear assembly  31  in the reducer  30  with the pinion gear  31 S. 
     The first planetary gear assembly  31  includes multiple planetary gears  311 P, multiple planetary gears  312 P, a first carrier  31 C, an internal gear  311 R, and an internal gear  312 R. 
     The planetary gears  311 P surround the larger-diameter portion  311 S of the pinion gear  31 S. The planetary gears  312 P surround the smaller-diameter portion  312 S of the pinion gear  31 S. The first carrier  31 C supports the planetary gears  311 P and the planetary gears  312 P. The internal gear  311 R surrounds the planetary gears  311 P. The internal gear  312 R surrounds the planetary gears  312 P. Each planetary gear  311 P has a smaller outer diameter than the planetary gear  312 P. A pin  31 A is located on the first carrier  31 C. The planetary gears  311 P and the planetary gears  312 P are supported by the pin  31 A in a rotatable manner. The first carrier  31 C supports the planetary gears  311 P and the planetary gears  312 P with the pin  31 A in a rotatable manner. The first carrier  31 C includes a gear on its outer periphery. 
     The second planetary gear assembly  32  includes a sun gear  32 S, multiple planetary gears  32 P, a second carrier  32 C, and an internal gear  32 R. The planetary gears  32 P surround the sun gear  32 S. The second carrier  32 C supports the planetary gears  32 P. The internal gear  32 R surrounds the planetary gears  32 P. The sun gear  32 S is located in front of the first carrier  31 C. The sun gear  32 S has a smaller diameter than the first carrier  31 C. The first carrier  31 C is integral with the sun gear  32 S. The first carrier  31 C and the sun gear  32 S rotate together. A pin  32 A is located on the second carrier  32 C. The planetary gears  32 P are supported by the pin  32 A in a rotatable manner. The second carrier  32 C supports the planetary gears  32 P with the pin  32 A in a rotatable manner. 
     The third planetary gear assembly  33  includes a sun gear  33 S, multiple planetary gears  33 P, a third carrier  33 C, and an internal gear  33 R. The planetary gears  33 P surround the sun gear  33 S. The third carrier  33 C supports the planetary gears  33 P. The internal gear  33 R surrounds the planetary gears  33 P. The sun gear  33 S is located in front of the second carrier  32 C. The sun gear  33 S has a smaller diameter than the second carrier  32 C. The second carrier  32 C is integral with the sun gear  33 S. The second carrier  32 C and the sun gear  33 S rotate together. Pins  33 A are located on the third carrier  33 C. The planetary gears  33 P are supported by the corresponding pins  33 A in a rotatable manner. The third carrier  33 C supports the planetary gears  33 P with the corresponding pins  33 A in a rotatable manner. 
     The reducer  30  includes a first speed switcher  34  and a second speed switcher  35 . The first speed switcher  34  is connected to the speed switch lever  12 . The second speed switcher  35  is connected to the speed switch lever  12 . 
     The first speed switcher  34  switches between an enabled mode and a disabled mode. In the enabled mode, the rotation reduction of the second planetary gear assembly  32  is enabled. In the disabled mode, the rotation reduction of the second planetary gear assembly  32  is disabled. The second planetary gear assembly  32  being placed in the enabled mode includes the rotation of the internal gear  32 R being restricted. The second planetary gear assembly  32  being placed in the disabled mode includes the rotation of the internal gear  32 R being allowed. The rotation of the internal gear  32 R is restricted to place the second planetary gear assembly  32  in the enabled mode. The rotation of the internal gear  32 R is allowed to place the second planetary gear assembly  32  in the disabled mode. 
     The first speed switcher  34  is movable in the front-rear direction inside the first casing  4 A. The first speed switcher  34  moves forward to place the second planetary gear assembly  32  in the enabled mode. The first speed switcher  34  moves backward to place the second planetary gear assembly  32  in the disabled mode. As the speed switch lever  12  moves in the front-rear direction, the first speed switcher  34  moves in the front-rear direction. 
     The internal gear  32 R in the embodiment is connected to the first speed switcher  34 . As the first speed switcher  34  moves in the front-rear direction, the internal gear  32 R moves in the front-rear direction together with the first speed switcher  34 . A cam ring  36  is located in front of the internal gear  32 R. The cam ring  36  has cam teeth on its inner circumferential surface. The internal gear  32 R has cam teeth on its outer circumferential surface. 
     As the first speed switcher  34  moves forward to place the internal gear  32 R at least partially inside the cam ring  36 , the cam teeth on the internal gear  32 R and the cam teeth on the cam ring  36  mesh each other. This restricts the rotation of the internal gear  32 R. As the first speed switcher  34  moves backward to remove the internal gear  32 R from inside the cam ring  36 , the cam teeth on the internal gear  32 R and the cam teeth on the cam ring  36  separate from each other. This allows the rotation of the internal gear  32 R. 
     When the second planetary gear assembly  32  is in the enabled mode, the internal gear  32 R meshes with the planetary gears  32 P alone. When the second planetary gear assembly  32  is in the disabled mode, the internal gear  32 R meshes with both the planetary gears  32 P and the first carrier  31 C. 
     The second speed switcher  35  switches between the first reduction mode and the second reduction mode. In the first reduction mode, the rotation of the internal gear  312 R in the first planetary gear assembly  31  is restricted, and the rotation in the internal gear  311 R is allowed. In the second reduction mode, the rotation of the internal gear  311 R in the first planetary gear assembly  31  is restricted, and the rotation of the internal gear  312 R is allowed. The second speed switcher  35  is movable in the front-rear direction inside the first casing  4 A. The second speed switcher  35  moves forward and enters the first reduction mode. The second speed switcher  35  moves backward and enters the second reduction mode. As the speed switch lever  12  moves in the front-rear direction, the second speed switcher  35  moves in the front-rear direction. 
