GB2270588A - Improvements in orreries. - Google Patents

Abstract

An orrery is driven by a spring motor having a first gear (42) integral with a lever (44) for winding the motor, the first gear (42) meshing with a second dual gear (46) which drives an arm for rotating a planet (18, Figure 1) about a star (14), and an elongate helical spring (50) connected between the lever and the second gear, said spring being expanded and curved when the lever is rotated to wind the motor, and wherein the speed of drive of the arm when the lever is released to allow the spring to contract and straighten is governed by the transmission chain between the spring motor and the rotating planet on the end of the arm. The inertia of the spinning earth (18) is employed as a governor. Thus the speed of operation of the orrery is controlled by appropriate selection of the mass of the earth (18). <IMAGE>

Description

Improvements in Orreries This invention relates to a mechanical device for demonstrating the relative movements of a star and its one or more planets, possibly together with the moons of the planet or planets, or possibly just a planet and its moon or moons. Such a device is referred to herein as an orrery.

The most common form of orrery is a device which demonstrates the movements of the earth relative to the sun and the movements of the moon relative to the earth. Optionally, one or more other planetary movements, for example of Mercury and Venus, may be simultaneously demonstrated.

Thus, an orrery typically comprises a central support for the sun and an arm rotatably mounted to the central support and carrying the earth and moon at its end remote from the central support. The arm incorporates a train of gears which, when the arm is rotated, drives the earth in rotation about an inclined axis and drives the moon in rotation about the earth. Usually, the central support is surrounded by an indicator on which the yearly seasons and equinoxes are marked, and the end of the arm carries a marker which moves around the indicator. The gear ratio of the gear train is such that reasonably accurate representations of the relative positions of the sun, earth and moon at different positions around the indicator are obtained, although in order to make the device practical, the relative sizes of the sun, earth and moon are effectively ignored.However, there exists a tilting attitude of the earth and there is therefore usually incorporated in the arm a second gear train to rotate the plane of inclination of the axis of the earth in synchronism with rotation of the arm. The orrery thus also reasonably faithfully reproduces the differing angles of incidence of the sun's rays on the earth at different times of the year.

Orreries as above described are usually undriven, the arm being moved by hand around the central support to demonstrate different conditions which can arise. However, orreries driven by an electric motor are also known.

It is an object of this invention to provide a powered orrery in which a planet-carrying arm can be driven around a starcarrying central support by a simple and inexpensive prime mover.

According to the invention, there is provided an orrery having a central star-carrying support, a planet-carrying arm mounted to the central support for rotation around it, a gear train incorporated in the arm for driving the planet in rotation about its axis, said gear train being driven when the arm is rotated, an energy storage device and means whereby, when the energy storage device releases its energy, the planet-carrying arm is driven in rotation about the central support, the arrangement being such that the transmission chain between the energy storage device and the rotating planet acts as a governor controlling the speed of rotation of the planet-carrying arm.

Preferably, the speed of rotation of the arm is primarily controlled by the inertia of the planet in rotation about its axis. The speed of rotation of the arm is thereby primarily determined by appropriate selection of the mass of the planet and the number of revolutions of the planet for one revolution of the arm around the central support.

Thus, in an embodiment, the planet is carried by an upstanding spindle inclined at an angle to the length of the arm, and the lower end of the spindle is friction driven in rotation about the spindle axis by a wheel driven in rotation by the gear train. Partly because of the inclination of the spindle, the rolling friction at its lower end is dependent on the mass of the planet carried by the spindle, and contributes to control of the speed of rotation of the arm. The wheel in question may be a wheel which carries a moon and drives it in rotation around the planet.

Preferably, a second gear train is incorporated in the arm for rotating the plane of inclination of the axis of the planet in synchronism with the rotation of the arm. The orrery then gives reasonably accurate representations of the relative movements of the sun, earth and moon in the solar system, and the changes throughout a year can be demonstrated by means of an indicator surrounding the central support and a marker on the end of the rotating arm.

The present invention, however, is especially concerned with the prime mover for the orrery. Thus, while it could conceivably be constituted by an elastic band, the energy storage device is preferably a spring forming part of a spring motor. In this motor, the spring is preferably an elongate helical spring.

In a preferred embodiment, the elongate helical spring is "loaded" by stretching it around an abutment, so that energy is released to drive the arm of the orrery in rotation as the spring contracts and straightens.

