MXPA00000313A - Piezoelectric motor - Google Patents

Abstract

A piezoelectric motor including a motor body, a compliant layer in communication with the motor body, and a predetermined number of legs in communication with the compliant layer, which urges the legs into engagement with a substrate. Each of the legs includes a piezoelectric wafer, preferably operated in the shear mode. The actuation of a piezoelectric wafer causes the corresponding leg to be displaced relative to a substrate. This displacement results in the transfer of strain energy to the compliant layer. The energy stored in the compliant layer may be released, causing the motor to advance along the substrate. The legs may be capable of moving independently from one another and also may be capable of moving sequentially or in predetermined groups or units. The legs also may be arranged in pairs with the leg pairs being capable of simultaneous actuation. The motor is capable of maintaining a high holding force in the absence of a power input.

Description

PIEZOELECTRIC MOTOR BACKGROUND OF THE INVENTION This application relates to piezoelectric motors, and more specifically, to a piezoelectric motor capable of storing energy that can be used to drive the motor.

In piezoelectric motors an electroactive material is used to convert electrical power directly into mechanical deformation. Piezoelectric motors use friction to convert microdeformations into macromotion.

Piezoelectric motors are useful for precision actuators and effectors, such as robotic manipulators. They generally have some advantages over conventional motors (ie, those based on electromagnetic couplings in air gaps) in precision control applications where features such as light weight, compact size, low power consumption, or the capacity of operate under cryogenic or extreme environmental conditions.

Conventional piezoelectric motors generally involve a series of mechanical steps. The motors do not store energy.

The components of conventional piezoelectric motors are quite small compared to stepped displacement. It may be difficult or expensive to manufacture engines that are capable of maintaining acceptable tolerances using conventional equipment and methods. They are also susceptible to failure if the wear exceeds these tolerances.

One of the objects of the present invention is to provide a piezoelectric motor capable of producing motive power by successively inducing small amounts of deformation in a substrate, and, specifically, a piezoelectric motor suitable for use in applications requiring compact high power-density actuators. and long embolado.

Another object of the present invention is to provide a piezoelectric motor capable of storing energy from the movement of a pin; energy that can be released to make the motor move in relation to a substrate, and that is able to sustain a constant force without consuming energy.

Yet another objective of the present invention is to provide a piezoelectric motor having an elastic surface that tends to push the motor so that it makes contact with the substrate, thereby avoiding the problems of tolerance and wear that previous inventions have.

Yet another objective of the invention is to provide a piezoelectric motor having a sufficient number of pins that contact the substrate to provide an acceptable level of redundancy and minimize faults in one place.

The above objects are achieved with a piezoelectric motor having a body, an elastic layer communicating with the motor body and a predetermined number of pins in communication with the elastic layer that pushes the pins into contact with a substrate. Each of the pins has a piezoelectric semiconductor plate, which is preferably operated in the shear mode. The action of a piezoelectric semiconductor plate causes the corresponding pin to move relative to a substrate. This displacement results in the transfer of deformation energy to the elastic layer. The energy stored in the elastic layer can be released, which causes the motor to move along the substrate.

The pins can move independently of each other; they are also capable of moving sequentially or in predetermined units or groups. In a preferred embodiment, the lugs may be arranged in pairs, the lugs being capable of acting simultaneously. The piezoelectric semiconductor plates of the pins can be operated by an analog voltage source arranged in parallel with the pairs of pins.

In another preferred embodiment, the piezoelectric motor can include a body and a predetermined number of pins connected to the body by means of an elastic contact surface that urges the pins to contact the substrate. Each pin includes at least one electroactive element, which is preferably a piezoelectric semiconductor plate operated as a shear.

The piezoelectric motor of another preferred embodiment is constituted by a body, an elastic layer capable of storing energy of deformation, communicating with the motor body, plus a predetermined number of pins communicating with the elastic layer, which keeps contact the pins with a substrate. Each pin includes a piezoelectric element. The action of a piezoelectric element causes the displacement of the corresponding pin. The discharge of the piezoelectric element transfers deformation energy to the elastic layer. The release of the energy stored in the elastic layer causes the motor to travel along a substrate. The motor is able to maintain a very high holding force in the absence of an input power.

