Effects of UV irradiation time on the molecular structure of typical engineering plastics and tribological properties under heavy load

Exposing engineering plastics to UV irradiation can easily destroy the original molecular structure of the materials and consequently affect their tribological properties. This study investigated the effects of UV irradiation on the molecular structure of typical engineering plastics, such as polytetrafluoroethylene (PTFE) and polyether ether ketone (PEEK), and on their tribological properties under heavy loads (20 MPa). The surface morphology results showed that the appearance of PEEK changed significantly under UV irradiation. However, the change in PTFE was negligible. Under micromorphology, the processing lines of the two materials gradually became lighter with increasing UV irradiation time. The resulting infrared spectra showed that the molecular chains of both materials were broken, and new functional groups were formed under UV irradiation. Tribology testing demonstrated that with prolonged UV irradiation, the average PTFE coefficient of friction remained relatively stable, whereas that of PEEK was approximately 0.55. As the UV irradiation time increased, the wear rate of PTFE increased significantly, whereas that of PEEK showed no significant change.

Grooved cam mechanism with a translating follower having an added ternary-roller intermediate link

The paper presents an analytical approach for designing grooved cam mechanisms with a modified arrangement of the common translating follower. That is, an intermediate link having three rollers is added between the cam and the common follower. On the basis of an existing cam mechanism with a common roller follower, an intermediate link that has three rollers is added between the cam and the common follower. Such a cam mechanism has two set of profile and can create multiple contact points between the cam and the follower at any instant. The two sets of profiles of such a cam mechanism can serve as the grooved types. Since the follower has three rollers that can simultaneously contact the cam at any instant, it can be positive driven along the guided groove of cam contour. The contact forces and contact stresses of such cam mechanisms are analyzed to illustrate the advantage of spreading force transmission and reducing contact stress of this uncommon follower. The obtained results indicate that the contact stress at the surface of the cam and the follower for such a cam mechanism can be reduced by 30% to 47% in comparison to those of cam mechanism with a common translating roller follower. In conclusion, the cam mechanism with a translating follower having an added ternary-roller intermediate link can be a preferable choice for the applications that follower is against heavy loads or move at high speed.

Towards a Modular Elbow Exoskeleton: Concepts for Design and System Control

In industrial workplaces, strenuous, repetitive, and long-term tasks at head level or above as well as carrying heavy loads may lead to musculoskeletal disorders of different task dependent body parts. With an increasing trend towards wearable support systems, there is already a large quantity of exoskeletons that may support the user during movements, or stabilize postures, in order to reduce strain on various parts of the body. However, most commercially available exoskeletons mainly focus on the back and shoulder support. Only a few of them address the elbow joint, despite it being prone to injury. Therefore, this paper discusses different possible design and control concepts of modular elbow exoskeletons. The modular architecture potentially enables coupling to existing commercial- and research-associated systems, through appropriate interfaces. Different morphological structures and control mechanisms are assessed in respect to their ability to extend common exoskeletons for back and shoulder support. Based on these considerations, a first functional passive prototype is presented, which supports the flexion of the elbow joint and can be coupled to an existing exoskeleton. In future work, the prototype may be used for further elaboration and practical investigations in laboratory settings to evaluate its technical functionality and biomechanical effects on the user.

