Dynamic Force Range Research Articles

Abraded optical fibre-based dynamic range force sensor for tissue palpation.

Tactile information acquired through palpation plays a crucial role in relation to surface characterisation and tissue differentiation - an essential clinical requirement during surgery. In the case of Minimally Invasive Surgery, access is restricted, and tactile feedback available to surgeons is therefore reduced. This paper presents a novel stiffness controllable, dynamic force range sensor that can provide remote haptic feedback. The sensor has an abraded optical fibre integrated into a silicone dome. Forces applied to the dome change the curvature of the optical fibres, resulting in light attenuation. By changing the pressure within the dome and thereby adjusting the sensor's stiffness, we are able to modify the force measurement range. Results from our experimental study demonstrate that increasing the pressure inside the dome increases the force range whilst decreasing force sensitivity. We show that the maximum force measured by our sensor prototype at 20 mm/min was 5.02 N, 6.70 N and 8.83 N for the applied pressures of 0 psi (0 kPa), 0.5 psi (3.45 kPa) and 1 psi (6.9 kPa), respectively. The sensor has also been tested to estimate the stiffness of 13 phantoms of different elastic moduli. Results show the elastic modulus sensing range of the proposed sensor to be from 8.58 to 165.32 kPa.

Experimental Study on Magnetorheological Damper Prototype and Obtaining Its Equivalent Damping Coefficients

In this work, a magnetorheological (MR) damper prototype that provides controllable damping force was designed, manufactured and tested. The design and dimensions of the MR damper piston were determined according to the static magnetic analysis results made in ANSYS/Emag (Electromagnetics) software. The MR damper’s damping performance was tested in laboratory by utilizing a damper testing device. The tests were carried out under different currents applied to coil of the MR damper. According to the test results, the equivalent damping coefficients of the MR damper were calculated for different currents. The test results show that the highest damping force is 169.4 N with frequency of 3.18 Hz and applied current of 2 A. In this case, the equivalent damping coefficient is 302 Ns/m. The equivalent damping coefficient is 181 Ns/m when no current is supplied to the coil. The area of the dynamic force range also becomes larger with increasing the applied current. In addition, according to the quarter car model based simulation results in MATLAB/Simulink, it was seen that the semi-active suspension system using MR damper was more effective and successful in vibration mitigation.

Design and performance of a 3D-Printed magnetorheological fluid-based adaptive vibration isolator

Emerging additive manufacturing (or 3D printing) can be advantageous for developing magnetorheological fluid (MRF)-based vibration isolators (MRVIs) because their designs can be easily and efficiently customized and also in-situ fabrication and repairing can be possible. In this study, a simple and compact adaptive MRVI was fabricated by using a 3D printing method. A masked stereolithography (MSLA) 3D printer was used for the fabrication of the rubber bellow and plastic lid parts of the MRVI. The electromagnet was mounted onto the lid, the reservoir was filled with an MRF, and the lid was simply assembled with the reservoir using a 3D-printed large thread without traditionally machined components. Using a material testing machine, the damper forces of the 3D-printed MRVI were measured under a constant velocity loading condition for different magnetic fields. From these tests, the magnetic field-controllable performances of the MRVI such as the MR yield force, the dynamic force range, the dissipated energy, and the secant stiffness were obtained. For the evaluation of the long-term performance reliability of the MRVI due to the MRF sedimentation, its magnetic field-controllable performances were tracked for 156 days with the variable testing intervals. Finally, the feasibility of the 3D-printed MRVI was experimentally confirmed.

