Robotic cylinder welding

A first embodiment of the present application is directed to a method and system used to weld a cylindrical workpiece. A substantially cylindrical workpiece is loaded into a workpiece support, and a robotic welding arm is positioned located at a start position. A value representing a size of the cylindrical workpiece is input into a robot controller via a system interface. Inputting of the size value to the robotic interface obtains a control program. Operation of the obtained control program is initiated by an operator, causing the robot arm to move a preprogrammed distance toward a work surface of the workpiece. Then a welding process is performed by the welder carried on the robot arm in accordance with the control program. The process includes initiating operation of the welder, and moving the welder in a pattern appropriate for the welding operation. The workpiece and welder are moved relative to each other so as to perform the welding process as determined by the control program.

The present application relates to the art of welding and, more particularly, to a robotic welding system designed to efficiently weld a cylindrical workpiece.

BACKGROUND OF THE INVENTION

The use of robotics to perform welding operations is well known. Typically, robots are used to increase production and/or to reduce human exposure to harsh and/or undesirable working conditions. Such systems may include an arc welding robot which moves a welder toward an object which is fixed to a welding jig. The system welds the object while moving the object and/or the welder. A control program controlling the movement of the robot, operates on the basis of certain stored input parameters, such as the type of welding object, geometric data of the welding portion, the depth of penetration, and the starting and termination points of the welding. Certain welding conditions which may be considered in the creation of the control program include welding current, welding voltage, distance between the welder and the welding object, speed of supplying a wire, as well as a relative velocity of the welder and the welding object. In an open-loop control system these welding parameters are applied without any alteration during the welding operation.

The inability to alter the welding process in an open-loop system has in certain situations been considered a drawback. Therefore robotic systems have been designed to include feedback control in order to alter the welding process during the welding operation. For example, U.S. Pat. No. 6,118,093, hereby incorporated by reference in its entirety, proposes a closed-loop design where real-time changes of welding conditions such as a welding voltage, welding current, welding speed and the like are performed without interruption of welding operation. These changes are achieved by the use of a temperature detection process, used to generate feedback data to a controller. Adjustments are made to the welding process dependent on the feedback data.

Other closed-loop robotic welding systems incorporate vision capabilities. In one example, a laser directs its beam across the seam of a welding area to generate a feed back signal for the robotic controller. Based on this feedback signal, adjustments to the welding operation are undertaken. For example, movement of the welding torch is adjusted based on the provided information.

The exemplary described robotic systems have various drawbacks. Specifically, with regard to existing open-loop robotic systems, the control programs are customized to operate for a specifically sized and shaped workpiece. To obtain an economic benefit when using these types of welding systems, a large number of the identically configured and sized workpieces must be batch processed. When another sized workpiece is to be welded, a separate unique customized control program must be created. Attempting to weld a workpiece using a control program created for a different sized workpiece will result in defective welding due to misplacement of the welder. Thus, existing open-loop welding systems do not provide, economical process to weld a number of differently sized cylindrical workpieces, where such a system is able to economically weld part-volumes as small as a single part.

On the other hand, while robotic systems having a closed-loop design permit for alterations to the welding process dependent upon existing conditions, the inclusion of these feedback systems greatly complicate and increase the cost of the welding systems. For example, a laser vision system incorporated with the robotic arm, may cost as much as the robotic system itself. Thus, the cost of adding feedback controls to alter a welding procedure creates economic inefficiencies when attempting to weld small numbers of workpieces. The economic benefit of automating the welding process is therefore offset by the high cost of incorporating the components needed for a closed-loop system.

A further drawback of existing robotic systems, is their failure to address the ability to weld two cylindrical workpieces not completely in the same horizontal plane. More specifically, in robotic welding, it has been defined that the cylindrical workpiece is rotated 360° while being welded. However, existing systems apparently only address the welding of two cylindrical workpiece portions which are in the same horizontal plane.

Another drawback in existing robotic systems, is the inability to provide for operator interaction during the welding process, which permits for refined operator control of the location of the welder, even while the welding control program is functioning.

