Method for monitoring a grinding process

Abstract

A method for monitoring a grinding process in which a workpiece is ground in a belt grinding machine, wherein the belt grinding machine has a grinding head comprising a contact roller and / or a grinding shoe and at least one deflection roller, wherein a grinding belt is guided by the at least one deflection roller or jointly by the at least one deflection roller and the contact roller, wherein the belt grinding machine has a mechanism for moving the workpiece relative to the grinding head during the grinding process, wherein the grinding belt is pressed onto a surface of the workpiece by the contact roller and / or the grinding shoe during grinding, wherein the belt grinding machine is further characterized by a sensor unit for scanning the surface of the workpiece, which is connected to an evaluation unit, in that the sensor unit scans the surface of the workpiece after grinding.wherein the sensor unit and the evaluation unit are configured to detect the presence of at least one chatter mark.

Description

Technical area

[0001] The invention relates to a method for monitoring a grinding process, a method for controlling and / or regulating a grinding process. State of the art

[0002] Belt grinding machines are known in the art. Devices and methods for controlling, regulating, and monitoring a grinding process are also known.

[0003] DE 199 15 909 C2, for example, proposes a method for controlling a grinding process. On the one hand, sensors are to be used to monitor the grinding process. On the other hand, a human, i.e., an operator, is still to be placed at the center of a control level. The operator is responsible, for example, for determining whether chatter marks are present by chalking the surface of a workpiece, such as a chipboard.

[0004] DE 10 2012 109 086 A1 also deals with the monitoring of a grinding process. For example, it proposes installing sensors for each position change of the workpiece being ground. Furthermore, it proposes installing a testing station downstream of the belt grinding machine, whose sensors examine the machined workpiece for compliance with certain parameters. If this examination reveals that the workpiece cannot be released, it is forwarded to an operator for further inspection.

[0005] In this context, reference is also made to EP 1 577 056 A1. This document describes a method for grinding a roll on a roll grinding machine, in which the roll surface is ground with a grinding wheel. Following automatic comparison of the test result with stored data on the condition of the roll surface, information on the evaluation result is output.

[0006] Further reference is made to EP 0 210 654 A2, which discloses a belt grinding machine in which the grinding belt is pressed onto a workpiece to be machined via bolts.

[0007] Furthermore, DE 10 2007 012 780 A1 discloses a scanner beam similar to the aforementioned inspection station. The scanner beam can be arranged in front of the grinding unit. The information acquired by the scanner beam can be transmitted to a control device of the belt grinding machine to determine which pressure elements of the pressure beam should be used to process the workpiece.

[0008] DE 10 2007 012 780 A1 further proposes arranging a scanner beam behind the grinding unit to capture information about the surface of the workpiece being machined. Such information can, for example, relate to the structure or color of the surface, as well as its roughness. This information can then be compared with reference values. This allows the grinding result and the wear of the abrasive to be assessed.

[0009] Conventional belt sanders typically require intensive and close monitoring of the sanding process by an operator. Furthermore, the desired sanding result is often not achieved. Furthermore, wear parts such as sanding belts are often replaced prematurely as a preventative measure to avoid keeping the sanding belt in operation for too long. The subsequent premature disposal of the sanding belts leads to high operating costs and pollutes the environment. Object of the invention

[0010] The object of the invention is to overcome the disadvantages of the prior art. Solution to the task

[0011] The features of claim 1 lead to the solution of the problem. Advantageous embodiments are described in the subclaims.

[0012] In a method according to the invention for monitoring a grinding process in which a workpiece is ground in a belt grinding machine, wherein the belt grinding machine has a grinding head which comprises a contact roller and / or a grinding shoe and at least one deflection roller, wherein a grinding belt is guided by the at least one deflection roller or jointly by the at least one deflection roller and the contact roller, wherein the belt grinding machine has a feed device for moving the workpiece relative to the grinding head during the grinding process, wherein the grinding belt is pressed onto a surface of the workpiece by the contact roller and / or the grinding shoe during grinding, wherein the belt grinding machine is further assigned a sensor unit for scanning the surface of the workpiece, which is connected to an evaluation unit, the sensor unit scans the surface of the workpiece after grinding, wherein the sensor unit and the evaluation unit are configured to detect the presence of at least one chatter mark.