Development and experimental characterization of a large-capacity magnetorheological damper with annular-radial gap

Magnetorheological (MR) dampers with bypass arrangements and combined annular-radial fluid flow channels have shown superior performance compared to conventional MR dampers with single annular/radial fluid flow gaps. Achieving a higher controllable dynamic force range with low off-state but high on-state damping force is yet a significant challenge for developing MR dampers for high payload ground vehicle suspensions. This paper presents the conceptual design, fabrication, and experimental characterization of a mid-sized large-capacity MR damper equipped with a compact annular-radial MR fluid bypass valve. Extensive experimental tests were conducted to investigate the dynamic characteristics of the proposed MR damper considering wide ranges of excitation frequency, loading amplitude, and electrical current. The equivalent viscous damping and the dynamic range were calculated as functions of loading conditions considered. The proposed damper initially realized the maximum dynamic range and damping force of 2.3 and 5.54 kN, respectively. With MR valve design modifications, the maximum dynamic range and damping force were substantially increased, reaching 5.06 and 6.61 kN, respectively. The effectiveness of the proposed MR damper was subsequently identified by comparing its dynamic range with other conventional MR dampers in previous studies. The results confirmed the superior performance of the proposed MR damper and its potential application for highly adaptive suspension systems for off-road wheeled and tracked vehicles.

Insight into the response time of fail-safe magnetorheological damper

The significant problem of magnetorheological (MR) dampers is their poor fail-safe ability. In the case of power supply failure, the damper remains in a low damping state which is dangerous for several technical applications. This can be solved by accommodating a permanent magnet to the magnetic circuit of the damper. Currently, the MR dampers are used in progressive semiactive (S/A) control of suspension systems. The dynamics (force response time) of the damper is an important parameter that affects the performance of S/A control. The main goal of this paper is to introduce the dynamic behavior of MR damper with a permanent magnet. The damper design with the permanent magnet in the magnetic circuit, transient magnetic simulation including magnetic hysteresis and eddy currents, and experiments are presented. The magnetic field response time and MR damper force response time are measured and also determined from magnetic simulation. The permanent magnet significantly influences the MR damper dynamics. The decrease of the damping force from a fail-safe state–medium damping to off-state–low damping is significantly faster (2 ms, −1 A) than the increase to on-state–high damping (12 ms, 1 A). The exact value is depending on the electric current magnitude and piston velocity. The damper achieved fail-safe damping force approximately 1/3 of the maximum damping force. The exact value of the fail-safe force is magnetization history-dependent. The maximum dynamic force range is 8.5 which is comparable with the common design of MR damper.

Tri-Modal Tactile Display and Its Application Into Tactile Perception of Visualized Surfaces.

Tactile representation on touchscreens plays an important role in improving realism and richness of users' interaction experience. The dynamic lateral force range and the efficient feedback dimensions are very critical in determining the fidelity of tactile displays. This article develops a tri-modal Electrovibration, Ultrasonic Vibration, and Mechanical Vibration (EUMV) tactile display integrating three types of representative principles, which enhances the dynamic lateral force range by leveraging electrostatic and ultrasonic vibrations stimuli, and induces the normal feedback dimension by utilizing mechanical vibration stimulus. Then, a tactile perception scheme with the EUMV display is proposed for simultaneously rendering contour and texture roughness features of visualized surfaces, in which the contour gradient-lateral force model and the texture gradient-perceived roughness model are determined respectively. Objective and subjective evaluations with 20 participants show that the novel scheme establishes significant improvements in both correct recognition ratios of geometric shapes and tactile perception realism of visualized images than the previous studies.

An In-Situ, Micro-Mechanical Setup with Accurate, Tri-Axial, Piezoelectric Force Sensing and Positioning

To enable accurate characterization of the mechanical behavior of materials at the micro-scale, e.g., in micro-systems, experiments are required that are representative of the actual (often multi-axial) loading conditions to which these materials are subjected during fabrication and operation. Equally important is the acquisition of mechanical data in the form of multi-axial force measurements, and the measurement of kinematics by in-situ microscopic techniques. To this end, a micro-mechanical testing rig is here realized using commercially available piezoelectric actuators. It is shown that the setup measures forces with a resolution of sim 0.3 [mN] in the x- and y-directions, and sim 50 [mN] in the z-direction, over a range of 5 [N], yielding a high dynamic (force) range. Furthermore, displacements can be imposed with a resolution of sim 1 [nm] over a range of 200 [μ m], in all three directions (x, y, z). The setup is compact, vacuum compatible, and specimens are loaded on top of the setup so that the field of view is unobstructed, allowing for in-situ testing with optical and scanning electron microscopy, and optical profilometry. A generic method is developed for extracting quasi-static forces from the piezoelectric actuators. Furthermore, challenges raised from the use of commercial actuators, for which the public technical specifications are generally incomplete, are overcome and the solution strategy is described. Proof-of-concept experiments on flexible, organic, light-emitting diodes demonstrate the potential of the setup to provide rich micro-mechanical data in the form of tri-axial force and displacement measurements. The commercial availability of the piezoelectric actuators, combined with the proposed engineering solutions lead to a generally accessible micro-mechanical test setup to investigate small-scale specimens under realistic, multi-axial loading conditions.

