Vibration reduction method for stepping motor system

Abstract

The invention belongs to the technical field of stepping motor control, and particularly relates to a stepping motor system vibration reduction method. The invention provides a stepping motor system vibration reduction method which reduces or eliminates pulse vibration caused by traditional PWM square waves by designing innovative stepping motor current control wave performance. According to the method, fixed bearings are symmetrically installed on the two sides of the stepping motor, so that vibration generation and conduction of the stepping motor are stabilized and weakened.

Description

Technical Field

[0001] The invention belongs to the technical field of stepper motor control, and more specifically, relates to a method for reducing vibration of a stepper motor system. Background Art

[0002] The stepper motor system can provide precise speed and angle control, provide various levels of torque, and is widely used in many fields such as measurement and control, engineering machinery, CNC equipment, and robotics. Due to the existence of the inherent frequency vibration of the stepper motor system, electromagnetic torque pulses, PWM high-frequency pulses, vibration caused by load swing, etc., especially when these frequencies overlap, it will cause non-negligible resonance in the stepper motor system.

[0003] There are generally two ways to solve the vibration and resonance problems of stepper motor systems: the first method is to slow down the current change input to the stepper motor rotor by increasing the subdivision of the PWM pulse output by the stepper motor controller, that is, by reducing the unit time change of the stepper motor input current, reducing the torque mutation caused by the current change, thereby reducing the vibration and resonance of the stepper motor system. Another way to solve the vibration and resonance of the stepper motor system is to increase the shock absorption damping, increase the torque load, and increase the reduction mechanism. Increasing the shock absorption damping is a physical shock absorption method, such as adding rubber gaskets to the system, implementing a rigid connection between the output shaft and the load, etc., which transmits the vibration of the stepper motor system to the outside of the system in a physical way, thereby reducing the vibration and resonance of the system. Therefore, this is a measure that cannot fundamentally reduce or eliminate the vibration and resonance of the system. Reducers are usually used to increase torque while reducing motor speed, but the increased rigidity helps to suppress the transmission of vibration from the motor to the load, and the gear friction helps to reduce overshoot and undershoot. At the same time, the reducer increases the load and power, which brings several defects: 1. While maintaining the output speed, the stepper motor drive current needs to be increased, which will bring more serious pulse torque and increase the risk of vibration and resonance. 2. In order to increase the output torque of the stepper motor, the speed of the stepper motor needs to be reduced, and the resonance range of the stepper motor is just in the lower speed range, and there is a risk of common frequency vibration of the stepper motor's natural frequency, pulse torque frequency, and PWM frequency. 3. Since the reducer is installed on one side of the stepper motor (the output shaft side), there is a torque imbalance problem for the stepper motor, which increases the risk of vibration in the stepper motor system. In addition, the traditional sinusoidal current control method has a period of zero current when the current passes through zero, which will cause the disappearance of torque and torque pulses, and then cause vibration and resonance of the stepper motor system. Summary of the invention

[0004] In order to solve the frequency pulse vibration and resonance caused by the rich harmonics of the traditional PWM square wave, it is necessary to further optimize the current control scheme of the stepper motor; eliminate the zero current at the zero crossing point; improve the vibration reduction scheme of the mechanical structure, etc. The present invention proposes a method for reducing vibration of a stepper motor system, which reduces or eliminates the pulse vibration caused by the traditional PWM square wave by designing an innovative stepper motor current control wave. The method stabilizes and weakens the vibration generation and conduction of the stepper motor by symmetrically installing fixed bearings on both sides of the stepper motor.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for reducing vibration of a stepper motor system comprises the following steps: the stepper motor system comprises a stepper motor, bearings are fixedly mounted on both sides of the stepper motor symmetrically, and the distance between the bearing and the stepper motor is L, which is defined as follows:

[0007]

[0008] Among them, F z is the typical torque value of the corresponding bearing model, r is the radius of the stepper motor rotor, J is the moment of inertia of the stepper motor rotor, and a is the typical operating angular acceleration of the stepper motor rotor;

[0009] The stepper motor controller current i k (t) are as follows:

[0010]

[0011] Where E is twice the amplitude, ω is the basic frequency of the PWM waveform, E=2, ω=0.5, k=2or 3.

[0012] This technical solution is further optimized, wherein k=3,

[0013] Δt=0.06*T

[0014] Where Δt is the duration of the current step when the stepper motor controls the sinusoidal current at the zero-crossing point, and T is the current control cycle of the stepper motor.

[0015] The technical solution is further optimized in that one side bearing of the stepper motor is connected to the load.

[0016] Different from the prior art, the above technical solution has the following beneficial effects:

[0017] 1. By designing an innovative stepper motor current control solution, the pulse vibration problem caused by the rich harmonics of the traditional PWM square wave is solved. It not only eliminates the high-order harmonic components of the square wave, but also maintains the characteristic of the constant current during the same phase period of the square wave to a certain extent, thereby improving the ability to output stable torque under the premise of vibration reduction.

[0018] 2. By maintaining the current step near the zero point of the stepper motor current (the current remains unchanged during the flat period and the current changes phase rapidly), the continuity of the current at the zero point is ensured to avoid the disappearance of torque due to the short-term disappearance of current and the resulting torque pulse vibration problem.

