GB2111380A

GB2111380A - Rocker members

Info

Publication number: GB2111380A
Application number: GB08229696A
Authority: GB
Inventors: Witold Zygmunt Paduch
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-12-09
Filing date: 1982-10-18
Publication date: 1983-07-06
Also published as: GB2111380B

Abstract

A rocker member (2) suitable for use in a baby's cradle (1), having a curved surface (3), the radius of curvature at any given point of the surface (3) displaced from a mid-point (7), varying according to the distance of that point from the mid-point (7) such that when the cradle (1) is in use, the cradle (1) will rock with substantially a constant desired frequency irrespective of the angle through which the cradle (1) is deflected. <IMAGE>

Description

SPECIFICATION Rocker members This invention relates to rocker members particularly, but not exclusively, rocker members for use in a baby's cradle, and to a cradle provided with such rocker members.

Hitherto, the rocking rate of cradles has not been an important consideration in the design of the rockers for a baby's cradle. Experiments have been carried out in order to try to determine a rocking speed which results in a maximum soothing effect for the baby lying in the cradle. It has been found that babies become much calmer and cry much less when they lie in a cradle which is being rocked at a "natural frequency" of between 60 and 70 rocks per minute.

In order to couple a rocking system (capable of rocking a cradle at a "natural frequency" of between 60 and 70 rocks per minute) to a conventionaily designed cradle, it would be necessary to empioy a complicated mechanical and control system, since it would have to be capable of operating regardless of the physical parameters and rocking characteristics of the cradle. Further difficulties would be encountered since the frequency at which a conventional cradle rocks (the rockers of the cradle having a curvature forming part of a circumference of a circle) increases with increasing deflection.

According to the present invention there is provided a rocker member suitable for use in a baby's cradle, the rocker having a curved edge, the edge having a mid-point which coincides with the point of contact between the edge and a surface on which the rocker is supported when the rocker is at rest, the edge having a radius of curvature, which, at any given point on the edge varies according to the distance of that point from the mid-point, such that when the rocker is deflected from its rest position through any angle, the rocker will rock with substantially the same frequency.

A rocker member embodying this invention, and as described hereinbelow, has its edge curved, such that when the rocker is deflected from its rest position, it rocks with substantially the same frequency. Hence, when a baby's cradle is attached to a pair of such rocker members, the cradle may be pushed and therefore deflected by any amplitude (within limits defined by the extent of the length of the rocker members, so that the cradle is not pushed over) and it will still rock at the same frequency.

Owing to damping effects on the rocking motion due to, among other things, friction between the rockers and the surface supporting the rockers, the amplitude of deflection, of the rocking cradle will decrease after the initial deflection. Although the cradle will always rock at the same frequency without external assistance, a mechanical device may be employed which is capable of applying pulses to the cradle, for example, once per 'rocking cycle', in order to maintain the rocking motion at the same amplitude. The pulses are activated or triggered by the rocking motion of the cradle itself, the device having no other influence other than to maintain the amplitude of rocking at the "natural frequency".

The present invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an end view of a baby's rocking cradle having a rocker edge with differing radii of curvature aiong its length; Figure 2 shows a side view of the baby's rocking cradle of Figure 1; and Figure 3 shows a pulse generator for compensating for frictional losses during rocking of the cradle of Figure 1.

Referring to Figure 1, there is shown an end view of a baby's rocking cradle 1, which comprises a rocker 2 having a curved edge 3, an end support 4, horizontal bars 5 and a bed 6. The cradle 1 is shown when in a rest position, that is, when it is not rocking, and therefore the point of contact of the edge 3 of the rocker 2 with its supporting surface (not shown) is at the mid-point 7 of the rocker 2. When the cradle 1 is deplaced from the rest position through a small angle and subsequently released, the cradle 1 rocks about the mid-point 7 at a frequency off rocks per minute. The curvature of the edge 3 is such that the cradle 1 will rock at substantially the same frequency for any amplitude of deviation, provided that one point of the curved edge 3 remains in contact with the supporting surface.

The rocker 2 of Figure 1 may be manufactured by the method described hereinbelow. The rocker 2 is initially provided with an edge 3 having a sufficiently large radius (rl) of curvature so that at all points along its length, this radius is greater than the radii required for ensuring a condition of constant rocking frequency at the "natural frequency" (that is between 60 and 70 rocks per minute). Firstly the distance g between the centre G and the mid-point 7 of the rocker edge 3 is determined as will be described later.Having established the distance g, the radii for construction of the first edge curvature 3 are determined using the following general relation:

where N=frequency of oscillation of the cradle 1 when rocking with a particular amplitude; K=constant at a particular amplitude of rocking; r=radius of curvature at a point on the rocker edge 3 of maximum deflection, when the cradle 1 rocks with the particular amplitude; g=distance between the G and the mid-point 7.

The relation (1) is derived by analogy from considerations of the rocking of floating bodies in fluids.

