The present invention relates to a particular configuration of a piezoelectric rotary motor of inertial type or "stick & slip" type which, operated with a particular command law, allows the increase of the transmitted torque, of the specified type in the preamble of the first claim.

The type of piezoelectric motors of the inertial type or "inertia Drive" is currently known, also known properly or in many cases improperly as "stick & slip" and is known in: patent literature, scientific literature and industrial literature, and it is the piezoelectric motor which has had the greatest success on the market thanks to its construction and control simplicity.

Ultrasonic piezoelectric motors are also known, for example described in US patent applications US 2013/307376 A1 , KR 2009 0011504 A, WO 92/10874 A1 US

2009/278421 A1. However, such motors are complex and expensive. For understanding the document, the operating principle underlying this type of motors is described.

With reference to Fig. 1a, the following basic components are identified: a piezoelectric type actuator (201), an element that moves in the "X" direction, called a cursor (204), as per the reference system (210), a spring (205), constraint means with respect to a fixed or ground-based framework (203, 202), a mobile slide equipped with a certain mass (206), rollers that allow the mobile slide to translate freely in the "X" direction (208 and others), an element called pin which is rigidly constrained to the cursor (204) but which rests, pushed by a fundamental preloading force (209), on the slide (206).

It is emphasized that while the slide (206) is capable of infinite rectilinear movements, the cursor moves exactly like the piezoelectric (201) as it is pushed on one side by said piezoelectric and on the other by the spring (205), said cursor (204) is to be considered integral with the piezoelectric actuator (201).

The piezoelectric actuator (201) is an element which, if powered with a voltage difference expressed in voltage, generally positive, deforms, usually exhibiting large forces and small displacements, it is a maximum of a few tenths of a millimeter.

In this document, piezoelectric actuators that deform are mainly considered, preferably by elongating, in one direction. The other directions are of minor interest.

The piezoelectric actuator (201) is powered, in the example, with a voltage ramp as shown in Fig. 1b between 0 and a maximum value called "V1" over time "TS", said actuator consequently extends by an amount called “α” by moving the cursor (204) in the same direction and compressing the spring (205).

Following the movement "α" the pin (207) which is integral with the slider (204) interacts with the slide by means of a frictional force which, in accordance with the simple Coulomb model, is proportional to the preload force through the relationship:

F _attr = μPrec (eq 1)

Where:

Fattr: friction force; μ: coefficient of friction;

Prec: preload force.

The friction force "Fattr" described by (eq 1) is the maximum force that the pin and the slide can exchange in the direction of motion "X".

If the pin (7) moves very slowly, the friction force is sufficient to accelerate the slide which will move integrally with the pin. If the pin moves rapidly such that: End> Fattr (eq 2)

Where:

End: is the inertia force of the slide (6);

Fattr: is the friction force as in (eq 1). So the slide (206) will tend to remain stationary while the pin (207) will slide on it.

We consider “TS” a short time such that the piezoelectric actuator (201) performs a rapid movement which causes the pin (207) to crawl on the slide.

In summary, if the piezoelectric actuator (201) is controlled with a linear voltage law between 0 and "V1" for a time "TS" called rising time, the slide remains stationary because its inertia force is greater than the maximum force of friction that develops between the pin (207) and the slide (206).

At this point the piezoelectric actuator (201) is controlled, again with linear law, from the voltage value “V1” to the value 0 for a time “TD” called descent time, as indicated in Fig. 1b. The piezoelectric actuator (201) contracts up to the resting dimension, that is the one corresponding to voltage 0.

During the contraction the piezoelectric actuator is followed by the cursor (204) because it is the spring (205) that pushes it and keeps it adherent to said piezoelectric actuator (201), therefore both the cursor (204) and the pin (207) will move in the "X" direction but in the opposite direction with respect to what was previously described.

The time 'TD" will be long enough that:

End < Fattr (eq 3)

The "End" inertia force of the slide (206) will be smaller than the maximum frictional force that pin (207) and slide (206) can exchange , therefore the slide (206) will be dragged by the pin (207) and will move as indicated in Figure 1 C in the “X +” direction.

