Instantaneous Center Research Articles

An interaction model for predicting brace migration and validation through walking experiment

Brace migration undermines therapeutic efficacy, which is traditionally evaluated through walking experiments. This study developed an interaction model that considered the instantaneous center of rotation (ICR) misalignment to predict migration. The model was validated by walking experiment. Results show a strong positive correlation for four-linkage (FL) (r = 0.952, p < 0.01, root mean squared error (RMSE) = 0.53 mm) and spur gear (SG) (r = 0.898, p < 0.01, RMSE = 1.35 mm) mechanisms. The FL exhibits lower migration than SG (p < 0.05). In conclusion, the interaction model accurately predicts migration, emphasizing the influence of mechanism on migration.

Cadaveric biomechanical studies of ADDISC total lumbar disc prosthesis

BackgroundMost total disc replacements provide excessive mobility and not reproduce spinal kinematics, inducing zygapophyseal joint arthritic changes and chronic back pain. In cadaveric lumbosacral spines, we studied if a new lumbar disc prosthesis kinematics mimics the intact intervertebral disc. MethodsIn eight cold preserved cadaveric lumbosacral spines, we registered the movement ranges in flexion, extension, right and left lateral bending, and rotation in the intact status, post-discectomy, and after our prosthesis implantation, comparing them for each specimen. FindingsComparing the intact lumbosacral spine with the L4-L5 prosthesis implanted specimens, we saw statistically significant differences in lateral bending and right rotation but not in the full range of rotation. Analyzing segments, we also noticed statistically significant differences at L4-L5 in flexion-extension and rotation. On the other hand, the L4-L5 discectomy, compared to the baseline spine condition, showed a statistically significant mobility increase in flexion, extension, lateral bending, and axial rotation, with an abnormal instantaneous center of rotation, which destabilizes the segment partly due to anterior annulus surgical removal. Disc prosthesis implantation reversed these changes in instantaneous center of rotation, but the prosthesis failed to restore the initial range of motion due to the destabilization of the ligaments in the operated disc. InterpretationThe ADDISC total disc replacement reproduces the intact disc kinematics and Instantaneous Center of Rotation, but the prosthesis fails to restore the initial range of motion due to ligament destabilization. More studies will be necessary to define a technique that restores the damaged ligaments when implanting the prosthesis.

An estimation method for dynamic vehicle turn center

The instantaneous vehicle turn center is of great significance in the design and analysis of vehicle steering and handling. Due to the influences of vehicle flexible components, the vehicle turn center is not intersected at one point and the traditional determination method for vehicle turn center is not applicable for multi-axle vehicles. In this paper, a novel instantaneous tire turn center (TTC) method is proposed to estimate the instantaneous vehicle turn center to provide a guidance for the design of vehicle steering and analysis of handling. The motivation of the tire turn center concept is introduced and the calculation method is developed. The instantaneous vehicle turn center is estimated based on the calculation of instantaneous TTC. The estimation results of the vehicle turn center of a two-axle vehicle and a three-axle off-road vehicle under different vehicle velocities and lateral accelerations during steering are presented based on the vehicle dynamics models built by ADAMS software. Since there is no simplifications of the vehicle in the proposed estimation method, the determined instantaneous vehicle turn center is more accurate and can reflect the actual vehicle motion better as compared to the traditional vehicle turn center in transient motion process. The estimated instantaneous vehicle turn center provides a guidance for design and optimization of vehicle steering as well as steering angles control strategies to make all tire turn centers controlled at the instantaneous vehicle turn center, thus reducing tire wears and improving the whole vehicle steering coordination performance.

