GB2075254A - Mode coupled tuning fork type piezo-electric resonator - Google Patents

Abstract

A mode coupled tuning fork type piezo-electric resonator (10) whose base portion (10') is supported from support structure (13) by at least one bent supporting member (11), to prevent leakage of vibrational energy. The tuning fork resonator may have projecting portions from the sides of its base portion. Numerous details of dimensions are given. <IMAGE>

Description

SPECIFICATION Mode coupled tuning fork type piezo-electric resonator This invention relates to a mode coupled tuning fork type piezo-electric resonator, e.g. a quartz crystal resonator.

According to the present invention there is provided a mode coupled tuning fork type piezo-electric resonator whose base portion is supported from support structure by at least one bent supporting member.

The or each bent support member may be bent through 180" so as to have inner and outer parts which are respectively disposed relatively nearer to and further from the resonator.

Each bent support member may be attached at one end thereof to the base portion of a major surface of the resonator.

Bent supporting members may be respectively attached to the opposite major surfaces of the resonator.

Preferably, the total height of the or each support member is in the range 0.4 to 5.0 mm., the widths of the said inside and outside portions are each in the range 0.1 to 0.3 mm., and the thickness of the or each support member is in the range 0.1 to 0.4 mm.

The thickness of the resonator is preferably 200y or less.

The base portion of the resonator may have projecting side portions which project outwardly of the arms of the tuning fork.

Each said projecting side portion may be rectangular in plan and have a width in the range 10 to 150u or a width which is not more than half the width of an arm of the tuning fork.

Alternatively, each said projecting side portion may be triangular in plan and may have a maximum width which is not more than two thirds that of an arm of the tuning fork.

The outer ends of the tuning fork arms may extend obliquely so that the length of each arm on its inner side is at least four fifths of its length on its outer side.

The projecting side portions may be provided adjacent to the arms of the resonator, the base portion having recessed side portions remote from the said arms.

Preferably, the length of each said recessed side portion is in the range 30 to 1000cm and the width of each said recessed side portion is in the range 10 to 3501l.

Preferably the resonator is such that in use an overtone of flexural vibration is coupled to a torsional vibration. The overtone is preferably the first overtone.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 shows a conventional mode coupled tuning fork type quartz crystal resonator, Figure2 is a diagrammatic drawing of a resonator illustrating how acoustic leaks occur, Figures 3A and 3B show embodiments of resonators according to the present invention, Figure 4 shows graphs illustrating the principle of the present invention, Figures 5, 6 and 7 respectively show a front view and a side view of other embodiments of resonators according to the present invention, Figures 8A, 8B and 8C are diagrams illustrating the shape and dimensions of various embodiments of the supporting member of the resonator, Figure 9 shows a side view, an elevation and a perspective view of a further embodiment of a resonator according to the present invention, Figure 10 is a graph showing the variation of the frequency of the resonator of Figure 9, Figure 11A shows a mode coupled tuning fork type quartz crystal resonator which may be used in the present invention and which has projecting side portions, Figure 11B is a graph which shows how A' of the flexural vibration and of the torsional vibration depend upon the width of the said projecting side portions, Figure 12A shows a mode coupled tuning fork type quartz crystal resonator which may be used in the present invention and which has projecting side portions at the upper part of the base portion and recessed side portions at the lower part of the base portion, Figure 12B is a graph which shows how ' of the flexural vibration and of the torsional vibration depend upon the width of the said recessed side portions, Figure 13 shows graphs illustrating the displacement of certain points on the resonator, and the variation of frequency of the resonator, when the resonator has the shape shown in Figure 12A and is supported as shown in Figure 3A, Figures 14A and 14B show further mode coupled tuning fork type quartz crystal vibrators which may be used in the present invention, Figure 15 shows graphs illustrating the variation of frequency of a vibrator as shown in Figure 1 1A, 14A or 14B when supported by a support member, Figure 16 shows further support members which may be used in the present invention, and Figures 17 and 18 are perspective views of further embodiments of the present invention.

Terms such as "upper" and "lower" as used in the description below are to be understood to refer to directions as seen in the accompanying drawings.

A mode coupled tuning fork type quartz crystal resonator should improve the resonance frequencytemperature characteristics of one of two different vibration modes of the resonator, that is, it should decrease the variation of the resonance frequency due to temperature variations by coupling the two vibration modes of the tuning fork type resonator.

