EP3028809B1

EP3028809B1 - Apparatus for automatically smoothing the rounded corners of prevalently flat panels made of wood and/or other material or other manufactured products

Info

Publication number: EP3028809B1
Application number: EP15197127.2A
Authority: EP
Inventors: Roberto Sorbini; Fabrizio Filippini
Original assignee: SORBINI Srl
Current assignee: SORBINI Srl
Priority date: 2014-12-03
Filing date: 2015-11-30
Publication date: 2017-03-01
Anticipated expiration: 2035-11-30
Also published as: ES2620510T3; EP3028809A1

Description

The invention relates to an apparatus for automatically sanding or smoothing the rounded corners of prevalently flat panels made of wood and/or of other material or other manufactured products, during a painting and/or finishing operation of the panels or manufactured products.
As closest prior art to the invention, which comes under the international class B24B9/00 and related subclasses, the document EP 293 341 is cited; this document describes an apparatus for automatically smoothing the rounded corners of a panel that moves along a rectilinear path, by means of a closed loop of sandpaper, mounted on three driven and rotation pulleys, supported by an arm oscillating on support means lateral to the path of the exposed longitudinal side of the panel with the end corners to be sanded and that is taken by suitable means from a position at rest to a position in contact with the corners, normally touching the corner areas first on the front or rear face, then curving around the corner and finally touching it along a section on the exposed side parallel to the direction of feed of the panel, also with the interposed action of an elastic pad and while said arm that supports the sanding unit oscillates about an axis perpendicular to the ideal plane on which the panel lies, so that the abrasive sandpaper progressively and with adequate pressure involves the whole of the rounded extension of the rounded corners of the panel.
When the profile of the sides and of the corners of the panels has rounded edges, in place of the closed sandpaper belt, the use is known of rotating sanding heads or brushes, the abrasive surface of which has a generatrix that reproduces the profile of the corners of the panels to be sanded.
Due to the fact that they are mounted able to oscillate on a fixed support and owing to their considerable mass and to the consequent inertia, prior art sanding apparatus negatively influence the feed speed of the panels, resulting in increased machining costs of the panels.
The invention intends to overcome this serious limitation of the prior art with an apparatus as claimed in claim 1) and in the subsequent dependent claims, which is able to operate on panels that are fed at a higher speed to those of the prior art and which makes use of the idea of solution below. The smoothing system, although still of oscillating type or of any other suitable type, is mounted on a carriage that can slide on guides parallel to the longitudinal side of the panel that has at the ends the corners to be smoothed and the carriage is motorised and means are provided that, to ensure that when the corner of the panel to be sanded reaches a predetermined position with respect to the smoothing means, the means remain aligned precisely with the panel and accompany this latter during feed, at the same speed, to sand the front or rear corner of the longitudinal side of the panel, with the speed required to perform sanding well, even at low speed, but no longer negatively influencing the feed speed of the panel, as the smoothing means follow the panel, after which the means move away from the longitudinal side of the panel and with a reverse movement of said supporting carriage are returned to the cycle start position, so that they are then able to sand the front or rear corner of a subsequent panel.
Further features of the invention and the advantages deriving therefrom will be more apparent from the following description of a preferred embodiment thereof, shown purely by way of non-limiting example in the figures of the five accompanying drawings, wherein:

Fig. 1 shows a top plan view of a possible shape of a rounded corner of a panel to be sanded with the apparatus of the invention;
Fig. 2 shows details of the rounded corner of the panel according to the section II-II of Fig. 1 and shows a rotating head or brush profiled for smoothing the rounded corner;
Figs. 3 and 4 show laterally and in relation respectively with the front side and with the rear side of the panel, the hook that ensures precise alignment and synchronism with the panel of the smoothing apparatus adapted to operate respectively on the front corner and on the rear corner of the panel;
Figs. 5 and 6 show a perspective view of the apparatus for sanding the front corner of the panel, respectively from the side facing the panel and from the opposite side;
Fig. 7 schematically shows a plan view of the main components of the apparatus shown in Figs. 5 and 6, together with a block diagram of the electrical and fluid pressure circuit required for operation of the apparatus;
Figs. 8 and 9 are perspective views of the apparatus according to the invention in the version useful for smoothing the rear corner of the panel, the apparatus being viewed respectively from the side facing the panel and from the opposite side.

