The Penn Jerboa: A Platform for Exploring Parallel Composition of Templates

We have built a 12DOF, passive-compliant legged, tailed biped actuated by four brushless DC motors. We anticipate that this machine will achieve varied modes of quasistatic and dynamic balance, enabling a broad range of locomotion tasks including sitting, standing, walking, hopping, running, turning, leaping, and more. Achieving this diversity of behavior with a single under-actuated body, requires a correspondingly diverse array of controllers, motivating our interest in compositional techniques that promote mixing and reuse of a relatively few base constituents to achieve a combinatorially growing array of available choices. Here we report on the development of one important example of such a behavioral programming method, the construction of a novel monopedal sagittal plane hopping gait through parallel composition of four decoupled 1DOF base controllers. For this example behavior, the legs are locked in phase and the body is fastened to a boom to restrict motion to the sagittal plane. The platform's locomotion is powered by the hip motor that adjusts leg touchdown angle in flight and balance in stance, along with a tail motor that adjusts body shape in flight and drives energy into the passive leg shank spring during stance. The motor control signals arise from the application in parallel of four simple, completely decoupled 1DOF feedback laws that provably stabilize in isolation four corresponding 1DOF abstract reference plants. Each of these abstract 1DOF closed loop dynamics represents some simple but crucial specific component of the locomotion task at hand. We present a partial proof of correctness for this parallel composition of template reference systems along with data from the physical platform suggesting these templates are anchored as evidenced by the correspondence of their characteristic motions with a suitably transformed image of traces from the physical platform.Comment: Technical Report to Accompany: A. De and D. Koditschek, "Parallel composition of templates for tail-energized planar hopping," in 2015 IEEE International Conference on Robotics and Automation (ICRA), May 2015. v2: Used plain latex article, correct gap radius and specific force/torque number

Modular Hopping and Running via Parallel Composition

Though multi-functional robot hardware has been created, the complexity in its functionality has been constrained by a lack of algorithms that appropriately manage flexible and autonomous reconfiguration of interconnections to physical and behavioral components. Raibert pioneered a paradigm for the synthesis of planar hopping using a composition of ``parts\u27\u27: controlled vertical hopping, controlled forward speed, and controlled body attitude. Such reduced degree-of-freedom compositions also seem to appear in running animals across several orders of magnitude of scale. Dynamical systems theory can offer a formal representation of such reductions in terms of ``anchored templates,\u27\u27 respecting which Raibert\u27s empirical synthesis (and the animals\u27 empirical performance) can be posed as a parallel composition. However, the orthodox notion (attracting invariant submanifold with restriction dynamics conjugate to a template system) has only been formally synthesized in a few isolated instances in engineering (juggling, brachiating, hexapedal running robots, etc.) and formally observed in biology only in similarly limited contexts. In order to bring Raibert\u27s 1980\u27s work into the 21st century and out of the laboratory, we design a new family of one-, two-, and four-legged robots with high power density, transparency, and control bandwidth. On these platforms, we demonstrate a growing collection of $\{$body, behavior$\}$ pairs that successfully embody dynamical running / hopping ``gaits\u27\u27 specified using compositions of a few templates, with few parameters and a great deal of empirical robustness. We aim for and report substantial advances toward a formal notion of parallel composition---embodied behaviors that are correct by design even in the presence of nefarious coupling and perturbation---using a new analytical tool (hybrid dynamical averaging). With ideas of verifiable behavioral modularity and a firm understanding of the hardware tools required to implement them, we are closer to identifying the components required to flexibly program the exchange of work between machines and their environment. Knowing how to combine and sequence stable basins to solve arbitrarily complex tasks will result in improved foundations for robotics as it goes from ad-hoc practice to science (with predictive theories) in the next few decades

EXPERIMENTAL EVALUATION AND SIMULATION OF TORQUE TRANSMISSIBILITY FREQUENCY RESPONSE FUNCTIONS OF VIBRATION ISOLATORS AND ABSORBERS FOR DRIVETRAIN APPLICATIONS

Four studies involving torsional vibration isolation performance of automotive drivetrain components, make up this dissertation. One study features a prototype planetary torsional vibration absorber, a unique device that targets low frequency torsion modes in automotive drivetrains. Two studies feature experiments on several torque converters, clutch locked and open, to validate models of the hardware. The last study details experiments on a centrifugal pendulum absorber in a torque converter, to characterize the viscous friction while submerged in automatic transmission fluid (ATF). The enclosed studies improve the state of the art of drivetrain vibration absorbers and isolators, by introducing a new vibration absorber concept and increasing understanding of the underlying physics of torque converters, lock-up clutch dampers, and centrifugal pendulum absorbers. The design and test of the planetary torsional vibration absorber concept demonstrated the utility of a gear reduction in increasing the apparent inertia of the absorber. By increasing its apparent inertia, the device successfully attenuated a ~20 Hz mode of vibration, and used less packaging volume and mass than a traditional torsional vibration absorber of equivalent performance. Various lockup clutch designs were characterized with torque transmissibility frequency response function (TTFRF) measurements while spinning at simulated vehicle operating conditions. This in situ testing lent itself useful in characterizing the speed dependent friction in a lockup clutch damper, while also confirming other damper parameters—like stiffness and damping. The torque converters were also tested in open mode (lockup clutch not engaged). The open mode testing revealed that the hydrodynamic torque converter transmits enough torsional vibration to excite the damper mode for the turbine damper architectures. The open clutch testing contributes a complete data set—encompassing a wide range of speed ratios—to verify torque converter models with. When comparing the test TTFRFs to model TTFRFs, a discrepancy in the damper mode’s natural frequency was revealed, and it was hypothesized that this error resulted from a reflected inertia effect of the ATF undergoing toroidal flow. The locked clutch testing provoked some questions about the centrifugal pendulum absorber (CPA)—a component of one of the tested torque converter clutch dampers. To validate an existing CPA model, and to characterize the equivalent viscous damping of the CPA mechanism, TTFRFs of custom made torque converters were measured. The custom hardware included: pinned damper (CPA active), pinned CPA (damper active), and pinned straight spring (CPA and arc spring active). The torques due to friction and viscous damping of the damper were effectively eliminated from the CPA, and the equivalent viscous damping of the CPA characterized