     A cam pin (not shown in  FIG.  5   ) is engaged with the second speed switcher  35 . The cam pin moves in the front-rear direction together with the second speed switcher  35  while being guided along a guide groove on the first casing  4 A. The cam pin is received in the guide groove and thus does not move in the circumferential direction. 
     When the second speed switcher  35  moves forward to surround the internal gear  312 R, the cam pin comes in contact with the cam teeth on the outer circumference surface of the internal gear  312 R. This restricts the rotation of the internal gear  312 R. More specifically, the second speed switcher  35  moves forward to restrict the rotation of the internal gear  312 R. This places the first planetary gear assembly  31  in the first reduction mode. 
     When the second speed switcher  35  moves backward to surround the internal gear  311 R, the cam pin comes in contact with the cam teeth on the outer circumference surface of the internal gear  311 R. This restricts the rotation of the internal gear  311 R. More specifically, the second speed switcher  35  moves backward to restrict the rotation of internal gear  311 R. This places the first planetary gear assembly  31  in the second reduction mode. 
     In the embodiment, the speed mode of the reducer  30  includes the low-speed mode, the medium-speed mode, and the high-speed mode. The speed switch lever  12  moves forward in its movable range to set the reducer  30  to the low-speed mode. The speed switch lever  12  moves to the middle in its movable range to set the reducer  30  to the medium-speed mode. The speed switch lever  12  moves backward in its movable range to set the reducer  30  to the high-speed mode. 
     The low-speed mode includes the first planetary gear assembly  31  being set to the first reduction mode and the second planetary gear assembly  32  being set to the enabled mode. The speed switch lever  12  moves forward in its movable range to set the first planetary gear assembly  31  to the first reduction mode, and set the second planetary gear assembly  32  to the enabled mode. 
     The medium-speed mode includes the first planetary gear assembly  31  being set to the first reduction mode and the second planetary gear assembly  32  being set to the disabled mode. The speed switch lever  12  moves to the middle in its movable range to set the first planetary gear assembly  31  to the first reduction mode, and set the second planetary gear assembly  32  to the disabled mode. 
     The medium-speed mode includes the first planetary gear assembly  31  being set to the second reduction mode and the second planetary gear assembly  32  being set to the disabled mode. The speed switch lever  12  moves forward in its movable range to set the first planetary gear assembly  31  to the second reduction mode, and set the second planetary gear assembly  32  to the disabled mode. 
     The spindle  81  is connected to the third carrier  33 C with the spindle locking assembly  50 . The spindle locking assembly  50  includes a lock cam  51  and a lock ring  52 . The lock cam  51  surrounds the spindle  81 . The lock ring  52  supports the lock cam  51  in a rotatable manner. The lock ring  52  is located inside the second casing  4 B. The lock ring  52  is fixed to the second casing  4 B. As the third carrier  33 C rotates, the spindle  81  rotates. 
     The spindle  81  is supported by a bearing  83  and a bearing  84  in a rotatable manner. In this state, the spindle  81  is movable in the front-rear direction. 
     The spindle  81  includes a flange  81 F. A coil spring  87  is located between the flange  81 F and the bearing  83 . The flange  81 F comes in contact with the front end of the coil spring  87 . The coil spring  87  generates an elastic force for moving the spindle  81  forward. 
     The chuck  82  can hold the tip tool. The chuck  82  is connected to a front portion of the spindle  81 . The spindle  81  has a threaded hole  81 R on its front end. The chuck  82  and the spindle  81  are fastened with a screw  88 . With the head of the screw  88  in contact with the chuck  82 , threads on the screw  88  are placed into the threaded hole  81 R, thus connecting the chuck  82  and the spindle  81  together. The chuck  82  rotates as the spindle  81  rotates. The chuck  82  holding the tip tool rotates. 
     The first cam  41  and the second cam  42  in the vibrator  40  are both located inside the second casing  4 B. The first cam  41  and the second cam  42  are located between the bearing  83  and the bearing  84  in the front-rear direction. 
     The first cam  41  is annular. The first cam  41  surrounds the spindle  81 . The first cam  41  is fixed to the spindle  81 . The first cam  41  rotates together with the spindle  81 . The first cam  41  has cam teeth on its rear surface. The first cam  41  is supported by a stop ring  44 . The stop ring  44  surrounds the spindle  81 . The stop ring  44  is located between the first cam  41  and the bearing  83  in the front-rear direction. An elastic force from the coil spring  87  causes the stop ring  44  to come in contact with a rear surface of the bearing  83 . 
     The second cam  42  is annular. The second cam  42  is located behind the first cam  41 . The second cam  42  surrounds the spindle  81 . The second cam  42  is rotatable relative to the spindle  81 . The second cam  42  has cam teeth on its front surface. The cam teeth on the front surface of the second cam  42  mesh with the cam teeth on the rear surface of the first cam  41 . The second cam  42  includes a tab on its rear surface. 
     A support ring  45  is located between the second cam  42  and the bearing  84  in the front-rear direction. The support ring  45  is located inside the second casing  4 B. The support ring  45  is fixed to the second casing  4 B. The support ring  45  receives multiple steel balls  46  on its front surface. A washer  47  is located between the steel ball  46  and the second cam  42 . The second cam  42  is rotatable while being restricted from moving forward and backward in a space defined by the support ring  45  and the washer  47 . 
