High Output Force Research Articles

Environmental Robust Position Control for Compact Solenoid actuators by Sensorless Simultaneous Estimation of Position and Force

This paper aims to realize compact actuation systems by sensorless approach. This study adopts solenoid actuators which have advantageous characteristics from the view point in inexpensive cost, simple structure, and high-output force in spite of difficulty in low cost position and force sensing. Some sensorless position estimation techniques for solenoid actuators were reported. However, position and force simultaneous estimation has not sufficiently been achieved. In addition, any real-time feedback control has not been reported. This paper proposes sensorless feedback position control for compact solenoid actuators. The force generation and position/force estimation are conducted by using a dc supply power superposed by an ac component. This control technique has three main features: 1) separation of the power supply into ac and dc components for the position estimation, 2) simultaneous real-time estimation of position and force, and 3) robust feedback position control. Simulations and experiments were conducted for verification of the proposed control with the above three features, and the results indicated that error between the estimation and actual positions was within 0.2 mm. This proposed system offers a new avenue for compact and inexpensive application field.

Visually guided targeting enhances bilateral force variability in healthy older adults

This study observed the effect of visual feedback on between-limb force variability relationships in young and older adults. Abduction force was examined in healthy young (n = 15, 25 ± 4 years) and older adults (n = 18, 71 ± 6 years) during simultaneous isometric contractions of both index fingers. Target forces ranged from 5% to 30% maximum voluntary contraction (MVC), where force variability and first dorsal interosseus activity were measured while (1) subjects viewed visual targets for both index fingers, (2) a visual target was provided for the dominant index finger only, and (3) visual targets were removed for both index fingers during bilateral isometric contractions. When subjects were provided with bilateral visual feedback during simultaneous contractions at low forces (5% and 10% MVC), older adults produced greater force variability than younger subjects (p = 0.002). However, when bilateral visual feedback was removed, age-related differences in variability were no longer present. Between-limb force variability differences existed at higher force outputs (20% and 30% MVC) when visual feedback was removed for the nondominant limb during bilateral isometric index finger abduction (p = 0.002). The control of bilateral force variability is compromised in older adults when visuomotor processes are engaged. However, age-related differences in force variability are abolished when no task-related visual feedback is available, and isometric contractions are based on internally guided feedback.

An inspection of force reduction in high force electromagnetic tweezers made of FeCo-V foil by laser cutting

One of the main goals in the design of magnetic tweezers is to obtain a high force output. In general, the force can be enhanced by adopting materials with high saturation magnetization and by using small sharp structures as magnetic pole tips. However, the practically achieved saturation forces are usually lower than predicted values. In this article, we inspect this issue in detail both by experiments and simulations. Our results show that the observed force reduction can be ascribed to two factors: magnetic performance deterioration near the cutting edges of the tips and a 3D geometrical effect. The high power laser used in cutting causes segregation and morphological roughness near the cutting edge. Moreover, the geometry of the magnetic tips plays an important role regarding the force behavior. As a matter of fact, there is a trade-off among high force, maneuverability, throughput, and manufacturing issues in practical design of magnetic tweezers.

A 3-DOF MEMS Electrostatic Piston-Tube Actuator

A three-degrees-of-freedom microelectromechanical systems (MEMS) electrostatic actuator was developed, fabricated, and tested. The actuator utilizes a piston-tube configuration that enables the use of electrodes with a wide area. Therefore, a large output force can be generated. The actuator also utilizes a flexure mechanism in which the in-plane (x-y) stiffness is high compared with the out-of-plane (z-axis) stiffness. This flexure mechanism enables a large translation stroke along the z-axis before experiencing lateral pull-in instability. A prototype of the actuator was able to achieve a pure translation (piston-style motion) of 28 μm at 80 V and an angle of rotation of 0.78° at 70 V. A mass of 1 mg was translated 24 μm at 80 V, indicating the ability of the actuator to provide high output force. The actuator was fabricated using the Micralyne MicraGEM-Si MEMS fabrication process, in which the pistons and tubes are fabricated in the device layers of two bonded Silicon on insulator (SOI) wafers. The misalignment between the pistons and the tubes using this process was ~0.005 of the gap between adjacent pistons and tubes. This amount of misalignment leads to a negligible lateral instability effect.

