The present invention relates to the fitting of abrasive belts to sanding machines, as per the preamble of claim 1. An example of such a device is disclosed in US-A-5 185 963.
At present, there are various types of sanding machines known to the trade; this invention is concerned with the so-called traverse sanders in which an endless abrasive belt is fitted over end pulleys which keep it tensioned and transmit drive motion to it. An example of this type of configuration is illustrated in Fig. 1 which shows a known type of double belt combination sander: the first belt N1 is fitted over a pair of end rollers or drums T1 and T2, whilst the second belt, N2, is fitted over three drums, two of which (T3 and T4) define a lower branch running parallel to the panel P to be worked, whilst the remaining drum T5 at the top acts as a tensioning element.
Inside the two lower drums (T3 and T4) of the second belt, there are a number of actuators or pushing shoes S which push the belt against the panel in order to improve the points or areas of contact between the abrasive and the work. A machine of this kind is described in patent publication US-4.651.474.
The most common problem encountered during operation of these machines is caused by the fact that the belts must be changed frequently, either because they are worn or because of differing work requirements. Changing may be necessary as often as ten or even more times a day. Each time the belt is changed, the operator must first slacken the belt rollers, remove the worn belt and fit a new belt from the spares department. The most critical stage in this operation is without doubt the placing of the belt over the drums, especially if it is considered that in some of the latter generation machines (superfine finishers), the belts are some metres long and wide and the upper drums are so high that the operator does not have direct access to them. This makes it difficult to handle the belts, creates hazardous situations for the operator and the possibility of damaging the abrasive surface of the belts themselves (extra fine grain), not to mention the downtime involved.
Various solutions have been devised to facilitate the belt changing operation, all based on the use of belt "guides" of various kinds. In one solution, the guides are fitted above and below the drums and, in practice, consist of fixed plates in the shape of cylinder or cone portions surrounding the visible end of the belt mounting drums. This solution does not, however, satisfy the aforementioned requirements and only partially facilitates belt changing.
Another solution, disclosed in patent publication US-5.185.963, envisages the use of an element formed by a "U" section hinged near the upper drum and driven by a pneumatic cylinder from a rest position, where the U section is vertical in such a way as to close the belt guards, to a work position, where it is at 90° to the previous position and with the cylindrical portion axially aligned with the generatrices of the upper drum. In this way, when removing the old belt and putting on the new one, the operator can rest the belt on the surface of the U section. The basic element of this solution, however, although it certainly facilitates belt changing, especially in the case of very tall machines, remains a passive element, in practice an appendage or guide of reducible size.
An improvement along the same lines is disclosed in patent publication JP-62-24957 where the supporting U section is no longer simply hinged to the machine frame but is mounted on an arm which can move vertically and rotate about the end of a first arm which is in turn hinged to the end of a second arm pivoted to the machine, all the said pivots being vertical. The U section can therefore assume a number of different configurations both in height and horizontally, while remaining parallel to itself, thus making it easier to manipulate the belt, even at considerable heights. In this solution, too, no automatic drive systems are envisaged and fitting the belt still depends on the operator's ability to manoeuvre the device using the handle.
Yet another disclosure is described in patent application IT-VI93A000019 where the supporting U section is hinged to a carriage which runs along a vertical rail attached to the machine frame. The carriage is equipped with a motor, which drives it along the rail in both directions, whilst the supporting U section can be turned on its hinge by a hydraulic cylinder linked to the carriage. This type of solution is expensive to make and must have at least two drive units, which, together with the front railing, unduly encumber the machine, making it difficult for the operator to gain access to the front of the machine itself.
The object of the present invention is to overcome the aforementioned disadvantages by providing a device for facilitating the fitting of abrasive belts to sanding machines that is at once simple and practical and that does not interfere with the other parts of the machine, allowing the abrasive belt to be rapidly changed thanks to a simple, economical mechanism structured in such a way as to also automate the handling of the abrasive belt.
