JPH08224672A - Device for detecting contact state of work in spot welding machine - Google Patents

Abstract

PURPOSE: To provide a device capable of automatically detecting a contact state between two works in the case of a spot welding. CONSTITUTION: A contact attaching plate 15 is provided at each circumference of electrode tips 3 so as to be elastically displaceable in the vertical-axial direction of a tip holder 2, and a pair of contact points 8, 9; 8a, 9a are attached to both contact attaching plates 15 to form a square with a vertical axis A as a center. A bridge circuit is structure for which a side to be measured on both sides is formed between points connecting one pair of contact points 8, 9 and the other pair of contact points 8a, 9a. The device is provided with an open state detector that detects the side to be measured is in an open state while a pair of contact points 8, 9; 8a, 9a are in contact with each other that belong to two sheets of work 5, 5a arranged between the electrode tips 3; an equilibrium state detector that detects the bridge circuit is in an equilibrium state; and a contact state discriminating means that produces welding OK signal when the open state detector fails to detect an open state and also when the equilibrium state detector detects an equilibrium state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a work contact state detection device for a spot welding machine for detecting the contact state of two works placed between electrode tips.

[0002]

2. Description of the Related Art In spot welding, when the electrode tip is pressed and welded with a gap between the workpieces, the workpieces in the spot-welded portion scatter and a normal nugget does not occur, or cracks occur. There is.

[0003]

SUMMARY OF THE INVENTION In view of the above, the present invention provides a work contact state detection device for a spot welding machine capable of automatically detecting the contact state between two works during spot welding. The purpose is to

[0004]

According to a first aspect of the present invention, in order to achieve this object, an electrode chip is fitted around each of the electrode chips fitted in the chip holders on opposite sides, rather than the electrode chips. A contact mounting plate is provided so as to be elastically displaceable in the longitudinal direction of the tip holder between the position projecting forward and the position retracting, and a pair of contacts are provided on both contact mounting plates so as to be located around the electrode tip. Along with mounting, these contact positions are positioned so as to form a rectangle centered on the vertical axis, and the measured point on both sides is between the connection point connecting one pair of contacts and the other pair of contacts. , A resistor is connected in series between the other pair of contacts to form proportional sides on both sides, and a power supply voltage is applied between the other pair of contacts to form a bridge circuit, which is arranged between the opposing electrode chips. Piece of With a pair of contacts belonging to each of the contacts being in contact with each other, the open state detection means for detecting that the measured sides on both sides are open and the voltage between the connection point and the series connection point of the resistor are detected. Accordingly, when the bridge circuit is in the balanced state, the balanced state detecting means and the open state detecting means do not detect the open state, and when the balanced state detecting means detects the balanced state, a welding OK signal is generated. A contact state determination means is provided.

According to the second aspect, one contact is attached to one of the contact attachment plates so as to be located around the electrode tip,
A pair of contacts are attached to the other contact mounting plate so as to be located around the electrode tip, and one contact position and a pair of contact positions are symmetric with respect to a line connecting the one contact and the vertical axis. It may be positioned so as to form an isosceles triangle, and a side between one contact and a pair of the other contacts may be measured sides on both sides.

[0006]

The function is to adjust the resistance for the proportional side in advance so that the bridge circuit is balanced in the state where the contacts on the belonging side are brought into contact with the two workpieces in perfect contact. In the welding operation, when the open state detecting means does not detect the open state in the state where the contacts of the belonging side are in contact with both sides of the work, and the equilibrium state detecting means detects the equilibrium state, the contact state determining means outputs a welding OK signal. . When the two workpieces are separated from each other, the open state detection means detects the open state and the welding OK signal is not output. If the resistance value ratio of the measured side deviates from the resistance ratio of the proportional side on both sides due to an abnormal contact state even if it is not open, the bridge circuit becomes unbalanced and the balanced state detection means becomes balanced. Cannot be detected, and similarly, a welding OK signal is not output.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A work contact state detecting device for a spot welding machine according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 shows, for example, spot welding guns on both sides which are attached to the tip of a robot arm of a spot welding machine and which face each other, and a tip holder 2 attached to the tips of gun arms 1 and 1a which face each other. Electrode tips 3 and 3a are fitted to the tip of 2a. These electrode tips are aligned with the vertical axis A of the tip holders 2 and 2a, and are driven to come into contact with and separate from each other by an air cylinder.

Around the respective electrode chips 3, 3a, contacts 8, 9 and 8 for contacting the two works 5, 5a are provided.
A contact device 10 equipped with a and 9a is attached. This device has a base 11 fixed to the gun arms 1 and 1a.
And a ring-shaped slider 13 which is slidably guided around the electrode chips 3 and 3a along the vertical axis A by the four guide poles 12 attached to this base, and this slider plate is biased forward. It is composed of a spring 14 and a contact attachment plate 15 attached to the slider 13 and having a hole 15a formed in the center thereof for inserting the electrode chips 3 and 3a therethrough. The contacts 8, 9 and 8a, 9a occupy positions projecting from the associated electrode tips 3 and 3a in the normal state, and can be retracted against the spring force.

