This present patent of invention refers to a robotic system designed for the orbital welding of pipelines, belonging to the field of industrial welding. A robotized system for the control and supervision that performs the automatic control of all the activities related to the welding procedure, using either one or two robot manipulators. There are the welding torches attached to the manipulators, which are connected to a welding machine with one or multiple wire feeders.

It is known that the welding of pipelines initiated in 1929, however it assumed productive characteristics only in 1933 (Widney, 1999). Nowadays, the welding of pipelines must have both the Welding Procedures Specifications (WPS), which is the specification or elaboration of the welding procedure, and qualified welders as ruled by the API 1104 norm from 1999. The most commonly used processes applied on the welding of pipelines and, at the same time, accepted by the API 1104 norm are: The SMAW (Shielded Metal Arc Welding) process which is the welding procedure that uses coated electrode; the GTAW (Gas Tungsten Arc Welding) process, also known as the TIG process, using a non-consumable electrode, nevertheless, it can be used an external material so as to fill the groove to be welded; the GMAW (Gas Metal Arc Welding) process, which is also known as the MIG/MAG process and, last, but not least, the FCAW (Flux Cored Arc Welding) process, which is the welding process that uses the tubular wire (AWS ₁ 1991). The equipment used for the GTAW and FCAW processes is the same, the difference is only on the type of wire used though: while it is used a solid wire in the GMAW process, it is used a tubular wire in the FCAW process. In general, it can be said that once the holding and the displacement of the welding torch is made by a human being over the welding bead then this is called a mechanized welding procedure. On the other hand, once the holding and displacement of the welding torch is made by a robot then it is called a robotized welding procedure (automatic welding procedure).

The continual performance of the orbital welding of pipes, (it is called orbital welding because the welding torch is moving around the pipe, while the pipe remains motionless) considering the use of the SMAW process, is something impossible because the electrodes have a limited length which produces welding beads with average length of 150 or 200 millimeters. On the other hand, the use of the GiVlAW process or the FCAW process makes it possible because on these processes the feeding of the wire is continual. However, despite the use of the GMAW or the FCAW processes, it is important to be mentioned that, at manual operation, the performance

of the welding procedure, over the over-head position, ascending vertical position and flat position, is not feasible without an intermission; what is something even worst when dealing with pipes with bigger diameters.

Considering the fact that on each welding position (flat, ascending vertical, descending vertical and over-head) there is a set of optimal welding parameters to be loaded (electric current, voltage, welding speed, stick-out and torch angle), then, there is the following question: How to perform tJhe controlled variation of these parameters while moving from one welding position to another without an intermission on the welding procedure? The answer is the se of a (automatic) robotic system. Accordingly to RIA (Robotics Industries Association) a "robot is a reprogrammable manipulator, multifunctional, designed to move materials, parts, tools and special devices through a variety of tasks" (Rivin, 1988). Based on the definition above, a robotic system must be completely programmable so as to allow all the activities related to the welding procedure in such an automatic way, i.e. switch on and off the electric arc, displacement of the welding torch controlling the welding speed, torch angle and stick-out, and also, control the electric current and voltage. The in field welding of pipelines using anthropomorphous robots is a possibility, however not practical considering the heavy weight to be moved to every new joint to be welded along the pipeline system. Besides this, to every new joint to be welded, due to irregularities in the site or due to changes on the diameter of the pipe, it is necessary to reprogram the whole trajectory of the torch around the pipe. An ideal robotic system to the in field welding of pipelines, not only to perform automatically all the activities related to the welding procedure, but it must be light so as to make easier the transportation of the equipment along the pipeline system. It must also have easiness in the determination of the trajectory of the torch around the pipe. However, such a system would not be completely multifunctional (it means the system would not be able to be used in a general task because its limitation to move around the pipe), yet it could be defined as a "robotic system to special tasks or a dedicated robotic system" (Romano, 2002). It js fundamental to state and emphasize the. importance of the data acquired by the control system, specially to the robotic system for orbital welding, because they determine which welding parameters must be loaded at that particular position according to the position of the manipulator, so as the points in which the electric arc is going to be switched on and off. These characteristics are essential for the

determination of the autonomy of the system. In this manner, it is possible to reduce the human participation during the orbital welding procedure.