     The vibration switch ring  43  switches between the vibration mode and the non-vibration mode. The mode switch ring  13  is connected to the vibration switch ring  43  with a cam ring  48  between them. The mode switch ring  13  is rotatable together with the cam ring  48 . The vibration switch ring  43  is movable in the front-rear direction. The vibration switch ring  43  includes a protrusion  43 T. The protrusion  43 T is placed in a guide hole in the second casing  4 B. The vibration switch ring  43  is movable in the front-rear direction while being guided along the guide hole in the second casing  4 B. The protrusion  43 T restricts the vibration switch ring  43  from rotating. The operator operates the mode switch ring  13  to move the vibration switch ring  43  in the front-rear direction. The vibration switch ring  43  moves in the front-rear direction between an advanced position and a retracted position rearward from the advanced position to switch between the vibration mode and the non-vibration mode. The mode switch ring  13  is operable to switch between the vibration mode and the non-vibration mode. 
     The vibration mode includes the state of the second cam  42  being restricted from rotating. The non-vibration mode includes the state of the second cam  42  being rotatable. When the vibration switch ring  43  moves to the advanced position, the second cam  42  is restricted from rotating. When the vibration switch ring  43  moves to the retracted position, the second cam  42  becomes rotatable. 
     In the vibration mode, the vibration switch ring  43  at the advanced position is at least partially in contact with the second cam  42 . This restricts the second cam  42  from rotating. When the motor  6  is driven in this state, the first cam  41  fixed to the spindle  81  rotates in contact with the cam teeth on the second cam  42 . The spindle  81  thus rotates while vibrating in the front-rear direction. 
     In the non-vibration mode, the vibration switch ring  43  at the retracted position is separate from the second cam  42 . This allows the second cam  42  to rotate. When the motor  6  is driven in this state, the second cam  42  rotates together with the first cam  41  and the spindle  81 . The spindle  81  thus rotates without vibrating in the front-rear direction. 
     The vibration switch ring  43  surrounds the first cam  41  and the second cam  42 . The vibration switch ring  43  includes an opposing portion  43 S facing the rear surface of the second cam  42 . The opposing portion  43 S protrudes radially inward from a rear portion of the vibration switch ring  43 . 
     When the mode switch ring  13  is operated to move the vibration switch ring  43  to the advanced position, the tab on the rear surface of the second cam  42  is in contact with the opposing portion  43 S of the vibration switch ring  43 . This restricts the second cam  42  from rotating. In this manner, the mode switch ring  13  is operated to move the vibration switch ring  43  to the advanced position and to switch the vibrator  40  to the vibration mode. 
     When the mode switch ring  13  is operated to move the vibration switch ring  43  to the retracted position, the opposing portion  43 S of the vibration switch ring  43  is separate from the second cam  42 . This allows the second cam  42  to rotate. In this manner, the mode switch ring  13  is operated to move the vibration switch ring  43  to the retracted position and to switch the vibrator  40  to the non-vibration mode. 
     Spindle Locking Assembly 
     The spindle locking assembly  50  will now be described.  FIG.  6    is a front perspective view of the spindle locking assembly  50  in the embodiment.  FIG.  7    is an exploded perspective view of the spindle locking assembly  50  in the embodiment as viewed from the front.  FIG.  8    is a rear perspective view of the spindle locking assembly  50  in the embodiment.  FIG.  9    is an exploded perspective view of the spindle locking assembly  50  in the embodiment as viewed from the rear.  FIG.  10    is a sectional view of the spindle locking assembly  50  in the embodiment taken along line A-A in  FIG.  6    as viewed in the direction indicated by arrows.  FIG.  11    is a sectional view of the spindle locking assembly  50  in the embodiment taken along line B-B in  FIG.  6    as viewed in the direction indicated by arrows.  FIG.  12    is a front perspective view of the spindle  81  in the embodiment.  FIG.  13    is a front perspective view of the third carrier  33 C in the embodiment.  FIG.  14    is a front view of the third carrier  33 C in the embodiment. 
     The spindle locking assembly  50  transmits a rotational force from the third carrier  33 C to the spindle  81  and blocks transmission of the rotational force from the spindle  81  to the third carrier  33 C. The spindle locking assembly  50  functions as a one-way clutch that transmits a rotational force from the third carrier  33 C to the spindle  81  in one direction alone. 
     The spindle locking assembly  50  is connected to each of the spindle  81  and the third carrier  33 C. The spindle locking assembly  50  includes the lock cam  51 , the lock ring  52 , and multiple pins  53  (cylindrical members). The lock cam  51  surrounds the spindle  81 . The lock ring  52  surrounds the lock cam  51 . The multiple pins  53  are located between the lock cam  51  and the lock ring  52 . 
     The spindle  81  is a rod elongated in the front-rear direction. The spindle  81  includes the flange  81 F and the threaded hole  81 R. The flange  81 F comes in contact with the front end of the coil spring  87 . The threads on the screw  88  are placed in the threaded hole  81 R. 
     The spindle  81  includes a rear portion with a flat surface  81 A, a flat surface  81 B, a curved surface  81 C, and a curved surface  81 D on the outer surface. Each of the flat surface  81 A, the flat surface  81 B, the curved surface  81 C, and the curved surface  81 D is parallel to the rotation axis AX. The flat surface  81 A and the flat surface  81 B are parallel to each other. The flat surface  81 A and the flat surface  81 B define flat edges on the rear portion of the spindle  81  extending frontward from the rear end of the spindle  81 . The curved surface  81 C connects the left end of the flat surface  81 A with the left end of the flat surface  81 B. The curved surface  81 D connects the right end of the flat surface  81 A with the right end of the flat surface  81 B. In the cross section orthogonal to the rotation axis AX, the curved surface  81 C and the curved surface  81 D are arcs being away from the rotation axis AX. 
