Valve controlled cylinder drives are an obvious choice whenever high loads are manipulated in translational motion with demanding requirements in terms of dynamic properties, accuracy, and costs. Improvements of energetic efficiency of valve control can be achieved by separating metering edges, allowing for different operating modes and thus adapting to different load scenarios.
In this paper, multiple-input-multiple-output closed loop control approaches are investigated in order to control cylinder speed and pressure in one cylinder chamber for a configuration with five 2/2-directional valves. By utilizing the flatness property of the system, the flatness-based tracking controller and the flatness based internal model controller will be described, developed and tested. They are adapted to the excessive number of command variables by introducing extended input. Based on validation on a test rig, the characteristics of both control approaches are pointed out.
The control strategy is fitted to a smooth mode switching algorithm published by the authors previously. It is shown that by making use of the degrees of freedom involved in the presented system, different operating modes can be switched smoothly in closed loop control. This contributes to the applicability of energetic potentials of independent metering.
In contrast to rotational hydraulic displacement units, such as pumps or motors, conventional hydraulic cylinder actuators do not allow a continuous variation of their displacement quantity: the piston area is regarded constant. In order to adapt to varying load and velocity requirements in a load cycle under torque restrictions of the driving motor, cylinder drives often implement pumps with variable displacement.
In this paper, cylinders with discretely variable effective piston area by means of variable circuitry of multi-chamber cylinders are discussed. Hydraulic symmetry or constant asymmetry of the hydraulic cylinder are traits of the cylinder that are required to fit the cylinder to pump structures for closed-circuit displacement control, as given in electro-hydrostatic compact drives (ECD). A methodology to generate all possible solutions of variable area cylinders under the constraint of ECD requirements is proposed.
A comprehensive description of the solution space is given, based on combinatorics and solution of equation systems. The methodology dealing with abstract cylinder areas is backed up by a general approach to describe the mechanical cylinder design space to combine multiple cylinder areas in one structural unit. Examples for design of three and four area cylinders are given and results are discussed. The paper concludes with the development of a demonstrator design to allow experimental validation in a subsequent step.
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