JPH0365602B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrical switches, and more particularly to electrical switches which operate under a predetermined load and create a conductive path that cannot be broken without destroying the switch when a predetermined overload is applied. Regarding electric switches. More particularly, the present invention relates to a pressure sensitive switch mat incorporating such an electric switch as a safety device.

Load sensitive mats incorporating electrical switches are well known and are commonly referred to as "switch mats." For example, switchmats are traditionally located near doors leading to exits from supermarkets, airports, and other public places, such that they are located in the path of pedestrians approaching the door. As the pedestrian approaches the door, the pine is stepped on by the pedestrian, thereby activating a mechanism that closes a normally open switch included in the pine and automatically opens the door. Switchmats are also used in industrial settings where switchmats may be used to limit access to hazardous machinery or to control the operation of machinery. Specifically, a switch mate may be used to activate a safety circuit that shuts down the machine if a person enters the hazardous area.

Well-known pressure sensitive switches and switch mats are disclosed in British Patent Publications Nos. 392936, 1185862 and British Patent Publications Nos.
1209564, 1351911, 1358006, 1369174, 1454805, 2064222,
2083858 and 2088637, U.S. Patent Publications 1775755, 2951921, and 3722086
No. 3812313, No. 3825277, No. 3825277, No. 3812313, No. 3825277, No.
4037069 and 4105899, French Patent Publication no.
1416570 and 2531178 and West German Publication No. 2148760.

Switchmats generally include first and second electrically conductive members, which are typically planar, and optionally include one or more intermediate electrically conductive elements located between the first and second electrically conductive members. Included in The typical structure of a switch pine is that there is no conductive path between the first and second conductive members, i.e. the switch is open, and when a load is applied to the switch pine, the first and second conductive members , compression of the non-conductive material and/or curvature of one or both of said conductive members to move towards each other, optionally through an intermediate conductive element, the first and second conductive elements. It is as if a conductive path is created between the active members and a switch is closed. When the load is removed, the first and second conductive members return to their spaced apart positions.

One of the problems with the use of many switchwoods known in the industry is that they are often not robust enough to withstand the harsh conditions of an industrial environment over an extended period of time. Switchmats used in the industry are subject to severe overloads, for example when heavy objects fall or when trolleys or trucks pass over them. As such, physical overuse of the switch mat can result in complete failure of the switch mechanism. If the switch mechanism of the switch mat is damaged, it will permanently close the switch and render it inoperable, i.e. there will be a permanent conductive path between the first and second conductive members, which will cause the mat to become inoperable. In order to complete electrical safety circuits, there is a demand in the industry for switch mats that are ``safe even if they fail.''

SUMMARY OF THE INVENTION An object of the present invention is to provide a switch mat with a switch that is safe even if the switch malfunctions.

According to the present invention, first and second conductive members are separated by a non-conductive material, and optionally one or more conductive members are located between the first and second conductive members. A normally open pressure sensitive switch mat, which may include an electrically conductive intermediate element, such that upon application of a predetermined actuating load, the first and second electrically conductive members move relative to each other to complete a conductive path therebetween. In the case where the switch mat is located between the first and second conductive members and only the predetermined operating load is applied, the a safety switch including a bridge member that does not form a conductive path in the switch, said bridge member including a conductive spring member held in compression by a frangible restraint device, and when a predetermined minimum overload is applied to the switch mat; The brittle restraint device ruptures, allowing the bridge member to move toward its released state and complete a conductive path between the first and second conductive members, which conductive path is caused by the overload. A normally open pressure sensitive switch is provided which is characterized in that it is retained even after being removed.

According to the present invention, when a normal predetermined operating load acts between the first and second conductive members, the first and second conductive members move relative to each other. An electrically conductive path is completed between the second electrically conductive member, allowing for example to detect when a person steps on the pressure sensitive switch mat. However, in this case, the bridge member does not form a conductive path, so when a person steps down from the top of the pressure-sensitive switch pine, the conductive path is opened and nothing is currently on the pressure-sensitive switch pine. It will let you know that there is no. However, if a car, rather than a person, accidentally lands on top of the pressure-sensitive switch mat, an overload is applied to the pressure-sensitive switch mat, destroying the aforementioned brittle restraint device and releasing the bridge member. to complete a conductive path between the first and second conductive members. The safety switch, which is a bridge member, will then remain closed, so that even if a vehicle steps off the top of the pressure-sensitive switch pine, the electrically conductive path will remain complete and nothing on top of the pressure-sensitive switch pine will remain closed. This pressure-sensitive switch continues to inform you of the information you are riding on.