The robotic system, which is the object of the present patent, was designed to perform the welding of pipelines in order to comply with the requirements above described. Using this robotic system, all needed passes at the welding of pipelines (root pass, filling pass and finishing pass) can be executed with the use of the GMAW process (solid wire) or the FCAW process (tubular wire). The robotic system includes all the necessary degrees of freedom that allow stick-out control, welding speed control, torch angle control and positioning of the welding torch control. Besides these variables just mentioned before, the voltage and the welding electric current are also controlled during the welding process. The system performs the controlled variation of the optimal welding parameters, what are function of the welding position of the torch over the pipe, in such a way that they are interpolated during the regions of transition of the welding positions (i.e., transition from the ascending vertical to the plain) in order to perform the welding procedure without an intermission during these transitions, aiming to increase the productivity and the quality of the welding beads. The system itself consists of a controller unit (the controller), what can be a computer that makes possible the control of all the activities related to the welding procedure. The controller is connected to the welding machine and through the direct operation of the controller on the variation of the welding voltage and electric current, during the execution of the welding procedure. Also, there are manipulators, which are responsible for the accurately displacement of the torch around the pipe, connected to the controller and welding machine. More technical details and the constructive and functional characteristics of the present robotic system can be better understandable when referring to the figures that follows, which contain numbered references combined with the description, with no restriction on its application reachability and its configuration in respect to its dimensions, proportions and eventual types of workmanship inserted. Figure 1 depicts a general illustration of the system. Figure 2 depicts a lateral view of the mechanical structure of the manipulator, displaying the base and the vertical support of its mechanisms.

Figure 3 is a portrayal of the lateral view of the structure shown by figure 2, displaying its transmission mechanisms. Figure 4 also depicts a lateral view of the mechanical structure of the manipulator, however displaying the welding torch positioning system.

Figure 5 portrays a lateral view of the same shown by figure 4, however showing the welding torch positioning mechanisms.

Figures 6, 7, 8, 9 are illustrations of the movement of the manipulators, displaying its displacement around the pipe, the torch up and down degree of freedom, the torch lateral degree of freedom and the torch angle degree of freedom, respectively.

Figures 10 and 11 portray, respectively, the used inclinometer in detail and its weight vector decomposition graphic.

Figure 12, 13 and 14 depicts diagrams of operation of the system controller. Accordingly to the figures presented and its numbered references, the present patent of invention refers itself to a robotic system for the orbital welding of pipelines that is composed by robotic manipulator (1), a controller system (2) and by a welding machine with duple, or multiple, wire feeders (3) which are interconnected among themselves; nevertheless, the manipulators (1) are basically mechanically constituted by three distinct subsystems: the base (11), the transmission (12) and the welding torch positioning system (13).

The base (11) is a unique part, whose function is to support all the other subsystem, sensors, cables, connections, wheels or any other auxiliary device that may be necessary to install. The base (11) still has two vertical supports (12) which support the transmission (12) and the welding torch positioning system (13). The base (11) is constructed to have all the holes and all the necessary clamps for the assembling of the other components.

The wheels (114) are responsible for the smooth movement of the manipulator (1) on the pipe surface (4), which are constructed with polymeric material resistant to heat, with furrows in order to improve the contact with the surface and bearing (115) on its enclosure to decrease bearing friction. The wheels (114) are linked to the base (11) by shafts (113); the shafts are screwed on the base (11). The base (11) is also useful in the support of the manipulators cover (116) which covers and protects the internal manipulators components from dust and bad weatfrier. The transmission (12) has two basic objectives: to move and to fix firmly the manipulator (1) against the pipe (4). In order to fix the manipulator on the pipe, a pair of chains, which are individually connected and surround the pipe diameter (4) and pass on the manipulator (1) simultaneously, however, depending on the number of manipulators to be used (1), also dependent on tfie diameter of the pipe, a higher or lower number of chains (121) can be used, so as other flexible mechanisms of transmission, such as cables and straps.

