Patent Publication Number: US-11396078-B2

Title: Grinder

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2019-108151, filed on Jun. 10, 2019, and Japanese Patent Application No. 2020-003071, filed on Jan. 10, 2020 the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a grinder. 
     2. Description of the Background 
     A grinder described in, for example, Japanese Unexamined Patent Application Publication No. 2013-119129, includes a spindle as a final output shaft facing downward at the front of a housing extending in the front-rear direction, and a tip tool, such as a grinding disc, attached at a lower end of the spindle, and performs grinding or other operations with the rotating tip tool. 
     BRIEF SUMMARY 
     Such a known grinder may have vibrations resulting from an unbalanced operation of a motor that rotates at high speed and an unbalanced operation of the tip tool attached to the spindle. The vibrations may be transferred to a hand of an operator through the housing accommodating the motor or a side handle attached to the housing, possibly annoying the operator or affecting the operability. 
     When the motor is activated or the tip tool receives a load, a reaction force may act on the housing in the direction opposite to the rotation of the tip tool, possibly lowering the operability. 
     One or more aspects of the present invention are directed to a grinder that effectively reduces vibrations and a reaction force transferred to an operator and improves usability and operability. 
     An aspect of the present invention provides a grinder, including:
         an inner housing accommodating a motor;   a final output shaft located in front of the motor;   a connecting shaft parallel to the final output shaft;   a front elastic member located in front of the connecting shaft; and   an outer housing enclosing the inner housing and holding, with the connecting shaft and the front elastic member in between, the inner housing in a relatively rotatable manner.       

     The structure according to the above aspect of the present invention effectively reduces vibrations and a reaction force transferred to an operator and improves usability and operability. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a grinder. 
         FIG. 2  is a plan view of the grinder. 
         FIG. 3  is a left side view of the grinder. 
         FIG. 4  is a longitudinal central sectional view of the grinder. 
         FIG. 5  is an enlarged partial sectional view taken along line A-A in  FIG. 4 . 
         FIG. 6A  is an enlarged cross-sectional view taken along line B-B in  FIG. 4 , and  FIG. 6B  is an enlarged cross-sectional view taken along line C-C in  FIG. 4 . 
         FIG. 7A  is an enlarged cross-sectional view taken along line D-D in  FIG. 4 , and  FIG. 7B  is an enlarged cross-sectional view taken along line E-E in  FIG. 4 . 
         FIG. 8A  is an enlarged cross-sectional view taken along line F-F in  FIG. 4 , and  FIG. 8B  is an enlarged cross-sectional view taken along line G-G in  FIG. 5 . 
         FIG. 9  is an exploded perspective view of an inner housing and a brushless motor, showing their holding structures. 
         FIG. 10  is an exploded perspective view of a handle detector. 
         FIG. 11  is an enlarged partial central sectional view of a grinder according to a modification, showing an elastic holding structure of an inner housing. 
         FIG. 12  is a cross-sectional view taken along line H-H in  FIG. 11 . 
         FIG. 13  is an exploded perspective view of the grinder according to the modification, showing the elastic holding structure of the inner housing. 
         FIG. 14  is a cross-sectional view taken along line I-I in  FIG. 11 . 
         FIG. 15A  is a cross-sectional view taken along line J-J in  FIG. 11 , and  FIG. 15B  is a cross-sectional view taken along line K-K in  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will now be described with reference to the drawings. 
       FIG. 1  is a perspective view of a rechargeable grinder as an example of a power tool.  FIG. 2  is a plan view of the grinder.  FIG. 3  is a left side view of the grinder.  FIG. 4  is a longitudinal central sectional view of the grinder. 
     A grinder  1  includes a housing including an outer housing  2 , an inner housing  3 , and a gear housing  5 . The outer housing  2  is cylindrical and extends in the front-rear direction. The inner housing  3  is cylindrical and is located inside the outer housing  2 . The inner housing  3  holds a brushless motor  4  and protrudes frontward. The gear housing  5  is connected to the front of the inner housing  3  and accommodates the spindle  6  protruding downward. 
     The outer housing  2  is formed from a resin and integrally includes a front cylinder  7  with a larger-diameter, a rear cylinder  8  with a smaller-diameter, and a battery mount  9 . The front cylinder  7  holds the inner housing  3 . The rear cylinder  8  is located behind and decentered upward from the front cylinder  7 . The battery mount  9  is located at the rear end of the rear cylinder  8 . The outer housing  2  is assembled by fastening a pair of right and left half housings  2   a  and  2   b  with screws. 
     The front cylinder  7  has, at its front end, a larger-diameter portion  10  with an increased diameter. The battery mount  9  can receive a battery pack  11  as a power supply in a manner slidable from above. 
     The rear cylinder  8  receives a main switch  12  including a plunger  13 , which protrudes downward. The main switch  12  includes a mechanical contact to be turned on to electrically connect a terminal mount  24  (described later) to a control circuit board  21 . The mechanical contact is switchable by operating the plunger  13 . A microswitch  14  including a button  15  protruding downward is located in front of the main switch  12  in the rear cylinder  8 . The microswitch  14  includes an electrical contact to be turned on to electrically connect the control circuit board  21  to the brushless motor  4 . The electrical contact is switchable by operating the button  15 . A switch lever  16  is vertically swingable on a lower surface of the outer housing  2 . The switch lever  16  is pivotable about its front end and extends rearward while bending in conformance with the lower surfaces of the front cylinder  7  and the rear cylinder  8 . A coil spring  17  between the rear of the switch lever  16  and the lower surface of the rear cylinder  8  urges the switch lever  16  downward to a protruding position in a normal state. 
