Permanent magnet synchronous motor based electro-mechanical actuation servo drives have widespread applications in the aviation field,such as unmanned aerial vehicle electric servos,electric cabin doors,and mechanical...Permanent magnet synchronous motor based electro-mechanical actuation servo drives have widespread applications in the aviation field,such as unmanned aerial vehicle electric servos,electric cabin doors,and mechanical arms.The performance of the servo drive,which encompasses the response to the torque,efficiency,control bandwidth and the steady-state positioning accuracy,significantly influences the performance of the aviation actuation.Consequently,enhancing the control bandwidth and refining the positioning accuracy of aviation electro-mechanical actuation servo drives have emerged as a focal point of research.This paper investigates the multi-source disturbances present in aviation electro-mechanical actuation servo systems and summarizes recent research on high-performance servo control methods based on active disturbance rejection control(ADRC).We present a comprehensive overview of the research status pertaining to servo control architecture,strategies for suppressing disturbances in the current loop,and ADRC-based strategies for the position loop.We delineate the research challenges and difficulties encountered by aviation electro-mechanical actuation servo drive control technology.展开更多
Stimuli-responsive shape-changing materials,particularly hydrogel and liquid crystal elastomer(LCE),have demonstrated significant potential for applications across various fields.Although intricate deformation and act...Stimuli-responsive shape-changing materials,particularly hydrogel and liquid crystal elastomer(LCE),have demonstrated significant potential for applications across various fields.Although intricate deformation and actuation behaviors have been obtained in either hydrogels or LCEs,they typically undergo reversible shape change only once(e.g.,one expansion plus one contraction)during one heating/cooling cycle.Herein,we report a study of a novel liquid crystalline hydrogel(LCH)and the achievement of dual actuation in a single heating/cooling cycle by integrating the characteristics of thermoresponsive hydrogel and LCE.The dual actuation behavior arises from the reversible volume phase transition of poly(N-isopropylacrylamide)(PNIPAM)and the reversible order-disorder phase transition of LC mesogens in the LCH.Due to a temperature window separating the two transitions belonging to PNIPAM and LCE,LCH actuator can sequentially execute their respective actuation,thus deforming reversibly twice,during a heating/cooling cycle.The relative actuation degree of the two mechanisms is influenced by the mass ratio of PNIPAM to LCE in the LCH.Moreover,the initial shape of a bilayer actuator made with an active LCH layer and a passive polymer layer can be altered through hydration or dehydration of PNIPAM,which further modifies the dual actuation induced deformation.This work provides an example that shows the interest of developing LCH actuators.展开更多
Polymeric microwave actuators combining tissue-like softness with programmablemicrowave-responsive deformation hold great promise for mobile intelligentdevices and bionic soft robots. However, their application is cha...Polymeric microwave actuators combining tissue-like softness with programmablemicrowave-responsive deformation hold great promise for mobile intelligentdevices and bionic soft robots. However, their application is challenged by restricted electromagneticsensitivity and intricate sensing coupling. In this study, a sensitized polymericmicrowave actuator is fabricated by hybridizing a liquid crystal polymer with Ti3C2Tx(MXene). Compared to the initial counterpart, the hybrid polymer exhibits unique spacechargepolarization and interfacial polarization, resulting in significant improvements of230% in the dielectric loss factor and 830% in the apparent efficiency of electromagneticenergy harvest. The sensitized microwave actuation demonstrates as the shortenedresponse time of nearly 10 s, which is merely 13% of that for the initial shape memory polymer. Moreover, the ultra-low content of MXene (upto 0.15 wt%) benefits for maintaining the actuation potential of the hybrid polymer. An innovative self-powered sensing prototype that combinesdriving and piezoelectric polymers is developed, which generates real-time electric potential feedback (open-circuit potential of ~ 3 mV) duringactuation. The polarization-dominant energy conversion mechanism observed in the MXene-polymer hybrid structure furnishes a new approachfor developing efficient electromagnetic dissipative structures and shows potential for advancing polymeric electromagnetic intelligent devices.展开更多
Bulk nanoporous(np)metallic actuators have attracted increasing attention due to their large strain and low stimulation voltage.However,studies focusing upon the combined effect of composition and structure on the act...Bulk nanoporous(np)metallic actuators have attracted increasing attention due to their large strain and low stimulation voltage.However,studies focusing upon the combined effect of composition and structure on the actuation performance of metallic actuators are relatively scarce,and its underlying mechanism needs to be clarified Herein,a series of bulk np-NiPd samples with differen compositions and microstructures were fabricated using a dealloying-coarsening-dealloying strategy and chargecontrolled electrochemical dealloying,and the process involves only one component of precursor alloy.It has been found that the np-NiPd cubes show a composition/structure-dependent mechanical property and electrochemical actuation performance.Specially,the npNi_(70)Pd_(30)sample with a homogeneously porous structure and good network connectivity exhibits significantly larger strain amplitude and faster strain rate than other hierarchically porous NiPd samples(np-Ni_(50)Pd_(50)and npNi_(20)Pd_(80)).Moreover,the np-Ni_(70)Pd_(30)sample demonstrates good actuation stability with high strain retention after hundreds of cycles.Notably,the maximum strain amplitude(1.17%)is even comparable to that of advanced leadfree piezoceramic,and the maximum strain rate exceeds those of many reported metallic actuator materials.Our work indicates that good network connectivity plays a vita role in facilitating large/fast strain response in metallic actuators.展开更多
3D printing of flexible piezoelectric composites(3D-FPCs)is increasingly attracting the attention due to its unique advantage for customized smart applications.However,current research mainly focuses on the 0-3 piezoe...3D printing of flexible piezoelectric composites(3D-FPCs)is increasingly attracting the attention due to its unique advantage for customized smart applications.However,current research mainly focuses on the 0-3 piezoelectric composites,in which the piezoelectric ceramics are embedded in polymer matrix in the form of particles.The poor connectivity between particles much reduces the conduction of strain and charge in the composites,seriously limiting its application in actuation.In this work,a continuous lead zirconate titanate(PZT)double-layer ceramic scaffold was prepared by 3D printing and assembled with epoxy resin and interdigital electrodes together to manufacture a multifunctional device.The 3D-FPCs exhibit a free strain of 1830 ppm in actuating and are able to actuate a stainless-steel cantilever beam to produce a tip displacement of 5.71 mm.Additionally,the devices exhibit a sensitivity of 26.81V/g in sensing applications.Furthermore,3D-FPCs are demonstrated as actuators for mobile small robots and wearable sensors for sensing joint activities.展开更多