In view of the foregoing problems and shortcomings of existing cylindrical robotic welding systems, the present application describes a method and apparatus to overcome these shortcomings, and provide an improved cylindrical robotic welding system.

SUMMARY OF THE INVENTION

A first embodiment of the present application is directed to a method and system used to weld a cylindrical workpiece. A substantially cylindrical workpiece is loaded into a workpiece support, and a robotic welding arm is positioned located at a start position. A value representing a size of the cylindrical workpiece is input into a robot controller via a system interface. Inputting of the size value to the robotic interface obtains a control program. Operation of the obtained control program is initiated by an operator, causing the robot arm to move a preprogrammed distance toward a work surface of the workpiece. Then a welding process is performed by the welder carried on the robot arm in accordance with the control program. The process includes initiating operation of the welder, and moving the welder in a pattern appropriate for the welding operation. The workpiece and welder are moved relative to each other so as to perform the welding process as determined by the control program.

In accordance with another aspect of the present application, the control program is one of a plurality of control programs stored in the robot controller, wherein the plurality of control programs correspond to different sizes of workpieces.

In accordance with another aspect of the present application, the control programs corresponding to different sizes of the workpieces include different welding speeds at which the welding process proceeds.

In accordance with still another aspect of the present application, the workpiece support includes a motor for rotating the workpiece, where the motor is integrated within the robot controller, wherein operation of the motor is controlled by the control program.

In accordance with still yet another aspect of the present application, the control program is a single control program stored in the robot controller, wherein inputting of a particular size of workpiece causes the control program to be loaded with values to replace variables within the control program, such replacement customizing the control program for the selected size.

Turning to still yet another aspect of the present application, the method is provided for manipulating the location of the welding torch via a manipulation control mechanism while the welding procedure is being performed.

With attention to still yet another aspect of the present invention, the workpiece support is positioned to permit the welding of a first cylindrical workpiece portion and a second cylindrical workpiece portion, where the second cylindrical workpiece portion includes a section in a plane substantially different from the plane of the first horizontal cylindrical workpiece portion.

PREFERRED EMBODIMENT OF THE PRESENT APPLICATION

Referring now to the drawings wherein the drawings are for the purpose of illustrating the preferred embodiments of the invention only, and not for the purpose of limiting same,FIGS. 1 and 2illustrate a robotic welding system10including a workpiece support assembly12, having an idle arm14and head stock16. Included as part of head stock16is a clamp or chuck element18, and a motor/gear arrangement20having a motor controller20a. The motor of motor/gear arrangement20may, in one embodiment, be a servo motor. Idle arm14and head stock16include wheels, bearings or other mechanisms to interface to a rail system22, and which permit workpiece support12to move along rails23. Idle arm14and head stock16each hold at least an end or portion of cylindrical workpiece portions24and26, which are to be welded.

Idle arm14and head stock16are further configured with pedestals28,30, providing a known distance between the ground and workpiece portions held by workpiece support12. Motor/gear arrangement20rotates the clamp element18, which in turn causes workpiece portions24,26to rotate at a predetermined speed. Workpiece portion26rotates with workpiece24, since in pre-welding preparation steps, the cylindrical workpiece portions have been either tacked together by a pipefitter or an internal clamp (not shown) has been used to hold the workpiece portions in a fixed relationship. For example, if the workpiece portions are pipes, and the weld is an open root weld, the ends of the portions will be brought into an abutting relationship, followed normally by a withdrawal of a selected amount to define a minimum open root in the joint. To maintain the proper alignment and distance, and to allow for the rotation which will be used in embodiments of the present application, the two workpiece portions24and26are connected via the mentioned tacking procedure or through the use of an internal clamp, which are concepts well known in the art.

Arrangement of workpiece support12on rails23, permit the workpiece to be manually or automatically moved to a predetermined position for the welding operation. For manual movement, an operator simply pushes the workpiece support12to a welding position. Automatic movement may be achieved by use of a motor arrangement (not shown).

