Stewart平台力控制系统研发

采用位移控制模式或称位姿控制的六自由度Stewart平台已经得到了广泛的应用,采用力控制模式(这里称之为力姿force posture控制)的研究和应用却很少,其中控制技术困难、稳定性差是重要的原因。而采用力姿控制在柔性加工、交会对接、实验边界模拟等方面具有非常广泛的应用前景。该文介绍了在Stewart平台上进行的力控制系统开发,实现了力姿控制。

Adaptive variable structure control based on backstepping for spacecraft with reaction wheels during attitude maneuver

An adaptive variable structure control method based on backstepping is proposed for the attitude maneuver problem of rigid spacecraft with reaction wheel dynamics in the presence of uncertain inertia matrix and external disturbances. The proposed control approach is a combination of the backstepping and the adaptive variable structure control. The cascaded structure of the attitude maneuver control system with reaction wheel dynamics gives the advantage for applying the backstepping method to construct Lyapunov functions. The robust stability to external disturbances and parametric uncertainty is guaranteed by the adaptive variable structure control. To validate the proposed control algorithm, numerical simulations using the proposed approach are performed for the attitude maneuver mission of rigid spacecraft with a configuration consisting of four reaction wheels for actuator and three magnetorquers for momentum unloading. Simulation results verify the effectiveness of the proposed control algorithm.

Attitude Control Experiments of Cubic Rover on Low-Gravity Testbed

In-situ exploration of asteroid surfaces is of great scientific significance.Internally actuated rovers have been released to asteroid surfaces but without enough controllability.To investigate the attitude control characteristics of the cubic rover for asteroid surface exploration,a series of experiments are carried out using the self-designed rover and the low-gravity testbed.The experiments focus on two major themes:The minimum flywheel speed for cubic rover to produce a walking motion in different conditions,and the relationship between the rover’s rotation angle and the flywheel speed in twisting motion.The rover’s dynamical descriptions of the walking and twisting motions are first derived.The features and design of the low-gravity testbed are then summarized,including its dynamics,setup,and validation.A detailed comparison between the dynamic model and the experimental results is presented,which provides a basic reference of the cubic rover’s attitude control in low-gravity environments.

The State of Arts of Hall Thruster

Electric propulsion is broadly defined as the acceleration of a working fluid for propulsion by electrical heating and/or by electric and magnetic body forces. Compared with chemical propulsion, electric propulsion has the characteristic of higher specific impulse, lower thrust, lighter weight and longer lifetime. So electric propulsion is generally suitable for satellite attitude control, the orbit transfer and raising, orbit correction, resistance compensate, position keeping, reposi- tion, space exploration and interplanetary flight.

Design of deep-water omnidirectional spirit level

Attitude adjustment is a key link in the installation process of underwater facilities in deep water.To solve this problem,an omnidirectional spirit level for deep water was developed.The sealing principle of the spirit level and the principle of deep-water pressure resistance are analyzed,and the threaded connection strength is checked.The mechanical simulation verifies that the spirit level can withstand the pressure of 2000 m water depth,and the water pressure test is carried out for 30 min in a 20 MPa hyperbaric chamber.After the experiment is completed,the appearance of the spirit level is intact and there is no leakage.The experiment results show that the deep-water omnidirectional spirit level can be used in the deep sea within 2000 m.

Changes in balance ability,power output,and stretch-shortening cycle utilisation after two high-intensity intermittent training protocols in endurance runners

