Apparartus for changing an abrasive sheet in an abrading machine

An apparatus for replacing an abrasive sheet in a sanding machine comprising a working head in which it is provided a support body having an engagement surface arranged to engage with an abrasive sheet. The sanding machine also comprises a handling device arranged to actuate the support body in space according to at least two degrees of freedom. The face of the abrasive sheet facing, in use, towards the support body and the engagement surface of this comprises a mutual engagement means of removable type. For example, the mutual engagement means can provide a layer of Velcro, i.e. a velvet layer on a face and a plurality of hooks on the other face, or an adhesive layer, in particular of reversible glue layer, or a plurality of projections and recesses mutually engageable with each other, or similar engagement elements. Furthermore, is provided a removal station in which it is installed a removal device having a sharp edge arranged to remove the sheet from the support body through a plurality of operations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National State of International Application No. PCT/M2015/051160, filed Feb. 17, 2015, which claims priority to Italian Patent Application No. PI2014A000015, filed Feb. 20, 2014, each of which is incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to sanding machines and, in particular it relates to an apparatus for changing an abrasive sheet in a sanding machine.

Furthermore, the invention relates to a method for carrying out a sandpaper change.

BACKGROUND

As well known, sanding, or abrading, is an operation that is made on surfaces of different materials, like plastic materials, metal materials, wood, for finishing the surfaces of objects of various type, normally for preparing them to next operations like painting their surface

The abrading, or sanding step, is usually effected manually by an operator that grips a hand-held tool. This is usually equipped with an abrasive disc, usually a disc of sandpaper, which is moved by an electric motor, or by a compressed air motor, which rotates the support to which it is fastened.

Among sanding machines of last generation there are the orbital sanders, in which the motor causes an orbital movement to the abrasive disc. In this type of machines, the support rotates about a rotation axis and at the time describes an orbital path. This way, owing to the particular motion the abrasive disc can make high quality sanding of the worked surfaces.

There are also automatic machine tools in which the abrasive disc is moved with respect to the surface to work.

In all the abrading or sanding machines, after a certain number of working cycles it is necessary to replace the abrasive disc that unavoidably is worn by the work and then produces a much less effective abrading action.

The change of the abrasive disc is made manually with subsequent loss of time and with the risk of applying in an incorrect way the abrasive disc to the support, with displacement from a correct working position and possibility to affect negatively the working step.

In U.S. Pat. No. 5,231,803 a method is described for positioning, at the end of a working cycle, a support body and the abrasive disc mounted to it in a known position. Once placed the support body in the known position, operations of removal and change of the abrasive disc are provided when it is worn.

However, in U.S. Pat. No. 5,231,803 a procedure of verification is not provided for controlling that the disc has been actually mounted to the support body. Therefore, if for any reasons, the position of the working head in the loading station is wrong, or the abrasive disc is not engaged, or the discs in the loading station are finished, then the abrasive disc is not mounted to the support body, and the working head is moved to the surface to work causing damages. In fact, not only the work of the surface of the working surface is compromised, since the abrasive action is not provided, but the support body and the working head can be damaged during when they hit the surface of the working surface.

Other prior art solutions with similar drawbacks are described also in EP2463056 and DE20213101858.

SUMMARY

In general terms, various embodiments are directed to an apparatus for replacing an abrasive sheet in abrading or sanding machines, which makes automatic the change of the abrasive sheet.

In addition, various embodiments are directed to an apparatus that ensures a highly precise positioning of the abrasive sheet.

Embodiments are directed to an apparatus that speeds up the change of the abrasive sheet.

It is still a further feature of the various embodiments to provide a method for replacing an abrasive sheet in abrading or sanding machines.

These and other objects are achieved by an apparatus or system, for changing an abrasive sheet in a sanding machine. In one embodiment, the system includes a sanding unit with a support body having an engagement surface arranged to engage the abrasive sheet. The sanding unit also includes a handling device configured to handle spatially the support body according to at least two degrees of freedom. The system also includes a removal station where the sheet can be removed from the support body. In one embodiment, the removal station includes a removal device having a sharp edge.

The handling device is arranged to actuate the support body with respect to the removal device to place the support body in a removal position in which the sharp edge is located between the abrasive sheet and the support body to detach at least one portion of the abrasive sheet from the engagement surface. In one embodiment, a detection device is provided which is arranged to measure the presence of the abrasive sheet on the engagement surface of the support body.

Preferably, the engagement surface has mutual engagement means of removable type with a side of the abrasive sheet facing, in use, towards the support body.

