Hopping Height Research Articles

Comparison of Time Needed to Meet Common Rehabilitation Milestones After Anterior Cruciate Ligament Reconstruction According to Graft Type

Background: The use of bone–patellar tendon–bone (BPTB) and hamstring tendon (HT) autografts is common in anterior cruciate ligament reconstruction (ACLR). After ACLR, patients typically progress through specific rehabilitation milestones, and graft type may play a role in patient progression. Purpose: To compare the time to meet rehabilitation milestones between BPTB and HT autografts after ACLR. Design: Cohort study; Level of evidence, 3. Methods: This was a single-institution study on patients who underwent ACLR with either BPTB or HT autograft between June 2018 and July 2021. The primary outcomes were time to meet return-to-sport criteria, including >90% limb symmetry index (LSI) for isokinetic quadriceps and hamstring strength, horizontal hop, 4-crossover hop, and single-hop height. The time to satisfaction of each criterion was compared between graft groups using Wilcoxon tests and Cox proportional hazards models. Results: Included in the analysis were 410 participants who underwent ACLR with either BPTB (n = 232) or HT (n = 178). The BPTB group took longer to achieve >90% LSI for knee extension than HT (11.1 ± 4.1 vs 7.63 ± 2.8 months; P < .001). Similarly, the BPTB group took longer than the HT group to achieve >90% LSI for horizontal hop (11.4 ± 3.5 vs 9.82 ± 2.8 months; P < .001), 4-crossover hop (11.8 ± 3.6 vs 10.4 ± 2.8 months; P = .002), and single-hop height testing (11 ± 3.7 vs 8.81 ± 3.2 months; P < .001). The median time to achieve >90% LSI for hamstring strength was similar between groups (7.18 ± 3 vs 7.56 ± 3.1 months; P = .2). Conclusion: Patients that underwent ACLR with BPTB autograft took longer than patients with HT to meet commonly used postoperative rehabilitation milestones. Clinicians should consider these differences when guiding patients regarding graft choice, postoperative expectations, and rehabilitation.

Relationship between hamstring strength and hop performance at 8 and 12 months after ACL reconstruction with hamstring tendon autografts

BackgroundThe relationship between hamstring strength and hop performance after anterior cruciate ligament (ACL) reconstruction with hamstring tendon (HT) autografts has not been well elucidated. The aim was to investigate the relationship between eccentric hamstring strength, assessed with the NordBord, and concentric hamstring strength, assessed with the Biodex, with hop performance at 8 and 12 months after ACL reconstruction.MethodsRegistry study. Patients ≥ 16 years who had undergone primary ACL reconstruction with HT autograft, followed by muscle strength and hop tests at 8 and 12 months were included. Correlations of the relative hamstring strength (Nm/kg or N/kg) and limb symmetry index (LSI) with hop performance were analyzed. Pearson’s correlation coefficient, and coefficient of determination (r2) were used for statistical analysis.ResultsA total of 90 patients were included, of which 48 (53%) were women. The mean age at ACL reconstruction was 27.0 ± 8.0 years. Relative hamstring strength had significant positive correlations with hop performance, ranging from r = 0.25–0.66, whereas hamstring strength LSI had significant positive correlations which ranged from r = 0.22–0.37 at 8 and 12 months after ACL reconstruction. At 12 months, the relative hamstring strength in the Biodex explained 32.5–43.6% of the hop performance in vertical hop height, hop for distance relative to height, and the total number of side hops, whereas the relative hamstring strength in the NordBord explained 15.2–23.0% of the hop performance.ConclusionThe relative hamstring strength in the Biodex test explained 32.5–43.6% of the hop performance, whereas the relative hamstring strength in the NordBord explained 15.2–23.0%. Thus, our findings suggest that relative hamstring strength, especially in the hip-flexed position may be a better indicator of hop performance at 8 and 12 months after ACL reconstruction in patients treated with HT autograft.

