Patent Publication Number: US-2023159208-A1

Title: Unwrapping apparatus and method for unwrapping articles

Description:
The present invention relates to an apparatus for unwrapping articles, such as palletized packages, by cutting the wraps around the articles, and to a method for autonomous unwrapping of articles. 
     Palletized articles are often wrapped with a flexible plastic wrap, in order to keep the articles from moving or even falling off the pallet, during transportation. 
     The wrap is usually applied to the articles about a vertical axis being orthogonal to the plane of the pallet. 
     In some situations, when for instance it is desired to keep the articles dry, it is further necessary to apply the wrap to the articles about a horizontal axis being parallel to the plane of the pallet. 
     The articles are unwrapped either manually using knifes, or an unwrapping apparatus. 
     Today, unwrapping apparatuses often use suction to pull a part of the wrap and subsequently pierce or cut the part of the wrap being pulled, using a knife or a pointed object. 
     EP 0625465 discloses an unwrapping apparatus, for removing the wrap from palletized articles, comprising suction cups for applying suction to a part of the wrap and for pulling that portion, a pointed object for piercing the part of the wrap being pulled, and removing devices, for removing the severed wrap. 
     However, articles are not always stacked in a way to form a cuboid on the pallet, but are sometimes stacked randomly, or forming a shape having a contour which forms steps. 
     The above mentioned EP document is only adapted to unwrap articles, that form a cuboid. It is not adapted to unwrap palletized articles, that are stacked in a way forming steps, or in a random way. It is further only adapted to initiate the unwrapping process on the sides of the articles, and not at the top for instance, and only when suction is applied. 
     Yet another problem with the prior art is, that an operator is required to operate the unwrapping apparatus, or to set the pathways for the wrap removing device(s) to follow the contour of the wrap, such that the unwrapping apparatus does not cut into the articles. 
     U.S. Pat. No. 5,463,841 discloses an unwrapping apparatus which is adapted to remove wraps from the top of palletized articles. It is however limited to only remove the wraps from articles on pallets of a certain size and height due to its construction, occupies much space due to its size, and is immobile. 
     The object of the present invention is inter alia to provide an unwrapping apparatus and a method for unwrapping palletized wrapped articles, which solves the above mentioned problems, and overcomes the above mentioned limitations. 
     SUMMARY 
     In view of this object, an unwrapping apparatus, configured to unwrap a stack of wrapped articles is provided, comprising an unwrapper head, which comprises a housing, a cutter head, a drive, the drive being configured to rotate the cutter head relative to the housing, the cutter head comprising a gripper, a knife, and a first actuator, being configured to move the gripper along a first path of movement relative to the housing, between a first retracted position and a first advanced position, a robotic manipulator arm, configured to move the unwrapper head, a registration device, configured to register a contour of the stack, and a controller, configured to control the robotic manipulator arm and the drive, in accordance with the registered contour, and the controller further being configured to control the first actuator. 
     In this way, a registration device will register a contour of the stacked articles, and sending the information to the controller, which then will calculate/establish a cutting path through the wrap, along the contour of the stack of articles. The cutting path preferably extends in a vertical plane, from the top of the stack to the bottom of the stack. 
     The controller then controls the robotic manipulator arm to move the unwrapper head along the cutting path, while the gripper is moved to the advanced position such as to get under a free edge of the wrap and drag the wrap towards an edge of the article, and then guide the wrap towards the knife while being moved along the surface of the articles, without damaging the stacked articles. 
     In another embodiment of the unwrapping apparatus, the unwrapper head further comprises a second actuator, configured to move the gripper and knife along a second path of movement, between a second retracted position and a second advanced position, the first path of movement and the second path of movement not being parallel, and wherein the controller further controls the second actuator, and a suction channel having a suction inlet at the knife, wherein the second retracted position is closer to the suction channel than the second advanced position. 
