Driving apparatus

A driving apparatus comprises: an electromechanical conversion element that expands and contracts in an extending direction of a given fiducial line; a driving shaft mounted on one end of the electromechanical conversion element in the extending direction; a driven member frictionally engaged with the driving shaft; a holder that supports the electromechanical conversion element from lateral sides with respect to extending direction; and an urging member that urges the electromechanical conversion element in the extending direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving apparatus suited for driving a lens or the like in a mobile telephone with a camera, a small-sized digital camera or the like.

2. Description of the Related Art

A driving apparatus, as known in the aforementioned technical field of the related art (as referred to JP-A-2006-91210, for example), comprises: an electromechanical conversion element for expanding and contracting in the extending direction of a given fiducial line; a driving shaft arranged on one end side of the electromechanical conversion element in the extending direction of the given fiducial line; a driven member frictionally engaged with the driving shaft; and a holder supporting the electromechanical conversion element and the driving shaft and urging the other end of the electromechanical conversion element and one end of the driving shaft so that the electromechanical conversion element and the driving shaft may come into abutment. There is also known a driving apparatus (as referred to JP-A-2007-49873, for example), which adopts a constitution for pushing the electromechanical conversion element from the other end side.

Moreover, a driving apparatus, as known in the aforementioned technical field of the related art (as referred to JP-A-2002-142470, JP-A-10-337055, and JP-A-2006-311794, for example), comprises: an electromechanical conversion element for expanding and contracting in the extending direction of a given fiducial line; a driving shaft mounted on one end of the electromechanical conversion element in the extending direction of the given fiducial line; a driven member frictionally engaged with the driving shaft; and a holder supporting the electromechanical conversion element and having a bearing hole of the driving shaft.

In these driving apparatus, driving pulses having saw-tooth waveforms are applied to the electromechanical conversion element so that the electromechanical conversion element is deformed in the state where an expanding rate and a contracting rate are different. When the electromechanical conversion element is deformed at a low rate, moreover, the driven member is caused by the friction to stand still with respect to the driving shaft. When the electromechanical conversion element is deformed at a high rate, on the contrary, the driven member is caused by the inertia to move with respect to the driving shaft. By applying the driving pulses having the saw-tooth waveforms repeatedly to the electromechanical conversion element, therefore, the driven member can be intermittently moved at a fine pitch.

In the driving apparatus thus far described, however, the other end of the electromechanical conversion element and the one end of the driving shaft are so urged by the holder that the electromechanical conversion element and the driving shaft may come into abutment. As a result, the electromechanical conversion element is improved in its supporting stability, but finds it difficult to make its expansion and contraction larger. On the other hand, a technique (as referred to JP-A-2007-74889, for example) for supporting the electromechanical conversion element elastically in the holder is effective for making the expansion and contraction of the electromechanical conversion element larger.

Here, the driving apparatus adopting the technique for supporting the electromechanical conversion element elastically in the holder is desired to improve the supporting stability of the electromechanical conversion element better. An extremely high optical performance is demanded especially for driving a lens or the like in the mobile telephone with the camera, the small-sized digital camera or the like. Therefore, a dislocation, as caused in the electromechanical conversion element by shocks due to a fall or the like, raises a serious problem even if the dislocation is small.

SUMMARY OF THE INVENTION

Therefore, the invention has been conceived in view of the background thus far described, and has an object to provide a driving apparatus, which can make the expansion and contraction of the electromechanical conversion element larger and which can improve the supporting stability of the electromechanical conversion element better.

In order to achieve the aforementioned object, a first driving apparatus according to the invention comprises: an electromechanical conversion element that expands and contracts in an extending direction of a given fiducial line; a driving shaft mounted on one end of the electromechanical conversion element in the extending direction; a driven member frictionally engaged with the driving shaft; a holder that supports the electromechanical conversion element from lateral sides with respect to extending direction; and an urging member that urges the electromechanical conversion element in the extending direction.

In this first driving apparatus, the electromechanical conversion element is elastically supported by the holder so that the expansion and contraction of the electromechanical conversion element can be made larger. At this time, the electromechanical conversion element is urged in its expanding and contracting direction by the urging member so that the supporting stability of the electromechanical conversion element can be improved better.

In the first driving apparatus according to the invention, it is preferred that the urging member urges the electromechanical conversion element in the extending direction on the other end side of the electromechanical conversion element. In this case, it is unnecessary to mount a weight member or the like on the other end of the piezoelectric element so as to displace the one end of the piezoelectric element more than the other end.

In the first driving apparatus according to the invention, it is preferred that the urging member is a screw so fastened in the holder as to push the other end of the electromechanical conversion element. In this case, the supporting stability of the piezoelectric element and the driving performance of the driving apparatus can be adjusted by the fastening extent of the screw.

