Model-based feedback control of an ultrasonic transducer for ultrasonic assisted turning using a novel digital controller

Ultrasonic turning has time variant parameters due to temperature effects and changing load conditions during the process. This results in a change of the resonance frequency and vibration amplitude. To realize constant vibration amplitudes it is necessary to control the ultrasonic transducer by a suitable feedback controller. One approach to drive such a system is to use the resonance frequency as operating point in connection with an amplitude feedback controller. The advantages of resonant driven low damped systems are low voltages and high values of effective power. This paper presents a digital system used for parameter identification and model-based feedback control of the ultrasonic turning tool. During the turning process the system load depends on several factors like chip formation, material inhomogeneity, warming and tool wear. To achieve a stable process and a uniform surface of the work piece the feedback controller has to guarantee constant vibration amplitudes of the ultrasonic tool. The controller used in this paper consists of a digital resonance controller and a current amplitude controller with a frequency of 500 Hz. The current amplitude and phase between the excitation voltage and current are determined by phase sensitive demodulation (PSD). To determine the feedback parameters a model-based approach is used

Ultrasonic friction reduction in elastomer - Metal contacts and application to pneumatic actuators

Ultrasonic friction reduction is well known in metal-metal contacts. Due to the vibration, the stick phase in the contact phase vanishes and only sliding occurs. As long as the macroscopic relative velocity of the contact partners is much lower than vibration velocity, the necessary force to move the parts tends to (nearly) zero. If the effect also exists in material combinations with a significant difference in stiffness and damping characteristic has not been investigated in the past. This contribution shows the effect for various material combinations, which are typical for sealings in pneumatic actuators. Further, a novel integrated transducer design for a pneumatic actuator is presented. In this design the transducer also acts as moving part within the pneumatic actuator. The design challenges are the two contact areas on the moving part, where the friction reduction and consequently high vibration amplitudes are needed. The first area is fixed on the transducer geometry, the other is moving along the piston. This novel design has been implemented in the laboratory; detailed experimental results are presented in this contribution

Modeling of ultrasonic processes utilizing a generic software framework

Modeling of ultrasonic processes is typically characterized by a high degree of complexity. Different domains and size scales must be regarded, so that it is rather difficult to build up a single detailed overall model. Developing partial models is a common approach to overcome this difficulty. In this paper a generic but simple software framework is presented which allows to coupe arbitrary partial models by slave modules with well-defined interfaces and a master module for coordination. Two examples are given to present the developed framework. The first one is the parameterization of a load model for ultrasonically-induced cavitation. The piezoelectric oscillator, its mounting, and the process load are described individually by partial models. These partial models then are coupled using the framework. The load model is composed of spring-damper-elements which are parameterized by experimental results. In the second example, the ideal mounting position for an oscillator utilized in ultrasonic assisted machining of stone is determined. Partial models for the ultrasonic oscillator, its mounting, the simplified contact process, and the workpiece's material characteristics are presented. For both applications input and output variables are defined to meet the requirements of the framework's interface.DF

Investigations on the effect of post treatment utilizing ultrasonic standing waves on the hardness of laser beam welds in stainless steel

Laser beam welding is precise, quick and highly automatable. Nevertheless, disadvantageous hardness profiles can result and promote cracking. By an ultrasonic post treatment, crystal defects, internal stress and grain structure can be altered to achieve uniform hardness. In the investigations round bars with 30 mm diameter made from stainless steel grade 1.4301 are welded by laser in a rotational process. Ultrasonic excitation is applied utilizing a longitudinal mode of the system. The weld pool is positioned in the node or the antinode of the amplitude distribution. The excitation amplitude varies at 0/2/4 µm and the treatment durations at 0/5/10 min. The welds are evaluated by metallographic cross sections and hardness measurements. The results indicate the effects of acoustic residual softening and hardening. With standard deviations of about 2 %, the weld hardness is decreased by 3 % with nodal excitation and increased by 4 % with antinodal excitation. The difference between weld and base material hardness is not reduced since the base material is hardened at all ultrasonic parameters used

Influence of the ultrasonic vibration amplitude on the melt pool dynamics and the weld shape of laser beam welded EN AW-6082 utilizing a new excitation system for laser beam welding

Laser beam welding is a commonly used technology for joining similar and dissimilar materials. In order to improve the mechanical properties of the weld, the introduction of ultrasonic vibration into the weld zone has been proposed [5]. The ultrasonic system consists of an electronic control, a power supply, a piezoelectric converter and a sonotrode, which introduces the vibration into the weld zone. Its proper design is of great importance for the process performance. Furthermore, the effects of ultrasound in a melt pool need to be understood to evaluate and optimize the process parameters. In addition, it is important to find out the limits of ultrasonic excitation with respect to a maximum vibration amplitude. Therefore, firstly different methods of ultrasonic excitation are investigated and compared with respect to their performance. A system which is based on using longitudinal vibrations turns out to be the best alternative. Secondly, the system design is described in detail to understand the boundary conditions of the excitation and finally, simulations about the influence of ultrasonic vibrations are done by using a simplified model. The system is used to perform experiments, which aim at detecting the maximum vibration amplitude doing bead on plate welds of EN AW-6082 aluminum alloy. The experiments reveal a significant change of the weld shape with increasing ultrasonic amplitude, which matches the simulative findings. If the amplitudes are small, there is a marginal effect on the weld shape. If the amplitudes are high, melt is ejected and the weld shape is disturbed. In the present case, amplitudes over 4 µm were found to disturb the weld shape. © 2021, The Author(s)

