Axial Transmission Research Articles

Flexural performance study of the CHC joint based on experimental methods

Joints are pivotal components in prefabricated station technology, requiring development to meet diverse requirements such as site conditions, safety, stability, operability and waterproofing. CHC joints, while addressing these factors, offer the advantages of easy assembly and clear force transmission. These advantages of CHC joints have been verified in the application of Pingxi station in Shenzhen, China. Furthermore, the mechanical transmission mechanism of CHC joints is novel and distinct from existing joint types. In this study, with the use of experimental methods, further investigation is conducted into the flexural mechanical properties of CHC joints, elucidating their flexural behaviour and failure modes. The findings indicate that the axial force transmission mechanism of CHC joints ensures stable tension transmission under bending moment loads; the flexural stiffness of joints exhibits pronounced non-linearity; and the failure mode of joints resembles that of reinforced concrete beams with adequate reinforcement, demonstrating ductile failure. This research offers valuable insights for the design of CHC joints.

Association between radius axial low-frequency ultrasound velocity and bone fragility in primary hyperparathyroidism.

Radius quantitative ultrasound measurement, that utilized a portable low-frequency (VLF) axial transmission ultrasound for assessing the properties of radius cortical bone in a non PHPT population revealed a possible role as a screening tool prior to DXA to evaluate fragility fracture. To evaluate this portable ultrasound device as a screening tool of skeletal fragility in PHPT patients. We enrolled 117 postmenopausal women with PHPT. Every subject had a DXA of femur, lumbar spine, non-dominant distal 1/3 radius, TBS measurement, VLF with a portable device and spine x- ray. The mean age of the patients was 68 ± 10 years. The measurement of agreement between radius DXA and VLF was: K = 0.43, p < 0.001. A lower radius US T-score, also adjusted for years since menopause and BMI, was associated with osteoporosis identified with DXA at lumbar and/or femoral neck sites: OR = 1.852 (CI 1.08, 3.18). All fractures were associated with femoral neck T-score: OR = 1.89 (95% CI 1.24, 2.89), as well as with total hip T-score: OR = 1.65 (95% CI 1.09, 2.50), and years since menopause: OR = 1.25 (95% CI 1.02, 1.54).Morphometric vertebral fractures were associated with years since menopause: OR = 1.28 (95% CI 1.02,1.61), femoral neck T-score OR = 1.96 (95% CI 1.227, 3.135), total hip T-score OR = 1.64 (95% CI 1.04, 2.60), TBS OR = 0.779 (95% CI 0.60-0.99), both ultra-distal radius T-score: OR = 1.50 (95% CI 1.05, 2.156), and radius US T-score: OR = 1.67 (95% CI 1.09, 2.56). VLF could be used for screening purposes prior to DXA to evaluate PHPT fracture risk, only in conditions in which DXA measurement cannot be performed.

CNN applied to ultrasonic guided wave spectrum image classification

Abstract Osteoporosis is a worldwide problem associated with an increasing number of fragility fractures. Currently, the standard for identifying patients at risk of fragility fracture is through Dual X-ray Absorptiometry (DXA). Different altenatives have been proposed, such as magnetic resonance imaging (MRI), three-dimensional X-rays, ultrasound or algorithms providing scores from clinical data. Among ultrasonic techniques, Bi-Directional Axial Transmission (BDAT) has been used to classify patients with or without fragility fractures, initially using ”classical” ultrasound parameters, such as velocities and latter using Support Vector Machine and automatic features, with performances close to the gold standard DXA. The aim of this study was to investigate the use of Convolutional Neural Networks (CNN) applied to patient classification using ultrasonic guided wave spectrum images, using a previous database of post menopausal women with or without fragility fractures. Two networks will be tested, a reference one, ResNet, successfully applied in classification and diagnosis in medical images, and a tailored one, denoted BDAT-Net, which hyperparameters will be optimized through a grid approach. The obtained accuracy, using BDAT-Net and clinical data (age, body mass index, cortisone intake) was found equal to 0.66 [0.64-0.69] comparable with the one obtained with DXA and significantly better than the one obtained with ResNet. These encouraging results open the door to the use of robust ultrasonic devices for fracture risk assessment, in particular in countries where DXA is not widely available.