The technical characteristics of the invention are laid out in the claims below and the advantages of the disclosure are apparent from the detailed description which follows, with reference to the accompanying drawings, which illustrate preferred embodiments of the invention by way of example and in which:
With reference to the above listed accompanying drawings, in particular, Fig. 2, the sanding machine equipped with the device disclosed by the present invention to facilitate the fitting of the abrasive belt is of the so-called "large-belt", traverse type. This kind of machine generally consists of a fixed frame 50 supporting one or more sanding units 1 for wooden panels 2; each of the said units 1 is made up of a plurality of parallel, end rollers or drums 4, over which an abrasive belt 3 is placed and of which one is motor-driven (usually the lower one 4i) while the other, 4s, is idle and acts as a tensioner. The rollers 4s and 4i are parallel to each other and mounted above a conveyor belt 5 which carries panels 2 in a direction F: the panel 2 therefore moves under the active branch of the belt 3 and its surface machined as it passes.
As shown schematically in Fig. 2, the top roller 4s is supported by a cradle 4c which is in turn linked to the stem of an actuating cylinder 4d which moves the cradle up and down in such a way as to tension and slacken the abrasive belt 3. The actuating cylinder 4d is located between the end rollers 4s and 4i and defines within the machine a hollow space 7 between said rollers 4s and 4i and said belt 3 whose size H (see Fig. 3) depends on the distance between the rollers themselves measured on a vertical axis Z of the machine from a horizontal reference plane (not illustrated) of the machine itself.
The rounded upper surface 6 of the top roller 4s over which the belt 3 runs corresponds to, and comes into alignment with, the U shaped upper surface 8s (in practice a U section) of a guide element 8 for the loading and unloading of the belt 3, the machine being equipped with one guide element 8 for each sanding unit 1 fitted.
In the solution disclosed by the present invention (again, see Fig. 2), the guide element 8 is axially parallel to the rollers 4s and 4i and is connected by a four-point linkage mechanism 12 to the frèe end of a supporting element 11 placed inside the aforesaid hollow space 7.
The four-point linkage mechanism 12 (described in more detail below) moves the guide element 8 between a plurality of intermediate positions in the two directions indicated by the arrow F1 in Fig. 2, while allowing the guide element itself to remain axially parallel to the end rollers 4s and 4i.
Fig. 2 shows the three main positions which may be assumed by the guide element 8, namely: a least extended rest position where the guide element 8 is completely inside the hollow space 7; a belt 3 loading/unloading position where the guide element 8 is partially outside the limits defined by the rollers 4s and 4i and at a height H1 less than the height of the top roller 4s from the aforesaid reference plane; and, lastly, a fully extended, work position where the guide element 8 is completely outside the limits defined by the rollers 4s and 4i and aligned with the top roller 4s in such a way that its upper surface 8s forms an extension of the roller itself.
Looking now in more detail, with reference also to Fig. 3, the four-point linkage mechanism 12 consists of a first arm 9 the ends of which 9a and 9b are pivoted to the aforesaid supporting element 11, which includes a second arm 10, and to the guide element 8, respectively. The arm 9 can rotate about its axis B, transverse to the axes of the rollers 4s and 4i, and located in the middle of the guide element 8. On the first end 9a of the first arm 9 pivoted to the second arm 10 there is envisaged a first sprocket-wheel 14 that meshes with a first endless chain 13 fitted over another first sprocket-wheel 15 that is driven by a known gearmotor unit 15m and located at the other end of the second arm 10.
Each of the first sprocket-wheels 14 and 15 is externally keyed through pins 14p and 15p to the first arm 9 and to the second arm 10, respectively, in such a way that, when the motor is activated, the first arm 9 can rotate about its axis B. Between the first arm 9 and the guide element 8 there is envisaged a second endless chain 16 fitted over second sprocket-wheels 17 and 18 (which, in the embodiment illustrated, have a double set of sprockets), one of which is internally keyed to the first arm 9 and attached to the corresponding sprocket-wheel 14 of the first chain 13, whilst the other is rotatably mounted on a pin 18p located inside the guide element 8 in such a way that, when the first arm 9 is rotated, the guide element 8 remains parallel to the end rollers 4s and 4i even when its position is changed in height.
In practice, the second chain 16 and the related sprocket-wheels 17 and 18 create a four-point linkage mechanism R-S-T-U forming a parallelogram-whose small sides RU and ST are defined by the diameter of the sprocket-wheels 17 and 18, whilst the long sides RS and UT are defined by the two branches of the second chain 16 (see Fig. 2).
