Abstract:
An obstruction detection device for use with a truss fabrication system including a table having spaced accessways. The obstruction detection device includes a support structure configured for movable attachment to a table having spaced accessways. An obstruction sensor is connected to the support structure and configured to detect obstructions in the spaced accessways of the table. The obstruction sensor has an activated state and a deactivated state. A control system is operatively connected to the obstruction sensor to activate and deactivate the obstruction sensor in response to a position of the obstruction sensor relative to the spaced accessways. The control system activates the obstruction sensor when the obstruction sensor is aligned with one of the spaced accessways of the table and deactivates the obstruction sensor when the obstruction sensor is out of alignment with the spaced accessways of the table.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to obstruction detection devices, and more specifically, to an obstruction detection device for use with a truss fabrication system. 
     BACKGROUND OF THE INVENTION 
     Truss fabrication systems typically include a truss assembly table and a gantry press. The truss assembly table includes several groups of planks forming the top of the table, and accessways or walkways spaced intermittently between the groups of planks providing operators access to portions of the table spaced from its edges. Operators place truss members and connector plates on the truss assembly table in predetermined configurations to form particular trusses. After the truss members and connector plates are placed on the table, the gantry press travels along the truss assembly table to press the connector plates into the truss members, joining them together. The gantry press typically includes a roller or hydraulic platen mounted on a gantry that engages the connector plates and presses them into the truss members. The gantry has wheels that run on rails or guides extending along the sides of the table or on the floor next to the table for guiding the gantry along the table. 
     Obstruction detection devices are mounted on the gantry press to detect whether obstructions are present on the table that may damage the press or be damaged by the press. For example, conventional obstruction detection devices for truss fabrication systems include push rods, light curtains, or light beams mounted on the gantry press above the table planks. If a push rod is contacted by an obstruction on the table, the push rods mechanically or electrically trigger a shut-off switch to stop the gantry press, preventing the obstruction from being contacted by the press. Similarly, if a light curtain or light beam is interrupted by an obstruction on the table, a shut-off switch is triggered to stop the gantry press and prevent the obstruction from being contacted by the press. However, if an obstruction is located beneath a level of the table planks, such as an operator bent over in a walkway extending between the planks of the table, the conventional push rods, light curtains, and light beams will not detect the obstruction. If an obstruction in a walkway rises to a level above the table planks after the push rods, light curtains, or light beams pass but before the roller passes, the roller may pinch the obstruction between the roller and truss members and/or connector plates positioned on the table planks, damaging the roller or the obstruction. Thus, there is a need for an obstruction detection device capable of detecting obstructions positioned in the walkways between the planks of the table. 
     SUMMARY OF THE INVENTION 
     In one aspect, an obstruction detection device for use with a truss fabrication system including a table having spaced accessways includes a support structure configured for movable attachment to a table having spaced accessways. An obstruction sensor is connected to the support structure and configured to detect obstructions in the spaced accessways of the table. The obstruction sensor has an activated state and a deactivated state. A control system is operatively connected to the obstruction sensor to activate and deactivate the obstruction sensor in response to a position of the obstruction sensor relative to the spaced accessways. The control system activates the obstruction sensor when the obstruction sensor is aligned with one of the spaced accessways of the table and deactivates the obstruction sensor when the obstruction sensor is out of alignment with the spaced accessways of the table. 
     In another aspect, a truss fabrication system includes a truss assembly table having a first side rail, a second side rail, and at least one accessway. A gantry press is movably mounted on the truss assembly table. A first obstruction detection device is mounted on the gantry press. A second obstruction detection device is mounted on the gantry press opposite the first obstruction detection device. Each of the first and second obstruction detection devices includes a support structure attached to the gantry press for movement with the gantry press along the truss assembly table. An obstruction sensor is connected to each support structure and configured to detect obstructions in the at least one accessway of the table. The obstruction sensor has an activated state and a deactivated state. A control system is operatively connected to each obstruction sensor for activating and deactivating the obstruction sensor in response to a position of the obstruction sensor relative to the at least one accessway. The control system activates the obstruction sensor when the obstruction sensor is aligned with the at least one accessway of the table and deactivates the obstruction sensor when the obstruction sensor is out of alignment with the at least one accessway of the table. A controller is configured to stop movement of the gantry press along the truss assembly table when an obstruction is detected in the at least one accessway of the table by the obstruction sensor. 
     In yet another aspect, a method of detecting obstructions in an accessway of a truss assembly table includes activating an obstruction sensor when the obstruction sensor moves into alignment with an accessway of a truss assembly table. The obstruction sensor is deactivated when the obstruction sensor moves out of alignment with the accessway of the truss assembly table. 
