An Industrial Robot Based Drilling System for Aircraft Structures

The use of industrial robots for welding automation is a major and expanding applications area. In a welding task, the robot should smoothly trace along the weldseam with appropriate tool poses. For welding a complex 3-D curve, a large number of points should be taught to make the weld path smooth. This is a very tedious job and is not an easy way to leach the robot. In this paper, the requirements of a CAD system to be used as a robotic off-line arc-welding programming system are discussed. An off-line programming system for such application was developed. The workpieces and the weldseam were represented by analytical geometries. The positions and orientations of the weldgun along the trajectory were analysed by the task requirement of the welding procedure and solved by differential geometry. Calibration process was discussed to ensure programs were properly executed. This system is especially useful for off-line programming for the welding of complex 3-D curves.

Grinding/lapping process is the final process for mold manufacturing, and is the criteria to check the quality of molds. However, this process depends on manual operation due to its work characteristics, and becomes the bottleneck process in the whole mold manufacturing process. To reduce mold manufacturing lead time, and to improve its productivity, multi joint robot system is implemented to automate grinding/lapping process. Total 8-axis redundancy grinding/ lapping robot system is developed as automation system which consists of 6-axis multi joint robot, 1-axis straight line carriage, 1-axis index table for walk rotation. Especially, we developed simulator which enables virtual drive simulation using OLP (Off Ling Programming) by importing 3D mold design data. In this study, we analyzed position error by measuring drive position command value and actual site robot driven automatic teaching using laser tracker, to optimize OLP simulation's operation program for grinding/lapping robot system. Based on this error analysis data, it will be able to compensate position for 3D walk model in virtual environment.

More and more robot control systems require intelligent extensions such as vision or virtual reality (VR) system in order to be capable of easy and flexible interaction with the environment or humans. This paper describes the stereo vision, virtual reality and off-line programming part of the intelligent control system of the Puma 560 robot and the dextrous hand developed at the Technical University of Budapest. With the use of the detailed graphic models of the VR system, efficient off-line robot programming and simulation of the contact forces between the hand and the grasped object is available. A simple robot programming language, which was written specifically for this robot-hand system, is introduced.

In this paper, a model is presented which, based on a description of the shape of a welding seam (the gab size and bevel angles), can be used to select variables controlling the welding of a root-bead. The model can be used in an off-line programming system as well as in a geometry-sensor based control system.The model is a stationary model and it is established on an empirical basis. Tests indicate that the model can be used to select control variables for seams with root gabs between 2 and 5 mm. The allowed deviation from the nominal value of the gab is app. 0.5 mm.The model has been implemented in an off-line programming system generating robot programs for welding thick walled large diameter nozzles perpendicular onto pipes. Tests with this off-line programming system indicate that if the workpiece geometry is defined sufficient well, a satisfactory weld quality is obtained when executing the control variables computed by the model.

Processing configuration off-line optimization for functionally redundant robotic drilling tasks

In recent years, industrial robots have been introduced to various production sites through teaching playback, enabling more efficient assembly lines and welding lines for large workpieces in automotive and other industries. Furthermore, offline programming is expected to be utilized for cutting workpieces that are becoming even larger in the next-generation EV giga-cast and construction industries. However, the machining accuracy of robots, in terms of motion accuracy, is lower than that of machine tools, and their low rigidity causes vibration. Therefore, in this study, we attempt to construct a system for the practical cutting of large workpieces by attaching a DC brushless motor controlled by a single-board computer and drill to the end-effector of a large industrial robot and examining the basic characteristics of this system. The relationship between the rotational speed and duty ratio of the pulse width modulation voltage is clarified, and the range where the rotation speed is stable is found such that any rotation speed can be output. It is also clarified that the mechanical time constant of the rotational speed of the motor changes when the temperature of the motor spindle changes.

