Patent Description:
In particular, the present belt sanding head is usable in a robotic machining station for sanding and finishing mechanical pieces.

The robotic stations allow the execution of different operations without the need for direct intervention by operators and an articulated robotic arm is generally housed inside them.

The use of robotic arms allows replacing the manual work of the operators and considerably reducing the machining time and the risks for the safety of the operators themselves.

The robotic arm is able to pick up a series of tool heads from special positions and bring them into contact with the mechanical pieces to be machined.

Among these, the belt sanding heads are used, e.g., for the removal of welding burrs and the final finishing of the mechanical piece through the use of special abrasive belts.

The abrasive belt, in particular, is closed in a loop and is mounted on the belt sanding head, which sets it in rotation.

More specifically, the movement is given by a series of swivel elements, suitably spaced apart from each other, around which the abrasive belt is wound and which keep, at the same time, the abrasive belt under tension.

The belt sanding heads of known type do have some drawbacks.

In particular, in order to carry out the machining of a mechanical piece, the robotic arm brings the belt sanding head closer to the mechanical piece itself to allow the sanding action of the abrasive belt.

However, the contact between the belt sanding head and the mechanical piece causes a reaction force to occur, opposite that applied by the belt sanding head to approach the mechanical piece.

The reaction force causes mechanical stress on the belt sanding head which stress can affect the machining of the mechanical piece or even lead to damage to the belt sanding head itself.

For this reason, the belt sanding heads of known type are provided with a basic frame, associable with the robotic arm, and with a movable frame, which supports the abrasive belt and is associated in a movable manner with the basic frame in order to undergo the reaction forces.

In use, the reaction forces operating on the belt sanding head are discharged onto the movable frame thus causing it to oscillate slightly with respect to the basic frame.

This oscillation is controlled by means of a compensation system adapted to counteract the reaction forces between the sanding head and the mechanical piece being machined.

However, this compensation system does not allow for the use of belt sanding heads of a known type for the machining of structurally complex mechanical pieces and/or in which very high sanding quality is required, unless the robotic arm continuously adjusts the movement and the position of the sanding head itself. This inevitably leads to a lengthening of the machining time and of the related costs.

In addition, during machining, the abrasive belt suffers a strong overheating caused by the interaction with the mechanical piece and the high rotational speed given by the swivel elements.

Such overheating leads to an inevitable deformation of the abrasive belt, specifically, to the elongation thereof.

The belt sanding heads of known type must therefore be provided with tensioning systems able to overcome this deformation of the abrasive belt.

In fact, inadequate tensioning of the abrasive belt can lead to an ineffective sanding action that risks compromising the entire machining cycle of the mechanical piece. Known tensioning systems, however, determine the displacement of one or more of the swivel elements with respect to the others, thus causing a change in the layout and weight distribution on board the sanding head that can inconveniently hinder the action of the compensation system.

Furthermore, during the machining, the abrasive belt may undergo crosswise displacements which may cause it to move away from the swivel elements.

The sanding heads of known type, however, are not always able to keep the abrasive belt in the correct position, i.e. around the swivel elements, for the entire machining cycle, with the risk of unwanted and frequent interruptions of the machining cycle aimed at repositioning the abrasive belt around the swivel elements, therefore, with an inconvenient extension of the machining time.

Belt sanding heads of known type are also disclosed in documents <CIT> and <CIT>. <CIT> is the basis for the preamble of claim <NUM>.

The main aim of the present invention is to devise a belt sanding head that allows carrying out sanding operations of the highest quality and precision.

A further object of the present invention is to devise a belt sanding head that allows effectively counteracting the reaction forces during the machining of structurally complex mechanical pieces in a quick and effective manner.

Another object of the present invention is to devise a belt sanding head that allows the abrasive belt to be tensioned in an adequate and constant manner even as a result of deformations due to overheating during the machining.

Yet another object of the present invention is to devise a belt sanding head that allows keeping the abrasive belt correctly wound around the swivel elements, for the entire machining cycle.

Another object of the present invention is to devise a belt sanding head that allows overcoming the above mentioned drawbacks of the prior art in a simple, rational, easy, effective to use and low cost solution.

