Passive Vision Research Articles

Adaptive control of deposited height in GMAW-based layer additive manufacturing

A passive vision sensor system has been developed to monitor the nozzle to the top surface distance (NTSD) in layer additive manufacturing (LAM) using gas metal arc welding (GMAW). The deviations in the NTSD are compensated by the movement of the working flat, and the adjustment of the deposition rate on next deposition layer. After simplification of the controlled process into a linear system, an adaptive control system has been designed to keep the NTSD constant. The effectiveness of the controller is evaluated through deposition of single-bead multi-layer walls, and the experimental results confirm that the process stability can be improved when applying the developed controller.

Online measurement of bead geometry in GMAW-based additive manufacturing using passive vision

Additive manufacturing based on gas metal arc welding is an advanced technique for depositing fully dense components with low cost. Despite this fact, techniques to achieve accurate control and automation of the process have not yet been perfectly developed. The online measurement of the deposited bead geometry is a key problem for reliable control. In this work a passive vision-sensing system, comprising two cameras and composite filtering techniques, was proposed for real-time detection of the bead height and width through deposition of thin walls. The nozzle to the top surface distance was monitored for eliminating accumulated height errors during the multi-layer deposition process. Various image processing algorithms were applied and discussed for extracting feature parameters. A calibration procedure was presented for the monitoring system. Validation experiments confirmed the effectiveness of the online measurement system for bead geometry in layered additive manufacturing.

Based on the CO<sub>2</sub> Gas Shielded Welding Molten Pool Image Edge Detection Algorithm

This paper use the passive vision system through high-speed camera collects molten pool images; and then according to the frequency domain characteristics of the weld pool image Butterworth low-pass filter; gradient method for image enhancement obtained after pretreatment. Research Roberts, Sobel, Prewitt, Log, Zerocross, and Canny 6 both traditional differential operator edge detection processing results. Through comparison and analysis of choosing threshold for [0.1, 0. Canny operator can get the ideal molten pool edge character, for subsequent welding molten pool defect recognition provides favorable conditions.

Rapid and accurate face depth estimation in passive stereo systems

In this paper, we introduce a novel approach for face depth estimation in a passive stereo vision system. Our approach is based on rapid generation of facial disparity maps, requiring neither expensive devices nor generic face models. It consists in incorporating face properties into the disparity estimation process to enhance the 3D face reconstruction. We propose a model-based method that is independent from the specific stereo algorithm used. Our method is a two-step process. First, an algorithm based on the Active Shape Model (ASM) is proposed to acquire a disparity model specific to the face concerned. Second, using this model as a guidance, the dense disparity is calculated and the depth map is estimated. Besides, an original post-processing algorithm is proposed in order to detect holes and spikes in the generated depth maps caused by wrong matches and uncertainties. It is based on the smoothness property of the face and a local and global analysis of the image. Experimental results are presented to demonstrate the reconstruction accuracy and the speed of the proposed method.

A robust algorithm for weld seam extraction based on prior knowledge of weld seam

PurposeThis paper aims to develop a method to extract the weld seam from the welding image.Design/methodology/approachThe initial step is to set the window for the region of the weld seam. Filter and edge‐operator are then applied to acquire edges of images. Based on the prior knowledge about characteristics of the weld seam, a series of routines is proposed to recognize the seam edges and calculate the seam representation.FindingsThe proposed method can be used to extract seams of different deviations from noise‐polluted images efficiently. Besides, the method is low time‐consuming and quick enough for real time processing.Practical implicationsWeld seam extraction is the key problem in passive vision based seam tracking technology. The proposed method can extract the weld seam even when the image is noisy, and it is quick enough to be applied in seam tracking technology. The method is expected to improve seam tracking results.Originality/valueA useful method is developed for weld seam extraction from the noise‐polluted image based on prior knowledge of weld seam. The method is robust and quick enough for real time processing.

