Adjusting the blade gap in fibrous material processing equipment.

Abstract

A loading device 10, arrangement and method for adjusting the size D of a blade gap 9 in a processing device 1 for processing fibrous material F,S. The loading device comprises a gearing 12 connected to and coupled to a processing element of a processing device for moving a processing element 6 relative to another processing element 5 of the processing device in order to adjust the size of the blade gap between the processing elements 5,6, a squirrel-cage induction motor 14 coupled to the gearing and including a shaft 15 for actuating the gearing, a position sensor 16 for measuring a rotational position M-RP of the motor shaft to indicate the position of the processing element relative to the other processing element, and a frequency converter 17 coupled to the position sensor and to the motor for controlling operation of the motor based on the measured rotational position of the motor shaft.

Description

[Technical field]

[0001] The present invention relates to a processing device for processing fibrous material, in particular to adjusting the size of the blade gap between substantially oppositely arranged processing elements in a processing device for processing fibrous material. [Background technology]

[0002] Refiners, such as refiners for refining lignocellulose-containing wood-based fibrous materials, plant-based fibrous materials or recycled fibrous materials, provide a type of processing device for processing fibrous materials. They typically comprise two opposingly arranged refining elements, one of which is typically a fixed refining element and the other a rotatable refining element arranged to rotate relative to the fixed refining element. Between the opposing refining elements there is a free distance, i.e. a blade gap or refining chamber, into which the fibrous material to be refined is fed. In the blade gap the fibrous material undergoes a refining effect which is determined by the characteristics of the refining surfaces in the refining elements and the operating characteristics of the refiner, such as the rotation speed of the rotatable refining element and / or the pressure in the blade gap.

[0003] A prior art arrangement for adjusting the size of the blade gap of a conical refiner comprises a loading device coupled to the rotatable refining element and for moving the rotatable refining element in the axial direction of the refiner relative to the fixed refining element. In this arrangement, the loading device comprises a gearing coupled to the shaft of the rotatable refining element and a motor coupled to the gearing for actuating the gearing, whereby the gearing and the motor coupled to the gearing together provide a gear motor for moving the rotatable refining element relative to the fixed refining element. However, the actual blade gap adjustment is performed based on the power control of the main motor of the refiner, i.e. the power control of the motor for rotating the rotatable refining element. The power required by the main motor to rotate the rotatable refining element provides an indication of the position of the rotatable refining element relative to the fixed refining element. Thereby, the closer the rotatable refining element is to the fixed refining element, the higher the power required by the main motor to rotate the rotatable refining element due to the pressure increase in the blade gap. In this solution, to prevent the rotatable refining element from getting too close to the fixed refining element, the loading device has a mechanical friction coupling that provides mechanical overload protection for the loading device, whereby the mechanical friction coupling is configured to slip if the force used to move the rotatable refining element towards the fixed refining element becomes too high, whereby the mechanical friction coupling limits the force applied to move the rotatable refining element towards the fixed refining element. Furthermore, this prior art configuration may include a sensor, which is located in the refiner to measure the position of the rotatable refining element in the refiner.The measurement information provided by this sensor may thereby be applied to prevent the rotatable refining elements from moving too close to the stationary refining elements and colliding with each other. Summary of the Invention

[0004] Despite the drawbacks of the gear ratio of the gear motor being very high, usually 1000:1 or more, which makes the implementation of the gearing substantially complicated and expensive, or the implementation of the mechanical friction couplings which require regular maintenance, the prior art arrangements for adjusting the size of the blade gap in conical refiners are very applicable in typical refining applications, which are intended to affect only the fiber properties without substantially affecting the fiber length of the fibrous material, i.e. without cutting the fibers substantially short. However, in particular refining applications in which the fiber length of the fibrous material is intended to be affected, i.e. the fibers are cut to have a relatively short length, e.g. in the production of microfibril cellulose (MFC) or nanofibril cellulose (NFC), where a very accurate constant blade gap is essential, the power control of the main motor of the refiner is less applicable as a method for adjusting the size of the blade gap.

