CN1918523A - System and method for adjusting a pid controller in a limited rotation motor system - Google Patents

Abstract

The invention discloses a diagnosis system for analyzing a limited rotating electric machine system, and the diagnosis system includes a first transformation unit, a second transformation unit, a closed-loop frequency response unit, and a diagnosis unit. The first transformation unit is configured to receive a first digital signal representing a motor control signal (35), and to provide a motor control frequency domain signal representing a frequency domain representation of the motor control signal. The second transformation unit is configured to receive a second digital signal representing a position detection signal (42), and to provide a position detection frequency domain signal representing a frequency domain representation of the position detection signal. The closed loop frequency response unit is operable to identify a representation of a frequency response of a constrained rotating electrical machine responsive to the position detection frequency domain signal and the motor control frequency domain signal. The diagnostic unit (50) is operable to compare the representation of the frequency response with a previously recorded representation of the frequency response to identify an error condition (52) associated with the limited rotating electric machine system.

Description

System and method for diagnosing a controller in a constrained rotating electric machine system

This application claims priority to U.S. Provisional Patent Application Serial No. 60/538,842, filed January 23, 2004, and claims priority to U.S. Provisional Patent Application Serial No. 60/575,255, filed May 28, 2004, and claims 2004 Priority to U.S. Provisional Patent Application Serial No. 60/613,962, filed September 28, 2009.

Background technique

The present invention relates generally to limited rotating electric machine systems, and more particularly to systems and methods for diagnosing and adjusting limited rotating electric machine systems.

Limited rotation motors generally include stepper motors and constant speed motors. Certain stepper motors are also suitable for applications requiring high duty cycle sawtooth scanning at high speeds and large scan angles. For example, US Patent No. 6,275,319 discloses an optical scanning device for raster scanning applications.

However, limited rotation motors for some applications require the rotor to move between two positions at a precise and constant speed rather than by stepping and settling in a sawtooth fashion. These applications require that the time required to reach a constant velocity be as short as possible, and that the amount of error in the attained velocity be as small as possible. Constant speed motors generally provide a higher torque constant and typically include a rotor and drive circuitry for rotating the rotor about a central axis, and a position transducer, such as a tachometer or position sensor, and a feedback circuit coupled to the transducer , which allows the rotor to be driven by a drive circuit that responds to input and feedback signals. For example, US Patent No. 5,424,632 discloses a conventional bipolar limited rotating electrical machine.

Limited rotating torque motors can be modeled or represented by a double integrator model plus several flexible modes and low frequency nonlinear effects. A typical closed-loop servo system for a galvanometer includes integrating action for low-frequency uncertainties and a notch filter for high-frequency resonant modes. The system was chosen to operate in the mid-frequency range where it can be well modeled using rigid solids. For a double integrator rigid solid model, there is a direct relationship between the open-loop gain and the crossover frequency on the frequency response curve. For example, in 1996, Y.H.Huang, S.Weerasooriya and T.S.Low, J.Applied Physics "Autotuning of aservowriter head positioning system with minimum positioning error" v.79pp.5674-5676 disclosed in the servo recorder head positioning system Auto-tuning system.

FIG. 1 illustrates a prior art limited rotation torque motor system 10 . System 10 includes a controller 12 (eg, a position, integral, derivative, or PID controller) that receives input commands 14 . A controller 12 provides control signals to a motor 16 that moves an optical element, such as a mirror, to provide a change in position 18 in response to an input command 14 . The system also includes a position detector 20 that provides a position detection signal 22 that is also provided to the controller 12 as is the input command 14 . If the controller cannot adapt to these changes, the system's open-loop gain (or 0dB cross-over variation) will affect the closed-loop system performance.

For example, such constrained rotation motors can be used in various laser scanning applications, such as high-speed surface metrology. Other laser processing applications include laser welding (e.g., high-speed spot welding), surface treatment, cutting, drilling, marking, cleaning welds, laser repair, rapid prototyping, forming microstructures, or forming densely packed nanostructures on various materials structure.