By repeating cyclically what described regarding the control of the piezoelectric actuator (201), or by controlling it with a command law called sawtooth as shown in the graph of Figures 1 C, the slide (206) will move in the "X" direction.

Even if the displacement of the piezoelectric actuator (201) is very small, the resulting movement of the slide (206) will be the sum of said displacements and its motion will appear as a rather fluid and continuous motion.

By inverting the times "TS" and "TD" or, by giving the time "TS" the value of the time "TD" and vice versa, the slide (206) will proceed in the opposite direction.

In this second case the spring (205) must be sufficiently rigid and such as to always keep the cursor (204) adhering to the piezoelectric actuator (201) so that if said piezoelectric actuator (201) retracts over time "TS" also the cursor (204) must follow it at the same time, otherwise the motor is not able to reverse the direction of travel. The known technique described includes some important drawbacks.

In particular, the force transmitted in the case of a linear motor and the torque transmitted in the case of a rotary motor is rather limited.

This drawback affects many applications to said type of engine.

Furthermore, stick slip motors generally have disturbances caused by orthogonal movements to the “X” movement direction which degrade the precision of the mechanism. This drawback limits the positioning accuracy of said motors, a quality which is important for this type of motors.

In this situation, the technical task underlying the present invention is to devise a piezoelectric rotary motor and a rotary movement method capable of substantially obviating at least part of the aforementioned drawbacks. Within the scope of said technical task, an important object of the invention is to obtain a piezoelectric rotary motor and a rotary motion method which allow to give a high torque.

Another important object of the invention is to provide a piezoelectric rotary motor and a rotary movement method which allow to obtain high precision.

The technical task and the specified aims are achieved by a piezoelectric rotary motor and a rotary motion method as claimed in the annexed independent claims.

Preferred technical solutions are highlighted in the dependent claims.

The characteristics and advantages of the invention are clarified below by the detailed description of preferred embodiments of the invention, with reference to the accompanying figures, wherein:

Fig. 1a shows a first example of prior art relating to the present invention;

Fig. 1b shows a first example of prior art relating to the present invention;

Fig. 1c shows a first example of prior art relating to the present invention;

Fig. 2 illustrates a section of the engine according to the invention;

Fig. 3 is an exploded view of the motor according to the invention;

Fig. 4a shows a diagram of the motor according to the invention;

Fig. 4b shows a portion of the engine according to the invention in axonometric view;

Fig. 4c shows a portion of the engine according to the invention in front view;

Fig. 5a shows a first operating diagram of the method according to the invention in a first configuration;

Fig. 5b shows a second method of operation diagram according to the invention in a first configuration;

Fig. 5c shows a third method of operation diagram according to the invention in a first configuration;

Fig. 6a shows a first operating diagram of the method according to the invention in a second configuration;

Fig. 6b shows a second method of operation diagram according to the invention in a second configuration;

Fig. 6c shows a third method of operation diagram according to the invention in a second configuration;

Fig. 7a shows a first operating diagram of the method according to the invention in a third configuration;

Fig. 7b shows a second method of operation diagram according to the invention in a third configuration;

Fig. 7c shows a third method of operation diagram according to the invention in a third configuration;

Fig. 8a shows an operating diagram of the method according to the invention in a third configuration; and

Fig. 8b shows an operation diagram of the method according to the invention in a third configuration.

In the present document, the measurements, values, shapes and geometric references (such as perpendicularity and parallelism), when associated with words like “about” or other similar terms such as “approximately” or “substantially”, are to be considered as except for measurement errors or inaccuracies due to production and/or manufacturing errors, and, above all, except for a slight divergence from the value, measurements, shape, or geometric reference with which it is associated. For instance, these terms, if associated with a value, preferably indicate a divergence of not more than 10% of the value. Moreover, when used, terms such as “first”, “second”, “higher”, “lower”, “main” and

“secondary" do not necessarily identify an order, a priority of relationship or a relative position, but can simply be used to clearly distinguish between their different components. Unless otherwise specified, as results in the following discussions, terms such as

“treatment”, “computing”, “determination", “calculation”, or similar, refer to the action and/or processes of a computer or similar electronic calculation device that manipulates and/or transforms data represented as physical, such as electronic quantities of registers of a computer system and/or memories in, other data similarly represented as physical quantities within computer systems, registers or other storage, transmission or information displaying devices.

