SE2251172A1

SE2251172A1 - Folding apparatus and method for controlling electric actuators of a folding apparatus

Info

Publication number: SE2251172A1
Application number: SE2251172A
Authority: SE
Inventors: Dennis Engman; Fredrik Lööw; Henrik Hedström; Marcus Kvist; Mikael Nilsson; Stefan Näslund
Original assignee: Valmet Oy
Priority date: 2022-10-07
Filing date: 2022-10-07
Publication date: 2023-11-07
Also published as: SE545596C2; WO2024076277A1

Abstract

Folding apparatus for folding ends of wrapping material around a pulp bale, the folding apparatus comprising at least two folding arms, each comprising a contact element at an end thereof, at least two electric actuators, each being arranged to co-act with one or more of the folding arms to displace its contact element for making contact with the wrapping material to fold said wrapping material around an edge of the pulp bale, and a control unit arranged in electrical contact with said at least two electric actuators, and arranged to determine, for each electric actuator, at least one operating parameter comprising a position parameter and/or a force parameter and/or a speed parameter, wherein said control unit is configured to control at least one electric actuator using said at least one operating parameter. A corresponding method is also provided.

Description

TECHNICAL FIELD The invention relates to the field of folding apparatuses for folding ends ofwrapping material around a pulp bale, the wrapping material being arranged around the circumference of the pulp bale and having a length being greater than a length of the pulp bale such that the ends of the wrapping material extend beyond opposite ends of the pulp bale.

BACKGROUND Folding apparatuses for folding ends of wrapping material around a pulp bale are known in the art. One example of such a folding apparatus is the Valmet Wrapper Folder, which comprises a plurality of folding arms actuated by hydraulic actuators, which folding arms fold the wrapping material around the edges of the pulp bale. Although such apparatuses provide high performance with low cycle times, a disadvantage is that the folding arms / hydraulic actuators need to be manually adjusted, for example during service of the folding apparatus or when a different bale size is to be used. This is time consuming and poses security problem since the operator needs to enter the security zone of the folding apparatus.

SUMMARY An object of the invention is to provide to provide a folding apparatus which at least partly solves or improves on the problems identified above.

These and other objects are achieved by the present invention by means ofa folding apparatus according to the independent claims.

According to a first aspect ofthe invention, there is provided a folding apparatus for folding ends of wrapping material around a pulp bale when positioned at a bale folding area in said folding apparatus. The wrapping material is arranged around the circumference of the pulp bale and having a length being greater than a length of the pulp bale such that the ends of the wrapping material extend beyond opposite ends of the pulp bale. The folding apparatus comprises at least two folding arms, each comprising a contact element at an end thereof, at least two electric actuators, each being arranged to co-act with one or more of the folding arms such as to displace its contact element for making contact with the wrapping material to fold said wrapping material around an edge of the pulp bale, and a control unit arranged in electrical contact with said at least two electric actuators, and arranged to determine, for each electric actuator, at least one operating parameter comprising a position parameter being correlated to a position of one or more contact element and/or a force parameter correlated or indicative of actuator torque or force and/ or a speed parameter correlated or indicative of a speed of rotation or displacement of the electric actuator, wherein said control unit is configured to control at least one electric actuator using said at least one operating parameter.

In other words, the folding apparatus comprises a bale folding area, which could also be referred to as a bale folding position, which area or position is where the pulp bale is to be positioned when the folding is to take place. The apparatus further comprises at least two folding arms, preferably arranged at opposite sides ofthe bale folding area. The folding arms may be displaceable and/ or rotatable, for example in the sense that they are rotatable around an axis of rotation or around a ball joint, which axis of rotation or ball joint is optionally displaceable. At least one, or each, of the folding arms comprises a contact element which may be arranged at, or in the vicinity of, an end thereof. The contact elements are adapted to make contact with the wrapping material to fold the wrapping material around an edge of the pulp bale. The apparatus further comprises at least two electric actuators, for example one electric actuator for each folding arm. Each electric actuator is arranged to co-act with one or more of the folding arms such as to displace its contact element. The control unit is arranged in wired or wireless electrical contact with the at least two electric actuators for control thereof. The control unit is arranged to determine, for at least one, or each, electric actuator, at least one operating parameter comprising a position parameter being correlated to a position of one or more contact element and/or a force parameter indicative of actuator torque or force and/or a speed parameter indicative of a speed of rotation or displacement of the electric actuator. The control unit is configured to control at least one, or each, electric actuator using the at least one operating parameter, i.e. the control unit uses the at least one operating parameter for feedback control of the electric actuator(s). It is understood that the circumference ofthe pulp bale refers to a circumference in a plane being substantially vertical to a length direction of the pulp bale. The pulp bale may be described as a rectangular cuboid in shape, where the wrapping material extends around the circumference to cover its long faces [i.e. the longer sides/faces extending in the lengthwise direction of the pulp bale). lt is understood that the wrapping material may be formed from one, two, or more sheets of wrapping material. The wrapping material has a length being greater than a length of the pulp bale such that not only the long faces/sides are covered, but also such that ends of the wrapping material extend beyond opposite ends of the pulp bale.

