Constant Force Research Articles

Anatomical and histological analyses of ankle plantar flexors: insights into connective tissue composition and muscle architecture.

The tibialis posterior (TP), flexor digitorum longus (FDL), and flexor hallucis longus (FHL) are muscles that contribute to the stability of foot and ankle movements, playing a crucial role in achieving optimal gait. However, a comprehensive examination of the anatomical characteristics and histological variances of each muscle has not been conclusively established. A total of 10 un-embalmed cadavers were dissected, and muscles from each cadaver were consistently harvested from the musculotendon junction. The ratio of collagen and elastic fibers was assessed through three immunohistological analyses, focusing on distinct histological characteristics in type I (slow twitch) and type II (fast twitch) fibers. Additionally, Ultrasonography was utilized to compare and analyze the thickness, fascicle angle, and muscle fiber length of each muscle. Concerning the relative proportion of elastic fibers to collagen, the TP exhibited the highest collagen content (21.9 ± 0.30%, mean ± standard deviation), while the FHL had the highest elastic fiber proportion (48.4 ± 0.44%). The TP predominantly comprised slow type muscle fibers (36.88 ± 0.83%), whereas the FHL contained a higher density of fast type muscle fibers (32.46 ± 4.02%). US analysis indicated that the thickness of the TP was relatively greater (2.0 ± 0.2mm) compared to the FDL (1.2 ± 0.1mm) and FHL (1.1 ± 0.1mm). Additionally, the fascicle length was notably longer in the TP (25.6 ± 4.1mm). Our anatomical and histological findings indicate that the tibialis posterior (TP) is the thickest with a significant physiological angle and a high collagen content. This characteristic enables the TP to provide stability by transmitting a constant force to the calf. On the other hand, the flexor hallucis longus (FHL) exhibits the highest elastic fiber content, confirming its ability to exert instantaneous, swift, and powerful force.

Design and experimental verification of programmable metastructures based on constant force cells

Abstract Mechanical metastructures consisting of periodic cells with adjustable output force charactersitics and ranges have received increasing attention in recent years owing to its unique capability to tune mechanical properties such as stiffness and Poisson’s ratio etc. In this paper, we present the design, simulation, and experimental characterization of a mechanical metastructure that realizes customized constant force output. The metastructure consists of periodic constant force units that are formed by combining a positive and negative stiffness element. Notably, the force unit also contains a unique flexure design with solid and hollow pins to reduce the lateral stress by 50%, which allows for precise control of the output force. By using a programmable design method, the force unit forms 2D and 3D metastructures via parallel and tendem stacking. Simulations were performed to optimize the design and predict the device performance. Finally, experiments were devised and performed to verify the simulation results of the metastructures. The promising results warrant the wide application of the new mechanical metastructure as well as the programmable design method, such as low-pass mechanical filters, noise and vibration cancellation devices etc.

Effect of friction on levelling of the maxillary canine with NiTi superelastic wire - an in silico experiment using a finite element method

ABSTRACT Purpose To clarify the effect of friction on the levelling process using a NiTi superelastic wire, the levelling process was simulated using a finite element method. Materials and methods The maxillary right canine, which was intruded by 2 mm, was levelled using a 0.014 inch or 0.016 inch NiTi round wire. The wire was supported by two fixed brackets with 0.018 × 0.025 inch slots. The canine, alveolar bone, and bracket were rigid bodies, while the periodontal ligament (PDL) was a nonlinear elastic material. Kinetic friction was caused by contact forces acting on the wire and the bracket slot. Additionally, when the wire was securely ligated to the bracket slot, a constant frictional force caused by the ligation was directly applied to the wire. As the levelling force was applied to the canine, it moved by accumulating the initial tooth movement caused by elastic deformation of the PDL. Results In the case without friction caused by ligation, although the kinetic friction decreased the levelling force during the early levelling stage, the progress of levelling remained unchanged. In the case with friction caused by ligation, as the ligation friction increased, the levelling force decreased, reducing the levelling speed. Furthermore, the levelling process was impeded when the friction caused by ligation reached a critical value. Conclusion When using passive self-ligating brackets, the friction is caused only by levelling forces, which have almost no effect. When the wire is ligated securely to the bracket, additional friction is generated, hindering the levelling process.

