The present invention relates to tape or ribbon switches and more particularly to such switches designed to be attached to gates, doors etc. as part of security systems as set forth in the preamble of claim 1. The invention furthermore relates to a manufacturing process for such switches and to an in-situ tailoring method to be used to fit the switch to a specific application.
Various types of tape- or ribbon switches have been known within the art for many years. Thus US 2,770,696 discloses a tape switch comprising a one-piece outer jacket preferably made of a rubber or plastics material, which tape switch can also be sued outdoors. Within said outer jacket there is contained two juxtaposed substantially plane contact strips separated from each other by means of strips of insulating material placed between the contact strips along the outer edges thereof.
US 4,293,752 discloses a self adhering tape switch the outer shape of the cover somewhat resembling that of the present invention, but as in the above mentioned case also provided with strips of insulating material placed between the contact strips along the outer edges of these for separation of the contact strips.
In US 4,551,595 the outer cover is not formed as a one-piece unit but rather welded together comprising separate top- and bottom portions. Also in this case strips of insulating material are placed between the contact strips along the outer edges of these for separation of the contact strips.
Neither of the above references discloses specific methods recommended for in-situ tailoring the switches to specific applications.
Prior art tape- or ribbon switches have typically suffered from a number of problems. One of these problems have been penetration of moisture through the outer insulating cover of the switch due for instance to the application of a hygroscopic (water-absorbing) material for the cover or to improper or unreliable tailoring of the switch during the specific application hereof. The penetration of water through the outer cover and into the contact region of the switch have often led to corrosion of the electrical contact surfaces in cases where the contacts have for instance been made of copper, leading to an unreliable electrical contact and hence possibly to dangerous situations, if the switch has formed part of a security system, for instance in connection with a heavy gate.
Document US 3 812 313 discloses a ribbon switch according to the preamble of claim 1.
According to the preceding description of some prior art problems it is thus an object of the present invention to provide an improved tape switch component that does not suffer from the above problems of moisture penetration through the outer cover of the switch and into the contact region of the switch.
It is a further object of the present invention to provide a tape switch component that can be manufactured in a simple manner.
It is a further object of the present invention to provide a tape switch comprising said tape switch component and appropriate terminating means so that said tape switch does not suffer from the above problems of moisture penetration through the terminating means (electrical leads to the contact strips of the tape switch and electrical terminating impedance) and into the interior of the tape switch.
It is a further object of the present invention to provide an improved method and system for in-situ tailoring of the switch to various specific applications.
These and other objects are attained with a tape switch component according to claim 1, a tape switch according to claim 5 and an in-situ tailoring method according to claim 10.
According to a first aspect of the present invention there is thus provided a tape switch component comprising a pair of parallel extending contact strips one of which is provided with a laterally extending corrugation in order to improve mechanical stability, said contact strips being completely surrounded by an outer cover to electrically isolate the contact strips from the surroundings and furthermore to prevent moisture from reaching the contact strips. The contact strips are held apart by suitable spacer means extending longitudinally over a portion of the surfaces of the contact strips facing one another, which spacer means according to the invention are formed as an integral part of said outer cover to provide a reliable spacing of the contact strips and furthermore to provide a simple and effective manufacturing process of the tape switch. In order to prevent moisture from penetrating the outer cover and reach the contact strips resulting in corrosion of these the outer cover is made of a water-impermeable (hygroscopic) material of suitable mechanical flexibility. In order to ensure reliable contact function throughout the life of the tape switch the contact strips are made from a material that is resistant against corrosion and that is not attacked by cleaning agents, oils etc. used in industries. In a preferred embodiment of the invention the contact strips are made of stainless steel.
A manufacturing process for said tape switch comprising component comprises the steps of providing two ribbons of metal sheets and passing one of said ribbons through a corrugation machine to provide said ribbon with a pattern of corrugations substantially lateral relative to the longitudinal extension of the ribbon and feeding said two ribbons into a torpedo provided in a transversal extruder head provided with an inlet for a melted plastics material supplied by an extruder. At the outlet of the torpedo the melted plastics material is joined with the metal ribbons and passed through a nozzle section to provide the desired cross section of the tape switch including the spacer means provided between the two metal ribbons as mentioned in the preceding paragraph. On leaving the transversal extruder head the tape switch finally passes through a water bath, whereby the temperature of the switch is reduced from its manufacturing temperature (for instance around 160 degrees centigrade) to room temperature. The fact that said spacer means are formed as integral parts of the outer cover provides for a very simple and straight forward manufacturing process.