Developing hydroscopic actuators with simultaneous high elasticity,shape programmability and tunable actuating behaviors are highly desired but still challenging.In this study,we propose an orthogonal composite design...Developing hydroscopic actuators with simultaneous high elasticity,shape programmability and tunable actuating behaviors are highly desired but still challenging.In this study,we propose an orthogonal composite design to develop such a material.The developed composite elastomer comprises carboxyl group-grafted polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene(SEBS-g-COOH)as the elastic substrate,and a synthesized azobenzene derivative as the functional filler(Azo12).By surface treatment using acidic and base solutions,the carboxyl groups on the surface can reversibly transform into carboxylate groups,which render the composite tunable hygroscopic actuating functionality.On another aspect,the added filler undergoes trans-to-cis isomerization when exposed to UV light irradiation,leading to liquefaction of the crystalline aggregates formed by Azo12 molecules.The liquefied Azo12 molecules can autonomously resotre their trans form and reform the crystalline structure.This reversible change in crystralline structure is utilized to realize the shape memory property,and 5 wt%of Azo12addition is adequate for the composite to exhibit photo-responsive shape memory behavior without compromising much of the elasricity.The regualtion of external geometry by shape memory effect is effective in altering the actuating behavior.The proposed method can be extend to designing different composites with the demonstrated functionalities.展开更多
Circular holes are commonly employed in engineering designs;however, they often serve as locations where cracks initiate and propagate. This paper explores a novel approach to structural repair by utilizing piezoelect...Circular holes are commonly employed in engineering designs;however, they often serve as locations where cracks initiate and propagate. This paper explores a novel approach to structural repair by utilizing piezoelectric actuators. The primary focus of this study is to investigate the influence of an adhesively bonded piezoelectric actuator patch placed above a circular hole on the stress intensity factor (SIF) in an aluminium plate. The plate is subjected to uniaxial tensile stress, while the piezoelectric actuator is excited with varying voltage levels. The analysis is conducted using the finite element method (FEM), a powerful numerical technique for simulating complex structures. The study assesses the stress distribution and employs the SIF as an adequate criterion for evaluating the impact of different patch configurations. The results indicate a strong correlation between the applied voltage and the SIF. Whether the SIF increases or decreases depends on the polarization of the piezoelectric actuator. Particularly noteworthy is the finding that rectangular patches in a horizontal orientation significantly reduce the SIF compared to other patch geometries. Moreover, double-sided patches exhibit a pronounced decrease in the SIF compared to single-sided patches. In summary, this research underscores the potential of piezoelectric actuators in mitigating stress intensity in structures with circular hole with crack initiation. It offers valuable insights into the influence of applied voltage, patch geometry, and patch placement on the SIF, thereby contributing to developing effective strategies for enhancing structural integrity.展开更多
Electrohydrostatic actuator（EHA） is a type of power-by-wire actuator that is widely implemented in the aerospace industry for flight control, landing gears, thrust reversers, thrust vector control, and space robots....Electrohydrostatic actuator（EHA） is a type of power-by-wire actuator that is widely implemented in the aerospace industry for flight control, landing gears, thrust reversers, thrust vector control, and space robots. This paper presents the development and evaluation of positionbased impedance control（PBIC） for an EHA. Impedance control provides the actuator with compliance and facilitates the interaction with the environment. Most impedance control applications utilize electrical or valve-controlled hydraulic actuators, whereas this work realizes impedance control via a compact and efficient EHA. The structures of the EHA and PBIC are firstly introduced. A mathematical model of the actuation system is established, and values of its coefficients are identified by particle swarm optimization. This model facilitates the development of a position controller and the selection of target impedance parameters. A nonlinear proportional-integral position controller is developed for the EHA to achieve the accurate positioning requirement of PBIC. The controller compensates for the adverse effect of stiction, and a position accuracy of 0.08 mm is attained.Various experimental results are presented to verify the applicability of PBIC to the EHA. The compliance of the actuator is demonstrated in an impact test.展开更多
Multilegged robots have the potential to serve as assistants for humans,replacing them in performing dangerous,dull,or unclean tasks.However,they are still far from being sufficiently versatile and robust for many app...Multilegged robots have the potential to serve as assistants for humans,replacing them in performing dangerous,dull,or unclean tasks.However,they are still far from being sufficiently versatile and robust for many applications.This paper addresses key points that might yield breakthroughs for highly dynamic multilegged robots with the abilities of running(or jumping and hopping)and self-balancing.First,21 typical multilegged robots from the last five years are surveyed,and the most impressive performances of these robots are presented.Second,current developments regarding key technologies of highly dynamic multilegged robots are reviewed in detail.The latest leg mechanisms with serial-parallel hybrid topologies and rigid–flexible coupling configurations are analyzed.Then,the development trends of three typical actuators,namely hydraulic,quasi-direct drive,and serial elastic actuators,are discussed.After that,the sensors and modeling methods used for perception are surveyed.Furthermore,this paper pays special attention to the review of control approaches since control is a great challenge for highly dynamic multilegged robots.Four dynamics-based control methods and two model-free control methods are described in detail.Third,key open topics of future research concerning the mechanism,actuation,perception,and control of highly dynamic multilegged robots are proposed.This paper reviews the state of the art development for multilegged robots,and discusses the future trend of multilegged robots.展开更多
To discover the characteristic of separated flows and mechanism of plasma flow control on a highly loaded compressor cascade, numerical investigation is conducted. The simulation method is validated by oil flow visual...To discover the characteristic of separated flows and mechanism of plasma flow control on a highly loaded compressor cascade, numerical investigation is conducted. The simulation method is validated by oil flow visualization and pressure distribution. The loss coefficients, streamline patterns, and topology structure as well as vortex structure are analyzed. Results show that the numbers of singular points increase and three pairs of additional singular points of topology structure on solid surface generate with the increase of angle of attack, and the total pressure loss increases greatly. There are several principal vortices inside the cascade passage. The pressure side leg of horse-shoe vortex coexists within a specific region together with passage vortex, but finally merges into the latter. Corner vortex exists independently and does not evolve from the suction side leg of horse-shoe vortex. One pair of radial coupling-vortex exists near blade trailing edge and becomes the main part of backflow on the suction surface. Passage vortex interacts with the concentrated shedding vortex and they evolve into a large-scale vortex rotating in the direction opposite to passage vortex. The singular points and separation lines represent the basic separation feature of cascade passage. Plasma actuation has better effect at low freestream velocity, and the relative reductions of pitch-averaged total pressure loss coefficient with different actuation layouts of five and two pairs of electrodes are up to 30.8% and 26.7% while the angle of attack is 2~. Plasma actuation changes the local topology structure, but does not change the number relation of singular points. One pair of additional singular point of topology structure generates with plasma actuation and one more reattachment line appears, both of which break the separation line on the suction surface.展开更多