[0013] The workpiece can be, for example, a board, such as a chipboard, an MDF board (medium density fiberboard or wood fiberboard), an OSB board (oriented strand board), a chipboard or a board made of another material such as wood, laminate or the like.

[0014] The feed device can be, for example, a transport table or a conveyor belt. The feed device moves the workpiece relative to the grinding head. Preferably, the workpiece is guided past the grinding head with the aid of the feed device in such a way that the grinding head can process the workpiece surface.

[0015] In order to monitor the grinding process, the sensor unit is conveniently arranged downstream or behind the grinding head in the feed direction in order to scan the surface of the ground workpiece.

[0016] The sensor unit comprises at least one sensor, but it can also comprise several sensors of the same or different types.

[0017] Chatter marks are surface defects. These usually occur in series and often have a characteristic appearance. The present invention aims to analyze and evaluate both the frequency with which chatter marks occur and the distances between them, as well as the properties and / or nature of individual chatter marks.

[0018] Numerous types and types of sensors can be considered. Non-contact sensors, such as optical sensors, are preferred.

[0019] The sensors are preferably suitable for scanning the surface of the workpiece after grinding and for detecting at least one property or condition of the workpiece's surface. This includes, for example, the presence, position, orientation, condition (e.g., dimensions or amplitude) of chatter marks, as well as roughness. Any other conditional characteristics can also be considered. Since chatter marks occur both as depressions and elevations, the amplitude of a chatter mark is understood to be its depth or height in comparison to the rest of the workpiece. On the one hand, the amplitude can be recorded and handled as an absolute value. On the other hand, the amplitude can also be recorded and handled as a signed quantity, so that not only the absolute value of the amplitude is determined, but also whether it is a height or elevation or a depth or depression.

[0020] The sensors can perform their functions individually or in combination, for example, by interconnecting them. The same applies to multiple sensor units.

[0021] Such sensors for determining, in particular, three-dimensional properties as well as texture characteristics and properties of surfaces are known. Suitable measurement methods include, for example, white light interferometry, focus variation, confocal measurement methods such as profilometry, interferometry, holographic measurement, and the like.

[0022] The belt grinder may include a control and / or regulating device. In this case, the evaluation unit may be integrated into the control and / or regulating device. However, the evaluation unit may also be implemented as a separate component or integrated into the sensor unit.

[0023] Wide belt sanders for carrying out the method according to the invention are understood to be, in particular, permanently installed, i.e., non-hand-guided sanders whose sanding belts have a width of more than one meter. The width of the sanding belts is typically between 1.3 and 3.3 meters.

[0024] A belt sander comprises at least one sanding head, often also called a sanding unit. The sanding head is understood to be the unit described above, which includes at least the components also described and supports or guides the sanding belt during sanding.

[0025] A belt grinder can comprise one or more grinding heads. If the belt grinder comprises several grinding heads, these can be housed in a single housing or in several housings. In the latter case, the housings can be joined together in a modular manner. Preferably, a belt grinder comprises at least two opposing grinding heads so that, in particular, both sides of a panel to be machined can be ground simultaneously. With respect to an imaginary plane within which the feed device lies, grinding heads arranged in pairs of this type are arranged essentially in mirror image above and below the imaginary plane. However, it is also possible to machine a workpiece to be machined from only one side and to provide individual grinding heads instead of grinding heads arranged in pairs.

[0026] If two opposing grinding heads are provided, the pressure applied to the workpiece can be adjusted by adjusting the pressure of the contact rollers and / or the sanding pads of the two grinding heads. However, if only one grinding head is present, the opposing grinding head, which acts as a counterbearing, is missing. This counterbearing function can be fulfilled either by the feed device or by a counterpressure roller. Such a counterpressure roller is preferably provided opposite the individually arranged grinding head and applies pressure from the non-machined side of the workpiece, or the side to be sanded, which is directed onto the sanding belt.