Abnormal Lower Limb Biomechanics During a Bilateral Vertical Jump Despite the Symmetry in Single-Leg Vertical Hop Height in Athletes After ACL Reconstruction.

A limb symmetry index (LSI) of >90% for single-leg horizontal hop distance is recommended as a cutoff point for safe return to sports after anterior cruciate ligament reconstruction (ACLR). Despite achieving this threshold, abnormal lower limb biomechanics continue to persist in athletes after ACLR. Symmetry in single-leg vertical hop height appears to be more difficult to achieve and can be a better representation of knee function than single-leg horizontal hop distance. To explore whether an LSI of >90% for single-leg vertical hop height can represent normal lower limb biomechanics in athletes during a bilateral vertical jump after ACLR. Controlled laboratory study. According to the LSI for single-leg vertical hop height, 46 athletes who had undergone ACLR with an autologous ipsilateral bone-patellar tendon-bone or hamstring tendon graft were divided into a low symmetry group (LSI <90%; n = 23) and a high symmetry group (LSI >90%; n = 23), and 24 noninjured athletes were selected as the control group. The kinematic and kinetic characteristics during a bilateral vertical jump were compared between the low symmetry, high symmetry, and control groups. During the propulsion phase of the bilateral vertical jump, the operated side in the high symmetry group showed a lower knee extension moment than the nonoperated side (P = .001). At peak vertical ground-reaction force, the operated side in the high symmetry group showed a lower knee internal rotation moment compared with the control group (P = .016). Compared with the nonoperated side, the operated side in the high symmetry group showed a higher hip extension moment (P = .002), lower knee extension moment (P < .001), lower ankle plantarflexion moment (P < .001), and lower vertical ground-reaction force (P = .023). Despite achieving an LSI of >90% for single-leg vertical hop height, athletes after ACLR showed abnormal lower limb biomechanical characteristics during the bilateral vertical jump. Symmetrical single-leg vertical hop height may not signify ideal biomechanical or return-to-sports readiness in this population.

Linking muscle mechanics to the metabolic cost of human hopping.

Many models have been developed to predict metabolic energy expenditure based on biomechanical proxies of muscle function. However, current models may only perform well for select forms of locomotion, not only because the models are rarely rigorously tested across subtle and broad changes in locomotor task but also because previous research has not adequately characterised different forms of locomotion to account for the potential variability in muscle function and thus metabolic energy expenditure. To help to address the latter point, the present study imposed frequency and height constraints to hopping and quantified gross metabolic power as well as the activation requirements of medial gastrocnemius (MG), lateral gastrocnemius (GL), soleus (SOL), tibialis anterior (TA), vastus lateralis (VL), rectus femoris (RF) and biceps femoris (BF), and the work requirements of GL, SOL and VL. Gross metabolic power increased with a decrease in hop frequency and increase in hop height. There was no hop frequency or hop height effect on the mean electromyography (EMG) data of ankle musculature; however, the mean EMG of VL and RF increased with a decrease in hop frequency and that of BF increased with an increase in hop height. With a reduction in hop frequency, GL, SOL and VL fascicle shortening, fascicle shortening velocity and fascicle to MTU shortening ratio increased, whereas with an increase in hop height, only SOL fascicle shortening velocity increased. Therefore, within the constraints that we imposed, decreases in hop frequency and increases in hop height resulted in increases in metabolic power that could be explained by increases in the activation requirements of knee musculature and/or increases in the work requirements of both knee and ankle musculature.

