Case Studies

FARO Laser Tracker Provides High Measurement Accuracy Essential for Assembling Astronomical Telescopes

FARO Laser Tracker Provides High Measurement Accuracy Essential for Assembling Astronomical Telescopes

There are eight* planets in the solar system. These include Venus – also known as the morning or the evening star, Mars – a planet that shares much of Earth’s characteristics and ability to support life, and Jupiter – the largest planet in the solar system with an apparent magnitude of minus two. Jupiter, interestingly, has at least 67* natural satellites surrounding it, including four large Galilean moons. The planet has captured man’s imagination, and been observed across the world since centuries ago. (*Accurate as of July 2016)

In June 2014, the University of Tokyo captured volcanic activity in the Daedalus Patera region, on “Io”, one of the Galilean moons that orbit Jupiter. This was done using an astronomical telescope, miniTAO, installed in the Atacama Desert of Chile. Although the results were achieved by a relatively small telescope with a caliber of 1m, it was an important contribution towards subsequent planetary observation research.

The miniTAO was manufactured and installed by Nishimura Co., Ltd (Nishimura). Based in Kyoto, Japan, the company focuses on designing, developing, manufacturing, and installing astronomical telescopes, domes, and special observation equipment for universities and research institutions. With growing public interest in space debris and satellites in recent years, Nishimura observed an increase in domestic and international orders for its large telescopes and astronomical domes.

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The miniTAO telescope used by the University of Tokyo. It is installed in Chile’s Atacama Desert.
 

High Precision Measurements Support Higher Levels of Accurate Assembly

90 years has passed since Nishimura manufactured its first domestic telescope in Japan, back in 1926. At the request of various local and international research institutions, the company installs telescopes and observation equipment in locations across the world. It is not unusual for Nishimura’s telescopes to be installed in places such as deserts and highlands, due to the clear air and low humidity conditions that these areas provide.

Large telescopes require high accuracy measurement support as they are computer-controlled to facilitate uninterrupted movement. Additionally, accurate measurements come in handy when large telescopes are installed in harsh environments to provide precise observation data. Amidst strong wind conditions, these environments also fluctuate immensely between day and night temperatures.

Recently, Nishimura was commissioned to manufacture and install an astronomical telescope for the King Saud University in Saudi Arabia. Upon installing the telescope, Mr. Takayuki Seki, General Manager of the Manufacturing Department at Nishimura, said, “Since a telescope will be installed in the open air and will have to withstand extreme weather conditions, we wanted to design a sturdier piece of equipment that can withstand the harsh outdoor environment. To do so, we need to secure high accuracy measurements that would enable the telescope to be assembled seamlessly.”
 

Portable 3D Measuring Device Perfects Large Volume Measurements and Delivers High Performance Even Under Harsh Conditions

An astronomical telescope, once manufactured and assembled at Nishimura, is then dissembled and transported, to be reassembled at its installation site. Each telescope component is significant in size – with the telescopic mirror measuring several meters in diameter, and the telescope base diameter ranging from 3 m to 12 m. The total weight of a telescope can therefore be well over 20 tons. In the past, Nishimura conducted its measurements using a level and dial gauge. Mr. Seki explained, “In assembling a telescope, we measure the roundness and flatness of the rotating rail of the pedestal, and the perpendicularity of a biaxial drive shaft. However, it can be time consuming, and depending on the measurement points, the process can take anywhere from two days to two weeks.”

In 2008, Nagoya University lent its FARO Laser Tracker ION, a high precision and high-speed measurement system, to Nishimura, allowing the manufacturer to measure its larger telescopic components. The device provided the manufacturer with immense support in completing measurement tasks quickly and accurately. However, as measurement requirements increased, it became increasingly inconvenient for Nishimura to borrow the equipment. Furthermore, the company wanted to have a measurement device to call their own.

In 2015, Nishimura purchased the FARO Laser Tracker Vantage, FARO’s latest compact and portable laser tracker with a measuring range of 80 m, to support its measurement processes. According to Mr. Seki, the laser tracker significantly reduced overall measurement time – from two days to half a day, and from two weeks to two days. Complex parts that were challenging to measure in the past could now be accomplished more easily and accurately with the laser tracker. Mr. Seki shared, “We could not measure the self-weight variations in barrel truss structures previously. As the direction of gravitational forces shifts as the telescope moves, we now measure the amount of displacement using the laser tracker. In assembling a telescope, the level of accuracy required is ± 20 μm. Since introducing the laser tracker, we have been able to conduct measurements more quickly, accurately, and easily.”

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The FARO Vantage is used to measure telescope components during production.

Pleased with the device, the company has plans to bring its Vantage along for installation overseas for future assemblies. Nishimura’s latest installation project is to assemble its TAO telescope in the Atacama Desert of Chile. Due to the success of the miniTAO project in withstanding extreme weather conditions in the highland desert, the University of Tokyo engaged Nishimura to install a unit of TAO, a larger astronomical telescope with a diameter of 6.5 m. The Atacama Desert is located in the highlands of Chile at about 5,600 m elevation. During the day, temperatures in the summer can average around 5 – 10°C, and drop to – 20 °C in the winter. Describing the performance of the Vantage in a harsh environment, Mr. Seki said, “We know that the miniTAO is sturdy to withstand extreme weather conditions, so we’re now confident to install the larger telescope, TAO. The Vantage performed exceptionally well with no issues, even at a high altitude of 5,600 m, and that is remarkable. It would be great if we can bring the Vantage for assemblies in Antarctica for future projects.”

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The TAO telescope base’s peripheral portion features a structure with a diameter of 12 m, with a top surface deviation of 0.05mm.
 

Telescopes for the Future

At the request of the Japan Aerospace Exploration Agency (JAXA), Nishimura is currently manufacturing a 60 cm telescope for the purpose of discovering space debris and communicating with satellites. After measuring the roundness of the telescope frame, and the trajectory of the motion where the lens is mounted, the telescope will be assembled in Nagano Prefecture. As requests for larger telescopes continue to grow, Nishimura plans to relocate its manufacturing plant to meet market demand.

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Dr. Otani measures the roundness of the telescope frame, designed for JAXA, with the laser tracker.

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The Vantage measures the trajectory of the scanner belonging to the Shanghai Astronomical Observatory.

Addressing future initiatives, Mr. Seki shared, “Over time, it is expected that a telescope will deviate from its original installed position due to gravitational influences. Before the Vantage, we had to be content with telescope data achieved using a charge-coupled device (CCD) camera and analysis. Now, we can expect to qualify displacement by using the Vantage, something that was not possible previously. By measuring the degree of displacement, we can track the secular change of the telescope every year. It will be possible for us to compile and utilize telescope data obtained with the Vantage, and also with the CCD camera. Both methods are valuable as they enable us to evaluate the data differently.” As Nishimura continues to support the industry with its professional equipment, Dr. Kazuto Otani, Ph.D. of the Optical Equipment Section at Nishimura, expressed the company’s desire to play a bigger role in facilitating the growth of satellite communication, “Right now, we manufacture telescopes and domes for research, but we hope to go beyond that to do more for the space industry.”
 

About Nishimura Co., Ltd.

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Nishimura Co., Ltd. designs, manufactures, sells and maintains telescope, astronomical observation equipment, astronomical observation domes, sliding roof, solar telescope, and other large special optical equipment for academic and research institutions. The company has been involved in high quality telescope manufacturing in the front lines. They have worked on projects with corporations and institutions based in Japan, China, Saudi Arabia, and Taiwan.

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