FIELD OF THE INVENTION

The invention relates to a feed roller used in forest- ry machines, such as harvesters and the like, for han ^¬ dling tree stems.

BACKGROUND OF THE INVENTION

A feed roller for moving a tree stem in its longitudi- nal direction or holding it in its position must have two somewhat opposite features. It must have a firm and tight grip of the stem so that the stem will move correctly, while also handling the stem gently so that its surface will not be damaged, at least deeper into the wood.

The currently used feed rollers are mostly full-metal steel rollers where a cylindrical jacket is coated with ribs having a sharp outwardly protruding edge, the ribs extending parallel to the axis of rotation and their length corresponding to the width of the roller. Depending on the size of the roller, there may be for example 15-25 ribs disposed at an even spacing over the circumference. Corresponding structures are also known, where a round plate-type flange serves as the roller body, the straight ribs being then welded to extend in the axial direction, either directly to the flange, or to a circumferential jacket fixed around the flange.

While the prior art structures work relatively well, there still is need for gentler handling of the stems. Too often are the stem surfaces left with such deep handling marks by the rollers that the use of the stems in further processing becomes limited or diffi- cult. Furthermore, the current steel rollers are rela ^¬ tively angulate, which causes vibrations and loud noise on the machine when the logs are being processed at a fast pace. Further problems are caused by the roller consisting of several separate parts, which re ^¬ quires a great deal of welding work and thus makes the roller expensive to manufacture. The known ribbed rollers also have a poor stem supporting capacity, i.e. the largest stems tend to slide out from the sup- port of the rollers when being processed.

OBJECT OF THE INVENTION

The object of the invention is to remedy the defects of the prior art mentioned above. Specifically, the object of the invention is to disclose a new feed roller that bites into a stem more smoothly and softly than the prior art feed rollers, causing less damage at the stem surface, less vibration in the machine, and less noise inside the machine and outside in the nature. A further object is to make the manufacture of the roller less expensive and improve the capacity of the roller to support the stem being processed.

SUMMARY OF THE INVENTION

The feed roller according to the invention comprises a round plate-type flange body, and radial ribs fixed at an even spacing over its outer circumference with gripping members for providing a firm grip of the surface of a tree stem being handled by the feed roller. According to the invention, the outer edge of the plate-type ribs, i.e. the edge of the ribs protruding outwards in the radial direction of the roller, is disposed at an oblique angle to the axis of the feed roller, and the outer edge of each rib comprises sev- eral gripping members having a straight blade edge, arranged such that the blade edges extend in the axial direction of the feed roller. In other words, the outer edges of the plate-type ribs as such are disposed at an oblique angle to the axial direction of the feed roller, while the sharp and straight blade edges of their gripping members are disposed parallel to said axis. As a result, in the invention each of the long axial ribs of the conventional ribbed roller are sepa ^¬ rated into several parts, their orientation remaining the same, i.e. axial, while the parts are circumferen- tially offset in a stepwise manner, so that a line of blade edges at an angle to said axis is formed, where the actual blade edges providing the grip are disposed in an optimal way, i.e. perpendicular to the direction of rotation of the roller. Said oblique angle is ap- propriately between 15 - 45°, for example approximate ^¬ ly 25° .

Preferably there are at least three gripping members at the edge of the same rib, for example 5-10 gripping members in a row at the outer edge of the rib. The number of the gripping members depends on the desired width of the feed roller being manufactured, and also on the thickness of the plate of which the ribs are made .

Preferably, the blade edges of the gripping members form a curved convex surface. When this convexity is suitably adjusted according to the oblique angle of the ribs, the blade edges of the gripping members of all ribs can be provided on the same cylindrical sur ^¬ face, i.e. the outer surface of the feed roller be ^¬ comes a cylindrical surface formed by the blade edges.

In a preferred embodiment of the invention, the rib with its gripping members is machined from a single one-piece steel plate. Thus, there are no other kinds of parts in the feed roller except one round plate- type flange body and a number of identical ribs welded over its circumference with the blade structures on their outer edges. In other words, in the invention the rib with its gripping members is an integral piece with no seams or joints, which is welded to the flange body .

ADVANTAGES PROVIDED BY THE INVENTION

The feed roller according to the invention provides considerable advantages over the prior art. The feed roller according to the invention is very simple and inexpensive to manufacture because the number of sepa ^¬ rate parts therein is just a fraction of the number of parts in the known rollers. In addition, the manufac ^¬ ture of the feed roller is easily automatizable, such that the machining of the billets of ribs welded to the flange body is carried out in a fully automatized manner. Further, the feed roller according to the in- vention bites into a tree stem more smoothly and firmly than the conventional rollers. In addition, the vibrations and loud noises caused by the known rollers are completely imperceptible with the feed roller ac ^¬ cording to the invention. The stepped edges formed by the gripping members according to the invention support the stem so effectively that the stem is not able to slide between the rollers, as it does in the prior art ribbed rollers. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to the accompanying drawings, in which

Fig. 1 is an oblique view of one feed roller according to the invention,

Fig. 2 shows the feed roller of Fig. 1 as seen along the circumference, and Fig. 3 is a side view of the feed roller of Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

The feed roller illustrated in the figures comprises a round plate-type flange body 1 having a central hole surrounded by installation holes 6 for bolting the feed roller to a machine to be operated. The outer circumference of the flange body 1 is provided with evenly spaced plate-type ribs 2 shaped at the ends facing the flange body so as to correspond to instal ^¬ lation recesses provided on the outer circumference of the flange body, the ribs being welded firmly to the outer circumference of the flange body so as to pro ^¬ trude away, i.e. outwardly from it.

The plate-type, substantially linear outer edge of the rib 2 is disposed at an oblique angle a to a line de ^¬ fined by the axis 4 of the roller. At the outer edge of the rib there are a number of gipping members 3, five in the figures, disposed one after another. The gripping members are formed by outwardly protruding straight blade edges 5, a straight line L of which is parallel to said axis 4. Thus, the blade lines of in ^¬ dividual gripping members 3 are parallel to the axis 4 of the feed roller, even though the gripping members 3 are disposed in a line angled at an angle a to said axial line 4.

As shown by rib A in Fig. 1, the gripping members are disposed in said straight line L, and the orientation S of the blade edge 5 of each of the gripping members is parallel to the axis 4 of the roller. In addition, as shown by rib B in Fig. 1, the gripping members 3 are disposed, in the radial direction of the roller, at different distances from the axis of the roller, such that their blade edges 5 form a slightly curved line. This curvature corresponds to the total curva ^¬ ture of the roller along the circumference. Thus, the greater the angle a, the greater said curvature is to be adjusted. This way, the sharp blade edges that are parallel to the axis 4 in all gripping members at the ends of all ribs will lie on the same cylindrical sur ^¬ face, moving perpendicular to the longitudinal direc ^¬ tion, i.e. the direction of movement, of a tree stem being processed. Thus, the grip of the tree stem is firm and tight, such that the roller feeds the stem being processed smoothly and noiselessly.

The invention has been described above by way of exam ^¬ ples with reference to the accompanying drawings; how ^¬ ever, various embodiments of the invention are possi ^¬ ble within the scope defined by the claims.