Patent Publication Number: US-2022212904-A1

Title: Work machine

Description:
TECHNICAL FIELD 
     The present invention relates to a work machine including a telescopic boom. 
     BACKGROUND ART 
     Conventionally, there is known a mobile crane including a telescopic boom is which a plurality of boom elements is disposed while being overlapped in a nested manner (also referred to as a telescopic manner) (see, for example, Patent Literature 1). The telescopic boom is configured to be telescopic stage by stage, for example, by a telescoping actuator disposed inside the innermost boom element. 
     Specifically, in the telescopic boom, boom elements adjacent to each other inside and outside are connected to each other by a boom-connecting pin (hereinafter, referred to as the “B pin”). When connection by the B pin is released, a boom element on an inner side is movable in a telescoping direction with respect to a boom element on an outer side. The movable boom element is connected to a movable portion of the telescoping actuator by a cylinder-connecting pin (hereinafter, referred to as the “C pin”). The telescoping actuator includes, for example, a hydraulic cylinder having a piston rod part and a cylinder part, and the cylinder part functions as a movable portion to telescope the boom element. 
     In addition, the insertion and removal operation of the B pin and the C pin is exclusively controlled by a pin insertion/removal actuator provided in the movable portion of the telescoping actuator, and a connection state between the boom elements by the B pin and a connection state between the cylinder and the boom by the C pin are not simultaneously released (so-called interlock). 
     CITATION LIST 
     Patent Literature 
     Patent literature 1: JP 2012-96928 A 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the invention 
     Incidentally, a hydraulic actuator is conventionally used as the pin insertion/removal actuator, and a pipe and a hydraulic circuit for supplying hydraulic oil to the actuator are provided around the telescopic boom. For this reason, design around the telescopic boom may be spatially limited, and this limitation in the design may restrict downsizing and light-weighting of the telescopic boom. 
     In addition, since the viscosity of the hydraulic oil varies according to environmental temperature or the like, operation time is unstable, and there is a large influence particularly in low temperature environments, which causes malfunction. 
     An object of the present invention is to provide a work machine that allows an improvement in the degree of freedom in terms of design around a telescopic boom and an increase in the reliability when the boom is telescoping. 
     Solutions to Problems 
     A work machine according to the present invention includes 
     a telescopic boom having a first boom and a second boom that are telescopically overlapped; 
     a telescoping actuator that moves the first boom in a telescoping direction with respect to the second boom; 
     an electrical drive source provided in a movable portion of the telescoping actuator; 
     a first fixing pin that connects the telescoping actuator and the first boom; 
     a first biasing mechanism that biases the first fixing pin to maintain a connection state between the telescoping actuator and the first boom; 
     a first connection mechanism that operates on the basis of the power of the electrical drive source and switches between the connection state and a disconnection state between the telescoping actuator and the first boom by inserting and removing the first fixing pin; 
     a second fixing pin that connects the first boom and the second boom; 
     a second biasing mechanism that biases the second fixing pin to maintain a connection state between the first boom and the second boom; 
     a second connection mechanism that operates on the basis of the power of the electrical drive source and switches between the connection state and a disconnection state between the first boom and the second boom by inserting and removing the second fixing pin; and 
     a clutch that is disposed in a power transmission path from the electrical drive source to the first connection mechanism and the second connection mechanism and discretionally intermittently transmits the power of the electrical drive source to the first connection mechanism and the second connection mechanism. 
     Effects of the Invention 
     According to the present invention, it is possible to improve the degree of freedom in terms of design around a telescopic boom and increase the reliability when the boom is telescoping. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating a state during traveling of a mobile crane according to an embodiment of the present invention. 
         FIG. 2  is a view illustrating a state of the mobile crane during work. 
         FIGS. 3A to 3C  are schematic views for describing a structure and extending operation of a telescopic boom. 
         FIGS. 4A to 4C  are schematic views for describing a structure and extending operation of the telescopic boom. 
         FIG. 5  is an overall perspective view of a telescopic device. 
         FIG. 6  is a perspective view of a pin insertion/removal actuator. 
         FIG. 7  is a plan view of the pin insertion/removal actuator as viewed from a +side in a Z direction. 
         FIG. 8  is a side view of the pin insertion/removal actuator as viewed from a +side in a Y direction. 
         FIG. 9  is a perspective view illustrating a state in which the pin insertion/removal actuator and a B pin holding part are engaged with each other. 
         FIG. 10  is a front view of a state in which the pin insertion/removal actuator and the B pin holding part are engaged with each other when viewed from a −side in an X direction. 
         FIG. 11  is a view illustrating an internal structure of the pin insertion/removal actuator. 
         FIG. 12  is a view illustrating the internal structure of the pin insertion/removal actuator. 
         FIG. 13  is a view illustrating the internal structure of the pin insertion/removal actuator. 
         FIG. 14  is a view schematically illustrating a configuration of the pin insertion/removal actuator. 
         FIGS. 15A and 15B  are views illustrating a removed state of a cylinder connection module and a removed state of a boom connection module. 
         FIGS. 16A to 16C  are schematic views for describing the operation and action of a lock mechanism. 
         FIGS. 17A to 17C  are schematic views for describing the operation of the cylinder connection module. 
         FIGS. 18A to 18C  are schematic views for describing the operation of the boom connection module. 
         FIG. 19  is a timing chart illustrating an example of control during the extending operation of the telescopic boom. 
         FIG. 20  is a timing chart illustrating an example of control during the extending operation of the telescopic boom to which motor assist processing is applied. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. 
     In the present embodiment, a mobile crane  1  that is an example of a work machine according to the present invention will be described. 
     &lt;Mobile Crane&gt; 
       FIG. 1  is a view illustrating a state during traveling of the mobile crane  1  according to an embodiment of the present invention.  FIG. 2  is a diagram illustrating a state of the mobile crane  1  during work. 
     The mobile crane  1  illustrated in  FIGS. 1 and 2  is a so-called rough terrain crane including an upper revolving body  10  and a lower traveling body  20 . 
     The upper revolving body  10  includes a revolving frame  11 , a cabin  12  (cab), a derricking cylinder  13 , a jib  14 , a hook  15 , a bracket  16 , a telescopic boom  30 , a counter weight CW, a hoisting device (winch, not illustrated), and the like. 
     The revolving frame  11  is revolvably supported by the lower traveling body  20  via a revolving suspension (not illustrated). The cabin  12 , the derricking cylinder  13 , the bracket  16 , the telescopic boom  30 , the counter weight CW, the hoisting device (not illustrated), and the like are attached to the revolving frame  11 . 
     The cabin  12  is disposed, for example, in front of the revolving frame  11 . In the cabin  12 , in addition to a seat on which an operator sits and various instruments, an operation part, a display part, a sound output part, and the like used when crane work and travelling operation are performed are disposed. 
     The derricking cylinder  13  is installed between the revolving frame  11  and the telescopic boom  30 . The telescopic boom  30  is derricked within a predetermined derricking angle range (for example, 0° to 84°) by the telescoping of the derricking cylinder  13 . 
     The jib  14  is rotatably attached to a distal end (boom head) of the telescopic boom  30  in a case where a lifting height is increased. The jib  14  is rotated forward, thereby being projected forward from the telescopic boom  30 . 
     The hook  15  is a hanging tool having a hook shape and has a main winding hook and an auxiliary winding hook. The hook  15  is attached to a wire rope  19  wound around a sheave at a distal end part of the telescopic boom  30  or a distal end part of the jib  14 . As the wire rope  19  wound up or paid out by a hoisting device (not illustrated), the hook  15  moves up and down. 
     The counter weight CW is attached to a rear part of the revolving frame  11 . The counter weight CW has a plurality of unit weights and can be set to have different weights depending on a combination of the unit weights. 
     The telescopic boom  30  is rotatably attached to the bracket  16  via a support shaft (foot pin, reference sign is omitted). The telescopic boom  30  has a plurality of boom elements including a distal end boom  31 , an intermediate boom  32 , and a proximal end boom  33 , and these boom elements are disposed while being overlapped in a nested manner (so-called telescopic structure). A telescoping actuator  40  (see  FIG. 5 ) disposed inside telescopes, whereby the distal end boom  31  and the intermediate boom  32  among the plurality of boom elements slide and telescope in a telescoping direction with respect to the proximal end boom  33 . Meanwhile, the proximal end boom  33  is riot movable in a telescoping direction. The state of the telescopic boom  30  changes from a contracted state illustrated in  FIG. 1  to an extended state illustrated in  FIG. 2  by extending the boom elements in order from the boom element disposed on an inner side (that is, the distal end boom  31 ). 
     In addition, a boom head (reference sign is omitted) having a sheave (reference sign is omitted) is disposed at a distal end part of the distal end boom  31 . In addition, a work attachment such as a bucket may be attached to the boom head. Note that in the telescopic boom  30 , the number of stages of the intermediate boom  32  is not particularly limited. 
     The lower traveling body  20  includes a vehicle body frame  21 , wheels  22  and  23 , outriggers OR 1  and OR 2 , an engine (not illustrated), and the like. 
     Driving force of the engine is transmitted to the wheels  22  and  23  via a transmission (not illustrated). The mobile crane  1  travels by the rotation of the wheels  22  and  23  by the driving force of the engine. In addition, steering angles (traveling directions) of the wheels  22  and  23  change in accordance with the operation of a steering wheel (not illustrated) provided in the cabin  12 . 
     The outriggers OR 1  and OR 2  are housed in the vehicle body frame  21  during traveling. Meanwhile, the outriggers OR 1  and OR 2  project in a horizontal direction and a vertical direction during work (during the operation of the upper revolving body  10 ), lift and support the entire vehicle body, and stabilize a posture. 
     As described above, the mobile crane  1  is a self-travelling crane using the wheels  22  and  23  for a travelling an it of the lower traveling body  20 , and travelling operation and crane operation can be performed from one cab. 
     Note that examples of the mobile crane  1  include an all-terrain crane, a truck crane, and a truck loader crane (also referred to as a cargo crane) in addition to a rough terrain crane. 
     &lt;Telescopic Boom&gt; 
       FIGS. 3A . to  3 C and  FIGS. 4A to 4C  are schematic views for describing a structure and extending operation of the telescopic boom  30 .  FIGS. 3A to 3C  and  FIGS. 4A to 4C  are vertical cross sections along a width direction of the telescopic boom  30 , the right side in the figures is the proximal end side of the telescopic boom  30 , and the left side in the figures is the distal end side of the telescopic boom  30 . Here, in order to simplify description, the telescopic boom  30  in which the intermediate boom  32  is of a one-stage composition will be described as an example. 
     As illustrated in  FIGS. 3A to 3C  and  FIGS. 4A to 4C , the telescopic boom  30  has a configuration substantially similar to a configuration of a conventionally known telescopic boom, The telescopic boom  30  has, for example, a structure symmetrical in the width direction with respect to a telescopic axis. A telescopic device A for telescoping the telescopic boom  30  is disposed inside the telescopic boom  30 . 
