WO2005088774A1

WO2005088774A1 - Deformable terminal and a strobe light unit that includes the terminal

Info

Publication number: WO2005088774A1
Application number: PCT/US2005/007258
Authority: WO
Inventors: Masami Ohsumi
Original assignee: 3M Innovative Properties Company
Priority date: 2004-03-09
Filing date: 2005-03-03
Publication date: 2005-09-22
Also published as: JP2005257808A; KR20060123786A; CN1930743A; EP1733457A1

Abstract

A non-soldered conductive connection terminal and a strobe light unit including the terminal are provided, wherein the terminal can be used, when the discharge tube is installed, in order to minimize the stress applied to an electrode of a discharge tube, generated by a drift of position of the electrode on a body of the discharge tube. [Means for Solving the Problem] A terminal (33) according to the present invention includes an electrode gripping part (332) having a groove or a slot (335) for receiving an electrode (151) of a discharge tube (15); a fixed part (333); and a deformable part (334) for connecting the electrode gripping part (332) to the fixed part (333). The deformable part (334) is generally U-shaped, and includes a first end (334a) connected to the electrode gripping part (332) and a second end (334b) connected to the fixed part. The first and second ends (334a and 334b) are configured such that these ends can be moved relative to each other in a direction generally perpendicular to a center axis of the discharge tube (15) and in a direction generally perpendicular to a depth direction of the slot.

Description

DEFORMABLE TERMINAL AND A STROBE LIGHT UNIT THAT INCLUDES THE TERMINAL

[Technical Field] [0001]

The present invention relates to a strobe light unit and, more particularly, to a terminal to which an electrode of a discharge tube of the strobe light unit can be conductively connected.

[Background] [0002] A strobe light, such as that used in a compact camera, a digital camera, a "film with lens", a mobile phone with a camera, etc., may conceptually be divided into a strobe light unit and other components such as a current source, a modulator, capacitors, etc. The strobe light unit includes a discharge tube, a reflective shade for reflecting light emitted by the discharge tube, terminals for conductively connecting electrodes of the discharge tube to other electrical components, a trigger electrode for initiating the emission of light by the discharge tube, and a cover for protecting the discharge tube. [003] The discharge tube itself includes a sealed cylindrical glass tube (the main body) that has been evacuated and then pressurized with a gas, such as xenon, and two electrodes each connected to either end of the main body. The positioning of the electrodes inside the main body does not require a high degree of accuracy, so that the electrodes are often positioned eccentrically with respect to the body (i.e., the centerline of the main body and the central axes of the electrodes inside the main body often do not coincide) . Accordingly, the external conductive connections between the electrodes of the discharge tube and their respective terminals are often accomplished by soldering, which does not require accurate positioning. Japanese ϋnexamined Patent Publication (Kokai) No. 2001-255576, for example, discloses a strobe apparatus in which the external conductive connections between electrodes of the discharge tube and their respective terminals and between a trigger electrode of the discharge tube and its respective terminal are soldered connections . [0004] The soldering process is generally labor-intensive and not easily automated. In addition, components connected by soldering may be less well electrically connected than the external appearance of the solder joint would indicate due to a defect known as "potato soldering" which yields a hollow solder joint that is prone to mechanical and electrical failure due to mechanical shock or vibration. Several Patent Documents disclose strobe light unit that have solder-free electrical connections between external terminals and electrodes of the discharge tubes of the strobe light unit. For example, Japanese Unexamined Patent Publication (Kokai) No. 11-218807 discloses a terminal having a U-shaped groove that maintains mechanical and electrical contact with an electrode of a discharge tube. Japanese Unexamined Patent Publication (Kokai) No. 7- 20541 discloses an apparatus having a U-shaped groove that supports an electrode of a discharge tube and a terminal elastically connected to the electrode. Japanese Unexamined Patent Publication (Kokai) No. 5- 165085 discloses a discharge tube supported by an electrically conductive elastomeric board that mechanically insulates the electrodes of the discharge tube from the effects of mechanical vibration and shock. [0005] The 11-218807 Japanese Published Application discloses a terminal with a U-shaped groove that maintains mechanical and electrical contact with the external ends of both electrodes of a discharge tube that is fixed to a board. If either electrode of the discharge tube is positioned eccentrically with respect to the main body of the discharge tube and if the central axes of the electrodes do not coincide, undesirable mechanical stress is placed on the discharge tube when the discharge tube is installed, particularly on the joint between the body of discharge tube and the electrode. This stress often causes cracks to develop on the joint or damages the main body of the discharge tube. The 7-20541 Japanese Published Application discloses a connecting part that includes an electrical terminal that is elastically connected to an electrode of a discharge tube. Although this terminal absorbs mechanical shock and vibration transmitted from the board to the discharge tube after the discharge tube has been installed, stress relaxation during installation of the discharge tube is unaffected. In other words, when the discharge tube is installed, the electrode of the discharge tube is supported by the U-shaped groove, and the position of the U-shaped groove is fixed relative to the board, so that mechanical stress on the discharge tube is unavoidably generated during installation of the tube, just as it is in the apparatus described in the 11-218807 Japanese Published Application. [0006] The electrically conductive elastomeric board briefly described above and disclosed in the 5-165085 Japanese Published Application is clearly capable of minimizing stress on the discharge tube when the discharge tube is installed. However, as the conductive board forces the electrode of the discharge tube in a single direction, it is necessary to minimize the pressure exerted by the conductive board in order to prevent excessive stress on the discharge tube. The electrical resistance between the discharge tube and the conductive board at the area of contact between them (i.e., at the connecting terminal) increases as the pressure between the board and the tube decreases. Accordingly it is difficult to simultaneously minimize both mechanical stress and contact resistance in the apparatus .

