Method of testing split ceramic alignment sleeve for an optical fibre connector and apparatus therefor

Abstract: A cylindrical part having an axial slit and called a split alignment sleeve (2) is used in an optical fiber connector for connecting optical fibers to each other. The split alignment sleeve (2) is made of a ceramic material, and the characteristics of the optical fiber connector can be largely improved. Since the split ceramic alignment sleeve (2), however, is brittle, its mechanical strength may be degraded, and the sleeve may be damaged during use for a long period of time. In order to proof the strength reliability of the split ceramic alignment sleeve (2), a predetermined stress is applied to it during a manufacturing inspection to perform a proof test having a criterion for ensuring not to damage the sleeve. The present invention provides an easy, low-cost test method and an apparatus therefor. More specifically, since a test load is applied from the inner circumferential surface (15a) of the split ceramic alignment sleeve, the shape, structure, and assembly of the loading part of a test apparatus are disclosed, and a proof test method of the split ceramic alignment sleeve by using the test apparatus is also disclosed.

Description: BACKGROUND OF THE INVENTION : Field of the Invention The present invention relates to a method of testing a split ceramic alignment sleeve used in an optical fiber connector used in optical fiber communications and a device therefor. Description of Prior Art A typical conventional optical fiber connector has a well-known structure in which an optical fiber is fixed at the center of a solid cylindrical ferrule, the resultant assembly is fitted in a hollow cylindrical alignment sleeve having an accurate inner diameter, and end faces of the ferrules are aligned with and abut against each other. The most popular alignment sleeve used in the above optical fiber connector is a split alignment sleeve having a slit in an axial direction of the solid cylindrical ferrule. A typical example of the conventional split alignment sleeve is made of phosphor bronze. However, split ceramic alignment sleeves are also manufactured. In particular, a split zirconia ceramic alignment sleeve having the same material as a zirconia ferrule is used in the connection of zirconia ceramic ferrules having mating portions made of zirconia ceramics. It is known that stabler connection characteristics than those obtained by using the split phosphor bronze alignment sleeve can be obtained (JAP-PAT-KOKAI NO. 33110/1990). The following conventional method is known as a method of evaluating a defective/nondefective split ceramic alignment sleeve before it is used in an optical fiber connector. First of all, flaw detection of a split alignment sleeve is generally performed as quality proof in the manufacture. More specifically, a flaw on the surface of a split alignment sleeve is dyed with a dyestuff, and the presence/absence of a flaw is visually checked. This method is called a color check method. Alternatively, light from a light source is transmitted through a split alignment sleeve to check the presence/absence of the flaw. In these test methods, a quantitative proof test of split ceramic alignment sleeves undesirably cannot be performed. A proof test method capable of applying a specific mechanical load on each split alignment sleeve to perform a quantitative proof test for lifetimes of split ceramic alignment sleeves, which test has been rarely satisfactorily performed by the conventional flaw detection methods, is disclosed (JAP-PAT-KOKAI NO. 2-231545/1990). Fig. 1 shows a test method in which L-shaped upper and lower loading parts A and B are inserted into a slit 3 of a split ceramic alignment sleeve 2 and test loads are applied to the L-shaped upper and lower loading parts A and B to open the slit 3. Fig. 2 shows another test method in which test loads are applied to flat upper and lower loading parts C and D so as to clamp the split ceramic alignment sleeve 2. These proof test methods can quantitatively perform a lifetime proof test of split ceramic alignment sleeves and can supply highly reliable split ceramic alignment sleeves. Regardless of these advantages, the method using a tensile strength test tool, as shown in Fig. 1, requires cumbersome operations for attaching the L-shaped upper and lower loading parts A and B into the slit 3 or detaching them from the slit 3, thus degrading operability. In addition, the size of the slit 3 is small, and excessive loads act on the L-shaped upper and lower loading parts A and B to test a high-strength member such as a split ceramic alignment sleeve, thus causing damage to the loading parts A and B. In the method shown in Fig. 2, tensile stresses act on the peripheral portions of the split alignment sleeve 2. This method is not suitable as a proof test method of a split alignment sleeve generally used to receive a tensile