The invention relates to a method and an arrangement for determining the profile of a roll surface and for controlling grinding in a paper machine, board machine, or the like according to the preambles of the independent claims presented below

In the machines of paper, board and film industry cylindrical rolls maintained by grinding are used. Grinding is necessary, because the form of the rolls and the quality of their surface changes due to wearing when the rolls are used. Grinding of a roll can be performed either by means of a separate roll grinding station, whereby the roll is removed from e.g. the paper machine for the time of grinding, or the roll can be ground in its own location, without removing it from the machine. For the grindings performed in the own location, separate linear guides or a guide beam are mounted in the paper machine, along which a grinding device equipped with a grinding head is driven back and forth in the direction of the rotation axis of the roll, and the roll is rotated at the same time.

However, a change in the profile of the roll surface in the direction of the rotation axis of the roll cannot be determined nor taken into account by means of present grinding devices placed in a paper machine. The grinding devices typically follow the surface of the object to be ground, often by the force of a constant pressure generated by means of a pneumatic cylinder. Thus, while grinding, they correct the quality and evenness of the surface, but do not substantially affect the longitudinal or rotation profile of the object to be ground, and thereby they are not able to correct possible profile defects. Even though the unevennesses of the roll surface can thus be eliminated by means of the present grinding devices, and the cross section of the roll at a certain location can be made fairly circular, the diameter of the roll can substantially vary in different locations of the roll. In order to estimate the need of maintenance and the condition of the roll, it would be preferable to observe the wearing of the roll and the changing of the form profile of the roll with respect to both the axis and the rotation direction of the roll. At separate grinding stations, in order to measure the form of the roll in the direction of the axis of the roll, typically a measuring arc is used, on the periphery of which measurement sensors are mounted, and the form of the roll is calculated on the values given by the measurement sensors. The roll to be ground is placed inside the measuring arc, whereby its form can be determined with respect to both the rotation axis and the rotation direction of the roll. It is, however, often difficult or even impossible to fit the measuring arc into a paper machine due to the space available, i.e. it cannot be easily utilised in a grinding process taking place in a paper machine.

The publication WO 99/10708 discloses a measuring method for measuring the straightness of the envelope surface of hollow drying cylinders, such as Yankee cylinders. A laser beam is used as a straightness reference, generated by means of a laser unit, which comprises a transmitter and a receiver. However, in the conditions of a paper mill machine room, the laser beam does not travel perfectly straight, due to variations in the refractive index of the air, for example the variations in temperature, humidity and flow. The problem becomes even worse at wide machines, whereby the inaccuracy of the measurement increases. In the disclosed solution, the problem has been tried to be reduced by protecting the beam by means of an enclosure, which leads to complex solutions. In addition, focusing of the laser beam can cause a problem as the laser beam does not necessarily remain completely unidirectional, but it can, for example, become wider or change focus as a function of distance, due to both the laser and the environmental effects. In the disclosed solution, while the distance between the transmitter and the receiver changes during the measurement, the image coming to the receiver spreads out as a patch from which an exact determining of the beam position is no more successful.

An object of this invention is to reduce or even completely eliminate the disadvantages and problems appearing in prior art.

An object of the invention is to provide a method and an arrangement with which an economical and a simple way to determine the profile of the roll surface both in the rotation direction of the roll and in the direction of the longitudinal axis of the roll can be performed, and with which the grinding of the roll can also be controlled. The present invention is characterised in what is defined in the characterising parts of the independent claims presented below.

Some preferred embodiments according to the invention are disclosed in the dependent claims presented below.

A typical method according to the invention for determining the profile of a roll surface and for controlling grinding in a paper machine, board machine or the like comprises

- arranging a straightness reference on one side of the roll, at a distance from the roll surface,

- measuring the distance of the roll surface from the straightness reference by means of a measurement sensor unit in order to obtain a measurement result, and

- determining the form of the roll and/or the profile of the roll surface and controlling the grinding on the basis of the obtained measurement result.

A typical arrangement for determining the profile of a roll surface and for controlling grinding comprises

- a grinding device,

- a straight straightness reference, which is arranged at a distance from the roll surface to be determined, in the direction of the longitudinal axis of the roll,

- at least one measurement sensor unit, which is arranged to measure the distance of the surface to be measured from the straightness reference,

- a control unit, which is arranged in a functional connection with the measurement sensor unit and/or the control system of the grinding device.

