GB2318042A - Drawer interlock for a cabinet - Google Patents

Abstract

A drawer interlock system has a rotary cam A,B,C for each drawer with their axes in vertical alignment. Vertical locking bars AB,BC are arranged end-to-end, each having upper and lower projections 23B,23C and 24A,24B which co-operate with the cams. Each drawer (not shown) has a finger 22B which engages and rotates the cam. Rotation of the cam on drawer opening causes the cam to engage the lower projection of the locking bar above and lifts it, whereby the upper projection(s) block rotation of the cam(s) above. At the same time the cam engages the upper projection of the lower bar, preventing the lower bar(s) from being raised thus blocking rotation of the lower cam(s). Closing the drawer reverses the earn rotation to release the blocked movements.

Description

"ImDrovements relations to Drawer Interlock Systems' This invention relates to drawer interlock systems.

It has become practically standard for multi-drawer filing cabinets to be fitted with an interlock mechanism whereby only one drawer can be opened at a time. To have two or more open could unbalance it, to the extent of causing it to topple forwards onto the person using the cabinet. That is obviously dangerous and to be avoided.

There have been a number of such systems proposed, usually involving a vertical locking bar that is actuated by any drawer that is pulled out. In several versions, this bar is divided into separate sections some of which are moved up and others held stationary or moved down when an intermediate drawer is pulled out. Some tend to rely on springs for return movements, but springs eventually weaken, and they are extra elements to manufacture and fit.

It is the aim of this invention to provide a reliable, compact drawer interlock system avoiding the use of springs.

According to the present invention there is provided a drawer interlock system comprising, for each drawer, a cam member rotatable about an axis fixed relative to the cabinet containing the drawers, vertically movable elements between each cam member with projections at opposite ends to cooperate with adjacent cam members at opposite sides of the axes thereof, and a finger on each drawer to co-operate with the associated cam member, the arrangement being such that, in an initial condition with all the drawers closed, adjacent elements abut and the cam members are in a first angular position allowing any drawer to be pulled out, wherein when a drawer is pulled out, its finger rotates the associated cam member to a second angular position before escaping therefrom, and that cam member: (a) raises any elements above it by acting on the lower projection of the element immediately above, and (b) blocks upward movement of any elements below by cooperation with the upper projection of the element immediately below, whereby (c) each raised element, through its upper projection engaging the associated cam member, prevents rotation of that member, which traps the associated drawer finger and stops the drawer being withdrawn, and (d) each other element, blocked against upward movement through its lower projection engaging the associated cam member, prevents rotation of that member, which traps the associated drawer finger and stops the drawer being withdrawn, and wherein the pulled out drawer, on being pushed in again, acts through its finger to rotate the associated cam member back from the second to the first rotated position, allowing any raised elements to lower and the initial condition to be resumed.

Preferably, the vertically movable elements are arranged so that their projections are in a vertical array containing the cam member axes.

Conveniently, rotation of each cam is limited by at least one of the associated projections acting as a stop.

Rotation beyond the first position may be limited by a notch in the periphery of the cam member, into which the projection on the element above enters, one flank of the notch providing a cam surface to lift that element when the cam member is rotated in the opposite direction. Rotation beyond the second position may be limited by a shoulder on the periphery of the cam member. In one form, the shoulder is the base of a U-shaped formation open circumferentially, an outer limb forming a resilient tongue to snap over an entering projection, and the inner limb being an arcuate portion centred on the axis of the cam member. At the mouth of the U the arcuate portion may have a tooth projecting towards the tip of the tongue.

In a preferred version there are two diametrically opposite shoulders which simultaneously engage projections on the elements above and below, and these shoulders may be at equal radii from the axis of the cam member.

The upper projection of each vertically movable element may be clear of the associated cam member when the drawers are closed and be abutted by an arcuate portion of the cam member periphery, centred on the axis of the cam member, when the associated drawer is opened and that cam member is rotated from its first angular position. When a drawer below is opened, that upper projection will be raised to engage a further shoulder on the cam member, preventing it from rotating.

The cam members may have associated damping means and stops, to ensure that they do not rotate too freely.

The system may be duplicated, with a mirror image one on the opposite side of the drawers.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a rotary cam member forming part of an anti-tilt mechanism, Figure 2 is a section on the line II-II of Figure 1, Figure 3 is a side elevation of an anti-tilt mechanism with three cam members such as those of Figure 1, with all drawers closed, and Figure 4 is a side elevation similar to Figure 3, but with one drawer opened.

