Patent Publication Number: US-11643232-B2

Title: Binding machine and method for testing the strength of a joint formed on a closed loop of an elongated binding element

Description:
FIELD OF THE INVENTION AND PRIOR ART 
     The present invention relates to a binding machine according to the description herein. The invention also relates to a method for forming a closed loop of an elongated binding element in the form of a wire or strap by means of a binding machine and testing the strength of a joint formed on said closed loop. 
     Automatic binding machines for applying a binding element in the form of a strap or wire in a loop around an object or a bundle of objects, drawing the binding element tightly around the object/bundle and thereafter joining two sections of the binding element in order to secure the binding element around the object/bundle are known in many different configurations. As an example, WO 2017/129679 A1 discloses a binding machine where a laser welding device is used for forming a joint between two sections at opposite ends of a piece of a binding element in the form of a wire or strap arranged in a loop around an object or a bundle of objects to thereby secure this piece of the binding element in a loop around the object or objects. As an alternative to laser welding, such a joint could be formed by any other suitable type of welding. When it comes to a binding element in the form of a metallic strap, it would also be possible to form the joint by punching locking seals and a securing seal in two mutually overlapping strap sections by means of punching members, for instance in the manner disclosed in EP 2 243 708 A1. 
     It is previously known from U.S. Pat. No. 4,314,131 A to test the strength of a welded butt joint formed on a loop of wire in a binding machine by gripping the wire on opposite sides of the joint by means of a stationary clamping member and a moveable clamping member and then moving the moveable clamping member away from the stationary clamping member in order to subject the joint to a tensile test. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to achieve a new and favourable manner of testing the strength of a joint formed in a binding machine on a loop of a binding element in the form of a wire or strap. 
     According to the invention, this object is achieved by means of a binding machine having the features defined herein. 
     The binding machine of the present invention comprises:
         a feeding and tensioning device for feeding an elongated binding element in the form of a wire or strap in a loop around a space configured for receiving one or more objects to be bound and subsequently retracting the binding element to draw it tightly around one or more objects received in said space;   a gripping arrangement for gripping and locking a first binding element section at the leading end of the binding element after the feeding of the binding element in a loop around said space;   a joining device for forming a joint between said first binding element section and an adjoining second binding element section at the trailing end of a piece of the binding element arranged in a loop in or around said space to thereby form a closed loop of this piece of the binding element; and   an electronic control device configured to control the feeding and tensioning device to exert a tensile force on the binding element after the formation of said joint in order to subject the joint to a tensile test and thereby check the strength of the joint, wherein the gripping arrangement during said tensile test is configured to keep the first binding element section secured in fixed position by engagement with a part of the first binding element section located between said joint and the leading end of the binding element.       

     Thus, according to the present invention, a tensile test for testing the strength of the joint formed on the binding element is effected by means of the feeding and tensioning device of the binding machine in a simple and efficient manner. The possibility to subject the joint to an efficient tensile test by pulling the binding element under the effect of the feeding and tensioning device has been made possible by making the gripping arrangement keep the first binding element section secured in fixed position by engagement with a part of the first binding element section located between the joint and the leading end of the binding element. Hereby, the gripping of the binding element and the pulling thereof are effected on opposite sides of the joint, which implies that the joint will take up the entire or at least almost the entire tensile force exerted by the feeding and tensioning device during the tensile test. 
     Further advantageous features of the binding machine according to the present invention will appear from the description following below. 
     The invention also relates to a method having the features defined herein. 
