Patent Publication Number: US-2022212885-A1

Title: Magnetic pouch clamp assembly and related methods

Description:
FIELD OF THE INVENTION 
     The present invention relates to pouching machines, and more particularly, to clamps for releasably holding the pouches through forming, filling and/or sealing operations. 
     BACKGROUND OF THE INVENTION 
     Most pouching machines employ pairs of track-mounted clamps which successively receive pouches and carry them to various stations where different operations are performed on the pouches, typically including filling and sealing and, depending on the type of pouching machine, initial forming operations. The clamps then release the filled and sealed pouches, which may be grouped and loaded in cartons or subject to further processing. 
     Most commonly, each clamp is held closed by spring pressure and, when receiving or releasing pouches, the clamp is urged open by application of an external mechanical force. While such clamps have been effectively used for many years, further improvements are possible. 
     SUMMARY OF THE INVENTION 
     According to one aspect, a magnetic pouch clamp assembly comprises: a first clamping arm having a first clamping surface; a second clamping arm having a second clamping surface opposed to the first clamping surface, the second clamping arm being slidably connected to the first clamping arm such that the first and second clamping arms are movable between open and closed positions, the first and second clamping surfaces being engaged in the closed position; a magnet assembly including a first magnet having a first polarity carried by the first clamping arm and a second magnet having a second polarity carried by the second clamping arm, the first and second polarities being oriented such that a closing attractive force therebetween holds the first and second clamping surfaces in the closed position. 
     In one implementation of the preceding aspect, the magnet assembly includes a third magnet having a third polarity carried by the second clamping arm, the second and third magnets being located on opposite sides of the first magnet and the first and third polarities being oriented such that an opening attractive force therebetween holds the first and second clamping surfaces in the open position. 
     In on implementation of the assembly of either of the preceding paragraphs, the first clamping arm defines a first guide slot and the second clamping arm defines a second guide slot, the first clamping arm includes a first magnet housing slidably received in the second guide slot and carrying the first magnet, and the second clamping arm includes a second magnet housing slidably received in the first guide slot and carrying the second magnet. 
     In on implementation of the assembly of any of the preceding paragraphs, the first magnet housing includes opposite sides within the second guide slot, wherein each of the opposite sides carries a plastic bearing in sliding contact with the second guide slot, wherein the second magnet housing includes opposite sides within the first guide slot, wherein each of the opposite sides of the second magnet housing carries a plastic bearing in sliding contact with the first guide slot. 
     In on implementation of the assembly of any of the preceding paragraphs, the magnet assembly includes a third magnet having a third polarity carried by the second clamping arm, the second and third magnets being located on opposite sides of the first magnet and the first and third polarities being oriented such that an opening attractive force therebetween holds the first and second clamping surfaces in the open position; and wherein the first clamping arm defines a third guide slot and the second clamping arm includes a third magnet housing slidably received in the third guide slot and carrying the third magnet. 
     In on implementation of the assembly of any of the preceding paragraphs, one of the first and second clamping arms includes mounting holes for mounting to a carriage. 
     In on implementation of the assembly of any of the preceding paragraphs, a first clamping arm distal end extends beyond a second clamping arm distal end, the first clamping arm distal end including a first end lateral extension, the first clamping surface being located on the lateral extension and facing the second clamping surface on the second clamping arm distal end. 
     In on implementation of the assembly of any of the preceding paragraphs, the second clamping arm distal end includes a second end lateral extension extending away from the first clamping arm and angled away from the second clamping surface. 
     In on implementation of the assembly of any of the preceding paragraphs, the first and second clamping surfaces are textured to increase grip. 
     In on implementation of the assembly of any of the preceding paragraphs, the first and second magnets are permanent magnets. 
     In on implementation of the assembly of any of the preceding paragraphs, the first clamping arm overlies the second clamping arm, wherein the second magnet housing extends upward into the first guide slot, wherein the first magnet housing extends downward into the second guide slot. 
     In on implementation of the assembly of any of the preceding paragraphs, at least one of the first clamping arm or the second clamping arm includes at least one slide slot, wherein a fastener extends through the slide slot and into the other of the first clamping arm or the second clamping arm to hold the first and second clamping arms together, wherein the fastener includes a shaft portion within the slide slot, wherein the shaft portion interacts with an end of the slide slot for limiting relative sliding movement between the first clamping arm and the second clamping arm. 
