Electricity: motive power systems – Positional servo systems – With stabilizing features
Reexamination Certificate
1999-10-12
2001-08-14
Ip, Paul (Department: 2837)
Electricity: motive power systems
Positional servo systems
With stabilizing features
C318S629000, C318S630000, C318S608000
Reexamination Certificate
active
06274995
ABSTRACT:
The present invention relates to a method for automatically parameterizing a quick-acting digital speed control loop, having branches excited separately by an excitation signal. The invention also related to a circuit arrangement for implementing a quick acting digital speed control in electro-drives.
DESCRIPTION OF RELATED ART
German Patent 195 16 402 Al, describes a circuit arrangement of a speed governor using a flexible feedback, where the feedback loop contains two models. A first model performs a partial approximation of the controlled system, a second model a full approximation of the controlled system. The output signal from the first model is fed back as a negative value while that of the second as a positive value, so that in the steady state condition the output signal from the two models should yield zero. A filter is arranged in the feedback loop, which uses as input signal the difference between the output signal from the second model and that from the controlled system. In this patent, the transfer function of the first model also includes the unstable poles of the controlled system.
One drawback of the method described above is the need to define two models, which can only be done with substantial outlay computational resources and with limited accuracy. The limited accuracy means that only an imprecise simulation of the controlled system is possible. The transfer functions of the models are high-order functions, so that the models are encumbered with many computational delays, leading to slow performance and additional inaccuracies.
German Patent 25 20 649 C2, describes a thermal power station having a side-water reactor, where a controlling system having frequency-dependent controlling elements is used. To prevent an unstable closed-loop feedback control, at least one resonant filter is arranged in the control loop, whose resonant frequency matches the frequency of the control loop. This prevents the control loop from becoming unstable. This document describes a resonant filter which is used in a control loop of a side-water reactor, not in a speed control loop. Furthermore, it also does not describe an automatic parameterizing of the filter in the control loop is.
German Patent 34 08 551 C2, describes a method for reducing tool path errors in computer-controlled machine tools, where positional setpoint values of the drive control loop are fed to a filter, which is active in response to changes in path vector. The response characteristic of the filter is the inverse of that of the drive's controlled system. A drawback of this implementation is that it requires determining the response characteristic of the drive's controller system as precisely as possible. However, this is only possible to accomplish with substantial effort and with limited accuracy. No provision is made for automatically assigning parameters to the filter in light of the control loop's resonant frequencies.
An arrangement and a method for determining optimal controller parameters for a closed-loop speed control are known from the German Patent 197 34 208.6. Test signals are applied to the electromotor of the installed machine, for whose speed controller the parameters are to be adjusted. These test signals activate selected controller components. A subsequent test is performed using an iterative method to determine at which amplification the stability limit of the individual control-loop components is reached. Depending upon the result, the amplification factors for the controller components are then adjusted. This method has the disadvantage that in one or more narrow-band resonant ranges of the mechanical system made up of the motor and the machine, vibrations can occur in response to low amplification factors of the speed controller. To avoid exciting the machine into vibrations in these resonant ranges, only low amplifications can be adjusted in the speed controller. Due to the low amplifications in the speed controller, setpoint values are reached only very slowly by the machine. Therefore, the so-called rise time is undesirably long.
SUMMARY OF THE INVENTION
The present invention is a method and a circuit arrangement that implements the method to permit automatic adjustment of the parameters of a speed control loop and of one or more filters provided in the speed control loop, to achieve a shortest possible rise time and an optimal feedback control performance, so that the machine is not excited into vibrations. The additional equipment and computational outlays required to obtain the necessary modules and process steps should be as small as possible.
Advantageous specific embodiments of the method and circuit arrangement according to the present invention follow from the features of each of the dependent claims.
To determine the optimal amplification of the speed controller, at least for the P- and I-branch of the speed controller, the resonant frequencies of the entire mechanical arrangement made up of the motor and the machine are determined at the same time in a frequency range relevant to the speed controller of the motor, at the stability limit of the speed control loop. Filters are located within the speed control loop, and their parameters are adjusted in such a way that instances of resonant rise in the frequency response characteristic are damped, and unwanted frequency ranges are suppressed. The output signal from the speed controller for resonant frequencies is damped in such a way that no more instances of resonant rise occur in the frequency response characteristic of the controller output signal. Thus, a signal is produced having an amplitude which is essentially constant over the frequency.
To achieve the desired rise time, the amplification factors of the controller are subsequently increased, and the determination is again made as to whether resonance occurs. If this is not the case, the adjustments in the filter and controller remain unchanged, since the desired rise time has now been achieved in this speed control loop without stability problems. If resonances are found, the filters are altered so as to damp the occurring resonant frequencies. After the filter coefficients are properly adjusted, the system checks again whether the desired rise time is reached and whether no resonance is occurring. If necessary, the resonant range of the mechanical arrangement is determined again, and amplification values in the controller, as well as filter coefficients of the filter are modified. In this manner, the filter parameters are additionally defined by using process steps which must be carried out in any case, to determine the controller parameters.
An especially short rise time can be advantageously achieved without the mechanical arrangement being excited in the process into continuing vibrations. Also, there is an additional benefit that there is no need for a mathematical modeling of the mechanical system. The mechanical arrangement is advantageously excited, as it is in regular operation with closed control loop, so that very realistic performance characteristics are determined for the mechanical system. The resonance ranges thereby determined are damped by filters, so that signals exciting a vibration are selectively damped. The amplification in the controller can be subsequently substantially increased.
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Dr. Johannes Heidenhain GmbH
Ip Paul
Kenyon & Kenyon
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