Design of a frictionless magnetorheological damper with a high dynamic force range

This article discusses an increase in dynamic force range in a spring–damper unit achieved by elimination of sealings’ friction. This friction is a part of damping force that cannot be controlled; therefore, it is undesirable in magnetorheological dampers. A new design of a magnetorheological damper with no friction force is described and compared with a traditional magnetorheological damper consisting of a piston and piston rod seals. In the traditional design, fluid is forced to flow by a hydraulic cylinder with high friction caused by sealings. In order to eliminate this friction, a frictionless unit made of metal bellows was designed. Elastic metal bellows can be sealed only by static seals. The measurement of force–velocity dependency was carried out for the original and the new damper with the same magnetorheological valve. The results indicate that the frictionless unit exhibits a significant improvement in the dynamic force range. In the case of adaptive-passive damping control, the increase in the dynamic force range enables the improvement of vibration elimination in the entire frequency range.

Piezoresistive strain sensor array using polydimethylsiloxane-based conducting nanocomposites for electronic skin application

PurposeThis paper aims to report a stretchable piezoresistive strain sensor array that can detect various static and dynamic stimuli, including bending, normal force, shear stress and certain range of temperature variation, through sandwiching an array of conductive blocks, made of multiwalled carbon nanotubes (MWCNTs) and polydimethylsiloxane (PDMS) composite. The strain sensor array induces localized resistance changes at different external mechanical forces, which can be potentially implemented as electronic skin.Design/methodology/approachThe working principle is the piezoresistivity of the strain sensor array is based on the tunnelling resistance connection between the fillers and reformation of the percolating path when the PDMS and MWCNT composite deforms. When an external compression stimulus is exerted, the MWCNT inter-filler distance at the conductive block array reduces, resulting in the reduction of the resistance. The resistance between the conductive blocks in the array, on the other hand, increases when the strain sensor is exposed to an external stretching force. The methodology was as follows: Numerical simulation has been performed to study the pressure distribution across the sensor. This method applies two thin layers of conductive elastomer composite across a 2 × 3 conductive block array, where the former is to detect the stretchable force, whereas the latter is to detect the compression force. The fabrication of the strain sensor consists of two main stages: fabricating the conducting block array (detect compression force) and depositing two thin conductive layers (detect stretchable force).FindingsCharacterizations have been performed at the sensor pressure response: static and dynamic configuration, strain sensing and temperature sensing. Both pressure and strain sensing are studied in terms of the temporal response. The temporal response shows rapid resistance changes and returns to its original value after the external load is removed. The electrical conductivity of the prototype correlates to the temperature by showing negative temperature coefficient material behaviour with the sensitivity of −0.105 MΩ/°C.Research limitations/implicationsThe conductive sensor array can potentially be implemented as electronic skin due to its reaction with mechanical stimuli: compression and stretchable pressure force, strain sensing and temperature sensing.Originality/valueThis prototype enables various static and dynamic stimulus detections, including bending, normal force, shear stress and certain range of temperature variation, through sandwiching an array of conductive blocks, made of MWCNT and PDMS composite. Conventional design might need to integrate different microfeatures to perform the similar task, especially for dynamic force sensing.

