Abstract:
A truss fabrication machine has processing circuitry for partially automating the fabrication of trusses. One or more workers place in jig stops on the tabletop a set of loose pre-cut truss members and the connector plates that get seated at the joints therebetween. The machine has a pressing head for seating the connector plates, which rides on a gantry above the tabletop in generally a Y-axis, wherein the gantry rides on a track generally along an X-axis. There are drivers to drive the gantry along the track and the pressing head along the gantry, as well an actuator for the pressing head. The processing circuitry is reliant on X- and Y-axis sensors for reckoning position on the tabletop. The processing circuitry is given control over the gantry, the pressing-head driver and actuator for coordinating movement of the gantry and pressing head between one given X and Y position to succeeding X and Y positions, and then actuating or not the actuating means. Alternatively the pressing head might pause in a standby mode following completion of a given truss sufficiently long to allow a worker to remove the completed truss and place back in the jig stops the loose pre-cut truss members and the connector plates, and so on, which will allow the fabrication of a succeeding truss, repetitively.

Description:
CROSS-REFERENCE TO PROVISIONAL APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 60/102,984, filed Oct. 03, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is directed to a machine for fabrication of roof trusses and, more particularly, to an automatic control system for such a machine for fabrication of roof trusses. A number of additional features and objects will be apparent in connection with the following discussion of preferred embodiments and examples. 
     Pitched roofs are commonly supported by roof trusses. Roof trusses are commonly constructed of wood, particularly for wood-framed structures and residences. Roof trusses are manufactured in a wide variety of shapes and sizes according to the needs encountered in erecting a specific building. Because the roof line is usually fairly uniform throughout much of the length of a single building, many identical trusses are needed for a single building. 
     It has long been known that such trusses can be fabricated more efficiently through use of a truss table than they can by manual methods at the job site. The truss table is setup so that each precut piece of a particular truss fits into a channel created by parallel raised members fastened to the top of the truss table. When all the pieces for a single truss have been put in place on the truss table, they are fastened together. Nails, staples, and other similar fasteners have long been used. For some time, it has been common practice to fasten many of the joints, particularly those bearing greater loads, with connector plates, which consist of a flat plate having a large number of downward projecting parallel spikes generally created by pressing a flat plate within a specially designed die. A connector plate is seated on both the top and bottom sides of the joint as the truss lies on the truss table. 
     The connector plates may be seated by hammering or the like. Substantial forces are required to seat the connector means of a machine. 
     A truss fabricating machine includes a gantry movable along an X-axis and a pressing cylinder suspended from the gantry which is movable along the Y-axis allowing the pressing cylinder to be located above a joint in a wooden truss. The pressing cylinder presses down to seat connector plates into selected joints of the truss. A joystick generates electrical signals proportional to the direction and extent of movement of the joystick by the operator, which are converted to pulse width modulated electrical signals in a driver, whose output controls proportional solenoids that drive infinite positioning four-way hydraulic valves to actuate hydraulic motors that drive the gantry and pressing mechanism along either the X-axis, or through a separate hydraulic circuit, the Y-axis. The pressing cylinder can be moved along both axes simultaneously. When the pressing cylinder is in the desired position, a thumb switch on top of the joystick is actuated, causing the ram of the pressing cylinder to descend until it seats the connector plate. Releasing the thumb switch causes the ram to move upward to the top of its stroke. 
     What is needed is an automatic or partially-automatic control system for such a truss fabrication machine to enhance the efficiency and ensure the maintenance of quality standards in the fabrication of trusses. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a truss fabrication machine with a processor or computer-implemented control system for automating or partially automating the fabrication of trusses thereon. 
     It is another object of the invention that such a processor or computer-implemented control system for a truss fabrication machine include access to storage devices for retrieval of pre-programmed or “canned” profiles of diverse truss configurations. 
     It is an alternate object of the invention that the above truss fabrication machine incorporate a manual command controller for not only operating the machine in a manual mode, but also for programmning the processor or computer-implemented control system by virtue of manually sequencing the machine through a given profile and having the processor or computer-implemented control system RECORD such sequence for automatic PLAY BACK later. 
     It is an additional object of the invention that the foregoing processor or computer-implemented control system include an editor for coding and/or editing the encoded instructions which govern such processor or computer-implemented control system. 
     These and other aspects and objects are provided according to the invention in a truss fabrication machine that is linked with processing circuitry for partially automating the fabrication of trusses. One or more workers place in jig stops on the tabletop a set of loose pre-cut truss members and the connector plates that get seated at the joints therebetween. The machine has a pressing head for seating the connector plates, which rides on a gantry above the tabletop in generally a Y-axis, wherein the gantry rides on a track generally along an X-axis. There are drivers to drive the gantry along the track and the pressing head along the gantry, as well an actuator for the pressing head. The processing circuitry is reliant on X- and Y-axis sensors for reckoning position on the tabletop. The processing circuitry is given control over the gantry, the pressing-head driver and actuator for coordinating movement of the gantry and pressing head between one given X and Y position to succeeding X and Y positions, and then actuating or not the actuating means. Alternatively, the pressing head might pause in a standby mode following completion of a given truss sufficiently long to allow a worker to remove the completed truss and place back in the jig stops the loose pre-cut truss members and the connector plates, and so on, which will allow the fabrication of a succeeding truss, repetitively. 
