Abstract:
An orbital welding apparatus includes a first housing defining a weld head assembly and a circular rotor disposed therein for rotation about a first axis. A welding electrode is carried by the rotor for welding. A second housing separate from the first housing forms a power transmission and has a second drive shaft extending therefrom. A flexible drive shaft connects the first drive shaft and the second drive shaft to conduct rotary drive forces from the first drive shaft to the second drive shaft while permitting the relative orientations of the first and second housings to be freely adjustable. A third and independent housing carries an electric drive motor and forms a power drive motor module with a rotary output shaft. A releasable clamping mechanism is provided for positioning and holding cylindrical members to be welded in an axially aligned relationship with their ends abutting in a single plane. A safety interlock mechanism is provided for sensing the releasable clamping mechanism in an operative position to prevent inadvertent operation or operation of the welding unit when the clamping mechanism is malaligned.

Description:
This application is a continuation-in-part of application Ser. No. 07/606,421 filed Oct. 31, 1990, now U.S. Pat. No. 5,136,134. 
    
    
     BACKGROUND OF THE INVENTION 
     The subject invention is directed toward the art of welding and, more particularly, to an orbital welding apparatus for circular products such as tubes or rods. 
     The invention is especially suited for incorporation in apparatus for welding small diameter tubing in closely confined spaces and will be described with references thereto. It should be appreciated, however, that the invention is capable of broader application and could be used in many different welding devices of widely varying sizes for many purposes. 
     Orbital arc welding equipment is often used to weld tubing and piping for use in fluid handling and processing system. Currently, there is significant interest in welding small diameter tubing, fittings, and control equipment such as valves, filters, and the like to form small, compact control and processing systems. Frequently, the various components must be welded in confined and nearly inaccessible areas. In addition, system designers are desirous of reducing, to the greatest extent possible, the size of the processing and control systems by reducing the distance between components. Much effort has been expended in miniaturizing tube fittings and system components; however, the space required by the welding apparatus has been a significant limitation on further system size reduction. 
     Safe use of potentially dangerous equipment has long been a concern in all areas of manufacturing and repair services. Fail-safe electrical interlocks are one of the various methods of ensuring operator safety during use of such equipment. Generally, electrical interlocks have met with great success and are therefore widely accepted in all areas of manufacturing and repair services. 
     The subject invention provides a unique combination of features which allows welds to be made safely in extremely confined spaces and under conditions which have heretofore prevented use of orbital welding equipment. The invention makes it possible to obtain the maximum system size reduction benefits through the use of miniaturized fittings and components. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with one aspect of the invention there is provided an orbital welding apparatus which comprises a first housing defining a weld head assembly and including a circular rotor disposed therein for rotation about a first axis. A welding electrode is carried by the rotor and extends radially inward toward the first axis. Suitable drive gears are carried in the first housing for rotating the rotor about the first axis and a first drive shaft is drivingly connected to the gears and extends from the first housing in a direction perpendicular to the first axis. A second housing separate from the first housing forms a power transmission and has a second drive shaft extending therefrom. A flexible drive shaft means connects the first drive shaft and the second drive shaft to conduct rotary drive forces from the first drive shaft to the second drive shaft while permitting the relative orientations of the first and second housings to be freely adjustable. A third separate and independent housing carries an electric drive motor and forms a power drive motor module with a rotary output shaft. Releasable connecting means are provided for quickly connecting the third housing with the second housing for permitting connection and disconnection of the rotary output shaft of the motor module with the second drive shaft so that the motor module can be manually connected and disconnected from the transmission and weld head assemblies quickly and easily. 
     The described arrangement permits the same motor module or power unit to be quickly changed between weld heads intended for welding tubing of different sizes. Moreover, because the weld head is connected to the transmission housing through a flexible drive, the motor module can have various desired orientations relative to the weld head module and the weld head module can be placed in extremely confined quarters without requiring that the motor module be associated therewith in a particular orientation. 
     In accordance with a more limited aspect, there is a gas line extending through the flexible drive shaft means to the housing to allow gas to be supplied to the weld head. Additionally, a gas supply connection extends through the motor module housing. A valved connecting arrangement joins the gas line in the motor module with the gas line in the flexible drive shaft whenever a motor module is connected thereto. Preferably, the valved connecting arrangement opens automatically when the motor module is connected to the flexible drive shaft. 
     In accordance with a further aspect of the invention, there are electrical power cables and safety interlock wires also extending through the flexible drive shaft. Suitable electrical connectors are provided so that power and safety signal connection takes place automatically when the motor module is connected to the flexible drive shaft. Thus, when changing orbital weld head modules, there is an automatic connection to the gas, the electric power and the safety interlock signal necessary for the operation of the weld head assembly. 