[0005] It is an object of the present invention to provide a novel loading device, arrangement and method for adjusting the blade gap in a processing device for processing fibrous material.

[0006] The invention is characterized by the features of the independent claims.

[0007] The invention is based on the idea of ​​combining a frequency converter, a squirrel-cage induction motor and a position sensor measuring the rotational position of the shaft of the squirrel-cage induction motor arranged to operate a gear of a loading device, and moving at least one processing element relative to at least one other processing element in order to adjust the size of the blade gap between the processing elements.

[0008] An advantage of the present invention is that it provides an accurate and simple closed loop position control application for adjusting the size of the blade gap. The combination of a frequency converter and a squirrel cage induction motor allows substantially low gear ratios, for example between 100:1 and 150:1, resulting in a simplified implementation of the gearing.

[0009] Some embodiments of the invention are disclosed in the dependent claims. [Brief description of the drawings]

[0010] The present invention will now be described in more detail with reference to preferred embodiments thereof with reference to the accompanying drawings.

[0011] [Figure 1] 13A and 13B show schematic diagrams of an arrangement for adjusting the size of the blade gap in a refiner. [Diagram 2] 1 illustrates a schematic of a method for adjusting the size of a blade gap in a processing device for processing fibrous material.

[0012] For clarity, the figures depict some embodiments of the invention in a simplified manner, and like reference numerals identify like elements in the figures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] FIG. 1 is a highly schematic side view, partly in section, of a conical refiner 1 for refining fibrous material. The refiner 1 is thus a type of processing device for processing fibrous material. The fibrous material to be refined is, for example, a lignocellulose-containing wood-based fibrous material, a plant-based fibrous material or a fibrous material derived from recycled fibrous material. The fibrous material to be refined is in the form of pulp, i.e. a mixture of water, fibrous material and possibly additives. The fiber consistency of the fibrous material to be refined may vary, for example depending on the source of the fibrous material, the fiber consistency may typically be between 3 and 40%.

[0014] Refiner 1 has an axial direction, generally indicated by an arrow with reference A, and a radial direction, generally indicated by an arrow with reference R. In the axial direction A, conical refiner 1 has a first end E1 with a smaller diameter and a second end E2 with a larger diameter.

[0015] The refiner 1 includes a frame 2, at least one supply connection 3 for supplying or inputting at least one stream of fibrous material to be refined into the refiner 1, as shown diagrammatically by the arrow indicated with the reference character S, and at least one discharge connection 4 for discharging at least one stream of fibrous material that has already been refined in the refiner 1, as shown diagrammatically by the arrow indicated with the reference character D (DISCHARGE).

[0016] The refiner 1 includes a stationary refining element 5, i.e. a stator 5, having a first end of smaller diameter facing a first end E1 of the refiner 1 and a second end of larger diameter facing a second end E2 of the refiner 1. Thus, for clarity, the reference sign E1 is further used to denote the first end of the stator 5 and the reference sign E2 is further used to denote the second end of the stator 5. The stator 5 is supported on a frame structure 2 of the refiner 1. The stator 5 thus forms a stationary processing element of the refiner 1.

[0017] The refiner 1 further comprises a rotatable refining element 6, i.e. rotor 6. The rotor 6 has a first end, facing the first end E1 of the refiner 1, with a smaller diameter, and a second end, facing the second end E2 of the refiner 1, with a larger diameter. For the sake of clarity, the reference sign E1 is therefore further used to denote the first end of the rotor 6, and the reference sign E2 is further used to denote the second end of the rotor 6. The rotor 6 is connected to a shaft 7, which extends substantially in the axial direction A of the refiner 1. The shaft 7 is connected to a main motor 8 of the refiner 1. The main motor 8 is arranged to rotate the shaft 7, and thus the rotor 6, by means of the shaft 7, for example in the direction of rotation indicated by the arrow RD in FIG. 1. The rotor 6 thus forms a rotatable processing element of the refiner 1.

