Mikko Huova

Jammed on/off Valve Fault Compensation with Distributed Digital Valve System

Abstract The digital valve system is an on/off valve based directional flow control valve capable of accurate control of hydraulic actuators. The presented system has good features concerning fault tolerance since it can detect, diagnose and compensate faults on-line. This paper concentrates on fault compensation when a valve has jammed in the open—position and the system has internal leakage. The system can adapt to the fault and continue operation with only a small degradation in performance. This feature is unique in the area of hydraulics since the system has no extra components added. The cost for this compensation is increased calculation in the controller and increased energy consumption if a fault occurs. If these downsides can be accepted the system can be considered fault-tolerant and it could be used even in critical applications where failing is not an option. Fault tolerance can also be introduced as standard in every modern hydraulic application where good performance and fault tolerance are needed.

Energy Efficiency of Three-Chamber Cylinder with Digital Valve System

ABSTRACT Commonly used hydraulic cylinders have a piston and a piston rod. The piston divides the inside of the cylinder in two chambers and pressures which affect how the piston generates the linear motion. Use of distributed valve system enables several control modes in a system of this type because different control edges can be controlled independently. These control modes can be used for decreasing energy consumption and improving controllability. The traditional hydraulic cylinder has only a limited number of control modes, but by utilizing a multi-chamber cylinder the number of control modes can be increased. In this paper, a three-chamber cylinder is studied using measurements and simulations. The control of the cylinder is presented and measurements are done in a 1-DOF boom mock-up to show the operation of the system in practice. A simulation model is built to investigate further the energy saving capability of the system. The studies show that losses can be significantly reduced by replacing traditional cylinder drives with multi-chamber cylinders.

Analysis by Simulation of Different Control Algorithms of A Digital Hydraulic Two-Actuator System

Many hydraulic systems have losses, which could be avoided with new technology. Because component efficiency can be optimized to a certain operation point, hydraulic machines are no worse than other machines. More important than the peak efficiency values of each individual component in a system is the efficiency of the whole power transfer line. In a system where the amount of required power and the velocity/force ratio are variables, components may but seldom operate at their optimal design points. A typical approach to mobile work hydraulics is to use a load-sensing pump for a hydraulic multi-actuator system. This approach is efficient but seldom, if many actuators are used simultaneously. Our recent prototype of an improved hydraulic power supply system is the Digital Hydraulic Power Management System (DHPMS), which can serve many actuators at optimised supply pressure but is also capable of motoring and transforming. This functionality holistically reduces losses in the system. Losses can be further reduced by using distributed valve systems with sophisticated control algorithms together with the DHPMS. In this study, we used digital hydraulic valves, which efficiency strongly depends on the control algorithms used. We studied here different control methods for a system with two actuators, a DHPMS, and digital valves.

Verification and Validation of a Pressure Control Unit for Hydraulic Systems

This paper describes the development, verification and model-based validation of a safety-critical pressure relief function for a digital hydraulic system. It demonstrates techniques to handle typical challenges that are encountered when verifying and validating cyber-physical systems with complex dynamical behaviour. The system is developed using model-based design in Simulink. The verification part focuses on verification of functional properties of the controller, where formal automated verification tools are employed. The validation part focuses on validating that the controller has the desired impact on the physical system. In the latter part search-based methods are used to find undesired behaviour in a simulation model of the system. The combination of techniques provides confidence in the resilience of the developed system.

Digital hydraulic multi-pressure actuator – the concept, simulation study and first experimental results

Abstract The decentralisation of hydraulic systems is a recent trend in industrial hydraulics. Speed variable drive is one concept where an actuator is driven by an integrated pump, thus removing the need for control valves or complex centralised variable displacement hydraulic units and long pipelines. The motivation for the development is the need to improve the energy efficiency and flexibility of drives. A similar solution to mobile hydraulics is not currently available. This paper studies a digital hydraulic approach, which includes a local hydraulic energy storage located together with the actuator, the means to convert efficiently energy from the storage to mechanical work and a small start-/stop-type pump unit sized according to mean power. The simulation results and first experimental results show that the approach has remarkable energy saving potential compared to traditional valve controlled systems, but further research is needed to improve the controllability.

Model-based force and position tracking control of an asymmetric cylinder with a digital hydraulic valve

Abstract This paper presents a model-based control solution for large inertia systems controlled by a fast digital hydraulic valve. The solution is based on model-based force control and it is shown that the cylinder chamber pressures have first order dynamics with the proper parameter selection. The robust stability is analyzed under unknown load mass, bulk modulus, and delay, and it is shown that a simple cascaded P + PID controller results in good control performance and robustness. The simulated results show smooth and stable response with good tracking performance despite large variations in the load mass and bulk modulus.

Model-based force and position tracking control of a multi-pressure hydraulic cylinder:

This article presents a force control solution for a throttle-free multi-pressure hydraulic cylinder actuator. A model-based force controller was developed and the position and velocity tracking control was implemented using low-order linear controllers. Special attention was paid to robustness against variations in the load mass, bulk modulus, and system delay. Experimental results demonstrated excellent energy efficiency and robustness, and acceptable tracking performance.

Analysis of Real-Time Properties of a Digital Hydraulic Power Management System

The paper presents a case study involving a Digital Hydraulics Power Management System (DHPMS). The system is a cyber-physical system, where actions need to be taken with high precision in order to ensure that the system works safely and energy efficiently. Here high precision actions demand very low latency of the control software. The contribution of this paper is an approach to analyse real-time properties of a common type of cyber-physical system. The paper also highlights the need to carefully analyse the effects of timing errors on performance and safety. The timing analysis is based on timed automata models and model-checking in the TIMES tool. Some lessons learned from the case study are also discussed.