New Dielectric Elastomers with Variable Moduli

Dielectric elastomers have been widely investigated for muscle‐like soft actuators and capacitive sensors. Mechanical properties play a central role in the performances of the active material. Most elastomers have specific moduli pre‐determined by the polymers' molecular structures, which are not suitable for applications in changing working conditions as natural muscles are capable of. Here new dielectric elastomers are described exhibiting variable moduli controlled via thermal treatment. The elastomers contain furan‐maleimide Diels–Alder adduct moieties to administer the crosslinking densities of the elastomeric networks via reversible Diels–Alder/retro‐Diels–Alder cycloaddition reaction, resulting in changes in the elastomers' moduli. One of the synthesized elastomers has moduli that can be controlled between 0.17 and 0.52 MPa incrementally and reversibly. Capacitive strain sensors based on this elastomer can be operated in both rigid and soft modes to achieve variable sensing response up to 30% linear strain. Actuators were fabricated and operated in both high strain mode (35% actuation area strain at 65 MV m−1) and high force output mode (0.55 MPa at 104 MV m−1). The elastomers can exhibit a range of stress–strain outputs in similar fashion as muscle.

Magnetic tweezers with high permeability electromagnets for fast actuation of magnetic beads.

As a powerful and versatile scientific instrument, magnetic tweezers have been widely used in biophysical research areas, such as mechanical cell properties and single molecule manipulation. If one wants to steer bead position, the nonlinearity of magnetic properties and the strong position dependence of the magnetic field in most magnetic tweezers lead to quite a challenge in their control. In this article, we report multi-pole electromagnetic tweezers with high permeability cores yielding high force output, good maneuverability, and flexible design. For modeling, we adopted a piece-wise linear dependence of magnetization on field to characterize the magnetic beads. We implemented a bi-linear interpolation of magnetic field in the work space, based on a lookup table obtained from finite element simulation. The electronics and software were custom-made to achieve high performance. In addition, the effects of dimension and defect on structure of magnetic tips also were inspected. In a workspace with size of 0.1 × 0.1 mm(2), a force of up to 400 pN can be applied on a 2.8 μm superparamagnetic bead in any direction within the plane. Because the magnetic particle is always pulled towards a tip, the pulling forces from the pole tips have to be well balanced in order to achieve control of the particle's position. Active video tracking based feedback control is implemented, which is able to work at a speed of up to 1 kHz, yielding good maneuverability of the magnetic beads.

A simple compact UHV and high magnetic field compatible inertial nanopositioner.

We present a novel simple piezoelectric nanopositioner which just has one piezoelectric scanner tube (PST) and one driving signal, using two short quartz rods and one BeCu spring which form a triangle to press the central shaft and can promise the nanopositioner's rigidity. Applying two pulse inverted voltage signals on the PST's outer and inner electrodes, respectively, according to the principle of piezoelectricity, the PST will elongate or contract suddenly while the central shaft will keep stationary for its inertance, so the central shaft will be sliding a distance relative to quartz rods and spring, and then withdraw the pulse voltages slowly, the central shaft will move upward or downward one step. The heavier of the central shaft, the better moving stability, so the nanopositioner has high output force. Due to its compactness and mechanical stability, it can be easily implanted into some extreme conditions, such as ultrahigh vacuum, ultralow temperature, and high magnetic field.

IPMC-Actuated Compliant Mechanism-Based Multifunctional Multifinger Microgripper

Over the past few decades, the Electro Active Polymer (EAPs) has become quite useful for vast applications in the field of robotic and bio-mimetic. Ionic Polymer Metal Composite (IPMC) is one of the EAPs which holds an excellent bending property at low actuation voltage resulting high force output; thus, it is capable of doing work as good as human finger tip when the same is employed as an actuator for micromanipulation. In the present investigation, a four-fingered micro gripper under the actuation of IPMC has been addressed. The microgripper consists of four fingers made of Polydimethyl Siloxane and each finger has three notches. The novelty of this gripping device is in its multifunction operation. It can manipulate microobject less than 1 mm diameter as well as macro object within the diameter of 10 mm. This finger design is compliant in nature. The development of micropart handling devices and allied research is a highly challenging task. The principle on which the gripper operates and its fabrication process are explained in detail in this article. It involves miniature part handling, integration, and assembly operation.

