Maximum Output Force Research Articles

Dynamic characteristics of piezoelectric jetting dispenser with a double spring recovery system

Piezoelectric jetting dispenser is widely used in microelectronic packaging field. The amplification mechanism with flexible hinge is often used in the piezoelectric jetting dispenser. Because the dynamic performance of the dispenser is affected by the deformation of flexure hinge, a model using rigid body amplification mechanism and double spring recovery is proposed in this paper. The mathematical model of the recovery system is established and the dynamic analysis is carried out. The working characteristics of piezoelectric ceramics are analyzed. With the increase of load stiffness, the maximum output force increases and the maximum output displacement decreases. With the decrease of needle stroke, the pressing force between the needle and the nozzle increases. Based on the double spring recovery system, the ADAMS simulation model is established, and the influence of the pre-compression of the double springs on the pressing force between the needle and the nozzle is studied.

Is the ‘reverse onion skin’ phenomenon more prevalent than we thought during intramuscular myoelectric recordings from low to maximal force outputs?

There are isolated instances in the literature that suggest the ‘onion skin’ phenomenon is not always present. That is, newly recruited high threshold motor units (MU) have higher discharge rates than previously recruited low threshold MUs. Therefore, the purpose of this paper was to investigate the presence of the ‘onion skin’ phenomenon in a large sample of intramuscular myoelectric recordings from low to maximal force outputs. Forty-eight participants performed rapid isometric dorsiflexion contractions at 20, 40, 60, 80 and 100 % MVC while intramuscular electrical activity was recorded. A bivariate frequency-distribution of the motor unit discharge rate and motor unit action potential peak-to-peak (P-P) amplitude was assessed. There was a significant difference in bivariate frequency-distribution across force levels (D’s = 0.1083−0.3094, p’s < 0.001). Newly recruited high threshold MUs did have lower discharge rates, but there was an increase in the presence of high threshold, large P-P amplitude MUs with higher discharge rates than lower threshold MUs (reverse onion skin) during the stable portion of the force output. The recruitment of high threshold MUs with higher discharge rates decreased the level of common drive from the cross-correlation (Rxy) = 0.79 at 20 % MVC to Rxy = 0.68 at 100 % MVC (p < 0.01), but it remained high. As the interference pattern becomes more complex with the recruitment of more motor units at higher force outputs, intramuscular electrodes may be more discriminating while recording motor unit activity leading to the identification of both the ‘reverse onion skin’ and ‘onion skin’ phenomenon being present.

Integrated optimal wind‐resistant design of super‐tall structures with toggle‐brace damper systems

SummaryWith the increasing heights of super‐tall buildings, the natural frequency of these structures approaches the predominant frequency of winds, causing the structures to be more sensitive to wind load. For the safety and economy of these structures, the formulation of a reasonable wind‐resistant design is crucial. In this paper, an optimal design of toggle‐brace damper systems for super‐tall buildings using a damping ratio limit method is presented to obtain the optimal placement, number, and damping coefficient of toggle‐brace dampers under different constraints. The constraints include the additional damping ratio under a 50‐year return period wind, the maximum power of the damper under a 50‐year return period wind, and the maximum output force of a moderate earthquake. The toggle‐brace damper systems improve the structural performance. Hence, the structural components produce design redundancy, which can be optimized using the sequential quadratic programming (SQP) algorithm and a multi‐grade constrained optimal design method to further improve the economic benefits of the structure. Based on the combination of the optimal design method of toggle‐brace damper systems, SQP algorithm, and multi‐grade constrained optimal design method, an integrated optimal wind‐resistant design for toggle‐brace damper systems is proposed. To demonstrate the effectiveness and applicability of this design, a 245‐m super‐tall building is employed as an engineering case.

Energy and Force Optimization of a Network of Novel Electromagnetic Soft Actuators

This paper discusses how to optimally design polygonal profiles of Electromagnetic Soft Actuators (ESAs) to be used in a network to achieve maximum output force with minimum energy consumption. The soft actuators work based on operating principle of solenoids but are made of intrinsically soft materials. It was, previously, confirmed that by miniaturizing the size, the amount of output force decreases for a single ESA however, by the ratio of force to volume increases. Therefore, networking small sized ESAs, would increase the output force. Initially, ESAs were made with circular cross-section profiles. However, we prove here that the shape of the cross-section profile can affect the output force. A polygonal shape with fewer sides would result in higher output force for a single ESA. However, with a network of ESAs, another parameter, packing density, plays an important role in the output force. Our optimization results suggest that even though triangular cross-section profiles lead to the highest amount of force for a single ESA, the best choice would be hexagonal shapes when they are networked.

