Force Control Mode Research Articles

Monitoring of the mechanical load and thermal history during friction stir channelling under constant position and constant force control modes

In the present investigation, constant position and constant force process control modes; and representative process temperature measurements were analysed during the application of the friction stir channelling process. The experimental tests were carried out using rolled plates of AA5083-H111 with thickness of 15 mm. Results show that the FSC process was found not stable during the forward traverse movement stage when it is performed via position control. For both control modes, the tool was subjected to a more severe loading during the initial plunge than during the channelling period. Moreover, it was found that the tool vertical position is not significantly affected during the channelling stage when the process was force controlled. From the temperature measurements carried out, it was recorded a maximum process temperature of about 330 °C.

Measurement of the bending of thin inclined nanowires as a method for determining elastic modulus

The method of measuring nanowires elastic modulus by scanning probe microscopy is presented. This method uses the measurement of nanowire bending profiles in the precise force control mode. The possibilities of the method are demonstrated by measuring the Young’s modulus of thin tapered InP nanowires.

Adjustable-length loop cortical button versus interference screw fixation in quadriceps tendon anterior cruciate ligament reconstruction – A biomechanical in vitro study

BackgroundThis biomechanical cadaveric in vitro study aimed to evaluate and compare the dynamic elongation behavior and ultimate failure strength of tibial adjustable-length loop cortical button versus interference screw fixation in quadriceps tendon-based anterior cruciate ligament reconstruction. MethodsSixteen human quadriceps tendons were harvested and fixed into porcine tibiae using either biodegradable interference screw (n = 8) or adjustable loop device (n = 8) fixation. An acrylic block was utilized for femoral adjustable loop device fixation for both groups. All constructs were precycled for 10 times at 0.5 Hz and manually retensioned before tested in position and force control mode each for 1000 cycles at 0.75 Hz according to in vitro loading conditions replicating the in vivo ACL environment. Subsequently, an ultimate failure test at 50 mm/min was performed with mode of failure noted. FindingsTibial IS fixation showed no statistically significant differences in the initial (−0.46 vs. −0.47 mm; P = 0.9780), dynamic (2.18 mm vs. 2.89 mm; P = 0,0661), and total elongation (1.72 mm vs. 2.42 mm; P = 0,0997) compared to adjustable loop device fixation. The tibial button fixation revealed an increased ultimate failure load (743.3 N vs. 606.3 N; P = 0.0027), while stiffness was decreased in comparison to screw fixation (133.2 N/mm vs. 153.5 N/mm; P = 0,0045). InterpretationAnterior cruciate ligament reconstruction for quadriceps tendon graft using a tibial adjustable-length loop cortical button provides for comparable dynamic stabilization of the knee with increased ultimate failure load at decreased stiffness compared to screw fixation.

Intraoperative Preconditioning of Fixed and Adjustable Loop Suspensory Anterior Cruciate Ligament Reconstruction With Tibial Screw Fixation—An In Vitro Biomechanical Evaluation Using a Porcine Model

To evaluate the effect of preconditioning according to intraoperative workflow on initial tension and elongation behavior for femoral adjustable loop devices (ALDs) and closed loop devices (CLDs) in suspensory anterior cruciate ligament reconstruction (ACLR) with tibial screw fixation in a biomechanical invitro study. Three ACLR groups with tibial screw fixation were biomechanically tested in a full-construct setup using porcine tibias. Groups (n= 8 per group) varied by femoral fixation method and consisted of a CLD (group 3) and ALD fixation with (group 2) and without simulated intraoperative preconditioning (group 1). The change in tension after screw insertion and the displacement to restore the initial loading situation were measured. Grafts underwent dynamic cycling (1,000 cycles at 0.75Hz) using both a position and a force control mode. Data are presented as mean [standard deviation]. Placement of an interference screw induced a graft tension loss of 62% (49.4 [0.4] N vs 19.0 [10.0] N, P < .001) by introducing a laxity of 0.53 [0.26] mm. Intraoperative preconditioning led to a higher initial load level (228.3 [19.8] N) compared with unconditioned ALD (156.1 [25.5] N, P < .001) and CLD groups (156.6 [12.8] N, P < .001) with less force decrease over position-controlled cyclic loading. Furthermore, initial (-0.22 [0.16] mm) and dynamic elongation (0.88 [0.23] mm) were reduced compared with the unconditioned ALD (0.65 [0.35] mm, P < .001; and 1.56 [0.19] mm, P < .001) and CLD groups (0.16 [0.26] mm, P < .001; and 1.64 [0.24] mm, P < .001). ACLR with femoral ALD fixation and intraoperative preconditioning allows for restoration of time-zero screw-imparted slack and leads to significantly reduced cyclic elongation in accordance with native ACL function. Both ALD and CLD control groups behaved similarly, with total elongation less than 3mm including time-zero slack. Although the clinical relevance of time-zero graft tension loss is uncertain, the use of an ALD in concert with tibial screw fixation may be favorable to allow for tension optimization.