Cortical bone plate properties assessment using inversion of axially transmitted low frequency ultrasonic guided waves.

Over the past few decades, early osteoporosis detection using ultrasonic bone quality evaluation has gained prominence. Specifically, various studies focused on axial transmission using ultrasonic guided waves and have highlighted this technique's sensitivity to intrinsic properties of long cortical bones. This work aims to demonstrate the potential of low-frequency ultrasonic guided waves to infer the properties of the bone inside which they are propagating. A proprietary ultrasonic transducer, tailored to transmit ultrasonic guided waves under 500 kHz, was used for the data collection. The gathered data underwent two-dimensional fast Fourier transform processing to extract experimental dispersion curves. The proposed inversion scheme compares experimental dispersion curves with simulated dispersion curves calculated through the semi-analytical iso-geometric analysis (SAIGA) method. The numerical model integrates a bone phantom plate coupled with a soft tissue layer on its top surface, mimicking the experimental bone phantom plates. Subsequently, the mechanical properties of the bone phantom plates were estimated by reducing the misfit between the experimental and simulated dispersion curves. This inversion leaned heavily on the dispersive trajectories and amplitudes of ultrasonic guided wave modes. Results indicate a marginal discrepancy under 5% between the mechanical properties ascertained using the SAIGA-based inversion and those measured using bulk wave pulse-echo measurements.

Unsupervised Learning-Based Measurement of Ultrasonic Axial Transmission Velocity in Neonatal Bone.

To develop a robust algorithm for estimating ultrasonic axial transmission velocity from neonatal tibial bone, and to investigate the relationships between ultrasound velocity and neonatal anthropometric measurements as well as clinical biochemical markers of skeletal health. This study presents an unsupervised learning approach for the automatic detection of first arrival time and estimation of ultrasonic velocity from axial transmission waveforms, which potentially indicates bone quality. The proposed method combines the ReliefF algorithm and fuzzy C-means clustering. It was first validated using an in vitro dataset measured from a Sawbones phantom. It was subsequently applied on in vivo signals collected from 40 infants, comprising 21 males and 19 females. The extracted neonatal ultrasonic velocity was subjected to statistical analysis to explore correlations with the infants' anthropometric features and biochemical indicators. The results of in vivo data analysis revealed significant correlations between the extracted ultrasonic velocity and the neonatal anthropometric measurements and biochemical markers. The velocity of first arrival signals showed good associations with body weight (ρ = 0.583, P value <.001), body length (ρ = 0.583, P value <.001), and gestational age (ρ = 0.557, P value <.001). These findings suggest that fuzzy C-means clustering is highly effective in extracting ultrasonic propagating velocity in bone and reliably applicable in in vivo measurement. This work is a preliminary study that holds promise in advancing the development of a standardized ultrasonic tool for assessing neonatal bone health. Such advancements are crucial in the accurate diagnosis of bone growth disorders.

