Doctor of Philosophy

dissertationShape Memory Alloy (SMA) actuators are compact and have high force-to-weight ratios, making them strong candidates to actuate robots, exoskeletons, and prosthetics. However, these actuators are thermomechanical in nature and slow cooling rates can limit their performance. Electricity can resistively heat the SMA actuators very quickly to produce contraction. To improve the convective cooling, SMA wires have been embedded in vascular networks, allowing cold fluid to pass across the actuators and extend them faster. The vascular network can also deliver hot fluid to heat and contract the wire. To minimize the weight and size of the control hardware for the vascular and electrical networks, a scalable NxN architecture has been implemented that allows for 2N control devices to be shared amongst N2 actuators. This Network Array Architecture (NAA) allows each actuator to be controlled individually or in discrete subarrays. However, this architecture does not allow all combinations of actuators to be activated simultaneously; therefore a sequence of control commands may be required to achieve the complete desired actuation. This dissertation presents the development of an intelligent controller for large arrays of wet SMA actuators with electric and thermofluidic inputs. The controller uses graph theory to identify a sequence to control commands to optimize the performance of the actuators. By treating each actuator as binary (contracted / extended), the collected states of an actuator array can be represented as nodes of the graph and the discrete NAA control commands as the graph edges. By weighting the costs of the graph edges (actuation times, energy), graph theory algorithms can find a set of control commands to transition the array to the desired state with specific performance characteristics. NAA results in a multi-graph that has a large number of nodes (2NxN) and is highly interconnected, causing problems with scalability. The search algorithm has incorporated an expanding wavefront algorithm to construct only a small portion of the graph as needed. The computational cost to construct the graph has been minimized by using bitwise operations and the discrete nature of the array of binary actuators and the NAA control commands. The algorithm was implemented in MATLAB and it is able to identify the optimal solution for a 4x4 array with more than 14 million edges. By using an expanding wavefront, the algorithm, on average, explored less than 100 edges (<0.01%) in 0.03 seconds. A 6x6 array was optimized in 0.7 seconds, exploring just 2400 edges

Nitinol shape memory alloy spring

Manufacturing, over the years, has evolved through three revolutions brought out by the impact of mechanization, electricity and Information Technology. The update in manufacturing has its root of intelligence. Necessity of miniaturization is shifted the use of conventional actuators with smart actuators. Conventional actuators generally produce the power in proportion to their volume, which reduce their application in micro applications. A concise review of the recent developments within nearly ten years on shape memory alloys has been presented. Besides other available shape memory alloys, Nitinol(Ni-Ti) is preferred due to its array of characteristicslike light weight, high power to weight ratio, noiseless operation, ease of actuation and muscle like movement. Shape memory effect and pseudo-elasticity play a crucial role in smart materials. Various actuation modes (Joule heating, hot water, laser assisted) and cooling methods are tabulated for Ni-Ti. The different forms of Nitinolare commercially available, but spring is used specially, due to its coiled structure

Nitinol shape memory alloy spring

446-453Manufacturing, over the years, has evolved through three revolutions brought out by the impact of mechanization, electricity and Information Technology. The update in manufacturing has its root of intelligence. Necessity of miniaturization is shifted the use of conventional actuators with smart actuators. Conventional actuators generally produce the power in proportion to their volume, which reduce their application in micro applications. A concise review of the recent developments within nearly ten years on shape memory alloys has been presented. Besides other available shape memory alloys, Nitinol(Ni-Ti) is preferred due to its array of characteristicslike light weight, high power to weight ratio, noiseless operation, ease of actuation and muscle like movement. Shape memory effect and pseudo-elasticity play a crucial role in smart materials. Various actuation modes (Joule heating, hot water, laser assisted) and cooling methods are tabulated for Ni-Ti. The different forms of Nitinolare commercially available, but spring is used specially, due to its coiled structure