However, limited rotational torque motors ultimately failed after limited use. Failure can come at unexpected times when it is more difficult to develop a method of driving a motor with limited rotation. The ability to measure the condition of a constrained rotating electric machine helps to predict the lifetime of the electric machine. Additionally, it would be desirable to be able to measure the condition of a constrained rotating motor in situ without requiring the motor to be returned to the factory for analysis.

Accordingly, there is a need for a method of monitoring a limited rotation torque motor, and more particularly a method of diagnosing the health and life of a limited rotation torque motor.

Contents of the invention

According to one embodiment, the present invention provides a diagnostic system for analyzing a limited rotating electric machine system. The diagnosis system includes a first conversion unit, a second conversion unit, a closed-loop frequency response unit and a diagnosis system. The first converting unit is used for receiving a first digital signal representing a motor control signal, and for providing a motor control frequency domain signal representing a frequency domain representation of the motor control signal. The second transformation unit is configured to receive a second digital signal representing the position detection signal, and to provide a position detection frequency domain signal representing a frequency domain representation of the position detection signal. The closed loop frequency response unit is for identifying a representation of a frequency response of a constrained rotating electrical machine in response to a position detection frequency domain signal and a motor control frequency domain signal. The diagnostic unit is operable to compare the representation of the frequency response with a previously recorded representation of the frequency response in order to identify an error condition related to the limited rotating electric machine system.

Description of drawings

The following description can be further understood with reference to the accompanying drawings, in which:

Figure 1 shows a schematic diagrammatic functional diagram of a constrained rotating electrical machine and a control system according to the prior art;

Figure 2 shows a schematic diagrammatic functional diagram of a constrained rotating electrical machine and diagnostic system according to one embodiment of the invention;

Figures 3A and 3B show schematic graphical representations of a pseudorandom binary sequence of excitation signals provided to a motor controller and associated position detection signals produced by the motor in response to the pseudorandom binary sequence;

Figure 4 shows a schematic diagrammatic representation of a diagnostic unit according to an embodiment of the invention;

Figure 5 shows a schematic graphical representation of the measured frequency response of a system according to one embodiment of the invention;

Figure 6 shows a schematic graphical representation of measured frequency responses showing changes in low frequency response, according to some embodiments of the invention;

Figure 7 shows a schematic graphical representation of the measured frequency response showing a change in torque constant according to another embodiment of the present invention;

Figure 8 shows a schematic graphical representation of a measured frequency response exhibiting asymmetric performance according to yet another embodiment of the present invention;

Figure 9 shows a schematic diagrammatic functional diagram of a limited rotation electric machine and diagnostic system according to yet another embodiment of the present invention;

The figures are shown for illustrative purposes only.

Detailed ways

According to various embodiments of the present invention, limited rotating electric machine performance data is captured from the electric machine system, and the data is analyzed to determine diagnostics of various conditions that may negatively affect system performance. In one embodiment, a Bode plot of the magnitude of the output signal in response to the input symbol waveform is determined for all operating frequencies. This figure is determined over a very small range (eg <1 degree). Another map can be determined later on a different range or on the same range. Comparing these graphs yields useful information about the galvanometer system. For example, inconsistencies in low frequencies over time on the same range may indicate impending bearing failure. Inconsistencies in the intermediate frequency over time may indicate a significant loss in torque constant. Inconsistencies over different parts of the frequency range (eg, +1 to +20 degree range compared to -1 to -20 degree range) may be indicative of asymmetric performance.

A common cause of failure in limited rotating electric machines is bearing failure, which typically occurs gradually over time. Other problems during operation may include changes in the torque constant or changes in the symmetry of the motor response about the zero-angle position response.

