1,721,003 research outputs found
Modeling and control of flexible-link robotic systems
Get PDFThe scientic activity presented in this Ph.D. thesis deals with the modeling and control of flexible-link robotic systems. Nowadays, the industrial demand for high performances, high speeds and low energy consume has highlighted the need to develop lightweight manipulators and robots. However, their design and control result more difficult and challenging with respect to traditional rigid-link robotic systems mainly due to the flexibility of the arms.
In the first part of my Ph.D., the research activity has been focused on the modeling and simulation of flexible-link mechanism, using an Equivalent Rigid-Link System (ERLS) formulation. In recent years, the ERLS approach, firstly implemented together with a Finite Element Method (FEM) formulation, has been extended through a modal approach and, in particular, a Component Mode Synthesis (CMS) technique. This novel formulation allows a reduced-order system of equations to be maintained even when a fine discretization is needed. After an analysis of the state of the art about dynamic modeling of flexible-link mechanisms, a numerical comparison between the ERLS-FEM and the ERLS-CMS approaches has been conducted. A benchmark manipulator has been implemented and the results have been compared in terms of accuracy and computational effort under different input conditions. The discretization of the mechanism and the number of considered vibrational modes have been as well discussed.
In the CMS approach, a classical Craig-Bampton reduction has been adopted. However, this is not the only technique capable of reducing the number of degrees of freedom of flexible-link mechanisms. For this reason, further developments of the work have seen the implementation and comparison of different Model Order Reduction Techniques, which can be applied to different benchmark robotic systems in order to highlight their advantages and disadvantages.
The second part of this thesis is focused on cable-driven parallel robots, which are a special class of
flexible-link mechanisms in which flexible cables, rather than rigid links, are employed to actuate the end-effector. A particular class of cable-driven robots is given by cable-suspended parallel robots, which rely on gravity to maintain the cables taut. These mechanisms are characterized by large workspaces, hig velocities and payload-to-weight ratios and can be employed for several different tasks such as handling and moving loads, pick-and-place and building tasks.
In collaboration with University of Trieste (Italy), a novel design of cable-suspended parallel robot based on variable radius drums has been developed and experimentally validated. A variable radius drum is characterized by the variation of the radius along the spool. This device is used in the cable-driven manipulator to move the end-effector through a planar working area, using just two actuated joints. Experimental results demonstrate a good agreement with the theoretical model.
Another example of cable-driven robot has been studied during the months that I spent at the Wearable Robotic Systems (WRS) Laboratory, Department of Mechanical Engineering, Stevens Institute of Technology (Hoboken, NJ, USA). The device consists of a 3-degree-of-freedom, under-actuated, pendulum-like robot. The mechanism is capable of performing planar point-to-point motions in its dynamic workspace by means of two actuated joints only, using parametric excitation in a way similar to playground swings. The control system is based on a feedback linearization that allows the dynamics of the variable-length pendulum to be decoupled from the dynamics of the rotation of the end-effector. Adaptive Frequency Oscillators have been introduced to estimate the phase of the pendulum-robot in real-time and without delay. The device has been experimentally validated showing the feasibility of the design and good performances of the control architecture
3-D ERLS based dynamic formulation for flexible-link robots: theoretical and numerical comparison between the Finite Element Method and the Component Mode Synthesis approaches
Get PDFThe industrial demand for high-performance and low energy consume has highlighted the need to develop lightweight manipulators and robots. However, their design and control result more difficult with respect to rigid-link robotic systems mainly due to the structural flexibility of the arms. To this end, the Equivalent Rigid-Link System (ERLS) approach for 3-D flexible link robots has been developed and, in this work, is considered in its recent developments. In particular, two recently published 3-D Equivalent Rigid-Link System formulations are discussed and compared by means of numerical simulations to highlight their strengths and possible
weaknesses. The former deals with the Equivalent Rigid-Link System concept extension to spatial manipulators and robots through a Finite Element Method approach (ERLS-FEM), whereas the latter reformulates the model through a Component Mode Synthesis technique (ERLS-CMS). After the definition and discussion of the kinematic and dynamic equations, which account for the coupling between rigid-body and flexible-body motions, an extensive comparison is made. A benchmark manipulator is implemented and the formulations numerically compared in terms of accuracy and computational load under different input conditions
A Framework for Improving the Energy Efficiency and Sustainability of Collaborative Robots
No full textExperimental Analysis and Comparison of Friction Models Applied to the UR5e Robot
No full textIn robotics, achieving precise and efficient dynamic modelling is paramount for the integration of robotic systems in diverse applications. A fundamental aspect influencing the dynamic behaviour of a robot is the effect of friction. In this paper we experimentally analyze and compare several friction models applied to the UR5e robot, leveraging only the data acquired from the robot real-time interface. The main objective is to provide a thorough assessment of each model performance, examining its ability to accurately represent the robot dynamics. This research contributes to the refinement of friction modelling for the UR5e, offering valuable insights for enhancing the accuracy of the whole dynamic model and its energy consumption prediction capabilities
Comparison of Model Order Reduction Techniques for Flexible Multibody Dynamics using an Equivalent Rigid-Link System Approach
Get PDFIn this paper we present a comparison of different model order reduction techniques for flexible multibody dynamics.
