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Explanation of the types of computer pattern machine drive circuit

Explanation of the types of computer pattern machine drive circuit

At this stage, andComputer pattern machineThe matching is mainly an asynchronous motor with a mechanical clutch. No matter whether the pattern sewing machine is working or not, the motor is always running. Step on the control pedal of the computer pattern machine, and when the clutch is closed, the power of the motor is transmitted through the friction plate; when the clutch is disengaged, the brake is realized by the friction plate.

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The disadvantage of the clutch motor matched with the computer pattern machine is the large waste of electric energy. Substituting a permanent magnet DC motor for the clutch motor can eliminate this waste of electric energy. Because the permanent magnet DC motor has the characteristics of large starting torque and convenient speed regulation and braking, its drive circuit can be controlled by the foot pedal, and it can be driven and stopped together with the computer pattern machine.

The permanent magnet motor of the computer pattern machine does not require an excitation current to generate the main magnetic field, and the speed is adjusted by changing the power supply voltage of the motor armature. Currently, two circuits are widely used. One is a more traditional thyristor drive circuit, that is, a single-phase half-controlled bridge rectifier circuit, which can obtain different voltages by changing the conduction angle of the thyristor to achieve the purpose of changing the motor speed. The disadvantages of this method are: First, it cannot brake; second, the harmonic pollution is serious; third, the control is not flexible. Thyristor trigger circuits are mostly implemented by hardware, which lacks flexibility. It is more difficult to adjust the acceleration time, control the starting current, or increase the intelligent malfunction protection function.

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Another commonly used drive circuit for computer pattern machines is more popular in recent years. The PWM circuit represented by new power electronic devices and single-chip microcomputers is a commonly used non-braking irreversible PWM motor drive circuit. When the single-chip microcomputer sends different duty cycle signals to the vm6 control terminal, a voltage of 0V-310V can be obtained on the motor armature, and the motor speed also changes accordingly. The motor power of the computer pattern machine is generally below 550W, enough to use power FETs, and the switching speed can reach above 40KHz. Since the armature currents of the above two circuits cannot flow in the opposite direction and cannot produce a braking effect, when the operator releases the pedal of the computer pattern machine, the machine will slowly stop under the action of inertia.

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