This paper presents the design of a low cost system that can be used as a spherical humanoid robot head to display expressive animations for social robotics. The system offers a versatile canvas for Human Robot Interaction (HRI), especially for face to face communication. To maximize flexibility, both in the style and apparent motion of the robot’s head, we exploit the relatively recent availability of low-cost portable projectors in a retro-projected animated face (RAF). The optical mechanical system is comprised of a projector whose light is reflected off a hemispherical mirror and onto a 360 degree section of the spherical head with sufficient resolution and illumination. We derive the forward and inverse mapping relation between the pixel coordinates on the projection plane of the projector, and the outer spherical surface to offer fast graphic generation. Calibration of the system is achieved by controlling three parameters of image translation and scaling, resulting in a specifically devised light cone whose edges are tangential to the hemispherical mirror. Several facial expressions are tested in illuminated indoor environments to show its potential as a modular low cost robot head for HRI.

Solar thermal energy is an alternative to provide heat for low-enthalpy processes at commercial and residential sectors in communities with energy sources scarcity. The present work is focused in the experimental performance analysis of a parabolic trough collector (PTC) designed and manufactured to minimize construction costs by setting the best parabolic profile and rim angle to improve thermal efficiency through enhancing light reflection in its parabolic surface, compound by conventional flat mirrors. The design considers an uncovered copper alloy receiver aligned with the focus of the reflective surface supported on a light metal structure. Sunlight collection area was defined at 1.2 m2 to allow installation of serial or parallel modular arrangements at reduced spaces like a building rooftop, the concentration ratio for this PTC is close to 33. This device was designed to use water as heat transfer fluid (HTF) and to be operated under environmental conditions of the city of Barranquilla, Efficiency curves were obtained based on experimental tests conducted with multiple HTF flow rate and varying reflecting surface slope for one PTC, obtaining a peak efficiency of 48 % and a without a tracking system. This device can be manufactured with a cost close to 80 USD/m2.

This paper presents the design and analysis of a portable forearm exoskeleton designed for rehabilitation and assistive purposes (FE.RAP). The design uses a direct-drive mechanism to actuate three degrees of freedom (DOFs) of the wrist, including: (1) wrist flexion and extension, (2) wrist radial and ulnar deviation, and (3) forearm supination and pronation. In recent decades, automated at-home recovery therapies have emerged as popular alternatives to hospital-based rehabilitation. Often in the case of lower arm rehabilitation, however, existing exoskeletons are not practical to use as home rehabilitation devices due to being non-transportable, bulky in size, and heavy in weight. In addition, compact sized exoskeletons often lack sufficient DOFs to mirror the natural movements of the hand. This paper proposes a design that addresses the drawbacks of current exoskeletons. The FE.RAP is designed to be portable and lightweight, while maintaining sufficient DOFs to help patients recover the range of motion needed by the wrist and forearm to support activities of daily living (ADL). Along with the design, the paper presents an analysis used to optimize the workspace for each DOF of the system. A kinematic analysis is performed to validate and compare the workspace of the system, as well as the coupling relationship between the DOFs, to that of the human hand and wrist. Finally, the torque required to support most ADLs is determined using static and dynamic analyses.