Order-of-magnitude increased range of constant force adjustment via section optimization

An adjustable constant force environment is critical in engineering applications, including precision manipulation, surgical robots, and advanced manufacturing, all requiring a wider range of force regulation and adjustment. Traditional adjustable constant force mechanisms (ACFMs) have significant limitations in achieving a wide range of constant force (CF) adjustments due to factors like stress and interference. Existing ACFMs typically offer only a 2–4 times change in CF, which is insufficient. This research aims to provide an order-of-magnitude increase in CF adjustment range while remaining compact and preserving CF quality through section optimization. An analytical model demonstrates the efficacy of adjusting CF by an order-of-magnitude in prismatic and non-prismatic beams for CF adjustment method selection. Additionally, finite element analysis and design optimization of the non-prismatic serpentine beam with an out-of-plumbness imperfection angle and polynomial section description were conducted to maximize CF adjustability and quality. Experimental validation showed a 38 times change in CF adjustability for 5 percent variation in the CF, 18 times improvement in compactness, and high Energy Similarity Index SCF compared to the prismatic benchmark mechanism. This proposed system may be implemented in several applications, including load control, impact and vibration mitigation, space exercise, wearables, etc.

Performance optimization of vessel sealing using a hemostatic ultrasonic scalpel.

Using ultrasound technology as one of the therapeutic methods, in which ultrasound waves of different frequencies and intensities are employed, has significantly contributed to enhancing and facilitating the treatment process of various diseases. A Hemostatic Ultrasonic Scalpel can entail considerable advantages by simultaneously performing two operations tissue cutting and coagulation of biological tissues. In the present study, employing experimental design through response surface methodology, the effect of ultrasonic power and the duration of vibration application on the tissue has been investigated. Two parameters, namely the burst pressure of the sealed vessel and the length of the thermal seal zone, were measured by pressure testing and analysis image of the thermal effect region at the sealed vessel area, respectively. The pressure test results demonstrated that an input power of 52 W and the application of vibrations for 8 s under a constant force of 10 N, showed the optimized maximum burst pressure equal to 1100 mmHg. Examination of the sealed vessel images revealed a linear increase in thermal damage with increasing input power.

Constant-force photonic projectile for long-distance targeting delivery

Abstract Optically controllable delivery of microparticles excites interesting research and applications in various fields because of the noninvasive and noncontact features. However, long-distance delivery with a static low-power light source remains challenging. Here, the constant-force photonic projectile (CFPP) is employed to achieve long-distance delivery of microparticles with a low-power laser beam. The CFPP takes advantage of photon absorption to create a constant optical force within a large range, surpassing traditional tweezers. The concept of CFPP has been experimentally corroborated by remote control over micrometer-sized absorptive particles (APs) using a simple tilted focused beam. At the laser focus, strong photon absorption results in a large constant optical force that ejects the APs along the optical axis. Furthermore, the additional thermal convection field, which attracts particles from a distance into the working range of the CFPP, is utilized to collect the unbound APs for reuse. Finally, we demonstrate the concept of drug delivery by transporting a small microparticle onto a host particle at a remote location. The proposed CFPP provides a new perspective for drug delivery and heat-enhanced photodynamic therapy.

Research on Fuzzy PID Compliant Grinding Control Based on DBO Algorithm Optimization

In order to achieve the requirements of high precision, fast response and low overshoot in the robot grinding process. An active compliant actuator at the end of the robot is designed, and a fuzzy PID constant force control method based on dung beetle optimizer (DBO) optimization is proposed. The force and gas flow model of the compliant actuator are analyzed, and the mathematical model of the actuator is established. On the basis of fuzzy PID algorithm, the fuzzy PID parameters optimized by DBO algorithm are adopted. The simulation system model is established by MATLAB, and the performance of PID control, fuzzy PID control and fuzzy PID control method optimized by DBO algorithm is compared. The simulation results show that the fuzzy PID control based on DBO algorithm has faster response speed, reaches stability in 0.5s, no overshoot, and the system is more stable.

