Patent Publication Number: US-2023150707-A1

Title: System and method for moving and unbundling a carton stack

Description:
TECHNICAL FIELD 
     The present invention relates to a method and a system for picking up and unbundling carton stacks. 
     BACKGROUND ART 
     Robots are often used for loading and unloading operations in the industry. Various types of products and objects can be handled by a robot. The products may be regular or irregular, and the size of an object may vary considerably. The robots can assemble products or they can be used to pack and stack the products. One common use for a robot is to move objects to a pallet in order to pack the pallet at the end of a production line. At the end of a production line, the products are often stored in regular boxes that will simplify the packing of products on a pallet. However, some products or product packages are shaped such that they can be packed on a pallet without the need to first pack them in a box. An example of such a product is a package containing a plurality of paper rolls, which is possible to pack on a pallet. 
     Another common use is to move products from a pallet onto a conveyor line at the beginning of a production line. One common product that is moved to a conveyor is flat-folded cartons or other flat sheet-like objects. These are often delivered in bundles wrapped together with a holding strap. Such a bundle must be moved from a pallet to an infeed station and the strap must be removed. 
     WO 2019/243674 A1 describes one way of transferring printed matter from a pallet to an entry section of a processing line. A vision system detects one side of the bundle and the position of the strap. A grasping member is positioned on top of the bundle, and the bundle is lifted in the strap by blades of the grasping member. The bundle is positioned in the entry section and the strap is cut by a cutting member and disposed of in a waste basket. 
     Such a system work well for some types of products, but there is still room for an improved system and method for moving carton bundles. 
     DISCLOSURE OF INVENTION 
     An object of the invention is therefore to provide an improved system for moving and unbundling carton stacks. Another object of the invention is to provide an improved method for moving and unbundling carton stacks. 
     The solution to the problem according to the invention is described in the characterizing part of claim  1  with regard to the system and in claim  10  regarding the method. The other claims contain advantageous embodiments and further developments of the system and method. 
     In a system for moving carton stacks from a pallet to a receiving position, where a stack is held together by a strap, where the receiving position comprises at least one carton support adapted to support the carton stack in a vertical position, where the system comprises an industrial robot provided with a gripping head, where the gripping head comprises a cutting module provided with a cutting means, where the system comprises at least one position for a pallet holding several carton stacks, a receiving position arranged to receive a carton stack in a vertical orientation, where the conveyor comprises at least one carton support adapted to support the carton stack in the vertical position, and a waste bin for receiving cut holding straps, the object of the invention is achieved in that the gripping head comprises an optical detection means adapted to detect the position of a print on a carton such that the orientation of the carton stack and the position of a strap can be determined, where the robot is arranged to move a carton stack from a horizontal position at the pallet to the vertical position at the receiving position, where the cutting means is arranged to cut off the strap at the receiving position, and that the gripping head is arranged to hold the cut strap and to be moved to the waste bin, where the gripping head is arranged to release the strap into the waste bin. 
     By this first embodiment of the system according to the invention, a system that allows horizontal carton stacks to be picked up and transferred to a vertical position, in which the strap holding the carton stack together is cut off and disposed of. The system is suitable for larger flat-folded cartons and other flat objects that are held together in a stack by a holding strap made of a plastic material. The size of such an object may be e.g. 30 cm*50 cm or more, and the number of objects in a stack may be e.g. 10-50 objects. The flat objects must be relatively rigid, since the complete stack is lifted by the upper object and the rest of the stack is lifted in the strap through the upper object. By positioning the carton stacks in a vertical position at a receiving position of e.g. a conveyor, the further handling of the cartons is simplified since the cartons can be forwarded in the proper orientation. 
     The orientation of the carton stack on the pallet is first detected, such that the carton stack can be positioned in the proper orientation at the receiving position. This will give the erected carton the proper orientation with regard to e.g. printing on the carton. The orientation of the carton is used to detect the position of the holding strap, which is applied with a specific tolerance. It is possible to use only the orientation of the carton to determine the position of the strap, or the position of the strap can also be detected by a detector. It is further possible to detect the presence of a strap with a strap detector. When the position of the strap is detected, the gripping head is positioned on the upper surface of the carton stack in a predefined position, such that a cutting means of the gripping head is positioned adjacent the strap. 
     The carton stack is lifted by the use of vacuum cups of the gripping head. By using vacuum cups, the carton stack can be lifted and moved in any direction and with any orientation. In this way, the carton stack can be placed in a vertical receiving position with a proper orientation. The carton stack is during the movement to the receiving position tilted to a more or less vertical orientation, and may at the same time be rotated such that the orientation of the printing of the carton stack is correct. 
