KR20070018009A - Controller Diagnosis System and Method of Rotational Restriction Motor System - Google Patents

Abstract

The diagnostic system of the present invention is for analyzing a rotation limiting motor system. The diagnostic system includes a first conversion unit, a second conversion unit, a closed loop frequency response unit, and a diagnostic system. The first conversion unit receives the first digital signal representing the motor control signal 35 and provides a motor control frequency domain signal corresponding to the frequency domain indication of the motor control signal. The second conversion unit receives the second digital signal representing the position detection signal 42 and provides a position detection frequency domain signal corresponding to the frequency domain representation of the position detection signal. The closed loop frequency response unit confirms the indication of the frequency response of the rotation limiting motor in response to the position detection frequency domain signal and the motor control frequency domain signal. The diagnostic unit 50 checks the error condition 52 for the rotational limiting motor system by comparing the indication of the frequency response with a previously recorded previous frequency response.

Rotating limiting motor system, conversion unit, FFT, closed loop frequency response

Description

SYSTEM AND METHOD FOR DIAGNOSING A CONTROLLER IN A LIMITED ROTATION MOTOR SYSTEM}

This application claims priority to US Provisional Patent Application No. 60 / 538,842, filed Jan. 23, 2004, and priority to US Provisional Patent Application No. 60 / 575,255, filed May 28, 2004, and 9, 2004. Claims priority to US Provisional Patent Application No. 60 / 613,962, filed May 28.

FIELD OF THE INVENTION The present invention relates generally to rotational limiting motor systems, and more particularly to design and adjusting systems and methods of rotational limiting motor systems.

Rotational limiting motors generally include stepper motors and constant velocity motors. Certain stepper motors are well suited for applications requiring high duty cycle sawtooth scanning at high speeds and large scan angles. For example, US Pat. No. 6,275,319 discloses an optical scanning device for raster scanning applications.

Rotational limiting motors for certain applications, however, require rotors that move between two positions at precise and constant speed, rather than sawing stepping and settling. This application requires a minimum time to reach a constant speed and a minimum amount of error in the speed obtained. Constant speed motors generally provide greater torque constants and typically position rotors, such as tachometers, as well as rotors and drive circuitry that causes the rotors to rotate about a central axis. Or a position sensor, and a feedback circuit coupled to the transducer that allows the rotor to be driven by a drive circuit in response to an input signal and a feedback signal. For example, US Pat. No. 5,424,632 discloses a conventional two-pole limited rotation motor.

The limited rotation torque motor can be designed or represented as a double-integrator model that includes several flexible modes and low frequency non-linear effects. Closed-loop servo systems for typical galvanometers include notch filters for high frequency resonant mode and integral actions for low frequency uncertainty. System operation is selected in the mid-frequency range in which the system is well designed by a rigid body. In the case of the double integrator rigid body model, there is a direct correlation between the open-loop gain and the cross-over frequency on the frequency response plot. For example, the automatic tuning system of a servowriter head positioning system is called Autotuning. of a servowriter head positioning system with minimum positioning error , YH Huang, S. Weerasooriya and TS Low, J. Applied Physics, v. 79 pp. 5674-5676 (1996).

1 shows a rotationally limited torque motor system 10 of the prior art. The system 10 includes a controller 12 (eg, position, integral, derivative or PID controller) that receives an input command 14. The controller 12 provides a control signal to the motor 16, which moves an optical element such as a mirror to provide a position change 18 in accordance with the input command 14. The system also includes a position detector 20 that provides a position detection signal 22 provided to the controller 12 with an input command 14. The open loop gain (or OdB cross-over variations) of the system adversely affects the closed loop system performance if the controller fails to adapt to these variations.

Such rotation limiting motors can be used in a variety of laser scanning applications, such as, for example, high speed surface metrology. Laser processing applications also include laser welding (such as high speed spot welding), surface treatment, cutting, drilling, marking, trimming, laser repair, rapid Rapid prototyping, microstructures, or the formation of dense arrays of nanostructures on a variety of materials.

Rotationally limited torque motors, however, eventually become defective after limited use. As methodologies have been developed to more robustly drive rotational limiting motors, defects can be reached at levels that are difficult to predict. The ability to measure abnormalities in rotational limiting motors also helps predict the life of the motor. In addition, it is desirable in that it can measure the abnormality of the rotation limiting motor in situ without sending it to the manufacturer for analysis.

