Inertial drive actuator

An inertial drive actuator includes a shift unit that generates a shift in a first direction and in a second direction opposite to the first direction, a base plate that moves with the shift of the shift unit, and a mover disposed on a surface of the base plate and having a magnetic field generating unit. The mover has a first yoke that guides magnetic flux generated by the magnetic field generating unit such that the magnetic flux concentrates on a surface of the mover facing the base plate with respect to both S and N poles. Also included is a second yoke provided on a side of the base plate facing away from the mover. The frictional force acting between the mover and the base plate is controlled by controlling a magnetic field generated by the magnetic field generating unit to drive the mover.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an inertial drive actuator that causes a movable member to move in a predetermined direction.

Description of the Related Art

There is a known actuator in which saw-tooth pulses are supplied to an electromechanical transducer coupled with a drive shaft to shift the drive shaft in the axial direction, thereby moving a movable member frictionally coupled with the drive shaft in the axial direction. (Such an actuator will be hereinafter referred to as an “impact drive actuator” or “inertial drive actuator”.)

Such an impact drive actuator is disclosed in Japanese Patent Application Laid-Open No. 2007-288828.FIG. 9Ashows the construction of the impact drive actuator. A vibration member103is inserted through holes provided in standing portions of a support member101and movable in the axial direction of the vibration member103. One end of the vibration member103is fixed to one end of a piezoelectric element102, the other end of which is fixed to the support member101. With this construction, the vibration member103vibrates in the axial direction with the vibration of the piezoelectric element102. A movable member104has two holes, through which the vibration member103is inserted. A leaf spring105is attached to the movable member104from below. A projection provided on the leaf spring105is pressed against the vibration member103. The pressure exerted by the leaf spring105brings the movable member104and the vibration member103into frictional coupling with each other.

FIGS. 9B and 9Cshow waveforms of driving pulses for driving the impact drive actuator.FIG. 9Bshows a waveform of driving pulses for moving the movable member104to the right, andFIG. 9Cshows a waveform of driving pulses for moving the movable member104to the left. The operation principle of the impact drive actuator will be described in the following with reference to these driving pulse waveforms. In the following description, it is assumed that the direction in which the piezoelectric element102expands is the left, and the direction in which the piezoelectric element contracts is the right.

When the movable member104is to be moved to the right, the driving pulse waveform shown inFIG. 9Bis used. The driving pulse waveform has steep rise portions and gradual fall portions. The steep rise portions of the driving pulse waveform cause the piezoelectric element102to expand quickly. Because the vibration member103is fixed to the piezoelectric element102, the vibration member103moves to the left at high speed with the quick expansion of the piezoelectric element102. During that time, the inertia of the movable member104overcomes the frictional coupling force between it and the vibration member103(i.e. frictional force between the vibration member103and the movable member104pressed against it by the leaf spring105), and therefore the movable member104does not move to the left but stays at its position.

The gradual fall portions of the driving pulse waveform causes the piezoelectric element102to contract slowly. Then, the vibration member103slowly moves to the right with the slow contraction of the piezoelectric element102. During that time, the inertia of the movable member104cannot overcome the frictional coupling force between it and the vibration member103, and therefore the movable member104moves to the right with the movement of the vibration member103.

On the other hand, when the movable member104is to be moved to the left, the driving pulse waveform shown inFIG. 9Cis used. The driving pulse waveform has gradual rise portions and steep fall portions. The gradual rise portions of the driving pulse waveform cause the piezoelectric element102to expand slowly. Then, the vibration member103moves slowly to the left with the slow expansion of the piezoelectric element102. During this time, the inertia of the movable member104cannot overcome the frictional coupling force between it and the vibration member103, and therefore the movable member104moves to the left with the movement of the vibration member103.

On the other hand, during the steep rise portions of the driving pulse waveform, the inertia of the movable member104overcomes the frictional coupling force between it and the vibration member103, as with the case described above with reference toFIG. 9B, and therefore the movable member104does not move to the right but stays at its position.