For example, the mutual engagement means can provide a layer of Velcro, i.e. a velvet layer on a face and a plurality of hooks on the other face, or an adhesive layer, in particular of reversible glue layer, a plurality of projections and recesses mutually engageable with each other, or a combination thereof.

Advantageously, the removal device is also comprised of a gripping element arranged to grip the abrasive sheet at the detached portion and to cause a relative movement between the gripping element and the support body determining a full disengagement of the abrasive sheet from the support body.

In a possible exemplary embodiment, the sharp edge is curvilinear, for example with substantially circular shape.

Advantageously, starting from a ready-for-removal position, the handling device is arranged to actuate the support body with respect to the sharp edge in order to cause the disengagement of a plurality of points of the abrasive sheet from the engagement surface. This way, a detached portion of the abrasive sheet from the support body is obtained assisting, thus a following full detachment.

In particular, the removal station has a gripping element arranged to grip the abrasive sheet at the detached portion, obtaining a gripping configuration. In this gripping configuration, a relative movement between the gripping element and the handling device causes the full disengagement of the abrasive sheet from the support body.

Preferably, the detection device is arranged at the removal station.

In particular, the detection device can be a sensor of colour recognition, i.e. a sensor responsive to a variation of the colour. In this case, therefore, the abrasive side of the abrasive sheet is of a colour different from the engagement surface of the support body. Therefore, according to the colour detected, the sensor of colour recognition can detect the presence, or the absence, of the abrasive sheet on the support body.

In one embodiment, the detection device is a diffuse-type laser sensor.

Furthermore, in a possible embodiment, in the removal station, can. be provided a delivery member of a jet of a pressurized gas. The delivery member may be arranged to deliver the jet of a pressurized gas on the engagement surface of the support body, in order to remove possible dust and fragments of abraded material from a working surface.

In another exemplary embodiment, the apparatus also includes at least one application station at which an abrasive sheet is mounted to the engagement surface of the support body. In particular, at the application station at least one container is arranged to contain at least one abrasive sheet, the handling device may be arranged to position the support body at said container, in order to cause the engagement of an abrasive sheet with the engagement surface of the support body.

Preferably, in the container a push element is provided to push the abrasive sheet against the engagement surface of the support body previously positioned at said container, to assist the engagement of the abrasive sheet with the engagement surface.

In an exemplary embodiment, the support body has at least one main suction hole in pneumatic connection with an air suction system, in order to cause the suction from the environment of surrounding dust and fragments removed from the working surface. Preferably, in this case, also the abrasive sheet has at least one secondary suction hole that may overlap the main suction hole.

Preferably a computing device is provided for computing the spatial orientation of the support body to assist positioning the support body in a position having a known spatial orientation.

In one embodiment, the handling device is arranged to position the support body at the device for computing the orientation with the support body free of rotating about a rotation axis. In particular, the spatial orientation computing device includes an actuation member that is arranged to cause a rotation of the support body about its rotation axis to place the support body in the position having known spatial orientation.

In a possible exemplary embodiment, the actuation member includes at least one roller arranged to rotate about a rotation axis and configured to contact the engagement surface at a distance from the rotation axis of the support body equal to the radial distance of the main suction hole. The rotation of the roller causes a rotation of the support body about the rotation axis until the roller moves to a respective suction hole. The actuation member also includes a motor and a transmission member. The transmission member is arranged to transmit the movement of the motor to the roller for causing it to rotate about the rotation axis.

In an exemplary embodiment, the handling device has a working head at which the abrasive sheet engages the working head has an axis.

In particular, the sanding machine can be of roto-orbital type where the support body can rotate about its axis and can move along an orbital eccentric path with respect to the axis of the working head.

In this case, a device for computing the position of the rotation axis of the support body with respect to the axis of a working head of the handling device at which the abrasive sheet engages is provided to calculate the space position of the rotation axis knowing the position of the axis, in such a way that the handling device can handle spatially the support body in a precise way.

In particular, the device for computing the position of the axis of the support body is arranged to determine the distance of the axis of the support body from the axis of the working head. This solution can be provided, for example, because the space position of the axis of the working head is known. For example, the device for computing the position of the axis of the support body can be configured to position the support body in a limit position, at which the distance of the axis of the support body with respect to the axis of the working head is maximum. For example, the device for computing the position of the rotation axis is configured to position the support body at a position where the axis of the support body is at a maximum distance from the axis of the working head. Since the maximum distance, i.e. the eccentricity, is known and since it is possible to know instant-by-instant the position in space of the working head owing to position sensors, it. is possible to determine also the position in space of the axis of the support body.

