Abstract:
A pipe bending system employing a sensing and indicating system that provides feedback to an operator regarding the position of components of the pipe bending system, such as the pin-up shoe and the stiffback. Apparatus for retrofitting a sensing and indicating system to existing pipe bending apparatus.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates in general to pipe bending apparatus, and more particularly to apparatus for improving the speed and accuracy of forming bends in large-diameter pipes such as the type utilized for pipelines carrying petrochemicals, and the like. 
   BACKGROUND OF THE INVENTION 
   Throughout the world liquids and gases, such as fuels, are distributed through pipeline networks. The pipelines generally constitute large 40 foot long, 6-60 inch diameter sections of pipe that are welded together and buried underground. The pipelines follow the general contour of the earth and must be routed around natural and man-made obstacles. Rather than forming curves in a pipeline by welding short sections of pipe at angles to each other, curves are formed by bending sections of pipe on site as the pipeline is being built. Bending the pipe minimizes the number of welds and enhances the reliability of the resulting pipeline. Because of the size of the pipes being bent, pipe bending equipment is generally massive in nature and hydraulically operated. Typically, hydraulic pressure for operating the pipe bending equipment is provided by a hydraulic pump driven by an internal combustion engine. Such pipe bending machines are disclosed in U.S. Pat. Nos. 3,834,210; 3,851,519; and 5,092,150, the disclosures of which are incorporated herein by reference. 
   As is customary with large diameter pipes, a bend in each pipe is accomplished by making numerous small bends, each spaced from the other along the length of the pipe. For example, several half-degree, incremental bends spaced along a length of pipe may be used to create an overall curve of several degrees. The operator of a pipe bending machine is in full control of the number of incremental bends to be made, the spacing between the incremental bends, as well as the extent of each incremental bend in the pipe. Skilled operators can efficiently control a pipe bending machine to consistently form accurate bends in the pipes, while minimizing pipes that are damaged, under bent, or over bent. While it is possible to make consistent bends, to a certain extent, variations occur due to the skill and judgment of an operator and to differences between operators. 
   As will be described below, consistently achieving accurate, consistent, damage-free, pipe bends is dependent on the proper positioning of the pipe, stiffback, and pin-up shoe of the pipe bending machine. Typically, positioning the stiffback and/or pin-up shoe is done by a combination of visual, tactile, and/or audible cues that an operator acquires through experience. For example, an experienced operator can determine when the pin-up shoe is properly positioned by listening for a change in the sound of the engine. However, a lack of experience, fatigue, distractions, and environmental considerations may lead to improper positioning of the stiffback and/or pin-up shoe, contributing to variations in pipe bends or even damage to a pipe. It would therefore be desirable to provide a system to aid the operator in positioning the pin-up shoe and stiffback. 
   Ensuring that the pipe and pin-up shoe are properly positioned is also time-consuming. First, the stiffback is raised to bring the pipe just to the point of contact with the bending die. This is called the ‘level’ or ‘zero’ position. The pin-up shoe is then brought up to support the free end of the pipe. The stiffback is then raised or pivoted to incrementally bend the pipe around the bending die. Finally, the stiffback and pin-up shoe are lowered. If further bends are required, the pipe is moved axially to a new bend position, the stiffback and pipe are brought to the level position, the pin-up shoe is raised to support the pipe, and then the stiffback is raised to bend the pipe. Bringing the stiffback and pipe to the level position prior to each bend so that the pin-up shoe can be accurately positioned reduces the throughput of the pipe bending machine. It would therefore be desirable to provide a system to speed up pipe bending by reducing the time needed to position the pipe, stiffback, and/or pin-up shoe. It would also be desirable to eliminate the need to bring a pipe to the level position prior to each bend. 
   It can be seen from the foregoing that a need exists for a system to aid the skilled operator in forming incremental bends with a high degree of repeatability and accuracy, and to improve the speed at which pipes may be bent. Because existing pipe bending machines lack such a system, a further need exists for a system that is easily retrofitted to existing pipe bending machines. 
