Miniature Actuation Research Articles

MPC-ESO Position Control Strategy for a Miniature Double-Cylinder Actuator Considering Hose Effects.

Miniature hydraulic actuators are especially suitable for narrow-space and harsh environment arrangement. However, when using thin and long hoses to connect components, the volume expansion caused by pressurized oil inside can have significant adverse effects on the performance of the miniature system. Moreover, the volumetric variation relates to many uncertain factors that are difficult to describe quantitatively. This paper conducted an experiment to test the hose deformation characteristics and presents the Generalized Regression Neural Network (GRNN) to describe the hose behavior. On this basis, a system model of a miniature double-cylinder hydraulic actuation system was established. To decrease the impact of nonlinearity and uncertainty on the system, this paper proposes a Model Predictive Control (MPC) based on Augmented Minimal State-Space (AMSS) model and Extended State Observer (ESO). The extended state space acts as the prediction module model for the MPC, and the disturbance of the ESO estimates is fed to the controller to improve the anti-disturbance capability. The full system model is validated by comparison between the experiment and the simulation. For a miniature double-cylinder hydraulic actuation system, the proposed MPC-ESO control strategy contributes to a better dynamic than conventional MPC and fuzzy-PID. In addition, the position response time can be reduced by 0.5 s and achieves a 4.2% reduction in steady-state error, especially for high-frequency motion. Moreover, the actuation system with MPC-ESO exhibits better performance in suppressing the influence of the load disturbance.

A novel miniature hydraulic actuation system and offset to long hose effect

For its compact and flexible design, a novel miniature hydraulic actuation scheme is proposed for use in applications especially where both size and power are extremely important. The system works on a volume-controlled method using miniature cylinders. In order to describe the impact of hose deformation on the system, a lumped-parameter hose model is proposed, and coefficients in the model are determined on the basis of experiments with an existing prototype. A position tracking controller with a disturbance observer is designed for a miniature hose-connecting hydraulic actuation system. Tracking control for the target displacement is arranged as an external circuit of pressure compensation to eliminate the tracking error and an inner circuit of pressure compensation which operates by observed disturbances and oil pressure in the hose. Lyapunov theory is employed to verify the stability of the system with the disturbance observer. The disturbance observer–based controller has much better tracking performance than conventional proportional–integral–derivative controllers, which can substantially offset negative effects of the hose.

Study on Precise Displacement Control of a Miniature Hydraulic System via RBF-DOB

For compact and efficient actuation, miniature hydraulic system has overwhelming superiority in power to weight ratio. However, it always involves nonlinear interferences like variable hose volume or oil bulk modulus, which greatly restricts control performance for the actuation. In this paper, a miniature hydraulic volume-controlled actuation system is introduced and the problem of precise displacement control of the system in presence of variable hose volume caused by uncertain external load is investigated. A radical basis function-disturbance observer (RBF-DOB) hybrid control strategy based on back-stepping theory is proposed. The system and the controller are mathematically modeled and simulation to demonstrate the validity of the RBF-DOB. Comparison to proportion-integral-differential and sliding model control (SMC) methods indicates that, the system using RBF-DOB has highest displacement precision and best dynamic performance. SMC is inclined to exhibit the best robustness but inferior jitter in control command output. As far as anti-disturbance capacity is concerned, RBF-DOB control strategy falls between other two counterparts. RBF-DOB hybrid control strategy can substantially solve the problems of nonlinear interferences resulted from uncertain system parameters and different load states in miniature hydraulic actuation systems.

Functional properties and morphology of NiTi articulated actuation elements during thermo-mechanical cyclic tests

Shape memory alloys (SMAs) are active materials able to recover large strains over several thermo-mechanical cycles. In the actuation field, this strain recovery is principally exploited on the mini and micro scales at which SMAs exhibit their highest power density with respect to common lightweight technologies. During the repetitive actuation of a SMA element, certain events occur: strain drift at the beginning of cyclic testing, the accumulation of plastic deformation, and strain stabilisation. In this study, these events as well as the overall mechanical response of an articulated NiTi element were monitored through calorimetry and scanning electron microscopy. Fatigue and cyclic stability were tested under different loads and under different aging conditions. In addition, the surface morphology was continuously observed via scanning electron microscopy to monitor crack growth and propagation during the fatigue test. Finally, before and after the fatigue test, samples were tested through calorimetry to investigate the overall microstructural homogeneity. Results confirm the high potential of the proposed geometry for the development of NiTi non-conventional active elements in the miniature actuation field.

Actuation and Control Strategies for Miniature Robotic Surgical Systems

During the past 20years, tremendous advancements have been made in the fields of minimally invasive surgery (MIS) and minimally invasive, robotically assisted (MIRA) cardiac surgery. Benefits from MIS include reduced pain and trauma, reduced risks of post-operative complications, shorter recovery times, and more aesthetically pleasing results. MIRA approaches have extended the capabilities of MIS by introducing three-dimensional vision, eliminating hand tremors, and enabling the precise articulation of smaller instruments. These advancements come with their own drawbacks, however. Robotic systems used in MIRA cardiac procedures are large, costly, and do not offer the miniaturized articulation necessary to facilitate tremendous advancements in MIS. This paper demonstrates that miniature actuation can overcome some of the limitations of current robotic systems by providing accurate, repeatable control of a small end effector. A 10× model of a two link surgical manipulator is developed, using antagonistic shape memory alloy wires as actuators, to simulate motions of a surgical end-effector. Artificial neural networks are used in conjunction with real-time visual feedback to “learn” the inverse system dynamics and control the manipulator endpoint trajectory. Experimental results are presented for indirect, on-line learning and control. Manipulator tip trajectories are shown to be accurate and repeatable to within 0.5mm. These results confirm that SMAs can be effective actuators for miniature surgical robotic systems, and that intelligent control can be used to accurately control the trajectory of these systems.