The present invention relates to an apparatus and a method for cutting a plastic optical fiber adapted for optical communication, which fiber has on its outer periphery a coating including a cladding layer.
Cutting of ends of plastic optical fibers for optical communication in order to mount the plastic optical fibers to optical signal connector plugs has been performed, for example, by pressing a sharp cutter to a plastic optical fiber, thereby shearing it with the pressing force (see Japanese Utility Model Registration No. 2573619). Such forcible cutting, however, causes an inconvenience that chips and/or cracks may occur in a cut plane of the plastic optical fiber, to degrade an accuracy of work in the subsequent step of forming an end face of the plastic optical fiber. To cope with such an inconvenience, an improved method has been disclosed, for example, in Japanese Patent Laid-open No. Hei 7-294748, wherein a plastic optical fiber is cut in a state that temperatures of both a cutter and the plastic optical fiber are raised by heating, thereby preventing occurrence of chips and/or cracks in a cut plane of the plastic optical fiber. Such a method, however, presents another problem that the raised temperature may give rise to deformation of a portion, other than an end face, of the plastic optical fiber, degradation of optical characteristics of the interior of the plastic optical fiber, and the like.
In most of plastic optical fibers (POFs), thermoplastic polymethyl methacrylate (PMMA) is used as a material of a core of the POF, and a fluorine based resin is used as a material of a cladding layer formed on an outer peripheral portion of the core. In addition, at present, a plurality of kinds of plastic optical fibers, each of which is of a multi-mode type, are being commercially available.
In the case of connecting a plastic optical cable led from one equipment to another equipment by mounting a POF of the cable to a connector plug and inserting the connector plug in a receptacle provided on another equipment, it is required that no change in optical transmission characteristics may occur even if the cable be replaced with a new cable. FIG. 1A is a typical sectional view showing a connector plug inserted in a receptacle. As shown in this figure, an end portion, inserted in a center hole of a connector plug 11, of a POF 1 is formed in a spherical plane R having a specific radius, and a distance xe2x80x9caxe2x80x9d between the end portion of the POF 1 and a light receiving element 11c in equipment is set to a specific length.
The structure shown in FIG. 1A is designed such that a positional relationship between the receptacle 11b and the connector plug 11 can be kept constant even if the connector plug 11 is replaced with a new connector plug. As a result, the replacement of the connector plug 11 with a new connector plug does not exert any effect on transmission characteristics of the POF 1 insofar as a position of the spherical plane R of the end of the POF 1 to the connector plug 11 is kept constant.
The formation of an end face of the POF 1 as shown in FIG. 1B is performed by making use of thermoplasticity of the POF 1. More specifically, a forming die 11d having at its one end a concave plane of a specific radius is heated and is pressed to an end face of the POF 1 mounted to the connector plug 11. The end face of the POF 1 is softened by heat of the forming die 11d, with a result that the concave plane of the forming die 11d is transferred to the end face of the POF 1 as a convex plane R.
A volume of the softened resin is regarded not to be changed after the forming work. Accordingly, to keep constant the distance xe2x80x9caxe2x80x9d shown in FIG. 1A, the POF 1 must be mounted to the connector plug 11 such that a position of the end face to the connector plug 11 before formation of the convex plane R of the POF 1 is kept constant. For this reason, there has been adopted a method of mounting the POF 1 to the connector plug 11 with a sufficient excess portion projecting from the connector plug 11, and cutting the POF 1 at a specific position associated with the connector plug 11, thereby keeping constant the position of the convex plane R formed in the subsequent step.
Cutting of POFs has been often performed by using sharp cutting tools such as a commercially available cutter or razor. In this case, however, as shown in FIG. 1C, chips of a resin forming the POF main body and/or cracks may occur in a cut plane perpendicular to the axial line of the POF. Such chips and/or cracks may remain in an end face to be formed in the subsequent step as shown in FIG. 1B, to cause failures that change transmission characteristics, such as deficiency of a convex plane or cracking.
If a POF is cut with a previously heated cutter, as shown in FIG. 1D, a cladding layer and the like may extend longer in the form of whiskers, and such whiskers may adhere on a cut plane, to be rolled in a convex plane at the time of forming an end face of the POF, to degrade transmission characteristics of the POF.
By the way, a method of cutting a plastic material by using a cutter blade mounted to an ultrasonic vibration exciter has been known, for example, from Japanese Patent Laid-open No. Sho 58-175630, wherein the plastic material is cut by concentrating ultrasonic vibration at a portion to be cut of the plastic material via the cutter blade and imparting a force to the cutter blade being in contact with the plastic material.
