289 research outputs found
Reducing the cogging torque effects in hybrid stepper machines by means of resonant controllers
Permanent magnet machines are not free from the interaction between magnets and the stator and rotor slots, which causes an undesired disturbing torque. Such cogging or detent torque is especially larger with salient pole machines, as it is the case of the Permanent Magnet Hybrid Stepper Machines (PMHSM). Depending on the application requirements, these torque perturbations can be unacceptable and the application of solutions that minimizes the cogging torque effects are mandatory. This paper originally faces the minimization of the cogging torque using resonant controllers. More specifically, the paper details the analysis and design of a speed-adaptive resonant controller, which not only is directly designed in Z domain but also considers the current (or torque) inner loop delay. Pole-zero placement and the disturbance rejection frequency response have been attained in the design of the speed and position speedadaptive controllers. Experimental results with two off-theshelf PMHSMs demonstrate the superior performance of the proposal in both speed and position closed-loop applications for tracking, as well as in disturbance (load impact) rejection tests and against inertia variations. A comparison with a conventional PI has been carried out from the design stage to experimental results and the improvement of the proposal has been numerically quantified.Postprint (published version
Derivative based control for LPV system with unknown parameters: An application on a Permanent Magnet Synchronous Motors
International audienceThis paper deals with the robust stabilization of a class of Linear Parameter Varying (LPV) systems in the continuous time case. Instead of using a state observer or searching for a dynamic output feedback, the controller is based on output derivative estimation. This allows the stabilization of the plant with very large parameter variation and uncertainties. The proof of stability is based on the polytopic representation of the closed loop, Lyapunov conditions and system transformations. The result is a control structure with only few parameters which are tuned via very simple conditions. This paper illustrates the usefulness on real application: Permanent Magnet Synchronous Motors (PMSM) position control
Cogging torque reduction in brushless motors by a nonlinear control technique
This work addresses the problem of mitigating the effects of the cogging torque in permanent magnet synchronous motors, particularly brushless motors, which is a main issue in precision electric drive applications. In this work, a method for mitigating the effects of the cogging torque is proposed, based on the use of a nonlinear automatic control technique known as feedback linearization that is ideal for underactuated dynamic systems. The aim of this work is to present an alternative to classic solutions based on the physical modification of the electrical machine to try to suppress the natural interaction between the permanent magnets and the teeth of the stator slots. Such modifications of electric machines are often expensive because they require customized procedures, while the proposed method does not require any modification of the electric drive. With respect to other algorithmic-based solutions for cogging torque reduction, the proposed control technique is scalable to different motor parameters, deterministic, and robust, and hence easy to use and verify for safety-critical applications. As an application case example, the work reports the reduction of the oscillations for the angular position control of a permanent magnet synchronous motor vs. classic PI (proportional-integrative) cascaded control. Moreover, the proposed algorithm is suitable to be implemented in low-cost embedded control units
Precision Control of a Sensorless Brushless Direct Current Motor System
Sensorless control strategies were first suggested well over a decade ago with the aim of
reducing the size, weight and unit cost of electrically actuated servo systems. The
resulting algorithms have been successfully applied to the induction and synchronous
motor families in applications where control of armature speeds above approximately one
hundred revolutions per minute is desired. However, sensorless position control remains
problematic.
This thesis provides an in depth investigation into sensorless motor control strategies for
high precision motion control applications. Specifically, methods of achieving control of
position and very low speed thresholds are investigated. The developed grey box
identification techniques are shown to perform better than their traditional white or black
box counterparts. Further, fuzzy model based sliding mode control is implemented and
results demonstrate its improved robustness to certain classes of disturbance. Attempts to
reject uncertainty within the developed models using the sliding mode are discussed.
Novel controllers, which enhance the performance of the sliding mode are presented.
Finally, algorithms that achieve control without a primary feedback sensor are
successfully demonstrated. Sensorless position control is achieved with resolutions
equivalent to those of existing stepper motor technology. The successful control of
armature speeds below sixty revolutions per minute is achieved and problems typically
associated with motor starting are circumvented.Research Instruments Ltd
Recent Advances in Robust Control
Robust control has been a topic of active research in the last three decades culminating in H_2/H_\infty and \mu design methods followed by research on parametric robustness, initially motivated by Kharitonov's theorem, the extension to non-linear time delay systems, and other more recent methods. The two volumes of Recent Advances in Robust Control give a selective overview of recent theoretical developments and present selected application examples. The volumes comprise 39 contributions covering various theoretical aspects as well as different application areas. The first volume covers selected problems in the theory of robust control and its application to robotic and electromechanical systems. The second volume is dedicated to special topics in robust control and problem specific solutions. Recent Advances in Robust Control will be a valuable reference for those interested in the recent theoretical advances and for researchers working in the broad field of robotics and mechatronics
Medical robots for MRI guided diagnosis and therapy
Magnetic Resonance Imaging (MRI) provides the capability of imaging tissue with fine resolution and
superior soft tissue contrast, when compared with conventional ultrasound and CT imaging, which
makes it an important tool for clinicians to perform more accurate diagnosis and image guided therapy.
Medical robotic devices combining the high resolution anatomical images with real-time navigation, are
ideal for precise and repeatable interventions. Despite these advantages, the MR environment imposes
constraints on mechatronic devices operating within it. This thesis presents a study on the design and
development of robotic systems for particular MR interventions, in which the issue of testing the MR
compatibility of mechatronic components, actuation control, kinematics and workspace analysis, and
mechanical and electrical design of the robot have been investigated. Two types of robotic systems
have therefore been developed and evaluated along the above aspects.
(i) A device for MR guided transrectal prostate biopsy: The system was designed from components
which are proven to be MR compatible, actuated by pneumatic motors and ultrasonic motors, and
tracked by optical position sensors and ducial markers. Clinical trials have been performed with the
device on three patients, and the results reported have demonstrated its capability to perform needle
positioning under MR guidance, with a procedure time of around 40mins and with no compromised
image quality, which achieved our system speci cations.
(ii) Limb positioning devices to facilitate the magic angle effect for diagnosis of tendinous injuries:
Two systems were designed particularly for lower and upper limb positioning, which are actuated and
tracked by the similar methods as the first device. A group of volunteers were recruited to conduct
tests to verify the functionality of the systems. The results demonstrate the clear enhancement of the
image quality with an increase in signal intensity up to 24 times in the tendon tissue caused by the
magic angle effect, showing the feasibility of the proposed devices to be applied in clinical diagnosis
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