FIELD OF THE INVENTION The invention relates to a device and a method for applying a cap to a package. More specifically the invention relates to a device and a method for applying a threaded cap to a threaded neck of a package. This type of devices comprises a conveyor, a package transport system, a cap dispenser and oppositely arranged and rotatable belts for rotating the cap on the package neck.

Packages of this type are generally used in connection with packages for liquid foodstuff, such as milk, juice, water, yoghurt and similar, but can be used for other types of packages having a threaded neck. One common type of packages of this type is carton packages having a neck and a cap of plas- tic materials.

PRIOR ART

There is a plurality of different types of devices for applying a threaded cap to a threaded neck of a package by means of rotating belts in the prior art. One such type of device comprises a conveyor and a pair of package supporting belts for transporting packages in a travel direction, wherein a cap is supplied to the top of the neck when the package passes a cap dispenser. Then, the cap is tightened by means of a cap tightening device having oppo- sitely arranged cap tightening belts for engaging and rotating the cap onto the neck. For example, a line of packages are transported on a continuously operating conveyor, wherein the continuously conveyed packages at short intervals pass the cap dispenser and wherein caps at short intervals are tightened by means of the cap tightening belts.

One problem with such prior art devices for applying a threaded cap to a threaded neck of a package is that a number of packages have tilted caps or caps not tightened correctly, which result in discarded packages and discarded content. SUMMARY OF THE INVENTION

An object of the invention is to provide a device and a method which result in a reduced number of tilted caps and caps not being applied properly, wherein the number of discarded packages and the amount of discarded content can be reduced.

The present invention relates to a device for applying a threaded cap to a threaded neck of a package, comprising a rotatable first belt and a rotat- able second belt arranged opposite to the first belt for engaging and rotating the cap between said first and second belts, and wherein the device comprises at least one motor for rotating at least one of the first and second belts characterised in that the motor is coupled to a control device and a sensor for monitoring velocity, acceleration, torque and/or current of the motor, that the control device is arranged for controlling the operation of the motor, that the control device is arranged for setting the motor in a thread entry detecting mode in which the first and second belts rotate the cap in a direction opposite to a cap tightening direction, that the control device is arranged for detecting a thread entry by means of variations in motor velocity, acceleration, torque and/or current, and that the control device is arranged for setting the motor in another mode as a response to the detected thread entry. By rotating the cap in a reversed direction and monitoring one or more of the mentioned values (velocity, acceleration, torque and/or current) of the at least one motor driving the belts the thread entries can be detected in an efficient manner, so that the tightening of the cap can be more precise and the number of tilted caps can be reduced.

A first motor can be connected to the first belt and a second motor can be connected to the second belt. The first motor can be coupled to a first sensor and the second motor can be coupled to a second sensor for monitoring the value, such as the velocity, of each of the motors. The control device can be arranged for calculating a resulting value, such as a resulting velocity, of the values, such as the velocities, of the first motor and the second motor and detecting a thread entry by means of said resulting value passing a threshold value. The resulting value, such as the resulting velocity, of the first and second motors provides a reliable parameter for detecting thread entries, wherein thread entries can be detected with great accuracy. The resulting value, such as the resulting velocity, can be a sum, a mean value or a difference of the values, such as the velocities, of the first motor and the second motor depending on the mechanical construction of the device and settings in the control device. Variations in motor values, such as velocities, appear more clearly when monitoring the resulting value, such as the resulting velocity, compared to monitoring the variations in motor values, such as motor velocities, separately. Alternatively, a resulting acceleration, torque or current can be calculated and used for detecting thread entries in a similar manner. Alternatively, a combination of measured values (velocity, acceleration, torque and/or current) or calculated resulting values are used for detecting thread entries.

The control device can be arranged for detecting a thread entry when a decreasing motor velocity or acceleration, such as the resulting velocity or acceleration, passes a predetermined threshold value followed by an increase in motor velocity or acceleration. Similarly, the control device can be arranged for detecting a thread entry when an increasing motor torque or motor current passes a predetermined threshold value followed by a de- crease in motor torque or motor current. The motor velocity decreases when the threads engage each other again after a thread entry has been passed and the friction between the threads increase. Then, when the friction between the threads momentarily is lost due to a thread entry the required torque is reduced and the velocity increases. Monitoring a motor velocity de- crease followed by a motor velocity increase has been found to result in a particularly favourable thread entry detection. Alternatively, the control device can be arranged for detecting a thread entry when an increasing motor velocity or acceleration, such as the resulting velocity or acceleration, passes a predetermined threshold value followed by a decrease in motor velocity or acceleration. Similarly, the control device can be arranged for detecting a thread entry when a decreasing motor torque or motor current passes a predetermined threshold value followed by an increase in motor torque or motor current. The motor velocity increases rapidly when the friction between the threads momentarily is lost due to a thread entry and the required torque is reduced. Then, when the threads engage each other again the friction increases, which results in increased torque requirement and reduced motor velocity. Hence, monitoring a motor velocity increase followed by a motor velocity decrease is also possible to increase the reliability of the thread entry detection.