In this way, the manager can know that an accident has occurred with the pressure-sensitive switch by continuing to be provided with this information.

If the safety switch made of such a bridge member adopted in the present invention is not provided, if an overload such as in an automobile is applied to the pressure-sensitive switch mate, Even if any damage occurs to any of the components and the pressure-sensitive switch can no longer be expected to operate reliably, the pressure-sensitive switch will still pick up and operate normally when the vehicle leaves the top of the pressure-sensitive switch. It may be that at some point in time the conductive path between the first and second conductive members is temporarily opened. Since the manager will not notice that a car has accidentally been placed on top of the pressure-sensitive switch, he will have no doubt that the pressure-sensitive switch will continue to operate normally. However, it is possible that certain components of the pressure-sensitive switch mat may have sustained significant damage due to the presence of a motor vehicle. Therefore, normal operation of this pressure-sensitive switch after that cannot be expected at all. If that's the case, in the event that a car is hit,
It goes without saying that it would be wiser to prohibit further use of the pressure-sensitive switch, inspect it, replace the safety switch, and use it again. Thus, in the present invention, the safety switch made of the bridge member constitutes a fail safe means.

The bridge member may take any desired configuration so long as the bridge member moves from its compressed state to its released state to complete the passage between the conductors upon failure of the restraint device.

The bridge member may be held in its compressed state by a restraint device that compresses the bridge member against one of the conductors, but preferably only the restraint device is involved in compressing the bridge member, and the electrical connection comprising the bridge member A switch forms another embodiment of the invention.

For example, the bridge member may consist of one or more turns of a helical spring that can be held in compression by a sleeve, collar or loop of a restrainer that compresses the spring. In practice, a helical spring has one or three turns, and when the overlapping turns of the spring are compressed together by a sleeve or bead of brittle material, each end of the spring wire has a contact plane with the conductor. It has been found that this provides an effective bridge member when bent up and down at right angles to.
The tip of the bridge member that comes into contact with the surface of the conductor is
Preferably, it is sharpened to penetrate any oxide or debris that may form on the surface. It will be readily appreciated that the bridge member may take many other shapes, for example a simple U-shape;
Other examples will be explained with reference to the drawings.

Conveniently, the restraint device is a collar or bead made of, for example, glass, ceramic or a brittle plastic material, such as Bakelite. The restraining device fixes the bridge member in a compressed state, ie, a restrained state, under a load that exceeds its breaking strength and causes the bridge member to break. Upon rupture, the bridge member moves toward its open state to complete and maintain the passage between the conductors.

In its simplest form, the switch pine is constructed from two semi-rigid metal sheets;
At least one of the sheets is an insulating elastic material,
For example, load-bearing sheets separated by strips of elastic material located around the periphery of the sheet, each metal sheet being connected to part of an electrical circuit. The switchmat further includes an electrically conductive intermediate element located between the metal plates so that when the elastic body is compressed, a conductive path is formed by the intermediate element between the metal sheets. By suitable selection and positioning of the intermediate element and the elastic body, the switchmat can be configured to operate with a predetermined minimum load, ^e.g. It should be sensitive to pressure, which is equivalent to a 20 kg load applied to the average foot area, which is significantly less than the load applied by an adult standing on or stepping on the pine. The intermediate element used in the switch pine according to the invention forms an electrical contact between the two metal sheets when the pine is compressed and is able to withstand significant overloads, e.g. at least 5 times the normal load applied to the pine. is sufficiently sturdy to support the load-bearing sheet when the load is applied, so that severe strain is not applied to the elastically compressible, elastomeric, electrically non-conductive material. Furthermore, the switch mate includes a safety switch according to the invention, so that if the overload is large enough to damage or deform the metal sheet or the intermediate element, the restraint device of the safety switch will fail and the bridge member will therefore move towards its released state. ,
An electrical path is formed between the metal sheets to prevent the switch mat from malfunctioning.

