EP2242604A1

EP2242604A1 - Portable work machine with double function of arc welder or of plasma cutter of metal objects

Info

Publication number: EP2242604A1
Application number: EP07866811A
Authority: EP
Inventors: Cristiano Dal Soglio
Original assignee: Ricerca & Distribuzione Srl
Current assignee: Ricerca & Distribuzione Srl
Priority date: 2007-12-18
Filing date: 2007-12-18
Publication date: 2010-10-27
Also published as: WO2009078043A1

Abstract

A portable work machine with double function of arc welder and of plasma cutter of metal objects comprises a shared electronic system (D, E, R) two distinct electrical transformers (N, 0) or a single core transformer with double primary and/or secondary windings and related secondary rectifying stages (P, Q); a shared powering circuit connectable to AC voltage mains, including a main switch (A), an EMC filter (B), a switching power supply (C) for said shared electronic system (D, E, R), a sensor (F) of the mains voltage generating a signal that is applied to an input of a core circuit (E) of said electronic control system, a shared primary rectifying stage (G) of the mains voltage and levelling capacitors (H) of the rectified DC voltage, a shared full wave primary inverter (I) and a routing circuit (M) of the AC voltage output by said primary inverter (I) towards the primary winding of one or the other of said, electrical transformers (N, 0); a first shared sensor (Rl) of the current flowing on output lines respectively of one or the other of said secondary rectifying stages (P, Q), generating a feedback signal that is applied to a second input (HPl) of the core circuit (E) of said electronic control system; a second sensor (R2) of the current flowing on an ancillary ground line connecting a metal body of an outlet nozzle of said plasma torch for signalling the lighting of a pilot arc between an inner spark electrode and the surrounding metallic body of the outlet nozzle of said plasma torch to the core circuit (E) of said electronic control system, through a third input (SENSE).

Description

"PORTABLE WORK MACHINE WITH DOUBLE FUNCTION OF ARC WELDER OR OF PLASMA CUTTER OF METAL OBJECTS"

The present invention relates in general to portable apparatuses for arc welding and for plasma cutting metal objects using an arc generated plasma torch fed with compressed air or inert gas.

Arc welders for welding metal objects according to one of the many common arc welding techniques such as SMAW (acronym for Shield Metal Arc Welding), TIG (acronym for Tungsten Inert Gas), GTAW (acronym per Gas Tungsten Arc Welding), MIG (acronym per Metal-Arc Inert Gas), MAG (Metal-Arc Active Gas), GMAW (Gas Metal Arc Welding), require forcing and controlling a relatively large DC current through a welding electrode and a return connection through the metal object being welded that, in case of a portable welder of medium-small power, may be in the range of 100-150 A or even larger, at a voltage difference between the electrode and the metal piece or pieces being welded that is generally comprised between 15 and 25 V.

To this end, the welding machine has an appropriate power supply circuit that converts the AC mains voltage to a (rectified) DC voltage, a regulation DC-DC converter and specific devices for delivering electric power to the welding electrode according to requirements.

Often, on-site jobs besides an arc welder that can be easily transported require also the availability of an equipment for cutting semi manufactured structural parts or partly finished metal pieces or metal structures. A traditional thermal plasma torch has an extremely poor portability because of the heaviness of standard sized commercial compressed combustible gas bottles and of the encumbrance of the relative implements such as the torch and relative flexible hose for connecting it to the compressed gas bottle and of the other accessories necessary for using it. Plasma cutting apparatuses specifically made for facilitating their transportation are known. In many of these portable apparatuses, the plasma is generated at the outlet of an electrode-nozzle of the torch by ionizing a stream of substantially inert gas by maintaining an electric arc between an inner spark electrode of the torch nozzle and the metal object to be cut using connection cables to respective terminals of the apparatus that is plugged into an AC mains socket.

Such an apparatus basically includes an AC-DC converter suitable to force a DC current of about 15-20 A through an inner spark electrode located at the nozzle outlet of the torch and a return connection through the metal object being cut, at a voltage appropriate to cause and maintain stably an electric arc that ionizes the pressurized gas jet upon passing through the nozzle of the torch and which may generally be comprised between about 100 and 130 V.

