Abstract:
A method of forming circumferential grooves in pipe elements using opposed rollers to cold work the pipe elements determines the diameter of the groove while the pipe element is rotated between the rollers. A device for executing the method uses the instantaneous determinations of the groove depth in a feed-back loop to control the operation of the device and halt groove formation when the groove depth is within a specified tolerance.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of and claims priority to U.S. patent application Ser. No. 13/964,671, filed Aug. 12, 2013 and hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention concerns methods and devices for forming a circumferential groove in a pipe element. 
       BACKGROUND 
       [0003]    Pipe elements, which include any pipe-like item such as pipe stock, as well as fittings, including, for example elbows, tees and straights and components such as valves, strainers, end caps and pump intakes and outlets, may be sealingly joined in end to end relation using mechanical pipe couplings, an example of which is disclosed in U.S. Pat. No. 7,086,131. The couplings are formed of two or more segments joined end to end by threaded fasteners. In use, the coupling segments are positioned surrounding the pipe elements and are drawn toward one another and into engagement with the pipe elements by tightening the threaded fasteners. The pipe elements may have circumferential grooves which are engaged by radially projecting keys on the pipe couplings to provide positive restraint to thrust loads experienced by the pipe elements when under internal pressure from the fluid within. An elastomeric gasket, often in the form of a ring, is positioned between the coupling segments and the pipe elements to ensure fluid tightness of the joint. The gasket may have glands which use the internal fluid pressure within the pipe elements to increase the maximum pressure at which it remains effective to prevent leaks. The gasket is compressed radially between the coupling segments and the pipe elements to effect the fluid tight seal desired. 
         [0004]    To form a fluid tight joint using a mechanical coupling with grooved pipe elements it is necessary to control the dimensions of the circumferential grooves of the pipe elements so that the grooves properly engage the keys of the coupling elements and also allow the segments to move toward one another and compress the gasket sufficiently to effect the fluid tight seal. Grooves may be formed by cold working the side wall of the pipe element between opposed rollers which are forced toward one another to displace material of the pipe element, typically by hydraulic means, while they are turning about substantially parallel axes of rotation. The pipe element rotates in response (or the rollers orbit around the pipe circumference) and the groove is formed about the pipe element circumference. Dimensional control of the grooves is made difficult by the allowable tolerances of the pipe dimensions. For example, for steel pipe, the tolerances on the diameter may be as great as +/−1%, the wall thickness tolerance is −12.5% with no fixed upper limit, and the out of roundness tolerance is +/−1%. These relatively large dimensional tolerances present challenges when forming the circumferential grooves by cold working. It would be advantageous to develop a method and an apparatus which actively measures a parameter, such as the groove diameter, and uses such measurements, as the groove is being formed, to control the motion of groove forming rollers as they form the groove. This will avoid the trial groove and measure/adjust procedure of the prior art. 
       SUMMARY 
       [0005]    The invention concerns a method of forming a circumferential groove in a pipe element having a longitudinal axis. The method is effected using a drive roller and a grooving roller. 
         [0006]    One example method of forming a circumferential groove in a pipe element having a longitudinal axis comprises:
       engaging the pipe element with the drive roller;   engaging the grooving roller with the pipe element;   measuring a diameter of the pipe element while rotating the pipe element about the longitudinal axis;   calculating a desired groove depth tolerance corresponding to a desired groove diameter tolerance;   forming the groove by rotating the pipe element about the longitudinal axis while forcing the grooving roller against the pipe element so as to displace material of the pipe element;   while rotating the pipe element, measuring the groove depth;   comparing the groove depth with the desired groove depth tolerance; and   repeating forming the groove, measuring the groove depth, and comparing the groove depth with the desired groove depth tolerance until the groove depth is within the desired groove depth tolerance.       
 
         [0015]    By way of further example, the step of measuring the diameter of the pipe element comprises:
       rotating the pipe element while the pipe element is engaged with the grooving roller, the grooving roller having a known diameter and rotating in response to the pipe element;   determining a number of revolutions of the grooving roller, including fractions thereof, for each revolution of the pipe element; and   calculating the diameter of the pipe element, wherein the number of revolutions of the grooving roller, including the fractions thereof, per revolution of the pipe element being proportional to the diameter of the pipe element.       
 
         [0019]    An example step of determining the number of revolutions of the grooving roller, including the fractions thereof, comprises counting the number of revolutions of the grooving roller, including the fractions thereof, for at least one the revolution of the pipe element. 
         [0020]    A specific example method of determining the at least one revolution of the pipe element comprises sensing a feature on the pipe element a first and a second time while rotating the pipe element. 
         [0021]    In a particular example the at least one revolution of the pipe element is determined by:
       marking an outer surface of the pipe element with a light reflecting surface that contrasts with the outer surface of the pipe element;   shining a light onto the outer surface of the pipe element;   sensing a first and a second reflection of the light from the light reflecting surface while rotating the pipe element.       
 
         [0025]    In another example, the at least one revolution of the pipe element is determined by:
       positioning a magnet on a surface of the pipe element;   sensing a first and a second magnetic field while rotating the pipe element.       
 