Bone Density Correlates With Depth of Subsidence After Expandable Interbody Cage Placement: A Biomechanical Analysis.

Biomechanical analysis. To evaluate the depth of subsidence resulting from an expandable interbody cage at varying bone foam densities. Expandable interbody cages have been shown to be associated with increased rates of subsidence. It is critical to evaluate all variables which may influence a patient's risk of subsidence following the placement of an expandable interbody cage. In the first stage of the study, subsidence depth was measured with 1Nm of input expansion torque. In the second stage, the depth of subsidence was measured following 150 N output force exerted by an expandable interbody cage. Within each stage, different bone foam densities were analyzed, including 5, 10, 15, and 20 pounds per cubic foot (PCF). Five experimental trials were performed for each PCF material, and the mean subsidence depths were calculated. Trials which failed to reach 150 N output force were considered outliers and were excluded from the analysis. There was an overall decrease in subsidence depth with increasing bone foam density. The mean subsidence depths at 150 N output force were 2.0±0.3mm for 5 PCF, 1.8±0.2mm for 10 PCF, 1.1±0.2mm for 15 PCF, and 1.1±0.2mm for 20 PCF bone foam. The mean subsidence depths at 1Nm of input torque were 2.3±0.5mm for 5 PCF, 2.3±0.5mm for 10 PCF, 1.2±0.2mm for 15 PCF, and 1.1±0.1mm for 20 PCF bone foam. Depth of subsidence was negatively correlated with bone foam density at both constant input torque and constant endplate force. Because tactile feedback of cage expansion into the subsiding bone cannot be reliably distinguished from true expansion of disc space height, surgeons should take bone quality into account when deploying expandable cages.

Analysis of Titanium Mesh Ti6Al4V Formation Using Die Press Forming Machine for Cranioplasty

Cranioplasty is required for patients with head defects, where the deformed part of the head is replaced with Ti6Al4V titanium wire implants. The titanium wire forming process is usually done manually, which can take a long time and give results that do not match the anatomical shape of the head. Therefore, it is important to develop domestic technology that can produce titanium wire automatically. This study aims to analyze the frame and mold of the automatic wire mesh molding machine before production. The tool is made using press forming method and finite element analysis with ANSYS software. The machine frame is made of 304 stainless steel material, while the mold uses ABS material. The analysis was performed with a constant load force of 100 N, corresponding to the maximum reading on the load cell. The simulation results show the deformation, strain, and von Mises stress of the machine frame and punch model, which are still far below the plastic deformation and UTS values of the material. However, the analysis results on the Ti6Al4V titanium die and mesh exceeded the UTS of the material in the cutting edge area of the die. Nevertheless, the die model can still be used because the maximum stress point is located at the edge of the die design area, where the titanium mesh will be cut when applied to the patient's skull implant. The results of this study are expected to help medical personnel in skull implant surgery and analysis of press machine manufacturing.

Real‐time hybrid simulation for investigating the seismic response of a bridge isolated with lead rubber bearings

AbstractThis study investigates the seismic response of lead rubber bearings (LRBs) under constant and time‐varying axial forces using real‐time hybrid simulation (RTHS). Although shake table testing can provide realistic seismic responses, it is often expensive and quite challenging for large‐scale structures. RTHS, however, offers a cost‐effective alternative by experimentally testing only the structural component of interest while analytically modeling the remaining structure. With the use of an advanced real‐time force control method, this study implemented RTHSs for a bridge isolated with two LRBs, where the LRBs are subjected to various constant axial forces due to self‐weight as well as time‐varying axial forces induced by vertical ground motions. The lateral response of LRBs was found to be significantly influenced by the magnitude of constant axial force, highlighting the importance of incorporating the effect of axial force due to self‐weight into numerical simulations. Additionally, it is crucial to satisfy the axial force boundary condition when conducting RTHS or cyclic loading tests to obtain more reliable test results. On the other hand, the time‐varying axial force generated by the vertical vibration of the bridge due to vertical ground motions has a limited impact on the lateral response of LRBs.

Artificial intelligence driven clustering of blood pressure profiles reveals frailty in orthostatic hypertension.