A Review of PZT Patches Applications in Submerged Systems.

Submerged systems are found in many engineering, biological, and medicinal applications. For such systems, due to the particular environmental conditions and working medium, the research on the mechanical and structural properties at every scale (from macroscopic to nanoscopic), and the control of the system dynamics and induced effects become very difficult tasks. For such purposes in submerged systems, piezoelectric patches (PZTp), which are light, small and economic, have been proved to be a very good solution. PZTp have been recently used as sensors/actuators for applications such as modal analysis, active sound and vibration control, energy harvesting and atomic force microscopes in submerged systems. As a consequence, in these applications, newly developed transducers based on PZTp have become the most used ones, which has improved the state of the art and methods used in these fields. This review paper carefully analyzes and summarizes these applications particularized to submerged structures and shows the most relevant results and findings, which have been obtained thanks to the use of PZTp.

A New Closed-loop Control Allocation Method with Application to Direct Force Control

A new closed-loop control allocation method is proposed to distribute the force and moment increment commands among multiple actuators at the same time. An innovative feedback configuration for the force and moment increment produced by the actuators deflections is added into the trajectory and attitude control loop, respectively. In addition, the trajectory and attitude controllers designed by nonlinear dynamic inversion are used to derive the desired force and moment increment commands. Then, the stability of the closed-loop system is guaranteed theoretically when the actuators are healthy and fail, where there is no a fault detection method to identify the failure. Finally, the proposed method is used to achieve direct force control for decoupling the attitude and flight trajectory in the longitudinal flight. The nonlinear simulation using Canard Rotor/Wing (CRW) aircraft longitudinal model in fixed-wing mode demonstrates that this method can achieve two direct force control modes: pitch pointing and direct lift, whether the actuators are healthy or fail.

Multi-parameter optimization of piezoelectric actuators for multi-mode active vibration control of cylindrical shells

A novel technique for the multi-parameter optimization of distributed piezoelectric actuators is presented in this paper. The proposed method is designed to improve the performance of multi-mode vibration control in cylindrical shells. The optimization parameters of actuator patch configuration include position, size, and tilt angle. The modal control force of tilted orthotropic piezoelectric actuators is derived and the multi-parameter cylindrical shell optimization model is established. The linear quadratic energy index is employed as the optimization criterion. A geometric constraint is proposed to prevent overlap between tilted actuators, which is plugged into a genetic algorithm to search the optimal configuration parameters. A simply-supported closed cylindrical shell with two actuators serves as a case study. The vibration control efficiencies of various parameter sets are evaluated via frequency response and transient response simulations. The results show that the linear quadratic energy indexes of position and size optimization decreased by 14.0% compared to position optimization; those of position and tilt angle optimization decreased by 16.8%; and those of position, size, and tilt angle optimization decreased by 25.9%. It indicates that, adding configuration optimization parameters is an efficient approach to improving the vibration control performance of piezoelectric actuators on shells.

Microstructure and mechanical properties of friction stir welded 8 mm pipe SAF 2507 super duplex stainless steel

The microstructure and mechanical properties of 8-mm-thick friction stir welded SAF 2507 super duplex stainless steel pipe was examined. High-quality welds were successfully produced using polycrystalline cubic boron nitride (PCBN) tool, force control mode of 38kN, travel speed of 50mm/min, rotational speed of 200rpm. Hardness and tensile tests were performed, showing hardness increase in the stir zone and failure on the base metal. Thermal simulation showed maximum global temperatures around 1176°C, and different thermal cycles along the joint thickness, providing microstructural and mechanical differences along the welded joint.

Real‐time force control for servo‐hydraulic actuator systems using adaptive time series compensator and compliance springs

SummaryServo‐hydraulic actuators have been widely used for experimental studies in engineering. They can be controlled in either displacement or force control mode depending on the purpose of a test. It is necessary to control the actuators in real time when the rate‐dependency effect of a test specimen needs to be accounted for under dynamic loads. Real‐time hybrid simulation (RTHS) and effective force testing (EFT) method, which can consider the rate‐dependency effect, have been known as viable alternatives to the shake table testing method. Due to the lack of knowledge in real‐time force control, however, the structures that can be tested with RTHS and EFT are fairly limited. For instance, satisfying the force boundary condition for axially stiff members is a challenging task in RTHS, while EFT has a difficulty to be implemented for nonlinear structures. In order to resolve these issues, this paper introduces new real‐time force control methods utilizing the adaptive time series (ATS) compensator and compliance springs. Unlike existing methods, the proposed force control methods do not require the structural modeling of a test structure, making it easy to be implemented especially for nonlinear structures. The force tracking performance of the proposed methods is evaluated for a small‐scale steel mass block system with a magneto‐rheological damper subjected to various target forces. Accuracy, time delay, and resonance response of these methods are discussed along with their force control performance for an axially stiff member. Overall, a satisfactory force tracking performance was observed by using the proposed force control methods.