The device can comprise a package conveyor and a pair of package supporting belts for continuously conveying the package. For example, the packages are conveyed during capping, including thread entry detection. For example, the control device is arranged to take a package conveying velocity into account for thread detection and capping operations. Hence, the packages can be conveyed continuously without stopping in a capping line, which results in efficient capping. The device can also comprise a detector for detecting the position of the cap along the conveyor before engaging the first and second belts. Hence, the position of the cap or the position of the package, which gives the position of the cap, e.g. by calculation, along the travel direction can be monitored by the device, e.g. by the control device.

The cap can be tightened by changing the operation of the first and second belts after detection of the thread entry. Alternatively, the device can comprise a cap tightening device arranged after the first and second belts in the travelling direction, said cap tightening device having a third belt and a fourth belt for engaging and tightening the cap.

The control device can be arranged for changing the first and second motors from the thread entry detecting mode to the other mode, such as a cap transport mode or a cap tightening mode, with a delay after thread entry detection, e.g. to compensate for motor operation change time and cap thread entries. Hence, the cap can be positioned in the desired position, such as in between thread entries to provide a stable and reliable tightening subsequent to thread entry detection. Hence, the cap can be positioned in the desired position on the neck, e.g. taking thread design into account and taking any system inertia into account. The device can comprise a cap top engaging element for biasing the cap towards the neck during thread entry detection. By means of the cap top engaging element the thread of the cap is pressed towards and against the thread of the neck to provide a suitable amount of friction between said threads when the threads are engaged and thus provide a suitable motor velocity increase when the friction is reduced or when the friction cease for a brief moment when a thread entry is passed during rotation of the cap.

The present invention also relates to a method for applying a threaded cap to a threaded neck of a package, comprising the steps of

a) supplying the cap to the neck,

b) engaging the cap by a rotatable first belt and a rotatable second belt arranged opposite to the first belt,

c) rotating the cap in a direction opposite to a cap tightening direction by means of at least one motor connected to the first and second belts,

d) monitoring velocity, acceleration, torque and/or current of the at least one motor by means of a sensor and a control device,

e) detecting a thread entry of the cap and neck by variations in motor velocity, acceleration, torque and/or current, and

f) subsequent to step e, tightening the cap on the neck. Further characteristics and advantages of the present invention will become apparent from the description of the embodiments below, the appended drawings and the dependent claims.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will now be described more in detail with the aid of embodiment examples and with reference to the appended drawings, in which

Fig. 1 is a schematic perspective view illustrating a part of a device for applying a cap to a package according to one embodiment of the present invention, in which a container conveyor, a package transport system, a part of a cap dispenser and belts for rotating the cap are illustrated schematically, and wherein a package is illustrated in the device, Fig. 2 is a schematic view according to Fig. 1 , illustrating an alternative embodiment, Fig. 3 is a schematic side view of a part of the device as illustrated in Fig. 1 , partly in section and in which a part of the device has been removed, wherein packages are transported by means of the conveyor and the package transport system, Fig. 4 is a schematic side view according to Fig. 3, illustrating a package passing the cap dispenser for supplying a cap onto the top of the package neck before engaging the cap rotating belts,

Fig. 5 is a schematic front view of a part of the device according to one em- bodiment, schematically illustrating a package in the device,

Fig. 6 is a schematic view of a part of the device seen from above,

Fig. 7 is a schematic front view according to Fig. 6, illustrating another alter- native embodiment,

Figs. 8 and 9 are schematic views from above, schematically illustrating a cap entering between first and second rotating belts and the rotation of the first and second belts in a cap transport mode according to one embodiment,

Figs. 10 and 1 1 are schematic views from above, schematically illustrating the cap between the first and second rotating belts and the rotation of said belts in a thread entry detecting mode according to one embodiment, Figs. 12 and 13 are schematic views from above, schematically illustrating the cap between the first and second rotating belts and the rotation of said belts in a cap transport mode according to one embodiment, Figs. 14 and 15 are schematic views from above, schematically illustrating the cap between third and fourth rotating belts and the rotation of said belts in a cap transport mode according to one embodiment, Figs. 16 and 17 are schematic views from above, schematically illustrating the cap between the third and fourth rotating belts and the rotation of said belts in a cap tightening mode according to one embodiment,

Figs. 18 and 19 are schematic views from above, schematically illustrating the cap between the third and fourth rotating belts and the rotation of said belts in a cap transport mode according to one embodiment,

Fig. 20 is a schematic diagram illustrating one example of detected velocities of first and second motors driving the first and the second belts, respectively, according to one example, and

Fig. 21 is a schematic diagram illustrating one example of a resulting velocity of detected velocities of the first and second motors for detecting a thread entry.