In order to achieve the aforementioned object, moreover, a second driving apparatus according to the invention comprises: an electromechanical conversion element that expands and contracts in an extending direction of a given fiducial line; a hollow driving shaft mounted on one end of the electromechanical conversion element in the extending direction; a driven member frictionally engaged with the driving shaft; a holder that supports the electromechanical conversion element and comprises a bearing portion for the driving shaft; a support member, disposed in the bearing portion, that comprises a fixing portion fixed in the holder and a fitted portion fitted from one end side in the driving shaft; and an urging member, arranged between the electromechanical conversion element and the fitted portion in the driving shaft, that urges the electromechanical conversion element in the extending direction.

In this second driving apparatus, the electromechanical conversion element is elastically supported by the holder so that the expansion and contraction of the electromechanical conversion element can be made larger. At this time, the electromechanical conversion element is urged in its expanding and contracting direction by the urging member, which is arranged in the hollow driving shaft between the electromechanical conversion element and the fitted portion of the support member, so that the supporting stability of the electromechanical conversion element can be improved better.

In the second driving apparatus according to the invention, it is preferred that the urging member is a spring arranged in a compressed state between the electromechanical conversion element and the fitted portion in the driving shaft. In this case, the supporting stability of the piezoelectric element and the driving performance of the driving apparatus can be adjusted by changing the spring constant of the spring.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the invention are described in detail in the following with reference to the accompanying drawings. Here, the same or corresponding portions in the individual drawings are designated by the common reference numerals, and their repeated descriptions are omitted.

FIG. 1Ais a perspective view showing a first embodiment of a driving apparatus according to the invention, andFIG. 2Ais a sectional view of a portion shown inFIG. 1Aand taken along line II-II.FIG. 1Bis a perspective view showing a second embodiment of the driving apparatus according to the invention, andFIG. 2Bis a sectional view of a portion shown inFIG. 1Band taken along line II-II. As shown inFIGS. 1A,1B,2A and2B, the driving apparatus1of the first embodiment and the driving apparatus10of the second embodiment are apparatus for driving a lens held by a lens frame (or a driven member)2, along an optical axis OA, and finds its preferred application in a mobile telephone with a camera, a small-sized digital camera or the like.

The driving apparatus1or10is provided with a holder3for housing the lens frame2. The holder3supports a piezoelectric element (or an electromechanical conversion element)4for expanding and contracting in the extending direction of a fiducial line FL parallel to the optical axis OA. Specifically, the piezoelectric element4is so elastically supported by the holder3as is held from lateral sides with respect to the extending direction of the fiducial line FL by a silicone cap5adhered to the holder3by a silicone adhesive. Here, the piezoelectric element4is provided with input terminals4aand4bfor applying driving pulses.

A driving shaft6is so fixed by an adhesive7to one end of the piezoelectric element4in the extending direction of the fiducial line FL as to extend along the fiducial line FL. In the second embodiment, the driving shaft6is made hollow. The driving shaft6is formed of a graphite composite, in which graphite crystals are firmly combined, such as carbon graphite, into a column shape in the first embodiment and into a cylindrical shape in the second embodiment.

The driving shaft6has its one end portion loosely fitted in a bearing hole11a(or a bearing portion) formed in a partition11of the holder3. On the other hand, the other end portion of the driving shaft6is inserted into a through hole12aformed in a partition12of the holder3. As a result, the driving shaft6can reciprocate along the fiducial line FL.

The driving shaft6is frictionally engaged by an engaging portion2aof the lens frame2, which is regulated in its moving region by and between the partitions11and12. Specifically, a plate member13of a V-shaped section fixed on the engaging portion2aand a plate member15of a V-shaped section urged toward the plate member13by a leaf spring14retained on the engaging portion2aclamp the driving shaft6, so that the engaging portion2ais so mounted on the driving shaft6as to establish a given frictional force as it moves. Here, a pin9, which is arranged in the groove of the U-shaped section of the lens frame2, is spanned in the extending direction of the fiducial line FL. In short, the driving shaft6functions as a guide pin, too, and the pin9functions as a rotation stopping pin of the lens frame2, too.

In the first embodiment, as shown inFIG. 1AandFIG. 2A, the piezoelectric element4is provided, on its other side in the extending direction of the fiducial line FL, with a screw (or an urging member)25, which is so fastened in the holder3as to push the other end of the piezoelectric element4. The screw25urges the piezoelectric element4toward the one side of the extending direction of the fiducial line FL.

