Body Stiffness Research Articles

Dynamics analysis of spur gears considering random surface roughness with improved gear body stiffness

In previous calculation of gear mesh stiffness, the gear body is typically treated as a deformable elastic ring, and the stiffness of the gear body is determined using Sainsot's empirical formula. In this paper, a new calculation method for determining the gear body stiffness based on the analytical finite element-potential energy method is proposed, and its feasibility is verified by the finite element method. A new nonlinear dynamic model for a spur gear system is established, taking into account the time-varying backlash and random surface roughness. This model aims to investigate the dynamical responses of the gear system under various parameters, including rotational speed, shaft hole radius and surface roughness. The results indicate that the proposed method for calculating the stiffness of the gear body is significantly more accurate than Sainsot's empirical formula, as it closely aligns with the finite element method. This leads to a more precise calculation of the time-varying mesh stiffness. The gear dynamics model incorporating random surface roughness exhibits a heightened degree of realism and complexity in its dynamic phenomena. This study provides a valuable reference for the future development of dynamic gear systems.

Research on the modification of the tool influence function for robotic bonnet polishing with stiffness modeling

Robotic bonnet polishing (RBP) technology is widely used in the polishing process of optical components, but industrial robots have the characteristics of a wide processing range and low body stiffness. Therefore, in the actual polishing process, there are different polishing forces due to different stiffnesses, which leads to different tool influence functions (TIF) affecting the surface quality of optical components. To achieve a uniform surface quality of the components polished by the RBP, we modeled the stiffness of the robot and modified the TIF in conjunction with the Preston equation, finally verifying the accuracy of the modified model through experiments. The results of the fixed-point polishing experiments show that the maximum relative error before the TIF correction is 12.5% and the maximum relative error after the correction is 2.8% within the robot's 600mm*600mm machining range. The results of the plane polishing experiments show that the maximum relative error before the TIF correction is 13% and the maximum relative error after the correction is 1.7%. Therefore, a method for TIF corrections from RBP based on stiffness modeling has important engineering implications.

Tendon-Driven Variable-Stiffness Pneumatic Soft Gripper Robot

In recent times, the soft robotics field has been attracting significant research focus owing to its high level of manipulation capabilities unlike traditional rigid robots, which gives room for increasing use in other areas. However, compared to traditional rigid gripper robots, being capable of controlling/obtaining overall body stiffness when required is yet to be further explored since soft gripper robots have inherently less-rigid properties. Unlike previous designs with very complex variable-stiffness systems, this paper demonstrates a soft gripper design with minimum system complexity while being capable of varying the stiffness of a continuum soft robotic actuator and proves to have potential applications in gripping objects of various shapes, weights, and sizes. The soft gripper actuator comprises two separate mechanisms: the pneumatic mechanism for bending control and the mechanical structure for stiffness variation by pulling tendons using stepper motors which compresses the actuator, thereby changing the overall stiffness. The pneumatic mechanism was first fabricated and then embedded into another silicon layer during which it was also merged with the mechanical structure for stiffness control. By first pneumatically actuating the actuator which causes bending and then pulling the tendons, we found out that the actuator stiffness value can be increased up to 145% its initial value, and the gripper can grasp and lift a weight of up to 2.075 kg.

A calibration method for predicting and compensating the flexible positioning errors of a 7-DOF series compliant robot caused by end-effector’s gravity

Due to low stiffness of compliant series robot body, the influence of joint flexible deformation caused by the gravity load of the end-effector on the absolute positioning accuracy cannot be ignored. In order to improve the flexible positioning accuracy of the robot end-effector, a calibration method for predicting and compensating the flexible positioning error of the 7-DOF series compliant robot due to the gravity load of the end-effector is proposed. The method identifies and predicts the pose configuration with similar flexible positioning error through the semi-parametric error model based on joint stiffness identification and of BP neural network. The feedforward method is used to compensate the positioning error. In this study, a 7-DOF series compliant robot is selected as the research object. Based on the principle of error similarity, the measurement points and the corresponding pose configurations are selected as the training data for the parameter identification of the semi-parametric error model, and the flexible positioning errors on the continuous trajectory of the end-effector are compensated according to the predicted values of the model. When the mass of the end-effector is 5 kg, by this method, the maximum value, mean value and mean square error of flexible positioning error on multiple straight-line trajectories on the plane are increased from 8.4779, 5.6039, and 1.8496 mm to 0.9720, 0.3079, and 0.2303 mm, respectively. It means the positioning accuracy are increased by 88.53%, 94.50%, and 87.55%, respectively, by which could observe that the precision of this robot’s end-effector was significantly improved.