Dipo: a miniaturized hopping robot via lightweight and compact actuator design for power amplification

Kangaroo rats are well known as representative hoppers in small-scale animals. Especially kangaroo rats show rapid movement when a predator approaches. If this amazing motion can be applied to small-scale robots, they will be able to traverse lands at high speed while overcoming size limitations. To take advantage of hopping locomotion, in this paper, we present a lightweight and small-scale clutch-based hopping robot called Dipo. To make this possible, a compact power amplifying actuation system has been developed using a power spring and an active clutch. The power spring is possible to take out and use the accumulated energy little by little whenever the robot starts to hop. Moreover, the power spring needs low torque to charge the elastic energy, and a only tiny space is required to install. The active clutch controls the motion of hopping legs by adjusting the timing of energy release and storage. Thanks to these design strategies, the robot weighs 45.07 g, has the height of 5 cm in the stance phase, and achieves the maximum hopping height of 54.9 cm.

Residual Deficits in Reactive Strength After Anterior Cruciate Ligament Reconstruction in Soccer Players.

Deficits in plyometric abilities are common after anterior cruciate ligament reconstruction (ACLR). Vertical rebound tasks may provide a targeted evaluation of knee function. To examine the utility of a vertical hop test for assessing function after ACLR and establishing factors associated with performance. Cross-sectional study. Rehabilitation program. Soccer players with a history of ACLR (n = 73) and matched control individuals (n = 195). The 10-second vertical hop test provided measures of jump height, the Reactive Strength Index (RSI), and asymmetry. We also examined possible predictors of hop performance, including single-legged vertical drop jump, isokinetic knee-extension strength, and the International Knee Documentation Committee questionnaire score. Between-limbs differences were identified only for the ACLR group, and asymmetry scores increased in those with a history of ACLR (P < .001) compared with the control group. The single-legged vertical drop jump, RSI, and knee-extension torque were significant predictors of 10-second hop height (R2 = 20.1%) and RSI (R2 = 47.1%). Vertical hop deficits were present after ACLR, even after participants completed a comprehensive rehabilitation program. This may have been due to reduced knee-extension and reactive strength. Vertical hop tests warrant inclusion as part of the return-to-sport test battery.

Functional outcomes after anterior cruciate ligament reconstruction: unravelling the role of time between injury and surgery, time since reconstruction, age, gender, pain, graft type, and concomitant injuries

BackgroundNumerous individual, temporal, injury- and surgery-specific factors impact the functional capacity during rehabilitation, return to sports (RTS), and re-injury prevention after an anterior cruciate ligament (ACL) reconstruction.PurposeThis multicentre cohort study evaluated the isolated and interactive contributions of time between injury and surgery, time since reconstruction, age, gender, pain, graft type, and concomitant injuries as to inertial sensor-assessed motor function after ACL reconstructions in multiple linear mixed model regressions.MethodsAnonymized data were retrieved from a nationwide German registry. In this cohort study, patients with an acute unilateral ACL rupture, with or without concomitant ipsilateral knee injuries, and having passed an arthroscopically assisted anatomic reconstruction were included. Potential predictors were age [years], gender/sex, time since reconstruction [days], time between injury and reconstruction [days], concomitant intra-articular injuries (isolated ACL tear, meniscal tear, lateral ligament, unhappy triad), graft type (hamstrings, patellar, or quadriceps tendon autograft), and pain during each measurement (visual analogue scale 0–10 cm). Repeated inertial motion unit-assessments of a comprehensive battery of classic functional RTS test were performed in the course of the rehabilitation and return to sports: Joint position sense/kinesthesia (Angle reproduction error [degrees]), Dynamic Balance Composite score [cm] of the Y-Balance test), drop jumps (Knee displacement [cm]), Vertical hop (Hopping height [mm]), Speedy jumps (Duration [seconds]), Side hops (Number of hops [n]), single leg hop for distance (hopping distance [cm]). Repeated measures multiple linear mixed models investigated the impact and nesting interaction of the potential predictors on the functional outcomes.ResultsData from 1441 persons (mean age 29.4, SD 11.8 years; 592 female, 849 male) were included. Most had an isolated ACL rupture: n = 938 (65.1%). Minor shares showed lateral ligament involvement: n = 70 (4.9%), meniscal tear: n = 414 (28.7%), or even unhappy triad: n = 15 (1%). Several predictors such as time between injury and reconstruction, time since reconstruction (estimates for ndays ranged from + .05 (i.e., an increase of the hopping distance of 0.05 cm per day since reconstruction occurs) for single leg hop for distance to + 0.17 for vertical hopping height; p < 0.001), age, gender, pain, graft type (patellar tendon graft: estimates between + 0.21 for Y-balance and + 0.48 for vertical hop performance; p < 0.001), and concomitant injuries contribute to the individual courses of functional abilities of the reconstructed side after ACL reconstruction. The unimpaired side was mostly influenced by sex, age, the time between injury and reconstruction (estimates between − 0.0033 (side hops) and + 0.10 (vertical hopping height), p < 0.001)), and time since reconstruction.ConclusionsTime since reconstruction, time between injury and reconstruction, age, gender, pain, graft type, and concomitant injuries are not independent but nested interrelating predictors of functional outcomes after anterior cruciate ligament reconstruction. It might not be enough to assess them isolated; the knowledge on their interactive contribution to motor function is helpful for the management of the reconstruction (earlier reconstructions should be preferred) deficit-oriented function-based rehabilitation (time- and function based rehabilitation instead of solely a time- or function based approach) and individualized return to sports strategies.