     Other objects and features will be in part apparent and in part pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective of a truss fabrication system having obstruction detection devices according to a first embodiment of the present invention; 
         FIG. 2  is a perspective of an obstruction detection device according to the first embodiment; 
         FIG. 3  is a fragmentary detail of  FIG. 2 , showing an arm of the obstruction detection device; 
         FIG. 4  is a fragmentary detail of  FIG. 1 , illustrating a first position of the obstruction detection device; 
         FIG. 5  is a fragmentary detail similar to  FIG. 4 , illustrating a second position of the obstruction detection device; 
         FIG. 6  is a perspective of a truss fabrication system having obstruction detection devices according to a second embodiment of the present invention; and 
         FIG. 7  is a fragmentary detail of  FIG. 6 , illustrating an obstruction detection device according to the second embodiment. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to drawings and more particularly to  FIG. 1 , a truss fabrication system is indicated in its entirety by the reference number  20 . The system  20  generally includes a truss assembly table (generally designated by  22 ), a gantry press (generally designated by  24 ), and an obstruction detection device (generally designated by  26 ). The obstruction detection device  26  generally includes a frame  28  (broadly, a support structure), upper obstruction sensors  30 , lower obstruction sensors  32 , and control sensors  34   a ,  34   b , as will be explained in further detail below. 
     As further illustrated by  FIG. 1 , the truss assembly table  22  has a support  40 , supporting a plurality of parallel elongate planks  42  extending across the support, perpendicular to a direction of gantry press  24  travel. The planks  42  provide a substantially planar working surface for holding structural members (not shown) and connector plates (not shown) in a desired configuration. The structural members (e.g., stick lumber) and connector plates can be arranged in a desired configuration on the planks  42  to form a truss as generally known in the art. Track tubes or rails  44  extend along sides of the support  40  for guiding the gantry press  24 . The support  40 , planks  42 , and rails  44  are omitted at intervals along the table  22  to form accessways or walkways  50  in the table  22 . The accessways  50  allow operators access to locations on the table  22  remote from its edges for properly positioning structural members and connector plates. 
     The gantry press  24  moves relative to the truss table  22 . As mentioned previously, the truss table  22  includes rails  44  for guiding the press  24  as it moves along the table. The gantry press  24  has conventional drive wheels (not shown) for moving the press back and forth along the table  22 . The press  24  also includes a conventional roller or hydraulic platen (not shown) for pressing connector plates into the structural members to form trusses. The roller is rotatably mounted for rotation on the gantry press  24  and extends entirely across the table  22 . The drive wheels and roller are connected in a conventional manner to one or more motors (not shown). A controller  52  is operatively connected to the drive wheels and roller to control movement of the gantry press along the rails  44  and rotation of the roller. Because the features of the gantry press  24  described above are conventional, they will not be described in further detail. Those skilled in the art will appreciate that the gantry press  24  can have other configurations, such as being guided by floor rails, without departing from the scope of the present invention. 
     Referring to  FIGS. 1-3 , the obstruction detection device  26  is mounted on the gantry press  24  so the device moves with the press along the rails  44  of the truss assembly table  22 . In the first illustrated embodiment, the truss fabrication system  20  has an obstruction detection device  26  mounted on opposite sides of the gantry press  24 . As mentioned previously, each obstruction detection device  26  includes a frame  28 , upper obstruction sensors  30 , lower obstruction sensors  32 , and control sensors  34   a ,  34   b . The frame  28  includes a horizontal upper element  60  having a vertical arm  62  extending downward from each end. Although the frame  28  may be made of other materials without departing from the scope of the present invention, in one embodiment the frame is made of aluminum. In the illustrated embodiment, the frame  28  is mounted on top of the gantry press  24 , but the frame may be mounted on other portions of the gantry press without departing from the scope of the present invention. 