In a mode coupled tuning fork type quartz crystal resonator according to this invention, flexural vibration and torsional vibration may, amongst other vibration modes, be used as the two vibration modes to be coupled together. When these particular two vibration modes are coupled together, the resonance frequency-temperature characteristics of the flexural vibration are improved. The time accuracy of an electronic timepiece can be greatly improved by providing the timepiece with such a resonator. A mode coupled tuning fork type quartz crystal resonator utilizing coupling between flexural vibration and torsional vibration is disclosed in Japanese laid-open patent No. 116191/79 and in British Patent Specification No.

2042796.

Afundamental vibration or an overtone can be used as the flexural vibration. From the view point of the improvement of time accuracy of the electronic timepiece, it is better to use the overtone. This is because there is in this case little variation of the resonance frequency with age, as the Q value of the overtone is generally higher than that of the fundamental vibration. Moreover, the overtone varies less than the fundamental vibration even when the resonance frequency is varied by changing the disposition of the mode coupled tuning fork type quartz crystal resonator with respect to the direction of gravity.

Although the use of the overtone has these two advantages, its use involves an increase in the resonance frequency of the resonator, so that it is natural to use the lowest overtone (hereinafter referred to as a first overtone). As a result, when such a mode coupled tuning fork type quartz crystal resonator is used in an electronic timepiece, a great increase in power consumption can be avoided.

Figure 1 shows a mode coupled tuning fork type quartz crystal resonator, as shown in the above-mentioned patents, in which the first overtone is coupled with the torsional vibration. As shown in Figure 1, a mode coupled tuning fork type quartz crystal resonator 1 is supported from a plug 4 by support members 2 which are electrically connected to the electrodes of the resonator. The support members 2 are secured to the resonator 1 by solder 3. The X, Y' and Z' axes in Figure 1 respectively indicate the electrical axis of the quartz crystal, the mechanical axis of the quartz crystal which is rotated about the electrical axis and the optical axis of the quartz crystal which is rotated about the electrical axis.These show the directions in which the mode coupled tuning fork type quartz crystal resonator 1 should be cut from the quartz crystal, when the X axis is parallel to the direction of the width of the quartz crystal resonator, theY' axis is parallel to the longitudinal direction of the resonator and the Z' axis is parallel to the direction of the thickness of the resonator. The oscillation frequency of the resonator of Figure 1 may be about 200 KHz, and the difference of the two resonance frequencies may be from 4 to 5 KHz.

Generally speaking, the Q value of the first overtone in the flexural vibration is higher than that of the fundamental vibration. However, since there is considerable displacement of the base portion of the mode coupled tuning fork type quartz crystal resonator, it was difficult to obtain a naturally high Q value of the first overtone when the resonator was supported as shown in Figure 1. Moreover, an acoustic leak could occur.

Further, this mode coupled tuning fork, type quartz crystal resonator uses torsional vibration, and the prevention of acoustic leaks had not hitherto been considered in relation to this mode. In particular, an acoustic leak of the torsional vibration causes the vibration in the resonance frequency-temperature characteristics to increse. Furthermore, if the resonator is clamped, abnormalities can occur in the resonance frequency temperature characteristics. Accordingly, it is necessary to suppress the acoustic leak of the torsional vibration.

An object of the present invention is therefore to reduce or eliminate the acoustic leak of the flexural vibration and of the torsional vibration, and to improve their Q values in a mode coupled tuning fork type quartz crystal resonator.

We will first deal with the reason why the 0 value decreases and the acoustic leak occurs in the resonator support structure shown in Figure 1. Figure 2 is provided as an explanatory diagram for this purpose. As shown in Figure 2, a tuning fork type resonator 5 is supported from a plug 7 by supporting members 6. 8 are arrows showing the directions of vibration of a base portion 5 of the tuning fork type resonator 5. 9 are arrows showing the directions of vibration of the plug 7. As shown in Figure 2, when the vibration amplitude of the base portion 5 is great, the resonator 5 makes the plug 7 vibrate. If the vibration amplitude of the base portion 5 is great, the loss of the vibration energy is great and the Q value decreases.Further, according to vibration theory, when a mass is added to a place where the vibration amplitude is not zero, the equivalent mass is not infinite and the frequency of the vibrating system decreases. Thus, if another mass is added to the plug 7, the resonance frequency of the resonator 5 decreases. If the mass added to the plug 7 moves in an unstable manner, the resonance frequency of the resonator 5 is similarly unstable. This is how the acoustic leak occurs.