THE INVENTION

Referring to Fig. 1 a device 10 for applying a threaded cap 1 1 to a threaded neck 12 of a package 13 is illustrated schematically. For example, the device 10 is arranged for applying caps 1 1 to packages 13, such as carton packages, plastic packages or packages of a combination of carton and plastic materials. For example, the packages 13 are packages for liquid foodstuff. According to one embodiment, the package 13 is formed with a flat top. Alternatively, the package 13 is formed with an inclined top or is a gable top package. For example, the cap 1 1 and neck 12 are of plastic materials. According to one embodiment the neck 12 is provided in the top of the package 13 and extends at least partially vertically. The neck 12 is, for example, formed as a closure spout. The device 10 comprises a package transport system 14, a cap dispenser 15 and a cap tightening device 16. The package transport system 14 is arranged for supporting and transporting packages 13 in a travel direction, such as a horizontal or substantially horizontal travel direction. The package transport system 14 is arranged for continuously supporting packages 13 along the package transport system 14, wherein the packages 13, e.g., form a line of packages 13. In the illustrated embodiment the package transport system 14 comprises a rotatable first package supporting belt 17 and an opposite rotatable second package supporting belt 18 for engaging and sup- porting the packages 13. The first and second package supporting belts 17, 18 of the package transport system 14 are arranged for engaging opposite sides, such as opposite vertical sides, of the package 13. The first and second package supporting belts 17, 18 are mounted to pulleys 19 and are operated by one or more motors 20. For example, the pulleys 19 are rotated around vertical axes for transporting the packages 13 in a horizontal direction. The pulleys 19 are supported by a supporting structure 21 , which is illustrated schematically in the drawings and which can be of various designs. In the illustrated embodiment the package bottoms are supported by a conveyor 22, such as a conventional conveyor for conveying the packages 13. The conveyor 22 is arranged as a rotating belt or similar moving the packages 13 in the travel direction. For example, the conveyor 22 rotates in the same speed as the first and second package supporting belts 17, 18 of the package transport system 14.

The cap dispenser 15 is arranged for supplying caps 1 1 to the necks 12 of the packages 13. In the illustrated embodiment the cap dispenser 15 comprises a chute 23 for feeding caps 1 1 to a cap supplying position, in which position packages 13 moving on the conveyor 22 and in the package transport system 14 engages the caps 1 1 . The chute 23 is, for example, connected to conventional cap storage and cap aligning means, which are not illustrated in the drawings.

The device 10 comprises a rotatable first belt 24 and a rotatable second belt 25 arranged opposite to the first belt 24 for engaging and rotating the cap 1 1 between said first and second belts 24, 25. In the illustrated em- bodiment the first belt 24 is connected to a first motor 26 and the second belt 25 is connected to a second motor 27 for rotating said belts 24, 25. Alternatively, a single motor is arranged for rotating the first and second belts 24, 25 The first and second belts 24, 25 are arranged for engaging the cap 1 1 and rotating the cap 1 1 of a package 13 being conveyed by the conveyor 22 and the package transport system 14. The first and second belts 24, 25 are arranged in parallel to the first and second package supporting belts 17, 18 of the package transport system 14. For example, the first and second belts 24, 25 are rotated around vertical axes. The first motor 26 and the second motor 27 are e.g. rotary actuators allowing for control of velocity. For example, the motors 26, 27 are electrical rotary actuators allowing for control of velocity, acceleration, angular position and current. For example, the motors 26, 27 are servomotors. For example, the motors 26, 27 are motors allowing measurement of velocity or rotational position in one or a few milliseconds intervals or less. The first motor 26 is coupled to a first sensor 28, wherein the second motor 27 is coupled to a second sensor 29, said sensors 28, 29 and a control device 30 being arranged for detecting velocity, acceleration, angular position and/or current of the motors 26, 27. For example, the sensors 28, 29 are arranged for detecting velocity, acceleration, angular position and/or torque, wherein the control device 30 is arranged for detecting current. The motors 26, 27 and the sensors 28, 29 are connected to the control device 30 for monitoring and controlling the operation of the motors 26, 27 and thereby also controlling the operation of the first and second belts 24, 25. For example, the control device 30 comprises a computer. In the illustrated embodi- ment the control device 30 comprises an input device and a monitor.

