Patent Publication Number: US-2023150085-A1

Title: Tool

Description:
TECHNICAL FIELD 
     The present invention relates to a tool configured to allow two types of accessories to be detachably attached thereto. 
     BACKGROUND 
     Various kinds of accessories may be detachably attached to a tool including a prime mover. For example, in the case of a grinder including a tool accessory configured to be rotationally driven, examples of detachably attachable accessories prepared therefor include a cover for covering a part of the tool accessory (also referred to as a wheel cover, a disk cover, a blade case, or the like), and a side handle to be held by the other hand of a user when the user holds a handle of the grinder with one of his/her hands. 
     For such a grinder, there is a demand for preventing the grinder from being used in a state that the accessory is not attached. For example, the following patent literature, PTL 1 discloses a grinder including a sensor that detects whether or not a cover is attached and a controller that prohibits a rotation of a tool accessory when the cover is not attached. Further, the following patent literature, PTL 2 discloses a grinder including a sensor that detects whether or not a cover is attached and a sensor that detects whether or not a side handle is attached. 
     Citation List 
     
         
         [PTL 1] International Publication No. 2017-051893 
         [PTL 2] US Patent Application Publication No. 2018/272494 
       
    
     SUMMARY 
     Technical Problem 
     However, according to the technique discussed in PTL 2, the configuration that prohibits the rotation of the tool accessory unless both the cover and the side handle are attached raises the necessity of providing an individual sensor for each of the cover and the side handle, thereby leading to a cost increase. Such problems are not limited to the grinder, and lie in common for any tool configured to allow two types of accessories to be detachably attached thereto. Under these circumstances, it is desired to allow the tool to be able to detect that the two types of accessories are attached using one sensor. 
     Solution to Problem 
     The present specification discloses a tool. This tool may include a first accessory, a second accessory, a first attachment portion configured to allow the first accessory to be detachably attached thereto, a second attachment portion configured to allow the second accessory to be detachably attached thereto, a first intermediate member configured to be displaced from a first non-attachment position to a first attachment position by the attachment of the first accessory to the first attachment portion, a second intermediate member configured to be displaced from a second non-attachment position to a second attachment position by the attachment of the second accessory to the second attachment portion, and a single sensor configured to detect a specific state in which the first intermediate member is located at the first attachment position and the second intermediate member is located at the second attachment position. 
     According to this tool, the tool detects that the first intermediate member is located at the first attachment position and the second intermediate member is located at the second attachment position using the single sensor. The first intermediate member located at the first attachment position means that the first accessory is attached, and the second intermediate member located at the second attachment position means that the second accessory is attached, and therefore the attachment of the two types of accessories can be detected using the single sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a vertical cross-sectional view of a grinder according to a first embodiment of the present invention, and illustrates a state in which a side grip and a wheel cover are attached thereto. 
         FIG.  2    is a vertical cross-sectional view of the grinder, and illustrates a state in which the side grip and the wheel cover are detached therefrom. 
         FIG.  3    is a partial enlarged view of the grinder illustrated in  FIG.  1   . 
         FIG.  4    is a partial enlarged view of the grinder illustrated in  FIG.  2   . 
         FIG.  5    is a perspective view of a first intermediate member. 
         FIG.  6    is a perspective view of a second intermediate member. 
         FIG.  7    is a perspective view of a holding member that holds the first intermediate member and the second intermediate member. 
         FIG.  8    is a perspective view of a sensor fixation member. 
         FIG.  9    illustrates the internal structure of the grinder and illustrates the state in which the side grip and the wheel cover are detached therefrom. 
         FIG.  10    illustrates the internal structure of the grinder and illustrates a state in which the side grip is attached thereto and the wheel cover is detached therefrom. 
         FIG.  11    illustrates the internal structure of the grinder and illustrates the state in which the side grip and the wheel cover are attached thereto. 
         FIG.  12    is a schematic view illustrating the positional relationship between a sensor, the first intermediate member  60 , and the second intermediate member  70  in the state that the side grip and the wheel cover are detached. 
         FIG.  13    is a schematic view illustrating the positional relationship between the sensor, the first intermediate member  60 , and the second intermediate member  70  in the state that the side grip is attached and the wheel cover is detached. 
         FIG.  14    is a schematic view illustrating the positional relationship between the sensor, the first intermediate member  60 , and the second intermediate member  70  in the state that the side grip and the wheel cover are attached. 
         FIG.  15    is a partial vertical cross-sectional view of a grinder according to a second embodiment of the present invention, and illustrates a state in which the side grip and the wheel cover are attached thereto. 
         FIG.  16    is a vertical cross-sectional view of the grinder according to the second embodiment, and illustrates a state in which the side grip and the wheel cover are detached therefrom. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In one or more embodiment(s), a tool may include a first accessory, a second accessory, a first attachment portion configured to allow the first accessory to be detachably attached thereto, a second attachment portion configured to allow the second accessory to be detachably attached thereto, a first intermediate member configured to be displaced from a first non-attachment position to a first attachment position by the attachment of the first accessory to the first attachment portion, a second intermediate member configured to be displaced from a second non-attachment position to a second attachment position by the attachment of the second accessory to the second attachment portion, and a single sensor configured to detect a specific state in which the first intermediate member is located at the first attachment position and the second intermediate member is located at the second attachment position. 
     According to this tool, the tool detects that the first intermediate member is located at the first attachment position and the second intermediate member is located at the second attachment position using the single sensor. The first intermediate member located at the first attachment position means that the first accessory is attached, and the second intermediate member located at the second attachment position means that the second accessory is attached, and therefore the attachment of the two types of accessories can be detected using the single sensor. 
     In one or more embodiment(s), the single sensor may be a photoelectric sensor including a light emitter and a light receiver, or an ultrasonic sensor. The first intermediate member may be configured to be displaced between a position of blocking light emitted from the light emitter or an ultrasonic wave emitted from the ultrasonic sensor and a position of not blocking the light or the ultrasonic wave due to the attachment or no attachment of the first accessory to the first attachment portion. The second intermediate member may be configured to be displaced between a position of blocking the light or the ultrasonic wave and a position of not blocking the light or the ultrasonic wave due to the attachment or no attachment of the second accessory to the second attachment portion. According to this configuration, the attachment of the two types of accessories can be easily detected using the single photoelectric sensor or the single ultrasonic sensor. 
