Technical field of the invention

This invention relates to a device for automatic grinding of a saw chain, which device comprises chain guides, means for feeding the saw chain forward along the chain guides, means for fixing the saw chain relative to the chain guides, and means for positioning a rotatable grinding disc which forms part of the device and which is switchable between two positions for grinding of right links and left links. The invention relates also to a method for automatic grinding of saw chains.

State of the art In the grinding of saw chains it is important that both the cutting tooth and the depth gauge are ground, which normally involves a number of grinding operations.

A grinding disc known from WO 2007/050006 is for simultaneous grinding of a cutting tooth which forms part of a saw chain and the relating depth gauge, which grinding disc has a first cutting surface in the region of its periphery and a second cutting surface which may have the shape of a circular cylinder or a truncated cone. As described in WO 2007/050006, the grinding disc has to be made in a number of configurations to suit different saw chains available on the market. The grinding disc is preferably faced with boron nitride, which makes it expensive.

Objects and features of the invention A primary object of the present invention is to propose a device of the kind defined above in which a grinding disc of standard configuration is used to grind both cutting teeth and depth gauges.

Another object of the present invention is that grinding of cutting teeth and depth gauges should take place in separate grinding processes.

A further object of the present invention is that grinding a cutting tooth and an associated depth gauge should take place in a number of consecutive grinding stages. Yet another object of the present invention is to effect grinding of the portion of the saw chain which extends between the cutting tooth and the depth gauge.

At least the primary object of the present invention is achieved by a device and a method having the features indicated in the independent claims set out below. Preferred embodiments of the inventions are defined in the dependent claims.

Brief description of the drawings

An embodiment of the invention is described below with reference to the attached drawings, in which: Fig. 1 depicts a side view of a device according to the present invention for automatic grinding of saw chains;

Fig. 2 depicts an end view of the device in Fig. 1; Fig. 3 depicts a plan view of the device in Fig. 1; Fig. 4 depicts a perspective view of the device in Fig. 1, in which a grinding disc forming part of the device assumes an inactive position;

Fig. 5 depicts a perspective view of the device in Fig. 1, in which a grinding disc forming part of the device assumes an active position;

Fig. 6A depicts a section along A-A in Fig. 1 or 4, illustrating in plan view a control mechanism of the device according to the present invention;

Fig. 6B depicts the position which the grinding disc of the device assumes when the control mechanism is in the position depicted; Fig. 7A depicts a section along A-A in Fig. 1 or 4, illustrating in plan view a new position for the control mechanism of the device according to the present invention;

Fig. 7B depicts the position which the grinding disc of the device assumes when the control mechanism is in the position depicted; Fig. 8A depicts a section along A-A in Fig. 1 or 4, illustrating in plan view a new position for the control mechanism of the device according to the present invention;

Fig. 8B depicts the position which the grinding disc of the device assumes when the control mechanism is in the position depicted;

Fig. 9A depicts a section along A-A in Fig. 1 or 4, illustrating in plan view a new position for the control mechanism of the device according to the present invention; Fig. 9B depicts the position which the grinding disc of the device assumes when the control mechanism is in the position depicted; Fig. 1OA depicts a section along A-A in Fig. 1 or 4, illustrating in plan view a new position for the control mechanism of the device according to the present invention; and

Fig. 1OB depicts the position which the grinding disc of the device assumes when the control mechanism is in the position depicted.