[0018] The stator 5 includes a refining surface 5a facing the rotor 6, and the rotor 6 includes a refining surface 6a facing the stator 5. The refining surfaces 5a, 6a typically include blade bars and blade grooves therebetween, in a manner well known to those skilled in the art. Therefore, for the sake of clarity, the refining surfaces 5a, 6a are not shown in detail in FIG. 1. Typically, the refining surface is implemented with a set of refining segments mounted adjacent to each other on the stator 5 and rotor 6, thereby providing a totality of refining surfaces 5a, 6a extending around the entire circumference of the stator 5 and rotor 6.

[0019] In the conical refiner 1, the rotor 6 is substantially arranged inside the stator 5 such that the stator 5 and the rotor 6 are substantially arranged opposite each other. Thereby, a blade gap 9 exists between the substantially oppositely arranged refining surfaces 5a, 6a of the stator 5 and the rotor 6. The blade gap 9, i.e. the refining chamber 9, forms a volume in which the fibrous material is refined. The free distance D between the opposing stator 5 and rotor 6 indicates the size of the blade gap 9. In FIG. 1, the size of the blade gap 9 relative to the other components of the refiner 1 is considerably exaggerated.

[0020] The operation of refiner 1 of FIG. 1 is as follows.

[0021] A flow of fibrous material is fed into the refiner 1 via a feed connection 3 at a first end E1 of the refiner 1, as shown diagrammatically by the arrows with reference S. The fibrous material to be refined enters the blade gap 9 at the first end E1 of the stator 5 and the rotor 6. When the rotor 6 rotates, the fibrous material flows forwards through the blade gap 9 from the first end E1 of the refiner 1 towards the second end E2 of the refiner 1. The fibrous material is subjected to a refining effect by the opposing refining surfaces 5a, 6a of the stator 5 and the rotor 6 until it leaves the blade gap 9 at the second end E2 of the refiner 1. The flow of the fibrous material in the blade gap 9 is shown diagrammatically by the arrows with reference F. The refined fibrous material in the blade gap 9 leaves the refiner 1 for further processing through a discharge connection 4 at the second end E2 of the refiner 1. For example, the refining effect imparted to the fibrous material in the blade gap 9 can be adjusted by adjusting the rotational speed of the rotor 6 and / or by adjusting the distance D between the stator 5 and the rotor 6, i.e. by adjusting the size of the blade gap 9.

[0022] 1 further shows, diagrammatically, a loading device 10 coupled to the shaft 7 of the rotor 6 of the refiner 1 by a coupling element 11. By actuating this loading device 10, the rotor 6 can be moved back and forth in the axial direction A of the refiner 1, as shown diagrammatically by the arrow AD, to adjust the distance D between the stator 5 and the rotor 6, i.e. the size of the blade gap 9. When the rotor 6 is moved towards the first end E1 of the refiner 1, the distance D between the stator 5 and the rotor 6 is reduced, i.e. the size of the blade gap 9 is reduced. When the rotor 6 is moved towards the second end E2 of the refiner 1, the distance D between the stator 5 and the rotor 6 is increased, i.e. the size of the blade gap 9 is increased. Since the stator 5 and rotor 6 are of conical construction, the amount of change in the distance D between the stator 5 and rotor 6, and therefore the size of the blade gap 9, depends on the amount of movement of the rotor 6 in the axial direction A of the refiner 1 and the rise angle of the conical construction of the stator 5 and rotor 6 relative to the axial direction A of the refiner 1. In the embodiment of Figure 1, the rotor 6 provides a movable refining element that is moved by a loading device 10 which adjusts the size of the blade gap 9.

[0023] The loading device 10 of Fig. 1 includes a gear arrangement 12 having a shaft 13. The shaft 13 of the gear arrangement 12 is connected and coupled to a shaft 7 of the rotor 6 of the refiner 1 by a coupling element 11. Furthermore, the coupling element 11 may be omitted if the gear arrangement 12 is directly connected to the shaft 7 of the rotor 6 or to another part of the rotor 6. Thus, by operating the gear arrangement 12, the rotor 6 can be moved in the axial direction A of the refiner 1 in order to adjust the size of the blade gap 9.