According to various embodiments of the invention, limited rotating electric machine performance data is captured from the electric machine system. A pseudo-random binary sequence (PRBS) excitation signal is input to the system. The signal input to the motor (motor input signal) is recorded, and the position signal (PD signal) received from the position detector is also recorded. A Fast Fourier Transform (FFT) is performed on each signal to compare the representations of the two signals by taking the ratio of the frequency response representation of the PD signal to the frequency response representation of the motor input signal. The ratio provides a sequence (ratio sequence) representing the open loop frequency response to the system. The open-loop frequency response is available as a Bode plot of magnitude versus frequency. This results in a mathematical system model representing the transfer function of the motor system. Knowing the mathematical model and angular range of motion for the motor system at a particular time allows the diagnostic system to compare that mathematical model with models used in other earlier applications, and/or with other positions along the range of rotor rotation .

This system assumes that the identifiers of open-loop crossover frequency changes in the electric machine system can be identified automatically (even with the aid of a remote digital network). Automatic identification can be performed in a closed loop so that the stability of the system is not affected during the process. The data collection process can be completed in milliseconds.

An automatic identification system according to an embodiment of the present invention may include system excitation using a pseudo-random binary sequence (PRBS), thus producing a Fast Fourier Transform on the captured time response. The system identification is then modeled using the FFT data.

FIG. 2 shows a schematic diagram of a system 30 according to one embodiment of the invention. System 30 includes a PID controller 32 that receives input commands 34 . A controller 32 provides control signals 35 to a motor 36 that moves an optical element, such as a mirror, to provide a change in position 38 in response to an input command 34 . System 30 also includes a position detector 40 that provides a position detection signal 42 that is provided to controller 42 as is input command 34 . The controller 32 includes a proportional amplifier 44 (k _p ), an integrating element 46 ( _ki ), and a differentiating element 48 (k _d ). The system also includes a diagnostic unit 50 that receives the motor control signal and the position detection signal 42 provided by the controller 32 and outputs an error signal 52 . The motor control signal and the position detection signal are provided in digital form to the FFT converter in the diagnosis unit 50 to determine the closed-loop frequency response, and the open-loop frequency response is obtained from the closed-loop frequency response.

In particular, a pseudo-random binary sequence (PRBS) is either input into the system as an input command 34 or provides a perturbation as an output of the controller 32 . The data points used for the PRBS excitation signal may be powers of 2. FIG. 3A shows a PRBS signal at 60 , and FIG. 3B shows at 62 position detection provided by the motor in response to the PRBS signal shown in FIG. 3A . For example, the input process may capture 1024 data points for each input signal. In further embodiments, other types of excitation signals may be used, such as a white noise generator excitation signal, a Gaussian noise generator excitation signal, or a swept sinusoidal excitation signal providing a sinusoidal signal across frequency.

As shown in FIG. 4 , if either of the captured control signal 35 and position detection signal 42 is not already in digital form, these two signals can be converted into digital signals by A/D converters 54 and 56 . Once the input signals are in digital form, they can be transmitted over an arbitrary distance, for example via a network, and the output PID regulation signals can also be transmitted via a network in a digital environment. The digital input time domain signal is converted to a frequency domain representation of the signal by FFT converter units 64 and 66 respectively. Each FFT provides a complex polynomial of _the form a ₀ w ₀ , a ₁ w ₁ , a ₂ w _{2 .} . . a _n w n where n can be 512 for example. A ratio sequence of a ₀ , a ₁ , a _{2 .} . . a _n values for the position detection signal 42 to respective a ₀ , a ₁ , a _{2 .} . . a _n values for the control signal generates an amplitude sequence m ₀ , m ₁ , m ₂ ... m _n . This ratio sequence is provided by a ratio sequence unit 68 . These magnitudes m ₀ , m ₁ , m _{2 .} . . m _n provide the open loop frequency of the system response and can be plotted graphically as shown at 90 in FIG. 5 . As shown in FIG. 5 , the system may experience some distortion at low frequencies 92 , some harmonic resonance at high frequencies 94 , and may operate in the mid-frequency range 96 . Data collection may take a short time, eg 13.44 microseconds for a 1024 PBRS sequence.