[0027] Furthermore, several belt grinders comprising one or more grinding heads can interact in such a way that a workpiece to be machined is machined sequentially by at least two belt grinders. For this purpose, the interacting belt grinders can, for example, use the same feed device or share this feed device. Furthermore, a transfer, in particular by means of an automatically operating transfer device, can also be considered, which transfers the workpiece machined by a first belt grinder to a second belt grinder for processing.

[0028] Several belt grinding machines interacting as described above can also be referred to as a grinding line.

[0029] If the belt grinding machine or grinding line comprises several grinding heads, it can be considered to arrange a sensor unit behind several grinding heads or even behind all grinding heads.

[0030] It may be considered to arrange exactly one sensor unit downstream or behind each belt grinder, even if at least one of the belt grinders has multiple grinding heads. It is usually sufficient to arrange one sensor unit behind each belt grinder, since the chatter marks caused by different grinding heads on the same belt grinder are usually different from one another. Furthermore, it may even be sufficient to arrange a single sensor unit downstream at the end of the grinding line, provided that all chatter marks generated by the various grinding heads on the various belt grinders can be distinguished from one another. Furthermore, it may be considered to arrange only one sensor unit behind one of the belt grinders or downstream at the end of the grinding line if not all grinding heads need to be detected as sources of chatter marks.

[0031] Of course, it is conceivable to arrange at least one further sensor unit upstream, i.e. in front of the at least one grinding head, in addition to the at least one sensor unit arranged downstream, i.e. after the at least one grinding head. In the case of a simply designed belt grinding machine comprising only one grinding head, a sensor unit would therefore be arranged in front of and behind the grinding head. The upstream sensor unit can scan the surface of the workpiece to be machined in the same way as already described with regard to the downstream sensor unit. Furthermore, the measurement data recorded by the upstream sensor unit can be compared with the measurement data recorded by the downstream sensor unit. This comparison can be carried out automatically, for example by subtracting the measurement data to be compared with regard to roughness or chatter marks.An upstream sensor unit can enable the grinding process monitoring method to automatically adapt to different workpieces with different properties or made of different materials.

[0032] The method described here for monitoring the grinding process is often superior to monitoring the grinding process by an operator, or can at least support the operator. Firstly, the often high feed rate or the high cycle rate mean that the operator does not have sufficient time to assess the grinding result. Furthermore, characteristics and properties of the surface of a workpiece can reach an undesirable level even if they are not yet visible to the operator's eye or can only be seen with great difficulty. Monitoring as described above is therefore often superior to monitoring by the operator in terms of precision, reliability and speed.

[0033] As described above, it can be envisaged that the sensor unit and the evaluation unit detect a property and / or a condition of the at least one chatter mark in the case of the presence of at least one chatter mark on the surface of the workpiece.

[0034] It may further be envisaged that, in the event of the presence of at least one chatter mark on the surface of the workpiece, the sensor unit and the evaluation unit determine, based on the property and / or the nature of the chatter mark, whether the chatter mark is caused by a belt connection of the grinding belt and / or by the contact roller and / or by the feed device and / or by another component of the belt grinding machine.

[0035] Sanding belts are typically designed as endless belts. Such an endless belt is created by joining a flat sanding belt to form a continuous belt, particularly by gluing. Methods for producing such an endless sanding belt, particularly by gluing, are known. At the point where the flat sanding belt is bonded to form a continuous belt, the thickness of the sanding belt often differs from the thickness of the rest of the sanding belt, which can lead to chatter marks.

[0036] There are numerous ways to assign at least one chatter mark to its cause or at least to its most probable cause.

[0037] For example, chatter marks can be created in preliminary tests through targeted manipulation. This could involve the targeted manipulation of a component or part of the belt grinder, or the targeted adjustment of at least one setting of the belt grinder, which leads to the formation of chatter marks. These chatter marks can then be examined and characterized. If the aforementioned preliminary test is carried out separately for different manipulations and the chatter marks caused by these differ from one another in at least one characteristic, this characteristic can be detected by the sensor unit in order to deduce the cause of the chatter mark based on this characteristic of the detected chatter mark.

