V-SHAPED GROOVE INSPECTING AND WORKING METHOD

Abstract: A method of inspecting V-shaped grooves, e.g. grooves for optical fibres, is carried out in the following steps. Coordinates of more than 20 points per groove (1) on a substate formed with V-shaped grooves ar emeasured with a stylus (3) moving in directions perpendicular to the longitudinal directions of the grooves. Data measured within regions of at least 10 µm at the edges (5) and bottom (6) of the grooves are removed from the data so obtained. Shapes formed by straight lines are then calculated on the basis of remaining data on effective measuring lengths of more than 40 µm. A method of working the V-shaped grooves is effected by the following steps. A circle (7) having a diameter substantially equal to that of fibres to be supported in the grooves is drawn inscribed in the interior of a V-shaped groove of shape calculated by the above method. The groove is then worked, while errors in the centre position of the circle are fed-back into the working process of the groove of the substrate to compensate for variation of depths and pitches of the V-shaped grooves being worked.

Description: This invention relates to a method of inspecting and working V-shaped grooves, for example, those as formed in a substrate of an optical fiber connector with high accuracy of the order of submicrons. In order to connect optical fibers having diameters of 100 µm plus several tens µm whose center axes are aligned with each other with high accuracy, connectors have been developed in which the optical fibers are to be embraced between a pair of chips formed in their surfaces with V-shaped grooves. Such chips are made of a hard material such as a ceramics, glass ceramics and quenched steel. The V-shaped grooves are formed by means of a rotating grinding wheel having a sharpened periphery edge. As any worked errors in the worked V-shaped grooves will directly cause deflections of axes of the optical fibers, the V-shaped grooves must be inspected with high accuracy. However, as the V-shaped grooves are very fine in the order of 100 µm depth and 150 µm width, the measurement of surface roughness determined in ISO cannot be applicable to the inspection of the grooves. Even if a surface roughness tester is used, significant measured values could not be obtained. In order to solve this problem, a following method has been proposed. In this method, as shown in Fig. 1, a master gauge 2 having a diameter equal to those of optical fibers to be used is arranged in a V-shaped groove 1 and a height of the master gauge 2 is measured by means of a stylus. A position and accuracy of the optical fiber in an actually used state are presumed with the aid of the measured value. With this method, however, the accuracy is likely to be detrimentally affected by unreliable master gauge, scores or scratches and located conditions of the master gauge. Therefore, it is quite impossible to measure pitches of V-shaped grooves with an accuracy higher than 1.0 µm. As shown in Fig. 2, moreover, a method has been proposed in which a V-shaped groove itself is directly measured with a stylus 3 to inspect whether a depth, width, pitch and the like are within allowable tolerances. In this method, however, errors would occur due to chipping, breaking off, caulking and the like at edges of V-shaped grooves. In addition, it is impossible with this method to accurately detect partial changes in angle ϑ of the V-shaped groove due to wear of tips of a grinding wheel. Direct measurement systems using styluses are illustrated in DE-A-35 43 906 and JP-A-57-10411. It is an object of the invention to provide a method of inspecting shapes and dimensions of fine V-shaped grooves with high accuracy less than 1.0 µm and a method of working the V-shaped grooves utilizing results of the inspection at least partly eliminating the disadvantages of the prior art above described. The method of inspecting V-shaped grooves according to the invention is set out in claim 1. The inspection may be performed at a plurality of locations spaced along the groove. In another aspect, a method of working V-shaped grooves according to the invention is set out in claim 4. The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings. Fig. 1 is a front elevation for explaining a inspecting method Of the prior art; Fig. 2 is a front elevation for explaining another inspecting method of the prior art; and Fig. 3 is a perspective view for explaining the inspecting method according to the invention. As shown in Fig. 3, according to the invention a stylus 3 is moved on surfaces 4 formed with V-shaped grooves 1 along broken lines in a direction perpendicular to a longitudinal direction of each of the V-shaped grooves 1 to measure coordinates of points on the surfaces 4 more than 20 per one groove. The stylus 3 is preferably a contacting type shape tester such as F available from Rank Tailor Hobson Co. A width (W) and a depth (M) of the V-shaped groove 1 are for example of the order of 150 µm and 100 µm. A pitch (L) of the V-shaped grooves 1 is of the order of 250 µm. An opening angle (ϑ) of the V-shaped groove 1 is more than 70°. Moreover, a stylus 3 having a tip end angle of 60° and a tip radius of 2 µm may be used. Coordinates of points more than 20 are measured, while the tip end of the stylus moves as indicated by the broken lines in fig.3. According to the invention, measured data within distances more than 10 µm at edges 5 and groove bottoms 6 of the grooves 1 as shown in Fig. 3 are removed from the data in order to avoid unstability in measured data. Remaining data over effective measuring lengths more than 40 µm are used to calculate shapes formed by straight lines with the aid of a calculating method such as the method of least squares or the like. In the present invention, the reason why measured points per one V-shaped groove are more than 20 is that errors in measurement may increase if the measured points are less than 20. Moreover, the measured data within the distances more than 10 µm from the edges and the groove bottom are excluded from all the measured data for the reason that the chipping, breaking off, caulking and the like are likely to occur within the portions in working and it is therefore difficult to cause the stylus 3 to follow along the lines exactly. Furthermore, only the measured data on the portions having the effective measured lengths of 40 µm are used for the calculations for the reason that the high accuracy can be obtained only from such data. With the above inspecting method according to the invention, the V-shaped grooves can be inspected with an accuracy of the order of 0.2 µm. The working method according to the invention will be explained hereinafter. In the working method, a circle 7 having a diameter D equal to those of bodies (optical fibers) to be supported in the V-shaped grooves is drawn so as to inscribe an interior of a V-shaped groove obtained in the calculation above described. Thereafter any shifting distance of a center O of the circle 7 from a set position of the center O is obtained and then fedback to a working process. Only the position of the center O of the circle 7 is considered in this manner for the reason that it is most important that centers of optical fibers and the like are accurately set when they are arranged in the V-shaped grooves. In other words, slight errors in shape of the grooves are acceptable so long as the centers of the optical fibers are accurately determined. When the shifting of the center position is fed-back to the working process, a relative position between a rotating grinding wheel and a chip is determined according to signals of the feed-back, and a depth Z from the surface of the tip to the center O of the circle 7 and a pitch L of V-shaped grooves are compensated for. In this manner, according to the invention even change in shape of the V-shaped grooves and the like caused by wear of the tip end of rotating grinding wheels can be accurately detected. If a machine tool having a resolving power of 0.1 µm, V-shaped grooves can be worked with high accuracy of 0.3-0.5 µm. As can be seen from the above explanation, according to the invention it is possible to accurately inspect with accuracy of the order of submicrons fine V-shaped grooves which would be impossible to be measured by usual surface roughness testers in view of measuring lengths and cut-off values, and it is also possible to work such grooves with the aid of results of the inspection. Therefore, methods according to the invention inspect and work with high accuracy fine V-shaped grooves of connector substrates, jigs for welding optical fibers, and jigs for assembling various kinds of sensors to prove great effectiveness in presumption of optical transmission losses and improvement of positioning accuracy. Accordingly, the invention greatly contributes to development of industries as inspection and working methods eliminating all the difficulties in the prior art.

