Patent Description:
Various types of balancing devices for rotating parts are currently known.

In particular, onboard of rotating devices, such as machine tools or other machinery, there are balancing devices capable of constantly maintaining the center of mass of the rotating portion in the selected position. Generally, the said center of mass of the rotating portion is kept in correspondence with the rotation axis, so that unwanted centrifugal forces are not created.

Said balancing devices are generally inserted in balancing apparatuses which also comprise imbalance measuring means, suitable for verifying and measuring the presence of an imbalance.

The imbalance is consequently regulated and canceled, or reduced to the maximum, by the said balancing device, constrained to the rotating portion.

The latter comprises two non-balanced masses, with respect to the rotation axis of the rotating piece, and therefore each comprising an appropriately identical imbalance, or rather of the same mass. The balancing device also comprises two motors, one for each mass, adapted to rotate said masses around the rotation axis itself.

The position of the non-balanced masses affects the center of mass of the rotating portion.

In fact, if the same masses are opposite, offset at <NUM> ° with respect to the rotation axis, their imbalances cancel each other out and the balancing device does not change the position of the center of mass of the assembly consisting of the rotating portion and the balancing device.

On the contrary, if the masses are not opposite, their imbalances do not cancel each other out and the balancing device generates an imbalance. Said imbalance at the same time is suitably made equal to and opposite to the unbalance of the rotating portion, so that the position of the center of mass of the assembly consisting of the rotating portion and the balancing device is modified and is positioned along the rotation axis or as close to it as possible.

The said masses are generally moved, with respect to the rotating piece and to modify the portion of the center of mass, by means of electric motors and mechanical connections. As described for example in patent application <CIT> by the same applicant or in patent <CIT>.

Patent application <CIT>, on the other hand, shows masses moved directly from the fixed portion.

Patent application <CIT>, by the same applicant, shows balancing masses moved by motors inside the masses themselves.

Patent application <CIT>, by the same applicant, shows moving balancing masses consisting of wires or tapes that can be wound around bobbins placed in eccentric positions with respect to the rotation axis, so that the winding and unwinding around a different bobbins result in a transfer of mass and a change in the center of mass of the balancing device.

The known technique described includes some drawbacks.

In particular, said devices are very complex and therefore could be subject to problems if not constantly revised.

A further drawback is that it is not possible to miniaturize very complex systems. The complexity and the problems are further accentuated by the considerable forces at play. In fact, said rotating pieces can reach speeds of the order of magnitude of tens of thousands of revolutions per minute.

In this situation, the technical task underlying the present invention is to devise a balancing device capable of substantially obviating at least part of the aforementioned drawbacks.

Within the scope of said technical task, it is an important object of the invention to obtain a balancing device which is simple and robust.

Another important object of the invention is to provide a balancing device which is precise.

Not least object of the invention is to provide an inexpensive balancing device. The technical task and the specified aims are achieved by a balancing device as claimed in the annexed claim <NUM>.

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 drawings, in which:.

With reference to the Figures, the balancing device according to the invention is globally indicated with the number <NUM>.

It is conveniently part of a balancing apparatus <NUM>, described below.

The balancing device <NUM> defines a central axis 1a and, in use, is connected to a rotating piece <NUM>.

Said rotating piece <NUM> is preferably constituted by the rotor of a machine tool or by other devices and defines a rotation axis 100a.

The balancing device <NUM> is preferably connectable to the rotating piece <NUM>, so that the central axis 1a substantially coincides with the rotation axis 100a. It has the purpose of eliminating the imbalances of the system comprising the balancing device <NUM> itself and the rotating piece <NUM>. These imbalances are eliminated when the center of mass of the balancing device <NUM> system and the rotating piece <NUM> lies along the rotation axis 100a.

The balancing device <NUM> preferably comprises at least one eccentric mass <NUM>, and more preferably two eccentric masses <NUM>, each independently rotatable about the central axis 1a and not balanced with respect to the same central axis 1a.

The eccentric masses <NUM> are for example constituted by two annular elements, with axis along the central axis 1a, having asymmetrically discharged portions 2a or similar.

The balancing device <NUM> preferably also comprises at least one balancing motor <NUM>, preferably one for each mass <NUM>, more preferably two motors <NUM>, each able to rotate an eccentric mass <NUM>, with respect to the rotating part <NUM> around the central axis 1a. The motor <NUM> is also capable of rotating the eccentric mass <NUM> with respect to the remaining part of the balancing device <NUM>.

Le eccentric masses <NUM> are preferably mutually opposed and/or mutually connected by second rotational bearings <NUM> around the central axis 1a, so that said masses <NUM> can rotate mutually freely and substantially without friction.