Development and analysis of a dynamic model for parasitic motion principle piezoelectric actuator

The main goal of this paper is studying characteristics of the parasitic motion principle (PMP) piezoelectric actuator and providing a dynamic model for possible control and optimization in future. Through analyzing motion principle of the PMP piezoelectric actuator and considering elastic deformation between the mover and the flexible mechanism, this paper first presents a dynamic model which is verified to be feasible through fitting experiment data. Then the model is used to analyze influence of the coupling angle, the driving signal symmetry, the mover mass and the preload force on performance of the PMP piezoelectric actuator, including the step length, the backlash ratio and the maximum output force. This research contributes to enhance the understanding of the PMP and provide a guidance for design of the PMP piezoelectric actuators.

A walking type piezoelectric actuator with two umbrella-shaped flexure mechanisms

A walking type piezoelectric actuator with two umbrella-shaped flexure mechanisms is proposed to reduce the backward motion. By utilizing two umbrella-shaped flexure mechanisms which could be treated as two ‘legs’, the ‘walking’ motion is accomplished. The structure and motion principle are described; Finite Element Method (FEM) is exploited to explore the static and modal performances of the umbrella-shaped flexure mechanism. Moreover, experiments have been carried out to investigate the working performance of the proposed walking type piezoelectric actuator. Results show that the walking type piezoelectric actuator with umbrella-shaped flexure mechanisms could achieve the ‘walking’ motion and reduce the backward motion. Additionally, the phase difference between two input signals U1 and U2 greatly influences the working performance. In the case of the phase difference Φ= 95°, the backward rate of the slider is able to achieve the minimum 0%; the minimum stepping displacement is 0.3 μm when the frequency f= 1 Hz; the maximum motion speed of the slider is up to 1132 μm s−1 when the input frequency f = 400 Hz and the input voltage U = 120 V; the maximum output force is 700 g while the input voltage U = 120 V and frequency f = 1 Hz.

Simulation of Shape Memory Alloy (SMA)-Bias Spring Actuation for Self-Shaping Architecture: Investigation of Parametric Sensitivity.

Parametric complexity of the thermomechanical shape memory alloy (SMA) model is one of the major barriers to advanced application of the SMA actuation in adaptive architecture. This article seeks to provide architectural practitioners with decision-making information about SMA actuator design parameters. Simulation-based global sensitivity analysis of an SMA-bias spring actuation model reveals that the SMA spring index (a spring’s outer diameter divided by its wire diameter) and stiffness of the bias spring are significant factors in both displacement and force exertion. Among all parameters, maximum output stroke and force largely depend on the temperature range at which the SMA spring operates. These findings also indicate a trade-off between the spring diameter and wire thickness, demonstrating that the output stroke and force tend to counter one another. Appropriate preloading and choice of an optimal spring index should be considered for desirable SMA motion.

A MEMS nanoindenter with an integrated AFM cantilever gripper for nanomechanical characterization of compliant materials

This work presents the development of a MEMS nanoindenter that uses exchangeable AFM probes for quasi-static nanomechanical characterization of compliant and ultra-compliant materials. While the electrostatic micro-force transducer of the MEMS nanoindenter provides a maximum indentation depth up to 9.5 µm with a maximum output force of 600 µN, experimental investigations reveal that it can achieve a depth and force resolution better than 4 pm Hz−1/2 and 0.3 nN Hz−1/2, in air for f≥ 1 Hz. A passive AFM probe gripper is integrated into the MEMS nanoindenter, allowing the nanoindenter to utilize various AFM probes as an indenter for material testing. A proof-of-principle experimental setup has been built to investigate the performance of the MEMS nanoindenter prototype. In proof-of-principle experiments, the prototype with a clamped diamond AFM probe successfully identified an atomic step (∼0.31 nm) within a Si < 111 > ultraflat sample using the scanning probe microscopy mode. The nanomechanical measurement capability of the MEMS nanoindenter prototype has been verified by means of measurements of reference polymer samples using a silicon AFM probe and by means of measurements of the elastic properties of a PDMS sample using a spherical diamond-coated AFM probe. Owing to its compact and low-cost but high-resolution capacitive readout system, this MEMS nanoindenter head can be further applied for in-situ quantitative nanomechanical measurements in AFMs and SEMs.