The cam member of Figure 1 has a central boss 1 with a horizontal axis through which a bush 2 extends, being mounted on the inside of a side wall of a filing cabinet by a screw 3. There will be one such cam member for each drawer, and they will be aligned vertically, as described later, at one side of the cabinet, although they could be mirrored by another set at the opposite side. The cam member can rotate on the bush 2, but its ease of movement may be damped by a friction pad or pads (not shown). There are also stops as described below to confine the movement to an arc.

The peripheral shape of the cam member will be described in terms of a clock face and x, y axes, and Figure 1 shows it in its usual position with the drawers closed.

At the 12 o'clock position there is a notch 4, and this has a side parallel to the y-axis providing a shoulder 5 just clockwise of its base. Then there is a straight portion 6, parallel to the x-axis, to about 1 o'clock, where it angles down into another straight portion 7 at 450 to both axes, terminating at about 2 o'clock. This is at the root of a clockwise facing U-shaped catch 8 whose outer limb is a resilient tongue 9 curving slightly inwards from the end of the portion 7 and whose inner limb is the beginning of an arcuate portion 10 centred on the boss 1 and extending round almost to 6 o'clock. Opposite the free end of the tongue 9 this portion has a small projecting tooth 11. At the end of the portion 10 the periphery steps inwards at another shoulder 12 followed by a straight portion 13 parallel to the x-axis out to 8 o'clock, where it forms the base of another clockwise facing U-shaped catch 14 diametrically opposite the catch 8. This has an outer limb 15 similar to the tongue 9, and an inner limb which is the beginning of an arcuate portion 16, of the same radius as the portion 10, centred on the boss 1 and extending round to about 10 o'clock. A tooth 17 on this portion 16 matches the tooth 11. Finally the portion 15 curves round in a lobe to a slope 18 which sweeps down into the notch 4.

On the side of the cam member away from the cabinet wall there are two projecting walls 19 and 20 forming a curved channel 21. At the boss its general direction is towards 4 o'clock, but then it bends round to point down in the y-axis direction. The shorter wall 19 terminates at the point of the shoulder 12 and the longer wall extends beyond the arcuate portion 10 and has a reverse curve at its end to flare the mouth of the channel 21.

Referring now primarily to Figures 3 and 4, these show an anti-tilt mechanism for three drawers. It will be understood that the same principles could apply to any number of drawers one above the other, but for simplicity just three are envisaged. There are three corresponding cam members as described, referenced A, B & C respectively.

These co-operate with vertical locking bars AB and BC, the bar AB being between the cams A and B and the bar BC being between the cams B and C. The various parts of the cam members and of the bars that co-operate with them have suffixes A, B or C as appropriate. The drawers are not shown, although the side of one is indicated in broken lines in Figure 2, but each carries a laterally projecting finger 22A, 22B and 22C to co-operate with the channels 21A, 21B and 21C respectively. Each bar is of flat rectangular shape and both ends have deep rectangular cutouts so that they can embrace the bosses 1 of the adjacent cam members. Just below and above these cutouts, and vertically aligned with the axes of the cam members, the bars have projecting pins 23B and 23C at the upper ends and 24A and 24B at the lower ends.

In an alternative arrangement, the cams are mounted on the base of an elongate, vertical, shallow channel member fixed to the side wall of the cabinet to form a housing for the locking bars. This base will have slots through which the pins 23 and 24 project. Such an arrangement avoids the need for the cut-outs in the ends of the bars, which can then be narrower than those illustrated.

Initially, with all drawers closed, the locking bars AB and BC abut, with the boss 1B of the central cam member B within the cutout at the lower end of the bar BC. The pins 24A and 24B rest in the notches 4A and 4B respectively, while the drawer figures 22A, 22B and 22C are within the channels 21A, 21B and 21C. The pins 23B and 23C are clear of their associated cam members.

Suppose the middle drawer is pulled out, being moved to the left as seen in the figures. The finger 22B, trapped in the channel 21B, pulls the cam member B round in a clockwise direction. This forces the pin 24B to ride up the slope 18B from the notch 4B, and consequently lifts the locking bar BC. By the time the finger 22B has escaped the channel 21B, the cam will have rotated by approximately 900 to the position shown in Figure 4, where the pin 24B has snapped into the catch 14B and the pin 23B into the catch 8B. These catches guard against 'bounce back' of the cam, which could happen if there was not much damping or if the drawer was pulled out very abruptly. Then the cam would be incorrectly positioned to receive back the finger 22B.