[0038] Furthermore, it may also be considered to assign certain properties of chatter marks to certain causes based on empirical values ​​or regularities and without prior tests and to ensure by suitable measures that the sensor unit can also make this assignment if it recognizes at least one specific property of a detected chatter mark.

[0039] The following properties of the chatter marks, individually or in combination, are taken into account: amplitude of the chatter mark in the workpiece, for example the amplitude at a specific position in the workpiece or the maximum amplitude or the average amplitude or a depth and / or height profile; a position of the chatter mark on the workpiece; an orientation of the chatter mark on the workpiece; a width of the chatter mark; a length of the chatter mark and the like.

[0040] In addition to the aforementioned properties of individual chatter marks, it is also possible to consider using properties relating to at least two chatter marks in a corresponding manner. These properties can of course also be used individually or in combination, even in combination with the aforementioned properties of individual chatter marks. For example, this could include a distance between at least two chatter marks; an average distance between at least three chatter marks; average values ​​of the properties described above with regard to individual chatter marks; and the change in such a property of individual chatter marks when comparing multiple chatter marks.

[0041] The characteristics of at least two chatter marks, such as their spacing, can also be attributed to specific causes in advance through preliminary tests. By evaluating these characteristics, a conclusion can be drawn about the cause, or at least the most likely cause. If, for example, the spacing of the chatter marks is indifferent to a change in the feed speed, a defect in the feed mechanism or feed system is suspected. For example, a transport roller in the feed mechanism could be defective or faulty.

[0042] A well-known rule is that a formula can be used to determine whether given chatter marks are caused by the belt joint. The distance M between two chatter marks caused by the belt joint is calculated by dividing the product of the sanding belt length L and the feed rate vv by the product of sixty times the sanding belt speed vs and the number of belt joints n of the sanding belt in question. The distance between the chatter marks and the sanding belt length are measured in mm. The feed rate is measured in meters per minute, and the sanding belt speed in meters per second. The formula is therefore M = ((L x vv ) / (vsx 60 x n)).

[0043] If chatter marks are caused by a faulty contact roller, for example, one that is running out of round, the chatter mark spacing M is calculated by dividing a thousand times the feed rate in meters per minute by the contact roller's speed n, measured in revolutions per minute. The formula is therefore M = ((vv x 1000) / n).

[0044] Preferably, the sensor unit and the evaluation unit detect all chatter marks on a workpiece and then determine whether the distances between some or all of the chatter marks satisfy at least one of the aforementioned rules. This allows even chatter mark series that have different causes and occur in superimposed fashion to be analyzed. For example, the sensor unit and the evaluation unit can detect the distances to all other chatter marks on a workpiece for each chatter mark present on the workpiece. In the next step, those chatter marks that satisfy one of the aforementioned rules can be identified and thus indicate, for example, the belt splices or an out-of-round contact roller.Of course, it is possible to differentiate between overlapping chatter mark series using the aforementioned process steps. This allows one to determine whether one or more causes of chatter mark are present, and to identify these causes at the same time.

[0045] Alternatively or complementarily, it may be possible to assign chatter marks to specific causes based on their properties or characteristics, or to verify an existing assignment using properties or characteristics. For example, if the spacing of an identified number or series of chatter marks indicates the contact roller as the cause, and it is further known that such chatter marks lie within certain limits with regard to certain characteristics, such as amplitude, depth and / or height profile, or width, then it can be verified by analyzing these characteristics and comparing them with the aforementioned limits whether the chatter marks in question are actually attributable to the contact roller as the cause.

[0046] The properties or characteristics of the chatter marks or individual chatter mark series can also be used to assess the quality of the workpiece. Assuming sufficient sensitivity of the sensor unit, it is possible that chatter mark series are detected, but the individual chatter marks in this series do not yet represent a quality defect in the workpiece due to their characteristics, particularly their amplitude or their depth and / or height profile. However, chatter marks usually initially appear to such an extent and to such an extent that no intervention is necessary. Without intervention, chatter marks then usually appear to such an extent and to such an extent that intervention is absolutely necessary.

