KR20070004523A - Ultrasonic lead screw motor - Google Patents

Abstract

An apparatus for driving a threaded shaft assembly that contains a threaded shaft with an axis of rotation and, engaged therewith, a threaded nut. Subjecting the threaded nut to ultrasonic vibrations causes the threaded shaft to simultaneously rotate and translate in the axial direction. The threaded shaft is connected to a load that applies an axial force to the threaded shaft. ® KIPO & WIPO 2007

Description

Ultrasonic lead screw motor

Miniature ultrasonic linear motor consisting of a threaded shaft and its associated nut.

Transducers using piezoelectric, electrostrictive, electrostatic or electromagnetic techniques are very useful for accurate positioning on the nanometer scale. In the case of piezoelectric devices, the ceramic is formed of a capacitor that changes shape when charged and discharged to create a force transducer or position actuator. When used as a position actuator, the shape change of the piezo ceramic is approximately proportional to the applied voltage. Piezo actuators are limited to a range of about 0.1% of the ceramic length corresponding to a typical stroke length of 10 μm. While the high hardness and nanometer accuracy of piezo actuators are very useful, longer strokes are required to be used in many applications.

Many piezo motor designs have been developed to "tune" small ceramic shape changes and make longer strokes.

Piezoelectric transducer (PZT) stepping motors are described in US Pat. No. 3,902,084, the entire disclosure of which is incorporated herein by reference. The motor combines many short PZT actuator cycles using a clamp-extend-clamp-retract operating sequence. This stepping linear actuator operates from 5 to 6 kHz frequency from DC, producing noise and vibration. The position is not maintained when the power is turned off. A resolution longer than 1 nanometer is obtained for a movement of 200 mm.

PZT inertial stick-slip motors are described in US Pat. No. 5,410,206; The entire disclosure of this US patent is incorporated herein by reference. The motor rotates the fine-threaded shaft using a split nut to form a "jaw" that holds the opposite shaft. PZT actuators move the jaw quickly in the opposite direction to the asymmetrical AC drive signal. Fast jaw movements overcome slipping friction and cause slippage. If the jaw moves slower, it will not slip and rotate the shaft. This attachment-slip motor produces similar noise and vibration as the stepping motor but is 100 times slower and remains in position when powered off. A resolution of better than 50 nm is achieved for a movement of 25 mm.

Ultrasonic motors use piezo-generated vibrations to create continuous motion with high speed, high torque, small size and quiet motion.

One of the earliest ultrasonic piezo motors is described in US Pat. No. 3,176,167, the entire contents of which are incorporated herein by reference. This unidirectional rotary motor uses a quartz crystal oscillator to drive a ratchet wheel with an external device that moves a thin rod and drives the instrument.

An example of a standing wave ultrasonic motor is described in US Pat. No. 5,453,653, the entire contents of which are incorporated herein by reference. The motor uses a rectangular PZT plate to generate ultrasonic vibrations of the contact points preloaded against the flow surface. The electrode pattern on the PZT plate is connected to an alternating signal and causes two-dimensional oscillation of the contact tip with the required amplitude and phase, resulting in a net force on the mating surface. This ultrasonic motor is quiet and 100 times faster than a stepping motor while producing about one third of the force. In general, ultrasonic motors are difficult to stop and start accurately. Reaching a submicrometer resolution typically requires an encoder with closed loop control.

A device for driving a threaded rod using ultrasonic vibrations is described, for example, in US Pat. No. 6,147,435 to Katsuyuki Fujimura. This patent disclosure and claims are incorporated herein by reference. The present patent discloses and claims: "... a device for driving a screw rod by ultrasonic vibrations comprising: a screw rod having a groove portion formed spirally along an axial direction; rotating the opposite end of the screw rod A pair of stands to hold the work piece; a work rack capable of partially enclosing the screw rod and sliding in an axial direction of the screw rod; fixed to one side of the work rack and the screw from the work rack At least one first threaded rod rotating device extending into the rod, the at least one first threaded rod rotating device having a first vibrator in contact with the groove portion of the threaded rod at a first specific angle, the screw at a specific pressure A first spring for urging the first vibrator toward the groove of the rod and the first vibrator by electrically vibrating A first piezo actuator for rotating said screw rod with said at least one second screw rod rotating device fixed to the other side of said actuation rack and extending from said actuation rack to said screw rod, said at least one The second screw rod rotating device of the second vibrator contacting the groove portion of the screw rod at a second specific angle opposite the first specific angle, pressurizing the second vibrator toward the groove portion of the screw rod at a specific pressure. And a second piezo actuator for vibrating the second vibrator with a second spring and electrically active to rotate the screw rod in a second direction. "

The apparatus of US Pat. No. 6,147,435 requires both a "first screw rod rotator" and a "second screw rod rotator"; These are for example shown in FIG. 3 as components 16a 'and 16d' (including such first threaded rod rotating device), and components 16b 'and 16c' (including such second threaded rod rotating device). Referring again to US Pat. No. 6,147,435, when components 16a 'and 16d' are activated by ultrasonic vibration, the screw rod 2 is rotated in one direction; When components 16b 'and 16c' are activated by ultrasonic vibration, the screw rod 2 rotates in the opposite direction.

