Piezoelectric drive device and electronic device

A piezoelectric drive device includes a piezoelectric actuator and a rotation transfer device. The piezoelectric actuator includes a vibrator and a rotor that is rotated in one specific direction by the vibrator. The rotation transfer device transmits rotational energy from the rotor to a driven rotating body, and includes an elastic device that stores rotational energy and a rotation limiting device having a drive wheel and a driven wheel. The rotation transfer device allows the driven wheel to rotate a specific angle, and restricts driving the drive wheel. The elastic device and the rotation limiting device are disposed so that rotational energy transmitted from the rotor is transmitted through one to the other of the elastic device and the rotation limiting device. The rotor, the elastic device, and the rotation limiting device render a serial path for transmitting rotational energy.

BACKGROUND

1. Technical Field

The present invention relates to a piezoelectric drive device having a piezoelectric actuator, and to an electronic device.

2. Related Art

Piezoelectric drive devices using piezoelectric devices that are resistant to the effects of magnetic fields, and are used as a drive device for driving the hands of an analog timepiece, for example, are known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-2008-245505.

The piezoelectric drive device taught in JP-A-2008-245505 has a piezoelectric actuator that has a piezoelectric element and a rotor that is rotationally driven by the piezoelectric element, a spiral spring that can store the drive power of the piezoelectric actuator as elastic energy, and a second rotor transfer wheel that is rotated by the elastic energy stored by the spiral spring.

With this piezoelectric drive device, rotation of the second rotor transfer wheel starts after the drive power of the piezoelectric actuator is stored as elastic energy by the spiral spring when the piezoelectric actuator is activated. As a result, the piezoelectric actuator is not subject to the load imposed by the inertial moments of the second rotor transfer wheel, the hand wheels, and the hands, the starting load is reduced, and the piezoelectric actuator can be driven with little power.

In addition, this piezoelectric drive device has a rotation limiting device that limits the angle of rotation of a driven rotating body to a specified angle, a first transfer path whereby the rotational energy of the rotor is transmitted to the rotation limiting device without passing through the elastic device, and a second transfer path whereby the rotational energy of the rotor is transmitted to the elastic device.

However, because the piezoelectric actuator is not subject to the load of the inertial moments of the wheels and other parts that are driven by the spiral spring with this piezoelectric drive device, the starting load of the piezoelectric actuator is reduced, but the elastic energy must be stored in the spiral spring on the second transfer path until the rotation limiting device on the first transfer path is released at startup, and a load is therefore always applied to the piezoelectric actuator when the piezoelectric actuator starts operating.

As a result, even when the load of the inertial moments of the hands is low because the hands are small, for example, a constant load is applied to the piezoelectric actuator until the rotation limiting device is released, and power consumption thus increases.

Another problem is that the timing of the first transfer path and the second transfer path must be matched, thus imposing design limitations.

SUMMARY

A piezoelectric drive device and an electronic device according to the present invention can drive with little power and eliminate the foregoing design limitations.

A first aspect of the invention is a piezoelectric drive device including a piezoelectric actuator including a vibrator having piezoelectric element, and a rotor that is rotated in one specific direction by the vibrator; and a rotation transfer device that transmits rotational energy from the rotor to a driven rotating body, includes an elastic device that can store rotational energy transmitted from the rotor as elastic energy, and a rotation limiting device that has a drive wheel and a driven wheel that rotates in conjunction with rotation of the drive wheel, allows the driven wheel to rotate a specific angle in conjunction with rotation of the drive wheel, and restricts driving the drive wheel from the driven wheel when the driven wheel rotates this specific angle. The elastic device and the rotation limiting device are disposed so that rotational energy transmitted from the rotor is transmitted through one to the other of the elastic device and the rotation limiting device; and the rotor, the elastic device, and the rotation limiting device render a serial path for transmitting rotational energy.

Note that the elastic device and the rotation limiting device may be connected in series to the rotor, or may be connected directly to the rotor, so that rotational energy is transmitted in series.

The vibrator oscillates when at least a drive signal is applied to a piezoelectric element, and is configured so that the resulting vibration causes the rotor to rotate in one specific direction. For example, the vibrator may be configured to make the rotor rotate by causing the piezoelectric element itself to oscillate, or it may be configured to make the rotor rotate by causing a laminated structure having flat piezoelectric elements disposed with a reinforcing plate therebetween to oscillate.

In addition, the rotor rotating in one specific direction means that when the rotor can rotate in a first direction and a second direction that is opposite the first direction, the rotor rotates in whichever one of the first direction and the second direction is set as the one specific direction.

Note that the driven rotating body that is driven by the piezoelectric drive device according to the invention may be any body that is rotationally driven by the rotation of the rotor transferred through the elastic device and the rotation limiting device. For example, when the piezoelectric drive device according to the invention is used as the drive device for an analog timepiece, the hands including the hour hand and minute hand, and the hour wheel and minute wheel to which the hands are attached, are driven rotating bodies.

Note, further, that rotational energy as used herein includes torque, and elastic energy includes elastic force.

Furthermore, the elastic device and the rotation limiting device being disposed so that rotational energy transmitted from the rotor is transmitted through one to the other of the elastic device and the rotation limiting device, and the rotor, the elastic device, and the rotation limiting device rendering a serial path for transmitting rotational energy, means that the rotor, the elastic device, and the rotation limiting device are disposed on the same path (serial path) as the path through which the rotational energy is transmitted. More specifically, examples of such serial configurations include the rotor, the elastic device, and the rotation limiting device being disposed in series so that the rotational energy is transmitted from the rotor through the elastic device to the rotation limiting device, and the rotational energy being transmitted from the rotor through the rotation limiting device to the elastic device.

When the piezoelectric actuator is started from a stopped state in this aspect of the invention, driven rotating bodies with a relatively large inertial moment, such as hands, are not directly rotated by the piezoelectric actuator because an elastic device is disposed to the rotation transfer device. Therefore, the inertial moment of the parts that are rotated directly by the piezoelectric actuator can be reduced by the inertial moments of the driven rotating bodies. As a result, the starting load of the piezoelectric actuator can be reduced and starting performance improved, and power consumption can be reduced. In addition, because the piezoelectric actuator drive time can be shortened when the driven rotating body is rotated only the specific angle, the drive signal supply time can also be shortened, and driving with low power is possible while also improving starting performance.

When the driven rotating body is made to rotate only a specific angle, the angle of rotation of the driven wheel can be limited to a specific angle by the rotation limiting device if the rotor is rotated at least the specific angle. More specifically, by using a rotation limiting device, the invention can hold the angle of rotation of the driven wheel constant while continuing to transfer rotational energy. The angle of rotation of the driven rotating body that rotates based on rotation of the driven wheel can therefore also be made constant.

Furthermore, because the rotor is rotated in one specific direction by the vibrator, the elastic energy transmitted from the rotor is stored in the same one specific direction, and the elastic device can easily and efficiently store the elastic energy.

Yet further, when the rotor is turned by the vibrator in the one specific direction and the direction opposite thereto, and the drive wheel is also turned in both directions, setting the position of the driven wheel in the direction of rotation becomes more difficult because of the backlash in the meshing of the drive wheel and the driven wheel. However, because the rotor turns in one specific direction and after turning is stopped by the vibrator in the invention, there is no such backlash effect and the angle of rotation of the drive wheel is therefore stable. As a result, the driven wheel can be reliably turned a specific angle, and the driven wheel can simultaneously be reliably prevented from turning the drive wheel.

Furthermore, because the rotor, the elastic device, and the rotation limiting device are disposed on the same path as the rotational energy transfer path of the rotor in the rotation transfer device, there is no need to match the timing of the first transfer path and the second transfer path as required with the related art taught in JP-A-2008-245505, the attendant design limitations can be eliminated, and the piezoelectric drive device can be easily designed and manufactured. In addition, because rotation of the drive wheel is not particularly restricted when the piezoelectric actuator starts, the load applied when the piezoelectric actuator starts can be reduced compared with the configuration taught in JP-A-2008-245505, and power consumption can be reduced accordingly.

Furthermore, because moving the hands at a constant interval is extremely important when the hands of a timepiece, for example, are driven by a piezoelectric actuator, the positions of the hands will shift and great problems can result if the piezoelectric drive device using a piezoelectric actuator cannot move the hands in steps of a constant angle.

With this embodiment of the invention, the rotation of the driven rotating body is always constant because the driven rotating body is limited to turning a specific angle of rotation by the rotation limiting device while the driven rotating body is rotated by rotor drive. Because overrun of the driven rotating body that is rotated by the piezoelectric actuator can thus be prevented, precisely controlling the angle of rotation of the rotor is not necessary, the precision of the angle of rotation of the driven rotating body can be improved, and the display precision of the hands or other display means that is rotated by the driven rotating body can be improved.

Furthermore, a rotation limiting device that can transmit rotational energy from a drive wheel to a driven wheel, and can prohibit the drive wheel being driven from the driven wheel side when the driven wheel rotates the specific angle in conjunction with rotation of the drive wheel, can normally be achieved by a Geneva gear mechanism or other type of non-reversing gear transfer mechanism. A non-reversing gear transfer mechanism such as a Geneva mechanism can transmit rotation from the drive wheel to the driven wheel, but reverse transfer of rotation from the driven wheel to the drive wheel is extremely inefficient and is normally not possible.

Therefore, by using a non-reversing gear transfer mechanism that thus inefficiently transmits rotation from the driven wheel to the drive wheel as the rotation limiting device, the invention can prohibit transfer of drive power from the driven wheel to the drive wheel when the driven wheel has rotated a specific angle. As a result, when the hands are subject to shock, such as by dropping the timepiece, torque from the hands is stopped by the rotation limiting device between the driven wheel and the drive wheel, and is prevented from being transferred to the rotor side. As a result, when the timepiece is dropped, the hands can be prevented from being moved by the force of the shock.

In a piezoelectric drive device according to another aspect of the invention, the rotational energy of the rotor is transmitted to the elastic device and stored as elastic energy, and the drive wheel of the rotation limiting device is rotationally driven by transfer of elastic energy stored in the elastic device.