In Fig. 1 the letter P indicates, in plan view, the panel on which it is necessary to smooth the rounded corners A, the upper edge B of which can in turn be rounded, as shown in Fig. 2. Preferably, the corners A, which can also be rounded on both sides, are smoothed using abrasive rotating brushes or heads T, of known type, provided with a lateral surface T1 made of consecutive inserts of abrasive material, mounted on a body partly made of pliable- elastic material and the generatrix of which reproduces the profile both of the rectilinear part of the lateral surface and of the curved part of the edge B of the panel P.
From Figs. 5 and 6 it can be seen that the panel P is arranged on a horizontal plane and is fed, by known conveying means, not shown, with a known and constant speed in the direction indicated by the arrow F, with the longitudinal side L bearing at the ends the rounded corners A (front A' and rear A") mentioned previously, arranged parallel to the direction of feed F, cantilevered from said conveyor means and facing the apparatus M1, which in the representation of Figs. 5 and 6 is responsible for smoothing the front corner in the direction of feed A' of the panel. Parallel to the longitudinal side L of the panel P, the apparatus M1 has a linear support structure 1, of adequate length, which if necessary can be arranged for adjustment in the position in height, by means of a guide and vertical slide assembly G1 and in the transverse orientation, also by means of an assembly G2 for rotation of the structure 1 around its longitudinal axis. The assemblies G1 and G2, shown schematically in Fig. 6, are known in machines for machining the rectilinear sides L and the corners A of panels P and therefore will not be described in greater detail herein.
Fixed longitudinally on the structure 1 is at least one rectilinear guide 2 on which a main and horizontal carriage 4 slides with precision, with the interposing of one or more slides 3 with low coefficient of friction, for example recirculating ball slides, and which through a downward facing appendix 5 is connected to the moving part of a rectilinear actuator 6 fixed on the structure 1, parallel to the guide 2 and for example of the type operated by a pneumatic piston cylinder assembly or of other suitable type, by means of which the carriage can be caused to slide first in the direction F of feed of the panels P and then in the opposite direction. At the start of each work cycle, the carriage 4 is positioned on the end of the guide 2 from which it reaches the front corner A' of the panel P travelling in the direction F, so that the carriage 4, on which the smoothing means described below are mounted, can be controlled to follow the panel to sand its front corner A' and to then allow the smoothing means to disengage from the panel and allow the actuator 6 to reverse its movement, to return the carriage 4 to the cycle start position, to operate on a subsequent panel. To ensure that the carriage 4 is moved strictly at the same feed speed as the panel P by its own movement means and with a relative arrangement or precise and constant alignment with respect to the front side LA of the panel, on the corner A' of which the smoothing means mounted on the carriage 4 must operate with consequent precision, a hook 7 is arranged on the side of the carriage 4 facing the panel P (Fig. 5), able to oscillate on an ideal vertical plane, oriented with its tooth 107 facing downward and in the direction F of feed of the panels, press fitted with its stem on a shaft 8 orthogonal to the longitudinal side L of the panel P, supported rotatably by supports 9 fixed on the carriage 4 and on the end of which that projects from the opposite side of the carriage 4 (Fig. 6), there is fixed a lever 10, connected to the rod of a pneumatic piston cylinder assembly 11 the body of which is anchored to a support 12 fixed to the carriage 4. By means of the cylinder 11, the hook 7 can be taken, see also Fig. 3, from a raised position at rest, shown with a continuous line, in which it does not in any way interfere with the panel P, to a lowered working position, shown with the dashed line and controlled by limit switch means, not shown as if necessary they can be built into the cylinder 11, in which the tooth 107 of the hook 7 is arranged with its vertical surface transverse and on the path of the front side LA of the panel P, to be coupled to the side and ensure that, also with the contribution of the linear actuator 6, the carriage 4 can follow with a precise alignment and with perfect synchronism the panel P being fed in the direction F. To ensure that these conditions are met, without the hook 7 causing even the slightest damage to the front side LA of the panel, the hook 7 is taken to the lowered working position before the side LA of the panel arrives and when the carriage 4 is in the cycle start position, the actuator 6 is already activated for movement in the direction F, with a thrust such as to balance the mass of the carriage 4 and of all the components mounted thereon, so that when the side LA of the panel touches the tooth 107 of the hook 7, the carriage 4 can be made to advance substantially drawn by the panel P, with an at least initially limited contact pressure between the tooth 107 of the hook 7 and the side LA of the panel, so as to prevent even the slightest damage to the front side LA.
