State Derivation of a 12-axis Gyroscope-free Inertial Measurement Unit

The derivation of linear acceleration, angular acceleration, and angular velocity states from a 12-axis gyroscope-free inertial measurement unit that utilizes four 3-axis accelerometer measurements at four distinct locations is reported. Particularly, a new algorithm which derives the angular velocity from its quadratic form and derivative form based on the context-based interacting multiple model is demonstrated. The performance of the system was evaluated under arbitrary 3-dimensional motion.

J. C. Lu and P. C. Lin, “State Derivation of a 12-axis Gyroscope-free Inertial Measurement Unit”, Sensors, Mar. 2011, vol.11, no.3, pp3145-3162

Design of a Leg-Wheel Hybrid Mobile Platform

We report on the design of a leg-wheel hybrid platform Quattroped. Comparing to most hybrid platforms which have separate mechanisms of wheels and legs, this robot is implemented with a transformation mechanism which directly changes the morphology of wheels (i.e. a full circle) into 2 degree-of-freedom legs (i.e. combining two half-circles as a leg). The mechatronics, software infrastructure, and the initial experimental test of the robot are also reported.

S. Y Shen, C. H. Li, C. C. Cheng, J. C. Lu, S. F. Wang, and P. C. Lin, “Design of a Leg-Wheel Hybrid Mobile Platform”, in IEEE/RSJ Int. Conf. Intelligent Robots and Systems (IROS), Oct. 2009

Design and Implementation of a Nine-Axis Inertial Measurement Unit

A nine-axis inertial measurement unit (IMU) that utilizes three-axis angular velocity measurements from rate gyroscopes and six-axis linear acceleration measurements from three two-axis accelerometers is reported. This system can derive linear acceleration, angular acceleration, and angular velocity via simple memoryless matrix operations, and eliminates the requirement for accelerometer installation at the center ofmass as in the traditional IMU. An optimal configuration of the system is proposed based on the analysis of rigid body dynamics and matrix theory. In this configuration, the computed angular acceleration is free of the gravity effect as well. Analyses of sensor position and orientation errors are reported. Experimental validation was executed to evaluate the performance of the system.

P. C. Lin, J. C. Lu, C. H. Tsai, and C. W. Ho, “Design and Implementation of a Nine-Axis Inertial Measurement Unit”, IEEE/ASME Transactions on Mechatronics (TMech) (in press)

The Electromechanical Characteristics of ZnO Grown on Polyethylene Terephthalate Substrates

We investigate the electromechanical properties of ZnO grown on poly
ethylene terephthalate (PET) and compare the results with those obtained from the counterparts on glass substrates. The elastic moduli of ZnO on PET
measured by a microstretcher are very close to those of ZnO grown on glass substrates
measured by nanoindentation: The moduli decrease then increase as the O2/Ar ratio increases. Films start to peel off from the plastic substrates when oxygen content reaches 50%. The in situ measurement of the ZnO resistance under uniaxial tensile stretching is influenced by the induced piezoelectric voltage, leading to a reduction in the electrical resistance for highly resistive ZnO films. The trend of the preferred orientation in relation to the oxygen content of the sputtering atmosphere is the same for ZnO films grown on either PET or glass substrates. The optical bandgap
(Eg) of the ZnO films on both substrates exhibits crystal orientation dependence, varying from 3.18 eV with
(002) preferred orientation to 3.25 eV, with a large number of (100) and (101) oriented crystals.

J. Chen, H. Shieh, I. Cheng, C. Hsiao, P. C. Lin, and Y. Yeh, “The Electromechanical Characteristics of ZnO Grown on Polyethylene Terephthalate Substrates”, Journal of The Electrochemical Society, May 2010, vol.157, no.7, H750-H754

Harnessing Surface Wrinkle Patterns in Soft Matter

Mechanical instabilities in soft materials, specifi cally wrinkling, have led to the formation of unique surface patterns for a wide range of applications that are related to surface topography and its dynamic tuning. In this progress report, two distinct approaches for wrinkle formation, including mechanical stretching/releasing of oxide/PDMS bilayers and swelling of hydrogel fi lms confi ned on a rigid substrate with a depth-wise modulus gradient, are discussed. The wrinkling mechanisms and transitions between different wrinkle patterns are studied. Strategies to control the wrinkle pattern order and characteristic wavelength are suggested, and some efforts in harnessing topographic tunability in elastomeric PDMS bilayer wrinkled fi lms for various applications, including tunable adhesion, wetting, microfl uidics, and microlens arrays, are highlighted. The report concludes with perspectives on the future directions in manipulation of pattern formation for complex structures, and potential new technological applications.

