Initial Posture Research Articles

Is the Force-Velocity Profile for Free Jumping a Sound Basis for Individualized Jump Training Prescriptions?

Formulating individualized optimized jump training prescriptions based on the force-velocity profile has become popular, but its effectiveness has been contested. Such training programs have opposite effects on 'maximal average force' and 'maximal average shortening velocity', and we set out to investigate which training-induced changes in the neuromuscular system could cause such effects. We used a musculoskeletal simulation model with four body segments and six muscle-tendon actuators to simulate vertical squat jumps with different loads. Independent input was muscle stimulation over time, which was optimized for maximal jump height. We determined the force-velocity profile for a reference model and investigated how it changed when we modified muscle properties and initial postures. We could not reproduce the reported training effects by realistically improving muscle properties (maximal force, shortening velocity and rate of force development) or modifying initial postures of the model. However, the profile was very sensitive to gains in jump height at low-loads but not high loads, or vice versa. Reaching maximal height in force-velocity profile jumps requires skill. We argued that submaximal performance in low-load or high-load jumps caused by lack of skill could be responsible for large imbalances in profiles before training. Differential skill training promoted by the individualized optimized approach could explain quick changes toward a balanced profile. If the success of individualized optimized training studies is explained by selective skill improvements, training effects are unlikely to transfer to other tasks, and individualized optimized training will not be superior to other types of training.

One-Side Weight Sports and the Impact of Their Load on the Feet and the Occurrence of Posture Disorders in Professional Football and Handball Players

The aim of this study was to evaluate center of pressure (CoP) changes in unilateral sports and examine how these changes affect the athlete’s feet, ankles, knees or posture. The study sample consisted of 40 professional male players (age: 19.4 ± 2.08 years; height: 165.78 ± 4.92 cm; weight: 59.04 ± 4.02 kg; BMI: 21.57 ± 2.22; foot size: 40.9 ± 1.6), divided by type of sport into group H—handball (n: 20) and group F—football (n: 20). To evaluate the monitored parameters, we used the instrumental diagnostic techniques: 3D laser footscan, baropodometric platform FreeStep and 2D Videography. We found no significant differences between the groups in the loading of the right and left foot (F: 8.3 ± 4.22; H: 7.7 ± 6.1) (p = 0.410). We found a significant difference in the load on the front and back of the left (p = 0.0079) and right foot (p = 0.0210) depending on the type of sport performed. Maximum and mean values of CoP (g/cm2) showed statistically significant differences depending on the sport performed (p < 0.0001). The shift in CoP (mm) from the norm depending on the sport performed was confirmed in the latero-lateral direction (p = 0.003), but not in the antero-posterior direction (p = 0.320). We found a difference in the angulation of the knees and heels depending on the sport played. Handball players showed higher knee varosity/valgosity (p = 0.015) and heel values than football players (p = 0.002). The handball players also confirmed a worse postural load and initial forward posture. The one-sided sports, handball and football, showed negative effects on the athlete’s movement system. These changes were more pronounced in handball players. Proper training programs should be applied in athletes’ daily routine to improve the negative effects of unilateral sports.

Corticospinal excitability during motor preparation of upper extremity reaches reflects flexor muscle synergies: A novel principal component-based motor evoked potential analyses.

Previous research has shown that noninvasive brain stimulation can be used to study how the central nervous system (CNS) prepares the execution of a motor task. However, these previous studies have been limited to a single muscle or single degree of freedom movements (e.g., wrist flexion). It is currently unclear if the findings of these studies generalize to multi-joint movements involving multiple muscles, which may be influenced by kinematic redundancy and muscle synergies. The objective of this study was to characterize corticospinal excitability during motor preparation in the cortex prior to functional upper extremity reaches. 20 participants without neurological impairments volunteered for this study. During the experiment, the participants reached for a cup in response to a visual "Go Cue". Prior to movement onset, we used transcranial magnetic stimulation (TMS) to stimulate the motor cortex and measured the changes in motor evoked potentials (MEPs) in several upper extremity muscles. We varied each participant's initial arm posture and used a novel synergy-based MEP analysis to examine the effect of muscle coordination on MEPs. Additionally, we varied the timing of the stimulation between the Go Cue and movement onset to examine the time course of motor preparation. We found that synergies with strong proximal muscle (shoulder and elbow) components emerged as the stimulation was delivered closer to movement onset, regardless of arm posture, but MEPs in the distal (wrist and finger) muscles were not facilitated. We also found that synergies varied with arm posture in a manner that reflected the muscle coordination of the reach. We believe that these findings provide useful insight into the way the CNS plans motor skills.