This and other objects of the invention will be obvious with the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of a piezoelectric linear motor of the present invention; Figure 2 is constituted by a series of schematic representations, from (a) to (h), showing the stepped operation of the piezoelectric motor of Figure 1 during a complete cycle; Figure 3 is a schematic diagram of a waveform that can be used to drive a piezoelectric motor pin of Figure 2; Figure 4 is a schematic representation of a linear and rotary piezoelectric motor of the present invention; Y Figure 5 is a schematic representation of a piezoelectric semiconductor plate, showing the operation of the semiconductor plate in the shear mode.

DESCRIPTION OF THE PREFERRED EMBODIMENT (S) The piezoelectric motor of the present invention has pins, formed of one or more piezoelectric semiconductor plates, which make contact with an axis or other substrate. The motor generates an output force by means of the frictional contact of the pins and the substrate. The invention provides applications in which the motor body is fixed and the lugs cause the substrate to move, as well as applications in which the substrate is fixed and the lugs cause the motor body to move along the substrate. .

With reference to the drawings, Figure 1 shows a schematic representation of the linear piezoelectric motor 10 of the present invention. The motor 10 has a predetermined number N of pins 12, and each of them includes at least one piezoelectric element, preferably, a piezoelectric-semiconductor plate. An elastic layer 14 located in the motor body 16 keeps the lugs 12 in contact with an axis or other substrate 18. A pre-charged force P can be applied to the motor body 16 to assist the lugs 12 to remain in contact with the motor. substrate 18. The frictional contact of the lugs 12 and the substrate 18, resulting from the action of the piezoelectric semiconductor plates, causes the motor 10 to move relative to the substrate 18, as described below. A contact layer 13 may be interposed between the lug 12 and the substrate 18 to further assist in maintaining that contact.

The size of the pins and the movement of the pins have been exaggerated in the drawings to better illustrate the structure and operation of the motor. In fact, the piezoelectric motor pins of the present invention are very small, and the movement of the pins generally can not be distinguished without an amplification. Finite steps are given to produce a macroscopic movement.

In the example shown, the lugs 12 are arranged linearly, with a certain distance between them, along an axis of the motor body 16. The pins N can also be arranged in pairs or even in larger multiples, with the pins of each pair or of another multiple unit separated from each other. Unless otherwise specified, the subsequent references to the N pins will also be applied to the N units constituted by two or more coupled pins. The use of a greater number of pins, provides a redundancy that allows the engine to continue operating efficiently even if some of the pins are damaged. This is especially valuable when the objective is to use the motor in applications where there is not easy access to it for repairs, or when the failure in a single place of the same could result in an unacceptable downtime, or even more serious consequences .

The pins 12 of the motor 10 can be able to move independently of one another. Alternatively, the control of the pins 12 in one or more multiple units can be coupled in such a way that they move at the same time in reaction to a control signal. The pins 12 can move on a single axis, as shown in the linear motor 10 of Figure 2, or they can be capable of moving along multiple axes, as shown in the rotary motor 10"of the Figure Four.

Figure 2 illustrates a series of schematic representations showing the complete operating cycle of a motor 10 'having four pins 12'. A pin, such as pin 2 of Figure 2 (a), is actuated, causing it to travel a distance s along the substrate 18 '. This pin 12 'can be displaced because the applied voltage is sufficient to cause the pin to be put into kinetic friction. However, the other pins remain in place, relative to the substrate 18 ', by means of static friction. In this way, when the motor 10 'is in the state represented by FIG. 2 (b), two external forces act on the motor body 16' by means of an elastic backrest 14 ', mainly the force of the pin. 2 which causes the motor to advance, and the sum of the forces of the rest of the pins does not allow the motor to advance. The static equilibrium of these forces causes the motor 10 'to advance through the subscale d. When the pin 2 is discharged, the deformation of its piezoelectric semiconductor plate is transferred to the elastic material 14 ', and then all the pins 12' are held in place relative to the substrate 18 'by means of static friction. In this way, the motor 10 'of the present invention is capable of maintaining a constant force without a voltage supply.