If the elastic device is disposed between the piezoelectric actuator and the rotation limiting device, the load of the inertial moments of rotating parts downstream from the driven wheel, including the driven wheel of the rotation limiting device, and the bearing load of those parts, can be removed from the load applied to the piezoelectric actuator when starting. As a result, the startup load on the piezoelectric actuator can be reduced, and power consumption can be reduced accordingly.

Furthermore, when a driven rotating body turns as a result of being dropped, for example, rotation (shock) from the driven rotating body can be received by the rotation limiting device without passing through the elastic device. As a result, high elastic force is not required in the elastic device, the load from the elastic device can be reduced when the piezoelectric actuator starts, and the piezoelectric drive device can be driven with low power.

A piezoelectric drive device according to another aspect of the invention also has a rotation detection wheel disposed between the rotor and the elastic device; a rotation detection device that detects if the rotation detection wheel has rotated a specific angle; and a drive control device that stops output of drive signals that drive the piezoelectric actuator when the rotation detection device detects that the rotation detection wheel has turned a specific angle after piezoelectric actuator drive starts.

The rotation detection device may detect rotation of the rotation detection wheel continuously or intermittently.

When the rotation detection wheel is disposed downstream of the elastic device in the rotational energy transfer path, for example, the rotation detection wheel detects rotation after a certain amount of elastic energy has been stored in the elastic device. In other words, the rotation detection wheel does not rotate until a specific amount of elastic energy has been stored in the elastic device after the rotor starts rotating. As a result, the rotation detection wheel does not rotate even of the rotor has rotated the specific angle, the rotation detection wheel starts rotating after a specific amount of elastic energy has been stored, and when the rotation detection device detects rotation of the rotation detection wheel to the specified position, the rotor that has continued rotating to that point may have rotated greater than the specific angle. More specifically, it is possible for the rotor to rotate too much.

Because excessive elastic energy will be stored in the elastic device due to excessive rotation of the rotor in this situation, it is possible that the drive wheel of the rotation limiting device is made to rotate more than the specified angle, and the driven rotating body is made to rotate passed the specified position. For example, when the driven rotating bodies are hands for indicating the time, the time may not be displayed accurately.

However, because the rotation detection wheel is disposed between the rotor and the elastic device in the invention, the rotation detection device can accurately detect the the specific angle of rotation of the rotor, and can therefore accurately store only a specific amount of elastic energy in the elastic device. As a result, because the drive wheel of the rotation limiting device is driven only a specific angle, and the driven wheel is also driven to a specific position, by releasing a specific amount of elastic energy stored in the elastic device, the driven rotating body can also be accurately driven to a specific position. Therefore, when the driven rotating bodies are hands for indicating the time, for example, the time can be displayed accurately.

In a piezoelectric drive device according to another aspect of the invention the rotation detection wheel is a wheel that accelerates rotation of the rotor.

Acceleration as used herein refers to rotation of a second wheel based on rotation of a first wheel, and means the angle of rotation rotated by the second wheel is greater than the angle of rotation rotated by the first wheel.

Because the rotation detection wheel is a wheel that accelerates rotation of the rotor in this aspect of the invention, the rotation angle of the rotation detection wheel can be large even when the rotation angle of the rotor is small, and rotation of the rotation detection wheel can be easily detected. For example, if the acceleration ratio from rotation of the rotor to the rotation detection wheel is six times, the rotation detection wheel will rotate 45 degrees when the rotor rotates 7.5 degrees, for example. Directly detecting if the rotor has rotated 7.5 degrees requires good precision because of the small angle of rotation, and is accordingly difficult. However, because rotation is detected by an accelerated rotation detection wheel, the rotor rotation detection accuracy of the rotation detection device can be improved. Driving the piezoelectric actuator by means of the drive control device can therefore be controlled with good precision.

In a piezoelectric drive device according to another aspect of the invention, a speed-increasing wheel train is disposed between the rotor and the rotation limiting device, and rotation of the rotor is accelerated by the speed-increasing wheel train and transmitted to the rotation limiting device; and a speed-reducing wheel train is disposed between the rotation limiting device and the driven rotating body, and rotation of the driven wheel of the rotation limiting device is slowed by the speed-reducing wheel train and transmitted to the driven rotating body.

In this aspect of the invention rotation of the rotor is accelerated by the speed-increasing wheel train and transmitted to the rotation limiting device (drive wheel), and is then reduced by the speed-reducing wheel train from the rotation limiting device (driven wheel) and transferred to the driven rotating body. The driven wheel of the rotation limiting device rotates in conjunction with rotation of the drive wheel. This speed-increasing wheel train refers to the wheel train that increases speed as described above.

Because the drive wheel rotates faster than the rotor and has a larger angle of rotation, and a large limiting range can be assured on the drive wheel for limiting rotation of the driven wheel, rotation of the driven wheel can be easily and reliably limited.

For example, even if the rotational angle of the rotor is small, the drive wheel can rotate through a large angle of rotation of 180 degrees. Of this 180 degree angle of rotation of the drive wheel, a 120 degree range is the limiting range in which the driven wheel does not turn, and the remaining 60 degree range may be the driving range in which the driven wheel turns. If thus configured and the drive wheel rotates more than the 60 degree driving range in which the driven wheel turns, the driven wheel can be rotated a specific angle even if there is some deviation in the amount of rotation in the limiting range. More specifically, by providing a relatively large limiting range, the driven wheel can be rotated a specific angle without being affected by variation in the drive wheel.

Furthermore, because rotation from the rotor is accelerated and transmitted to the drive wheel of the rotation limiting device in the invention, even if the drive wheel rotates 180 degrees, the rotor can have a small angle of rotation determined by the speed-increasing gear ratio. If the angle of rotation of the rotor can be small, the drive time of the piezoelectric actuator can also be shortened, and power consumption can be reduced accordingly.

Furthermore, because the output of the driven wheel of the rotation limiting device is slowed by the speed-reducing wheel train, the gear ratio of the speed-increasing wheel train can be easily set with consideration for the piezoelectric actuator drive time and drive wheel rotation (angle of rotation) irrespective of the speed of the driven rotating body.

In a piezoelectric drive device according to another aspect of the invention, the rotation limiting device is rendered by a non-reversing gear transfer device that does not transfer rotation from the driven wheel to the drive wheel; and the non-reversing gear transfer device is a Geneva mechanism including a Geneva drive wheel and a Geneva driven wheel.

Because this aspect of the invention renders the rotation limiting device using a Geneva gear device, the configuration of the rotation limiting device can be simplified and the parts count reduced. In addition, if a Geneva mechanism is used, the hands, for example, can be accurately driven an angle of rotation equal to one step without being affected by variations in the angle of rotation of the rotor when the driven rotating body is moved intermittently.

In a piezoelectric drive device according to another aspect of the invention, the Geneva drive wheel has a finger that engages a tooth of the Geneva driven wheel and causes the Geneva driven wheel to rotate, and a limiting part that is contacted by a tooth of the Geneva driven wheel and stops the Geneva driven wheel from rotating. A driving range in which the finger contacts a tooth of the Geneva driven wheel and causes the Geneva driven wheel to rotate, and a limiting range in which the limiting part contacts a tooth of the Geneva driven wheel and stops rotation of the Geneva driven wheel, are disposed in the rotational range of the Geneva drive wheel. The limiting range is set to an angle of rotation range that is greater than or equal to the driving range.

Because a relatively large limiting range can be disposed to the Geneva drive wheel in this aspect of the invention, the drive wheel can be prevented from exceeding the limiting range and jumping to the next driving range even if drive wheel rotation overruns due to the inertia of the rotating rotor or residual vibration after the vibrator is stopped. As a result, driving the piezoelectric actuator can be easily controlled so that the Geneva driven wheel rotates only a specific angle.

In a piezoelectric drive device according to another aspect of the invention, the elastic device has a spiral spring.

The spiral spring may be a hairspring or a main spring such as used in timepieces.

Because the elastic device has a spiral spring in this aspect of the invention, the spiral spring can be provided without particularly increasing the installation space compared with a configuration that uses a U-shaped spring or cantilever spring even if the number of winds in the spiral spring is increased to assure a large displacement. In addition, if a large displacement is assured, substantially constant elastic energy can be produced irrespective of the displacement of the elastic device. Therefore, because the driven rotating body receives substantially constant elastic energy from the elastic device irrespective of the size of any external shock, operation of the driven rotating body can be stabilized.

In a piezoelectric drive device according to another aspect of the invention, the rotation transfer device has a rotor transfer wheel to which rotation is transmitted from the rotor; the rotor transfer wheel and the drive wheel of the rotation limiting device are disposed to the same rotating shaft; and one end of the elastic device is engaged with the rotor transfer wheel, and the other end is engaged with the drive wheel.

This aspect of the invention can render the elastic device compactly because the elastic device can be disposed between the rotor transfer wheel and the drive wheel of the rotation limiting device disposed on the same shaft.

Furthermore, if the drive wheel is disposed on top of the rotor wheel disposed coaxially to the rotor, and the elastic device is disposed therebetween, the rotor, the rotor wheel, the elastic device, and the drive wheel will be stacked in the axial direction, and the thickness increases accordingly. However, because the rotor transfer wheel can be disposed on a different shaft than the rotor in this aspect of the invention, only the rotor transfer wheel, elastic device, and drive wheel are stacked together, and the thickness can be reduced by the amount of the rotor.

In a piezoelectric drive device according to another aspect of the invention, the rotation transfer device has a transfer wheel that is disposed on the same rotating shaft as the driven wheel of the rotation limiting device; and one end of the elastic device is engaged with the driven wheel, and the other end is engaged with the transfer wheel.

Because the driven wheel of the rotation limiting device and the transfer wheel of the rotation transfer device are disposed to the same shaft in this aspect of the invention, the elastic device can be compactly disposed when the elastic device is located on the output side of the rotation limiting device.

In a piezoelectric drive device according to another aspect of the invention, the vibrator is preferably flat and has a contact probe that contacts the outside surface of the rotor, and a pressure means that presses either one of the vibrator and rotor to the other of the vibrator and rotor.