It has now been surprisingly found out that by using a straight straightness reference placed at a distance from the roll it is easy to determine the form of the roll and its surface both in the rotation direction of the roll and in the direction of the longitudinal axis of the roll. The distance between the roll surface and the straight straightness reference is preferably measured at least partly in a non-contacting manner, and on the basis of the obtained measurement result the profile of the roll surface is determined in a desired direction. The determining of the form of the roll can thus be easily performed only from one side also when the roll is in its place in a paper machine or the like, and the roll does not need to be moved to a separate grinding station for the form determination. By using the obtained measurement results it is possible to determine even more accurately than before the need for grinding of the roll, whereby unnecessary or too frequent grinding can be avoided. In addition, the obtained measurement results can be used for controlling the grinding itself, whereby defects in the form of the roll can be corrected even better than before both in the rotation direction and in the direction of the longitudinal axis of the roll. In this application a change of the form of the roll means a change in the diameter or the radius as a function of the axial position, i.e. in the direction of the longitudinal axis of the roll. A change in the roll profile i.e. the rotation profile means a change in the circularity of the roll in the direction of the roll radius or a radial eccentricity of the roll, which comprises both a change of the roll radius as a function of the rotation angle, and a change of the position of the roll surface in the radial direction as a function of the angle.

According to an embodiment of the invention, the control unit comprises calculation means for determining the distance of the surface to be measured by calculation on the basis of the measurement values obtained from the measurement sensor unit.

In an embodiment of the invention, a possible change, for example sag, of the straightness reference as a function of position can be corrected by calculation. The correction can be performed by means of the calculation means of the control unit. When, for example, a tensioned steel wire functions as a straightness reference, it is tightened by a known force, for example by means of a spring or a compressed air cylinder to a distance from the roll in the direction of the roll axis. A possible sag of a steel wire tightened by a known force can be calculated when the properties of the steel wire are known, such as diameter, length, tension force, etc., and in this manner the effect of a possible sag can be eliminated by correction by calculation. A disturbance caused by a possible vibration of the steel wire functioning as a straightness reference can also be eliminated by means of calculation means, by using mean filtration.

According to an embodiment of the invention, the grinding interval of the roll surface is determined on the basis of the obtained measurement result. The measurement sensor unit can be a separate unit from the grinding device, with which unit the determination of the profile of the roll surface and the form of the envelope surface of the roll is performed at predetermined time intervals and/or when the process operator considers it to be necessary. The measurement sensor unit can perform the determination of the profile of the roll surface, and if the profile of the roll surface deviates too much from the original profile or from the limiting values defined for the profile of the roll, the measurement sensor unit can call a grinding device to perform grinding of the roll or notify the need for grinding to the process operator. In this manner, an individual grinding time interval based on real wearing and form change can be guaranteed for each roll. This provides significant cost savings, especially in arrangements in which the roll needs to be transferred to a separate roll grinding station for to be ground.

According to an embodiment of the invention, the control unit can comprise a memory unit for storing the measurement values obtained from the measurement sensor unit and/or the values calculated with the calculation means. Also limiting values describing the profile of the roll surface either in its rotation direction or in its longitudinal direction, i.e. in the direction of the rotation axis, can be stored in the memory unit. The control unit of the arrangement compares the measurement results obtained from the measurement sensor to the limiting values stored in the memory unit. If the measurement result describing the profile of the roll surface is below/over the allowable limiting value, the control unit can carry out an alarm. The alarm can be forwarded to the process operator, who in this way receives an information on an incorrect profile of the roll surface, and can start the preparations for the grinding of the roll, or the alarm can be forwarded automatically to the grinding device's own control system, which is arranged to start the grinding of the roll in question within a certain delay from the alarm. The grinding device can use in the grinding event the measurement results obtained from the control unit or directly from the measurement sensor unit.

Also moments of grinding of individual rolls and the measurement results of several consecutive measurement events obtained therefrom can be stored in the memory unit. By means of this data the grinding interval and grinding profile of individual rolls can be determined by calculation if regularities in wearing of the roll can be observed in consecutive measurement results. Measurement results collected and stored in the memory unit can be utilised also when choosing roll coatings, their materials and thicknesses. In an embodiment, the arrangement comprises several measurement sensor units and one or more grinding devices, however so that the number of grinding devices is smaller than the number of sensor units. Each measurement sensor unit performs determinations of the roll surface profile constantly or at predetermined time intervals at a single roll or on a roll group, and calls the grinding device to grind or correct the profile of the roll surface preferably only when needed. One grinding device is thus responsible for the grinding of several rolls or roll groups. The call for grinding can be transmitted via the control unit to the grinding device or to the process operator responsible for the grinding device. Thereby the number of grinding devices can also be low in a paper industry mill comprising several rolls, which provides distinct savings in the investment costs.

