Rebar tying machine

The disclosure herein discloses a rebar tying machine. The rebar tying machine may include a feed motor, a current sensor configured to detect a current flowing through the feed motor, and a control unit configured to control an operation of the feed motor. The rebar tying machine may be configured to perform: a feeding-out process in which a wire is fed out around rebars by driving the feed motor, a gripping process in which a vicinity of a tip of the wire is gripped, a pulling-back process in which the wire is pulled back by driving the feed motor, a cutting process in which the wire is cut, and a twisting process in which the wire is twisted. The control unit may be configured to determine a diameter of the rebars based on a history of a current value flowing through the feed motor in the pulling-back process.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2021-029232, filed on Feb. 25, 2021, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The technique disclosed herein relates to rebar tying machines.

BACKGROUND

Japanese Patent Application Publication No. 2001-140471 describes a rebar tying machine. The rebar tying machine incudes a feed motor, a current sensor configured to detect a current flowing through the feed motor, a control unit configured to control an operation of the feed motor, and a determination mechanism configured to determine the diameter of rebars. The rebar tying machine is configured to perform a feeding-out process in which a wire is fed out around the rebars by driving the feed motor, a cutting process in which the wire is cut, and a twisting process in which the wire is twisted. The rebar tying machine operates depending on the diameter of the rebars determined by the determination mechanism.

SUMMARY

The rebar tying machine above requires the determination mechanism for determining the diameter of the rebars and thus has a complex mechanical configuration. The disclosure herein provides techniques that enable a rebar tying machine to operate depending on a diameter of rebars without a determination mechanism for determining the diameter of the rebars.

The disclosure herein discloses a rebar tying machine. The rebar tying machine may comprise a feed motor, a current sensor configured to detect a current flowing through the feed motor, and a control unit configured to control an operation of the feed motor. The rebar tying machine may be configured to perform a feeding-out process in which a wire is fed out around rebars by driving the feed motor, a gripping process in which a vicinity of a tip of the wire is gripped, a pulling-back process in which the wire is pulled back by driving the feed motor, a cutting process in which the wire is cut, and a twisting process in which the wire is twisted. The control unit may be configured to determine a diameter of the rebars based on a history of a current value flowing through the feed motor in the pulling-back process.

The disclosure herein also discloses another rebar tying machine. The rebar tying machine may comprise a feed motor, a current sensor configured to detect a current flowing through the feed motor, and a control unit configured to control an operation of the feed motor. The rebar tying machine may be configured to perform a feeding-out process in which a wire is fed out around rebars by driving the feed motor, a gripping process in which a vicinity of a tip of the wire is gripped, a pulling-back process in which the wire is pulled back by driving the feed motor, a cutting process in which the wire is cut, and a twisting process in which the wire is twisted. The control unit may be configured to, in the pulling-back process, stop the feed motor when a stop condition is satisfied. The control unit may be configured to change the stop condition according to a history of a current value flowing through the feed motor in the pulling-back process.

DETAILED DESCRIPTION

In one or more embodiments, a rebar tying machine may comprise a feed motor, a current sensor configured to detect a current flowing through the feed motor, and a control unit configured to control an operation of the feed motor. The rebar tying machine may be configured to perform a feeding-out process in which a wire is fed out around rebars by driving the feed motor, a gripping process in which a vicinity of a tip of the wire is gripped, a pulling-back process in which the wire is pulled back by driving the feed motor, a cutting process in which the wire is cut, and a twisting process in which the wire is twisted. The control unit may be configured to determine a diameter of the rebars based on a history of a current value flowing through the feed motor in the pulling-back process.

In the pulling-back process, the diameter of a loop formed by the wire fed around the rebars is reduced and the wire is appressed to the rebars. During this time, the behavior of the current value flowing through the feed motor changes at a timing when the wire starts to be appressed to the rebars and a timing when the wire is completely appressed to the rebars. As the diameter of the rebars is larger, the timing when the wire starts to be appressed to the rebars and the timing when the wire is completely appressed to the rebars come earlier. To the contrary, as the diameter of the rebars is smaller, the timing when the wire starts to be appressed to the rebars and the timing when the wire is completely appressed to the rebars come later. In the rebar tying machine above, the diameter of the rebars is determined based on the history of the current value flowing through the feed motor, taking advantage of the fact that the current value flowing through the feed motor in the pulling-back process exhibits different behaviors depending on the diameter of the rebars. Thus, the rebar tying machine can operate in accordance with the diameter of the rebars without a determination mechanism for determining the diameter of the rebars.

In one or more embodiments, the control unit may be configured to, in the pulling-back process, calculate a time rate of change of the current value flowing through the feed motor after an inrush current of the feed motor has peaked, and determine the diameter of the rebars based on a timing at which the time rate of change reaches a time rate of change threshold value.

In the pulling-back process, the current value flowing through the feed motor gradually decreases after the inrush current has peaked. Then, the current value flowing through the feed motor stops decreasing and starts to increase at the timing when the wire starts to be appressed to the rebars, and then stops to increase and starts decreasing again at the timing when the wire is completely appressed to the rebars. According to the configuration above, the diameter of the rebars can be determined at the timing when the current value flowing through the feed motor stops decreasing and starts to increase after the inrush current has peaked, namely at the timing when the wire starts to be appressed to the rebars. Thus, the rebar tying machine can perform the latter half of the pulling-back process in accordance with the determined diameter of the rebars.

In one or more embodiments, the control unit may be configured to, in the pulling-back process, stop the feed motor when a stop condition is satisfied. The control unit may be configured to change the stop condition according to the determined diameter of the rebars.

As the diameter of the rebar is larger, the timing when the wire starts to be appressed to the rebars comes earlier, and thus the feed motor needs to be stopped earlier accordingly. To the contrary, as the diameter of the rebars is smaller, the timing when the wire is completely appressed to the rebars comes later, and thus the feed motor needs to be stopped later accordingly. According to the configuration above, the feed motor can be stopped at an appropriate timing since the stop condition is changed according to the determined diameter of the rebars.

In one or more embodiments, the control unit may be configured to, in the pulling-back process, determine a minimum value of the current value flowing through the feed motor after the inrush current of the feed motor has peaked, and calculate an increase in the current value flowing through the feed motor from the minimum value. The stop condition may include that the increase reaches an increase threshold value. The control unit may be configured to change the increase threshold value according to the determined diameter of the rebars.

In the pulling-back process, as the diameter of the rebars is larger, the timing when the wire starts to be appressed to the rebar comes earlier, and thus the current value flowing through the feed motor does not decrease much after the inrush current has peaked. Therefore, the minimum value of the current value flowing through the feed motor after the inrush current has peaked is relatively large and an increase in the current value therefrom until the wire is completely appressed to the rebars is small. To the contrary, as the diameter of the rebars is smaller, the timing when the wire starts to be appressed to the rebars comes later, and thus the current value flowing through the feed motor significantly decreases after the inrush current has peaked. Therefore, the minimum value of the current value flowing through the feed motor after the inrush current has peaked is relatively small and an increase in the current value therefrom until the wire is completely appressed to the rebars is large. According to the configuration above, the increase threshold value is changed according to the determined diameter of the rebars, and thus the feed moto can be stopped at an appropriate timing.

In one or more embodiments, a rebar tying machine may comprise a feed motor, a current sensor configured to detect a current flowing through the feed motor, and a control unit configured to control an operation of the feed motor. The rebar tying machine may be configured to perform a feeding-out process in which a wire is fed out around rebars by driving the feed motor, a gripping process in which a vicinity of a tip of the wire is gripped, a pulling-back process in which the wire is pulled back by driving the feed motor, a cutting process in which the wire is cut, and a twisting process in which the wire is twisted. The control unit may be configured to, in the pulling-back process, stop the feed motor when a stop condition is satisfied. The control unit may be configured to change the stop condition according to a history of a current value flowing through the feed motor in the pulling-back process.

In the rebar tying machine above, the stop condition for the feed motor is changed based on the history of the current value flowing through the feed motor, taking advantage of the fact that the current value flowing through the feed motor in the pulling-back process exhibits different behaviors depending on the diameter of the rebars. Thus, the rebar tying machine can operate in accordance with the diameter of the rebars without a determination mechanism for determining the diameter of the rebars.

In one or more embodiments, the control unit may be configured to, in the pulling-back process, calculate a time rate of change of the current value flowing through the feed motor after an inrush current of the feed motor has peaked, and change the stop condition according to a timing at which the time rate of change reaches a time rate of change threshold value.

According to the configuration above, the stop condition for the feed motor can be changed at the timing when the current value flowing through the feed motor stops decreasing and starts to increase after the inrush current has peaked, namely at the timing when the wire starts to be appressed to the rebars.

In one or more embodiments, the control unit may be configured to, in the pulling-back process, determine a minimum value of the current value flowing through the feed motor after the inrush current of the feed motor has peaked, and calculate an increase in the current value flowing through the feed motor from the minimum value. The stop condition may include that the increase reaches an increase threshold value. The control unit may be configured to change the increase threshold value according to the timing at which the time rate of change reaches the time rate of change threshold value.

According to the configuration above, the increase threshold value is changed according to the timing when the time rate of change of the current value flowing through the feed motor reaches the time rate of change threshold value, and thus the feed motor can be stopped at an appropriate timing.

