Grinding machine and method for operating a grinding machine

Abstract

The grinding machine (1) for centerless grinding includes a grinding disk (2) and an adjustment disk (3), between which a grinding gap (4) is formed. In addition, there is a workpiece support assembly (6) located below the grinding gap (4), a workpiece cover rail (9), and a plurality of solid-state sound sensors (14) distributed over the length of the workpiece cover rail (9) and coupled to a display device (20), which is formed to display information obtained by the individual solid-state sound sensors (14) in an array that reflects the array of the solid-state sound sensors (14). This allows visualization of the grinding gap (4) during centerless grinding during operation.

Description

[Technical Field]

[0001] The present invention relates to a grinding machine for centerless grinding, in which the workpiece is ground in a through-feed manner. Furthermore, the present invention relates to a method for operating such a grinding machine. [Background technology]

[0002] WO 2018 / 162002 discloses a loading device for a plunge grinding machine for centerless peripheral grinding and a method for centerless peripheral grinding. The plunge grinding machine is intended for machining an unmachined workpiece guided between a grinding disc and an adjusting disc.

[0003] The centerless grinding machine described in DE 1402590 comprises a grinding disc and an adjusting disc that rotates opposite to each other, and the grinding disc and the adjusting disc are movable relative to each other. The centerless grinding machine according to DE 1402590 further comprises a stepwise rotatable workpiece carrier disc that transports workpieces from a supply station to a grinding position between the grinding disc and the adjusting disc, and from the grinding position to a discharge station.

[0004] German Patent No. 860468 discloses an apparatus for centerless grinding of cylindrical surfaces, which envisages an arrangement for external grinding being ensured, in which the workpiece is guided during the grinding process by a driving adjusting disc and a support guide, which in principle can be replaced by a support roller.

[0005] Machining processes on various types of machines can be monitored, inter alia, by detecting acoustic signals. For example, the surface processing device described in Swiss Patent No. 702248, which processes with a dish-shaped grinding tool, is equipped with a sensor for detecting noise. By detecting noise, in the case of Swiss Patent No. 702248, the position of the spindle holder is determined at the moment the grinding tool contacts the workpiece. This provides information about the plunge depth of the grinding tool.

[0006] Further grinding machines combined with acoustic sensors are described, for example, in Chinese Utility Model No. 2928386 and Chinese Patent No. 105215852.

[0007] In the context of a method for tool wear detection in cylindrical grinding, disclosed in the former East German Patent Application No. 263489, detection of solid-state sound near the cutting position is contemplated. The signal processing used for wear detection is particularly concerned with signals having frequencies below 1 kHz. Further grinding devices equipped with solid-state sound sensors are described, for example, in the German Patent Application No. DE 102007063200 A1.

[0008] A method for monitoring the wear state of a grinding disc is described in DE 41 06 053 A1, in which not only the noise generated during grinding but also the power of the drive motor is sensed. Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to provide a particularly user-friendly method of acoustic monitoring in centerless peripheral grinding, which is further developed relative to the above-mentioned prior art. [Means for solving the problem]

[0010] This problem is solved according to the invention by a grinding machine designed for centerless grinding having the features of claim 1. Likewise, the problem is solved by a method for operating a grinding machine according to claim 8. The embodiments and advantages of the invention described below in relation to the operating method also apply to the device, i.e., the centerless grinding machine, and vice versa.

[0011] The components of the grinding machine are a grinding disc and an adjusting disc, between which a grinding gap is formed in a manner known per se. The grinding machine further comprises a workpiece support assembly located below the grinding gap and a workpiece cover rail covering the workpiece. A plurality of structure-borne sound sensors, for example at least six, in particular eight or more, are distributed over the length of the workpiece cover rail and are data-technically linked to a display device, which is configured to display information obtained by the individual structure-borne sound sensors in an array that reflects the given linear array of the structure-borne sound sensors.

[0012] By positioning the information obtained using the structure-borne sound sensors in a pattern that corresponds to the pattern of arrangement of the structure-borne sound sensors on the grinding machine, a particularly simple and intuitive perception of the information by the operator is possible.

[0013] Generally, when operating a grinding machine, multiple workpieces are fed through a grinding gap formed between a grinding disc and an adjusting disc, and during grinding, acoustic signals are acquired at multiple positions formed together in a row along the grinding gap and converted into optical signals, and the signal arrangement reproduces the above-mentioned positions, i.e., the detection positions. In this way, visualization of the grinding gap is achieved in centerless outer diameter grinding.

[0014] In order to set up an acoustic detection device that can be classified as a solid-state sound sensor, also known as a hydrophone, a reference part can first be machined to a known configuration and geometry as accurately as possible before machining the parts to be manufactured in series, and during this reference machining, vibration signals are generated, which are acquired at detection positions formed together in a row, sensed as reference signals, and stored at least indirectly, in particular in digital form.