         [0028]    Further by way of example, the step of engaging the grooving roller with the pipe element comprises pinching the pipe element between the grooving roller and the drive roller with sufficient force to hold the pipe element therebetween. Specifically by way of example, the step further comprises engaging an inner surface of the pipe element with the drive roller and engaging an outer surface of the pipe element with the grooving roller. 
         [0029]    Another example embodiment of the method comprises selecting a rotational speed for rotating the pipe element based upon at least one characteristic of the pipe element. By way of example the at least one characteristic of the pipe element is selected from the group consisting of a diameter, a wall thickness, a material of the pipe element and combinations thereof. 
         [0030]    A further example of the method comprises selecting a force for forcing the grooving roller against the pipe element based upon at least one characteristic of the pipe element. In this example the at least one characteristic of the pipe element is selected from the group consisting of a diameter, a wall thickness, a material of the pipe element and combinations thereof. 
         [0031]    Again by way of example, the method further comprises selecting a feed rate of the grooving roller for forming the groove in the pipe element based upon at least one characteristic of the pipe element. Specifically by way of example, the at least one characteristic of the pipe element is selected from the group consisting of a diameter, a wall thickness, a material of the pipe element and combinations thereof. 
         [0032]    In an example embodiment of the method, the step of measuring the groove depth while rotating the pipe element comprises:
       projecting a fan-shaped beam of light onto the pipe element;   sensing a reflection of the fan-shaped beam of light;   using triangulation methods to calculate the groove depth.       
 
