This article addresses mainly questions about the roles of fluid systems, in particular of digital ones, in an “Industrie 4.0 (I4.0)” environment. There are three roles: the general machines’ subsystems/components’ role in machines of an I4.0 production system, the role of subsystems/components of machines which are produced under I4.0 conditions, and the manufacturing of fluid systems’ components in an I4.0 setting. These roles are discussed and examples of digital hydraulic solutions which fulfill these roles excellently are presented. They feature simplicity and robustness of hardware components and transfer of functionality to software. It is concluded that components and subsystems can support the successful realization of I4.0-type production systems decisively.
This paper studies a novel on/off-valve-based fine positioning method for hydraulic drives. The method proposed utilizes four on/off-valves in independent metering configuration to reach good positioning accuracy and low power losses. Previously, servo valves have been used in precise position control of hydraulic double acting cylinders. Another approach uses on/off-valves, which are typically driven by using pulse width modulation (PWM) or, if there are parallel connected valves, pulse code modulation (PCM). Typically, both cylinder sides are modulated simultaneously. The new concept proposed uses a cylinder model to calculate a correct opening sequence for the on/off-valves, such that the target piston position is reached. The method proposed modulates single cylinder side at a time in order to achieve small piston position step sizes. Despite relying on the modelled compressibility of the fluid, the method presented requires no knowledge about the bulk modulus of the fluid. It is enough that the bulk modulus of the fluid in both cylinder chambers can be assumed equal. The paper includes the design of the control method, a simulation study proving the validity of the method, and an experimental part investigating the performance in practice. The experimental results show a positioning accuracy of +/− 1 μm with an on/off-valve-based hydraulic drive, the maximum velocity of which is 0.7 m/s.
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