Body stiffness is a mechanical property that facilitates contact-mediated mate recognition in Caenorhabditis elegans

Physical contact is prevalent in the animal kingdom to recognize suitable mates by decoding information about sex, species, and maturity. Although chemical cues for mate recognition have been extensively studied, the role of mechanical cues remains elusive. Here, we show that C.elegans males recognize conspecific and reproductive mates through short-range cues, and that the attractiveness of potential mates depends on the sex and developmental stages of the hypodermis. We find that a particular group of cuticular collagens is required for mate attractiveness. These collagens maintain body stiffness to sustain mate attractiveness but do not affect the surface properties that evoke the initial step of mate recognition, suggesting that males utilize multiple sensory mechanisms to recognize suitable mates. Manipulations of body stiffness via physical interventions, chemical treatments, and 3D-printed bionic worms indicate that body stiffness is a mechanical property for mate recognition and increases mating efficiency. Our study thus extends the repertoire of sensory cues of mate recognition in C.elegans and provides a paradigm to study the important roles of mechanosensory cues in social behaviors.

Towards the optimization of passive undulatory locomotion on land: mathematical and physical models.

The current study investigates the body-environment interaction and exploits the passive viscoelastic properties of the body to perform undulatory locomotion. The investigations are carried out using a mathematical model based on a dry frictional environment, and the results are compared with the performance obtained using a physical model. The physical robot is a wheel-based modular system with flexible joints moving on different substrates. The influence of the spatial distribution of body stiffness on speed performance is also investigated. Our results suggest that the environment affects the performance of undulatory locomotion based on the distribution of body stiffness. While stiffness may vary with the environment, we have established a qualitative constitutive law that holds across environments. Specifically, we expect the stiffness distribution to exhibit either an ascending-descending or an ascending-plateau pattern along the length of the object, from head to tail. Furthermore, undulatory locomotion showed sensitivity to contact mechanics: solid-solid or solid-viscoelastic contact produced different locomotion kinematics. Our results elucidate how terrestrial limbless animals achieve undulatory locomotion performance by exploiting the passive properties of the environment and the body. Application of the results obtained may lead to better performing long-segmented robots that exploit the suitability of passive body dynamics and the properties of the environment in which they need to move.

Investigating the dynamic influence of passive effects on undulatory locomotion in viscous environment and unleashing the potential of hybrid friction

This study encompasses the passive interdependence of body material (internal damping, stiffness, and geometry) and environmental (frictional anisotropy and frictional coefficients) properties on the performance and adaptability of undulatory locomotion. Undulatory locomotion is modeled in viscous and hybrid environments. The body’s ability to adapt passively results in different locomotion gaits, such as swimming and crawling. Results show that, in swimming gaits, body stiffness dominates frictional forces, whereas in crawling gaits, frictional forces dominate body stiffness. Our result showed that the interdependence between endogenous and exogenous dynamics can be utilized to achieve the desired speed. The hybrid frictional environment is modeled as the combination of dry and viscous frictions and recognized as a valuable asset in the modeling of undulatory locomotion in granular media. In the hybrid environment the respective ratios of dry and viscous frictions play an essential role in the speed optimization. The optimal combination of dry and viscous frictions can be found depending on the characteristics of the body and environment. We validate the viscous based frictional model using the properties of the body of Caenorhabditis Elegans from the state of the art, in a viscous environment. The results can be employed to design robotic solutions to perform optimally in different environments and with customized body properties.