[Summary] [0007] An object of at least one embodiment of the present invention is thus to provide an electrical terminal for a strobe light unit that furnishes a low resistance electrical connection for the electrodes of the strobe light's discharge tube but does not also generate excessive mechanical stress on any part of the discharge tube during installation of the discharge tube. [0008] Claim 1 presents an embodiment of the present invention that is a terminal for retaining, and being electrically connected to, an electrode of a discharge tube having a body, the terminal comprising: an electrode gripping part capable of gripping the electrode of the discharge tube by equal forces from at least two directions; and a fixed part to prevent the terminal from moving, the electrode gripping part gripping the electrode such that the electrode is displaced in an arbitrary direction generally perpendicular to a center axis of the discharge tube relative to the fixed part. [0009] Claim 2 presents a terminal as described in Claim 1, in which: the terminal further comprises a deformable part which connects the electrode gripping part to the fixed part such that the gripping part comprising a slot for receiving the electrode by press-fitting, the deformable part may deform such that the electrode gripping part is displaced in a direction generally perpendicular to an extending direction of the slot and in a direction generally perpendicular to the center axis of the discharge tube. [0010] Claim 3 presents a terminal as described in Claim 2, in which the slot is configured to receive the electrode such that the depth of the press-fitting of the electrode into the slot is variable. [0011] Claim 4 presents a terminal as described in the Claim 2, in which the deformable part comprises two curved portions which bend approximately 90 degrees, the deformable part and fixed part being connected by the two curved portions . [0012] Claim 5 presents a strobe light unit comprising at least one terminal described in one of claims 1 to 4 and a discharge tube having two electrodes, at least one of the two electrodes being gripped by the electrode gripping part of a terminal.

[Brief Description of the Drawings] [0013] [Fig. 1] (a) is a perspective view of the preferred embodiment of the strobe light unit of the present invention; and (b) is an exploded perspective view of the embodiment depicted in Fig. 1(a) . [Fig. 2] An exploded perspective view of the strobe light unit depicted in Fig. 1 (b) . [Fig. 3] A perspective view of a first embodiment of the terminal of the present invention that illustrates the spatial relationship between the terminal of the present invention and an electrode of the discharge tube of the strobe light unit. [Fig. 4] (a) is a perspective view of the first embodiment of the terminal of the present invention; and (b) is a perspective view of the terminal depicted in Fig. 4(a) looking from the different angle. [Fig. 5] A perspective view of the inside of the cover of the strobe emit part. [Fig. 6] A perspective view of the second embodiment of the terminal of the present invention. [Fig. 7] A perspective view of the third embodiment of the terminal of the present invention; and [Fig. 8] A perspective view of the fourth embodiment of the terminal of the present invention.