The characteristics of the power circuits required for forcing a DC current through the electrode that establishes the electric arc at the outlet of the nozzle of a torch for plasma cutting a metal object and those of the power circuits required for forcing a DC current through the welding electrode of an electrical arc welder are antithetical and this has so far obliged to have distinct apparatuses specifically designed for the two functions with evident overall aggravation of their costs, encumbrance and weight and, when at the site of intervention, also of the time necessary for readying for use one of the other of the two apparatuses, according to needs.

Vis-a-vis this state of the art, the applicant has now found a way of effectively and efficiently overcoming such aggravations, inconveniences and drawbacks by providing for an outstandingly improved transportability, reduced overall costs of these apparatuses and an enhanced practicalness in using one of the other apparatus as may be dictated by often unpredictable needs during the intervention at the job site.

These important results are attained by integrating the two distinct functions of electric arc welder and of plasma cutter of metal objects by an arc-generated plasma in a single work machine more easily transportable and wherein numerous functional parts and/or relative power components and electronic circuitry of selection and control of the two functions are "shared", such to function when the apparatus is set and utilized as an electric welder as well as when the apparatus is set and utilized as a plasma cutter, thus greatly reducing costs, encumbrance and weight of such a bi-functional work machine as a whole.

Basically, the transportable work machine having the double function of electric welder and of plasma cutter of metal objects of the present invention comprises:

a shared electronic control system of the apparatus for functioning as arc welder or as a torch cutter with arc-generated plasma;

either two distinct transformers or a single transformer with double secondary and/or primary windings and two distinct secondary rectifying stages for electrically powering through distinct electric terminals a pair of arc welding pincers and an arc generated plasma torch, respectively;

a shared powering circuit connectable to the AC mains, including a main switch, an EMC filter, a switching power supply circuit for said electronic control system, a sensing circuit of the AC mains voltage generating a signal that is applied to a first signal input of a core circuit of said electronic control system, a shared primary rectifying stage and leveling capacitors of the rectified DC voltage, a shared full wave primary inverter and a routing circuit of the AC voltage produced by said primary inverter to a respective primary winding of said distinct secondary transformers or single transformer;

a first shared sensor of the current flowing on output lines of one and of the other of said secondary rectifying stages, respectively, generating a feedback signal applied to a second signal input of said core circuit of the electronic control system;

a second sensor of the current flowing on a ground line connected to a metallic body of the plasma torch, for signaling the lighting of a pilot arc between said inner spark electrode and said metallic body of the torch to said core circuit of the electronic control system.

Supply of compress air or compressed inert gas to the outlet nozzle of the plasma torch may take place through a coupling and an external hose connecting the coupling to an outlet of a distribution piping of compressed air or other inert gas or of an external air compressor. Alternatively, the apparatus may optionally comprise an on-board compressor or a pressurized bottle capable of ensuring a certain autonomy and be replaceable upon exhaustion.

Preferably, the bi-functional work machine of the present invention further includes:

a chassis or frame suitable to accommodate and hold operative parts and components for one and/or the other of the two selectable functions of the apparatus;

a lower shell containing said chassis and having a cooling air intake with dust filter, a cooling fan and an air outlet with protection grid;

a tray fastened onto said lower shell and having a raised perimeter wall for defining a space capable of accommodating a power cable with relative plug, insulated electric wires and relative arc welder pliers, a plasma torch and relative hose for feeding compressed gas to the torch nozzle and insulated electric wires for connecting the inner spark electrode and the metallic body of the torch, respectively, and a control panel in said perimeter wall of the tray;

a cover fastened onto the rim of said perimeter wall of the tray when transporting or storing the work machine;

electrical cable means of inner electrical connection of said arc welder pliers and said arc generated plasma torch trough the bottom of said tray to respective electrical connection terminals of parts and components held in said chassis and at least a coupling trough the bottom of said tray for connecting said plasma torch nozzle to a source of compressed gas.

The invention and particularly effective embodiments thereof are defined in the annexed claims.

Figure 1 is a block diagram of the electrical circuit of the transportable work machine of the present invention with double function of arc welder and of arc generated plasma torch for cutting metal objects.