     Referring to  FIG. 3 , the obstruction detection device  26  includes an upper obstruction sensor  30  positioned above the table  22  to detect obstructions above the table. The corresponding upper sensors  30  of each detection device  26  are aligned, forming a light curtain or detection plane extending entirely across the table  22 . When light passing between the sensors  30  is interrupted, the sensors send a signal to the controller  52  indicating an obstruction is present. The upper sensor  30  is positioned high enough above the planks  42  so structural members on the table  22  are not in the detection plane formed between the sensors. When an obstruction is detected, the upper sensor  30  sends a signal to the controller  52  to stop the motor system, thereby stopping the gantry press  24  traveling before the press contacts the obstruction. Although other sensors may be used without departing from the scope of the present invention, in one embodiment the upper sensor  30  is a model MLD520-T2L/MLD520-R2L sensor available from Leuze Electronic. In the illustrated embodiment, the arms  62  are pivotable relative to the upper element  60  so the upper sensors  30  move out of alignment with each other when either of the arms contacts an obstruction positioned immediately beside the table  22  so the gantry press  24  stops traveling. As will be appreciated by those skilled in the art, whenever the gantry press  24  is traveling, the leading pair of upper sensors  30  (relative to gantry press direction of travel) is operational to signal the controller  52  and stop the gantry press when the sensors senses obstructions to prevent damage to the obstruction or gantry press. In some embodiments, the trailing pair of upper sensors  30  is not energized to reduce power consumption. In other embodiments, the trailing pair of upper sensors  30  is energized but is ignored by the controller  52 . The direction of travel determines which sensors are active and which sensors are ignored. If an object is detected while the gantry is traveling, the gantry will stop and the electrical system will prevent the gantry from moving again in the first direction. The gantry will be permitted to travel in a second direction opposite from the first direction without the operator resetting the system until an obstruction is encountered in the second direction. Permitting travel in the second direction allows the operator to move the gantry away from a detected obstruction to clear the area. Once a direction has been disabled, the operator must perform a reset and acknowledge that the area has been cleared for the required travel direction. As will also be appreciated, dampers or gas springs  64  are mounted between the arms  62  and upper element  60  to prevent the arms from freely pivoting as the gantry press  24  moves. 
     As further illustrated in  FIG. 3 , the obstruction detection device  26  includes a lower obstruction sensor  32  positioned below the planks  42  of the table  22  to detect obstructions in the accessways  50  of the truss assembly table  22 . The corresponding lower sensors  32  of each detection device  26  are aligned, forming a light curtain or detection plane extending entirely across the table  22 . Although other sensors may be used without departing from the scope of the present invention, in one embodiment the lower sensor  32  is a model MLD520-T1/MLD520-R1 sensor available from Leuze Electronic. As will be appreciated by those skilled in the art, obstructions below the table  22  are physically blocked from contacting the gantry press  24  by the planks  42  except in the accessways  50  where obstructions can rise as the gantry press  24  passes to contact the press without breaking the light curtain formed between the upper sensors  30 . To avoid sensing obstructions below the table  22  outside of the accessways  50  and unnecessarily stopping the gantry press  24 , the leading pair of lower sensors  32  is only operational to signal the controller  52  and stop the gantry press when those sensors are moving across the accessways. In some embodiments, the trailing pair of lower sensors  32  is not energized for sensing objects to reduce power consumption. In other embodiments, the trailing pair of lower sensors  32  is energized but is ignored by the controller  52 . In the latter case, the direction of travel determines which set of sensors are actively armed for detection, as described above in relation to the upper sensors  30 . 
     Referring still to  FIG. 3 , two control sensors  34   a ,  34   b  mounted on brackets  70  extend from each arm  62  of the frame  28 . The control sensors identified as  34   a  are spaced farther from the gantry press  24  than the control sensors identified as  34   b . The control sensors  34   a ,  34   b  are positioned on opposite sides of the lower sensor  32 . The corresponding control sensors  34   a ,  34   b  of each detection device  26  are aligned to detect a particular feature on the table  22  as will be explained below. Although other sensors may be used without departing from the scope of the present invention, in one embodiment each control sensor  34   a ,  34   b  is a model GM705S sensor available from IFM Efector, Inc. The leading and trailing control sensors  34   a ,  34   b , respectively, associated with a particular pair of lower sensors  32  control when that pair of control sensors is operational to signal the controller  52  to stop the gantry press  24 . The control sensors  34   a ,  34   b  are operatively connected to the lower sensors  32  and are configured to detect when the lower sensor is aligned with an accessway  50  of the truss assembly table  22 . The control sensors  34   a ,  34   b  detect when the lower sensors  32  are aligned with an accessway  50  by detecting the presence of a target. In one embodiment, the target is a top surface of the side rail  44  of the truss table  22 , but the control sensors  34   a ,  34   b  can be configured to detect the presence of other targets without departing from the scope of the present invention. 
     As shown in  FIG. 1 , the obstruction detection device  26  may include cover plates  72  mounted on the arms  62  to protect the sensors  30 ,  32 ,  34   a ,  34   b  from physically contacting obstructions to prevent the sensors from becoming misaligned. 