S. Yang, K. Khare, and P. C. Lin, “Harnessing Surface Wrinkle Patterns in Soft Matter”, Advanced Functional Materials, Aug. 2010, vol.20, no.16, pp2550-2564

Mechanically switchable wetting on wrinkled elastomers with dual-scale roughness

We report the fabrication of a new superhydrophobic surface with dual-scale roughness by coating silica nanoparticles on a poly(dimethylsiloxane) (PDMS) elastomer bilayer film with micro-scaled ripples. The wetting behavior of the surface can be reversibly tuned by applying a mechanical strain, which induces the change in micro-scale roughness determined by the ripples. The dual-scale roughness promotes the wetting transition of the final dual-structure surface from Wenzel region into the Cassie region, thus, reducing the sliding angle at least three times in comparison to that from the surfaces with single-scale roughness (either from the nanoparticle film or the wrinkled PDMS film). In addition, three-times and fast-response tunability of the sliding angle by applying mechanical strain on this dual-roughness surface is demonstrated.

P. C. Lin, and S. Yang, “Mechanically Switchable Wetting on the Wrinkled Elastomers with Dual-scale Roughness”, Soft Matter, Feb. 2009, vol.5, 1011-1018

Mechanically tunable dry adhesive from wrinkled elastomers

supplementary video

We report a new dry adhesive structure using a rippled poly(dimethylsiloxane) (PDMS) elastomer bilayer film, whose surface roughness and adhesion can be reversibly regulated by applying mechanical strain. It has a set of advantages not offered by other techniques for regulation of adhesion, including real-time tunability, no requirement of specific surface chemistry, operability under ambient conditions, and relative ease of control. To understand the mechanism for adhesion regulation quantitatively, we have modeled the mechanics of adhesion in the limits of small- and large-amplitude ripples, and show good agreement with indentation experiments. We demonstrate the real-time tunability of the new adhesive structure by repeatedly picking and releasing a glass ball simply by modulating the mechanical stretch of the rippled PDMS film.

P. C. Lin, S. Vajpayee, A. Jagota, C. Hui, S. Yang, “Mechanically Tunable Dry Adhesive from Wrinkled Elastomers”, Soft Matter, Aug. 2008, vol.4, 1830-1835

One-Step Nanoscale Assembly of Complex Structures via Harnessing of an Elastic Instability

supplementary video

We report on a simple yet robust method to produce orientationally modulated two-dimensional patterns with sub-100 nm features over cm2 regions via a solvent-induced swelling instability of an elastomeric film with micrometer-scale perforations. The dramatic reduction of feature size (∼10 times) is achieved in a single step, and the process is reversible and repeatable without the requirement of delicate surface preparation or chemistry. By suspending ferrous and other functional nanoparticles in the solvent, we have faithfully printed the emergent patterns onto flat and curved substrates. We model this elastic instability in terms of elastically interacting “dislocation dipoles” and find complete agreement between the theoretical ground-state and the observed pattern. Our understanding allows us to manipulate the structural details of the membrane to tailor the elastic distortions and generate a variety of nanostructures.

Y. Zhang, E. A. Matsumoto, A. Peter, P. C. Lin, R. D. Kamien, and S. Yang, “One-step nanoscale assembly of complex structures via harnessing of an elastic instability”, Nano Letters, 2008 , vol.8, no.4, 1192-1196 (pdf), supplementary information

Strain responsive concave and convex microlens arrays

We report the fabrication of single-component, strain responsive microlens arrays with real-time tunability. The concave lens array is fabricated by patterning hard oxide layer on a bidirectionally prestretched soft elastomer, poly
dimethylsiloxane
PDMS followed by confined buckling upon release of the prestrain. The convex microlens array is replica molded from the concave lenses in PDMS. Due to difference in lens formation mechanisms, the two types of lenses show different tunable range of focal length in response to the applied strain: large focal length change is observed from the concave microlens array, whereas that from the convex microlens array is much smaller.

