FR2803978A1 - PLASMA TORCH WITH HEAD, ELECTRODE OR TIPE IDENTIFICATION SYSTEM - Google Patents

Abstract

The invention relates to an electric arc work torch, in particular a plasma torch, comprising a torch body (3) comprising means for supplying electric current and at least one fluid passage; a torch head (2) comprising electrode holder means capable of receiving an electrode and nozzle holder means capable of receiving a nozzle. The torch optionally includes assembly and disassembly means making it possible to associate and / or dissociate the torch head (2) from the torch body (3). According to the invention, the torch head (2), the electrode and / or the nozzle or any other consumable part are equipped with an identification element (5) from which a signal of specific value can be extracted or determined. and identifiable, for example a voltage or current value.

Description

-1 The present invention relates to an arc work torch

  electric, in particular a plasma torch, in particular a torch with a removable head, lo said torch being provided with a recognition and identification system of

  the torch head or wearing parts equipping said torch head.

  There are currently two families of plasma torches, namely, on the one hand, "blown plasma" torches used in marking, projection of surface coating, heating (in the blast furnace), and the like and, on the other hand apart, the "transferred plasma" torches used in welding, cutting

and the like.

  In the field of automatic plasma cutting, that is to say when the plasma torch is arranged on a cutting machine, two types of torches can be used, namely monobloc type torches or

  torches in two parts, that is to say with removable nose or head.

  A monoblock torch usually includes a torch assembly

  complete with its bundle of cables and various pipes.

  More specifically, such an assembly conventionally comprises a holder

  electrode, acting as cathode, associated via an insulating material with a nozzle holder acting as an anode and carrying an ejection nozzle

of the plasma arc.

  The electrode holder and the nozzle holder are connected, via cables

  electric, to one or more electric current generators.

  During their operation, the electrode holder and the nozzle holder need to be cooled to prevent their deterioration too quickly and to do this, they are connected, via pipes, to a source of cooling fluid, generally from the water. The set of cables and pipes

  feeding the torch is called a beam.

  In addition, the torch has active parts, namely in particular a dip tube bringing the coolant as close as possible to their active end thereof; an electrode formed of a particular material, that is to say an emissive insert of tungsten, zirconium, hafnium or the like, chosen as a function, for example, of the gas used, of the intensity of the current or of the 'thickness to be cut; a specific gas diffuser according to the gas used or the current intensity range; a nozzle specific to each gas and intensity; an outer protective cap forming a sleeve around

  io of the nozzle and also serving as a cooling chamber; and a room-

  nut used to hold the cap and the nozzle in place on the active end of the torch; this nut-piece can be replaced by a device with

  water vortex or by a gaseous "double flow" device.

  The architecture and operation of such one-piece type torches are described in particular in the following documents: EP-A-144267, EP-A-

  410875, EP-A-772957, EP-A-902606, EP-A-810052, EP-A-845929, EP-A-

  790756, EP-A-196612, WO-A-89/11941, US-A-4,521,666, US-A-4,059,743,

US-A-4,163,891 and US-A-5,591,357.

  Furthermore, a torch in two parts, also called a torch with a head or a demountable nose, generally comprises a torch body or base comprising the bundle of cables and fluid lines (cooling water and gas), as explained above. , and being able, in addition, to receive one or more different torch heads, the torch head

  comprising the active parts of the torch, namely the electrode, the nozzle ...

  The architecture and operation of such torches with heads or noses

  removable are described in particular in the following documents: EP-A-

  599709, EP-A-872300, EP-A-801882 and EP-A-941018.

  In the case of a torch with a removable head or nose, a torch head is generally dedicated to a particular process and / or to a range of intensity

limited.

  In other words, each torch head is equipped with active parts having variable characteristics and which are a function of the process to be implemented or the current intensity supplying the torch and serving to generate

the plasma arc.

  Thus, the process to be implemented can vary and must be chosen according to the nature of the gas or gas mixture to be used, the type of

  gas distribution (single distribution, vortex, double flow, post-

  water injection ....), depending on the nature of the material to be cut (steel, stainless steel, aluminum, ...), depending on its thickness, depending on the suitability of the

  cut piece to be welded or other requirements.

  Conventionally, the main gases or gas mixtures usable in plasma cutting are nitrogen, oxygen, compressed air or mixtures

  argon / hydrogen or nitrogen / hydrogen.

  Furthermore, it is known that a current intensity must be chosen which is a function of the thickness of the material to be cut; thus, the thicker the material

  the higher the intensity to be implemented.

