Motor unit buckling in variable recruitment fluidic artificial muscle bundles: implications and mitigations

Fluidic artificial muscles (FAMs) are a popular actuation choice due to their compliant nature and high force-to-weight ratio. Variable recruitment is a bio-inspired actuation strategy in which multiple FAMs are combined into motor units that can be pressurized sequentially according to load demand. In a traditional ‘fixed-end’ variable recruitment FAM bundle, inactive units and activated units that are past free strain will compress and buckle outward, resulting in resistive forces that reduce overall bundle force output, increase spatial envelope, and reduce operational life. This paper investigates the use of inextensible tendons as a mitigation strategy for preventing resistive forces and outward buckling of inactive and submaximally activated motor units in a variable recruitment FAM bundle. A traditional analytical fixed-end variable recruitment FAM bundle model is modified to account for tendons, and the force-strain spaces of the two configurations are compared while keeping the overall bundle length constant. Actuation efficiency for the two configurations is compared for two different cases: one case in which the radii of all FAMs within the bundle are equivalent, and one case in which the bundles are sized to consume the same amount of working fluidvolume at maximum contraction. Efficiency benefits can be found for either configuration for different locations within their shared force-strain space, so depending on the loading requirements, one configuration may be more efficient than the other. Additionally, a study is performed to quantify the increase in spatial envelope caused by the outward buckling of inactive or low-pressure motor units. It was found that at full activation of recruitment states 1, 2, and 3, the tendoned configuration has a significantly higher volumetric energy density than the fixed-end configuration, indicating that the tendoned configuration has more actuation potential for a given spatial envelope. Overall, the results show that using a resistive force mitigation strategy such as tendons can completely eliminate resistive forces, increase volumetric energy density, and increase system efficiency for certain loading cases. Thus, there is a compelling case to be made for the use of tendoned FAMs in variable recruitment bundles.

Corticospinal excitability remains unchanged in the presence of residual force enhancement and does not contribute to increased torque production

Background Following stretch of an active muscle, muscle force is enhanced, which is known as residual force enhancement (rFE). As earlier studies found apparent corticospinal excitability modulations in the presence of rFE, this study aimed to test whether corticospinal excitability modulations contribute to rFE. Methods Fourteen participants performed submaximal plantar flexion stretch-hold and fixed-end contractions at 30% of their maximal voluntary soleus muscle activity in a dynamometer. During the steady state of the contractions, participants either received subthreshold or suprathreshold transcranial magnetic stimulation (TMS) of their motor cortex, while triceps surae muscle responses to stimulation were obtained via electromyography (EMG), and net ankle joint torque was recorded. B-mode ultrasound imaging was used to confirm muscle fascicle stretch during stretch-hold contractions in a subset of participants. Results Following stretch of the plantar flexors, an average rFE of 7% and 11% was observed for contractions with subthreshold and suprathreshold TMS, respectively. 41–46 ms following subthreshold TMS, triceps surae muscle activity was suppressed by 19–25%, but suppression was not significantly different between stretch-hold and fixed-end contractions. Similarly, the reduction in plantar flexion torque following subthreshold TMS was not significantly different between contraction conditions. Motor evoked potentials, silent periods and superimposed twitches following suprathreshold TMS were also not significantly different between contraction conditions. Discussion As TMS of the motor cortex did not result in any differences between stretch-hold and fixed-end contractions, we conclude that rFE is not linked to changes in corticospinal excitability.

Reduced Equations of Slope-Deflection Method in Structural Analysis

This paper presents an update of the slope-deflection method, which is used in the analysis of statically indeterminate structures. In this study, new reduced equations are presented based on including both the effects of the member rotations and the fixed end moments in one term, rather than two terms, in order to simplify the application of the slope-deflection method. The reduced equations are developed, then three numerical examples with comprehensive cases of beams are solved by applying both the original and the proposed reduced equations. The analysis outputs indicated that the reduced equations are applicable for all cases that can be analyzed by the slope-deflection method, and give identical results compared with the original equations. It is found that the reduced equations require less computations when the structure has no support settlement, compared with the original equations, whereas the computations are approximately similar when the structure has a support settlement.