Claims: A method of inspecting a V-shaped groove (1) in a surface of a substrate which receives an optical fibre in an optical fibre connector, comprising the steps of (a) measuring coordinates of more than 20 points of the V-shaped groove on the surface (4) of the substrate, (b) discarding from the measured data so obtained the data obtained within regions which respectively extend from the edges (5) and the bottom (6) of the groove, to points not less than 10 µm from the respective edge or the bottom of the groove, and (c) calculating the shape of the V-groove as a V-groove shape consisting of straight lines on the basis of the remaining measured data, said remaining measured data relating to portions of said surface having effective measured lengths of more than 40 µm. A method according to claim 1 wherein said coordinates are measured by moving a stylus (3) of a contacting type shape tester in a direction perpendicular to the longitudinal direction of the V-shaped groove. A method according to claim 1 or claim 2 wherein said effective measured lengths consist of or include flank regions of the groove. A method of working a V-shaped groove (1) in a substrate, comprising calculating the position of the center of a circle (7) having a diameter substantially equal to that of an element to be supported in the V-shaped groove, which circle is inscribed in an interior of a V-groove shape calculated by the method as set forth in claim 1, and working the V-shaped groove while feeding back errors in the thus calculated center position of the circle relative to a predetermined center position into the working process of the V-shaped groove. A method of working as set forth in claim 4, wherein the relative position between a tool for working the V-shaped groove and the substrate is determined according to the feed-back signals to compensate for the shape of the V-shaped groove being worked. A method according to any one of claims 1 to 5 wherein said substrate is a part of an optical fibre connector and said surface of said substrate is a surface which receives an optical fibre in an optical fibre connector.

Inventors: NOMOTO, SUSUMU, OTA, TAKASHI, TSUJI, HIROYUKI
Applicants: NGK INSULATORS, LTD.
Application year: 1989
Main classification: G01B21
IPC codes: G01B21, G02B6