     In the telescopic boom  30 , the distal end boom  31  and the intermediate boom  32  are connected to each other with a boom-connecting pin (hereinafter, referred to as the “B pin”)  315  provided in the distal end boom  31 , and the intermediate boom  32  and the proximal end boom  33  are connected to each other with a B pin  325  provided in the intermediate boom  32 . In addition, each of the distal end boom  31 , the intermediate boom  32 , and the proximal end boom  33  is connected to the telescoping actuator  40  by a cylinder-connecting pin (hereinafter, referred to as the “C pin”)  150 . The distal end boom  31  or the intermediate boom  32  connected to the telescoping actuator  40  by the C pin  150  is a boom element to be telescoped. 
     The distal end boom  31  has a cylindrical shape and has an internal space capable of accommodating the telescopic device A. The distal end boom  31  has a C pin receiving part  311 , a B pin holding part  314 , and the B pin  315  at a proximal end part. 
     Each of a pair of the C pin receiving parts  311  is configured to be engageable with and disengageable from the C pin  150  (first fixing pin) provided in a pin insertion/removal actuator  50 . The C pin receiving parts  311  are disposed, for example, coaxially with each other. 
     The B pin holding part  314  is fixed to a frame of the distal end boom  31  on the proximal end side of the C pin receiving part  311  and holds the B pin  315  (second fixing pin) so that the B pin  315  is movable forward and backward. A pair of the B pins  315  is disposed, for example, coaxially at the B pin holding part  314  and is biased in directions opposite to each other toward the intermediate boom  32  on the outer side by the biasing force of a biasing member. That is, in normal times in which the distal end boom  31  is not telescoped, the B pin  315  is inserted into a proximal end side B pin receiving part  322  or a distal end side B pin receiving part  323  of the intermediate boom  32  by the biasing force of the biasing member, and the B pin  315  is maintained in this state. 
     The intermediate boom  32  has a cylindrical shape and has an internal space capable of accommodating the distal end boom  31 . The intermediate boom  32  has a C pin receiving part  321 , the proximal end side B pin receiving part  322 , and a B pin holding part  324  at a proximal end part and includes the distal end side B pin receiving part  323  at a distal end part. 
     Bach of a pair of the C pin receiving parts  321  is configured to be engageable with and disengageable from the C pin  150  (first fixing pin). The C pin receiving parts  321  are disposed, for example, coaxially with each other. 
     A pair of the proximal end side B pin receiving parts  322  is provided on the proximal end side of the C pin receiving part  321  and is disposed coaxially with each other. A pair of the distal end side B pin receiving parts  323  is provided at a distal end part of the intermediate boom  32  and disposed coaxially with each other. Each of the proximal end side B pin receiving part  322  and the distal end side B pin receiving part  323  is configured to allow insertion and removal of the B pin  315  of the distal end boom  31 . 
     The B pin holding part  324  is fixed to a frame of the intermediate boom  32  on the proximal end side of the proximal end side B pin receiving part  322 , and holds the B pin  325  (second fixing pin) so that the B pin  325  is movable forward and backward. A pair of the B pins  325  is disposed, for example, coaxially at the B pin holding part  324  and is biased in directions opposite to each other toward the proximal end boom  33  on the outer side by the biasing force of the biasing member. That is, in normal times in which the intermediate boom  32  is not telescoped, the B pin  325  is inserted into a proximal end side B pin receiving part  332  or a distal end side B pin receiving part  333  of the proximal end boom  33  by the biasing force of the biasing member and is maintained in this state. 
     The proximal end boom  33  has a cylindrical shape and has an internal space capable of accommodating the intermediate boom  32 . The proximal end boom  33  has the proximal end side B pin receiving part  332  at a proximal end part and the distal end side B pin receiving part  333  at a distal end part. 
     A pair of the proximal end side B pin receiving parts  332  is disposed coaxially with each other. A pair of the distal end side B pin receiving parts  333  is provided at a distal end part of the proximal end boom  33  and disposed coaxially with each other. Each of the proximal end side B pin receiving part  332  and the distal end side B pin receiving part  333  is configured to allow insertion and removal of the B pin  325  of the intermediate boom  32 . 
     The B pins  315  and  325  are displaced in an axial direction thereof on the basis of the operation of a boom connection module  200  included in the pin insertion/removal actuator  50 . 
     Specifically, the B pin  315  is inserted so as to be bridged over the proximal end side B pin receiving part  322  or the distal end side B pin receiving part  323  of the intermediate boom  32 . As a result, the distal end boom  31  and the intermediate boom  32  are connected to each other and brought into a connection state. Meanwhile, when the B pin  315  is removed from the proximal end side B pin receiving part  322  or the distal end side B pin receiving part  323  of the intermediate boom  32 , the connection between the distal end boom  31  and the intermediate boom  32  is released, and the distal end boom  31  and the intermediate boom  32  are brought into a disconnection state. 
     The B pin  325  is inserted so as to be bridged over the proximal end side B pin receiving part  332  or the distal end side B pin receiving part  333  of the proximal end boom  33 . As a result, the intermediate boom  32  and the proximal end boom  33  are connected to each other and brought into a connection state. Meanwhile, when the B pin  325  is removed from the proximal end side B pin receiving part  332  or the distal end side B pin receiving part  333  of the proximal end boom  33 , the connection between the intermediate boom  32  and the proximal end boom  33  is released, and the intermediate boom  32  and the proximal end boom  33  are brought into a disconnection state. 
     The distal end boom  31  is not movable in the telescoping direction with respect to the intermediate boom  32  in the connection state in which the distal end boom  31  is connected to the intermediate boom  32  with the B pin  315 , and the distal end boom  31  is movable in the telescoping direction with respect to the intermediate boom  32  in the disconnection state. Similarly, the intermediate boom  32  is not movable in the telescoping direction with respect to the proximal end boom  33  in the connection state in which the intermediate boom  32  connected to the proximal end boom  33  with the B pin  325 , and the intermediate boom  32  is movable in the telescoping direction with respect to the proximal end boom  33  in the disconnection state. 
     The C pin  150  is displaced in an axial direction thereof on the basis of the operation of a cylinder connection module  100  included in the pin insertion/removal actuator  50 . 
     Specifically, the distal end boom  31  and the intermediate boom  32  take either one of an engaged state in which the C pin  150  is engaged with the C pin receiving parts  311  and  321  and a disengaged state in which the C pin  150  is detached from the C pin receiving parts  311  and  321 . 
     In the engaged state, the distal end boom  31  and the intermediate boom  32  are movable in the telescoping direction together with a movable portion of the telescoping actuator  40  (cylinder part  42  in the present embodiment). When the intermediate boom  32  moves, the distal end boom  31  connected to the intermediate boom  32  via the B pin  315  also moves together in the telescoping direction. 
     The extending operation of the telescopic boom  30  will be briefly described as follows. 
       FIG. 3A  illustrates a fully retracted state of the telescopic boom  30 . In this state, the distal end boom  31  is accommodated in the intermediate boom  32 , is connected to the intermediate boom  32  via the B pin  315 , and is not movable in an extending direction (see  FIG. 3C ). In addition, the C pin  150  is engaged with the C pin receiving part  311  of the distal end boom  31 , and the distal end boom  31  and the cylinder part  42  are in an engaged state. 
     As illustrated in  FIG. 3B , the B pin  315  is removed from the proximal end side B pin receiving part  322  of the intermediate boom  32  (see a part surrounded by a broken line in  FIG. 3B ), the distal end boom  31  and the intermediate boom  32  are brought into the disconnection state, and the distal end boom  31  is movable in the extending direction. 
     As illustrated in  FIG. 3C , the distal end boom  31  moves to the distal end side as the telescoping actuator  40  operates to move the cylinder part  42  in the extending direction. 
     As illustrated in  FIG. 4A , after the distal end boom  31  moves to a predetermined position, the B pin  315  is inserted into the distal end side B pin receiving part  323  of the intermediate boom  32  (see a part surrounded by a broken line in  FIG. 4A ), the distal end boom  31  and the intermediate boom  32  are brought into the connection state, and the distal end boom  31  is not movable in the extending direction. 
     As illustrated in  FIG. 4B , engagement between the C pin receiving part  311  of the distal end boom  31  and the C pin  150  is released (see a part surrounded by a broken line in  FIG. 4B ), and only the cylinder part  42  can be restored to a contracted state after being separated from the distal end boom  31 . 
     Then, as illustrated in  FIG. 4C , the cylinder part  42  is restored to the contracted state, the C pin receiving part  321  of the intermediate boom  32  and the C pin  150  are engaged with each other, and the intermediate boom  32  and the cylinder part  42  are brought into an engaged state. 
     Note that in a case where the intermediate boom  32  is extended, operation similar to the operation described above is performed. In addition, in a case where the distal end boom  31  or the intermediate boom  32  is contracted, operation in a direction opposite to a direction described above is performed. &lt;Telescopic Device&gt; 
     The extending operation and the contraction operation of the telescopic boom  30  described above are performed by the telescopic device A incorporated in the telescopic boom  30 . The telescopic device A is disposed in the internal space of the distal end boom  31  in the fully retracted state (state illustrated in  FIG. 3A ) of the telescopic boom  30 . A detailed configuration of the telescopic device A will be described below. [ 0036 ] 
       FIG. 5  is an external perspective view of the telescopic device A. Hereinafter, each component constituting the telescopic device A will be described using an orthogonal coordinate system (X, Y, Z) on the basis of a state in which each component is incorporated in the telescopic device A. Also in figures to be described later, each component is illustrated by the common orthogonal coordinate system (X, Y, Z). In the orthogonal coordinate system (X, Y, Z), an X direction coincides with the telescoping direction of the telescopic boom  30 . A +side in the X direction is the distal end side of the telescopic boom  30 , and a −side in the X direction is the proximal end side of the telescopic boom  30 . For example, a Z direction coincides with an up-and-down direction of the mobile crane  1  in a fallen state in which a derricking angle of the telescopic boom  30  is 0°. A Y direction is orthogonal to the X direction and the Z direction and coincides with, for example, the width direction of the telescopic boom  30 . 
     As illustrated in  FIG. 5 , the telescopic device A includes the telescoping actuator  40  and the pin insertion/removal actuator  50 . The pin insertion/removal actuator  50  is disposed, for example, on the proximal end side of the telescoping actuator  40  so that the pin insertion/removal actuator  50  is movable together with the cylinder part  42 . 
     The telescoping actuator  40  is a hydraulic cylinder having a piston rod part  41  (see  FIG. 3A  and the like) and the cylinder part  42 . The telescoping actuator  40  moves the boom element (for example, the distal end boom  31  or the intermediate boom  32 ) connected to the cylinder part  42  via the C pin  150  (see  FIG. 3A  and the like) in the telescoping direction. The cylinder part  42  has, for example, a cylinder frame  43  with a rail. The rail (not illustrated) of the cylinder frame  43  is engaged with a rail groove provided in the telescopic boom  30 . As a result, the cylinder part  42  can slide along the telescopic boom  30  is a stable posture in the telescoping direction. Note that since a main structure of the telescoping actuator  40  is substantially similar to a main structure of a publicly known hydraulic cylinder, detailed description thereof will be omitted. 
