Patent Publication Number: US-2023158644-A1

Title: Impact tool and method for manufacturing output block

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is based upon, and claims the benefit of priority to, Japanese Patent Application No. 2021-188794, filed on Nov. 19, 2021, and Japanese Patent Application No. 2022-149335, filed on Sep. 20, 2022, the entire disclosure of which is hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present disclosure generally relates to an impact tool and a method for manufacturing an output block. More particularly, the present disclosure relates to an impact tool including a hammer and an output block including an anvil claw, against which the hammer collides, and a method for manufacturing an output block for use in such an impact tool. 
     BACKGROUND ART 
     JP 2021-070108 A discloses an electric tool (impact tool), which includes a motor, an impact mechanism, an output shaft, and a torque measuring unit. The impact mechanism receives motive power from the motor and thereby generates impacting force. The output shaft holds a tip tool thereon. The impact mechanism includes a hammer and an anvil. The output shaft is subjected by the impact mechanism to rotational impact around an axis. The torque measuring unit measures, as measured torque, the torque applied to the output shaft. The torque measuring unit may be, for example, a magnetostrictive strain sensor (magnetostrictive sensor) with the ability to detect torsional strain. 
     In the electric tool of JP 2021-070108 A, the impact caused through the impact operation, involving generation of rotational impact, by the impact mechanism places load on an output block (which includes the anvil in this case). Thus, the output block is sometimes required to have its mechanical strength increased sufficiently to withstand such impact. 
     SUMMARY 
     The present disclosure provides an impact tool including a magnetostrictive sensor and an output block, of which the mechanical strength is increased sufficiently for the output block to withstand the impact caused by an impact operation, and also provides a method for manufacturing an output block for use in such an impact tool. 
     An impact tool according to an aspect of the present disclosure includes a motor, an output block, a hammer, and a magnetostrictive sensor. The output block holds a tip tool thereon. The hammer receives motive power from the motor and collides against the output block. The magnetostrictive sensor includes a magnetostrictive member and a coil portion covering the magnetostrictive member. The hammer includes a hammer body and a hammer claw connected to the hammer body. The output block includes a claw block and a body block. The claw block includes an anvil claw, against which the hammer claw collides. The claw block has been subjected to quenching treatment. The body block includes a thermally sprayed portion and is coupled to the claw block. The thermally sprayed portion includes, on a surface thereof, the magnetostrictive member made of a magnetostrictive material. 
     A method for manufacturing an output block according to another aspect of the present disclosure is designed to manufacture an output block for use in an impact tool to hold a tip tool thereon. The output block includes: a claw block including an anvil claw; and a body block. The method includes a first step, a second step, and a third step. The first step includes subjecting the claw block to quenching treatment. The second step includes thermally spraying a magnetostrictive material onto a surface of a thermally sprayed portion that forms a predetermined part of the body block and thereby forming a magnetostrictive member on the surface. The third step includes coupling the body block and the claw block to each other after the first step and the second step have been performed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The figures depict one or more implementations in accordance with the present teaching, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements. 
         FIG.  1    is an exploded perspective view of an output block for an impact tool according to a first embodiment as viewed obliquely from behind the output block; 
         FIG.  2    is an exploded perspective view of the output block for the impact tool as viewed obliquely from in front of the output block; 
         FIG.  3    is an exploded perspective view of the output block, a hammer, and a transmission shaft of the impact tool; 
         FIG.  4    is a side cross-sectional view of the impact tool; 
         FIG.  5    is a side cross-sectional view of a main part of the impact tool; 
         FIG.  6    is a flowchart showing the procedure of a method for manufacturing an output block for the impact tool; 
         FIG.  7    is an exploded perspective view of an output block for an impact tool according to a second embodiment as viewed obliquely from behind the output block; and 
         FIG.  8    is a flowchart showing the procedure of a method for manufacturing an output block for the impact tool. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of an impact tool and method for manufacturing an output block according to the present disclosure will now be described with reference to the accompanying drawings. Note that the embodiments to be described below are only exemplary ones of various embodiments of the present disclosure and should not be construed as limiting. Rather, the exemplary embodiments may be readily modified in various manners depending on a design choice or any other factor without departing from the scope of the present disclosure. The drawings to be referred to in the following description of embodiments are all schematic representations. Thus, the ratio of the dimensions (including thicknesses) of respective constituent elements illustrated on the drawings does not always reflect their actual dimensional ratio. 
