The hottest PLC realizes the automatic shift of ma

PLC realizes automatic shift of machine tool spindle

spindle is the moving mechanism of machine tool rotating at high speed, and it is the key component of machine tool. Its performance directly affects the processing quality of parts. In the actual machining process, for different materials, in order to ensure the surface roughness, geometric tolerance and cutting force of parts, it is necessary to have different rotational speeds of the spindle. The speed change of the main shaft is generally realized by electric control or gearbox. The electric spindle directly adopts frequency conversion. At present, many large PE pipes in the market require low system speed control of the spindle, while the spindle gearbox adopts different gear combinations to realize the control of several gears and different speeds. Many machine tools adopt the form of spindle gearbox. The speed and output power of the spindle must be matched. If a single gear ratio is used, although the speed of the spindle can be changed, it is impossible to make full use of the power of the spindle motor. In order to take into account the speed and power of the spindle, different gear combinations must be used

at the beginning of this year, we successfully completed the technical transformation of a five axis CNC gantry milling machine. Its main shaft adopts gearbox speed change, the control system is Siemens SINUMERIK840C numerical control system, and the coordinates and main shaft drive adopt Siemens simodriver611a. According to the spindle shift structure of the machine tool and the characteristics of the control system, the spindle shift is automatically controlled through the built-in PLC control program

1 spindle shift mechanism

the spindle shift mechanism of the machine tool is controlled by two two two-way solenoid valves (SOL1 ~ sol4) to drive two gear sets to move up and down respectively. Each group of gears has two positions up and down, changing the gear speed ratio and generating the fourth gear speed. Four gear detection switches (SW1 ~ SW4) are installed in the spindle box. The pressure relay (PS1) detects the shift hydraulic pressure. The shift structure is shown in Figure 1

2 signal and data interface of the control system

the control system is composed of NC reserved data interface K and PLC module, and messages are transmitted between them by data blocks. The input and output points of the machine tool are connected to the input and output module of PLC. The NC system sends speed command voltage to the spindle. The main shaft data block of the system stores the relevant data of the main shaft shift, and these data are operated in real time through the PLC program. The system can have 8-speed control. The machine tool adopts four gears, and there can be speed crossing between adjacent gears

in order to realize the automatic shift of the spindle, four shift speed ranges of the spindle are preset in the machine tool data. The L value of the NC control system takes the average value of the measured values on both sides of the test piece and sends different command voltages to the spindle drive device according to different gears, corresponding to different speeds of the spindle motor

input signal: gear detection signal SW1 ~ SW4, shift hydraulic pressure PS1, spindle motor stalling Nmin, actual spindle motor speed NACT

output signal: shift solenoid valves SOL1 ~ sol4, motor drive command voltage vist

the spindle data block of the system includes swing speed, swing frequency, built-in shift range, current gear, shift command, target gear, shift end flag, spindle motor operation status, spindle prohibition, spindle PLC control and other data. The signal flow of the control system is shown in Figure 2

the system can use the state combination code of SW1 ~ SW4 detection switch as the mark of the current spindle gear. See Table 1 for the status of solenoid valve and detection switch

Table 1 shift status of main shaft shift number sol1sol2sol3sol4sw1sw3sw4

first gear

second gear

third gear

fourth gear

PLC implementation of automatic shift of main shaft

the control process of main shaft shift is realized in PLC. After receiving the shift command sent by Nck, PLC first checks whether the spindle motor is in the stopped state. If it is not stopped, PLC sends the "spindle prohibition" command to the spindle to stop the spindle. It determines the size of the fixture structure and the labor intensity of fixture operation. PLC sets a specific timer to send output commands to the corresponding shift hydraulic cylinders (SOL1 ~ sol4) according to the target gear to promote the corresponding gear movement. At the same time, start the spindle swing mode and set the swing frequency to make the gears mesh during movement. After the timer is timed, the PLC detects whether the corresponding gear switch is effective. If it is effective, it indicates that the shift gear is meshed in place. At the same time, it reports that the Nck shift is effective, and fills in the "current gear" to the data block. At this time, the spindle automatically enters the next gear speed. Otherwise, PLC will handle the error alarm. See Figure 3 for the main shaft shift control process

in the PLC design, it must be noted that:

in order to avoid confusion in the shift of the spindle, in the initialization module of the PLC program, the system will scan the gear detection switch of the machine tool as soon as it is powered on, and set the "current gear" in the data block to initialize the system state

the rotation speed of the main shaft must be reduced to zero before shifting the running main shaft, otherwise the gear will be damaged

before the spindle turns to the next gear speed, the corresponding shift cylinder must move in place to mesh the corresponding gears

is