Components 16a '/ 16d', and 16b '/ 16c' are never activated at the same time; Doing so would waste energy and leave the screw rod 2 stationary.

However, there is a waste of energy even when such components are not active at the same time 16a '/ 16d' and 16b '/ 16c'. Inactive component pairs still contact the threads of threaded rod 2, causing drag friction.

This frictional drag is a problem with the device of US Pat. No. 6,147,435. As in claim 2 of the patent, in order to solve this problem more or less, the device of such patent is “... when one of the first and second piezo actuators is electrically activated, a small amount of current is applied to the first and second. To the other of the piezo actuators. " The efficiency of the device of US Pat. No. 6,147,435 is not so high.

It is an object of the present invention to provide a threaded shaft with ultrasonic vibrations that provides substantially higher efficiency than that of US Pat. It is to provide a device for driving.

According to the invention, there is provided an apparatus for driving a threaded shaft assembly consisting of a threaded shaft and a nut engaged therewith. This assembly includes means for ultrasonically vibrating the nut to cause the shaft to translate simultaneously with rotation in the axial direction. The assembly also consists of means for exerting an axial force on the shaft.

The invention is described by the specification, the appended claims, and the drawings, wherein like numerals refer to like components.

1-6 show a motor comprising four rectangular piezo plates: where FIG. 1 is a perspective view of the motor, FIG. 2 is an enlarged view of the motor, FIG. 3 is an end view of the motor, and FIG. 4 5 shows an electrical connection to the motor, FIG. 5 is a cutaway view of the motor along the AA 30 line of FIG. 3, and FIG. 5A is an enlarged view of screw engagement with an external preload when the motor is off (FIG. 5B shows the same enlarged view of FIG. 5A when the motor is operating, FIG. 6 shows a cutaway view along the line BB 32 of FIG.

7-12 show a motor comprising four piezo stacks: where FIG. 7 is a perspective view of the motor, FIG. 8 is an enlarged view of the motor, FIG. 9 is an end view of the motor, FIG. 10 shows an electrical connection to the motor, FIG. 11 is a cutaway view along line AA of FIG. 9, FIG. 12 is a cutaway view along line BB 46 of FIG. 9,

13 to 17 show a motor comprising a piezo tube having four external electrodes: where FIG. 13 is a perspective view of the motor, FIG. 14 is an enlarged view of the motor, and FIG. 15 is an end view of the motor. 16 shows an electrical connection to the motor, FIG. 17 is a cutaway view along line AA of FIG. 15,

18 is a schematic illustration of the orbital movement of the threaded nut for the motor of FIG. 1 showing the rotation and translation of the threaded shaft;

FIG. 19 is a schematic illustration of the electric drive signal required to produce the motion shown in FIG. 18,

20-25 show applications of the motor of FIG. 1 packed and integrated into a linear stage, where FIG. 20 is a perspective view of the motor assembly, FIG. 21 is an enlarged view of the motor assembly, and FIG. 22 is a motor. FIG. 23A is an opposite perspective view of the motor assembly of FIG. 20, FIG. 23B is a perspective view illustrating how the motor assembly rotates and translates in the advancing direction, and FIG. 23C is a perspective view of the motor assembly in the opposite direction. 24A shows a motor assembly integrated into a linear stage in the advancing direction, FIG. 24B shows a motor assembly integrated into a linear stage operating in the opposite direction, and FIG. 25 shows a three-axis stage. Represents a motor assembly integrated into a three-axis stage system.