Figure 3A shows one embodiment of the present invention. As shown in Figure 3A, a mode coupled tuning fork type piezo-electric quartz crystal resonator 10 has a base portion 10' which is supported from a plug 13 by way of bent supporting members 11 whIch are secured to the resonator 10 by electrically conductive solder 12. Each supporting member 11 is bent back on itself through 1800 to provide it with an inner part 12' and an outer part 12" which respectively have horizontally aligned straight portions. The inner and outer parts 12', 12" are respectively disposed relatively nearer to and further from the resonator 10. Each of the support members 11 is attached at its inner end to the base portion 10' of a major surface of the resonator 10. The dimensions of the supporting members 11 are respectively as follows: the length of each straight portion is s, the thickness of each supporting member 11 is t, the width of the inner parts 12' is w, and the width of the outer parts 12" is w2. 14 is one particular point of contact of a supporting member 11 and the plug 13. 15 is one particular point on the edge of the base of the plug 13.

Figure 1 3B shows a resonator similar to that of Figure 3A and therefore will not be described in detail, like reference numerals indicating like parts. In the construction of Figure 3B, however, the supporting members 11 are respectively attached to the opposite major surfaces of the resonator 10 and not to the same major surface thereof, as in Figure 3A. Moreover, in Figure 3B the supporting members 11 extend throughout the greater part of the tuning fork arms, whereas in Figure 3Athey extend throughout only a minor part of the tuning fork arms.

The principle of the present invention will now be explained with reference to Figure 4(a), (b), (c) and (d).

Figure 4(a) shows the variation of frequency of the flexural vibration and that of the torsional vibration in terms of s when the shape and the dimensions of everything except the straight portion of a supporting member 11 are held fixed. A curve 16 shows the variation of frequency of the flexural vibration, and a curve 17 shows that of the torsional vibration. The ordinate represents the variation of frequency in relation to a certain s.

Figure 4(b) shows the displacement of the point 14 in relation to s. The ordinate represents the relative value when the maximum displacement at the top of a tuning fork arm is regarded as 1. A curve 18 shows the displacement of the flexural vibration, and a curve 19 shows that of the torsional vibration.

Figure 4(c) shows the amount of displacement of the point 15 in relation to s. The ordinate is the same as that of Figure 4(b). A curve 20 shows the displacement of the flexural vibration, and a curve 21 shows that of the torsional vibration.

Figure 4(d) shows the variation of X against s.

If the frequency of the plug 13 when completely free isfFREE and that of the plug 13 when completely clamped is CLAMP, X fFREE fCLAMP ,,, (1 ) fCLAMP A curve 22 shows the displacement of the flexural vibration and a curve 23 shows that of the torsional vibration. The abscissae of Figures 4(a), (b), (c) and (d) are all on the same scale.

In Figure 4(a), the vibration indicated by the curves 16, 17 is small in the zones S1 and S2, even if s is varied. In the zones other than S1 and S2, the variation offrequency is very great and there are jumps in the frequency. If the mounting portion of the resonator 10 (i.e. the portion of the resonator 10 where the supporting members 11 are attached with the solder 12) is completely fixed, the frequency is constant regardless of the value of s. However, in fact, because of the vibration of the said mounting portion, coupling between the supporting members 11 and the resonator 10 occurs. Thus, in the zones where the frequency jumps, the coupling between the supporting members 11 and the resonator 10 increases very markedly.

Further, in the zones S1 and S2, the variation of frequency is small because the coupling between the supporting members 11 and the resonator 10 decreases.

As shown in Figure 4(b), the displacement of the point of contact 14 of a supporting member 11 and the plug 13 is small in the zones S1 and S2, and it suddenly increases in the areas outside the zones S1 and S2. In other words, in the zones where the coupling between the resonator 10 and the supporting members 11 is weak, the point 14 is nearly at the node, and in the zones where the coupling is strong, it is nearly at the loop.

