Hysteresis Control in Pump-Controlled Systems—A Way to Reduce Mode-Switch Oscillations in Closed and Open Circuits

There is growing interest in using electric motors as prime movers in mobile hydraulic systems. This increases the interest in so-called pump-controlled systems, where each actuator has its own drive unit. Such architectures are primarily appealing in applications where energy efficiency is important and electric recuperation is relevant. An issue with pump-controlled systems is, however, mode-switch oscillations which can appear when the pressure levels in the system are close to the switching condition. In this paper, the mode-switching behavior of different generalized closed and open circuit configurations is investigated. The results show that the choice of where to sense the pressures has a huge impact on the behavior. They also show that, if the pressure sensing components are properly placed, closed and open circuits can perform very similarly, but that mode-switch oscillations still can occur in all circuits. Active hysteresis control is suggested as a solution and its effectiveness is analyzed. The outcome from the analysis shows that active hysteresis control can reduce the risk for mode-switch oscillations significantly.

Role of MicroRNAs and Long Non-Coding RNAs in Regulating Angiogenesis in Human Breast Cancer- A Molecular Medicine Perspective

: MicroRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are proficient in regulating gene expression post-transcriptionally. Considering the recent trend in exploiting non-coding RNAs (ncRNAs) as cancer therapeutics, the potential use of miRNAs and lncRNAs as biomarkers and novel therapeutic agents against angiogenesis is an important scientific aspect. An estimated 70% of the genome is actively transcribed, only 2% of which codes for known protein-coding genes. Long noncoding RNAs (lncRNAs) are a large and diverse class of RNAs > 200 nucleotides in length, and not translated into protein, and are of utmost importance and it governs the expression of genes in a temporal, spatial, and cell context-dependent manner. Angiogenesis is an essential process for organ morphogenesis and growth during development, and it is relevant during the repair of wounded tissue in adults. It is coordinated by an equilibrium of pro-and anti-angiogenic factors; nevertheless, when affected, it promotes several diseases, including breast cancer. Signaling pathways involved here are tightly controlled systems that regulate the appropriate timing of gene expression required for the differentiation of cells down a particular lineage essential for proper tissue development. Lately, scientific reports are indicating that ncRNAs, such as miRNAs, and lncRNAs, play critical roles in angiogenesis related to breast cancer. The specific roles of various miRNAs and lncRNAs in regulating angiogenesis in breast cancer, with particular focus on the downstream targets and signaling pathways regulated by these ncRNAs with molecular medicine perspective, are highlighted in this write-up.

Extended Analysis of a Valve-Controlled System with Multi-Chamber Actuator

This paper outlines an extended analysis on how multi-chamber actuators can improve the efficiency of valve-controlled systems. Resistive control is a major source of energy losses in valve-controlled systems that share the same pump to drive multiple loads. By combining different chambers, the load on multi-chamber actuators can be transformed into different pressure and flow rate levels. This allows the adaptation of its load to the loads on other actuators. This can lead to a reduction of resistive control energy losses that occur between pump and actuators when driven simultaneously. As a case study to highlight how the system efficiency can be improved, a load sensing system with a conventional and a multi-chamber actuator is analysed. The equations that describe the system steady state behaviour are presented to evaluate the effect of the load transformations on the system efficiency. A disadvantage of such architecture is the fact that load transformations result in different actuator speeds. To reduce this effect, a compensation factor for the command signal to the proportional valve is presented. The highlight from this paper is the potential for efficiency improvement enabled by the adoption of multi-chamber actuators in a valve-controlled architecture. Further research is required for the selection of number of chambers and their areas since they directly affect the system efficiency.

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.

The properties of the solution for a class of switched systems with internally forced switching

In this paper, the dynamic behavior of a class of switched systems with internally forced switching (IFS) is investigated. By introducing the definitions of continuous dependence and differentiability, the continuous dependence and differentiability of the solution relative to the control function are obtained. In the past studies, the optimal control problem given by IFS mainly focused on a special class of controlled systems (the piece affine system). Our results lay a good foundation for studying the more general internally forced switching problem.

Grey FNN control and robustness design for practical nonlinear systems

To ensure asymptomatic stability and improve vehicle ride comfort, this paper develops a fuzzy neural network (FNN) based on the evolved bat algorithm (EBA) to design adaptive backstepping controllers with gray signal predicators. A recoil method is used to evaluate the nonlinearity of the controlled systems and to derive the control law which is evolved for the tracking of the signals. A group of grey differential equations are applied for the grey model (GM) (n, h), which is an active model where h is the number of considered variables and n is the order of the grey differential equations. In the article, the Discrete GM (2.1) is used to obtain the advanced motion of the nonlinear system, so that the command controller can prove the Lyapunov stability and feasibility of the entire scheme through the Lyapunov-like lemma. The controller design criteria are demonstrated for mechanical elastic wheels (MEW) to establish a viable mathematical framework for the new wheels.

Design and Efficiency Analysis of Closed Loop Pump Controlled Circuit Hydraulic Lifting System of Wheel Loaders Based on Gravity Self-Balancing Hydraulic Cylinder

In the hydraulic lifting systems of wheel loaders, the valve controlled systems are used to drive the hydraulic cylinder to complete frequent lifting and falling operations. The gravitational potential energy of the lifting system, accumulated in the lifting process, is converted into heat energy through the throttling port of the valve during the falling processes, which results in significant throttling loss and severe system overheating. To solve the problems, a potential energy regeneration and utilization system is proposed, where the closed loop pump controlled circuit based on the gravity self-balancing hydraulic cylinder is adopted to eliminate throttling loss, and the gravity self-balancing chamber of the cylinder is directly connected with accumulator to recycle gravity potential energy. In the research, the structure and working principle of the proposed hydraulic system is analyzed first, then the co-simulation model and the test prototype are established to investigate the working and energy characteristics of the proposed system. Test results indicate that, compared with the traditional valve controlled hydraulic system, 58.9% energy consumption reduction can be expected for the hydraulic pump by adopting the proposed system under the same working condition.