Abstract:
A press apparatus for pressing connector plates into opposing surfaces of structural members which are to be secured together to form a structure such as a roof truss. The apparatus includes a frame particularly constructed to reduce stress concentrations and failure. Forces applied to the frame are transmitted in a loadpath which is smooth and free from discontinuity to inhibit concentration of stress and thereby strengthen the frame against fatigue damage. The frame includes ribs spanning and connecting an inner rim and outer rim for strengthening the frame. A powered actuator has a body which is removably attachable to the frame, and a timer control operates the press to make sure the connector plates are fully embedded.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to the assembly of structures, and in particular to a press for manufacturing trusses which provides several advantageous features. 
   Pre-manufactured structural frameworks, such as trusses, are widely used in the construction industry for forming a roof, wall panel, floor, or other building component. The truss is assembled to the correct specifications at a factory and then shipped to a construction site. Each truss includes a collection of structural members made of wood, plastic, or metal which are held together by fasteners, such as nailing or connector plates. Efficient assembly of the truss is facilitated by a press apparatus which drives the connector plates into assembled precut structural members where they intersect or abut each other. 
   In one widely used type of system, a press is suspended from an overhead carriage for movement between several splice pedestals (or stands) supporting the structural members in assembled position. Each of the pedestals includes a holder for holding a lower connector plate at a position below the structural members and bridging lower surfaces of the structural members at their intersection or abutment. An upper connector plate is placed over the joint so that it bridges upper surfaces of the structural members. The press has a C-shaped frame which carries upper and lower platens adapted to be positioned above and below the respective upper and lower connector plates. Actuation of a hydraulic powered cylinder causes the upper platen to move downwardly toward the lower platen and press the joint so that the connector plates are driven into the structural members thereby connecting the structural members. 
   There has been growing demand for larger, heavier trusses using larger sizes of connector plates, such as 8×8 inches and 10×12 inches, which require a larger capacity press, e.g., on the order of about 37.5 to 50 tons instead of 25 tons. Unfortunately, existing presses have a number of drawbacks which degrade their effectiveness in applying such a large force without substantial increases in size and weight of the frame. 
   Frames of the prior art are prone to fatigue damage. Typically, a frame has two major structural parts including an inner peripheral rim defining the inside edge of the C-shape and an outer peripheral rim defining the outer edge. For lower cost manufacturing (e.g., by forging of steel), the frame has a profile which is not a substantially rounded “C”, but rather a generally rectangular “C”. Consequently, the frame has two substantially 90° turns at corners of the C-shape, separating the generally horizontal and vertical portions of the “C”. During operation, the frame is exposed to a reaction force urging apart the upper and lower platens. Unfortunately, stress concentrations arise at each turn which produce a local stress greater than a nominal stress. Consequently, the frame tends to develop fatigue cracks and fail sooner than should be expected for its size and loading. Aggravating this problem is that the majority of the load is transmitted through the inner peripheral rim, which consequently exhibits the earliest fatigue damage. The inner and outer rims are divided such that the loads carried by each are separate, without the added stability or efficiency if the load was shared in a structural framework. 
   Systems of the prior art are not designed for rapid maintenance and repair. The hydraulic cylinder for driving the upper platen includes a tubular body holding a reciprocally movable piston connected to a movable rod. That body is typically welded to the frame. Consequently, the body carries load and is subject to fatigue damage, particularly along the weld. Replacement of the cylinder is difficult and requires substantial down time. Moreover, maintenance work on the cylinder or its replacement with a new or differently sized cylinder and piston is a major repair effort. There is no flexibility in quickly substituting differently sized cylinders for carrying different loads tailored to the truss. The cylinder and its tubular body are not “off the shelf” items. 
   The upper platen is subject to failure when used with high loadings. Periodically, the platen inadvertently presses a non-flat object, such as due to operator error or due to an incorrectly positioned stop on the pedestal. That exposes a portion of the platen to an even greater load which frequently leads to permanent deflection or failure. 
