Abstract:
A method and apparatus for installing corner protectors onto picture frames, to protect the corners from damage during shipment, uses preforms made of a thin, flat sheet of cardboard having left and right flap sections, one of which, e.g., the right one, is bendable from the plane of the sheet to form an upper cover flap, the left flap section forming a lower cover flap. Left and right flap sections are joined at parallel vertical sides thereof to opposite vertical sides of a vertically elongated, rectangularly-shaped inner spine flap for covering a vertical side of a “right hand” picture frame molding. A horizontally elongated, rectangularly-shaped outer spine flap protrudes from a lateral edge of the lower cover flap, and a trapezoidally-shaped securement flap protrudes from the outer spine flap. A preform is positioned below a frame corner, with outside walls of left and right intersecting picture frame moldings aligned with the base and inner vertical side, respectively, of the lower cover flap, and above a pair of left and right folder mechanisms that include flap folder arms which fit into worktable recesses. A hot-melt adhesive applicator head sprays a first blob of adhesive onto an upper surface of the left-hand frame molding, whereupon a first flap folder arm is elevated to bend the outer spine flap and securement flap into a vertical position adjacent the outer vertical side of the left-hand frame molding; the first flap folder arm is then rotated towards the inside of the frame, bending the securement flap over the adhesive blob on the frame molding. A second adhesive blob is then sprayed onto the upper surface of the securement flap. Next, the second flap folder arm is elevated to bend the inner spine flap and upper cover flap into a vertical position adjacent the outer side of the right-hand frame molding, whereupon the second flap folder arm is rotated inwardly to bend the upper cover flap into a horizontal position over the second adhesive blob on the securement flap. The applicator head is then pressed against the upper cover flap, thus adhering the second adhesive blob to the upper cover flap and securement flap to form a corner protector, and adhering the first adhesive blob to the securement flap and left-hand frame molding to secure the corner protector to the frame.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    A. Field of the Invention  
           [0002]    The present invention relates to methods and apparatus for protecting the corners of rectangularly-shaped frames such as picture frames, from impact damage during shipping. More particularly, the invention relates to a method and apparatus for adhesively bonding corner protectors onto the corners of a picture frame.  
           [0003]    B. Description of Background Art  
           [0004]    Picture frames for holding and displaying paintings, photographs, diplomas, certificates and similar flat articles are manufactured in prodigious quantities worldwide. Although picture frames vary in shape and construction details, most frames have a rectangular plan view shape. Moreover, the structure of most picture frames consists essentially of four elongated, straight channel members or moldings, each having formed therein an inner longitudinally disposed channel that intersects channels of adjacent members at ninety degree angles. Four such channel members fastened together form a rectangular ring-shaped frame. The channels or recesses in the moldings face inwardly of the frame, and comprise spaces for receiving a rectangularly-shaped flat display piece such as a photograph or painting, and sometimes, a backing panel, mat and protective cover glass.  
           [0005]    Picture frames of the type described above are made from a variety of materials including, wood, metal and plastic. Whatever material the frame is made of, the geometry of a rectangular picture frame dictates that it have four peripheral members or moldings of generally uniform thickness which are joined to each other at forty-five degree miter angles to form ninety-degree corners. Since the sides of each molding intersect at an acute angle, i.e., 45 degrees, the frame corners as well as the molding corners are sharp, and are therefore highly subject to breakage, denting or cosmetic damage during shipment. Accordingly, most picture frames, whether empty or occupied, are fitted with some sort of corner protectors during shipment. Such corner protectors are usually made of a relatively inexpensive recyclable material such as cardboard or polystyrene foam. Typical corner protectors of this type are disclosed in U.S. Pat. Nos. 3,955,677, 4,598,825, and 5,447,233. Other patents, related to protecting corners of objects during shipping include U.S. Pat. No. 4,407,898. Also, U.S. Pat. No. 5,255,458 discloses a three-dimensional picture corner and U.S. Pat. No. 4,787,553 discloses a corner fastening device.  
           [0006]    In addition to the above-referenced patents related to corner protectors and the like, a variety of machines for bending sheet metal or cardboard of the type used for corner projectors have been disclosed in the following U.S. Pat. Nos: 4,132,102, 4,585,432, 4,713,957, 4,857,038, 4,956,961, and 5,184,998.  
           [0007]    None of the aforementioned references disclose a machine for automatically attaching corner protectors to picture frames. Accordingly, the task of attaching corner protectors to picture frames was formerly labor intensive and time consuming. In response to those limitations of the prior art, the present inventor disclosed an automatic Method and Apparatus For Attaching Corner Protectors to Picture Frames, in U.S. Pat. No. 6,018,934. In that patent, the present inventor disclosed a method and apparatus for installing covers to protect picture frame corners from damage during shipment, utilizing thin cardboard preforms having symmetric, left and right-hand, right-triangular coverflaps joined at vertical sides thereof to opposite vertical sides of a vertically elongated, rectangular spine flap, the left-hand triangular cover flap having depending downwardly from its base a horizontally elongated rectangular side cover flap, and depending downwardly from the lower lateral edge of the side cover flap a trapezoidally-shaped securement flap. The preform is positioned below a picture frame corner, with intersecting side members of the frame vertically aligned with the sides of the left-hand right-triangular cover flap, which serves as a lower face cover flap. The apparatus includes folder mechanisms including flap folder arms which are retractable into recesses provided in a work table, and which are extendible and rotatable to thereby bend the side cover flap and securement flap into a vertical position adjacent a first side of the frame corner and perpendicularly inwardly to overlie the first frame member, bend the spine flap and right-hand triangular coverflap into a vertical position adjacent the second frame member, and bend the right-hand triangular flap perpendicularly inwards from the spine flap to overlie the second and first frame members. An automatic staple gun then inserts a staple downwardly through the right-triangular cover flap into the securement flap and left-hand frame member, securing the corner protector in a folded disposition over the frame corner. The present invention was conceived of to provide a method and apparatus for adhesively bonding corner protectors on the corners of picture frames, the method and apparatus being suitable for use with picture frames made of metal or plastic, as well as wood.  
