Patent Publication Number: US-7902484-B2

Title: Method and apparatus for remotely controlling a welding system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a divisional and claims priority of U.S. patent application Ser. No. 10/904,172 filed Oct. 27, 2004, the disclosure of which is incorporated herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to welding machines and, more particularly, to a method and apparatus for remotely controlling operation of a power source of a welding-type system through the transmission of control signals across a weld cable. 
     MIG welding, formerly known as Gas Metal Arc Welding (GMAW), combines the techniques and advantages of TIG welding&#39;s inert gas shielding with a continuous, consumable wire electrode. An electrical arc is created between the continuous, consumable wire electrode and a workpiece. As such, the consumable wire functions as the electrode in the weld circuit as well as the source of filler metal. MIG welding is a relatively simple process that allows an operator to concentrate on arc control. MIG welding may be used to weld most commercial metals and alloys including steel, aluminum, and stainless steel. Moreover, the travel speed and the deposition rates in MIG welding may be much higher than those typically associated with either Gas Tungsten Arc Welding (TIG) or Shielded Metal Arc Welding (stick) thereby making MIG welding a more efficient welding process. Additionally, by continuously feeding the consumable wire to the weld, electrode changing is minimized and as such, weld effects caused by interruptions in the welding process are reduced. The MIG welding process also produces very little or no slag, the arc and weld pool are clearly visible during welding, and post-weld clean-up is typically minimized. Another advantage of MIG welding is that it can be done in most positions which can be an asset for manufacturing and repair work where vertical or overhead welding may be required. 
     A wire feeder is operationally connected to the power source and is designed to deliver consumable wire to a weld. To further enhance the operability of the wire feeder of a MIG welding system, known welding systems have connected the power source and the wire feeder to one another across a dedicated control cable that is in addition to a dedicated weld cable such that control signals defining the operational parameters of the power source are transmitted or fed back from the wire feeder to the power source, generally referred to as remote control. 
     One type of remote control device is used to regulate the operational welding parameters, and switch the welding power source output ON and OFF as well as change the power source mode via a pendant that connects to the power source by a multi-conductor cable. The solution is schematically illustrated in  FIG. 1A . A wire feeder  2 A is connected to a power source  4 A by a control cable  6 A that includes a 14-pin connector. The cable  6 A used to transmit operational information to, and in some cases, from the power source may incorporate 2 to 14 conductors depending on how many functions are to be controlled. Separately connected between the power source  4 A and wire feeder  2 A is a high voltage weld cable  8 A that delivers welding power to the wire feeder and creates a voltage potential between an electrode and a workpiece. 
     A significant drawback to this control cable-based scheme is that the control cable is typically fragile relative to the welding cables designed to carry high currents at high voltages. Welding machines are commonly used at construction sites or shipyards where it is not uncommon for the welding machines to be periodically relocated or surrounded by other mobile heavy equipment operating in the same area. As such, the remote control cable can become damaged by being crushed or snagged from contact with surrounding machines and/or traffic. This can cause damage to the wire feeder and/or the welding power source if internal power conductors become shorted to signal leads that are connected to sensitive signal level circuitry. 
     Referring now to  FIG. 1B , another remote controlled system includes a radio transmitter type remote control. This approach has several disadvantages. First, electric arc welding can create radio frequency interference that negatively affects the communication between a transceiver  9 A of the wire feeder  2 B and the transceiver  9 B of the power source  4 B. Second, if the system is used inside metal structures such as tanks, ships, or large aircraft, the radio link can be lost due to the shielding effect of the metallic surroundings. Third, if multiple welding stations use a radio link for remote control, each control loop would require a separate security code to prevent cross-talk or mis-transmission of control signals to the wrong welding machine. 
     Another remote control solution is described in U.S. Ser. No. 10/604,482, which is assigned to the Assignee of the present application. Notwithstanding the numerous advancements achieved with the invention of the aforementioned pending application, such a system relies upon pulse width modulation to remotely transmit operational data from a wire feeder to a power source across a weld cable. By using pulse width modulated signals to remotely control operation of a power source, the amount of data as well as variability in the types of data that could be transmitted between the wire feeder and a power source is limited when compared to that which may be achieved with serialized or encoded communications. Further, with the system described in the aforementioned pending application, the wire feeder is constructed without a contactor and thus requires an internal DC power supply to power the electronics of the wire feeder. That is, the invention of the above-referenced application teaches the avoidance of an open circuit voltage (OCV) between the wire feeder and power source. As a result, absent a DC power supply, the wire feeder cannot be minimally powered so as to communicate with the power source to initiate the welding process. 
