Cylinders having a smooth surface must be reground from time to time.

Hitherto roll grinding machines or so-called profile grinding machines have been used, in particular for great tissue (yankee) or machine glazed cylinders. Such profile or tangential grinding machines grind a smooth contour during traversing at the rotating cylinder. However, profile machines of this kind have a weight in excess of 4 tons, causing transport and space problems. Profile or tangential grinding is much more involved than a polishing procedure which has hitherto been used to remove smaller surface damage (roughness), and furthermore requires considerable reinstallation work. With the profile or tangential grinding machines as hitherto used to recondition great tissue (yankee) or machine glazed cylinders, large bench type grinders have to be installed leading to the following disadvantages: -heavy and bulky to ship around the world -long transport ways due to sea freight -takes a relative long time to install and prepare the equipment underneath the cylinder -major paper machine components must be removed and reinstalled to allow space for the grinder.

With the application of polish grinding machines, hitherto used only for polishing, transport costs and installation and dismounting time could be reduced. Such polish grinding machines are small and have a weight of about 0.5 tons. Polish grinding machines are usually formed by belt or band grinding machines as disclosed, e. g., in WO 9803304 and WO 9302835. Machines of this kind provide a sufficiently great power but are usually not used to change the contour of the cylinder, i. e. only compensate for scratches, markings and the like. Band grinding machines are mounted on the scraping blade holder of the cylinder and can, without greater expenditure, be laid out for traversing along the cylinder.

Polish grinding machines do not influence the contour or the concentricity of the cylinder and therefore are pneumatically pressed against the cylinder with constant pressure. However, a control of the pressure is only possible when a reference is provided. In contrast to profile grinding machines where such a reference is given by the great machine bed, or by a physical reference plane on the grinding machine, polish grinding machines are not provided with such a reference. In particular, the scraper blade cannot be used as such a reference when, e. g., the contour or the concentricity of the cylinder must be reestablished.

The object of the invention is to provide a grinder of the above-mentioned kind, the basic structure of which can principally be that of a grinding machine as disclosed, e. g., in the above-referenced WO 9803304 and WO 9302835, but by which profile grinding can also be carried out.

This object is achieved by the following features: A measuring system associated and displaceable with said grinding mechanism is provided for determining the position of said displaceable grinding mechanism relative to said roll and relative to at least one reference line provided outside of said roll and adjusted parallel to the axis of said roll, with the relative position being determined in a plane preferably perpendicular to said reference line. The grinding effected by said grinding mechanism is controlled on the basis of the measurement values obtained from said measuring system.

With the virtual reference that is provided a corresponding control of the application force or contact pressure force of the polish grinding or profile grinding machine is possible. Even if the grinder is used for profile grinding, due to the virtual reference that is provided, the basic structure can principally be the same as with a usual polish grinding machine, e. g., a polish grinding machine such as as disclosed in WO 9803304 and WO 9302835, the disclosures of which are hereby incorporated herein by reference.

The measuring system is preferably a laser measuring system.

In accordance with a further preferred embodiment at least one reference line is provided as a wire spanned parallel to the axis of the roll.

In practice, the grinding mechanism is preferably controlled so that only elevations are removed.

When at least two parallel reference lines are provided, the measuring system can additionally be laid out for determining the inclination of the grinding mechanism in a plane preferably perpendicular to the reference lines and/or for determining the angular position of the roll.

The measuring system may comprise triangular path measuring means, e. g., for carrying out measurements by triangulation.

In accordance with a further advantageous embodiment the measuring system is provided for determining the outer surface contour of the roll.

In principle, the grinder can be controlled so that measurement and grinding cycles are executed in parallel or alternately. However, it is preferred to control the grinder so that measurement and grinding cycles are executed alternately.

The grinding mechanism is preferably a band grinding mechanism.

According to a preferred embodiment the grinder is controlled to provide for profile grinding.

The grinding mechanism is preferably mounted on a scraper blade holder associated with the roll or on a rail temporarily replacing said scraper blade, and displaceable along said scraper blade and rail, respectively.

Embodiments of the subject matter of the invention are described in more detail hereinafter in connection with schematic drawings which show: Fig. 1 a measuring principle which may be used for the measurement system of a grinder, Fig. 2 a schematic sideview of a grinder comprising a band grinding mechanism mounted on a scraper blade holder associated with the roll and displaceable along said blade, Fig. 3 a possible measuring trace obtained from a measuring cycle, Fig. 4 the measuring results obtained on the basis of measurements according to Fig. 3, and Fig. 5 the surface topography representation visualized by interpolation.