RESEARCH OF OPERATION TECHNOLOGY OF HEAVY LOADS PROCESSING POINTS

Target. The transportation of oversized and heavy cargo is considered one of the most important transport services that bring the greatest profit. This requires powerful equipment and highly qualified specialists. The modern system of organizing transportation provides for the acceptance and delivery of small shipments of heavy cargo yards, during which each shipment can be reloaded several times at the cargo sites. Despite the relatively average transportation distances within Ukraine, the number of processing can reach 3 times, and the time spent at such sites is several days. Therefore, an increase in the delivery time for heavy small consignments arises due to their long stay at the cargo yards. Improvement of the technology of cargo yards and their technical equipment is of paramount importance for improving the organization of transportation of heavy cargo by small consignments. Methods. Comprehensive analysis of technical equipment and technology of work of points for processing heavy cargo on railway transport, statistical analysis, mathematical theory of inventory management, methods of correlation analysis. Results. The analysis of the technology and technical equipment of heavy cargo handling points is carried out, recommendations for their improvement are given. The nature of the arrival of vehicles on the cargo front has been studied, the mode of using loading and unloading machines has been studied, and a method for optimizing the technical equipment of the cargo front has been provided. The method for determining the optimal capacity of sites for heavy cargo has been improved. Practical significance. The studies carried out have shown that there are reserves for improving the transportation of goods by heavy small shipments through the development and application of optimal technology. The main direction in reducing the idle time of wagons is to optimize the processes of handling heavy cargo: increasing the capacity of technical equipment, improving the system of operational planning and management of the operation of points for processing heavy cargo. The application of the methodology makes it possible to evaluate various options for technical equipment at reduced costs, to calculate the optimal capacity of processing points for local and transit heavy cargo using the mathematical theory of inventory management and methods of correlation analysis. The task of drawing up an optimal operational plan for sorting heavy cargo is reduced to a linear programming transport problem and is solved with the help of computer technology.

Prevalence and Risk Factors Analysis for Low Back Pain Among Occupational Groups in Key Industries of China

Background: With the acceleration of industrialization and the growth of population aging, LBP has become the main disease of life loss caused by disability, which brings huge economic burden to society and is a global public health problem that needs to be solved urgently. The purpose of this study is to carry out epidemiological investigation and research on a large sample of people in key industries in different regions of China, to find out the incidence and distribution characteristics of LBP in key industries in China, to explore the epidemic law, and to provide reference basis for alleviating the global public health problems caused by LBP.Methods: This study adopts the modified epidemiological cross-sectional survey method and the stratified cluster sampling method. From the representative enterprises in key industries in seven regions of North China, East China, central China, South China, southwest, northwest and Northeast China, all workers on duty and fulfill the criteria are taken as the research objects. The Chinese version of musculoskeletal disease questionnaire modified by a standardized Nordic Questionnaire was used to collect information, and a total of 57501 valid questionnaires were received. Descriptive statistics were used and multivariate logistic regression analysis (p < 0.05) was performed to explore the associations between musculoskeletal disorders and potential risk factors.Results: The annual incidence of LBP in key industries or workers in China is 16.4%. There was significant difference in the incidence of LBP among occupational groups in different industries (P < 0.05). The results of multivariate regression model show that always make the same movements with your trunk, working in the same positions at a high pace, trunk position, always turn round with your trunk, often work overtime, lift heavy loads (more than 20 kg), education level, staff shortage, working age (years), cigarette smoking, use vibration tools at work Body mass index (BMI), lift heavy loads (more than 5 kg) and age (years) were risk factors for LBP. Physical exercise, standing often at work and absolute resting time are protective factors.Conclusion: The incidence of LBP in key industries or workers in China is high. It is urgent to take relevant measures according to individual, occupational and psychosocial factors of LBP to reduce the adverse impact of LBP on workers' health.

A finite-element-aided ultrasonic method for measuring central oil-film thickness in a roller-raceway tribo-pair

Roller bearings support heavy loads by riding on an ultra-thin oil film (between the roller and raceway), the thickness of which is critical as it reflects the lubrication performance. Ultrasonic interfacial reflection, which facilitates the non-destructive measurement of oil-film thickness, has been widely studied. However, insufficient spatial resolution around the rolling line contact zone remains a barrier despite the use of miniature piezoelectric transducers. In this study, a finite-element-aided method is utilized to simulate wave propagation through a three-layered structure of roller-oil-raceway under elastohydrodynamic lubrication (EHL) with nonlinear characteristics of the i) deformed curvature of the cylindrical roller and ii) nonuniform distribution of the fluid bulk modulus along the circumference of the oil layer being considered. A load and speed-dependent look-up table is then developed to establish an accurate relationship between the overall reflection coefficient (directly measured by an embedded ultrasonic transducer) and objective variable of the central oil-film thickness. The proposed finite-element-aided method is verified experimentally in a roller-raceway test rig with the ultrasonically measured oil-film thickness corresponding to the values calculated using the EHL theory.