         [0036]    The invention further encompasses a device for forming a circumferential groove in a pipe element having a longitudinal axis. In one example embodiment, the device comprises a drive roller rotatable about a drive roller axis. The drive roller is engageable with an inner surface of the pipe element when the drive roller axis is oriented substantially parallel to the longitudinal axis of the pipe element. A grooving roller is rotatable about a grooving roller axis oriented substantially parallel to the drive roller axis. The grooving roller has a known diameter. The grooving roller is movable toward and away from the drive roller so as to forcibly engage the outer surface of the pipe element and form the groove therein upon rotation of the pipe element. A first sensor is used to determine a degree of rotation of the grooving roller and generate a first signal indicative thereof. A second sensor is used to determine a degree of rotation of the pipe element and generate a second signal indicative thereof. A control system is adapted to receive the first and second signals, use the first and second signals to determine a diameter of the groove, and control motion of the grooving roller toward and away from the drive roller in response to the diameter of the groove. 
         [0037]    By way of example, the first sensor may comprise a rotational encoder operatively associated with the grooving roller. Also by way of example, the second sensor may comprise a light reflecting surface affixed to an outer surface of the pipe element. The light reflecting surface contrasts with the outer surface of the pipe element. A light projector is positioned to project light onto the outer surface of the pipe element and the light reflecting surface affixed thereto. A detector, adapted to detect light projected by the light projector upon reflection from the light reflecting surface, generates the signal indicative thereof. By way of example, the light projector may comprise a laser. Further in example, the light reflecting surface may be selected from the group consisting of a specular reflecting surface, a diffuse reflecting surface, a contrasting color reflecting surface and combinations thereof. In another example embodiment, the second sensor comprises a magnet affixed to a surface of the pipe element. A detector is adapted to detect a magnetic field. The detector generates a signal indicative thereof. In another example embodiment, the device may further comprise a third sensor for measuring a surface profile of at least a portion of the pipe element and generating a signal indicative thereof. The third sensor may, for example, comprise a laser adapted to project a fan-shaped beam along a at least the portion of the pipe element. A detector receives a reflection of the fan-shaped beam from the portion of the pipe element. A calculator unit converts the reflection into measurements representing the surface profile using triangulation. The calculator unit then generates the signal indicative of the measurements and transmits the signal to the control system. 
         [0038]    By way of example, the grooving roller may be mounted on an actuator controlled by the control system, the actuator comprising a hydraulic ram for example. 
         [0039]    The invention further encompasses a device for forming a circumferential groove in a pipe element having a longitudinal axis. In an example embodiment, the device comprises a drive roller rotatable about a drive roller axis. The drive roller is engageable with an inner surface of the pipe element when the drive roller axis is oriented substantially parallel to the longitudinal axis of the pipe element. A grooving roller is rotatable about a grooving roller axis oriented substantially parallel to the drive roller axis. The grooving roller is movable toward and away from the drive roller so as to forcibly engage an outer surface of the pipe element so as to displace material of the pipe element and form the groove therein upon rotation of the pipe element. An idler roller is rotatable about an idler roller axis oriented substantially parallel to the drive roller axis. The idler roller has a known diameter. The idler roller is movable toward and away from the drive roller so as to engage an outer surface of the pipe element so as to rotate upon rotation of the pipe element. A first sensor determines a degree of rotation of the idler roller and generates a first signal indicative thereof. A second sensor determines a degree of rotation of the pipe element and generates a second signal indicative thereof. A control system is adapted to receive the first and second signals and use the first and second signals to determine a diameter of the groove, and control motion of the grooving roller toward and away from the drive roller in response to the diameter of the groove. 
         [0040]    In a particular example embodiment, the first sensor comprises a rotational encoder operatively associated with the idler roller. By way of further example, the second sensor may comprise a light reflecting surface affixed to an outer surface of the pipe element. The light reflecting surface contrasts with the outer surface of the pipe element. A light projector is positioned to project light onto the outer surface of the pipe element and the light reflecting surface affixed thereto. A detector is adapted to detect light projected by the light projector upon reflection from the light reflecting surface, the detector generating a signal indicative thereof. The light projector may, for example, comprise a laser. 
         [0041]    In another example embodiment, the second sensor may comprise a magnet affixed to a surface of the pipe element. A detector is adapted to detect a magnetic field. The detector generates a signal indicative thereof. The example device may further comprise a third sensor for measuring a surface profile of at least a portion of the pipe element and generating a signal indicative thereof. In a particular example embodiment, the third sensor comprises a laser adapted to project a fan-shaped beam along at least the portion of the pipe element. A detector is adapted to receive a reflection of the fan-shaped beam from the portion of the pipe element. A calculator unit converts the reflection into measurements representing the surface profile using triangulation. The sensor generates the signal indicative of the measurements and transmits the signal to the control system. 
         [0042]    In a particular example embodiment, the grooving roller is mounted on an actuator that is controlled by the control system. Similarly by way of example, the idler roller may be mounted on an actuator that is controlled by the control system. 
         [0043]    In another example embodiment of a device for forming a circumferential groove in a pipe element having a longitudinal axis, the device comprises a drive roller rotatable about a drive roller axis. The drive roller is engageable with an inner surface of the pipe element when the drive roller axis is oriented substantially parallel to the longitudinal axis of the pipe element. A grooving roller, rotatable about a grooving roller axis oriented substantially parallel to the drive roller axis, has a known diameter. The grooving roller is movable toward and away from the drive roller so as to forcibly engage an outer surface of the pipe element and form the groove therein upon rotation of the pipe element. A sensor is used to measure a surface profile of at least a portion of the pipe element and generate a signal indicative thereof. A control system, adapted to receive the signal, uses the signal to determine a diameter of the groove and control motion of the grooving roller toward and away from the drive roller in response to the diameter of the groove. 
         [0044]    In a particular example embodiment, the sensor comprises a laser adapted to project a fan-shaped beam along at least the portion of the pipe element. A detector receives a reflection of the fan-shaped beam from the portion of the pipe element. A calculator unit converts the reflection into measurements representing the surface profile using triangulation, generates the signal indicative of the measurements and transmits the signal to the control system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]      FIGS. 1 and 1A  are isometric views of example embodiments of devices for forming circumferential grooves in pipe elements; 
           [0046]      FIG. 2  is an isometric view of a portion of the device shown in  FIG. 1 ; 
           [0047]      FIGS. 3, 3A, 4 and 5  are sectional views of a portion of the device shown in  FIG. 1 ; 
           [0048]      FIG. 6  is a flow chart illustrating an example method of forming a circumferential groove in a pipe element; 
           [0049]      FIG. 7  is a sectional view of the portion of the device shown in  FIG. 1 ; 
           [0050]      FIG. 8  is a longitudinal sectional view of a pipe element having a circumferential groove; and 