According to a second aspect of the present invention there is thus provided a tape switch comprising a suitable length of said tape switch component and furthermore provided with suitable terminating means. One end of the cut off tape switch component is thus provided with electrical contact leads to establish electrical contact to the two contact strips of the tape switch and the electrical leads and a suitable length of the tape switch component is surrounded by a body of heat shrinking foil, the inner surface of which is provided with an adhesive agent that when initially heated and subsequently cooled down to ambient temperature adheres firmly to the outer surface of said outer cover of the tape switch and to the outer surface of terminal lead electrically connected to the contact strips of the switch. The other end of the cut off tape switch component is sealed in a similar manner and may instead of said electrical leads be provided with an electrical terminating impedance component, such as a resistor of suitable electrical resistance. The end could also be left electrically open if desired for specific applications.
According to a third aspect of the present invention there is provided an in-situ tailoring method for said tape switch, said tailoring method comprising the following main steps:
Providing heat for instance by means of an appropriate shrinking tool to said tubular body until a tight seal is established between the tape switch and the tubular body and around said second contact plate with said terminating impedance component;
The claimed tape switch component and corresponding tape switch adapted to specific applications using said tailoring method offers the advantageous effects of highly reduced humidity intrusion through the outer cover and the end portions of the switch. An error free operation is furthermore ascertained by the choice of contact material of stainless steel. The described in-situ tailoring method and a corresponding system comprising the necessary components and tool's provide for an easy and reliable fitting of the switch for the specific application. Furthermore the switch is characterised by a lack of deformation by bending up to 90 degrees and by a small activation force of approximately 3N.
The invention will now be described in more detail with reference to the accompanying drawings, in which
In the following a detailed description of the invention is given.
With reference to figure 1a and 1b there is shown a tape switch component according to the invention generally referred to by reference numeral 1. The tape switch component comprises two juxtaposed electrical contact strips 5, 6 of which one in the present embodiment of the invention is provided with a laterally oriented corrugation provided in order to increase mechanical stability of the switch. According to this specific embodiment of the invention the contract strips 5, 6 are made of thin sheets of stainless steel, which is considerably more resistant to oxidation than other materials normally used in such switches such as copper. According to this specific embodiment of the invention the upper contact strip has a thickness of 0,05 mm and the lower contact strip 0,1 mm, although it is understood that other choices of thickness of the contact strips could also be made.
Surrounding and tightly encapsulating said contact strips there is provided an outer cover 2 formed as one longitudinally extending piece by means of a suitable extrusion process. The cover 2 is provided with an outwardly extending longitudinal protrusion 3 provided in order to ensure a reliable contact action of the switch, when this is exposed to an external pressure, and two internal longitudinally extending thin protrusions 4 acting as spacer means between the two contact strips 5, 6. Formation of these spacer means 4 as an integral part of the outer cover 2 is advantageous both from a manufacturing and a reliability point of view.
With reference to figure 2 there is shown a tape switch comprising a suitable length of the tape switch component 1 described above and furthermore comprising terminating means 8, 9 at either end of the tape switch component. As described in the summary of the invention - and in detail in the subsequent section on in-situ tailoring of the switch - these terminating means 8, 9 are formed by pieces of heat shrinking foil, the inner surfaces of which are provided with an adhesive agent which heat shrinking foil and adhesive agent upon heating and subsequent cooling to ambient temperature forms a tight seal around the ends of the tape switch component 1. The terminating means 8 comprises an electrical lead 10 broad in contact with the contact strips 5, 6 in the tape switch component for instance by the method described in the following. Similarly the other terminating means 9 may comprise an electrical terminating impedance element, such as a resistor, although an open ended electrical termination could also be conceived (i.e. infinite impedance).
With reference to figure 3a and 3b there is very schematically shown the main steps to be performed during tailoring of the tape switch according to the invention for a specific application. These steps comprises:
Although various embodiments of the present invention have been shown and described in the preceding parts of the detailed description it is understood that a person skilled in the art may conceive other embodiments of the invention without departing from the scope of the invention as defined by the following claims.