Since the vibration member103is always pressed by the leaf spring105, the movable member104is frictionally supported by the vibration member103. In consequence, when the movable member104is stationary, its position is maintained.

As described above, the impact drive actuator utilizes the frictional coupling of the movable member104and the vibration member103provided by the leaf spring105and the inertia, and it can move the movable member104using driving pulse waveforms shown inFIGS. 9B and 9C.

The impact drive actuator disclosed in Japanese Patent Application Laid-Open No. 2007-288828 uses a leaf spring to provide a frictional force between the vibration member103and the movable member104.

SUMMARY OF THE INVENTION

An inertial drive actuator according to the present invention comprises a shift unit that generates a small shift in a first direction and in a second direction opposite to the first direction, a vibration base plate that moves to and fro with the small shift of the shift unit, and a mover disposed on a flat surface of the vibration base plate and having a first magnetic field generating unit, wherein the mover comprises a first yoke that guides magnetic flux generated by the first magnetic field generating unit in such a way that the magnetic flux generated by the first magnetic field generating unit concentrates on a surface of the mover facing the vibration base plate with respect to both S and N poles, the inertial drive actuator further comprises a second yoke disposed on a side of the vibration base plate facing away from the mover, and a frictional force acting between the mover and the vibration base plate is controlled by controlling a magnetic field generated by the first magnetic field generating unit to drive the mover.

DETAILED DESCRIPTION OF THE INVENTION

The construction, operations, and advantages of inertial drive actuators according to several embodiments will be described. It should be understood that the present invention is not limited by the embodiments. Although a lot of specific details will be described in the following description of the embodiments for the purpose of illustration, various modifications and changes can be made to the details without departing from the scope of the invention. The illustrative embodiments of the invention will be described in the following without any intension of invalidating the generality of or imposing any limitations on the claimed invention.

FIGS. 1A, 1B, and 1Cshow an inertial drive actuator according to a first embodiment.FIG. 1Ais a side view of the inertial drive actuator, andFIG. 1Bis a cross sectional view taken along line A-A inFIG. 1A.

The inertial drive actuator100according to the first embodiment includes a piezoelectric element (shift unit)3, a vibration base plate4, a mover10, and a stator20. The piezoelectric element3and the vibration base plate4are disposed on top of the stator20, and the mover10is disposed on top of the vibration base plate4.

The mover10includes a coil11(first magnetic field generating unit) and a first yoke12a. The first yoke (magnetic flux guide member)12ais a grooved member having a groove (or recess), which is partitioned by a T-shaped member at its center. The coil11is wound in a cylindrical shape around a coil core surrounding the T-shaped member. Wiring L for supplying electric current to the coil11extends out of the first yoke12a. The grooved member and the T-shaped member are connected with each other.

The piezoelectric element3and the vibration base plate4are both plate-like members. The vibration base plate4is made of a non-magnetic material. One end of the piezoelectric member3and one end of the vibration base plate4are mechanically connected. Their connection is not limited to mechanical connection, but they may be adhered to each other. The piezoelectric element3and the vibration base plate4are disposed on top of the stator20. The piezoelectric member3generates a small shift or displacement, which causes the vibration base plate4to move to and fro.

The stator20includes a permanent magnet21(second magnetic field generating unit) and a second yoke (magnetic flux guide member)22a. The permanent magnet21is a cuboid component having an N-pole on one side and an S-pole on the other side. The second yoke22ais a box-like component. The permanent magnet21is disposed inside the second yoke22awith its N-pole side facing upward. The permanent magnet21is fixed on the bottom of the second yoke22a.

Now, the operation of the inertial drive actuator100will be described. The principle of driving (or method of driving) will be described with reference toFIG. 6. Current is supplied to the coil11in such a way that the S-pole is generated in the downward direction in the drawing. The yoke12ais arranged on both sides of the coil11. Therefore, the first yoke12acan prevent magnetic flux generated by the coil11from leaking to the outside. In consequence, the S-pole concentrates to the center P1of the lower part of the first yoke12a, and the N-pole concentrates to both ends P2of the lower part of the first yoke12a.