[Detailed Description] [0014] At least one embodiment of the present invention provides a solder-free terminal for an electrode of a discharge tube, where the terminal is capable of providing a low contact-resistance, electrically conductive connection for the electrode without exerting excessive mechanical stress on the discharge tube. A very reliable strobe light unit that includes this solder-free terminal is also provided. [0015] An embodiment of the present invention is described immediately below with reference to the accompanying drawings .

As shown in Fig. 1(a), a strobe light unit 1 has a socket 3 mounted on a printed circuit board 2 (for example, by soldering) and a cover 11 engaged to the socket 3. As shown in Fig. 1(b), the strobe light unit 1 also has an electrically conductive reflective shade 12 that would fit in the space defined by the cover 11 and the socket 3; and a discharge tube 15 extending through both openings 121 of the reflective shade 12. The printed circuit board 2 is provided with holes 21a to 21c which can receive a part of terminals and a trigger electrode that will be described later-. The discharge tube 15 includes a sealed, hollow glass cylinder 152 (i.e., the main body of the discharge tube) that is evacuated and then refilled with an inert gas, such as xenon, and two conducting, preferably cylindrical electrodes 151 that extend from inside to outside the glass cylinder at either end of the main body 152. The length of the glass cylinder is roughly 1 to 3 cm and the length of each of the two electrodes 151 is roughly 3 to 5 mm. [0016] Fig. 2 is an exploded view of the detail of the strobe light unit 1. The socket 3 includes a case 36, two electrically conductive terminals 33 for engaging the two electrodes 151 of the discharge tube 15, and an electrically conductive trigger electrode 34. The two terminals 33 and the trigger electrode 34 are previously positioned in the case 36 by, for example, press-fitting or insertion-molding and are typically fabricated from a copper alloy to have high conductivity. The trigger electrode 34 includes a tail portion 341, a spring portion 342, and a connecting portion 343 that conductively contacts the convex outer surface of the reflective shade 12 when the reflective shade 12 is positioned in the socket 3. The trigger electrode 34 and the reflective shade 12 are electrically connected because the reflective shade 12 is fabricated from a conductive material . [0O17] The two terminals 33 according to the present invention will be described with reference to Fig. 3. As shown in Fig. 3 and Figs. 4(a) and 4(b), each of the terminal 33 includes: an electrode gripping portion 332 having a groove or slot 335 for receiving and retaining one of the electrodes 151 of the discharge tube 15; a fixed part 333 that is fastened to the case 36 when the strobe light unit is assembled; and a pin portion 331, preferably adjacent to the fixed part, that is inserted into the hole 21a or 21b and then soldered to the printed circuit board 2 when the strobe light unit is assembled. The electrode gripping portion 332 and fixed part 333 are mechanically joined by a substantially U-shaped deformable portion 334. The terminal 33 is typically punch-pressed from a copper or copper alloy sheet preferably 0.1 to 0.5 mm thick into a planar piece, which is then bent into a three-dimensional piece with a desired shape. [0O18] The width of the slot 335 in the electrode gripping portion 332 is slightly les than the width (i.e., diameter) of the electrode 151 of the discharge tube 15. Therefore, the electrode 151 is engaged in the slot 335 by press-fitting or interference-fitting. When the electrode 151 is press-fitted into the slot 335, the bottom 336 of the electrode gripping portion 332 transfers the force exerted on the electrode 151 to the case 36, so that the electrode an be easily and reliably press-fitted. The depth of the slot 335 (i.e., the dimension of the slot in the direction of press-fit of an electrode 151) is preferably greater than the diameter of the electrode 151. A slot 335 into which an electrode 151 is inserted is accordingly capable of accommodating variations in the depth of insertion of the electrode 151, and two slots 335 into which the two electrodes 151 of a discharge tube 15 are simultaneously inserted are thus capable of accommodating eccentric placements of the electrodes 151 with respect to the centerline of the discharge tube in the insertion direction. That is, when the two electrodes 151 of a discharge tube 15 are simultaneously inserted into the respective slots 335 of a terminals 33 and the component of the vector displacement of the first electrode from the center axis of the discharge tube along the insertion direction is not the same as the component of the vector displacement of the second electrode from the center axis of the discharge tube along the insertion direction, the structure of the terminals 33 is significantly ameliorates mechanical stress on both the discharge tube body 152 and on the joints between the discharge tube body 152 and the electrodes 151. [0019J As shown in Figs. 3 and 4, the deformable portion 334 that connects the electrode gripping portion 332 and the fixed part 333 is substantially U-shaped and includes: a first end part 334a that is connected to the electrode gripping portion 332; and a second end part 334b that is connected to the fixed part 333. The first end part 334a and the second end part 334b of the deformable portion 334 are capable of relative displacements parallel to the line B shown in Fig. 3, that is, in directions that are roughly perpendicular to the central axis of the discharge tube 15 and also roughly perpendicular to the insertion direction. With this structure, the electrode gripping portion