The above mentioned objects are achieved by the present belt sanding head having the characteristics of claim <NUM>.

Other characteristics and advantages of the present invention will be more evident from the description of a preferred, but not exclusive, embodiment of a belt sanding head, illustrated by way of an indicative, yet non-limiting example in the attached tables of drawings in which:.

With particular reference to these figures, reference numeral <NUM> globally indicates a belt sanding head.

The sanding head <NUM> is usable inside a machining station <NUM> for sanding and finishing at least one mechanical piece M.

In the context of the present treatise, the term "mechanical piece" means a production product intended to be used as a component in mechanical applications. In particular, the mechanical piece is made of metal material and may have welding burrs to be polished and/or surface portions to be finished.

The machining station <NUM> also comprises at least one movement device A adapted to move the sanding head <NUM> inside the machining station <NUM>.

Preferably, the movement device A is of the type of an automated robotic arm that allows doing without the intervention of an operator and displacing the sanding head <NUM> inside the machining station <NUM> in order to approach / move away from the mechanical piece M.

The machining station <NUM> is also suitably provided with at least one management and control system <NUM> operationally connected to at least one of either the sanding head <NUM> or the movement device A.

The management and control system <NUM>, in this case, is of the type of a computerized electronic system which is configured to automatically manage the movement of the movement device A and the operation of the sanding head <NUM>. The management and control system <NUM> will be described in more detail later in the present discussion.

The sanding head <NUM> according to the invention comprises at least one basic frame <NUM> associable with at least one movement device A and with at least one operating assembly <NUM>.

The operating assembly <NUM> is associated with the basic frame <NUM> and is provided with a plurality of swivel elements 6a, 6b, 6c and with at least one abrasive belt <NUM> closed on itself in a loop and wound at least partly around the swivel elements 6a, 6b, 6c for the machining of the mechanical piece M.

During the machining of the mechanical piece M, the operating assembly <NUM> is movable in rotation in both directions of rotation around at least one axis of rotation R.

In particular, during the machining, the operating assembly <NUM> comes into contact with the mechanical piece M and causes the occurrence of a reaction force, opposite that applied by the sanding head <NUM> to come into contact with the mechanical piece M.

For this purpose, the operating assembly <NUM> is hinged to the basic frame <NUM> so as it is subjected to such a reaction force and to avoid possible damage to the sanding head <NUM> and/or to the mechanical piece M.

More specifically, the operating assembly <NUM> comprises at least one holding frame <NUM> hinged to the basic frame <NUM> around the axis of rotation R and supporting at least one of the swivel elements 6a, 6b, 6c.

In this case, the basic frame <NUM> comprises a hub portion 4a inside which a corresponding tubular portion 8a of the holding frame <NUM> is at least partly housed.

Specifically, the operating assembly <NUM> is movable between a balance position, wherein the operating assembly <NUM> and the basic frame <NUM> are aligned along an axis of equilibrium E substantially perpendicular to the axis of rotation R, and an unbalance position, wherein the operating assembly <NUM> is rotated with respect to the axis of equilibrium E by an angle of rotation α.

In particular, the angle of rotation α is comprised between -<NUM>° and +<NUM>°, wherein the negative values represent the rotation in a clockwise direction and the positive values represent the rotation in a counterclockwise direction.

In the balance position the angle of rotation α is zero and the operating assembly <NUM> extends towards the mechanical piece M, moving away from the basic frame <NUM>. The sanding head <NUM> is suitably provided with a pair of counterweighted elements <NUM> associated with the holding frame <NUM>, each one arranged on opposite sides of a plane of equilibrium P passing through the axis of rotation R and through the axis of equilibrium E.

The counterweighted elements <NUM> have the function of balancing the weight of the operating assembly <NUM> on the axis of rotation R.

During machining, the operating assembly <NUM> can be subjected to reaction forces in the opposite direction and can be made to rotate clockwise and counterclockwise.

The operating assembly <NUM> is, in fact, able to machine the mechanical piece M by operating on opposite sides of the mechanical piece itself with respect to the plane of equilibrium P, in order to optimize the machining time and thus reduce the costs related thereto.