The measurements and data reported in this text are to be considered, unless otherwise indicated, as performed in the International Standard Atmosphere ICAO

(ISO 2533:1975). With reference to the figures, the piezoelectric rotary motor 1 according to the invention is globally indicated with the number 1.

It comprises, briefly, a rotor 2 that can be rotated around an axis of rotation 1a, and comprises an abutment surface 2a basically, preferably substantially lying on a plane perpendicular to the axis of rotation 1a and preferably substantially annular.

The piezoelectric rotary motor 1 further comprises a stator 3, and at least one movable element 4, preferably at least three movable elements 4, constrained in a complaint way to the stator 3.

Each movable element 4 is preferably movable at least partially in the circumferential direction with respect to the rotation axis 1a, and comprises at least one, and preferably only one for each movable element 4, contact element 40 protruding in the direction of the rotation axis 1a.

The piezoelectric rotary motor 1 also preferably comprises thrust means 5 capable of pressing the contact elements 40 against the abutment surface 2a. The thrust means 2 preferably comprise an elastic element. The thrust means 5, and the structure of the motor 1 preferably have all the contact elements 40 simultaneously in contact with the abutment surface 2a.

Furthermore, preferably, the motor means 6 comprise at least one piezoelectric actuator 60, capable of moving, preferably selectively, the movable elements 4 so that the relative contact elements 40 are movable, preferably selectively, at least partially in the circumferential direction with respect to the axis of rotation 1 a.

The motor means 6 are also, preferably, capable of moving said movable element

4 rapidly, so as to cause the sliding of said contact element 40 against said abutment surface 2a, and also slowly, so as to cause the dragging of said surface abutment

2a by said contact element 40, as further specified below. Furthermore, the motor means 6 preferably comprise at least one return element 61 of the movable element 4, preferably an elastic return element, more preferably a leaf spring. This elastic element conveniently connects each movable element 4 to the stator 3.

The invention further defines a method of rotary movement which takes place preferably by means of a piezoelectric rotary motor 1 of the type described above.

In this method, the motor means 6 move the mobile element 4 quickly, so as to cause the sliding of said contact element 40 against said abutment surface 2a, or, alternatively, slowly, so as to drag said abutment surface 2a from part of said contact element 40. In this way they can realize a stick-slip type motor. Furthermore, the motor means 6 preferably quickly move the movable elements 4 not simultaneously, and preferably in rapid succession. Preferably, the fast movement of a subsequent mobile element 4 takes place after the previous mobile element 4 has finished its fast movement.

Furthermore, preferably, the movable elements 4, when moved slowly, are moved simultaneously.

More in detail, the motor means 6 are arranged in correspondence with a motor element 24, preferably mainly arranged on a plane perpendicular to the axis 1 a, which comprises the motor means 6 and preferably a plurality of contact element 40.

Preferably, the abutment surface 2a consists of a slewing ring 21 or a ring preferably made of hard metal, tungsten carbide or ceramic or similar, said slewing ring or ring rests on said contact element 40.

The motor element 30 in turn is constrained to the stator 3 which constitutes the fixed part of the motor as opposed to the moving part.

The "Prec" preload force which pushes the slewing ring 21 against the multiplicity of contact element 40 is preferably achieved by means of thrust means 5 consisting of a spring 25 which, in turn, is preferably compressed between a nut 26 with washer

29 and a bearing 23 or a generic rolling body.

Said nut 26 is preferably integral with the rotor 2, it is screwed onto it, therefore the spring 25 pushes the rotor against the bearing 23. Preferably, the bearing 23 rests in turn on the stator 3 to which the motor element

24 is integral, said bearing allows rotor 2 to rotate around its own axis 1 a while stator

3 remains stationary and said stator exchanges the preload force with rotor 2.