     A configuration of the pin insertion/removal actuator  50  is illustrated in  FIGS. 6 to 10 .  FIGS. 6 to 8  are a perspective view of the pin insertion/removal actuator  50 , a plan view as viewed from a +side in the Z direction, and a side view as viewed from a +side in the Y direction, respectively.  FIGS. 9 and 10  are a perspective view of a state in which the pin insertion/removal actuator  50  and the B pin holding part  314  are engaged with each other and a front view seen from the −side in the X direction, respectively. 
     In  FIGS. 6 to 10 , a pair of the C pins  150  is distinguished as “C pins  150 A and  150 B”. In addition, in  FIGS. 9 and 10 , the pair of B pins  315  is distinguished as “B pins  315 A and  315 B”. 
     As illustrated in  FIGS. 6 to 8 , the pin insertion/removal actuator  50  is disposed on the −side in the X direction (proximal end side) of the cylinder part  42  and is configured to move in the telescoping direction together with the, cylinder part  42 . The pin insertion/removal actuator  50  includes an electric motor  51  (electrical drive source), a brake  52 , a transmission mechanism  53 , a position detection device  54 , a lock mechanism  55  (see  FIG. 11  and the like), the cylinder connection module  100  (first connecting device), and the boom connection module  200  (second connecting device). The transmission mechanism  53  includes a clutch  61 , a speed reducer  62 , and a torque limiter  63  (see  FIG. 14 ). 
     Each component is disposed in a housing  58  and unitized. As a result, it is possible to downsize the pin insertion/removal actuator  50 , improve productivity, and increase the reliability of a system. Specifically, the housing  58  has a box-shaped first housing  581  and a box-shaped second housing  582 . 
     The first housing  581  accommodates the cylinder connection module  100  in an internal space. Each of the C pins  150 A and  150 B of the cylinder connection module  100  is disposed so as to be movable forward and backward, for example, from both end parts of the first housing  581  in the Y direction. The piston rod part  41  (see  FIG. 3A  and the like) of the telescoping actuator  40  is inserted into the first housing  581  in the X direction. An end part of the cylinder part  42  is fixed to a side wall of the first housing  581  on the side in the X direction. 
     The second housing  582  is provided on the +side in the Z direction of the first housing  581 . The second housing  582  accommodates the boom connection module  200  in an internal space. A B pin rack bar  220 A of the boom connection module  200  is disposed so as to be movable forward and backward, for example, from one end part of the second housing  582  in the Y direction, and a B pin rack bar  220 B is disposed so as to be movable forward and backward, for example, from the other end part. In addition, a transmission shaft  56  (see  FIG. 12 ) of the transmission mechanism  53  is in into the second housing  582  in the X direction. 
     The electric motor  51  is an electrical drive source that operates the, cylinder connection module  100  and the boom connection module  200 . The electric motor  51  includes, for example, a rotary motor that uses electromagnetic force to output rotational motion. 
     As the rotary motor, for example, various electromagnetic motors such as a brush motor (direct current (DC) motor), a brushless DC motor, and a stepping motor can be applied. The operation of the electric motor  51  is controlled by a control device  70  (see  FIG. 14 ). 
     The electric motor  51  is supported by the second housing  582  via the transmission mechanism  53 . An output shaft (not illustrated) of the electric motor  51  extends in the X direction. For example, the electric motor  51  is disposed so that a ring gear (not illustrated) disposed on the outer periphery of the piston rod part  41  as a mechanical element of the transmission mechanism  53  meshes with the output shaft of the electric motor  51 . By disposing the electric motor  51  in this manner, it is possible to downsize the pin insertion/removal actuator  50  in the Y direction and the Z direction. 
     The electric motor  51  can be disposed in the cylinder frame  43  by applying a flat motor such as a large thin motor or a surface facing motor. In this case, a compact configuration is possible, and the cylinder frame  43  functions as a protective cover, so that the risk of damage due to interference during boom expansion/contraction operation can be reduced. 
     In addition, by taking advantage of a large cuter diameter of the motor, power is directly transmitted from the output shaft of the electric motor  51  to the large-diameter ring gear, whereby a deceleration ratio can be reduced and inertia during insertion operation by a C pin biasing mechanism  160  or a B pin biasing mechanism  240  can be reduced. 
     The electric motor  51  is connected to, for example, a power supply device (not illustrated) disposed on the upper revolving body  10  (see  FIG. 1 ) via a power supply cable. In addition, the electric motor  51  is connected to, for example, the control device  70  disposed on the upper revolving body  10  via a control signal transmission cable. These cables can be paid out and wound by a cord reel provided at a proximal end part of the telescopic boom  30  or the upper revolving body  10  (see  FIG. 1 ). 
     Since the power supply cable and the control signal transmission cable requires a small wiring space and can be freely routed, the degree of freedom in design around the telescopic boom  30  is significantly improved as compared with a case where a pipe of a hydraulic actuator or a hydraulic circuit is provided. 
     In addition, the electric motor  51  has a manual operation part  511  that can be operated by a manual handle (not illustrated). The manual operation part  511  is for manually changing a state of the pin insertion/removal actuator  50  (specifically, the cylinder connection module  100  and the boom connection module  200 ). The manual operation part  511  is turned with the manual handle when the electric motor  51  fails or the like, whereby the output shaft of the electric motor  51  rotates to change a state of the pin insertion/removal actuator  50 , and the B pins  315  and  325  and the C pin  150  can be inserted and removed. 
     In the present embodiment, the cylinder connection module  100  and the boom connection module  200  are operated by one electric motor  51 . Note that as the electric motor  51 , a motor for the cylinder connection module  100  and a motor for the boom connection module  200  may be separately provided. For example, in a case where the output shaft of the electric motor  51  is connected to a ring gear (not illustrated) of the transmission mechanism  53 , since the disposition of the electric motor  51  is not particularly limited as long as the electric motor  51  is disposed on the outer periphery of the ring gear, a plurality of small motors can be easily disposed as the electric motor  51  in addition, since it is possible to obtain required torque by increasing or decreasing the number of the electric motors  51 , the electric motor  51  can be composed of one type of motors, and can be easily applicable to the design of other models. 
     The brake  52  applies braking force to the electric motor  51 . The brake  52  includes, for example, an electromagnetic brake that performs braking using electromagnetic force. 
     The operation of the brake  52  is controlled by the control device  70 . 
     The brake  52  restricts the rotation of the output shaft of the electric motor  51  is a stopped state (non-energized state) of the electric motor  51 . The brake  52  operates, for example, in a removed state of the cylinder connection module  100  or in a removed state of the boom connection module  200 . As a result, the removed states of the cylinder connection module  100  and the boom connection module  200  are maintained in the stopped state of the electric motor  51 . In addition, it is possible to achieve power saving and prevent the electric motor  51  from generating heat due to the electric motor  51  being brought into a locked state as compared with a case where the removed state is maintained by motor torque. 
     In addition, in a case where external force of a predetermined magnitude acts on the cylinder connection module  100  or the boom connection module  200  at the time of braking, the brake  52  may allow the rotation (that sliding) of the electric motor  51 . As a result, it is possible to prevent mechanical elements (for example, the electric motor  51 , Gears, and the like) of the pin insertion/removal actuator  50  from being damaged by overload. 
     The brake  52  is preferably disposed in a stage preceding the speed reducer  62  of the transmission mechanism  53 . The stage preceding is an upstream side (−side in the X direction) in a power transmission path through which the power of the electric motor  51  is transmitted to the cylinder connection module  100  or the boom connection module  200 , and the stage preceding includes an upstream side of the electric motor  51 . Meanwhile, a stage following is a downstream side (+side in the X direction) in the power transmission path of the electric motor  51 . In the present embodiment, the brake  52  is disposed coaxially with the electric motor  51  on the −side in the X direction of the electric motor  51  (that is, a side opposite to the transmission mechanism  53  with the electric motor  51  as the center). By disposing the brake  52  in this manner, it is possible to downsize the pin insertion/removal actuator  50  in the Y direction and the Z direction. In addition, in a case where the brake  52  is disposed in the stage preceding the speed reducer  62 , since brake torque required for maintaining the stopped state of the electric motor  51  is smaller than that in a case where the brake  52  is disposed in a stage following the speed reducer  62 , it is possible to downsize the brake  52 . 
     Note that various brake devices such as a mechanical brake device and an electromagnetic brake device can be applied to the brake  52 . In addition, the position of the brake  52  is not limited to a position in the present embodiment. 
     The transmission mechanism  53  transmits the power (that is, rotational motion) of the electric motor  51  to the cylinder connection module  100  and the boom connection module  200 . 
     The transmission mechanism  53  is disposed in the second housing  582 . The transmission mechanism  53  has the clutch  61 , the speed reducer  62 , the torque limiter  63 , and the like (see  FIG. 14 ). The transmission mechanism  53  has, for example, the ring gear (not illustrated) disposed on the outer periphery of the piston rod part  41  and a transmission gear meshing with the ring gear, and the clutch  61 , the speed reducer  62 , and the torque limiter  63  are disposed on the transmission shaft  56  connected to the transmission gear. 
     The clutch  61  is disposed in the power transmission path for transmitting the power of the electric motor  51  and discretionally intermittently transmits the power to the cylinder connection module  100  and the boom connection module  200 . The clutch  61  is disposed, for example, in the stage preceding the speed reducer  62  (between the electric motor  51  and the speed reducer  62  in the present embodiment) in the power transmission path. By disposing the clutch  61  in this manner, it is possible to reduce a transmission torque capacity of the clutch  61  and downsize the clutch  61 . 
     For example, an electromagnetic clutch, a mechanical clutch, or a torque diode can be applied to the clutch  61 . Since these configurations are publicly known, the configurations will be briefly described. 
     The electromagnetic clutch is a mechanical element that electromagnetically transmits or cuts off power transmission from an input shaft to an output shaft. In a case where the electromagnetic clutch is applied, the operation of the clutch  61  is controlled, for example, by the control device  70 . Note that in a case where the operation of the clutch  61  is interlocked with the electric motor  51 , it is not necessary to individually control the clutch  61 . 
     The mechanical clutch is a mechanical element that transmits power by engagement between the input shaft and the output shaft. In a case where the mechanical clutch is applied, the clutch  61  is preferably a one-way clutch that transmits power from an input shaft to an output shaft while cutting off power from the output shaft to the input shaft and transmits power only in one direction. 
     The torque diode is a mechanical element that transmits power from an input shaft to an output shaft while cutting off power from the output shaft to the input shaft. 
     In a case where the mechanical clutch and the torque diode are applied, electrical control by the control device  70  or the like is unnecessary. 
     The speed reducer  62  decelerates the rotation of the electric motor  51  and outputs the decelerated rotation. The speed reducer  62  includes, for example, a planetary gear mechanism accommodated in a speed reducer case (reference sign is omitted), and an input shaft and an output shaft extend in the X direction. By disposing the speed reducer  62  in this manner, it is possible to downsize the pin insertion/removal actuator  50  in the Y direction and the Z direction. 