The invention is based on the insight to use electric actuators rather than hydraulic actuators, which electric actuators allows or facilitates control of the actuators based on at least one measured or determined operating parameter such as position and/ or, actuator torque/force and/or speed. Such control of the actuators based on Operating parameters, which may also be referred to as feedback control, may reduce or eliminate the need for manually adjusting the folding arms. A further advantage with electric actuators rather than hydraulic actuators is that energy consumption is reduced since the electric actuators only consume energy while actuating. A further advantage is that cycle times may be reduced since having [accurately controllable] electric actuators along with having knowledge of the position of each contact element allows the electric actuators to be actuated in such a manner that contact elements precisely pass each other. Present hydraulic actuators require large margins to avoid collisions between the contact elements.

It is understood that the directions referred to herein are defined in relation to the folding apparatus, where the bale folding area is defined as horizontal. For example, lateral movement thus refers to a movement comprising movement in the horizontal direction.

In embodiments, one or more ofthe at least two electric actuators each comprises an electric motor, wherein the control unit is configured to determine the position parameter using data obtained from one or more position sensors connected to the electric motor and/or to a thereto connected folding arm. The position sensor[s) may be pulse sensor[s) connected directly or indirectly to the shaft of the electric motor. Having accurate knowledge of the position of the contact elements provides several advantages. For example, the start and stop positions can be adjusted when a different bale size is to be used. Furthermore, the position of each actuator/contact element can also be monitored during operation of the apparatus and used for feedback control.

In embodiments, the electric motor is connected to a corresponding folding arm via a gearbox for rotation of the folding arm. For example, the folding arm rotates around an axis of rotation coinciding with the outgoing axle of the gearbox.

In other embodiments, the electric motor forms part of a mechanical linear actuator connected to a corresponding folding arm. The mechanical linear actuator may be screw actuator such as a traveling-nut linear actuator.

In embodiments, at least one, or each, of the electric motors is controlled using a variable frequency drive [VFD] controller, which may also be referred to as an inverter.

In embodiments, the control unit is configured to determine at least one target displacement parameter for one or more of the electric actuators. The folding apparatus may further comprise a Human Machine Interface, HMI, being arranged in communication with the control unit, wherein the HMI is configured to receive user input comprising the at least one target displacement parameter, or user input indicative thereof, and to transmit to the control unit one or more signals indicative of the user input, and wherein the control unit is configured to determine the at least one target displacement parameter using the one or more signals. The at least one target displacement parameter may be one or more of a start position [of the contact element or an actuator member), an end position [ofthe contact element or an actuator member), rotation speed [of the folding arm or of an electric motor axle), displacement speed [of the folding arm or of a linear actuator), actuator torque and actuator force. The target displacement parameters may also be referred to as target parameter values, for example target start and end positions, target speed/torque/force etc. The HMI may be a device in wired or wireless communication with the control unit. Alternatively, the HMI may be a software adapted to be executed on a handheld device or on a computer.

In embodiments, the folding apparatus comprises four folding arms arranged symmetrically around the bale folding area, for instance at opposing corners thereof, wherein a corresponding electric actuator for each of the four folding arms is arranged to co-act therewith such that the contact elements of the four folding arms are, independently of each other, displaceable into the bale folding area to make contact with wrapping material at a corresponding edge of the pulp bale. The four folding arms are preferably displaceable laterally into the bale folding area, i.e. displaceable in a substantially horizontal plane. It is understood that although a corresponding electric actuator for each of the four folding arms is arranged to co-act therewith, it is also foreseen that one or more additional electric actuators are provided, which each co-act with one or more of the four folding arms.