The motor <NUM> is preferably of the piezoelectric type, or, alternatively, of the "impact drive" type or a generic ultrasonic motor. The motor <NUM> is also, in addition or alternatively, preferably of the stick-slip type.

As known, a motor of the piezoelectric type uses motor means constituted by piezoelectric elements, such as crystals or ceramics known per se. Said piezoelectric elements are deformed, generally expanded or contracted, or elongated or restricted, following an electrical stimulus or an electrical voltage. The stick-slip motors, on the other hand, are motors that exploit the phenomenon called stick-slip for handling. The stick-slip is a known mechanical phenomenon that involves the friction between two mutually connected surfaces. In such motors, for example in a first direction, one surface is moved very quickly with respect to another, so that the inertia force exceeds that of friction and slippage is obtained. On the contrary, in the opposite direction, the same moving surface can move more slowly, with reduced accelerations, so as not to overcome the static friction between the two portions and drag the second surface in this second movement. To obtain the inversion of the motion it is sufficient to invert the law of command. That is, by first applying the slow movement which drags the rotating mass <NUM> and then the rapid movement where the return action of the spring, suitably sized, causes the slippage. The balancing device <NUM> preferably comprises a rotor portion 1b, in use integral with the rotating piece <NUM>, and not movable with respect to it. With respect to the fixed portion 1b, the eccentric masses <NUM> can be moved by the motors <NUM>. The balancing device <NUM> preferably comprises a stator portion 1c, preferably connected to the balancing apparatus <NUM> and integral with a support and preferably with the ground. The stator portion 1c preferably faces radially, or axially, to the rotor portion 1b.

Each eccentric mass <NUM> is therefore preferably constrained to the rotor portion 1b by means of first rotational bearings <NUM>, around the central axis 1a, so as to be able to rotate freely, and as commanded, with respect to the same central axis 1a.

According to the invention, each balancing motor <NUM> comprises at least one active portion <NUM>, movable with respect to the rotor portion 1b and connected to the fixed portion 1b by means of at least one piezoelectric thrust element.

The piezoelectric thrust element <NUM> is therefore able to move, by means of its own active deformation following electrical pulses, at least part of the active portion <NUM> in a circumferential direction with respect to the central axis 1a.

More in detail, the active portion <NUM> is connected to the fixed portion 1a by means of elastic return means <NUM>, capable of bringing, in the absence of other external stimuli, the active portion <NUM> to an initial position following movement by said thrust element <NUM>. The elastic return means are preferably leaf springs or the like or magnetic elements.

For example, as illustrated in the <FIG>, the active portion <NUM> can be arranged in a radial position close to the edge end of an eccentric mass <NUM> and comprise a piezoelectric thrust element <NUM> having a prevalent extension in the radial direction and extending, following an electrical stress, along the same radial direction. The piezoelectric thrust element <NUM> is, in this case, suitably connected to a portion at the circumferential end of the active portion <NUM>. Furthermore, in the illustrated example, there are two leaf springs which constitute the elastic return means <NUM> for each active portion <NUM>: a first leaf spring 32a preferably aligned on the joining radius of the center of the system 1a with the center of the support <NUM> described hereinafter. The elastic return means <NUM> also preferably comprise a second leaf spring 32b preferably arranged so that its axis passes through the center of rotation of the first leaf spring 32a and furthermore partly radially and partly circumferentially. Furthermore, a plurality of active portions <NUM> are preferably present, preferably three, arranged, preferably symmetrically, more preferably at <NUM>°, along a circumference perpendicular to the central axis 1a.

Structurally, preferably, the said active portions <NUM> are connected to a motor element <NUM>, integral with the fixed portion 1b and constituting part of the same. Preferably, the active portions <NUM> are constrained to the motor element <NUM>, preferably by means of the elastic return means <NUM> and the piezoelectric thrust element <NUM>, more preferably all the active portions <NUM> arranged along the same circumference and constituting a balancing motor <NUM> for an eccentric mass <NUM>.

Each motor element <NUM> is substantially, but not necessarily, structured as a ring and also preferably comprises an annular flange 30a. On the one hand, an eccentric mass <NUM> can be connected to said annular flange 35a, through said first rotational bearings <NUM>. It is also pointed out that the device would function correctly even if said eccentric mass <NUM> were connected through said first rotational bearings <NUM> to the stator portion 1c.

The device <NUM> further comprises electrical connection means <NUM>, between the piezoelectric thrust elements <NUM> and an electrical power supply. Said connection means <NUM> are electric cables, metal discs or similar.