Embodiments

As illustrated inFIG.1, a rebar tying machine2is configured to tie a plurality of rebars R with a wire W. For example, the rebar tying machine2can tie small-diameter rebars R having a diameter of less than 15 mm (e.g., a diameter of 10 mm or 13 mm), medium-diameter rebars R having a diameter of 15 mm or more and 25 mm or less (e.g., a diameter of 16 mm or 22 mm), and large-diameter rebars R having a diameter of 25 mm or more (e.g., a diameter of 25 mm or 32 mm) with the wire W. The diameter of the wire W is, for example, in a range from 0.5 mm to 2.0 mm.

The rebar tying machine2comprises a body4, a grip6, a battery mount10, a battery B. and a reel holder12. The grip6is a member configured to be gripped by a user. The grip6is positioned at a lower rear portion of the body4. The grip6is integral with the body4. A trigger8is attached to an upper front portion of the grip6. The grip6houses a trigger switch9(seeFIG.2) configured to detect whether the trigger8is pushed in or not. The battery mount10is positioned at a lower portion of the grip6. The battery mount10is integral with the grip6. The battery B is detachably attached to the battery mount10. The battery B is, for example, a lithium-ion battery. The reel holder12is disposed below the body4. The reel holder12is disposed forward of the grip6. In the present embodiment, a longitudinal direction of a twisting mechanism30, which will be described later, is termed a front-rear direction, a direction orthogonal to the front-rear direction is termed an up-down direction, and a direction orthogonal to the front-rear direction and the up-down direction is termed a right-left direction.

The reel holder12comprises a holder housing14and a cover member16. The holder housing14is attached to a lower front portion of the body4and a front portion of the battery mount10. The cover member16is attached to the holder housing14such that it is pivotable about a pivot shaft14aat a lower portion of the holder housing14. The holder housing14and the cover member16define a housing space12a(seeFIG.2). A reel18on which the wire W is wound is disposed in the housing space12a. That is, the reel holder12houses the reel18therein.

A display unit12band a manipulatable unit12care disposed on a rear surface of the reel holder12. The manipulatable unit12creceives, from the user, manipulations regarding various settings such as tying force of the rebar tying machine2. The display unit12bis configured to display information about the present setting of the rebar tying machine2.

As illustrated inFIG.2, the rebar tying machine2comprises a control board20and a display board22. The control board20is housed in the battery mount10. The control board20controls the operation of the rebar tying machine2. The display board22is housed in the reel holder12. The display board22is connected to the control board20via wiring, which is not illustrated. The display board22comprises a setting display LED22a(seeFIG.20) configured to emit light toward the display unit12band a setting switch22b(seeFIG.20) configured to detect manipulations of the user on the manipulatable unit12c.

The rebar tying machine2comprises a feed mechanism24, a guide mechanism26, a cutting mechanism28, and the twisting mechanism30. The feed mechanism24is housed in the lower front portion of the body4. The feed mechanism24performs a feeding-out operation by which the wire W is fed out to the guide mechanism26and a pulling-back operation by which the wire W is pulled back from the guide mechanism26. The guide mechanism26is disposed at a front portion of the body4. The guide mechanism26guides the wire W, which has been fed out from the feed mechanism24, around the rebars R in a loop shape. The cutting mechanism28is housed in a lower portion of the body4. The cutting mechanism28performs a cutting operation by which the wire W wound around the rebars R is cut. The twisting mechanism30is housed in the body4. The twisting mechanism30performs a twisting operation by which the wire W around the rebars R is twisted.

(Configuration of Feed Mechanism24)

As illustrated inFIG.3, the feed mechanism24comprises a feed motor32, a reducer34, and a feeder36. The feed motor32is connected to the control board20via wiring, which is not illustrated. The feed motor32is driven by electric power supplied from the battery13. The feed motor32is controlled by the control board20. The feed motor32is connected to a drive gear42of the feeder36via the reducer34. The reducer34reduces the rotation of the feed motor32, for example, by a planetary gear mechanism and transmits it to the drive gear42.

In the present embodiment, the feed motor32is a brushless motor. As illustrated inFIG.18, the feed motor32comprises a stator174including teeth172on which coils170are wound, a rotor176disposed inside the stator174, and a sensor board178fixed to the stator174. The stator174is constituted of a magnetic body. The rotor176comprises a permanent magnet in which magnetic poles are circumferentially arranged. As illustrated inFIG.19, the sensor board178comprises a Hall sensor180. The Hall sensor180includes a first Hall element180a, a second Hall element180b, and a third Hall element180c. The first Hall element180a, the second Hall element180b, and the third Hall element180cdetect magnetic forces from the rotor176. The Hall sensor180is positioned on the sensor board178such that an electrical angle is advanced by 25 degrees for the forward rotation of the feed motor32and the electrical angle is delayed by 25 degrees for the reverse rotation of the feed motor32. In the present embodiment, for the reverse rotation of the feed motor32, the control board20outputs a pattern offset by an electrical angle of 60 degrees. Thus, for the forward rotation of the feed motor32, control is performed such that the electrical angle is advanced by 25 degrees, while for the reverse rotation of the feed motor32, control is performed such that the electrical angle is advanced by 35 degrees (=60 degrees−25 degrees).

As illustrated inFIG.3, the feeder36comprises a base member38, a guide member40, the drive gear42, a first gear44, a second gear46, a gear supporting member48, and a biasing member52. The guide member40is fixed to the base member38. The guide member40includes a guide hole40a. The guide hole40ahas a tapered shape that is broad at its lower end and narrower at its upper end. The wire W is inserted through the guide hole40a.

The drive gear42is coupled to the reducer34. The first gear44is rotatably supported by the base member38. The first gear44meshes with the drive gear42. The first gear44is rotated by the rotation of the drive gear42. The first gear44includes a groove44a. The groove44ais formed in an outer circumferential surface of the first gear44and extends along a rotation direction of the first gear44. The second gear46meshes with the first gear44. The second gear46is rotatably supported by the gear supporting member48. The second gear46includes a groove46a. The groove46ais formed in an outer circumferential surface of the second gear46and extends in a rotation direction of the second gear46. The gear supporting member48is swingably supported by the base member38via a swing shaft48a. The biasing member52biases the gear supporting member48such that the second gear46is brought closer to the first gear44. Thus, the second gear46is pressed against the first gear44. As a result, the wire W is held between the groove44aof the first gear44and the groove46aof the second gear46. When the gear supporting member48is pushed against the biasing force of the biasing member52, the second gear46separates from the first gear44. This facilitates the insertion of the wire W between the groove44aof the first gear44and the groove46aof the second gear46when the reel18is replaced.

The wire W is moved by the feed motor32rotating with the wire W held between the groove44aof the first gear44and the groove46aof the second gear46. In the present embodiment, when the feed motor32rotates in reverse, the drive gear42rotates in a direction D1illustrated inFIG.3, and thus the wire W is fed out toward the guide mechanism26. When the feed motor32rotates forward, the drive gear42rotates in a direction D2illustrated inFIG.3, and thus the wire W is pulled back from the guide mechanism26.

(Configuration of Guide Mechanism26)

As illustrated inFIG.4, the guide mechanism26comprises a wire guide56, an upper guide arm58, and a lower guide arm60. The wire W fed out from the feed mechanism24passes through the inside of the wire guide56. A protrusion56ais arranged on the inside of the wire guide56.

The upper guide arm58is disposed at an upper front portion of the body4. The upper guide arm58includes an upper guide path58a. The wire W that has passed through the inside of the wire guide56passes the upper guide path58a. A first guide pin61and a second guide pin62are disposed at the upper guide path58a. Once the wire W passes through the upper guide path58awhile contacting the protrusion56aof the wire guide56, the first guide pin61, and the second guide pin62, the wire W is downwardly curled.

The lower guide arm60is disposed at a lower front portion of the body4. The lower guide arm60includes a lower guide path60a. The wire W that has passed through the upper guide path58apasses the lower guide path60a. InFIG.4, portions of the wire W that are hidden by the lower guide arm60and the twisting mechanism30are indicated by broken lines.

As illustrated inFIG.5, the cutting mechanism28comprises a cutting member66and a link68. The cutting member66is a member configured to cut the wire W. As illustrated inFIG.4, the cutting member66is disposed on a route that the wire W follows from the feed mechanism24to the guide mechanism26. The wire W passes through the inside of the cutting member66. The cutting member66is supported such that it is rotatable about a rotation shaft66a(seeFIG.5) with respect to the body4. When the cutting member66is rotated in a direction D3illustrated inFIG.4, the wire W is cut by the cutting member66.

As illustrated inFIG.5, the link68comprises a link member70, an operable member72, and a biasing member74. The link member70links the cutting member66and the operable member72. The operable member72is supported such that it is rotatable about a rotation shaft72awith respect to the body4. The operable member72is normally biased by the biasing member74to be at an initial position. When a force that is larger than the biasing force of the biasing member74is applied to the operable member72, the operable member72is thereby rotated about the rotation shaft72a. As a result, the link member70is moved forward and the cutting member66is rotated about the rotation shaft66a. When the operable member72is rotated about the rotation shaft72afrom the initial position to a predetermined position illustrated inFIG.6, the wire W is cut by the rotation of the cutting member66. Hereinafter, the predetermined position of the operable member72is termed a cutting position.

As illustrated inFIG.7, the twisting mechanism30comprises a twisting motor76, a reducer78, and a holder82. The twisting motor76is connected to the control board20via wiring, which is not illustrated. The twisting motor76is driven by electric power supplied from the battery B. The twisting motor76is controlled by the control board20. The twisting motor76is connected to a screw shaft84of the holder82via the reducer78. The reducer78reduces the rotation of the twisting motor76, for example, by a planetary gear mechanism, and transmits it to the screw shaft84.

