Displacement-controlled (DC) actuation has been under investigation by the authors' group since its conception in 1998 as a highly efficient alternative to its valve controlled counterpart. The major advantages of DC actuation include the complete elimination of losses due to resistive control and the recuperation of energy due to overriding loads. One obstacle for the introduction of DC actuation to the market is the increased machine production costs due to the one-pump-per-actuator requirement. To overcome this impediment, the authors' research group propose the idea of pump switching. The idea consists on utilizing a distributing manifold comprising a set of on/off valves utilized to direct flow either from/to a hydraulic unit to/from a particular actuator. Then, the concept allows for the reduction of machine installed pump power for multi-actuator machines, thereby minimizing parasitic losses and production costs. In this paper, the challenges and implications, as well as the control strategies developed to realize this technology are outlined for a multi-actuator system. Furthermore, an extension of work previously proposed by the author's research group is made by presenting a validation of the proposed control strategies on an excavator prototype. Measurement results show that the pump switching concept is attainable while maintaining the same basic DC concept and relatively simple actuator-level control algorithms.

View full abstract

A proper cushioning of the spool and armature of a switching valve at the end stops is important for a high lifetime and a low impact sound. Squeeze gap concepts are often employed. Oil between two basically parallel surfaces, which come into contact and which form the mechanical end stop, provides an excellent damping mechanism. But this oil film may exhibit high stiction forces, which cause a high response delay or even a total failure of the valve, unless cavitation in the oil film limits the stiction force. A new cushioning concept based on a notched groove is presented in this paper. Its basic functional principle is studied by compact mathematical models. The basic differences to squeeze gap cushioning are worked out and basic dimensioning rules are derived. This concept overcomes the stiction force problem fully.

View full abstract

Previously, a newly designed electro-magnetic actuator composed of an armature and a stator with multi-convex teeth to control oil hydraulic valves was introduced. Each of the convex teeth forms a magnetic pole, and a large thrust force is generated in the actuator. This actuator produces about 300N at an electronic power consumption of 15W. This thrust force was examined experimentally by using a prototype actuator. In this study, magnetic flux flow in the actuator is investigated by using Finite Element Method Analysis. Difference of magnetic flux flow between several tooth shapes, and the flow of the front and rear edge of a tooth of the actuator are examined. Furthermore, to augment heat transfer of the actuator, a stator with fins made with round slots is examined.

View full abstract

Hydraulic drives are widely found in industrial manufacturing, energy power plants and other important application domains, due to their high power density and robustness. However, one major problem facing modern hydraulic drives is their considerably lower efficiency compared to other drives. Switched hydraulic systems present a possible solution to this challenge. By using a number of different operating modes, these systems can adapt themselves to current load conditions, thereby maximizing efficiency. Despite their great energy-saving potential, care must be taken when using such systems due to the possibility of unstable mode switching and non-smooth physical behavior not desired by operators. This paper reviews recent theoretical and practical developments in the category of switched hydraulics by specifically discussing an innovative design for mobile applications called STEAM.

View full abstract

The modeling and design of a hybrid bicycle with hydraulic transmission conducted at the University of Minnesota are introduced in this paper. The work is under the scope of 2013-2014 Parker Chainless Challenge with the initiative of building a chainless drivetrain for a bicycle. A hydraulic transmission, either a hydrostatic transmission (HST) or a hydro-mechanical transmission (HMT), provides a powerful solution to this competition. A pump coupled to the pedal shaft provides flow to a hydraulic motor coupled to the drive wheel shaft, constituting the simplest hydrostatic drivetrain. A hydraulic accumulator is added to provide large acceleration when needed. This turns the bicycle into a hydraulic hybrid. A multi-functional hydraulic circuit was designed to achieve different bicycle functions including human-powered mode, hydraulic-powered mode, regenerative braking and charge mode. A mathematical model was developed to help the system parameters design. A dynamic simulation model was developed to evaluate the system performance.

View full abstract

This paper is concerned with displacement control of water hydraulic McKibben muscle. In general, control performance of conventional PI control is not enough because the muscle has strong nonlinearities. Moreover, a load connected with the muscle affects in the performance. For these problems, we propose combination of model-based control and adaptive parameter estimation. First, model predictive control is introduced and its control performance is validated. However, the performance is degraded under loaded condition because the characteristics of the muscle are changed and the one-step-ahead estimation, which is used to generate control inputs, should fail. In order to compensate the effect of characteristic change under the condition, we combine an adaptive parameter estimation algorithm with the proposed control. In particular, recursive least squares algorithm is applied as an adaptive algorithm. As a result, effect of load can be compensated and the performance under loaded condition can be improved.

View full abstract

In wearable pneumatic driving system, the small-sized and lightweight valve is important. In addition, the bulky battery to drive valves will be required. The purpose of our study is to develop a valve with lower electric energy consumption that can be used for a long time with a small battery. In our previous study, the valve with self-holding function that consumes electric power for a very short time (0.01s) only when the valve changes to open or close was proposed and tested. In this paper, the analytical model of the valve with self-holing function using permanent magnets is proposed and improved to estimate the performance of the valve theoretically. The behavior of magnets was observed by using high speed camera to know the detail behavior of both magnets and to identify system parameters. As a result, we can predict the whole response of the valve using the proposed model.

View full abstract

In wearable pneumatic driving system, the small-sized and light-weight control valve and wearable actuator are important. Mostly, the total cost of control system depends on the cost of valves, because a popular industrial servo valve is very complex and expensive compared with a wearable actuator. The purpose of our study is to develop a small-sized and low-cost control valve that can be safe enough to be mounted on the human body. In our previous study, the low-cost servo valve using buckled tube was proposed and tested. However, the valve has relatively larger hysteresis in a relation between the motor rotational angle and output flow rate. In this paper, the improved servo valve with less hysteresis characteristics of output flow rate is proposed and tested. In addition, the configuration of the buckled tube on the valve is redesigned in order to reduce an overlap of the valve. Then, the improved valve is applied to the position control of the rubber artificial muscle. As a result, the position control performance of the muscle was also improved.

View full abstract