     The subject invention also provides an improved tube clamping assembly for use with the weld head to hold the cylindrical tube ends in axially aligned abutting relationship while the welding is performed to join the tube ends. The clamp assembly generally comprises a rectangular base with an opening extending therethrough defining a path of movement for slidably receiving the orbital weld head. A first pair of transversely spaced clamp arms extend from the base on opposite sides of the base opening. A second pair of transversely spaced clamp arms extend from the base on opposite sides of the opening in alignment with the first pair of clamp arms. The first and second pairs of arms include cooperating clamp jaws for gripping on opposite sides of the tube ends and maintaining them coaxially aligned with a first axis. The second pair of arms are mounted for pivotal movement about a second axis which extends parallel to the first axis and is in a common plane therewith which is aligned with the path of movement of the weld head into the opening in the base member. Additionally, actuating means are provided for moving the second pair of clamp arms between their open and closed positions. Further, in the closes position, the clamp arms mate along a line which includes the common plane. 
     The described arrangement of the arms opening in the manner described allows the clamp assembly to be moved into position around tubes confined in corners and closely adjacent walls since the movement of the clamping of the arms takes up a minimum amount of space and does not require any significant amount of space in the area beyond the outermost extent of the arms. That is, the clamp arms engage in the manner of a pair of pliers being moved into position on the tubing. Access to the side of the tubing opposite the weld head is not required. Further, the design requires a minimum amount of space on the lateral sides of the clamp assembly. 
     A further aspect of the invention contemplates that the arms of the clamp assembly are moved between their open and closed position through the use of a cam actuating assembly wherein the assembly is located in an enclosed position between the arms and the base plate in a concealed and confined manner and wherein the operating portions of the actuating means are located at a position spaced remotely from the outer end of the clamp assembly. Thus, when used in confined spaces, the actuating means are readily operable even through the clamp elements are enclosed and confined by surrounding environmental structure. 
     In accordance with another aspect of the invention, the operating portions of the clamp assembly actuating means are arranged such that when the orbital weld head assembly is in operating position in the clamp assembly, interengaging portions prevent opening or operating of the clamp arms. Thus, the clamp arms cannot inadvertently open during a welding operation. 
     In accordance with a further limited aspect of the invention, there are provided safety interlock wires extending through the flexible drive shaft means, which wires terminate at a transducer mounted to the orbital weld head assembly. The transducer is sensitive to the respective portions of the clamp assembly actuating means and the weld head assembly being in said interengaging operating position to inhibit the weld cycle when out of position. 
     As is apparent from the foregoing, a primary object of the invention is the provision of an orbital welding apparatus which is capable of being used safely in extremely confined spaces and which can weld extremely small fittings and produce miniaturized piping and control systems. 
     A further object of the invention is the provision of an orbital welding apparatus of the general type described wherein the various modules used to make up the system can be oriented at selectively different arrangements relative to one another while the unit is being fitted to the components being welded and while the apparatus in use and actually making a weld. 
     A further object is the provision of a system of the type described wherein the same power and control module can be used with a variety of different weld head modules so that the system is capable welding tubing of many different sizes while being operated off a single power module. 
     A further object of the invention is the provision of a system of the general type described wherein a flexible drive connection conveys rotary power, electrical power, and weld environment gas simultaneously and wherein connection and disconnection of the power unit from the weld head assembly automatically connects and disconnects not only the rotary power but also the electrical power and weld environment gas. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangement of parts, preferred and alternate embodiments of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein: 
     FIG. 1 is a pictorial view showing the overall construction and arrangement of the orbital welding assembly of the subject invention; 
     FIGS. 2 and 2A are exploded pictorial views of the transmission and orbital weld head units, respectively, which together make up module B of the assembly illustrated in FIG. 1; 
     FIG. 3 is an exploded pictorial view of the drive motor module A of the assembly illustrated in FIG. 1; 
     FIG. 4 is an exploded pictorial view of the tube clamping and holding module C of the assembly illustrated in FIG. 1; 
     FIGS. 5-8 are partial side elevational views of the tube clamping and holding module, somewhat diagrammatic, showing the operation of the clamp arm actuating mechanism; 
     FIG. 9 is a cross-sectional view taken on line 9--9 of FIG. 1 and showing the mounting and side loading arrangement for the electrode holder; 
     FIGS. 10 and 10A are pictorial views in partial cross-section illustrating the manner in which the motor module is joined to the transmission module; 
     FIG. 11 is an exploded partial pictorial view of the orbital weld head unit comprising module B of the assembly illustrated in FIG. 1; 
     FIGS. 12 and 12A are pictorial views showing the tube clamp and holding module received on and removed from the welding head module respectively; 
     FIG. 13 is an electrical schematic representing the control logic executed by the weld head controller of the preferred embodiment; and, 
     FIG. 14 is a flow chart illustrating the control algorithm used in the weld head controller of the preferred embodiment to prevent inadvertent operation of the orbital welding assembly with safety interlock of the subject invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring more particularly to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting same, FIG. 1 shows the overall construction and arrangement of an orbital welding assembly formed according to the subject invention and comprising a motor and drive module A which is arranged releasably connected to a transmission and welding head module B which is associated with a tube clamp and holding module C. Merely by way of explanation and general background, the various modules are arranged to be quickly and rapidly assembled and disassembled so that, for example, the motor and drive module A can be used with different transmission and weld head modules B. For example, a single motor and drive module can be used with a variety of different sizes of transmission and weld head modules. Additionally, and for further example, the tube clamp and holding assembly C is quickly and easily releasable from the transmission and welding head assembly B such that it can be separately connected to and positioned relative to the tubing to be joined and a multiple number of such tube clamping and holding units or modules can be used with a single transmission and weld head module to allow welding to take place while additional tube ends are clamped in alignment by additional clamping and holding modules in preparation for welding operation. 
