Search

Considering the load uncertainty and unmodeled dynamics in multicylinder hydraulic systems, this paper proposes a balance control algorithm based on safe reinforcement learning to release the restrictions of classical model-based control methods that depend on fixed gain. In this paper, the hydraulic press is controlled by a trained agent that directly maps the system states to control commands in an end-to-end manner. By introducing an action modifier into the algorithm, the system states are kept within security constraints from the beginning of training, making safe exploration possible. Furthermore, a normalized exponential reward function has been proposed. Compared with a quadratic reward function, the precision is greatly improved under the same training steps. The experiment shows that our algorithm can achieve high precision and fast balance for multicylinder hydraulic presses while being highly robust. To the best of our knowledge, this research is the first to attempt the application of a reinforcement learning algorithm to multi-execution units of hydraulic systems. [ABSTRACT FROM AUTHOR]

This paper presents the formulation of a variable load sense control strategy suitable to achieve power savings in hydraulic systems using postcompensated load sensing (LS) hydraulic control architectures. Such architecture is typical in off-road construction machinery. The paper also describes the application of the proposed control strategy referred to as variable load sensing margin (VLM) on a full-size wheel loader. The paper first presents the rationale for the proposed strategy, showing how the state-of-the-art LS architecture present in commercial machines has a margin for lowering the throttling losses present at the control valves. A feedforward controller, derived from an empirical study on a reference vehicle, is used to control the flow to the front-end loader functions. Test results show improvements of the hydraulic power consumption up to 45%, based on the commanded speed of each front-end loader actuator. The paper also describes a gain scheduling pressure feedback control strategy, which is used to allow controlling also functions that include priority. For the case of off-road vehicles, this is typically the steering function. The experimental results show good performances with an error in controlled velocity below 5%, which is achieved when the front-end loader functions are used concurrently with the steering. [ABSTRACT FROM AUTHOR]

Digital hydraulics is a novel alternative to proportional or servovalve-controlled systems in fluid power engineering, providing hydraulic systems with high-energy efficiency, good controllability, and insensitivity to contamination. Switched inertance hydraulic converters (SIHCs) are new digital hydraulic devices that can adjust flow and pressure by digital switching instead of throttling the flow. In this paper, an efficient closed-loop control system is proposed for SIHCs subject to time-varying loading conditions in which the load pressure and/or flow varies with time. The control system is designed to operate SIHCs at optimized switching frequencies and ratios that maximize system efficiency when the load varies. With the proposed controller, the SIHC can effectively adapt to the time-varying load and has achieved up to 10% efficiency improvement and up to 65% pressure ripple reduction without affecting the system's dynamic responses, compared with using a nonoptimized controller. The work shows the feasibility and advantages of simultaneously controlling the switching ratio and switching frequency of SIHCs with a time-varying load. As time-varying loading conditions are commonly found in hydraulic applications, the research outcomes constitute an important aspect in the design and development of highly efficient SIHCs and their practical use in hydraulic machinery. [ABSTRACT FROM AUTHOR]

Counterbalance valves (CBVs) are widely used in hydraulic machines handling gravitational loads. They are usually adopted in hydraulic circuits that set the flow to the actuator with either metering control strategies or primary control strategies. In these circuits, the CBV does not determine the actuator velocity, but it establishes a proper counterpressure that balances the actuator during overrunning loads. A well-known problem of CBVs is the excessive power consumption introduced into the circuit, which is due to an excessive pressurization of the flow supply. This paper presents a solution for using CBVs to control the actuator velocity while also reducing energy consumption. The method consists in controlling the pilot port of the CBV through an external pressure source (adjustable pilot). The solution is first studied analytically, considering all the possible loading conditions at the actuator. Two different control strategies are presented: the "Smart CBV," where the CBV does not control the actuator velocity but it minimizes the system pressure; and the "Smart System" that uses the CBV to efficiently control the actuator velocity during overrunning load conditions. An experimental validation of the proposed solutions is also provided, taking as reference a truck-mounted hydraulic crane. The results of the proposed solutions are compared to those achieved by the traditional circuit of the reference hydraulic crane which uses standard CBVs. For both cases of smart CBV and smart system, a remarkable power saving, respectively, up to 75% and up to 90% is observed. [ABSTRACT FROM AUTHOR]