The optional types of power source and actuator in the aircraft are more and more diverse due to fast development in more electric technology, which makes the combinations of different power sources and actuators beco...The optional types of power source and actuator in the aircraft are more and more diverse due to fast development in more electric technology, which makes the combinations of different power sources and actuators become extremely complex in the architecture optimization process of airborne actuation system. The traditional ＂trial and error＂ method cannot satisfy the design demands. In this paper, firstly, the composition of more electric aircraft （MEA） flight control actuation system （FCAS） is introduced, and the possible architecture quantity is calculated. Secondly, the evaluation criteria of FCAS architecture with respect to safe reliability, weight and efficiency are proposed, and the evaluation criteria values are calculated in the case that each control surface adopts the same actuator configuration. Finally, the optimization results of MEA FCAS architecture are obtained by applying genetic algorithm （GA）. Compared to the traditional actuation system architecture, which only adopts servo valve controlled hydraulic actuators, the weight of the optimized more electric actuation system architecture can be reduced by 6%, and the efficiency can be improved by 30% based on the safe reliability requirements.展开更多
This article carries out synthetic measurements and analysis of the characteristics of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuation. The rotational and vibrational temperatures of a...This article carries out synthetic measurements and analysis of the characteristics of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuation. The rotational and vibrational temperatures of an N2 （ C3 Ⅱu ） molecule are measured in terms of the optical emission spectra from the N2 second positive system. A simplified collision-radiation model for N2 （C）and N2 ＋ （B）is established on the basis of the ratio of emission intensity at 391.4 nm to that at 380.5 nm and the ratio of emission intensity at 371. 1 nm to that at 380.5 nm for calculating temporal and spatial averaged electron temperatures and densities. Under one atmosphere pressure, the electron temperature and density are on the order of 1.6 eV and 10H cm-3 respectively. The body force induced by the plasma aerodynamic actuation is on the order of tens of mN while the induced flow velocity is around 1.3 m/s. Starting vortex is firstly induced by the actuation ; then it develops into a near-wall jet, about 70 mm downstream of the actuator. Unsteady plasma aerodynamic actuation might stimulate more vortexes in the flow field. The induced flow direction by nanosecond discharge plasma aerodynamic actuation is not parallel, but vertical to the dielectric layer surface.展开更多
Plasma flow control is an active flow control technology that based on the plasma aerodynamic actuation. It can be used to enhance the aerodynamic characteristics of aircraft and propulsion systems. To study the pheno...Plasma flow control is an active flow control technology that based on the plasma aerodynamic actuation. It can be used to enhance the aerodynamic characteristics of aircraft and propulsion systems. To study the phenomena occurring in plasma aerodynamic actuation and the mechanism of plasma flow control, the induced flow velocity of the plasma aerodynamic actuator is experimentally investigated under a variety of parameter conditions. The results indicate that plasma aerodynamic actuation accelerates the near surface air at velocities of a few meters per second, and there is an angle about 5° between the mainstream and the actuator wall and a spiral vortex is formed when the induced flow is moving along the wall. Besides, with the fixed frequency, the induced flow velocity increases linearly with the applied voltage, but it is insensitive to the frequency when the applied voltage is fixed. And the configuration is an effective factor for the performance of the plasma aerodynamic actuator.展开更多
This paper proposes an active fault-tolerant control strategy for an aircraft with dissimilar redundant actuation system （DRAS） that has suffered from vertical tail damage. A damage degree coefficient based on the e...This paper proposes an active fault-tolerant control strategy for an aircraft with dissimilar redundant actuation system （DRAS） that has suffered from vertical tail damage. A damage degree coefficient based on the effective vertical tail area is introduced to parameterize the damaged flight dynamic model. The nonlinear relationship between the damage degree coefficient and the corresponding stability derivatives is considered. Furthermore, the performance degradation of new input channel with electro-hydrostatic actuator （EHA） is also taken into account in the damaged flight dynamic model. Based on the accurate damaged flight dynamic model, a composite method of linear quadratic regulator （LQR） integrating model reference adaptive control （MRAC） is proposed to reconfigure the fault-tolerant control law. The numerical simulation results validate the effectiveness of the proposed fault-tolerant control strategy with accurate flight dynamic model. The results also indicate that aircraft with DRAS has better fault-tolerant control ability than the traditional ones when the vertical tail suffers from serious damage.展开更多
A servo press is a new type of mechanical press that is driven by programmable motors and offers superior performance such as low noise, excellent efficiency and high precision for metal forming operations. Similar to...A servo press is a new type of mechanical press that is driven by programmable motors and offers superior performance such as low noise, excellent efficiency and high precision for metal forming operations. Similar to multi-link mechanical presses, a servo mechanical press tends to grow in size as the tonnage increases that calls for larger, heavy duty servo motors, which could be expensive and may not even be available. In this paper, a new concept of servo mechanical press with redundant actuation is proposed firstly using two servo motors driving one input shaft, i.e. one-point-two-motor mode that makes it possible to produce a larger press with available servomotors. Then the punching mechanism design is detailed. The performance indices are set up including mechanical advantage reciprocal and link force ratios. A bounded feasible solution space is constructed for dimensional synthesis based on non-dimensional link lengths and assembly conditions. The performance atlases are depicted over the bounded feasible solution space that lead to a visual solution of the punching mechanism with global optimization. Finally, case studies are given to illustrate the design method with visual global optimization, and a prototype with 200 t punching force is being developed in our laboratory to demonstrate efficacy of the new concept for servo mechanical press. The presented research provides a feasible solution to the development of heavy-duty servo mechanical presses and finds potential applications in the development of other types of heavy equipments with electric drive.展开更多
