Mihaita Horodinca

Active damping of chatter in machine tools: demonstration with a “hardware-in-the-loop” simulator

Abstract The motivation of the work is twofold: (a) understand the physics behind regenerative chatter and the influence of structural damping and (b) demonstrate an active damping technique based on collocated actuator/sensor pairs. A numerical stability analysis is performed using the root locus method and it is shown that, along with the structural poles, eigenvalues due to the delay parameter may contribute to instability. Since experimental demonstration of chatter in real machines is difficult, an alternative way of demonstration via a mechatronic simulator is presented, using the ‘hardware-in-the-loop’ concept. The mathematical model of the regenerative cutting process in turning is simulated in a computer and this is interfaced to a beam, representing the structural dynamics of the machine, via a displacement sensor and force actuator. In this way, a hardware and a software loop are combined. In a second step, an additional control loop is added, consisting of an accelerometer sensor and a collocated inertial actuator. Numerical and experimental stability lobe diagrams are compared, with and without active damping.

Vibration Isolation of Precision Payloads: A Six-Axis Electromagnetic Relaxation Isolator

This paper describes a passive six-axis vibration isolation system for space applications. The system consists of a Stewart platform with cubic architecture; each leg is equipped with an electromagnetic transducer connected to a RL circuit. The system behaves like a relaxation isolator and its transmissibility exhibits an asymptotic decay rate of ―40 dB/decade. The performances are very similar to that of an active isolator based on a skyhook controller.

SAM : A 7-DOF portable arm exoskeleton with local joint control

This paper presents the development of SAM, the Sensoric Arm Master, a 7-DOF portable exoskeleton with integrated actuation and sensors. Local joint control is implemented to improve performances of the device. Some experiments have been conducted with the system to show the functionality of the exoskeleton device linked to a virtual reality.

Computer Controlled Rotational MR-brake for Wrist Rehabilitation Device

This aricle presents a novel, computer controlled, magneto-rheological (MR) brake actuated, muscular rehabilitation, and evaluation device. The first part discusses various MR brake architectures and compares them. Simple analytical formulae are developed for a set of figures of merit, which point out the role played by the various parameters. Based on this analysis, a prototype with a T-shaped rotor has been designed, built and integrated into a portable rehabilitation device. In the second part of the article, the various exercise modes of the device and its control are described. Finally, results validating the performances of the device for the pronation/supination motion of the wrist are shown.

Rotational vibration absorber for the mitigation of rail rutting corrugation

Torsional vibrations of metro wheel sets are known to be involved in the wavelength-fixing mechanism of the rutting-type rail corrugation. In the first part of this paper, the basic conditions for this type of wear to appear are established using a theory developed in the frequency domain. The efficiency of a dynamic vibration absorber tuned to the first torsional resonance of the wheel set to mitigate rutting corrugation is evaluated numerically. In the second part, the phenomenon is studied on a quarter-scale test bench. The scaling laws for wheel–roller wear predictions are established. The efficiency of the dynamic vibration absorber is evaluated on the scaled bench. The results are compared with theoretical predictions from a linear model. Additionally, the measurements are compared with numerical results from a multi-body model portraying the experiment.

Parallel Piezoelectric Shunt Damping of Rotationally Periodic Structures

This paper considers the RL shunt damping of rotationally periodic structures with an array of regularly spaced piezoelectric patches. The technique is targeted to the damping of a specific mode with nodal diameters. For this particular case, one can take advantage of the shape of the targeted mode to organize the piezoelectric patches as a modal filter (in parallel loops) which reduces the demand on the inductors of the tuned inductive shunt. In the case of a perfectly rotationally periodic structure, it is possible to organize 4 piezoelectric transducers (PZT patches) in two parallel loops of 2 patches each. In this way, the demand on the inductors is reduced by as compared to independent loops, which may allow a fully passive integration of the RL shunt in a turbomachinery application. The method is first illustrated experimentally on a circular plate; it is then applied to a prototype of an industrial bladed drum. The influence of blade mistuning is investigated.

Simulation and Active Control of Chatter in Milling via a Mechatronic Simulator

This paper presents a 2 degree of freedom “Hardware in the Loop” mechatronic simulator for the study of regenerative chatter in milling. The main motivation behind the construction of the simulator is to propose active damping as a strategy for control of chatter in milling. A good comprehension of regenerative chatter in milling is essential for that purpose. Characterization of chatter in a real machining environment may be difficult, and the mechatronic simulator provides an alternative way to conduct investigations on chatter in milling in a laboratory environment, without conducting actual cutting tests. The simulator is found to realistically reproduce various kinds of bifurcation phenomena normally expected in milling operations. Active damping is then implemented on the system to investigate its effect on stability. It is shown experimentally that stability lobes are enhanced by the application of active damping, which fulfils the original objective of proposing active damping as a chatter stabilizing strategy.

Segmented bimorph mirrors for adaptive optics: segment design and experiment

We discuss the concept of lightweight segmented bimorph mirrors for adaptive optics. The segment consists of a monocrystal silicon substrate actuated by an array of in-plane piezoceramic (PZT) actuators with honeycomb electrodes. We focus on technological aspects of the segment design that are critical for space applications and describe a single segment demonstrator. The morphing capability of the segment is evaluated experimentally. We also discuss the local deformations (dimples) associated with the shape of the electrodes acting on the PZT array.

Portable smart wrist rehabilitation device driven by rotational MR-fluid brake actuator for telemedecine applications

This paper reports on the current status of the effort conducted at ULB in order to develop a portable muscular rehabilitation device for telemedicine applications. It is divided into four parts. The first part recalls the basic modes of muscular rehabilitation and gives a brief overview of commercial rehabilitation machines as well as portable devices under development. The second part describes the design of the proposed device and justifies the selection of MR-fluid brake actuation. The third part is devoted to the description of the control strategies implemented on the device. Finally, the last part describes preliminary results obtained with the device for the various exercise modes.

Prototype of a Small Low Noise Absolute Displacement Sensor

Inertial seismic sensors typically have a velocity readout, to offer a large dynamic range in a large frequency range. However, in some precision engineering applications, it can be preferable to have access to the displacement. An example is the so-called sky-hook spring strategy used for active vibration isolation. In this paper, we present a prototype of small inertial sensor with a displacement readout. It is based on a commercial low cost geophone, which has been modified to measure the displacement with a capacitive sensor. It results in a compact sensor with a resolution which is a factor 10 better than the commercial geophone, but a limited range of amplitudes. This paper finished with an attempt to extend the bandwidth of the sensor at low frequency.