     In one or more embodiment(s), the single sensor may be a reflection-type photosensor. In one or more embodiment(s), the single sensor may be a transmission-type photosensor. 
     In one or more embodiment(s), the tool may include an electric motor, and a controller configured to control driving of the electric motor. The controller may permit the electric motor to be driven when the single sensor detects the specific state and prohibit the electric motor from being driven when the single sensor does not detect the specific state. 
     In one or more embodiment(s), the tool may be a grinder including a tool accessory configured to be rotated by the electric motor. The first accessory may be a side grip, and the second accessory may be a cover that partially covers the tool accessory. 
     In one or more embodiment(s), the first attachment portion may include at least two side grip attachment portions for selectively attaching the side grip. The first intermediate member may be a single member provided in common for the at least two side grip attachment portions and configured to be rotatable about a rotational axis of the electric motor. The at least two side grip attachment portions may be located at positions spaced apart from each other in a circumferential direction around the rotational axis, respectively. The first intermediate member may include at least one pressed portion configured to, when the side grip is attached to one side grip attachment portion arbitrarily selected from the at least two side grip attachment portions, be directly or indirectly pressed by the side grip, and the first intermediate member may be rotated about the rotational axis when the at least one pressed portion is pressed. According to this configuration, regardless of which is selected from the at least two side grip attachment portions to attach the side grip, this attachment can be detected. In addition, the single first intermediate member is used in common for the at least two side grip attachment portions, and therefore the number of components can be reduced. 
     In one or more embodiment(s), the first intermediate member may have an annular shape or a partially annular shape. According to this configuration, the first intermediate member is shaped to correspond to the layout of the at least two side grip attachment portions, and therefore the single first intermediate member can be used in common for the at least two side grip attachment portions with a simple structure. 
     In one or more embodiment(s), the at least one pressed portion may protrude radially outward from a first intermediate member main body. The at least one pressed portion may be provided at at least two positions respectively corresponding to positions of the at least two side grip attachment portions, respectively. According to this configuration, the first intermediate member can be easily rotated. 
     In one or more embodiment(s), the at least one pressed portion may include a pressed surface angled with respect to a longitudinal direction of the side grip in such a manner that the first intermediate member is displaced in a direction different from the longitudinal direction of the side grip. The longitudinal direction of the side grip is a longitudinal direction of the side grip when the side grip is attached to the one side grip attachment portion. According to this configuration, the first intermediate member can be easily rotated. 
     In one or more embodiment(s), the first intermediate member main body may include a first through-hole having a circular-arc shape centered at the rotational axis. The first intermediate member main body may be attached rotatably along the circular-arc shape using a screw via the first through-hole. According to this configuration, the first intermediate member can be held rotatably with a simple structure. 
     In one or more embodiment(s), the first intermediate member may include a second through-hole. The light or the ultrasonic wave may pass through the second through-hole when the first intermediate member is located at the position of not blocking the light or the ultrasonic wave. According to this configuration, the first intermediate member can have a compact size. 
     In one or more embodiment(s), the second intermediate member may be configured to be linearly moved by being directly or indirectly pressed by the cover when the cover is attached to the second attachment portion. According to this configuration, the tool does not have to include a direction conversion mechanism by being designed in such a manner that the attachment direction of the cover matches a linear motion direction of the second intermediate member, thereby allowing the second intermediate member to be displaced with a simple structure. 
     In one or more embodiment(s), the second intermediate member may include a third through-hole in the form of an elongated hole having a longitudinal direction extending along a direction in which the second intermediate member is linearly moved. The second intermediate member may be attached linearly movably along the elongated hole using a screw via the third through-hole. According to this configuration, the second intermediate member can be held linearly movably with a simple structure. 
     In one or more embodiment(s), the tool may include a single holding member that holds the first intermediate member and the second intermediate member. According to this configuration, mounting each of the first intermediate member and the second intermediate member on the holding member automatically determines the relative positions of the first intermediate member and the second intermediate member. In other words, the relative positions of the first intermediate member and the second intermediate member do not have to be adjusted when the tool is assembled. 
     In the following description, the embodiments of the present invention will be described in further detail with reference to the drawings. First, a first embodiment of the present invention will be described with reference to  FIGS.  1  to  14   . In the embodiments that will be described below, a handheld-type electric disk grinder (hereinafter simply referred to as a grinder)  10  will be cited as an example of the tool. 
     As illustrated in  FIGS.  1  and  2   , the grinder  10  is configured to rotationally drive a generally disk-like tool accessory  28  mounted around a spindle  25 . The spindle  25  is rotated by a rotational driving force provided from an electric motor  31  as the prime mover. A grinding stone, a rubber pad, a brush, a blade, and the like are prepared as the tool accessory  28  mountable on the grinder  10 . A user selects the appropriate tool accessory  28  according to desired processing work and mounts it on the grinder  10 . According to the grinder  10 , processing work such as grinding, polishing, and cutting can be performed on a processing target material according to the type of the tool accessory  28 . 
     In the following description, a direction in which a rotational axis AX1 of the electric motor  31  (i.e., a motor shaft  32 ) extends is defined to be a front-rear direction of the grinder  10 . One side in the front-rear direction on which the tool accessory  28  is located is defined to be a front side, and the opposite side therefrom is defined to be a rear side. Further, a direction in which a rotational axis AX2 of the spindle  25  (i.e., a rotational axis of the tool accessory  28 ) extends is defined to be a vertical direction of the grinder  10 . One side in the vertical direction on which the tool accessory  28  is located is defined to be a lower side, and the opposite side therefrom is defined to be an upper side. Further, a direction perpendicular to the vertical direction and the front-rear direction is defined to be a left-right direction of the grinder  10 . A right side in the left-right direction when the front side is viewed from the rear side is defined to be a right side of the grinder  10 , and the opposite side therefrom is defined to be a left side of the grinder  10 . 
     As illustrated in  FIGS.  1  and  2   , the grinder  10  includes a gear housing  20 , a motor housing  30 , and a handle housing  40 . The electric motor  31  is contained in the motor housing  30 , which is located between the gear housing  20  and the handle housing  40  in the front-rear direction, i.e., the longitudinal direction of the grinder  10 . The electric motor  31  is configured to be driven by electric power supplied from outside (alternating-current power supplied from an AC power source in the present embodiment, but may be direct-current power supplied from a battery). Further, a controller  33  is contained between the electric motor  31  and a switch  41  in the front-rear direction in the handle housing  40 . The controller  33  receives the electric power supplied from outside and supplies this electric power to the electric motor  31  and a sensor  80 , which will be described below. The controller  33  controls the driving of the electric motor  31  by controlling the electric power supplied to the electric motor  31 . 