This paper deals with the dynamics and control of a novel 3-degrees-of-freedom （DOF） parallel manipulator with actuation redundancy. According to the kinematics of the redundant manipulator, the inverse dynamic equa...This paper deals with the dynamics and control of a novel 3-degrees-of-freedom （DOF） parallel manipulator with actuation redundancy. According to the kinematics of the redundant manipulator, the inverse dynamic equation is formulated in the task space by using the Lagrangian formalism, and the driving force is optimized by utilizing the minimal 2-norm method. Based on the dynamic model, a synchronized sliding mode control scheme based on contour error is proposed to implement accurate motion tracking control. Additionally, an adaptive method is introduced to approximate the lumped uncertainty of the system and provide a chattering-free control. The simulation results indicate the effectiveness of the proposed approaches and demonstrate the satisfactory tracking performance compared to the conventional controller in the presence of the parameter uncertainties and un-modelled dynamics for the motion control of manipulators.展开更多
Non-contact actuated microbeads have attracted a lot of attention in recent years because of its enormous potential in medical, biological, and industrial applications. Researchers have proposed a multitude of electro...Non-contact actuated microbeads have attracted a lot of attention in recent years because of its enormous potential in medical, biological, and industrial applications. Researchers have proposed a multitude of electromagnetic actuation(EMA) systems consisting of a variety of coil pairs. However, a unified method to design and optimize a coil pair according to technical specifications still does not exist. Initially, this paper presented the modeling of an untethered ferromagnetic particle actuated by externally applied magnetic field. Based on the models, a simple method of designing and optimizing the EMA coil pair according to technical specifications, was proposed. A loop-shaped coil pair generating uniform magnetic and gradient fields was chosen to demonstrate this method clearly and practically. The results of the optimization showed that the best distance to radius ratio of a loop-shaped coil pair is 1.02 for a uniform magnetic field and 1.75 for a uniform gradient field. The applicability of the method to other shapes of coil configuration was also illustrated. The best width to distance ratio for a square-shaped coil pair is 0.558 and 0.958 for uniform magnetic and gradient fields, respectively. The best height to width ratio and distance to width ratio for a rectangle-shaped coil pair is h/w =[0.9,1.1], d/w =[0.5,0.6] for uniform magnetic field and h/w =[1.0,1.2], d/w =[0.9,1.1] for uniform gradient field. Furthermore, simulations of a microparticle tracking the targeted trajectory were conducted to analyze the performance of the newly designed coils. The simulations suggested the ability of manipulating microparticles via the coils designed by our proposed method. The research mainly proposed a unified design and optimization method for a coil pair, which can support researchers while designing a specific coil pair according to the technical requirements. This study is aimed at researchers who are interested in EMA system and microrobots.展开更多
As the essential technology of human-robotics interactive wearable devices,the robotic knee prosthesis can provide above-knee amputations with functional knee compensations to realize their physical and psychological ...As the essential technology of human-robotics interactive wearable devices,the robotic knee prosthesis can provide above-knee amputations with functional knee compensations to realize their physical and psychological social regression.With the development of mechanical and mechatronic science and technology,the fully active knee prosthesis that can provide subjects with actuating torques has demonstrated a better wearing performance in slope walking and stair ascent when compared with the passive and the semi-active ones.Additionally,with intelligent human-robotics control strategies and algorithms,the wearing effect of the knee prosthesis has been greatly enhanced in terms of stance stability and swing mobility.Therefore,to help readers to obtain an overview of recent progress in robotic knee prosthesis,this paper systematically categorized knee prostheses according to their integrated functions and introduced related research in the past ten years(2010−2020)regarding(1)mechanical design,including uniaxial,four-bar,and multi-bar knee structures,(2)actuating technology,including rigid and elastic actuation,and(3)control method,including mode identification,motion prediction,and automatic control.Quantitative and qualitative analysis and comparison of robotic knee prosthesis-related techniques are conducted.The development trends are concluded as follows:(1)bionic and lightweight structures with better mechanical performance,(2)bionic elastic actuation with energy-saving effect,(3)artificial intelligence-based bionic prosthetic control.Besides,challenges and innovative insights of customized lightweight bionic knee joint structure,highly efficient compact bionic actuation,and personalized daily multi-mode gait adaptation are also discussed in-depth to facilitate the future development of the robotic knee prosthesis.展开更多
In this article, numerical investigation of the effects of different plasma actuation strengths on the film cooling flow characteristics has been conducted using large eddy simulation （LES）. For this numerical resea...In this article, numerical investigation of the effects of different plasma actuation strengths on the film cooling flow characteristics has been conducted using large eddy simulation （LES）. For this numerical research, the plasma actuator is placed downstream of the trailing edge of the film cooling hole and a phenomenological model is employed to provide the electric field generated by it, resulting in the body forces. Our results show that as the plasma actuation strength grows larger, under the downward effect of the plasma actuation, the jet trajectory near the cooling hole stays closer to the wall and the recirculation region observably reduces in size. Meanwhile, the momentum injection effect of the plasma actuation also actively alters the distributions of the velocity components downstream of the cooling hole. Consequently, the influence of the plasma actuation strength on the Reynolds stress downstream of the cooling hole is remarkable. Furthermore, the plasma actuation weakens the strength of the kidney shaped vortex and prevents the jet from lifting off the wall. Therefore, with the increase of the strength of the plasma actuation, the coolant core stays closer to the wall and tends to split into two distinct regions. So the centerline film cooling efficiency is enhanced, and it is increased by 55% at most when the plasma actuation strength is 10.展开更多
The lower-mobility parallel mechanism has been widely used in the engineering field due to its numerous excellent characteristics.However,little work has been devoted to the actuator selection and placement that best ...The lower-mobility parallel mechanism has been widely used in the engineering field due to its numerous excellent characteristics.However,little work has been devoted to the actuator selection and placement that best satisfy the system's functional requirements during concept design.In this study,a unified approach for synthesizing the actuation spaces of both rigid and flexure parallel mechanisms has been presented,and all possible combinations of inputs could be obtained,laying a theoretical foundation for the subsequent optimization of inputs.According to the linear independence of actuation space and constraint space of the lower-mobility parallel mechanism,a general expression of actuation spaces in the format of screw systems is deduced,a unified synthesis process for the lower-mobility parallel mechanism is derived,and the efficiency of the method is validated with two selective examples based on screw theory.This study presents a theoretical framework for the input selection problems of parallel mechanisms,aiming to help designers select and place actuators in a correct and even optimal way after the configuration design.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52177059 and 52407064).
