Robots are starting to transition from the confines of the manufacturing floor to homes, schools, hospitals, and highly dynamic environments. As, a result, it is impossible to foresee all the probable operational situations of robots, and preprogram the robot behavior in those situations. Among human-robot interaction technologies, haptic communication is an intuitive physical interaction method that can help define operational behaviors for robots cooperating with humans. Multimodal robotic skin with distributed sensors can help robots increase perception capabilities of their surrounding environments.
Electro-Hydro-Dynamic (EHD) printing is a flexible multi-modal sensor fabrication method because of its direct printing capability of a wide range of materials onto substrates with non-uniform topographies. In past work we designed interdigitated comb electrodes as a sensing element and printed piezoresistive strain sensors using customized EHD printable PEDOT:PSS based inks. We formulated a PEDOT:PSS derivative ink, by mixing PEDOT:PSS and DMSO. Bending induced characterization tests of prototyped sensors showed high sensitivity and sufficient stability.
In this paper, we describe SkinCells, robot skin sensor arrays integrated with electronic modules. 4x4 EHD-printed arrays of strain sensors was packaged onto Kapton sheets and silicone encapsulant and interconnected to a custom electronic module that consists of a microcontroller, Wheatstone bridge with adjustable digital potentiometer, multiplexer, and serial communication unit. Thus, SkinCell’s electronics can be used for signal acquisition, conditioning, and networking between sensor modules. Several SkinCells were loaded with controlled pressure, temperature and humidity testing apparatuses, and testing results are reported in this paper.
Poly(3,4-ethyle- nedioxythiophene)-poly(styrenesulfonate) or PEDOT:PSS is a flexible polymer which exhibits piezo-resistive properties when subjected to structural deformation. PEDOT:PSS has a high conductivity and thermal stability which makes it an ideal candidate for use as a pressure sensor. Applications of this technology includes whole body robot skin that can increase the safety and physical collaboration of robots in close proximity to humans. In this paper, we present a finite element model of strain gauge touch sensors which have been 3D-printed onto Kapton and silicone substrates using Electro-Hydro-Dynamic ink-jetting. Simulations of the piezoresistive and structural model for the entire packaged sensor was carried out using COMSOLR , and compared with experimental results for validation. The model will be useful in designing future robot skin with predictable performances.
Robotic skins with multi-modal sensors are necessary to facilitate better human-robotic interaction in non-structured
environments. Integration of various sensors, especially onto substrates with non-uniform topographies, is challenging
using standard semiconductor fabrication techniques. Printing is seen as a technology with great promise that can be
used for sensor fabrication and integration as it may allow direct printing of different sensors onto the same substrate
regardless of topology. In this work, we investigate Electro-Hydro-Dynamic (EHD) printing, a method that allows
printing of micron-sized features with a wide range of materials, for fabricating pressure sensor arrays using Poly(3,4-
ethylenedioxythiophene):Polystyrene Sulfonate (PEDOT:PSS). Fabrication of such sensors has been achieved by prepatterning
gold or platinum metallized interdigitated comb electrode arrays on a polyimide substrate, with three custom
made PEDOT:PSS based inks printed directly onto the electrode arrays. These three inks include a formulation of
PEDOT:PSS and NMP; PEDOT:PSS, PVP, and NMP; and PEDOT:PSS, PVP, Nafion, and NMP. All these inks were
successfully printed onto sensor elements. The initial results of bending-induced strain tests on the fabricated sensors
display that all the inks are sensitive to strain. This confirms their suitability for pressure and strain sensor applications;
however, the behavior of each ink; including sensitivity, linearity, and stability; is unique to the type.
This paper presents development of a new MEMS-based tactile microsensor to replicate the delicate sense of touch in robotic surgery. Using an epoxy-based photoresist, SU-8, as substrate, the piezoresistive type sensor is flexible, robust, and easy to fabricate in mass. Sensor characteristic tests indicate adequate sensitivity and linearity, and the multiple sensor elements can match full range of surgical tissue stiffness. Such characteristic nearly match the most delicate sense of touch at the human fingertip. It is expected such a sensor is essential for delicate surgeries, such as handling delicate tissues and microsurgery.
