WO1990012345A1

WO1990012345A1 - Clock mechanisms

Info

Publication number: WO1990012345A1
Application number: PCT/GB1990/000523
Authority: WO
Inventors: Rodney Philip Jackson
Original assignee: Chronos (Cumbria) Limited
Priority date: 1989-04-07
Filing date: 1990-04-06
Publication date: 1990-10-18
Also published as: GB8907883D0

Abstract

In a clock mechanism of the ''Congreve'' type, in which escapement is controlled by a ball (24) rolling down a tiltable track (22) the ball striking a lever (50) to release the escapement (34) at each end of the track and to tilt the track in the opposite direction, the ball is given impetus in the opposite direction when the track is released by spring means (56) as illustrated and/or by the track being inclined upwards slightly at each end.

Description

Title: Clock Mechanisms

DESCRIPTION

This invention concerns improvements in and relating to clock mecanisms and, in particular, "Congreve" clock mechanisms.

In the Congreve clock, the escapement is controlled by a steel ball rolling down a zigzag track on a tilted brass plate. Each complete journey takes almost 30 seconds, at the end of which the ball strikes a lever releasing the escapement and tilting the table in the opposite direction, causing the ball to retrace its path exactly 30 seconds after the start from the other end. A normal clock train tilts the table through a cranked arm, hours and minutes are shown on separate dials, seconds by marks on the track of the tilting table. Normally spring-driven, Congreve's original clock employed small cannon balls as driving weights. These clocks are poor timekeepers yet many replicas have been made in recent years, for they have a hypnotic effect upon the viewer.

The principle of the rolling-ball clock was defined by Galileo; a ball rolling down a constant slope takes the same time to cover the same distance at any part of the slope. This principle was first put to practical use by Christof Margref of Vienna in 1597, and in the early 17th Century others makers such as Hans Schlotheim and Johan Sayllert followed suit. John Evelyn described such a clock presented to Charles I and was later in the possession of Cromwell. This clock had a crystal ball, but the usual practice was to use a steel one. The idea was, superseded by the invention of the pendulum clock, but it was revised in the early 19th Century by William Congreve.

Many clocks of the Congreve rolling ball type have been made over the years. All without exception have proved very poor timekeepers, being inaccurate by 15 minutes per day and more, very prone to stopping, through dirt and inaccurate setting up of the clock on a level surface.

The clock has normally had to be wound every day and/or weekly. A further innovation was to use two trains and two mainsprings. One mainspring drove a conventional and modern platform escapement to give accurate timekeeping. Whilst the other mainspring and train drove the table which was thus actually a purely aesthetic function and had no functional use, other than a decoration and an appealing feature. It sells at relatively low cost but can only be considered as a poor imitation.

Balancing of these clocks is very critical and usually it is achieved by means of a spirit level, either separate to the clock or incorporated in the base.

The mainspring being of high strength invariably utilise a fusee system, with appropriate maintaining power to be used during winding, whilst the fusee evens out the variations of power between the fully wound and unwound condition of the mainspring.

In all cases, the table release is through two arms, suspended from the clock, and passing through the track at each end, the release arms having attached at the clock end a detent engaging with a two pin escape wheel, which is released every 30 seconds, and of course also serves as the locking mechanism.

The table lift is also actuated by a connecting rod system, associated with the two pin escape wheel and the table.

The drawbacks of typical Congreve clocks are that the timekeeping is grossly affected by the slightest change of angle of the table. The typical Congreve is inherently poor in maintaining a consistant angle of tilt. Despite the fusee, power variations are considerable because of the strong springs required to drive the clock.

Changes in oil consistency, dirt and grease inherent from, and as a result of exposure to air due to the frequent winding, and temperature all cause major timekeeping changes.

An object of this invention is to provide improvements in and relating to the Congreve clock mechanism.- According to the present invention there is provided a clock mechanism of the "Congreve" type in which escapement is controlled by a ball rolling down a tiltable track, the ball striking a lever to release the escapement at each end of the track and to tilt the track in the opposite direction, characterised in that the ball is given impetus in the opposite direction when the track is released.

A particular aim of the invention is to provide for the rolling ball to travel at a substantially constant speed over a substantial length of the track.

Helping the ball reach its terminal speed quickly may serve to achieve that aim.

The impetus may be imparted to the ball upon striking the release lever, the lever being spring biased to impart said impetus on release of the track.

Additionally or alternatively impetus may be imparted to the ball by the track being inclined upwardly at its ends. The inclination of the track ends relative to the remainder of the track may be up to about 20 degrees, preferably up to about 10 degrees, especially up to about 5 degrees.

In a preferred embodiment the release lever carries a lug, preferably in the form of a jewel and the track has a pallet associated therewith to be held down by said lug when the ball is travelling towards that end of the track, striking of the lever by the ball releasing the track. The release lever and hence its lug is preferably height adjustable and the force of the spring means is preferably adjustable.

One or more of the following features may be applied to a Congreve clock mechanism of the invention:

1) Constant force mainspring(s) , i.e. having about 5% variation in torque output from fully wound to run down, possibly with elimination of fusees;

2) Sun and planets winding system preferably with an epicycloidal gear train;

3) Wire ball track, preferably in stainless steel and preferably also hardened and tempered;

4) Table release being detached from the gear train. Further features of the present invention will be apparent from the following description given, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a front view of a clock housing;

Figure 2 is a side view of a clock housing;

Figure 3 shows schematically a clock regulating mechanism;

Figures 4 and 5 shows schematically a clock regulating mechanism;

Figure 6 shows a track for the mechanism of Figures 4 and 5; Figure 7 shows a track cover;

Figures 8, 9 and 10 show a track release mechanism;

Figure 11 shows a track support system; and

Figure 12 shows an alternative table release mechanism.

