Rubble-strewn corridors, stairs and steep natural terrain all present a challenge for wheels and tracks. Legs are a solution in these cases because foot placement allows the traversal of discontinuous terrain. Legged robots, however, currently lack the performance needed for practical applications. This work seeks to address an aspect of the problem, foot placement while running. A novel hopping height controller for a spring-loaded legged robot is presented. It is simple and performs well enough to allow control of the ballistic trajectory of hops and therefore foot placement. Additionally, it can adapt to different ground properties using the result from previous hops to update control gains. A control strategy of extending the leg at a fixed rate during the stance phase and modulating the rate of extension on each hop was used to control the hopping height. The extension rate was then determined by a feed-forward + proportional control loop. This performed sufficiently well allowing the ballistic trajectory of hops to be controlled. In simulation, the spring-loaded inverted pendulum (SLIP) model was extended to include actuation and losses due to friction. The control strategy was developed using this model then, in a planar simulation, the controller was run to perform foot placement while running over a series of platforms which vary in their horizontal and vertical spacing. To experimentally validate and further develop the control strategy, a one-legged hopping robot, constrained to move vertically, was used. The leg had 2 links, hydraulically actuated hip and knee joints and a spring-loaded foot. Results showed that the controller developed could be used to perform hops of randomly varying size on grounds with different properties and while running on a treadmill at different speeds. As an aside, the dynamics of hydraulic actuators presented a problem for foot repositioning during flight using a simple PID controller. This was solved through the novel implementation, in hydraulics, of a `zero-vibration' (ZV) filter in a closed-loop. Simulation and experimental results demonstrating this are presented.

The medical community has expressed a need for flexible medical instruments. Hence, this work investigates the possibility to use "flexible fluidic actuators" to develop such flexible instruments. These actuators are driven by fluid, i.e. gas or liquid, and present a flexible structure, i.e. an elastically deformable and/or inflatable structure. Different aspects of the study of these actuators have been tackled in the present work: • A literature review of these actuators has been established. It has allowed to identify the different types of motion that these actuators can develop as well as the design principles underlying. This review can help to develop flexible instruments based on flexible fluidic actuators. • A test bench has been developed to characterize the flexible fluidic actuators. • A interesting measuring concept has been implemented and experimentally validated on a specific flexible fluidic actuator (the "Pneumatic Balloon Actuator", PBA). Ac- cording to this principle, the measurements of the pressure and of the volume of fluid supplied to the actuator allow to determine the displacement of the actuator and the force it develops. This means being able to determine the displacement of a flexible fluidic actuator and the force it develops without using a displacement sensor or a force sensor. This principle is interesting for medical applications inside the human body, for which measuring the force applied by the organs to the surgical tools remains a problem. The study of this principle paves the way for a lot of future works such as the implemen- tation and the testing of this principle on more complex structures or in a control loop in order to control the displacement of the actuator (or the force it develops) without using a displacement or a force sensor. • A 2D-model of the PBA has been established and has helped to better understand the physics underlying the behaviour of this actuator. • A miniaturization work has been performed on a particular kind of flexible fluidic actu- ator: the Pleated Pneumatic Artificial Muscle (PPAM). This miniaturization study has been made on this type of actuator because, according to theoretical models, minia- turized PPAMs, whose dimensions are small enough to be inserted into MIS medical instruments, could be able to develop the forces required to allow the instruments to perform most surgical actions. The achieved miniaturized muscles have a design similar to that of the third generation PPAMs developed at the VUB and present a total length of about 90 mm and an outer diameter at rest of about 15 mm. One of the developed miniaturized PPAMs has been pressurized at p = 1 bar and it was able to develop a pulling force F = 100 N while producing a contraction of 4 %. Propositions have been made regarding a further miniaturization of the muscles.