Passive vision based seam tracking system for pulse-MAG welding

Welding robots have been widely used in manufacturing process to substitute for human welders. However, most of them are rigid and cannot adjust to variations in the weld seam positions caused by natural welding environmental factors. To address this problem, this paper presents a passive vision-based robotic welding system, which can realize the seam tracking function for pulse-MAG welding. In this paper, the light spectrum of the welding process is analyzed to determine the optical filters used during the image capture. Then, a robust image processing method is proposed to extract the offset from the image which contains much noise. The transformation formula is calibrated to obtain the relationship between the image coordinate system and the robot coordinate system. The tracking strategy is designed to improve the tracking precision and the stability of the welding process. Finally, experiments are conducted on straight line and curved line seam to verify the feasibility of the developed system.

A Simple 3D Scanner Based On Passive Vision for Geometry Reconstruction

Acquire spatial information of a 3D model is very useful in many applications in the computer science field. A device broadly used as acquisition hardware of models is the 3D scanner. With a 3D scanner is possible to obtain the geometric structure based on points and triangles of a model, and use it on several computing applications. According the hardware and algorithms employed, the scanners can be classified as passive and active vision. The passive vision scanners are lower cost devices which require geometrics algorithms to obtain a 3D reconstruction. In this paper, we present a design and implementation of a simple 3D scanner of lower cost based on passive vision. The scanner consists in the design of hardware and algorithms where two webcam are placed on a controlled environment. Several experiments demonstrate excellent results on the geometric reconstruction of the scanned objects.

Anatomical Imag(inari)es: The Cultural Impact of Medical Imaging Technologies

The 'eyes' made available in modern technological sciences shatter any idea of passive vision; these prosthetic devices show us that all eyes, including our own organic ones, are active perceptual systems, building on translations and specific ways of seeing, that is, ways of life. There is no unmediated photograph or passive camera obscura in scientific accounts of bodies and machines; there are only highly specific visual possibilities, each with a wonderfully detailed, active, partial way of organising worlds. (Haraway 1988: 583)

Real‐time image capturing and processing of seam and pool during robotic welding process

Purpose – The purpose of this paper is to analyze the technology of capturing and processing weld images in real‐time, which is very important to the seam tracking and the weld quality control during the robotic gas tungsten arc welding (GTAW) process.Design/methodology/approach – By analyzing some main parameters on the effect of image capturing, a passive vision sensor for welding robot was designed in order to capture clear and steady welding images. Based on the analysis of the characteristic of the welding images, a new improved Canny algorithm was proposed to detect the edges of seam and pool, and extract the seam and pool characteristic parameters. Finally, the image processing precision was verified by the random welding experiments.Findings – It was found that the seam and pool images can be clearly acquired by using the passive vision system, and the welding image characteristic parameters were accurately extracted through processing. The experiment results show that the precision range of the i...

Real-time seam tracking control technology during welding robot GTAW process based on passive vision sensor

This paper presents a technology about real-time seam tracking, which is necessary to overcome the deficiencies of the teaching-playback welding robots in seam tracking control during gas tungsten arc welding (GTAW) process. A set of vision sensor system has been designed for the welding robot, which can acquire clear and steady welding images. By analyzing the features of welding images, a new improved Canny algorithm has been proposed to detect the edges of seam and pool, and extract the characteristic parameters of welding images. Based on the analysis of the characteristic of the real-time seam tracking, a segmented self-adaptive PID controller is introduced to the system, and some experiments have been done to testify whether the accuracy of the technology can meet the requirements of quality control of seam forming.

Detecting falls with 3D range camera in ambient assisted living applications: A preliminary study