     The torque limiter  63  is an overload protection device that is disposed in the power transmission path for transmitting the power of the electric motor  51  and maintains torque acting on mechanical elements (for example, the electric motor  51 ) constituting the power transmission path at a predetermined value or less. The torque limiter  63  is disposed, for example, in a stage following the speed reducer  62  in the power transmission path. By disposing the torque limiter  63  in this manner, it is possible to reduce influence of tolerances and variations of a torque setting value as compared with a case where the torque limiter  63  is disposed in the stage preceding the speed reducer  62 . In addition, for example, the torque limiter  63  may be disposed in the stage preceding the speed reducer  62  in the power transmission path. In this case, since the torque setting value is decreased, it is possible to downsize the torque limiter  63 . 
     Note that the torque limiter  63  continues to slide while the electric motor  51  is driven, whereby predetermined torque can continue to be given to the cylinder connection module  100  and the boom connection module  200 . Therefore, the torque limiter  63  can be used as a substitute for the brake  52  to maintain the removed states of the cylinder connection module  100  and the boom connection module  200 . In addition, since the electric motor  51  is not brought into the locked state, heat generation due to overload does not occur. 
     The torque limiter  63  includes, for example, a friction torque limiter that is attached to an output shaft of the clutch  61  (transmission shaft  56  of the transmission mechanism  53 ) and in which an input side element and an output side element are joined together while sliding when torque larger than a predetermined value is generated. 
     The position detection device  54  detects the displacement of the C pin  150  and the B pins  315  and  325  on the basis of the output (for example, the rotation of the output shaft) of the electric motor  51 . The position detection device  54  detects, for example, a moving direction (rotation direction) and a moving amount (rotation angle) from a reference position of the C pin  150  or each of the B pins  315  and  325  (see  FIGS. 17A and 18A ). 
     The position detection device  54  includes, for example, an angle sensor such as a rotary encoder or a potentiometer and outputs information (for example, a pulse signal, a code signal) corresponding to a rotation amount of the output shaft of the electric motor  51 . The rotary encoder detects and outputs the rotational displacement of the input shaft using a built-in lattice disk. The potentiometer converts a change in the rotation angle into a change in a resistance value and outputs the change in the resistance value. 
     An output method of the rotary encoder is not particularly limited and may be an incremental method of outputting a pulse signal (relative angle signal) according to a rotation amount (rotation angle) from a measurement start position, or an absolute method of outputting a code signal (absolute angle signal) corresponding to an absolute angle position with respect to a reference point. 
     In a case where the position detection device  54  includes an absolute type rotary encoder, absolute positions of the C pin  150  and the B pins  315  and  325  can be detected even when the non-energized state is restored to an energized state. 
     The position detection device  54  may be provided directly on the output shaft of the electric motor  51  or may be provided on a rotating member (for example, a rotation shaft, a gear, or the like) that rotates together with the output shaft of the electric motor  51 . 
     In the present embodiment, the position detection device  54  is provided on the transmission shaft  56  in a stage following (on the +side in the X direction of) the transmission mechanism  53  (torque limiter  63 ) and outputs information corresponding to a rotation amount of the transmission shaft  56 . In this case, a rotary encoder capable of obtaining sufficient resolution with respect to the number of rotations (rotation speed) of the transmission shaft  56  is suitable for the position detection device  54 . 
     Note that since a C pin toothless gear  110  of the cylinder connection module  100  and a B pin toothless gear  210  of the boom connection module  200  are fixed to the transmission shaft  56 , a detection result of the position detection device  54  can also be said to be information corresponding to rotation amounts of the C pin toothless  110  and the B rein toothless gear  210 . 
     Note that the position detection device  54  is not limited to the above-described rotary encoder and may include, for example, a limit switch or a proximity sensor. The limit switch is disposed in the stage following the speed reducer  62  and mechanically operates on the basis of the output of the electric motor  51 . In addition, the proximity sensor is disposed in the stage following the speed reducer  62  so that the proximity sensor faces the rotating member that rotates on the basis of the output of the electric motor  51 , and the proximity sensor outputs a detection signal on the basis of a distance from the rotating member described above. The detection result of the position detection device  54  is output to the control device  70 . 
     However, the proximity sensor and the limit switch are provided, for example, at positions where an inserted state and a removed state of each of the C pin  150  and the B pins  315  and  325  can be detected, and at least as many proximity sensors and limit switches as the C pin  150  and the B pin rack bars  220 A and  220 B are required. In contrast to this, in a case where the rotary encoder is applied, since a state of each of the C pin  150  and the B pins  315  and  325  can be detected by one detection sensor, it is possible tn reduce the number of parts, and it is possible to reduce a cost. 
     In addition, the disposition of the position detection device  54  is not limited to the present embodiment. For example, the position detection device  54  may be disposed in the stage preceding the speed reducer  62 . That is, the position detection device  54  may acquire information to be output to the control device  70  on the basis of the rotation of the electric motor  51  before being decelerated by the speed reducer  62 . In a case where the position detection device  54  is disposed in the stage preceding the speed reducer  62 , high resolution can be obtained as compared with a case where the position detection device is disposed in the stage following the speed reducer  62 . 
     The control device  70  is, for example, an in-vehicle computer having a central processing unit (CPU) as an arithmetic/control device, a read only memory (ROM) and a random access memory (RAM) as main storage devices, an input terminal, an output terminal, and the like. The control device  70  calculates information on a position of the C pin  150  or positions of the B pins  315  and  325  on the basis of the output of the position detection device  54 . In the calculation, data (tables, maps, and the like) indicating a correlation between the output of the position detection device  54  and the information on the positions of the C pin  150  and the B pins  315  and  325  (for example, the moving amount from the reference position) is used. This data is stored, for example, in the ROM. 
     For example, the, control device  70  determines whether the C pin  150  is in the engaged state (for example, in a state illustrated in  FIG. 3A ) or in the disengaged state (for example, in a state illustrated in  FIG. 4B ) with respect to the C pin receiving part  311  of the distal end boom  31  or the C pin receiving part  321  of the intermediate boom  32 , that a connection state between the pin insertion/removal actuator  50  and the distal end boom  31  or the intermediate boom  32 , by calculation on the basis of the output of the position detection device  54 . 
     In addition, in a case where an object to be telescoped is the distal end boom  31 , the control device  70  determines whether the B pin  315  of the distal end boom  31  and the intermediate boom  32  are in the engaged state (see  FIGS. 3A, 3C , and the like) or in the disengaged state (see  FIG. 3B ), that is, the connection state between the distal end boom  31  and the intermediate boom  32  by calculation on the basis cf the detection result of the position detection device  54 . Similarly, in a case where an object to be telescoped is the intermediate boom  32 , the control device  70  determines the connection state between the intermediate boom  32  and the proximal end boom  33  by calculation on the basis of the detection result of the position detection device  54 . 
     The control device  70  executes various types of control cf the pin insertion/removal actuator  50 , including, for example, operation control of the electric motor  51 , the brake  52 , the clutch  61 , and the like on the basis of a calculation result. Note that, in executing the various types of control of the pin insertion/removal actuator  50 , for example, various sensors provided in the telescopic boom  30  or the telescoping actuator  40  may be used to acquire information indicating a state of the telescopic boom  30  or the telescoping actuator  40 . 
     Referring to  FIGS. 11 to 14 , the cylinder connection module  100  and the boom connection module  200  will be described.  FIGS. 11 to 13  are views illustrating an internal structure of the pin insertion/removal actuator  50 .  FIG. 14  is a view schematically illustrating the configuration of the pin insertion/removal actuator  50 . 
       FIGS. 11 to 14  illustrate a neutral state in which the electric motor  51  is in the stopped state and the cylinder connection module  100  and the boom connection module  200  are not operating. In the neutral state, both the cylinder connection module  100  and the boom connection module  200  are in an inserted state. The neutral state is maintained, for example, by the movement of the C pin rack bar  120  and the B pin rack bars  220 A and  220 B being mechanically restricted by a stopper (not illustrated). Note that the neutral state may be maintained by the biasing force of the C pin biasing mechanism  160  and the biasing force of the B pin biasing mechanism  240  being balanced with each other. 
     In addition,  FIGS. 15A and 15B  illustrate the removed state of the boom connection module  200  and the removed state of the cylinder connection module  100 . As illustrated in  FIG. 15A , in the removed state of the cylinder connection module  100 , the boom connection module  200  is maintained in the inserted state. As illustrated in  FIG. 15B , in the removed state of the boom connection module  200 , the cylinder connect on module  100  is maintained in the inserted state. 
     The cylinder connection module  100  operates on the basis of the power (that is, rotational motion) of the electric motor  51  and changes between the inserted state (see  FIG. 11 ) and the removed state (see  FIG. 15A ). 
     The inserted state of the cylinder connection module  100  is a state in which the C pin receiving part  311  of the distal end boom  31  or the C pin receiving part  321  of the intermediate boom  32  are engaged with the C pin  150  to connect the respective boom elements and the pin insertion/removal actuator  50 . In this connection state, the distal end boom  31  and the intermediate boom  32  are movable together with the cylinder part  42  and the pin insertion/removal actuator  50  (see  FIG. 3B ,  FIG. 15B , and the like). 
     Meanwhile, the removed state of the cylinder connection module  100  is a state in which the C pin  150  is detached from the C pin receiving parts  311  and  321  of the distal end boom  31  or the intermediate boom  32 , and the respective boom elements are separated from the pin insertion/removal actuator  50 . In this disconnection state, the cylinder part  42  and the pin insertion/removal actuator  50  are movable independently from the respective boom elements (see  FIG. 4B ,  FIG. 15A , and the like). 
     The boom connection module  200  operates on the basis of the power (that is, rotational motion) of the electric motor  51  and changes between the inserted state (see  FIG. 11 ) and the removed state (see  FIG. 15B ). 
     The inserted state of the boom connection module  200  is, for example, a state in which the B pin  315  is inserted into the proximal end side B pin receiving part  322  or the distal end side B pin receiving part  323  of the intermediate boom  32  to connect the distal end boom  31  and the intermediate boom  32 . In this connection state, the distal end boom  31  is not movable in the telescoping direction with respect to the intermediate boom  32  (see  FIG. 3A ,  FIG. 15A , and the like). 
     Meanwhile, the removed state of the boom connection module  200  is, for example, a state in which the B pin  315  is detached from the proximal end side B pin receiving part  322  or the distal end side B pin receiving part  323  of the intermediate boom  32 , and the distal end boom  31  is separate from the intermediate boom  32 . 
     In this disconnection state, the distal end boom  31  is movable in the telescoping direction with respect to the intermediate boom  32  (see  FIG. 3B ,  FIG. 15B , and the like). 
     As illustrated in  FIGS. 11 to 14 , the cylinder connection module  100  has the C pin toothless gear  110 , the C pin rack bar  120 , a first gear group  130 , a second gear group  140 , the C pin  150 , and the C pin biasing mechanism  160 . Each of the mechanical elements  110  to  160  is an example of constituent members of the first connection mechanism. In the following description, the C pin  150  is distinguished as the “C pins  150 A and  150 B”. 
     Note that in the present embodiment, a pair of the C pins  150 A and  150 B is incorporated in the cylinder connection module  100 , but the C pins  150 A and  150 B may be provided independently from the cylinder connection module  100 . 