Thus, a preferred spring motor is incorporated in the central support, and comprises a hand operable lever carrying a first gear and a second gear coupled to gearing which drives the arm of the orrery in rotation, the elongate helical spring being connected between the lever and the second gear. The lever is preferably rotatable around a central pivot with which the lever gear is coaxial, and when rotated by hand stretches the spring around the axis of the central pivot. Release of the lever enables its reverse rotation, thereby to drive the second gear as the spring contracts and straightens.

A clutch is preferably incorporated, enabling the lever to be moved to load the spring without driving the second gear.

This clutch conveniently comprises a sliding pivot defining the axis of rotation of the second gear, whereby the teeth of the first gear are able to ride over the teeth of the second gear during "winding" of the motor. The clutch also enables the orrery to be operated by hand, as will often be desired for demonstration purposes, in either the clockwise or the anti-clockwise direction.

A practical embodiment of orrery in accordance with the invention is now described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevational view of the orrery; Figure 2 is a diagrammatic representation of two gear trains incorporated in the arm of the orrery; and Figures 3 and 4 show a spring motor incorporated in the central support of the orrery, respectively in the unwinding and the winding condition.

The orrery shown in Figure 1 comprises a central support generally referenced 10 and which includes an upstanding stem 12 carrying a representation of the sun 14 at its upper end.

The stem 12 serves as a shaft on which a skeletal arm generally referenced 16 is mounted for rotation at its inner end. The outer end of the arm carries a representation of the earth 18 at the upper end of an inclined spindle 20, and a representation of the moon 22 at the upper end of an upstanding stem 24.

A spring motor later described is able to drive the skeletal arm 16 in rotation, and rotation of the arm causes upper and lower gear trains, respectively 26 and 28, incorporated along the length of the skeletal arm, to be driven. These gear trains are shown diagrammatically in Figure 2.

At the outer end of the arm 16, the upper gear train 26 drives a wheel 30 carrying a mount 32 for the stem 24 supporting the moon 22. This moon wheel 30 is recessed at its upper surface to form a rim 34 against which bears a roller 36 fixed on the lower end of the inclined spindle 20 carrying the earth 18. Thus, when the moon wheel 30 is driven in rotation, the earth 18 is rotated about its inclined axis.

The earth spindle 20 is held in its inclined position by a fitting 38 fixed on a slightly inclined cam disc 40, which is driven in rotation by the lower gear train 28.

The moon stem 24 is vertically slidable through its mount 32, and the bottom end of this stem 24 rests on the edge of the inclined cam disc 40. Thus, as the moon 22 is driven in rotation around the earth 18, it is also subject to a periodic lifting and lowering motion brought about by rotation of the cam disc 40, thus defining an orbit for rotation of the moon about the earth in a plane parallel to that of the inclined cam disc 40.

A second purpose of the cam disc 40 is to rotate the plane of inclination of the axis of the earth 18 in synchronism with rotation of the arm 16, in order to reproduce the tilted attitude of the axis of the earth which brings about the annual seasons, which may be marked on an annular indicator plate (not shown) and pointed to by a marker 41 on the arm 16. The lower gear train 28 thus has a 1 : -1 ratio, so that the cam disc 40 performs one complete revolution for one complete revolution of the arm 16. The upper gear train 26, on the other hand, has a ratio, having due regard to other factors such as the diameter of the earth spindle roller 36, for rotating the earth about its inclined axis approximately 365 times for each complete revolution of the arm 16.

The present invention is more particularly concerned with the spring motor which is incorporated in the central support 10 to drive the skeletal arm 16. This spring motor is shown in Figures 3 and 4.

The motor comprises a first gear 42 integral with a manually operable lever 44, the first gear normally being in mesh with the inner teeth of a second dual gear 46, the outer teeth 47 of which drive the skeletal arm 16 through a gear 48 (see Figure 1). Connected between the lever 44 and the second gear 46 is an elongate helical spring 50.

When, as shown in Figure 4, the lever is rotated about a central pivot 52, the spring 50 is expanded and bent around the pivot 52, which acts as an abutment for an intermediate point in the length of the spring. Thus, when the lever 44 is released, energy is released as the spring contracts and straightens, the reverse rotation of the first gear 42 (and lever 44) driving the second gear 46, in turn to drive the skeletal arm 16. Thereby, by means of gears 54, 56 on the inner end of the skeletal arm 16 (see Figure 1), the upper and lower gear trains 26, 28 are also driven.

The motor also incorporates a clutch, whereby the second gear 46 is not driven when the motor is wound by rotation of the lever 44 (in the clockwise direction as shown in Figure 4), but only when the lever is released to rotate reversely (in the anti-clockwise direction as shown in Figure 3).