     In on implementation of the assembly of any of the preceding paragraphs, the first magnet housing includes a first magnet housing retention lug at a first magnet housing distal end and the second guide slot includes a second guide slot retention lug passage extending across a width thereof, engagement between the first magnet housing retention lug and the second clamping arm preventing removal of the first magnet housing from the second guide slot except when the first magnet housing retention lug and the and the second guide slot retention lug passage are aligned. 
     In on implementation of the assembly of any of the preceding paragraphs, the second clamping arm includes a second clamping arm guide slot cover connected thereto outwardly of the first magnet housing retention lug, the second clamping arm guide slot cover having a magnet housing blocking protrusion extending inwardly therefrom positioned to prevent the first magnet housing retention lug from sliding into aligned with the second guide slot retention lug passage. 
     In on implementation of the assembly of any of the preceding paragraphs, the second magnet housing includes a second magnet housing retention lug at a second magnet housing distal end and the first guide slot includes a first guide slot retention lug passage extending across a width thereof, engagement between the second magnet housing retention lug and the first clamping arm preventing removal of the second magnet housing from the first guide slot except when the second magnet housing retention lug and the and the first guide slot retention lug passage are aligned. 
     In a further aspect, a pouch handling system includes a carriage mounted for movement along a continuous conveyor track. The magnetic pouch clamp assembly of any of the preceding paragraphs is mounted to the carriage for movement therewith. A first assembly actuator positioned at a pouch drop location along the continuous conveyor track, the first assembly actuator configured to interact with the magnetic pouch clamp assembly to shift the first and second clamping arms to the open position for pouch dropping. A second assembly actuator positioned at a pouch receive location along the continuous conveyor track, the second assembly actuator configured to interact with the magnetic pouch clamp assembly to shift the first and second clamping arms to the closed position for pouch holding. The system is configured such that the magnetic pouch clamp assembly (i) receives a pouch at the pouch receive location, (ii) drops the pouch at the pouch drop location and (iii) remains in the open position while traversing along the continuous conveyor track from the pouch drop location back to the pouch receive location to receive another pouch. 
     These and other objects, aspects and advantages of the present invention will be better appreciated in view of the drawings and following detailed description of preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a magnetic pouch clamp assembly, according to an embodiment of the present invention; 
         FIG. 2  is another perspective view of the magnetic pouch clamp assembly of  FIG. 1 , with a guide slot cover removed to show internal details; 
         FIG. 3  is a partially exploded perspective view of the magnetic pouch clamp assembly of  FIG. 1 ; 
         FIGS. 4A and 4B  are sectional views taken along line  4 - 4  of  FIG. 1  with clamping surfaces in the open and closed positions, respectively; 
         FIG. 5  is a perspective view of a pair of magnetic pouch clamp assemblies mounted to carriages, according to another embodiment of the present invention; 
         FIG. 6-9  show perspective views of another embodiment of a magnetic pouch clamp assembly; 
         FIG. 10  shows an exploded perspective view of the magnetic pouch assembly of  FIG. 9 ; 
         FIGS. 11-14  show perspective views of another embodiment of a magnetic pouch assembly (in  FIGS. 12 and 14  clamping arm  212  is shown transparent of ease of understanding); 
         FIG. 15  shows one clamping arm of the assembly; 
         FIG. 16  shows another clamping arm of the assembly; 
         FIG. 17  is another perspective view of the assembly; and 
         FIG. 18  is a schematic plan view a pouch handling system employing magnetic pouch clamp assemblies. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     According to an embodiment of the present invention, referring to  FIGS. 1-3 , a magnetic pouch clamp assembly  10  includes slidably connected clamping arms  12 ,  14  carrying a magnet assembly  16 . The magnet assembly  16  is operable to engage opposed clamping surfaces  20 ,  22  of the clamping arms  12 ,  14  in the open ( FIG. 4A ) and closed positions ( FIG. 4B ). 