The load-bearing sheets used in the switch mats are extremely rigid, ie, have only limited elasticity and are generally non-deformable during normal use. When a heavy load, e.g. the weight of a pedestrian, is applied to the ^middle part of a metal sheet, a moderate area of most metal sheets, e.g. curved to Although a limited amount of elasticity or curvature is acceptable in a preferred switch pine to increase the sensitivity of the central portion of the switch pine, such susceptibility is not essential; Preferably, the mode of operation of the switchmat is determined by the compressibility of the non-conductive material separating the metal sheets. The second metal sheet is
Due to its thickness and strength, or support device,
It is preferred that it is non-deformable in the operating state, for example by providing a reinforcing plate or a surface for attaching a switch mat.

As used herein, the term "load-bearing" means that the load-bearing metal sheet contributes no more than 50% of the deformation required to make electrical contact. That is, a deformation of at least 50% is achieved by compressing the elastically compressible non-conductive material.
Preferably in this non-conductive material at least
Most preferably, 75% deformation occurs and at least 90% or 95% deformation occurs in the elastically compressible, non-conductive material.

In one construction of the switchmat according to the invention, the intermediate element consists of a raised projection from one or both sides of the metal sheet. The projections are preferably arranged at regular intervals over the entire surface of the metal sheet and may be formed by scoring from the outermost surface of said sheet. The height and sufficient number of said protrusions is such that when the mat is loaded, the protrusions support the upper metal sheet on the lower metal sheet so that the non-conductive material is not compressed to the point where damage occurs. It is intended to do so.

According to another construction, the intermediate element is in the form of an insert made of electrically conductive material, located between two metal sheets. These inserts advantageously consist of metal balls, such as ball bearings, or barrel-shaped bodies made of metal or plastic made electrically conductive, for example by incorporating electrically conductive particles of metal. These inserts do not need to be welded or glued to one of the two metal sheets;
A section of compressible non-conductive material may be provided in any desired location by forming a closed cell between the metal sheets.

In practice, it has been found that a good and stable electrical contact between the intermediate element and the metal sheet is obtained if the intermediate element is curved towards the metal sheet.

The invention will now be described with reference to the accompanying drawings.

Referring to FIG. 1, there is shown a partial perspective view of a switch mat to which the present invention can be applied. The switchmat comprises a basic metal plate 1 made of aluminum, for example 2 mm thick, which has a series of projections 4 at regular intervals over its area. Conveniently, the projections are formed by scoring from below and raising them to a height of about 3-4 mm above the surface of the metal plate. Around the periphery of the base plate 1 is provided a fixing strip 5 of compressible, electrically non-conductive material, such as a strip of cell-tight foamed neoprene rubber, 1.5 cm wide and 0.45 cm thick.
If desired, flanges 3 may be provided along one or more sides or edges of the mat to enable it to be secured to the floor. A top plate 2 is fixed to the peripheral wall of non-conductive material 5. The top plate constitutes a 2 mm thick aluminum "treadboard" whose top surface is engraved with a pattern of five raised horizontal lines to act as a walking surface for pedestrians. The switch mat is intended to operate at very low voltages, so that direct electrical connections can be made to the two plates 1 and 2 that are exposed to the user. Switch Matsutto is sensitive to loads of 20Kg or less,
This load is sufficient to compress the rubber wall and bring the projection 4 into contact with the top plate 2, so that when a person's foot rests on the mat, the pressure exerted thereby is easily detected. The use of 2 mm thick "treads" makes the pine resistant to damage and accepts overloads by supporting the weight of the top plate and its load on the projections 4. By providing the protrusion immediately adjacent the edge, sensitivity of the entire edge is achieved. It is readily possible to form projections on the top plate instead of the bottom plate, or on both plates, without interfering with the operation of the switch.

The switch mat may be constructed from materials other than aluminum sheet or plate; for example, in the food industry it may be necessary to use stainless steel for hygiene reasons. The metal sheet may be constructed from any metal or combination of metals commonly available in the art. The practical advantages of aluminum: availability in suitable dimensions, light weight, cost, good appearance without painting, and sufficient strength make it a convenient and desirable material in most cases. Become. It is well known that aluminum readily forms an oxide layer on its surface, inhibiting further corrosion. Not only is this oxide a good insulator, its obvious drawbacks in electrical properties can be easily overcome by forming intermediate elements that break through the oxide layer.