  However, it is also necessary to take into account the type of cut desired: cut of

  high quality or simple separation cut.

  Usually, the intensity range used can range from ten to

more than a thousand amps.

  From there, there are therefore many types of parts of different wear and

  therefore torches adapted to the different intensities that can be adopted.

  In the case of a monoblock torch, the presence of the torch, i.e.

  say its operation, can be detected using a direct link between two pins at a harness connector and this, via a simple

  electrical assembly detecting the presence of the connection.

  However, each monoblock torch being dedicated to an eVtou cutting process at an intensity range, when the operator or cutter wishes to cut first a first material, for example a sheet of stainless steel 70 mm thick, then a second material, for example a 3 o aluminum sheet 5 mm thick, it must: - either change the torch used during the cutting of the first material and replace it with a torch suitable for cutting the second material, which requires uncoupling the harness from the current generator, dismantling the harness on the machine, removing the torch from its support or dismantling the torch and its support, before proceeding in reverse to install the new torch on the support; - either disassemble all the parts of the active part of the torch (electrode, nozzle ...) after cutting the first material and replace them with

  active parts suitable for cutting the second material.

  It is easy to understand that, in one case as in the other, these 1o operations are impractical, generate a significant loss of time

  and can lead to assembly errors.

  To remedy these problems, a nose torch or

  removable and interchangeable head.

  Thus, the operator can prepare the second removable head with the appropriate active parts which he will need to cut the second material, while the other torch head is in use, that is to say

  while cutting the first material.

  Then it will only take a few seconds to change the torch head and cut the second material since, in this case, the torch body fixed to the machine or to the support frame remains the same and therefore does not

not to be disassembled.

  However, a problem arises with torches with removable heads, namely that there are a large number of potential combinations of torch bodies and torch heads, which are all possible sources of errors.

for the operator.

  In other words, the operator must not be able to give inappropriate intensity adjustment instructions with the selected head, or else risk damaging the torch head or obtaining

poor quality cutting.

  For example, if active parts (electrodes, nozzles, etc.) provided for

  withstand a current of 30 A are used with a current of 300 A, these

  these will be destroyed by fusion and this will generally result in

  at least part of the torch body.

  Furthermore, the same applies to the fluids used.

  For example, a tungsten electrode designed to operate under nitrogen will not work for long if the gas is oxygen or another oxidizing gas. Such unexpected destruction of the torch elements generates significant costs in time and / or money which are unacceptable from the

industrial point of view.

  In order to solve this problem, the simplest solution would be to put

  a color mark or marking on each torch head.

  However, this solution is not ideal because, with time and soiling due to the fumes, there can be confusion between different torch heads since the paint or ink can fade, sufficiently strong lighting is necessary to being able to visually distinguish a color or a marking, engraved marks can become dirty and become illegible .... Another solution would be to use a photoelectric sensor

  for detecting the presence of the torch head on the torch body.

  However, here again the solution is not ideal, since the information that can be collected is then of binary type, i.e. 0 or 1, which does not

  not allow to differentiate different torch heads from each other.

  Furthermore, quite similar problems arise when it comes to being able to recognize a specific wearing part, such as an electrode or a nozzle, having been mounted on the head of a plasma torch, whatever is

  separable or not from the torch body.

  Indeed, a similar problem arises with wearing parts for electric arc torches, namely that there are a large number of types of nozzles and electrodes each having their own characteristics and variable 3 o according to the process to implement, for example, as mentioned above, an electrode with a tungsten insert intended to operate under nitrogen will not work for a long time if the gas used during cutting is oxygen or another oxidizing gas and such unexpected destruction of these wearing parts generate significant costs in

  time and / or money which are unacceptable from an industrial point of view.

  Again, the great diversity of existing wearing parts creates

  many potential errors for the operator.

  From there, the operator must not be able to give unsuitable intensity adjustment instructions with the wear part selected, at the risk of causing deterioration of the wear part or of the head.

  1o torch, and thus obtain a poor quality cut.

  The object of the present invention is therefore to solve the above-mentioned problem arising with electric arc work torches, in particular with a removable head, in particular plasma torches, equipped with a system making it possible to avoid or minimize any error in mounting the torch head on the torch body or incorrect or inappropriate choice of wear parts fitted to the torch head, warning the operator that the torch head or the wear part fitted by mistake does not correspond to

  selected operating conditions to be obtained.