The influence of elastic ankle exoskeletons on lower limb mechanical energetics during unexpected perturbations.

Passive elastic ankle exoskeletons have been used to augment locomotor performance during walking, running and hopping. In this study, we aimed to determine how these passive devices influence lower limb joint and whole-body mechanical energetics to maintain stable upright hopping during rapid, unexpected perturbations. We recorded lower limb kinematics and kinetics while participants hopped with exoskeleton assistance (0, 76 and 91 Nm rad-1) on elevated platforms (15 and 20 cm) which were rapidly removed at an unknown time. Given that springs cannot generate nor dissipate energy, we hypothesized that passive ankle exoskeletons would reduce stability during an unexpected perturbation. Our results demonstrate that passive exoskeletons lead to a brief period of instability during unexpected perturbations - characterized by increased hop height. However, users rapidly stabilize via a distal-to-proximal redistribution of joint work such that the knee performs an increased energy dissipation role and stability is regained within one hop cycle. Together, these results demonstrate that despite the inability of elastic exoskeletons to directly dissipate mechanical energy, humans can still effectively dissipate the additional energy of a perturbation, regain stability and recover from a rapid unexpected vertical perturbation to maintain upright hopping.

Particle saltation trajectories in supercritical open channel flows: Roughness effect

AbstractBed load sediment transport governed by particle saltation in supercritical open channel flows causes bedrock incision in high‐gradient mountain streams and hydro‐abrasion at hydraulic structures. Hence, a better understanding of turbulent flow characteristics and particle dynamics is of prime importance for the prediction of river and landscape evolution, and for a sustainable design of hydraulic structures. To this end, we experimentally investigated single‐particle dynamics in supercritical open channel flows over fixed planar and abraded beds covering smooth, transitionally rough, and hydraulically rough regimes. The experiments were performed at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zürich in a wide range of hydraulic conditions with various channel width‐to‐depth aspect ratios (b/ho) and Froude numbers (F). We investigated the motions of five particle groups differing in shape, hardness, and diameter. By means of a high‐speed camera, the particle velocities and trajectory parameters—such as hop height and hop length—were determined using particle tracking velocimetry. The results reveal that at least 120 individual particles should be used in the tests to determine sound statistics of particle trajectories. In the present test conditions, the particles are dominantly transported in saltation. The effects of particle properties such as shape and diameter on the particle trajectories are negligible, while the rolling probability of the particles for a given flow condition increases with increasing diameter. Bed roughness was found to be the key parameter having a significant effect on the saltation trajectories and horizontal energy transfer. Hop height, hop length, and particle velocities, as well as horizontal energy transfer, increase with increasing bed roughness. Based on the saltation trajectory data, non‐dimensional equations are developed for each hydraulic regime and used to enhance the saltation–abrasion model of Sklar and Dietrich. The present findings contribute to a better understanding of particle motion characteristics under different hydraulic and roughness conditions, and their effect on the mechanics and prediction of bedrock incision and hydro‐abrasion in three‐dimensional supercritical open channel flows occurring in steeply sloped rivers and at hydraulic structures.