In embodiments, the control unit is configured to, based on at least one operating parameter for each of the electric actuators co-acting with the four folding arms, determine if the pulp bale is misaligned, and if so, control at least one of the electric actuators co-acting with the four folding arms in response thereto. The control unit may be configured to determine if the pulp bale is misaligned by comparing at least one operating parameter with a corresponding target displacement parameter [or with a maximum value) for each of the electric actuators co-acting with the four folding arms. For example, the position parameter of each of the actuators/contact elements [an operating parameter) may be compared with the corresponding end position [a target displacement parameter), and if for instance two of the position parameters are within a predetermined interval from the corresponding end positions, whereas the other two position parameters are outside the interval, it can be determined that the pulp bale is misaligned. Alternatively, or additionally, the force parameter indicative of actuator torque (an Operating parameter) may be compared with the corresponding (target) actuator torque (a target displacement parameter) or a predetermined (or via the HMI user adjustable) maximum torque, and if for instance two of the force parameters differ less than a predetermined amount from the corresponding actuator torque, whereas the other two force parameters differ more, it can be determined that the pulp bale is misaligned. ln response to a determination that the pulp bale is misaligned, various control actions are possible. For example, if the force parameter indicative of actuator torque for two diagonally opposing actuator has reached the corresponding actuator torque, while not having reached their corresponding end positions, the control unit can attempt to align the pulp bale by increasing the torque further to these two actuators until the end positions are reached.

In embodiments, two lower folding arms, or two sets oflower folding arms, are arranged symmetrically at opposing sides of the bale folding area, wherein, for each of the two lower folding arms or sets oflower folding arms, at least one electric actuator is arranged to co-act therewith such that the thereto connected contact element(s) is /are vertically displaceable towards (and above) the bale folding area from below for making contact with wrapping material at a corresponding lower edge of the pulp bale.

In embodiments, two upper folding arms, or two sets of upper folding arms, are arranged symmetrically at opposing sides of the bale folding area, wherein, for each of the two upper folding arms or sets of upper folding arms, at least one electric actuator is arranged to co-act therewith such that the thereto connected contact element(s) is /are vertically displaceable towards the bale folding area from above for making contact with wrapping material at a corresponding upper edge of the pulp bale.

It is understood that the contact elements of the lower and upper folding arms are not necessarily displaceable solely in a vertical direction (such as along a plumb line). For example, the folding arms are typically rotatable around an axis of rotation at an end thereof, which means that the thereto connected contact elements are displaced along a curved path, i.e. not solely in the vertical direction.

In embodiments, a rotation device, which may also be referred to as a turn table, is arranged at the pulp folding area and comprise a rotatable contact member adapted to engage with a pulp bale when positioned at the bale folding area to rotate the pulp bale, for instance 90 degrees. The rotation device may comprise one or more electric, pneumatic or hydraulic actuator to rotate the contact member. The one or more actuator is advantageously directly or indirectly electrically connected to the control unit for control thereof.

In embodiments, for each ofthe two lower or upper folding arms or sets of folding arms, at least one electric actuator is arranged co-act therewith such that the contact elements are laterally displaceable, wherein the control unit is configured to, prior to controlling the rotation device to rotate the pulp bale to a position where the ends of the wrapping material are directed towards the two folding arms, controlling the electric actuators co-acting with the two folding arms or sets of folding arms to: - displace (raise or lower) the contact elements to a vertical level being above the bale folding area (the vertical level being lower than the height of the pulp bale), and thereafter - displace the contact elements ofthe two folding arms towards each other for pushing opposite sides of the pulp bale until target positions are reached, which target positions are determined based on the pulp bale size.

According to a second aspect ofthe invention, there is provided a method for controlling electric actuators of a folding apparatus for folding ends ofwrapping material around a pulp bale, said folding apparatus comprising at least two folding arms, each comprising a contact element at an end thereof, and at least two electric actuators, each being arranged to co-act with one or more of the folding arms such as to displace its contact element for making contact with the wrapping material to fold said wrapping material around an edge of the pulp bale, the method comprising - determining, for each electric actuator, at least one operating parameter comprising a position parameter being correlated to a position of one or more contact element and/or a force parameter indicative of actuator force or torque and/or a position or speed indicative of actuator or folding arm position or speed; - controlling the at least two electric actuators using said at least one operating parameter.

