The present invention relates to a method and a device for conveying objects, especially objects on a moving surface, for example a conveyor belt, the method and the apparatus being of the types stated in the preambles of claims 1 and 2, respectively.

In industry, a variety of objects are frequently transported on different types of conveyors, and in many cases it is desirable that certain objects, for example objects having a given weight or volume or conforming to other production requirements, or defective objects, can be removed at predetermined locations along the conveying path.

Some examples of applications where there is need of an efficient removal of objects are the following. In the tobacco industry, snuff-boxes not coming up to full weight must be sorted out for refilling. The postal services must be able to sort parcels according to weight, size and destination. In the food industry, chocolates, potatoes, eggs etc must be sorted quickly and efficiently. For example, it is desirable that potatoes classified according to size can be removed at preselected stations along the conveying path.

In addition, it is desirable that such removal can be effected quickly and economically and in a manner which does not damage the objects or interfere with the progress of other objects.

Methods and devices for removing objects from a conveying path of this type are in existence.

If the conveying path is in the form of an uninter- rupted surface, ^" especially an endless loop, the removal device is preferably positioned beside or above the con¬ veying path. If the conveying path is defined by a succession of rollers or the like, the removal device can be positioned beside, above and even underneath or

in the conveying path proper. For example, use is made of trapdoors, sprocket means seizing each object for transfer from one conveyor to another, and different types of arms and plungers. It is evident that the objects conveyed along the conveying path need not take up the entire width of the conveying path; they can also lie within specific conveying tracks, and in the following description the term "conveying track" is used for an area of the conveying path which extends in the longitudinal direction thereof. The conveying track requires no physical boundary means, such as barriers or the like. Although the con¬ veying tracks can be as wide as the conveying path, two or more parallel but spaced-apart conveying tracks can be arranged on the conveying path without completely filling it. Several conveying tracks are used for example when different frozen vegetables are to be mixed in specific proportions, and then each conveying track carries a string of, for example, peas or grains of maize. At an unloading station, suitable quantities are removed and filled as a vegetable mix into bags for freezing. In those cases where plungers are positioned adjacent the conveying path, these plungers project sub¬ stantially perpendicular to the longitudinal direction of the path, strike the object which is thrown off the path, and then return into their initial position. If the objects lie after one another in a conveying track, but are laterally offset within this track, the objects must lie fairly far apart because the plunger must have time to reach out across the entire width of the con¬ veying track and go back again between two successive objects. Furthermore, a great deal of energy is required since the plunger must first be accelerated, then decelerated to a stop position, again accelerated in the opposite direction, and finally decelerated when returning into its initial position.

Another prior art device comprises an arm which,

in the normal initial position, is parallel to the travelling direction of the conveying path and which, upon actuation, is swung out in a plane parallel to the plane of the conveying path, and strikes an object which is thrown off. Also in this case, one has essen¬ tially the same difficulties as in the arrangement described above.

Also when the arm merely blocks the conveying track for gentle deflection of the object, similar difficulties are encountered.

The above-mentioned devices thus suffer from the shortcoming that it is difficult to remove the object both quickly and in a gentle and efficient manner.

According to a further solution, the objects are blown off the conveying track by compressed air. Besides high losses of energy in the expelled compressed air, this system causes considerable environmental problems in that it is exceedingly noisy and produces a great deal of dust. DE 449,392 discloses a device for removing objects from a conveyor belt, said device comprising an impeller which lifts the objects from the conveying track when the objects have reached the end of the conveyor belt. The objects are flung over the impeller. This device removes every object to ensure that the objects do not follow the conveyor belt over the end thereof.

NO 104,444 discloses a device comprising a swinging arm which, upon contact with an object, first turns the object about a vertical axis and then rakes it off the conveying track. The device is mounted above the conveying track, and the arm swings substantially across the conveying path. In its initial position, the arm is located in the highest point of its path of travel. A motor drives the arm and causes it to sweep down across the conveying belt in clockwise or anticlockwise direction. Admittedly, the Norwegian patent is capable, to some extent, to solve the above-mentioned problems

but only at the cost of a low working speed.

US 4,057,138 discloses a spider-like device for transferring logs from a first conveyor to a second conveyor travelling in a direction perpendicular to that of the first conveyor. The objects handled by this device are entirely different from those of the present invention, and further this prior art device does not have the control system required in a device for handling fragile objects. With the present invention, the above-mentioned problems are solved and the following aims achieved.