stress on the inner circumferential surface of the split alignment sleeve 2. It is therefore an object of the present invention to provide a highly reliable method of testing a split ceramic alignment sleeve so as to easily allow lifetime proof. It is another object of the present invention to provide a test method capable of easily performing a test of a split ceramic alignment sleeve. DISCLOSURE OF THE INVENTION : A split alignment sleeve is used in an optical fiber connector for connecting optical fibers to each other. When the split alignment sleeve is made of a ceramic material, characteristics of the optical fiber connector can be greatly improved. However, a split ceramic alignment sleeve is a brittle material, its quality must be proven by a proof test prior to use in an optical fiber connector. It is an object of the present invention to provide a highly reliable method of testing a split ceramic alignment sleeve so as to easily ensure lifetime proof, and a test device therefore. In order to achieve the above object of the present invention, there is provided a test device as defined in claim 1 and a test method as defined in claim 5 and using this device. A piezoelectric device or a dielectric sandwiched between electrodes is stacked on the stationary member. The test load can be detected by this piezoelectric device or dielectric. BRIEF DESCRIPTION OF THE DRAWINGS : Fig. 1 is a view showing a conventional method of testing a split ceramic alignment sleeve, wherein test loads are applied to increase the size of a slit; Fig. 2 is a view showing another conventional method of testing a split ceramic alignment sleeve, wherein test loads are applied to compress the split alignment sleeve; Figs. 3(a) and 3(b) are views showing the structure of a split ceramic alignment sleeve; Figs. 4(a) and 4(b) are views showing the first embodiment of the test device used in the proof test of a split ceramic alignment sleeve according to the present invention; Figs. 5(a) and 5(b) are views showing the second embodiment of the test device used in the proof test of a split ceramic alignment sleeve according to the present invention; Fig. 6 is a view showing the third embodiment of the test device used in the proof test of a split ceramic alignment sleeve according to the present invention; Figs. 7(a) and 7(b) are views showing the fourth embodiment of the test device used in the proof test of a split ceramic alignment sleeve according to the present invention; Fig. 8 is a view showing the fifth embodiment of the test device used in the proof test of a split ceramic alignment sleeve according to the present invention; and Fig. 9 is a flow chart showing the proof test sequence of a split ceramic alignment sleeve according to the present invention. BEST MODE OF CARRYING OUT THE INVENTION The present invention will be described in detail with reference to the accompanying drawings. Figs. 3(a) and 3(b) are views showing the structure of a split ceramic alignment sleeve, in which Fig. 3(a) is a front view thereof, and Fig. 3(b) is a side view thereof. A split alignment sleeve 2 has a slit 3 having a width W₁, and its inner diameter is d . (First Embodiment) Figs 4(a) and 4(b) show an arrangement of a split ceramic alignment sleeve test device according to the first embodiment of the present invention, in which Fig. 4(a) is a front view thereof, and Fig. 4(b) is a partially cutaway side view thereof. Referring to Figs. 4(a) and 4(b), reference numeral 1 denotes a loading part divided into an upper, stationary member 1a and a lower, movable member 1b. The movable and stationary members are in contact with each other through their inclined surfaces 4 descending to the lower right direction along the longitudinal direction of the loading part 1. The upper, stationary member 1a is held in a holder 6 fixed by a projection 5, and a clearance 7 is present between the projection 5 and the holder 6. The upper, stationary member 1a can be vertically moved with respect to the holder 6. The upper, stationary member 1a is stacked with a piezoelectric device 10 to sandwich the inclined surfaces 4, and the piezoelectric device 10 extends in a direction normal to the axial direction. The lower movable member 1b is connected to an actuator 11 and can be moved in a horizontal direction indicated by α. In the state of Figs. 4(a) and 4(b), the distance ℓ between the ridgelines 9 and 9′ is slightly smaller than the inner diameter of the split alignment sleeve 2 shown in Figs. 3(a) and 3(b). Procedures of a method of testing the split ceramic alignment sleeve 2 by using the test method of the first embodiment will be described below. The split alignment sleeve 2 is fitted on the loading part 1. Since the relationship between the thickness ℓ of the loading part 1 and the inner diameter d of the split alignment sleeve 2 is given by ℓ < d, the split alignment sleeve can be easily fitted on the loading part 1. The actuator 11 