Optimizing PID control for enhanced stability of a 16‐DOF biped robot during ditch crossing

AbstractThe current research article discusses the design of a proportional–integral–derivative (PID) controller to obtain the optimal gait planning algorithm for a 16‐degrees‐of‐freedom biped robot while crossing the ditch. The gait planning algorithm integrates an initial posture, position, and desired trajectories of the robot's wrist, hip, and foot. A cubic polynomial trajectory is assigned for wrist, hip, and foot trajectories to generate the motion. The foot and wrist joint angles of the biped robot along the polynomial trajectory are obtained by using the inverse kinematics approach. Moreover, the dynamic balance margin was estimated by using the concept of the zero‐moment point. To enhance the smooth motion of the gait planner and reduce the error between two consecutive joint angles, the authors designed a PID controller for each joint of the biped robot. To design a PID controller, the dynamics of the biped robot are essential, and it was obtained using the Lagrange–Euler formulation. The gains, that is, KP, KD, and KI of the PID controller are tuned with nontraditional optimization algorithms, such as particle swarm optimization (PSO), differential evolution (DE), and compared with modified chaotic invasive weed optimization (MCIWO) algorithms. The result indicates that the MCIWO‐PID controller generates more dynamically balanced gaits when compared with the DE and PSO‐PID controllers.

Influence of initial belt torso contact on the kinematics and kinetics of booster-seated ATDs in frontal-oblique impacts

Objective Varying initial belt torso contact (i.e., belt gap) on belt-positioning boosters may have implications for potential shoulder belt slip-off in low-speed evasive vehicle maneuvers and differences in dynamic outcomes in frontal sled tests. This study evaluated the influence of initial booster belt gap and belt fit conditions on the kinematic and kinetic outcomes during frontal oblique impacts. Methods Frontal oblique (+15° from frontal) sled tests (n = 18; 23.6 ± 0.1 g at 12.4 ± 0.1 ms) were conducted using the Q-Series 6-year-old (Q6) and 10-year-old (Q10) and the Large Omni Directional Child (LODC) anthropomorphic test devices (ATDs). Various initial belt fit and belt gap conditions were investigated by evaluating each ATD on 2 high-back (HB), 3 low-back (LB), and 1 low-profile (Low) booster. Initial belt fit and belt gap were quantified, and boosters were categorized as “smaller gap” or “larger gap” for comparison. Results Larger-gap boosters produced greater peak lumbar FY and MZ (HB: −23.2 ± 8.8 Nm, LB: −23.6 ± 9.7 Nm) compared to smaller-gap boosters (HB: −12.6 ± 4.4 Nm, LB/Low: −12.4 ± 7.2 Nm) for the LODC and Q10. Peak axial torso rotations were also observed for larger-gap LB (38.6°) compared to smaller-gap LB boosters (23.8°), and the LODC experienced greater peak thoracic rotations on larger-gap boosters compared to smaller-gap boosters. These results suggest that ATDs on larger-gap boosters experienced greater torso rotation and lumbar MZ due to lack of initial contact between the shoulder belt and inferior torso. No ATDs experienced complete shoulder belt slip-off; however, larger-gap boosters displayed more visual evidence of outboard shoulder belt positioning at the time of peak forward head excursion. Conclusion This study provides a novel investigation on the role of initial belt fit and belt gap metrics on the dynamic response of booster-seated ATDs in frontal oblique impacts. Larger-gap boosters allowed the torso to undergo greater axial rotation before restraint was provided by the shoulder belt to the lower torso. Increased shoulder rotations may indicate greater propensity for shoulder belt slip-off in more severe crashes, in oblique maneuvers, or with variations in initial occupant posture. These results suggest the importance of continued evaluation of the implications of initial belt gap provided by boosters and the importance of evaluating lumbar FY and MZ and useful metrics for discrimination of differences in ATD response across booster designs.

Tree frogs Polypedates Dennysi landing on horizontal perches: the effects of perch diameters.