The above action and discharge steps can be repeated for each of the pins N, as shown with respect to pins 1, 3 and 4 of Figures 2 (c) to 2 (h), until the motor 10 ' He has fully started the step s. During this process, the number of pins 12 holding the motor 10 'gradually decreases, while the number of pins 12' which cause the motor 10 'to advance increases. The entire cycle can be repeated until the desired displacement is achieved.

In the example shown, a pin 12 'is independently actuated. However, the pins can also be operated in pairs, or in larger multiples, to increase the speed at which the motor moves (not shown in the drawings). The control signals used to drive the motor 10 'do not need to be synchronized because the elastic contact surface 14' can indiscriminately store the deformation energy.

Figure 3 is a schematic diagram illustrating a shape wave 20 that can be used to cause the pin 12 'of the motor of Figure 2 to advance in a single step. Each pin 12 'individually actuated by a voltage pulse, which switches the voltage from Vm? N to Vma ?. The pulse results in a high rotation rate (slope) 22 sufficient to cause an intermittent slip reaction on a pin, such as pin 2 of Figure 2 (a). Once the pin 12 'is in its advance state, the voltage is discharged through a resistor, so as to form the low slope portion 24 of the sawtooth waveform, and the pin 12' is maintained in place by means of static friction.

The speed of the motor can be controlled by regulating the frequency of the signals, the peak voltage (the size of the step), or both. Speed reductions up to zero can be achieved by controlling the frequency or voltage of the signal applied to the piezoelectric elements. Finite steps can be taken at any desired frequency, as required by the application.

For example, the control signal shown in Figure 3 can be generated using a combination of digital and analog circuits. Timed waveforms can be generated using a control unit, such as an MCU, (magnetic card unit) with a digital-analog converter (D / A). The output of the MCU is constituted by low power N signals used to control a series of high voltage amplifiers. The intermittent phase of the control sequence can be amplified using a field effect power transistor voltage switch of oxidometallic semiconductor material (MOSFET). The impulse phase of the control sequence can be achieved by unloading all the actuators of the pins by means of an RL circuit. Alternatively, the shape of the waveform during the drive phase can be controlled using two power transistors with different current limits. The high slope phase can be charged through a high current limit, and the low slope phase can be charged through a low current limit. Of course, a person with ordinary knowledge in this matter will be able to devise other control signals to control the motor pins.

The static displacement capability of the pins determines the extent of the positioning.

The amount of displacement s is determined by the constant d? 5 of the piezoelectric material (for operation in shear mode) and by the applied voltage. A very precise micropositioning can be achieved by arranging the pins in pairs and operating all pairs of pins, together and in parallel, with a load amplifier or analog voltage.

The direction of travel can be controlled by reversing the polarity of Vmax. Alternatively, the input signal can be changed from the ascending slow sawtooth shape of Figure 3 to the slow sawtooth sawtooth shape.

The peak voltage Vmax applied to each pin may be the same, but in fact it is not needed because the elastic layer stores energy indiscriminately. However, it may be necessary to modify the voltage applied to one or more pins, in order to achieve a displacement of a distance s, especially when the pins are operated sequentially. For example, if the elastic layer is especially efficient with regard to storing energy of deformation, it might be necessary to reduce the peak voltage applied to one or more of the driven pins, and close to the end of the cycle, to prevent the distance s from suffering an overshoot.