     It is therefore desirable to design a remote controlled welding machine that receives command signals from a wire feeder across a weld cable to control or otherwise regulate operation of a power source. It would also be desirable to design a remote controlled welding system having with a battery-less wire feeder whereupon electronics of the wire feeder are powered in a conventional manner, but the OCV between the wire feeder and power source is used as the backbone of a communications link between the wire feeder and power source for the transmission of control commands. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention provides a system and method of remotely controlling operation of a welding machine via control commands transmitted across a weld cable connecting the welding machine to a peripheral, such as a wire feeder, that overcomes the aforementioned drawbacks. 
     A remote control uses a weld cable as a communication link to transfer control information to a welding power source. The information to be communicated to the power source includes welding power source output command information (amperage/voltage control), welding circuit on/off information (power source output contactor control), power source mode control (constant voltage/constant current), and the like. The control information may be transmitted in a serial communication and/or encoded using frequency and or voltage decoding. The control information may be transmitted during dedicated transmission intervals or as an offset to an OCV between the power source and wire feeder. 
     Therefore, in accordance with one aspect, the present invention includes a welding system having a battery-less wire feeder designed to feed consumable material to a weld and a power source designed to provide a welding power and having a power output connected to the battery-less wire feeder via a weld cable. The welding system includes a controller to periodically disable the power output and receive power source control commands from the battery-less wire feeder across the weld cable when the power output is disabled. 
     In accordance with another aspect, a MIG welder is disclosed and includes a wire feeder designed to deliver consumable welding wire to a weld. A power source is connected to the wire feeder via a weld cable. The weld cable is designed to carry an OCV thereacross during standby operation of the wire feeder. The MIG welder includes a communications link between the wire feeder and the power source extending across the weld cable. The communications link is designed to translate control commands between the power source and wire feeder manifested in a voltage offset from the OCV. 
     According to yet another aspect, the present invention includes a method of remotely controlling a welding process. The method includes the steps of periodically disabling an output of a power source designed to provide welding power to a weld and receiving control commands from a wire feeder remote from the power source when the output of the power source is disabled. The method further includes the step of, following reception of the control commands, re-enabling the output of the power source to provide power to the weld at a level consistent with that embodied in the control commands. 
     Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention. 
       In the drawings: 
         FIGS. 1A-1B  are schematic block diagrams illustrating examples of known remotely controlled welding and wire feeder systems. 
         FIG. 2  is a pictorial view of a welding system in accordance with one aspect of the present invention. 
         FIG. 3  is a schematic of the welding system illustrated in  FIG. 2 . 
         FIG. 4  is a flow chart setting forth the steps of remotely controlling a power source in accordance with one aspect of the present invention. 
         FIG. 5  is an exemplary circuit schematic for providing an OCV offset according to another aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be described with respect to regulation of a power source and a wire feeder of a MIG welding system based on feedback provided from a transceiver remote from the power source to a receiver incorporated within the power source. However, the present invention is equivalently applicable with power sources of TIG, stick, flux cored, and the like welding systems. Moreover, the present invention is also applicable with non-welding, high power systems such as plasma cutters and induction heaters. 
     Referring to  FIGS. 2 and 3 , a MIG welding system  10  includes a welding power source  12  designed to supply power to a wire feeder  14  through a weld cable  16 . The power source is designed to run in one of a number of modes including constant voltage (CV) and constant current (CC). Also connected to the power source is a secondary work weld cable  18  that connects the power source to a clamp  20  designed to receive cable  18  to workpiece  22 . Also connected to wire feeder  14  is a welding gun or torch  24  configured to supply consumable welding wire to a weld. Welding system  10  may further include a gas cylinder  26  connected to wire feeder  14  such that shielding gas can be provided through gas hose  28  for the MIG welding process. 
     Power source  12  is designed to condition raw power supplied from a utility line or engine driven power supply and output power usable by the welding process. As such, power source  12  includes one or more transformer assemblies or power conditioner  29  to condition the raw power into a usable form for welding. The output of the power source is generally controlled by a controller  38  and associated operational circuitry that regulates the secondary or output side of the power conditioning components  29 . As such, the power source may provide a welding output when the secondary power circuit  39  and the contactor  41  or other power switching device is closed to a conductive state. As will be described in greater detail below, switch device  39  may be regulated such that a secondary or welding power output is periodically not provided to wire feeder  14  across weld cable  16  during non-welding intervals. In this regard, the typically otherwise present OCV between the power source and wire feeder is temporarily lost. During these moments of disablement of the power source output, transceiver  36  will await control commands across weld cable  16  which then operates as the backbone of a communication link between the wire feeder and the power source. 
