Hydraulic cylinder

Abstract: A hydraulic actuator is described which has a layered structure and a flattened piston assembly to enhance production speed and reduce the costs of assembly. A system for performing surgery is also described incorporating the hydraulic actuator, having a sensory glove, a computer, and a slender robot manipulator which can be inserted into the human body through a small incision. The robot manipulator has a layered structure with integrated hydraulic pistons. This design allows the use of a novel manufacturing process in which all of the parts are formed from laminated sheets of material. Seals are formed to prevent leakage of hydraulic fluid by introducing castable rubber into enclosed channels in the structure.

Abstract: This paper presents a novel approach to the design of road adaptive active suspensions via a combination of linear parameter-varying control and nonlinear backstepping techniques. Two levels of adaptation are considered: the lower level control design shapes the nonlinear characteristics of the vehicle suspension as a function road conditions, while the higher level design involves adaptive switching between these different nonlinear characteristics, based on the road conditions. A quarter car suspension model with a nonlinear dynamic model of the hydraulic actuator is employed. The suspension deflection, car body acceleration, hydraulic pressure drop, and spool valve displacement are used as feedback signals. Nonlinear simulations show that these adaptive suspension controllers provide superior passenger comfort over the whole range of road conditions.

Abstract: A method for operating a hydraulic control system for the speed selection mechanism on a motor vehicle with first and second double-acting hydraulic actuators (114,115) and a main control valve (150), which is suitable for the selected connection of one side of the hydraulic actuator to a supply source (275) with pressurised hydraulic fluid, or to a volume equalisation vessel (278).

Abstract: A hydraulic circuit may include a proportional control solenoid valve controlling hydraulic pressure such that an operating hydraulic pressure required by the friction member is supplied to the friction member; a supply hydraulic path connecting the proportional control solenoid valve with the friction member, and adapted to supply hydraulic pressure controlled by the proportional control solenoid valve to the friction member; and a switch valve disposed in the supply hydraulic path so as to selectively open/close the supply hydraulic path

Abstract: Series elastic actuators have a spring intentionally placed at the actuator output. Measuring the spring strain gives an accurate measurement for closed-loop actuator force control. The low spring stiffness allows for high control gain while maintaining actuator stability. This gives series elastic actuators many desirable properties including high bandwidth at moderate force amplitudes, low output impedance, large dynamic range, internal error rejection and tolerance to shock loading. However, as a consequence of the elasticity, the large force bandwidth capabilities of the actuator are reduced when operating at power saturation limits. Series elasticity is examined with three models. First, it is generalized by using a minimal actuator model. This mathematical model consists of an ideal velocity source actuator, linear spring and proportional controller. Series elasticity is then demonstrated in two case studies of physical actuator systems. The first is a linear hydraulic piston with a servo valve and the second is an electric motor with a geared linear transmission. Both case studies have a linear spring and low complexity control systems. The case studies are analyzed mathematically and verified with physical hardware. A series elastic actuator under simple closed-loop control is physically equivalent to a second order system. This means that an equivalent mass defined by the control system and physical parameters, is effectively in series with the physical spring connected to the actuator load. Nondimensional analysis of the dynamics clarifies important parametric relationships into a few key dimensionless groups and aids understanding when trying to scale the actuators. The physical equivalent abstractions and non-dimensional dynamic equations help in the development of guidelines for choosing a proper spring stiffness given required force, speed and power requirements for the actuator. Thesis Supervisor: Gill A. Pratt Title: Associate Professor of Electrical Engineering and Computer Science