     The switch lever  16  includes a pressing plate  18  and a lock-off lever  19 . The pressing plate  18  is pressed upward to press the plunger  13 . The lock-off lever  19  is located in front of the pressing plate  18 . The lock-off lever  19  in a normal state is urged rotationally into a vertical posture shown in  FIG. 4 , restricting the switch lever  16  from being pressed. The lock-off lever  19  in  FIG. 4  is rotatable counterclockwise to allow the switch lever  16  to be pressed. The rear cylinder  8  is used as a main handle. An operator rotates the lock-off lever  19  counterclockwise with fingers holding the rear cylinder  8  and then grips the switch lever  16 . This causes the pressing plate  18  to press the plunger  13  and subsequently the lock-off lever  19  to press the button  15 . 
     A controller  20  behind the main switch  12  is supported in a tilt posture with its lower end more frontward than its upper end with respect to the axis of the rear cylinder  8 . The controller  20  includes a dish-shaped case  22 , which is formed from aluminum. The case  22  accommodates the control circuit board  21 . The control circuit board  21  receives, for example, six field-effect transistors (FETs) (not shown) corresponding to coils  37  in the brushless motor  4 , a capacitor, and a microcomputer (not shown). The battery mount  9  has inlets  23  as slits on its right and left side surfaces behind the controller  20 . The terminal mount  24  is held vertically behind the inlets  23 . The terminal mount  24  is electrically connectable when the battery pack  11  is slide-attached from above. 
     The electric components other than the brushless motor  4  are accommodated in the outer housing  2  behind the inner housing  3  as described above. 
     The inner housing  3  is formed from a resin and has a smaller diameter than the front cylinder  7  to be enclosed in the front cylinder  7 . As shown in  FIG. 5 , the inner housing  3  has a flared portion  30  and an expanded portion  31  at its front end protruding frontward from the outer housing  2 . The flared portion  30  has diameters increasing frontward. The expanded portion  31  extends frontward from the front end of the flared portion  30  and has substantially the same outer diameter as the larger-diameter portion  10 . 
     The brushless motor  4  is an inner-rotor motor including a cylindrical stator  32  and a rotor  33  extending through the stator  32 . The stator  32  includes a cylindrical stator core  34 , a front insulator  35 , a rear insulator  36 , and the coils  37 . The stator core  34  includes multiple steel plates stacked on one another. The front insulator  35  is located on the axially front end face of the stator core  34 . The rear insulator  36  is located on the axially rear end face of the stator core  34 . The coils  37  are wound around the stator core  34  with the front and rear insulators  35  and  36  in between. A sensor circuit board  38  and a wire connection member  40  are attached to the rear insulator  36 . The sensor circuit board  38  detects the positions of permanent magnets  67  placed in a rotor core. The wire connection member  40  includes a terminal fitting  41  for connecting the coils  37  with fuse terminals  39 . 
     As shown in  FIGS. 6A, 6B, and 9 , the inner housing  3  has, on its inner front surface, four protrusions  42  elongated in the front-rear direction and protruding toward the axis. The protrusions  42  are arranged at circumferentially equal intervals. Each protrusion  42  has a first projection  43  and a second projection  44  on its front. The first projection  43  and the second projection  44  project more from the inner surface (or become thicker) in a stepwise manner toward the front of the inner housing  3 . 
     The front insulator  35  has a pair of upper and lower fitting recesses  45  and a pair of right and left flat edges  46 . The pair of upper and lower fitting recesses  45  are fitted with the second projections  44  when circumferentially aligned with the upper and lower protrusions  42 . The pair of right and left flat edges  46  are in no contact with the second projections  44  when circumferentially aligned with the right and left protrusions  42 . 
     The stator  32  is placed into the inner housing  3  from the rear with the fitting recesses  45  circumferentially aligned with the upper and lower protrusions  42  and the flat edges  46  circumferentially aligned with the right and left protrusions  42 . The fitting recesses  45  are fitted with the second projections  44  on the upper and lower protrusions  42 , thus locking the stator  32  in a nonrotatable manner. The stator core  34  is in contact with the first projections  43  on the protrusions  42 . This defines an advanced position of the stator core  34 . In this state, the inner surfaces of the protrusions  42  excluding the first and second projections  43  and  44  are in contact with the outer surface of the stator core  34  as shown in  FIG. 6B , thus holding the stator core  34 . 
     A ring baffle plate  47  is fitted onto the fronts of the protrusions  42  from the front in the inner housing  3 . As shown in  FIGS. 5 to 6B , the baffle plate  47  includes right and left hooks  48 , which are engaged with, outside the flat edges  46  of the front insulator  35 , the second projections  44  on the right and left protrusions  42 . This positions the baffle plate  47 . 
     A metal bearing retainer  50  is fitted onto the rear end of the inner housing  3  from the rear. The bearing retainer  50  is disk-shaped and includes a bearing holder  51 , multiple arch-shaped through-holes  52 , and a joint  53 . The bearing holder  51  is at the center of the bearing retainer  50  and has an opening facing frontward. The arch-shaped through-holes  52  surround the bearing holder  51  as shown in  FIGS. 7A and 9 . The joint  53  is at the rear of the bearing holder  51 . The joint  53  protrudes rearward and has a through-hole  54  extending vertically. 