In the present embodiment, the twisting motor76is a brushless motor. In the present embodiment, the twisting motor76comprises the same configuration as the configuration of the feed motor32. As illustrated inFIG.18, the twisting motor76comprises a stator186including teeth184on which coils182are wound, a rotor188disposed inside the stator186, and a sensor board190fixed to the stator186. The stator186is constituted of a magnetic body. The rotor188comprises a permanent magnet in which magnetic poles are circumferentially arranged. As illustrated inFIG.19, the sensor board190comprises a Hall sensor192. The Hall sensor192includes a first Hall element192a, a second Hall element192b, and a third Hall element192c. The first Hall element192a, the second Hall element192b, and the third Hall element192cdetect magnetic forces from the rotor188. The Hall sensor192is disposed on the sensor board190such that an electrical angle is advanced by 25 degrees for the forward rotation of the twisting motor76and the electrical angle is delayed by 25 degrees for the reverse rotation of the twisting motor76. In the present embodiment, for the reverse rotation of the twisting motor76, the control board20outputs a pattern offset by an electrical angle of 60 degrees. Thus, for the forward rotation of the twisting motor76, control is performed such that the electrical angle is advanced, by 25 degrees, while for the reverse rotation of the twisting motor76, control is performed such that the electrical angle is advanced by 35 degrees (=60 degrees−25 degrees).

In the present embodiment, the twisting motor76and the feed motor32comprises the same configuration. Thus, the common components are used for the stator174and the stator186, the common components are used for the rotor176and the rotor188, and the common components are used for the sensor board178and the sensor board190.

As illustrated inFIG.7, the holder82comprises the screw shaft84, a clamp guide86(seeFIGS.8,9), a biasing member92(seeFIGS.8,9), a sleeve88, and a holder member90.

The screw shaft84is connected to the reducer78. When the twisting motor76rotates forward, the screw shaft84rotates counterclockwise as viewed from the back of the screw shaft84. When the twisting motor76rotates in reverse, the screw shaft84rotates clockwise as viewed from the back of the screw shaft84.

As illustrated inFIG.8, the screw shaft84comprises a large diameter portion84aand a small diameter portion84b. The large diameter portion84ais positioned at a rear portion of the screw shaft84, and the small diameter portion84bis positioned at a front portion of the screw shaft84. A helical ball groove84cis formed in an outer circumference surface of the large diameter portion84a. Balls94fit in the ball groove84c. An annular washer96is disposed at a step between the large diameter portion84aand the small diameter portion84b. An engagement groove84dis formed in a front portion of the small diameter portion84b.

As illustrated inFIG.9, the front portion of the small diameter portion84bis inserted in a recess86aof the clamp guide86. An engagement pin86bof the clamp guide86is inserted in the engagement groove84dof the small diameter portion84bof the screw shaft84and is engageable with a front surface and a rear surface of the engagement groove84d. A step86cis arranged on an outer circumferential surface of the clamp guide86. A portion of the outer circumferential surface of the clamp guide86that is rearward of the step86chas a larger diameter than a portion of the outer circumferential surface of the clamp guide86that is forward of the step86c.

The small diameter portion84bis inserted through the biasing member92. The biasing member92is disposed between the washer96and the clamp guide86. The biasing member92biases the clamp guide86in a direction that brings it away from the washer96.

The screw shaft84and the clamp guide86are inserted in the sleeve88. The sleeve88comprises an inner sleeve100and an outer sleeve102. The large diameter portion84aof the screw shaft84is inserted through the inner sleeve100. Ball holes (not illustrated) are formed in the inner sleeve100. The balls94fit in the ball holes. The inner sleeve100is connected to the screw shaft84via the balls94fitted between the ball groove84cand the ball holes, i.e., via a ball screw. When the screw shaft84rotates with respect to the inner sleeve100, the inner sleeve100moves in the front-rear direction with respect to the screw shaft84in the range where the ball groove84cis formed.

The screw shalt84, the clamp guide86, and the inner sleeve100are inserted in the outer sleeve102. The outer sleeve102has a cylindrical shape extending in the front-rear direction. A step102ais formed on an inner surface of the outer sleeve102. A portion of the inner surface of the outer sleeve102that is positioned forward of the step102ahas a smaller diameter than a portion of the inner surface of the outer sleeve102that is positioned rearward of the step102a. The outer sleeve102is fixed to the inner sleeve100with a set screw106. The outer sleeve102moves (i.e., translates or rotates) along with the inner sleeve100. In the range where the ball groove84cis formed, the outer sleeve102moves, along with the inner sleeve100, in the front-rear direction with respect to the screw shaft84when the screw shaft84rotates with respect to the inner sleeve100. Further, the outer sleeve102moves with respect to the clamp guide86between an advance position and a receding position when the screw shaft84rotates with respect to the inner sleeve100. Hereinafter, “the outer sleeve102advances” means that the outer sleeve102moves toward the advance position (i.e., forward) with respect to the clamp guide86, and “the outer sleeve102recedes” means that the outer sleeve102moves toward the receding position (i.e., rearward) with respect to the clamp guide86.

The holder82further comprises a support member104. The support member104covers an outer surface of the outer sleeve102. The support member104is rotatable with respect to the outer sleeve102. The support member104is movable in the front-rear direction with respect to the outer sleeve102. The outer sleeve102is supported by the body4via the support member104.

The holder member90is supported at a front portion of the clamp guide86. The holder member90is supported by two guide pins110(seeFIG.8) of the outer sleeve102such that it is movable with respect to the outer sleeve102. The holder member90is configured to hold the wire W. The holder member90opens and closes in conjunction with the rotation of the screw shaft84.

The holder member90comprises an upper holder member114and a lower holder member116. The upper holder member114faces the lower holder member116in the up-down direction. As illustrated inFIG.10, the upper holder member114comprises an upper base118, a first upper projection120, an upper connection121, and a second upper projection122. The upper base118is a portion supported by the clamp guide86and the guide pins110. The upper base118comprises two upper guide holes118a. The two upper guide holes118ahas the same shape. The two upper guide holes118aextend in the front-rear direction, and are inclined rightward from the rear toward the front when the upper base118is viewed from above.

The first upper projection120extends forward from a left front end of the upper base118. The upper connection121extends rightward from a right end of a center portion of the first upper projection120. The second upper projection122extends forward from the upper connection121. The first upper projection120is separated from the second upper projection122in the right-left direction. A first wire path124is defined between the first upper projection120and the second upper projection122. The wire W passes the first wire path124after fed out from the feed mechanism24and before reaching the upper guide path58aof the guide mechanism26.

The holder member90further comprises a first retainer123as illustrated inFIG.12. The first retainer123is integral with the upper holder member114. The first retainer123extends downward from a front end of the second upper projection122. The first retainer123partially overlaps the lower holder member116in the front-rear direction. The first retainer123prevents the wire W held by the holder member90from slipping out of the holder member90.

As illustrated inFIG.11, the lower holder member116comprises a lower base126, a first lower projection128, a lower connection129, and a second lower projection130. The lower base126is a portion supported by the clamp guide86and the guide pins110. The lower base126comprises two lower guide holes126a. With respect to a plane orthogonal to the right-left direction, the shape of the lower guide holes126aas the lower base126is viewed from above is symmetrical to the upper guide holes118aas the upper base118is viewed from above. That is, the two lower guide holes126aextend in the front-rear direction, and are inclined leftward from the rear toward the front as the lower base126is viewed from above.

The first lower projection128extends forward from a right front end of the lower base126. The lower connection129extends leftward from a left end of a center portion of the first lower projection128. The second lower projection130extends forward from a front end of a center portion of the lower connection129. The first lower projection128is separated from the second lower projection130in the right-left direction. A second wire path132is defined between the first lower projection128and the second lower projection130. The wire W passes the second wire path132after having passed through the lower guide path60aof the guide mechanism26.

The holder member90further comprises a second retainer131. The second retainer131is integral with the lower holder member116. The second retainer131extends leftward from a left front end of the second lower projection130. The second retainer131prevents the wire W held by the holder member90from slipping out of the holder member90. The second retainer131is separated from the lower connection129in the front-rear direction. An auxiliary path134is defined between the second retainer131and the lower connection129.

As illustrated inFIG.8, the guide pins110of the outer sleeve102are inserted in the upper guide holes118aand the lower guide holes126awhen the upper holder member114and the lower holder member116overlaps each other in the up-down direction. When the outer sleeve102moves in the front-rear direction with respect to the clamp guide86, the guide pins110move in the front-rear direction within the upper guide holes118aand the lower guide holes126a. When the guide pins110are in front portions of the upper guide holes118aand the lower guide holes126a, the first wire path124and the second wire path132are open as illustrated inFIG.12. This state of the holder member90is termed a fully open state.

When the outer sleeve102recedes with respect to the clamp guide86, the guide pins110move rearward within the upper guide holes118aand the lower guide holes126a. When the upper holder member114moves rightward with respect to the clamp guide86, the lower holder member116moves leftward (i.e., in the opposite direction to the direction in which the upper holder member114moves) with respect to the clamp guide86. The distance the upper holder member114moves rightward is equal to the distance the lower holder member116moves leftward. As the holder member90is viewed in the up-down direction, the upper holder member114and the lower holder member116move toward each other. When the guide pins110move to intermediate positions within the upper guide holes1l8aand the lower guide holes126aas illustrated inFIG.13, the second wire path132is blocked by the second upper projection122, while the first wire path124is open due to the auxiliary path134formed in the second lower projection130. This state of the holder member90is termed a half open state. If the wire W is in the second wire path132, the wire W is held and fixed at a first holding site P1between the second upper projection122and the first lower projection128. Hereinafter, a portion of the wire W that is held at the first holding site P1is termed a first held portion WP1. In the half open state, the first retainer123blocks the first holding site P1from the front. InFIG.13, the position of the first retainer123with respect to the front-rear direction is indicated by the broken line. The first retainer123is positioned between the rebars R (not illustrated inFIG.13) and the first holding site P1.

