A rotor cutter

Abstract: A rotor cutter comprises a cutting member (1) adapted to be driven into rotation about an axis of rotation (3). The cutting member (1) comprises a knife holder (6) connected with a knife (12). The knife (12) comprises a blade (14, 64), which during the rota­ tion of the cutting member (1) rotates in a plane substantially perpendicular to the axis of rotation (3) of the cutting member (1). The knife (12, 62) comprises furthermore a shank (13) rotatably jour­ nalled relative to the knife holder (6) about a swivel axis (11), said swivel axis (11) forming an acute angle (α) with the axis of rotation (3) of the cutting member (1), the angle space of said angle (α) facing upwards.

Description: The invention relates to a rotor cutter comprising a cutting member adapted to be driven into rotation about an axis of rotation and being of the type mentioned in the preamble of claim 1. The expression "rotor cutter" includes all cutters comprising a rotating cutting member, such as rotary lawn mowers, reapers, topping machines etc. GB-A-1.220,353 discloses a rotor cutter of the above type, which comprises a cutting member arranged on a vertical rotary shaft. The cutting member comprises a knife holder mounted at the lower end of the shaft, a plurality of knives with a shank extending downwards and outwards from said knife holder, and a blade formed integral with said shank and adapted to rotate in a plane perpendicular to the longitudinal axis of the rotary shaft. At the upper end the shank of the knife is pivotally connected to the knife holder by means of a pin. The longitudinal axis of the pin forms an acute angle with the rotary shaft. DE-C-29 20 244 discloses a rotor cutter where the knife holder of the cutting member is a disk. On the bottom side of the disk, knives are rotatably arranged about an axis parallel to the axis of rotation of the cutting member, said knives projecting radially outwards from the disk when the cutting member is rotating. As a result the knives turn and clear possible obstacles such as a small stone or a stump. Experience has, however, shown that this type of cutting members involves a high risk of said cutting member and the driving device causing said member to rotate being seriously damaged when the cutting member bumps into a large object such as a large stone or a large stump. The object of the invention is to provide a rotor cutter of the above type , which compared to the conventional rotor cutters eliminates or minimizes the risk of damages of the cutting member and the driving device when the cutting member hits obstacles. The rotor cutter according to the invention is characterised in the blade is rotatably journalled relative to the shank about an axis of rotation substantially parallel to the axis of rotation of the cutting member. In connection with a possible obstacle the knife swivels backwards and upwards about the swivel axis so as to clear the obstacle. However, only the blade and not the entire knife turns when said blade bumps into an obstacle. The latter is considered to very advantageous for obtaining a uniform cutting result, as the blade reverts to its cutting position faster than when the entire knife is turned. In addition the knife holder is situated at a higher level compared to the blade of the knife whereby the risk of said holder bumping into an obstacle is highly reduced. Accordingly, the risk of the cutting member and its driving device being damaged when a knife bumps into an obstacle is minimized. According to the invention the blade may be replaceably connected to the shank. In addition, according to the invention the angle formed by the swivel axis of the knife and the axis of rotation of the cutting member may be in the range 30-60°, and preferably 40-50°, said ranges having proved to be particularly advantageous in practice. Moreover, according to the invention the rotatable journalling of the knife relative to the knife holder may be situated a short distance from the axis of rotation of the cutting member, said rotatable journalling forming the swivel axis. As a result the knife holder can advantageously be shaped such that transverse to the axis of rotation of the cutting member said holder is of a small dimension which minimizes the risk of exactly this portion of the cutting member bumping into an obstacle in the ground and of the cutting member and/or its driving device being damaged. The invention is explained in greater detail below with reference to the accompanying drawing, in which Figure 1 is an axial, sectional view through a first embodiment of a cutting member for a rotor cutter according to the invention. The cutting member 1 of Figure 1 is fixedly connected to a substantially vertical shaft 2 adapted to cause the cutting member to rotate about a vertical axis of rotation 3 by means of a driving device not shown. The cutting member 1 comprises a hub 4 fixedly connected to the shaft 2. A knife holder 6 is bolted onto the hub 4 by means of screws 5, said knife holder 6 comprising a disk 7. Two diametrically opposing notches 8 are shaped at the periphery of the disk 7, only one notch appearing from the drawing. A bushing 9 is situated in each notch and is welded at 10 to the disk 7 in such a manner that the axis 11 of the bushing forms an angle a of about 45° with the axis of rotation 3 of the cutting member. The angle can, however, be arbitrarily chosen in the range 0-90°. The axis 11 of the bushing 9 is a swivel axis for a knife 12 comprising a shank 13 and a blade 14. The shank 13 is shaped like a two-legged fork and is formed by two flat bars welded together at one end at 17 and forming the legs 15, 16 of the fork at the opposite end. The distance between the legs of the fork corresponds substantially to the length of the bushing 9. Each leg is at its free end provided with an opening 18, 19, and a bolt 20 extends through each of these openings 18, 19 and through the bushing 9. A nut 21 is screwed onto the end of the bolt 20. Accordingly the bolt 20 forms the swivel axis 11 for the knife 12. The opposite end of the fork-shaped shank 13 is provided with an opening 22 allowing passage of a bolt 23. The bolt 23 is secured by means of a nut 24. The bolt 23 comprises a shank portion 25 of a larger diameter than the opening 22. The blade 14 is situated on the shank portion 25 and comprises at one end an opening 26 of an inner diameter slightly larger than the outer diameter of the shank portion. As a result the blade 14 is rotatably arranged about an axis of rotation 27 formed by the axis of the bolt 23 and being substantially parallel to the axis of rotation 3 of the cutting member 1. When the cutting member 1 is rotating, the blade 14 sweeps a plane substantially perpendicular to the axis of rotation 3, and the shank 13 and the blade 14 of the knife 12 are in the position shown in Figure 1 where they project radially outwards from the axis of rotation 3 of said cutting member 1. When only the blade 14 bumps into an obstacle, said blade swivels backwards and clears said obstacle. When also the shank 13 bumps into the obstacle, said shank 13 and consequently also the blade 14 swivels backwards and upwards about the swivel axis 11 and clears the obstacle. The swivel axis 11 of the knife and the axis of rotation 3 of the cutting member may be skewly situated relative to one another instead of being situated in a common plane, in case such a solution is advantageous. Furthermore the rotor cutter may be provided with a plurality of cutting members.