     The bearing retainer  50  includes four pins  55  protruding from its front surface. The pins  55  are arranged concentrically at equal intervals. Each pin  55  has a larger diameter at a basal portion  56 . 
     The inner housing  3  has a thick portion  58  raised from its inner rear surface. The thick portion  58  has an inner diameter fittable with the bearing retainer  50 . Four V-shaped notches  59  are formed on the outer circumference of the rear insulator  36  at circumferentially equal intervals as shown in  FIG. 7B . 
     The pins  55  are circumferentially aligned with the corresponding notches  59  in the rear insulator  36  to place the bearing retainer  50  into the thick portion  58  of the inner housing  3  from the rear. The pins  55  are then engaged with the notches  59  and in contact with the rear surface of the stator core  34  as shown in  FIG. 7B . The basal portions  56  are thus located adjacent to the rear surface of the rear insulator  36 . 
     The bearing retainer  50  has an internal thread  60  on its inner circumference at the rear. With the bearing retainer  50  being placed in the thick portion  58 , a resin lock ring  61  is screwed onto the internal thread  60 . The lock ring  61  thus presses the bearing retainer  50  from the rear, preventing the bearing retainer  50  from slipping off. In this state, the joint  53  protrudes rearward from the inner housing  3  through the center of the lock ring  61 . 
     The rotor  33  includes a rotational shaft  65 , a rotor core  66 , and the four permanent magnets  67 . The rotational shaft  65  is aligned with the axis of the rotor  33 . The rotor core  66  surrounds the rotational shaft  65 . The rotor core  66  is substantially cylindrical and includes multiple steel plates stacked on one another. The permanent magnets  67  are plates fixed inside the rotor core  66 . 
     The rotational shaft  65  has its rear end axially supported by the bearing  68 . The bearing  68  is held in the bearing holder  51  of the bearing retainer  50 . The rotational shaft  65  has its front end axially supported by the bearing  70 . The bearing  70  is held on a partition  69  attached between the gear housing  5  and the expanded portion  31  of the inner housing  3 . The distal end of the rotational shaft  65  protrudes into the gear housing  5 . The rotational shaft  65  receives a centrifugal fan  71  behind the partition  69 . The centrifugal fan  71  is in front of the baffle plate  47  and is accommodated in the flared portion  30  and the expanded portion  31 . 
     The inner housing  3  holding the brushless motor  4  is elastically held on the outer housing  2 . An elastic holding structure will now be described in detail. 
     In the bearing retainer  50 , a through-hole  54  in the joint  53 , which protrudes rearward from the inner housing  3 , receives a metal connecting rod  75  extending vertically. The connecting rod  75  has upper and lower ends supported in a pair of upper and lower rod receivers  76 , which are hollow prisms as shown in  FIGS. 8A and 9 . The pair of upper and lower rod receivers  76  each include two half parts on the half housings  2   a  and  2   b  of the outer housing  2  that are combined together. The rod receivers  76  each have an insertion hole  77  for receiving the connecting rod  75  at the interface between the half parts. The rod receivers  76  each hold a rubber cap  78 , which receives an end of the connecting rod  75  extending through the insertion hole  77 . The rubber cap  78  has a pair of ends  79  extending laterally. Each end  79  is placed into and supported in the corresponding half parts of the rod receiver  76 . 
     The connecting rod  75  extending through the joint  53  is supported in the rod receivers  76 , thus holding the inner housing  3  in a laterally swingable manner about the connecting rod  75 . The upper and lower ends of the connecting rod  75 , which serves as a pivot, are elastically held in the rod receivers  76  with the rubber caps  78 . 
     A rubber cylinder  80  is externally mounted on the outer circumference of the inner housing  3  to cover from the flared portion  30  to a rear portion. The rubber cylinder  80  is held between the larger-diameter portion  10  of the outer housing  2  and the inner housing  3 . The rubber cylinder  80  has flanges  80   a  on the right and left edges. The flanges  80   a  are arch-shaped in conformance with the rear surface of the flared portion  30 . The inner housing  3  laterally swingable about the connecting rod  75 , which is elastically held in the rubber caps  78 , is elastically held on the outer housing  2  along its entire front circumference with the rubber cylinder  80  in between. The rubber cap  78  has a lower hardness than the rubber cylinder  80 . 
     A fixing ring  81  is externally mounted on the rubber cylinder  80  between the flared portion  30  and the larger-diameter portion  10 . The fixing ring  81  is formed from a metal and has the same outer diameter as the larger-diameter portion  10 . The fixing ring  81  has a pair of flat surfaces  82  extending vertically on its right and left side surfaces. 
     As shown in, for example,  FIGS. 2 and 5 , a pair of handle mounts  83  are integrally formed on the right and left side surfaces at the front end of the outer housing  2 . The pair of handle mounts  83  protrude laterally outward and extend frontward to cover the outer surfaces of the gear housing  5  without being in contact with the outer surfaces of the inner housing  3  and the partition  69 . Each handle mount  83  is used to attach a side handle  25  (e.g.,  FIGS. 1 and 2 ). Each handle mount  83  is flat on a plane defined in vertical and lateral directions. As shown in  FIG. 8B , the handle mounts  83  in contact with the flat surfaces  82  of the fixing ring  81  at their inner surfaces are fastened to the fixing ring  81  with pairs of upper and lower screws  84 , which are screwed from outside, or from the right and the left. The right and left half housings  2   a  and  2   b  of the outer housing  2  are thus fastened to the fixing ring  81  through the handle mounts  83 , in addition to being directly fastened to each other with the screws. 
