Dynamic Modeling and Experimental Validation of a Water Hydraulic Soft Manipulator Based on an Improved Newton—Euler Iterative Method

Compared with rigid robots, soft robots have better adaptability to the environment because of their pliability. However, due to the lower structural stiffness of the soft manipulator, the posture of the manipulator is usually decided by the weight and the external load under operating conditions. Therefore, it is necessary to conduct dynamics modeling and movement analysis of the soft manipulator. In this paper, a fabric reinforced soft manipulator driven by a water hydraulic system is firstly proposed, and the dynamics of both the soft manipulator and hydraulic system are considered. Specifically, a dynamic model of the soft manipulator is established based on an improved Newton–Euler iterative method, which comprehensively considers the influence of inertial force, elastic force, damping force, as well as combined bending and torsion moments. The dynamics of the water hydraulic system consider the effects of cylinder inertia, friction, and water response. Finally, the accuracy of the proposed dynamic model is verified by comparing the simulation results with the experimental data about the steady and dynamic characteristics of the soft manipulator under various conditions. The results show that the maximum sectional error is about 0.0245 m and that the maximum cumulative error is 0.042 m, which validate the effectiveness of the proposed model.

Seismic performance of a continuous bridge with winding rope device activated by a fluid viscous damper

The seismic requirements of piers with fixed bearings (the fixed pier) for continuous girder bridges are relatively high, while the potential seismic capabilities of piers with sliding bearings (the sliding piers) are not fully utilized. To solve this contradiction, a new type of winding rope shock absorption device activated by a fluid viscous damper (WRD-D) was proposed. The WRD-D was installed on the top of the sliding piers, and the both ends of a fluid viscous damper were connected to the superstructure by winding ropes. During an earthquake, the damping force rises with the increase of relative speed between the sliding piers and the superstructure, activating the WRD-D and producing large frictional resistance, subsequently causing the sliding piers and the fixed pier to bear the seismic load cooperatively. In this study, the working mechanism of the WRD-D was researched. The shaking table test of a scaled continuous girder bridge model employing the WRD-D was conducted. The test results reveal that the WRD-D can effectively reduce the seismic requirements of the fixed pier and the superstructure displacements.

A minimum transmitted load control method for shock isolation mounts with magnetorheological energy absorbers

This paper proposed a minimum transmitted load (MTL) control method for drop-induced shock isolation mounts (SIM) with magnetorheological energy absorbers (MREAs). MTL control method consists of two parts of maximum damping force (MDF) control and one part of constant acceleration (CA) control, which can make the payload stop after fully utilize MREA stroke (soft landing) with minimum transmitted load. The control algorithm of MTL control method is derived in a single-degree-of-freedom (SDOF) system. The relationship between the controllable velocity range of MTL control method and parameters of shock isolation mounts is also derived. An optimal control method selection criterion between Bingham number (BN) control method and MTL control method is developed. The performance of MTL control method and selection criterion are shown by applying to the SIM system with variable drop velocities and system parameters. Results shows that MTL control method has the minimum transmitted load and the selection criterion is feasible.

Modeling and control of hybrid MR seat damper and whole body vibration evaluation for bus drivers

This paper describes the design, simulation, and performance evaluation of hybrid MR damper on quarter bus semi-active seat suspension coupled with human biodynamic model. Also, the whole body vibration (WBV) exposures were evaluated based on the international standard ISO 2631 (1997), and its parameters were used to measure the level of discomfort for bus drivers. The hybrid MR damper was proposed to enhance the damping force within low current supplied and achieve a fail-soft capability in case of electrical failure. The characteristics of the proposed hybrid MR damper were compared to the conventional MR damper by considering the same size, materials, and current input. The designed damper was incorporated to seat suspension system coupled with biodynamic lumped model, and the governing equations of motion of the full model were derived. Skyhook controller was used to control the amount of current to be supplied to hybrid MR damper. The controlled semi-active hybrid MR and conventional MR seat suspension are compared to uncontrolled system for two types of road excitation. The simulated results show that the driver seat comfort was improved by the skyhook controller than the uncontrolled case. The evaluated WBV showed that the hybrid MR damper can improve the driver life from fairly uncomfortable to little discomfort.

Analysis and optimisation design on damping orifice of oleo-pneumatic landing gear

This paper investigates the feasibility of improving the aircraft landing performance by design the damping orifice parameters of the landing gear using lattice Boltzmann method coupled with the response surface method. The LBM is utilised to simulate characteristics of the damping orifice after model validation. The numerical model of the landing gear using simulated damping force is validated by single landing gear drop test. Based on the numerical model and the response surface functions, the sensitivity analysis and the optimisation design are performed. The maximum error of mean velocity simulated using LBM with experimental data is 7.07% for sharp-edged orifices. Moreover, the numerical model predicts the landing responses adequately, the maximum error with drop test data is 2.51%. The max overloading of the aircraft decreases by 5.44% after optimisation, which proves that this method is feasible to design the damping orifice for good landing performance.

