196,009 research outputs found
Optimization of a Rotary Part Feeder with Circular Blades
No full textPart feeding can be a source of inefficiencies in kitting operations: in common applications, hoppers are used to batch parts, but such hoppers require a double motion for each operation. In previous works, a rotating feeding device has been proven to be more efficient than hoppers, . This rotating device uses blades to compartmentalize parts, and such blades can be optimized to achieve specific design goals. In this paper circular blades are investigated due to their ease of manufacturing, and results show how this shape is suitable for the required design goals
DEVELOPMENT OF A HYBRID HARVESTER FOR COLLECTING ENERGY FROM WIND AND VIBRATIONS IN LIGHT VEHICLES
No full textA bicycle experiences road-excited vibrations and is impacted by a wind flow. Both these phenomena can be exploited for energy harvesting. Previous research showed that the tuning of the harvester to road-excited vibrations requires a low natural frequency that can be achieved by means of a large tip mass. This tip mass can be used to equip the harvester with a bluff body for energy harvesting from wind-excited vibrations. The interaction between the bluff body and the wind flow generates a vortex shedding phenomenon that at a certain wind velocity is able to excite the harvester in resonance condition. Moreover, the turbulence of the incoming wind is able to excite the bluff body in the high velocity range (buffeting excitation). The paper deals with mathematical and experimental analyses for the development of a hybrid piezoelectric harvester able to scavenge energy from road-excited vibrations and wind. A multi-physical mathematical model that takes into account the couplings between the mechanical, electrical and fluid domains is developed. The coupled equations are solved in Matlab and are used for the harvester design. Two prototypes are developed and tested. The results of experimental tests carried out in a wind tunnel and in open space show the potentialities of the proposed harvester layout
Design and Analysis of a 5-DOF Dynamically Balanced Serial Robot with Variable Payloads
No full textRobotic manipulators are indispensable tools in various industrial contexts and play critical roles in remote operations. However, conventional manipulators often lack dynamic balance, which means that when they move from one location to another they exert shaking forces and moments on the robot base. However, for many applications the zeroing of the shaking forces and moments is required, therefore the robot has to be designed to be dynamically balanced. Furthermore, this becomes more challenging when it comes to maintain balance under varying loads. In this paper, a -degree of freedom (DOF) dynamically balanced robot able to guarantee perfect balancing also in the presence of a variable payload is proposed. The design of the -DOFs robot is explained and then numerical results are reported to show the validity of the proposed system. The robot is simulated in a low-gravity environment and successful demonstrations of a pick and place operation are carried out considering an unilaterally constrained base
Vibration Energy Harvesting from Plates by Means of Piezoelectric Dynamic Vibration Absorbers
No full textIn this paper, the possibility of harvesting energy from the vibrations of a plate is analyzed. The harvester takes the form of a cantilever dynamic vibration absorber equipped with a piezoelectric layer and tuned by means of a tip mass to the first mode of vibration of the plate. A mathematical model of the coupled system composed of the plate and the harvester is presented. The validity of the proposed harvester is proved by means of simulations carried out with the modal expansions approach. Simulation results highlighting the effects of harvester tuning and location are presented as well. Then, the validity of the harvester is confirmed by experimental tests carried out both with a concentrated impulsive load and with a distributed pressure load. Simulations and experimental tests are performed on the cantilever piezoelectric dynamic vibration absorber and on the same piezoelectric layer directly bonded to the plate surface. Results show an improvement in terms of generated voltage when the proposed novel device is used in place of the simple layer
Motion Planning of Differentially Flat Planar Underactuated Robots
No full textDifferential flat underactuated robots have fewer actuators than degrees of freedom (DOFs). This characteristic makes it possible to design light and cost-effective robots with great dexterity. The primary challenge associated with these robots lies in effectively controlling the passive joint, in particular, when collisions with obstacles in the workspace have to be avoided. Most of the previous research focused on point-to-point motions without any control on the actual robot trajectory. In this work, a new method is presented to plan trajectories that include one or more via points. In this way, the underactuated robot can avoid the obstacles in the workspace, similarly to traditional fully actuated robots. First, a trajectory planning strategy is analytically described; then, numerical results are presented. The numerical results show the effects of the via points and of the order of the polynomials adopted to define the motion laws. In addition, experimental tests performed on a two-DOF underactuated robot are presented, and their results validate the proposed method
SIMPLIFIED MODEL FOR DYNAMIC ANALYSIS OF ROBOTIC MANIPULATORS
