Application Advantage of Linear Motor Zero Drive in Machine Tool Feed System

Date: 2018-12-25
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In the feed system of machine tool, linear motor is used to drive directly. The biggest difference between the drive mode of the original rotary motor and that of the original rotary motor is that the mechanical intermediate transmission link between the motor and the worktable (trailer) is cancelled. That is to say, the length of the feed chain of the machine tool is reduced to zero. Therefore, this transmission mode is called 'direct drive' or 'zero drive'. Direct drive avoids the shortcomings of reverse clearance, inertia, friction and rigidity in screw drive. The development and application of linear motor system has caused a sudden change in the traditional feeding mechanism structure of machine tool industry. Through advanced electrical control, not only the feeding mechanism has been simplified, but also the performance index of machine tool has been greatly improved, which is mainly manifested in the following aspects:

(1) High-speed responsiveness

Generally speaking, the dynamic response time of mechanical transmission parts is several orders of magnitude longer than that of electrical components. The dynamic response performance of the closed-loop control system is greatly improved by eliminating some mechanical transmission parts with large response time constants, such as lead screw, which makes the response abnormally sensitive and fast.

(2) High accuracy

Because the mechanical transmission mechanism such as screw is cancelled, the tracking error caused by the lag of transmission system in interpolation is reduced. Through feedback control of linear position detection, the positioning accuracy of machine tools can be greatly improved.

(3) High transmission stiffness and stable thrust

Direct drive improves its transmission stiffness. At the same time, the layout of linear motor can be arranged according to the surface structure of the machine tool guide and the force acting on the worktable when it moves. Usually, it is designed to be symmetrical and uniformly distributed, so that its motion thrust is stable.

(4) Fast speed, short acceleration and deceleration process

Linear motors were first mainly used in maglev trains (up to 500 km/h per hour). Now they are used in machine tool feed drive. It is no problem to satisfy the maximum feed speed of ultra-high speed cutting (up to 60-100 m/min or higher). Because of the high-speed responsiveness of 'zero drive', the acceleration and deceleration process is greatly shortened, so that it can achieve high-speed instantaneously when starting and quasi-stop instantaneously when running at high speed. Generally, the acceleration can reach 2-10g (g=9.8m/s2).

(5) Travel length is unrestricted

The travel length of the moving parts can be indefinitely extended by connecting the fixed parts of the linear stepping motor in series on the guide rail.

(6) Low noise during operation

Because the mechanical friction of the transmission screw and other parts is eliminated, and the slideway pair can also adopt rolling guideway or magnetic cushion suspension guideway (without mechanical contact), the motion noise is greatly reduced.

(7) high efficiency

Because there is no intermediate transmission link, the energy loss caused by mechanical friction is eliminated.

(8) Fully closed-loop control system

Because the motor of the linear motor and the worktable of the machine have been combined into one, the feed unit of the linear motor can only adopt the full closed-loop control system, which is different from the feed unit of the ball screw.

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