Furthermore, each active portion <NUM> preferably comprises a support <NUM>, protruding in the direction of the central axis 1a and resting, in the direction of the central axis 1a, on an eccentric mass <NUM>. The support <NUM> is preferably constituted by a pin and/or a hemispherical portion, preferably of metal, more preferably of hard metal, such as tungsten carbide, or ceramic or similar. It is preferably placed in proximity to the portion of the active portion <NUM> with a greater radial distance from the central axis. Preferably, the support <NUM> is opposed to abutment ring 2t preferably thin and preferably made of hard metal, tungsten carbide, or ceramic, or similar, integral with the eccentric mass <NUM>. These elements have the advantage of reducing wear.

The balancing device <NUM> also comprises axial thrust means <NUM> capable of pressing the support <NUM> against the eccentric mass <NUM>. Preferably they consist of a spring, preferably spiral or circular, with a center along the central axis. Preferably there is a single element which constitutes the thrust means <NUM> and is able to push both motors <NUM> in the direction of their own eccentric masses <NUM>, locking them and allowing reciprocal rotation thanks to the second rotational bearings <NUM>. In particular, the axial thrust means <NUM> include an elastic joint <NUM>. Said element also contributes to the elimination of the backlash at the inversion of the motion of the pressed part, which would have been introduced by any other type of mechanical constraint (e.g. spines). Clearly, the elimination of backlash and inversion is also guaranteed by the configuration of the engine itself and by the absence of transmission systems between the engine and the rotating elements <NUM>.

Preferably, each engine element <NUM> is connected to an eccentric mass <NUM> exclusively by means of the supports <NUM> and the first rotational bearings <NUM>.

The balancing device <NUM>, as a whole, has preferably arranged in the direction of the central axis 1a, in the center the two eccentric masses <NUM>, mutually separated by the second rotational bearings <NUM>, at the sides of the two eccentric masses <NUM> the two balancing motors <NUM>, composed of the motor elements and the connected active elements <NUM> with their own electrical connections <NUM>, to the side of only one of the motors the element constituting the axial thrust means <NUM>. The device <NUM> is also preferably closed by a casing <NUM>, part of the rotor portion 1b and preferably including a tubular portion 8a on which all the items described. The casing <NUM> preferably has the task of making the rotor part 1b of the balancing device <NUM> watertight. The casing <NUM>, preferably, constitutes a watertight protective shell and also houses the electronic and electromagnetic circuitry for the transmission of power and data bi-directional with the control unit placed upstream and part of the balancing apparatus <NUM>. The apparatus <NUM> therefore comprises the said balancing device <NUM> and, preferably means for detecting the imbalance <NUM>, such as accelerometers known per se which can be inserted in the device <NUM> or not, electrical power supply means <NUM>, connected to said electrical connections <NUM> and to said piezoelectric thrust elements <NUM>, control means <NUM>, suitable for receiving information, transmitting it and controlling the piezoelectric elements <NUM> and other elements. The apparatus <NUM> may further comprise sensor means suitable for sensing the contact between the rotating piece <NUM> and the workpiece, in particular when the former consists of a grinding wheel or similar tool.

The operation of the balancing device <NUM>, and of the balancing apparatus <NUM>, previously described in structural terms, is as follows.

Within it, a new process is defined for moving an eccentric mass <NUM>, around a central axis 1a, to modify the center of mass of a rotating piece <NUM>. In this process, the eccentric mass <NUM> is preferably moved by a balancing motor <NUM> of the piezoelectric type, preferably of the type described above. Furthermore, in this process the eccentric mass <NUM> is preferably moved by a balancing motor <NUM> of the stick-slip type, preferably of the type described above.

The process takes place preferably through the balancing device <NUM> previously described and, preferably through the balancing apparatus <NUM> previously described.

In detail, the balancing device <NUM> is integrally constrained, in particular through the fixed portion 1b and more particularly through the casing <NUM>, to a shaft of the rotating piece <NUM>, so that the central axis 1a substantially coincides with the axis of rotation 100a.

Initially, if the rotating piece is balanced, the two eccentric masses <NUM> are offset by <NUM>°, so that the balancing device <NUM> is also balanced and also the whole of the two objects.

If an imbalance occurs in the rotating piece <NUM>, the imbalance detection means <NUM> perceives it, measures it and sends it to the control means <NUM>.

These control the electrical power supply means <NUM> and, through the electrical connections <NUM>, the balancing motors of one or two eccentric masses.

In particular, an electrical impulse is sent to the piezoelectric element <NUM> which deforms, in particular it expands or contracts according to the direction of rotation of the mass <NUM>, moving, according to the degree of freedom allowed by the elastic return means <NUM>, the active portion <NUM>.

In particular, (<FIG>) in a first case, all the piezoelectric elements <NUM>, part of the same balancing motor <NUM> and therefore preferably of the same motor element <NUM>, are activated simultaneously, hence the electrical pulse arrives simultaneously to all the piezoelectric elements <NUM> connected to the motor element <NUM>.