Visual-Based Kinematics and Pose Estimation for Skid-Steering Robots

To build commercial robots, skid-steering mechanical design is of increased popularity due to its manufacturing simplicity and unique mechanism. However, these also cause significant challenges on software and algorithm design, especially for the pose estimation (i.e., determining the robot’s rotation and position) of skid-steering robots, since they change their orientation with an inevitable skid. To tackle this problem, we propose a probabilistic sliding-window estimator dedicated to skid-steering robots, using measurements from a monocular camera, the wheel encoders, and optionally an inertial measurement unit (IMU). Specifically, we explicitly model the kinematics of skid-steering robots by both track instantaneous centers of rotation (ICRs) and correction factors, which are capable of compensating for the complexity of track-to-terrain interaction, the imperfectness of mechanical design, terrain conditions and smoothness, etc. To prevent performance reduction in robots’ long-term missions, the time-and location-varying kinematic parameters are estimated online along with pose estimation states in a tightly-coupled manner. More importantly, we conduct in-depth observability analysis for different sensors and design configurations in this paper, which provides us with theoretical tools in making the correct choice when building real commercial robots. In our experiments, we validate the proposed method by both simulation tests and real-world experiments, which demonstrate that our method outperforms competing methods by wide margins. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This paper was motivated by the problem of long-term pose estimation of the commonly commercial-used skid-steering robots with only low-cost sensors. Skid-steering robots change their orientation with a skid, which poses a significant challenge for pose estimation when using the wheel encoders. We propose to online estimate the robot’s kinematics, which succeeds in compensating for the complexity of track-to-terrain interaction, due to the slippage, the imperfectness of mechanical design, terrain conditions and smoothness. It is critical to estimate the kinematics and poses jointly to prevent performance reduction in robots’ long-term missions. We further theoretically analyze whether the kinematics parameters can be estimated under different sensor configurations, and find out the special degrade motions that make the parameters unobservable.

Adaptive core cervical total disc arthroplasty device replicates biomechanical instantaneous center of rotation in cadaver model

Adaptive core cervical total disc arthroplasty device replicates biomechanical instantaneous center of rotation in cadaver model

Instantaneous Center of Rotation Tracking Control of Four-Wheel Independent Steering Vehicles Under Large-Curvature Turning Conditions

Instantaneous Center of Rotation Tracking Control of Four-Wheel Independent Steering Vehicles Under Large-Curvature Turning Conditions

Estimation of Cervical Spinal Loading and Internal Motion at Adjacent Segments after C5–C6 Fusion Using a Musculoskeletal Multi-Body Dynamics Model during the Head Flexion–Extension Movement

Cervical spinal fusion is the standard of care for treating intractable spinal diseases. However, frequent adjacent segment disease (ASD) has recently drawn a great deal of attention among clinicians and researchers. At present, the etiology of ASD remains controversial. The investigation of cervical spine biomechanics after fusion may contribute to understanding the causes of ASD. In the present study, a cervical spinal musculoskeletal fusion model, with multi-body dynamics method, was established. Dynamic head flexion–extension movements were simulated for both a fusion subject and a normal subject. The cervical spinal loading pattern, load sharing ratios, and translations of instant centers of the rotation at adjacent segments were then predicted. The average intervertebral compressive forces, shear forces, and facet joint forces against the intervertebral angle were also obtained. By comparison, some obvious differences in cervical spinal loading patterns were found between the fusion subject and the normal subject. Fusion surgery would alter the postoperative biomechanical surrounding of the cervical spine, especially the adjacent segments. These changes might affect the intervertebral disc-bearing capacity, and even weaken the physiological structure. From a purely biomechanical perspective, the cervical spinal fusion model can contribute to comprehending the etiology of ASD after spinal fusion.

Development of four-bar polycentric knee joint with stance-phase knee flexion

A conventional 4-bar polycentric knee and solid ankle cushion heel foot (SACH foot) have been commonly used in developing countries. However, they cannot perform stance-phase knee flexion, which makes a person with an amputation walk unnaturally and with less stability. This research proposes a novel design of a 4-bar polycentric knee with stance-phase knee flexion ability (4BSF), which can perform both stance and swing-phase knee flexion, like able-bodied gait. In the proposed conceptual design, the instantaneous center of rotation (ICR) path is repositioned during the stance phase. The ICR was placed in front of the ground reaction force (GRF) to initiate knee flexion during the loading response. The prototype was validated by a single-subject pilot study at the Gait analysis laboratory. The results showed that a person with an amputation walks with stance-phase knee flexion using the proposed 4BSF. The maximum knee flexion angle is more than 10° during the stance phase. Furthermore, when the 4BSF was used with a SACH foot, the amount of time to achieve the foot flat was shorter, and the foot flat duration time was twice as long as the conventional 4-bar polycentric knee.