     A mechanism for transmitting the rotational driving force of the electric motor  31  to the tool accessory  28  is contained in the gear housing  20 . More specifically, a small bevel gear  23 , a large bevel gear  24 , and the spindle  25  are contained in the gear housing  20 . The small bevel gear  23  is fixed around the motor shaft  32  at the front end portion of the motor shaft  32  of the electric motor  31 . The spindle  25  is supported rotatably about the rotational axis AX2 by bearings disposed so as to be vertically spaced apart from each other. The rotational axis AX2 intersects with (more specifically, intersects perpendicularly to) the rotational axis AX1 of the electric motor  31 . The large bevel gear  24  is fixed around the spindle  25  on the upper side of the spindle  25 , and is meshed with the small bevel gear  23 . The gear housing  20  includes a second attachment portion  22  at the lower edge portion thereof. The second attachment portion  22  is used to detachably attach a cover  300 . The second attachment portion  22  has a vertically extending cylindrical shape. The spindle  25  extends vertically in the gear housing  20 , and extends out of the gear housing  20  (more specifically, the second attachment portion  22 ) on the lower side. 
     An inner flange  26  is attached around the spindle  25  at the lower end portion of the spindle  25  extending out of the gear housing  20 . A male screw portion is formed on a lower portion of the spindle  25  with respect to the inner flange  26 , and a lock nut  27  is attached to this male screw portion. The position of the tool accessory  28  relative to the spindle  25  is fixed by interposing the tool accessory  28  between the inner flange  26  and the lock nut  27  and tightening the lock nut  27 . 
     The handle housing  40  is a portion to be held by the user with one of his/her hands when the grinder  10  is in use. The handle housing  40  has a hollow circular cylindrical shape extending generally in the front-rear direction. The switch  41  for driving the electric motor  31  is contained inside the handle housing  40 . An operation member  50  is provided under the handle housing  40 . The operation member  50  is configured to be displacable between an OFF position of bringing the switch  41  into an OFF state and an ON position of bringing the switch  41  into an ON state.  FIGS.  1  and  2    illustrate the operation member  50  located at the OFF position. A lock-off switch  57  is provided near the front end of the operation member  50  in the front-rear direction. The lock-off switch  57  is used to engage the operation member  50  at the OFF position, thereby prohibiting the operation member  50  from being displaced to the ON position. 
     When the operation member  50  is operated from the OFF position to the ON position by the user, the switch  41  detects that and transmits a detection signal to the controller  33 . Upon receiving this detection signal, the controller  33  supplies the electric power to the electric motor  31 , thereby driving the electric motor  31 . When the electric motor  31  is driven, the rotation of the motor shaft  32  is transmitted to the spindle  25  while being slowed down via the small bevel gear  23  and the large bevel bear  24 . At this time, the direction of the rotational motion is converted from the direction around the motor shaft  32  into the direction around the rotational axis AX2 of the spindle  25 . According to this mechanism, the spindle  25  is rotated about the rotational axis AX2 in response to the rotation of the motor shaft  32 , and the tool accessory  28  fixed by the inner flange  26  and the lock nut  27  is rotated together with the spindle  25  as a result thereof. 
     As illustrated in  FIG.  1   , the grinder  10  further includes a side handle  200  and the cover  300  as the accessories thereof. The side handle  200  is prepared to be held by the user with the opposite hand from his/her hand holding the handle housing  40 . The user can further stably hold the grinder  10  by using the side handle  200 . The side handle  200  includes a grip portion  210  to be held by the user, and an attachment portion  220  to be attached to the gear housing  20 . The attachment portion  220  has a circular columnar shape extending in the longitudinal direction of the side handle  200 , and extends out of one end of the grip portion  210  in the longitudinal direction of the side handle  200 . A male screw is formed on the outer peripheral surface of the attachment portion  220 . 
     As illustrated in  FIG.  9   , the gear housing  20  includes three first attachment portions  29   a  to  29   c  for detachably attaching the side handle  200 . The first attachment portions  29   a  to  29   c  are disposed at positions spaced apart from each other in the circumferential direction around the rotational axis AX1. More specifically, the first attachment portion  29   a  is formed on the left surface of the gear housing  20 , the first attachment portion  29   b  is formed on the upper surface of the gear housing  20 , and the first attachment portion  29   c  is formed on the right surface of the gear housing  20 . The three first attachment portions  29   a  to  29   c  are provided at positions rotational symmetric with respect to the rotational axis AX1, respectively. Each of the first attachment portions  29   a  to  29   c  is provided in the form of a through-hole that establishes communication between the inside and the outside of the gear housing  20 . A female screw threadedly engageable with the male screw of the attachment portion  220  is formed on the inner surface forming this through-hole. 
     The side handle  200  can be attached to the gear housing  20  by screwing the attachment portion  220  of the side handle  200  into selected one from the three first attachment portions  29   a  to  29   c . The user can arbitrarily select the attachment portion of the side handle  200  from the first attachment portions  29   a  to  29   c  according to the type of the work intended to perform using the grinder  10  or according to whether the user is right-handed or left-handed. The three first attachment portions  29   a  to  29   c  are provided in the present embodiment, but the number of first attachment portions is not especially limited and may be any number equal to or greater than 1. For example, the grinder  10  may include only two first attachment portions  29   a  and  29   c . 
     As illustrated in  FIG.  1   , the cover  300  includes a cover main body  310  to cover a part of the tool accessory  28  therewith, and an attachment portion  320  to be attached to the second attachment portion  22 . The cover main body  310  covers an approximately rear half portion of the tool accessory  28 . The cover main body  310  covers the upper surface, the lower surface, and the circumferential surface between the upper surface and the lower surface of the tool accessory  28  in the present embodiment, but may cover only the upper surface and the circumferential surface depending on the type of the tool accessory  28  in use. The attachment portion  320  has a generally annular shape with an opening, and extends upward from the upper surface of the cover main body  310 . The attachment portion  320  includes opposing two flanges at two distal ends in the circumferential direction, although they are not illustrated because the structure of the attachment portion  320  is well known. A bolt is inserted into a screw hole formed at each of the flanges and is tightened in a state that the attachment portion  320  is disposed so as to surround the second attachment portion  22  of the gear housing  20 , by which the radius of the annular shape of the attachment portion  320  reduces and the attachment portion  320  is fixed to the second attachment portion  22 . 