In one embodiment of the invention, the model ultrasonic linear motor rotates the lead screw to make linear movement. The cylinder supports the threaded nut with a first bending mode resonance frequency in the ultrasonic range. The cylinder and nut are excited by the transducer at this resonant frequency to dislodge the nut from the end of the cylinder. The transducer may be any device capable of stimulating piezo, electrical, electrostatic, electromagnetic or resonance vibrations. At least two transducers are needed to simultaneously excite orthogonal bending modes of a cylinder with + or-90 degree of mobility to create a circular orbit. The closed-assembly threaded shaft is installed inside the nut. A resilient axial load is applied to the shaft through low frictional engagement. At the resonant frequency, the nut orbits and the inertia of the shaft keeps it centered. The trajectory of the nut causes torque to rotate the shaft and make linear movement. At least two AC drive signals are needed for the transducers. The drive frequency must excite the mechanical frequency and control phase to complete the circular nut trajectory. Modulation of the drive signal amplitude and duration controls the speed. The phase shift between the drive signals can be + or-, which reverses the direction of the nut trajectory and the rotation / translation of the shaft. This and other preferred embodiments will be described in more detail herein.

Without combining with any particular theory, Applicant excites the first bending resonance of the cylindrical tube with the principle of operation of one of its ultrasonic linear actuators, thereby allowing the cylinder axis to be rotated without rotating one or two ends of the tube. It is believed to orbit around. In this embodiment, one end of the tube receives a threaded nut which orbits around the paired shaft and distributes tangential force through friction to rotate the threaded shaft as it turns around the track. Let's do it. Friction at this thread is useful because it drives the screw directly. This is totally the opposite of conventional lead screw driving, where the thread contact friction is parasitic and causes windup, backlash and slow response. Another important advantage of the helical thread used in this embodiment is the direct conversion of rotation to vibration, along with a large mechanical advantage, ie expanding axial force and reducing linear speed, resulting in increased accuracy.

In this embodiment, the transducer inside or outside the load path is preferably used to excite the first bending mode. Some transducers that can be used include, for example, piezo components and stacks, magnetostrictive materials, and electrostatic materials. This list does not include all transducer materials, but if such materials or devices can be used to excite the first bending resonance or similarly formed blocks of a cylindrical tube and complete the trajectory of one or two tube ends, Anything should be understood as being implemented in the present invention. The embodiments described herein use piezo material but can also be readily implemented with other alternative transducer materials described above.

1-6, in the preferred embodiment described herein, an ultrasonic linear motor 10 is depicted. In the depicted embodiment, four spherical piezo plates are used to generate ultrasonic vibrations. In another embodiment, although not shown in FIG. 1, other means may be used to generate ultrasonic vibrations.

As used herein, the term ultrasonic waves means operating frequencies in excess of 20,000 hertz. In one embodiment, the operating frequency is at least about 25,000 hertz. In yet another embodiment, the operating frequency is at least about 50,000 hertz. In yet another embodiment, the operating frequency is at least about 100,000 hertz.

As used herein, the term linear motor refers to an actuator that generates force and / or displacement to cause movement in a substantially straight line. See, for example, US Pat. No. 5,982,075 (ultrasonic linear motor); 5,134,334 (ultrasonic linear motors); 5,036,245 (ultrasonic linear motors); 4,857,791 (linear motors). The entire disclosure of each of these US patents is incorporated herein by reference.

Referring again to FIGS. 1-6, it can be seen in the preferred embodiment described herein that a threaded shaft 12 with a spherical ball tip 26 rotates and causes axial force and movement.

The threaded shaft 12 is preferably installed to be movable in the housing 14. The length 15 (see FIG. 5) of the threaded shaft 12 preferably exceeds the length 13 of the housing 14 by at least about 10 mm. In one embodiment, the length 15 exceeds the length 13 by at least 25 mm. In another embodiment, the length 15 exceeds the length 13 by at least 50 mm.

In one embodiment, the threaded shaft 12 has a first natural frequency less than 0.2 times the magnitude of the first natural frequency of the housing 14. In another embodiment, the first natural frequency of the threaded shaft 12 is about 0.1 times less than the magnitude of the first natural frequency of the housing 14.

As used herein, the term first natural frequency means the frequency of the first normal mode of vibration: see, for example, the McGraw-Hill Dictionary of Scientific and Technical Terms, in terms of science and technology. (McGraw-Hill Book Company, New York, New York, 1989.). In addition, the Eugene A. Avallone et al.'S "Mark's Standard Handbook for Mechanical Engineers" (McGraw-Hill Book Company, New York, New York, 1978) Reference may be made from 5 to 59 p to 5 to 70 p of "Natural Frequencies of Simple Systems." Also, US Pat. Nos. 6,125,701; 6,591,608; 6,525,456; 6,439,282; 6,170,202; 6,101,840 Reference may be made to the entire disclosure of each of these US patents.

In the embodiments depicted in the figure, the orbital movement of the nut 16 occurs due to the presence of two normal vibration modes, as best described in FIG. 18, which are at the axis centerline (see FIG. 2). They are in parallel planes and are orthogonal to each other.