Purpose：This study aimed to describe the acute effects of 2 different high-intensity intermittent trainings（HIITs） on postural control,countermovement jump（CMJ）,squat jump（SJ）,and stretch-shortening cycle（SSC） utilisation,and to compare the changes induced by both protocols in those variables in endurance runners.Methods：Eighteen recreationally trained endurance runners participated in this study and were tested on 2 occasions：10 runs of 400 m with 90 s recovery between running bouts（10×400 m）,and 40 runs of 100 m with 30 s recovery between runs（40 × 100 m）.Heart rate was monitored during both HIITs;blood lactate accumulation and rate of perceived exertion were recorded after both protocols.Vertical jump ability（CMJ and SJ） and SSC together with postural control were also controlled during both HIITs.Results：Repeated measures analysis revealed a significan improvement in CMJ and SJ during 10 × 400 m（p〈0.05）,whilst no significan changes were observed during 40×100 m.Indexes related to SSC did not experience significan changes during any of the protocols.As for postural control,no significan changes were observed in the 40×100 m protocol,whilst significan impairments were observed during the 10×400 m protocol（p〈0.05）.Conclusion：A protocol with a higher number of shorter runs（40×100 m） induced different changes in those neuromuscular parameters than those with fewer and longer runs（10×400 m）.Whereas the 40×100 m protocol did not cause any significan changes in vertical jump ability,postural control or SSC utilisation,the 10×400 m protocol impaired postural control and caused improvements in vertical jumping tests.

Effects of static aeroelasticity on composite wing characteristics under different flight attitudes

Composite wing static aeroelasticity was analyzed through a loosely coupled method and the effects on composite wing characteristics under different flight attitudes were presented. Structural analysis and aerodynamic analysis were carried out through finite element method (FEM) software NASTRAN and computational fluid dynamics (CFD) software FLUENT, respectively. Correlative data transfer and mesh regenerate procedure were applied to couple the results of computational structure dynamics (CSD) and CFD. After static aeroelasticity analysis under different flight attitudes, it can be seen that lift increases with the increase of flight speed and the incremental value enlarges gradually in both rigid and elastic wings. Lift presents a linear increment relationship with the increase of attack angle when the flight speed is 0.4Ma or 0.6Ma, but nonlinear increment in elastic wing when flight speed is 0.8Ma. On the effect of aeroelasticity, the maximum of deformation increases with the increase of flight speed and attack angle, and the incremental value decreases with the increase of flight speed while uniform with different attack angles. The results provide a reference for engineering applications.

Attitude Stabilization of a Novel Flying Robot by Dynamic Compensation

This paper gives details about the controller design that aims to stabilize the novel twinrotor flying robot, Toruk. Toruk is an experimental test bench to study center of gravity steering, effect of the location of the center of gravity, controller design and implementation, etc. Physical components are also briefly discussed in this paper. Attitude dynamics of the system is inherently unstable. It is stabilized by a regulator. In addition, an observer is designed and utilized to estimate the unmeasured states. Thrust force generated by the propulsion unit is estimated by using the identified mathematical model of the unit. An experimental setup is employed to identify the mathematical model that expresses the relation between the applied input voltage to the propulsion unit and thrust produced by the propeller. Mathematical model for the attitude dynamics of Toruk is built. Then controllability and observability analysis are carried out for the system. Dynamic compensator composed of a state observer and a regulator, is designed on the mathematical model. Physical implementation on the system will be performed.

The relationship between intermittent limit cycles and postural instability associated with Parkinson’s disease

Background:Many disease-specific factors such as muscular weakness,increased muscle stiffness,varying postural strategies,and changes in postural reflexes have been shown to lead to postural instability and fall risk in people with Parkinson's disease(PD).Recently,analytical techniques,inspired by the dynamical systems perspective on movement control and coordination,have been used to examine the mechanisms underlying the dynamics of postural declines and the emergence of postural instabilities in people with PD.Methods:A wavelet-based technique was used to identify limit cycle oscillations(LCOs) in the anterior–posterior(AP) postural sway of people with mild PD(n = 10) compared to age-matched controls(n = 10).Participants stood on a foam and on a rigid surface while completing a dual task(speaking).Results:There was no significant difference in the root mean square of center of pressure between groups.Three out of 10 participants with PD demonstrated LCOs on the foam surface,while none in the control group demonstrated LCOs.An inverted pendulum model of bipedal stance was used to demonstrate that LCOs occur due to disease-specific changes associated with PD:time-delay and neuromuscular feedback gain.Conclusion:Overall,the LCO analysis and mathematical model appear to capture the subtle postural instabilities associated with mild PD.In addition,these findings provide insights into the mechanisms that lead to the emergence of unstable posture in patients with PD.

