Application of a Camera for Measuring Robot Position Accuracy

New Technologies - Trends, Innovations and Research, 2012

IEEE Transactions on Robotics and Automation, 1996

A sensor has been developed and successfully implemented to automate robot calibration. Its simple design makes it ideal for production environments. It works in conjunction with precision spheres that are mounted in the workspace. The relative positions of the spheres are measured in advance, and the sensor is positioned over them automatically and precisely. The positioning of the sensor is governed by three light beams that define position with respect to the sensor. This eliminates the problems experienced by other short range devices in that it acts digitally and without contact. Design of the sensor and its autonomous control from a PC are presented along with proven measurement tactics and results of performance tests.

Robotics and Computer-Integrated Manufacturing, 2015

The paper deals with geometric calibration of industrial robots and focuses on reduction of the measurement noise impact by means of proper selection of the manipulator configurations in calibration experiments. Particular attention is paid to the enhancement of measurement and optimization techniques employed in geometric parameter identification. The developed method implements a complete and irreducible geometric model for serial manipulator, which takes into account different sources of errors (link lengths, joint offsets, etc). In contrast to other works, a new industry-oriented performance measure is proposed for optimal measurement configuration selection that improves the existing techniques via using the direct measurement data only. This new approach is aimed at finding the calibration configurations that ensure the best robot positioning accuracy after geometric error compensation. Experimental study of heavy industrial robot KUKA KR-270 illustrates the benefits of the developed pose strategy technique and the corresponding accuracy improvement.

1994

Abstract This paper addresses the problem of calibrating a camera mounted on a robot arm. The objective is to estimate the camera's intrinsic and extrinsic parameters. These include the relative position and orientation of camera with respect to robot base as well as the relative position and orientation of the camera with respect to a pre-defined world frame. A calibration object with a known 3D shape is used together with two known movements of the robot.

2002

In the field of industrial robotics, many different calibration methods exist to reduce error in the robot system. Locating the manipulator home position is a common calibration technique, which can be divided into three main categories — relative, optimal and leveling based ...

Mechanisms and Machine Science, 2012

The paper focuses on the accuracy improvement of geometric and elasto-static calibration of industrial robots. It proposes industry-oriented performance measures for the calibration experiment design. They are based on the concept of manipulator test-pose and referred to the end-effector location accuracy after application of the error compensation algorithm, which implements the identified parameters. This approach allows the users to define optimal measurement configurations for robot calibration for given work piece location and machining forces/torques. These performance measures are suitable for comparing the calibration plans for both simple and complex trajectories to be performed.

Journal of physics, 2018

The issue of determining industrial robot's kinematic errors does seem to be already fully addressed.However, due to the recent influx of new technological possibilities, it was decided to verify and apply new methods of determining both robot's and its mounted equipment's errors. It is possible for industrial robot with integrated scanning head to become a reliable, automatic system; one that could allow direct coordinate measuring on assembly line even in places that are both difficult to access and dangerous for a worker. However, determination of kinetic errors as well as measuring errors is going to be a start to improving accuracy of the device and modelling errors' matrix. Due to better software correction, the matrix is going to allow installation of cheaper components in devices.

Advances in Mechanical Engineering

Robot kinematic calibration used to be carried out with the partial pose measurements (position only) of dimension 3 in industry, while full pose measurements (orientation and position) of dimension 6 sometimes could be considered to improve the calibration performance. This paper investigates the effects of measurement dimensions on robot calibration accuracy. It compares the resulting robot accuracies in both partial pose and full pose cases after calibrating three structural types of robot manipulators such as a serial manipulator (Hyundai HA-06 robot), a single closed-chain manipulator (Hyundai HX-165 robot), and a multiple closed-chain manipulator (Hyundai HP-160 robot). These comparative studies show when the full-pose based calibration need to be considered and how much it contributes the improvement of robot accuracy to the different structural type of robot manipulators.

SAE International Journal of Aerospace, 2013

The purpose of this work is to evaluate the efficiency of several calibration methods applied to a six-axis industrial (serial) robot. Specifically, the absolute position accuracy of a Fanuc LR Mate 200 iC industrial robot is improved using two calibration models. The first model is purely kinematic, and takes into account all geometric parameters. The second model considers, in addition, five compliance parameters related to the stiffness in joints 2, 3, 4, 5, and 6. For both models, the so-called calibration (or identification) robot configurations are selected based on an observability analysis. For each model, the efficiency of five different observability indices are compared. The parameter identification is based on the forward kinematic approach, where only the residual of the calibration positions is minimized. The data collection process is completely automated, by using Matlab, a FARO laser tracker, communication modules, and a special end-effector with three optical targets (SMRs). The comparisons of the observability indices and of the two calibration models are made through an exhaustive experimentation (7000 measurements). Results show that the robot's mean position error is reduced from 0.622 mm (before calibration) to 0.250 mm, when using the kinemetic model, and to 0.142 mm, when using the complete calibration model.