As shown in Figure 4(c), the displacement of the point 15 of the plug 13 similarly decreases in the zones where the point of contact 14 is approaching the node, and it suddenly increases in the zones where the point of contact 14 is approaching the loop. This is to be expected having regard to the fact that the plug 13 is made to vibrate by the supporting members 11 and to the fact that the point of contact 14 is at the contact between a supporting member 11 and the plug 13. As in the cases of Figure 4(a) and Figure 4(b), in the zones where the vibration amplitude of the plug 13 is small, the coupling between the supporting members 11 and the resonator 10 is weak. Even if the value of s is varied, the variation of the frequency is small. In the zones where the vibration amplitude of the plug 13 is great, the coupling is strong and the frequency suddenly changes when s is varied.When, however, s is in the zone S1 or S2, the vibration amplitude of the plug 13 is small.

That is to say, in the total vibration system comprising the resonator 10, the supporting members 11 and the plug 13, the equivalent mass of the plug 13 increases. Accordingly, even if another mass is added to the plug 13, the variation of the frequency in the total vibration system is extremely small. For this reason, any acoustic leak will be extremely small.

On the contrary, when s is in a zone outside the zones S1 and S2, the vibration amplitude of the plug 13 increases. Accordingly, if another mass is added to the plug 13, the frequency of the total vibration system decreases markedly and an acoustic leak occurs.

As shown in Figure 4(c), as the displacement of the plug 13 is small in relation to the flexural vibration and the torsional vibration in the zones S1 and S2, acoustic leaks can be substantially prevented in relation to both modes. This is shown in Figure 4(d). When another mass is added to the plug 13, the boundary condition which is realized in practice is between the conditions when the plug 13, is completely free and when it is completely fixed. So, if the value of X is small, even if another mass is added to the plug 13, the variation of the frequency is small as compared with the case in which nothing is added. That is to say, the acoustic leak is small.In Figure 4(d), the curvature of the curve 22 of the flexural vibration and of the curve 23 of the torsional vibration is extremely small in the zones S1 and S2 and thus an acoustic leak can be substantially prevented in relation to both the modes.

Figures 5, 6 and 7 show other embodiments according to the present invention. In the respective Figures, (a) is a front view and (b) is a side view. A mode coupled tuning fork type quartz crystal resonator is indicated at 24,27 and 30. The supporting members of these resonators are indicated at 25,28 and 31. The plugs of these resonators are indicated at 26, 29 and 32. In the embodiments of Figures 5-7, the manner in which an acoustic leak can be prevented is the same as described above with reference to Figure 4. Any supporting member 11,25,28 or 31 used in the constructions shown in Figures 3A, 3B, 5,6 or7 which are embodiments of the present invention may have the shape shown in Figure 8A, 8B or 8C. Each such supporting member has a portion 33 which is bent through 180 degrees.When such a supporting member has a total height h, an inner part whose width is w1, an outer part whose width is w2 and a thickness t, h = 400 to 2,600cm w1 and W2 = 100 to 200Ft, and t =100to400CI.

In the case of the construction shown in Figures 8B and 8C, the heightofthe support members is represented by h and h', the thickness of the support members is d and d', the widths of the inner parts are w1 and w', and the widths of the outer parts are w2 and w'2. These dimensions depend upon the material of the support members and the size of the resonator to be supported.If the thickness of the resonator is 200put or less and the support members are made from carbon steel, the respective dimensions are as follows: h, h' = 1.0 to 4.5 mm w1,w'1 = 0.1 to 0.3 mm w2,w2 = 0.1 to 0.3 mm d,d' =0.1 to 0.3 mm If the thickness of the quartz crystal vibrator is 2001t or less and the support members are made from the material sold under the Trade Mark Kovar, the respective dimensions are as follows:: h,h' =2.5to 5.0 mm w1,w'1 = 0.15 to 0.3 mm w2,w'2 =0.15to 0.3 mm d, d' = 0.15 to 0.3 mm In the constructions of Figures 3A and 5, two supporting members, each of which has a bent portion, are attached to one only of the major surfaces of the resonator. However, in the constructions of Figures 6 and 7, at least one supporting member having a bent portion is respectively attached to each of the said major surfaces. In either case, the effects are the same in respect of the prevention of the acoustic leak. The term "major surface" is intended to indicate a face of the resonator in which lie surfaces of the two tuning fork arms. There are thus two major surfaces. Further, the effect is the same if a plurality of bent portions are bent through given angles.

