15,592 research outputs found
Control and Filtering for Discrete Linear Repetitive Processes with H infty and ell 2--ell infty Performance
No full textRepetitive processes are characterized by a series of sweeps, termed passes, through a set of dynamics defined over a finite duration known as the pass length. On each pass an output, termed the pass profile, is produced which acts as a forcing function on, and hence contributes to, the dynamics of the next pass profile. This can lead to oscillations which increase in amplitude in the pass to pass direction and cannot be controlled by standard control laws. Here we give new results on the design of physically based control laws for the sub-class of so-called discrete linear repetitive processes which arise in applications areas such as iterative learning control. The main contribution is to show how control law design can be undertaken within the framework of a general robust filtering problem with guaranteed levels of performance. In particular, we develop algorithms for the design of an H? and dynamic output feedback controller and filter which guarantees that the resulting controlled (filtering error) process, respectively, is stable along the pass and has prescribed disturbance attenuation performance as measured by and – norms
Development of a multi-channel concentric tube robotic system with active vision for transnasal nasopharyngeal carcinoma procedures
No full textTowards hybrid control of a flexible curvilinear surgical robot under visual/haptic guidance
No full textComprised of multiple telescoptic precurved tubes that can independently rotate and translate, concentric tube robots (<i>CTRs</i>) are favorable in minimally invasive surgeries thanks to their small size and considerable dexterity along with curvilinear accessibility. However, there is a lack of investigation on improvement of the surgeons' perception which in turn can be used to guide the telemanipulation. In this work, we proposed an eye-in-hand configuration for the concentric tube robot by adding an endoscope to the tip of the inner tube, which provides direct and intuitive visual sensing ability for the operator. Based on this visual feedback, we further developed two frameworks for the hybrid control of <i>CTR</i>, namely Teleoperation Before Visual Servoing (<i>TBVS</i>) and Teleoperation During Visual Servoing (<i>TDVS</i>). The structures of these two frameworks were elaborated with key algorithms derived. The effectiveness of the proposed methods were demonstrated through a series of experiments both in free space and in a confined environment (inside a skull model). The results manifested that the visual guidance had the potential of assisting the operator to control the CTR more efficiently
Acoustic radiation due to scattering of T-S wave by the mean-flow distortion induced by steady local suction
No full textSubstantial sound waves can be generated by boundary-layer instability modes when the latter are scattered by a rapid mean-flow distortion. This is a rather generic mechanism and operates when an oncoming T-S wave is scattered by a steady local suction slot. This paper focuses on this problem by extending a recently developed Local Scattering Theory (Wu & Dong, J. Fluid Mech. submitted), where a so-called transmission coefficient, defined as the ratio of the T-S wave amplitude downstream of the scatter to that upstream, is introduced to characterize the effect of a local scatter on boundary-layer instability and transition. As in the earlier work, the mathematical formulation is based on triple-deck formulism, but in order to accommodate the acoustic far field, which was not considered in the paper mentioned, the unsteady terms in the upper deck, which play a leading-order role in radiation, are retained, and the influence of the radiated sound on the near-wall perturbation is included. The upper deck equation for the pressure is the Helmholtz equation rather than the Laplace equation. This leads to a modified pressure-displacement relation, which is coupled with the linearized boundary-layer equations in the lower deck. Discretization of the whole system formulates a generalized eigenvalue problem, which is solved numerically. It is found that suction suppresses oncoming T-S waves, and this effect increases with the suction velocity and the slot width. The directivity is ndependent of the flow parameters only when the Mach number is low. The intensity of the radiated sound in general increases with the frequency, the suction velocity and the width of the suction slot. Interestingly, for O(1) suction velocities, the radiated sound is very weak, indicating that the gain of stabilizing effect does not cause aeroacoustic penalty
An image based targeting method to guide a tentacle-like curvilinear concentric tube robot
No full textConcentric tube robot (CTR) comprises several precurved concentric tubes which can rotate and translate independently with respect to each other. Each pre-curved tube of a CTR can be controlled to rotate axially and translate along its axis, which enables the tip to bypass obstacles and finally reach the target position. The concentric tube robots enable surgeons to perform delicate procedures by combining the flexibility of elastic catheters with the use of operation tools, such as needles, forceps and grippers. Hence, many clinical applications of concentric tube robots are promising, such as transnasal robotic neurosurgery. Concentric tube robots are suitable for such minimally invasive surgeries because they are able to present various flexible shapes with great dexterity, which strengthens the ability of collision avoidance and enlarges the reachability of operation tools. This paper describes an image based visual servoing method to control the concentric tube robot so that it can reach a desired position. A model-less control algorithm is developed by first estimating and adjusting the Jacobian matrix based on measurement of each incremental movement traced by a single camera, and then generating the next motion using the estimated Jacobian matrix. Therefore, no kinematic model is required to control the CTR during experiments and the experimental results reveal the feasibility and accuracy of the proposed method. To the best of our knowledge, this is the first work that realizes model-less feedback control of concentric tube robots based on visual servoing
