Arc start ancillary apparatus

Abstract: In an arc start ancillary apparatus, which is connected in parallel to a welding power source for supplying electric power necessary for arc discharge to between an electrode and a base metal, for supplying a pulse-form electric current in transferring from spark discharge to arc discharge, an object of the present invention is to solve a problem in that arc is not started, and to keep the effective value of current low. A capacitor (16) with a relatively high capacitance is connected to secure a current for transferring from spark discharge to arc discharge, and a D.C. high voltage of a high voltage generator (15) is applied according to a pulse in a period to which the period of pulse signals of a fixed period type high voltage controller (14) is set so that the effective value of the current between an electrode (9) and a base metal (8) is kept low.

Description: Field of the Invention The present invention relates to an arc start ancillary apparatus according to the preamble of claim 1. Such an arc start ancillary apparatus for an arc welding machine has been disclosed in Japanese Patent Application Laid-Open No. 8-215843. As shown.in FIG. 6, a conventional arc welding machine is made up of an arc start ancillary apparatus 19, a welding power source 10, a wire 6, a wire feeding motor 7, a base metal 8, and an electrode 9. This arc welding machine is configured so that welding current is supplied to between the electrode 9 and the base metal 8 by means of the low-voltage welding power source 10 on receipt of a welding start signal, and thereby the wire feeding motor 7 is driven to feed the wire 6 to a weld location, by which arc welding is performed. At the time of arc start, spark discharge is generated between the base metal 8 and the electrode 9 by applying a pulse-form D.C. high voltage, so that an insulating substance (for example, slug) at the tip end of the wire is destroyed by an electric shock of the generated spark discharge, or arc is induced by the creeping discharge on the insulating substance on the base metal 8. Thereby, the arc start performance is improved, and the safety is secured by restricting the effective value of current caused to flow at the time of discharge by the application of the pulse-form D.C. high voltage. The conventional arc start ancillary apparatus 19 is made up of a D.C. high-voltage power source 1 for generating spark discharge, a capacitive load 2 for checking whether discharge is generated between the electrode 9 and the base metal 8, a timer circuit 3 for turning on/off the D.C. high-voltage power source 1 with a fixed period, a switch 4, and a drooping resistor 5. The following operation is repeated: A D.C. high voltage is applied by the D.C. high-voltage power source 1 according to the input of a welding start signal, the current of spark discharge at the time when spark discharge is generated is detected by the capacitive load 2, the switch 4 of the D.C. high-voltage power source 1 is turned off according to the timer circuit 3, and the switch 4 of the D.C. high-voltage power source 1 is turned on again after an elapse of certain time. To make the D.C. high voltage of the D.C. high-voltage power source 1 pulse-form is an effective means for decreasing the effective value of current caused to flow by discharging. However, there arises a problem in that the current in transferring from spark discharge to arc discharge cannot sometimes be secured, so that arc is not started. Also, although the aforesaid current can sometimes be secured by the floating capacitance by a cable or the like, the aforesaid current cannot be secured depending on the laying condition of cable. Also, although the capacitive load 2 is provided in the conventional arc start ancillary apparatus 19, this capacitive load 2 serves to detect discharge, but is not intended to improve the arc start performance. Disclosure of the Invention An object of the present invention is to provide an arc start ancillary apparatus which improves the arc start performance for transferring from spark discharge to arc discharge, and keeps the effective value of current low by applying a pulse-form D.C. high voltage. This object is achieved by the features of claim 1. The arc start ancillary apparatus in accordance with the present invention is configured so that a capacitor with a relatively high capacitance is connected to secure a current for transferring from spark discharge to arc discharge, and a pulse-form D.C. high voltage is applied to keep the effective value of the current low. According to the present invention, the problem in that arc is not started is solved, and the effective value of current can be kept low by the improvement in arc start performance and the application of D.C. high voltage. The apparatus of the invention can improve the arc start performance by adding the discharge current of the capacitor to the output current of the high voltage generator. Also, when the effective value of current of D.C. high voltage exceeds the specified value at the effective current value detector, the effective value of current can be decreased by feeding back the change in pulse duty to the variable duty type high voltage controller so that the effective value of current does not exceed the specified value. More specifically, the apparatus is characterized in that when the capacitance of the capacitor is about 3 × 2.35 × 10 3 pF, the frequency of pulse signals is 1.5 Hz or near that value. As described above, according to the arc start ancillary apparatus in accordance with the present invention, the capacitor with a relatively high capacitance is connected, and the period of application and stoppage of D.C. high voltage is set by the controller. Thereby, sufficient electric charges are supplied when spark discharge is generated, so that the current for transferring to arc discharge can be supplied, and also the effective value of the current can be kept low and decreased to a safe value. Therefore, the problem in that arc is not started can be solved, and the arc