VLT Cassegrain Adapter-Rotators


The complete adapter-rotator units comprise two major subsystems: the opto-mechanical part and the control system.The Opto-Mechanical part consists of three main sub-components listed below.

  • the Large Structure
  • the Sensor Arm
  • the Maintenance and Integration Equipment

The figure shows the general sectional view of the Cassegrain Adapter-Rotator indicating the main elements.

The Large Structure

The Large is composed of two main sub-components, the Instrument Rotator and the Adapter plus some smaller assemblies (Safety Brake,Limit Switch systems, Cable Wrap, Hoses and Cables).

The Instrument Rotator consists of a large flange to which the scientific instrument is attached. The flange is mounted on a bearing which is driven by a Drive Unit to allow the instrument to be rotated around the telescope optical axis to follow the rotation of the telescope field. The other part of the bearing is directly fixed to the telescope primary mirror cell (M1-Cell Adapter flange) and support the Adapter.

The Adapter consists of the Adapter Structure, the Adapter Box and the Drive Unit. The Adapter Structure is fixed to the fixed part of the Instrument Rotator bearing and supports the Adapter Box.

Like the Instrument Rotator, the Adapter Box is supported by a large bearing. The Drive Unit allows the Adapter Box to be rotated about the telescope optical axis. The Adapter Box, in turn, supports the Sensor Arm described below. The Cable Wrap transports Cables And Hoses from the Adapter Structure to the Adapter Box and Sensor Arm. The Safety Brake prevents motion of the Instrument Rotator when the Rotator Drive Unit is not powered. The Limit Switch Systems control the limits of rotation of the Adapter.

The Sensor Arm

The Sensor Arm comprises a Turntable, a Supporting Arm, Supporting Arm Structure, a Focusing Device, a Reference System and an Optical System.

The Supporting Arm assembly is attached to the Adapter Boxby means of the Turntable which allows it to rotate about an axis at the edge of the telescope optical field. At the end of the Supporting Arm is a pick-up mirror which directs light from the telescope beam, through the Optical System, to two CCDsensors. The Focusing Device allows the adjustment of the CCD sensor focus position.

The Reference System inserts an optical fibre into the beam for calibration purposes. The combined movements of the Sensor Arm and the Adapter Box allow the pick-up mirror to be placed anywhere inthe telescope field.

The Maintenance and Integration Equipment

This component comprises a number of assemblies which are used for the assembly, alignment, handling and maintenance.