GB575127A - Improvements in or relating to transmissions for converting rectilineal movement of a driving member to rotary movement of a driven member or vice versa - Google Patents

Abstract

575,127. Linkwork. SMITH & SONS (ENGLAND), Ltd., S., (formerly SMITH & SONS (MOTOR ACCESSORIES), Ltd., S.), and DAVIS, W. O. June 3, 1943, No. 8938. [Class 80 (iii)] [Also in Group XIX] Consists in linkwork, particularly applicable to dial gauges, for giving a constant ratio between the angular movement of one member and the rectilinear displacement of another member. In Fig. 1, the rectilinearly moving member is shown at 10 and the angularly moving member 11 pivoted at 12. A link 16 pivoted at 116 carries a pin 13 and is displaceable through a small angle from a reference line 117. The distance between the points 12 and 116 is R/2 where 3R/2 is the distance between the points 13 and 116, R being the distance of the pin 13 from 12 when the angle # which the line 12, 13 makes with the reference line is zero. The pin 13 engages a straight edge 14 on the member 10 extending at right angles to the line of motion of this member at right angles to line 117. The pin also engages a straight edge 15 on the member 11. It is found that, for small values of #, the pin 13 moves along a path approximating very closely to the desired curve y=R#, where y is the linear movement of the member 10. In practice, the straight edges 14, 15 are inconvenient and the necessary relative movements may be obtained by linkwork as in Fig. 2. The pin 13 is connected to the member 10 by a link 17 which is parallel to the member when the link is midway between the limits of its movement. The pin 13 is also connected to the member 11 by a link 18 which, when midway between its limits of movement, is at rightangles to a line joining the pivot centre 12 to the pin. Two errors will be introduced by this construction but these may be made to cancel each other by making the link 17 four times the length of the link 18. As applied to a dial gauge, Fig. 4, the angularly moving member is a sector 11 pivoted at 12. The equivalent of the pin 13 is the end 4 of the link 16 which is pivoted at 6 so that the distance between 4 and 6 is about 1.5 times the distance between 4 and 12. The end 4 is coupled by a link 17 through a pin-and-slot connection to an abutment 7 on the member 10. Spring pressure keeps the pin at the bottom of the slot. The end 4 is coupled by a link 18 to a point 19 on the sector, the link 18 being at right angles to the.line 12, 4 when half way between its limits of movement. The link 17 is four times the length of the link 18. The sector has a rack 8 which drives the usual amplifying gear 9 for rotating the scale pointers. A modified linkage, also described, avoids the feature of the lever 16 and links 17, 18, all joining at the pin 4.