Search

This paper presents a low-cost pose measuring device capable of simultaneously measuring all six coordinates (3 translations and 3 rotations) of a rigid body with respect to a given reference frame. The proposed system consists of a mechanical chain of rigid bodies and two encoders. The mechanism is a spatial four-bar linkage system with a symmetrical Revolute-Spherical-Spherical-Revolute (RSSR) kinematic structure, where two encoders measure the rotation of the revolute joints. The mechanism is investigated theoretically and solved kinematically using a numerical estimation method. The uncertainty of the pose determination, caused by the repeatability of the sensors, is estimated, as well as the achievable measurement range. A low uncertainty is achieved by a suitable design of the proposed kinematic chain. The mechanism is easy to realize with low tolerances and the correct definition of the length of the links allows a quite large workspace. The system can be profitably used in the calibration of robots or multi-axis machine tools where the actual pose of the gripper or spindle must be measured over the workspace of the machine. An experimental prototype is described, and the first experimental results are reported. • Six-coordinate low-cost pose measuring device. • Simple RSSR kinematic structure, easy realized with high accuracy and low backlash. • Great linear and angular accuracy of about 1 ⋅ 1 0 − 5 [m] and 1 ⋅ 10−4 [rad]. • Useful for kinematic calibration of robots or multi-axis machine. [ABSTRACT FROM AUTHOR]

Modeless industrial robot calibration plays an important role in the increasing employment of robots in industry. This approach allows to develop a procedure able to compensate the pose errors without complex parametric model. The paper presents a study aimed at comparing neural-kinematic (N-K) architectures for a modeless non-parametric robotic calibration. A multilayer perceptron feed-forward neural network, trained in a supervised manner with the back-propagation learning technique, is coupled in different modes with the ideal kinematic model of the robot. A comparative performance analysis of different neural-kinematic architectures was executed on a two degrees of freedom SCARA manipulator, for direct and inverse kinematics. Afterward the optimal schemes have been identified and further tested on a three degrees of freedom full SCARA robot and on a Stewart platform. The analysis on simulated data shows that the accuracy of the robot pose can be improved by an order of magnitude after compensation. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the results of a research project whose aim is investigating, from both a theoretical and an experimental point of view, all the aspects connected to the optimal design and use of a 6 DoF draw-wire sensors based measuring system in the kinematic calibration of industrial robots context. One essential operation in calibration is the measurement of the pose of the robotic gripper in a predefined set of points inside the working space. For this purpose optical devices, like laser trackers, are usually employed due to their precision, although they are very expensive. Therefore, the study of a low-cost measuring system and the investigation of the reachable performances could represent a relevant outcome in the evolution of the calibration task. With this aim the design of a wire-sensors based measuring system was developed and applied to a six revolute degrees of freedom anthropomorphic robot. In a preliminary phase, with the aid of simulations tools, the measuring system was optimized to obtain isotropic accuracy and high sensitivity, while in the following experimental phase the same system was employed for the kinematic calibration of the robot, achieving an accuracy lower than the robot repeatability, which practically represents a physical limit. [Copyright &y& Elsevier]

This paper deals with the implementation of a hybrid force/velocity controller for the automatic edge following of two-dimensional unknown planar contours performed by an industrial robot manipulator. In particular, the authors address the problem of compensating the joint friction effects that have to be taken into account in the controller design in order to achieve a reasonable performance with regards to normal force and tangential velocity errors. For that reason, two model-based friction-compensation methods are compared: a static method, based on a previously identified model, and an adaptive method, where joint friction parameters are recursively updated. By means of an extensive experimental activity, it is shown that, in spite of its simplicity and despite the friction effects changing in time during the robot operations, the devised adaptive procedure obtains a high performance in different operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: Motion planning for free-flying robots can be quite complex due to the fact that any movement of the joints influences the position and the orientation of the spacecraft which carries the manipulator. Several studies have been carried out to plan joint trajectories which eliminate the effects of the dynamic disturbances. Approximate solutions to this problem have been proposed using the concept of the Disturbance Map. The authors have already studied this problem for the case of 2 DOF and 3 DOF planar robots connected with revolute joints developing an exact solution based on the concept of dynamic singularities. Aim of this paper is to extend the proposed methodology to the case of planar polar manipulators, analyzing the peculiarities of these robot arm configurations. A numerical procedure for the evaluation of zero disturbance trajectories is also presented and application examples are developed. The adoption of the proposed strategy improves the performances of spacecraft’s attitude control system. [Copyright &y& Elsevier]

Examines the use of different control strategies for the trajectory tracking control of an industrial selective compliance. Use of proportional-integral-derivative-based and sliding mode; Estimation of the dynamic model of the manipulator; Kinds of industrial robot.