     When the carton stack is placed at the receiving position and is standing still, the cutting module is moved from a start position adjacent the strap to a cutting position in which the cutting means of the trimming module encloses the strap. In this position, a lower blade and an upper blade of the cutting means is positioned on each side of the strap. A cutting actuator moves the blades with the cutting edges towards each other such that the strap is cut off. At the same time, a holding means is lowered towards the lower blade. The holding means will clamp the strap between the holding surface and the lower blade such that the strap is held securely by the holding means. Thereafter, the gripping head releases the carton stack and moves to a waste bin, where the strap is released. 
     The gripping head comprises a plurality of vacuum cups, a trimming module provided with a cutting means and an optical detection means. The cutting module of the trimming module is adapted to move from a start position in which the cutting means is positioned adjacent the strap to a cutting position in which the strap is embraced by the cutting means, with lower blade and an upper blade arranged on each side of the strap. The trimming module further comprises a holding means adapted to hold the strap when the cutting module has cut the strap. Since the gripping head will move a carton stack to a receiving position, unbundle the carton stack and move the cut strap to a waste bin, there is no need for an operator to constantly monitor or oversee the operation of the system. 
     In a method for moving a carton stack from a pallet to a receiving position and to cut a strap holding the carton stack together, the steps of: detecting the position of a print on a carton with an optical detection means such that the orientation of the carton stack can be determined, determining the position of the strap from the detected position of the print on the carton, positioning a gripping head in a predefined position relative the strap, lifting the carton stack with a plurality of vacuum cups arranged on the gripping head, placing the carton stack in a vertical position at the receiving position, moving a cutting module provided in the gripping head from a start position to a cutting position in which the cutting module embraces the strap, cutting the strap with the cutting module, holding the strap with a holding means arranged on the gripping head, moving the gripping head to a waste basket, and releasing the strap in the waste basket are disclosed. 
     By this first embodiment of the method according to the invention, a simplified way of moving and unbundling a carton stack is provided. By the method, a carton stack is moved from a horizontal position to a vertical position, and is unbundled at the vertical position. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will be described in greater detail in the following, with reference to the embodiments that are shown in the attached drawings, in which 
         FIG.  1    shows a schematic view of a system according to the invention, 
         FIG.  2    shows an example of a gripping head used in the system according to the invention, 
         FIG.  3    shows an example of a trimming module in a start position, 
         FIG.  4    shows the trimming module in a cutting position, 
         FIGS.  5   a - 5   c    show details of the trimming module in cut views, and 
         FIG.  6    shows a flow chart of an example of a method according to the invention. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way to limit the scope of the protection provided by the patent claims. In the described example, an example of moving a stack of folded cartons from a pallet is described. The method and system may as well be used for other flat objects held together by a holding strap. Reference to directions such as vertical, horizontal etc. are related to normal earth plane directions, i.e. the floor of a production plant is horizontal. 
       FIG.  1    shows a system according to the invention, and  FIG.  2    shows a gripping head used in the system. The system  1  comprises a robot  4  provided with a gripping head  20 . The robot may be a standard industrial robot having a multi axle robot arm  5  that can be moved in any direction, and is in the described example a collaborate robot that does not require a protection cage. The arm is provided with a gripping head  20  that is adapted to pick up and move a carton stack by using vacuum cups  22 . The gripping head is provided with a safety shroud  21  that will detect if the gripping head hits something and will in this case stop the robot. The robot is arranged at one end of a conveyor  6 , which is adapted to transport the cartons from a vertical position at a receiving position  7  to a carton handling station, e.g. a carton erecting station at the other end of the conveyor. The carton stacks are arranged in a horizontal direction on a pallet  2  arranged beside the robot and the conveyor. The system may be provided with one or more pallets from which the robot can pick up carton stacks. The pallets are positioned at specific, predefined positions such that the system does not have to identify the exact position of a pallet. With two pallets, there will be no interruption when a pallet is empty and needs to be exchanged. 
     In the shown example, the robot is adapted to move a carton stack  3  from a pallet  2  to a vertical receiving position  7  at one end of a conveyor  6 . A carton is provided with a print of some sort, e.g. a logotype that is arranged on the upper side of a carton, such that it is visible from above. The gripping head  20  will detect the print with an optical detection means  40 , e.g. a vision system comprising a camera  25 . When the print is detected, the system can determine the orientation of the carton stack. The actual orientation of the carton stack is important e.g. when the cartons are to be fed to a carton erecting station, such that the folded cartons are erected with the proper orientation. From the position of the print on the carton, the position of the strap  36  holding the carton stack together can also be determined, since the strap is applied to the carton stack in a known manner with a known tolerance. 