A single-modal linear ultrasonic motor based on multi vibration modes of PZT ceramics

We have developed a single-modal linear motor which contains two kinds of PZT ceramics. The linear motor works by exciting the transverse vibration mode of the PZT ceramic on the upper surface of stator elastomer and the shear vibration mode of PZT ceramics at two ends simultaneously. The operation principle of the motor is analyzed in detail. And the rule of the driving foot amplitude varies with the size of the end protruding structure has been further researched by FEM analysis. The prototype is manufactured, and its operating characteristics are experimentally studied and analyzed. The no-load velocity and the maximum output force are tested to be 169.4 mm/s and 1.1 N, respectively. The results show that extra arrangement of PZT ceramics which works on shear vibration mode can efficiently improve the output of motor.

Sex differences in motor unit discharge rates at maximal and submaximal levels of force output.

This study evaluated potential sex differences in motor unit (MU) behaviour at maximal and submaximal force outputs. Forty-eight participants, 24 females and 24 males, performed isometric dorsiflexion contractions at 20%, 40%, 60%, 80%, and 100% of a maximum voluntary contraction (MVC). Tibialis anterior electromyography was recorded both by surface and intramuscular electrodes. Compared with males, females had a greater MU discharge rate (MUDR) averaged across all submaximal intensities (Δ 0.45 pps, 2.56%). Males exhibited greater increases in MUDR above 40% MVC, surpassing females at 100% MVC (p's < 0.01). Averaged across all force outputs, females had a greater incidence of doublet and rapid discharges and a greater percentage of MU trains with doublet and rapid (5-10 ms) discharges (Δ 75.55% and 61.48%, respectively; p's < 0.01). A subset of males (n = 8) and females (n = 8), matched for maximum force output, revealed that females had even greater MUDR (Δ 1.38 pps, 7.47%) and percentage of MU trains with doublet and rapid discharges (Δ 51.62%, 56.68%, respectively; p's < 0.01) compared with males at each force output, including 100% MVC. Analysis of the subset of strength-matched males and females suggest that sex differences in MU behaviour may be a result of females needing to generate greater neural drive to achieve fused tetanus. Novelty Females had higher MUDRs and greater percentage of MU trains with doublets across submaximal force outputs (20%-80% MVC). Differences were even greater for a strength matched subset. Differences in motor unit behaviour may arise from musculoskeletal differences, requiring greater neural drive in females.

Design, fabricate, and experimental verification of an ultrasonic linear motor derived from V-type motors.

In this work, a novel ultrasonic linear motor is proposed. The proposed motor has two driving feet and a simple structure. The torque applied to the motor is converted into a normal preload between the driving feet and the mover, avoiding the use of a large preloading mechanism. The vibration characteristics of the motor are studied by the finite element analysis method. Finally, the prototype is fabricated. The experimental system is established, and a series of experiments has been carried out to evaluate the performance of the motor in terms of maximum velocity and maximum output force, and the feasibility of the proposed motor is verified. The experimental results show that the maximum no-load velocities of the motor moving to the right and left are 85.2 mm/s and 76 mm/s, respectively, and the maximum output force is 1.96 N. The numerical simulation results show that the stator of the motor can be used as a displacement amplifying structure, which can effectively amplify one or two orders of magnitude deformation of the piezoelectric stack.

The Effect of Mental Fatigue on Neuromuscular Function is Similar in Young and Older Women.

The purpose of this study was to examine the effect of a mentally fatiguing task on neuromuscular function in young and older women. Neuromuscular measures were obtained prior to and following 20 min of a mentally fatiguing task. Maximal force output significantly decreased after the mental fatigue task (p = 0.02) and this was not different between age groups (p = 0.32). Increases in cortical silent period duration approached significance in both young and older groups (p = 0.06), suggesting that mental fatigue may cause increased cortical inhibition. Measures of peripheral neuromuscular function (contractile properties of the muscle, M-wave) did not change (p ≥ 0.09), suggesting that changes in force production with mental fatigue are more likely due to supraspinal than peripheral mechanisms. These findings provide further evidence of an interaction between mental fatigue and physical function.

A Novel Hydraulic Actuation System Utilizing Magnetorheological Fluids for Single-Port Laparoscopic Surgery Applications.

Single-port laparoscopic surgery (SLS), which utilizes one major incision, can deliver favorable cosmetic outcomes with fewer patient hospitalization stays and less postoperative pain. However, current SLS instruments, which are rigid and slender, have been suffering from several drawbacks, including their inability to provide the optimum articulation required to complete certain SLS tasks. This paper reports on the development of a lightweight smart hydraulic actuation system that is proposed to be embedded at selected joints along current SLS instruments, in order to enhance their adaptability with a higher level of stiffness and degrees-of-freedom. The developed smart actuation system utilizes both conventional hydraulic and magnetorheological (MR) fluid actuation technologies. Electromagnetic finite element analyses were conducted to design the electromagnetic circuit of the smart actuator. A prototype of the developed actuation system was manufactured, and its performance was assessed using a dedicated experimental arrangement, which was found to agree well with the results obtained using a Bingham plastic theoretical model. Finally, the present design of the developed smart actuation system permits an angulation of about 90° and a maximum force output in excess of 100 N, generated under a magnetic excitation of about 1.2 Tesla, which should be sufficient to resist torques of up to 500 mNm.