The workpiece24,26is positioned within the range of a robotic arm welding system32of robotic welding system10. As illustrated inFIGS. 1 and 2, robotic arm welding system32includes a welding head assembly (also called herein a welder)34having a welding head or torch36. Welder34is considered to include a welding cable which supplies gases, an electrode and/or a welding flux to welding head36. Welder34is attached to robotic arm40, designed to move welder34to and from the workpiece portions24,26. Robotic arm40is supported on base42. A robotic arm motor and indexer unit44moves and controls the position of robotic arm40. Power supply46supplies power to welding station10. A robotic controller48controls operation of workpiece support12, including operation of motor/gear arrangement20, and the robot arm system32. A control station (or system interface)50includes, among other elements, a data entry section52, a start button54, a manipulation refinement position control mechanism, such as a joystick56and a teach pendent58to manually position the robot arm. In one embodiment the data entry section52may include a programmable logic controller or other device which will accept data inputs, and the teach pendent can be used as a manual data entry input.

The mentioned components, including motor/gear arrangement20, robotic arm motor/indexer42, welding head assembly (or welder)34and robot controller48, among other elements, are connected to each other via known wire connections (not shown, for convenience) and/or by a radio frequency (RF) design. Thus, for example, information input to data entry section52is transmitted to robotic controller48, although it is shown a distance from interface50. Power to the elements of robotic welding system10is supplied using well-known cabling arrangements.

In one embodiment, a movable table60is constructed to have its top portion60a, which carries robot arm40, move horizontally and/or vertically. Table motor/gear arrangement62, including table motor controller62a, is provided to move the tabletop section60ain each of these directions. In this embodiment, tabletop60ais carried on an intersecting rail system64, wherein motor/gear arrangement62moves tabletop section60ain x and y directions of a horizontal plane. Legs66are, in one embodiment, telescoping legs moved by motor/gear arrangement62, permitting vertical movement of the tabletop60a, as referenced to ground. Control of table60can, in one embodiment, be accomplished through the operation of joystick56. Signals generated by movement of joystick56are transmitted to a table motor controller62aof table motor/gear arrangement62. Receipt of signals from joystick56initiates operation of table motor/gear arrangement62, causing horizontal and/or vertical movement of tabletop60a. Operation of teach pendent58, which in one embodiment could be a joystick controller, permits an operator to manually move the robot arm40to a desired position. In one instance, manual control will be used to place the welder34, carried by robot arm40, to a start position prior to initiation of a welding operation. In an alternative embodiment, motor/gear arrangement is designed to make the tabletop62ain x, y and z directions, thereby not requiring use of the telescoping legs.

It is to be appreciated that whileFIGS. 1 and 2illustrate a specific arrangement of the components, the robotic welding system may be configured using different arrangements which are equally applicable to the concepts of the present application. For example, system interface50is shown separate from robotic controller48. However, in other embodiments the interface and robotic controller elements may be combined as a single unit. Also, whereas table60is described in one embodiment as being movable, in other embodiments table60may be stationary, and a motorized hinged manipulator connector70is used to hold welder34. In this design, joystick56is used to control movement of hinged connector70to refine the position of welder34. Still further, other system signals from joystick56may be used to move the entire welding platform, shown inFIGS. 1 and 2, when the platform is provided with appropriate motors and gears.

A further feature of the present application is the integration of motor/gear arrangement20into the welding system10, which permits the system to be informed when cylindrical workpiece (24,26) has been rotated 360°. By providing this integration, it is possible for welding system10to shut off the motor/gear arrangement20upon completion of a welding process or pass.

The operation of robotic welding system10will now be described with continuing reference toFIGS. 1 and 2, and additional reference to flowchart80ofFIGS. 3A-3B. In a first step, a workpiece is loaded into the workpiece support82. The workpiece may be manually and/or automatically loaded to the workpiece support. Preferably an operator, not shown, loads the cylindrical workpiece, such as tubes, pipes, tanks, cylinders, columns, or other cylindrical weldable material. The weldable material is perferably a type of metal. However, the described system may also be usable with other weldable material such as weldable plastics and ceramics. As previously mentioned, one end of workpiece portion26lies on the idle arm14and the other workpiece portion24is held in clamp18. Once the workpiece has been securely attached, the workpiece support is moved, if necessary, to locate the area to be welded into a region accessible by the robot arm84. The location may be a specific point, or somewhere within an envelope of the robot arm's range of operation. This movement can be manual, or the workpiece support may be provided with a motorized transport system as would be known to one of ordinary skill in the art.

