Apparatus for cutting reinforcing fibre material

TECHNICAL FIELD

The present invention refers to an apparatus for cutting fibrous reinforcement material in relationship with an ejector nozzle, comprising at least two feeding rollers and a rotary cutter which is provided with a substantially cylindric mantle surface with attachments for a number of knife means and which cooperate with a support roller with an elastic surface layer for forming a thread nip.

BACKGROUND OF THE INVENTION

In robot-controlled production, there are usually a high demand for precision in the delivery of raw material. For example, when feeding fibre thread to a robot-controlled fibre feeding apparatus, the feeding rate may be about 10 meters per second. If jerks occur in feeding, the thread may be torn off or damaged, which will lead to serious losses in production.

When cutting fibre thread, a cutting apparatus of the above described type is normally used. Each time the fibre thread is hit by the sharp edge of the knife means, the fibre is folded in V-shape around said edge while being pressed into the elastic layer of the support roller. This operation occurs at a high frequency during a space of time of some fractions of a second. The mechanical deformation leads to fracture of the single fibres of the thread.

Known apparatuses for this purpose are adapted to cutting of fibres of a certain thread length. The distance between two cuts normally depends upon the distance between the knife means of the cutter. Thus, the feeding rate of the feeding rollers and the cutter is synchronized.

It would be desirable to be able to vary the length of the cut fibre pieces infinitely variable. Besides, a drawback with the method lies in that a sudden jerk is developed in the thread each time it is hit by a knife means, because the thread is momentary accelerated while being folded around the knife edge. These rapid jerks can lead to tearing off of the fibre thread at wrong places.

THE TECHNICAL PROBLEM One object of the present invention is therefore to provide a cutting apparatus which enables infinitely variable length of the cut fibre pieces, and which is able to dampen the jerks which are developed when the edge of the knife means hit the fibre thread.

THE SOLUTION

For this purpose the invention is characterized in that the mantle surface of the cutter is provided with slot-shaped recesses for the fibre thread, which recesses extend peripherally along the mantle surface between the knife means enabling the thread to be fed forward by means of the feeding rollers at a feeding rate which deviates from the speed of the cutter, for adaption of the cutting length of the fibre thread.

DESCRIPTION OF THE DRAWINGS

The invention will be described here below with reference to an embodiment shown in the accompanying drawing, in which Fig. 1 schematically shows a fibre feeding device in a view from the side,

Fig. 2 shows in a plane view in somewhat larger scale the nip between the cutter and the support roller, and Fig. 3 is a section along the line III-III in Fig. 2.

DESCRIPTION OF EMBODIMENTS

The feeding apparatus schematically shown in Fig. 1 is used mounted upon a not shown robot arm, for feeding out fibre thread 10 and binding agent in the form of powder from not shown magazines, for example to moulds for plastic products.

Preferably, the robot arm is freely movable in the room and is governed by a micro processor, which can be programmed.

The fibre thread 10 is drawn from its magazine into the feeding apparatus by means of two feeding rollers 11, 12, which form a nip for the fibre thread and comprises a first motor driven roller 11 and a second co-rotating roller 12.

The roller 12 has a displaceable bearing which is pressed in the direction towards the roller 11 by means of a compression spring 13. The roller 11 is driven in a speed adjustable manner by means of a not shown driving motor.

The rollers 11, 12 feed the fibre thread 10 forward via a compressed air ejector 14 and a tube 15, which is bent to about 90° and emerges into the nip between a knife roller 16 and a support roller 17.

The fibre thread pieces 18 cut by the knife roller 16 can be blown out through an ejector pipe 19 which is provided with a connection 20 for compressed air. Also, the ejector pipe 19 is provided with a connection 21 to a conduit for supply of a pulverulent bonding agent.

The cutter 16 is provided with three knife blades 22 which are distributed with equal spacing around the periphery of the roller. The cutter 16 can be driven in a speed adjustable manner by means of a not shown driving motor. The support roller 17 is provided with an elastic surface layer 17a is manoeuvrable by means of a pneumatic piston 23. Cutting of the fibre thread 10 is started by manoeuvring the

support roller 17 by means of the piston 23 toward the cutter 16. Uncut thread 10 can be fed out through the nozzle 19 when the support roller 17 is manoeuvred away from the cutter 16.

Figs. 2 and 3 show that the mantle surface of the cutter 16 is provided with slot-shaped recesses 24 for the fibre thread 10, which recesses extend peripherally along the mantle surface from a point 25 adjacent the rear side of the respective knife blade 22, as seen in the direction of rotation, to a point 26 somewhat in front of the next following knife blade 22.

The recesses makes it possible to feed the thread 10 through the cutting device, without moving the support roller 17 from the cutter 16. This enables the variation of the length of the fibre pieces within comparatively wide limits. For example, the feeding rollers 11, 12 can be driven more slowly than the cutting device, so that very short fibre pieces are produced. Alternatively, the feeding rollers 11, 12 can be driven at a higher speed than the cutting device, so that very long fibre pieces are produced.

At each time the fibre thread 10 is cut, it is drawn forward intermittently a short length at a higher speed than the normal feeding speed of the thread. The slot-shaped recesses enable the forming of a short slack in the thread adjacent its end, at the moment from when the cut has occurred and until the next following knife blade hits the thread at a distance from the free end of the thread, which slack is enough to prevent development of jerks in the thread which can lead to uncontrolled tearing of the thread or to increased wear in the feeding rollers 11, 12. The length of this slack is controlled by the depth of the recesses and is sufficient to compensate for the variations in the pulling force, when the knife hits the thread and folds it while it

is pressed into the elastic surface layer 17a of the support roller 17.

Because the point 25 is located at some distance before the next following knife blade 22, the free end of the thread is caught up by the nip between the cutter 16 and the support roller 17, before the knife blade hits the thread 10.

The piston 23 is preferably connected to a micro-processor which enables compensation for wear upon the elastic surface layer 17a of the support roller 17.

The invention is not limited to the embodiments described here above, but several variants are conceivable within the scope of the following claims. For example, the cutter 16 may be provided with parallel groves 24 for two or more fibre threads 10, wherein the cutter may have a corresponding number of support rollers 17, which may be individually manoeuvrable.