Electrical connector with shorting contacts which wipe against each other

Abstract: A pair of shorting contacts (16,16) on mated electrical contact members (10,10) are protrusions on the respective contact members (10), which protrusions are laterally reversed mirror images of each other. The respective shorting contacts (16,16) confront each other in a substantially transverse configuration. Initial engagement between the respective shorting contacts (16,16) is at an initial contact point (25) at a high stress. The shorting contacts (16,16) thereafter wipe against one another and come to engage at a final contact point (26). The path from the initial contact point (25) to the final contact point (26) constitutes a line between the respective contact members (10,10).

Description: The present invention relates to shorting electrical contacts of an electrical connector for a printed circuit board and more particularly to shorting contacts which wipe against one another and engage one another at a final point contact. A mother board and one or more daughter boards are used to transfer signals between respective assemblies used in a computer or other electronic equipment. The mother and daughter boards may be arranged perpendicular to each other, as in an "edge card" configuration, depending upon the design of the overall product. Edge card connector contacts are formed on the mother card so that when the daughter card is removed, the opposing contacts come together to form an electrical shorting circuit. The reliability of these shorting contacts is very important to the efficiency of the overall equipment. Due to the environment in which the boards are located, there is the possibility of debris being collected at the interface between the mother board and the daughter board or of a film being formed on the opposing contacts on the mother card. In this type of situation, the electrical connection between the opposing contacts may be imperfect or unreliable and may result in malfunction of the electronic equipment. The known art utilizes opposing contacts which are usually bent or bowed members, parallel to one another and which engage across the entire width of the respective contacts. Alternatively a dimple has been used on a surface to obtain contact stress against the opposing contact. CH-A-534 435 discloses opposing contact members which are laterally bent and have radiused protrusions biased into contact such that the protrusions wipe against each other as they become engaged or disengaged from one another It is important to have opposing contacts which can reliably and simply effect an electrical connection when the daughter board is removed from the mother board and which can overcome film deposits and debris on the surfaces of the contacts. The present invention consists in a pair of shorting electrical contacts of an electrical connector for a printed circuit board alternately inserted and withdrawn between the contacts, comprising resilient members having longitudinal axes and mutually opposed radiused protrusions with axes extending transversely to the longitudinal axes of the resilient members, said protrusions having arcuate surfaces biased into engagement, characterised in that each protrusion has a base, a top and at least one of the sides between the base and the top disposed at an acute angle to the longitudinal axis of the associated resilient member, and in that the opposed protrusions are arranged as laterally reversed mirror images of each other, whereby, after initial engagement at an initial contact point, the protrusions wipe against each other and come to engage each other at a final contact point, the path from the initial contact point to the final contact point constituting a line between the respective protrusions. In one embodiment, each protrusion is a substantially bisected cone frustum in shape. The contacts are in opposing relationship so that their respective angled protrusions confront one another substantially in a transverse configuration. In this manner, the base of each protrusion is opposite the top of each confronting protrusion so that the respective sides of the confronting protrusions of the contacts initially engage each other at an initial point contact. A very high stress concentration is provided therebetween. The protrusions thereafter wipe against each other and come to engage each other at a final point contact. The path from the initial point contact to the final point contact constitutes a line between the respective contacts, In another embodiment, each protrusion is a radiused protrusion disposed at an acute angle with respect to the longitudinal axis of the respective resilient member. The resilient members are in opposing relationship so that their respective angled radiused protrusions confront one another substantially in a transverse configuration. The respective resilient members may be twisted about their longitudinal axes so that the contacts initially engage each other at an initial point contact, thereby providing a very high stress concentration therebetween. The protrusions thereafter wipe against each other and come to engage each other at a final point contact. The path from the initial point contact to the final point contact constitutes a line between the respective contact members. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a perspective view of a mated pair of electrical contacts showing the shorting contacts of the present invention. Fig. 2 is a perspective view of one contact showing the right side of the shorting contact. Fig. 3 is a perspective view of the contact of Fig. 2 showing the left side of the shorting contact. Fig. 4 is a side view of the contact of Fig. 2. Fig. 5 is a partial front view of the contact of Fig. 2 showing the shorting contact. Figs. 6A-6B are end views of the mated pair of contacts of Fig. 1 showing the wiping movement of the shorting contacts. Fig. 7 is a cross sectional view taken across the lines 7-7 of Fig. 6B. Figs. 8A-8B are cross sectional views showing the insertion of a daughter board between the mated electrical contacts . Fig. 9 is a sketch showing contacting edges being substantially parallel to one another and the forces attendant thereto. Fig. 10 is a sketch showing contacting edges meeting at an angle with the forces attendant thereto. Fig. 11 is a perspective view of a mated pair of electrical contacts showing the shorting contacts of another embodiment of the present invention. Figs. 12A-12D are perspective views of the embodiment of Fig. 11 showing the forming of the shorting contacts. Fig. 13A-13C are end views of the embodiment of Fig. 11 showing the wiping movement of the shorting contacts. With reference to Fig. 1-8, a first embodiment of the present invention is shown. A plurality of electrical contacts 10 are secured to a mother board 11 (Figs 8A and 8B). The contact 10 is a member of electrically conductive material (preferably beryllium copper) formed with a U-shaped bend 12 at the upper end, a front leg 13, a rear leg 14, an upper board contact 15 at the approximate midpoint of the front leg 13 and a shorting contact 16 at the lower end of the front leg 13. The bent configuration of the contact 10 provides a resiliency to the contact 10 so that the shorting contact 16 is biased in a direction away from the rear leg 14. Preferably the contacts 10 are secured in mating opposing pairs in cavities 42 of a dielectric housing 40 wherein the respective upper contacts 15 and shorting contacts 16 are mutually facing. In the normal condition, the respective upper contacts 15 of the opposing front legs 13 are spaced apart and the respective shorting contacts 16 of the opposing contacts 10 are touching one another to provide an electrical connection (a shorting connection) between the mated contacts 10. A daughter board 17 having an electrical circuit thereon may be inserted in a slot 44 in housing 40 between the mated contacts 10. The daughter board 17 initially makes electrical contact with the upper board contacts 15 on the respective mating contacts 10. As the daughter board 17 is further inserted, the opposing shorting contacts 16 are separated. Upon removal of the daughter board 17 from between the mated contacts 10, the opposing shorting contacts 16 are urged together due to the resiliency of the respective contacts 10 and a shorting type electrical connection is effected between the mated contacts 10. The present invention is directed toward the shorting contacts 16 to assure a high reliability electrical connection. The development of a film such as an oxide or the deposition of debris such as dust on the engaging surfaces of the respective shorting contacts 16 are common causes of poor electrical contact. The present invention overcomes these problems. In one embodiment, the shorting contact 16 is a protrusion 16 formed on the longitudinal axis of the contact strip. The protrusion 16 is in the shape of a bisected frustum cone having a base 20, a top 21, an upper side 22 and a lower side 23. The altitude of the protrusion 16 is between the base 20 and the top 21 and is also perpendicular to the longitudinal axis of the front leg 13. The upper side 22 is disposed at an angle of approximately 30°-60° with respect to the altitude of the protrusion 16 with a particularly preferred disposition of approximately 45°. The lower side 23 is disposed at an angle of approximately 0°-45° with respect to the altitude of the protrusion 16. In this manner, both sides 23, 24 of the protrusion 16 are disposed at an acute angle with respect to the longitudinal axis of the front leg 13. The respective protrusions 16 on the mated contacts 10 are laterally-reversed mirror images of one another. In this manner, the base 20 of the protrusion 16 on one contact 10 is disposed opposite the top 21 of the protrusion 16 on the mated contact 10 and the respective protrusions 16 confront one another in a transverse configuration. As the respective protrusions 16 initially contact one another there is an initial contact point 25 on the curved edge of each respective protrusion 16. Due to the resiliency of the contacts 10, and there being only a point contact between the contacts 10, the contact point 25 is under high stress. Also due to such resiliency and the arcuate nature of the contacting edges of the respective protrusions 16, the protrusions 16 wipe against one another in a sliding movement and come to engage one another at a final contact point 26, the path between the initial contact point 25 and the final contact point 26 constituting a line. When the mated contacts 10 are viewed from the end and as the daughter board 17 is inserted between the contacts 10, the shorting contacts move slightly sideways with respect to one another and then outwardly from one another in a letter "L" like movement. The advantage of having the contact surfaces at an angle with respect to one another is further shown in Figs. 9 and 10. Fig. 9 shows the contacting edges being substantially parallel to one another as is common practice in the field. In this situation the spring force (S F ) is equal and opposite to the contact interface force. However, when the opposing contacts meet at an angle with respect to one another (Fig. 10) the interface force (I F ) is greater than the direct spring force (S FD ). To illustrate, S FD is spring force direct, F F is friction force, S FL is spring force lateral, I F is interface force. Let F X = any