Design and Modeling of a High Force Soft Actuator for Assisted Elbow Flexion

Over the past decade, soft robotics have found its way into many applications that span across different length scales. Studies have since been done in respective research fields to characterize soft robots and understand their actuation process. On the nano to micro scale, soft robots are used to study and replicate movements of living organisms in bioinspired robots. While on the macro scale, soft actuators have found their niche in assistive and rehabilitative exoskeletons due to their compliant nature, as compared to traditional rigid rehabilitative robots, making them less injury prone. Modeling the kinematics and force output of soft actuators have been the main research focuses so that actuator performance may be tuned for specific scenarios and use cases. Kinematics studies have been adequate in describing the actuation patterns of these soft actuators. However, modeling the force output of soft robotic actuators remains a challenge due to their highly compliant material characteristics and complex deformation throughout the actuation process. In addition, the maximum force output of soft robots are often several magnitudes lesser than that of rigid robots. Force modeling and profiling of soft robots are thus of paramount importance towards fine tuning the force output from soft actuators. State-of-the-art upper limb assistive exoskeletons focus on improving the mobility of fingers and wrists joints that are lesser in anatomical weight. Developing exoskeletons for heavier joints, such as elbow and shoulder, remain a technical challenge. In this letter, we describe our work in the development of a 3D printable, high force soft exoskeleton that aims to assist the user in elbow flexion. The soft actuator can provide up to 100 N of tip force. We also describe a force model that allows tuning the dimensions of the bellow based actuator to cater to different payloads should the actuator be used in other applications, which are not described in this letter.

Fabrication and Actuation of Cu-Ionic Polymer Metal Composite.

In this study, Cu-Ionic polymer metal composites (Cu-IPMC) were fabricated using the electroless plating method. The properties of Cu-IPMC in terms of morphology, water loss rate, adhesive force, surface resistance, displacements, and tip forces were evaluated under direct current voltage. In order to understand the relationship between lengths and actuation properties, we developed two static models of displacements and tip forces. The deposited Cu layer is uniform and smooth and contains about 90% by weight of copper, according to the energy-dispersive X-ray spectroscopy (EDS) analysis data obtained. The electrodes adhere well (level of 5B) on the membrane, to ensure a better conductivity and improve the actuation performance. The penetration depth of needle-like electrodes can reach up to around 70 μm, and the structure shows concise without complex branches, to speed up the actuation. Overall the maximum displacement increased as the voltage increased. The applied voltage for the maximum force output is 8–9 V. The root mean square error (RMSE) and determination coefficient (DC) of the displacement and force models are 1.66 and 1.23, 0.96 and 0.86, respectively.

A Compact Cantilever-Type Ultrasonic Motor With Nanometer Resolution: Design and Performance Evaluation

A cantilever ultrasonic motor with nanometer resolution is designed, fabricated, and tested in this article. Two orthogonal first bending vibration modes are used to form elliptical movements on driving tip to move slider. The structure of this motor is depicted, and its geometric dimensions are determined by modal analysis. The total size of this motor is 30 × 30 × 34.2 mm along the X-, Y-, and Z-direction. The working principle of the proposed motor is illustrated, and the motion characteristics of the driving tip are studied by transient analysis. A prototype of this motor is manufactured to investigate its vibration performances and mechanical characteristics. The tested results denote that this motor generates an output speed of 344.35 mm/s when the frequency and voltage are 22.7 kHz and 200 Vp-p, respectively. The maximum output force is tested as about 8 N under the voltage and preload of 100 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-p</sub> and 50 N, respectively. Furthermore, the proposed ultrasonic motor obtains a high displacement resolution of 48 nm under the resonant working state.

Neuromuscular Mechanisms Underlying Changes in Force Production during an Attentional Focus Task.