The cradle 1 (having the rockers 2 of the initial radius rl) is first displaced by a small angle (less than 50) about the mid-point 7 and the frequency of oscillation Nl at this small angle is measured.

Substituting into the equation (1)

where KO=constant for small angles of deflection.

Denoting the required "natural frequency" N then for the same small angle of deflection.

where r0=the required radius of the rocker at the mid-point 7.

Eliminating K0

Hence the radius rio is evaluated.

It is noted that the radius of curvature r0 ensures the required frequency condition only for small displacement of the cradle 1, that is, at about 50 either side of the mid-point 7.

Displacements through larger angles causes the cradle 1 to rock at higher frequencies to the frequency Nr. Further radii of curvature for ensuring the constant frequency condition for points on the rocker edge 3 displaced from the mid-point 7 (that is, for displacement of the cradle 1 through angles greater than 50) are determined using the same procedure as for determination of the radius rO.

The cradle 1 is displaced through known angles greater than 50 either side of the midpoint 7, for example, firstly to point A and secondly to point B (which may, for example, correspond to the cradle being deflected through 100 and 200 respectively) as shown in Figure 1.

The frequency of rocking for displacements to these points is then measured giving rise to frequency measurements N a and Nb respectively.

For the "natural frequency" Nr the radius r required at point A is evaluated from the equation:

and the radius r2 required at the point B, from equation:

The initial rocker edge 3 of the rocker 2 may be adjusted by being placed so that the appropriate radius of curvature is formed at the appropriate points on the edge 3.

Although the radius of curvature has been determined at 3 points, namely themid-point 7, A and B, on the edge 3, more values may be determined as required. The more values obtained, than the closer the shape of the edge 3 will turn out to be to the ideal shape which will result in a "natural frequency" rocking at all deflections.

The centre of gravity G may be located by, for example, suspending the cradle from 2 points in turn and locating the intersection of vertical lines passing through each point of suspension. The intersection corresponds to the position of the centre of gravity G. Alternatively, the cradle may be rocked, for small deflections, on its edge 3 having the initial radius of curvature r1 and the frequency of rocking N. being measured. The cradle 1 is then inverted so that it rocks on an edge 8 having a radius of curvature ra (Figure 1), and then rocked through small deflections and the frequency of rocking Na is measured. Hence, from equation (1), the constant K can be eliminated and the value g fround (see equations (2)).

(for rocking on the edge 3)

(for rocking on the edge 8) where d is equal to the distance between points of rocking on the edges 3 and 8 respectively.

A mechanical device 10 may be associated with the cradle 1 in order to compensate for frictional losses in the rocking motion. As shown in Figure 3, a pulse generator is shown comprising a pair of solenoids 11, 12 at either end of a tube 13 (alternatively there may be only one solenoid situated at one end of the tube).

Inside the tube 13, there is a plunger 14 made from a ferromagnetic material which can slide from one end of the tube 13 to the other Electric current from a power supply 1 5 is fed to the coils 11 and 12 via a mercury switch 16. The device 10 is then attached to the cradle 1. When the cradle is deflected (manually), the mercury switch 16 is tilted with the cradle and one pair of contacts in the mercury switch is closed thereby allowing current to pass through the corresponding coil, thus causing the plunger 14 to accelerate within the tube 13 and to strike the end of the tube 13, thus supplying a push to the cradle 1. With a two-coil generator, the swing of the cradle in the opposite direction opens a first pair of contacts and cioses a second pair of contacts in the mercury switch 16, thus energising the second coil and causing the plunger 14 to accelerate in the opposite direction.

An adjustable resistor 1 7 is provided in the mechanical device 10 so that the amplitude of the rocking of the cradle 1 may be varied by varying the force acting on the plunger 14 and hence the energy of the pulses delivered to the tube 13.

Although the embodiment described hereinabove relates to a rocker of a baby's cradle, the rocker may be used on, for example, a rocking chair. Furthermore, rockers designed to rock at particular frequencies for varying amplitudes may have application in mechanical systems used in industry, for instance rocker systems are used in some types of crystallizers.

Claims

1. A rocker member suitable for use in a baby's cradle, the rocker having a curved edge, the edge having a mid-point which coincides with the point of contact between the edge and a surface on which the rocker is supported when the rocker is at rest, the edge having a radius of curvature, which, at any given point on the edge varies according to the distance of that point from the mid-point, such that when the rocker is deflected from its rest position through any angle, the rocker will rock with substantially the same frequency.

2. A baby's cradle having rocker members according to claim 1.

3. A cradle provided'with rocker members according to claim 1, and provided with a mechanical device capable of maintaining rocking motion of the cradle.

4. A rocker member substantially as herein described with reference to, and as illustrated in, Figures 1 and 2 of the accompanying drawings.

5. A baby's cradle according to claim 1, substantially as herein described with reference to, and as illustrated in, Figures 1 and 2 of the accompanying drawings.