A three degrees of freedom (3-DOF) piezoelectric micromanipulator (PEMMR) based on symmetric and antisymmetric bending of a cross-shaped beam is proposed in this work. Different from typical scheme ...of combining piezoelectric stack actuator (PSA) and flexible mechanism in previous micromanipulation devices, this work only utilizes eight piezoelectric ceramic plates to construct actuation units and further to realize 3-DOF motions; it overcomes the disadvantages of complex structure, high capacitance and relatively high cost of traditional micromanipulation devices constructed on PSAs. The structure design and motion principle are presented, and the finite element analysis (FEA) method is used to simulate output motions and analyze output characteristics; then a prototype is fabricated and an experimental system is established to implement experiments. The experimental results show that the prototype achieves operating range of 99.28 μm×99.09 μm×24.19 μm, displacement resolution of 15.74 nm, output force of 57.76 mN and force resolution of 0.067 mN, which successfully verifies the design and analysis. The static capacitance of the PEMMR is only about 13.34 nF per axis. Furthermore, a preliminary application experiment is implemented, in which the non-contact posture adjustment of microsphere with diameter of 500 μm in liquid is successfully achieved by the developed PEMMR.
Structural changes in electrical energy systems are occurring rapidly. Due to the development of technology and the increase in energy consumption, the importance and impact of nanogrids in the ...energy system is increasing. It is very difficult to sustain nanogrids as offgrid. Therefore, this study thoroughly examines the most efficient controller designs for nanogrids that use fuel cells as their primary source of energy. In addition, Dwarf Mongoose Optimization (DMO), a new effective optimization technique, is used to determine controller gains in nanogrid systems for the first time in the literature. Controller gains for different objective functions such as ISE, IAE, ITSE and ITAE are determined using classical PID controllers and two degrees of freedom (2 DOF) PID controllers.
Moreover, sensitivity analysis is carried out for both variable and constant load scenarios. The constant load is selected as 0.25 pu, and variable load is chosen from values ranging from 0.15 pu to 0.75 pu. In addition, the response of the system to parameter changes is examined by increasing or decreasing the time constants in all load cases. The system parameters are changed from −20 % to +40 % in 0.05 intervals. It has been noted that the suggested controller topologies perform differently depending on the objective functions. Thus, a significant contribution has been made to researchers to indicate the effectiveness of various control structures in fuel cell powered nanogrids.
Display omitted
•Classical and 2 DOF PID controllers are investigated in fuel cell powered nanogrids.•DMO algorithm is proposed to determine the controller gains.•Sensitivity analyses are examined for different load cases.•The performances are analysed for different objective functions.•The controllers demonstrate different performance for different objective functions.
Active intelligent reflecting surface (IRS) is a revolutionary technique for the future 6th generation mobile networks. The conventional far-field single-IRS-aided directional modulation (DM) ...networks have only one (no direct path) or two (existing direct path) degrees of freedom (DoFs). This means that there are only one or two streams transmitted simultaneously from base station to user and will seriously limit its rate gain achieved by IRS. How to create multiple DoFs more than two for DM? In this paper, single large-scale IRS is divided to multiple small IRSs and a novel multi-IRS-aided multi-stream DM network is proposed to achieve a point-to-point multi-stream transmission by creating K (≥3) DoFs, where multiple small IRSs are placed distributively via multiple unmanned aerial vehicles (UAVs). The null-space projection, zero-forcing (ZF) and phase alignment are adopted to obtain the transmit beamforming, receive beamforming and phase shift matrix (PSM), respectively, called NSP-ZF-PA. Here, K PSMs and their corresponding beamforming vectors are independently optimized. The weighted minimum mean-square error (WMMSE) algorithm is involved in alternating iteration for the optimization variables by introducing the power constraint on IRS, named WMMSE-PC, where the majorization-minimization (MM) algorithm is utilized to address the total PSM. To achieve a lower computational complexity, a maximum trace method, called Max-TR-SVD, is proposed by optimizing the PSM of all IRSs. Simulation results have shown that the proposed NSP-ZF-PA performs much better than Max-TR-SVD in terms of rate. In particular, the rate of NSP-ZF-PA with sixteen small IRSs is about five times that of NSP-ZF-PA with combining all small IRSs as a single large IRS. Thus, a dramatic rate enhancement may be achieved by multiple distributed IRSs.