is actuated to give a displacement α to the lower, movable member 1b in a direction indicated by the arrow in Fig. 4(b). The lower movable member 1b is slid along the inclined surface 4 of the upper, stationary member 1a, so that the upper, stationary member 1a is pushed upward through the inclined surface 4 of the movable member 1b. At this time, since a clearance 7 is formed between the projection 6 and the holder 6, the upper, stationary member 1a floats upward to increase the thickness ℓ of the body of the loading part. When the displacement α is appropriately set, condition ℓ > d is established. A test load β (Fig. 3(a)) in a direction to increase the width of the slit 3 is applied through the loading part uniformly in the circumferential and longitudinal directions of the split alignment sleeve 2. Since the piezoelectric element 10 on the upper, stationary member 1a has the nature of generating a voltage corresponding to the load, the test load β can be monitored by measuring the voltage of the piezoelectric device 10 during the test. Therefore, the displacement α can be controlled. (Second Embodiment) Figs. 5(a) and 5(b) show an arrangement of a split ceramic alignment sleeve test device according to the second embodiment of the present invention, in which Fig. 5(a) is a front view thereof, and Fig. 5(b) is a partially cutaway sectional view thereof. The second embodiment is different from the first embodiment in that the upper, stationary member 1a has a stop projection 8 at its free end, and the stop projection has a height slightly smaller than the width W₁ of the slit 3 of the split alignment sleeve 2. The procedure of the method of testing a split ceramic alignment sleeve 2 by using the test device of the second embodiment are substantially the same as those of the first embodiment, except that the stop projection 8 is fitted in the slit 3 of the split alignment sleeve 2, and the split alignment sleeve 2 is fitted on a loading part 1, the split alignment sleeve 2 is rotated about its axis upon passing of the slit 3 over the stop projection 8, and the end face of the split alignment sleeve 2 abuts against the rear end of the stop projection 8, as shown in Fig. 5(b). The methods of testing the split ceramic alignment sleeves by using the test devices of the first and second embodiments have the following features. (1) Since a test can be performed by inserting the loading part 1 into the split alignment sleeve 2 and displacing the lower movable member 1b, the test can be simply performed at low cost, and productivity of split ceramic alignment sleeves can be improved. (2) Since the loading part 1 receives a uniform compression force and a small tension along its longitudinal direction, it is rarely deformed. As compared with conventional methods, the loading portion and the portion for supporting the loading portion need not be increased in size. The test device can be made small at low cost. (3) Since the piezoelectric device for detecting the load during the test is arranged on the upper, stationary member, the test can be performed with high precision. In the first or second embodiment, it is possible to fix the lower, movable member 1b and apply the displacement α to the upper, stationary member 1a in a reverse direction by connecting the actuator 11 to the holder 6, to give a front shape to the loading part 1 other than that shown in Fig. 4(a) or 5(a), and to divide the loading part 1 into three or more parts. In addition, the test load β is further increased to destroy the split alignment sleeve 2 and to measure the mechanical strength of the split alignment sleeve 2 from the piezoelectric device voltage obtained at the time of destruction. (Third Embodiment) The third embodiment of the present invention will be described below. Fig. 6 is a partially cutaway sectional side view showing an arrangement of a split ceramic alignment sleeve test device according to the third embodiment. In the third embodiment, a dielectric 14 sandwiched between electrodes 12 and 13 is stacked in place of the piezoelectric element 10 of the second embodiment shown in Fig. 5(b). The reference numerals as in the second embodiment denote the same parts in the third embodiment. In the third embodiment, the load reaction acting on the split alignment sleeve 2 acts on the dielectric 14, and the thickness of the dielectric 14 is changed in accordance with this reaction. The electrostatic capacitance between the electrodes 12 and 13 is changed. The electrostatic capacitance of the dielectric 14 is measured to monitor the test load β acting on the split alignment sleeve. Other functions in the third embodiment are the same as those of the second embodiment. The same features as in the first or second embodiment can be obtained in the third embodiment. (Fourth Embodiment) The fourth embodiment of the present invention will be described below. Figs. 7(a) and 7(b) show an arrangement of a split