Patent Publication Number: US-2021187674-A1

Title: Device for cutting structure and method for cutting structure

Description:
TECHNICAL FIELD 
     The present invention relates to a device used to cut a cutting object such as a steel member and a method for cutting the cutting object. 
     BACKGROUND ART 
     Examples of known methods for cutting a cutting object such as a steel member include a method of cutting the cutting object by using a hydraulic cutter mounted on a construction machine such as a hydraulic excavator. However, this method has a limit for the size of a steel member or the like to be cut by the method; therefore, there can be a case of failing to completely cut a large steel member used in a large-scale structure or the like. In this case, performed is cutting a cutting object as deeply as possible by use of a hydraulic cutter or cutting down to some extent manually by a worker with a gas cutting machine and then twisting off it by use of a hydraulic cutter or the like. The former case has a possibility of failing to make a cut in the steel member by a sufficient depth to thereby cause an excessive load on the hydraulic cutter to twist off the steel member, which may shorten the life of the working device. The latter case involves a problem of forcing the worker to work at a high and unstable location. 
     As means for solving the above-described problems, for example, Patent Literature 1 discloses a cutting device including: a plurality of steel clumps (grasp unit) axially spaced to support a steel member to be cut; a plurality of cutting tools; a moving means for moving the plurality of cutting tools along a slide frame, and a controller to which the size and other information of the steel member is input in advance. The controller moves the cutting device through remote control in the axial direction, the transverse direction, and the height direction of the steel member to enable the cutting device to cut the steel member. 
     Besides, Patent Literature 2 discloses a demolition attachment including: a holding device provided to a distal end of a boom of a construction machine to hold a cutting object; a shifter attached to a frame of the holding device, and a cutting device mounted on the moving device and including a cutting torch. The shifter moves the cutting device relatively to the holding device to allow the cutting device to cut a steel member that is held by the holding device. 
     The cutting device disclosed in Patent Literature 1, however, requires the size and other information of the steel member to be input in advance to the controller for controlling the operation of the cutting device. Moreover, the plurality of cutting tools has to make respective individual and independent movements of each other, which makes the operation thereof difficult and generates necessity of a complex mechanism and structure. 
     The demolition attachment disclosed in Patent Literature 2, in which respective positions at which the cutting device starts and stops a cutting operation cannot be specified, has a possibility of needless operation of the cutting device. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. 2007-146571 
     Patent Literature 2: Japanese Unexamined Patent Publication No. 2005-002688 
     SUMMARY OF INVENTION 
     It is an object of the present invention to provide a device and a method for efficiently cutting a cutting object to be cut. 
     To achieve the above-mentioned object, the inventors of the present application have come up with the idea of detecting the position of a cutting object by utilization of a grasp unit that grasps the cutting object and make use of the detected position in positioning a cutting unit. 
     Provided is a cutting device for cutting a cutting object included in a structure, the cutting device comprising: a grasp unit including a first grasper and a second grasper that are movable in an opening and closing directions, in which direction the first grasper and the second grasper come close to each other or go away from each other, to grasp the cutting object therebetween in the opening and closing directions; a drive mechanism that moves the first grasper and the second grasper relatively to each other in the opening and closing directions; a cutting unit disposed side by side with the first grasper and the second grasper and configured to cut the cutting object with movement of the cutting unit in a cutting direction along with the opening and closing directions; a main unit supporting the first and second graspers movably in the opening and closing directions and supporting the cutting unit movably in the cutting direction; a feed mechanism that moves the cutting unit in the opening and closing directions; and a position setting means that sets a cutting start position and a cutting end position based on respective positions of the first grasper and the second grasper that are grasping the cutting object, respectively. The cutting start position is a position at which an operation of the cutting unit and the movement of the cutting unit for cutting the cutting object are started, and the cutting end position is a position at which the operation of the cutting unit and the movement of the cutting unit for cutting the cutting object are ended. The limitation “sets a cutting start position and a cutting end position based on respective positions of the first grasper and the second grasper” does not necessarily require that the cutting start position exactly agrees with the position of the first grasper and the cutting end position exactly agrees with the position of the second grasper, but encompasses the aspect to set the cutting start position to allow the operation of the cutting unit is started at a position slightly before the position of the first grasper and the aspect to set the cutting end position to allow the operation of the cutting unit to be stopped at a position slightly ahead of the position of the second grasper. 
     Also provided is a method for cutting a cutting object included in a structure by using a cutting device, the method comprising: a cutting device preparation step of preparing the cutting device that includes a grasp unit including a first grasper and a second grasper that are movable in an opening and closing directions, in which direction the first grasper and the second grasper come close to each other or go away from each other, to grasp the cutting object therebetween in the opening and closing directions, a drive mechanism that moves the first grasper and the second grasper relatively to each other in the opening and closing directions, a cutting unit disposed side by side with the first grasper and the second grasper to cut the cutting object with a movement of the cutting unit in a cutting direction along with the opening and closing directions, a main unit supporting the first and second graspers movably in the opening and closing directions and supporting the cutting unit movably in the cutting direction, and a feed mechanism that moves the cutting unit in the opening and closing directions; a grasp unit positioning step of positioning the cutting device to locate the cutting object between the first grasper and the second grasper; a grasping step of moving the first grasper and the second grasper relatively to each other in a closing direction that is one of the opening and closing directions, the first grasper and the second grasper coming close to each other in the closing direction, to thereby cause the first grasper and the second grasper to grasp the cutting object; a position setting step of setting a cutting start position based on the position of the first grasper and setting a cutting end position based on the position of the second grasper when the first grasper and the second grasper are grasping the cutting object; a cutting unit positioning step of causing the feed mechanism to move the cutting unit in the opening and closing directions to position the cutting unit at the cutting start position; and a cutting step of causing the feed mechanism to move the cutting unit from the cutting start position to the cutting end position to cut the cutting object. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic side view of a demolition machine to which a cutting device according to a first embodiment of the present invention is attached. 
         FIG. 2  is an elevational view of essential components of the cutting device according to the first embodiment. 
         FIG. 3  is a side view of the essential components of the cutting device according to the first embodiment. 
         FIG. 4  is a sectional view taken along line IV-IV of  FIG. 3 . 
         FIG. 5  is a perspective view of a part of the cutting device according to the first embodiment. 
         FIG. 6  is a perspective view of another part of the cutting device according to the first embodiment. 
         FIG. 7  is a perspective view for explaining a state of the cutting device according to the first embodiment when cutting a cutting object. 
         FIG. 8  is an enlarged perspective view of a grasp unit of the cutting device according to the first embodiment. 
         FIG. 9  is a sectional view taken along line IX-IX of  FIG. 8 . 
         FIG. 10  is a perspective view of a cutting unit of the cutting device according to the first embodiment. 
         FIG. 11  is an enlarged perspective view of part of a cutting unit of a cutting device according to a second embodiment of the present invention. 
         FIG. 12  is an enlarged perspective view of part of a cutting unit of a cutting device according to a third embodiment of the present invention. 
         FIG. 13  is an elevational view of a grasp unit and a cutting unit of a cutting device according to a fourth embodiment of the present invention. 
         FIG. 14  is a perspective view of a grasp unit and a cutting unit of a cutting device according to a fifth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below will be described embodiments of the present invention with reference to the accompanying drawings. It should be understood that the preferred embodiments described hereinafter are merely illustrative, and are not intended to limit the scope, application and use of the present invention in any way. 
       FIG. 1  shows a demolition machine  1  according to a first embodiment 1 of the present invention. The demolition machine  1  includes: a lower travelling body  2 ; un upper slewing body  3  mounted on the lower travelling body  2  so as to be slewable; a boom  6 ; a crushing device  7 ; and a cutting device  20  that is an example of a cutting device according to the present invention. On the upper slewing body  3  are mounted a cab  4  and a machine room  5 . The boom  6  is attached to a front part of the upper slewing body  3  in a raisable and lowerable manner. The crushing device  7  is detachably attached to a distal end of the boom  6 . In the present invention, directional terms such as “front and rear direction” “vertical direction” and “left and right directions”, unless otherwise specified, refer to the front and rear direction, the vertical direction, and the left and right directions when viewed by an operator seated in the driver&#39;s cab  4  of the demolition machine  1  who is facing forward. 