In embodiments of the method according to the second aspect ofthe invention, the method further comprises determining at least one target displacement parameter for one or more (or each] of the electric actuators by means of receiving user input from a HMI comprising the at least one target displacement parameter, or user input indicative thereof. The at least one target displacement parameter may be one or more of a start position (of the contact element or an actuator member), an end position (of the contact element or an actuator member), rotation speed (of the folding arm or of an electric motor axle], displacement speed [of the folding arm or of a linear actuator), actuator torque and actuator force.

In embodiments of the method according to the second aspect ofthe invention, the method further comprises determining if the pulp bale is misaligned, and ifso, control at least one of the electric actuators co-acting with the four folding arms in response thereto, wherein it is determined if the pulp bale is misaligned by comparing at least one operating parameter with a corresponding target displacement parameter (or with a maximum value) for each of the electric actuators co-acting with the four folding arms.

According to a third aspect of the invention, there is provided a data processing device comprising means for carrying out the method according to the second aspect ofthe invention or embodiments thereof.

According to a fourth aspect of the invention, there is provided a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to the second aspect of the invention or embodiments thereof.

According to a fifth aspect of the invention, there is provided a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to the second aspect of the invention or embodiments thereof.

The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features. Further, all features and advantages of embodiments described above with reference to the first aspect of the invention may be applied in corresponding embodiments of the second, third, fourth and fifth aspects of the invention and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS Above discussed and other aspects of the present invention will now be described in more detail using the appended drawings, which show presently preferred embodiments of the invention, wherein: fig. 1 shows an embodiment of a folding apparatus according to the first aspect of the invention; fig. 2 shows the same embodiment as in fig. 1 (without the control unit and the HMI) along with a schematic illustration of a pulp bale entering the folding apparatus, and fig. 3 shows a detail view of one side of the folding apparatus in fig. 1 and 2.

DETAILED DESCRIPTION Figures 1-3 show an embodiment of a folding apparatus according to the first aspect of the invention. The folding apparatus 1 is configured for (see fig. 2] folding ends (for example 2a-d, corresponding ends are present at the opposite end of the pulp bale) of wrapping material 2 around a pulp bale 3 when positioned at the bale folding area 4 in the folding apparatus. As can be seen in fig. 2, the wrapping material is arranged around the circumference of the pulp bale and has a length being greater than a length of the pulp bale such that ends (Za-d for example] of the wrapping material extend beyond opposite ends (3a for example] of the pulp bale. The folding apparatus comprises folding arms 5a-d, 6a-b, 7a-d, each comprising a contact element 8a-d; 9a; 10a-b at an end thereof.

Four folding arms 5a-d are arranged symmetrically around the bale folding area 4 at opposing corners thereof. A corresponding electric actuator (each comprising an electric motor 11a-d and a gear box 11a'-d') for each of the four folding arms is arranged to rotate the folding arms such that the contact elements 8a-d of the four folding arms are, independently of each other, laterally displaceable into the bale folding area to make contact with wrapping material at a corresponding edge (3" for example, see fig. 2] of the pulp bale. The contact elements 8a-d are connected to the respective folding arm 5a-d in a rotatable/pivotable manner around axes of rotation which are parallel to the axes of rotation of the folding arms 5a-d. Springs are arranged to pre-load the contact elements to the shown position. Assuming that the folding apparatus is arranged horizontally (with the bale folding area horizontal), the mentioned axes of rotation are substantially vertical.

Two lower folding arms 6a-b are arranged symmetrically at opposing sides ofthe bale folding area 4, wherein, for each of the two lower folding arms, one electric actuator (each comprising an electric motor 12a-b and a gear box 12a'-b') is arranged to rotate the folding arms 6a-b such that the contact element (9a for example, arm 6b comprises a corresponding contact element which is not seen in the figures] is vertically displaceable towards the bale folding area from below for making contact with wrapping material at a corresponding lower edge (3' for example, see fig. 2) of the pulp bale. The contact elements (9a for example) are connected to the respective folding arm 6a-b in a rotatable/pivotable manner around axes of rotation which are parallel to the axes of rotation of the folding arms 6a-b. Springs are arranged to pre-load the contact elements to the shown position, as can be seen in fig. 3. Assuming that the folding apparatus is arranged horizontally (with the bale folding area horizontally), the mentioned axes of rotation are substantially horizontal.