     First Embodiment 
     Overview 
     As shown in  FIGS.  1  and  4   , an impact tool  1  according to an exemplary embodiment includes a motor  3 , an output block  8 , a hammer  9 , and a magnetostrictive sensor  5 . The output block  8  holds a tip tool thereon. The hammer  9  receives motive power from the motor  3  and collides against the output block  8 . The magnetostrictive sensor  5  includes a magnetostrictive member  51  and a coil portion  52  covering the magnetostrictive member  51 . The hammer  9  includes a hammer body  90  and a hammer claw  95  (see  FIG.  3   ) connected to the hammer body  90 . The output block  8  includes a claw block  81  and a body block  82 . The claw block  81  includes an anvil claw  812 , against which the hammer claw  95  collides. The claw block  81  has been subjected to quenching treatment. The body block  82  includes a thermally sprayed portion  821  and is coupled to the claw block  81 . The thermally sprayed portion  821  includes, on a surface thereof, the magnetostrictive member  51  made of a magnetostrictive material. 
     If the claw block  81  and the body block  82  were formed as a single integral member, then not only the body block  82  but also the claw block  81  would be heated while the magnetostrictive material is being thermally sprayed, thus possibly lessening the effect of increasing the impact resistance of the claw block  81  to be achieved by the quenching treatment. In contrast, according to this embodiment, the claw block  81  and the body block  82  are provided as two separate members, thus enabling maintaining the impact resistance of the claw block  81 . 
     Thus, this embodiment enables forming a magnetostrictive member  51  on the thermally sprayed portion  821  of the body block  82  and increasing the impact resistance of the claw block  81  by quenching treatment at the same time. That is to say, this enables providing an impact tool  1  including a magnetostrictive sensor  5  and an output block  8 , of which the mechanical strength is increased sufficiently for the output block  8  to withstand the impact caused by an impact operation. 
     In addition, this impact tool  1  may make the magnetostrictive sensor  5  measure torque and control the motor  3  based on the torque thus measured. 
     Details 
     (1) Structure 
     In the following description, a direction in which the claw block  81  of the output block  8  and a tip portion  823  thereof (to be described later) are arranged side by side will be hereinafter defined as a “forward/backward direction” with the tip portion  823  supposed to be located forward of the claw block  81  and with the claw block  81  supposed to be located backward of the tip portion  823 . Also, in the following description, a direction in which a barrel  21  and a grip  22  (to be described later) are arranged one on top of the other will be hereinafter defined as an “upward/downward direction” with the barrel  21  supposed to be located upward of the grip  22  and with the grip  22  supposed to be located downward of the barrel  21 . Nevertheless, these definitions should not be construed as limiting the directions in which the impact tool  1  is supposed to be used. 
     The impact tool  1  according to this embodiment is a portable electric tool. As shown in  FIG.  4   , the impact tool  1  includes a housing  2 , the motor  3 , a transmission mechanism  4 , an operating member  24 , the magnetostrictive sensor  5 , a circuit section  6 , and a control unit  7 . The transmission mechanism  4  includes the output block  8  and the hammer  9 . 
     The housing  2  houses the motor  3 , the transmission mechanism  4 , the magnetostrictive sensor  5 , the circuit section  6 , and the control unit  7 . The housing  2  includes the barrel  21 , the grip  22 , and an attachment  23 . The barrel  21  has a circular cylindrical shape. The grip  22  protrudes from the barrel  21 . More specifically, the grip  22  protrudes from a side surface of the barrel  21 . A tip portion, opposite from the portion connected to the barrel  21 , of the grip  22  is connected to the attachment  23 . 
     A rechargeable battery pack is attached removably to the attachment  23 . The impact tool  1  is powered by the battery pack. That is to say, the battery pack is a power supply that supplies a current for driving the motor  3 . In this embodiment, the battery pack is not a constituent element of the impact tool  1 . However, this is only an example and should not be construed as limiting. Alternatively, the impact tool  1  may include the battery pack as one of constituent elements thereof. The battery pack includes an assembled battery formed by connecting a plurality of secondary batteries (such as lithium-ion batteries) in series and a case in which the assembled battery is housed. 
     The operating member  24  protrudes from the grip  22 . The operating member  24  accepts an operating command for controlling the rotation of the motor  3 . As used herein, “the rotation of the motor  3 ” refers to the rotation of a drive shaft  311  of the motor  3 . The ON/OFF states of the motor  3  may be switched by pulling the operating member  24 . In addition, the rotational velocity of the motor  3  is adjustable by the manipulative variable indicating how deep the operating member  24  has been pulled. Specifically, the greater the manipulative variable is, the higher the rotational velocity of the motor  3  becomes. Besides, according to the manipulative variable indicating how deep the operating member  24  has been pulled, the control unit  7  also makes the motor  3  start or stop running and controls the rotational velocity of the motor  3  as well. 
     The tip tool is held by the output block  8 . More specifically, the tip tool is attachable to, and removable from, the output block  8 . In this embodiment, the tip tool is attached to the output block  8  via a chuck. However, this is only an example and should not be construed as limiting. Alternatively, the tip tool may be directly attached to the output block  8 . 