Industrial applications increasingly require actuators that offer a combination of high force output, large stroke and high accuracy. The ElectroHydraulic Actuator (EHA) was designed by Drs. Habibi and Goldenberg originally as a high-performance actuator for use in robotics. However, it was determined that the EHA had the potential to achieve high positional accuracy. Little research has been performed in the area of high-accuracy hydraulic positioning systems. Therefore, the objective of this study to achieve nano-scale positional accuracy with the EHA while maintaining large stroke and high force output. It was planned to achieve this objective through modification of the prototype EHA and the use of fuzzy control. During this research project, both hardware and control system modifications to the EHA were performed. A high-precision optical encoder position sensor with a 50 nm resolution was mounted on the inertial load to directly measure the position of the load. A number of device drivers were written to interface the MATLAB real-time control environment with the optical encoder and servo motor amplifier. A Sugeno-inference fuzzy controller was designed and implemented in MATLAB. For comparison purposes, a switched-gain controller and a proportional controller were also implemented in the control environment. The performance of the fuzzy controller was compared to the switched-gain controller and the proportional controller in a number of tests. First, the regulatory and tracking performance of the EHA with an inertial load of 20 kg was examined. It was determined in the regulatory tests that the positional accuracy of the EHA with the fuzzy controller was excellent, achieving a steady state error of 50 ± 25 nm or less for step inputs in the range 5 cm to 200 nm. The positional accuracy during the tracking tests was found to be reduced compared to the regulatory tests since the actuator did not have sufficient time to settle to final accuracy due to the timevarying input signals. In all cases, it was found that the positional accuracy of the EHA with the fuzzy controller was significantly greater than with the switched-gain and proportional controllers for both regulatory and tracking signals. Testing with the inertial load eliminated or changed was not performed because the position sensor was mounted to the load, making it unfeasible to alter the load during the time frame of this study. The regulatory and tracking performance of the EHA with an inertial load of 20 kg plus external resistive loads of 90 to 280 N were investigated. It was found that the positional accuracy of the EHA decreased with the application of an external load to 3.10 ± 0.835 µm for a 1 cm step input (90 N load) and 8.45 ± 0.400 µm for a 3 cm step input (280 N load). Again, the positional accuracy of the EHA decreased during the tracking tests relative to the regulatory tests, for the reason stated above. This implies that the positional accuracy of the EHA with a resistive load is in the microscale, rather than the nano-scale as was put forth as the objective of this study. Nevertheless, the positional accuracy of the EHA with the fuzzy controller was found to be significantly greater than with the switched-gain and proportional controllers. It is postulated that the increase in positional error observed during the external load tests was due to an increase in cross-port leakage, relative to the inertial load tests, caused by the pressure differential induced across the actuator by the external load. Methods of reducing the increase in positional error caused by external loads on the EHA remains an area for future study.

Industrial applications increasingly require actuators that offer a combination of high force output, large stroke and high accuracy. The ElectroHydraulic Actuator (EHA) was designed by Drs. Habibi and Goldenberg originally as a high-performance actuator for use in robotics. However, it was determined that the EHA had the potential to achieve high positional accuracy. Little research has been performed in the area of high-accuracy hydraulic positioning systems. Therefore, the objective of this study to achieve nano-scale positional accuracy with the EHA while maintaining large stroke and high force output. It was planned to achieve this objective through modification of the prototype EHA and the use of fuzzy control. During this research project, both hardware and control system modifications to the EHA were performed. A high-precision optical encoder position sensor with a 50 nm resolution was mounted on the inertial load to directly measure the position of the load. A number of device drivers were written to interface the MATLAB real-time control environment with the optical encoder and servo motor amplifier. A Sugeno-inference fuzzy controller was designed and implemented in MATLAB. For comparison purposes, a switched-gain controller and a proportional controller were also implemented in the control environment. The performance of the fuzzy controller was compared to the switched-gain controller and the proportional controller in a number of tests. First, the regulatory and tracking performance of the EHA with an inertial load of 20 kg was examined. It was determined in the regulatory tests that the positional accuracy of the EHA with the fuzzy controller was excellent, achieving a steady state error of 50 ± 25 nm or less for step inputs in the range 5 cm to 200 nm. The positional accuracy during the tracking tests was found to be reduced compared to the regulatory tests since the actuator did not have sufficient time to settle to final accuracy due to the timevarying input signals. In all cases, it was found that the positional accuracy of the EHA with the fuzzy controller was significantly greater than with the switched-gain and proportional controllers for both regulatory and tracking signals. Testing with the inertial load eliminated or changed was not performed because the position sensor was mounted to the load, making it unfeasible to alter the load during the time frame of this study. The regulatory and tracking performance of the EHA with an inertial load of 20 kg plus external resistive loads of 90 to 280 N were investigated. It was found that the positional accuracy of the EHA decreased with the application of an external load to 3.10 ± 0.835 µm for a 1 cm step input (90 N load) and 8.45 ± 0.400 µm for a 3 cm step input (280 N load). Again, the positional accuracy of the EHA decreased during the tracking tests relative to the regulatory tests, for the reason stated above. This implies that the positional accuracy of the EHA with a resistive load is in the microscale, rather than the nano-scale as was put forth as the objective of this study. Nevertheless, the positional accuracy of the EHA with the fuzzy controller was found to be significantly greater than with the switched-gain and proportional controllers. It is postulated that the increase in positional error observed during the external load tests was due to an increase in cross-port leakage, relative to the inertial load tests, caused by the pressure differential induced across the actuator by the external load. Methods of reducing the increase in positional error caused by external loads on the EHA remains an area for future study.