The construction of the switchmat described in connection with FIGS. 1 and 2 provides a sturdy and stable switchmat of reasonable size for use in industrial environments that are not significantly contaminated by liquids.

If a switch pine has a large area, such as a top plate with a span of 400 mm or more, the middle part may flex due to the weight of the plate. To eliminate the risk of accidental contact, it is advisable to provide further supports of compressible non-conductive material, for example foamed neoprene strips, at intervals of approximately 300 mm to provide sufficient support for the top plate. .

It has been found that if the metal plate is aluminum, the tips of the protrusions should be sufficiently sharp to be able to pierce the oxide layer on the surface of the plate upon contact. In practice, a protrusion with the desired contact points is provided by punching a round indentation from the opposite side of the sheet. To further increase stability, the protrusions should be positioned at a spacing such that the foot of the pedestrian at any point exerts sufficient pressure to ensure that the weight makes good electrical contact at that point. 50 for the aforementioned aluminum sheets
Experiments have shown that spacings of between 150 mm and preferably between 60 and 120 mm are satisfactory, with the most satisfactory performance being achieved at 75 mm. If it is 120 mm or more, the sensitivity will decrease when a load is applied to the contact point in the middle, and the above distance will decrease.
Sensitivity decreases rapidly beyond 150 mm. If the protrusions are too closely spaced on the aluminum sheet, the individual contact pressure of each protrusion will not be sufficient to penetrate the oxide layer. The use of a strip of cell-sealed foamed neoprene rubber as a compressible non-conductive material around the plate provides protection from various contaminants within the switch mate. Suitable cell-sealed expanded neoprene rubber strips are available under the trade name "Neontrice".
Florist and Company Limited (C.
B.Frost & Company Limited).
The neoprene strips are coated with oil and manufactured by 3M United Kingdom PLC, for example under the trade name "Scotchgrip".
It can be attached to both metal plates with a water-resistant adhesive, such as vinyl adhesive, commercially available from PLC). However, due to the inevitable movement of the switchpine as it is loaded and unloaded, "air leaks" can occur through small gaps in its edge seals. According to one embodiment of the invention, each projection is protected by a gasket made of cell-tight expanded neoprene rubber in the form of a square or disc-shaped material with a hole in the center for receiving the projection. An example of the circular gasket is shown in FIG. Typical dimensions of the circular gasket are 25 mm in diameter, the diameter of the central hole is 5 mm and the thickness is equal to that of the peripheral wall 5. Other configurations may be used as long as the width of the wall protecting the protrusion is thick enough to withstand strain and avoid failure as a result. The use of said gasket, which can be conveniently secured with a contact adhesive, provides a second barrier to the ingress of contaminants into the contact area, resulting in significantly increased stability and the ability of the top plate in large span mats. It can also act as a support means.

The switch mat shown in FIGS. 1 and 2 further includes, in accordance with the invention, one or more safety switches, examples of the configuration of which are shown in FIGS. 6 through 9 below. The compressed bridge member is
Preferably, it can be placed inside a gasket of the type shown in FIG. 3 and easily positioned between the protrusions (section A in FIG. 2).

FIG. 4 shows an alternative switch mat to that of FIG. 1 to which the invention may be applied, in which the conductive intermediate element is provided separately and the base plate is not machined to form the projections. Tomoyoshi. The same reference numerals as in FIG. 1 are used in FIG. The base plate 1 consists of a flat metal sheet, and the intermediate elements are provided by a series of metal balls 6, which are sealed in the interior space of a gasket 7 similar to that shown in FIG. The diameter of the sphere is smaller than the thickness of the peripheral wall and gasket, typically 1 to 1.5
Millimeter smaller. The inner diameter of the gasket is typically about 1.5-5 times larger than the diameter of the ball to allow the ball to float within the gasket cavity, occasionally providing a new contact surface and reducing wear overall. The spherical shape of the sphere provides high pressure contact to each plate when the switchmat is loaded, and acts as a conductive bridge between the two plates. As in the case of projections, the spacing of the contact points of the spheres is preferably between 50 and 150 mm. Preferably, the ball is constructed from stainless steel and is commercially available in a variety of sizes.