     The output block  8  receives motive power from the motor  3  to rotate along with the tip tool. As the rotational velocity of the motor  3  is controlled by operating the operating member  24 , the rotational velocity of the tip tool is also controlled. 
     In this embodiment, the tip tool is not a constituent element of the impact tool  1 . Nevertheless, the impact tool  1  may include the tip tool as one of constituent elements thereof. 
     The tip tool may be, for example, a screwdriver bit. The tip tool is fitted into a fastening member as a work target (such as a bolt or a screw). The work of tightening or loosening the screw may be performed by turning the tip tool that is fitted into the screw. 
     The motor  3  according to this embodiment may be, for example, a brushless motor. Also, the motor  3  according to this embodiment is a servomotor. The torque and rotational velocity of the motor  3  vary under the control of the control unit  7  (which is a servo driver). More specifically, the control unit  7  controls the operation of the motor  3  by feedback control for bringing the torque and rotational velocity of the motor  3  closer toward target values. In addition, the control unit  7  may control the operation of the motor  3  based on the torque detected by the magnetostrictive sensor  5 . 
     The transmission mechanism  4  includes an impact mechanism  40 . The impact tool  1  according to this embodiment is an electric impact screwdriver for fastening a screw while performing an impact operation using the impact mechanism  40 . During the impact operation, the impact mechanism  40  generates impacting force based on the motive power of the motor  3  and applies the impacting force to the tip tool. 
     The transmission mechanism  4  preferably includes not only the impact mechanism  40  but also a planetary gear mechanism  48 . The impact mechanism  40  includes a transmission shaft  41 , the hammer  9 , a return spring  43 , the output block  8 , and two steel spheres  49 . The rotational power of the drive shaft  311  of the motor  3  is transmitted to the transmission shaft  41  via the planetary gear mechanism  48 . The transmission mechanism  4  transmits the torque of the motor  3  to the output block  8  via the transmission shaft  41 . The transmission shaft  41  is interposed between the motor  3  and the output block  8 . 
     The hammer  9  is made of a metallic material. The hammer  9  moves relative to the output block  8  and applies impacting force to the output block  8  upon receiving motive power from the motor  3 . As shown in  FIG.  3   , the hammer  9  includes a hammer body  90  and two hammer claws  95 . The hammer body  90  has a disk shape. The two hammer claws  95  protrude from the front surface of the hammer body  90 . The hammer body  90  has a through hole  91  to pass the transmission shaft  41  therethrough. 
     The hammer body  90  has two grooves  93  on an inner peripheral surface of the through hole  91 . The transmission shaft  41  has a circular columnar shape. The transmission shaft  41  has two grooves  413  on an outer peripheral surface thereof. The two grooves  413  are connected to each other. The two steel spheres  49  (see  FIG.  4   ) are sandwiched between the two grooves  93  and two grooves  413 . The two grooves  93 , the two grooves  413 , and the two steel spheres  49  together form a cam mechanism. While the two steel spheres  49  are rolling, the hammer  9  may move along the axis of the transmission shaft  41  with respect to the transmission shaft  41  and rotate with respect to the transmission shaft  41 . As the hammer  9  moves either forward or backward along the axis of the transmission shaft  41 , the hammer  9  rotates with respect to the transmission shaft  41 . 
     The output block  8  is made of a metallic material. As shown in  FIGS.  1 - 3   , the output block  8  includes the claw block  81  and the body block  82 . The claw block  81  corresponds to a so-called “anvil” of the impact tool  1 . The claw block  81  includes a first coupling portion  811  and two anvil claws  812 . The body block  82  includes the thermally sprayed portion  821 , a second coupling portion  822 , and the tip portion  823 . 
     The first coupling portion  811  has a circular cylindrical shape. That is to say, the first coupling portion  811  has a through hole as its center hole. The first coupling portion  811  is a boss having a through hole, of which the inner surface has a gear-shaped groove portion  8110  to be fitted into a spline shaft. 
     The two anvil claws  812  protrude from the first coupling portion  811  to extend along the radius of the first coupling portion  811 . One of the two anvil claws  812  protrudes toward the opposite end from the other anvil claw  812 . The anvil claws  812  are located in front of, and faces, the hammer body  90 . 
     The thermally sprayed portion  821  of the body block  82  has a circular columnar shape in appearance. The surface of the thermally sprayed portion  821  is covered with the magnetostrictive member  51  (see  FIG.  4   ). Note that in  FIGS.  1 - 3   , illustration of the magnetostrictive member  51  is omitted. The axis of the thermally sprayed portion  821  is aligned with the forward/backward direction. A first end (rear end) of the thermally sprayed portion  821  is connected to the second coupling portion  822 . A second end (front end) of the thermally sprayed portion  821  is connected to the tip portion  823 . 
