Photoelectric device for stroke induction in the control of dials and coded disks

Abstract

Currently photoelectric devices for stroke induction are widely used in systems for controlling dials (coded disks). As a rule the induction is effected with the aid of a photoelectric microscope (PEM) with a movable slit, located in the plane of analysis, i.e., in the plane of the sensitive area of the phototransducer. To eliminate error associated with variation in the width of the stroke, the induction is performed on its center [1]. Stroke induction using a PEM requires special conditions and accessories. First, they place strict requirements on the initial exposure of the optical axis of the PEM relative to the axis of rotation of the attachment and on the focusing of the microscope on the surface of the piece being tested. Second, when the axis of rotation of the attachment is not parallel to the optical axis of the PEM (the inclination of the reading microscope) an additional error appears due to wobble in the axes of the rotating attachment and sphericity in the dial, since these factors cause variation in the distance of the diaI from the microscope [2]. Third, the PEM have significant structural parameters (mass, dimensions) and should be equipped with complex electronic units [3]. These factors to a significant degree limit application of PEM in systems for the dynamic control of dials and coded disks constructed, for example, on the basis of a laser goniometer [4] the speed of rotation of the rotating base of which is equal to 90~ Fiber optics has permitted development of light field intensity distribution gauges for relative motion of the gauge and the field. Figure 1 shows a measurement diagram of such a device. Fiber light conductor 2 is mounted on carrier 3. The input end of the light conductor is optically treated and transparent to the wavelength of the field being tested. The output end of the light conductor is connected optically to the sensitive area of phototransducer 1 and mechanically to its chassis. The design incorporates special measures to exclude the incidence of background radiation onto the sensitive area of the phototransducer. Moreover, the gauge is equipped with a device 5 for rotation around two mutually orthogonal axes and a device 4 for translation along a third axis which is perpendicular to the first two axes and which coincides with the axis of the fiber light conductor. This light field intensity gauge permits practical application of classical diffraction theory to problems of dial stroke (coding path window) induction. The dial is a plane-parallel plate with strokes the dimensions of which may vary within broad limits for different dials. Independently of the method of applying the stroke to the surface of the dial the stroke may be regarded as an opaque screen with finite dimensions and, without loss of generality, the rectilinearity of the edge of any stroke may be assumed. The portion of the dial with the strokes is shown in Fig. 1. Here 2h is the width of the stroke, 2H is its height, M is the distance between neighboring strokes along the diameter of the graduated circumference. Let us introduce a rectangular coordinate system X, Y, Z, the center of which is the point O which coincides with the center of symmetry of the stroke, while the axes OX and OY are directed along the short 2h and the long 2H sides of the stroke, respectively. The OZ axis is perpendicular to the surface of the stroke (screen). Let us connect a linear laser equipped with a collimating system and generating in space a light field of intensity E to the gauge in such a way that the optical axes of the laser and the gauge coincide and coincide with the O'Z" of the fixed rectilinear coordinate system X'Y'Z" associated with the gauge. The input end of the fiber light conductor lies in the X'O'Y" plane. The gauge registers the field intensity I r determined by the square of the modulus I El 2 as a constant quantity. Into the gap between the laser mirror and the input end of the fiber light conductor we introduce the dial in such a way that the axes of the XYZ and X'Y'Z" coordinate systems are collinear and the distance OO" is equal to L. Then, taking into account that for dials and coding disks 2H >> 2h in accordance with [5] we write the field intensity beyond the stroke in the near diffraction zone (taking into account that Ir(Y') = const) as