     The clamping arm  12  includes a magnet housing  24  extending laterally therefrom through the clamping arm  14 . Magnet housing retention lugs  26  extend upwardly and downwardly from a distal end  30  of the housing  24 . Guide slots  32 ,  34  are defined in the clamping arm  12  extending across a width thereof. 
     Guide slot retention lug passages  36  are defined extending upwardly and downwardly from the guide slots  32 ,  34 . A guide slot cover  40  is attached to the clamping arm  12  over outer ends of the guide slots  32 ,  34 . Magnet housing blocking protrusions  42  extend into the guide slot retention lug passages  36  from an inner surface of the cover  40 . 
     The clamping arm  14  includes magnet housings  44 ,  46  extending laterally therefrom and slidably accommodated, respectively, in the guide slots  32 ,  34  of the first clamping arm  12 . The clamping arm  14  defines a guide slot  50  extending across a width thereof, which slidably receives the magnet housing  24  of the first clamping arm  12 . 
     Magnet housing retention lugs  26  extend upwardly and downwardly from the distal ends  52 ,  54  of the magnet housings  44 ,  46 . The guide slot  50  defines guide slot retention lug passages  36  extending downwardly and upwardly therefrom. A guide slot cover  56  is attached to the clamping arm  14  over outer ends of the guide slot  50  and includes a magnet housing blocking protrusion  42  extending inwardly therefrom into the passages  36 . 
     Each of the lugs  26  extend upwards or downwards beyond the height of respective guide slot  32 ,  34 ,  46 , which prevents lateral separation of the clamping arms  12 ,  14  by retaining each magnet housing  26 ,  44 ,  46  within its respective guide slot  32 ,  34 ,  36 . The clamping arms  12 ,  14  are only separable by sliding them to align each lug  26  with a respective one of the passages  36 . Because the blocking protrusions  42  extend into the passages  36  with the guide slot covers  40 ,  56  in place, the covers  40 ,  56  must be removed prior to separating the arms  12 ,  14 —preventing inadvertent separation during normal opening and closing operations of the clamp assembly  10 . 
     The magnet assembly  16  includes magnets  60 ,  62 ,  64 , each located in a respective one of the magnet housings  24 ,  44 ,  46 . The magnets  60 ,  62 ,  64  are preferably rare earth magnets, such as neodymium or samarium-cobalt magnets, although electromagnets could be used within the scope of the present invention. 
     The polarities +/−(see  FIGS. 4A, 4B ) of the magnets  60 ,  62  are oriented such that an attractive force therebetween holds the clamping surfaces  20 ,  22  in the closed position. The polarity +/− of the magnet  64  is preferably oriented relative to that of the magnet  60  such that an attractive force therebetween holds the clamping surfaces  20 ,  22  in the open position, and more particularly, a fully open position. 
     This is advantageous in that application of force is required only to transition the clamping surfaces  20 ,  22  between the open and closed position, and not to maintain the surfaces  20 ,  22  in either position. Alternately, the polarity (+)/(−) of the magnet  64  is oriented relative to that of the magnet  60  such that a repulsive force therebetween urges the clamping surfaces  20 ,  22  toward the closed position, reducing the energy required for this transition. 
     Advantageously, each magnet  60 ,  62 ,  64  is situated in its respective magnet housing  24 ,  44 ,  46  with a plurality of shims  66 . The spacing between the magnets  60 ,  62  and between the magnets  60 ,  64  can be adjusted by moving some or all of the shims  66  in a magnet housing  24 ,  44 ,  46  to the other side of the magnet  60 ,  62 ,  64 . The guide slot covers  40 ,  50  help ensure that the magnets  60 ,  62 ,  64  and shims  66  remain in their respective housings  24 ,  44 ,  46 . 
     The use of three magnets in each magnet assembly is preferred because it minimizes the number of magnets while still allowing the clamp assembly to be held by magnetic attraction in both the closed and open positions. It will be appreciated that two or more pairs of magnets could be used to the same effect simply by modifying the clamping arms to include a corresponding number of additional magnet housings and guide slots. Likewise, the present invention could be used with only a single pair of magnets, such that magnet attraction only holds the clamp assembly to be held closed (or open). 