In this work the transformation induced fatigue of Ni-rich NiTi shape memory alloys (SMAs) was investigated. The aerospace industry is currently considering implementing SMA actuators into new applications. However, before any new applications can be put into production they must first be certified by the FAA. Part of this certification process includes the actuator fatigue life. In this study, as-received and polished at dogbone SMA specimens underwent transformation induced fatigue testing at constant loading. The constant applied loading ranged from 100 MPa to 200 MPa. Specimens were thermally cycled through complete actuation (above Af to below Mf ) by Joule heating and environmental cooling. There were three cooling environments studied: liquid, gaseous nitrogen and vortex cooled air. It was shown that polished specimens had fatigue lives that were two to four times longer than those of as-received specimens. Test environment was also found to have an effect on fatigue life. Liquid cooling was observed to be corrosive, while the gaseous nitrogen and vortex air cooling were observed to be non-corrosive. The two non-corrosive cooling environments performed similarly with specimen fatigue lives that were twice that of specimens fatigue tested in the corrosive cooling environment. Transformation induced fatigue testing of polished specimens in a non-corrosive environment at 200 MPa had an average fatigue life of 14400 actuation cycles; at 150 MPa the average fatigue life was 20800 cycles and at 100 MPa it was 111000 cycles. For all specimens constant actuation from the beginning of testing until failure was observed, without the need for training. Finally, a microstructural study showed that the Ni3Ti precipitates in the material were one of the causes of crack initiation and propagation in the actuators.

The goal of the research of this Dissertation is using actuation redundancy to reduce backlash in parallel manipulators (PMs.) Initially, 3-RRR and 3-RPR PM layouts where 3 is the number of branches, R is a revolute joint and P is a prismatic joint, are introduced. Actuated joints will later be underlined in the PM desciptions. A method for determining PM working area for rotated payload platforms, based on a mechanism inversion, is presented. Force solutions for non-redundantly actuated 3-RRR, 3-RRR, 3-RPR and 3-RPR PMs are formulated in terms of screw coordinates. The reciprocal product of screw coordinates is demonstrated to be invarient under changes in reference location and orientation. As examples, the PMs execute basic circle, logarithmic spiral and arc displacement and force trajectories. All non-redundantly-actuated PMs, encounter two backlash-prone zero-actuator-output configurations when executing any of the trajectories. Therefore, non-redundantly actuated PMs are found inadequate for precision applications. Force-uncertainties, where PMs cannot sustain or apply forces in uncertain directions, are examined. For typically actuated 3-RRR and 3-RPR PMs, force uncertainties are identified using screw system arguments based on the existance of 3 actuated forces forming degenerate (rank = 2) planar pencils of forces. These degenerate force pose make arbitrary force and moment application impossible and cause singularities in the force solutions. The working area of the 3-RRR PM is found compatible with all trajectories. This compatibility is due to zero minimum branch length being possible with the limitless angular displacements possible with stacked R joints. In comparison, the 3-RPR PM with minimum joint lengthes imposed on the P joints, has a smaller working area, and is not compatible with any of the trajectories. A P joint modification allowing relative length minimums of zero and a compatible working area identical to the 3-RRR PM, is considered. To address inadequacies, symmetric actuation-redundant 3-RRR and 3-RPR PMs are considered. Pseudo (right Moore-Penrose) inverse of the 3×6 ARS (associated reciprocal screw) matrix is considered to solve for the required actuation. This solution, while providing a minimum 2-norm of the vector of required actuator outputs, does not reduce backlash-prone configurations with all actuators still having two backlash-prone zero-output configurations. An algorithm for reducing backlash, using MATLAB’s constrained optimization routine FMINCON is applied. Minimizing the 2-norm of the vector of actuator outputs, subject to the backlash-free constraint of having outputs ≥ 0 or ≤ 0 depending on the initial values, is considered. Actuators providing the best conditioned ARS matices are utilized for the particular solutions. / Graduate

Neural probes are a promising tool in understanding the brain, alleviating symptoms of various diseases like Parkinson’s Disease and allowing for applications like controlling prosthetics directly using the mind. However, current probes suffer from deleterious glial tissue buildup, poor insulation and low electrode yield. In this work, to improve upon current probes, ultra-compliant probes are fabricated and integrated with biodissolvable needles. Mechanically compliant probes allow for reduction in the body’s immune response chronically whereas biodissolvable needles provide sufficient stiffness during insertion. To achieve this, contributions are made in the categories of probe design concepts, device level processes, and processes in support of final probe assembly. Major contributions include incorporation of interleaved atomic layer deposited ceramics to create hybrid materials that provide better insulation properties, reducing the distance between the electrode and the site-of-interest by developing a gray scale lithography based technique to fabricate protruding electrodes and creating probes that improve electrode yield by integrating liquid crystal polymers into the parylene-C probe structure, which allows the parylene-C probe to actuate. To allow for integration of the biodissolvable needle with the probe, a peel-based process is developed that controls the adhesion between parylene-C to Si using different HMDS conditions and a transfer based process is developed that enables hightemperature annealing. In addition, a generalized design of neural probes using meandering interconnect structures is developed, allowing for rapid mechanical design of probes. This is key for neural probes because of the application specific nature of neural probe design.