Rigid body dynamic response of a floating offshore wind turbine to waves: Identification of the instantaneous centre of rotation through analytical and numerical analyses

Rigid body dynamic response of a floating offshore wind turbine to waves: Identification of the instantaneous centre of rotation through analytical and numerical analyses

Sidewinding locomotion of flatworm-like mesh robot WORMESH-II

WORMESH-II, which is the second prototype in the WORMESH series, is inspired by a flatten and soft-bodied fatworm, and its uniqueness is the use of multiple travelling waves for locomotion. In this paper, the sidewinding locomotions for WORMESH-II are talked about. This is because sidewinding is one of the most effective ways to traverse sandy terrain. The mathematical model of the sidewinding locomotion kinematics of WORMESH-II explains how synchronous multiple sidewinding waves can be used to control the movement of the robot effectively. Unlike WORMESH’s pedal-wave locomotion, sidewinding gaits allow the robot to be manoeuvred in any direction without changing the joint sequence. Relative to the wave propagation direction, velocity in the longitudinal direction is dependent on the vertical component of sidewinding travelling waves. Moreover, velocity in the transverse direction depends on the horizontal component of sidewinding travelling waves. The velocity in the longitudinal direction becomes zero when the phase shift of the travelling waves equals pi rad. The angular velocity around the instantaneous centre of rotation depends on the wave amplitude of the horizontal component of the sidewinding travelling wave along the kinematic chains, and the turning radius is proportional to the amplitude gradient along the kinematic chains. The dynamic simulation of WORMESH-II and testing with the WORMESH-II prototype confirmed the proposed method, which was based on the metamathematical explanation of locomotion.

Design and optimization of a new integrated hip and knee prosthesis structure.

Conventional hip disarticulation prostheses (HDPs) are passive devices with separate joint structures, limiting amputees' ability to control and resulting in abnormal gait patterns. This study introduces a new HDP integrating the hip and knee joints for amputees' natural gait. The new HDP restores the physiological rotation center of the hip with a remote center of motion (RCM) structure, and simulates the knee motion with a four-bar structure. Nonlinear programming was employed to optimize the hip-knee joint structure. A hybrid multi-objective drive structure with a series-parallel connection was also designed to ensure motion synergy between the hip and knee joints. Finally, a prototype of the prosthesis was tested using the HDP test system. The optimization results demonstrate that the new HDP accurately restores the rotation center of the femur in amputees, with the knee's instantaneous center of rotation (ICR) trajectory closely resembling that of the human knee (Pearson correlation coefficient is 0.999). The study shows that the new HDP achieves a motion reproduction accuracy of over 95% for the human hip joint at walking speeds above 1.5 km/h, 38% higher than conventional prosthesis. Similarly, at the same walking speed, the new HDP replicates the motion of the human knee at 82.89%, surpassing conventional prosthesis by 57.85%. The new HDP restores symmetry and replicates synergistic movement in amputees' lower limbs, exhibiting superior movement characteristics compared to conventional prostheses. This innovative HDP has the potential to enhance the quality of life for amputees.

Kinematics Model Estimation of 4W Skid-Steering Mobile Robots Using Visual Terrain Classification

Accurate real-time kinematics model is very important for the control of a skid-steering mobile robot. In this study, the kinematics model of the skid-steering mobile robots was first designed based on instantaneous rotation centers (ICRs). Then, the extended Kalman filter (EKF) technique was applied to obtain the parameters of ICRs under the same specific terrain online. To adapt to different terrain environments, the fractal dimension-based SFTA (segmentation-based fractal texture analysis) method was used to extract features of different terrains, and the k-nearest neighbor (KNN) method was used to classify the terrains. In the case of real-time terrain recognition, the filter parameters of the EKF for estimating the ICRs are adjusted adaptively. Experiments on a real skid-steering mobile robot show that this method can quickly estimate the kinematics model of the robot in the case of terrain changes, and can meet the needs of practical applications. The average error of odometer estimation based on visual terrain classification is 0.06 m, while the average error of odometer estimation without terrain classification is 0.14 m.