It is easy to understand, however, that in order to carry out its function effectively and keep the abrasive belt <NUM> in contact with the mechanical piece M, the operating assembly <NUM> must be able to counteract the reaction forces generated on contact with the mechanical piece M and return to the balance position.

For this purpose, the sanding head <NUM> is provided with bi-directional pneumatic compensation means <NUM> adapted to counteract the rotation of the operating assembly <NUM> around the axis of rotation R from the balance position to the unbalance position in both directions of rotation.

In other words, the bi-directional pneumatic compensation means <NUM> tend to bring the operating assembly <NUM> back to the balance position and keep it in contact with the mechanical piece M in order to allow the sanding action of the abrasive belt <NUM>. The bi-directional pneumatic compensation means <NUM> comprise at least one pair of compensation elements <NUM> inserted at least partly into a housing chamber <NUM> defined in the basic frame <NUM>.

The compensation elements <NUM> interact with the operating assembly <NUM> during the rotation towards the unbalance position.

Each of the compensation elements <NUM> is movable between a home position and a counteracting position, wherein the compensation element <NUM> is pushed inside the housing chamber <NUM> by the operating assembly <NUM> as a result of the rotation.

The compensation elements <NUM> are substantially aligned along an axis of compensation C that is substantially orthogonal to the axis of rotation R and perpendicular to the axis of equilibrium E.

In more detail, the axis of compensation C is substantially perpendicular to the plane of equilibrium P.

The compensation elements <NUM> are arranged on opposite sides of the plane of equilibrium P and are movable with respect to the housing chamber <NUM> sliding along the axis of compensation C between the home position and the counteracting position, in opposite directions.

In other words, the housing chamber <NUM> extends along the axis of compensation C and the compensation elements <NUM> partly protrude from the housing chamber <NUM>, from opposite sides thereof.

After having been pushed inside the housing chamber <NUM> in the counteracting position, the compensation elements <NUM> are brought back to the home position to bring, in turn, the operating assembly <NUM> back to the balance position.

For this purpose, the bi-directional pneumatic compensation means <NUM> comprise actuation means which are adapted to move at least one of the compensation elements <NUM> from the counteracting position to the home position.

In particular, the actuation means comprise injection means <NUM> of at least one operational fluid into the housing chamber <NUM>.

The operational fluid is able to counteract the displacement of the compensation elements towards the counteracting position and thus to push the operating assembly <NUM> towards the balance position.

In more detail, the operational fluid is injected inside the housing chamber <NUM> at a predetermined pressure value.

Conveniently, the predetermined pressure value is more than <NUM> bar.

In other words, in the housing chamber <NUM> the operational fluid is overpressure compared to the atmospheric pressure.

Preferably, the predetermined pressure value is comprised between <NUM> and <NUM> bar.

In addition, the operational fluid is preferably compressed air.

The bi-directional pneumatic compensation means <NUM> comprise at least one thrust element <NUM> associated with the operating assembly <NUM> and adapted to abut against at least one of the compensation elements <NUM> between the home position and the counteracting position.

In particular, the bi-directional pneumatic compensation means <NUM> comprise at least one pair of the thrust elements <NUM> arranged from opposite sides with respect to the plane of equilibrium P, in the balance position, each adapted to abut against a corresponding compensation element <NUM>.

In more detail, each of the thrust elements <NUM> is associated with a corresponding counterweighted element <NUM>.

Advantageously, the sanding head <NUM> comprises at least one position sensor <NUM> adapted to detect the position of the operating assembly <NUM> with respect to the basic frame <NUM>, i.e. to determine the angle of rotation α, and to generate at least one electronic positioning data of the operating assembly <NUM>.

In other words, the position sensor <NUM> allows detecting the instant when the contact occurs between the operating assembly <NUM> and the mechanical piece M, which determines the displacement from the balance position to the unbalance position. Preferably, the position sensor <NUM> is of the magnetic type.

In particular, the position sensor <NUM> comprises a first sensor element 15a associated with the basic frame <NUM> and a second sensor element 15b associated with the holding frame <NUM>.

In the balance position, the first sensor element 15a and the second sensor element 15b face each other and generate a predetermined magnetic field.

For example, the first sensor element 15a is a Hall effect sensor while the second sensor element 15b consists of a permanent magnet.

