Robotic Manufacturing Research Articles

How to minimize cycle times of robot manufacturing systems

The employment of industrial robot systems especially in the automotive industry noticeably changed the view of production plants and led to a tremendous increase in productivity. Nonetheless, rising technological complexity, the parallelization of production processes, as well as the crucial need for respecting specific safety issues pose new challenges for man and machine. Our goal is to develop algorithms, guidelines, and tools that make the commissioning of industrial robot systems more reliable by verifying the programs of robots and logical controllers. This in particular includes optimizing the schedule of the robot systems in order to ensure desired period times as well as conflict-free timetables already in the planning stage. The applicability of the Periodic Event Scheduling Problem proposed by Serafini and Ukovich (SIAM J Discrete Math 2(4):550–581, 1989) is investigated to tackle this cycle time minimization task, and we establish a variant of the classical formulation in order to cover the special characteristics of our scenario. We want to demonstrate how this key element forms a part of a range of developed software tools that support engineers and programmers throughout the commissioning of real-world robot production systems.

Deadlock-free Supervisor Design for Robotic Manufacturing Cells With Uncontrollable and Unobservable Events

In this paper, a deadlock prevention policy for robotic manufacturing cells with uncontrollable and unobservable events is proposed based on a Petri net formalism. First, a Petri net for the deadlock control of such systems is defined. Its admissible markings and first-met inadmissible markings (FIMs) are introduced. Next, place invariants are designed via an integer linear program (ILP) to survive all admissible markings and prohibit all FIMs, keeping the underlying system from reaching deadlocks, livelocks, bad markings, and the markings that may evolve into them by firing uncontrollable transitions. ILP also ensures that the obtained deadlock-free supervisor does not observe any unobservable transition. In addition, the supervisor is guaranteed to be admissible and structurally minimal in terms of both control places and added arcs. The condition under which the supervisor is maximally permissive in behavior is given. Finally, experimental results with the proposed method and existing ones are given to show its effectiveness.

Concurrent geometry- and material-based process identification and optimization for robotic CMT-based wire arc additive manufacturing

Additive Manufacturing (AM) is a novel manufacturing method where a component is fabricated by accumulating material layer-by-layer therefore facilitating customized near-net-shape components while maximizing design freedom. A metal AM technology suited for large-scale component fabrication that has been emerging in recent years and is commonly referred to as Wire and Arc AM (WAAM) uses Gas Metal Arc Welding (GMAW) technology to deposit material and large-scale robotic serial manipulator systems (reach >1 m cubed). One of the requirements for applying GMAW welding technology to AM is to identify and optimize deposition parameters in order to achieve a desired deposition quality measured in terms of geometrical, mechanical and metallurgical consistency. In this work, deposition process parameters qualitatively and quantitatively influencing the geometrical, mechanical and metallurgical consistency are identified and statistically validated. A deposition parameter combination is found that optimizes the quality of single-track wall benchmark components made from low-carbon steel. Moreover, correlations are found between accumulated heat during fabrication and the geometrical variations of the benchmark components due to bead slumping. Additionally, correlations between microstructure variations and geometrical variations are found. Finally, based on the presented analyses, in-situ temperature monitoring methods are proposed in order to achieve optimal component quality.

Robotic additive manufacturing with toy blocks

We develop and study a block-type three-dimensional (3D) printer that can assemble toy blocks based on 3D CAD models. Our system automatically converts a 3D CAD model into a block model consisting of toy blocks in basic shapes. Next, it automatically generates a feasible assembly plan for the block model. An industrial robot then assembles the block sculpture layer-by-layer, from bottom to top, using this assembly plan. This approach has advantages including the ease of combining multiple types of materials and reusing them which is difficult for conventional 3D printers to accomplish. We also introduce a technique to reliably determine the order of block placement to assemble block models from various patterns. This technique includes converting unassemblable shapes in the models to assemblable ones with support blocks and/or decomposing them into subassemblies. In addition, we implement a robot control system that automatically generates a stable sculpture according to a predetermined placement order. We also demonstrate the assembly of various toy block models using our system.