These two orthogonal steady vibration modes are generated by the interaction of the activated transducer with the activated transducer (such as plates 18, 20, 22, and 24); And such interaction causes orbital movement of the nut 16, alternating rotation and translation of the threaded shaft 12.

In one embodiment, the first natural resonance frequency of the nut 16 is preferably at least five times the magnitude of the operating frequency of the motor assembly 10. Therefore, the nut 16 is preferably a substantially rigid body.

In one embodiment, the threaded shaft 12 is made of substantially stainless steel metal. In this embodiment, the threaded shaft 12 meshes with a threaded nut 16 made of substantially brass metal.

It is clear that it is desirable to use a combination of materials for the threaded shaft 12 and threaded nut 16 in order to minimize abrasion and galling. Different combinations of materials to minimize wear and tear can also be used in the present invention.

Referring again to FIG. 1, the threaded shaft 12 consists of a plurality of threads 17, preferably configured in the form of a spiral groove. In one embodiment, the thread 17 has a pitch less than about 250 threads per inch, preferably less than about 200 threads per inch. In another embodiment, the threads 17 have a pitch less than about 100 threads per inch. In one aspect of this embodiment, the threads 17 have a pitch of about 40 to 80 threads per inch.

The thread 17 is preferably engaged with the internal thread 19 of the nut 16, as best described in FIG. 18. In one preferred embodiment, the pitch of the inner thread 19 is substantially the same as the pitch of the outer thread 17.

For the sake of simplicity, the threads 17, 19 are shown as fully engaged (except for FIGS. 5A, 5B and 18), but the diametrical clearance between the threads 17, 19 is threaded. (17) and / or less than about 0.5 times the thread depth 33/35 of the thread 19. This relative clearance is well illustrated in Figure 5A. Means for determining the relative clearance are well known. US Patent No. 6,145,805; 5,211,101; 5,211,101; 4,781,053; 4,277,948; 4,277,948; 6,257,845; 6,257,845; 6,142,749, etc .; The disclosures of each of these US patents are incorporated herein by reference. See also, 8-9 et seq. ("Machine Elements"), above, "A Trademark Standard Handbook for Mechanics."

Referring to FIG. 5A, a preferred mode of engagement between threads 17 and 19 is described. As can be seen from this figure, each of the threads 17 has a tip 29, and the threads 19 have a tip 31. In addition, threads 17 and 19 each have thread depths 33 and 35, respectively.

Referring again to FIG. 1, in the preferred embodiment depicted herein, the rotation of the threaded shaft 12 is made by the ultrasonic trajectory of the threaded nut 16 connected to the vibration housing 14. In the embodiment depicted, the threaded nut 16 is preferably connected to the housing 14. This is well illustrated in FIG.

Referring to FIG. 2, in the preferred embodiment depicted herein, it can be seen that the nut 16 is installed in an orifice 11. The nut 16 is fixed in the hole 11 by conventional means, for example a press fit, and / or an adhesive means.

In the preferred embodiment depicted in FIGS. 1 and 2, the nut 16 is a cylindrical nut. In another embodiment, although not shown, the nut 16 is a polygonal nut that may have a square, hexagonal shape, octagonal shape, or the like.

Referring again to FIGS. 1 and 2, in the preferred embodiment depicted therein, a number of ceramic plates 18 can be seen attached to the outer surface 37 of the housing 14, see below.

It is preferable that the ceramic plates change their respective lengths in accordance with a voltage, in particular a change in voltage. As used herein and described herein, these ceramic plates may be described as "active ceramic plates." In one embodiment, the ceramic plates 18 are selected from the group consisting of piezo plates, electrostatic plates and mixtures thereof. For simplicity of discussion, at least the embodiment of FIGS. 1 and 2 will be described with reference to piezo plates.

In the embodiment depicted in FIG. 2, four piezo plates 18, 20, 22 and 24 are coupled to the outer surface 37 of the housing and the electrical drive signal of the electrodes 21 and 23 of each piezo plate. The nuts 16 orbital oscillate when excited by replacing them (see FIG. 4).

In one embodiment, only two piezo plates, plates 18 and 20 are used. In another embodiment, eight or more piezo plates are used. Regardless of how many piezo plates are used, a sufficient number of such plates are used to excite movement in orthogonal planes 39 and 41 (see FIG. 2).

For simplicity of explanation, four piezo plates 18, 20, 22 and 24 will be described. These plates are preferably coupled to the corresponding outer surface 37 of the housing 14 such that the plates are in complete contact with the outer surface 37.

