Rapid lossless identification method for resonant frequency of heavy-load mechanism

Abstract

The invention provides a rapid lossless identification method for resonant frequency of a heavy-load mechanism. A speed step response method and a current step response method are respectively utilized to obtain a load end speed curve and a motor end speed curve in a motor end speed closed-loop state and a motor end speed open-loop state, FFT conversion is carried out on the two speed curves, a harmonic peak is obtained, and the structural resonant frequency and the comprehensive resonant frequency can be rapidly measured. According to the method, the cost of additionally purchasing a set of resonance analyzer is saved, the measurement cost is reduced, the damage of sine frequency sweep measurement to a large heavy-load servo mechanism is also avoided, and the method can be used for quickly identifying the resonant frequency of the structure and can also be used for guiding the design of a servo controller.

Description

Technical Field

[0001] The invention belongs to the field of servo systems, and in particular relates to a method for fast and lossless identification of the resonance frequency of a heavy-load mechanism. Background Art

[0002] Structural resonance has a significant impact on radar servo systems, especially for large load inertia servo systems such as large measurement and control phased array radar servo systems. Structural resonance can usually be considered to be caused by the flexibility of the transmission chain and the load inertia. The impact of structural resonance characteristics on the performance of the servo system is reflected in the limitation of the bandwidth of the servo system. Structural resonance will also couple with the electrical system, which will cause the servo system to have a low frequency and small damping coefficient. The comprehensive resonance acts on the radar motor end speed loop, directly affecting the dynamic performance of the speed loop. For shipborne measurement and control radars, it will also limit the effective improvement of ship shaking isolation. Therefore, it is necessary to identify the structural resonance and comprehensive resonance characteristics, so as to lay the foundation for the design of the bandwidth of each link of the servo system and the adjustment of controller parameters. Summary of the invention

[0003] To this end, the present invention proposes a method for fast and non-destructive identification of the resonant frequency of a heavy-duty mechanism. First, the theoretical relationship between the motor end speed and current, and the load end speed and the motor end speed under open loop is established. On this basis, a step response method is proposed to measure the resonant frequency. The speed step response method and the current step response method are used to obtain the load end speed curve and the motor end speed curve under the closed-loop and open-loop states of the motor end speed, respectively. By performing FFT transformation on the two speed curves, the resonant peak is obtained, and the structural resonant frequency and the comprehensive resonant frequency can be quickly measured. The present invention saves the cost of purchasing an additional set of resonance analyzers, reduces the measurement cost, and avoids the damage of sinusoidal sweep frequency measurement to large heavy-duty servo mechanisms. It can not only be used to quickly identify the structural resonant frequency, but also can be used to guide the design of servo controllers.

[0004] A method for rapid and non-destructive identification of the resonant frequency of a heavy-duty mechanism of the present invention specifically comprises the following steps:

[0005] 1) Resonance generation

[0006] The stiffness of the electromechanical servo system is expressed as torsional stiffness. The stiffness affects the dynamic performance of the system by affecting the resonance characteristics of the system. The structural resonance frequency ω of the electromechanical servo system is defined as l and damping ξ l , comprehensive resonant frequency ω z and damping ξ z ,but:

[0007]

[0008] In the formula, K ml is the torsional stiffness of the system, Jm and J l are the rotational inertia of the motor and load respectively, C l is the velocity damping coefficient.

[0009] Define the motor speed ω m (s) and electromagnetic torque M m (s), motor end speed ω m (s) and the antenna end speed ω l The transfer function relationship between (s) is expressed as:

[0010]

[0011] Where i0 is the reduction ratio of the system.

[0012] The response curve under the motor speed step is a unit step response curve of a typical second-order underdamped system. Its transition process is a decaying oscillation process, and the oscillation frequency is the structural resonance frequency. The response curve under the unit electromagnetic torque step is approximately considered to be an decaying oscillation curve superimposed on the ramp curve, and the decaying oscillation frequency is the comprehensive resonance frequency.

[0013] 2) Rapid identification of resonant frequency

[0014] First, keep the antenna still and assume that the antenna is not subject to external load. Then open the speed loop and close only the current loop. Set the speed command value to 0. At this time, the current loop set value is 0. On this basis, give a step torque current, observe the motor speed output curve, and then perform FFT transformation on the motor speed output curve. The resonant peak of the amplitude-frequency characteristic is identified as the comprehensive resonant frequency.