Claims: A rotor cutter comprising a cutting member (1) adapted to be driven into rotation about an axis of rotation (3), said cutting member comprising a knife holder (6) connected with a knife (12) having a shank (13) extending downwards from the knife holder (6) and being at its upper end rotatably journalled thereto about a swivel axis (11) forming an acute upwardly open angle (α) with the axis of rotation (3) of the cutting member (1), said knife (12) further having at the lower end of the shank (13) a blade (14) which during the rotation of the cutting member (1) rotates in a plane substantially perpendicular to the axis of rotation (3) of the cutting member (1) characterised in that the blade (14) is rotatably journalled relative to the shank (17) about an axis of rotation (27) substantially parallel to the axis of rotation (3) of the cutting member (1). A rotor cutter as claimed in claim 1, characterised in that the blade (14) is replaceably connected to the shank (13). A rotor cutter as claimed in claim 1, characterised in that the angle (α) formed by the swivel axis (11) of the knife and the axis of rotation (3) of the cutting member is in the range of 30-60°, and preferably 40-50°. A rotor cutter as claimed in claim 1 or 3, characterised in that the rotatable journalling of the knife (12) relative to the knife holder (6) is situated a short distance from the axis of rotation (3) of the cutting member, said rotatable journalling forming the swivel axis (11).

Inventors: ANDERSEN BERNT, ANDERSEN, BERNT
Applicants: SPRAGELSE MASKINFABRIK AS, SPRAGELSE MASKINFABRIK A/S
Application year: 1990
Main classification: A01D34
IPC codes: A01D34