  In other words, the object of the invention is to propose a torch equipped with a system making it possible to verify that the torch head and / or the wearing parts present on the torch are compatible with the selected process.

  and with the current intensity range to be used.

  The solution of the present invention is then an electric arc work torch, in particular a plasma torch, comprising: - a torch body comprising means for supplying electric current and at least one fluid passage, - a torch head comprising electrode holder means capable of receiving an electrode and nozzle holder means capable of receiving a nozzle, and 3 o - assembly / disassembly means making it possible to associate and / or dissociate the torch head of the torch body, characterized in that the torch head further comprises an identification element from which a value signal can be extracted or determined

  specific prefixed and identifiable.

  In addition, the invention also relates to an electric arc work torch, in particular a plasma torch, comprising a torch body comprising means for supplying electric current and at least one

  fluid passage, and a torch head comprising means

  electrode capable of receiving an electrode and nozzle-carrying means capable of receiving a nozzle, characterized in that the electrode carried

  o10 by the electrode holder means and / or the nozzle carried by the holder means

  nozzle includes (s) an identification element from which it can be extracted

  or determined a signal of specific value prefixed and identifiable.

  According to yet another aspect, the invention also relates to an electric arc work torch, in particular a plasma torch, comprising a torch body comprising means for supplying electric current and at least one passage for fluid, and a torch head, the torch head and / or the torch body comprising consumable part-holder means capable of receiving at least one consumable part chosen from the nozzles, the electrodes, the cartridge and nozzle-electrode combination assemblies, dip tubes and gas or water diffusers, characterized in that at least one of said consumable parts includes an identification element from which a value signal can be extracted or determined

  specific prefixed and identifiable.

  In the context of the present invention, the term "signal" is considered to be synonymous with the term "information"; therefore, we will use

  either of these terms.

  Depending on the case, the torch of the invention may include one or more of the following characteristics: - the torch body comprises signal transmission means making it possible to route the signal coming from the identification element through to the at least part of said torch body and preferably up to

a signal processing unit.

  - the identification element is chosen from resistors, capacitors, diodes (such as signal diodes or Zener diodes), coils, reflecting pads, systems using the principle of infrared or radio frequency remote controls, "smart card" elements and magnetic or magnetic elements, or combinations of several of these elements, for example an RLC assembly combining resistance, coil and capacitor, preferably the identification element is

chosen from the resistors.

  the signal of specific value is at least one signal of intensity, voltage, capacity, frequency, light wavelength, infrared

  or radio, preferably an intensity or voltage signal.

  The signal processing unit is connected to a command director, preferably the command director controls at least one current source, at least one source of fluid and / or means for moving the torch along at least one X, Y and / or Z axis. According to another aspect, the invention also relates to a plasma torch head comprising electrode-holder means capable of receiving an electrode and nozzle-holder means capable of receiving a nozzle, characterized in what it includes, in addition, an identification element from which a specific value signal can be extracted or determined

prefixed and identifiable.

  Depending on the case, the plasma torch head of the invention may include one or more of the following characteristics: - the identification element is chosen from resistors, capacitors, diodes, coils, reflective pads , systems using the principle of infrared or radio frequency remote controls, magnetic or magnetized elements, smart card elements and their combinations, preferably the identification element is chosen

among the resistances.

  According to yet another aspect, the invention relates to a method for controlling an electric arc work torch, in particular a plasma torch, comprising a torch head according to the invention fixed on a torch body, wherein one proceeds according to the steps of: (a) determining and / or extracting a signal of specific value prefixed from said identification element; (b) processing said specific value signal determined or extracted in step (a) by comparing the value of said signal with at least one reference or reference value; (c) control of the supply of torch with electric current and at

  lo at least one fluid according to the result of the comparison carried out in step (b).

  Depending on the case, the method of the invention may include one or more of the following characteristics - the signal of specific value is at least one signal of intensity, voltage, capacity, magnetic, frequency, length light, infrared or radio wave, preferably an intensity or voltage signal. the control of the supply of the torch with electric current and with fluid comprises at least one of the following steps: (i) allowing the supply of the torch with electric current and with fluid so as to start a working operation at l arc, when the comparison carried out in step (b) shows that the value of the specific signal determined is equal to or close to the reference or reference value; and (ii) prohibit the supply of electric power and fluid to the torch so as to prevent the start of an arc work operation, when the comparison carried out in step (b) shows that the value of the specific signal

  determined is different from the reference or setpoint value.

  The invention also relates to a nozzle or an electrode for an electric arc work torch, in particular a plasma torch, comprising a

  identification element as mentioned above.