Traditional thermal management techniques such as air-cooled plate- and pin-fin heat sinks are today being pushed to their limits by the increasing power densities of computing hardware (power supplies, controllers, processors, and integrated circuits). In comparison, direct immersion cooling within an alternative cooling medium such as commercial dielectric fluids offers the ability to handle high power densities while also accommodating tighter printed circuit board spacing. Together, these attributes are critical to facilitating higher computing densities. However, this type of high density setup also requires that any heat sink present be low profile so as to not obstruct adjacent printed circuit boards. Such a stringent limit on heat sink height can make achieving cooling targets challenging with existing designs. In this work, the performance of several low profile (height less than 6 mm) heat sinks of varying design are evaluated within a carefully controlled direct immersion cooling environment. Commercial copper heat sinks fabricated through conventional manufacturing (CM) approaches serve as baselines for these performance tests. These same heat sink designs are also replicated via additive manufacturing (AM) utilizing a conductive, carbon-filled printable polylactic acid (PLA) composite material. The performance of these AM heat sinks are then compared to the CM heat sinks, with special emphasis on differences in thermal conductivity between the constituent materials. Finally, novel bio-inspired heat sink designs are developed which would be difficult or impossible to achieve using CM approaches. The most promising of these designs were then created using AM and their performance evaluated for comparison. The overall goal of this is to ascertain whether the design and fabrication flexibility offered by AM can facilitate low profile heat sink designs that can meet or exceed the performance of conventional heat sinks even with perceived deficiencies in material properties for AM parts. Experiments were carried out within Novec 7100 dielectric fluid for single-phase natural convection scenarios as well as two-phase subcooled boiling conditions at atmospheric pressure. A custom test rig was constructed consisting of mirror-polished stainless steel plates and polycarbonate viewing ports to allow visual access. A rotating sample stage allows for data to be obtained at varying heat sink orientation angles from 0° to 90°. For two-phase experiments, multi-angle video capture allows for analysis of the two-phase dynamics occurring at the heat sink samples to be visualized and temporally linked to the associated temperature and heat flux data.

Fourier transform based frequency representation makes an underlying assumption of stationarity and linearity for the target signal whose spectrum is to be computed, and thus it is unable to track time varying characteristics of non-stationary signals that also widely exist in the physical world. Time-frequency representation (TFR) is a technique to reveal useful information included in the signals, and thus the TFR methods are very attractive to the scientific and engineering world. Local mean decomposition (LMD) is a TFR technique used in many fields, e.g. machinery fault diagnosis. Similar to Hilbert-Huang transform, it is an alternative approach to demodulate amplitude-modulation (AM) and frequency-modulation (FM) signals into a set of components, each of which is the product of an instantaneous envelope signal and a pure FM signal. TFR can then be derived by the instantaneous envelope signal and the pure FM signal. However, LMD based TFR technique still has two limitations, i.e. the end effect and the mode mixing problems. Solutions for the two limitations greatly depend on three critical parameters of LMD that are boundary condition, envelope estimation, and sifting stopping criterion. Most reported studies aiming to improve performance of LMD have focused on only one parameter a time, and thus they ignore the fact that the three parameters are not independent to each other, and all of them are needed to address the end effect and the mode mixing problems in LMD. In this paper, a robust optimization approach is proposed to improve performance of LMD through an integrated framework of parameter selection in terms of boundary condition, envelope estimation, and sifting stopping criterion. The proposed optimization approach includes three components. First, the mirror extending method is employed to deal with the boundary condition problem. Second, moving average is used as the smooth algorithm for envelope estimation of local mean and local magnitude in LMD. The fixed subset size is the only parameter that usually needs to be predefined with a prior knowledge. In this step, a self-adaptive method based on the statistics theory is proposed to automatically determine a fixed subset size of moving average for accurate envelope estimation. Third, based on the first and the second steps, a soft sifting stopping criterion is proposed to enable LMD to achieve a self-adaptive stop for each sifting process. In this last step, we define an objective function that considers both global and local characteristics of a target signal. Based on the objective function, a heuristic mechanism is proposed to automatically determine the optimal number of sifting iterations in the sifting process. Finally, numerical simulation results show the effectiveness of the robust LMD in terms of mining time-frequency representation information.