Nonlinear Rolling Control Technology of Liquid Launch Vehicle Based on Single Engine

New program was proposed in LM-6 rolling control technology that using high-pressure staged combustion gas. Launch vehicle rolling control by just one engine was realized. Under the limit of the rolling control moment of the launch vehicle, a new attitude dynamic model is established. Interference source and how to reduce the effect was analyzed, and method of designing a pre-compensated robust controller was proposed. Simulation and flight resuits showed that the attitude dynamic model established and the pre-compensation robust controller proposed in this paper could solve the key problems with a strong coupling attitude controller, and realize high quality and high reliability control in wind areas, and improve the capability of the launch vehicle.

On all-propulsion design of integrated orbit and attitude control for inner-formation gravity field measurement satellite

The inner-formation gravity field measurement satellite （IFS） is a novel pure gravitational orbiter. It aims to measure the Earth＇s gravity field with unprecedented accuracy and spatial resolution by means of precise orbit determination （POD） and relative state measurement. One of the key factors determining the measurement level is the outer-satellite control used for keeping the inner-satellite flying in a pure gravitational orbit stably. In this paper the integrated orbit and attitude control of IFS during steady-state phase was investigated using only thrusters. A six degree-of-freedom translational and rotational dynamics model was constructed considering nonlinearity resulted from quaternion expression and coupling induced by community thrusters. A feasible quadratic optimization model was established for the integrated orbit and attitude control using con- strained nonlinear model predictive control （CNMPC） techniques. Simulation experiment demonstrated that the presented CNMPC aigorithm can achieve rapid calculation and overcome the non-convexity of partial constraints. The thruster layout is rational with low thrust consumption, and the mission requirements of IFS are fully satisfied.

A novel posture alignment system for aircraft wing assembly

A novel 6-degree of freedom (DOF) posture alignment system, based on 3-DOF positioners, is presented for the assembly of aircraft wings. Each positioner is connected with the wing through a rotational and adsorptive half-ball shaped end-effector, and the positioners together with the wing are considered as a 3-PPPS (P denotes a prismatic joint and S denotes a spherical joint) redundantly actuated parallel mechanism. The kinematic model of this system is established and a trajectory planning method is introduced. A complete analysis of inverse dynamics is carried out with the Newton-Euler algorithm, which is used to find the desired actuating torque in the design and path planning phase. Simulation analysis of the displacement and actuating torque of each joint of the positioners based on inverse kinematics and dynamics is conducted, and the results show that the system is feasible for the posture alignment of aircraft wings.

Observation of the effects of back-Shu and front-Mu points combination needling on balance and walking function in patients after stroke and its mechanism

Objective:To observe the clinical efficacy of back-Shu and front-Mu points combination needling on balance and walking function in patients after stroke and its mechanism.Methods:A total of 79 patients with post-stroke balance and walking dysfunction were randomly divided into a control group and an observation group.Both groups received conventional treatments such as dietary guidance and oral medications as well as rehabilitation training.On this basis,the control group was treated with additional conventional acupuncture,and the observation group was treated with additional back-Shu and front-Mu points combination needling.Both groups were treated for 4 consecutive weeks.The thickness of abdominal muscle group(transverse abdominal muscle,rectus abdominis,obliquus internus abdominis,and obliquus externus abdominis),the scores of Berg balance scale(BBS),Fugl-Meyer assessment(FMA),and functional ambulation categories(FAC),and walking velocity and stride were compared between the two groups.Results:During the trial,there was 1 dropout case in the control group and 4 dropout cases in the observation group.Before treatment,there were no statistical differences in the abdominal muscle group thickness,scores of BBS,FMA,and FAC,and walking velocity and stride between the two groups(P>0.05).After 4 weeks of treatment,the thickness of abdominal muscle groups,scores of BBS,FMA,and FAC,and walking velocity and stride in both groups were improved(P<0.01),and the observation group was superior to the control group(P<0.05).Conclusion:Both conventional acupuncture and back-Shu and front-Mu points combination needling are conducive to the improvement of balance and walking function in patients after stroke.The back-Shu and front-Mu points combination needling method has better curative efficacy.Strengthening the core muscle group strength may be one of the mechanisms of back-Shu and front-Mu points combination needling treatment.