   Operationally, presses of the prior art are inefficient. An operator controls a switch to activate the hydraulic cylinder and apply force through the cylinder to the joint. The operator makes a visual judgment of whether the connector plates are completely embedded into the structural members, and releases the switch so that the platens may separate. Often, the operator misjudges that time and must conduct one or more repetitive cycles of force application. Further, the press may be limited in magnitude of force due to the aforementioned structural drawbacks and cylinder size and requires several cycles to embed larger connector plates. Thus, substantial delays may occur in the construction of a roof truss. 
   SUMMARY OF THE INVENTION 
   Among the several objects and features of the present invention may be noted the provision of an apparatus for pressing connector plates into structural members which inhibits fatigue damage; the provision of such an apparatus which distributes load effectively; the provision of such an apparatus which is easy to maintain and repair; the provision of such an apparatus which applies greater force without a corresponding increase in mass of the frame; and the provision of such an apparatus which is operationally efficient. 
   In general, a press according to the present invention is for use in pressing connector plates into opposing surfaces of structural members which are to be secured together at one or more joints to form a structure. The press comprises first and second platens sized and shaped for engaging connector plates to press the connector plates into the structural members. A frame includes a first mounting portion mounting the first platen, a second mounting portion mounting the second platen and a third portion interconnecting the first and second mounting portions. The frame positions the first and second platens in generally opposed relation for relative movement toward each other to press connector plates into the structural members and away from each other to clear the structural members and connector plates. An actuator is mounted on the frame for applying a force to at least one of the first and second platens to forcibly move the platen. The third portion of the frame is free of straight sections thereby to inhibit the concentration of stress in one location of the frame in operation of the press. 
   In another aspect, a press of the present invention is for use in pressing connector plates into opposing surfaces of structural members which are to be secured together at one or more joints to form a structure. The press comprises first and second platens sized and shaped for engaging connector plates to press the connector plates into the structural members. A frame mounts the first and second platens in generally opposed relation for relative movement toward each other to press connector plates into the structural members and away from each other to clear the structural members and connector plates. An actuator is mounted on the frame for applying a force to at least one of the first and second platens to forcibly move the platen. The frame includes a peripheral inner rim, a peripheral outer rim and ribbing spanning and connecting the inner rim to the outer rim. 
   In yet another aspect, a press of the present invention is for use in pressing connector plates into opposing surfaces of structural members which are to be secured together at one or more joints to form a structure. The press comprises first and second platens sized and shaped for engaging connector plates to press the connector plates into the structural members. A frame mounts the first and second platens in generally opposed relation for relative movement toward each other to press connector plates into the structural members and away from each other to clear the structural members and connector plates. An actuator is mounted on the frame for applying a force to at least one of the first and second platens to forcibly move the platen. A timer control is adapted for automatically holding the actuator at a preselected force for a preselected period of time and then to move at least one of the first and second platens away from the other platen to release the force. 
   In still a further aspect, a press of the present invention is for use in pressing connector plates into opposing surfaces of structural members which are to be secured together at one or more joints to form a structure. The press comprises first and second platens arranged for placement proximate the opposing surfaces of the structural members and relatively movable toward and away from one another. The platens are configured for pressing the connector plates into the structural members. A frame mounts the platens, the frame having a generally C-shaped contour with an inner peripheral load carrying surface and an outer peripheral load carrying surface. The inner peripheral load carrying surface of the frame has a shape which defines a segment of a circle such that forces applied to the frame while the platens are pressing the connector plates are transmitted in a loadpath through the inner peripheral load carrying surface which is smooth and substantially free from discontinuity to inhibit concentration of stress at any position along the inner peripheral load carrying surface and thereby strengthen the frame against fatigue damage. 
   Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevation of a press system and support pedestals holding a truss; 
       FIGS. 2 and 3  are front and side elevations, respectively, of a press of the press system; 
       FIG. 4  is similar to  FIG. 3  but shows the press pressing connector plates into opposing surfaces of structural members which are to be secured together; 
       FIG. 5  is a section on line  5 — 5  of  FIG. 3 ; 
       FIG. 6  is a section on line  6 — 6  of  FIG. 3 ; 
       FIG. 7  is a section on line  7 — 7  of  FIG. 5 ; 
       FIG. 8  is a vertical section of a frame of the press; 
       FIG. 9  is a section on line  9 — 9  of  FIG. 8 ; 
       FIG. 10  is a perspective of a cylinder mount of the apparatus; 
       FIGS. 11 and 12  are front and right side elevations, respectively, of the cylinder mount of  FIG. 10 ; 
       FIG. 13  is a fragmentary elevational section showing the engagement of the cylinder mount and the C-frame; and 
       FIG. 14  is a schematic of a control system of the invention. 
