New Damped-Jerk trajectory for vibration reduction

This paper derives a jerk-shaped profile to address the vibration reduction of underdamped flexible dynamics of motion system. The jerk-limited profile is a widespread smooth command pattern used by modern motion systems. The ability of the jerk-limited profile to cancel the residual vibration of an undamped flexible mode is clearly explained using an equivalent continuous filter representation and the input shaping formalism. This motivates the design of a new jerk-shaped profile, named Damped-Jerk profile, to extend the previous result to the more common case of underdamped systems. Both simulations and experimental results demonstrate the effectiveness of the proposed Damped-Jerk profile to reduce damped vibration

Etat de l’art de la compensation de vibration par la generation de trajectoire – application a la robotique industrielle

Dans un contexte d’amélioration constante de la productivité et de la flexibilité des machines de production, les vibrations mécaniques demeurent un phénomène limitant les performances dynamiques. Le problème de réduction des vibrations induites par les perturbations extérieures (environnement dynamique, procédés de coupe) est généralement abordé par le biais de la mise en oeuvre de systèmes de dissipation passifs ou actifs. Quant aux vibrations induites par le mouvement des axes de la machine, elles peuvent être efficacement prises en compte lors de la synthèse de la trajectoire du système. Ce papier dresse un état de l’art des méthodes de réduction de vibration s’appuyant sur une adaptation de la trajectoire du système. Une analyse unifiée des méthodes applicables au domaine de la machine de production est réalisée. Des essais menés sur un robot industriel 6 axes viennent illustrer cette analyse

Feedrate planning for machining with industrial six-axis robots

The authors want to thank Stäubli for providing the necessary information of the controller, Dynalog for its contribution to the experimental validations and X. Helle for its material contributions.Nowadays, the adaptation of industrial robots to carry out high-speed machining operations is strongly required by the manufacturing industry. This new technology machining process demands the improvement of the overall performances of robots to achieve an accuracy level close to that realized by machine-tools. This paper presents a method of trajectory planning adapted for continuous machining by robot. The methodology used is based on a parametric interpolation of the geometry in the operational space. FIR filters properties are exploited to generate the tool feedrate with limited jerk. This planning method is validated experimentally on an industrial robot

Etat de l’art de la compensation de vibration par la generation de trajectoire – application a la robotique industrielle

Dans un contexte d’amélioration constante de la productivité et de la flexibilité des machines de production, les vibrations mécaniques demeurent un phénomène limitant les performances dynamiques. Le problème de réduction des vibrations induites par les perturbations extérieures (environnement dynamique, procédés de coupe) est généralement abordé par le biais de la mise en oeuvre de systèmes de dissipation passifs ou actifs. Quant aux vibrations induites par le mouvement des axes de la machine, elles peuvent être efficacement prises en compte lors de la synthèse de la trajectoire du système. Ce papier dresse un état de l’art des méthodes de réduction de vibration s’appuyant sur une adaptation de la trajectoire du système. Une analyse unifiée des méthodes applicables au domaine de la machine de production est réalisée. Des essais menés sur un robot industriel 6 axes viennent illustrer cette analyse

Improving the Accuracy of Industrial Robots by offline Compensation of Joints Errors

The use of industrial robots in many fields of industry like prototyping, pre-machining and end milling is limited because of their poor accuracy. Robot joints are mainly responsible for this poor accuracy. The flexibility of robots joints and the kinematic errors in the transmission systems produce a significant error of position in the level of the end-effector. This paper presents these two types of joint errors. Identification methods are presented with experimental validation on a 6 axes industrial robot, STAUBLI RX 170 BH. An offline correction method used to improve the accuracy of this robot is validated experimentally