In a preferred embodiment of the invention, by means of the obtained measurement result, the grinding device's grinding parameters, such as grinding pressure of the grinding device's grinding member and/or the axial feeding speed of the grinding member and/or the rotation speed of the roll to be ground, are controlled during grinding. The measurement results obtained from the measurement sensor unit are thus transmitted immediately or within a suitable delay from the control unit of the arrangement to the control system of the grinding device, which control system changes or maintains, on the basis of the measurement result, the grinding pressure of the grinding device's grinding member, such as the grinding head, and/or the axial feeding speed of the grinding member and/or the rotation speed of the roll to be ground. The grinding device is thereby preferably provided with a real time or almost real time feedback control function, which is controlled by means of the obtained measurement result. In this manner, it is possible to ensure an even more accurate correct grinding of the profile of the roll surface both in the rotation direction of the roll and in the direction of the rotation axis of the roll.

In an embodiment of the invention, the measurement sensor unit is moved in the direction of the longitudinal axis of the roll between the first and the second edges of the roll, preferably from the first edge to the second edge. By moving the measurement sensor unit in the direction of the rotation axis, i.e. the longitudinal axis of the roll, measurement results describing the distance of the roll surface from the straightness reference are obtained from different locations of the roll. These measurement results can be used to determine an exact profile of the roll surface in the direction of the rotation axis of the roll, whereby it is possible to detect if the form of the roll has changed from the original. It is for example possible to detect if the central part of the roll wears more than the ends of the roll, whereby the form of the roll tapers in the centre part. By means of the obtained measurement results and the determined exact profile of the roll surface, the grinding can be controlled so that the generated changes are compensated and corrected with it.

When the form of the roll is determined both in its rotation direction and in the direction of its longitudinal axis, by using the method and arrangement of the present invention it is possible to rotate the roll during the measurement at a speed, which is lower than the normal production speed of the roll. Production speed means in this context the speed with which the roll is rotated when it is in normal use in an industrial process, for example in paper making.

In an embodiment of the invention, the roll is rotated at the production speed, the distance of the roll surface from the straightness reference is measured with a measurement sensor unit in order to obtain a measurement result, the profile of the roll surface is determined at the production speed, and the roll grinding is controlled on the basis of the obtained measurement result. In this manner it is possible to find out the dynamic form of the roll at the production speed, i.e. bulging of the roll form during rotation caused by the rotating movement of the roll is found out. In an embodiment of the invention, the dynamic form of the roll at the production speed is thus determined, and the roll is ground into a form with which the change in the roll form at the production speed is compensated. Usually the rolls are not entirely homogeneous with respect to their rigidity in the rotation direction, due to for example welding seams, rolling and/or differences in thickness. When the roll is rotated at the production speed, it is bulged due to inertial forces, but as it is not homogeneous in its rigidness, it does not bulge evenly in the circular direction, and the circularity of the roll is deteriorated i.e. the dynamic form of the roll is changed. The bulging has an effect both in the rotation direction and in the direction of the longitudinal axis of the roll. By means of the present embodiment the dynamic form of the roll can be more accurately determined than before to determine and, if need be, the roll can be ground into a form with which a change of the roll form in the production speed can be compensated. The roll can be ground into a so-called counter form.

The grinding device and the measurement sensor unit of the arrangement can be arranged to travel along a guide in the direction of rotation axis i.e. the longitudinal axis, of the roll to be ground, which guide extends from the first edge of the surface to be ground towards its second edge, preferably from the first edge to the second edge. Thus, the arrangement thereby comprises a guide, which extends from the first edge of the surface to be ground to its second edge, and the grinding device and the measurement sensor unit are arranged to travel along the guide. If the determination of the profile of the surface and/or the grinding are performed when the roll is in its own location in the paper machine or the like, for example a guide beam arranged in a connection with the paper machine or the like can function as a guide. The guide beam can be realised in different ways depending on the application and purpose, either by making an entirely new guide beam structure or by utilising already existing beam or guide structures in the paper machine. For example, a steel beam provided or machined with linear guides or a guide surface can function as a guide. The guide can be arranged so as to be movable or it can be arranged as a solid structure. A solid guide can be arranged for example by casting in concrete to the floor structures.

