Investigations on Actuator Dynamics through Theoretical and Finite Element Approach

This paper gives a new approach for modeling the fluid-structure interaction of servovalve component-actuator. The analyzed valve is a precision flow control valve-jet pipe electrohydraulic servovalve. The positioning of an actuator depends upon the flow rate from control ports, in turn depends on the spool position. Theoretical investigation is made for No-load condition and Load condition for an actuator. These are used in finite element modeling of an actuator. The fluid-structure-interaction (FSI) is established between the piston and the fluid cavities at the piston end. The fluid cavities were modeled with special purpose hydrostatic fluid elements while the piston is modeled with brick elements. The finite element method is used to simulate the variation of cavity pressure, cavity volume, mass flow rate, and the actuator velocity. The finite element analysis is extended to study the system's linearized response to harmonic excitation using direct solution steady-state dynamics. It was observed from the analysis that the natural frequency of the actuator depends upon the position of the piston in the cylinder. This is a close match with theoretical and simulation results. The effect of bulk modulus is also presented in the paper

Investigations on Actuator Dynamics through Theoretical and Finite Element Approach

This paper gives a new approach for modeling the fluid-structure interaction of servovalve component-actuator. The analyzed valve is a precision flow control valve-jet pipe electrohydraulic servovalve. The positioning of an actuator depends upon the flow rate from control ports, in turn depends on the spool position. Theoretical investigation is made for No-load condition and Load condition for an actuator. These are used in finite element modeling of an actuator. The fluidstructure-interaction FSI is established between the piston and the fluid cavities at the piston end. The fluid cavities were modeled with special purpose hydrostatic fluid elements while the piston is modeled with brick elements. The finite element method is used to simulate the variation of cavity pressure, cavity volume, mass flow rate, and the actuator velocity. The finite element analysis is extended to study the system's linearized response to harmonic excitation using direct solution steady-state dynamics. It was observed from the analysis that the natural frequency of the actuator depends upon the position of the piston in the cylinder. This is a close match with theoretical and simulation results. The effect of bulk modulus is also presented in the paper

Design of SMA actuated light weight parallel manipulator with intelligent controller

Parallel manipulators are best known for their high load carrying capacity, stiffness, fast, accurate positioning etc., compared to their serial counterparts. Lightweight parallel manipulators are typical parallel mechanisms in which the linear-rotary actuators and spherical-rotary joints are replaced by smart actuators and with or without flexure joints. This paper describes about a lightweight miniature parallel manipulator of size 17.5mm diam. 25mm height, made of Beryllium-Copper spring steel and actuated by Shape Memory Alloy (SMA) actuators. The system modelling which includes dynamics and kinematics analysis is briefly described. The possibility of incorporating an Intelligent Fuzzy Controller is investigated. Preliminary simulation results are presented

Recent advances in nonlinear control technologies for shape memory alloy actuators

This paper reviews recent developments in nonlinear control technologies for shape memory alloy (SMA) actuators in robotics and their related applications. SMA possesses large hysteresis, low bandwidth, slow response, and non-linear behavior, which make them difficult to control. The fast response of the SMA actuator mostly depends upon, (1) type of controller, (2) rate of addition and removal of heat, and (3) shape or form of the actuator. Though linear controllers are more desirable than nonlinear ones, the review of literature shows that the results obtained using nonlinear controllers were far better than the former one. Therefore, more emphasis is made on the nonlinear control technologies taking into account the intelligent controllers. Various forms of SMA actuator along with different heating and cooling methods are presented in this review, followed by the nonlinear control methods and the control problems encountered by the researchers

A compliant miniature parallel manipulator with shape memory alloy actuators

Light weight parallel manipulators are most desirable for aerospace, medical applications etc., where flexibility, low inertia, simplicity in operation, low stowed volume are important parameters. This paper presents the design and simulation of a flexible parallel manipulator with central elastic column that is made of superelastic nitinol. The actuators are shape memory SMA wires of 300um diameter. Unlike conventional rigid link parallel manipulators, the proposed manipulator does not have any joints, which is the major advantage. The proposed manipulator is investigated for its degree of freedom with virtual rigid segment concept and its large deflection is analyzed based on elastica approach. Its control aspect is briefly described and numerical simulation results are presented

Critical review of current trends in shape memory alloy actuators for intelligent robotic devices

Purpose \u2013 The purpose of this paper is to review the current application areas of shape memory alloy (SMA) actuators in intelligent robotic systems and devices. Design/methodology/approach \u2013 This paper analyses how actuation and sensing functions of the SMA actuator have been exploited and incorporated in micro and macro robotic devices, developed for medical and non-medical applications. The speed of response of SMA actuator mostly depends upon its shape and size, addition and removal of heat and the bias force applied. All these factors have impact on the overall size of the robotic device and the degree of freedom (dof) obtained and hence, a comprehensive survey is made highlighting these aspects. Also described are the mechatronic aspects like the software and hardware used in an industrial environment for the control of such nonlinear actuator and the type of sensory feedback devices incorporated for obtaining better control, positioning accuracy and fast response. Findings \u2013 SMA actuators find wide applications in various facets of robotic equipments. Selecting a suitable shape, fast heating and cooling method and better intelligent control technique with or without feedback devices could optimize its performance. Research limitations/implications \u2013 The frequency of SMA actuation purely depends on the rate of heat energy added to and removed from the actuator, which in turn depends upon interrelated nonlinear parameters. Practical implications \u2013 For increasing the dof of robots, number of actuators also have to be increased that leads to complex control problems. Originality/value \u2013 Explains the suitability of SMA as actuators in smart robotic systems, possibility of miniaturisation. It also highlights the difficulties faced by the SMA research community