Experimental Behaviour of Tensioner for Rigid Hangers of Arch Bridges

In steel tied arch bridges where the hangers are made of rigid bars, the replacement of damaged hangers is rather complex. In fact, while generally the cable hangers are already prepared with anchors at the ends and their replacement traces the initial stages of construction with their prestressing, on the contrary, the rigid bars are welded to the arch and the deck, so their replacement must include the design of a new suspension system that allows the insertion of a pretension where this had never been considered. To check the reliability of this new system, a prototype of tensioner was studied for the case of a steel arch bridge in which the high level of corrosion made it necessary to replace all the original hangers with new ones. This entailed the need to test the tensioner performance with the aim of ensuring the axial force transmission between the two hanger segments without slippage in the threads, as well as to test the correct tension setting before construction and putting into service the hangers to be replaced. For this reason, a predictive experimental campaign was carried out on a prototype by means of tests for the mechanical characterization of the materials used, tensile tests of the system, and tensioning tests under load, measuring the displacements and strains of the system elements. The results of the tests, with slippage in the threads limited to the 2% of total elongation, and the turnaround-stressing curves were useful for the definition of the pieces to be assembled during on-site work and for addressing the operating procedures of the tensioning phases on-site during hanger replacement. Validation with the on-site monitoring of stressing operation was conducted at the end; the monitoring of tension through dynamic tests confirmed the agreement of on-site results with the predictive loading tests of the experimental campaign on the tensioner prototype.

Swirling Capillary Instability of Rivlin–Ericksen Liquid with Heat Transfer and Axial Electric Field

The mutual influences of the electric field, rotation, and heat transmission find applications in controlled drug delivery systems, precise microfluidic manipulation, and advanced materials’ processing techniques due to their ability to tailor fluid behavior and surface morphology with enhanced precision and efficiency. Capillary instability has widespread relevance in various natural and industrial processes, ranging from the breakup of liquid jets and the formation of droplets in inkjet printing to the dynamics of thin liquid films and the behavior of liquid bridges in microgravity environments. This study examines the swirling impact on the instability arising from the capillary effects at the boundary of Rivlin–Ericksen and viscous liquids, influenced by an axial electric field, heat, and mass transmission. Capillary instability arises when the cohesive forces at the interface between two fluids are disrupted by perturbations, leading to the formation of characteristic patterns such as waves or droplets. The influence of gravity and fluid flow velocity is disregarded in the context of capillary instability analyses. The annular region is formed by two cylinders: one containing a viscous fluid and the other a Rivlin–Ericksen viscoelastic fluid. The Rivlin–Ericksen model is pivotal for comprehending the characteristics of viscoelastic fluids, widely utilized in industrial and biological contexts. It precisely characterizes their rheological complexities, encompassing elasticity and viscosity, critical for forecasting flow dynamics in polymer processing, food production, and drug delivery. Moreover, its applications extend to biomedical engineering, offering insights crucial for medical device design and understanding biological phenomena like blood flow. The inside cylinder remains stationary, and the outside cylinder rotates at a steady pace. A numerically analyzed quadratic growth rate is obtained from perturbed equations using potential flow theory and the Rivlin–Ericksen fluid model. The findings demonstrate enhanced stability due to the heat and mass transfer and increased stability from swirling. Notably, the heat transfer stabilizes the interface, while the density ratio and centrifuge number also impact stability. An axial electric field exhibits a dual effect, with certain permittivity and conductivity ratios causing perturbation growth decay or expansion.

Axial transfer characteristics of a drillstring in conjunction with bit penetration behavior in horizontal wells

Nonlinear friction and interaction between bit and rock often result in a lower weight on bit (WOB) than the intended design value. The analysis of the dynamic transmission mechanism of a drillstring in complex horizontal wells is a crucial engineering problem that aims to enhance drilling efficiency. In this paper, a mechanical model was developed, integrating nonlinear bit penetration behavior and variable axial loads, aiming to unveil the nonlinear axial vibration characteristics and elucidate the transmission mechanisms within the drillstring. Notably, the mean value of axial force distributed along the drillstring is dictated by wellhead pulling force, while the amplitude is shaped by the interaction between bit and rock, and rotary speed. In calculated examples for horizontal wells, the analysis reveals that significant losses in power axial transmission, resulting in WOB is only 38% of the intended value. And reducing the wellhead pulling force by 30 kN leads to a maximum increase in WOB only of 9.51 kN. Extended region in drillstring with negative axial forces exhibit maximum values 5–6 times higher than the WOB. Specific zones, such as 20 m–40 m and 0–20 m from the bit, experience axial force fluctuation amplitudes of 40.5% and 138.8% of the mean value respectively, with the latter identified as an intense vibration zone, while the acceleration values 0–10 m from the bit signal a high-risk zone. In prolonged horizontal section, stability issues manifest, with spiral buckling observed in the holding section and sinusoidal buckling in the horizontal section. Mitigating the synchronous vibrations between the bit and the surrounding drillstring can effectively reduce the intensity of axial vibration. To ensure successful drilling to target formation, adjusting the wellhead pulling force to keep the WOB in the range of 60–90 kN and limiting the rotary speed to 90 r/min are recommended practices. This comprehensive analysis offers valuable insights for optimizing drilling parameters, pinpointing high-vibration zones, and mitigating risks associated with drilling, providing a holistic approach to enhancing drilling efficiency.

