Center Of Gravity Position Research Articles

Iterative control decoupling tuning for precision MIMO motion systems: A matrix update method

Control decoupling is the basic control step for precision MIMO (Multi-Input-Multi-Output) motion systems. After decoupling, the MIMO logical controlled plant can be diagonal dominant so that the control design for each DOF (Degree of Freedom) can be separately treated. However, due to the manufacturing tolerances and the assembling errors, the actual CoG (Center of Gravity) and actuator positions are inconsistent with the designed values. The nominal static control decoupling matrix is inaccurate, which significantly deteriorates the decoupling performance. To address the problem, this paper develops a matrix update based iterative control decoupling tuning method. Tuning with feedback control signals to achieve accurate tuning is its first distinct feature. By employing rigid-body model information to construct more accurate basis functions, fast tuning can also be achieved, especially for relatively low control bandwidth occasions. Differing from the feedforward compensation based iterative control decoupling tuning method, the matrix update method improves the dynamics of the logical controlled plant, does not increase the control complexity and is more robust to the inaccuracy of the model information. Experimental results on the short-stroke module of a precision motion stage which is the key subsystem of the lithographic projection lens testing system present significant control decoupling performance improvement (for example the peak value of the Rx-DOF servo error caused by the Z-DOF movement is reduced from 1.29 ×10−5 m to 3.19 ×10−6 m) after just two trials.

Tiltwing eVTOL Transition Trajectory Optimization

This paper studies transition trajectory optimization for a tiltwing electrical vertical takeoff and landing (eVTOL) aircraft configuration and evaluates the benefits of equipping it with fluid injection active flow control (AFC). Using a three-degree-of-freedom model of the aircraft’s longitudinal dynamics, both hover-to-cruise (forward) and cruise-to-hover (backward) transition are investigated for a range of center-of-gravity (CG) positions to determine minimum-energy trajectories that achieve zero altitude variation while avoiding wing aerodynamic stall. It is demonstrated that constant-altitude transition can be achieved in the forward direction (with or without AFC), whereas the use of AFC in backward transition reduces the total altitude change by 24%. A comparative constant-altitude backward transition solution using a different airfoil with a higher stall limit suggests that a redesign of the tail wing of this unique tiltwing aircraft could better leverage the benefits of using AFC in this application. Additionally, it is also shown that, in the case of forward transition, AFC can be used to decrease the total transition time and increase the range of CG positions where constant-altitude transition can occur.

Application of Continuous Stability Control to a Lightweight Solar-Electric Vehicle Using SMC and MPC

This paper investigates the application of contusion stability yaw control of a lightweight solar-electric vehicle. The vehicle’s customized design envelope makes it more sensitive to variations in load due to its low weight and relatively large size. To address this issue, control strategies were developed using differential motor torques to generate direct yaw moments using the vehicle’s rear in-wheel motors. This paper introduces the working conditions of solar vehicles and demonstrates the necessity of stability control. Vehicle parameters such as mass and center of gravity position are obtained to apply control to the real vehicle. The paper then describes two stability control strategies, using (i) sliding-mode control (SMC) and (ii) model predictive control (MPC). To account for the road bank angle of the test area and the impact of additional weight from a driver and passenger, a Kinematic-Based Observer is designed to estimate the vehicle’s side-slip based on measured values. To collect real-time data, a dSPACE MicroAutobox was installed on the solar vehicle. The results show the effect of the observer and controllers under different vehicle speeds and load conditions. Finally, closed-loop simulation results are presented to support the findings from the open-loop testing.

Real-time estimation of barycenter position for fuel cell distributed drive electric tractor based on derived UKF

ABSTRACT The FCDET is considered as a promising and advanced agricultural machinery due to its convenience and controllability. To enhance the control performance of the FCDET unit dynamic system, understanding the accurate position of the center of gravity (CoG) of the tractor unit in longitudinal motion and the operating environment is essential. In this paper, we proposed a real-time estimation method of CoG position of longitudinal motion for FCDET plowing and transportation conditions. CoG height and longitudinal axis distance distribution coefficients are used as state estimation variables, and the data obtained from displacement and velocity sensors are used as state observation variables, establishing a discrete system state space model and proving the observability. The proposed Derived UKF algorithm introduces the Sage-Husa adaptive noise equation within the Square-Root UKF framework to address the non-positive definite matrix problem. The research shows that the precise CoG longitudinal position effectively reflects changes in operational pavement load. The Derived UKF algorithm exhibits high state estimation accuracy in plowing and transportation conditions, with mean absolute errors of 14.2% and 5.0% of the state amplitude, respectively. This study supports the practical application of real-time state parameter estimation algorithms in controlling advanced agricultural machinery distributed drive systems.