[0015] After the reference machining is completed, machining of the parts to be produced in series can begin, and the parts to be machined in the targeted operation, i.e., the serially produced parts, will correspond, at least approximately, to the geometry of the reference part. During the grinding of the reference part, the acquired acoustic signals are already Fourier transformed, thereby obtaining the set frequency. In a corresponding manner, during the production of the serially produced parts, the acquired acoustic signals are also Fourier transformed, thereby determining the actual frequency. The comparison of the actual frequency with the set frequency can finally be graphically depicted in the form of a display matrix. In the display matrix, the horizontal axis represents the row of structure-borne sound sensors along the length of the workpiece cover rail, while the vertical axis represents the deviation between the set frequency and the actual frequency for each structure-borne sound sensor.

[0016] The structure-borne sound sensors can be mounted directly on the workpiece cover rail. In this case, five or more structure-borne sound sensors are arranged in a single row. Instead of multiple structure-borne sound sensors, other methods for sensing vibration signals, such as laser-assisted methods, can be used. Regardless of the exact location and type of structure-borne sound sensors, a signal processing unit for frequency determination, i.e., performing a Fourier transform, can be connected to the sensor system, and each structure-borne sound sensor can be assigned a separate signal processing unit. Similarly, a common signal processing unit can be provided for all structure-borne sound sensors or other vibration sensor systems.

[0017] A data processing unit, which can be realized either as a separate unit or as an integral component of the signal processing unit, is suitable for carrying out the comparison between the actual frequency determined in the targeted operation on the one hand and the predetermined set frequency on the other hand.

[0018] The information obtained using the data processing unit and to be output can be displayed on a display unit, which may have, for example, several display columns, each assigned to a structure-borne sound sensor. In each display column, for example, a central display point signals a perfect match between the set frequency and the actual frequency. The display moves upward if the set frequency is exceeded and downward if the set frequency is exceeded. In this case, only the frequency at which the structure-borne sound signal is greatest is considered. In an improved embodiment, more complex set and actual signals can also be compared. In this case, the respective signals are presented in the form of signal patterns, and the set and actual patterns are compared, in particular using artificial intelligence. Even in the case of complex signal evaluation, the degree of deviation between the set and actual signals can be graphically displayed in a clear manner.

[0019] For calibration purposes, each individual structure-borne sound sensor can be assigned a separate setting element. The setting elements are provided to determine the display position of the set frequency and may each be located at an extension of the corresponding display row. Overall, the setting elements are arranged in a row that reflects the row of structure-borne sound sensors provided on the grinding machine.

[0020] The assignment of setting elements, for example in the form of rotary knobs or operating fields on a touch panel surface, to the individual structure-borne sound sensors is self-evident by arranging the respective setting elements directly below or above the display row representing the structure-borne sound sensor.

[0021] In the following, an embodiment of the invention will be explained in more detail with reference to the drawings, in which a part of the drawing is shown in outline form. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a simplified diagram of a grinding machine for centerless grinding. [Figure 2] FIG. 1 is a front view of components of a grinding machine. [Figure 3] FIG. 1 is a diagram of an ideal structure-borne sound signal acquired using a sensor on a grinding machine. [Figure 4] FIG. 4 is a diagram of the Fourier transform of the signal according to FIG. [Figure 5] FIG. 10 is a frequency spectrum diagram of an actual signal acquired by an acoustic sensor of a grinding machine. [Figure 6] FIG. 10 is a diagram of a comparison between the set frequency and the actual frequency measured at various positions on the grinding machine. DETAILED DESCRIPTION OF THE INVENTION

[0023] The grinding machine, generally designated 1, comprises, in a basic concept known per se, a grinding disc 2 and an adjusting disc 3, between which a grinding gap 4 is formed. A workpiece 5 is ground in the centerless throughfeed method and, during grinding, is positioned on a workpiece support assembly generally designated 6. The workpiece support assembly includes a height-adjustable bearing rail 7 and a swiveling guide clamp 8. The height adjustment mechanism for the bearing rail 7 is designated 13, and the swiveling mechanism for the guide clamp 8 is designated 11. Furthermore, there is a workpiece cover rail 9, which is placed on top of the workpiece 5.