Effects of body stiffness on propulsion during fish self-propelled swimming

Many fish propel themselves using wave-like lateral flexion of their body and tail in the water. The undulatory body is driven by the distributed muscles, and locomotion is achieved by internal muscular stimulation and the external action of the fluid. As one of the material properties, the stiffness of the body being propelled plays an important role in the deformation process, especially for the muscle power input and phase lag. In this paper, a three-dimensional self-propelled elongated body model is employed to numerically investigate the effects of stiffness on the propulsion performance, including the forward speed, energy consumption, and energy-utilization ratio. According to various deformation characteristics and energy-utilization ratios, three deformation modes corresponding to high, medium, and low stiffness are identified. Our results indicate that a deforming body with medium stiffness has the highest efficiency, and its corresponding deformation is closest to that of fish in nature. When the stiffness of the fish body is higher than the normal level, more muscle energy is needed to sustain the tail beating of the same amplitude. A lower level of stiffness produces a more obvious phase lag in the fish body, which might lead to slow control responses. We also show that the stiffness of the fish body affects the scaling relationship between the swimming speed and the tail beating velocity. The upper and lower limits of the scaling exponent correspond to high and low levels of stiffness, respectively, and are also affected by the wavelength of the muscle contraction.

Computational Study of Stiffness-Tuning Strategies in Anguilliform Fish.

Biological evidence demonstrates that fish can tune their body stiffness to improve thrust and efficiency during swimming locomotion. However, the stiffness-tuning strategies that maximize swimming speed or efficiency are still unclear. In the present study, a musculo-skeletal model of anguilliform fish is developed to study the properties of variable stiffness, in which the planar serial-parallel mechanism is used to model the body structure. The calcium ion model is adopted to simulate muscular activities and generate muscle force. Further, the relations among the forward speed, the swimming efficiency, and Young's modulus of the fish body are investigated. The results show that for certain body stiffness, the swimming speed and efficiency are increased with the tail-beat frequency until reaching the maximum value and then decreased. The peak speed and efficiency are also increased with the amplitude of muscle actuation. Anguilliform fish tend to vary their body stiffness to improve the swimming speed and efficiency at a high tail-beat frequency or small amplitude of muscle actuation. Furthermore, the midline motions of anguilliform fish are analyzed by the complex orthogonal decomposition (COD) method, and the discussions of fish motions associated with the variable body stiffness and the tail-beat frequency are also presented. Overall, the optimal swimming performance of anguilliform fish benefits from the matching relationships among the muscle actuation, the body stiffness, and the tail-beat frequency.

The first and foremost unilateral pallidothalamic tractotomy done in India for Parkinson’s Disease

Background. Pallidothalamic tractotomy” can be effective in Parkinson’s disease by exhibiting anti-parkinsonian effects. Case presentation. The patient was a 53 years old gentleman, having Parkinson’s disease for the last 14 years. The disease onset was on the left side and slowly moved to the right side. He had tremors, slowness of body movements and stiffness of the movements. The first right Pallidotomy was done in January 2019. There was a noticeable improvement in a few weeks. He continued to have symptoms on the right side. The preoperative Unified Parkinson Disease Rating Scale (UPDRS) part 3 score in 2019 was 53 while the postoperative score was only 26 showing drastic improvement after right Pallidotomy. After 2 years of the first surgery, a new technique called Pallido Thalamic Tractotomy (PTT), an MRI-guided stereotactic surgery was done on the left side. Tremors reduced gradually by 99% in 3 weeks after surgery. This is the first case of PTT performed on a patient with Parkinson’s disease in India. Conclusion. PTT is an effective procedure in PD that acts by disconnecting the pallidothalamic tract. Unilateral pallidothalamic tractotomy done on the left side improved contralateral side rigidity, tremors and bradykinesia.

The Flexible Armor of Chinese Sturgeon: Potential Contribution of Fish Skin on Fracture Toughness and Flexural Response.