Piezo plates 18 are connected to the voltage source by electrodes 21 and 23, as well shown below in FIG. 4. For simplicity of depiction, the connection of electrodes 21 and 23 is only shown with respect to the piezo plate, and the connection with respect to the other piezo plates is made equivalent.

Referring to FIG. 4, with reference to the preferred embodiment described herein, it will be seen that all four electrodes 23 are connected to ground 25. In this embodiment, the piezo material is a generally available "hard" composition with low dielectric loss and high depollng voltage. Thus, for example, one may use a piezo solid material marketed as "PZT-4" by Morgan Matroc of Bedford, Ohio. This preferred material typically has several important properties.

Therefore, the preferred material preferably has a dielectric loss factor of less than about 1%, preferably less than 0.5%, at frequencies greater than about 20,000 hertz. In one embodiment, the dielectric loss factor is about 0.4% at frequencies greater than about 20,000 hertz.

Therefore, the preferred material has a d33 piezoelectric charge coefficient of at least about 250 pC / N (picoCoulomb / Newton's), preferably at least about 270 pC / N. In one embodiment, the preferred material has a d33 piezo charge coefficient of about 285 pC / N.

Therefore, preferred materials have a d31 piezo charge coefficient of at least about -90 pC / N, more preferably at least about -105 pC / N. In one embodiment, the d31 piezo charge coefficient is about −115 pC / N.

In one embodiment, the preferred material is a single crystal material having a d33 piezo charge coefficient of at least about 2500 pC / N and a d31 piezo charge coefficient of at least about 900 pC / N.

For discussion of some suitable materials, reference is made, for example, to US Pat. Nos. 3,736,532 and 3,582,540 for purposes of explanation. The entire disclosures of these US patents are incorporated herein by reference.

By further description, low dielectric loss piezomaterials are known to those skilled in the art. U.S. Patent No. 5,792,379 (Low Loss PZT Ceramic Composition) may be referred to by way of example; The entire disclosure of these US patents is incorporated herein by reference.

In one embodiment, the piezo material is a single crystal piezo material. These materials are known in the art. US Patent No. 5,446,330; No. 5,739,624; 5,814,917; 5,814,917; 5,763,983 (Single Crystal Piezo Transformer); 5,739,626; 5,739,626; 5,127,892, and the like. The entire disclosure of each of these US patents is incorporated herein by reference.

Referring again to FIG. 4, in the preferred embodiment depicted here, the axial length of the piezo plates 18, 20, 22 and 24 is dependent on the applied voltages (Vx / 86 and Vy / 88) and d ₃₁ piezo charge coefficients. Change proportionally.

The piezo plates 18, 22 and 20, 24 respectively act in pairs to bend the housing 14 (see FIGS. 1 and 2) and to excite orbital resonance. It is preferred to apply the electric drive signals 86 and 88 to the plates 20, 24 and 18, 22, respectively, alternately in the polarizing direction 43. As is well known to those skilled in the art, polarization direction 43 is the direction in which dipoles in the piezo material are arranged during manufacture. For example, US Pat. No. 5,605,659 (method of polarizing ceramic piezo plates); 5,663,606 (apparatus for polarizing piezo actuators); No. 5,045,747 (apparatus for polarizing piezo ceramics) may be referred to. The disclosures of each of these US patents are incorporated herein by reference.

For each plate pair 18, 22 and 20, 24, the electric field is positive with respect to the polarization direction 43 on one plate and negative with respect to the polarization direction 43 on the opposite plate. The drive signal Vx86 is preferably applied to the plates 20, 24 and simultaneously expands in one plate and contracts in the other, so that the plane 39 (see FIG. 2) and in the X direction 72a / 72b (see FIG. 18). The housing 14 is bent (see FIG. 18). In a similar manner, the drive signal Vy88 is applied to the plates 18, 22 and bends the housing 14 in the plane 41 (see FIG. 2), and in the Y direction 74a / 74b (see FIG. 18).

The housing end 45 opposite the threaded nut 16 preferably supports a guide bushing 28 having a small gap between the outer diameter of the threaded shaft 12 and the inner diameter of the bushing (FIG. 2). The threaded shaft 12 supports the elastic axial force 27 (see FIGS. 5 and 6), which is applied through a spherical ball tip 26 using a hard, flat surface with low friction.

During operation of the motor, the axial force 27 preferably transmitted through the ball 26 is preferably about 0.1 to about 100N. The axial force 27 is preferably similar in magnitude to the output driving force.