In the embodiment of Fig. 1 the device 10 comprises a rotatable third belt 31 and a rotatable fourth belt 32 for engaging and rotating the cap 1 1 . The third belt 31 is connected to a third motor 33 and the fourth belt 32 is connected to a fourth motor 34 for operating the third and fourth belts 31 , 32. For example, the third and fourth motors 33, 34 are coupled to a third and fourth sensor, respectively, and are connected to the control device 30. Supporting structures for the belts 25, 26, 33, 34 are not illustrated in the drawings or are simplified. However, such supporting structures are conventional. In the embodiment of Fig. 1 the third and fourth belts 31 , 32 form the cap tightening device 16, wherein the first and second belts 24, 25 are arranged for detecting a thread entry of the cap 1 1 and neck 12 and the third and fourth belts 31 , 32 are arranged for tightening the cap 1 1 . The cap tightening device 16 is arranged for tightening caps 1 1 on the necks 12 of the packages 13 by rotating the caps 1 1 . The third belt 31 is arranged opposite to the fourth belt 32 for tightening the cap 1 1 on the package neck 12 by rotation. The third and fourth belts 31 , 32 are arranged for engaging the cap 1 1 and rotating the cap 1 1 of a package 13 being conveyed by the conveyor 22 and the package transport system 14. The third and fourth belts 31 , 32 are for example aligned with the first and second belts 24, 25. For example, the third and fourth belts 31 , 32 are rotated around vertical axes.

The device 10 comprises a detector 35a and a position sensor 35b for detecting the position of the package 13, with or without the cap 1 1 , before the cap 1 1 engages the first and second belts 24, 25. The detector 35a and the position sensor 35b are connected to the control device 30. For example, the detector 35a is a sensor, such as a photocell or similar, detecting when a package 13 passes the detector 35a. In the illustrated embodiment, the position sensor 35 b is connected to the motor 20 driving one of the package supporting belts 17, 18 to monitor a distance the motor 20 has driven the package supporting belt 17, 18 and hence the distance the package 13 has travelled since detection by the detector 35a. Alternatively, the position sensor 35b is connected to one of the pulleys 19, one of the axes driving the conveyor 22 or the motor driving the conveyor 22 to monitor the position of the package 13. For example, the position sensor 35b is a rotation sensor measuring the number of revelations on the axis it is connected to. The control device 30 uses the measured value from the position sensor 35b to calculate a distance that the package supporting belts 17, 18 or the conveyor 22 has travelled since the measurement was initiated by a package 13 passing the detector 35a. Hence, by means of the detector 35a and the position sensor 35b the control device 30 calculates the position of the package 13 or the cap 1 1 in relation to the position in which the detector 35a was affected by the same package 13 or cap 1 1 . For example, the position sensor 35b com- prises a pulse transducer or similar connected to the control device 30 for monitoring the position of the package 13 and/or cap 1 1 along the conveyor. Alternatively, the position of the cap 1 1 is monitored by the time lapsed since the package 13 passed the detector 35a, wherein a clock for indicating the lapsed time is started by the detector 35a. Alternatively, the position of the cap 1 1 in relation to the belts 24, 25 are detected or monitored in another suitable manner. For example, the control device 30 includes a shift register (FIFO) or similar for monitoring the position of a plurality of packages 13 in the device 10 simultaneously. A cap top engaging element 36 for biasing the cap 1 1 towards the neck 12 when the cap 1 1 passes between the first and second belts 24, 25 is provided. For example, the cap top engaging element 36 is arranged for biasing the cap 1 1 towards the neck 12 when the cap 1 1 passes between the first, second, third and fourth belts 24, 25, 31 , 32. For example, the cap top engaging element 36 is arranged as a top glide, wherein the top of the cap 1 1 at least partially slides along the cap top engaging element 36 during its transport by the first and second belts 24, 25 or during its transport by the first, second, third and fourth belts 24, 25, 31 , 32. Alternatively, the cap top engaging element 36 comprises a rotating belt or similar. With reference to Fig. 2 an alternative embodiment is illustrated, wherein the first and second belts 24, 25 form the cap tightening device 16. Hence, the operations of the first, second, third and fourth belts 24, 25, 31 , 32 in Fig. 1 are combined to the first and second belts 24, 25 in the embodiment according to Fig. 2. In such an embodiment the length of the first and second belts 24, 25 are for example longer than in the embodiment of Fig. 1 .