Therefore, there is a need for a method of monitoring the rotational limit torque motor, and more particularly, a method for diagnosing the condition and life of the rotational limit torque motor.

[Summary of invention]

According to one embodiment, the present invention provides a diagnostic system for analyzing a rotational limiting motor system. The diagnostic system includes a first transform unit, a second transform unit, a closed-loop frequency response unit, and a diagnostic system. The first conversion unit receives a first digital signal indicative of a motor control signal and receives a motor control frequency domain signal corresponding to a frequency domain representation of the motor control signal. control frequency domain signal). The second conversion unit receives the second digital signal representing the position detection signal and provides a position detection frequency domain signal corresponding to the frequency domain indication of the position detection signal. The closed loop frequency response unit checks the display of the frequency response of the rotational limiting motor in response to the position detection frequency domain signal and the motor control frequency domain signal. The diagnostic unit checks the error condition for the rotational limiting motor system by comparing the indication of the frequency response with the indication of the previously recorded previous frequency response.

The following detailed description may be understood by reference to the accompanying drawings:

1 is a schematic diagram of a rotation limiting motor and control system according to the prior art;

2 is a schematic diagram of a rotation limiting motor and diagnostic system according to an embodiment of the invention;

3A and 3B are graph diagrams of a pseudo random binary sequence excitation signal provided to a motor controller and an associated position detection signal generated by a motor in response to the pseudo random binary sequence;

4 is a schematic diagram of a diagnostic unit according to an embodiment of the invention;

5 is a graphical representation of a measured frequency response of a system according to an embodiment of the invention;

6 is a graphical representation of a measured frequency response showing a change in low frequency response in accordance with certain embodiments of the present invention;

7 is a graphical representation of a measured frequency response illustrating a change in torque constant in accordance with another embodiment of the present invention;

8 is a graphical representation of measured frequency response showing asymmetrical performance in accordance with another embodiment of the present invention; And

9 is a schematic diagram of a rotation limiting motor and diagnostic system according to another embodiment of the invention.

The drawings are shown for illustrative purposes only.

According to various embodiments of the present invention, rotational limit motor performance data is captured from the motor system, and this data is analyzed to diagnose various abnormalities that may negatively affect the performance of the system. In one implementation, a Bode plot of the magnitude of the output signal in response to an input sign wave is measured at all operating frequencies. This plot is measured in a very small range (eg <1 degree). Another plot can be measured for the same range at a later time, or at another range. Comparison of these plots yields useful information about galvanometer systems. For example, inconsistency in low frequency over time in the same range can mean impending bearing failure. The discrepancy of intermediate frequencies over time can mean a serious loss of torque constant. Mismatches in different parts of the range (eg, in the +1 degree to +20 degree range and the -1 degree to -20 degree range comparison) may mean asymmetric performance.

A common cause of faults in rotational limiting motors is bearing faults, which typically occur gradually over time. Another problem during operation may include a change in torque constant or a change in the symmetry of the motor's response to zero angle position.

According to various implementations of the invention, rotational limit motor performance data is captured from a motor system. A pseudo random binary sequence (PRBS) excitation signal is input to the system. The signal (motor input signal) input to the motor 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, and the two are compared 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) that represents the open loop frequency response of the system. The open loop frequency response can be obtained as a board plot of magnitude versus frequency. A mathematical system model can then be generated that represents the transfer function of the motor system. By knowing the mathematical model of the motor system at a particular time and angular range of operation, the diagnostic system can compare the mathematical model with the previous model and / or with the model at different locations along the rotational range of the rotor.

With this system confirmation of the open loop crossover frequency change of the motor system can be automatically verified (even via a remote digital network). Automatic identification can be performed on a closed loop so that system stability is not affected during this process. The data collection process may be performed in milliseconds.

Automated Confirmation System According to an Embodiment of the Invention The present invention includes system excitation using a pseudo random binary sequence (PRBS), and can then perform fast Fourier transform on the captured time response. The system identification is then modeled using FFT data.