Note: A rigid piezo motor with large output force and an effective method to reduce sliding friction force

We present a completely practical TunaDrive piezo motor. It consists of a central piezo stack sandwiched by two arm piezo stacks and two leg piezo stacks, respectively, which is then sandwiched and spring-clamped by a pair of parallel polished sapphire rods. It works by alternatively fast expanding and contracting the arm/leg stacks while slowly expanding/contracting the central stack simultaneously. The key point is that sufficiently fast expanding and contracting a limb stack can make its two sliding friction forces well cancel, resulting in the total sliding friction force is <10% of the total static friction force, which can help increase output force greatly. The piezo motor's high compactness, precision, and output force make it perfect in building a high-quality harsh-condition (vibration resistant) atomic resolution scanning probe microscope.

Infrared-Actuated Recovery of Polyurethane Filled by Reduced Graphene Oxide/Carbon Nanotube Hybrids with High Energy Density

Optically actuated shape recovery materials receive much interest because of their great ability to control the creation of mechanical motion remotely and precisely. An infrared (IR) triggered actuator based on shape recovery was fabricated using polyurethane (TPU) incorporated by sulfonated reduced graphene oxide (SRGO)/sulfonated carbon nanotube (SCNT) hybrid nanofillers. Interconnected SRGO/SCNT hybrid nanofillers at a low weight loading of 1% dispersed in TPU showed good IR absorption and improved the crystallization of soft segments for a large shape deformation. The output force, energy density and recovery time of IR-triggered actuators were dependent on weight ratios of SRGO to SCNT (SRGO:SCNT). TPU nanocomposites filled by a hybrid nanofiller with SRGO:SCNT of 3:1 showed the maximum IR-actuated stress recovery of lifting a 107.6 g weight up 4.7 cm in 18 s. The stress recovery delivered a high energy density of 0.63 J/g and shape recovery force up to 1.2 MPa due to high thermal conductivity (1.473 W/mK) and Young's modulus of 23.4 MPa. Results indicate that a trade-off between the stiffness and efficient heat transfer controlled by synergistic effect between SRGO and SCNT is critical for high mechanical power output of IR-triggered actuators. IR-actuated shape recovery of SRGO/SCNT/TPU nanocomposites combining high energy density and output forces can be further developed for advanced optomechanical systems.

Development and Application of a High-Thrust Voice Coil Motor

A Voice Coil Motor (VCM) for precise positioning with high output force was designed. The stability and heat dissipation of VCM were analyzed. The performance of VCM was also compared with that of the same type VCM produced by SMAC. Uniaxial ratcheting behavior of solder wire (Sn63/Pb37) was studied by uniaxial cyclic stress controlled tension deformation tests,to verify the VCM systematically.

Cellular Force Measurement Using a Nanometric-Probe-Integrated Microfluidic Chip with a Displacement Reduction Mechanism

This paper presents noncontact nanometric positioning of a probe tip with high output force in a microfluidic chip. To measure cellular force in a microfluidic chip on the basis of cell deformation, we employed an on-chip probe with a magnetic drive method with actuation on the order of millinewtons. A reduction mechanism was proposed to realize nanometric resolution for positioning the probe tip. This mechanism utilizes a combination of springs with different stiffness levels and is driven bymagnetic force. The performance of the prototype device was examined and results indicated that, as ameasure of repetitive positioning accuracy, standard deviation of probe tip displacement was under 0.18 µm. Deformation was successfully measured for an oocyte on the order of 0.1 mN, demonstrating, as a consequence, nanometric order noncontact actuation of the on-chip probe with high output force. Using this on-chip probe, cellular force measurement was achieved for the microfluidic chip.