The vibrator is not limited to a flat configuration, and may have a diamond, trapezoidal, or parallelogram shape.

Furthermore, the contact probe must be disposed to touch at least the outside surface of the rotor, and may be formed protruding from an end part of a flat vibrator or from a corner part of a flat vibrator.

The pressure means may push the rotor to the vibrator, or push the vibrator to the rotor. The direction of pressure from the pressure means is substantially perpendicular to the rotary shaft of the rotor, and the direction of this pressure and the oscillation direction of the vibrator are preferably on the same plane.

By using a flat vibrator, this aspect of the invention helps render a thinner piezoelectric drive device. In addition, because a pressure means is provided, friction between the contact probe and the outside surface of the rotor can be increased, and drive power can be reliably transferred when the rotor is caused to rotate by vibration of the vibrator.

Another aspect of the invention is an electronic device having the piezoelectric drive device according to the invention, and a driven unit that is driven by the piezoelectric drive device.

This aspect of the invention enables rendering various types of electronic devices that use a piezoelectric drive device as the drive power source. This prevents driving the driven body by means of the piezoelectric drive device being affected by magnetic fields, and can reduce power consumption when driving.

In an electronic device according to another aspect of the invention, the driven unit is a time information display unit that displays time information kept by a timekeeping unit.

Because a time information display unit such as the hands of a timepiece can be driven by a piezoelectric drive device with this aspect of the invention, driving the hands can be prevented from being affected by magnetic fields, and the hands of the time information display unit, for example, can be driven with low power.

DESCRIPTION OF EMBODIMENTS

A first embodiment of the invention is described next with reference to the accompanying figures.

Note that in the second and third embodiments described below components that are identical to and components that have the same function as components described in the first embodiment are identified by the same reference numerals, and further description thereof is omitted or simplified.

General Configuration

FIG. 1is a plan view schematically showing the configuration of an electronic timepiece1as an example of an electronic device using a piezoelectric drive device according to this embodiment of the invention.FIG. 2andFIG. 3are section views showing selected parts of the configuration.

FIG. 1is a view from the opposite side of the electronic timepiece1to the side on which the time is displayed (the “time display side”), that is, from the back cover side.

Note that when the electronic timepiece1is seen as shown inFIG. 1, the direction from the center to the time adjustment mechanism80is the 3:00 o'clock side of the electronic timepiece1; the direction from the center to the rotation transfer device40is the 9:00 o'clock side; the opposite direction to the direction from the center to the piezoelectric actuator20is the 12:00 o'clock side; and the direction from the center to the piezoelectric actuator20is the 6:00 o'clock side.

When seen as shown inFIG. 2andFIG. 3, the time display side (the main plate3side) of the electronic timepiece1is down, and the back cover side (the train wheel bridge4side) is up.

As shown inFIG. 1, the electronic timepiece1includes a piezoelectric drive device10that drives hands for displaying the time, a battery2, an IC chip5, and a quartz oscillator6. The IC chip5and quartz oscillator6, for example, are disposed to a circuit board not shown. The battery2is held by a battery presser.

Note also that the electronic timepiece1according to this embodiment of the invention is a two-hand analog wristwatch having an hour hand and a minute hand as hands for displaying time.

Piezoelectric Drive Device

As shown inFIG. 1toFIG. 3, the piezoelectric drive device10that drives the hands includes a piezoelectric actuator20, and a rotation transfer device40that transfers output from the piezoelectric actuator20to the hands, which are driven rotating bodies.

Piezoelectric Actuator

The piezoelectric actuator20includes a vibrator21and a rotor30. As shown inFIG. 2, the vibrator21has a laminated structure in which two flat, rectangular piezoelectric elements22are disposed with a stainless steel reinforcing plate23therebetween, the reinforcing plate23being thinner than and substantially the same shape as the piezoelectric elements22.

The piezoelectric elements22can be made from a variety of materials including lead zirconate titanate (PZT(R)), quartz, lithium niobate, barium titanate, lead titanate, lead metaniobate, polyvinylidene fluoride, lead zinc niobate, and lead scandium niobate, for example.

The vibrator21has a contact probe25at the widthwise edge of one short side. This contact probe25is formed by cutting or otherwise shaping the reinforcing plate23, and the gently curving distal end part of the contact probe25protrudes from the piezoelectric elements22. The vibrator21is positioned so that the distal end of this contact probe25contacts the outside surface of the rotor30.

Note that because the contact probe25is formed eccentrically positioned to the widthwise center of the vibrator21, the weight is unbalanced widthwise to the vibrator21, and the piezoelectric actuator20can be easily made to produce a bending oscillation.

Note, further, that a contact probe26identical to the contact probe25is formed on the other short side of the vibrator21at a position symmetrical to the plane center of the vibrator21so that a bending oscillation can be produced even more easily.

A support unit27is formed on one long side of the piezoelectric actuator20. The support unit27is formed in unison with the reinforcing plate23. This support unit27is fastened, for example, to the main plate with a screw.

A circuit board for the piezoelectric elements is also disposed to this support unit27, and is extended with a wire lead disposed on the surface of the circuit board connected to a drive electrode disposed on the surface of the piezoelectric elements22so that the piezoelectric elements22can be driven.

Applying a voltage of a specific frequency to the drive electrode of the vibrator21excites vibrations in a longitudinal primary vibration mode in which the piezoelectric elements22expand and contract lengthwise. Because contact probe25and contact probe26are disposed at diagonally opposite ends of the vibrator21, the weight of the vibrator21is unbalanced to the longitudinal center line. This imbalance excites vibrations in a bending secondary vibration mode in which the vibrator21bends in the direction substantially perpendicular to the length. The vibrator21thus produces vibrations combining this longitudinal primary vibration mode and the bending secondary vibration mode, and causes the contact probe25to oscillate on a substantially elliptical path.

Rotor

The rotor30that is driven by contact with the vibrator21is supported freely rotatably by a rotor guide320. The rotor30and rotor guide320together render a rotor block. A rotor wheel31that rotates in unison with the rotor30is also disposed to the rotor30.

As shown inFIG. 1, the rotor guide320is disposed to pivot freely on a pivot pin321, and one end of a pressure spring35used as a pressure means is disposed in contact with a pin322disposed to the rotor guide320.

The other end of this pressure spring35is engaged by a stationary pin36disposed on the main plate, for example, so that the pressure spring35disposed between the stationary pin36and the rotor guide320deflects and urges the rotor guide320.

As a result of the rotor guide320being urged by the pressure means (pressure spring35), the rotor30contacts the contact probe25of the piezoelectric actuator20with a specific contact force (contact pressure). As a result, when the vibrator21of the piezoelectric actuator20vibrates and the contact probe25oscillates on a substantially elliptical path, contact of the contact probe25with the side of the rotor30causes the rotor30to turn. In this embodiment of the invention the rotor30rotates clockwise as seen inFIG. 1. The one specific direction in which the rotor30thus turns in this embodiment of the invention is therefore the clockwise direction inFIG. 1.

Rotation Transfer Device

The rotation transfer device40transfers the rotational energy of the rotor30to a driven rotating body, and as shown inFIG. 2toFIG. 4includes a rotation detection wheel41, an elastic device42, a rotation limiting device43, the third wheel44, the second wheel45, the day wheel46, and hour wheel47.

Rotation Detection Wheel

The rotation detection wheel41includes a pinion411that meshes with the rotor wheel31, and a wheel412that rotates in unison with the pinion411, and is supported freely rotatably by the main plate3and train wheel bridge4.

The wheel412has a boss part412A disposed in the center, an annular rim part412B disposed around the outside, and a plurality of spoke parts412C disposed radiating from the boss part412A to the rim part412B. Holes are thus formed between the boss part412A and rim part412B in the areas between the spoke parts412C.

Elastic Device

The elastic device42includes a pinion421, a spindle422, a spring engaging member423, a bearing ring424and engaging pin425fastened to the Geneva drive wheel431of the rotation limiting device43, a spiral spring426, and a cover427. The Geneva drive wheel431is rotatably disposed on the spindle422by means of the bearing ring424fixed in the center of the Geneva drive wheel431.

The pinion421rotates in unison with the spindle422, which is supported freely rotatably by the main plate3and the train wheel bridge4, and meshes with the wheel412of the rotation detection wheel41.

The spring engaging member423is fit on and rotates in unison with the spindle422, and is engaged by the inside circumference end of the spiral spring426. The outside circumference end of the spiral spring426is engaged by the engaging pin425. In this embodiment of the invention a rotor transfer wheel whereby rotation from the rotor30is transmitted through the rotation detection wheel41is rendered by the pinion421, spindle422, and spring engaging member423rotating in unison. One end of the spiral spring426is engaged by this rotor transfer wheel.

The cover427is fixed in a specific plane position to the spindle422, and prevents the middle of the spiral spring426from popping out to the train wheel bridge4side. In addition, by being fastened to the spindle422in this specific plane position, the side of the cover427can meet and position the engaging pin425that secures the outside end of the spiral spring426as shown inFIG. 4. By thus positioning the engaging pin425, the elastic force of the spiral spring426holds the Geneva drive wheel431in a specific rotational position, that is, in the position where the engaging pin425meets the side of the cover427.

The spiral spring426is formed by winding thin flat spring stock that is rectangular in section view in a counterclockwise spiral from the center to the outside circumference side as seen in plan view inFIG. 4. The spiral spring426is elastically deformed in the direction increasing the number of windings as a result of the pinion421, spindle422, and spring engaging member423turning clockwise in advance of the Geneva drive wheel431, and can thus store the drive power transferred to the pinion421as elastic energy.