     In operation, the clamping arm  14  is mounted to a carriage via the mounting holes  70 , with the clamping arm  12  slidably mounted thereto. An engagement roller  72  extending from the clamping arm  12  is engaged by an external mechanism to transition the magnetic clamp assembly  10  between open and closed positions. 
     Pouch retention when closed is enhanced by knurled or otherwise textured finishes on opposing faces of the clamping surfaces  20 ,  22 . Since the clamping arms  12 ,  14  are laterally adjacent, a lateral extension  74  at the distal end  76  of the clamping arm  14  to allow the clamping surface  22  to be located coaxially along a clamping axis opposed to the clamping surface  20 . A lateral extension  82  at the distal end  84  of the clamping arm  12  is angled away from the clamping surface  20  and facilitates pouch loading. 
     The abutting inner sides of the clamping arms  12 ,  14  preferably completely cover the inner openings of the guide slots  32 ,  34 ,  50  while the outer openings of the guide slots  32 ,  34 ,  50  are completely covered by the covers  40 ,  56 . This arrangement advantageously inhibits fine particulates commonly encountered during pouching operations from entering the guide slots  32 ,  34 ,  50  and interfering with the opening and closing of the clamp assembly  10 . 
     Referring to  FIG. 5 , according to another embodiment of the present invention, a pair of magnetic pouch clamp assemblies  10 A,  10 B are each mounted on adjacent carriages  90 A,  90 B. The clamp assemblies  10 A,  10 B are mirror-images of one another, such that lateral extensions  74 A/B,  82 A/B on the distal ends  76 A/B,  84 A/B of the clamping arms  12 A/B,  14 A/B extend toward one another, allowing both side of a pouch to accommodated therebetween. 
     It will be noted that, in the clamp assemblies  10 A,  10 B, the outboard clamping arms  14 A,  14 B carry the engagement rollers  72 A,  72 B while the inboard clamping arms  12 A,  12 B are mounted to the carriages  90 A,  90 B. A roller engagement mechanism  92  is positioned to engage the rollers  72 A,  72 B to simultaneously urge both the clamp assemblies  10 A,  10 B into the open position. 
     To help counteract the force exerted on the clamp assemblies  10 A,  10 B and carriages  90 A,  90 B, retentions mechanisms  94 A,  94 B (such as the depicted hooks) are located on proximal ends  96 A,  96 B of the mounted clamping arms  12 A,  12 B. These mechanisms  94 A,  94 B are able to engage a rail or other fixed structure at opening positions for the assemblies  10 A,  10 B, thereby preventing unwanted movement thereof. 
     According to another embodiment, referring to  FIGS. 6-10 , a magnetic pouch clamp assembly  110  includes slidably connected clamping arms  112 ,  114  carrying a magnet assembly  116 . The magnet assembly  116  is operable to engage opposed clamping surfaces  120 ,  122  of the clamping arms  112 ,  114  in open and closed positions. 
     The clamping arm  112  includes a magnet housing  124  extending laterally therefrom through the clamping arm  114 . Magnet housing retention lugs  126  extend upwardly and downwardly from a distal end  130  of the housing  124 . Guide slots  132 ,  134  are defined in the clamping arm  112  extending across a width thereof. 
     Guide slot retention lug passages  136  are defined extending upwardly and downwardly from the guide slots  132 ,  134 . A guide slot cover  140  is attached to the clamping arm  112  over outer ends of the guide slots  132 ,  134 . Magnet housing blocking protrusions  142  extend into the guide slot retention lug passages  136  from an inner surface of the cover  140 . 
     The clamping arm  114  includes magnet housings  144 ,  146  extending laterally therefrom and slidably accommodated, respectively, in the guide slots  132 ,  134  of the first clamping arm  112 . The clamping arm  114  defines a guide slot  150  extending across a width thereof, which slidably receives the magnet housing  124  of the first clamping arm  112 . 
     Magnet housing retention lugs  126  extend upwardly and downwardly from the distal ends  152 ,  154  of the magnet housings  144 ,  146 . The guide slot  150  defines guide slot retention lug passages  136  extending downwardly and upwardly therefrom. A guide slot cover  156  is attached to the clamping arm  114  over outer ends of the guide slot  150  and includes a magnet housing blocking protrusion  142  extending inwardly therefrom into the passages  136 . 