文摘Permanent magnet synchronous motor based electro-mechanical actuation servo drives have widespread applications in the aviation field,such as unmanned aerial vehicle electric servos,electric cabin doors,and mechanical arms.The performance of the servo drive,which encompasses the response to the torque,efficiency,control bandwidth and the steady-state positioning accuracy,significantly influences the performance of the aviation actuation.Consequently,enhancing the control bandwidth and refining the positioning accuracy of aviation electro-mechanical actuation servo drives have emerged as a focal point of research.This paper investigates the multi-source disturbances present in aviation electro-mechanical actuation servo systems and summarizes recent research on high-performance servo control methods based on active disturbance rejection control(ADRC).We present a comprehensive overview of the research status pertaining to servo control architecture,strategies for suppressing disturbances in the current loop,and ADRC-based strategies for the position loop.We delineate the research challenges and difficulties encountered by aviation electro-mechanical actuation servo drive control technology.
基金financial support from the Natural Sciences and Engineering Research Council of Canada(NSERC),le Fonds de recherche du Québec:Nature et technologies(FRQNT),and The Centre québécois sur les matériaux fonctionnels.
文摘Stimuli-responsive shape-changing materials,particularly hydrogel and liquid crystal elastomer(LCE),have demonstrated significant potential for applications across various fields.Although intricate deformation and actuation behaviors have been obtained in either hydrogels or LCEs,they typically undergo reversible shape change only once(e.g.,one expansion plus one contraction)during one heating/cooling cycle.Herein,we report a study of a novel liquid crystalline hydrogel(LCH)and the achievement of dual actuation in a single heating/cooling cycle by integrating the characteristics of thermoresponsive hydrogel and LCE.The dual actuation behavior arises from the reversible volume phase transition of poly(N-isopropylacrylamide)(PNIPAM)and the reversible order-disorder phase transition of LC mesogens in the LCH.Due to a temperature window separating the two transitions belonging to PNIPAM and LCE,LCH actuator can sequentially execute their respective actuation,thus deforming reversibly twice,during a heating/cooling cycle.The relative actuation degree of the two mechanisms is influenced by the mass ratio of PNIPAM to LCE in the LCH.Moreover,the initial shape of a bilayer actuator made with an active LCH layer and a passive polymer layer can be altered through hydration or dehydration of PNIPAM,which further modifies the dual actuation induced deformation.This work provides an example that shows the interest of developing LCH actuators.
基金supported by the National Natural Science Foundation of China(No.52373280,52177014,51977009,52273257)。
文摘Polymeric microwave actuators combining tissue-like softness with programmablemicrowave-responsive deformation hold great promise for mobile intelligentdevices and bionic soft robots. However, their application is challenged by restricted electromagneticsensitivity and intricate sensing coupling. In this study, a sensitized polymericmicrowave actuator is fabricated by hybridizing a liquid crystal polymer with Ti3C2Tx(MXene). Compared to the initial counterpart, the hybrid polymer exhibits unique spacechargepolarization and interfacial polarization, resulting in significant improvements of230% in the dielectric loss factor and 830% in the apparent efficiency of electromagneticenergy harvest. The sensitized microwave actuation demonstrates as the shortenedresponse time of nearly 10 s, which is merely 13% of that for the initial shape memory polymer. Moreover, the ultra-low content of MXene (upto 0.15 wt%) benefits for maintaining the actuation potential of the hybrid polymer. An innovative self-powered sensing prototype that combinesdriving and piezoelectric polymers is developed, which generates real-time electric potential feedback (open-circuit potential of ~ 3 mV) duringactuation. The polarization-dominant energy conversion mechanism observed in the MXene-polymer hybrid structure furnishes a new approachfor developing efficient electromagnetic dissipative structures and shows potential for advancing polymeric electromagnetic intelligent devices.
基金financially supported by the National Natural Science Foundation of China(Nos.U23A20554 and 52371158)the Key Research and Development Program of Shan dong Province(No.2021ZLGX01)+2 种基金Taishan Scholar Foundation of Shandong Province,the Natural Science Foundation of Shan dong Province(No.ZR2022QB169)the Excellent Youth Science Fund Project of Shan dong Province(Overseas)(No.2023HWYQ-018)the Postdoctoral Science foundation of China(No.2022M710077)。
文摘Bulk nanoporous(np)metallic actuators have attracted increasing attention due to their large strain and low stimulation voltage.However,studies focusing upon the combined effect of composition and structure on the actuation performance of metallic actuators are relatively scarce,and its underlying mechanism needs to be clarified Herein,a series of bulk np-NiPd samples with differen compositions and microstructures were fabricated using a dealloying-coarsening-dealloying strategy and chargecontrolled electrochemical dealloying,and the process involves only one component of precursor alloy.It has been found that the np-NiPd cubes show a composition/structure-dependent mechanical property and electrochemical actuation performance.Specially,the npNi_(70)Pd_(30)sample with a homogeneously porous structure and good network connectivity exhibits significantly larger strain amplitude and faster strain rate than other hierarchically porous NiPd samples(np-Ni_(50)Pd_(50)and npNi_(20)Pd_(80)).Moreover,the np-Ni_(70)Pd_(30)sample demonstrates good actuation stability with high strain retention after hundreds of cycles.Notably,the maximum strain amplitude(1.17%)is even comparable to that of advanced leadfree piezoceramic,and the maximum strain rate exceeds those of many reported metallic actuator materials.Our work indicates that good network connectivity plays a vita role in facilitating large/fast strain response in metallic actuators.
基金supported by the National Key R&D Program of China(2020YFA0711700)the National Natural Science Foundation of China(Grant No.U19A2087,52172134,52102150)the Science and Technology Innovation Program of Hunan Province(No.2022RC1029).
文摘3D printing of flexible piezoelectric composites(3D-FPCs)is increasingly attracting the attention due to its unique advantage for customized smart applications.However,current research mainly focuses on the 0-3 piezoelectric composites,in which the piezoelectric ceramics are embedded in polymer matrix in the form of particles.The poor connectivity between particles much reduces the conduction of strain and charge in the composites,seriously limiting its application in actuation.In this work,a continuous lead zirconate titanate(PZT)double-layer ceramic scaffold was prepared by 3D printing and assembled with epoxy resin and interdigital electrodes together to manufacture a multifunctional device.The 3D-FPCs exhibit a free strain of 1830 ppm in actuating and are able to actuate a stainless-steel cantilever beam to produce a tip displacement of 5.71 mm.Additionally,the devices exhibit a sensitivity of 26.81V/g in sensing applications.Furthermore,3D-FPCs are demonstrated as actuators for mobile small robots and wearable sensors for sensing joint activities.