     Torch  24  is equipped with a pushbutton trigger  30  that when depressed causes contactor  41  of the wire feeder to close and make a welding voltage available to the torch. As shown in  FIGS. 2 and 3 , a separate control cord connecting the wire feeder and power source to one another is avoided. 
     The incorporation of a transceiver within wire feeder  14  that communicates with a transceiver in power source  12  directly through weld cable  16  eliminates the need for a separate control/power cable. The control cable adds to the complexity, weight, and overall cost of the welding system. Additionally, as previously noted, the control cord is typically less durable than the welding cables and, as such, is prone to nicks and snags typically associated with industrial locations. 
     This invention includes a pair of transceivers  36 ,  32 : one in the power source  12  and one in the wire feeder  14 . In this regard, bi-directional communication is supported between the wire feeder and the power source. It is contemplated, however, that the wire feeder may be equipped with a transmitter and the power source with a receiver to support uni-directional communication between the two components. The transceiver in the wire feeder is designed to transmit serialized and modulated packets of feedback or commands to a transceiver  36  in the power source  12  across the weld cable  16 . 
     The signal includes information regarding desired operational parameters of the wire feeder  14  and instructs the transceiver  36  of the power source  12  to set the magnitude of the output of the welding power source (volts or amperes), the mode of the welding power source (CC or CV), and wire feed speed among other parameters. The transceiver  32  is also configured to transmit commands regarding JOG and PURGE functions. That is, when the JOG button is pushed on the wire feeder  14 , the transmit automatically repeats the minimum reference command each time the open circuit voltage of the welding power source falls to zero. In accordance with known wire feeder construction, the operator may select operational parameters on a user panel of the wire feeder. In a further embodiment, the user panel may be integrated with the electrode holder or torch  24  to allow user control of the welding process without leaving the weld. 
     Referring again to  FIG. 3 , the welding system  10  is designed to provide serialized and/or encoded communication between the wire feeder  14  and power source  12 . In this regard, controller  34  of wire feeder  14  also includes an encoder  40 , serializing circuitry  42 , and modulator  43 . Serializing circuitry  42  is designed to serialize communications between the wire feeder and the power source based on user input to a user panel  44  and for feedback provided from the weld. Encoder  40  is designed to encode the serialized transmission for improved and more efficient transmission to the power source  12 . Modulator  43  is designed to modulate the serialized data before transmission. A number of transmission techniques is envisioned including, but not limited to spread spectrum and psuedo-random sequenced using amplitude and/or phase-shifting. Spread spectrum technology is a method of communication that is typically implemented to secure communications and/or to overcome narrow-band constraints of a transmission line, i.e. a weld-cable. It is also contemplated that voltage and frequency level encoding may be used. 
     As described above, user panel  44  is designed to receive discrete inputs from an operator that collectively define operation of a welding process. As wire feeder  14  supports digitized control of the welding process, the operator is able to input, with a certain degree of specificity, exact operating parameters via user panel  44 . However, as welding system  10  is a remotely controlled system, controller  34  of wire feeder  14  receives the user inputs whereupon those inputs are fed to serializing circuit  42  to arrange the user input data into a serialized communication that supports streamlined transmission of the control commands across weld cable  16 . 
     Power source  12  also includes a decoder  46  and demodulator  47  that are matched with the encoder  40  of the wire feeder so as to demodulate and decipher the encoded signal received from transceiver  32  across weld cable  16 . Based on the deciphered commands, controller  38  will regulate operation of power source  12  in accordance with the user inputs to the wire feeder  14 . In a further embodiment, each transmission includes a checksum that allows decoder  46  to verify the accuracy of the transmitted data based on the particular encoding used. 
     Referring now to  FIG. 4 , a flow chart is shown setting forth steps of remotely controlling a welding-type power source according to one embodiment of the present invention. Preferably, the power source controller  38  carries out the steps of process  48  through the execution of one or more programs stored on a readable storage medium (not shown) in the power source. Process  48  begins at  50  with powering up at  52  of the power source to provide an OCV between the power source and the wire feeder across the weld cable. This OCV is provided in a conventional manner. Specifically, the power conditioning components, i.e. transformer, of the power source receives a raw power input from either a utility source or an engine-driven generator and conditions that power input into a form usable by a welding-type process. The OCV will be maintained between the wire feeder and the power source across the weld cable and used to power the electronics of the wire feeder when the wire feeder is in a standby mode. In a conventional manner, when the contactor or other switch mechanism in the wire feeder is closed, the voltage across the weld cable will be available at the welding torch or gun for creation of an arc between an electrode, i.e. consumable wire, and the workpiece. When this welding circuit is formed, the wire feeder as well as the power source preferably operate consistent with the parameters identified by the operator and transmitted from the wire feeder remotely to the power source. In this regard, process  48  is preferably executed prior to the commencement of a welding-type process and also re-executed during non-welding intervals. 