Secure landing is indispensable for both leaping animals and robotics. Tree frogs, renowned for their adhesive capabilities, can effectively jump across intricate 3D terrain and land safely. Compared to jumping, the mechanisms underlying their landing technique, particularly in arboreal environments, have remained largely unknown. In this study, we focused on the landing patterns of the tree frogs Polypedates Dennysi on horizontally placed perches, explicitly emphasizing the impact of perch diameters. Tree frogs demonstrated diverse landing postures, including the utilization of (1) single front foot, (2) double front feet, (3) anterior bellies, (4) middle bellies, (5) posterior bellies, (6) single hind foot, or (5) double hind feet. Generally, tree frogs favour bellies on slimmer targets but double front feet on large perches. Analysis of limb-trunk relationships revealed their adaptability to modifying postures, including body positions and limb orientations, for successful landing. The variations in the initial landing postures affect the succeeding landing procedures and, consequently, the dynamics. As the initial contact position was switched from front foot to hind foot, the stabilization time decreased first, reaching the minimum in middle belly landings, and then increased. The maximum vertical forces changed in an inverse trend, whereas the maximum fore-aft forces continuously increased as the initial contact position switched. As the perch diameter rose, the time expenses dropped, whereas the maximum impact increased. These findings not only added to our understanding of frog landings but also highlighted the necessity of considering perch diameters and landing styles when studying the biomechanics of arboreal locomotion.

Influence of car front-end designs on motorcyclists’ trajectory in head-on and side-on-head crashes

Motorcyclists are highly vulnerable road users, and cars are one of their primary crash opponents. This study investigates the influence of car front-end designs on motorcyclist trajectory in head-on and side-on-head crashes. The analysis is based on a dataset of 120 multi-body crash simulations conducted using MADYMO and post-processed with MATLAB. An analysis of 1412 real-world Powered Two-Wheeler (PTW) to car accidents was conducted to determine the most common crash configurations and the associated ranges of the variables, such as vehicle speeds and contact points. Three PTW styles (sport-touring, scooter, and sport) and four car front-end designs (Sport utility vehicle (SUV), Family Car/Sedan (FCR), Roadster (RDS), and Multi-purpose vehicle (MPV)) were considered.The study examined the riders’ thrown distance in both collision types. It was observed that, regardless of the collision type, the head was identified overall as the primary body region coming into contact with the opposing vehicle, followed by the chest and neck. In frontal collisions, an augmented bonnet height corresponded to an increased incidence of head contact, whereas a lower bonnet height resulted in a higher frequency of chest contact. Moreover, the thrown distance depended also on PTW speed, particularly for sport and sport-touring motorcycles. Notably, contact with the car windscreen was only observed at velocities exceeding 60 km/h, whereas impact with the bonnet leading edge occurred exclusively below this threshold. Due to the shielding effect of their PTW’s fairing, scooter riders predominantly experienced no contact with the opposing vehicle. Sport-touring motorcycles exhibited a more vertical trajectory upon ejection, leading to a greater likelihood of overturning and subsequent rearward head impact with the vehicle. In contrast, sport motorcycles tended to forward projections with a high likelihood of chest contact. In the case of lateral impacts, it was observed that vehicles with a more prominent profile, such as SUVs and MPVs, equipped with protruding bumpers, effectively restrained riders. In this case, vehicle speed did not exert a significant influence on the thrown distance. Additionally, the presence of a conspicuous fuel tank and the initial posture of the rider on the PTW played a crucial role in determining the final thrown distance. Due to their upright postures and the absence of a pronounced fuel tank, scooter dummies were thrown further than others, thus causing head contact with the windscreen.These findings highlight the importance of car front-end design and PTW fairings in mitigating riders’ injuries and provide valuable insights to vehicle manufacturers for developing tailored safety measures for riders.