[0024] The loading device 10 of FIG. 1 further comprises a squirrel-cage induction motor 14 (motor 14) having a shaft 15 (motor shaft 15). The shaft 15 of the squirrel-cage induction motor 14 is coupled to a gearing 12 which operates the gearing 12 to move the rotor 6 relative to the stator 5 to adjust the size of the blade gap 9. The gearing 12 and the squirrel-cage induction motor 14 coupled to the gearing 12 together provide a gear motor, the gearing 12 being arranged to double the output torque available from the squirrel-cage induction motor 14. The gearing 12 provides the output torque of the loading device 10 required to move the rotor 6 without substantially increasing the power consumption of the squirrel-cage induction motor 14, allowing the size or output power of the squirrel-cage induction motor 14 to be moderate. Furthermore, squirrel-cage induction motors are inexpensive, simple in construction, reliable and easy to control.

[0025] The loading device 10 of FIG. 1 further comprises a position sensor 16 in the squirrel-cage induction motor 14 for measuring the rotational position of the shaft 15 of the squirrel-cage induction motor 14. The position sensor 16 is typically arranged on the shaft 15 of the squirrel-cage induction motor 14, but does not exclude other positions at which the position sensor 16 can measure the rotational position of the shaft 15 of the squirrel-cage induction motor 14. If the geometry of the coupling between the rotor 6 of the refiner 1 and the loading device 10 and the gear ratio of the gearing 12 are known, the rotational position of the shaft 15 of the squirrel-cage induction motor 14 may be used to determine the position of the rotor 6 relative to the stator 5. The output signal of the position sensor 16, i.e. the measured rotational position of the shaft 15 of the squirrel-cage induction motor 14, is indicated in FIG. 1 with the reference M-RP. The position sensor 16 may be, for example, a pulse transducer or a pulse sensor.

[0026] The loading device 10 of Fig. 1 further comprises a frequency converter 17, which is coupled to the squirrel cage induction motor 14 and controls the operation of the squirrel cage induction motor 14 by controlling the power supply to the squirrel cage induction motor 14. The frequency converter 17 includes a position control module PCM, which is configured to determine the current position of the rotor 6 relative to the stator 5, i.e. the current distance D between the rotor 6 and the stator 5, i.e. the current size of the blade gap 9, based on the measured rotational position M-RP of the shaft 15 of the squirrel cage induction motor 14 inputted into the position control module PCM, the known geometry of the coupling between the rotor 6 and the loading device 10 and the gear ratio of the gearing 12. The position control module PCM may be implemented by hardware or software or a combination thereof.

[0027] Furthermore, the position control module PCM of the frequency converter 17 is configured to receive as input a set value SET-D of the distance D between the rotor 6 and the stator 5 of the refiner 1 to be applied during the refining operation, i.e. a set value for the size of the blade gap 9. Based on the measured rotational position M-RP of the shaft 15 of the squirrel-cage induction motor 14 and the set value SET-D for the size of the blade gap 9, the position control module PCM is further configured to determine a control signal RP-CO for controlling the operation of the gearing 12 to move the rotor 6 relative to the stator 5 if the current size of the blade gap 9 differs from the set value SET-D for the size of the blade gap 9.

[0028] If the current size of the blade gap 9 is greater than a set value SET-D for the size of the blade gap 9, the frequency converter 17 is configured to control the squirrel-cage induction motor 14 to move the rotor 6 towards the stator 5 according to a control signal RP-CO supplied from the frequency converter 17 (frequency controller 17).

[0029] If the current size of the blade gap 9 is smaller than the set value SET-D for the size of the blade gap 9, the frequency converter 17 is configured to control the squirrel-cage induction motor 14 according to a control signal RP-CO provided by the frequency converter 17 (frequency controller 17) to move the rotor 6 away from the stator 5. Alternatively, if the current size of the blade gap 9 is smaller than the set value SET-D for the size of the blade gap 9, and it is expected that the size of the blade gap 9, i.e. the distance D between the rotor 6 and the stator 5, will soon follow the set value SET-D, for example due to wear of the refining surfaces 5a, 6a of the stator 5 and the rotor 6, the frequency converter 17 may be configured not to provide a control signal that causes the squirrel-cage induction motor 14 to move the rotor 6 relative to the stator 5.

