Parametric virtual concept design of heavy machinery: a case study application

Virtual prototyping enables the validation and optimization of machinery equivalent to physical testing, saving time and costs in the product development, especially in case of heavy machines with complex motions. However, virtual prototyping is usually deployed only at the end of the design process, when product architecture is already developed. The present paper discusses the introduction of virtual prototypes since conceptual design stage as Virtual Concepts in which coarse models of machinery design variants are simulated obtaining useful information, sometimes fundamental to support best design choices. Virtual Concept modeling and preliminary validation and its later integration to a Virtual Prototype are expressly investigated using Multi Body Dynamics software. A verification case study on a large vibrating screen demonstrates that dynamic Virtual Concepts enable easier and effective evaluations on the design variants and increase the design process predictability

Analysis and Conceptual Design of a Passive Upper Limb Exoskeleton

This paper reports a preliminary design of a passive upper limb exoskeleton with 6 degrees of freedom to support workers in industrial environments in a vast range of repetitive tasks. Leveraging the detailed analytical model developed in previous research, the best springs configuration to balance the system during motion is designed through an efficient optimization routine. The model is validated with commercial software for specific overhead tasks, and aspects of the proposed balancer physical implementation are evaluated. Index Terms—Upper Limb Exoskeleton, Wearable Devices, Design Optimization, Virtual Prototyping, Gravity balancing

Design, modeling, and control of a variable stiffness elbow joint

New technological advances are changing the way robotics are designed for safe and dependable physical human–robot interaction and human-like prosthesis. Outstanding examples are the adoption of soft covers, compliant transmission elements, and motion control laws that allow compliant behavior in the event of collisions while preserving accuracy and performance during motion in free space. In this scenario, there is growing interest in variable stiffness actuators (VSAs). Herein, we present a new design of an anthropomorphic elbow VSA based on an architecture we developed previously. A robust dynamic feedback linearization algorithm is used to achieve simultaneous control of the output link position and stiffness. This actuation system makes use of two compliant transmission elements, characterized by a nonlinear relation between deflection and applied torque. Static feedback control algorithms have been proposed in literature considering purely elastic transmission; however, viscoelasticity is often observed in practice. This phenomenon may harm the performance of static feedback linearization algorithms, particularly in the case of trajectory tracking. To overcome this limitation, we propose a dynamic feedback linearization algorithm that explicitly considers the viscoelasticity of the transmission elements, and validate it through simulations and experimental studies. The results are compared with the static feedback case to showcase the improvement in trajectory tracking, even in the case of parameter uncertainty

A Minimal Touch Approach for Optimizing Energy Efficiency inPick-and-Place Manipulators

The interest in novel engineering methods andtools for optimizing the energy consumption in robotic systemsis currently increasing. In particular, from an industry pointof view, it is desirable to develop energy saving strategiesapplicable also to established manufacturing systems, beingliable of small possibilities for adjustments.Within this scenario,an engineering method is reported for reducing the totalenergy consumption of pick-and-place manipulators for givenend-effector trajectory. Firstly, an electromechanical model ofparallel/serial manipulators is derived. Then, an energy-optimaltrajectory is calculated, by means of time scaling, starting froma pre-scheduled trajectory performed at maximum speed (i.e.compatible with actuators limitations). A simulation case studyfinally shows the effectiveness of the proposed procedure

A Practical Method for Determining the Pseudo-rigid-body Parameters of Spatial Compliant Mechanisms via CAE Tools

Compliant Mechanisms (CMs) are employed in several applications requiring high precision and reduced number of parts. For a given topology, CM analysis and synthesis may be developed resorting to the Pseudo-Rigid Body (PRB) approximation, where flexible members are modelled via a series of spring-loaded revolute joints, thus reducing computational costs during CM simulation. Owing to these considerations, this paper reports about a practical method to determine accurate PRB models of CMs comprising out-of-plane displacements and distributed compliance. The method leverages on the optimization capabilities of modern CAE tools, which provide built-in functions for modelling the motion of flexible members. After the validation of the method on an elementary case study, an industrial CM consisting of a crank mechanism connected to a fully compliant four-bar linkage is considered. The resulting PRB model, which comprises four spherical joints with generalized springs mounted in parallel, shows performance comparable with the deformable system

Hyperelastic Modeling of Rubber-Like Photopolymers for Additive Manufacturing Processes

Constituive models of polymers for rapid prototypin

A Simulation Tool for Computing Energy Optimal Motion Parameters of Industrial Robots

