This invention relates to a device for feeding an endless conveyor belt which, along part of its length, travels in a helical path.

In conveyors of this type, the endless conveyor belt is driven at several points along its path of travel, and it may therefore be desirable that the belt tension at a certain point outside the helical path should have a pre¬ determined value, for instance the minimum value enabling a stretched belt. If a desired value of the belt tension is to be con¬ tained, it is essential that the belt tension can be mea¬ sured with sufficient accuracy.

The object of this invention is, therefore, to pro¬ vide, in a belt conveyor of the above type, a belt-feed- ing device enabling the belt tension to be accurately determined ad acent to the device, so as to make it pos¬ sible to set and maintain a desired belt tension.

This object is achieved by a device for feeding an endless conveyor belt, said device comprising a driving pulley engaging the conveyor belt outside the helical path and between two belt-path sections essentially tan¬ gent to the driving pulley. The device is characterised in that the driving pulley is rotatably mounted in a holder, which is so mounted in a stationary frame as to be pivotable about an axis extending essentially through the one belt-path section transversely of the longitudi¬ nal direction thereof.

Consequently, a sensor for sensing the compressive force can be provided between the holder and the frame, preferably on the same side of the axis as the other belt-path section. The sensor is able to provide an accu¬ rate value of the compressive force, since it is only the belt tension that exerts a torque on the holder as long as the above-mentioned position of the pivot axis of the holder is maintained.

With the aid of a suitable control means, the feed¬ ing force applied to the driving pulley can be so con¬ trolled as a function of the compressive force between the holder and the frame that it falls within a predeter- mined range, whose lower limit value has to be above zero if the conveyor belt is to be kept stretched adjacent to the feeding device.

One embodiment of the invention will be described in more detail below with reference to the accompanying drawings, in which

Fig. 1 is a perspective view showing an example of different belt-path sections of a conveyor belt;

Fig. 2 is a side view of a feeding device according to the invention; Fig. 3 is an enlarged view of a detail in Fig. 2; and

Fig. 4 is a top plan view of the feeding device in Fig. 2.

The present invention is intended for a conveyor belt 1 of the design shown in Fig. 1. To be more precise, the conveyor belt 1 shown in Fig. 1 has a helical belt- path section 2, which forms a pile and with which connect two straight belt-path sections 3, 4. Between the latter belt-path sections 3, 4, the belt 1 travels in a return- path section 5.

The conveyor belt 1 can leave the pile 2 via the belt-path section 3, as indicated by an arrow A, or enter the pile 2 via the belt-path section 3, as indicated by an arrow B. In both instances, a feeding device 6 accord- ing to the invention may be provided between the belt- path section 3 and the return-path section 5.

Figs 2-4 illustrate the preferred embodiment of the feeding device 6, which comprises a holder 7 for a driv¬ ing pulley 8 rotatably mounted therein. The holder 7 includes two lateral plates 9 and 10, which are fixedly interconnected by means of one transverse plate 11 and two transverse support beams 12 and 13.

The holder 7 further supports an electric motor 14 for driving the pulley 8, for instance via a V-belt 15.

The lateral plates 9, 10 are equipped with apertured lugs 16 for mounting of the holder 7, such that it can pivot about a shaft 17 mounted in two posts 18 forming part of a stationary frame.

Moreover, the frame comprises two sliding rails 19, 20 extending essentially tangentially in towards the upper periphery of the driving pulley 8, as well as two sliding rails 21, 22 extending essentially tangentially in towards the lower periphery of the driving pulley 8. The shaft 17 is disposed transversely of the sliding rails 21, 22, such that the conveyor belt 1 cannot, when travelling over the sliding rails 21, 22, transmit any torque to the holder 7 with respect to the shaft 17.

Apart from a V-belt pulley 23 for driving the driv¬ ing pulley 8 by means of the motor 14, the driving pulley 8 has two sprockets 24, 25 for engaging links at each longitudinal edge of the conveyor belt 1, as well as a plurality of support rollers 26 for supporting the con¬ veyor belt 1 when fed approximately half a turn round the driving pulley 8.

The holder 7 strives to rotate clockwise in Fig. 2 about the shaft 17, but is prevented therefrom by the fact that it is connected to the stationary frame by means of a screw 27, a sleeve 28 and a spring 29, which together determine a maximum as well as a minimum dis¬ tance between the holder 7 and the frame when the holder 7 is pivoted about the shaft 17. Adjacent to the screw 27, there is mounted a force sensor 30, for instance a load cell, for sensing the force with which the holder 7 is pressed against the sta¬ tionary frame as a result of the feeding of the conveyor belt 1 by the driving pulley 8. More specifically, the holder 7 is equipped with a movable pin 31 which, by a spring 32, is pressed against the force sensor 30.

The spring 29 balances the torques of the holder 7 about the shaft 17, and the sleeve 28 limits the force applied to the force sensor 30.

There are two different modes of operation. In the one mode of operation, the pile 2 is so driven by a driv¬ ing means that the conveyor belt 1 moves in the direction indicated by the arrow A and leaves the pile 2 in the belt-path section 3. In the other mode of operation, the pile 2 is driven in the opposite direction, such that the conveyor belt 1 moves in the direction indicated by the arrow B and enters the pile 2 in the belt-path section 3. In both cases, it is desirable that the force acting on the belt, and hence the belt tension, is small adja¬ cent to the feeding device 6. According to the invention, this can be achieved by supplying the compressive force, which is exerted between the holder 7 and the frame and sensed by the force sensor 30, in the form of an actual- value signal to a control means (not shown) which, for instance by suitable operation of the motor 14 and, hence, of the driving pulley 8, may cause the actual- value signal to agree with a reference-value signal representing the aimed-at low value of the belt tension.

The invention thus provides a belt-feeding device enabling accurate determination of the belt tension adja- cent to the device and, hence, expedient maintenance of a desired belt tension. It goes without saying that several modifications of the feeding device are conceivable with¬ in the scope of the invention as defined in the appended claims.