Piezo motor

A piezo motor has a stator and a rotor as well as a drive finger which is held by the stator, drives the rotor and interacts with at least one piezo element. In order to improve the force transmission, the free end of the drive finger moves a driver jaw, which can be pressed against a ring surface of the rotor. The free end of the drive finger is held such that it can move in the longitudinal direction between two stops on the driver jaw, and the driver jaw can be pressed against the rotor, in time with the drive movement of the drive finger, by at least one piezo actuator during the drive movement of the drive finger, and can be pivoted in the drive direction and back about the rotor axis, together with the piezo actuator, corresponding to the magnitude of a deflection of the drive finger.

TECHNICAL FIELD

This application relates to a piezo motor having a stator and a rotor and at least one drive finger which is held by the stator, drives the rotor and interacts with at least one piezo element. The rotor can rotate about the stator which is secured by a stator axle. This rotor has a hollow-cylindrical annular face on which the drive finger acts. However, the rotor can also be arranged next to the stator, and the drive finger which is held at one end by the stator acts on a cylindrical annular face of the rotor.

BACKGROUND OF THE INVENTION

Piezo motors of this type are known from the following documents: DE 10 2006 004 194; EP 0 951 078; WO 01/41228; and EP 1 192 704.

In these piezo motors, electrical oscillations are converted into mechanical oscillations by means of the reciprocal piezo effect, and these mechanical oscillations of a drive finger are used to drive a rotor. Even if the deflections of the drive finger are very small, a sufficiently high rotational speed of the rotor is achieved owing to the high speed of these deflections.

In the known piezo motors, the drive finger is formed by a resonance body which is made to oscillate by an oscillation generator made of a piezo-electric material. The oscillating end of the drive finger is pressed against an annular face of a rotor by a spring device, and as a result a frictional contact is brought about.

The frictional contact of the drive finger with the rotor has the disadvantage that the oscillating contact face of the drive finger wears relatively quickly and the component which runs in the drive direction is not fully utilized. In addition, only very small forces can be transmitted from the drive finger to the rotor.

Accordingly, it would be desirable to provide a piezo motor in which the transmission of force from the drive finger to the rotor is improved.

SUMMARY OF THE INVENTION

According to the system described herein, a piezo motor includes a drive finger that moves, with its free end, a driver jaw which can be pressed against an annular face of the rotor wherein the free end of the drive finger is held in a radially displaceable fashion between two stops of the driver jaw, and during the drive movement of the drive finger the driver jaw can be pressed against the rotor by at least one piezo actuator in time with the drive movement of the drive finger, and can be pivoted in the drive direction and back about the rotor axis, together with the piezo actuator, in accordance with the magnitude of a deflection of the drive finger.

In this piezo motor, the oscillations of the drive finger are taken up by a driver jaw which is pressed against a hollow cylindrical or cylindrical annular face of the rotor by a further piezo actuator in time with the oscillation of the drive finger. As a result, slip losses are largely avoided and relatively large forces can also be transmitted from the drive finger to the rotor via the driver.

The contact face of the driver jaw is relatively large and constructed in such a way that a good frictional connection comes about between the rotor and the driver jaw.

The free end of the drive finger is held between the stops of the driver jaw in such a way that the free end can move in the longitudinal direction of the drive finger and at a right angle thereto. The free end of the drive finger can then not only oscillate in the drive direction and back but also in a circle or in an oval.

The drive finger can be formed as a bending piezo which is non-rotatably held with its fixed end in the stator, is coated with piezo crystals on one side or on both sides and can be bent on one or two sides, and is partially composed of an elastic material which serves as a resetting spring.

However, the drive finger can also be held with its fixed end on the stator in such a way that it can pivot about the rotor axis, and can be made to oscillate by a stack actuator and a resetting spring or a second stack actuator.

Two or more driver jaws which are moved by drive fingers act on the rotor, the drive piezos and pressing piezo actuators of said driver jaws acting on the rotor with the same frequency and with an at least partial phase offset.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The piezo motor according toFIGS. 1 and 2has a stator1and a rotor2which can rotate about the axis11and is driven by a drive finger3. The drive finger3has a fixed end4which is held by the stator1, and a free moveable end5. The drive finger3interacts with at least one piezo element17which moves the free end5of the drive finger3in a drive direction. The free end5of the drive finger3is held such that it is radially displaceable between two stops8and9of a driver jaw7which, during the drive movement of the drive finger3, is pressed against the annular face6of the rotor2by at least one piezo actuator10which changes its length under voltage. The piezo actuator10which presses the driver jaw7against the rotor2may be, for example, a piezo stack actuator.