The measurement sensor unit can also be arranged in a fixed connection with the grinding device. Thus the measurement sensor unit and the grinding device form a single unitary and inseparable measurement and grinding unit. Preferably however, a unitary measurement and grinding unit can be transferred from one roll or roll group to another, whereby one unit measures and grinds several rolls or roll groups. The transfer can take place at predetermined time intervals. The measurement and grinding unit or the guide, onto which the unit in question is arranged, can for example be turned so that two adjacent rolls can be measured and ground with the unit. The turning can be performed for example in a hydraulic manner. Alternatively the process operator can transfer the measurement and grinding unit from a roll or a roll group to another at desired and/or determined times. Typically the grinding device comprises a grinding member and a feeding device for feeding the grinding member against the roll surface. The grinding device comprises as a feeding device for example a grinding slide, into which the grinding member is fixed. The grinding member can be pressed towards the roll by means of a mechanic, pneumatic or hydraulic actuator which generates a linear movement. In a grinding situation, the grinding surface of the grinding member grinding the roll is arranged substantially parallel with the roll surface. Preferably, the grinding device comprises a grinding member, which is provided with a slowly moving grinding band and in which the grinding power is taken substantially from the rotation of the workpiece i.e. the roll to be ground. This kind of a grinding device is useful especially in the maintenance grindings in paper industry, in which the amounts of material to be ground out are small and the obtained grinding result needs to be of high quality. It is clear that in the arrangement according to the invention also other kinds of grinding devices can be used, such as grinding devices using a grinding band or a grinding disc, which are provided with an own motor.

In an embodiment of the invention, the distance between the measurement sensor unit and the roll surface is determined in a contacting manner, the distance between the measurement sensor unit and the straightness reference is measured in a non-contacting manner, and the form of the roll and/or the profile of the roll surface are determined by calculation on the basis of the obtained distances. The measurement sensor unit can comprise a measurement arm having in its end a contact member, such as a reel. The length of the measurement arm determines the distance of the measurement sensor unit from the roll surface. Alternatively, the measurement sensor unit can comprise a contact member, which is a contacting electro-mechanic sensor, with which the distance and the profile of the roll surface can be determined by calculation on the basis of the distances measured by the sensors. The contact member of the measurement sensor unit is thus in contact with the roll surface during the determination of the distance between the surface and the measurement device. The measurement sensor unit can move on its own guide rails on the basis of the surface contact of the contact member in the direction of the roll radius, or the measurement sensor unit can be arranged in a connection with the grinding member, whereby it moves in the direction of the roll radius together with the grinding member. The distance of the roll surface from the straightness reference can thus be obtained by calculation when the distance of the measurement sensor unit from the straightness reference and the distance of the measurement sensor unit from the roll surface are known.

In an embodiment, the measurement sensor unit can be arranged to the grinding member of the grinding device in a fixed manner, the measurement sensor unit comprising a non-contacting distance sensor, for example a laser sensor, with which the distance and the profile of the roll surface can be determined in a non- contacting manner by calculation on the basis of the distances measured by the sensor.

According to an embodiment of the invention, after the determination of the profile of the roll surface, the surface to be ground is arranged to travel via the outer surface of the roll, and the distance of the surface to be ground from the straightness reference is measured by means of a measurement sensor. Thereafter, the profile of the surface to be ground is determined by calculation by using the obtained measurement results for the roll surface and for the surface to be ground, and the grinding of the surface to be ground is preferably controlled on the basis of the calculated surface profile. In this manner it is easy to grind for example metallic belts or the like used in connection with calenders and/or presses. In this case the roll functions as a support roll for the belt to be ground, which is arranged to travel via the roll surface. When the measurement result which has been obtained earlier for the support roll is subtracted from the measurement result obtained for the belt to be ground, it is easy to determinate the thickness and profile of the belt to be ground by calculation. This makes it considerably easier to grind wide belts into an even thickness and accelerates the grinding process.

In principle, the guide along which the measurement sensor unit and/or the grinding device are moved could simultaneously serve as a straightness reference. In practice, the available guides are difficult to build completely straight at current paper machine widths, which typically are 8-12 m, i.e. the guide may possibly serve as a straightness reference in machines whose width is less than 2,5 m, i.e. the length of the roll to be ground is less than 2,5 m.