When the guide pins110move to rear portions of the upper guide holes118aand the lower guide holes126aas illustrated inFIG.14, the first wire path124is blocked by the second lower projection130, and the second wire path132remains blocked by the second upper projection122. This state of the holder member90is termed a fully closed state. If the wire W is in the first wire path124, the wire W is held and fixed at a second holding site P2between the first upper projection120and the second lower projection130, while the first held portion WP1of the wire W remains held at the first holding site P1of the holder member90. Hereinafter, a portion of the wire W that is held at the second holding site P2is termed a second held portion WP2. In the fully closed state, the first retainer123blocks the first holding site P1from the front and the second retainer131is positioned immediately below and forward of the second holding site P2. InFIG.14, a front end of the second retainer131is depicted by a shorter-dashed line than the dashed line depicting the first retainer123. The second retainer131is positioned between the rebars R (not illustrated inFIG.14) and the second holding site P2.

As illustrated inFIG.7, the holder82further comprises a push plate140. The push plate140is held between a rib100aarranged on a rear end portion of the inner sleeve100and a rear end portion of the outer sleeve102. In response to the rotation of the screw shaft84by the twisting motor76, the push plate140moves in the front-rear direction with respect to the screw shaft84, along with the inner sleeve100and the outer sleeve102.

As illustrated inFIGS.5and6, the push plate140operates the operable member72of the cutting mechanism28. As illustrated inFIG.5, the push plate140is normally separated from a projection72bof the operable member72. In this state, the operable member72is at the initial position. When the push plate140recedes with respect to the screw shaft84in response to the rotation of the screw shaft84, the push plate140contacts the projection72band pushes the operable member72rearward. As a result, the operable member72rotates about the rotation shaft72a, the link member70moves forward, and the cutting member66rotates about the rotation shaft66a. The push plate140can operate the cutting member66by operating the operable member72. When the operable member72rotates to the cutting position as illustrated inFIG.6, the wire W passing through the inside of the cutting member66is cut by the cutting member66. Then, when the push plate140advances with respect to the screw shaft84in response to the rotation of the screw shaft84, the operable member72is biased by the biasing member74and rotates about the rotation shaft72ato the initial position. As a result, the link member70and the cutting member66also return to their states illustrated inFIG.5.

The push plate140includes an initial state detecting magnet140aand a grip detecting magnet140b. As illustrated inFIG.7, the twisting mechanism30comprises an initial state detection sensor136configured to detect magnetism from the initial state detecting magnet140aand a grip detection sensor138configured to detect magnetism from the grip detecting magnet140b. The positions of the initial state detection sensor136and the grip detection sensor138are fixed with respect to the body4. When the twisting mechanism30is in an initial state, the initial state detection sensor136is opposed to the initial state detecting magnet140a. Thus, the initial state detection sensor136can detect whether the twisting mechanism30is in the initial state or not. When the holder member90is in the half open state in the twisting mechanism30, that is, when the holder member90grips the distal end of the wire W, the grip detection sensor138is opposed to the grip detecting magnet140b. Thus, the grip detection sensor138can detect whether the holder member90is gripping the distal end of the wire W in the twisting mechanism30or not.

As illustrated inFIG.7, fins144are arranged on an outer surface of the rear portion of the outer sleeve102. The fins144extend in the front-rear direction. The fins144permit or prohibit the rotation of the outer sleeve102. In the present embodiment, eight fins are arranged at intervals of 45 degrees on the outer surface of the outer sleeve102. Further, in the present embodiment, the fins144comprise seven short fins146and one long fin148. The length of the long fin148in the front-rear direction is greater than the length of the short fins146in the front-rear direction. With respect to the front-rear direction, a front end of the long fin148is at the same position as positions of front ends of the short fins146. To the contrary, with respect to the front-rear direction, a rear end of the long fin148is positioned rearward of rear ends of the short fins146.

The rebar tying machine2further comprises a rotation restrictor150illustrated inFIG.15. As illustrated inFIG.17, the rotation restrictor150is positioned adjacent to the outer sleeve102. The rotation restrictor150permits or prohibits the rotation of the outer sleeve102in cooperation with the fins144. As illustrated inFIG.15, the rotation restrictor150comprises a base member152, an upper stopper154, a lower stopper156, swing shafts158,160, and biasing members162,164. The base member152is fixed to the body4. The upper stopper154is swingably supported by the base member152via the swing shaft158. The upper stopper154comprises a restriction piece154a. The restriction piece154ais positioned at a lower portion of the upper stopper154. The biasing member162biases the restriction piece154ain a direction that opens the restriction piece154aoutward (i.e., in a direction that brings the restriction piece154aaway from the base member152).

When the screw shaft84rotates clockwise as viewed from the rear, the short fins146and the long fin148push in the restriction piece154a. Thus, the upper stopper154does not prohibit the rotation of the outer sleeve102. To the contrary, when the screw shaft84rotates counterclockwise as viewed from the rear, the short fins146and the long fin148contact the restriction piece154ain the rotation direction of the outer sleeve102. Thus, the upper stopper154prohibits the rotation of the outer sleeve102. When the screw shaft84rotates clockwise as viewed from the rear corresponds to when the twisting mechanism30has finished twisting the wire W around the rebars R and returns to its initial state. When the screw shaft84rotates counterclockwise as viewed from the rear corresponds to when the twisting mechanism30holds and twists the wire W around the rebars R.

The lower stopper156is swingably supported by the base member152via the swing shaft160. The lower stopper156comprises a restriction piece156a. The restriction piece156ais positioned at an upper portion of the lower stopper156. The restriction piece156ais opposed to the restriction piece154a. A rear end of the restriction piece156ais positioned rearward of a rear end of the restriction piece154a. A front end of the restriction piece156ais positioned rearward of a front end of the restriction piece154a. The biasing member164biases the restriction piece156ain a direction that opens the restriction piece156aoutward (i.e., in a direction that brings the restriction piece156aaway from the base member152).

When the screw shaft84rotates clockwise as viewed from the rear, the short fins146and the long fin148contact the restriction piece156ain the rotation direction of the outer sleeve102. Thus, the lower stopper156prohibits the rotation of the outer sleeve102. To the contrary, when the screw shaft84rotates counterclockwise as viewed from the rear, the short fins146and the long fin148push in the restriction piece156a. Thus, the lower stopper156does not prohibit the rotation of the outer sleeve102.

Regarding the mechanical configuration of the rebar tying machine2, various changes and modifications may be added to the configuration described above. For example, the reel holder12may be positioned at the rear portion of the body4and the feed mechanism24may be positioned between the reel holder12and the guide mechanism26of the body4in the rebar tying machine2. In this case, the reel18, the feed motor32, and the twisting motor76are positioned above the grip6. Alternatively, the control board20and/or the display board22may be housed inside the body4. In this case, the control board20and/or the display board22are positioned above the grip6.

Referring toFIGS.4,9,16, and17, how the rebar tying machine2ties the rebars R with the wire W will be described. To tie the rebars R with the wire W by the rebar tying machine2, a feeding-out process, a distal end gripping process, a pulling-back process, a proximal end gripping process, a cutting process, a pulling process, and a twisting process are sequentially performed. As illustrated inFIG.9, in an initial state in which the rebar tying machine2has not started an operation of tying the rebars R with the wire W yet, only the front portion of the screw shaft84is inserted within the inner sleeve100. Further, the long fin148is positioned between the restriction piece154aof the upper stopper154and the restriction piece156aof the lower stopper156. Further, the outer sleeve102is at the advance position with respect to the clamp guide86. The two guide pins110are positioned in the front portions of the two upper guide holes118aand the two lower guide holes126a, and the holder member90is in the fully open state. As illustrated inFIG.5, the push plate140is separated from the projection72bof the operable member72and the operable member72is at the initial position.

When the feed motor32rotates in reverse in the initial state, the feed mechanism24feeds out a predetermined length of the wire W wound on the reel18. The distal end of the wire W sequentially passes through the inside of the cutting member66, the first wire path124, the upper guide path58a, the lower guide path60a, and the second wire path132. As a result, the wire W is arranged around the rebars R in a loop shape as illustrated inFIG.4.

When the twisting motor76rotates forward in that state, the screw shaft84rotates counterclockwise. The long fin148contacts the restriction piece154aof the upper stopper154in the rotation direction of the outer sleeve102, and thus the counterclockwise rotation of the outer sleeve102is prohibited. Thus, the outer sleeve102recedes with respect to the clamp guide86, along with the inner sleeve100. As the outer sleeve102recedes, the two guide pins110move from the front portions to the intermediate positions within the two upper guide holes118aand the two lower guide holes126a. The holder member90transitions from the fully open state to the half open state, and a portion of the wire W that is near the distal end (i.e., the first held portion WP1) is held and fixed at the first holding site P1between the second upper projection122and the first lower projection128. Thus, the portion of the wire W that is near the distal end is held by the holder member90. In this state, the first retainer123blocks the first holding site P1of the holder member90from the front.

