Jiyun Zhang

The rotation of a rotary table inevitably induces six typical motion errors. To improve the measurement efficiency and accuracy of rotary table motion error detection, this paper proposes a novel system for the simultaneous online measurement of six-degree-of-freedom (6-DOF) motion errors. The system consists of a 5-DOF measurement module and an independent angular position error measurement module. The proposed system innovatively integrates an axial motion error measurement module into the original 4-DOF measurement framework. Based on the optical collimation principle, the system employs a beam-splitting flat plate to split the light beam of the original 4-DOF optical path, enabling real-time monitoring of the axial motion error of the rotary table. Meanwhile, an optical path adjustment strategy for axial motion error detection is proposed. Based on geometric analysis, an error model is constructed to eliminate the interference of radial and tilt motion errors on axial motion measurement, thereby achieving accurate acquisition of six-dimensional motion errors. The experimental results indicate that the angular error measurement accuracy of the proposed system is ±2″ within a measurement range of ±100″, with a standard deviation ( σ ) of 1.3″. For linear error measurement, the accuracy reaches ±3 μm over the ±100 μm range, accompanied by a standard deviation of 1.7 μm. The experimental results confirm the favorable accuracy and stability of the proposed 6-DOF measurement system for rotary table error measurement. Therefore, the system is applicable to precision rotary tables (⩾2 σ ), and future work will focus on performance optimization to extend its capability to ultra-precision rotary axis measurement.

1. Driven by the Industry 5.0 paradigm and the rapid advancement of intelligent manufacturing, industrial robots have become pivotal enablers of digital transformation in modern production systems....

Highly reflective surfaces often cause overexposure in fringe projection profilometry, leading to missing or distorted point cloud data. To overcome this limitation, this study proposes a mask-based method for generating adaptive fringe patterns, combining surface reflectance distribution characteristics with fringe projection principles. First, dynamic masks for non-saturated and saturated regions are generated according to pixel intensity values. Second, a linear regression equation is determined using the least squares method, and the light intensity scaling factor is calculated by combining the camera-projector coordinate mapping relationship to dynamically generate adaptive fringe sequences that match local reflectivity. Finally, the encoded fringes are projected onto the surface of the measured object for 3D reconstruction. Experimental results demonstrate that, compared with the traditional phase-shifting method, the point cloud coverage in highly reflective areas of typical metal workpieces increases significantly from 65.4% to 90.1%, with the use of only one set of masks, thereby improving measurement efficiency. Moreover, the proposed method exhibits good applicability for typical metal parts and plastics. The point cloud coverage in highly reflective regions shows an increase of over 22%.

This work presents the development of a 3-D passive scale tracker (3DPST) for industrial robot pose accuracy detection. A nonlinear optimization error parameter identification approach based on a geometric error model is given in order to acquire geometric errors of the instrument precisely and simply. The spatial measurement accuracy of 3DPST has greatly increased after new error parameters adjustment. Additionally, the robot pose errors are measured by 3DPST, and a laser tracker (LT) is employed as a reference tool for simultaneous comparison and verification. Moreover, as a result of the presence of Abbe offsets between the measurement points of the two instruments, orientation errors will affect positioning errors in the comparison procedure. Therefore, it is crucial to apply the Abbe principle while transferring the error values from the LT measurement points to the 3DPST measurement points. According to ISO 9283, the pose accuracy is measured using a cube in the robot workspace. The maximum measurement difference of positioning errors and orientation errors between the two instruments is $\pm 33.1 \mu \text{m}$ and 0.0723°, respectively. This demonstrates that the two instruments’ calibration capabilities are comparable, and 3DPST can complete the pose accuracy calibration of industrial robots.

Laser trackers are usually used to measure spatial positional error of the moving targets on large-scaled objects, such as the airplane profile. It is a spherical coordinate system with a dual-axis tracking mirror actively controlled by the built-in servo system to direct the laser interferometer beam always toward the reflecting target. It is very expansive when used in testing the spatial positional accuracy of industrial robots, which are rapidly growing for factory automation in recent years. Therefore, simplified from the laser tracker structure, a 3D passive laser tracker (3DPLT) for measuring spatial trajectory of a moving target is proposed. It is composed of a 2D rotary stage and a linear telescopic mechanism with an end-ball, which can be magnetically sucked by the moving target. The rotational angles of the 2D rotary stage are measured by two respective encoders, and the radial displacement of the telescopic mechanism is detected by an equipped laser interferometer. The world coordinate of the target can be obtained by the coordinate transformation from the spherical measuring system of 3DPLT. Multibody system error modeling is used to analyze the measurement error of the instrument, and testing methods of the main error sources are also proposed. After accuracy calibration and error compensation, the measurement error of the 3DPLT is 49.2 μm, which is good enough to calibrate the spatial trajectory error of the robot.

This paper proposes a five degrees-of-freedom measurement system for measuring geometric errors of the rotary axis. To align the measured rotary axis with the reference axis, a diode laser is used to represent the rotary axis of the measured rotation stage. Based on the proposed measurement system, a model for separating the position independent geometric errors and position dependent geometric errors of the measured rotary axis from the measured value is established and verified by measurement experiments. The results of measurement experiments repeated for five times show that the measurement uncertainty of the proposed measurement system is less than ±1.6 µm for radial motion, the measurement uncertainty is less than ±1.7 arc sec for tilt motion, and the measurement uncertainty is less than ±1.3 arc sec for angle position.

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