JPS58129815A - Manufacture of small-sized crystal piece - Google Patents

Abstract

PURPOSE:To obtain a small-sized crystal piece with good characteristics efficiently by finishing the small-sized crystal piece near ends with adhesive grains of larger grain size than at the center part. CONSTITUTION:A crystal piece blank 4 is placed in a pipe made of cast iron together with abrasive grains of grain side (#400-1,000) and the pipe is rotated to perform so called piping work. Consequently, blank 4 is shaped into a crystal piece blank 7. In this case, curved surface 8 of ends of the crystal piece are nearly finished to finally necessary curved surfaces, but a little bit thicker. Then, the blank 7 is finished by lapping and/or polishing while using abrasive grains of less grain size (#2,000-4,000) to obtain flat parts 10 as center part of main surfaces. Lastly, the shape of the crystal blank 9 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a small crystal piece having both main surfaces having curved surfaces having a predetermined curvature.

In recent years, the time accuracy of mobile watches has improved dramatically since crystal oscillators were used as frequency standards, and the time accuracy of mechanical watches, which used to be a few seconds per day, has now increased to 5 to 10 seconds per month. Accuracy is now achieved.

However, the requirements for precision are becoming increasingly strict, and the reality is that recently there has been a particularly strong demand for high-precision clocks with a time accuracy of several seconds per year.

The time standard for such a high-precision clock is difficult to achieve using a simple method using a 32Kf (Z tuning fork type crystal oscillator). Thickness-slip crystal oscillators attracted attention, and more efforts were put into research and development.

However, this thickness-sliding crystal resonator is easy to design and manufacture to avoid the secondary vibration peculiar to this resonator in relatively large size devices used in communication equipment, clocks, etc. However, for small-sized watches that can be used in portable watches (approximately 6 cm or less), various ingenuity is required in the manufacturing method.

As shown in the cross-sectional view shown in Fig. 1, a conventional method for manufacturing a thickness-sliding crystal blank is to take a crystal blank 1 whose thickness dimension has been finished and whose surface has a circular or square external shape, and which has a predetermined curvature. The curvature of one end of the crystal was formed by rubbing little by little while supplying abrasive grains 3 with a bowl-shaped rotating plate 2.

Although this method is easy, it is not efficient because it involves molding one piece at a time, and the accuracy of forming the curved surface is also poor because the center of the axis of the main surface of the crystal piece may be misaligned with the center of curvature of the curved surface.

Therefore, in recent years, a method called piping, as shown in the perspective view shown in FIG. 2, has also been used.

This method has the advantage of being able to produce a large amount of crystal pieces at one time, but it also has the advantage of being able to produce a large amount of crystal pieces at once.

Since abrasive grains as coarse as GC are sometimes used, the principal surface is also roughened at the same time as the curved surface is formed, resulting in a dimensional change.

In particular, when it comes to crystal units used in mobile watches with a side ratio (ratio of thickness to outer diameter or side length) of 15 or less, the processing precision of the shape has a large effect on the characteristics. It is clear that changing the thickness dimension due to piping makes it difficult to fix the frequency of the secondary vibration with respect to the main vibration, which deteriorates the frequency of the crystal resonator characteristics and the temperature characteristics of the CI value. It is necessary that the surface roughness of the surface be good, but if the surface is rough, it becomes difficult to obtain good aging characteristics such as those aiming for yearly differences.

An object of the present invention is to improve the above-mentioned drawbacks of the manufacturing method and to efficiently manufacture a small crystal piece with good characteristics that can be used in portable watches.

The key point of the present invention to achieve this object is to use the piping method explained in FIG. However, by using abrasive grains with a coarser grain size near the ends of the crystal piece than in the center, the surface roughness is intended to be rougher than in the center.

Next, a method for manufacturing a crystal blank according to the present invention will be explained. The outer shape of the surface of the crystal blank can of course be any shape, such as square, diamond, circle, polygon, etc., but here we will show an example of the processing method for a blank that is circular and has a flat part near the center. This will be explained using figures.

First, as shown in FIG. 3a, the outer diameter of the crystal blank is finished using a rounding machine or the like so that it is slightly thicker in plan than the finished dimension, and then the thickness is processed to be thicker than the finished dimension. In addition, in FIG. 3a, the dotted line portion indicates the finished dimensions.

This crystal blank 4 is connected to a cast iron pipe 5 as shown in Figure 2.
A so-called piping process is performed in which several hundreds of abrasive grains 6 of a grain size (#400 to #1000) are placed in a pipe and a lid 6 is placed on the side, and then the pipe is rotated at a predetermined number of revolutions. If the rotation is fast, a uniform curved surface cannot be formed, and if the rotation is slow, the efficiency of forming the curved surface is poor. The cross section of the crystal blank 7 taken out after about 5 to 6 days of rotation has a shape as shown in Figure 3. At this stage, the curved surface 8, which is the end of the crystal piece, has the final required curved shape, but the thickness is slightly thicker (the dotted line is the finished thickness dimension).

At this point, the thickness is uneven, and the surface condition of the flat portion of the main surface is also rough.

Next, by piping the crystal piece blank 7 of this shape,
The flat portion 10, which is the center of the main surface, is finished by lapping or polishing using finer abrasive grains (#2000 to #4000), or both. FIG. 4 shows a partial sectional view of the lapping process. 7 is a crystal blank, 11 is an upper and lower lapping machine, and 12 is a carrier.The lapping machine 11 is rotated and the central flat part 1 is cut by abrasive grains 13.
Finish processing 0. As a result, the flat part 10 having a large vibration amplitude can obtain a better surface condition than the curved part 8, and the thickness accuracy can be reliably finished within a predetermined dimension. The cross section of the final crystal blank 9 is shown in FIG. 3C.Of course, the processed strain layer on the surface is removed by light etching.

By using this manufacturing method, a large amount of bevels can be formed efficiently by piping, while the thickness accuracy of the flat part on the main surface is increased by lapping and bolishing, and the vibration amplitude is It has become possible to mass produce small crystal blanks with uniform thickness and dimensional accuracy and a good surface condition of the large flat part.

Note that the processing method for the center and end portions may be reversed by performing abrasive processing other than piping on the end portions (for example, covering the center portion with a mask and then honing or etching). The center doesn't need to be particularly flat as long as it's grainy.

Furthermore, in the case of a rectangular crystal piece, by changing the surface roughness of the main surface and side surfaces of the center part and the surface roughness of the main surface and side surfaces of the end parts by the above method, 1. Improve the crystal characteristics and achieve good vibration. can have a child.

By carrying out the present invention as described above, the thickness of the thickness-sliding crystal resonator using a small crystal piece can be controlled, so that the secondary vibration can be reliably fixed to the main vibration, and the surfaces of the center and end parts can be reliably fixed. Since the roughness can be changed, good frequency and CI value temperature characteristics can be obtained, and the surface condition of the main surface has the effect of achieving good aging characteristics.
It is very useful as a time standard for mobile watches that display yearly differences.

[Brief explanation of the drawing]

Claims (1)

[Claims] In a method for manufacturing a small crystal piece having curved surfaces on both main surfaces with a predetermined curvature, a step of final forming the vicinity of the center portion by at least one of lapping and polishing, and a step of final forming the vicinity of the center portion of the small crystal piece with a curved surface having a predetermined curvature; A method for manufacturing a small crystal piece, characterized by comprising a final forming process using abrasive grains with a coarser grain size than the previous one.