           [0051]      FIGS. 9-17  are flow charts illustrating example methods of forming grooves in the pipe element shown in  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0052]      FIG. 1  shows an example embodiment of a device  10  for forming a circumferential groove in a pipe element. Device  10  comprises a drive roller  12  rotatable about an axis  14 . In this example, drive roller  12  is rotated about axis  14  by an electric motor  16  positioned within a housing  18  on which the drive roller is mounted. Drive roller  12  has an outer surface  20  which is engageable with an inner surface of a pipe element as described below. An idler roller, which, in this example embodiment, is a grooving roller  22  is also mounted on housing  18  for rotation about an axis  24 . Axes  14  and  24  are substantially parallel to one another which permit them to cooperate when forming a circumferential groove. 
         [0053]    Grooving roller  22  is mounted to housing  18  via a yoke  26  which permits the grooving roller to be moved toward and away from the drive roller in the direction indicated by arrow  28  while maintaining axes  14  and  24  in substantially parallel relationship. Movement of the yoke  26  and hence the grooving roller  22  is effected by an actuator  30 . Hydraulic actuators are advantageous because they provide a great range of high force adjustable in fine increments capable of locally yielding the pipe material to progressively form the groove. Other types of actuators are of course feasible. 
         [0054]    As shown in  FIG. 2 , the device also includes a first sensor  32  for determining the degree of rotation of the grooving roller  22  about axis  24  during formation of the circumferential groove in the pipe element. In this example embodiment, the first sensor  32  comprises a rotary encoder. Rotary encoders are advantageous because they have excellent reliability, repeatability, accuracy and resolution, typically allowing a revolution to be divided into 600,060 discrete steps for great accuracy in measuring the rotation of the grooving roller  22 . Rotary encoder model LM10IC005BB20F00 supplied by RLS of Ljubjana, Slovenia serves as a practical example appropriate for device  10 . 
         [0055]    In general, at least one revolution of the pipe element may be determined by sensing a feature on the pipe element a first and a second time while rotating the pipe element. The feature, for example, could be a naturally occurring feature, such as a unique scratch, tool marking, seam or other feature which is not placed on the pipe for any particular purpose. However, it is advantageous to position a feature on the pipe element which will be readily detectable so as to ensure reliable and accurate determination of a revolution of the pipe element. Two examples are described below, it being understood that other detection methods are also feasible. 
         [0056]    With reference again to  FIG. 1 , device  10  comprises a second sensor  34  for determining the degree of rotation of the pipe element.  FIG. 3  shows an example of second sensor  34  which comprises a light projector  36 , for example, a laser, a detector  38 , which detects light from the projector as it is reflected from the pipe element  40 , and a light reflecting surface  42  which is affixed to the outer surface  40   b  of the pipe element  40 . Light reflecting surface  42  may be specular, diffuse, or have a different color from that of the outer surface  40   b  of the pipe element  40  and thus provides a contrast with the pipe element outer surface. Sensor  34  is also known as a contrast sensor because the detector  38  detects the difference between projected light reflected from the pipe outer surface  40   b  and the contrasting light reflecting surface  42 . Contrast sensors such as  34  are manufactured by Leuze Electronics of New Hudson, Mich., with model number HRTL 3B/66-S8 being feasible for the device  10  disclosed herein. Each time the light reflecting surface  42  passes beneath light from projector  36  the detector detects the reflection therefrom and generates a signal which can be used to detect and count the revolutions of the pipe element. 
         [0057]    In an alternate embodiment, shown in  FIG. 3A , the second sensor  34  may comprise a magnetic sensor  35 . Magnetic sensor  35  is also a non-contact proximity sensor which uses inductive or capacitive principles to sense the passing of a magnet  37  affixed to a surface, for example, the outer surface  40   b  of the pipe element  40 . Each time the magnet  37  passes the magnetic sensor  35  it generates a signal which can be used to detect and count the revolutions of the pipe element. 
         [0058]    As shown in  FIG. 1 , device  10  may also have a third sensor  46  for measuring a surface profile of at least a portion of the pipe element. As shown in  FIG. 7 , the third sensor  46  is a triangulation sensor and comprises a laser  48  adapted to produce a fan-shaped beam  50  along a portion of the outer surface  40   b  of the pipe element  40  where the profile  52  is to be measured. A detector  54  is adapted to receive the reflection of the fan-shaped beam from the outer surface portion of the pipe element. The third sensor  46  also includes a calculator unit  55  which uses triangulation to convert the reflection of the fan-shaped beam into measurements representing the outer surface profile. 
         [0059]    With reference again to  FIG. 1 , device  10  also includes a control system  56 . Control system  56  is in communication with the sensors  32 ,  34  and  46  as well as with the electrical motor  16  and the actuator  30 . Communication may be through dedicated electrical lines  58 . The control system receives signals generated by the sensors  32 ,  34  and  46  and sends commands to the actuator  30  and the motor  16  to control operation of the various parts of the device  10  to form the groove in the pipe elements. Sensor  32  generates signals indicative of the rotation of the grooving roller  22 ; sensor  34  generates signals indicative of the rotation of the pipe element  40  (see also  FIG. 3 ); and sensor  46  generates signals indicative of the outer surface profile of the pipe element  40  (see also  FIG. 7 ). These signals are transmitted to the control system. Control system  56  may comprise a computer or programmable logic controller having resident software which interprets the signals from the sensors  32 ,  34  and  46  and then issues commands to the actuator  30  and the motor  16  to effect the various functions associated with forming the circumferential grooves in the pipe elements. Together the control system  56 , actuator  30 , motor  16  and sensors  32 ,  34  and  46  operate in a feed-back loop to automatically form the grooves in an operation described below. 
         [0060]      FIG. 1A  shows a device  10   a  having a second idler roller  23  that is separate from the idler roller  22 . In this example embodiment, idler roller  22  is a grooving roller mounted on yoke  26  as described above, and second idler roller  23  is mounted on an actuator  25  which is mounted on device  10   a . Actuator  25  is controlled by control system  56  and moves the idler roller  23  toward and away from the drive roller  12  to engage and disengage the idler roller  23  with the pipe element. Idler roller  23  is rotatable about an axis  27  substantially parallel to axis  14  and will rotate about axis  27  when engaged with a pipe element that is mounted on and rotated by the drive roller  12 . In this embodiment, the idler roller  23  is used to determine the pipe element diameter and the groove diameter, and the idler (grooving) roller  22  is used to support the pipe element and form a circumferential groove. To that end, first sensor  32  is operatively associated with the idler roller  23  and used to determine the degree of rotation of the idler roller  23  about axis  27  during determination of the pipe element diameter and formation of the circumferential groove in the pipe element. In this example embodiment, the first sensor  32  may again comprise a rotary encoder as described above. The rotary encoder counts the number of revolutions and fractions thereof of the idler roller  23  and generates a signal indicative thereof which is transmitted to the control system  56  via a communication link such as hardwired lines  58 . The control system  56  uses the information transmitted in the signals to determine the diameter of the pipe element and control the machine operation during groove formation as described below. 
       Device Operation 