Having determined the open loop frequency responses, the system can store these responses for later comparison of identified changes over time. In particular, the system may periodically generate a closed-loop frequency response and compare the current response to previous responses, as determined in comparison unit 70 . If there is a significant change in the low frequency range (as determined by the low frequency analysis unit 72 ), the system will identify a potential problem in the bearing as shown at 74 . FIG. 6 illustrates two closed loop frequency responses 100 and 102 . Response 100 was recorded at some point prior to response 102 . As shown in Figure 6, a significant change in the low frequency range as shown at 104 indicates that the bearing is beginning to fail.

If a significant change occurs in the mid-frequency range (as determined by the mid-frequency analysis unit 76 ), the system will recognize that the torque constant has changed, as indicated at 78 . FIG. 7 illustrates two closed loop frequency responses 110 and 112 . Response 110 was recorded at some point prior to response 112 . As shown in FIG. 7, due to the shift in the response curve, as indicated at 114, a significant change occurs at the intersection point of the specified magnitude. This change in the intersection point indicates a change in the torque constant of the system.

The system can also compare the closed-loop frequency response to the closed-loop frequency response for other portions of the range (eg, +20 degrees to -20 degrees). If the closed-loop frequency response is determined using a range of movement of less than 1 degree, many points along that range can be determined. As shown in FIG. 4, the closed loop frequency response may be compared (at comparator 80) to a previously recorded (eg, earlier recorded directly) closed loop frequency for other portions of the range. If the change is greater than the threshold change (as determined by unit 82 ), then an error condition is flagged by asymmetry unit 84 . For example, FIG. 8 shows a desired symmetric torque constant representation 120 over the range -20 degrees to +20 degrees and a measured torque constant representation 122 over the same range. As shown, in the range of -20 degrees to +20 degrees, the measured torque constant is not symmetric about the 0 degree angle. If left undetected, this asymmetry can seriously negatively affect the performance of a constrained rotating electrical machine. Once detected, the system either makes adjustments to use only the portion of the range that is symmetrical about its midpoint, or actually establishes PID tuning for a different portion of the range.

The diagnostic unit 50 then outputs an error signal 52 which is indicative of any existing error conditions, such as a bearing being in a bad condition, a change in torque constant or an asymmetrical condition.

As shown in FIG. 9 , a diagnostic system for a limited rotation electric machine system 130 according to a further embodiment of the present invention may include a PID controller 132 that receives input commands 134 . Controller 132 provides control signals 135 to motors 136 , which move optical elements, such as mirrors, to provide position changes 138 in response to input commands 134 . System 130 also includes a position detector 140 that provides a position detection signal 142 that is also provided to controller 142 along with input commands 134 . The controller 132 includes a proportional amplifier 144(k _p ), an integrating element 146 ( _ki ), and a differentiating element 148 (k _d ). The system also includes a diagnostic unit 150 that receives motor control signals and position detection signals 142 provided by the controller 132 . The motor control signal and the position detection signal are provided in digital form to the FFT converter in the diagnosis unit 150 to determine the closed-loop frequency response, and the open-loop frequency response is obtained from the closed-loop frequency response.

In the embodiment of FIG. 9, the diagnostic unit 150 determines an appropriate adjustment for the PID controller in order to adapt the coefficients _kp , _ki , respectively, of the corrections of the proportional unit, the integral unit and/or the derivative unit for the detected error state, k _d required changes. For example, if the detected error condition indicates that the torque constant has been changed by a factor of, say, 2, then each of the _kp , _ki , and _kd coefficients is also increased by a factor of 2. Thus, the system 130 assumes that if an error condition is identified, then the system can attempt to correct for the detected error condition.

Those skilled in the art will appreciate that many modifications and changes can be made to the above disclosed embodiments without departing from the spirit and scope of the invention.