基金financially supported by the National Natural Science Foundation of China(Nos.51803115 and 21636006)the Fundamental Research Funds for the Central Universities(Nos.GK201901001,2021CSLY008,2021CSZL003 and GK202103032)the Innovation Capability Support Program of Shaanxi(No.2020TD-024)。
文摘Developing hydroscopic actuators with simultaneous high elasticity,shape programmability and tunable actuating behaviors are highly desired but still challenging.In this study,we propose an orthogonal composite design to develop such a material.The developed composite elastomer comprises carboxyl group-grafted polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene(SEBS-g-COOH)as the elastic substrate,and a synthesized azobenzene derivative as the functional filler(Azo12).By surface treatment using acidic and base solutions,the carboxyl groups on the surface can reversibly transform into carboxylate groups,which render the composite tunable hygroscopic actuating functionality.On another aspect,the added filler undergoes trans-to-cis isomerization when exposed to UV light irradiation,leading to liquefaction of the crystalline aggregates formed by Azo12 molecules.The liquefied Azo12 molecules can autonomously resotre their trans form and reform the crystalline structure.This reversible change in crystralline structure is utilized to realize the shape memory property,and 5 wt%of Azo12addition is adequate for the composite to exhibit photo-responsive shape memory behavior without compromising much of the elasricity.The regualtion of external geometry by shape memory effect is effective in altering the actuating behavior.The proposed method can be extend to designing different composites with the demonstrated functionalities.
文摘Circular holes are commonly employed in engineering designs;however, they often serve as locations where cracks initiate and propagate. This paper explores a novel approach to structural repair by utilizing piezoelectric actuators. The primary focus of this study is to investigate the influence of an adhesively bonded piezoelectric actuator patch placed above a circular hole on the stress intensity factor (SIF) in an aluminium plate. The plate is subjected to uniaxial tensile stress, while the piezoelectric actuator is excited with varying voltage levels. The analysis is conducted using the finite element method (FEM), a powerful numerical technique for simulating complex structures. The study assesses the stress distribution and employs the SIF as an adequate criterion for evaluating the impact of different patch configurations. The results indicate a strong correlation between the applied voltage and the SIF. Whether the SIF increases or decreases depends on the polarization of the piezoelectric actuator. Particularly noteworthy is the finding that rectangular patches in a horizontal orientation significantly reduce the SIF compared to other patch geometries. Moreover, double-sided patches exhibit a pronounced decrease in the SIF compared to single-sided patches. In summary, this research underscores the potential of piezoelectric actuators in mitigating stress intensity in structures with circular hole with crack initiation. It offers valuable insights into the influence of applied voltage, patch geometry, and patch placement on the SIF, thereby contributing to developing effective strategies for enhancing structural integrity.
基金completed in the Fluid Power and Tele-Robotics Research Laboratory at the University of Manitobathe supports of the Natural Sciences and Engineering Research Council(NSERC)of Canada+1 种基金China Scholarship Council(CSC)the National Natural Science Foundation of China(Nos.51275021 and 61327807)
文摘Electrohydrostatic actuator（EHA） is a type of power-by-wire actuator that is widely implemented in the aerospace industry for flight control, landing gears, thrust reversers, thrust vector control, and space robots. This paper presents the development and evaluation of positionbased impedance control（PBIC） for an EHA. Impedance control provides the actuator with compliance and facilitates the interaction with the environment. Most impedance control applications utilize electrical or valve-controlled hydraulic actuators, whereas this work realizes impedance control via a compact and efficient EHA. The structures of the EHA and PBIC are firstly introduced. A mathematical model of the actuation system is established, and values of its coefficients are identified by particle swarm optimization. This model facilitates the development of a position controller and the selection of target impedance parameters. A nonlinear proportional-integral position controller is developed for the EHA to achieve the accurate positioning requirement of PBIC. The controller compensates for the adverse effect of stiction, and a position accuracy of 0.08 mm is attained.Various experimental results are presented to verify the applicability of PBIC to the EHA. The compliance of the actuator is demonstrated in an impact test.
基金Supported by National Natural Science Foundation of China(Grant Nos.51575337,U1613208)Equipment Pre-research Aerospace Joint Fund(Grant No.6141B06220407)Key Laboratory Fund of Science and Technology on Space Intelligent Control(Grant No.HTKJ2019KL502011).
文摘Multilegged robots have the potential to serve as assistants for humans,replacing them in performing dangerous,dull,or unclean tasks.However,they are still far from being sufficiently versatile and robust for many applications.This paper addresses key points that might yield breakthroughs for highly dynamic multilegged robots with the abilities of running(or jumping and hopping)and self-balancing.First,21 typical multilegged robots from the last five years are surveyed,and the most impressive performances of these robots are presented.Second,current developments regarding key technologies of highly dynamic multilegged robots are reviewed in detail.The latest leg mechanisms with serial-parallel hybrid topologies and rigid–flexible coupling configurations are analyzed.Then,the development trends of three typical actuators,namely hydraulic,quasi-direct drive,and serial elastic actuators,are discussed.After that,the sensors and modeling methods used for perception are surveyed.Furthermore,this paper pays special attention to the review of control approaches since control is a great challenge for highly dynamic multilegged robots.Four dynamics-based control methods and two model-free control methods are described in detail.Third,key open topics of future research concerning the mechanism,actuation,perception,and control of highly dynamic multilegged robots are proposed.This paper reviews the state of the art development for multilegged robots,and discusses the future trend of multilegged robots.