When the twisting motor76stops and the feed motor32rotates forward in that state, the feeder36pulls back the wire W around the rebars R. Since the portion of the wire W that is near the distal end is held by the holder member90, the diameter of the loop formed by the wire W around the rebars R is reduced.

When the twisting motor76rotates forward again in that state, the outer sleeve102further recedes with respect to the clamp guide86, along with the inner sleeve100. As the outer sleeve102recedes, the two guide pins110move from the intermediate positions to the rear portions within the two upper guide holes118aand the two lower guide holes126a. The holder member90transitions from the half open state to the fully closed state, and a portion of the wire W that is near the proximal end (i.e., the second held portion WP2) is held and fixed at the second holding site P2between the first upper projection120and the second lower projection130. Thus, the portion of the wire W that is near the proximal end is held by the holder member90. In this state, the first retainer123blocks the first holding site P1of the holder member90from the front and the second retainer131is positioned immediately below the second holding site P2of the holder member90. Further, the first retainer123and the second retainer131are positioned between the rebars R and the wire W.

As the twisting motor76rotates forward in that state, the outer sleeve102further recedes with respect to the clamp guide86. As illustrated inFIG.6, the push plate140recedes along with the outer sleeve102, contacts the projection72bof the operable member72, and pushes it rearward. When the operable member72rotates about the rotation shaft72ato the cutting position, the cutting member66rotates about the rotation shaft66ato a predetermined position. The wire W passing through the inside of the cutting member66is thereby cut. The wire W around the rebars R is held by the holder member90at the portion of the wire W that is near the distal end and the portion thereof that is near the proximal end.

When the outer sleeve102further recedes with respect to the clamp guide86in that state in response to the forward rotation of the twisting motor76, the step102aof the outer sleeve102contacts the step86cof the clamp guide86as illustrated inFIG.16. The outer sleeve102thereby cannot recede any more with respect to the clamp guide86and thus recedes integrally with the clamp guide86. As a result, the holder member90recedes (i.e., the holder member90moves away from the rebars R) and the wire W around the rebars R is pulled away from the rebars R. While the pulling process is performed, the first retainer123blocks the first holding site P1from the front and the second retainer131is positioned immediately below and forward of the second holding site P2. Thus, when the wire W moves forward with respect to the holder member90due to the tension applied to the wire W as the wire W is pulled, the portion WP1of the wire W that is near the distal end contacts the first retainer123and the portion WP2of the wire W that is near the proximal end contacts the second retainer131. The wire W is thus pulled away from the rebars R without slipping out of the holder member90.

In the state, when the outer sleeve102recedes along with the clamp guide86in response to the forward rotation of the twisting motor76, the long fin148comes out of contact with the restriction piece154aof the upper stopper154in the rotation direction of the outer sleeve102as illustrated inFIG.17. This permits the counterclockwise rotation of the outer sleeve102. In this state, the biasing member92is compressed and applies to the clamp guide86a biasing force that brings the clamp guide86away from the washer96. Thus, frictional forces act between the balls94fitted in the ball holes of the inner sleeve100and the ball groove84cof the screw shaft84. Consequently, when the clamp guide86rotates, the outer sleeve102does not recede with respect to the screw shaft84but rotates counterclockwise integrally with the screw shaft84. As a result, the clamp guide86and the holder member90rotate counterclockwise, and thus the wire W held by the holder member90is twisted. While the twisting process is performed, as in the pulling process, the first retainer123blocks the first holding site P1from the front and the second retainer131is positioned immediately below and forward of the second holding site P2. Thus, when the wire W moves forward with respect to the holder member90due to the tension applied to the wire W as the wire W is twisted, the portion WP1of the wire W that is near the distal end contacts the first retainer123and the portion WP2of the wire W that is near the proximal end contacts the second retainer131. The wire W is thus twisted without slipping out of the holder member90.

Thereafter, the twisting motor76rotates in reverse and the screw shalt84rotates clockwise. The outer sleeve102rotates clockwise and one of the short fins146or the long fin148contacts the restriction piece156aof the lower stopper156, and thus the clockwise rotation of the outer sleeve102is prohibited. Since the biasing member92is applying to the clamp guide86the biasing force that brings the clamp guide86away from the washer96, the outer sleeve102advances along with the clamp guide86. When the engagement pin86bcontacts the front end of the engagement groove84d, the outer sleeve102advances with respect to the clamp guide86. When the two guide pins110have moved within the two upper guide holes118aand the two lower guide holes126afrom their rear portions to front portions, the holder member90transitions to the fully open state. This allows the wire W held by the holder member90to be released from the holder member90. In a case where the short fin146is in contact with the restriction piece156a, when the outer sleeve102advances with respect to the clamp guide86and the short fin146moves forward than the front end of the restriction piece156a, the outer sleeve102rotates clockwise again. When the long fin148is in contact with the restriction piece156a, the rotation of the outer sleeve102is prohibited. The twisting mechanism30thereby returns to its initial state.

(Circuit Configuration of Control Board20)

As illustrated inFIG.20, the control board20comprises a regulated power supply circuit200, an MCU (micro control unit)202, a motor control signal output switching circuit204, a motor rotation signal input switching circuit206, gate driver circuits208,210, inverter circuits212,214, a current detection circuit216, brake circuits218,220, etc.

The regulated power supply circuit200adjusts the electric power supplied from the battery B to a predetermined voltage and supplies the electric power to the MCU202, brake circuits218,220, etc.

As illustrated inFIG.21, the inverter circuit212comprises switching elements222a,222b,224a,224b,226a,226b. Each of the switching elements222a,222b,224a,224b,226a,226bis a field-effect transistor, specifically a MOSFET including an insulated gate. The switching element222aconnects a positive-side potential line228to a motor power line232. The switching element222bconnects a negative-side potential line230to the motor power line232. The switching element224aconnects the positive-side potential line228to a motor power line234. The switching element224bconnects the negative-side potential line230to the motor power line234. The switching element226aconnects the positive-side potential line228to a motor power line236. The switching element226bconnects the negative-side potential line230to the motor power line236. The positive-side potential line228is connected to a positive-side power potential of the battery B. The negative-side potential line230is connected to the current detection circuit216. The motor power lines232,234,236are connected to the coils170of the feed motor32(seeFIGS.18,19).

Similarly, the inverter circuit214comprises switching elements238a,238b,240a,240b,242a,242b. Each of the switching elements238a,238b,240a,240b,242a,242bis a field-effect transistor, specifically a MOSFET including an insulated gate. The switching element238aconnects a positive-side potential line244to a motor power line248. The switching element238bconnects a negative-side potential line246to the motor power line248. The switching element240aconnects the positive-side potential line244to a motor power line250. The switching element240bconnects the negative-side potential line246to the motor power line250. The switching element242aconnects the positive-side potential line244to a motor power line252. The switching element242bconnects the negative-side potential line246to the motor power line252. The positive-side potential line244is connected to the positive-side power potential of the battery B. The negative-side potential line246is connected to the current detection circuit216. The motor power lines248,250,252are connected to the coils182of the twisting motor76(seeFIGS.18,19).

The gate driver circuit208controls the operation of the feed motor32by switching the switching elements222a,224a,226a,222b,224b,226bof the inverter circuit212between a conducting state and a non-conducting state according to motor control signals UH1, VH1, WH1, UL1, VL1, WL1. When the gate driver circuit208switches all of the switching elements222a,224a,226a,222b.224b,226bto the non-conducting state while the feed motor32is rotating, the power supply to the feed motor32is cut off, and thus the feed motor32stops after continuing to rotate fora while according to inertia. To the contrary, when the gate driver circuit208switches the switching elements222a,224a,226ato the non-conducting state and the switching elements222b,224b,226bto the conducting state while the feed motor32is rotating, a so-called short-circuit brake is applied to the feed motor32, and thus the rotation of the feed motor32stops immediately. Hereinafter, the motor control signals UH1, VH1, WH1, UL1, VL1, WL1in which UL1, VL1, WL1all have an H potential (in this case, the switching elements222b,224b,226bare all switched to the conducting state) may be termed a short-circuit brake signal.

Similarly, the gate driver circuit210controls the operation of the twisting motor76by switching the switching elements238a,240a,242a,238b,240b,242bof the inverter circuit214between a conducting state and a non-conducting state according to motor control signals UH2, VH2, WH2, UL2, VL2, WL2. When the gate driver circuit210switches all of the switching elements238a,240a,242a,238b,240b,242bto the non-conducting state while the twisting motor76is rotating, the power supply to the twisting motor76is cut off, and thus the twisting motor76stops after continuing to rotate for a while according to inertia. To the contrary, when the gate driver circuit210switches the switching elements238a,240a,242ato the non-conducting state and the switching elements238b,240b,242bto the conducting state while the twisting motor76is rotating, a so-called short-circuit brake is applied to the twisting motor76, and thus the rotation of the twisting motor76stops immediately. Hereinafter, the motor control signals UH2, VH2, WH2, UL2, VL2, WL2in which UL2, VL2, WL2all have the H potential (in this case, the switching elements238b,240b,242bare all switched to the conducting state) may be termed a short-circuit brake signal.

As illustrated inFIG.20, the current detection circuit216is disposed between the negative-side power potential of the battery B and the inverter circuits212,214. The current detection circuit216detects magnitudes of currents flowing through the inverter circuits212,214. The current detection circuit216outputs detected current values to the MCU202.