     In this way, the unwrapping apparatus can be used to start cutting on any surface of the stacked articles. The unwrapper head will use suction at a suction inlet of the unwrapper head to pull a part of the wrap towards the knife which is retracted towards a retracted position, in order not to damage the wrap, until the controller controls the second actuator to move the knife to an advanced position, thereby piercing the part of the wrap being pulled, thereby allowing the gripper to get below a now free end of the damaged wrap, and drag the wrap towards an edge of the article, or simply guide the wrap towards the knife. The unwrapping may for instance begin at a vertical surface of a stacked article, or at a horizontal surface of an article, which is wrapped on a top surface and therefore has no free edge to be grabbed by the gripper. 
     In another embodiment, the first actuator and the gripper are linked to each other by a pivoting lever, the first actuator acting on one end of the pivoting lever and the gripper is arranged on another end of the pivoting lever. 
     In this way, the first actuator can move the gripper between a retracted position, which is desirable in a situation, where a measurement is to be conducted and an advanced gripper would provide an obstacle, and prevent a precise measurement, and an advanced position, which is desirable when for instance a free end of a wrap is to be gripped. 
     In one embodiment, the gripper can only be fully retracted to the second retracted position by the second actuator, when the gripper is retracted towards the first retracted position by the first actuator. In this way, the gripper will not collide with a wall of the suction inlet when being retracted towards the second retracted position by the second actuator. 
     In another embodiment, the unwrapper head further comprises a spring, configured to bias the gripper towards the first advanced position, and wherein the first actuator is configured to counteract the spring and move the gripper towards the first retracted position, when activated. 
     Pressing the gripper towards the first advanced position using a spring, allows the gripper to follow the contour of the stack of articles while being advanced, thereby being able to catch a free end of the wrap, and drag it towards an edge of the article, and stay under the uncut wrap while following the contour, and guiding the uncut wrap portions towards the knife, being arranged at a top portion of the gripper, but arranged further within the suction channel than the gripper, in order only to cut the portion of wrap that is guided towards it by the gripper, and not cut into the surface of the articles. 
     In another embodiment, the registration device comprises one of the following: a camera or scanner, or a device for registering the rotation of wheels arranged on the unwrapper head, or a device for registering the force resisting the movement of the robotic manipulator arm, or sensors configured to detect distances, or a combination of two or more of the above mentioned registering options. 
     In this way, a contour of the stacked articles can either be registered by taking a picture of the contour, or scan the contour and get a digital representation of it, or registering the distances that the wheels travelled along the surfaces of the stacked articles thereby getting measurements of the lengths of the surfaces of the articles, or getting measurements of the lengths by registering where and when the unwrapper head moved by the robotic manipulator arm has reached a surface or an edge of the stack of articles, or measuring distances and using sensors, or using a combination of two or more of the above mentioned techniques, to register the contour of the stacked articles. The information will then be sent to the controller, which will calculate and determine a cutting path, based on the information obtained by the registering device, and control the robotic manipulator arm to move the unwrapper head, based on the determined cutting path. 
     In the case where the registration device comprises a camera or a scanner, the registration device will be configured to obtain, capture, record, or scan an image of a contour of the stack, and send a digital representation of the image to the controller, which then will process and/or analyse that digital representation and determine a cutting path. The processing and/or analysis of the digital representation of the image may be conducted by the camera or scanner, which then will determine a cutting path, and send information about the cutting path to the controller. 
     In view of the above mentioned object, a method for unwrapping a stack of wrapped articles using an unwrapping apparatus is provided, using an unwrapping apparatus with an unwrapper head comprising: 
     a) a wrapping gripper, such as i) a wrapping gripper comprising an arm with a free end for wrapping gripping or ii) a wrapping gripper with suction inlets for gripping the wrapping by applying suction to the wrapping, optionally rotatably mounted to a housing of the unwrapper head, and 
     b) a knife, the unwrapping apparatus further comprising: 
     a robotic manipulator arm, configured to move the unwrapper head, 
     a registration device, configured to register a contour of the stack, 
     a controller, configured to control the robotic manipulator arm, 
     the method comprising the steps of: 
     registering the contour of the stack using the registration device, establishing a cutting path which follows said registered contour of stack, and 
     moving the unwrapper head to a top surface portion of the stack, and gripping by the gripper a free end edge of the wrapping of the stack at the top surface portion, such as by applying suction by the gripper to the wrapping at the free end edge, and dragging by the gripper the free end edge of the wrap towards an edge of the top surface portion, and cutting the wrap along the cutting path by moving the unwrapper head. The established cutting path preferably extends in a vertical plane, and preferably from the top of the stack to the bottom of the stack. 