Spatial-temporal pattern of change in production-living-ecological space of Nanchong City from 2000 to 2020 and underlying factors.

This study analyzed the spatial-temporal change pattern and underlying factors in production-living-ecological space (PLES) of Nanchong City, China, over the past 20 years using historical land use data (2000, 2010, 2020). A land use transfer matrix was calculated from the historical land use maps, and spatial analysis was conducted to analyze changes in the land use dynamics degree, standard deviation ellipse, and center of gravity. The results showed that there was a rapid spatial evolution of the PLES in Nanchong from 2000 to 2010, followed by a stabilization in the second decade. The transfer of ecological-production space occurred mainly in the Jialing and Yilong River basins, while the reduction of production space and the increase of living space were most prominent in the intersection of three districts (Shunqing, Jialing, and Gaoping districts). The return of production-ecological space was observed in the south and northeast of Yingshan, and there was little notable transfer of other types. The distribution of production space in Nanchong evolved in a north-south to east-west trend, with the center of gravity moving from Yilong to Peng'an County. The living space and production space expanded in a north-south direction, and the center of gravity position was in Nanbu, indicating a more balanced growth or decrease in the last 20 years. The changes in the spatial-temporal pattern of PLES in Nanchong were attributed to the intertwined factors of national policies, economic development, population growth, and the natural environment. This study introduced a novel approach towards rational planning of land resources in Nanchong, which may facilitate more sustainable urban planning and development.

Design and numerical study of foldable wing module of air-launched underwater glider

Launching underwater gliders by aircraft could greatly expand the application of underwater gliders. However, during the process of the glider entry into the water, it will be subjected to significant impact loads, especially during the process of wing entry into the water. In this paper, a foldable wing module is proposed to reduce the water entry impact loads of the glider caused by the wings entering into the water. The effect of the foldable wing module on impact loads reduction and the influence of the foldable wing module on the water entry trajectory are studied by numerical method. The results show that the differences in mass and gravity center position caused by the foldable wing module have little effect on the water entry impact loads of the glider until the wings impact the water. When the glider enters the water obliquely, the wing module reduces the peak radial acceleration of the glider. In addition, the trajectory and time of the glider to reach the horizontal attitude are also reduced. These conclusions will be helpful for the designing of the wings of air-launched underwater gliders.

Biomechanical Analysis of Walking Shoes with Different Center of Gravity Positions on Gait

Biomechanical Analysis of Walking Shoes with Different Center of Gravity Positions on Gait

P1E5-19 Effects of shoes with different center of gravity positions on gait

P1E5-19 Effects of shoes with different center of gravity positions on gait

Localization of center of gravity of helmet systems in the human anatomical frame using 3D laser scanners

Introduction: An accurate assessment of the Center of Gravity (CoG) and mass properties of aircrew helmets and helmet-mounted devices is an essential requirement to predict neck injury potential. Conventionally, trifilar pendulum method is used for the assessment of CoG shift and calculation of force moment and mass moment. In this study, a new procedure is described to obtain a more precise measurement of the CoG of the helmet as well as the combined head and helmet system. Material and Methods: Measurement of the helmet mass and CoG properties was done using a trifilar pendulum and the geometrical properties of the helmet and head were obtained using a 3D laser scanner. The required coordinate transformations from the laboratory frame to the anatomical frame using the 3D scanner as a coordinate digitizer. The head sizes used in the calculations ranged from small female head to large male head and a single average head CoG position was used to calculate the combined head and helmet CoG. Results: The error of the 3D scanner method for combined head and helmet CoG measurement as compared to the trifilar pendulum method varied between 0.3 mm and 0.4 mm with an average error of 0.4 mm. This method could also successfully calculate the combined CoG of the helmet on various head sizes ranging from small female to large male heads. Conclusion: The 3D laser scanner-based CoG measurement gave similar results as compared to the present method of CoG measurement when the medium-sized anthropomorphic test dummy head was considered. The localization of helmet CoG in the anatomical frame would allow more accurate measurements of force moment and mass moment. The same methodology could also be used to calculate the combined head and helmet CoG of different head and helmet masses.