According to a preferred embodiment of the invention, preferably a tensioned wire, for example a steel wire, an interferometric straightness measurement device or a laser beam serves as a straightness reference of the arrangement. The straightness reference is especially preferably a tensioned steel wire, which is tensioned with a known force, for example by means of a spring or a compressed air cylinder. Steel wire is preferred, as the form of the wire is not dependent on the pressure, temperature or humidity prevailing in the machine room. Typically the straightness reference is arranged at a distance from the surface to be determined and/or ground, in parallel therewith. In an embodiment of the invention, triangulation is used for the determination of the profile of the roll surface. By means of triangulation, the profile of the roll surface both in the rotation direction and in the direction of the rotation axis can be determined in an easy and simple manner. When using triangulation, the straightness reference can be, for example, a tensioned steel wire or the like, and the triangulation itself can be performed by means of a laser sensor or other optical sensor, such as a camera sensor. Thus, the measurement sensor unit comprises an optical sensor, such as a camera sensor or a laser sensor. In an embodiment of the invention, the rotation profile and the longitudinal form of the roll surface can be determined by means of a three-point measurement at the same time as the total position of the measurement sensor is determined from the straightness reference.

When using triangulation, the measurement sensor unit comprises a triangulation sensor, which comprises a laser beam transmitter unit and a camera unit provided with an image processing unit, such as a line camera or a matrix camera,. The camera unit is arranged in an angle with respect to the laser beam emitted by the laser beam transmitter unit. When measuring the distance of the measurement sensor unit from the straightness reference, the laser beam transmitter unit emits a laser beam to the straightness reference. The laser beam is reflected from the straightness reference to the camera unit of the measurement sensor unit, which camera unit is arranged in an angle with respect to the laser beam emitted by the laser beam transmitter unit. Depending on the distance of the straightness reference, the laser beam is reflected to a different point on the camera unit so that the position of the camera unit seems to be dependent on the distance. By using a matrix camera instead of a line camera it is possible to measure with one triangulation sensor in a two-dimensional manner, for example, also a sag of the guide. According to a preferred embodiment of the invention, the distance of the measurement sensor unit from the tensioned steel wire serving as a straightness reference is measured by using triangulation. Also a side-observing camera technology can be used for measuring the distance between the measurement sensor unit and the straightness reference. In that case a camera sensor, such as a line camera, is arranged in the measurement sensor unit, and the distance of the measurement sensor unit from the straightness reference, such as a steel wire, is measured by observing the straightness reference from the side against a suitable light source or shade. Then, by means of the camera sensor, it is possible to determine the location of the straightness reference, such as a tensioned steel wire, with respect to the camera sensor. By adding a second camera sensor into an angle, preferably vertically, with the first camera sensor, it is possible to measure also the sag of the guide, if desired.

In an embodiment of the invention, the distance of the roll surface is measured with at least three measurement sensors, preferably mounted in an angle, and the movement of the central axis of the roll is compensated by calculation on the basis of the measurements of these sensors. The form of the roll in the rotation direction can thus be calculated for example by using a three-point method. By means of a three-point measurement the circularity of an object is measured by subtracting the movement of the central axis of the object. The three-point measurement is known as such to a person skilled in the art, and it is not described more in detail here. The three-point measurement should not be confused with the triangulation described above.

The straightness reference can be arranged in a connection with the guide, for example when using a steel wire as a straightness reference, it can be tensioned between the ends of the guide. Alternatively, a transmitter unit and a receiver unit of the laser beam of the interferometric straightness measurement device can be arranged in the first end of the guide and a returning prism for the laser beam of the straightness measurement device in the other end of the guide. The beam of the straightness measurement device then travels via the measurement prism of the measurement sensor unit. Still alternatively a member generating the laser beam, such as a laser projector, can be arranged in the first end of the guide, whereby the laser beam operates as a straightness reference, and travels via the sensor, for example an electronic XY-position-sensor or a matrix camera, of the measurement sensor unit.

In an embodiment of the invention, the straightness reference is arranged to be entirely separate from the guide, in parallel with the guide but within a distance therefrom.