[0030] If the current size of the blade gap 9 is substantially the same as the set value SET-D for the size of the blade gap 9, then no control action to move the rotor 6 relative to the stator 5 is necessary.

[0031] FIG. 2 illustrates, in a schematic manner, an embodiment of a method for adjusting the size of a blade gap in a processing device for processing fibrous material.

[0032] The combination of the squirrel cage induction motor 14, position sensor 16, and frequency converter 17 provides a closed loop position control application that controls the position of the rotor 6 of the refiner 1 relative to the stator 5 of the refiner 1 to regulate the size of the blade gap 9 within the refiner 1. This closed loop position control application provides an accurate manner of determining and controlling the current size of the blade gap 9 in a simple manner. This allows sensors that may be placed within the refiner 1 to measure the position of the rotor 6 within the refiner 1 to be omitted.

[0033] The combination of the frequency converter 17 and the squirrel cage induction motor 14 provides precise control, whereby the gear ratio of the gearing 12 may be selected to be substantially low, for example between 100:1 and 150:1, which simplifies the implementation of the gearing 12 and leads to cost savings in the implementation of the loading device 10.

[0034] The precise adjustment of the size of the blade gap 9 is particularly important in the production of microfibril cellulose (MFC) or nanofibril cellulose (NFC). The term "nanofibril cellulose" refers here to a collection of separated cellulose microfibrils or microfibril bundles derived from plant-based, especially wood-based, fibrous materials. Synonyms for nanofibril cellulose (NFC) are, for example, nanofibrillated cellulose, nanocellulose, microfibril cellulose, cellulose nanofibers, nanoscale cellulose, microfibrillated cellulose (MFC) or cellulose microfibrils. Depending on the degree of comminution, the particle size of the separated cellulose microfibrils or microfibril bundles is expressed in nanometers (nm) or micrometers (μm). The average length of the separated cellulose microfibrils or microfibril bundles is, for example, 0.2 to 200 μm, and the average diameter is, for example, 2 to 1000 nm.

[0035] According to an embodiment, the frequency converter 17 is configured to determine a torque TQ of the squirrel-cage induction motor 14 to be applied to move the rotor 6 relative to the stator 5 while adjusting the size of the blade gap 9 according to the position control signal RP-CO. The torque TQ may be determined by the frequency converter 17 based on the power and frequency used to operate the squirrel-cage induction motor 14. The determined torque TQ may be calculated based on a maximum torque limit value TQ MAX The determined torque TQ and the maximum torque limit value TQ MAX The torque TQ determined is compared with the maximum torque limit value TQ MAXIf this is the case, the frequency converter 17 is arranged to stop the squirrel-cage induction motor 14, thereby interrupting the movement of the rotor 6 relative to the stator 5. Determination of the torque TQ and the maximum torque limit value TQ MAX In comparison with the conventional technique, electrical overload protection of the squirrel-cage induction motor 14 is realized. This allows the mechanical friction coupling applied in the prior art to be omitted. This further leads to cost reduction in the implementation of the loading device 10.

[0036] According to one embodiment, the frequency converter 17 includes a torque control module TCM that determines the torque TQ of the squirrel cage induction motor 14 to be applied to move the rotor 6 relative to the stator 5 and adjusts the determined torque to a maximum torque limit value TQ. MAX The determined torque TQ is compared with the maximum torque limit value TQ MAX The determined torque TQ is compared with the maximum torque limit value TQ MAX In response to this indication, the frequency converter 17 is configured to stop the squirrel cage induction motor 14 by a specific torque control signal TQ-CO or by interrupting the power supply to the squirrel cage induction motor 14. The torque control module TCM may be implemented by hardware or software or a combination thereof.