     The boom  6  according to this embodiment includes a first boom member  6   a  having a proximal end attached to the front part of the upper slewing body  3  in a raisable and lowerable manner and a distal end opposite to the proximal end, a second boom member  6   b  having a proximal end and a distal end opposite thereto, the crushing device  7  being detachably attached to the distal end, and a coupling member  6   c  coupling the proximal end of the second boom  6   b  to the distal end of the first boom  6   a  in a raisable and lowerable manner. The first boom member  6   a  is raised and lowered through extension and retraction of a boom cylinder  8   a,  and the second boom member  6   b  is raised and lowered through extension and retraction of a boom cylinder  8   b.  The crushing device  7  is brought into vertical rotational movement about a horizontal axis by extension and retraction of the working cylinder  8   c.    
     The crushing device  7  includes, for example, a crusher body  9  detachably attached to the distal end of the second boom member  6   b,  a pair of hydraulic cylinders  10 ,  10  connected to the crusher body  9  through a not-graphically-shown rotary mechanism, and a pair of crusher claws  11  supported on the crusher body  9  rotatably about an axis J. The paired hydraulic cylinders  10  is extended and retracted to thereby move respective proximal ends of the paired crusher claws  11 , respectively, in a direction in which the paired crusher claws  11  come close to each other or go away from each other, thereby moving respective distal ends of the paired crusher claws  11  in opening and closing directions. Being moved in the opening and closing directions, the crusher claws  11  make crushing actions such as grasping a cutting object T shown in  FIG. 7 , for example, a steel member, or twisting off the cutting object T while grasping it. 
     To be used for cutting the cutting object T, the cutting device  20  is connected to the second boom member  6   b  through an arm  12  and a suspension support member  13 . The arm  12  includes a proximal end coupled to the second boom member  6   b  in a raisable and lowerable manner and a distal end opposite to the proximal end. The cutting device  20  includes a proximal end to be attached to the distal end of the arm  12 . In the first embodiment  1 , illustrated as the cutting object T is an H-section steel member including a web and a pair of flanges. The cutting object T, however, is not limited to an H-section steel member but permitted to be other steel materials. In addition, the cutting object according to the present invention is not limited to a steel member. 
     The arm  12  includes, for example, four cylindrical members  12   a  to  12   d  forming a telescopic structure. The cylindrical members  12   a  to  12   d  are aligned in this order from their distal end. With regard to adjacent ones of the cylindrical members  12   a  to  12   d,  the tubular member on the proximal side has a greater diameter than that of the tubular member on the distal side. The arm  12  is attached with not-graphically-shown telescoping means, which moves the tubular members  12   a  to  12   d  relatively to each other in a retracting direction such that the tubular members  12   a  to  12   c  are retracted into their respective adjacent tubular members  12   b  to  12   d  on the proximal side thereof, thereby shortening the entire arm  12 ; in contrast, the telescoping means moves the tubular members  12   a  to  12   d  relatively to each other in a direction such that the tubular members  12   a  to  12   c  are protruded to the distal side from the respective adjacent tubular members  12   b  to  12   d  located on the proximal side, thereby lengthening the entire arm  12 . The tubular member  12   d  located at the rearmost end and having the largest diameter has a rear end, which is connected to a lower surface of the second boom member  6   b  rotatably, for example, through a not-graphically-shown pin. 
     The tubular member  12   d  is connected with an arm cylinder  14  to raise and lower the arm  12 . The arm cylinder  14  includes a rod  14   a  and a rear end opposite thereto, the rod  14   a  having a distal end connected to the rear end of the tubular member  12   d,  the rear end being connected rotatably to the second boom member  6   b.  The arm cylinder  14  is extended and retracted to thereby raise and lower the arm  12 . 
     The tubular member  12   d  has a lower surface, from which a hook  17  is suspended. The hook  17 , which is provided to hang the cutting device  20  in a stored state, is able to be engaged with an engagement portion  20   a  provided in a lower end of the cutting device  20 . 
     As shown in  FIG. 1 , the suspension support member  13  is connected to a distal end of the tubular member  12   a  located at the most distal end and having the smallest diameter in the arm  12 , extending downward in a direction substantially orthogonal to the tubular member  12   a.  The suspension support member  13  includes an upper end to be connected to the tubular member  12   a  and a lower end that forms a suspension connection portion  13   a,  from which the cutting device  20  is suspended through a direction change mechanism  16 . 
     The cutting device  20  includes: a grasp unit  40  that is actuated in the opening and closing directions to grasp the cutting object T, a main unit  21  that supports the grasp unit  40 , a drive mechanism  49  that actuates the grasp unit  40  in the opening and closing directions, a cutting unit  60  for cutting the cutting object T, a feed mechanism  65  that moves the cutting unit  60 , a first detector  70   a,  a second detector  70   b,  and a controller. The grasp unit  40  includes a first grasper  50   a  and a second grasper  50   b,  and the drive mechanism  49  includes a first hydraulic cylinder  45   a  and a second hydraulic cylinder  45   b  that are connected to the first and second graspers  50   a  and  50   b,  respectively, to form a first drive mechanism  49   a  and a second hydraulic cylinder  49   b,  respectively. The first and second detectors  70   a,    70   b  detect respective positions of the first and second graspers  50   a,    50   b,  respectively. 
     As shown in  FIGS. 2, 3, and 7 , the main unit  21  includes a first main section  21 A, and a second main section  21 B coupled to the first main section  21 A through a turning mechanism  26 . The first main section  21 A includes a suspension plate  22  and a main plate  23 , and the second main section  21 B includes a support bracket  24 , a pair of holding pieces  25   a  and  25   b,  a pair of guide shafts  41   a  and  41   b,  a pair of upper and lower support plates  44 , and a position adjustment mechanism  43 . 
     The suspension plate  22  is formed of a plate shaped to extend in the opening and closing directions (in the vertical direction in  FIGS. 2, 3, and 7 ), including an upper end connected to the direction change mechanism  16  and a lower end opposite to the upper end. The main plate  23  is joined to a side surface of the lower end of the suspension plate  22  to extend in a left and right directions substantially orthogonal to the suspension plate  22 . The support bracket  24  is connected to the main plate  23  through the turning mechanism  26  so as to be turnable about a predetermined turn axis. The turn axis extends in a turn-axis direction (in the front and rear direction in this embodiment) that is orthogonal to both the opening and closing directions and the left and right directions. The support bracket  24  includes a proximal wall  24   a  and left and right side walls  24   b.  The proximal wall  24   a  is coupled to the turning mechanism  26  so as to extend along a plane orthogonal to the turn axis. The left and right side walls  24   b  protrude from the left and right edges of the proximal wall  24   a  in a direction orthogonal thereto (frontward in this embodiment). In  FIG. 7 , the support bracket  24  is partially omitted for descriptive purpose. 
     As shown in  FIGS. 1, 3, 5, and 7 , the upper end of the suspension plate  22  has a shape curved to protrude frontward, provided with a suspension hole  22   a.  Through a pin or the like inserted into the suspension hole  22   a  and the direction change mechanism  16 , the whole cutting device  20  including the suspension plate  22  is coupled to a lower part of the direction change mechanism  16 . An upper part of the direction change mechanism  16  is connected to the suspension connection portion  13   a  rotatably about a horizontal axis relatively to the suspension support member  13 . 
     The turning mechanism  26  is provided to turn the support bracket  24  and the other components constituting the second main section  21 B about the turn axis relatively to the suspension plate  22  and the main plate  23  constituting the first main section  21 A, including a turning motor  26   a  as shown in  FIGS. 3 and 7 . The turning motor  26   a  is mounted on a rear surface of the main plate  23 , that is, a surface opposite to a front surface that faces the support bracket  24 . The turning motor  26   a  includes an output shaft connected to the support bracket  24 , and makes an action of turning the support bracket  24  about the turn axis within a predetermined angular range. The turn of the support bracket  24  enables a grasping direction in which the grasp unit  40  grasps the cutting object T to be changed, as described later. 
     As shown in  FIG. 5 , the first and second guide pieces  25   a  and  25   b  are provided to longitudinally (verticaly in  FIG. 5 ) opposite ends of the support bracket  24  at respective positions different from each other with respect to the left and right directions of the support bracket  24 , being integrally secured to the support bracket  24 , for example, by welding. The first and second guide pieces  25   a  and  25   b  arc formed with respective through-holes that allow the first and second guide shafts  41   a  and  41   b  to pass through the first and second guide pieces  25   a  and  25   b,  respectively. 