Fish skin is a biological material with high flexibility and compliance and can provide good mechanical protection against sharp punctures. This unusual structural function makes fish skin a potential biomimetic design model for flexible, protective, and locomotory systems. In this work, tensile fracture tests, bending tests, and calculation analyses were conducted to study the toughening mechanism of sturgeon fish skin, the bending response of the whole Chinese sturgeon, and the effect of bony plates on the flexural stiffness of the fish body. Morphological observations showed some placoid scales with drag-reduction functions on the skin surface of the Chinese sturgeon. The mechanical tests revealed that the sturgeon fish skin displayed good fracture toughness. Moreover, flexural stiffness decreased gradually from the anterior region to the posterior region of the fish body, which means that the posterior region (near the tail) had higher flexibility. Under large bending deformation, the bony plates had a specific inhibition effect on the bending deformation of the fish body, especially in the posterior region of the fish body. Furthermore, the test results of the dermis-cut samples showed that the sturgeon fish skin had a significant impact on flexural stiffness, and the fish skin could act as an external tendon to promote effective swimming motion.

Influence of Maintain Bumpers on Vehicle Hood Modal Response

Abstract Vehicle hood modal analysis is an essential step in the design and development process of a hood system. It involves studying the dynamic response of the vehicle’s hood structure under different operational conditions and helps in designing a proper geometry that can withstand durability and fatigue. There are many parameters in the hood system that can influence its modal response as: hood stiffness, body stiffness, equipment stiffness and position and others. Our paper summarizes some research on this topic and then provides a case study on a numerical modal analysis of a steel hood on body with and without maintain bumpers. The resonant frequencies, mode shapes, global and local displacement responses are presented for each of the selected configurations. The influence of the maintain bumpers on the dynamic response of the hood is highlighted and conclusions are made for each of the computed configuration. Finally, the paper presents a general view of the future studies on hood modal response.

Seizure After Ischemic Stroke; A Diagnostic and Management Challenge in a Resource Limited Setting: A Case Report

Background: Poststroke seizures occur in 6-8% of the adult population that suffer an ischaemic stroke. This pathological process increases metabolic stress and cell death, the extent of vascular obstruction in the brain, the mortality rate and long term morbidity. Poststroke seizures represent one of the most important complications of stroke that must be recognised and treated in a timely fashion. These are classified as either early or late depending on the time of onset after stroke. Case Report: A 51 year old woman presented to the Emergency Department of RSUD Dr Murjani following a generalised tonic-clonic seizure 3 hours prior that had lasted for two minutes. On arrival the patient subsequently had two further generalised tonic-clonic seizures with a one hour interval between. Whole body stiffness and a fixed upward gaze were observed. A non-contrast CT Head displayed a diffuse infarct of the left frontotemporoparietooccipital lobes. The patient had a history of stroke one year previously and a second stroke one month ago with resultant persistent weakness of the right upper and lower limbs. This patient was diagnosed with poststroke seizure of late onset and treated in hospital with diazepam 10mg and phenytoin 100mg three times per day. Discussion: Poststroke seizure is described as either early-onset (occurring in the first week after a stroke) or late-onset (occurring after the first week). Based on the International League Against Epilepsy (ILAE) definition, a single unprovoked late-onset poststroke seizure occurring more than seven days after a stroke is considered as epilepsy with a high risk (>60%) of recurrent seizures that may occur for up to ten years thereafter. Hence this risk factor must be identified and treated correctly to prevent significantly increased morbidity for the patient

Body Stiffness Control for Using Body-Environment Interaction with a Closed-Link Deformable Mobile Robot

It is necessary for the robot to use interactions from the environment through the body in order to adaptively move through various environments. When the robot is faced with a narrow path or a space with many pillars, it should be able to use its interaction with the environment to thin its own shape, i.e., it should have a flexible body. In contrast, in the case where we want the robot to move forward powerfully on a slope or uneven terrain (small steps), it is preferable for the robot to rigidify its own body and exert a strong propulsive force in response to interactions from the environment. In this paper, we present an idea of a mobile robot that can adjust its body flexibility (stiffness) to realize such adaptive behavior, and furthermore, we demonstrate its validity through experiments. Specifically, we propose a closed-link deformable mobile robot whose stiffness can be adjusted by indirectly driving joints. We design a function that increases the stiffness of the body by controlling the joints to follow the target angle quickly, and a function that decreases the stiffness of the body by controlling the joints to follow the angle slowly. The effectiveness of a robot that can adjust its stiffness is demonstrated through experiments of traversing narrow paths and steps. We also discuss propulsion control that takes advantage of the deformable mobile robot and its applicability to uneven slopes due to the flexibility of the links.

