JP7484381B2 - Chatter Detection System - Google Patents

Description

The present invention relates to a chatter detection system.

In general, when grinding a workpiece, vibrations may occur due to uncut areas on the ground surface of the workpiece, wear of the grinding wheel, etc., which may cause chatter. If chatter occurs during grinding, it may cause a deterioration in the surface properties of the workpiece, so it is extremely important to detect whether chatter is occurring. For this reason, the techniques disclosed in Patent Documents 1 and 2 have been known.

Patent Document 1 discloses a technique for measuring the vibration of a machine tool in operation using a vibration detector and a frequency analyzer, inputting the obtained measurement data into a data processing means, and comparing it with a preset chatter discrimination criterion to detect chatter. Patent Document 2 discloses a technique for comparing the vibration level at a specific frequency obtained by frequency decomposition with a threshold value, and determining that the grinding wheel has deteriorated if the vibration level is greater than the threshold value.

Japanese Patent Application Laid-Open No. 8-174379 JP 2008-290203 A

Chattering that occurs in finish machining can occur suddenly, for example, when unevenness, i.e., uncut areas, are formed by rough grinding and the subsequent finish machining is unable to remove the uncut areas. When chattering occurs in this way, for example, during offline inspection, the finished workpiece will be defective. Therefore, in order to suppress chattering (including chattering that occurs suddenly), it is necessary to remove the uncut areas by finish machining, and in order to accurately detect chattering, it is important to base it on whether or not the uncut areas created by rough grinding have been removed.

The present invention aims to provide a chatter detection system that can accurately detect the occurrence of chatter during grinding.

The chatter detection system includes a grinding device in which a grinding wheel grinds a workpiece through a plurality of grinding steps controlled by a control device, a detector that detects status data related to the grinding resistance of the grinding wheel that is observable during the grinding step and outputs the detected status data, and a chatter detection device that detects chatter that occurs during the grinding step. The chatter detection system includes a frequency analysis unit that divides status data having frequency characteristics obtained from the detector into a plurality of frequency components by frequency analysis for each of the rough grinding step in the grinding step and the finish processing step in the finish processing step, an amplitude extraction unit that extracts, from the plurality of frequency components divided by the frequency analysis, an amplitude of the grinding wheel rotation frequency corresponding to the rotation speed of the grinding wheel of the grinding device for each of the rough grinding step and the finish processing, and a chatter judgment unit that judges that chatter will occur in the subsequent grinding step if the magnitude of the amplitude of the grinding wheel rotation frequency for the finish processing extracted is less than a predetermined judgment value, because the unevenness formed on the ground surface of the workpiece by the rough grinding step has not been removed by the finish processing .

According to this, during grinding of a workpiece, status data related to grinding resistance is detected by a detector for each of rough grinding and finish grinding, and the occurrence of chatter during finish grinding can be determined using the amplitude of the grinding wheel rotation frequency during finish grinding extracted from the status data having the detected frequency characteristics. The amplitude of the grinding wheel rotation frequency indicates an increase or decrease in grinding resistance, i.e., whether or not the grinding surface of the workpiece is being ground by the grinding wheel.

Therefore, based on the amplitude of the grinding wheel rotation frequency during finishing, it is possible to accurately determine whether or not the remaining cutting material during rough grinding has been removed during finishing. This makes it possible to accurately detect the occurrence of chatter (including chatter that occurs suddenly) caused by the remaining cutting material during grinding, particularly during finishing, and ultimately reduces the number of workpieces that are defectively machined.

FIG. 1 is a diagram showing a configuration of a chatter detection system. FIG. 2 is a diagram illustrating an example of a grinding device. FIG. 2 is a diagram showing a functional block configuration of a chatter detection system. FIG. 4 is a diagram for explaining a change in grinding resistance. FIG. 11 is a diagram illustrating an example of state data having frequency characteristics. 6 is a diagram for explaining a feature amount extracted from the state data of FIG. 5 . FIG. FIG. 13 is a diagram for explaining uncut portions generated in rough grinding. 8 is a diagram for explaining a case where the uncut portion in FIG. 7 is removed in finish processing. FIG. 13 is a flowchart showing a sudden chatter detection program. 13 is a flowchart showing a grindstone condition determination routine (subroutine). 10 is a flowchart showing a sudden chatter detection program according to a first modified example.

(1. Grinding Machine to Which Chatter Detection System is Applied)
The chatter detection system detects chatter that occurs in a grinding machine that performs grinding through multiple grinding processes. In particular, the chatter detection system is effective in detecting chatter that occurs suddenly during grinding. Grinding machines of various configurations, such as cylindrical grinding machines, cam grinding machines, and surface grinding machines, can be used. The grinding processes performed by the grinding machine include a rough grinding process and a fine grinding process, a fine grinding process, and a spark-out process as finishing processes.