With reference to Figs. 3-5 packages 13 are conveyed in the travel direction by means of the conveyor 22 and the package transport system 14, which travel direction is illustrated by means of the arrow A in the drawings. The conveyor 22 and the package transport system 14 is arranged for con- veying the packages 13 continuously in the travel direction A, e.g. at a constant speed. The conveyor 22 and the package transport system 14 is arranged for conveying a single line of packages 13, so that one single pack- age 13 at a time passes the detector 35a and so that one single package 13 at a time passes the cap dispenser 15. For example, packages 13 are conveyed continuously and are continuously transported through the cap dispenser 15 and through the gap between the first and second belts 24, 25. During transport along the conveyor 22 and the package transport system 14 the package 13 passes the detector 35a, wherein the position thereof along the conveyor 22 is detected. Alternatively, the detector 35a is arranged at the cap dispenser 15 or between the cap dispenser 15 and the first and second belts 24, 25 to detect the position of the cap 1 1 along the conveyor 22. In the cap dispenser 15 the neck 12 engages a cap 1 1 and, by further movement of the package 13 in the travel direction A, pulls a cap 1 1 from the cap dispenser 15, wherein a cap 1 1 is applied on the top of the neck 12 without being tightened onto the neck 12, which is illustrated in Fig. 4. For example, the cap 1 1 is tilted or inclined in relation to the neck 12, wherein a front edge of the neck 12 of the package 13 travelling in the travel direction A is brought into contact with an inner surface of the cap 1 1 , wherein the cap 1 1 is removed from the cap dispenser 15 and falls down on the neck 12, so that the cap 1 1 is carried by the neck 12. Then, the package 13 with the cap 1 1 being carried on the top of the neck 12 is conveyed to the first and second belts 24, 25, wherein the cap 1 1 is rotated in a direction opposite to the tightening direction, such as counter clockwise, to detect the thread entry and position the cap in a desired position on the neck, which is described in more detail below. Then, after detection of the thread entry and positioning of the cap in the desired position the package 13 with the cap 1 1 is conveyed to the cap tightening device 16, wherein the cap 1 1 is tightened by rotation by means of the third and fourth belts 31 , 32. Then, the package 13 exits the cap tightening device 16 for further handling. For example, after the thread entry has been detected or the cap 1 1 has been disengaged from the first and second belts 24, 25 the cap 1 1 of the next package 13 is introduced be- tween the first and second belts 24, 25.

With reference to Fig. 6 a part of the device 10 is illustrated from above, wherein the cap top engaging element 36 has been removed. In the embodiment of Fig. 6 a number of packages 13 are conveyed on the con- veyor 22. In the embodiment of Fig. 6 the packages 13 are supported by the first and second package supporting belts 17, 18. In the illustrated example, the packages 13 are conveyed continuously and adjacent each other. Alternatively, the packages 13 are conveyed with a gap between them. The de- tector 35a is arranged for detecting when a front part of the cap 1 1 carried by the package 13 passes the detector 35a in the travel direction A. Hence, the detector 35a is arranged in a position after the cap 1 1 has been applied to the neck 12 in the cap dispenser 15 and before the cap 1 1 engages the first and second belts 24, 25. The detector 35a and the control device 30 is ar- ranged for monitoring the position of the cap 1 1 to determine the mode of operation of the first and second belts 24, 25 and also the third and fourth belts 31 , 32 when applicable. For example, the detector 35a and the control device 30 are connected to a pulse transducer of the motor operating the conveyor 22 or the motor 20 operating the package supporting belts 17, 18 or similar to monitor the position of the cap 1 1 along the travel direction A. With reference to Fig. 7 the detector 35a is arranged for detecting when a rear part of the cap 1 1 carried by the package 13 passes the detector 35a in the travel direction A.

With reference to Figs. 8-19 one example of the operations of the belts 24, 25, 31 , 32 are illustrated schematically for one package 13 passing through the device 10. However, it is to be understood that packages 13 are conveyed continuously with suitable or no distance between the packages 13. For example, packages 13 are conveyed adjacent to each other or with a gap between them. In Figs. 8 and 9 a package 13 has been provided with a cap 1 1 in the cap dispenser 15 and the position of the cap 1 1 has been detected by the detector 35a. Before the cap 1 1 engages the first and second belts 24, 25 they are put in a transport mode, wherein the first and second belts 24, 25 rotate to transport the cap 1 1 in the travel direction A at the same speed as the conveyor 22 without rotating the cap 1 1 . Hence, the control device 30 is arranged to set the first and second belts 24, 25 in the transport mode a predetermined time after detecting the cap 1 1 by the detector 35a or after the package 13 has travelled a predetermined distance after detection of the cap 1 1 by the detector 35a. Hence, the first and second belts 24, 25 rotate in the same velocity and in opposite directions, which is illustrated by the arrows B and C in Fig. 9. The rotations of the first and second package supporting belts 17, 18 are illustrated by means of the arrows H and I. The third and fourth belts 31 , 32 are, for example, tightening or transporting another cap (not illustrated) simultaneously as the first and second belts 24, 25 are transporting the cap 1 1 , which is illustrated by means of the dash and dot arrows.

