Design of large aperture focal plane shutter

Abstract

ABSTRACT Abstract oTo satisfy the requirement of large telescope, a large aperture focal plane shutte r with aperture size of 3 200mm was researched and designed to realize, which could be star ted and stopped in a relative short time with precise position, and also the blades could open and close at the same time at any orientation. Timing-belts and stepper motors were adopted as the drive mechanism. Velocity and position of the stepper motors were controlled by the PWM pulse generated by DSP. Exponential curve is applied to control the velocity of the stepper motors to make the shutter start and stop in a short time. The closing/open time of shutter is 0.2s, which meets the performance requirements of large telescope properly. Keywords olarge telescope; shutter; timing-belt, aperture size, closing/open time OMT12-OM100-18 1. INTRODUCTION With the requirement of a large telescope, a large aperture focal plane shutter which is mounted before the CCD is needed, while Camera exposure shutters with apertures in excess of 100 mm are hard to find on the ¯market °. Traditional shutters can be generally assorted to two categories by framework, lamina-type shutter and center-type shutter. The mechanism of lamina-type shutter is motor drive each lamina move by linkage mechanism, which is usually used in camera. The mechanism of center-type shutter is electromagnet control the movement of each blade by linkage mechanism ewhich is mostly used in telescope with small aperture. A ll kinds of shutters can't be simply enlarged with the similar framework. Shutter technology abroad leads us, their structure are complicated, and BONN shutter is famous among them, while the dimension can't satisfy our need. And most shutters abroad used in each large telescope are specifically designed according to different dimensional limitation and speed requirement. They are practically unavailable to our telescope. We have to design a shutter of the whole dimension less than 3 500mm and thinner than 20mm with aperture of 3 200mm, and the open/close time less than 0.2s.