     As shown in  FIGS. 4 and 6 , the first and second guide shafts  41   a  and  41   b  extend vertically inside the left and right side walls  24   b  of the support bracket  24 . Specifically, the first and second guide shafts  41   a  and  41   b  are retained by the first and second guide pieces  25   a  and  25   b  so as to extend vertically beyond the upper and lower ends of the support bracket  24 , in a state that the first guide shaft  41   a  passes through the through-hole of the first guide piece  25   a  and the second guide shaft  41   b  passes through the through-hole of the second guide piece  25   b.  The upper one of the paired mounting plates  44  interconnects respective upper ends of the first and second guide shafts  41   a  and  41   b,  and the lower one of the paired mounting plates  44  interconnects respective lower ends of the first and second guide shafts  41   a  and  41   b.    
     The first grasper  50   a  of the grasp unit  40  includes a first base plate  58   a  serving as a base member, a first restriction wall  57   a,  and a first grasping contact member  52   a.  The second grasper  50   a,    50   b  includes a second base plate  58   b  serving as a base member, a second restriction wall  57   b,  and a second grasping contact member  52   b.    
     Each of the first and second base plates  58   a  and  58   b  has a front part and a rear part aligned in the front and rear direction. Respective front parts of the first and second base plates  58   a,    58   b  forms a first grasp plate portion  51   a  and a second grasp plate portion  51   b  shown in  FIGS. 6 and 7 , respectively. The first and second grasp plate portions  51   a  and  51   b  are paralleled and opposed to each other in the opening and closing directionse so as to come into contact with the cutting object T to grasp the cutting object T. 
     The first and second restriction walls  57  protrude inward in the opening and closing directions from respective longitudinally middle parts of the first and second base plates  58   a,    58   b,  respectively, each of the middle parts setting the boundary between the front part and the rear part in each of the first and second base plates  58   a,    58   b.  The first and second restriction walls  57   a  and  57   b  can come into contact with the cutting object T when the first and second graspers  50   a  and  50   b  are moved by the operated hydraulic cylinders  45   a  and  45   b  to cause the grasp unit  40  to grasp the cutting object T thereby preventing the first and second graspers  50   a  and  50   b  from contact with the first and second hydraulic cylinders  45   a  and  45   b.    
     Respective rear ends (on the back side of the drawing sheet of  FIG. 7 ) of the first and second base plates  58   a,    58   b  are formed with a first hole  55   a  and a second hole  55   b,  respectively. The first and second guide shafts  41   a  and  41   b  pass through the first hole  55   a  and the second hole  55   b,  whereby the first and second graspers  50   a  and  50   b,  which include the first and second base plates  58   a  and  58   b,  respectively, are supported on the second main section  21 B slidably in the opening and closing directions along the first and second guide shafts  41   a  and  41   b.    
     As shown in  FIGS. 8 and 9 , in the first and second grasp plates  51   a  and  51   b,  the first and second grasping contact members  52   a,    52   b  are disposed on respective inner sides, i.e., respective sides where the first and second grasping contact members  52   a,    52   b  being capable of making direct contact with the cutting object T, of the front parts of the first and second base plates  58   a,    58   b  with respect to the opening and closing directions. The first and second grasping contact members  52   a  and  52   b  are made of, for example, a heat-resistant resin. While  FIGS. 8 and 9  show only the first grasper  50   a  for descriptive purpose, the second grasper  50   b  has the same configuration. 
     The first and second grasping contact members  52   a,    52   b  are mounted on respective front parts of the first and second base plates  58   a,    58   b,  respectively, through a plurality of pins  54  and a plurality of springs  53  each serving as a biasing member. In a state where the first and second grasping contact members  52   a,    52   b  ( FIG. 9  shows only the first grasping contact member  52   a ) are overlaid on respective front parts of the first and second base plates  58   a,    58   b  ( FIG. 9  shows only the first base plate  58   a ) in the plate thickness direction thereof, each of pins  54  penetrates either of the first and second grasping contact members  52   a,    52   b  and either of the front parts in the plate thickness direction, thereby coupling respective front parts of the first and second base plates  58   a,    58   b  and the first and second grasping contact member  52   a,    52   b,  respectively, with allowing the first and second grasping contact members  52   a,    52   b  to make relative movement in the plate thickness direction (opening and closing directions) to respective front parts of the first and second base plates  58   a,    58   b,  respectively. The plurality of springs  53  are disposed around the plurality of pins  54 , respectively, to be interposed between either of respective front parts of the first and second base plates  58   a,    58   b  and either of the first and second grasping contact members  52   a,    52   b.    
     Respective front parts of the first and second base plates  58   a,    58   b  and the first and second grasping contact members  52   a,    52   b  mounted thereon as mentioned above form the first grasp plate portion  51   a  and the second grasp plate portion  51   b,  respectively, wherein the first and second grasping contact members  52   a  and  52   b  are biased by the resilient force of the springs  53 , with respect to the first and second base plates  58   a  and  58   b,  in respective closing directions each being a direction in which the first and second grasping contact members  52   a  and  52   b  come close to each other in the opening and closing directions. The biasing force effectively restrains the first and second grasping contact members  52   a  and  52   b  constituting the first and second graspers  50   a  and  50   b  from being moved in respective opening directions in which they go away from each other, thereby enabling the first and second grasping contact members  50   a  and  50   b  to grasp the cutting object T more reliably and stably. Respective surfaces of the first and second grasping contact members  52   a  and  52   b  are provided with not-graphically-shown fine irregularities, which hinder the surfaces from slipping against the grasped cutting object T. 
     The second main section  21 B further includes a pair of first projecting portions  56   a  and a pair of second projecting portions  56   b.  The first projecting portions  56   a  project from the rear end of the first base plate  58   a  to be interposed between the first restriction wall  57   a  and the rear end. The second projecting portions  56   b  project from the rear end of the second base plate  58   b  to be interposed between the second restriction wall  57   b  and the rear end. 
     The first and second hydraulic cylinders  45   a  and  45   b  constituting the drive mechanism  49  are hydraulic actuators that are extended and retracted by supply of hydraulic fluid to thereby move the first grasper  50   a  and the second grasper  50   b,  respectively, in the opening and closing directions, specifically, in opposite directions to move them to come close to each other and to go away from each other. The first hydraulic cylinder  45   a  includes a first rod  46   a  having a distal end, i.e. a longitudinally outer end, which is connected to the first projecting portions  56   a.  The second hydraulic cylinder  45   b  includes a second rod  46   b  having a distal end, i.e. a longitudinally outer end, which is connected to the second projecting portions  56   b.  In the present embodiment, the first hydraulic cylinder  45   a  constituting the first drive mechanism  49   a  for moving the first grasper  50   a  and the second hydraulic cylinder  45   b  constituting the second drive mechanism  49   b  for moving the second grasper  50   b  are able to move the first and second graspers  50   a  and  50   b  individually, which allows the cutting object T to be grasped efficiently and reliably. Alternatively, it is also possible to move both the first and second graspers  50   a  and  50   b  through a single drive mechanism. 
     As shown in  FIG. 7 , through the extension and retraction of the first rod  46   a  of the first hydraulic cylinder  45   a,  the first grasper  50   a  is moved in the opening and closing directions (vertically) along the first guide shaft  41   a  while being guided by the first guide shaft  41   a.  Similarly, through the extension and retraction of the second rod  46   b  of the second hydraulic cylinder  45   b,  the second grasper  50   b  is moved in the opening and closing directions along the second guide shaft  41   b  while being guided by the second guide shaft  41   b.    
     When the first and second rods  46   a  and  46   b  of the first and second hydraulic cylinders  45   a  and  45   b  extend to move the first and second graspers  50   a  and  50   b  greatly in the respective opening directions, respectively, the mounting plate  44  abuts against the first and second graspers  50   a  and  50   b  thereby hindering further movement of the first and second graspers  50   a  and  50   b.    
     The position adjustment mechanism  43  is to adjust the midway position between the first and the second graspers  50   a  and  50   b  relative to the second main section  21 B, namely, the exact middle position between the first and the second graspers  50   a  and  50   b  in the grasping direction, so as to allow the first and second graspers  50   a  and  50   b  to grasp the cutting object T regardless of the relative position of the main unit  21  to the cutting object T, the position adjustment mechanism  43  including a first block  42   a  holding the first hydraulic cylinder  45   a,  a second block  42   b  holding the second hydraulic cylinder  45   b,  a first spring  43   a  biasing the first block  42   a  upward, and a second spring  43   b  biasing the second block  42   b  downward. 