In one embodiment, if the support body and the abrasive sheets have main and secondary suction holes, respectively, the container of the application station has a reference element, in particular a reference bolt. More in detail, the reference element is arranged to engage with one of the suction holes of the support body, in order to keep the support body to a correct position during the application of the abrasive sheet.

Preferably, the container has a cover arranged to pass from a closed position of the container in order to avoid that dust and other material can make dirty a new abrasive sheet, and an open position, in which the abrasive sheet can exit from the container for application to the support body.

In one embodiment, the wall of the container ⋅ is associated with at least one protruding element towards the housing in which the stack of abrasive sheets is arranged. The latter are arranged in the container with respective abrasive sides facing each other and, accordingly, two sheets could adhere to each other and could be erroneously applied together to the support body. The presence of the protruding elements, instead, provides a separating action of the two sheets and avoids the disadvantage.

In particular, the protruding element can be a knurled, or indented, for example threaded.

According to another embodiment, a method for changing an abrasive sheet in a sanding machine is described. The method includes a sanding machine having a support body with an engagement surface arranged to engage with said abrasive sheet. The sanding machine also has a handling device configured to handle spatially the support body according to at least two degrees of freedom.

The method further includes providing a removal device having a sharp edge. Also, the method includes handling by the handling device the support body with respect to the removal device to place the support body in a removal position in which the sharp edge is located between the abrasive sheet and the support body. This detaches at least one portion of the abrasive sheet from the engagement surface. The method also includes controlling the presence of the abrasive sheet on the engagement surface of said support body.

DETAILED DESCRIPTION

InFIG. 1, an apparatus is diagrammatically shown100, according to the invention, for replacing an abrasive sheet25in a sanding machine120. It comprises a working head50in which a support body10is provided having an engagement surface15arranged to engage with an abrasive sheet25. The support body10has normally at least one rotation movement about a rotation axis110with respect to the working head50. The sanding machine120can also be of roto-orbital type and therefore in this case, in operating conditions, the support body10describes an orbital eccentric path with respect to an axis150of the working head50.

The sanding machine120also comprises a handling device40arranged to handle spatially the support body10according to at least two degrees of freedom. As diagrammatically shown inFIG. 1, the handling device40can be an anthropomorphic robot, for example with six rotational degrees of freedom.

Normally, the side26of the abrasive sheet25facing, in use, the support body10and the engagement surface15of the latter comprise a mutual engagement means of removable type. For example, the mutual engagement means can provide a layer of Velcro, i.e. a velvet layer on a face and a plurality of hooks on the other face, or an adhesive layer, in particular of reversible glue layer, or a plurality of projections and recesses mutually engageable with each other, or similar engagement elements.

According to the invention, the apparatus100, in addition to the sanding machine as described above, comprises a removal station30in which a removal device35is installed having an sharp edge31arranged to remove the sheet25from the support body10through the operations described below. More in detail, the handling device40is arranged to position the support body10in a removal position in which the sharp edge31is located between the abrasive sheet25and the support body10.

Through this step the mutual engagement means that engage the face26of the abrasive sheet25and the engagement surface15of the support body10and pass, at least at the beginning, from an engagement configuration to a configuration of disengagement in which at least one portion of the abrasive sheet25does not adhere any more to the engagement surface15.

More in detail, once arranged the support body10in a ready-for-removal position, i.e. the first position, in which the support body10has at least one portion located opposite to the abrasive sheet25with respect to the sharp edge31, the handling device40can actuate the support body10with respect to the sharp edge31, in order to bring the sharp edge21between the support body10and the abrasive sheet25at a plurality of points. This way, a detached portion of the abrasive sheet from the support body10is obtained, comprising all the points of the abrasive sheet25detached from the engagement surface15of the support body10.

In the exemplary embodiment ofFIGS. 1, 4 and 6, the sharp edge31is circular, but it may also have different shape, for example substantially linear, or it can have an open curved profile, or a combination of linear and curved segments.

In case of a sharp edge31having substantially circular shape, the support body10can be advantageously moved by the handling device40along a substantially circular trajectory, or elliptical, such that a disengagement of more points of the abrasive sheet25from the support body10is obtained.

The removal station30is, advantageously, equipped with a gripping element38arranged to grip the abrasive sheet25at the detached portion. In particular, in this case, the handling device40is arranged to position the abrasive sheet25, advantageously the detached portion thereof, at the gripping element38. When the gripping element38is arranged in the gripping configuration in which it grips the sheet25, a relative movement between the gripping element38and the support body10, for example made by the handling device40, causes a full disengagement of the abrasive sheet25from the support body10. In the example shown inFIGS. 4 and 5, the gripping element38comprises two parts and precisely a first part38aand a second part38bmovable with respect to each other. For example, the part38acan be connected to the removal device35and the part38bcan be slidingly mounted towards/away from the part38a, for example along a direction substantially orthogonal to the plane on which the sharp edge31lays.