According to Figs. 1 and 2, a grinder 10 is provided for grinding an outer surface 12 of a roll 14, such a paper machine roll, in particular a tissue (yankee) cylinder or machine glazed cylinder.

The grinder 10 comprises a grinding mechanism 16 displaceable in a direction essentially parallel to said roll 14 and displaceable towards and away from said roll 14 in a direction perpendicular to the roll axis.

A measuring system 18 associated and displaceable with said grinding mechanism 16 is provided for determining the position of said displaceable grinding mechanism 16 relative to said roll 14 and relative to at least one reference line 20,22 provided outside of said roll 14 and adjusted parallel to the axis of said roll 14. The relative position is determined in a plane perpendicular to said at least one reference line 20, 22. The grinding effected by the grinding mechanism 16 is controlled on the basis of the measurement values obtained from said measuring system 18.

The measuring system 18 is mounted on the grinding mechanism 16.

The measuring system 18 is preferably a laser measuring system.

According to a preferred embodiment at least one reference line 20,22 is provided as a wire spanned parallel to the axis of the roll 14.

The grinding mechanism 16 is preferably controlled so that only elevations are removed.

When using at least two parallel reference lines 20,22 as in the present case, said measuring system 18 can additionally be laid out for determining the inclination of the grinding mechanism 16 in a plane preferably perpendicular to the reference lines 20,22 and/or for determining the angular position of the roll 14.

The measuring system 18 preferably comprises triangular path measuring means. The measuring means is preferably used for determining the outer surface contour of the roll 14. Principally, the grinder 10 can be controlled so that measurement and grinding cycles are executed parallel or alternately. However, it is preferred to control the grinder so that measurement and grinding cycles are executed alternately.

In the present case, as can be seen from Fig. 2, the grinding mechanism is a band grinding mechanism.

The grinding mechanism 16 can be mounted on a preferably curved or bent scraper blade holder 24 and/or the associated scraper beam 24'.

Alternatively, the grinding mechanism 16 can be mounted on a rail temporarily replacing said scraper blade 14. The mounted grinding mechanism 16 is displaceable along said scraper blade 24 and rail, respectively.

Thus, the principle structure of the grinder can be similar to that of a usual polish grinding machine as disclosed, e. g., in WO 9803304 and WO 9302835. However, with the provided virtual reference the grinder can also be used for providing profile or tangential grinding. In doing so, the grinding mechanism 16 is preferably controlled in such a way that only elevations are removed.

In Fig. 1, xi, yl and X2, y2 are the co-ordinates of the two adjusted wires 20,22 relative to the measuring system 18, and X3 is the distance between the measuring system 18 and the outer surface 12 of the roll 14 having a radius r. In Fig. 2, the respective laser beams generated by the measuring system 18 are indicated by"26". The roll 14 can be, e. g., a yankee cylinder. The radius r itself can be determined by the following function: r = f (XI, 2, 3, Yl, 2, C), wherein"C"are calibrated parameters (wire position etc.). As already mentioned, the measuring system 18 may comprise triangular path measuring means. Preferably a 2D scanning (device) is provided.

Consequently, a conventional polish grinding machine can be provided with the necessary hardware and software so that such a polish grinding machine can also be applied for profile or tangential grinding.

The information on how much the roll surface topography deviates from the measured target crown line can be processed in a way eliminating this deviation by a corresponding control of the force and/or pressure applied by the wheel heads of the grinding mechanism 16.

The functional structure of the total system can be, e. g., as follows: Measuring system -Systems for topography measurement and positioning -Calibration of the required measurement standards -Accuracy analysis Control svstem -Calculation of the machining allowance -Synchronisation of kinematic sequences -Exact control in cross direction -Grinding force control of both wheelheads according to default -Consideration of special states -Determination of the abrasive characteristics (grinding curve) in experiment Attachment modification -Auxiliary driven axes for grinding force control -Synchronisation attachment The measuring system can be laid out for recording the roll's (yankee cylinder's) crown or crowning line topography consisting, e. g., of the following components: 1. measuring system for determining the roll's angular position, 2. measuring system for finding out the position in cross direction (cd), 3. adjustment of the at least one spanned wire, 4. measuring device for determining the radial distance between the at least one spanned wire and the crown line surface, 5. control processor (PC) for calculating the crown line topography.

The components 1 and 2 can be used to find out the current local co- ordinates on the roll's crown line during the roll's rotation thereby simultaneously moving the measuring equipment in cross direction (cd).

To define the angular position, an incremental measuring band (self- adhesive) with reference mark can be provided on the roll's circumference.