Robot end-effector position measurement is very essential to determine the error between the commanded position and actual position reached by the robot end-effector. This also ensures the error with which the robot end-effector traces the commanded path. Conventionally position measuring devices like laser trackers, coordinate measuring machine and other non-contact-based position measuring devices are widely used to measure the position of the end-effector due to their high accuracy and precision, even though they are very expensive. This paper presents a cost effective solution for the measurement of position of robot end-effector. An end-effector position measuring device is designed and developed in spherical coordinate system using two absolute rotary encoders and a draw-wire sensor. A mathematical model for the end effector position measuring device is developed to determine the position of the end-effector with respect to a reference coordinate system using 3D homogeneous transformation approach. End-effector position measuring device is tested for ABB IRB 1600 for numerous poses and for a straight line path. The newly developed end-effector position measuring device is found to be capable of measuring the end effector position with an accuracy of 2 mm and hence can be implemented in calibration of industrial robots.

In this article, an orthogonal 6-degree-of-freedom (DOF) parallel robot with redundant actuation is studied as an earthquake motion simulator. Taking the practical simulation of earthquake waves into consideration, the general characteristics of natural earthquakes are analysed and complexity and variety of seismic waves, three-dimensional and multi-DOF movement, and strong devastating force are regarded as the three obvious features in this article. Based on the characteristics of this orthogonal 6-DOF parallel robot with redundant actuation and the features of earthquakes, the feasibility of using this parallel robot as an earthquake motion simulator is analysed from three aspects: orthogonal 6-DOF structure, decoupling feature, and redundant actuation module. In order to simulate an earthquake motion using this parallel robot, its inverse kinematics and dynamics models are derived. The control system of this earthquake simulator is developed based on the PXIbus development platform. The computed-torque control algorithm based on the inverse dynamics is used in the controller of this equipment. A typical three-directional earthquake motion, the El Centro earthquake, is simulated on the end-effector of this parallel robot by means of its mathematical models and control system. Three main motion parameters of simulated seismic waves, displacements, velocities, and accelerations, are measured, respectively, by laser tracker and acceleration sensors. The experimental results show this equipment is appropriate to be used as an earthquake simulator.

The optimization of re-production processes in the industrial manufacturing has long been the main interest in order to stay competitive. Only lately the idea spreads that optimizing the pro- duction, in the sense of innovation, could bring further improvement. This paper discusses aspects of introducing automation technology into the manufacturing of one-of-a-kind products. The co-ordination of 3D-optical feed-back with a graphic layout-, off-line programming and simulation system, and with a dual robot cell for flame-cutting, arc-welding and assembly is being developed at the BIBA as a demonstrator and testbed. The main emphasis is put on the active structured lighting for optical 3D-measurement with LCD-line projectors. The concept of the coded light approach and the phase shifting method for the 3D- data acquisition are described. With attention to the application in a robot cell for one-of-a- kind production the components of the measurement system are designed as robot based tools. For calibration and inspection purposes operation sequences are planned with the graphic simulation system. For the extraction of special points out of the 3D-clusters a simple and pragmatic method is applied.

This paper presents an automated calibration method for industrial robots, based on the use of (1) a novel, low-cost, wireless, 3D measuring device mounted on the robot end-effector and (2) a portable 3D ball artifact fixed with respect to the robot base. The new device, called TriCal, is essentially a fixture holding three digital indicators (plunger style), the axes of which are orthogonal and intersect at one point, considered to be the robot tool center point (TCP). The artifact contains four 1-inch datum balls, each mounted on a stem, with precisely known relative positions measured on a Coordinate Measuring Machine (CMM). The measurement procedure with the TriCal is fully automated and consists of the robot moving its end-effector in such as a way as to perfectly align its TCP with the center of each of the four datum balls, with multiple end-effector orientations. The calibration method and hardware were tested on a six-axis industrial robot (KUKA KR6 R700 sixx). The calibration model included all kinematic and joint stiffness parameters, which were identified using the least-squares method. The efficiency of the new calibration system was validated by measuring the accuracy of the robot after calibration in 500 nearly random end-effector poses using a laser tracker. The same validation was performed after the robot was calibrated using measurements from the laser tracker only. Results show that both measurement methods lead to similar accuracy improvements, with the TriCal yielding maximum position errors of 0.624 mm and mean position errors of 0.326 mm.

