Simulation of light sources using photometric data can result in realistic scenes which is necessary in many applications such as planning autonomous visual inspection. However, most computer graphics softwares like Blender are not capable of doing simulations for luminaires that are non-point sources, like bar or ring lights. Since a wide variety of non-point lights are being used in the real world, filling the existing gap, and simulating them is a valuable step. In the present paper, a method is presented to model the light texture of a bar light using multiple point lights. The proposed method is evaluated in DIALux which is a lighting software with accurate light calculations. By utilizing multiple sets of point lights in the simulations, the proper number of point lights for the luminaire based on the application requirements is studied. After showing the feasibility, the method is implemented in Blender software and the simulation results are compared with DIALux software to confirm the applicability of the method in Blender. Moreover, a rough light calculation method based on exposure values and false color representation is studied for Blender software and evaluated with results of DIALux which can result in a useful index for some applications.
This work investigates the force-moment capabilities of different redundant-actuation configurations for planar-parallel manipulators. A previously developed methodology for determining the force-moment capabilities of redundantly-actuated parallel manipulators using optimization and scaling factors is employed. The preliminary results show that different, symmetric redundant-actuation schemes yield substantial variations in the force-moment capabilities for the three-branch, three-revolute joints per branch (3-RRR) manipulator. Configurations where all base and wrist joints are actuated or all elbow and wrist joints are actuated yielded better force-moment capabilities when compared to the actuation configuration where all base and elbow joints are actuated. The biggest difference in terms of force-moment capabilities was found to be the maximum moment that could be sustained. The actuation configuration where all base and elbow joints were actuated yielded the lowest maximum moment that could be sustained.
Mobile-manipulator systems (MMS) are extremely useful tools in teleoperation tasks. However, the current command strategy is strenuous and difficult and requires extensive training. A new command strategy is presented where control of the entire MMS is done using a single joystick. Rather than modeling the system as a redundant manipulator, control of the manipulator and mobile base is decoupled. In two separate states, the operator either controls the manipulator or the base. The system automatically switches between states based on the configuration of the manipulator. Testing is performed using the Omnibot MMS, a holonomic platform with a 3-DOF manipulator. The results showed that less time is required for completion of the tasks. In addition, the tasks are completed with greater accuracy and lower power consumption. Operators who used the system agreed the new command strategy was easier and more intuitive.
Inspections of pressure tubes in CANDU® reactors are a key part of maintaining safe operating conditions. The current inspection system, the channel inspection and gauging apparatus for reactors (CIGAR), performs the job well but is limited by the fact that it can only inspect one channel at a time. A multidisciplinary team is currently developing a novel robotic inspection system. As part of this work, a Monte Carlo N-particle (MCNP) model has been developed in order to predict the dose rates that the improved inspection system will be exposed to and, from this, predict the component lifetime. This MCNP model will be capable of predicting in-core dose rates at any location within the reactor, and as such could be used for other situations where the in-core dose rate needs to be known. Based on estimates from this model, it is expected that at 7 days after shutdown, the improved inspection system could survive in core for approximately 7 h, providing it uses a tungsten shield 2.5 cm in thickness around the integrated circuit components. This is expected to be sufficient to perform a single inspection.
Advanced robotic systems are expected to be smartly reconfigurable to adapt to new needs for versatile operations in rapidly changing unknown, uncertain environments. The evolution has led to worldwide research interest in developing reconfigurable mechanisms and robots as intelligent-mechanical systems which have the ability to change their mobility, configurations, kinematics, and dynamics performance for various application scenarios in industrial automation, healthcare, space, field exploration, maintenance, domestic operations, human assistance, and augmentation. This Special Section features 14 papers that highlight the latest theories, designs, analyses, and deployments of reconfigurable mechanisms and robots with contributions from papers presented in the IEEE/IFToMM International Conference on Reconfigurable Mechanisms and Robots (ReMAR 2021) [1] as well as an Open Call for Papers.Mechanism and robot reconfiguration stems from geometric constraint changes based on innovative design and control operation. Systematic design synthesis theory and use-oriented design methodologies are critical to generating more reconfigurable mechanism and robot concepts. Reconfiguration has been extended from basic reconfigurable joints and linkages, to various mechanisms, and to various robot functions including ground mobile motion, flying navigation, manipulation, soft robotics, and sensing interaction. Fundamental modeling and analysis of those newly developed designs are the basis to verify the reconfiguration process and guide application-based development with experimental validation. In this special issue, reconfiguration highlights numerous exemplars in the form of modular manipulators, deployable linkages, reconfigurable grippers, origami mechanisms, and reconfigurable parallel mechanisms with both rigid links and cable-driven designs.Modular design enables flexible manipulator design and reconfiguration. Ju et al. present a cable-driven manipulator with a lightweight and expandable structure based on a modular U-joint unit for flexible environment adaptability. A fast heuristic inverse kinematics model is developed for the hyper-redundant system and provides a reference solution for other reconfigurable redundant designs. A similar modular cable-driven continuum arm is developed by Sitler and Wang for free-floating underwater manipulation onboard a remotely operated vehicle (ROV). In addition to the flexible arm design based on the modular unit, a reconfigurable dual arm configuration is also realized for crawling gait, dexterous, and seafloor manipulation. Modular units-based serial chain arm could be redundant and self-reconfigurable, requiring intensive dynamic calculations in simulation. To reduce the computational load, Fass et al. present a general novel analytical approach to formulate the Newton–Euler dynamics of self-reconfigurable chains in a single vectorized differential equation which enables efficient parallel computing.Reconfigurable linkages provide a fundamental basis for mechanism reconfiguration in a wide range of application scenarios. Tang et