The principal aim of the present invention is to eliminate the shortcomings of the prior art con¬ structions and to make the handling of objects on a conveyor belt more efficient.

A first particular aim is to remove objects following closely upon one another.

A second particular aim is to remove the objects in a gentle manner. A third particular aim is to remove specific objects and to allow the remaining objects to pass unhindered.

A fourth particular aim is to remove the objects with a minimum of noise. A fifth particular aim is to remove objects con¬ veyed at high speed in a conveying track on a conveyor belt.

These aims are achieved by the method and the device defined in the characterising clauses of claims 1 and 2, respectively, and by a blade as defined in claim 8. Preferred embodiments are defined in the dependent claims. The invention will be described in more detail hereinafter, reference being had to the accompanying drawings. Figs 1A and IB illustrate schematically an embodiment of a device for removing objects from a belt or roller conveyor.

Fig. 2 is a front view of an impeller included in the device according to the invention.

Fig. 3 is a front view of another embodiment of the impeller. Fig. 4 illustrates schematically the function of the device according to the invention.

Fig. 5 illustrates schematically the device according to the invention, especially the impeller operation. Fig. 6 is a time-dependency diagram of signals generated during the operating cycle of the device.

A number of objects 1a, 1b are lying on a conveying track 20 of a conveyor 2 moving toward the right in Fig. 1A. Above the conveyor 2, a device for removing the objects from the conveyor is mounted. The device comprises a geared motor 3 which drives a motor shaft 4 carrying at one end a driving disc 5. The motor 3 preferably is a three-phase a.c. motor, and the motor shaft 4 rotates continuously. The driving disc 5 is disposed within a clutch housing 6 which also contains a brake disc 7 and a clutch disc 8. The clutch disc is mounted on one end of a shaft 9, the other end of which enters a hub 10. The hub carries substantially radially projecting blades 11a-e.

When the clutch disc 8 engages the driving disc 5, - the shaft 9 and the hub 10 are caused to rotate. When, on the other hand, the clutch disc 8 engages the brake disc 7, the movement is braked.

The clutch disc is engaged and disengaged electronic¬ ally, as will be explained below. When the hub 10 rotates and one of the blades 11 strikes an object 1b, the object is knocked off into a receptacle B beside the conveyor.

Fig. 1B illustrates an alternative disposition of the device. In this case, the conveyor is in ^' the form of a number of rollers 12 between which a blade 11 can be introduced for actuation of the object.

In Fig. 2, the hub 10 is shown with five blades

1la-e, the hub and the blades being identified herein¬ after by the collective term impeller 10a.

The blades 11a-e of the impeller substantially comprise two parts, i.e. a striking part 13 and a radially directed main part 14 to which the striking part is fixed. The striking part 13 has a striking surface 15 and forms an angle with the main part 14 of the blade. If the device is positioned underneath the conveyor, the striking part 13 is angled rearwardly in the direction of rotation. If the device is positioned above the conveyor, the striking part 13 is angled forwardly in the direction of rotation. When the striking surface 15 hits the object 1b, the surface is not po¬ sitioned vertically, but is slightly inclined, which means that the object is moved substantially parallel to the plane of the conveyor 2 or, possibly, in a direc¬ tion away from the conveyor 2, and therefore there is no risk that the object 1b is caught between the blade and the conveyor 2. During normal operation, the impeller 10a always rotates in the same direction (clockwise in Fig. 2), but it is possible to reverse the movement, and even to selectively swing the blade to and fro across the conveying track, in which case the striking portion should be provided with two angled striking surfaces, one on each side of the blade.

The impeller function will now be described with reference to Fig. 2. The object 1b is conveyed within its conveying track on the conveyor 2 in a direction away from the viewer. A surface 17 defines the area within which objects may occur. This means that the width of the surface 17 is determined by the conveying track, and that the height of the surface 17 is determined by the maximum height of the objects. The impeller is positioned at a location along the conveying track where it is desired to remove objects of a specific type. As long as a free passage of objects is desired, the impeller

is in a predetermined position in which all blades 11a-e are outside the surface 17. In the embodiment illustrated, the impeller is rotated in clockwise direction. When an object is to be removed from the conveyor 2, the clutch disc 8 is engaged with the driving disc 5 (Fig. 1). The propeller begins practically instantaneously a rotational movement, and the blade 11b which in Fig. 2 is to the right of the surface 17 in the initial position I, is moved to the left in the Figure. The striking surface 15 of the blade strikes the object 1b, as shown by dash-dot lines at position II. The blade continues its movement until it has reached a position of rest III to the left of the surface 17 in Fig. 2. It will be appreciated that the next blade lie simultaneously has assumed its initial position I to the right of the surface 17.