     In one example of the invention, pressing-unit moving means may comprise a motor, a drive shaft, and a drive transmission for driving the pressing unit along the gantry. That way, the Y-axis sensing means might comprise a shaft encoder coupled to the motor shaft for generating signals corresponding to Y-axis displacement. The drive transmission might comprise a chain and sprocket arrangement. 
     Also, the X-axis sensing means might comprise a photoelectric encoder mounted to one of the gantry or a carriage of the track and carriage means. The photoelectric encoder is preferably aimed at a strip on the tabletop, or otherwise somewhere else with the table. The stip will include photoelectric graduations allowing the photoelectric encoder to generate signals corresponding to X-axis displacement of the gantry. Such photoelectric graduations might be a marking stripe having dark and light alternations, or else a series of uniform notches, and so on. 
     An inventive aspect relates to the processing circuitry being configured with communication paths and ports sufficient for accessing pre-programmed profiles or instruction sets from storage in or on any of the following:—ie., chip memory, a hard disk, a floppy disk, a CD, or from alternative other remote devices accessible through either network- or modem-interfaces. That way, the profiles or instruction sets can be downloaded from a link through an intranet or the internet, and so on. 
     Another aspect of the invention is if it further includes a manual command means. The manual command means not only operating the machine in a manual mode, but also programming or entering profiles for storage and retrieval by the equivalent of a RECORD mode. Thus the manual command means, more particularly, is provided for electrically controlling the gantry moving means, the pressing-unit moving means and the actuating means. It includes a manually-operated control having electrical outputs and signal delivery means for delivering signals at said outputs representative of movement of said manual control corresponding to desired X and Y directions of movement of the gantry and pressing unit, responsive means for responding to said signals for driving said gantry moving means and pressing unit moving means, and a switch for actuating the actuating means. 
     The processing circuitry is linked to the manual command means for recording in the RECORD mode a given instruction set corresponding to the manually-inputted movements entered by the manual command means of the gantry and pressing unit movements from one given X and Y coordinate to another, succeeding X and Y coordinate. The processing circuitry also associates each X and Y coordinate with an instruction to actuate the actuating means or not, or pausing in the PAUSE mode. That way, in a PLAYBACK mode, the processing circuitry can play back the given manually-recorded instruction set, as well as include pauses in the PAUSE mode during which a worker might remove one or more completed trusses and place back in the jig means sets of loose pre-cut truss members and connector plates. This all allows the repetitive fabrication of succeeding trusses during the corresponding play backs of the given manually-recorded instruction set. 
     It is preferred if the manually-operated control comprises a joystick, as configured with a centered neutral position. The aforementioned signals are related to the displacement of said joystick away from said centered neutral position. Alternatively, the manually-operated control may comprise either a keypad or keyboard and the like. 
     A way of achieving some of the above may include having the gantry moving means comprise an infinitely adjustable gantry valve operatively connected to at least one fluid-driven motor and a pair of proportional solenoids operatively connected to said gantry valve. Likewise, the pressing-unit moving means might have a similar infinitely adjustable valve, a fluid-driven motor and a pair of proportional solenoids. Given the foregoing, the signal delivery means would likely provide the signals in response to displacements of the joystick from the neutral position in order to drive the proportional solenoids. 
     Additional aspects and objects of the invention will be apparent in connection with the discussion further below of preferred embodiments and examples. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There are shown in the drawings certain exemplary embodiments of the invention as presently preferred. It should be understood that the invention is not limited to the embodiments disclosed as examples, and is capable of variation within the scope of the appended claims. In the drawings, 
     FIG. 1 is a perspective view of a truss fabricating machine according to the present invention including an automatic control system therefor and in accordance with the invention. 
     FIG. 2 is a front elevational view of the operator booth and truss fabricating machine of FIG.  1 . 
     FIG. 3 is a side elevational view thereof. 
     FIG. 4 is a side elevational view of the joystick in the operator booth and used to control manually the truss fabricating machine of FIG.  1 . 
     FIG. 5 is a schematic diagram of the electro-hydraulic control mechanisms, in part. of the truss fabricating machine of FIG.  1 . 
     FIG. 6 is a schematic top plan view of the joystick illustrating the direction along which it can be displaced from its vertically centered neutral position. 
     FIG. 7 is a schematic block diagram of the automatic control system for the truss fabricating machine of FIG.  1 . 
     FIG. 8 is a schematic of assorted program events for a control program therefor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown the truss fabricating machine  10  for joining precut pieces of lumber with pronged connector plates to form a roof truss or similar structure. The truss fabricating machine  10  includes a jigging table  12  for positioning the truss members and a pressing mechanism, generally  16 . 