Figure 9 shows a side view, an elevation and a broken away perspective view of a mode coupled tuning fork type quartz crystal resonator according to this invention which is similar to that of Figure 7.

Referring to Figure 9, a mode coupled tuning fork type quartz crystal resonator 34 is supported from a plug 35 by supporting members 36 having mounting portions 37 where they are connected to the resonator 34 and mounting portions 38 where they are connected to the plug 35. The mode coupled tuning fork type quartz crystal resonator 34 of Figure 9 is different from the resonator 10 of Figure 3B in the shape of the base portion, and, unlike Figure 3B, projecting portions are not provided at the sides of the base portion.

It is obvious that the mode coupled tuning fork type quartz crystal resonator 34 is a resonating member, and the supporting members 37 can also be resonating members. As two vibrating members are connected at the mounting portions 37,38 coupling will occur therebetween.

Figure 10 shows this coupling, The S shown on the abscissa of Figure 10 is the same as the S of Figure 9, and represents the length of the straight portion of the supporting members 36. The ordinate shows the frequency variation of the mode coupled tuning fork quartz crystal resonator. That is to say, the solid line shows the variation of the frequency of the resonator when S is changed. If the mounting portions 37 are completely fixed, such coupling does not occur and the frequency of the quartz crystal resonator keeps constant value independently of the change of S. However, in practice, as the mounting portions 37 vibrate considerably, the coupling with the supporting members 36 increases and the frequency of the quartz crystal resonator varies with the changes in the value of S. Also, as the vibrating displacement of the mounting portions 11 is considerable, even if the vibration decays a little at the supporting members 36, the vibration is transmitted to the plug 35 and the plug 35 vibrates. Accordingly, if another object touches the plug 35 friction occurs between them. As a result, vibrating energy is lost, the Q value decreases, and the CI value increases.

Further, as the resonating system containing the support members 36 and the plug 35 changes, the frequency of the quartz crystal vibrator 34 coupled with the support members 36 changes, too. Such an acoustic leak appears particularly in the most intense coupling zones enclosed by the broken lines. So, if a value of S near S1, 52 and S3 is adopted, the mode coupled tuning fork type quartz crystal resonator is better than the conventional embodiment as shown in Figure 1.

UY', UZ' and UX are values of the vibration displacement of the mounting portions 38 of the quartz crystal resonator. As for UZ' and UX, if the width, the thickness and the length of the supporting members 36 are properly chosen, UZ' and UX can be got near zero at the mounting portions 38 of supporting members 36.

That is to say, as for the vibration displacement of the directions of axis of Z' and X, the mounting portions 38 of the supporting members 36 can be made the nodal points of the vibration. However, as for UY', the mounting portions 38 of supporting members 36 cannot be made the nodal points of the vibration. The plug is therefore caused to vibrate. Moreover, as UY' is the largest of all, it also causes the coupling of the quartz crystal resonator and the supporting members to be more intense. Accordingly, in order to decrease the coupling between the quartz crystal resonator and the supporting members 36 and not to transmit the vibration to the plug 35, it is necessary to make UY' of the mounting portions 36 small.

In the embodiment of this invention described above, the acoustic leak of the flexural vibration and of the torsional vibration can be supressed to a degree which does not matter in a practical application. However, when one considers the variations which occur during manufacture it is necessary to suppress the acoustic leak to a much greater extent and to improve the Q value. For that purpose, the displacement of the mounting portion of the resonator needs to be decreased. This point will now be described with reference to Figures 11A, 11B, 12A and 12B.

Figure 1 1A shows a mode coupled tuning fork type quartz crystal resonator 41 whose base portion is provided with a side projecting portion 43 which projects outwardly of the arms of the vibrator and which is rectangular in plan, the said base portion being the portion of the resonator 41 other than the two tuning fork arms. The length of the base portion is LB, its width is WB, and the width of the projecting portion 43 is B. 42 is a mounting portion.