The arrangement and the method according to the invention can preferably be used for grinding different kinds of rolls used in paper industry or in film industry. The invention is applicable for grinding the rolls of a paper machine or a board machine, for grinding the rolls of calenders, and for grinding the rolls used in coating units.

In the following, the invention is described in more detail with reference to the enclosed schematic drawings:

Figure 1 shows an arrangement according to an embodiment of the invention in connection with a roll to be ground,

Figure 2 shows an arrangement according to an embodiment of the invention as seen from the side,

Figure 3 shows an arrangement according to a second embodiment of the invention as seen from the side,

Figure 4 shows an arrangement according to a third embodiment of the invention as seen from the side,

Figure 5 shows an arrangement according to a fourth embodiment of the invention as seen from the side,

Figure 6 shows arrangements according to an embodiment of the invention when a steel belt is being ground, Figure 7 shows an arrangement according to an embodiment of the invention when a steel belt is being ground in the maintenance device of a calender belt, and Figure 8 shows an arrangement according to a further embodiment of the invention as seen from the side and in which a three-point measurement is utilised.

Figure 1 shows an arrangement according to an embodiment of the invention in connection with a roll to be ground. The arrangement comprises a guide beam 1 , which is arranged to extend from a first end 30' to the second end 30" of the roll 30 to be determined and ground. In connection with the guide beam 1 is arranged a first and a second linear guide 2, 2', along which a grinding slide 3 is arranged to travel. The grinding slide 3 comprises a grinding member 5, which can be moved along guide rails 4 further away and closer to the surface 31 of the roll 30 to be ground. For the sake of clarity, only one guide rail 4 is shown in Figure 1 , but it is clear that there can be several of them. The distance of the grinding member 5 from the roll 30 surface 31 can be adjusted by using a cylinder means 6, which can be for example a hydraulic or a pneumatic cylinder. The grinding of the roll 30 is performed with the grinding surface 8 of the grinding member 5, in this case with a grinding band, which is arranged to travel from a first guide reel 9 to a second guide reel 9' via a contact reel 7.

In Figure 1 , fixing means 10, 10' are arranged in the first and the second ends 1 ', 1 " of the guide beam, between which fixing means a steel wire 11 functioning as a straightness reference is tensioned. A measurement sensor unit 13 is arranged beside the grinding member 5, which measurement sensor unit is arranged to measure the distance of the roll 30 surface 31 from the steel wire 11 functioning as a straightness reference. The measurement sensor unit 13 comprises a measurement arm having in its end a contact member 16, such as a reel. The length of the measurement arm determines the distance of the measurement sensor unit 15 from the surface 31 of the roll 10. The contact member 16 is in contact with the roll 30 surface 31 during the determination of the distance of the surface. The measurement sensor unit 13 moves on its own guide rails (not shown) in the direction of the radius of the roll 30 on the basis of the surface contact of the contact member 16. The distance of the roll 30 surface 31 from the straightness reference 11 can thus be obtained by calculation when the distance of the measurement sensor unit 13 from the straightness reference 11 and the distance of the measurement sensor unit 13 from the roll 30 surface 31 are known. The grinding member 5 and the measurement arrangement shown in Figure 1 are described more in detail in Figure 3. Figure 2 shows an arrangement according to an embodiment of the invention as seen from the side. The grinding member 5 is arranged on the grinding slide 3, which is arranged to travel along the first and the second linear guides 2, 2', which are in a fixed contact with the guide beam 1. The fixing means 10 is arranged in the first end of the guide beam, into which fixing means an end 11 Of the steel wire functioning as a straightness reference is fixed.

The grinding member 5 comprises 5 the grinding surface 8, such as a grinding band, which is arranged to travel from the first guide reel 9 to the second guide reel 9' via the contact reel 7. The distance of the grinding member 5 from the surface of the roll 30 can be altered by means of the cylinder means 6. The measurement sensor unit 13 is arranged in a connection with the grinding member 5, which measurement sensor unit measures the distance of the grinding member 5 from the steel wire functioning as a straightness reference. The measurement sensor unit 13 is arranged, by means of the connecting arm 14, in a fixed connection with the grinding member 5, whereby it moves together with the grinding member 5.