     The third carrier  33 C is located frontward from the internal gear  33 R and the planetary gears  33 P. The internal gear  33 R surrounds the planetary gears  33 P. The third carrier  33 C supports the planetary gears  33 P. The multiple pins  33 A are supported on the third carrier  33 C. The pins  33 A protrude rearward from the rear surface of the third carrier  33 C. The pins  33 A support the corresponding planetary gears  33 P in a rotatable manner. The third carrier  33 C supports the planetary gears  33 P with the corresponding pins  33 A in a rotatable manner. 
     The third carrier  33 C includes a plate  330 , a protrusion  331 , a protrusion  332 , a protrusion  333 , a protrusion  334 , a land  335 , and a land  336 . 
     The plate  330  is substantially disk-shaped. The front surface of the plate  330  is parallel to the rear surface of the plate  330 . The plate  330  has a hole  337  at its center. The hole  337  extends through the front surface of the plate  330  and the rear surface of the plate  330 . 
     Each of the protrusions  331  to  334  protrudes frontward from the front surface of the plate  330 . The protrusions  331  to  334  protrude by substantially equal amounts. The amount by which each of the protrusions  331  to  334  protrudes refers to the amount by which each protrusion protrudes from the front surface of the plate  330 . The protrusions  331  to  334  are spaced apart from one another to surround the hole  337  (about the rotation axis AX of the third carrier  33 C). The protrusion  331  is located at the upper left of the hole  337 . The protrusion  332  is located at the upper right of the hole  337 . The protrusion  333  is located at the lower left of the hole  337 . The protrusion  334  is located at the lower right of the hole  337 . In a plane orthogonal to the rotation axis AX, each of the protrusions  331  to  334  extends along the outer shape of the hole  337 . The protrusions  331  to  334  are substantially arc-shaped in a plane orthogonal to the rotation axis AX. 
     Each of the lands  335  and  336  protrudes frontward from the front surface of the plate  330 . The land  335  and the land  336  protrude by substantially equal amounts. The amount by which each of the lands  335  and  336  protrudes refers to the amount by which each land protrudes from the front surface of the plate  330 . In the circumferential direction, the land  335  is located between the protrusions  331  and  332 . In the circumferential direction, the land  336  is located between the protrusions  333  and  334 . The land  335  protrudes by a lesser amount than each of the protrusions  331  and  332 . The land  336  protrudes by a lesser amount than each of the protrusions  333  and  334 . In a plane orthogonal to the rotation axis AX, each of the lands  335  and  336  extends along the outer shape of the hole  337 . The lands  335  and  336  are substantially arc-shaped in a plane orthogonal to the rotation axis AX. 
     As shown in  FIGS.  13  and  14   , the third carrier  33 C has a flat surface  3371 A, a flat surface  3371 B, a flat surface  3372 A, a flat surface  3372 B, a curved surface  337 C, and a curved surface  337 D. Each of the flat surface  3371 A, the flat surface  3371 B, the flat surface  3372 A, the flat surface  3372 B, the curved surface  337 C, and the curved surface  337 D is parallel to the rotation axis AX. 
     The flat surface  3371 A includes a portion of the inner surface of the hole  337  and a portion of the inner surface of the land  335  facing the hole  337 . The flat surface  3372 A includes a portion of the inner surface of the hole  337  and a portion of the inner surface of the land  335  facing the hole  337 . 
     The flat surface  3371 B includes a portion of the inner surface of the hole  337  and a portion of the inner surface of the land  336  facing the hole  337 . The flat surface  3372 B includes a portion of the inner surface of the hole  337  and a portion of the inner surface of the land  336  facing the hole  337 . 
     The flat surfaces  3371 A and  3372 A are adjacent to each other. The flat surface  3371 A is located leftward from the flat surface  3372 A. The angle between the flat surface  3371 A and the flat surface  3372 A is greater than 180°. The flat surface  3371 B and the flat surface  3372 B are adjacent to each other. The flat surface  3371 B is located rightward from the flat surface  3372 B. The angle between the flat surface  3371 B and the flat surface  3372 B is greater than 180°. The flat surface  3371 A and the flat surface  3371 B are parallel to each other. The flat surface  3372 A and the flat surface  3372 B are parallel to each other. 
     The curved surface  337 C includes a portion of the inner surface of the hole  337 . The inner surface of the hole  337  includes the curved surface  337 C connecting the left end of the flat surface  3371 A with the left end of the flat surface  3372 B. The curved surface  337 D includes a portion of the inner surface of the hole  337 . The inner surface of the hole  337  includes the curved surface  337 D connecting the right end of the flat surface  3372 A with the right end of the flat surface  3371 B. In the cross section orthogonal to the rotation axis AX, the curved surfaces  337 C and  337 D are arcs being away from the rotation axis AX. 
     The land  335  has a support surface  335 A and a support surface  335 B. The support surface  335 A connects to the front surface of the plate  330  and to the inner surface of the protrusion  331  facing radially inward. The support surface  335 B connects to the front surface of the plate  330  and to the inner surface of the protrusion  332  facing radially inward. 
     The land  336  includes a support surface  336 A and a support surface  336 B. The support surface  336 A connects to the front surface of the plate  330  and to the inner surface of the protrusion  333  facing radially inward. The support surface  336 B connects to the front surface of the plate  330  and to the inner surface of the protrusion  334  facing radially inward. Each of the support surface  335 A, the support surface  335 B, the support surface  336 A, and the support surface  336 B is parallel to the rotation axis AX. 
