Development of Faster SMA Actuators

Large cycle time, resulted from slow cooling, is the core hindrance to the wide spread applications of shape memory alloys (SMAs) as actuators. This chapter discusses a novel cooling technique to decrease the cycle time of SMAs. Under this technique, the SMA actuator of 0.15 mm diameter was run through a grease-filled Polytetrafluoroethylene (PTFE) tube of 0.5 mm outside diameter. Later, same tests were repeated with oil filled PTFE tube. The test results conducted in ambient air were used as standard for comparison. The actuation current in ambient air was set at 210, 310 and 410 mA. While testing with heat sink, i.e. grease and oil, the SMA was heated with 210, 310, 410, 500, 615 and 720 mA currents for 1 and 2 seconds, whereas the SMA was heated for 1 second only with 810 mA current. It was found that the grease cooling reduced the cooling time up to 30% and oil cooling by 20%, as compared to the ambient air-cooling time. However, the grease-cooled actuators had shown less strain, and their response was non-linear at many instances. Heat loss to the sinks resulted to more power consumption than that in ambient air cooling for equivalent amount of strain

Design and simulation of a shape memory alloy bundle actuated robotic finger

In this research, commercially available Nickel-Titanium based shape memory alloy actuators are used to design and develop a novel bundled actuator. The bundled actuators are then used in a special configuration to actuate and control a low cost one degree of freedom (dof) anthropomorphic finger. SMAs possess hysteretic and nonlinear behaviour when heated (actuated) and cooled (relaxed). Hence, a full understanding of the behaviour of these actuators is essential to control them. In order to characterise the behaviour of the actuators, an instrumented test rig was designed and developed to characterise the commercially available Nickel-Titanium SMA actuators obtained from the two manufacturers. The test rig was equipped with the laser displacement sensor, the load cell and the thermocouple. All the measurements were taken by a PC based data acquisition system. Nickel-Titanium based SMA actuators (Flexinol® and Biometal'") obtained from the two manufacturers were characterised using the test rig. The Flexinol'" actuator was selected for the use in the bundled actuator on the basis of better drift property. The existing bundle designs are merely a parallel arrangement of individual actuators crimped or screwed to the end plates on both sides. However, this may cause uneven strains (and forces) in individual actuators of the bundle. The novel bundle proposed in this research used a single 960 mm long actuator looped around frictionless supports to form a 12-string bundled actuator. Design and simulation of a one dof finger was carried out by using a set of three bundled actuators arranged in a special configuration. This made it possible to use a simple control to achieve seven possible for the proposed finger.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Actuation Characteristics of 0.15mm Diameter Flexinol® and Biometal ® Wire Actuators for Robotic Applications

In this paper the actuation properties of two NiTi (Nickel Titanium) SMA (Shape Memory Alloy) actuators available under the commercial names of Flexinol ® and Biometal ® are investigated and compared with each other. Both actuators have diameter of 0.15mm and transformation temperature of 70 o C. The diameter of 0.15mm is selected because of best combination of force and cooling time. An experimental test rig specially designed and developed by the first author was used to conduct tests on the actuators. Both actuators were tested by supplying actuation voltages of 5 and 5.5V. Actuators were thermomechanically loaded for 100 cycles and their strains were recorded. The results of the tests show that 5.5V actuation resulted in greater strain. It was found from the test results that Biometal ® actuators produced more strain as compared to Flexinol ® actuators for both the actuation voltages. However, the drift results showed that higher strains in Biometal ® are due the permanent deformation of the same. This shows that Flexinol ® actuators possess better actuation characteristics as compared to Biometal ® actuators

Modeling of Static Characteristics of Switched Reluctance Motor

To investigate the running characteristics of a switched reluctance motor, the static characteristics and related input data tables are required. The static characteristics comprise of flux linkage, co-energy and static torque characteristics. The co-energy and static torque are calculated once data of magnetization characteristics is available. The data of co-energy is required for the calculation of static torque characteristics. The simulation model includes the data of static characteristics for prediction of the instantaneous and steady state performance of the motor. In this research a computer based procedure of experiments is carried out for measurement of the magnetization characteristics. For every set of measurements, the removal of eddy current is carefully addressed. The experiments are carried out on an existing 8/6 pole rotary switched reluctance motor. Additionally, the instantaneous phase current, instantaneous torque and flux waveforms are produced by using linear, which is by default and spline data interpolation separately. The information obtained from theses simulation results will help in an improved simulation model for predicting the performance of the machine