     The table  12  is disposed between two parallel tracks or rails  18  secured to the floor, upon which the pressing mechanism  16  rides in mating guides  20 . The pressing mechanism  16  rides on the tracks or rails  18  along the X-axis, that is, the elongated dimension of the table  12 . 
     The table  12  includes a working platform, or top  22 , which is supported by a plurality of parallel shiftable supporting units  24  comprising legs that depress upon contact from the pressing mechanism  16  as it moves along the X-axis in either the positive (to the right in FIG. 1 as viewed from the operator s platform  56 ) or the negative X direction (to the left as viewed in FIG. 1 from the operator s platform  56 ), to permit the anvil portion of the pressing mechanism to pass beneath the tabletop according to principles well known in the prior art. 
     The platform or tabletop  22  has a base formed of any sturdy flat surface, but typically made from sheets of ¾ inch (1.9 cm) tongue and groove solid core plywood set edge to edge to form the base. As shown in U.S. Pat. No. 3,826,188—Eberle (the disclosure of which is fully incorporated herein by this reference thereto), a plurality of parallel, upwardly opening steel channels secured to the base may extend the length of the table  12  and have inwardly turned flanges which accommodate adjustable jigging pads. Fitted between the channels are filler pieces of wood such as ¾ inch (1.9 cm) plywood that in turn are covered by top pieces which may be ⅛ inch (0.3 cm) fiberboard. The upper surfaces of the top pieces should lie flush with the flanges on the channels. 
     The pressing mechanism  16  includes a frame  32  which in plan view extends parallel to the Y-axis and includes vertical support members  34  for holding the gantry  36  above the table  12  and parallel to the top of the table  12 . The pressing mechanism  16  includes wheels  62  (see FIG. 2) contained within the carriages or guides  20 , which ride on the tracks  18 . Each carriage  20  includes a hydraulic motor  102  connected to the carriage wheels  62  through sprocket and chain drives for driving the pressing mechanism  16  along the X-axis. The frame  32  is welded to the carriages  20 . A bridge bearing (not shown), that is, a pivot block attaching one carriage to one vertical support member  34  of the gantry  36 , allows the carriage wheels to remain engaged on the tracks  18  even if the tracks  18  are not precisely parallel or have irregularities. 
     The pressing mechanism further includes a cross beam  42  that is parallel to the gantry  36 , but travels under the table  12  and is also seated on bridge bearings. The cross beam  42  is used as an anvil to absorb the force of the press  44  when it drives down onto the truss  26 . The truss  26  includes a plurality of truss members  28  laid on the tabletop  22  in the desired pattern with a connector plate  29  below the joints formed by adjoining members and a truss plate  29  lying on top of each joint, as the truss members are lying on the tabletop  22 . 
     The cross beam  42  carries a top plate  46  that is somewhat wider than the box beam  42  and provides the surface of the anvil. The top plate is located at a height very slightly under the bottom surface of the table  12  so that it does not drag along the table when the pressing mechanism  16  is moved along the X-axis. Six rollers, with three positioned along each longitudinal edge of the top plate  46  contact the bottom of the table top  12  until the press  44  is actuated. 
     Referring to FIG. 2, the pressing mechanism  16  carries an operator&#39;s platform  56  where the operator stands to control the truss fabricating machine  10  by manipulating the joystick  48 . The platform  56  includes protective side guard rails  50  and horizontal guard rails  52 . Two safety switch stop bars  54  are mounted on the platform  56 . The stop bars  54  are pivotally attached to the floor of the platform  56  by the pivot joints  58  and actuate a safety switch that stops all operation of the truss fabricating machine  10  when either one is pushed upward by a moderate force, such as that which would be encountered if the pressing mechanism  16  were to run into a person while traveling on the rails  18 . 
     Still referring to FIG. 2, one X-axis or direction motor  102  is visible on the left-hand side of the working platform  22 . Two drive motors  102  operating in unison are required, one on each side of the pressing mechanism  16 , to provide true parallel travel of the two ends of the gantry  36  and to reduce the probability of the carriages  20  binding on the tracks  18 . 
     The operator&#39;s platform  56  is joined to gantry  36  by suitable means such as welding. As an alternative, a separate operator s platform may be located on each side of the table  12  along with a separate joystick  48 , allowing the truss fabricating machine to be operated from either side of the table. The gantry  36  also carries the control box  33  which includes much of the electrical circuitry and hydraulic equipment described below. 
