Neural control of rhythmic limb motion is shaped by size and speed

Over many size and time scales, behaviors such as locomotion or feeding require mechanical movements. Size and time in turn determine a behavior’s dominant mechanical properties: mass, stiffness or viscous damping. The constraints for limbed behaviors can thus be quantified by two variables: limb size and limb speed, defining a ‘mechanics space’ that shows the relative magnitude of each mechanical property for animals ranging from fruit fly to elephant. The mechanics space has three distinct regions: 1) an inertia-dominated region; 2) a gravity or elastic-force-dominated region; and 3) a viscous-force-dominated region. In the mass-dominated region, associated with large limbs moving rapidly, muscle work is translated into primarily kinetic energy. Thus, stable motion requires compensatory control and active damping. In the elastic-force-dominated region, associated with small limbs moving slowly, muscle energy is translated into primarily gravitational or elastic potential energy. Thus, compensatory control and active damping are unnecessary. Lastly, in the viscous region, associated with small limbs moving quickly, joint viscosity acts to damp actuation, resulting in exclusively stable movements. Control and stability of a limb thus depends almost entirely on the size and speed of limb movement, and this has fundamental implications for neural control.

Design of a Five-Degrees of Freedom Statically Balanced Mechanism with Multi-Directional Functionality

A statically balanced mechanism is designed as a potential solution for the positioning of surgical instruments. Its kinematics with five degrees of freedom that decouples linear and angular motions is proposed for that objective. The linear motion of its end effector is provided by a classical parallelogram linkage. To enhance its adaptability, a mechanical system allows re-orienting the position mechanism in three different working modes (horizontal, upward and downward) while preserving its static balance. Based on the mechanical concept, a uniformized static balancing condition that considers all working modes is given. The orientation of the end effector is provided by a spherical decoupled mechanism. It generates a remote center of motion which is highly representative of kinematics in surgery requirements. Based on the mechanism kinematics, the evolution of its gravitational potential energy is studied. Two different mechanical concepts are then proposed to generate a compensating elastic potential energy. A CAD model of the entire mechanism has allowed the estimation of all mechanical parameters for the selection of the appropriate tension springs and for carrying out validation simulations. A prototype of the statically balanced mechanism is fabricated and successfully tested.

A gravity balancing assistant arm design in 3-D for rehabilitation of stroke patients

A gravity balancing assistant arm design in 3-D is a mechanical mechanism consisted of springs, rigid rods, joints and sliders, which can be modified to the geometry and inertia of the arm of stroke patients. This mechanism is designed without any controllers and motors, based solely on mechanical principles, to achieve a relative balance of gravitational potential energy and elastic potential energy, thereby reducing the burden on the arm of a stroke patient to facilitate rehabilitation. To achieve this function, first, the center of gravity of the patient’s arm will be positioned, and then the mounting position of the spring on the assistant arm will be determined. In this paper, the following objectives will be achieved: (i) the calculation of the gravitational potential energy and the elastic potential energy in the mechanism (ii) the simplification of the potential energy equation and the elimination of the coefficient of the items related to the angle. (iii) The comparison between 2-D and 3-D cases of the mechanism. (iv) The motion process of simulating the mechanism using MATLAB (v) Using MATLAB to create the energy plots (vi) Using SolidWorks to construct the prototype of the mechanism (vii) Describe the practical application and future extensions of this mechanism.

Bioinspired high-power-density strong contractile hydrogel by programmable elastic recoil

Stimuli-responsive hydrogels have large deformability but—when applied as actuators, smart switch, and artificial muscles—suffer from low work density due to low deliverable forces (~2 kPa) and speed through the osmotic pressure–driven actuation. Inspired by the energy conversion mechanism of many creatures during jumping, we designed an elastic-driven strong contractile hydrogel through storing and releasing elastic potential energy in polymer network. It can generate high contractile force (40 kPa) rapidly at ultrahigh work density (15.3 kJ/m3), outperforming current hydrogels (~0.01 kJ/m3) and even biological muscles (~8 kJ/m3). This demonstrated elastic energy storing and releasing method endows hydrogels with elasticity-plasticity switchability, multi-stable deformability in fully reversible and programmable manners, and anisotropic or isotropic deformation. With the high power density and programmability via this customizable modular design, these hydrogels demonstrated potential for broad applications in artificial muscles, contractile wound dressing, and high-power actuators.