Detailed description of a preferred embodiment of the invention

A saw chain comprises cutting teeth which are normally angled respectively to left and right alternately. The device in Figs. 1-3 for grinding of saw chains comprises generally a frame 1 which has means for supporting rotatably a grinding disc 3 which performs grinding operations on the saw chain S, only part of which is depicted in Figs. 1- 3. The saw chain S is supported by chain guides 4. The means for supporting the grinding disc 3 comprises a support arm 5 and a cover 9 which is attached pivotably to the support arm 5 via a first articulation 7 and which itself supports a first electric motor 10 which has the grinding disc 3 mounted on its shaft. The support arm 5 is connected to a first support element 11 which has an extent in the height direction of the device. The support arm 5 has a shoulder 6. The first support element 11 has an upper first bracket 12, a lower second bracket 13 and an intermediate third bracket 14. The device according to the present invention has also a generally U-shaped second support element 15, the bottom 16 of the U is in the plane of the paper in Fig. 4 and the limbs 17 of the U are perpendicular to the paper. In the region of its one end, the first support element 11 is connected pivotably via the brackets 12, 13 to the second support element 15 by means of a first spindle 18 which is accommodated pivotably in the limbs 17 of the U-shaped second support element 15 and which has its ends connected to the brackets 12, 13. In the region of its other end, the U-shaped second support element 15 is connected pivotably to the frame 1, which connection is effected by means of a second spindle 19. Changing over between grinding of right and left links respectively involves the second support element 15 being pivoted relative to the frame via the second spindle 19. This is effected by means of a second electric motor 20 (not depicted in Fig. 4) connected via a strut 21 to the second support element 15. The result is that the first support element 11 and the grinding disc 3 attached to it move in conjunction and assume a new grinding position. Pivoting the grinding disc 3 relative to the frame 1 is in principle prior art, but the constructional configuration with an articulatable fastening between the first support element 11 and the second support element 15 is novel and unique to the present invention. An aperture 22, see Figs. 4 and 5, the function of which will be explained below, is provided in the bottom 16 of the second support element 15. A stop screw 23, see Fig. 7A, the function of which will be explained below, is also fitted in the bottom 16 of the second support element 15. A lifting arm 25 generally comprising two portions at an angle to one another is disposed close to the support arm 5 of the device according to the present invention. The lifting arm 25 is fastened articulatedly to the support arm 5 via the first articulation 7. When the lifting arm 25 moves relative to the first articulation 7, the cover 9 and the grinding disc 3 move in conjunction with it.

The lifting arm 25 can be acted upon in various ways. To effect a marked change of position of the lifting arm 25, the device according to the present invention is provided with a wire 27 which has its end anchored in a first abutment 28 attached to the first support element 11. One end of the wire sleeve 29 is anchored in the lifting arm 25 and the other end of the wire sleeve 29 is anchored in the frame 1. The wire 27 can be acted upon by a third electric motor 30 to cause it to move relative to the wire sleeve 29, resulting in the lifting arm 25 rotating about the first articulation 7. The rotation of the lifting arm 25 about the first articulation 7 results in the cover 9 with the grinding disc 3 being transferred between the raised position, see Fig. 4, in which no grinding takes place, and a lowered position, see Fig. 5, in which grinding takes place. This movement of the cover 9 and the grinding disc 3 between inactive and active positions is prior art. A generally triangular guide element 35 fastened pivotably via a second articulation 36 to the intermediate bracket 14 is disposed in the region of the free end of the intermediate bracket 14. A first link 37 extends between the triangular guide element 35 and a rotating disc 38 connected to the shaft of a fourth electric motor 39 which is attached to the first support element 11 on the opposite side from the intermediate bracket 14. The fourth electric motor 39 can cause the disc 38 to rotate in the direction of the arrow Pl. According to the embodiment depicted, the first link 37 is articulatedly fastened to the triangular guide element 35 on its upper side and has attached to its lower side a first contact element in the form of a first ball bearing 40 depicted in continuous lines in Fig. 6A despite being masked. According to the embodiment depicted, the articulated fastening of the first link 37 coincides with the centre of rotation of the first ball bearing 40. According to the embodiment depicted, the first link 37 and the first ball bearing 40 are disposed in the region of a first corner of the triangular guide element 35. A second contact element in the form of a second ball bearing 41 is attached rotatably to the underside of the triangular guide element 35 in the region of a second corner of the triangular guide element 35. As most clearly illustrated in Figs. 6A-8A, the triangular guide element 35 is partly accommodated in the aperture 22, see Figs. 4 and 5, during certain parts of the grinding operation which the device according to the present invention performs.

A second link 42 has its one end fastened articulatably to a third corner of the triangular guide element 35 and has its other end fastened adjustably to a second abutment 43 on the lifting arm 25. The adjustable fastening comprises a threaded rod 44 and a nutlike wheel 45 which can be moved along the threaded rod 44. The device according to the present invention has a spring arrangement 50 which urges the free end of the intermediate bracket 14 towards the bottom 16 of the second support element 15. This is not visible in the drawings. The spring arrangement 50 comprises a threaded rod 51 with a compression spring 52 at its one end, a third abutment 53 integrated with the intermediate bracket 14, and a penetration for the threaded rod 51 in the bottom 16 of the second support element 15. Nuts 54 are fitted on the ends of the threaded rod 51. The compression spring 52 is clamped between the one nut 54 and the third abutment 53.