     The second coupling portion  822  is coupled to the first coupling portion  811 . The second coupling portion  822  is a spline shaft to be fitted into the groove portion  8110  of the first coupling portion  811 . The second coupling portion  822  has a generally circular columnar shape. When taken along a plane intersecting at right angles with the center axis of the second coupling portion  822 , the second coupling portion  822  has a gear shape. 
     The tip portion  823  has a circular columnar shape in appearance. The tip portion  823  has a through hole  8230  to be coupled to the chuck. 
     As shown in  FIG.  3   , the body block  82  is coupled to the claw block  81 , thus making the thermally sprayed portion  821  protruding forward from the claw block  81 . 
     More specifically, the second coupling portion  822  of the body block  82  is passed through the center through hole of the first coupling portion  811  to be fitted into the groove portion  8110 . In this manner, the second coupling portion  822  is coupled to the first coupling portion  811 . That is to say, the body block  82  is coupled to the claw block  81 . 
     The body block  82  and the claw block  81  are preferably coupled to each other by press fitting. This may reduce the backlash between the body block  82  and the claw block  81 , thus cutting down the energy transfer loss between the body block  82  and the claw block  81 . As a result, this makes it easier to express the impact received by the claw block  81  from the hammer  9  as a strain of the magnetostrictive member  51  provided for the body block  82 , thus contributing to increasing the sensitivity of the magnetostrictive sensor  5 . 
     In addition, the first coupling portion  811  and the second coupling portion  822  have a spline shape, thus allowing the claw block  81  and the body block  82  to be firmly coupled to each other. 
     As shown in  FIGS.  4  and  5   , the return spring  43  is disposed behind the hammer  9 . The return spring  43  according to this embodiment is a conical coil spring. The hammer  9  receives forward biasing force from the return spring  43 . The hammer  9  may rotate with respect to the return spring  43 . The impact mechanism  40  further includes a ring  42  interposed between the hammer  9  and the return spring  43 . 
     While the impact mechanism  40  is performing no impact operation, the hammer  9  and the output block  8  rotate along with each other with the two hammer claws  95  of the hammer  9  and the two anvil claws  812  of the output block  8  kept in contact with each other in the rotational direction of the transmission shaft  41 . Thus, at this time, the transmission shaft  41 , the hammer  9 , and the output block  8  rotate along with each other. 
     When a torque condition on the magnitude of the torque applied to the body block  82  of the output block  8  (hereinafter referred to as “load torque”) is satisfied, the impact mechanism  40  starts performing an impact operation. The impact operation is an operation of applying impacting force from the hammer  9  to the output block  8 . In this embodiment, the torque condition is a condition that the load torque become equal to or greater than a predetermined value. That is to say, as the load torque increases, the proportion of a force component having a direction that causes the hammer  9  to retreat increases with respect to the force generated between the hammer  9  and the output block  8 . When the load torque increases to the predetermined value or more, the hammer  9  retreats while compressing the return spring  43 . In addition, as the hammer  9  retreats, the hammer  9  rotates while the two hammer claws  95  of the hammer  9  are going over the two anvil claws  812  of the output block  8 . Thereafter, the hammer  9  advances upon receiving recovery force from the return spring  43 . Then, when the transmission shaft  41  goes approximately half around, the two hammer claws  95  of the hammer  9  collide against the side surface  8120  of the two anvil claws  812  of the output block  8 . In this impact mechanism  40 , every time the transmission shaft  41  goes approximately half around, the two hammer claws  95  of the hammer  9  collide against the two anvil claws  812  of the output block  8 . That is to say, every time the transmission shaft  41  goes approximately half around, the hammer  9  applies impacting force (rotational impacting force) to the output block  8 . 
     As can be seen, in this impact mechanism  40 , collisions between the hammer  9  and the output block  8  occur repeatedly. The torque caused by these collisions allows the screw to be fastened more tightly than in a situation where no collisions occur between the hammer  9  and the output block  8 . 
     As shown in FIG. 4 , the impact tool  1  further includes a bearing  16 . The bearing  16  is housed in the housing  2 . The bearing  16  is in contact with the body block  82  of the output block  8 . More specifically, the bearing  16  is in contact with a part, located forward of the thermally sprayed portion  821 , of the body block  82  (i.e., in contact with the tip portion  823 ). The bearing  16  holds the output block  8  rotatably. 
     As shown in  FIG.  5   , the magnetostrictive sensor  5  includes the magnetostrictive member  51 , the coil portion  52 , and a coil bobbin  53 . 
     The magnetostrictive member  51  is formed on the surface of the thermally sprayed portion  821 . Examples of magnetostrictive materials for the magnetostrictive member  51  include iron-cobalt based alloys, iron-nickel based alloys, and nickel-based ferrite. 