In the second embodiment, as shown inFIG. 1BandFIG. 2B, a support member20for supporting the driving shaft6is mounted in the bearing hole11aof the partition11. This support member20is provided with a fixing portion21of a rectangular plate shape adhered and fixed to the holder3, and a fitted portion22loosely fitted in the driving shaft6from one end side of the same. Between the other end face of the fitted portion22and the one end face of the driving shaft6, there is formed a clearance for keeping those end faces out of contact even when the piezoelectric element4extends to its largest stroke. A spring (or an urging member)26is arranged in a compressed state in the driving shaft6between the one end face of the piezoelectric element4and the other end face of the fitted portion22. The spring26urges the piezoelectric element4toward the other side of the extending direction of the fiducial line FL. Here, the fixture of the fixing portion21on the holder3is not limited to the use of the adhesion but may also be made by means of a screw or the like.

In the driving apparatus1or10thus constituted, the piezoelectric element4is elastically supported by the holder3. Therefore, the expansion and contraction of the piezoelectric element4can be made larger than those of the case, in which the other end of the piezoelectric element4and the one end of the driving shaft6are so urged by the holder3that the piezoelectric element4and the driving shaft6come into abutment. In the first embodiment, moreover, the piezoelectric element4is urged toward the one side of the extending direction (or the expanding and contracting direction) of the fiducial line FL by the screw25. In the second embodiment, on the other hand, the piezoelectric element4is urged toward the other side of the extending direction (or the expanding and contracting direction) of the fiducial line FL by the spring26, which is arranged in the hollow driving shaft6between the piezoelectric element4and the fitted portion22of the support member20. Therefore, the supporting stability of the piezoelectric element4by the holder3can be better improved than that of the case, in which a weight member is mounted on the other end of the piezoelectric element4with neither the screw25nor the spring26, for example. As a result, the piezoelectric element4can be prevented from dislocation, as might otherwise be caused by shocks due to a fall or the like. When the lens or the like is driven in the mobile telephone with the camera, the small-sized digital camera or the like, for example, the drive can keep an extremely high optical performance.

Here, the hardness (or the hardness of the silicone cap5, for example) at the time when the piezoelectric element4is elastically supported by the holder3is suitably a durometer A 90 or less and is preferably a durometer A 20 to 60.

In the first embodiment, moreover, the screw25urges the piezoelectric element4toward the one side of the extending direction of the fiducial line FL. This makes it unnecessary to mount a weight member or the like on the other end of the piezoelectric element4so as to displace the one end of the piezoelectric element4more than the other end.

Moreover, the supporting stability of the piezoelectric element4by the holder3and the driving performance of the driving apparatus1can be adjusted by the fastening extent of the screw25.

In the second embodiment, on the other hand, the supporting stability of the piezoelectric element4and the driving performance of the driving apparatus1or10can be adjusted by changing the spring constant of the spring26.

The actions of the driving apparatus1or10are described hereinafter.FIG. 3is a circuit diagram of a driving circuit for activating the piezoelectric element shown inFIGS. 1A and 1B.FIGS. 4A and 4Bare waveform diagrams of an input signal to be inputted to the driving circuit shown inFIG. 3.FIGS. 5A and 5Bare waveform diagrams of an output signal to be outputted from the driving circuit shown inFIG. 3.

As shown inFIG. 3, a driving circuit31is disposed in a control unit30. This control unit30performs the entire control of the driving apparatus1, and includes a CPU, a ROM, a RAM, an input signal circuit and an output signal circuit. The driving circuit31functions as a drive circuit for the piezoelectric element4, and outputs a driving electric signal to the piezoelectric element4. The driving circuit31inputs a control signal from the control signal generating unit of the control unit30, and amplifies the control signal in voltage or amplitude and outputs an electric signal for driving the piezoelectric element4. The driving circuit31used has its input stage constituted of logic circuits U1to U3, for example, and its output stage equipped with field effect type transistors (FET) Q1and Q2. These transistors Q1and Q2can output a Hi-output (or a high-potential output), a Lo-output (or a low-potential output) and an OFF-output (or an open output) as their output signals.

FIG. 4Aillustrates the input signal, which is inputted when the lens frame2is moved so that the engaged portion2amay approach the piezoelectric element4, andFIG. 4Billustrates the input signal, which is inputted when the lens frame2is moved so that the engaged portion2amay leave the piezoelectric element4. On the other hand,FIG. 5Aillustrates the output signal, which is outputted when the lens frame2is moved so that the engaged portion2amay approach the piezoelectric element4, andFIG. 5Billustrates the output signal, which is outputted when the lens frame2is moved so that the engaged portion2amay leave the piezoelectric element4.