When the front corner A' of the panel has been sanded, the hook 7 is raised by the cylinder 11, while in correct phase the actuator 6 decreases its thrust and, if necessary, accelerates in the direction F, so that the tooth 107 of the hook can move away from the side LA of the panel without any rubbing on the side. This condition is also guaranteed by the fact that the fulcrum 8 of the hook 7 is positioned above the panel P, so that the upward oscillation of the hook 7 takes place with simultaneous detachment of its tooth 107 from the front side LA of the panel.
After this phase, the actuator 6 is operated to move the carriage 4 in the opposite direction to the feed path F of the panels and to return it to the useful position to start a new work cycle on a subsequent panel.
In Figs. 5 and 6 it can be seen that the abrasive brush T for sanding the corner A' of the panel is press fitted onto the lower end of the shaft 113 of a vertical spindle 13 fixed with interposing of a support 114 on the distal end of an arm 14 pivoted on a vertical axis 15 and fixed on the arm, with interposing of a support 214, is an electric motor 16, which by means of the belt and toothed pulley drive 17 transmits rotation to the shaft 113 and to the brush T at the correct speed and in the correct direction. A specific casing, removable and not shown, protects said drive 17.
The fulcrum 15 of the arm 14 is supported by a support 115 fixed on a secondary carriage 18 that by means of recirculating ball slides 19 slides on at least one rectilinear precision guide 20 fixed on the main carriage 4 and orthogonal to the guide 2 of the main carriage and the secondary carriage 18, by means of a downward facing appendix 21, is connected to the rod of a pneumatic piston cylinder assembly 22 fixed with the body to a support 23 anchored laterally to the main carriage 4. Due to the action of the cylinder 22, the arm 14, with the spindle 13 and with the abrasive brush T, can be taken in a movement perpendicular to the longitudinal side L of the panel P. This movement is used so that a cam follower 24 positioned coaxially and idle on the section of shaft 113 above the abrasive brush T, can read the oblique profile (see below) of a cam 25 positioned above the longitudinal side L of the panel P, which with its longitudinal axis is parallel to the longitudinal side L and which is mounted on a guide and slide structure 26 located on the front of the main carriage 4 facing the panel P and provided with lead screw means 27 to adjust the longitudinal position of the cam 25, to adapt it with precision to the needs of the apparatus and also to allow the progressive wear on the abrasive brush T to be taken up.
In Fig. 6 it can be seen that laterally to the support 114 of the motor 16 there is fixed a small arm 314, to which there is articulated the rod of a pneumatic piston cylinder assembly 28 articulated with the body to a support 29 fixed on the main carriage 4. The assembly 28 is permanently urged in extension, with the correct pressure values, to maintain the cam follower 24 constantly in contact with the profile of the cam 25. When the apparatus M1 is in the cycle start position, with the hook 7 in the lowered position for coupling to the front side LA of a panel P, the cylinder 28 has the rod extended, as shown in Fig. 5 and the rod of the cylinder 22 is retracted, as shown in Fig. 5, to arrange the secondary carriage 18 at the end of the stroke towards the flow of the panels P. As a result of said condition, respectively extended and retracted, of the cylinders 28 and 22, the arm 14 is initially positioned substantially parallel to the longitudinal side L of the panel and the cam follower 24 reads the initial convex section 125 of the profile of the cam 25, to arrange the working surface of the brush T in contact with correct interference with the front side LA of the panel, in front of the corner A' to be sanded and suitably distanced from the hook 7.
While the main carriage 4 moves forward with the panel P, to which the front side LA of which the hook 7 is anchored, the cylinder 22 of Fig. 5 is extended progressively to move the secondary carriage 18 with the fulcrum 15 of the arm 14 away from the panel, so that as the cylinder 28 of Fig. 6, which maintains the cam follower 24 adhering to the profile of the cam 25, remains pressurised, the follower is taken to read the intermediate section 225 of the profile of the cam 25, which carries the abrasive brush T to sand the whole of the extension of the curved corner A' and to be arranged on the longitudinal side L of the panel, with precise interference guaranteed by the fixed position of the cam 25 with respect to the hook 7 and by the temporary fixed anchoring of the hook to the front side LA of the panel P passing through.
During the last section of the return stroke of the secondary carriage 18, the cam follower 24 is taken to read the last section 325 of the profile of the cam 25, with the effect of moving the abrasive brush T away from the longitudinal side L of the panel, so that after or in correct phase with raising of the hook 7, the actuator 6 can be operated to reverse the stroke of the main carriage 4 and to return the apparatus to the cycle start position, behind the sanded panel and in front of a subsequent panel and, when the panel arrives, the cylinder 22 is retracted to return the apparatus to the condition shown in Figs. 5 and 6, with the cam follower 24 that once again reads the initial section 125 of the profile of the cam 25 and arranges the abrasive brush T, T1 in front of the front side LA of the subsequent panel.