  The invention also relates to a plasma cutting process of at least one metal part, in which a plasma torch is used, a plasma torch head and / or in which a control method is implemented.

  according to the invention for controlling a plasma torch.

  In other words, the solution provided by the present invention is essentially based on the incorporation in the torch head of an identification system which can immediately and effectively signal to the operator that the torch head in place does not is not compatible with the selected process and / or with the current intensity and / or with another operating parameter. The invention will now be described in more detail using the figures

  lo appended given by way of illustration but not limitation.

  Figure 1 is a block diagram of an operating torch

  removable head according to the present invention.

  The plasma torch 1, quite similar to that described for example in document EP-A-599709 incorporated herein by reference, comprises a torch body or base 3, on which the torch head 2 fitted with the identification system according to the invention. The torch 1 is supplied with fluids from fluid sources 100, in particular plasma gas and cooling water, and is also supplied with electric current from a current generator 110 connected, on the one hand, to the part to cut 120 and else

  2 o share, at the electrode of torch 1 and the nozzle.

  The identification system of the invention consists of an identification element 5 and signal transmission means 4 connecting this element 5

  identification to a signal processing unit 6 which communicates

  even with a torch control director 8 making it possible in particular to control or not to move the torch 1 along the axis Z. The identification element 5 included in the head 2 of the torch 1 is, for example, a resistor, a capacitor or a coil having a determined value known for each nose or head 2 of the torch. It is also possible to envisage other types of identification elements 5 such as in particular a 3o reflecting patch, a system using the principle of infrared or radio frequency remote controls, or even a chip card element or a l1

  magnetic or magnetic element, or combinations thereof.

  By smart card element is meant the active part of the card,

  ie the integrated circuit or "chip" encapsulated in the plastic serving as a support. There are several different types that can be envisaged, for example a first type with an apparent connector such as that of bank or similar payment cards which have two operating modes, namely the reading of the magnetic strip located on one of the faces of the card and / or writing information stored in the memory; a second type such as that of access badges possibly with remote reading system, 1o for example by radio link; in this case, an antenna is associated with the chip used for the power supply and for the transfer of digital information. Since the identification element 5 can take different values, it is possible to thus differentiate a large number of different torch heads 2 from each other, since each torch head 2 is provided with an element 5 identification with a specific value prefixed and identifiable. This identification element 5 is connected to a signal processing unit 6 making it possible to warn the operator if he has made a wrong choice, to check the presence of the necessary fluids, to detect the presence of the torch head 2 adapted to the process to be implemented and thus authorize or not the start of the cutting process. The signal processing unit 6 is managed by a command director 8 whose role is to supervise all the

  components necessary for the smooth running of the cutting operation.

  2 5 Signal processing is ensured by measuring, for example, either: - a current or a voltage if a resistor supplied respectively by a fixed voltage or current source, - a capacity if a capacitor is used, - a frequency if a coil is used, - a light wavelength if a reflector is used, - an infrared or radio receiver, and

  - from another device such as a smart card reader.

  The measurement is then processed, for example, using a converter

  analog / digital of the type appropriate to the signal.

  The management software of the command director 8 can warn the operator, in the event of an error in the choice of torch head 2, as shown schematically

  on the flowcharts of Figures 2 and 3.

  For example, if the operator wants to cut a part in a 4 mm thick carbon steel sheet, he consults a scale or a correspondence table provided by the manufacturer who tells him to use the process

  lo under dry oxygen at 60 A, as well as the type of active parts to use.

  The operator therefore equips a second torch head with these while cutting, for example, a 10 mm thick stainless steel sheet with a 120 A process using nitrogen and a vortex of water and using a first torch head having characteristics

different.

  Once the workpiece is finished, it replaces the first torch head with the second torch head, program 60 A and modifies the cutting speed as specified on the scale before starting the execution program. In the event of a wrong choice of head or a program not suited to the chosen torch head, the operator will be immediately notified by the system

identification of the invention.

  Preferably, use is preferably made, as an identification system mounted on the torch with removable head, of an element 5 of the resistive type (resistance, etc.) since such an element is simple to implement, little

  expensive, reliable and not very sensitive to parasites from an industrial environment.

  Example of differentiation with 12 combinations.

  Using a constant current source of 20 mA and desiring a discrimination of 1V to avoid confusion, the resistance values will be between 50 and 600 Q with a step of 50 Q to measure respectively a voltage from 1 to 12 V with a step of 1 V; the power of

  the resistance being 1/4 of Watt.