2 is a schematic diagram of a system 30 in accordance with an embodiment of the present invention. System 30 includes a PID controller 32 that receives an input command 34. The controller 32 provides a control signal 35 to the motor 36, which moves an optical element such as a mirror to provide a position change 38 in accordance with the input command 34. The system 30 also includes a position detector 40 which provides a position detection signal 42 which is provided to the controller 32 with an input command 34. The controller 32 includes a proportional amplifier 44 (k _p ), an integrating element 46 (k _i ), and a derivative element 48 (k _d ). . The system also includes a diagnostic unit 50 that receives the motor control signal and 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 an FFT converter in the diagnostic unit 50 to measure 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 entered into the system as an input command 34 or provided as a perturbation to the output of the controller 32. The data point for the PRBS excitation signal can be n powers of two. FIG. 3A shows a PRBS signal 60 and FIG. 3B shows a position detection 62 provided by the motor in response to the PRBS signal shown in FIG. 3A. The input process may, for example, capture 1024 data points of each input signal. In another implementation, other types of excitation signals may be used, such as noise generator excitation signals, Gaussian noise generator excitation signals, or swept sine excitation signals that provide sine signals at all frequencies.

As shown in Fig. 4, none of the captured control signals 35 and position detection signals 42, which can be converted into digital signals by the A / D converters 54 and 56, are yet in digital form. Once the input signals are in digital form, they can be sent anywhere over the network, for example, and output PID adjustment signals can also be sent over the network in a digital environment. The digital input time domain signals are then converted by the FFT converter units 64 and 66 into signals of frequency domain representation. Each FFT provides a complex polynomial of the form a _o w _o , a _l w _l , a ₂ w ₂ ... a _n w _n , where n may be, for example, 512. A _o , a _l , a ₂ ... a _n for each control signal A _o , a _l , a ₂ ... a _n for the position detection signal 42 over a value The sequence of ratios of values gives a sequence of magnitudes m _o , m _l , m ₂ ... m _n . This ratio sequence is provided by ratio sequence unit 68. These magnitudes m _o , m _l , m ₂ ... M _n provide the open loop frequency response of the system 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 frequency 92, some harmonic resonance at high frequency 94, and may be operated at intermediate frequency 96. have. The data collection process requires little time, for example 13.44 μsec in a 1024 PBRS sequence.

After measuring the open loop frequency response, the system stores these responses and compares them later to see how they change over time. In particular, the system periodically generates a closed loop frequency response and compares the current response with the previous response measured at the comparison unit 70. If there is a significant change in the low frequency range (as measured by the low frequency analysis unit 72), the system will be able to identify potential problems present in the bearing as shown at 74. 6 shows two closed loop frequency responses 100 and 102. The response 100 is recorded at a time earlier than the response 102. As shown in FIG. 6, a significant change occurs in the low frequency range, as shown at 104, which means that the bearings are starting to fail.

If there is a significant change in the intermediate frequency range (as measured by the intermediate frequency analysis unit 76), the system will confirm that the torque constant has changed as shown by 78. 7 shows two closed loop frequency responses 110 and 112. The response 110 is recorded at a time earlier than the response 112. As shown in FIG. 7, a significant change occurs at the designated magnitude crossing point due to the shift in the response curve, as shown at 114. This change in crossover means a change in the torque constant of the system.

The system also compares the closed loop frequency response with the closed loop frequency response of another portion of the range (eg, +20 degrees to -20 degrees). If the closed loop frequency response is measured with a range of motion of less than 1 degree, many points in that range can be identified. As shown in FIG. 4, the closed loop frequency response can be compared (at comparator 80) to the previously recorded (eg, just before) closed loop frequency response of another portion of the range. If the variance is greater than the threshold variance (measured by unit 82), the error condition is indicated by asymmetry unit 84. For example, FIG. 8 shows the ideal symmetric torque constant indication 120 for the range of -20 degrees to +20 degrees, as well as the measured torque constant indication 122 for the same range. As shown, the measured torque constant is asymmetric with respect to the zero angle for the range of -20 degrees to +20 degrees, and if this asymmetry is not detected, it will have a significant negative impact on the performance of the rotational limiting motor. will be. Once detected, the system can adjust using only a constant range symmetrical with respect to the intermediate point, or make PID adjustments to substantially other parts of the range.

The diagnostic unit 50 then outputs an error signal 52 indicating the presence of any fault condition, such as a bearing in a vulnerable state, a change in torque constant, or an asymmetric state.

