Control method of spot welder

Abstract

To provide a control method of a spot welder which can perform high speed dotting even with a small-sized motor while keeping required welding pressure.SOLUTION: A control method of a spot welder makes, when a spot welder performs spot weld at a plurality of dots and when a movable electrode is operated at a maximum rotational speed of a servo motor and at a shortest acceleration / deceleration time, the acceleration / deceleration time tv of the servo motor longer at the dots where execution torque per dot exceeds rating torque so that the execution torque is the rating torque or less.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for controlling a spot welding machine that performs spot welding while applying pressure to workpieces. [Background technology]

[0002] In the production process of automobiles, etc., spot welding is performed by resistance welding while applying pressure to the workpiece such as the body of the automobile with an electrode. As a spot welding machine, for example, a servo gun is known, which uses a servo motor as a driving source for a movable electrode, and converts the rotational motion of the servo motor into linear motion with a ball screw to move the movable electrode and apply pressure to the workpiece. There is a demand for such a servo gun to be compact and yet obtain a high pressurizing force. For example, if the lead of the ball screw is reduced to make the ball screw smaller and the reduction ratio is increased, a high pressurizing force can be obtained even with a small motor. In addition, Patent Document 1 describes a welding gun in which a large motor is required to generate high torque by increasing the lead when the lead of the ball screw is increased to make the hard ball diameter larger and the number of threads is increased to make it compatible with high loads (pressure), although a large motor is required to generate high torque by increasing the lead.

[0003] However, if the lead is made smaller or the reduction ratio is increased by adding a reducer, a high pressure force can be obtained, but the tradeoff is that the arm pressure speed (opening and closing speed) slows down, and the welding work time per welding point becomes longer. Also, to increase the speed, it is necessary to obtain torque to drive the lead that has been enlarged in order to lower the reduction ratio, which poses the problem that a large motor must be used to generate the pressure. For example, to generate a pressure force of 400 kgf and a pressure speed of 200 mm / s, the servo motor output must be 1500 W. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5437841 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above problems, and has an object to provide a method for controlling a spot welding machine that can perform high-speed welding while maintaining a required welding force even with a small motor. [Means for solving the problem]

[0006] The control method of a spot welding machine of the present invention is a control method for a spot welding machine comprising a fixed electrode, a movable electrode movable toward or away from the fixed electrode, a servo motor for driving the movable electrode, and a crank mechanism for converting rotational motion of the servo motor into linear motion to move the movable electrode, and which spot welds a material to be welded while applying pressure between the fixed electrode and the movable electrode, and when spot welding a plurality of welding points with the spot welding machine, when the movable electrode is operated at the maximum rotational speed of the servo motor and with the shortest acceleration and deceleration times, for welding points where the effective torque for each welding point exceeds a rated torque, the acceleration and deceleration times of the servo motor are lengthened so that the effective torque becomes equal to or less than the rated torque. Effect of the Invention

[0007] According to the present invention, for striking points where the effective torque for each striking point exceeds the rated torque, the acceleration and deceleration time of the servo motor is lengthened so that the effective torque is equal to or less than the rated torque, so that the effective torque can be reduced without changing the reduction ratio and pressure torque by lowering the acceleration and deceleration torque. Therefore, even a small motor can perform high-speed striking while maintaining the necessary pressure force. [Brief description of the drawings]

[0008] [Figure 1]1 is a diagram illustrating an example of the configuration of a spot welder controlled by a method for controlling a spot welder according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a diagram showing the relationship between torque and rotational speed of a servo motor and time. [Diagram 3] FIG. 11 is another diagram showing the relationship between the torque and rotational speed of the servo motor and time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0010] 1 is a diagram showing an example of the configuration of a spot welder 1 controlled by a method for controlling a spot welder according to an embodiment of the present invention. The spot welder 1 includes a fixed electrode 10, a movable electrode 20 that is movable so as to approach or move away from the fixed electrode 10, a servo motor 30 that drives the movable electrode 20, and a crank mechanism that converts the rotational motion of the servo motor 30 into linear motion to move the movable electrode 20. This spot welder 1 spot welds a workpiece M while applying pressure between the fixed electrode 10 and the movable electrode 20, and can be used by being attached to, for example, an industrial robot.