A Soft-Bodied Aerial Robot for Collision Resilience and Contact-Reactive Perching.

Current aerial robots demonstrate limited interaction capabilities in unstructured environments when compared with their biological counterparts. Some examples include their inability to tolerate collisions and to successfully land or perch on objects of unknown shapes, sizes, and texture. Efforts to include compliance have introduced designs that incorporate external mechanical impact protection at the cost of reduced agility and flight time due to the added weight. In this work, we propose and develop a lightweight, inflatable, soft-bodied aerial robot (SoBAR) that can pneumatically vary its body stiffness to achieve intrinsic collision resilience. Unlike the conventional rigid aerial robots, SoBAR successfully demonstrates its ability to repeatedly endure and recover from collisions in various directions, not only limited to in-plane ones. Furthermore, we exploit its capabilities to demonstrate perching where the three-dimensional collision resilience helps in improving the perching success rates. We also augment SoBAR with a novel hybrid fabric-based bistable (HFB) grasper that can utilize impact energies to perform contact-reactive grasping through rapid shape conforming abilities. We exhaustively study and offer insights into the collision resilience, impact absorption, and manipulation capabilities of SoBAR with the HFB grasper. Finally, we compare the performance of conventional aerial robots with the SoBAR through collision characterizations, grasping identifications, and experimental validations of collision resilience and perching in various scenarios and on differently shaped objects.

Evolution Mechanism and Control of Floor Heave in the Deep Roadway with Retained Bottom Coal

Roadways with retained bottom coal are common in thick coal seam mining, and floor heaving is a prominent problem. In this study, based on the interaction between the floor and two sides of the roadway-surrounding rock, a Winkler elastic foundation beam model is established to analyze the floor heave problem. A 3DEC model was used to analyze the failure range, failure mode, and migration law of the floor-surrounding rock with different bottom coal thicknesses and coal body strengths. The results show that (1) an increase in the thickness of the bottom coal results in a decrease in the stiffness of the roadway side coal body (the foundation of the supporting rock layer) and an increase in the bending deformation range, the amount of floor rock beam deformation, and the extrusion force. This leads to an expansion in the range of the sides of the coal body that are squeezed by the floor rock layer, resulting in additional failure and deformation of the coal body sides. Therefore, the damage to the floor rock layer is extended and increased. (2) The expansion of the floor pressure-bearing arch and surrounding rock in the arch are the causes of floor heave in the deep coal roadway with retained bottom coal. (3) Because of an increase in the thickness of the bottom coal and a decrease in the coal body strength, the floor pressure-bearing arch expands to the deeper part; thus, the range of surrounding rock in the arch with deformation and failure increases, resulting in an increase in floor heave. The field practice indicates that the support strategy of the “high prestressed strong rock bolt (cable) supporting two sides and bottom corners in time” can effectively control the floor heave of a roadway with retained bottom coal.

Stiffness of gangue backfilling body in goaf and its influence mechanism on rock strata control and stress evolution in gangue backfill mining

To study the influence mechanism of gangue backfilling material (GBM) with different particle sizes on overburden deformation, the particle movement characteristics and the mechanism of stiffness difference with different particle sizes of GBM were analysed by physical compression and particle flow numerical simulations. Then, combined with a similar material simulation method, the deformation characteristics of roof overburden and the evolution process of floor stress in backfill mining with backfilling bodies of different stiffness levels were studied. The results indicate that the subsidence decreased monotonously with a decrease in the particle size, and the stiffness of the GBM increased significantly under the same vertical load. The small-particle gangue moved downward in the layered law under the same load conditions, while the large-particle gangue moved downward through rotation, rubbing, crushing, and filling interaction processes. In the treatment of goaf by the backfilling method, the entire process of overlying strata movement mainly experienced bending, micro-fracture, separation, compaction, and new fracture, and the anti-deformation capacity of the backfilling body directly determined the deformation and movement of the overburden strata in a goaf. In the backfilling method, the greater the stiffness of the filling body, the smaller the advanced support pressure, and the more effective it was to inhibit pressure relief from the floor.

