API’s Multi-Tracker Measurement Solution Reduces Aspheric Optical Error by 80%

19 July 2023 · 3 min read

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API’s Multi-Tracker Measurement Solution Reduces Aspheric Optical Error by 80%

Radian Pro Laser Tracker Assists IOE’s Technical Breakthrough on Large Mirror Measurement

Aspheric lenses and mirrors are manufactured with dimensions and surfaces that are not perfectly spherical or cylindrical. These features reduce spherical aberration and other aberrations, resulting in less complex optical systems. These benefits have led to large-scale aspheric optical systems becoming more and more sought after for astronomical observation and space optics. But the additional features that make the lenses and mirrors aspheric add a great deal of complexity in the design, manufacture, and quality assurance processes, especially at the scales and tolerances demanded for outer space viewing. To break this technical bottleneck, the Chinese Academy of Sciences’ Institute of Optics and Electronics (IOE) worked with API to develop a measurement system using multiple Laser Trackers to apply swing arm contour detection for high-precision in-position detection. Using API’s Radian Pro Laser Tracker, this process:

  • Realized 6 degree of freedom (6 DoF) dynamic and high-precision measuring of the target
  • Reduced measurement uncertainty from 11.8” to 2.4”
  • Improved measurement accuracy nearly five times

IOE, also known as the Chengdu Institute of Optics and Electronics, was founded in 1970. Since its foundation, IOE has made many significant achievements in the fields of adaptive optics, beam control, applied optics and so on, and obtained over 500 scientific research awards including top prizes of the National Science and Technology Progress Award. With support from China’s National “863” and “Light of the West” Programs, IOE set out to improve the manufacturing process for large-scale aspheric lenses and mirrors by measuring the working volume of the swing arm’ rotational axis.

Researchers from IOE contacted API to discuss their Radian Laser Tracker Series, and together API and IOE developed a high-precision measurement system using four laser trackers to calculate the working volume of the swing arm profiler’s rotational axis. The four Laser Tracker setup solved the problem of low accuracy when using a single laser tracker to this working volume.

System Composition

1. API Radian Pro Laser Tracker

API’s Radian Pro Laser Tracker is equipped with ADM (absolute laser) and IFM (interferometry laser) lasers; IFM interferometry laser is the standard for length measurement, which provides a high precision guarantee and data traceability for the whole system.

2. TTL (or other) Data Synchronization System

A Data Synchronization System is a device which can trigger multiple Laser Trackers to collect data at the same time. There is a special signal generator in this system, and this generator uses the pulse signal to order the trackers to collect data at the same time. The user can trigger the trackers selected together during the measurement task.

3. API Signal Synchronous Processing Software

This software was invented by API and is used to analyze the data which are collected from the multiple trackers. The software can fulfill various customer requirements, including unifying the coordinates of multiple trackers, defining the coordinates of the target, and synchronously analyzing the collected data.

As a micron (μm) level precision measuring instrument, Laser Tracker measurement accuracy has been recognized by many advanced manufacturing industries in the last three decades and has been used in various key projects globally. A single Laser Tracker has been able to achieve ultra-high precision measurement, but in some precision engineering with more stringent requirements for measurement accuracy, the multi-tracker solution can further improve measurement accuracy.

The source of measurement error in a single laser tracker is 90% from angular error. In a multi-tracker measurement solution, several Laser Trackers measure one point at the same time and calculate this point’s position according to data collected on the tracker’s own position as well as the point’s location, so as to maximumly avoid tracker angle error and get relatively more accurate measurement data.


Using multiple Radian Pro Laser Trackers, IOE carried out spatial layout measurements and measurement algorithm research, and the measurement uncertainty was decreased from U=11.8″ to U=2.4″ and improved measuring accuracy by nearly five times. On this basis, the first practical engineering prototype based on swing-arm profile detection technology has been formed, which can

meet the requirements of actual engineering measurements. At present, there are no other reports of such engineering practical prototypes in China.

The work of IOE and API is just one example of a multi-tracker measurement solution that realizes the 6 DoF dynamic high-precision measuring and monitoring of a target and greatly improving measurement accuracy. To learn more about multi-tracker applications or any of API’s other dimensional metrology products and services, please fill out the form below to contact a Real Metrologist today.

Four Laser Trackers are Used to Measure Large Aspheric Mirrors with High Precision

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