Figure 2 illustrates an embodiment of the electrical circuit of the bi-functional machine of this invention in relation to the functional blocks M to T of the diagram of Figure 1.

Figure 3 illustrates possible embodiments of the electrical circuits relative to the blocks C, D and E of the diagram of Figure 1.

Figure 4 is a simplified exploded view of a first embodiment of the apparatus of the present invention.

Figure 5 is a simplified rendering of parts of the exploded view of Figure 4.

Figure 6 illustrates how the cover of the apparatus may be alternatively equipped with glass panes, to be used as a welding mask, or with a tub coverable by a sliding panel for orderly carrying an inventory of substitute plasma torch nozzles.

In the block diagram of Figure 1 are identified by shadings of different tonalities the shared blocks that function when the apparatus is used as an arc welder as well as when the apparatus is used as an arc generated plasma cutter; the blocks specific for functioning as arc welder, and the blocks specific for functioning as arc generated plasma cutter, according to the legend.

In the sample embodiment illustrated in the figure, the bi-functional apparatus has shared devices or parts such as the main power switch A and the EMC filter block B, the presence of which is dictated by rules that limits injection of disturbances on the mains to which the apparatus is connected, such as the high frequency noise that is generated by rectifiers directly connected to the AC mains, and which normally consists of a low pass filter of appropriate characteristics.

The AC voltage source may be monophase or three-phase, typically at 230V or 400V. The main switch A may be of mechanical type (e.g. turnable on and off) or of static analog type (e.g. an integrated switch).

The bi-functional apparatus of the present invention employs a shared unified electronic control system, a core circuit block E of which regulates the electric output parameters for the welding electrode pliers or for the arc generating inner spark electrode of the plasma torch, depending on the selection of one or of the other function, using for these purposes feedback information produced by the same block R which is also substantially shared. The core circuit block E besides generating indications and eventual luminous and/or acoustical alarms, actuates the appropriate configuration of the electrical power stages depending on the operator's selection of the function of the bi-functional apparatus.

A common control panel D provides the command interface for turning on the machine, selecting and eventually setting the working parameters of the selected function and hosts the indicators and eventual luminous and/or acoustical alarm means. The control panel D communicates with the core circuit block E for the necessary interaction with the operator.

The core circuit E may be realized on a printed circuit card with traditional (analog) logic or preferably with digital logic circuitry, employing in the latter case either a micro controller (μP) or a digital signal processor device (DSP), programmed for executing appropriate algorithms in function of the selection and settings and of internally generated monitoring and feedback signals and consequently generating configuration and control signals of the power circuitry of the apparatus.

The electronic control system is powered by a dedicated switching power supply C and optionally may be a circuit F for monitoring conditions of significant variation of the AC voltage on the mains to which the apparatus is connected, in order to permit to the core circuit E on the control system to automatically compensate within certain limits for significant variations of the mains voltage.

Other "shared" functional circuits are: a primary full bridge rectifying stage G of the AC mains voltage, related leveling capacitors H of the rectified primary DC voltage or equivalent "forward" or "pfc" stabilizers, and a primary inverter I, designed for outputting an AC voltage at a frequency that may be fixed or adjustable between about 15KHz and 200KHz, of a value that may also be adjustable, for example between about 200 V and 260 V.

The primary inverter I may have any one of the known many switching mode topologies, such as for example of type "forward", "fly-back", "full-bridge", "half- bridge", "chopper", resonant or alike.

Connected in cascade of the shared primary inverter I there is a routing circuit M of the output of the primary inverter I towards one of the two distinct secondary rectifying stages P and Q for one and for the other, respectively, of the two selectable functions of the apparatus. The routing circuit M may be realized using either dynamic or static relays that ensure an adequate safety of operation in implementing the selection commanded through the core circuit E of the electronic control system of the apparatus.

The routing circuit M implements a "mutually exclusive" selection of one or of the other function of the bi-functional apparatus thus preventing a simultaneous activation of the pliers for arc welding and of the inner spark electrode of the plasma torch and a consequently excessive power absorption from the AC mains.