Flux distribution around the parabolic trough receiver being typically non-uniform, only a certain portion of the receiver circumference receives the concentrated solar irradiance. However, radiative and convective losses occur across the entire receiver circumference. This paper attempts to introduce the idea employing transparent heat mirror to effectively reduce the heat loss area and thus improve the thermal efficiency of the solar collector. Transparent heat mirror essentially has high transmissivity in the solar irradiance wavelength band and high reflectivity in the mid-infrared region thus it allows the solar irradiance to pass through but reflects the infrared radiation back to the solar selective metal tube. Practically, this could be realized if certain portion of the conventional low iron glass envelope is coated with Sn-In 2 O 3 so that its acts as a heat mirror. In the present study, a parabolic receiver design employing the aforesaid concept has been proposed. Detailed heat transfer model has been formulated. The results of the model were compared with the experimental results of conventional concentrating parabolic trough solar collectors in the literature. It was observed that while maintaining the same external conditions (such as ambient/initial temperatures, wind speed, solar insolation, flow rate, concentration ratio etc.) the heat mirror-based parabolic trough concentrating solar collector has about 3–12% higher thermal efficiency as compared to the conventional parabolic solar collector. Furthermore, steady state heat transfer analysis reveals that depending on the solar flux distribution there is an optimum circumferential angle ( θ = θ optimum , where θ is the heat mirror circumferential angle) up to which the glass envelope should be coated with Sn-In 2 O 3 . For angles higher than the optimum angle, the collector efficiency tends to decrease owing to increase in optical losses.

Given the largely untapped solar energy resource, there has been an ongoing international effort to engineer improved solar-harvesting technologies. Towards this, the possibility of engineering a solar selective volumetric receiver (SSVR) has been explored in the present study. Common heat transfer liquids (HTLs) typically have high transmissivity in the visible-near infrared (NIR) region and high emission in the mid-infrared region, due to the presence of intra-molecular vibration bands. This precludes them from being solar absorbers. In fact, they have nearly the opposite properties from selective surfaces such as cermet, TiNO x , and black chrome. However, liquid receivers which approach the radiative properties of selective surfaces, can be realized through a combination of anisotropic geometries of metal nanoparticles and transparent heat mirrors. Solar selective volumetric receivers represent a paradigm shift in the manner in which solar thermal energy is harnessed and promise higher thermal efficiencies (and lower material requirements) than their surface-absorption based counterparts. In this paper, the ‘effective’ solar absorption to infrared emission ratio has been evaluated for a representative SSVR employing copper nanospheroids and Sn-In 2 O 3 based heat mirrors. It has been found that a solar selectivity comparable to (or even higher than) cermet-based Schott receiver is achievable through control of the cut-off solar selective wavelength. Theoretical calculations show that the thermal efficiency of Sn-In 2 O 3 based SSVR is 6 to 7% higher than the cermet-based Schott receiver. Furthermore, stagnation temperature experiments have been conducted on a lab-scale SSVR to validate the theoretical results. It has been found that higher stagnation temperatures (and hence higher thermal efficiencies) compared to conventional surface absorption-based collectors are achievable through proper control of nanoparticle concentration.

Recently, various precision products such as lenses or mirrors are produced by the ultra-precision machine tools. Then, the single-point diamond cutting is mainly carried out using the ultra-precision machine tool. In order to generate the high accuracy and high quality machined surfaces, the high stiffness and precise rotational accuracy of the spindle is required for the ultra-precision machining tools. The water driven spindle had been developed for the precision machine tool spindle. This spindle is driven by the generated torque due to the water flow power. Then, the rotational speed can be controlled by the supplied flow rate of water. In addition, the spindle has the water hydrostatic bearings that achieve the high bearing stiffness and precise motion accuracy. Furthermore, it is expected that the water driven spindle has the high thermal stability since the water with low viscosity is used as a coolant media. If the thermal deformation of the spindle is caused during the machining process, the deformation degrades the machining accuracy, accordingly. Thus, it is desirable that the thermal deformation and the temperature change of each part of the spindle and machine tool structure can be controlled and minimized during machining process. In this paper, in order to investigate the thermal stability of the water driven spindle, the measurement tests of the temperature of the water driven spindle were carried out. In addition, the power loss due to the water viscosity between the rotor and the casing of the spindle is calculated. As a result, this paper considers the temperature change and considers the thermal stability of the water driven spindle from the results of experiments.