Temporal segmentation of motion propagation in response to an external impulse

In high-density crowds, local motion can propagate, amplify, and lead to macroscopic phenomena, including ”density waves”. These density waves only occur when individuals interact, and impulses are transferred to neighbours. How this impulse is passed on by the human body and which effects this has on individuals is still not fully understood. To further investigate this, experiments focusing on the propagation of a push were conducted within the EU-funded project CrowdDNA. In the experiments the crowd is greatly simplified by five people lining up in a row. The rearmost person in the row was pushed forward in a controlled manner with a punching bag. The intensity of the push, the initial distance between participants and the initial arm posture were varied. Collected data included side view and top view video recordings, head trajectories, 3D motion using motion capturing (MoCap) suits as well as pressure measured at the punching bag. With a hybrid tracking algorithm, the MoCap data are combined with the head trajectories to allow an analysis of the motion of each limb in relation to other persons.The observed motion of the body in response to the push can be divided into three phases. These are (i) receiving an impulse, (ii) receiving and passing on an impulse, and (iii) passing on an impulse. Using the 3D MoCap data, we can identify the start and end times of each phase. To determine when a push is passed on, the forward motion of the person in front has to be considered. The projection of the center of mass relative to the initial position of the feet is a measure of the extent to which a person is displaced from the rest position. Specifying the timing of these phases is particularly important to distinguish between different types of physical interactions. Our results contribute to the development and validation of a pedestrian model for identifying risks due to motion propagation in dense crowds.

Investigation on vehicle occupant dummy applicability for under-foot impact loading conditions

PurposeUnder-foot impact loadings can cause serious lower limb injuries in many activities, such as automobile collisions and underbody explosions to military vehicles. The present study aims to compare the biomechanical responses of the mainstream vehicle occupant dummies with the human body lower limb model and analyze their robustness and applicability for assessing lower limb injury risk in under-foot impact loading environments. MethodsThe Hybrid III model, the test device for human occupant restraint (THOR) model, and a hybrid human body model with the human active lower limb model were adopted for under-foot impact analysis regarding different impact velocities and initial lower limb postures. ResultsThe results show that the 2 dummy models have larger peak tibial axial force and higher sensitivity to the impact velocities and initial postures than the human lower limb model. In particular, the Hybrid III dummy model presented extremely larger peak tibial axial forces than the human lower limb model. In the case of minimal difference in tibial axial force, Hybrid III's tibial axial force (7.5 KN) is still 312.5% that of human active lower limb's (2.4 KN). Even with closer peak tibial axial force values, the biomechanical response curve shapes of the THOR model show significant differences from the human lower limb model. ConclusionBased on the present results, the Hybrid III dummy cannot be used to evaluate the lower limb injury risk in under-foot loading environments. In contrast, potential improvement in ankle biofidelity and related soft tissues of the THOR dummy can be implemented in the future for better applicability.

Biomimetic learning of hand gestures in a humanoid robot.

Hand gestures are a natural and intuitive form of communication, and integrating this communication method into robotic systems presents significant potential to improve human-robot collaboration. Recent advances in motor neuroscience have focused on replicating human hand movements from synergies also known as movement primitives. Synergies, fundamental building blocks of movement, serve as a potential strategy adapted by the central nervous system to generate and control movements. Identifying how synergies contribute to movement can help in dexterous control of robotics, exoskeletons, prosthetics and extend its applications to rehabilitation. In this paper, 33 static hand gestures were recorded through a single RGB camera and identified in real-time through the MediaPipe framework as participants made various postures with their dominant hand. Assuming an open palm as initial posture, uniform joint angular velocities were obtained from all these gestures. By applying a dimensionality reduction method, kinematic synergies were obtained from these joint angular velocities. Kinematic synergies that explain 98% of variance of movements were utilized to reconstruct new hand gestures using convex optimization. Reconstructed hand gestures and selected kinematic synergies were translated onto a humanoid robot, Mitra, in real-time, as the participants demonstrated various hand gestures. The results showed that by using only few kinematic synergies it is possible to generate various hand gestures, with 95.7% accuracy. Furthermore, utilizing low-dimensional synergies in control of high dimensional end effectors holds promise to enable near-natural human-robot collaboration.