[0019] 3. By symmetrically installing fixed bearings at designated positions on both sides of the stepper motor shaft, the vibration generation and transmission of the stepper motor can be stabilized and weakened. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the current control scheme of the stepper motor controller;

[0021] Figure 2 This is a schematic diagram of the current zero-crossing processing;

[0022] Figure 3 Schematic diagram of the axially symmetrical installation of fixed bearings on both sides of the stepper motor. DETAILED DESCRIPTION

[0023] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0024] 1. Stepper motor controller current solution

[0025] The stepper motor controller uses PWM square wave current to accurately control the speed and angle of rotation of the stepper motor. Since the square wave contains rich harmonics, when the harmonics overlap or partially overlap with the natural frequency of the stepper motor and its multiples, the motor torque pulse frequency and its multiples, the stepper motor system will resonate and vibrate, causing failures and accidents such as loss of steps, abnormal load operation, and runaway. Although the traditional sinusoidal current control of the stepper motor can reduce the impact of harmonics, it loses the characteristic that the current in the same phase period of the square wave remains unchanged, that is, the ability of the stepper motor to continuously output stable and large torque is reduced, which is not conducive to stable load driving. For this reason, it is necessary to improve the PWM square wave current and sinusoidal current driving methods, so as to maintain the sine wave to reduce the impact of harmonics, and to maintain the characteristic of the sine wave in the same phase period to a certain extent. The current formula of the stepper motor controller of the present invention is as follows

[0026]

[0027] Where E is twice the amplitude, ω is the basic frequency of the PWM waveform. When E=2, ω=0.5, k=1,2,3,4, the current i k The waveform of (t) is as follows Figure 1 As shown in the figure, it is a schematic diagram of the current control scheme of the stepper motor controller. Figure 1It can be seen that when k is 1, the current wave still retains a large high-frequency pulse; when k is 2 or 3, the high-frequency pulse basically disappears, while maintaining a relatively flat current constant platform curve, so the present invention takes k=2or3; when k is 4, the current platform becomes narrower to a level close to a sine wave, which is also undesirable.

[0028] 2. Current zero-crossing processing

[0029] When the stepper motor switches phases, if the current changes slowly, such as in a sinusoidal current control method, the current will remain at zero for a period of time at the zero crossing point. During this period of time, the torque of the stepper motor disappears due to the zero current, which in turn causes a torque pulse. This can easily cause vibration and resonance of the stepper motor system. In order to solve this defect of the traditional sinusoidal current control method, the current change rate of the stepper motor is increased at the zero crossing point to ensure the continuity of the current. The present invention also increases the continuity of the current by maintaining a current step near the current zero crossing point (the current remains unchanged during the flat step period). Taking k in formula (1) as 3 as an example, the control current waveform is as follows: Figure 2 As shown, this is a schematic diagram of the processing at the current zero crossing. Figure 2 The total width of the steps in the stepper motor needs to be adjusted according to the stepper motor speed, stepper motor structure, and working conditions. The empirical value of the present invention is

[0030] Δt=0.06*T (2)

[0031] Among them, Δt is the duration of the current step when the stepper motor controls the sinusoidal current at the zero crossing point, that is, the total duration of keeping the current constant (including positive and negative steps). Figure 2 There are specific marks in . T is the current control period of the stepper motor.

[0032] 3. Vibration reduction by installing fixed bearings symmetrically on both sides of the stepper motor

[0033] Reducers are usually used to increase torque while reducing motor speed, but the increased rigidity helps to suppress vibration transmission from the motor to the load. In terms of control stability, the role of the reducer is similar to installing a fixed bearing on the output shaft of the stepper motor to stabilize and reduce the vibration transmission of the stepper motor. However, since the reducer is installed on one side of the stepper motor (the output shaft side), there is a torque imbalance problem for the stepper motor, which increases the risk of vibration in the stepper motor system. The present invention stabilizes and reduces the vibration generation and transmission of the stepper motor by axially symmetrically installing fixed bearings on both sides of the stepper motor, such as Figure 3 The figure shows a schematic diagram of the fixed bearings installed symmetrically on both sides of the stepper motor. Figure 3It can be seen that in order to stabilize the vibration of the stepper motor, the distance L between the bearing and the stepper motor should be able to meet the working conditions of the bearing and the torque requirements of the stepper motor rotor. The distance L of the present invention is defined as follows:

[0034]

[0035] Among them, F z is the typical torque value of the corresponding bearing model, r is the radius of the stepper motor rotor, J is the moment of inertia of the stepper motor rotor, and a is the typical operating angular acceleration of the stepper motor rotor.

[0036] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or terminal device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or terminal device. In the absence of further restrictions, the elements defined by the sentence "include..." or "comprise..." do not exclude the existence of other elements in the process, method, article or terminal device including the elements. In addition, in this article, "greater than", "less than", "exceed" and the like are understood to exclude the number itself; "above", "below", "within" and the like are understood to include the number itself.

[0037] Although the above embodiments have been described, once those skilled in the art know the basic creative concepts, they can make additional changes and modifications to these embodiments. Therefore, the above description is only an embodiment of the present invention and does not limit the patent protection scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the specification and drawings of the present invention, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for reducing vibration of a stepper motor system, characterized in that: The stepping motor system includes a stepping motor, and bearings are fixedly installed on both sides of the stepping motor in a symmetrical manner. The distance between the bearing and the stepping motor is L, which is defined as follows: Among them, F z is the typical torque value of the corresponding bearing model, r is the radius of the stepper motor rotor, J is the moment of inertia of the stepper motor rotor, and a is the typical operating angular acceleration of the stepper motor rotor; The stepper motor controller current i k (t) are as follows: Where E is twice the amplitude, ω is the basic frequency of the PWM waveform, E=2, ω=0.5, k=2 or 3.

2. The method for reducing vibration of a stepper motor system as claimed in claim 1, characterized in that: k=3, Δt=0.06*T Where Δt is the duration of the current step when the stepper motor controls the sinusoidal current at the zero-crossing point, and T is the current control cycle of the stepper motor.

3. The method for reducing vibration of a stepper motor system as claimed in claim 1, characterized in that: One side bearing of the stepper motor is connected to a load.

Images