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5-AXIS ION BEAM MIRROR POLISHING MACHINE

AMOS has developed a 5-axis manipulator to test the process of final mirror polishing by ion beam etching. This process will permit to correct the last irregularities that remain after classic mechanical polishing. All types of optical surfaces (concave, convex, aspherical and out of axis) can be corrected.
This technique involves the ejection of atoms from the surface of the mirror material as a result of variable angle bombardment by a beam of energetic ions.
The process is activated under secondary vacuum conditions,with argon as working gas. A neutraliser emits charge balancing electrons.
The manipulator has been designed to determine the performances that can be obtained with this technique, and to study the influence of different parameters (distance, angle, speed, vacuum, beam opening,..).

The system is composed of:

• a stainless steel vacuum chamber of Ø 1200 mm and 1450 mm height;
• a turbomolecular pumping system of 1500 l/s;
• a two-stages rotary pump;
• a 5-axis positioning mechanism;
• a Ø 3 cm ion beam source with neutraliser;
• a mirror support that can be oriented (maximum mirror Ø205 mm);
• a control cabinet.

The 5 axes are motorised by vacuum stepper motors. The translations are motorised by means of precision ball screws. The rotation axes are realised by means of precision gear boxes. Each axis is equipped with a precision zero-reference switch. All end of travels are protected by limit switches.
The ion beam source is mounted on a 4-axis mechanism.
Two horizontal translation axes have each 300 mm stroke, precision is 0.05 mm, speed is continuously variable between 0.1 and 50 mm/s.
Two rotation axes permit to direct the ion beam source, precision is 0.01°, speed is continuously variable between 0.1 and 20 °/s.
The mirror support is motorised by a vertical translation axis of 500 stroke, precision is 0.01 mm, speed is continuously variable between 0.05 and 5 mm/s. This axis is equipped with a security brake.
The motors are controlled in open loop from two 3-axis PC-bus stepper motor controllers. The software permits to control all the axes in a so-called time-distance mode. In this mode a 5-axis motion profile is computed from the mirror surface profile. This motion profile is then sampled with a sampling period of typically 5 to 10 ms. These position samples are communicated continuously to the axis controllers that are synchronised. A total motion profile can be as long as several hours. A total polishing cycle takes typically 10 hours.

CUSTOMER : CSL (Centre Spatial de Liège) - BELGIUM

Creation & Hosting : REALITY MEDIA