The MCU202comprises motor control signal output ports202a, motor rotation signal input ports202b, and general-purpose input-output ports202c. The motor control signal output ports202aare for output of motor control signals UH, VH, WH, UL, VL, WL to the brushless motors and are capable of processing signals faster than the general-purpose input-output ports202c. The motor rotation signal input ports202bare for input of Hall sensor signals Hu, Hv, Hw from the brushless motors and are capable of processing signals faster than the general-purpose input-output ports202c. The setting display LED22aand the setting switch22bof the display board22, the trigger switch9, the initial state detection sensor136, the grip detection sensor138, and the current detection circuit216are connected to the general-purpose input-output ports202cof the MCU202.

The motor control signal output ports202aof the MCU202are connected to the motor control signal output switching circuit204. The motor control signal output switching circuit204switches output destinations of the motor control signals UH, VH, WH, UL. VL, WL outputted from the motor control signal output ports202abetween the gate driver circuit208and the gate driver circuit210according to a switching signal SW outputted from the general-purpose input-output port202cof the MCU202.

As illustrated inFIG.22, the motor control signal output switching circuit204may comprise a demultiplexer260. When the switching signal SW outputted from the MCU202has the H potential, the demultiplexer260outputs the motor control signal UH outputted from the MCI202to the gate driver circuit208as the motor control signal UH1. When the switching signal SW outputted from the MCU202has an L, potential, the demultiplexer260outputs the motor control signal UH outputted from the MCU202to the gate driver circuit210as the motor control signal UH2. In order to facilitate the understanding, the details have been described only for the motor control signal UH, however, the motor control signal output switching circuit204operates the same for the other motor control signals VH, WH, UL, VL, WL, as well.

Alternatively, as illustrated inFIG.23, the motor control signal output switching circuit204may comprise FETs262,264and a NOT gate266. When the switching signal SW outputted from the MCU202has the H potential, the FET262is turned on and the FET264is turned off. In this case, the motor control signal output switching circuit204outputs the motor control signal UH outputted from the MCU202to the gate driver circuit208as the motor control signal UH1. When the switching signal SW outputted from the MCU202has the L potential, the FET262is turned off and the FET264is turned on. In this case, the motor control signal output switching circuit204outputs the motor control signal UH outputted from the MCU202to the gate driver circuit210as the motor control signal UH2. In order to facilitate the understanding, the details have been described only for the motor control signal UH, however, the motor control signal output switching circuit204operates the same for the other motor control signals VH, WH, UL, V L, WL, as well.

Alternatively, as illustrated inFIG.24, the motor control signal output switching circuit204may comprise NOR gates268,270and NOT gates272,274. When the switching signal SW outputted from the MCU202has the H potential, the NOR gate268outputs the motor control signal UH outputted from the MCU202and the NOR gate270outputs the L potential. In this case, the motor control signal output switching circuit204outputs the motor control signal UH outputted from the MCU202to the gate driver circuit208as the motor control signal UH1. When the switching signal SW outputted from the MCU202has the L potential, the NOR gate268outputs the L potential and the NOR gate270outputs the motor control signal UH outputted from the MCU202. In this case, the motor control signal output switching circuit204outputs the motor control signal UH outputted from the MCU202to the gate driver circuit210as the motor control signal UH2. In order to facilitate the understanding, the details have been described only for the motor control signal UH, however, the motor control signal output switching circuit204operates the same for the other motor control signals VH, WH, UL, VL, WL as well.

As illustrated inFIG.25, the brake circuit218is connected to signal lines for the motor control signals UL1, VL1, WL1that are outputted from the motor control signal output switching circuit204to the gate driver circuit208. The brake circuit218applies the short-circuit brake on the feed motor32according to a brake signal BR1outputted from the general-purpose input-output port202cof the MCU202. The brake circuit218comprises transistors274a,274b,274c,274dand resistors276a,276b,276c,276d,276e,276f,276g,276h. When the brake signal BR1inputted from the MCU202has the L potential, the transistor274ais turned off and all the transistors274b,274c,274dare thus turned off. As a result, the motor control signals UL1, VL1, WL1outputted from the motor control signal output switching circuit204are inputted to the gate driver circuit208without being changed. When the brake signal BR1inputted from the MCU202has the H potential, the transistor274ais turned on and all the transistors274b,274c,274dare thus turned on. As a result, the motor control signals UL1, VL1, WL1to be inputted to the gate driver circuit208all have the H potential. In this case, the short-circuit brake signal is inputted to the gate driver circuit208and the short-circuit brake is applied on the feed motor32.

Similarly, the brake circuit220is connected to signal lines for the motor control signals UL2, VL2, WL2that are outputted from the motor control signal output switching circuit204to the gate driver circuit210. The brake circuit220applies the short-circuit brake on the twisting motor76according to a brake signal BR2outputted from the general-purpose input-output port202cof the MCU202. The brake circuit220comprises a similar configuration to that of the brake circuit218. The brake circuit220comprises transistors278a,278b,278c,278dand resistors280a,280b,280c,280d,280e,280f,280g,280h. When the brake signal BR2inputted from the MCU202has the L potential, the transistor278ais turned off and all the transistors278b,278c,278dare thus turned off. As a result, the motor control signals UL2, VL2, WL2outputted from the motor control signal output switching circuit204are inputted to the gate driver circuit210without being changed. When the brake signal BR2inputted from the MCU202has the H potential, the transistor278ais turned on and all the transistors278b,278c,278dare thus turned on. As a result, the motor control signals UL2, VL2, WL2to be inputted to the gate driver circuit210all have the H potential. In this case, the short-circuit brake signal is inputted to the gate driver circuit210and the short-circuit brake is applied on the twisting motor76.

As illustrated inFIG.20, the Hall sensor180of the feed motor32and the Hall sensor192of the twisting motor76are connected to the motor rotation signal input switching circuit206. The motor rotation signal input switching circuit206is connected to the motor rotation signal input ports202bof the MCU202. The motor rotation signal input switching circuit206inputs one of a group of Hall sensor signals Hu1, Hv1, Hw1from the feed motor32and a group of Hall sensor signals Hu2, Hv2, Hw2from the twisting motor76to the motor rotation signal input ports202bof the MCU202according to the switching signal SW outputted from the MCU202.

As illustrated inFIG.26, the motor rotation signal input switching circuit206may comprise a multiplexer282. When the switching signal SW outputted from the MCU202has the H potential, the multiplexer282outputs the Hall sensor signal Hu1from the feed motor32to the MCU202as the Hall sensor signal Hu. When the switching signal SW outputted from the MCU202has the L potential, the multiplexer282outputs the Hall sensor signal Hu2from the twisting motor76to the MCU202as the Hall sensor signal Hu. In order to facilitate the understanding, the details have been described only for the Hall sensor signal Hu, however, the motor rotation signal input switching circuit206operates the same for the other Hall sensor signals Hv, Hw, as well.

Alternatively, as illustrated inFIG.27, the motor rotation signal input switching circuit206may comprise FETs284,286and a NOT gate288. When the switching signal SW outputted from the MCU202has the H potential, the FET284is turned on and the FET286is turned off. In this case, the motor rotation signal input switching circuit206outputs the Hall sensor signal Hut from the feed motor32to the MCU202as the Hall sensor signal Hu. When the switching signal SW outputted from the MCU202has the L potential, the FET284is turned off and the FET286is turned on. In this case, the motor rotation signal input switching circuit206outputs the Hall sensor signal Hu2from the twisting motor76to the MCU202as the Hall sensor signal Hu. In order to facilitate the understanding, the details have been described only for the Hall sensor signal Hu, however, the motor rotation signal input switching circuit206operates the same for the other Hall sensor signals Hv, Hw, as well.

Alternatively, as illustrated inFIG.28, the motor rotation signal input switching circuit206may comprise NOR gates290,292,294and a NOT gate296. When the switching signal SW outputted from the MCU202has the H potential, the NOR gate290inverts the Hall sensor signal Hu1from the feed motor32and outputs it and the NOR gate292outputs the L potential. As a result, the NOR gate294outputs the Hall sensor signal Hu1from the feed motor32. In this case, the motor rotation signal input switching circuit206outputs the Hall sensor signal Hu1from the feed motor32to the MCU202as the Hall sensor signal Hu. When the switching signal SW outputted from the MCU202has the L potential, the NOR gate290outputs the L potential and the NOR gate292inverts the Hall sensor signal Hu2from the twisting motor76and outputs it. As a result, the NOR gate294outputs the Hall sensor signal Hu2from the twisting motor76. In this case, the motor rotation signal input switching circuit206outputs the Hall sensor signal Hu2from the twisting motor76to the MCU202as the Hall sensor signal Hu. In order to facilitate the understanding, the details have been described only for the Hall sensor signal flu, however, the motor rotation signal input switching circuit206operates the same for the other Hall sensor signals Hv, Hw, as well.

As illustrated inFIG.20, the Hall sensor180of the feed motor32and the Hall sensor192of the twisting motor76are connected to the general-purpose input-output ports202cof the MCU202, as well. The MCU202can monitor the Hall sensor signals Hu1, Hv1, Hw1and the Hall sensor signals Hu2, Hv2, Hw2inputted to the general-purpose input-output ports202cfrom the feed motor32and the twisting motor76.

The MCU202executes the process illustrated inFIG.29when the trigger switch9is switched from off to on. In the process ofFIG.29, the MCU202sequentially executes a first feed motor driving process in S2(seeFIG.30), a first twisting motor driving process in S4(seeFIG.31), a second feed motor driving process in S6(seeFIG.32), a second twisting motor driving process in S8(seeFIG.35), and a third twisting motor driving process in S10(seeFIG.36).

