Dynamic Measurement of 6-DOF Platform (Simulation Platform)

In the manufacturing and R&D processes of modern aircraft, spacecraft, vehicles, ships, etc., conducting 6D dynamic simulation experiments has become an indispensable project. Consequently, the dynamic pose metrics for a 6-bar platform used in 6D simulation have become a critical performance indicator for such platforms. In practical applications, factors such as mechanics and control can generate dynamic motion trajectory errors in the 6D platform; excessive errors may prevent the platform from meeting expected precision requirements.

Among the many causes of error, evaluating dynamic 3D spatial error is particularly important. This data requires measurement under dynamic, high-precision conditions, which poses a challenge to traditional measurement methods, as conventional static techniques struggle to capture effective dynamic 3D data. Therefore, finding a method capable of large-range, high-precision, dynamic data acquisition has become key to solving simulation platform testing issues.

API Laser Tracker Dynamic 3D Precision Testing Solution

To address the difficulty of measuring dynamic 3D spatial positional accuracy, API developed the 3D point dynamic measurement target - ActiveTarget (as shown in Figure 1, hereinafter referred to as AT Target). Similar to traditional SMR targets used with trackers, the AT Target reflects the tracker's laser beam back via a mirror body to complete spatial positioning. Its distinguishing feature is that it possesses drive motors in both horizontal and vertical directions, enabling automatic positioning of the reflective target, effectively functioning as a mobile SMR.

Figure 1: API Series Laser Trackers

Figure 2: Performance Overview of Various Laser Tracker Models

Figure 3: API Laser Tracker (Radian Plus) and ActiveTarget

In practical measurement operations, the AT Target offers the following advantages:

- Regardless of its orientation or movement in space, the AT Target always locks onto the laser beam; even during rapid and arbitrary movement measurements, the laser tracker will not lose the signal;

- During measurement, the AT Target automatically tracks any rotating target without manual intervention, completing coordinate acquisition of its 3D dynamic position;

- The introduction of the AT Target makes high-precision dynamic 3D spatial positioning measurement of large 5-axis/6-axis machine tools, robots, simulation platforms, and mechanisms easily achievable.

3D Dynamic Measurement Requirements for Simulation Platforms

For measuring 3D dynamic data of simulation platforms, the platform must be started and operated along a planned path. Data at various positions along the dynamic trajectory should be collected and analyzed to achieve the following:

1. Compare the measured dynamic point coordinates with the theoretical trajectory model to determine spatial error values, yielding maximum angular displacement error and maximum linear displacement error;

2. By comparing changes in distance between measured points and angle changes relative to the center of point pairs against corresponding time intervals, derive maximum linear velocity and angular velocity;

3. Project dynamic trajectory points onto three orthogonal planes to evaluate the dynamic matching performance during operation among moving bodies.

Figure 4: On-site Inspection of 6-DOF Platform

Actual Measurement and Target Achievement

During actual measurement, simply set up the Radian or iLT laser tracker at an appropriate location, aim the laser at the AT target mounted on the target end, and begin measuring. As the target end moves along a predetermined trajectory, the API laser tracker performs dynamic measurements at a sampling rate of 1000 points per second, transmitting data in real time to the measurement software for recording, enabling both real-time and post-processing analysis.

Throughout the entire measurement process, the AT target continuously faces the laser tracker in its optimal orientation and locks onto the laser beam, automatically adjusting its attitude without manual intervention, ensuring smooth and efficient measurement throughout.

The ActiveTarget active target features a highly integrated design with a compact form factor, weighing only 0.9 kg. It boasts extremely high optical centering accuracy and can rotate infinitely in all horizontal directions (360°), allowing it to be easily mounted on the end of the measured target in any orientation, providing maximum convenience for measurement tasks. Additionally, its battery-powered operation eliminates cable constraints entirely, and its standard operating life of over 16 hours provides strong assurance for the seamless execution of measurement operations.

Figure 5: Introduction to the ActiveTarget Moving Target

Conclusion

In summary, the combination of API's Radian or iLT laser trackers with the ActiveTarget moving target offers a system that is easy and quick to install, simple to operate. With just a few straightforward setup steps for the tracker and the AT moving target, it can effectively handle dynamic 3D trajectory measurements for simulation platforms, laying a solid foundation for enhancing overall simulator performance.

Figure 6: Introduction to API Laser Tracker Functional Extension Accessories

More Extensions

Beyond the ActiveTarget moving target introduced in this article, based on continuous exploration and deep understanding of measurement sites, API has developed other functional extension accessories for laser trackers. These include the STS six-axis sensor capable of dynamically detecting six-dimensional parameters, and the vProbe intelligent probe head designed for measuring deep holes and hidden points. Please refer to Figure 6 for brief introductions to the functions of each accessory product.