     Further advantageous features of the method according to the present invention will appear from the description following below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       With reference to the appended drawings, a specific description of preferred embodiments of the invention cited as examples follows below. In the drawings: 
         FIG.  1    is an outline diagram of a binding machine according to an embodiment of the present invention, 
         FIGS.  2   a - 2   j    are partly cut outline diagrams of parts included in the binding machine of  FIG.  1   , as seen at different stages during the process of securing a binding element in a loop around a bundle of objects and testing the strength of a joint formed on the binding element, 
         FIGS.  3   a - 3   e    are partly cut outline diagrams of parts included in the binding machine of  FIG.  1   , as seen at different stages during the process of forming a closed loop of a binding element and testing the strength of a joint formed on the binding element, 
         FIG.  4    is a schematic illustration of a support member and a pressing element included in the binding machine of  FIG.  1   , as seen with the pressing element in a retracted position at a distance from an associated recess in a support member, and 
         FIG.  5    is a schematic illustration of the support member and pressing element, as seen with the pressing element in an advanced position received in the recess in the support member. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Some of the parts included in a binding machine  1  according to an embodiment of the present invention are very schematically illustrated in  FIG.  1   . The binding machine  1  comprises:
         a guide track  2  for guiding an elongated binding element  3  in the form of a wire or strap in a loop around a space  4  configured for receiving one or more objects  10  to be bound;   a sealing unit  20  for securing the binding element  3  around said one or more objects  10 ;   a feeding and tensioning device  5  for feeding the binding element  3  from a supply coil  6 , through the sealing unit  20 , into said guide track  2 , along the guide track in a loop around said object receiving space  4  and then back into the sealing unit  20  and subsequently retracting the binding element  3  to draw it tightly around one or more objects  10  received in said space  4 ; and   an accumulator  9  for temporarily accumulating a part of the binding element  3  when the binding element is retracted by the feeding and tensioning device  5  and then releasing the accumulated part of the binding element when the binding element thereafter is fed forwards by the feeding and tensioning device  5 .       

     The guide track  2  may for instance have the form of a rail with a longitudinal opening facing said object receiving space  4 . As an alternative, the binding element may also be fed in a loop around the object or objects to be bound without using any guide track. This may be accomplished by feeding the binding element through a bending device that is configured to bend the binding element in such a manner that it will move in free space, without contact with any guide track or the similar, in an essentially circular path around the object or objects  10  to be bound, wherein a funnel-shaped guiding element may be arranged at the end of said path in order to catch the leading end of the binding element and guide it into the sealing unit. 
     The object or objects  10  to be bound may be positioned in the object receiving space  4  before, during or after the feeding of the binding element  3  in a loop around this space  4 . 
     As an alternative to the use of an accumulator  9 , the slackening of the binding element  3  when the binding element is retracted by the feeding and tensioning device  5  may be taken up or avoided by rotating the supply coil  6  in a reversed direction. 
     Some of the parts included in the above-mentioned sealing unit  20  are very schematically illustrated in  FIGS.  2   a - 2   j  and  3   a - 3   e   . The sealing unit  20  comprises a gripping arrangement  30  for gripping and locking a first binding element section  7   a  at the leading end of the binding element  3  after the feeding of the binding element in a loop around the object receiving space  4 . The sealing unit  20  further comprises a joining device  40  for forming a joint  8  between said first binding element section  7   a  and an adjoining second binding element section  7   b  at the trailing end of a piece  3   a  of the binding element arranged in a loop in or around the object receiving space  4  to thereby form a closed loop  11  of this piece  3   a  of the binding element. 
     The binding machine  1  may have the form of a strapping machine, wherein the binding element  3  is a strap of metallic or plastic material. In this case, the above-mentioned joining device  40  may comprise punching members for punching locking seals and a securing seal at mutually overlapping ends of a piece of a binding element in the form of a metallic strap applied in a loop around said one or more objects  10 . As an alternative, the joining device  40  of the strapping machine may be a welding device, for instance a laser welding device, which is configured to form the joint  8  between the above-mentioned first and second binding element sections  7   a ,  7   b  as a lap joint with the second binding element section  7   b  overlapping the first binding element section  7   a.    
     The binding machine  1  may also have the form of a wire binding machine, wherein the binding element  3  is a wire of metallic material. In this case, the above-mentioned joining device  40  is a welding device, for instance a laser welding device, which is configured to form a welded joint between the above-mentioned first and second binding element sections  7   a ,  7   b . In this case, the joining device  40  is configured to form the joint as a longitudinal welded joint at the interface between the first and second binding element sections  7   a ,  7   b , wherein the second binding element section  7   b  is located in parallel with and at the side of the first binding element section  7   a.    
     In the illustrated embodiment, the binding machine  1  is a strapping machine provided with a joining device  40  in the form of a laser welding device provided with a laser welding head  42 , wherein the joint  8  between the first and second binding element sections  7   a ,  7   b  is formed by means of a laser beam  43  (see  FIGS.  2   g  and  3   d   ) emitted from the laser welding head. The laser welding device  40  comprises means of conventional type for directing and focusing the emitted laser beam  43  onto a desired target area. 