[0015] Furthermore, before identifying the resonant frequency, the motor speed signal needs to be processed, specifically: the motor speed curve when considering the comprehensive resonance is subtracted from the motor speed curve when not considering the comprehensive resonance, and then the error curve is transformed by FFT. At this time, only the peak near the comprehensive resonant frequency exists in the amplitude-frequency characteristic, and the low-frequency signal introduced by the ramp signal is eliminated, thereby avoiding misjudgment of the comprehensive resonant frequency.

[0016] Furthermore, when the antenna remains stationary and there is no external load, the speed of the motor is given a step, and the speed closed-loop control system responds quickly, so that the motor quickly reaches and maintains the given speed. Through the action of the transmission structure, the speed of the antenna end resolver can be obtained, and then the speed of the antenna end resolver is transformed by FFT. The resonant peak of the amplitude-frequency characteristic is identified as the structural resonant frequency.

[0017] Since the angle measurement at the antenna end is usually obtained through a rotation transformer, if you want to obtain the rotation speed of the antenna end rotation transformer, you need to perform differential processing on the angle output curve.

[0018] The beneficial effects of the present invention are

[0019] 1. A theoretical model of the radar servo transmission system including the structural resonant frequency is established. The structural resonant frequency and the comprehensive resonant frequency of the transmission system can be obtained through the current and speed step response curves respectively.

[0020] 2. Utilize the existing components of the servo control system, including the driver, motor and transmission system, and obtain information such as the resonant frequency through the step response method without adding new hardware.

[0021] 3. Compared with the resonant frequency measurement method using a resonance analyzer, this method does not require additional hardware, simplifies the measurement system architecture, and greatly reduces hardware costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the block diagram of electromechanical transmission when considering the structural torsional stiffness.

[0023] Figure 2 This is the unit electromagnetic torque step and motor speed step response curve.

[0024] Figure 3 This is the schematic diagram of the comprehensive resonant frequency test of the radar servo system.

[0025] Figure 4 Transfer function block diagram of the comprehensive resonant frequency test system for the radar servo system.

[0026] Figure 5 This is a diagram of the comprehensive resonant frequency identification process.

[0027] Figure 6 This is a flow chart of the comprehensive resonant frequency identification process.

[0028] Figure 7 This is the schematic diagram of the radar servo system structure resonant frequency test.

[0029] Figure 8 The transfer function block diagram of the radar servo system structural resonant frequency test system.

[0030] Fig. 9 This is the speed curve of the pitch motor when the enable is turned off instantly.

[0031] Fig.10 The curve diagram of the pitch antenna speed when a 15% step motor speed command is given.

[0032] Fig.11 The amplitude-frequency characteristic curve of the pitch antenna speed when a 15% step motor speed command is given. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The method for rapid and non-destructive identification of the resonant frequency of a heavy-duty mechanism proposed in the present invention specifically comprises the following steps:

[0035] 1) Analysis of resonance generation mechanism

[0036] For electromechanical servo systems with low resonant frequencies, such as large inertia radar servo systems, the influence of system stiffness on the dynamic performance of the servo system cannot be ignored. The stiffness of an electromechanical servo system is usually expressed as torsional stiffness. Stiffness mainly affects the dynamic performance of the system by affecting the resonant characteristics of the system. The block diagram of the electromechanical transmission system considering the torsional stiffness of the system is shown in the attached figure. Figure 1 As shown, R and L in the figure are the equivalent resistance and inductance of the motor respectively.

[0037] Among them, the structural resonant frequency ω l and damping ξ l , comprehensive resonant frequency ω z and damping ξ z It can be expressed as:

[0038]

[0039] In the formula, K ml is the torsional stiffness of the system, J m and J l are the rotational inertia of the motor and load respectively, C l is the velocity damping coefficient.

[0040] Motor speedω m (s) and electromagnetic torque M m (s), motor end speed ω m (s) and the antenna end speed ω l The transfer function relationship between (s) can be expressed as:

[0041]

[0042] Where i0 is the reduction ratio of the system.

[0043] The response curves for unit electromagnetic torque step and unit motor speed step are shown in the attached figure. Figure 2As shown in the figure, the response curve under the unit motor speed step is a unit step response curve of a typical second-order underdamped system, and its transition process is a decaying oscillation process, and the oscillation frequency is the structural resonance frequency; and the response curve under the unit electromagnetic torque step can be approximately regarded as a decaying oscillation curve superimposed on the ramp curve, and the decaying oscillation frequency is the comprehensive resonance frequency.