     The above-described grinder  10  is configured to permit the electric motor  31  to be driven only in a state that the side handle  200  is attached to any of the first attachment portions  29   a  to  29   c  of the gear housing  20  and the cover  300  is also attached to the second attachment portion  22  of the gear housing  20 . In a state that at least one of the side handle  200  and the cover  300  is not attached, the controller  33  prohibits the electric motor  31  from being driven even when the user operates the operation member  50  to the ON position and the detection signal is transmitted from the switch  41  to the controller  33 . The state in which both the side handle  200  and the cover  300  are attached is detected by the single sensor  80 , which will be described below, and is output from the sensor  80  to the controller  33  via a signal line (not illustrated). In the following description, a configuration for this detection will be described in detail with reference to the drawings. 
     As illustrated in  FIGS.  1  and  2   , the grinder  10  further includes a first intermediate member  60 , a second intermediate member  70 , a holding member  140 , and the sensor  80 . First, the first intermediate member  60 , the second intermediate member  70 , the holding member  140 , and the sensor  80  will be described in outline. 
     The first intermediate member  60  is configured to be pressed and displaced by the attachment portion  220  of the side handle  200  by the attachment of the side handle  200  to any of the first attachment portions  29   a  to  29   c . The first intermediate member  60  is rotated by a predetermined angle about the rotational axis AX1 as such a displacement operation in the present embodiment. The position of the first intermediate member  60  when the side handle  200  is attached to none of the first attachment portions  29   a  to  29   c  of the gear housing  20  will be referred to as a first non-attachment position (refer to  FIGS.  4  and  9   ). The position of the first intermediate member  60  when the side handle  200  is attached to any of the first attachment portions  29   a  to  29   c  will be referred to as a first attachment position (refer to  FIGS.  3 ,  10 , and  11   ). The first intermediate member  60  is a generally annular member, and is disposed inside the gear housing  20  so as to surround the motor shaft  32  on the front side with respect to the electric motor  31 . 
     The second intermediate member  70  is configured to be pressed and displaced by the attachment portion  320  of the cover  300  by the attachment of the cover  300  to the second attachment portion  22 . The second intermediate member  70  is linearly moved upward as such a displacement operation in the present embodiment. The position of the second intermediate member  70  when the cover  300  is not attached to the second attachment portion  22  of the gear housing  20  will be referred to as a second non-attachment position (refer to  FIGS.  4 ,  9 , and  10   ). The position of the second intermediate member  70  when the cover  300  is attached to the second attachment portion  22  will be referred to as a second attachment position (refer to  FIGS.  5  and  16   ). The second intermediate member  70  is disposed between the motor shaft  32  and the tool accessory  28  on the front side with respect to the first intermediate member  60 . 
     The holding member  140  is disposed on the front side with respect to the first intermediate member  60 , and holds the first intermediate member  60  and the second intermediate member  70  together. 
     The sensor  80  detects a state in which the first intermediate member  60  is located at the first attachment position and the second intermediate member  70  is located at the second attachment position. In the present embodiment, the sensor  80  is a photoelectric sensor. 
     In the following description, the first intermediate member  60 , the second intermediate member  70 , the holding member  140 , and the sensor  80  will be described in detail. First, the first intermediate member  60  will be described. As illustrated in  FIG.  5   , the first intermediate member  60  is a single member, and is provided in common for the first attachment portions  29   a  to  29   c . The first intermediate member  60  includes a first intermediate member main body  61 . The first intermediate member main body  61  has an annular shape centered at the rotational axis AX1 of the electric motor  31  in the present embodiment. However, the first intermediate member  60  may have a partially annular shape (i.e., an unclosed annular shape). A through-hole is formed at the central portion of the first intermediate member main body  61 . The motor shaft  32  extends through this through-hole. 
     The first intermediate member  60  further includes three pressed portions  62   a  to  62   c  and a second through-hole  64 . The three pressed portions  62   a  to  62   c  are disposed so as to be circumferentially spaced apart from each other. The pressed portion  62   a  is a portion pressed by the side handle  200  (more specifically, the distal end of the attachment portion  220 ) when the side handle  200  is attached to the first attachment portion  29   a  of the gear housing  20 . Similarly, the pressed portion  62   b  is a portion pressed by the side handle  200  when the side handle  200  is attached to the first attachment portion  29   b , and the pressed portion  62   c  is a portion pressed by the side handle  200  when the side handle  200  is attached to the first attachment portion  29   c . Therefore, the pressed portions  62   a  to  62   c  are disposed at angular positions corresponding to the angular positions of the first attachment portions  29   a  to  29   c , respectively (refer to  FIG.  14   ). Each of the pressed portions  62   a  to  62   c  protrudes radially outward from the first intermediate member main body  61 . 
     As described above, the first intermediate member  60  is configured to be rotated about the rotational axis AX1 when any of the pressed portions  62   a  to  62   c  is pressed by the side handle  200 . A comparison between  FIG.  9    and  FIG.  10    makes it understandable that, due to the attachment of the side handle  200  to the first attachment portion  29   c , the pressed portion  62   c  is pressed by the side handle  200 , and the first intermediate member  60  is rotated in the counterclockwise direction from the position illustrated in  FIG.  9    to the position illustrated in  FIG.  10   . 
     As illustrated in  FIGS.  5  and  9   , the pressed portion  62   a  includes a pressed surface  63   a  angled with respect to the longitudinal direction of the side handle  200  when the side handle  200  is attached to the first attachment portion  29   a  (i.e., the attachment direction of the side handle  200 ). Similarly, the pressed portion  62   b  includes a pressed surface  63   b  angled with respect to the longitudinal direction of the side handle  200  when the side handle  200  is attached to the first attachment portion  29   b . Similarly, the pressed portion  62   c  includes a pressed surface  63   c  angled with respect to the longitudinal direction of the side handle  200  when the side handle  200  is attached to the first attachment portion  29   c . The pressed surfaces  63   a  to  63   c  are angled at approximately 45 degrees with respect to the corresponding longitudinal direction of the side handle  200  (refer to  FIG.  9   ). This angle can be set to any angle so as to allow the first intermediate member  60  to be displaced in a direction different from the longitudinal direction of the side handle  200 . In an alternative embodiment, this angle may be set within a range of 30 degrees or larger and 60 degrees or smaller. According to the pressed surfaces  63   a  to  63   c  angled in this manner, the first intermediate member  60  can be easily rotated. 
     The second through-hole  64  extends through the first intermediate member  60  in the front-rear direction. When the first intermediate member  60  is located at the first non-attachment position illustrated in  FIG.  9   , the second through-hole  64  is located at an angular position offset from the lowermost portion of the first intermediate member  60  slightly to the left side and the upper side (i.e., a position at which the second through-hole  64  does not overlap a blocking portion  73  of the second intermediate member  70 , which will be described below, as viewed in the front-rear direction). On the other hand, when the first intermediate member  60  is located at the first attachment position illustrated in  FIG.  10   , the second through-hole  64  is located at an angular position of the lowermost portion of the first intermediate member  60  (i.e., a position at which the second through-hole  64  overlaps the blocking portion  73  of the second intermediate member  70 , which will be described below, as viewed in the front-rear direction). 
