| 1. |
- Hillerström, Gunnar, et al.
(författare)
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Adaptive rejection of periodic disturbances with unknown period
- 1996
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Ingår i: Journal of Dynamic Systems Measurement, and Control. - : ASME International. - 0022-0434 .- 1528-9028. ; 118:3, s. 606-610
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Tidskriftsartikel (refereegranskat)abstract
- A disturbance cancellation extension by means of Youla parametrization to a stabilizing nominal controller is investigated. In the case of known disturbance model, disturbance frequencies or period time, it may be implemented directly as an add-on device to the existing control system. The nominal control system may be designed without consideration of the deterministic disturbances. This way it may suffice with a PID controller. It may also be a more complex one e.g., designed to obtain certain robustness properties. For known relation between the disturbance frequencies (one or more periodic signals) but unknown fundamental frequency, a frequency shaped disturbance model estimarion scheme is utilized. This makes it possible to e.g., adapt the disturbance model to minimize the error directly with respect to the output. For periodic disturbances the scheme implements a self-tuning discrete time repetitive controller. To illustrate the feasibility of the approach taken it is used for rejecting a periodic disturbance acting on a nonminimum-phase plant.
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| 2. |
- Hillerström, Gunnar
(författare)
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Adaptive suppression of vibrations : a repetitive control approach
- 1995
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Ingår i: Proceedings of the 1995 American Control Conference. - Piscataway, NJ : IEEE Communications Society. - 0780324455 - 0780324463 ; , s. 3820-3824
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Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to present an adaptive solution to suppression of vibrations. Adaptation is appropriate whenever the fundamental frequency is unknown or drifting, e.g. when the vibration is caused by a rotational machine with unknown rotational speed. The approach presented here has its roots in repetitive control based on models of isolated frequencies rather than the commonly used delay model. The relationship between different modeled frequencies is fixed by the model structure, and the fundamental frequency is obtained by gradient descent. To show the feasibility of this approach, it was used to reduce vibrations on a lever that were caused by a motor with imbalance in its rotation. As actuator, a standard loudspeaker was used, and the vibration was sensed by an accelerometer.
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| 3. |
- Hillerström, Gunnar
(författare)
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Adaptive suppression of vibrations : a repetitive control approach
- 1996
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Ingår i: IEEE Transactions on Control Systems Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-6536 .- 1558-0865. ; 4:1, s. 72-78
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to present an adaptive solution to suppression of vibrations. Adaptation is appropriate whenever the fundamental frequency is unknown or drifting, e.g., when the vibration is caused by a rotational machine with unknown rotational speed. The approach presented here has its roots in repetitive control based on models of isolated frequencies rather than the commonly used delay model. The relationship between different modeled frequencies is fixed by the model structure, and the fundamental frequency is obtained by gradient descent or Newton's method. To show the feasibility of this approach, it was used to reduce the vibrations on a lever that were caused by a motor with imbalance in its rotation. As an actuator, a standard loudspeaker was used, and the vibration was sensed by an accelerometer.
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| 4. |
- Hillerström, Gunnar, et al.
(författare)
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Application of repetitive control to a peristaltic pump
- 1993
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Ingår i: Proceedings. - : IEEE Communications Society. - 0780308611 ; , s. 136-140
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Konferensbidrag (refereegranskat)abstract
- In many machinery there are rotating axis, which sometimes give problems with mechanically coupled disturbances from e.g. imperfect roundness or loads. These disturbance can be modeled as a nonlinear feedback, and treated under the framework of repetitive control.
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| 5. |
- Hillerström, Gunnar, et al.