Two sets of upper folding arms 7a-b, 7c-d, are arranged symmetrically at opposing sides of the bale folding area, wherein, for each of the two sets of upper folding arms, one electric actuator (each comprising an electric motor 13a-b and a gear box 13a'-b') is arranged to rotate the folding arms such that the thereto connected contact elements 10a-b are vertically displaceable towards the bale folding area from above for making contact with wrapping material at a corresponding upper edge of the pulp bale.

The folding apparatus further comprises a rotation device 17 arranged to engage with a pulp bale 3 when positioned at the bale folding area 4 to rotate said pulp bale.

The folding apparatus further comprises a conveying arrangement comprising two chains 18a-b arranged to convey the pulp bale from an inlet of the folding apparatus to the bale folding area and further to an outlet ofthe folding apparatus. ln fig. 2, the bale can be seen at an inlet ofthe folding apparatus.

The four folding arms are pairwise, along with one lower folding arm and one upper arm, connected to a sliding device [19a-b for example, see fig. 3) at opposing sides of the bale folding area. The sliding devices are displaceable towards and away from each other by means of a respective electric actuator (13a-a', 14a-a'] being arranged in electrical contact with control unit.

As can be seen in fig. 3, the electric motor 14a is coupled to the sliding device via a rack and pinion arrangement to translate the rotational movement of the motor into linear movement of the sliding device. Thus, when the respective electric actuator of the sliding device is actuated, the axes of rotation of the thereto connected folding arms are displaced (laterally) towards or away from the bale folding area. By actuating the electric actuator of the respective folding arm, it is furthermore rotated for lateral or vertical displacement of its contact element.

A control unit 15 is arranged in electrical contact with each electric motor 11a-b, 12a-b, 13a-b, 14a-b (indicated by dotted lines to motors on one side of the apparatus). The control unit is arranged to determine, for each electric actuator, three Operating parameters: a position parameter (being correlated to a position of the contact elements which is inﬂuenced by the actuator), a force parameter indicative of electric motor torque and a speed parameter indicative of a speed of rotation of the electric motor. The control unit is configured to control the electric motors/actuators using the Operating parameters.

The control unit 15 is configured to determine the position and speed parameters using data obtained from position sensors being pulse sensors connected to the shaft of the respective electric motor. The force parameters are determined using the current output to the respective electric motor (which current is known by the control unit).

The rotation device 17 is pneumatically driven (not shown in the figure), which pneumatic drive is also electrically controlled by the control unit 15.

The folding apparatus further comprises a Human Machine Interface, HMI, 16 being arranged in electric communication with the control unit. The control unit 15 is configured to determine target displacement parameters for each electric actuator: start and end positions of its contact element, rotation speed and motor torque. The HMI is configured to receive user input indicative of the displacement parameters, and to transmit to the control unit signals indicative of the user input. The control unit is configured to determine the target displacement parameters using the signals.

When a pulp bale enters the folding apparatus, it normally enters with its long sides in parallel with the conveying arrangement, as can be seen in fig. 2. When the pulp bale has been conveyed to the center of the bale folding area 4, having its center at the rotation device 17, an optional aligning procedure may be executed. In this procedure, the control unit 15 orders electric motors 12a-b to raise contact elements of the two lower folding arms 6a-b and the thereto connected contact elements (9a for example) to a vertical level being above the bale folding area, and thereafter control electric motors 14-a-b to displace the sliding devices such that contact elements of the two lower folding arms are displaced towards each other for pushing opposite sides of the pulp bale (to align the pulp bale) until target positions are reached, which target positions are determined based on the pulp bale size. The aligning procedure is finalized by controlling the electric motors 12a-b and 14a-b to return to their previous positions. Thereafter, the control unit 15 controls the rotation device 17 to rotate the pulp bale 90 degrees such that the ends of the wrapping materials are directed to the sides. Thereafter, the control unit controls the electric motors 14a, 14b to displace the sliding devices towards the pulp bale, whereafter electric motors 11a-d are activated to displace the contact elements Ba-d laterally, i.e. in a substantially horizontal plane, to make contact with the wrapping material to fold it around the standing edges (3" for example) of the pulp bale. Thereafter, electric motors 12a-b are 11 controlled to displace lower contact elements (9a for example) along a curved path (defined by the length of the folding arms) upwards to make contact with the wrapping material to fold it around respective lower edge (3' for example). When contact elements 8a-d, 9a make contact with the wrapping material, they pivot around their axes of rotation (against the pre-loading of the Springs). Thereafter, electric motors 13-ab are controlled to displace upper contact elements 10a, 10b along a curved path downwards to make contact with the wrapping material to fold it around respective upper edge of the pulp bale. Finally, electric motors 14a, b are controlled again to displace the sliding devices away from the pulp bale, and the finished pulp bale with folded wrapping material is conveyed out from the folding apparatus using the conveying arrangement 18a-b.