332 can easily move in A directions parallel to the B directions. Namely, when the discharge tube 15 is connected to the terminal 33, the relative displacement of the axes of the electrodes 151 in the A directions (that is, perpendicular to the press-fitting direction) toward the central axis of the body of the discharge tube 15 will be accommodated by the structure of the terminal 33. When the discharge tube 15 is connected to the terminal 33 and the displacement of one electrode relative to the other electrode has a component perpendicular to the insertion direction, mechanical stress on the main body 152 of the discharge tube and on the joints between the main body

152 and the electrodes 151 is significantly ameliorated by the structure of the terminal 33. [0020] As shown in Figs. 3 and 4(a), the second terminal part 334b of the deformable portion 334 may include two curved portions 337 that bend approximately 90 degrees. The deformable portion 334 and the fixed part

333 are connected to each other via the two curved portions 333. With this structure, the electrode gripping portion 332 is capable of moving in the direction of press-fitting of the electrode 151, so that it is not necessary to control the depth of the insertion of the electrode 151 into the slot 335.

[0021] As described above, by press-fitting an electrode 151 of a discharge tube 15 into a slot 335, by means of a terminal 33 having a slot 335 described above or a curved portion 337 and a deformable portion 334, the electrode gripping portion 332 is capable of gripping after transferring the electrode 151 in the fixed part 333 in a direction perpendicular to the central axis of the discharge tube 15. So the mechanical stress on the discharge tube due to eccentric placement of the electrodes with respect to the central axis of the discharge tube will be dramatically minimized in comparison with the prior art when an electrode (the electrodes) is (are) press-fitted and damage to the discharge tube is accordingly prevented. In addition, plastic deformation of the deformable portion 334 during installation of the discharge tube 15 is acceptable, for example in order to continuously use the strobe light unit when the discharge tube is replaced, elastic deformation of the deformable portion, as described above, is preferable. [0022] Due to a mechanical structure of the slot 335 that exerts a force of the same magnitude on the electrode 151 from each of at least two directions (the terminal 33 of the preferred embodiment of course exerts a force of the same magnitude on the electrode from exactly two directions) , the terminal of the present invention has the advantageous capability of subjecting the electrode 151 to high pressure, which minimizes contact resistance. By combining the slot 355 and the deformable portion 334, terminal of the present invention is able to provide an electrically conductive contact having a small contact-resistance without exerting a large stress on the discharge tube when the discharge tube is installed. This is a significant advantage. In the terminal of the preferred embodiment, deformation of the joint between the electrode 151 and the slot 335 is accomplished primarily by the sides of slot 335, which is different from a conventional pressure-type engagement, in which the terminal breaks into the side of the electrode side. However, the slot 335 breaking into the electrode 151, as in a conventional terminal, would be acceptable. [0023] In view of reducing the number of different parts of the strobe light unit, terminals 33 that include deformable portions 334 are preferably used for the two electrodes 151 of the discharge tube, but may be used for only one of the two electrodes. However, in the latter case, it would be possible to use, as the other electrode, another terminal that does not include a deformable portion. [0024] The fixed part 333 is fixed to the case 36 when the strobe light unit is assembled. In order to achieve firmer fixing, teeth or a wedged portion 333a may be employed in the fixed part 333, as shown Fig. 4(a) . [0025]

