The main shaft system of the hydraulic press is divided into the main shaft system of the stepless variable speed hydraulic machine, the main shaft system of the continuously variable hydraulic machine and the main shaft system of the sectional continuously variable hydraulic machine according to the mode of speed change. The stepped variable speed hydraulic machine spindle system is mostly used in economical CNC hydraulic machine tools. At present, most CNC hydraulic machine tools use a continuously variable speed hydraulic machine spindle system and a segmented continuously variable hydraulic machine spindle system.
1. Main shaft system of step-variable hydraulic press
The main shaft motor of the hydraulic press in the main shaft drive system of the step-variable hydraulic press is mostly an ordinary three-phase asynchronous motor, and the start and stop of the main shaft of the hydraulic press are controlled by an electric circuit. The speed control of the main shaft drive system of a step-variable hydraulic press is realized by changing the motor winding connection (delta to double star) or changing the gearbox transmission ratio.
2. Continuously variable hydraulic machine spindle system
CNC hydraulic machine tools generally adopt a DC hydraulic machine spindle drive system or an AC drive system to realize the stepless speed change of the hydraulic machine spindle. DC hydraulic press spindle drive system is often used in early CNC hydraulic machine tools. DC motors have shortcomings such as easy wear of brushes, narrow constant power speed regulation range, large size, and difficult maintenance. AC motors and their drives have no brushes, will not produce sparks, have a long service life, and their performance has reached the level of DC drive systems. Therefore, the main shaft drive system of AC hydraulic press gradually replaces the DC drive system and is widely used.
However, when using general frequency converters for speed regulation, AC motors do not have the excellent speed regulation characteristics of DC motors, so vector frequency conversion control technology is required. At present, vector frequency conversion is an ideal method for speed regulation and control of AC motors, and it has become a mature technology. The basic idea of vector frequency conversion is to simulate an AC motor into a DC motor for control through a series of coordinate transformations, so that the speed regulation performance similar to that of a DC motor can be obtained. At present, the hydraulic spindle drive system of most CNC hydraulic machine tools is composed of a squirrel cage AC asynchronous motor and a vector frequency converter.
The working characteristic curve of the spindle motor of the hydraulic press is shown in Figure 1. In the constant torque region, the power of the motor decreases with the decrease of the speed. In the constant power region, the maximum output torque of the motor decreases with the increase of the spindle speed of the hydraulic press. The speed regulation characteristic of the three-phase asynchronous motor is that the constant torque speed regulation range is large, while the constant power speed regulation range is small.
3. Subsection stepless variable speed hydraulic machine main shaft system
In actual production, the spindle motor of the hydraulic press is generally required to have a constant torque transmission when running at low speeds, and a constant power transmission when running at medium and high speeds. It is not necessary for the entire variable speed range to be constant power. The constant torque speed range of the continuously variable motor meets the constant torque speed range required by CNC hydraulic machine tools, but its constant power speed range cannot meet the needs of CNC hydraulic machine tools. Therefore, generally a group of gear transmission groups are connected in series after the continuously variable transmission mechanism as a stepwise transmission mechanism to expand the constant power transmission range of the motor.
