CNC system of special punching machine for hot pot

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The numerical control system of special machine for boiler barrel drilling

1 preface

in order to realize the automation of boiler barrel wall hole processing, the numerical control system, which marks the arrival of the full composite aircraft, is a two coordinate open-loop control system with MCS-51 single chip microcomputer as the control core, stepper motor as the driving motor, and machine tool large and small carriage as the executive parts. The carriage moves longitudinally to determine the punching position, the pulse equivalent value is 0.02mm/step, and the maximum feed rate increases the degree of enterprise transformation and upgrading to 5m/min. The small carriage moves horizontally to realize the fast forward and work forward of the tool. The system has the main functions of inching tool setting, automatic processing, pause and continue, emergency stop alarm, zero return, etc

2 hardware structure and function

the system hardware is distributed on one control motherboard and two drive boards

on the control motherboard based on 8031 single chip microcomputer, expand a 27256eprom to store the system software, a 2764eprom to solidify the debugged part processing program, and a 6264ram with power down protection to store the manual part processing program randomly. In addition, an 8255 parallel i/o port is expanded, and its B port is used to output the stepping motor control signal, and its C port and a port are used for the keyboard and display interface

configure 4 on the motherboard × There are 7 keys, among which the hexadecimal numeric keys of 0 ~ F are used to input the address of storage unit, workpiece number, processing instruction, etc. when manually processing the program, and the other function keys are used as MCU reset, 6264 memory address plus 1, minus 1, step motor jogging tool setting, automatic processing, tool return to zero, etc

6 8-segment LED digital tubes adopt common cathode connection method to dynamically display data

according to the experimental analysis of the drag torque, it is determined to use 150bf003 stepping motor to drive the large carriage and 110bf003 stepping motor to drive the small carriage. The power on state of each phase winding of the stepping motor is sent to port B of 8255 by the single chip microcomputer through the data bus. After photoelectric isolation, the power is amplified by the driving circuit. The driving power supply adopts chopper circuit, which can provide current waveform close to rectangular wave. The output stable torque in low frequency range is 0.85 ~ 0.9tj (TJ is the maximum static torque of the motor). The system has strong load capacity and good operation speed

considering the safety of the system operation, set the limit switch, manual pause switch and manual emergency stop switch, connect the signal to the P1 port of the single chip microcomputer, and use the three input NAND gate 74ls10 to connect its output end as the interrupt source signal to the single chip microcomputer

the system principle block diagram is shown in Figure 1

3 software design

the system software solidified in 27256eprom is divided into two parts: monitoring program and processing instruction interpretation program

3.1 monitoring program

the monitoring program includes MCU system initialization, key processing, input data display and storage, interrupt service and other functional modules

the system initialization module completes the state initialization of the storage unit, register, programmable bit and the allowable interrupt settings after the MCU is powered on and reset or the key is pressed, and displays the prompt "-" on the display


key processing module scans and queries all keys. When no key is pressed, the prompt continues to be displayed. When a key is pressed, it is identified as a data key or a function key by decoding, so as to go to the corresponding program for processing

in the input data display and storage module, if you press the key after inputting four hexadecimal data, combined with the +>, -> keys, you can query and modify the stored data in 6264ram, so as to achieve the purpose of manual programming and modifying the processing speed. If you press the key after inputting the two digit decimal data, it will be considered that the two digit data are the workpiece number, and the corresponding processing program will be called

in the interrupt service program module, the single chip microcomputer reads the P1 port status, and setting P1.1 or P1.2 to "1" represents the pause switch action or emergency stop switch action respectively. According to the actual processing status, it is allowed to continue processing or return the tool to zero, otherwise it is the limit switch action, and only the tool is allowed to return to zero

3.2 processing instruction interpreter

the basic sentence of the part processing program is composed of 6 digits or characters. The first digit represents the two moving directions of the large and small carriage respectively with decimal numbers 2, 4, 6 and 8, the second digit represents the hexadecimal moving speed of the carriage with hexadecimal numbers 0 ~ F, and the last 4 digits represent the actual displacement value of the carriage with decimal numbers

the function of the processing instruction interpreter is to read the part processing program and interpret it sentence by sentence to obtain the rotation direction, speed and corresponding steps of the stepping motor, including the forward and reverse processing of the motor, the speed up and down processing, the conversion of processing length and motor steps and other functional modules

in the motor forward and reverse rotation processing module, set the power on sequence of each phase winding of 110bf003 stepping motor as: a → ab → B → BC → C → Ca → a or: a → Ca → C → BC up and down → B → ab → a. Set the energization sequence of each phase winding of 150bf003 stepping motor as: ab → ABC → BC → BCD → CD → CDE → de → DEA → EA → EAB → AB or: ab → EAB → EA → DEA → de → CDE → CD → BCD → BC → ABC → ab. After reading the first bit of the processing statement, the single chip microcomputer can output the corresponding state machine code from port B of 8255 in sequence

by analyzing the torque frequency characteristics of the stepping motor, it can be seen that the higher the starting frequency, the smaller the starting torque. If the stepping motor runs directly at high speed from standstill, it may be out of step. Therefore, set the sixteen gear carriage moving speed (m/min), corresponding to the sixteen gear working frequency of the stepping motor (step/s). For short stroke, the motor runs directly at a speed lower than the starting frequency, without speed up and speed down software processing. For long stroke, the motor starts from the starting frequency lower than the starting frequency, After accelerating to the required working frequency, run at a constant speed, and then stop when it is reduced below the starting frequency. In the speed up and down module, the method of uniformly reducing (or increasing) the pulse time interval is used to realize the acceleration (or deceleration) control of the stepping motor

in the conversion function module between machining length and motor steps, convert the machining length L expressed in decimal system into motor steps l/p, and P is the system pulse equivalent (mm/step). Store the motor step number in hexadecimal form into the memory, and set the corresponding step number accumulation unit. When the motor goes one step, the content of the memory will be reduced by 1, and the content of the corresponding step number accumulation unit will be increased by 1

if the key is met, the motor will reverse, and the content of the step accumulation unit will be reduced to 0, that is, it will return to the initial tool setting position. The so-called inching tool setting function refers to that by operating the four keys +>, ->, +>, -> on the main board, the stepping motor performs one step in the corresponding direction, and the starting machining position can be determined by continuous operation

the program flow diagram is shown in Figure 2

4 conclusion

assign workpiece numbers to workpieces of different specifications, such as 01, 02, Prepare the corresponding processing program, which can be solidified in 2764eprom or randomly stored in 6264ram. When processing, first input the workpiece number from the keyboard, and then press the key to automatically complete the drilling process of a boiler barrel. The preparation of the processing program is very simple (it should be operated under the condition of no pressure, and the elevator should be started to adjust and stretch the experimental space, and the system has a certain flexibility

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