Inverse Dynamics Approach Research Articles

Reduction of the dynamic coupling in an underwater vehicle-manipulator system using an inverse dynamic model approach

This paper proposes a control strategy for station keeping of an underwater vehicle- manipulator system when the manipulator is asked to perform a certain task. The control structure consists of an inverse dynamic feedforward controller, the interaction forces between subsystems and a PILIM feedback controller for pitch control of the vehicle. The UVMS includes a 6-DOF vehicle and a 3-link manipulator, where the manipulator has a significant mass compared to the vehicle. The equations of motion are based on a tree representation of the UVMS and are described with the Newton-Euler algorithm. Hydrodynamic effects and friction considerations are taken into account in the forward dynamic model, while in the inverse dynamic model they are ignored. Simulation results show the validity of the inverse dynamic model approach without perfect knowledge of the system for station keeping of the vehicle. A key contribution of the study is that it is based on a lightweight underwater system. The main problem addressed in this paper is the station keeping of an underwater vehicle when the attached manipulator is moving. It is demonstrated that an inverse dynamic model used as a feedforward controller is a viable solution in the presence of system uncertainties.

A subject-specific inverse-dynamics approach for estimating joint stiffness in sideways fall

Sideways fall has been identified as the most critical situation leading to hip fracture in the elderly. The stiffness and damping property of the body joints are necessary for constructing effective biomechanical models to study fall dynamics. However, very little has been known about the joint behaviour when the body is in fall. We developed a subject specific inverse-dynamics approach to estimate the joint stiffness and damping property. The anthropometric parameters required for constructing the inverse-dynamics model was extracted from the subject's whole body dual energy X-ray absorptiometry (DXA) image. The motion data of the body in sideways fall were obtained by protected fall tests using the same subject. The joints were represented by the Kelvin-Voigt model with undetermined stiffness and damping parameters, which were then determined by solving the inverse problems. For validation purpose, the obtained joint stiffness and damping parameters were substituted back into the dynamics equations and the forward problems were solved. The predicted fall kinematic variables were compared with those measured from the fall tests. Good agreements were observed, indicating that the proposed approach is reliable and reasonably accurate.

A novel measurement of intersegmental forces exerted on human lower limbs during forward falling and regaining balance motions

This study proposes an analysis system for evaluating the intersegmental forces exerted on human lower limbs. In existing analysis systems, the ground reaction force exerted on the feet is generally measured using force plates fixed on the motion trajectory, and the intersegmental forces are then estimated using an inverse dynamics approach. However, force plates are inconvenient and expensive. Accordingly, the present study proposes a method for evaluating the intersegmental forces without the need for force plates. In the proposed approach, the supporting and striding legs are modeled as a seven-link manipulator system, and the intersegmental forces is then derived using Newton–Euler theory. It is found that the estimated results are in good agreement with the actual measurement datum. Thus, the basic validity of the proposed analysis system is confirmed. For application, the intersegmental force would be the major reference datum to design the artificial joints.

Ground reaction forces and lower-limb joint kinetics of turning gait in typically developing children

Turning is a common locomotor task essential to daily activity; however, very little is known about the forces and moments responsible for the kinematic adaptations occurring relative to straight-line gait in typically developing children. Thus, the aims of this study were to analyse ground reaction forces (GRFs), ground reaction free vertical torque (TZ), and the lower-limb joint kinetics of 90° outside (step) and inside (spin) limb turns. Step, spin, and straight walking trials from fifty-four typically developing children were analysed. All children were fit with the Plug-in Gait and Oxford Foot Model marker sets while walking over force plates embedded in the walkway. Net internal joint moments and power were computed via a standard inverse dynamics approach. All dependent variables were statistically analysed over the entire curves using the mean difference 95% bootstrap confidence band approach. GRFs were directed medially for step turns and laterally for spin turns during the turning phase. Directions were reversed and magnitudes decreased during the approach phase. Step turns showed reduced ankle power generation, while spin turns showed large TZ. Both strategies required large knee and hip coronal and transverse plane moments during swing. These kinetic differences highlight adaptations required to maintain stability and reorient the body towards the new walking direction during turning. From a clinical perspective, turning gait may better reveal weaknesses and motor control deficits than straight walking in pathological populations, such as children with cerebral palsy, and could potentially be implemented in standard gait analysis sessions.