This paper presents the experimental characterization and vibration control of a flexible robotic system. For this work, a test bench was built to characterize the harmonic drive (HD) and joint components, while control algorithms were designed and compared to minimize vibration. Encoder accuracy was critical since the difference in the measurements between two encoders was used to evaluate the vibrational behavior of the test set-up. Therefore, a laser tracker was used to characterize the error of the output encoder. Real-time compensation using this technique achieved an angular position accuracy of 50 µrad. Four rosette strain gauges were fixed to the HD’s flexible spline to determine its torsion. To reduce torque ripple, a real-time correcting function was applied. It was thus possible to reduce the error to 0.3% of the full-scale error. Two vibration control strategies were developed, namely, singular perturbation and feed-forward control. Simulation results showed that both control strategies greatly reduced vibration response compared to a common rigid control. However, test results showed that good vibration control could only be achieved with the feed-forward approach: the singular perturbation technique generated too much torque ripple to the motor. A feed-forward controller can quickly stabilize the link, achieving the same settling time as with the rigid control algorithm.

The paper describes the improvement in drilling efficiency obtained in five mature North Sea fields, by using a systems approach. The drilling program was managed by a drilling efficiency group consisting of a service company, drilling contractor and operator engineers drawn from several disciplines. All of the well sections were geometrically complex. Data was gathered using downhole pressure and vibration sensors, and acoustic caliper sensors. MWD annular pressure measurements had shown that conventional steerable motor/bit combinations required extensive circulation and occasional back reaming to ensure adequate hole cleaning. MWD vibration measurements and BHA modeling had proved that particularly high levels of vibration were caused by both circulating and back reaming. This was directly associated with MWD, motor and other downhole tool failures. It was concluded that the basic problem was hole quality and attention was directed to eliminating hole spiraling deduced from MWD logs and calipers. A new combination of compatible steerable PDM and long gauge bit was designed with input from the operator. This was designed to achieve improved hole quality from long gauge bits without losing the rapid deviation response of conventional motor/bit combinations. The aim was to improve overall drilling system efficiency, particularly poor hole cleaning, excessive torque and drag, and slow ROP when sliding. The paper discusses the initial data gathering and diagnosis and how measurement and modeling of downhole conditions led to the optimal solution. Comparison between 8 conventionally drilled hole sections and 8 hole sections drilled utilising the new drilling system showed more than 50% reduction in overall drilling time. Significant time savings have been made when drilling in the orientated mode. Other benefits are reduced drilling WOB from 30,000 lb to 3,000 lb, reduced drilling torque and drag, and an overall improvement in hole quality reflected by improved hole cleaning.

In this paper, the path planning method of a redundant robotic work cell consisting of an overhead linear rail and a FANUC 6-joint robot mounted on it is studied for the continuous-trajectory tracking task. The existence of the solution of the inverse kinematics problem of the rail-mounted industrial robot (RMIR) is discussed and an analytical redundancy resolution scheme for RMIR is proposed based on the workspace. The path planning method with the performance evaluation mechanism makes the end-effector (EE) of robot reach the target position and posture and avoid joint limit, which makes the best of the redundant degree of freedom to improve the robot performance. The results of simulation and experiment prove that the proposed method is effective in the application of the long and closed-trajectory tracking. The above research findings are integrated into the robot off-line programming (OLP) software developed based on the UG platform and successfully applied to the robotic induction hardening for the chamfers of the large automobile panel dies.

A knowledge-based multipass welding distortion estimation method for a multi-robot welding off-line programming and simulation software

The abrasive waterjet technology (AWJ) is a non-traditional method of machining which offers a productive alternative to conventional techniques. Aerospace composite materials although possessing special properties such as high strength to weight ratio and stability, are known to be difficult to machine, or even impossible to be machined by conventional methods. However, by using abrasive waterjet these composite materials can be efficiently machined. In this paper, two-dimensional and three-dimensional AWJ cuttings are addressed and a focus is placed on the challenging three-dimensional waterjet trial and due to its much more complexity involved, very little work has been done so far. The following subjects were studied: Off-line programming and simulation using IGRIP software, setup and control of the three-dimensional system etc. Finally, a few two-dimensional and three-dimensional abrasive waterjet machining conclusions and future research work are given that reflect our ongoing research.