Fig. 5 is a perspective view of the interior of a preferable cover 11. The cover 11 may be brought to the configuration shown in Fig. 1(a) by seating the reflecting shade 12, which includes the discharge tube 15, into the socket 3 to the configuration shown in Fig. 1(b) . In order that the cover 11 include a space 111 that can accommodate the reflective shade 12; a first groove 112 that is able to press the electrode 151 of the discharge tube 15 when the reflective shade 13 is seated in the cover; and a second groove 113 that is able to receive the terminal 333. Such a construction enables the electrode 151 of the discharge tube 15 to be inserted into the slot 335 of the terminal 33 at the same time as the reflective shade 12 is seated in the socket 3. As described above, the electrode gripping portion 332 of the terminal 33 may be deformed in a direction perpendicular to the central axis of the discharge tube 15 by the displacement of the electrode 151 when the electrode 151 is inserted into the slot 335. As the shape of first groove 112 is not perfectly complementary to the shape of the electrode 151, the groove 112 preferably has a slightly larger radius of curvature than the cylindrical electrode 151. For the same reason, the second groove 113 of the cover 11 is preferably slightly larger than the terminal 33. [0026]

Figs . 6 to 8 respectively illustrate a second, a third and a fourth embodiments of the present invention, all of which are modifications of the preferred embodiment. The terminal 43 of the second embodiment of the present invention, which is shown in Fig. 6, is identical to the terminal 33 except for the tail part 431 of the terminal 43, which is the counterpart of the pin part 331 of the terminal 33. In order to establish an electrical connection to the terminal 43, the tail part 431 may be soldered to a printed circuit board 2 without making a hole in the printed circuit board 2. [0027] The terminal 53 depicted in Fig. 7 and the terminal 63 depicted in Fig. 8, which are the third and the fourth embodiments, respectively, of the present invention, both include structural features that enable an electrically conductive connection with an cable, but not with a printed circuit board. In lieu of the pin part 331 of the terminal 33, the terminal 53 shown in Fig. 7 includes a cable connecting part 531 having a slit 531a into which an electrical cable may be inserted or to press- fit. The other structural features of the terminal 53 are as same as the corresponding features of the terminals 33 and 43. In place of the pin part 331 that is a distinguishing feature of the terminal 33, the terminal 63 shown in Fig. 8 includes a cable connecting part 631 with a substantially flat surface that facilitates the soldering of a cable to the terminal 63. Each of the other distinguishing features of the terminal 63 is same as the corresponding feature of terminal 33, 43, and 53. [0028] Each of the terminals 43, 53 and 63 may include the same type of teeth 333a as were explained in connection with the terminal 33 in lieu of engaging with the fixed part, that is, the socket 3. [0029] The purpose of each of the terminals 33, 43, 53 and 63 described in detail is to provide a low-resistance, electrically conductive connection for an electrode of the discharge tube of a strobe light unit without generating excessive mechanical stress on any part of the discharge tube. The characteristics of the terminals described above render them capable of fitting with other components, such as terminals which have poor accuracy of fit with respect to the discharge tube.

Claims

[Claims] 1. A terminal for retaining, and being electrically connected to, an electrode of a discharge tube having a body, the terminal comprising: an electrode gripping part capable of gripping the electrode of the discharge tube by equal forces from at least two directions; and a fixed part to prevent the terminal from moving, the electrode gripping part gripping the electrode such that the electrode is displaced in an arbitrary direction generally perpendicular to a center axis of the discharge tube relative to the fixed part.

2. A terminal according to claim 1, wherein the terminal further comprises a deformable part which connects the electrode gripping part to the fixed part such that the gripping part may be moved relative to the fixed part, the electrode gripping part comprising a slot for receiving the electrode by press-fitting, the deformable part may deform such that the electrode gripping part is displaced in a direction generally perpendicular to an extending direction of the slot and in a direction generally perpendicular to the center axis of the discharge tube.

3. A terminal according to claim 2, wherein the slot is configured to receive the electrode such that the depth of the press- fitting of the electrode into the slot is variable.

4. A terminal according to claim 2 , wherein the deformable part comprises two curved portions which bend approximately 90 degrees, the deformable part and the fixed part being connected by the two curved portions .

5. A strobe light unit comprising at least one terminal according to one of claims 1 to 4 and a discharge tube having two electrodes, at least one of the two electrodes being gripped by the electrode gripping part of a terminal.