Mohamed Slamani

Assessment of the positioning performance of an industrial robot

– The purpose of this paper is to investigate the use of a laser tracker, a laser interferometer system and a telescopic ballbar for assessing the positioning performance of a six‐axis industrial serial robot. The paper also aims to illustrate the limitations of these three metrology instruments for the assessment of robot positioning performance and to demonstrate the inadequacy of simplistic performance tests., – Specific test methods in the case of the laser interferometer system and the telescopic ballbar are proposed. Measurements are analyzed in accordance to the ISO 9283 norm., – It is found that, in static conditions and after a relatively short warm‐up, the unidirectional position repeatability of the non‐calibrated industrial robot under study (an ABB IRB 1600) is better than 37 μm, the unidirectional orientation repeatability is at worst 87 μrad, the linear position accuracy is better than 650 μm, and the rotation accuracy is at worst 2.8 mrad (mainly because of the sixth robot axis). It was also found that the dynamic (radial) errors due to vibrations can be up to approximately ±250 μm along a small circular path at TCP speed of 700 mm/s., – It is pointed out that the use of a laser tracker (or any other large range portable 3D measurement system) is questionable for assessing – let alone analyzing in depth – the unidirectional position repeatability of some of todays industrial robots. It is also demonstrated that the laser interferometer system can be used for measuring linear errors along a linear path of motion as well as angular errors about axes orthogonal to the path of motion. Finally, it is shown that the telescopic ballbar is an excellent, comparably low‐cost, high‐precision tool for assessing the static and dynamic positioning performance of industrial robots and its use in robotics should be further developed., – This work is the first to detail the use of three metrology equipments for assessing the positioning performance of an industrial robot. Experimental results are presented and discussed. Some guidelines for optimizing the positioning performance of an industrial robot are provided.

Comparison of two calibration methods for a small industrial robot based on an optical CMM and a laser tracker

The absolute accuracy of a small industrial robot is improved using a 30-parameter calibration model. The error model takes into account a full kinematic calibration and five compliance parameters related to the stiffness in joints 2, 3, 4, 5, and 6. The linearization of the Jacobian is performed to iteratively find the modeled error parameters. Two coordinate measurement systems are used independently: a laser tracker and an optical CMM. An optimized end-effector is developed specifically for each measurement system. The robot is calibrated using fewer than 50 configurations and the calibration efficiency validated in 1000 configurations using either the laser tracker or the optical CMM. A telescopic ballbar is also used for validation. The results show that the optical CMM yields slightly better results, even when used with the simple triangular plate end-effector that was developed mainly for the laser tracker.

Kinematic calibration of a 3‐DOF planar parallel robot

Purpose – The purpose of this paper is to describe a calibration method developed to improve the absolute accuracy of a novel three degrees‐of‐freedom planar parallel robot. The robot is designed for the precise alignment of semiconductor wafers and, even though its complete workspace is slightly larger, the accuracy improvements are performed within a target workspace, in which the positions are on a disc of 170 mm in diameter and the orientations are in the range ±17°.Design/methodology/approach – The calibration method makes use of a single optimization model, based on the direct kinematic calibration approach, while the experimental data are collected from two sources. The first source is a measurement arm from FARO Technologies, and the second is a Mitutoyo coordinate measurement machine (CMM). The two sets of calibration results are compared.Findings – Simulation confirmed that the model proposed is not sensitive to measurement noise. An experimental validation on the CMM shows that the absolute acc...

Modeling and assessment of the backlash error of an industrial robot

This paper proposes an experimental approach for evaluating the backlash error of an ABB IRB 1600 industrial serial robot under various conditions using a laser interferometer measurement instrument. The effects of the backlash error are assessed by experiments conducted on horizontal and vertical paths. A polynomial model was used to represent the relationship between the backlash error and the robot configuration. A strategy based on statistical tests was developed to choose the degree of polynomial representing the effect of the tool center point (TCP) speed and payload. Results show that the backlash error strongly affects the repeatability of the industrial robot. Statistical analyses prove that the backlash is highly dependent on both robot configuration and TCP speed, whereas it remains nearly unaffected by changes in the payload. It was discovered that the backlash error as measured at the TCP may exceeds 100 µm, and that the positive backlash error increases and the negative backlash error decreases when there is increase in TCP speed.

Characterization and experimental evaluation of gear transmission errors in an industrial robot

Purpose – This paper proposes a simple technique for assessing the effect of gear transmission errors in a six‐axis industrial serial robot, as these errors can vitally affect the industrial robots positioning accuracy.Design/methodology/approach – The experimental procedure is developed using a laser interferometer system to measure bidirectional linear position errors for an ABB IRB 1600 industrial robot. A simple technique based on fast Fourier transformation (FFT) analysis is devised and implemented for the characterization, evaluation, and quantification of gear transmission errors. Structural deformation and backlash error are also discussed.Findings – The authors found that the major sources of error affecting the performance of the robot come from joints two and three. They also found that eccentricity errors, structural deformations, and backlash are the most important sources of error affecting the accuracy and the repeatability of the industrial robot studied. Additional tests show that the ro...

A comparative evaluation of three industrial robots using three reference measuring techniques

Purpose – The purpose of this paper is to present a technique for assessing and comparing the static and dynamic performance of three different models of small six-axis industrial robots using a Renishaw XL80 laser interferometer system, a FARO ION laser tracker and a Renishaw QC20-W telescoping ballbar. Design/methodology/approach – Specific test methods are proposed in this work, and each robot has been measured in a similar area of its working envelope. The laser interferometer measurement instrument is used to assess the static positioning performance along three linear and orthogonal paths. The laser tracker is used to assess the contouring performance at different tool center point (TCP) speeds along a triangular tool path, whereas the telescoping ballbar is used to assess the dynamic positioning performance for circular paths at different TCP speeds and trajectory radii. Findings – It is found that the tested robots behave differently, and that the static accuracy of these non-calibrated robots var...

Issues and Challenges in Robotic Trimming of CFRP

Thanks to their adaptability, programmability, high dexterity and good maneuverability, industrial robots offer more cutting-edge and lower-cost than machine tools to bring molded Carbon Fibre Reinforced Polymers (CFRPs) parts to their final shapes and sizes. However, the quality of CFRP parts obtained with robotic machining must be comparable to that obtained with a CNC machine. In addition, the robot itself has to be very stiff and accurate to provide the same consistency and accuracy as their machine tool counterparts. If the robot is not sufficiently stiff, chatter, overall vibrations and deviations in shape and position of the workpieces will occur. Furthermore, during robotic machining of Carbon Fibre Reinforced Polymer, the anisotropic and highly abrasive nature of CFRPs combined with the higher cutting forces and the lower stiffness of the robot, lead to numerous machining problems. Therefore, robotic machining of CFRPs stills a big challenge and need further research. In this position paper, a methodology has been developed and implemented to identify, understand and quantify the machining errors that can alter parts accuracy during high speed robotic trimming of CFRPs.