al. present a novel quadruped robot using a single-loop metamorphic mechanism to enable the ability of transforming between different working modes. This paves the way for developing versatile mobile robots using reconfigurable linkages. By applying Hoberman’s linkage as the modular design, Zhang et al. present a snake-inspired swallowing robot that can synchronously deploy and fold both axially and radially. The work creatively demonstrates an application of reconfigurable linkages in bio-inspired robot designs. To match demands of rapid development in the automotive industry, Lyu et al. present a reconfigurable modular fixture with high modularity and flexibility. The design method has a potential in generating more flexible fixture systems in industrial applications with frequent object size changes.Robot grasping requires high flexibility and adaptability in interacting with objects of various sizes and geometry. Sun et al. propose a reconfigurable robotic gripper based on a metamorphic finger mechanism which can have both expanding and grasping functions. The work expands reconfigurable mechanism applications into robotic grippers aiming at improving object grasping performance. To have an adaptable grasping function, soft materials are applied to gripper designs. However, their grasping force is generally low. To solve this problem, Cheng et al. introduce a limiting fiber into a soft finger design which largely increases the grasping force capacity and bending response speed. The method can be applied to similar soft robotic designs.Origami designs are a kind of reconfigurable mechanisms based on their folding/unfolding functions. Combining with a hydraulic power source, an origami actuator is developed by Liu et al. and integrated into a 6DOF Stewart-Gough parallel mechanism to realize translational and rotational motions. The design shows potential to be implemented in constructing dexterous and lightweight soft robotic applications. To quantify and improve folding reliability of origami systems, Liu et al. propose a biasing method to model the folding process through the origami hyperbolic paraboloid (hypar) when folding into one of two possible configurations. The results show an increased folding accuracy from 50% to 70% and provide insights for folding reliability analysis in more complex origami patterns with various reconfigurations.Reconfigurable parallel mechanisms can change their output motion types through constraint singularity, reconfigurable joints, re-assembly, or reconfigurable base/platform and links. The first three methods are demonstrated by three papers in this Special Section. Ye et al. present a new reconfigurable parallel mechanism that can reconfigure into 1R2T and 2R1T operation modes through a constraint singularity when the platform is parallel to the base. Zhao et al. present unified kinematics and dynamics modeling of a n(3RR1S) reconfigurable manipulator based on the principle of recursive virtual power. The work provides a method for solving high-redundant series-parallel systems with reconfigurable parallel modules for potential space object grasping applications. Through module re-assembly, Feng et al. investigate all possible non-isomorphic configurations of a reconfigurable hexapod robot using Pólya enumeration theorem. The method is applicable for other similar reconfigurable robot and mechanism designs using modular combinations.Cable-driven parallel robots (CDPRs) with movable anchor points can reconfigure into infinite configurations for flexible manipulation tasks with the anchor points attached to mobile ground or aerial vehicles. To solve their real-time planning, Xiong et al. present a dynamic control method through a reconfiguration value function, which is defined to value possible RCDPR configurations for optimal selection and planning. The developed method creatively treats the planning problem as a reconfiguration model and can be extended to other similar mobile robot planning tasks.We hope this Special Section will contribute to the research on reconfigurable mechanisms and robots as a key trend in mechanisms and robotics. We would like to show our great thanks to the general chair of ReMAR 2021, Professor Fengfeng Xi, and to the Editor-in-Chief, Professor Venkat Krovi, for his guidance and huge support throughout the whole process. We are also grateful to the journal administrative team and all the authors and reviewers for their valuable support and contributions.
Series elastic actuators with passive compliance have been gaining increasing popularity in force-controlled robotic manipulators. One of the reasons is the actuator's ability to infer the applied torque by measuring the deflection of the elastic element as opposed to directly with dedicated torque sensors. Proper deflection control is pinnacle to achieve a desired output torque and, therefore, small deviances in positional measurements or a nonlinear deformation can have adverse effects on performance. In applications with larger torque requirements, the actuators typically use gear reductions which inherently result in mechanical backlash. This combined with the nonlinear behaviour of the elastic element and unmodelled dynamics, can severely compromise force fidelity.This paper proposes a backlash compensating active disturbance rejection controller (ADRC) for multi-input series elastic actuators. In addition to proper deflection control, a multiinput active disturbance rejection controller is derived and implemented experimentally to mitigate any unmodelled nonlinearities or perturbations to the plant model. The controller is experimentally validated on a hybrid motor-brake-clutch series elastic actuator and the controller performance is compared against traditional error-based controllers. It is shown that the backlash compensated ADRC outperforms classical PID and ADRC methods and is a viable solution to positional measurement error in elastic actuators.
In this research, autonomous inspection of steel pipe weld lines for a single class of defects is done using a frequency analysis combined YOLOv5 (You Only Look Once) model.Since steel pipes are vastly implemented in high-risk applications, it is essential to accurately inspect them for defects.A new method is presented to enhance the training process of YOLOv5 using frequency analysis.Two YOLOv5 models are trained using frequencymodified and original images, and the results and training process of these two models are compared.In order to produce frequencymodified images, the first 50 frequencies are removed from the Fourier transform, resulting in a new image set.Results revealed that removing lower frequencies leads to more smooth behavior in indices of the YOLOv5 model during different epochs and reduces training time by 15%.I.
A quasi-Newton optimization routine and Grashof criteria for geared five-bar mechanisms are used to develop a Grashof five-bar mechanism synthesis routine. Sequential transformations mapping Grashof mechanism parameters satisfying sub-type specific upper and lower constraints are used. Convergence criteria of: (i) objective function value change, (ii) mechanism parameter change, and (iii) task satisfaction are used. These criteria, combined with search restarts, ensure the synthesis of an acceptable mechanism. Example results demonstrate the effectiveness of the routine.
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