The spiral spring426is held by the spring engaging member423and the engaging pin425when initially deflected (in the initial elastic deformation position). More specifically, the elastic force of this initial deflection is set so that the engaging pin425of the Geneva drive wheel431reliably contacts the side wall of the cover427when the piezoelectric actuator20is stopped, that is, when the pinion421, spindle422, and cover427are stopped. In this position, a tooth436and a tooth437of the Geneva driven wheel435contact the limiting part433of the Geneva drive wheel431, the Geneva driven wheel435is positioned in the direction of rotation, and rotation of the Geneva driven wheel435is prohibited even if torque is produced from the Geneva driven wheel435side. In addition, when the spiral spring426is thus initially deflected, the hands can be driven easily even when the hour hand, minute hand, or other hands are heavy (the inertial moment is high).

Rotation Limiting Device

The rotation limiting device43is positioned so that rotational energy from the rotor30is transmitted through the elastic device42. More specifically, the rotation limiting device43together with the rotor30and elastic device42render a serial path for transmitting rotational energy from the rotor30. This rotation limiting device43is configured using a Geneva mechanism, which is a non-reversing gear transfer device, and includes a Geneva drive wheel431(drive wheel) and a Geneva driven wheel435(driven wheel) that is turned by the Geneva drive wheel431.

The Geneva drive wheel431is supported freely rotatably on the spindle422by means of the bearing ring424affixed in the center. Fingers (teeth)432that engage the Geneva driven wheel435are disposed symmetrically to the axis of rotation of the Geneva drive wheel431, that is, at two positions 180 degrees apart in the rotation direction of the Geneva drive wheel431. The limiting part433is rendered by the curved outside circumference surfaces between the two fingers432. The radius of this limiting part433from the center axis is greater than the radius of the base circle of the fingers432(teeth), and is smaller than the radius of the tip circle.

The Geneva driven wheel435has teeth436formed at five places72degrees apart in the direction of rotation on the outside circumference, teeth437corresponding to each of the teeth436, and a pinion438disposed on the center shaft.

The interval between the teeth436and teeth437is a small interval of approximately20degrees from one tooth436to the tooth437adjacent thereto in the counter-rotation direction, and a large interval of approximately50degrees from the tooth436to the tooth437adjacent thereto in the direction of rotation.

As shown inFIG. 5A, when two teeth437and436on opposite sides of this large gap contact the limiting part433of the Geneva drive wheel431, the Geneva driven wheel435cannot turn in either the direction of rotation or the counter-rotation direction. More specifically, the Geneva driven wheel435is prevented from turning by means of the Geneva drive wheel431.

Rotation of the Geneva driven wheel435is thus limited until the Geneva drive wheel431turns and a finger432contacts a tooth436. In this embodiment of the invention, rotation of the Geneva driven wheel435is restricted from the position shown inFIG. 5Auntil the Geneva drive wheel431rotates 120 degrees.

As shown inFIG. 5B, when the Geneva drive wheel431rotates further from the position where a finger432of the Geneva drive wheel431contacts a tooth436of the Geneva driven wheel435, the Geneva driven wheel435also rotates in conjunction therewith as shown inFIG. 5C. Rotation of the Geneva driven wheel435then stops after returning to the position shown inFIG. 5A.

In this embodiment of the invention, therefore, when the Geneva drive wheel431turns 180 degrees, the Geneva driven wheel435is prevented from turning through a 120 degree portion of this rotation (rotation-limited range), but during the remaining 60 degrees, the Geneva driven wheel435rotates 72 degrees in conjunction with the Geneva drive wheel431. The Geneva driven wheel435thus turns intermittently in conjunction with rotation of the Geneva drive wheel431.

As described above, rotation of the Geneva drive wheel431causes the Geneva driven wheel435to turn intermittently, and the angle of rotation of the Geneva driven wheel435is set to a specific angle. On the other hand, even if the Geneva driven wheel435side turns, this rotation is limited by the Geneva drive wheel431and is not transmitted to the Geneva drive wheel431side. The Geneva drive wheel431and Geneva driven wheel435thus render a non-reversing gear transfer device, and render a rotation limiting device whereby the Geneva driven wheel435turns a specific angle (72 degrees) in conjunction with rotation of the Geneva drive wheel431, and driving the Geneva drive wheel431from the Geneva driven wheel435is prohibited when the Geneva driven wheel435has turned this specific angle.

In addition, the fingers432are asymmetrical tooth forms having the distal ends thereof sloped in the direction of rotation of the Geneva drive wheel431. As a result, as shown inFIG. 5B, when the Geneva drive wheel431turns in the direction of the arrow inFIG. 5Band contacts a tooth436of the Geneva driven wheel435, the finger432pushes the tooth436in the rotation direction of the Geneva driven wheel435, and the Geneva driven wheel435is thus driven rotationally.

Furthermore, while the finger432contacts a tooth437when the Geneva drive wheel431turns in the opposite direction, the finger432pushes the tooth437toward the center of rotation of the Geneva driven wheel435because the surface of the distal end of the finger432on the opposite side as the side that contacts the tooth436inFIG. 5Bis sloped, and rotation can therefore not be transmitted to the Geneva driven wheel435.

Wheels Train Configuration Downstream from the Geneva Driven Wheel

As shown inFIG. 1toFIG. 4, the pinion438of the Geneva driven wheel435meshes with the third wheel44, and the pinion441of the third wheel44meshes with the second wheel45. A second pinion451is disposed to the second wheel45, this second pinion451meshes with the day wheel46, and the pinion461of the day wheel46meshes with the hour wheel47.

A minute hand not shown is disposed to the distal end of the second pinion451of the second wheel45. An hour hand not shown is attached to the distal end of the hour wheel47. These wheels44to46are axially supported on the main plate3and train wheel bridge4.

Note that if a second hand is provided, a fourth wheel and a seconds pinion that rotates in unison with the fourth wheel may be disposed in the second pinion451and a second hand attached thereto as in a common timepiece. However, because a second hand is not provided in this embodiment of the invention, a shaft member48that supports the second pinion451freely rotatably is disposed in the second pinion451.

Rotation Detection Device

The electronic timepiece1according to this embodiment of the invention has a rotation detection device70(seeFIG. 6) that detects rotation of the rotation detection wheel41.

The rotation detection device70detects if the rotation detection wheel41has turned a specific angle by detecting the spoke parts412C of the rotation detection wheel41or the holes between the spoke parts412C.

More specifically, the rotation detection device70uses a reflection or a transmission photosensor having an LED or other light-emitting device and a phototransistor or other photoreception device. In this embodiment of the invention a reflection photosensor is used, light is projected from the back cover side of the wheel412, and the photosensor is set to receive the light that passes through the holes and is reflected by the main plate3, or the light that is reflected by the spoke parts412C, and rotation is detected from the output of this photosensor.

More specifically, in this embodiment of the invention light from the rotation detection device70that passes through the holes in the rotation detection wheel41and is reflected by the main plate3is picked up and detected by the photosensor. As a result, if the spoke parts412C are formed at 45 degree intervals in the direction of rotation, the detection of reflected light passing through these holes switches between an on state in which the output of the photoreceptor is greater than or equal to a specified value, and an off state in which the output is less than the specified value, every time the rotation detection wheel41turns 45 degrees. Therefore, whether the rotation detection wheel41has turned 45 degrees can be detected by comparing photoreceptor output with a specified threshold value.

Note that a reflection photosensor requires a specific distance between the photoreception surface of the photosensor and the reflecting surface. Therefore compared with a configuration detecting reflection from the spoke parts412C, detecting reflections from the main plate3has the advantage of enabling placing the photosensor closer to the main plate3and rendering the electronic timepiece1accordingly thinner.

Note that the rotation detection device70is not limited to detecting the movement (the angle of rotation) of the rotation detection wheel41, and may directly detect the movement of the rotor30or rotor wheel31, for example. More specifically, the rotation detection device70is disposed between the rotor30and the spiral spring426, and may detect the movement of the rotor30or any member that rotates in conjunction with the rotor30.

Furthermore, in addition to optical sensing devices, the rotation detection device70may use a spring or other type of mechanical contact, a magnetic sensor, or other type of sensor that can detect the movement (the amount of movement, such as the angle of rotation) of the rotor30or rotation detection wheel41.

Time Adjustment Mechanism

A time adjustment mechanism80for adjusting the time by means of operating a crown is also disposed in the electronic timepiece1according to this embodiment of the invention. This time adjustment mechanism80is a typical mechanism known from the literature, and includes a winding stem81that turns when a crown attached thereto turns, a setting lever82, a yoke83, a clutch wheel84, and a setting wheel85.

When the crown is pulled out and the crown is turned with the clutch wheel84engaged with the setting wheel85due to the operation of the setting lever82and yoke83, the day wheel46engaging the pinion851of the setting wheel85turns as the crown turns. Because the Geneva driven wheel435is prevented from turning by means of the Geneva drive wheel431, the third wheel44and second wheel45do not turn, the second pinion451rotates slipping on the second wheel45, and the position of the minute hand is adjusted. Because the hour wheel47also turns when the day wheel46turns, the position of the hour hand is also adjusted at the same time.

Timepiece Circuit Configuration

The circuit configuration of the timepiece1is described next with reference toFIG. 6.

The drive circuit of the timepiece1includes an oscillation circuit102, a frequency division circuit103, and a control circuit104that are driven by a power supply101including a battery2such as a primary battery or a secondary battery.

The oscillation circuit102has a reference oscillation source such as a quartz oscillator6, and outputs an oscillation signal to the frequency division circuit103.

The frequency division circuit103receives the oscillation signal input from the oscillation circuit102, and based on this oscillation signal outputs a time reference signal (such as a 1-Hz signal).

The control circuit104counts the time based on the reference signal output from the frequency division circuit103, and tells the timepiece drive circuit106to output a timepiece drive signal according to the timepiece specifications.

For example, to advance the movement in steps at 1-second intervals, such as when the timepiece1has an hour hand, a minute hand, and a second hand, the control circuit104controls the timepiece drive circuit106to output a timepiece drive signal once every second.

On the other hand, if the timepiece1is a two hand timepiece having an hour hand and a minute hand as in this embodiment of the invention, and the minute hand is advanced3times at 20-second intervals, the control circuit104controls the timepiece drive circuit106to output the timepiece drive signal time once every 20 seconds.

The control circuit104is connected to the rotation detection device70described above, and controls operation of the timepiece drive circuit106triggered by the detection signal output from the rotation detection device70.