     More specifically, and as best shown in FIG. 3, the motor and drive module comprises a relatively elongated housing assembly 10 formed by a pair of clam shell type housing halves 12 and 14 (shown in FIG. 1) and a traverse end plate 16. The components 12, 14 and 16 are formed from any suitable material such as a non-conductive thermoplastic or other non-conductive material having adequate strength and wear characteristics. An elongated shell diameter electric motor 18 is supported within the housing by having its output end suitably connected to the end plate 16. The drive shaft 20 of motor 18 extends freely through a suitable opening in the end plate 16 into a comparatively large diameter counterbored section 22. A drive connection element 24 is pinned or otherwise positively connected to the drive shaft 20 and has an enlarged diameter end portion 26 which carries axially extending pins 28. The pins 28 are retained in portion 26 and provide a rotary drive connecting with the transmission and weld head module in a manner subsequently to be described. 
     At the opposite end of the housing assembly 10 there is provided a central inlet opening or passage 30 through which the electrical power lines or cables 32 and 34 enter the motor drive housing. The cables 32 and 34 are of sufficient gage to carry the maximum anticipated current necessary to effect a wide range of welding operations at the welding head module. In addition, a pair of lighter gage safety interlock wires 31 and 33 pass through the central inlet opening or passage 30 en route to a transducer mounted on the orbital weld head unit 52 discussed below. Similarly, a pair of medium gage electric motor control cables 35 and 37 pass through the central inlet opening or passage 30 and are directly connected to the motor 18 within the housing assembly 10. The motor control cables 35 and 37 may be fused at the motor 18 or may provide a fusible link between a power supply and the motor 18. In the preferred embodiment, each of the above electrical conductors exit the housing 10 through the opening 30 and in turn are received into a weld head controller 300 described below. 
     Also entering through the opening 30 is a gas supply line 36 which supplies an inert gas to provide a suitable inert gas atmosphere about the welding operation which takes place in the weld head module. Many different types of gas are used to provide the necessary inert atmosphere and such are well known in the art. 
     The gas line 36 is connected to the head or end plate 16 and a flow line 38 is provided through the head end for connection with the transmission and weld head module. A check valve 39 is provided in flow line or opening 38 as shown in FIG. 10. In the preferred embodiment, the check value 39 is a simple ball member 39a which is biased toward a seated, sealed position by a spring 39b. The ball member 39a is moved open against the bias of spring 39b when the motor and drive module A is joined to the transmission and welding head module as will subsequently be described. 
     As also seen in FIG. 1, the power cables 32, 34 and the safety interlock wires 31, 33 are provided at their ends with electrical socket connectors 40 and 41 respectively that, as will become apparent, allow a simple plug-in connection with the cooperating elements of the transmission and weld head module in a manner which will subsequently be discussed. The arrangement of the socket type connectors 40, 41 is conventional and they are suitably retained in the end plate 16 while being insulated therefrom. 
     At the entrance end to the housing assembly 10, the power cables 32, 34, the safety interlock wires 31, 33, the motor control cables 35, 37 and the gas line 36 are suitably enclosed by a resilient protective hose member 29 which has its end clamped between the housing half sections 12 and 14 (as shown in FIG. 1). Additionally, it should be noted that the housing sections are releasably clamped together in any convenient manner such as through the use of a plurality of socket head machine screws 42 or the like. 
     Referring again to FIG. 1, it will be noted that the motor and drive module A is connected with the transmission and welding head module B through the use of a conventional over center type, lever actuated toggle or latch mechanism indicated generally with the reference number 46. The use of such latch mechanisms is well known and many different types of quick release connections could equally well be used to allow positive connection of these components while permitting ready disconnection when it is desired to change the particular weld head assembly being used with the motor and drive assembly or module A. 