         OBJECTS OF THE INVENTION  
         [0008]    An object of the present invention is to provide a method for attaching protective covers to the corners of a picture frame, using an adhesive bonding process.  
           [0009]    Another object of the invention is to provide an apparatus for automatically attaching protective covers to the corners of picture frames using adhesive bonds.  
           [0010]    Another object of the invention is to provide a method and apparatus for automatically attaching protective covers to the corners of picture frames, in which a cover is bonded to the corner of a frame by an adhesive bond, not requiring penetration of the frame by a fastener.  
           [0011]    Another object of the invention is to provide a method and apparatus for automatically attaching protective covers to corners of a picture frame in which adhesive is applied to a surface of a frame molding, a protective cover is positioned over the cover, and the cover pressed against the adhesive to bond the cover to the frame molding.  
           [0012]    Another object of the invention is to provide an apparatus for depositing a quantity of adhesive on a surface of a picture frame molding, folding a flat sheet of flexible material over the corner of a picture frame, depositing a quantity of adhesive on a surface of the sheet, securing the folds of the sheet together by pressing an upper portion of the folded sheet against a lower portion having adhesive on its surface to form a protective cover, and adhering the cover to the picture frame by pressing the cover against adhesive on the molding surface.  
           [0013]    Another object of the invention is to provide an apparatus for bending a cardboard preform cut to a pre-determined shape over the corner of the picture frame, securing the folded portions of the cardboard preform by compressing a liquid adhesive therebetween and allowing the liquid adhesive to solidify, thereby forming a corner protector, and securing the corner protector to a molding of the frame by compressing a liquid adhesive between the molding and corner protector and allowing the liquid adhesive to solidify, thereby adhesively bonding the corner protector to the frame.  
           [0014]    Another object of the invention is to provide a picture frame corner protector attaching apparatus which includes means for clamping and holding a corner of a picture frame, positioning under the picture frame corner a preform sheet of flexible material, the preform sheet having the shape of left and right, lower and upper right triangular-shaped cover flaps joined at their inner vertical edges by a vertically elongated, rectangular-shaped inner spine flap to form a shape approximating that of a truncated isosceles triangle, the preform having a horizontally elongated, rectangularly-shaped outer spine flap depending downwardly from the left triangular corner flap and shaped similarly to the inner spine flap, and having depending downwardly therefrom a trapizoidally-shaped securement flap, means for spraying a first quantity of adhesive onto the upper surface of a first frame molding overlying the lower triangular-shaped cover flap, bending the outer spine flap vertically upwards into contact with the outer lateral side of the first frame molding, bending the securement flap down into a horizontal position in contact with the adhesive on the surface of the first frame molding, bending the inner spine flap and upper triangular cover flap vertically upwards into contact with the outer lateral surface of the second frame molding, spraying a second quantity of adhesive onto the upper surface of the securement flap overlying the first quantity of adhesive and bending the upper triangular cover flap into compressive contact with the second quantity of adhesive, thereby securing the upper triangular cover flap to the securement flap to form a completed cover protector, and pressing the first quantity of adhesive between the lower surface of the securement flap and the upper surface of the first frame molding to thereby secure the corner protector to the frame.  
           [0015]    Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims.  
           [0016]    It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, I do not intend that the scope of my exclusive rights and privileges in the invention be limited to details of the embodiments described. I do intend that equivalents, adaptations and modifications of the invention reasonably inferable from the description contained herein be included within the scope of the invention as defined by the appended claims.  
         SUMMARY OF THE INVENTION  
         [0017]    Briefly stated the present invention comprehends a method and apparatus for automatically and adhesively bonding protective covers made of a sheet of flexible material, e.g., cardboard, stock to the corners of frames, particularly rectangularly-shaped frames of the type used to hold pictures, documents and the like, the covers being intended to protect the corners of the frame from damage during shipment.  
           [0018]    A preferred embodiment of an automatic adhesive bonding method and apparatus according to the present invention preferably utilizes corner protectors made from thin, flat sheets of cardboard, each pre-cut, by die cutting, for example, into a generally triangular shape which includes panel sections which are bent out from the plane of the sheet to form cover flaps which are to be folded over and enclose a corner and adjacent portions of the side channel members of a conventional rectangularly-shaped picture frame. Four such corner protectors are used to cover the four corners of the frame.  
           [0019]    In a preferred embodiment of the invention, the plan view shape of the upper, larger portion of the corner protector preform includes two mirror symmetric, left and right, right-triangularly-shaped, panel sections having collinear horizontal bases joined to opposite vertical sides of a vertically elongated rectangular, inner, or right-hand spine panel section. The left and right triangularly-shaped panel sections serve as lower and upper cover flaps, while the inner spine panel section serves as a first, right-hand spine cover flap for a picture frame corner, as will be described below. Thus shaped, the upper portion of the preform has the appearance of an isosceles triangle whose vertex is horizontally truncated. The preform preferably includes a lower portion that has a horizontally elongated, rectangularly shaped outer, or left-hand spine flap panel section which depends downwardly from the base of one of the right-triangle flap panels, the left one, for example, and has the same width as that panel. A trapezoidally-shaped securement flap panel section depends downwardly from the bottom edge of the outer spine flap panel, the securement flap panel having a lower edge wall parallel to but shorter than that of the outer spine flap panel. In a preferred embodiment, the horizontal width of the vertically elongated inner spine flap panel and the vertical height of the horizontally elongated outer spine flap panel have a common value which is slightly greater than the thickness of a picture frame which is to be protected, e.g., about {fraction (16/16)} inch for a frame thickness of ⅝ inch. Preferably, the vertical side walls of the vertical inner spine flap panel and the horizontally disposed upper and lower edges of the outer spine flap panel are scored to facilitate folding those respective flaps to contact adjacent perpendicular channel members or moldings of a picture frame.  