ceramic alignment sleeve test device according to the fourth embodiment, in which Fig. 7(a) is a front view thereof and Fig. 7(b) is a partially cutaway side view thereof. Referring to Figs. 7(a) and 7(b), reference numeral 15 denotes a loading part for applying a load on a split ceramic alignment sleeve 2. The loading part 15 is divided into an outer, stationary member 15a and an inner, movable member 15b. The inner circumferential surface of the outer, stationary member 15a is frustoconical. The outer, stationary member 15a has a cylindrical shape having a slit 15c extending along the longitudinal direction. The outer, stationary member 15a is held in a holder 17 fixed by a projection 16. A clearance 18 is formed between the projection 16 and the holder 17, and the outer, stationary member 15a can be deformed in a direction to open the slit 15c. The inner, movable member 15b is a rod-like member having an outer circumferential frustoconical surface, connected to an actuator 19, and moved in a horizontal direction indicated by the arrow α. The outer, stationary member 15a and the inner, movable member 15b are in contact with each other through the inclined surface 20 (outer, stationary member) as a frustoconical inner circumferential surface and the inclined surface 21 (inner, movable member) as an outer circumferential surface. In a state shown in Fig. 7(b), an outer diameter ℓ of the outer, stationary member 15a is slightly smaller than the inner diameter d of the split alignment sleeve 2. A test method of the split ceramic alignment sleeve 2 by using the test device according to the fourth embodiment will be described below. The split alignment sleeve 2 is inserted onto the outer, stationary member 15a of the loading part 15. At this time, since the relationship between the outer diameter ℓ of the outer, stationary member 15a and the inner diameter d of the split alignment sleeve 2 satisfies condition ℓ < d, the split alignment sleeve 2 can be easily inserted into the outer, stationary member 15a. The actuator 19 is actuated to give a displacement α to the inner, movable member 15b in the direction of the arrow. The inclined surface 21 of the inner movable member 15b and the inclined surface 20 of the outer, stationary member 15a slide over each other, and the outer, stationary member 15a is deformed in a direction to increase the width of the slit 15c, thereby increasing the distance ℓ. When the displacement α is appropriately set as in the first to third embodiments, the outer diameter ℓ of the outer, stationary member 15a is set to be larger than the inner diameter d of the split alignment sleeve 2 (ℓ < d). A load is applied from the loading part 15 to increase the width of the slit 3 uniformly in the circumferential and longitudinal directions of the split alignment sleeve. Therefore, a test load β (Figs. 3(a) and 3(b)) acts on the split alignment sleeve 2. A method of testing the split ceramic alignment sleeve 2 using the test device of the fourth embodiment has the feature that no relative motion between the outer, stationary member 15a and the split alignment sleeve 2 is present. In the fourth embodiment, when a piezoelectric device is stacked on the outer, stationary member 15a, the test load β can be monitored. The same effect as in the first or second embodiment can be obtained in the fourth embodiment. In addition, even if the outer, stationary member 15a and the inner, movable member 15b have any shape other than cylindrical and columnar shapes, the same effect as in the fourth embodiment can be obtained if the given shape has the same function as that of the fourth embodiment. (Fifth Embodiment) The fifth embodiment of the present invention will be described below. Fig. 8 shows an arrangement of a split ceramic alignment sleeve test device according to the fifth embodiment. Referring to Fig. 8, reference numeral 30 denotes a loading part for applying a test load to a split ceramic alignment sleeve 2. The loading part 30 comprises a lower, stationary member 30a and an upper, movable member 30b. The lower, stationary member 30a and the upper, movable member 30b are in contact through their inclined surfaces 40. Although the upper, movable member 30b is held by a holder 34, the upper, movable member 30b can be vertically moved and can be moved in a right-and-left direction in accordance with the holder 34. The lower, stationary member 30a is fixed on a base 33. The holder 34 is fixed on a guide mechanism 32, and the guide mechanism 32 is connected to an actuator 31. The upper, movable member 30b is driven by a displacement γ by means of the actuator 31 in the right-and-left direction. A position detector 35 detects the position of the right-and-left displacement γ of the guide mechanism 32, and consequently the position of the upper, movable member can be detected. A controller 36 controls the operation of the actuator 31 on the basis of the detection signal 38 of position