D. Chandra, S. Yang, P. C. Lin, “Strain Responsive Concave and Convex Microlens Arrays”, Applied Physics Letters (APL), Dec. 2007, vol.91, 251912

Design of a Bio-inspired Dynamical Vertical Climbing Robot

Supplementary videos:

  Front view

  Side view

This paper reviews a template for dynamical climbing originating in biology, explores its hypothetical utility , and offers a preliminary look at empirical data bearing on the feasibility of adapting it to build a robot that “runs” vertically upward. The recently proposed pendulous climbing model abstracts remarkable similarities in dynamic wall scaling behavior exhibited by radically different animal species. The present paper’s first contribution summarizes a continuing numerical study of this model to hypothesize that these animals’ apparently “wasteful” commitments to lateral oscillations may be justified by a significant gain in the dynamical stability and, hence, the robustness of their resulting climbing capability. We explore numerically a scaled version of this template devised to inform the design of a physically realizable robotic mechanism with the same climbing behavior. The paper’s second contribution documents the design and offers very preliminary empirical data arising from a physical instantiation of this model. Notwithstanding the significant differences between the proposed bio-inspired template and its physical robot model, these intial data suggest the mechanical climber may be capable of roughly reproducing both the motions and ground reaction forces characteristic of dynamical climbing animals. Even without proper tuning the robot’s steady state trajectories manifest a substantial exchange of kinetic and potential energy, resulting in vertical speeds of 0.14 m/s (0.35 bl/s) and claiming its place as the first bio-inspired dynamical legged climbing platform.

J. E. Clark, D. I. Goldman, P. C. Lin, G. Lynch, T. S. Chen, H. Komsuoglu, R. J. Full, D. E. Koditschek, “Design of a Bio-inspired Dynamical Vertical Climbing Robot”, in Robotics: Science and Systems (RSS), Jun. 2007

Spontaneous formation of 1D ripples in transit to highly-ordered 2D herringbone structures through sequential and unequal 2D mechanical force

Spontaneous formation of periodic structures with controlled morphologies on surfaces has been of great interest for many potential applications. We report the formation of various submicron wrinkle patterns using mechanical force coupled with oxygen plasma treatment on PDMS. It allows us to control the amount and timing of strain applied to the substrate on both planar directions (either simultaneously or sequentially), which appears to be critical to maneuver the pattern formation of 1D ripple, 2D herringbone, and patterns in between in real time. We observe clear transitions from ripple, to ripple with bifurcation, to ripple/herringbone mixed features, and to completely 2D herringbone structure. More specifically, we demonstrate the well-controlled formation of a highly-ordered zigzag-based herringbone structure, and elucidate the mechanisms of pattern formation and transition at a large strain level (up to 60%).

P. C. Lin, S. Yang, "Spontaneous Formation of 1D Ripples in Transit to Highly-ordered 2D Herringbone Structures through Sequential and Unequal 2D Mechanical Force", Applied Physics Letters (APL), Jun. 2007, vol.90, 241903

RHex-SLIP: A Model of the Robotic Hexapod RHex in the Sagittal Plane

The spring-loaded inverted pendulum (SLIP) is a simple, passively-elastic two-degree-of-freedom model for legged locomotion that describes the saggital-plane center of mass (COM) dynamics of many animal species and some legged robots. In previous work we have extended SLIP to model three-dimensional COM motions and to incorporate multiple stance legs. To better understand the agile hexapedal robot RHex, here we incorporate key details of leg design and motor specifications into SLIP, allowing us to match SLIP gaits with experimental data from RHex, and to investigate their stability properties. We find that motor and leg characteristics, and leg touchdown and liftoff protocols, can significantly influence stability, and that non-periodic "chaotic" gaits can occur.

(in collaboration with Dr. J. Seipel and Prof. P. Holmes at Princeton University)

Distributed Mechanical Feedback in Arthropods and Robots Simplifies Control of Rapid Running on Challenging Terrain

some movies

Terrestrial arthropods negotiate demanding terrain more effectively than any search-and-rescue robot. Slow, precise stepping using distributed neural feedback is one strategy for dealing with challenging terrain. Alternatively, arthropods could simplify control on demanding surfaces by rapid running that uses kinetic energy to bridge gaps between footholds. We demonstrate that this is achieved using distributed mechanical feedback, resulting from passive contacts along legs positioned by pre-programmed trajectories favorable to their attachment mechanisms. We used wire-mesh experimental surfaces to determine how a decrease in foothold probability affects speed and stability. Spiders and insects attained high running speeds on simulated terrain with 90% of the surface contact area removed. Cockroaches maintained high speeds even with their tarsi ablated, by generating horizontally oriented leg trajectories. Spiders with more vertically directed leg placement used leg spines, which resulted in more effective distributed contact by interlocking with asperities during leg extension, but collapsing during flexion, preventing entanglement. Ghost crabs, which naturally lack leg spines, showed increased mobility on wire mesh after the addition of artificial, collapsible spines. A bioinspired robot, RHex, was redesigned to maximize effective distributed leg contact, by changing leg orientation and adding directional spines. These changes improved RHex’s agility on challenging surfaces without adding sensors or changing the control system.