Intraoperative Workflow for All-Inside Anterior Cruciate Ligament Reconstruction: An In Vitro Biomechanical Evaluation of Preconditioning and Knot Tying

To evaluate and compare the effect of preconditioning according to intraoperative workflow on the elongation behavior of single-side and fully knotted all-inside anterior cruciate ligament (ACL) reconstruction configurations in a biomechanical invitro study. Four full construct all-inside ACL reconstruction groups (n= 8 per group) were tested using porcine tibias and bovine tendons. Groups included both an all-inside configuration with one- (group 1) and both-side knotted adjustable loop-length devices (group 2), without and with performing intraoperative preconditioning (group 1-intraoperative preconditioned [IPC], group 2-IPC). Adjustable loop-length devices for control groups were knotted according to test configurations. Intraoperative preconditioning specimens were further precycled for 10 times at 0.5Hz and manually retensioned before knotting. All groups underwent dynamic cycling in position and force control mode each for 1,000 cycles at 0.75Hz according to invitro loading parameters replicating the invivo ACL environment. Finally, a load-to-failure test at 50mm/min was performed. Intraoperative preconditioning increases initial graft tension for single- (242 ± 22N vs 174 ± 13N; P < .0001) and both-side knotted configurations (225 ± 15N vs 159 ± 10N; P < .0001) compared with controls and allows maintained graft tension at higher levels until reaching the end of position-controlled cyclic loading. Furthermore, dynamic elongation is reduced for one- (1.93 ± 0.28 vs 0.76 ± 0.12; P < .0001) and both-side knotted (1.84 ± 0.20 vs 0.96 ± 0.32; P < .0001) configurations by 61% and 47%, respectively. No intergroup (group 1 vs group 2 and group 1-IPC vs group 2-IPC) statistically significant differences could be found between one- and both-side knotted configurations. All-inside ACL reconstruction with preconditioning according to intraoperative workflow leads to a statistically significant improved mechanical behavior and may allow for optimizing initial graft tension and elongation for all-inside ACL reconstruction to reduce knee laxity. A single-side knotted configuration achieves similar stabilization strength to fully knotted constructs. Graft insertion until tunnel docking increases the intratunnel graft portion that may optimize graft incorporation. Eliminating a suture knot stack may improve intraoperative workflow and reduce postoperative knot irritation.

Distributed microscopic actuation analysis of paraboloidal membrane shells of different geometric parameters

Abstract Paraboloidal membrane shells of revolution are commonly used as key components for advanced aerospace structures and aviation mechanical systems. Due to their high flexibility and low damping property, active vibration control is of significant importance for these in-orbit membrane structures. To explore the dynamic control behavior of space flexible paraboloidal membrane shells, precision distributed actuation and control effectiveness of free-floating paraboloidal membrane shells with piezoelectric actuators are investigated. Governing equations of the shell structronic system are presented first. Then, distributed control forces and control actions are formulated. A transverse mode shape function of the paraboloidal shell based on the membrane approximation theory and specified boundary condition is assumed in the modal control force analysis. The actuator induced modal control forces on the paraboloidal shell are derived. The expressions of microscopic local modal control forces are obtained by shrinking the actuator area into infinitesimal and the four control components are investigated respectively to predict the spatial microscopic actuation behavior. Geometric parameter (height-radius ratio and shell thickness) effects on the modal actuation behavior are explored when evaluating the micro-control efficiency. Four different cases are discussed and the results reveal the fact that shallow (e.g., antennas/reflectors) and deep (e.g., rocket/missile fairing) paraboloidal shells exhibit totally different modal actuation behaviors due to their curvature differences. Analytical results in this paper can serve as guidelines for optimal actuator placement for vibration control of different paraboloidal structures.