Stiffness characteristics analysis of a Biglide industrial parallel robot considering the gravity of mobile platform and links

For the machining process of industrial parallel robots, the gravity generated by the weight of mobile platform and links will lead to the deviation of the expected machining trajectory of the tool head. In order to evaluate this deviation and then circumvent it, it is necessary to perform the robotic stiffness model. However, the influence of gravity is seldom considered in the previous stiffness analysis. This paper presents an effective stiffness modeling method for industrial parallel robots considering the link/joint compliance, the mobile platform/link gravity, and the mass center position of each link. First, the external gravity corresponding to each component is determined by the static model under the influence of gravity and mass center position. Then, the corresponding Jacobian matrix of each component is obtained by the kinematic model. Subsequently, the compliance of each component is obtained by cantilever beam theory and FEA-based virtual experiments. In turn, the stiffness model of the whole parallel robot is determined and the Cartesian stiffness matrix of the parallel robot is calculated at several positions. Moreover, the principal stiffness distribution of the tool head in each direction over the main workspace is predicted. Finally, the validity of the stiffness model with gravity is experimentally proved by the comparison of the calculated stiffness and measured stiffness in identical conditions.

Model-Based Estimation of Vehicle Center of Gravity Height and Load

AbstractWith an increasing number of driver assistance functions and the upcoming trend of autonomous driving, knowledge of the current state and changeable parameters of the vehicle becomes more and more important. One particularly significant parameter with regard to vehicle dynamics is the center of gravity (COG) height, which mainly accounts for its roll dynamics in combination with the mass of the vehicle. Thus, a highly increased vehicle mass and COG height might lead to rollover during cornering, which underlines the need for accurate knowledge of the load of the vehicle. Based on that, an improved rollover prevention could be implemented, for instance, by enhancing the electronic stability program (ESP) of the vehicle. Therefore, the main contribution of this work is the model-based online estimation of the additional load of the vehicle, comprising its COG position and mass. This is achieved by applying a joint extended Kalman Filter (EKF) for the simultaneous state and parameter estimation. Based on a nonlinear model with roll, pitch, and vertical dynamics, an accurate and reliable estimation is possible. One major novelty of this work is the consideration of air suspension systems on top of conventional steel spring suspension systems. Therefore, a nonlinear air spring model with sufficient complexity is proposed, making it suitable for real-time applications. Further, a system theoretical observability analysis allows for an online adaptation of the Kalman Filter weights in order to account for different driving situations. The proposed estimation method is tested and validated by considering a wide range of driving situations, considering distinct loading conditions on both a test track and public roads. The estimation accuracy lies within roughly 50 kg and 1.5 cm for the vehicle mass and COG height, respectively.

Approach for Measuring a Ship to Shore Crane Actual Wheel Load

Knowing the real crane deadweight, center of gravity (COG) and wheel loads instead of nominal ones is crucial for many reasons. One of the reasons relates to the checking the quay strength where the crane is going to be installed and it should be based on the crane maximum real wheel loads. Another example could be the crane transportation by sea on the deck of the vessel (Starykov & Van Hoorn, 2017). In this case predicting the precise value of the crane deadweight and its COG plays a key role in accurate calculation of the vessel stability, acceleration calculation from the ship motions and the vessel’s deck strength. This paper demonstrates a new approach to finding the crane wheel load and in the result the deadweight and COG position. This method does not need special arrangement and uses combination of strain gauge measurements and Finite Element (FE) analysis only. The application of the method is demonstrated on example of the ship loader for which the possibility of capacity increase has been assessed.

Joint Estimation of Mass and Center of Gravity Position for Distributed Drive Electric Vehicles Using Dual Robust Embedded Cubature Kalman Filter

The accurate estimation of the mass and center of gravity (CG) position is key to vehicle dynamics modeling. The perturbation of key parameters in vehicle dynamics models can result in a reduction of accurate vehicle control and may even cause serious traffic accidents. A dual robust embedded cubature Kalman filter (RECKF) algorithm, which takes into account unknown measurement noise, is proposed for the joint estimation of mass and CG position. First, the mass parameters are identified based on directly obtained longitudinal forces in the distributed drive electric vehicle tires using the whole vehicle longitudinal dynamics model and the RECKF. Then, the CG is estimated with the RECKF using the mass estimation results and the vertical vehicle model. Finally, different virtual tests show that, compared with the cubature Kalman algorithm, the RECKF reduces the root mean square error of mass and CG by at least 7.4%, and 2.9%, respectively.