     The Transmission and Weld Head Module Assembly B 
     Referring in particular to FIGS. 2 and 2A, the overall construction and arrangement of the components which make up the transmission and weld head module are shown in some detail in exploded pictorial form. In general, the module B comprises a transmission unit 50 and an orbital weld head unit 52. In the subject embodiment and in the preferred form of the invention, the transmission unit 50 and the weld head unit 52 are drivingly interconnected by a flexible drive shaft assembly 54. However, in certain environments and under certain conditions of operation, the flexible drive shaft assembly 54 could be dispensed with and a direct connection provided between the noted components. In FIGS. 2 and 2A, the flexible drive shaft assembly 54 is shown as of indeterminate length with opposite ends thereof shown connected to each of the components 50, 52. 
     Referring more particularly to FIG. 2, it will be seen that the transmission unit 50 includes a three-part housing including side elements or housing components 56 and 58 (see FIG. 1), which are basically mirror images of one another. The side elements 56 and 58 cooperate to form a clam shell type housing which is interconnected in a releasable manner to the end plate member or wall 64 through the use of a suitable mechanical fastener such as socket head machine screws 60. The outer configuration of the housing as formed by the components 56, 58 has an overall size and external shape which generally corresponds to the shape of the motor module unit. More particularly, it should be noted that when assembled as shown in FIG. 1, the outer end of the motor module end plate 16 is closely received in the open end 62 of the housing of a transmission unit 50. This provides a close coupling and sealing and encloses the electrical connections as well as the drive elements. 
     Positioned within the housing components 56, 58 and located inwardly from the outer end 62 is the rigid end plate member 64 which is also releasably connected to the housing components 56, 58 in any convenient manner such as through the use of machine screws or the like (not shown). A counterbored section or opening 66 is formed in the end plate member 64 at the location shown. (See FIG. 10 also). Carried within the counterbored section 66 and freely rotatable in suitable bearings located internally of the opening 66, is a gear-like drive element or member 68. The external periphery of the larger diameter end of the drive element 68 is provided with a multiplicity of uniformly spaced, generally semi-cylindrical recesses 70 which are sized and spaced so as to closely and drivingly engage the axially extending pins 28 on the drive connection element 24 (see FIG. 3) when the units are in the coupled condition shown in FIG. 1. 
     It should be noted that the opposite end of the housing component 56, as well as housing component 58, including integral wall sections formed to provide an outer end wall. The two housing components 56, 58 have mating semi-cylindrical recesses which together define a cylindrical opening 72 which is sized to closely receive the end 74 of the flexible drive shaft assembly 54. End 74 is a rigid metal collar and is clamped between the housing components 56, 58 and held therein through cooperating grooves as illustrated. 
     The flexible drive shaft assembly 54 is a conventional flexible drive assembly. The outer housing or sheath 55 of this flexible drive assembly is formed of a braided Teflon hose covered with a stainless steel braided outer layer. Extending axially through the center of the outer housing or sheath 55 is the flexible drive shaft element 76 which terminates in a rigid drive connection or end 78. The space available within the outer housing or sheath 55 is sized so as to be capable of holding the electrical cables 32a, 34a and safety interlock wires 31a, 33a. In the preferred embodiment illustrated, it is not necessary that sheath 55 accommodate the motor control cables 35, 37 as they terminate at the motor 18 within the motor and drive module A. 
     However, as an alternative to the electrical connection scheme of the preferred embodiment, the motor 18 and the safety interlock transducer 101 discussed below may be series-connected. In this topology, the outer housing or sheath 55 must be large enough to accommodate the electrical cables 32a , 34a and two wires sized according to the capacity of the motor control cables 35, 37. That is, in the alternative series connection, a first motor control cable is connected directly from the weld head controller 300 to a first terminal of the motor 18 in the drive module A. The second motor control cable is routed directly from the weld head controller 300 to a first contact of the safety interlock transducer 101 at the welding head unit 52 through the transmission unit 50 and the outer housing or sheath 55. To complete the circuit of course, a motor control cable-sized wire must connect a second contact of the safety interlock transducer 101 at the welding head unit 52 to the second terminal of the motor 18 in the drive module A. 
     Referring once again to the preferred embodiment, there is additionally sufficient space through the interior of the housing so as to allow free passage of the gas line 36 connecting with opening 38 (as shown in FIG. 3). In this regard, a suitable opening 80 is formed through the end wall 64 at a location corresponding to opening 38 in the end wall 16 of the motor and drive module A. A suitable sealed connection is provided between openings 80, 38 by an O-ring 81 which is located in a recess about opening 80 and engaged by boss 38a which extends out about opening 38 as shown in FIGS. 10 and 10A. It should also be seen that the ends of cables 32a and 34a are connected to suitable plug type electrical connectors 82 and 84 respectively. Similarly, ends of the safety interlock wires 31a and 33a are connected to suitable plug type electrical connectors 81 and 83 respectively. Connectors 81-84 are of conventional design, size and shape. The electrical connectors 82 and 84 are suitably mounted in the end wall 64 at locations corresponding to the locations of the socket connectors 40 of the motor module A. Similarly, the electrical connectors 81 and 83 are suitably mounted in the well wall 64 at locations corresponding to the locations of the socket connectors 41 of the motor module A. 