     In this way, a registration device will register a contour of the stacked articles, and send the information to the controller, which then will calculate/establish a cutting path, along the contour of the stack of articles. The controller then controls the robotic manipulator arm to move the unwrapper head along the cutting path, while the gripper is moved to the advanced position such as to get under a free edge of the wrap and drag the wrap towards an edge of the article, and then guide the wrap towards the knife while being moved along the cutter head, without damaging the stacked articles. 
     In another embodiment, the method of the registering of a contour of the stack by the registering device, comprises one of the following steps:
         recording one or more images using a camera or a scanner, or   counting the number of rotations of wheels arranged on the unwrapper head during the moving of the cutter head along the contour, or   using sensors sensing during the moving of the cutter head along the contour the presence of obstacles or measuring distances, or   measuring during the moving of the cutter head along the contour loads resisting the movement of the robotic manipulator arm, or   a combination of two or more of the above mentioned steps.       

     In another embodiment, the registering of a contour of the stack by the registering device, comprises the steps of:
         moving the unwrapper head in a horizontal direction towards a portion of the stack of wrapped articles until a force is measured resisting a further movement of the unwrapper head in the horizontal direction or an obstacle is detected using sensors, and
           moving the unwrapper head in a vertical direction, until either
               1 an edge is detected by registering the absence of a force resisting a further movement in the vertical direction, or using sensors detecting the absence of an obstacle, or   2 a corner is detected by measuring the presence of a force resisting a further movement in the vertical direction, or using sensors detecting the presence of an obstacle, and   
               moving the unwrapper head in a horizontal direction, and   repeating the above mentioned steps, until a free end of the wrap is detected, and   sending location information of the change in directions of movements of the unwrapper head and the location of the free end of the wrap from the registering device to the controller, while conducting the above mentioned steps of registering the contour of the stack.   
               

     In this way, measurements of the lengths of the surfaces of the stack are obtained, by registering where and when the unwrapper head, moved by the robotic manipulator arm, has reached a surface or an edge of the stack of articles, and thereby needs to change the direction of movement, in order to continue following the contour of the stack. 
     In another embodiment, the method comprises the steps of:
         using a spring to bias the gripper towards a first advanced position relative to a housing comprising the cutter head along a first path of movement,   using a first actuator to apply a load on one end of a lever connecting the first actuator with the gripper to counteract the pressing force of the spring and moving the gripper towards a first retracted position along the first path of movement.       

     In this way, the gripper will be in an advanced position, thereby following the contour of the stack of articles, while being retractable towards a retracted position, when the first actuator is activated. Retracting the gripper is desired when for instance a process of registering the contour of the stack of articles is conducted, and it is desired that the gripper is not in an advanced position in order to not become an obstacle hindering an accurate acquisition of information. 
     In another embodiment, the method comprises the step of moving the gripper and knife between a second retracted position and a second advanced position along a second path of movement using a second actuator, wherein the first and second path of movement not being parallel. 
     In this way, the second actuator is able to retract the gripper and the knife towards a second retracted position, in a direction away from the suction inlet. This is desired, when for instance the unwrapping process is to be started on a vertical surface of the stack of wrapped articles, or on a top surface of the stack without the presence of a free end of the wrap. A portion of the wrap is pulled towards the suction inlet. If the gripper is not retracted, it will make an obstacle preventing the portion of the wrap from being pulled properly into the suction chamber of the cutter head, and if the knife is not retracted, the pulled portion of the wrap would immediately be pierced. This may not be desired. Therefore, the gripper and the knife are retractable using the second actuator, towards a second retracted position along a second path of movement, being further inside the suction chamber. This will further allow the portion of pierced wrap to be pulled towards the suction chamber along the second path of movement, and allow the gripper to be moved towards the first advanced position, along the first path of movement, and eventually get under the wrap, since the first path of movement and the second path of movement not being parallel. 