   SUMMARY OF THE INVENTION 
   In accordance with the principles and concepts of the present invention, there is disclosed an system of sensors and indicators, and a method of operation thereof, which overcome the disadvantages and shortcomings of the prior art. In accordance with the preferred embodiment of the invention, a system of sensors and indicators is disclosed, which enables a skilled operator to quickly and consistently position and bend a pipe. 
   According to one form of the invention, one or more sensors are coupled to the stiffback and/or pin-up shoe. The position sensors are connected to a display or to indicators that provide information to the operator on the position of the pin-up shoe and stiffback. Additional sensors and indicators may provide information on the axial movement of the pipe. With the aid of feedback provided by the sensors and indicators, the skilled operator can control the pipe bending system so as to rapidly and consistently form accurate bends in pipes. 

   
     BRIEF DESCRIPTIONS OF THE DRAWINGS 
     Further features and advantages of the present invention will become more apparent from the following detailed description of various preferred embodiments of the invention, taken in conjunction with the accompanying drawings, in which like reference characters generally refer to the same parts throughout, and in which: 
       FIGS. 1A-C  are side views of a typical pipe bending system, showing the operation of placing a bend in a pipe; 
       FIG. 2  is a schematic representation of a sensor and indicator system in accordance with the principles of the invention; 
       FIG. 3  is a first illustrative position sensor; 
       FIG. 4  is a first illustrative embodiment of an indicator panel; 
       FIG. 5  is a second illustrative position sensor; and 
       FIGS. 6A and 6B  are views of an alternative illustrative embodiment of an indicator panel in accordance with the principles of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1A-C  show a simplified representation of pipe bender  10  for forming bends in large diameter pipe, such as pipes  12  preferably having diameters between 22-36 inches, as well as other pipe diameters. Pipe bender  10  can accommodate pipes  12  of standard length, which in the industry is about 40 feet. Longer or shorter pipes as well as pipes having larger or smaller diameters can, of course, be operated upon by pipe bender  10 . In general, pipe bender  10  includes a number of components mounted on frame  11 . 
   The primary components of pipe bender  10  include bending die  14 , stiffback  16 , and pin-up shoe  18 . Bending die  14  has a saddle-shaped bottom surface against which pipe  12  is forced during the bending operation. Bending die  14  is stationary with respect to frame  11 . As can be seen in  FIGS. 1A-C , bending die  14  is engaged with the top surface of pipe  12 . Pipe  12  is supported on its bottom surface by stiffback  16  and pin-up shoe  18 . 
   Stiffback  16  cradles pipe  12 , and is movable or pivotable about horizontal axis  13  to raise one end of pipe  12  so as to bend the pipe around bending die  14 . Hydraulic clamps hold the ends of pipe  12 . Bending die  14  and stiffback  16  operate in conjunction with an internal pipe bending mandrel (not shown), which allows pipe  12  to be bent without crushing or otherwise internally deforming the circular nature of pipe  12  at the bend. Internal mandrels are well known in the art. 
   Hydraulic cylinder  17  raises or lowers one end of stiffback  16 . Raising stiffback  16  forces one end of pipe  12  upward. The opposite end of pipe  12  is supported by pin-up shoe  18 , which is raised or lowered by hydraulic cylinder  19 . Pin-up shoe  18  is raised to support pipe  12  in a fixed position while the pipe is bent, and then lowered so that the pipe can be moved axially to another location for forming another incremental bend. 
     FIG. 1B  illustrates stiffback  16  being pivoted in the direction of arrow  21  to form a bend in pipe  12  around the curved surface in bending die  14 . Each pipe is generally individually bent through a specific angle at a specific location along the pipe. Each bend placed in pipe  12  by pipe bender  10  is limited to a certain number of degrees to avoid damage to pipe  12 . Typical pipe benders can generally form bends of one degree or less during a single bending operation. Thus, if a greater curvature is required in a specific pipe  12  than is possible with a single bending operation, pipe  12  must undergo a number of incremental bending operations, spaced apart from each other a specified distance along the length of pipe  12 . For example, to bend a pipe through a total of five degrees a series of five one-degree, incremental bends spaced approximately 12 inches apart may be used. Winch  22  and cable  24  can be used to move pipe  12  axially by engaging the end of pipe  12  with hook  26 . Alternatively, pipe  12  may be moved axially by a set of power rollers as described in detail in U.S. Pat. No. 5,092,150, by Cunningham. 