           [0020]    According to the method of the present invention, a preform, score lines up, is positioned below a corner of a picture frame. The corner of the frame is oriented with respect to a preform with a pair of perpendicularly intersecting adjacent molding side walls defining the corner of the frame vertically aligned with the perpendicular sides of the left-hand, lower right-triangular cover flap having the downwardly depending outer spine and securement flaps. A first quantity of adhesive is then deposited on the upper surface of left-hand frame molding, near its intersection with the right-hand frame molding. Preferably, the first quantity of adhesive consists of one or more blobs of molten hot melt adhesive sprayed onto the upper surface of the molding from one or more nozzles of a pressurized hot melt glue gun positioned above the frame. The outer spine flap and securement flap are then folded vertically upwards as a planar unit along the upper or inner score line defining the junction between the base of the left, lower, right triangularly-shaped lower cover flap and the outer spine flap. Next, the securement flap is folded downwardly and inwardly along the lower or outer score line towards a horizontal position, and the securement flap is pressed down onto the semi-liquid glue blobs on the upper surface of the frame member overlying the left, lower triangularly-shaped cover flap. A second quantity of adhesive is then deposited on the upper surface of the securement flap by the glue gun. Then, the second, right-hand, right-triangularly-shaped upper cover flap and inner spine flap are bent upwards as a unit along the innermost vertical fold line, i.e., the left-hand vertical edge of the inner spine flap, to a vertical position. The right-hand, upper triangular cover flap is then bent downwardly and laterally along the outermost, right-hand vertical fold line of the inner spine flap to a horizontal position overlying the securement flap and pressed down against the second quantity of adhesive on the upper surface of the securement flap, thus securing the overlying, upper right-hand triangular cover flap to the securement flap.  
           [0021]    The apparatus according to the present invention includes a base plate or work table having a flat upper surface for supporting a corner of a picture frame, and a frame holder clamping jig for receiving and holding the corner of the picture frame on the surface of the table.  
           [0022]    Mounted on the table is a corner protector installation mechanism which includes a pair of corner protector flap folder actuators positioned on opposite sides of the corner of a picture frame held in the clamping jig. Each corner folder actuator includes a flat, rectangularly-shaped flap-contacting arm mounted near a longitudinal end thereof on the upper end of a post which is actuable by a linear actuator from a lower inactive position in which the arm resides within a rectangularly-shaped recess in the upper surface of the base plate, with the upper surface of the arm flush with the upper surface of the base plate, to an upper, active position. Each post also includes a 90-degree rotary actuator means, which is effective in rotating a flap contacting arm, when raised, from an outer position contacting the outer vertically disposed side of a flap to an inner position effective in exerting an inwardly and downwardly directed folding force on the flap.  
           [0023]    In operation, the first corner folder actuator arm is extended vertically, folding the outer spine flap and securement flap upwardly into a vertical position adjacent one side of a frame. An automatic hot melt adhesive gun applicator head having nozzles pressurized by air then deposits sprays a first quantity of hot melt adhesive onto the upper surface of the frame molding adjacent to the first folder actuator arm. The arm is then rotated inwards, bending the securement flap inwardly and downwardly into contact with the first quantity of semi-liquid adhesive on the upper surface of the first frame molding strip, thus bonding the securement flap to the frame.  
           [0024]    Next, the actuator arm of the second corner folder actuator is elevated, folding the upper triangular corner protector flap upwardly to a position vertically adjacent the outer edge of the second frame molding strip. The arm of the first corner folder actuator is then rotated outwardly from its position overlying and holding down the securement flap. A second quantity of molten hot melt adhesive is then sprayed onto the upper surface of the securement flap. The arm of the second actuator is then rotated inwardly, bending the upper triangular cover flap down into contact with the securement flap. This action presses the upper triangular cover flap down against the second quantity of adhesive on the upper surface of the underlying securement flap, thereby securing adhering the flaps to each other. The applicator head is then moved forcibly downwards by a pneumatic actuator, causing a pair of fingers protruding downwardly from the head to press downwardly on the upper surface of the upper triangular cover flap, causing secure adhesive bonds to be formed between the securement flap and frame, and between the upper triangular cover flap and securement flap. Both actuator arms are then automatically rotated and retracted to their recessed positions, flush with the work table surface. At the same time, the frame holding clamp is also automatically released, allowing the frame with attached corner protector to be removed from the clamp.  
           [0025]    The apparatus according to the present invention may optionally include means for automatically and substantially simultaneously initiating operation of a pair of corner protector installation mechanisms of the type described above, each time two adjacent corners of a picture frame are fully inserted into and correctly oriented with respect to clamping jigs of the mechanisms. In a preferred embodiment, apparatus components for implementing this automatic operation include a pair of guide plates in each clamping jig that have inner vertically disposed wall surfaces that define therebetween a ninety degree intersection angle or vertex, which is cut off or truncated by a plane oriented at forty-five degrees to the guide bars, to thereby form an opening for insertably receiving the corner of picture frame, with the intersecting channel moldings of the frame aligned with the guide plates.  
