GB983961A - Improvements in or relating to electro optical micrometers - Google Patents

Abstract

983,961. Electro optical micrometer. CONTINENTAL ELEKTROINDUSTRIE A.G., [trading as CONTINENTAL ELEKTROINDUSTRIE A.G. ASKANIA-WERKE]. Aug. 2, 1961 [Aug. 2, 1960], No. 28084/61. Heading G1A. An electro optical micrometer device, for the interpolation of a rotatable graduated circular scale, comprises two reading microscopes disposed on the circumference of the scale and angularly displaced from one another by 180 degrees with respect to the axis of rotation of the scale, a photo-electric device associated with each microscope ray path serving to determine the position of the graduation marks observed in the image plane of the reading microscopes and from which electrical control signals are derivable, first means for causing the images of the graduation marks as seen through the microscopes to undergo translatory motions in the same direction as each other and second means for causing the images to undergo motions in opposite directions to each other, the control signals serving to adjust the first and second means. In the embodiment shown, the graduated transparent disc 3, eccentrically mounted on rotatable shaft 1, has its angular position roughly measured in whole degrees by counter 8 and has its graduations viewed at two diametrically opposite points by two viewing systems, each comprising a light source 10 and lenses 12 and 14, focussing an image of a graduation mark on to an image plane 15. Interposed between each lens 14 and image plane 15 are image diverting rotatable discs 19 and 30, equivalent discs of each viewing system being mechanically coupled and rotated by motors 27 and 35 respectively. The two halves A and B 1 and A<SP>1</SP> and B<SP>1</SP> of each field 15 and 16 are viewed alternately by means of beam splitting devices 50 and 51 and rotating shutters 60 and 61. Due to the eccentricity of the disc mounting, the images 40, 41 (Fig. 2a) of two normally opposite graduation marks appear as in Fig. 2a, the centre of the graduations being at 45<SP>1</SP>. The resulting differences in the light content of the two halves of each field are represented as electrical signals which are fed to motors 27 and 35. Discs 19 and 20 are then similarly rotated to bring the centre 45<SP>1</SP> into line with the axis of observation 42 (Fig. 2b) and discs 30 and 31 are oppositely rotated to rotate and centralize the graduation marks (Fig. 2c) to give zero outputs from the photo-cell differential circuits. The apparent degree of rotation of the graduation marks can be read from counter 8<SP>1</SP>. Alternatively, motor 35 may be omitted and a desired degree of rotation can be finely set manually on counter 8<SP>1</SP> and the graduated disc made to follow by a motor coupled to the shaft having a control signal fed from photo-cell 62 (Fig. 3, not shown). Alternatively the apparent motion of the graduation lines by the rotating discs may be replaced by a real displacement of the reading assembly and the apparent rotation of the graduation marks may be caused by actual rotation of the scale on the shaft.