(2. Overview of the Configuration of Chatter Detection System 1)
An outline of the configuration of the chatter detection system 1 will be described with reference to Fig. 1. The chatter detection system 1 includes at least one grinding machine 10 and one computing device 20. The chatter detection system 1 may target one grinding machine 10, or may target multiple grinding machines 10 as shown in Fig. 1. In this example, the chatter detection system 1 includes multiple grinding machines 10.

The grinding device 10 is equipped with at least a detector 13 that detects observable state data during grinding of the workpiece W. The computing device 20 detects the occurrence of sudden chatter based on the state data detected by the detector 13, and determines the state of the grinding wheel T that may cause unevenness in the grinding surface that causes chatter.

(3. Details of the Configuration of Chatter Detection System 1)
The configuration of the chatter detection system 1 will be described in more detail with reference to Fig. 1. The chatter detection system 1 includes a plurality of grinding machines 10 and a plurality of computing devices 20 provided in a one-to-one correspondence with each of the grinding machines 10. In this example, the computing devices 20 are configured as chatter detection devices 20 that detect the sudden occurrence of chatter during grinding processing.

Each grinding device 10 mainly comprises a grinding machine 11 that uses a grinding wheel T to grind the workpiece W, a control device 12 that controls the grinding machine 11, a detector 13, and an interface 14. The control device 12 includes a CNC device and a PLC device, and controls the drive device of the grinding machine 11. The interface 14 is a device that enables communication between the grinding machine 11, the control device 12, the detector 13, and the outside. The outside includes a server that stores the surface roughness of the ground surface of the workpiece W ground by each grinding device 10 and condition data detected by the detector 13.

The detector 13 detects status data related to the grinding resistance (in other words, the remaining part) of the grinding wheel T that can be observed on the grinding machine 11 during grinding of the workpiece W. Specifically, the detector 13 detects the grinding resistance (processing load) and the driving load of the driving device as status data. The detector 13 is, for example, a displacement sensor that detects the relative position (or distance) data between the grinding wheel T and the workpiece W, a current sensor that detects the driving current data of the motor serving as the driving device, a torque sensor that detects the torque data of the motor, etc. In other words, the status data detected by the detector 13 is, for example, position (displacement) data, driving current data, torque data, vibration data (acceleration data), etc. that change depending on the grinding resistance (remaining part).

The chatter detection device 20 is configured with a processor 21, a storage device 22, an interface 23, etc. The chatter detection device 20 is disposed integrally in a position close to each grinding device 10, and functions as a so-called edge computer. It is also possible to provide the chatter detection device 20 separately from the grinding device 10.

The chatter detection device 20 detects chatter that occurs during grinding of the workpiece W by the grinding device 10, based on the status data detected by the detector 13 during grinding of the workpiece W. If the chatter detection device 20 detects the occurrence of chatter, it changes the content of the finishing process to remove unevenness, i.e., uncut areas, that exist on the ground surface of the workpiece W during the finishing process.

The chatter detection system 1 includes a plurality of individual display devices 30. However, the chatter detection system 1 may be configured without including the individual display devices 30. The individual display devices 30 are arranged corresponding to each of the grinding devices 10.

(4. Examples of Grinding Machine 11)
2, a wheelhead traverse type cylindrical grinding machine 40 is taken as an example of the grinding machine 11 in this embodiment. Note that the grinding machine 11 may also be of a table traverse type.

The cylindrical grinding machine 40 is a machine for grinding a workpiece W. The cylindrical grinding machine 40 mainly comprises a bed 41, a headstock 42, a tailstock 43, a traverse base 44, a grinding wheel head 45, a grinding wheel 46 (grinding wheel T), a sizing device 47, a grinding wheel adjustment device 48, and a coolant device 49.

The bed 41 is fixed on the installation surface. The headstock 42 is provided on the upper surface of the bed 41, on the front side in the X-axis direction (lower side in FIG. 2) and on one end side in the Z-axis direction (left side in FIG. 2). The headstock 42 supports the workpiece W so that it can rotate around the Z-axis. The workpiece W is rotated by driving a motor 42a provided on the headstock 42. The tailstock 43 is provided on the upper surface of the bed 41 in a position facing the headstock 42 in the Z-axis direction, that is, on the front side in the X-axis direction (lower side in FIG. 2) and on the other end side in the Z-axis direction (right side in FIG. 2). As a result, the workpiece W is rotatably supported at both ends by the headstock 42 and the tailstock 43.