     The first and second blocks  42   a,    42   b  are mounted on respective middle parts of the first guide shafts  41   a,    41   b  so as to be slidable in respective longitudinal directions of the first and second guide shafts  41   a,    41   b  (in directions parallel to the opening and closing directions; vertically in this embodiment), respectively. The first block  42   a  and the second block  42   b  are integrally coupled to each other at their respective positions different from each other with respect to the axial direction of the first and second guide shafts  41   a  and  41   b.  The first spring  43   a  is disposed around the first guide shaft  41   a  to be interposed between the first guide piece  25   a  and the first block  42   a,  thereby biasing the first block  42   a  upward, i.e. in the opening direction of the first grasper  50   a.  The second spring  43   b  is disposed around the second guide shaft  41   a  to be interposed between the second guide piece  25   b  and the second block  42   b,  thereby biasing the second block  42   b  downward, i.e. in the opening direction of the second grasper  50   b.    
     The first and second hydraulic cylinders  45   a,    45   b  are disposed frontward of the first and second guide shafts  41   a,    41   b  in parallel thereto, respectively, being secured to the first and second blocks  42   a,    42   b,  respectively. Specifically, a pair of first brackets  47   a  protrude from the first block  42   a  toward the first hydraulic cylinder  45   a,  i.e. frontward, and a pair of second brackets  47   b  protrude from the second block  42   b  toward the second hydraulic cylinder  45   b,  i.e. frontward. On the other hand, the first hydraulic cylinder  45   a  has an upper end, which is provided with a first connecting portion  48   a,  and the second hydraulic cylinder  45   b  has a lower end, which is provided with a second connecting portion  48   b.  The first connecting portion  48   a  is interposed between the paired first brackets  47   a,  and a pin or the like penetrates them to thereby connect the upper end of the first hydraulic cylinder  45   a  to the first block  42   a  rotatably about an axis extending in the left and right directions. The second connecting portion  48   b  is interposed between the paired second brackets  47   b,  and a pin or the like penetrates them to thereby connect the upper end of the second hydraulic cylinder  45   b  to the second block  42   b  rotatably about an axis extending in the left and right directions. 
     As shown in  FIGS. 2, 6 and 7 , the first and second detectors  70   a  and  70   b  detect information on respective positions of the first and second graspers  50   a  and  50   b,  respectively, when they are grasping the cutting object T. 
     The first detector  70   a  includes a first detector body  71   a  and a first stroke guide  72   a,  and the second detector  70   b  includes a second detector body  71   b  and a second stroke guide  72   b.  The first detector body  71   a  is mounted on the first connecting portion  48   a  of the first hydraulic cylinder  45   a,  that is, the portion close to that where the first rod  46   a  is protruded from and retracted into the cylinder body of the first hydraulic cylinder  45   a.  The first stroke guide  72   a  is shaped like a long shaft penetrating the first detector body  71   a,  being secured to the distal end, i.e., the longitudinally outer end, of the first rod  46   a  so as to be moved integrally with the first rod  46   a  longitudinally thereof. The first detector body  71   a  detects a first passing amount by which the first stroke guide  72   a  has passed through the first detector body  71   a  and outputs a detection signal corresponding to the first passing amount. Similarly, the second detector body  71   b  is mounted on the second connecting portion  48   b  of the second hydraulic cylinder  45   b,  that is, the portion close to that where the second rod  46   b  is protruded from and retracted into the cylinder body of the second hydraulic cylinder  45   b.  The second stroke guide  72   b  is shaped like a long shaft penetrating the second detector body  71   b,  being secured to the distal end, i.e., the longitudinally outer end, of the second rod  46   b  so as to be moved integrally with the second rod  46   b  longitudinally thereof. The second detector body  71   b  detects a second passing amount by which the second stroke guide  72   b  has passed through the second detector body  71   b  and outputs a detection signal corresponding to the second passing amount. 
     The first and second detectors  70   a  and  70   b  are included in a position setting means for setting a cutting start position and a cutting end position that are described later. The first and second detectors  70   a  and  70   b  detect the respective positions of the first and second graspers  50   a  and  50   b  when they are brought into a state of grasping the cutting object T, by being moved by the first and second hydraulic cylinders  45   a  and  45   b,  from their respective full-opening positions where they are spaced at the greatest interval, i.e. where the first and second graspers  50   a  and  50   b  abut against the upper and lower mounting plates  44 , respectively. Specifically, the first and second rods  46   a,    46   b  are retracted into respective cylinder bodies of the first and second hydraulic cylinders  45   a,    45   b  by respective amounts corresponding to respective movement amounts of the first and second graspers  50   a,    50   b,  while the first and second stroke guides  72   a,    72   b  secured to the first and second rods  46   a,    46   b,  respectively, pass through the first and second detector bodies  71   a,    71   b,  respectively, by respective amounts corresponding to the above-mentioned movement amounts. Therefore, respective passing amounts of the first and second stroke guide  72   a,    72   b,  namely, the first and second passing amounts, detected by the first and second detector bodies  71   a,    71   b,  respectively, correspond to the amounts by which the first and second rods  46   a,    46   b  are protruded from or retracted into respective cylinder bodies of the first and second hydraulic cylinders  45   a,    45   b  and further corresponds to respective movement amounts of the first and second graspers  50   a,    50   b.  This enables the respective positions of the first and second graspers  50   a  and  50   b  and the dimension of the cutting object T in the opening and closing directions to be calculated based on the first and second passing amounts. 
     Thus, the first and second detectors  70   a  and  70   b  according to the present embodiment detect the respective positions of the first and second graspers  50   a  and  50   b  grasping the cutting object T not directly but indirectly based on the respective amounts by which the first and second rods  46   a  and  46   b  are retracted into respective cylinder bodies of the first and second hydraulic cylinders  45   a  and  45   b.  The detector according to the present invention may alternatively be configured to detect the respective moving strokes of the first and second graspers  50   a  and  50   b  directly. 
     As shown in  FIGS. 2, 4, and 10 , the cutting unit  60  is disposed side by side with the grasp unit  40  to cut the cutting object T. Specifically, the grasp unit  40  and the cutting unit  60  are disposed adjacent to each other in the left and right directions orthogonal to the opening and closing directions. The present embodiment employs as the cutting unit  60  a torch operable to emit a flame, for example, by use of gas to perform fusion cutting of the cutting object T. 
     The second main section  21 B further includes a box  61 , a plurality of (two in this embodiment) guide rails  62 , and a torch holding section  63 , the box  16  provided for supporting the cutting unit  60  movably in a cutting direction parallel to the opening and closing directions, which is vertical in this embodiment. The box  61  has a vertically elongated rectangular parallelepiped shape with one face thereof which faces the cutting object T (front face) being opened, accommodating the cutting unit  60  while allowing the cutting unit  60  to slide vertically in the box  61 . The box  61  includes longitudinally opposite ends, that is, upper and lower opposite ends, which are connected to the paired mounting plates  44 , respectively. In  FIG. 10 , the box  61  is partially omitted to show the configuration of the cutting unit  60  and other components. The plurality of guide rails  62  are housed in the box  61  while extending in the longitudinal direction of the box  61  (in the direction parallel to the opening and closing directions of the grasp unit  40 ) to guide the cutting unit  60  in the longitudinal direction. 
     The torch holding section  63  holds the cutting unit  60 , while being mounted on the plurality of guide rails  62  so that the guide rails  62  pass through the torch holding section  63  vertically, thereby being supported on the guide rails  62  movably along the guide rails  62  in the direction parallel to the opening and closing directions of the grasp unit  40  (in the vertical direction in this embodiment). 
     The cutting unit  60  includes a torch section  64 . The torch section  60  includes a flame outlet through which a flame is emitted, and is held on the torch holding section  63  so as to be movable integrally with the torch holding section  63  in the cutting direction with the flame outlet facing frontward, which is a direction orthogonal to the opening and closing directions of the grasp unit  40 . 
     The feed mechanism  65  operates to move the torch holding section  63  and the cutting unit  60  held thereon in the longitudinal direction of the guide rails  62 , i.e. in the cutting direction. The feed mechanism  65  is, for example, a ball screw mechanism. The ball screw mechanism includes ball screws constituting the guide rails  62 , respective nuts screwed to the ball screws, and a motor disposed in the torch holding section  63  to rotate the nuts. 
