The traditional "rotary motor + ball screw" feed drive mode on the machine tool is difficult to achieve breakthrough improvement in feed speed, acceleration and rapid positioning accuracy due to its own structure limitation. Ultra-precision machining puts higher requirements on the servo performance of the machine feed system. Linear motors convert electrical energy directly into linear motion mechanical energy without the need for any intermediate conversion mechanism. It has the advantages of large starting thrust, high transmission rigidity, fast dynamic response, high positioning accuracy and unlimited stroke length.
In the machine feed system, the biggest difference between the direct drive of the linear motor and the original rotary motor drive is that the mechanical drive between the motor and the table (the carriage) is eliminated, and the length of the machine feed chain is shortened to zero. Therefore, this type of transmission is also called "zero transmission". It is precisely because of this "zero transmission" mode that the performance indicators and advantages that the original rotating motor drive method cannot achieve.
1, high speed response
Because the mechanical transmission parts (such as the lead screw) with large response time constant are directly eliminated in the system, the dynamic response performance of the whole closed-loop control system is greatly improved, and the reaction is extremely sensitive and quick.
2, accuracy
The linear drive system eliminates the transmission gap and error caused by the mechanical mechanism such as the lead screw, and reduces the tracking error caused by the delay of the transmission system during the interpolation motion. Through the linear position detection feedback control, the positioning accuracy of the machine tool can be greatly improved.
3. The dynamic stiffness is high due to the “direct driveâ€, which avoids the movement hysteresis caused by the elastic deformation, friction and wear and backlash of the intermediate transmission link during starting, shifting and reversing, and also improves the transmission rigidity.
4, fast speed, short acceleration and deceleration process
Since linear motors were first used mainly for maglev trains (up to 500km/h), they are used in machine feed drives to meet the maximum feed rate for ultra-high-speed cutting (required to be 60-100M/min or higher). Of course there is no problem. Due to the high-speed responsiveness of the above-mentioned "zero transmission", the acceleration and deceleration process is greatly shortened. In order to achieve high speed at the moment of starting, it can be quasi-stop at high speed. Higher accelerations are available, typically up to 2 to 10 g (g = 9.8 m/s2), while the maximum acceleration of a ball screw drive is typically only 0.1 to 0.5 g.
5. The length of the stroke is not limited. By connecting the linear motor on the guide rail, the stroke length can be extended indefinitely.
6, the movement is quiet, low noise. Since the mechanical friction of the components such as the drive screw is eliminated, and the guide rail can adopt the rolling guide or the magnetic pad suspension guide (no mechanical contact), the noise during the movement will be greatly reduced.
7, high efficiency. Since there is no intermediate transmission link, the energy loss during mechanical friction is eliminated, and the transmission efficiency is greatly improved.
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