Dynamic characterization of machining robot and stability analysis

Abstract

Machining robots have major advantages over cartesian machine tools because of their flexibility, their ability to reach inaccessible areas on a complex part, and their important workspace. However, their lack of rigidity and precision is still a limit for precision tasks. Innovations and design optimization of robotic structure, links, and power transmission allow robot manufacturers to propose business solutions for machining applications. Beyond accuracy problems, it is also necessary to quantify the vibration phenomena that may affect, as in machine tools, the quality of machined parts and the tools and spindle lifespan. These vibrations occurred at specific machining conditions depending on robot and spindle dynamic properties. The robot's posture evolved significantly in its workspace and induces dynamic's changes observed at the tool tip that in turn impact the stability of the machining process. The objective of this paper is to quantify the dynamic behavior's variation of an ABB IRB 6660 robot equipped with a high-speed machining (HSM) spindle in its workspace and analyze the consequences in terms of machining stability. Through an experimental modal characterization, significant variability of modal parameters is observed at the tool tip and impacts the stability of machining. The results show that an adjustment of the cutting conditions must accompany the change of robot posture during machining to ensure stability.

Industrial robotic machining: a review

“…Their results showed that cutting force was reduced by 50-70% compared with using a fluting machine. In a high-speed machining category, Mejri et al [115] observed dynamic characterisation of robotic machining system. Cutting conditions should be adaptively changed along with robot posture to ensure stability in terms of dynamic property differences, as shown in Fig.…”

Analysis of the Compliance Properties of an Industrial Robot with the Mozzi Axis Approach

“…The modulus plot highlights the presence of the fundamental mode at about 13 Hz, and the phase plot corroborates this fact, showing large phase changes at the same frequency. The tests were carried out with the modal analysis approach [20], which is widely used in the fields of automotive engineering [21,22], aerospace engineering [23], automatic machines [24], and robotics [25]. A grid of measurement points was defined on the robot (see Figure 5); points 10 and 11 were used to monitor base vibrations.…”

Dynamic modeling and stability prediction in robotic machining

“…The experimental identification carried out by Mejri et al [5] enables the determination of the actual modal parameters of the robot structure in a given position and configuration where the tests are performed. It is not valid for other positions and configurations of the robot, but they are usually required as an effective means to calibrate numerical models.…”

“…Mejri et al [5] experimentally investigated the end-effector position effect on the dynamic behavior of an ABB IRB6660 robot. They observed modifications in the robot's dynamic behavior depending on changes in its posture.…”