Study on the Control Algorithm of Automatic Emergency Braking System (AEBS) for Commercial Vehicle Based on Identification of Driving Condition

Automatic emergency braking systems (AEBS) significantly improve the active safety performance of commercial vehicles, but their effectiveness is affected by the vehicle’s driving conditions, which mainly include the vehicle load and road conditions. In order to improve the adaptability of the AEBS, an AEBS control strategy with adaptive driving conditions was proposed and validated using a simulation and experimentation. This AEBS control strategy was designed based on an estimation of the vehicle mass, the center of gravity position, road grade, and the tire-road friction coefficient. In the simulation and experimental verification, the braking deceleration and braking distance under different driving conditions were compared. The results show that the AEBS control strategy proposed in this paper can avoid collisions in all test scenarios and maintain a parking spacing of approximately 5 m. In an extreme test scenario with a full load and low tire–road friction, as compared with the fixed threshold control strategy, the warning can be issued 0.2 s earlier and the maximum intensity braking can be carried out 0.5 s earlier.

Game-based virtual reality solution for post-stroke balance rehabilitation

In recent years, there has been a remarkable decline in stroke-related mortality. However, it remains one of the leading causes of death and the most prominent cause of lifelong disability in adults. This positive development results from increased accessibility to various stroke treatment options. In addition, the use of virtual reality in rehabilitation offers a possible alternative to traditional methods of medical rehabilitation of the upper limbs, improving muscle strength or balance. An early diagnosis of equilibrium deficits brings an incredible contribution to recovery. Analysis tests using stabilometric platforms have begun to be used more recently due to the advantages offered. This assessment method highlights and analyzes balance disorders and determines the body's center of gravity position through several sensors or arrays of sensors that transmit information to the processing software. This work aimed to develop a low-cost, stabilometric platform that could be used to build a recovery system using virtual reality-based games. The developed platform uses an Arduino UNO microcontroller that takes data from 4 force sensors. Two applications have been created. The first one was for balance maintenance and the second for execute balance exercises in the anteroposterior and mediolateral direction.

A Research of Design, Lateral Stability and Simulation for a Chassis Running in Forest

Forest roads are short of structured terrain. Individual wheels often cannot contact the ground when conventional chassis is driving, and the mobility is weak. In addition, the lateral rollover usually occurs. In this article, a forestry chassis with a novel articulated structure with three degrees of freedom (FC-3DOF(II)) is proposed. Compared with conventional chassis, the novel articulated structure is designed, which contributes to achieving full-time contact between wheels and ground. The mobility is improved. For the lateral stability, the previous lateral rollover model of chassis is often established by the geometrical position of COG (center of gravity) of the frame. This method is applied with limitations, which is not universal. Therefore, a new accurate lateral rollover model for FC-3DOF(II) is derived, which predicts the lateral stability by analyzing tire contact forces. The new lateral rollover model is more general and recovers the previous model. To verify the theoretical analysis exactly, the virtual prototype of FC-3DOF(II) is established in SolidWorks, and simulations of lateral rollover are carried out in ADAMS. In simulation experiments, the lateral stability is predicted by analyzing tire contact forces when the inclination of terrain is increasing. Two conditions are considered in simulations. The lateral stability of FC-3DOF(II) and FC-3DOF(II) installed rectangular objects. Compared to the simulation and theoretical results, for FC-3DOF(II), the maximum absolute percent difference of the contact force with the theoretical analysis relative to the simulation is only 1.83%. For FC-3DOF(II) installed rectangular objects, the simulation results show that the lateral rollover is caused by the rear up-slope wheel when the inclination of terrain reaches 34°. The theoretical result relative to the simulation is only 2.90%. The maximum absolute percent difference of the contact force with the theoretical analysis relative to the simulation is only 2.50%. Simulation results validate the effectiveness of the proposed lateral rollover model in two conditions.

Development and evaluation of new simple mechanisms for shock absorption of the ankle

Diverse types of high-precision body modeling have been proposed to improve the efficiency of rehabilitation work and exercise in sports and other activities. In this study, a simple below-knee model of the body was created. First, the moment of inertia around the ankle was calculated, and the center of gravity position on the sole of the foot, which is decided by the body inclination, the ball of the thumb, and the reaction force on the heel, was used as the basic model. Based on this basic model, the force acting on the center of gravity of the body was calculated as a first-order lagging element, and it was found that in order to reduce the ankle torque, it is not necessary to increase the proportional gain of the force output per body displacement (how much force can be produced), but to reduce the time constant T In order to reduce the ankle torque, it was observed that making the time constant T small (how fast the force can be generated) is a major factor. When the spring-damper system was added to the model as well as the force generation mechanism, it was found that increasing the damper coefficient was also effective in reducing the ankle torque. Increasing the damper coefficient means how quickly a large force can be generated when an impact is applied. In other words, to reduce the burden on the ankle, it is effective to have a flexible body with the agility to produce quick and large forces.