In particular, we adopt a formulation based on a Equivalent Rigid-Link System (ERLS). This approach is suitable in
the case of large displacements and small elastic deformations and it allows the kinematic equations of motion to be
decoupled from the compatibility equations of the displacements at the joints. The ERLS approach, recently extended
through a modal formulation, is here implemented in combination with different reduction techniques, i.e. Craig-
Bampton, Interior Mode Ranking (IMR), Guyan, Least Square Model Reduction (LSMR) and Mode Displacement
Method (MDM). In order to assess the advantages and disadvantages of the different methodologies, these techniques
are applied to a benchmark mechanism under different input conditions, i.e. gravitational force and step torque input.
The accuracy of each reduced model is numerically evaluated through the comparison of computational time, the
behaviour in frequency domain and by means of vector correlation methods, i.e. the Modal Assurance Criterion (MAC),
the Cross-Orthogonality (CO) and the Normalized Cross-Orthogonality (NCO)
Airbrush robotic painting system: experimental validation of a colour spray model
No full textThis research is focused on developing a robotic painting
system for artistic and graphic applications by means of an anthropomorphic
robot equipped with an airbrush. Firstly, we introduce a mathematical
colour spray model, based on a radially symmetric Gaussian
distribution of colour intensity within the spray cone. Then, we present
an experimental characterization of colour intensity in a spot, by varying
the distance between airbrush and target surface and the spraying time.
The experimental results of this pilot study validate the paint intensity
model and provide the basis for further investigations
Anti-hedonistic mechatronic systems
Get PDFIn this paper the concept of anti-hedonistic mechatronic systems interacting with humans is discussed. Up to this time, people have used their creativity to design machines which could reduce human efforts (i.e. robots) or enhance the perceived pleasure (i.e. entertainment tools and virtual reality systems). Nowadays, new machines designed to prevent people from doing something are emerging. Examples are: intragastric balloons to prevent people from eating, timed cigarettes boxes to prevent people from smoking, bracelets to prevent people from nail biting, alcohol-testers connected to car starter to avoid driving under alcohol influence. The aim of this work is to present a survey about anti-hedonistic machines, providing general definitions and a possible classification. In particular a mechatronic system designed to motivate users to do push-ups exercises, by controlling the television energy supply, is presented
Cable-Based Robotic Crane (CBRC): Design and Implementation of Overhead Traveling Cranes Based on Variable Radius Drums
Get PDFIn this paper, we present a new family of overhead traveling cranes based on variable radius drums (VRDs), called cable-based robotic cranes (CBRCs). A VRD is characterized by the variation of the spool radius along its profile. This kind of device is used, in this context, for the development of a cable-robot, which can support and move a load through a planar working area with just two degrees of freedom. First we present the kinematic analysis and the synthesis of the geometry of a VRD profile. Then, the schema of a bidimensional horizontal moving mechanism, based on the VRD theory, and an experimental prototype of a three-dimensional CBRC are presented. The features of this wire-based overhead crane and an analysis of cables tensions are discussed. Finally, the performance of this mechanism is evaluated, demonstrating a deviation between the end-effector and the nominal planar surface of less than 1% throughout the whole working area
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