Dynamic linear motor
Many scholars and research institutes at home and abroad have studied dynamic linear motors, but most of them focus on the optimization of the structure and materials of permanent magnets, the overall structure of the motor, and the control circuit and chip design combined with efficient control strategies. field. However, there are not many researches on its power-to-power ratio and time delay from start-up to steady state. This part has made in-depth discussion on this part.
The moving coil linear motor can continuously convert the externally input voltage signal into a linear displacement of reciprocating linear motion, and can generate electromagnetic force of about 2.5 times of the same size structure, and is widely used with high linearity and small hysteresis characteristics. attention. However, during the movement of the single-coil coil assembly of the conventional structure, eddy current is easily generated inside the magnetic material, so that the electromagnetic force generated by the coil is reduced. At the same time, due to the inherent impedance characteristics of the coil component, there are certain limitations in both response time and response speed. The development of large-output electromagnetic force and high-response moving-coil linear motors is a trend in the field of electrical engineering.
To this end, a new type of moving coil linear motor with two-way reversible control is proposed in this paper. A new type of coil splitting, parallel and parallel conversion combination is adopted for the current-carrying coil, and the loading response time of both ends of the coil is improved by changing the resistance and time constant. The PWM pulse width modulation control method is used to control the magnitude and direction of the coil current, which can not only achieve stable and undisturbed motor switching control, but also realize the large electromagnetic force output and high frequency response characteristics of the device.
Structure and principle
The structure of the moving coil type linear motor is as shown in Fig. 1. A plurality of annular permanent magnets are arranged on the circumference of the inner wall of the casing, and the armature is located in the annular permanent magnet body, and is fixed to one end of the casing by screws. The current-carrying coil is wound around the electromagnetic force coil bobbin and connected to the output shaft, floats through an air gap between the permanent magnet and the armature through a guide pin, and is separated from the outside by a sealing bowl.
The control principle is shown in Figure 3. First, the input signal voltage ui is processed by the amplifier and then loaded into the control coil. The current-carrying control coil together with the electromagnetic force coil bobbin is generated by the electromagnetic force Fcd in the constant magnetic field provided by the permanent magnet. The displacement xc is such that the core is moved together. The coil assembly detects the position error by the displacement sensor and then converts it into a signal voltage, which is compensated to the input signal ur as a correction voltage ue to ensure that the coil assembly remains in the correct position as needed. The magnitude and direction of the electromagnetic force depends on the magnitude and direction of the control current i in the coil. The direction of the electromagnetic force Fcd is changed by changing the direction of the input voltage signal, thereby achieving bidirectional motion. In this way, the system is controlled by closed loop, which also improves its control accuracy and response speed.
The electromagnetic force Fcd is always proportional to the armature current i, and the induced electromotive force E is always proportional to the mover speed vc. The proportional coefficients are called the electromagnetic force constant and the back electromotive force constant, respectively, and the values of the two are slightly different. The effect of the armature reaction, but substantially the same, is approximately the product of the air gap magnetic induction Bg and the effective winding length la. In addition, it does not need to change direction within the stroke range, and the coil inductance is basically unchanged within the stroke range, so the moving coil type linear motor has good controllability.
Combined coil design
The coil is a key component of the moving coil linear motor. Its main function is to convert electrical energy into mechanical energy, which is widely used in the field of actuator control. At present, the commonly used coil winding method is a single coil combination method, and the response speed and electromagnetic force are limited, and the conversion efficiency is low, which is difficult to meet the requirements of energy saving, environmental protection, high efficiency and high speed. In this paper, the original coil is divided into multiple sections equally and used in parallel. Not only greatly reduces the weight and energy consumption of the coil, but also reduces the loss of material energy, and can meet the requirements of large electromagnetic force and high frequency responsiveness.
Under the same voltage, a single set of moving coil coil series component circuit can reduce the response time and improve the response speed, but it is difficult to realize the large electromagnetic force output of the device. Only by maintaining the length of the coil in the magnetic field in the coil of the circuit can the large electromagnetic force output of the device be ensured, and the length of the energized coil in the circuit can be increased by the way of the parallel coil group to increase the electromagnetic force, relative to the opposite of the single coil. The electromotive force does not increase. Uniform splitting and parallel connection of the moving coil coil can reduce the resistance and inductance of the device, reduce the resistance and amplify the current, and greatly improve the electromagnetic force output of the device; however, since the inductance is relatively too small, the response to the moving coil linear motor is not affected. Big.
If the passing current is too large, the generated magnetic field interacts with the air gap magnetic field, resulting in a nonlinear limitation of the magnetic field; a large current is passed for a long time, and the working temperature rises rapidly to cause heat damage, and the working time and life of the motor are limited; the inductance of the coil The presence of the operating current is always easy to reach steady state.
in conclusion
Under the same voltage working condition, compared with the moving coil assembly in series, the single-group moving coil assembly has small circuit resistance and small inductance, which can reduce the response time and improve the response speed, but it is difficult to realize the large electromagnetic force output of the device. Only by maintaining the length of the coil in the magnetic field in the coil of the circuit can the large electromagnetic force of the device be ensured, and the length of the energized coil in the circuit is increased by the way of the parallel coil group to increase the electromagnetic force, and the back electromotive force of the single coil is not increase. In this paper, it is verified that the evenly split coil assembly is designed in parallel, and the step response of the displacement reaches about 1mm, which is reduced from greater than 14.6ms to less than 9.94ms, and the response speed is more than doubled. The electromagnetic force is 10.8N. Increasing to 93.2N, the acceleration has also increased by 8 times. Combined with the PWM control mode, the control of higher frequency response can be realized. The response time of the electromagnetic force reaching the maximum value is reduced to 0.688 ms, which greatly improves the high-frequency response characteristics of the whole device, and achieves short output response time and large electromagnetic force. Features. The moving coil type linear motor can be widely applied to various types of automatic control systems requiring high response speed, such as direct drive type numerical control products, and has a good prospect.