     As shown in  FIGS. 5 and 9 , each handle mount  83  has, in a middle portion in the front-rear and vertical directions, a screw hole  85  that is a laterally extending through-hole. The side handle  25  includes a threaded portion  26  at its distal end, which is screwed into the screw hole  85  and is fixed. Each handle mount  83  includes a handle detector  86  that detects the side handle  25  attached in the screw hole  85 . 
     Each handle detector  86  includes a detection plate  87  and a photointerrupter  88  as shown in  FIG. 10 . The detection plate  87  is at a different position depending on whether the side handle  25  has been attached. The photointerrupter  88  detects the position of the detection plate  87  when the side handle  25  is attached, and outputs a detection signal to the controller  20 . In response to the detection signal about the side handle  25 , the controller  20  allows the brushless motor  4  to operate. 
     A pivot pin  90  is vertically supported in a frame  89  protruding on the outer surface of the handle mount  83 . The detection plate  87  has a front portion pivotably attached to the pivot pin  90  and a rear portion swingable laterally. The detection plate  87  has, behind the pivot pin  90 , a through-hole  91  located outside the screw hole  85 . The through-hole  91  can receive the threaded portion  26  of the side handle  25 . 
     The detection plate  87  has a rear end bending inward toward the handle mount  83 . The rear end is placed into a holder  92  accommodating the photointerrupter  88  in the handle mount  83 . The detection plate  87  includes a light shield  93  at its rear end, or an end to be placed. The handle mount  83  includes a stopper  94  adjacent to the inlet of the holder  92 . The stopper  94  comes in contact with the light shield  93  when the detection plate  87  swings outward, restricting the swingable position of the detection plate  87 . The handle mount  83  receives, behind the through-hole  91 , a coil spring  95  that urges the detection plate  87  toward an outward position at which the detection plate  87  comes in contact with the stopper  94 . 
     The photointerrupter  88  includes a substrate  96 . The substrate  96  is held in the lateral direction in a rear portion of the holder  92 . The substrate  96  includes a photoreceiver  97  on its front surface. The photoreceiver  97  can detect the light shield  93  placed in the holder  92  in a contactless manner. 
     When the detection plate  87  is at the outward position, the light shield  93  is outside the photoreceiver  97  without blocking the light entering the photoreceiver  97 . The photoreceiver  97  thus enters a non-detection state with no detection signal being output. When the detection plate  87  swings inward against the urging force from the coil spring  95 , the side handle  25  comes in contact with a receiver  98  on the outer surface of the handle mount  83 . At this inward position, the light shield  93  blocks light entering the photoreceiver  97 . The photoreceiver  97  thus enters a detection state with a detection signal being output. The photointerrupter  88  includes a dust cover  88   a  covering the photoreceiver  97  and a part of the substrate  96  excluding a slit  88   b  through which the light shield  93  passes. 
     The gear housing  5  is fastened to the inner housing  3  with four screws  100  at four corners viewed from the front, which are placed from the front with the partition  69  between the gear housing  5  and the inner housing  3 . A bevel gear  101  is fixed on the front end of the rotational shaft  65  protruding into the gear housing  5 . As shown in  FIG. 4 , the bevel gear  101  meshes with a bevel gear  102  fixed on the upper end of the spindle  6 . The gear housing  5  has, on its front surface, outlets  103  that communicate with the inner housing  3  through a through-hole (not shown) in the partition  69 . A shaft lock  104  is located in front of the outlets  103 . The shaft lock  104  can lock the spindle  6  not to rotate via the bevel gear  102  when pressed. 
     The spindle  6  is axially supported by upper and lower bearings  106 , and protrudes downward. The upper bearing  106  is held on the gear housing  5 . The lower bearing  106  is held on a bearing box  105  attached to the bottom of the gear housing  5 . The spindle  6  has a lower end to receive a tip tool  107  ( FIG. 4 ), such as a grinding disc. The bearing box  105  can receive, on its outer circumference, a wheel cover (not shown) covering a rear half of the tip tool  107 . 
     In the grinder  1  according to the present embodiment, the threaded portion  26  of the side handle  25  is screwed into the screw hole  85  in either the right or left handle mount  83  through the through-hole  91  in the detection plate  87 . The side handle  25  has a distal end  27  holding the threaded portion  26 . The distal end  27  presses the detection plate  87  inward against the urging force from the coil spring  95 , thus pressing the detection plate  87  against the receiver  98 . In response to the side handle  25  attached, the detection plate  87  swings to the inward position and causes the light shield  93  to block light entering the photoreceiver  97  in the photointerrupter  88 . 
     The operator rotates the lock-off lever  19  with fingers holding the rear cylinder  8  to unlock the lock-off lever  19 , and then grips the switch lever  16 . The pressing plate  18  presses the plunger  13  to first turn on the main switch  12 . This allows the battery pack  11  to power the control circuit board  21  in the controller  20 . The control circuit board  21  determines whether the photointerrupter  88  outputs a detection signal. 
