BELT SANDING MACHINE

Abstract: When sanding for instance panelled doors in a belt sanding machine it must be prevented that transverse­ ly extending parts (16) are sanded since it would be harmful to sand across the direction of the veins of the wood. A machine according to the invention is therefore provided with a combined sensing and con­ trol device which in a simple and effective manner will prevent damage caused by the sanding process by controlling the contact of the sanding belt with the workpiece. The device consists of a disc (14, 20) which is mounted on the sanding equipment. The disc (14, 20) protrudes a distance beyond the sanding position of the sanding belt (15), in order that the disc will sense the workpiece when this is moved under the sanding belt. When the disc (14, 20) rolls across a frame piece (16) the sanding belt (15) is pivoted up above the wood, and when the disc (14, 20) meets a sunken part (18), the sanding belt (15) is pivoted to a non-sanding position.

Description: The invention relates to a belt sanding machine having at least a lower and an upper turning roller and an endless sanding belt extending around said turning rollers for sanding wooden workpieces consisting of frame pieces around panellings, said panellings being recessed in relation to the frame pieces, and where the workpieces are carried forward on a conveyor belt below the sanding belt. Machines of this type are particularly used within the furniture industry for sanding and polishing panelled doors and similar objects which are built of wooden frame pieces whose grains extend in opposite directions. In order to avoid causing damage to the wood, it has to be sanded along its grains, and this means that a workpiece must be sanded in at least two varying directions in order for the frame parts to be sanded along its grains. Add to this that the sanding must be commenced and finished in the centre part of the workpiece in order to avoid damage to the frame pieces that extend transversly along the outer side. Hitherto known machines for this purpose are extremely complicated and difficult to use, because they require a uniform product and a correspondingly precise conveyance below the sanding belt for each setting. Moreover, such machines are very expensive. The machines are based on a sanding principle that comprises one or more thrust pads extending behind the sanding belt, which thrust pads can be actuated for pressing down the sanding belt towards the workpiece on a signal from an impulse transmitter. Similarly, the pressure against the sanding belt may be discontinued and the sanding stopped when the pressure of the thrust pad against the sanding belt is discontinued. An example of such a construction is described in German published specification no. 1,148,465. This known construction thus comprises a separate sensing device which senses the item during its travelling below the sanding belt, and which produces a signal to a thrust pad which adjusts the position of the sanding belt in relation to the surface of the item. This is a complicated and poor solution, in that it cannot be avoided that considerable friction between the thrust pad and the sanding belt occurs when the sanding belt is pressed against the item. Add to this the complex construction of the sensory and adjustment equipment, and the use of signals which must be converted into adjustment signals for the pressure device. It is the object of the invention to overcome these drawbacks of the known machines, and this object is obtained by a belt sanding machine of the initially mentioned type the said belt sanding machine according to the invention being characteristic in that the lower turning roller cooperates with the workpieces and performs the sanding operation, that the lower and upper turning roller are mounted on a plate part, which is pivotally mounted on the machine frame in such a manner that when the plate part rotates, the lower turning roller is lifted from or lowered to the workpiece, and that a mechanical sensing device is adjustably connected to the plate part and projects from the bottom of the lower turning roller towards the workpiece in order to sense the panellings and lift the lower turning roller from the workpiece, when the mechanic sensing device contacts a frame piece, which must not be sanded. By an extremely simple and reliable method a sanding belt machine is hereby achieved where the lower turning roller with the sanding belt is capable of adjusting itself to the shape of the workpiece merely by means of a mechanical sensing device which exerts a direct influence on the position of the lower turning roller in relation to the workpiece. Programming, remote monitoring, thrust pads and connection means are hereby eliminated. By, as described in claim 2, designing the mechanical sensing device as a disc which can roll across the workpiece when this is conveyed below the sanding belt and which by its contact to the workpiece determines the position of the sanding belt, there is obtained a completely reliable and precise adjustment of the sanding process. By, as described in claim 3, attaching the disc to an arm the sensing may be displaced in relation to the actual sanding belt, and it becomes possible to sand items where the lowering is displaced in relation to the required sanding point. It is expedient, as described in claim 4, to be able to adjust the position of the disc in relation to the sanding belt in that it thereby becomes possible to adapt the machine to any required workpiece. By, as described in claim 5, mounting the disc directly on the axle of the lower turning roller, there is obtained a simple and strong construction. Finally, it is expedient, as described in claim 6, to arrange the disc on the axle of the lower turning roller by means of an eccentric ring which can be secured to the axle, because this construction is very simple and reliable. In the following the sanding belt machine according to the invention will be described in closer detail with reference to the drawing, wherein fig. 1 is a cross section of a sanding belt machine according to the invention seen in the direction I-I in fig. 3, fig. 2 shows the machine seen from the feed end of the workpiece, fig. 3 is a top view of the machine. fig. 4 is a cross section of a second embodiment of the sanding belt machine according to the invention, and fig. 5 shows this embodiment seen from the feed end of the workpiece. In the drawing there is shown an example of two embodiments of a belt sanding machine according to the invention, and in schematic form, in that the frame of the machine is not shown, whereas merely those components as take part in the actual sanding and adjusting operation of the machine are shown. The actual sanding unit comprises a plate part 5 which is pivotally mounted to an axle 6 extending across the machine. On this plate part 5 a drive motor 7 is provided which over a shaft 4 drives an upper turning roller 3. At the lower end of the plate a lower turning roller 1 is mounted, said roller rotating on an axle 2. An endless sanding belt 15 runs on these two turning rollers 1, 3. At the top of the plate part 5 there is moreover mounted a horizontally extending pin 8 on which a bearing 9 is arranged. Moreover, a sliding part 10 is mounted on the frame of the machine above this bearing 9, said sliding part being vertically adjustable. When the plate part 5 is tilted around the axle 6 the lower turning roller 1 is lifted and lowered in relation to the underlying conveyor belt 19 extending endlessly in the direction of the arrow. The sliding part 10 forms a stop for the position of the sanding belt 15 in relation to the conveyor belt 19 so that it is possible to adjust the sanding depth by adjusting the vertical position of the sliding part 10. A disc or roll 14 is mounted on the plate part 5, as shown in figs. 1-3, said disc being rotatably mounted on a spindle 13 fitted to an arm 12 which in turn is attached to the plate part 5 over a stay 11. The disc 14 protrudes a distance down below the sanding belt 15 and may furthermore be adjusted in relation to the lower turning roller 1 and the sanding belt 15, both in relation to the workpiece and in relation to the point of contact between the sanding belt and the workpiece. This may take place by extending the arm 12 and/or by changing its angle in relation to the plate part 5. In a second embodiment shown in figs. 4 and 5 a disc 20 is rotatably mounted directly in continuation of the axle 2 of the lower turning roller 1, which simplifies the construction considerably. This embodiment may of course only function if the disc 20 has a radius which is larger than the total radius of the lower turning roller 1 and the sanding belt 15 in order to ensure that the sanding belt may be lifted free from the workpiece by pivoting around the axle 6 when the rim of the disc 20 encounters an obstacle. Furthermore, the disc 20 is mounted on an eccentric ring 21, shown by a dotted line in fig. 4, which can be attached to the end of the axle 2 by means of a disc 22 and a clamping bolt 23 screwed into the end of the axle 2. By slackening the bolt 23 the eccentric ring 21 can be turned in relation to the axle whereby the position of the disc 20 in relation to the sanding belt 15 can be adjusted. This is expedient, especially in connection with workpieces with a small difference of level between those areas that must be sanded and those that should be sensed by the disc 20. The mode of operation of the device will now be described in closer detail. The workpiece, as shown in the drawing, is a panelled door, which is built of wooden frame pieces 16 surrounding a panel 17 so that there is a difference in level between the frame and the panelling. The panel 17 is moreover chamfered at the frame 16 in order that a depression 18 is formed along the frame 16. When the workpiece is inserted on the conveyor belt 19 the frame 16 which is to be sanded, is placed opposite the sanding belt. The conveyor belt conveys the workpiece, and the disc 14, 20 will at the beginning of the movement roll on the frontmost transverse wooden frame piece thereby lifting the sanding belt and preventing sanding across the wooden frame piece, as shown in fig. 2, thereby avoiding to cause damage to this piece. When the workpiece is further conveyed, the disc 14, 20 will slide down in the depression 18, as shown in figs. 1, 3, 4 and 5, and the sanding belt will be lowered and reach sanding contact with the longitudinal frame part 16 in the direction of its grains. When sanding of this frame part 16 is finished, the disc 14, 20 will again roll across the rearmost longitudinal frame part 16 and thereby lift up the lower turning roller 1 and the sanding belt 15 to an inactive position. In this manner it will be possible to sand the inner frame pieces along their grains without touching the parts extending across the sanding direction, merely by adjusting the disc 14, 20 in relation to the recessed part. By adjusting the sliding part 10, it becomes possible to adjust the sanding depth and thereby ensure that the workpiece obtains the required thickness.