Energy-Based Vibration Modeling and Solution of High-Speed Elevators Considering the Multi-Direction Coupling Property

Vibration of a high-speed elevator is one of the major factors contributing to a safe, stable and comfortable ride. Vibration control and systematic optimization rely on the establishment of an accurate and reliable model. An energy-based vibration model (EVM) is proposed in this paper to describe the multi-directional coupling properties of high-speed elevators. After analyzing the structural and kinematic characteristics, a combination of the kinematic energy, elastic potential energy and virtual works is implemented to describe the vibrational characteristics. The Gaussian precise integration method is implemented to obtain accurate solutions because of the infinite degrees of freedom and the time-varying parameters. An example study is conducted using the KLK2 high-speed elevator. EVM is established to obtain the Max(Pk)/Pk and A95 indices of the X, Y, Z axis vibrational acceleration through simulations. A comparison is proposed between the proposed EVM method, conventional methods based on differential-equation vibration model (DVM) and real prototype experimental data. Results show that the proposed EVM method could achieve more accurate results than the conventional DVM method. Deviations of these indicators are less than 5%, which suggest the efficiency, precision and reliability of the proposed EVM.

Triple-Cell Origami Structure for Multistable Transition Sequences

With the infinite design space and the excellent folding-induced deformability, origami has been recognized as an effective tool for developing reconfigurable structures. Particularly, the multistable origami structure, which possesses more than one stable configuration that is distinct in shape and mechanical properties, has received wide research attention. Generally, the origami structure reaches a kinematic singularity point when switching among different stable configurations. At this critical state, multiple switching sequences are possible, and the actual transition is generally hard to predict. In this paper, evolving from the conventional bistable Miura-ori unit, a triple-cell origami structure with eight potential stable configurations is proposed, which serves as a platform for investigating the transition sequences among different stable configurations. To quantify the overall elastic potential of the structure, besides the conventional elastic energy originating from the rigid folding creases, extra elastic potential induced by the mismatch among the cells are introduced, so that folding of the triple-cell structure is no longer a strict single degree-of-freedom mechanism. Instead, the three cells can deform asynchronously to avoid reaching the kinematic singularity point. Hence, under displacement loading, the transition sequence of the multistable structure is predicted by performing optimization on the elastic potential energy. It shows that sequences with multifarious characteristics are possible, including reversible and irreversible transitions, and transitions with symmetric and asymmetric energy barriers. Considering that the fundamental transition mechanisms are of great significance in understanding the quasi-static and dynamic behaviors of multistable structures, the results could be potentially employed for developing morphing structures, adaptive metamaterials, and mechanical logic gates.

Free Vibration Analysis of Arbitrary-Shaped Plates Based on the Improved Rayleigh–Ritz Method

In this investigation, an improved Rayleigh–Ritz method is put forward to analyze the free vibration characteristics of arbitrary-shaped plates for the traditional Rayleigh–Ritz method which is difficult to solve. By expanding the domain of admissible functions out of the structural domain to form a rectangular domain, the admissible functions of arbitrary-shaped plates can be described conveniently by selecting the appropriate admissible functions. Adopting the spring model to simulate the general boundary conditions, the problems of vibration of the arbitrary plate domain can be solved perfectly. Then, a numerical method is introduced to figure out the structure strain energy, kinetic energy, and elastic potential energy of the boundary. Finally, comparing the result with the simulation results and reference examples, the accuracy and convergence of this method are testified. Therefore, an effective new method is proposed for the guidance of the related research and practical engineering problems.