Patent GB-1489310-A (GB)
Title: Measuring instrument
IPC: G01B7/02
Filed: 1975-04-03
Abstract: 1489310 Measuring instrument ROLLSROYCE Ltd 25 March 1976 [3 April 1975] 13587/75 Headings G1A and G1M A measuring instrument comprises a bar 12 formed of two detachable portions 13, 14, a first anvil 10 secured to the bar portion 14, a carriage 15 movable along the bar portion 13 and positionable at a series of equally spaced positions defined by detent means along the bar portion 13, a second anvil mounted on the carriage for movement parallel to the bar over a distance at least equal to the spacing of the positions, and first and second means for indicating, in the same units of measurement, the position of the carriage relative to the first anvil and the position of the second anvil relative to the carriage. The bar 12 comprises a metal bar 13, and a carbon fibre extension 14 selected from a set of such extensions according to the dimension to be measured. The carriage 15 is positionable at locations 1 cm apart along bar 13 by means of a pin 18 which engages holes 19 in the bar, a push button member 26 being operable to raise and lower the pin 18 and having a cam surface 27 which acts to push the pin tightly into a selected hole 19 when member 26 is rotated. A hexagonal rod 16 carries a cm scale on each side, each scale corresponding to a respective extension 14. When an extension 14 is located in member 13, a rack and pinion arrangement (not shown) operates so that rod 16 turns to present the side having the corresponding scale to a read-out window (17), Fig. 4 (not shown). Anvil 11 is mounted on the base 21 of carriage 15 by means of crossed roller bearings 30 and is movable over a range of 12 mm corresponding to the 10 mm between the positions set by two adjacent holes 19, and an extension of 1 mm at each end. The anvil is biased to the left or right end of this range, according to whether an outside or inside measurement is to be taken, by means of a spring 31 anchored at one end to base 21 and at the other end to a rotatable pin 32. Pin 32 carries a handle 33 which may be located in alternative angularly displaced positions by means of a pin 35 engaging holes 36, 37 according to which end position is required. The position of the anvil 11 relative to the carriage is measured by a Moire fringe device and displayed digitally in window 17, (Fig. 4). The Moire fringe device comprises a grating 101 mounted on the carriage and, mounted on the anvil 11, four smaller gratings 102, 103, 104, 105 and associated light emitting diodes 106, 107, 108, 109 respectively and photo-electric detectors 110, 111, 112, 113 respectively, the gratings 102-105 being staggered from each other along grating 101  by a quarter of a grating spacing. The outputs of the detectors 110-113 are combined in unit 100 to produce count pulses on line 131, and to produce a high or low voltage on line 127 according to whether it is an up or down count. The count pulses are counted in decode counters 140, 150, 160, and the counts are passed to LED displays  206, 207, 208 via a multiplex arrangement. This consists of inverters 170, 180, 190, a decoder 200, a multiplex oscillator 210, and a counter 216 having its input connected to the oscillator and having its 1, 3 and 6 outputs connected to invertors 190, 180, 170 respectively so that displays 206, 207, 208 are energized in turn. Initially, before the anvils contact a workpiece, the anvil 11 will be biased to the left or right end of its range, and a micro-switch 250 actuated by pin 35, Fig. 3, signals the chosen range end to the counting circuit so that with the anvil in its left or right end position, display 206-208 will show 900 or 100 respectively. Positioning of the anvil in either of the 1 mm extensions of its 10 mm central range is signalled by means of LED's 240, 241. The power supply circuit, Fig. 6C, includes a press button switch 222 and a pair of relays 223, 229 which are operated when switch 222 is depressed prior to taking a reading and which have contacts 223A, 229A, connecting the battery 45 to the counting circuit, and producing a voltage on line 232. The voltage on line 232 sets the display 206-208 to 900 or 100 depending on micro-switch 250. Contacts 229A also supply voltage to Nand gates 141, 151, 161 which enable counters 140, 150, 160 to count. With switch 222 depressed, the operator positions the anvils to engage the workpiece and then releases switch 222. This causes relay contacts 229A to open immediately, thus freezing the count, and the instrument is then withdrawn without affecting the count displayed. The count is displayed until capacitor 224 has discharged causing relay contacts 223A to open.