To ensure that the impeller blades 11a-e assume their predetermined positions, a sensor 504 is mounted opposite the hub 10 (see Fig. 5). The sensor may be of the optical, mechanical or, as in the embodiment illustrated, the inductive type. In the embodiment illustrated, metal plates 18 are mounted on the hub 10 radially within each blade 11a-e.

This means that, even if the blades are not posi- tioned at exact mutual angular distances, one blade 11 will always, after each operating step, be placed in the initial position I adjacent the surface 17. The operation is controlled such that the predetermined blade positions are attained, which may imply, for example, that the driving disc is engaged only during an initial phase of the rotational movement. If the removed object has a large mass, the peripheral speed of the blade may decrease considerably, for which reason a further engagement of the clutching means may be necessary.

In the embodiment illustrated, the impeller has five blades 11a-e. The number of blades, their length

and specific design must be adapted to each specific type of objects. Fig. 3 shows an alternative embodiment comprising eight blades, which may be suitable for tall and narrow objects. It will be noted that the blades in this case do not reach all the way down to the surface of the conveyor 2.

In some installations, it may be desirable to convey large amounts of objects on one and the same conveyor. It may then be suitable to dispose the objects in side by side relation in spaced-apart conveying tracks on the conveyor, and also with this disposition the conveyor according to the invention is useful since two impeller-like conveying means can be provided adjacent one another as long as the blades of one impeller do not interfere with the working surface 19 of the other impeller. Fig. 2 shows a second working surface 19 beside the working surface 17.

The striking surface 15 should strike the object in such a manner that, vectorially seen, the impulse generated by the speed goes through the mass centre of the object. The object 1b will leave the conveying track 20 in a direction determined by several factors. Mechanically seen, the impact is more or less elastic, and regard should therefore be paid to the mass of the object, the speed of the conveyor, the speed of the blade at the time of the impact, and the coefficient of friction between the object 1b and the conveyor 2. If the speed of the blade is sufficiently high in relation to the speed of the conveyor, the speed of the blade may, however, be regarded as the most important factor. The object-will thus be removed in a trajectory that lies substantially in the plane of the impeller. The less the deviation from this plan, the smaller the risk that other objects on the conveyor are hit by the object thrown off.

With fragile objects such as potatoes, raw eggs etc, it may be suitable tomake the blades of some

resilient material, preferably plastic. This contributes to low sound levels. Preferably, the blade is made replaceable since it is subjected to a large number of impacts during operation. Fig. 4 illustrates schematically and from above the function of the conveyor according to the invention. In this case, the conveyor 2 forms the entire conveying track 20 and moves at a speed V2 to the right in Fig. 4. A blade is moving at a substantially constant speed V11 upwardly in Fig. 4. The width of the blade is designated 111. The blade will sweep across a surface 113 which is represented by the dotted zone in Fig. 4 and within which only one object must be positioned. To enable the next blade to strike the next object, the latter must not be placed within a zone 114 surrounding the surface 113 by a comfortable margin.

When the blade 11 has reached a far side 115, the next blade 11 is in its initial position I (see Fig. 2) adjacent a first side 116. To enable the next blade to strike the next object adjacent the side 115, the object must lie outside the zone 114. The ideal minimum spacing of two successive objects will thus be a distance 117.

In a prior art construction, a plunger is moving across the conveyor. However, since the plunger must return into its initial position between each strike, the objects must be spaced apart a larger distance 118. The banned zone 200 is shown in Fig. 4.

The electronic control of the impeller will now be described with reference to Figs 5 and 6.

A transducer 503 for which the term belt trans¬ ducer is used hereinafter, transmits pulses in time with the forward movement of the conveyor belt 2. The pulses are counted by a microcomputer 501. A posi- tional detector 502 which, in a simple construction, may comprise a photocell, senses when an object on the conveyor belt has rached a given position. The

positional detector then instructs the microcomputer to read a number of belt transducer pulses. The object is classified by additional information, for example by weighing or image analysis. This classification is not shown in Fig. 5 and, besides, is no part of the invention. Because normally a number of impellers are provided along the conveyor belt, the classification enables one to decide which impeller is to sort out the object 1b from the conveyor belt. The distances to the impellers are stored in the microcomputer.