While controlling the respective electric motor, the control unit repeatedly determines the operating parameters (position, speed and force) and repeatedly compares the operating parameters with the target displacement parameters and/ or limit values such as maximum torque. For instance, when it is determined for an electric actuator that the position parameter is within a predetermined interval from the end position, the control unit stops the movement. Furthermore, the control unit may be configured to determine if the pulp bale is misaligned for example by comparing the position parameter (operating parameter) of contact elements 8a-d with the corresponding end position (a target displacement parameter), and if for instance two of the position parameters are within than a predetermined interval from the corresponding end positions, whereas the other two position parameters are outside the interval, it can be determined that the pulp bale is misaligned. In response to a determination that the pulp bale is misaligned, various control actions are possible. For example, if the force parameter indicative of actuator torque for two diagonally opposing actuator has reached the corresponding actuator torque, while not having reached their corresponding end positions, the control unit can attempt to align the pulp bale by increasing the torque further to these two actuators until the end positions are reached. Alternatively, all actuators can be controlled back to their initial positions, and the pulp rotated back 90 degrees, whereafter the above-mentioned aligning procedure may be executed.

The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. In particular, although a total of four folding arms and contact elements are provided at each side of the folding apparatus, it is foreseen within the scope of the invention that fewer folding arms can be used. For example, the upper and lower folding arms 6a, 10a could be replaced by a single folding arm which axis of 12 rotation is vertically displaceable using an additional electric actuator such as to be able to fold the wrapping material around both the upper and lower edges. Correspondingly, folding arms 5a, 5b could be replaced by a single folding arm. Further, the sliding devices along with the corresponding actuators may be omitted. Further, by choosing start positions of contact elements Bb, 8d which is more spaced apart, the folding apparatus could be arranged to receive the pulp bale at its inlet rotated 90 degrees compared to the position shown in fig. 2. In such an embodiment, the rotation device may be omitted. Furthermore, the control unit may be configured to determine fewer than the three operating parameters, for instance only the position parameter. Furthermore, the above-described springs arranged to pre-load the contact elements may be replaced with pneumatic cylinders or other devices having corresponding function. Furthermore, although the sliding devices are shown comprising wheels rolling in a track/profile to allow displacement thereof, different arrangements are possible, for example comprising sliding blocks.

Claims

1. Folding apparatus (1) for folding ends (Za-d) ofwrapping material (2) around a pulp bale (3) when positioned at a bale folding area (4) in said folding apparatus, said wrapping material being arranged around the circumference of the pulp bale and having a length being greater than a length of the pulp bale such that said ends (Za-d) of the wrapping material extend beyond opposite ends (Sa) of the pulp bale, said folding apparatus comprising: - at least two folding arms (Sa-d, 6a-b, 7a-d), each comprising a contact element (8a-d; 9a; 10a-b) at an end thereof; - at least two electric actuators (lla-d, 11a'-d', 12a-b, 12a'-b', 13a-b, 13a'-b',14-a-b, 14a'-b'), each being arranged to co-act with one or more ofthe folding arms such as to displace its contact element for making contact with the wrapping material to fold said wrapping material around an edge (3', 3") of the pulp bale; - a control unit (15) arranged in electrical contact with said at least two electric actuators, and arranged to determine, for each electric actuator, at least one operating parameter comprising a position parameter being correlated to a position of one or more contact element and/or a force parameter indicative of actuator torque or force and/or a speed parameter indicative ofa speed of rotation or displacement of the electric actuator, wherein said control unit is configured to control said at least two electric actuators using said at least one operating parameter. Z.

