Gramian-constrained optimization process for the stiffness model identification of industrial manipulators

This work deals with the elastostatic identification of industrial manipulators. By reviewing the basics of the physical elastic properties of both links and joints in the framework of the lumped stiffness modeling techniques, the Gramian nature of the stiffness matrices has been found out adequate to do so. Then, a novel optimization method has been developed, which incorporates the Gramian matrix formulation along a non-linear optimization process, acting as an intrinsic constraint for the conservativeness of the elastostatic modeling. Numerical and experimental analyses evince the effectiveness of the proposed method, as the elastostatic models obtained by means of the proposed technique predict more than 93.7% of the compliance deviations of a real industrial robot. The proposed method is simple enough to be jointly applicable to the most recent elastostatic model reduction techniques.

Calculation of accuracy with the coordinate-positional method of basing

The article is devoted to the assessment of assembly accuracy when positioning with the use of industrial manipulators (robots). Classic assembly technologies are outdated and have many disadvantages that can be solved by the automation of industrial processes, which became possible due to the rapid development of robotization. In the material there are investigation the possibility of using industrial robots for positioning structural elements of aircraft from the point of view of achieving the required assembly accuracy. For the analysis, foreign literature sources and the current experience of introducing similar technologies by large aircraft manufacturers were used. To assess the assembly accuracy, the formulas for the functional size error were used. An enlarged technological assembly process is presented, graphic materials with basing schemes are presented. Based on the data obtained, the advantages and disadvantages of basing with the help of industrial robots at this stage of technology development are formulated, taking into account the existing production experience.

Evaluation of Kinematic and Compliance Calibration of Serial Articulated Industrial Manipulators

As long as industrial robots are programmed by teach programming, their positioning accuracy is unimportant. With a wider implementation of offline programming and new applications such as machining, ensuring a higher positioning accuracy of industrial robots over the entire working space has become very important. In this paper, we first review the measurement schemes of end effector poses. We then outline kinematic models of serial articulated industrial manipulators to quantify the positioning accuracy with a focus on the extension of the classical Denavit-Hartenberg (DH) models to include rotary axis error motions. Subsequently, we expand the discussion on kinematic models to compliant robot models. The review highlights compliance models that are applied to calculate the elastic deformation produced by forces, namely gravity and external loads. Model-based numerical compensation plays an important role in machine tool control. This paper aims to present state-of-the-art technical issues and future research directions for the implementation of model-based numerical compensation schemes for industrial robots.

Quasi-Static Compliance Calibration of Serial Articulated Industrial Manipulators

This article presents a procedure for the quasi-static compliance calibration of serial articulated industrial manipulators. Quasi-static compliance refers to the apparent stiffness displayed by manipulators at low-velocity movements, i.e., from 50 to 250 mm/s. The novelty of the quasi-static compliance calibration procedure lies in the measurement phase, in which the quasi-static deflections of the manipulator’s end effector are measured under movement along a circular trajectory. The quasi-static stiffness might be a more applicable model parameter, i.e., representing the actual manipulator more accurately, for manipulators at low-velocity movements. This indicates that the quasi-static robot model may yield more accurate estimates for the trajectory optimization compared with static stiffness in the implementation phase. This study compares the static and apparent quasi-static compliance. The static deflections were measured at discretized static configurations along circular trajectories, whereas the quasi-static deflections were measured under circular motion along the same trajectories. Loads of different magnitudes were induced using the Loaded Double Ball Bar. The static and quasi-static displacements were measured using a linear variable differential transformer embedded in the Loaded Double Ball Bar and a Leica AT901 laser tracker. These measurement procedures are implemented in a case study on a large serial articulated industrial manipulator in five different positions of its workspace. This study shows that the measured quasi-static deflections are bigger than the measured static deflections. This, in turn, indicates a significant difference between the static and apparent quasi-static compliance. Finally, the implementation of the model parameters to improve the accuracy of robots and the challenges in realizing cost-efficient compliance calibration are discussed.

KINEMATICS OF POSITIONING DEVICE FOR MATERIAL HANDLING IN MANUFACTURING

Different types of robots are used in many areas of industry. Industrial manipulators are used to ensure productivity and flexibility in automated production lines. Most of them is used for tasks that automatically repeat the same operation in a familiar environment. The key element in the development and analysis of industrial robots is their kinematic analysis. The article deals with the kinematic analysis of this positioning equipment. Individual relations of kinematic quantities are plotted graphically. Matrix methods were used for the analysis.