Distributed microscopic actuation analysis of deformable plate membrane mirrors

Abstract To further reduce the areal density of optical mirrors used in space telescopes and other space-borne optical structures, the concept of flexible membrane deformable mirror has been proposed. Because of their high flexibility, poor stiffness and low damping properties, environmental excitations such as orbital maneuver, path changing, and non-uniform heating may induce unexpected vibrations and thus reduce working performance. Therefore, active vibration control is essential for these membrane mirrors. In this paper, two different mirror models, i.e., the plate membrane model and pure membrane model, are studied respectively. In order to investigate the modal vibration characteristics of the mirror, a piezoelectric layer is fully laminated on its non-reflective side to serve as actuators. Dynamic equations of the mirror laminated with piezoelectric actuators are presented first. Then, the actuator induced modal control force is defined. When the actuator area shrinks to infinitesimal, the expressions of microscopic local modal control force and its two components are obtained to predict the spatial microscopic actuation behavior of the mirror. Different membrane pretension forces are also applied to reveal the tension effects on the actuation of the mirror. Analyses indicate that the spatial distribution of modal micro-control forces is exactly the same with the sensing signals distribution of the mirror, which provides crucial guidelines for optimal actuator placement of membrane deformable mirrors.

Light-induced vibration control of parabolic cylindrical shell panels

Parabolic cylindrical shell panel is useful in the aerospace. Light-activated shape memory polymer is a novel kind of smart materials. It is capable of offering a non-contact control way at the room temperature. In this study, the parabolic cylindrical shell panel laminated with light-activated shape memory polymer actuators is analyzed. First, the dynamic equations of the parabolic cylindrical shell panel coupled with light-activated shape memory polymer actuators are established; the modal control force of light-activated shape memory polymer actuators is derived with the modal expansion method. Then, the strain variation of light-activated shape memory polymer actuators is modeled based on the chemical kinetics. Furthermore, Young’s modulus of light-activated shape memory polymer actuators is measured through the biaxial tension experiments. The strain variation of light-activated shape memory polymer actuator with initial strain is also measured. The established strain model is validated by the experimental data of strain variation. In this case study, the snap-back control effects of the first four modes, that is, the (1,3), (1,4), (2,4), and (2,5) modes are evaluated. The study shows light-activated shape memory polymer actuators are effective to control the vibration of parabolic cylindrical shell panels. Light-activated shape memory polymer actuators have potential applications for the vibration control of double-curvature shells.

Velocity-dependent characteristics of magnetorheological fluids in squeeze mode considering the hydrodynamic and the magnetic field interactions

This work presents an experimental investigation on the behavior of magnetorheological (MR) fluids in squeeze mode and a theoretical analysis of its MR mechanism. Relative to the well-known large normal stress in squeeze mode, the exciting velocity-dependent characteristics and the normal stress variation tendency of MR fluids are emphasized. The characteristics of MR fluids are tested under displacement-control and force-control modes. It is shown from the tests that along with the exciting velocity, the tensile stress shows an increasing tendency before saturation, but the compressive stress exhibits a decreasing tendency. In addition, under force-control mode (10 N/s) test, after the initial elastic deformation the elastic-plastic deformation occurs instead of plastic flow. As a consequence, in order to fully understand the exciting velocity-dependent characteristics of MR fluids in squeeze mode, a new concept considering both the hydrodynamic interaction between the particles and continuous phase and ...

A new modified independent modal space control approach toward control of seismic-excited structures

In this paper, a new modified independent modal space control, namely independent modal space proportional-integral-derivative control (IMSPIDC), is proposed. The proposed control approach is developed through combining the well-known idea of proportional- integral- derivative control with the independent modal space control theory. IMSPIDC is applied to the problem of structural control under seismic excitation. A good trade-off between the conflicted modal structural responses and modal control force is crated using a multi-objective cuckoo search. Considering two different control devices includes: (1) an active tuned mass damper and (2) a system of active tendons, the performance of the proposed controller is evaluated in comparison with an independent modal space Linear–quadratic–Gaussian control (IMSLQRC). The Simulation results show that the IMSPIDC performs significantly better than the IMSLQRC in reduction of seismic responses of the structure. The proposed controller has several advantages in terms of simplicity and reduction of required sensors to the number of controlled stories. Furthermore, an evaluation of robustness against stiffness uncertainties indicates that the IMSPIDC gives a better performance than IMSLQRC in this term.