           [0026]    Each guide plate is provided, near the opening between the inner longitudinal ends of the guide plate, with a sensor which provides an electrical signal indicating that a frame corner molding has been fully inserted into the clamping jig. The electrical signals from each pair of sensors for each of the two clamping jigs are logically ANDed, producing a command signal to initiate automatic operation of the machine only when all three outer sides of the frame channel moldings defining two adjacent corners of the frame are fully inserted into and properly aligned with the guide plates of the two clamping jigs for proper operation of the corner protector folding and attaching operation. This command signal initiates a sequence of operations by which a pair of corner protectors are automatically attached in tandem to the two corners of a picture frame. Upon completion of this automatic operation, the holding clamps of both clamping jigs are automatically released, allowing the frame with a pair of attached corner protectors installed to be withdrawn from engagement with the apparatus. The frame may then be rotated one hundred and eighty degrees in a horizontal plane, and re-inserted into the apparatus to initiate attachment of a pair of corner protectors to the remaining two corners of the picture frame. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIG. 1 is a front perspective view of an apparatus for adhesively bonding corner protectors onto picture frames according to the present invention, showing a hot melt adhesive machine comprising part of the apparatus.  
         [0028]    [0028]FIG. 2 is a fragmentary upper rear perspective view of the apparatus of FIG. 1 on an enlarged scale, and showing guide rods and preforms used therewith removed to show details of the apparatus.  
         [0029]    [0029]FIG. 3 is a front perspective view of an adhesive applicator head comprising part of the apparatus of FIG. 1.  
         [0030]    [0030]FIG. 4 is a front elevation view of the applicator head of FIG. 3.  
         [0031]    [0031]FIG. 5 is a side elevation view of the applicator head of FIG. 3.  
         [0032]    [0032]FIG. 6 is a lower plan view of the applicator head of FIG. 3.  
         [0033]    [0033]FIG. 7 is an upper plan view of a corner protector preform or blank usable with the apparatus of FIG. 1.  
         [0034]    [0034]FIG. 8 is a rear perspective view of the apparatus of FIG. 2 showing a supply of corner protector preforms or blanks of the type shown in FIG. 7 in a stack preparatory to feeding individual preforms into a clamping position on the apparatus.  
         [0035]    [0035]FIG. 9 is a rear perspective view similar to that of FIG. 8, but showing an individual corner protector preform advanced to a clamping location, and showing a corner protector in a stack from which the individual corner protector was advanced.  
         [0036]    [0036]FIG. 10 is a view similar to that of FIG. 9, but showing a corner of a picture frame inserted into a clamping jig comprising part of the apparatus, the picture frame corner being positioned above the individual corner protector preform of FIG. 9, and showing a clamp bar of the clamping jig brought down into compressive contact with the upper surface of the picture frame.  
         [0037]    [0037]FIG. 11 is a view similar to that of FIG. 10, but showing streams of adhesive issuing from the adhesive applicator head of FIGS. 3 through 6, the streams impinging on the upper surface of a channel member of the picture frame to thereby deposit thereon a first adhesive blob consisting of two glue dots.  
         [0038]    [0038]FIG. 12 is a view similar to that of FIGS. 10 and 11, but showing a first corner flap actuator comprising part of the apparatus in an upwardly actuated position.  
         [0039]    [0039]FIG. 13 is a view of the apparatus of FIG. 1 similar to that of FIG. 12, but showing a fold-effecting arm of the first corner flap actuator rotated to contact and fold down a securement flap of the corner protector preform into a position overlaying the picture frame.  
         [0040]    [0040]FIG. 14 is a view similar to that of FIG. 13, but showing streams of adhesive issuing from the adhesive applicator head of FIGS. 2 through 6, the streams impinging on the upper surface of the securement flap to thereby deposit thereon a second adhesive blob consisting of two glue dots.  
         [0041]    [0041]FIG. 15 is a view of the apparatus similar to that of FIG. 13, but showing a second corner flap actuator of the apparatus in an upwardly actuated position.  
         [0042]    [0042]FIG. 16 is a view of the apparatus of FIG. 1 similar to that of FIG. 15, but showing a fold-effecting arm of the second corner flap actuator rotated to contact and fold down a triangularly-shaped upper cover flap of the corner protector preform into a position overlying the securement flap of the corner protector preform.  
         [0043]    [0043]FIG. 17 is a view of the apparatus of FIG. 1 similar to that of FIG. 16, but showing the fold-effecting arm of the first corner flap actuator rotated back into an inactive, home position, and showing an adhesive applicator head comprising part of the apparatus actuated downwardly to thereby press a flat lower portion of the head forward of nozzles protruding downwardly from the head into compressive contact with the upper surface of that portion of the second, triangularly-shaped upper cover flap overlying the securement flap of the corner protector preform, thereby pressing the glue dots between the flaps together to thereby adhere the flaps together and thereby pressing the lower surface of the securement flap against the glue dots on the picture frame channel molding, thereby adhering the securement flap to the picture frame.  
         [0044]    [0044]FIG. 18 is a fragmentary side elevation view of the apparatus of FIG. 17, showing the applicator head on an enlarged scale, but in a partially lowered position.  
         [0045]    [0045]FIG. 19 is a view similar to that of FIG. 18, but showing the applicator head in a fully lowered position, as shown in FIG. 17. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]    FIGS.  1 - 19  depict a method and apparatus according to the present invention for adhesively bonding corner protectors onto picture frames and the like. The structure and function of certain portions of the apparatus according to the present invention are described in detail in the present inventor&#39;s U.S. Pat. No. 6,018,934, the entire specification, claims, drawings, and abstract which are hereby incorporated by reference into the present application.  
         [0047]    Referring now to FIGS. 1 and 2, an apparatus  20  for adhesively bonding corner protectors onto the corners of picture frames and the like may be seen to include a corner protector installation mechanism  30 . Mechanism  30  is similar in structure and function to the apparatus disclosed in U.S. Pat. No. 6,018,934. Notably, however, as will be described in detail below, mechanism  30  according to the present invention utilizes an adhesive dispensing gun rather than the staple gun disclosed in the &#39;934 patent. Thus, corner protector installation mechanism  30 , in contrast to the apparatus disclosed in the &#39;934 patent, can be used to install corner protectors on frames, such as metal or plastic frames, where it would not be feasible to staple the protector to the frame.  