On the other hand, in the stator20opposed to the first yoke12a, the permanent magnet21is surrounded by the second yoke22a. Therefore, the second yoke22acan prevent magnetic flux generated by the permanent magnet21from leaking to the outside. In consequence, the N-pole concentrates to the upper part of the permanent magnet21, and the S-pole concentrates to both ends P3of the upper part of the second yoke22a.

As described above, in the inertial drive actuator100according to this embodiment, magnetic flux is prevented from leaking out of the mover10or out of the stator20, whereby the S-pole and the N-pole can be concentrated to predetermined regions. Consequently, magnetic attractive force can be generated efficiently in the downward direction in the drawing between the mover10and the stator20.

Conversely, when current is supplied to the coil11in such away that the S-pole is generated in the upward direction in the drawing, the N-pole concentrates to the center P1of the lower part of the first yoke12a, and the S-pole concentrates to both ends P2of the lower part of the first yoke12a. On the other hand, in the stator20opposed to the first yoke12a, the N-pole concentrates to the upper part of the permanent magnet21, and the S-pole concentrates to both ends P3of the upper part of the second yoke22a. Consequently, magnetic repulsive force can be generated efficiently in the upward direction in the drawing between the mover10and the stator20.

The magnitude of the normal force acting between the mover10and the vibration base plate4(or the magnetic attractive or repulsive force acting between the mover10and the stator20) can be varied by varying the amount of current supplied to the coil11. This enables controlling the frictional force between the mover10and the vibration base plate4.

As described above, the inertial actuator100according to this embodiment utilizes a magnetic force to move or drive the mover10. Thus, the inertial drive actuator100according to this embodiment is free from an elastic member that might wear by driving. Therefore, moving or driving the mover10does not lead to wearing. Consequently, it is possible to move or drive the mover10(i.e. to move it to a desired position and to keep it at a desired position) stably for a long period of time. Moreover, the use of the yoke in the inertial drive actuator100according to this embodiment enables prevention of the leakage of magnetic flux to the outside. Consequently, the magnetic attractive force and the magnetic repulsive force can be generated efficiently. Therefore, the mover10can be moved or driven efficiently, while the inertial drive actuator is simple in structure and can be made at low cost.

Next, an inertial drive actuator according to a second embodiment will be described. The components same as those in the first embodiment will be denoted by the same reference characters to eliminate redundant descriptions.

FIG. 2is a cross sectional view of the inertial drive actuator similar toFIG. 1B.

The inertial drive actuator200according to the second embodiment includes a piezoelectric element3(not shown inFIG. 2), a vibration base plate4, a mover10, and a stator20. The piezoelectric element3and the vibration base plate4are disposed on top of the stator20, and the mover10is disposed on top of the vibration base plate4.

In the mover10of the inertial drive actuator100according to the first embodiment, the first yoke12acovers two portions of the coil11. In contrast, in the mover10of the inertial drive actuator200according to this embodiment, the first yoke12bcovers only one of the two portions of the coil11. In other words, while in the inertial drive actuator100according to the first embodiment, the first yoke12ais provided for two side portions of the coil11, in the inertial drive actuator200according to this embodiment, the first yoke12bis provided only for one side portion of the coil11.

Referring to the stator20, while in the inertial drive actuator100according to the first embodiment the second yoke22ais provided on both sides of the permanent magnet21, in the inertial drive actuator200according to this embodiment the second yoke22bis provided on only one side of the permanent magnet21.

As described above, the inertial drive actuator200according to this embodiment partly differs in structure from the inertial drive actuator100according to the first embodiment. Nevertheless, the inertial drive actuator200according to this embodiment has advantages in magnetic attractive and repulsive forces substantially the same as the inertial drive actuator100according to the first embodiment. In the inertial drive actuator200according to this embodiment, the first yoke12band the second yoke22bare disposed on only one side of the coil11and the permanent magnet21. Therefore, if the overall size of the inertial drive actuator is the same as the first embodiment, the number of turns of the coil can be made larger in this embodiment than in the first embodiment. Consequently, if the current supplied to the coil11is the same as the first embodiment, higher magnetic flux density can be achieved, leading to increased magnetic attractive and repulsive forces.