We examined the effects of attentional focus cues on maximal voluntary force output of the elbow flexors and the underlying physiological mechanisms. Eleven males participated in two randomized experimental sessions. In each session, four randomized blocks of three maximal voluntary contractions (MVC) were performed. The blocks consisted of two externally and two internally attentional focus cued blocks. In one of the sessions, corticospinal excitability (CSE) was measured. During the stimulation session transcranial magnetic, transmastoid and Erb’s point stimulations were used to induce motor evoked potentials (MEPs), cervicomedullary MEP (CMEPs) and maximal muscle action potential (Mmax), respectively in the biceps brachii. Across both sessions forces were lower (p = 0.024) under the internal (282.4 ± 60.3 N) compared to the external condition (310.7 ± 11.3 N). Muscle co-activation was greater (p = 0.016) under the internal (26.3 ± 11.5%) compared with the external condition (21.5 ± 9.4%). There was no change in CSE. Across both sessions, force measurements were lower (p = 0.033) during the stimulation (279.0 ± 47.1 N) compared with the no-stimulation session (314.1 ± 57.5 N). In conclusion, external focus increased force, likely due to reduced co-activation. Stimulating the corticospinal pathway may confound attentional focus. The stimulations may distract participants from the cues and/or disrupt areas of the cortex responsible for attention and focus.

A Traveling-Wave Linear Ultrasonic Motor Driven by Two Torsional Vibrations: Design, Fabrication, and Performance Evaluation

In this study, we design and fabricate a tank-track-shaped stator working in two torsional modes to form a traveling-wave (TW) linear ultrasonic motor (USM). The stator comprises two torsional transducers and two kidney-shaped vibrating bodies. When voltages with a certain phase are applied to the transducers, two in-phase TWs are excited on the vibrating bodies to frictionally drive the slider. Here, the torsional vibration guarantees strong electromechanical coupling, and meanwhile, the tank-track shape ensures plural driving points and low weight; these features may facilitate realizing high thrust force density and high power density of linear motors. To examine the feasibility, first, we constructed a stator prototype 116 mm in length, 91 mm in width, and 32 mm in thickness and explored its vibration properties. The minimal standing wave (SW) ratio reaches 1.21 and the small SW components are desirable for TW motors. Then, we measured the load characteristics and found that, at the working frequency of 54.34 kHz and the phase shift of -110°, the maximal thrust force and maximal output power were 96.1 N and 27.8 W, respectively. Moreover, the thrust force density and power density reached respectively 234.1 N/kg and 67.8 W/kg, relatively high compared to the values of most conventional linear motors. This study verifies the feasibility of our proposal and paves a new way of designing powerful linear USMs.

Design Optimization of a Novel Networked Electromagnetic Soft Actuators System Based on Branch and Bound Algorithm

This paper presents a design optimization framework based on Branch and Bound Algorithm for novel networked electromagnetic soft actuators. The soft actuators work based on the operating principle of solenoids but are made of intrinsically soft materials. We confirmed that by scaling down the size of the soft actuators, their force to volume ratio increases. This suggests that by miniaturizing the actuators size and attaching them as a network based on the arrangement of actin and myosin filaments in skeletal muscles, the output force can be enhanced. In order to achieve the maximum output force, design parameters of a single soft actuator as well as those of a network are considered as design variables. The maximum available volume (thickness, width and length) and deflection range of the network are considered design constraints. The cost function, i.e. the output force is a non-linear mixed-integer function. A Branch and Bound optimization algorithm based on interval analysis is then proposed to solve the optimization problem. Numerical simulations are presented for a representative example of an active soft brace for the human elbow joint. The results suggest that an electromagnetic soft actuator network can provide sufficient torque to be used as a drive train for an active elbow brace for both flexion and extension over a range of around 93 degrees.

Resonant-Type Piezoelectric Screw Motor for One Degree of Freedom Positioning Platform Application

A resonant-type piezoelectric screw motor for one degree of freedom (1-DOF) positioning platform is proposed, fabricated, and investigated in this article. The motor comprises a driver and a screw rod. The driver is composed of four transducers, a nut seat, and a flange nut. The flange nut is bolted connected on the nut seat, and the four piezoelectric transducers are connected with the nut seat by right-angle flexible hinges. Each piezoelectric transducer comprises two piezoelectric stacks and one displacement amplifier. Driven by the four piezoelectric transducers, elliptical vibration is generated by the driver, which is used to actuate the screw rod to realize the linear movement. The driver is analyzed using the finite element analysis software ANSYS. The proposed motor and positioning platform prototype are manufactured, assembled, and tested. The performance of the developed piezoelectric screw motor shows its applicability and effectiveness for the 1-DOF positioning platform with a large force. Experiments demonstrate that the maximum velocity of this motor is 10.53 mm/s without mechanical load and the maximum output force of the platform can reach 17.19 N when the excitation voltage is 230 at 365 Hz.