   

   Corresponding reference characters indicate corresponding parts throughout the views of the drawings. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings,  FIG. 1  shows a press system according to the present invention, generally indicated at  10 , for assembling structures such as trusses. The apparatus  10  includes a press, indicated generally at  12 , which is suspended by a suspension assembly  14  from an overhead rail  16  for movement between a series of conventional splice pedestals  18 . The suspension assembly  14  includes a carriage assembly  20  movable along the rail, a pivotal boom  22  attached to the carriage by a hanger  24  and swivel  26 , and a yoke  28  suspended from one end of the boom. The press is counterbalanced by a power and control assembly  30  including a hydraulic power unit  32 , counterweight (not shown), electrical panel and control unit  34 , and manifold  36  on the opposite end of the boom. The press  12 , suspension assembly  14 , and power and control assembly  30  are considered collectively to be a press system. Pedestals  18  hold structural members  38 , such as pre-cut timbers, which are to be secured together by the press at their intersections with connector plates  40 . Although the press  12  is shown operating on wooden components (i.e., pre-cut timbers), the press may be used to press connector plates into components made of other materials. 
   Referring to  FIGS. 2 and 3 , the press  12  comprises a frame  44  which supports first and second platens  46 ,  48  for relative movement toward one another to press the connector plates into the timbers, and away from one another so that the platens may clear the timbers and connector plates so that the press may be moved to another position. In the illustrated embodiment, the first platen  46  is a lower platen and is fixedly attached to a first portion  50  of the frame  44 , such as by welding, and strengthened by two lateral support plates  52 . The second platen  48  is an upper platen movable via a hydraulic powered cylinder  53  (broadly, “actuator”) having a tubular body  56  ( FIG. 4 ) holding a movable piston and rod assembly  54 . The cylinder body  56 , and hence the upper platen  48 , are mounted on an actuator mount  58 , constituting a second portion of the frame  44 . The platens  46 ,  48  are generally rectangular in planform shape and of sufficient size for engaging an entire extent of a connector plate  40 , with an exemplary size of each platen being 10×16 inches. An exemplary diameter of the bore of cylinder body  56  is six inches. However, the platens and cylinder may have other shapes and sizes (not shown)  FIG. 4  shows the second platen  48  moved downwardly such that the platens press the connector plates into opposing surfaces of the structural members  38 . 
   The cylinder  53  is interconnected to the hydraulic power unit  32  by conventional hydraulic fluid lines  60  for providing hydraulic fluid under pressure to forcibly move the second platen  48  toward and away from the first platen  46 . A protective guard  62  is provided over the frontmost hydraulic fluid line  60  and its attachment to the cylinder  53 . Conventional pistol grip handles  64  are provided on opposite sides of the frame  44  so as to enable an operator readily to control the movement and operation of the press. Push button electrical switches  66  are mounted on the handles  64  for movement of the carriage  20  along the overhead rail  16 . Additional push button electrical switches  68  are provided on the handles for controlling operation of the platens of the press  12 . Other arrangements, shapes, number and orientations of the platens, including configurations where all platens are movable, and other power sources (i.e., non-hydraulic) do not depart from the scope of this invention. 