The face of the driver jaw7which comes into contact with the rotor2is such that in the case of abutment a good frictional connection with the rotor2comes about. Because the driver jaw7pivots with the rotor2about the axis11during the drive phase, the driver jaw7must also be pivotable, together with its piezo actuator10, about the rotor axis11. The driving piezo element17and the pressing piezo actuator10operate with the same frequency and with the same timing with the result that at the end of the drive movement the contact of the driver jaw7to the rotor2is eliminated and the drive finger3quickly moves back into the home position together with the driver jaw7, and a new drive step can begin. The quick return movement of the drive finger3can take place on the basis of the material property and elasticity of the drive finger3or else also by means of a further piezo actuator which operates with the same frequency but with a phase offset. The lifting off of the driver jaw7from the annular face6can take place with the aid of a resetting spring.

The free end5of the drive finger3can also be held between the stops8and9of the driver jaw7such that it is displaceable not only in the longitudinal direction of the drive finger3but also at a right angle thereto and at a right angle to the drive direction, with the result that the free end5of the drive finger3can also carry out oval movements.

The drive finger3advantageously operates as a resonator which is excited to oscillate at its natural frequency by piezo crystals. The oscillations can occur in the drive direction and back or else also in accordance with an elliptical path or circular path.

The piezo crystals17are arranged on one side of the drive finger3with the result that under voltage the drive finger bends toward this side and in the process entrains the driver jaw7. Because at the end of this movement the driver jaw7ceases its contact with the hollow cylindrical annular face6of the rotor2, the drive finger3jumps back with the driver jaw7, into the home position. The drive finger3can also be coated on both sides with piezo crystals, with the result that the rotor2can rotate both in the clockwise direction and in the counterclockwise direction if in each case only one side of the drive finger3is connected to voltage, and the drive finger3bends to the left or the right.

In order to bring about better synchronicity of the rotor2and a higher power of the piezo motor, two or more drive fingers, and driver jaws cooperating therewith, act on the rotor2.

As is shown byFIG. 2, drive fingers3,3′ which interact with the driver jaws7,7′ are arranged on both sides of a disk-shaped stator1. The drive fingers3,3′ and the driver jaws7,7′ operate at the same frequency but offset by half a wavelength or phase. In the case of three drive fingers with driver jaws, the phase offset should be a third of a phase and in the case of four drive fingers with driver jaws it should be a quarter of a wavelength or phase.

In the case of the embodiment of a piezo motor according toFIGS. 3 to 5, the method of operation is in line with the piezo motor according toFIGS. 1 and 2. The parts which act in the same way are provided with the same reference symbols. The rotor2surrounds the stator1on the housing side and is mounted so as to rotate about a fixed stator axle13by means of two housing covers21,22and by means of roller bearings12. The stator1has at least one drive finger3which acts, with at least one driver jaw7, on a hollow-cylindrical annular face6of the rotor2. The stator is composed of an upper stator disk1which is permanently connected to the fixed stator axle13and in which the fixed end4of the drive finger3is held, and of a lower stator disk1′ in which the fixed end4′ of the drive finger3′ is held. The two stator disks1,1′ are rigidly connected to one another by means of bolts25.

In this embodiment, the driver jaws7,7′ are pressed by one piezo curving disk23,23′ each against the inner face6of the rotor2when the drive fingers3,3′ make a movement in the drive direction with their free ends5,5′. The piezo curving disks23,23′ have, on one side, a layer of piezo crystals which cause the disks to curve when voltage is applied. In the process, the circumference of the disks23,23′ decreases. If the disks23,23′ are without voltage, they are flat and have a relatively large circumference, with the result that the driver jaws7,7′ are pressed against the rotor2.

InFIG. 3, a fixed intermediate disk26, which has a sliding ring27against which the driver jaws7and7′ bear, is arranged between the upper and the lower driver jaws7,7′.

In the basic illustration according toFIG. 4, the drive finger3interacts with the driver jaw7, and the drive finger3′ interacts with the driver jaw7′. The piezo curving disks23,23′ are connected rigidly, and if appropriate in one piece, to the associated driver jaws7,7′. The piezo curving disk23of the upper drive finger3is without voltage and lies flat in one plane with the result that the driver jaws7are pressed by the piezo curving disk23against the inner face6of the rotor2. At the same time, the piezo curving disk23′ of the lower drive finger3′ is under voltage, as a result of which this curving disk23′ curves, its circumference decreases and the driver jaw7′ becomes detached from the rotor2.