As shown in FIG. 9, the diagnostic system of the rotation limiting motor system 130 according to another embodiment of the present invention may include a PID controller 132 that receives an input command 134. The controller 132 provides a control signal 135 to the motor 136, which moves an optical element, such as a mirror, to provide a position change 138 according to the input command 134. System 130 also includes a position detector 140 that provides a position detection signal 142 provided to controller 132 with an input command 134. The controller 132 includes a proportional amplifier 144 (k _p ), an integral element 146 (k _i ), and a derivative element 148 (k _d ). The system also includes a diagnostic unit 150 for receiving 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 transducer in the diagnostic unit 150 to measure 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 is configured with respective coefficients k _p , k _i for the proportional unit, the integral unit and / or the derivative unit to correct the detected error condition. And Determine the appropriate adjustments to the PID controller to match the changes that need to be made for k _d . For example, if an error condition is detected that indicates that the torque constant has changed by, for example, two factors, then k _p , k _i , respectively. And The k _d coefficient can also be increased by 2 factors. Thus, if the error condition is identified, the system 130 will also attempt to correct the detected error condition.

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

Claims (21)

Diagnostic system for analysis of limited rotation motor system, including: A motor control frequency domain signal corresponding to a frequency domain representation of the motor control signal by receiving a first digital signal representing a motor control signal First transform means for providing a; Second conversion means for receiving a second digital signal representative of a position detection signal and providing a position detection frequency domain signal corresponding to a frequency domain representation of the position detection signal; Closed loop frequency response means for confirming an indication of said frequency response of said rotational limiting motor in response to said motor control frequency domain signal and said position detection frequency domain signal; And Diagnostic means for confirming an error condition for the rotational limiting motor system by comparing the indication of the frequency response with an indication of a previously recorded previous frequency response. 2. The system of claim 1, wherein the first transform means and each transform receiving means perform a Fast Fourier Transform. The system according to claim 1, wherein said indication of said frequency response identified by said closed loop frequency response means comprises a ratio of said position detection frequency domain signal and said motor control frequency domain signal. 4. The system of claim 3, wherein the ratio is provided by dividing the position detection frequency domain signal by the motor control frequency domain signal. 2. The system of claim 1, wherein said diagnostic means compares said frequency response in the low frequency range with said previous frequency response. 6. A system according to claim 5, wherein said diagnostic means provides a faulty bearing error signal indicating that there is a risk of bearing failure. 2. The system of claim 1, wherein said diagnostic means compares said frequency response in the intermediate frequency range with said previous frequency response. 8. A system according to claim 7, wherein said diagnostic means provides a torque constant error signal indicative of a change in the torque constant of said rotational limiting motor. 2. A system according to claim 1, wherein the diagnostic means provides an asymmetry error signal indicating whether the range of motion of the rotor shaft of the rotational limiting motor is symmetrical with respect to the torque constant. 10. The system of claim 1, wherein the rotational limiting motor system comprises a proportional, integral, and derivative controller. 12. The system of claim 10, wherein said diagnostic means provides corrective signals to said proportional, integral, and derivative controller. Diagnostic system for analysis of rotational limiting motor systems, including: First FFT means for receiving a first digital signal representing a motor control signal and providing a motor control frequency domain sequence corresponding to a frequency domain representation of the motor control signal at various frequencies; Second FFT means for receiving a second digital signal representing a position detection signal and providing a position detection frequency domain sequence corresponding to a frequency domain representation of the position detection signal at the various frequencies; Closed loop frequency response means for confirming an indication of said frequency response at said various frequencies of said rotational limiting motor in response to said motor control frequency domain signal and said position detection frequency domain signal; And Diagnostic means for confirming an error condition for said rotational limiting motor system by comparing said indication of said frequency response with an indication of a previously recorded previous frequency response. 13. The system according to claim 12, wherein said indication of said frequency response identified by said closed loop frequency response means comprises a ratio of said position detection frequency domain signal and said motor control frequency domain signal. 14. The system of claim 13, wherein the ratio is provided by dividing the position detection frequency domain signal by the motor control frequency domain signal. 13. The system of claim 12, wherein the diagnostic means compares the frequency response in the low frequency range with the previous frequency response. 16. The system of claim 15, wherein said diagnostic means provides a fault bearing error signal indicating that a bearing may be defective. 13. The system of claim 12, wherein said diagnostic means compares said frequency response in the intermediate frequency range with said previous frequency response. 18. The system according to claim 17, wherein said diagnostic means provides a torque constant error signal indicative of a change in torque constant of said rotational limiting motor. 13. The system according to claim 12, wherein the diagnostic means provides an asymmetric error signal indicating whether the range of motion of the rotational axis of the rotational limiting motor is symmetrical with respect to the torque constant. 13. The system of claim 12, wherein the rotational limiting motor system includes a proportional, integral, and derivative controller. 21. The system of claim 20, wherein said diagnostic means provides a calibration signal to said proportional, integral, and derivative controller.

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