       [0061]    An example method of forming a circumferential groove in a pipe element using the device  10  is illustrated in  FIGS. 1-5  and in the flow chart of  FIG. 6 . As shown in  FIG. 3 , pipe element  40  is engaged with the drive roller  12  (see box  62 ,  FIG. 6 ). In this example, the inner surface  40   a  of the pipe element  40  is placed in contact with the drive roller. Next, as described in box  64  of  FIG. 6 , grooving roller  22  is moved by the actuator  30  (under the command of control system  56 ) toward the drive roller  12  until it engages the outer surface  40   b  of pipe element  40 . It is advantageous to pinch pipe element  40  between the drive roller  12  and the grooving roller  22  with sufficient force to securely hold the pipe element on the device  10 . At this point, it is possible to determine the diameter of the pipe element  40  in order to either accept the pipe element and form the circumferential groove, or reject the pipe element because its diameter is outside of the accepted tolerance range and thus be incompatible with other pipe elements of the same nominal size. Determining the pipe element diameter is represented by box  66  in  FIG. 6  and is effected by measuring the circumference of the pipe while rotating the pipe element  40  about its longitudinal axis  68  using drive roller  12  powered by motor  16 . Drive roller  12  in turn, rotates pipe element  40 , which causes grooving roller  22  to rotate about its axis  24 . For greater accuracy of the measurement, it is advantageous if grooving roller  22  rotates in response to pipe element  40  without slipping. The diameter of pipe element  40  may then be calculated by knowing the diameter of the surface  22   a  of the grooving roller  22  that is in contact with the pipe element  40 , and counting the number of revolutions of the grooving roller, including fractions of a rotation, for each revolution of the pipe element. If the diameter D of the grooving roller surface  22   a  is known, then the circumference C of the pipe element  40  can be calculated from the relation C=(D×rev×Π) where “rev” equals the number of revolutions of the grooving roller  22  (including fractions of a rotation) for one revolution of the pipe element. Once the circumference C of the pipe element is known, the pipe element diameter d can be calculated from the relation d=C/Π. 
         [0062]    In device  10 , sensor  32 , for example, a rotary encoder, counts the number of revolutions and fractions thereof (rev) of the grooving roller  22  and generates a signal indicative thereof. Each revolution of the pipe element  40  is detected and/or counted by the sensor  34 , which generates signals indicative thereof. For example, if sensor  34  is a contrast sensor as described above (see  FIG. 3 ), it senses a first and a second reflection from the light reflecting surface  42 , which indicate it has detected or counted one revolution of the pipe element. If sensor  34  is a magnetic sensor ( FIG. 3A ), it senses a first and a second magnetic field, which indicates that it has detected or counted one revolution of the pipe element. Signals from the sensor  32  and the sensor  34  are transmitted to the control system  56 , which performs the calculations to determine the diameter of the pipe element  40 . The control system may then display the pipe element diameter to an operator for acceptance or rejection, or, the control system itself may compare the pipe element diameter with a tolerance range for pipes of a known nominal size and display an “accept” or “reject” signal to the operator. Note that for such automated operation the control system is programmed with dimensional tolerance data for pipe elements of various standard sizes. The operator must mount the grooving roller appropriate for the standard pipe size and groove being formed and input to the control system the particular standard pipe elements being processed. In response to these inputs the resident software within the control system will then use the proper reference data to determine if the pipe element has a diameter which falls within the acceptable tolerance range for pipe elements of the selected standard size. 
         [0063]    Box  70  of  FIG. 6  and  FIG. 4  illustrate forming of a groove  72  in pipe element  40 . Drive roller  12  is rotated, thereby rotating pipe element  40  about its longitudinal axis  68 , which rotates the grooving roller  22  about axis  24 . Note that the axis of rotation  14  of the drive roller  12 , the axis of rotation  24  of the grooving roller  22  and the longitudinal axis  68  of the pipe element  40  are substantially parallel to one another. “Substantially parallel” as used herein means within about 2 degrees so as to permit rotation without significant friction but also allow for tracking forces to be generated which maintain the pipe element engaged with the drive and grooving rollers during rotation. During rotation of the pipe element, the actuator  30  ( FIG. 1 ) forces the grooving roller  22  against the pipe element  40 , thereby cold working the pipe element, displacing the pipe element material, and forming the circumferential groove  72 . Note that the force exerted by the actuator  30 , as well as the feed rate of the grooving roller  22  (i.e., the rate at which the grooving roller moves toward the drive roller) and the rotational speed of the pipe element may be selected based upon one or more characteristics of the pipe element  40 . Such characteristics include, for example, the pipe element diameter, the wall thickness (schedule), and the material comprising the pipe element. Selection of the operational parameters such as force, feed rate and rotational speed may be established by the operator, or, by the control system  56  in response to inputs from the operator specifying the particular pipe being processed. For example, the control system may have a database of preferred operational parameters associated with particular standard pipe elements according to diameter, schedule and material. 
         [0064]    For compatibility of the pipe element  40  with mechanical couplings, it is necessary that the final diameter  74   b  (see  FIG. 5 ) of the groove  72  be within an acceptable tolerance for the particular diameter pipe element being processed. As indicated in box  76  (see also  FIG. 4 ), to produce an acceptable groove  72 , the instantaneous groove diameter  74   a  (i.e., the groove diameter before it achieves its final diameter) is determined at intervals while the pipe element  40  is rotating. The instantaneous groove diameter  74   a , as shown in  FIG. 4 , is determined using signals from the sensor  32  and the sensor  34  as described above for determining the diameter of the pipe element  40  ( FIG. 6 , box  66 ). Signals from the sensor  32 , indicative of the number of revolutions (and fractions thereof) of the grooving roller  22 , and signals from the sensor  34 , indicative of the number of revolutions of the pipe element constitute a measurement of the instantaneous circumference of the pipe element  40  within groove  72 . These signals are transmitted to the control system  56  which uses the information in the signals to determine (i.e., calculate) the instantaneous diameter  74   a  of the groove  72  (note that the diameter of the surface  22   a  of the grooving roller  22  forming the groove is known). As shown in Box  78 , the control system then compares the instantaneous diameter of the groove with the appropriate tolerance range for groove diameters for the particular pipe being processed. As shown in Box  80 , if the instantaneous groove diameter is not within the appropriate tolerance range, for example, the instantaneous groove diameter is larger than the largest acceptable diameter for the particular pipe element being processed, then the control system  56  continues to form the groove  72  by rotating the pipe element  40  about its longitudinal axis  68  while forcing the grooving roller  22  against the pipe element so as to displace material of the pipe element, determining the instantaneous diameter  74   a  of the groove  72  while rotating the pipe element  40 , and comparing the instantaneous diameter of the groove with the tolerance range for the diameter of the groove until the groove diameter is within the tolerance range acceptable for the diameter of the groove. 
         [0065]    Once the final groove diameter  74   b  is at a predetermined target diameter the control system  56  halts the motion of the grooving roller  22  toward the drive roller  12 , but continues rotation of the pipe element for at least one full rotation to ensure a uniform grooving depth. The rotation is then halted and the grooving roller  22  is moved away from the drive roller  12  so that the pipe element  40  may be removed from the device  10 . 