Gravity, an invisible but constant force , challenges the regulation of blood pressure when transitioning between postures. As physiological reserve diminishes with age, individuals grow more susceptible to such stressors over time, risking inadequate haemodynamic control observed in orthostatic hypotension. This prevalent condition is characterized by drops in blood pressure upon standing; however, the contrary phenomenon of blood pressure rises has recently piqued interest. Expanding on the currently undefined orthostatic hypertension, our study uses continuous non-invasive cardiovascular data to explore the full spectrum of blood pressure profiles and their associated frailty outcomes in community-dwelling older adults. Given the richness of non-invasive beat-to-beat data, artificial intelligence (AI) offers a solution to detect the subtle patterns within it. Applying machine learning to an existing dataset of community-based adults undergoing postural assessment, we identified three distinct clusters (iOHYPO, OHYPO and OHYPER) akin to initial and classic orthostatic hypotension and orthostatic hypertension, respectively. Notably, individuals in our OHYPER cluster exhibited indicators of frailty and sarcopenia, including slower gait speed and impaired balance. In contrast, the iOHYPO cluster, despite transient drops in blood pressure, reported fewer fallers and superior cognitive performance. Surprisingly, those with sustained blood pressure deficits outperformed those with sustained rises, showing greater independence and higher Fried frailty scores. Working towards more refined definitions, our research indicates that AI approaches can yield meaningful blood pressure morphologies from beat-to-beat data. Furthermore, our findings support orthostatic hypertension as a distinct clinical entity, with frailty implications suggesting that it is worthy of further investigation.

Nonequilibrium Molecular Dynamics Method to Generate Poiseuille-Like Flow between Lipid Bilayers.

There are various flows inside and outside cells in vivo. Nonequilibrium molecular dynamics (NEMD) simulation is a useful tool for understanding the effects of these flows on the dynamics of biomolecules. We propose an NEMD method to generate a Poiseuille-like flow between lipid bilayers. We extended the conventional equilibrium MD method to produce a flow by adding constant external force terms to the water molecules. Using the Lagrange multiplier method, the center of mass of the lipid bilayer is constrained so that the flow does not sweep away the lipid bilayer, but the individual lipid molecules fluctuate. The temperature of the system is controlled properly in the solution and membrane by using the Nosé-Hoover thermostat. We found that the flow velocity increases linearly as the applied external force term increases. It is possible to estimate the appropriate value of acceleration to generate a flow with an arbitrary velocity using this proportional relation once a single short MD simulation is performed. We also found that the flow between two lipid bilayers is slower than the analytical solution of the Navier-Stokes equations between rigid parallel plates due to the interactions between water molecules and the membrane. This method can be applied not only to a flow on lipid membranes but also to a flow on soft surfaces generally.

Parallel Force Feedback Device Design With Constant Jacobian Matrix and Net Weight Fully Balanced

Abstract Force feedback devices offer realistic and intuitive feedback to operators, and achieving higher accuracy and transparency has been a prominent research focus in this field. However, errors in real-time force or position calculations are inevitable, which can have adverse effects on the accuracy of the equipment. This article presents the design of a parallel mechanism that incorporates a constant force and velocity mapping relationship based on the type synthesis of the constant Jacobian matrix. Specifically, the mechanism maintains a fixed direction of force applied to the operating platform by the drive pair, which is mounted on the fixed platform in each limb, irrespective of position changes. This unique feature enables the mechanism to achieve a complete net weight balance. The implementation method is detailed in this article, which involves adding appropriate counterweights to achieve a balance between the weight of the connecting rod and the overall gravity of the operating platform. Furthermore, the optimization of structural parameters helps to improve the performance of the developed prototype. The proposed design scheme not only addresses the fundamental reduction of errors caused by real-time force and position mapping solving but also enhances operational transparency. Finally, simulation and experimental tests are conducted to validate the proposed theory.

Absolute negative mobility of an inertial Brownian particle in an oscillating potential.