[0037] According to one embodiment, the determination of the torque TQ applied in the adjustment of the size of the blade gap 9 is applied during the operation of the refiner 1, for example, to prevent the application of an overload to the fibrous material to be refined and / or to prevent the opposing refining elements 5, 6 from colliding with each other. In practice, the determination of the torque TQ applied in the adjustment of the size of the blade gap 9 may be used at least at the time when the rotor 6 is moved towards the stator 5 in order to reduce the size of the blade gap 9. However, the determination of the torque TQ applied in the adjustment of the size of the blade gap 9 may also be used when the rotor 6 is moved away from the stator 5 in order to increase the size of the blade gap 9. Thereby, possible malfunctions in the internal operation of the loading device 10 or its coupling to the rotor 6 can be observed based on an increase in the torque TQ required by the squirrel cage induction motor 14 to move the rotor 6.

[0038] According to one embodiment, the determination of the torque TQ to be applied in adjusting the size of the blade gap 9 is used for the calibration of the loading device 10, which is performed in the non-operating state of the refiner 1. During the calibration of the loading device 10, the rotor 6 is moved towards the stator 5 until the rotor 6 comes into contact with the stator 5, i.e. meets the stator 5. This means that the determined torque TQ is adjusted to a corresponding torque limit value TQ LIMIT This torque limit value may be observed based on being greater than or equal to the maximum torque limit value TQ MAX or it may be a specific limit applied during the calibration of the loading device 10. This kind of calibration operation is also called zero-point calibration. The rotational position of the shaft 15 of the squirrel-cage induction motor 14 at the moment when the rotor 6 meets the stator 5 may be stored, for example in a position control module PCM, and may be applied later when adjusting the size of the blade gap 9.

[0039] According to one embodiment, the loading device 10 comprises a blade gap control module BGCM configured to control the operation of the frequency converter 17 in order to control the adjustment of the size of the blade gap 9, for example to determine a setpoint value SET-D for the size of the blade gap 9 and / or a maximum torque limit value TQ of the torque to be applied in the adjustment of the size of the blade gap 9 during the operation of the refiner 1. MAX and / or a torque limit value TQ applied during calibration of the loading device 10. LIMIT The blade gap control module BGCM may be configured to determine the measured rotational position M-RP of the shaft 15 of the squirrel cage induction motor 14 and the determined torque TQ. The measured rotational position M-RP of the shaft 15 of the squirrel cage induction motor 14 and the determined torque TQ may be input as measurements to the blade gap control module BGCM and used there for controlling the loading device 10, for example for determining a setpoint SET-D for the size of the blade gap 9. The blade gap control module BGCM may be implemented by hardware or software, or a combination thereof.

[0040] In the embodiment of Fig. 1, the blade gap control module BGCM is implemented in a higher-level process control system, which may for example be arranged to control the operation of the entire fibre mass production section, whereby the blade gap control module BGCM is functionally part of the loading device 10. Alternatively to this, the blade gap control module BGCM may further be implemented in the frequency converter 17. The higher-level process control system is shown highly diagrammatically in Fig. 1 in a box designated with the reference PCS.

[0041] The process control system PCS may contain or receive information related to the fiber pulp to be produced, such as, for example, the quality or other desired characteristics of the fiber pulp to be produced, the quality or other characteristics of the fibrous raw materials used, and also the additives and their characteristics to be mixed into the fiber pulp to be produced. Based on the information received from the process control system PCS, the blade gap control module BGCM determines setting parameters for the operation of the frequency converter 17, such as, for example, a set value SET-D for the size of the blade gap 9 and / or a maximum torque limit value TQ to be applied in adjusting the size of the blade gap 9. MAX etc., so as to impart a desired refining effect to the fibrous material being refined.

[0042] According to one embodiment, the blade gap control module BGCM is configured to estimate the wear of the opposing refining surfaces 5a, 6a during refining, for example based on the characteristics of the refining surfaces 5a, 6a, the characteristics of the fibrous material to be refined and possibly other characteristics related to refining, and is also configured to determine a setpoint SET-D for the size of the blade gap 9 taking into account the estimated wear of the refining surfaces 5a, 6a.