FIG. 5with the individual drawings a), b), c), d), e), f), g), h), i) and j) shows individual parts of the piezo motor according to the system described herein in a comprehensive overview.

FIG. 5a) is a smaller version ofFIG. 3.

FIG. 5b) shows a sectional view of the piezo motor with a section parallel to the rotor axis11and parallel to the drive fingers3,3′.

FIG. 5c) shows a view along the sectional line B-B inFIG. 5b) of the piezo curving disk23with the driver jaws7and the connecting bolt25of the stator1.

FIG. 5d) shows a perspective view of the part according toFIG. 5c).

FIG. 5e) shows a view along the sectional line A-A inFIG. 5b) with a plan view of the lower stator disk1′, the lower drive finger3′ and the lower driver jaws7′ with the stops8,9between which the free end5of the drive finger3′ is held in a longitudinal displaceable fashion.

In addition, the size of a drive section30, which comes about as a result of the bending deformation of the drive finger3′ is indicated.

FIG. 5f) shows a perspective view of the upper housing cover21which can be screwed onto the rotor2or onto the gear wheel20.

FIG. 5g) shows a perspective view of the upper stator disk1with the stator axle13.

FIG. 5h) shows a perspective view of the upper drive finger3which is held with its free end5between the stops8and9of the driver jaw7.

FIG. 5i) shows a perspective view of the sliding ring27, of the stator connecting bolts25and of the lower driver jaws7′.

FIG. 5j) shows a perspective view of the rotor2with its hollow-cylindrical face6and the lower stator disk1′ with the lower drive finger3′.

FIG. 6shows that the drive finger3is driven by a stack piezo actuator28. The stack piezo actuator28can be arranged on one side of the drive finger3or else on both sides of the drive finger3in order to bend the drive finger3to one side or else bend to one side or to the other side, with the result that the rotor2is driven in the clockwise direction or in the counterclockwise direction. The stack piezo actuator28can be straight in the known fashion or else also be curved in the form of a circular arc in order to increase the number of piezo actuator disks, as is shown byFIGS. 7 and 8.

FIG. 7shows a plan view of three driver jaws7,7′ and7″, which are held in abutment against the hollow-cylindrical annular face of the rotor2by a piezo curving disk23which is integrally connected to said driver jaws7,7′ and7″. When voltage is applied, the piezo curving disk23curves, as a result of which its circumference decreases and the driver jaw7lifts off from the hollow-cylindrical face6of the rotor2.

As is shown, in particular byFIG. 7, passage openings33for the bolts25which rigidly connect the disk-shaped parts of the stator1to one another are formed in the piezo curving disk23. These passage openings33are shaped in such a way that the curving disk23can pivot at least by the magnitude of a deflection30relative to the bolts25. In addition, these openings33are shaped and arranged in such a way that in the curved position the curving disk23bears against these three bolts and therefore centers itself with respect to the rotor axis11. This ensures that the driver jaws7,7′ lift off from the annular face6of the rotor2when the circumference of the curving disk23becomes smaller.

InFIGS. 1 to 5, the drive finger3is non-rotatably held with its fixed end4in the stator1and the deflection30occurs as a result of bending of the drive finger3. The resetting of the drive finger takes place as a result of its elasticity.

InFIG. 7, the drive finger3is moved by a stack actuator29in the drive direction and by a second stack actuator29′ into the home position. In this case, the drive finger3is mounted at its fixed end4so as to be rotatable about the rotor axis. The oscillations of the drive finger3are generated by the stack actuators29,29′.

As is shown byFIGS. 8 and 9, the piezo motor according to the system described herein can also operate as a micro servo motor if the annular face6of the rotor2and the driver jaw7have toothings31and32which engage one in the other during the pressing on of the driver jaw7. The pitch of this toothing corresponds here to a deflection30of the drive finger3.

The piezo motor according to the system described herein is illustrated and described with a rotor2which surrounds the stator1. However, in a kinematic reversal the stator can also surround the rotor or be arranged next to a rotor, and the drive finger and the driver jaws act on a cylindrical annular face of the rotor. This embodiment of a piezo motor is not as compact as the piezo motor which is described and illustrated and the structural complexity is greater.