     The end 78 of the flexible drive shaft element 76 is connected to the drive member 68 by a cooperating flat and a C-ring or spring clip. The C-ring 86 and the flat 78a provide a rotary drive connection in which the shaft end 78 can axially move by sliding as is required when the flexible drive unit undergoes substantial bending. As can be appreciated, the overall arrangement thus far described allows rapid connection and disconnection of the motor module from the transmission unit 50. Additionally, as can be seen, the electrical and gas connections are made automatically upon a simple plugging together of the two components. 
     The orbital weld head is, as previously mentioned, connected to the opposite end of the flexible drive shaft assembly 54. The details of construction of the weld head are best illustrated in FIG. 2A. As shown therein the orbital weld head 52 generally comprises an outer frame and housing 90 which is defined by a pair of opposed body sections or members 92 and 94. These sections are suitably molded or machined from a non-conductive, high strength, high temperature resistant material. The body sections 92, 94 are joined in mating relationship in any suitable manner such as through the use of socket head machine screws 96. It should be seen that the body sections 92, 94 each include a first generally rectangular end portion or body section 92a and 94a respectively. These sections cooperate to define an internal chamber of generally rectangular shape into which a right angle drive assembly 96 is releasably received. The details and arrangement of the drive assembly 96 will subsequently be described. For the present, however, it should be noted that the body members 92 and 94 each further include relatively thinner and smaller generally rectangular sections or members 92b and 94b respectively. These sections are arranged to house the gearing and transmission members for connecting rotary motion from the right angle drive assembly 96 to the rotor or electrode holder 98. In this regard, FIG. 9 together with FIG. 2A shows the overall arrangement for the electrode holder and the mounting thereof. More particularly, each of the sections 92b and 94b cooperate to define a tube receiving through opening 100 and a laterally open entrance area 102. This arrangement allows the tube ends to be positioned in abutment and the weld head moved laterally thereover to bring the abutted tube ends into alignment with the electrode holder at the location necessary for performing the weld. The tube ends are suitably held in proper alignment and position by the tube holding and clamping assembly C in a manner subsequently to be described. 
     As shown, the rotor or electrode holder 98 is generally circular in shape but has an open side or opening 103 which is of a width sufficient to allow the holder to pass over the exterior diameter of the particular size of tubing which the weld head 52 is intended to weld. Both sides of the rotor or electrode holder 98 have a continuous convex configuration as illustrated to define circular guide surfaces 106, 108. In the embodiment under consideration, the electrode holder 98 is formed from a relatively hard copper; however, any suitable wear resistant and electrically conductive material could be used. The body section 92b is provided with an inwardly extending machined grooved 110 which is concentric with the opening 100 and provides a guide track which receives the guide surface 106. In the body section 94b, there is a circular recess 112 which is coaxial with the housing 100 and is machined to receive a circular brush member 114. The brush member 114 has a circular shape with its upper surface shafted to form a complementary guide track for the guide surface 108 on the rotor or electrode holder 98. The surface is identified with the numeral 116 and extends circumferentially about the opening 100. The brush member 114 is connected through an electrical bus bar 118 with a connector 120 which is joined to the end of the power cable 34a (shown in FIG. 2). The power cable 32a (shown in FIG. 2) is electrically connected with a plug element 122 which extends outwardly adjacent the sections 92b and 94b as illustrated in FIG. 2A. This completes an electrical circuit from cable 32b to the tube holding and clamping module C in a manner subsequently to be described. 
     With reference now to FIG. 11, the body sections 92a and 94a are further provided with suitable matching grooves 93a and 95a respectively for receiving the safety interlock wires 31a and 33a while permitting the body sections 92 and 94 to matingly engage as described above using socket head machine screws 96. The grooves 93a and 95a are inwardly extending in a manner similar to groove 110 and recess 112. Of course, either one of the matching grooves may be dispensed with should it be desired to machine only one of the body sections 92 or 94. However, as would be understood from the FIGURE, if only a single groove is used, the overall dimension must be sufficient to receive the safety interlock wires 31a and 33a which may be single strands twisted together or any other suitable two-wire configuration. 