[0044] 2) Rapid identification method of resonant frequency

[0045] Velocity step response and electromagnetic torque step response are one of the most commonly used methods to test the dynamic performance of a servo system, and are often used to evaluate the bandwidth, stability, and accuracy of the system. Figure 3 The figure shows the test principle of comprehensive resonance identification in the control framework of the existing radar servo system. The test principle is to first keep the antenna stationary and assume that the antenna is not subject to external loads. Then open the speed loop and close only the current loop. Set the speed command value to 0. At this time, the current loop set value is 0. On this basis, a step torque current is given (to prevent the current value from being too large and causing the antenna to accelerate too fast and cause uncontrollable conditions, the current value can generally be 5%-10% of the rated value). Since the response of the current loop is very fast compared to the speed response, it can be considered that the step electromagnetic torque has been added before the antenna starts to rotate. From the attached Figure 3 Establish the transfer function of the test system, as shown in the attached Figure 4 As shown, observing the motor speed output curve, theoretically it should be consistent with the attached Figure 2 At this time, the motor speed output curve is transformed by FFT, and the resonance peak of the amplitude-frequency characteristic is identified as the comprehensive resonance frequency.

[0046] Since the motor speed output curve is superimposed with an approximate ramp output, performing FFT on the ramp signal will reveal a large signal component in the low frequency band, which may drown out the resonance peak. Therefore, before identifying the resonance frequency, the motor speed signal needs to be processed to some extent, as shown in the attached figure. Figure 5 The principle is to subtract the motor speed curve when the comprehensive resonance is considered from the motor speed curve when the comprehensive resonance is not considered, and then perform FFT transformation on the error curve. At this time, only the peak near the comprehensive resonance frequency exists in the amplitude-frequency characteristic, and the low-frequency signal introduced by the ramp signal is eliminated, thereby avoiding misjudgment of the comprehensive resonance frequency.

[0047] The comprehensive resonant frequency identification process flow chart is as follows: Figure 6 As shown, through the above process, the identification of the comprehensive resonant frequency can be completed.

[0048] The transfer function from the motor speed to the load antenna speed is a typical second-order underdamped system transfer function. Figure 2As shown in the figure, when the step motor speed is given, the antenna speed will have attenuated oscillation, and the oscillation frequency is the structural resonant frequency. Therefore, the following can be constructed Figure 7 The structural resonance frequency test system shown in the figure has the following test principle: when the antenna remains stationary and there is no external load, a step motor speed is given, and the speed closed-loop control system responds quickly, so that the motor quickly reaches and remains at a given speed. Through the action of the transmission structure, the rotation speed of the antenna end resolver can be obtained. Since the angle measurement of the antenna end is usually obtained through the resolver, if you want to get the rotation speed of the antenna end, you also need to perform differential processing on the angle output curve to get the antenna rotation speed. Then perform FFT transformation on the antenna rotation speed, and identify the resonance peak of the amplitude-frequency characteristic to obtain the structural resonance frequency.

[0049] In the step motor speed test, you can refer to the conventional step response test process, and give a step speed of about 10-15% of the rated value. At the same time, in order to be able to excite the structural resonance frequency, the speed loop bandwidth must be large enough, and must be greater than 0.7 times the structural resonance frequency. In order to ensure that the motor speed has a high steady-state accuracy, the speed loop bandwidth cannot be too large. Since the motor inertia is smaller than the load inertia, after designing appropriate speed controller parameters, it can be considered that the motor speed responds fast enough compared to the load speed. The motor speed quickly reaches the given speed and stabilizes at the given speed with high precision. At this time, the antenna speed is almost 0. Similarly, from the attached Figure 7 Establish the transfer function of the test system, as shown in the attached Figure 8 As shown, observe the load speed output curve, theoretically it should be consistent with the attached Figure 2 The step motor speed response curve in is similar.

[0050] In order to verify the effectiveness of the proposed test method, an experimental study was carried out on the pitch axis of a radar. The motor moment of inertia of the pitch axis is J m =0.07kgm 2 , the load moment of inertia converted to the motor end is J l =0.32kgm 2 , if the structural resonance frequency is ω l =3Hz, the comprehensive resonant frequency is ω z =About 7Hz.