Stable posture tracking for modular spatial hyper-redundant serial arms using selective control points

ABSTRACT Robotic arms with redundant degrees of freedom are known to exhibit characteristics that make them more suitable than their non-redundant counterparts in many manipulation tasks. These redundant degrees of freedom allow for multiple control objectives to be pursued simultaneously leading to increased efficiency, dexterity and versatility. Redundancy however brings about structural complexity, difficulties in tasks specification, challenging kinematics and dynamics and high computational cost. This work tackles kinematic hyper redundancy resolution in the context of posture (shape) control of a modular serial link arm by proposing a new take on formulating and solving the problem. In the proposed formulations, strategic points along the arm (termed control points) are explicitly controlled in such way that their overall motion steers the posture of the arm toward the desired target posture. These control points stem from the modular structure of the arm and are chosen in order to achieve specific control characteristics. Desired target posture outlines are specified intuitively and arbitrarily with continuous spline curves. The proposed method has demonstrated the ability to safely steer the arm towards intermediate postures which reduce the overall posture tracking error. It copes well with singularities and is capable of tracking target postures that are significantly distinct from the arm's initial posture. Numerical simulations on a 40 DOF arm are conducted to assess the validity and performance of the method.

PoseNormNet: Identity-Preserved Posture Normalization of 3-D Body Scans in Arbitrary Postures

3D human models accurately represent the shape of the subjects, which is key to many human-centric industrial applications, including fashion design, body biometrics extraction, and computer animation. These tasks usually require a high-fidelity human body mesh in a canonical posture (e.g., ‘A’ pose or ‘T’ pose). Although 3D scanning technology is fast and popular for acquiring the subject's body shape, automatically normalizing the posture of scanned bodies is still under-researched. Existing methods highly rely on skeleton-driven animation technologies. However, these methods require carefully-designed skeleton and skin weights, which is time-consuming and fails when the initial posture is complicated. In this work, a novel deep learning-based approach, dubbed PoseNormNet, is proposed to automatically normalize the postures of scanned bodies. The proposed algorithm provides strong operability since it does not require any rigging priors and works well for subjects in arbitrary postures. Extensive experimental results on both synthetic and real-world datasets demonstrate that the proposed method achieves state-of-the-art performance in both objective and subjective terms.

Discovering individual-specific gait signatures from data-driven models of neuromechanical dynamics.

Locomotion results from the interactions of highly nonlinear neural and biomechanical dynamics. Accordingly, understanding gait dynamics across behavioral conditions and individuals based on detailed modeling of the underlying neuromechanical system has proven difficult. Here, we develop a data-driven and generative modeling approach that recapitulates the dynamical features of gait behaviors to enable more holistic and interpretable characterizations and comparisons of gait dynamics. Specifically, gait dynamics of multiple individuals are predicted by a dynamical model that defines a common, low-dimensional, latent space to compare group and individual differences. We find that highly individualized dynamics-i.e., gait signatures-for healthy older adults and stroke survivors during treadmill walking are conserved across gait speed. Gait signatures further reveal individual differences in gait dynamics, even in individuals with similar functional deficits. Moreover, components of gait signatures can be biomechanically interpreted and manipulated to reveal their relationships to observed spatiotemporal joint coordination patterns. Lastly, the gait dynamics model can predict the time evolution of joint coordination based on an initial static posture. Our gait signatures framework thus provides a generalizable, holistic method for characterizing and predicting cyclic, dynamical motor behavior that may generalize across species, pathologies, and gait perturbations.

ANALISIS ERGONOMIS PADA ALAT MINI CULTIVATOR PENGOLAH LAHAN PERTANIAN BERDASARKAN METODE NBM DAN OWAS

This research aims to: (1) Analyzing the ergonomics of mini cultivator tools based on the Nordic Body Map (NBM) method, and (2) Analyzing the ergonomics of mini cultivator tools based on the Ovako Working Posture Analysis System (OWAS) method. The method in this study was experimental, and the data were analyzed by quantitative descriptive method. The research sample amounted to 5 farmers. The results showed that in the initial posture, namely the upright back position, a score of 1122 category 1 was obtained, which means that the posture is not dangerous and does not need to be improved. In the work posture when running the mini cultivator tool, a score of 2173 category 3 is obtained, which means that the straight work posture must be improved immediately. The results of filling out the NBM questionnaire show that farmers still feel "a little sick" in straight work postures. Meanwhile, the turning posture obtained a score of 4173 category 3 which means that immediate improvement is needed. The results of filling out the NBM questionnaire show that farmers still feel "very sick" in the turning posture. Thus, the mini cultivator tool still needs improvement in several aspects of ergonomics and is discussed in the results of this study

A Radiotherapy Positioning Method for Both Coarse Guidance and Precise Verification Based on Integration of AR and Optical Surface Imaging