As shown in FIG. 2, the contacts 8 and 9 occupy positions symmetrically spaced from each other around the electrode chip 3 on the contact mounting plate 15 with respect to the orthogonal line of the vertical axis A, and the other contact. 8a and 9a also occupy similar positions around the electrode tip 3 on the associated contact mounting plate 15, and these four contacts are positioned so as to form a rectangle centered on the vertical axis A. That is, the line connecting the contacts 8 and 9a and the line connecting the contacts 9 and 8a are equidistant from each other and intersect the vertical axis A passing through the centers of the electrode chips 3 and 3a.

The circuit device shown in the figure is connected to these contacts 8, 8a, 9, 9a. That is, the connection point connecting the pair of contacts 8 and 9 on the one hand and the pair of contacts 8 on the other hand.
A and 9a are the sides to be measured on both sides, and contacts 8a and 9a
The variable resistors RV1 and RV2 are connected in series between them to form proportional sides on both sides, and the AC power supply voltage S1 is applied between the pair of contacts 8a and 9a, so that the connection point between the contacts 8 and 9 and the variable resistors RV1 and RV2. A bridge circuit 20 is configured to detect the voltage between the serial connection points. Variable resistors RV1, RV2
The resistance value of is in a state in which the pair of contacts 8, 9 and 8a, 9a on the side belonging to the two workpieces 5, 5a in perfect contact arranged between the opposing electrode tips 3, 3a are in contact with each other. The bridge circuit 20 is preset so as to be balanced, corresponding to the resistance values R1 and R2 exhibited by the measured sides on both sides.

Further, the bridge circuit is provided with an open state detecting means 21 for detecting that both sides to be measured are in an open state, a voltage between a connection point of the contacts 8 and 9 and a series connection point of the variable resistors. By detecting, when the bridge circuit 20 is in the equilibrium state, the equilibrium state detection means 22 and the open state detection means 21 do not detect the open state, and the equilibrium state detection means 22 detects the equilibrium state. Contact state determination means 23 for generating a welding OK signal
And a notifying means 24 for notifying a contact abnormality by light or sound unless a welding OK signal is generated.

The open state detecting means 21 includes a work 5,
Since the resistance value R1 between the contacts 8 and 9a and the resistance value R2 between the contacts 9 and 8a both become infinite in a state where 5a are completely separated from each other, either one of the contact pairs, for example, the contacts 8 and 9a. Detects that no voltage is generated between them. The equilibrium state detection means 22 outputs an OK signal as the equilibrium state when the workpieces 5 and 5a are completely in contact with each other and the detected voltage is in a minute allowable range. The resistance values R1 and R2 are
In principle, when the workpieces 5 and 5a are in complete contact with each other, even if they are of the same type or of different thicknesses, they have the same resistance.
Or, they differ from each other because the work shapes are not symmetrical. In this state, the variable resistor RV1,
Fine-tune RV2. On the other hand, if there is a slight gap near the region where the electrode chips 3, 3a of the works 5, 5a are in pressure contact, the resistance values R1, R2 will change from the standard state even if they exhibit minute resistance, and these resistances Variable resistance RV
An unbalanced voltage is generated due to a deviation from the resistance ratio of 1 and RV2.

The operation of the work contact state detecting device thus constructed is as follows. In the spot welding operation, the pair of contacts 8, 9 and 8a, 9a belonging to the workpieces 5 and 5a, which are confirmed to be in perfect contact with each other, are brought into contact with each other, and the variable resistance RV1 for the proportional side is connected. ,
The RV2 is adjusted and set so that the bridge circuit 20 is balanced.

When the welding work is started, the electrode tips 3 and 3a are moved to both sides of the loaded works 5 and 5a by the robot arm, and the air cylinder is driven by a smaller air pressure than that at the time of welding, and the contacts 8 and 9 and 8a, 9a are brought into contact with the associated works 5, 5a. In this state, the circuit device is operated, and the open state detecting means 21 measures the voltage divided by the resistance values R1 and R2 to output an OK signal if the open state is not established, and the balanced state detecting means 22 then. If the detected voltage is near zero voltage within the allowable range, an OK signal is output. That is, as shown in FIG. 3, two work pieces 5,
Balanced state of the combined resistance of the resistances of the paths (shown by the solid lines) from the contact 9a to the contact 9 to the contact 5a and the resistances of the paths (shown by the dotted line) from the contact 8a to the contacts 8 and 9 Is detected.

