Patent GB-675343-A (GB)
Title: Improved scale arrangements for measuring instruments of the micrometer type
IPC: G01B3/18
Filed: 1950-10-25
Abstract: 675,343. Linear-dimension gauges. LEITZ GES., E. Oct. 25, 1950 [Oct. 1, 1948], No. 25961/50. Class 106 (ii). A micrometer having a rotatable barrel needing at least two revolutions to move it along one unit of a main scale, includes at least one slide co-operating with the barrel and means for controlling a movement of the slide such that some of the numerals for reading off the result on an auxiliary scale are covered or uncovered according to the revolutions made by the barrel. In Figs. 1 and 2, when the knob 4 is rotated relatively to the body member 15, the spindle 3 and therewith the free edge of a barrel 6 in a protecting sleeve 5 are on each complete revolution of the knob 4, rotated so as to be longitudinally displaced by one half of a unit of the main scale 17 on the body 15. During such rotation, each of two diametrically opposed followers 11a and 11b slide in endless grooves 12a and 12b in a non-rotating member 13 moving axially with the spindle 3 and barrel 6 and, on reaching a region 12c, Fig. 3, where the two grooves cross each other, the relevant follower is displaced longitudinally of the barrel 6 in one or other sense to cause corresponding movement of its associated slide 8a or 8b, these slides having graduated ends 9a and 9b respectively. The arrangement is such that when the free edge of the barrel 6 passes, at the region of the index line 18, through the first half of a unit of the main scale 17, the respective free end 9a or 9b of the slide 8a or 8b is retracted so as to be covered by the protecting sleeve 5 whereby at the said region the auxiliary scale 19 engraved on the barrel 6 is visible and allows <SP>1</SP>/50 of half a unit of the main scale 17, that is to say <SP>1</SP>/ 100  of such a full unit, to be directly read off on the auxiliary scale 19 against the index line 18. When, on the other hand, the free edge of the barrel 6 passes, at the region of the index line 18, through the second half of a unit of the main scale 17, the respective free end 9a or 9b of the slide 8a or 8b protrudes from the protecting sleeve 5 and covers the numerals engraved on the barrel 6 at the region of the index line 18 while the numerals engraved on the protruding end 9a or 9b are now uncovered and thus visible and allow fractions between <SP>50</SP>/ 100  and <SP>59</SP>/ 100  of a full unit of the main scale 17 to be read off directly on the auxiliary scale 19 against the index line 18. In Figs. 5 and 7, the member 13 has four endless grooves 20 with four crossing regions to which are connected five slides 21 moving beneath a sleeve 5 having five windows 22. The five slides 21 are arranged to carry respectively the numerals 00, 75, 25, 50; 05, 80, 30, 55; and so on, the fifth slide carrying the numerals 20, 95, 45, 70. Owing to the longitudinal displacements of the five slides 21 caused by the endless grooves 20 in co-operation with a follower on each slide, either the numerals 00, 05, 10 and so on to 25, or the numerals 30, 35 ... 50, and so on are visible through the windows 22, Fig. 5, depending on whether at the region of the index line 18 the auxiliary scale indicates fractions of the first, second, third or fourth quarter of a unit of the main scale 17. Four complete revolutions of the operating knob thus correspond to a longitudinal displacement of the measuring spindle 3 through one unit of the main scale 17, which may be <SP>1</SP>/ 10  of an inch. For increasing the precision, a vernier scale 23, Fig. 5 is provided on the body 15. In Fig. 8, the ends 9a<SP>1</SP> and 9b<SP>1</SP> of the slides (of which only slide 8b is visible in the drawing) do not carry any numerals. Instead, two rows of numerals 0 to 45 and 50 to 95 respectively are engraved side by side on the barrel 6, which are alternatively covered by the ends 9a<SP>1</SP> and 9b<SP>1</SP> of the slides, the slides being longitudinally displaceable and controlled in an analogous manner to the control of the slides 8a and 8b of the first embodiment. For clarity, one of the rows of numerals in Fig. 8 has been indicated as being visible through the end 9b<SP>1</SP> of the slide 8b, although the ends 9a<SP>1</SP> and 9b<SP>1</SP> are opaque so that only one of the rows of numerals is visible at a time. In the embodiment of Figs. 9 and 10, two slides 25a are provided which are displaceable circumferentially. They extend through recesses in the protecting sleeve 5 and have windows 24 through which numerals on the barrel 6 are visible, namely either the numerals 10, 20 ... 50 or the numerals 55, 65 ... 95 according to the position of the slides. The rotation of the slides is effected by control members each provided with two followers 27a, 27b, which are longitudinally displaced when passing the region 12c where the branches of the endless grooves on the member 13 cross each other. Thereby, a rotational movement of the respective arm 30a of each control member is caused, the rotational movement being transmitted to a pivot 29a respectively of the slides 25a, whereby the respective slide is circumferentially rotated.