     The feeding and tensioning device  5  may be of any desired type suitable for use in a binding machine of the type here in question. The feeding and tensioning device  5  is for instance of the type described in closer detail in EP 3 398 866 A1. 
     In the illustrated embodiment, the feeding and tensioning device  5  comprises two rotatable feeding rollers  5   a ,  5   b  for feeding and retracting the binding element  3  and tensioning members in the form of two rotatable tensioning rollers  5   c ,  5   d  for tensioning the binding element  3 . Under the effect of the feeding rollers  5   a ,  5   b , the binding element  3  is first fed forwards in a loop around the object receiving space  4  and thereafter retracted in order to be pulled into contact with one or more objects  10  to be bound, wherein the binding element  3  is subjected to an initial stretching when being retracted by the feeding rollers  5   a ,  5   b . Thereafter, the binding element  3  is subjected to a final stretching under the effect of the tensioning rollers  5   c ,  5   d  before being secured around said one or more objects  10 . 
     The feeding rollers  5   a ,  5   b  are located opposite each other and configured to be in contact with opposite sides of a part of the binding element  3  received in the nip between the feeding rollers. At least one of the feeding rollers  5   a ,  5   b  is rotatably driven by an actuator (not shown) in the form of a reversible drive motor in order to move the binding element  3  in its longitudinal direction. The drive motor is configured to rotate the driven feeding roller at high speed and low torque. The drive motor is preferably an electric motor, but it could as an alternative be a hydraulic or pneumatic motor. 
     Also the tensioning rollers  5   c ,  5   d  are located opposite each other and configured to be in contact with opposite sides of a part of the binding element  3  received in the nip between the tensioning rollers. At least one of the tensioning rollers  5   c ,  5   d  is rotatably driven by an actuator (not shown) in the form of a drive motor in order to pull the binding element  3  in its longitudinal direction backwards away from the sealing unit  20 . The drive motor is configured to rotate the driven tensioning roller at low speed and high torque. The drive motor is preferably an electric motor, but it could as an alternative be a hydraulic or pneumatic motor. The rotatably driven feeding roller and the rotatably driven tensioning roller may be driven by one and the same drive motor. As an alternative, the feeding and tensioning device  5  may comprise a first drive motor for rotating each rotatably driven feeding roller and a second drive motor for rotating each rotatably driven tensioning roller. 
     As an alternative to tensioning members in the form of tensioning rollers  5   c ,  5   d , the feeding and tensioning device  5  may comprise tensioning members in the form of two clamping and pulling jaws for tensioning the binding element  3 , wherein the clamping and pulling jaws are located opposite each other and configured to be moveable by an actuator, for instance in the form of a hydraulic cylinder, into gripping contact with opposite sides of a part of the binding element  3  received between them in order to establish a firm grip on the binding element. When the clamping and pulling jaws have been made to establish a firm grip on the binding element, they are together moved in the longitudinal direction of the binding element by an actuator, for instance in the form of a hydraulic cylinder, in order to exert a tensile force on the binding element. 
     According to the invention, the feeding and tensioning device  5  is used in order to exert a tensile force on the binding element  3  after the formation of the above-mentioned joint  8  in order to subject the joint  8  to a tensile test and thereby check the strength of the joint  8 . During this tensile test, the gripping arrangement  30  is configured to keep the first binding element section  7   a  secured in fixed position by engagement with a part  13  of the first binding element section located between the joint  8  and the leading end  12  of the binding element. The tensile test may be performed when a piece  3   a  of the binding element has been secured in a closed loop  11  around one or more objects  10  to be bound, as illustrated in  FIG.  2   h   . As an alternative, the tensile test may be performed during a test procedure when a closed loop  11  of a piece  3   a  of the binding element has been formed in the object receiving space  4  without any object received inside the closed loop  11 , i.e. with the closed loop  11  hanging freely below the gripping arrangement  30 , as illustrated in  FIG.  3   e   . The tensile tests may be performed at any desired intervals, for instance each time the use of a new supply coil  6  begins. 
     During the tensile test, the tensile force may be exerted on the binding element  3  under the effect of the tensioning members  5   c ,  5   d  included in the feeding and tensioning device  5  or under the combined effect of the feeding rollers  5   a ,  5   b  and the tensioning members  5   c ,  5   d.    