     The C pin toothless Gear  110  is a substantially discoid gear and has a tooth part  111  (see  FIG. 12 ) on a part of the outer peripheral surface. The C Pin toothless gear  110  is externally fitted and fixed to the transmission shaft  56  of the transmission mechanism  53  and rotates together with the transmission shaft  56 . The C pin toothless gear  110  constitutes a switch gear G (see  FIG. 14 ) together with the B pin toothless gear  210  of the boom connection module  200 . The power of the electric motor  51  is alternatively transmitted to either one of the cylinder connection module  100  and the boom connection module  200  by the switch gear G. 
     In the present embodiment, the C pin toothless gear  110  and the B pin toothless gear  210  constituting the switch gear G are incorporated in the cylinder connection module  100  that is the first connection mechanism and the boom connection module  200  that is the second connection mechanism, respectively. However, the switch gear C may be provided independently from the first connection mechanism and the second connection mechanism. 
     In addition, the switch gear G only needs to function as the C pin toothless gear  110  and the B pin toothless gear  210  and for example, may include one toothless gear, as illustrated in  FIG. 14 . 
     In the following description, a rotation direction (R 1  direction in  FIG. 14 ) of the C pin toothless gear  110  when the cylinder connection module  100  changes from the inserted state (see  FIG. 11 ) to the removed state (see F  15 A) is referred to as the “forward direction”, and a rotation direction (R 2  direction in  FIG. 14 ) of the C pin toothless gear  110  when the cylinder connection module  100  changes from the removed state to the inserted state is referred to as the “reverse direction”. 
     Among projections constituting the tooth part ill of the C pin toothless gear  110 , a projection provided at an end part in the forward direction of the C pin toothless gear  110  is a positioning tooth (not illustrated). 
     The C pin rack bar  120  is, for example, a shaft member extending in one direction and is disposed along the Y direction on a lower side (−side in the Z direction) of the C pin toothless gear  110 . 
     The C pin rack bar  120  has an input side rack part  121  on a surface closer to the C pin toothless gear  110  (+side in the Z direction) and has two output side rack parts  122  and  123  on a surface farther from the C pin toothless gear  110  (−side in the Z direction). 
     The input side rack part  121  meshes with the tooth part  111  of the C pin toothless gear  110  only when the cylinder connection module  100  changes from the inserted state (see  FIG. 11 ) to the removed state (see  FIG. 15A ). 
     Specifically, in the inserted state of the cylinder connection module  100 , a first end face (not illustrated) of the input side rack part  121  on the +side in the Y direction abuts on the positioning tooth (not illustrated) in the tooth part  111  of the C pin toothless gear  110  or faces the positioning teeth (not illustrated) in the Y direction via a slight gap. In this state, when the C pin toothless gear  110  rotates in the R 1  direction, the positioning tooth pushes the first end face to the +side in the Y direction, and the C pin rack bar  120  moves to the +side in the Y direction. Then, the tooth part  111  formed in the reverse direction from the positioning tooth sequentially mesh with the input side rack part  121 . As a result, the C pin rack bar  120  moves to the +side in The Y direction along with the rotation of the C pin toothless gear  110  in the R 1  direction. 
     Note that in a case where the C pin toothless gear  110  rotates in the R 2  direction in the inserted state of the cylinder connection module  100  illustrated in  FIG. 11 , the input side rack part  121  does not mesh with the tooth part  111  of the C pin toothless gear  110 . 
     As described above, the C pin rack bar  120  moves in a longitudinal direction (Y ion) thereof with the rotation of the C pin toothless gear  110 . The C pin rack bar  120  is positioned on the most −side in the Y direction in the inserted state of the cylinder connection module  100  (see  FIG. 11 ) and is positioned on the most +side in the Y direction in the removed state (see  FIG. 15A ). 
     That is, when the C pin toothless gear  110  rotates in the R 1  direction in the inserted state (neutral state) of the cylinder connection module  100 , the C pin rack bar  120  moves to the +side in the Y direction and changes to the removed state. Meanwhile, when the C bin toothless gear  110  rotates in the R 2  direction in the removed state of the cylinder connection module  100 , the C pin rack bar  120  moves to the −side in the Y direction and changes to an inserted state. 
     The output side rack parts  122  and  123  mesh with the first gear group  130  and the second gear group  140 , respectively. 
     The first gear group  130  has, for example, a drive gear  131 , an intermediate gear  132 , and a driven gear  133 . Each gear element includes a spur gear. 
     Specifically, the drive gear  131  meshes with the output side rack part  122  of the C pin rack bar  120  and the intermediate gear  132 . The intermediate gear  132  meshes with the drive gear  131  and the driven gear  133 . The driven gear  133  meshes with the intermediate gear  132  and a pin side rack part  151  of one C pin  150 A, 
     When the cylinder connection module  100  is in the inserted state, the drive gear  131  meshes with an end part on the +side in the Y direction or a part close to the end part in the output side rack part  122  of the C pin rack bar  120 . In addition, the driven gear  133  meshes with the end part on the −side in the Y direction of the pin side rack part  151  of the one C pin  150 A, 
     The second gear group  140  has, for example, a drive gear  141  and a driven gear  142 . Each gear element includes a spur gear. 
     Specifically, the drive gear  141  meshes with an output side rack part  123  of the C pin rack bar  120  and the driven gear  142 . The driven gear  142  meshes with the drive gear  141  and the pin side rack part  151  of the other C pin  1508 , 
     When the cylinder connection module  100  is in the inserted state, the drive gear  141  meshes with an end part on the +side in the Y direction or a part close to the end part in the output side rack part  123  of the C pin rack bar  120 . In addition, the driven gear  142  meshes with the end on the +side in the Y direction in the pin side rack part  151  of the other C pin  150 B. 
     In the first gear group  130 , the drive gear  131  and the driven gear  133  are connected via the intermediate gear  132 , whereas in the second gear group  140 , the drive gear  141  and the driven gear  142  are directly connected. Therefore, a rotation direction of the driven gear  133  of the first gear group  130  and a rotation direction of the driven gear  142  of the second gear Group  140  are opposite to each other. 
     The pair of C pins  150 A and  150 B is disposed, for example, coaxially with each other in the Y direction. The C pins  150 A and  150 B are preferably symmetric with respect to the center of the piston rod part  41  of the to actuator  40 . As a result, it is possible to prevent bending stress from being generated in the piston rod part  41  and to reduce a dimension in a height direction (Z direction). 
     Note that the C pins  150 A and  150 B only need to be disposed symmetrically with respect to the telescoping direction (X direction), and for example, may be disposed at positions shifted from each other in the Z direction or may be provided at positions eccentric to the piston rod part  41  (for example, the −side in the Z direction of the piston rod part  41 ). 
     Hereinafter, distal end parts of the C pins  150 A and  150 B are end parts on sides far from each other, and proximal end parts thereof are end parts on sides close to each other. 
     The C pins  150 A and  150 B each have a pin side rack part  151  on the outer peripheral surface. 
     The pin side rack part  151  of the one C pin  150 A meshes with the driven gear  133  of the first gear group  130 . The pin side rack part  151  of the other C pin  150 B meshes with the driven gear  142  of the second gear group  140 . 
     The C pins  150 A and  150 B move in an axial direction thereof (Y direction) with the rotation of the driven gears  133  and  142 , respectively. Specifically, the one C pin  150 A moves to the −side in the Y direction when the cylinder connection module  100  changes from the inserted state to the removed state, and the one C pin  150 A moves to the +side in the Y direction when the cylinder connection module  100  changes from the removed state to the inserted state. The other C pin  150 B moves to the +side in the Y direction when the cylinder connection module  100  changes from the inserted state to the removed state, and the other C pin  150 B moves to the −side in the Y direction when the cylinder connection module  100  changes from the removed state to the inserted state. That is, in the above-described state change, the C pins  150 A and  150 B move in directions opposite to each other in the Y direction. 
     The C pin biasing mechanism  160  biases the C pins  150 A and  150 B in directions away from each other. The C pin biasing mechanism  160  includes, for example, a pair of compression coil springs. In the present embodiment, the C pin biasing mechanism  160  is disposed on each of the proximal end sides of the C pins  150 A and  150 B and biases the C pins  150  and  150 B toward the distal end side. 
     When the electric motor  51  rotates in the R 1  direction to bring the cylinder connection module  100  into the removed state (see  FIG. 15A ) and then the operation of the electric motor  51  stops, the cylinder connection module  100  is automatically restored to the inserted state by the biasing force of the C pin biasing mechanism  160 . However, in a case where the brake  52  is operating, the cylinder connection module  100  is not automatically restored to the inserted state, and the removed state is maintained. 
     Note that the C pin biasing mechanism  160  may directly apply biasing force to the C pins  150 A and  150 B or may apply biasing force via another member. In addition, the C pin biasing mechanism  160  may be omitted, and the cylinder connection module  100  may be configured to change from the removed state to the inserted state on the basis of the power of the electric motor  51 . Even in this case, from the viewpoint of fail-safe, it is preferable to provide the C pin biasing mechanism  160  and configure so that the cylinder connection module  100  is restored to the inserted state that is a safe side when the electric motor  51  fails. 
     As illustrated in  FIGS. 11 to 13 , the boom connection module  200  has the B pin toothless gear  210 , a pair of the B pin rack bars  220 A and  220 B, a synchronous gear  230  (see  FIG. 14 ), and the B pin biasing mechanism  240 . Each of the mechanical elements  210  to  240  is an example of constituent members of the second connection mechanism. In the following description, the B pin  315  is distinguished as the “B pins  315 A and  315 B”. 
     In addition, a case where the boom connection module  200  acts on the B pin  315  will be described, but the same applies to a case where the boom connection module  200  acts on the B pin  325 . 
     The B pin toothless gear  210  is a substantially discoid gear and has a tooth part  211  on a part of the outer peripheral surface. The B pin toothless gear  210  is externally fitted and fixed to the transmission shaft  56  on the +side in the X direction of the C pin toothless gear  110  and rotates together with the transmission shaft  56 . As described above, the B pin toothless gear  210  constitutes the switch gear G (see  FIG. 14 ) together with the C pin toothless gear  110  of the cylinder connection module  100 . 
     In the following description, a rotation direction (R 2  direction in  FIG. 14 ) of the B pin toothless gear  210  when the boom connection module  200  changes from the inserted state (see  FIG. 11 ) to the removed state (see  FIG. 15B ) is referred to as the “forward direction.”, and a rotation direction (R 1  direction in  FIG. 14 ) of the B pin toothless gear  210  when the boom connection module  200  changes from the removed state to the inserted state is referred to as the “reverse direction”. 
     Among projections constituting the tooth part  211  of the B pin toothless gear  210 , a projection provided at an end part in the forward direction of the B pin toothless gear  210  is a positioning tooth (reference sign is omitted). 
     That is, the rotation direction R 2  of the B pin toothless gear  210  when the boom connection module  200  changes from the inserted state to the removed state is opposite to the rotation direction R 1  of the C pin toothless gear  110  when the cylinder connection module  100  changes from the inserted state to the removed state. 
     The pair of B pin rack bars  220 A and  220 B is, for example, shaft members extending in one direction and is disposed parallel to each other along the Y direction on an upper side (+side in the Z direction) of the B pin toothless gear  210 . In addition, the B pin rack bars  220 A and  220 B are disposed around the synchronous gear  230  (see  FIG. 14 ) in the X direction. 