   The frame  44  includes a central (or third) portion  70 , shown in section in  FIG. 8 , which has a generally C-shape and a uniform width. The central portion  70  is laterally bounded by two side plates  72  ( FIG. 2 ) attached to the central portion. Referring to  FIGS. 8 and 9 , the frame  44  is adapted to inhibit fatigue damage. The frame has an inner peripheral load carrying surface  74  and an outer peripheral load carrying surface  76  which each have a shape that is smooth and free from discontinuity (i.e., generally no sharp or distinct localized bends in slope). Preferably the shapes generally define arcs, and more preferably segments of circles, such as semicircles, having noncoincident centers  78 . The arcs each have a rate of change of slope which ideally is close to a constant value along the extent of the respective load carrying surface  74 ,  76 . That avoids discontinuity and stress concentration. Moreover, the central portion  70  of the frame and its arcs are free of any straight sections. Accordingly, there are no tight bends defining corners in which stress concentrations occur. Forces applied to the frame  44  while the platens  46 ,  48  are pressing the connector plates are transmitted in loadpaths through the inner load carrying surface  74  and outer load carrying surface  76  which do not produce appreciable concentrations in stress beyond a nominal stress. Other smooth but non-circular shapes do not depart from the scope of this invention, nor do frames with only one peripheral load carrying surface having a shape free from discontinuity. 
   The frame  44  has an inner structural rim  80  ( FIG. 8 ) having a generally uniform thickness and which defines the inner peripheral load carrying surface  74 . Similarly, an outer structural rim  82  has a generally uniform thickness (less than the inner rim) and defines the outer peripheral load carrying surface  76 . The inner rim  80  is generally semicircular, but the outer rim  82  extends to a greater angular extent on the lower side of the frame  44  such that the outer rim forms a chin  84  for supporting the second platen  48 . The centers  78  are noncoincident, with an upper region of the frame  44  being generally thicker than the lower region, because stress levels are generally greater in the upper. A central web  86  ( FIG. 9 ) is positioned between the inner and outer rims  80 ,  82  at the chin  84  and is oriented generally vertically. A shoulder  88  is provided for engagement by the actuator mount  58 , as discussed below. 
   Internal ribs  90  (collectively, “ribbing”) span and connect the inner and outer rims  80 ,  82  for strengthening the frame  44  and distributing load. As seen in  FIG. 8 , the ribs  90  are arranged in a triangular web pattern between the inner and outer rims. In this way, the frame itself becomes a truss for resisting applied loads, with the ribs  90  not only rigidifying the inner and outer rims  80 ,  82  but transferring loads between them. The ribs facilitate a more efficient distribution of load between the inner and outer rims. In use, the frame  44  of this invention has permitted application of double the pressing load (from 25 tons to 50 tons) without increasing size or weight of the frame and without formation of fatigue cracks after repeated use. The ribs  90  have thicknesses which are large enough to transmit loads and minimize sharp edges at triangle corner radii, while small enough to avoid substantial weight penalty. Preferably, all the ribs  90  have a uniform thickness, such as ⅜ inch, although the thicknesses may vary depending on design loads. Further, the number and arrangement of ribs which extend between the inner and outer rims may vary without departing from the scope of this invention. 
   The inner rim  80 , outer rim  82 , ribs  90 , and central web  86  are preferably formed as one piece (comprising the central portion  70  of the frame), such as a one piece casting. That minimizes manufacturing cost and improves structural integrity. The frame  44  is formed of a suitable strong material, such as ASTM A148 steel. Frames which are formed with more than one piece or from other materials do not depart from the scope of this invention. 
   The frame  44  includes a foot  92  for supporting the frame in an upright position when it is lowered to a floor. Two guide bars  94  ( FIGS. 3 and 5 ) extend from the second platen  48  on opposite sides of the frame for preventing rotation of the cylinder  54  and second platen relative to the frame. The guide bars  94  are mounted in a cantilever arrangement with an end portion of each guide bar engaging a slide pad  96  which is fixedly mounted on the frame  44 . As the second platen  48  moves up and down relative to the frame, the end portion of each guide bar  94  also moves and slides along the respective pad  96 . The engagement prevents rotation of the cylinder and platen. 
   The actuator mount  58  is attached to the central portion  70  of the frame  44  and configured for mounting the cylinder body  56 . Referring to  FIGS. 10-12 , the mount  58  includes a platform  98  and two sloping sidewalls  100  attached to the platform and forming lateral sides of the mount. The platform  98  has a counterbored hole  102  therein adapted for receiving the cylinder rod  54  and forming a seat for the cylinder body  56 . The platform  98  is configured for stable engagement with the shoulder  88  of the frame, as seen in  FIG. 13 , and the sidewalls  100  are fixedly attached to the side plates  72  of the frame, as by welding. The press  12  is suspended by attaching the sidewalls  100  to the yoke  28  at pivots  104  ( FIGS. 2 and 3 ) which are located at a position generally aligned with a center of gravity so that the frame is maintained at a desired orientation. 