Preferably, the motor element 24 is composed of a stator part 24a of a plurality of movable elements 4, said movable elements can be greater than or equal to three, by the piezoelectric actuators 60 interposed between the stator part and the movable elements.

Preferably, said piezoelectric actuators 60 push the movable elements 4, said movable elements are the equivalent of the cursor 204 seen above, they can move by the same amount as the piezoelectric actuator or more or less depending on whether there is a further lever mechanism between piezoelectric actuators and moving elements or the moving element itself is a lever.

Preferably, the multiplicity of mobile elements 4 is arranged radially, they are constrained by means of hinges 33, preferably coinciding with said return elements

61 , to the stator part 24a, the movement of said mobile elements takes place around said hinges.

Preferably, the contact elements 40 or pins are constrained to the movable elements. Preferably, said contact elements 40 are positioned along the radial axis that passes through the hinges 33 in such a way that a small rotation of said movable elements 4 around said hinges 33 produces a repositioning 35 which, in approximation of the small repositioning, can be considered tangential to the ideal circumference 101 which passes through all the contact elements 40. In fact, preferably, the contact elements 40 all recline on the same perpendicular circumference and with a center along the axis 1a.

Preferably, said small tangential repositioning 35 of the contact elements 40 rotate the rotor 2 by exploiting the "stick & slip" principle described above.

The Fig. 4d represents a preferred diagram of how the architecture of the mobile element 4 can be understood, the piezoelectric actuator pushes on it at a distance

"W" with respect to the hinge 33 while the contact element 40 is placed at the distance "J + W" with respect to the hinge 33. The described piezoelectric rotary motor configuration considerably limits the disturbance caused by movements perpendicular to the direction of movement, since the rotor 2, preferably, always remains in contact only with the contact elements 40 and said contact elements 40 are constrained to the ground by means of the stator part 24a which fixes the rolling element or bearing and does not act directly on the rotor 2 but acts on the spring 25, said rolling element acts between the spring 25 and the stator 3, Its possible "run out" is therefore eliminated because it is compensated by the spring 25.

Preferably, the use of the slewing ring or ring 21 which rests on the contact elements

40 allows to choose hard materials such as tungsten carbide, other carbides or ceramics in order to increase the “Prec" preload force, therefore the friction force, and therefore the transmitted torque.

The Fig. 5b is a preferred operating diagram of the piezoelectric motor in the rotary configuration, in the classical operating mode and in the "slip" phase or rather sliding.

The Fig. 5a is the preferred command as seen previously, the piezoelectric actuators 60 are powered in voltage or other way so that they lengthen over time

"TS", called rising time, said actuators move the movable elements 4 in Fig. 5b, which consequently they move the contact elements 40 which interact with the fifth slewing ring 21 by means of the friction forces "Fatt1 , Fatt2, Fatt3" in the direction tangent to the ideal circumference 101.

The balance of the torques are in Fig. 5c, the external torque "Cext " is added to the friction torques (Fattr1 , Fattr2, Fattr3), said addition must be equal to the inertia torque of the rotating parts of the motor according to the formula:

Cine = Cext + (Fattr1 + Fattr2 + Fattr3), (eq4) The motor functions and transmits more torque in the "slip" or sliding phase only if the mass of the rotating parts of the motor is increased, substantially of the rotor 2 and of the slewing ring 21.

Assuming that the rising time "TS" is a tenth of the descent time "TD", the motor operates in the "slip" phase if the rotating inertia is: lne≥ ((Fattr1 + Fattr2 + Fattr3 + Cext) [TS] ^Λ 2) /0.2SC (eq5)

Where:

TS: is the rising time;

SC: is the tangential displacement of the contact elements 40.