     When the operator grips the switch lever  16  further, the lock-off lever  19  presses the button  15  in the microswitch  14  to turn on the microswitch  14 . In response to a detection signal from the photointerrupter  88  and an on signal from the microswitch  14 , the control circuit board  21  controls the battery pack  11  to power the brushless motor  4  and activate the brushless motor  4 . More specifically, the microcomputer in the control circuit board  21  receives, from a rotation detection element in the sensor circuit board  38 , a rotation detection signal indicating the positions of the permanent magnets  67  in the rotor  33 , and determines the rotational state of the rotor  33 . The microcomputer in the control circuit board  21  controls the on-off state of each FET in accordance with the determined rotational state, and applies a current through the coils  37  in the stator  32  sequentially to rotate the rotor  33 . The rotational shaft  65  thus rotates and causes the spindle  6  to rotate (rotate clockwise as viewed from above) via the bevel gears  101  and  102  to allow grinding or other operations with the tip tool  107 . 
     The rotor  33  in the brushless motor  4  that rotates at high speed and the tip tool  107  attached to the spindle  6  may cause unbalanced operations. This may cause vibrations to be transferred to the inner housing  3  and the gear housing  5 . 
     The rubber cylinder  80  is held between the inner housing  3  and the outer housing  2  in the present embodiment. This structure effectively isolates such vibrations, thus reducing vibrations transferred to the outer housing  2 . The operator is thus less likely to receive vibrations on his or her hand holding the rear cylinder  8  as a main handle. The side handle  25  is attached to the handle mount  83  on the outer housing  2 , which also isolates vibrations. The operator is thus less likely to receive vibrations on his or her hand holding the side handle  25 . This structure achieves lower vibrations. 
     When the brushless motor  4  is activated or the tip tool  107  receives a load during rotation, the inner housing  3  is urged to rotate counterclockwise (in a direction in which a reaction force is applied) about the connecting rod  75  as viewed in plan. The rubber cylinder  80  is held between the inner housing  3  and the outer housing  2  in the present embodiment. The rubber cylinder  80  thus absorbs the rotation of the inner housing  3  to reduce a reaction transferred to the outer housing  2  and the side handle  25  attached to the outer housing  2 . 
     When the centrifugal fan  71  rotates together with the rotational shaft  65 , the outside air is drawn through the inlets  23  behind the centrifugal fan  71 , passes under the controller  20 , and advances through the outer housing  2 . This cools the controller  20  and the terminal mount  24 . 
     The airflow in the outer housing  2  passes through the main switch  12  and the microswitch  14  while cooling them, enters the inner housing  3  through the through-holes  52  in the bearing retainer  50 , and passes between the stator  32  and the rotor  33  in the brushless motor  4  to cool the brushless motor  4 . The airflow then passes through the flared portion  30  and expanded portion  31  to the gear housing  5  through the partition  69 , and is then discharged through the outlets  103 . 
     The grinder  1  according to the present embodiment includes the inner housing  3  accommodating the brushless motor  4  (motor), the spindle  6  (final output shaft) in front of the brushless motor  4 , and the outer housing  2  enclosing the inner housing  3  and integral with the rear cylinder  8  (handle). The inner housing  3  and the outer housing  2  are connected in a relatively rotatable manner with the connecting rod  75  (connecting shaft) parallel to the spindle  6 . The inner housing  3  is held on the outer housing  2  with the rubber cylinder  80  (front elastic member) in between in front of the connecting rod  75 . This structure effectively reduces vibrations and a reaction force transferred to the operator and improves usability and operability. 
     In particular, the connecting rod  75  is held with the rubber cap  78  (rear elastic member) in the outer housing  2 . This effectively reduces vibrations transferred from the connecting rod  75  to the outer housing  2 . 
     The outer housing  2  includes the handle mounts  83  (mounts to which the side handle is attachable). This also effectively prevents vibrations and a reaction force from being transferred to the side handle  25 . 
     The outer housing  2  includes the pair of right and left half housings  2   a  and  2   b  that are assembled together. The half housings  2   a  and  2   b  are fixed to the fixing ring  81  (ring), which is externally mounted on the inner housing  3  with the rubber cylinder  80  in between. The half housings  2   a  and  2   b  are thus firmly joined together with the fixing ring  81  between them. 
     The joint  53  (a joint portion connected to the connecting shaft) in the inner housing  3  is formed from a metal to provide sufficient strength. 
     The inner housing  3  accommodates the brushless motor  4  in a cylindrical holder. The rubber cylinder  80  thus effectively isolates vibrations along the entire circumference. 
     The outer housing  2  accommodates the electric components other than the brushless motor  4 , such as the main switch  12 , the microswitch  14 , the controller  20 , and the terminal mount  24 . These electric components are located apart from the brushless motor  4  and the tip tool  107 , which are vibration sources, and located in a manner isolated from vibrations. This protects the electric components against vibrations. 
     The outer housing  2  includes the battery packs  11  (batteries) serving as a power supply. The outer housing  2  thus has an increased weight, effectively reducing vibrations. 
     The rubber cap  78  has a lower hardness than the rubber cylinder  80 . This effectively prevents transfer of a reaction force. 
     The connecting shaft may be integral with the joint in the bearing retainer, instead of being separate from the bearing retainer, similarly to the connecting rod  75  in the present embodiment. The connecting shaft may be directly located on the inner housing without using a separate member such as a bearing retainer. The rear elastic member for elastically holding the connecting shaft may be eliminated. 