Complete 3D Kinematics Parameters of the Temporo-Mandibular Joints Using in Vivo Data Fusion

ObjectivesThe temporo-mandibular joint (TMJ) has implications in vital functions and its disorder prevalence is between 5% and 12%. The mandible motions rely on two joints where mandibular condyles are generally asymmetric and highly individual. They rotate during jaw opening and closing and translate vertically and anteroposteriorly. Quantitative motion analysis tools are of interest to better understand normal and abnormal TMJ behavior. Previous studies have reported the asymmetrical behavior of the mandible compared to the skull as well as the synchronism of rotation and translation during its motions. But none of them has developed an experimental protocol using in vivo motion data fused with a tridimensional (3D) model. Therefore, we aim to provide the detailed kinematic parameters of the mandible compared to the skull, of the 2 condyles compared to their sockets and the instantaneous helicoidal axis (IHA) calculation through a clearly described new technology: in vivo data motion fused with virtual palpation on 3D models. We also compare the accuracy and the consistency of our results with the existing literature. Material and methodsFive healthy subjects fitted with a tailor-made dental and head clusters performed mouth opening/closing, diduction and chewing motions. 15 anatomical landmarks (ALs) were palpated on their skull and their mandible. The trajectory of the markers and ALs was recorded by opto-electronic cameras. 3D models created from magnetic resonance imaging (MRI) from the 5 subjects were processed through a segmentation procedure and imported into a musculo-skeletal data processing software. Virtual palpation was used to locate specific ALs and to build coordinate systems following the ISB recommendations. The ALs coordinates, the motion files and the morphological model were fused. Motion cycles were normalized from 1 to 100% of rotations and translations duration in coordinate systems, instantaneous helical axis (IHA) parameters were computed for the 3 motions. ResultsMedian RMSE between manually and virtually palpated ALs was 8,0 mm.During opening motion, rotation around the Z-axis (median 24,9°), translations along the X-axis and the Y-axis (median 9,7 mm and 6,3 mm respectively) were happening all at once. The IHA was obliquely orientated.During diduction motion, rotations around the Y-axis and the X-axis (median 10,7° and 3.3° respectively), translation on the Z-axis is (median −9.4 mm) occurred simultaneously. The IHA orientation was oblique and changed accordingly to the diduction side.During chewing motion, median rotation around the Z-axis was −2.2° and median translation on the Y-axis −1.0 mm. The IHA pathway high asymmetry coincided with typical movements of working and balancing condyles. ConclusionComplete 3D kinematics parameters of the TMJs, corresponding to the ISB recommendations, have been extracted with our methodology. Our values matched previous studies if available and the palpation RMSE was within the bounds of precedent experimental protocol. It is therefore efficient to study in vivo motion.Motion data have been registered in an open access data repository, allowing other researchers to exploit them and develop their own TMJ model.

Optimization of stationary shoulder friction stir welding numerical model based on instantaneous velocity center

Optimization of stationary shoulder friction stir welding numerical model based on instantaneous velocity center

The move-C cervical artificial disc can restore intact range of motion and 3-D kinematics