     In another embodiment, the method comprises the steps of:
         arranging the unwrapper head at a surface of the wrap, and   retracting the gripper towards the first retracting position, and   pulling a portion of the wrap, using suction, towards a suction, inlet of a suction channel comprised in the unwrapper head, and   piercing the portion of wrap being pulled towards the suction inlet using the knife arranged at the suction inlet.       

     In view of the above mentioned object, another method for unwrapping a stack of wrapped articles using an unwrapping apparatus as described in the previously mentioned embodiments, is provided, the method comprising the steps of:
         determining a cutting path which follows the registered contour of the stack, and   moving the cutter head to a top surface portion of the stack, and   gripping a free end edge of the wrapping of the stack at the top surface portion, and   dragging the free end edge of the wrap towards an edge of the top surface portion, and   initiating a cutting of the wrap along the cutting path while dragging uncut portions of the wrap downwards along the determined cutting path.       

     In this way, a registration device will register a contour of the stacked articles, and sending the information to the controller, which then will calculate a cutting path through the wrap, along the contour of the stack of articles. The controller then controls the robotic manipulator arm to move the unwrapper head along the calculated cutting path, while the gripper is moved to the advanced position such as to get under a free edge of the wrap and drag the wrap towards an edge of the article, and then guide the wrap towards the knife while being moved along the cutter head, without damaging the stacked articles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view of a stack of wrapped articles on a pallet and an unwrapper head of the apparatus of the invention, placed on top of the stack. 
         FIG.  2    is a view of a front portion of the unwrapper head. 
         FIG.  3    is a view of the unwrapper head. 
         FIG.  4    is a schematic cross-sectional view of the unwrapper head. 
         FIG.  5    is a schematic cross-sectional side view of the unwrapper head showing the gripper fully retracted in a first retracted position. 
         FIG.  6    is a schematic cross-sectional side view of the unwrapper head showing the gripper fully advanced in a first advanced position. 
         FIG.  7    is a schematic side view of the unwrapper head, showing the cutter head dragging a wrap by its top edge, along the top side of a wrapped article, towards the edge of the article. 
         FIG.  8    is a schematic side view of the unwrapper head shown in  FIG.  7   , having reached the edge of the wrapped article. 
         FIG.  9   a    is a schematic side view of the unwrapper head shown in  FIG.  7   , while removing the wrap at a corner, defined by two stacked articles. 
         FIG.  9   b    is a schematic side view of the unwrapper head shown in  FIG.  7   , while removing the wrap along a corner of a stacked article. 
         FIG.  10   a    is a schematic side view of the unwrapper head shown in  FIG.  7   , showing a portion of the wrap on a top side of a wrapped article, being pulled towards the cutter head, using suction. 
         FIG.  10   b    is a schematic side view of the unwrapper head shown in  FIG.  10   a   , while piercing through the portion of the wrap being pulled, using a knife. 
         FIG.  10   c    is a schematic side view of the unwrapper head shown in  FIG.  10   b   , while cutting the wrap along a top side of the wrapped article. 
         FIGS.  11   a - 11   d    show an alternative embodiment of the unwrapper head, in perspective and cross-sectional view, and in a first position cutting at the top of a stack and in a second position cutting along the side of a stack, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the invention will now be explained in more detail below by reference to the figures. 
       FIG.  1    shows the unwrapper head  1 , positioned on top of a stack S of wrapped articles  50 ,  50 ′, arranged on a pallet  60 . The wrap  40  wrapping the stack S of articles  50 ,  50 ′ is indicated by shaded lines. 
       FIG.  2    shows a closer view of a part of the unwrapper head  1 , comprising a housing  2 , the housing  2  comprising wheels  3  and a cutter head  10 , the cutter head  10  comprising: a gripper  11  having in the shown embodiment an arm  11   a  with a free end defining a gripping tip  11   b , a knife  12 , and a suction inlet  13  in communication with a suction channel  14 . The shown gripper  11  is spring loaded using a spring (not shown). The knife  12  is arranged at a top portion of the gripper  11 , and arranged closer to the suction channel  14  than the gripper  11 . 