When the operating assembly <NUM> rotates around the axis of rotation R towards the unbalance position, the second sensor element 15b tilts with respect to the first sensor element 15a, thus changing the magnetic field and generating the electronic positioning data of the operating assembly <NUM>.

Appropriately, the management and control system <NUM> comprises at least one balancing unit 3a operationally connected to the position sensor <NUM> and to the actuating means and configured to operate the actuating means based on the electronic positioning data of the operating assembly <NUM>.

In more detail, depending on the electronic positioning data of the operating assembly <NUM> generated by the position sensor <NUM>, the balancing unit 3a can intervene dynamically on the injection means <NUM>, so as to increase or decrease the pressure of the operational fluid inside the housing chamber <NUM> according to pre-established conditions of use.

The operational fluid operates on the compensation element <NUM> to bring it back to the home position; the thrust of the compensation element <NUM> on the thrust element <NUM> causes the operating assembly <NUM> to rotate in the opposite direction, towards the balance position.

The application of greater or lesser pressure of the operational fluid in the housing chamber <NUM> thus results in greater or lesser pressure of the abrasive belt <NUM> on the mechanical piece M.

As described above, the operating assembly <NUM> is provided with swivel elements 6a, 6b, 6c around which the abrasive belt <NUM> is at least partly wound.

The swivel elements 6a, 6b, 6c define at least partly a working seat S of the abrasive belt <NUM>.

Advantageously, the operating assembly <NUM> comprises rotational means <NUM> adapted to set at least one of the swivel elements 6a, 6b, 6c in rotation.

The rotation of the swivel elements 6a, 6b, 6c causes the movement of the abrasive belt <NUM> in order to allow the sanding of the mechanical piece M.

In particular, the swivel elements 6a, 6b, 6c comprise at least one motor-driven wheel 6a associated with the rotational means <NUM>.

The rotational means <NUM> comprise at least one motor assembly <NUM> provided with a casing 17a associated with the holding frame <NUM> and a drive shaft 17b associated with the motor-driven wheel 6a for setting the motor-driven wheel 6a in rotation around an axis coinciding with the axis of rotation R.

In particular, the drive shaft 17b is mounted inside the casing 17a which, in turn, is partly inserted inside the tubular portion 8a of the holding frame <NUM>.

The motor assembly <NUM> drives the rotation of the motor-driven wheel 6a for the movement of the abrasive belt <NUM>.

In order to allow an adequate sanding action of the mechanical piece M, the abrasive belt <NUM> must be kept taut around the swivel elements 6a, 6b, 6c.

The operating assembly <NUM> conveniently comprises tensioning means <NUM> adapted to keep the abrasive belt <NUM> taut around the swivel elements 6a, 6b, 6c.

In particular, the swivel elements 6a, 6b, 6c comprise at least one tensioning wheel 6b associated with the tensioning means <NUM>.

The tensioning wheel 6b is movable in rotation with respect to the holding frame <NUM> as a result of the rotation of the abrasive belt <NUM> by the motor-driven wheel 6a.

Advantageously, the tensioning means <NUM> comprise at least one supporting arm <NUM> of the tensioning wheel 6b associated in a movable manner with the holding frame <NUM> and adapted to move the tensioning wheel 6b along a direction of tensioning D to tension the abrasive belt <NUM>.

In particular, the supporting arm <NUM> extends along the direction of tensioning D, towards the mechanical piece M.

In the balance position, the direction of tensioning D coincides with the axis of equilibrium E.

In other words, on the sanding head <NUM>, the tensioning wheel 6b is arranged in a distal position, i.e. in an opposite direction with respect to the basic frame <NUM> and to the movement device A, and interacts with the mechanical piece M during machining.

It is important to underline that the rotation of the abrasive belt <NUM> occurs at very high speeds and this, together with the friction generated by the interaction between the abrasive belt <NUM> and the mechanical piece M, leads to an overheating of the abrasive belt itself and its consequent deformation.

In particular, the abrasive belt <NUM> tends to stretch and lose its initial tensioning degree.