Transient Magnetic Model of Magnetorheological Damper and Its Experimental Verification

The present paper deals with the transient magnetic model of the magnetorheological (MR) damper and its experimental verification. The response time of MR damper affects the quality of semi-active control of this damper. The lower the response time, the higher the system efficiency. The most important part of the response time of the MR damper is the response time of magnetic field of the MR damper which can be determined by transient magnetic model. The transient magnetic model was created by the software Ansys Electromagnetics 17.1 as 2D axisymmetric and verified by measurement of magnetic field in the gap of MR damper piston. The maximum difference between the model and the experiment was 28 %. The response time depends on the electric current in the coil of MR damper. The transient magnetic model was used for determination of influence of MR fluid type, material of cover and material of magnetic circuit on the response time of magnetic field of MR damper. The type of MR fluid has a significant influence on the response time. The lower the mass concentration of ferromagnetic particles, the lower the response time of magnetic field. A material selection of magnetic circuit is always a trade-off between the response time and the maximum magnetic flux density (dynamic force range) in the gap of the MR damper. According to the verified transient magnetic model, it is possible to find a suitable material of magnetic circuit for specific application (response time).

Design and testing of magnetorheological valve with fast force response time and great dynamic force range

The paper deals with design, simulation and experimental testing of a magnetorheological (MR) valve with short response time. The short response time is achieved by a suitable design of an active zone in combination with use of a ferrite material for magnetic circuit. The magneto-static model and the simplified hydraulic model of the MR valve are examined and experimentally verified. The development the MR valve achieves an average response time 4.1 ms and the maximum dynamic force range of eight.

A novel all-elastomer MEMS tactile sensor for high dynamic range shear and normal force sensing

A novel all-elastomer MEMS tactile sensor with high dynamic force range is presented in this work. Conductive elastomeric capacitors formed from electrodes of varying heights enable robust sensing in both shear and normal directions without the need for multi-layered assembly. Sensor geometry has been tailored to maximize shear force sensitivity using multi-physics finite element simulations. A simple molding microfabrication process is presented to rapidly create the sensing skins with electrode gaps of 20 m and sensor spacing of 3 mm. Shear force resolution was found to be as small as 50 mN and tested up to a range of 2 N (dynamic range of ). Normal force resolution was found to be 190 mN with a tested range of 8 N (dynamic range of ). Single load and multiload tests were conducted and the sensor exhibited intended behavior with low deviations between trials. Spatial tests were conducted on a sensor array and a spatial resolution of 1.5 mm was found.

Development of a Wireless, Modular Centrifuge Force Microscope for Use in a Commercial Benchtop Centrifuge

A few years ago, we introduced the Centrifuge Force Microscope (CFM) as a new platform for massively parallel single-molecule manipulation. Our original prototype instrument used a microscope on a rotary stage to generate uniform centrifugal forces, which were applied to thousands of microspheres at once, hundreds of which formed single molecule tethers. Here we present a second generation CFM that is fully integrated into a commercial benchtop centrifuge, further increasing the accessibility of the method and greatly expanding the dynamic force range. We have condensed a complete video microscope to fit into a centrifuge bucket, along with battery power and an onboard computer. The result is a fully wireless “CFM module” that can be placed inside a swinging bucket, while still retaining full control of the instrument (even during centrifugation) from a wifi enabled computer. We have demonstrated the unit up to 1000g, which gives a force range of ∼70fN to 70pN using 2.8 micron microspheres. Our current device can save images at near USB 2.0 speeds with up to 5-megapixel resolution, and we are working toward improving the bandwidth further. While a number of single-molecule applications exist, one of our primary interests will be to probe the structure and function of various non-coding RNAs.

Physical Microscopic Model of Proteins Under Force

Nature has evolved proteins to counteract forces applied on living cells, and has designed proteins that can sense forces. One can appreciate Nature's ingenuity in evolving these proteins to be highly sensitive to force and to have a high dynamic force range at which they operate. To achieve this level of sensitivity, many of these proteins are composed of multiple domains and linking peptides connecting these domains, each of them having their own force response regimes. Here, using a simple model of a protein, we address the question of how each individual domain responds to force. We also ask how multidomain proteins respond to forces. We find that the end-to-end distance of individual domains under force scales linearly with force. In multidomain proteins, we find that the force response has a rich range: at low force, extension is predominantly governed by "weaker" linking peptides or domain intermediates, while at higher force, the extension is governed by unfolding of individual domains. Overall, the force extension curve comprises multiple sigmoidal transitions governed by unfolding of linking peptides and domains. Our study provides a basic framework for the understanding of protein response to force, and allows for interpretation experiments in which force is used to study the mechanical properties of multidomain proteins.