       FIG.  3    shows the unwrapper head  1  comprising a drive  4 , which may be a motor, preferably a gear motor, preferably mounted to the housing  2 . The drive  4  is configured to rotate the cutter head  10 , in order to allow the cutter head  10  to adapt to any surface of an article  50  to be unwrapped. 
       FIG.  4    shows a first actuator  15 , in connection with the gripper  11 , configured to move the gripper  11  along a first path of movement FP between a first retracted position ( FIG.  5   ) and a first advanced position ( FIG.  6   ). 
     For clarity reasons, the first path of movement FP is in the figures shown parallel to the gripper  11 . However, the first path of movement FP also follows a longitudinal axis of the gripper  11  or is also aligned with the direction of movement of the gripper  11 . 
       FIG.  4    further shows a second actuator  16 , which is in connection with both the gripper  11  and the knife  12 , and is configured to simultaneously move the gripper  11  and the knife  12  in the same direction along a second path of movement SP between a second retracted position ( FIG.  10   a   ) and a second advanced position ( FIG.  10   b   ), wherein the second advanced position is closer to a suction inlet  13  than the second retracted position is. 
     For clarity reasons, the second path of movement SP is in the figures shown parallel to the cutter head  10 . However, the second path of movement SP also follows a longitudinal axis of the cutter head  10  or is also aligned with the direction of movement of the knife  12 , which also is the direction of movement/action of the second actuator  16 . 
     As shown in  FIGS.  4 - 6   , the connection between the second actuator  16  and the gripper  11  and knife  12  may be a direct connection, whereas the connection between the first actuator  15  and the gripper  11  may have a link in-between, such as a mechanism comprising a pivoting lever  18 , acting as a tilt, wherein the first actuator  15  acts on one side of the pivoting lever  18 , and the gripper  11  is arranged on the other side of the pivoting lever  18 . A spring (not shown) will keep the gripper  11  in tension, biasing it into the first advanced position, until the first actuator  15  counteracts the spring force, and acts on one side of the pivoting lever  18 , thereby moving the gripper  11 , which is arranged on the other side of the pivoting lever  18 , towards the first retracted position. When the first actuator  15  is deactivated, the spring load will move the gripper  11  towards the first advanced position, and keep pressing on the gripper  11  to keep it in that position. This situation is seen in  FIG.  6   . 
     It is further seen, that the first path of movement FP brought about by the first actuator  15 , and the second path of movement SP brought about by the second actuator  16 , are not parallel. 
     The unwrapping apparatus further comprises a controller C and a robotic manipulator arm  5 , controlled by the controller C and configured to move the unwrapper head  1  along the top surfaces and side surfaces of the stack S of articles. 
     The controller C further controls the first and second actuators  15 ,  16 , the drive  4 , and the suction. 
     When fully advanced by the first actuator  15 , the tip part  11   b  of the gripper  11  is reaching beyond the foremost front end of the cutter head  10  as seen in  FIG.  6   , while the gripper  11  when fully retracted, is arranged as seen in  FIG.  5   . 
     The gripper  11 , when fully advanced by the second actuator  16 , is positioned at a foremost front end of the cutter head  10  and in front of the suction inlet  13 , as seen in all figures other than  FIG.  10   a   , whereas when the gripper  11  is fully retracted by the second actuator, the tip part  11   b  of the gripper  11  is positioned within the suction chamber  14 , as seen in  FIG.  10     a.    
     The figure further shows holes in the rear end of the housing  2 , for mounting of the robotic manipulator arm  5 . 
       FIG.  5    shows schematically a cross-sectional side view of the unwrapper head  1  shown in  FIG.  3   , wherein the gripper  11  is fully retracted. In this situation, the first actuator  15  acts on the pivoting lever  18  to counteract the spring, and force the gripper  11  into a fully retracted position. 
