Henrique Simas

The dynamic performances of an innovative robotic total station (RTS) are assessed while tracking a moving target; also, the results of these performance evaluations are exploited to design its control system. The proposed methodology is novel and uses ad hoc virtual experiments implemented on the digital twin of the studied RTS. This methodology is general and is also applicable for the design of other mechatronic systems. The proposed ad hoc virtual experiments constitute a benchmark for assessing the tracking performances of pointing systems. The application of this methodology to the studied RTS will help complete the RTS’s design by determining the most suitable actuators and the control system constants necessary to obtain the assigned dynamic performances. A 3D-printed prototype of the designed RTS was built and is shown in this paper.

Robotic Total Stations (RTS) are fully automated theodolites with electronic distance measurement (EDM) that include a number of additional tools (e.g., camera, laser rangefinder, onboard computer, and tracking software, etc.) enabling them to work autonomously. The added tools make RTSs able to track mobile targets on civil structures thus opening to the use of RTSs in structural monitoring. Unfortunately, the available RTSs are able to track a target up to a motion rate of 3 Hz. Reducing mobile masses is a viable design strategy for extending this frequency border. Such a strategy is pursued in this study by proposing the use of parallel pointing systems (PPS) as basic mechanical architectures for RTSs. The literature on PPSs is reviewed and the applicable PPS architectures are selected. Successively, the selected architectures are sized according to RTSs’ functional requirements, and the positioning precision of the sized mechanisms is evaluated. The result of this study is that there are three PPS architectures suitable for RTSs, whose detailed comparison is also presented.

Product assembly is the final step in a manufacturing process where the individual components of a product are joined together. Assembly sequence planning (ASP) can be defined as the problem of finding a collision-free sequence of operations that allow the product assembly. Considering that during assembly individual modules cannot pass through a gap only as large as a module side, the ASP problem can be extended to modular robots, more specifically to rectangular modular robots. The main ASPs presented in the literature that are applicable to rectangular modules do not allow configurations with narrow corridors, i.e., corridors which are too narrow for a robot to transverse. Furthermore, these ASPs do not allow preassembled substructures or the free selection of the assembly starting point. Thus, the main goal of this work is to extend the classes of rectangular modular robot configurations that can be assembled without violating the accessibility condition. This paper introduces three novel ASP for constructing planar target structures composed of rectangular modular robots. Each ASP is adequate for a different scenario. Original implementation results and mathematical proofs for the three novel ASPs are also presented. To the best of the authors’ knowledge, this is the first work that presents, considering the accessibility condition, how to obtain centralized ASPs for assembling planar structures composed of rectangular modules with narrow corridors. Furthermore, the novel ASPs allow structures composed of subsets of preassembled modules and configurations with internal holes. They also allow the choice of the assembly starting point. Moreover, the third ASP proposed in this work allows achieving discontinuous assembly paths, i.e., wherever possible, the ASP allows a novel module to not connect to the latest added robot.

3-XXRRU parallel manipulators (PMs) constitute a family of six-degrees-of-freedom (DOF) PMs with three limbs of type XXRRU, where R and U stand for revolute pair and universal joint, respectively, and XX indicates any actuated two-DOF mechanism that moves the axis of the first R-pair. The members of this family share the fact that they all become particular 3-RRU structures when the actuators are locked. By exploiting this feature, the present paper proposes a general approach, which holds for all the members of this family, to analyze the instantaneous kinematics, workspace, and kinetostatic performances of any 3-XXRRU PM. The results of this study include the identification of singularity conditions without reference to a specific actuation system, the proposal of two specific dimensionless performance indices ranging from 0 to 1, the determination of the optimal actuation system, and the demonstration that 3-XXRRU PMs, when appropriately sized and actuated, possess a broad singularity-free workspace that is also fully isotropic. These findings hold significance in the context of the dimensional synthesis and control of 3-XXRRU PMs. Moreover, when combined with the closed-form solutions for their positional analysis, as demonstrated in a previous publication by the same authors, 3-XXRRU PMs emerge as intriguing alternatives to other six-DOF PMs. The efficacy of the proposed approach is further illustrated through a case study.

This study addresses the development of smart neural sensors to predict the powder mass flow and track clogging in real time during laser cladding. The challenges posed by powder granulometry and challenging environmental conditions that can lead to delivery failures are considered. An extensive experimental setup was conducted that included manipulation of key factors, such as laser power, travel speed, Z-step, N-layers, nozzle-to-substrate distance, and two types of process patterns. The mass flow rate of the powder was used as an independent variable to evaluate the predictive ability of the neural sensor with respect to the mass flow rate. Several models were trained and evaluated with different datasets and images of the cladding equipment. The model that integrated all data and images showed the best accuracy and precision also showed a strong predictive power for real-time estimation of the powder mass flow rate. Considering two practical rules—an error detection time of no more than one second and a confidence interval of less than 1.8 g/min—two strategies were proposed to meet these criteria. The first recommends the use of the comprehensive “all-features” model, while the second proposes a simplified model (with Z-step, N-slices, and the external camera as inputs) for efficient real-time error detection. The study provides an understanding of powder clogging prediction in laser cladding and suggests strategies for leaders in the field. Future research should validate these results and test these models in different environments to predict complex cladding properties and support the development of stand-alone laser cladding systems.

Geometric Design and Tolerancing (GD&T) is the language that specifies several design features and, in this paper, is used to deal with the tolerances of Translational Parallel Manipulators (TPMs). TPMs intend to make a platform have only translational motion with respect to the frame (base), but, in practice, TPMs’ platforms present undesirable rotation motions due to unavoidable geometric errors in links’ sizes. During the machine-element design, geometric errors can be limited by imposing given tolerances on links’ sizes and the tighter tolerances are the higher manufacturing costs are. Therefore, dealing with tolerances is the key for designing a TPM with assigned requirements in terms of platform’s rotation limits. In this context, this paper moves from the fact that machining processes generate link sizes with values distributed according to Gaussian distributions, whose mean values are the nominal sizes and whose standard deviations depend on the machining process accuracy, to build a novel method that makes a designer able to satisfy an assigned maximum orientation error on the TPM platform. The proposed method consists of two main phases: (a) identification of the geometric parameters that affect platform’s position and orientation, and (b) an analysis, based on numerical simulations, that relates the tolerances assigned to the identified parameters and the positioning precision of the platform. The method can be adapted to other types of lower-mobility robots (LMRs). A case study is also discussed to better illustrate the method.

Anais do XXV Colóquio de Usinagem (978-65-272-0075-8) - Usinagem Robotizada: Análise Da Capacidade De Forças De Robôs Cooperativos