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Publication A Scalable Strategy for Open Loop Magnetic Control of Microrobots Using Critical Points(2016-05-11) Guerrero-Bonilla, Luis; Bhattacharya, Subhrajit; Kumar, VijayA novel scalable strategy for open loop control of ferromagnetic microrobots on a plane using a scalable array of electromagnets is presented. Instead of controlling the microrobot directly, we create equilibrium points in the magnetic force field that are stable and attractive on the plane in which the microrobot is to be controlled. The microrobot moves into these equilibrium points rapidly in presence of low viscous forces, and thus controlling the equilibrium points let us control the microrobot precisely. An unit/cell in the array of electromagnets allows precise control of the microrobot in the unit/cell’s domain. Motion synthesis across multiple overlapping domains allows control of the microrobot in large regions across the array. We perform numerical analysis and demonstrate the control of the ferromagnetic microrobot using the proposed method through simulations.Publication The Penn Baxter Face Database(2017-03-23) Fitter, Naomi T.; Kuchenbecker, Katherine J.The Penn Baxter Face Database is composed of Baxter robot face images designed in a variety of expressions and colors. Each of these images was photographed on the physical Baxter robot and assessed by internet raters (N = 568) in an Amazon Mechanical Turk survey. Raters assessed the pleasantness and energeticness of each robot face and also shared how safe and pleased each face made them feel. This project was published in our ICSR 2016 paper entitled “Designing and Assessing Expressive Open-Source Faces for the Baxter Robot.” After hearing of interest from other researchers, we previously released our Baxter face database on GitHub at https://github.com/nfitter/BaxterFaces. This dataset, now additionally available on Scholarly Commons, includes the developed Baxter faces, photographs used in the Mechanical Turk survey, editable source files for the studied faces, and bonus faces developed in our subsequent design work with Baxter. These contents may benefit any Baxter users who publish images to the robot's face. The organization of the database is explained in the included ReadMe file.Publication The Penn Hand-Clapping Motion Dataset(2016-11-27) Fitter, Naomi T; Kuchenbecker, Katherine JThe Penn Hand-Clapping Motion Dataset is composed of inertial measurement unit (IMU) recordings from the hand motions of 15 naïve people. Each of these individuals participated in an experiment during which they were asked to pantomime various sequences of 10 different motions: back five, clap, double, down five, front five, lap pat, left five, right five, right snap, and up five. The examined motions comprise most typical actions from hand-clapping games like “Pat-a-cake” and “Slide.” This project was published in our IROS 2016 paper entitled “Using IMU Data to Demonstrate Hand-Clapping Games to a Robot.” After hearing of interest from other researchers, we are releasing the corresponding motion dataset, which was originally collected to help us investigate whether we could train highly accurate and rapid classifiers to label hand-clapping game motions performed by everyday people. This dataset, explained further in the included ReadMe file, may interest researchers who investigate human motion.Publication Refined Methods for Creating Realistic Haptic Virtual Textures from Tool-Mediated Contact Acceleration Data(2012-03-01) Culbertson, Heather; Romano, Joseph M; Castillo, Pablo; Mintz, Max; Kuchenbecker, Katherine JDragging a tool across a textured object creates rich high-frequency vibrations that distinctly convey the physical interaction between the tool tip and the object surface. Varying one’s scanning speed and normal force alters these vibrations, but it does not change the perceived identity of the tool or the surface. Previous research developed a promising data-driven approach to embedding this natural complexity in a haptic virtual environment: the approach centers on recording and modeling the tool contact accelerations that occur during real texture interactions at a limited set of force-speed combinations. This paper aims to optimize these prior methods of texture modeling and rendering to improve system performance and enable potentially higher levels of haptic realism. The key elements of our approach are drawn from time series analysis, speech processing, and discrete-time control. We represent each recorded texture vibration with a low-order auto-regressive moving-average (ARMA) model, and we optimize this set of models for a specific tool-surface pairing (plastic stylus and textured ABS plastic) using metrics that depend on spectral match, final prediction error, and model order. For rendering, we stably resample the texture models at the desired output rate, and we derive a new texture model at each time step using bilinear interpolation on the line spectral frequencies of the resampled models adjacent to the user’s current force and speed. These refined processes enable our TexturePad system to generate a stable and spectrally accurate vibration waveform in real time, moving us closer to the goal of virtual textures that are indistinguishable from their real counterparts.Publication Effective properties of nonlinear inhomogeneous dielectrics(1992) Ponte-Castañeda, Pedro; deBotton, G.; Li, G.We develop a general procedure for estimating the effective constitutive behavior of nonlinear dielectrics. The procedure is based on a variational principle expressing the effective energy function of a given nonlinear composite in terms of the effective energy functions of the class of linear comparison composites. This provides an