Tuned muscle and spring properties increase elastic energy storage

Elastic recoil drives some of the fastest and most powerful biological movements. For effective use of elastic recoil, the tuning of muscle and spring force capacity is essential. While studies of invertebrate organisms that use elastic recoil show evidence of increased force capacity in their energy loading muscle, changes in the fundamental properties of such muscles have yet to be documented in vertebrates. Here we used three species of frogs (Cuban tree frogs, bullfrogs, and cane toads) that differ in jumping power to investigate functional shifts in muscle-spring tuning in systems using latch-mediated spring actuation (LaMSA). We hypothesized that variation in jumping performance would result from increased force capacity in muscles and relatively stiffer elastic structures resulting in greater energy storage. To test this, we characterized the force-length property of the plantaris longus muscle-tendon unit (MTU), and quantified the maximal amount of energy stored in elastic structures for each species. We found that the plantaris longus MTU of Cuban tree frogs produced higher mass-specific energy and mass-specific forces than the other two species. Moreover, we found that the plantaris longus MTU of Cuban tree frogs had higher pennation angles than the other species suggesting that muscle architecture was modified to increase force capacity through packing of more muscle fibers. Finally, we found that the elastic structures were relatively stiffer in Cuban tree frogs. These results provide a mechanistic link between the tuned properties of LaMSA components, energy storage capacity and whole system performance.

Direct Actuation of Large Sized Valves by a Hydraulically Relieved Electromechanical Actuation System

Extensive actuation forces and strokes are required for the actuation of large sized valves normally implemented in high power hydraulic systems. A hydraulically piloted operation is, for now, the most suitable solution and state of the art. However, there are some applications where electromechanical valve actuation systems are at advantage against common pilot operation systems. In this contribution it is analyzed in which cases the application of electro-mechanical actuators can be of advantage and why displacement-controlled systems may be one of these applications. A novel electromechanical valve actuation system for large sized 4/3-way directional control valves for the use in displacement-controlled systems is presented. This new actuation system is characterized by a hydraulic relief of the centering springs. Therefore, the springs are only active in safety-critical conditions, such as a power outage. Since the actuator is not working against the spring force during every displacement, the necessary actuation force is reduced drastically. Thus, common electromechanical actuators can be used. In case of a power outage, the spring relief is deactivated causing the stored energy to center the spool in its neutral position. The performance of the novel actuation system is examined through measurements conducted on a manufactured demonstrator for valves of nominal size 25 with a flow rate of up to 600 l/min.

Study on Improving the Sealing Reliability of Fluid Connector

Aiming at the problem of sealing reliability of fluid connector products commonly used in hydraulic system, this paper studies the static seal and the sliding seal. The factors affecting the sealing such as spring force, sealing ring and life of spring are considered one by one and the sealing effect is teseted. The results showed that improved fluid connector can ensure that the hydraulic system is in the state of not even air intake or oil leakage while connecting and disconnecting at any time. The connector has been successfully applied to a certain model of launch vehicle.

F-Actin Bending Facilitates Net Actomyosin Contraction By Inhibiting Expansion With Plus-End-Located Myosin Motors

We investigate whether a microscopic system of two semi-flexible actin filaments with an attached myosin motor can facilitate contraction. Based on energy minimisation, we derive and analyse a partial differential equation model for a two-filament-motor structure embedded within a dense, two-dimensional network. Our method enables calculation of the plane stress tensor, providing a measure for contractility. After deriving the model, we use a combination of asymptotic analysis and numerical solutions to show how F-actin bending facilitates net contraction as a myosin motor traverses two symmetric filaments. Myosin motors close to the minus-ends facilitate contraction, whereas motors close to the plus-ends facilitate expansion. The leading-order solution for rigid filaments exhibits polarity-reversal symmetry, such that the contractile and expansive components balance to zero. Surprisingly, after introducing bending the first-order correction to stress indicates expansion. However, numerical solutions show that filament bending induces a geometric asymmetry that brings the filaments closer to parallel as a myosin motor approaches their plus-ends. This decreases the effective spring force opposing motion of the motor, enabling it to move faster close to filament plus-ends. This reduces the contribution of expansive stress, giving rise to net contraction. Further numerical solutions confirm that this applies beyond the small bending regime considered in the asymptotic analysis. Our findings confirm that filament bending gives rise to microscopic-scale actomyosin contraction, and provides a possible explanation for network-scale contraction.

Analysis of Racing Greyhound Path Following Dynamics Using a Tracking System

The University of Technology Sydney (UTS) has been working closely with the Australasian greyhound industry for more than 5 years to reduce greyhound race-related injuries. During this period, UTS has developed and deployed several different techniques including inertial measurement units, drones, high-frame-rate cameras, track geometric surveys, paw print analysis, track soil spring-force analysis, track maintenance data, race injury data, race computer simulation and modelling to assist in this task. During the period where the UTS recommendations have been adopted, the injury rate has dropped significantly. This has been achieved by animal welfare interventions that lower racing congestion, and lower transient forces and jerk rates the greyhounds experience during a race. This study investigated the use of a greyhound location tracing system where small and lightweight signal emitting devices were placed inside a pocket in the jackets of racing greyhounds. The system deployed an enhanced version of a player tracking system currently used to track the motion of human athletes. Greyhounds gallop at speeds of almost 20 m/s and are known to change their heading direction to exceed a yaw rate of 0.4 rad/s. The high magnitudes of velocity, acceleration and jerk posed significant technical challenges, as the greyhounds pushed the human tracking system beyond its original design limits. Clean race data gathered over a six-month period were analysed and presented for a typical 2-turn greyhound racing track. The data confirmed that on average, greyhounds ran along a path that resulted in the least energy wastage, which includes smooth non-linear paths that resemble easement curves at the transition between the straights to the semi-circular bends. This study also verified that the maximum jerk levels greyhounds experienced while racing were lower than the jerk levels that had been predicted with simulations and modelling for the track path. Furthermore, the results from this study show the possibility of such a systems deployment in data gathering in similar settings to greyhound racing such as thoroughbred and harness horse racing for understanding biomechanical kinematic performance.