The spherical ball 26 (see FIG. 2) is one means of coupling the threaded shaft 12 to its load 27 with low frictional torque (see FIG. 5). As will be apparent to those skilled in the art, one skilled in the art can use other means to combine movement from the rotating threaded shaft to the moving load. Thus, for example, one person may use a rolling element bearing, and one person may use an arcuate load that contacts a flat surface, such as a threaded shaft 12. See US Pat. No. 5,769,554 (kinematic coupling method), 6,325,351 (damped kinematic coupling for precision instrument); The disclosures of each of these patents are incorporated herein by reference.

1 and 2, the end 45 of the housing 14 opposite the threaded nut 16 incorporates the flanges, which are the connection points of the stop cover 58 (FIG. 21). The thread pitch on the shaft 12 and nut 16 transmits the orbital tangential force and movement in axial force and axial movement. The pitch can be selected to optimize force expansion, speed reduction, resolution increase and off-power holding force.

With reference to FIGS. 7-12, in the preferred embodiment depicted here, the ultrasonic linear motor 30 uses four piezo stacks 36, 40, and 42 (see FIGS. 7 and 8) to generate ultrasonic vibrations. desirable. Threaded shaft 12 with spherical ball tip 26 rotates to create axial force and axial movement. The rotation takes place by the ultrasonic trajectory of the threaded nut 16 connected to the vibrating cylinder 32. Four piezo stacks 36, 38, 40 and 42 are coupled to the end of the cylinder opposite the threaded nut and to the base ring 34. The four stacks 36 are constructed using a known assembly with internal stack leads and an electrical internal connection method 44, see below, wherein the internal stack leads are preferably connected together to a common ground 35. The axial length of the stack varies in proportion to the applied voltage and d ₃₃ piezo charge coefficient. Piezomaterials are generally available "hard" compositions with low dielectric loss and high polarization voltage. Electrical drive signals 86 and 88 are alternately connected to the external leads of each piezo stack 44 and counter-orbital vibration of the nut. Piezo stacks 36 and 40 and 38 and 42 respectively work together in pairs to rotate the tube and excite orbital resonance. The electrical drive signals Vx86 and Vy88 are alternately connected to stacks 38, 42, 36 and 40 in the polarization direction, respectively. For each stack pair 38, 42 and 36, 40 the electric field is positive for the polarization direction 43 in one stack and negative for the polarization direction in the opposite stack. The drive signal Vx 86 is applied to stacks 38 and 42 to simultaneously expand in one stack and contract in the opposite stack; So this rotates the tube in the X direction 72a / 72b (see FIG. 18). In a similar manner, the drive signal Vy 88 is applied to stacks 36 and 40 and moves the end of the tube in the Y direction 74a / 74b (see FIG. 18). The base ring 34 opposite the threaded nut 16 supports a guide bushing 28 having a small gap between the bushing inner diameter and the outer diameter of the threaded shaft. The threaded shaft 12 supports a flexible axial force 27 applied through a spherical ball tip 26 that uses a hard, flat surface that produces less friction. The base ring 34 is a connection point for a stationary cover 58 (FIG. 21). The thread pitch of the shaft 12 and nut 16 converts orbital tangential and tangential movements into axial and axial movements. The pitch may be selected to optimize force expansion, speed reduction, resolution increase and off-power holding force.

Referring to Figures 13-17, the ultrasonic linear motor 50 generates ultrasonic vibrations using a piezo tube 54 having quadrant electrodes. Threaded shaft 12 with spherical ball tip 26 rotates and generates axial force and axial movement. The rotation is caused by the ultrasonic trajectory of the threaded nut 16 connected to the vibrating piezo tube 54. The inner diameter of the tube is a continuous electrode 61 grounded 63, and the outer diameter of the tube is divided into four separate electrodes 60, 62, 64 and 66. The piezo material is a generally available "hard" composition with low dielectric loss and high depolarization voltage. The axial length of the piezotube section below each electrode 60, 62, 64 and 66 varies in proportion to the applied voltage and d ₃₁ piezoelectric charge coefficient. Electrode sections 60, 64 and 62, 66 each work together in pairs to bend the tube and excite the orbital resonance. Electrical drive signals 86 and 88 are alternately applied to plates 60, 64, 62 and 66 in polarization direction 43, respectively. For each electrode pair 60, 64 and 62, 66 the electrode field is positive for the polarization direction at one electrode and negative for the polarization direction at the opposite electrode. The drive signal Vx86 is applied to electrodes 60, 64 and simultaneously causes expansion under one electrode and contraction under the opposite electrode: this bends the tube in the X direction 72a / 72b (see FIG. 18). In a similar manner the drive signal Vy 88 is applied to the plates 62, 66 and the tube is bent in the Y direction 74a / 74b direction (see FIG. 18).