Instead of a sphere, other shapes of conductive material may be used, such as a barrel-shaped resin member made conductive by incorporating conductive particles.
However, such an electrically conductive intermediate element must be sufficiently sturdy to support the loads applied to the top plate of the switch pine during overload conditions.

To facilitate rapid assembly of a switch mat incorporating individual intermediate elements, such as balls, the rubber gasket may be in the form of a perforated strip, as shown in FIG. The strip may be formed from closed cell foamed neoprene rubber and is perforated with closely spaced holes. To use the strips coated with pressure-sensitive adhesive on both sides, place the strips parallel to the edges at intervals of 50 to 150 mm across the base plate, and Insert the intermediate element into the holes drilled at the desired spacing of 50 to 150 mm across. By providing a plurality of holes in the strip, the resistance to compression under load is reduced and the sensitivity of the switch mat is maintained.

Examples of dimensions for strip gaskets are as follows.

No.1 No.2 Gasket width 12 mm 19 mm Hole diameter 7 mm 12.7 mm Distance between hole centers 25 mm 19 mm Gasket thickness 5 mm 5.5 mm The gasket has an intermediate diameter including a metal ball with a diameter of 4 mm. Suitable for use with elements. The length of the strip will vary depending on the size of the switch pine to be constructed.

An alternative method of constructing a switch mat using individual intermediate elements is to provide a number of spaces on the base plate for inserting intermediate elements at the desired spacing.
The first step is to place a perforated sheet or grid of elastic material. This direction of construction allows for the provision of a peripheral wall of compressible material as well as an internal gasket. However, it is important to avoid using such large amounts of elastic material to increase the degree of support to the top plate to the extent that it impairs the sensitivity of the switch mat.

The switch mat shown in FIG. 4 further includes at least one safety switch used in the present invention having a structure shown in any of FIGS. 6 to 9, which will be described later. Conveniently, the compressed bridge member of the safety switch is located within one of the holes in the gasket.

For some applications, the lower plate of the switchpine must be completely insulated from its surrounding environment, for example when the switchpine is mounted on a metal country crane or the like. In that case, insulation can be easily accomplished by placing a sheet of insulating material below the lower base plate. The insulating sheet may be made of plywood, plastic, or any other insulating material. The insulating sheet may be configured to have a high load-bearing capacity, and therefore, the main load is transmitted to the insulating sheet, so the lower conductive sheet can be configured without much consideration regarding the load-bearing capacity. In that case, the lower conductive sheet may be thin or may be perforated to some extent. If drilled, the hole should have a smaller diameter than any of the intermediate elements used for contact purposes to ensure electrical contact is achieved.

Although the switchmat may be small to accommodate only one intermediate element, in practice the area of the switchmat will be large enough to accommodate multiple intermediate elements. Practical dimensions for switch mats of the type described above range from a 100mm wide strip to a 1.4m x 1.2m rectangle, the largest size of aluminum sheet currently readily available from material stores in the UK. span. However, large switchmats are difficult to handle and may be damaged during transportation unless reinforced. It is often desirable to join them edge-to-edge and electrically connect them in series. A small switch pine can be handled by one person and is sturdy enough that only the edges need to be protected during transportation.

Typical pine is 9 mm thick, which is similar in size to some floor coverings in this country, so it does not pose a significant hindrance to walking.

While the foregoing dimensions have been found to be practical and the pine is constructed from materials that are readily available commercially, the specific dimensions of the switch pine will vary depending on the type of material used and the specific application. It is recognized that it can be used. Generally, the height of the intermediate element, either in the form of a protrusion or a separate element such as a ball, is between 25% and 95% of the thickness of the elastic material separating the metal sheets when they are in the open state.
It turns out that it should be. Preferably, the height of the intermediate element is between 70% and 80% of this height.

The electrical system connected to the switch mate may be of any preferred type requiring low voltage contact, such as a 5 volt electrical system controlling a TTL logic circuit, or a 12 volt relay may be connected directly to the switch mate. good. If the metal conductor is to be accessible directly by the user, it is essential that the voltage present at the switch mate is low voltage and that adequate grounding is provided. The conductive wires may be suitably fixed to the metal plates by screws or rivets; generally double connections are made to each plate, so a four-wire system with continuous loops is employed. good.
An example of a commercially available control system that may be used with a switchmat is the "Safety Switchmat Device" marketed by 3M United Kingdom PLC.
(“Safety switchmat system”).