Edge Structural Health Monitoring (E-SHM) Using Low-Power Wireless Sensing

Effective Structural Health Monitoring (SHM) often requires continuous monitoring to capture changes of features of interest in structures, which are often located far from power sources. A key challenge lies in continuous low-power data transmission from sensors. Despite significant developments in long-range, low-power telecommunication (e.g., LoRa NB-IoT), there are inadequate demonstrative benchmarks for low-power SHM. Damage detection is often based on monitoring features computed from acceleration signals where data are extensive due to the frequency of sampling (~100–500 Hz). Low-power, long-range telecommunications are restricted in both the size and frequency of data packets. However, microcontrollers are becoming more efficient, enabling local computing of damage-sensitive features. This paper demonstrates the implementation of an Edge-SHM framework through low-power, long-range, wireless, low-cost and off-the-shelf components. A bespoke setup is developed with a low-power MEM accelerometer and a microcontroller where frequency and time domain features are computed over set time intervals before sending them to a cloud platform. A cantilever beam excited by an electrodynamic shaker is monitored, where damage is introduced through the controlled loosening of bolts at the fixed boundary, thereby introducing rotation at its fixed end. The results demonstrate how an IoT-driven edge platform can benefit continuous monitoring.

An Experiment to Design an Operation and Maintenance System Integrating Apriori Association Rules for a Telecom Platform

The operation and maintenance management of telecom platforms puts more emphasis on operation and alarm monitoring and less on business flow, and it is difficult to have a seamless connection between operation and maintenance and sales. To improve the cooperative efficiency and the informatization level of telecom platform operation and maintenance, a new operation and maintenance system integrating Apriori association rules for a telecom platform is proposed. In this paper, the Apriori algorithm is firstly used to analyse the fault correlation of the operation and maintenance system of the telecommunications platform to get the alarm message. Then, the fault risk of the operation and maintenance platform is evaluated intelligently by the system-business alarm causality model. Finally, based on the fixed end and the mobile end, the dynamic presentation of the system running state and alarm monitoring, device query and positioning, and online and offline inspection are implemented and designed, respectively. Experimental results show that the proposed operation and maintenance systems integrating Apriori association rules for the telecom platform innovate the cooperative mode between the operations and sales team, and the average time reduces to 3.9 minutes from 4.7 minutes and the risk forecasting accuracy increases from 8% to 26%. The assumed method can significantly improve the operational efficiency and intelligent level of the telecom platform’s system and business.

DYNAMIC PERFORMANCE OF ADHESIVELY BONDED SINGLE LAP JOINTS WITH DIFFERENT FIBER ANGLE ORIENTATIONS OF ADHERENDS

This work aims to investigate the dynamic response of the adhesive bonding of Single Lap Joints (SLJs) using a free vibration technique. For this purpose, the joints with fixed-end conditions were subjected to the vibration test, and the results were compared with the numerical ones which were obtained from the Finite Element Method (FEM) via the ANSYS package program. The materials used in this study are an adhesive film, AF163 2K produced by 3M, and adherends, manufactured from a glass reinforced polymer matrix composite, produced by Hexcel. While four different adherends with different fiber orientations were used, the thickness of the adhesive layer in bonded region was kept constant, 0.2 mm. In doing so, the main concentration was given to the adherends as the energy dissipation was believed to come mainly from them. The main objective was to get high damping values without compromising any decrease in the structural performance of the joints. The experimental natural frequency, flexural rigidity and damping values of the joints were obtained as a parameter of the different adherend types. The results were also validated using numerical modal analysis.

DESIGN ASPECTS OF INSTALLATION DEVICES OF THE SUPPORT RINGS

The processes of manufacturing machines and appliances show a continuous tendency to increase the degree of automation. An important role in the automation of manufacturing processes is played by the constructive technologicality of the product. It is important to use a minimum number of components, which have a construction as technological as possible in terms of automation. In this context, the use of supporting rings as fasteners is welcome. The design of the installation devices of these rings requires the knowledge of their deformation forces, information that is missing in the profile literature. The authors set their goal to develop the method for calculating the forces required to deform the supporting rings with a rectangular transverse profile and their maximum allowable deformations. The calculation relationships were obtained by formalizing the supporting ring through a bar with a fixed end and studying its deformation using Mohr's integral. The article lists some types of the supporting rings used in the construction of machines and appliances, their advantages and disadvantages, aspects of their automatic installation: deformation and installation methods, precision of joint orientation, optimal design, calculation of forces required for deformation and the maximum permissible deformation value. As a result of the research carried out, recommendations were developed regarding the calculation of some constructive parameters of the devices for installing the supporting rings.