Referring toFIG.30, the first feed motor driving process will be described. In S12, the MCU202outputs the H potential as the switching signal SW to switch the motor control signal output switching circuit204and the motor rotation signal input switching circuit206to the feed motor32side.

In S14, the MCU202outputs the motor control signals UH, VH, WH, UL, VL, WL to rotate the feed motor32in reverse. As a result, the feed motor32rotates in reverse and the feeding-out process in which the wire W is fed out starts.

In S16, the MCU202waits until a fed-out amount of the wire W reaches a predetermined value. The fed-out amount of the wire W can be calculated, for example, by counting the Hall sensor signals Hu, Hv, Hw. When the fed-out amount of the wire W reaches the predetermined value (YES), the process proceeds to S18.

In S18, the MCU202outputs the short-circuit brake signal as the motor control signals UH, VH, WH, UL, VL, WL to stop the feed motor32. Further, the MCU202outputs the H potential as the brake signal BR1. Thus, the feed motor32is braked. After S18, the process ofFIG.30ends.

Referring toFIG.31, the first twisting motor driving process will be described. In S22, the MCU202outputs the L potential as the switching signal SW to switch the motor control signal output switching circuit204and the motor rotation signal input switching circuit206to the twisting motor76side.

In S24, the MCU202outputs the motor control signals UH, VH, WH, UL, VL, WL to rotate the twisting motor76forward. As a result, the twisting motor76rotates forward and the distal end gripping process in which the distal end of the wire W is gripped starts.

In S26, the MCU202waits until the distal end of the wire W is gripped. Whether the distal end of the wire W has been gripped or not can be determined based on the detection signal of the grip detection sensor138. When the distal end of the wire W is gripped (YES), the process proceeds to S28.

In S28, the MCU202outputs the short-circuit brake signal as the motor control signals UH, VH, WH, UL, VL, WL to stop the twisting motor76. Further, the MCU202outputs the H potential as the brake signal BR2. Thus, the twisting motor76is braked. After S28, the process ofFIG.31ends.

Referring toFIG.32, the second feed motor driving process will be described. In S32, the MCU202outputs the H potential as the switching signal SW to switch the motor control signal output switching circuit204and the motor rotation signal input switching circuit206to the feed motor32side.

In S34, the MCU202outputs the motor control signals UH, VH, WH, UL, VL, WL to rotate the feed motor32forward. As a result, the feed motor32rotates forward and the pulling-back process in which the wire W is pulled back starts.

In S36, the MCU202determines whether a time elapsed since the feed motor32started being driven in S34(which may be termed a feed motor driving time, hereinafter) is no less than a predetermined upper time limit. When the feed motor driving time is equal to or greater than the upper time limit in S36(in case of YES), the MCU202determines that the feed motor32is not rotating normally due to some sort of abnormality and performs an error process in S38. When the feed motor driving time is less than the upper limit time in S36(in case of NO), the process proceeds to S40.

In S40, the MCU202determines whether a pulled-back amount of the wire W is no less than a predetermined upper limit value. The pulled-back amount of the wire W can be calculated, for example, by counting the Hall sensor signals Hu, Hv, Hw. When the pulled-back amount of the wire W is equal to or greater than the upper limit value in S40(in case of YES), the MCU202determines that the distal end of the wire W is not normally gripped and performs the error process in S38. When the pulled-back amount of the wire W is less than the upper limit value in S40(in case of NO), the process proceeds to S42.

In S42and the following steps, the MCU202determines whether the pulling-back of the wire W has been completed or not, based on a history of a current value I flowing through the feed motor32detected by the current detection circuit216. Hereinafter, changes in the current value I flowing through the feed motor32over time will be described referring toFIGS.33and34.

InFIG.33, a change in the current value I overtime with large-diameter rebars is indicated by a broken line, while a change in the current value I over time with small-diameter rebars is indicated by a solid line. As illustrated inFIG.33, after the feed motor32starts to be driven at a time t0, the current value I increases up to a peak of inrush current at a time t1and then gradually decreases. Then, when the wire W is started to be appressed to the rebars R, the current value I starts increasing again (at a time t2with large-diameter rebars, and at a time t4with small-diameter rebars). Then, when the wire W is completely appressed on the rebars R, the current value I starts decreasing again (at a time t3with large-diameter rebars, and at a time t5with small-diameter rebars).

FIG.34schematically illustrates relationships between the wire W and the rebars Rat the times t1, t2, t3, t4, and t5inFIG.33. With large-diameter rebars, the wire W starts to be appressed to the rebars R earlier (at the time t2) and the wire W is appressed completely to the rebars R earlier (at the time t3). Thus, as indicated by the broken line inFIG.33, the current value I stops decreasing and starts increasing earlier, and then stops increasing and starts decreasing earlier. Further, a minimum value Imin1of the current value I after the peak of the inrush current is not so small, and an increase ΔI1in the current value I thereafter is not so large. To the contrary, as illustrated inFIG.34, with small-diameter rebars, the wire W starts to be appressed to the rebars R later (at the time t4) and the wire W is appressed completely to the rebars R later (at the time t5). Thus, as indicated by the solid line inFIG.33, the current value I stops decreasing and starts increasing later, and then stops increasing and starts decreasing later. Further, a minimum value Imin2of the current value I after the peak of the inrush current is smaller and an increase ΔI2in the current value I thereafter is larger.

In the present embodiment, the MCU202determines the rebar diameter based on the timing when the current value I stops decreasing and starts increasing after the peak of the inrush current, that is, based on a timing when a time rate of change dI/dt of the current value I becomes equal to or greater than a time rate of change threshold value α. Further, the MCU202changes a determination condition for the completion of the pull-back based on the determined rebar diameter.

In S42ofFIG.32, the MCU202determines whether the current value I has passed the peak of the inrush current or not. The MCU202determines that the current value I has passed the peak of the inrush current, for example, when the feed motor driving time exceeds a predetermined lower limit time. When the current value I has not passed the peak of the inrush current (in case of NO), the process returns to S36. When the current value I has passed the peak of the inrush current (in case of YES), the process proceeds to S44.

In S44, the MCU202determines whether the rebar diameter has been already determined or not. When the rebar diameter has not been determined yet (in case of NO), the process proceeds to S46. When the rebar diameter has been already determined (in case of YES), the process proceeds to S56.

In S46, the MCU202updates the minimum value Iminof the current value I of the feed motor32. Specifically, when the currently detected current value I is smaller than the stored minimum value Imin, the MCU202replaces the latter with the former.

In S48, the MCU202calculates a time rate of change dI/dt of the current value I of the feed motor32.

In S50, the MCU202determines whether the time rate of change dI/dt is no less than the time rate of change threshold value α. The time rate of change threshold value α is a predetermined positive constant. When dI/dt is less than α (in case of NO), the process returns to S36. When dI/dt is equal to or greater than α (in case of YES), the process proceeds to S52.

In S52, the MCU202specifies the rebar diameter bused on the feed motor driving time. For example, when the feed motor driving time as of S52is less than a first predetermined time, the MCU202determines that the rebar diameter is large. When the feed motor driving time as of S52is equal to or greater than the first predetermined time and less than a second predetermined time which is greater than the first predetermined time, the MCU202determines that the rebar diameter is medium. When the feed motor driving time as of S52is equal to or greater than the second predetermined time, the MCU202determines that the rebar diameter is small.

In S54, the MCU202sets an increase threshold value ΔImaxof the current value I based on the rebar diameter determined in S52. A smaller increase threshold value ΔImaxis set for a larger rebar diameter.

In S56, the MCU202calculates an increase ΔI of the current value I by subtracting the minimum value Iminupdated in S46from the currently detected current value I.

In S58, the MCU202determines whether the increase ΔI calculated in S56is no less than the increase threshold value ΔImaxset in S54. When the increase ΔI is less than the increase threshold value ΔImax(in case of NO), the process returns to S36.

When the increase ΔI is equal to or greater than the increase threshold value ΔImaxin S58(in case of YES), the MCU202determines that the pull-back of the wire W is completed and the process proceeds to S60.

In S60, the MCU202outputs the short-circuit brake signal as the motor control signals UH, VH, WH, UL, VL, WL to stop the feed motor32. Further, the MCU202outputs the H potential as the brake signal BR1. As a result, the feed motor32is braked. After S60, the process ofFIG.32ends.

In S52ofFIG.32, the MCU202determines the rebar diameter based on the time elapsed since the feed motor32started to be driven in S34(the feed motor driving time). Instead of this, for example, the MCU202may specify the timing when the inrush current of the feed motor32peaks and then determine the rebar diameter in S52based on a time elapsed since the peak of the inrush current.

In the process ofFIG.32, regarding the current value I flowing through the feed motor32, the MCU202specifies the minimum value Iminafter the peak of the inrush current and then stops the feed motor32when the increase ΔI from the minimum value Iminreaches the increase threshold value ΔImax. Instead of this, for example, the MCU202may stop the feed motor32when a time elapsed since the time rate of change dI/dt of the current value I flowing through the feed motor32reached the time rate of change threshold value α in S50reaches a time threshold value. In this case, similar to the process ofFIG.32, the stop condition for the feed motor32can be changed according to the rebar diameter by setting the time threshold value to a small value when the rebar diameter specified in S52is large and setting time threshold value to a large value when the rebar diameter specified in S52is small.