A Reconfigurable Leg for Walking Robots

We present the design of a robotic leg that can seamlessly switch between a spring-suspended-, and unsuspended configuration. Switching is realized by a mechanism that exploits the alternative configuration of the two-link leg. The mechanism is lightweight, does not require additional actuation, and only relies on the leg movement for engagement. We validated the performance of the prototype leg on a single-leg testbed and investigated the power consumption during standing, crouching, and hopping in both configurations. The experiments showed that the efficiency of hopping and cyclic base height control is better with the spring-suspended configuration. However, it can undermine the leg's performance in position control and requires higher torque to maintain low base height, where the unsuspended configuration has advantages. Overall, the switching ability allows for seamlessly selecting the optimal mode for a specific locomotion task.

Spherical robot with spring energy storage type hopping mechanisms: design, dynamics and experimental evaluation

PurposeSpherical robot plays an essential role in the field of mobile robot because of its unique shape and omni-directional mobility, especially in the application of planet detection. Although spherical robot has many advantages over leg robot, its obstacle climbing performance is still not satisfactory, that is exactly the motivation of this paper. The purpose of this paper is to propose a high-performance hopping mechanism for spherical robot, which can adapt to different terrain and effectively cross obstacles.Design/methodology/approachThe hopping system uses torque spring as part of the energy storage mechanism, and converts the kinetic energy of rotation into elastic potential energy with a particularly designed turntable. Moreover, the track of the turntable, based on the Archimedes spiral principle, has the attributes of equidistance and equivelocity that enable better stability of energy storage process.FindingsExperiments show that the proposed hopping mechanism can make a 250 g spherical robot jump up to 58 cm with the take-off angle of 60°. Finally, the influence of friction and take-off angle on the hopping height and distance of the robot is also analyzed, which provides a prior guidance for optimizing its jumping process.Originality/valueThis paper shows how to easily design a lightweight, compact and embedded spring hopping structure so that a spherical hopping robot with detection ability can be developed.

Muscle Actuators, Not Springs, Drive Maximal Effort Human Locomotor Performance.

The current investigation examined muscle-tendon unit kinematics and kinetics in human participants asked to perform a hopping task for maximal performance with variational preceding milieu. Twenty-four participants were allocated post-data collection into those participants with an average hop height of higher (HH) or lower (LH) than 0.1 m. Participants were placed on a customized sled at a 20º angle while standing on a force plate. Participants used their dominant ankle for all testing and their knee was immobilized and thus all movement involved only the ankle joint and corresponding propulsive unit (triceps surae muscle complex). Participants were asked to perform a maximal effort during a single dynamic countermovement hop (CMH) and drop hops from 10 cm (DH10) and 50 cm (DH50). Three-dimensional motion analysis was performed by utilizing an infrared camera VICON motion analysis system and a corresponding force plate. An ultrasound probe was placed on the triceps surae muscle complex for muscle fascicle imaging. HH hopped significantly higher in all hopping tasks in comparison to LH. In addition, the HH group concentric ankle work was significantly higher in comparison to LH during all of the hopping tasks. Active muscle work was significantly higher in HH in comparison to LH as well. Tendon work was not significantly different between HH and LH. Active muscle work was significantly correlated with hopping height (r = 0.97) across both groups and hopping tasks and contributed more than 50% of the total work. The data indicates that humans primarily use a motor-driven system and thus it is concluded that muscle actuators and not springs maximize performance in hopping locomotor tasks in humans.