     Each of the B pin rack bars  220 A and  220 B has an engaging part  221  that engages with a locking piece  314   a  of the B pin holding part  314 . The locking piece  314   a  is provided, for example, at both end parts in the Y direction (in the vicinity of the B pins  315 A and  315 B) in the B pin holding part  314 . 
     One B pin rack bar  220 B has a drive side rack part  222  on a surface close to the B pin toothless gear  210 . In addition, the B pin rack bars  220 A and  220 B have synchronization side rack parts  223  (see  FIG. 14 ) on surfaces facing each other in the X direction. Each of the synchronization side rack parts  223  meshes with the synchronous gear  230 . 
     The drive side rack part  222  meshes with the tooth part  211  of the B pin toothless gear  210  only when the boom connection module  200  changes from the inserted state (see  FIG. 11 ) to the removed state (see  FIG. 15B ). 
     Specifically, in the inserted state of the boom connection module  200 , a first end face (not illustrated) of the drive side rack part  222  on the +side in the Y direction abuts on the positioning tooth (not illustrated) in the tooth part  211  of the B pin toothless gear  210  or faces the positioning teeth (not illustrated) in the Y direction via a slight gap. In this state, when the B pin toothless gear  210  rotates in the R 2  direction, the positioning tooth pushes the first end face to the +side in the Y direction, and the one B pin rack bar  220 B moves to the +side in the Y direction. 
     In addition, when the one B pin rack bar  220 B moves to the +side in the Y direction, the synchronous gear  230  rotates, and the other B pin rack bar  220 A moves to the −side in the Y direction (that is, a side opposite to the B pin rack bar  220 B). 
     Note that in a case where the B pin toothless gear  210  rotates in the R 1  direction in the inserted state of the boom connection module  200  illustrated in  FIG. 11 , the drive side rack part  222  does not mesh with the tooth part  211  of the B pin toothless gear  210 . 
     As described above, each of the B pin rack bars  220 A and  220 B moves in a longitudinal direction (Y direction) thereof with the rotation of the B pin toothless gear  210 . 
     The one B pin rack bar  220 B is positioned on the most −side in the Y direction in the inserted state of the boom connection module  200  (see  FIG. 11 ) and is positioned on the most side in the Y direction in the removed state (see  FIG. 15B ). In addition, the other B pin rack bar  220 A is positioned on the most +side in the Y direction in the inserted state of the boom connection module  200  (see  FIG. 11 ) and is positioned on the most −side in the Y direction in the removed state (see  FIG. 15B ). 
     As the one B pin rack bar  220 B moves in the Y direction, one locking piece  314   a  of the B pin holding part  314  and the engaging part  221  of the B pin rack bar  220 B abut on each other. Then, a member of the B pin holding part  314  that supports the B pin  315 B moves in the Y direction, whereby the B pin  315 B changes to an inserted state or a removed state. 
     Similarly, as the other B pin rack bar  220 A moves in the Y direction, the other locking piece  314 a of the B pin holding part  314  and the engaging pare  221  of the B pin rack bar  220 A abut on each other. Then, a member of the B pin holding part  314  that supports the B pin  315 A moves in the Y direction, whereby the B pin  315 A changes to an inserted state or a removed state. 
     In the above-described state change, the B pins  315 A and  315 B move in directions opposite to each other in the Y direction. 
     Note that the movement of the one B bin rack bar  220 B toward the side in the Y direction and the movement of the other B pin rack bar  220 A toward the −side in the Y direction are restricted, for example, by abutment on a stopper (not illustrated) provided in the housing  58 . 
     The B pin biasing mechanism  240  biases the B pin rack bars  220 A and  220 B in directions away from each other. The B pin biasing mechanism  240  includes, for example, a pair of compression coil springs. In the present embodiment, the B pin biasing mechanism  240  is incorporated in the B pin rack bars  220 A and  220 B and biases the B pin rack bars  220 A and  220 B toward the distal end side. 
     When the electric motor  51  rotates in the R 2  direction to bring the boom connection module  200  into the removed state (see  FIG. 15B ) and then the operation of the electric motor  51  stops, the boom connection module  200  is automatically restored to the inserted state (see  FIG. 11 ) by the biasing force of the B pin biasing mechanism  240 . However, in a case where the brake  52  is operating, the boom connection module  200  is not automatically restored to the inserted state, and the removed state is maintained. 
     Note that the B pin biasing mechanism  240  may directly apply biasing force to the B pin rack bars  220 A and  220 B or may apply biasing force via another member. In addition, the B pin biasing mechanism  240  may be omitted, and the boom connection module  200  may be configured to change from the removed state to the inserted state on the basis of the power of the electric motor  51 . Even in this case, from the viewpoint of fail-safe, it is preferable to provide the B pin biasing mechanism  240  and configure so that the boom connection module  200  is restored to the inserted state that is a safe side when the electric motor  51  fails. 
     The lock mechanism  55  prevents external force other than power from the electric motor  51  from acting on the cylinder connection module  100  (for example, the C pin rack bar  120 ) or the boom connection module  200  (for example, the B pin rack bars  220 A and  220 B) to cause the cylinder connection module  100  and the boom connection module  200  to change to the removed state simultaneously. That is, in a state in which one connection mechanism of the boom connection module  200  and the cylinder connection module  100  is operating, the lock mechanism  55  blocks the operation of the other connection mechanism. 
     Referring to  FIGS. 16A to 16C , the lock mechanism  55  will be described.  FIG. 16A  illustrates a state in which the cylinder connection module  100  and the boom connection module  200  are in the inserted state (neutral position), and  FIGS. 16B and 16C  each illustrate a state when the boom connection module  200  changes from the inserted state to the removed state. Note that in  FIGS. 16A to 16C , the C pin toothless gear  110  or the cylinder connection module  100  and the B pin toothless gear  210  of the boom connection module  200  are illustrated as an integrally formed switch gear G. 
     As illustrated in  FIG. 16A  and the like, the lock mechanism  55  has a first projection  551 , a second projection  552 , and a cam member  553  (lock side rotating member). 
     The first projection  551  is provided integrally with the C pin rack bar  120  of the cylinder connection module  100 . Specifically, the first projection  551  is provided at a position adjacent to the input side rack part  121  of the C pin rack bar  120 . 
     The second projection  552  is provided integrally with the one B pin rack bar  220 B of the boom connection module  200 . Specifically, the second projection  552  is provided at a position adjacent to the drive side rack part  222  of the one B pin rack bar  220 B. 
     The cam member  553  is a plate-shaped member having a substantially crescent shape. The cam member  553  has a first cam receiving part  553   a  at one end in a circumferential direction and a second cam receiving part  553   b  at the other end. 
     For example, the cam member  553  is externally fitted and fixed to the transmission shaft  56  at a position shifted in the N direction from a position where the switch gear G is externally fitted and fixed. Note that in the present embodiment, the cam member  553  is externally fitted and fixed between the C pin toothless gear  110  and the B bin toothless gear  210 . That is, the cam member  553  is provided coaxially with the switch year C and rotates around the transmission shaft  56  as a central axis together with the switch gear G with the rotation of the transmission shaft  56 . 
     Note that the cam member  553  may be provided integrally with the switch gear G. In addition, the cam member  553  may be provided integrally with at least one of the C pin toothless Gear  110  and the B pin toothless gear  210 . 
     As illustrated in  FIG. 16B , in a state in which a tooth part G 1  of the switch gear C meshes with the drive side rack part  222  of the B pin rack bar  220 B, the first cam receiving part  553 a of the cam member  553  is positioned on the +side in the Y direction from the first projection  551 . 
     That is, the first cam receiving part  553   a  and the first projection  551  face each other via a slight gap in the Y direction. In this state, even if external force (external force Fa in  FIG. 16B ) acts on the C pin rack bar  120  toward the +side in the Y direction, the external force is absorbed by the gap. 
     When larger external force Fa is applied to the C pin rack bar  120  toward the +side in the Y direction, the C pin rack bar  120  moves from a position illustrated by a two-dot chain line in  FIG. 16B  to a position illustrated by a solid line. In this state, the projection  551  abuts on the first cam receiving part  553   a,  and the movement of the C pin rack bar  120  toward the +side in the Y direction is prevented. 
     In addition, as illustrated in  FIG. 16C , in a state in which the tooth part G 1  of the switch gear G meshes with the input side rack part  121  of the C pin rack bar  120 , the second cam receiving part  553   b  of the cam member  553  is positioned on the +side in the Y direction of the second projection  552 . That is, the second cam receiving part  553   b  and the second projection  552  face each other via a slight gap in the Y direction. In this state, even if external force on the +side in the Y direction (external force Fb in  FIG. 16C ) is applied to the B pin rack bar  220 B, the external force is absorbed by the gap. 
     When larger external force Fb is applied to the B pin rack bar  220 B toward the +side in the Y direction, the B pin rack bar  220 B moves from a position illustrated by a two-dot chain line in  FIG. 16C  to a position illustrated by a solid line in the +side in the Y direction. In this state, the second projection  552  abuts on the second cam receiving part  55  Sb, and the movement of the B pin rack bar  220 B toward the +side in the Y direction is prevented. 
     &lt;Operation of Cylinder Connector Module  100  and Boom Connection Module  200 &gt; 
     Referring to  FIGS. 17A to 17C  and  FIGS. 18A to 18C , an example of operation of the cylinder connection module  100  and the boom connection module  200  will be described. The operation illustrated in  FIGS. 17A to 17C  and  FIGS. 18A to 18C  is, for example, the removal operation of the cylinder connection module  100  and the boom connection module  200  in a case where the distal end boom  31  is extended. 
     Hereinafter, the rotation of the electric motor  51  when the boom connection module  200  is changed from the inserted state to the removed state is referred to as “forward rotation”, and the rotation of the electric motor  51  when the cylinder connection module  100  is changed from the inserted state to the removed state is referred to as “reverse rotation”. 
       FIGS. 17A to 17C  are schematic views for describing the operation of the cylinder connection module  100 .  FIGS. 17A to 17C  illustrate operation in a case where the cylinder connection module  100  changes from the inserted state to the removed state. In  FIGS. 17A to 17C , the C pin toothless gear  110  and the B pin toothless gear  210  are illustrated as the integrally formed switch gear G. In addition, in  FIGS. 17A to 17C , the lock mechanism  55  is omitted. 
     As illustrated in  FIG. 17A , in a contracted state of the distal end boom  31  before being extended, the cylinder connection module  100  is in the neutral state. That is, the C pin  150  is engaged with the C pin receiving part  311  of the distal end boom  31 , and the distal end boom  31  and the cylinder connection module  100  are in a connection state. 
     In a case where the cylinder connection module  100  changes from the inserted state to the removed state, the power of the electric motor  51  is transmitted to the C pins  150 A and  150 B through the following first path and second path. 
     The first path is the C pin toothless gear  110 →the C pin rack bar  120 →the first gear group  130 →the one C pin  150 A. The second path is the C pin toothless gear  110 →the C pin rack bar  120 →the second gear group  140 →the other C pin  150 B. 