This clutch comprises a slot mounting 58 for the second gear 46. When at the inner end of the slot 58, the second gear 46 is fully in mesh with the first gear 42, but when the second gear is at the outer end of the slot, where a resilient lip 60 limits further displacement of this second gear, the first gear is able to ride over although not fully disengage from the inner teeth of the second gear as the lever is manually rotated. The action of starting to wind the motor (Figure 4) automatically initiates movement of the second gear 46 to the outer end of the slot 58. However, when the lever is released (Figure 3), the second gear 46 is instantaneously forced back to the inner end of the slot 58 to bring about the required drive to the skeletal arm 16.

An essential feature of the invention concerns the manner in which the speed of rotation of the skeletal arm 16 (and thus the speed of the complete mechanism) is controlled when the spring motor is unwinding.

In the mechanism above-described, the inertia of the spinning earth 18 is employed as a governor. Thus, the principal work performed by the energy of the spring when the motor is unwinding is that of rotating the earth 18 about its axis through the friction coupling between the moon wheel 30 and the roller 36 on the earth spindle 20.

The mass of the earth 18 is thus both a direct and indirect factor in the speed governing action. More effort is required to spin an earth 18 of greater mass, and additionally, because the axis of the earth is inclined, a greater rolling friction exists at the wheel/roller coupling if the earth 18 is of greater mass. Thus, in the mechanism above-described, and having due regard to the strength of the motor spring 50, the speed of drive of the mechanism is controlled by appropriate selection of the mass of the earth 18 and the number of revolutions of the earth for one revolution of the arm.

It will be appreciated that various modifications of the above-described mechanism are possible within the scope of the invention as hereinbefore described. For example, it is possible to incorporate additional arms driving other inner planets, and it is even possible to apply the mechanism to other star/planet systems, real or imaginery.

Claims (14)

Claims

1. An orrery having a central star-carrying support, a planet-carrying arm mounted to the central support for rotation around it, a gear train incorporated in the arm for driving the planet in rotation about its axis, said gear train being driven when the arm is rotated, an energy storage device and means whereby, when the energy storage device releases its energy, the planet-carrying arm is driven in rotation about the central support, the arrangement being such that the transmission chain between the energy storage device and the rotating planet acts as a governor controlling the speed of rotation of the planetcarrying arm.

2. An orrery as claimed in claim 1, wherein the speed of rotation of the arm is primarily controlled by the inertia of the planet in rotation about its axis.

3. An orrery as claimed in claim 1 or claim 2, wherein the planet is carried by an upstanding spindle inclined at an angle to the length of the arm, and the lower end of the spindle is friction driven in rotation about the spindle axis by a wheel driven in rotation by the gear train.

4. An orrery as claimed in claim 3, wherein, partly due to the inclination of the spindle, the rolling friction at its lower end is dependent on the mass of the planet carried by the spindle, and thereby contributes to control of the speed of rotation of the arm.

5. An orrery as claimed in claim 4, wherein the wheel is a wheel which carries a moon and drives it in rotation around the planet.

6. An orrery according to any of claims 1 to 5, wherein a second gear train is incorporated in the arm for rotating the plane of inclination of the axis of the planet in synchronism with the rotation of the arm.

7. An orrery according to any of claims 1 to 6, wherein the prime mover for the orrery is constituted by a spring forming part of a spring motor.

8. An orrery according to claim 7, wherein the spring is an elongate helical spring.

9. An orrery according to claim 8, wherein, in use, the elongate helical spring is "loaded" by stretching it around an abutment, so that energy is released to drive the arm of the orrery in rotation as the spring contracts and straightens.

10. An orrery according to claim 9, wherein the spring motor is incorporated in the central support, and comprises a hand operable lever carrying a first gear and a second gear coupled to gearing which drives the arm of the orrery in rotation, the elongate helical spring being connected between the lever and the second gear.

11. An orrery according to claim 10, wherein the lever is rotatable around a central pivot with which the lever gear is coaxial, and when rotated by hand stretches the spring around the axis of the central pivot, whereby release of the lever enables its reverse rotation, thereby to drive the second gear as the spring contracts and straightens.

12. An orrery according to claim 10 or claim 11, wherein a clutch is incorporated, enabling the lever to be moved to load the spring without driving the second gear.

13. An orrery according to claim 12, wherein the clutch comprises a sliding pivot defining the axis of rotation of the second gear, whereby the teeth of the first gear are able to ride over the teeth of the second gear during "winding" of the motor.

14. An orrery substantially as hereinbefore described with reference to the accompanying drawings.