         [0048]    As shown in FIGS. 1 and 2, corner protector installation mechanism  30  includes a generally rectangular box-shaped enclosure  31  surmounted by a generally flat, upper base plate or work table  32 . As may be seen best by referring to FIG. 1, apparatus  30  includes an elongated, generally straight frame holder/clamping jig  33  mounted on the upper surface  34  of work table  32 . Preferably, clamping jig  33  is disposed obliquely, e.g., at 45 degrees, with respect to the rectangular plan-view shape of work table  32 . As shown in FIGS. 1, 8,  10  and  18 , clamping jig  33  is spaced above upper surface  34  of table  32 , and includes a longitudinally elongated, horizontally disposed, generally rectangular-shaped upper straight beam member  35 , supported at opposite transverse ends thereof by a pair of laterally opposed, left and right guide plates  36 L,  36 R, respectively. Guide plates  36  have flat and parallel lower and upper surfaces,  236  and  237 , these surfaces supporting clamp beam member  35  so that its lower surface  37  is parallel to and spaced above upper surface  34  of work table  32 .  
         [0049]    As shown in FIG. 1, enclosure  31  of mechanism  30  has parallel, vertically disposed left and right side panels  72  and  73 , which are perpendicular to front and rear vertically disposed panels  75 ,  74 . Front panel  75  is preferably joined to left and right side panels  72 ,  73  by left and right vertically disposed transition panels  28 ,  29 . The latter are obliquely angled to front panel  75 , e.g., at 45 degrees. This construction enables pairs of mechanisms  30  to be oriented with longitudinal axes of the mechanism, defined by a horizontal line centered in work table  32  and perpendicular to front panel  75 , perpendicular to one another, with transition panels  29 ,  28  of mechanisms  20  spaced closely next to one another. Thus arranged, pairs of mechanisms  30  may optionally be employed in tandem, in a manner similar to that described in co-pending application Ser. No. 09/687,358, filed Oct. 13, 2000, the entire disclosure of which is hereby incorporated by reference into this present application.  
         [0050]    As shown in FIGS. 1 and 18, left and right guide plates  36 L and  36 R have inner longitudinally disposed vertical wall surfaces  238 L and  238 R, respectively. If extended inwardly or rearwardly towards the center of work table  32 , inner vertical surfaces  238 L and  238 R of guide plates  36 L and  36 R would intersect to form a right angle corner. However, as shown in FIGS. 1, 2, and  18 , inner ends of guide plates  36 L and  36 R are truncated by an obliquely disposed cutting plane which forms obliquely disposed inner vertical transverse face walls  239 L and  239 R, respectively, that are coplanar with the cutting plane, and angled at 45 degrees to inner vertical side walls  238 L and  238 R. Thus arranged, inner vertical side walls  238 L and  238 R form guide surfaces along which may be slid the outer side walls of side channel members or moldings of a rectangular picture frame that intersect each other at a ninety-degree corner. A laterally disposed space  240  between opposed inner corners  241 L and  241 R of guide plates  36 L and  36 R allows the corner of a picture frame to protrude inwardly beyond inner face walls  239 L and  239 R of the guide plates.  
         [0051]    As may be seen best by referring to FIGS. 1, 8,  10 , and  18 , clamping jig  33  includes a horizontally disposed, elongated straight clamp bar  38  located below and in vertical alignment with clamp beam member  35 . Clamp bar  38  is vertically movably held with respect to clamp beam member  35 . Thus, as shown in FIGS. 1, 8, and  18 , clamping jig  33  includes a linear actuator comprising a double acting pneumatic cylinder  40 , for raising and lowering clamp bar  38 . Clamp bar cylinder  40  is mounted on the upper surface  41  of clamping jig support beam  35 , and has a piston rod  42  which protrudes vertically downwards through a bore  43  provided through the thickness dimension of the support beam. The lower end of piston rod  42  has a square transverse sectional shape which protrudes through a similarly shaped bore through clamp bar  38 , and is secured to the clamp bar by a screw  39 . Since pneumatic cylinder  40  is of the type in which piston rod  42  is non-rotatable, clamp bar  38  is maintained in a fixed horizontal orientation when moved vertically with respect to work table  32 .  
         [0052]    As shown in FIGS. 2 and 18, clamp bar cylinder  40  has an upper pressurized “down” air inlet port  44  connected to a first “down” air inlet hose  45 , and a second, lower, “up” air inlet port  46  connected to a second, “up” air inlet hose  47 . Hoses  45  and  47  connect to tubular fittings  48  and  49  which protrude downwards through upper surface  34  of work table  32 , to control valves and a source of pressurized air, as will be discussed in detail below. When pressurized air is supplied to “up” inlet port  46  of clamp air cylinder  40 , pressurized air on the lower side of a piston within the cylinder forces the piston, attached piston rod  42 , and attached clamp bar  38  upwards to an upper, unlocked position, as shown in FIG. 1. Conversely, when pressurized air is supplied to “down” inlet port  44  of clamp air cylinder  40 , pressurized air on the upper side of the piston within the cylinder forces the piston and clamp bar  38  downwards to a lower position in clamping contact with a picture frame A, as shown in FIG. 10.  
         [0053]    A preferred embodiment of mechanism  30  according to the present invention includes a feeder mechanism  70  for automatically feeding a single corner protector preform  50  at a time to a pre-determined position beneath clamping bar  38  of clamping jig  33 , prior to inserting a frame to be protected into the clamping jig. The structure and function of feeder mechanism  70  may be best understood by first reviewing the construction of corner protector preforms  50  used with apparatus  30 . FIG. 7, shows a corner protector preform  50  of the type the apparatus  30  is intended to be used with.  