     The handle mounts may not be on the outer housing. A known structure including a side handle attached to a gear housing may also provide certain vibration reduction with the elastically held inner housing. 
     The outer housing may not be halved as in the present embodiment, but may be an integral cylinder similarly to the inner housing. The grinder may operate on an alternating current (AC) without including batteries or may include a motor other than a brushless motor. 
     The grinder  1  (power tool) according to the present embodiment includes the inner housing  3  accommodating the brushless motor  4  (motor), the spindle  6  (final output shaft) drivable by the brushless motor  4 , and the outer housing  2  enclosing the inner housing  3  and integral with the rear cylinder  8  (handle). The inner housing  3  is held on the outer housing  2  with the rubber cylinder  80  (elastic member) in between. The outer housing  2  includes the handle mounts  83  (mounts to which the side handle is attachable) and the handle detectors  86  each for detecting the side handle  25  attached. More specifically, the handle detectors  86  are located on the outer housing  2 , which is isolated using the rubber cylinder  80  from vibrations generated by the brushless motor  4  and the spindle  6  (tip tool  107 ). The grinder  1  thus includes the handle detectors  86  that are less susceptible to vibrations and are highly durable and reliable. 
     In particular, the handle detectors  86  each detect the side handle  25  attached, in response to an attaching operation of the side handle  25 . The handle detectors  86  do not cause any additional operation for detection. 
     The handle detectors  86  are provided at multiple (two in the embodiment) locations. The side handle  25  attached is thus independently detectable on each handle mount  83 . 
     The handle detectors  86  are located in right and left portions of the outer housing  2 . The side handle  25  is thus detectable on either the right or left handle mount  83 . 
     The inner housing  3  is connected to the outer housing  2  with the connecting rod  75  (connecting shaft) parallel to the spindle  6 . This structure effectively reduces a reaction force transferred to the operator generated when the brushless motor  4  is activated or the tip tool  107  receives a load. 
     The handle detectors  86  operate in a contactless manner. The handle detectors  86  are less likely to have failures or erroneous detection caused by foreign matter such as dust, and are expected to have higher durability and reliability. 
     Each side handle detector  86  includes the detection plate  87  (detection member) having the front portion swingable about the pivot pin  90  (pivot). The detection plate  87  comes in contact with the side handle  25  when the side handle  25  is attached. The photointerrupter  88  (detector) located behind the detection plate  87  detects the detection plate  87  that swings when in contact with the side handle  25 . The receiver  98  is located between the pivot pin  90  and the photointerrupter  88  to receive the side handle  25 . The detection plate  87  thus reliably swings in response to an attaching operation of the side handle  25  to allow the photointerrupter  88  to detect the side handle  25  attached. 
     The photointerrupter  88  is covered with the dust cover  88   a . This effectively prevents foreign matter such as dust from entering and improves the reliability of detection. 
     In the present embodiment, the positional relationship between the pivot pin and the photointerrupter is not limited to the relationship described above and may be modified as appropriate in accordance with the power tool used. For example, the pivot pin and the photointerrupter may be reversed in the front-rear direction or may be arranged in the vertical direction. 
     The sensor is not limited to a photointerrupter. The sensor may be another contactless sensor such as a proximity sensor including a magnet, or may be a contact sensor such as a microswitch or a pressure switch. 
     In the present embodiment, the handle detector is provided for each handle mount. In some embodiments, a single handle detector may be used for multiple handle mounts. 
     The present invention is applicable not only to a grinder but also to other power tools with a mount to which a side handle is attachable, such as an angle drill or a sander. When the inner housing and the outer housing are connected with the connecting shaft in a structure including a final output shaft facing other than downward, the connecting shaft may be aligned parallel to the final output shaft. 
     The tool may operate on an alternating current (AC) without including batteries or may include a motor other than a brushless motor. 
     Modifications 
     In the above embodiment, both the upper and lower ends of the connecting rod  75  are elastically held in the rod receivers  76  with the rubber caps  78 . In this structure, the connecting rod  75  may be tilted in the vertical direction when the rubber caps  78  are press-fitted into the rod receivers  76 , possibly causing the inner housing  3  to be assembled in a tilted manner. In the tilted inner housing  3 , the spindle  6  is also tilted with respect to the rear cylinder  8 . This structure insufficiently reduces vibrations and a reaction force. A modification for avoiding such erroneous assembly will now be described. The same components as in the above embodiment are given the same reference numerals and will not be described repeatedly, and the components different from those in the above embodiment will be described. 
     The assembly of a stator  32  will be described first. For a grinder  1 A shown in  FIGS. 11 and 12 , the stator  32  is placed into an inner housing  3  from the front. The inner housing  3  has, on its inner surface, four receiving surfaces  110  protruding toward the axis as shown in  FIGS. 13 and 15A . The receiving surfaces  110 , which extend in the front-rear direction, are arranged at circumferentially equal intervals. Each receiving surface  110  includes an engagement portion  111  at its rear as shown in  FIG. 15B . The engagement portion  111  has a triangle cross section and protrudes more toward the axis than its front portion. 
     The inner housing  3  includes, in its rear portion, a bearing holder  51  that is axially integral with the inner housing  3  with four connecting plates  51   a . The connecting plates  51   a  each extend radially and connect to the inner surface of the inner housing  3 . 