     Each of the lugs  126  extend upwards or downwards beyond the height of respective guide slot  132 ,  134 ,  146 , which prevents lateral separation of the clamping arms  112 ,  114  by retaining each magnet housing  126 ,  144 ,  146  within its respective guide slot  132 ,  134 ,  136 . The clamping arms  112 ,  114  are only separable by sliding them to align each lug  126  with a respective one of the passages  136 . Because the blocking protrusions  142  extend into the passages  136  with the guide slot covers  140 ,  156  in place, the covers  140 ,  156  must be removed prior to separating the arms  112 ,  114 —preventing inadvertent separation during normal opening and closing operations of the clamp assembly  110 . 
     The magnet assembly  116  includes magnets  160 ,  162 ,  164 , each located in a respective one of the magnet housings  124 ,  144 ,  146 . The magnets  160 ,  162 ,  164  are preferably rare earth magnets, such as neodymium or samarium-cobalt magnets, although electromagnets could be used within the scope of the present invention. In this embodiment, shims are not used, and therefore the magnet housings are sized to closely match the magnet dimensions. 
     The polarities +/− of the magnets  160 ,  162  are oriented such that an attractive force therebetween holds the clamping surfaces  120 ,  122  in the closed position. The polarity +/− of the magnet  164  is preferably oriented relative to that of the magnet  160  such that an attractive force therebetween holds the clamping surfaces  120 ,  122  in the open position, and more particularly, a fully open position. 
     The use of three magnets in each magnet assembly is preferred because it minimizes the number of magnets while still allowing the clamp assembly to be held by magnetic attraction in both the closed and open positions. It will be appreciated that two or more pairs of magnets could be used to the same effect simply by modifying the clamping arms to include a corresponding number of additional magnet housings and guide slots. Likewise, the present invention could be used with only a single pair of magnets, such that magnet attraction only holds the clamp assembly to be held closed (or open). 
     In operation, the clamping arm  114  is mounted to a carriage via the mounting holes  170  and fasteners  171 , with the clamping arm  112  slidably mounted thereto. An engagement post  172  extending from the clamping arm  112  is engaged by an external mechanism to transition the magnetic clamp assembly  110  between open and closed positions. 
     Pouch retention when closed is enhanced by knurled or otherwise textured finishes on opposing faces of the clamping surfaces  120 ,  122 . Since the clamping arms  112 ,  114  are laterally adjacent, a lateral extension  174  at the distal end  176  of the clamping arm  114  to allow the clamping surface  122  to be located coaxially along a clamping axis opposed to the clamping surface  120 . A lateral extension  182  at the distal end  184  of the clamping arm  112  is angled away from the clamping surface  120  and facilitates pouch loading. 
     The abutting inner sides of the clamping arms  112 ,  114  preferably completely cover the inner openings of the guide slots  132 ,  134 ,  150  while the outer openings of the guide slots  132 ,  134 ,  150  are completely covered by the covers  140 ,  156 . This arrangement advantageously inhibits fine particulates commonly encountered during pouching operations from entering the guide slots  132 ,  134 ,  150  and interfering with the opening and closing of the clamp assembly  110 . Here, a top cover  190  is also provided over the adjacent clamping arms for reducing ingress of dust or particles into the sliding joint between the two clamping arms. 
     Each of the magnet housings  124 ,  144  and  146  includes upper and lower sides that carry a plastic bearing  192  (e.g., here in plate form attachable via openings  194  in the magnet housings). The external surfaces of the plastic bearings  192  are in sliding contact with the guide slots and facilitate the relative sliding of the first and second clamping arms  112 ,  114 . The plastic bearings  192  are particularly useful when the first and second clamping arms are formed of metal (e.g., aluminum or stainless steel). 
     According to another embodiment, referring to  FIGS. 11-17 , a magnetic pouch clamp assembly  210  includes slidably connected clamping arms  212 ,  214  carrying a magnet assembly  216 . The magnet assembly  216  is operable to engage opposed clamping surfaces  220 ,  222  of the clamping arms  212 ,  214  in open and closed positions. 