Additive manufacturing by means of parametric robot programming

3D printing or additive manufacturing (AM) is now becoming a common technology in industry. The research activities in this area are constantly increasing, because with the high level of automation and the possibility to produce individual and complex structures, the advantages of additive manufacturing are promising. Most materials used in the construction industry can be used for additive manufacturing, for example steel and concrete. The print head (for example, a welding torch in the AM of steel) is mainly led by industrial robots, whose movements must be transferred from the 3D geometry files to be manufactured. In contrast to all-in-one systems, where hardware, software and printed material are coordinated, most robot-based AM systems are made of components from different manufacturers and branches. The objects to be manufactured are complex and the manufacturing parameters, which significantly influence the geometry and quality of the manufactured part, are manifold. This makes the workflow from the 3D model to the finished object difficult, especially because it is almost impossible to predict the exact manufactured structure geometry or layer height (which would be indispensable for accurate slicing). During the manufacturing process, deviations between the target and actual geometry can occur. In this paper, parametric robot programming (PRP) is presented, which allows flexible motion programming, and a quick and easy reaction to deviations between target and actual geometry during the manufacturing process. Complex geometries are divided into iso-curves whose mathematical functions are determined by means of polynomial regression. The robot can calculate the coordinates to be approached from these functions itself. This allows a simple adjustment of the manufacturing coordinates during the process as soon as target–actual deviations occur. The workflow from the file to the manufactured object is explained. The principle of PRP is transferable and applicable to all robot manufacturers and all conceivable printing processes. In the following article, it will be presented using wire + arc additive manufacturing, in which welding robots or portals can be used to produce steel structures with high deposition rates. Furthermore, the project “AM Bridge 2019” is presented, in which a steel bridge was manufactured in situ over a little creek and the presented PRP was applied.

An integrated review of automation and robotic technologies for structural prefabrication and construction

AbstractBuilding construction has developed from the use of primitive tools to that of machinery, with a tendency toward automation. Automation of processes and robotics can improve efficiency, accuracy and safety in construction. On the other hand, structural prefabrication for construction is increasingly being adopted worldwide to enhance productivity and to alleviate the environmental impact of conventional construction processes. The combination and application of automation and prefabrication technologies may therefore introduce new developments to the construction industry. This paper provides a comprehensive review of the use of automation technology for structural prefabrication and construction, including recent developments, challenges and future trends. Five stages following the sequence of construction are proposed: design, construction management, robotic manufacturing, autonomous transportation and automatic structural assembly. The paper concludes that the widespread use of automation technology is preferable to structural prefabrication for construction, and that the design for robotic construction introduced through connection innovations may be beneficial as a means of avoiding complex operations and thus improving the efficiency of robotic assembly processes.

Online Process Monitoring Based on Vibration-Surface Quality Map for Robotic Grinding

In robotic manufacturing, the machining vibration can easily affect the quality of the processed surfaces due to poor stiffness and variable stiffness of the robot arm. It is important to monitor the processing quality. Therefore, an online process monitor method for robotic grinding is proposed in this article. Since the surface quality is difficult to be measured directly online, a vibration-surface quality map is proposed to show the mapping relationship between the vibration signals and the surface images. Based on this map, the grinding states are classified to lack, normal, and overgrinding, which formed the training set data. Then a convolutional neural network classifier is trained to detect the grinding states during robotic machining only with the vibration signals. To establish the vibration-surface quality map, the symmetrized dot pattern and sparse autoencoder methods are utilized to extract the features from the raw vibrations and images data, and a gray-level co-occurrence matrix index is further used to build the bridge between them. The experimental results in this article have proved the effectiveness and potential of our method for online robotic grinding quality monitoring.

Framework for Performance Assessment of Heterogeneous Robotic Systems

In a dynamic environment, a manufacturing system should be reconfigurable to make the products with lot size of one and a high product mix in mass customization. A manufacturing system is continuously evolved to make new products at different time scales and ensure uninterrupted productions when internal or external changes occur. System evolution relates to add, remove, upgrade components, and reconfigure the system at different levels and scopes. However, scientific methods and tools are lacking to support designers in reconfiguring a system subject to given changes. This becomes a big hurdle to adopt automated solutions in small- and medium-sized enterprises. To support system reconfiguration, we propose a generic framework and methods to assess the performance of heterogeneous robotic systems or components. The proposed methods can also help 1) designers to select components for an integrated solution based on the needs and 2) robot manufacturers to identify the weaknesses of their products.

