CNC cutting machine manufacturers introduce stepper motor related knowledge CNC cutting machine has high requirements on power supply in many times. Servo motor and stepping motor have different applications in different cutting. Here we will introduce you about stepping. Some general knowledge of the application of the motor open loop servo system.
I. Introduction to the application of stepper motor open-loop servo mechanism
In the automatic line of the combined machine tool, three kinds of sliding tables are generally set according to different processing precision requirements.
a. Hydraulic slide table, used in roughing process with large cutting amount and low processing precision;
b. Mechanical sliding table, used in semi-finishing process with medium cutting amount and certain processing precision requirements;
c. CNC slide table, used in the finishing process with small cutting amount and high processing precision. Programmable controller (referred to as PLC) is widely used in industry for its versatility, high reliability, simple command system, easy programming, easy to master, small size, less maintenance work, and convenient installation of field interface. Automatic control. Especially in the control of the automatic production line of the combined machine tool and the S, T, M function control of the CNC machine tool, it shows its excellent performance. The PLC-controlled stepping motor open-loop servo is applied to the CNC slide control on the automatic production line of the combined machine tool. The CNC system of the unit can be omitted to reduce the control system cost of the unit by 70~90%, or even occupy the automatic line control unit. 3~5 I/O interfaces of PLC and 2 CNC sliding table structure controlled by PLC
The numerical control slide in the automatic line of the general combined machine tool adopts an open-loop servo mechanism driven by a stepping motor. The CNC sliding table controlled by PLC is composed of programmable controller, circular pulse distributor, stepping motor driver, stepping motor and servo transmission mechanism. The gears Z1 and Z2 in the servo transmission mechanism should adopt anti-backlash measures to avoid The reverse dead zone is generated or the machining accuracy is lowered; and the screw drive pair should determine whether to use the ball screw pair according to the machining accuracy requirements of the unit. The ball screw pair has the advantages of high transmission efficiency, good system rigidity, high transmission precision and long service life, but the cost is high and cannot be self-locking.
3, PLC control method of CNC sliding table
There are three main control factors for the CNC slide:
1, stroke control
The stroke control of the general hydraulic slide and the mechanical slide is realized by the position or pressure sensor (stroke switch / dead stop iron); and the travel of the numerical control slide is realized by digital control. According to the structure of the numerical control slide table, the stroke of the slide table is proportional to the total rotation angle of the stepping motor, so it is only necessary to control the total rotation angle of the stepping motor. It is known from the working principle and characteristics of the stepping motor that the total rotation angle of the stepping motor is proportional to the number of control pulses input; therefore, the number of pulses output by the PLC can be determined according to the displacement of the servo mechanism:
n= DL/d
(1) DL - displacement amount of the servo (mm) d - pulse equivalent of the servo (mm / pulse)
Second, feed speed control
The feed rate of the servo is determined by the speed of the stepper motor, and the speed of the stepper motor depends on the input pulse frequency; therefore, the pulse frequency of the PLC output can be determined according to the feed rate required by the process:
f=Vf/60d (Hz) (2) where Vf——feedrate of servo mechanism (mm/min)
Third, the feed direction control
The feed direction control is the steering control of the stepper motor. The steering of the stepper motor can change its steering by changing the energization sequence of each winding of the stepping motor;
When the three-phase stepping motor is energized in the order of A-AB-B-BC-C-CA-A... the stepping motor rotates forward; when the winding is energized in the order of A-AC-C-CB-B-BA-A... The motor is reversed. Therefore, it can be realized by changing the output sequence of the hardware loop distributor by the direction control signal of the PLC output, or changing the order of the output pulses by programming to change the power-on sequence of the stepping motor windings.
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