•Profile division method based on heterogeneous modules is proposed.•Configuration design of heterogeneous deployable mechanism is accomplished.•The performance characteristics of deployable antenna ...mechanism are described..
The truss-type deployable antenna is the core equipment for information acquisition and transmission in aerospace engineering. As an important implementation method for large-aperture and high-precision space deployable antennas, the truss-type deployable antenna mechanism has advantages in surface accuracy, deployable ratio, and brace stiffness. However, existing parabolic deployable antennas based on isomorphic modules have shortcomings such as insufficient surface accuracy, complex actuation, and low deployable ratio. We propose a parabolic deployable antenna mechanism with single-DoF and deployable ratio, which combines research content such as parabolic reflector surface division, configuration synthesis, performance analysis and experimental verification of the deployable antenna mechanism. The research results indicate that the proposed mechanism has the characteristics of high surface accuracy, high deployable ratio, and single actuation. The research work provides a solid theoretical foundation and technical reserves for the application and research and development of high-precision and ultra large parabolic truss-type deployable antenna mechanisms.
Energy consumption is a problem for robotic manipulators, which are popular in manufacturing, assembly, and process handling. Some of the most significant energy consumption comes from the weight of ...the large moving mass of the manipulator. This paper proposes a new multi-degree-of-freedom (DOF) manipulator with a wire-driven gravity compensation mechanism. The most significant problem of a wire system is the durability of the wire, which is improved in this study by using a multiwinding mechanism. The tension of the wire is reduced in proportion to the number of windings. Timing belts are used to design a multi-DOF manipulator and the lightweight gravity compensation mechanism reduces inertia forces during operation. Static analysis and design issues are presented. A robotic prototype is assembled and the torque-reduction performance is verified experimentally. The proposed mechanism can be applied to industrial manipulators for efficient robotic operation.
The digital twin (DT), which effectively represents the actual real-world physical system or process, has reshaped the classic manufacturing, construction, as well as healthcare industry. As for ...realizing DT, both sensing and communication functionalities are demanded, which fully builds the connectivity between the physical world and the digital world. We first conducted a survey on the current situation of DT combined with communication and sensing. Inspired from this survey and the current development of communication and sensing, in this paper, we attempt to study the communication annd sensing technologies of physical layer in DT, to reduce the hardware and spectrum overhead. First, we studied the degree of freedom (DoF) problem in general communication and sensing system, and contribute to the DoF definition in the sensing system. Then, in order to improve the spectrum efficiency in DT system, we proposed an iterative optimization framework to address the coexistence of communication and sensing, and some examples are provided. Finally, in order to pursue a better integration gain, we proposed a new waveform design method based on DoF completion. The proposed optimization method can achieve the mean square error (MSE) lower bound. Simulation results demonstrate the effectiveness of various problems in the above scenarios.
In this paper, we study the degrees of freedom (DoF) region and sum DoF of the time-selective <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-user interference channel in ...the presence of intelligent reflecting surfaces (IRSs). We consider both active and passive IRSs. While both types of IRS can attenuate the amplitude and change the phase of a reflected electromagnetic wave, active IRSs are also capable of amplifying the wave. We derive inner and outer bounds for the DoF region and lower and upper bounds for the sum DoF of the <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-user interference channel in the presence of an active IRS and prove that the maximum value of <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula> for the sum DoF can be achieved if the number of IRS elements exceeds a certain finite value. The analysis framework developed for active IRSs forms the basis for our analysis of passive IRS-assisted systems. In particular, we present probabilistic inner and outer bounds for the DoF region and probabilistic lower and upper bounds for the sum DoF of the <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-user interference channel in the presence of a passive IRS and prove that the lower bound for the sum DoF asymptotically approaches <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula> as the number of IRS elements grows large.
This paper for the first time presents a finite screw approach to type synthesis of three-degree-of-freedom (DOF) translational parallel mechanisms (TPMs). Firstly, the finite motions of a rigid ...body, a TPM and its limbs are described by finite screws. Secondly, given the standard form of a limb with the specified DOF, the analytical expressions of the finite screw attributed to the limb are derived using the properties of screw triangle product, resulting in a full set of the 3-, 4- and 5-DOF limbs that can readily be used for determining all the potential topological structures of TPMs. Finally, the assembly conditions for type synthesis of TPMs are proposed by taking into account the inclusive relationship between the finite motions of a TPM and those of its limbs. The merit of this approach lies in that the limb structures can be formulated in a justifiable manner that naturally ensures the full cycle finite motion pattern specified to the moving platform.