Multiple solutions and corresponding power output of a nonlinear bistable piezoelectric energy harvester

We examine multiple responses of a vibrational energy harvester composed of a vertical beam and a tip mass. The beam is excited horizontally by a harmonic inertial force while mechanical vibrational energy is converted to electrical power through a piezoelectric patch. The mechanical resonator can be described by single or double well potentials depending on the gravity force from the tip mass. By changing the tip mass we examine the appearance of various solutions and their basins of attraction. Identification of particular solutions of the energy harvester is important as each solution may provide a different level of power output

Investigation of process forces of ultrasonically assisted scratch tests

Due to their abrasive qualities, machining of hard and brittle materials is predominantly performedusing tools with geometrically indefinite cutting edge. However, these processingmethods offer only low productivity, which often can be increased by superimposing ultrasonicvibrations to the process. At the same time this hybrid process design involves great uncertainties,as influencing factors and the mechanism of action are not sufficiently describedyet. In order to close this knowledge gap, firstly the occurrences on the scale of single abrasivegrains shall be observed. This should increase the overall process understanding andreveal fundamental interrelations of machining with geometrically indefinite cutting edge. Toachieve this, scratch tests with well-defined boundary conditions will be performed, analyzedand compared. As a result of the experiments the interdependencies of process forces, cuttingspeed, ultrasonic amplitude and depth of cut will be presented

Defibrillation of soft porous metal-organic frameworks with electric fields

Tuning porosity with electric fields Many metal-organic framework (MOF) compounds exhibit soft porosity—i.e., their lattices can undergo considerable deformation. Knebel et al. formed membrane layers of the MOF ZIF-8 and found that it was converted into a polar polymorph with a stiffer lattice in response to an applied electric field (see the Perspective by Gascon). This change reduced gas transport but, for certain gas mixtures such as propane and propene, also improved their separation factor. Science , this issue p. 347 ; see also p. 303 </jats:p

Dynamic Acoustic Levitator Based On Subwavelength Aperture Control

Abstract Acoustic levitation provides a means to achieve contactless manipulation of fragile materials and biological samples. Most acoustic levitators rely on complex electronic hardware and software to shape the acoustic field and realize their dynamic operation. Here, the authors introduce a dynamic acoustic levitator that is based on mechanically controlling the opening and (partial) closing of subwavelength apertures. This simple approach relies on the use of a single ultrasonic transducer and is shown to permit the facile and reliable manipulation of a variety targets ranging from solid particles, to fluid and ferrofluidic drops. Experimental observations agree well with numerical simulations of the Gor'kov potential. Remarkably, this system even enables the generation of time‐varying potentials and induces oscillatory and rotational motion in the levitated objects via a feedback mechanism between the trapped object and the trapping potential. This is shown to result in long distance translation, in‐situ rotation and self‐modulated oscillation of the trapped particles. In addition, dense ferrofluidic droplets are levitated and transformed inside the levitator. Controlling subwavelength apertures opens the possibility to realize simple powerful levitators that nevertheless allow for the versatile dynamic manipulation of levitated matter

A control system for ultrasound devices utilized for inactivating E. coli in wastewater

Sonochemical processes applied to wastewater treatment have an influence on the behavior of ultrasonic systems. This is especially due to the load characteristic of the sonochemical process itself and the temperature increase caused by internal damping within the converter. Hence, a controlling device is needed to guarantee the operation in resonance and to keep the vibration amplitude constant. This paper presents a digital control system for the operation of weak to strong damped ultrasonic devices and its application for inactivating Escherichia coli in wastewater. In an experimental investigation, the electric data during a sonochemical process to inactivate E. coli in wastewater is taken into account to analyze the efficacy of the treatment process and the reaction of the vibration system to the process. Frequency response measurements depict that the resonance frequency changes with the sonicated medium and the vibration amplitude decreases with driving current. In addition to a common continuous operation of the system, different pulsed modes are investigated. The experiments prove the common dependencies between inactivation and power level or treatment time. Additionally, it is pointed out that the control of the sonochemical device is of utmost importance to guarantee an efficient treatment of water, because fast process changes, especially in pulsed operation modes, need to be controlled to a steady state as fast as possible. Although a water treatment efficiency increase using pulsed modes was not proved, it is shown, that the performance of the control unit is capable of using different driving modes in water treatment