In general, the convention lens grinding apparatus can be largely divided into two kinds, depending on whether a holder shaft in the tip direction is always pressing the spherical center of a grinding dish or not. The present invention relates to the former apparatus wherein lenses are ground by being swung about the spherical center of the grinding dish as a grinding center. In this type of apparatus, there is a system wherein the grinding dish is swung and a system wherein the holder shaft on which the lens is mounted is swung. In the latter, the adjustment of the machine is so difficult that the swing angle will vary and due to the error the lens will be pressed in an unbalanced state resulting in low reproducibility of the lens radius R. In addition, as a result of this unbalance, the grinding dish will be worn unevenly and the grinding dish radius R and swinging state will have to be frequently readjusted. In the latter situation, concave lenses will present few problems, but with convex lenses many problems will arise. Also, in this method, as the holder shaft (upper shaft) is swung, the control in the structure will be complicated and the stability of the machine will be low.
Therefore, the method wherein the grinding dish is swung about the spherical center of the dish has come to be conventionally adopted. In this method, however, as the entire dish support is swung like a pendulum through the rotation of a cam or crank, usually by a motor or the like, the weight of the entire dish support, swung by the rotating angle of the cam or crank, will be added, the swinging speed will become unstable and the swinging frequency will be difficult to increase.
As a result, there will be produced the following defects:
(1) When the swinging direction rises, all the weight including that of the swinging base will be added, but on the contrary, when the swinging direction lowers, the dish support will be pushed in by the weight of the load and the swinging speed will become non-uniform.
(2) For the foregoing reason at the turning point of swinging, the cam and crank will be braked so suddenly that the grinding dish will be instantaneously swung in the reverse direction. At this time, a severe shock will be caused. In order to make the apparatus endure such shock, structural and economical problems must be overcome.
(3) In order to adjust the cam and crank, the fulcrum must be changed. In order to change the swinging angle and amplitude, they must be separately set. Further, as adjustments by hand and sense are required, there will be no reproducibility. Needless to say, fine adjustments are quite impossible.
Further, in the conventional lens grinding systems, as only one lens can be ground at any one time, the work efficiency is low and further, as the steps of conveying, feeding and removing the lenses are made by hand, it is impossible to grind many lenses at once.
It is the object of the present invention to solve such problems as are mentioned above by providing the following:
(1) An air cylinder or oil pressure cylinder is used for the swinging power so that within the swinging range, the swinging speed will be very natural as in a pendulum and, near the turning point of swinging, the air within the cylinder will acts as an air cushion to reduce the sudden shock of turning;
(2) All the so called grinding steps of feeding, grinding and removing the lenses are automated and these operations are continuous;
(3) The lenses are conveyed continuously between the respective operating steps;
(4) The mechanical adjustment, so far made only by the human sense, can be made numerically, so that errors will be few and the finished lenses will be of a good and high quality;
(5) The operations of conveying the lenses to the lens grinding tank and positioning the lenses are made by an air cylinder;
(6) The grinding apparatus is provided with a lens conveying and positioning device wherein four basic shafts are rotated at a pitch of 1/4 rotation and a lens conveying and positioning device wherein two horizontal basic shafts are operated simultaneously;
(7) Further, the entire apparatus itself is unified and compacted.