Axisymmetric Predictions of Fluid Flow inside a Rotating Cavity System

Accurate prediction of fluid flow in the rotating cavity system is of practical interest as it is most commonly used in the gas turbine engines and compressors. This paper presents the numerical predictions of a rotating cavity flow system for Reynolds numbers of the range 1x105 < Re? < 4x105 and two different mass flow rates Cw=1092 and 2184. A finite-difference technique is employed for a Steady-state solution in the axisymmetric cylindrical polar coordinate frame of reference. The two low Reynolds number turbulence models, the low Reynolds number k-? model and the low Reynolds number second moment closure have been used to compute the basic characteristics of the flow inside the rotating cavity flow system. Different flow regions have been identified by computing flow structures and dimensions of those regions have also been studied under different flow rates. A comparison of the computed variation of moment coefficient of both the turbulence models are presented for the above mentioned parameters and the parametric effects on the moment coefficients have been discusse

Introducing Dual Suspension System in Road Vehicles

The main objective of suspension system is to reduce the motions of the vehicle body with respect to road disturbances. The conventional suspension systems in road vehicles use passive elements such as springs and dampers to suppress the vibrations induced by the irregularities in the road. But these conventional suspension systems can suppress vibrations to a certain limit. This paper presents a novel idea to improve the ride quality of roads vehicles without compromising vehicle?s stability. The paper proposes the use of primary and secondary suspension to suppress the vibrations more effectively

Tolerance Analysis in Straight-Build Mechanical Assemblies Using a Probabilistic Approach-2D Assembly

Product quality in mechanical assemblies is determined by the dispersion of manufacturing variance during the structure building. This paper focuses on straight-build assembly and proposes a probabilistic approach based on connective assembly model to analyze the effect of individual component variations on the eccentricity of the straight-build assembly. The probabilistic approach calculates the pdf (probability density function) of key assembly variation of rotor assembly of high speed rotating machines. The probabilistic approach considers two straight-build scenarios: (i) Best Build; and (ii) Direct Build, for 2D (Two-Dimensional) "axi-symmetric" assemblies. Numerical examples are presented to investigate the probabilistic approach for its efficiency and accuracy in comparison to MCS (Monte Carlo simulation)

Challenges for practical applications of shape memory alloy actuators

Shape memory alloy (SMA) actuators present opportunities for the development of novel actuating systems. High force-to-weight ratio, silent operation, muscle-like motion, biocompatibility, and simple design possibilities have attracted researchers to SMA actuators. Many SMA actuated systems in engineering and medical domains have been reported in the literature. Recently, SMAs have also being used to develop soft robotic systems. However, low absolute force and high cycle time have limited the widespread use of these actuators. Moreover, non-linear and unpredictable behaviour caused by hysteresis results in difficulties to accurately control it. Some work detailing the strategies to overcome these shortcomings has been reported in the literature, this paper presents an articulated brief review of the techniques to overcome low force, long cycle time, and material non-linearity issues

Predictions of Buoyancy-induced Flow in Asymmetrical Heated Rotating Cavity System

This paper presents the finite difference solutions for buoyancy-induced flow in the asymmetrical heated rotating cavity system for the range of rotational Reynolds numbers Reθ =6.13x10^5 <Reθ =4.4x106 and the mass flow rates Cw<28000<Cw < 3000. All the simulations have been carried out through the CFD (Computational Fluid Dynamics) commercial code, ANSYS Fluent 12.0, by adopting axisymmetric, Steadystate and elliptic technique. Two well know models namely k-ε and the Reynolds stress models have been employed. The simulated results illustrate the important aspects of the heated rotating cavity flow system. The noteworthy influence of buoyancy-induced flow have been observed on the predicted stream lines, static temperature contours and the local Nusselt numbers for the rotating cavity space. A comparison of the predicted local Nusselt numbers for the hot and cold discs showed a good level of agreement with the measurements