A Theory of (Sexual) Justice: the roboethician's edition

Sex robots have been gaining significant traction in the media and in pop culture. Each new launch of an updated model or a new entrepreneurial innovation on the sex robot market was signaled and discussed at length in the media. Simultaneously, Hollywood productions and popular TV series have graphically illustrated and brought forth serious questions regarding human – sex robot relationship. Unsurprisingly, philosophical interest is already extensive, with a series of papers and books tackling a wide array of issues related to sexbots. The purpose of my paper is that of exploring one potential deployment of sex robots: as a solution for addressing claims of sexual justice. I will begin with a short overview of the debate regarding sex rights for people with disabilities and argue that a Rawlsian account of sexual justice is possible. One of the main claims of the paper will be that there might be a strong link between sex rights and Rawlsian primary goods. I will then argue that, from a Rawlsian framework, it makes sense to adopt an anthropocentric meta-ethical approach to human – sex robot interactions. In the last part of the paper, I will present and criticize the main objections that have been brought against the manufacture and selling of sex robots. Even assuming that the objections were correct, they do not hold in the case of the use of sex robots by people with mental or physical disabilities.

Hybrid calibration and detection approach for mobile robotic manufacturing systems

PurposeThe purpose of this paper is to present a visual detection approach to predict the poses of target objects placed in arbitrary positions before completing the corresponding tasks in mobile robotic manufacturing systems.Design/methodology/approachA hybrid visual detection approach that combines monocular vision and laser ranging is proposed based on an eye-in-hand vision system. The laser displacement sensor is adopted to achieve normal alignment for an arbitrary plane and obtain depth information. The monocular camera measures the two-dimensional image information. In addition, a robot hand-eye relationship calibration method is presented in this paper.FindingsFirst, a hybrid visual detection approach for mobile robotic manufacturing systems is proposed. This detection approach is based on an eye-in-hand vision system consisting of one monocular camera and three laser displacement sensors and it can achieve normal alignment for an arbitrary plane and spatial positioning of the workpiece. Second, based on this vision system, a robot hand-eye relationship calibration method is presented and it was successfully applied to a mobile robotic manufacturing system designed by the authors’ team. As a result, the relationship between the workpiece coordinate system and the end-effector coordinate system could be established accurately.Practical implicationsThis approach can quickly and accurately establish the relationship between the coordinate system of the workpiece and that of the end-effector. The normal alignment accuracy of the hand-eye vision system was less than 0.5° and the spatial positioning accuracy could reach 0.5 mm.Originality/valueThis approach can achieve normal alignment for arbitrary planes and spatial positioning of the workpiece and it can quickly establish the pose relationship between the workpiece and end-effector coordinate systems. Moreover, the proposed approach can significantly improve the work efficiency, flexibility and intelligence of mobile robotic manufacturing systems.

Spherical slicing method and its application on robotic additive manufacturing

This article presents a spherical slicing method for additive manufacturing (AM) which is used to lay additive layers on a spherical surface, thus removing the stair stepping effect, increasing structural integrity and tensile strength. A toolpath is required to guide the extruder in the three-dimensional space and deposit the material in the desired locations. These tool paths are computed using slicing algorithms. The well-established method in AM industry is the planar slicing. In this method, the Computer Aided Design model is sliced using planes and as a result, two-dimensional tool paths are formed. With the introduction of multi-axis AM machines, development of new non-planar slicing algorithms has started. In this article, a novel non-planar, spherical slicing, is introduced. In the proposed spherical slicing method, the model is sliced by spherical shells such as that of an onion. These spherical slices are then used to generate the appropriate tool paths for guiding the robotic manipulator in three-dimensional space together with the corresponding orientation to lay the spherical layers on top of the previously manufactured planar base. Results are verified by manufacturing a model using a six-axis robotic serial manipulator by fused deposition modeling.

