Configurable Slit Unit (CSU)
The most striking feature in the EMIR mechanical design is the choice of a fully cryogenic robotic system which can be remotely reconfigured to form the multislit pattern in the instrument focal plane, the Configurable Slit Unit (CSU), developed by JANSSEN Precision Electronics. This subsystem has obvious functional and operational advantages with respect to the more classical approach of interchangeable multislit masks.
The CSU is attached onto the front plane of the cold bench. It consists of the following elements:
- A field of view, the aperture left for the optical beam.
- Sliding bars, which coming in and out from the field of view block a portion of the light beam, creating slit patterns. Bars are laid in two groups of 55 bars, symmetrically with respect to the central symmetry plane of the CSU. The multislit pattern is achieved by positioning each of the bar pairs into the field of view. The long slit pattern is a multislit pattern with all the slits lined up in a single, longer slit.
- Spools, these act as guiding bearings.
- The bars that carry the spools (which bear and guide the sliding bars) are attached to a main frame which is the fixed reference of the system.
- Brake clutches are mounted onto the main frame (and therefore do not move), one per sliding bar. They consist of a electromagnet and a flexure.
- Ratchet clutches are similar to brake clutches.
Each bar has 4 sensors (capacitors) and using a lookup table calibrated we are able to get its position using an reconstruction algorithm, independently of its orientation and temperature.