[0047] According to the present invention, problems can be detected early, before intervention is absolutely necessary, and can be remedied during planned downtimes of the belt grinding machine, for example due to belt changes or operator changes, without the need for an unplanned downtime to resolve the problem.

[0048] Each of the processes described above can be used to simultaneously check the quality of the workpiece.

[0049] Furthermore, it can be considered that the sensor unit and the evaluation unit record the roughness of the surface of the workpiece.

[0050] It can be considered that in the event of a change in the setting of the belt grinder, the sensor unit and the evaluation unit record the roughness both before and after the change is made.

[0051] If at least one desired or necessarily occurring or expected effect, which is to be achieved by making the change in the setting described above, is a change in the roughness, it can be determined by the before-and-after measurement described above whether the desired effect occurs.

[0052] Such a change could, for example, be replacing a sanding belt, as sanding belts vary in their properties and, for example, differ in whether they produce a coarser or finer finish. Whether the finish is coarser or finer can depend, among other things, on the following sanding belt parameters: grain type, grain shape, grain size, grain distribution, as well as the selection of a binder and filler.

[0053] Such a change can also be a change in the pressure with which, for example, the contact roller or the sanding pad applies to the sanding belt, thus pressing it against the workpiece to be machined. If, in two consecutive sanding heads, the first sanding head performs a coarser, so-called calibration grind and the second sanding head performs a so-called fine grind, the pressure of the sanding pad in the second sanding head is preferably increased to reduce roughness.

[0054] If, for example, this pressure is adjusted to direct the roughness in the desired direction and it is determined using the before-and-after measurement described above that the desired effect is not achieved, this may indicate that the sanding belt or one of the sanding belts has reached its maximum service life and the so-called service life has been exceeded.

[0055] Furthermore, it can be considered that measurement data recorded by the sensor unit and evaluated by the evaluation unit are compared with predetermined limit values, whereby a signal is output if a predetermined limit value is exceeded or undershot.

[0056] The measurement data recorded by the sensor unit and evaluated by the evaluation unit relate in particular to roughness and chatter marks, but can also relate to other characteristics of the workpiece.

[0057] The specified limit values ​​can be set, for example, by an operator. Depending on which characteristics or properties are detected by the sensor unit and transmitted to the evaluation unit as measured data, it may be appropriate to specify an upper limit or a lower limit. If the characteristic to be detected is to remain within a certain range and thus not exceed an upper limit or fall below a lower limit, it may also be considered to specify both an upper limit and a lower limit.

[0058] The output signal can be a warning signal or a control signal. Of course, it's also possible to output both a warning signal and a control signal.

[0059] In the case of a warning signal, this can be an acoustic, a visual, or another type of warning signal, either individually or in combination. The warning signal can also be transmitted to a suitable signaling device, such as a siren or a horn. The signal can also be displayed on the belt grinder's control panel.

[0060] In the case of a control signal, it can be envisaged that a control signal is generated when the limit value is exceeded or undershot and is transmitted to the belt grinder, in particular to its control and / or regulating device. If a limit value regarding roughness is exceeded and the surface of the workpiece is therefore too rough, a control signal can be generated, for example, which increases the pressure with which the contact roller or the sanding pad applies to the sanding belt. If a characteristic is detected that indicates a malfunction of the belt grinder that requires repair, a control signal can be generated that causes the belt grinder to stop in emergency mode.Accordingly, it is conceivable to record and evaluate a variety of quality characteristics and, after comparing them with a specified limit value, generate a control signal, particularly to intervene in the grinding process in a regulating manner. This allows for automatic readjustment of at least one, but preferably several, settings of the belt grinding machine during operation.

[0061] In a similar way to what was described above with reference to just one limit value, it is also conceivable to assign multiple limit values ​​and multiple signals to one another in different ways. On the one hand, it is conceivable that, for example, exceeding a limit value triggers the output of multiple signals, including multiple control signals. Furthermore, it is conceivable that exceeding different limit values ​​triggers the output of the same signal. For example, both certain chatter marks and a certain roughness can trigger an emergency stop. Other assignments of limit values ​​and signals are conceivable.