Traditional methods of radiotherapy positioning have shortcomings such as fragile skin-markers, additional doses and lack of information integration. Emerging technologies may provide alternatives for the relevant clinical practice. We proposed a noninvasive radiotherapy positioning method integrating augmented reality (AR) and optical surface, and evaluated its feasibility in clinical workflow. AR and structured light-based surface were integrated to implement the coarse-to-precise positioning through two coherent steps, i) the AR-based coarse guidance. To implement quality assurance, recognition of face and pattern was used for patient authentication, case association and accessory validation in AR scenes. The holographic images reconstructed from simulation computed tomography (CT) images, guided the initial posture correction by virtual-real alignment. ii) optical surface-based precise verification. The point clouds were fused, with the calibration and pose estimation of structured light cameras, and segmented according to the preset regions of interest (ROIs). The global-to-local registration for cross-source point clouds was achieved to calculate couch shifts in 6 degrees-of-freedom (DoF), which were ultimately transmitted to AR scenes. The evaluation based on phantom and human-body (4 volunteers) included, i) quality assurance workflow, ii) errors of both steps and correlation analysis, and iii) receiver operating characteristic (ROC). The maximum errors in phantom evaluation were 3.4±2.5 mm in Vrt and 1.4±1.0° in Pitch for the coarse guidance step, while 1.6±0.9 mm in Vrt and 0.6±0.4° in Pitch for the precise verification step. The Pearson correlation coefficients between precise verification and cone beam CT (CBCT) results were distributed in the interval [0.81, 0.85]. In ROC analysis, the areas under the curve (AUC) were 0.87 and 0.89 for translation and rotation respectively. In human body-based evaluation, the errors of thorax and abdomen (T&A) were significantly greater than those of head and neck (H&N) in Vrt (2.6±1.3 vs. 1.7±1.1, p<0.01), Lng (2.4±1.3 vs. 1.4±0.1, p<0.01) and Rtn (0.8±0.5 vs. 0.6±0.4, p = 0.03) while relatively similar in Lat (1.7±1.0 vs. 1.9±1.1, p = 0.13). The combination of AR and optical surface has utility and feasibility for patient positioning, in terms of both safety and accuracy.

One-piece knitted embedded hang-needle sensor for shoulder posture recognition

Wearable products have significant applications in medical assistance, posture correction, and humancomputer interaction. In this study, we present a knitting method for a one-piece knitted embedded hang-needle sensor. This method involves simultaneously knitting conductive yarn into the sensing zone while creating the monitoring garment in a seamless manner. By implementing a tight hanging needle structure in the sensing zone design and adjusting knitting parameters, the effect of pre-stretching on the sensor caused by the base garment is minimized. Furthermore, integrating the sensing area of the hang-needle structure with the monitoring garment eliminates the need for additional sensor integration steps and simplifies the preparation process, resulting in reduced time and material costs. Moreover, the monitoring garment offers a comfortable wearing experience without any foreign body sensation and accurately captures the initial shoulder posture of the wearer.

Grip selection without tool knowledge: end-state comfort effect in familiar and novel tool use.

A well-known phenomenon for the study of movement planning is the end-state comfort (ESC) effect: When they reach and grasp tools, individuals tend to adopt uncomfortable initial hand postures if that allows a subsequent comfortable final posture. In the context of tool use, this effect is modulated by tool orientation, task goal, and cooperation. However, the cognitive bases of the ESC effect remain unclear. The goal of this study was to determine the contribution of semantic tool knowledge and technical reasoning to movement planning, by testing whether the ESC effect typically observed with familiar tools would also be observed with novel tools. Twenty-six participants were asked to reach and grasp familiar and novel tools under varying conditions (i.e., tool's handle downward vs. upward; tool transport vs. use; solo vs. cooperation). In our findings, the effects of tool orientation, task goal and cooperation were replicated with novel tools. It follows that semantic tool knowledge is not critical for the ESC effect to occur. In fact, we found an "habitual" effect: Participant adopted uncomfortable grips with familiar tools even when it was not necessary (i.e., to transport them), probably because of the interference of habitual movement programming with actual movement programming. A cognitive view of movement planning is proposed, according to which goal comprehension (1) may rely on semantic tool knowledge, technical reasoning, and/or social skills, (2) defines end-state configuration, which in turn (3) calibrates beginning-state comfort and hence the occurrence of the ESC effect.

