Patent GB-605331-A (GB)
Title: Improvements in or relating to averaging devices
IPC: G06G3/08
Filed: 1945-07-11
Abstract: 605,331. Sextants. GENERAL TIME INSTRUMENTS CORPORATION..July 11, 1945, No. 17678. Convention date, Feb. 24. [Class 97 (ii)] [Also in Groups XVIII and XIX] In order to determine the average reading of a sextant over a predetermined period of time the angle-indicating member is geared to an averaging member with a ratio which varies continuously with time during the averaging period, the averaging member being manually returned to zero at the end of the averaging period while remaining geared to the indicator with the ratio obtaining at the end of the period, the indicator thus finally showing the required average. The invention is shown applied to a bubble-type sextant, Fig. 1, in which a prism 6 is adjusted through worm gearing by a knob 8, the readings being indicated on an angle indicator or counter 10 and also being transmitted by gearing to a shaft 11, Fig. 4, which projects through the side of the sextant casing into the casing containing the averaging mechanism the shaft there being releasably connected to a disc 18. The disc 18 drives a cylinder 19 through transmission mechanism comprising two balls 30, 31 mounted in a carriage 33 which, during the period of observation, is driven by clockwork radially across the disc 18 from the centre at a uniform rate so that the transmission ratio between the disc 18 and the cylinder 19 is increased from zero to a maximum in dependence upon the passage of time. The amount and direction of rotation imparted to the cylinder 19 are indicated on drums 44, 47 respectively. The clockwork is manually released at the beginning of an observation period and is automatically stopped at the end of the period, a shutter being simultaneously moved across the viewing field. The prism-actuating knob 8 is then again rotated to turn the drums 44, 47 backwards to zero while the transmission mechanism 30, 31 remains in its outer position. The final reading of the angle indicator 10 is then the average reading over the period of observation. A hand driven by the clockwork indicates onehalf the duration of this period. The clockwork driving the ball carriage 33, Fig. 8, comprises springs 38 which are moved to the stretched position shown by winding the carriage to the right to the shown position by turning clockwise through 180 degrees a winding knob 69, Fig. 15, fixed to a stub shaft 70 ending on a plate 117 carrying a pin 121 which thus engages and drives a pin 122 on a winding gear 67 engaging a gear 66 on a shaft 63 geared with a rack 59 on the ball carriage. When the winding knob 69 is released, it is returned by a spiral spring 119. The carriage is held and, when released, its motion is time-controlled, by an escapement driven by a gear 64, Fig. 15, connected to the shaft 63 by a ratchet clutch. A hand 41 on the end of the shaft 63 indicates against a time scale one-half the true time the carriage is moving. The escapement is released and the carriage started at the commencement of the observation period by pressing a button which removes a detent away from the balance wheel, the detent being returned by a spring to stop the action when the button is released. If, as is normally the case, the action be allowed to proceed until the carriage has reached the limit of its travel, this taking, e.g. two minutes, a pin 136, Fig. 11, on the winding gear 67 lifts a latch 133 to release a disc 128 fixed to a shaft 68 urged to rotate anticlockwise by a spring. The lifting of latch 133 lifts a bar 139 to abut the balance wheel and stop the motion thereof and the shaft 68 when released turns to interpose a shutter in the field of view. When the winding knob 69 is turned to energize the springs the indicating drums 44, 47, Figs. 4, 17, are automatically zeroized. A pin 116, Fig. 1, on the plate 117 fixed to the knob spindle rocks a lever 113, 111, Fig. 17, to move to the right a rod 104 which moves the gear 58 driving the indicating drum 47 out of engagement with a friction ring 101 on the indicating drum. Continued motion of the lever 111 then moves to the right a sleeve 108 carrying both drums 44, 47 to move the lefthand drum 47 to break the frictional driving connection 100 between this drum and its driving gear 46. Rollers 94 carried on spring- pressed levers pivoted within the drums and bearing on a heart cam 91 then cause the drums to turn to zero.