Claims: 1. Belt sanding machine having at least a lower (1) and an upper turning roller (3) and an endless sanding belt (15) extending around said turning rollers (1, 3) for sanding wooden workpieces consisting of frame pieces (16) around panellings (17), said panellings (17) being recessed in relation to the frame pieces (16), and where the workpieces are carried forward on a conveyor belt (19) below the sanding belt (15), characterized in that the lower turning roller (1) cooperates with the workpieces and performs the sanding operation, that the lower (1) and upper turning roller (3) are mounted on a plate part (5), which is pivotally mounted (6) on the machine frame in such a manner that when the plate part (5) rotates, the lower turning roller (1) is lifted from or lowered to the workpiece, and that a mechanic sensing device (14, 20) is adjustably connected to the plate part (5) and projects from the bottom of the lower turning roller (1) towards the workpiece in order to sense the panellings (17) and lift the lower turning roller (1) from the workpiece, when the mechanic device (14, 20) contacts a frame piece (16), which must not be sanded. 2. Belt sanding machine according to claim 1, characterized in that the mechanical sensing device comprises a roll or disc (14) which is rotatably mounted to a spindle (13) extending parallel to the axle of rotation (2) of the lower turning roller (1), which disc (14) protrudes a distance beyond the sanding belt (15) where this has sanding contact with the workpiece (16). 3. Belt sanding machine according to claim 2, characterized in that the axle of rotation (13) of the disc (14) is attached to an arm (12) being attached to the plate part (5) parallel to the axle of rotation (2) of the lower turning roller (1). 4. Belt sanding machine according to claim 3, characterized in that the position of the disc (14) in relation to the sanding belt (15) can be adjusted. 5. Belt sanding machine according to claim 1, characterized in that the mechanical sensing device comprises a roll or disc (20) which is rotatably mounted on the axle (2) of the lower turning roller (1) and has a radius which is somewhat larger than the total radius of the lower turning roller (1) and the sanding belt (15). 6. Belt sanding machine according to claim 5, characterized in that the disc (20) is arranged on the axle (2) of the lower turning roller (1) by means of an eccentric ring (21) which can be secured (22, 23) to the axle (2).

Inventors: HUNDEBOL, KELD OTTING
Applicants: HH PATENT APS
Application year: 1988
Main classification: B24B21
IPC codes: B24B21, B24B19