     The controller is included in the position setting means together with the first and second detectors  70   a  and  70   b.  The controller sets the cutting start position and the cutting end position, based on the positions of the first and second graspers  50   a  and  50   b  detected by the first and second detectors  70   a  and  70   b,  and controls the operation of the cutting unit  60  based on the set cutting start position and cutting end position. Specifically, upon the start of cutting the cutting object T, the controller controls the feed mechanism  65  so as to position the cutting unit  60  (the torch holding section  63  in this embodiment) at the cutting start position which corresponds to the position of the first grasper  50   a  when the first and second graspers  50   a  and  50   b  are grasping the cutting object T, and controls the cutting unit  60  so as to cause the torch section  64  to emit a flame at the cutting start position. Besides, the controller controls the feed mechanism  65  to stop the movement of the cutting unit  60  when cutting unit  60  (the torch holding section  63  in this embodiment) reaches the cutting end position which corresponds to the position of the second grasper  50   b,  and controls the cutting unit  60  so as to cause the torch section  64  to stop the flame emission at the cutting end position. 
     Now will be described a method for cutting a cutting object T by using the above-described cutting device  20 . 
     (0) Preparation Step 
     In advance of the above-mentioned cutting operation, the crushing device  7  of the demolition machine  1  is operated to make a rearward rotational movement to retreat to a position for not interfering the cutting performance of the cutting device  20 . There can be a case of no requirement for the rearward rotational movement of the crushing device  7  depending on a certain work site or a certain structure of the cutting object T. 
     Besides, the cutting device  20  is shifted from the not-graphically-shown stored state to a state of being suspended from the boom  6  as shown in  FIG. 1 . 
     (1) First Step (Grasp Unit Positioning Step) 
     In the first step, performed is approaching the cutting device  20  to the cutting object T indicated by the two-dot chain line in  FIG. 7 , through an operation provided by an operator in the cab  4 . The cutting device  20  is brought to a position where the front face thereof is opposed to the cutting object T. The cutting device  20  is thereafter operated to reach a position where the cutting object T is located between the first and second graspers  50   a  and  50   b.    
     (2) Second Step (Grasping Step) 
     After confirmation of the position of the cutting device  20  relatvive to the cutting object T, performed is the second step of actuating the first and second graspers  50   a  and  50   b  through the first and second drive mechanisms  49   a  and  49   b.  Specifically, the first and second hydraulic cylinders  45   a  and  45   b  are operated so that the first and second rods  46   a  and  46   b  are retracted into the cylindrical bodies of the first and second hydraulic cylinders  45   a  and  45   b,  respectively, i.e. operated in the respective retracting directions, thereby moving the first and second graspers  50   a  and  50   b  in their respective closing directions. This movement brings the first and second graspers  50   a  and  50   b  into contact with the cutting object T to grasp it. The controls for moving the first and second graspers  50   a  and  50   b  including the movement, may be performed by the above-described controller. 
     The first and second graspers  50   a  and  50   b  rarely come into contact with the cutting object T exactly at the same time through the above movement; usually, one of the first and second graspers  50   a  and  50   b  comes into contact with the cutting object T earlier than the other. Even in this case, the position adjustment mechanism  43  can absorb the load to be applied to the cutting device  20 . For example, when the first grasper  50   a  comes into contact with the cutting object T earlier than the second grasper  50   b,  a force will continue acting on the first grasper  50   a  to move it further in the closing direction; however, this force causes the first block  42   a  holding the first hydraulic cylinder  45   a  for driving the first grasper  50   a  to press the first spring  43   a  to and contract it while the second spring  43   b  is extended. The respective resilient restoring forces of the first and second springs  43   a  and  43   b  at this time act on the first grasper  50   a  so as to push back it in the opening direction, which allows the relative position of the grasp unit  40  to the cutting object T to be adjusted so as to locate the first and second graspers  50   a  and  50   b  at respective positions having the same distance from the longitudinally central position of the support bracket  24 . Through the action of thus equalizing the resilient restoring forces of the first and second springs  43   a  and  43   b  of the position adjustment mechanism  43  are equalized, the midway position between the first and second graspers  50   a  and  50   b  and respective positions of the first and second hydraulic cylinders  45   a  and  45   b  of the drive mechanism  49  are adjusted so as to enable the first and second graspers  50   a  and  50   b  to grasp the cutting object T regardless of the relative position of the main unit  21  to the cutting object T. This suppresses the load to be applied to the grasper that is one of the first and second graspers  50   a  and  50   b  and having come into contact with the cutting object T earlier than the other, protecting the grasp unit and the cutting device  20  from their breakages due to the load. 
     (3) Third Step (Position Fixing Step) 
     In the third step, the first and second detectors  70   a  and  70   b  detect the positional information of the first and second graspers  50   a  and  50   b  when the first and second graspers  50   a  and  50   b  have grasped the target objet T and, based on the detected positional information, the cutting start position and end position are set. In this embodiment, the controller sets respective positions of the first and second graspers  50   a  and  50   b  that are grasping the cutting object T as the cutting start position and the cutting end position respectively, based on respective detection signals input from the first and second detectors  50   a  and  50   b.  Thus, in this embodiment, the first and second detectors  70   a  and  70   b  and the controller are included in the position setting means that sets the cutting start position and end position to respective positions of the first and second graspers  50   a  and  50   b  that are grasping the cutting object T. 
     Meanwhile, the first and second springs  43   a  and  43   b  of the position adjustment mechanism  43  exert biasing forces to the first and second blocks  42   a  and  42   b  so as to retain the first and second blocks  42   a  and  42   b  at the longitudinally central position of the support bracket  24 , thereby allowing not only respective positions of the first and second hydraulic cylinders  45   a,    45   b  connected to the first and second blocks  42   a,    42   b,  respectively, but also respective positions of the first and second detector body  71   a,    71   b  of the first and second detectors  70   a,    70   b  mounted on the first second connecting portion  48   a,    48   b  of the first and second hydraulic cylinder  45   a,    45   b  to be adjusted. Thus, respective positions of the first and second hydraulic cylinders  45   a  and  45   b  are adjusted to equalize respective protruding or retracting amounts of the first and second rods  46   a  and  46   b  from or into their respective cylinder bodies. This enables the first and second detectors  70   a  and  70   b  to accurately detect the protruding or retracting amounts of the first and second rods  46   a  and  46   b,  that is, to accurately detect the positional information of the first and second graspers  50   a  and  50   b  grasping the cutting object T. 
     (4) Fourth Step (Cutting Unit Positioning Step) 
     In the fourth step, the torch holding section  63  of the cutting unit  60  is moved by the feed mechanism  65  in the opening and closing directions of the grasp unit  40  and positioned at the cutting start position, based on the positional information of the first grasper  50   a  obtained in the third step. In this embodiment, the controller controls the feed mechanism  65  to position the cutting unit  60  (the torch holding section  63  in this embodiment) at the cutting start position having been set based on the positional information of the first grasper  50   a.    
     (5) Fifth Step (Cutting Step) 
     In the fifth step, by the controller, the cutting unit  60  is controlled to operate the torch section  64  constituting the cutting unit  60  and the feed mechanism  65  is controlled to move the torch section  64  from the cutting start position to the cutting end position. This allows the cutting unit  60  to cut the cutting object T. Specifically, the operation of the cutting unit  60  is started at the cutting start position to cause the torch section  64  to emit a flame from the flame outlet while sliding toward the cutting end position in the cutting direction along the opening and closing directions of the grasp unit  40 , thereby performing fusion cutting of the cutting object T. Subsequently, the controller controls the cutting unit  60  and the feed mechanism  65  to stop the movement and the flame emission of the torch section  64  when the cutting unit  60  has reached the cutting end position. The fusion cutting of the cutting object T is thereby ended. 
     The cutting start position of the cutting unit  60  does not necessarily have to agree with the position of the first grasper  50   a;  for example, in order to start the cutting operation smoothly, the cutting start position may be set to a position slightly before the position of the first grasper  50   a  and the operation of the cutting unit  60  is started at the set cutting start position. In other words, the cutting unit  60  including the torch section  64  according to the first embodiment may be conveyed in the cutting direction along the opening and closing directions while the torch section  64  has already started to emit a flame. Similarly, in order to complete the cutting operation reliably, the cutting end position may be set to a position slightly ahead of the position of the second grasper  50   b  to continue the operation of the cutting unit  60  until it reaches the set cutting end position. In other words, the torch section  64  may continue emitting a flame even after the completion of the cutting operation. 