Due to their merits of low areal density, in-orbit deploying and low manufacturing cost properties, membrane-like deformable mirrors meet the ultra-lightweight and large aperture demand of space optical mirror systems well. Membrane-like mirrors has therefore become a hot spot in the field of space science research now. Surface of these in-orbit membrane-like structures are susceptible to external environment variation on account of their low stiffness and high flexibility properties. Once excited by external excitations, the membrane vibration endures and this would not only degrade its performance, but also lead to system or structural failures. So dynamic vibration control of the membrane-like mirror is indispensable. When the orbiting mirror passes from Earth’s shadow into sunlight, the surface temperature of the mirror changes and this will render membrane thermal distortion. Hence, quasi-static surface error adjustment of the mirror is also requisite. In this paper, a 0.2m diameter scaled-down Kapton membrane-like mirror is taken as the experiment subject. Polyvinylidene Fluoride (PVDF) patches are laminated on the non-reflective side of the mirror as in-plane actuators. High precision laser displacement sensors are used to measure the surface deviation of the mirror. A modal vibration control system based on the positive position feedback (PPF) algorithm and a quasi-static surface control system based on the proportional error feedback algorithm are established respectively. Several mirror control experiments are performed and the results indicate that the methods proposed could suppress the membrane vibration and alleviate the membrane thermal deformation effectively.

The Lanthanum-doped lead zirconate titannate (PLZT) ceramic can be able to drive a micro-mirror according to its excellent advantages such as less susceptible to electromagnetic interference, non-contact optical control and other features. However, the slow response of the photo-deformation and inherent hysteresis extremely limit its wide applications, especially in the dynamic fields of high frequency. To solve above-mentioned problems, this paper proposes an optical-electrostatic driving approach to actuate a device including two parallel electrode plates and a micro-mirror. For the experiment, the SMF-28 fiber with a diameter of 8.2um was selected and the displacement and photovoltage of the PLZT ceramic when irradiated with ultraviolet light of 200mWcm −2 were measured and analyzed. The results show that the response time of the PLZT ceramic obtains 20s when the deformation displacement reaches over 8.2um. Based on the proposed hybrid optical-electrostatic driving device, the deformation displacement is demonstrated to be 9.17um by applying 300V voltage to the parallel electrode plates. Furthermore, the response time reduces to almost 1s when the photovoltage of PLZT is applied with 300V, which indicates that the proposed hybrid optical-electrostatic driving mechanism can significantly eliminate the effect of slow response of photo-deformation.

3D printing was used to produce custom and anatomically-faithful prototype prosthesis device as a missing hand replacement. 3D-printed bones (ABS) were actuated electromagnetically activated copper wire coils (resulting in field of about 9 mT) via nylon lines being attached to one side of the metacarpal bones of the hand, one for each finger, and the other attached to the distal phalanges providing sufficient force for finger bending and functioning. For emotional factors, the device was wrapped in an exact replica of the amputee’s hand anatomy obtained by mirror-imaging the other existing hand.

In ultra-precision machining to produce various precision products such as lenses or mirrors, the single-point diamond cutting is mainly carried out to achieve the high accuracy and high quality machined surfaces. Thus, the precise rotation accuracy is required to the spindle of the ultra-precision machining tool. The water driven spindle had been developed for the precision machining tool spindle. This spindle is driven by the torque of water flow power. Then, the rotational speed can be controlled by supplied flow rate of water. However, the rotational spindle speed during cutting operation is changed due to the influence of the cutting forces during the machining processes. The change in the rotational speed causes the change in the cutting speed, as a result, it degrades the machined surface quality as well. In order to reveal and reduce the influence of this phenomenon, the mathematical model of the rotational speed control system for water driven spindle was derived. This rotational speed control system consists of the water driven spindle and the flow control valve. From the simulation results using a derived transfer function of the rotational speed control system, it is clarified that the rotational speed changes depending on the external load torque. Then, based on the mathematical model, the feedback rotational speed control system with a conventional P-I controller is designed. The effectiveness of the proposed feedback control system is verified by the turning tests. Furthermore, a disturbance observer to minimize the influence of cutting forces on the rotational speed was added to the feedback control system. As a result, this paper shows the performance of the rotational speed control system.