Figure 11 B shows ' in relation to B. If the frequency when the mounting portion 42 is completely free is fFREE, and the frequency when it is completely clamped is CLAMP then = = fFREE - fCLAMP . . . (2) CLAMP In Figure 11 B 44 is a curve which represents the dependence of ' on the value of B in relation to the flexural vibration. 45 is a curve representing the dependence of ' on the value of B in relation to the torsional vibration. As will be appreciated from Figure 11 B, ' is at a minimum at a position Bo in relation to the flexural vibration, and ' increases with the increase of Bin relation to the torsional vibration.In relation to the two modes, it is necessary to arrange that ' S 1 ppm . . . (3) and this is very difficult to arrange in the case of the shape shown in Figure 1 A.

In the case of the resonator of Figure 12A, however, this resonator is provided with a projecting portion which has a width B and which is disposed on the upper part of the base portion of the resonator and with a recessed portion 46 which has a width WC and a length LC, and which is disposed on the lower part of the said base portion. Thus the projecting side portions are provided adjacent to the arms of the resonator, the base portion of the resonator having recessed side portions which are remote from the said arms. The length of the base portion is LB, and its width is WB.

Figure 1 2B shows the value of ' in relation to WC when LB, WB and B are values at the minimum of the curve 44 shown in Figure 11 B and when LC is given suitable values. Curves 47,48 show respectively how ' depends upon WC. From Figure 12B it will be appreciated that, when WC is greater than WCo, the condition (3) is satisfied in relation to the two modes. Thus, the fact that there is only a small difference between the frequency when the mounting portion is completely free and the frequency when it is completely clamped means that the displacement of the mounting portion is small. This is the same condition as that described with reference to Figure 4(c) and 4(d) wherein the displacement of the plug can be said to be small in the zone where A is small.

Accordingly, when the resonator is given the shape shown in Figure 12A, the displacement of the mounting portion decreases in relation to the two modes and the coupling between the resonator and the supporting members becomes much weaker than in the case of the constructions of Figures 3A, 3B, 5, 6,7,9 and 10. When curves are prepared in relation to the resonator of Figure 12A corresponding to those of Figures 4a, 4b, 4c and 4d, the curves 16, 17 of Figure 4(a) become smoother, the minimum values of the curves 18, 19,20 and 21 of Figures 4(b) and 4(c) become smaller, and, as regards Figure 4(d), the zone of s where h is small increases and the acoustic leak can be almost entirely prevented.Further, the fact that the zone of s where? is small increases in Figure 4 means that the acoustic leak does not occur even if there is some variation in manufacture whereby mass production is made easier.

The above-mentioned state of affairs is illustrated by the curves of Figure 13 where the displacement of the points 14 and 15 and the variation of the frequency of the resonator are represented when a resonator, which has a shape as shown in Figure 12A, is supported in the manner shown in Figure 3A, Figures 13(a), (b), (c) and (d) to Figures 4(a), (b), (c), and (d) respectively. Curves 16', 17', 18', 19', 20', 21', 22' and 23' correspond to the curves 16, 17, 18, 19,20,21,22 and 23 respectively. S1' and S2' correspond to S1, S2 respectively. It can be seen from Figure 13 that S1' and S2' are widerthan S1, S2 in Figure 4 and that the minimum values of 18', 19' 20' and 21 ' are smaller than those of 18, 19,20 and 21 respectively.These effects are similarly obtained if the mounting of the resonator is as shown in Figures 5,6,7,9 and 10. In the zones of S1' and S2', X is almost zero and the acoustic leak can be almost entirely prevented in relation to the two modes. Si' and S2' have values from 400 to 500pot, which are sufficient to cope with manufacturing variations.

Experimentally,? S 0.5 ppm in relation to the flexural vibration and? S 5 ppm in relation to the torsional vibration, and there is no difficulty in providing such values in practice.

The dimensions of the various parts of the resonator of Figure 1 2A having a thickness of 200pot or less are as follows: LB = 500to2,000u WB = 400 to 1,500kit B = 30to1501 LC =100to1,0001* WC = 30 to 350it Additionally, a resonator having a shape as shown in Figure 12A can be easily manufactured by a photo-lithographic process.

When a resonator having a shape as shown in Figure 12A is supported by any of the supporting means described above, each Q value of the flexural vibration and of the torsional vibration turns out to be 300,000 or more. Also, the CI of the flexural vibration turns out to be 2kQ or less. This is because the displacement of the mounting portion decreases.