•A finite screw approach to type synthesis of TPMs is proposed.•The finite motions of a TPM and its limbs are described by finite screws.•3-, 4- and 5-DOF TPM limbs are synthesized in a parametric and hierarchical manner.•All the derivations are based upon analytical manner using algebraic methods.
In the context of coded caching in the <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-user broadcast channel, our work reveals the surprising fact that having multiple ...(<inline-formula> <tex-math notation="LaTeX">L </tex-math></inline-formula>) transmitting antennas, dramatically ameliorates the long-standing subpacketization bottleneck of coded caching by reducing the required subpacketization to approximately its <inline-formula> <tex-math notation="LaTeX">L </tex-math></inline-formula>th root, thus boosting the actual DoF by a multiplicative factor of up to <inline-formula> <tex-math notation="LaTeX">L </tex-math></inline-formula>. In asymptotic terms, this reveals that as long as <inline-formula> <tex-math notation="LaTeX">L </tex-math></inline-formula> scales with the theoretical caching gain, then the full cumulative (multiplexing + full caching) gains are achieved with constant subpacketization. This is the first time, in any known setting, that unbounded caching gains appear under finite file-size constraints. The achieved caching gains here are up to <inline-formula> <tex-math notation="LaTeX">L </tex-math></inline-formula> times higher than any caching gains previously experienced in any single- or multi-antenna fully connected setting, thus offering a multiplicative mitigation to a subpacketization problem that was previously known to hard-bound caching gains to small constants. The proposed scheme manages for the first time to virtually decompose the fully connected cache-aided channel into <inline-formula> <tex-math notation="LaTeX">L </tex-math></inline-formula> parallel channels. The scheme is practical; it works for all the values of <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">L </tex-math></inline-formula> and all cache sizes, and its gains show in practice: e.g., for <inline-formula> <tex-math notation="LaTeX">K = 100 </tex-math></inline-formula>, when <inline-formula> <tex-math notation="LaTeX">L = 1 </tex-math></inline-formula> the theoretical caching gain of <inline-formula> <tex-math notation="LaTeX">G = 10 </tex-math></inline-formula>, under the original coded caching algorithm, would have needed subpacketization <inline-formula> <tex-math notation="LaTeX">S_{1} = \binom {K}{G} = \binom {100}{10} > 10^{13} </tex-math></inline-formula>, while if extra transmitting antennas were added, the subpacketization was previously known to match or exceed <inline-formula> <tex-math notation="LaTeX">S_{1} </tex-math></inline-formula>. Now for <inline-formula> <tex-math notation="LaTeX">L = 5 </tex-math></inline-formula>, our scheme offers the theoretical (unconstrained) cumulative DoF <inline-formula> <tex-math notation="LaTeX">d_{L} = L + G = 5 + 10 = 15 </tex-math></inline-formula>, with subpacketization <inline-formula> <tex-math notation="LaTeX">S_{L} = \binom {K/L}{G/L} = \binom {100/5}{10/5} = 190 </tex-math></inline-formula>. The work extends to the multi-server and cache-aided IC settings, while the scheme's performance, given subpacketization <inline-formula> <tex-math notation="LaTeX">S_{L} = \binom {K/L}{G/L} </tex-math></inline-formula>, is within a factor of 2 from the optimal linear sum-DoF.
This work considers a general fully coupled autonomous underwater vehicle (AUV) for applying nonlinear suboptimal control. In most cases, AUV models are nonlinear and affine in control, especially ...without modeling rudders and fins. The aim of this work is to address the challenges of nonlinear non-affine AUVs for implementing the controllers, as this aspect of control design has received little attention in this field of research. The NPS II is a well-known AUV that is often mentioned in research on nonlinear, non-affine modeling. This model is considered for applying the state-dependent Riccati equation (SDRE) controller with a non-affine structure for point-to-point motion that generates a suboptimal path. Furthermore, the control, design and simulation results are provided without any simplification or decoupling of the entire system. The design approach of this paper is implemented on NPS II; nonetheless, this point of view can be actualized on any AUV using the same technique.
Display omitted
•Non-affine structure of the SDRE is expressed.•The SDC parameterization of the SDRE for AUV NPS II is presented.•Fully coupled six-DOF controller of an AUV is designed.•Regulation and trajectory tracking problems are simulated.
PDF