It is believed that step size s is reached with the following formula d15 * Vmax * N where d? S is the piezoelectric displacement constant, V ^ a * is the applied voltage, and N is the number of shear semiconductor plates that each pin has. For a semiconductor plate layer and a di5 value of 800 e-12m / V and Vmax of 400V, the unit displacement is calculated to be 0.32 microns. If five semiconductor shear plates are used in each step, the unit displacement is estimated to be 1.6 microns. Because the piezoelectric material is not moving an inert mass, the resonance of the semiconductor plate will be high (at least as high as 50 kHz). If the engine is operated at 25 kHz, which is a frequency that is quite consistent with the power MOSFET capacity, it is estimated that the engine capacity is 40 mm / sec. The speed can be increased by increasing the number of shear semiconductor plates per pin. In addition, the speed of the motor can be controlled by regulating the frequency of the signals or the peak voltage, as described above.

It is also believed that the output power of the motor can be calculated assuming that the force generated will be whatever is lower than the piezoelectric force or the frictional force. For a shear semiconductor plate 10 mm wide x 0.25 mm thick, the blocked piezoelectric force is approximately 110 N. The frictional force is determined by the preload applied to the motor body. It is taken for granted that the coefficient of static friction will dominate the contact interaction. As an example, it can be said that the coefficient of static friction of the steel on a ceramic material, generally fluctuates between 0.1 and 0.5. If an SMA band is used as the preload mechanism, a 250 N preload can be achieved. In this example, the lower limit of the projected motor output force would be 25 N and the upper limit would be the blocked piezoelectric force, which it is approximately 110 N.

As shown in Figure 4, the piezoelectric motor 10"of the present invention can also be configured to have a rotary motion, alone or in combination with a linear movement, the motor 10" is constituted by a predetermined number N of piezoelectric arms 12 '' attached to the motor body 16 '' by means of an elastic layer (not shown in the drawing) The motor 10 '' generates an output force through the frictional contact of the motor 10 '' with a axis 18 '' The motor body 16 '' can be moved linearly (in the direction A) or rotatably (in the direction B), or both, relative to the axis 18 ''.

The elastic layer ensures that the pins are always in contact with the substrate. It also stores deformation energy to allow the pins to move without complex synchronization. The elastic material must be rigid enough to hold the pins in communication with the substrate; but it must also be resilient enough to store the energy imparted by the deformation release on the pins and not to unduly interfere with the performance of the pins. Any material having a wide range of properties may be suitable for one or more applications of the present invention; This will depend, among other things, on the environment in which the motor will be used and the forces expected to act on the elastic layer during the use or transport of the motor. Examples of materials that may be useful for forming the elastic layer include moderately rigid elastomeric materials, plastics and polyurethanes. The elastic layer can be formed independently of the motor body and subsequently adhered to it. Depending on the material chosen for the elastic layer, it could also be possible to shape the elastic layer by coating the motor body with it or by applying it in some other way.

The temples can be attached to the elastic layer with any method that holds them and puts them in contact with the elastic layer and allows them to impart deformation energy to the elastic layer. For example, the lugs can be attached to the elastic layer with an adhesive material. Other methods may also be used to attach the lugs to the elastic layer, such as for example inserting them directly into an elastic layer without solidifying or partially solidifying. A contact surface can be interposed between the lower part of the piezoelectric semiconductor plate of a pin and the substrate. The contact surface can be formed with any suitable material having suitable wear and friction properties (high static friction and low kinetic friction to assist the movement of the pin relative to the substrate).

Each active pin includes at least one piezoelectric semiconductor plate, although additional semiconductor plates can be stacked together on a single pin to increase force or displacement. Generally piezoelectric materials have a low tensile strength, so the semiconductor plate or plates must be held within the pins in a manner that reduces the possibility of a traction fault in piezoelectric semiconductor plates.

Preferably, the semiconductor plates are operated in the shear mode, in order to maximize the displacement output by voltage input. Figure 5 illustrates the operation of a piezoelectric semiconductor plate 30 in the shear mode. As explained above, a high piezoelectric constant corresponds to a large displacement output per voltage input. The highest piezoelectric constant d is di (di5> d33> d31), so that the performance of the piezoelectric material in the "15" direction, referred to as shear mode, will maximize the displacement output by voltage input . In the shear mode, the polarization direction P is perpendicular to the applied field E, which allows the piezoelectric semiconductor plate to operate at a high bipolar operating voltage (ie, the motor can be operated with positive and negative high acting voltages, without risk of depolarization). The maximum field is limited only by the dielectric breakdown voltage. (In "3x" applications, the negative field is limited in the negative direction by depolarization, and in the positive direction by the dielectric break). In addition, the operation of the piezoelectric material in the shear mode allows the pins to be preloaded on the shaft when they can still be deformed, and reduces non-linearity, fatigue alteration and aging.

