Patent Number: 
Section: claims

1. A method of manufacturing a rotation detector that comprises a semiconductor chip, a nonmagnetic case body, a biasing permanent magnet and a nonmagnetic cap fixed to the case body for accommodating therein the semiconductor chip and the biasing permanent magnet, wherein: the case body has a joint surface; and the cap has an inside surface in contact with the joint surface, the method comprising:assembling the semiconductor chip, the case body and the biasing permanent magnet into a unit;forming at least one groove adjacent to the joint surface so as to form a space between the joint surface and the inside surface when the cap is fixed to the case body;fixing the cap to the case body so that the inside surface of the cap can be in contact with the joint surface;irradiating a laser beam at portions behind the inside surface of the cap under a prescribed pressure to melt materials of the case body and the cap and to make melted materials flow to the space;filling the melted materials in the space under the prescribed pressure;stopping irradiation of the laser beam when the melted materials function to gradually stop reducing a height of the inside surface of the cap from the joint surface of the case body; andcooling the melted materials to re-crystallize. 2. A method as in claim 1, wherein the laser transmittance of the case body is less than the laser transmittance of the cap. 3. A method as in claim 2, wherein:each of the case body and the cap is made of polyphenilene sulfide; andthe case body contains more carbon black than the cap. 4. A method as in claim 1, further comprising rotating the case body and the cap while irradiating a laser beam. 5. A method as in claim 4, wherein the pressure in irradiating is applied to the bottom end of the cap. 6. A method as in claim 1, wherein:the joint surface of the case body is tapered; andthe inside surface of the cap is shaped conical to be in close contact with the joint surface. 7. A method as in claim 1, wherein:the joint surface of the case body is tapered;the joint surface of the case body has a plurality of ring-shaped grooves, including the at least one groove, that circumferentially surround the joint surface on the opposite sides thereof; andthe inside surface of the cap is shaped conical and the conical inside surface confronts the tapered joint surface.