Once the workpiece support is at an appropriate location, the robot arm is moved to a start position, or if the start position does not change, the previous position of the robot arm is maintained86. Next, the operator inputs a size, i.e., diameter of the workpiece to a robotic controller88. The inputting of the diameter of the workpiece will in one embodiment cause selection of a robot control program, from a family of robot control programs, corresponding to the workpiece diameter. In another embodiment, operational data corresponding to the input diameter size is input into a robot control program template90. Next, the selected robot control program or the template control program is initiated to control operation of the robot arm and motor/gear arrangement92. The robot control program directs the robot arm to move a preprogrammed distance to a weld start position94. For example, when the welding operation is designed to weld a pipe joint having an open-root joint, the move is in a horizontal position to a bevel of a workpiece portion to be welded. In many operations, the welder is preferably positioned at a location of the workpiece between 10 and 2 o'clock. Once in proper position, the program initiates the welding operation (e.g., an arc weld is struck)96. When the operation is for an open root weld, the robot will move back to its initial start position98. Thereafter, the robot is controlled to move the welder in an appropriate manner for the intended welding application100. For example, when an open-root welding process is undertaken, the robot arm will move the welding torch in a weaving pattern as is well-known in the art.

During the welding operation, the motor/gear arrangement operates to rotate the cylindrical workpiece to perform a welding operation in a welding time which has a correspondence to the diameter of the workpiece102. The welding operation continues until an initial welding pass has been completed104, where the initial welding pass welds the full 360° of the cylindrical workpiece. Next, a determination is made by the control program as to whether an additional welding pass is required106. When it is determined such an additional welding pass is not required, the procedure ends108. However, if it is determined an additional welding pass is required, the welder is moved a preselected distance from its welding position110. The preprogrammed distance is sufficient so the welder is moved from the just-deposited weld material a distance sufficient to permit a second welding pass. Particularly, during the first welding pass, the depositing of the weld material decreases the depth of the weld area. Therefore, the welder is pulled back a sufficient distance so a proper arc may be formed.

Next, and optionally, the workpiece is rotated, via operation of the workpiece support, a predetermined number of degrees from the start position of the first pass112. This step insures that the start and end welds of additional passes are not layered on top of each other. In one embodiment, for example, the workpiece is rotated 180° from the original start position such that the second start position will be 180° distanced from the first start weld position. Once the workpiece is rotated, the next welding pass procedure is initiated114. The second pass may be a different welding process than that of the first welding process. For example, if the first welding pass undertakes a surface tension transfer process (STT, a trademark of Lincoln Electric Corporation), the control program may institute different welding processes (e.g., conventional CV welding, pulse welding, pulse-on-pulse welding, etc.) for the next or additional passes. Upon initiation, the robot arm moves the welding torch in a path appropriate for the second or further welding procedure116. At the same time, the integrated motor rotates the workpiece during this subsequent welding pass118. As previously mentioned, the rotation of the workpiece will normally be 360° to provide the full weld area of the workpiece to the welding operation. Following the second pass, an inquiry is made whether an additional welding pass is required120. When it is determined no additional welding is required, the process ends122. However, if additional welding passes are necessary, steps110-124are repeated.

The order of the steps described in connection with flowchart80ofFIGS. 3A-3Bmay be processed in an order other than as presented therein. For example, where movement of the robot arm to a start position (step86) is recited prior to the input of the size (e.g., diameter) of the workpiece to the control program (step88), in other embodiments, the inputting step (88) may occur prior to the positioning of the robot arm (86). It is to be understood the foregoing is presented as an example, and the order of other steps may also be altered. Further, a number of the steps ofFIGS. 3A-3Bare optional and/or directed to a particular welding process, such as an open-root application. It is to be appreciated flowchart80is considered to be applicable to alternative welding procedures other than open root welding.

