An ActiveVision System for Recognition of Pre-Marked Objects

Abstract -In this paper, a new 3D-object-recognition method for robotic assembly workcells is presented. The proposed method is focused on two basic concepts, namely active vision and object preconditioning. The paper will briefly present the main aspects of the proposed system. The Proposed Recognition Method [l] Herein, it is proposed to model an object using only a small number of 2D topologically-distinct perspective views. These are referred to as standardviews, each with a corresponding standard-view-axis. For successful recognition purposes, the input image of' an object must be one of its standard perspective views. Thus, a mobile camera is used, such that its optical axis can be aligned with one of the standardview-axes of the object in order to acquire a standardview. Then, the matching process is performed between h e acquired 2D standard-view of the object and the library of 2D standard-views of a set of objects. To enable the vision system to acquire standardviews, standard-view-axes must be pre-defined. This can be accomplished by defining a local surface normal for each distinct view of an object. The local surface normals can be defined by pre-marking the objects using circular markers. In the context of the above scheme, active vision is used for two purposes: (1) Acquiring only specific views of an object (i.e., standard views) by controlling the external parameters of the camera; and (2) Acquiring additional images (standard views) if needed by virtuc of the possibility that the recognition process is not successful after the analysis of the first image, either due to significant distortion and noise, or, insufficient visual information in the image initially acquired. On the other hand, object pre-marking, servcs the following purposes: (1) Specifying a set of object surfaces to be viewed; (2) Defining a local surface normal --a standard axis-of-view --(which can be cstimatcd from the shape of a marker in the imagc plane); and (3) Conveying local 3D orientation and 3D position of a surface of an object, which can be subsequently used for 3D-location estimation of the objcct with respect to a refercnce frame. Based on the above scheme, the major steps for the identification and 3D-location estimation of a premarked object can be listed as follows: In the context of on-line issues and system implementation, the following aspects of the new technique have been addressed: a sequential distortioncompensation procedure, marker boundary detection to a sub-pixel accuracy, elliptical parameter estimation [71, and 3D-location estimation of circular markers [8]. For a complete presentatior? of each of the above issues and the proposed solution method and experimental results, please refer to the corresponding refcrences indicated above. An Experimental Prototype of the Active-Vision System [3] In an attempt to verify the validity and performance of the presented active object recognition technique, a prototype of the system was developed. The prototype is able to recognize the idcntity of manufactured objects which appear randomly oriented in thc field of view of a camera, provided that the standard views of all objects are available and stored in a standard-view database. In this particular implementation, the functions of the active object recognition are distributed between a loosely-coupled vision subsystem and robot-control subsystem. The system is an integration of the follow

Three-dimensional kinematic motion analysis of a daily activity drinking from a glass: a pilot study

BACKGROUND: Development of reliable and objective evaluation methods is required, particularly for natural and goal-oriented upper-extremity tasks. Three-dimensional imaging measurement techniques have turned out to be a powerful tool for a quantitative and qualitative assessment of multijoint movements. The purpose of this study was to develop and test a method of three-dimensional motion analysis for the activity "drinking from a glass" and describe the drinking task with kinematic variables in control subjects. METHODS: A protocol was developed for the drinking activity including the set-up of cameras and positions of the markers and the subject. The drinking task included reaching, forward transport with glass, drinking, back transport and returning the hand to the initial position. An optoelectronic system was used for the three-dimensional kinematic motion capture. Movement times, velocities, joint angles and interjoint coordination for shoulder and elbow were computed and analyzed for twenty control subjects. Test-retest consistency was evaluated for six subjects. RESULTS: The test protocol showed good consistency in test-retest. Phase definitions for the drinking task were defined and verified. Descriptive kinematic variables were obtained for movement times, positions, velocities and joint angles for shoulder and elbow joint. Interjoint coordination between shoulder and elbow joint in reaching phase showed a high correlation. CONCLUSION: This study provides a detailed description of the three-dimensional kinematic analysis of the drinking task. Our approach to investigate and analyze a goal-oriented daily activity has a great clinical potential. Consequently, the next step is to use and test this protocol on persons with impairments and disabilities from upper extremities

Kinematic analysis of the daily activity of drinking from a glass in a population with cervical spinal cord injury