Master of Science

thesisThis thesis presents the design and optimization of a biologically inspired wet shape memory alloy (SMA) actuated pump that can provide thermal energy via fluidic convection to actuate external wet SMA subsystems. Furthermore, the pump draws from its own fluidic output to assist in the actuation of its own internal SMA actuators. A thorough analysis of the previous wet SMA robotic heart is conducted by searching for opportunities for improvement. Methods of improving the pump's output-to-input ratio included modifying the pumping chambers, actuation cycle timing, implementing electrical actuation, and continuously adding heat to the system. Dynamic modeling was performed to provide a baseline indicator of what was to be expected during actual implementation and testing. The effects of changing various parameters were explored to determine optimal configurations. Key parameters affecting performance include mechanical advantage, actuator length, flow durations, and water temperature. Implemented design changes and testing confirmed the modeling results. Continuous heating of the hot water within the pressurized accumulator greatly enhanced the pump's performance. Using only fluidic induced actuation, the output-to-input ratio peaked at 1.4. The pump reached an output-to-input ratio of 2.1 with the aid of electrical actuation. This is the first successful implementation of a self-sustaining thermofluidically powered SMA pump. Furthermore, unlike other SMA micropumps that typically output 1 mL/min or less, this pump is capable of a macroscale net output of 66 mL/min. While the pump's output exceeds the required input, the power efficiency and power density of the pump do not compare to that of the human heart due to the amount of power required to keep the hot water continuously heated. Viable options for improving efficiency and power density include minimizing pump mass, optimizing pumping chamber design, and reducing the amount of heat necessary to keep the hot water at an elevated temperature

Shape memory Alloy Actuator for cross-feed in turning operation

A shape memory alloy (SMA) is an intermetallic compound able to recover, in a continuous and reversible way, a predetermined shape during a thermal cycle while generating mechanical work. In this thesis, its use in developing an actuator for a machining process is investigated. The actuator is to drive the tool cross feed into an aluminium workpiece in a finishing lathe operation. The actuator structure was designed with an output shaft to transfer the movement and force of the SMA wire outside the device. The actuator was fabricated and the experimental setup was assembled which also included a power supply control circuit, displacement sensor, temperature sensor and current sensor for feedback, and data collection and monitoring within software. PID control was implemented within the software that regulated the power supplied to the SMA, thereby providing the position control. This study covers the mechatronics system design and development of the actuator, the experiments carried out to determine performance and the results. Open loop tests were conducted to determine the maximum stroke, the effect of cooling and response to radial forces. These tests revealed the expected non-linearity of the SMA. The actuator achieved the rated maximum stroke of 3-4 percent. The forced cooling test showed a general improvement of approximately 65 percent with fans. The radial force tests showed the value of the maximum stroke remained unaffected by force. The results from the closed loop tests responses with a tuned PID controller produced a stable system for various displacement setpoints. The actuator had a feed rate of 0.25 mm/s and an accuracy of 0.0153mm, which was within the acceptable accuracy for turning operations. The system was deemed accurate for a conventional lathe machine cross feed

Shape memory Alloy Actuator for cross-feed in turning operation

A shape memory alloy (SMA) is an intermetallic compound able to recover, in a continuous and reversible way, a predetermined shape during a thermal cycle while generating mechanical work. In this thesis, its use in developing an actuator for a machining process is investigated. The actuator is to drive the tool cross feed into an aluminium workpiece in a finishing lathe operation. The actuator structure was designed with an output shaft to transfer the movement and force of the SMA wire outside the device. The actuator was fabricated and the experimental setup was assembled which also included a power supply control circuit, displacement sensor, temperature sensor and current sensor for feedback, and data collection and monitoring within software. PID control was implemented within the software that regulated the power supplied to the SMA, thereby providing the position control. This study covers the mechatronics system design and development of the actuator, the experiments carried out to determine performance and the results. Open loop tests were conducted to determine the maximum stroke, the effect of cooling and response to radial forces. These tests revealed the expected non-linearity of the SMA. The actuator achieved the rated maximum stroke of 3-4 percent. The forced cooling test showed a general improvement of approximately 65 percent with fans. The radial force tests showed the value of the maximum stroke remained unaffected by force. The results from the closed loop tests responses with a tuned PID controller produced a stable system for various displacement setpoints. The actuator had a feed rate of 0.25 mm/s and an accuracy of 0.0153mm, which was within the acceptable accuracy for turning operations. The system was deemed accurate for a conventional lathe machine cross feed

A Methodology Towards Comprehensive Evaluation of Shape Memory Alloy Actuators for Prosthetic Finger Design