The tube end opposite the threaded nut 16 is coupled to a base flange 52 and holds a guide bushing 28 having a small gap between the bushing inner diameter and the threaded shaft outer diameter. The threaded shaft 12 supports a flexible axial force 27 applied through a spherical ball tip 26 that uses a hard, flat surface that produces a small frictional force. The base flange is the connection point of the stop cover 58 (see FIG. 21). The thread pitch of the shaft 12 and the nut 16 converts the orbital tangential force and movement into axial force and movement. The pitch may be selected to optimize force expansion, speed reduction, resolution increase and off-power bearing capacity.

Referring to FIGS. 18 and 19, the operation of the motor 10 (see FIG. 1) and the corresponding drive signals 86 and 88 used to influence such operation are shown. The piezo plate pairs work together, one expanding (70) and the other constricting (69) at the same time to bend the housing. The AC drive signals Vx 86 and Vy 88 are preferably sinusoidal having the same amplitude 90/91 and 90 degree phase shift 92 to create a circular trajectory. Positive phase shift 92 produces positive nut 16 orbital direction and positive shaft 12 rotation 96 / translation 98, while negative phase shift 92 has negative orbital direction and negative shaft rotation / translation. Create For one direction of rotation, one orbital cycle of the motor, and its corresponding drive signal amplitudes 90 and 91, appear to be continuously increasing 90 degrees (76, 78, 80, 82, and 84). The cylindrical bending and orbital movements appear in the X 72a / 72b and Y 74a / 74b directions. The nut contacts the side of the threaded shaft at one position 74a where a gap 73b is created on the opposite side, thereby distributing tangential forces and movements into the contact so that the shaft 12 with respect to each orbital cycle. Minor rotation 96 and translation 98. The magnitude of rotation and translation per cycle depends on the surface finish of many factors and threads, including orbital amplitude, magnitude of force 27 acting on the shaft, and coefficient of friction. If a zero-slip condition can be achieved between the contact 73a of the nut and the shaft, the movement per cycle is generally proportional to the diameter gap between the threads. In general, as the driving amplitudes 90 and 91 increase, the raceway diameter increases, the normal contact force between the shaft 12 and the nut 16 increases, slippage decreases and speed increases. , And torque / force increases.

The ultrasonic frequency is the inverse of the period (see periods 94a and 94b of FIG. 19); And such an ultrasonic frequency is preferably the same for the two signals and coincides with the first bending resonance frequency of the housing 14.

20 to 25, the motor assembly 100 is a composite motor 10 having a cover 58 and a knurled knob 102. The threaded shaft 112 is installed in the motor 10. As best shown in FIG. 21, the threaded shaft 112 is similar to the threaded shaft 12 (see FIG. 1), except that it has a smooth spindle 113 integrally attached thereto. The spindle 113 is applied to attach to the knurled knob 102. The cover 58 is attached to the motor 10 at the flange 45. The knurled knob 102 rotates and translates with the shaft 112 without the contact cover 58.

21 is an enlarged view of the motor assembly 100. 22 is a cross-sectional view of the motor assembly 100.

23A, 23B and 23C show the motor assembly 100. FIG. 23A is a perspective view of the motor assembly 100 upside down from FIG. 20. 23B illustrates the operation of the motor assembly 100 to rotate the knob 102 and shaft 112 clockwise 103 and to translate in the direction of the arrow 105. In comparison, FIG. 23C illustrates the operation of the motor assembly 100 to rotate the knob 102 and the shaft 112 in the counterclockwise direction 107 and to translate in the direction of the arrow 109.

For simplicity of description, it will be apparent that the physical means for electrically connecting the various components of the motor assemblies have been removed from the drawings.

It is also clear that the presence of the knurled knob 102 makes it possible to move the motor assembly 100 by manual means in addition to or in place of moving such motor assembly 100 by electrical means. Thus, for example, the assembly 100 can be used as a micrometer's drive replacement device that allows the user to use both manual and manual adjustment means as well as electrically automated additional adjustment means.

In one embodiment, although not shown, the knurled knob 102 may be mechanically connected to an external motor to become a second means of mechanical movement of the assembly.

24A and 24B illustrate applicable linear stages 106 comprised of motor assemblies 100 operably connected to a linear translation stage 104a / 104b. In this embodiment the cover 58 of the motor assembly 100 is connected to the lower stage portion 104b and the ball 26 is in contact with the upper stage portion 104a. When the nulling knob 102 moves clockwise 103, a linear movement in the direction of the arrow 105 occurs. Conversely, when the nulling knob 102 moves in the counterclockwise direction 107, linear movement in the direction of the arrow 109 occurs.

