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The purpose of this paper is to resolve the problem of 3D modelling of small objects lacking or without real texture, using an automatic, practical, convenient and effective method.

For each space feature point projected on the surface of the target small object, there are two corresponding 2D points existing. One is an image point in one of the image sequences from the digital camera; another is a point in the slide from the projector. Using the image processing method, the image point can be extracted out accurately so that its 2D coordinates are gained. At the same time, the slide point is designed first so that its 2D coordinates are calculated by the known data. The 3D coordinates of the space feature point can be computed by the space forward intersection.

The projector‐camera system is composed of a slide projector, a digital camera, a control ground, and a computer. The computer controls the other three pieces of equipment, working together automatically and efficiently.

According to the size of the grid, the target object is relatively small. The planar grid is functioned as the calibration of the slide projector and the digital camera.

The paper presents a very effective approach for 3D reconstruction of small objects.

According to the traditional method of the digital camera taking images, the projector is steered so that the projector‐camera system is formed. After being calibrated, respectively, in advance, the projector‐camera system is similar to the binocular vision system in the principle of 3D modelling.

In some three-dimensional (3D) printing application scenarios, e.g., model manufacture, it is necessary to print large-sized objects. However, it is impossible to implement large-size 3D printing using a single projector in digital light processing (DLP)-based mask projection 3D printing because of the limitations of the digital micromirror device chips.

A multi-projector DLP with energy homogenization (EHMP-DLP) scheme is proposed for large-size 3D printing. First, a large-area printing plane is established by tiling multiple projectors. Second, the projector set’s tiling pattern is obtained automatically, and the maximum printable plane is determined. Third, the energy is homogenized across the entire printable plane by adjusting gray levels of the images input into the projectors. Finally, slices are automatically segmented based on the tiling pattern of the projector set, and the gray levels of these slices are reassigned based on the images of the corresponding projectors.

Large-area high-intensity projection for mask projection 3D printing can be performed by tiling multiple DLP projectors. The tiled projector output energies can be homogenized by adjusting the images of the projectors. Uniform ultraviolet energy is important for high-quality printing.

A prototype device is constructed using two projectors. The printable area becomes 140 × 210 mm from the original 140 × 110 mm.

The proposed EHMP-DLP scheme enables 3D printing of large-size objects with linearly increasing printing times and high printing precision. A device was established using two projectors to practice the scheme and can easily be extended to larger sizes by using more projectors.

Stiffness control of redundant robot arm, aimed at using extra degrees of freedom (DoF) to shape the robot tool center point (TCP) elastomechanical behavior to be consistent with the essential requirements needed for a successful part mating process, i.e., to mimic part supporting mechanism with selective quasi-isotropic compliance (Remote Center of Compliance – RCC), with additional properties of inherent flexibility.

Theoretical analysis and synthesis of the complementary projector for null-space stiffness control of kinematically redundant robot arm. Practical feasibility of the proposed approach was proven by extensive computer simulations and physical experiments, based on commercially available 7 DoF SIA 10 F Yaskawa articulated robot arm, equipped with the open-architecture control system, system for generating excitation force, dedicated sensory system for displacement measurement and a system for real-time acquisition of sensory data.

Simulation experiments demonstrated convergence and stability of the proposed complementary projector. Physical experiments demonstrated that the proposed complementary projector can be implemented on the commercially available anthropomorphic redundant arm upgraded with open-architecture control system and that this projector has the capacity to efficiently affect the task-space TCP stiffness of the robot arm, with a satisfactory degree of consistency with the behavior obtained in the simulation experiments.

A novel complementary projector was synthesized based on the adopted objective function. Practical verification was conducted using computer simulations and physical experiments. For the needs of physical experiments, an adequate open-architecture control system was developed and upgraded through the implementation of the proposed complementary projector and an adequate system for generating excitation and measuring displacement of the robot TCP. Experiments demonstrated that the proposed complementary projector for null-space stiffness control is capable of producing the task-space TCP stiffness, which can satisfy the essential requirements needed for a successful part-mating process, thus allowing the redundant robot arm to mimic the RCC supporting mechanism behavior in a programmable manner.

Tony Crocker concludes his two‐part article on using projected still pictures with some advice on projectors and screens.

Tony Crocker in the first of a two‐part article discusses some of the problems of using projected still pictures

In a typical additive manufacturing (AM) system, it is critical to make a trade-off between the resolution and the build area for applications in which varied dimensions, feature sizes and accuracies are desired. Conventional solutions to this challenge are based on curing of multiple areas with a single high resolution and stitching them to form a large layer. However, because of the lack of the capability in adjusting resolution dynamically, such stitching approaches will elongate the build time greatly in some cases. To address the challenge without sacrificing the build speed, this paper aims to design and develop a novel AM system with dynamic resolution control capability.