Leg stiffness and muscle power vs manometer in sportswomen with symptoms of stress urinary incontinence

BackgroundPelvic floor muscle training can cure or alleviate stress urinary incontinence. This study aimed to evaluate maximum voluntary contractions of the pelvic floor muscle in sportswomen and verify the association with leg stiffness and muscle power, both maximal and submaximal. MethodsThe sample consisted of 41 sportswomen between 18 and 42 years of age. Pelvic floor muscle strength was measured by the manometer. The sportswomen were instructed to perform 3 maximum voluntary contractions of the perineum, held for 3 seconds. Maximal and submaximal leg stiffness and muscle power were measured with a force platform, in two conditions: 1st condition was the sub-maximal, double leg hop test, which was performed allowing sportswomen to self-select their preferred frequency and 2nd condition was the maximal double leg hop test, which was performed asking athletes to maximize hop height and minimize contact time on the top of the force platform for 6 consecutive hops. FindingsMaximal and submaximal leg stiffness values increase with increasing age, weight, height, and body mass index, showing positive and significant (p <0.05) or close correlations. There are strong positive correlations between maximal and submaximal leg stiffness (r = 0.759) and between maximal and submaximal muscle power. Maximum voluntary contractions values decrease with increasing leg stiffness: the correlation is significant with maximal leg stiffness. InterpretationMaximum voluntary contractions values decrease with increasing leg stiffness and increase with increasing muscle power values. If the training program aims to increase muscle power, it may also increase maximum voluntary contractions.

Including jump height when normalizing single hop impact kinetics can change the directionality of findings

BackgroundAssessing landing kinetics during hop testing could improve return to sport decisions following anterior cruciate ligament reconstruction (ACL) reconstruction. However, different methods for normalizing kinetic outcomes could influence the interpretation of landing kinetics and therefore the clinical recommendations. MethodsTwenty-one females who had returned to sport following primary unilateral ACL reconstructed completed two single hops for maximum distance on each limb. Hop distance, hop height, peak impact force, and impulse were computed for each hop, and peak impact force and impulse magnitudes were assessed when 1) non-normalized 2) normalized by bodyweight, and 3) normalized by peak potential energy during the hop. FindingsAlong with hop distance and height, peak impact force and impulse were found to be lower on the surgical limb relative to the non-surgical limb for both non-normalized data and when normalized to bodyweight only (p < 0.001, d > 0.95). However, peak impact force and impulse were found to be higher on the surgical limb relative to the non-surgical limb when normalizing outcomes to peak potential energy (p < 0.001, d > 1.03). InterpretationDifferent normalization methods result in different interpretations of single hop kinetics. ACL reconstruction patients have shorter hop distances, lower hop heights, lower force magnitudes, and worse energy absorption when hopping on their surgical limb, relative to their non-surgical limb. We believe that normalizing landing kinetics using bodyweight and using peak potential energy provide different information, and as such, we suggest that future research use both methods based on the research question.

Active Muscle Work, Not Springs, Determine Maximal Effort Hopping Performance in Humans