(författare)
-
Application of repetitive control to a peristaltic pump
- 1994
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Ingår i: Journal of Dynamic Systems Measurement, and Control. - : ASME International. - 0022-0434 .- 1528-9028. ; 116:4, s. 786-789
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to study angular velocity control of a rotating axis, a peristaltic pump where the disturbance is associated with certain angular positions. The use of constant sampling rate then implies varying disturbance period. A discrete repetitive control scheme based on a reduced order disturbance model tuned to the setpoint of the angular velocity is shown to reject the modeled disturbance with asymptotically zero error. With axis angle synchronization of sampling, the plant model is time-varying but it gives a static discrete disturbance model independent of the angular velocity. If the deviation from the nominal working point is not too large this is to prefer while it gives faster convergence
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| 6. |
- Hillerström, Gunnar
(författare)
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On repetitive control
- 1994
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis will concern control systems ability to enhance performance by repeating, while maintaining a stable and sufficiently fast closed loop performance. Iterative techniques can be divided into repetitive and learning control. In principle these techniques only differ in that the learning systems initial condition is reset at the beginning of each cycle while the repetitive system runs continuously. Repetitive controllers, the main theme of this thesis, can be used for rejecting periodic disturbances as well as tracking periodic references with ideally zero error. To accomplish this an internal signal model is utilized. This model is either a delay with a positive feedback around it modeling a general periodic signal, or a combination of harmonic frequencies adding up to a band-limited signal. The delay internal model has some uncomplicated, easy to grasp interpretation. Robustness properties may however not be the best. But if the plant is well determined over a frequency band this may be an excellent approach. With increased sampling rate the robustness properties of the delay model controller will however deteriorate. To cure this, disturbance rejection/tracking properties may be traded against robustness using lowpass filtering. As an alternative the internal model consisting of a number of isolated frequencies is exploited. This model has better robustness properties while preserving the zero error property for a bandlimited input signal. In addition it is shown how fundamental frequency adaptation can be incorporated for the case of unknown or drifting input signal frequencies. In this thesis repetitive controllers have successfully been implemented with two test plants; a peristaltic blood pump used in dialysis treatments, and a process where vibrations caused by a motor with an imbalance are suppressed.
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| 7. |
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| 8. |
- Hillerström, Gunnar, et al.
(författare)
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Rejection of periodic disturbances with unknown period : a frequency domain approach
- 1994
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Ingår i: Proceedings of the 1994 American Control Conference. - Piscataway, NJ : IEEE Communications Society. - 0780317831 ; , s. 1626-1631
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Konferensbidrag (refereegranskat)abstract
- A self-tuning discrete time repetitive controller comprising a gradient descent disturbance model estimation and a pseudo feedforward controller is investigated. To illustrate the feasibility of the approach considered an example is given for rejecting a periodic disturbance acting on a nonminimum-phase plant.
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| 9. |
- Hillerström, Gunnar, et al.
(författare)
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Repetitive control theory and applications : a survey
- 1996
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Ingår i: Elsevier IFAC Publications / IFAC Proceedings series. - 1474-6670. - 0080429084 ; 29:1, s. 1446-1451
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to present repetitive control, controllers for rejecting periodic disturbances or tracking periodic reference signals, This survey covers both continuous and discrete time theory, together with a number of applications
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| 10. |
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| 11. |
- Hillerström, Gunnar, et al.
(författare)
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Repetitive control using low order models
- 1994
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Ingår i: Proceedings of 1994 American Control Conference. - Piscataway, NJ : IEEE Communications Society. - 0780317831 ; , s. 1873-1878
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Konferensbidrag (refereegranskat)abstract
- In repetitive control based on the internal model principle of Francis and Wonham (1976) much interest has been focused around the model comprising a time delay with a memoryless positive feedback around it. A definite merit of this model is that, when used in the closed loop, it will generate an arbitrary periodic signal. In discrete-time the model order increases proportionally to the rise in sampling rate, giving a high order model. The input (disturbance or reference) signal may however be concentrated to some frequencies rather than the whole band up to the Nyquist frequency. Then the model is too large in the sense that it models frequencies that are not present in the input. The inactive part of the model can produce oscillations in the closed loop. Oscillations can be reduced by introducing a lowpass filter (or Q-filter) in the feedback path of the model, but thereby the asymptotic zero error property is lost. A lower order model is shown to overcome this problem and feasibility illustrated by a simulation example.
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| 12. |
- Hillerström, Gunnar, et al.
(författare)
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Robustness properties of repetitive controllers
- 1996
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Ingår i: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 65:6, s. 939-961
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Tidskriftsartikel (refereegranskat)abstract
- Stability robustness properties of sampled data repetitive control systems are examined. Due to the infinite loop gain at periodic frequencies originating from the included internal model (Internal Model Principle), repetitive systems are, if properly designed, not very sensitive towards possibly time-varying gains. Uncertainty in plant delay is, however, a problem. Controller action timing becomes more or less out of order and may result in severe performance degradation, depending on model type and the number of frequencies included in the design. With a Linear Time-Invariant (LTI) controller comprising the commonly used time delay internal model, the closed loop system is stable for nominal time delay plus/minus at most one sampling interval. A controller based on a reduced order model, perhaps not modelling all harmonics, is utilized to enhance robustness properties. Simulation runs with different controllers show how different models work in the closed loop, and also that synchronization in time is of utmost importance in order to utilize the delay internal model.Stability robustness properties of sampled data repetitive control systems are examined. Due to the infinite loop gain at periodic frequencies originating from the included internal model (Internal Model Principle), repetitive systems are, if properly designed, not very sensitive towards possibly time-varying gains. Uncertainty in plant delay is, however, a problem. Controller action timing becomes more or less out of order and may result in severe performance degradation, depending on model type and the number of frequencies included in the design. With a Linear Time-Invariant (LTI) controller comprising the commonly used time delay internal model, the closed loop system is stable for nominal time delay plus/minus at most one sampling interval. A controller based on a reduced order model, perhaps not modelling all harmonics, is utilized to enhance robustness properties. Simulation runs with different controllers show how different models work in the closed loop, and also that synchronization in time is of utmost importance in order to utilize the delay internal model.