Referring to the accompanying drawings, a clock of the "Congreve" type comprises an upper gear train housing 10 is shown supported on pillars 14, the choice of which is principally aesthetic, from a base 16, the base having height adjustable feet 18 so that the clock can be accurately positioned. The base 16 has supports 20 for a tiltable table track 22 on which a ball 24 travels. The clock is in a glass case 19 to keep out dust. The table track 22 (Figure 6) is made of hardened and tempered stainless steel, although other materials may be used. The table track has to be very accurately made and must have a very smooth surface finish to reduce friction. The table track is supported in or on a low friction system 23 such as ball races, jewelled bearings, "V" agate or sapphire jaws, flexible crossed springs, a frictionless suspension system. It is believed that making the table track by photoetching may achieve the required accuracy.

The track support system is shown in Figure 11 which shows support posts 90 holding up the track 22, the posts 90 being on arms 92 that are height adjustable by means of vertical screw threaded rods 94 themselves also being supported on posts 96 from the base 16.

The table track 22 may be used alone or in combination with a track cover 26 (Figure 7) secured thereto to prevent the ball 24 jumping or otherwise being dislodged from the track.

At one end the track is connected by a connecting rod 30 and crank rod 32 to a two position escape wheel 34, which forms part of the gear illustrated schematically in Figure 3 and described in the accompanying TABLE. In one position that end of the track is raised and at its other position that track end is lowered. Once the track is in either postion it is locked by a combined locking/releasing mechanism, of which there is one at each end of the track. The 2 position release wheel is held in position, not locked, by the relative position of the table in its locked state. The mass of the release wheel is adjustable to compensate for the efficiency of the gear train. The release wheel may be balanced with a counterpoise weight to offset the weight of the crank arm and associated parts.

The locking/releasing mechanisms comprise a pivotable arm 50 from the base of the clock which arm has a locking jewel 52 that in a locking condition holds down a pallet 54 of the track. The pivotable arm 50 is urged onto a locking position by a spring 56. As the ball 24 reaches the arm 50 it pushes it backwards to release the pallet 54 from the jewel 52, whereupon the escape wheel rotates to its other position to tilt the track the other way. As it does so the spring 56 applies pressure on the arm 50 which pushes the ball off on its return journey. When the track has reached its full tilt position the other way, the locking/releasing mechanism at the opposite end of the track comes into play and locks the track in position until the ball reaches the end of the track and so on.

The pivotable arm 50 is adjustable in a number of ways. Firstly, it has an upper part 60 screw threaded into a holder 62 which itself is pivotably mounted on a shaft 64 with a jewel bearing 66. Thus, the upper part 60, which carries the jewel 52 can be height adjusted by means of a spanner on a square head 68 of the part 60. Secondly, the vertical positioning of the arm 50 can be adjusted by means of a screw 70 through a support post 72, the screw bearing upon the holder 62.

Adjustment of the locking/releasing mechanism is important for accuracy of timekeeping. Slight adjustment to the pivotable arm 50 such as a 1 turn to change its height may alter the timekeeping by as much as 12 seconds in a day.

Turning to Figure 12, an alternative table release mechanism involves a track 100 such as of the type shown in Figure 6 except for its ends 102 being inclined by about 5 degrees relative to the rest of the track. The track 100 is mounted on a carrier (not shown) with a part associated therewith that is latched by pallet 104 of lever 106 when the ball 108 is travelling in that direction. The lever 106 is spring biased by spring member 110.

As the ball 108 reaches the inclined track section it slows down but retain sufficient speed to strike the lever and release the pallet and hence the track to tilt in the opposite direction. The inclined track section then serves to accelerate the ball on its journey back along the track. The overall effect is that the speed of the ball travelling along the track is evened out over the length of the track rather than being slower at the start and quicker at the end of a run.

Clearly the precise balancing of components is desirable and the use of materials that are relatively unaffected by temperature changes and that are low friction in order to obtain optimum accuracy from the clock.

The clock of the invention is generally constructed and operated in a conventional manner otherwise than specified above.

Claims

1. A clock mechanism of the "Congreve" type in which escapement is controlled by a ball rolling down a tiltable track, the ball striking a lever to release the escapement at each end of the track and to tilt the track in the opposite direction, characterised in that the ball is given impetus in the opposite direction when the track is released.

2. A mechanism as claimed in claim 1, characterised in that impetus is imparted to the ball upon striking the release lever, the lever being spring biased to impart said impetus on release of the track.

3. A mechanism as claimed in claim 1 or claim 2, characterised in that impetus is imparted to the ball by the track being inclined upwardly at its ends.

4. A mechanism as claimed in claim 3, wherein said inclination relative to the remainder of the track is up to about 20 degrees, preferably up to about 10 degrees, especially up to about 5 degrees.

5. A mechanism as claimed in any one of claims 1 to 4, characterised in that the release lever carries a lug and the track has a pallet associated therewith to be held down by said lug when the ball is travelling towards that end of the track, striking of the lever by the ball releasing the track.

6. A mechanism as claimed in claim 5, characterised in that the release lever and hence its lug is height adjustable.

7. A mechanism as claimed in any one of claims 2 to 6, characterised in that the spring force is adjustable.

8. A mechanism as claimed in any one of claims 1 to 7, characterised in that the ball track comprises parallel wires forming a sinuous path for the ball.

9. A mechanism as claimed in claim 8, characterised in that the track is formed by photo-etching.

10. A mechanism as claimed in any one of claims 1 to 9, characterised by one or more constant force main springs.

11. A mechanism as claimed in any one of claims 1 to 10, characterised by a sun and planets winding systems with an epicycloidal gear train.