Abstract: This paper briefly introduces the working principle of the welding arc tracking control system for rotating arc sensing arc welding robot, and explains the application of AC1820A data acquisition card in this system.
Keywords : AC1820A, data acquisition, rotating arc, weld tracking
Intelligent welding process control system is an important means to improve labor productivity, improve welding quality and improve working conditions. Arc welding robot plays an important role in the automation of welding process. It is widely used in industrial production of arc welding robot. The meaning of reality. In the arc welding arc welding robot welding seam correction system, it is very important to collect the current signal data in the welding process. AC1820A is a 12-digit 1000KH A/D board based on PC ISA bus of Beijing Shuangnuo Measurement and Control Technology Co., Ltd. Suitable for medium and high speed signals, waveform acquisition and recording applications. It is therefore suitable for weld tracking control systems for rotary arc sensing.
1 system working principle and implementation plan
Arc sensing is a method of obtaining lateral, high and low information between the torch and the weld from changes in arc and voltage. The basic principle is: for the melting arc welding, according to the self-adjusting principle of the arc, when the distance between the torch and the surface of the workpiece, that is, the distance between the end of the electrode tip and the surface of the workpiece (hereinafter referred to as the torch height) changes The dry elongation and the length of the arc column will change, and the arc current and voltage will change accordingly to maintain the original melting rate. Therefore, the change of arc current or voltage reflects the change of the height of the torch. The arc scans the groove to obtain the change of the torch height from the change of the arc parameter, and derives the torch and the welding according to the geometric relationship between the torch and the weld. The relative relationship of the seams is obtained to obtain weld bevel information. The block diagram of the weld trimming system is shown in Figure 1.
Fig.1 Block diagram of arc welding robot weld seam correction system
The arc sensor current varies with its rotational position. Therefore, in order to perform the weld deviation analysis, the arc sensing signal must include a rotational speed signal reflecting the position of the starting point of the welding pitch and a position reflecting the instantaneous position of the welding pitch in addition to the welding current signal. Signal, for this purpose, the optical encoder speed measurement and positioning system is added to the rotating arc sensing mechanism. The shape of the optical code disc is shown in Figure 2. The outer ring of the optical code disc is 64 indexing teeth, and the inner ring is # indexing teeth. In this way, two pulse signals can be generated, and the pulse signal generated by the outer ring reflects the moment of rotation. Position, the pulse signal generated by the inner ring reflects the rotational speed and can be used as the starting position of the rotation. The waveforms of the two pulse signals are shown in Fig. 3 (a) and Fig. 3 (b), respectively.
When the speed signal is detected as high level, A/D acquisition is started, which ensures that the starting position of each acquisition is the same; the position signal is used as the trigger signal for A/D acquisition, and each rising edge comes for A/D acquisition. Once, this ensures that each acquired data corresponds to a rotational position. In order to achieve evenly spaced sampling, it is also necessary to use the speed signal for closed loop control of the speed.
2 Introduction to AC1820A
2.1 Performance and working methods
The AC1820A has a resolution of 12 bits, a sampling speed of 1000KHZ (multi-channel), and 16 single-ended inputs. The analog input supports three ranges of 0 to 5V, 0 to 10V, and ±5V. The input channel is automatically scanned, and it can be programmed to start from any channel to any channel. The input uses DB25 socket (P1 port). With 8 input and 8 output switch DIO, TTL level, input current less than 0.5mA, output current greater than 5mA, 20PIN flat cable socket (P2 port).
The AD boot has two modes: software start and external trigger (TTL level rising edge is valid). On-board clock 4MHZ reference, 16-bit resolution. The AD conversion control can be an on-board 16-bit timer (4 MHz reference) or an external clock input. Interrupts can be selected IRQ10, 11, 12, 15, switch selection. The AD data is read using a 16-bit ISA bus with 16-bit operation.
2.2 I / O decoding address and use
AC1820A occupies 16 IO decoding addresses, corresponding to four address lines AO-A3, the base address is set by A4~A9, the default address is 300H, and the address offset is assigned as follows (OFFSET):
3 AC1820A hardware and software design
To properly use the AC1820A, you must ensure that the correct connection of the hardware circuit and software programming are correct.
3.1 hardware design
The position signal and the speed signal sent by the arc sensor are respectively connected to the 12-pin and 2-pin of the P18 port of the AC1820A data acquisition card through the limiting, shaping, and off-signal conditioning circuits, so that the position signal is used as the trigger signal for the A/D acquisition. The speed signal is connected to analog channel 1 to ensure that the starting position of the acquisition is the same. The welding current signal is converted into a voltage signal of 0~5V through the Hall sensor through the linear isolation circuit and then connected to the 1st pin of the P1 port of the AC1820A, that is, the analog channel 0. The 3 to 9 pins of the P1 port are connected and grounded, corresponding to the simulated ground of the welding current. 10, 11, and 13 feet are suspended, 14 to 22 feet are connected, and 22 feet and 25 feet (digital ground) are connected at the same time, corresponding to the position signal ground, and also the speed signal ground. The signal conditioning circuit for position and speed is shown in Figure 4. Linear isolation circuit is shown in Figure 5.
Figure 4 position, speed signal conditioning circuit
Figure 5 welding current isolation circuit
Since the AC1820A has 8 to 8 output D/O, it can be used for the output of the correction signal. The correction signals for controlling the up, down, left, right and motion of the robot are respectively connected to the 11 to 14 of the P2 port of the AC1820A. The foot, so that the correction signal sent by the A/D capture card is isolated, amplified and sent to the internal interface of the robot.
3.2 Software Design Some of the source programs related to AC1820A are as follows:
The system has been implemented and the experiment proved to be very effective.
references
1 AC1820A User Manual, W&W LAB, 2001.10
2 Xiong Zhenyu, Rotating arc sensing arc welding robot welding seam correction intelligent control system [D], Nanchang University PhD thesis, 2002
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