FIELD OF THE INVENTION This invention relates to a forklift truck accessory and, more particularly, to an accessory aimed at facilitating alignment of the load carrying forks of a forklift truck or the like with a load to be lifted. Whilst the term forklift truck will be used throughout this specification it is to be understood that any other analogous lifting vehicle having a generally upright mast with a carriage carrying load engaging members such as forks movable up and down the mast and wherein the mast is capable of being tilted out of the vertical orientation is intended to be included within the scope of the invention.

BACKGROUND TO THE INVENTION The driver of a forklift truck generally has at least some difficulty in aligning the free ends of the forks with apertures provided in, for example, a pallet, and simultaneously ensuring that the forks extend in a substantially horizontal direction. The danger is that the forks may foul either the pallet or its load on one hand, or the supporting ground or floor and the other hand, as they enter beneath the load to their full extent. It can happen, and often has, that some form of damage results from misalignment of the forks and apertures and very often this can be attributed at least in part to the fact that the forks were not properly orientated in a horizontal plane.

OBJECT OF THE INVENTION It is an object of the invention to provide an accessory which will contribute towards facilitating the orientation of the forks of a forklift truck when aligning them with a load to be moved.

SUMMARY OF THE INVENTION In accordance with this invention there is provided a forklift truck accessory comprising a housing adapted to be secured relative to the generally upright mast of a forklift truck, a relatively rotatable operating member located within the housing and gravity biased towards a fixed position relative to the vertical at least within the general operating parameters of a forklift truck; and indicator means associated with the operating member for indicating when the operating member is in a particular position relative to the housing which in use corresponds to a horizontal position of the forks of a forklift truck.

Further features of the invention provide for the relative rotatable operating member to be rotatable about a generally horizontal axis; for the operating member to have at least a part cylindrical surface associated with it and rotatable in unison with it with the surface carrying demarcated zones which cooperate with one or more indicators associated with the housing in which case the combination of the demarcated zones and indicators constitute said indicator means; for the indicators to be lines marked on a window in a wall of the housing through which the cylindrical surface is visible; and for the demarcated zones to include a central longitudinally extending stripe of a preselected colour, such as green, with contrasting coloured zones on each circumferentially adjacent region of said stripe.

The accessory may be provided with illuminating means for facilitating viewing thereof, and it may also have audible signal generating means to

alert a forklift truck driver to a particular condition of the mast, for example that it is, or is not, in a vertical orientation.

The invention also provides a forklift truck having fixed to the mast thereof an accessory as defined above. The accessory is preferably fitted to the mast at substantially the eye level of a driver of the forklift truck and is attached to the mast in a manner such that it is ajustable in angular orientation relative to the axis of rotation of the operating member and is also preferably ajustable in height to allow for adjustment to suit different sizes of drivers.

In order that the above and other features of the invention may be more fully understood one embodiment thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:- Figure 1 is a perspective illustration showing an accessory according to the invention fitted to a forklift truck; Figure 2a is an orthographic projection of the accessory itself with the indicator means indicating a horizontal orientation of the forks of an associated forklift truck; Figure 2b is an elevation of the front face of the accessory illustrating the indicator means indicating a rearwardly inclined orientation of the mast of the forklift truck; Figure 2c is similar to Figure 2b but showing the indicator means indicating a forwardly inclined orientation of the mast;

Figure 3 is a sectional side view showing the interior of the accessory; Figure 4a illustrates schematically the orientation of the mast corresponding to the rearwardly inclined orientation indicated by the indicator means in Figure 2b; and, Figure 4b is similar to Figure 4a but showing the forwardly inclined orientation of the mast as indicated by the indicator means in Figure 2c.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS Referring firstly to Figure 1, there is shown a forklift truck, generally indicated by numeral (1), and having an upwardly extending mast (2) of conventional type with a carriage (3) movable up and down the mast and having a pair of forwardly projecting load engaging forks (4). The mast (2) is capable of tilting forwardly (as shown in Figure 4b) and rearwardly (as shown in Figure 4a) in order to manipulate the forks relative to a load to be engaged, and to provide for safety of transport of a load in the rearwardly inclined position.

A level indicating accessory (5) according to the invention is, in this instance, secured by way of brackets which are more fully described below to a generally horizontal cross brace (6) at about the eye-level of a driver (7) of the forklift truck. The cross brace extends between the two main parallel uprights (8) of the mast.

Turning now to the construction of the level indicating accessory itself, and with particular reference to Figures 2 to 4, the accessory of this embodiment of the invention comprises a housing (9) of generally rectangular configuration and having within it an operating member in the form of a

generally horizontal, freely rotatable circular cross-sectioned cylinder (10).

The cylinder has a weight (11) attached at one point to its periphery so that the cylinder tends to adopt a fixed position relative to the vertical with the axis of the cylinder being generally horizontal whilst the housing is free to rotate relative to the cylinder.

A window (12) is provided through the front wall (13) of the housing immediately opposite the outer surface of the cylinder so that the central region of the surface of the cylinder can be viewed through it. The window has a pair of horizontal indicator lines (14) extending across its width, the lines being vertically spaced apart about the centre of the height of the window so that they divide the height of the window into three roughly equal sized lateral strips.

The surface of the cylinder has a green stripe (15) extending along its length and corresponding in width to the vertical space between the indicator lines.

The areas (16) adjacent the green stripe are coloured to contrast with it.

They may thus be a bright yellow for example. The green stripe is arranged to fill the space between the indicator lines (14) when a horizontal position of the forks is being indicated.

As indicated above, the housing (9) is attached to the cross brace (6) by means of brackets. These brackets may assume the form of the vertically extending brackets (17) illustrated in Figure 2a. A series of holes (18) along the length of the brackets enables vertical height adjustment of the housing to be made and the size of the holes is adequate to allow for adjustment of the housing about a horizontal and transverse axis to adjust the orientation in which the green stripe (15) is located between the two indicator lines (14).

Installation of the level indicating accessory described above is extremely simple in that the brackets are simply bolted to the cross brace; a suitable height of the housing is determined; and the housing is secured to the

brackets in this position. The forks of the forklift truck are then adjusted to a level condition using a spirit level or the like and the position of the housing is adjusted so that the green stripe is located exactly between the two indicator lines (14). The housing is then fixed in this position.

A forklift truck driver will be most easily able to see when the forks of the forklift truck are horizontal simply by viewing the green stripe through the window (12) of the housing of the level indicating accessory. In the event that the mast and forks are tilted rearwardly, as illustrated in Figure 4a, then the green stripe will be located at least partly above the space between the indicator lines (14) as shown in Figure 2b. If, on the other hand, the forks are inclined forwardly, as shown in Figure 4b, the green stripe (15) will be located at least partly below the space below the indicator lines (14) as shown in Figure 2c.

It will be understood that numerous variations may be made to the embodiment of the invention described above without departing from the scope hereof. In particular, additional functions can be added such as, for example, an illuminating light so that the indicator means is easily visible even under poor lighting conditions. Also, the device could embody sensing means for triggering an audible signal indicating when the vertical condition of the mast is achieved or, on the other hand, indicating that the mast is not in a vertical condition. Such an audible signal could be intermittent or continuous as may be required.

Also, numerous different arrangements of operating member are possible within the scope of the invention, the cylindrical member described above simply being illustrative of the invention.