When the detection signal is output from the rotation detection device70, that is, when the rotor30is detected to have moved a specific amount, the control circuit104controls the timepiece drive circuit106to stop outputting the drive signal, that is, applies control that stops the piezoelectric actuator20.

For example, when the second hand is moved in steps at a 1-second interval, the control circuit104instructs the timepiece drive circuit106to output a drive signal every second. In this situation the rotation detection device70is set to detect when the rotor30has rotated a specific angle corresponding to the minute hand moving the distance of 1 minute, that is, 6 degrees, and when the rotation detection device70detects that the rotor30has rotated this specific angle, the control circuit104instructs the timepiece drive circuit106to stop outputting the drive signal. As a result, the piezoelectric actuator20drives the second hand at a 1-second interval to move the distance of one second.

When the minute hand is advanced 3 times at a 20-second interval such as in a two-hand timepiece, the control circuit104instructs the timepiece drive circuit106to output a drive signal every 20 seconds. In this configuration the rotation detection device70is set to detect rotation of the rotor30equal to the specific angle corresponding to the minute hand moving the amount of 20 seconds or 3 times, and when the rotation detection device70detects that the rotor30has moved this specific angle, the control circuit104causes the timepiece drive circuit106to stop outputting the drive signal.

An operation detection unit109for detecting operation of the time adjustment mechanism80, such as the crown or a button, is also connected to the control circuit104. When the operation detection unit109detects a specific operation of the time adjustment mechanism80, the operation detection unit109outputs a corresponding detection signal to the control circuit104. Based on the signal from the operation detection unit109, the control circuit104instructs the timepiece drive circuit106to output the drive signal, that is, to start driving the piezoelectric actuator20, or to stop outputting the drive signal, that is, to stop driving the piezoelectric actuator20.

For example, when the crown is pulled out to adjust the time, the movement of the hands must be stopped. Therefore, when the operation detection unit109outputs a detection signal indicating the crown was pulled out, the control circuit104outputs a control signal for stopping driving the piezoelectric actuator20to the timepiece drive circuit106. When the operation detection unit109outputs a detection signal indicating that the crown was pushed in, the control circuit104outputs a control signal to start driving the piezoelectric actuator20to the timepiece drive circuit106.

A drive control device that controls driving the piezoelectric actuator20is thus rendered by the control circuit104.

The timepiece drive circuit106receives control signals from the control circuit104, and outputs drive signals to the piezoelectric actuator20. More specifically, the timepiece drive circuit106applies a drive voltage of a specific frequency to and drives the piezoelectric elements22of the piezoelectric actuator20by means of an AC signal (pulse signal).

It should be noted that the method of controlling the drive frequency of the piezoelectric actuator20is not specifically limited. As taught in Japanese Unexamined Patent Appl. Pub. JP-A-2006-20445, for example, a method of driving the piezoelectric actuator20reliably by causing the frequency of the drive signal supplied to the piezoelectric elements22to sweep (change) through a wide range including the drivable frequency range may be used. Alternatively, as taught in Japanese Unexamined Patent Appl. Pub. JP-A-2006-33912, a method that changes the frequency of the drive signal so that the phase difference of the frequency of the drive signal supplied to the piezoelectric elements22and the detection signal acquired from the oscillation state of the piezoelectric elements22goes to a specified target phase difference suitable for driving the piezoelectric actuator20may be used. Further alternatively, the piezoelectric actuator20may be driven using a fixed frequency preset according to the temperature.

Further alternatively, a detection electrode to which voltage is not applied may be disposed to the piezoelectric elements22of the piezoelectric actuator20, and the detection signal output from this detection electrode may be fed back to the control circuit104to control the frequency of the drive signal. This detection signal enables the control circuit104to check the drive status of the piezoelectric actuator20, and enables feedback control of the drive signal frequency.

The output of the piezoelectric actuator20is transmitted through the rotation transfer device40as described above.

The rotation transfer device40converts the rotational energy output from the piezoelectric actuator20to an amount of movement suitable for displaying the time, and transmits this movement to the time display unit110(hands), that is, the time information display unit. In this embodiment of the invention a speed-increasing wheel train is rendered from the rotor wheel31to the rotation detection wheel41and Geneva drive wheel431, and a speed-reducing wheel train is rendered from the Geneva driven wheel435through the third wheel44, second wheel45, day wheel46, and hour wheel47. As a result, the movement of the piezoelectric actuator20(rotation of the rotor30) is converted at a specific speed increasing/reducing ratio to the movement of the time display.

Operation of the Piezoelectric Drive Device when Starting

The operation of starting the piezoelectric drive device is described next.

First, when a drive signal (drive voltage) is applied by the timepiece drive circuit106to the vibrator21of the piezoelectric actuator20when the piezoelectric actuator20is stopped, the vibrator21vibrates and the rotor30turns. Rotational energy is thus transmitted from the rotor30through the rotor wheel31and rotation detection wheel41to the pinion421.

The spindle422and spring engaging member423rotate in conjunction with rotation of the pinion421, the spiral spring426is thereby wound up and elastically deformed, and the transmitted rotational energy is stored as elastic energy in the spiral spring426.

When winding the spiral spring426starts, the elastic energy stored in the spiral spring426is weak. As a result, the rotational energy applied from the spiral spring426to the Geneva drive wheel431is low and the Geneva drive wheel431remains stopped.

However, when the elastic energy stored in the spiral spring426increases and the rotational energy applied to the Geneva drive wheel431reaches a specific level, the Geneva drive wheel431starts turning.

However, as described above, the rotational energy of the Geneva drive wheel431is not transmitted to the Geneva driven wheel435from when the Geneva drive wheel431starts turning until a finger432thereof contacts a tooth436of the Geneva driven wheel435. Therefore, in order to make the Geneva drive wheel431turn, the rotational energy applied from the spiral spring426must only be of a magnitude equal to the load equal to the load from the inertial moment of the Geneva drive wheel431plus the bearing load, and is not affected by the bearing load or the load from the inertial moments of the rotating bodies from the Geneva driven wheel435to the hands. The time lag from when piezoelectric actuator20drive starts until the Geneva drive wheel431turns can therefore be made very short.

When the Geneva drive wheel431rotates approximately 120 degrees from the start of rotation, a finger432contacts a tooth436of the Geneva driven wheel435, and the Geneva driven wheel435starts turning. Note that to make the Geneva driven wheel435turn, rotational energy equal to the combined load of the load from the inertial moments of the rotating bodies (the Geneva driven wheel435, third wheel44, second wheel45, day wheel46, hour wheel47, and each of the hands in this embodiment of the invention) and the bearing load of each of these rotating bodies is required.

Therefore, if this specified rotational energy cannot be applied to the Geneva driven wheel435when the finger432of the Geneva drive wheel431contacts the tooth436of the Geneva driven wheel435, the Geneva drive wheel431stops, the spiral spring426is wound and the elastic energy stored, and when the rotational energy applied by this elastic energy becomes equal to or greater than this specified level, the Geneva drive wheel431and Geneva driven wheel435start turning.

When the finger432of the Geneva drive wheel431contacts the tooth436of the Geneva driven wheel435, the Geneva drive wheel431turns the specified angle, and the finger432and Geneva driven wheel435disengage, the Geneva driven wheel435stops even if the Geneva drive wheel431continues turning.

For example, if the speed-increasing ratio from the rotor wheel31to the rotation detection wheel41is 6 times and the rotor30and rotor wheel31rotate 7.5 degrees, the rotation detection wheel41rotates 45 degrees. Because the spoke parts412C of the rotation detection wheel41are located at 45 degree intervals, the rotation detection device70outputs a detection signal every time the rotation detection wheel41turns 45 degrees.

Furthermore, because the speed-increasing ratio from the rotation detection wheel41to the Geneva drive wheel431is 4 times in this embodiment of the invention, the Geneva drive wheel431turns 180 degrees when the rotation detection wheel41turns 45 degrees. When the Geneva drive wheel431turns 180 degrees, rotation of the Geneva driven wheel435is restricted and the Geneva driven wheel435cannot turn while the Geneva driven wheel435is in contact with the Geneva drive wheel431through the limiting range (120 degrees in this embodiment of the invention), but the Geneva driven wheel435turns 72 degrees through the drive range (60 degrees in this embodiment of the invention) in which the finger432is in contact with the tooth436of the Geneva driven wheel435, and then stops.

When the rotation detection device70detects that the rotation detection wheel41turned 45 degrees, the piezoelectric actuator20stops as a result of the detection signal output therefrom.

When the Geneva driven wheel435turns 72 degrees, the second pinion451to which the minute hand is attached rotates 3 degrees and the hour wheel47to which the hour hand is attached rotates approximately 0.17 degree as a result of the speed-reducing wheel train from the Geneva driven wheel435to the hour wheel47. Therefore, by outputting a drive signal from the timepiece drive circuit106and driving the piezoelectric actuator20at a 20-second interval, and stopping the piezoelectric actuator20when the rotation detection wheel41turns 45 degrees, the minute hand and hour hand can be moved in steps at a 20-second interval and the time can be indicated.

Effect

The effect of this embodiment of the invention is described next.

(1) In a rotation transfer device40that transmits rotational energy output from a piezoelectric actuator20, an elastic device42that stores rotational energy from the piezoelectric actuator20as elastic energy, and a rotation limiting device that is composed of a Geneva drive wheel431and a Geneva driven wheel435, rotates the Geneva driven wheel435intermittently, and limits the angle of rotation of the Geneva driven wheel435to a specific angle, are disposed on the same path. More specifically, the rotor, the elastic device, and the rotation limiting device are disposed on the same path (a serial path) that transmits rotational energy. As a result, the starting load of the piezoelectric actuator20is the bearing load and the load from the inertial moments of rotating bodies including the rotor30, the rotor wheel31, the rotation detection wheel41, the pinion421, and the spindle422that are before the spiral spring426on the rotation transfer path, and the bearing load and the load from the inertial moments of the rotating bodies from the Geneva drive wheel431to the hands do not act on the piezoelectric actuator20. As a result, the load applied when the piezoelectric actuator20starts can be reduced, starting performance is improved, and power consumption can be reduced.