Transport of an inertial Brownian particle in an oscillating potential is numerically investigated in the presence of an external constant force. The oscillating potential can break thermodynamic equilibrium. Within appropriate parameter regimes, the particle moves in a direction opposite to the constant force, which means that the system can exhibit the phenomenon of absolute negative mobility (ANM). Furthermore, it may be inferred from the bifurcation diagrams that ANM originates from chaotic-periodic transitions, where the particle subjected to a constant force performs reverse periodic motion due to continuous reverse driving by the oscillating potential. Based on GPU acceleration techniques, we present the distribution of ANM in the parameter space and analyze how the ANM depends on the system parameters. These results are robust in a wide range of parameters and may pave the way to the experimental realization of ANM.

Equivalent spring-like system for two nonlinear springs in series: application in metastructure units design

The paper deals with the problem of design of unit in auxetic metastructure. The unit is modeled as a two-part spring-like system where each part is with individual stiffness. To overcome the problem of analyzing of each of parts separately, the equivalent spring is suggested to be introduced. In the paper, a method for obtaining the equivalent elastic force of the unit is developed. The method is the generalization of the procedure suggested for substitution of a hard and a soft spring in series with an equivalent one. The nonlinearity of original springs is of quadratic order. As a results, it is obtained that the equivalent elastic force for two equal springs remains of the same type as of the original springs (soft or hard). For two opposite type springs in series with equal coefficients, the equivalent force is soft. The method is applicable for any hard and soft nonlinear springs or spring-like systems. Thus the hexagonal auxetic unit which contains a soft and a hard part in series is analyzed. In the paper, a new analytic method for determination of the frequency of vibration for the unit under action of a constant compression force acting along the unit axis is introduced. The method is applied for units which contain two parts: hard–hard, soft–soft, hard–linear, soft–linear and opposite. The obtained approximate vibration results are compared with numerically obtained ones and show good agreement. The advantage of the method is its simplicity as it does not require the nonlinear equation of motion to be solved.

Cortical drive may facilitate enhanced use of the paretic leg induced by random constraint force to the non-paretic leg during walking in chronic stroke.

The goal of this study was to determine the effects of applying random vs. constant constraint force to the non-paretic leg during walking on enhanced use of the paretic leg in individuals post-stroke, and examine the underlying brain mechanisms. Twelve individuals with chronic stroke were tested under two conditions while walking on a treadmill: random vs. constant magnitude of constraint force applied to the non-paretic leg during swing phase of gait using a custom designed robotic system. Leg kinematics, muscle activity of the paretic leg, and electroencephalography (EEG) were recorded during treadmill walking. Paretic step length and muscle activity of the paretic ankle plantarflexors significantly increased after walking with random and constant constraint forces. Cortico-cortical connectivity between motor cortices and cortico-muscular connectivity from the lesioned motor cortex to the paretic ankle plantarflexors significantly increased for the random force condition but not for the constant force condition. In addition, individuals post-stroke with greater baseline gait variability showed greater improvements in the paretic step length after walking with random force condition but not with the constant force condition. In conclusion, application of random constraint force to the non-paretic leg may enhance the use of the paretic leg during walking by facilitating cortical drive from the lesioned motor cortex to the paretic ankle plantarflexors. Results from this study may be used for the development of constraint induced locomotor intervention approaches aimed at improving locomotor function in individuals after stroke.

Analysis of the seismic fragility of slender piers on prestressed concrete viaducts

This research aims to study the seismic fragility evaluations of slender piers with single-column sections on prestressed concrete viaducts to investigate how pier height, prestressing force, and ground motion intensity are related, not only in terms of mean values but also in their probability density functions (PDFs), which inherently imply parameters such as dispersion indices. A detailed nonlinear numerical analysis was performed using a finite element model that incorporated the realistic response of concrete, steel, and infrm-FB element types for the columns. To this end, fragility curves were developed based on a probabilistic procedure that accounted for the variability of material properties, pier geometry, and seismic loading. The results show that the fragility function of high piers is hardly dependent on the shear span efficiency. Conversely, slender piers exhibit an increased level of fragility when the effect is confined to a constant prestressing force. This study highlights the need to account for the nonlinearity of pier members and variation in seismic loading when estimating the seismic fragility of slender piers. The conclusions of this study are beneficial for designing and retrofitting strategies for prestressed concrete viaducts in seismic regions.