The static modeling of a bi-axial torsional micro-mirror with sidewall electrodes is investigated. The mirror and sidewall electrodes experience different voltages. As a result of the potential difference, the mirror rotates about x and y axes with the torques generated from electrostatic forces by the sidewall and bottom electrodes. The rotations about two axes are made possible using a gimbal frame and serpentine springs. An analytical model is presented that is a simplified model of a previous study based on independent excitation of the two rotation angles. The simplified model enables prediction of the rotation angles with good accuracy and faster computation time.

Thermal management systems for space equipment commonly utilize static solutions such as insulation, optical coatings or reflective mirrors. The simplicity of static systems is advantageous, but the inability to adapt to environmental changes leads to systems designed for extreme conditions. Active control of radiative surface properties would increase the operational capabilities of spacecraft thermal management systems. This study investigates a dynamic solution that allows for real-time control of radiative surface properties based on origami-inspired designs. The extent to which the absorptivity and emissivity of a surface may be varied is demonstrated experimentally. Linear actuation of origami-based structures provides the avenue to alternating between flat and cavity-like surface geometries where the number of reflections, and hence the radiative surface properties are controlled. Flat and folded aluminum foil samples were alternately irradiated with a blackbody emitter at 1000 °C then shielded from the radiation source while the transient temperature was recorded using thermocouples and an IR camera. Thermal models relating the apparent absorptivity of the radiation shield to the time-dependent surface temperature are presented, and methods to invert these models are described. Preliminary results show a significant increase in irradiated steady state temperature for a high fold density as compared to unfolded configurations of the same thickness and material. These results indicate that origami-inspired designs have the potential to provide dynamic control of the apparent absorptivity of radiation shields and surfaces.

This paper presents a novel tool path planning approach for polygonal mirror scanning based Stereolithography (SL) process. Compared with traditional laser scanning and mask projection based SL process, the polygonal mirror scanning based process can build part with high surface quality and precision without losing the fabrication efficiency. As an emerging additive manufacturing process, no efficient tool path planning algorithm is available in current system. This paper presented a direct tool path planning algorithm without converting the 3-Dimentional model into 2-Dimentional contours. Different test cases are used to verify its efficiency and effectiveness. Compared with the commercial software, the proposed algorithm is several times faster. Physical parts are also built using the tool path generated by the proposed algorithm.

Hundreds of mirror segments are needed to realize the laser fusion system and the next generation ground based extra-large telescopes. In order to manufacture the mirror segments, the ultra-precise optics grinding machine is essential equipment. As the most widely used motion transfer device in these machines, the ball screw mechanism need predetermine its positional accuracy. And the positional accuracy is based on load distribution of ball screw. This will be discussed in the article. Based on existing analytical models, an improved model is developed to accurately predict load distribution of ball screw. In this model, variation of contact angle is considered. And a simple approach considering of the influence of the geometry errors on the load distribution is developed. The results of this model demonstrate the load distribution of ball screw is not average and load of every ball falls from the position near the load to further. Downward trend is more marked when introducing the variation of contact angle into the model. Besides, the effect of geometry errors on the load distribution is not as remarkable as existing models. Based on the model, the larger ratio of helical pitch to screw diameter is, the worse the nonuniformity of load distribution is. This will impair the stiffness of ball screw and its positional accuracy. The calculated results are significant to ball screw design.

In order to deal with the shortage in energy using clean renewable energy, a highly efficient and economical solution is needed to meet consumer energy needs. To achieve that, a solar dish collector was established with some major modification in the collection of solar energy to decrease manufacturing cost and increase efficiency. In addition, the focal point of the system was modified using an optical system to establish greater light concentration. This was done using a series of tests, on the different optical assemblies, which affected the performance, efficiency, durability, and cost of the system. Finally, an optical assembly that was used has shown that it can reduce the shadow on the primary mirror, decrease the manufacturing cost of the structure, and increase the efficiency of the system.