force component acting along X axis F Y = any force component acting along Y axis Then, for system in static equilibrium: ΣF x = 0 and ΣF Y = 0 As a reasonable example assume: spring force direct S FD = 50 grams interface angle Θ = 45° coefficient of friction µ = 0.2 Then ΣF Y = S FD - F F sin Θ - I F cos Θ = 0 Where F F = µ I F So S FD - µ I F sin Θ - I F cos Θ - 0 50 - .2 I F sin 45° - I F cos 45° = 0 50 - .1414 I F - .707 I F = 0 50 - .8485 I F = 0 I F = 58.9 grams, this is higher than S FD Also Σ F X = 0 Σ F X = S FL + F F cos Θ - I F sin Θ = 0 S FL + µ I F cos Θ - I F sin Θ = 0 S FL + .2 (58.9) cos 45 - 58.9 sin 45 = 0 S FL + 8.3 - 41.6 = 0 S FL = 33.3 grams As shown, the interface force is greater than the spring force. This can be viewed as a wedge effect. An increase in the force at the interface further increases the surface stress. Thus, the wiping movement between the respective protrusions consists of a moving point of contact which effectively overcomes any film or debris on the respective shorting contacts 16 and provides a highly reliable electrical contact. In another embodiment (Figs. 11-13) the shorting contacts 16 on the respective contacts 10 are formed as a radiused protrusion 30 which is at an acute angle with respect to the longitudinal axis of the front leg 13 of the respective contact 10. The method of forming the radiused protrusion 30 is shown in Figs. 12A-12D. The radiused protrusion 30 is formed in the contact at approximately 30°-60° with respect to longitudinal axis and at an especially preferred angle of 45°. The mated opposed contact 10 also has a radiused protrusion 30 formed therein, the radiused protrusion being a laterally-reversed mirror image of the opposite and confronting radiused protrusion. In the preferred configuration, where the respective radiused protrusions 30, 30 are disposed at an angle of 45° with respect to the longitudinal axis of the front leg, the radiused protrusions on the mated contacts 10 are at 90° with respect to one another. In order to further improve the reliability of the connection, the respective front legs 13 of the contacts are twisted through approximately 45° so that when the radiused protrusions 30, 30 on the contacts 10 engage one another, the angle of the contact is approximately 45°. When the opposing radiused protrusions 30, 30 initially engage one another, there is an initial contact point on the curved edge of each respective protrusion 30. As in the previously described embodiment, the contact point is under high stress and due to the resiliency of the connecting bodies and the arcuate nature of the contacting edges, the protrusions wipe past one another in a sliding movement until the resilient forces equalize and the motion stops at a final contact point. The path between the initial contact point and the final contact point constitutes a line. As will be appreciated by those skilled in the art, the present invention provides features and advantages as follows: (1) contact between opposing shorting contacts is reliable, (2) point contact is made under high stress and (3) a wiping movement between the opposing shorting contacts overcomes film and debris on the contact surfaces.

Claims: A pair of shorting electrical contacts (10) of an electrical connector for a printed circuit board (11) alternately inserted and withdrawn between the contacts, comprising resilient members (13) having longitudinal axes and mutually opposed radiused protrusions (16, 30) with axes extending transversely to the longitudinal axes of the resilient members, said protrusions having arcuate surfaces biased into engagement, characterised in that each protrusion (16, 30) has a base (20), a top (21) and at least one of the sides (22,23) between the base and the top disposed at an acute angle to the longitudinal axis of the associated resilient member (13), and in that the opposed protrusions (16, 30) are arranged as laterally reversed mirror images of each other, whereby, after initial engagement at an initial contact point (25), the protrusions wipe against each other and come to engage each other at a final contact point (26), the path from the initial contact point to the final contact point constituting a line between the respective protrusions. A pair of shorting electrical contacts as claimed in claim 1, wherein each protrusion (16) is in the shape of a bisected frustum of a cone, the protrusions being disposed in opposed relationship with one another, substantially in a transverse configuration, with the base (20) of each protrusion being opposite the top (21) of the opposing protrusion so that the respective surfaces of the protrusions initially engage each other at the initial contact point (25), thereby providing a very high stress concentration therebetween, and so that the protrusions thereafter wipe against each other and come to engage each other at the final contact point (26). A pair of shorting contacts as claimed in claim 1 or 2, wherein the acute angle of said at least one side (22, 23) is in the range from 30° to 60°. A pair of shorting contacts as claimed in claim 1, wherein each protrusion is a radiused protrusion (30) and the associated resilient member (13) is twisted about its longitudinal axis. A pair of shorting contacts as claimed in claim 4, wherein the protrusion is disposed at an acute angle in a range of 30° to 60° with respect to the longitudinal axis of the resilient member. A pair of shorting contacts as claimed in claim 3 or 5, wherein the acute angle is approximately 45°.

Inventors: PICKLES CHARLES SANDS, THUMMA MARK RICHARD, PICKLES, CHARLES SANDS, THUMMA, MARK RICHARD
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1993
Main classification: H01R13
IPC codes: H01R13, H01R12