Development of Control System for Parallel Seam Welding Machine

Parallel seam welders are used to package integrated circuit chips. At present, the equipment used to package integrated circuit chips in China is basically from countries such as the United States and Japan, and the price is expensive. Therefore, it is of far-reaching significance to make it domestic and have a low price.
1 The main composition and function system of the system consists of two parts: the upper computer (PC machine) and the lower computer (SCM). The hardware structure is shown in Figure 1.
The host computer (PC) software is developed using the visual programming language VB6.0, uses the Mscomm control to complete the data communication between the PC and the microcontroller, and transfers the control information, status information and welding parameters; and utilizes the various databases that VB6.0 has. Operational ability to achieve the humanization of welding. The lower computer (single-chip microcomputer) receives the commands sent by the PC through the serial interface, starts the working program, and controls six stepping motors (two x-axis, one y-axis, two z-axis, and one rotating θ-axis). The angular displacement of the motor is converted into linear displacement through the lead Screw, which drives the welding electrode to run according to the designed track and transmits the current running state to the PC in real time. The main functions of the system are:
1 The upper computer monitors the working status of the lower computer in real time and controls the working process of the lower computer; sets the operating parameters of the lower computer, receives and sends data information, control information and status information; and records welding parameters of the history chip. When the system is re-powered, the latest welding parameters are taken as the default values ​​of the welding parameters; data processing and data and working status are displayed to guide the operation process;
2 The lower position machine controls the rotation of the 6 stepping motors to ultimately control the movement of the welding electrodes; control the size of the welding power and achieve intermittent control; and fine tuning of the welding electrodes.
3 The precision of each welding axis of the system shall not be less than 0.1mm.

Figure 1 System hardware block diagram

2 System Resource Utilization and Communication Mechanism 2.1 Utilization of System Resources In order to make full use of the PC's powerful data processing capabilities, massive storage space, and effectively play the role of the single-chip data storage, system resources must be allocated reasonably. One of the specific methods is that when the PC sends welding data, the welding parameters stored in the floating-point number are converted to pulses according to the step angle and screw ratio of the stepper motor. The second is the number of bits occupied by the number of pulses. Slightly larger than the single-byte integer multiple N bits, under the premise of meeting the accuracy requirements are: sent data = original data / 2n, then rounding the sending data, the microcontroller receives the integer data, left shift N bit Can restore real data. This not only improves the communication efficiency, but also reduces the occupancy of the microcontroller's RAM.
2.2 The baud rate of the system communication protocol is set to 4800 bps; the data frame structure is set to: 1 bit for the start bit, 8 bits for the data bit, and 1 bit for the stop bit.
The packets sent by the PC to the MCU include data packets and control packets. The data information includes a structure that begins with an "S" character followed by a 22-byte hexadecimal number. When sending, it is sent in ASCII format (text format), actually sending 44 ASCII codes. After the lower machine is correctly received, it sends “K” to the PC as a confirmation response signal. If the PC does not receive the "K" signal within the stipulated time, it will resend it. If three unsuccessful, the display information is given on the screen. The PC must ensure 44 ASCII packet lengths to avoid system misoperation. The control packet structure is: a control word that begins with a capital “O” followed by a single-byte hexadecimal number, actually transmits two bytes of ASCII code, and also uses “K” as the response signal, and adopts the equal code 3 /8. When sending, the high is in the front and the low is in the back.
The information received by the PC from the MCU includes the main contents of the structure as data information and status signals, and the data information and the status information are simultaneously transmitted. This information is switched with "S" followed by 32 1-bit hexadecimal ASCII codes with "K" as the end signal. If the PC receives a complete packet from the MCU, a screen prompt will appear to indicate the user's operation.
The above information is composed of a mixture of double bytes and single bytes. The non-hexadecimal ASCII characters are used to distinguish between the head and the tail of the packet. The receiver then unpacks according to the algorithm specified by the parties to the agreement, and the sender organizes the packets according to the data structure specified by both parties.

3 The main components and design ideas of the lower computer 3.1 The hardware components of the module communication module make it simple to use a MAX232 to complete the level conversion function, eliminating the use of ±12V～15V voltage for common chips. The troubles, and the connection with the PC is the simplest, no need for a hard handshake, a lot of work is done by the software.
Its main program design method is as follows:
1 The lower computer receives the data packet sent by the PC and receives it in an interrupt mode (and is set as an advanced interrupt) to meet the real-time requirements of the communication. This is only to trigger the execution of the receive interrupt service routine and receive the first byte. Once the interrupt routine is entered, the remaining bytes are received by program polling. The receiving flag RI is set by hardware and reset by software. After the data, the protocol specifies that the data is decoded and verified, and the verification information is returned to the PC. 2 The subroutine sending the operating status information to the PC by the lower computer is called according to the needs of the working process of the program. In order to ensure the clarity of the program logic in the call process, the CPU shuts off, uses the program query to send the flag TI (TI's use is similar to RI), according to the protocol requirements for data conversion and send a complete information packet, and then make the CPU open interrupt, The entire program has been executed.