FIR filter-based online jerk-constrained trajectory generation

In the context of human-robot manipulation interaction for service or industrial robotics, the robot controller must be able to quickly react to unpredictable events in dynamic environments. In this paper, a FIR filter-based trajectory generation methodology is presented, combining the simplicity of the analytic second-order trajectory generation, i.e. acceleration-limited trajectory, with the flexibility and computational efficiency of FIR filtering, to generate on the fly smooth jerk-constrained trajectories. The proposed methodology can generate synchronized (fixed-time) and time-optimal jerk-limited trajectories from arbitrary initial velocity and acceleration conditions within 20 microsecond. Other jerk-constrained trajectories such as jerk-time fixed trajectories, which are particularly suitable for vibration reduction, can be easily generated. Experimental validations carried out on a seven axis Kuka LBR iiwa are presented

Industrial equipment for Powder transportation using piezoelectric “friction control” method

This paper presents a new powder transportation system that uses a high frequency flexural stationary wave coupled with a low frequency horizontal displacement of a beam to produce the transport of the powder. The ultrasonic wave is produced with the help of piezoelectric cells glued under the beam and is used to decrease the friction coefficient between the powder and the beam surface

Task-oriented rigidity optimization for 7 DOF redundant manipulators

In this work, redundancy resolution has been employed to increase the Cartesian mechanical rigidity of 7 DOF robot manipulators during tasks requiring stiff interactions with the environment (e.g. milling or drilling). The Cartesian static stiffness of the end-effector for a given joint configuration is deduced from an identified joints stiffness model. The Cartesian reflected rigidity evolution over an analytically computed self-motion of the manipulator shows significant variations that clearly highlight the need to select the right set of joint angles among the possible ones. A global optimization scheme of the redundant DOF is proposed to determine the stiffest robot configurations for a given pose of the end-effector. An experimental study on 7 DOF KUKA LBR iiwa then shows the relevance of the proposed approach in finding the redundant robot joint angles that optimize this rigidity criteria

A Modified DLS Scheme With Controlled Cyclic Solution for Inverse Kinematics in Redundant Robots

Redundancy in robotic manipulators has many advantages. It is successfully used to achieve better dexterity, and to avoid obstacles, singularities, or the kinematic limitations. However, redundancy makes the inverse kinematics (IK) problem harder to solve. The damped least squares (DLS) is a powerful method for calculating the IK of redundant robots, but it suffers from noncyclicity issue, where a closed curve motion in the Cartesian space of the end-effector (EEF) does not map into a closed curve in the joint space. This results in nonrepetitive motion in the joint space, even though the EEF motion is repetitive. In this article, we present a solution for the noncyclicity problem in the DLS method. The proposed scheme was successfully tested both in simulation (9 DoF robot) and on a real robotic manipulator (7 DoF robot)

A Pragmatic Approach to Exploiting Full Force Capacity for Serial Redundant Manipulators

Considering a set of robotic tasks which involve physical interaction with the environment, the theoretical knowledge of the full force capacity of the manipulator is a key factor in the design or development of an efficient and economically attractive solution. Carrying its own weight while countering forces may be too much for a robot in certain configurations. Kinematic redundancy with regard to a task allows a robot to perform it in a continuous space of articular configurations; space in which the payload of the robot may vary dramatically. It may be impossible to withstand a physical interaction in some configurations, while it may be easily sustainable in others that bring the end-effector to the same location. This becomes obviously more prevalent for a limited payload robot. This letter describes a framework for these kind of operations, in which kinematic redundancy is used to explore the full extent of a force capacity for a givenmanipulator and task (in this letter, the terms “force” and “wrench” may interchangeably refer to two-, three-, or six-dimensional forces depending on the dimension of the problem and on whether they may or may not include components of translational forces and/or moments. Their dimensional definition will be explicitly given whenever specifically needed). A pragmatic force capacity index (FCI) is proposed. The FCI offers a sound basis for redundancy resolution via optimization or complete redundancy exploration, and may provide good hints for end-effector design. A practical use case involving 7-DOFs KUKA LBR iiwa was used to demonstrate the relevance of the proposed method