Martin Hosek

Active Vibration Control of Distributed Systems Using Delayed Resonator With Acceleration Feedback

The Delayed Resonator (DR) and Dual Frequency Fixed Delayed Resonator (DFFDR) are newly introduced control techniques for active vibration absorption. Both methods propose a delayed position feedback within the absorber section of the structure to impart ideal resonance features to the absorber. When installed on an oscillating primary body, they form notch filters at their resonance frequencies attenuating the response of the primary structure. The DR absorber is shown to be real-time tunable to time varying disturbance frequencies. In this article, a number of new issues are considered. First, the basic theory is modified for acceleration feedback instead of position, which was originally proposed for the DR methodology. Second, the new absorption methods are implemented on distributed parameter structures which are under high frequency excitation (around 1 KHz). Stability of the combined structure is studied on a reduced order multi-degree-of-freedom primary structure together with the DR absorber. Experimental tests are conducted on a steel beam to verify the analytical findings. Piezoelectric actuators are used both to generate harmonic disturbances and to implement the control. The correspondence observed between the theoretical and experimental results is encouraging. The efficiency of the DR and DFFDR absorption techniques is demonstrated.

A new perspective and analysis for regenerative machine tool chatter

Abstract The paper contains a practical perspective on regenerative machine tool chatter. Chatter is a well known phenomenon, occurrence of which is undesired in manufacturing. Aggressive machining conditions, in the sense of removing more metal rapidly, usually cause chatter. In most cases, these conditions can be determined a priori to the operation. A chatter stability study and its reasoning based on root locus plot analysis of time delayed systems is presented as a new and practical perspective in the field. At the junction of root locus and chatter concepts an area of particular interest to the authors arises: a new method for active vibration suppression, the Delayed Resonator. It is an active vibration absorber tuning of which is achieved utilizing a simple time delayed feedback. The cross linking between the Delayed Resonator study and the subject matter, machine tool chatter, is exciting to share. This is the primary motivation in pursuing this study. One of the highlights of the work appears at the phenomenon called Dual Frequency Delayed Resonator. This feature has been conjectured in the literature using the well known “stability lobes”, but never discussed with detail.

Active Vibration Absorption Using Delayed Resonator With Relative Position Measurement

A novel active vibration absorption technique, the Delayed Resonator, has been introduced recently as a unique way of suppressing undesired oscillations. It suggests a control force on a mass-spring-damper absorber in the form of a proportional position feedback with a time delay. Its strengths consist of extremely simple implementation of the control algorithm, total vibration suppression of the primary structure against a harmonic force excitation and full effectiveness of the absorber in a semi-infinite range of disturbance frequency, achieved by real-time tuning. All this development work was done using the absolute displacements of the absorber in the feedback. These measurements, however, may be difficult to obtain and for some applications impossible. This paper deals with the operating and design repercussions caused by the substituting of an easier measurement: the relative motion of the absorber with respect to the primary structure. Although the proposition sounds like a trivial extension to the prior work it gives rise to important concerns such as system stability. Theoretical foundations for the Delayed Resonator (DR) are briefly recapitulated and its implementation on a single-degree-of-freedom primary structure disturbed by a harmonic force is discussed utilizing both absolute and relative position measurement of absorber mass. Methods for stability range analysis and transient behavior are presented as design tools. Properties observed for the same system with these two different feedbacks are compared. Another important advantage of the relative position feature is is to decouple the operation of the absorber from the primary structure entirely.

A single-step automatic tuning algorithm for the delayed resonator vibration absorber

The delayed resonator (DR) is an active vibration control approach where a passive mass-spring-damper arrangement is converted into an undamped real-time tunable dynamic absorber using partial state feedback with time delay. In the presented work, robustness of the control strategy against fluctuations in the structural parameters of the controlled system is addressed. A single-step automatic tuning algorithm based on online parameter identification is developed as a means of increasing robustness against uncertainties and variations in the mechanical properties of the absorber arrangement. The tuning process is completed within the absorber section of the controlled system with no external information from the primary structure. Implementation of the algorithm is illustrated by a numerical example, and demonstrated experimentally on a clamped-clamped flexible beam.

The Centrifugal Delayed Resonator as a Tunable Torsional Vibration Absorber for Multi-Degree-of-Freedom Systems

The centrifugal delayed resonator (CDR) is a novel active vibration absorption technique for elim inating undesired torsional oscillations in rotating mechanical structures. The key idea is to reconfigure the dynamics of a damped centrifugal pendulum arrangement so that it mimics an ideal real-time tunable ab sorber. This objective is achieved by applying a control torque based on proportional position feedback with variable gain and time delay. Theoretical fundamentals of the technique are explained, its implementation on a multi-degree-of-freedom primary structure is presented, stability of the controlled system is discussed, and real-time tuning ability is elaborated upon and demonstrated via simulations. The strengths of the CDR control consist of complete vibration elimination of the fundamental frequency component of torsional oscil lations at the location where the absorber is attached to the rotating structure, automatic tuning to time-varying frequencies, decoupling of the feedback control from the mechanical and dynamic properties of the rotating structure, relatively simple implementation of the control algorithm, and fault-tolerant performance in the case of control failure.

Observer-corrector control design for robots with destabilizing unmodeled dynamics

Industrial robotic manipulators and other mechatronic systems often possess undesirable higher order dynamics exhibited in the form of resonance conditions which affect closed-loop stability when feedback control is applied. In this study, an alternative reduced-complexity control design strategy is presented. The fundamental idea of the proposed approach is to synthesize a substitute feedback signal which reflects the dominant dynamics essential for operation of the system subject to control but does not include the undesirable higher order dynamic effects. A unique arrangement of a band-limited state observer and a low-pass filter corrector is employed for this purpose, providing a mechanism to extract the dominant dynamics from the output of the system with minimal amplitude and phase distortion. The resulting synthetic signal is used as a controller input, effectively eliminating destabilizing effects of the undesirable higher order dynamics. As a result, the controller can be designed practically without taking the higher order dynamic effects into account, which allows for use of conventional control techniques, and translates into reduced modeling requirements, simplified controller design and shorter development time when compared to a complete dynamic analysis. The effectiveness of the proposed concept is demonstrated experimentally on motion control of a four-axis direct-drive robotic manipulator for automated pick-place operations in semiconductor manufacturing applications. It is concluded that the proposed control design strategy provides improved control performance, increased stability margin, and added robustness against variations in system parameters in comparison to common methods adopted currently in the engineering practice.

Application of optimal trajectory algorithms to a solar-panel handling industrial manipulator: A case study

Several algorithms have been proposed in the last 25 years on the problem of generating time-optimal trajectories for robot manipulators along specified paths. This article describes an application of an optimal trajectory algorithm to an industrial manipulator used in the transfer of solar panel substrates between process modules. These manipulators operate in a vacuum environment and have constraints on substrate accelerations as well as available motor torques. The article shows that a trajectory profile optimized for both substrate acceleration and motor torques can reduce substrate transport time by 25 percent over the commonly used “S-curve” based algorithms.

Torsional vibration control of MDOF systems using the Centrifugal Delayed Resonator

The Centrifugal Delayed Resonator (CDR) is a novel active vibration absorption technology for eliminating undesired torsional oscillations in rotating mechanical structures. The key idea is to reconfigure the dynamics of a damped centrifugal pendulum arrangement so that it mimics an ideal real time tunable absorber. This objective is achieved by applying a control torque based on proportional position feedback with variable gain and time delay. Theoretical fundamentals of the technology are explained, its implementation on a multi-degree of freedom primary structure is presented, and stability of the controlled system is discussed.