3.2 Stepper Motor Control Modules Stepper motors are one of the most important actuators in mechatronic products. For a three-phase reactive stepper motor, its operation is divided into two types. The system uses three-phase single, double six-shot power, this method is not easy to lose step, in the vicinity of the equilibrium position of the rotor is not easy to produce oscillation, the stability of the operation is better, and the control accuracy is also doubled, to make steps Into the motor running more stable, higher control accuracy, the system uses a subdivided stepper motor driver to control. The speed of the stepper motor depends on the frequency of the step pulse sequence. The hardware interface circuit shown in Figure 2. In the figure, only the connection diagram of the stepping motor on the left side of the X-axis is shown. The connections of other motors are similar to those in the figure, but the other pins of the 8155A are used. CP+ and CP- of the stepper motor driver are step pulse input terminals, U/D+ and U/D- are direction control inputs, PD+ and PD- are offline control inputs (not used in this system), and each has The photoelectric isolation circuit is conducive to the safety and reliability of the system work. The common anode connection method is used in the connection because the load current capacity of the logic circuit is usually greater than the load capacity of the pull current; DC and GND are the power supply terminals. The requirements are DC 20 ~ 60V, current 4A; output terminals A + and A-, B + and B-, C + and C-, respectively, with the stepper motor A, B, C three-phase outlet corresponding connection. The control of the stepper motor mainly includes logic control and speed control.
Logic control includes motor rotation direction control and sending step pulse sequence. Since the access to the 8155 PA port and PB port need to be performed in bytes, according to the needs of the rotation direction control and step pulse sequence transmission, the two logic control bits are set and reset, and are alternately output to the corresponding ports. Can control the rotation of the motor. The system controls up to two motors at the same time and has a total of 16 control words. The specific programming idea is that the number of pulses can be proportional to the linear displacement after the number of pulses reaches the angular displacement through the step angle and then through the screw to the displacement.
Speed ​​control is achieved by inserting a delay subroutine during the alternating output of set and reset of two control words, so the speed is determined by the execution time of the delay subroutine. In the low speed zone of the motor in this system, the control line speed is 4mm/s in non-welding operation; the line speed in welding operation is 1~8mm/s, which is controlled in real time by the PC.
3.3 PWM module In order to meet the technical condition of seam welding of IC chip, the power loading of the welding process is required to be intermittent. Therefore, a PWM pulse width modulation module is designed to realize intermittent control of power. Figure 3 shows the circuit composition of this module. The core device is SG3524. Its output is a periodic pulse train whose period is controlled by the RT and CT end-to-end access resistance RT and the access capacitor CT. The period T is 0.77Rt×Ct, so the digital potential is connected here. X9C104 is used to control T. According to the use of the digital potentiometer in the figure, the expression of its resistance R is: R=(99-n)×100kΩ, where n is controlled through programming. The duty cycle of the SG3524's output signal is controlled programmatically by the D/A converter circuit. The system has achieved T = 40ms ~ 80ms, the duty cycle is 0 ~ 100%, controlled by the host computer.

Figure 4 Power control module circuit Figure 3.4 Welding function The control of the welding power of the control module is actually implemented indirectly by controlling the output voltage. SCM output digital signal to DAC0832 for digital / analog conversion, the results of the conversion by the SG3524 control of the analog switch, and then control the solid-state voltage regulator module EUV-40A, so that the output AC voltage and the input digital signal linear ratio. The output voltage is transferred to the welding transducer, which converts the low voltage and high current to the welding electrode. The IC chip is seam welded by generating a high temperature. The circuit is shown in Figure 4. In addition, due to the residual voltage in the actual operation process of the EVA-40A voltage regulator module, the electrode welding wheel is ignited when the welding parameters are adjusted, resulting in unnecessary losses. Therefore, the input loop of the voltage regulator module is connected in series with the AC solid state relay. GJH25-W is blocked.
The control method for the control of the welding power module is as follows: The MCU receives the power control information of the host computer and writes the DAC0832 chip with an address of 6000H. At the same time, the GJH25-W sends an effective control signal to make it conductive, and the welding electrode has a corresponding power output. Seam welding. When the welding is not performed, the GJH25-W is turned off and the OFFH is sent to the DAC0832 to completely disconnect the welding.
4 experimental test results X, Y axis screw displacement / angular displacement = 4mm / 360 degrees, Z-axis screw displacement / angular displacement = 1.5mm / 360 degrees, step angles are 0.36 degrees. The experimental method is: use the computer to send the pulse number and calculate the theoretical value, use the micrometer to actually measure and calculate the absolute error value (see Table 1). The analysis results meet the design requirements.
Table 1 Test data test table

After a period of test operation, this system proves that communication has good real-time performance and high control precision, which meets the design requirements.