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| 13. |
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| 14. |
- Hillerström, Gunnar
(författare)
-
Vibration suppression with frequency adaptation
- 1995
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Ingår i: Proceedings of the 4th IEEE Conference on Control Applications. - Piscataway, MJ : IEEE Communications Society. - 0780325508 ; , s. 890-895
-
Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to present an adaptive solution to suppression of vibrations. Adaptation is appropriate whenever the fundamental frequency is unknown or drifting, e.g. when the vibration is caused by a rotational machine with unknown rotational speed. The approach presented here has its roots in repetitive control based on models of isolated frequencies rather than the commonly used delay model. The relationship between different modeled frequencies is fixed by the model structure, and the fundamental frequency is obtained by a Newton method. To show the feasibility of this approach, it was used to reduce vibrations on a lever that were caused by a motor with imbalance in its rotation. As an actuator, a standard loudspeaker was used, and the vibration was sensed by an accelerometer
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| 15. |
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| 16. |
- Medvedev, Alexander, et al.
(författare)
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An external model control system
- 1995
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Ingår i: Control : Theory and Advanced Technology. - 0911-0704. ; 10:4, s. 1643-1665
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Tidskriftsartikel (refereegranskat)abstract
- A new observer-based approach to disturbance rejection and control in linear continuous systems is introduced. A recently developed technique of continuous deadbeat observation is exploited to estimate the process states and disturbance signal described by a known dynamic model. A realization condition in the form of linear algebraic equations is derived. When there is no reliable disturbance model available, it is suggested that a neural network-based structure be used. An application example illustrates the feasibility of the approach taken
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| 17. |
- Medvedev, Alexander, et al.
(författare)
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External model control of a peristaltic pump
- 1994
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Ingår i: Advanced control of chemical processes (ADCHEM '94). - Oxford : Pergamon Press. - 0080422292 ; , s. 519-524
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Konferensbidrag (refereegranskat)
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| 18. |
- Medvedev, Alexander, et al.
(författare)
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External model control of a peristaltic pump
- 1994
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Ingår i: Elsevier IFAC Publications / IFAC Proceedings series. - 1474-6670. - 0080422292 ; 27:2, s. 519-524
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Tidskriftsartikel (refereegranskat)abstract
- An observer-based approach to perfect disturbance rejection in linear continuous systems with delayed control is presented and exemplified by an application to a peristaltic pump. Disturbance rejection properties of the Smith Predictor are studied. A recently developed technique of continuous deadbeat observation is exploited to predict the disturbance signal which is described by a known dynamic model. It is shown that under certain algebraic conditions a disturbance estimate based control law is able to provide a disturbance-free output signal. The disturbance rejection scheme can be used in combination with any conventional control technique such as stabilizing or servo controller.
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| 19. |
- Medvedev, Alexander, et al.
(författare)
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On perfect disturbance rejection
- 1993
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Ingår i: Proceedings of the 32nd IEEE Conference on Decision and Control. - Piscataway, NJ : IEEE Communications Society. - 0780312988 ; , s. 1324-1329
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Konferensbidrag (refereegranskat)abstract
- A new observer-based approach to perfect disturbance rejection in linear continuous systems is introduced. A technique of continuous deadbeat observation is exploited to estimate the disturbance signal described by a known dynamic model. A realization condition in the form of linear algebraic equations is derived. It is shown that the introduced disturbance rejection scheme can be used in combination with any conventional control technique such as stabilization or servo control
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| 20. |
- Medvedev, Alexander, et al.
(författare)
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Periodic disturbance rejection : a neural network approach
- 1993
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Ingår i: Proceedings of the International Conference on Artificial Neural Networks. - London : Encyclopedia of Global Archaeology/Springer Verlag. - 0387198393 ; , s. 814-817
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Konferensbidrag (refereegranskat)
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| 21. |
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