start performance can be improved. Also, specifically, the period of application and stoppage of D.C. high voltage is made about 1.5 Hz by connecting the capacitor with a capacitance of 3 × 2.35 × 10 3 pF, by which sufficient electric charges are supplied when spark discharge is generated, so that the current for transferring to arc discharge can be supplied, the arc start performance can be improved, and the effective value of current can be kept low. Brief Description of the Drawings FIG. 1 is a schematic view of an illustrative consumable electrode type arc welding machine; FIG. 2 is a schematic view of an illustrative arc start ancillary apparatus; FIG. 3 is a schematic view of an arc start ancillary apparatus in accordance with the present invention; FIG. 4 is a characteristic diagram showing the relationship between capacitor capacitance and effective current value; FIG. 5 is a characteristic diagram showing the relationship between applied frequency and effective current value and FIG. 6 is a schematic view of a conventional arc welding machine. The arc start ancillary apparatus in accordance with the present invention will now be described with reference to illustrative examples and to a specific embodiment. (First example) An example in which the arc start ancillary apparatus is applied to a consumable electrode type arc welding machine is explained below. This illustrative example is not covered by the claims, because the controller described is not a variable duty type high voltage controller. As shown in FIG. 1, a consumable electrode type arc welding machine is so configured that welding current is supplied to between an electrode 9 and a base metal 8 by means of a low-voltage welding power source 10 on receipt of a welding start signal, and thereby a wire feeding motor 7 is driven to feed a wire 6 to a weld location, by which arc welding is performed. An arc start ancillary apparatus of the first embodiment of the present invention is, as shown in FIG. 1, made up of an arc detector 11, a disconnector 12, a high voltage generator 15, a capacitor 16, and a controller, for example, a fixed period type high voltage controller 14. In transferring from spark discharge to arc discharge at the time of arc start, the fixed period type high voltage controller 14 on receipt of a welding start signal generates pulse signals with a fixed period to the high voltage generator 15 via the disconnector 12. The high voltage generator 15 executes the generation and stoppage of D.C. high voltage with the period of the aforesaid pulse signals, so that a high voltage is supplied to between the electrode 9 and the base metal 8. By the capacitor 16 connected in parallel to the output of the high voltage generator 15, the current caused by the discharge of the capacitor 16 is added to the output current of the high voltage generator 15, by which the transfer from spark discharge to arc discharge is facilitated to improve the arc start performance. The addition of the current caused by the discharge of the capacitor 16 increases the effective value of current. For the change of the effective value of current with respect to the change in capacitor capacitance at the time of continuous application of D.C. high voltage, as can be seen in FIG. 4, the effective value of current increases with an increase in the capacitor capacitance. The data in this figure are those in the case where discharge is generated via a resistance estimated for a human body, 500Ω, in the condition that the cable length is 25 m, the spark gap is 0.5 mm, and the discharge atmosphere is air. For example, when the capacitor capacitance is 1 × 2.35 x 10 3 pF, the effective value of current is about 14.8 mA, and when the capacitor capacitance is 6 × 2.35 × 10 3 pF, the effective value of current is about 15.8 mA, increasing by about 1 mA. However, the effective value of current can be kept low by selecting the period of application and stoppage of D.C. high voltage of the fixed period type high voltage controller 14. For example, for the relationship between the applied frequency of D.C. high voltage and the effective value of current in the case where a capacitor capacitance of 3 x 2.35 × 10 3 pF is connected, as can be seen in FIG. 5, the effective value of current fluctuates with the change in the applied frequency of D.C. high voltage. The data in this figure, too, are those in the case where discharge is generated via a resistance estimated for a human body, 500Ω, in the condition that the cable length is 25 m, the spark gap is 0.5 mm, and the discharge atmosphere is air, and also in the condition of a high voltage application duty of 50%. The increase/decrease in the effective value of current depends on the applied frequency of D.C. high voltage and the times of discharge, and when the applied frequency and the times of discharge agree with each other, the effective value of current is the lowest. However, if the applied frequency of D.C. high voltage is too high, the voltage of spark discharge cannot be reached, so that an applied frequency of D.C. high voltage in the vicinity of 1.5 Hz is selected. The effective value of current-in the vicinity of the selected 1.5 Hz is about 8 mA, which meets the requirement of the IEC Standard and other standards. It is to be noted that when the welding current is detected by the arc detector 11, the pulse signals are cut off by the disconnector 12, so that the output is stopped. Also, the apparatus is configured so that D.C. high voltage is not applied to the low-voltage portion of the welding power source and the like by using a diode 13. Thus, the capacitor 16 with a relatively high capacitance is connected, and the period of application and stoppage of D.C. high voltage is set by the fixed period type high voltage controller 14. Thereby, sufficient electric charges are supplied when spark discharge is generated, so that the current for transferring to arc discharge can be supplied, and also the effective value of the current can be kept low. When a welding current is detected by the arc detector 11, the