     The clamping arm  212  includes a magnet housing  224  extending downwardly therefrom into the clamping arm  214 . Upwardly extending guide slots  232 ,  234  are defined in the clamping arm  212  extending across a width thereof. Here, the guide slots  232 ,  234  are closed at the top by a wall portion  212   a  of the clamping arm  212 . The clamping arm  212  also includes fastener receiving openings  215 . 
     The clamping arm  214  includes magnet housings  244 ,  246  extending upwardly therefrom and slidably accommodated, respectively, in the guide slots  232 ,  234  of the first clamping arm  212 . The clamping arm  214  defines a guide slot  250  extending across a width thereof, which slidably receives the magnet housing  224  of the first clamping arm  212 . The guide slot  250  is closed at the bottom by wall portion  214   a  of the clamping arm  214 . The clamping arm  214  also includes slide slots  217  though which fasteners  219  extend (into the openings  215 ) in order to hold the first and second clamping arms together. Shaft segments of the fasteners  219  move along the slide slots  217  during transition of the first and second clamping arms between the open and closed positions. 
     The magnet assembly  216  includes magnets  260 ,  262 ,  264 , each located in a respective one of the magnet housings  224 ,  244 ,  246 . The magnets  260 ,  262 ,  264  are preferably rare earth magnets, such as neodymium or samarium-cobalt magnets, although electromagnets could be used within the scope of the present invention. In this embodiment, shims are not used, and therefore the magnet housings are sized to closely match the magnet dimensions. 
     The polarities +/− of the magnets  260 ,  262  are oriented such that an attractive force therebetween holds the clamping surfaces  220 ,  222  in the closed position. The polarity +/− of the magnet  264  is preferably oriented relative to that of the magnet  260  such that an attractive force therebetween holds the clamping surfaces  220 ,  222  in the open position, and more particularly, a fully open position. 
     In operation, the clamping arm  214  is mounted to a carriage via the mounting holes  270  and fasteners  271 , with the clamping arm  212  slidably mounted thereto. An engagement post  272  extending from the clamping arm  212  is engaged by an external mechanism to transition the magnetic clamp assembly  210  between open and closed positions. 
     Pouch retention when closed is enhanced by knurled or otherwise textured finishes on opposing faces of the clamping surfaces  220 ,  222 . Here, first clamping arm  112  overlies the second clamping arm  214 . The distal end  276  of clamping arm  214  includes an upward extension  273  with a lateral extension  274  to allow the clamping surface  222  to be located coaxially along a clamping axis opposed to the clamping surface  220 . 
     Each of the magnet housings  224 ,  244  and  246  includes upper and lateral sides that carry a plastic bearing  292  (e.g., here in plate form attachable via openings  294 , represented in dashed line in  FIG. 16 , in the magnet housings). The external surfaces of the plastic bearings  292  are in sliding contact with the guide slots and facilitate the relative sliding of the first and second clamping arms  212 ,  214 . The plastic bearings  292  are particularly useful when the first and second clamping arms are formed of metal (e.g., aluminum or stainless steel). 
     Referring now to  FIG. 18 , an exemplary pouch handling system  300  (e.g., a pouch filling system) is shown. The system includes carriages  302  mounted for independent movement along a continuous conveyor track  304 . Opposed pairs of magnetic pouch clamp assemblies  306  (e.g., any of the assemblies  10 ,  110  or  210 ) are mounted to each of the carriages  302  for movement therewith. An assembly actuator  312  is positioned at a pouch drop location or zone  314  along the continuous conveyor track  304 . The assembly actuator  312  is configured to interact with the magnetic pouch clamp assemblies to shift the first and second clamping arms to the open position for pouch dropping. An assembly actuator  308  is positioned at a pouch receive location or zone  310  along the continuous conveyor track  304 . The assembly actuator  308  is configured to interact with the magnetic pouch clamp assemblies to shift the first and second clamping arms to the closed position for pouch holding. The actuators  308  and  312  may, for example, be linear actuators (e.g., pneumatic motor driven) which move a paddle or plate that interacts with the clamp assemblies  306 . The system  300  is configured such that the magnetic pouch clamp assemblies (i) receive a pouch at the pouch receive location  308 , (ii) drops the pouch at the pouch drop location  314  and (iii) remains in the open position while traversing along the continuous conveyor track  304  (in the direction of the arrows) from the pouch drop location back to the pouch receive location to receive another pouch. The system may include various processes that act on or with respect to the pouches between locations  308  and  314 . 