Background Three-dimensional kinematic analysis equipment is a valuable instrument for studying the execution of movement during functional activities of the upper limbs. The aim of this study was to analyze the kinematic differences in the execution of a daily activity such as drinking from a glass between two groups of patients with tetraplegia and a control group. Methods A total of 24 people were separated into three groups for analysis: 8 subjects with metameric level C6 tetraplegia, 8 subjects with metameric level C7 tetraplegia and 8 control subjects (CG). A set of active markers that emit infrared light were positioned on the upper limb. Two scanning units were used to record the sessions. The activity of drinking from a glass was broken down into a series of clearly identifiable phases to facilitate analysis. Movement times, velocities, and the joint angles of the shoulder, elbow and wrist in the three spatial planes were the variables analyzed. Results The most relevant differences between the three groups were in the wrist. Wrist palmar flexion during the back transport phase was greater in the patients with C6 and C7 tetraplegia than in the CG, whereas the highest wrist dorsal flexion values were in forward transport in the subjects with C6 or C7 tetraplegia, who required complete activation of the tenodesis effect to complete grasping. Conclusions A detailed description was made of the three-dimensional kinematic analysis of the task of drinking from a glass in healthy subjects and in two groups of patients with tetraplegia. This was a useful application of kinematic analysis of upper limb movement in a clinical setting. Better knowledge of the execution of this movement in each of these groups allows therapeutic recommendations to be specifically adapted to the functional deficit present. This information can be useful in designing wearable robots to compensate the performance of AVD, such as drinking, in people with cervical SCI

IEEE Pacific Rim Conference on Communications, Computers and Signal Processing MORPHOLOGICAL SKELETON TRANSFORMS FOR DETERMINING POSITION AND ORIENTATION OF PRE-MARKED OBJECTS

Abstract In this paper, the feasibility of a pre-marking scheme for 3-D object recognition is presented. The proposed scheme is based on the assumption that an object can be modeled by a small number of its distinct 2-D perspective projections, referred to as "standard-views". Circular markers are used to identify these views by determining their surface normals passing through their centers. Since a circular marker would always appear as an ellipse on all acquired images, its shape can be related to the orientation of the surface, on which it is located, with respect to the camera's optical axis. The surface normal of the marker can be determined by analysing the geometrical features of its acquired pseudo-ellipse image using morphological skeleton transforms. The position of the marker, on the other hand, has to be determined by acquiring two images from different viewing-angles. The experimental results illustrate that the specific pseudo-Euclidean skeleton transform used in this paper can accurately determine the features of the ellipse to allow the succesful aplication of the proposed pre-marking scheme

Motion recovery for uncalibrated turntable sequences using silhouettes and a single point

LNCS v. 5259 is the conference proceedings of ACIVS 2008This paper addresses the problem of self-calibration and motion recovery for turntable sequences. Previous works exploited silhouette correspondences induced by epipolar tangencies to estimate the image invariants under turntable motion and recover the epipolar geometry. These approaches, however, require the camera intrinsics in order to obtain an Euclidean motion, and a dense sequence is required to provide a precise initialization of the image invariants. This paper proposes a novel approach to estimate the camera intrinsics, the image invariants and the rotation angles from a sparse turntable sequence. The silhouettes and a single point correspondence are extracted from the image sequence. The point traces out a conic in the sequence, from which the fixed entities (i.e., the image of the rotation axis, the horizon, the vanishing point of the coordinates, the circular points and a scalar) can be recovered given a simple initialization of the camera intrinsic matrix. The rotation angles are then recovered by estimating the epipoles that minimize the transfer errors of the outer epipolar tangents to the silhouettes for each pair of images. The camera intrinsics can be further refined by the above optimization. Based on a given range of the initial focal length, a robust method is proposed to give the best estimate of the camera intrinsics, the image invariants, the full camera positions and orientations, and hence a Euclidean reconstruction. Experimental results demonstrate the simplicity of this approach and the accuracy in the estimated motion and reconstruction. © 2008 Springer Berlin Heidelberg.link_to_subscribed_fulltextThe 10th International Conference on Advanced Concepts for Intelligent Vision Systems (ACIVS 2008), Juan-les-Pins, France, 20-24 October 2008. In Lecture Notes in Computer Science, 2008, v. 5259, p. 796-80

Motion Recovery for Uncalibrated Turntable Sequences Using Silhouettes and a Single Point

This paper addresses the problem of self-calibration and motion recovery for turntable sequences. Previous works exploited silhouette correspondences induced by epipolar tangencies to estimate the image invariants under turntable motion and recover the epipolar geometry. These approaches, however, require the camera intrinsics in order to obtain an Euclidean motion, and a dense sequence is required to provide a precise initialization of the image invariants. This paper proposes a novel approach to estimate the camera intrinsics, the image invariants and the rotation angles from a sparse turntable sequence. The silhouettes and a single point correspondence are extracted from the image sequence. The point traces out a conic in the sequence, from which the fixed entities (i.e., the image of the rotation axis, the horizon, the vanishing point of the coordinates, the circular points and a scalar) can be recovered given a simple initialization of the camera intrinsic matrix. The rotation angles are then recovered by estimating the epipoles that minimize the transfer errors of the outer epipolar tangents to the silhouettes for each pair of images. The camera intrinsics can be further refined by the above optimization. Based on a given range of the initial focal length, a robust method is proposed to give the best estimate of the camera intrinsics, the image invariants, the full camera positions and orientations, and hence a Euclidean reconstruction. Experimental results demonstrate the simplicity of this approach and the accuracy in the estimated motion and reconstruction