         [0066]    Another example method of forming a circumferential groove in a pipe element is described using the device  10   a  shown in  FIG. 1A . This embodiment has two separate idler rollers, idler roller  22 , which is a grooving roller, and idler roller  23 , which is a measuring roller. As described above, the pipe element is engaged with the drive roller  12  (see box  62 ,  FIG. 6 ). Next, as described in box  64  of  FIG. 6 , grooving roller  22  is moved by the actuator  30  (under the command of control system  56 ) toward the drive roller  12  until it engages the outer surface of the pipe element. It is advantageous to pinch pipe element between the drive roller  12  and the grooving roller  22  with sufficient force to securely hold the pipe element on the device  10 . Control system  56  also commands actuator  25  to move idler roller  23  into engagement with the outer surface of the pipe element. At this point, it is possible to determine the diameter of the pipe element in order to either accept the pipe element and form the circumferential groove, or reject the pipe element because its diameter is outside of the accepted tolerance range and thus would be incompatible with other pipe elements of the same nominal size. Determining the pipe element diameter is represented by box  66  in  FIG. 6  and is effected by measuring the circumference of the pipe element while rotating it about its longitudinal axis using drive roller  12  powered by motor  16 . Drive roller  12  in turn, rotates the pipe element, which causes idler roller  23  to rotate about its axis  27 . For greater accuracy of the measurement, it is advantageous if idler roller  23  rotates in response to the pipe element without slipping. The diameter of the pipe element may then be calculated by knowing the diameter of the surface of the idler roller  23  that is in contact with the pipe element, and counting the number of revolutions of the idler roller  23 , including fractions of a rotation, for each revolution of the pipe element. If the diameter D of the idler roller  23  is known, then the circumference C of the pipe element can be calculated from the relation C=(D×rev×Π) where “rev” equals the number of revolutions of the idler roller  23  (including fractions of a rotation) for one revolution of the pipe element. Once the circumference C of the pipe element is known, the pipe element diameter d can be calculated from the relation d=C/Π. 
         [0067]    In device  10   a , sensor  32 , for example, a rotary encoder, counts the number of revolutions and fractions thereof of the idler roller  23  and generates a signal indicative thereof. Each revolution of the pipe element is detected and/or counted by the sensor  34  (for example, a contrast sensor or a magnetic sensor), which generates signals indicative thereof. Signals from the sensor  32  and the sensor  34  are transmitted to the control system  56 , which performs the calculations to determine the diameter of the pipe element. The control system may then display the pipe element diameter to an operator for acceptance or rejection, or, the control system itself may compare the pipe element diameter with a tolerance range for pipes of a known nominal size and display an “accept” or “reject” signal to the operator. 
         [0068]    Box  70  of  FIG. 6  illustrates forming of a groove in pipe element. Drive roller  12  is rotated, thereby rotating the pipe element about its longitudinal axis, which rotates the grooving roller  22  about its axis  24  and the idler roller  23  about its axis  27 . Note that the axis of rotation  14  of the drive roller  12 , the axis of rotation  24  of the grooving roller  22 , the axis of rotation  27  of the idler roller  23  and the longitudinal axis of the pipe element are substantially parallel to one another. During rotation of the pipe element, the actuator  30  forces the grooving roller  22  against the pipe element, thereby cold working the pipe element, displacing the pipe element material, and forming the circumferential groove. Also during rotation of the pipe element, the actuator  25  maintains the idler roller  23  in contact with the pipe element within the groove being formed by the grooving roller  22 . 
         [0069]    For compatibility of the pipe element with mechanical couplings, it is necessary that the final diameter of the groove be within an acceptable tolerance for the particular diameter pipe element being processed. As indicated in box  76 , to produce an acceptable groove, the instantaneous groove diameter (i.e., the groove diameter before it achieves its final diameter) is determined at intervals while the pipe element is rotating. The instantaneous groove diameter is determined using signals from the sensor  32  and the sensor  34  as described above for determining the diameter of the pipe element ( FIG. 6 , box  66 ). Signals from the sensor  32 , indicative of the number of revolutions (and fractions thereof) of the idler roller  23 , and signals from the sensor  34 , indicative of the number of revolutions of the pipe element, constitute a measurement of the instantaneous circumference of the pipe element within the groove being formed by the grooving roller  22 . These signals are transmitted to the control system  56  which uses the information in the signals to determine (i.e., calculate) the instantaneous diameter of the groove (note that the diameter of the idler roller  23  in contact with the pipe element is known). As shown in Box  78 , the control system then compares the instantaneous diameter of the groove with the appropriate tolerance range for groove diameters for the particular pipe being processed. As shown in Box  80 , if the instantaneous groove diameter is not within the appropriate tolerance range, for example, the instantaneous groove diameter is larger than the largest acceptable diameter for the particular pipe element being processed, then the control system  56  continues to form the groove by rotating the pipe element about its longitudinal axis while forcing the grooving roller  22  against the pipe element so as to displace material of the pipe element, determining the instantaneous diameter of the groove (via the idler roller  23  and its associated sensor  32 ) while rotating the pipe element, and comparing the instantaneous diameter of the groove with the tolerance range for the diameter of the groove until the groove diameter is within the tolerance range acceptable for the diameter of the groove. 
         [0070]    Once the final groove diameter is at a predetermined target diameter the control system  56  halts the motion of the grooving roller  22  toward the drive roller  12 , but continues rotation of the pipe element for at least one full rotation to ensure a uniform grooving depth. The rotation is then halted and the grooving roller  22  and the idler roller  23  are moved away from the drive roller  12  so that the pipe element may be removed from the device  10   a.    
         [0071]    As shown in  FIG. 7 , the triangulation sensor  46  may also be used to measure a plurality of dimensions of the pipe element  40  proximate to the groove  72 . As shown in  FIG. 8 , dimensions such as the distance  88  from the end of pipe  40  to the groove  72 , the width  90  of the groove, the depth  92  of the groove, and the flare height  94  of the pipe element may be measured to create a profile of the pipe end. Flare may occur as a result of the grooving process and flare height is the height of the end of the pipe element above the pipe diameter. This information may be transmitted to the control system for comparison with acceptable tolerances for these dimensions for a standard pipe element. 
         [0072]    As depicted in  FIGS. 7 and 9 , measurement of the plurality of dimensions is effected while rotating the pipe element and comprises projecting a fan-shaped beam of light  50  along a length of the surface of the pipe element  40  which includes the circumferential groove  72  (see  FIG. 9 , box  96 ). The reflection of the beam  50  is detected by a sensor  54  (box  98 ). A calculator unit  55 , operatively associated with the sensor  54  uses triangulation methods to calculate the dimensions of the region of the pipe element  40  swept by the beam  50  (box  100 ). The dimensional information is encoded into signals which are transmitted to the control system  56  (see  FIG. 1 ), in this example over hardwired lines  58 . The dimensional information thus acquired may be displayed and/or evaluated against a database to characterize the pipe element as processed. 
         [0073]    Another example method of forming a circumferential groove in a pipe element having a longitudinal axis and using a drive roller and a grooving roller is shown in  FIG. 10 . This example method comprises:
       engaging the pipe element with the drive roller (box  102 );   engaging the grooving roller with the pipe element (box  104 );   forming the groove by rotating the pipe element about its longitudinal axis while forcing the grooving roller against the pipe element so as to displace material of the pipe element (box  106 );   measuring a plurality of circumferences of the groove while rotating the pipe element (box  108 );   determining a plurality of diameters of the groove using the plurality of circumferences of the groove (box  110 );   calculating a change in diameter of the groove per revolution of the pipe element (box  112 );   calculating a number of revolutions of the pipe element needed to form a groove of a desired diameter using the change in diameter per revolution of the groove (box  114 );   counting the number of revolutions of the pipe element (box  116 ); and   stopping forcing the grooving roller against the pipe element upon reaching the number of revolutions needed to form the groove of the desired diameter (box  118 ).       
 