       FIG.  6    shows schematically a cross-sectional side view of the unwrapper head  1 , in a situation, where the first actuator  15  no longer acts on the pivoting lever  18 , and the spring therefore has forced the gripper  11  into the advanced position. 
     As shown in  FIGS.  5  and  6   , when the gripper  11  is in the first and second advanced positions, the gripper  11  may touch a surface of an article, while when in the first retracted position, the gripper  11  will not be suitable to touch a surface of an article. 
     To describe the unwrapping method, an example of a process is made, using reference to the figures. Reference is made again to  FIG.  1   . 
     A scanning process is initiated prior to a cutting process, whereby a cutting path is determined which follows a vertical contour of the stacked articles  50 ,  50 ′, using sensors arranged on the unwrapper head  1  or the resisting forces measured resisting the further movement of the robotic manipulator arm  5 . This is to ensure a fully automatic cutting process without cutting into the stacked articles  50 ,  50 ′. 
     When a stack of wrapped articles  50 ,  50 ′ as seen in  FIG.  1    is to be unwrapped, the unwrapper head  1  is brought to the bottom of the wrapped articles  50 ,  50 ′ or the pallet  60 , using the robotic manipulator arm  5 . 
     At this point, the gripper  11  and the knife  12 , are fully retracted in both first and second retracted positions, and the cutter head  10  is pushed towards the vertical side of the lowest article  50  or towards the pallet  60 . 
     The robotic manipulator will begin moving the unwrapper head  1  upwards along the vertical contour of the stack S of articles  50 ,  50 ′, while pushing the cutter head  10  against the sides of the articles  50 ,  50 ′, but without damaging the articles  50 ,  50 ′. The wheels  3  of the housing  2  reduce the friction between the unwrapper head  1  and the wrap wrapping the articles. 
     The registering device will record the vertical and horizontal contour of the stack S of articles  50 ,  50 ′ during the entire movement of the unwrapper head  1 , using the sensors mounted to the unwrapper head  1  or using the registered resisting forces, until the unwrapper head  1  reaches the top edge of the highest article  50  of the stack S of articles  50 ,  50 ′, and sending the registered information to the controller C, which determines a cutting path based on these information. 
     Thus, the controller C will let the unwrapper head  1  travel upwards along the vertical side of an article  50 , until it detects an edge of that article. From that point, the controller C will let the unwrapper head  1  travel horizontally along the horizontal top side of the article  50 , until it detects a vertical side of an article  50 ′, wherefrom it again lets the unwrapper head  1  travel upwards along the vertical side of the article  50 ′. 
     Once the top of the stack S of articles has been reached, the controller C will move the unwrapper head  1  horizontally on top of the stack S of articles, until an edge  41  of the wrap  40  has been detected. This situation is depicted in  FIG.  7   . 
     Reference is now made to  FIG.  7   . At this point, the controller C deactivates the first actuator  15  in order to allow the spring to force the gripper  11  towards a first advanced position, and controls the second actuator  16  to bring the gripper  11  and the knife  12  towards a second advanced position, as seen in  FIG.  7   . 
     As seen in  FIG.  7   , the gripper  11  will travel towards the first advanced position, until the top side surface of an article  50  is reached. From here, the controller C will control the robotic manipulator arm  5  to move the unwrapper head  1  backwards along the previously scanned pathway. The gripper  11  will eventually grip an edge  41  of the wrap  40 , and drag that free end edge  41  of the wrap  40  towards an edge of the top surface portion of the article, as seen in  FIGS.  7 - 8   . 
     When the unwrapper head  1  reaches the edge of the article  50 , and continues following the pathway vertically downwards, as seen in  FIG.  8   , the knife  12  which is put in the second advanced position, will eventually press against a portion of the wrap  40  beginning with the dragged edge  41  of the wrap  40 , and eventually cut that portion, beginning with the edge  41  of the wrap  40 . The cutting process of the unwrapping process has thus begun. 
       FIG.  9   a    shows schematically a situation, where the unwrapper head  1  has reached a corner defined between two articles  50 ,  50 ′. The drive  4  has rotated the cutter head  10  relative to the housing  2 , such that the cutting of the wrap  40  continues, following the cutting path along the horizontal surface of the article  50  below. In this situation it is seen, that the gripper  11 , due to the tension from the spring load, still functions as a guide, guiding the wrap  40  towards the knife  12 . 
