Electronically controlled variable slit width focal plane shutter

Abstract

A focal plane shutter includes first and second shutter blades mounted for forming a slit that is scanned across an aperture. The shutter blades are shaped to form the slit between a trailing edge of the first blade and a leading edge of the second blade, the width of the slit being determined by the relative position of the first and second blades with respect to each other. The velocity of the slit across the aperture is determined by the velocity of the two blades. A pair of moving coil actuators are connected to the blades, for moving the blades relative to the aperture, and a pair of position sensors are connected, one to each shutter blade, for producing signals indicating the positions of the shutter blades relative to the aperture. A shutter controller electrically connected to the moving coil actuators and the position sensors is responsive to the signals from the position sensors for applying power to drive the actuators to control the width of the slit formed by the shutter blades and the rate of movement of the slit across the aperture. The controller includes a velocity controller for the first blade to control the velocity of the slit across the aperture, and a position controller for controlling the position of the second blade relative to the first blade to maintain a constant slit width as the slit is moved relative to the aperture.