It is evident how the orientation of the hook 7 and of the abrasive brush T from the top downwards and the positioning of the whole apparatus M1 at a level higher than the level at which the panels P pass through prevents dust from falling and accumulating on the various operating components of the apparatus, with the important advantages that this brings. Appropriate and simple suction means, not shown, can be provided to collect and remove the dusts produced by the sanding operation performed by the abrasive brush T.
The apparatus M1 as described above, and also the apparatus M2 described below, will be controlled by a respective processor 30 as shown schematically in Fig. 7, which will receive information on the conditions of feed and on the position in space of the front and rear sides of the panel P to be sanded, by the processing unit 31, known and belonging to the conveying system of the panels P. The processor 30 will also receive information 106, 111, 122, 128 from the limit switch means, not shown, associated with the cylinders 11, 22, 28 and with the actuator 6, or associated with the components operated by the cylinders and the processor 30 will also control an electro-pneumatic interface 32 that will operate the various pneumatic piston cylinder assemblies of the apparatus. The processor 30 will also be equipped with a connection 33 for operation of the electric motor 16 and optionally with a connection 34 to detect through optional sensors the thrust that the hook 7, in the lowered position and in the working stroke, exerts on the front LA or rear LP side (see below) of the panel, in order to operate, in a logic and safe way, the actuator 6 that drives the main carriage 4, to ensure and maintain contact between the hook 7 and the panel P, but to prevent even the slightest damage of the surface of the sides LA and LP (see below) touched by the tooth 107 of the hook 7.
Optional pressure sensors useful for the object indicated above, for example of resistive, piezoelectric or similar type, can be positioned on the tooth 107 of the hook 7 or on parts associated therewith, or can be of the type suitable to detect the degree of torsion to which the shaft 8 is subjected, or can be mounted, in the form of pressure transducers, on the cylinder 11 responsible for lifting and lowering of the hook 7, maintaining this latter in the lowered working position, to oppose the thrust exerted by the actuator means 6 and by the reaction of the panel, which tends to cause upward oscillation of the hook 7. The use of an encoder, not shown, to detect the speed of the working stroke of the carriage 4 and to allow the processing unit 30 to compare and synchronize it with the feed speed of the panels P, also falls within the scope of the invention.
An apparatus M2, shown in Fig. 8 and 9, is responsible for smoothing the rear corner A" of the panels P, the apparatus having a structure similar and substantially symmetrical with respect to that of the apparatus M1 described above and differing from this latter due to the fact that the hook 7 and the abrasive brush T will be inserted at the back of the rear side LP of the panel passing through and that the actuator 6 will be arranged to operate the main carriage 4 so as to take the hook 7, when it is lowered, into contact with the rear side LP, with a limited impact and to maintain this contact for the whole of the working stroke of the main carriage 4, with a pressure that is adequate but always limited between the hook 7 and the rear side LP of the panel. Subsequent disengagement of the hook 7 from the rear side LP of the panel is now facilitated as raising of the hook can take place simultaneously to reversal of the motion of the actuator 6.
In the claims, the references provided in brackets are purely indicative and do not limit the scope of protection of the claims.

Claims

Apparatus for automatically smoothing also rounded corners (A) of prevalently flat panels (P) made of wood and/or other material or other manufactured products, during a painting and/or finishing operation of the panels or manufactured products that by suitable means are fed along a rectilinear path, in a predetermined direction (F) and at a speed that can also be high and is known, with each subsequent panel (P) that has, parallel to the path, a longitudinal side (L) with the front (A') and with the rear (A") corners to be smoothed facing smoothing means (T), characterised in that the smoothing means (T) are mounted on a carriage (4) sliding on a guide (2) rectilinear and parallel to the direction (F) of feed of the panels (P), the carriage (4) being connected to reciprocating motion means (6) and such that, with the help of alignment and hooking means (7), the carriage (4) can be controlled to accompany the panel (P) in its forward movement, proceeding at the same speed as it and with a fixed and predetermined relative position or alignment, so that the smoothing means (T) located on the carriage (4) can sand the rounded front (A') or rear (A") corner of the panel (P) and can then be moved away from the longitudinal side (L) of the panel to allow the return of the carriage (4) with the smoothing means to the cycle start position, be able to operate on a subsequent panel, it be provided that, on the side of the carriage (4) facing the longitudinal side (L) of the panel (P) there is arranged a hook (7), forming said alignment and hooking means, which is connected to motion means (11) adapted to take the hook (7) from a raised position at rest, above the panel (P) and without interfering with it, to a lowered working position controlled by limit switch means, in which the tooth (107) of the hook (7) is arranged with a vertical surface thereof, transverse on the path of the front side (LA) or of the rear side (LP) of the panel (P), to be able to be coupled to the side and so that, also with the contribution of its linear motion actuator (6), the carriage (4) can follow the panel (P) that is fed in the direction (F), with precise alignment and perfect synchronism.