     As illustrated in  FIG.  5   , the first intermediate member main body  61  includes first through-holes  65  and  66 . Each of the first through-holes  65  and  66  has a circular-arc shape centered at the rotational axis AX1. The first through-holes  65  and  66  are disposed at positions rotational symmetric by 180 degrees with respect to the rotational axis AX1. The first intermediate member  60  is attached to the holding member  140  using screws via these first through-holes  65  and  66 . More specifically, bolts  91  are inserted in the first through-holes  65  and  66  as illustrated in  FIGS.  9  to  11   . These bolts  91  are threadedly engaged with screw holes  143   a  and  144   a  of the holding member  140 , which will be described below. Actually, a sensor board holding member  85  (refer to  FIG.  8   ), which will be described below, is disposed between the first intermediate member  60  and the heads of the bolts  91 , and the bolts  91  are disposed so as to extend through through-holes  87  and  88  of the sensor board holding member  85  and the first through-holes  65  and  66 , respectively, although this is not illustrated in  FIGS.  9  to  11   . Due to a predetermined clearance secured between the holding member  140  and/or the sensor board holding member  85  and the first intermediate member  60 , the first intermediate member  60  is held by the holding member  140  rotatably along the circular-arc shapes of the first through-holes  65  and  66 . According to this configuration, the first intermediate member  60  can be held with a simple structure. 
     The first intermediate member  60  further includes a protrusion  67 . The protrusion  67  extends forward from the front surface of the first intermediate member main body  61 . This protrusion  67  is used to bias the first intermediate member  60  toward the first non-attachment position (refer to  FIGS.  4  and  9   ) by a spring  68  (refer to  FIG.  7   ), which will be described below. 
     Next, the second intermediate member  70  will be described. As illustrated in  FIG.  6   , the second intermediate member  70  includes a base  71 , a pressed portion  72 , a blocking portion  73 , support portions  74  and  75 , and a spring seat  78 . The base  71  is a portion shaped like a flat plate which has a longitudinal direction extending along the front-rear direction and lies perpendicularly to the vertical direction. The pressed portion  72  is a portion pressed upward by the attachment portion  320  of the cover  300  when the cover  300  is attached to the second attachment portion  22 , and is located at the front edge of the second intermediate member  70 . The pressed portion  72  is shaped like a flat plate lying in parallel with the base  71 . A stepped portion is formed between the base  71  and the pressed portion  72 . The displacement amount of the second intermediate member  70  when the cover  300  is attached can be reduced due to this stepped portion. More specifically, when the cover  300  is attached, the second intermediate member  70  is not displaced since the attachment portion  320  of the cover  300  is in a state of being raised to the same position as the base  71  until the attachment portion  320  is brought into a state of abutting against the pressed portion  72 , and therefore the displacement amount of the second intermediate member  70  is reduced by an amount corresponding the step compared to a configuration in which the pressed portion  72  is located at the same vertical position as the base  71 . This can lead to a reduction in a space for the displacement of the second intermediate member  70 . In other words, this can cut down an increase in the vertical size of the grinder  10 . 
     The blocking portion  73  is a portion that blocks light emitted from the sensor  80  when the second intermediate member  70  is located at the second attachment position. The blocking portion  73  is located at the rear edge of the second intermediate member  70 , and extends upward from the rear edge of the base  71 . The blocking portion  73  is shaped like a flat plate extending perpendicularly to the front-rear direction. 
     The support portions  74  and  75  are disposed opposite from each other in the left-right direction on the front side with respect to the blocking portion  73  near the blocking portion  73 . The support portions  74  and  75  have generally L-like shapes extending from the base  71  in directions away from each other in the left-right direction, and then bent and extending upward after that. Third through-holes  76  and  77  are formed on the support portions  74  and  75 , respectively. The third through-holes  76  and  77  extend through the support portions  74  and  75  in the front-rear direction, respectively. The third through-holes  76  and  77  are each in the form of an elongated hole having a longitudinal direction extending along the vertical direction (i.e., a direction in which the second intermediate member  70  is linearly moved when being pressed by the cover  300 ). The second intermediate member  70  is attached to the holding member  140  using screws via these third through-holes  76  and  77 . More specifically, bolts  92  are inserted in the third through-holes  76  and  77  as illustrated in  FIGS.  9  to  11   . These bolts  92  are threadedly engaged with screw holes  145   a  and  146   a  of the holding member  140 , which will be described below. Due to predetermined clearances secured between the heads of the bolts  92  and the support portions  74  and  75 , respectively, the second intermediate member  70  is held by the holding member  140  linearly movably along the third through-holes  76  and  77 . According to this configuration, the second intermediate member  70  can be held with a simple structure. 
     The spring seat  78  is provided so as to protrude upward from the base  71 . A spring  79  (refer to  FIG.  4   ) is held between the spring seat  78  and a spring seat  148  of the holding member  140  (refer to  FIG.  7   ). The spring  79  biases the second intermediate member  70  toward the second non-attachment position (refer to  FIGS.  4 ,  9 , and  10   ). 
     Next, the holding member  140  will be described. As illustrated in  FIG.  7   , the holding member  140  includes an annular portion  141 , a hollow circular cylindrical portion  142 , protrusion portions  143  and  144 , protrusion portions  145  and  146 , the spring seat  148 , and a spring housing portion  149 . The annular portion  141  has a disk-like shape centered at the rotational axis AX1 of the electric motor  31 , and a through-hole is formed at the center thereof. A cutout  147  is formed on the lower side of the annular portion  141  to secure the space for the displacement of the second intermediate member  70 . 
     The hollow circular cylindrical portion  142  has a hollow circular cylindrical shape extending rearward from the annular portion  141 . The diameter of the hollow circular cylindrical portion  142  is smaller than the diameter of the annular portion  141 . The spring housing portion  149  is formed at the upper side of the hollow circular cylindrical portion  142  adjacently to the hollow circular cylindrical portion  142 . The spring housing portion  149  is formed to have a circular-arc shape centered at the rotational axis AX1. The spring  68  is housed in the spring housing portion  149 . The spring  68  is extensible and compressible along the circular-arc shape of the spring housing portion  149 . The rear side of the spring housing portion  149  is opened, and the protrusion  67  of the first intermediate member  60  is inserted in the spring housing portion  149  via this opening. One end of the spring  68  is supported on the inner surface of the spring housing portion  149  (a flat surface located at one end portion of the circular-arc shape), and the other end of the spring  68  is engaged with the protrusion  67 . Due to this configuration, the first intermediate member  60  is biased in the clockwise direction (i.e., toward the first non-attachment position). 
     The protrusion portions  143  and  144  are disposed so as to be spaced apart from each other in the left-right direction. The protrusion portions  143  and  144  extend rearward from the annular portion  141  at approximately vertically central positions of the annular portion  141 . The protrusion portions  143  and  144  include the screw holes  143   a  and  144   a  having female screws formed thereon, respectively. The screw holes  143   a  and  144   a  extend forward from the rear end surfaces of the protrusion portions  143  and  144 , respectively. The bolts  91  are threadedly engaged with the screw holes  143   a  and  144   a  to mount the first intermediate member  60  to the holding member  140  in the above-described manner (refer to  FIG.  9   ). 