A switchmat needs to be stable throughout its life, especially if it is required to act as an industrial safety device. Switchmats are rigorously tested to determine their performance. When contact is made, it is believed that satisfactory electrical performance will be obtained if the resistance across the switch mat is less than 1 ohm.

The switch mat according to the present invention has a circular steel plate of approximately 45 cm ² for 1000 cycles at the same point of the mat.
It withstood a 75 kg impact transmitted at 2.5 m/s without any significant deterioration in performance. However, scratches appeared on the aluminum tread. When the impact velocity was reduced to a few centimeters per second and the impact was applied closer to the feet for 4000 cycles, there was no visible or measurable effect on the performance of the Switchmat.

Another switch pine according to the invention having an internal gasket around the intermediate element was immersed in regular tap water and operated occasionally. After 16 consecutive days, it broke down due to water intrusion.

To test the shear strength between the switch pine aluminum top plate and the base plate, a car was driven on the switch pine and the rear wheels were parked on the pine. The car was then accelerated. As a result, no deterioration in the appearance or performance of the pine was observed.

The switch pine constructed using a metal ball as an intermediate element shown in Fig. 4 exhibits a sensitivity of 10 to 20 for a 1 m ² switch pine, and can simulate a foot pedal by applying a load over a circular area of about 45 cm ² . distributed. The sensitivity is more than sufficient to detect pedestrian footsteps on any part of the mat.

In the embodiments described above, the projections and ball bearings are used individually, but the intermediate elements may be combined on one mat if desired.

Although the mat is basically configured to be used on a horizontal floor, it functions equally well at any angle relative to the horizontal, even when inverted.

FIG. 6 shows a compressed bridge member of a safety switch that may be used in the switch mat of the present invention. The bridge member, generally designated 8, has a spring wire
It comprises a helix 10 with 1.3 turns, so that the end of the spring, in the released state, has a non-conductive compressibility equal to the distance between the two conductive plates of the switch mat, i.e. the non-conductive compressibility shown in FIGS. 1, 2 and 4. Separate by more than the height of the strip of material. The helix 10 is held in compression by a brittle collar or bead 12, which may be formed of glass, ceramic material or brittle plastic material. spiral 10
The ends are elastically separated in the horizontal plane and each pass through the restraint device 12 in opposite directions, so that they are juxtaposed within the restraint device. The ends of the helix are therefore free in the horizontal plane but restrained in the vertical plane. The restraint device 12 includes friction and
The curvature of the wire and the downturned end 14 prevent movement over the length of the spring wire.

In use, the safety switch is held in a horizontal position and between two conductors, and the restrained bridge member 8 cannot span the distance between said two conductors. If a sufficient load is applied to one of the conductors to pinch the restraint between the conductors, the restraint 12 will break between the two conductors and the ends of the helix 10 will no longer be restrained. actuating a switch that springs apart and forms an electrical bridge between the two conductors. The bridge member continues to splice the conductor whether or not the compressive force is subsequently removed from the mat.

For example, in the switch mat shown in Fig. 4,
The bridge member may be replaced with one metal ball 6. During normal operation, the ball will slightly indent into the aluminum plates under a load, such as the weight of a pedestrian, but this will not be sufficient to close the air gap between the plates to near the point of failure of the restraint device. It is.
Under conditions of severe overload, the ball can dig into the aluminum plate to the extent that normal operating sensitivity is impaired, ie, the human weight does not close the switch. Under such circumstances, the air gap between the plates is closed to the extent that the restraint device is destroyed, thereby causing the bridge member to move to its released position and permanently shorting the aluminum plates. In this way, the switch pine malfunctions but leaves the associated machinery in a safe state.

In practice, the restrained bridge used in the switch according to the invention is intended to prevent accidental destruction of the restraint device caused by sudden local loads, for example loads when the operator drops a tool. It is often desirable for the member to have two or more spherical switches in close proximity.

