Plane motor control and its application prospects Zhang Qi (Electronics Forty-fifth Institute of Information Industry, Pingliang 744000, Gansu) 1 Plane motor structure characteristics Planar motor originated from linear motor, also known as x y magnetic air-floating motor. The linear motor is manufactured according to the Sawyer principle, and its overall structure can be divided into two parts: a stator and a mover.
The stator is used as the base platform, and the mover is filled with compressed air by its bottom aperture to form a layer of air cushion suspended on the surface of the stator, which is a movable component. The linear motor mover can only perform uniaxial linear motion on the stator, and the planar motor can do parallel vertical biaxial linear motion. Therefore, the planar motor is also called a two-dimensional motor, as shown in Figures 1 to 3.
2 Planar motor control principle The plane motor is a hybrid motor with stepper motor features for open loop control. However, due to its limited processing accuracy, the processing width of the cogging on the mover and stator is about 0.5. The stepping equivalent is 1/4 cogging width. This step resolution is far from the need of a higher positioning accuracy workbench in practical applications. Therefore, it is necessary to perform subdivision control according to actual requirements. The electronic control system is relatively complicated. The control block diagram is shown in Figure 4.
The control system can be designed to be managed by a separate subsystem under the master computer and exchange commands and data with the P A T bus. The subsystem is based on a single-chip microcomputer, which controls the total movement of the mover on the stator. This structure is beneficial to the combination of software and hardware inside the subsystem, implements high-speed operation control, self-monitoring fault processing, and can realize other components under the supervision of the host. Coordinating and working in parallel to lay the foundation for improving the efficiency of the whole machine.
The key technologies of control hardware design are roughly 4: special equipment for electronic industry (1) smooth subdivision technology. It not only satisfies high resolution, improves the accuracy of the order of magnitude, but also improves the operating characteristics, reduces the oscillation caused by the air cushion rigidity, and makes the operation smooth and stable.
(2) A large number of hardware control triggers are used. It makes high-frequency pulse frequency division, frequency modulation and timing efficient and accurate, and compensates for the weakness of software with low operation speed and poor accuracy, and solves the contradiction between high subdivision rate and high speed step, and achieves good dynamic performance.
(3) Acceleration dynamic closed-loop detection technology. The suppression of the mover oscillation reduces the vibration time to less than 20 s, which consolidates the dynamic performance.
(4) Full-stroke array automatic compensation technology. Planar motors have inherent errors due to their unique processing methods. The accuracy error of the machining of the cogging of the mover can cause periodic error. The accuracy of the machining error of the stator cogging can cause linear accumulation error, the straightness error of the machining of the stator cogging, the verticality error caused by the orthogonal machining, and the running process. The nonlinear expansion error of the mover and stator caused by the heat of the mover, the hysteresis error between the mover and the stator, and the like. These errors reduce the positioning accuracy, repeatability and orthogonality of the planar motor. Only by accurately measuring the various error distributions, and performing data processing according to the specific conditions, and finally determining the accurate compensation data, can effectively compensate the inherent processing of the planar motor. The error ensures the positioning accuracy of the plane motor.
3 Planar motor table characteristics and its application prospects Planar motors with their unique structural features are unique in the field of two-dimensional workbench applications, with many advantages. The mover acts as a moving body actuator with air cushion isolation from the stator, which is a frictionless operation. It has long life and good dynamic performance. The air cushion has a resonance that suppresses the self-oscillation of the mover during the starting and stopping operations and possibly the components that may be extended. The mover itself is lightweight and easy to load on all the required mechanisms. In practice, a high-efficiency two-dimensional table with good dynamic characteristics can be designed with large acceleration and speed and stability.
As a two-dimensional workbench, the flat motor has a simple structure, large working stroke and small volume. Compared with the two-dimensional table with double-layer lead screw guide structure, the height and its inertia are greatly reduced, and there is no mechanical wear, which simplifies the workbench. structure.
The plane motor double-dimensional workbench has been applied for the first time in the LT-109 automatic probe station of the national 85 practical research project I have undertaken, and the high-precision and high-speed performance of the workbench is realized. The design level of the control system is obtained. The improvement has been affirmed by the experts.
Limited to the processing level of domestic flat motors, there is no production self-sufficiency in China. The series of planar motors used by EG in the United States are excellent in performance but expensive. The performance of the series of flat motors produced in Belarus is slightly lacking. The plane motor I introduced has small static thrust, poor carrying capacity, easy heat generation of the mover and causes such as low acceleration, and large nonlinear expansion error caused by the temperature rise of the mover, which restricts the reasonable application and reduces the performance of the equipment.
Therefore, the cost-effectiveness of integrated equipment and the rational introduction of high-performance planar motor worktables are promising. In the low, medium and high-grade mid-measures of the US EG company, the plane motor workbench maintains an eternal position. It has also proved its superiority in practice, and as a basic technology, it can be extended to a wide range of fields. For example, in the DSW equipment, the servo system uses a planar motor and uses a closed-loop control of the grating. The structure is greatly simplified and has good dynamic and static performance. This is the way we are worth learning and the new world worth exploring.
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