Both the efficiency of the energy conversion in the motor of the present invention and the response time depend on the properties of the active material that is selected. Suitable piezoelectric materials may include lead zirconium titanate (PZT), magnetorestrictive materials (eg, Terfinol-D), and electrorestrictive materials (eg, magnesium lead niobate (PMN)) that have a factor of loss-response time adequate. Generally piezoelectric materials are characterized by having a fast response time, so that the response time of the motor of the present invention can be less than one-second.

The motor of the present invention has advantages over conventional electromagnetic motors and over other piezoelectric motors. It provides a large force and speed output in a single reliable package.

Although a specific embodiment of the invention has been described in detail in this specification, it should be understood that those who have knowledge of the subject will be able to make variations thereof without departing from the spirit of the invention or from the scope of the claims set forth below. k -k k k -k k

Claims (20)

We claim:

1. A piezoelectric motor consisting of: the body of the engine; an elastic layer communicated with the motor body; Y a predetermined number of pins communicating with the elastic layer, each of the pins having a piezoelectric semiconductor plate.

2. The piezoelectric motor according to Claim 1, wherein the pins are capable of moving independently of one another.

3. The piezoelectric motor according to Claim 2, wherein the pins are capable of moving sequentially.

4. The piezoelectric motor according to Claim 1, wherein the actuation of a piezoelectric semiconductor plate causes displacement of the corresponding pin.

5. The piezoelectric motor according to Claim 4, wherein the displacement of the pin causes energy to be stored within the elastic layer.

6. The piezoelectric motor according to claim 4, wherein the release of energy stored within the elastic layer causes the motor to travel along a substrate.

7. The piezoelectric motor according to Claim 1, wherein the elastic layer urges the pins to contact a substrate.

8. The piezoelectric motor according to Claim 1, wherein a piezoelectric semiconductor plate is operated in the shear mode.

9. The piezoelectric motor according to Claim 1, wherein the pins are arranged in pairs, and the pins in pairs are capable of acting simultaneously.

10. The piezoelectric motor according to claim 9, which further includes: an analog voltage source arranged in parallel with the pairs of pins, said voltage source being capable of driving the piezoelectric semiconductor plates of the pins.

11. A piezoelectric motor, which includes the following: the body of the engine; Y a predetermined number of pins connected to the motor body by means of an elastic contact surface;

12. The piezoelectric motor according to the Claim 11, wherein the elastic contact surface urges the pins to contact a substrate.

13. The piezoelectric motor according to the Claim 11, wherein each of the pins includes at least one electroactive element.

14. The piezoelectric motor according to Claim 13, wherein the electroactive element is a piezoelectric semiconductor plate.

15. The piezoelectric motor according to Claim 14, wherein the piezoelectric semiconductor plate is operated in the shear mode.

16. A piezoelectric motor that includes the following: the body of the engine; an elastic layer capable of storing energy of deformation, which communicates with the motor body; Y a predetermined number of lugs communicating with the elastic layer, each of the lugs having a piezoelectric element, and the elastic layer keeping the lugs in contact with a substrate.

17. The piezoelectric motor according to Claim 16, wherein the actuation of a piezoelectric element causes displacement of the corresponding pin.

18. The piezoelectric motor according to Claim 16, wherein the discharge of the piezoelectric element transfers deformation energy to the elastic layer.

19. The piezoelectric motor according to Claim 16, wherein the release of energy stored within the elastic layer causes the motor to travel along a substrate.

20. The piezoelectric motor according to Claim 16, wherein the motor is capable of maintaining a high holding force in the absence of an input power. k k k -k