The traverse base 44 is provided on the upper surface of the bed 41 so as to be movable in the Z-axis direction. The traverse base 44 is moved by the drive of a motor 44a provided on the bed 41. The grinding wheel head 45 is provided on the upper surface of the traverse base 44 so as to be movable in the X-axis direction. The grinding wheel head 45 is moved by the drive of a motor 45a provided on the traverse base 44. The grinding wheel 46 is rotatably supported on the grinding wheel head 45. The grinding wheel 46 rotates by the drive of a motor 46a provided on the grinding wheel head 45. The grinding wheel 46 is composed of multiple abrasive grains fixed with a bond material.

The sizing device 47 measures the dimensions (diameter) of the workpiece W. The grinding wheel correction device 48 corrects the shape of the grinding wheel 46. In other words, the grinding wheel correction device 48 is a device that performs truing of the grinding wheel 46. The grinding wheel correction device 48 may also be a device that performs dressing of the grinding wheel 46 in addition to or instead of truing.

Truing here refers to a reshaping process, which involves shaping the grinding wheel 46 to match the shape of the workpiece W when the grinding wheel 46 has worn down due to grinding, and removing runout of the grinding wheel 46 caused by uneven wear. Dressing refers to a dressing process, which involves adjusting the amount of protrusion of the abrasive grains and creating the cutting edges of the abrasive grains. Dressing is a process for correcting dullness, clogging, and overflow, and is usually performed after truing.

The coolant device 49 supplies coolant to the grinding point of the workpiece W by the grinding wheel 46. The coolant device 49 cools the collected coolant to a predetermined temperature and supplies it again to the grinding point.

The control device 12 provided on the cylindrical grinding machine 40 controls each drive device based on an NC program generated based on operation command data such as the shape of the workpiece W, the processing conditions, the shape of the grinding wheel 46, and coolant supply timing information. That is, the control device 12 inputs the operation command data and generates an NC program based on the operation command data.

The control device 12 then performs grinding of the workpiece W by controlling the motors 42a, 44a, 45a, 46a and the coolant device 49 based on the NC program. The control device 12 then performs grinding until the workpiece W has a finished shape based on the diameter of the workpiece W measured by the sizing device 47. The control device 12 also performs correction (truing and dressing) of the grinding wheel 46 by controlling the motors 42a, 44a, 45a, 46a and the grinding wheel correction device 48 at the timing for correcting the grinding wheel 46.

The control device 12 also outputs the status data outputted in a chronological order (continuously) from the detector 13 to the chatter detection device 20. The control device 12 also links and adds to the status data process information identifying the current grinding process, i.e., the rough grinding process, fine grinding process, fine grinding process, and spark-out process, which is outputted in a chronological order based on the NC program generated according to the operation command data.

Here, in the grinding process, the grindstone feed speed is greatest in the rough grinding process, and in the finish processing for adjusting the surface shape of the workpiece W, it decreases in the order of the fine grinding process, the fine grinding process, and the spark-out process. Also, in the grinding process, the cutting depth is greatest in the rough grinding process, and decreases in the order of the fine grinding process, the fine grinding process, and the spark-out process. In the spark-out process, the cutting depth is set to zero.

The control device 12 of the cylindrical grinding machine 40 includes a counter. The counter counts the number of workpieces W ground by the cylindrical grinding machine 40. The counter of the control device 12 can count the number of workpieces W that have been ground since the grinding wheel correction device 48 trued or dressed the grinding wheel 46. The counter can be provided in the detector 13 itself, or in a separate external device, in addition to the control device 12.

(5. Functional Block Configuration of Chatter Detection System 1)
The functional blocks of the chatter detection system 1 will be described with reference to Fig. 3. The chatter detection system 1 includes a control device 12, a detector 13, a chatter detection device 20, and a display device 30.

As described above, in this example, the detector 13 outputs drive current data that has a high correlation with the grinding resistance as status data related to the grinding resistance observable in the cylindrical grinding machine 40 during grinding of the workpiece W. The drive current data is detected and output, for example, for each grinding process, i.e., the rough grinding process, the fine grinding process, the fine grinding process, and the spark-out process, from the start to the end of processing of one workpiece W. Here, the drive current data is detected when the cylindrical grinding machine 40 is performing grinding, and is status data that has multiple frequency components associated with the operation of the cylindrical grinding machine 40, i.e., has frequency characteristics.