With more particular attention to step90, in one embodiment, and as shown inFIG. 4A, robotic controller48includes a storage area130which stores a family of control programs132a,132b,132n. Each control program132a-132n, includes steps for welding cylindrical workpieces. For example, program132amay be for welding pipes two inches in diameter, program132bfor welding 4.5-inch diameter pipes, and program132nfor welding 18-inch diameter pipes. The recited diameters are presented only as examples and, programs for different types and sizes of cylindrical workpieces may also be stored in storage area130.

Each of the programs of the family of programs132a-132nemploy the same welding processes and/or procedures. More particularly, the programming logic and instructions are substantially identical. The similarity of the programming logic within a family of programs is taken advantage of to decrease the programming burden and increase the ease by which the programs of a family of programs are replicated.

In generating a family, initially one control program for a cylindrical workpiece of a certain diameter is created. Thereafter, the programming logic is copied for the number of control programs in the family of programs. Once the additional family members are copied, only minor changes are made to enable the family members to be used with different sized cylindrical workpieces. The basic change to the programs is the time taken to rotate the workpiece, i.e., the speed at which the workpiece is rotated. Thus, the present application takes advantage of the inventor's investigation into the similarity of cylindrical objects of a same class (e.g., class=metal pipes, class=metal tanks, class=plastic tubes, etc.) irrespective of diameter sizes, and the corresponding similarity of welding steps employed to weld such cylindrical objects irrespective of their diameters. Due to fundamentally similar geometric shape of a class of cylindrical workpieces, a family of control programs will employ the same welding steps, which differ only in the time taken to rotate the workpiece.

With attention to the time necessary to rotate the cylindrical object 360°, it has been observed that the larger the cylindrical workpiece diameter (for a class such as pipes), the thicker the cylindrical workpiece material. Therefore, more weld material needs to be applied to the weld area. As a consequence, for high quality welding, the larger the cylindrical workpiece, the slower the speed of rotation in order to provide the thicker layers of weld material into the weld area. The welding time for a specific diameter is simply inserted into the replicated programs of the first generated program. The inserted welding time replaces the welding time existing in the original program. It is to be understood that the speed at which a workpiece is rotated may be consistent throughout the welding operation, or alternatively, may vary depending upon the instructions of the control program.

In a preferred embodiment, the robot arm is moved to a start position by manual operation of the teach pendent58. However, in an optional embodiment, unique start positions which are dependent on the diameter of the workpieces being welded, are directly incorporated into the individual programs of the family of programs in a manner similar to the welding time.

By appreciating the similarity between cylindrical objects of a class, irrespective of diameter, the different sized diameter workpieces will employ substantially identical welding procedures and/or processes. This understanding permits for the implementation of a family of easily reproducible computer programs which employ the same incremental moves to control the welding operation irrespective of diameter size. The parameters which vary between the different sized workpieces, are a very small percentage of the overall robotic control program. Therefore, any two programs of a family of programs will be at least 90 percent identical in content, and more preferably over 95 percent identical in content, wherein content is the programming logic of the programs, as embodied in the coding of the control programs. Thus, most preferably the instructions among the programs are 100% identical and only variables (e.g., rotation speed) are different.

Maintaining attention toFIG. 4A, by the design described above, when an input request134is received via interface50ofFIGS. 1 and 2, and the operator inputs a specific pipe size (e.g., 4.5 inches) the program corresponding to that diameter is selected and downloaded for operation by robotic controller48.

In an alternative embodiment as shown inFIG. 4B, instead of the family of programs132a-132nof FIG.4A—and again using the knowledge of similarity between cylindrical workpieces of varying sizes—a program template136is designed and used in place of the family of programs132a-132n. Template program136provides the incremental moves required by robotic welding system10to weld workpiece portions24,26. In one embodiment, a lookup table138includes a Diameter reference column140linked to a Welding Time column142and, optionally, a Start Position column144. An operator input command145requesting a particular diameter (e.g., for 8-inch pipe), is directed to the lookup table138, where the corresponding variable information is selected and inserted to template program136.