Figure 3 shows an arrangement according to a second embodiment of the invention as seen from the side, and the reference numbers correspond to the reference numbers of Figure 2, i.e. the same reference numbers are used for the same parts. In Figure 3, the measurement sensor unit 13 is arranged in a connection with the measurement arm 15, the end of the said measurement arm 15 being provided with a contact member 16, such as a reel. The contact member 16 is in contact with the roll 30 surface 31 during determination of the distance of the surface. Thus, the distance of the roll 30 surface 31 from the straightness reference can be determined directly by means of the measurement sensor unit 13. In this case, the measurement sensor unit 13 is provided with its own guide rails, which allows an independent movement of the measurement sensor unit and the contact member with respect to the grinding member.

Figure 4 shows an arrangement according to a third embodiment of the invention as seen from the side, and the reference numbers correspond to the reference numbers of Figure 2, i.e. the same reference numbers are used for the same parts. In Figure 4, the measurement sensor unit 13 is fixedly arranged to the grinding member 5, which measurement sensor unit determines the distance of the grinding member 5 from the straightness reference 11. The measurement sensor unit 13 comprises a laser sensor 17, by means of which the distance and the profile of the roll 30 surface 31 can be determined in a non-contacting manner by calculation on the basis of the distances measured by the sensors.

Figure 5 shows an arrangement according to a fourth embodiment of the invention as seen from the side. The reference numbers correspond again to the reference numbers of the previous Figures 2-3, i.e. the same reference numbers are used for the same parts. In Figure 5, the measurement sensor unit 13 is arranged to the grinding member 5 in a fixed manner, which measurement sensor unit determines the distance of the grinding member 5 from the straightness reference 11. The measurement sensor unit 13 comprises also a contacting electro-mechanic sensor 18, by means of which the distance and the profile of the roll 30 surface 31 can be determined by calculation on the basis of the distances measured by the sensors.

Figure 6 shows arrangements according to an embodiment of the invention when a steel belt is being ground in a production machine, i.e. in the case of the Figure, in a metal belt calender. The steel belt 32 to be ground is arranged to travel via the outer surfaces of the rolls 30, 30', 30", 30"' so that the steel belt remains suitably tensioned and straight. Measurement and grinding units 101 , 101 ', 101 " according to the invention are used to determine the profile of the surface of the steel belt 32 and to grind its surface into an even thickness.

Before the steel belt 32 is arranged to travel via the outer surfaces of the rolls 30, 30', 30", 30'", the profile of the surface of each roll 30, 30', 30", 30"' is determined by means of the measurement and grinding units 101 , 101 ', 101 ". Thereafter, the steel belt 32 is arranged to travel via the outer surfaces of the rolls 30, 30', 30", 30"' and the measurement of the profile of the surface is performed again. Now, as a result of the measurement a summed up profile of the roll 30, 30', 30" surface and the steel belt 32 is obtained, from which the earlier measured roll 30, 30', 30" profile can be subtracted by calculation, whereby the profile of the steel belt 32 is obtained as a result. The information on the profile of the steel belt 32 can be used for controlling the grinding so that the steel belt can be ground into an even thickness. The rolls are rotated by means of their own driving motors (not shown). Figure 7 shows an arrangement according to an embodiment of the invention when the steel belt is ground in a maintenance device of the calender belt. The steel belt 32 to be ground is tensioned around a support roll 30 by means of a tension roll 311. The belt is rotated by rotating the support roll 30 or the tension roll 311 by means of an electric motor (not shown) and the steel belt is ground by means of the measurement and grinding unit 101. Before grinding, the profile of the support roll 30 surface is determined by means of the measurement and grinding unit 101.

Figure 8 shows an arrangement according to a further embodiment of the invention as seen from the side. The reference numbers correspond to the reference numbers of the previous Figures, i.e. the same reference numbers are intended to be used for the same parts. In Figure 8, the measurement sensor unit 13 is arranged to the slide 3 in a fixed manner, which measurement sensor unit determines the distance of the slide 3 from the straightness reference, whose end 11 ' is shown in the Figure as being fixed to the fixing means 10. The measurement sensor unit 13 comprises an arc member 19, which is arranged in a fixed connection with the slide 3, preferably in an immobile manner. Several laser sensors 17, 17', 17" are arranged in the arc member 19, by means of which laser sensors the distance and the profile of the roll 30 surface 31 can be determined in a non-contacting manner by calculation on the basis of the distances measured by the laser sensors 17, 17', 17". The number of the laser sensors in the arc member can be 3 or more, preferably 3-6.

It is apparent to a person skilled in the art that the invention is not limited exclusively to the examples presented above, but that the invention may vary within the scope of the claims presented below.