No full textThe dynamic analysis of robotic manipulators is a well-known problem, but very often the inertia tensors of the links are unknown and the computational complexity is high. Tliis paper introduces a simplified approach, based on the use of a limited set of lumped masses placed along the joint axes, which provides an efficient and sufficiently accurate estimation of joint torques, linear momentum, and kinetic energy along a given trajectory. One of the main advantages brought by this approach is that its implementation does not require the knowledge of the inertia tensors of the links. Compared to traditional methods, the proposed approach offers a good balance between accuracy’ and complexity, since the normalized root mean square error (NRMSE) in kinetic energy is lower than 3% with a consistent reduction in computation time (8%). Tlierefore, it is a valuable tool for the design and control of robotic manipulators in a wide range of industrial and service applications. Moreover, the quick calculation of linear momentum and kinetic energy is useful for the prediction of collision severity. The detailed description of the proposed method is completed with numerical simulations dealing with three different robotic manipulators
Oscillation-free point-to-point motions of planar differentially flat under-actuated robots: a Laplace transform method
No full textDifferentially flat under-actuated robots are characterized by more degrees of freedom (DOF) than actuators: this makes possible the design of lightweight cheap robots with high dexterity. The main issue of such robots is the control of the passive joint, which requires accurate dynamic modeling of the robot. Friction is usually discarded to simplify the models, especially in the case of low-speed trajectories. However, this simplification leads to oscillations of the end-effector about the final position, which are incompatible with fast and accurate motions. This paper focuses on planar n-DOF serial robotic arms with n − 1 actuated rotational joints plus one final passive rotational joint with stiffness and friction properties. These robots, if properly balanced, are differentially flat. When the non-actuated joint can be considered frictionless, differentially flat robots can be controlled in open loop, calculating the motor torques demanded by point-to-point motions. This paper extends the open-loop control to robots with a passive joint with viscous friction adopting a Laplace transform method. This method can be adopted by exploiting the particular structure of the equations of motion of differentially flat under-actuated robots in which the last equations are linear. Analytical expressions of the motor torques are obtained. The work is enriched by an experimental validation of a 2-DOF under-actuated robot and by numerical simulations of the 2- and 4-DOF robots showing the suppression of unwanted oscillations
Influence of Joint Stiffness and Motion Time on the Trajectories of Underactuated Robots
No full textUnderactuated robots have fewer actuators than degrees of freedom (DOF). Nonactuated joints can be equipped with torsional springs. Underactuated robots can be controlled in a point-to-point motion if they have a particular mass distribution that makes them differentially flat. The trajectory described by the robot moving from the start point to the end point largely depends on the torsional stiffness of the nonactuated joints and on motion time. Thus, the same point-to-point motion can be obtained by sweeping different parts of the workspace. This property increases the dexterity of the robot. This paper focuses on the trajectories of a 3-DOF robot moving in the horizontal plane with two actuators and a torsional spring. Parametric analyses showing the effect of torsional stiffness and motion time are presented. The existence of combinations of torsional stiffness and motion time that minimize the motion torques or the swept area is discussed. The area swept by the underactuated robot is compared with the one swept by an equivalent actuated robot performing the same task. Reductions in the swept area of up to 36% are obtained. Finally, numerical results are validated by means of experimental tests on a simplified prototype
Differentially Flat Robots with Compliance in Actuated Joints
No full textMost robots and mechanisms are fully actuated, i.e., the number of actuators is equal to the number of degrees of freedom (DOFs). Thus, the robot’s configuration is fully determined by imposing the position of the actuators. However, a class of robots exists, the under-actuated robots, in which the number of actuators is smaller than the number of degrees of freedom. In this case, the non-actuated joints cannot be directly controlled. When an under-actuated robot with n-DOFs and n-1 actuators is designed with specific inertial properties of the links, it becomes differentially flat. In this case, the non-actuated joint, which is equipped with a torsion spring, can be controlled by the motion of the actuated joints. In the previous works dealing with differentially flat underactuated robots the compliance of the actuated joints was neglected. In this paper, the effect of actuated joint compliance in differentially flat underactuated robots is investigated. A mathematical model is proposed and numerical simulations are carried out to highlight the effect of joint compliance in the precision of point-to-point motions
Planning of Underactuated Differentially Flat Robot Trajectories with a via Point
No full textUnderactuated robots usually perform point-to-point motions exploiting the differential flatness property. This paper aims to extend the capabilities of this class of robots considering a via point in the workspace. A method for trajectory planning in the space of flat variables is presented. Flat variables are described by means of polynomials and have to guarantee the continuity of motor torques. Numerical results and experimental tests carried out on a 2 degree of freedom prototype show the validity of the method, which allows the robot to avoid an obstacle in the workspace
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