A laser projector is adopted in a vat photopolymerization system. The laser projection system has unique properties, including focus-free operation and capability to produce dynamic mask image irrespective of any surface (flat or curved). By translating the projector along the building direction, the pixel size can be adjusted dynamically within a certain range. Consequently, the build area and resolution could be tuned dynamically in the hardware testbed. Besides, a layered depth image (LDI) algorithm is used to construct mask images with varied resolutions. The curing characteristics under various resolution settings are quantified, and accordingly, a process planning approach for fabricating models with dynamically controlled resolutions is developed.

A laser projection-based stereolithography (SL) system could tune resolution dynamically during the building process. Such a dynamic resolution control approach completely addresses the build size-resolution dilemma in vat photopolymerization AM processes without sacrificing the build speed. Through fabricating layers with changing resolutions instead of a single resolution, various build areas and feature sizes could be produced precisely, with optimized build speed.

A focus-free laser projector is investigated and adopted in a SL system for the first time. The material curing characteristics with changing focal length and therefore changing light intensities are explored. The related digital mask image planning and process control methods are developed. In digital mask image planning, it is the first attempt to adopt the LDI algorithm, to identify proper resolution settings for fabricating a sliced layer precisely and quickly. In the process of characterizing material curing properties, parametric dependence of curing properties on focal length has been unveiled. This research contributes to the advancement of AM by addressing the historical dilemma of the resolution and build size, and optimizing the build speed meanwhile.

16MM FILMS ARE BECOMING AVAILABLE IN INCREASING numbers for training purposes and are now being produced in the UK specifically to serve the needs of the training officer. In addition to those being made on a commercial basis, many organisations, such as the National Coal Board, British Rail, ICI and British Oxygen, who make their own training films, are making them available to other users, whilst many of the several hundreds of industrial films sponsored each year have a direct or indirect training application. With their particular power to motivate and stimulate, to overcome barriers of time, space and distance and to slow down or speed up motion, to simulate direct experience and create understanding — with all these attributes, film has immense, but as yet largely unrealised, potential.

Marking and inspecting are key steps in hull structure construction. However, currently most marking and inspecting operations are still carried out manually, which leads to low assembly efficiency and quality. This paper aims to solve these problems through the application of digital technology: the optical projection and machine vision.

First, the assembly process model of hull construction is established in 3D design environment. Second, the process information is presented to workers in a virtual form through optical projector, which provides accurate guidance for the manual operation. On this basis, the workers can complete welding and assembly operations readily. Finally, the machine vision method is used to check the assembly results, which can decrease the subjective errors.

A rapid and accurate assembly positioning for hull structure construction is realized based on optical projection, which can avoid the pollution caused by the marking machine and the error caused by human.

This paper combines the advantages of optical projection and machine vision to the field of shipbuilding. The shortcomings of the traditional marking and inspection methods is effectively solved, which may provide a new way for enhancing the assembly efficiency and quality.

Tony Crocker, of the National Centre for Audio Visual Aids, reviews equipment trends

The nose radii of cutting inserts are normally measured using a profile projector or toolmaker's microscope. Since only a sector of a circle is available for the measurement using such instruments, the radii determined from these methods are inaccurate. The purpose of this paper is to present an alternative method of determining the nose radii more accurately using machine vision.

The 2D images of the cutting inserts were captured using a CCD camera with the aid of back lighting. The tool nose center in each digitized image was located based on the tool geometry. The curved nose profile was transformed into a linear profile using polar‐radius transformation. The nose radius was then varied within ten pixels of the nominal radius and the average deviation from a straight line profile in the nose region in the polar‐radius plot was evaluated. The radius corresponding to the minimum average deviation is identified as the most accurate radius value.

For the 15 simulated images of cutting inserts tested, the error in radii determine by the proposed method varied from −4.9 to 3.7 percent. But, the radii were about 9 to 22 percent higher than those measured using the profile projector on commercially available inserts. The radii measured using the profile projector was closer to the nominal radii with an average deviation of −3.2 percent compared to those measured using the proposed method.

The cutting inserts must be clean and free from dust particles when capturing the images; and the insert must be aligned accurately so that the plane of the nose profile is perpendicular to the optical axis of the CCD camera.

The proposed method can be used to determine the nose radii accurately. If the exact nose radius of an insert is known, the tool path can be programmed precisely to obtain high‐dimensional accuracy in the finished product.

The paper shows how a new method of determining the tool nose radii of cutting inserts more accurately compared to the conventional methods, based on a sector of the nose profile, has been developed.