Boots – shoes – and leggings
Patent
1986-12-03
1988-07-19
Smith, Jerry
Boots, shoes, and leggings
364553, 364148, 364149, 364179, 318561, 318636, 318610, G05B 1302
Patent
active
047589434
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for adjusting the setting of a digital process regulator with the aid of the result obtained from a simple relay feedback experiment.
BACKGROUND OF THE INVENTION
A serious problem encountered with all digital regulators is one of obtaining in a simple fashion those parameters which are to be used for tuning the regulator. Applicants' U.S. Pat. No. 4,549,123 describes a method which utilizes the fact that many processes experience periodic oscillation with relay feedback. A simple relay feedback experiment is carried out, and the amplitude and period of the resultant oscillation is used to tune a PID-type regulator (PID stands for Proportional, Integrated, Derivating) on the basis of the control concept according to Zeigler-Nichols-like design methods. This prior art tuning method is thus based solely on knowledge of the amplitude and period of the oscillation. Although this method is successful in the majority of cases, it is encumbered with the fundamental drawback that the model is based solely on one point in the frequency curve of the open loop system in a Nyquist diagram.
A process model can also be determined experimentally by first selecting a sampling period and introducing pertubation signals, whereafter the process mode is obtained with the aid of some suitable parameter assessment method. In those cases in which the regulator is tuned automatically, the oscillations are generated by conventional feedback and the parameters determined recursively and progressively, as further measurements become available.
The sampling period is a critical parameter, both in respect of conventional parameter estimation and of adaptive control. In order to estimate the sampling period, it is necessary to have prior knowledge of the time scale of the model and of the system engaged. This has long been the stumbling block in achieving automatic model construction and adaptive regulation or tuning.
SUMMARY OF THE INVENTION
In accordance with the invention, the result of a simple relay feedback experiment is used to acquire the requisite knowledge of the process. The difference between the above-mentioned earlier method employing a relay feedback experiment and the method according to the invention, is that instead of using solely amplitude and period of the oscillating signal obtained on the output when carrying out the experiment, the method according to the invention also utilizes the knowledge of the shape of the curve obtained in the form of an output signal from a process effected with relay feedback during one stage of the experiment. Accordingly, the curve obtained within one period is sampled at a plurality of points thereon and the sampling values obtained at these points on the curve are used to make an accurate calculation of a regulator means suitable for adaptive modification of the process concerned. This calculation must be made in accordance with certain rules, in a manner such that a computer device, such as a microprocessor, is able to calculate an efficient regulator in a simple and ready manner, directly from the sampling values obtained. As a result of the method according to the invention there is obtained a model which is directly adapted for digital regulation. Distinct from the known prior art method, the calculated or computed Regulator does not have the form of a PID-regulator. The method according to the invention also provides the possibility of calculating the dead-time of the process in a simple fashion. Dead-time is a factor which is often found problematic with adaptive regulators and which has in fact led to the limited use of adaptive systems.
The sampling points may be uniformly distributed over one period, although the selection of irregular sampling point distribution is also a conceivable procedure. According to a further development of the invention, the number of sampling points can be varied.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more clearly understood, reference will no
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patent: 4549123 (1985-10-01), Hagglund et al.
Astrom Karl J.
Hagglund Tore
Hightech Network AB
Hoang Steve
Smith Jerry
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