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.

Design, analysis, and validation of an orderly recruitment valve for bio-inspired fluidic artificial muscles

Biological musculature employs variable recruitment of muscle fibers from smaller to larger units as the load increases. This orderly recruitment strategy has certain physiological advantages like minimizing fatigue and providing finer motor control. Recently fluidic artificial muscles (FAM) are gaining popularity as actuators due to their increased efficiency by employing these bio-inspired recruitment strategies such as active variable recruitment (AVR). AVR systems use a multi-valve system (MVS) configuration to selectively recruit individual FAMs depending on the load. However, when using an MVS configuration, an increase in the number of motor units in a bundle corresponds to an increase in the number of valves in the system. This introduces greater complexity and weight. The objective of this paper is to propose, analyze, and demonstrate an orderly recruitment valve (ORV) concept that enables orderly recruitment of multiple FAMs in the system using a single valve. A mathematical model of an ORV-controlled FAM bundle is presented and validated by experiments performed on an ORV prototype. The modeling is extended to explore a case study of a 1-DOF robot arm system consisting of an electrohydraulic pressurization system, ORV, and a FAM-actuated rotating arm plant and its dynamics are simulated to further demonstrate the capabilities of an ORV-controlled closed-loop system. An orderly recruitment strategy was implemented through a model-based feed forward controller. To benchmark the performance of the ORV, a conventional MVS with equivalent dynamics and controller was also implemented. Trajectory tracking simulations on both the systems revealed lower tracking error for the ORV controlled system compared to the MVS controlled system due to the unique cross-flow effects present in the ORV. However, the MVS, due to its independent and multiple valve setup, proved to be more adaptable for performance. For example, modifications to the recruitment thresholds of the MVS demonstrated improvement in tracking error, albeit with a sacrifice in efficiency. In the ORV tracking performance remained insensitive to any variation in recruitment threshold. The results show that compared to the MVS, the ORV offers a simpler and more compact valving architecture at the expense of moderate losses in control flexibility and performance.

Peran Rekrutmen dan Penempatan Kerja pada PT. Indomarco Adi Prima Surabaya

This study examines the role of recruitment and job placement at PT. Indomarco Adi Prima Surabaya influence work productivity. This research with a quantitative approach has 60 populations. The tests performed were data analysis of validity, reliability, and classic assumption tests, including normality test, autocorrelation test, multicollinearity test, and heteroscedasticity test. Furthermore, hypothesis testing includes test (R2), T statistical test, F statistical test, and multiple linear regression test. Data collection use observations, interviews and (primary) questionnaires. Data analysis use multiple linear regression with SPSS (v.18). The results showed that partially and simultaneously, the variables of recruitment and job placement had a significant positive effect on employee work productivity. Partially the better the recruitment system, the better work productivity will be. Likewise, a good job placement will increase employee work productivity. Furthermore, simultaneously the variable recruitment and good work placement will increase employee productivity.

Modeling of Resistive Forces and Buckling Behavior in Variable Recruitment Fluidic Artificial Muscle Bundles

Fluidic artificial muscles (FAMs), also known as McKibben actuators, are a class of fiber-reinforced soft actuators that can be pneumatically or hydraulically pressurized to produce muscle-like contraction and force generation. When multiple FAMs are bundled together in parallel and selectively pressurized, they can act as a multi-chambered actuator with bioinspired variable recruitment capability. The variable recruitment bundle consists of motor units (MUs)—groups of one of more FAMs—that are independently pressurized depending on the force demand, similar to how groups of muscle fibers are sequentially recruited in biological muscles. As the active FAMs contract, the inactive/low-pressure units are compressed, causing them to buckle outward, which increases the spatial envelope of the actuator. Additionally, a FAM compressed past its individual free strain applies a force that opposes the overall force output of active FAMs. In this paper, we propose a model to quantify this resistive force observed in inactive and low-pressure FAMs and study its implications on the performance of a variable recruitment bundle. The resistive force behavior is divided into post-buckling and post-collapse regions and a piecewise model is devised. An empirically-based correction method is proposed to improve the model to fit experimental data. Analysis of a bundle with resistive effects reveals a phenomenon, unique to variable recruitment bundles, defined as free strain gradient reversal.

Qualitative analysis of a diffusive SEIR epidemic model with linear external source and asymptomatic infection in heterogeneous environment

<p style='text-indent:20px;'>This paper is devoted to an SEIR epidemic model with variable recruitment and both exposed and infected populations having infectious in a spatially heterogeneous environment. The basic reproduction number is defined and the existence of endemic equilibrium is obtained, and the relationship between the basic reproduction number and diffusion coefficients is established. Then the global stability of the endemic equilibrium in a homogeneous environment is investigated. Finally, the asymptotic profiles of endemic equilibrium are discussed, when the diffusion rates of susceptible, exposed and infected individuals tend to zero or infinity. The theoretical results show that limiting the movement of exposed, infected and recovered individuals can eliminate the disease in low-risk sites, while the disease is still persistent in high-risk sites. Therefore, the presence of exposed individuals with infectious greatly increases the difficulty of disease prevention and control.</p>

PENGARUH REKRUTMEN TERHADAP KINERJA KARYAWAN DI KOPERASI LEMBAGA PENGEMBANGAN PERBANKAN INDONESIA

This study aims to determine the effect of recruitment on improving cooperative performance. This analysis uses the independent variable, recruitment, and the dependent variable is employee performance.The population in this study were all supervisors, managers and associations of Indonesian banking development cooperatives. Samples were conducted using the non-probability sampling method using saturated samples obtained 30 people as samples. The type of data used is primary data. The testing method in this thesis uses IBM SPSS 22 processing. The results of the questionnaire have been tested for validity, reliability testing, data normality test, regression analysis and hypothesis testing.The results of the study prove that the proposed partial hypothesis is accepted because it shows significant test results. This means a significant increase in employee performance by 81.0% while 19.0% requires other factors.