Research on a high power density mechanical-electrical-hydraulic regenerative suspension system for high-speed tracked vehicles

High power density energy regeneration is one of the effective solutions to solve the contradiction between improving the damping performance and energy consumption of active suspension. The hydraulic commutator is used to realize hydraulic rectification and hydraulic variable speed/pump/motor with few teeth difference gear pairs is used to match the speed, combined with permanent magnet motor power generation and power supply to put forward kilowatt level high power density mechanical-electrical-hydraulic regenerative suspension system for high-speed tracked vehicles. The mathematical model and fluid-solid-thermo-magnetic multiphysics coupling model are built to analyze the damping performance and regenerative characteristics of the system under passive and semi-active working conditions. The simulation results show that the damping force of the system increases with the increase of the road excitation amplitude and the semi-active control can be realized by adjusting the duty cycle with the PWM control rectifier module. The high power density mechanical-electrical-hydraulic regenerative suspension system can realize kilowatt level energy regeneration, and the regenerative efficiency is more than 50% under low-frequency excitation. The temperature rise of the system is low during operation, which is helpful to improve the reliability and service life.

Wave Energy Converter’s Slack and Stiff Connection: Study of Absorbed Power in Irregular Waves

Two different concepts of wave energy converter coupled to the novel C-GEN linear generator have been studied numerically, including the evaluation of different buoy sizes. The first concept has a slack connection between the buoy and the generator on the seabed. Another concept is based on a stiff connection between the buoy and the generator placed on an offshore platform. Three different approaches to calculate the damping force have been utilized within this study: the optimal damping coefficient, R-load, and RC-load. R-load is a model for the load applied to a grid-connected generator with passive rectification. RC-load is a model for a phase angle compensation applied to a system with active rectification. The radiation forces originating from the oscillatory motion of the buoy have been approximated using the transfer function in the frequency domain and the vector fitting algorithm. A comparison of the approximation methods is presented, and their accuracy has been evaluated. The advantage of the vector fitting method has been shown, especially for higher approximation orders which fit the transfer function with high accuracy. The study’s final results are shown in terms of the absorbed power for the sea states of March 2018 at Wave Hub, UK.

Shape optimization of magnetorheological damper piston based on parametric curve for damping force augmentation

Making full use of the magnetically controllable rheological properties of magnetorheological (MR) fluid, MR actuators have been applied in many engineering fields. To adapt to different application scenarios, parameters of MR actuators often need to be optimized. Previous MR actuator optimization was focused on finding optimal combinations of geometric dimensions and physical parameters that meet certain requirements. The parts with optimized dimensions were still in regular shape, which might not bring optimal damping performance. Therefore, in this paper, shape optimization of MR damper piston based on parametric curve is performed for the first time. First, the regional magnetic saturation problem in the previous prototype is stated. Then, the MR damper with normal piston is simulated as a reference. Later, Bezier curve, one of the typical parametric curves, is used to form the piston with optimized parameters, and the MR damper with optimized piston is also simulated. Finally, prototypes of the MR dampers with normal and optimized pistons are fabricated and tested. Compared with the MR damper with normal piston, the one with optimized piston has larger field dependent force and total damping force under relatively large current, with about 52% and 24% maximum increasing percentage, respectively. The controllable force range of the MR damper with optimized piston is also larger than that with normal piston.

A High-Speed Current Source for Magnetorheological Application

Current source is an indispensable component of magnetorheological (MR) systems. Though MR fluid has a phase change as fast as in 1 ms, the response of MR damper (MRD) to generate the damping force may be two orders of magnitude longer. Therefore, the rapid response of current source is a key to realize the real-time semi-active control of MR devices. This study proposes a programmable high-speed, low-cost current source exclusively for MR devices based on the synergy between supercapacitor and Buck converter (i.e., SSBC current source). SSBC current source features a strategy consisting of a lifting phase of supercapacitor and a following maintaining phase of Buck converter. Specifically, the high power density of supercapacitor contributes to rapidly lifting/raising the initial current, and then, like a “relay race”, the expected output is maintained through a Buck converter. Theoretical modeling and experiments are performed systematically. The response times (@ 95% of expected outputs) measured are 0.44, 0.84 and 1.88 ms for the outputs of 3, 6 and 9 A, respectively; these values are highlighted as the fastest level in this field. Besides, the response can be up to 24.6 and 43.7 times faster than the cases using supercapacitor and Buck converter to directly drive the MRD, respectively. SSBC current source is employed to generate a sequence of currents/magnetic inductions, only four variables of which need to be controlled programmatically: the order of lifting and maintaining phases, switching time of lifting phase, PWM duty cycle of Buck converter and duration of maintaining phase. The response time stability is verified by 100 cycles of on/off tests, showing a fluctuation of only 1.1%, which indicates a very reliable high-speed response. This study provides an exclusive power supply with a novel strategy for MR devices, which is believed to be an important promotion for MR technologies.