Speed regulation method of CNC lathe machining spindle

In order to meet the requirements of the main transmission of CNC lathe processing, CNC machine tools often adopt a motor stepless speed regulation system. In order to expand the speed adjustment range and meet the requirements of low speed and large torque, a combination of gear stepped speed regulation and motor stepless speed regulation is also commonly used. Method to realize spindle speed control.

1. Mechanical gear shift

In the main transmission system of CNC lathe processing, the traditional spindle box structure is greatly simplified due to the stepless speed regulation of the motor. However, due to the limitation of the spindle motor and the drive power supply, it is often output with a constant torque at its low speed. In order to enable the spindle to provide the maximum output power of the main motor within the entire speed range as much as possible, and to meet the needs of CNC machine tools for low-speed and powerful cutting, a combination of 1 to 4 gears and stepless speed regulation is often used, the so-called segmentation Stepless speed regulation. The use of mechanical gear reduction not only amplifies the output power, but also expands the speed range.

When CNC lathe processing is cutting, the spindle runs automatically at the speed specified by the S command in the part processing program. Therefore, there must be two types of spindle speed command signals in the numerical control system, that is, analog or digital signals (S codes) are used to control the drive speed regulation circuit of the spindle motor, and switching signals (M codes) are used to control the speed of mechanical gears. Actuating mechanism for automatic shifting. The automatic gear shifting actuator is an electric-mechanical conversion device, commonly used hydraulic shift forks and electromagnetic clutches.

2. Motor speed regulation

The speed-regulating motors used for the spindle drive of CNC lathes are mainly divided into two categories: DC and AC.

(1) DC motor speed regulation-usually CNC machine tools have a large speed regulation range, and the DC motor speed regulation adopts both voltage regulation and magnetic regulation. The characteristic curve of its typical DC spindle motor is shown in Figure 6-1. It can be seen from its characteristic curve that the motor is a constant torque speed regulation below the speed n0, that is, it is realized by changing the armature voltage; it is a constant power speed regulation above the speed n0, which is realized by changing the excitation current.

The more commonly used FANUC DC-excited spindle motor adopts a three-phase fully controlled thyristor non-circulating current reversible speed regulation system, which can realize voltage and magnetic speed regulation, and the speed range is 35~3500r/min .

(2) AC motor speed regulation

At present, cage induction motors are used in AC spindle drives of CNC machine tools, and vector control frequency conversion speed regulation methods are widely used.

With the improvement of new DC and AC spindle speed motors, motor speed regulation will be widely used. However, in order to reduce costs in economical CNC machine tools, mechanical gear shifting is often used to change the spindle speed.