The two secondary rectifying stages P and Q may be as in the shown sample embodiment, distinct and separate from each other and respectively connected to secondary windings of two distinct transformers N and O of the high frequency AC voltage output by the primary inverter I. Of course, the two distinct transformers N and O may be combined in a single core transformer having two distinct primary windings that will be selected in a mutually exclusive manner by the routing circuit M, and two distinct secondary windings or even a single secondary winding. The two distinct secondary windings or the single secondary winding may be operatively connected to the input or either two distinct secondary rectifying stages or even to a single secondary rectifying stage that would be shared for the two functions of the apparatus, by replicating a second routing circuit toward the respective output terminals for the selected function.

Controlled current and/or voltage delivered or applied to the respective electrode during functioning of the apparatus as an arc welder or during the functioning of the apparatus as an arc generated plasma torch cutter, are monitored by dedicated feedback signal generating circuits contained in the shared block R which convey signals representative of the controlled output parameters to dedicated signal inputs of the core circuit E of the electronic control system.

The apparatus has distinct electrical connection terminals T and S to which are respectively connected the insulated cables for the arc welder pliers, one for holding a welding electrode and another for the metal object being welded, and for the inner spark electrode within the outlet nozzle of the plasma torch and for a metal body of the plasma torch for first establishing a pilot arc, and for establishing a return path of the electric current through the metal object being cut.

The functional devices and circuit blocks A, B, C, F, G, H and I of Figure 1 may be chosen or realized according to any known configuration as long as they are designed for the maximum power that can be absorbed by the apparatus connected to the AC mains and other design figures.

As will be evident to a skilled person, the topography of the relative circuits may be any one of the different topographies that are commonly used for the specific function and their circuital definition may be immediately prefigured having established the maximum power, the AC mains voltage and the AC voltage and frequency to be produced at the output of the shared primary inverter I.

Figure 2 shows a suitable circuit diagram of the bi-functional apparatus of the present invention, for the important part of the power circuitry that is connected in cascade to the output of the shared primary inverter I.

The common node of the two switches SWl and SW2 is connected to a respective output node of the shared primary inverter I and their state is determined by the pair of relays SWrI and SWr2, respectively controlled by the COMl and COM2 signals coming from the core circuit E of the electronic control system.

As may be observed from the notations and the connections to the primary windings of the two distinct transformers Tl and T2 (corresponding to the blocks N and O, respectively, of the basic diagram of Figure 1), the pair of switches SWl and SW2 (corresponding to the functional block M of the basic diagram of Figure 1) actuates the routing in a mutually exclusive mode of the AC voltage output by the shared primary inverter I, towards one or the other of the two transformers Tl and T2.

To the secondary windings of the two transformers Tl and T2 are connected two full-bridge rectifying stages P and Q that are designed, as their respective input transformers Tl and T2, for the specific voltage and current values of the selectable two distinct functions of arc welder and of arc-generated plasma torch cutter of the bi-functional work machine of this invention.

The rectified voltage output by either one or the other of the two rectifying stages P and Q is commonly leveled by a battery of leveling capacitors connected between the output lines of the rectified voltages and ground, according to common DC power supply topologies.

The electrical diagram of Figure 2 shows also an embodiment of the feedback signal generating means that is of a way information on the current delivered by the apparatus either during operation as an arc welder or during operation as a plasma torch cutter, is produced in for providing it through a dedicated feedback signal input (HPl) of a printed circuit card hosting most parts of the electronic control system.

Also this feed back signal generating circuit is shared and, in the depicted example, is realized by employing a Hall-effect probe that detects the current on one or on the other of the conductors that cross a sensible zone of the probe, in practice the return current conductor (i.e. through the electrical terminal 03) of the plasma torch and the conductor of connection of either the pliers that hold the welding electrode or the metal object being welded (i.e. through the electrical terminals 04 or 05, depending on the specific arc welding technique that is implemented).

