GB2312032A - Buffer stops for radar tracking heads - Google Patents

Abstract

A plunger 7 providing a buffer stop for an arm (5, Fig. 1) of an oscillating radar antenna acts on friction springs 14, 15 via pistons 16, 17 and the cam piston head 7b. The cam head 7b provides a non-linear relationship between the plunger deflection and spring force (Fig. 3).

Description

RADAR TRACKING HEADS AND BUFFER STOPS THEREFOR The present invention relates to radar tracking heads and to buffer stops therefor.

In radar tracking heads having a radar antenna which is oscillatingly rotatable between two positions there are certain extreme operational conditions which necessitate the head being oscillated rapidly.

In such conditions it is a requirement that the radar head be decelerated at the end of its travel in each direction in a way which will keep its traversing time to a minimum whilst at the same time not imposing undesirably high loads on either the radar antenna itself or its supporting structure.

In order to achieve this a buffer stop is provided at each end of the rotary travel of the radar antenna to cater for these extreme circumstances, the purpose of each buffer stop being to progressively absorb the kinetic energy of the radar head as it approaches the end of its travel.

It is known to employ hydraulic buffers which on the one hand are capable of absorbing the high kinetic energy of the rotating antenna, which may weigh several tons, at the end of its travel without generating excessive loads on the antenna or support structure, whilst at the same time being sufficiently compact to fit in the space available in the particular application.

However, it has been found that the performance of such hydraulic buffers is variable depending, for example, upon how long they have been left unoperated and upon the ambient temperature particularly when low. They also require regular maintenance. There is therefore a requirement for a buffer which overcomes this problem whilst at the same time being sufficiently compact.

This problem is especially acute in cases where the radar antenna is designed to be mounted on a ship's mast. The present invention is particularly applicable to this type of application although it could be used in other applications.

The present invention is concerned with providing a buffer stop, particularly for the aforementioned application to a radar antenna head, which will be relatively compact and capable of operating for lengthy periods without any adjustment or servicing being required and thus instilling confidence in the user.

According to the present invention a buffer stop comprises a mechanical energy absorber and means for transmitting to it the kinetic energy of movement of a member to be arrested, the said means being designed to enable a non-linear relationship to exist between the deflection of the transmission means and the force applied by it to the said mechanical energy absorber.

According to a preferred aspect of the invention the mechanical energy absorber comprises a friction spring as hereinafter defined..

This arrangement has a number of advantages. A simple wholly mechanical buffer stop can be constructed which is more reliable and operationally consistent over a wide temperature range as compared with the known hydraulic types described earlier. Furthermore by the use of the non-linear transmission means for imparting the kinetic movement of the member to be arrested to the spring, the energy absorbing characteristics of the buffer stop can be designed in such a way as to minimise the overall dimensions of the buffer stop.

The term "friction spring" is intended to relate to a device which comprises interlaced columns of rings which interface with one another at mutually contacting cam surfaces so that any compression of the spring results in the dissipation of energy by the frictional forces between the contacting cam surfaces and by the expansion and contraction of the rings..

How the invention may be carried out will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagramatic side-elevational view of a radar antenna head to which a buffer stop according to the present invention may be applied; Figure 2 is an enlarged cross-sectional view of one of the two buffer stops shown in Figure 1; and Figure 3 is a graph illustrating the operating characteristics of the buffer stop shown in Figure 2.

Figure 1 This is a side-elevational view showing a pedestal 1 on which is mounted two buffer stops 2 and 3 constructed according to the present invention. A radar antenna (not shown) is mounted from both ends of a torque tube 4 to oscillatingly rotate around the head of the pedestal 1 as indicated by the double-headed arrow..

The torque tube 4 carries an arm 5 having at its outer radial end a stop member 6.

In certain operational conditions the oscillating antenna reaches either end of its angular traverse so that the stop member 6 abuts the head 7a or 8a of two plungers 7 and 8 respectively which form part of the buffer stops 2 and 3 respectively.

The kinetic energy of the rotating antenna is then dissipated by the action of the head 6 driving the plunger 7 or 8 into its respective buffer stop 2 or 3.

The way in which this is achieved will now be described with reference to Figures 2 and 3.

Figures 2 and 3 Figure 2 shows the buffer stop 2 but the buffer stop 3 is of the same construction.

The buffer stop 2 has a housing 9 which has an end cap 10 removably secured to it by nuts and bolts 11. The housing 9 is secured to a support 22 by means of a bracket 23 which is welded to both the housing 9 and the support 22.

The tubular housing 9 has an aperture 12 formed substantially mid-way along its length.

Extending outwardly from the housing 9 and the aperture 12 is a tubular guide 13 stepped at 13a.

The purpose of this tubular guide 13 is to locate and guide the plunger 7 as it moves inwardly and outwardly as indicated by the double-headed arrow in Figure 2. As mentioned earlier the plunger 7 has a head 7a at its exposed end, a wedge shaped cam member 7b, having a cam surface 7c, being formed on the inner end of the plunger 7, the ends of the cam member normal to Figure 2 being flat. The exact shape of the cam surface 7c will be discussed later in relation to Figure 3.

There are located within the housing 9 two friction springs 14 and 15.

The spring 14 is contained between an end cap 20 (which is sandwiched between the end of the spring and the closed end 9a of the housing 9) and a piston like member 16 which is slidable within the housing 9.

In a similar manner the second identical opposing spring 15 is contained between the end cap 10 of the housing 9 and a second piston like member 17 which is slidable within the tubular portion of the housing 9.

The detailed construction of the ring friction springs 14 and 15 will be described later in more detail.

The piston like members 16 and 17 have head portions 16a and 17a respectively, each of these head portions having cam surfaces 18 and 19 respectively against which the cam shaped head 7b of the plunger 7 is adapted to abut.