     The protrusion portions  145  and  146  are disposed so as to be spaced apart from each other in the left-right direction on the lower side with respect to the protrusion portions  143  and  144 . The protrusion portions  145  and  146  include the screw holes  145   a  and  146   a  having female screws formed thereon, respectively. The screw holes  145   a  and  146   a  extend forward from the rear end surfaces of the protrusion portions  145  and  146 , respectively. The bolts  92  are threadedly engaged with the screw holes  145   a  and  146   a  to mount the second intermediate member  70  to the holding member  140  in the above-described manner (refer to  FIG.  9   ). The lengths of the protrusion portions  145  and  146  in the front-rear direction are shorter than the lengths of the protrusion portions  143  and  144  in the front-rear direction to allow the second intermediate member  70  to be held on the front side with respect to the first intermediate member  60 . 
     The above-described spring seat  148  is formed at the lower edge of the hollow circular cylindrical portion  142 . This holding member  140  is fitted in the gear housing  20  so as to bring the outer periphery of the annular portion  141  and the inner periphery of the hollow circular cylindrical portion  142  into abutment with the gear housing  20  in a state that the first intermediate member  60  and the second intermediate member  70  are mounted thereto. As a result, the holding member  140  is fixed to the gear housing  20 . Mounting the first intermediate member  60  and the second intermediate member  70  to the single holding member  140  automatically determines the relative positions of the first intermediate member  60  and the second intermediate member  70 , and therefore the relative positions of the first intermediate member  60  and the second intermediate member  70  do not have to be adjusted when the grinder  10  is assembled. In addition, as described above, the holding member  140  holds the sensor board holding member  85  holding the sensor  80 , and the first intermediate member  60  together. Therefore, mounting the sensor board holding member  85  also automatically determines the relative position of the sensor  80  to the first intermediate member  60  and the second intermediate member  70 , and therefore the position of the sensor  80  neither has to be adjusted. 
     Next, the sensor  80  will be described. The sensor  80  is a reflection-type photosensor in the present embodiment. As illustrated in  FIG.  4   , the sensor  80  includes a light emitter  82 , a light receiver  83 , and a sensor board  81  on which the light emitter  82  and the light receiver  83  are mounted together. The light emitter  82  and the light receiver  83  are disposed on the front surface of the sensor board  81 . The sensor  80  is disposed near the bottom portion of the gear housing  20  to detect the displacements of the first intermediate member  60  and the second intermediate member  70 . More specifically, the sensor board  81  and the light emitter  82  are disposed behind the first intermediate member main body  61  in proximity to the first intermediate member main body  61 . 
     This sensor  80  is held by the sensor board holding member  85  illustrated in  FIG.   8   . The sensor board holding member  85  is a generally Y-shaped plate-like member. The sensor board  81 , on which the light emitter  82  and the light receiver  83  are mounted, is held at a proximal portion from which the sensor board holding member  85  is forked. The sensor board  81  is fixed to the sensor board holding member  85  by any method (for example, screwing, snap-fit, or engagement using a partial heated deformation). Further, the through-holes  87  and  88  are formed near the forked distal ends of the sensor board holding member  85 , respectively. 
     The first intermediate member  60  is displaced between a position of blocking light emitted from the light emitter  82  and a position of not blocking this light due to the attachment of the side handle  200 . Similarly, the second intermediate member  70  is displaced between a position of blocking the light emitted from the light emitter  82  and a position of not blocking this light due to the attachment of the cover  300 . The sensor  80  detects the state in which the side handle  200  and the cover  300  are attached, based on whether or not the light receiver  83  receives the light based on these differences in the positions of the first intermediate member  60  and the second intermediate member  70 . In the following description, this will be described more specifically. 
       FIG.  12    schematically illustrates the positional relationship between the first intermediate member  60  and the second intermediate member  70  (refer to  FIGS.  4  and  9   ), and the sensor  80  when neither of the side handle  200  and the cover  300  is attached. In the state that neither of the side handle  200  and the cover  300  is attached, the first intermediate member  60  is located at the position where the first intermediate member main body  61  blocks the light emitted from the light emitter  82  as illustrated in  FIG.  12   . Since the first intermediate member main body  61  is disposed in proximity to the light emitter  82  and the light receiver  83 , the light receiver  83  cannot receive the light emitted from the light emitter  82 . In the state that only the cover  300  of the side handle  200  and the cover  300  is attached, the first intermediate member main body  61  is also located at the position illustrated in  FIG.  12    and therefore the light receiver  83  can neither receive the light emitted from the light emitter  82 , although this is not illustrated. 
     When only the side handle  200  is attached in the state illustrated in  FIG.  12   , the first intermediate member  60  is displaced to the first attachment position illustrated in  FIGS.  3  and  10   . At this time, light  89  emitted from the light emitter  82  passes through the second through-hole  64  and therefore is not blocked by the first intermediate member main body  61 , as illustrated in  FIG.  13   . Further, at this time, the blocking portion  73  of the second intermediate member  70  is located at the position of not blocking the light  89 , and therefore the light receiver  83  cannot receive the light emitted from the light emitter  82 . 
     When the cover  300  is attached in the state illustrated in  FIG.  13   , the second intermediate member  70  is displaced to the second attachment position illustrated in  FIGS.  3  and  11   . At this time, the light  89  emitted from the light emitter  82  is blocked by the blocking portion  73  after passing through the second through-hole  64 , as illustrated in  FIG.  14   . As a result, the light  89  is reflected by the blocking portion  73  and is received by the light receiver  83 . 
     In this manner, according to the above-described grinder  10 , the light  89  emitted from the light emitter  82  can be received by the light receiver  83  on the single sensor  80  only in the state that both the side handle  200  and the cover  300  are attached. In other words, the state in which both the side handle  200  and the cover  300  are attached can be detected using the single sensor  80 . Therefore, the present configuration can reduce the number of components and the cost compared to a configuration in which an individual sensor is prepared for each of the side handle  200  and the cover  300 . 
     Further, the first intermediate member  60  is configured to be rotated about the rotational axis AX1 when any of the pressed portions  62   a  to  62   c  is pressed by the side handle  200 . This eliminates the necessity of securing a space for the displacement of the first intermediate member  60  in the front-rear direction, thereby allowing the grinder  10  to have a compact size in the front-rear direction. 
     Further, the second intermediate member  70  is pressed by the cover  300  (more specifically, the attachment portion  320 ) and is linearly moved in the attachment direction of the cover  300  (i.e., upward) when the cover  300  is attached. This eliminates the necessity of a direction conversion mechanism, thereby contributing to the simplification of the apparatus configuration. 
