Subrack for telecommunication equipments

Abstract: The subrack accoridng to the invention, supporting cards and printed circuit boards (PCS) for telecommunication equipments, allows to use in a complete manner the space at disposal for these circuits respecting the Standars DIN 41494-IEC 297 and with mi­ nimum pitch (P'min) by least 4 times lower than the pitch (Pmin) foreseen by this standard. It includes undrilled crosspieces, but provided only with grooves, one of which being associated to a positioning toothing with teeth forming a rack, having a pitch (P'min) equal to the half of the pitch of drillings of conventional crosspieces. The teeth must be housed into seats machined into the guide of PCS, each seat being offset by a quarter of Pitch P'min, there­ fore, each time turning the boardguide by 180°, the eccentricity of the seat allows to obtain a series of real pitches multiple by a quarter of Pmin foreseen by the standard.

Description: The present invention refers to a subrack for housing electronic circuits, in particular in the form of cards or printed circuit boards (PCS) for telecommunication equipments, formed by four crosspieces supplied with means offset by a certain pitch along the axis of each crosspiece, for being engaged with corresponding insertion means provided on the bottom of boardguides, each crosspiece being provided with grooves for being fixed to the sides and with a groove for snap insertion with said boardguides. The importance of subracks in telecommunication systems is well-known; they must include the maximum number of printed circuit boards in the least possible volume, respecting the international standards such as DIN 41494-IEC 297. Further, there is a continuous tendency to miniaturize the electronic circuits, that may be at least partially impeded by the lack of timely and suitable modifications of the mechanical structures to house them. In practice, subracks are made up of four crosspieces that are redundantly provided with drillings. A second drawback is added to this first drawback, arising from the fact that the pitch of the drillings is 5.08 mm, consequently the minimum pitch (Pmin) of the housing of printed circuits is made, according to standard DIN 41494-IEC 297, as a multiple of 5.08 mm (1/5 inch). This pitch Pmin is too restrictive for telecommunication equipment (in which there is a continuous development) as it offers only the possibility of making unit dimensions that are multiples of 5.08 mm (e.g. 20.32 mm, 25.4 mm, 30.48 mm, etc.). DE-A-3 110 719 discloses a subrack which has the features recited in the first part of claim 1. The known subrack employs toothed detent bars inserted in grooves of subrack crosspieces, to avoid the necessity of providing holes in the crosspieces. The teeth are arranged with the conventional pitch. It is an object of the present invention to provide a subrack which allows optimum use of the space available for arranging printed circuit boards, yet taking account of existing standards. This object is met by the subrack defined in claim 1. Due to the fact that the seats provided on the boardguides for engagement by the teeth are offset from the centre of the boardguides, rotating anyone of the adjacent boardguides by 180° will provide a variety of positions of the individual circuit boards on the subrack and a variety of spacings between adjacent circuit boards. Preferred embodiments of the invention are set forth in the dependent claims. The invention will now be explained in more detail with respect to the drawings, in which Figures 1 and 2 are partial perspective views of a single crosspiece and, respectively, a partial subrack arrangement in accordance with the prior art, Figures 3 and 4 are views similar to Figure 1 of a crosspiece of a subrack according to the invention; Figure 5 is a schematic exploded perspective view of a base of the subrack according to the invention with five boardguides designed from A to E; Figures from 6a and 6h are partial section views of the different possible eccentricities or misalignments of the seats (SEi) of the boardguides and different possible couplings and real pitches with the teeth of a positioner according to the invention, the Figure 6i being on the contrary a similar schematic section of a crosspiece of the prior art, Figure 6 is a schematic plan view of the Figures 5 and 6i; Figure 7 is a schematic exploded perspective view of a subrack completed according to the invention; Figure 8 is an exploded perspective view of a subrack according to another embodiment of the invention and related upright of the frame; Figures 9 and 9a are schematic exploded perspective views of an embodiment of the invention with positioners formed directly on the crosspiece; and Figure 10 is a perspective view in enlarged scale of a crosspiece according to the invention, that shows better the different grooves, the positioner being removed. The Figure 1 shows a conventional crosspiece Tc having a long series of holes FO and four grooves S1, S2, S3, S4; the preparation of this crosspiece requires machining of a certain complexity. As can be seen from Figure 2, two cross-pieces Tc1 and Tc2, each one having holes FO at a pitch of 5.08 mm, (1/5 inch) receive the boardguides GS1, GS2, GS3, each of which has two pins Pio1, Pio2 to be engaged into the aligned holes FO3, FO'3 and two legs ZA1, ZA2 to be snap-engaged into the related grooves S1-S'1. Owing to its difficult machining the holes must have a minimum suitable diameter. e.g. of 2.5 mm, its minimum pitch (Pf) according to DIN 41494 IEC 297 was 5.08 mm (1/5 inch), therefore the housing pitch Pmin (distance between two adjacent printed circuits) was necessarily a multiple of Pf. According to the invention (Figures 3 and 4) the new crosspiece Tin no longer has drillings, but has two grooves S1 and S3 for fastening the same crosspiece to the body side F1 of the subrack, a groove SSC for snap-fastening the boardguide GSi, and a groove SPOS that houses or receives a positioner POS having a series of teeth DE1 and DEn forming a rack (Figures 4 and 5). In the Figures, SST indicates the conventional groove for inserting threaded bars normally used for fastening front plates, connector-holder brackets, rear parts (back panels), etc.. As Figure shows, the pitch between the teeth is e.g. P= 2.54 mm (that is 1/10 inch). The minimum pitch P'min now becomes a quarter of the minimum conventional pitch P'min = Pmin/4 = 5.08/4 = 1.27 that is 1/20 inch. This is very advantageous as it allows to obtain a dimension of unit housing which is a multiple of 1.27 mm (e.g. 20.32 mm, 21.59mm, 22.86mm; 24.13mm; 25.4mm), thus permitting optimal use of the available space for the printed circuits without violating the standard DIN 41494 IEC 297. In a first embodiment, the toothed positioner POS is constituted by a part that is formed separately and is then inserted into the groove SPOS. Preferably the positioner POS is molded from plastics material. In another embodiment, the positioner POS is directly provided on the crosspiece and/or formed integrally therewith, e.g. with the groove SPOS. The tooth DEi of the positioner POS is received by a seat SEi (Figure 5) machined in the boardguide GSi. As can be seen in better detail in the Figures 6-6h, the seats SEI have a fork form with two protruding legs Gz-Gz' suitable for being placed onto a tooth DEi of the positioner (POS). The seats SEi have critically an eccentricity or misalignment DIS that, in the most preferred embodiment, is equal to a fourth of the tooth pitch P, that is DIS = P/4 = 2.54mm: 4 = 0.635 mm (that is 1/40 inch). Turning to the boardguide by 180°, the misalignment (DIS) can be made positive (+0.635) or negative (-0.635) with respect to the axis of the positioner tooth, so that the following actual housing pitches (PE) may be obtained: PE1= (n x P) - (2 x DIS) = (10 x 2.54mm) - (2 x 0.635mm) = 24.13mm PE2= (n x P) - (2 x DIS) = (10 x 2.54mm) - (2 x 0.635mm) = 26.67mm PE3= (n x P) - DIS+DIS = (10 x 2.54mm)- 0.635mm+0.635mm= 25.4mm (with n being equal to 10). The Figure 5 shows in perspective view a crosspiece Tin with a positioner indicated by POS, that receives five boardguides A, B, C, D, E. Figure 6 shows that the boardguides A and B just as C and D are turned with respect to one another, while the boardguide E is not turned with respect to D or with respect to B. Figures from 6a to 6h show respectively: Figures 6 and 6h are front views of the boardguides A, B, C, D, E in different possible assembly positions/ rotations. Figures 6a, 6b, 6c and 6d show respectively the change of the pitch by progressive increments e.g. of 1.27 (equal to 1/20 inch) passing in increasing order from one figure to the next. Starting from the position of Figure 6d, the position of Figure 6c is obtained by rotation by 180° of SEiA and SEiB, keeping constant the tooth (DEi) engaged between 1 and 2. The position of Figure 6b is obtained from the position of Figure 6d without rotation, but inserting the teeth 2 and 3 with one another. Figure 6a is similar to the Figure 6b, but showing further the rotation of the boardguides by 180°. Figures 6e, 6f and 6g represent respectively the real pitches PE1, PE2 and PE3 where. considering e.g. PE1 as start pitch. PE2 is obtained by turning Gsi1 by 180° and engaging the seat of the same boardguide always onto the tooth 1 of the positioner and turning GSi2 by 180° and keeping always engaged the tooth of the positioner. PE3 is obtained by turning GSi1 by 180° with respect to GSi1 of the Figure 6f keeping engaged the tooth 1 of the positioner and keeping GSi2 fixed with respect to the same GSi2. The Figure 7 shows in perspective partial exploded view a subrack with four crosspieces Tin1, Tin2, Tin3, Tin4, each provided with a positioner (POS) and each being fixed to the body sides FI, FI' by self-threading screws V (Figure 8), that are engaged into the grooves S1 and S3; the crosspieces are of the type represented in enlarged scale in Figure 10, which shows an end groove SCL for engaging insertion levers and releasing the electronic devices in addition to a groove SSC for snap-engaging with legs ZA of the boardguides (GSi), Figure 8 is a perspective exploded view of a subrack according to the second embodiment (Figure 9), where the positioner is formed integrally with the crosspiece; Figure 9a shows in enlarged scale the engagement of a boardguide GS with its seat SEi onto the teeth of the positioner POS.In.