   The mount  58  is configured such that the cylinder  53  and its body  56  are removably attachable for rapid repair and maintenance. Upper and lower cylinder blocks  106  ( FIG. 2 ) are provided for holding the body  56  on the actuator mount  58 . Four connecting rods  108  interconnect the upper and lower blocks  106 . Each rod  108  is received through the upper block and is threaded on an upper end for receiving a cap nut  110 . Each rod  108  is threaded on a lower end for being received in a threaded hole (not shown) on the lower block. Bolt fasteners  112  ( FIG. 2 ) hold the assembled blocks  106  and body  56  to the mount  58 . The fasteners  112  extend through the lower block  106  and are received in threaded holes  114  ( FIG. 10 ) positioned on the platform  98 . A differently sized cylinder  53  may be substituted for applying a larger or smaller load, or a malfunctioning cylinder may be replaced, by unfastening the blocks  106  from the mount, detaching the hydraulic lines  60 , and installing a new body  56 . There are no welds or fixed attachment which must be broken, and downtime is minimized. The cylinder and its tubular body are therefore “off the shelf” replaceable units. Other attachable/detachable mounting configurations of the cylinder do not depart from the scope of this invention. 
   The second platen  48  is designed for strength for applying relatively greater forces, such as 50 tons. Referring to  FIGS. 5-7 , the platen  48  has a bottom side  116 , comprising its front side, for engaging the connector plate  40  and a top side  118 , comprising its back side. A boss  120  extends from the top side  118  for receiving the cylinder rod  54 . A conventional coupler  122  having a collar and a ring of axial fasteners attach the cylinder rod  54  to the second platen  48 . Four gussets  124  are in spaced arrangement on the top side  118  of the second platen, extending at an inclined angle between the boss  120  and the top side for providing added strength and stability. Each gusset  124  slopes in height from a maximum height near a top of the boss  120  to the surface of the top side  118 . Preferably, the second platen  48 , boss  120 , and gussets  124  are formed in one piece. The gussets  124  inhibit deflections of the second platen  48  and do so without increasing thickness of the platen which would increase weight and cost. When the platen  48  inadvertently presses a non-flat object, such as due to operator error, the load is not distributed across the platen but rather is concentrated at one, usually eccentric location on the platen. The gussets  124  inhibit deflection and failure by transmitting the concentrated load to the boss  120  and more effectively distributing the load until the operator releases the press. Other configurations, such as a different size, number, or configuration of gusset(s), do not depart from the scope of this invention. Further, similar gussets could be included on the first platen  46 . 
   The apparatus of the present invention includes a timer and controller unit  126 , indicated schematically in  FIG. 14 , for operational efficiency. The unit  126  is part of the control unit  34  shown in  FIG. 1 , and it is adapted to automatically hold the cylinder rod  54  at a preselected force for a preselected period of time. The timer and controller unit  126  is selectively adjustable for selecting the force and time period. Typically, the preselected force is a maximum force which is to be applied by the press  12  and the time period is sufficient for completely embedding the connector plates  40  in the structural members  38 . The time period, also known as “dwell time” to those skilled in the art, is an automated hold at the selected maximum force to permit the fasteners on the connector plates  40  to more fully embed in pre-cut timbers. A typical period is 3 seconds. When the operator presses the push button electrical switches  68 , the hydraulic power unit  32  is activated to move the cylinder rod  54  and second platen  48  and press the connector plates  40  into the structural members  38 . When the applied force reaches the preselected or maximum force, as measured by conventional sensors (not shown), the power unit holds the force relatively constant for the preselected dwell time before beginning release. The automation of the timer permits a more exact and repeatable process which avoids delays of manual inspection/estimation and repetitive cycles of force application. 
   In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results obtained. 
   When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
   As various changes could be made in the above without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.