Occlusion Avoidance Research Articles

Visual Servoing in an Optimization Framework for the Whole-Body Control of Humanoid Robots

In this paper, we show that visual servoing can be formulated as an acceleration-resolved, quadratic optimization problem. This allows us to handle visual constraints, such as field of view and occlusion avoidance, as inequalities. Furthermore, it allows us to easily integrate visual servoing tasks into existing whole-body control frameworks for humanoid robots, which simplifies prioritization and requires only a posture task as a regularization term. Finally, we show this method working on simulations with HRP-4 and real tests on Romeo.

Geometry optimization of branchings in vascular networks.

Progress has been made in developing manufacturing technologies which enable the fabrication of artificial vascular networks for tissue cultivation. However, those networks are rudimentary designed with respect to their geometry. This restricts long-term biological functionality of vascular cells which depends on geometry-related fluid mechanical stimuli and the avoidance of vessel occlusion. In the present work, a bioinspired geometry optimization for branchings in artificial vascular networks has been conducted. The analysis could be simplified by exploiting self-similarity properties of the system. Design rules in the form of two geometrical parameters, i.e., the branching angle and the radius ratio of the daughter branches, are derived using the wall shear stress as command variable. The numerical values of these parameters are within the range of experimental observations. Those design rules are not only beneficial for tissue engineering applications. Moreover, they can be used as indicators for diagnoses of vascular diseases or for the layout of vascular grafts.

1P2-S02 自律移動型プロジェクタロボットによる投影画像欠落時の回避方法 : 輝度値による遮蔽物体の認識

1P2-S02 自律移動型プロジェクタロボットによる投影画像欠落時の回避方法 : 輝度値による遮蔽物体の認識

Opacity optimization for 3D line fields

For the visualization of dense line fields, the careful selection of lines to be rendered is a vital aspect. In this paper, we present a global line selection approach that is based on an optimization process. Starting with an initial set of lines that covers the domain, all lines are rendered with a varying opacity, which is subject to the minimization of a bounded-variable least-squares problem. The optimization strives to keep a balance between information presentation and occlusion avoidance. This way, we obtain view-dependent opacities of the line segments, allowing a real-time free navigation while minimizing the danger of missing important structures in the visualization. We compare our technique with existing local and greedy approaches and apply it to data sets in flow visualization, medical imaging, physics, and computer graphics.

Comparison of Two Sequencing Techniques to Perform a Vision-Based Navigation Task in a Cluttered Environment

We address the problem of multi-sensor-based navigation in a cluttered environment for a non-holonomic robot. To perform such a successful and safe navigation, three controllers realizing, respectively, nominal vision-based navigation, obstacle bypassing and occlusion avoidance have been designed using the task function approach. Then it suffices to sequence them to realize the complete mission. To guarantee the control continuity when switching between two successive controllers, two sequencing approaches have been used and compared. Simulation results validate our work.

REACTIVE SELF COLLISION AVOIDANCE WITH DYNAMIC TASK PRIORITIZATION FOR HUMANOID ROBOTS

We propose a self collision avoidance system for humanoid robots designed for interacting with the real world. It protects not only the humanoid robots' hardware but also expands its working range while keeping smooth motions. It runs in real-time in order to handle unpredictable reactive tasks such as reaching to moving targets tracked by vision during dynamic motions like e.g. biped walking. The collision avoidance is composed of two important elements. The first element is reactive self collision avoidance which controls critical segments in only one direction — as opposed to other methods which use 3D position control. The virtual force for the collision avoidance is applied to this direction and therefore the system has more redundant degrees of freedom which can be used for other criteria. The other second element is a dynamic task prioritization scheme which blends the priority between target reaching and collision avoidance motions in a simple way. The priority between the two controllers is changed depending on current risk. We test the algorithm on our humanoid robot ASIMO and works while the robot is standing and walking. Reaching motions from the front to the side of the body without the arm colliding with the body are possible. Even if the target is inside the body, the arm stops at the closest point to the target outside the body. The collision avoidance is working as one module of a hierarchical reactive system and realizes reactive motions. The proposed scheme can be used for other applications: We also apply it to realizing a body schema and occlusion avoidance.

