Energy efficient and environment conscious solutions are currently in high demand. This paper illustrates the
potential of pump-controlled actuators such as directly driven hydraulic drives (DDH) for various zonal
hydraulics applications. A novel pump-controlled actuator, powered directly by a servo motor is considered for
industrial and mobile applications replacing conventional valve-controlled hydraulics. This solution is targeting
improvements in energy efficiency, especially for continuous operation systems, however, due to the nature of
the solution, system response has high dependency on electric motor dynamics. Therefore, adaptive controller is
designed to realise benefits of the DDH. Study presents results of performance by simulation of this new
concept.

The paper presents an optimal reference tracking algorithm for electrohydraulic steering systems which is based
on multivariable system identification, linear quadratic control and Kalman filtering for state estimation. A
laboratory test-bench composed of electrohydraulic-steering unit (EHSU), steering cylinder, 32-bit
microcontroller, steering wheel and joystick supports experimental work. Traditional approach for reference
tracking in steering usually is based on classical control algorithms such digital PI regulator or non-digital hydromechanical
feedback. In contrast the control theory suggests advanced control techniques, which can take into
account multivariable nature of the process. In this way a higher closed-loop performance can be achieved.

Functionality and performance of novel hydraulic systems under real life stress can usually be examined in field tests only. In order to gather information about the behavior under stress during the development process as soon as possible, system components as well as systems get tested on test rigs. In hydraulics, applying passive loads e.g. to linear actuators can easily be done by throttling the outflow. For rotatory units, loads can either be applied with ropes and masses or other rotatory units. Especially applying active loads i.e. loads with the same orientation as the motion of the cylinder, is difficult and usually connected to a high complexity. At Karlsruhe Institute of Technology (KIT), a hydraulic load unit for hydraulic cylinders was developed to be used at various test rigs. The load units’ controller design allows for the application of either active or passive loads in variable directions and intensities. The following paper introduces the load unit, its open- and closed-loop control concept and the verification results from simulation, which show the potential of the load unit.

Fault tolerance is the most important feature in safety-critical applications, including aircraft flight controls,
nuclear systems, and medical devices, but it is a desirable property of any mechatronic system. In this paper, the
fault tolerance of a multi-outlet digital hydraulic pump-motor is studied. This machine has actively controlled
on/off valves to independently connect each piston to the tank or one of its outlets. Furthermore, the pump-motor
can control an actuator directly without having directional control valves in the system; thus, the on/off control
valves of the machine are the most vulnerable components of failure. A valve can either become jammed on (not
able to close) or off (not able to open), whether the fault is electrical or mechanical. The effect of a defective
valve is studied through simulations, and a method for fault compensation is proposed with a control algorithm
adapted for each fault case. The simulations and experimental results show that the valve faults can be
effectively compensated for by reconfiguring the software. Only slight degradation in the control performance
can be expected.

An independent metering valve control system (IMVCS) controls the meter-in and meter-out orifices of a valve independently. This innovative structure achieves a better energy saving performance, but also requires a more complex control algorithm. A flow and pressure coupling control system is proposed to control both the flow rate of the load and the pressure in each chamber. A DSP controller with TI-RTOS real-time operating system and digital driving module is adopted for fast response and accurate control. A two level fuzzy PID control algorithm and a lookup table algorithm are applied to improve the performance of the IMVCS. Experimental results show that the created control system can effectively control an IMVCS, and realize the function of flow and pressure coupling control.