It can be applied a strong tension to each chain (121) by means of the use of stretching mechanisms, which are located at the manipulator extremities (1), in order to sustain the chain steady relatively to the pipe while the manipulator (1) moves itself around it (4) (the manipulator translational movement around the pipe, fig.6) based on friction effects. The stretcher is mainly composed by a split shaft (122) that has a bearing between the two halves (the half-shafts) in order to allow the individual action of each half. On each of these halves, there exists a lever arm (124) with a low friction bushing or with a pinion so as to apply the tension onto the chains (121). Each lever arm (124) is kept fixed to the half-shafts (124) by holes, whose diameter equals the half-shaft diameters, in the lever arm structure, however the lever arms are free to spin up to a certain degree because they are not completely independent from the motion of the half-shafts. The lever arms are connected to torque springs (125) which, in turn, are connected to the half-shafts as well. There is a ratchet system (126) that guarantees the maintenance of the amplitude of the tension applied to the chains by disabling the half-shafts spinning (121).

The configuration described just before allows the spin of each half-shaft, in a first moment, until the lever arms (124) touch the chains (121), what eliminates every existing looseness; however, in a second moment, any further spin of the half-shafts is going to move the torque springs (125), which are responsible for maintaining the tension constant on the chains(121). In order to install the manipulator on the pipe, the stretchers can be driven either manually, i.e., using open-end wrenches on the existing notches on the half-shafts or electronically assisted.

Toothed wheels (127) are used as ending-effector's elements so as to perform the translational movement of the manipulator (1) on the surface of the pipe (4) (fig. 6). The toothed wheels exert their action directly on each chain (121 ) which, in turn, when installed in proper manner, surrounds the pipe (4) (it passes around the pipe) and contacts the chain links on the stretchers and on the pinions. The latter are kept fixed on a driver-shaft by a chock or any other compatible mechanical systems that perform this function. Yet, the driver-shaft is fastened by two auto-alignment bearings (128), which, in turn, are screwed onto the manipulator base. Nevertheless, also fixed onto the driver-shaft, there is a straight-toothed gear (129) (46 teeth) which is driven by means of an electric motor (M) that supplies the necessary torque to perform the movement of the manipulator around the pipe. Both the manipulator absolute position on the pipe and the manipulator speed around it are variables measured and monitored

by optical encoders (E). In order to measure the manipulator speed, one encoder is attached to the driver-shaft related to this degree of freedom.

The welding torch (131) contains, preferably, four degrees of freedom (i.e., two linear moves (fig. 7 and 8) and two rotational moves (fig. 9)) in order to allow its vertical, lateral and angular movements in relation to the manipulator (1) and to the welding groove of the joint to be welded. So as to perform the linear moves, the welding torch (131) is mounted onto two linear guidance systems (132) that are moved by spindles (133) or any other driving means for linear move. The motion of every degree of freedom is provided by electric motors which can be identical or not. On the other hand, the rotational moves (fig. 9), which have rotational axes on the welding torch (131), are performed by means of gears (134) or any other compatible transmission system for rotational movement.

Every motion mechanism of the welding torch (131) is connected to the welding torch positioning mechanism (13) which can be effortlessly dispersed. The welding torch (131) is fastened by means of an adjustable tab, which is capable of hosting any type of welding torch and also enabling the maintenance and change to be easy. The linear vertical move (fig.7) has as function, besides that, it also allows the compensation of the pipe curvature (4) and adjusts itself in order to keep constant the distance between the pipe (4) and the welding torch (131) during the manipulator (1) translational motion on the pipe (4) (fig. 6). The linear horizontal move (fig.8) is suitable for moving the welding torch (131) orthogonally to the joint to be welded, so that the welding torch can be adjusted and aligned over the groove and to maintain the alignment of the torch with the groove during the manipulator (1) translational motion on the pipe (4) with the feedback of the seam tracker sensor (126). The angular horizontal move (fig. 9) is suitable for adjusting the welding torch angle (131) in relation to the orthogonal axis at the welding point, then defining whether the welding procedure is performed pulling or pushing the welding pool. The performance of angular horizontal motion synchronistically to the linear vertical motion of the welding torch (fig.7) and to the manipulator (1) translational motion on the pipe (4) (fig.6) allows the system to keep the welding speed and the stick-out as the desired parameter the whole time. The angular lateral move (fig.9) has as objective to adjust the angle formed by the normal axis at the point to be welded and by the orthogonal axis at the welding groove; therefore, it is capable to control the welding bead geometry by means of moving this degree of freedom synchronistically to the linear vertical move (fig. 7) and to the linear horizontal move, so that, at every moment, during the manipulator (1)