Output signals ofFIGS. 5A and 5Bare the pulse signals, which are turned ON/OFF at the same timings as those of the input signals ofFIGS. 4A and 4B. The two signals ofFIGS. 5A and 5Bare inputted to the input terminals4aand4bof the piezoelectric element4. Although pulse signals having saw-tooth waveforms may be inputted to those input terminals4aand4b, the piezoelectric element4can be actuated, too, even if it is fed with pulse signals having rectangular waveforms, as shown inFIG. 5. Tn this case, the driving signals of the piezoelectric element4may be pulse signals having the rectangular waveforms so that the signal generations are facilitated.

The output signals ofFIGS. 5A and 5Bare constituted of two pulse signals of the common frequency. These two pulse signals are changed, by making their phases different each other, into either signals having such a potential difference as becomes stepwise large and abruptly small, or signals having such a potential difference as becomes abruptly large and stepwise small. By inputting these two signals, the expanding rate and the contracting rate of the piezoelectric element4can be made different to move the engaged portion2aand accordingly the lens frame2.

InFIGS. 5A and 5B, for example, the signals are set such that, after one was changed from Hi (High) to Lo (Low), the other becomes Hi. These signals are set such that the other signal becomes Hi after a given time lag tOFFelapsed when one signal becomes Lo. In case both the two signals are Lo, moreover, the output is turned OFF (or Open).

Signals of frequencies exceeding an audible frequency are used as the output signals ofFIGS. 5A and 5B, that is, the electric signals for activating the piezoelectric element4. InFIGS. 5A and 5B, the two signals are made to have frequencies exceeding the audible frequency, such as 30 to 80 KHz, preferably 40 to 60 KHz. The operating noise in the audible range of the piezoelectric element4can be reduced by using the signals of such frequency.

Thus, the driving apparatus1or10acts in the following manners. Specifically, the electric signals are inputted to the piezoelectric element4so that the piezoelectric element4is caused to repeat the expansion and contraction by the inputs of the electric signals. In response to these expansion and contraction, the driving shaft6reciprocates. By making different the expanding rate and the contracting rate of the piezoelectric element4, the velocity of the driving shaft6to move in one direction and the velocity to move in the other direction become different. As a result, the engaged portion2a, accordingly the lens frame2is moved in the desired direction.

The invention should not be limited to the aforementioned embodiments.

In the first embodiment, for example, an elastic member (or an urging member)126of a spring or rubber may also be arranged in a compressed state between the other end of the piezoelectric element4and the holder3, as shown inFIG. 6. In this case, too, the piezoelectric element4is urged toward the one side of the extending direction of the fiducial line FL by the elastic member126. Therefore, the supporting stability of the piezoelectric element4by the holder3can be better improved than that of the case, in which the elastic member126is not provided but a weight member is mounted on the other end of the piezoelectric element4, for example.

In the aforementioned first embodiment, on the other hand, the piezoelectric element4is urged toward the one side of the extending direction of the fiducial line FL, but the urging mode is not limited thereto. By mounting a tension spring or the like between the other end of the piezoelectric element4and the holder3, for example, the piezoelectric element4may also be urged toward the other side of the extending direction of the fiducial line FL.

Moreover, the piezoelectric element4may also be urged in the extending direction of the fiducial line FL not by pushing or pulling the other end of the piezoelectric element4directly but by pushing or pulling the other end of the piezoelectric element4indirectly through some member.

In the second embodiment, on the other hand, an elastic member of rubber or the like may be arranged in a compressed state in the driving shaft6, for example, between the one end face of the piezoelectric element4and the other end face of the fitted portion22. In this case, too, the piezoelectric element4is urged toward the other side of the extending direction of the fiducial line FL by the elastic member. Therefore, the supporting stability of the piezoelectric element4by the holder3can be better improved than that of the case, in which the elastic member is not provided but a weight member is mounted on the other end of the piezoelectric element4, for example.

In the aforementioned second embodiment, on the other hand, the piezoelectric element4is urged toward the other side of the extending direction of the fiducial line FL, but the urging mode is not limited thereto. By mounting a tension spring or the like in the driving shaft6between the one end face of the piezoelectric element4and the other end face of the fitted portion22, for example, the piezoelectric element4may also be urged toward the one side of the extending direction of the fiducial line FL.

In the driving shaft6, moreover, the piezoelectric element4may also be urged in the extending direction of the fiducial line FL not by pushing or pulling the one end face of the piezoelectric element4or the other end of the fitted portion22directly but by pushing or pulling the one end face of the piezoelectric element4or the other end face of the fitted portion indirectly through a member.

On the other hand, the support of the piezoelectric element4by the holder3should not be limited to the lateral sides one with respect to the extending direction of the fiducial line FL, but may also be made from the other side of the extending direction of the fiducial line FL, if the support is elastic.

According to the invention, it is possible to make the expansion and contraction of the electromechanical conversion element larger and to improve the supporting stability of the electromechanical conversion element better.