       FIG.  15    is a front perspective view of the lock cam  51  and the pins  53  in the embodiment.  FIG.  16    is a rear perspective view of the lock cam  51  and the pins  53  in the embodiment. 
     The lock cam  51  surrounds the spindle  81  frontward from the front surface of the plate  330  in the third carrier  33 C. The lock cam  51  includes a cylindrical portion  511 , a protrusion  512 , and a protrusion  513 . 
     The outer surface of the lock cam  51  includes a flat surface  511 A, a flat surface  511 B, a curved surface  511 C, and a curved surface  511 D. Each of the flat surface  511 A, the flat surface  511 B, the curved surface  511 C, and the curved surface  511 D is parallel to the rotation axis AX. The flat surface  511 A and the flat surface  511 B are parallel to each other. The curved surface  511 C connects the upper end of the flat surface  511 A with the upper end of the flat surface  511 B. The curved surface  511 D connects the lower end of the flat surface  511 A with the lower end of flat surface  511 B. In the cross section orthogonal to the rotation axis AX, the curved surface  511 C and the curved surface  511 D are arcs being away from the rotation axis AX. 
     The cylindrical portion  511  surrounds the rear portion of the spindle  81 . The outer surface of the cylindrical portion  511  includes a portion of the flat surface  511 A, a portion of the flat surface  511 B, the curved surface  511 C, and the curved surface  511 D. The portion of the flat surface  511 A is located on the left of the cylindrical portion  511 . The portion of the flat surface  511 B is located on the right of the cylindrical portion  511 . 
     The cylindrical portion  511  has a hole  514  at its center. The hole  514  extends through the front surface and the rear surface of the cylindrical portion  511 . The rear portion of the spindle  81  is received in the hole  514 . 
     The inner surface of the hole  514  includes a flat surface  514 A, a flat surface  514 B, a curved surface  514 C, and a curved surface  514 D. Each of the flat surface  514 A, the flat surface  514 B, the curved surface  514 C, and the curved surface  514 D is parallel to the rotation axis AX. The flat surface  514 A and the flat surface  514 B are parallel to each other. The curved surface  514 C connects the left end of the flat surface  514 A with the left end of the flat surface  514 B. The curved surface  514 D connects the right end of the flat surface  514 A with the right end of the flat surface  514 B. In the cross section orthogonal to the rotation axis AX, the curved surface  514 C and the curved surfaces  514 D are arcs being away from the rotation axis AX. 
     Each of the protrusions  512  and  513  protrudes rearward from the rear surface of the cylindrical portion  511 . The portion of the flat surface  511 A is located on the side surface of the protrusion  512 . The portion of the flat surface  511 B is located on the side surface of the protrusion  513 . The protrusions  512  and  513  protrude by substantially equal amounts. The amount by which each of the protrusions  512  and  513  refers to the amount by which each protrusion protrudes from the rear surface of the cylindrical portion  511 . The protrusion  512  is located leftward from the hole  514 . The protrusion  513  is located rightward from the hole  514 . Each of the protrusions  512  and  513  is located without protruding radially outward from the outer surface of the cylindrical portion  511 . 
     The lock ring  52  supports the lock cam  51  in a rotatable manner. The lock ring  52  surrounds the lock cam  51 . The lock ring  52  is fixed to the second casing  4 B. The lock ring  52  does not rotate. 
     The multiple (two in the embodiment) pins  53  surround the lock cam  51 . One pin  53  faces the flat surface  511 A of the lock cam  51 . The other pin  53  faces the flat surface  511 B of the lock cam  51 . In the front-rear direction, the flat surface  511 A and the corresponding pin  53  have substantially equal dimensions. In the front-rear direction, the flat surface  511 B and the corresponding pin  53  have substantially equal dimensions. 
       FIG.  17    is a front view of the third carrier  33 C, the lock cam  51 , and the pins  53  in the embodiment, describing the positional relationship between them. 
     As shown in  FIGS.  11  and  17   , the lock cam  51  is located radially inward from the multiple protrusions  331 ,  332 ,  333 , and  334 . As shown in  FIG.  11   , the lock ring  52  is at least partially located radially outward from the multiple protrusions  331 ,  332 ,  333 , and  334 . 
     The pins  53  are located between the outer surface of the lock cam  51  and the inner surface of the lock ring  52 . The pins  53  are located between the lock cam  51  and the lock ring  52  to allow the central axis of each pin  53  to be parallel to the rotation axis AX of the spindle  81 . 
     The pin  53  facing the flat surface  511 A is located between a lower end face  331 T of the protrusion  331  and an upper end face  333 T of the protrusion  333  in the circumferential direction. The pin  53  facing the flat surface  511 B is located between a lower end face  332 T of the protrusion  332  and an upper end face  334 T of the protrusion  334  in the circumferential direction. 
     The cylindrical portion  511  of the lock cam  51  is located radially inward from the protrusions  331  to  334  and the lands  335  and  336 . The rear surface of the cylindrical portion  511  faces the front surfaces of the lands  335  and  336 . 
     The protrusion  512  is located between the support surface  335 A of the land  335  and the support surface  336 A of the land  336 . The rear surface of the protrusion  512  faces the front surface of the cylindrical portion  511  leftward from the hole  337 . The protrusion  513  is located between the support surface  335 B of the land  335  and the support surface  336 B of the land  336 . The rear surface of the protrusion  513  faces the front surface of the cylindrical portion  511  rightward from the hole  337 . 
     As shown in  FIG.  11   , one pin  53  is located between the flat surface  511 A of the lock cam  51  and the inner surface of the lock ring  52 . The other pin  53  is located between the flat surface  511 B of the lock cam  51  and the inner surface of the lock ring  52 . 
