Accuracy Improvement of Robot-Based Milling Using an Enhanced Manipulator Model

Abstract

The paper is devoted to the accuracy improvement of robot-based milling by using an enhanced manipulator model that takes into account both geometric and elastostatic factors. Particular attention is paid to the model parameters identification accuracy. In contrast to other works, the proposed approach takes into account impact of the gravity compensator and link weights on the manipulator elastostatic properties. In order to improve the identification accuracy, the industry oriented performance measure is used to define optimal measurement configurations and an enhanced partial pose measurement method is applied for the identification of the model parameters. The advantages of the developed approach are confirmed by experimental results that deal with the elastostatic calibration of a heavy industrial robot used for milling. The achieved accuracy improvement factor is about 2.4.

Robots in machining

“…The procedure of Klimchik et al from Refs. [61] and [62] is illustrative of the general strategy used for offline compensation (Fig. 14).…”

Automatic pose optimization for robotic processes

“…Due to lack of sufficient identification data, a linear description of joint stiffness, or compliance (inverse of the stiffness) is used. Abele and Klimchik propose virtual joints where they add two DoF per joint which results in three rotational compliances per joint [12], [13]. Yet, the model is limited to linear descriptions of the compliances as well.…”

“…Yet, the model is limited to linear descriptions of the compliances as well. As literature agrees, that the compliances of robot arms are neglectable for robots with payload beyond 100 kg, the compliance is concentrated in the robot joints [5], [11], [12], [13]. In order to describe the joint stiffness in detail, the following model is introduced: stiffness in six DoF is modeled in each joint, three translational and three rotational stiffness.…”

Robotic Milling: A New Era of Machining

“…Most industrial robots are constructed as a cantilever, in which each of the arms is supported by motors, brakes and reduction gears, they struggle to achieve high positioning accuracy level, being limited to 0.5-2mm (Vergeest & Tangelder, 1996) and at the same time are more prone to disturbances from the process forces [1] .…”