Figure 6 schematically represents the "stick" or adhesion phase, the piezoelectric actuators 60 retract because they are commanded with a decreasing voltage from the value "V1" to "0" in the 'TD" descent time, the movable elements 4 move following the piezoelectric actuators and consequently moving the contact elements

40 so as to exert friction forces on the fifth wheel 21 (Fattr1 , Fattr2, Fattr3) tangent to the ideal circumference 101 contained in the fifth wheel 21 and concentric to it. The frictional forces work against the inertia torque "Cine" and the external torque

(Cext) as shown in Figure 6 C1 , and in accordance with the equation:

Cext + Cine = R (Fattr1 + Fattr2 + Fattr3), (eq6)

These frictional forces accelerate the rotating parts of the motor up to a constant angular speed, at this point the maximum torque that can be transmitted by the motor can be defined as:

Cext <= R (Fattr1 + Fattr2 + Fattr3), (eq7)

The equation (eq7) is schematized in Fig. 6c and based on this equation the motor improves the transmissible torque if the inertia of the rotating parts or the "Cine" component is reduced but this is contrary to what is stated for improve the transmissible torque in the "slip" phase. A new control mode is described for the piezoelectric motor configuration described in this document as schematized in Figs. 7a-7c.

With regard to said Figs. 7a-7c describes a "slip" phase, that is, only a piezoelectric actuator is activated, it could be any one but in Fig. 7b for simplicity the piezoelectric actuator 60 is activated with a voltage command as indicated by the graph of Fig.

7a, while the other actuators 60 and others not shown remain stationary.

The balance of the torques is described by the equation:

Cine = Cext + Fattr1-Fattr3-Fattr2, (eq8)

From (eq8) it can be clearly deduced that the inertia torque, in order for the "slip" to occur, is less than that described by (eq4).

It is necessary to repeat the actuation phase illustrated in Figure 7 C as many times as there are contact elements 40 so that said "slip" phase can be considered completed and it is possible to move on to the next "stick" phase, i.e. dragging the rotating part of the motor. As shown by the graph in Fig. 7c, the external torque "Cext" in this case is balanced by the inertia torque "Cine" and by a multiplicity of friction couples exerted by the contact elements 40 which are not activated.

The necessary inertia referred to the "slip" phase in Figure 7 is governed by the equation: lne _n ≥ ((Cext- (R (Fattr1 + Fattr2 + Fattr3)) / 3) TS ^Λ 2) /0.2SC, (eq9)

It can be unequivocally asserted that the inertia necessary for the slip phase to work is less than that necessary if the command law is like the one in Fig. 5.

As regards the "stick" phase or grip, there are no differences except when there is a type of motor with a multiplicity of pins (22) greater than three. With reference to Figs. 8a-8b, we call the command law D1 the one in Fig. 8a which is the classic one, which refers to an inertia of the rotating part necessary for correct operation which we call "Ine" while we call D2 the new command law in Fig. 8b, which refers to an inertia of the rotating part that we call “Inen” as indicated in (eq9).

In the simplified hypothesis that:

Fattr1 = Fattr2 = Fattr3 = Fattr, (eq10)

The relationship between "Inen" and "Ine" becomes:

Ine _n / Ine = (Cext-R (Fattr)) / (Cext + 3R (Fattr)), (eq11)

It is clear that by controlling the motor with the command law D2 the inertia necessary to make the motor work is lower than in case it feeds on the D1 law. For simplicity we note that if the external couple were zero then the inertia "Inen" would be one third of "Ine".

It is further stated that the new control law called D2 allows to improve the performance of the motor in terms of torque transmitted if the multiplicity of contact elements 40 are increased beyond the number of three. In Fig. 9 there is a comparison between the balances of the pairs in play relative to the two command laws "D1" and "D2" as the number of contact elements 40 increases, if said pins increase, in the case of power supply with the D1 command, more and more inertia is required, for example an ever-shorter rise time called "TS", on the contrary, using a command law of the "D2" type, as the number of pins increases less and less inertia is required and this can increase the transmissible torque.

The invention is susceptible of variants falling within the scope of the inventive concept defined by the claims.

In this context, all the details can be replaced by equivalent elements and the materials, shapes and dimensions can be any.