     That is, when the OCV is available across the weld cable at  52 , the controller  38  will periodically disable the output of the power source at  58 . It should be noted that, in a preferred embodiment, the power output is only disabled when a welding process is not actively being carried out at  54 ,  56 . In this regard, the controller will determine that the contactor in the wire feeder has closed the welding circuit when the OCV is lost. While the power source output is disabled, the controller will query the receiver for control commands transmitted across the weld cable. That is, if the operator indirectly opens the contactor in the wire feeder to open the welding circuit, and the OCV between the wire feeder and power source is re-established, the controller of the power source will briefly disable the power source output  58  and await control commands  60  across the weld cable during this period of disablement. It is noted that the OCV will be briefly lost between the wire feeder and power source when the power source output is disabled. As such, any signal detected across the weld cable when the power source output is disabled will include control data from the wire feeder to the remote power source, and vice versa. 
     If control commands are received  60 ,  62  across the weld cable, the controller processes the control data and adjusts  64  operation of the power source accordingly. On the other hand, if control data is not received  60 ,  66  during the brief disablement of the power source output, the controller will cause re-enablement  68  of the power source output, which will cause re-establishment of the OCV at  52  between the wire feeder and power source. The re-establishment of the OCV at  52  will be maintained across the weld cable for delivery to the weld upon closure of the contactor in the wire feeder and triggering of the welding gun or torch. In this regard, upon commencement of a welding-type process  54 ,  70 , the controller will enter a standby mode with respect to the reception of remote control commands and wait for a non-welding interval at  72 . During the non-welding interval  72 , the OCV will be re-established at  52  and the controller will re-execute steps  58 - 68  as described above following a re-verification that welding has not re-commenced at  54 ,  56 . As such, during re-establishment of the OCV, the power source will be periodically disabled and during these periods of disablement, the transceiver will, if transmitted from the wire feeder, receive remote control commands to be processed and implemented by the controller in regulating operation of the power source. 
       FIG. 4  has been described with respect to the transmission of control commands from the wire feeder to the power source across the weld cable during non-welding intervals. It is also contemplated, however, that control commands may also be transmitted across the weld cable from the power source to the wire feeder during these non-welding intervals. In this regard, the present invention supports bi-directional communication between the power source and wire feeder. It is contemplated, however, that the advantages of the present invention may also be achieved with a uni-directional system. 
     Referring now to  FIG. 5 , an exemplary circuit schematic illustrating another embodiment of the present invention is shown. Circuit  74  provides a general topology for providing an offset voltage to the OCV otherwise present between the power source and the wire feeder during non-welding intervals. In contrast to the periodic disabling of the power source output to receive control data, the circuit of  FIG. 5  is designed to provide an offset to the OCV whereby the voltage offset is used to convey control data between the remote wire feeder and the power source. While a particular exemplary circuit will be described, it is recognized that other circuit topologies apart from that specifically illustrated in  FIG. 5  may be used to provide a voltage offset for the transmission of control or operational data. 
     As shown in  FIG. 5 , the remote transmission of operational and/or control data in accordance with the present invention includes a transmission circuit  76  and a reception circuit  78  connected to one another across weld cable. The transmission circuit  76  resides in the wire feeder  14 ,  FIG. 3 , whereas the reception circuit  78 ,  FIG. 5 , resides in the power source  12 . In the transmission circuit  76 , a transmitter  80  is designed to provide a transient signal encoded and/or modulated with operational control data to be transmitted to the controller of the power source. The transient signal has a voltage sufficient to overcome diode D 2  such that the voltage at node  82  exceeds the OCV. In this regard, a DC with transient voltage signal is input to linear operational amplifier  84  across weld cable  16 ,  FIG. 3 , schematically represented in lead line  86 ,  FIG. 5 . The DC portion of input  82  is then filtered out using a capacitive element C 3  such that the input to operational amplifier  84  is limited to the transient signal. The operational amplified  84  then provides a single output  85  that is the difference between the pair of inputs to the operational amplifier. Specifically, the output is equal to the transient voltage input to the linear op-amp. As such, for example, if transmitter  80  provides a transient signal of seven volts coupled with a DC voltage of 80 volts, then the output provided by the operational amplifier will have a voltage of seven volts. The data embodied in this seven volts signal may then be processed by the controller to adjust the operating parameters of the power source consistent with those parameters input at the wire feeder. 