Alternatively, a frictional wheel path sensor and a reference mark can be provided on the roll. The position in cross direction (cd) can be measured by a suitable control path sensor (absolute measurement).

The current local co-ordinates are necessary to generate a measuring grid for topography as well as to find out the grinding (abrading) position.

The installation of the span-wire (s) consisting of one or more wires spanned equidistantly to the roll's axis serves as the reference to the roll axis which is not accessible for measurement. The adjustment of the span-wire (s) is the measuring base to find out position-related radii differences on the roll's crown line. The use of such a virtual reference takes account of the fact that the mechanical guidance of the distance measuring units cannot usefully act as a base according to the required accuracy.

The current positions of the distance measuring unit inside the roll's section plane can be determined by means of the span-wire (s) comprising one or more axially spanned wires.

Therefore, two orthogonal positions as well as the measuring device's angular location to the normal line in the measuring point on the crown line will have to be found out.

The angular position can be determined by means of an electronic inclinometer. Alternatively, the angular position can be determined by means of two reference lines, e. g., two wires spanned in parallel.

The distance measuring unit can consist of: -a laser scanning system for determining the location and inclination of the measuring system in the roll's cross section plane (if only one spanned wire is used, an inclinometer may be used to measure the inclination), -a laser triangulation path measuring instrument for determining the distance to the roll's surface, and -a platform to fix the above-mentioned components in a fixed manner.

The distance measuring unit is not guided in the cross direction (cd) on its own. It is to be mounted on the abrasive unit equipped with a feed drive in a mechanically reliable way.

In a control processor (PC) the current radii differences of the roll's crown line are calculated from the current measuring values and known parameters on the wire suspension as well as the adjustment geometry and saved in conjunction with the local co-ordinates. Hereby, the parameters on the wire suspension and installation geometry are to be input into the PC off-line. When co-ordinating roll speed, feedrate and CPU time, the roll crown line's topography can be recorded in a predefined grid on a helix spanning the whole roll's crown line.

On the yankee stands to be considered, there are no doctors which are precisely adjusted equidistant to the yankee axes which could be used as measuring bases to determine the crown line profile. Thus, the real problem in the measurement of the crown line's topography (profile) is to realize a sufficiently precise measuring base.

Under the given circumstances at the yankee stands, the measuring base is preferably provided by at least one reference line, preferably at least one spanned wire, although a laser beam could also be used in principle. One of the advantages of the use of at least one spanned wire is that it can be adjusted to the roll (yankee cylinder) axis and mounted at the crown line's base and end, whereas a laser beam can only be adjusted and fixed at one end of the roll's crown line.

To measure the topography of the entire yankee cylinder by means of the distance measuring unit, i. e. measuring system, the topography must be traversable on the abrasive attachment in cross direction (cd) by an exactly defined path value. Therefore, no special NC axis is necessary. It can also be traversed, e. g., manually from stop to stop.

In order to put the measuring system into operation, the following steps could be provided: 1. mount grinding attachment in conjunction with the distance measuring unit on the stripper, 2. fix holders and chucks for adjusting the span-wire (s), 3. calculate the mean yankee's crown line radii from circumference measurements, 4. span and adjust wire (s), 5. radially adjust the laser triangulation measuring means or instruments.

The following measuring aids can, e. g., be used for the initiation: -a nonius band chain for measuring the roll diameter, -a levelling device for horizontally adjust the spanned wire (s).

The local radius of the yankee cylinder cannot be measured immediately.

Only the radial distance to a straight reference line (spanned wire (s)) located equidistantly to the yankee cylinder axis can be measured.

In the span-wire (s) measuring technique, a map of the wire (s) (silhouette with contour lines) can be created by a measuring microscope and evaluated afterwards.

For an automated silhouette measurement, e. g., a mapping lens with telecentric beam path can be used. The spanned wire (s) in the telecentering region of the lenses can be illuminated by a light source and the silhouette can be mapped into a diode line. Afterwards, the wire diameter, the wire's centroidal position and the location of the wire in the object field can be evaluated.

In the scanning method, a parallel laser beam with small beam section can be commonly moved over the issue to be measured. A laser beam can be deflected over rotating mirror surfaces located in the focus of lenses or concave mirrors. Therefrom, during rotation of the mirror, the beam is shifted in parallel over a scanning field and can be received on the counter side by a receiver.

The location of the wire (s) in the object field is necessary for the desired case of application. This application can also be put out by several devices (suspension control, definition of position). The scanning method provides higher accuracy and lower measurement uncertainties by multiple measurements and averaging.