Presently, DC motors are the actuator of choice within intelligent upper limb prostheses. However, the weight and dimensions associated with suitable DC motors are not always compatible with the geometric restrictions of a prosthetic hand; reducing available degrees of freedom and ultimately rendering the prosthesis uncomfortable for the end-user. As a result, the search is on-going to find a more appropriate actuation solution that is lightweight, noiseless, strong and cheap. Shape memory alloy (SMA) actuators offer the potential to meet these requirements. To date, no viable upper limb prosthesis using SMA actuators has been developed. The primary reasons lie in low force generation as a result of unsuitable actuator designs, and significant difficulties in control owing to the highly nonlinear response of SMAs when subjected to joule heating. This work presents a novel and comprehensive methodology to facilitate evaluation of SMA bundle actuators for prosthetic finger design. SMA bundle actuators feature multiple SMA wires in parallel. This allows for increased force generation without compromising on dynamic performance. The SMA bundle actuator is tasked with reproducing the typical forces and contractions associated with the human finger in a prosthetic finger design, whilst maintaining a high degree of energy efficiency. A novel approach to SMA control is employed, whereby an adaptive controller is developed and tuned using the underlying thermo-mechanical principles of operation of SMA wires. A mathematical simulation of the kinematics and dynamics of motion provides a platform for designing, optimizing and evaluating suitable SMA bundle actuators offline. This significantly reduces the time and cost involved in implementing an appropriate actuation solution. Experimental results show iii that the performance of SMA bundle actuators is favourable for prosthesis applications. Phalangeal tip forces are shown to improve significantly through bundling of SMA wire actuators, while dynamic performance is maintained owing to the design and implementation of the selected control strategy. The work is intended to serve as a roadmap for fellow researchers seeking to design, implement and control SMA bundle actuators in a prosthesis design. Furthermore, the methodology can also be adopted to serve as a guide in the evaluation of other non-conventional actuation technologies in alternative applications

Design optimisation of shape memory alloy linear actuator applications

Shape memory alloy (SMA) actuators have drawn much attention and interest in recent decades due to their unique properties; and, are expected to be increasingly integrated within commercial automotive applications. Key advantages of SMA actuators include: potentially simplified construction, whereby the SMA can act as both sensor and actuator simultaneously; compatibility with Joule heating and convective ambient cooling; and, potential mass advantages over competing actuation technologies. These attributes potentially allow for the development of simpler, more reliable and cost effective actuation systems with significant reduction in mechanical complexity and size. SMA is readily available in commercial quantities and exhibits high wear resistance and durability, which make it an ideal candidate for application in automotive grade applications. Despite these identified advantages, SMA actuators are subject to a series of technical challenges associated with: &amp;nbsp;- Relatively small strain (displacement or stroke) &amp;nbsp;- Achievable frequency (actuation speed) &amp;nbsp;- Controllability (and stability) &amp;nbsp;- Positional accuracy &amp;nbsp;- Energy efficiency These technical challenges contribute to a relatively low success rate of commercial SMA actuator applications; and, provide motivation for this program to generate relevant research outcomes that enhance the commercialisation of SMA actuators. An extensive literature review of over 500 journal and patent documents was conducted to provide a clear roadmap for the commercial imperatives for SMA design. The formulated research methodology identifies milestones required for achieving the research objectives, which were addressed as research themes. Based on this literature review, the following research themes were identified: &amp;nbsp;- Design methods to resolve SMA actuator limitations &amp;nbsp;- Development of simple and practical numerical models for SMA actuator response &amp;nbsp;- Data for SMA linear actuator design Specific research contributions within these themes are presented within the thesis, with the objective of enhancing the commercial application of shape memory alloy (SMA) linear actuators, and include: &amp;nbsp;- A comprehensive analysis of SMAs: history, commercial applications, strength and limitations, design challenges and &amp;nbsp; &amp;nbsp; &amp;nbsp; &amp;nbsp; opportunities. &amp;nbsp;- A novel investigation of transient heat transfer scenarios for cylindrical systems associated with their crossover and critical radii. &amp;nbsp;- Development of novel latent heat models for analytical and numerical applications, and proposal of readily applied activation and deactivation charts compatible with the requirements of SMA actuator designers. &amp;nbsp;- A novel investigation of the morphological effects of SMA-pulley systems (i.e. pulley diameter, SMA and lagging diameter) on structural and functional fatigue