Next, an inertial drive actuator according to a third embodiment will be described.

FIG. 3Ais a side view of the inertial drive actuator, andFIG. 3Bis a cross sectional view taken along line A-A inFIG. 3A. The components same as those in the inertial drive actuator according to the first embodiment will be denoted by the same reference characters to eliminate descriptions thereof. Wiring is not illustrated in these drawings.

The inertial drive actuator300according to the third embodiment includes a piezoelectric element3, a mover10, and a vibration base plate40. The mover10is disposed on top of the vibration base plate40. One end of the piezoelectric member3and one end of the vibration base plate are mechanically connected.

The mover10includes a coil11and a first yoke12c. The structure of the mover10is the same as that of the mover10in the first embodiment and will not be described further. The mover10in this embodiment plays the same role as the mover10in the first embodiment. The vibration base plate40includes a permanent magnet40and a second yoke22c. The vibration base plate40plays the same role as the stator20in the first embodiment as well as the vibration base plate4.

The inertial drive actuator300according to this embodiment includes components having the same functions as components in the inertial drive actuator100according to the first embodiment, and has the same advantages as the inertial drive actuator100according to the first embodiment accordingly. Since the vibration base plate40in the inertial drive actuator300according to this embodiment plays multiple roles, reduction in the size of the actuator can be achieved.

Next, an inertial drive actuator according to a fourth embodiment will be described.

FIG. 4is a cross sectional view of the inertial drive actuator similar toFIG. 1B. The components same as those in the first embodiment will be denoted by the same reference characters to eliminate descriptions thereof.

The inertial drive actuator400according to the fourth embodiment includes a piezoelectric element3(not shown inFIG. 4), a vibration base plate4, a mover10, and a stator20. The piezoelectric element3and the vibration base plate4are disposed on top of the stator20, and the mover10is disposed on top of the vibration base plate4.

The mover10includes a coil11, a first yoke12d, and a permanent magnet13. The first yoke12dis a grooved member having a groove, which is partitioned by a T-shaped member at its center. The coil11is wound in a cylindrical shape around a coil core surrounding the T-shaped member. The grooved member and the T-shaped member are separated from each other, and the permanent magnet13is arranged between them. The permanent magnet13is disposed with its N-pole facing the T-shaped member. The stator20has a second yoke22d.

This embodiment differs from the first embodiment in that it lacks the permanent magnet21(second magnetic field generating unit) in the first embodiment.

In the inertial drive actuator400having the above-described construction, when current is supplied to the coil11, for example, in such a way that the N-pole is generated in the downward direction in the drawing. Then, the N-pole concentrates to the center of the lower part of the first yoke12d, and the S-pole concentrates to both ends of the lower part of the first yoke12d.

As to the magnetic flux generated by the permanent magnet13also, the N-pole concentrates to the center of the lower part of the first yoke12d, and the S-pole concentrates to both ends of the lower part of the first yoke12d. In the stator20opposed to the first yoke12d, magnetization in the reverse polarity is induced in the second yoke22d. Specifically, an S-pole is induced at the center of the second yoke22d, and N-poles are induced at both ends of the second yoke22d. Consequently, a magnetic attractive force stronger than that in the case where no current is supplied to the coil11acts on the mover10in the downward direction in the drawing.

On the other hand, when current is supplied to the coil11in such a way that the N-pole concentrates to the upward direction in the drawing, a magnetic attractive force weaker than that in the case where no current is supplied to the coil11is generated. The magnitude of the normal force acting between the mover10and the vibration base plate4can be varied by varying the current supplied to the coil11. This enables controlling the frictional force between the mover10and the vibration base plate4.

