GB2172748A - Pressure mat switch assemblies - Google Patents

Abstract

A safety mat assembly of the type used for protecting personnel from dangerous machinery and the like in which a conventional mat switch 2 is positioned between a plate assembly 1, comprising a plurality of edge-to-edge plates 4, and the floor surface. The plates 4 have a small gap in between to allow for relative movement between plates as the assembly is stepped upon, this gap being sealed against ingress of particulate material. A frame surrounds the complete assembly to protect the edges of the plates. <IMAGE>

Description

SPECIFICATION Improvements relating to safety pressure mats This invention relates to pressure mat assemblies, particularly of the type used for protecting personnel from potentially dangerous machinery and the like. Such mats are usually arranged strategically around the machine to be protected and operate to automatically make the machine safe, for example by switching it off, when the mat is stepped on.

Many types of mat are available; the mostoften seen types work on the principle of electrical contacts which make or break when the mat is stepped on, or change in electrical resistance or capacitance, or pneumatically by restriction of air flow in rubber tubing. Many of these mats have an upper surface of flexible material, for example rubber or plastics material. However there are many applications where a rigid upper surface is preferable due to its improved ruggedness or for other reasons. Such rigid upper surfaces are usually made from metal, hard plastics material or timber, all of which materials suffer from difficulties in obtaining specimens in sheet form which are flat to begin with, and which will remain flat in service.These difficulties result in an operating sensitivity which is not substantially uniform over the whole mat surface, a problem which can be compounded by the floor surface on which the mat is mounted itself being uneven.

In order to overcome or reduce this problem, the present invention provides that the top surface of the mat assembly is composed, not of a single sheet, but of a plurality of plates of rigid material which are arranged to cover the area to be protected, and wherein there is further provided means for inhibiting particulate material from dropping down between adjacent plates.

The plates may be rectangular, but are conveniently square; typically in the size range 10 to 25 cm2. Larger or smaller plates could be used in certain circumstances, depending upon the required degree of uniformity of sensitivity and the flatness of the floor. The plates are typically of wood, for example plywood, rigid plastics material, or metal, and may be embossed or ribbed on their upper surfaces to provide a non-slip finish. As an alternative the upper surface may be coated with a film of anti-slip material.

The means for inhibiting particulate material from passing between adjacent plates advantageously comprises some form of tongue and groove joint between adjacent plates in which the tongue is relatively loose in the groove in order to permit a degree of flexing between adjacent plates. In one embodiment, two adja cent edges of each plate are formed with an integral tongue, while the other two edges are formed with a cooperating groove wider than the tongue. The plates may then loosely fit together with the tongues of one plate entering the grooves of adjacent plates. In an alternative embodiment, all edges of each plate are formed with a groove, and a loose tongue is inserted between adjacent plates during assembly. Such a loose tongue could be fabricated, for example, from strip stainless steel, phosphor bronze or spring steel.

The plate assembly described above can be used as an actuating surface for many types of pressure mat assembly. Preferably one or more protective layers are inserted between the mat itself and the plate assembly in order to provide mechanical protection for the mat and also, if necessary, protection against ingress of liquids, which latter may be corrosive. Such protective layers should be flexible and are preferably also resilient, to allow flexing of the plates relative to one another. A suitable material would be a thin layer of foam plastics, for example polyethylene foam, or foam rubber.

Preferably also, the pressure sensitive element is itself mounted on a relatively rigid base plate, for example of sheet aluminium or aluminium alloy, thus forming a sandwich construction of base plate-pressure sensitive element-protective layer(s) (if used)-plate assembly. Individual layers are attached together, for example, by adhesive. Advantageously the base plate is made thin enough to conform to the contours of an uneven floor.

In order that the invention may be better understood, several embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a plan view of a pressure mat incorporating the plate assembly of the invention; Figure 2 is a partial section through the mat of Fig. 1; and Figures 3 and 4 are partial sections showing two further embodiments of the plate assembly only.