The contact state determination means 23 outputs a welding OK signal when both OK signals are input, and the electrode tips 3, 3a are pressed against the workpieces 5, 5a by normal air pressure by the cylinder to perform welding work. Thereafter, the welding point is moved in order, and the welding operation is performed while detecting the same contact state.
The same applies when a new work 5, 5a is loaded.
When the open state detecting means 21 or the equilibrium state detecting means 22 does not output the OK signal when the circuit device is operating, the informing means 24 informs of the contact abnormality between the works 5 and 5a. When performing the welding work of the works 5 and 5a of different types, since the resistances in the symmetrical positional relationship are measured, the ratio may remain unchanged even if the absolute values of the resistance values R1 and R2 change. , The variable resistor R is usually used in order to be affected by the change of the peripheral work shape.
Finely adjust V1 and RV2 to reset to equilibrium.

FIG. 4 shows another embodiment in which the number of contacts is three. One contact 28 is attached to one of the contact mounting plates 15 so as to be located around the electrode tip 3, and a pair of contacts 28a and 29a are provided so as to be located around the electrode chip 3a on the other contact mounting plate 15. Is installed. The contacts 28a and 29a are positioned symmetrically with respect to the line connecting the contact 28 and the vertical axis A, and these three contacts form an isosceles triangle. In this case, 1
The contact 28 is replaced with a connection point that connects the pair of contacts 8 and 9 in the bridge circuit 20 of FIG. 2 to form a bridge circuit, and the measured sides on both sides are between the contact 28 and the contacts 28a and 29a. And Thereby, the electrode chips 3, 3
The contact state of the work region where a is pressed is monitored by detecting the deviation of the resistance ratio of the two sides of the aforementioned isosceles triangle from the standard state.

[0017]

According to the present invention, it is possible to automatically judge the quality of the contact state between two works during spot welding. By using a bridge circuit that positions the contacts on both sides of the work symmetrically with respect to the pressure contact position of the electrode tip and uses them as the measured sides on both sides, it is difficult to change the equilibrium condition even if the type of work is different, By finely adjusting the resistance on the proportional side, it is possible to accurately detect the contact state for various works with simple preliminary adjustment.

[Brief description of drawings]

FIG. 1 is a diagram showing a side view of essential parts of a work contact state detection device for a spot welding machine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a circuit device portion of the same device.

FIG. 3 is a diagram illustrating an operation principle of the device.

FIG. 4 is a schematic perspective view of a main part of a work contact state detection device according to another embodiment.

[Explanation of symbols]

 2, 2a Tip holder 3, 3a Electrode tip 5, 5a Work piece 8, 8a, 9, 9a, 28, 28a, 29a Contact point 15 Contact point attachment plate

Claims (2)

[Claims] 1. A contact, which is elastically displaceable in the longitudinal direction of the tip holder between positions retracted from positions projecting ahead of the electrode chip, around each of the electrode chips fitted to the opposite chip holders. A mounting plate is provided, and a pair of contacts are respectively mounted on both of the contact mounting plates so as to be located around the electrode tip,
These contact positions are positioned so as to form a square centered on the vertical axis, and one side between the connection point connecting the pair of contacts and the other pair of contacts is the measured side on both sides. , A resistor is connected in series between the other pair of contacts to form proportional sides on both sides,
A bridge circuit is configured by applying a power supply voltage between the other pair of contacts, and the pair of contacts belonging to two workpieces arranged between the opposing electrode chips are in contact with each other, The bridge circuit is in the equilibrium state by detecting the voltage between the open state detection means for detecting that the measured sides on both sides are in the open state and the series connection point of the connection point and the resistor. An equilibrium state detecting means for detecting a welding state and a contact state determining means for generating a welding OK signal when the open state detecting means does not detect the open state and the equilibrium state detecting means detects the equilibrium state. A work contact state detection device for a spot welding machine, which is characterized in that 2. A contact, which is elastically displaceable in the longitudinal direction of the tip holder, between each of the periphery of the electrode tip fitted to the tip holders on both sides facing each other and the position retracted from the position projecting ahead of the electrode tip. A mounting plate is provided, one contact mounting plate is mounted on one of the contact mounting plates so as to be located around the electrode chip, and one contact mounting plate is mounted on the other contact mounting plate around the electrode chip. While mounting a pair of contacts, the one contact position and the pair of contact positions are positioned so as to form an isosceles triangle symmetrical with respect to a line connecting the one contact and the vertical axis, Between the one contact and the other pair of contacts is a measured side on both sides, a resistor is connected in series between the pair of contacts to form a proportional side on both sides, and a power supply voltage is applied between the pair of contacts. By applying It is detected that the sides to be measured on both sides are in an open state in a state where the pair of contacts belonging to the two workpieces arranged between the opposing electrode chips are in contact with each other. Open state detecting means, a balanced state detecting means for detecting that the bridge circuit is in a balanced state by detecting a voltage between the one contact and the series connection point of the resistor, and the open state Work contact state for spot welding machine, characterized in that the detection means does not detect the open state, and the contact state determination means generates a welding OK signal when the equilibrium state detection means detects the equilibrium state. Detection device.