As described above, in the inertial drive actuator400according to this embodiment, a magnetic force is used in moving or driving the mover10. Thus, the inertial drive actuator400according to this embodiment is free from an elastic member that might wear by driving. Therefore, moving or driving the mover10does not lead to wearing. Consequently, it is possible to move or drive the mover10(i.e. to move it to a desired position and keep it at a desired position) stably for a long period of time. Moreover, the use of the yoke in the inertial drive actuator400according to this embodiment enables prevention of the leakage of magnetic flux to the outside. Consequently, the magnetic attractive force and the magnetic repulsive force can be generated efficiently. Therefore, the mover10can be moved or driven efficiently.

Next, an inertial drive actuator according to a fifth embodiment will be described.FIG. 5is a cross sectional view of the inertial drive actuator similar toFIG. 1B. The components same as those in the first embodiment will be denoted by the same reference characters and will not be described further.

The inertial drive actuator500according to the fifth embodiment includes a piezoelectric element3(not shown inFIG. 5), a vibration base plate4, a mover10, and a stator20. The piezoelectric element3and the vibration base plate4are disposed on top of the stator20, and the mover10is disposed on top of the vibration base plate4.

The inertial drive actuator500according to the fifth embodiment differs from the inertial drive actuator100according to the first embodiment in the structure of the vibration base plate. While the vibration base plate4in the first embodiment is made only of non-magnetic material, the vibration base plate4in this embodiment includes a magnetic part41and a non-magnetic part42. The magnetic part functions as a yoke. The magnetic part41includes three separate parts, which are arranged at the center of the vibration base plate4and on both sides of the center. The center magnetic part41is substantially opposed to the T-shaped member (of the first yoke12e). The side magnetic parts41are substantially opposed to the edges of the grooved member (of the first yoke12e).

In the inertial drive actuator500according to this embodiment, magnetic flux guided by the first yoke12eof the mover10and magnetic flux guided by the second yoke22eof the stator20flow through the magnetic parts41in the vibration base plate4. Therefore, better prevention of leakage of magnetic flux can be achieved advantageously. In particular, leakage of magnetic flux to the outside in the region near the lower edges of the first yoke12eand the upper edges of the second yoke22ecan be reduced greatly by virtue of the two side magnetic parts41existing between them.

Next, the method of driving in the inertial drive actuator according to the embodiments will be described.FIG. 6illustrates the method of driving in an inertial drive actuator, e.g. the inertial drive actuator100according to the first embodiment. InFIG. 6, the horizontal axis represents time, and the vertical axis represents shift of the piezoelectric element3, where expanding shifts of the piezoelectric element3to the left inFIG. 1Aare expressed by positive values.

During the time period from time0to time A, the piezoelectric element3is expanding. During this period, current is supplied to the coil11in such away that the S-pole is generated in the downward direction in the drawing. Then, the magnetic attractive force acting on the mover10in the direction toward the vibration base plate4increases. In consequence, the friction between the mover10and the vibration base plate4increases. Consequently, as the vibration base plate4moves to the left in the drawing with the expansion of the piezoelectric member3, the mover10moves to the left in the drawing accordingly.

During the time period from time A to time B, the piezoelectric element3is contracting. During this period, current supply to the coil11is suspended. Then, no magnetic attractive force generated by the coil11acts on the mover10. In consequence, the frictional force between the mover10and the vibration base plate4decreases. This means that the amount of slippage of the mover10arelative to the movement of the vibration base plate4increases. Consequently, while the vibration base plate4moves to the right in the drawing with the contraction of the piezoelectric element, the mover10apparently stays stationary at the shifted position. In this way, while the piezoelectric element3is contracting, the mover10slips to the left relative to the vibration base plate4, which moves to the right in the drawing. Thus, the mover10shifts to the left in the drawing during the time period from time0to time B.

As the same operation is performed repeatedly in the time period from time B to time C, the time period from time C to time D and so on, the mover10moves or shifts to the left in the drawing. The mover10can also be moved to the right in the drawing by reversing the timing of current supply to the coil11shown inFIG. 6. Specifically, the mover10is moved to the right in the drawing, by supplying the coil11with current with which a magnetic repulsive force acting between the mover10and the vibration base plate4is generated instead of current with which a magnetic attractive force acting between the mover10and the vibration base plate4is generated, during the time period from time0to time A.

