Patent Description:
Various types of balancing devices of workpieces are currently known.

In particular, on board 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, 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 include imbalance measuring means, capable of 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 a conveniently identical imbalance, or rather of the same mass. The balancing device also comprises two motors, one for each mass, suitable for rotating the said masses around the rotation axis itself.

The portion 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 and opposite to the imbalance 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 application <CIT>.

Patent applications <CIT> and <CIT> instead show 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 handled balancing masses consisting of wires or tapes that can be rolled-up around coils placed in eccentric positions with respect to the rotation axis, so that the winding and unwinding around a different coils result in mass transfer 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.

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.

Furthermore, in the patent application <CIT> the motors which move the eccentric masses are always active, even when the masses must not be moved, with respect to the rotating piece. Consequently, the device can entail considerable problems, in particular if the rotation speeds of the rotating piece are high.

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 precise balancing device.

The technical task and the specified aims are achieved by a balancing procedure as claimed in the annexed claim <NUM>.

The features and advantages of the invention are clarified below by the detailed description of preferred embodiments of the invention, with reference to the accompanying figures, in which:
<FIG> shows a section of the device on which the procedure according to the invention is carried out.

With reference to the Figures, the balancing device 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 at least partially constrained to a rotating part <NUM>.

Said rotating part <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 part <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 part <NUM>. Such imbalances are eliminated when the center of mass of the balancing device <NUM> system and the rotating part <NUM> lies along the axis of rotation 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 or weighted portions or the like.

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 capable of rotating 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>.

The balancing motor <NUM> is preferably an electric motor, more preferably three-phase, with permanent magnets, also called a brushless motor and per se known to the person skilled in the art. It is a direct current electric motor (BLDCM, Brushless Direct Current Motor) having a permanent magnet rotor.

Each balancing motor <NUM> preferably comprising a stator <NUM> and a rotor <NUM>, and, preferably, the rotor <NUM> is integral with an eccentric mass <NUM>.

More in detail, the rotor <NUM> comprises permanent magnets, preferably present in a number of pairs of magnets with different poles preferably greater than <NUM>.

Said magnets are preferably arranged in the outer portion of the rotor <NUM>.

The stator <NUM> preferably comprises electromagnetic windings, such as coils and the like, distributed or concentrated, known per se. It is preferably external to the rotor <NUM>. The number of electromagnetic windings is suitably defined on the basis of the pairs of permanent magnets present on the rotor.

Preferably, the stator <NUM> is fixed and does not rotate with said rotating part <NUM>. For example, it is fixed to the ground or to other supports and does not rotate during the rotation of the part <NUM>.

In a different example, however, the stator <NUM> is integral with the rotating part <NUM>. The rotor <NUM>, on the other hand, is always integral with the rotating part <NUM> except for the moments in which the position of the eccentric masses <NUM> must vary in order to balance the rotating part <NUM>.

The stator <NUM> also comprises electrical connections <NUM> between the electromagnetic windings 30a (for example in distributed or concentrated configuration) and a source of electrical energy, preferably alternating, more preferably three-phase.

The balancing device <NUM> also comprises first detection means <NUM> of the angular position of the overall rotor and preferably also second detection means <NUM> for each rotating mass <NUM>, preferably with respect to the stator <NUM>. They are known per se and consist for example of Hall effect sensors or by an encoder per se known to the person skilled in the art or similar. For example, if Hall effect sensors are used: a first and a second Hall sensor are positioned respectively in correspondence with each stator <NUM> and each are capable of detecting a corresponding magnet or other suitable reference placed on the rotor <NUM> or on the masses <NUM>. A third Hall sensor, always integral with the stator body (or suitably available on the stator of the whole system including the host machinery) is capable of detecting a corresponding magnet or other appropriate reference that rotates integral with the axis 1a or <NUM>. They also include suitable electrical connections <NUM>.

The balancing device <NUM> also preferably comprises rotational bearings <NUM>, around the central axis 1a, capable of connecting the eccentric mass <NUM>, each with an independent bearing <NUM>, with the rotating part <NUM> or with portions integral with it. The balancing device <NUM> therefore defines a stator portion 1b. Said stator portion 1b preferably comprises the stator <NUM>, the electric connections <NUM>, part of the fixed detection means <NUM>, <NUM>, relative connections <NUM> and a first casing <NUM>, suitable for enclosing the elements forming the stator portion 1b. The first casing <NUM> is preferably provided with a central seat 6a, hollow and preferably cylindrical or cylindrical sector. The balancing device <NUM> also defines a rotor portion 1c. It preferably comprises the rotor <NUM>, the eccentric masses <NUM>, the rotational bearings <NUM>, part of the movable detection means <NUM>, <NUM>, and relative connections and a second casing <NUM>, capable of containing the said elements. The second casing <NUM> is preferably inserted, in use, inside the central seat 6a, which is hollow and preferably cylindrical or cylindrical sector.