Trajectory planning method for docking of large aircraft components

PurposeIn the digital assembly system of large aircraft components (LAC), the docking trajectory of LAC is an important factor affecting the docking accuracy and stability of the LAC. The main content of docking trajectory planning is how to move the LAC from the initial posture and position to the target posture and position (TPP). This paper aims to propose a trajectory planning method of LAC based on measured data.Design/methodology/approachFirst, the posture and position error model of the wing is constructed according to the measured data of the measurement points (MPs) and the fork lug joints. Second, the particle swarm optimization algorithm based on the dynamic inertia factor is used to optimize the TPP of the wing. Third, to ensure the efficiency and stability of posture adjustment, the S-shaped curve is used as the motion trajectory of LAC, and the parameters of the trajectory are solved by the generalized multiplier method. Finally, a series of docking experiments are carried out.FindingsDuring the process of posture adjustment, the motion of the numerical control locator (NCL) is stable, and the interaction force between the NCLs is always within a reasonable range. After the docking, the MPs are all within the tolerance range, and the coaxiality error of the fork lug hole is less than 0.2 mm.Originality/valueIn this paper, the measured data rather than the theoretical design model is used to solve the TPP, which improves the docking accuracy of LAC. Experiment results show that the proposed trajectory method can complete the LAC docking effectively and improve the docking accuracy.

Choice of end-state comfort is dependent upon the time spent at the beginning-state and the precision requirement of the end-state

Choice of posture while grasping an object typically depends upon several factors including the time spent in that posture, what postures were held prior to choosing that posture, and the precision required by the posture. The purpose of this study was to test choice of end-state thumb-up posture based on time spent at the beginning-state and the precision requirement of the end-state. To determine choice of thumb-up based on time or precision, we varied how long a subject had to hold the beginning state before moving an object to an end location. We made end-state precision either small or large and eliminated the precision needed to stand the object up at the end of the movement. A choice between “comfort” at the beginning or precision at the end-state would be demanded by the conditions with long beginning-state hold times and high precision demands. We aimed to determine which aspect of movement was of greater importance to individuals, overall “comfort” or precision. When the requirement was to hold the initial grasp longer, and the end-target was large, we predicted that we would see more thumb-up postures adopted at the beginning state. When the final placement was small and the initial posture was not constrained, we predicted we would see thumb-up postures adopted at the end state. On average, we found that, as beginning-state grasp time increased, more individuals chose beginning-state thumb-up postures. Perhaps, not surprisingly, we found distinct individual differences within our sample. Some individuals seemed to choose beginning-state thumb-up postures nearly 100% of the time, while other individuals chose end-state thumb-up postures nearly 100% of the time. Both the time spent in a posture and its precision requirements influenced planning, but not necessarily in a systematic way.

Humans need only 200 ms to generate posture-specific muscle activation patterns for successful vertical jumps in reaction to an auditory trigger.

It is currently unknown how the central nervous system controls ballistic whole-body movements like vertical jumps. Here we set out to study the time frame of generating muscle activation patterns for maximum-effort jumps from different initial postures. We had ten healthy male participants make a slow countermovement from an upright position and initiate a maximal vertical jump as soon as possible following an auditory trigger. The trigger was produced when hip height dropped below one of three preselected values, unknown in advance to the participant, so that the participant was uncertain about the posture from which to initiate the jump. Furthermore, we determined the ensuing bottom postures reached during jumps, and from these postures had the participants perform maximum-effort squat jumps in two conditions: whenever they felt ready, or as soon as possible following an auditory trigger. Kinematics and ground reaction forces were measured, and electromyograms were collected from gluteus maximus, biceps femoris, rectus femoris, vastus lateralis, gastrocnemius and soleus. For each muscle, we detected activation onsets, as well as reaction times defined as the delay between trigger onset and activation onset. In the jumps preceded by a slow countermovement, the posture from which to initiate the jump was unknown before trigger onset. Nevertheless, in these jumps, posture-specific muscle activation patterns were already released within 200 ms after trigger onset and reaction times were not longer and jump heights not less than in squat jumps from corresponding bottom postures. Our findings suggest that the generation of muscle activation patterns for jumping does not start before trigger onset and requires only about 200 ms.