Apparatus according to claim 1,
wherein said carriage (4) and the smoothing means (T) located on the carriage, are positioned at a higher level than the level at which the panels (P) pass through, so as not to be soiled by the dusts produce by smoothing.
Apparatus according to claim 1,
characterised in that the hook (7) positioned on the side of the carriage (4) facing the part of the longitudinal side (L) of the panel (P), is press fitted with its stem on a shaft (8), orthogonal to said longitudinal side (L) of the panel (P), supported rotatably by supports (9) fixed on the carriage (4) and on the end of which that projects from the opposite side of the carriage (4) there is press fitted a lever (10), connected to the rod of a pneumatic piston cylinder assembly (11), which with its body is anchored to a support (12) fixed to the carriage (4), all so that by means of the cylinder (11), the hook (7) can be taken from said raised position at rest, above the panel (P) and without interfering with it, to said lowered working position.
Apparatus according to claim 3,
characterised in that in the version (M1) of the apparatus responsible for smoothing the front corner (A') of each panel (P), the hook (7) is oriented so as to be able to couple to the front side (LA) of the panels, there being provided means through which the hook (7) can be taken to the lowered working position in front of and before the front side (LA) of the panel arrives and there also being provided means to ensure that already when the carriage (4) is in the cycle start position, the related rectilinear motion actuator (6) is activated in the working stroke with a thrust such as to balance the mass of the carriage (4) and of all the smoothing components mounted thereon, so that when the front side (LA) of the panel touches the tooth (107) of the hook (7), the carriage (4) is made to advance substantially drawn by the panel (P), with a limited but constant contact pressure between the tooth (107) of the hook (7) and the front side (LA) of the panel, so as to prevent even the slightest damage to the front side (LA).
Apparatus according to claim 3,
characterised in that in the version (M2) of the apparatus responsible for smoothing the rear angle (A") of each panel (P), said hook (7) is oriented so that it can be coupled to the rear side (LP) of the panels and in that it comprises means through which the hook (7) can be taken to the lowered working position, behind the rear side (LP) of the panel that has passed by it and there are provided means through which the motion actuator (6) advances the carriage (4) with the smoothing means (T) so as to bring the tooth (107) of the lowered hook (7) into contact with the rear side (LP) of the panel, with an impact that is limited and such as to maintain the contact for the whole of the working stroke of the main carriage (4), with a pressure between the hook (7) and the rear side (LP) of the panel that ensures said conditions of synchronism and alignment, but prevents even the slightest damage of the rear side (LP) of the panel.
Apparatus according to one of the preceding claims, characterised in that it comprises sensors to detect the pressure between the tooth (107) of the hook (7) and the front (LA) or rear (LP) side of the panel (P) during the working stroke of the main carriage (4) by its motion means (6), the sensors being positioned on the tooth (107) of the hook (7) or on parts associated therewith, and which can be of resistive, piezoelectric or similar type, or suitable to detect the degree of torsion to which the pivot shaft (8) of said hook (7) is subjected, or be positioned, in the form of pressure transducers, on the cylinder 11 responsible for lifting and lowering of the hook (7).
Apparatus according to one of the preceding claims, characterised in that each apparatus (M1, M2) is controlled by a respective processor (30) that receives information on the conditions of feed and on the position in space of the front (LA) and rear (LP) sides of the panels (P) to be sanded, by the processing unit (31), known and belonging to the conveying system of the panels (P) and which also receives information (106, 111, 122, 128) from the limit switch means associated with the pneumatic cylinders or with the components of the apparatus (M1, M2) operated by the cylinders, there being provided means to allow the processor (30) to control an electro-pneumatic interface (32) that provides for logic operation of the various pneumatic piston cylinder assemblies of the apparatus, the processor (30) also be provided with a connection (33) for operation of the rotation motor of the smoothing means (T) and with an optional connection (34) for detecting the signal coming from said sensors of the thrust occurring between the hook (7) and the front or rear (LA, LP) side of the panel, in order to operate the drive actuator (6) of the main carriage (4) logically, to ensure and maintain the contact between the hook (7) and the panel (P), simultaneously preventing even the slightest damage of the surface of the sides (LA, LA) touched by the tooth (107) of the hook (7).