With continuing attention to the speed at which the workpiece is to be welded, the inventor performed extensive research and experimentations. This investigation included welding pipes of a certain size at certain rates of rotation. For example, a 2-inch pipe diameter was welded in accordance with a welding procedure of a first welding time. Following the welding procedure, that welded pipe was reviewed for a variety of quality control features, including but not limited to completeness of the weld and weld strength. Additional 2-inch pipes were welded using the same welding procedure but at different welding times. The welded pieces were then also quality control tested, and the pipe having the highest quality weld was selected. The rotation welding time for this pipe was then plotted as a point on a chart of pipe sizes versus welding time. Next, pipes of other sizes (e.g., 4-inch and 6-inch pipes, etc.) were then welded. The welding procedures for each of the different sized pipes being the same. Following the welding and testing of the different sized pipes, a best welded pipe for each size was selected. Thereafter, the welding time for each best weld was also plotted to obtain a variety of test points. Using the plotted points, welding times for non-tested pipes of different sizes were obtained through known extrapolation and/or regression plotting mathematics and techniques. In one instance, and as shown inFIGS. 5 and 6, plots representing the welding time versus the size (diameter) of a cylindrical workpiece, may be obtained by use of statistical software for line plotting, such as Excel or Minitab software.

As previously noted, in one embodiment, the first pass of the welding process may be an open root welding operation.FIG. 5illustrates a regression plot146for a root pass, with seconds versus the size of the nominal pipe. This regression plot is for a welding process to weld a V-joint, which is commonly used for the joining of two pipes. As illustrated, regression plot146is substantially linear where, as the pipe size increases, the rotation speed of the workpiece decreases.

As previously noted, in many instances more than a single weld pass is required to complete the weld operation.FIG. 6depicts a regression plot148for a V-joint welding process for total welding time versus a nominal pipe size. As can be seen in this plot, the total time necessary (i.e., the initial open root plot and a second pass) increases at a greater rate as the pipe size increases.

Using the research and experimentation undertaken by the inventor, a generalized welding time formula has been obtained for the first pass open-root weld of a V-joint welding operation. The time in seconds for the root pass may be found by:
FirstPassseconds=a+(b×nominal diameter)+(c×nominal diameter)2,
where a is in a range from 10 to 50 seconds, and preferably 44.5942 seconds, b is in a range from 10 to 25 seconds, and preferably 19.6200 seconds, c is in a range of 0.10 to 0.75 seconds, and preferably 0.522950 seconds, and nominal diameter is the stated workpiece diameter.

Similarly, the inventor has determined a generalized formula for a V-joint welding process for a total welding time in seconds, which may be found by:
TotalTimeseconds=x+(y×nominal diameter)+(z×nominal diameter)2,
where x is in a range from 10 to 70 seconds, and preferably 67.3598 seconds, y is in a range from 10 to 40 seconds, and preferably 33.8308 seconds, and z is in a range of 0.10 to 10 seconds, and preferably 5.67906 seconds, and nominal diameter is the stated workpiece diameter.

The foregoing formulas used to obtain the welding time in accordance with concepts of the present application are appropriate for V-joint welding. However, it is to be appreciated that dependent upon a particular welding process employed by a user, the range and specific statements of time described herein may be inappropriate. Provision of this formula, and the specific times set out herein are not intended to be warranties of any type that a weld made in accordance with these formulas will meet any existing welding standards, or be appropriate for any specific welding application. Further, in one embodiment the stated nominal diameter is the diameter provided by a manufacturer, or supplier. However, in other embodiments the stated diameter may be an actual measured diameter. Also, while a diameter measurement is used in this embodiment, the formulas may be adjusted for use with the measurements of a cylinder, such as a circumference.

With continuing attention to the control programs, it is known that in some uses, the welding material used may result in metallurgical changes in workpieces. In such situations, it is a requirement that the welding temperature decreases prior to a second welding pass. If the temperature is not permitted to decrease prior to a second welding pass, a defective weld may occur. Therefore, when the welding process is used in these situations, either the family of control programs or the template control program will include a time delay which permits an interpass temperature to decrease to an acceptable level. Instructions for this time delay would be undertaken during the coding of the first of program of the family of programs, and would then be transferred to the other family members during the replication operation.