THE USE OF THE TWO-HANDED COLLABORATIVE ROBOT IN NON-COLLABORATIVE APPLICATION

The article deals with possibilities of using of a two-handed collaborative robot in automated production. The introductory part of this paper is about robot manufacturers’ proposed ways of use of collaborative robots and a consideration of correctness of this stance. In this matter, an alternative point of view is proposed and tested, where a collaborative robot does not cooperate with a worker but replaces him/her completely. The main part of the study focuses on a specific installation of the YuMi collaborative robot into an already existing production line of a leading Czech supplier in the automotive industry. This real application is verified in simulations with an alternative solution consisting of two traditional industrial robots ABB IRB 120 instead. These data are evaluated and the advantages of deploying the collaborative robot and the industrial robots in the specific assembly application are compared. Economic return and productivity in high production cycle applications are considered. The article then describes the difficulties caused by the low load capacity of the YuMi collaborative robot and an alternative approach using the FEM methodology and topology optimization in the robot grip jaws design.

Interlayer closed-loop control of forming geometries for wire and arc additive manufacturing based on fuzzy-logic inference

Abstract The deposition process of wire and arc additive manufacturing (WAAM) is usually planned based on a bead geometry model (BGM), which represents the relationship between bead geometries (e.g. width, height) and required deposition parameters. However, the actual deposition situation may deviate from the one in which the BGM is built, such as varied heat dissipation conditions, resulting in morphological changes of deposited beads and geometrical errors in the formed parts. In this paper, a novel control mechanism for enhancing the fabrication accuracy of WAAM based on fuzzy-logic inference is proposed. It considers the geometrical errors measured on already deposited layers and deposition context to adjust deposition parameters of beads in the subsequent layer, forming an interlayer closed-loop control (ICLC) mechanism. This paper not only presents the theoretical fundamentals of the ICLC mechanism but also reports the technical details about utilizing this mechanism to control the forming height of multi-layer multi-bead (MLMB) components. A fuzzy-logic inference machine was applied as the core component for calculating speed change of bead deposition based on height error and previously applied change. In terms of validation, the effectiveness of the proposed control mechanism and the implemented controller was investigated through both simulative studies and real-life experiments. The fabricated cuboid blocks showed good accuracy in height with a maximum error of 0.20 mm. The experimental results implied that the proposed ICLC approach facilitates deposition continuity of WAAM, and thus enables process automation for robotic manufacturing.

A novel multi-brand robotic software interface for industrial additive manufacturing cells

A novel multi-brand robotic software interface for industrial additive manufacturing cells

Increasing deposition height stability in robotic GTA additive manufacturing based on arc voltage sensing and control

Abstract Robotic gas tungsten arc (GTA)-based additive manufacturing (AM) is a promising technique to produce high-quality and large-scale metal parts with low cost. Despite this fact, the key issue of ensuring deposition height stability has not been fully solved. In this study, an arc voltage sensing and control approach with little delay is proposed to increase the forming height stability in GTA-based AM. The deposition height stability is indirectly characterized by arc voltage signals sampled using a designed arc voltage detection system. A novel de-noising method, combining the anti-impulse interference moving average with the wavelet packet transform, is proposed to filter out interferences in the original arc voltage. A Fuzzy-PID controller is developed to control the arc voltage by adjusting the wire feed speed on next deposition layer. Constant parameter and closed-loop control experiments are compared via fabricating thin-walled parts. The more stable arc voltage and more excellent forming appearance in the closed-loop control test indicate that applying the arc voltage sensing and control system can greatly improve the forming height stability in robotic GTA-based AM.

Fabrication of metallic parts with overhanging structures using the robotic wire arc additive manufacturing

Abstract Robotic wire arc additive manufacturing (WAAM) technology has been widely employed to fabricate medium to large scale metallic components. It has the advantages of high deposition rates and low cost. Ideally, the deposition process is carried out in a flat position. The build direction is vertically upward and perpendicular to a horizontal worktable. However, it would be difficult to directly deposit complex parts with near horizontal ‘overhangs’, and temporary supports may be required. Thus, it is necessary to find an alternative approach for the deposition of ‘overhangs’ without extra support in order to simplify the deposition set-up. This paper proposed a fabrication method of producing metallic parts with overhanging structures using the multi-directional wire arc additive manufacturing. Firstly, based on the metal droplet kinetics and weld bead geometry, two different Gas Metal Arc Welding (GMAW) metal transfer modes, namely short circuit transfer and free flight transfer, were evaluated for the multi-directional wire arc additive manufacturing. Subsequently, the effects of process parameters, including wire feed speed (WFS), torch travel speed (TS), nozzle to work distance (NTWD) and torch angle, on the stability of positional deposition were investigated. Finally, the effectiveness of the proposed strategy was verified by fabricating three complex samples with overhangs.

