[The Horological Journal. Vol. ??, No. ?? (December, 1877): 49-53.]
(Continued from page 23.)
Fig. 1 - Remontoire1 of the first class (see page 22), exhibited by M. Couet at the 1862 Exhibition. The maintainer2 here is a helical spring, seen in side view; it actuates the escape wheel thru auxiliary wheel H, and is re-wound by the train 60 times in a minute. (Auxiliary wheel H rides on the arbor of N.)
Fig. 1 - Couet's Remontoire
The train is locked under detent P s, which has a safety-pad to prevent more than one leg passing at a time, by pins on the five legged fly wheel v, driven by the seconds wheel N of the train ; it is unlocked (and so arms the maintainer) by arm b, fixed to the anchor A, by means of a passing piece c as the pendulum is completing its vibration to the left of the figure.
|Train wheel N||has||120||teeth.|
|Auxiliary wheel H||"||96||"|
Gravity Escapements. – Principle I. – For a successful gravity escapement the lifting and the locking actions must be separated so as, while making the lifting as effective as possible, to reduce the locking to a practical mini mum, and since this latter pressure will be so trifling, a fly3 is necessary to steady the motion, and make the beat on the detents dead.
Fig. 2 - Mudge arranged à la Denison
This principle being unknown and violated the early gravity escapements failed from tripping4 approximate tripping5 and the heavy pressure on the detents affecting the pendulum.
To make the principle clear, that form of Denison is shown, which describes on page 128 and 129, fourth edition of Sir E. Beckett's book. See preceeding page, fig. 2. The escape wheel of Mudge (fig. 3) is here made the rewinder only and the locking is done by the three-legged wheel carrying a fly. Tripping is prevented by the fly, and approximate tripping is rendered impossible, because no sufficient force can arrive at the lockings to hold up the gravity arms; should they by any extraordinary force be jerked up, they will fall down by their own weight to the proper place.
Fig. 3 - Mudge's Gravity Escapement
6Kater's7 escapement (fig. 4) was an attempt to entirely detach the pendulum by making the maintainers unlock the train, by falling alternatively on the anchor B (it will be seen that though the arm may approximately trip, and prevent the arms falling down place before the unlocking commences), but it was quite a failure.
Fig. 4 - Kater's detached Escapement
In Professor Bloxam's8 escapement, fig. 5, (notice the improvement in the lift which is done at the line of centres from a pinion) the difference between the locking and lifting (i.e., the difference between the radii of the pinion and locking wheel) is carried out but is not enough, and Bloxam's escapement would only succeed with an almost faultless train.
Fig. 5 - Bloxam's detached Escapement
Massey came very near to a satisfactory solution of the gravity escapment9; in fact, both tripping and approximate tripping were impossible with his arrangement, see fig. 6; the pressure at the lockings being less than one-fifteenth of that at the liftings, and he also proposed a fly; but the method of locking reduces his escapement to a dead beat with a gravity impulse, for the locking stops are on an anchor moving with the pendulum. Nevertheless, great credit is due to this old master, who nearly forty years even before Professor Bloxam, came so near success.
Fig. 6 - Massey's Gravity Escapement
It is perhaps needless to point out a really successful gravity escapement – everybody knows it is Sir Edmund Beckett's; but, since no drawing of it has appeared in the journal, it is here given (fig. 7 on the preceding page). The lifting is from a sort of lantern pinion (by an easy push across the line of centres), and the pressure on the stops is about one-twelfth of the lifting power.
The Escapement by Voss and Monnington of Hamburg10 (figs. 8, 9, 10), is a variety of the second class, i.e., the arming of the maintainer takes place while the pendulum is in connection with it, but in this form the maintainer acts directly on the pendulum.
The maintainer is the inverted "T" shaped piece w pivoted at q, which is rocked from side to side by the prism, and so tenses springs s1 s2 down on the standards 1 1', fixed on arms a a1 of the pendulum.
The prism is fixed on the arbor of the last wheel of the train; the pins on this wheel lock alternately on either side of the pallet r.
Fig. 7 - Denison double 3 legged Gravity Escapement
Fig. 811 shows the pendulum, having just received its impulse from the left hand spring, moving towards the right where standard l1 on arm a1 finds the spring s2 in the position shown,
one of the pins of the escape wheel being locked on double pallet r, the pendulum continuing its vibration to the right arm l1 pressing against spring s2 releases the train which runs on and the point of the prism forcing w to the right
(see fig. 9) tenses the spring s2 down on arm of of the pendulum, which thus receives its impulse.
Fig. 10 is a side view of this escapement.
Figs. 8, 9, 10 - Voss & Monnington's Escapement
Fig. 11, a remontoire by Gehrckens of Hamburg12 is of the third class (sec page 22). The maintainer consists of the two springs r and r1 which are armed by prism a b c, pivoted at d, through the medium of the inverted T shaped piece B S B1 pivoted at h as in Voss and Monnington's above; but whereas in theirs the springs are screwed to the bottom of the rocking piece, here they are screwed to the top chops of the pendulum, and they are so actuated that the pendulum always finds one of them tensed when it comes up to it.