For this reason, the supporting arm <NUM> is constantly moved with respect to the holding frame <NUM>, so that the tensioning wheel 6b keeps the abrasive belt <NUM> taut. The tensioning means <NUM> comprise at least one movement system <NUM>, <NUM> of the supporting arm <NUM> comprising:.

More specifically, the actuator element <NUM> is of the type of a compressed air cylinder and allows the supporting arm <NUM> to slide on the guiding element <NUM> in extension with respect to the holding frame <NUM>, to tension the abrasive belt <NUM>. Conveniently, the actuator element <NUM> also allows the supporting arm <NUM> to slide on the guiding element <NUM> in contraction with respect to the holding frame <NUM>, to release the abrasive belt <NUM>, e.g., during the replacement of the latter.

Advantageously, the tensioning means <NUM> comprise sensor means <NUM> associated with the supporting arm <NUM> and adapted to detect the position of the tensioning wheel 6b with respect to the holding frame <NUM> and to generate at least one electronic positioning data of the tensioning wheel 6b.

In fact, the variation of the position of the tensioning wheel 6b must be followed by an adjustment of the position of the sanding head <NUM> with respect to the mechanical piece M, so that the tensioning wheel 6b is in contact with the mechanical piece itself during machining.

The sensor means <NUM> comprise at least one extension sensor <NUM>, <NUM> adapted to detect the extension of the supporting arm <NUM> with respect to the holding frame <NUM> along the direction of tensioning D.

In particular, the extension sensor <NUM>, <NUM> comprises a fixed portion <NUM> associated with the holding frame <NUM> and a movable portion <NUM> associated with the supporting arm <NUM>.

The movable portion <NUM> is associated in a sliding manner with the fixed portion <NUM> and a variation of the mutual position between the two portions <NUM> and <NUM>, due to the movement of the supporting arm <NUM> along the direction of tensioning D, generates the electronic positioning data of the tensioning wheel 6b.

The tensioning wheel 6b represents, in fact, the machining point of the sanding head <NUM> and must be kept in contact with the mechanical piece M to allow the machining of the mechanical piece itself.

Therefore, the management and control system <NUM> must be able to constantly detect the position of the tensioning wheel 6b.

Appropriately, the management and control system <NUM> comprises at least one locating unit 3b operationally connected to the sensor means <NUM> and to the movement device A and configured to control the movement device A based on the electronic positioning data of the tensioning wheel 6b.

When the extension sensor <NUM>, <NUM> generates the electronic positioning data of the tensioning wheel 6b, the locating unit 3b controls the movement device A to displace the sanding head <NUM> so as to move the basic frame <NUM>, and then the motor-driven wheel 6a, away from the mechanical piece M and to keep, this way, the tensioning wheel 6b in contact with the latter.

The operating assembly <NUM> conveniently comprises tilting means <NUM> positioned between the supporting arm <NUM> and the tensioning wheel 6b and adapted to rotate the tensioning wheel 6b around at least one tilting axis B substantially parallel to the direction of tensioning D.

The tilting means <NUM> allow the tensioning wheel 6b to adapt to the surface of the mechanical piece M so that the abrasive belt <NUM> always remains in contact with the mechanical piece itself.

In particular, the tilting means <NUM> comprise a supporting portion <NUM> of the tensioning wheel 6b associated in rotation with the supporting arm <NUM> along the tilting axis B.

The supporting portion <NUM> is provided with a rotational pin 26a which extends along the tilting axis B and is inserted in a corresponding rotational seat 19a defined on the supporting arm <NUM>.

In addition, the supporting portion <NUM> is provided with a clamping pin 26b, inserted into a corresponding clamping seat 19b defined on the supporting arm <NUM>, which binds the tensioning wheel 6b to rotate according to a predefined tilting angle.

The clamping pin 26b has a substantially cylindrical shape and has a diameter measurement substantially smaller than the diameter measurement of the clamping seat 19b.

The oscillation of the clamping pin 26b inside the clamping seat 19b allows the rotation by a tilting angle comprised between -<NUM>° and +<NUM>° with respect to the tilting axis B.

During the machining of the mechanical piece M, the abrasive belt <NUM> is subjected to mechanical stress that may cause it to move away from its working seat S. Advantageously, the operating assembly <NUM> comprises positioning means <NUM> adapted to keep the abrasive belt <NUM> wound around the swivel elements 6a, 6b, 6c.