基金National Natural Science Foundation of China(50906100, 10972236)Foundation for the Author of National Excellent Doctoral Dissertation of PR China (201172)Postgraduate Technology Innovation Foundation of Air Force Engineering University(DX2010103)
文摘To discover the characteristic of separated flows and mechanism of plasma flow control on a highly loaded compressor cascade, numerical investigation is conducted. The simulation method is validated by oil flow visualization and pressure distribution. The loss coefficients, streamline patterns, and topology structure as well as vortex structure are analyzed. Results show that the numbers of singular points increase and three pairs of additional singular points of topology structure on solid surface generate with the increase of angle of attack, and the total pressure loss increases greatly. There are several principal vortices inside the cascade passage. The pressure side leg of horse-shoe vortex coexists within a specific region together with passage vortex, but finally merges into the latter. Corner vortex exists independently and does not evolve from the suction side leg of horse-shoe vortex. One pair of radial coupling-vortex exists near blade trailing edge and becomes the main part of backflow on the suction surface. Passage vortex interacts with the concentrated shedding vortex and they evolve into a large-scale vortex rotating in the direction opposite to passage vortex. The singular points and separation lines represent the basic separation feature of cascade passage. Plasma actuation has better effect at low freestream velocity, and the relative reductions of pitch-averaged total pressure loss coefficient with different actuation layouts of five and two pairs of electrodes are up to 30.8% and 26.7% while the angle of attack is 2~. Plasma actuation changes the local topology structure, but does not change the number relation of singular points. One pair of additional singular point of topology structure generates with plasma actuation and one more reattachment line appears, both of which break the separation line on the suction surface.
基金National Natural Science Foundation of China （50675009） International Science ＆ Technology Cooperation Program of China （2010DFA72540）
文摘The optional types of power source and actuator in the aircraft are more and more diverse due to fast development in more electric technology, which makes the combinations of different power sources and actuators become extremely complex in the architecture optimization process of airborne actuation system. The traditional ＂trial and error＂ method cannot satisfy the design demands. In this paper, firstly, the composition of more electric aircraft （MEA） flight control actuation system （FCAS） is introduced, and the possible architecture quantity is calculated. Secondly, the evaluation criteria of FCAS architecture with respect to safe reliability, weight and efficiency are proposed, and the evaluation criteria values are calculated in the case that each control surface adopts the same actuator configuration. Finally, the optimization results of MEA FCAS architecture are obtained by applying genetic algorithm （GA）. Compared to the traditional actuation system architecture, which only adopts servo valve controlled hydraulic actuators, the weight of the optimized more electric actuation system architecture can be reduced by 6%, and the efficiency can be improved by 30% based on the safe reliability requirements.
基金National Natural Science Foundation of China(50906100)China Postdoctoral Science Foundation(20090450373)
文摘This article carries out synthetic measurements and analysis of the characteristics of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuation. The rotational and vibrational temperatures of an N2 （ C3 Ⅱu ） molecule are measured in terms of the optical emission spectra from the N2 second positive system. A simplified collision-radiation model for N2 （C）and N2 ＋ （B）is established on the basis of the ratio of emission intensity at 391.4 nm to that at 380.5 nm and the ratio of emission intensity at 371. 1 nm to that at 380.5 nm for calculating temporal and spatial averaged electron temperatures and densities. Under one atmosphere pressure, the electron temperature and density are on the order of 1.6 eV and 10H cm-3 respectively. The body force induced by the plasma aerodynamic actuation is on the order of tens of mN while the induced flow velocity is around 1.3 m/s. Starting vortex is firstly induced by the actuation ; then it develops into a near-wall jet, about 70 mm downstream of the actuator. Unsteady plasma aerodynamic actuation might stimulate more vortexes in the flow field. The induced flow direction by nanosecond discharge plasma aerodynamic actuation is not parallel, but vertical to the dielectric layer surface.
基金Supported by the National High Technology Reserach and Development Program of China("863"program)(2005AA753031)the New Century Educational Talents Plan of Ministry of Education of China(NCET-05-0907)~~
文摘Plasma flow control is an active flow control technology that based on the plasma aerodynamic actuation. It can be used to enhance the aerodynamic characteristics of aircraft and propulsion systems. To study the phenomena occurring in plasma aerodynamic actuation and the mechanism of plasma flow control, the induced flow velocity of the plasma aerodynamic actuator is experimentally investigated under a variety of parameter conditions. The results indicate that plasma aerodynamic actuation accelerates the near surface air at velocities of a few meters per second, and there is an angle about 5° between the mainstream and the actuator wall and a spiral vortex is formed when the induced flow is moving along the wall. Besides, with the fixed frequency, the induced flow velocity increases linearly with the applied voltage, but it is insensitive to the frequency when the applied voltage is fixed. And the configuration is an effective factor for the performance of the plasma aerodynamic actuator.
基金supported by the National Basic Research Program of China (No 2014CB046402)the National Natural Science Foundation of China (No.51575019)111 Project of China
文摘This paper proposes an active fault-tolerant control strategy for an aircraft with dissimilar redundant actuation system （DRAS） that has suffered from vertical tail damage. A damage degree coefficient based on the effective vertical tail area is introduced to parameterize the damaged flight dynamic model. The nonlinear relationship between the damage degree coefficient and the corresponding stability derivatives is considered. Furthermore, the performance degradation of new input channel with electro-hydrostatic actuator （EHA） is also taken into account in the damaged flight dynamic model. Based on the accurate damaged flight dynamic model, a composite method of linear quadratic regulator （LQR） integrating model reference adaptive control （MRAC） is proposed to reconfigure the fault-tolerant control law. The numerical simulation results validate the effectiveness of the proposed fault-tolerant control strategy with accurate flight dynamic model. The results also indicate that aircraft with DRAS has better fault-tolerant control ability than the traditional ones when the vertical tail suffers from serious damage.
基金supported by National Natural Science Foundation of China (Grant No. 50875161, No. 50405017)National Hi-Tech Research and Development Program of China (863 Program, Grant No. 2006AA04Z118)
文摘A servo press is a new type of mechanical press that is driven by programmable motors and offers superior performance such as low noise, excellent efficiency and high precision for metal forming operations. Similar to multi-link mechanical presses, a servo mechanical press tends to grow in size as the tonnage increases that calls for larger, heavy duty servo motors, which could be expensive and may not even be available. In this paper, a new concept of servo mechanical press with redundant actuation is proposed firstly using two servo motors driving one input shaft, i.e. one-point-two-motor mode that makes it possible to produce a larger press with available servomotors. Then the punching mechanism design is detailed. The performance indices are set up including mechanical advantage reciprocal and link force ratios. A bounded feasible solution space is constructed for dimensional synthesis based on non-dimensional link lengths and assembly conditions. The performance atlases are depicted over the bounded feasible solution space that lead to a visual solution of the punching mechanism with global optimization. Finally, case studies are given to illustrate the design method with visual global optimization, and a prototype with 200 t punching force is being developed in our laboratory to demonstrate efficacy of the new concept for servo mechanical press. The presented research provides a feasible solution to the development of heavy-duty servo mechanical presses and finds potential applications in the development of other types of heavy equipments with electric drive.