     As illustrated in  FIG. 17B , when the electric motor  51  performs reverse rotation, the C pin toothless gear  110  rotates in the R 1  direction. With the rotation of the C pin toothless gear  110 , the C pin rack bar  120  is displaced to the +side in the Y direction (right side in  FIGS. 17A to 17C ). Accordingly, in the first path, the one C pin  150 A is displaced to the −side in the Y direction (left side in  FIGS. 17A to 17C ) via the first gear group  130 . In The second path, The other C pin  150 B is displaced to the +side in the Y direction (right side in  FIGS. 17A to 17C ) via the second gear group  140 . That is, when the cylinder connection module  100  changes from the inserted state to the removed state, the one C pin  150 A and the other C pin  150 B are displaced in directions approaching each other. 
     Finally, as illustrated in  FIG. 7C , the C pins  150 A and  150 B are completely detached from the C pin receiving part  311 , and the cylinder connection module  100  and the distal end boom  31  are brought into a disconnection state. Note that a state change of the cylinder connection module  100  from the removed state to the inserted state is automatically performed on the basis of the biasing force of the C pin biasing mechanism  160 . 
       FIGS. 18A to 18C  are schematic views for describing the operation of the boom connection module  200 .  FIGS. 18A to 18C  illustrate operation in a case where the boom connection module  200  changes from the inserted state to the removed state. In  FIGS. 18A to 18C , the C pin toothless gear  110  and the B pin toothless gear  210  are illustrated as the integrally formed switch gear G. In addition, in  FIGS. 18A to 18C , the lock mechanism  55  is omitted. 
     As illustrated in  FIG. 18A , in the contracted state of the distal end boom  31  before being extended, the cylinder connection module  100  and the boom connection module  200  are in the neutral state. That is, the distal end boom  31  is connected to the intermediate boom  32  via the B pin  315  and is not movable in the telescoping direction with respect to the intermediate boom  32 . 
     In a case where the boom connection module  200  changes from the inserted state to the removed state, the power of the electric motor  51  is transmitted through a path of the B pin toothless gear  210 →the one B pin rack bar  220 B→the synchronous pear  230 →the other B pin rack bar  220 A. 
     As illustrated in  FIG. 18B , when the electric motor  51  performs forward rotation, the B pin toothless gear  210  rotates in the R 2  direction. With the rotation of the B pin toothless gear  210 , the one B pin rack bar  220 B is displaced to the side in the Y direction (right side in  FIGS. 18A to 18C ). In addition, the synchronous gear  230  rotates, and the other B pin rack bar  220 A is displaced to the −side in the Y direction (left side in  FIGS. 18A to 18C ) in response to the rotation of the synchronous gear  230 . That is, when the boom connection module  200  changes from the inserted state to the removed state, the one B pin rack bar  220 B and the other B pin rack bar  220 A are displaced in directions approaching each other. As a result, the B pin holding part  314  connected to the B pin rack bars  220 A and  220 B also contracts, and the B pin  315  held by the B pin holding part  314  is Gradually removed from the proximal end side B pin receiving part  322 . 
     Finally, as illustrated in  FIG. 18C , the B pins  315 A and  315 B are completely detached from the proximal end side B pin receiving part  322 , and the distal end boom  31  and the intermediate boom  32  are brought into the disconnection state. Note that a state change of the boom connection module  200  from the removed state to the inserted state is automatically performed on the basis of the biasing force of the B pin biasing mechanism  240 . 
     &lt;Control During Telescoping Operation&gt; 
       FIG. 19  is a timing chart illustrating an example of control during the extending operation of the telescopic boom  30 . For convenience, a case where the distal end boom  31  is extended from a fully retracted state will be described. Note that the inserted state and the removed state of the B pin  315  correspond to the inserted state and the removed state of the boom connection module  200 , respectively and the inserted state and the removed state of the C pin  150  correspond to the inserted state and the removed state of the cylinder connection module  100 , respectively. Switching between on and off of the electric motor  51 , the brake  52 , and the clutch  61  is controlled by the control device  70 . 
     Sections T 0  to T 1  in  FIG. 19  are initial contracted states of the extending operation, and the cylinder connection module  100  and the boom connection module  200  are in the neutral state (see  FIGS. 17A and 18A ). That is, the distal end boom  31  is connected to the intermediate boom  32  via the B pin  315  and is not movable in the telescoping direction with respect to the intermediate boom  32 . In addition, the C pin  150  is engaged with the C pin receiving part  311  of the distal end boom  31 , and the distal end boom  31  and the cylinder part  42  are in a connection state. 
     States of respective mechanical elements in the sections T 0  to T 1  are as follows. 
     Electric motor  51 : Off 
     Clutch  61 : Off 
     Brake  52 : Off 
     C pin  150  (cylinder connection module  100 ): Inserted state 
     B pin  315  (boom connection module  200 ): Inserted state 
     When receiving the extension operation of the telescopic boom  30  by the operator (timing T 1 ), the control device  70  controls the clutch  61  to bring the clutch  61  into an on state (connected state) and causes the electric motor  51  to perform forward rotation. The B pin  315  gradually changes from the inserted state to the removed state. 
     States of respective mechanical elements in the sections T 1  to T 2  are as follows. 
     Electric motor  51 : On 
     Clutch  61 : On 
     Brake  52 : Off 
     C pin  150  (cylinder connection module  100 ): Inserted state 
     B pin  315  (boom connection module  200 ): Inserted state→Removed state (removal operation) 
     At this time, when the B pin  315  is difficult to remove, for example, due to being caught by the proximal end side B pin receiving part  322  of the intermediate boom  32 , rotating elements in the power transmission path from the electric motor  51  to the boom connection module  200  cannot rotate smoothly, and an overload occurs. Then, there is a risk that a large current flows through the electric motor  51 , resulting is heat generation and burnout. 
     In the present embodiment, the torque limiter  63  is disposed in the power transmission path, and a load applied to the mechanical element is the power transmission path is maintained at a predetermined value or less. Therefore, it is possible to prevent the mechanical element from being damaged due to difficulty in removal of the B pin  315  during the removal operation of the B pin  315 . 
     The control device  70  determines a state of the B pin  315  on the basis of the detection result of the position detection device  54  and the like, and when the B pin  315  changes to the removed state (timing T 2 ), the control device  70  stops the electric motor  51  while maintaining the clutch  61  in an on state. In addition, the brake  52  is turned on to maintain the removed state of the B pin  315 . 
     Note that timing to turn off the electric motor  51  and timing to turn on the brake  52  are appropriately controlled by the control device  70 . For example, by turning on the brake  52  and then turning off the electric motor  51 , it is possible to reliably maintain the removed state of the B pin  315 . 
     At timing T 2 , the B pin  315  is completely detached from the proximal end side B pin receiving part  322 , and the distal end boom  31  and the intermediate boom  32  are brought into the disconnection state. Although not illustrated, in sections T 2  to T 3 , the control device  70  controls the telescoping actuator  40  to move the cylinder part  42  in the extending direction. Accordingly, the distal end boom  31  connected to the cylinder part  42  via the cylinder connection module  100  moves in the extending direction. 
     States of respective mechanical elements in the sections T 2  to T 3  are as follows. 
     Electric motor  51 : Off 
     Clutch  61 : On 
     Brake  52 : On 
     C pin  150  (cylinder connection module  100 ): Inserted state 
     B pin  315  (boom connection module  200 ): Removed state 
     When the distal end boom  31  moves to a predetermined position and is brought into the extended state (timing T 3 ), the control device  70  controls the clutch  61  and the brake  52  to bring the clutch  61  and the brake  52  into an off state. The boom connection module  200  is restored to the neutral state by the biasing force of the B pin biasing mechanism  240 . Accordingly, the B pin  315  changes from the removed state to the inserted state and is inserted into the distal end side B pin receiving part  323 . 
     States of respective mechanical elements in sections T 3  to T 4  are as follows. 
     Electric motor  51 : Off 
     Clutch  61 : Off 
     Brake  52 : Off 
     C pin  150  (cylinder connection module  100 ): Inserted state 
     B pin  315  (boom connection module  200 ): Removed state→Inserted state (insertion operation) 
     As described above, in the insertion operation of the B pin  315 , the boom connection module  200  is restored to the neutral state using the B pin biasing mechanism  240  In this case, when the power transmission path from the electric motor  51  to the boom connection module  200  is connected, the electric motor  51  rotates in a direction opposite to the rotation direction during the removal operation in accordance with the insertion operation of the B pin  315 . Then, the rotating elements including the electric motor  51  may not stop at the neutral position due to inertial force, and thrust for rotating the switch gear G in a direction in which the C pin  150  is removed due to overrun may be generated. 
     In this regard, in the present embodiment, the clutch  61  is disposed in the power transmission path, and the transmission of power from the boom connection module  200  to the electric motor  51  is cut off when the boom connection module  200  is restored to the neutral state using the B pin biasing mechanism  240 . Therefore, during the insertion operation of the B pin  315 , it is possible to prevent the C pin  150  from changing to the removed state temporarily and becoming unstable in operation. 
     When the B pin  315  is completely engaged with the distal end side B pin receiving part  323  (timing T 4 ), the control device  70  changes the C pin  150  to the removed state in order to return the telescoping actuator  40  to a contracted state. That is, at timing T 5 , the control device  70  controls the clutch  61  to bring the clutch  61  into the on state (connected state) and causes the electric motor  51  to perform reverse rotation. The C pin  150  gradually changes from the inserted state to the removed state. 
     States of respective mechanical elements in the sections T 5  to T 6  are as follows. 
     Electric motor  51 : On 
     Clutch  61 : On 
     Brake  52 : Off 
     C pin  150  (cylinder connection module  100 ): inserted state→Removed state (removal operation) 
     B pin  315  (boom connection module  200 ): Inserted state 
     At this time, when the C pin  150  is difficult to remove, for example, due to being caught by the C pin receiving part  311  of the distal end boom  31 , the rotating elements in the power transmission path from the electric motor  51  to the cylinder connection module  100  cannot smoothly rotate, and an overload occurs. Then, there is a risk that a large current flows through the electric motor  51 , resulting in heat generation and burnout. 
     In the present embodiment, the torque limiter  63  is disposed in the power transmission path, and a load applied to the mechanical element in the power transmission path is maintained at a predetermined value or less. Therefore, it is possible to prevent the mechanical element from being damaged due to difficulty in removal of the C pin  150  during the removal operation of the C pin  150 . 
     The control device  70  determines a state of the C pin  150  on the basis of the detection result of the position detection device  54  and the like, and when the C pin  150  changes to the removed state (timing T 6 ), the control device  70  stops the electric motor  51  while maintaining the clutch  61  in the on state. In addition, the brake  52  is brought into an on state, and the C pin  150  is maintained in the removed state. 
     At timing T 6 , the C pin  150  is completely detached from the C pin receiving part  311  of the distal end boom  31 , and the cylinder connection module  100  and the distal end boom  31  are brought into a disconnection state. Although not illustrated, in sections T 6  to T 7 , the control device  70  controls the telescoping actuator  40  to move the cylinder part  42  in a contraction direction. At this time, since the cylinder part  42  is in a disconnection state with respect to the distal end boom  31 , the intermediate boom  32 , and the proximal end boom  33 , the cylinder part  42  moves alone in the contraction direction. 
