Method and apparatus for making a spark plug with a predetermined spark gap

#The present invention relates to a method and apparatus for making a spark plug.

#In a spark plug for use in an internal combustion engine, the accuracy in positioning a ground electrode and a center electrode is important. For example, there possibly occurs such a case in which the center lines of the ground electrode and center electrode with a spark gap being disposed therebetween are eccentric due to defective bending of the ground electrode, displacement of a noble metal attached to one of or each of the electrodes, etc. Such eccentricity will lead to, for example, a short life due to a partial electrode consumption and a trouble of misfire. Further, a spark gap larger than a predetermined value requires an excessively high discharge voltage so as to disable the spark plug to fire. On the other hand, a spark gap smaller than a predetermined value tends to cause short of the spark gap, etc.

#For adjustment of the eccentricity between the electrodes and the spark gap, it is known a method of treating the ground electrode by an adjustment bending by means of a bending machine having a pressing punch. For example, in Japanese Patent Unexamined Publication No. 3-64882 is disclosed a method of repeatedly pressing the ground electrode by means of a pressing punch until the spark gap is adjusted to a target value while monitoring the spark gap by means of a CCD camera. In this instance, a target spark gap is set smaller than an ideal spark gap by a predetermined value with consideration of spring back of the ground electrode upon release of a pressing force on the ground electrode.

#FIG. 1 is a schematic view of an electronic photography system of an apparatus for carrying out a method of making a spark plug according to the present invention;

#FIG. 2 is a block diagram showing a main control section of the apparatus for controlling an adjustment bending device that is used in the method of the present invention for performing an adjustment bending process;

#FIG. 3 is a schematic view showing a field of vision of a camera;

#FIG. 1 shows an electronic photography system 22 of an apparatus 1 for carrying out a method of making a spark plug according to an embodiment of the present invention. In the figure, a spark plug (hereinafter also referred to simply as work) 50 includes a center electrode 53 that is disposed inside an insulator 52 and a ground electrode 54 that has a base end side attached to a leading end surface 51a of a metallic shell 51 disposed outside the insulator 52. The ground electrode further has a leading end side disposed opposite to the center electrode 53 so as to form a spark gap g between the center electrode 53 and the ground electrode 54. More specifically, the work 50 is of such a kind that the ground electrode 54 is bent toward the center electrode 53 side so as to have a leading end side surface that faces the leading end surface of the center electrode 53 and form therebetween a spark gap g. In this embodiment, the leading end portion of the center electrode 53 is comprised of a noble metal chip 53a (hereinafter also referred to as leading end portion 53a) made of a Ni alloy and welded to a leading end of a center electrode main body (no numeral).

#The photography system 22 includes a light 19 and a camera 4. The camera captures an image VA of the work 50 while lighting the work 50 by the light 19.

#Based on the image VA obtained by this photography operation, information on the positions of the ground electrode 54 and the center electrode 53 is analyzed and acquired. The analysis and acquisition of the information on the positions is executed by a computer 10 (refer to FIG. 2) that functions as an analysis device and a control device.