Matti Linjama

Hardware-in-the-loop environment for servo system controller design, tuning and testing

Abstract The paper analyses the possibility to replace the hydraulic and mechanical parts of a hydraulic position servo with a real-time simulation model. The aim is to test the controller hardware against the simulation model that includes the dynamics of the servo system as well as the feedback sensors and amplifier card. The requirements caused by this hardware-in-the-loop (HIL) approach are analyzed. A special attention is paid to the correct modeling of incremental encoders that are widely used as a feedback sensor. Experimental results show that there is no remarkable difference between the responses of the real system and HIL model and so the HIL model can replace the real system.

Is the future of fluid power digital

This article presents digital fluid power as a new branch of fluid power which offers high potential for innovative solutions. The variety of digital concepts is quite large and digital concepts have long been successfully applied in low-power applications. Research and development is now becoming more intensive, being undertaken by several research groups and also more and more in industry. First applications will be brought to industry soon. A successful application requires new components, a sound understanding of system and new control principles.

Improved Digital Hydraulic Tracking Control of Water Hydraulic Cylinder Drive

Abstract A position tracking control system is implemented by utilizing parallel-connected on/off valve series. The pulse code modulation method is used to achieve stepwise flow control and four valve series, each having four two-way solenoid valves, are used. A cost function based controller is used to control simultaneously and independently flow paths from supply to cylinder chambers and from chambers to tank. It is shown that controllability can be improved especially at low velocities by allowing three or four valve series to be open simultaneously instead of using classical inflow-outflow control.

Effect of Cavitation in Water Hydraulic Poppet Valves

Abstract In this paper, cavitation in water hydraulic poppet valves is investigated by an experimental method with a half cut test model. The situation of cavitation appearance, the effects of cavitation on the characteristics of flow rate, noise level, pressure distributions and the boundary of inception of the cavitation are investigated. Comparison between a poppet valve with sharp edged seat and another, which has a length on the seat, is made. The effects of change in the shape of the seat are discussed as well as the effect of cavitation appearance. As a result, it is revealed that the sharp edged seat valve is less influenced by the cavitation on its characteristics.

Novel bistable hammer valve for digital hydraulics

ABSTRACT This paper presents a fast and small on/off actuator—called the bistable hammer actuator—which requires only a small amount of work to switch between two stable positions. This actuator is combined with a suitable hydraulic part. The combination—called the hammer valve—is analyzed with multiphysical models including dynamic electromagnetic and static fluid mechanic models. A prototype is built and measured to verify the analysis. Smaller and faster valves are critical in digital hydraulics, and the results show the presented valve is competitive for the needs of digital hydraulics.

Accurate Trajectory Tracking Control of Water Hydraulic Cylinder with Non-Ideal on/off Valves

Abstract The aim of the work is to develop an on/off valve based trajectory tracking control solution without fast and/or continuous switching of valves. The pulse code modulation method is used to realise stepwise control of inflow and outflow of the actuator. Both inflow and outflow paths have five parallel-connected two-way solenoid valves, each having different flow capacity according to binary series, and a four-way on/off valve is used for changing direction of movement. Cost function based open-loop and closed-loop control solutions are developed and it is demonstrated how the cost function weights can be used to find a reasonable trade-off between tracking performance and pressure surges. Closed-loop results show accurate and reasonably smooth position tracking and simultaneous pressure level control. Achieved control performance is close to that of water hydraulic servo systems.

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.

ITER Divertor Maintenance: Development of a Control System for the Remote Handling of the Divertor Cassette Mover

Remote handling devices are being used to carry out the maintenance tasks in the divertor area of the ITER. One of the main challenging operations is the installation and transportation of Divertor Cassettes in and out from the vessel. This paper deals with the development of the control system for such remotely operated devices, with special emphasis on the tools, mock-ups and virtual prototypes employed to develop the high level control software and the water-hydraulics position servos controllers. Preliminary studies showing the effect of irradiation in hydraulic cylinder seals are also presented.