Fig. 11 - Gehrcken's Remontoire
The pendulum moving towards the left, finds spring r tensed, pushes it up a little more, and the pressure of spring r1 draws B S B1 a little on one side, and so disengages tooth e1 from pallet p1; the train thus released runs on and locks by tooth e on pallet p, at the same time arming spring r2. Spring r being no longer supported (by pin f on arm b), is at liberty to fall, which it does as soon as the pendulum begins to descend, and the difference between the height where screw v on arm b found r and where r springs down to (owing to B S B2 being rocked to the other side), is the impulse given to the pendulum.
Figs. 12 & 13 - Gehrcken's Remontoire
Gehrcken's other arrangement (fig. 12 and 13) is inserted as a beacon, as despite disguise, it is a Mudge, and would fail as that failed from actual or approximate tripping.
[Correction.-In answer to a enquiry the courteous Edior of "Revue Chronometrique," informs me that Breguet applied the escapement (figs. 5 & 6, page 5) to a regulator in 1796 or 1798.
It was another entirely detached gravity escapement by Garnier, which was exhibited in Paris, in 1827. - H.M.F.]
1 Adapted from "Revue Chronometrique," Vol. IV., page 613.
2 Maintainer — The weight or spring, armed by the re-winder, which maintains the oscillations of the pendulum or balance. Re-winder - That wheel of the train which serves to re-wind (or arm) the maintainer. Cumming, throughout his Essay, calls the force which sustains the oscillations of the pendulum the maintaining power. What is now called by that name was known then as a going-in-time of winding.
3 It appears that nothing less than an angular motion of 45° is enough to render a fly effective.
4 Tripping — More than one tooth passing the detents at a time.
5 Approximate Tripping — Variation of the angle of impulse. The success of the escapement evidently depends on this being a constant quantity: the maintainer acting directly on the pendulum, the impulse angle consists of the difference between the angle at which the pendulum takes up the maintainer and that at which it leaves it. This is of course the difference between the place to which the maintainer is lifted by the train and that to which it is allowed to fall down when the train escapes. The latter place is either the re-winding wheel itself or a banking pin on the frame (except in certain entirely detached escapements as Kater's, see fig. 4), so the angle of impulse can only vary by the maintainer being jerked up, owing to some extraordinary force, and kept in that position. The force is not enough to make the escapement trip, but the arm is knocked out and kept out owing to the pressure of the wheel on the detent.
6On the Ramsgate Harbour Clock. See Bloxam's paper Astronomical Society's Memoirs. Vol. 22, p. 140.
7Philosophical Transactions, Vol. 130, Part 2, page 335.
8Royal Astronomical Society's Memoirs. Vol. 22, pp. 143, 145. Fig. 5 is from the original plate by favour of the R. A. Society.
9From Massey's Specification 3854, A.D. 1814. "a, the swing wheel of 30 teeth, b, b, a wheel of 120 teeth fixed on the same axle as the swing wheel, and acts in a pinion of 12, which pinion is on the same axle as c, a wheel of 75 teeth, which acts in d, a wheel of 50 teeth, the axle of which wheel also carries e, e, a lever of two equal arms which comes in contact with f, f, the locking detents, which should extend one-fourth of the circle described by the lever, and which locking detents are secured on a cradle verge, which is pivoted in a cock, and connected with the crutch in the usual way. The wheels c and d may be pivoted in the inside of the pillar plate, and in cocks fastened to that plate, or they may be taken to the back of the plate, in which case they will require additional cocks at the back of the plate. g, a cross piece, which is also secured to the verge at h, which immediately before the lever is disengaged from the locking detents at e, by the vibration of the pendulum, touches a pin at i on the raised pallet k; and when the detent is unlocked the wheels advance and raise the opposite pallet o, and the ball l2 (which is on the same axle as the pallet k, and fixed on light pivots in the cock, which is in the centre of the cradle verge), descends on the return of the pendulum, and communicates an impulse to the pendulum by means of its gravitation. The other ball n and pallet o are fixed in like manner in the cock in the centre of the cradle verge, and thus alternately give an impulse to the pendulum. It will be seen that the length of the lever e, e, is about equal to the diameter of the swing wheel, and performs one fourth of a revolution for each vibration of the pendulum, and of consequence passes through about fifteen times the space that the swing wheel does during each vibration, thus lessening the pressure against the locking detents, which may also be made considerably shorter than usual, and by these means relieving the pendulum from the greatest part of the friction; a fly may also be added to the axle of the lever for the purpose of equalising its motion."
10In Soul's patent 2822, 1868.
1`The escapement shown in fig. 8 and 9 resembles in appearance something very different in principle, viz., an arrangement of M. Detouche's, by which the impulse to the pendulum is given through the suspension spring.
The idea will be understood if the reader will imagine the rocking piece w to be the top chops of the suspension spring of the pendulum P, and the wheel locked by detents, whose ends act lower down the rod (arms and springs of the fig. being supposed non-existent), so that the spring is tensed as the pendulum begins the downward movement, i.e., at the commencement of each oscillation. Notwithstanding the dangers to isochronism of which this method seems full, the inventor states that when the tensing is done as described above, the going is regular and uninfluenced by the train. - [See Revue Chronometrique, Exhibition - part of Volume IV., p. 293.]
12See Soul's patent 850, 1871.
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