     One skilled in the art will fully appreciate that the resistive values selected for R 4 , R 5 , R 6 , and R 7  are relatively arbitrary, but are preferably selected such that a unity gain factor is present at the output  85 . Additionally, when the transmitter  80  is not applying providing a transient voltage, the OCV, which is DC, is seen across the weld cable, but filtered out by capacitive elements C 2  and C 3 . As such, a negligible output is provided at  85 . Further, during these intervals when the transmitter is not providing a transient voltage, the OCV is used to charge one or more capacitors or other energy storage devices (not shown) in the wire feeder, generally referenced at C_bulk. In this regard, the OCV is used to power the electronics of the wire feeder. 
     While the present invention has been described with respect to a battery-less wire feeder, it is contemplated that a DC energy source may be used to separately power the electronics of the wire feeder and thus avoid the need for a contactor in the wire feeder. In this regard, a contactor in the power source is used to control the presence of the OCV between the power source and the wire feeder. As such, the contactor in the power source may be closed to create a voltage potential between the welding torch and the power source. This OCV may be temporarily interrupted to receive control commands or used as a communications link between the power source and wire feeder as heretofore described. 
     Additionally, the present invention contemplates the incorporation of a state machine or other processing device to ignore, for a pre-set period, changes in current at initiation of welding. That is, absent such a state machine, the controller may interpret initial changes in current at welding start-up as an arc outage. As such, the present invention also is directed to the incorporation of a timed loop whereby initial changes in current are ignored for a fixed period of time after, i.e. 100 msec., after welding start-up. Such a system is in contrast to known systems that may be susceptible to false detection of arc outages. With these systems, the power source may try to power down to a non-welding state in response to a rapid change in current, notwithstanding that the operator has initiated a welding event. Accordingly, the controller in the power source is further configured to control the power source to enter a start-up state when the gun trigger is pressed, but not allow transition to an “arc end” state until the pre-set time has expired. 
     Therefore, the present invention includes a welding system. The welding system includes a battery-less wire feeder designed to feed consumable material to a weld and a power source designed to provide a welding power and having a power output connected to the battery-less wire feeder via a weld cable. The welding system includes a controller to periodically disable the power output and receive power source control commands from the battery-less wire feeder across the weld cable when the power output is disabled. 
     A MIG welder is disclosed and includes a wire feeder designed to deliver consumable welding wire to a weld. A power source is connected to the wire feeder via a weld cable. The weld cable is designed to carry an OCV thereacross during standby operation of the wire feeder. The MIG welder includes a communications link between the wire feeder and the power source extending across the weld cable. The communications link is designed to translate control commands between the power source and wire feeder manifested in a voltage offset from the OCV. 
     The invention also includes a method of remotely controlling a welding process. The method includes the steps of periodically disabling an output of a power source designed to provide welding power to a weld and receiving control commands from a wire feeder remote from the power source when the output of the power source is disabled. The method further includes the step of, following reception of the control commands, re-enabling the output of the power source to provide power to the weld at a level consistent with that embodied in the control commands. 
     As stated above, the present invention is also applicable with non-MIG welding systems such as TIG and stick welders. Further, the aforedescribed circuitry may be implemented to automatically adjust the output of a power source to compensate for losses that occur across weld cables. That is, in some manufacturing and/or industrial settings, the weld is a relatively great distance from the power source. As such, the weld cables may be dozens to over a hundred feet in length. This weld cable length results in losses from the output terminal of the power source to the weld. Simply, the voltage at the output terminals of the power source (where the weld cable is connected to the power source) may be significantly more than the voltage across the weld. Accordingly, the present invention may be used to transmit a voltage feedback signal at the weld to the power source whereupon a controller in the power source compares the voltage at the terminal to the voltage at the weld and adjusts the voltage at the terminal such that after the losses experienced across the weld cables, the voltage at the weld is at the level requested by the user. 
     As one skilled in the art will fully appreciate, the heretofore description of welding devices not only includes welders, but also includes any system that requires high power outputs, such as heating and cutting systems. Therefore, the present invention is equivalently applicable with any device requiring high power output, including welders, plasma cutters, induction heaters, aircraft ground power units, and the like. Reference to welding power, welding-type power, or welders generally, includes welding, cutting, heating power, or ground power for aircraft. Description of a welding apparatus illustrates just one embodiment in which the present invention may be implemented. The present invention is equivalently applicable with many high power systems, such as cutting and induction heating systems, aircraft ground power systems or any similar systems. 
     The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.