The circuit of Figure 2 shows also a second sensor of what is referred to as "pilot arc", that is the arc that is initially established between the inner spark electrode and a surrounding metal body of the outlet nozzle of the ionized compressed gas (i.e. through the electrical terminals 01 and 02) which is commanded by the operator to light in air for thereafter bringing the metal body of the outlet nozzle of the torch in electrical contact with the metal surface of the object to be cut, through which the electrical circuit will preferentially close itself (i.e. through the electrical terminals 01 and 03) for maintaining the arc between the spark electrode of the torch and the metal object to be cut itself that is then directly impinged upon by the plasma generated by ionization of the compressed gas that is released in a jet through the nozzle of the torch.

The "pilot arc" sensor is generally imposed by the need of ensuring interruption of the pilot arc in air in case it lasts in excess of few seconds (generally for not longer than 4-8 seconds). The passage of current along such an auxiliary conduction path for lighting for a brief period of time a pilot arc practically ceases upon touching with a metal tongue of the torch the surface of the metal object to be cut. This avoids that the pilot arc be maintained for an undetermined time that would lead to a damage of the outlet nozzle of the torch.

The two sensors that generate current detection signals that are conveyed to the respective feedback signal inputs HPl and SENSEl of the core circuit E of the electronic control system, represent an embodiment of the functional block R of the basic diagram of Figure 1.

As may be observed in Figure 2, the electrical connection terminals of the plasma torch are three, namely: 01, 02 and 03, for the above mentioned reasons, while the electrical connection terminals of the arc welder pliers are two, namely 04 and 05, (for the pliers for holding a welding electrode and the pliers for connecting the metal object to be welded), being possible to invert the connection of the two pliers depending on the type of arc welding technique to be used (the connections depicted in Figure 2 being suitable for performing M.M.A. or T.I.G.).

In the sample embodiment depicted in Figure 3, on a printed circuit board is organized the majority of the distinct functional blocks of the basic diagram of Figure 1, singled out by rectangular boxes. A common switching power supply corresponding to the functional block C of the basic diagram of Figure 1, and a primary rectifying stage corresponding to the functional block G of the basic diagram of Figure 1, are directly connected to the AC mains through an EMC filter corresponding to the functional block B of the basic diagram of Figure 1 and the electrical connection terminal Ll-IN and L2-IN.

In Figure 3 may also be recognized the battery of leveling electrolytic capacitors of the output DC voltage of the primary rectifier corresponding to the functional block H of the basic diagram of Figure 1. The functional block F is implemented with a light emitting diode and a photocell for providing to the programmable micro controller μP (or alternatively a DSP device) information on the current level of the AC voltage on the mains to which the apparatus is connected.

The same printed circuit card hosts also the primary inverter, corresponding to the functional block I of the basic diagram of Figure 1. The integrated component PTl contains a driver circuit at a programmed frequency of the four power devices that form the output bridge of the primary inverter that generates the high frequency (15-200 KHz) AC voltage on the output electrical connection terminals TRl-IN and TR2-IN, and the core circuit of electronic control system, corresponding to the functional block E of the basic diagram of Figure 1 , The integrated device PRG serves for programming the μP (or alternatively a DSP).

The functional block D of function selection, setting of the desired power and of light indicators and alarms may be implemented in a traditional form of a control panel and connected to dedicated leads of the integrated μP (or DSP device) by flexible isolated wires or multi conductor cable extending from the rear of the control panel to the printed circuit card of the electronic control system.

The core circuit E has common over voltage protection of the signal input nodes HPl and SENSEl connected to the sensors of delivered current and common analog buffer stages for controlling, through the electrical connection terminals COMl, COM2 and COM, the control nodes of the relays SWrI and SWr2 that implement the selection of a specific function.

Figure 4 is a simplified exploded view of a sample embodiment of a bi-functional work machine of the present invention.

According to a preferred embodiment, the portable bi-functional work machine of the present invention has a bottom shell 1 having rest feet 2 and a plurality of channels 3 for accommodating common clasps for fastening together the shell 1 and a tray 4 having a raised perimeter wall and the tray to a top cover 5, and optionally even transportation slings.

Two openings on opposite side of the bottom shell 1 with respective gratings 6 and 7, the first of which incorporates a dust filter 6a, permits circulation of cooling air inside the shell 1.