Linear magnetorheological brake with serpentine flux path as a high force and low off-state friction actuator for haptics

In robotics and haptics, actuators that are capable of high force output with compact size are desired for stable and stiff interfaces. Magnetorheological brakes are viable options for such implementations since they have large force-to-volume ratios. Existing linear magnetorheological brakes have limited strokes, are relatively large, and have high off-state friction forces mainly due to the piston-cylinder internal design. The main contribution of this research is a new alternative internal design for linear magnetorheological brakes. The proposed approach uses the serpentine flux path concept to eliminate the piston-cylinder arrangement. It leads to significantly less off-state friction and infinite stroke. To the best of our knowledge, this is the first such linear magnetorheological brake. Our new brake can produce 173-N force. In comparison, a conventional linear magnetorheological brake with the same size can only produce about 27-N force. Our results showed that the ratio of the off-state friction force to the maximum force output in the prototype linear brake is about 3% compared with more than 10% for most similar devices in the literature and 27% for a commercial brake. At the same time, the compactness was improved as our prototype is about half the size of a commercially available product.

Design and Analysis of Tubular Linear Machines with Dual Halbach Arrays

Linear machines are widely employed in robotics, transportation and manufacturing industries because complex rotation-to-translation conversion mechanism is no longer required. This paper proposed a novel tubular linear machine with dual permanent magnet (PM) Halbach arrays to achieve high force output performance. Based on Lorentz force law, the magnetic force output and force ripple for three-phase winding linear machine is formulated in analytical way. By taking advantage of the analytical models, the force output is simulated with respect to the motion of the mover. Numerical result is then obtained to validate the analytical force models. In addition, based on the technology of non-dimensionalization, the mathematical force models are employed to analyze the influence among the structure parameters on the force output and force ripple for design purpose of the tubular linear machines. The study in this paper could contribute to the design analysis and optimization of electromagnetic linear machines with similar poles patterns.

A piezo motor based on a new principle with high output force, rigidity and integrity: The Tuna Drive

We present a linear piezoelectric motor as simple as one piezoelectric scanner tube (PST) spring-clamping a central shaft at both ends with roughly equal clamping forces. The clamping points are aligned with ±X electrodes at one end and ±Y electrodes at the other end. Thus, the ±X (or ±Y) push-pull motions of the PST can cause the push-pull motions of the clamping points on the shaft (called push-pull rubbing), which reduces the total dynamic friction force at one (or the other) end of the PST. This new piezo motor advances one step by fast push-pull rubbing at one end while slowly retracting the PST followed by fast push-pull rubbing at the other end while slowly elongating the PST. Apart from the obvious advantages of simplicity, rigidity, integrity, etc., we will also show that this motor can produce a large output force, which we believe is because of the huge drop of the clamping friction force when the push-pull rubbing occurs.

Dynamic Behaviour of a Novel Compliant MEMS Force Amplifier by MATLAB/SIMULINK

High force amplification in micro-scale can be achieved by MEMS compliant systems and such systems have been recently preferred to obtain high output forces in micro actuators due to its monolithic structure and ease of fabrication. We studied the mechanism of novel MEMS force amplifier in dynamic mode by modeling its rigid body mechanism with Matlab/Simulink programming. Kinematic analysis and dynamic response of the MEMS compliant system was obtained by modeling of velocity and acceleration parameters, and ramp input function, respectively. We found that the output force goes to infinity at zero-crank angle and there is 2650 times force amplification by a given very small crank rotation about 2.30.