Hydrodynamic Characteristics at Intersection Areas of Ship and Bridge Pier with Skew Bridge

Ships sailing in the area of a bridge are vulnerable to the influence of complex water flow, due to the complex flow pattern around the bridge pier. Ships often crash into bridge piers, leading to serious economic losses and threating personal safety. Based on the common forms of piers of skew bridges, the hydrodynamic problems encountered during ship–bridge interactions in the area of a skew bridge were studied using particle image velocimetry-based flume testing, physical model testing, and numerical simulation. The influence of the flow angle of attack of a round-ended pier on the force and center of gravity of a ship moving on both sides of a pier is discussed under various ship–bridge transverse spacings. The results show that as a ship passes through the bridge area, the bow roll moment exhibits three peak values: ‘positive’, ‘negative’, and ‘positive’, and the curve of the center of gravity position forms the shape of a ‘straw hat’. With an increase in the flow angle of attack of the pier, the negative peak value and the second positive peak value of the bow roll moment of the ship passing through the back flow side of the pier become greater than those on the upstream side. Moreover, the ship’s navigation attitude is more unstable compared to that upstream, and the ship is at risk of colliding with the pier and sweeping. The width of the restricted water area, determined by the hydrodynamic action between the ship and bridge in the skew bridge area, is the same as that determined by the critical lateral velocity. For the ship class referred to in this study, the current code can also be used in channel design, to safeguard ship and personal safety with piers with a large flow angle of attack.

Effects of Galvanic Vestibular Stimulation on Subjective Visual Vertical and Sitting Balance in Patients with Stroke

ObjectiveThis study aimed to examine the effects of galvanic vestibular stimulation (GVS) on visual vertical cognition and sitting balance in stroke patients. Materials and MethodsPatients with unilateral supratentorial infarction and hemorrhagic lesions and healthy controls were recruited. Bipolar GVS was performed through the bilateral mastoid processes with an 1.5-mA electric current. Each participant received three stimulation patterns: right anode-left cathode, left anode-right cathode, and sham. The subjective visual vertical (SVV) and center of gravity positions in the sitting posture were measured in three groups of participants: patients with right hemisphere lesions, patients with left hemisphere lesions, and in healthy controls. Changes in the SVV and center of gravity positions before and during galvanic vestibular stimulation were assessed. ResultsIn each group, eight individuals were recruited for SVV measurements and nine individuals for center of gravity measurements. We found changes due to polarity of stimulation on the SVV and mediolateral changes in the center of gravity in the sitting position of patients with stroke, while there was no significant difference between groups or interaction of the two factors (polarity vs. group). ConclusionChanges in the visual vertical cognition and sitting balance occur during GVS in patients with stroke. GVS is a potential tool for ameliorating balance dysfunction in patients with stroke.

Numerical study of shallow-draft air-cavity hull with two-step bottom in deep and shallow water

Air-cavity boats utilize air injection to the bottom hull surface to reduce water drag. While being attractive due to potentially large energy savings, this technology has not yet found broad applications due to challenges in confidently predicting air-cavity flows and a lack of standard development practices for air-cavity vessels. In this work, computational fluid dynamics modeling is undertaken to demonstrate the air-cavity system implementation on a simple shallow-draft hull. After conducting verification and validation study with data available for a displacement barge-type air-cavity boat, its hull is numerically modified with intention to operate at higher speeds up to the planing regime. The modifications include replacement of a sloping beach in the bottom recess with additional step and reduction of skeg volume. Computational simulations are carried out for the modified hull at several speeds and center of gravity positions. Numerically obtained resistance, trim, heave, and air-cavity shapes are reported and discussed. A favorable loading condition is identified. In addition, simulations were conducted for shallow-water scenarios. In steady-state regimes, significant performance degradation is found near the critical speed, while performance gains are demonstrated in the supercritical regime. In one case of extremely shallow water, the hull exhibited vertical-plane instability resulting in cyclic motions.