2.Folding apparatus according to claim 1, wherein one or more of the at least two electric actuators each comprises an electric motor (11a-d, 12a-b, 13a-b, 14a-b), wherein said control unit (15) is configured to determine said position parameter using data obtained from one or more position sensors connected to the electric motor and/or to a thereto connected folding arm.

3. Folding apparatus according to claim 2, wherein said electric motor is connected to a corresponding folding arm via a gearbox (11a'-d', 12a'-b', 13a'-b', 14a'-b') for rotation of the folding arm. 4-.

4.Folding apparatus according to claim 2, wherein said electric motor forms part of a mechanical linear actuator connected to a corresponding folding arm.

5.Folding apparatus according to any of the preceding claims, wherein said control unit (15) is configured to determine at least one target displacement parameter for one or more of the electric actuators, and wherein said folding apparatus further comprises a Human Machine Interface, HMI, [16] being arranged in communication with said control unit, wherein said HMI is configured to receive user input comprising said at least one target displacement parameter, or user input indicative thereof, and to transmit to the control unit one or more signals indicative of said user input, and wherein said control unit is configured to determine said at least one target displacement parameter using said one or more signals.

6.Folding apparatus according to claim 5, wherein said at least one target displacement parameter comprises at least one of a start position, an end position, rotation speed, displacement speed, actuator torque and actuator force.

7.Folding apparatus according to any of the preceding claims, comprising four folding arms (Sa-d) arranged symmetrically around the bale folding area [4] , wherein a corresponding electric actuator (1 la-d, 11a'-d') for each ofthe four folding arms is arranged to co-act therewith such that the contact elements [8a-d] of the four folding arms are, independently of each other, laterally displaceable into the bale folding area to make contact with wrapping material at a corresponding edge (3"] ofthe pulp bale.

8.Folding apparatus according to claim 7, wherein said control unit is configured to, based on at least one operating parameter for the each of the electric actuators co-acting with the four folding arms, determine if the pulp bale is misaligned, and if so, control at least one ofthe electric actuators co-acting with the four folding arms in response thereto.

9.Folding apparatus according to claim 8, wherein the control unit is configured to determine if the pulp bale is misaligned by comparing at least one operating parameter with a corresponding target displacement parameter for each of the electric actuators co-acting with the four folding arms.

10.Folding apparatus according to any of the preceding claims, wherein two lower folding arms (Ga-b) are arranged symmetrically at opposing sides of the bale folding area (4), wherein, for each of the two lower folding arms, at least one electric actuator [12a-b, 12a'-b'] is arranged to co-act therewith such that the contact element (9a] is vertically displaceable towards the bale folding area from below for making contact with wrapping material at a corresponding lower edge [3'] of the pulp bale.

11.Folding apparatus according to any of the preceding claims, further comprising a rotation device [17] arranged to engage with a pulp bale [3] when positioned at said bale folding area (4) to rotate said pulp bale, said rotation device being electrically controlled by said control unit (15).

12.Folding apparatus according to claim 11 as dependent on claim 10, wherein, for each of the two lower folding arms (óa-b), at least one electric actuator (14a-b, 14a'-b') is arranged to co-act therewith such that the contact element [9a) is laterally displaceable, wherein the control unit is configured to, prior to controlling the rotation device to rotate the pulp bale, controlling the electric actuators (12a-b, 12a'-b', 14a-b, 14a'-b') co- acting with the two folding arms to: - raise the contact elements (9a] of the two folding arms to a vertical level being above the bale folding area (4), and thereafter - move the contact elements [9a) of the two folding arms towards each other for pushing opposite sides of the pulp bale.

13.Method for controlling electric actuators of a folding apparatus for folding ends of wrapping material around a pulp bale, said folding apparatus comprising: - at least two folding arms, each comprising a contact element at an end thereof, and - at least two electric actuators, each being arranged to co-act with one or more of the folding arms such as to displace its contact element for making contact with the wrapping material to fold said wrapping material around an edge of the pulp bale, the method comprising: - determining, for each electric actuator, at least one operating parameter comprising a position parameter being correlated to a position of one or more contact element and/or a force parameter indicative of actuator force or torque and/or a position or speed indicative of actuator or folding arm position or speed; - controlling the at least two electric actuators using said at least one operating parameter.

14. A data processing device comprising means for carrying out the method of claim

15. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of claim

16. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of claim 13.