JP3275201B2 - Control device for welding robot - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a welding robot having a welding gun at the tip of a robot arm.

[0002]

2. Description of the Related Art As a conventional control device of this type, for example, Japanese Patent Publication No. 3-28265 discloses a control device for a welding robot provided with a welding transformer and a welding gun at the tip of a robot arm. And a drive control device that controls a servomotor for driving a welding robot and a welding inverter device that supplies electric power to the welding robot are housed in one housing to form a single control device.

[0003] The structure of the drive control device is, for example, as disclosed in Japanese Patent Application Laid-Open No. 5-204422, in which an amplifier called a servo controller for controlling a plurality of axes (three axes) of servomotors includes a welding robot. In the case of a 5-axis welding robot, for example, two are connected in parallel according to the number of axes. As shown in FIG. 4, in one amplifier 1A, PWM generators 11, 12, and 13 for outputting pulse width modulation (PWM) signals corresponding to each of three servomotors M controlled by the amplifier 1A. And PW
Inverters 21, 22, and 23 for supplying three-phase currents to the respective servo motors M based on the PWM signals from the M generators 11, 12, and 13 are provided. Among the currents supplied from the inverters 21, 22 and 23 to the servomotor M, the currents of the U-phase and the V-phase are detected by the current sensors and input to the multiplexer 3. The multiplexer 3 sequentially switches the U-phase and V-phase current signals for each servo motor M and outputs the signals to the A / D converters 41 and 42. Thus, the current supplied to the servo motor M is feedback-controlled. A pulse generator PG that outputs a signal corresponding to the rotation speed of the servomotor M is connected to the rotation shaft of each servomotor M, and the rotation speed signals output from the pulse generator PG are output to interfaces 51, 52, and 53. The feedback control of the rotation speed of the take-in servo motor M is carried out via the.

[0004]

SUMMARY OF THE INVENTION In the above prior art,
Although the welding inverter and the drive control device are housed in one housing, the welding inverter device and the drive control device are configured separately,
A problem arises in that the housing becomes large and the layout of the welding device is restricted. Also, since the welding inverter device and the drive control device are separate bodies, when teaching the welding robot, the teaching of the welding inverter device and the teaching of the drive control device must be performed separately. Must
The trouble that the teaching operation becomes troublesome occurs.

An object of the present invention is to solve the above problems.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention relates to a control device for a welding robot having a welding gun at the tip of a robot arm , comprising a plurality of inverters.
A servo motor that drives the robot arm by an amplifier provided in the plurality of inverters.
A part of the data is used for controlling the welding current, and the welding current supplied to the welding gun is controlled by the amplifier.

According to the present invention, the operation of the robot and the control of the welding current can be performed by one amplifier.
Because the size of the entire control device is miniaturized, and can perform the teaching operation easily.

[0008] The sampling period of the welding current is determined by the frequency of the alternating current supplied to the welding transformer. On the other hand, the sampling period for detecting the drive current to the servomotor is determined by the characteristics of the servomotor. If the sampling period is too long, the characteristics of the servomotor cannot be fully exhibited. If the sampling period is too short, arithmetic processing cannot be performed. In general, the sampling cycle of the drive current of the servomotor is shorter than the sampling cycle of the welding current. Therefore, it is necessary to set the sampling cycle of the drive current of the servo motor shorter than the sampling cycle of the welding current. On the other hand, since the control of the welding current and the control of the drive current of the servomotor are performed by one amplifier, the sampling periods of the two cannot be freely set. If the sampling period of the drive current of the servomotor is set to be a value obtained by dividing the sampling period of the welding current by an integer, for example, when the integer is 2, the drive current of the servomotor is sampled every period, and the welding current is 2 Sampling may be performed once at a time. However, the sampling period of the servomotor cannot be longer than a certain period in order to exhibit the characteristics of the servomotor. Further, when the sampling period is shortened, the number of times of the arithmetic processing in the control device increases, so that there is a limit due to the arithmetic capability of the control device. Therefore, it is necessary to set the sampling cycle of the drive current of the servo motor so as to fall between the two.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, RO is a welding robot. In this embodiment, a five-axis control robot having five servomotors is used. A welding gun GA is attached to the tip of the robot arm via a welding transformer TR. The attitude of the welding robot RO can be freely changed by controlling each servomotor by the control device C. Welding robot RO
When the welding gun GA is moved to a desired welding position by controlling the attitude of the welding gun GA, spot welding is performed with a work (not shown) sandwiched by the welding gun GA. At this time, an AC welding current having a predetermined frequency f is supplied from the control device C to the transformer TR.