The paper is devoted to the geometrical calibration of industrial robots employed in precise manufacturing. To identify geometric parameters, an advanced calibration technique is proposed that is based on the non-linear experiment design theory, which is adopted for this particular application. In contrast to previous works, the calibration experiment quality is evaluated using a concept of the user-defined test-pose. In the frame of this concept, the related optimization problem is formulated and numerical routines are developed, which allow user to generate optimal set of manipulator configurations for a given number of calibration experiments. The efficiency of the developed technique is illustrated by several examples.

IEEE/CAA Journal of Automatica Sinica, 2021

With the continuous improvement of automation, industrial robots have become an indispensable part of automated production lines. They widely used in a number of industrial production activities, such as spraying, welding, handling, etc., and have a great role in these sectors. Recently, the robotic technology is developing towards high precision, high intelligence. Robot calibration technology has a great significance to improve the accuracy of robot. However, it has much work to be done in the identification of robot parameters. The parameter identification work of existing serial and parallel robots is introduced. On the one hand, it summarizes the methods for parameter calibration and discusses their advantages and disadvantages. On the other hand, the application of parameter identification is introduced. This overview has a great reference value for robot manufacturers to choose proper identification method, points further research areas for researchers. Finally, this paper analyzes the existing problems in robot calibration, which may be worth researching in the future.

Presented in this paper is a project in which an autonomous camera-based calibration system is being developed. As with all other calibration methods, the desired goal is to improve the accuracy of a robot to the same degree as its repeatability. The distinct feature of this system is that it will employ the novel Relative Measurement Concept (RMC) to identify the discrepancies between nominal robot parameters, defined by its specified geometry, and the actual parameters defined by its manufacture. The geometry of a KUKA KR 15/2 was chosen for the simulation as a preliminary experiment was performed with this particular serial robot, however, substitution of other serial robot geometries is possible. Derivation of the error model will be presented along with discussion on the components of the simulation. Program components include Pieper's solution method to the inverse kinematic problem and Singular Value Decomposition (SVD). Results from the absolute measurement case and the relative measurement case, in its current form, will be presented. The RMC method allows for the identification of 20 of the 24 robot parameters, in its present state, and will be experimentally validated with a Thermo CRS A465 six-axis serial robot.

Journal of Robotic Systems, 1990

This article presents a local calibration method that is philosophically different from the more contemporary global calibration methods. Local methods seek models of robot performance at the robot distal link measured relative to parts in localized part regions. In contrast, global methods seek to model various sources of robot inaccuracy internal to the robot. For example, a significant global research area is the determination of the actual robot arm structural parameters. Given more accurate estimates of these parameters, global compensation methods propose perturbation techniques or improved kinematic models that can be used to control the as-manufactured robot. To implement local calibration methods, calibration procedures have been developed to locate tool and sensor tool control frames (TCF's) and to measure robot inaccuracy in localized regions. Using the measured position and orientation (pose) data obtained by hardware sensors, the components of operational inaccuracy are integrated into compensation models. This article discusses compensating model effectiveness and considers the interactions between hardware sensors and part features necessary to extract robot pose measurements automatically and effectively. Applying the relative calibration methodologies presented in this article to a GMF S-200 six-axis robot, robot repeatability was reduced by 39% and average localized robot inaccuracy was reduced from 3.4 mm (0.134 inch) to less than 0.86 mm (0.034 inch). The compensated robot inaccuracy is near the unstructured robot repeatability.

A measurement system was designed to meet high positioning accuracy requirements for trajectory-determined industrial robots in its partial workspace. Positioning error was calculated and its varying laws were analyzed by tracking the spatial position of the tool center point (TCP) of the industrial robot using a laser tracker and then transforming the relevant coordinate system. A neural network model of the difference between the commanded TCP position and the positioning error of the industrial robot was built. A reverse compensation model of the positioning error of the industrial robot was constructed based on the reverse compensation principle of positioning error, after which the commanded TCP position coordinates were revised accordingly. The experimental results show that the proposed method is feasible and effective, the average positioning error of the robot decreased to 0.028 from 3.232mm, the standard deviation decreased to 0.100 from 2.987, and the positioning accuracy increased by more than two orders of magnitude. The proposed method is suitable for situations that involve determined trajectory, high positioning accuracy, and sealed robot control systems, and is easily incorporated into engineering applications.

2012

A high level of positioning accuracy is an essential requirement in a wide range of industrial robots’ applications. Robot calibration is a process by which robot positioning accuracy can be improved. During a manipulator control system design, and periodically in the course of task performing, manipulator geometry calibration is required. Nowadays robot calibration plays an increasingly important role in robot production as well as in robot implementation and operation within computer-integrated manufacturing where the simulated robot must reflect the real robot geometry (Elatta, et al. 2004; Khalil & Dombre, 2004; Perez, et al. 2009).