automatic procedure for converting well-known information for linear composites, in the form of estimates and bounds for their effective dielectric constants, into corresponding estimates and bounds for the effective behavior of nonlinear composites. Further, the procedure is easily implemented, and leads in some cases to exact results. This, exact estimates are given herein for isotropic weakly nonlinear composites with general nonlinearity, and bounds of the Hashin-Shtrikman type are given for the class of two-phase, isotropic dielectric composites with strongly and perfectly non-linear constitutive behavior. The optimality of the bounds is addressed briefly.Publication Regular and Irregular Splashing of Drops on Geometric Targets(2012-09-17) Juarez, Gabriel; Gastopoulos, Thomai; Zhang, Yibin; Siegel, Michael L; Arratia, Paulo EThe effect of target cross-sectional geometry on drop splashing is investigated using surfaces with length scales comparable to the drop diameter. The target cross-sectional geometries are regular polygon shapes that vary from a triangle (n = 3) to a decagon (n = 10), where n is the number vertices. The impacting cross-sectional surface area of all targets is constrained to equal the cross-sectional area of the impacting drop which is 6.38 mm2.Publication An Approach to Simultaneous Control of Trajectory and Interaction Forces in Dual-Arm Configurations(1991-10-01) Yun, Xiaoping; Kumar, Vijay R.Multiple arm systems, multifingered grippers, and walking vehicles all have two common features. In each case, more than one actively coordinated articulation interacts with a passive object, thus forming one or more closed chains. For example, when two arms grasp an object simultaneously, the arms together with the object and the ground (base) form a closed chain. This induces kinematic and dynamic constraints and the resulting equations of motion are extremely nonlinear and coupled. Furthermore, the number of actuators exceeds the kinematic mobility of the chain in a typical case, which results in an underdetermined system of equations. An approach to control such constrained dynamic systems is described in this short paper. The basic philosophy is to utilize a minimal set of inputs to control the trajectory and the surplus inputs to control the constraint or interaction forces and moments in the closed chain. A dynamic control model is derived for the closed chain that is suitable for designing a controller, in which the trajectory as well as the interaction forces and moments are explicitly controlled. Nonlinear feedback techniques derived from differential geometry are then applied to linearize and decouple the nonlinear model. In this paper, these ideas are illustrated through a planar example in which two arms are used for cooperative manipulation. Results from a simulation are used to illustrate the efficacy of the method.Publication Kinematics of Redundantly Actuated Closed Chains(1990-04-01) Kumar, Vijay; Gardner, John F.The instantaneous kinematics of a hybrid manipulation system, which combines the traditional serial chain geometry with parallelism in actuation, and the problem of coordination is discussed. The indeterminacy and singularities in the inverse kinematics and statics equations and measures of kinematic performance are analyzed. Finally, coordination algorithms that maintain an optimal force distribution between the actuators while avoiding or exploiting singularities are presented.Publication Recreating the Feel of the Human Chest in a CPR Manikin via Programmable Pneumatic Damping(2012-03-01) Kuchenbecker, Katherine J; Stanley, Andrew A; Healey, Simon K; Maltese, Matthew RIt is well known that the human chest exhibits a strong force displacement hysteresis during CPR, a stark contrast to the non hysteretic behavior of standard spring manikins. We hypothesize that individuals with experience performing CPR on humans would perceive a manikin with damping as more realistic and better for training. By analyzing data collected from chest compressions on real patients, we created a dynamic model that accounts for this hysteresis with a linear spring and a one-way variable damper, and we built a new high-fidelity manikin to enact the desired force displacement relationship. A linkage attached to the chest plate converts vertical compression motions to the horizontal displacement of a set of pneumatic dashpot pistons, sending a volume of air into and out of the manikin through a programmable valve. Position and pressure sensors allow a microcontroller to adjust the valve orifice so that the provided damping force closely follows the desired damping force throughout the compression cycle. Eight experienced CPR practitioners tested both the new manikin and an identical looking standard manikin; the manikin with damping received significantly higher ratings for haptic realism and perceived utility as a training tool.Publication Abstraction and Control for Groups of Fully-Actuated Planar Robots(2003-09-14) Belta, Calin; Kumar, R. VijayThis paper shows how a large number of robots can be coordinated by designing control laws on a small dimensional manifold, independent on the number and ordering of the robots. The small dimensional description of the team has a product structure of a Lie group, which captures the dependence of the ensemble on world frame, and a shape manifold, which is an intrinsic description of the team. We design decoupled controls for group and shape. The individual control laws which are mapped to the desired collective behavior can he realized by feedback depending only on the current state of the robot and the state on the small dimensional manifold, so that the robots have to broadcast their states and only have to listen to some coordinating agent with small bandwidth.