Comparisons of increases in knee and ankle joint moments following an increase in running speed from 8 to 12 to 16 km·h− 1

BackgroundKnowledge regarding knee and ankle joint load across a range of running speeds is important, if running related injuries are to be prevented. The purpose of the present study was to test the hypothesis that peak plantar flexion moment increases relatively more than peak knee extension moment when running speed is increased. MethodsKinematic and ground reaction force data were collected from 33 recreational runners during steady-state running at three different speeds: 7.96km·h−1 (SD 0.18), 11.92km·h−1 (SD 0.25) and 15.91km·h−1 (SD 0.36). Peak plantar flexion moment and peak knee extension moment were calculated using a standard three-dimensional inverse dynamics approach. FindingsThere was a significant interaction between the joint location and the running speed (P=0.03): When running speed increased from 7.96 to 15.91km·h−1, mean peak plantar flexion moment increased by 0.74N·m·kg−1 (95% CI: 0.64; 0.85) which was more than the 0.52N·m·kg−1 (95% CI: 0.42; 0.63) increase in mean peak knee extension moment. InterpretationA greater increase in biomechanical load occurs for the plantar flexors of the ankle joint than for the extensors of the knee joint when running speed increases. This may indicate that at an excessive running speed, the structures at the posterior part of the lower leg and underneath the foot are relatively more vulnerable to injury compared with the structures at the anterior part of the knee. As a considerable load reduction is achieved, a decrease in running speed may benefit rearfoot striking recreational runners experiencing pain in the posterior lower leg or underneath the foot.

Muscle co-contraction around the knee when walking with unstable shoes

Walking with unstable shoes has been discussed to decrease joint loading. Typical estimates of joint loading using an inverse dynamic approach only account for net joint moments, not considering the potential role of muscular co-contraction. Therefore, the purpose of this study was to compare muscular co-contraction levels when walking with two different unstable shoe constructions (rocker-bottom and toning shoes) compared to walking with regular shoes. For each shoe condition, 12 healthy subjects walked with both, a regular shoe and with an unstable shoe at self-selected walking speed at a 10-m walkway. Surface EMG data of selected muscles were recorded and time normalized for calculating co-contraction indices (CCI) for opposing muscle groups.Results showed an increase of co-contraction primarily for vastii and gastrocnemius muscles for the first and second half of stance when walking with an unstable shoe construction. Therefore, when using an inverse dynamic approach to analyze joint loading differences between regular shoes and unstable shoes, one should be cautious in interpreting the data, as these methods base their estimates of joint moments upon the net joint torque.

Hybrid force and motion control of flexible joint parallel manipulators using inverse dynamics approach

An inverse dynamics control algorithm is developed for hybrid motion and contact force trajectory tracking control of flexible joint parallel manipulators. First, an open-tree structure is considered by the disconnection of adequate number of unactuated joints. The loop closure constraint equations are then included. Elimination of the joint reaction forces and the other intermediate variables yield a fourth-order relation between the actuator torques and the end-effector position and contact force variables, showing that the control torques do not have an instantaneous effect on the end-effector contact forces and accelerations because of the flexibility. The proposed control law provides simultaneous and asymptotically stable control of the end-effector contact forces and the motion along the constraint surfaces by utilizing the feedback of positions and velocities of the actuated joints and rotors. A two degree of freedom planar parallel manipulator is considered as an example to illustrate the effectiveness of the method.

The Fuel Economy of Hybrid Buses: The Role of Ancillaries in Real Urban Driving

In the present context of the global economic crisis and environmental emergency, transport science is asked to find innovative solutions to turn traditional vehicles into fuel-saving and eco-friendly devices. In the last few years, hybrid vehicles have been shown to have potential benefits in this sense. In this paper, the fuel economy of series hybrid-electric and hybrid-mechanical buses is simulated in two real driving situations: cold and hot weather driving in the city of Taranto, in Southern Italy. The numerical analysis is carried out by an inverse dynamic approach, where the bus speed is given as a velocity pattern measured in the field tests performed on one of the city bus routes. The city of Taranto drive schedule is simulated in a typical tempered climate condition and with a hot temperature, when the air conditioning system must be switched on for passenger comfort. The fuel consumptions of hybrid-electric and hybrid-mechanical buses are compared to each other and with a traditional bus powered by a diesel engine. It is shown that the series hybrid-electric vehicle outperforms both the traditional and the mechanical hybrid vehicles in the cold weather driving simulation, reducing the fuel consumption by about 35% with respect to the traditional diesel bus. However, it is also shown that the performance of the hybrid-electric bus gets dramatically worse when the air-cooling system is continuously turned on. In this situation, the fuel consumption of the three different technologies for city buses under investigation is comparable.