         [0054]    As shown in FIG. 7, preform  50  is made of a thin sheet of readily bendable material, such as corrugated cardboard. Preform  50  has two laterally mirror symmetric, left and right right triangularly-shaped panel sections bendable out the plane of the sheet to form lower and upper triangular cover flaps  51  and  52 , respectively. In the orientation of preform  50  shown in FIG. 7, flap  51  is on the left-hand side of the figure, and will be referred to as the left-hand flap as a matter of convenience throughout the ensuing discussion. Left and right, lower and upper triangular coverflaps  51  and  52  have collinear horizontal bases  53  and  54  joined at their respective ninety degree corner angles to opposite vertical sides  55  and  56  of a vertically elongated, rectangular panel section comprising an inner spine flap  57 , which has a base  58  collinear with the bases of the triangles. Thus shaped, preform  50  has an appearance approximating that of an isosceles triangle having a horizontal base  53 - 58 - 54  and an upper vertex truncated by a horizontal edge  59  parallel to the base.  
         [0055]    Referring still to FIG. 7, preform  50  may be seen to include a horizontally elongated, rectangularly shaped panel section comprising an outer spine flap  60  which depends downwardly from base  53  of left-hand triangular flap  51 , and has the same width as that flap. A trapezoidally-shaped securement flap  61  depends downwardly from the bottom edge wall  62  of outer rectangular spine flap  60 , the securement flap having an upper edge wall coextensive with bottom edge wall  62  of the outer spine flap, and a lower edge wall  63  parallel to but shorter than edge wall  62 .  
         [0056]    In a preferred embodiment of corner protector preform  50 , the width of inner, vertical spine flap  57  and the height of outer, horizontal spine flap  60  are each equal to a common value which is slightly greater than the thickness of a typical picture frame, e.g., about {fraction (15/16)} inch, for a frame thickness of ⅞ inch. As shown in FIG. 7, preform  50  is preferably scored along edge walls  55  and  56  of inner, vertical spine flap  57 , and along edge walls  53  and  62  of outer, horizontal spine flap  60 . These score lines are located along boundaries between adjacent flaps, and facilitate folding the flaps out from the plane of a preform and around a picture frame corner, as will be explained below.  
         [0057]    Referring again to FIGS. 2 and 8, corner protector feeder mechanism  70  may be seen to include a longitudinally elongated, rectangularly shaped guide plate  71  having a generally flat upper surface mounted above and parallel to upper surface  34  of work table  32 . Guide plate  71  is oriented with its long axis parallel to left and right side walls  72  and  73  of enclosure  31 , and protrudes rearwardly beyond rear side wall  74  of the enclosure. As shown in FIGS. 1, 2, and  8 , guide plate  71  of feeder mechanism  70  has through its thickness dimension a perforation  76  having substantially the same outline shape as corner protector preform  50 . Guide plate  71  is spaced above upper surface  34  of table  32  by longitudinally disposed support ribs  82 , at a distance slightly greater than the thickness of corner protector preform  50 , e.g., {fraction (5/16)} inch for preforms having a thickness of about ¼ inch. Thus, a corner protector preform  50  placed conformally over perforation  76  will drop through the aperture onto work table surface  32 , allowing the preform to be slid into operating position under clamping jig  33 , as will be described in detail below.  
         [0058]    As may be seen best by referring to FIG. 9, feeder mechanism  70  includes a pusher plate  79  longitudinally slidably mounted in longitudinally disposed guideways consisting  11  of grooves  80  provided in inner facing walls  81  of guide plate support ribs  82 . Pusher plage  79  has a generally uniform thickness, and has a front edge wall  83  in which is formed a groove shaped complementarily to the lower edge wall of preform  50 . Preferably, pusher plate  79  is made of DELRIN, NYLON, or a similar structural polymer that has good lubricity.  
         [0059]    As shown in FIG. 9, pusher plate  79  has protruding perpendicularly from a rear edge  85  thereof an elongated straight push rod member  84  which protrudes rearwardly of rear vertical wall panel  74  of enclosure  31 . Push rod  84  is reciprocally and cyclically actuated longitudinally, i.e., perpendicularly to rear edge  85  of pusher plate  79 , in a forward direction to feed a preform  50  forward under clamping jig  33 , and rearwardly to retract front edge  83  of the pusher plate into alignment with the rear edge wall of aperture  76  through guide plate  71 , to thereby enable a next preform  50  in a stack to drop through the aperture preparatory to its being fed forward for installation on another picture frame corner. In a preferred embodiment, push rod  84  is coupled to the piston of a double acting pneumatic cylinder (not shown) used to cyclically advance and retract pusher plate  79 .  
         [0060]    In a preferred embodiment of apparatus  20 , as shown in FIG. 1, corner protector installation mechanism  30  includes a plurality of vertically disposed guide rods  77  which protrude perpendicularly upwards from upper surface  34  of work table  32 . Guide rods  77  define between tangents to the outer wall surfaces of inner facing sides of the rods a uniform transverse cross-section, vertically disposed bore  78  which is vertically aligned with guide plate perforation  76  and which is adapted to receive a vertical stack of preforms  50 .  