     In the following description, a second embodiment of the present invention will be described with reference to  FIGS.  15  and  16   . The second embodiment is different from the first embodiment in terms of using a sensor  180  instead of the sensor  80 , using a first intermediate member  160  instead of the first intermediate member  60 , and using a second intermediate member  170  instead of the second intermediate member  70 . In  FIGS.  15  and  16   , components similar to the components in the first embodiment are identified by the same reference numerals as the first embodiment. In the following description, the second embodiment will be described focusing only on differences from the first embodiment. The sensor  180  is a transmission-type photosensor in the present embodiment. As illustrated in  FIGS.  15  and  16   , the sensor  180  includes a light emitter  182 , a light receiver  183 , and a sensor board  181  on which the light emitter  182  and the light receiver  183  are mounted together. The first intermediate member  160  does not include the second through-hole  64 , but instead includes a cutout on the radial outer edge portion thereof. The second intermediate member  170  includes a blocking portion  173  instead of the blocking portion  73 . The blocking portion  173  extends downward from the rear edge of the base  71 . 
     The light emitter  182  and the light receiver  183  are arranged in such a manner that the blocking portion  173  and the first intermediate member main body  61  are located between the light emitter  182  and the light receiver  183  in the front-rear direction. In this configuration, the first intermediate member main body  61  is located at a position of blocking light emitted from the light emitter  182  when the first intermediate member  160  is located at the first non-attachment position, and the blocking portion  173  is located at a position of blocking the light emitted from the light emitter  182  when the second intermediate member  170  is located at the first non-attachment position (refer to  FIG.  16   ). In other words, when at least one of the side handle  200  and the cover  300  is not attached, the light emitted from the light emitter  182  is blocked by at least one of the first intermediate member  160  and the second intermediate member  170 . Therefore, the light receiver  183  cannot receive the light emitted from the light emitter  182 . On the other hand, the light emitted from the light emitter  182  can pass through the cutout of the first intermediate member  160  when the first intermediate member  160  is located at the first attachment position, and the blocking portion  173  is displaced to the position of not blocking the light emitted from the light emitter  182  when the second intermediate member  170  is located at the first attachment position (refer to  FIG.  15   ). In other words, when both the side handle  200  and the cover  300  are attached, the light emitted from the light emitter  182  is received by the light receiver  183 . Therefore, the state in which both the side handle  200  and the cover  300  are attached can be detected using the single sensor  180 . 
     Having described the embodiments of the present invention, the above-described embodiments are intended to only facilitate the understanding of the present invention, and are not intended to limit the present invention thereto. The present invention can be modified or improved without departing from the spirit thereof, and includes equivalents thereof. Further, each of the elements described in the claims and the specification can be combined in any manner or omitted in any manner within a range that allows it to remain capable of achieving at least a part of the above-described objects or bringing about at least a part of the above-described advantageous effects. 
     For example, the shapes and the forms of the components of the above-described grinder  10  are merely examples, and can be changed in any manner as long as the functions of these components can be maintained. For example, the pressed portions  62   a  to  62   c  of the first intermediate member  60  may protrude forward or rearward instead of protruding radially outward. Alternatively, the first intermediate member  60  may include a blocking portion protruding radially outward from the first intermediate member main body  61  instead of the second through-hole  64 . In this case, the light emitted from the light emitter  82  is blocked by the blocking portion when the first intermediate member  60  is located at the first non-attachment position, and the blocking portion is brought into a state of being displaced to the position of not blocking the light emitted from the light emitter  82  when the first intermediate member  60  is located at the first attachment position. 
     Further, the first intermediate member  60  may be indirectly pressed by the side handle  200  when the side handle  200  is attached. More specifically, an additional member that is displaced by being pressed by the side handle  200  may be provided, and the first intermediate member  60  may be displaced by this additional member. Similarly, the second intermediate member  70  may be indirectly pressed by the cover  300  when the cover  300  is attached. 
     Further, the first intermediate member  60  may be configured to be tilted by being pressed by the side handle  200  when the side handle  200  is attached instead of being configured to be rotated when the side handle  200  is attached. For example, the first intermediate member  60  may include a support shaft on the lower side of the first intermediate member  60  and be tilted about this support shaft in such a manner that the lower edge of the first intermediate member  60  approaches the front side. 
     Further, the second intermediate member  70  may be located at the position of blocking the light emitted from the light emitter  82  when being located at the second non-attachment position, and located at the position of not blocking the light emitted from the light emitter  82  when being located at the second attachment position. In this case, for example, a low-reflective coating material may be applied to the second intermediate member  70  in advance, and a reflection board may be disposed in such a manner that the first intermediate member  60  and the second intermediate member  70  are located between the reflection plate and the sensor  80  in the front-rear direction. Employing this layout allows the light receiver  83  to receive the light emitted from the light emitter  82  only in the state that both the side handle  200  and the cover  300  are attached. 
     Each of the sensors  80  and  180  is not limited to the photoelectric sensor, and may be any other known type of sensor. For example, an ultrasonic distance sensor may be employed. In this case, the state in which both the side handle  200  and the cover  300  are attached can also be detected if the first intermediate member  60  and the second intermediate member  70  are each configured to be displaced between a position of blocking an ultrasonic wave emitted from the sensor (hereinafter also referred to as a blocking position) and a position of not blocking this ultrasonic wave (hereinafter also referred to as a non-blocking position) according to whether the side handle  200  or the cover  300  is attached. For example, the first intermediate member  60  may be located at the blocking position when the side handle  200  is not attached, and be located at the non-blocking position when the side handle  200  is attached. Further, the second intermediate member  70  may be located at the blocking position when the cover  300  is not attached, and be located at the non-blocking position when the cover  300  is attached. Employing this configuration allows the sensor  80  or  180  to detect the state in which both the side handle  200  and the cover  300  are attached based on a difference in the detected distance. Alternatively, an eddy current displacement sensor may be employed. In this case, each of the first intermediate member  60  and the second intermediate member  70  is at least partially made from metal. Alternatively, a color sensor may be employed. In this case, the first intermediate member  60  and the second intermediate member  70  are colored in different colors from each other. 
     Further, the grinder  10  may include a notification unit for notifying the user that at least one of the side handle  200  and the cover  300  is not attached instead of or in addition to the configuration that permits or prohibits the driving of the electric motor  31  according to the attachment states of the side handle  200  and the cover  300 . The notification method may be light emission, a sound output, a character display, or a combination of them. For example, the notification unit may include at least one of a light-emitting element such as an LED, a GUI screen, and a speaker. 
     Further, the above-described embodiments can be applied to not only the grinder  10  but also any tool configured to allow two types of accessories to be detachably attached thereto. 
     