from the position detector 35. More specifically, a control signal 39 is sent to the actuator 31 to control its operation. Test procedures of the split ceramic alignment sleeve 2 by using the test device of the fifth embodiment will be described below. The split ceramic alignment sleeve 2 is inserted onto the loading part 30. The diameter of the loading part 30 is slightly smaller than the inner diameter d of the split ceramic alignment sleeve 2. In this state, when the actuator 31 is driven by the control signal 39, the upper, movable member 30b is driven through the guide mechanism 32 and the holder 34. As in the first to third embodiments, a test load is applied to the split ceramic alignment sleeve 2. In the process wherein the test load is applied, the position signal 37 is input from the guide mechanism 32 to the position detector 35 upon a displacement of the upper, movable member 30b, and the position detector 35 sends the detection signal of position to the controller 36. When the controller 36 detects a displacement of the upper, movable member 30b corresponding to a predetermined test load, the controller 36 sends the control signal 39 to the actuator 31, thereby stopping the actuator 31. The controller 36 then sends an instruction in the form of the control signal 39 to the actuator 31 to move the upper, movable member 30b in the direction to release the test load acting on the split ceramic alignment sleeve 2. The guide mechanism 32 is moved by the actuator 31. when the controller 36 detects through the position detector 36 that the upper, movable member 30b returns to the position where the split ceramic alignment sleeve 2 is inserted, the controller 36 sends a control signal to the actuator 31, thereby stopping the actuator 31 and hence completing the proof test. Since the proof test of the split ceramic alignment sleeve by using the test device according to the fifth embodiment can be performed automatically, test efficiency can be improved, and the test cost can be reduced. It is possible to use any one of the loading parts of the first to fourth embodiments as the loading part of the fifth embodiment, as a matter of course. Procedures of a proof test method using the split ceramic alignment sleeve test devices of the first to fourth embodiments will be described below. Fig. 9 is a flow chart of the procedures of the proof test method of the split ceramic alignment sleeve of the present invention. The proof test procedures are represented by the following steps. (1) The movable and stationary members of the loading part are located so that the thickness of the body is slightly smaller than the inner diameter of the split ceramic alignment sleeve. At this time, the relative position between the movable and stationary members is defined as the initial position. (2) The split alignment sleeve is inserted onto a portion of the loading part which has a cantilevered structure (i.e., a beam portion) from the free end of the beam portion along the longitudinal direction of the split alignment sleeve until the split alignment sleeve entirely overlaps the beam portion. (3) The movable member of the loading part is driven to be in slidable contact with the stationary member through the inclined sliding contact surfaces in the longitudinal direction of the beam portion an in a direction to increase the thickness of the body until one of the following conditions is satisfied, i.e., (a) until the piezoelectric device or the dielectric stacked on the loading part detects the predetermined test load, or (b) until the split alignment sleeve is enlarged by an amount corresponding to the predetermined test load. (4) The movable member is returned to the initial position. (5) The split alignment sleeve is removed from the free end of the beam portion of the loading part along the longitudinal direction of the split alignment sleeve. (6) The test result is evaluated. An evaluation criterion is given such that the split alignment sleeve is not damaged during movement of the movable member along the stationary member for a period of time immediately after procedure (1) is started and immediately before procedure (5) is completed. As described above, since a test method and an device therefor according to the present invention facilitate a proof test of a split ceramic alignment sleeve by simple procedures, the test efficiency can be improved, and the test cost can be reduced. Since the loading part is not susceptible to deformation and a uniform load acts on the split ceramic alignment sleeve with a simple structure, the test device can be made compact at low cost. Since the test device comprises a device for detecting a load during a test, a highly accurate test can be performed. The proof test method and the device therefor according to the present invention are also effective to proof the strength reliability of a C-shaped ceramic ring in addition to split ceramic alignment sleeves.