Claims (21)

1, a kind of diagnostic system that is used to analyze the limited rotation motor system, described diagnostic system comprises:

First converting means is used to receive first digital signal of expression motor control signal, and the Electric Machine Control frequency-region signal that is used to provide the frequency domain representation of representing described motor control signal;

Second converting means is used to receive second digital signal of expression position detection signal, and the position probing frequency-region signal that is used to provide the frequency domain representation of representing described position detection signal;

The closed loop frequency response device is used to discern the expression in response to the frequency response of the limited rotation motor of described Electric Machine Control frequency-region signal and described position probing frequency-region signal; And

Diagnostic device is used for the expression of the frequency response in advance of the expression of more described frequency response and precedence record, to discern the error condition of relevant described limited rotation motor system.

2, system according to claim 1, each of wherein said first converting means and described conversion receiving trap all carried out fast fourier transform.

3, system according to claim 1, wherein the expression of the described frequency response by the identification of described closed loop frequency response device comprises the ratio of described position probing frequency-region signal and described Electric Machine Control frequency-region signal.

4, system according to claim 3, wherein said ratio provides divided by described Electric Machine Control frequency-region signal by described position probing frequency-region signal.

5, system according to claim 1, wherein said diagnostic device is made comparisons the low-frequency range and the described frequency response in advance of described frequency response.

6, system according to claim 5, wherein said diagnostic device provides the fault bearing error signal in the danger of indicating bearing whether to be in fault.

7, system according to claim 1, wherein said diagnostic device is made comparisons the intermediate frequency range and the described frequency response in advance of described frequency response.

8, system according to claim 7, wherein said diagnostic device provides the torque constant error signal of the variation in the torque constant of indicating described limited rotation motor.

9, system according to claim 1, wherein said diagnostic device provides the asymmetric error signal, and whether described asymmetric error signal indicates the moving range of rotating shaft of described limited rotation motor asymmetric about described torque constant.

10, system according to claim 1, wherein said limited rotation motor system comprises ratio, integration, derivative controller.

11, system according to claim 10, wherein said diagnostic device provides correction signal for described ratio, integration, derivative controller.

12, a kind of diagnostic system that is used to analyze the limited rotation motor system, described diagnostic system comprises:

The one FFT device is used to receive first digital signal of expression motor control signal, and is used to a plurality of frequencies that the Electric Machine Control frequency domain sequence of the frequency domain representation of the described motor control signal of expression is provided;

The 2nd FFT device is used to receive second digital signal of expression position detection signal, and is used to described a plurality of frequency that the position probing frequency domain sequence of the frequency domain representation of the described position detection signal of expression is provided;

The closed loop frequency response device is used to discern the expression in response to the frequency response of described a plurality of frequencies of the limited rotation motor of described Electric Machine Control frequency-region signal and described position probing frequency-region signal; And

Diagnostic device is used for more described frequency response and represents expression with the frequency response in advance of precedence record, to discern the error condition of relevant described limited rotation motor system.

13, system according to claim 12, wherein the expression of the described frequency response by the identification of described closed loop frequency response device comprises the ratio of described position probing frequency-region signal and described Electric Machine Control frequency-region signal.

14, system according to claim 13, wherein said ratio provides divided by described Electric Machine Control frequency-region signal by described position probing frequency-region signal.

15, system according to claim 12, wherein said diagnostic device is made comparisons the low-frequency range and the described frequency response in advance of described frequency response.

16, system according to claim 15, wherein said diagnostic device provides the fault bearing error signal in the danger of indicating bearing whether to be in fault.

17, system according to claim 12, wherein said diagnostic device is made comparisons the intermediate frequency range and the described frequency response in advance of described frequency response.

18, system according to claim 17, wherein said diagnostic device provides the torque constant error signal of the variation in the torque constant of indicating described limited rotation motor.

19, system according to claim 12, wherein said diagnostic device provides the asymmetric error signal, and whether described asymmetric error signal indicates the moving range of rotating shaft of described limited rotation motor asymmetric about described torque constant.

20, system according to claim 12, wherein said limited rotation motor system comprises ratio, integration, derivative controller.

21, system according to claim 20, wherein said diagnostic device provides correction signal for described ratio, integration, derivative controller.

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