Customised gearbox aids extraterrestrial search

Cone Drive enlisted the help of sister company David Brown to upgrade the shutter motion of the world's largest optical and infra-red telescope.

The second stage of an upgrade project has seen Cone Drive working with Dangel Robots and Machinery to provide another specialist solution for the world famous WM Keck Observatory at the summit of Hawaii's Mauna Kea.

Cone Drive had already been involved in a successful project to replace exterior mounted worm boxes in 2004 and this time returned with additional expertise provided by its sister company David Brown to upgrade the shutter motion of the world's largest optical and infra-red telescope.

The latest stage of the project involved installation of new drives for the two massive shutters on the dome that encloses the Keck I telescope.

The upper and lower shutters weigh around 47 and 23 tonnes, respectively.

Central drive motors were replaced with synchronised drives on each side of the shutters.

Cone Drive and David Brown - both Textron companies - worked together to provide custom gearbox input and output shafting to match the drive train requirement and simplify the installation which was an onerous task given the telescope's location at 4300m elevation and the requirement to complete the work during a scheduled shutdown.

It was critical to minimise the length of the shutdown required to perform this work in order to avoid losing valuable observing time.

Dangel Robots was engaged to assist with the drive train design and provide the motion control system and software.

The new motion control system incorporates a number of unique features not available previously.

The most significant operational improvements are the ability to use the shutters to track the vertical motion of the telescope to minimise the effect of wind buffeting, and faster shutter speed to close up quickly if the weather turns bad.

Other new capabilities are to move the shutters together with a minimum gap for daytime maintenance, to independently operate the left and right side drives for alignment, and to control shutter speed during portions of the move profile.

For the power transmission, Dangel Robots specified a David Brown G14 right angle bevel-helical gearbox to combine the functions of both the original mitre and helical reduction boxes.

A motor bracket was designed to mount both the motor and the G14 gearbox using some of the existing holes in the shutter frame to ensure the drive train output alignment.

The close working relationship between Cone Drive and David Brown provided custom gearbox input and output shafting to match up the drive train requirement.

This drop-in solution greatly simplified installation on the shutter.

Dangel Robots built a custom enclosure for the motion controller, 40hp inverter drives and drive components to fit inside the curvature of the dome.

Dangel Robots also created a twentieth-scale model of the shutters with 1hp motors to test the motion control electronic components and the software.

The mechanical model and motion control system were interfaced to the Keck telescope operating computer to test all of the motion control functions prior to installation on the actual dome.

Keck Observatory personnel installed the new drive train hardware and control system during a shutdown in the late summer of 2005.

Installation went smoothly and was completed on time.

Shutter motion is faster, smoother and quieter than it was with the old power transmission.

The Keck I telescope is one of two operated by the California Association for Research in Astronomy at the summit of Mauna Kea.

Each telescope stands eight storeys tall and weighs 300 tonnes, yet operates with nanometre precision, probing the deepest regions of the universe.

The dome and shutters for the Keck II telescope were originally built using Cone gearboxes in 1995 and they are still performing today.

Cone Drive provided a "drop in" solution to replace the reducers on the shutters for the Keck I telescope that was built in 1991.

The original reducers were undersized and causing maintenance problems.

Seal leaks were of special concern because of the low temperatures and dry air at such high altitude.

The observatory presents obvious maintenance problems and the aim was to find a replacement reducer that would require minimum modification at the summit, and which offered an increased service factor and improved seal arrangement.

For the final stage of the project four David Brown G14 gearboxes with a ratio of 41.6:1 were added to the 14 previously installed Cone custom 8.000in centre distance HP double enveloping worm reducer units with a special ratio of 9.75:1.

Modified shafting, housings, mounting flanges and keeper plates were provided to mount the gearboxes and connect them together.

The gearboxes incorporate taconite seal arrangements on both input and output shafts.

Oil expansion chambers were supplied to provide sealed units since the gearboxes change attitude as the shutters move up and down over the dome.

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