The casing <NUM> preferably has the task of making the entire rotor assembly airtight and protected.

Preferably there is no direct contact between the portions <NUM> and <NUM> but an air cushion, preferably a few tenths of a millimeter. It can also comprise a second seat 7a for a portion of the rotating part <NUM>.

The balancing device <NUM> also preferably comprises locking means <NUM>, capable of locking, preferably by friction, the two eccentric masses <NUM> when not stressed by the motors <NUM>. Preferably they act in the axial direction 1a. They can be constituted by one or more thrust elements acting in an axial direction or similar, or made with magnetic elements.

The balancing device <NUM> also preferably comprises detection means of the imbalance <NUM>, preferably consisting of piezoelectric elements known per se. They are preferably placed inside the device <NUM> and can be integral with the casing <NUM>.

The balancing device <NUM> also preferably comprises a contact sensor <NUM> of the rotating part <NUM> with a part being processed, especially if the part in rotation is a tool such as a grinding wheel or similar.

The balancing device <NUM> also preferably comprises a sensor <NUM> for detecting the position or proximity sensor between the rotor and the stator.

The balancing apparatus <NUM> therefore comprises said balancing device <NUM> and, preferably, electrical power supply means <NUM>, connected to said electric connections <NUM> and <NUM> and data connection means of the wired or wireless type. It also preferably comprises control means <NUM>, capable of receiving information, transmitting it and controlling the motors <NUM>.

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

In detail, the rotor portion 1c, in particular by means of the second casing <NUM>, is rigidly constrained to a shaft of the rotating part <NUM>, so that the central axis 1a substantially coincides with the rotation axis 100a.

The rotor portion 1c is also inserted in the central seat 6a of the first casing <NUM>, and therefore in functional connection with the stator portion 1b and the proximity sensor system perceives the correct positioning of the elements.

When the rotating part <NUM> is initiated, the locking means <NUM> keep the eccentric masses <NUM> fixed with respect to the rotor <NUM> and the rotating part <NUM>. The masses <NUM> and the rotor <NUM> are therefore dragged by the rotating psrt <NUM> and therefore have the same rotation speed as the latter.

Initially, for example if the rotating part 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. Or the masses <NUM> are in the starting position in which they keep the part <NUM> balanced.

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>. The latter, preferably, knowing the position of the eccentric masses <NUM>, by means of the detection means <NUM>, <NUM>, and the position and extent of the imbalance, by the imbalance detection means <NUM>, calculate the position that the eccentric masses <NUM> must assume and the direction and angle of rotation, around the central axis 1a, which must implement the masses <NUM>, to balance the assembly consisting of the rotating part <NUM> and the device <NUM>.

To move the eccentric masses <NUM>, the control means <NUM> acquire, by the first detection means <NUM>, the speed of the rotor <NUM> and control, obtaining for example a vector control, at or to the eccentric mass <NUM> a speed, with respect to the stator <NUM>, slightly higher or lower than this speed of the rotor <NUM>, so that the eccentric mass <NUM> is based of an angular distance equal to a maximum of half a turn with respect to the rest of the rotor <NUM>. This speed is controlled by selecting the respective alternation of electrical power supply to the electromagnetic windings of the stator <NUM>.

Basically, the control means <NUM> control the power supply means <NUM> and, through the electric connections <NUM>, the balancing motors <NUM> of one or both of the eccentric masses <NUM> arranging them, with respect to the position of the rest of the rotor <NUM>, in the required position, or rather, preferably, until the imbalance of the balancing device <NUM> is not equal and opposite to the imbalance of the part <NUM>, in such a way as to balance it. Once the ideal position has been reached, the electric control is switched off.

The eccentric masses <NUM>, following this movement, remain blocked by the locking means <NUM> and continue to be dragged with the rotor <NUM> by the rotating part <NUM>.

The balancing device <NUM> according to the invention achieves important advantages. In fact, the balancing device is simple and robust, since the motors are of the brushless type and therefore not subject to wear. It can therefore also be arranged on board rotating members that exceed tens of thousands of revolutions per minute. For the same reasons it is also economical.

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

The two masses can also be moved in both directions, since they can assume a selected speed.

Claim 1:
A balancing procedure, carried out on 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, at least partially, 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), wherein,
- said balancing motor (<NUM>) is an electric motor with permanent magnets comprising a stator (<NUM>) and a rotor (<NUM>),
- said rotor (<NUM>) is integral with said eccentric mass (<NUM>),
- said rotor (<NUM>) is driven and dragged by said rotating part (<NUM>) when no balancing operation is required for said rotating part (<NUM>),
characterized in that said electric motor is a brushless electric motor.