In recent years several world-wide ambient assisted living (AAL) programs have been activated in order to improve the quality of life of older people, and to strengthen the industrial base through the use of information and communication technologies. An important issue is extending the time that older people can live in their home environment, by increasing their autonomy and helping them to carry out activities of daily livings (ADLs). Research in the automatic detection of falls has received a lot of attention, with the object of enhancing safety, emergency response and independence of the elderly, at the same time comparing the social and economic costs related to fall accidents. In this work, an algorithmic framework to detect falls by using a 3D time-of-flight vision technology is presented. The proposed system presented complementary working requirements with respect to traditional worn and non-worn fall-detection devices. The vision system used a state-of-the-art 3D range camera for elderly movement measurement and detection of critical events, such as falls. The depth images provided by the active sensor allowed reliable segmentation and tracking of elderly movements, by using well-established imaging methods. Moreover, the range camera provided 3D metric information in all illumination conditions (even night vision), allowing the overcoming of some typical limitations of passive vision (shadows, camouflage, occlusions, brightness fluctuations, perspective ambiguity). A self-calibration algorithm guarantees different setup mountings of the range camera by non-technical users. A large dataset of simulated fall events and ADLs in real dwellings was collected and the proposed fall-detection system demonstrated high performance in terms of sensitivity and specificity.

The influence of age management policies on older employee work relationships with their company

The negative consequences of age-related discrimination are now well documented. Employee relationships have become looser both with their work and their workplace. On the other hand, there is far less research analyzing how employees cope when confronted with negative stereotypes associated with human resource management (HRM) measures of discrimination. The field remains imprisoned in a passive vision of the individual faced with stigmatization. This research analyses how and with what resources senior employees manage the discrimination they are subjected to. Far from being homogeneous, this work shows that individual reactions are marked by a diversity of adaptation tactics, which go from accepting the constraint passively to putting its burden into perspective. We suggest a typology, which is an invitation to re-read the effects of discrimination by integrating the role of work and of the company in the development of the individual.

On the possibility of reduction of the scattering background in passive vision systems during observation of objects emitting polarized light

We consider a simple method that considerably reduces the effect of the scattering background of a medium during observation of spatial self-luminous objects emitting polarized light.

Experiential blindness revisited: In defence of a case of embodied cognition

The sensorimotor theory ( Noë, 2004; Noë, in press) discusses a special instance of lack of perceptual experience despite no sensory impairment. The phenomenon dubbed “experiential blindness” is cited as evidence for a constitutive relation between sensorimotor skills and perceptual experience. Recently it has been objected ( Adams & Aizawa, 2008; Aizawa, 2007) that the cases described by Noë as experiential blindness are cases of pure sensory deficit. This paper argues that while the objections bring out limitations of Noë’s sensorimotor theory they do not do enough to challenge a robust perception–action interdependence claim. There are genuine cases of experiential blindness and these are better explained by the hypothesis of the interdependence of perception and action rather than by a passive vision approach. The cases provide support for a strong thesis of embodied cognition where ongoing sensorimotor dynamics non-trivially constrain perceptual content.

Systematic distortions of perceived planar surface motion in active vision

Recent studies suggest that the active observer combines optic flow information with extra-retinal signals resulting from head motion. Such a combination allows, in principle, a correct discrimination of the presence or absence of surface rotation. In Experiments 1 and 2, observers were asked to perform such discrimination task while performing a lateral head shift. In Experiment 3, observers were shown the optic flow generated by their own movement with respect to a stationary planar slanted surface and were asked to classify perceived surface rotation as being small or large. We found that the perception of surface motion was systematically biased. We found that, in active, as well as in passive vision, perceived surface rotation was affected by the deformation component of the first-order optic flow, regardless of the actual surface rotation. We also found that the addition of a null disparity field increased the likelihood of perceiving surface rotation in active, but not in passive vision. Both these results suggest that vestibular information, provided by active vision, is not sufficient for veridical 3D shape and motion recovery from the optic flow.

Robot welding seam tracking method based on passive vision for thin plate closed-gap butt welding

A passive vision sensor is added to a teaching and playback welding robot for pulsed gas tungsten arc welding, which is normally used in the welding of thin plate closed-gap butts. This paper presents a seam tracking method based on this sensor through period visual measurement of the offset between the torch and the seam center. A robust image processing algorithm is developed to extract the seam center. A kind of ARX(auto-regressive with exogenous input) model is studied to describe the relationship between the rectifying voltage and the offset. The fuzzy PID(proportional-integral-derivative) seam tracking controller is analyzed and designed in consideration of various offsets based on the ARX model. The experimental results on straight line weld display a good seam tracking capability of the proposed method.