Homopolymer Based Magnetorheological Elastomer

Magnetorheological rubber belongs to the class of ‘Smart Material’ whose mechanical properties can be altered continuously and reversibly by an applied magnetic field. Magnetorheological rubber (MRE’s) are composites that consists of magnetically polarisable particles mixed into rubber matrix. With suitable controlled algorithms, they respond to change in their environment. Purpose of this work is to know more about magnetorheological rubber for active stiffness, vibration control and dampening applications. Although few applications of these materials have been reported in the literature, the possibilities are numerous. They can be used for various applications such as vibration absorber, vibration isolator, variable stiffness bush, spring, force sensors, actuators etc.

Performance of a friction ring DVA for vibration control of a flywheel

A flexible ring DVA with friction contact interfaces (essentially a viscoelastic-friction DVA) is proposed to suppress vibration of a flywheel, two other cases are also studied, i.e., viscoelastic DVA and friction DVA. Based on an equivalent 3 degrees of freedom (DOFs) dynamic model, displacement response of the flywheel-DVA are obtained by using harmonic balance method (HBM). It is shown that all three types of DVA can suppress vibration of the flywheel effectively, bandwidth of the viscoelastic-friction DVA is enlarged due to the existence of friction interface. Performances of the DVA are evaluated by analyzing the displacement responses and forces (i.e., spring force, damping force and friction force). It is shown that the frequency corresponding to the turning point on the response curve is the critical frequency at which dynamic vibration absorption takes place, and it is also the frequency at which the friction force begins to take effect. In the process of emergence and disappearance of the dynamic vibration absorption, the friction force plays a role similar to a "switch"

DEVELOPMENT OF THE OPTIMAL DESIGN OF MANUAL GARDEN FORK WITH THE ABILITY TO QUICKLY CLEAN THE WORKING SURFACE

Manual garden tools help a lot with different types of work with soil: digging, removing roots and weeds, harvesting root crops and bulbs, and much more would be much more difficult if it were not for the forks. This tool has a wide range of features. There are many varieties of this tool differing in shapes and sizes: manure, harvesting, hay, flower, pointed, fork-shovel, telescopic, digging, ball-pointed. A common problem for all manual garden forks is clogging of the tines. This reduces the productivity of those who use them. Attempts are constantly being made to solve the problem of quick cleaning of the tines of manual garden forks. Many technical solutions to this problem are patented and are actively used in practice. The employee of the FSBEI of Higher Education “Pskov State University” has developed a manual self-cleaning fork. The design of the manual self-cleaning fork consists of a handle and a frame with many elongated spaced tines, which is fixed at one end of the handle, as well as a cleaning plate that is fixed to the movable handle, and a spring located on top of the handle inside the movable handle. The movable handle has lateral longitudinal grooves. The movable handle provides movement of the cleaning plate relative to the handle, and, consequently, compression and releasing of the spring. The overall dimensions of the proposed device are accepted according to the existing standards for such structures. The principle of operation of the proposed device: during the operation of the fork, the cleaning plate is pressed against the frame by spring force. Cleaning of the tines is made by a cleaning plate, which is moved along the tines. To do this, the user withdraws the movable handle, overcoming the resistance of the spring. By doing so, the frame passes through the longitudinal grooves and serves as one guide for the movable handle, and the handle serves as the second guide. The fork returns to its original state by releasing the spring after the user releases the movable handle. The main technical result of the proposed device is an increase in the operational characteristics of the fork, reduction in the time and effort spent on cleaning of the tines.

Vibration Attenuation Investigations on a Distributed Phononic Crystals Beam for Rubber Concrete Structures

Locally resonant phononic crystals (LRPCs) beam is characterized by the band gaps; some frequency ranges within which flexural waves cannot propagate freely. So, the LRPCs beam can be used for noise or vibration isolation. In this paper, a LRPCs beam with distributed oscillators is proposed, and the general formula of band gaps and transmission spectrum are derived by the transfer matrix method (TMM) and spectrum element method (SEM). Subsequently, the parameter effects on band gaps are investigated in detail. Finally, a rubber concrete beam is designed to demonstrate the application of distributed LRPCs beam in civil engineering. Results reveal that the distributed LRPCs beam has multifrequency band gaps and the number of the band gaps is equal to that of the oscillators. Compared with others, the distributed LRPCs beam can reduce the stress concentration when subjected to vibration. The oscillator interval has no effect on the band gaps, which makes it more convenient to design structures. Individual changes of oscillator mass or stiffness affect the band gap location and width. When the resonance frequency of oscillator is fixed, the starting frequency of the band gap remains constant, and increasing oscillator mass of high-frequency band gap widens the high-frequency band gap, while increasing oscillator mass of low-frequency gap widens both high-frequency and low-frequency band gaps. External loads, such as the common uniform spring force provided by foundation in civil engineering, are conducive to the band gap, and when the spring force increases, all the band gaps are widened. Taken together, a configuration of LRPCs rubber concrete beam is designed, and it shows good isolation on the vibration induced by the railway. By the presented design flow chart, the research can serve as a reference for vibration isolation of LRPCs beams in civil engineering.