GB1150243A - Automatic X-Ray Apparatus for Crystal Z-Axis Orientation Determination and Sorting. - Google Patents

Abstract

1,150,243. Photo-electric examination of crystals. AIKEN INDUSTRIES Inc. Feb.15, 1967, No. 7302/67. Heading G1A. [Also in Division H5] Quartz crystal wafer blanks are examined by X-ray diffraction apparatus to determine the angle of orientation of the surface of each crystal with respect to its Z-(or optical) axis, and then sorted into a plurality of separate bins in dependence on this determination. A plurality of crystal blanks are contained in a magazine which is inserted into a nest 40. Motor 62, operating through a magnetic clutch 66, causes a blade 48 to feed crystals in sequence from the magazine into position at station 70. Here a crystal 16 is held in position during Z-axis determination by a vacuum, applied to holes (70) in a crystal holding block (76 Fig. 3 not shown), through conduit 75.and solenoid-controlled valve V. Before determination, the crystal is tapped by a solenoidcontrolled plate 90 to ensure that it is securely seated on the ledge of the block (76). After determination, air pressure is applied through the holes (70) to blow the crystal down an exit shoot 32 to a sorter 30, where the crystal is sorted into one of a plurality, for example, sixty four, bins, by a digitally operated tree-type sorting system under the control of circuit 28. The Z-axis determination involves directing X-rays from source 12 through collimator 14 and cut-away portion 97 of the crystal holding block to the crystal and detecting the diffracted radiation with Geiger-Muller counter 20 while the crystal mounting table 18 is rotated through a predetermined angle of arc. The drive for the table 18 comes from a motor 24 which rotates a cam (116 Fig.6 not shown) operating through a cam follower lever (146) on to an arm (98 Fig.4 not shown) integral with the table 18. Use of a cam provides that once the table 18 has turned through the predetermined arc it returns in the opposite direction to the original position relatively quickly so that the determination of a fresh sample can be started from the same reference orientation. As the crystal is rotated through the predetermined angle, at one particular angle depending on the orientation of the Z-axis a peak in the output of the detector 20 is obtained. The time this peak occurs after the start of the determination is measured by peak sensing circuit 22, Fig. 8 (not shown), which includes a circuit inverting the peak pulse, a pulse height limiter, a differentiator, and a crossing detector producing a squarewave pulse which is fed through a multi-vibrator, and matching and relay circuits on to the terminal of the shaft encoder 26. This is driven by motor 24 and produces an encoded digital indication of the angular position of the driving shaft (110) of the motor. When the pulse from the peak sensing circuit arrives, this is converted by the encoder into a digital coded output on its six output lines, representative of the angle at which the peak occurred. The output lines are connected to six identical channels comprising a silicon controlled rectifier, followed by a holding relay and a sorting relay which sets a sequence of sorting gates in the tree-type sorter. The setting of all the sorting gates can thus be controlled to guide a crystal into a bin in dependence on its Z-axis orientation. The circuitry is provided with error detecting means for detecting jamming or sticking of a sorting gate, incorrect feeding of a crystal to the determination position 70 (including jamming of the feed motor), and the absence of crystals passing a checking photo-cell 34 on the way to the sorter 30. A warning lamp may be lit and/or the motors deenergized.