     In the above-described cutting step, the position adjustment mechanism  43  can also contribute to the grasping stability and the prevention of breakage of the cutting device  20 . For example, even when the grasp unit  40  is vibrated by the own load of the cutting object T acting on the cutting device  20  during the thermal cutting of the cutting object T or rebound or vibration due to the residual strain after the thermal cutting of the cutting object T, the first and second springs  43   a  and  43   b  of the position adjustment mechanism  43  is able to absorb the vibration. This makes it possible to improve the grasping stability and to prevent breakage of the cutting device  20 . The first spring  43   a  and the second spring  43   b  constituting the position adjustment mechanism  43 , thus, is capable of not only exerting respective biasing forces to the first and second blocks  42   a  and  42   b  to keep them at the longitudinally central position of the support bracket  24  but also absorbing vibration and the like of the grasp unit  40  to thereby minimize the influence of the vibration and the like on the cutting device  20 . 
     ( 6 ) Sixth Step (Finishing Step) 
     After the completion of the thermal cutting of the cutting object T, the first and second drive mechanisms  49   a  and  49   b  move the first and second graspers  50   a  and  50   b  in the respective opening directions to release the grasping of the cutting object T. The movements of the first and second graspers  50   a  and  50   b  also can be controlled by the controller. 
     The cutting device  20  is thereafter moved away from the cutting object T and the next operation is started. If there is a need for further fusion cutting at another position in the cutting object T at this stage, the cutting device  20  is brought to the position to perform additional fusion cutting of the cutting object T through steps similar to the above. 
     In the first step (grasp unit positioning step), the turning mechanism  26  can turn the second main section  21 B relatively to the first main section  21 A in either of the directions shown by the arrows X in  FIG. 7  about the turn axis extending in the front and rear direction in accordance with the shape of the cutting object T to thereby enable the grasp unit  40  to grasp the cutting object T and enable the cutting unit  60  to cut the cutting object T regardless of the shape of the cutting object T. Specifically, the turning motor  26   a  attached to the turning mechanism  26  can operate to turn the support bracket  24  to turn the first and second graspers  50   a  and  50   b  integrally with the cutting unit  60 . For example, in the case where the cutting object T is a columnar steel frame column extending vertically, it allows the cutting operation to be efficiently performed that the turning mechanism  26  turns the grasp unit  40  and the cutting unit  90  degrees to bring the grasp unit  40  into a position to allow the grasp unit  40  to grasp the columnar steel frame laterally and that the feed mechanism  65  moves the cutting unit  60  in the cutting direction extending in the left and right directions that is the opening and closing directions of the grasp unit  40 . 
     Thus, in this embodiment, the cutting start position and the cutting end position are set to respective positions of the first grasper  50   a  and the second grasper  50   b  that are grasping the cutting object T, respectively, and the cutting unit  60  cuts the cutting object T with the movement thereof from the cutting start position to the cutting end position in the cutting direction along the opening and closing directions of the grasp unit  40 . In other words, the position of the cutting unit  60  is determined based on the positional information of the pair of first and second graspers  50   a  and  50   b  that are grasping the cutting object T and the cutting unit  60  cuts the cutting object T with the movement thereof in the cutting direction along the opening and closing directions of the graspers  50   a  and  50   b.  This makes it possible to perform a cutting work efficiently with no need for a complex structure. Besides, the simple structure allows the operation to be made easily and has excellent durability against shock and vibrations, which is suitable for use in a work site where strong vibrations and shocks are likely to occur. 
     Next will be described a second embodiment of the present invention with reference to  FIG. 11 . The following description of a cutting device according to the second embodiment only deals with differences from the cutting device  20  according to the first embodiment. 
     The cutting device according to the second embodiment includes a displacement mechanism  84  in addition to the constituent elements of the cutting device  20  according to the first embodiment. The displacement mechanism  84 , as shown by the two-dot chain line  64 A in  FIG. 11 , displaces the flame outlet of the torch section  64  linearly in the front and rear direction orthogonal to the cutting direction (i.e. the direction in which the torch section  64  slides along the lengths of the guide rails  62 ), that is, in the direction in which the torch section  64  emits a flame through the flame outlet. This displacement enables the position of the flame outlet relative to a target objet T to be adjusted. The displacement mechanism  84  preferably includes, for example, a gear mechanism having a rack and a pinion and a motor that actuates the gear mechanism. The displacement mechanism  84 , alternatively, may be a cylinder device configured to extend and retract in a direction to displace the flame outlet of the torch section  64 . 
     The cutting method according to the second embodiment differs from the method according to the first embodiment in that the above-described fourth step, namely, the cutting unit positioning step, further includes displacing the flame outlet of the torch section  64  linearly in the front and rear direction to thereby adjust the distance between the flame outlet of the torch section  64  and the cutting object T. 
     The displacement of the torch section  64  enables efficient cutting of the cutting object T to be performed. For example, in the case of fusion cutting of a cutting object T that is an H-section steel member so as to cut a flange thereof and thereafter cut a web, it allows the fusion cutting of the H-section steel member to be performed efficiently to displace frontward the cutting unit  60  that had been positioned with reference to the flange through the displacement mechanism  84  to bring the cutting unit  60  close to the web and to perform the fusion cutting in a situation where the flame outlet is as close to the web as possible. 
     Moreover, the displacement mechanism  84  is able to displace the cutting unit  60  closer to or farther away from the cutting object T even during the cutting operation, which allows also a fusion cutting of also a cutting object T having an irregular surface on the side facing the cutting unit  60  to be efficiently performed. 
     Next will be described a third embodiment of the present invention with reference to  FIG. 12 . The following description of a cutting device according to the third embodiment only deals with differences from the cutting device according to the first embodiment. 
     The cutting device according to the third embodiment includes a tilting mechanism  85  in addition to the constituent elements of the cutting device  20  according to the first embodiment. The tilting mechanism  85 , as shown by the two-dot chain lines  64 B and  64 C in  FIG. 12 , has a function of tilting the cutting unit  60  so as to bring the distal end of the cutting unit  60  away from a reference axis extending in the front and rear direction orthogonal to the cutting direction in which the feed mechanism  65  moves the cutting unit  60 , that is, a function of tilting the flame outlet of the torch section  64 . Specifically, the torch section  64  is mounted on the torch holding section  63  rotatably about an axis extending in the left and right directions, and the tilting mechanism  85  includes an actuator, for example, mounted on the torch holding section  63 , to rotate the torch section  64  to thereby tilt the flame outlet in the moving direction of the cutting unit  60 . Thus, the torch section  64  is supported on the torch holding section  63  pivotally to be able to be tilted upward and downward so as to bring the distal end thereof away from the reference axis. The tilting mechanism  85  preferably includes, for example, a motor or a cylindrical device. 
     The cutting method according to the third embodiment differs from the method according to the first embodiment in that the above-described fourth step, namely, the cutting unit positioning step, further includes tilting the distal end (flame outlet) of the torch section  64  in such a way as to swing it vertically. 
     The tilting of the torch section  64  also makes it possible to cut a cutting object T more efficiently. For example, in the case of fusion cutting of the cutting object T, which is an H-section steel member, wherein the joint between an upper flange and a web of the H-section steel member is cut, tilting the torch section  64  upward so as to orient the distal end of the torch section  64  to the joint enables the joint between the flange and the web of the H-steel member to be cut efficiently. 
     The titling mechanism  85  shown in  FIG. 12  may be added to the cutting device instead of or together with the above-described displacement mechanism  84 . The latter case allows the torch section  64  to make both of linear displacement as shown by the two-dot chain line  64 A and a tilt as shown by the two-dot chain lines  64 B and  64 C in  FIG. 12 . 
     Next will be described a fourth embodiment of the present invention with reference to  FIGS. 13 and 14 . The following description of a cutting device according to the fourth embodiment only deals with differences from the cutting device  20  according to the first embodiment. 
     The cutting device according to the fourth embodiment includes a first stopper  90   a  and a second stopper  90   b  as a position setting means for setting the cutting start position and the cutting end position of the cutting unit  60  to respective positions of the first and second graspers  50   a  and  50   b  that are grasping a cutting object T, respectively, in place of the first and second detectors  70   a  and  70   b  according to the first embodiment, that is, in place of the means for detecting the positions of the first and second graspers  50   a  and  50   b  that are grasping a cutting object T. The first and second stoppers  90   a  and  90   b  restrict the moving range of the cutting unit  60  within a range between the first and second graspers  50   a  and  50   b  that are grasping the cutting object T, thereby setting the cutting start position and the cutting end position to respective positions of the first and second graspers  50   a  and  50   b,  respectively. 