     In examples: 
     A magnetic pouch clamp assembly includes a first clamping arm having a first clamping surface; a second clamping arm having a second clamping surface opposed to the first clamping surface, the second clamp arm being slidably connected to the first clamping arm such that the first and second clamping arms are movable between open and closed positions, the first and second clamping surfaces being engaged in the closed position; and a magnet assembly including a first magnet having a first polarity carried by the first clamping arm and a second magnet having a second polarity carried by the second clamping arm, the first and second polarities being oriented such that a closing attractive force therebetween holds the first and second clamping surfaces in the closed position. 
     In implementations, the magnet assembly includes a third magnet having a third polarity carried by the second clamping arm, the second and third magnets being located on opposite sides of the first magnet and the first and third polarities being oriented such that an opening attractive force therebetween holds the first and second clamping surfaces in the open position. 
     In implementations, the first clamping arm defines a first guide slot and the second clamping arm defines a second guide slot, the first clamping arm includes a first magnet housing slidably received in the second guide slot and carrying the first magnet, and the second clamping arm includes a second magnet housing slidably received in the first guide slot and carrying the second magnet. 
     In implementations, the magnet assembly further includes at least one first magnet shim located in the first magnet housing with the first magnet, the first magnet shim being repositionable to adjust a spacing between the first and second magnets. 
     In implementations, the magnet assembly further includes at least one second magnet shim located in the second magnet housing with the second magnet, the second magnet shim being repositionable to further adjust the spacing between the first and second magnets. 
     In implementations, the first magnet housing includes a first magnet housing retention lug at a first magnet housing distal end and the second guide slot includes a second guide slot retention lug passage extending across a width thereof, engagement between the first magnet housing retention lug and the second clamping arm preventing removal of the first magnet housing from the second guide slot except when the first magnet housing retention lug and the and the second guide slot retention lug passage are aligned. 
     In implementations, the second clamping arm includes a second clamping arm guide slot cover connected thereto outwardly of the first magnet housing retention lug, the second clamping arm guide slot cover having a magnet housing blocking protrusion extending inwardly therefrom positioned to prevent the first magnet housing retention lug from sliding into aligned with the second guide slot retention lug passage. 
     In implementations, the second magnet housing includes a second magnet housing retention lug at a second magnet housing distal end and the first guide slot includes a first guide slot retention lug passage extending across a width thereof, engagement between the second magnet housing retention lug and the first clamping arm preventing removal of the second magnet housing from the first guide slot except when the second magnet housing retention lug and the and the first guide slot retention lug passage are aligned. 
     In implementations, the magnet assembly includes a third magnet having a third polarity carried by the second clamping arm, the second and third magnets being located on opposite sides of the first magnet and the first and third polarities being oriented such that an opening attractive force therebetween holds the first and second clamping surfaces in the open position; and wherein the first clamping arm defines a third guide slot and the second clamping arm includes a third magnet housing slidably received in the third guide slot and carrying the third magnet. 
     In implementations, one of the first and second clamping arms includes mounting holes for mounting to a carriage. 
     In implementations, another of the first and second clamping arms includes an engagement roller for engagement to move the first and second clamping surfaces between the open and closed positions. 
     In implementations, a first clamping arm distal end extends beyond a second clamping arm distal end, the first clamping arm distal end including a first end lateral extension, the first clamping surface being located on the lateral extension facing the second clamping surface on the second clamping arm distal end. 
     In implementations, the second clamping arm distal end includes a second end lateral extension extending away from the first clamping arm and angled away from the second clamping surface. 
     In implementations, the first and second clamping surfaces are textured to increase grip. 
     In implementations, the first and second magnets are permanent magnets. 
     The above-described embodiments are provided for illustrative purposes; the present invention is not necessarily limited thereto. Rather, those skilled in the art will appreciate that various modifications, as well as adaptations to particular circumstances, will fall within the scope of the invention herein shown and described, and of the claims appended hereto.