     In the illustrated embodiment, the gripping arrangement  30  comprises a support member  34  for supporting the first and second binding element sections  7   a ,  7   b  during the formation of the welded joint  8 . The support member  34  is configured to be located between the binding element sections  7   a ,  7   b  and an outer surface of the object or objects  10  to be bound during the formation of the welded joint  8 . When the welded joint  8  has been formed, the support member  34  is moved laterally out of the area between the bounded object/objects  10  and the closed loop formed around the object/objects to thereby release the closed loop from the sealing unit  20 . 
     In the illustrated embodiment, the gripping arrangement  30  also comprises a pressing element  37 , which has a shape adapted to the shape of a recess  35  provided in an upper support surface  36  on the support member  34  so as to allow the pressing element  37  to be received in this recess  35 . The pressing element  37  has an upper surface  38  which is flush or at least essentially flush with the upper support surface  36  on the support member  34  when the pressing element  37  is received in the recess  35  in the support member, as illustrated in  FIGS.  2   a    and  3   a.    
     An actuating device  39  (very schematically illustrated in  FIG.  1   ) included in the gripping arrangement  30  is configured to move the pressing element  37  and the support member  34  in relation to each other between a first mutual position (see for instance  FIGS.  2   c    and  4 ), in which the pressing element  37  is located outside and at a distance from the recess  35  in the support member  34 , and a second mutual position (see for instance  FIGS.  2   a    and  5 ), in which the pressing element  37  is received in said recess  35 . The pressing element  37  and the support member  34  are configured to form a bulge  14  on the first binding element section  7   a  when the pressing element  37  and the support member  34  are moved in relation to each other by the actuating device  39  from said first mutual position to said second mutual position with a part  13  of the first binding element section  7   a  received in the space between the pressing element  37  and the support member  34 , wherein this bulge  14  is formed at a position between the leading end  12  of the binding element  3  and the welded joint  8  to be formed by the joining device  40 . 
     In the illustrated embodiment, the actuating device  39  is configured to achieve said relative movement between the pressing element  37  and the support member  34  by moving the pressing element  37  in relation to the support member  34 . In this case, the pressing element  37  is moved downwards towards the support member  34  in order to achieve the movement from the first mutual position to the second mutual position and upwards away from the support member  34  in order to achieve the movement from the second mutual position to the first mutual position, wherein the support member  34  remains in a fixed position during the movements of the pressing element  37 . As an alternative, the actuating device  39  may be configured to achieve said relative movement between the pressing element  37  and the support member  34  by moving the support member  34  in relation to the pressing element  37  or by moving the pressing element  37  as well as the support member  34  in relation to each other. 
     The pressing element  37  is also moveable horizontally by means of the actuating device  39  in order to allow the pressing element to be moved laterally out of the bulge  14  when the first and second binding element sections  7   a ,  7   b  have been secured to each other by the joining device  40  and the closed loop  11  thereby formed is to be released from the sealing unit  20 . According to a first alternative, the pressing element  37  is formed as a single-part element and moveable out of the bulge  14  by a displacement in a horizontal direction. According to another alternative, the pressing element  37  is divided into two parts, which are located opposite each other and moveable out of the bulge  14  by being displaced laterally in opposite directions away from each other. 
     The support member  34  may comprise first and second support jaws located opposite each other in the manner shown in WO 2017/129679 A1, wherein the support jaws are moveable in relation to each other between an advanced supporting position, in which the support jaws form a support for the first binding element section  7   a , and a retracted releasing position, in which the support jaws are retracted from each other in order to allow the first and second binding element sections  7   a ,  7   b , after having been joined to each other, to pass through a gap between the support jaws. Each support jaw may be fixed to a pivot arm, which in its turn is pivotally mounted to a housing  21  of the sealing unit  20 . Thus, in this case, the support jaws are pivotable between the supporting and releasing positions. As an alternative, the support jaws could be linearly moveable between the supporting and releasing positions. The support jaws are moveable between the supporting and releasing positions by means of the actuating device  39 . As an alternative, the support member  34  is formed as a single-part member and moveable between the supporting and releasing positions by a displacement in a horizontal direction. 
     The actuating device  39  may be electrically, pneumatically or hydraulically driven and may comprise one or more electrically, pneumatically or hydraulically driven actuators. 
     In the illustrated example, the recess  35  and the pressing element  37  have a cross-sectional shape in the form of an isosceles trapezoid, as seen in a vertical plane. However, the recess  35  and the pressing element  37  may also have any other suitable cross-sectional shape. 