It can be seen that the bar AB cannot rise since the pin 23B bears against the portion 10B as soon as the shoulder 12B moves, and it ends firmly trapped in the catch 8B. This keeps the pin 24A at the lower end of the bar AB in the notch 4A, preventing any movement of the cam member A and trapping the finger 22A. The lowermost drawer there fore cannot be pulled out. The upper bar BC meanwhile has shifted its pin 23C upwards past the shoulder 12C. This prevents the cam member C turning clockwise, and so the upper drawer is also trapped by its finger 22C in the channel 21C.

When the middle drawer is pushed in again, the finger 22B re-enters the channel 21B and the cam member B is turned back to the Figure 3 position. The upper bar BC drops back as well.

It will be seen that if the lower drawer is pulled out, both bars are raised to block the shoulders 12B and 12C, while if the upper drawer is pulled out, both bars are held down by the pin 23C and the pins 24A and 24B stop their cams rotating and thus prevent the two lower drawers opening.

The upper cam C will only be retained by the single catch 8C when the top drawer is opened. To lessen further the chances of bounce-back, there could be a short vertically movable bar above the bar BC equipped with a pin and bifurcated like the lower ends of the bars shown. When the top drawer is opened this will be lifted by the slope 18C and the pin will engage in the catch 14C.

At the lower end, an extra stop for the cam A can simply be a fixed pin projecting from the cabinet wall to be engaged by the catch 8A.

While U-shaped catches 8 and 14 are preferred, the tongues 9 and 15 may be dispensed with, leaving radial abutments or shoulders for the pins 23 and 24 to engage.

The teeth 11 and 17 may also be redundant.

Claims (13)

1. A drawer interlock system comprising, for each drawer, a cam member rotatable about an axis fixed relative to the cabinet containing the drawers, vertically movable elements between each cam member with projections at opposite ends to co-operate with adjacent cam members at opposite sides of the axes thereof, and a finger on each drawer to co-operate with the associated cam member, the arrangement being such that, in an initial condition with all the drawers closed, adjacent elements abut and the cam members are in a first angular position allowing any drawer to be pulled out, wherein when a drawer is pulled out, its projection rotates the associated cam member to a second angular position before escaping therefrom, and that cam member: (a) raises any elements above it by acting on the lower projection of the element immediately above, and (b) blocks upward movement of any elements below by cooperation with the upper projection of the element immediately below, whereby (c) each raised element, through its upper projection engaging the associated cam member, prevents rotation of the that member, which traps the associated drawer finger and stops the drawer being withdrawn, and (d) each other element, blocked against upward movement through its lower projection engaging the associated cam member, prevents rotation of that member, which traps the associated drawer finger and stops the drawer being withdrawn, and wherein the pulled out drawer, on being pushed in again, acts through its projection to rotate the associated cam member back from the second to the first rotated position, allowing any raised elements to lower and the initial condition to be resumed.

2. A drawer interlock system as claimed in claim 1, wherein the vertically movable elements are arranged so that their projections are in a vertical array containing the cam member axes.

3. A drawer interlock system as claimed in claim 1 or 2, wherein rotation of each cam is limited by at least one of the associated projections acting as a stop.

4. A drawer interlock system as claimed in claim 3, wherein rotation beyond the first position is limited by a notch in the periphery of the cam member, into which the projection on the element above enters, one flank of the notch providing a cam surface to lift that element when the cam member is rotated in the opposite direction.

5. A drawer interlock system as claimed in claim 3 or 4, wherein rotation beyond the second position is limited by a shoulder on the periphery of the cam member.

6. A drawer interlock system as claimed in claim 5, wherein the shoulder is the base of a U-shaped formation open circumferentially, an outer limb forming a resilient tongue to snap over an entering projection, and the inner limb being an arcuate portion centred on the axis of the cam member.

7. A drawer interlock system as claimed in claim 6, wherein at the mouth of the U the arcuate portion has a tooth projecting towards the tip of the tongue.

8. A drawer interlock system as claimed in claim 5, 6 or 7, wherein there are two diametrically opposite shoulders which simultaneously engage projections on the elements above and below.

9. A drawer interlock system as claimed in claim 8, wherein the shoulders are at equal radii from the axis of the cam member.

10. A drawer interlock system as claimed in any preceding claim, wherein the upper projection of each vertically movable element is clear of the associated cam member when the drawers are closed, abuts a further shoulder on the periphery of that cam member when the element is raised, and is abutted by an arcuate portion of the cam member periphery, centred on the axis of the cam member, when that cam member is rotated from its first angular position.

11. A drawer interlock system as claimed in any preceding claim, wherein the cam members have associated damping means to reduce their freedom of movement.

12. A drawer interlock system as claimed in any preceding claim, duplicated, with mirror image systems on opposite sides of the drawers.

13. A drawer interlock system substantially as hereinbefore described with reference to the accompanying drawings.