New Multi-d.o.f. Haptic Device Using a Parallel Mechanism with a Wide Rotational Working Area

A parallel mechanism is a multi-legged kinematic structure with actuators fixed on the base. In recent years, parallel mechanisms have been implemented in haptic devices due to their benefits, such as high rigidity, high output force, high accuracy and high backdrivability. Multi-d.o.f. haptic devices with rotational motion have become increasingly important as haptic applications have become diversified (e.g., in surgical training). However, typical multi-d.o.f. parallel mechanisms (e.g., Stewart platform and HEXA) have limitations on the working area for rotational motions. A multi-d.o.f. haptic device can be designed by stacking the translational and rotational mechanisms by decoupling these motions. However, this dedoupling can have an adverse effect on inertia because of the weight of the stacking mechanism. Eventually, the operability of the device deteriorates. Therefore, a parallel mechanism with both a translational and rotational multi-d.o.f. structure can effectively apply the full advantages of a parallel mechanism to a multi-d.o.f. haptic device. In this paper, a 6-d.o.f. (five active: three translations, two rotations and one passive rotation) parallel mechanism, called the D-8, is presented. In the D-8, a new redundant parallel mechanism is introduced to overcome the problem of operability.

Central and Peripheral Fatigue during Passive and Exercise-Induced Hyperthermia

Hyperthermia was induced during prolonged exercise (ExH) and passive heating (PaH) to isolate the influence of exercise on neuromuscular function during a maximal voluntary isometric contraction (MVC) of the quadriceps under heat stress. The influence of cardiovascular strain in limiting endurance performance in the heat was also examined. On separate days, eight males cycled to exhaustion at 60% maximal oxygen uptake or were immersed in a water bath (∼41°C) until rectal temperature (Tre) increased to 39.5°C. The ExH and PaH interventions were performed in ambient conditions of 38°C and 60% relative humidity with Tre reaching 39.8°C during exercise. Before (control) and after each intervention, voluntary activation and force production capacity were evaluated by superimposing an electrically stimulated tetanus during a 45-s MVC. Force production decreased immediately after PaH and ExH compared with control, with the magnitude of decline being more pronounced after ExH (P < 0.01). Mean voluntary activation was also significantly depressed after both interventions (P < 0.01 vs control). However, the extent of decline in voluntary activation was maintained at ∼90% during both PaH and ExH MVC. This decline accounted for 41.5% (PaH) and 33.1% (ExH) of the decrease in force production. In addition, exhaustion coincided with a marked increase in HR (∼96% of maximum) and a decline in stroke volume (25%) and mean arterial pressure (10%) (P < 0.05). The loss of force production capacity during hyperthermia originated from central and peripheral fatigue factors, with the combination of heat stress and previous contractile activity exacerbating the rate of decline. Thus, the observed significant rise in thermal strain in ExH and PaH impaired neuromuscular function and was associated with an exercise performance limiting increase in cardiovascular strain.

An experimental study on the normal stress of magnetorheological fluids

The dependence of the normal stress on the shear rate and magnetic field strength in theshear flow of magnetorheological (MR) fluids has been studied experimentally. An obviousnormal stress could be observed when the applied magnetic field was higher thana critical value. The normal stress increases considerably with increase of theshear rate and magnetic field, and decreases suddenly and significantly uponthe onset of shear thickening in MR fluids. The ratio of shear stress to normalstress, an analogue of the friction coefficient, increases with increase of the shearrate, but decreases with increase of the applied magnetic field. Along with theshear stress, the normal stress in MR fluids could provide a more comprehensiveunderstanding of the MR effect, and the evolution of the particle structure inshear flow, and may have important implications for preparing high performancemagnetostrictive elastomers with high force output along the magnetic field direction.

A model of magnetostrictive actuators for active vibration control

One of the most frequent applications of magnetostrictive actuator technology is the active structural vibration control (AVC). Magnetostrictive actuators (MAs) can deliver high-output forces and can be driven at high frequencies. These characteristics make them suitable for a variety of vibration control applications. The use of this technology, however, requires an accurate knowledge of the dynamics of such actuators. Several models are available in the literature. However, their use in control applications, characterized by high dynamics, is often limited by nonlinearities and complexity of the model. To overcome this difficulty, the paper introduces a linear model of magnetostrictive actuators that is valid in a range of frequencies below 2 kHz. The assumptions supporting the linearity of the system are discussed and the theoretical model is presented. Finally the model is validated through experimental tests carried out on two different magnetostrictive actuators.