Further, the control programs as designed, especially in the family of programs, are portable in one instance, since the family of programs are created from a single base member of the family. The single base program may be easily transmitted electronically to remote sites via an e-mail transmission or other well-known electronic communication connection. Thereafter, the receiving party is able to easily construct the program family using the replication techniques previously discussed.

Implementation of the robotic cylindrical welding processes of the present application results in an improved process capability with an increased welding performance than has previously been achieved.FIG. 7is a chart of a process capability analysis for weld times150. The chart defines an upper specification limit152, and lower specification limit154defining an acceptable pipe welding time range. Bar graphs156represent a histogram of an amount of 8-inch diameter pipes welded within a certain welding time range (e.g., approximately 525 seconds to 528 seconds per weld). As can be seen here, the welding of the pipes shown by bar graphs156are all within the acceptable range as emphasized overall averaged curve158.

Turning toFIG. 8, and with continuing attention toFIGS. 1 and 2, operation of joystick56will now be discussed in greater detail. Operational joystick flowchart160, includes movement of the joystick which represents movement in at least one of a horizontal or vertical direction162. Movement of the joystick generates a joystick position signal164, which is transmitted to a controlled component166(such as a movable table60of FIG.1). Reception of the joystick signal activates the controlled component in accordance with movement of the joystick168. Therefore, and with continuing reference toFIGS. 1 and 2, when joystick56is moved in a selected direction (and when the first embodiment is used with movable table60), the location of robotic arm40is altered from the location prescribed by the robotic control program. This refinement control is useful, as it is known that while smaller cylindrical workpieces have a very high degree of accuracy in their diameters and their geometric shape, as the diameters of cylindrical workpieces increase, manufacturing imperfections become apparent. These imperfections result in a less than ideal cylindrical workpiece having non-cylindrical features. The present application provides a welding system with an open-loop type robotic control program. Therefore, the control programs are not provided with feedback signals to address these imperfections. Rather, an operator can directly address the imperfections by use of the joystick56. The operator is able to alter the position of the robotic arm40, with reference to the workpiece when it is determined the shape of the pipe does not correspond to the expected cylindrical workpiece for which the robotic arm has been programmed. Use of joystick control provides a manual assist to the robotic control program without requiring the high infrastructure costs of a closed-loop feedback system. This feature also permits the operator to provide adjustments to the location of the welder to address imperfect cylindrically formed workpieces, without interrupting operation of the robotic control program.

FIG. 9illustrates the concepts of the refinement control provided by the joystick control system56. Illustrated in side view is robotic arm40, with movable table60, including telescoping legs66. In this embodiment, the cylindrical workpiece170shown in a solid line is a substantially true cylindrical geometric shape. In this instance, welder34is directed to the proper welding position with regard to cylindrical workpiece170. However, imperfections172in the cylindrical shape may occur, especially in cylindrical workpieces of larger dimensions (e.g., 12 inches and above). In this example, imperfection172would result in the welder34being too far into the welding area. An operator will visually note this imperfection and as the rotation of cylindrical workpiece170is occurring, the operator uses joystick56to adjust or refine the welding process by moving the entire robotic arm via operation of the joystick56. The operator moves joystick56to activate telescoping legs66increasing the height of tabletop60a(in the direction shown by arrow174), raising the entire welding arm to a location for welding of imperfection172. As the cylindrical workpiece170continues its rotational path, and imperfection172is passed, the operator moves joystick56to reposition the telescoping legs66to their original position. In alternative uses, joystick56is used to move tabletop60ahorizontally to address other imperfections in the cylindrical workpiece.

Turning toFIG. 10, depicted is a welding system180incorporating dual workpiece supports182,184similar to those previously described. This design permits the robotic arm to improve the efficiency of its work processes by removing idle time once workpiece of one workpiece support has been welded and then must be removed prior to a next welding operation. By use of dual workpiece supports182,184. Once welding of a workpiece186carried on workpiece support182is completed, the robotic arm moves to welding of another workpiece188held in workpiece support184. This figure also illustrates the present concept may flexibly weld cylindrical workpieces (e.g., workpieces186and188) of different diameters.

