Bistability and delayed acceleration feedback control analytical study of collocated and non-collocated cases

Stability and bifurcation analysis of a non-rigid robotic arm controlled with a time-delayed acceleration feedback loop is addressed in this work. The study aims at revealing the dynamical mechanisms leading to the appearance of limit cycle oscillations existing in the stable region of the trivial solution of the system, which is related to the combined dynamics of the robot control and its structural nonlinearities. An analytical study of the bifurcations occurring at the loss of stability illustrates that, in general, hardening structural nonlinearities at the joint promote a subcritical character of the bifurcations. Consequently, limit cycle oscillations are generated within the stable region of the trivial solution. A nonlinear control force is then developed to enforce the supercriticality of the bifurcations. Results illustrate that this strategy enables to partially eliminate limit cycle oscillations coexisting with the stable trivial solution. The mechanical system is analysed in a collocated and a non-collocated configuration, depending on the position of the sensor

Stability Analysis of a One Degree of Freedom Robot Model with Sampled Digital Acceleration Feedback Controller in Turning and Milling

This study is interested in the stability of robots in machining. The goal is to improve the dynamic performance of robots using an additional acceleration signal fed back through the conventional built-in proportional-derivative controller provided by the manufacturer. The structure of the robot is modelled with a simple one degree of freedom lumped model and the control signals are fed back via a linear spring and damping. The time delays of feedback controllers are considered zero-order holds, which results in sawtooth-like time-periodic time delays. The resulting equation of motion is an advanced delay differential equation. The semidiscretization method is shown for such systems having multiple sampled digital delays and continuous delays. First, we establish the stable regions in the plane of the sampling delay and the gain of the acceleration signal without machining. Then we show the possibility to improve stability in turning and milling using the additional acceleration feedback controller compared to the cases without any controller or using only the built-in proportional-derivative controller

Analyses of Key Variables to Industrialize a Multi-Camera System to Guide Robotic Arms

Robotic arms are widely used in sectors such as automotive or assembly logistics due to their flexibility and cost. Other manufacturing sectors would like to take advantage of this technology, however, higher accuracy is required for their purposes. This paper integrated a multi-camera system to achieve the requirements for milling and drilling tasks in aeronautic parts. A closed-loop framework allows the position of the robot’s end-effector to be corrected with respect to a static reference. This is due to the multi-camera system tracking the position of both elements due to the passive targets on their surface. The challenge is to find an auxiliary system to measure these targets with an uncertainty that allows the desired accuracy to be achieved in high volumes (>3 m3). Firstly, in a reduced scenario, a coordinate measuring machine (CMM), a laser tracker (LT), and portable photogrammetry (PP) have been compared following the guidelines from VDI/VDE 2634-part 1. The conclusions allowed us to jump into an industrial scenario and run a similar test with a higher payload than in the laboratory. The article ends with an application example demonstrating the suitability of the solution

Online compliance error compensation system for industrial manipulators in contact applications

Industrial manipulators are rarely used in high-force processes even though they provide flexibility, adaptability, relatively low cost, and a large workspace. This limited utilization is mainly due to their inherent low stiffness, which results in significant deformation. Hence, it is necessary to improve their accuracy in order to achieve high-precision requirements while performing tasks under load. This paper focuses on the development and implementation of an online compliance error compensation system for industrial manipulators. The proposed algorithm computes the compensation based on an elasto-geometric robot model and process forces measured with a force sensor mounted between the robot mechanical interface and the end effector. The performance of the compensation system is evaluated experimentally in two high payload robots from different manufacturers in which the compensation was carried out to reduce the mean deformation of circular trajectories under load.QC 20220404COMAC

Diseño de un amortiguador activo para la eliminación de chatter en máquina herramienta

National audienceLa aparición de chatter o retemblado en el proceso de mecanizado es uno de los mayores inconvenientes a la hora de incrementar el ratio de arranque de viruta, debido a que puede conllevar un mal acabado superficial y la rotura de elementos mecánicos. Este problema está cada día más vigente debido a que los requerimientos de precisión de las piezas hace a los diseñadores huir de la fricción en los guiados, a que las piezas son cada vez más ligeras y a que los requerimientos de productividad van aumentando. Los amortiguadores activos comandados por una estrategia de control permiten aumentar el amortiguamiento estructural sin modificar la máquina, aumentando de esta manera la zona libre de vibraciones. En este trabajo se muestra el actuador electromagnético diseñado íntegramente en IK4-IDEKO para la eliminación de chatter en operaciones de mecanizado. Además del diseño del mismo, se pueden observar los diferentes ensayos de validación (temperatura, linealidad...) que se han llevado a cabo en dicho actuador y los resultados de mejora que se han obtenido al introducirla en un centro de mecanizado