In a second case (<FIG>), on the other hand, the piezoelectric elements <NUM>, part of the same balancing motor <NUM> and therefore preferably of the same element motor <NUM>, are activated (<FIG>) or deactivated (<FIG>) in sequence, preferably one at a time. Therefore the electrical impulse, in the "slip" phase only, arrives in sequence and not simultaneously to all the piezoelectric elements <NUM> connected to the motor element <NUM>, while in the "stick" phase the impulse is simultaneous. This second solution has the advantage of increasing the torque transferred during the slip phase.

Conveniently, the electrical impulse is given in such a way, and the piezoelectric is chosen in such a way that the acceleration and speed imposed on the active portion <NUM> overcomes the static friction between the supports <NUM> and the connected eccentric mass <NUM>. In this phase, therefore, only the active portions <NUM> are moved, while the connected eccentric mass <NUM> and, obviously, the motor element <NUM>, remain stationary. There is therefore the phenomenon of "slip" of the stick-slip mechanism described above.

At the end of this movement, the electrical impulse decreases in voltage or intensity or power, more slowly, and the piezoelectric returns to its original position preferably also under the action of the elastic return means <NUM>.

The latter, thanks to the waveform of the power supply, is slower and the static friction between the supports <NUM> and the connected eccentric mass <NUM> is not exceeded. Consequently, there is the "stick" phase of the movement described and the active portions drag, in their return movement, the connected eccentric mass <NUM> making it rotate by a fraction of the circumference, for a linear even sub-micrometric movement, around the central axis 1a.

In detail, the piezoelectric material is preferably a piezoelectric ceramic, preferably of the "stack" type, fed with a suitable waveform (example <FIG>) characterized in voltage and frequency. In particular, for the "slip" to occur, the piezoelectric must be fed with sufficient speed (increase or decrease for the two directions of rotation).

Similarly, for the "stick" to occur, the piezoelectric must be fed with adequate slowness (increase or decrease for the two directions of rotation).

The eccentric masses <NUM> are then rotated until the unbalance of the balancing device <NUM> is equal and opposite to the imbalance of the piece <NUM>, in such a way as to balance it.

The balancing device <NUM> according to the invention achieves important advantages. In fact, the balancing device is simple and robust, not including complex rotational motors and the like. It can therefore also be placed on board rotating elements that exceed tens of thousands of revolutions per minute.

For the same reasons it is very economical.

The device <NUM> itself is also very precise, since it can move the masses of micrometric portions.

The eccentric mass <NUM> are also locked in the absence of activation of the motors <NUM>, without the need for braking devices.

A further advantage is given by the fact that the motor <NUM> is intrinsically resistant to the centrifugal force since it is designed with the following innovation. The lever 30t is such as to allow the insertion of the active element <NUM> (piezoelectric example) in the radial direction. Therefore, the centrifugal force is an axial stress for it and damages it. The center of gravity of the element 30t is opposite to the piezoelectric <NUM> with respect to the axis joining the center of the pin <NUM>, the center of rotation of the leaf spring 31b and the center of rotation 1a. This causes the centrifugal force to increase the preload on the piezoelectric <NUM>. Otherwise, the mechanism would not work, since under the effect of the centrifugal force it would tend to open.

Claim 1:
A balancing device (<NUM>) for a rotating part (<NUM>),
- said rotating part (<NUM>) defining a rotation axis (100a),
- said balancing device (<NUM>) defining a central axis (1a) and being able to be bound to said rotating part (<NUM>) so that said central axis (1a) basically coincides with said rotation axis (100a), and comprising:
- at least one eccentric mass (<NUM>) that can be rotated about said central axis (1a) and that is not balanced in relation to said central axis (1a),
- at least one balancing motor (<NUM>), designed to rotate said eccentric mass (<NUM>), in relation to said rotating part (<NUM>) around said central axis (1a),
- a fixed portion (1b), which is integral, in use, with said rotating part (<NUM>), and being characterised in that said balancing motor (<NUM>) comprises piezoelectric type motor means,
- said balancing motor (<NUM>) comprising at least one active portion (<NUM>), which is movable in relation to said fixed portion (1b) and connected to said fixed portion (1b) by at least one piezoelectric element (<NUM>), said piezoelectric element (<NUM>) being designed to move, by its active deformation following electrical impulses, at least part of said active portion (<NUM>) in the circumferential direction in relation to said central axis (1a),
- wherein said active portion (<NUM>) comprising a support (<NUM>), protruding in the direction of said central axis (1a), and said support (<NUM>) resting, in the direction of said central axis (1a), on said eccentric mass (<NUM>),
- and said balancing device (<NUM>) comprises axial thrust means (<NUM>) designed to press said support (<NUM>) against said eccentric mass (<NUM>).