Comparative Analysis of Armature Structure on Constant Force Characteristics in Long-Stroke Moving-Iron Proportional Solenoid Actuator

The influence of key design parameters on the constant force characteristics of long-stroke moving-iron proportional solenoid actuators (MPSAs) has been explored by a method combining finite element modelling and correlation analysis. First, the finite element model (FEM) of long-stroke MPSA was developed and validated. Subsequently, the two evaluation indexes, the average-output solenoid force and maximum-output solenoid force variability, were introduced to disclose the influence law of pole shoe parameters on the constant force characteristics of a long-stroke MPSA. After that, correlation analysis was employed to quantify the influence of several parameters and parameter interaction factors on the constant force characteristics. The results indicate a strong contradiction between the average-output solenoid force and maximum-output solenoid force variability; however, increasing the inner diameter of the cone helps enhance the average-output solenoid force without causing maximum-output solenoid force variability to increase. Among all the parameters examined, the cone angle is the most significant parameter affecting the constant force characteristics. Additionally, interactions between the cone angle and the cone length, the cone angle and the inner cone diameter, the cone angle and the outer cone diameter, the cone length and the outer cone diameter, as well as the inner cone diameter and the outer cone diameter also have an important influence on the constant force characteristics. This study deepens our understanding of how the key parameters affect the constant force characteristics and assists designers in optimizing these parameters for developing new structures.

Enhancing Robot End‐Effector Trajectory Tracking Using Virtual Force‐Tracking Impedance Control

This article presents an extended Cartesian space robot control framework that features a virtual force tracking impedance control to enhance the end‐effector trajectory tracking performance. Initially, the concept of a virtual surface is introduced, which is assumed to be at some constant distance from the desired end‐effector trajectory. This virtual surface generates a virtual contact force when interacting with the torque‐controlled robot end‐effector. The interaction is then manipulated using an impedance control model to track a constant desired force. If the robot end‐effector deviates from the desired trajectory, the constant force‐tracking impedance control generates a compliance trajectory that regulates the end‐effector movements, constraining it to the desired trajectory. For robust force tracking, impedance parameters are optimally tuned using a closed‐loop dynamic model incorporating both robot and impedance dynamics. Additionally, super twisting sliding mode control (STSMC) is integrated to overcome uncertainties and the impact of robot dynamics on force‐tracking performance. Experimental validation confirms the theoretical claims of the proposed approach. It demonstrates that force‐tracking impedance control improves the end‐effector trajectory tracking by quickly reacting to the dynamic trajectories compared to position control only and effectively maintains it on the desired trajectories.

A rheological constitutive model to predict the anisotropic biaxial bending behavior of spiral strands subjected to variable axial force

Spiral strands exhibit dissipative bending behavior when subjected to external axial force. To the best of the authors’ knowledge, only the uniaxial bending behavior of spiral strands subjected to constant axial force has been studied in the literature so far. Thanks to a recently developed mixed stress–strain driven computational homogenization for spiral strands, this paper is the first to study the biaxial bending behavior of spiral strands subjected to variable tensile force. Based on the observed anisotropic behavior, a rheological constitutive model equivalent to multilayer spiral strands is proposed to predict their behavior under such loading. For an Nl-layer strand, the proposed model consists of several angularly distributed uniaxial spring systems, referred to as a multiaxial spring system, where each uniaxial spring system consists of a spring and Nl slider-springs. In a uniaxial spring system, the spring represents the slip contribution of all wires to the bending stiffness of the strand, while each slider-spring represents the stick contribution of each layer. A major advantage of the proposed scheme is its straightforward parameter identification, requiring only several monotonic uniaxial bendings under constant axial force. The proposed rheological model has been verified against the responses obtained from the mixed stress–strain driven computational homogenization through several numerical examples. These examples consist of complex uniaxial and biaxial load cases with variable tensile force. It has been shown that the proposed scheme not only predicts the response of the strand, but also provides helpful insight into the complex underlying mechanism of spiral strands. Furthermore, the low computational cost of the proposed models makes them perfect candidates for implementation as a constitutive law in a beam model. Using a single beam with the proposed constitutive law, spiral strand simulations can be performed in a few seconds on a laptop instead of a few hours or days on a supercomputer.