[0043] According to an embodiment, the loading device 10 comprises a vibration sensor 18 arranged to measure the vibrations of the refiner 1 during its operation. In the embodiment of FIG. 1, the vibration sensor 18 is arranged on the frame 2 of the refiner 1, but other positions of the vibration sensor 18 on the refiner 1 are also applicable, if the vibration sensor 18 is able to detect exceptional vibrations of the refiner 1 resulting from collisions of opposing refining elements during the operation of the refiner 1. The vibration sensor 18 delivers a vibration measurement signal M-VB which indicates whether, during the operation of the refiner 1, the stator 5 and the rotor 6 start to collide. If, during the operation of the refiner 1, the stator 5 and the rotor 6 start to collide, the level of the vibration measurement signal M-VB increases significantly with respect to the vibration level of the refiner 1 during normal operation of the refiner 1. The vibration measurement signal M-VB is, for example, forwarded to a blade gap control module BGCM and used to determine a set value SET-D for the size of the blade gap 9.

[0044] In the above example, the rotor 6 is arranged to move relative to the stator 5 when adjusting the size of the blade gap 9. However, instead, the stator 5 may be arranged to move relative to the rotor 6 in order to adjust the size of the blade gap 9.

[0045] Furthermore, in the above example, the disclosed solution for adjusting the size of the blade gap 9 is applied to a conical refiner 1. However, for adjusting the size of the blade gap 9, the disclosed solution is correspondingly also applicable to disc refiners with fixed and rotatable disc-shaped refining elements, whereby the change in the size of the blade gap takes place in the axial direction of the refiner.

[0046] Furthermore, in the above examples, the disclosed solutions for adjusting the size of the blade gap 9 are applied to refiners including a stator and a rotor opposing the stator, however, the disclosed solutions are correspondingly applicable for adjusting the size of the blade gap 9 in refiners in which both opposing refining elements are rotors.

[0047] The disclosed loading device 10 may alternatively be applied in a disperser, which is also a kind of processing device for processing fibrous material, as in the different embodiments described above. Thus, a disperser is a dispersing device whose purpose is to disperse fibrous material in the blade gap between oppositely arranged dispersing elements. The dispersed fibrous material may be, for example, a lignocellulose-containing wood-based fibrous material, a plant-based fibrous material or a fibrous material derived from recycled fibrous material. The dispersed fibrous material is in the form of pulp, i.e. a mixture of water, fibrous material and possibly additives. The fiber consistency of the dispersed fibrous material may vary, for example, depending on the raw material of the fibrous material, the fiber consistency may typically be between 3 and 40%.

[0048] In a disperser, the dispersing element is a processing element that imparts a processing or dispersing effect to the fibrous material in the blade gap, and the blade gap forms a dispersing chamber or volume in which this dispersing effect is imparted to the fibrous material being processed. The basic structure and operation of a disperser is substantially similar to that of a refiner, despite some characteristics of the dispersing surface of the dispersing element as compared to the characteristics of the refining surface of the refining element. Thereby, the loading device 10 disclosed above in relation to the refiner 1 and its different embodiments are equally applicable when the loading device 10 is applied in relation to a disperser for adjusting the size of the blade gap of the disperser.

[0049] It will be obvious to those skilled in the art that with the advancement of technology, the concept of the present invention may be implemented in various ways. The present invention and its embodiments are not limited to the examples described above, but may be modified within the scope of the claims.

Claims

1. 1. A loading device for adjusting a blade gap size in a processing apparatus for processing fibrous material, comprising: a gear device connected and coupled to at least one processing element of the processing device for moving at least one of the processing elements relative to at least one other processing element of the processing device to adjust the size of the blade gap between the processing elements; a squirrel-cage induction motor including a shaft, the shaft coupled to the gearing and actuating the gearing to move at least one of the processing elements relative to at least one of the other processing elements; a position sensor for measuring a rotational position of the shaft of the squirrel cage induction motor to indicate a position of at least one said processing element relative to at least one other said processing element; and a frequency converter coupled to the position sensor and to the squirrel cage induction motor for controlling operation of the squirrel cage induction motor based at least on the measured rotational position of the shaft of the squirrel cage induction motor.