     Referring to FIG. 3, the joystick  48  is attached to electrical circuitry explained below by the electrical lead set  64 , which transmits the electrical signals fed from the joystick  48  to the driver  100  (FIG.  5 ), described below. The signals developed by manipulation of the joystick  48  are related to the direction and magnitude of displacement of the joystick  48  from its central upright neutral position  49  (FIG.  6 ). Referring to FIG. 6, which is a schematic plan view of the joystick  48 , it is shown that the top of the joystick  48  can be moved along the X-axis of the tabletop  22  with either positive (to the right) or negative (to the left) polarity and along the Y-axis of the table  22  with either positive (up in FIG. 6, or away from the operator s platform  56  in FIG. 1) or negative polarity (down in FIG. 6 or toward the operator s platform  56  in FIG.  1 ). As illustrated by the ghost-image  51  of the joystick  48 , the joystick  48  can also be moved in any pattern or direction within the limits of its movements. Moving toward the ghost-image  51  produces signals causing the press  44  to move along both the X-axis and the Y-axis simultaneously. Regarding the axes, it could also be said that the joystick  48  itself has an X-axis and a Y-axis that are each parallel to the corresponding axes of the tabletop  22 . The essential feature of use of the joystick  48  for control is that the movements of the press  44  mimic the movements of the joystick  48 . 
     Referring now to FIG. 4, there is shown an enlarged side elevation of the joystick  48 , which includes a pistol grip  66  having cross-hatched friction ridge surfaces  68  and a trigger  70 , which operates as a safety switch, for whenever the trigger  70  is released, the truss fabricating machine  10  stops. The trigger  70  is a normally open switch that controls a relay in the main control panel so that the entire truss fabricating machine  10  is deactivated when the trigger is released. When the trigger is depressed, the truss fabricating machine  10  is activated. The stem  72  supports the pistol grip  66  and its opposite end terminates in a ball and socket joint (not shown) inside the housing  74 , wherein electrical circuitry converts the motion of the pistol grip  66  into related electrical signals that are ultimately used to actuate hydraulic valves for controlling motion of the press unit or pressing cylinder  44  along the X-axis and the Y-axis. 
     A thumb switch  76  is located in the top of the joystick  48  and can be moved either to the left or to the right as the operator faces the table  12 . When moved in either direction, the thumb switch  76  energizes a relay  138  (FIG. 5) which controls operation of the hydraulic pressing cylinder  44  that, in turn, controls the up and down motion of its pressing head  45 , as will be described in greater detail below. 
     The speed of the motion of the press  44  along either the X-axis or the Y-axis is proportional to the distance that the joystick is moved relative to its centered vertical normal position, which represents neutral and will not cause the gantry  36  or the press  44  to move along either the X-axis or the Y-axis. 
     A suitable joystick  48  is now manufactured by and available from P-Q Controls. Inc. of Bristol, Conn., U.S.A., and several other suppliers, and may include a 20° maximum travel along the Y-axis on either side of the vertical neutral position, a maximum of 15° on either side of the vertical neutral position along the X-axis, and a maximum 27° travel in any direction not directly along the X-axis or the Y-axis. The trigger has 0.28 inch (7 mm) total pull and requires 0.1 inches (2.5 mm) to switch. The voltage supply may be from 5 to 15 volts DC. The reference voltage is 50 percent of the voltage supply. The output when the pistol grip  66  handle is vertically centered is also 50 percent of the voltage supply, that is, the same as the reference voltage. Full positive deflection in any direction results in a signal of 60 percent of the voltage supply, while full negative deflection in any direction generates a signal having 40 percent of the voltage supply. 
     Referring now to FIG. 5, there is shown a schematic illustration of the electrohydraulic circuitry that controls the movement of the press  44 . Other fluid-driven circuits. e.g. pneumatic, could easily be substituted for the hydraulic components of the system. The joystick  48  is schematically illustrated in the lower left-hand portion of FIG.  5 . The joystick  48  utilizes a source voltage +V on the lead  80  from the control box  33  (FIG.  1 ), which may be between 5 and 15 volts DC and which is supplied to two grounded resistors, resistor  82  for the X-axis motion detection and resistor  84  for the Y-axis motion detection. The resistors  82 ,  84  are portions of potentiometers that are centered with the reference voltage, VR, along the lead  86 . The point of contact of the lead  88  on the resistor  82  changes when the joystick  48  is moved from the centered vertical neutral position along the X-axis. The x output on the lead  92  thereby becomes a DC voltage that is proportional to the displacement of the joystick  48  away from its neutral centered position. The full positive deflection of 15° to the right as viewed from the operator&#39;s platform in FIG. 1 produces a signal of 60 percent of the voltage power supply, whereas the full negative deflection of 15° to the operator&#39;s left as viewed in FIG. 1 produces a voltage signal of 40 percent of the voltage supply. 
     Similarly, the y output on the lead  94  changes as the potentiometer contact  96  moves along the resistor  84  in response to movements of the joystick along the Y-axis. The y output signal on the lead  94  is also at the reference voltage when the joystick  48  is in the centered neutral position, 60 percent of the voltage supply when the joystick is in the full positive deflection, that is, away from the operator as illustrated in FIG. 1 by a maximum of 20° deflection from the vertical neutral position, and 40 percent of the voltage supply upon full negative deflection, that is, 20° away from the centered neutral position and toward the operator. 