[0062] It may further be envisaged that measurement data recorded by the sensor unit and evaluated by the evaluation unit are compared with limit values, whereby a signal is output when a predetermined limit value is exceeded or undershot, whereby the limit value depends on at least one property or setting of the belt grinding machine.

[0063] The limit value(s) do not have to be fixed and unchangeable for each belt grinder, but can be adapted to the settings and properties, i.e. to the configuration of the belt grinder.

[0064] The aforementioned properties and settings of the belt sander include, for example, a quality or type of the sanding belt, a grain sequence, i.e. properties and quality of a grain of several successive sanding belts, a predetermined and / or an actually measured feed or feed speed, a feed direction, a sanding belt speed, a quality or type of the sanding head, a quality or type of the sanding shoe and a quality or type of the contact roller.

[0065] The limit value(s) can either be set by an operator or specified automatically.

[0066] If the limit value is set by an operator, the operator selects the limit value based on his or her experience or specific work instructions and depending on the aforementioned characteristics and settings or the configuration of the belt grinder.

[0067] If the limit value is specified automatically, it can be envisaged, for example, that an operator enters the aforementioned properties and settings of the belt grinding machine via a control panel and the control and / or regulation device calculates the limit value based on this input.

[0068] Furthermore, it is also possible to automatically record the properties and settings of the belt grinder using suitable sensors, and to calculate the limit values ​​automatically and without operator intervention. Suitable sensors are preferably used to detect the condition or type of the grinding belt, grinding head, grinding pad, contact roller, etc. Furthermore, sensors for detecting the feed rate and direction can be considered.

[0069] Furthermore, it can be envisaged that measurement data recorded by the sensor unit and evaluated by the evaluation unit are recorded over a period of time and combined to form a measurement curve, whereby a property of the measurement curve is calculated, whereby a signal is output if the property of the measurement curve deviates to a certain extent from a specification with regard to this property.

[0070] With regard to the calculated properties of the measurement curve, for example, all properties that can be determined using mathematical methods and in an automated manner can be considered. For example, the following properties can be recorded, as well as the changes in these properties over the specified period: local or global minima and maxima, regression curves and regression lines, as well as their gradients, limits, fluctuations, inflection points, symmetries, derivatives, and integrals. Of course, it is possible to calculate not just one but several properties of the measurement curve simultaneously, as described above, and, if necessary, use them to generate a signal.

[0071] In contrast to one or more point measurements, a measurement over a period of time is often more meaningful. Which of the aforementioned characteristics of the measurement curve is meaningful enough to be used to output the signal can be determined in preliminary tests.

[0072] The time period can be adapted to the grinding process. It is also possible to combine the recorded measured values ​​into different measurement curves based on different time periods. For example, it might be possible to calculate fluctuations or maxima of the measurement curve both on a specific day and over the previous 10 days. If the fluctuations or maxima on the observed day deviate significantly from the fluctuations and maxima of the previous 10 days, this may require intervention in the grinding process, which can be achieved by outputting a signal.

[0073] The present invention further proposes a method for controlling and / or regulating a grinding process, in which the method steps of monitoring as described above are first carried out, wherein subsequently, depending on the acquired measurement data and / or depending on the output signal, at least one of the following actions is carried out: Stopping the belt grinder or the grinding process, changing at least one setting of the belt grinder.

[0074] The aforementioned method allows for the first time to control and / or regulate the grinding process based on measurement data recorded during operation.

[0075] In order to carry out the control and / or regulation method described above, a belt grinding machine is expediently usually equipped with the control or regulation device already described. The settings and their changes, which are effected depending on the output signal, are described above with reference to the exemplary embodiments of the monitoring method. With the aforementioned change of at least one setting, the belt grinding machine can be readjusted during operation and thus corrective intervention in the ongoing grinding process can be carried out. Through continuous monitoring, it can then be monitored whether the change made has the desired effect.