The removal station30can also have a device for detecting the presence of the abrasive sheet25on the engagement surface15of the support body10. For example, the detection device can be a sensor of colour recognition36, i.e. sensing the variation of the colour. In this case, the abrasive side26of the abrasive sheet25is of a colour different from the engagement surface15of the support body10. Therefore, the sensor of colour recognition36can recognize the presence, or the absence, of the abrasive sheet25on the support body10according to the detected colour. The sensor36can also be a sensor of different type, normally a presence sensor.

The removal station can also be equipped with a delivery member37of a jet of air, or other pressurized gas, arranged to deliver the jet on the engagement surface15of the support body10, once removed the abrasive sheet25, for removing possible dust and fragments of abraded material from the working surface.

The apparatus100can also comprise at least one application station70in which an abrasive sheet25′ is mounted at the engagement surface15of the support body10. At the application station70of the abrasive sheet at least one container75is arranged, containing at least one abrasive sheet25, but preferably a stack of abrasive sheets25. More in particular, the handling device40is arranged to position the support body10at the container75up to cause the engagement of an abrasive sheet25with the engagement surface15of the support body10.

More in detail, at the application station70several containers75can be provided, for example each containing a sheet25, or, more in general a stack of abrasive sheets25that have a different sand size, i.e. smaller or larger, and then used for a variety of Works, or for different sanding steps.

The or each container75has a cover76arranged to pass from a closed position of container75, in order to avoid that dust and other material can make dirty the abrasive sheets25(FIG. 9), to an open position, in which it allows the access of the support body10, moved by the handling device40, to the mouth79of the container75, for being able, then, to apply a sheet25to the support body10(FIG. 10).

In the container75a push element can be provided of arranged to push the abrasive sheet25, or the stack of sheets25, towards the opening79, in order to push the abrasive sheet25against the engagement surface15previously positioned at the opening79. For example, the push element can be an actuator, such as a pneumatic piston85, arranged to translate longitudinally in the container75, and to act on a support body on which the abrasive sheets25are arranged, or directly on the first abrasive sheet25of the stack, i.e. farther from opening78.

The actuator85can be associated with at least one stop element, for example two stop elements86aand86b, arranged to stop the withdrawal during a step of back stroke towards the starting position after having applied the abrasive sheet25to support body10.

According to a further aspect of the invention, the wall77of container75has at least one protruding element87, for example at opening79. The protruding element87is arranged to protrude towards the inside of the container75, i.e. in a recess77, and is configured to cause the separation of two abrasive sheets25that can adhere to each another. The abrasive sheets25, in fact, are arranged in the container75with the abrasive side of one sheet oriented towards the engagement side of the next one and, accordingly, the two sheets can adhere to each other and could erroneously applied together to the support body10, with subsequent waste of material and with the risk of affecting the sanding step. The presence of the protruding elements87, instead, produces an action of separating the two sheets25that can adhere to each other and allows, therefore, to avoid said disadvantage. In particular, the protruding element87can be a knurled element, or indented, for example having a screwed surface. Therefore, when translating the abrasive sheets25towards the support body, the protruding element87separates by friction the two abrasive sheets25.

In the exemplary embodiment shown for example inFIG. 13, the support body10has at least one main suction hole18, for example three suction holes18at an angle of 120° from one another. The or each main suction hole18, is in pneumatic connection with an air suction system diagrammatically shown inFIG. 13with a block300. This way, when sanding a workpiece it is possible to cause the suction from the environment of surrounding dust and fragments from the working surface ensuring, on the one hand, to possible operators in the working area to work in safety conditions and, on the other hand, to avoid that dust and fragments material removed by the working surface can affect the sanding step.

Also the abrasive sheet25can be advantageously equipped with at least one secondary suction hole28. In this case, therefore, it is necessary to provide a device for overlapping the, or each, main suction hole18with the, or a respective, secondary suction hole28.

Alternatively, or in addition, to the device for overlapping, a computing device can be provided for determining the spatial orientation of the support body10. More in detail, the spatial orientation computing device of the support body10is arranged to position the support body10to a position whose orientation is known.

An example of spatial orientation computing device of the support body10is shown inFIGS. 14 to 17.

The handling device40is configured to position the support body10at the device for computing the orientation60in such a way that the support body10is free of rotating about its own rotation axis110. In particular, the handling device40is arranged to position the support body10with the engagement surface15in contact of rollers65, whose operation is disclosed in detail hereinafter. The device60can provide a side wall62to define laterally a housing61, to avoid possible side movements of the support body10during the step of computing the spatial orientation.