A grinding operation performed by the device described above is described below. Grinding operation in this context means the grinding stages effected between two feed-forward movements of the saw chain S. Feeding the saw chain S forward may be effected as described in the applicant's older Swedish patent 0401028-6 (527 002), which is hereby incorporated in the description pertaining to the present patent application.

Figs. 6A and 6B depict the introductory stage of a grinding operation, which stage comprises grinding a cutting tooth T which forms part of the saw chain S. For this grinding stage to take place, the grinding disc 3 has to be transferred from an inactive raised position to an active lowered position. This is done by using the third electric motor 30 to activate the wire 27, which can be caused to move relative to the wire sleeve 29. The result is a transfer of the grinding disc 3 from the position in Fig. 4 to the position in Fig. 5. The grinding disc 3 assuming the position in Fig. 5 results in the lifting arm 25 coming to abut against the shoulder 6. During the transfer from the position in Fig. 4 to the position in Fig. 5, the grinding disc 3 is caused to rotate by means of the first electric motor 10. When the grinding disc 3 has assumed the position in Fig. 5, it remains in this position for a certain predetermined time during which grinding of the cutting tooth T takes place. When the predetermined time has passed, the fourth electric motor 39 comes into action, causing the disc 38 to rotate in the direction of the arrow Pl. The triangular guide element 35 will thus be transferred from the position in Fig. 6A to the position in Fig. 7A, i.e. the guide element 35 will move in the direction of the arrow P2 about the second articulation 36. At the same time, the first ball bearing 40 comes to abut against the stop screw 23 and the continuing rotation of the triangular guide element 35 about the articulation 36 results in rotation/pivoting of the first support element 11 relative to the second support element 15 via the first spindle 18. This rotation/pivoting of the first support element 11 is represented by the angle α in Fig. 7A. As the grinding disc 3 is firmly connected, via the cover 9 and the support arm 5, to the first support element 11, the rotation/pivoting of the first support element 11 will be converted to a movement of the grinding disc 3 away from the position for grinding the cutting tooth T, see Fig. 6B, towards the depth gauge R, see Fig. 7B. The grinding disc 3 will thus effect grinding of the depression between the cutting tooth T and the depth gauge R. This is an advantage in that repeated grinding of the cutting tooth T may result in the formation of a "ridge" in an intermediate portion of the depression. While the grinding disc 3 is executing the movement illustrated in Figs. 6B and 7B, the lifting arm 25 abuts against the shoulder 6, i.e. there is a clearance between the second abutment 43 and the wheel 45, see Figs. 6A and 7A.

Upon continued rotation of the disc 38 in the direction of the arrow Pl, the triangular guide element 35 will move in the direction of the arrow P3, see Fig. 8A, about the second articulation 36, i.e. away from the stop screw 23. The spring arrangement 50 urges the free end of the intermediate bracket 14 to abut against the bottom 16 of the second support element 15, and the first support element 11 assumes relative to the second support element 15 a position similar to that in Fig. 6A. This means that the cutting tooth T undergoes a further grinding by the grinding disc 3.

Upon continued rotation of the disc 38 in the direction of the arrow Pl, the fastening of the second link 42 to the triangular guide element 35 will move in the direction of the arrow P3, about the second articulation 36, from the position in Fig. 8A to the position in Fig. 9A. The result is that immediately after the position in Fig. 8A, the wheel 45 comes to abut against the second abutment 43, and the continuing movement of the fastening of the second link 42 to the triangular guide element 35 about the articulation 36 causes raising of the grinding disc 3 as a result of the wheel 45 coming to abut against the second abutment 43 on the lifting arm 25. In the position in Fig. 9A, a rise corresponding to the height of the depth gauge R relative to the bottom of the depression between it and the cutting tooth T will have taken place.