translational motion on the pipe (4) (fig.6) the welding torch end (131) is kept over the groove on the desired position and height.

In order to commute the optimal welding parameters during the orbital welding process, it is necessary to determine the position of the torch in relation to the horizon. Therefore, the manipulator (1) has an inclinometer (I) sensor which measures the manipulator inclination in relation to the horizon. The inclinometer (I) is a sensor, whose size is suitable for being embedded into the manipulator interior, that is robust enough to the aggressive welding environment; its output is the most as possible immune from electromagnetic noise created by the electric arc, 360° range operation, minimum acceptable error, 0.18° resolution; which are relevant characteristics to the control of the parameters. The inclinometer (I) is basically composed by a high-resolution incremental encoder (E), by an electronic unit and by a specially designed pendulum so as to change the welding parameters during the orbital welding of pipelines.

The inclinometer working principle is mainly based on the pendulum (fig.10) center of gravity and on the weight vector (its components). There is an encoder (E) attached to the pendulum. The more the sensor is inclined, the stronger is the torque, what is due to the x component of the weight vector (fig. 11), that tends to align the pendulum with the normal vector (orthogonal vector to the earth surface). Therefore, a rotational motion is produced on the encoder that is sent to the electronic unit, whose function is to suit the information and to produce an 11 -bits digital output. The output of the electronic unit is, then, sent to the controller system and to the external environment by a liquid crystal display.

The controller system (2) consists of a (desktop) personal computer (PC) in which digital and analog boards are added in order to allow the driving and control of the manipulator axes, so as the control of the welding machine (3). However, in order to facilitate the transportation of the controller system, it can be replaced the desktop PC by a notebook PC.

The start-up procedure of the present robotic system is the same start-up procedure applied onto any welding industrial robot. The first step is the calibration of the welding torch position (or the center of tool definition) (131); the second step is the calibration of the welding machine (3); then, in the third step, the manipulator (1) trajectory and the welding parameters are programmed on the controller system.

The calibration of the welding torch (131) is performed so as to decrease the accuracy error of the system. The welding parameters to be programmed are: the stick-out, longitudinal position, angular position and the manipulator position around the pipe. The stick-out parameter refers to the distance between the contact tube and the pipe (4) surface. The longitudinal position parameter is the lateral move of the welding torch whose calibration is accomplished by defining the central position, where the welding bead is going to be deposited (zero position). The angular position parameter refers to the angle constituted by the torch axis and the axis orthogonal to the pipe surface, whose calibration is accomplished when the two axes are coincident (i.e., 9O°). The manipulator position parameter is the welding torch position around the pipe whose calibration is accomplished by moving the manipulator (1) around the pipe (4) in order to define the zero position on the inclinometer (I).

The calibration of the welding machine (3) is performed only when the type (chemical composition) or the diameter of the electrode or the type of protection gas are altered. This is a procedure necessary in order to assure the loyal reproduction of the current and voltage adjusted by the manipulator (1) controller on the welding machine (3). Also, as its is performed on welding industrial robots, references curves for the electric arc voltage and for the welding current are determined as function of the wire and protection gas which, in turn, are saved on the controller system (2). These reference curves are used as they are needed.

The definition of the trajectory of the robot is performed by saving points around the pipe (4), among which the manipulator (1) will move in a pre-programmed velocity. It is on the programming procedure of the trajectory that the points for opening and closing the electric arc are defined. The welding parameters to be used along the trajectory are saved on pre-programmed welding files. On these files, the necessary variation of the welding parameters, as a function of the position of the welding torch (131), around the pipe is programmed. It is possible to store on the controller system different files which are function of the activities to be performed during the welding of a pipeline.