BACKGROUND CONTEXTIn contrast to cervical discectomy and fusion, total disc replacement (TDR) aims at preserving the motion at the treated vertebral level. Spinal motion is commonly evaluated with the range of motion (ROM). However, more qualitative information about cervical kinematics before and after TDR is still lacking. PURPOSEThe aim of this in vitro study was to investigate the influence of cervical TDR on ROM, instantaneous centers of rotation (ICR) and three-dimensional helical axes. STUDY DESIGNAn in vitro study with human spine specimens under pure moment loading was conducted to evaluate the kinematics of the intact cervical spine and compare it to cervical TDR. METHODSSix fresh frozen human cervical specimens (C4–5, median age 28 years, range 19–47 years, two female and four male) were biomechanically characterized in the intact state and after implantation of a cervical disc prosthesis (MOVE-C, NGMedical, Germany). To mimic in vivo conditions regarding temperature and humidity, water steam was used to create a warm and humid test environment with 37°C. Each specimen was quasistatically loaded with pure moments up to ±2.5 Nm in flexion/extension (FE), lateral bending (LB) and axial rotation (AR) in a universal spine tester for 3.5 cycles at 1 °/s. For each third cycle of motion the ROM was evaluated and an established method was used to determine the helical axis and COR and to project them into three planar X-rays. Statistical analysis was conducted using a Friedman-test and post hoc correction with Dunn-Bonferroni-tests (p<.05). RESULTSAfter TDR, total ROM was increased in FE from 19.1° to 20.1°, decreased in LB from 14.6° to 12.6° and decreased in AR from 17.7° to 15.5°. No statistical differences between the primary ROM in the intact condition and ROM after TDR were detected. Coupled rotation between LB and AR were also maintained. The position and orientation of the helical axes after cervical TDR was in good agreement with the results of the intact specimens in all three motion directions. The ICR in FE and AR before and after TDR closely matched, while in LB the ICR after TDR were more caudal. The intact in vitro kinematics we found also resembled in vivo results of healthy individuals. CONCLUSIONThe results of this in vitro study highlight the potential of artificial cervical disc implants to replicate the quantity as well as the quality of motion of the intact cervical spine. CLINICAL SIGNIFICANCEPhysiological motion preservation was a driving factor in the development of cervical TDR. Our results demonstrate the potential of cervical TDR to replicate in vivo kinematics in all three motion directions.

Design, Control, and Validation of a Polycentric Hybrid Knee Prosthesis

This paper presents a novel polycentric hybrid knee prosthesis (PHKP) by enabling a multi-bar linkage to work for high-torque activities in active mode and for low-torque activities in passive mode. The mode transition is implemented by a servo-controlled telescopic slide rails. Distinguished from the single-axis hybrid knee prostheses, the PHKP Knee provides geometric stability in stance and notably increases toe clearance in swing by using an optimally designed instantaneous center of rotation (ICR) trajectory. In active mode, the PHKP Knee provides high transmission ratio and continuous peak torque offering sufficient support for torque-demanding activities. Impedance control was employed to regulate joint torque as a response to knee motion in the active mode. It was found that due to the inherent geometric stability of the polycentric mechanism in stance, the damping coefficient of the controller can be tuned much smoother than the single-axis knees leading to more compliant and comfortable interactions among the wearer, the prosthesis and the ground. The stair ascent tests showed that the joint angle and torque profiles of the PHKP Knee are similar to those of the able-bodied by demonstrating a step-over-step pattern with a peak angle of 73 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\deg$</tex-math></inline-formula> and a maximum torque of 0.92 Nm/Kg.

Parameters optimization and trajectory planning of a novel 3-UPU parallel mechanism for ankle rehabilitation

AbstractAnkle rehabilitation robots are widely used due to nerve injuries and sports injuries leading to decreased mobility of the ankle joint. However, the motion of most ankle rehabilitation robots has distinctions with human ankle physiological structure. In order to achieve more accurate rehabilitation training of the ankle joint, this paper proposes a novel 3-UPU parallel rehabilitation mechanism. In a certain range, the mechanism can perform rotation around any axis within the midplane, which means that the mechanism can achieve non-fixed-point rotation around the instantaneous axis of the ankle joint. The mechanism has three degrees of freedom and can perform ankle pronation/supination and inversion/eversion movements. Taking into account the structural differences of different human bodies, the rotating axis of the mechanism can be adjusted in both height and angle. Then, the workspace of the mechanism was solved, and the size parameters of the mechanism are analyzed based on the characteristics of the size parameters of the mechanism and the motion range of the ankle. A genetic algorithm was employed to optimize the mechanism’s parameters. Next, the motion trajectory of the mechanism was planned, and the length change of the mechanism driving pair during the motion planning of the angle was obtained through kinematics simulation. Finally, experimental verification of the above rehabilitation training methods indicates that the mechanism meets the requirements of ankle rehabilitation.