In practice, all functional blocks of the basic diagram of Figure 1, with the exception of the control panel D that is mounted on an outer surface of the raised perimeter wall of the tray 4, the electrical transformers 8, 9 and 10, the finned heat sink 11 on which are mounted the power devices of the rectifying stages and of the inverters, the electrolytic capacitors 12 for levelling rectified DC voltages, the compressor 13 and one or two cooling fans 14 are all installed in a chassis or frame 15, that is closed at the two opposite ends by secondary anti-tampering gratings 16 and 17, respectively aligned with the outer gratings 6 and 7 that by contrast may be extracted from outside for cleaning and substitution of the dust filter 6a.

The tray 4 that closes at the top the bottom shell 1, over the perimeter edge of which is fastened by four common clasps (not shown in the Figure), a control panel 18 for manually turning on and off the machine, selecting the function and eventually setting the operating parameters, has common luminous indicators of state and of eventual alarm condition.

The perimeter walled tray 4 is instrumental to orderly accommodate thereon the various electrical cables 19, 21, 23 and flexible sleeve 25 with their relative terminations, namely the plug 20 for connecting to a mains socket, the welding electrode pliers 22, the plasma torch 26 and the pliers 24 for connecting the metal object to be welded or to be cut, that operatively connect to the AC power terminals Ll-IN, L2-IN and PE-IN and to the output terminals 01, 02, 03, 04 and 05 of the circuit diagram of Figures 2 and 3. This greatly facilitate an orderly transportation and storage of the bi-functional work machine, minimizing the operations required for readying the machine at the job site.

The flexible sleeve 25 terminating with the plasma torch 26 orderly envelopes a hose that supplies compressed gas to the outlet nozzle of the plasma torch and two insulated wires of connection of the arc generating inner spark electrode and of a surrounding metal body of the outlet nozzle of the torch for providing a DC current return path through the electrical terminal 02 of the circuit diagram of Figure 2, thus allowing the lighting of a pilot arc in air between the inner spark electrode and the surrounding metal body of the nozzle through which a jet of compressed air that is ionized by the electric arc is emitted.

Respective socket or terminals for the electrical connection of the various cables and coupling for connecting the hose may be organized through the bottom of the tray 4 and are internally connected to the respective electrical output terminals for one and for the other function alternatively selectable of the bi-functional apparatus by common insulated flexible cables and flexible hose.

Similarly, all the devices installed in the control panel 18, among which a main power switch of the machine, at least a selector of the function desired and eventually also optional selectors of parameters of regulation and operation of the apparatus and relative light indicators connect to respective electrical terminals that may for example be organized on a printed circuit card as depicted in Figure

3, through mono and/or multi-conductor flexible cables. All the interconnection elements between parts installed on the tray 4 and in control panel 18 and the parts contained in the bottom shell 1, including an eventual compressed gas hose 27 and air intake pipe 28 are flexible and/or have a length sufficient to permit to unfasten and lift off the tray 4 sufficiently for accessing the parts contained into the bottom shell 1.

In the depicted sample embodiment, delivery of compressed air to the plasma torch 26 takes place though a hose 27 connecting the outlet of an on-board air compressor 13 and a coupling (not visible) mounted across the bottom of the tray

4, to the outer part of which a similar hose connects the outlet nozzle of the plasma torch 26, hidden inside the flexible sleeve 25 together with the pair of insulated wires that electrically connect the spark electrode and the surrounding metal body of the nozzle of the torch.

The bi-functional work machine may also be provided with an ancillary hose coupling for permitting connection through an external hose to an external source of suitable compressed gas, for example an external compressor or a distribution pipe of compressed air or inert gas if available at the job site. Such an ancillary hose coupling which may be of quick-coupling type, may always substitute the function of the inner compressor 13 of the sample embodiment of transportable bi-functional work machine depicted in Figure 4. he on-board air compressor, though preferred, is not essential for the use of the transportable bi-functional machine of the present invention, being the function of such an optional inner compressor 13 be substitutable by a customized small size bottle of either air or other suitable inert compressed gas that can be installed in the chassis 15, in place of the compressor 13, capable of ensuring a certain autonomy of operation of the plasma torch that may vary from about one up to several tens of minutes and be eventually replaceable upon exhaustion.

