Patent Application
20100109639
1. Technical Field
The present disclosure relates to analysis systems and methods, and particularly to a frequency spectrum analysis system and method.
2. Description of the Related Art
In the machining field, machining performances of a servo system not only depend on driver, motor, and characteristics of the servo system itself, but also optimum control parameters of the machine. It is important to get the optimum control parameters for the servo system working according to different machining conditions. When the servo system has optimum control parameters, the frequency range of the output signal of the servo system is greatest when the servo system is stable. The greatest frequency range is taken as a desired frequency bandwidth. Generally, a simulation module of the servo system is employed for a frequency spectrum analysis to determine the optimum control parameters. However, this method is not as precise as desired in practice.
Referring to
The control platform 100 includes a first transmission device 102, such an such as an RS-232 interface, an RS-485 interface and so on The driver 200 includes a second transmission device 202, a signal source 204, and a data logger 206. The first transmission device 102 of the control platform 100 is connected to the second transmission device 202 of the driver 200. The second transmission device 202, such as an RS-232 interface, an RS-485 interface and so on, is connected to the signal source 204. The signal source 204 is connected to the data logger 206 and the motor 300. The data logger 206 is connected to the motor 300 and the second transmission 202. The signal source 204 is capable of providing different frequencies, such as a chirp source (e.g., a short, sharp frequency source) for example, but the disclosure is not limited thereto. In one exemplary embodiment, the attenuation value of output signals of the motor 300, functioning as output signals of the servo system, is −3 dB. That is to say, the output signal divided by the input signal is 0.707, and the logarithm of 0.707 multiplied by 20 dB is −3 dB. When an output signal is 0.707 times an input signal of the motor 300, the frequency bandwidth of a control loop of the servo system 400 can be obtained by adjusting the PI plus of the control loop if the servo system 400 is stable.
Referring to
In block S1, the control platform 100 sets a frequency response condition of a control loop of the servo system 400, such as an offset value, a magnitude value, and a sampling time of the input signal of the control loop of the servo system 400.
In block S2, the control platform 100 transmits a trigger command to the signal source 204 via the first transmission device 102 and the second transmission device 202 to trigger the signal source 204.
In block S3, the signal source 204, according to the trigger command, provides a frequency response trigger signal as the input signal of the control loop of the servo system 400, and transmits the input signal to the motor 300 and the data logger 206.
In block S4, the motor 300 outputs an output signal according to the input signal, and the output signal of the motor 300 functioning as an output signal of the servo system 400 is transmitted to the data logger 206.
In block S5, the data logger 206 records the input signal and output signal of the motor 300, and transmits the input signal and output signal of the motor 300 to the control platform 100.
In block S6, the control platform 100 stores the input signal and the output signal of the motor 300 in a memory (not shown).
In block S7, the input signal and the output signal of the motor 300 are processed by the control platform 100 by processing the input signal and the output signal using a fast Fourier transform.
In block S8, the control platform 100 draws a magnitude-frequency characteristic curve of the input signal and the output signal of the motor 300 using the fast Fourier transform, and determines an attenuation value of the output signal thereby to obtain the frequency range of the output signal of the servo system 400.
Then, a determination is made whether the frequency range is the frequency bandwidth according to state performance of the servo system 400. The state performance of the servo system 400 may be according to steady state performance of the servo system 400, and the PI plus of the control loop of the servo system 400 can be adjusted as needed. In one embodiment, the determination may be done by an operator of the servo system 400. Hereinafter, the speed control loop and the current control loop of the servo system 400 are used to provide a detailed explanation about the frequency spectrum analysis system 10 and the method for the same.
The control platform 100 stores the speed input signal V1 and the speed output signal V2 in the memory, and processes the speed input signal V1 and the speed output signal V2 using the fast Fourier transform for transforming the speed input signal V1 and the speed output signal V2 from the time domain to the frequency domain. Then, the control platform 100 draws a magnitude-frequency characteristic curve of the speed input signal V1 and the speed output signal V2 as shown in
If the servo system 400 is determined to be stable, that is to say, noise and vibration of the motor 300 are in a permitted range, the frequency range may be less than the frequency bandwidth. Therefore, the frequency range of the speed control loop of the servo system 400 can be increased by increasing the PI plus of the speed control loop so as to obtain the frequency bandwidth. However, the servo system 400 may become unstable when the PI plus of the speed control loop is increased to a certain value. When the servo system 400 is unstable, that is to say, the noise and the vibration of the motor 300 exceed the permitted range, the frequency range may be more than the frequency bandwidth. Therefore, the frequency range can be decreased by reducing the PI plus of the speed control loop so as to obtain the frequency bandwidth. When the frequency bandwidth is determined, the PI plus, functioning as a control parameter of the speed control loop of the servo system 400, is determined.
The control platform 100 stores the current input signal I1 and the current output signal I2 in the memory, and processes the current input signal I1 and the current output signal I2 by the fast Fourier transform for transforming the current input signal I1 and the current output signal I2 from the time domain to the frequency domain. Then the control platform 100 draws a magnitude-frequency characteristic curve of the current input signal I1 and the current output signal I2 as shown in
If the servo system 400 is determined to be stable, that is to say, noise and vibration of the motor 300 are in a permitted range, the frequency range of the current control loop of the servo system 400 may be less than the frequency bandwidth. Therefore, the frequency range can be increased by increasing the PI plus of the current control loop so as to obtain the frequency bandwidth. However, the servo system 400 may become unstable when the PI plus of the current control loop is increased to a certain value. When the servo system 400 is unstable, that is to say, the noise and the vibration of the motor 300 exceed the permitted range, the frequency range may be more than the frequency bandwidth. Therefore, the frequency range can be decreased by reducing the PI plus of the current control loop so as to obtain the frequency bandwidth. When the frequency bandwidth is determined, the PI plus functioning as a control parameter of the current control loop of the servo system 400, is determined.
In one exemplary embodiment, the control parameters such as PI plus values of other control loops of the servo system 400, such as a pressure control loop of the servo system 400, can be determined by using the frequency spectrum analysis system and method mentioned above. The selection of attenuation value of 3 dB can be other values.
It is to be understood, however, that even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200810305333.X | Oct 2008 | CN | national |