     The coil bobbin  53  is fixed to the housing  2 . The coil bobbin  53  is disposed behind the bearing  16 . The coil portion  52  includes one or more coils wound around the coil bobbin  53 . The coil portion  52  surrounds the magnetostrictive member  51 . 
     When torque is applied to the output block  8 , stain is caused in the thermally sprayed portion  821  of the output block  8 , and strain is also caused in the magnetostrictive member  51  accordingly. The magnetostrictive sensor  5  makes the coil portion  52  detect a variation in the permeability of the magnetostrictive member  51  due the strain caused in the magnetostrictive member  51  upon the application of the torque to the output block  8 , and outputs, as a result of detection, a voltage signal proportional to the strain. 
     The circuit section  6  (see  FIG.  4   ) includes, for example, a board and an electric circuit mounted on the board. The circuit section  6  is electrically connected to the coil portion  52 . The circuit section  6  allows a current to flow through the coil portion  52 . In addition, the circuit section  6  measures the strain of the output block  8 . That is to say, the circuit section  6  acquires a voltage signal, which is proportional to the strain caused in the output block  8  and the magnetostrictive member  51 , from the coil portion  52  and calculates the strain of the output block  8  based on the voltage signal. 
     (2) Manufacturing Method 
     Next, a method for manufacturing the output block  8  will be described with reference to  FIG.  6   . Note that the flowchart shown in  FIG.  6    shows only an exemplary procedure of the manufacturing method according to the present disclosure. Thus, the processing steps shown in  FIG.  6    may be performed in a different order as appropriate, an additional processing step may be performed as needed, or at least one of the processing steps shown in  FIG.  6    may be omitted as appropriate. 
     First, quenching treatment is conducted on the claw block  81  and body block  82  that have been molded (in Step ST 1 ). Next, tempering treatment is conducted on the claw block  81  and the body block  82  (in Step ST 2 ). The quenching temperature in the quenching treatment is higher than the tempering temperature in the tempering treatment. 
     Next, a magnetostrictive material is thermally sprayed onto the thermally sprayed portion  821  of the body block  82  (in Step ST 3 ). Specifically, a film of the magnetostrictive material is formed on the surface of the thermally sprayed portion  821  by spraying and solidifying a heated magnetostrictive material onto the thermally sprayed portion  821 . This film is the magnetostrictive member  51  (see  FIG.  5   ). The surface temperature of the body block  82  while the magnetostrictive material is being thermally sprayed thereto is lower than the quenching temperature. Also, the surface temperature of the body block  82  while the magnetostrictive material is being thermally sprayed thereto is higher than the tempering temperature. 
     Next, the claw block  81  and the body block  82  are coupled to each other (in Step ST 4 ). More specifically, the second coupling portion  822  of the body block  82  is inserted into the first coupling portion  811  of the claw block  81  by press fitting. 
     The output block  8  is manufactured by performing these process steps. 
     In the process step of thermally spraying the magnetostrictive material, the member as a target onto which the magnetostrictive material is sprayed comes to have so high a temperature that annealing could occur to cause a decline in the mechanical strength of that member. Thus, in this embodiment, the claw block  81  and the body block  82  are provided as two separate members and the process step of thermally spraying the magnetostrictive material includes spraying the magnetostrictive material onto only the body block  82 . This enables avoiding causing a decline in the mechanical strength of the claw block  81 . In particular, the claw block  81  includes (two) anvil claws  812  to collide against the hammer  9 , and therefore, is required to have higher mechanical strength than the body block  82 . This embodiment enables ensuring sufficient mechanical strength for the claw block  81  and thereby increasing the reliability of the impact tool  1 . 
     In addition, this also enables reducing, in a situation where the surface of the output block  8  has been subjected to carburizing treatment, the chances of the carburized layer on the surface of the claw block  81  changing its properties due to the heat in the process step of thermally spraying the magnetostrictive material. 
     Also, if the body block  82  were subjected to the quenching treatment after the magnetostrictive material has been thermally sprayed thereto, then the quenching treatment could alter the properties of the magnetostrictive member  51  and impair the magnetostrictive sensor&#39;s  5  capability of detecting the strain of the output block  8 . In contrast, this embodiment allows the magnetostrictive sensor  5  to maintain its capability by thermally spraying the magnetostrictive material onto the body block  82  after the quenching treatment. 