Validation of a Biomechanical Injury and Disease Assessment Platform Applying an Inertial-Based Biosensor and Axis Vector Computation.

Inertial kinetics and kinematics have substantial influences on human biomechanical function. A new algorithm for Inertial Measurement Unit (IMU)-based motion tracking is presented in this work. The primary aims of this paper are to combine recent developments in improved biosensor technology with mainstream motion-tracking hardware to measure the overall performance of human movement based on joint axis-angle representations of limb rotation. This work describes an alternative approach to representing three-dimensional rotations using a normalized vector around which an identified joint angle defines the overall rotation, rather than a traditional Euler angle approach. Furthermore, IMUs allow for the direct measurement of joint angular velocities, offering the opportunity to increase the accuracy of instantaneous axis of rotation estimations. Although the axis-angle representation requires vector quotient algebra (quaternions) to define rotation, this approach may be preferred for many graphics, vision, and virtual reality software applications. The analytical method was validated with laboratory data gathered from an infant dummy leg's flexion and extension knee movements and applied to a living subject's upper limb movement. The results showed that the novel approach could reasonably handle a simple case and provide a detailed analysis of axis-angle migration. The described algorithm could play a notable role in the biomechanical analysis of human joints and offers a harbinger of IMU-based biosensors that may detect pathological patterns of joint disease and injury.

Probabilistic analysis of the instantaneous center of rotation of a floating structure under regular and irregular beam waves

Accurate prediction of roll motion is crucial to the safety of ships and floating structures. The “roll center” mentioned in the literature is ambiguous and various definitions exist. Hence, the instantaneous center of rotation (ICR) is preferred, being an established kinematic concept. Understanding the ICR is important on account of its significant influence on roll damping. A previous study postulated that the ICR moves in a straight line for regular beam waves, based on experimental observations. In this paper, the probability distribution of the ICR coordinates (y1, y2) is derived analytically for regular and irregular beam waves. For regular waves, it is proven a fortiori that the ICR lies on a straight line, and that y1 and y2 follow the Cauchy distribution, for which the mean and variance are undefined. For irregular waves, it is shown that the joint probability density of y1 and y2 is a bivariate Cauchy distribution, thus the iso-density contour lines are concentric ellipses. Regular and irregular wave experiments are performed to investigate realistic conditions. The analytical solutions are found to be quite accurate, notwithstanding some discrepancies arising from nonlinearities and experimental imperfections. The theoretical results presented herein have potential practical applications, for example since the ICR governs damping, the ICR distribution allows damping to be modeled as a stochastic process.

Cervical Disc Arthroplasties Fail to Maintain Physiological Kinematics Under Lateral Eccentric Loads.

In vitro human cadaveric biomechanical analysis. Optimization of prostheses for cervical disc arthroplasties (CDA) reduces the risk of complications. The instantaneous helical axis (IHA) is a superior parameter for examining the kinematics of functional spinal units. There is no comprehensive study about the IHA after CDA considering all 3 motion dimensions. Ten human functional spinal units C4-5 (83.2 ± 7.9yrs.) were examined with an established measuring apparatus in intact conditions (IC), and after CDA, with 2 different types of prostheses during axial rotation, lateral bending, and flexion/extension. Eccentric preloads simulated strains. The IHA orientation and its position at the point of rest (IHA0-position) were analyzed. The results confirmed the existing data for IHA in IC. Lateral preloads showed structural alterations of kinematics after CDA: During axial rotation and lateral bending, the shift of the IHA0-position was corresponding with the lateral preloads' applied site in IC, while after CDAs, it was vice versa. During lateral bending, the lateral IHA orientation was inclined, corresponding with the lateral preloads' applied site in the IC and oppositely after the CDAs. During flexion/extension, the lateral IHA orientation was nearly vertical in the IC, while after CDA, it inclined, corresponding with the lateral preloads' applied site. The axial IHA orientation rotated to the lateral preloads' corresponding site in the IC; after CDA, it was vice versa. Both CDAs failed to maintain physiological IHA characteristics under lateral preloads, revealing a new aspect for improving prostheses' design and optimizing their kinematics.