     The gripping head  20  is positioned on the carton stack by the robot such that the cutting module  28  of the trimming module  24  is positioned on one side of the strap  36 , in a start position  37 . The trimming module  24  is arranged on the frame  23  of the gripping head, and is in one example arranged with a resilient suspension such that the trimming module is spring-loaded in a vertical direction. The trimming module extends out from the gripping plane of the gripping head, i.e. below the vacuum cups  22  and the safety shroud  21  of the gripping head, when the gripping head is empty, and will bear on the upper carton in a carton stack when the gripping head is arranged on the carton stack. The resilient suspension assures that the lower blade  30  of the cutting module will be in contact with the upper carton. In the shown example, the lower blade  30  is provided with a spring-loaded catch finger  26  that is adapted to bear against the upper carton in a carton stack, even if the carton is not totally flat or if the lower blade  30  is positioned slightly above the upper carton. In this way, a strap will always be caught by the lower blade, even when the lower blade is not in contact with the upper carton or when the upper carton is somewhat warped. The catch finger can catch the strap such that it can slide up on the lower blade when the cutting module moves from the start position to the cutting position. 
     When the gripping head bears on the upper carton of the carton stack, the vacuum cups are engaged by an under pressure source arranged at the robot. The vacuum cups will attach the gripping head to the carton stack such that the carton stack can be lifted and manipulated by the robot. The vacuum cups will hold the uppermost carton and the strap holds the complete stack together. By lifting a carton stack in this way, the cartons must be relatively stiff since most of the cartons are held only by the strap. The gripping head is thus not suitable for lifting soft or flexible products, even if they are held together by a strap. The surface of the carton must also be relatively flat, such that the vacuum cups can get a good grip. 
     When the gripping head is attached to the carton stack, the cutting module  28  of the trimming module  24  is moved from the start position  37 , as shown in  FIG.  3   , to the cutting position  38 , as shown in  FIG.  4   . The catch finger  26  and the lower blade  30  of the cutting module are bevelled at the front, such that they will easily slide under the strap when the cutting module is moved towards the cutting position, even if the upper carton is not totally flat. In the cutting position, the strap  36  is enclosed by the cutting module  28 , where the lower blade  30  with a lower edge  32  is positioned under the strap, and where the upper blade  31  with an upper edge  33  is positioned above the strap. 
     The gripping head  20  may also be provided with a strap detector (not shown), which in one example may be a photoelectric sensor that will detect the position of the strap. The photoelectric sensor can be used to determine the position of the strap, which may be helpful for fine adjustment of the gripping head before the gripping head is positioned on the carton stack. The photoelectric sensor may also be used to ensure that the carton stack is provided with a strap. Since the strap is applied to a carton stack in a predictable manner, at the same position for every carton stack, the strap detector is optional. 
     In the described example, the cutting module is moved from the start position to the cutting position before the carton stack is lifted. It is also possible to move the cutting module to the cutting position when the carton stack is positioned at the receiving position  7 . 
     The trimming module  24  is provided with a linear actuator  27  on which the cutting module  28  is mounted. The linear actuator will move the cutting module from the start position  37  to the cutting position  38 . The cutting position may be a fixed position corresponding to the end position of the linear actuator. The cutting module may also be provided with a detector, e.g. a micro switch, which detects when the cutting module has reached the strap and stops the linear actuator. 
     When the carton stack is held by the gripping head, the carton stack is lifted and moved to the receiving position  7  at the conveyor  6 . Depending on the orientation of the carton stack on the pallet, the carton stack may also be rotated such that the carton stack is positioned at the receiving position with the correct orientation with regards to the print on the cartons. When the carton stack is bearing on the conveyor at the receiving position, the strap can be cut by a cutting means comprising an upper blade  31  and a lower blade  30 . The strap is cut off by engaging a cutting actuator  34  of the cutting module  28 , as is shown in  FIGS.  5   a - 5   c   . The cutting actuator will move the upper blade  31  provided with an upper edge  33  towards the lower blade  30  provided with a lower edge  32  such that the edges perform a cutting action. Since the system with the gripping head is a collaborative system where a human may work in the reach area of the robot arm, it is important that there is no sharp or pointed edges at the cutting module. The edges are thus not sharp or pointed, but are two 90 degrees edges that cut the strap when the blades pass each other. 
     At the same time, a holding means  35  arranged at the cutting means, together with the upper blade, will move towards the lower blade and will clamp the strap between the holding means and the lower blade, as shown in  FIG.  5   b   . The strap is now securely held by the cutting module. The holding means may e.g. comprise a pointed pattern or a protruding part that cooperates with a recess in the lower blade. The holding means is preferably spring-loaded such that it will be able to grip a strap in a secure way regardless of the thickness of the strap. When the holding means bears on the strap, the upper blade of the cutting means continues downwards and cuts off the strap, as shown in  FIG.  5   c   . The strap is now cut off and is securely held in the gripping head by the holding means. 