     States of respective mechanical elements in the sections T 6  to T 7  are as follows. 
     Electric motor  51 : Off 
     Clutch  61 : On 
     Brake  52 : On 
     C pin  150  (cylinder connection module  100 ): Removed state 
     B pin  315  (boom connection module  200 ): Inserted state 
     When the telescoping actuator  40  is brought into the contracted state (timing  17 ), the control device  70  controls the clutch  61  and the brake  52  to bring the clutch  61  and the brake  52  into the off state. The cylinder connection module  100  is restored to the neutral state by the biasing force of the C pin biasing mechanism  160 . Accordingly, the C pin  150  changes from the removed state to the inserted state and engages with the C pin receiving part  321  of the intermediate boom  32 . In addition, the B pin holding part  324  of the intermediate boom  32  is engaged with the B pin rack bars  220 A and  220 B. 
     States of respective mechanical elements in sections T 7  to T 8  are as follows. 
     Electric motor  51 : Off 
     Clutch  61 : Off 
     Brake  52 : Off 
     C pin  150  (cylinder connection module  100 ): Removed state→Inserted state (insertion operation) 
     B pin  315  (boom connection module  200 ): Inserted state 
     As described above, in the insertion operation of the C pin  150 , the cylinder connection module  100  is restored to the neutral state using the C pin biasing mechanism  160 . In this case, when the power transmission path from the electric motor  51  to the cylinder connection module  100  is connected, the electric motor  51  rotates in a direction opposite to the rotation direction during the removal operation in accordance with the insertion operation of the C pin  150 . Then, the rotating elements including the electric motor  51  may not stop at the neutral position due to inertial force, and thrust for rotating the switch gear G in a direction in which the B pin  325  is removed due to overrun may be generated. 
     In this regard, in the present embodiment, the clutch  61  is disposed in the power transmission path, and the transmission of power from the cylinder connection module  100  to the electric motor  51  is cut off when the cylinder connection module  100  is restored to the neutral state using the C pin biasing mechanism  160 . Therefore, it is possible to prevent the B pin  325  from changing to the removed state temporarily during the insertion operation of the C pin  150  and becoming unstable in operation. 
     When the C pin  150  is completely engaged with the C pin receiving part  321  of the intermediate boom  32  (timing T 8 ), the neutral state is maintained. Note that in a case where the intermediate boom  32  is extended, operation similar to the operation described above is performed. In addition, in a case where the distal end boom  31  or the intermediate boom  32  is contracted, operation in a direction opposite to a direction described above is performed. 
     Here, lubricant oil is generally applied to the mechanical elements constituting the pin insertion/removal actuator  50  so that the removal operation and the insertion operation of the B pin  315  and the C pin  150  are smoothly performed. In this case, if the viscosity of the lubricant oil increases due to ambient environmental temperature or aging, the insertion and removal operation of the B pin  315  and the C pin  150  may be hindered. In particular, since the insertion operation of the B pin  315  and the C pin  150  is performed using the biasing force, the lubricant oil of high viscosity may become resistance and operation time may become unstable. 
     Therefore, in the present embodiment, when the C pin  150  is restored to the inserted state by the biasing force of the C pin biasing mechanism  160  and when the B pin  315  is restored to the inserted state by the biasing force of the B pin biasing mechanism  240 , the control device  70  executes motor assist processing of operating the electric motor  51 . 
       FIG. 20  is a timing chart for describing the extending operation of the telescopic boom  30  to which the motor assist processing is applied. 
     As illustrated in  FIG. 20 , in a case where the insertion operation of the B pin  315  is performed in the sections T 3  to T 4 , the control device  70  causes the electric motor  51  to perform reverse rotation for a short period of time (for example, 0.01 to 0.5 sec). In addition, in a case where the insertion operation of the C bin  150  is performed. in the sections T 7  to T 8 , the control device  70  causes the electric motor  51  to perform forward rotation. As a result, it is possible to release a state in which the C pin  150  or the B pin  315  is difficult to move due to the viscosity of the lubricant oil by the power of the electric motor  51 , and thereafter it is possible to smoothly restore to the neutral state by the subsequent biasing force of the C pin biasing mechanism  160  or the B pin biasing mechanism  240 . 
     This motor assist processing may be always performed during the insertion operation of the B pin  315  and the C pin  150  or may be performed only in a case where a predetermined condition is satisfied. The predetermined condition includes ambient environmental temperature (for example, −10° C. or less), use time, and the like. In addition, the operator may manually set whether to perform the motor assist processing. In addition, the motor assist processing may be selectively performed on the B pin  315  and the C pin  150 . 
     Furthermore, the control device  70  may determine the drive start timing and drive time of the electric motor  51  in the motor assist processing according to the environmental temperature. As a result, since appropriate motor assist processing is performed, it is possible to prevent thrust from being generated in a direction in which the C pin  150  or the B pins  315  and  325  are removed due to overrun. 
     As described above, the mobile crane  1  (work machine) according to the present embodiment includes: the telescopic boom  30  having the first boom (for example, the distal end boom  31 ) and the second boom (for example, the intermediate boom  32 ) that overlap each other in a telescopic manner; the telescoping actuator  40  that moves the first boom in the telescoping direction with respect to the second boom; the electric motor  51  (electrical drive source) provided in the cylinder part  42  (movable portion) of the telescoping actuator  40 ; the C pin  150  (first fixing pin) that connects the telescoping actuator  40  and the first boom; the C pin biasing mechanism  160  (first biasing mechanism) that biases the C pin  150  to maintain a connection state between the telescoping actuator  40  and the first boom; the cylinder connection module  100  (first connection mechanism) that operates on the basis of power of the electric motor  51  and switches between the connection state and a disconnection state between the telescoping actuator  40  and the first boom by inserting and removing the C pin  150 ; the B pins  315  and  325  (second fixing pins) that connect the first boom and the second boom; the B pin biasing mechanism  240  (second biasing mechanism) that biases the B pins  315  and  325  to maintain a connection state between the first boom and the second boom; the boom connection module  200  (second connection mechanism) that operates on the basis of the power of the electric motor  51  and switches between the connection state and a disconnection state between the first boom and the second boom by inserting and removing the B pins  315  and  325 ; and the clutch  61  that is disposed in the power transmission path from the electric motor  51  to the cylinder connection module  100  and the boom connection module  200  and discretionally intermittently transmits the power of the electric motor  51  to the cylinder connection module  100  and the boom connection module  200 . 
     Specifics the clutch  61  cuts off the power of the electric motor  51  (electrical drive source) at least when the C pin  150  (first fixing pin) is restored by the biasing force of the C pin biasing mechanism  160  (first biasing mechanism) and/or when the B pins  315  and  325  (second fixing pins) are restored by the biasing force of the B pin biasing mechanism  240  (second biasing mechanism). 
     According to the mobile crane  1 , since the cylinder connection module  100  and the boom connection module  200  are electric, it is not necessary to provide a hydraulic circuit as is conventional structures in the internal space of the telescopic boom  30 . Therefore, it is possible to improve the degree of freedom in terms of design in the internal space of the telescopic boom  30  by effectively utilizing a space used by the hydraulic circuit. 
     In addition, the clutch  61  is disposed in the power transmission path, and the transmission of the power from the cylinder connection module  100  or the boom connection module  200  to the electric motor  51  is cut off when the neutral state is restored using the C pin biasing mechanism  160  or the B pin biasing mechanism  240 . Thus, it is possible to prevent the C pin  150  or the B pins  315  and  325  from changing to the removed state temporarily during the insertion operation of the B pins  315  and  325  or the C pin  150  and becoming unstable in operation. 
     Therefore, according to the mobile crane  1 , it is possible to improve the degree of freedom in terms of design around a telescopic boom  30  and an increase in the reliability when the boom  30  is telescoping. 
     In addition, the mobile crane  1  includes the speed reducer  62  that decelerates a driving speed of the electric motor  51  (electrical drive source) and outputs the decelerated driving speed, and the clutch  61  is disposed between the electric motor  51  and the speed reducer  62 . As a result, it is possible to reduce the transmission torque capacity of the clutch  61  and downsize the clutch  61 . 
     In addition, in the mobile crane  1 , the clutch  61  includes an electromagnetic clutch, a mechanical clutch, or a torque diode. As a result, it is possible to appropriately select a general-purpose clutch as necessary and easily switch between transmission and cutoff of the power from the electric motor  51 . 
     Although the invention made by the present inventors has been specifically described above on the basis of the embodiment, the present invention is not limited to the embodiment described above, and can be modified without departing from the gist thereof. 
     For example, as the electric motor  51 , a hollow motor having a hollow stator disposed on the inner side and a rotor disposed on the outer side may be applied, the hollow motor may be disposed on the outer periphery of the piston rod part  41 , and a transmission gear (not illustrated) of the transmission mechanism  53  may mesh with a Gear provided on the rotor. 
     In addition, the disposition of the electric motor  51  described in the embodiment is an example, and the electric motor  51  may be disposed so that the output shaft (not illustrated) extends in the Y direction or the Z direction. 
     In addition, the electric motor  51  is not limited to the rotary motor, and a linear motor (linear motion actuator) that outputs linear motion can also be used. 
     In addition, the work machine according to the present invention is not limited to the mobile crane and can also be applied to other work machines (for example, a vehicle for work at height) including a telescopic boom. 
     It should be understood that the embodiment disclosed herein is illustrative in all respects and not restrictive. The scope of the present invention is indicated not by the description above but by the claims, and it is intended that meanings equivalent to the claims and all modifications within the scope are included. 
     All disclosed contents of the description, drawings, and abstract included in the Japanese application of Japanese Patent Application No. 2019-151521 filed on Aug. 21, 2019 are incorporated by reference into the present application. 
     REFERENCE SIGNS LIST 
     
         
           1  Mobile crane (work machine) 
           30  Telescopic boom 
           31  Distal end boom 
           311  C pin receiving part 
           314  B pin holding part 
           315 ,  315 A,  315 B B pin 
           32  Intermediate boom 
           321  C pin receiving part 
           322  Proximal end side B pin receiving part 
           323  Distal end side B pin receiving part 
           324  B pin holding part 
           325  B pin 
           33  Proximal end boom 
         A Telescopic device 
           40  Telescoping actuator 
           41  Piston rod part 
           42  Cylinder part (movable portion) 
           50  Pin insertion/removal actuator 
           51  Electric motor (electrical drive source) 
           52  Brake 
           53  Transmission mechanism 
           54  Position detection device 
           55  Lock mechanism 
           56  Transmission shaft 
           61  Clutch 
           62  Speed reducer 
           63  Torque limiter 
           100  Cylinder connection module (first connection mechanism) 
           110  C pin toothless gear 
           120  C pin rack bar 
           130  First gear group 
           140  Second gear group 
           150 ,  150 A,  150 B C pin 
           160  C pin biasing mechanism (first biasing mechanism) 
           200  Boom connection module (second connection mechanism) 
           210  B pin toothless gear 
           220 A,  220 B B pin rack bar 
           230  Synchronous gear 
           240  B pin biasing mechanism (second biasing mechanism)