   Pin-up shoe  18  is of conventional design such that it can support pipe  12  irrespective of the orientation of the pipe. In practice, pin-up shoe  18  will initially clamp to the end of the pipe, which at that time is level or horizontal over its entire length. After the first incremental bend, both ends of pipe  12  can no longer be at a level or horizontal position. Rather, the stiffback end of pipe  12  is always maintained at a level position, while the pin-up end of pipe  12  is allowed to become elevated above the level position. This is shown in  FIG. 1C . After each incremental bend, the pin-up end of pipe  12  raises higher to enable the stiffback end to maintain its level orientation. Hence, pin-up shoe  18  is structured to grasp the respective end of the pipe at whatever elevation it may assume, and to accurately and firmly maintain such elevation during the next incremental bending operation. 
   Typically, stiffback  16  and pin-up shoe  18  are positioned by hydraulic cylinders. A control station is provided from which an operator of pipe bender  10  initiates and otherwise controls a bending operation. Controls are provided to selectively applying hydraulic pressure to the hydraulic cylinders. For example, a control may apply hydraulic pressure to hydraulic cylinder  17  to raise or lower stiffback  16 . When raising pipe  12  to the level position, the operator may look for the position of pipe  12  with respect to bending die  14  and may also monitor hydraulic pressure. Similarly, another control applies hydraulic pressure to hydraulic cylinder  19  so as to raise or lower pin-up shoe  18  to pipe  12 . Additional controls are used to operate other components of pipe bending machine  10 , such as winch  22  and/or power rollers, if provided. The controls may be hydraulic or electrical. 
   When moving stiffback  16  or pin-up shoe  18 , the hydraulic pressure needed corresponds to the amount of resistance to the desired motion. When pin-up shoe  18  is raising pipe  12  relatively little hydraulic pressure is needed. However, when pipe  12  comes into contact with die  14 , the hydraulic pressure in the cylinder begins to increase, loading the engine. Based on experience, the operator stops moving pin-up shoe  18  when support for the end of the pipe is ensured. For example, proper pin-up shoe position may be indicated by a change in the sound of the engine driving the hydraulic pump. Hydraulic pressure or the lifting of a pressure relief valve can also be used to determine proper pin-up shoe position. 
   Judging the position of the stiffback and/or pin-up by experience is imprecise and error prone. Therefore, in accordance with the principles of the present invention, sensors and indicators are provided to directly sense, detect, and display the position of the pipe, pin-up shoe, and/or stiffback. Specific sensors and indicators may be used to implement the present invention depending on operational requirements. 
   The major system components are shown schematically in  FIG. 2 . As described above, stiffback  16  and pin-up shoe  18  are positioned by hydraulic cylinders  17  and  19 , respectively, under the control of an operator at control panel  25 . Sensors  28  and  30  are coupled to stiffback  16  and pin-up shoe  18 , respectively, to obtain position information. Display panel  29 , which is coupled to the outputs of sensors  28  and  30 , provides the operator a visual indication of the positions of stiffback  16  and pin-up shoe  18 . 
   In a first embodiment of the invention, the positions of the pin-up shoe and/or stiffback are detected by limit switches and displayed by indicator lights. For example, one or more limit switches may be mounted on frame  11  in the vicinity of stiffback  16  and/or pin-up shoe  18 , or their respective operating cylinders and related structures. If needed, the limit switches may be mounted on a stanchion, bracket, or other rigid support attached to pipe bending machine  10 . The limit switches are located such that the limit switches open or close when the stiffback  16  or pin-up shoe  18  are in predetermined positions. 
