Optical displacement indicator

Abstract

Abstract An optical device for measuring the displacement of a remote object. In a preferred embodiment, the device consists of two major subassemblies. One assembly consists of a light source which projects a collimated light beam towards the object whose displacement is to be measured. Associated with the light source is a beamsplitter which diverts any light reflected back from the direction of the object onto a photoelectric cell. The other assembly is located near the object and in the path of the collimated light beam. This assembly consists of a hollow cone whose inside surface is specularly reflective. A plunger is fixed to slide along the axis of the cone. The plunger protrudes through a hole cut into the apex of the cone. A small flat mirror is fastened to the end of the plunger that projects inside the cone. The other end of the plunger rests against the object. The plunger is spring loaded to maintain contact with the object. The light in the collimated beam that enters the open end of the cone is reflected by the inner surface of the cone in such a manner that all the rays of light cross the axis of the cone. The apex angle of the cone is chosen so that, even by multiple reflections within the cone, any rays emerging from the mouth of the cone do not find their way back to the photocell; that is, the cone alone is not a retroreflector. The small mirror on the end of the plunger, however, intercepts a portion of the light rays as they cross the cone axis and redirects them so that, upon reflection from the opposite wall of the cone, the light rays emerge travelling in the direction of the photocell. As the object moves, the plunger slides along the axis of the cone (the cone being stationary) and the amount of light reflected back to the photocell changes. Furthermore, the amount of light reflected back to the photocell is a linear function of the position of the plunger and, hence, of the position of the object. The photocell current is measured by a meter whose scale is calibrated in units of length.

Inventors

• 👤 D Mary

Bibliographic Details