In one embodiment, outlined in FIGS. 24A and 24B, the spring assembly 111 (contoured in dashed lines) consisting of pins 115 and 116 is moved to the previous stage 104a / 104b in the direction of the arrow 109. Bias. In the depicted embodiment, the pin 115 is attached to the movable top 104a of the assembly, which pin 116 is attached to the fixed bottom 104b of the assembly. It is clear that the spring assembly 111 can be produced to produce the axial force 27 (see FIGS. 5 and 6).

25 is a perspective view of a micromanipulator 120 capable of moving its stages 106a 106b and 106c in the X, Y and Z axes.

While the invention has been described in any particular preferred form, the teachings of the preferred form of the invention may vary in details of construction and other combinations and arrangements of parts may be made again without departing from the spirit of the invention. It can be seen that it can be produced.

In an earlier part of this specification, a device for driving a threaded shaft assembly comprising a threaded shaft having an axis of rotation and a threaded nut engaged therewith, wherein the assembly provides a means for applying the threaded nut to ultrasonic vibrations. And thereby allow the shaft to rotate and translate simultaneously in the axial direction. One may manufacture a corresponding means consisting of means for vibrating the threaded shaft assembly, which allows the threaded nut to translate simultaneously with rotation.

The present invention provides a device for driving a screw shaft with ultrasonic vibrations having substantially higher efficiency than that of US Pat. No. 6,147,435 while providing higher accuracy, force and speed than would normally be achieved with other ultrasonic motors of similar size. To provide.

Claims (20)

A threaded shaft with a shaft of rotation, a threaded nut engaged therewith, where a. Said assembly comprising means for ultrasonically vibrating said threaded nut to simultaneously translate said threaded shaft while axially rotating it; b. The threaded shaft is operably connected to the load, and c. And said assembly further comprises means for applying said axial force to said threaded shaft. 2. A screw shaft assembly drive according to claim 1 wherein said assembly comprises means for moving said screw nut in an orbital direction. 2. The threaded shaft assembly drive of claim 1 wherein said threaded nut is a substantially rigid body. The drive mechanism of claim 1 wherein the device further comprises a housing in which the threaded shaft assembly is installed. 5. The threaded shaft assembly drive of claim 4 wherein said threaded nut is attached to said housing. 6. A screw shaft assembly drive according to claim 5 wherein said housing has a first bending resonance frequency of at least 20,000 cycles per second and said first bending mode lies in a plane parallel to said axis of rotation. 7. The threaded shaft assembly of claim 6, wherein the housing has a second bending resonance frequency equal to the first bending resonance frequency, and wherein the second bending mode lies on a plane perpendicular to the first bending mode. Drive system. 7. The threaded shaft assembly drive of claim 6, wherein the device further comprises means for orbiting the threaded nut at a frequency of at least about 20,000 orbits per second. 9. The threaded shaft assembly drive of claim 8 wherein the device further comprises means for moving the threaded shaft in a direction substantially parallel to the axis of rotation. 9. The drive unit of claim 8 further comprising means for rotating said threaded shaft while moving said threaded shaft in a direction substantially parallel to said axis of rotation. 8. A screw shaft assembly drive according to claim 7, wherein said means for orbiting said threaded nut comprises at least two transducers for converting electrical energy into force. 12. A screw shaft assembly drive according to claim 11 wherein said transducer is selected from the group consisting of piezo transducers, former transducers, magnetostrictive transducers, electrostatic transducers, electromagnetic transducers and mixtures thereof. 13. The threaded shaft assembly drive of claim 12 wherein the transducer is a piezo transducer. 14. A screw shaft assembly drive according to claim 13 wherein said piezo transducer is a piezo plate. 15. The threaded shaft assembly drive of claim 14, wherein the piezo plate is made of piezo material having a dielectric loss factor of less than about 1% at frequencies greater than about 20,000 hertz. 15. The threaded shaft assembly drive of claim 14 wherein the piezo plate is comprised of a piezo material having a dielectric loss factor of less than about 0.5% at a frequency greater than about 20,000 hertz. 2. The drive mechanism of Claim 1 wherein said threaded shaft consists of a plurality of threads having a thread pitch of about 40 to 250 threads per inch. The drive mechanism of claim 1 wherein said threaded shaft is installed in a housing and said threaded shaft is connected to a knob. 19. The drive mechanism of claim 18 wherein the device further comprises a movable stage coupled to the threaded shaft and the housing. An apparatus comprising at least two movable stages adjacent to each other, wherein each of the at least two movable stages consists of the apparatus of claim 19.

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