     The rear portion of the spindle  81  is received in the hole  337  in the third carrier  33 C. The flat surface  81 A of the spindle  81  comes in contact with one of the flat surfaces  3371 A and  3372 A. The flat surface  81 B of the spindle  81  comes in contact with one of the flat surfaces  3371 B and  3372 B. The curved surface  81 C of the spindle  81  faces the curved surface  337 C. The curved surface  81 D of the spindle  81  faces the curved surface  337 D. 
     When the flat surface  81 A of the spindle  81  comes in contact with the flat surface  3371 A, the flat surface  81 B of the spindle  81  comes in contact with the flat surface  3371 B. In this case, the flat surface  81 A is separate from the flat surface  3372 A, and the flat surface  81 B is separate from the flat surface  3372 B. 
     When the flat surface  81 A of the spindle  81  comes in contact with the flat surface  3372 A, the flat surface  81 B of the spindle  81  comes in contact with the flat surface  3372 B. In this case, the flat surface  81 A is separate from the flat surface  3371 A, and the flat surface  81 B is separate from the flat surface  3371 B. 
     In the example described below, the state in which the flat surface  81 A is in contact with the flat surface  3371 A and the flat surface  81 B of the spindle  81  is in contact with the flat surface  3371 B is referred to as a first contact state. The state in which the flat surface  81 A is in contact with the flat surface  3372 A and the flat surface  81 B is in contact with the flat surface  3372 B is referred to as a second contact state. 
     In the embodiment, the spindle  81  and the third carrier  33 C can rotate slightly relative to each other to change between the first contact state and the second contact state. 
     The rear portion of the spindle  81  is received in the hole  514  in the lock cam  51 . The flat surface  81 A of the spindle  81  faces the flat surface  514 A. The flat surface  81 B of the spindle  81  faces the flat surface  514 B. The curved surface  81 C of the spindle  81  faces the curved surface  514 C. The curved surface  81 D of the spindle  81  faces the curved surface  514 D. The lock cam  51  is rotatable together with the spindle  81 . 
     When the third carrier  33 C rotates in the direction indicated by arrow Ra shown in  FIGS.  11 ,  14 , and  17    as driven by the motor  6 , the spindle  81  rotates together with the third carrier  33 C in the direction indicated by arrow Ra in the first contact state in which the flat surface  81 A is in contact with the flat surface  3371 A and the flat surface  81 B of the spindle  81  is in contact with the flat surface  3371 B. The lock cam  51  rotates together with the spindle  81  in the direction indicated by arrow Ra. The pin  53  facing the flat surface  511 A rotates together with the third carrier  33 C in contact with the lower end face  331 T of the protrusion  331 . The pin  53  facing the flat surface  511 B rotates together with the third carrier  33 C in contact with the upper end face  334 T of the protrusion  334 . 
     When the third carrier  33 C rotates in the direction indicated by arrow Rb shown in  FIGS.  11 ,  14 , and  17    as driven by the motor  6 , the spindle  81  rotates together with the third carrier  33 C in the direction indicated by arrow Rb in the second state in which the flat surface  81 A is in contact with the flat surface  3372 A and the flat surface  81 B of the spindle  81  is in contact with the flat surface  3372 B. The lock cam  51  rotates together with the spindle  81  in the direction indicated by arrow Rb. The pin  53  facing the flat surface  511 A rotates together with the third carrier  33 C in contact with the upper end face  333 T of the protrusion  333 . The pin  53  facing the flat surface  511 B rotates together with the third carrier  33 C in contact with the lower end face  332 T of the protrusion  332 . 
     Thus, when the third carrier  33 C rotates as driven by the motor  6 , the rotational force from the third carrier  33 C is transmitted to the spindle  81 . The third carrier  33 C and the spindle  81  rotate together, with the relative positions of the lock cam  51  and the pin  53  in the circumferential direction being unchanged. 
     When, for example, attaching a tip tool to the output unit  8 , the operator may apply a force in the rotation direction to the spindle  81 . For example, the spindle  81  may rotate when the chuck  82  is tightened. To attach the tip tool smoothly to the output unit  8 , the rotation of the spindle  81  is to be restricted. In attaching the tip tool, the spindle locking assembly  50  blocks transmission of a rotational force from the spindle  81  to the third carrier  33 C. In other words, the rotation of the spindle  81  is restricted. This allows the tip tool to be smoothly attached to the output unit  8 . 
     When a force is applied in the rotation direction to the spindle  81  and the spindle  81  is about to rotate, the lock cam  51  is also about to rotate together with the spindle  81 . The lock ring  52  surrounds the lock cam  51 . The lock ring  52  is fixed to the casing  4  and does not rotate. As the lock cam  51  rotates, the pin  53  facing the flat surface  511 A moves and is pushed radially outward by the flat surface  511 A. The pin  53  facing the flat surface  511 B then moves and is pushed radially outward by the flat surface  511 B. The one pin  53  is sandwiched between the flat surface  511 A and the inner surface of the lock ring  52 . The other pin  53  is sandwiched between the flat surface  511 B and the inner surface of the lock ring  52 . The pins  53  serve as wedges that restrict rotation of the lock cam  51 . This restricts the rotation of the lock cam  51 , thus restricting the rotation of the spindle  81 . Transmission of a rotational force from the spindle  81  to the third carrier  33 C is blocked. 