2. The loading device of claim 1 , wherein the position sensor is disposed on the shaft of the squirrel cage induction motor.

3. 2. The loading device of claim 1, wherein the frequency converter includes a position control module configured to determine a position control signal for controlling operation of the squirrel cage induction motor based at least on the measured rotational position of the shaft of the squirrel cage induction motor.

4. 4. The loading device of claim 3, wherein the position control module is configured to determine the position control signal based at least on the measured rotational position of the shaft of the squirrel cage induction motor and a set point established for the size of the blade gap.

5. The frequency converter includes a torque control module; 5. The loading device of claim 1, wherein the torque control module is configured to determine a torque of the squirrel cage induction motor to be applied to move at least one of the processing elements relative to at least one of the other processing elements, compare the determined torque to a maximum torque limit value, and stop the squirrel cage induction motor if the determined torque is equal to or greater than the maximum torque limit value.

6. 5. A loading device according to any one of claims 1 to 4, comprising a blade gap control module configured to determine setting parameters for operation of the frequency converter.

7. The loading device of claim 6 , wherein the blade gap control module is configured to determine at least one parameter of a set point for the size of the blade gap and a maximum torque limit.

8. 5. The loading device according to claim 1 , wherein the loading device is configured to be used to adjust the size of the blade gap in a refiner for refining fibrous material or in a disperser for dispersing fibrous material.

9. 1. A configuration for adjusting a blade gap size in a processing device for processing fibrous material, comprising: a processing apparatus for processing fibrous material, the processing apparatus including at least two substantially oppositely disposed processing elements, at least one of the processing elements being movable in an axial direction of the processing apparatus to adjust the size of the blade gap between the processing elements; 5. The loading device of claim 1 , further comprising: a loading device coupled to the processing device and configured to move at least one processing element in the axial direction of the processing device relative to at least one other processing element to adjust the size of the blade gap between the processing elements.

10. The arrangement of claim 9 , wherein the processing device is a refiner for refining fibrous material or a disperser for dispersing fibrous material.

11. 5. A method for adjusting a blade gap size in a processing device for processing fibrous material, the method comprising: moving at least one processing element of the processing device relative to at least one other processing element of the processing device in order to adjust the size of the blade gap between the processing elements by means of at least one loading device according to any one of claims 1 to 4, measuring a rotational position of the shaft of the squirrel cage induction motor to indicate a position of at least one of the processing elements relative to at least one other of the processing elements; determining a position control signal for controlling operation of the squirrel-cage induction motor based at least on the measured rotational position of the shaft of the squirrel-cage induction motor; and controlling operation of the squirrel-cage induction motor by the frequency converter in accordance with the determined position control signal to control a position of at least one of the processing elements relative to at least one other of the processing elements to adjust the size of the blade gap between the processing elements.

12. moreover, determining a set point for the size of the blade gap; and determining the position control signal based at least on the measured rotational position of the shaft of the squirrel cage induction motor and the determined set point for the size of the blade gap.

13. 12. The method of claim 11, further comprising the step of actuating the gear arrangement coupled to at least one of the processing elements by the squirrel-cage induction motor to move the at least one processing element relative to at least one other of the processing elements.

14. moreover, determining a torque of the squirrel cage induction motor when at least one of the processing elements is moved relative to at least one of the other processing elements; comparing the determined torque to a maximum torque limit; The method of claim 11 , further comprising: suspending movement of at least one of the processing elements relative to at least one of the other processing elements in response to the determined torque being equal to or greater than the maximum torque limit.

15. The method of claim 11 , wherein the processing device is a refiner for refining a fibrous material or a disperser for dispersing a fibrous material.

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