After selection of the impeller to be activated, the microcomputer counts the number of belt transducer pulses corresponding to the distance to the desired impeller 10a. In the embodiment shown in Fig. 1A, the clutch 6 is of the electromagnetic type. The motor 3 is constantly activated, and the rotational impeller thus is controlled by the clutch.

A sensor 504 is mounted opposite the impeller 10a. In the embodiment illustrated (Fig. 1A) , the sensor is of the inductive type and connected to a power stage 500 comprising a simple logic circuit. If the sensor is not actuated by any of the metal plates 18 (Fig. 2) on the hub 19, the power stage will supply a current to the electromagnetic clutch 6, such that the clutch disc 8 is engaged with the driving disc 5. Current is supplied until the sensor senses one of the metal plates 18, and the sensor then supplies a braking order signal to the power stage which inter- rupts the clutching current and supplies a braking current to the clutch so that the clutch disc is engaged with the brake .disc 7. One of the blades 11a-e now is in the initial position I. When the microcomputer has calculated the time when an object is to be knocked off the conveyor belt, it supplies a starting signal to the power stage 500 which in turn supplies a clutching current to the clutch 6. The starting signal to the

power stage overrides the braking order signal from the sensor, for which reason a clutching current is supplied to the clutch in spite of the fact that the sensor is opposite a metal plate. The impeller 10a begins to rotate, and the starting signal from the microcomputer ceases after a short while, but the impeller does not stop until the sensor 504 is actuated by a new metal plate, such that a new blade comes into the initial position. By this construction, there is always one blade in the initial position after an interference, if any, such as a current failure, when the interference has been eliminated, i.e. an operating cycle is not begun until a blade is in the initial position. The arrangement according to the invention can cope with the variations of the belt speed as long as the objects do not slide on the belt after the position determination in that the microcom¬ puter counts the number of pulses from the belt transducer. The power stage is supplied with current from a mains supply 505.

It has heretobefore been difficult to remove the objects at high speed. This problem has been solved by the present invention in that the electromagnetic clutch has a relatively long response time before the magnetic fields have been built up sufficiently to make the electromagnets operative. By intermittently applying a high voltage across the magnetic cores, the current will increase more rapidly. When the current has increased, the voltage can then be reduced to prevent overheating of the clutch and excessive current consumption.

The clutching current has, furthermore, been adapted such that the clutch slips just enough, and this, in combination with the resilient blades, makes it possible to sort also extremely fragile products at high speed. One example is fifteen raw eggs per second

By varying the clutching current, an efficient overload protection is obtained.

Fig. 6 is a diagram of four signals comprised by the operating cycle of the device. Diagram A shows that a starting pulse is supplied from the microcomputer 501 to the power stage 500 at a time 0. The starting signal lasts only until the time t„, or for a fraction of the operating cycle. Diagram C illustrates the built-up voltage across the clutch coil, beginning at the time 0. After a certain period, the voltage is lowered and completely interrupted at the time t.. which is determined by the sensor. Diagram B shows the signal of the sensor, and it appears that the braking order signal of the sensor remains after the time 0 but, like before, the starting signal from the microcomputer overrides the braking order signal. After a time t- , the braking order signal is inter¬ rupted because the metal plate has left the sensing area of the sensor 504. Diagram D shows the voltage which is supplied to the brake coil in the clutch. At the time t-. , the sensor 504 supplies a braking order signal to the power stage which immediately begins to build up a voltage across the brake coil in the clutch. Like the voltage across the clutch coil, the voltage across the brake coil is given a high initial value and fades towards a constant voltage which remains until the voltage is interrupted at a time t. corresponding to the time 0 at the beginning of the operating cycle which thus lasts from 0 to t.. In diagrams A-D, a new operating cycle is thus begun at the time t. , and this is controlled by the microcomputer and the information supplied thereto by the classifying device mentioned above.

Closely packed objects can be sorted if the micro- computer also pays regard to the lateral position of the objects on the conveyor belt. By measuring and calculating the size and positions of the centres

of gravity, the blade width can be reduced such that the objects can be placed more closely together even though they vary in size.

In the preferred embodiment of the invention, removal is achieved by means of an almost elastic impact, the object following a trajectory away from the conveying track. The microcomputer may be supplied by signals indicating the mass, extent and volume of an object, and the engagement of the blade with the object can be controlled such that the object is thrown off in a controlled trajectory.

The man skilled in the art can design alternative embodiments without departing from the protective scope of the invention as defined by the appended claims.