     The cutting device according to the fourth embodiment does not include the box  61  according to the first embodiment, and the first stopper  90   a  is secured to the first grasper  50   a  while the second stopper  90   b  is secured to the second grasper  50   b.  The first stopper  90   a  is secured to respective upper ends of a plurality of guide rails  62  supporting the first and second graspers  50   a  and  50   b.  The second stopper  90   b  includes a plurality of slide holes  91 , through which the guide rails  62  vertically pass, respectively, to thereby allow respective inner circumferential surfaces of the second stopper  90   b  defining the slide hole  91  to slide against and along the guide rails  62 . The plurality of guide rails  62  shares a stoppage piece  92 , which is secured to respective lower ends of the guide rails  62  to prevent the second stopper  90   b  from slipping off the guide rails  62 . A second main section  21 B of the cutting device according to the fourth embodiment includes a torch holding section  63  that is similar to the torch holding section  63  according to the first embodiment, the torch holding section  63  of the fourth embodiment being disposed across the plurality of guide rails  62  to be movable in the opening and closing directions of the first and second graspers  50   a  and  50   b.  In addition, the upper limit position of the torch holding section  63  and a torch section  64  held thereon, namely, the cutting start position, is defined by contact of the torch holding section  63  with a lower surface of the stopper  90   a  as shown in  FIGS. 13 and 14 , while the lower limit position of the torch holding section  63  and the torch section  64  held thereon, namely, the cutting end position, is defined by contact of the torch holding section  63  with an upper surface of the second stopper  90   b.    
     The second stopper  90   b  includes a loose-fit hole  93  and a cutout  94 . The loose-fit hole  93  has a shape of allowing the first guide shaft  41   a  located between the plurality of guide rails  62  and the second grasper  50   b  to loosely fit with the second stopper  90   b  moving together with the second grasper  50   b  to thereby prevent the second stopper  90   b  from interfering with the first guide shaft  41   a.  The cutout  94  has a shape of preventing the second stopper  90   b  during the above mentioned movement from interfering with the first hydraulic cylinder  45   a.    
     In the cutting device according to the fourth embodiment, the first and second stoppers  90   a  and  90   b  move involved by respective movements of the first and second graspers  50   a  and  50   b  in the respective closing directions of coming close to each other. Specifically, as shown in  FIG. 14 , accompanying a downward movement of the first grasper  50   a  and the first stopper  90   a  secured thereto, the plurality of guide rails  62  having respective upper ends secured to the second stopper  90   a  pass downward through the slide holes  91  of the second stopper  90   b,  and the second stopper  90   b  secured to the second grasper  50   b  moves upward while being guided along the guide rails  62 , causing a part of the guide rails  62  to protrude downward beyond the stopper  90   b.  Thus, with decrease in the distance between first and second graspers  50   a  and  50   b  in the opening and closing directions decreases, the distance between the first and second stoppers  90   a  and  90   b  in the opening and closing directions is also decreased. The first and second stoppers  90   a  and  90   b  prevent the cutting unit  60  from movement beyond the first and second stoppers  90   a  and  90   b  to thereby restricting the moving of the cutting unit  60  within the range between the first and second stoppers  90   a  and  90   b,  that is, the range between the first and second graspers  50   a  and  50   b,  suppressing undesired movement of the cutting unit  60 . 
     The position setting means for setting the cutting start position and the cutting end position of the cutting unit  60  may include only one of the first and second stoppers  90   a  and  90   b.  Also in this case, the position setting means can set either the cutting start position or the cutting end position to the position of the one stopper and define the other position through measurement or inference. 
     The first and second stoppers  90   a  and  90   b  make it possible to set the cutting start position and the cutting end position structurally with no need for the first and second detectors  70   a  and  70   b  according to the first embodiment. Hence, the first and second stoppers  90   a  and  90   b  according to the fourth embodiment also form the position setting means for setting the cutting start position and the cutting end position to the positions of the first and second graspers  50   a  and  50   b  that are grasping the cutting object T, respectively. 
     The above-described fourth embodiment is not intended to exclude simultaneous use of at least one of the first and second stoppers  90   a  and  90   b  and a detector. For example, it is also permissible to provide one of the graspers  50   a  and  50  with a stopper while providing the other with a detector. 
     The present invention is not limited to the above-described embodiments. The present invention also encompasses, for example, the following embodiments. 
     (A) Regarding Detector 
     Although the first embodiment includes the first and second detectors  70   a  and  70   b  which are provided to the first and second graspers  50   a  and  50   b,  respectively, the detector according to the present invention may be configured to directly detect only the position of one of the first and second graspers and infer the position of the other grasper. Such detector also enable the cutting start position and end position to be set. 
     It is also possible to detect respective movement amounts of the first and second graspers  50   a  and  50   b  and the dimension of the cutting object T in the opening and closing directions without direct detection of the positions of the first and second graspers  50   a  and  50   b  that have been moved, because respective strokes of the first and second rods  46   a,    46   b  can be calculated based on the amount of hydraulic fluid supplied to the first and second hydraulic cylinder  45   a,    45   b  respectively. Based on the detected information, respective positions at which the cutting should be started and ended can be obtained, enabling the cutting unit  60  to be set to the cutting start position corresponding to the position of the first grasper  50   a.    
     Modified Embodiments 
     While the cutting start position and the cutting end position of the cutting unit  60  according to the above-described first embodiment are set based on the moving distance of the grasp unit  40 , the method for setting the cutting start position and the cutting end position is not limited. For example, the first embodiment may be modified to include a switch configured to be activated to perform a switching action for cutting start or cutting end of the cutting operation when the cutting unit  60  on the plurality of guide rails reaches respective positions corresponding to the first grasper and the second grasper that are grasping the target objet T. For example, it is also possible to provide the first and second graspers  50   a  and  50   b  with respective proximity sensors or like and to set the cutting start position and end position based on the position of the cutting unit  60  at the time when it passes through each of the proximity sensors. 
     In the present invention, the position setting means capable of setting the cutting start position and the cutting end position without a detector is not limited to the first and second stoppers  90   a  and  90   b  according to the fourth embodiment. Any configuration including restriction means that allows the cutting unit to move freely between the first and second graspers but prevents the cutting unit from moving beyond the first or second grasper enables the cutting start position and the cutting end position to be set to respective positions of the first and second graspers. 
     The cutting method according to the present invention may include swinging the arm  12  in the left and right directions (in the direction orthogonal to the drawing sheet surface of  FIG. 1 ) depending on the shape and position of the cutting object T to thereby move the cutting device  20  to a position facilitating the grasping of the cutting object T, after which the operation of the cutting device  20  should be started. 
     The cutting device according to the present invention is not necessarily mounted on the above-described demolition machine  1 . The cutting device may be mounted, for example, on a crane, or may be directly mounted to the distal end of the boom  6  shown in  FIG. 1 . 
     The place where the remote control of the cutting device  20  should be performed by an operator is not limited to the cab  4 . The remote control of the cutting device according to the present invention may be performed outside a construction machine. 
     The cutting unit according to the present invention is not limited to those that perform fusion cutting with a gas torch like the above-described cutting unit  60 . The cutting unit may be configured to perform fusion cutting through plasma or laser. Alternatively, may be used one that cuts a cutting object by means other than fusion cutting, for example, a mechanical cutting machine such as a high speed cutter. 
     As described above, provided are a device and a method capable of cutting a cutting object efficiently. 
     Provided is a cutting device for cutting a cutting object included in a structure, the cutting device comprising: a grasp unit including a first grasper and a second grasper that are movable in an opening and closing directions, in which direction the first grasper and the second grasper come close to each other or go away from each other, to grasp the cutting object therebetween in the opening and closing directions; a drive mechanism that moves the first grasper and the second grasper relatively to each other in the opening and closing directions; a cutting unit disposed side by side with the first grasper and the second grasper and configured to cut the cutting object with a movement of the cutting unit in a cutting direction along with the opening and closing directions; a main unit supporting the first and second graspers movably in the opening and closing directions and supporting the cutting unit movably in the cutting direction; a feed mechanism that moves the cutting unit in the opening and closing directions; and a position setting means that sets a cutting start position and a cutting end position based on respective positions of the first grasper and the second grasper that are grasping the cutting object, respectively. The cutting start position is a position at which an operation of the cutting unit and the movement of the cutting unit for cutting the cutting object are started, and the cutting end position is a position at which the operation of the cutting unit and the movement of the cutting unit for cutting the cutting object are ended. The limitation “sets a cutting start position and a cutting end position based on respective positions of the first grasper and the second grasper” does not necessarily require that the cutting start position exactly agrees with the position of the first grasper and the cutting end position exactly agrees with the position of the second grasper, but encompasses the aspect to set the cutting start position to allow the operation of the cutting unit is started at a position slightly before the position of the first grasper and the aspect to set the cutting end position to allow the operation of the cutting unit to be stopped at a position slightly ahead of the position of the second grasper. 