     In addition to the grooves 93a and 95a, the body sections 92a and 94a are further provided with suitable matching recesses 97a and 99a respectively for receiving a safety interlock transducer 101 while permitting the body sections 92 and 94 to matingly engage as described above. The recesses 97a and 99a are inwardly extending in a manner similar to grooves 93a and 95a and are disposed in the respective body portions to permit direct electrical/mechanical connecting of leads of the transducer 101 to the appropriate safety interlock wires 31a and 33a. Of course a single recess may be used if the transducer size permits. However, as described above, if only a single recess is used, the overall dimension must be sufficient to receive the entire safety interlock transducer 101 therein. The transducer may be a photo-sensor, a proximity switch or a simple mechanical micro-switch as will be subsequently described. In addition, the transducer may be provided with a raised portion circumferentially extending about the body thereof in a manner as to be matingly received in corresponding recesses in the respective recesses 97a and 99a. Other fastening schemes may similarly be employed including the use of epoxies or the like. 
     As a result of the above described expedient, a complete electrical safety interlock circuit is established from the weld head controller 300 to the transducer in the welding head module B through the flexible drive shaft assembly 54. The motor control cables 35 and 37 extend from the weld head controller 300 and into the motor and drive module A where they connect with the electric motor 18. 
     With reference once again to FIGS. 2 and 2A, the electrode holder 98 carries a suitable tungsten electrode 126 which is adjustably clamped in the holder by a set screw 128. As can be appreciated, rotation of the electrode holder about the axis of opening 100 allows a weld to be performed on abutting tube ends suitably positioned within the opening 100 in a manner well known in the art. 
     The rotation of the electrode holder 98 is accomplished through a gear train connected with the right angle drive assembly 96. In this regard, it should be noted that the outer periphery of the electrode holder 98 is provided with gear teeth 130 which mate with corresponding teeth carried on the individual mating gears 132 and 134. Gears 132 and 134 are positioned as shown and carried on suitable axles and bearings mounted in the section 94b as illustrated. Drive gear 136 is in driving engagement with the gears 132 and 134 to provide two separate drive trains from the right angle drive unit 96. This allows drive to be maintained even though the electrode holder 98 includes the opening 104. That is, the gears 132 and 134 are spaced apart a distance greater than the opening 104 so that one or the other of the gears is always in contact with the geared periphery of the electrode holder 98 at all times. The drive gear 136 is, of course, in driving engagement with the output gear 140 of the right angle drive assembly 96. 
     It should be noted that the right angle drive assembly 96 includes a machined block frame or housing element 142 which is preferably formed from a high strength thermoplastic and sized to be closely received and located by the recesses formed within the body sections 92a and 94a in the manner illustrated. The output gear 140 is suitably carried on a bearing and pin assembly which extends upwardly from the bottom of the housing or frame element 142. A bevel gear element 144 is formed integrally with the output gear 140 and mates with a corresponding bevel gear 146 mounted horizontally in a pair of bearings 148. The bearings 148 are suitably received in an opening 151 formed at the right hand end of block 142. The drive lug from the flexible drive element 76 is received in the interior of the shaft joined to the bevel gear 146 and is connected therewith through the use of a C-ring 152. This connecting is also arranged to allow axial movement of the shaft portion 150 relative to the bevel gear 146 to permit axial movement as required during bending of the flexible drive cable 54. This connection is merely flats formed on the sides of shaft portion 150 which slidably engage the C-ring 152. By forming the right angle drive unit as a separate component with its own frame, maintenance, repair, and replacement of the drive is simplified. 
     The exterior housing of the flexible drive cable assembly 54 is connected at its end through a metal sleeve or end portion 156 that is clamped between the body sections 92a and 94a and joined thereto through a socket head machine screw 158. 
     In addition, connecting means 152 is provided to provide section 92a. Connecting means 153 is hinged to body sections 92a with pin means 155. 
     The Tube Clamping and Holding Module C 
     The module C can best be understood by reference to FIG. 4 which shows the module in somewhat of an exploded pictorial view. Broadly, the tube clamping and holding module is designed so as to be of minimum size capable of performing the function to thereby allow it to be used in extremely tight cramped spaced and to assembly miniature tube fittings in extremely compact small assemblies. The module is preferably formed from a high strength metal such as stainless steel and generally comprises a first substantially rectangular base assembly 160 comprising a pair of side members 162 which are joined by end members 164. The base defines a rectangular opening 166 which is sized to closely but slidably receive members 92b and 94b of the weld head assembly 90. FIG. 1 shows the weld head 90 and the fixture block module C in the assembled condition. When in this assembled condition, the members 92b and 94b extend through the base assembly 160 such that the opening 100 is located outwardly thereof or to the left as viewed in FIG. 4. Additionally, it should be understood that the base includes a bloss with an opening or socket to receive plug element 122 (see FIG. 2A) to assure a good electrical connection with electrical cable 32a. In addition, the base includes a pad 103 (FIGS. 12 and 12A) on the side opposite the boss described above for communication of the presence of the clamping assembly properly received on the tube holding assembly. In the preferred embodiment, the pad 103 is a reflective surface for operative communication with a photo-sensor variety safety interlock transducer 101. Of course, other types transducers may be employed including micro-switches, magnetic proximity sensors or the like as would be understood by those skilled in the art. 