Initial Experience of Pacing with a Lumenless Lead System in Patients with Congenital Heart Disease

Long-term pacing is frequently necessary in patients with congenital heart disease (CHD). Preservation of ventricular function and avoidance of venous occlusion is important in these patients. Site-selective pacing with a smaller diameter lead is achievable with the model 3830 lead (SelectSecure, Medtronic Inc., Minneapolis, MN, USA), which was specifically designed to target these complications. We describe our initial experience with the Model 3830 lead in patients with CHD. Retrospective analysis of all patients undergoing site-selective implantation of a Model 3830 lead(s) from two congenital heart centers (Bristol, UK, and Dublin, Ireland) from October 2004 until February 2008. We implanted 139 SelectSecure leads (atrial n=70; ventricular n=69) in 90 patients (57 male) with CHD. Median age at implantation: 13.4 years (1.1-59.2 years), median weight: 43 kg. Sixty-nine patients (76%) were children (<18 years). Indications for lead implantation included atrioventricular block (n=55), sinus node disease (n=18), implantable cardiac defibrillator (n=12), antitachycardia pacing (n=4), and cardiac resynchronization (n=1). Twenty-two patients underwent pre-existing lead extraction during the same procedure. All the attempted procedures resulted in successful pacing. One patient had a significantly raised threshold at implantation. There was no procedural mortality. There were two procedural complications. Three patients required lead repositioning for increasing thresholds early postprocedure (<6 weeks). Four leads (2.9%) had displaced on median follow-up of 21.8 months (0.5-42 months). The Model 3830 lead is safe and effective in patients with CHD. This is a technically challenging patient group yet procedural complication and lead displacement rates are acceptable.

Occlusion Avoidance for Microassembly Using A Variable View Imaging System

Occlusion is an important issue in conventional microscopes using in the microassembly and micromanipulation. This paper presents an occlusion avoidance method using a variable view imaging system that enable adjustment of the view orientation and position to avoid occlusion and keep target in side field of view. The system integrates a telecentric scanner and a double wedge prisms system which can supply a flexible view with adjustable zenith and azimuth angles. This design simplified the operation of system by decoupling the scanning mirror angle with the view zenith and azimuth angles. In order to obtain a desired view direction to avoid occlusion, the artificial potential field was applied for calculation of rotation angles double wedge prisms. Different interested surfaces can be combined in the artificial potential field and the angles of prisms for the best view direction without occlusion can be obtained. The view position is steered by visual feedback method, which eliminates the requirement of accurate system calibration. Simulations and microassembly experimental results are provided to verify the feasibility of the proposed approach.

Hand-Assisted Laparoscopic Partial Nephrectomy in the Porcine Model Using Gelatin Matrix Hemostatic Sealant Without Hilar Occlusion

Gelatin matrix hemostatic sealant (GMHS) has been used for hemostasis during partial nephrectomy with hilar clamping. The objective of this study was to determine the ability of GMHS to achieve hemostasis without hilar clamping in the porcine model. In this feasibility study, eight farm pigs underwent a left-hand-assisted laparoscopic partial nephrectomy (HALPN). The lower fourth of the kidney was removed with cold scissors, and GMHS was applied laparoscopically. Samples were collected for measurement of serum hemoglobin (Hb) and creatinine (Cr) prior to surgery and at 4 and 30 days after HALPN. The kidneys were harvested at 30 days, and retrograde pyelograms and pathologic analysis were performed. Application of GMHS achieved complete hemostasis in all eight animals. The mean estimated blood loss was 40 mL, and the operating time was short (mean 92.5 minutes). In three kidneys, a significant collecting system opening was noted but not repaired. At harvest, there were no hematomas, infections, or urine leaks in any animals. In one animal, a 2-cm contained fluid collection was identified. There was no difference in the preoperative and harvest Hb (9.63 v 9.21 g/dL; P = 0.49), but there was a slight increase in Cr (1.21 v 1.46 mg/dL; P = 0.01) possibly because of the decreased renal mass after partial nephrectomy. Even without hilar occlusion, GMHS was 100% safe and effective in controlling bleeding after HALPN in the porcine model. Avoidance of hilar occlusion may reduce the risk associated with warm renal ischemia and the extra dissection required to isolate the hilum in preparation for clamping.