J. C. Spagna, D. I. Goldman, P. C. Lin, D. E. Koditschek and Robert J. Full, "Distributed mechanical feedback in arthropods and robots simplifies control of rapid running on challenging terrain",  Bioinspiration and Biomimetics, Mar. 2007, vol.2, no.1, pp9-18, (Journal cover)

Sensor Data Fusion for Body State Estimation in a Hexapod Robot with Dynamical Gaits

We report on a hybrid 12 dimensional full body state estimator for a hexapod robot executing a jogging gait in steady state on level terrain with regularly alternating ground contact and aerial phases of motion. We use a repeating sequence of continuous time dynamical models that are switched in and out of an Extended Kalman Filter to fuse measurements from a novel leg pose sensor and inertial sensors. We implement this estimation procedure offline, using data extracted from numerous repeated runs of the hexapod robot RHex (bearing the appropriate sensor suite) and evaluate its performance with reference to a visual ground truth measurement system, comparing as well, the relative performance of different fusion approaches implemented via different model sequences.

P. C. Lin, H. Komsuoglu, D. E. Koditschek, “Sensor Data Fusion for Body State Estimation in a Hexapod Robot with Dynamical Gaits”, IEEE Transactions on Robotics (TRO), Oct. 2006, vol.22, no.5, pp932-943

A Context-Based State Estimation Technique for Hybrid Systems

This paper proposes an approach to robust state estimation for mobile robots with intermittent dynamics. The approach consists of identifying the robot’s mode of operation by classifying the output of onboard sensors into mode-specific contexts. The underlying technique seeks to efficiently use available sensor information to enable accurate, high-bandwidth mode identification. Context classification is combined with multiple-model filtering in order to significantly improve the accuracy of state estimates for hybrid systems. This approach is validated in simulation and shown experimentally to produce accurate estimates on a jogging robot using low-cost sensors.

S. Skaff, A. Rizzi, H. Choset, P. C. Lin, “A Context-Based State Estimation Technique for Hybrid Systems”, in Proc. IEEE Int. Conf. Robotics and Automation (ICRA), Apr. 2005, Barcelona, Spain, pp3935-3940

A Leg Configuration Measurement System for Full-Body Pose Estimates in a Hexapod Robot

We report on a continuous-time rigid-body pose estimator for a walking hexapod robot. Assuming at least three legs remain in ground contact at all times, our algorithm uses the outputs of six leg-configuration sensor models together with a priori knowledge of the ground and robot kinematics to compute instantaneous estimates of the 6-degrees-of-freedom (6-DOF) body pose. We implement this estimation procedure on the robot RHex by means of a novel sensory system incorporating a model relating compliant leg member strain to leg configuration delivered to the onboard CPU over a customized cheap high-performance local wireless network. We evaluate the performance of this algorithm at widely varying body speeds and over dramatically different ground conditions by means of a 6-DOF vision-based ground-truth measurement system (GTMS). We also compare the odometry performance to that of sensorless schemes—both legged as well as on a wheeled version of the robot—using GTMS measurements of elapsed distance.

P. C. Lin, H. Komsuoglu, D. E. Koditschek, “A Leg Configuration Measurement System for Full Body Pose Estimates in a Hexapod Robot”, IEEE Transactions on Robotics (TRO), Jun. 2005, vol.21, no.3, pp411-422

Magnetic Torque Compensating Methods for Cam Indexing Devices

In automatic production processes, cam indexing devices are frequently utilized to transportworkpieces intermittently to the appointed manufacturing positions. However, because of alternating working forces and rotational inertia, indexing devices tend to generate vibration during each positioning process, which retards working speed and degrades positioning accuracy. To minimize positioning vibration, we developed a magnetic compensation concept and diverse devices based on the concept. A magnetic torque compensator basically consists of a magnetic loop with field generator and soft-magnetic elements. The soft-magnetic elements are designed to generate relative motion to each other to realize variable distribution of magnetic field and induce a compensation torque to suppress the positioning vibration. In addition to our experimental research, we investigated analytically the influential parameters of the compensating torque and their relationships by using the equivalent magnetic circuit method and the finite-element method. We found that modifications of magnetic arrangement or geometric parameters of functional elements lead to different characteristics of the magnetic torque curve. On the basis of the verified function and parameters of the magnetic torque compensator, we built some configurations to synthesize the compensating torque needed for countering vibration.

K. Huang, P. C. Lin, S. Tsai, “Magnetic Torque Compensating Methods for Cam Indexing Devices”, IEEE Transactions on Magnetics (TMAG), Mar. 2007, vol.43, no.3, pp1061-1071