   An illustrative arrangement of limit switches is shown in  FIG. 3 , wherein limit switches  35 - 37  are attached to stanchion  32  at various points along its length. Stanchion  32  is mounted to bending machine  10  such that the limit switches are close enough to a portion of stiffback  16  so that one or more of the limit switches are operated by stiffback  16  as it is raised or lowered. As shown in  FIG. 3 , when stiffback  16  is in the position shown in solid lines switch  35  has been actuated; whereas switches  36  and  37  are actuated when the stiffback is at positions  16 ′ and  16 ″ shown in dashed lines. Preferably, the positions of limit switches  35 - 37  are mounted to stanchion  32  in such a manner that their position along the length of stanchion  32  may be adjusted as desired. 
   The limit switches are connected to a display device to indicate when the stiffback and/or pin-up shoe are in predetermined positions. An exemplary display is shown in  FIG. 4 , wherein indicator lights are used to inform the operator of the position of the monitored element of machine  10 . In one embodiment of the invention, limit switches  35 - 37  directly switch the corresponding indicator lights on a display panel. For example, when stiffback  16  is at the level position, limit switch  35  may be closed causing indicator light  42  to illuminate. Additional indicator lights may indicate other positions. For example, limit switch  37  may turn on indicator light  44  to indicate that stiffback  16  is at the desired height at the end of a bending operation. Indicator lights  46  to  49  may indicate that pin-up shoe  18  is in positions corresponding to performing a first, second, or third bend. Preferably, the positions of limit switches  35 - 37  along the length of stanchion  32  are adjustable so that positions to be indicated can be established depending on the size and/or type of pipe being bent. 
   The sensor and indicator system disclosed above may be used as follows. When putting a first bend in a first pipe, the operator operates the controls of machine  10  to position stiffback  16  and pin-up shoe  18  in the conventional manner, i.e., by monitoring hydraulic pressure and other visual, tactile, and audible cues. At each step, the position of one or more of the limit switches is adjusted so that the stiffback  16  or pin-up shoe  18  can be returned to the same position based on the indicators. For example, when the pipe is at the level position, the limit switch connected to indicator light  42  is adjusted so that when the stiffback  16  is being raised to the level position on a subsequent bend, indicator light  42  illuminates when the stiffback  16  reaches the current position, e.g., the level position. Similarly, other limit switches may be adjusted to indicate the desired maximum raised position of the stiffback  16  during a bend, as well as the desired positions of the pin-up shoe  18  before the pipe is bent as well as after certain numbers of bends. For example, limit switches  35 - 37  may be adjusted so that limit switch  35  indicates the desired position of the pin-up shoe  18  when the pipe is unbent, limit switch  36  indicates the desired position when performing a second bend, and switch  37  indicates the desired position for performing a third bend. 
   The limit switches and indicators of  FIG. 3  are sufficient to indicate discrete positions of the stiffback  16  and/or pin-up shoe  18 . However, adjusting the switches to accommodate different pipes requires physically moving the limit switches, which may be burdensome and time consuming. In an alternative illustrative embodiment of the present invention, the limit switches are replaced by a continuous position sensor or transducer. For example, the extent of movement of pin-up shoe  18  may be monitored and otherwise measured by position transducer  52  of  FIG. 5 . Similarly, the extent of movement of stiffback  16  may be monitored and otherwise measured by a similar position transducer. In the preferred form of the invention, position transducer  52  constitutes a cable-extension position transducer such as that identified as model P8510, obtainable from Celesco of Canoga Park, Calif. Clearly other types of transducers from other companies may also be suitable for use in the present invention. For example, optical, magnetic, ultrasonic, and/or electronic position sensors may be used. 
   The body of the position transducer  52  is fixed to the frame or other portion of pipe bending machine  10 . Cable  54 , which extends from position transducer  52  includes end  56  adapted to be coupled to stiffback  16 . Accordingly, when stiffback  16  is raised or lowered the cable is either extended from or retracted into the body of position transducer  52 . The extension or retraction of cable  54  is measured by position transducer  52 , and a signal indicative of the measurement is provided. Typically, the signal is an analog signal, but can also be digital in nature. As can be appreciated, the position of stiffback  16  is directly related to the extent of a bend formed in pipe  12 . Thus, the position of stiffback  16 , as measured by position transducer  52 , is an indication of the pipe bend angle. The signal from position transducer  52  is coupled to an indicator, wherein appropriate circuitry analyzes the signal and provides a display of the position of the stiffback. 