     The gripping arrangement  30  may of course also have any other suitable design in addition to the design illustrated in  FIGS.  2   a - 2   j  and  3   a   - 3   e.    
     In the illustrated embodiment, the sealing unit  20  comprises a squeezing device  50  for squeezing the second binding element section  7   b  against the first binding element section  7   a  with the second binding element section  7   b  overlapping the first binding element section  7   a , wherein the squeezing device  50  is configured to keep the second binding element section  7   b  squeezed against the first binding element section  7   a  during the moment when a welded joint  8  between the first and second binding element sections  7   a ,  7   b  is formed by the laser welding device  40 . In the illustrated example, the squeezing device  50  comprises a squeezing member  51  which is configured to co-operate with the support member  34  and which is moveably mounted to the housing  21  of the sealing unit  20 . The first and second binding element sections  7   a ,  7   b  are receivable in a space between the squeezing member  51  and the support member  34 , and the squeezing member  51  is moveable in relation to the support member  34  between a retracted first position (see for instance  FIGS.  2   a    and  4 ), in which the squeezing member  51  is retracted from the support member  34 , and an advanced second position (see for instance  FIGS.  2   g    and  5 ), in which the squeezing member  51  is pressed against the support member  34  in order to squeeze together the first and second binding element sections  7   a ,  7   b . The squeezing member  51  is provided with a passage  52 , through which a laser beam  43  from the laser welding head  42  of the laser welding device  40  may be directed towards an area on the second binding element section  7   b , in order to form the welded joint  8  between the first and second binding element sections  7   a ,  7   b , when the squeezing member  51  is in said second position and keeps the first and second binding element sections  7   a ,  7   b  squeezed together between the squeezing member  51  and the support member  34 . The squeezing member  51  is moveable between said first and second positions by means of an actuator (not shown), which may be electrically, pneumatically or hydraulically driven. The actuator is with advantage a hydraulic cylinder. 
     The binding machine  1  further comprises an electronic control device  60  (very schematically illustrated in  FIG.  1   ) for controlling the operation of the binding machine. The electronic control device  60  is connected to the feeding and tensioning device  5  and configured to control the actuator or actuators of the feeding rollers  5   a ,  5   b  and tensioning members  5   c ,  5   d . The electronic control device  60  is also connected to the laser welding device  40  and configured to control the laser welding device to direct and focus the laser beam  43  of the laser welding device onto a desired part of the binding element  3 . Furthermore, the electronic control device  60  is connected to the actuating device  39  of the gripping arrangement  30  and to the actuator of the squeezing device  50  and configured to control the operation thereof. 
     The electronic control device  60  may be implemented by one single electronic control unit or by two or more mutually co-operating electronic control units. 
     During the execution of a tensile test, the electronic control device  60  may be configured to make the feeding and tensioning device  5  exert a tensile force of a given magnitude on the binding element  3  to thereby subject the joint  8  to a tensile force of a given magnitude. If the joint  8  withstands this tensile force, the result of the tensile test is deemed to be positive and the binding of objects may continue. If the joint  8  does not withstand the tensile force exerted during the tensile test, the joint  8  will break and the result of the tensile test is deemed to be negative. A negative result of a tensile test may for instance be due to the use of a binding element of a material with inappropriate properties or due to inappropriate welding parameters. Before proceeding with a binding of objects after a negative tensile test, the cause thereof has to be analysed and taken care of. 
     As an alternative, the electronic control device  60  may, during the execution of a tensile test, be configured to make the feeding and tensioning device  5  exert a tensile force with a magnitude that is made to gradually increase until the joint  8  breaks. In this case, the tensile test will give a value of the maximum strength of the joint  8 . 
     The electronic control device  60  may be configured to control the laser welding device  40  to direct a laser beam  43  (see  FIG.  2   i   ) onto an area at the trailing end of the second binding element section  7   b , i.e. at the end of the second binding element section  7   b  facing the feeding and tensioning device  5 , in order to cause the binding element to be broken or cut off at the trailing end of the second binding element section  7   b . Hereby, the closed loop  11  arranged around the object or objects  10  to be bound is released from the remaining part  3   b  of the binding element. When the joint  8  is to be subjected to a tensile test under the effect of the feeding and tensioning device  5 , the release of the closed loop  11  from the remaining part  3   b  of the binding element is of course effected after the performance of the tensile test. 