Obviously, an eventual ancillary hose coupling for permitting to connect the portable machine to an external source of compressed gas or the eventual gas bottle hosted inside the transportable machine will need to have the conduit of compressed gas fed to the torch 26 intercepted by a solenoid valve controlled by the electronic control system of the apparatus and an eventual pressure reducer.

Compressed air or inert gas is fed to the torch nozzle at a pressure that may generally be comprised between about 25 and about 40 bar and at a flow rate generally comprised between about 20 and 40 litres/minute, depending on the rated power of the portable machine.

As schematically shown in the exploded view of Figure 4 wherein the presence of an inner compressor 13 is contemplated, the air intake of the compressor 13 may be organized through a rubber tube 28 through which external air is ducted to the intake port of the compressor 13, through a dust filter (not visible in the Figure) that may be mounted on the tray.

The intake tube 28 may be for example of flexible rubber tube. The electrical motor of the compressor 13 is powered through the cable 27e.

The rendering of Figure 5 permits to better observe the control panel 18 besides giving a clearer indication of the peculiar architecture of the bi-functional work machine of the present invention though, for simplifying the rendering, cables and pipes that connects the functional components and parts hosted in the bottom shell 1 to the components and parts mounted in the control panel 18 and to the cables, hoses and intake air dust filter accommodated on the tray 4 are not shown.

The transportable bi-functional work machine finally includes an upper cover 5 that may be coupled to and fastened over the perimeter edge of the raised perimeter wall of the tray 4 with ordinary clasps similar to those used for fastening the tray 4 onto the rim of the bottom shell 1, such to orderly accommodating in a confined space over the bottom of the tray 4 all the cables, flexible sleeve and respective terminations, thus making the machine outstandingly suited for transportation and storage.

According to a preferred embodiment, the upper cover 5 has a structure such to permit to adapt its secondary usefulness according to specific needs or preferences of the user. In fact, the cover 5, once unfastened from the tray, may be used as a welding mask or screen, being provided of an inner handle 31, that may be hingedly raised from a rest position where it is retained by a clip, and blocked in an operative position for permitting to safely hold the cover-mask as a any common welding mask.

For this purpose, the cover 5 has an opening or window in the first half of an area defined by rectangular frame 29 that has lateral guides in which a blinding panel 30 can slid from a position over the other blind half of the rectangular area to an extended position for covering the opening or window area. The frame 29 accommodates in the opening or window of its first half an inattinic glass pane 33 coupled to a similar pane of common transparent glass 32 for protecting the inattinic glass from scratches.

During transportation or storage of the machine, the pair of glass panels is protected from accidental impacts with external objects by the blinding panel 30 purposely slid over the pair of glass panes. Alternatively, the cover 5 instead of being so equipped to be usable as a welding mask may be differently equipped, by substituting the pair of glass panes with a tub 34, useful to contain a number of plasma torch nozzles, that is closed by the same sliding panel 30 of the frame 29. Thus the cover 5 may offer a different utility that may be preferred in case the primary contemplated use of the bi- functional transportable work machine of this invention be that of plasma cutter. In this case, the cover 5, equipped with the nozzle holding tub 34, provides a practical way of having a more immediate availability of plasma torch nozzles of different shapes and flow rate among which choosing the one more suited for the material to be cut.

Preferably, the bottom shell 1 , the outer gratings 6 and 7, the perimeter walled tray 4 and the cover 5 are all made by injection molding employing a suitable plastic material such as for example a polycarbonate, ABS or mixtures of the two resins.

Claims

C L A I M S

1. A transportable work machine with double function of arc welder and of plasma cutter of metal objects comprising

a shared electronic system (D, E, R) for selecting and controlling operation of the machine as electric arc welder or as plasma cutter with arc generated plasma;

two distinct electrical transformers (N, O) or a single core transformer with double primary and/or secondary windings and related secondary rectifying stages (P, Q) for electrically powering through distinct terminals (S, T), respectively a pair of arc welding pliers or arcing means of an arc generated plasma torch fed with compressed air or inert gas;

