Mikko Heikkilä

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.

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.

Comparison of Proportional Control and Displacement Control Using Digital Hydraulic Power Management System

The Digital Hydraulic Power Management System (DHPMS) is a solution based on the digital pump-motor technology and has shown to be a promising approach to improve the energy efficiency of hydraulic systems. The DHPMS is controlled by active on/off valves, but unlike the digital pump-motors the DHPMS has multiple independent outlets; hence, the DHPMS can operate also as a transformer. In this experimental study, a proportional control of a mobile boom is compared with a displacement control when a six-piston DHPMS is used. In the proportional control, the system pressure is controlled by the DHPMS and a lift cylinder with a proportional valve. In the displacement control, the cylinder fluid volumes are controlled directly using the DHPMS. Firstly, the systems under study are presented along with the control methods. Then the control performance of the DHPMS is studied and finally, the energy losses in the systems are analysed. The results show the versatility of the DHPMS; it is capable of fast and accurate pressure control but also handles the direct flow control. According to the measurements, the losses are significantly smaller in the displacement controlled system thanks to the minimised throttling losses and the energy recovery. Nevertheless, the energy losses in the prototype DHPMS are rather high due to the leakage in the control valves and their low flow capacity, and therefore improvements in the design are needed.Copyright

Analysis of Signals and Power Flow in a Digital Hydraulic Multi Actuator Aplication

A combination of digital hydraulic four notch control valves and the digital hydraulic power management system (the DHPMS) has many controller levels, both parallel and series. The DHPMS is a multi-port sink/source of hydraulic power. Digital hydraulic valves are used to control the actuators. Both the DHPMS and the digital valves are based on the idea that all complexity is in the software and the hardware is based on arrays of mechanically simple base units. Controllers work together merging into a power flow system where the whole power transfer line is controlled from a single pumping piston within the pump to the movement of the tip of the boom. Or vice versa, if the operating conditions allow negative power to be routed backwards. In the paper certain measurements are looked into; second by second and a signal by a signal. The paper presents and verifies functionality of the novel combination of technologies. How signals flow in the controllers and how they actually control the power flow in the system is explained. The test system is a two-actuator boom, and as two is the smallest example of multi, the controller is designed by a simple and robust control method.Copyright