     As can be seen, a method for manufacturing an output block  8  according to this embodiment is designed to manufacture an output block  8  for use in an impact tool  1  to hold a tip tool thereon. This manufacturing method includes a first step (step ST 1 ) including subjecting a claw block  81 , including anvil claws  812 , to quenching treatment. This manufacturing method further includes a second step (step ST 3 ) including thermally spraying a magnetostrictive material onto a surface of a thermally sprayed portion  821  that forms a predetermined part of the body block  82  and thereby forming a magnetostrictive member  51  on the surface. This manufacturing method further includes a third step (step ST 4 ) including coupling the body block  82  and the claw block  81  to each other. The third step is performed after the first step and the second step have been performed. More specifically, it is not until not only the quenching treatment in the first step but also the tempering treatment are finished that the third step is performed. 
     Variations of First Embodiment 
     Next, variations of the first embodiment will be enumerated one after another. The variations to be described below may be adopted in combination as appropriate. 
     The output block  8  may have another structure to be coupled to either the chuck or the tip tool instead of, or in addition to, the through hole  8230 . 
     In the first embodiment described above, the claw block  81  and the body block  82  are coupled to each other with the body block  82  inserted inside the claw block  81 . However, this is only an example and should not be construed as limiting. Alternatively, the claw block  81  and the body block  82  may be coupled to each other with the claw block  81  inserted inside the body block  82 . Still alternatively, the claw block  81  and the body block  82  may also be coupled to each other in some way other than insertion. For example, the claw block  81  and the body block  82  may also be coupled to each other by having a projection, extending from one member selected from the group consisting of the claw block  81  and the body block  82 , held by the other member selected from the claw block  81  and the body block  82 . 
     The first coupling portion  811  and the second coupling portion  822  do not have to have a spline shape. For example, the first coupling portion  811  and the second coupling portion  822  may be coupled to each other by inserting the second coupling portion  822  having a circular columnar shape in appearance into the first coupling portion  811  having a circular cylindrical shape. 
     The number of the anvil claws  812  provided does not have to be two but may also be one or three or more. Likewise, the number of the hammer claws  95  provided does not have to be two but may also be one or three or more. 
     The process step of conducting quenching treatment on the body block  82  is not an essential process step for the method for manufacturing the output block  8 . 
     Second Embodiment 
     Next, an output block  8 A of an impact tool according to a second embodiment will be described with reference to  FIGS.  7  and  8   . In the following description, any constituent element of this second embodiment, having the same function as a counterpart of the first embodiment described above, will be designated by the same reference numeral as that counterpart&#39;s, and description thereof will be omitted herein. 
     (1) Structure 
     As shown in  FIG.  7   , an output block  8 A according to this embodiment further includes a tip block  83 . The tip block  83  holds a tip tool thereon. The tip block  83  is to be coupled to a body block  82 A. The tip block  83  has been subjected to quenching treatment. 
     That is to say, the output block  8 A includes the claw block  81 , the body block  82 A, and the tip block  83 . The claw block  81  has the same configuration as its counterpart of the first embodiment described above. 
     The body block  82 A includes the thermally sprayed portion  821 , the second coupling portion  822 , and a third coupling portion  824 . The tip block  83  includes a tip portion  831  and a fourth coupling portion  832 . 
     The axis of the thermally sprayed portion  821  is aligned with the forward/backward direction. A first end (rear end) of the thermally sprayed portion  821  is connected to the second coupling portion  822 . A second end (front end) of the thermally sprayed portion  821  is connected to the third coupling portion  824 . 
     The third coupling portion  824  is coupled to the fourth coupling portion  832 . The third coupling portion  824  is a spline shaft to be fitted into a groove portion  8320  of the fourth coupling portion  832 . The third coupling portion  824  has a generally circular columnar shape. When taken along a plane intersecting at right angles with the center axis of the third coupling portion  824 , the third coupling portion  824  has a gear shape. 
     The tip block  83  has a circular columnar shape in appearance. The tip portion  831  of the tip block  83  has a configuration corresponding to that of the tip portion  823  according to the first embodiment. The tip portion  831  has a circular columnar shape in appearance. The tip portion  831  is to be coupled to a tip tool via a chuck. The tip portion  831  has a through hole  8310  to be coupled to the chuck. 
     The fourth coupling portion  832  has a circular cylindrical shape. That is to say, the fourth coupling portion  832  has an opening as its center hole. The fourth coupling portion  832  is a boss having an opening, of which the inner surface has a gear-shaped groove portion  8320  to be fitted into a spline shaft (third coupling portion  824 ). The tip portion  831  and the fourth coupling portion  832  are connected to each other in the forward/backward direction. 
     The body block  82 A is coupled to the tip block  83 . More specifically, the third coupling portion  824  of the body block  82 A is inserted into the opening as the center hole of the fourth coupling portion  832  and fitted into the groove portion  8320 . In this manner, the third coupling portion  824  is coupled to the fourth coupling portion  832 . That is to say, the body block  82 A is coupled to the tip block  83 . As a result, the tip portion  831  protrudes forward from the body block  82 A. 