  According to Ohm's law U = RI, the current being constant, the voltage is directly a function of the value of the resistance. It then suffices to assign in a correspondence table, opposite each voltage value, an intensity limit and a process which by

  therefore requires fluids (gas, water vortex, double flow, etc.).

  Table I below shows an example of possibilities.

Table I

IDENTIFICATION CODING

  Intensity Resistance Voltage Cutting intensity Process (in mA) (in Q) (in V) (in A) (gas) 50 1 <90 Ar / H2

100 2 <90 02

150 3 <90 N2

200 4 <90 N2 + VE

250 5 <90 02 + DF

  300 6 90 Ar / H2 + DF 350 7 from 120 to 150 Ar / H2 400 8 from 120 to 150 02 450 9 from 120 to 150 N2 500 10 from 120 to 150 N2 + VE 550 11 from 120 to 150 02 + DF 600 12 from 120 to 150 Ar / H2 + DF VE: "vortex" of water - DF: double flow As detailed in figure 6, the electrical connections of the identification element can be ensured at the level of the head 2 of torch by a socket 15 of male jack type 3.5 mm in diameter and, as shown in FIG. 7, in the base 3 by a socket 16 of female jack type, which allows the torch head 2 to be easily coupled to the base 3 by a simple movement from bottom to top; the rotational position is already imposed by the other connections (plasma gas, nozzle connection, actuator controls, ...). As shown in Figure 1, two electrical conductors are sufficient

  to connect the base 2 to the processing unit as part of the bundle.

  However, in other cases, a single electrical conductor may suffice,

  others more than two drivers will be required.

  o10 Figures 4 and 5 represent, for their part, possible industrial versions of torch heads 2 according to the invention shown, respectively, devoid of active parts and / or wearing parts (fig. 4) and equipped with such wearing parts (fig. 5), in particular a nozzle 22 and an electrode 20 these torch heads 2 can be mounted on the base 3 of FIG. 7.

  The torch head 2 includes electrode holder means 10 capable of receiving, for example by screwing, an electrode 20 provided with an emissive insert 21, and nozzle holder means 12 capable of receiving and maintaining, for example also by screwing, the nozzle 22 pierced with an orifice

  axial 23 of the plasma jet ejection.

  Assembly / disassembly means, comprising a ball cage 18 and an axially movable external part 19 cooperating with said ball cage 18, as explained in EP-A-599709, make it possible to associate and / or

  easily and quickly dissociate the torch head 2 from the torch body 3.

  According to the invention, the identification element 5 is carried by the torch head 2 and is, in this case, a resistor from which can be extracted or determined a signal of specific value prefixed and identifiable, namely a

intensity or voltage signal.

  Although the embodiments above relate only to an identification system for the torch head of a plasma torch with a removable 3o head, this identification system is applicable strictly speaking to the identification of wearing parts or consumable parts for an electric arc torch, such as nozzles, electrodes, a "cartridge" assembly

  comprising a nozzle and an electrode as described in the document EPA-

  326445, the dip tube or the gas diffuser for a torch or the additional devices capable of equipping an arc torch, such as a device for creating a water vortex, such as a water diffuser, or dual system flow with a second nozzle situated downstream from the first nozzle, since all these devices each include a body and one or more removable parts and it is therefore necessary to identify the presence for each device

  global and each of the active parts.

Claims (16)