     Associated with the base element 160 are a pair of outwardly extending clamp arms 168 which are joined to the base or formed integrally therewith to extend perpendicularly outward on opposite sides of the opening 166 to closely enclose the members 92b and 94bof the weld head assembly 90. In the embodiment under consideration, the pair of arms 168 are rigidly positioned and interconnected by a cross piece 170. Associated with the first pair of arms 168 is a second pair of clamp arms 172 which extend outwardly from the base assembly 160 in opposed aligned relationship with the first pair of rams 168. Each of the arms 172 are mounted for independent pivotal movement relative to the arms 168. The actual mounting and actuating mechanism will subsequently be described; however, it should be noted that each arm of the first pair of arms, as well as each arm of the second pair of arms, carries a tube clamp jaw 174. Although they could vary in construction, each of the clamp jaws 174 are identical and are of generally semi-circular shape and define a semi-cylindrical clamp face 176. The individual jaws 174 are provided with internal machined cuts 178 to produce resilient clamp portions such that the clamp faces themselves can resiliently engage the periphery of the tube ends being clamped. This design and the resilient nature of the clamp faces is the subject of a prior U.S. Pat. No. 4,868,367 and a pending application commonly assigned, Ser. No. 373,029, filed Jun. 28, 1989 for &#34;Collet Assembly for Cylindrical Workpieces&#34; which are incorporated by reference herein. Each of the individual clamp jaws is provided on its outer surface with a flange 180 which is engaged with a corresponding counterbore 182 formed in the circular recess into which it is respectively received in the corresponding arm element. Preferably, the individual clamp jaws are welded or otherwise positively connected in position in their respective clamp arms. It should be noted that each of the jaws is located such that when the movable second set of clamp arms 172 is actuated to the closed position illustrated in FIG. 1, the clamp jaws define spaced tube holding cylindrical sections which are located closely adjacent and coaxial with the electrode holder 98 of the weld head assembly 90. Additionally, it is preferable that the individual arms of the first and second sets of arms be provided with means to assure proper mating and alignment when they are in the tube clamping or closed position illustrated. For this purpose, the arms 172 are provided along their mating edge with a tongue element 184 which is arranged to be received within a corresponding groove 186 formed along a mating edge of the first pair of arms 168. Thus, when the arms are in the closed or tube clamping position, these cooperating tongues and grooves assure proper alignment of the individual arms relative to the orbital weld head 90. 
     Of particular importance to the tube clamping and holding module C is the manner in which the movable arms 172 are mounted and actuated. As illustrated in FIG. 4, each of the arms 172 are independently mounted for rotation about an axis 188 which extends transversely through the opening 166 and generally perpendicular to the path of insert movement of the weld head into the module C. This path of movement is illustrated generally by the arrow 190. Additionally, the two arms mate along a plane which includes the axis of opening 100 of the weld head module 90 as well as the axis 188. It has been found that when the jaws can be opened in this manner, the weld head and tube clamp assembly are capable of being inserted into extremely confined areas and can make welds on tubes located in structural corners and other confined areas not otherwise weldable with typical prior art units. 
     Although the particular manner of mounting the movable arms 172 could vary, in the subject embodiment a pair of shoulder screws 192 are received through suitable openings formed in the arms 172 and threadedly engaged with the sides 162 of the base assembly 160. Each of the arms 17 are independently actuated by a separate actuating means which takes the form in the subject embodiment of separate cam actuating assembly 194 and 194a. These cam actuating assemblies are independently operable and move the associated arm 172 independently between open and closed positions. They are, however, mirror images of one another as can be readily appreciated. For present purposes, a detailed description of the assembly 194 and its method of operation should be understood as equally applicable to assembly 194a subject to the understanding that 194a is a mirror image of 194. Referring in particular to FIGS. 4-8, the operation of the operating or actuating assembly 194 can be understood. Specifically, as shown, the actuating assembly 194 includes a cam plate member 196 which is mounted for pivotal movement about a pine 198 which is positioned such that the axis of rotation of the cam plate member 196 is parallel to the axis 188. The cam plate is located in an enclosed position between the lateral side 162 and the associated arm 172 as best seen in FIG. 4. Each of the arms 172 includes a cam surface 200 which is inclined as best shown in FIG. 5. The cam surface 200 extends transversely of the arm and is engaged by an outwardly extending cam lobe 202 carried on plate member 196. Additionally, the overall shape of plate member 196 is best illustrated in FIG. 5 and includes a laterally extending handle portion or actuating member 204 which is accessible from the ends of the module C. The cam plate 196 also carries a pin 205 which extends outwardly through the arm 172. As best illustrated in FIGS. 4 and 5, the arm includes a somewhat L-shaped opening 206 into which the pin 205 and the outer end of pivot pin 198 can extend. 