[0024] The grinding machine 1 can furthermore be equipped with an evaluation device 10, which is designed to monitor the grinding process by means of structure-borne sound measurements. The evaluation device 10 works together with a number of structure-borne sound sensors 14, eight in the illustrated case, which are located on the workpiece cover rail 9. The structure-borne sound sensors 14 form eight detection positions 15, which are evenly distributed over the length of the workpiece cover rail 9. Overall, this forms an array 16 of detection positions 15 which extends in the longitudinal direction of the grinding machine 1, i.e. in the feed direction of the workpiece 5, and thus in the axial direction of the rotation axes of the grinding disc 2 and the adjusting disc 3.

[0025] In addition to the structure-borne sound sensors 14, the evaluation device 10 includes a signal processing unit 17, the wiring of the structure-borne sound sensors 14 to the signal processing unit 17 and further wiring inside the evaluation device 10 being designated with 18. In the illustrated embodiment, a separate signal processing unit 17 is assigned to each structure-borne sound sensor 14, and all signal processing units 17 are connected to a data processing unit 19. Wireless signal transmission, in particular wireless transmission of digital signals, is also possible inside the evaluation device 10. In this case, the structure-borne sound signals K S acquired by the structure-borne sound sensors 14 are digitized using the signal processing unit 17. In FIG. 3, an ideal structure-borne sound signal K S i in the shape of a sine curve can be seen. In general, the structure-borne sound signal is designated K S . The amplitude of the structure-borne sound signals K S , K S i is designated with A.

[0026] The data processing unit 19 generates a corresponding signal frequency spectrum using a Fourier transform from the structure-borne sound signal KS provided by the structure-borne sound signal sensor 14. In Figure 4, the Fourier transformed structure-borne sound signal KSFi can be seen, which corresponds to the signal shape according to Figure 3.

[0027] In reality, each structure-borne sound signal KS contains signal components of different frequencies. A possible actual structure-borne sound signal KSFr, compared to the ideal scenario according to FIGS. 3 and 4, is illustrated in FIG. 5. Optionally, the structure-borne sound signal KSFr is subjected to filtering, in particular low-pass filtering, in the data processing unit 19. For further data processing, the structure-borne sound signals KSFr acquired at a total of eight detection positions 15 are assigned the following frequencies F1, F2, F3, F4, F5, F6, F7, and F8, respectively. In this case, F1 refers to the first detection position 15, F2 refers to the next adjacent detection position 15, and so on. The different frequencies F1, F2, ... F8 may differ significantly from one another during operation of the grinding machine 1.

[0028] To calibrate the evaluation device 10, the grinding machine 1 can be first operated on a test basis with a geometrically nearly ideal workpiece 5. During the calibration run, a set frequency FS, shown by the dotted line in FIG. 6, is determined. The set frequency FS lies within the frequency range FB, but does not have to be the same for all detection positions 15. After the calibration run is completed, the grinding machine 1 is operated with the workpieces 5 that will be processed in series production, i.e., that will be ground rotationally symmetrically around their outer diameters. The actual frequencies F1, F2, F3, F4, F5, F6, F7, F8 determined in this case are compared with the set frequency FS, as visualized in FIG. 6, where SQ stands for signal quality, which in the simplest case may assume only the values ​​0 and 1.

[0029] The results of the comparison performed using the data processing unit 19 are displayed on a display unit 20, which is typically located on or near the grinding machine 1. In this case, eight display columns 21, 22, 23, 24, 25, 26, 27, 28 are displayed on the display unit 20, representing the individual detection positions 15. Each display column 21, 22, ... 28 indicates whether the set frequency FS is maintained, exceeded, or fallen below the assigned detection position 15. A display field 29 crosses the display matrix 33 formed by the columns 21, 22, ... 28 as a whole in the form of a horizontal line that can be interpreted as a reference line and indicates that the frequency is maintained within the permissible frequency range FB. On the other hand, if frequencies F1, F2, ... F8 higher than the assigned set frequency FS are measured, a display field 30 located above the display field 29 is used for the graphical display. In the opposite case, that is, when the frequency is lower than the set frequency FS, the graphic signal is output to the display field 31 located below the display field 29.

[0030] The set frequency FS does not have to be known at the start of the evaluation device 10. Rather, it is sufficient to know that a pure structure-borne sound signal KS is measured with an intact grinding machine 1 during the machining of a workpiece 5 used as a reference part. The frequency of this pure structure-borne sound signal constitutes the set frequency FS, which is set at the height of the display field 29, i.e. at the center height, by means of the setting element 32 located below the columns 21-28.