With reference to Figs. 10 and 1 1 the first and second belts 24, 25 are set in a thread detection mode, wherein the cap 1 1 is rotated in a direction opposite to the cap tightening direction, which is illustrated by means of the arrow on the cap 1 1 in Fig. 10. Hence, in the illustrated embodiment the mode of operation of the first and second belts 24, 25 are changed by means of the control device 30 from the transport mode to the thread detection mode after the cap 1 1 has entered between the first and second belts 24, 25. Alternatively, the first and second belts 24, 25 are set in the thread detection mode before the cap 1 1 engages the first and second belts 24, 25. In the thread detection mode the velocity of the first belt 24 is increased in relation to the second belt 25 for reversed rotation of the cap 1 1 . In the illustrated embodiment the direction of rotation of the second belt 25 is changed. The rotations of the first and second belts 24, 25 are illustrated by means of the arrows D and E in Fig. 1 1 . The third and fourth belts 31 , 32 are, for example, tightening or transporting another cap 1 1 (not illustrated) simultaneously as the first and second belts 24, 25 are rotating the cap 1 1 , which is illustrated by means of the dash and dot arrows. With reference to Figs. 12 and 13 the first and second belts 24, 25 are set in the transport mode after detection of the thread entry. Hence, after detection of the thread entry and positioning of the cap 1 1 in the desired rotational position the mode of operation of the first and second belts 24, 25 are changed from the thread entry detecting mode to the transport mode for feeding out the cap 1 1 from the first and second belts 24, 25 without further rotation and, e.g., for receiving the cap of the next package 13 between the first and second belts 24, 25. Hence, the rotation of the first and second belts 24, 25 are set to rotate in the same speed and in opposite directions, which is illustrated by means of the arrows B and C in Fig. 13. Hence, according to the illustrated embodiment the control device 30 is arranged for controlling the first and second motors 26, 27 to operate in the cap transport mode when the cap 1 1 enters between the first and second belts 24, 25, and then to op- erate in the thread entry detecting mode followed by a change back to the transport mode. Alternatively, the control device 30 is arranged to operate the first and second motors 26, 27 in the thread entry detecting mode when the cap 1 1 engages the first and second belts 24, 25, followed by a change to the cap transport mode after detection of the thread entry. Optionally, the control device 30 is also arranged to position the cap 1 1 in the desired position taking into account the thread design of the cap 1 1 and the time or rotational distance for the first and second motors 26, 27 to stop and/or change speed and/or change direction once the thread entry has been detected. The third and fourth belts 31 , 32 are, for example, tightening or transporting an- other cap 1 1 (not illustrated) simultaneously as the first and second belts 24, 25 are transporting the cap 1 1 , which is illustrated by means of the dash and dot arrows.