In a typical switch mat with plates spaced 6 mm apart, a helical spring bridge switch is housed in a resilient ring with an inner diameter of 12.5 mm. The outer diameter of the helix (as shown in Figure 7) is 11 mm, the width is 2 mm, the locking projection is 5 mm long, and the ends of the helix in the open state are at least 7 mm in the vertical plane. is seperated. The helix is made from a spring wire with a diameter of 0.45 mm, whose ends are bent up and down to form a "spike" about 1 mm in diameter. A suitable glass bead for use with this helix is in the form of a tube 3 mm long, 2 mm outside diameter, and 0.35 mm wall thick. Such a bead would require a radial load of approximately 1.3 Kg to break and release the spring.

It is clear that the bridge member described above is only suitable for operation in a horizontal plane unless it is fixed to one of the conductors. There is a small possibility that particles of the broken suppressor will accumulate between the helix and one of the conductors and prevent electrical conductivity between the conductors. 7th
The figure shows a modified bridge member in which the basic helical shape 20 of the spring wire is reversed in its natural shape by a bend 22 at a point opposite the overlap.
It has been modified by adding . The end 24 of the spring wire is bent both upward and downward by a length slightly greater than the wall thickness of the brittle restraint device 25. Said inverted bend 22 is used as a fixing projection and can be fixed to one of the conductors and restrained to keep the plane of the helix parallel to the surface of the conductor. This is done by inserting said protrusion under the edge of the insulating strip 5, i.e. the gasket, so that the helix lies flush with one side of the conductor, as shown in FIGS. and can be conveniently achieved in the switch mat shown in FIG. This allows the switch to operate in any direction. The ends of the spring wire are preferably sharp to ensure good metal-to-metal contact when the switch is actuated. Additionally, the length of the bent portion is sufficient to prevent fragments of a destroyed suppressor from causing the switch to malfunction.

Figures 8A to 8D illustrate other variations of bridge members suitable for use in the present invention, which may be stamped and formed from sheet metal, such as strips of phosphor bronze, beryllium copper, etc., as required. and annealed in a kiln. The structure of each of the bridge members includes two arms 30 which are held in a horizontal plane in a restrained state by a restraining device 32. When the restrainer is broken, the ends 30 spring apart and come into contact with the respective conductors. The bridge member may include a protrusion 34 for securing the bridge member within the switch. Alternatively, the bridge member may be fixed by a portion of its periphery. The bridge member shown in FIGS. 8A to 8D has the advantage that it can be inexpensively mass-produced using an automatic mechanical press.

The arms 30 of the bridge member need not overlap, but may each be inserted into the end of a restraining device, such as a glass bead, so that they rest on each other in the center of the opening of the bead. The beat can be prevented from moving by tapering the end of the arm 30.

9A and 9B illustrate alternative bridge members that may be used in the present invention in compressed and released states, respectively, and use the same reference numerals as in FIG. 7. The bridge member is generally rectangular and in the form of a spring wire sized to provide a wide base to prevent twisting of the bridge member during use.

In addition to being used in a switch mat, the safety switch may be incorporated into a fire alarm circuit, and the switch is operated by a person by mounting it vertically on a wall or the like and manually compressing the switch. In such constructions, the insulation separating the two conductors comprises a relatively soft compressible material, such as a foamed elastic material.
If the suppressor fails, the switch completes an alarm circuit that cannot be reset without replacing the bridge device.

The pressure sensitive switch according to the invention can also be used as a "motion limit" switch by mounting a machine having movable parts, such as a crane, on the frame. The switch is positioned such that when unauthorized or unspecified movement occurs, the switch is compressed, destroying the suppressor and activating the switch, completing an alarm or disable circuit.

To protect against metal shavings that could short out the top plate of the switch pine, the bottom plate is made larger than the top plate by, for example, 25 mm, and a load-bearing plate of the same dimensions as the enlarged bottom plate is placed above it. to fix the upper plate. Thus, the additional top plate is electrically insulated from the upper conductive plate by, for example, plastic spacers, and the edges of the mat are then sealed with an insulating material, such as, for example, foam rubber. The lower flange may be provided with a flange that allows mechanical attachment to the floor.