This paper presents a novel robot simulation tool, fully interfaced with a common Robot Offline Programming software (i.e. Delmia Robotics), which allows to automatically compute energy-optimal motion parameters, for a given end-effector path, by tuning the joint speed/acceleration during point-to-point motions whenever allowed by the manufacturing constraints. The main advantage of this method, as compared to other optimization routines that are not conceived for a seamless integration with commercial industrial manipulators, is that the computed parameters are the same required by the robot controls, so that the results can generate ready-to-use energy-optimal robot code

Virtual Prototyping of a Compliant Spindle for Robotic Deburring

At the current state-of-the-art, Robotic Deburring (RD) has been successfully adopted in many industrial applications, but it still needs improvements in terms of final quality. In fact, the effectiveness of a RD process is highly influenced by the limited accuracyof the robot motions and by the unpredictable variety of burr size/shape. Tool compliance partially solves the problem, although dedicated engineering design tools are strictly needed, in order to identify those optimized parameters and RD strategies that allow achieving the best quality and cost-effectiveness. In this context, the present paper proposes a CAD-based Virtual Prototype (VP) of a pneumatic compliant spindle, suitable to assess the process efficiency in different case scenarios. The proposed VP is created by integrating a 3D multi-body model of the spindle mechanical structure with the behavioural model of the process forces, as adapted from previous literature. Numerical simulations are provided, concerning the prediction of both cutting forces and surface finishing accuracy

Design and Virtual Prototyping of a Variable Stiffness Joint via Shape Optimization in a CAD/CAE Environment

During the latest decade, collaborative robots, namely machines specifically designed for the physical interaction with humans, have been gradually making their transition from laboratories to real-world applications [1]. Naturally, whenever the envisaged task would benefit form physical human-machine interaction, safety and dependability become issues of paramount importance [2]. Nonetheless, especially when dealing with collaborative operations in the manufacturing industry, safety regulations may lead the plant designer to face opposite goals. On one hand, robots should indeed be designed so as to never cause harm to people (both during regular functioning or in case of failure). On the other hand, the wide-spread use of industrial manipulators traditionally leverages on their capabilities to carry rather high payloads, while achieving a very fast and precise positioning of the end-effector. These requirements are usually pursued by coupling powerful actuation systems with extremely rigid mechanical structures, which hardly comply with safety needs whenever the workers are supposed to enter the robot workspace. Therefore, the engineering challenge when designing collaborative robotics systems, which have to be safe and efficient at the same time, is usually tackled via the following strategies: i) by enhancing the robot sensory apparatus; ii) by adopting active control strategies; iii) by reducing the inertia of any moving part employing lightweight materials whenever possible. In parallel, as previously proven by several researchers [3], another way to actually implement safe machines for collaborative tasks is to increase (rather than minimize) the inherent compliance of their mechanical structure [4], simultaneously introducing the possibility to actively vary such compliance during the robot movements. This capability can be implemented, for instance, by means of Variable Stiffness Joints (VSJ), namely particular actuation systems which allow to independently control the position of an output link along with the transmission stiffness. In light of this consideration, the present talk describes the design of a novel VSJ architecture, depicted in Fig. 1a. The VSJ can achieve stiffness modulation via the use of a pair of compliant mechanisms with distributed compliance, which act as nonlinear springs with proper torque-deflection characteristic. These elastic elements are composed of slender beams whose neutral axis is described by a spline curve with non-trivial shape. The beam geometry is determined by leveraging on a CAD/CAE framework that allows for the shape optimization of complex flexures. In particular, the design method makes use of the modeling and simulation capabilities of a parametric CAD seamlessly connected to a FEM tool. For validation purposes, proof-concept 3D printed prototypes of both elastic elements (Fig. 1a) and overall VSJ (Fig. 1b) are finally produced and tested (Fig. 1c). Experimental results fully confirm that the VSJ behaves as expected. BIBLIOGRAFY [1] Heyer, C., 2010. \u201cHuman-robot interaction and future industrial robotics applications\u201d. Proceeding of the IEEE/RSJ International Conference on Intelligent Robots and Systems, pp. 4749\u20134754. [2] Fryman, J., and Matthias, B., 2012. \u201cSafety of industrial robots: From conventional to collaborative applications\u201d. Proceeding of ROBOTIK, 7th German Conference on Robotics, May, pp. 1\u20135. [3] Bicchi, A., and Tonietti, G., 2004. \u201cFast and soft arm tactics: Dealing with the safety-performance trade-off in robot arms design and control\u201d. IEEE Robotics and Automation Magazine, 11(2), pp. 22\u201333. [4] Berselli, G., Guerra, A., Vassura, G., and Andrisano, A. O., 2014. \u201cAn engineering method for comparing selectively compliant joints in robotic structures\u201d. IEEE/ASME Transactions on Mechatronics, 19(6), pp. 1882\u20131895