During the movement of the triangular guide element 35 in the direction of the arrow P3 which took place by transfer from the position in Fig. 8A to the position in Fig. 9A, the second ball bearing 41 will have come to abut against the bottom 16 of the second support element 15, resulting in rotation/pivoting of the first support element 11 relative to the second support element 15. This rotation/pivoting is represented by the angle βl in Fig. 9A. This rotation/pivoting will also have entailed the grinding disc 3 being moved from the position in Fig. 8B to the position in Fig. 9B. Upon continued rotation of the disc 38 in the direction of the arrow Pl, the first link 37 will impart to the triangular guide element 35 a continuing movement in the direction of the arrow P3 about the articulation 36. Continuing contact will thus be established between the wheel 45 and the second abutment 43 of the lifting arm 25. This means that the grinding disc 3 will remain at substantially the same level during the transfer between the position in Fig. 9A and the position in Fig. 1OA. Since the fastening of the second link 42 to the triangular guide element 35 moves along a circular arc about the articulation 36, a certain height variation, albeit in principle negligible, will occur. The continuing movement of the triangular guide element 35 in the direction of the arrow P3 also causes further rotation/pivoting of the first support element 11 relative to the second support element 15, as may be seen from the fact that β2 > βl. The angle difference between β2 and βl corresponds to the distance by which the grinding disc 3 will have moved from the position in Fig. 9B to the position in Fig. 1OB as a result of the aforesaid further rotation/pivoting having been imparted to the support arm 5 which supports the grinding disc 3. During the movement of the grinding disc 3 from the position in Fig. 9B to the position in Fig. 1OB, the grinding disc 3 will have performed grinding of the depth gauge R.

Upon continued rotation of the disc 38 in the direction of the arrow Pl, the continuing movement of the triangular guide element 35 in the direction of the arrow P3 about the articulation 36 will cease once the fastening of the first link 37 to the disc 38 has passed the point furthest away from the triangular guide element 35. Further continued rotation of the disc 38 causes the triangular guide element 35 to move in the direction of the arrow P2, see Fig. 6A, resulting in cessation of contact between the second ball bearing 41 and the bottom 16 of the second support element 15. This means that contact between the second abutment 43 and the wheel 45 ceases and the spring arrangement 50 urges the free end of the intermediate bracket 14 to abut against the bottom 16 of the second support element 15. The grinding disc 3 then drops down to the level where the lifting arm 25 abuts against the shoulder 6, i.e. the position in Fig. 6A is reverted to and a third grinding of the cutting tooth T takes place during the grinding operation described, which is thereby completed.

In this context it should be noted that the rotatable fastening of the ball bearings 40, 41 to the guide element 35 results in no sliding in the contact region between the ball bearings 40, 41 and the stop screw 23 and the bottom 16 of the second support element 15. A new grinding operation is commenced by the grinding disc 3 being raised by the wire 27 and the saw chain S being fed forward. A further cutting tooth with opposite oblique positioning (right-left) relative to the cutting tooth which has just been ground is normally fed forward. The first support element 11 has then to be pivoted about the second spindle 19 so that the grinding disc assumes a correct position for grinding the cutting tooth fed forward.

Conceivable modifications of the invention

In the embodiment described above there is grinding of the depression between the cutting tooth T and the depth gauge R. Within the scope of the present invention, however, it is conceivable that grinding the depression is omitted, i.e. grinding the cutting tooth T is followed by grinding the depth gauge R. To achieve this, the device described above is modified in such a way that the stop screw 23 is removed.

The embodiment described above of the device according to the present invention performs a grinding operation comprising the following stages:

1) grinding a cutting tooth (T) ,

2) grinding a depression between the cutting tooth (T) and the depth gauge (R) ,

3) grinding the cutting tooth (T) , 4) grinding the depth gauge (R) ,

5) grinding the cutting tooth (T) .

The cutting tooth (T) being ground several times is an advantage in that such a procedure eliminates any burrs which arise during the grinding. In this context it should however be noted that the method according to the present invention is in no way limited to the grinding operation defined above. Thus, as indicated above, grinding the depression of the saw chain (S) may be eliminated, nor need a grinding operation involve grinding the cutting tooth (T) three times. Thus it is possible within the scope of the present invention to conceive of a method whereby a grinding operation comprises only grinding a cutting tooth T and grinding a depth gauge R, both of these two stages being effected by the same grinding disc 3.