In particular, the swivel elements 6a, 6b, 6c comprise at least one positioning wheel 6c associated with the positioning means <NUM> and movable in rotation between a home position, wherein it partly defines the working seat S of the abrasive belt <NUM>, and at least one adjustment position, wherein it brings the abrasive belt <NUM> back which winds around the motor-driven wheel 6a and the tensioning wheel 6b.

The positioning wheel 6c is in turn movable in rotation with respect to the holding frame <NUM> as a result of the rotation of the abrasive belt <NUM> by the motor-driven wheel 6a.

The positioning means <NUM> have the function of keeping the abrasive belt <NUM> in its working seat S by moving the positioning wheel 6c between the home position and the adjustment position.

In more detail, the positioning wheel 6c is hinged to the holding frame <NUM> and is movable in rotation around an axis of adjustment F, substantially parallel to the direction of tensioning D.

In particular, the positioning wheel 6c can rotate around the axis of adjustment F, towards the adjustment position, in both directions of rotation.

The positioning means <NUM> comprises at least one actuating device <NUM> connected to the positioning wheel 6c and adapted to move the positioning wheel 6c between the home position and the adjustment position.

The actuating device <NUM> is of the type of an electric servomotor and comprises an adjustment element 28a associated with the positioning wheel 6c, movable by sliding along an axis of positioning G substantially parallel to the axis of rotation R.

The movement of the adjustment element 28a along the axis of positioning G results in a rotary movement of the positioning wheel 6c around the axis of adjustment F.

The positioning means <NUM> also comprises at least one position detecting device <NUM> of the abrasive belt <NUM> adapted to generate at least one electronic positioning data of the abrasive belt <NUM>, to which the actuating device <NUM> is subordinate.

The position detecting device <NUM> is of the type of a laser sensor.

In more detail, the position detecting device <NUM> is adapted to emit a laser beam towards the working seat S and detects the presence of the abrasive belt <NUM>.

The displacement of the abrasive belt <NUM> from its working seat S leads to the generation of the electronic positioning data of the abrasive belt <NUM>.

Conveniently, the positioning means <NUM> comprise a plurality of position detecting devices <NUM>.

Specifically, the positioning means <NUM> comprise a pair of position detecting devices <NUM> each adapted to emit the laser beam L towards the opposite sides of the working seat S.

This way, the position detecting devices <NUM> are able to detect even the slightest movement of the abrasive belt <NUM> with respect to its working seat S, both on one side and on the other, and to allow immediate operation of the actuating device <NUM>.

Appropriately, the above mentioned management and control system comprises at least one positioning unit 3c operationally connected to the position detecting device <NUM> and to the actuating device <NUM> and configured to operate the actuating device <NUM> based on the electronic positioning data of the abrasive belt <NUM>.

In more detail, when the position detecting device <NUM> generates the electronic positioning data of the abrasive belt <NUM>, the positioning unit 3c operates the actuating device <NUM> in order to displace the positioning wheel 6c from the home position to the adjustment position.

Conveniently, the sanding head <NUM> is also provided with removal means <NUM> associated with the operating assembly <NUM> and adapted to remove the machining residues generated by the mechanical piece M during the sanding operation.

In particular, the removal means <NUM> are adapted to blow compressed air in the proximity of the tensioning wheel 6b, where the machining of the mechanical piece M takes place, in order to space the machining residues apart from the mechanical piece itself.

The removal means <NUM> also have the function of cooling the tensioning wheel 6b, which, due to the rotation and interaction with the mechanical piece M, tends to overheat considerably.

The operation of the belt sanding head <NUM> inside the machining station <NUM> is as follows.

Initially, the sanding head <NUM> is mounted on the movement device A for the movement of the belt sanding head itself with respect to the mechanical piece M. The abrasive belt <NUM> is installed in its own working seat S, wound around the swivel elements 6a, 6b, 6c.

At this point, the tensioning means <NUM> extend the supporting arm <NUM> along the direction of tensioning D to tension the abrasive belt <NUM> and, at the same time, the rotational means <NUM> set the motor-driven wheel 6a in rotation to move the abrasive belt <NUM>.