[0076] If at least one sensor unit is arranged upstream, it is also possible to use the measurement data acquired by this sensor unit to control and / or regulate the grinding process in the same way as already described for the downstream sensor unit. For example, the roughness of a workpiece to be machined can be measured and then at least one setting, such as the pressure of a grinding shoe, can be adjusted accordingly.

[0077] The method according to the invention proposes a monitoring system for a belt grinding machine with a sensor unit for scanning a surface of a workpiece and an evaluation unit, wherein the sensor unit and the evaluation unit are configured to detect the presence of at least one chatter mark.

[0078] The sensor unit and the evaluation unit can be designed as described above with regard to the monitoring method. It is conceivable to integrate the monitoring system into belt grinding machines already in operation or to retrofit them with the monitoring system. If available, an evaluation unit already installed in the belt grinding machine can be used.

[0079] It can be envisaged that the sensor unit and the evaluation unit are configured to determine, in the case of the presence of at least one chatter mark on the surface of the workpiece, based on a property and / or on a nature of the chatter mark, whether the chatter mark is caused by a belt connection of the grinding belt and / or by the contact roller and / or by the feed device.

[0080] Such detection and assignment is carried out in the same manner as described above with reference to the method for monitoring the grinding process.

[0081] Furthermore, it can be envisaged that the sensor unit for scanning the surface of the workpiece and the evaluation unit are configured to transmit control or regulation commands to a control or regulation device based on measurement data acquired by the sensor unit and evaluated by the evaluation unit. This is also described above with reference to the method for monitoring the grinding process.

Claims

1. Method for monitoring a sanding process in which a disc-shaped workpiece is sanded in a belt sanding machine, wherein the belt sanding machine has a sanding head which comprises a contact roller and / or a sanding shoe and at least one deflection roller, wherein a sanding belt is guided by the at least one deflection roller or jointly by the at least one deflection roller and the contact roller, wherein the belt sanding machine has a feed device for moving the workpiece relative to the sanding head during the sanding process, wherein the sanding belt is pressed onto a surface of the workpiece by the contact roller and / or by the sanding shoe during the sanding process, wherein the belt sanding machine is also assigned a sensor unit for scanning the surface of the workpiece, which is connected to an evaluation unit, characterized in that the sensor unit scans the surface of the workpiece after the sanding, wherein the sensor unit and the evaluation unit detect the roughness of the surface of the workpiece and, in the event of a change in a setting of the belt sanding machine, detect the roughness both before and after the change is made, wherein the sensor unit and the evaluation unit are set up to detect the presence of at least one chatter mark, wherein, if at least one chatter mark is present on the surface of the workpiece, a property and / or a condition of the at least one chatter mark is detected by the sensor unit and the evaluation unit, wherein the condition of the chatter mark is used to determine whether the chatter mark is caused by a belt connection of the sanding belt and / or by the contact roller and / or by the feed device and / or by another component of the belt sanding machine, wherein measurement data recorded by the sensor unit and evaluated by the evaluation unit are compared with predetermined limit values, wherein a signal is output if a predetermined limit value is exceeded or not reached, wherein, for monitoring the sanding process, the sensor unit is expediently arranged downstream or behind the sanding head in the feed direction in order to scan the surface of the sanded workpiece, whereby at least one of the following actions is then carried out depending on the measurement data recorded and / or depending on the signal output: - Stopping the belt sanding machine or the sanding process, changing at least one setting of the belt sanding machine, whereby non-contact sensors, such as optical sensors, are used.

2. Method according to claim 1, characterized in that measurement data recorded by the sensor unit and evaluated by the evaluation unit are compared with limit values, a signal being output if a predetermined limit value is exceeded or undercut, the limit value depending on at least one property or setting of the belt sanding machine.

3. Method according to claim 1, characterized in that measurement data recorded by the sensor unit and evaluated by the evaluation unit are recorded over a period of time and combined to form a measurement curve, wherein a property of the measurement curve is calculated, wherein a signal is output if the property of the measurement curve deviates to a certain extent from a predetermined value with regard to this property.