Dynamic stall occurs on helicopter rotor blades, wind turbine blades, and even insect and bird wings. Although most studies on dynamic stall are conducted assuming two-dimensional behavior, it has been shown that this phenomenon is highly three-dimensional. Recent studies of dynamic stall on a rotating blade of helicopter in forward flight and wind turbines in yaw have shown that the nature of the radial flow near the surface has first-order significance in the stalled flow field. Past literature suggests that the boundary layer over a rotating disk has been correlated to that over a swept wing. Drawing a similar parallel it is hypothesized that fundamental insights into dynamic stall may be derived from studying the boundary layer over a rotating blade in dynamic stall is similar to that over a rotating disk. Particle image velocimetry (PIV) is used to investigate the boundary layer development on a rotating disk. The first set of measurements was conducted using PIV with a micro lens attachment to the camera. Next, a microscope was used to conduct μ-PIV measurements. The measured radial velocity profiles show substantially higher radial jet peak velocities than the analytical solution for a mirror-smooth disk. This difference is narrowed down to the effect of surface roughness of the painted disk, representative of reality on rotor blades used in PIV. This results in a much higher effective viscosity in the near-surface layer, contributing to additional radial flow, as seen from the centrifugal pump literature. However, the non dimensional radial velocity profile exhibits the expected self similar behavior at various radial locations.

Optical disk drives (ODD) have become one of the most popular solutions for large storage capacity applications and are widely used in consumer electronics. For precise positioning in optical disk drives (ODD), the actuating system using MEMS technology has been considered as a very promising solution. This paper aims to optimize a recently proposed microactuator design as a fine-tracking device for high-density ODD. The microactuator device is electrothermally driven and consists of suspended bimorph beams that are connected to electric heater through linkage hinges on a micromirror platform. Static and dynamic characteristics of the microactuator device are analyzed using coupled electrothermal-mechanical finite element models. Our modeling results reveal that the performance of the original design is undesirable as the central mirror platform is undergoing a lateral shift and is bent concave down when the microactuator is activated. In order to maintain the relative flatness of the mirror surface, a new design with a folded-arm structure is proposed. The design is further optimized using experimental design and response surface method to achieve large actuation displacement and improved resonant frequency response. Overall, the results show that the optimized design outperforms the original design in achieving large displacement, fairly small lateral shift and mirror flatness under the same actuating voltage, while maintaining a compact size and supporting the high bandwidth servo control.

In the last ten years, a new type of advanced polymer known as swelling elastomer has been extensively used as sealing element in the oil and gas industry. These elastomers have been instrumental in various new applications such as water shutoff, zonal isolation, sidetracking, etc. Though swell packers can significantly reduce costs and increase productivity, their failure can lead to serious losses. Integrity and reliability of swelling-elastomer seals under different field conditions is therefore a major concern. Investigation of changes in material behavior over a specified swelling period is a necessary first step for performance evaluation of elastomer seals. Current study is based on experimental and numerical analysis of changes in compressive and bulk behavior of an elastomeric material due to swelling. Tests and simulations were carried out before and after various stages of swelling. Specimens were placed in saline water (0.6% and 12% concentration) at a temperature of 50°C, total swelling period being one month. Both compression and bulk tests were conducted using disc samples. A small test rig had to be designed and constructed for determination of bulk modulus. Young’s modulus (under compression) and bulk modulus were determined for specimens subjected to different swelling periods. Shear modulus and Poisson’s ratio were calculated using isotropic relations. Experiments were also simulated using the commercial finite element software ABAQUS. Different hyperelastic material models were examined. As Ogden model with second strain energy potential gave the closest results, it has been used for all simulations. The elastomer was a fast-swell type. There were drastic changes in material properties within one day of swelling, under both low and high salinity water. Values of elastic and shear modulus dropped by more than 90% in the first few days, and then remained almost constant during the rest of the one-month period. Poisson’s ratio, as expected, showed a mirror behavior of a sharp increase in the first few days. Bulk modulus exhibited a fluctuating pattern; rapid initial decrease, then a slightly slower increase, followed by a much slower decrease. Salinity shows some notable effect in the first 5 or 6 days, but has almost no influence in the later days. Very interestingly, Poisson’s ratio approaches the limiting value of 0.5 within the first 10 days of swelling, justifying the assumption of incompressibility used in most analytical and numerical models. In general, simulations results are in good agreement with experimental ones.