The spatial orientation computing device60comprises an actuation member63,64and65, arranged to cause the rotation of the support body10up to bring it in a position whose spatial orientation is known. The actuation member for causing the rotation of the support body10can rotate the support body10up to place the suction holes18in a predetermined angular known position. Therefore, when the handling device40draws the support body its spatial orientation and, in particular the angular position of the holes18, is known with precision. This allows moving in the application station70above described with the reliability of overlapping precisely the secondary suction holes28, i.e. those made on the abrasive sheets25, with the main suction holes18, i.e. those of the support body10.

In a possible exemplary embodiment, the device63,64,65is arranged to cause the rotation of the support body10about its rotation axis110up to a known position, comprising an element of transmission63arranged to transmit the movement of a motor, or a gear motor66, to at least one roller65at a distance from the rotation axis110of the support body10corresponding to the radial distance of one of the main suction holes18. More in detail, the roller65can rotate about an axis165, for example substantially horizontal. The rotation of the roller65causes the rotation of the support body10positioned on it. For increasing the grip of the surface of the or each roller65on the engagement surface15of the support body10it is possible to provide that the roller surface is knurled, or indented. When the rotation of the support body10has brought the roller65at the suction hole18, the rotation of the support body10stops.

The means for transmitting the movement of the gear motor66to the rollers65can provide, as shown in detail inFIG. 17, a rotatable plate63. The rotation of the plate about an axis160causes the rotation of the rollers65. For example, the or each roller65can be pivotally engaged to a pin69connected to a plate67. This is in turn fastened, for example by a bolt68, to the wall delimiting laterally the housing61. Therefore, the rotation of plate63about its axis160causes the rotation of the or each roller65about the respective rotation axis165. For increasing the friction between the plate63and the roller65it is possible to provide a layer of a high friction material, such as rubber.

Therefore, by knowing the angular position of the rollers65the spatial orientation of the support body10is determined and, in particular, the angular position of each suction hole18present on it is known. This makes it possible to arrange precisely the support body10by the handling device40at the application station of the abrasive sheet25, and, in particular to cause the suction holes18of the support body10to overlap the suction holes28of the abrasive sheets25housed within the container75.

To assist the relative positioning of the support body10and the stack of abrasive sheets25in container75, it is possible to provide a reference element, in particular a reference bolt78. For example, the reference element78is arranged to engage with one of the holes18of the support body10, in order to keep the support body10to a correct position during the approaching movement of the stack of sheets25and the following application of an abrasive sheet25on the surface15.

In case of a sanding machine of roto-orbital type the support body10, in addition to rotate about its own axis110, moves along an orbital eccentric path with respect to the axis150of the working head50of the handling device40to which it is constrained.

The detection device36above described with reference toFIGS. 5, 6 and 7, can be used both for testing the correct removal of the abrasive sheet25from the engagement surface15of the support body10and to check the successful application of the abrasive sheet25to the engagement surface15and then to test the correct removal carried out by removal station30and the correct application in the application station70.

Therefore, in this case, a device can be provided for computing the position of the rotation axis110of the support body10, for determining the position of the axis110in space and then execute the different operations with high precision.

In an exemplary embodiment of the invention, the axis150of the working head50has a ‘known position, and so it is enough to know the relative position of the axis110of the support body10from axis150. Therefore, in this case, the device for computing the position of the axis110can be arranged to determine the distance of the axis110from the axis of the working head50.

An example of the process through which it is possible to determine the position of the axis110with respect to the axis150is shown inFIG. 18. In this case, the handling device40is arranged to actuate the working head50, and then the support body10to it constrained, in order to bring the axis110of the support body10to a known position, for example at a maximum distance from the axis150. This can be made by the handling device40, for example by forcing the support body10against a wall200up to maximize the distance from axis150. In fact, by knowing the eccentricity of the support body, i.e. a maximum distance dmaxof the axis110from axis150, and by knowing the position of the latter, it is possible to determine the spatial position of the axis110.

Notwithstanding the abrasive sheet shown inFIGS. 1 to 18is substantially circular, i.e. It is an abrasive disc, this structure is to be intended as an exemplary one, since it is possible to use the apparatus, according to the present invention, for replacing abrasive sheets with different shape, for example rectangular.

The foregoing description of specific exemplary embodiments will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt in various applications the specific exemplary embodiments without further research and without parting from the invention, and, accordingly, it is meant that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology that is employed herein is for the purpose of description and not of limitation.