Arrangement in Working Lamps

The subject invention concerns an arrangement in working lamps of the kind comprising an upper pivotable arm supporting the light fittings proper, and a lower pivotable arm which is arranged for pivotal movements about a horizontal shaft provided in a housing at the lower end of the lower arm, said pivotable arms being interconnected by a segment and hingedly connected thereto for pivotal movement, each about its respective pivot shaft.

Working lamps for close-range illumination of working areas, such as desks, working benches, machines and the like are usually provided with pivotable arms of the above-mentioned kind in order to maximize the range and positions of adjustment of the lamp. Since in this kind of lamps the light fittings are normally positioned at the extreme end of the upper pivotable arm, i.e. at the remote end from the point of attachment of the lamp, the lamp has a tendency to buckle up about its attachment.

It is known to arrange the upper and/or the lower pivotable arm as double parallel rods including spring means to counter-act the moments tending to tilt the pivotable arms supporting the fittings. The parallel rods form levers with which the springs can cooperate. In addition, this arrangement has the advantage that when the lower arm is lowered to move the light laterally, the angle of the light fittings to the illuminated surface remains substantially the same.

Similar types of lamps are known showing combinations of frictional joints and lever-arm joints and springs cooperating therewith.

The subject invention provides a working lamp the construction of which is less complicated than conventional lamps while at the same time it provides maximum safety against unwanted tilting or buckling up, in addition to which it is both sturdy and durable. A further advantage is that when the lower arm is displaced in order to move the light fittings in the lateral direction, the level of the lamp above the illuminated surfaces remains substantially unchanged.

The invention is characterised by a rail which extends essentially in parallel with the lower pivotable arm and which is pivotally connected to the segment about a third pivot shaft, said rail being axially displaceable in a guide means relative to the lower pivotable arm and cooperating with the housing by means of a pin-and-slot coupling arrangement, wherein the slot serves as a track to guide the pin and extends in a curve from a maximum radial distance from the lower pivot shaft of the lower pivotable arm to a minimum distance from said shaft, in addition to which said slot serves to take on one of its edges any moments of load exerted by the light fittings in any one of their set positions and transmitted via the upper pivotable arm, the segment and the rail.

In accordance with one aspect of the invention the rail is provided with said pin and said slot is formed in the wall of the housing.

One embodiment of the invention will be described in closer detail in the following with reference to the accompanying drawings, wherein

FIG. 1 shows the improved working lamp in accordance with the invention attached to a table top,

FIGS. 2 and 3 show in a broken view and on an enlarged scale the lower pivotable arm of the lamp in various angular positions,

FIG. 4 illustrates schematically the forces acting on a guide track included in the lamp arrangement in accordance with the invention.

The working lamp illustrated in FIG. 1 is secured to a table top 2 by means of an attachment fitting 1. A horizontal shaft 3 forms the pivot axis about which the lower end of a lower pivotable arm 4 is arranged to pivot while the upper end of the arm is pivotally connected to an upper pivotable arm 6 via a joint segment 5. The upper pivotable arm 6 supports light fittings 7 of a well-known type.

The joint segment 5, see FIGS. 2 and 3, is pivotally connected to the lower pivotable arm 4 via a shaft 8. The upper pivotable arm 6 is arranged to pivot about a shaft 9 in a frictional-type of joint provided in the segment 5.

Between a housing 10 in which the lower arm 4 is mounted on the shaft 3 and the segment 5 extends a rail 11 which is connected to the segment via a pivot shaft 12. The shaft 3 is formed with a groove 13 in which the rail 11 is arranged to move in its lengthwise direction and which groove serves to guide the rail. In the embodiment illustrated in the drawings, the rail 11 is provided at its lower end with a pin 14 engaging in a slot 15 formed in the wall of the housing 10. The slot 15 forms a guiding track to guide the pin 14 and describes a curve from a radially maximum distance from the lower pivot shaft 3 of the lower arm 4 to a minimum distance from said shaft.

Irrespective of in which position the working lamp is set the moment of load of the light fittings 7 is transferred in accordance with the invention via the upper pivotable arm 6, the segment 5, the rail 11 and the pin 14 to the outer edge of the slot 15. FIG. 4 illustrates the manner in which the forces involved act in a predetermined set position of the lamp. The vector A indicates the force tending to pull the upper pivotable arm 6 downwards. The vector B indicates the force tending to pivot the lamp downwards about the horizontal shaft 3. If the vector A is of a sufficient magnitude, that is, if the moment of leverage exerted by the light fittings 7 is of a necessary minimum magnitude, the resultant R will be directed radially outwards from the slot 15, as illustrated in FIG. 4. This means that the working lamp will remain stable in any position in which it is set. Should the load increase, for instance if the light fittings 7 are replaced by other, heavier fittings, the pressure exerted by the pin 14 on the edge of the slot 15 will increase, and consequently the force acting to retain the lamp in any position wherein it is set is increased accordingly. Inversely, by raising the light fittings 7 somewhat, that is, by reducing the vector A somewhat, the lamp will automatically move from the position shown in FIG. 1 in continuous lines to the position shown in dash-and-dot lines therein. During this movement, the light fittings 7 move in parallel with the table top 2.

The working lamp in accordance with the invention thus offers the considerable advantage that one and the same arm structure can be used for light fittings of various sizes and weights without any adaptation whatsoever of the structure to new conditions with regard to the moments of leverage involved.

The invention is not limited to the embodiment as shown and described in the aforegoing but a variety of modifications are possible within the scope of the appended claims. For instance, the slot 15 may be positioned elsewhere than in the wall of the housing, such as below the shaft 3 and may extend in another direction towards the shaft centre, in which case the pin 14 will abut against the opposite edge of the slot.

In addition, the rail 11 may be guided in another manner than by means of the groove 13 in the shaft 3.

Within the scope of the principal claim it is likewise possible to provide a pin-and-slot coupling arrangement in a mirror fashion to the one shown, that is to provide the pin 14 on the inner face of the wall of the housing 10 whereby the pin will travel in a slot formed in the rail 11. In this case the rail 11 should be broader than as illustrated in the drawings.