RU2793010C1 - Control device for the mechanism of pulse feeding of wire to the welding zone - Google Patents

Abstract

FIELD: welding equipment.

SUBSTANCE: invention can be used in devices for pulse feeding of welding wire into the welding zone. The device contains a microcontroller connected to a power switch unit, which is configured to be connected to the electric motor of the wire feed mechanism, a motor current sensor and a data input unit connected to the corresponding inputs of the microcontroller. The device is also equipped with a supply voltage attenuator, a communication unit with an external control device and a display, appropriately connected to the microcontroller, which is configured to programmatically generate a PWM signal supplied to the control device of the bridge circuit of the power switch unit with the possibility of adjusting the corresponding feeds of the mechanism.

EFFECT: use of the invention makes it possible to expand the technological capabilities of the device and simplify its design.

1 cl, 3 dwg

Description

The device relates to technological welding equipment, in particular, to devices for pulsed supply of welding wire into the welding zone.

A device is known that contains a microcontroller unit for generating a rotation speed setting and a frequency change in the speed of rotation of the motor shaft and a dual-circuit motor control system with an internal current loop and an external speed loop to control the speed and frequency of multidirectional rotation of the motor shaft (utility model patent RU 199206 U1, published 08/21/2020 Bull. No. 24).

Unlike analog, in the claimed device, the motor speed control is performed not by a two-level algorithm, but by a software pulse-width modulator (PWM) with a changeable voltage polarity. In this case, the claimed device allows you to separately adjust the main parameters of the wire feed mode: the duration of the forward feed, the speed of the forward feed, the duration of the reverse feed. Reverse feed speed, forward and reverse feed acceleration, pause between forward and reverse feed.

The task is to create a compact control device that can be included in any commercially available welding wire feeder with a DC motor, which, depending on the generated task, can synchronize the feed and reciprocating (pulse) movement of the wire during welding.

EFFECT: simplifying the design by eliminating the speed feedback loop and the speed sensor, increasing the accuracy of controlling the speed of rotation of the electric motor and changing the direction of rotation due to pulse-width modulation, the possibility of separate regulation of the forward feed speed; feed back speed; acceleration duration; duration of braking; duration of forward feed, duration of reverse feed, duration of the pause between forward and reverse feed, the ability to quickly change the parameters of pulses from an external control device, the ability to work with a wide range of supply voltages, the ability to integrate into industrial wire feed systems without modifications to their mechanical parts and to control electric motors with different electrical characteristics (supply voltages, speeds, powers).

The control device for pulsed wire feeding into the welding zone is configured to control the speed and frequency of multidirectional rotation of the electric motor shaft, contains a microcontroller, power switches, a current sensor, a supply voltage attenuator, a communication unit, a data input device, a display. The device controls the motor and can receive control signals from an external control device.

The principle of operation of the device is illustrated in the figures, where in Fig. 1 shows a diagram of the control device for the pulse wire feed mechanism, in Fig. 2 is a diagram of the motor voltage and motor speed, in Fig.3 is a diagram of the operation of the wire feeder in reverse mode and in non-reverse mode.

The control device (figure 1) consists of: microcontroller MK (1), power switches SC (2), current sensor DT (3), supply voltage attenuator A (4), communication unit BS (5), data input device UV ( 6), display D (7). The control device controls the electric motor ED (8) and can receive control signals from the external control device VUU (9).

In this case, the arrows in the diagram show the direction of data or energy transfer of the power supply, but not the number of signals, that is, one arrow can correspond to one signal or several (signal bus).

The microcontroller is supposed to be standard, with the number of discrete inputs of at least three for UV6, one for the built-in asynchronous universal receiver (UART), the number of analog inputs of at least 2 (for analyzing signals from A4 and DT3), the number of discrete outputs of at least 6 for D7 and two discrete outputs (PWM and Voltage).

In the practical implementation of the device, the ATmega8 microcontroller was used, but other universal microcontrollers of the ATtinyxxx, ATmegaxxx, ATxmegaxxx, PICxx, STM32 families or other manufacturers with the above characteristics can also be used.

The algorithm of the microcontroller is determined by the control program developed by the authors of the application and is registered separately as a computer program.

The program analyzes signals from VUU9, UV6, A4, DT3 and generates control signals D7, as well as PWM and Eg.

Signal Direct - digital signal of the direction of movement of the electric motor: 1 - wire movement forward, 0 - wire movement backward.

PWM signal - output digital signal from the PWM modulator. The waveform is shown in Fig. 2.

The CK2 block contains 4 power switches (field-effect transistors) connected in a bridge circuit, as well as a control unit for them. Since the authors of the application used the standard LMD18200 chip, which structurally contains all of the above elements, in the implementation of the patented device, they are designated in the description of the device (Fig. 1) as one functional block CK2.

In the claimed device, a standard bridge inverter was used as SC2. A standard bridge inverter works as follows: the control unit CU receives the Vd and PWM signals (not shown in the figure). A discrete high-level signal arrives at the KU1 device if Dir=1 and PWM=1, a high-level discrete signal arrives at the KU2 device if Dir=0 and PWM=1. Devices KU1 and KU2 control pairs of transistor switches, respectively VT1, VT4 and VT2, VT3, as a result of which a PWM modulated voltage of direct or reverse polarity from the power source E is supplied to the load Rn. In the claimed device, the supply voltage in Fig. 1 denoted +U _p .