To realize cutting of a POF with desirable optical transmission characteristics thereof kept, an attempt has been made to cut POFs by making use of such a high-frequency mechanical vibration cutting method or ultrasonic vibration cutting method. Even in the case of adopting this method, however, there may occur an inconvenience. Since a cladding layer and the like are provided on an outer peripheral surface of a core of a POF, when a cutter blade and the optical fiber are excessively heated (such heating occurs even by using a high-frequency mechanical vibration exciter), the cladding layer and the like may often extend longer in the form of whiskers and such whiskers may adhere on a cut plane, to be entrained in an end face of the POF at the time of forming the end face, thereby degrading transmission characteristics of the POF. Further, according to the related art high-frequency mechanical vibration cutting method, it is difficult to optimize working conditions required for obtaining a uniform finish cut plane, for example, a condition of determining the length of a cutoff piece of a POF.
An object of the present invention is to provide a method and an apparatus for cutting a plastic optical fiber, which are capable of reducing a load applied the plastic optical fiber upon cutting, thereby reducing degradation of transmission characteristics of the plastic optical fiber after cutting.
To achieve the above object, according to a first aspect of the present invention, there is provided a cutting apparatus for cutting a plastic optical fiber, including cutting means for cutting a plastic optical fiber, and positioning means for positioning the cutting means to at least a first position at which the plastic optical fiber is to be subjected to rough cutting, and to at least a second position at which the plastic optical fiber is to be subjected to finish cutting.
The cutting apparatus preferably includes vibration means for giving high-frequency mechanical vibration to a portion, being in contact with the plastic optical fiber, of the cutting means, and allowing the cutting means to heat and cut the contact portion of the plastic optical fiber.
To achieve the above object, according to a second aspect of the present invention, there is provided a cutting method of cutting a plastic optical fiber by using cutting means, including the steps of positioning the cutting means to a first position at which the plastic optical fiber is to be subjected to rough cutting, cutting the plastic optical fiber at the first position by the cutting means, positioning the plastic optical fiber to a second position at which the plastic optical fiber is to be subjected to finish cutting, and cutting the plastic optical fiber at the second position by the cutting means.
In the cutting method, preferably, in each of the cutting steps, the cutting means is heated by high-frequency mechanical vibration, to cut the plastic optical fiber.
The apparatus and method for cutting a plastic optical fiber according to the present invention, which are configured as described above, has the following effects:
Since a portion to be cut of a plastic optical fiber is finely cut while being heated by a sharp cutter blade representative of the cutting means, it is possible to significantly reduce a force applied to the plastic optical fiber upon cutting, and hence to prevent occurrence of chips and/or cracks in a cut plane of the plastic optical fiber and to prolong a service life of the cutter blade and reduce a cost required for replacement and adjustment of the cutter blade. Since the plastic optical fiber is thinly cut in the finish cutting step, it is possible to form an accurate, smooth cut plane of the plastic optical fiber, and hence to improve, in the subsequent step, an accuracy of forming an end face of the plastic optical fiber while preventing occurrence of a failure in this forming step.
In addition to the above-described basic configurations of the present invention, according to a preferable form of the present invention, an optimum temperature control may be performed in the finish cutting step. With this configuration, it is possible to prevent occurrence of an inconvenience caused by extension of a cladding layer and the like of the softened plastic optical fiber, without the need of any additional post treatment.
According to another preferable form of the present invention, the cutting apparatus having a large flexibility in working condition may be provided. More specifically, the working condition of the cutting apparatus can be changed variously in a wide range, for example, from a working condition adapted for cutting of plastic optical fibers in a very small quantity of a lot at a service shop to a working condition adapted for cutting of plastic optical fibers in a very large quantity of a lot at a factory, by changing a combination of basic cutting operations such as movement of a cutter blade representative of the cutting means in the cutting direction, movement of a plastic optical fiber in the direction perpendicular to the movement direction of the cutter blade, and control of a heating condition of the cutter blade due to high-frequency mechanical vibration.
According to a further preferable form of the present invention, the cutting means may be configured as a two-piece cutter blade element having a rough cutter blade and a finish cutter blade, with the two-piece cutter blade element mounted to one cutter haft. With this configuration, it is possible to simplify the cutting apparatus and the cutting works, and hence to reduce the cost required for cutting a plastic optical fiber.
According to still a further preferable form of the present invention, a plastic optical fiber may be mounted to a connector plug with a relatively longer excess portion projecting from the connector plug and the excess portion of the plastic optical fiber be repeatedly cut by several times. With this configuration, since the excess portion is repeatedly cut, it is possible to obtain a desirable cut plane of the plastic optical fiber, and since initial cutting of the excess portion of the plastic optical fiber may be roughly performed, it is possible to reduce the working cost, although the cutting is repeated by several times.
According to an additional preferable form of the present invention, a peripheral device such as a cooling device may be combined with the cutting device. With this configuration, the cutting device can be easily modified into that having a function satisfying a user""s specification. Further, since the cutting device can be modified into that having a function satisfying the minimum user""s specification, it can be matched with each user""s specification at a low cost.