     Referring to  FIGS. 4 and 5 , operation of the obstruction detection device will be described. As shown in  FIG. 4 , when the leading control sensor  34   a  detects the presence of the rail  44 , it sends a signal to deactivate or mute the lower sensor  32  to prevent the obstruction sensor from stopping the gantry press  24  when the frame  40  of the table  22  breaks the light curtain. Referring to  FIG. 5 , when the trailing control sensor  34   b  enters one of the spaced accessways  50  of the side rail  44 , it sends a signal to activate or unmute the lower sensor  32  so the lower sensor can then detect obstructions in the accessways  50  of the table  22 , and signal the controller  52  to stop the gantry press  24  if an obstruction is detected. 
       FIGS. 6 and 7  illustrate a second embodiment of an obstruction detection device  126 . The obstruction detection device  126  is similar to the obstruction detection device  26  described above, except for the differences pointed out below. In this embodiment, the obstruction detection device  126  includes upper obstruction sensors  130 , lower obstruction sensors  132 , and control sensors  134   a ,  134   b  mounted on collapsible bumpers  128  (broadly, support structures). 
     The obstruction detection device  126  is configured for use on the truss assembly table  22 , as described above in reference to the obstruction detection device  26 . The obstruction detection device  126  is mounted on the gantry press  24  so the device moves with the press along the rails  44  of the truss assembly table  22 . In the illustrated embodiment, the obstruction detection device  126  includes four collapsible bumpers  128  mounted on the gantry press  24 . Each collapsible bumper  128  includes a support  160  mounting the bumper to the gantry press  24  and a bumper flag  162 , as will be described in further detail below. Although the collapsible bumpers may be made of other materials without departing from the scope of the present invention, in one embodiment the bumpers are made of aluminum. 
     Referring still to  FIGS. 6 and 7 , the obstruction device  126 , like the obstruction detection device  26 , includes an upper obstruction sensor  130  positioned above the table  22  to detect obstructions above the table. The corresponding upper sensors of opposed collapsible bumpers  128  are aligned, forming a light curtain or detection plane extending entirely across the table  22 . When light passing between the sensors  130  is obstructed, the sensors send a signal to the controller  52  indicating that an obstruction is present. The upper sensors  130  are positioned high enough above the planks  42  so structural members on the table  22  are not in the detection plane formed between the sensors. When an obstruction is detected, the upper sensors  130  send a signal to the controller  52  to stop the motor system, thereby stopping movement of the gantry press  24  before the press contacts the obstruction. Although other sensors may be used without departing from the scope of the present invention, in one embodiment the upper sensor  130  is a model PA46-2-500-Q2-NO1-PN sensor available from Omron Scientific Technologies, Inc. 
     In the illustrated embodiment, a scanner  168  is mounted on each side of the gantry press  24  at or near the center of the press. The scanners  168  can be used in addition to the upper sensors  130 , or in some cases can be used instead of the upper sensors. The scanners  168  scan at least about 180 degrees on each side of the gantry press  24  to detect obstructions. If an obstruction is detected, the scanners  168  send a signal to the controller  52  to stop the motor system, thereby stopping movement of the gantry press  24  before the press contacts the obstruction. Although other scanners may be used without departing from the scope of the present invention, in one embodiment each scanner  168  is a model 0532C-BP scanner available from Omron Scientific Technologies, Inc. It is understood that the scanners  168  could also be used with the obstruction detection device  26  in addition to or instead of the upper sensors  30 . 
     In the embodiment of  FIGS. 6 and 7 , each bumper  128  is collapsible so the bumper flag  162  breaks the light curtain or detection plane of the upper sensors  130  when the bumper contacts an obstruction positioned immediately beside the table  22  so the gantry  24  stops moving. A gas spring  170  mounted to the support  160  permits movement of the bumper  128  relative to the gantry press  24 . The bumper flag  162  is positioned relative to the upper sensor  130  such that minimal movement of the flag towards the gantry  24  will break the light curtain of the upper sensors and signal the controller  52  to stop the gantry. As will be appreciated by those skilled in the art, whenever the gantry press  24  is moving, the leading (relative to the gantry press direction of travel) pair of upper sensors  130  is operational to signal the controller  52  to stop the gantry press when the sensors sense obstructions to prevent damage to the obstruction or gantry press. In some embodiments, the trailing pair of upper sensors  130  is not energized to reduce power consumption. In other embodiments, the trailing pair of upper sensors  130  is energized but is ignored by the controller  52 . The direction of travel from the controller  52  determines which sensors are actively looking for an obstruction and which sensors are ignored. If an object is detected while the gantry travels in a first direction, the gantry will stop and the electrical system will be disabled from traveling again in the first direction. The gantry will be permitted to move in a second direction opposite from the first direction without the operator resetting the system until an obstruction is encountered in the second direction. Permitting the gantry to move in the second direction allows the operator to move the gantry away from a detected obstruction to clear the area. Once a direction has been disabled, the operator must perform a reset to acknowledge the area has been cleared for the required travel direction. 