In the process ofFIG.32, the MCU202determines the rebar diameter and changes the stop condition of the feed motor32, based on the history of the current value I flowing through the feed motor32with respect to the time t. Unlike this, the MCU202may determine the rebar diameter and change the stop condition of the feed motor32, for example, based on a history of the current value I flowing through the feed motor32with respect to a number of rotations N of the feed motor32. For example, the MCU202may calculate a rate of change dI/dN of the current value I flowing through the feed motor32with respect to the number of rotations N of the feed motor32in S48, and determine whether the calculated rate of change dI/dN has reached a rate of change threshold value β in S50.

Referring toFIG.35, the second twisting motor driving process will be described in detail. In S62, the MCU202outputs the L potential as the switching signal SW to switch the motor control signal output switching circuit204and the motor rotation signal input switching circuit206to the twisting motor76side.

In S64, the MCU202outputs the motor control signals UH, VH, WH, UL, VL, WL to rotate the twisting motor76forward. The twisting motor76thereby rotates forward, and the proximal end gripping process in which the proximal end of the wire W is gripped, the cutting process in which the wire W is cut, the pulling process in which the wire W is pulled, and the twisting process in which the wire W is twisted are sequentially performed.

In S66, the MCU202waits until the twisting of the wire W is completed. For example, the MCU202determines that the twisting of the wire W is completed when the current value detected at the current detection circuit216exceeds a predetermined value in accordance with a setting value of tying force for the wire W. This predetermined value may be varied depending on the rebar diameter determined in the second feed motor driving process or may be a constant value regardless of the rebar diameter. When the twisting of the wire W is completed (YES), the process proceeds to S68.

In S68, the MCU202outputs the short-circuit brake signal as the motor control signals UH1, VH, WH, UL, VL, WL to stop the twisting motor76. The twisting motor76is thereby braked. After S68, the process ofFIG.35ends.

Referring toFIG.36, the third twisting motor driving process will be described in detail.

In S72, the MCU202outputs the motor control signals UH, VH, WH, UL, VL, WL to rotate the twisting motor76in reverse. The twisting motor76thereby rotates in reverse, and the initial state returning process in which the twisting mechanism30returns to its initial state starts.

In S74, the MCU202waits until the twisting mechanism30returns to the initial state. Whether the twisting mechanism30has returned to the initial state or not can be determined based on a detection signal from the initial state detection sensor136. When the twisting mechanism30has returned to the initial state (YES), the process proceeds to S76.

In S76, the MCU202outputs the short-circuit brake signal as the motor control signals UH, VH, WH, UL, VL, WL to stop the twisting motor76. The twisting motor76is thereby braked. After S76, the process ofFIG.36ends.

As described, in one or more embodiments, the rebar tying machine2comprises the feed motor32, the current detection circuit216(an example of the current sensor) configured to detect the current flowing through the feed motor32, and the MCU202(an example of the control unit) configured to control the operation of the feed motor32. The rebar tying machine2is configured to perform the feeding-out process in which the wire W is fed out around the rebars R by driving the feed motor32, the gripping process in which the vicinity of the distal end of the wire W is gripped, the pulling-back process in which the wire W is pulled back by driving the feed motor32, the cutting process in which the wire W is cut, and the twisting process in which the wire W is twisted. The MCU202is configured to determine the diameter of the rebars R based on the history of the current value I flowing through the feed motor32in the pulling-back process.

In the pulling-back process above, the diameter of the loop formed by the wire W fed around the rebars R is reduced and the wire W is appressed to the rebars R. During this time, the behavior of the current value I flowing through the feed motor32changes at the timing when the wire W starts to be appressed to the rebars R and the timing when the wire W is completely appressed to the rebars R. As the diameter of the rebars R is larger, the timing when the wire W starts to be appressed to the rebars R and the timing when the wire W is completely appressed to the rebars R come earlier. To the contrary, as the diameter of the rebars R is smaller, the timing when the wire W starts to be appressed to the rebars R and the timing when the wire W is completely appressed to the rebars R come later. In the rebar tying machine2described above, the diameter of the rebars R is determined based on the history of the current value I flowing through the feed motor32, taking advantage of the fact that the current value I flowing through the feed motor32in the pulling-back process exhibits different behaviors depending on the diameter of the rebars R. Thus, the rebar tying machine2can operate in accordance with the diameter of the rebars R without a determination mechanism for determining the diameter of the rebars R.

In one or more embodiments, the MCU202is configured to, in the pulling-back process, calculate the time rate of change dI/dt of the current value I flowing through the feed motor32after the inrush current of the feed motor32has peaked, and determines the diameter of the rebars R based on the timing at which the time rate of change dI/dt reaches the time rate of change threshold value α.

In the pulling-back process, the current value I flowing through the feed motor32gradually decreases after the inrush current has peaked. Then, the current value I flowing through the feed motor32stops decreasing and starts to increase at the timing when the wire W starts to be appressed to the rebars R, and then stops increasing and starts to decrease again at the timing when the wire W is completely appressed to the rebars R. According to the configuration above, the diameter of the rebars R can be determined at the timing when the current value I flowing through the feed motor32stops decreasing and starts to increase after the inrush current has peaked, namely at the timing when the wire W starts to be appressed to the rebars R. Thus, the rebar tying machine2can perform the latter half of the pulling-back process in accordance with the determined diameter of the rebars R.

In one or more embodiments, the MCU202is configured to, in the pulling-back process, stop the feed motor32when the stop condition is satisfied. The MCU202is configured to change the stop condition according to the determined diameter of the rebars R.

As the diameter of the rebars R is larger, the timing when the wire W starts to be appressed to the rebars R comes earlier, and thus the feed motor32needs to be stopped earlier accordingly. To the contrary, as the diameter of the rebars R is smaller, the timing when the wire W is completely appressed to the rebars R comes later, and thus the feed motor32needs to be stopped later accordingly. According to the configuration above, the feed motor32can be stopped at an appropriate timing since the stop condition is changed according to the determined diameter of the rebars R.

In one or more embodiments, the MCU202is configured to, in the pulling-back process, specify the minimum value Iminof the current value I flowing through the feed motor32after the inrush current of the feed motor32has peaked, and calculate the increase ΔI in the current value I flowing through the feed motor32from the minimum value Imin. The stop condition includes that the increase ΔI reaches the increase threshold value ΔImax. The MCU202is configured to change the increase threshold value ΔImaxaccording to the determined diameter of the rebars R.

In the pulling-back process, as the diameter of the rebars R is larger, the timing when the wire W starts to be appressed to the rebars R comes earlier, and thus the current value I flowing through the feed motor32does not decrease much after the inrush current has peaked. Therefore, the minimum value Iminof the current value I flowing through the feed motor32after the inrush current has peaked is relatively large and the increase ΔI in the current value I therefrom until the wire W is completely appressed to the rebars R is small. To the contrary, as the diameter of the rebars R is smaller, the timing when the wire W starts to be appressed to the rebars R comes later, and thus the current value I flowing through the feed motor32significantly decreases after the inrush current has peaked. Therefore, the minimum value Iminof the current value I flowing through the feed motor32after the inrush current has peaked is relatively small and the increase ΔI in the current value I therefrom until the wire W is completely appressed to the rebars R is large. According to the configuration above, the increase threshold value ΔImaxis changed according to the determined diameter of the rebars R, and thus the feed motor32can be stopped at an appropriate timing.

In one or more embodiments, the rebar tying machine2comprises the feed motor32, the current detection circuit216(an example of the current sensor) configured to detect the current flowing through the feed motor32, and the MCU202(an example of the control unit) configured to control the operation of the feed motor32. The rebar tying machine2is configured to perform the feeding-out process in which the wire W is fed out around the rebars R by driving the feed motor32, the gripping process in which the vicinity of the distal end of the wire W is gripped, the pulling-back process in which the wire W is pulled back by driving the feed motor32, the cutting process in which the wire W is cut, and the twisting process in which the wire W is twisted. The MCU202is configured to, in the pulling-back process, stop the feed motor32when the stop condition is satisfied. The MCU202is configured to change the stop condition according to the history of the current value I flowing through the feed motor32in the pulling-back process.

In the rebar tying machine2described above, the stop condition for the feed motor32is changed based on the history of the current value I flowing through the feed motor32, taking advantage of the fact that the current value I flowing through the feed motor32in the pulling-back process exhibits different behaviors depending on the diameter of the rebars R. Thus, the rebar tying machine2can operate in accordance with the diameter of the rebars R without a determination mechanism for determining the diameter of the rebars R.

In one or more embodiments, the MCU202is configured to, in the pulling-back process, calculate the time rate of change dI/dt of the current value I flowing through the feed motor32after the inrush current of the feed motor32has peaked, and change the stop condition according to the timing at which the time rate of change dI/dt reaches the time rate of change threshold value α.

According to the configuration above, the stop condition for the feed motor32can be changed at the timing when the current value I flowing through the feed motor32stops decreasing and starts to increase after the inrush current has peaked, namely at the timing when the wire W starts to be appressed to the rebars R.

In one or more embodiments, the MCU202is configured to, in the pulling-back process, specify the minimum value Iminof the current value I flowing through the feed motor32after the inrush current of the feed motor32has peaked, and calculate the increase ΔI in the current value I flowing through the feed motor32from the minimum value Imin. The stop condition includes that the increase ΔI reaches the increase threshold value ΔImax. The MCU202is configured to change the increase threshold value ΔImaxaccording to the timing at which the time rate of change dI/dt reaches the time rate of change threshold value α.

According to the configuration above, the increase threshold value ΔImaxis changed according to the timing when the time rate of change dI/dt of the current value I flowing through the feed motor32reaches the time rate of change threshold value α, and thus the feed motor32can be stopped at an appropriate timing.