Since the resonator has little acoustic leak, a high Q value of 300,000 or more and a high oscillation frequency of 22 kHz, there is little change of frequency with age. Accordingly, when a resonator according to the present invention is used in an electronic watch, there is a great improvement in its accuracy and there are excellent frequency-temperature characteristics. The time error is only a few seconds a year. Further, when the resonator of the present invention is used in an electronic watch, a great increase in power consumption is avoided on account of the low CI value oftheflexural vibration of 2kQ and thus it is also advantageous in terms of the long operating life of the battery.When the oscillation frequency is 200 kHz, the sum total of the oscillating current and the dividing current is from 0.5 to 0.SuA.

The resonator supporting means and the shape of the mode coupled tuning fork type quartz crystal resonator described above can be used for a mode coupled tuning fork type quartz crystal resonator employing a vibration mode other than the first overtone as a flexural vibration. In addition, they can be used for a resonator employing a vibration mode other than flexural vibration and torsional vibration.

Figure 14B shows a resonator 50 which may be used in substitution for the resonator 41 of Figure 1 The resonator 50 has projecting side portions 51 which are triangular in plan and which have a maximum width B2 outwardly of the tuning fork arms.

Figure 1 4B shows another resonator 52 which may be used in substitution for the resonator 41. The outer ends 53 of the tuning fork arms 54 extend obliquely through a longitudinal distance B3.

The value of B in the resonator 41 may be half or less of the width of the tuning fork arms. The value of B2 is 2/3 or less of the width of the tuning fork arm, and the value of B3 is 1/5 or less of the length L of the tuning fork arms. Thus the length of each arm 54 on its inner side is at least four fifths of its length L on its outer side.

If such values of B, B2 and B3 are used and the resonator is supported by the supporting members as shown in Figures 3B and 9, the value of UY' of the supporting members can be almost reduced to the same order as the UX. If the values of B, B2 and B3 are made greater than the above-mentioned values, UY' increases conversely. Moreover, if desired, the features of the resonator 52 may be combined with those of the resonators 41 or 50. Resonators of the shape as shown in Figures 1 1A, 14A, 14B can be easily manufactured by a photo-lithographic process.

Figure 15 shows the variation of frequency of the quartz crystal resonator in relation to S when the mode coupled tuning fork type quartz crystal resonator as shown in Figures 11A, 14A, 14B is supported bythe supporting members as shown in Figures 3B and 9. UY' of the mounting portions 37 decreases so much that the coupling between the quartz crystal resonator and the supporting members 36 decreases. Especially when S is in the ranges 55, 56, 57, the coupling decreases greatly and the frequency of the quartz crystal resonator keeps almost a constant value.Only when the resonance frequency of the supporting members approaches that of the quartz crystal resonator does a coupling occur as shown by 60,61,62,63. In the ranges 55, 56, 57, since the displacement of vibration of the mounting portions 38 of the supporting members 36 is small and the coupling between the supporting members 36 and the quartz crystal resonator decreases, the acoustic leak does not occur. In the ranges 60, 61,62, 63, since the coupling between the supporting members 36 and the quartz crystal resonator increases and the plug 35 vibrates greatly, the acoustic leak occurs.

Further, in the ranges 55, 56,57, the frequency does not change even if the mounting portions 38 of the supporting members 36 are loosened by shock, e.g. from dropping the resonator. That is to say, a quartz crystal resonator in the ranges 55, 56, 57 is not substantially affected by shock.

Figure 16 shows part of one embodiment of the invention which uses supporting members 58 whose shape is slightly different from that of the supporting members shown in the other Figures.

Figure 17 shows another embodiment of the present invention. Referring to Figure 17, a mode coupled tuning fork type quartz crystal resonator 64 is supported from a plug 66 by way of supporting members 65.

The supporting members 65 are secured to the resonator 64 by solder 67. The Figure 17 embodiment, however is different from the embodiments described above. Thus resonator 64 is supported by two supporting members 65 having no portion which is bent However, the reason why the acoustic leak can be prevented in relation to the flexural vibration and to the torsional vibration is the same as in the case in which each supporting member has a portion which is bent through 180 degrees.

In the Figure 17 construction, the effective length d of each supporting member 65 corresponds to the distance s in the construction of Figure 3A.

