Abstract
The power supply circuit of the welding robot system is analyzed, and the working principle of its start-up circuit, trigger circuit, overvoltage alarm and protection circuit is discussed in detail. Specific circuit diagrams are also provided.
Keywords: Power supply, robot, overvoltage protection
1 Introduction
In recent years, with the development of technology, an increasing number of robots of various types have been put into use. Among them, industrial robots used in industrial production constitute the largest branch. They are characterized by high efficiency, stable processing quality, and strong environmental adaptability, playing an increasingly important role in many industrial fields. Since the 1980s, China has imported a large number of industrial robots, which have played a significant role in promoting China's economic development. However, with the increase in the use of imported robots, their maintenance has become particularly important. At present, there are still many problems regarding robot maintenance, such as untimely after-sales service from many foreign suppliers, expensive spare parts with long procurement cycles, and a lack of necessary maintenance information. Under these circumstances, reverse engineering to draw circuit diagrams and analyze their working principles is of particular significance, providing an important guarantee for better use, maintenance, fault analysis, and improvement in the future.
This article takes the welding robot of Shenlong Automobile Co., Ltd. as an example to analyze the power circuit of the robot system for reference by peers.
2. Power Supply Circuit Analysis
2.1 Power Supply Unit Composition
The power supply unit of the welding robot includes three power supplies, as shown in Figure 1.
The first group (U1, V1, W1) is a three-phase 226V supply, which is rectified to DC 328V (L+, L-) by a three-phase thyristor rectifier bridge to supply the main circuit of the shaft control unit. The rectifier bridge is triggered by EIN. Its control circuit has overvoltage alarm, processing, and fault reset functions.
The second group (U2, V2, W2) is a three-phase 20V circuit. After rectification by a three-phase rectifier bridge, one part provides DC 24V power to other parts of the robot (KRC, VER, INTERN, INTERFACE), and the other part is regulated by a 7815 to power the control circuit of the first group (U1, V1, W1).
The third group (U3, V3, W3) is a three-phase 25V power supply. After rectification by a three-phase rectifier bridge, it provides the brake power supply UB to the shaft control unit. UB is then converted by the switching power supply in the shaft control unit into 7 power supplies to provide power to the control circuit and inverter control circuit of the shaft control unit respectively.
Of the three power supply groups above, the second and third groups are relatively simple and will not be discussed further. Only the first group will be introduced here.
2.2 First group of power supply circuits
The first power supply main circuit consists of a rectifier bridge composed of three thyristor modules as shown in Figure 2. VT1 and VD1 are one module, and the output terminals (L+, L-) are connected to the filter capacitor C and the discharge resistor R. The wavefront signal X2 (1, 3, 16) of each phase is sent to the control circuit, and after processing, the gate trigger signal X2 (9, 13, 11) of the corresponding thyristor is obtained.
2.3 Control Loop
The first power control circuit consists of a three-phase trigger circuit, starting conditions, overvoltage alarm and protection circuits.
2.3.1 Startup Conditions
The power supply startup circuit is shown in Figure 3. When the controller sends the EIN (start) signal, pin 1 of the optocoupler I1 is at a low potential. After being inverted by pins 3 and 4 of the Schmitt-N gate driver IC1B, it becomes a high potential. This high potential is then used to charge C9 through R13, eliminating signal jitter. After being inverted twice by IC1C and IC1D, it remains at a high potential, providing the opening signal SEIN to the three-phase trigger circuit and the normal output circuit, respectively.
2.3.2 Three-phase trigger circuit
Taking phase U as an example, the thyristor triggering circuit is shown in Figure 4. The AC wavefront signal (X2(1)-L+) of the main circuit is taken, isolated by optocoupler IC8, so that pin 6 outputs a low potential, and is inverted to a high potential by Darlington inverting driver IC5A. With EIN providing the gate opening signal SEIN to pin 6 of IC6, IC6B(4) outputs a high potential, and is inverted to a low potential by IC5B, so that the primary side of the pulse high voltage transformer TC3 generates a pulse signal, and the secondary side outputs a trigger signal GU to the gate of VT1, so that the thyristor is triggered to conduct. When the wavefront signal of this phase disappears, its trigger signal also disappears. When U1 < L+, the thyristor of this phase is turned off by negative voltage. In this way, the thyristors of each phase are turned on and off in sequence to complete the three-phase half-controlled rectification.
2.3.3 Overvoltage alarm and protection circuit
As shown in Figure 5, when the output voltage of the rectifier circuit is too high, the voltage divider circuit composed of R29 and R27 raises the potential of the non-inverting input terminal of IC2, while the inverting input terminal of IC2 remains at a constant potential. It first forms a voltage divider circuit composed of R19, R18, R16, RP1, and R20. After being regulated by VD6 (9 V), it is then divided by R16, RP1, and R20, with RP1 adjusting the set protection voltage value. Once the voltage at terminal 3 exceeds this set voltage, the output of IC2 is high, VT1 conducts, VT2 and VT3 conduct, causing VT01 to conduct. The smoothing loads R+ and R- are connected to the rectifier output terminal, and simultaneously, pin 1 of optocoupler I2 is at a low potential, which is inverted to a high potential by IC1A. One path drives the BAL lamp to light up via IC4C inverting, indicating overvoltage and the activation of the smoothing load; another path inverts twice via IC11E and IC1F, charging C11 via VD3 and self-holding it, then drives the fault lamp BAF to light up via I1A, simultaneously inputting a low level to terminal 3 of IC3 via IC4, extinguishing the normal operation lamp BTB, and informing the controller of the fault information via terminal X1 (2). When the overvoltage disappears, VT01 is cut off, the smoothing load is disconnected, the BAL lamp goes out, C11 discharges via R25, IC1A outputs a low level, and the fault lamp BAF goes out. If the EIN signal is still present, the normal operation lamp BTB lights up, and the circuit returns to normal operation. Alternatively, after the fault disappears, the controller can be notified by pressing the reset button to restore normal operation.
3. Conclusion
This article focuses on the working principle of a robot's rectifier power supply unit and provides a detailed circuit diagram. It is of great significance for users to better utilize and maintain robots, and also serves as a reference for other related organizations.
References
1 KUKA Automatisme + Robotique Service & Formation Version, 1994, 6
2. Editorial Committee of Electronic Engineer's Handbook. Electronic Engineer's Handbook. Beijing: Machinery Industry Press, 1995, p. 4.