pulse signals are cut off by the disconnector 12, so that the output is stopped. Also, even when the capacitor has a capacitance other than about 3 × 2.35 × 10 3 pF in the first embodiment, the same effect can be achieved by setting the frequency of pulse signals which keep the effective value of current low. Also, although the case where the arc start ancillary apparatus is applied to the consumable electrode type arc welding machine has been explained in the first embodiment, the same effect can be achieved when the apparatus is applied to a non-consumable electrode type arc welding machine or some other welding machines. (Second example) The arc start ancillary apparatus is, as shown in FIG. 2, made up of a high voltage generator 15, a capacitor 16, and a controller, for example, a fixed period type high voltage controller 14. This illustrative example is not covered by the claims, because the controller described is not a variable duty type high voltage controller. The fixed period type high voltage controller 14 to which a welding start signal is input generates pulse signals with a fixed period to the high voltage generator 15. The high voltage generator 15 repeats the application and stoppage of D.C. high voltage according to the pulse signals. By the capacitor 16 connected in parallel to the output of the high voltage generator 15, the current caused by the discharge of the capacitor 16 is added to the output current of the high voltage generator 15. Thus, the capacitor 16 with a relatively high capacitance is connected, and the period of application and stoppage of D.C. high voltage is set by the fixed period type high voltage controller 14. Thereby, sufficient electric charges are supplied when spark discharge is generated, so that the current for transferring to arc discharge can be supplied, and also the effective value of the current can be kept low. Embodiment of the invention The arc start ancillary apparatus in accordance with the present invention is, as shown in FIG. 3, made up of a variable duty type high voltage controller 18, a high voltage generator 15, a capacitor 16, and an effective current value detector 17. The high voltage generator 15 repeats the application and stoppage of D.C. high voltage according to the pulse signals from the variable duty type high voltage controller 18. The capacitor 16 is connected in parallel to the output of the high voltage generator 15. Specifically, the capacitor 16 is connected to a point between the plus side of the output of the high voltage generator 15 and the effective current value detector 17 and the minus side of the output of the high voltage generator 15. The current value is maintained by storing electric charges by using the capacitor 16 in the application of D.C. high voltage and by supplying the electric charges in transferring from spark discharge to arc discharge. The effective current value detector 17, which is connected in series to the plus side of the output of the high voltage generator 15, detects the effective value of current of spark discharge when D.C. high voltage is applied, and outputs it to the variable duty type high voltage controller 18. The variable duty type high voltage controller 18 to which a welding start signal is input starts the output of pulse signals. When the effective value of current exceeds the specified value at the effective current value detector 17, the pulse duty is decreased, and the pulses are output so that the effective value of current does not exceed the specified value. Thus, the capacitor 16 with a relatively high capacitance is connected, and when the effective value of current exceeds the specified value at the effective current value detector 17, the pulse duty is decreased by the variable duty type high voltage controller 18, and the pulses are output so that the effective value of current does not exceed the specified value. Therefore, sufficient electric charges are supplied when spark discharge is generated, so that the current for transferring to arc discharge can be supplied, and also the effective value of the current can be kept low.

Claims: An arc start ancillary apparatus, which is connected in parallel to a welding power source (10) for supplying electric power necessary for arc discharge between an electrode (9) and a base metal (8), for supplying a pulse-form electric current in transferring from spark discharge to arc discharge, which comprises: a high voltage generator (15) for executing the generation and stoppage of a D.C. high voltage with the period of pulse signals; a capacitor (16) connected in parallel to the output of said high voltage generator (15); a controller (18) for generating said pulse signals; characterized in that an effective current value detector (17), which is connected in series to the plus side of the output of said high voltage generator (15), for detecting and outputting the effective value of a current supplied to said electrode in transferring from spark discharge to arch discharge; and a variable duty type high voltage controller (18) for changing the duty of said pulse and outputting pulse signals according to a welding start signal, wherein the effective current value outputted from the detector (17) is fed back to the variable duty type high voltage controller (18) which is arranged to change and set the pulse duty so that the effective value of the current between said electrode (9) and said base metal (8) is kept below a specified value. The arc start ancillary apparatus according to claim 1, wherein when the capacitance of the capacitor is about 3 x 2.35 x 10 3 pF, the frequency of pulse signals is 1.5 Hz or near that value. The arc start ancillary apparatus according to claim 1, comprising a disconnector (12) for cutting off and stopping pulse signals according to the welding current value of the effective current value detector (17).

Inventors: IHARA HIDEKI, INNAMI TETSU, WANG JING BO, IHARA, HIDEKI, INNAMI, TETSU, WANG, JING BO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1998
Main classification: B23K9
IPC codes: H02M9, B23K9