Mechanical Properties of GFRP Bolts and Its Application in Tunnel Face Reinforcement

As a new type of pre-reinforcement material for tunnel faces, glass fiber-reinforced polymer (GFRP) bolts can effectively and safely improve the stability of tunnel faces in soft surrounding rocks and speed up excavation. Therefore, in this paper, systematic research is carried out on the bond strength of GFRP bolts in tunnel faces and their relative pre-reinforcement parameters. Firstly, the effects of rebar diameter, anchorage length, and mortar strength on the bonding properties of GFRP bars were studied by indoor pull-out tests. The bond strength-slip curves under different working conditions were obtained, and the curves showed that the ultimate bond strength between GFRP bars and mortar was negatively correlated with the diameter of GFRP bars but positively correlated with the strength of the mortar. In addition, the increase in anchorage length led to a reduction in bonding strength. Secondly, inverse analysis was used to analyse the mechanical parameters of the bond performance of the anchor bars by the finite difference software FLAC3D, and the results indicated that 1/5 of the compressive strength of the GFRP bar grouting body can be taken as the ultimate bond strength to calculate the cohesive strength of the grout. Additionally, the formula of GFRP bar grouting body stiffness was revised. Finally, based on the results of laboratory tests and the inverse analysis, the numerical simulation analysis results showed that the optimal reinforcement configuration for a shallow buried tunnel face surrounded by weak rock is to use GFRP bars with a length of 17 m arranged in the center circle of the tunnel face with a reasonable reinforcement density of 1.0 bolt/m2. The calculation formula of the stiffness and cohesion strength of the GFRP bar grouting body and the reinforcement scheme proposed in this paper can provide a reference for the construction of shallowly buried rock tunnels in soft surrounding rock.

AI Application for Body Stiffness in Parkinsons Disease

Abstract: National projections indicate that the number of people over 60 years old is expected to increase, bringing with it an increase in the number of people affected by Parkinson's Disease (PD). This makes PD an important public health problem. Therefore, the development of effective approaches for intervention in people with Parkinson's disease needs to be more thoroughly investigated. End-to-end application will make exercising at home more convenient for patients. We can project prescribed exercises and determine whether the patient is completing them correctly. The Flutter app enables patients to register themselves, communicate with specialists over the app, and make virtual appointments. The pose detection library will help us detect angles of the exercises, and determine whether patients are performing them correctly

Mechanics and optimization of undulatory locomotion in different environments, tuning geometry, stiffness, damping and frictional anisotropy.

One of the oldest yet most common modalities of locomotion known among limbless animals is undulatory, also recognized for its stability compared to legged locomotion. Multiple forms of active mechanisms, e.g. active gait control, and passive mechanisms, e.g. body morphology and material properties, have adapted to different environments. The current research explores the passive role of body stiffness and internal losses in meeting terrain requirements. Furthermore, it addresses the influence of the environment on the resultant gait and how the interplay between various environments and body properties can lead to different speeds. We modelled undulatory locomotion in a dry friction environment where frictional anisotropy determines propulsion. We found that the body stiffness, the moment of inertia, the dry frictional coefficient ratio between normal and tangential frictional constants, and the internal damping of the body play an essential role in optimizing speed and animal adaptability to external conditions. Furthermore, we demonstrate that various known gaits like swimming, crawling and polychaete-like locomotion are achieved as a result of the interaction between body and environment parameters. Moreover, we validated the model by retrieving a corn snake's speed using data from the literature. This study demonstrates that the dependence between morphology, body material properties and environment can be exploited to design long-segmented robots to perform in specialized situations.