During the rotation of the first arm 9, therefore, the two chains 13 and 16 rotate in opposite directions but the latter enables the axial position of the guide element 8 to remain unchanged irrespective of the angular position assumed by the first arm 9.
To avoid interference between the first arm 9 and the guide element 8 during the rotation of the first arm 9, a gap 8a is envisaged at the end of the arm nearest the pivot point B between the two elements (see Fig. 5 in particular).
With reference to Fig. 2 again, it may be noted that the aforesaid hollow space 7 contains a frame 19 formed partly by the aforesaid actuating cylinder 4d, which is connected to a first unit 20 that supports the top roller 4s, while at the bottom there is a vertical bar, constituting the aforesaid support element 11 and joining the first support unit 20 to a similar second unit 21 that supports the lower roller 4i; the vertical bar 11 is also linked to the second arm 10 which extends horizontally.
The hollow space 7 also contains means 22 for detecting the guide element 8 when the latter is at the aforesaid rest and work positions. The detecting means 22 may consist of microswitches 22i mounted on the vertical bar 11 inside the hollow space 7 and on one of the outer corners of the first support unit 20 of the top roller 4s. The microswitches 22i operate directly on the motor 15m so as to stop or start the four-point linkage mechanism 12 when the two positions are reached.
Fig. 4 illustrates an improved embodiment of the guide element 8, used preferably for tall machines, where the guide element 8 itself is equipped with means 23 for moving the abrasive belt 3 towards and away from the top roller 4s. The means 23 consist of a first endless conveyor belt 24 fitted over two transmission pulleys 25, one keyed at the end of the guide element 8 and the other at a point in the central portion of the guide element 8 near the pivot point B. The latter pulley, labelled 25a, is driven by a gearmotor 26 mounted by the guide element itself and designed to drive the conveyor belt 24 in both directions.
Another improved embodiment of the abovementioned solution is illustrated in Fig. 5, where the guide element 8 is again equipped with a first endless conveyor belt 24 fitted over the transmission pulleys 25 but where the first pulley 25a is driven indirectly through a first endless transmission belt 26 fitted over a second pair of pulleys 27 and 28: the first of these pulleys 27 is keyed to a first shaft 29 coaxially and directly to the aforesaid first pulley 25a, whilst the other pulley 28 is keyed to the end of a second shaft 30 passing through the guide element 8 at the linkage point B.
At the same end where the second pulley 28 is keyed, the second shaft 30, which is concentric with the pin 18p but separate from it, rotatably mounts a third pulley 31 over which there is a second endless transmission belt 32 driven by a fourth pulley 33 driven by a gearmotor 33m and keyed to the second arm 10 through a corresponding third shaft 34. This solution too is capable of automating the handling of the abrasive belt 3 but at the same time lightens the structure of the guide element 8.
The dashed line in Fig. 5 shows a constructional variation of the first conevyor belt 24. In this variation, the conveyor belt 24 may be divided into two smaller belts 24a and 24b (or toothed belts), both narrower but longer than those of the previous solutions, extending along the entire length of the guide element 8 and located on opposite sides of the first arm 9. Each belt 24a and 24b is endless and fitted over corresponding pairs of wheels 24r mounted on the vertical sides of the guide element 8, two of the said wheels being motor-driven in the same way described in the previous paragraph.
To fully automate the handling mechanism of abrasive belt 3 in the two embodiments just described, the device may be equipped with abrasive belt 3 loading means 40, placed above the top roller 4s and operating in both directions parallel and in contact with the upper surface 6 of the top roller. The loading means 40 consist of a second endless belt 41, which can run in both directions, hinged at one of its end pulleys 41a and driven by a cylinder 42 to rotate about the said pulley from a working position in which it is in contact with the upper surface of the roller 4s (see Fig. 2) to a rest position in which it is not in contact with the roller 4s, that is to say, it is in a raised position.
The device disclosed by the present invention can be used to change the abrasive belt 3 as follows, starting with the machine idle.
The machine guard or door is opened and the change routine started, using preferably a control unit CE located inside the hollow space 7. The routine runs as follows:
Although the routine described above could be varied slightly and the various stages combined differently, it shows the basic operation of the device and the considerable advantages for the operator in terms of safety and easy operation. These advantages are particularly evident when the abrasive belt to be changed is very wide and long and the top roller of the machine is so high up as to be out of the operator's reach.