With reference to Figs. 14 and 15 the cap 1 1 engages the third and fourth belts 31 , 32 for tightening the cap 1 1 on the neck 12. Hence, after de- tection of the thread entry and positioning of the cap 1 1 in the desired rotational position by means of the first and second belts 24, 25 the package 13 with the cap 1 1 is conveyed to the third and fourth belts 31 , 32 for tightening the cap 1 1 . Alternatively, the cap 1 1 is tightened in a corresponding manner by means of the first and second belts 24, 25 as illustrated in Fig. 2. In the illustrated embodiment the control device 30 is arranged to operate the third and fourth belts 31 , 32 in a cap transport mode by means of the motors 33, 34 before the cap 1 1 engages the third and fourth belts 31 , 32, which is illustrated by means of the arrows F and G in Fig. 15. In the cap transport mode the cap 1 1 is transported without rotation thereof. Then, the operation of the third and fourth belts 31 , 32 are changed to a cap tightening mode in which the cap 1 1 is tightened on the neck 12 by rotating the cap 1 1 by means of the third and fourth belts 31 , 32, which is illustrated in Figs. 16 and 17. Hence, the velocities of the third and fourth belts 31 , 32 are changed. In the illustrat- ed embodiment the direction of the third belt 31 is changed and the speed thereof is reduced, wherein the speed of the fourth belt 32 is increased while the direction thereof is maintained, which is illustrated by means of the arrows J and K in Fig. 17, so as to provide a rapid tightening of the cap 1 1 by rotation. For example, the cap 1 1 is tightened to a predetermined torque, which is measured on the third and/or fourth motors 33, 34, optionally taking into account the time or rotational distance for the third and fourth motors 33, 34 to change their speed or mode of operation back to the transport mode, which is illustrated in Figs. 18 and 19. Hence, after tightening the cap 1 1 to the desired torque by means of the third and fourth belts 31 , 32 the mode of operation is changed to the transport mode, wherein the third and fourth belts 31 , 32 are operated in a velocity and direction so as to transport the cap 1 1 without further rotation thereof, which is illustrated by means of the arrows F and G in Fig. 19. The control device 30 is, for example, arranged to operate the third and fourth motors 33, 34 to drive the third and fourth belts 31 , 32 in the cap transport mode before the cap 1 1 engages the third and fourth belts 31 , 32 and then to change the mode of operation to the cap tightening mode followed by a change back to the cap transport mode once the cap has been tightened to the desired torque as measured on one or both of the third and fourth motors 33, 34. The first and second belts 24, 25 are, for example, rotating or transporting another cap 1 1 (not illustrated) simultaneously as the third and fourth belts 31 , 32 are tightening or transporting the cap 1 1 , which is illustrated by means of the dash and dot arrows.

With reference to Figs. 20 and 21 detection of thread entry is illustrated according to one embodiment by simplified and schematic examples of diagrams of the velocities of the first and second motors 26, 27 over time.

Hence, in the diagrams the horizontal x-axis represents time. Alternatively, the x-axis represents a distance travelled by the package 13. The first and second motors 26, 27 drive the first and second belts 24, 25, respectively, in the thread detection mode and the transport mode by means of the control device 30, the detector 35a and the first and second sensors 28, 29 as described above. For example, a continuous and constant speed command is applied to the first and second motors 26, 27 in the thread detection mode. The variation in resulting or single motor velocity is monitored and taken into account for detecting the thread entry. Alternatively, variations in acceleration or torque/current is monitored and taken into account to detect the thread entry. With reference to Fig. 20 the dashed line 37 represents the velocity of the first motor 26 driving the first belt 24, wherein the continuous line 38 represents the velocity of the second motor 27 driving the second belt 25. A first thin line 39 represents detection of a package 13 or a cap 1 1 by the detector 35a. A second thin line 40 represents detection of a thread entry. In the illus- trated example, the first and second motors 26, 27 operate at a substantially constant speed or at a substantially constant current during the cap transport mode. For example, the first and second motors 26, 27 operate at a predetermined speed command. A predetermined time or travelled distance after detection of a cap 1 1 or a package 13 by the detector 35a the mode of op- eration of the first and second motors 26, 27 is changed from the cap transport mode to the thread entry detecting mode, wherein the velocities of the first and second motors 26, 27 are changed. This is illustrated in Fig. 20 by the continuous line 38 going down steeply and extensively, which indicates that the velocity of the second motor 27 increases rapidly and substan- tially in a direction opposite of the first motor 26. The dashed line 37, on the other hand, goes up steeply and extensively, which indicates that the velocity of the first motor 26 increases rapidly and substantially. For example, the first and second motors 26, 27 are operated in the cap transport mode when the cap 1 1 engages the first and second belts 24, 25. Alternatively, the first and second motors 26, 27 are operated in the thread detection mode when the cap 1 1 engages the first and second belts 24, 25. In the thread detection mode the cap 1 1 is rotated in the direction opposite the tightening direction, such as counter-clockwise. During rotation in the direction opposite the tightening direction the threads of the cap 1 1 and the neck 12 are intermittently engaged and result in friction between the threads. The friction between the threads is, for example, partially determined by the cap top engaging portion 36 and the pressure applied to the cap 1 1 by it. For example, the pressure applied on the cap 1 1 by the cap top engaging element 36 is adjustable. After the cap 1 1 has reached its uppermost position by rotation in the direction opposite tightening direction the threads are disengaged for a moment and the cap 1 1 falls down, wherein the cap 1 1 and neck 12 are positioned in a thread entry position. When the threads are disengaged and the cap 1 1 drops down the friction between the threads drops suddenly and the velocities of the first and second motors 26, 27 increase suddenly for a short moment. Then the threads engage again and the cap 1 1 is rotated upwards along the thread of the neck 12, which results in an increase in friction between the threads and a temporary reduction in the velocities of the first and second motors 26, 27 as the speed command applied to the first and second motors 26, 27 are constant but the controlling device 30 cannot immediately correct the velocities of the first and second motors 26, 27 due to mechanical inertia. These variations in velocities of the first and second motors 26, 27 are illustrated by small peaks of the continuous line 38 and the dashed line 37 in the diagram of Fig. 20. Every time a thread entry is encountered variations in the velocities of the first and second motors 26, 27 are detected. The velocities of the first and second motors 26, 27 are monitored by means of the first and second sensors 28, 29 and the control device 30. For example, the control device 30 is arranged to detect a thread entry when the velocities of the first and second motors 26, 27 are increased to a predetermined value. For example, the control device 30 is arranged to detect a thread entry when at least one of the velocities of the first and second motors 26, 27 is increased to a predetermined value. For example, the control device 30 is arranged to detect a thread entry when at least one of the velocities of the first and sec- ond motors 26, 27 is increased to a predetermined value followed by a decrease. Moment of detection of a thread entry is illustrated by means of the second thin line 40. Alternatively, the control device 30 is arranged to detect a thread entry when at least one of the velocities of the first and second motors 26, 27 is decreased followed by an increase, wherein at least one of the velocity decrease and velocity increase passes a predetermined threshold value. According to one embodiment the mode of operation of the first and second motors 26, 27 is changed by means of the control device 30 from the thread entry detecting mode to the cap transport mode after detection of a thread entry. For example, the control device 30 is arranged to stop the thread entry detecting mode and change to the cap transport mode a predetermined time or a predetermined package transport distance after detecting a thread entry to position the cap 1 1 in the desired position, e.g. taking into account the cap design, such as the number and positions of thread entries, and e.g. compensating for motor inertia, i.e. the time it takes for the motors 26, 27 to stop, change velocity and/or change direction. For example, the cap 1 1 is positioned so that the thread entry of the cap 1 1 is positioned in between two thread entries, such as in the middle between two thread entries. Hence, after detecting the thread entry and positioning the cap 1 1 in the desired position on the neck the operation of the first and second belts 24, 25 is changed from reversed rotation of the cap 1 1 to the cap transport mode for conveying the package 13 without further rotation of the cap 1 1 by the first and second belts 24, 25. Alternatively, the operation of the first and second belts 24, 25 is changed from reversed rotation to a cap tightening mode after detection of the thread entry as described with reference to Fig. 2.