   In one embodiment of the present invention, position transducer  52  provides analog signals indicative of the positions of the stiffback  16  and pin-up shoe  18 . For example, position transducer  52  may comprise a potentiometer that provides an analog voltage or current signal related to the extension of cable  54 . Appropriate comparison circuitry may be used to turn an indicator light on when the voltage of an analog signal is within a preset range. The circuitry may be analog circuitry such as one or more comparators that detect when the signal is within the preset range. Threshold values of the comparators may be adjustable so that bending machine  10  may be used to bend pipes having different bending characteristics. 
   Alternatively, the circuitry may comprise an analog-to-digital converter to convert the analog signal to a digital value. A suitably programmed processor may then compare the digital value to previously stored threshold values. An output of the processor may then drive a display based on the comparison. For example, the processor could simply turn on an indicator light, such as those in  FIG. 4 , when it determines that the converted digital value lies within a preset range of values. 
   Instead of an analog signal, position transducer  52  may provide a digital signal related to the extension of cable  54 . The transducer my indicate the extension of the cable by directly outputting a digital value indicative of the amount of cable extension. Or, the transducer may be an encoder that outputs pulses indicative of the movement of cable  54 . The output of the transducer may be transmitted by a wired or wireless connection to a microprocessor, which is programmed to interpret the digital signal and drive a display. Preferably, the processor is programmed to enable easily changing various set points and indicators used by the processor software so that different pipes can be accommodated. A general purpose processor, such as a programmable logic controller, SLC500 series, obtainable from Allen-Bradley, of Milwaukee, Wis., is suitable for use in the present invention. 
   The display may comprise simple indicator lights such as those shown in  FIG. 4 , or may comprise a video screen, such as a CRT, LCD, or other type of display. An exemplary illustrative display is shown in  FIGS. 6A and 6B , wherein display panel  60  includes an LCD display with a touch screen in accordance with a preferred embodiment of the present invention. During operation, the signal from position sensors  28  and  30  of  FIG. 2  are received by the processor and displayed on a display panel. In  FIG. 6 , the positions of stiffback  16  and pin-up  18  are indicated on virtual gauges  62  and  64  as a percent of full range. For example, virtual gauges  62  and  64  show, respectively, that stiffback  16  is at approximately 38% and pin-up  18  is at approximately 59% of full range. In addition, various target positions are indicated by pointers  65   a - b  and  67   a - d.    
   While operating bending machine  10 , the indications shown on virtual gauges  62  and  64  changes while stiffback  16  and/or pin-up shoe  18  are raised an lowered. Pointers  65   a - b  and  67   a - d  mark specific positions of these bending machine components. For example, pointers  65   a  and  67   a  may correspond to the zero or level position of the stiffback  16  and pin-up shoe  18 ; whereas, pointer  65   b  indicates the maximum bend position of the  37  and pointers  67   b - d  indicate pin-up shoe  18  positions for the second, third, and fourth bend. The pointers are set when performing bends on a first pipe. The pointers may then be relied on while bending subsequent pipes. 
   First, pipe  12  is inserted horizontally through the pin-up shoe  18  until the front end of the pipe rests fully on the stiffback  16 . The internal mandrel is then driven into the pipe until it is registered with respect to the bending die  14  in the manner described in U.S. Pat. No. 5,651,638 by Heggerud, the disclosure of which is incorporated herein by reference. Stiffback  16  is raised until pipe  12  is level and it just touches the lowest point of the undersurface of bending die  14 . When in this position, the operator accesses the setup screen by touching on the display panel  60  in the area of setup button  68  shown in  FIG. 6A . An illustrative setup screen is shown in  FIG. 6B . 
   As the operator proceeds through the steps of bending the first pipe, the various pointers are set by touching the corresponding button on the setup screen. For example, when the stiffback  16  is at the zero or level position, the operator touches STIFFBACK LEVEL button  70 , whereupon the processor stores an indication of the present position of the stiffback as determined by position sensor  28  of  FIG. 2 , and adjusts the display of pointer  65   a  accordingly. Similarly, when stiffback  16  is raised to the maximum bend position, the operator touches STIFFBACK BEND button  72  and the processor stores the position information and updates pointer  65   b . Pointers  67   a - d  are set in a similar fashion by positioning pin-up shoe  18  and touching the corresponding button. When all the setpoints and pointers have been set, touching MAIN button  80  returns the display to the operational screen of  FIG. 6A . 