     The position setting means according to this cutting device, setting the cutting start position and the cutting end position based on respective positions of the first grasper and the second grasper that are grasping the cutting object, respectively, make it possible to cut the cutting object efficiently with no need for a complex structure. 
     It is preferable that the position setting means includes, for example, a detector that detects positional information of at least one of the first grasper and the second grasper that are grasping the cutting object, the position setting means being configured to set the cutting start position and the cutting end position based on the positional information detected by the detector. 
     The position setting means can set the cutting start position and the cutting end position appropriately, based on the actual positional information of the first and second graspers detected by the detector. 
     Alternatively, it is preferable that the position setting means includes a stopper provided for at least one of the first grasper and the second grasper, the stopper being coupled to the one grasper so as to be moved together with the one grasper in the opening and closing directions and configured to prevent the cutting unit, by contact of the stopper with the cutting unit, from moving beyond a position corresponding to the one grasper. 
     With the movement together with one of the first grasper and the second grasper and contact with the cutting unit, the stopper enables at least one of the cutting start position and the cutting end position to be set to the position corresponding to the one grasper without actually detecting the position of the one grasper. 
     It is preferable that the cutting device further includes a displacement mechanism that displaces the cutting unit relatively to the main unit in an intersecting direction that intersects the cutting direction, the cutting unit coming close to the cutting object and going away from the cutting object in the intersecting direction. 
     The displacement mechanism allows the distance between the cutting unit and the cutting object to be adjusted with no need for movement of the main unit, thereby enabling the cutting operation to be performed more efficiently. 
     It is preferable that the cutting device further includes a tilting mechanism that tilts the cutting unit with respect to the main unit in the cutting direction so as to bring a distal end of the cutting unit away from a reference axis orthogonal to the cutting direction. 
     The tilting mechanism allows the tilt of the cutting unit relatively to the cutting object to be adjusted with no need for tilt of the main unit, thereby enabling the cutting operation to be performed more efficiently. 
     The drive mechanism preferably includes a first drive mechanism that moves the first grasper in the opening and closing directions and a second drive mechanism that moves the second grasper in the opening and closing directions independently of the first grasper. 
     The first drive mechanism and the second drive mechanism, being capable of move the first grasper and the second grasper individually, enables the cutting object to be grasped efficiently and reliably. 
     It is preferable that at least one of the first grasper and the second grasper includes a base portion to be moved by the drive mechanism, a grasping contact portion capable of making direct contact with the cutting object, the grasp contact portion being mounted on the base portion on an inner side of the base portion in the opening and closing directions so as to be displaceable relatively to the base portion in the opening and closing directions, and a biasing member that biases the grasping contact portion with respect to the base portion in a closing direction in which the first grasper and the second grasper come close to each other. 
     The biasing member, exerting a biasing force to the grasping contact portion in the closing direction to restrain the grasping contact portion from movement in an opening direction in which the first grasper and the second grasper go away from each other, enables the first and second graspers to grasp the cutting object more reliably. 
     It is preferable that the main unit includes a first main section, a second main section supporting the grasp unit and the cutting unit, and a turning mechanism coupling the second main section to the first main section so as to allow the second main section to turn about a turn axis extending in a front and rear direction orthogonal to the opening and closing directions, the front and rear direction being a direction toward and away from the cutting object, the turning mechanism being configured to turn the second main section relatively to the first main section. 
     The turning mechanism makes it possible to cope with a cutting object in any orientation, with no need for moving the first main section, by turning the grasp unit and the cutting unit together with the second main section about the turn axis extending in the front and rear direction depending on the orientation of the cutting object, such as the direction in which a steel member extends. 
     It is preferable that the cutting device further includes a position adjustment mechanism that adjusts a midway position between the first and second graspers relative to the second main section so as to allow the first and second graspers to grasp the cutting object regardless of the relative position of the main unit to the cutting object. 
     The position adjustment mechanism allows the first and second graspers to stably grasp the cutting object even when the first grasper and the second grasper come into contact with the cutting object at different timings depending on a relative position of the main unit to the cutting object, through adjusting the midway position between the first and second graspers so as to allow the first and second graspers to properly grasp the cutting object to thereby prevent an uneven load from acting on the cutting device. 
     Also provided is a method for cutting a cutting object included in a structure by using a cutting device, the method comprising: a cutting device preparation step of preparing the cutting device that includes a grasp unit including a first grasper and a second grasper that are movable in an opening and closing directions, in which direction the first grasper and the second grasper come close to each other or go away from each other, to grasp the cutting object therebetween in the opening and closing directions, a drive mechanism that moves the first grasper and the second grasper relatively to each other in the opening and closing directions, a cutting unit disposed side by side with the first grasper and the second grasper to cut the cutting object with a movement of the cutting unit in a cutting direction along with the opening and closing directions, a main unit supporting the first and second graspers movably in the opening and closing directions and supporting the cutting unit movably in the cutting direction, and a feed mechanism that moves the cutting unit in the opening and closing directions; a grasp unit positioning step of positioning the cutting device to locate the cutting object between the first grasper and the second grasper; a grasping step of moving the first grasper and the second grasper relatively to each other in a closing direction that is one of the opening and closing directions, the first grasper and the second grasper coming close to each other in the closing direction, to thereby cause the first grasper and the second grasper to grasp the cutting object; a position setting step of setting a cutting start position based on the position of the first grasper and setting a cutting end position based on the position of the second grasper when the first grasper and the second grasper are grasping the cutting object; a cutting unit positioning step of causing the feed mechanism to move the cutting unit in the opening and closing directions to position the cutting unit at the cutting start position; and a cutting step of moving the cutting unit from the cutting start position to the cutting end position to cut the cutting object. 
     The above method, including setting the cutting start position and the cutting end position based on the positions of the first and second graspers that are grasping the cutting object and cutting the cutting object while moving the cutting device from the thus set cutting start position to the cutting end position in the cutting direction along with the opening and closing directions of the first and second graspers, makes it possible to efficiently cut the cutting object with no need for a complex structure. 
     It is preferable that the cutting unit positioning step includes displacing the cutting unit relatively to the main unit in an intersecting direction which intersects the cutting direction, the intersecting direction being a direction in which the cutting unit comes close to and away from the cutting object. This makes it possible to adjust the distance between the cutting unit and the cutting object easily, thereby enabling the cutting operation to be performed more efficiently. 
     It is preferable that the cutting unit positioning step includes tilting the cutting unit with respect to the main unit in the moving direction of the cutting unit so as to bring a distal end of the cutting unit away from a reference axis orthogonal to the cutting direction. This makes it possible to adjust the tilt of the cutting unit with respect to the cutting object easily, thereby enabling the cutting operation to be performed more efficiently. 
     It is preferable that the position setting step includes, for example, detecting a position of at least one of the first grasper and the second grasper that are grasping the cutting object, setting the cutting start position to a position corresponding to the position of the first grasper, and setting the cutting end position to a position corresponding to the second grasper, based on the detected position. Thus detecting the position of at least one of the first grasper and the second grasper and setting the cutting start position and the cutting end position to respective positions corresponding to the first grasper and the second grasper, respectively, based on the detected positional information enables the cutting start position and the cutting end position to be set to proper positions more reliably. 
     The position setting step, alternatively, may include providing a stopper for at least one of the first grasper and the second grasper to couple the stopper to the one grasper so as to cause the stopper to be moved together with the one grasper in the opening and closing directions and preventing the cutting unit, by contact of the stopper with the cutting unit, from moving beyond a position corresponding to the one grasper. This makes it possible to set at least one of the cutting start position and the cutting end position to the position corresponding to the one grasper with no need for actually detecting the position of the one grasper. 
     In the above method, it is preferable that the cutting device preparation step includes the cutting device in which the main unit includes a first main section and a second main section supporting the grasp unit and the cutting unit, the second main section being coupled to the first main section turnably about a turn axis extending in a front and rear direction orthogonal to the opening and closing directions, the front and rear direction being a direction toward and away from the cutting object, and the grasp unit positioning step includes turning the grasp unit together with the second main section relatively to the first main section. This makes it possible to cope with a cutting object in any orientation by turning the grasp unit easily about the turn axis depending on the orientation of the cutting object, such as the direction in which a steel member extends.