     As described above, the spindle  81  and the third carrier  33 C can rotate slightly relative to each other to change between the first contact state and the second contact state. When the spindle  81  and the third carrier  33 C cannot rotate relative to each other, the lock cam  51  may not rotate until the wedge effect of the pins  53  is produced. In the embodiment, the spindle  81  and the third carrier  33 C can rotate slightly relative to each other, and thus the lock cam  51  can rotate until the wedge effect of the pins  53  is produced. 
     The driver drill  1  according to the embodiment includes the motor  6 , the third planetary gear assembly  33 , the spindle  81 , and the spindle locking assembly  50 . The third planetary gear assembly  33  is at least partially located frontward from the motor  6 . The third planetary gear assembly  33  is rotatable with a rotational force from the motor  6 . The spindle  81  is at least partially located frontward from the third planetary gear assembly  33 . The spindle locking assembly  50  transmits a rotational force in one direction from the third carrier  33 C of the third planetary gear assembly  33  to the spindle  81 . The rear portion of the spindle  81  is received in the hole  337  in the third carrier  33 C. 
     The rear portion the spindle  81  has the outer surface including the two flat surfaces  81 A and  81 B. The inner surface of the hole  337  of the third carrier  33 C includes the two flat surfaces  3371 A and  3371 B ( 3372 A and  3372 B) that come in contact with the two flat surfaces  81 A and  81 B of the spindle  81 . The spindle locking assembly  50  includes the lock cam  51  surrounding the spindle  81  frontward from the front surface of the plate  330  in the third carrier  33 C and rotatable together with the spindle  81 . The spindle locking assembly  50  includes the lock ring  52  surrounding the lock cam  51 . The spindle locking assembly  50  includes the two pins  53  (cylindrical members) between the lock cam  51  and the lock ring  52 . 
     In the above structure, the inner surface of the hole  337  in the third carrier  33 C includes the two flat surfaces  3371 A and  3371 B ( 3372 A and  3372 B) that come in contact with the two flat surfaces  81 A and  81 B of the spindle, allowing a rotational force from the third carrier  33 C to be directly transmitted to the spindle  81 . The inner surface and the flat surfaces  3371 A and  3371 B ( 3372 A and  3372 B) of the hole  337  in the third carrier  33 C and the flat surfaces  81 A and  81 B of the outer surface of the spindle  81  in contact with each other can reduce the concentration of stress in the third carrier  33 C and the spindle  81 . Thus, damage to the third carrier  33 C and the spindle  81  is reduced. The spindle locking assembly  50  transmits a rotational force from the third carrier  33 C to the spindle  81  and blocks transmission of the rotational force from the spindle  81  to the third carrier  33 C. 
     The outer surface of the lock cam  51  includes the first flat surface  511 A and the second flat surface  511 B in the embodiment. The pins  53  include a first pin  53  between the flat surface  511 A of the lock cam  51  and the inner surface of the lock ring  52  and a second pin  53  between the flat surface  511 B of the lock cam  51  and the inner surface of the lock ring  52 . 
     In the above structure, when a force is applied in the rotation direction to the spindle  81  and the spindle  81  is about to rotate, the lock cam  51  is also about to rotate together with the spindle  81 . The lock ring  52  surrounds the lock cam  51 . The lock ring  52  does not rotate. As the lock cam  51  rotates, the first pin  53  moves and is pushed radially outward by the flat surface  511 A, and the second pin  53  moves and is pushed radially outward by the flat surface  511 B. The first pin  53  is sandwiched between the flat surface  511 A and the inner surface of the lock ring  52 . The second pin  53  is sandwiched between the flat surface  511 B and the inner surface of the lock ring  52 . The first and second pins  53  serve as wedges that restrict rotation of the lock cam  51 . This restricts the rotation of the lock cam  51 , thus restricting the rotation of the spindle  81 . This blocks transmission of a rotational force from the spindle  81  to the third carrier  33 C. 
     In the embodiment, the flat surface  511 A and the first pin  53  have substantially equal dimensions, and the flat surface  511 B and the second pin  53  have substantially equal dimensions in the front-rear direction parallel to the rotation axis AX of the spindle  81 . 
     In the above structure, the first pin  53  is located appropriately between the flat surface  511 A and the inner surface of the lock ring  52 . Similarly, the second pin  53  is located appropriately between the flat surface  511 B and the inner surface of the lock ring  52 . 
     In the embodiment, the inner surface of the hole  337  in the third carrier  33 C includes a first pair of two flat surfaces  3371 A and  3371 B and a second pair of two flat surfaces  3372 A and  3372 B. The spindle  81  and the third carrier  33 C are rotatable relative to each other to change between a first contact state and a second contact state. In the first contact state, the two flat surfaces  81 A and  81 B of the spindle  81  are in contact with the first pair of two flat surfaces  3371 A and  3371 B and are not in contact with the second pair of two flat surfaces  3372 A and  3372 B. In the second contact state, the two flat surfaces  81 A and  81 B of the spindle  81  are in contact with the second pair of two flat surfaces  3372 A and  3372 B and are not in contact with the first pair of two flat surfaces  3371 A and  3371 B. 
     In the above structure, when a force is applied in the rotation direction to the spindle  81 , the lock cam  51  rotates until the wedge effect of each of the first and second pins  53  is produced. When the spindle  81  and the third carrier  33 C cannot rotate relative to each other, the lock cam  51  may not rotate until the wedge effect of each of the first and second pins  53  is produced. The spindle  81  and the third carrier  33 C can rotate slightly relative to each other, and thus the lock cam  51  can rotate until the wedge effect of the first and second pins  53  is produced. 