With reference to Fig. 21 a schematic diagram of a resulting velocity of a detected velocity of the first motor 26 and a detected velocity of the second motor 27 is illustrated by means of a resulting velocity line 41 . In the illus- trated embodiment the resulting velocity is a subtraction between the two velocities. Alternatively, the resulting velocity is obtained as a mean value or a sum of the velocities.

The detection of a cap 1 1 or a package by the detector 35a is illustrated by the first thin line 39. In the illustrated embodiment the cap 1 1 is then conveyed into engagement with the first and second belts 24, 25 operated in the cap transport mode by the first and second motors 26, 27 and the control device 30. Then the mode of operation is switched from cap transport mode to thread entry detecting mode, wherein the thread entry is detected as illustrated by means of the second thin line 40. A thread entry is detected as an increase in the resulting velocity such as the difference of the velocity of the first motor 26 and the velocity of the second motor 27, by a predetermined value. Velocity increases and decreases are indicated as peaks in the resulting velocity line 41 . For example, a thread entry is detected as an increase in the resulting velocity followed by a decrease. Alternatively, a thread entry is detected as a decrease in the resulting velocity followed by an increase. For example said increase and decrease must be within a predetermined package travel distance or within a predetermined period of time to be construed as a thread entry. For example, said increase and said decrease must reach predetermined threshold values for the monitored resulting velocity to be construed as a thread entry. When a thread entry is detected, as illustrated by the second thin line 40, the cap 1 1 is further rotated in the reversed direction, wherein further thread entries are passed, which is illustrated by the peaks following the second thin line 40 in Fig. 21 , before the mode of operation of first and second motors 26, 27 has changed from the thread entry detecting mode to the cap transport mode. The change in operation of the first and second motors 26, 27 is, for example, performed with a deliberate and predetermined delay. Hence, the cap 1 1 is positioned in the desired rotation- al position on the neck for subsequent tightening.

According to different alternative embodiments one or more values in the form of velocity, acceleration, torque and/or current of a single motor is monitored to detect the thread entry as mentioned above. Alternatively, acceleration, torque and/or current of the first and second motors are monitored to detect the thread entry.