The hands of an analog timepiece in particular have a large inertial moment, and the shapes of the hands differ according to the design (model) of the timepiece. As a result, the inertial moment of the hands differs according to the model of the timepiece, and power consumption therefore also changes with drive methods according to the related art. This means that the battery life also changes in a timepiece that is driven by a battery.

By providing a spiral spring426according to this embodiment of the invention, however, the load from the inertial moment of the hands does not act on the piezoelectric actuator20, the effect of change in the inertial moment of the hands can be cancelled, low power drive is possible, and changes in battery life due to model changes can be prevented.

In addition, disc-shaped hands having a larger inertial moment than conventional hands can also be used, and the freedom of timepiece design can be improved.

(2) By using a Geneva mechanism, which is a type of non-reversing gear transfer mechanism, as the rotation limiting device43, the angle of rotation of the Geneva driven wheel435can be limited to a specific angle, which is specifically 72 degrees in this embodiment of the invention, while transmitting rotational energy from the piezoelectric actuator20to the driven rotating body side through the Geneva drive wheel431and Geneva driven wheel435. As a result, it is not necessary to render in a timepiece1according to this embodiment of the invention a first transfer path for transmitting the rotational energy of a rotor to a rotation limiting device without passing through the elastic device, and a second transfer path for transferring the rotational energy of the rotor to the elastic device, as taught in Japanese Unexamined Patent Appl. Pub. JP-A-2008-245505. The design limitations on the electronic timepiece1are thus reduced, and design and manufacturing are simplified.

In addition, because the rotor30is rotated in one specific direction by the vibrator21, the elastic energy stored by the rotational energy transmitted from the rotor30is stored in the same one specific direction, and the spiral spring426can easily and efficiently store the elastic energy.

Yet further, when the rotor30is turned by the vibrator21in the one specific direction and the direction opposite thereto, and the Geneva drive wheel431is also turned in both directions, setting the position of the Geneva driven wheel435in the direction of rotation becomes more difficult because of the backlash in the meshing of the Geneva drive wheel431and the Geneva driven wheel435. However, because the rotor30turns in one specific direction and after turning is stopped by the vibrator21in this embodiment of the invention, there is no such backlash effect and the angle of rotation of the Geneva drive wheel431is therefore stable. As a result, the Geneva driven wheel435can be reliably turned a specific angle, and the Geneva driven wheel435can simultaneously be reliably prevented from turning the Geneva drive wheel431.

(3) A further problem with the technology taught in JP-A-2008-245505 is that the elastic energy of a spiral spring must be stored in an elastic device on a second transfer path until restriction by the rotation limiting device is released, and a load is therefore always applied when the piezoelectric actuator20is started.

However, because rotation of the Geneva drive wheel431is not specifically limited when the piezoelectric actuator20starts in this embodiment of the invention, the load applied when the piezoelectric actuator20starts can be reduced compared with JP-A-2008-245505, and power consumption can be reduced accordingly.

(4) Because the amplitude of the piezoelectric actuator20can be driven to a specific amplitude and the rotor speed can be increased to a desired speed in a short time, and the startup time can be shortened, by providing a spiral spring426and reducing the starting load on the piezoelectric actuator20, power consumption can be further reduced.

(5) Because the rotation of the Geneva driven wheel435is restricted by the Geneva drive wheel431while the teeth436and437are in contact with the limiting part433of the Geneva drive wheel431, shaking of the hands can be suppressed when an external shock acts on the hands, such as when the timepiece1is dropped.

In addition, because a spiral spring426is provided, even if the shock of being dropped is applied from the Geneva driven wheel435to the Geneva drive wheel431, the force of impact is buffered by the spiral spring426and can be prevented from being transmitted to the piezoelectric actuator20side, and operation of the piezoelectric actuator20can be stabilized.

Yet further, because rotation of the Geneva driven wheel435can be limited on the Geneva drive wheel431side, a separate limiting means for limiting rotation of the third wheel44, for example, does not need to be provided for adjusting the time by operating the crown, and the parts count can be reduced.

(6) Because a spiral spring426is provided, great displacement can be easily assured by increasing the number of winds in the spiral spring426, and the spiral spring426can be provided without particularly increasing the installation space compared with a configuration that uses a U-shaped spring or cantilever spring.

In addition, because a spiral spring426is provided, great displacement can be assured as described above, and substantially constant elastic energy can be produced irrespective of the displacement of the spiral spring426. Therefore, because the Geneva drive wheel431receives substantially constant elastic energy from the spiral spring426irrespective of the size of any external shock, operation of the Geneva drive wheel431and the Geneva driven wheel435can be stabilized.

Yet further, even if shock is applied from the hands, the shock can be received by the rotation limiting device43, the spiral spring426does not need to absorb the force, and the elastic force of the spiral spring426does not need to be set high. As a result, the load applied by the spiral spring426when the piezoelectric actuator20starts up can be reduced, and the piezoelectric drive device10can be driven with less power.

(7) The Geneva drive wheel431has fingers432for causing the Geneva driven wheel435to turn disposed 180 degrees apart. As the Geneva drive wheel431turns 180 degrees, a finger432engages the Geneva driven wheel435and causes the Geneva driven wheel435to turn while the Geneva drive wheel431rotates through the 60 degree drive range. The range of the remaining 120 degrees is the limiting range in which the limiting part433contacts the teeth436and437of the Geneva driven wheel435and restricts rotation of the Geneva driven wheel435.

As a result, because rotation of the Geneva driven wheel435remains limited after the finger432and Geneva driven wheel435disengage even if the Geneva drive wheel431overruns due to the attenuating oscillation of the vibrator21and the inertia of the rotor30after the rotation detection device70detects that the rotation detection wheel41rotated a specific angle (45 degrees) when the piezoelectric actuator20is driven, and driving the piezoelectric actuator20is stopped, the Geneva driven wheel435can be driven intermittently and the angle of rotation can be kept constant (72 degrees in this embodiment of the invention). As a result, the movement of the hands to which rotation of the Geneva driven wheel435is transmitted can be held constant, and the positioning precision of the hands that are moved in steps can be assured.

(8) Because the piezoelectric elements22is rectangular, the piezoelectric drive device10can be rendered even thinner.

(9) The distance the hands move can be accurately controlled because the rotation detection device70, that is, the rotation detection wheel41, detects the movement of the rotor30. The reason for this is described next.

Because the vibrator21of the piezoelectric actuator20and the rotor30transfer torque by means of friction, accurately setting the amount of rotor30rotation by controlling the drive time of the piezoelectric actuator20is difficult. In this embodiment of the invention the rotor30, that is, the hands, can be moved accurately because the movement of the rotor30and the directly driven rotation detection wheel41is detected by the rotation detection device70, and drive stops when the rotation detection device70detects that the rotor30has moved a specific amount. In addition, by disposing the rotation detection wheel41between the rotor30and the elastic device42(particularly the spiral spring426), rotation of the rotor30can be detected before the rotational energy of the rotor30is stored as elastic energy in the spiral spring426. Rotation of the rotor30due to driving the piezoelectric actuator20can therefore be more accurately detected, and the rotor30and hands can be moved more precisely than when the rotation detection wheel41is disposed on the back side of the elastic device42(the opposite side to the rotor).

A piezoelectric drive device10A in a timepiece1A according to a second embodiment of the invention is described next with reference toFIG. 7.

In the first embodiment of the invention, the rotational energy of the piezoelectric actuator20is stored as elastic energy in the spiral spring426of the elastic device42in the rotation transfer device40, and the Geneva drive wheel431and the Geneva driven wheel435are then made to rotate using this elastic energy.

In this second embodiment of the invention, the Geneva drive wheel431A and the Geneva driven wheel435A are rotated by the rotational energy of the piezoelectric actuator20, and the spiral spring426A is wound by the rotation of the Geneva driven wheel435A.

More specifically, in the second embodiment of the invention the rotor30, the rotation limiting device, and the elastic device are disposed so that the rotational energy of the rotor30is transferred through the rotation limiting device composed of the Geneva drive wheel431A and Geneva driven wheel435A to the spiral spring426A of the elastic device. The rotor30, the rotation limiting device, and the elastic device thus render a serial path that transmits the rotational energy of the rotor30.

More specifically, rotation of the rotation detection wheel41that is rotated by the rotor30is transmitted to a pinion434that rotates in unison with the Geneva drive wheel431A. Although the size differs, the Geneva drive wheel431A has fingers432formed 180 degrees apart, and the period between the fingers432renders a limiting part433similarly to the Geneva drive wheel431of the first embodiment.

The Geneva driven wheel435A has teeth436formed around the outside, rotation is limited when two teeth436contact the limiting part433, and the Geneva driven wheel435A rotates a specific angle when the finger432of the Geneva drive wheel431A contacts a tooth436. Therefore, the Geneva mechanism in this second embodiment of the invention also enables the Geneva driven wheel435A to intermittently turn a specific angle in conjunction with rotation of the Geneva drive wheel431A. Because the Geneva driven wheel435A cannot turn after the Geneva driven wheel435A rotates this specific angle, the rotational position of the Geneva driven wheel435A is set. The Geneva driven wheel435A is also prohibited from driving the Geneva drive wheel431A at this time.

The outside circumference end of the spiral spring426A is fastened to the Geneva driven wheel435A, and the inside circumference end of the spiral spring426A is fastened to a shaft member disposed in the center of the Geneva driven wheel435A. The third wheel44is also turned by the pinion438that rotates in unison with this shaft member, and the second wheel45, day wheel46, and hour wheel47are driven by the third wheel44as described in the first embodiment. The Geneva driven wheel435A is rotatably supported on this shaft member. In this embodiment of the invention, therefore, the pinion438that rotates in unison with the shaft member is disposed coaxially to the Geneva driven wheel435A, is connected to the other end of the spiral spring426A, and is also a transfer wheel.