       FIG.  9   b    shows schematically a similar situation as in  FIG.  9   a   , but where the unwrapper head  10  has to follow a part of the contour of the stack S defining a cavity, and the drive  4  therefore has rotated the cutter head  10  to form an appropriate angle with the housing  2 . 
       FIG.  10   a    shows a situation where the unwrapping begins on top of an article, where no wrap edge  41  is present. This may be a situation, where the top surface of the article or stack S is wrapped. However, the same process would apply when the unwrapping is to begin on a vertical side surface of an article  50 . 
     In this situation, the drive  4  has rotated the cutter head  10  into an appropriate vertical position. In a situation where the unwrapping begins on a vertical side surface of an article  50 , the drive  4  would rotate the cutter head  10  into a horizontal position. 
     In this situation, the suction is activated, thereby pulling a part of the wrap  40  towards the suction inlet  13  at the front end of the cutter head  10 , keeping that particular part of the wrap  40  under tension. The gripper  11  and the knife  12  are seen retracted in the second path of movement SP, such as not to damage the part of the wrap  40  being pulled. The gripper  11  is in this situation retracted in the horizontal (first path of movement FP) and the vertical (second path of movement SP) direction by both the first and second actuators  15 ,  16 , respectively. 
     As schematically illustrated in  FIG.  10   b   , the second actuator  16  then moves the knife  12  and the gripper  11  into the second advanced position in the vertical direction along the second path of direction, thereby piercing the part of the wrap  40  held under tension. The gripper  11  is however still retracted in the horizontal direction by the first actuator  15 . 
     The wrap  40  may also be pierced by simply retracting the gripper  11  towards the second retracting position, while the knife  12  is in the second advanced position, as seen in  FIG.  10   b   , wherein when suction is activated, a portion of the wrap  40  will be pulled towards the knife  12 , and thereby be pierced. 
     During the two alternative situations mentioned above, the suction is still activated, and the severed part of the wrap  40  is pulled towards the suction inlet  13 . This in turn allows the gripper  11  to get below a part of the wrap  40  near the newly created free end edge  41  of the wrap  40 . 
     From here, the unwrapping process arrives at a situation similar to that illustrated in  FIG.  7   , where suction no longer is necessary, and where the gripper  11  drags the edge  41  of the wrap  40  towards an edge of the article, where after the cutting process may begin. This situation is schematically illustrated in  FIG.  10     c.    
       FIG.  10   c    further schematically shows the gripper  11  having been put into the first advanced position in the horizontal direction by the first actuator  15 , in order to improve the process of guiding the wrap  40  towards the knife  12 . 
       FIGS.  11   a - 11   d    show an alternative unwrapper head  1 ′ with an alternative type of gripper  11 ′, rotatably mounted to a housing  2 ′ of the unwrapper head  1 ′, by which gripper  11 ′ the wrap  40  is gripped at its free end edge  41  by applying suction to the wrap  40  via suction inlets  13 ′ defining the alternative gripper  11 ′ that does not have the arm  11   a  with the gripping tip  11   b  discussed above, wherein the applied suction pulls the wrapping  40  away from the wrapped articles  50 ,  50 ′ towards one or more knives  12 ′ mounted to the unwrapper head  1 ′ in the vicinity of the one or more suction inlets  13 ′, such as between the suction inlets  13 ′ of a pair of such suction inlets  13 ′. The alternative gripper  11 ′ preferably is controlled to rotate relative to the housing  2 ′ from a position wherein the suction inlets  13 ′ face downwards towards horizontal portions of the wrap  40 , as shown in  FIG.  11   c   , such as at the top of the stack of wrapped articles  50 ,  50 ′, and the unwrapper head  1 ′ has wheels  3 ′ bearing against the side of the stack of wrapped articles (as the unwrapper head  1 ′ is in one embodiment initially moved upwards for the registration of the contour), during the cutting along the sides by the knives  12 ′.