Apparatus according to claim 1,
characterised in that the smoothing means comprise an abrasive brush (T) whose working surface (T1) has a generatrix that reproduces the profile of the corner (A', A") to be smoothed and the brush is press fitted on the lower end of the shaft (113) of a vertical spindle (13) fixed on the distal end of an arm (14) pivoted on a vertical axis (15) and on the arm there is fixed an electric motor (16) that by means of a drive (17) rotates said shaft (113) with the brush (T, T1) at the correct speed and in the correct direction, said fulcrum (15) being supported by a support (115) fixed on a secondary carriage (18) that by means of slides (19) slides on at least one rectilinear guide (20) fixed on the carriage (4) and orthogonal to the guide (2) of the carriage (4) and the secondary carriage (18) is connected to the rod of a pneumatic piston cylinder assembly (22) anchored with the body laterally to the carriage (4) and due to the action of which, a cam follower (24) positioned coaxially and rotatably on the section of shaft (113) above the abrasive brush (T, T1), can read the oblique profile of a cam (25) positioned above the longitudinal side (L) of the panel (P), which with its longitudinal axis is parallel to the longitudinal side (L) and which is mounted on a guide and slide structure (26) fixed on the front of the main carriage (4) facing the panel (P) and provided with lead screw means (27) to adjust the longitudinal position of the cam (25), to adapt it with precision to the needs of the apparatus and also to allow the progressive wear on the abrasive brush (T, T1) to be taken up.
Apparatus according to claim 8,
characterised in that said cam follower (24) is constantly thrust against said cam (25) by a pneumatic piston cylinder assembly (28) that interacts between said arm (14) and a support (29) anchored to the carriage (4), it being provided that when the apparatus (M1, M2) is in the work cycle start position, with the hook (7) in the lowered position to be coupled to the front (LA) or to the rear (LP) side of a panel (P), said cylinder (28) has the rod extended and said cylinder (22) has the rod retracted, to arrange the secondary carriage 18 at the end of the stroke towards the flow of panels (P), with the arm (14) substantially parallel to the longitudinal side (L) of the panel and with the cam follower (24) that reads an initial convex section (125) of the profile of the cam (25) to arrange the working surface of the brush (T,T1) in contact with correct interference with the front or rear side (LA, LP) of the panel, in front of or behind the corner (A', A") to be sanded and suitably distanced from the alignment hook (7).
Apparatus according to one of the preceding claims, characterised in that due to the action of said processing unit (30), while the main carriage (4) advances with the panel (P) to the front (LA) or rear (LP) side of which the hook (7) is anchored, said cylinder (22) is extended progressively to move the secondary carriage (18) with the fulcrum (15) of the arm (14) away from said panel, so that as the cylinder (28) that maintains the cam follower (24) adhering to the profile of the cam (25) remains pressurised, the follower (24) is taken to read an intermediate section (225) of the profile of the cam (25), which takes the abrasive brush (T, T1) to sand the whole of the extension of the curved corner (A', A") of the panel and to be arranged on the longitudinal side (L) of the panel, with precise interference guaranteed by the fixed position of the cam (25) with respect to the hook (7) and by the temporary fixed anchoring of the hook to the front or rear side (LA, LP) of the panel (P) passing through, it being provided that during the last section of the return stroke of the secondary carriage (18), the cam follower (24) is taken to read a last section (325) of the profile of the cam (25), with the effect of moving the abrasive brush (T) away from the longitudinal side (L) of the panel, so that in correct phase with raising of the hook (7), the actuator (6) can optionally be operated to modify its speed and to reverse the stroke of the main carriage (4), to return the apparatus (M1, M2) to the cycle start position, in front of or behind a subsequent panel (P) and when the panel arrives, the cylinder (22) is retracted so that the cam follower (24) once again reads the initial section (125) of the profile of the cam (25), with the abrasive brush (T, T1) positioned in front of or behind the front or rear side (LA, LP) of the subsequent panel (P).