     The laser welding head  42  may comprise one or more computer-controlled scanning mirrors for controlling the direction and movement of the laser beam  43  emitted from the laser welding head. As an alternative, the direction and movement of the laser beam  43  may be controlled by computer-controlled movements of the entire laser welding head  42 . The laser welding head  42  is provided with a focusing lens  44 , through which the laser beam  43  leaves the laser welding head. 
     In the illustrated embodiment, the laser welding device  40  further comprises a laser source  45  (see  FIG.  2   a   ) for generating the laser power required for producing the laser beam  43  used for forming the welded joint  8  between the first and second binding element sections  7   a ,  7   b  and for releasing the closed loop  11  from the remaining part  3   b  of the binding element. The laser source  45  can be of any type commonly used for welding. In the illustrated example, the laser source  45  is connected to the laser welding head  42  via an optical fibre cable  46 , which is configured to guide the laser power generated by the laser source  45  to the laser welding head  42 . The optical fibre cable  46  is in a conventional manner connected to the laser welding head  42  by means of an optical connector  47  comprising focusing optics. The focal point of the laser beam  43  emitted from the laser welding head  42  may be adjusted by computer-controlled movements of one or more optical members included in the focusing optics of the optical connector  47 . 
     An operating sequence for securing a binding element  3  in the form of a strap in a loop around a bundle of objects  10  and performing a tensile test by means of the above-described binding machine  1  will now be described with reference to  FIGS.  2   a   - 2   j.    
     In a first step, the drive motor of the feeding rollers  5   a ,  5   b  is operated in a first direction in order to feed the binding element  3  forwards from the supply coil  6 , through the sealing unit  20 , in a loop around the object receiving space  4  of the binding machine  1  and then back into the sealing unit  20 . The leading end  12  of the binding element is first moved over the support member  34  and the pressing element  37 , thereafter in a loop around the object receiving space  4  and then into a space between the pressing element  37  and the recess  35  in the support surface  36  on the support member  34 , wherein the feeding of the binding element  3  is stopped when the leading end  12  of the binding element has reached a given end position. 
     During the feeding of the binding element  3 , the squeezing member  51  is in its retracted first position. 
     In the illustrated example, the pressing element  37  is positioned in the recess  35  in the support member  34  before the initial feeding of the leading end  12  of the binding element through the sealing unit  20  and maintained in the recess  35  until the leading end  12  of the binding element has passed over the upper surface  38  of the pressing element  37  and the upper support surface  36  on the support member  34 , as illustrated in  FIGS.  2   a  and  2   b   . Thus, in this case the upper surface  38  of the pressing element  37  is flush or at least essentially flush with the upper support surface  36  on the support member  34  when the leading end  12  of the binding element is fed through the sealing unit  20  before being fed around the object receiving space  4 . The actuating device  39  thereafter effects a relative movement between the pressing element  37  and the support member  34  in order to cause the pressing element  37  to be positioned at a distance from the recess  35  in the support member  34 , wherein the binding element  3  is lifted by the pressing element  37  from the upper support surface  36  on the support member  34 , as illustrated in  FIG.  2     c.    
     When the binding element  3  has been fed through the guide track  2  in a loop around the object receiving space  4 , the leading end  12  of the binding element  3  will leave the guide track  2  and pass through the gap between the pressing element  37  and the support member  34  (see  FIG.  2   d   ), whereupon the leading end  12  of the binding element  3  actuates a stop member (not shown) and the drive motor of the feeding rollers  5   a ,  5   b  is stopped. The actuating device  39  thereafter effects a relative movement between the pressing element  37  and the support member  34  in order to cause the pressing element  37  to be received in the recess  35  (see  FIG.  2   e   ) and thereby effect gripping and locking of the first binding element section  7   a  at the leading end of the binding element  3  while forming a bulge  14  on the first binding element section  7   a . In the next step, the drive motor of the feeding rollers  5   a ,  5   b  is reversed in order to retract the binding element  3  and thereby pull the binding element  3  out of the guide track  2  and into contact with the objects  10  received in the object receiving space  4 , as illustrated in  FIG.  2   f   . Thereafter, the drive motor of the tensioning rollers  5   c ,  5   d  is operated in order to draw the binding element  3  more tightly around the objects  10 . As illustrated in  FIGS.  2   e  and  2   f   , the sealing unit  20  and the guide track  2  are moveable in relation to the objects  10  and configured to move towards the objects  10  when the binding element  3  is tightened around the objects. 