         [0083]    The method shown in  FIG. 10  is a predictive method which uses the rate of change of the diameter per revolution of the pipe element to predict when to stop forming the groove by displacing the material of the pipe element. As it is possible that the prediction might not yield as precise a groove diameter as desired, additional steps, shown below, may be advantageous:
       measuring the diameter of the groove (box  120 );   comparing the diameter of the groove to the desired diameter (box  122 );   repeating the forming, measuring, determining, calculating, counting and stopping steps (box  124 ).       
 
         [0087]      FIG. 11  shows a similar predictor-corrector method of forming the groove. However, this method is based upon the circumference of the groove, not the diameter. In a particular example the method comprises:
       engaging the pipe element with the drive roller (box  126 );   engaging the grooving roller with the pipe element (box  128 );   forming the groove by rotating the pipe element about the longitudinal axis while forcing the grooving roller against the pipe element so as to displace material of the pipe element (box  130 );   measuring a plurality of circumferences of the groove while rotating the pipe element (box  132 );   calculating a change in circumference of the groove per revolution of the pipe element (box  134 );   calculating a number of revolutions of the pipe element needed to form a groove of a desired circumference using the change in circumference per revolution of the pipe element (box  136 );   counting the number of revolutions of the pipe element (box  138 ); and   stopping forcing the grooving roller against the pipe element upon reaching the number of revolutions needed to form the groove of the desired circumference (box  140 ).       
 
