GB963595A - Improvements in or relating to apparatus for checking and/or measuring dimensions - Google Patents

Abstract

963,595. Investigation of turbine blades &c. by photo-electric means. ROLLS-ROYCE Ltd. May 16, 1962 [May 5, 1961], No.16505/61. Heading G1A. [Also in Division H4] The invention relates to apparatus for checking or measuring a selected dimension of successive blades, teeth or the like on the periphery of an article such as a turbine rotor, and comprises a light source and collimating means producing a beam, photo-electric means which receives the said beam and gives an electrical output representative of its illumination thereby, means for mounting the said article adjacent the said beam and moving the article so that its projecting blades or teeth are passed successively through the beam, and indicator means which produces a visual indication under the control of the said output, and means for providing correlation of said visual indication with the corresponding blades, comprising a disc attached coaxially with said article, said disc carrying projecting studs of magnetically permeable material, and stationary magnetic pick ups mounted to give electric pulse outputs upon passage of the studs past the pick ups. In the embodiment shown in Fig. 1 the blades 1 of a rotating turbine rotor pass successively between a light source 2 having a collimating lens to produce a parallel beam and a photomultiplier tube 3 fitted with a projecting tube of internal diameter similar to the diameter of the light beam, the beam diameter being wider than the spacing between adjacent blades so that maximum illumination of the photomultiplier tube 3 occurs when the whole width of a gap between adjacent blades is within the beam. The output of the tube 3 is fed to a D.C. amplifier in a display unit 5 which includes a cathode-ray tube having a time-base generator to provide X-deflection giving one scan of the cathode ray tube for every revolution of the turbine rotor. The output of the amplifier provides Y-deflection of the cathode ray tube in the form of a number of blips on the scan each blip representing a different gap between two successive blades and the height of each blip representing the width of its corresponding gap on the rotor. In order to identify gaps represented by the blips and particularly in investigating a rotor having a large number of blades the display unit may be used in conjunction with a synchronizing device shown in Fig. 2 in which a disc 6 having ten studs of magnetically permeable material 7 disposed in circular formation round the disc and one stud 8 offset, is secured to the turbine rotor for rotation therewith. A pick-up 11 produces a pulse when the stud 8 passes it, and is connected to the time base generator of the display unit 5 to trigger the return stroke back along the X-axis. A further pick-up 10 produces a pulse when each of the studs 7 pass it, these pulses serving to initiate the forward sweep of the time base, but these pulses do not pass direct to the time base generator but to a gate circuit associated with a delay unit 12 which receives each pulse from the pick-up 11 and, after a delay determined by the setting of a manual control on the unit 12, opens the gate to complete the connection between the pickup 10 and the time base generator. Thus a group of blips corresponding to any chosen sector of the rotor may be selected for display on the cathode ray tube. If the synchronizing device is so arranged that the output for only one gap is allowed to pass the gate during each revolution of the rotor the cathode ray tube may be replaced by a voltmeter. The output from the studs may alternatively be used simply to produce marker blips on the tube.