       
         
           
               
               
             
               
                 DESCRIPTION OF MUMERALS 
               
             
            
               
                 
                   10 
                 
                 grinder 
               
               
                 
                   20 
                 
                 gear housing 
               
               
                 
                   22 
                 
                 second attachment portion 
               
               
                 
                   23 
                 
                 small bevel gear 
               
               
                 
                   24 
                 
                 large bevel gear 
               
               
                 
                   25 
                 
                 spindle 
               
               
                 
                   26 
                 
                 inner flange 
               
               
                 
                   27 
                 
                 lock nut 
               
               
                 
                   28 
                 
                 tool accessory 
               
               
                   29   a  to  29   c 
 
                 first attachment portion 
               
               
                 
                   30 
                 
                 motor housing 
               
               
                 
                   31 
                 
                 electric motor 
               
               
                 
                   32 
                 
                 motor shaft 
               
               
                 
                   33 
                 
                 controller 
               
               
                 
                   40 
                 
                 handle housing 
               
               
                 
                   41 
                 
                 switch 
               
               
                 
                   50 
                 
                 operation member 
               
               
                   60 ,  160   
                 first intermediate member 
               
               
                 
                   61 
                 
                 first intermediate member main body 
               
               
                   62   a  to  62   c 
 
                 pressed portion 
               
               
                   63   a  to  63   c 
 
                 pressed surface 
               
               
                 
                   64 
                 
                 second through-hole 
               
               
                 
                   65 
                 
                 first though-hole 
               
               
                 
                   67 
                 
                 protrusion 
               
               
                 
                   68 
                 
                 spring 
               
               
                   70 ,  170   
                 second intermediate member 
               
               
                 
                   71 
                 
                 base 
               
               
                 
                   72 
                 
                 pressed portion 
               
               
                   73 ,  173   
                 blocking portion 
               
               
                 
                   74 
                 
                 support portion 
               
               
                 
                   76 
                 
                 third through-hole 
               
               
                 
                   78 
                 
                 spring seat 
               
               
                 
                   79 
                 
                 spring 
               
               
                   80 ,  180   
                 sensor 
               
               
                   81 ,  181   
                 sensor board 
               
               
                   82 ,  182   
                 light emitter 
               
               
                   83 ,  183   
                 light receiver 
               
               
                 
                   85 
                 
                 sensor board holding member 
               
               
                   87 ,  88   
                 through-hole 
               
               
                 
                   89 
                 
                 light 
               
               
                   91 ,  92   
                 bolt 
               
               
                 
                   140 
                 
                 holding member 
               
               
                 
                   141 
                 
                 annular portion 
               
               
                 
                   142 
                 
                 hollow circular cylindrical portion 
               
               
                   143 ,  144 ,  145 ,  146   
                 protrusion portion 
               
               
                   143   a ,  144   a ,  145   a ,  146   a   
                 screw hole 
               
               
                 
                   147 
                 
                 cutout 
               
               
                 
                   148 
                 
                 spring seat 
               
               
                 
                   149 
                 
                 spring housing portion 
               
               
                 
                   200 
                 
                 side handle 
               
               
                 
                   210 
                 
                 grip portion 
               
               
                 
                   220 
                 
                 attachment portion 
               
               
                 
                   300 
                 
                 cover 
               
               
                 
                   310 
                 
                 cover main body 
               
               
                 
                   320 
                 
                 attachment portion 
               
               
                 AX 1 , AX 2 
 
                 rotational axis