     With four notches  59  circumferentially aligned with the corresponding engagement portions  111 , the stator  32  is placed into the inner housing  3  from the front. As shown in  FIG. 15B , the notches  59  are engaged with the corresponding engagement portions  111  to lock the stator  32  in a nonrotatable manner and restrict the stator  32  from moving rearward. In this state, the inner surfaces of the receiving surfaces  110 , excluding the engagement portions  111 , are in contact with the outer surface of a stator core  34 , thus holding the stator  32 . 
     The inner housing  3  has a pair of slits  112  at upper and lower positions that are point-symmetric to each other about the axis. Each slit  112  has a front end in a flared portion  30  and is elongated rearward. Screw bosses  113  are located adjacent to the rear ends of the slits  112  on the same axis as the front ends of the slits  112 . The screw bosses  113  protrude from the outer surface of the inner housing  3 . 
     The inner housing  3  has a fitting protrusion  114  on its left side surface. The fitting protrusion  114 , which is a rib with a predetermined vertical width, extends in the front-rear direction from the flared portion  30  to the rear end of the inner housing  3 . The inner housing  3  has, on its right and left outer surfaces, a pair of inner projections  115  elongated in the front-rear direction. 
     A baffle plate  47 , which is attached to the front of the stator  32 , includes a pair of small cylinders  116  on its upper and lower portions. The small cylinders  116  protrude radially outward. The small cylinders  116  are fitted into the slits  112  in the inner housing  3  and come in contact with the screw bosses  113  from the front. Each small cylinder  116  is integral with a front stopper  117  located on its radially inner surface. The front stopper  117  has an arch-shaped cross section and protrudes radially inward from the inner circumferential surface of the inner housing  3 . 
     The baffle plate  47  presses, rearward, the upper and lower small cylinders  116  received in the slits  112  and placed in front of the screw bosses  113 . As shown in  FIG. 11 , the front stoppers  117  are fitted into the fitting recesses  45  on the front insulator  35  to come in contact with the front surface of the stator core  34 , positioning the stator  32  from the front. 
     After the positioning, the flared portion  30  and the baffle plate  47  define a bowl-shaped flow regulating portion  118  behind a centrifugal fan  71 . The flow regulating portion  118  is defined by the flared portion  30  located radially outside the inner housing  3  and the baffle plate  47  located radially inside the inner housing  3 . 
     The flow regulating portion  118  has, between the flared portion  30  and the baffle plate  47 , circular holes  119  in front of the screw bosses  113  and the front stoppers  117 . The circular holes  119  are each defined by a semicircular front end of the slit  112  cut in the flared portion  30  as viewed from the front and by a semicircular cutout  120  in the outer circumferential surface of the baffle plate  47  as viewed from the front. The baffle plate  47  has, on its left front end, a projection  121  for closing a cutout defined by the fitting protrusion  114  in the front surface of the flared portion  30 . 
     In this state, screws  122  are screwed into the screw bosses  113  from the front through the circular holes  119  and the small cylinders  116 . The baffle plate  47  is fastened with the front surface continuously connected to the front surface of the flared portion  30 , defining the flow regulating portion  118 . The baffle plate  47  also stably holds the stator  32  between the baffle plate  47  and the engagement portions  111 . 
     The elastic holding structure of the inner housing  3  will now be described. A connecting rod  75 A is directly held in rod receivers  76 A without rubber caps in the rear portion of the inner housing  3 . The connecting rod  75 A includes portions with two different diameters, or specifically a smaller-diameter portion  125  in the middle and larger-diameter portions  126  at the upper and lower ends. The smaller-diameter portion  125  extends through a through-hole  54  in a joint  53  in the inner housing  3 . The larger-diameter portions  126  protrude upward and downward from the joint  53 . The rod receivers  76 A each have semicircular receiving recesses  127  on their surfaces facing each other. The receiving recesses  127  hold the larger-diameter portion  126  from the right and the left. 
     A rubber sleeve  128  is externally fitted on the smaller-diameter portion  125 . The rubber sleeve  128  is thick in the radial direction. 
     The rubber sleeve  128  has catchers  129  on its outer circumferences at both ends as shown in  FIG. 13 . One catcher  129  flares toward the other. The catcher  129  has multiple cutouts  130  on its outer circumference at circumferentially equal intervals. 
     The rubber sleeve  128  is inserted in the through-hole  54  in the joint  53  together with the connecting rod  75 A. The leading catcher  129  guides the rubber sleeve  128  to be placed in the through-hole  54 . Once the connecting rod  75 A is placed through the joint  53 , the catchers  129  on the two ends are engaged with the upper and lower ends of the joint  53  to position the rubber sleeve  128  as shown in  FIG. 14 . The inner housing  3  and the connecting rod  75 A are thus elastically connected with the rubber sleeve  128  between them. 
     As shown in  FIG. 15A , a rubber cylinder  80  has, at upper and lower positions of its inner circumferential surface, a pair of grooves  131  extending in the front-rear direction. With the rubber cylinder  80  externally mounted on the inner housing  3 , the screw bosses  113  are fitted into the grooves  131 . 
     The rubber cylinder  80  has, on its left inner surface, a positioning groove  132  extending in the front-rear direction. With the rubber cylinder  80  externally mounted on the inner housing  3 , the fitting protrusion  114  is fitted into the positioning groove  132 . 