In its rest or extended position the plunger 7 is in the position indicated by B in Figure 2 and in its fully loaded or retracted position it is in the position shown by C in Figure 2.

As the plunger 7 is moved by the rotating arm 5, and associated head 6, from its fully extended or rest position B to its fully retracted and fully loaded position C the cam shaped head 7b of the plunger progressively deflects the two piston heads 16a and 1 7a outwardly with respect to the centre line of the plunger.

In other words the pistons 16 and 17 are moved towards their respective end caps 20 and 21 to progressively compress the friction springs 14 and 15 respectively.

In Figure 2 the spring 14 is shown in its fully extended condition as permitted by the fact that plunger head 7b is in its fully retracted position, and the spring 15 is shown in its fully compressed condition under the action of the plunger head 7b which is in its fully retracted position.

In being compressed each spring dissipates energy due to the friction forces generated between its adjacent and abutting rings and due to the expansion and contraction of the inner and outer columns of rings 22 and 23 respectively as described later in more detail below. It is in this way that the kinetic energy of the rotating radar antenna head is dissipated to bring the latter to a stop. The way in which this is done will be described in more detail in relation to Figure 3. Each spring comprises a series of separate inner 22 and outer 23 rings with mating tapered cam surfaces.

In the relatively uncompressed condition, but subject to a small pre-load, as shown by spring 14 on the left-hand side of Figure 2, there are gaps between adjacent rings of the inner 22 and outer 23 columns of rings respectively.

As the spring is compressed by the application of an axial load the wedge action of the abutting internaUexternal tapered surfaces on the inner 22 and outer 23 rings expands the outer rings 23 and contracts the inner rings 22 radially to dissipate energy..

One effective tapered face, i.e. one half inner ring and one half outer ring is defined as one element. Thus each of the springs shown in the drawings consists of twelve elements.

Compared with an ordinary coil spring having little or no frictional loss between adjacent coils of the spring as it is compressed, the amount of force required to compress the friction springs 14 and 15 is significantly greater. It is this excess force which enables the friction springs to dissipate a greater amount of kinetic energy of the rotating antenna for a given size of spring. Approximately two-thirds of the energy capacity of the spring is converted into frictional heat.

An example of this type of frictional spring is available from Ringfeder Limited and sold under the name RINGFEDER (Registered Trademark).

It has already been indicated earlier that the outward deflection of the pistons 16a and 17a, and therefore the compression of the respective springs 14 and 15, is not linear with respect to the travel of the piston 7. The non-linear characteristics will now be described in more detail with respect to Figure 3.

As indicated earlier one of the problems in designing a buffer stop, particularly for the application to a rotating radar antenna, is that a relatively large amount of energy has to be dissipated by means of a device which must occupy relatively little space. Furthermore, the loads being transmitted within the structure must be kept below certain critical levels otherwise damage to the structure will occur. This is particularly so where the rotatable radar antenna is mounted on a mast of a ship, for example.

Essentially the head 7b of the plunger 7 has a cam surface shape 7c designed to ensure that the load on the plunger 7 is partially equalised throughout its full stroke and so that the reactive load limitations of the supporting structure are not exceeded. In other words it is designed so that these loads will remain substantially constant throughout a wide temperature range.

Figure 3 is a graph of the plunger movement in millimetres against the total force applied to the plunger in thousands of Newtons.

The amount of energy dissipated is increased by pre-loading the two springs 14 and 15, this being represented in Figure 3 by the graph not starting at zero, the pre-load being of approximately 8000 Newtons at zero plunger deflection.

The objective is to maximise the area under the curve whilst at the same time keeping the maximum instantaneous loading below the critical value which would otherwise damage the structure.

The cam surface 7c of the head 7b is shaped to produce the curve shown in Figure 3 in which the maximum plunger load is 31200n, the total plunger movement is 68mm and the total energy absorbed during that plunger movement is 1640Nm.

The embodiment shown in Figure 2 is designed for a specific application. However, the invention could be applied to other detailed constructions of buffer stop employing the invention.

For example, the buffer stop could be designed to incorporate only one of the springs illustrated in Figure 2, i.e. the construction would be substantially that part illustrated on the lefthand-side of the centre line of the plunger 7.

In contrast a buffer stop could be designed to have more than two springs and in fact any number of spring/plunger cam surface combinations could be incorporated in such a buffer stop.

For example, there could be four springs in a cruciform shaped housing equivalent to housing 9 shown in Figure 2, a substantially conical cam head 7b acting on each of the four springs.

Although a specific type of energy dissipating spring has been described in relation to the construction shown in Figure 2, the invention could incorporate other suitable mechanical energy dissipating resilient elements or devices.

Claims (7)

1. A buffer stop comprises a mechanical energy absorber and means for transmitting to it the kinetic energy of movement of a member to be arrested, the said means being designed to enable a non-linear relationship to exist between the deflection of the transmission means and the force applied by it to the said mechanical energy absorber.

2. A buffer stop as claimed in Claim 1 in which the mechanical energy absorber comprises a friction spring.

3. A buffer stop as claimed in Claim 1 or 2 in which there are two diametrically opposed mechanical energy absorbers operated on by a single plunger.

4. A buffer stop as claimed in Claim 3 in which the plunger has a cam surface shaped so that the buffer stop has the operating performance characteristics shown in Figure 3.

5. A radar antenna head fitted with a buffer stop as claimed in any previous claim.

6. A buffer stop substantially as hereinbefore described with reference to and as shown in Figures 2 and 3 of the accompanying drawings.

7. A radar antenna arrangement substantially as hereinbefore described with reference to and shown in Figures 1 to 3 of the accompanying drawings.