Note that rotation of the rotation detection wheel41is detected by the rotation detection device40as described in the first embodiment. More specifically, rotation of the rotor30a specific amount is detected by the rotation detection device40detecting that the rotation detection wheel41has turned a specific amount, and driving the piezoelectric actuator20is stopped by detecting this.

When the rotor30of the piezoelectric actuator20rotates in this second embodiment of the invention, the Geneva drive wheel431A is turned by the rotation detection wheel41, and in conjunction therewith the Geneva driven wheel435A intermittently rotates a specific angle.

The spiral spring426A is wound and elastic energy is stored in conjunction with rotation of the Geneva driven wheel435A. When the stored elastic energy equals or exceeds a specific amount, the pinion438rotates and causes the rotating bodies from the third wheel44to the hands to rotate.

This embodiment of the invention has substantially the same effect as the first embodiment described above.

A piezoelectric drive device10B in a timepiece1B according to a third embodiment of the invention is described next with references toFIG. 8-FIG.11. Other than having piezoelectric drive device10B instead of the piezoelectric drive device10used in the first embodiment of the invention, a timepiece1B according to this third embodiment of the invention has the same configuration as the timepiece1described above. This piezoelectric drive device10B has the same configuration as the piezoelectric drive device10described above except for having a rotation transfer device40B instead of the rotation transfer device40in the first embodiment. Similarly to the rotation transfer device40described above, this rotation transfer device40B transmits drive power produced by the piezoelectric actuator20to the minute hand and hour hand, and causes the minute hand and hour hand to rotate.

In the first embodiment of the invention the Geneva drive wheel431has two fingers432disposed 180 degrees apart, and when the rotor wheel31turns 7.5 degrees, the rotation of the rotor wheel31is accelerated by the rotation detection wheel41so that the Geneva drive wheel431rotates 180 degrees.

With the rotation transfer device40B according to this embodiment of the invention, however, the Geneva drive wheel509has three fingers5091disposed 120 degrees apart. When the rotor wheel31turns 12 degrees, rotation of the rotor wheel31is accelerated by the rotation detection wheel49and the Geneva drive wheel509rotates 120 degrees. Described in further detail below, the third wheel52of the rotation transfer device40B renders a torque slip mechanism.

This rotation transfer device40B has substantially the same configuration as the rotation transfer device40of the first embodiment, and differs therefrom in replacing the rotation detection wheel41, elastic device42, and rotation limiting device43of the first embodiment with a rotation detection wheel49, elastic device50, rotation limiting device51, and third wheel52as shown inFIG. 8.

Rotation Detection Wheel

The rotation detection wheel49is disposed between the rotor30and the elastic device50, accelerates the rotation of the rotor30, and transfers the rotational energy of the rotor30to the elastic device50. More specifically, the rotation detection wheel49renders a speed-increasing wheel train with a velocity ratio of 10 times disposed between the rotor30and the elastic device50. This rotation detection wheel49has a pinion491that meshes with the rotor wheel31, a wheel492that rotates coaxially to and in unison with the pinion491, and a plurality of holes493that pass through the wheel492. This rotation detection wheel49is supported freely rotatably by the main plate3and the train wheel bridge4.

The plural holes493are disposed30degrees apart on a virtual circle of a specific radius centered on the rotational axis of the491. These holes493are used by the foregoing rotation detection device70when detecting rotation of the rotation detection wheel49.

Elastic Device

FIG. 9andFIG. 10are oblique views of the elastic device50,FIG. 9showing the elastic device50from the opposite side as the side shown inFIG. 8, andFIG. 10showing the elastic device50from the same side shown inFIG. 8.

The elastic device50converts rotational energy from the rotor30through the rotation detection wheel49to elastic energy stored in an internally disposed spiral spring504, and also transmits the received rotational energy to the rotation limiting device51. As shown inFIG. 8toFIG. 10, the elastic device50has a pinion501, a shaft502, a spring catch503, a spiral spring504, spring retainers505, a spring catch506, a pressure unit507, a pin508, and the Geneva drive wheel509.

As shown inFIG. 8andFIG. 9, the pinion501meshes with the wheel492of the rotation detection wheel49, and rotates in unison with the shaft502supported freely rotatably on the main plate3and the train wheel bridge4.

As shown inFIG. 9andFIG. 10, the spring catch503is rendered in unison with the shaft502, and rotates in conjunction with rotation of the shaft502. This spring catch503holds the inside circumference end part of the spiral spring504stored inside the elastic device50coaxially to the shaft502.

As shown inFIG. 8toFIG. 10, the spiral spring504is formed by winding flat spring stock in a counterclockwise spiral from the center to the outside circumference side when seen in plan view as inFIG. 8. As a result of the pinion501, the shaft502, and the spring catch503rotating clockwise in advance of the Geneva drive wheel509, the spiral spring504is elastically deformed in the direction increasing the number of winds, and thus stores drive power transferred to the pinion501as elastic energy.

As shown inFIG. 9andFIG. 10, the spring retainers505are disposed at three positions at equal intervals around the outside circumference of the spiral spring504. The inside walls of these spring retainers505contact the outside surface of the spiral spring504, and the spiral spring504is thereby held inside the elastic device50. Note that each of these spring retainers505has a boss5051that protrudes toward the shaft502. These bosses5051prevent the spiral spring504from escaping in the axial direction of the shaft502.

As shown inFIG. 8toFIG. 10, the spring catch506is disposed adjacent to one of the three spring retainers505, and together with said adjacent spring retainer505holds the outside circumference end part of the spiral spring504surrounded by the spring retainers505. When the outside circumference end part of the spiral spring504is thus held, and the shaft502and the spring catch503holding the inside circumference end of the spiral spring504are rotated in unison, the number of winds in the spiral spring504increases.

The pressure unit507and pin508fix the initial deflection position of the spiral spring504.

More specifically, as shown inFIG. 8andFIG. 10, the pressure unit507is disposed to the shaft502on the opposite side to the pinion501, and the pin508protrudes from the opposite side of the Geneva drive wheel509to the pinion501. When the spiral spring504is set to the initial deflection (initial elastic deformation) position by the pressure unit507and the pin508, the spiral spring504is engaged by the spring catch503and the spring catch506.

The pressure unit507and the spring catch503are disposed in unison with the shaft502, and hold the Geneva drive wheel509rotatably therebetween with a slight gap to the Geneva drive wheel509in the axial direction of the shaft502.

The Geneva drive wheel509renders part of the elastic device of the invention, and is equivalent to a drive wheel used in the rotation limiting device of the invention.

As shown inFIG. 8toFIG. 10, this Geneva drive wheel509is substantially round when seen in plan view, and has three sets each including a finger5091that protrudes to the outside from the outside surface and a pair of recesses5092that are recessed to the inside on opposite sides of each finger5091formed 120 degrees apart. These fingers5091and recesses5092engage the teeth5111and5112of the Geneva driven wheel511part of the rotation limiting device51, and contribute to rotation of the Geneva driven wheel511.

The curved outside surfaces between the fingers5091of the Geneva drive wheel509are formed as limiting parts5093that restrict rotation of the Geneva driven wheel511.

Note that the Geneva drive wheel509includes the spring retainers505, the spring catch506, and the pin508molded in unison with each other from a plastic resin. Compared with a configuration in which discrete components are assembled together, this configuration reduces the parts count of the elastic device50and makes elastic device50assembly easier. This configuration also reduces the inertial moment of the elastic device50(particularly the Geneva drive wheel509) when compared with a configuration using metal components. As a result, the thickness of the fingers5091can be increased with consideration for the meshing with the teeth5111.

Rotation Limiting Device

The rotation limiting device51is disposed so that the rotational energy of the rotor30is transmitted through the elastic device50. More specifically, the rotation limiting device51, rotor30, and elastic device50together render a serial transfer path for transferring rotational energy from the rotor30. This rotation limiting device51includes the Geneva drive wheel509and the Geneva driven wheel511to which torque is transmitted from the Geneva drive wheel509. More specifically, the Geneva drive wheel509is part of the elastic device50and the rotation limiting device51.

As shown inFIG. 8the Geneva driven wheel511has teeth5111formed at five locations 72 degrees apart in the direction of rotation on the outside circumference surface, a tooth5112corresponding to each of the teeth5111, and a pinion5113disposed to a center shaft.

The gap between each tooth5111and the tooth5112positioned on the counterclockwise side of that tooth5111is a small gap of approximately 20 degrees, and the gap to the tooth5112positioned in the direction of tooth5111rotation is a large gap of approximately 50 degrees.

FIG. 11shows the Geneva drive wheel509and Geneva driven wheel511. More specifically,FIG. 11shows when rotation of the Geneva driven wheel511is restricted by a tooth5111of the Geneva driven wheel511touching a limiting part5093of the Geneva drive wheel509.

As shown inFIG. 11, when two teeth5112and5111on opposite sides of one of the foregoing large gaps are in contact with the limiting part5093of the Geneva drive wheel509, the Geneva driven wheel511cannot turn in either the direction of rotation or the direction of counter-rotation. More specifically, rotation of the Geneva driven wheel511is restricted by the Geneva drive wheel509.

Rotation of the Geneva driven wheel511is restricted until the Geneva drive wheel509turns, a tooth5111fits into a recess5092of the Geneva drive wheel509on the direction of rotation side, and a finger5091contacts the tooth5111. More specifically, in this embodiment of the invention rotation of the Geneva driven wheel511is restricted until the Geneva drive wheel509rotates, the engaged finger5091separates from the tooth5111, and the Geneva drive wheel509turns 120 degrees.

When the Geneva drive wheel509then rotates further from the position where a finger5091of the Geneva drive wheel509contacts a tooth5111of the Geneva driven wheel511, the Geneva driven wheel511also turns pushed by the finger5091. Rotation of the Geneva driven wheel511then stops when the finger5091and the tooth5111separate.