Human-robot interaction can be made more sophisticated and intuitive if the entire body of a robot is covered with multimodal sensors embedded in artificial skin. In order to efficiently interact with humans in unstructured environments, robotic skin may require sensors such as touch, impact, and proximity. Integration of various types of sensors into robotic skin is challenging due to the topographical nature of skin. Printing is a promising technology that can be explored for sensor integration as it may allow both sensors and interconnects to be directly printed into the skin. We are developing Electrohydrodynamic (EHD) inkjet printing technology in order to co-fabricate various devices onto a single substrate. Using strong applied electrostatic forces, EHD allows the printing of microscale features from a wide array of materials with viscosities ranging from 100 to 1000cP, highly beneficial for multilateral integration. Thus far we have demonstrated EHD’s capability at printing patterns of Poly(2,3-dihydrothieno-1,4-dioxin)-poly(styrenesulfonate) for pressure sensor applications, generating patterns with modified commercial photoresist for mask-less lithography, and obtaining ZnO microstructures for direct device printing. Printed geometries range from a few tens of microns to millimeters. We have used inks with viscosities ranging from 230 to 520cp and from non-conductive to 135μS/cm. These results clearly show that the EHD is a promising multi-material printing platform and would be an enabling technology that can be used to co-fabricate various devices into robotic skin.
Future robot skin will consist of massive numbers of sensors embedded in flexible and compliant elastomer substrate. To test and characterize pressure-sensitive skin prototypes, we have built an experimental testbed capable of applying controlled loading profiles, using the data to create reduced-order models of skin sensors for simulation and control. Measurement data from a load applicator and embedded taxel is acquired using National Instruments real-time control technology. Reduced-order models were proposed to relate the load applied to robot skin to the load sensed by the embedded taxel. Experiments for soft skin material characterization and taxel characterization were also undertaken with the testbed to better understand their nonlinear behavior. With this setup current and future skin sensor designs undergoing a range of loading profiles can be tested and modeled.
This paper focuses on robotic technologies and operational capabilities of multiscale robots that demonstrate a
unique class of Microsystems with the ability to navigate diverse terrains and environments. We introduce two
classes of robots which combine multiple locomotion modalities including centimeter scale Discrete and Continuous
robots which are referred here by D-Starbot and C-Starbot, respectively. The first generation of the robots were
obtained to allow rapid shape reconfiguration and flipping recovery to accomplish tasks such as lowering and raising
to dexterously go over and under obstacles, deform to roll over hostile location as well as squeezing through opening
smaller than its sizes. The D-Starbot is based on novel mechanisms that allow shape reconfiguration to accomplish
tasks such as lowering and raising to go over and under obstacles as well as squeezing through small voids. The CStarbot
is a new class of foldable robots that is generally designed to provide a high degree of manufacturability. It
consists of flexible structures that are built out of composite laminates with embedded microsystems. The design
concept of C-Starbot are suitable for robots that could emulate and combine multiple locomotion modalities such as
walking, running, crawling, gliding, clinging, climbing, flipping and jumping. The first generation of C-Starbot has
centimeter scale structure consisting of flexible flaps, each being coupled with muscle-like mechanism. Untethered
D-Starbot designs are prototyped and tested for multifunctional locomotion capabilities in indoor and outdoor
environments. We present foldable mechanism and initial prototypes of C-Starbot capable of hopping and squeezing
at different environments. The kinematic performance of flexible robots is thoroughly presented using the large
elastic deflection of a single arm which is actuated by pulling force acting at variable angles and under payload and
This paper presents the statistical formulation of misalignments of optical components. As a case study, sensitivity
analysis is performed to evaluate the optical performance of an assembled Fourier Transform (FT) microspectrometer.
Precision alignment of optical components is a critical factor to achieve high sensitive measurement. Positional and
angular misalignments of optical components are propagated and accumulated from one part to another as the beam is
delivered. Optical paths are modeled as kinematic variables of a linked chain, and its propagation is calculated using
forward kinematics with homogeneous transform matrices. This approach not only formulates the deviation of beam
paths as traditional optics do, but also accommodates statistical variables to represent the mean and variance of
kinematic errors. With the assumption of Gaussian distribution of the errors, the statistical equation was linearly
propagated. The beam deviation was further combined with a light coupling model at the detector to evaluate the
degradation of optical. Its prototype and experimental results were also reported.
This paper presents the design, analysis, and fabrication of an array of microflap actuators that can produce a substantial
aerodynamic force for course corrections of Micro Air Vehicles (MAVs) and low speed projectiles. In the past, several
actuation principles, including microjet, magnetic and bubble actuators, and flapping wings have been proposed, and had
varying degrees of success. In this paper, we discuss the benefits and drawbacks of past attempts, and the technology that
can be used to address the microflap steering problem. We propose a hybrid microflap actuation scheme that combines
two types of actuators including: 1) a MEMS fabricated "active" microactuator connected to a microflap, and 2) a
"passive" fluidic channel system that harvests the potential energy in the high pressure field on the leading edge of the
MAV or high speed projectile to achieve a desired deflection. An array of microflap actuators was prototyped using
silicon MEMS fabrication and microassembly. A Silicon On Insulator (SOI) wafer with 100 micron thick device layer
was used to as a substrate material to fabricate microflap structures with springs. Front and back side DRIE process was
used to etch and release the microstructures including microflaps. Then, the microactuator was assembled on top of the
microflap. The static and dynamic behaviors of a microflap were measured using a laser displacement sensor and were
compared to the analytic model. In the near future, a prototyped microflap will be tested inside of a wind tunnel to
measure the lift and drag at various air speeds.