Phase shifting-based debris effect detection in USV-assisted AFM nanomachining

Atomic force microscopy (AFM) mechanical-based lithography attracts much attention in nanomanufacturing due to its advantages of low cost, high precision and high resolution. However, debris effects during mechanical lithography often lead to an unstable machining process and inaccurate results, which limits further applications of AFM-based lithography. There is a lack of a real-time debris detection approach, which is the prerequisite to eventually eliminating the influence of the debris, and of a method that can solve the above problems well. The ultrasonic vibration (USV)-assisted AFM has the ability to sense the machining depth in real time by detecting the phase shifting of cantilever. However, whether the pile-up of debris affect the phase response of cantilever is still lack of investigation. Therefore, we analyzed the mechanism of the debris effect on force control mode and investigated the relationship between phase shifting and pile-up of debris. Theoretical analysis and experimental results reveal that the pile-up of debris have negligible effect on phase shifting of cantilever. Therefore, the phase shifting-based method can detect the debris effect on machining depth in force control mode of AFM machining.

Analysis of Startup Process and Its Optimization for a Two-Stand Reversible Cold Rolling Mill

Dynamic characteristic analysis of a two-stand reversible cold rolling mill in the startup process was carried out. The delay algorithm of the interstand thickness was proposed. A new method combined with the accelerated secant and the tangent methods was established to solve the simultaneous equations. The thickness and interstand tension transition processes with different static tension establishing processes were analyzed. Both mills were operated under constant rolling force control mode in the above process. The results show that the strip thickness in the rolling gap reduces in the static mill screwdown process. The entry stand runs inversely to establish the static interstand tension. This area becomes an abnormal thickness reduction area of the incoming strip. It results in several abnormal interstand tension increases in the subsequent startup process. The tension increase leads to an impact force on the strip that is the main reason of the strip breakage in the startup process. So the static tension establishing process was optimized, and the interstand tension fluctuation and the strip breakage accidents both reduced significantly. The results are beneficial to the startup process of the two-stand reversible cold rolling mill.

Modelling and Testing of the Piezoelectric Beam as Energy Harvesting System

Abstract The paper describes modelling and testing of the piezoelectric beam as energy harvesting system. The cantilever beam with two piezo-elements glued onto its surface is considered in the paper. As result of carried out modal analysis of the beam the natural frequencies and modes shapes are determined. The obtained results in the way mentioned above allow to estimate such location of the piezo-actuator on the beam where the piezo generates maximal values of modal control forces. Experimental investigations carried out in the laboratory allow to verify results of natural frequencies obtained during simulation and also testing of the beam in order to obtain voltage from vibration with help of the piezo-harvester. The obtained values of voltage stored on the capacitor C 0 shown that the best results are achieved for the beam excited to vibration with third natural frequency, but the worst results for the beam oscillating with the first natural frequency.

A structural experimental technique to characterize the viscoelastic behavior of concrete under restrained deformations

AbstractAn innovative variable restraint frame is proposed to characterize the viscoelastic behavior of concrete under tensile stresses induced by restraints to shrinkage deformations (mainly due to drying). Two concrete specimens with the same cross section are used, subjected to equal thermal and moisture conditions: one is made of plain concrete, to assess the “free” deformations due to shrinkage and temperature; the other is reinforced with two steel threaded rods, which induce a manually controlled axial restraint to shrinkage. The restrained specimen is installed on a reaction frame, being stretched in force control mode. The concrete and the rods are instrumented with strain gauges and temperature sensors, which allow separation of the different components of concrete strains with the aid of equations based on equilibrium and compatibility conditions. This permits identifying the elastic and tensile creep concrete strains, as well as the concrete tensile stresses induced by the restrained shrinkage. The device also allows assessing the concrete modulus of elasticity during the test and remains operational even upon concrete cracking, features of great interest for the intended material characterization.

Quasi-optimal locations of piezo-elements on a rectangular plate

The optimal location of piezo-actuators and piezo-sensors for the vibration control of a rectangular plate with SFSF (Simply Supported - Free - Simply Supported - Free) boundary conditions is presented in the paper. Based on bending moments, \(M_{x}(x,y)\) and \(M_{y}(x,y)\), the modal control forces generated by the piezo-stripes are calculated for the first five mode shapes. Calculations are carried out for different locations of two piezo-strips directed along the X and Y axes. The obtained results are used to define performance indexes of modal control forces for the two considered directions of vibration. In a similar way the modal unit elongations of the piezo-sensors are calculated for two different orientations of the piezos on the plate. Based on these results the objective cost functions \( J_{\varepsilon - odd}\) and \( J_{\varepsilon - even}\) are defined separately for odd and even modes. The quasi-optimal locations of the piezo-actuators and piezo-sensors are determined by maximizing the proposed cost functions. After analytical and numerical investigations the process of the full model identification is carried out at the laboratory stand. A chirp signal is applied in the identification process. The rectangular plate is excited with the chirp force while output signals are measured by the piezo-sensors oriented in the perpendicular directions X and Y. In such a way two mathematical models are obtained to control the vibration of the plate separately for odd and even natural modes.-1