Design and Analysis of MR Damper with Radial Duct for Tracked Vehicle Suspension

This study presents the development of a MR damper applied to the suspension of tracked vehicles to improve the ride comfort and mobility. The MR valve is constrained to a specific cylindrical volume in order to keep the same geometry with the original damper. Radial duct is selected for its high efficiency and small volume requirement. The design rule is to enlarge the dynamic force range of the damper under the condition that the off-state force accords with the fail-safe principle. So the mechanical modeling is established and the influencing factors of adjustable coefficient are analyzed so as to determine the geometry parameters of MR valve. A set of experiments are performed to verify the theoritical analysis. The experimental results illustrate the designed MR damper has a good performance of energy dissipation and can be used to practical applications.

Typical Characteristics of Magnetorheological Grease and Its Application to a Controllable Damper

This paper describes a successful application of Magnetorheological (MR) grease to controllable dampers for general use. MR fluid is known to have a great potential as intelligent material to be applied to many devices such as dampers, clutches and engine mounts. However, ferromagnetic particles in MR fluid settle out of the suspension over time due to the density difference between the particles and their carrier fluid. Consequently, devices using MR fluid is difficult to achieve the desired performance. We have solved the problem by developing MR grease using grease as the carrier fluid which holds the particles in its thickener networks. The typical characteristics of MR grease have been measured by using a rotational rheometer specially designed for MR suspensions. The relationship of shear stress to shear rate and magnetic flux density in the MR grease is as same as MR fluid. The performance of a prototype controllable damper using the MR grease has been verified to be a wide dynamic force range and high time response. The ratio of maximum damping force in on-state to that in off-state is approximately 13. The time constant of damping force is 45 ms in off to on-state and 33 ms in on to off-state.

Modeling and testing of a field-controllable magnetorheological fluid damper

In this study, an experimental and a theoretical study were carried out to predict the dynamic performance of a linear magnetorheological (MR) fluid damper. After having designed and fabricated the MR damper, its dynamic testing was performed on a mechanical type shock machine under sinusoidal excitation. A theoretical flow analysis was done based on the Bingham plastic constitutive model to predict the behavior of the prototyped MR damper. The theoretical results were then validated by comparing them against experimental data, and it was shown that the flow model can accurately capture the dynamic force range of the MR damper. In addition to the flow model, a modified parametric algebraic model was proposed to capture the hysteretic behavior of the MR damper. The superiority of the proposed modified model was shown by comparing it with the Alg model as well as with a widely adopted modified Bouc–Wen model through an error analysis. It is observed that although all the three models are comparable at the excitation velocities of 0.05, 0.10, and 0.15 m/s, the mAlg model is remarkably successful at the highest excitation velocity of 0.2 m/s over the other two. The improvements in the predictions were found to be over 50%, relative to unmodified model especially at lower current inputs. Therefore, it was concluded that the present flow model can be successfully adopted to design and predict the dynamic behavior of MR dampers, while the mAlg model can be used to develop more effective control algorithms for such devices.

A New Bypass Magnetorheological Fluid Damper

This study presents theoretical and experimental investigations of a novel external bypass, fail-safe, magnetorheological fluid (MRF) damper. A fail-safe MRF damper is referred to as a device that retains a minimum required damping capacity in the event of a power supply or electronic system failure. The new MRF device has a simple design, is compact, is capable of generating a considerable dynamic force range, and can be sized for specific vibration control applications. The theoretical formulation is developed based on the Herschel–Bulkley constitutive model for an annular flow. Experimental results are obtained to demonstrate the validity of the theoretical analysis.