         [0096]    Again, in order to account for imprecise groove formation using the prediction, the following steps may be added:
       measuring the circumference of the groove (box  142 );   comparing the circumference of the groove to the desired circumference (box  144 );   repeating the forming, measuring, calculating, counting and stopping steps (box  146 ).       
 
         [0100]    The methods thus far described use substantially continuous feed of the grooving roller toward the pipe element. However, there may be advantages in efficiency and precision if the grooving roller is advanced in discrete increments as described in the method shown in  FIG. 12  and described below:
       engaging the pipe element with the drive roller (box  148 );   engaging the grooving roller with the pipe element (box  149 );   forming the groove by rotating the pipe element about the longitudinal axis while forcing the grooving roller a discrete distance into the pipe element so as to displace material of the pipe element for a revolution of the pipe element (box  150 );   measuring a circumference of the groove while rotating the pipe element (box  152 );   determining a diameter of said groove using said circumference of said groove (box  154 );   comparing the diameter of the groove with a tolerance range for the diameter of the groove (box  156 ); and   until the groove diameter is within the tolerance range:   repeating said forming, determining and comparing steps (box  158 ).       
 
         [0109]    It may be further advantageous to vary the size of the discrete distance over which the grooving roller moves, for example by decreasing the discrete distance for each the revolution as the diameter approaches the tolerance range. This may permit more precision in groove formation and decrease the time needed to form a groove. 
         [0110]    The example method described in  FIG. 13  also uses discrete increments of the distance traveled by the grooving roller, but bases control of the grooving roller on measurements of the circumference of the groove, as described below:
       engaging the pipe element with the drive roller (box  160 );   engaging the grooving roller with the pipe element (box  162 );   forming the groove by rotating the pipe element about the longitudinal axis while forcing the grooving roller a discrete distance into the pipe element so as to displace material of the pipe element for a revolution of the pipe element (box  164 );   measuring a circumference of the groove while rotating the pipe element (box  166 );   comparing the circumference of the groove with a tolerance range for the circumference of the groove (box  168 ); and   until the circumference of the groove is within the tolerance range:   repeating said forming, measuring and comparing steps (box  170 ).       
 
         [0118]    Again, it may be further advantageous to vary the size of the discrete distance over which the grooving roller moves, for example by decreasing the discrete distance for each the revolution as the diameter approaches the tolerance range. This may permit more precision in groove formation and decrease the time needed to form a groove. 
         [0119]    In the example method shown in  FIG. 14 , the predictor-corrector aspects are combined with the discrete step-wise motion of the grooving roller as described below:
       engaging the pipe element with the drive roller (box  172 );   engaging the grooving roller with the pipe element (box  174 );   forming the groove by rotating the pipe element about the longitudinal axis while forcing the grooving roller a discrete distance into the pipe element so as to displace material of the pipe element for a revolution of the pipe element (box  176 );   calculating a number of revolutions of the pipe element needed to form a groove of a desired diameter using the discrete distance per revolution of the groove (box  178 );   counting the number of revolutions of the pipe element (box  180 ); and   stopping forcing the grooving roller into the pipe element the discrete distance upon reaching the number of revolutions needed to form the groove of the desired diameter (box  182 ).       
 
         [0126]    Again, it may be advantageous to add the following steps to the method shown in  FIG. 14 :
       measuring the diameter of the groove (box  184 );   comparing the diameter of the groove to the desired diameter (box  186 );   repeating the forming, measuring, calculating, counting and stopping steps (box  188 ).       
 
         [0130]    In the example method embodiment of  FIG. 15 , the groove depth  92  (see also  FIG. 8 ) is used to control the motion of the grooving roller as described below:
       engaging the pipe element with the drive roller (box  190 );   engaging the grooving roller with the pipe element (box  192 );   measuring a diameter of the pipe element while rotating the pipe element about the longitudinal axis (box  194 );   calculating a desired groove depth tolerance corresponding to a desired groove diameter tolerance (box  196 );   forming the groove by rotating the pipe element about the longitudinal axis while forcing the grooving roller against the pipe element so as to displace material of the pipe element (box  198 );   while rotating the pipe element, measuring the groove depth (box  200 );   comparing the groove depth with the desired groove depth tolerance (box  202 ); and   repeating forming the groove, measuring the groove depth, and comparing the groove depth with the desired groove depth tolerance until the groove depth is within the desired groove depth tolerance (box  204 ).       
 
         [0139]      FIG. 16  shows an example method where the groove diameter is used to control the motion of the grooving roller, as described below:
       engaging the pipe element with the drive roller (box  205 );   engaging the grooving roller with the pipe element (box  206 );   determining a diameter of the pipe element while rotating the pipe element about the longitudinal axis (box  208 );   determining a desired groove diameter tolerance based upon the diameter of the pipe element (box  210 );   forming the groove by rotating the pipe element about the longitudinal axis while forcing the grooving roller against the pipe element so as to displace material of the pipe element (box  212 );   determining the groove diameter while rotating the pipe element (box  214 );   comparing the groove diameter with the desire groove diameter tolerance (box  216 );   repeating the forming the groove and determining the groove diameter until the groove diameter is within the desired groove diameter tolerance (box  218 ).       
 
         [0148]      FIG. 17  illustrates an example method wherein the groove circumference is used to control the motion of the grooving roller, as described below:
       engaging the pipe element with the drive roller (box  220 );   engaging the grooving roller with the pipe element (box  224 );   measuring a circumference of the pipe element while rotating the pipe element about the longitudinal axis (box  226 );   determining a desired groove circumference tolerance based upon the diameter of the pipe element (box  228 );   forming the groove by rotating the pipe element about the longitudinal axis while forcing the grooving roller against the pipe element so as to displace material of the pipe element (box  230 );   measuring the groove circumference while rotating the pipe element (box  232 );   comparing the groove circumference with the desired groove circumference tolerance (box  234 );   repeating the forming the groove, the measuring the groove circumference, and the comparing the groove circumference steps until the groove circumference is within the desired groove circumference tolerance (box  236 ).       
 
         [0157]    The methods and apparatus disclosed herein provide increased efficiency in the formation of grooved pipe elements which reduce the probability of human error as well as the frequency of mal-formed grooves.