Light‐Driven Liquid Crystalline Networks and Soft Actuators with Degree‐of‐Freedom‐Controlled Molecular Motors

AbstractDesign and fabrication of photomechanical soft actuators has attracted intense scientific interest because of their potential in the manufacture of untethered intelligent soft robots and advanced functional devices. Trifunctional and monofunctional polymerizable molecular motors are judiciously designed and synthesized. Novel light‐driven liquid crystalline networks (LCN) are prepared by crosslinking overcrowded‐alkene‐based molecular motors with different degrees of freedom into the anisotropic LCN. The photoisomerization and thermal helix inversion of light‐driven molecular motors are reversible when only the upper part of the molecular motor is linked to the network, endowing the LCN film with remarkable photoactive performance. However, photochemical geometric change of the light‐driven molecular motor does not work after crosslinking both the upper and lower part of the motor by polymer chains. Interestingly, it is found that the fastened motor can transfer the light energy into localized heat instead of performing photoisomerization. The light‐driven molecular‐motor‐based LCN soft actuators are demonstrated to function as a grasping hand, where the continuous motions of grasping, moving, lifting, and releasing an object are successfully achieved. This work may provide inspiration to the preparation of next‐generation photoactive advanced functional materials toward their wide applications in the areas of photonics, optoelectronics, soft robotics, and beyond.

The Ethical Dimensions of Public Opinion on Smart Robots

This article investigates public opinion about smart robots, with special focus on the ethical dimension. In so doing, the study reviews relevant literature and analyzes data from the comments sections of four publically available online news articles on smart robots. Findings from the content analysis of investigated comments suggest that public opinion about smart robots remains fairly negative, and that public discussion is focused on potentially negative social and economic impacts of smart robots on society, as well as various liability issues. In particular, many comments were what can only be called “apocalyptical”, suggesting that the rise of smart robots is a threat to the very existence of human beings, and that the replacement of human labour by smart robots will lead to deepening the socio-economic gap, and concentrating power and wealth in the hands of even fewer people. Further, public discussion seems to pay little attention to the debate on whether robots should have “rights”, or on the increasing environmental effects of the growth in robotics. This study contributes to the extant literature on “roboethics”, by suggesting a dendrogram approach to illustrate themes based on a qualitative content analysis. It suggests that smart robot manufacturers should ensure better transparency and inclusion in their robotics design processes to foster public adoption of robots.

Layer-by-layer generation of optimized joint trajectory for multi-axis robotized additive manufacturing of parts of revolution

This work focuses on additive manufacturing by Directed Energy Deposition (DED) using a 6-axis robot. The objective is to generate an optimized trajectory in the joint space, taking into account axis redundancy for parts of revolution produced with a coaxial deposition system. To achieve this goal, a new layer-by-layer method coupled with a trajectory constrained optimization is presented. The optimization results are theoretically compared to a non-optimized trajectory and a point-by-point optimized trajectory. The layer-by-layer generation of optimized trajectories is validated experimentally on a 6-axis robot using a PLA extrusion system. Experimental results show that the layer-by-layer trajectory optimization strategy applied to parts of revolution provides better geometrical accuracy while improving the efficiency of the manufacturing device compared to non-optimized solutions.

Shape Control of Lotus Leaf Induced by Surface Submillimeter Texture

AbstractAutomatic slant of lotus leaf achieving self‐motive unidirectional fluid transport is significant for self‐cleaning, decreasing load, enhancing respiration, and receiving more sunlight, which is the consequence of natural evolution. In this study, the mechanism of the automatic gradual slant process in its development is exposed and this function is successfully replicated. The special distribution of submillimeter papillae (SP) on the leaf surface generates anisotropic deflection and induces the leaf edge to warp asymmetrically. These effects shift the center of gravity, slant the leaf, and bend the petiole gradually, thereby guiding the liquid away from the surface with synergy effect. The behaviors of lotus leaf are realized with stimulus of temperature on artificial lotus leaf. This work uncovers a new theory for shape control of soft materials and opens up new horizons for artificial intelligence, flexible robot, flexible sensor, and membrane manufacture industry.