Referring to Figs. 1 and 2 there is shown a complete mat switch panel incorporating a plate assembly 1, mat switch 2 and backing plate 3. The plate assembly comprises a plurality of flat square plates 4 made for example of plywood, metal or plastics material. The upper surface 5 of each plate is advantageously rendered slip-resistant by ribbing or scoring or by providing an anti-slip layer (not shown). One particular commercially available item which is thought to be particularly suitable is Acme anti-skid panels made by Acmeflooring Ltd. These comprise W.B.P. plywood panels which are seal coated with an epoxy resin in which is embedded graded cal cined bauxite to provide an extremely effective non-slip surface.

The plates are arranged in any suitable pat tern, one such being illustrated in Fig. 1, and are surrounded by a frame 6 (not shown in Fig. 2) which covers the exposed edges of the assembly and has an upper surface which is flush with the upper surface 5 of the plates 4. The purpose of the frame 6 is to protect the exposed edges of the assembly and also keep the plate 4 in position.

Each plate 4 is provided around all four of its edges with a groove 7 arranged such that, when assembled, the grooves 7 of adjacent plates face one another to form an elongate slot in which a strip 8 of metal, for example stainless steel, or plastics material or similar can be incorporated. The grooves 7 are fabricated to be of greater width than the thickness of the strips 8-typically a ratio of 10:1-in order to permit relative movement as between adjacent plates 4 so that the plate assembly as a whole has a degree of flexibility. This also allows the strips 8 to cross over at the corner junctions of adjacent plates 4 without affecting relative plate movement and this in turn means that a single strip 8 can be used for each straight run between plates-in other words, in the Fig. 1 example, 5 strips in one direction and 3 in the other.The strips 8 act to prevent the ingress of grit and dirt into the assembly which could cause damage to the mat switch 2. Typical dimensions for the plate assembly are as follows: Overall size of each plate : 200 mm square Overall thickness of each plate : 6 mm Width of groove 7 : 1-2 mm Width of strips 8 : 12 mm Thickness of strips 8 0.1-0.2 mm Distance between adjacent plates: 1 mm The construction of the mat switch 2 is not shown in detail since this is well known. Typically, the switch 2 comprises two sheets of stainless steel between which is sandwiched a thin layer of perforated insulating material.

Pressure on one of the sheets causes the sheets to touch through the insulating material, and a contact is made. Leads are connected to the two sheets and taken to external circuitry. The assembly is usually enclosed in a pocket of rubber or flexible plastics material for protection. Other types of mat switch may be used, depending upon the circumstances.

Interposed between the plate assembly 1 and the mat switch 2 is a thin layer 9 of foam plastics material such as polyethylene foam. The layer 9 is glued to the top surface of the mat switch 2 and the plates 4 are in turn glued to the top surface of the layer 9.

The plates 4 are thus kept in position by virtue of all being glued to a common base layer, and damage at the edges is prevented by the aforsaid frame 6.

The mat switch 2 is glued to the backing plate 3 either directiy, as shown, or via the intermediary of a further thin layer of foam plastics material similar to layer 9. The backing plate can be rigid or non-rigid and is typically of aluminium which is rigid enough to properly support the assembly, and yet flexible enough to conform to the shape of an uneven floor, thus providing a reasonably uniform sensitivity of switch operation over the whole area of the switch panel. A rigid backing plate may be desirable if the floor surface is particularly uneven.

In the above, it has been assumed that the switch panel shown in Fig. 1 is made up as a single unit. However, as will be seen from the typical sizes quoted above, this leads to the 4X6 plate arrangement of Fig. 1 being of inconveniently large size. In practice therefore it is anticipated that the switch panel will in fact be assembled from a plurality of smaller switch mat modules, each comprising say six plates in a 2X3 array. Each such module will have an associated mat switch 2 and backing plate 3, as described above; however, the switch panel of Fig. 1, when constructed in this manner would actually comprise four separate 2X3 plate modules, each having their own separate mat switches and backing plates. Adjacent modules are held in place by strips 8 extending in the outside facing grooves 7 of the plates 4 and the whole assembly is kept together by frame 6.It is envisaged that for a typical installation around a large machine, several tens or even hundreds of such modules will be needed.