In order to vary the manipulator (1) position around the pipe (4) (fig.6) and to control its velocity, there is a rotative motor with velocity control. In particular, it was selected a c.c. motor (M) which is driven by a PWM (pulse width modulation) amplifier. The pulse width is proportional to a differential analog signal applied to the PWM amplifier input.

This differential analog signal is, in turn, generated by an analog/digital board located in the personal computer.

There were also used rotative motors for the other degrees of freedom (i.e., linear vertical move (fig.7), linear horizontal move (fig. 8), angular lateral move and angular horizontal move (fig. 9)). In particular, in order to provide high torque with small motors, which are compatible with the manipulator dimensions, and, at the same time, providing higher positioning precision without sensor feedback, it was selected high torque step motors. These motor are driven by amplifiers which generate input currents on the necessary sequence for the motion. So as to command the amplifiers, it is necessary digital signals indicating the motion direction and the rotation speed as a proportional relation to the frequency of the pulses.

In the controller system (2), there were added both digital and analog input and output boards so as to be possible to drive and control the robot axes and the welding machine, as well. During the execution of the program implemented on the controller system (2), it is generated values of reference of velocity for the first axis and the position for the remaining axes. The translatiortal velocity values, the welding torch angle values (131) and the stick-out values are loaded from the parameter table (T). Therefore, in each position of the manipulator around the pipe (4), which is informed by the inclinometer (I), it is possible to generate the references (A, B, C and D) with the optimal parameters from points located on the table or from the interpolation of points. The alignment of the welding torch (131) with trie welding groove is obtained by the reading of the seam tracker sensor (S) and casual corrections are performed by the motor for the torch lateral position (131).

Ordinary welding machines possess potentiometers for the adjustment of welding voltage and for the adjustment of the welding current (wire feeders speed).

Both potentiometers mentioned above are operated manually, i.e., the operator must adjust the voltage and current before beginning the welding procedure. The process robotization, however, requires the parameters (welding current and welding voltage) to be adjusted by the controller system (2). Hence, an electronic board (21) was designed in order to interface the manipulator (1) controller system (2) and the welding machine (3). The board (21) is capable of varying the electric resistance among 3 terminals, working as a 3-terminal resistor (tripot). The desired resistance is commanded by the controller system (2) by means of an 8-bit digital signal. Therefore, it is allowed a

resolution of 256 steps between the maximum and the minimum resistance values. The substitution of the resistor that adjusts the welding machine voltage (3) allows the adjustment of 256 different levels of voltage. The same substitution occurs on the wire feeders in which the potentiometers that adjust the welding current are replaced by the circuitry of the electronic board (21 ).

In order to generate the correct digital values to be commanded on trie electronic board (21) so as to obtain the desired voltage (22) and current (24), it is necessary to calibrate the welding machine (3). It was implemented on the controller system (2) the capability to the user to plot calibration curves (24 and 25) composed by experimental data (i.e., the actual values are measured and used to plot the curve for each value of reference of voltage (26) and current (27)). Therefore, by means of interpolation among experimental data, the controller system (2) is capable to command suitable digital references so as to obtain the desired welding parameters (28).

Once the controller system (2) knows the references for the parameters, it implements the velocity control of the manipulator around the pipe (4). The measuring of the velocity is performed by means of a sensor (Sv) which is located on the shaft of the driving pinions. In particular, it was selected an incremental encoder. It is capable to measure precisely the manipulator (1) actual velocity by measuring trie encoder pulses frequency. Just in case there is an error between the reference and the manipulator actual velocity (28), the input voltage on the driving motor (M) is adjusted so as to minimize the error (make it equal to zero). After calculating the new input voltage, an analog signal is generated by the D/A board, and, then, sent to the amplifier that supplies the motor (M). It is used drivers (29) that energize the coil on the right order so as the step motors are moved accordingly to the personal computer.

The present robotic system show itself as a viable and productive alternative for the welding of pipelines above 10 inches of external diameter, and it is characterized by the great repeatability, high deposition rates and working factor.