Claims: A device for testing the quality of a split alignment sleeve on the basis of a criterion which ensures that said split alignment sleeve is not damaged by a predetermined load applied before said split alignment sleeve is used in an optical fibre connector, said split alignment sleeve (2) having a longitudinal slit and being made of a ceramic material, and being intended to be used in an optical fibre connector for aligning end faces of a pair of ferrules fitted in said split alignment sleeve, said device comprising a loading part (1,15,30) having a two-part body, said loading part being insertable into said split alignment sleeve to apply the predetermined load to said split alignment sleeve, said body consisting of a movable member (1b,15b,30b) and a stationary member (1a,15a,30a) having a form suitable for mounting as a cantilever, the cantilever mounting end of said stationary member being opposite to the end which is to be inserted into said sleeve, wherein said members have inclined sliding surfaces which are kept in slidable contact with each other along the axial direction of said sleeve when the body is inserted therein, a holder holding the stationary member at its mounting end (5, 16), detecting means (10,14) for detecting the load applied to the inner circumference of said sleeve and mounted in said stationary member, and an actuator (11,19,31) for moving said movable member relative to said stationary member, wherein said mounting end (5, 16) of said stationary member is freely movable along a normal to said axial direction, said movable member is reciprocatively moveable in said axial direction, so that said inclined surfaces slide relative to each other, such that the thickness of said body in the direction of said normal increases, thus causing the predetermined load to be applied to the inner circumferential surface of said sleeve, said thickness of the body depending on the relative position of the moveable and the stationary member such that the minimum thickness is smaller than and the maximum thickness is larger than the inner diameter of said split alignment sleeve. A device according to claim 1, wherein said detecting means (10, 14) is a piezoelectric device stacked between parts of said stationary member (1a, 15a, 30a) of said loading part (1, 15, 30) in the direction of said normal. A device according to claim 1, wherein said detecting means (10, 14) is a dielectric sandwiched between electrodes and stacked between parts of said stationary member (1a, 15a, 30a) of said loading part (1, 15, 30) in the direction of said normal. A device according to claim 1, further comprising a position detector (35) for detecting the position of said movable member (1b, 15b, 30b) of said loading part (1, 15, 30), and a controller (36) for controlling reciprocal motion of said movable member on the basis of an output signal from said position detector (35). A method of testing a split alignment sleeve (2) on the basis of a criterion which ensures that said split alignment sleeve is not damaged by a predetermined load applied before said split alignment sleeve is used in an optical fibre connector, said method using a test device comprising a loading part (1, 15, 30) having a two-part body, said loading part (1, 15, 30) being insertable into said split alignment sleeve (2) to apply the predetermined load to said split alignment sleeve, said body consisting of a movable member (1b, 15b, 30b) and a stationary member (1a, 15a, 30a) and said members having inclined sliding surfaces (4, 20, 21) which are kept in slidable contact with each other along the axial direction of said sleeve when the body is inserted therein, the body having a thickness defined by the movement of the two members (1a, 1b, 15a, 15b, 30a, 30b) over their sliding surfaces, and being able to apply a load to the inner circumferential surface of the split alignment sleeve (2), said load having a magnitude determined by the thickness of the two part body, said test method comprising the steps of : locating the movable member (1b, 15b, 30b) in an initial position in which the thickness of the two part body is smaller than an inner diameter of said sleeve (2), inserting the body into the split alignment sleeve (2), moving said movable member (1b, 15b, 30b) by a moving distance calculated in advance until the thickness of the body reaches a value at which the predetermined load is applied to said sleeve (2), or calculating whether a predetermined test load is achieved by load detecting means (10, 14) subsidiarily provided to said stationary member (1a, 15a, 30a), if the predetermined load is achieved, removing the load ; and determining whether the split alignment sleeve is damaged.

Inventors: IWANO SHIN ICHI, KANAYAMA KAZUNORI, NAGASE RYO, SUGITA ETSUJI, IWANO, SHIN'ICHI, KANAYAMA, KAZUNORI, NAGASE, RYO, SUGITA, ETSUJI
Applicants: NIPPON TELEGRAPH & TELEPHONE, NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Application year: 1990
Main classification: G02B6
IPC codes: G01N3, G02B6, G01N33