• Smooth and efficient interpolation between different angular poses. • Singularity-free rotation interpolation algorithm. • C 2 angular motion generation. This paper proposes a new methodology for the interpolation of a given set of 3D rotation poses that have to be reached in successive times by preserving continuity in orientation, angular velocity and angular acceleration. The discussed algorithm ensures the generation of smooth angular trajectories without singularities. The distinctive features of the proposed approach are the straightforward formulation, the reduced computational burden and the lack of iterative procedures. The presented methodology has applications in the generation of spatial motion of mechanical systems (e.g. robotics, flying devices) or in 3D computer graphics. After a theoretical introduction, the proposed algorithm is compared with other methods available in literature and some possible applications are presented. [ABSTRACT FROM AUTHOR]

Identifies the number of accelerometers necessary to measure rigid body acceleration. Reasons for not applying accelerometer-based rotation; Number of accelerometers to measure angular velocity; Conditions for the sensor placement.

A wide variety of mechatronic products undergoes major changes to miniaturize them and integrate a larger number of functions. They require advanced technologies for their manipulation and assembly, that become even more challenging due to the different properties and tiny size of their components. Innovative devices are necessary to enable the automation of such operations, such as sorting and feeding systems able to singularize and deliver micro-parts precisely and reliably at high-speed. To this aim, an original "Store&Place device" was developed for micro-sphere singularization and deposition (Fontana et al., 2018) [3], based on the novel operating principle proposed in Fontana et al. (2017) [1]. A potential application of this device concerns the automatic rework of electronic components, more specifically the reballing of Ball Grid Array packages, that basically consists in restoring their electrical connection to the board by attaching new solder balls. When the release of a single solder ball is commanded, the device singularizes it from a storage of identical balls and places it onto the corresponding circular land on the package. The paper presents the assessment of the device performance resulting from a structured experimental analysis on the manipulation of micro-spheres with diameter of 300 μm. It was applied to highlight the main process parameters influencing its performance, optimize them, and enhance the tool use. The performance indices to quantitatively evaluate the precision of the micro-sphere release were calculated according to Ruggeri et al. (2019) [5], and merged with other indices related to the reliability of the release and the time needed to execute it. • Experimental analysis of the parameters influencing the device release performance. • Maximum throughput of 1.66 spheres/second to achieve 100% reliability. • Precision is more influenced by the release height than pressure and vacuum values. • Best precision with the lowest pressure and vacuum values and null release height. • Best repeatability of 62.9 μm and accuracy of 10.7 μm for micro-spheres of 300 μm. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a new model for joint dynamic friction of industrial robot manipulators is presented. In particular, the effects of the temperature in the joints are considered. A polynomial-based model is proposed and the parameter estimation is performed without the need of a joint temperature sensor. The use of an observer is then proposed to compensate for the uncertainty in the initial estimation of the temperature value. A large experimental campaign show that the model, in spite of the simplifying assumptions made, is effective in estimating the joint temperature and therefore the friction torque during the robot operations, even for values of velocities that have not been previously employed. [ABSTRACT FROM AUTHOR]