     The body block  82 A and the tip block  83  are preferably coupled to each other by press fitting. This may reduce the backlash between the body block  82 A and the tip block  83 . 
     In addition, the body block  82 A is also coupled to the claw block  81  in the same way as in the first embodiment described above. 
     (2) Manufacturing Method 
     Next, a method for manufacturing the output block  8 A will be described with reference to  FIG.  8   . Note that the flowchart shown in  FIG.  8    shows only an exemplary procedure of the manufacturing method according to the present disclosure. Thus, the processing steps shown in  FIG.  8    may be performed in a different order as appropriate, an additional processing step may be performed as needed, or at least one of the processing steps shown in  FIG.  8    may be omitted as appropriate. 
     First, quenching treatment is conducted on the claw block  81 , body block  82 A, and tip block  83  that have been molded (in Step ST 1 ). Next, tempering treatment is conducted on the claw block  81 , the body block  82 , and the tip block  83  (in Step ST 2 ). The quenching temperature in the quenching treatment is higher than the tempering temperature in the tempering treatment. 
     Next, a magnetostrictive material is thermally sprayed onto the thermally sprayed portion  821  of the body block  82 A (in Step ST 3 ). The surface temperature of the body block  82 A while the magnetostrictive material is being thermally sprayed thereto is lower than the quenching temperature. Also, the surface temperature of the body block  82 A while the magnetostrictive material is being thermally sprayed thereto is higher than the tempering temperature. 
     Next, the claw block  81  and the body block  82 A are coupled to each other and the tip block  83  and the body block  82 A are also coupled to each other (in Step ST 4 ). More specifically, the second coupling portion  822  of the body block  82 A is inserted into the first coupling portion  811  of the claw block  81  by press fitting. In addition, the third coupling portion  824  of the body block  82 A is inserted into the fourth coupling portion  832  of the tip block  83  by press fitting. 
     The output block  8 A is manufactured by performing these process steps. 
     In this embodiment, the body block  82 A and the tip block  83  are provided as two separate members and the process step of thermally spraying the magnetostrictive material includes spraying the magnetostrictive material onto only the body block  82 A. This enables avoiding causing a decline in the mechanical strength of the tip block  83 . In particular, the tip block  83  is configured to hold the tip tool thereon and receive force applied directly from the tip tool, and therefore, is required to have higher mechanical strength than the body block  82 A. This embodiment enables ensuring sufficient mechanical strength for the tip block  83  and thereby increasing the reliability of the impact tool  1 . 
     As can be seen, a method for manufacturing an output block  8 A according to this embodiment further includes, in addition to the first, second, and third process steps of the method for manufacturing an output block  8  according to the first embodiment, a fourth step including subjecting the tip block  83  to quenching treatment and a fifth step including coupling the body block  82 A to the tip block  83 . The fifth step is performed after the second step and the fourth step have been performed. More specifically, it is not until not only the quenching treatment in the fourth step but also the tempering treatment are finished that the fifth step is performed. The tip block  83  holds a tip tool thereon. The tip block  83  is to be coupled to the body block  82 A. 
     Variations of Second Embodiment 
     Next, variations of the second embodiment will be enumerated one after another. The variations to be described below may be adopted in combination as appropriate. In addition, the variations of the first embodiment described above are also applicable to the second embodiment as appropriate. 
     In the second embodiment described above, the body block  82 A and the tip block  83  are coupled to each other with the body block  82 A inserted inside the tip block  83 . However, this is only an example and should not be construed as limiting. Alternatively, the body block  82 A and the tip block  83  may be coupled to each other with the tip block  83  inserted inside the body block  82 A. Still alternatively, the body block  82 A and the tip block  83  may also be coupled to each other in some way other than insertion. For example, the body block  82 A and the tip block  83  may also be coupled to each other by having a projection, extending from one member selected from the group consisting of the body block  82 A and the tip block  83 , held by the other member selected from the body block  82 A and the tip block  83 . 
     The third coupling portion  824  and the fourth coupling portion  832  do not have to have a spline shape. For example, the third coupling portion  824  and the fourth coupling portion  832  may be coupled to each other by inserting the fourth coupling portion  832  having a circular columnar shape in appearance into the third coupling portion  824  having a circular cylindrical shape. 
     Recapitulation 
     The embodiments and their variations described above may be specific implementations of the following aspects of the present disclosure. 