Motion planning of continuum tubular robots based on centerlines extracted from statistical atlas
No full textContinuum tubular robots, which are constructed by telescoping pre-curved elastic tubes, are capable of balancing the force application and steerability during minimally invasive surgeries. These devices are able to reach the desired surgical sites in body cavities without colliding with critical blood vessels, nerves and tissues. However, the motion planning of continuum tubular robots is quite challenging because of their complicated kinematics as well as the high dimensional configuration space. In this paper, a sampling-based motion planning method is proposed based on the Rapidly-exploring Random Tree (RRT) algorithm for continuum tubular robots in 3D environments, such as medullary cavities. The proposed motion planner enables a continuum tubular robot to maneuver roughly along the central axis of the statistical humerus atlas in an approximate follow-the-leader manner. The experiment results have demonstrated the effectiveness and superiority of the proposed motion planning algorithm
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Tim Wu & “The Curse of Bigness”
No full textHost Nicholas Lemann sits down with Tim Wu, author of The Curse of Bigness, to discuss the politics of Louis Brandeis and Theodore Roosevelt as antitrust has reemerged this year as a major issue in the run-up to the 2020 U.S. Presidential Election.
Model-free image guidance for intelligent tubular robots with pre-clinical feasibility study: Towards minimally invasive trans-orifice surgery
No full textComprised of multiple precurved concentric tubes, continuum tubular robots are capable to reach surgical targets while bypassing critical anatomical obstacles during minimally invasive surgeries, such as transnasal and transoral surgeries. To automatically track the surgical target and compensate undesired disturbance, an eye-in-hand image-based visual servoing algorithm is presented in this paper to control in-house continuum tubular robots. The proposed visual servoing approach does not require any prior knowledge on kinametic models of the robots in order to avoid the errors introduced by imaging-sensor calibration and 3D position reconstruction. Preclinical cadaveric experiments have been demonstrated in the paper to illustrate the feasibility of the model-free automatic visual servoing method
Measurement of dwell times of spin polarized rubidium atoms on octadecyltrichlorosilane- and paraffin-coated surfaces
No full textWe report the measurement of dwell times of spin polarized Rb atoms on octadecyltrichlorosilane OTS- and paraffin-coated surfaces. We find that at a cell temperature of 72 °C the dwell times for OTS- and paraffin-coated surfaces are 0.9+-0.1 microsecond and 1.8 +-0.2 microsecond , respectively. Since the relaxation probability on paraffin is almost one order of magnitude smaller than that on OTS, the longer dwell time for paraffin indicates that the average strength of the interactions experienced by Rb atoms while they are inside paraffin is much weaker than while they are inside OTS.Peer reviewe
[[alternative]]A Study on History of Shin-Wu Elementary School at Tao-Yuan（1905-2003）
No full text[[abstract]]To explore the school cultural development in Shin-Wu Elementary school in the last hundred years and the significance of school history research in educational history, this study examines documents and files in the school history room of Shin-Wu Elementary school and has oral history interviews as well. The main findings of this study are as follows.
1. In late Meiji, most of the teachers were Japanese or Taiwanese from the nearby common schools, however, the turnover was high. At that time, only affluent students attended schools while later, more students were from poor families. Yet, the drop-out rate was relatively high.
2. As for the age, most students went to school in their teens, for they had to share responsibilities in home chores.
3. In Taisyo period, there were more and more teachers who had been Shin-Wu graduates and students were from different sources.
4. Owing to the air raid during the war, schools got closed very often and the content of education was mainly about laboring.
5. Post-war education, compared with that before, varied little in educational contents and forms because of the position-retaining teachers and staff.
6. For the last hundred years, nearly one-third of Shin-Wu teachers were their graduates and principals and teachers of branch schools came form Shin-Wu Elementary School, too. Therefore, Shin-Wu Elementary School had played an influential role in the elementary education and the local people cultivation in Shin-Wu area.
7. Shin-Wu Elementary School had always followed the national educational policy, seldom did they have local standpoints, which meant, they had to strengthen their autonomy and capacity when faced with new challenges especially after the lifting of Martial Law.
8. Through elaborative school cultural analysis, relationship among education, politics, economy and society, in particular, individual area development will be more carefully investigated.
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