An amplifier 1A shown in FIG. 4 is incorporated in the control device C, and controls the operation of three of the five-axis servo motors of the welding robot RO. The control of the remaining two-axis servomotors is performed by the amplifier 1 shown in FIG. The two amplifiers 1 and 1A are connected in parallel in the control device C. The amplifier 1 shown in FIG.
2 except that the welding current is supplied to the transformer TR via the inverter 21. Further, in order to detect the drive current to the servomotor M, it is necessary to detect the U-phase and V-phase currents of the three-phase current. However, since the welding current is a single-phase current, the transformer T
Only the current on one side of the two wires on the primary current side connected to R needs to be detected. On the secondary current side, the current on one side of the two electric wires connected to the welding gun GA is detected and input to the multiplexer 3. However, only one of the primary current and the secondary current may be detected. Since it is not necessary to attach the pulse generator PG to the transformer TR, the interface 51 is left unconnected. The interface 51 need not be provided in the amplifier 1, but in the present embodiment, the amplifier 1 is shared with the amplifier 1A, so that the amplifier 1 is left unconnected.

Incidentally, in order to sample the welding current supplied to the transformer TR, it is necessary to sample at the peak of the welding current which is a single-phase current. Therefore, the sampling cycle of the welding current is determined by the frequency of the welding current. Since the secondary current is full-wave rectified, it may be sampled at the same cycle as the sampling cycle of the primary current.

Referring to FIG. 3 and Table 1 below, the welding current frequency f (Hz) uniquely determines the sampling period T (μsec) of the welding current.

On the other hand, if the servo motor M is equivalent to, for example, 5 kW, 5 kW unless the current of the U phase and the V phase is sampled in a sampling cycle shorter than 150 μsec.
Can not draw a considerable performance. Further, in the present embodiment, if the sampling period is shorter than 100 μsec, the arithmetic operation cannot be performed. Therefore, when switching the data sampled by the multiplexer 3 and taking the data into the A / D converters 41 and 42, the sampling data is taken in at a cycle of T / 2 with respect to the sampling cycle T of the welding current, and the sampling data of the taken welding current is taken. Is ignored once every two times. Then, the welding current can be sampled at cycle T, and the motor current can be sampled at cycle T / 2. If the period is still long in the period T / 2, the motor current is sampled in the period T / 4, which is a further half, or in the period T / 8, which is a further half.

[0014] From Table 1, when the motor current is sampled at a period T / 2, the frequency f of the welding current is 1700 Hz to 200 Hz.
It is understood that a range of 0 Hz is sufficient. When sampling is performed at the cycle T / 4, the frequency f of the welding current is 900
It can be seen that the frequency range is from Hz to 1200 Hz. In addition, in the present embodiment, when sampling is performed at the cycle T / 8, it can be seen that the sampling cycle of the motor current becomes too short to be performed.

In the above embodiment, the sampling cycle of the motor current is set to 1/2 ⁿ of the sampling cycle T of the welding current. However, it may be set to 1/3 or another integer.

[Brief description of the drawings]

FIG. 1 shows a schematic configuration of a welding robot.

FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between sampling periods.

FIG. 4 is a block diagram illustrating a configuration of a conventional amplifier.

[Explanation of symbols]

 1 amp 1A amp C controller RO welding robot TR transformer

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshiaki Nagasawa 1-10-1 Shinsayama, Sayama City, Saitama Prefecture Inside Honda Engineering Co., Ltd. (72) Inventor Tetsuya Ozawa 1-10-1, Shinsayama, Sayama City, Saitama Prefecture (56) References JP-A-6-31462 (JP, A) JP-A-8-132253 (JP, A) JP-A-4-349501 (JP, A) JP-B-3-28265 ( JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 11/11 B23K 11/24

Claims (2)

(57) [Claims] 1. A control device for a welding robot having a welding gun at a tip of a robot arm, comprising:
The amplifier comprises a capacitor in which controls a servo motor for driving the robot arm, the plurality of Lee
A control device for a welding robot, wherein a part of an inverter is used for controlling a welding current, and the welding current supplied to the welding gun is controlled by the amplifier. 2. The amplifier according to claim 1, wherein the amplifier has a sampling function of sampling a welding current and a sampling of a motor current. The sampling cycle of the motor current is a value obtained by dividing the sampling cycle of the welding current by an integer. 2. The control device for a welding robot according to claim 1 , wherein the control value is set to a value that falls within a range of a predetermined sampling period defined from a characteristic of the motor and a calculation capability of the control device.