Assessment of cortical bone phantom properties using ultrasonic guided waves transduced with a multi-element transducer

The past decade has seen extensive exploration of alternative methods for the early diagnosis of osteoporosis through the assessment of the the bone quality. Previous research on axial transmission of ultrasonic guided waves demonstrated their sensitivity to the intrinsic properties of elongated cortical bones. This study highlights the capacity of low-frequency guided waves to ascertain bone properties through the inversion of dispersion curves. The proposed inversion scheme relies on dispersion curves simulated using the semi-analytical iso-geometric analysis (SAIGA) method. The model incorporates the excitability of ultrasonic guided wave modes to ensure that the inversion uses both the dispersive trajectories and amplitudes of the modes. Two models were examined: (1) a cortical bone phantom plate covered with a soft tissue mimicking material and (2) a quasi-cylinder cortical bone phantom surrounded by a soft tissue mimicking material. A proprietary axial transmission multielement ultrasonic transducer, designed for exciting guided waves under 500 kHz, was employed to capture experimental dispersion curves on phantoms through the 2D-FFT. The mechanical properties of the bone phantoms were inferred by minimizing disparities between experimental and simulated dispersion curves. Inverse properties exhibited an error of less than 4% compared to reference values. The axial transmission probe demonstrated its proficiency in accurately measuring modes propagating inside the cortical layer.

Building Vibration Measurement and Prediction during Train Operations

Urban societies face the challenge of working and living in environments filled with vibration caused by transportation systems. This paper conducted field measurements to obtain the characteristics of vibration transmission from soil to building foundations and within building floors. Subsequently, a prediction method was developed to anticipate building vibrations by considering the soil and structure interaction. The rigid foundation model was simplified into a foundation–soil system connected via spring damping, and the building model is based on axial wave transmission within the columns and attached floors. Building vibrations were in response to measured input vibration levels at the ground and were validated through field measurements. The influence of different building heights on soil and structure vibration propagation was studied. The results showed that the predicted vibrations match well with the measured vibrations. The proposed prediction model can reasonably predict the building vibration caused by train operations. The closed-form method is an efficient tool for predicting floor vibrations prior to construction.

Numerical and analytical models of the mechanism of torque and axial load transmission in a shock absorber for drilling oil, gas and geothermal wells