The Use of axially loaded flexures for vibration isolation in the OMEGA laser facility target positioner

The OMEGA Laser Facility is used for laser driven inertial confinement fusion research at the University of Rochester\u27s Laboratory for Laser Energetics. This facility requires 1 millimeter diameter spherical targets placed at the center of an experimental chamber to remain stable to within 5 microns (0.0002 ). Occasionally a mounted target will exceed this stability specification due to ambient vibration, so an isolation stage is proposed as a means of eliminating this problem. This isolation stage consists of six parallel flexures that are axially loaded to reduce the resonant frequency of the isolator. Frequency versus axial load, damping, and linearity are measured and compared to results in the literature. Difficulties in achieving the required performance are discussed, and a simplified isolator geometry is proposed

Wireless Sensor Integrated Tool for Characterization of Machining Dynamics in Milling

A first step towards practical sensing in the machining environment is the development and use of low cost, reliable sensors. Historically, the ability to record in-process data at an end mill tool tip has been limited by the sensor location. Often, these sensors are mounted on the material workpiece or the machine spindle at significant physical distance from the cutting process. Of specific interest are the problems of tool chatter which causes limitations to productivity and part quality. Although tool chatter is a substantial issue in machining, it remains an open research topic. In this research, a sensor integrated cutting tool holder is developed to specifically analyze the problems related to tool chatter. With the sensor integrated cutting tool holder, the signal to noise ratio is higher than traditional sensing methods. Because of the higher sensitivity, new data analysis methods can be explored. Specifically, the sensor is used in conjunction with a data dependent linear predictive coding algorithm to demonstrate effective prediction of chatter frequencies from stable cutting

Model Identification and Robust Nonlinear Model Predictive Control of a Twin Rotor MIMO System

PhDThis thesis presents an investigation into a number of model predictive control (MPC) paradigms for a nonlinear aerodynamics test rig, a twin rotor multi-input multi-output system (TRMS). To this end, the nonlinear dynamic model of the system is developed using various modelling techniques. A comprehensive study is made to compare these models and to select the best one to be used for control design purpose. On the basis of the selected model, a state-feedback multistep Newton-type MPC is developed and its stability is addressed using a terminal equality constraint approach. Moreover, the state-feedback control approach is combined with a nonlinear state observer to form an output-feedback MPC. Finally, a robust MPC technique is employed to address the uncertainties of the system. In the modelling stage, analytical models are developed by extracting the physical equations of the system using the Newtonian and Lagrangian approaches. In the case of the black-box modelling, artificial neural networks (ANNs) are utilised to model the TRMS. Finally, the grey-box model is used to enhance the performance of the white-box model developed earlier through the optimisation of parameters using a genetic algorithm (GA) based approach. Stability analysis of the autonomous TRMS is carried out before designing any control paradigms for the system. In the control design stage, an MPC method is proposed for constrained nonlinear systems, which is the improvement of the multistep Newton-type control strategy. The stability of the proposed state-feedback MPC is guaranteed using terminal equality constraints. Moreover, the formerly proposed MPC algorithm is combined with an unscented Kalman filter (UKF) to formulate an output-feedback MPC. An extended Kalman filter (EKF) based on a state-dependent model is also introduced, whose performance is found to be better compared to that of the UKF. Finally, a robust MPC is introduced and implemented on the TRMS based on a polytopic uncertainty that is cast into linear matrix inequalities (LMI)

Development of a force-feedback laparoscopic surgery simulator

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (p. 77-78).The work presented here addressed the development of an electro-mechanical force-feedback device to provide more realistic and complete sensations to a laparoscopic surgery simulator than currently available. A survey of the issues surrounding haptic (touch) displays and training for laparoscopic or "keyhole" procedures was performed. A number of primary and secondary sources including surgeon consultation , operating room observations, and task analyses were used to accumulate a list of needs. Subsequent requirements analysis translated these into a set of specifications for the kinematics, dynamics and actuators, and configuration of the device. These suggested a design with five actuated axes (pitch and yaw about the entrance to the abdomen, insertion, rotation about the tool axis, and gripper feedback) amenable to a configuration including two actuated tools in a lifelike torso. These specifications were the basis for the generation and selection of design concepts. The PHANTOM haptic interface from Sensable Devices was chosen from among a number of existing devices and original designs to actuate the pitch, yaw, and insertion degrees of freedom. A separate end effector actuator was specified to supply feedback to the handle rotation and gripper. Mechanisms were proposed for each of these axes; a linear cable capstan was selected for the gripper and a cable capstan/drum for the rotation. The kinematics, bearings, transmissions, and user interface for both axes were designed in detail, and first- and second generation prototypes were built. The finished devices were integrated with the PHANTOM hardware, electronics, and software. Performance and design evaluations were performed, and plans for future device improvements and user studies were outlined.by Ela Ben-Ur.S.M