Patent GB-639131-A (GB)
Title: Improvements in or relating to apparatus for optically gauging profiles
Inventor: SMITH HARRY JOHN
IPC: G02B21/00
Filed: 1947-03-18
Abstract: 639,131. Optical gauging apparatus. OPTICAL MEASURING TOOLS, Ltd. March 18, 1947, No. 7500. [Class 106 (ii)] An apparatus for gauging by optical means the contour of a profiled work-piece comprises a plurality of contact members mounted in a carriage so as to be presented by the carriage to different faces of the work-piece, means to urge each contact member in turn into engagement with the work-piece, means to cause relative movement between the carriage and the workpiece so that that contact member which is in engagement with a face of the work-piece is caused to traverse the face, a movable index controlled by relative movement between the work-piece and the carriage and an optical system for displaying the movements of the index on a screen bearing a master profile. A turbine blade 12, Fig. 7, is fixed at its root 11 in a plunger 54 urged downwardly inside a holder 47 by a spring 56. The holder 47 is fitted within a sleeve 33 in a bore 32 of a boss 31 of a bracket arm 16 and its flange 48 is connected by a pin 49 to a ring 50 secured to the sleeve 33. A stop 37 on the ring 50 co-operates with two stops 39 on plates 38 secured on a disc 41 secured to the boss 31 to limit the angular movement of the sleeve 33 which may be clamped by a screw 44 threaded into a split portion 45 of the boss 31. The arm 16, Fig. 3, is vertically movable on a pillar 15 between two stops 24, 25 and can be clamped in any desired position. Below the work-holder on a table 14 are two carriages 60, 61, Figs. 3 and 5, the lower one 61 of which is movable towards and away from the pillar 15 by rotation of a knob 63. The upper carriage 60 is transversely movable in ball-bearing guideways on the carriage 61 and has a downwardly extending tubular part 68. Two adjustable ball-tipped stylii 72, 73 project radially inwards over the part 68 and either of them can be brought into contact with the adjacent surface of the depending turbine blade 12 and as the carriage 61 is moved such stylus traverses the contacting surface and the carriage 60 is accordingly moved transversely. A toggle spring unit 81, Fig. 5, under the carriage 61, acts through a bell-crank lever 76 to urge the carriage 60 in such a direction as to keep the stylus against the blade 12. When the contacting stylus reaches the end of the adjacent face of the blade 12 the toggle unit 81 is tripped and the carriage 60 is moved to bring the other stylus against the other side of the blade 12. A roller 132, Fig. 4 (not shown) on an arm on the carriage 60 co-operates with two cams on the carriage 61 for correctly positioning the carriage 60 at the limits of travel of the stylii. The upper carriage 60 has an arm 86 carrying a transparent glass disc 87 with two black circles 123, Fig. 9, corresponding respectively to the stylii 72, 73 so that upon movement of a stylus as described above the corresponding circle 123 traces a contour similar to that over which the stylus is moving. By means of the optical system, Fig. 1, an image 108 of the circle 123 is projected on to a screen 103 which bears a " master " contour 107 and by observing the projection 108 as a blade is tested, departure from standard form is shown by the image 108 departing from or being intersected by the curve 107. The tolerance limits are allowed for by having spots 88 inside and circles 124 outside the circles 123. To gauge the alignment of a blade the stylii 72, 73 are positioned, by means of a special tool 116, Fig. 11, in a horizontal line passing through the axis of the holder and are thereby separated by the distance between the centres of the circles 123 of a disc 87 which in this case, Fig. 10, has crossed lines 111, 112. The screen also bears crossed lines, Fig. 12 (not shown), which are brought into coincidence with the projected image of the crossed lines 111, 112. The blade to be tested is then positioned in the holder and the stylii moved over adjacent blade surfaces as before when misalignment will be shown by the projected image of the circles 123 tracing a contour which is displaced from the master contour. Specification 586,071 is referred to.