     When the binding element  3  has been drawn tightly around the objects  10 , the squeezing member  51  is moved to its advanced second position in order to squeeze together the first and second binding element sections  7   a ,  7   b  between the squeezing member  51  and the support member  34  (see  FIG.  2   g   ). The laser welding device  40  is then operated to focus a laser beam  43  onto the mutually overlapping binding element sections  7   a ,  7   b  in order to form a welded joint  8  between the binding element sections  7   a ,  7   b . A piece  3   a  of the binding element  3  is thereby secured in a closed loop  11  around the objects  10 . 
     In the next step, the squeezing member  51  is moved to its retracted first position, as illustrated in  FIG.  2   h   , whereupon the drive motor of the tensioning rollers  5   c ,  5   d  is operated so as to make the tensioning rollers  5   c ,  5   d  exert a tensile force of a given magnitude on the binding element  3  in order to subject the joint  8  to a tensile test and thereby check the strength of the joint  8 . During this tensile test, the pressing element  37  is maintained in the recess  35  in the support member  34  and the gripping arrangement  30  thereby keeps the first binding element section  7   a  secured in fixed position in the sealing unit  20  by engagement with the part  13  of the first binding element section located between the joint  8  and the leading end  12  of the binding element. 
     If the joint  8  withstands the tensile test, the squeezing member  51  is in the next step (see  FIG.  2   i   ) moved back to its advanced second position, whereupon the laser welding device  40  is operated to direct a laser beam  43  onto an area at the trailing end of the second binding element section  7   b  in order to break or cut off the binding element  3  at the trailing end of the second binding element section  7   b  and thereby release the closed loop  11  around the objects  10  from the remaining part  3   b  of the binding element. Finally, the squeezing member  51  is returned to its retracted first position and the pressing element  37  and support member  34  are removed from the first binding element section  7   a  in order to release the closed loop  11  from the sealing unit  20 , as illustrated in  FIG.  2     j.    
       FIGS.  3   a - 3   e    illustrate an alternative operating sequence for forming a closed loop  11  of a binding element  3  in the form of a strap and performing a tensile test by means of the above-described binding machine  1 . In this case, the tensile test is performed during a separate test procedure without having the closed loop  11  secured around any object to be bound. At first, the binding element  3  is feed forwards by the feeding rollers  5   a ,  5   b , and the first binding element section  7   a  at the leading end of the binding element is gripped by the gripping arrangement  30  in the manner described above with reference to  FIGS.  2   a - 2   e   . In the next step, the drive motor of the feeding rollers  5   a ,  5   b  is reversed in order to retract the binding element  3  and thereby pull the binding element  3  out of the guide track  2 , as illustrated in  FIG.  3   c   . Thereafter, the squeezing member  51  is moved to its advanced second position in order to squeeze together the first and second binding element sections  7   a ,  7   b  between the squeezing member  51  and the support member  34 . The laser welding device  40  is then operated to focus a laser beam  43  onto the mutually overlapping binding element sections  7   a ,  7   b  in order to form a welded joint  8  between the binding element sections  7   a ,  7   b . A closed binding element loop  11  is hereby formed in the object receiving space  4 . In the next step, the squeezing member  51  is moved to its retracted first position, as illustrated in  FIG.  3   e   , whereupon the drive motor of the tensioning rollers  5   c ,  5   d  is operated so as to make the tensioning rollers  5   c ,  5   d  exert a tensile force of a given magnitude on the binding element  3  in order to subject the joint  8  to a tensile test and thereby check the strength of the joint  8 . During this tensile test, the pressing element  37  is maintained in the recess  35  in the support member  34  and the gripping arrangement  30  thereby keeps the first binding element section  7   a  secured in fixed position in the sealing unit  20  by engagement with the part  13  of the first binding element section located between the joint  8  and the leading end  12  of the binding element. 
     The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims. The binding machine according to the present invention may for instance be design for co-operation with a compacting machine in order to bind a coil of wire compacted by the compacting machine. In the latter case, several sealing units are mounted to the compacting machine and used simultaneously in order to apply binding element loops at different positions around the compacted coil of wire, wherein each binding element loop extends along the inside of the coil through a central axial opening therein and along the outside of the coil.