Biological systems typically require movement patterns that involve either efficiency or maximal power. Mammalian propulsion systems consist of the active and passive work elements of muscle actuators and a muscle and tendon springs. These components can be used in an array of motor-driven or spring-driven models to optimize performance and task accomplishment. The purpose of this investigation was to examine muscle-tendon unit kinematics and kinetics in human subjects asked to perform a locomotor task (hopping) for maximal performance with variational preceding milieu. Based on previous evidence it was hypothesized that a motor-driven model would be utilized. Twenty-four subjects were allocated post-data collection into those subjects with an average hop height lower than 0.1 m (LH, n = 11, age = 22.3 ± 2.7 yrs, height = 1.68 ± 0.09 m, body mass = 64.8 ± 13.7 kg, avg hop hght = 0.08 ± 0.01 m) or higher than 0.1 m (HH, n = 13, age = 21.5 ± 2.1 yrs, height = 1.79 ± 0.05 m, body mass = 83.1 ± 15.2 kg, avg hop hght = 0.13 ± 0.01 m). Subjects were placed on a carriage attached to rails on a customized sled at a 20 degree angle while standing on a force plate. Subjects only used their dominant ankle for all testing and their corresponding knee was completely immobilized and thus all movement was isolated to that single ankle joint and corresponding propulsive unit (triceps surae muscle complex). Subjects were asked to hop as high as possible during a single dynamic countermovement hop (CMH) and drop hops from 10 cm (DH10) and 50 cm (DH50). Drop hops involved dropping the carriage from the afore mentioned heights and asking the subject to hop upwards after impact with the force plate. Three-dimensional motion analysis was performed by utilizing an infrared 9-camera VICON motion analysis system and a corresponding force plate. In addition, an ultrasound probe was placed at the mid-muscle belly of the triceps surae muscle complex of the subject for muscle fascicle imaging. HH hopped significantly higher in all hopping tasks in comparison to LL. The HH group concentric ankle work (CMH = 2.55 ± 0.93 J•kg-1, DH10 = 2.72 ± 0.75 J•kg-1, DH50 = 4.48 ± 1.56 J•kg-1) was significantly higher in comparison to LL (CMH = 1.49 ± 0.56 J•kg-1, DH10 = 1.98 ± 0.59 J•kg-1, DH50 = 3.14 ± 1.43 J•kg-1) during all of the hopping tasks as well (Figure 1). In addition, active muscle work was significantly higher in HH (CMH = 3.26 ± 1.18 J•kg-1, DH10 = 3.74 ± 0.90 J•kg-1, DH50 = 4.98 ± 3.22 J•kg-1) in comparison to LH (CMH = 1.01 ± 0.79 J•kg-1, DH10 = 1.85 ± 1.34 J•kg-1, DH50 = 2.66 ± 2.0 J•kg-1). However, passive tendon and passive muscle work were not significantly different between the groups. Across both groups and hopping tasks, active muscle work was significantly correlated with hopping height (r = 0.97) and contributed to approximately 49% of the total work. The data indicates that humans primarily use a motor-driven system. Thus, muscle actuators and not springs maximize performance in hopping locomotor tasks in humans.

Design, Optimization and Evaluation of a New Cylinder Attachment Geometry to Improve the Hopping Height of the Bionic One-Legged Robot

Due to the high power-to-weight ratio and robustness, hydraulic cylinders are widely used in the actuation area of the legged robot systems. Most of these applications are focused on the motion stability, gait planning, and impedance control. However, the energy efficiency of the legged robotic system is also a very important point to be considered. Hopping locomotion requires a fast extension of the tibia leg at the end of the take-off phase, which causes a continuous increment of the cylinder velocity under the normally direct attachment geometry (DAG) of the cylinder. This leads to a high flow requirement, large pressure drop, and low energy efficiency. Therefore, we propose a four-bar mechanism attachment geometry (FMAG) to improve the energy efficiency by refining the relationship between the joint angle and cylinder displacement trend. The kinematic and dynamic models of the bionic one-legged robot are built to calculate the hopping process during the take-off phase. Based on the established dynamic models, the design parameters in both the DAG and FMAG are optimized to maximize the hopping height, respectively. The hopping experiments are conducted to verify the effectiveness of the new attachment geometry. The experimental results show that the robot hopping energy at the end of the take-off phase increases 14.8% under the FMAG.

Vertical and Horizontal Hop Performance: Contributions of the Hip, Knee, and Ankle.