Figure 18 illustrates another embodiment of this invention. Referring to Figure 18, a mode coupled tuning fork type quartz crystal resonator 67 is supported from a plug 69 by supporting members 68 which are secured to the resonator 67 by solder 70. In this embodiment, there are two supporting members 68 which respectively support the major surfaces of the resonator. In this case, the effect is the same as in the embodiment of Figure 17 in respect to the prevention of the acoustic leak. When each supporting member 68 has a thickness t, a width w, and a length l, which is the distance between the bottom of the resonator 67 and the plug 69, w = 0.05 to 0.3 mm t = 0.05 to 0.3 mm f = 0.2to1.0mm

Claims (23)

1. A mode coupled tuning fork type piezo-electric resonator whose base portion is supported from support structure by at least one bent supporting member.

2. A resonator as claimed in claim 1 in which the or each bent support member is bent through 180" so as to have inner and outer parts which are respectively disposed relatively nearer to and further from the resonator.

3. A resonator as claimed in claim 1 or 2 in which the or each bent support member is attached at one end thereof to the base portion of a major surface of the resonator.

4. A resonator as claimed in any preceding claim in which bent supporting members are respectively attached to the opposite major surfaces of the resonator.

5. A resonator as claimed in claim 2 or in any claim appendantthereto in which the total height of the or each support member is in the range 0.4 to 5.0 mm, the widths of the said inside and outside portions are each in the range 0.1 to 0.3 mm, and the thickness of the or each support member is in the range 0.1 to 0.4.

mm.

6. A resonator as claimed in claim 5 in which the total height is in the range 0.4 to 2.6 mm, and the widths are in the range of 0.1 to 0.2 mm.

7. A resonator as claimed in claim 5 in which the total height is in the range 1.0 to 4.5 mm, and the thickness is in the range 0.1 to 0.3 mm.

8. A resonator as claimed in claim 5 in which the total height is in the range 2.5 to 5.00 mm, the widths are in the range 0.15 to 0.3 mm, and the thickness is in the range 0.1 to 0.3 mm.

9. A resonator as claimed in any preceding claim in which the thickness of the resonator is 200lot or less.

10. A resonator as claimed in claim 5 in which the length of the base portion of the resonator is in the range 500 to 2000lot, and the width of the said base portion is in the range 300 to 1500cm.

11. A resonator as claimed in any preceding claim in which the base portion ofthe resonator has projecting side portions which project outwardly of the arms of the tuning fork.

12. A resonator as claimed in claim 11 in which each said projecting side portion is rectangular in plan and has a width in the range 10 to 150.

13. A resonator as claimed in claim 11 in which each said projecting side portion is rectangular in plan and has a width which is not more than half the width of an arm of the tuning fork.

14. A resonator as claimed in claim 11 in which each said projecting side portion is triangular in plan and has a maximum width which is not more than two thirds that of an arm of the tuning fork.

15. A resonator as claimed in any preceding claim in which the outer ends of the tuning fork arms extend obliquely so that the length of each arm on its inner side is at least four fifths of its length on its outer side.

16. A resonator as claimed in claim 11 in which the projecting side portions are provided adjacent to the arms of the resonator, the base portion having recessed side portions remote from the said arms.

17. A resonator as claimed in claim 16 in which the length of each said recessed side portion is in the range 30 to 1 000tut and the width of each said recessed side portion is in the range 10 to 350lot.

18. A resonator as claimed in any preceding claim in which, when the resonator is in use, an overtone of flexural vibration is coupled to a torsional vibration.

19. A resonator as claimed in claim 18 in which the overtone is the first overtone.

20. A resonator as claimed in any preceding claim in which the resonator has been made by a photolithographic process.

21. A mode coupled tuning fork type piezo-electric vibrator whose base portion is supported from support structure by at least one straight supporting member whose width is in the range 50 to 300lot, whose thickness is in the range 50 to 300,tt, and whose length between the support structure and the resonator is in the range 200 to 1000fit.

22. A mode coupled tuning fork type piezo-electric resonator in which there is in use coupling between the first overtone of flexural vibration and torsional vibration, the base portion of the resonator being supported from support structure by at least one supporting member.

23. A mode coupled tuning fork type piezo-electric vibrator substantially as hereinbefore described with reference to and as shown in any of Figures 3A, 3B, 5, 6,7 and 9 of the accompanying drawings.