In use, the whole switch panel, such as that shown in Fig. 1 is placed in a strategic position, for example in front of a dangerous machine. An operator who steps on the panel will depress one or more of the plates 4 to cause actuation of the mat switch 2 which in turn causes actuation of a safety function-- warning lights or bells, switching off of the machine or similar.

Figs. 3 and 4 are views of the plate assembly only and show two further embodiments.

In Fig. 3, each plate 4 is provided with a groove 10 along two adjacent edges and a tongue 11 along the other two adjacent edges. The relative dimensions of the tongue and groove are such that the plates can move relative to each other, as described above.

The plates are fitted together in the manner illustrated to form a panel such as that shown in Fig. 1.

Fig. 4 shows a further alternative plate assembly in which each plate is provided on all four edges with a tongue 12. The facing free ends of the tongues 12 are sealed by an extruded plastics or rubber section 13 which extends between the plates in a manner similar to the strips 8 of the embodiment of Fig. 2.

Both the assemblies of Figs. 3 and 4 are completed in the manner of Fig. 2 to provide a complete mat switch panel.

Claims (16)

1. A pressure mat assembly comprising a pressure switch mat operable to activate an alarm function when pressure is applied, said switch mat being sandwiched between a floor surface and a plate assembly comprising a plurality of plates of rigid material arranged edge to edge to cover the area to be protected.

2. An assembly as claimed in claim 1 wherein a gap is present between the facing edges of adjacent plates and wherein means are provided for inhibiting particulate material from dropping through the gap.

3. An assembly as claimed in claim 2 wherein the means for inhibiting particulate material comprises a tongue and groove joint between the facing edges of adjacent plates.

4. An assembly as claimed in claim 3 wherein the perimeter edge of each plate is provided with a slot and wherein the assembly further comprises a plurality of loose tongues in the form of strip material, which tongues are loosely housed in the slots in such a way as to act as a bridge between adjacent plates.

5. An assembly as claimed in claim 4 wherein said strip material is stainless steel.

6. An assembly as claimed in claim 3 wherein the plates are such that, when arranged together, the facing edges of adjacent plates are formed, on the one hand, with a tongue and, on the other hand, with a cooperating groove, the arrangement being such that the tongue is a loose fit in the groove to permit a degree of relative movement between adjacent plates.

7. An assembly as claimed in claim 2 wherein the means for inhibiting particulate material comprises a strip of elastomeric material arranged between the facing edges.

8. An assembly as claimed in claim 7 wherein the facing edges of adjacent plates are each formed with a short tongue and wherein the strip of elastomeric material is fitted between the facing tips of these tongues and is shaped in such a way as to be securely located thereby.

9. An assembly as claimed in any one of the preceding claims further comprising a protective layer of sheet material sandwiched between the plate assembly and the pressure switch mat.

10. An assembly as claimed in any one of the preceding claims wherein the pressure switch mat is mounted on a relatively rigid base plate which latter is mounted on the floor surface.

11. An assembly as claimed in claim 10 wherein the base plate is made of sheet metal.

12. An assembly as claimed in either one of claims 10 or 11 further comprising a protective layer of sheet material sandwiched between the pressure switch mat and the base plate.

13. An assembly as claimed in either one of claims 9 or 12 wherein said protective layer or layers is/are made from foam plastics material.

14. An assembly as claimed in any one of the preceding claims wherein the top surface of each of said plates is formed with a nonslip surface.

15. A pressure mat assembly substantially as hereinbefore described with reference to the accompanying drawings.

16. A plate assembly for incorporation into the pressure mat assembly as claimed in any one of the preceding claims, said plate assembly comprising a plurality of plates of rigid material arranged edge to edge to cover an area to be protected and operable to actuate a pressure switch mat positioned between the plate assembly and a floor surface when pressure is applied to the top surface of the plate assembly.