Analytical model for estimating intersegmental forces exerted on human lower limbs during walking motion

Existing methods for evaluating the intersegmental forces acting on the human lower limbs during walking generally measure the ground reaction force exerted on the feet using force plates and estimate the intersegmental forces using an inverse dynamics approach. However, force plates are inconvenient and expensive. Accordingly, the present study proposes an approach for evaluating the intersegmental forces without the need for force plates by modeling the human lower limbs as a seven-link manipulator system. In the proposed approach, the intersegmental forces are derived directly from the analytical model using Newton–Euler theory based on the posture information obtained from a system of gyroscopes and accelerometers during walking motion. The results obtained from the analytical model are compared with the experimental data obtained using load cells. It is found that the estimated results are in good agreement with the measured results. Thus, the basic validity of the proposed analysis system is confirmed.

Modeling the biomechanics of swine mastication – An inverse dynamics approach

A novel reconstructive alternative for patients with severe facial structural deformity is Le Fort-based, face-jaw-teeth transplantation (FJTT). To date, however, only ten surgeries have included underlying skeletal and jaw-teeth components, all yielding sub-optimal results and a need for a subsequent revision surgery, due to size mismatch and lack of precise planning. Numerous studies have proven swine to be appropriate candidates for translational studies including pre-operative planning of transplantation. An important aspect of planning FJTT is determining the optimal muscle attachment sites on the recipient׳s jaw, which requires a clear understanding of mastication and bite mechanics in relation to the new donated upper and/or lower jaw. A segmented CT scan coupled with data taken from literature defined a biomechanical model of mandible and jaw muscles of a swine. The model was driven using tracked motion and external force data of one cycle of chewing published earlier, and predicted the muscle activation patterns as well as temporomandibular joint (TMJ) reaction forces and condylar motions. Two methods, polynomial and min/max optimization, were used for solving the muscle recruitment problem. Similar performances were observed between the two methods. On average, there was a mean absolute error (MAE) of <0.08 between the predicted and measured activation levels of all muscles, and an MAE of <7N for TMJ reaction forces. Simulated activations qualitatively followed the same patterns as the reference data and there was very good agreement for simulated TMJ forces. The polynomial optimization produced a smoother output, suggesting that it is more suitable for studying such motions. Average MAE for condylar motion was 1.2mm, which reduced to 0.37mm when the input incisor motion was scaled to reflect the possible size mismatch between the current and original swine models. Results support the hypothesis that the model can be used for planning of facial transplantation.

An Instrumented Footbar for Evaluating External Forces in Pilates

The intensity of Pilates exercises is almost exclusively based on experience. Therefore, knowing the precise amount of effort that is exerted during exercises could be useful for professionals conducting exercise assessments and for future research using inverse dynamics (ID) analyses. The reformer is an apparatus that contains a carriage on rails to which resistance is applied via springs attached to the carriage. Subjects apply force to a footbar to displace the carriage, but the magnitude and direction of this force are unknown and need to be quantified if the ID approach is to be used. This study aimed to develop and describe a device built with commercial load cells attached to the reformer's footbar, with the device capable of measuring the direction and magnitude of the force exerted on the reformer's footbar, and to compare the force found using the device with the force estimated using the springs' parameters. To illustrate the device's use, one volunteer performed footwork exercises at different speeds and with different foot support positions and loads. External force estimated by the springs' level of deformation was significantly different (P < .001) from the magnitude of force acquired using the device, showing that the estimation is imprecise.

The effect of muscle weakness on the capability gap during gross motor function: a simulation study supporting design criteria for exoskeletons of the lower limb.

BackgroundEnabling persons with functional weaknesses to perform activities of daily living (ADL) is one of the main challenges for the aging society. Powered orthoses, or exoskeletons, have the potential to support ADL while promoting active participation of the user. For this purpose, assistive devices should be designed and controlled to deliver assistance as needed (AAN). This means that the level of assistance should bridge the capability gap, i.e. the gap between the capabilities of the subjects and the task requirements. However, currently the actuators of exoskeletons are mainly designed using inverse dynamics (ID) based calculations of joint moments. The goal of the present study is to calculate the capability gap for the lower limb during ADL when muscle weakness is present, which is needed for appropriate selection of actuators to be integrated in exoskeletons.MethodsA musculoskeletal model (MM) is used to calculate the joint kinematics, joint kinetics and muscle forces of eight healthy subjects during ADL (gait, sit-to-stand, stand-to-sit, stair ascent, stair descent). Muscle weakness was imposed to the MM by a stepwise decrease in maximal isometric force imposed to all muscles. Muscle forces were calculated using static optimization. In order to compensate for muscle weakness, ideal moment actuators that represent the motors of an exoskeleton in the simulation were added to deliver AAN required to perform the task.ResultsThe ID approach overestimates the required assistance since it relies solely on the demands of the task, whereas the AAN approach incorporates the capabilities of the subject. Furthermore, the ID approach delivers continuous support whereas the AAN approach targets the period where a capability gap occurs. The level of muscle weakness for which the external demands imposed by ADL can no longer be met by active muscle force production, is respectively 40%, 70%, 80% and 30%.ConclusionsThe present workflow allows estimating the AAN during ADL for different levels of muscle weakness, which can be used in the mechatronic design and control of powered exoskeletons. The AAN approach is a more physiological approach than the ID approach, since the MM accounts for the subject-specific capabilities of the user.