     Referring more particularly to FIGS. 5-8, the overall operation of the actuating mechanism can best be understood. FIG. 5 shows the arm 172 in its tube clamping or closed position. In this position, the cam lobe 202 is in somewhat of an over center position and the pin 205 is spaced from the sides of the L-shaped opening 206. If the actuating member 204 is pulled in the direction of the arrow shown i FIG. 6, the pin 205 engages the side of opening 206 as shown. With further movement in the direction of the arrow, the cam plate is rotated rotating the pin 205 to engage the surface and drive the arm 172 in a counter-clockwise direction. Continued movement moves the arm to a full open non-clamping position as illustrated in FIG. 8. In this position, the spacing between the outer ends of the arms 172 and the cooperating arms 168 are such as to allow the jaws to be moved into and out of engagement with the tube ends which are being welded or have just been welded. 
     When the cam plate member is actuated in the opposite direction, the cam lobe 202 engages with the surface 200 and applies a closing force to move the associated arm 172 back in a clockwise direction to a closed direction as viewed in FIG. 5-8. It should be noted that throughout this movement that a positive drive takes place and when in the FIG. 5 position, the cam plate 196 is generally in a slightly over center position so that it tends to maintain its clamped position until it is manually moved in the opening direction. It should be noted further that during the closing operation, the pin 205 does not act to move the arm 172. 
     The safety interlock control logic will now be described with reference to FIGS. 13 and 14. FIG. 13 illustrates the weld head controller 300 executed in simple &#34;ladder logic&#34; diagram form comprising relays, pushbutton and a limit switch. In FIG. 13, the safety interlock transducer 101 is represented schematically as a normally open double pole signal throw limit switch LS1. A pushbutton PB on an operator panel of the weld head controller 300 momentarily energizes relay coil CR1 when depressed by the operator. When the clamping assemble C is properly received over the welding head B as described above and illustrated in FIG. 12, the transducer 101 produces a signal indicative of a safe condition. This is represented schematically in FIG. 13 as the closure of normally open limit switch LS1. When the clamping assemble C is not properly received over the welding head B as described above or completely removed therefrom as illustrated in FIG. 12A, the transducer 101 does not produce the safe signal. This is represented schematically in FIG. 13 as the normally open limit switch LS1 opened. 
     With the switch LS1 closed, actuation of the pushbutton PB energizes the coil of relay CR1. This closes the contacts R 11  in turn energizing the coil of relay CR2. Relay CR2 closes the contacts R 21 , R 2  and R 23 . It can be seen that the contacts R 21  are used as a latch to maintain the coil of relay CR2 energized. Should the clamping assemble C move or otherwise shift from a position of not being properly received over the welding head B as illustrated in FIG. 12A, the safe signal from the transducer 101 will be removed. This is represented schematically in FIG. 13 as the limit switch LS1 opening. When in an operating condition, the contacts R 22  and R 23  energize a motor control circuit MCC and a weld head control logic circuit WCL respectively. The motor control circuit MCC may be a simple fixed voltage signal or a more sophisticate profile as may be provided by a PLC, a computer numerical control or the like. The weld head control logic circuit WCL may similarly be a PLC, a computer numerical control or the like. The motor control circuit MCC and the weld head control logic circuit WCL share a common proprietary control platform in the preferred embodiment. 
     The process for initiating a weld cycle is illustrated in FIG. 14. The process may be executed in software on the weld head controller 300 or in any other arrangement such as in hardware or the like. In the preferred embodiment, the method comrpises the steps of first reading a condition of the start pushbutton 502. If the button is actuated, the controller 300 inspects the transducer 101 to determine 504 the clamping assembly C as being properly received over the welding head B. If not properly received, an error signal is generated 506 which may include a visual and/or audio signal to alert the operator. If the clamping assembly C is properly received over the welding head B, the weld cycle is initiated 510. Once initiated, monitoring of the position of the clamping assemble C is not longer necessary. In the event that the clamping assembly C is moved to an unseen position or the like 512, the weld cycle is immediately halted 514. That is, if the clamping assembly C is detached from the welding head B, the current to the electrode 126 is interrupted by virture of the physical separation of the components. An appropriate message or other signal is generated 516 to alert the operator of this condition using various sensing means well known in the art. When the weld cycle completes 520, the control logic returns to an idle state 530 where the pushbutton is monitored. Of course, some provisions may be made for resuming a welding cycle which may have been interrupted 514 as understood by one of ordinary skill in the art. 
     The invention has been described with reference to the preferrred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.