     In the preferred embodiment, the internal mechanism of the joystick  48  allows the joystick to be moved at any angle within the cone described, leading to a maximum travel between axes of 27°. These movements create simultaneous x output and y output signals and will be acted on simultaneously by a driver  100 , to produce movement of the press  44  along both the X-axis and the Y-axis simultaneously. That movement may describe a straight line at an angle of 45° from the origin  0  of FIG. 1, a curve, or any other of an infinite number of curves between two points, depending upon the combination of X-axis input and Y-axis input that the operator selects through his motions of the joystick  48 . 
     The X output signal on the lead  92 , the reference signal on the lead  86 , and the Y output signal on the lead  94  are all transmitted to the driver  100 , which is an electronic interface between a command source, namely the joystick  48 , and an electrically modulated valve or transmission stroker such as the proportional solenoids employed here to actuate the hydraulic valves. A suitable driver is the model  516  currently manufactured by P-Q Controls, Inc. of Bristol, Conn., U.S.A. The driver  100  provides a ramp, or acceleration and deceleration, function causing a smoothed output to the valve regardless of the abruptness of signal changes from the command source, or joystick  48 . 
     The driver  100  provides a current source output that can be configured to drive single coil, dual coil, or single coil polarity reversal (floating coil) valves. The electrical current output remains constant within  10  percent over a wide voltage supply swing, typically 10 to 30 volts DC, and a wide resistance shift, which occurs as the valve coil heats up. The command source can be a potentiometer, switch, or a joystick as is employed in the preferred embodiment. 
     Using the driver  100  to control the solenoids and valves described below enables the joystick  48  to be readily replaced by a programmable control or computer interface, which obviates the need for an operator to visually direct the machine from the operator&#39;s platform  56 . 
     The output from the proportional channel outputs of the driver  100  is a pulse width modulated electrical signal with current monitoring to drive the proportional solenoids on the hydraulic valves. The frequency of the pulse width modulated output is more critical with some hydraulic valves, so the driver  100  is calibrated for both the frequency and voltage required to meet the operational specifications of the particular valve it drives. The frequency and magnitude of the driver outputs are also adjusted to counteract oscillations in hydraulic fluid output and excessive hysteresis. 
     The driver board  100  is powered by a regulated power supply (not shown), but can be operated from a vehicle battery in the field. The supply voltage +V should be free from AC ripple and DC spikes and have power capable of driving all functions under full load. 
     The leads  86 ,  92 ,  94 , which provide the command source inputs to the driver  100  are shielded cables having grounded shields to eliminate interference. 
     Two hydraulic motors  102  control movement of the pressing mechanism  16  along the X-axis. The electrical signals on the leads  104 ,  106 ,  108 ,  110  actuate a pair of opposed proportional solenoids  112 , which in turn control an infinite positioning four-way valve  114 . A hydraulic pressure source  116  supplies the source of motive power through the hydraulic lines  118 ,  120  and the hydraulic fluid is returned to a reservoir  122  on the drain side of the hydraulic circuit. 
     Each of the proportional solenoids  112  shifts its armature a distance that is proportional to the strength of the triggering electrical signal delivered to the proportional solenoid  112 . This action, in turn, causes the infinite positioning four-way valve  114  to regulate the flow of hydraulic fluid through the valve, and hence through the motors  102  throughout an infinite continuum of flow rates between the on and off states. This allows the motors  102  to control the speed at which the pressing mechanism  16  moves along the X-axis. This allows the operator to delicately control the rate of acceleration, deceleration. and the speed of the pressing mechanism  16  along the X-axis. 
     A similar arrangement drives the pressing cylinder  44  along the gantry itself, that is, along the Y-axis. The press  44  is suspended from the gantry  36  and rides therealong transversely of the table  12  in the manner as disclosed in the aforesaid Eberle &#39;188 patent. A hydraulic motor  124  on the top of the gantry  36  is driven by hydraulic fluid flowing through the hydraulic lines  123 ,  125  from a hydraulic pressure source  116 , and is routed through the hydraulic lines  125  into the drain side reservoir  122  when its energy has been expended. The direction of drive and rate of acceleration, deceleration and speed of the motor  124  are controlled by an infinite positioning four-way valve  126 , whose flow rates are regulated by a pair of opposed proportional solenoids  128 . The degree of engagement of the solenoids  128 , in turn, is controlled by electrical signals from the driver  100  transmitted along the leads  130 ,  132 ,  134  and  136 . The hydraulic motor  124  is connected to the press  44  by a sprocket and chain drive (not shown). 