Avoidance of arterial occlusion from injection of soft tissue fillers

In recent years, several cases of blindness, stroke, and skin necrosis have occurred after injection of soft tissue fillers. To avoid such complications, the author recommends using larger, blunt cannulas and epinephrine at the injection site, while avoiding the injection of large boluses of soft tissue filler in the face. ( Aesthetic Surg J 2002;22:555-557.)

Variable resolution depth imaging by using elliptical mirrors

We describe a novel optical sensor to acquire two-dimensional depth maps of a viewed scene, based on the well established principle of triangulation. The principal contribution of the research lies in the design, which employs planar elliptical mirrors to allow sensor reconfiguration. This enables continuous variation of the triangulation geometry, so that depth maps can be acquired either at a low-depth resolution but with minimal occlusion or at a high-depth resolution but with higher occlusion, depending on the object geometry. The predicted precision of the system is modeled, and the avoidance of occlusion is demonstrated.

Dynamic Sensor Placement Using Controlled Active Vision

The working region of a camera providing visual feedback to guide manipulation tasks can be greatly extended if the camera can move in real-time. Proper camera motion depends on several different criteria, such as object motion, maximum manipulator tracking speed, manipulator configuration, camera depth-of-field, field-of-view, spatial resolution, occlusion avoidance, etc. In this paper, the controlled active vision framework is extended to include dynamically determined sensor placement criteria. The criteria considered include focus, spatial resolution, and manipulator configuration, as well as object motion. Experimental results are presented.

Occlusion avoidance of visual sensors based on a hand-eye action simulator system: HEAVEN

In order to construct an intelligent robot system, the implementation of sensor systems is a prime requirement. With the increasing demands for hand-eye coordinating systems, problems of how to design, construct, and utilize hand-eye systems effectively have been realized which have to be solved. For example, teaching tasks to a hand-eye system requires off-line programming of the visual sensors as well as the manipulators. Although much attention has been paid recently to robot simulators for assisting the off-line programming of manipulators, less work has been done on simulators of the sensors. We have developed a hand-eye action simulator system called HEAVEN. This system provides model-based functions to assist the hand-eye system in visual recognition and monitoring the robot environment. This paper describes a function of assisting cameras in occlusion avoidance to input adequate image data without occlusion. The problem to select the best viewpoint for a camera is defined as to evaluate the viewpo...

Epidural analgesia for elective Caesarean section. Technique and its assessment.

A technique is described of epidural anaesthesia for electric Caesarean section which has a 98% success rate, and an acceptably low incidence of intra-operative pain. The essentials of the technique are to produce and maintain complete sensory block from S5 to T6, employing a two-stage injection of bupivacaine 0.5% (mean dose 23 ml) and the use of gravity to ensure sacral block. Despite the use of preoperative fluid loading and avoidance of caval occlusion, transitory hypotension occurred in 16% of patients. Vomiting, which occurred in 18% of patients, is a minor but distressing complication.

Extrathoracic bypass for stenosis of innominate artery

Stenosis of the innominate artery usually occurs in older patients in whom the risks of conventional, corrective procedures such as transthoracic endarterectomy or aorto-innominate arterial bypass grafting are quite high. An axillo-axillary bypass procedure was performed in a high-risk patient with innominate arterial stenosis who had repeated episodes of transient cerebral ischemia due to decreased blood flow through the right carotid artery and reversal of blood flow through the right vertebral artery. Postoperatively, he has had dramatic improvement in his symptoms. Because of its simplicity, avoidance of major thoracotomy, avoidance of temporary occlusion of the carotid artery, and excellent late results, axillo-axillary bypass grafting is being proposed as the procedure of choice for stenosis of the innominate artery.