Compliant mechanisms are flexible structures that utilize elastic deformation to achieve their desired motions. Using this unique mode of actuation, the compliant mechanisms have two distinct advantages over traditional rigid machines: (1) They can create highly repeatable motions that are critical for many high precision applications. (2) Their high degrees-of-freedom motions have the potential to achieve mechanical functionalities that are beyond traditional machines, making them especially appealing for miniature robots that are currently limited to only having simple rigid-body-motions and gripping functionalities. Unfortunately, despite the potential of compliant mechanisms, there are still several key challenges that restrict them from realizing their full potential. To facilitate this discussion, we first divide the compliant mechanisms into two categories: (1) the stiffer flexural mechanisms that are ideal for high precision applications, and (2) the more compliant miniature soft robots that can reshape their geometries to achieve highly complex mechanical functionalities. The key limitation for existing flexural mechanisms is that their stiffness and dynamic properties cannot be optimized when they have multi-degrees-of-freedom. This limitation has severely crippled the performance of flexural mechanisms because their stiffness and dynamic properties dictate their workspace, transient responses and capabilities to reject disturbances. On the other hand, miniature soft robots that have overall dimensions smaller than 1 cm, are unable to achieve their full potential because existing works do not have a systematic approach to determine the required design and control signals for the robots to generate their desired time-varying shapes.

Photoacoustic (PA) Imaging is an emerging biomedical imaging modality based on the laser-generated ultrasound. The method has unique advantages in providing microvessel structure visualization, neuroimaging, and functional imaging provided by its physical principle. Photoacoustic microscopy (PAM) is one of the PA imaging instruments which provides high resolution and contrast imaging of a near-field target. Relying on the acoustic focusing, Acoustic-resolution PAM (AR-PAM) is capable of reaching a sub-centimeter of penetration depth with sub-millimeter resolution and is optimized for tissue samples and small animals. However, the state-of-art AR-PAMs are large in size and expensive in cost, which hinders its democratization. There are previous researches conducted on reducing the cost by introducing a low-cost optical source or ultrasound acquisition device. Few research has investigated the possibility of modification on actuator design. The total system cost should be further reduced by substituting the translation stage while maintaining the imaging quality. In this research, a delta configuration actuation is introduced to the AR-PAM. The delta-configuration actuation adapted from a low-cost off-the-shelf 3D printer has been implemented in the design. An economical PAM system that integrates the combination of hardware and software enhancement is designed and tested in this research. With the software approach, advanced beamforming methods such as Delay-and-Sum with Coherence Factor (DAS+CF) and Delay-Multiply-and-Sum (DMAS) algorithms are applied to obtaining the high-resolution PA image through 3D reconstruction. The preliminary phantom study demonstrated the applicability of low-cost delta configuration actuators for AR-PAM imaging. The simulation study shows the beamforming algorithms has capability to remove the device precision error and increasing the tolerance. The research suggests that the 3D reconstruction algorithms significantly improve the resolution and contrast of the image quality.

Polymer based microelectromechanical systems (MEMS) micromachining is finding more interest in research and applications. This is due to its low cost and less time processing compared with silicon MEMS. SU-8 is a photo-patternable polymer that is used as a structural layer for MEMS and microfluidic devices. In addition to being processed with low cost, it is a biocompatible material with good mechanical properties. Also, amorphous silicon (α-Si) has found use as a sacrificial layer in silicon MEMS applications. α-Si can be deposited at large thicknesses for MEMS applications and also can be released in a dry method using XeF2 which can solve stiction problems related to MEMS applications. In this thesis, an SU-8 MEMS process is developed using amorphous silicon (α-Si) as a sacrificial layer. Electrostatic actuation and sensing is used in many MEMS applications. SU-8 is a dielectric material which limits its direct use in electrostatic actuation. This thesis provides a MEMS process with two conductive metal electrodes that can be used for out-of-plane electrostatic applications like MEMS switches and variable capacitors. The process provides the fabrication of dimples that can be conductive or non-conductive to facilitate more flexibility for MEMS designers. This SU-8 process can fabricate SU-8 MEMS structures of a single layer of two different thicknesses. Process parameters were tuned for two sets of thicknesses which are thin (5-10μm) and thick (130μm). Chevron bent-beam structures and different suspended beams (cantilevers and bridges) were fabricated to characterize the SU-8 process through extracting the density, Young’s Modulus and the Coefficient of Thermal Expansion (CTE) of SU-8. Also, the process was tested and used as an educational tool through which different MEMS structures were fabricated including MEMS switches, variable capacitors and thermal actuators.