[Brief explanation of drawings]

1 is a partially cross-sectional perspective view of a part of a switch pine to which the present invention can be applied; FIG. 2 is a plan view of the switch pine shown in FIG. 1 with the top metal sheet removed; FIG. FIG. 4 is a perspective view, partially in section, of another switch mate to which the present invention may be applied; FIG. FIG. 6 shows a compressed bridge member of a safety switch that can be used in the switch mate of the invention; FIG. Figures 8A to 8D are diagrams showing other variations of the bridge member for use in safety switches that may be used in the present invention; Figures 9A and 9B; FIG. 6 shows another modification of the bridge member for a safety switch that can be used in the present invention. In the figure, 1...plate, 2...top plate, 4...protrusion, 5...fixing strip, 6...ball (conductive intermediate element), 7...gasket, 8...
Bridge member, 10... spiral, 12... collar, 14... end, 20... spiral, 22... end, 24... end, 25... suppressing member, 30...
Arm, 32... suppressing member, 34... protrusion.

Claims (1)

[Scope of Claims] 1. A device comprising a first and a second conductive member separated by a non-conductive material, and optionally a first and a second conductive member separated by a non-conductive material.
a normally open pressure sensitive switch mat which may include one or more electrically conductive intermediate elements positioned between said first and second electrically conductive members; In a switch mate configured for relative movement of members to complete a conductive path therebetween, the switch is located between said first and second conductive members and has only the predetermined operating load applied thereto. In some embodiments, the safety switch includes a bridge member that does not form a conductive path between the first and second conductive members, the bridge member comprising a conductive spring member held in compression by a frangible restraint. When a predetermined minimum overload is applied to the switch mate, the brittle restraint device ruptures and the bridge member moves toward its released state, causing electrical conduction between the first and second conductive members. A normally open pressure sensitive switch mat, characterized in that the conductive path is maintained even after the overload is removed. 2. The pressure-sensitive switch mat according to claim 1, wherein the conductive spring member is held in a compressed state only by the brittleness suppressing device. 3. The switch mat according to claim 1 or 2, wherein the conductive spring member includes at least one turn of spring wire, and adjacent turns are compressed together by the brittle suppression device;
A pressure-sensitive switch mat characterized in that both ends of the spring wire are bent vertically at right angles to the plane of the compressed spring. 4. The pressure-sensitive switch mat according to claim 1 or 2, wherein the bridge member is a helical spring obtained by pressing a sheet material. 5. In the switch mat according to any one of claims 1 to 4, a protrusion is formed on the conductive spring member, and the protrusion is used for positioning the bridge member inside the switch mat. A pressure sensitive switch is used. 6. A pressure-sensitive switch mat according to any one of claims 1 to 5, characterized in that the brittleness suppressing device comprises a brittle collar or bead. 7. The switch mat according to claim 1, wherein the non-conductive material is an elastic compressible non-conductive material, and the first and second conductive members have conductive surfaces. and a metal sheet separated from the load-bearing sheet, with one or more of the conductive intermediate elements interposed between the conductive surface of the load-bearing sheet and the metal sheet; The intermediate element is adapted to form a conductive path between the conductive surface of the load-bearing sheet and the metal sheet when the non-conductive material is compressed, and the load-bearing sheet is arranged to being generally rigid under operating loads, the load-bearing sheet being configured to be supported by the intermediate element to minimize damage to the non-conductive material when overloaded; Pressure sensitive switch. 8. The pressure-sensitive switch mat according to claim 7, wherein the intermediate element comprises a protrusion on one or both of the load-bearing sheet and the metal sheet, or a metal ball. 9. The switch mat according to claim 7 or 8, wherein the height of the intermediate element is between 25% and 95% of the thickness of the compressible non-conductive material in the released state, A pressure sensitive switch mat according to claim 1, wherein the intermediate element is surrounded by a gasket of the compressible non-conductive material affixed to the load-bearing sheet and the metal sheet. 10. The switch mat according to any one of claims 7 to 9, wherein the conductive spring member is held in a compressed state only by the brittleness suppressing device. Pressure sensitive switch. 11. The switch mat according to claim 7, wherein the conductive spring member comprises at least one turn of spring wire, adjacent turns being compressed together by the brittle restraint device, and an end portion of the spring wire. is bent upward and downward, respectively, at right angles to the plane of the compressed spring. 12. The pressure-sensitive switch mat according to claim 7, wherein the bridge member is a helical spring obtained by pressing a sheet material. 13. The pressure-sensitive switchmat according to claim 7, wherein the brittleness suppressing device comprises a collar or a bead.