More specifically, when the rotor30and rotor wheel31rotate 12 degrees and the Geneva drive wheel509rotates 120 degrees in this embodiment of the invention, the Geneva driven wheel511rotates according to rotation of the Geneva drive wheel509while the finger5091and the tooth5111are in contact (in the drive range). When a finger5091and a tooth5111are not engaged (in the movement-limiting range), the Geneva driven wheel511does not turn even if the Geneva drive wheel509does. The Geneva driven wheel511turns turns intermittently in conjunction with rotation of the Geneva drive wheel509.

As described above, the Geneva driven wheel511rotates intermittently as a result of rotation from the Geneva drive wheel509, and the angle of rotation is set to a specific angle (72 degrees). Even if the Geneva driven wheel511side turns, this rotation is limited by the Geneva drive wheel509and is not transmitted to the Geneva drive wheel509side. The Geneva drive wheel509and Geneva driven wheel511thus render a non-reversing gear transfer device, and render a rotation limiting device51whereby the Geneva driven wheel511turns 72 degrees when the Geneva drive wheel509turns120degrees, and when the Geneva driven wheel511turns, transfer of rotation from the Geneva driven wheel511to the Geneva drive wheel509is restricted.

Furthermore, similarly to the fingers432described above, the fingers5091are asymmetrical tooth forms having the distal ends thereof sloped in the direction of rotation of the Geneva drive wheel509. As a result, when the finger5091contacts a tooth5111, the finger5091pushes the tooth5111in the direction of rotation of the Geneva driven wheel511and the Geneva driven wheel511is driven rotationally.

Furthermore, while the finger5091contacts a tooth5112when the Geneva drive wheel509turns in the opposite direction, the finger5091pushes the tooth5112toward the center of rotation of the Geneva driven wheel511because the surface of the distal end of the finger5091on the opposite side as the side of the finger5091that contacts the tooth5112when the Geneva drive wheel509rotates forward is sloped, and rotation can therefore not be transmitted to the Geneva driven wheel511.

Positioning of the Fingers and Teeth

As shown inFIG. 11, the positions of the fingers5091on the Geneva drive wheel509and the positions of the teeth5111on the Geneva driven wheel511are set so that when a tooth5111contacts the limiting part5093and rotation of the Geneva driven wheel511(in the direction of arrow S inFIG. 11) is limited, the direction in which force is applied to the tooth5111(the direction of arrow V inFIG. 11, that is, the friction angle) at the point of contact between the tooth5111and the limiting part5093is, at this point of contact A1, in the opposite direction to direction S, which is the direction of rotation of the Geneva driven wheel511, relative to line W, which is the line connecting the point of contact A1and the center of rotation C1of the Geneva driven wheel511.

As described above, it is necessary that the Geneva driven wheel511does not turn even if the Geneva drive wheel509turns while the tooth5111and the limiting part5093are touching. However, if the working direction of force applied to the tooth5111(the direction of arrow V, which is the working direction of the force determined by the force working tangentially to the direction of rotation of the Geneva drive wheel509at the point of contact A1, and the force working radially to the Geneva drive wheel509) is to the side of direction S from line W, the tooth5111may ride onto (bite into) the limiting part5093in conjunction with rotation of the Geneva drive wheel509. If this happens, the Geneva driven wheel511that should normally not rotate may become damaged and rotate freely.

However, by positioning the teeth5111and the limiting parts5093(that is, positioning the teeth5111and the fingers5091) as described above so that the direction of force applied to the tooth5111contacting the limiting part5093(the direction indicated by arrow V) is in the direction opposite direction S relative to line W, the teeth5111can be prevented from thus riding onto (biting into) the limiting part5093. Rotation of the Geneva driven wheel511can thus be reliably prevented when a tooth5111is in contact with the limiting part5093as a result of disposing the teeth511172 degrees apart around the outside of the Geneva driven wheel511, disposing the teeth5112offset 22 degrees to an opposite direction side to the S direction side of the teeth5111, and disposing the fingers5091120 degrees apart around the outside of the Geneva drive wheel509.

Configuration of Wheel Train Downstream from the Geneva Driven Wheel

As shown inFIG. 8, the third wheel52and second wheel45are disposed in series between the Geneva driven wheel511and the day wheel46, and render a speed-reducing wheel train.

The third wheel52has a third transfer wheel521around the outside circumference of which teeth5211are formed, and a pinion522axially supported to the third transfer wheel521. The third transfer wheel521meshes with the pinion5113of the Geneva driven wheel511, and the pinion522meshes with the second wheel45.

The third transfer wheel521has a pair of support ribs5212and5213that hold the rotating shaft of the pinion522therebetween. These support ribs5212and5213are formed to be elastically deformable, are pushed together from the outside to the center of the rotating shaft of the pinion522, and assure a specific friction torque with the pinion522. The third transfer wheel521and the pinion522therefore normally rotate in unison.

When the crown is operated to adjust the positions of the hands, a powerful rotational torque works on the pinion522of the second wheel45through the time adjustment mechanism80. In this situation rotation of the Geneva driven wheel511is restricted by the Geneva drive wheel509, and the support ribs5212and5213of the third transfer wheel521friction slip when the pinion522is turned with great force. As a result, applying a load in the opposite direction from normal to the upstream side of the third wheel52(such as the piezoelectric actuator20side) can be prevented.

When external shock is produced by, for example, dropping the timepiece1, the minute hand attached in an unbalanced condition to the second pinion451of the second wheel45, and the hour hand attached in an unbalanced condition to the hour wheel47, are made to turn, and a high rotational torque could be applied through the second wheel45to the pinion522. In this situation rotation of the Geneva driven wheel511is limited by the Geneva drive wheel509, and rotation of the third transfer wheel521is locked. At the same time, the pinion522is held by friction without slipping between the support ribs5212and5213. As a result, the minute hand and hour hand are held in the correct positions without moving therefrom even when subject to external interference. As a result, the hands will not move and the displayed time will not be changed even when external shock is applied.

Note that the specific friction torque of the support ribs5212and5213holding the pinion522therebetween is set so that when the crown is operated, the pinion522slips between the support ribs5212and5213, but during normal operation and when an external shock is applied, the pinion522does not slip between the support ribs5212and5213and can rotate in unison with the third transfer wheel521.

The configuration of the third wheel52thus described enables compatibility with the torque of a large minute hand, and can improve the freedom of design in minute hand selection.

More specifically, wheels that may be caused to turn idly as a result of a high torque load transferred from the minute hand conceivably include the second wheel45in addition to the third wheel52. However, because the second wheel45and the third wheel52render a speed-reducing wheel train, the slip torque is higher when the slip torque is applied to the second wheel45than when the slip torque is applied to the third wheel52. On the other hand, because slip torque can be set low when the slip torque is disposed to the third wheel52, the third wheel52can be processed stably, freedom of design is increased in minute hand selection, and the freedom of timepiece1B design is improved.

The timepiece1B according to this embodiment of the invention has the same effect as the timepiece1described above.

Variations

It will be obvious to one with ordinary skill in the related art that the invention is not limited to the foregoing embodiments and can be modified and improved in many ways without departing from the scope of the accompanying claims.

For example, the rotation limiting device of the invention is not limited to a Geneva mechanism such as described above, and many be any device that can transmit rotational energy and limit the angle of rotation to a specific angle.

Note, further, that a speed-increasing wheel train is rendered by the configuration from the rotor30to the Geneva drive wheel431in this embodiment of the invention, but rotation may be transferred without acceleration.

In addition, a rotation detection wheel41,49is disposed between the rotor wheel31and the elastic device42,50in the foregoing embodiments, but the rotation detection wheel41,49may be omitted. In this configuration it is sufficient if rotation can be detected at the rotor wheel31part, for example. Note, further, that the rotation detection wheel may be disposed to a transfer path other than the transfer path whereby rotational energy from the rotor wheel is transmitted to the elastic device and the rotation limiting device. Further alternatively, the rotation detection wheel may be disposed downstream from the elastic device.

In the first and second embodiments of the invention the fingers432of the Geneva drive wheel431,431A are disposed180degrees apart on the outside of the Geneva drive wheel431,431A, and in the third embodiment of the invention the fingers5091of the Geneva drive wheel509are disposed 120 degrees apart on the outside circumference of the Geneva drive wheel509, but the invention is not so limited. For example, the fingers may be disposed90degrees apart, the interval between the fingers may be set appropriately, and the positions of the teeth on the Geneva driven wheel can be set appropriately according to the position of the fingers.

The third wheel52in the third embodiment of the invention has support ribs5212,5213that hold the pinion522to impart slip torque to the third wheel52, but the invention is not so limited. More specifically, the pinion522may be axially supported by a different configuration, and a configuration that imparts slip torque to the second wheel45is also conceivable.

In the foregoing embodiments of the invention driven rotating bodies rotate due to elastic energy from an elastic device, but the bodies that are driven by the elastic device may be non-rotationally driven. Non-rotationally driven as used herein refers to linear drive, linear bidirectional drive, and bidirectional drive on a curve, for example.

The piezoelectric drive device according to the invention is not limited to timepieces, and can also be used as a drive power source in other types of electronic devices. More specifically, electronic devices using the piezoelectric drive device according to the invention include, for example, measurement instruments that drive needle indicators using a piezoelectric drive device, and other types of electronic devices that drive a driven body such as a turntable. More particularly, the piezoelectric drive device according to the invention has superior magnetic resistance than a stepping motor, and can be widely used as a power supply where magnetic resistance is required.

The best modes and methods of achieving the present invention are described above, but the invention is not limited to these embodiments. More specifically, the invention is shown in the figures and described herein with particular reference to specific embodiments thereof, but it will be obvious to one with ordinary skill in the related art that the shape, material, number, and other detailed aspects of these configurations can be varied in many ways without departing from the technical concept or the scope of the object of this invention.

Therefore, description of specific shapes, materials and other aspects of the foregoing embodiments are used by way of example only to facilitate understanding the present invention and do not limit the scope of this invention, and descriptions using names of parts removing part or all of the limitations relating to the form, material, or other aspects of these embodiments are also included in the scope of this invention.

The entire disclosure of Japanese Patent Application Nos: 2009-005616, filed Jan. 14, 2009 and 2009-271567, filed Nov. 30, 2009 are expressed incorporated by reference herein.