The paper proposes an improved design of a shock absorber used in drilling deep oil and gas and geothermal wells with polycrystalline diamond compact (PDC) bits. The proposed innovations successfully combat the dangerous phenomenon of self-excited vibrations, which can lead to malfunctions such as stick-slip and whirling of the drilling tool. Most conventional drill shock absorbers are designed to only absorb longitudinal vibrations, which was sufficient when using roller cutter bits for the drilling process. However, the design features of PDC bits and the phenomenon of interaction of their cutters with interlayered rocks during deep drilling impose new requirements on the properties of the drill shock absorber. To protect the downhole tool from abnormal torque values and torque oscillations, it is proposed to equip the shock absorber with a special torque transmission unit in the form of a fourteen-thread self-releasing screw pair. This unit is capable of transforming increases in external torque into increases in the force that loads the elastic element of the shock absorber. The numerical and analytical models of the mechanism of transferring external axial load and torque to the elastic element of the drill shock absorber are constructed. The distribution of contact pressures on the interacting surfaces of the screw pair and the distribution of equivalent stresses in the screw pair parts are analysed. The strength of the proposed drill shock absorber assembly was evaluated using the Huber-von Mises energy criterion. The dependence of the load transmitted to the elastic element of the shock absorber on changes in the external torque and external axial force is investigated. In general, it is determined that the external load is distributed evenly between all turns of the screw pair, and the limit state of the parts of the proposed assembly is not reached even under high-torque operating load. The obtained analytical dependencies will allow to effectively determine the required strength and stiffness of the elastic element of the drill shock absorber at the design stage. The obtained analytical results were verified using a finite element model.

Cortical bone properties assessment using axially transmitted low frequency (&amp;lt;500 kHz) guided waves

The early diagnosis of osteoporosis through bone quality assessment has been extensively studied in the past decade. Research in axial transmission using ultrasonic guided waves has shown the method to be sensitive to intrinsic properties of long cortical bone. The aim of this work is, therefore, to show the capability of low frequency guided waves to enable the inversion of dispersion curves into bone properties. The proposed inversion scheme relies on dispersion curves simulated using the semi-analytical iso-geometric analysis (SAIGA) method. The model used in simulation comprised a bone phantom plate with a layer of soft tissue attached to the top surface in accordance with experimental bone phantom plates. A proprietary axial transmission multielement ultrasonic transducer specifically designed to excite ultrasonic guided waves under 500 kHz was used for measurements. Acquired data were processed using the 2-D Fast Fourier Transform to extract dispersion curves. The mechanical properties of the bone phantom plates were obtained by minimizing the difference between the experimental and simulated dispersion curves. The inversion was based on the dispersive properties of ultrasonic guided waves as well as their amplitudes. Results show a difference around 5% between the mechanical properties found with the SAIGA based inversion and those provided by the manufacturer of the plates.

A Highly Flexible Piezoelectric Ultrasonic Sensor for Wearable Bone Density Testing.

Driven by the loss of bone calcium, the elderly are prone to osteoporosis, and regular routine checks on bone status are necessary, which mainly rely on bone testing equipment. Therefore, wearable real-time healthcare devices have become a research hotspot. Herein, we designed a high-performance flexible ultrasonic bone testing system using axial transmission technology based on quantitative ultrasound theory. First, a new rare-earth-element-doped PMN-PZT piezoelectric ceramic was synthesized using a solid-state reaction, and characterized by X-ray diffraction and SEM. Both a high piezoelectric coefficient d33 = 525 pC/N and electromechanical coupling factors of k33 = 0.77, kt = 0.58 and kp = 0.63 were achieved in 1%La/Sm-doped 0.17 PMN-0.47 PZ-0.36 PT ceramics. Combining a flexible PDMS substrate with an ultrasonic array, a flexible hardware circuit was designed which includes a pulse excitation module, ultrasound array module, amplification module, filter module, digital-to-analog conversion module and wireless transmission module, showing high power transfer efficiency and power intensity with values of 35% and 55.4 mW/cm2, respectively. Finally, the humerus, femur and fibula were examined by the flexible device attached to the skin, and the bone condition was displayed in real time on the mobile client, which indicates the potential clinical application of this device in the field of wearable healthcare.