     In the shown example, the conveyor comprises two spaced apart conveyor belts, such that the centre of the conveyor is open. This will simplify the removal of a strap that is positioned in a vertical direction of the carton stack at the receiving position. Since the conveyor is open at the centre, the carton stack will not stand on the strap, and the strap can easily be removed. The strap may also be positioned in a horizontal direction, in which case also a closed conveyor belt may be used. The conveyor is provided with a vertical carton support that will support the carton stack. The conveyor may also be provided with additional grippers that hold the carton stack. The orientation of the carton stack at the receiving position is substantially vertical, i.e. the cartons are arranged with an angle between 70-90 degrees with respect to a horizontal plane. 
     The carton stack is released from the gripping head by evacuating the under pressure from the vacuum cups. The robot moves the gripping head from the receiving position to a position above a waste bin, where the strap is released from the trimming module by returning the cutting actuator to its idle position. The strap falls down into the waste bin and the gripping head is ready to pick up a new carton stack. 
     The system is further provided with a control unit adapted to control the movement of the robot and the gripping head. The control unit is preferably connected to the control system for the complete manufacturing system including the conveyor system. In this way, the robot can move carton stacks to the receiving position when needed. The control unit can also adapt the system to different types of cartons, e.g. having different sizes or different printing. 
     A further advantage of the system is that the gripper head can also be used to remove interposing sheets or liners arranged between different layers of carton stacks. A liner can easily be picked up and placed in a vertical direction on a pallet next to the pallet with the carton stacks. 
     In the method for moving a carton stack from a pallet to a receiving station and to unbundle the carton stack, the following steps are comprised. 
     In a first step  100 , the position of the print on the carton is detected with an optical detection means. From the position of the print, the orientation of the carton pack can be determined. The optical detection means may e.g. comprise a vision system having a camera that will detect the position and orientation of a print on a carton. 
     In a second step  110 , the position of the strap holding the carton stack together is determined from the detected position of the print on the carton. The position of the strap may be estimated from the position of the print, since the strap is applied to a carton stack in the same position for all carton stacks, or the position of the strap may be detected individually by the optical detection means. 
     In step  120 , the gripping head is positioned on the upper carton in a carton stack in a predefined position relative the strap. In this position, the cutting module of the trimming module is positioned on one side of the strap, adjacent the strap. 
     In step  130 , the carton stack is lifted by using a plurality of vacuum cups arranged on the gripping head. The gripper head lift the upper carton of the carton stack, and the rest of the cartons in the carton stack follows the upper carton due to the strap holding the carton stack together. 
     In step  140 , the carton stack is placed in a vertical position at the receiving position. The carton stack may be placed with the strap in a vertical direction or in a horizontal direction. 
     In step  150 , the cutting module is moved from a start position to a cutting position in which the cutting means of the cutting module embraces the strap. In this position, the lower blade with a lower edge will be positioned under the strap, and the upper blade with an upper edge will be positioned above the strap. This step may also be performed after the gripping head has attached to the carton stack, but before the carton stack is lifted. 
     In step  160 , the strap is cut with the cutting module, by moving the upper blade with the upper edge towards the lower blade with the lower edge by the use of a cutting actuator. At the same time, a holding means is moved downwards towards the lower blade. The holding means is arranged adjacent the upper blade. 
     In step  170 , the strap is held by the holding means arranged on the cutting module. The holding means will clamp the strap between the holding means and the lower blade in a secure way. 
     In step  180 , the gripping head is moved away from the receiving position to a position above a waste bin. 
     In step  190 , the strap is released into the waste bin by returning the cutting actuator to its idle state, such that the holding means releases the grip of the strap. The gripping head can now return to the pallet to pick up a new carton stack. 
     A further step that may be included, depending on how the position of the strap is detected. If the position of the strap is determined only by using the position of the print, it may be of advantage to detect if a carton pack comprises a strap. The presence of a strap may be detected by an optical detector, e.g. a photoelectric sensor, which detects the presence of a strap. This sensor may be used to detect the presence of a strap, or if the strap is misaligned. If the strap is misaligned, the holding position of the gripper head may be adjusted such that the gripper head is aligned correctly with regards to the strap. 
     The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims. 
     REFERENCE SIGNS 
     
         
           1 : System 
           2 : Pallet 
           3 : Carton stack 
           4 : Robot 
           5 : Robot arm 
           6 : Conveyor 
           7 : Receiving position 
           8 : Waste bin 
           20 : Gripping head 
           21 : Safety shroud 
           22 : Vacuum cup 
           23 : Frame 
           24 : Trimming module 
           25 : Vision system 
           26 : Catch finger 
           27 : Linear actuator 
           28 : Cutting module 
           29 : Cutting means 
           30 : Lower blade 
           31 : Upper blade 
           32 : Lower edge 
           33 : Upper edge 
           34 : Cutting actuator 
           35 : Holding means 
           36 : Strap 
           37 : Start position 
           38 : Cutting position 
           39 : Gripping plane 
           40 : Optical detection means