[0051] First, we conduct a comprehensive resonant frequency test experiment. The test method here is different from the previous one: first, the motor end speed is controlled at a constant speed, and then the motor is turned off instantly, which is equivalent to applying a step load torque, and the effect is similar to applying a step electromagnetic torque. Therefore, according to the above analysis, the motor speed curve is also a ramp curve superimposed with a decaying oscillation curve, and the oscillation frequency is the comprehensive resonant frequency. The motor end speed curve is obtained according to the above method, as shown in the attached figure. Fig. 9As shown, the oscillation period is about 0.164s, from which the comprehensive resonance frequency of the pitch axis can be inferred to be about 6.1Hz.

[0052] When a 15% step motor speed is given, the antenna speed curve can also be obtained as shown in the attached figure. Fig.10 As shown in the figure, it can be seen that under the step motor speed, the antenna speed output curve is a decaying oscillation curve with an oscillation period of about 0.33s. By performing FFT transformation on the antenna speed curve, the amplitude-frequency characteristic curve can be obtained, as shown in the attached figure. Fig.11 As shown in the figure, the amplitude-frequency characteristic curve has a resonance peak near 3Hz, from which it can be determined that this frequency is the structural resonance frequency.

[0053] The present invention is not limited to the above specific implementations, and the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made to the above implementations based on the technical essence of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for rapid and non-destructive identification of the resonant frequency of a heavy-duty mechanism, characterized in that: The specific steps include: 1) Resonance generation The stiffness of the electromechanical servo system is expressed as torsional stiffness. The stiffness affects the dynamic performance of the system by affecting the resonance characteristics of the system. The structural resonance frequency ω of the electromechanical servo system is defined as l and damping ξ l , comprehensive resonant frequency ω z and damping ξ z ,but: In the formula, K ml is the torsional stiffness of the system, J m and J l are the rotational inertia of the motor and load respectively, C l is the velocity damping coefficient; Define the motor speed ω m (s) and electromagnetic torque M m (s), motor end speed ω m (s) and the antenna end speed ω l The transfer function relationship between (s) is expressed as: In the formula, i0 is the reduction ratio of the system; The response curve under the motor speed step is a typical unit step response curve of a second-order underdamped system. Its transition process is a decaying oscillation process, and the oscillation frequency is the structural resonance frequency. The response curve under the unit electromagnetic torque step is approximately considered to be a decaying oscillation curve superimposed on the ramp curve, and the decaying oscillation frequency is the comprehensive resonance frequency. 2) Rapid identification of resonant frequency First, keep the antenna still and assume that the antenna is not subject to external load. Then open the speed loop and close only the current loop. Set the speed command value to 0. At this time, the current loop set value is 0. On this basis, give a step torque current, observe the motor speed output curve, and then perform FFT transformation on the motor speed output curve. The resonant peak of the amplitude-frequency characteristic is identified as the comprehensive resonant frequency.

2. A method for rapid non-destructive identification of the resonant frequency of a heavy-duty mechanism according to claim 1, characterized in that: Before identifying the resonant frequency, the motor speed signal needs to be processed. Specifically, the motor speed curve when the comprehensive resonance is considered is subtracted from the motor speed curve when the comprehensive resonance is not considered, and then the error curve is transformed by FFT. At this time, there is only a peak near the comprehensive resonant frequency on the amplitude-frequency characteristic, and the low-frequency signal introduced by the ramp signal is eliminated, thereby avoiding misjudgment of the comprehensive resonant frequency.

3. The method for rapid non-destructive identification of the resonant frequency of a heavy-duty mechanism according to claim 1 is characterized in that: When the antenna remains stationary and there is no external load, the speed of the motor is given a step speed, and the speed closed-loop control system responds quickly, so that the motor quickly reaches and maintains the given speed. Through the action of the transmission structure, the speed of the antenna end resolver can be obtained. The speed of the antenna end resolver is then transformed by FFT, and the resonance peak of the amplitude-frequency characteristic is identified as the structural resonance frequency.

4. A method for rapid non-destructive identification of the resonant frequency of a heavy-duty mechanism according to claim 3, characterized in that: Since the angle measurement at the antenna end is usually obtained through a rotation transformer, if you want to obtain the rotation speed of the antenna end rotation transformer, you need to perform differential processing on the angle output curve.

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