         [0061]    Referring now to FIGS. 1, 2 and  8 , it may be seen that corner protector installation mechanism  30  includes an adhesive dispensing apparatus  101  for dispersing quantities of adhesive used for bonding corner protectors  50  to picture frames. In a preferred embodiment, adhesive dispensing apparatus  101  includes a hot melt adhesive machine, such as the Autotech Model AT15 Hotmelt Unit, manufactured by the Slautterback Corporation, located at 5 Lower Ragsdale Drive, Monterey, Calif. 93940-5779. As shown in FIG. 2, this embodiment of an adhesive dispensing apparatus includes a machine  102  for melting solid polymer sticks and pumping the molten polymer, and a thermally blanketed, high pressure hose  103  for conveying hot, molten polymer adhesive to an applicator head  104 . As shown in FIGS.  3 - 6 , applicator head  104  has a horizontally elongated body  105  including a generally rectangular block-shaped front portion  106  having a flat, horizontally disposed lower surface  107  from which protrude one or preferably two adhesive dispensing nozzles  108 . Hot melt adhesive dispensing apparatus  101  includes a pressurized air hose  109  and electrical control cable  110  which are interconnected between hot melt pumping machine  102  and applicator head  104 . Machine  102  includes a melting tank (not shown) located below a hinged lid  111  for receiving and melting sticks of hot melt polymer adhesive, such as H. B. Fuller type HL 9254 hot melt adhesive received into the tank. This type adhesive has a working temperature range of about 270° F. to 325° F. Machine  102  includes an internal heater, and internal control mechanisms which, in response to electrical command signals supplied from an external source, pump molten hot melt adhesive from the melting tank through delivery hose  103  to applicator head  104 . Internal control mechanisms within machine  102  also provide electric signals through control cable  110  to applicator head which control pressurized air supplied to the had through hose  109 .which operate valves within the head, causing jets of pressurized liquid hot melt adhesive to be sprayed from nozzles  108  upon receipt of an external command signal.  
         [0062]    As may be seen best by referring to FIGS. 2, 8, and  18 , corner protector installation apparatus  20  includes an adjustable support structure  118  for holding and supporting at an adjustable longitudinal distance, or throat depth, applicator head  104  of the apparatus relative to a picture frame held in clamp jig  33 .  
         [0063]    Support structure  118  is mounted on the upper end of a compressor/elevator actuator mechanism  119  which lowers applicator head  104  to force a pair of fingers  141  having flat, co-planar horizontally disposed anvil surfaces  142  which protrude downwards from a front flat anvil portion  120  of head  104  into compressive contact with a corner protector  50  on a picture frame to press flaps of the corner protector preform into bonding contact with semi-liquid hot melt adhesive, upon completion of the adhesive application operation, as will be explained in detail below.  
         [0064]    As may be seen best by referring to FIGS. 2, 8, and  18 , compressor/elevator actuator  119  of hot melt adhesive dispensing apparatus  101  includes a row of three vertically disposed, laterally spaced apart and aligned support rods  121  fastened at the upper ends thereof to the lower portion of spray gun applicator head support structure  119 A. Support rods  121  are vertically slidably supported in sleeve bearings  122  located below an elongated rectangular base plate  123 . Base plate  123  is fastened to a structural member  124  within enclosure  31 , and is located below a similarly-shaped aperture  125  through work table  32 .  
         [0065]    Referring now to FIGS. 2 and 8- 1   0 , corner protector installation mechanism  30  may be seen to include a pair of corner flap folder actuators  130 L and  130 R located on the left and right sides, respectively, of a longitudinal center line of work table  32  of the apparatus. As shown in FIG. 2, flap folder actuators  130 L and  130 R are located longitudinally inwards of clamping jig  33 , in a location that places the actuators adjacent to the sides of a frame inserted inwardly under clamp bar  38  of clamping jig  33 . Flap folder actuators  130 L and  130 R are identical in structure and function. Therefore, in the ensuing description, the flap folder actuators will be referred to generally without a subscript.  
         [0066]    As shown in FIGS. 2 and 8, each flap folder actuator  130 , such as left-hand folder actuator  130 L, may be seen to include a flat, rectangularly-shaped flap folder arm  131  which fits into a complementarily shaped recess  129  provided in upper surface  34  of work table  32 , flush with the upper surface. Arm  131  is oriented with a long, inner longitudinal edge  132  thereof parallel and adjacent to a side of a picture frame protruding diagonally inwardly from beneath clamp bar  38  of clamping jig  33 .  
         [0067]    As may be seen best by referring to FIG. 12, each flap holder arm  131  is mounted on the upper transversely disposed horizontal end wall  133  of a vertically disposed, cylindrically-shaped support post  134 . Also, corner protector installation mechanism  30  includes a linear actuator for elevating support post  134  along its longitudinal axis, to thereby elevate flap folder arm  131  attached to the upper end of the support post upwardly from its rest position recessed in upper surface  34  of work table  31 , and a rotary actuator for reciprocally rotating elevator support post  134  about its longitudinal axis, to thereby rotate the flap folder arm ninety degrees away from and back to its rest position, where the linear actuator retracts the flap folder arm into recess  129 .  
         [0068]    Corner protector installation mechanism  30  according to the present invention also includes preferably sensor means which provides a signal indicating that a corner of a picture frame has been fully inserted into clamping jig  33 , with the frame moldings adjacent the corner parallel to and proximate inner vertical wall surfaces  238 R,  238 L of guide plates  36 R,  36 L.  
         [0069]    Various types of proximity or optical sensors suitable for the foregoing purpose are well known to those skilled in the art. In an example embodiment of apparatus  20  tested by the present inventor, each sensor  170  consisted of a UZJ-111, fixed-focus type micro-photo sensor, manufactured by Matsushita Electric Works, Ltd., Automation Controls Group, 1048 Kadoma, Osaka 571, Japan. That sensor contains an infrared light emitting diode and phototransistor arranged within a circuit module with their optical axes generally parallel, and their respective exit and entrance pupils adjacent each other behind an infrared window comprising the outer face of the module. When a surface such as the outer surface of a picture frame molding is positioned within about 5 mm±2.5 mm of the outer face of the sensor, an output transistor within the sensor is turned on, providing a logic TRUE current through a load resistor connected in series with a collector supply voltage, and the emitter and collector output terminals of the sensor.  