[0011] The fixed electrode 10 spot-welds the workpiece M between the fixed electrode 10 and the movable electrode 20 while applying pressure therebetween. The fixed electrode 10 is disposed, for example, at a one-end-side installation portion 51 of the support 50 so as to face the movable electrode 20. The movable electrode 20 is attached, for example, to a movable arm 21. The movable arm 21 is disposed, for example, at a crank mechanism, specifically, by being connected to a nut 42 of a ball screw 40 described later. The servo motor 30 is disposed, for example, at a other-end-side installation portion 52 of the support 50. The servo motor 30 has, for example, a motor body 31 and a motor transmission means 32 such as a gear that transmits the power of the motor body 31 to the crank mechanism 40.

[0012] The crank mechanism has, for example, a ball screw 40 that extends in the opposing direction of the fixed electrode 10 and the movable electrode 20 and is driven by the servo motor 30. The ball screw 40 has, for example, a screw shaft 41 that rotates by the servo motor 30, a nut 42 that is disposed on the screw shaft 41 and interlocks with the movable electrode 20, a ball (not shown) disposed between the screw shaft 41 and the nut 42, and a ball screw transmission means 43 such as a gear that transmits the power of the servo motor 30 to the screw shaft 41. One end side of the ball screw 41 is disposed relative to an intermediate disposition portion 53 provided between a one end side disposition portion 51 and an other end side disposition portion 52 of the support body 50, and the other end side is disposed relative to the other end side disposition portion 52 of the support body 50.

[0013] In this embodiment, for example, when spot welding a plurality of welding points using the spot welder 1, the servo motor 30 is selected and the drive of the servo motor 30 is controlled as follows. Figures 2 and 3 are diagrams showing the relationship between the torque and rotational speed of the servo motor 30 and time, and show one welding point cycle from the spot welding operation at one welding point to the spot welding operation at the next welding point. Also, Figure 2 shows a case where the effective torque exceeds the rated torque, and Figure 3 shows a case where the acceleration and deceleration times of the servo motor 30 are extended so that the effective torque is equal to or less than the rated torque.

[0014] First, the servo motor 30 is selected so that the instantaneous maximum torque of the servo motor 30 satisfies the required pressurizing torque Tp at each welding point. The instantaneous maximum torque of the servo motor 30 is the maximum torque that the servo motor 30 can use instantaneously (for a short period of time). In other words, the instantaneous maximum torque is set to be equal to or greater than the pressurizing torque. In this case, it is preferable to select a servo motor 30 whose instantaneous maximum torque is as low as possible within a range that satisfies the required pressurizing torque Tp, since this allows the servo motor 30 to be made smaller. The pressurizing torque Tp is a value determined based on the lead and gear ratio of the ball screw 41 from the welding conditions (required pressurizing force) of each welding point.

[0015] Moreover, the servo motor 30 is selected so that its maximum rotation speed is equal to or less than the allowable rotation speed of the ball screw 41. The maximum rotation speed of the servo motor 30 is the maximum rotation speed at which the servo motor 30 can rotate. The allowable rotation speed of the ball screw 41 is the fastest feed speed determined based on the lead and gear ratio of the ball screw 41.

[0016] Next, the effective torque for each impact point is obtained when the movable electrode 20 is operated at the maximum rotation speed and the shortest acceleration / deceleration time of the selected servo motor 30. That is, when the movable electrode 20 is brought close to the fixed electrode 10, the rotation speed of the servo motor 30 is accelerated from zero to the maximum rotation speed in the shortest acceleration / deceleration time, the movable electrode 20 is moved close to the fixed electrode 10 at the maximum rotation speed, and then the rotation speed of the servo motor 30 is decelerated from the maximum rotation speed to zero at the shortest acceleration / deceleration speed to apply pressure and current, and then, when the movable electrode 20 is separated from the fixed electrode 10, the rotation speed of the servo motor 30 is accelerated from zero to the maximum rotation speed in the shortest acceleration / deceleration time, the movable electrode 20 is moved away at the maximum rotation speed, and then the rotation speed of the servo motor 30 is decelerated from the maximum rotation speed to zero at the shortest acceleration / deceleration speed to obtain the effective torque for each impact point.

[0017] The execution torque for each welding point is the execution torque for each welding point in one welding cycle from the spot welding operation at one welding point to the spot welding operation at the next welding point. The execution torque for each welding point is calculated by the following equation 1.