Claims   1. Torch (1) for working with an electric arc, in particular a plasma torch, comprising: - a torch body (3) comprising means for supplying electric current and at least one fluid passage, a head (2) torch comprising electrode holder means (10) capable of receiving an electrode (20) and nozzle holder means (12) 1o capable of receiving a nozzle (22), and - assembly / disassembly means for associating and / or dissociating the torch head (2) from the torch body (3), characterized in that the torch head (2) further comprises an identification element (5) from which can be extracted or determined a   signal of specific value prefixed and identifiable.   2. Torch (1) for working with an electric arc, in particular a plasma torch, comprising a torch body (3) comprising means for supplying electric current and at least one fluid passage, and a head ( 2) torch, the torch head (2) and / or the torch body (3) comprising consumable workpiece carrier means capable of receiving at least one consumable part chosen from the nozzles (22), the electrodes (20) , the cartridge assemblies combining nozzle and electrode, the dip tubes and the gas or water diffusers, characterized in that at least one of said consumable parts comprises an identification element (5) from which can be extracted or determined a signal of specific value prefixed and identifiable. 3. Torch (1) for working with an electric arc, in particular a plasma torch, comprising a torch body (3) comprising means for supplying electric current and at least one fluid passage, and a head ( 2) torch comprising electrode holder means (10) capable of receiving an electrode (20) and nozzle holder means (12) capable of receiving a nozzle (22), characterized in that the electrode (20) carried by the   electrode holder means (10) and / or the nozzle (22) carried by the holder means   nozzle (12) has an identification element (5) from which can be   extract or determine a signal of specific value prefixed and identifiable.   4. Torch according to one of claims 1 to 3, characterized in that the   torch body (3) comprises signal transmission means (4) for routing the signal coming from the identification element (5) through at least a part of said torch body (3) and, preferably , until   a signal processing unit (6).   5. Torch according to one of claims 1 to 4, characterized in that the identification element (5) is chosen from resistors, capacitors, coils, diodes, reflecting pads, systems using the principle infrared or radio frequency remote controls, smart card elements, magnetic or magnetic elements, and combinations of several of these elements, preferably   the identification element (5) is chosen from among the resistors.   6. Torch according to one of claims 1 to 5, characterized in that the signal of specific value is at least one signal of intensity, voltage, capacity, frequency, light wavelength, infrared or radio , or   magnetic, preferably an intensity or voltage signal.   7. Torch according to one of claims 1 to 6, characterized in that the signal processing unit (6) is connected to a command director (8), preferably the command director (8) pilot at least a current source (110), at least one fluid source (100) and / or means for moving the torch (1) along at least one axis X, Y and / or Z. 8. Torch according to claim 1, characterized in that it comprises assembly / disassembly means making it possible to associate and / or   dissociate the torch head (2) from the torch body (3).   9. Head (2) of plasma torch comprising electrode holder means (10) capable of receiving an electrode (20) and nozzle holder means (12) capable of receiving a nozzle (12), characterized in that it further comprises an identification element (5) from which can be   extract or determine a signal of specific value prefixed and identifiable.   10. torch head (2) according to claim 9, characterized in that the identification element (5) is chosen from resistors, diodes, capacitors, coils, reflective pads, systems using the principle infrared or radio frequency remote controls, magnetic or magnetized elements, smart card elements, and combinations thereof, preferably the identification element (5) is chosen from the resistors. 11. Nozzle (22) for electric arc work torch (1), in particular a plasma torch, comprising an identification element (5) from which a signal of specific value prefixed can be extracted or determined and identifiable, preferably the identification element (5) is chosen from resistors, diodes, capacitors, coils, reflective pads, systems using the principle of infrared or radio frequency remote controls, magnetic or magnetized elements , the   smart card elements, and combinations thereof.   12. Electrode (20) for torch (1) for working with an electric arc, in particular a plasma torch, comprising an identification element (5) from which a signal of specific value can be extracted or determined and identifiable, preferably the identification element (5) is chosen from resistors, diodes, capacitors, coils, reflective pads, systems using the principle of infrared or radio frequency remote controls, magnetic or magnetized elements , the   smart card elements, and combinations thereof.   13. Method for controlling a torch (1) for working with an electric arc, in particular a plasma torch, comprising a torch (1) according to one of   Claims 1 to 3, in which the following steps are carried out:   (a) determining and / or extracting a signal of specific value prefixed from said identification element (5); (b) processing said specific value signal determined or extracted in step (a) by comparing the value of said signal with at least one reference or reference value; (c) control of the supply of the torch (1) with electric current and at least one fluid as a function of the result of the comparison carried out in step (b). 14. Control method according to claim 13, characterized in that the signal of specific value is at least one signal of intensity, voltage, capacity, frequency, magnetic, light wavelength, infrared or radio, preferably an intensity signal or o tension.   15. Control method according to one of claims 13 or 14,   characterized in that the control of the supply of the torch (1) with electric current and of fluid comprises at least one of the following steps: (i) allowing the supply of the torch (1) with electric current and of so as to start an arc work operation, when the comparison carried out in step (b) shows that the value of the specific signal determined is equal to or close to the reference or reference value; and (ii) prohibit the supply of torch (1) with electric current and fluid so as to prevent the start of an arc work operation, when the comparison carried out in step (b) shows that the signal value   specific value is different from the reference or set value.   16. Plasma cutting process for at least one metal part, in   which is used a plasma torch according to one of claims 1 to 3 and / or   in which one implements a control method according to one of   Claims 13 to 15 for piloting a plasma torch.