   Thus, an operator sets the setpoints by raising the stiffback  16  to the level position and pressing the STIFFBACK LEVEL button  70 . The operator then raises the pin-up shoe  18  for engagement with the pipe  12 . This constitutes the initial position of the pin-up shoe  18  for starting the first incremental bend of pipe  12 . The position of the pin-up is entered into the processor by operating the PIN-UP LEVEL button  74 . 
   The maximum extent by which a pipe will be bent constitutes a “bend maximum set point”, which relates to the maximum raised position of the stiffback  16  in forming a curvature in the pipe, including any spring back of the pipe  12 . This may also be the maximum position that the stiffback cylinder will travel. Any attempt to bend the pipe  12  beyond the bend maximum set point may result in damage to the pipe. 
   Pipe  12  is bent by raising stiffback  16  upwardly until pipe  12  “fills” the concave undersurface of bending die  14 , i.e., until the pipe  12  is in contact with the die surface from the center of the bending die  14  to the frontal edge thereof, and until the pipe has been bent through the desired bend angle, taking into account any expected spring back. As with the level position of stiffback  16 , this position of the stiffback may be entered into the processor by pressing the STIFFBACK BEND  72  button on the setup screen. Pin-up shoe  18  and stiffback  16  are then lowered. The mandrel is retracted and pipe  12  is moved axially to prepare for the next incremental bend. 
   In a most preferred embodiment of the present invention, pipe bending machine  10  also includes a sensor to determine the axial movement of pipe  12  such as when pipe  12  is positioned for a second or third incremental bend. The display panel may then indicate when pipe  12  has been moved by a specified distance. For example, display panel  60  may include an indicator light that illuminates when pipe  12  has been moved axially a distance of 12 inches relative to the prior bend. Alternatively, a running indication may be kept of the total axial movement of pipe  12 . An exemplary sensor for axial movement of pipe  12  is disclosed in U.S. Pat. No. 6,253,595 to Donald Lewis. 
   Note that the first time a particular incremental bend in a series of bends is performed, the corresponding position of the pin-up shoe is saved in the processor by an appropriate button on the setup screen. For example, in  FIG. 6B  buttons are provided for storing the position of the pin-up shoe after one, two, or three incremental bends have been performed. Advantageously, the setup procedure only has to be done the first time a given bend is performed. When bending subsequent pipes of the same size and characteristics the values stored during setup may be used. 
   In accordance with the principles of the present invention, once the positions of stiffback  16  and/or pin-up shoe  18  are established, e.g, by adjusting the limit switches or storing the position signals from the position transducers, is no longer necessary to level or zero a pipe before placing a bend in the pipe. That is, after a pipe is loaded into pipe bender  10 , pin-up shoe  18  is raised to a previously established pin-up shoe position. Then stiffback  16  is raised to a previously established stiffback position. This eliminates the leveling step, thereby reducing the time needed to place a bend in a pipe. 
   From the foregoing, a sensor and indicator system is disclosed which provides operator feedback on the operation of a pipe bending machine and thereby enables the operator to perform highly accurate bends in the pipe in a repeatable manner. While the preferred embodiments of the method and apparatus have been disclosed with reference to a specific pipe bending system, it is to be understood that many changes in detail may be made as a matter of engineering and software choices without departing from the scope of the invention as defined by the appended claims. For example, instead of using a touch screen for an operator interface, as shown in  FIGS. 6A and 6B , separate display and buttons may be used. Indeed, those skilled in the art may prefer to embody the apparatus in other forms, and in light of the present description it will be found that such choice can be easily implemented. Also, it is not necessary to adopt all of the various advantages and features of the present disclosure into a single composite pipe bending system in order to realize the individual advantages. Accordingly, such features are individually defined in the appended claims.