     As further illustrated in  FIG. 7 , the obstruction detection device  126  includes a lower obstruction sensor  132  positioned below the planks  42  of the table  22  to detect obstructions in the accessways  50  of the truss assembly table  22 . The lower obstruction sensor  132  of the obstruction detection device  126  works as described above with reference to the lower obstruction sensor  32  of the obstruction detection device  26 . The corresponding lower sensors  132  on each bumper  128  are aligned, forming a light curtain or detection plane extending entirely across the table  22 . If the collapsible bumper  128  contacts an obstruction and collapses, the corresponding lower sensor  132  moves out of alignment with the other sensor, breaking the light curtain extending between the lower sensors. The light curtain between the lower sensors  132  is also broken by an obstruction positioned between the sensors. Although other sensors may be used without departing from the scope of the present invention, in one embodiment the lower sensor is a model MLD520-T1/MLD520-R1 sensor available from Leuze Electronic. As will be appreciated by those skilled in the art, obstructions below the table  22  are physically blocked from contacting the gantry press  24  by the planks  42  except in the accessways  50  where the obstructions can rise as the gantry press passes to come in contact with the press without breaking the light curtain formed between the upper sensors  130 . To avoid sensing obstructions below the table  22  outside of the accessways  50  and unnecessarily stopping the gantry press  24 , the leading pair of lower sensors  132  is only operational to signal the controller  52  and stop the gantry press when those sensors are moving across the accessways. In some embodiments, the trailing pair of lower sensors  132  is not energized for sensing objects to reduce power consumption. In other embodiments, the trailing pair of lower sensors  132  is energized but is ignored by the controller  52 . In the latter case, the direction of travel determines which set of sensors are actively armed for detection, as described above in relation to the upper sensors  130 . 
     Referring still to  FIGS. 6 and 7 , two control sensors  134   a ,  134   b  are mounted on each bumper  128 . The control sensors  134   a ,  134   b  can be mounted on a bracket (not shown) mounted to a front plate  172  of the bumper  128 , to the support  160 , on the front plate of the bumper, or any combination thereof. The control sensor  134   a  is spaced farther from the gantry press  24  than the control sensor  134   b . The control sensors  134   a ,  134   b  are positioned on opposite sides of the lower sensor  132 . The corresponding control sensors  134   a ,  134   b  of opposing bumpers  128  are aligned to detect a particular feature on the table  22 . Although other sensors may be used without departing from the scope of the present invention, in one embodiment each control sensor  134   a ,  134   b  is a model GM705S sensor available from IFM Efector, Inc. The leading and trailing control sensors,  134   a ,  134   b , respectively, associated with a particular pair of lower sensors  132  control when that pair of control sensors is operational to signal the controller  52  to stop the gantry press  24 . The control sensors  134   a ,  134   b  are operatively connected to the lower sensors  132  and are configured to detect when the lower sensor is aligned with an accessway  50  of the truss assembly table  22 . The control sensors  134   a ,  134   b  detect when the lower sensors  132  are aligned with an accessway  50  by detecting the presence of a target. In one embodiment, the target is a top surface of the side rail  44  of the truss table  22 , but the control sensors  134   a ,  134   b  can be configured to detect the presence of other targets without departing from the scope of the present invention 
     As illustrated, the front plates  172  of each bumper  128  protect the sensors  132 ,  134   a ,  134   b  from physically contacting obstructions to prevent the sensors from becoming misaligned or physically damaged. A cover plate  174  can also be included to protect the upper sensors  130  from physically contacting obstructions. 
     The operation of the obstruction detection device  126  is similar to the operation of the obstruction detection device  26  described above. When the leading control sensor  134   a  detects the presence of the rail  44 , it sends a signal to deactivate or mute the lower sensor  132  to prevent the obstruction sensor from stopping the gantry press  24  when the frame  40  of the table  22  breaks the light curtain. When the trailing control sensor  134   b  enters one of the spaced accessways  50  of the side rail  44 , it sends a signal to activate or unmute the lower sensor  132  so the lower sensor can then detect obstructions in the accessways  50  of the table  22 , and signal the controller  52  to stop the gantry press  24  if an obstruction is detected. 
     Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. 
     When introducing elements of the present invention or the preferred embodiments(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. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
     As various changes could be made in the above products and methods 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.