Redeployable, 4D printed wave spring actuators

Wave springs are a novel type of axial compression spring that offer complete axial load transmission and a significant free height reduction when compared to coil springs. In this paper, it is shown that direct 4D printing using bilayers on a fused filament fabrication system can be used to create deployable, polymer wave springs that do not suffer from layering effects, as is common in other cyclically loaded additively manufactured parts. Bilayer actuators enable a flat print configuration and subsequent deployment by a thermal stimulus that then aligns the layers in the direction of the wave in the spring. Due to this, the springs exhibit exceptional performance under cyclic loading, reaching 104 cycles without failure. After plastic deformation caused by extended cyclic loading, the springs can be redeployed to recover their original mechanical properties using cold programming. These findings show the great potential of direct 4D printing in fused filament fabrication to create functional, 4D printed components with complex geometry and greatly increased lifespan compared to conventional 3D printed parts. The presented approach to compression spring fabrication further provides a standard component that enables the design of highly integrated, monolithically printed, and tunable mechanical systems.

A novel vertical waterproofing joint with trapezoidal steel plate connections for steel–concrete underground silos: Bending test and numerical simulation

Steel-concrete silo is a popular option in green grain storage project due to its pretty stiffness and better waterproof. However, the structural form and mechanical properties of vertical joints in the prefabricated steel–concrete silo are two key problems, which restrict its wide application. Consequently, a novel vertical waterproofing joint with trapezoidal steel plate (TSP) connections is proposed for steel–concrete underground silos. The TSP is welded laterally between the adjacent prefabricated silo walls, and it also needs to undertake part of the axial force transmission of underground silos. Firstly, the steel–concrete specimen of two-TSPs’ deformation, interior force, failure mode and mechanism are analyzed comprehensively. Secondly, two numerical model of the steel–concrete silo wall with non-TSP and two-TSP are established on ABAQUS. Finally, the effect of different parameters on mechanical properties are analyzed. Experimental results show that, compared with the specimens with non-TSP, the deflection of the proposed two-TSP connection is decreased by 270% and the yield load of internal waterproof steel plate is increased by 29%. When the internal waterproof steel plate is yield, the compressive strain of external waterproof steel plate and TSP in the upper part are similar, while its internal tensile strain in the lower part have a little gap. TSP can cooperative work with both internal and external waterproof steel plates. Numerical results are difference from test results by only 5.34% and 4.48% respectively, which verifies that the numerical model is effective and feasible. Meanwhile, it is also found that the proposed novel connection has the greatest strength enhancement effect on flexural bearing capacity of vertical joint, and the greatest effect on improving the flexural bearing capacity of vertical joint.

PREDICTION OF FRAGILE FRACTURE USING DEEP LEARNING BASED ON ULTRASOUND RADIOFREQUENCY SIGNAL: A PILOT STUDY

Quantitative ultrasound (QUS) is a promising tool to estimate bone structure characteristics and predict fragile fracture. The aim of this pilot cross-sectional study was to evaluate the performance of a multi-channel residual network (MResNet) based on ultrasonic radiofrequency (RF) signal to discriminate fragile fractures retrospectively in postmenopausal women.MethodsRF signal and speed of sound (SOS) were obtained using an axial transmission QUS at one‐third distal radius for 246 postmenopausal women. Based on the involved RF signal, we conducted a MResNet, which combines multi-channel training with original ResNet, to classify the high risk of fragility fractures patients from all subjects. The bone mineral density (BMD) at lumber, hip and femoral neck acquired with DXA was recorded on the same day. The fracture history of all subjects in adulthood were collected. To assess the ability of the different methods in the discrimination of fragile fracture, the odds ratios (OR) calculated using binomial logistic regression analysis and the area under the receiver operator characteristic curves (AUC) were analyzed.ResultsAmong the 246 postmenopausal women, 170 belonged to the non-fracture group, 50 to the vertebral group, and 26 to the non-vertebral fracture group. MResNet was discriminant for all fragile fractures (OR = 2.64; AUC = 0.74), for Vertebral fracture (OR = 3.02; AUC = 0.77), for non-vertebral fracture (OR = 2.01; AUC = 0.69). MResNet showed comparable performance to that of BMD of hip and lumbar with all types of fractures, and significantly better performance than SOS all types of fractures.Conclusionsthe MResNet model based on the ultrasonic RF signal can significantly improve the ability of QUS device to recognize previous fragile fractures. Moreover, the performance of the proposed model modified by age, weight, and height is further optimized. These results open perspectives to evaluate the risk of fragile fracture applying a deep learning model to analyze ultrasonic RF signal.