With continuing reference toFIG. 10, in one embodiment robotic arm40has six axes of movement, including movement in the x,y,z direction and for yaw, roll and pitch movements. Robots of this type are known to exist. However, a feature of the described system provides a seventh axis of movement through the integration of the motor/gear arrangement190as part of robotic system180and controlled by robot controller48. Thus, workpiece support182, provides a seventh axis of movement. Additionally, an eighth axis of movement is provided by the dual workpiece support system by integration of workpiece support184, which has a separate motor/gear arrangement192also integrated into the robotic system and controlled by robotic controller48.

With continuing attention toFIGS. 1,2and10, the workpiece supports have been constructed to incorporate pedestals (e.g.,28and30ofFIG. 1) such that the cylindrical workpieces are a predescribed distance above the ground. By this design it is possible to weld workpiece portions which are not entirely within the same horizontal plane. For example, inFIG. 11, all of workpiece portion200is substantially entirely in the same horizontal plane. Workpiece portion202(which may be understood to be an elbow portion) is only partly within the same horizontal plane as workpiece portion200. Where the two portions come together in welding area204, the portions are in the same plane to permit an alignment of the surface edges. However, the form of workpiece portion202includes a section206in a separate plane. Without use of pedestals28and30, when workpiece portions200and202are rotated, section206of workpiece portion202would come into contact with the ground, blocking further movement and resulting in an inability of the system to weld these workpiece portion combinations. Thus, by this design, irregular objects not entirely in each other's horizontal plane may be welded together. The heights of pedestals28and30are adjustable by known height adjustment mechanisms.

The movable workpiece supports also provide a capability of welding extended lengths of cylindrical workpieces. Particularly, inFIG. 1, by adding additional idle arms, such as idle arm14, on the rail system23, additional workpiece portions may be added. Then in operation, once a first weld is accomplished, the workpiece support is moved to a next area to be welded within the welding envelope. Thereafter, these portions may be welded and the process repeated. By this design, lengths up to fifty feet or more may be welded, providing an appropriate number of the idle arms are used, and a motor with sufficient power to turn the various workpiece portions are used.

Cylindrical workpieces as small as one inch in diameter have been welded using this process, and the upper diameter limit would appear to only be limited by the physical size of the system.

An additional benefit of the present application is that there is not a requirement of a pipe edge (land) to weld the workpiece portions. This is particularly possible when the welding process employed is the surface tension transfer process, which allows a very fine control of heat input. Further, the use of a variable power control supply is used in this system for the changing from a first welding process to a second or subsequent welding process on-the-fly. One particular power source which permits this switching capability is an STT/Powerwave 455 from Lincoln Electric Corporation.

As described, the robotic welding system incorporates a family of control programs (or a template control program), these programs may be considered to provide open-loop control. Use of a manipulator such as joystick56permits an operator to adjust the path of welding based on a visual observation. Thus, operator intervention is able to adjust the open-loop control of the control program(s). This refinement control is especially beneficial in connection with welding of large cylindrical diameter workpieces which may not be ideally round. A combination of the open-loop control program with the refined control available through the use of the manipulator joystick, permits the present application to provide on-the-fly procedure adjustment and on-the-fly process adjustment. On-the-fly process adjustment is incorporated during the coding of the control programs, wherein during a first pass a first welding process is performed, (e.g., conventional CV, STT, etc.), and then during a second pass operation transitions to another welding process (e.g., pulse welding, pulse-on-pulse welding, etc.). The on-the-fly procedure adjustment is obtained through the use of the manipulator joystick, where based on visual inspection, an operator provides refined positioning above what is achievable by the control program.

Through use of the present system, including the ability to select a variety of workflow programs for cylindrical welding, it becomes economical to use a robotic welding system to weld single pieces rather than requiring large runs of the same-sized pieces.

The invention has been described with reference to a preferred embodiment and alternatives thereof. It is believed that many modifications and alterations to the embodiments disclosed will readily suggest themselves to those skilled in the art upon reading and understanding the detailed description of the invention. It is intended to include all such modifications and alterations insofar as they come within the scope of the present invention.