     When the operator has moved the press  44  to a position directly above the connector plates, he actuates the thumb switch  76  at the top of the joystick  48 , which is schematically represented in the lower right-hand portion of FIG.  5 . The thumb switch  76  operates a relay  138  driven by the 12 volt power supply  140 . The thumb switch  76  is normally in a neutral or off vertical position and can be toggled either to the left or the right with the same effect, namely engaging the pair of normally open switch contacts  142 , which closes the 12 volt circuit along the lead  141  to actuate the relay coil  143  of the relay  138 . This closes the normally open relay contacts  142 , delivering 12 volts to the solenoid  146  along the lead  144 . The solenoid  146  opens the four-way hydraulic valve to allow hydraulic fluid to be pumped into the upper chamber of the double acting hydraulic cylinder  161 , causing the ram of the press  44  to move down through the full length of its stroke, thereby seating the connector plate. The operator must keep the thumb switch  76  engaged until the connector plate is seated. 
     Then the operator releases the thumb switch  76 , cutting off the 12 volt supply that actuated the relay  138 , and cutting off the electricity to the solenoid  146 . While the relay  143  is actuated the normally closed contacts  150  of the relay  143  are opened, preventing current from reaching the relay coil of the time delay relay  152 . When the operator releases the thumb switch  76  the contacts  150  of the relay  138  close, thereby delivering excitation from the 120 volt power source  145  to the time delay relay  152 , which closes the contacts  154 . This delivers 12 volts from the 12 volt power supply  140  along the lead  158  to the solenoid  156 , which actuates the four-way valve  148  and allows hydraulic fluid to be pumped into the bottom chamber of the double acting hydraulic cylinder  161 , thereby drawing the ram of the press  44  up to the top of its stroke. The time delay relay  152  remains on and keeps its contacts  154  closed long enough for the ram to rise to the top of its stroke without action by the operator. When the pressing ram reaches the top of its stroke, the time delay relay times out despite still being connected to the 120 volt power, and the contacts  154  are opened, the solenoid  156  is de-energized and the four-way valve  148  returns to a neutral position and releases pressure on the hydraulic fluid inside the cylinder  161 , but keeps the ram stationary by not allowing fluid to flow into or out of the cylinder  161 . 
     While certain forms of this invention have been illustrated and described herein, the invention is not limited thereto, except insofar as such limitations are included in the following claims. 
     FIG. 7 shows an automatic control system  200  in accordance with the present invention. It includes a processor  204  for running an application program  210  having characteristics as shown by FIG. 8, which application program  210  manages the control system&#39;s operation. 
     The machine  10  of FIGS. 1-3 for fabricating trusses is given the following signal generators to track the X-Y displacement of the press-head. The Y-position of the press-head  44  is sensed by means of a shaft encoder  222  coupled to the shaft  124 ′ of the motor  124  for the press-head  44 . That is, the motor  124  shuttles the press-head  44  back and forth across the Y-axis by means of a chain and sprocket drive. The motor  124  turns drive shaft  124 ′ which carries a drive sprocket which is meshed with a drive chain. The drive chain extends between opposite tag ends which forms nearly a perfect loop extending in a circuit around the drive sprocket on one extreme end of the gantry  32 , to an idler sprocket on the opposite extreme end (ie., this opposite extreme being the end nearest the operator booth  56 ). The drive chain&#39;s tag ends are secured to the press head  44 , which slides on complementary tracks for it in the gantry  32  top beam  36 . Clockwise and counterclockwise rotation of the drive motor  124  causes back and forth traversing of the press-head  44  on the gantry  32  top beam  36 . 
     By configuring the drive shaft  124 ′ of drive motor  124  with the shaft encoder  222 , the shaft encoder generates signals which though routine calibration can be corresponded to the differential displacement of the press-head  44  in the Y-axis. Referring to FIG. 7, the shaft encoder is conventional and comprises a photoelectric transceiver aimed at the motor shaft  124 ′. The motor shaft  124 ′ configured with marking which can comprise, for example, alternating hatches of light and dark bars, or else absorptive and reflective bars and the like. The shaft encoder senses interruptions of the emitted beam and corresponds successive interruptions with frequency. Frequency, in turn, corresponds to not only shaft speed but also—by means of calibration—the actual physical displacement of the presshead  44 . All this is well-known in the art. The shaft encoder  222  moreover tracks clockwise and counterclockwise rotation of the shaft  124 ′, which corresponds to reverse directions of travel for the press-head  44 . 
     A similar photoelectric encoder  224  device is used to signal the X-axis displacement of the gantry  32  over the tabletop  22 . With joint reference to FIGS. 1 and 7, the tabletop  22  is configured with a marking stripe  226  that extends between the left and right edges of the tabletop  22 . The marking stripe can comprise a series of uniform notches, the passage over of which by the photoelectric device on its boom  224 ′ results in a series of interruptions in the reception of the emitted beam. As previously described in connection with the shaft encoder  222 , the photoelectric encoder  224  corresponds the interruptions of the emitted beam with linear velocity. Linear velocity, by means of calibration, corresponds to the actual physical displacement of the gantry  32  in the X-axis over the tabletop  22 . The photoelectric encoder  224  moreover tracks reversals in direction of travel of the gantry  32 , which corresponds to flip-flops in positive- and negative-direction displacement of the gantry  32 . 