Human walking dynamics: modeling, identification and control

Human gait simulation is a complex dynamical problem that requires, in addition to the mechanical model, the observance of muscle activations, neural excitations, and energetic and aesthetic considerations. After an short review on the historical development two- and three-dimensional models using multibody system dynamics are presented. The identification of the muscle actuation during human walking is based on data in literature comparing the resultant torques to each other. The control design uses inverse dynamics approaches and an optimization framework minimizing the metabolical energy consumption and improving the aesthetics. Numerical simulation results are shown for planar as well as spatial models.

건강한 성인의 슬개건 반사 시 무릎 감쇠효과를 고려한 대퇴사두근의 근력 및 근활성도 예측

Most analytical models of the human body have focused on conscious responses. A patellar tendon reflex, a representative example of spinal reflexes, occurs without a neural command. Muscle forces and activation of the quadriceps femoris muscles in healthy adults during patellar tendon reflex are identified in this study. The model is assumed to move in the sagittal plane, and the thigh and the trunk are assumed to be fixed in a sitting position so that the shank can move similar to a pendulum. The knee joint is modeled as a revolute joint, and the ankle joint is modeled as a fixed joint so that the shank and the foot can be regarded as one rigid body. Muscle forces are calculated following the inverse dynamic approach. Kinematic data obtained from an experiment (Mamizuka, 2007) are used as input data. Muscle activations are identified using a Hill-type muscle model. The obtained simulation results are compared with experimental results for validating the model and the underlying assumptions. † Corresponding Author, hhyoo@hanyang.ac.kr C 2014 The Korean Society of Mechanical Engineers

Analysis System of Intersegmental Force Exerted on Human Lower Limbs During Walking Motion

This study proposes an analysis system for evaluating the intersegmental forces exerted on human lower limbs during walking motion. In existing analysis systems, the ground reaction force exerted on the feet is generally measured using force plates and the intersegmental forces are then estimated using an inverse dynamics approach. However, force plates are inconvenient and expensive. Accordingly, the present study proposes a new method for evaluating the intersegmental forces exerted on human lower limbs during walking without the need for force plates. In the proposed approach, the legs are modeled as a seven-link parallel manipulator. The kinematics and dynamics of the leg model are formulated, and the intersegmental forces are then derived using Newton-Euler theory based on the posture information obtained by gyroscopes accelerometers during walking motion. The results obtained from the analysis system for the intersegmental forces during walking motion are compared with experiment data obtained by using an load cells. It is found that the estimated results are in good agreement with measurement results. Thus, the basic validity of the proposed analysis system is confirmed.

Alterations in lower‐extremity sagittal plane joint moments due to experimental knee pain and effusion during walking

Methods Nineteen able-bodied subjects walked four different conditions (control, effusion, pain, and pain+effusion), with a week between each condition. We used previouslyused injury models of pain [1] and joint effusion [2] to the right side of the knee. The control condition consisted of no injection. For each condition, subjects completed three walking trials at three times: precondition (prior to injection(s)), condition (3 minutes post injection(s)), and postcondition (30 minutes post injections). We used a standard inverse dynamics approach (combining high speed video, ground reaction force, and anthropometric

Musculoskeletal Analysis of Driving Fatigue: The Influence of Seat Adjustments

Main causes for discomfort experienced by vehicle drivers during driving were investigated using a rigid-body model originally developed in the AnyBody Modeling System [. The interactions between the human body and the car-seat in various combinations of seat-pan/backrest inclinations and the effect of pedal spring stiffness were analyzed using an inverse dynamics approach. To deal with the muscle redundancy problem, (i.e. the problem with the human-body containing more muscles than necessary to drive its degrees of freedom) a minimum-fatigue criterion [ was utilized. The results show that various seat adjustments (e.g., seat-pan and backrest inclinations) and the pedal spring stiffness have complex influences on the muscle activation and spinal joint forces of the human body. From the results, an optimal adjustment for the car-seat is proposed, i.e. the backrest inclination is 10° and the seat-pan inclination is between 0o to 5 o. This study can in general capture the overall interactions between human body and environment (i.e. the maximum muscle activity and spine forces), which is thought to be the factors of driving fatigue.