     An impact tool ( 1 ) according to a first aspect includes a motor ( 3 ), an output block ( 8 ,  8 A), a hammer ( 9 ), and a magnetostrictive sensor ( 5 ). The output block ( 8 ,  8 A) holds a tip tool thereon. The hammer ( 9 ) receives motive power from the motor ( 3 ) and collides against the output block ( 8 ,  8 A). The magnetostrictive sensor ( 5 ) includes a magnetostrictive member ( 51 ) and a coil portion ( 52 ) covering the magnetostrictive member ( 51 ). The hammer ( 9 ) includes a hammer body ( 90 ) and a hammer claw ( 95 ) connected to the hammer body ( 90 ). The output block ( 8 ,  8 A) includes a claw block ( 81 ) and a body block ( 82 ,  82 A). The claw block ( 81 ) includes an anvil claw ( 812 ), against which the hammer claw ( 95 ) collides. The claw block ( 81 ) has been subjected to quenching treatment. The body block ( 82 ,  82 A) includes a thermally sprayed portion ( 821 ) and is coupled to the claw block ( 81 ). The thermally sprayed portion ( 821 ) includes, on a surface thereof, the magnetostrictive member ( 51 ) made of a magnetostrictive material. 
     This configuration enables forming a magnetostrictive member ( 51 ) on the thermally sprayed portion ( 821 ) of the body block ( 82 ,  82 A) and increasing the impact resistance of the claw block ( 81 ) by quenching treatment at the same time. That is to say, this enables providing an impact tool ( 1 ) including a magnetostrictive sensor ( 5 ) and an output block ( 8 ,  8 A), of which the mechanical strength is increased sufficiently for the output block ( 8 ,  8 A) to withstand the impact caused by an impact operation. 
     In an impact tool ( 1 ) according to a second aspect, which may be implemented in conjunction with the first aspect, the output block ( 8 A) further includes a tip block ( 83 ). The tip block ( 83 ) holds the tip tool thereon. The tip block ( 83 ) is coupled to the body block ( 82 A). The tip block ( 83 ) has been subjected to the quenching treatment. 
     This configuration enables increasing the mechanical strength of not only the claw block ( 81 ) but also the tip block ( 83 ) as well. 
     In an impact tool ( 1 ) according to a third aspect, which may be implemented in conjunction with the second aspect, the body block ( 82 A) and the tip block ( 83 ) are coupled to each other by press fitting. 
     This configuration may reduce the backlash between the body block ( 82 A) and the tip block ( 83 ), thus cutting down the energy transfer loss between the body block ( 82 A) and the tip block ( 83 ). 
     In an impact tool ( 1 ) according to a fourth aspect, which may be implemented in conjunction with any one of the first to third aspects, the body block ( 82 ,  82 A) and the claw block ( 81 ) are coupled to each other by press fitting. 
     This configuration may reduce the backlash between the body block ( 82 ,  82 A) and the claw block ( 81 ), thus cutting down the energy transfer loss between the body block ( 82 ,  82 A) and the claw block ( 81 ). In addition, this also makes it easier to express the impact received by the claw block ( 81 ) as a strain of the magnetostrictive member ( 51 ), thus contributing to increasing the sensitivity of the magnetostrictive sensor ( 5 ). 
     Note that the constituent elements according to the second to fourth aspects are not essential constituent elements for the impact tool ( 1 ) but may be omitted as appropriate. 
     A method for manufacturing an output block ( 8 ,  8 A) according to a fifth aspect is designed to manufacture an output block ( 8 ,  8 A) for use in an impact tool ( 1 ) to hold a tip tool thereon. The output block ( 8 ,  8 A) includes: a claw block ( 81 ) including an anvil claw ( 812 ); and a body block ( 82 ,  82 A). The method includes a first step, a second step, and a third step. The first step includes subjecting the claw block ( 81 ), to quenching treatment. The second step includes thermally spraying a magnetostrictive material onto a surface of a thermally sprayed portion ( 821 ) that forms a predetermined part of the body block ( 82 ,  82 A) and thereby forming a magnetostrictive member ( 51 ) on the surface. The third step includes coupling the body block ( 82 ,  82 A) and the claw block ( 81 ) to each other after the first step and the second step have been performed. 
     This method enables providing an impact tool ( 1 ) including a magnetostrictive sensor ( 5 ) and an output block ( 8 ,  8 A), of which the mechanical strength is increased sufficiently for the output block ( 8 ,  8 A) to withstand the impact caused by an impact operation. 
     In a method for manufacturing an output block ( 8 A) according to a sixth aspect, which may be implemented in conjunction with the fifth aspect, the output block ( 8 A) further includes a tip block ( 83 ). The tip block ( 83 ) holds the tip tool thereon and is to be coupled to a body block ( 82 A). The method further includes: a fourth step including subjecting the tip block ( 83 ) to the quenching treatment; and a fifth step including coupling the body block ( 82 A) to the tip block ( 83 ) after the second step and the fourth step have been performed. 
     This method enables increasing the mechanical strength of not only the claw block ( 81 ) but also the tip block ( 83 ) as well. 
     While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all modifications and variations that fall within the true scope of the present teachings.