For reasons of accuracy and also technical suppositions, this scanning method should be preferably used to record the wire position.

For scanning the yankee cylinder surface, many instruments or devices for distance measurement are available, e. g. incremental distance sensors (displacement transducers), inductive probes, eddy current sensors and optical sensors.

As regards the non-contact procedures, especially the triangulation sensors based on optical principles would provide a suitable solution. A triangulation sensor can be described as follows: A ray of light (preferably a laser beam) is incident under a defined angle on the crown line of the yankee cylinder. The luminous spot is mapped on a receiver at changed positions depending on the corresponding distance of the sensor. This position shift is received by analogous photo receivers (sensors reacting sensitive on position) or digital sensors (photodiode lines (CCD)).

The span-wire (s) has to be adjusted equidistantly to the yankee cylinder axis. Therefore, the radial distances from the beginning of the wire and the wire end are to be adjusted to the yankee cylinder axis and both wire ends are, e. g., to be horizontally aligned.

The radial distance between span-wire (s) and yankee cylinder axis is adjusted by two measurable radial distances-located near to the front side and rear front of the yankee cylinder-to the crown line surface.

Therefore the yankee cylinder diameter at both of those adjustment points must be known. The measurement of the mean yankee cylinder diameter at both adjustment points can be carried out by a nonius steel band measurement means to determine the yankee cylinder's circumference.

The mean yankee cylinder radius is calculated from the measured circumference. From this value, one can define the radial distances to the crown line of the yankee cylinder at the adjustment points which are to be adjusted.

All calculations may be based on consecutively executed measuring cycles.

The measuring values (cd, angle, md) are recorded on a predefined trajectory (helix) keeping defined angular distances. The results of an exemplary measuring cycle are illustrated in Fig. 3 (measuring trace) and Fig. 4 (measuring result) in a simplified manner.

The surface representation can be visualized by interpolation (cf. Fig. 5).

Grinding by means of the polish grinding apparatus is performed as follows: During grinding, a material height which can be derived from the grinding force of the grinding curve is homogeneously removed over the whole width of the abrasive band (grinding band).

Hereby, the grinding force is determined in a way removing as much material as possible without reaching the lower tolerance.

The optimization of the grinding cycle is based on the grinding trajectories which are to be kept precisely since the grinding forces to be specifically realised must be calculated beforehand.

Optimization can be separately performed for each angular cylinder position (in the same grid as used for the measuring cycle). Now, one can derive from the concrete shape of the grinding trajectory, at which moment of time each of both grinding heads applies at the points used during measuring-hereunder named as check points. Since each position of the surface is ground repeatedly, a grinding force input acts on several check points.

To reduce the yankee cylinder's wall thickness as little as possible, it should be ensured that no check point is ground below nominal size.

Since a usual polish grinding should be performed before the first measuring cycle in order to achieve accurate measurement, it may be assumed that only very small gradients appear in the cross direction.

Consequently, the residual over allowance remaining from the optimization approach can be accepted.

The allowance can be calculated separately for all (correspondingly discrete defined) angular locations of the yankee cylinder. Solving the optimization problem (for each angle) demands for calculations to be repeated correspondingly.

The required computing and memory capacities can be provided by a control processor (PC).

The measuring values as well as the grinding force should be exactly assigned to cd and angle. In general, and especially in the case of necessary interrupts and following direct continuation, the reference with the measuring system for cd and angle should be ensured.

The required extensions of a conventional polish grinding machine include the installation of the measuring system, the controlled driving axes and a control processor (PC) to compute and co-ordinate the measuring and grinding cycles.

Measuring systems standing for components to be integrated into the grinding system must be installed additionally. Making use of commercially available components, the smooth interaction with the control processor (PC) is to be ensured. The measuring system is preferably mounted on the used polish grinding machine so that it is moved in machine direction (md) together with this grinding machine.

Controlled driving axes are provided in cross direction and machine direction.

As to the cross direction, the polish grinding machine used is equipped with a drive in the cross direction (CD) which is to be extended by a controller. The controller guarantees that the necessary measuring or grinding trajectories are maintained.

As to the machine direction, the respective time signals must be calculated for the grinding pressure acting adequately on the wheel head.

A controlled (hydraulic) drive could be used in this case also. The measuring signal necessary for the controller could be fed back as a check value (trace) to the control processor.

List of reference signs 10 grinder 12 outer surface 14 roll 16 grinding mechanism 18 measuring system 20 reference line, spanned wire 22 reference line, spanned wire 24 scraper blade 24'scraper beam