     The rubber cylinder  80  has, on its right and left rear, a pair of ribs  133  raised radially outward. Each rib  133  has a middle slit  134  extending from the rear end of the rubber cylinder  80 . With the rubber cylinder  80  externally mounted on the inner housing  3 , the inner projections  115  are engaged with the corresponding middle slits  134 . Each rib  133  has a pair of upper and lower outer slits  135 , which are parallel to the middle slit  134 , extending from the rear end of the rubber cylinder  80 . 
     The rubber cylinder  80  has a pair of positioning projections  136  at upper and lower front positions of its inner circumferential surface. The positioning projections  136  are fitted into the circular holes  119  in the flow regulating portion  118  and close the circular holes  119 . 
     The outer housing  2  has, on its right and left inner surfaces, a pair of recesses  140  as shown in  FIGS. 13 and 15A . The recesses  140  are engaged with the ribs  133  on the rubber cylinder  80 . A pair of upper and lower outer projections  141  are located above and under the recesses  140 . Each outer projection  141  is elongated in the front-rear direction. The outer projections  141  are engaged with the corresponding outer slits  135 . 
     The handle mounts  83  in front of the recesses  140  each have a receiving hole  142  that is a laterally extending through-hole. A fixing ring  81  includes screw cylinders  143 . The screw cylinders  143  protrude outward from right and left flat surfaces  82  of the fixing ring  81 . The screw cylinders  143  are fitted into the receiving holes  142 . A threaded portion  26  of a side handle  25  is screwed into the screw cylinder  143  ( FIG. 12 ). 
     In the present modification, the inner housing  3  and the connecting rod  75 A are connected with the rubber sleeve  128  (rear elastic member) between them. The connecting rod  75 A is more accurately positioned and supported in the rod receivers  76 A without tilting. The inner housing  3  can thus support the spindle  6  positioned accurately without tilting. 
     In particular, the connecting rod  75 A is directly held in the rod receivers  76 A on the outer housing  2 . The connecting rod  75 A is thus accurately positioned and supported once the connecting rod  75 A is placed in the rod receivers  76 A. 
     The inner housing  3  includes the inner projections  115  (first engaging portions). The rubber cylinder  80  has the middle slits  134  (first receiving portions) engageable with the inner projections  115  in the rotation direction about an axis in the front-rear direction and the ribs  133  (second engaging portions). The outer housing  2  has the recesses  140  (second receiving portions) engageable with the ribs  133  in the rotation direction. This structure restricts rattling between the outer housing  2  and the inner housing  3  in the circumferential direction (rotation direction) of the rubber cylinder  80 , thus allowing highly reliable positioning. 
     The inner housing  3  has, on its outer surface, the inner projections  115  (projections) to be the first engaging portions. The rubber cylinder  80  has the middle slits  134  engageable with the inner projections  115 . Further, the ribs  133  (second engaging portions) raised from the outer surface of the rubber cylinder  80  include portions with the middle slits  134 . The outer housing  2  has, on its inner surface, the recesses  140  to be the second receiving portions. The outer housing  2  and the inner housing  3  are thus effectively positioned in the rotation direction with the rubber cylinder  80  in between. 
     In some modifications, the connecting rod may have a uniform diameter along the full length rather than including portions with two different diameters, or the catchers on the rubber sleeve may be eliminated. The rubber sleeve may not be a single sleeve. Multiple shorter rubber sleeves may be used. 
     The engagement structures for the inner housing and the rubber cylinder may also be modified by changing, for example, the number of inner projections and their shapes or positions, or the number of ribs and their shapes or positions. The numbers of middle slits and outer slits and their shapes or positions may also be changed. These slits may be replaced by through-holes or recesses. The recesses and the outer projections may also be changed. 
     Although the inner housing includes the projections (first engaging portions) and the rubber cylinder has the middle slits (first receiving portions) in the above modification, the rubber cylinder may include the first engaging portions such as projections on its inner surface and the inner housing may have the first receiving portions such as recesses or through-holes. Similarly, although the rubber cylinder includes the ribs (second engaging portions) and the outer housing has the recesses (second receiving portions) in the above modification, the outer housing may include the second engaging portions such as projections on its inner surface and the rubber cylinder may have the second receiving portions such as recesses or through-holes. 
     REFERENCE SIGNS LIST 
     
         
           1 ,  1 A rechargeable grinder 
           2  outer housing 
           3  inner housing 
           4  brushless motor 
           5  gear housing 
           6  spindle 
           7  front cylinder 
           8  rear cylinder 
           9  battery mount 
           10  larger-diameter portion 
           11  battery pack 
           20  controller 
           25  side handle 
           26  threaded portion 
           30  flared portion 
           31  expanded portion 
           32  stator 
           33  rotor 
           50  bearing retainer 
           51  bearing holder 
           53  joint 
           61  lock ring 
           65  rotational shaft 
           75 ,  75 A connecting rod 
           76 ,  76 A rod receiver 
           78  rubber cap 
           80  rubber cylinder 
           81  fixing ring 
           83  handle mount 
           86  handle detector 
           87  detection plate 
           88  photointerrupter 
           93  light shield 
           97  photoreceiver 
           98  receiver 
           107  tip tool 
           115  inner projection 
           125  smaller-diameter portion 
           126  larger-diameter portion 
           128  rubber sleeve 
           133  rib 
           134  middle slit 
           135  outer slit 
           140  recess 
           141  outer projection