Claims: A subrack for housing electronic circuits, particularly in the form of cards or printed circuit boards for telecommunication equipment, formed by four crosspieces (Tin), each having a first groove (S1, S3) for connection to body sides (FI) of the subrack, a second groove (SSC) for snap-insertion of board guides (GSi), and a third groove (SPOS) including a positioner (POS) having teeth (DEi) projecting away from the bottom of the third groove (SPOS) for engaging corresponding seats (SEi) projecting from the bottom of the board guides (GSi), characterised in that the seats (SEi) are disposed with a misalignment (DIS) with respect to the centre of the board guides (GSi). The subrack of claim 1, wherein the misalignment (DIS) is equal to one-fourth the pitch (P) of the positioner teeth (DEi). The subrack of claim 1 or 2, wherein the pitch (P) of the positioner teeth (DEi) is one-half the standard pitch (Pmin) according to DIN 41494 IEC 297. The subrack of claim 1 or 2, wherein the pitch (P) of the positioner teeth is 2.54 mm and said misalignment (DIS) is 0.635 mm. The subrack of any preceding claim, wherein the positioner (POS) is a preformed piece, preferably made of plastics material, inserted into said third groove (SPOS). The subrack of any of claims 1 to 4, wherein the positioner (POS) is formed integrally with said third groove (SPOS). The subrack of any preceding claim, wherein the seats (SEi) to be engaged by the positioner teeth (DEi) are formed at least by two lateral walls (Gz) spaced apart in accordance with the tooth thickness.

Inventors: OREGLIO MAURIZIO, RONCHI DOMENICO, ZINGRINI CARLO, OREGLIO, MAURIZIO, RONCHI, DOMENICO, ZINGRINI, CARLO
Applicants: ALCATEL ITALIA, ALCATEL ITALIA S.P.A
Application year: 1990
Main classification: H05K7
IPC codes: H05K7