The device works as follows. The microcontroller (1) outputs two control signals to the power switches - a pulse-width modulated signal and a signal for the direction of rotation (For example) of the electric motor. Power switches (2), made according to the bridge circuit, switch the supply voltage (Up) in a pulsed mode and supply it to the electric motor. In this case, the output voltage of the switches can take one of three values: + Up, 0, - Up. The current sensor (3) measures the average value of the motor current and transmits the measured value to the microcontroller (1), which is used as a feedback signal.

The attenuator (4) lowers the supply voltage to a level equal to the input voltage of the analog-to-digital converter of the microcontroller and is converted into a digital code by means of the microcontroller. This value is used to stabilize the motor voltage when the circuit supply voltage changes.

By measuring the supply voltage of the circuit, the device stabilizes the motor voltage as follows. When the supply voltage deviates from the nominal value, the deviation of the supply voltage and the adjustment of the PWM control signals are calculated in order to maintain the average supply voltage of the electric motor at a given level, which ensures the independence of the speed of rotation of the electric motor shaft from an increase in the supply voltage.

To set the operating mode of the device, an input device (ID) is used, which includes a keyboard and a display (D).

The device can be integrated into the control system of the welding machine, for which it has a communication unit (BS). This block provides galvanic isolation of control circuits and level matching of control signals. When controlling the device through the communication unit, the external control device transmits control signals containing information about the operating mode: enabled / disabled, forward feed rate, reverse feed rate, duration of forward feed and reverse feed, pause between forward feed and reverse feed, acceleration and deceleration time of the motor .

Pulse-width modulation (Fig. 2) implies the issuance of a voltage of one of three values: + Up, 0, -Up. In this case, the pulse duration (ti) is changed while maintaining the pulse repetition period (T) unchanged. This makes it possible to smoothly regulate the average value of the motor voltage (Ud) in the range from -Up to +Up, and, consequently, smoothly control the speed of rotation of the electric motor (Vd) and change the direction of rotation.

The operation algorithm of the control device allows you to separately adjust the following parameters of the rotation of the motor shaft of the wire feed mechanism (Fig. 3):

- direct feed speed (Vp);

- reverse feed rate (Vo);

- duration of acceleration (tp) or acceleration during acceleration;

- duration of braking (tp) or acceleration during deceleration;

- duration of forward feed (tp);

- the duration of the return feed (to);

- the duration of the pause between forward and reverse feed (tp).

In this case, the speeds of forward and reverse feeds can be either of a different sign or the same, or equal to zero. In this case, the feed algorithm can be implemented with reverse (Vp and Vo of different sign), without reverse (Vp and Vo of the same sign) or feed with pauses (Vo or Vp equal to zero).

The exclusion of the feedback loop and speed sensor from the system simplifies the device and eliminates the need to modify the mechanical part of the wire feeder (eliminating the need to install a speed sensor), since regular wire feeders, as a rule, do not have a speed sensor. Since the motor shaft is rigidly (through a mechanical gearbox) connected to the feed rollers, control of the wire speed is not necessary.

By measuring the supply voltage of the circuit, the device stabilizes the motor voltage as follows. When the supply voltage deviates from the nominal value, the deviation of the supply voltage and the adjustment of the PWM control signals are calculated in order to maintain the average supply voltage of the electric motor at a given level, which ensures the independence of the speed of rotation of the electric motor shaft from an increase in the supply voltage.

Controlling the acceleration and deceleration time (accelerations during acceleration and deceleration) allows you to limit the load on the mechanical parts of the wire feed mechanism, limit the motor currents, and also set the required acceleration of the wire movement to ensure the mode of "reset" of a drop of molten metal from the wire.

A pause between the forward and reverse strokes eliminates voltage surges that occur when the motor voltage polarity is reversed.

Separate smooth control of the forward and reverse pulse parameters allows you to flexibly adjust the wire feed parameters for various welding modes when studying welding processes, working out welding modes and searching for the optimal mode, as well as during welding with the optimal wire feed mode.

The use of a communication unit with an external control device allows you to quickly change the parameters of the wire feed mode directly in the welding process to correct the mode when welding conditions change.

The device can be integrated into existing continuous wire feed systems with DC motors and different characteristics (supply voltage, power, shaft speed) without modifications to the mechanical parts.

Claims (1)

A device for controlling a mechanism for pulsed wire feed into the welding zone, comprising a microcontroller connected to a block of power switches connected in a bridge circuit, having its own control device, which is configured to be connected to the electric motor of the mentioned mechanism, a current sensor of the mentioned electric motor and a data input unit, associated with the corresponding inputs of the microcontroller, characterized in that it is equipped with a supply voltage attenuator, a communication unit with an external control device and a display, respectively connected to the microcontroller, which is configured to programmatically generate a PWM signal supplied to the control device of the bridge circuit of the power switch unit providing the possibility of separate adjustment of the forward feed rate, reverse feed rate, acceleration duration, braking duration, forward feed duration, reverse feed duration and pause duration between forward and reverse feed of the said mechanism.

Images