     In the embodiment, the third carrier  33 C includes the protrusions  331  to  334  spaced about the rotation axis AX of the third carrier  33 C and protruding frontward from the front surface of the third carrier  33 C. The lock cam  51  is located radially inward from the protrusions  331  to  334 . The first pin  53  is located between the protrusions  331  and  333 . The second pin  53  is located between the protrusions  332  and  334 . 
     In the above structure, the lock cam  51  is located radially inward from the multiple protrusions  331  to  334  without any excess torque being applied to the lock cam  51 . This reduces the concentration of stress in the lock cam  51  and thus damage to the lock cam  51 . The first pin  53  is located between the pair of protrusions  331  and  333 . The second pin  53  is located between the pair of protrusions  332  and  334 . Thus, when the third carrier  33 C rotates with a rotational force from the motor  6 , the pins  53  rotate together with the third carrier  33 C. In other words, the pins  53  rotate (revolve) about the rotation axis AX as the third carrier  33 C rotates. This transmits a rotational force from the third carrier  33 C to the spindle  81 . 
     Other Embodiments 
     In the embodiment described above, the outer surface of the rear portion of the spindle  81  includes the two flat surfaces  81 A and  81 B, and the inner surface of the hole  337  in the third carrier  33 C includes the two flat surfaces  3371 A and  3371 B ( 3372 A and  3372 B) that come in contact with the two flat surfaces  81 A and  81 B of the spindle  81 . The outer surface of the rear portion of the spindle  81  may include three or more flat surfaces, and the inner surface of the hole  337  in third carrier  33 C may include three or more flat surfaces that come in contact with the three or more flat surfaces of the spindle  81 . 
     In the embodiment described above, the spindle locking assembly  50  includes the two pins  53  (cylindrical members) between the lock cam  51  and the lock ring  52 . The spindle locking assembly  50  may include three or more pins  53  (cylindrical members) between the lock cam  51  and the lock ring  52 . 
     In the above embodiment, the driver drill  1  is powered by the battery pack  20  attached to the battery mount  5 . The driver drill  1  may use utility power (alternating current power supply). 
     The electric work machine in the above embodiment is a driver drill (vibration driver drill), which is an example of a power tool. The power tool is not limited to a driver drill. Examples of the power tool include an impact driver, an angle drill, a screwdriver, a hammer, a hammer drill, a circular saw, and a reciprocating saw. 
     REFERENCE SIGNS LIST 
     
         
           1  driver drill 
           2  housing 
           2 L left housing 
           2 R right housing 
           2 S screw 
           3  rear cover 
           3 S screw 
           4  casing 
           4 A first casing 
           4 B second casing 
           4 C bracket plate 
           4 D stop plate 
           4 E screw 
           4 F screw 
           4 S screw 
           5  battery mount 
           6  motor 
           7  power transmission 
           8  output unit 
           9  fan 
           10  trigger lever 
           11  forward-reverse switch lever 
           12  speed switch lever 
           13  mode switch ring 
           14  lamp 
           15  interface panel 
           16  dial 
           17  controller 
           18  inlet 
           19  outlet 
           20  battery pack 
           21  motor compartment 
           22  grip 
           23  battery holder 
           24  operation unit 
           25  display 
           26  controller case 
           27  panel opening 
           28  dial opening 
           30  reducer 
           31  first planetary gear assembly 
           31 A pin 
           31 C first carrier 
           31 S pinion gear 
           32  second planetary gear assembly 
           32 A pin 
           32 C second carrier 
           32 P planetary gear 
           32 R internal gear 
           32 S sun gear 
           33  third planetary gear assembly 
           33 A pin 
           33 C third carrier 
           33 P planetary gear 
           33 R internal gear 
           33 S sun gear 
           34  first speed switcher 
           35  second speed switcher 
           36  cam ring 
           40  vibrator 
           41  first cam 
           42  second cam 
           43  vibration switch ring 
           43 S opposing portion 
           43 T protrusion 
           44  stop ring 
           45  support ring 
           46  steel ball 
           47  washer 
           48  cam ring 
           50  spindle locking assembly 
           51  lock cam 
           52  lock ring 
           53  pin (cylindrical member) 
           61  stator 
           61 A stator core 
           61 B front insulator 
           61 C rear insulator 
           61 D coil 
           61 E sensor circuit board 
           61 F short-circuiting member 
           62  rotor 
           62 A rotor core 
           62 B permanent magnet 
           63  rotor shaft 
           64  bearing 
           65  bearing 
           81  spindle 
           81 A flat surface 
           81 B flat surface 
           81 C curved surface 
           81 D curved surface 
           81 F flange 
           81 R threaded hole 
           82  chuck 
           83  bearing 
           84  bearing 
           87  coil spring 
           88  screw 
           311 P planetary gear 
           312 P planetary gear 
           311 R internal gear 
           312 R internal gear 
           311 S larger-diameter portion 
           3125  smaller-diameter portion 
           330  plate 
           331  protrusion 
           331 T lower end face 
           332  protrusion 
           332 T lower end face 
           333  protrusion 
           333 T upper end face 
           334  protrusion 
           334 T upper end face 
           335  land 
           335 A support surface 
           335 B support surface 
           336  land 
           336 A support surface 
           336 B support surface 
           337  hole 
           3372 A flat surface 
           3372 B flat surface 
           337 C curved surface 
           337 D curved surface 
           511  cylindrical portion 
           511 A flat surface 
           511 B flat surface 
           511 C curved surface 
           511 D curved surface 
           512  protrusion 
           513  protrusion 
           514  hole 
           514 A flat surface 
           514 B flat surface 
           514 C curved surface 
           514 D curved surface 
           3371 A flat surface 
           3371 B flat surface 
         AX rotation axis