         [0070]    As shown in FIG. 1, a pair of sensors  170 R,  170 L of the type described above with their outer faces installed in guide plates  36 R,  36 L, flush with inner surfaces  238 R,  238 L of guide plates  36 R,  36 L, respectively, near the inner transverse vertical end walls  171 R,  171 L thereof, and near upper surface  34  of work table  32 . Each sensor  170  produces a logic TRUE signal when a frame molding is parallel to and a predetermined distance from inner surface  238 R,  238 L adjacent the outer face of the sensor. Moreover, apparatus  20  includes an electronic AND circuit  172  for logically ANDING signals from the output terminals of two sensors  170 R,  170 L of corner protector installation mechanism  30 . The output signal from the AND circuit is false when either of the 2 sensors  170 R,  170 L outputs a false signal, indicating that a picture frame molding near that sensor is not substantially close to and parallel to the sensor. However, when the corner of a frame has been fully inserted into and properly aligned with clamping jig  33  of corner protector installation mechanism  30  of apparatus  20 . The logical AND circuit produces a TRUE output signal which initiates a sequence of automatic operations of the corner protector installation mechanism, which are described below. Electronic circuitry for performing the foregoing functions is well known to those skilled in the art, and therefore need not be described in further detail here. For example, such circuitry can be implemented in a Programmable Logic Controller, PLC  133 , or a general purpose microprocessor or micro controller.  
         [0071]    Operation of the Invention  
         [0072]    In response to a TRUE output signal from AND circuit  172  when both sensors  170 L,  170 R produce TRUE output signals, Programmable Logic Controller (PLC)  133  issues in sequence drive signals to the various actuators of corner protector installer mechanism  30  of apparatus  20  according to the present invention, as follows:  
         [0073]    1. Vertical stacks of corner protector preforms  50  are loaded into bores  78  between guide rods  77  of feeder mechanisms  70  of installer mechanism  30 . (FIGS. 1 and 8)  
         [0074]    2. Power is turned on and PLC  133  resets and checks mechanism  30  of apparatus  20 , readying the PLC for outputting sequential drive signal commands to the various actuators of the apparatus. A program for the operational sequence of apparatus  20  is stored in electronic memory means in PLC  133 . This program can be executed via an internal or external computer. (FIG. 2)  
         [0075]    3. Actuator cylinder  92  of feeder mechanism  70  in installer mechanism  30  is actuated to reciprocate piston rod  94 , thereby moving an individual corrugated corner protector blank preform  50  forward into position below clamp bar  38  of the installer mechanism. (FIG. 9)  
         [0076]    4. A first corner C 1  of a picture frame A having left and right channel moldings D and B is inserted into position beneath clamp bars  38  and over blank  50  of installer mechanism  30 . (FIG. 10)  
         [0077]    5. Frame A is positioned relative to apparatus  20  so that corner C 1  of the frame is fully inserted into clamping jig  33  of mechanism  30 . (FIG. 10)  
         [0078]    6. Sensors  170 L,  170 R of installer mechanism  30  output TRUE signals, causing AND circuit  172  to output a TRUE signal, in turn causing PLC  123  to simultaneously issue drive signals to the installer mechanism, as follows: (FIG. 10)  
         [0079]    7. Hold down clamp bar  38  of clamping jig  33  of mechanism  30  is forced downward onto the adjacent molding channels D and B of frame A which intersect at corner C 1 . (FIG. 10)  
         [0080]    8. Hot melt adhesive machine  102  is then actuated, causing applicator head  104  to spray blobs E of semi-liquid hot melt adhesive onto the upper surface of left-hand frame molding D. (FIG. 11)  
         [0081]    9. Blank preform  50  under corner C 1  of frame A is automatically manipulated as follows: First, rectangular outer spine flap  60  and securement flap  61  of preform  50  are bent upwardly in unison into a vertically disposed orientation by elevating right-hand flap folder arm  131 R of mechanism  30  from its recess  129 R, with the flap folder arm in its clockwise position. (FIG. 12)  
         [0082]    10. Securement flap  61  of preform  50  is bent inwardly and downwardly over left frame channel D by rotating right-hand flap folder arm  131 R counterclockwise. (FIG. 13)  
         [0083]    11. Hot melt adhesive applicator head  104  is again actuated to spray blobs F of semi-liquid adhesive onto the upper surface of securement flap  61 . (FIG. 14)  
         [0084]    12. Right-hand, upper triangular cover flap  52  and inner spine flap  57  of preform  50  are bent as a unit into a vertically disposed orientation by extending right-hand flap folder arm  162 R upwardly from recess  129 R. (FIG. 15)  
         [0085]    13. Upper cover flap  52  of preform  50  is bent inwardly and downwardly over right-hand frame channel B by rotating flap folder arm  152 L ninety degrees clockwise. (FIG. 16)  
         [0086]    14. Right flap folder arm  131 R is rotated ninety degrees clockwise to its angular rest position, and retracted downwardly into recess  129 R to its vertical rest position. (FIG. 17)  
         [0087]    15. Hot melt adhesive applicator head gun  104  of mechanism  30  is lowered toward frame A, pressing fingers  141  protruding downwardly from front flat anvil portion  120  of the head, located forward of nozzles  108 , down against upper flap  52 , thereby pressing the flap down into blobs of adhesive between it and securement flap  61 . (FIGS. 17, 18,  19 )  
         [0088]    16. Left flap folder arm  131 L of mechanism  30  is rotated ninety degrees counterclockwise to its angular rest position. (FIG. 2)  
         [0089]    17. Left flap folder arm  131  L of mechanism  30  is retracted downwardly into recess  129 L to its vertical rest position. (FIG. 2)  
         [0090]    18. Hold down clamp bar  38  of clamping jig  33  of mechanism  30  is retracted vertically upwards to its rest position, unclamping corner C 1  of frame A. (FIG. 9)  
         [0091]    19. Frame A is retracted from apparatus  20 , disengaging corner C 1  from clamping jig  33 .  
         [0092]    20. Frame A is rotated ninety degrees in a horizontal plane, and steps 4-18 repeated to attach a corner protector  50  to a second corner C 2  of frame A.  
         [0093]    21. Step 20 is repeated for the remaining two corners C 3 , C 4  of frame A.