While in the above-described illustrative case, current supply is suspended during the time period from time A to time B, the coil11may be supplied with current with which a magnetic repulsive force acts between the mover10and the vibration base plate4during this period. This also enables the mover10to move in the same manner as described above.

Next, an inertial drive actuator according to a sixth embodiment will be described.

FIG. 7is a side view of the inertial drive actuator similar toFIG. 1B.FIGS. 8A, 8B, and 8Cillustrate a method of driving in the inertial drive actuator100according to the sixth embodiment.

The inertial drive actuator according to the sixth embodiment has two movers10like that in the inertial drive actuator100in the first embodiment. Specifically, the inertial drive actuator600according to the sixth embodiment includes a piezoelectric element3, a vibration base plate4, a mover10a, a mover10b, and a stator20. The piezoelectric element3and the vibration base plate4are disposed on top of the stator20, and the mover10aand the mover10bare disposed on top of the vibration base plate4. Wiring is not illustrated inFIG. 7.

The method of driving in the inertial drive actuator600will be described. InFIGS. 8A, 8B, and 8C, the horizontal axis represents time, and the vertical axis represents shift of the piezoelectric element3, where expanding shifts of the piezoelectric element3to the left inFIG. 7are expressed by positive values.

During the time period from time0to time A, the piezoelectric element3is expanding. During this period, current is not supplied to the coil11in the mover10a. Then, no magnetic attractive force acts on the mover10a. Consequently, the mover10astays stationary without changing its position. On the other hand, current is supplied to the coil11in the mover10bin such a way that the S-pole is generated in the downward direction in the drawing. Then, a magnetic attractive force acts on the mover10bin the direction toward the vibration base plate4, as described above with reference toFIG. 6. In consequence, the mover10bmoves to the left in the drawing.

During the time period from time A to time B, the piezoelectric element3is contracting. During this period, current is supplied to the coil11in the mover10ain such a way that the S-pole is generated in the downward direction in the drawing. Then, a magnetic attractive force acts on the mover10ain the direction toward the vibration base plate4, as described above with reference toFIG. 6. In consequence, the mover10amoves to the right in the drawing. On the other hand, current is not supplied to the coil11in the mover10b. Then, no magnetic attractive force acts on the mover10b. Consequently, the mover10bstays stationary without changing its position.

As described above, during the time period from time0to time A, the mover10astays stationary, and the mover10bmoves to the left in the drawing or toward the mover10a. On the other hand, during the time period from time A to time B, the mover10amoves to the right in the drawing or toward the mover10b, and the mover10bstays stationary. Consequently, the mover10aand the mover10bcan be brought closer to each other. By performing the driving operation during the time period from time0to time B repeatedly, the mover10aand the mover10bcan be brought further closer to each other. Moreover, by changing the driving method, it is also possible to move the mover10aand the mover10bin the same direction or to move the mover10aand the mover10baway from each other.

While a construction with two movers and a method of driving thereof have been described by way of illustration with reference toFIGS. 7, 8A, 8B, and 8C, more than two movers can be moved independently from each other on the same vibration base plate according to the same principle. Moreover, because the mover includes a coil in all of the first to fifth embodiments, the principle of driving illustrated inFIGS. 7, 8A, 8B, and 8Ccan be applied to all the embodiments. Therefore, it is possible to move a plurality of movers independently from each other on the same vibration base plate in the inertial drive actuators according to the embodiments.

Various modification can be made without departing from the essence of the present invention.

As described above, the present invention can suitably be applied to an inertial drive actuator capable of operating stably for a long period of time, for example in moving a mover to a desired position, stopping the mover at a desired position, and keeping the mover stationary.

The present invention can provide an inertial drive actuator that uses a magnetic force to reduce adverse effects of wearing etc. and can move or drive a mover efficiently by using a yoke.