The paper presents an integrated approach to suspension design with educational purposes. A dedicated design tool was created to instruct automotive engineering students in the whole process of suspension design across the various CAE tools involved, from early kinematics studies to CAD, vehicle dynamics simulations and FEM modelling. The tool has given birth to a proven design procedure that the authors would like to share in this paper with focus on the educational side, although suspension kinematics design is not certainly a novel subject in itself. The tool includes geometries like the widely used McPherson strut, complex five-link schemes for high-end road cars, and typical racing car geometries like the so-called push/pull rod systems used on Formula 1 and Le Mans racecars. It has been applied successfully to various projects developed by professionals as well as by students, including the latest three Formula SAE (FSAE) single-seaters of the University of Brescia (Brescia, Italy) team. The paper is structured as follows. The introduction describes the role student design competitions play in higher engineering education, and within the frame of the Automotive Engineering course at UniBS in particular. A selection of relevant bibliography on the topic is listed. The Educational scenario section deals with the specific case of the Automotive Engineering course at UniBS and the requirements posed by student competitions, also in the frame of the Dublin Descriptors, and shows how suspension design can play a pivot role in a FSAE project. The A tool for suspension kinematics: requirements, description, solution section presents the software tool in itself. The math underlying the user interface is outlined. Finally, the integration features towards other CAE tools are presented with the related advantages. [ABSTRACT FROM AUTHOR]

A non-overconstrained three-DOF parallel orientation mechanism that is kinematically equivalent to the Agile Eye is presented in this paper. The output link (end-effector) of the mechanism is connected to the base by one spherical joint and by another three identical legs. Each leg comprises of, in turns from base, a revolute joint, a universal joint, and three prismatic joints. The three lower revolute joints are active joints, while all other joints are passive ones. Based on a special configuration, some three projective angles of the end-effector coordinates are fully decoupled with respect to the input actuated joints, that is, by actuating any revolute joint the end-effector rotates in such a way that the corresponding projective angle changes with the same angular displacement. The fully decoupled motion is analyzed geometrically and proved theoretically. Besides, the inverse and direct kinematics solutions of the mechanism are provided based on the geometric reasoning and theoretical proof. [ABSTRACT FROM PUBLISHER]

The selection of a motor-reducer unit in electrical servo-systems has a profound impact on the dynamic performance of a machine. This choice must be made considering all the limits imposed by each component of the system and all the operational constraints. This article proposes a useful and practical methodology for the correct sizing of a motor-reducer unit. The relationships between motor and transmission are investigated by introducing some easily calculated factors useful for comparing all the available motor-reducer couplings and selecting the best solution. The article suggests an innovative approach for the selection of a motor-reducer unit that involves solving the problem with the use of graphs that would allow showing all the possible alternatives. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new method, which is based on an iterative-learning-control (ILC) algorithm, for the contour tracking of an object of unknown shape performed by an industrial robot manipulator. In particular, we consider (both implicit and explicit) hybrid force/velocity control whose performance is improved by repeating the task. Here, a time-based reference signal is not present, and therefore, a new approach has been developed, which is different from the typical applications of ILC. Experimental results show the effectiveness of the technique. [ABSTRACT FROM AUTHOR]

The article presents the study of the pedalling rates obtained by minimizing a cost function based on a kinetic approach and which can be estimated with more easily achievable experimental data as input than other cost functions. Simulations based on data available in the literature were used to compare the cadences obtained by minimizing well-known joint moment-based cost functions and the proposed cost function. The influence of the power output and of the body mass index on the pedalling rates that minimize the cost function was investigated. Experimental tests performed by four competitive cyclists in the field were used as comparison for the results based on simulations. From simulations emerged that results obtained with the cost function proposed in this work were similar to those based on the absolute average joint moments. We found that the upper limit of the more convenient pedalling rate range decreases linearly with the body mass index, while it increases non-linearly with power output. Furthermore, a polynomial regression of the correlation of the pedalling rate obtained through the method and body mass index and power was found. Experimental results confirmed that the proposed model, finding an approximation of the minimum of muscular effort (not including negative muscular work), is able to estimate the upper limit of an optimal range of cadence. All tested cyclists freely choose to pedal at a cadence under this limit. [ABSTRACT FROM AUTHOR]

SUMMARY: Cladding through laser metal deposition is a promising application of additive manufacturing. On the one hand, industrial robots are increasingly used in cladding because they provide wide wrist reorientation, which enables manufacturing of complex geometries. On the other hand, limitations in robot dynamics may prevent cladding of sharp edges and large objects. To overcome these issues, this paper aims at exploiting the residual degrees of freedom granted by the cladding process for the optimization of the deposition orientation. The proposed method optimizes the robot head orientation along a predefined path while coping with kino-dynamic constraints as well as process constraints. Experimental tests and results are reported and used to validate the approach. [ABSTRACT FROM AUTHOR]