Single-leg vertical and horizontal hop tests are commonly used to assess performance of healthy athletes and as a measure of progress during rehabilitation from knee injury. It is unclear if they measure similar aspects of leg function, as the relative joint contributions of the hip, knee, and ankle joints during propulsion and landing are unknown. The proportion of work done by the hip, knee, and ankle will not be the same for these 2 jump types and will vary for propulsive and landing phases. Cross-sectional cohort study. Level 3. Twenty physically active participants completed instrumented single-leg hop analysis in both vertical and horizontal directions. Joint peak power, work generated or absorbed, and percentage contribution of each joint during propulsive and landing phases were compared between tasks using paired t tests. Vertical hop was performed with roughly similar contributions of the hip, knee, and ankle for both propulsion (31%, 34%, 35%, respectively) and landing (29%, 34%, 37%, respectively). Horizontal hop distance was mostly (87%) determined by the hip and ankle (44% and 43%), but landing was mostly (65%) performed by the knee with lesser contribution from the hip and ankle (24% and 11%). Propulsive phase showed a proximal-to-distal temporal sequence for both hop types, but landing was more complex. Performance during vertical and horizontal hops (jump height and jump distance, respectively) measures different aspects of hip, knee, and ankle function during the propulsive and landing phases. Assessment of knee joint function during rehabilitation should not be done using a horizontal hop. The knee contributes about a third to vertical hop height, but only about an eighth to horizontal hop distance. Practitioners carrying out performance testing using either vertical or horizontal hops should be mindful of the relative contributions for meaningful training inferences to be derived.

Compensation of nonlinear dynamics for energy/phase control of hopping robot

Hopping height control is one of the difficult problems in legged control. Many kinds of research employ a leg spring for the supplement of energy, and model the robot as a spring-mass model. Feedback linearization enables to cancel the nonlinear terms theoretically. However, it is difficult to identify the nonlinear terms including the parameters precisely in the real world.This paper nominalizes the robot dynamics as the desired spring-mass system applying a disturbance observer. In order to realize the desired characteristics of the spring and the mass, the disturbance including the nonlinear terms is rejected firstly by a disturbance observer. To make the mass in the workspace as constant, the nominal inertia of the disturbance observer in the joint space is varied. Next, by adding the desired virtual elastic force, the robot dynamics is nominalized as the desired spring-mass system.Based on the nominalized spring-mass dynamics, hopping-height control using energy/phase control is implemented. While energy control is often used for hopping height control, the energy/phase control enables the hopping-height control and the spring-mass oscillation simultaneously.Constant hopping-height and stepwise hopping height are realized experimentally through the proposed control method. The simulations in the case of the ideal dynamics are also conducted for comparison.

Lower Leg Characteristics Influance on Hopping Height

Lower Leg Characteristics Influance on Hopping Height

Vibratory Feeding Performance Improvement Through Discrete Element Analysis for High-Speed Optical Detection of LED Chips

A high-speed vibratory bowl feeder is a key equipment of the optical detection of light emitting diode (LED) chips. Addressing the stationarity-losing problem induced by transporting small-size and light-weight LED chips, this study designs a vibratory bowl feeder for the high-speed detection of small LED chips based on theoretical and numerical analyses. To understand the influence of the structural parameters of the feeder on its performance, we create a mathematical model of the part's behavior base on the Hertz-Mindlin contact theory. The numerical model indicates that the property of the part, the track angle and the friction coefficient of the track are the main factors that affect the behavior of the part in the feeding process. Through the discrete element method (DEM) simulation, we observe the part behavior under different track angles and friction coefficients of the feeder. The motion stationary of the LED chip is evaluated by its standard deviation (STD) of velocity and hopping height. Thus, we can appropriately determine these parameters of the vibratory feeder in order to get the optimal feeding performance. Finally, an experimental platform of the LED chip detection device is built to verify the performance of the vibratory bowl feeder. The experimental results show that the performance of the feeder was in good agreement with the simulation results. With the theoretical analysis and experimental verification, the vibratory bowl feeder was successfully implemented for LED transportation and reached a high feeding velocity of 1516.5 pieces/min at the working frequency of 223 Hz.