Microassembly is an enabling technology to build 3D microsystems consisting of microparts made of different materials and processes. Multiple microparts can be connected together to construct complicated in-plane and out-of-plane microsystems by using compliant mechanical structures such as micro hinges and snap fasteners.
This paper presents design, fabrication, and assembly of an active locking mechanism that provides mechanical and electrical interconnections between mating microparts. The active locking mechanism is composed of thermally actuated Chevron beams and sockets. Assembly by means of an active locking mechanism offers more flexibility in designing microgrippers as it reduces or minimizes mating force, which is one of the main reasons causing fractures in a microgripper during microassembly operation.
Microgrippers, microparts, and active locking mechanisms were fabricated on a silicon substrate using the deep reactive ion etching (DRIE) processes with 100-um thick silicon on insulator (SOI) wafers. A precision robotic assembly platform with a dual microscope vision system was used to automate the manipulation and assembly processes of microparts. The assembly sequence includes (1) tether breaking and picking up of a micropart by using an electrothermally actuated microgripper, (2) opening of a socket area for zero-force insertion, (3) a series of translation and rotation of a mating micropart to align it onto the socket, (4) insertion of a micropart into the socket, and (5) deactivation and releasing of locking fingers. As a result, the micropart was held vertically to the substrate and locked by the compliance of Chevron beams. Microparts were successfully assembled using the active locking mechanism and the measured normal angle was 89.2°. This active locking mechanism provides mechanical and electrical interconnections, and it can potentially be used to implement a reconfigurable microrobot that requires complex assembly of multiple links and joints.
Microassembly process plays a key role in building 3-dimensional heterogeneous microsystems. This paper presents a miniaturized Fourier transform spectrometer (FTS) implemented by combining silicon micromachining and microassembly techniques. The FTS is based on a Michelson interferometer where a scanning mirror mechanism creates an interferogram, and the recorded interferogram is converted to a spectrum by Fourier transform. The miniaturized Michelson interferometer is integrated on a microoptical bench, which is fabricated using Deep RIE (Reactive Ion Etching) process on a SOI (Silicon On Insulator) wafer. Key components of the FTS optical bench are a linear translation stage, mechanical assembly sockets, a beam splitter, and assembled mirrors. An electrothermal actuator with stroke amplification mechanisms provides the amplified scanning motion of a scanning mirror. The sockets are female mechanical flexure structures that allow a precise snap-fit assembly with micromachined silicon mirrors. The dimension of the FTS optical bench is 1cm2, and its embedded thermal actuator has a couple of V-beam structures whose beam length is 1mm. The mirrors are Deep RIE micromachined structures with reflection area 500x450μm2 and 750μm long flexure structures for pick & place assembly. The flexure structure allows large deflection so that a microgripper can pick up the mirror by inserting the gripper tip into the structure, and snap-fit assembles it into the mechanical socket of the bench. The linear translation stage generates up to 30μm scanning stroke at 22V input, which corresponds to a spectral resolution of 10nm at 775nm wavelength. While this microassembly method is designed to self-align the mirror in the socket, the mirror slightly tilts after assembly due to the slope of side wall of DRIE processed structures. The measured tilting angles of assembled mirrors range from -2.5° to 0.8° from several assembly trials. The tilting angle combined with beam divergence can cause the loss of power and resolution, spectrum shift and phase error. A He-Ne laser was used as a light source to create interferogram with the assembled microspectrometer. Formation of fringe patterns was successfully conducted with a prototype. Mirrors with a large tilting misalignment resulted in stripe pattern fringes, whereas an improved alignment generated circular pattern fringes. A detector was used to measure light power with respect to input voltage, and the displacement of a scanning mirror was measured and curve-fitted. The relationship between light power changes versus the displacement of a scanning mirror represents interferogram. Spectrum profiles showed a peak around 632nm with FWHM (Full Width Half Magnitude) 25nm approximately. While further research is on going to improve spectrum quality and microassembly technique for the integration of various components with heterogeneous materials and shapes, this approach is expected to facilitate the design and manufacturing of MOEMS from the constraints of micromachining processes.