     Referring more particularly to the automatic control system  200  of FIG. 7, it comprises a CPU for processing the functions of the system. The CPU is served by memory which may take the format of chip memory alone or in combination with storage media such as a main disk or hard drive (eg., a c:\drive for the CPU). The CPU is linked for communication of signals with the joystick  48 , the Y-displacement (ie., shaft) encoder  222 , the X-displacement encoder  224 , and the press-head electro-hydraulic circuits as well as the gantry electro-hydraulic circuits (see, eg., driver  100  and the rest of the circuits illustrated by and described in connection with FIG.  5 ). The CPU and its memory can be physically configured in any suitable package including any off-the-shelf laptop computer or the like. Such an off-the-shelf laptop configuration would also include a display or monitor or virtual monitor, a keyboard or at least an abbreviated keypad, and perhaps a cursor-controlling device such as a track-ball or graphic tablet. In whatever physical format the CPU and its memory are packaged, the package is preferably stationed in or around the operator booth  56  for convenience for the operator to dually handle both the joystick and the CPU keyboard/keypad device(s). 
     Also, the CPU and its memory are provided with set(s) of communication ports for attaching or communicating with floppy or CD drives, another CPU memory (eg., which may alternatively be chip memory alone or else other main hard disk media or “c:” drive thereof, or combinations thereof), or else take the format of a printer port, a network interface and cable jack, or modem and phone jack, and so on. The use(s) of these ports will be described more particularly below in connection with loading programs and/or data files into the processor of the present invention. 
     FIG. 8 shows an assortment of various program events for the example application program  210  for controlling the processor of FIG. 7 axis given in connection with this written description. In one mode of its operation, the program allows an operator to manually press all the connector plates of a first truss in a series. Each time he lines up the press-head  44  for stroking down on a connector-plate/truss-joint, the operator concurrently signals the processor to “Record.” After having recorded every position in sequence for the first truss in a batch, every successive truss in the batch can be run automatically by signaling the processor to “Playback.” This is akin to a Re-dial function on a telephone. However, the application program  210  in accordance with the invention is configured with much higher level programming than that. 
     Execution of the program is begun by the Run command, which might alternatively be achieved by clicking an icon or the like. The program has multiple modes including “Begin Recording,” “Play,” “Save,” “Edit,” “Copy ” and so on. The following various program events are associate with “Begin Recording” mode. 
     By way of background, it is conventional to set-up the truss machine  10  to run a batch of like identical trusses. There are appropriate jig stops that are set-up for holding all the pre-cut lumber pieces in the correct place. That way the joints (and the corresponding placement of the connector plates) more or less always land on the same spot on the tabletop  22 . In other words, these “spots” or positions are effectively the “same” given that the press plate  45  measures quite big as the connector plates correspondingly present a relatively small target. More simply, there is room for minor overshoot in both the X- and Y-directions. The large press plate  45  is going to sufficiently compress any connector plates within the neighborhood. 
     An inventive aspect of the present invention is that once the processor is supplied with a profile of a given truss representative of a batch of identical or substantially “like” trusses, the processor can automatically sequence the press-head into all the positions of all the connector plates and stroke down at the appropriate positions. The processor can operate in various ways. It can be given a Home position, which might be the left near (eg., left near in FIG. 1) comer of the tabletop  22 . That way, the press-head  44  and gantry  32  can be commended to cycle or “run” through the sequence of a given truss profile, and finish up by returning to Home and pausing there in a “standby” mode. The operator stacks aside the completed truss, reloads pre-cut lumber and connector plates for the next truss, and then commands the processor to “Playback” the profile. Which in response, the press-head  44  and gantry  32  are cycled through the sequence of the same given truss profile, after which they return to Home and standby. Hence a second truss has been completed and is ready for stacking aside. 
     In an alternate mode of operation, perhaps the gantry sweeps right for odd-numbered trusses, and after idling at the right-side of the tabletop  22  it reverses and sweeps left for even-numbered trusses (idling on the left after completion of left-direction sweep). 
     By either mode (eg., return to Home after every circuit or alternately sweep left and then right), the advantages of the present invention include that the press-head can be run as fast and efficiently as desired, and at a more repetitively consistent rate than can ever be accomplished by hand alone. More significantly, the processor directs the press-head  44  to proceed between successive press positions on a straight line, accelerating and decelerating at pre-programmed-defined extremes of speed-up and speed-down rates in accordance with design protocols established for the equipment. An operator can never consistently run the equipment at its optimum speed-up and speed-down rates unerringly each time; running the equipment too hard results in needless wear and tear while running the equipment at sub-par levels results in lost efficiency. Moreover, some truss profiles are used for the production of such a large number of trusses that the execution routines which correspond to such programs justify optimization. Such an optimization of the profile would include coursing the press-head  44  through the most efficient route possible, with the greatest speed, to reach and hit every press position. These and other aspects and objects will be apparent with the following brief discussion of FIG.  8 . 