基金supported by National Natural Science Foundation of China(Nos.51075222 and E050101)Priority Academic Program Development of Jiangsu Higher Education Institutions(No.6,2011)+1 种基金Zhenjiang Municipal Key Technology R&D Program(No.NY2011013)Postgraduate Research and Innovation Program of Jiangsu Higher Education Institutions(No.1221140046)
文摘This paper deals with the dynamics and control of a novel 3-degrees-of-freedom （DOF） parallel manipulator with actuation redundancy. According to the kinematics of the redundant manipulator, the inverse dynamic equation is formulated in the task space by using the Lagrangian formalism, and the driving force is optimized by utilizing the minimal 2-norm method. Based on the dynamic model, a synchronized sliding mode control scheme based on contour error is proposed to implement accurate motion tracking control. Additionally, an adaptive method is introduced to approximate the lumped uncertainty of the system and provide a chattering-free control. The simulation results indicate the effectiveness of the proposed approaches and demonstrate the satisfactory tracking performance compared to the conventional controller in the presence of the parameter uncertainties and un-modelled dynamics for the motion control of manipulators.
基金Supported by Aerospace Research Project(Grant No.040102)
文摘Non-contact actuated microbeads have attracted a lot of attention in recent years because of its enormous potential in medical, biological, and industrial applications. Researchers have proposed a multitude of electromagnetic actuation(EMA) systems consisting of a variety of coil pairs. However, a unified method to design and optimize a coil pair according to technical specifications still does not exist. Initially, this paper presented the modeling of an untethered ferromagnetic particle actuated by externally applied magnetic field. Based on the models, a simple method of designing and optimizing the EMA coil pair according to technical specifications, was proposed. A loop-shaped coil pair generating uniform magnetic and gradient fields was chosen to demonstrate this method clearly and practically. The results of the optimization showed that the best distance to radius ratio of a loop-shaped coil pair is 1.02 for a uniform magnetic field and 1.75 for a uniform gradient field. The applicability of the method to other shapes of coil configuration was also illustrated. The best width to distance ratio for a square-shaped coil pair is 0.558 and 0.958 for uniform magnetic and gradient fields, respectively. The best height to width ratio and distance to width ratio for a rectangle-shaped coil pair is h/w =[0.9,1.1], d/w =[0.5,0.6] for uniform magnetic field and h/w =[1.0,1.2], d/w =[0.9,1.1] for uniform gradient field. Furthermore, simulations of a microparticle tracking the targeted trajectory were conducted to analyze the performance of the newly designed coils. The simulations suggested the ability of manipulating microparticles via the coils designed by our proposed method. The research mainly proposed a unified design and optimization method for a coil pair, which can support researchers while designing a specific coil pair according to the technical requirements. This study is aimed at researchers who are interested in EMA system and microrobots.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.62003060,51975070 and 62033001)the National Key Research and Development Program of China under Grant 2020YFB1313000.
文摘As the essential technology of human-robotics interactive wearable devices,the robotic knee prosthesis can provide above-knee amputations with functional knee compensations to realize their physical and psychological social regression.With the development of mechanical and mechatronic science and technology,the fully active knee prosthesis that can provide subjects with actuating torques has demonstrated a better wearing performance in slope walking and stair ascent when compared with the passive and the semi-active ones.Additionally,with intelligent human-robotics control strategies and algorithms,the wearing effect of the knee prosthesis has been greatly enhanced in terms of stance stability and swing mobility.Therefore,to help readers to obtain an overview of recent progress in robotic knee prosthesis,this paper systematically categorized knee prostheses according to their integrated functions and introduced related research in the past ten years(2010−2020)regarding(1)mechanical design,including uniaxial,four-bar,and multi-bar knee structures,(2)actuating technology,including rigid and elastic actuation,and(3)control method,including mode identification,motion prediction,and automatic control.Quantitative and qualitative analysis and comparison of robotic knee prosthesis-related techniques are conducted.The development trends are concluded as follows:(1)bionic and lightweight structures with better mechanical performance,(2)bionic elastic actuation with energy-saving effect,(3)artificial intelligence-based bionic prosthetic control.Besides,challenges and innovative insights of customized lightweight bionic knee joint structure,highly efficient compact bionic actuation,and personalized daily multi-mode gait adaptation are also discussed in-depth to facilitate the future development of the robotic knee prosthesis.
文摘In this article, numerical investigation of the effects of different plasma actuation strengths on the film cooling flow characteristics has been conducted using large eddy simulation （LES）. For this numerical research, the plasma actuator is placed downstream of the trailing edge of the film cooling hole and a phenomenological model is employed to provide the electric field generated by it, resulting in the body forces. Our results show that as the plasma actuation strength grows larger, under the downward effect of the plasma actuation, the jet trajectory near the cooling hole stays closer to the wall and the recirculation region observably reduces in size. Meanwhile, the momentum injection effect of the plasma actuation also actively alters the distributions of the velocity components downstream of the cooling hole. Consequently, the influence of the plasma actuation strength on the Reynolds stress downstream of the cooling hole is remarkable. Furthermore, the plasma actuation weakens the strength of the kidney shaped vortex and prevents the jet from lifting off the wall. Therefore, with the increase of the strength of the plasma actuation, the coolant core stays closer to the wall and tends to split into two distinct regions. So the centerline film cooling efficiency is enhanced, and it is increased by 55% at most when the plasma actuation strength is 10.
基金Supported by National Natural Science Foundation of China(Grant No.51775475).
文摘The lower-mobility parallel mechanism has been widely used in the engineering field due to its numerous excellent characteristics.However,little work has been devoted to the actuator selection and placement that best satisfy the system's functional requirements during concept design.In this study,a unified approach for synthesizing the actuation spaces of both rigid and flexure parallel mechanisms has been presented,and all possible combinations of inputs could be obtained,laying a theoretical foundation for the subsequent optimization of inputs.According to the linear independence of actuation space and constraint space of the lower-mobility parallel mechanism,a general expression of actuation spaces in the format of screw systems is deduced,a unified synthesis process for the lower-mobility parallel mechanism is derived,and the efficiency of the method is validated with two selective examples based on screw theory.This study presents a theoretical framework for the input selection problems of parallel mechanisms,aiming to help designers select and place actuators in a correct and even optimal way after the configuration design.