[0018]

number

[0019] In the formula 1, Tp is the pressure torque, tp is the pressure current time, Tv is the acceleration / deceleration torque, tv is the acceleration / deceleration time, and tc is the time for one welding cycle from the spot welding operation at one welding point to the time before the spot welding operation at the next welding point is performed. The acceleration / deceleration time tv occurs four times in one welding cycle, specifically, when the rotation speed of the servo motor 30 is accelerated from zero to the maximum rotation speed when the movable electrode 20 is brought close to the fixed electrode 10, when the rotation speed of the servo motor 30 is decelerated from the maximum rotation speed to zero when the movable electrode 20 is moved close to the fixed electrode 10, when the rotation speed of the servo motor 30 is accelerated from zero to the maximum rotation speed when the movable electrode 20 is separated from the fixed electrode 10, and when the rotation speed of the servo motor 30 is decelerated from the maximum rotation speed to zero when the movable electrode 20 is separated from the fixed electrode 10 to a predetermined position.

[0020] If the calculated effective torque for each impact point is equal to or less than the rated torque, the servo motor 30 is controlled to operate the movable electrode 20 at the maximum rotation speed and the shortest acceleration and deceleration times. In other words, the acceleration and deceleration times tv of the servo motor 30 are set to the shortest acceleration and deceleration times. The rated torque is the torque output when the servo motor 30 is operated at the rated output and rated rotation speed.

[0021] On the other hand, for the impact point where the effective torque exceeds the rated torque, the acceleration / deceleration time tv of the servo motor 30 is set to be longer so that the effective torque is equal to or less than the rated torque. For example, as shown in Fig. 3, if the acceleration / deceleration time tv of the servo motor 30 is lengthened, the acceleration / deceleration torque Tv decreases, and the effective torque can be reduced.

[0022] Furthermore, for a welding point where the effective torque exceeds the rated torque, as described above, the acceleration / deceleration time tv of the servo motor 30 may be lengthened and the stop time when welding is stopped after the spot welding operation at that welding point is completed and before the spot welding operation at the next welding point is set to be long, so that the effective torque becomes equal to or less than the rated torque. The torque required when welding is stopped is low because it is to keep the movable electrode 20 separated from the fixed electrode 10, and therefore the effective torque can be reduced by lengthening the stop time.

[0023] In this way, the servo motor 30 is controlled based on the acceleration / deceleration time tv and the welding stop time set for each welding point, and spot welding is performed.

[0024] In this way, according to this embodiment, for striking points where the effective torque for each striking point exceeds the rated torque, the acceleration / deceleration time tv of the servo motor 30 is lengthened so that the effective torque is equal to or less than the rated torque, so that the effective torque can be reduced by lowering the acceleration / deceleration torque Tv without changing the reduction ratio and the pressure torque Tp. Therefore, even a small motor can perform high-speed striking while maintaining the necessary pressure force.

[0025] In addition, the effective torque can also be reduced by lengthening the acceleration / deceleration time tv of the servo motor 30 and by lengthening the stop time when welding is stopped after the spot welding operation at that welding point is completed and before the spot welding operation at the next welding point is performed.

[0026] Although the present invention has been described above with reference to the embodiment, the present invention is not limited to the above embodiment and can be modified in various ways. For example, in the above embodiment, each component is specifically described, but it is not necessary to include all the components, and other components may be included. Furthermore, the requirements of each component may be different. [Explanation of symbols]

[0027] 1...spot welding device, 10...fixed electrode, 20...movable electrode, 21...movable arm, 30...servo motor, 31...motor body, 32...motor transmission means, 40...ball screw, 41...screw shaft, 42...nut, 43...ball screw transmission means, 50...support, 51...one end side arrangement portion, 52...other end side arrangement portion, 53...middle arrangement portion

Claims

1. A control method for a spot welding machine comprising: a fixed electrode; a movable electrode that is movable so as to approach or move away from the fixed electrode; a servo motor that drives the movable electrode; and a crank mechanism that converts rotational motion of the servo motor into linear motion to move the movable electrode, the spot welding machine performing spot welding while applying pressure to workpieces with the fixed electrode and the movable electrode, the method comprising: When spot welding a plurality of welding points by the spot welding machine, the movable electrode is operated at the maximum rotation speed of the servo motor with the shortest acceleration and deceleration times, and for welding points where the effective torque for each welding point exceeds a rated torque, the acceleration and deceleration times of the servo motor are lengthened so that the effective torque becomes equal to or less than the rated torque. A method for controlling a spot welding machine.

2. 2. The spot welding machine control method according to claim 1, wherein, for a welding point where the effective torque exceeds the rated torque, the acceleration / deceleration times of the servo motor are lengthened and a stop time when welding is stopped after the spot welding operation at the welding point is completed and before the spot welding operation at the next welding point is started is set long, thereby making the effective torque equal to or less than the rated torque.

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