Knee Adduction Moment and Medial Contact Force – Facts about Their Correlation during Gait

The external knee adduction moment is considered a surrogate measure for the medial tibiofemoral contact force and is commonly used to quantify the load reducing effect of orthopedic interventions. However, only limited and controversial data exist about the correlation between adduction moment and medial force. The objective of this study was to examine whether the adduction moment is indeed a strong predictor for the medial force by determining their correlation during gait. Instrumented knee implants with telemetric data transmission were used to measure tibiofemoral contact forces in nine subjects. Gait analyses were performed simultaneously to the joint load measurements. Skeletal kinematics, as well as the ground reaction forces and inertial parameters, were used as inputs in an inverse dynamics approach to calculate the external knee adduction moment. Linear regression analysis was used to analyze the correlation between adduction moment and medial force for the whole stance phase and separately for the early and late stance phase. Whereas only moderate correlations between adduction moment and medial force were observed throughout the whole stance phase (R2 = 0.56) and during the late stance phase (R2 = 0.51), a high correlation was observed at the early stance phase (R2 = 0.76). Furthermore, the adduction moment was highly correlated to the medial force ratio throughout the whole stance phase (R2 = 0.75). These results suggest that the adduction moment is a surrogate measure, well-suited to predicting the medial force ratio throughout the whole stance phase or medial force during the early stance phase. However, particularly during the late stance phase, moderate correlations and high inter-individual variations revealed that the predictive value of the adduction moment is limited. Further analyses are necessary to examine whether a combination of other kinematic, kinetic or neuromuscular factors may lead to a more reliable prediction of the force magnitude.

Analysis of the musculoskeletal loading of the thumb during pipetting – A pilot study

Previous epidemiological studies indicate that the use of thumb-push mechanical pipettes is associated with musculoskeletal disorders (MSDs) in the hand. The goal of the current study was to analyze the loading in the muscle–tendon units in the thumb during pipetting. The hand is modeled as a multi-body linkage system and includes four fingers (index, long, ring, and little finger), a thumb, and a palm segment. Since the current study is focused on the thumb, the model includes only nine muscles attached to the thumb via tendons. The time-histories of joint angles and push force at the pipette plunger during pipetting were determined experimentally and used as model input; whereas forces in the muscle–tendon units in the thumb were calculated via an inverse dynamic approach combined with an optimization procedure. Results indicate that all nine muscles have force outputs during pipetting, and the maximal force was in the abductor pollicis brevis (APB). The ratio of the mean peak muscle force to the mean peak push force during the dispensing cycle was approximately 2.3, which is comparable to values observed in grasping tasks in the literature. The analysis method and results in the current study provide a mechanistic understanding of MSD risk factors associated with pipetting, and may be useful in guiding ergonomic designs for manual pipettes.

Determination of reaction forces and moments in the foot joints using multibody dynamics and Fe analysis—A clinical application

This study aimed to assess the effects of backrest inclination and vibration frequency on muscle activity in a dynamic environment using a musculoskeletal model.The muscle activity modeling method was used to analyze a full body musculoskeletal system of a seated person with a public domain rigid body model in an adjustable car seat. This model was established using AnyBody Modeling System, based on the inverse dynamic approach. And the min/max criterion in dealing with the muscle redundancy problem. Ten healthy subjects were exposed to whole body vibration (WBV) with five frequencies (3, 4.5, 6, 7, and 8 Hz) in the vertical direction in a randomized order on three separate days. The displacement of the seat-pan and head was measured using a hybrid Polaris spectra system to obtain the seat-to-head (STH) transmissibility. Muscle oxygenation was measured using near-infrared spectroscopy. The validity of the model was tested using STH transmissibility and muscle oxygenation.Increased vibration frequency caused high muscle activities of the abdomen and the right leg with a backrest forward inclination angle. The muscle activities of the left leg decreased at a backrest backward inclination except at inclination angles of 15° and 30°. Muscle activity of the lumbar suddenly increased at a backrest inclination angle of 5° and vibration frequency of 5 Hz. Muscle activities were higher under vibration than that without vibration.Vibration frequency significantly affected the muscle activity of the lumbar area. Likewise, the inclination degree of the backrest significantly affected the muscle activities of the right leg and the abdomen. The combination of vibration and forward inclination of the backrest can be used to maximize the muscle activity of the leg, similar to the abdomen and lumbar muscles.The musculoskeletal model established in the present study provides a method that can be used to investigate the biomechanical response of seated drivers to WBV. This model helps protect drivers from occupational injury.