The Evolution of Blood Flow Restricted Exercise

The use of blood flow restricted (BFR) exercise has become an accepted alternative approach to improve skeletal muscle mass and function and improve cardiovascular function in individuals that are not able to or do not wish to use traditional exercise protocols that rely on heavy loads and high training volumes. BFR exercise involves the reduction of blood flow to working skeletal muscle by applying a flexible cuff to the most proximal portions of a person’s arms or legs that results in decreased arterial flow to the exercising muscle and occluded venous return back to the central circulation. Safety concerns, especially related to the cardiovascular system, have not been consistently reported with a few exceptions; however, most researchers agree that BFR exercise can be a relatively safe technique for most people that are free from serious cardiovascular disease, as well as those with coronary artery disease, and also for people suffering from chronic conditions, such as multiple sclerosis, Parkinson’s, and osteoarthritis. Potential mechanisms to explain the benefits of BFR exercise are still mostly speculative and may require more invasive studies or the use of animal models to fully explore mechanisms of adaptation. The setting of absolute resistive pressures has evolved, from being based on an individual’s systolic blood pressure to a relative measure that is based on various percentages of the pressures needed to totally occlude blood flow in the exercising limb. However, since several other issues remain unresolved, such as the actual external loads used in combination with BFR, the type of cuff used to induce the blood flow restriction, and whether the restriction is continuous or intermittent, this paper will attempt to address these additional concerns.

Modeling and Control of Underactuated Three-Dimensional Overhead Crane Systems

Overhead crane systems play a vital role in different factories to transport heavy loads. This paper provides an overview of recent developments in the modeling and control of three-dimensional overhead crane systems. It provides a categorized survey of the published work. Different control methodologies when applied to overhead crane are examined, outlined and assessed to aid for future work.

Correlation between Individual Characteristics and Work Position with Work Fatigue on Workers

Introduction: Work fatigue is a condition of decreased efficiency and resilience of workers, which can interfere the companys’ productivity. Job fatigue can be caused by the performance, duration, and effort (work position) of the workers. Based on the observations, workers at the expedition sub units of PT X needed to lift 200 to 400kg heavy loads. The activity of lifting very heavy weights can cause fatigue. One form of physical fatigue indicators is an increase in lactic acid in the blood. The purpose of this study was to analyze the correlation between workers’ characteristics and work position with work fatigue among workers in the expedition sub units of PT X. Methods: This research was a quantitative study with a cross sectional design. The population of this study was 36 people. This research used total sampling. The independent variable were individual characteristics and work position as measured using REBA tools, and the dependent variable was work fatigue as measured using lactic acid levels in blood. Data was analyzed using statistical tools to obtain the value of correlation coefficient between variables. Result: The results showed that there was a weak positive correlation between workers’ characteristics and physical fatigue. The results showed that the coefficient value between work position and physical fatigue was 0.354. The coefficient figure indicated a weak positive correlation between work position and work fatigue. Conclusion: There was a correlation between work position and work fatigue in workers.Keywords: ergonomics, lactic acid, REBA, work fatigue, work position .

A Review of the Conceptualization and Operational Management of Seaport Microgrids on the Shore and Seaside

Seaports are well known as the medium that has evolved into the central link between sea and land for complex marine activities. The growth in maritime logistics particularly necessitates a large volume of energy supply in order to maintain the operation of sea trade, resulting in an imbalance between generation and demand sides. Future projections for three major concerns show an increase in load demand, cost of operation, and environmental issues. In order to overcome these problems, integrating microgrids as an innovative technology in the seaport power system appears to be a vital strategy. It is believed that microgrids enhance seaport operation by providing sustainable, environmentally friendly, and cost-effective energy. Although microgrids are well established and widely used in a variety of operations on land, their incorporation into the seaport is still limited. The involvement of a variety of heavy loads such as all-electric ships, cranes, cold ironing, and buildings infrastructure renders it a complicated arrangement task in several aspects, which necessitates further research and leaves space for improvement. In this paper, an overview of the seaport microgrids in terms of their concepts and operation management is presented. It provides the perspectives for integrating the microgrid concept into a seaport from both shore side and seaside as a smart initiative for the green port’s vision. Future research directions are discussed towards the development of a more efficient marine power system.