The sensor means <NUM> generate an electronic positioning data of the tensioning wheel 6b and the locating unit 3b controls the movement device A to bring the tensioning wheel 6b in contact with the mechanical piece M.

The interaction with the mechanical piece M generates a reaction force that causes the rotation of the operating assembly <NUM> around the axis of rotation R in one of the directions of rotation, towards the unbalance position.

The rotation causes one of the compensation elements <NUM> to be displaced towards the counteracting position by the corresponding thrust element <NUM>.

The pressure of the operational fluid in the housing chamber <NUM> opposes the displacement of the compensation elements <NUM> and thus determines the force with which the abrasive belt <NUM> is pushed onto the mechanical piece M.

During machining, the position sensor <NUM> detects the rotation and generates the electronic positioning data of the operating assembly <NUM>.

At the same time, the tilting means <NUM> allow the partial rotation of the tensioning wheel 6b along the tilting axis B to adapt to the surface of the mechanical piece M and allow the abrasive belt <NUM> to remain in contact with the latter, even if there are irregularities on the surface of the mechanical piece M.

During cutting, the removal means <NUM> blow compressed air at the point where the tensioning wheel 6b is located to remove the machining waste and cool the tensioning wheel itself.

Due to the high speed of rotation of the swivel elements 6a, 6b, 6c and of the interaction with the mechanical piece M, the abrasive belt <NUM> overheats and tends to deform.

As a result, the supporting arm <NUM> tends to extend along the direction of tensioning D in order to keep the abrasive belt <NUM> taut.

The sensor means <NUM>, therefore, generate an additional electronic positioning data of the tensioning wheel 6b and the locating unit 3b controls the movement device A to keep the tensioning wheel 6b in contact with the mechanical piece M.

In the event of a possible movement of the abrasive belt <NUM> away from its working seat S, the position detecting devices <NUM> generate an electronic positioning data of the abrasive belt <NUM>.

The positioning unit 3c then operates the actuating device <NUM> in order to move the positioning wheel 6c between the home position and the adjustment position to bring the abrasive belt back to its working seat S.

At the end of the machining or in the event of the abrasive belt <NUM> being replaced, the movement device A moves the sanding head <NUM> away from the mechanical piece M, the rotational means <NUM> stop the rotation of the motor-driven wheel 6a and the tensioning means <NUM> move the supporting arm <NUM> in contraction to release the abrasive belt <NUM>.

It has in practice been ascertained that the described invention achieves the intended objects and in particular the fact is emphasized that the belt sanding head according to the present invention allows carrying out high quality and precision sanding operations and to effectively counteract the reaction forces during the machining of structurally complex mechanical pieces quickly and effectively, thanks to the bi-directional pneumatic compensation means.

In addition, the present belt sanding head allows adequate and constant tensioning of the abrasive belt even as a result of deformations due to overheating during machining, through the action of the tensioning means.

Claim 1:
Belt sanding head (<NUM>), usable in a machining station (<NUM>) of at least one mechanical piece (M), comprising:
- at least one basic frame (<NUM>) associable with at least one movement device (A) adapted to move said sanding head (<NUM>) inside said machining station (<NUM>);
- at least one operating assembly (<NUM>) provided with a plurality of swivel elements (6a, 6b, 6c) and with at least one abrasive belt (<NUM>) closed on itself in a loop and wound at least partly around said swivel elements (6a, 6b, 6c) for the machining of said mechanical piece (M), wherein said operating assembly (<NUM>) is associated with said basic frame (<NUM>) and movable in rotation in both directions of rotation around at least one axis of rotation (R), during said machining, between a balance position, wherein said operating assembly (<NUM>) and said basic frame (<NUM>) are aligned along an axis of equilibrium (E) substantially perpendicular to said axis of rotation (R), and an unbalance position, wherein said operating assembly (<NUM>) is rotated with respect to said axis of equilibrium (E) by an angle of rotation (α);
characterized in that it comprises bi-directional pneumatic compensation means (<NUM>) adapted to counteract the rotation of said operating assembly (<NUM>) around said axis of rotation (R) from said balance position to said unbalance position in both directions of rotation.