     The operator has the choice of a “Select Record Mode—Joystick Mode.” In this mode, the press-head  44  is moved to a position and then the operator enters that position in memory. The coordinates of that position are given cooperatively by the X- and Y-displacement encoders,  224  and  222  respectively. Also, the operator must “Select” or preselect a parameter or command to be associated with that position. For example. the first position the operator might enter is the Origin position, which corresponds to the (x=0, y=0) coordinate. In the industry there is already some acceptance among truss designers that the origin position corresponds to the “heel” of the truss, which in FIG. 1 corresponds to the far left corner of the truss on the table. 
     For a second example, the operator might move the gantry (ie., indicated by reference numeral  32 ) five feet (1.5 m) to the left of the Origin position. While doing so, the X- and Y-displacement encoders  224  and  222  are feeding the CPU with signals corresponding to the physical displacement of the press-head  44  from the Origin position. At the remote position, the operator might enter the coordinates and associate the Home parameter with these coordinates. Hence this second position becomes the Home position. Home is where (or at least one place where) the gantry  32  and press-head  44  might stand-by while a worker removes completed trusses and sets-up next trusses. Following entry of the Home position, the operator might cycle through all the press positions, entering each into memory, and associating each with the command “Move Head to press position (x,y) and Press.” At the completion of the cycle, the operator might move the gantry  32  and press-head  44  in a remote spot and enter “Move Head to this standby position (x,y) and Standby.” Other available commands to the operator include “Home,” which is a command to move Head to the Home position and idle in Standby mode. The “Origin” command commands the Head to move to the Origin position and idle in Standby mode, and so on. 
     After having cycled through a profile, the operator may next enter the “Save and compile” command. The current sequence of commands—which comprise the current or open “document” for the application program  210 —is then compiled into an executable file, and saved in memory. The operator is queried for a filename, and automatically the programs quits the “Begin Recording” mode. 
     If the next entry is “Play” the processor will cycle the gantry  32  and press-head  44  through the subject profile, which at the finish finds the gantry  32  and press-head  44  idle and standing by. 
     An alternative mode of loading a profile is simply manually keying-in the positions and associated commands by the keyboard/keypad device(s). For this purpose there is a “Select Record Mode—Key-In Mode.” 
     A “Pause” command is provided to Pause Recording or Playing. What is briefly described next are various program events associated with “Play,” “Edit, ” and “Copy” modes and so on. 
     The “Play” command begins Play or resumes Play after Pause or standby with the current document or executable file. “Edit” allows editing of commands, parameters, the actual x- and y-cordinates associated with each command or parameter, or change the sequence thereof. The “Close” command closes the current document (ie., profile) and allows the operator to enter in memory or retrieve from memory another profile. As a safeguard, the Close command queries if it Closes the current document without saving changes. 
     The “Copy” utility allows several advantages. Copy allows copying into memory the execution files, merge files or data files from any other folder or linked media or drive. By way of background, an execution file is a complete file with both commands and x- and y-coordinate data. A data file is more basically a table of x- and y-coordinate data, which is non-executable unless associated with corresponding commands. A merge file contains such corresponding commands. The “Merge” command associates such a merge tile with an applicable data file. The “Command editor” allows development of merge files. 
     To return to the “Copy” utility, it allows loading into memory a canned profile either by way of a floppy disk or by cable from the drive of another processor. It is foreseeable that designers of trusses might provide canned routines on floppy or over the Internet for loading into the memory of such an automatic control system in accordance with the invention. That way, profiles are pre-programmed and these pre-programmed routines may be provided as a service by the original designers of the trusses. For loading such pre-programmed routines, the CPU is attached to one or more floppy port(s) and other port(s) as may allow a cable and/or modem connection. 
     To call a pre-programmed routine from memory, the operator enters “Open” and then selects the file by its filename. The operator then has available all the utilities of this application program  210 , including “Play” and “Edit” and so on. Needless to say, the application program  210  preferably includes a Quit option to quit the program. 
     For convenience of configuring the processor  200  in accordance with the invention, it can be operated by any suitable readily-available off-the-shelf operating system such as a Microsoft® Windows® product, including for example Windows 98®. The program  210  in accordance with the invention as shown by FIG. 8 is substantially adapted from the “Macro” utility of the WordPerfect® word processing program, versions 6.0 and higher (nowadays a product of the Corel Corporation, Ltd.). Indeed, incorporated herein by this reference thereto are both the chapter from the “WordPerfect® version 6.0 for Windows User&#39;s Guide” entitled “Macros,” and Lesson 31 thereof also entitled “Macros,” as if both passages were reproduced fully herein. 
     The invention having been disclosed in connection with the foregoing variations and examples additional variations will now be apparent to persons skilled in the art. The invention is not intended to be limited to the variations specifically mentioned, and accordingly reference should be made to the appended claims rather than the foregoing discussion of preferred examples, to assess the scope of the invention in which exclusive rights are claimed.