Analysis of axial force transmission characteristics and contact mechanism of coiled tubing in the spoolable compliant guide during injection

The spoolable compliant guide (SCG) maintains S-shaped dynamic stability in the marine environment. At present, limited studies have been reported on the mechanical laws of coiled tubing (CT) injection by employing SCG. In this study, an experimental platform was developed to simulate the CT injection process in SCG. The axial force transmission characteristics, buckling laws, and contact mechanism of the CT were investigated. The results showed that an increase in the diameter of the inner pipe delayed the occurrence of sinusoidal and helical buckling and improved the transmission efficiency by 13.0%. An increase in the outer pipe diameter showed no significant effect on the efficiency, however, it increased the injection length of the inner pipe by 30.4%. The friction force increased significantly after the helical buckling of the inner pipe. Based on the results, the presented research is beneficial in establishing CT's theoretical framework and enhancing operational effectiveness.

Axial transmission technique for screening bucked shin in a horse leg

For the safe and simple screening of equine leg bones, we applied an ultrasonic axial transmission (AT) technique to an equine bone sample with a weak bucked shin. Both experimental and simulation studies have been conducted. To simulate by the finite-difference time-domain method, a digital model of the equine leg bone was fabricated. The experimental and simulation results showed a similar tendency. The obtained apparent wave velocities in the axial direction were almost constant in the healthy part but strongly fluctuated in the bucked shin part because of the small surface irregularities. The standard deviation values of the wave velocities in the bucked shin parts were large. These results indicate that a weak bucked shin in the equine leg bone may be screened clinically by a simple evaluation of velocity fluctuation using the AT technique.

Bilateral bony fusion of sacroiliac joint- A rare case report

SI joint dysfunction is responsible for about 15-30% of low backache causes. It is crucial for locomotor activity as well as delivery during labour. It aids in axial body weight transmission and distribution from the sacrum to the pelvis. Limited gliding movements occur within joint cavity of this synovial joint. They are a category of inflammatory illnesses that affect the vertebral spines and peripheral joints, with stiffness as a common symptom. Anatomical differences in SI joint morphology, such as auxiliary SI joint, ilio sacral complex and sacral defect, and dismorphic joint, are of compelling interest when it comes to SI joint diseases. Obese people suffer from a variety of health problems related to sacroiliac joint.

Analytical and experimental validation of vibration isolation system with complementary stiffness and composite control

In the spacecraft, optical payloads are greatly disturbed by micro-vibration. Therefore, the active-passive vibration isolation system (APVIS) with stable performance and high efficiency has become the focus of many scholars, with the increasing demand for vibration isolation. The voice coil motor (VCM) is often used to verify the APVIS. However, due to processing and installation errors, noncontact and low stiffness between the mover and stator of the VCM, the normal operation of the system will be affected. An APVIS based on the complementary pair of axial and radial stiffness is proposed in this paper. Structurally, the flexible joint and the membrane are used to compensate for each other and explained and verified from the mechanism and experiment. In the control algorithm, feedback control and feedforward control are used to build an active composite control (ACC) algorithm, and the two compensate each other to solve the problems of feedback control time delay and feedforward control instability. Experimental results show that the errors of the axial force transmission and the output force of the VCM are only 1.09% and −1.5%, respectively. The designed structure can ensure the co-axiality of the mover and stator, and the VCM can work normally. After control, the ACC algorithm can achieve vibration attenuation of 95.8%, the amplitude at natural frequency is decreased by 27.53 dB, which verifies the effectiveness of the ACC algorithm.