Al alloy weld pool control of welding robot with passive vision

PurposeThe purpose of this paper is to describe work aimed to control the Al alloy welding penetration through the passive vision for welding robot.Design/methodology/approachFirst a passive vision system was established. The system can capture the Al alloy welding image. Based on the analysis of the characteristic of the welding image, the composite edge detectors were developed to recognize the shape of the weld seam and the weld pool. To realize the automatic control of the Al alloy‐weld process, the relation between the welding parameter and the quality of the weld appearance was established through the random welding experiment. The wire feed was chosen with PID controller adjusting the wire feed rate according to the weld gap variation.FindingsThis paper finds that the passive vision system can be captured the clear weld seam and weld pool image simultaneously. the method of composite edge detectors can be effectively and accurately recognize the weld seam edges. The wire feed rate controller ensured the welding robot to adjust the wire feed rate according to the gap variation.Research limitations/implicationsThis system has been applied to the industrial welding robot production.Originality/valueThe weld seam and weld pool image can be simultaneously captured by the passive vision system. The composite edge detectors have been developed for the passive vision method. The controller has been set up for Al alloy welding process based on the neural network.

Dense range map reconstruction from a versatile robotic sensor system with an active trinocular vision and a passive binocular vision

One major research issue associated with 3D perception by robotic systems is the creation of efficient sensor systems that can generate dense range maps reliably. A visual sensor system for robotic applications is developed that is inherently equipped with two types of sensor, an active trinocular vision and a passive stereo vision. Unlike in conventional active vision systems that use a large number of images with variations of projected patterns for dense range map acquisition or from conventional passive vision systems that work well on specific environments with sufficient feature information, a cooperative bidirectional sensor fusion method for this visual sensor system enables us to acquire a reliable dense range map using active and passive information simultaneously. The fusion algorithms are composed of two parts, one in which the passive stereo vision helps active vision and the other in which the active trinocular vision helps the passive one. The first part matches the laser patterns in stereo laser images with the help of intensity images; the second part utilizes an information fusion technique using the dynamic programming method in which image regions between laser patterns are matched pixel-by-pixel with help of the fusion results obtained in the first part. To determine how the proposed sensor system and fusion algorithms can work in real applications, the sensor system is implemented on a robotic system, and the proposed algorithms are applied. A series of experimental tests is performed for a variety of configurations of robot and environments. The performance of the sensor system is discussed in detail.

Arc welding robot system with seam tracking and weld pool control based on passive vision

The automatic control in square-wave alternating current (AC) gas tungsten arc welding (GTAW) is significant for a “teach and playback” robot to overcome the variation of the seam trajectory and the seam gap in the welding process. This paper presents a welding robot system based on the real-time visual measurement in the different levels of the welding current. The primary objective is to measure the offset of the torch to the seam center and the size of seam gap by passive vision, track the seam and control the weld pool in real time. A novel visual image analysis algorithm was developed for seam tracking and seam gap measuring, free from robot calibration. The control algorithm based on the knowledge base was established to control the weld formation by regulating the welding current and wire feed rate. The welding practice for the rocket storage tank demonstrates the efficiency of the proposed system.

Pedestrian tracking routine for passive automotive night vision systems

Purpose – This paper aims to present a new approach to implement a pedestrian tracking algorithm for a passive automotive night vision application.Design/methodology/approach – First, the basic information of passive and active night vision systems is presented, with implementation methods adopted in previous work. The proposed thermal‐image processing is a combination of seed detection, boundary detection and seed growth computations, based on a temperature thresholding scheme.Findings – The processing routine performance is assessed when implemented to a continuous sequence of thermal acquisitions, from a commercial automotive night vision module. Experimental results show good tracking performance for both pedestrians and passing vehicles.Research limitations/implications – A strategy of multi‐seed growth, directional seed growth and image fusion is proposed to improve the current tracking algorithm.Originality/value – New thermal image processing routines are applied to commercial, automotive night vi...