a shared powering circuit connectable to AC voltage mains, including a main switch (A), an EMC filter (B), a switching power supply (C) for said shared electronic system (D, E, R), a sensor (F) of the mains voltage generating a signal that is applied to an input of a core circuit (E) of said electronic control system, a shared primary rectifying stage (G) of the mains voltage and levelling capacitors (H) of the rectified DC voltage, a shared full wave primary inverter (I) and a routing circuit (M) of the AC voltage output by said primary inverter (I) towards the primary winding of one or the other of said electrical transformers (N, O);

a first shared sensor (Rl) of the current flowing on output lines respectively of one or the other of said secondary rectifying stages (P, Q), generating a feedback signal that is applied to a second input (HPl) of the core circuit (E) of said electronic control system;

a second sensor (R2) of the current flowing on an ancillary ground line connecting a metal body of an outlet nozzle of said plasma torch for signalling the lighting of a pilot arc between an inner spark electrode and the surrounding metallic body of the outlet nozzle of said plasma torch to the core circuit (E) of said electronic control system, through a third input (SENSEl).

2. The work machine according to claim 1, characterized in that said core circuit (E) of said shared electronic control system (D, E, R) comprises an integrated DSP device capable of executing pre-programmed algorithms upon selecting a certain function from a control panel (D) of the machine and in function of said signals applied thereto for generating configuration and control signals of power circuits of the machine.

3. The work machine according to claim 1, characterized in that said first shared sensor (Rl) is a Hall-effect sensor, through an active area of which pass the lines of the DC current delivered to arc welding or to plasma cutting implements by one or to other of said distinct secondary rectifying stages (P, Q).

4. The work machine according to claim 1, wherein said second sensor (R2) is a on-off sensor.

5. The work machine according to claim 1, characterized in that it comprises a compressor for a supplying compressed air to an outlet nozzle of said plasma torch for cutting a metal object with arc-generated plasma of ionized compressed air.

6. The work machine according to claim 1, characterized in that it comprises means for connecting to an external source of compressed air or other inert gas for supplying it to an outlet nozzle of said plasma torch for cutting a metal object with arc-generated plasma of the supplied compressed gas.

7. The work machine according to claim 1, characterized in that it comprises a compressed gas bottle and at least a solenoid valve for supplying compressed gas to an outlet nozzle of said plasma torch for cutting a metal object with arc-generated plasma of ionized compressed air.

8. The work machine according to claim 1, characterized in that it further comprises a chassis (15) accommodating functional parts and components for both selectable functions;

a lower shell (1) containing said chassis (15) having a cooling air intake provided with a grating (6) and a dust filter (6a) and at least a cooling fan (14) associated to an air outlet grating (7);

a tray (4) having a raised perimeter wall on an external surface of which is installed a control panel (18), the tray closing at the top said lower shell (1) to which is releasably fastened, and suited to accommodate electrical cable extensions (19, 21, 23) respectively terminating with a plug (20) of connection to a mains socket, first welding electrode pliers (22), second electrical connecting pliers (24) of the metal object to be welded or cut, a flexible sleeve (25) enveloping a supply hose of compressed gas and two insulated electrical wires for biasing at a certain DC voltage an inner spark electrode and a metal body of said outlet nozzle of the plasma torch (26);

a cover (5) releasably fastened to the perimeter wall of said tray (4) during transportation and storage of the machine.

9. The work machine according to claim 8, characterized in that said cover (5) has an opening or window in the first half of an area defined by a rectangular frame (29) having guides for a blinding panel (30) to slide from a position over the other blind half of said rectangular area to a position over said opening or window for blinding it;

an inattinic glass pane and a protective transparent glass pane mounted in said opening or window for using the cover (5) as a welding mask or a nozzle holding tub mounted in said opening or window in lieu of said pair of glass panes for carrying substitute nozzles of different configuration for said plasma torch (26).

10. The machine according to claim 9, wherein said cover (5) has a handle (31) and means for blocking it in an operative raised position on the inner side of said cover and at least a clip for keeping the handle (31) in a abated non operative position.

11. The machine according to claim 8, wherein said lower shell (1), said gratings (6, 7), said perimeter walled tray (4) and said cover (5) are of molded plastic material belonging to the group composed by polycarbonate, ABS and mixtures thereof.