[0031] If the structure-borne sound signal KSFr leaves the display field 29 during continuous operation, this can be interpreted as a deviation from the intended operation. The cause of such a deviation can be, for example, the nature of the grinding disc 2 and / or the workpiece 5. In either case, the columns of the display 21, 22, ... 28 correspond to the columns of the structure-borne sound sensors 14, so that the evaluation device 10 not only signals the occurrence of a deviation from the intended operation, but also the localization of the detected fault. In a simplified manner, the display matrix 33 visualizes the grinding gap 4 being produced by the grinding machine 1 during centerless peripheral grinding in the currently running operation. In this case, not only can the zero-point state of the displayed curve, which in an ideal case extends only across the display field 29 and indicates the intended shape of the grinding gap 4, be calibrated, but the sensitivity of the display can also be optionally set. [Explanation of symbols]

[0032] 1 grinding machine 2 grinding discs 3 Adjustment discs 4 Grinding gap 5 Workpiece 6 Workpiece Support Assembly 7 Bearing rail 8 Guide Clamp 9 Workpiece cover rail 10 Evaluation equipment 11 Swivel mechanism 12 Sensor Array 13 Height adjustment mechanism 14 Solid-state sound sensor 15 Detection position 16 Detection position column 17 Signal Processing Unit 18 Wiring 19 Data Processing Unit 20 Display device 21 First Display Column 22 Second Display Column 23 Third Display Column 24 Fourth Display Column 25 5th display column 26 6th Display Column 27 7th Display Column 28 8th Display Column 29 Display field: Match with set signal 30 Display field: Displacement above set signal 31 Display field: Displacement below set signal 32 Configuration Elements 33 Display Matrix A amplitude f frequency F1…F8 Actual measured frequencies FB frequency range FS setting frequency KS solid sound signal KSi ideal solid-state sound signal KSF Structure-borne Sound Signal (Frequency Domain) KSFi Ideal Structure-Borne Sound Signal (Frequency Domain) KSFr Actual structure-borne sound signal (frequency domain) SF signal strength SQ Signal Quality (binary) t time

Claims

1. 1. A grinding machine (1) for centerless through-feed grinding, comprising a grinding disc (2) and an adjusting disc (3), a grinding gap (4) formed between the grinding disc (2) and the adjusting disc (3), a workpiece support assembly (6) located below the grinding gap (4), and a workpiece cover rail (9), wherein a plurality of acoustic detection devices (14) for sensing acoustic signals are distributed over the length of the workpiece cover rail (9) and are connected to a display device (20), the display device (20) being configured to display information obtained by each of the acoustic detection devices (14) in an array, the array reflecting the array of the acoustic detection devices (14).

2. 2. Grinding machine (1) according to claim 1, characterized in that the acoustic detection device (14) is attached to the workpiece cover rail (9).

3. 3. Grinding machine (1) according to claim 1 or 2, characterized in that at least six acoustic detection devices (14) are arranged in a row.

4. 2. Grinding machine (1) according to claim 1, characterized in that the acoustic detection device (14) is connected to at least one signal processing unit (17) provided for frequency determination.

5. 5. Grinding machine (1) according to claim 4, characterized in that it is equipped with a data processing unit (19) for carrying out a comparison between the frequency determined using the acoustic detection device (14) and the signal processing unit (17) on the one hand and a set frequency on the other hand.

6. 6. The grinding machine (1) according to claim 5, characterized in that the display device (20) connected to the data processing unit (19) is provided for graphically displaying the undershooting and overshooting of the set frequency in individual display columns (21, 22, ... 28), each display column (21, 22, ... 28) being assigned to one of the acoustic detection devices (14).

7. 7. The grinding machine (1) according to claim 6, characterized in that a setting element (32) is assigned to each individual acoustic detection device (14), is provided for setting the display position of the set frequency, and is located in an extension of the associated display row (21, 22, ... 28), the setting elements (32) being arranged in a row, the row reflecting the row of the acoustic detection devices (14).

8. A method for operating a grinding machine (1) for centerless through-feed grinding, wherein a plurality of workpieces (5) are fed through a grinding gap (4) formed between a grinding disc (2) and an adjusting disc (3), and during grinding, acoustic signals are acquired by an acoustic detection device (14) at a plurality of positions (15) formed together in a row on a workpiece cover rail (9) along the grinding gap (4) and converted into optical signals, and the arrangement of the optical signals is displayed on a display device reproducing the row of the above-mentioned positions (15).

9. 9. The method according to claim 8, wherein, before approving a targeted grinding process, a reference part is machined in the grinding gap (4), and vibration signals acquired at the aligned positions (15) during the machining of the reference part are sensed and at least indirectly stored as reference signals.

10. 10. The method according to claim 9, characterized in that a workpiece (5) is machined after the reference part, the geometry of which corresponds at least approximately to the geometry of the reference part, and during the machining of the workpiece (5), the acoustic signals are Fourier transformed, the results of this Fourier transformation output in the form of actual frequencies are compared with set frequencies also determined by Fourier transformation from the reference signals and graphically depicted as a display matrix (33).

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