The chatter detection device 20 performs frequency analysis on the state data having frequency characteristics acquired from the detector 13 in the corresponding cylindrical grinding machine 40, and detects the occurrence of chatter based on the magnitude of the amplitude of a specific frequency as a feature value among multiple frequency components obtained from the analysis result. As shown in FIG. 3, the chatter detection device 20 includes a state data acquisition unit 51, a grinding process determination unit 52, a feature value extraction unit 53, a chatter determination unit 54, a period change unit 55, a spark out execution control unit 56, and an output unit 57.

The status data acquisition unit 51 acquires status data detected by the detector 13 in a time series manner via the control device 12 during machining of the workpiece W. In this example, the status data acquisition unit 51 acquires, as status data, drive current data that is highly correlated with the grinding resistance that changes depending on the amount of remaining material.

Here, in the finish process, when the grinding wheel 46 removes the remaining cutting residue (protrusions) present on the ground surface of the workpiece W, the grinding resistance increases when the grinding wheel 46 comes into contact with the remaining cutting residue (protrusions). In other words, in order for the grinding wheel 46 to remove the remaining cutting residue (protrusions), the grinding wheel 46 needs to rotate against the grinding resistance, and as a result, the drive current increases according to the grinding resistance.

That is, as shown by the thick dashed line in FIG. 4, for example, when the rotational speed ratio of the grinding wheel 46 and the workpiece W is an integer multiple, the remaining cut portions (protrusions) are not removed, so there is no change in grinding resistance, i.e., drive current, over time. On the other hand, as shown by the thick solid line in FIG. 4, for example, when the rotational speed ratio of the grinding wheel 46 and the workpiece W is not an integer multiple, there is a change in grinding resistance, i.e., drive current, over time, because the remaining cut portions (protrusions) are removed. Therefore, since there is a strong correlation between the drive current and the grinding resistance, it is possible to observe changes in the grinding resistance, which are difficult to observe, by using drive current data that can be easily observed as state data.

The grinding process determination unit 52 determines the current grinding process based on process information linked to the status data (drive current data) that the status data acquisition unit 51 acquires chronologically (continuously) from the control device 12. The grinding process determination unit 52 determines whether the grinding process is a rough grinding process or a finishing process, i.e., a fine grinding process, a fine grinding process, or a spark process.

The feature extraction unit 53 extracts features related to grinding resistance from the status data acquired by the status data acquisition unit 51. As shown in FIG. 3, the feature extraction unit 53 includes a frequency analysis unit 53a and an amplitude extraction unit 53b.

The frequency analysis unit 53a performs frequency analysis, specifically, FFT (Fast Fourier Transform), on the drive current data having frequency characteristics as shown in FIG. 5. Then, the frequency analysis unit 53a performs frequency analysis (FFT) on the drive current data to extract the amplitudes of the divided multiple frequency components as shown in FIG. 6.

As shown in FIG. 6, the amplitude extraction unit 53b extracts the amplitude of a specific frequency as a feature from the amplitudes of the multiple frequency components divided and extracted by the frequency analysis unit 53a. As described above, the unevenness associated with the uncut portion that occurs on the ground surface of the workpiece W after the rough grinding process is mainly caused by the rotation of the grinding wheel 46 of the cylindrical grinding machine 40. In other words, the uncut portion that exists on the ground surface is formed in response to the rotation speed of the grinding wheel 46.

Therefore, in the finishing process, the drive current data required to remove the remaining cutting residue has a rotation frequency component of the grinding wheel 46. For this reason, the amplitude extraction unit 53b extracts, as a feature, the amplitude A for the grinding wheel rotation frequency F corresponding to the rotation speed of the grinding wheel 46 as a specific frequency from among the multiple frequency components of the drive current data, as shown in FIG. 6.

Returning to FIG. 3, the chatter judgment unit 54 compares the magnitude of the amplitude A extracted by the amplitude extraction unit 53b of the feature extraction unit 53 with the magnitude of a preset judgment value D. If the magnitude of the amplitude A is equal to or greater than the judgment value D, the chatter judgment unit 54 judges that the remaining cutting portion has been ground and therefore chatter will not occur unexpectedly. On the other hand, if the magnitude of the amplitude A is less than the judgment value D, the chatter judgment unit 54 judges that the remaining cutting portion has not been ground and therefore chatter will occur unexpectedly.

The period change unit 55 changes the rotation period so that the rotation speed ratio between the grinding wheel 46 of the cylindrical grinding machine 40 and the workpiece W during finishing (fine grinding, fine grinding, and spark-out) is not an integer multiple. This is explained in detail below.

When grinding the workpiece W, rough grinding is generally performed in the rough grinding process. In this case, in the cylindrical grinding machine 40, the control device 12 sets the feed speed and cutting depth of the rotating grinding wheel 46 to a large value, and grinds the grinding surface of the workpiece W.

For this reason, the surface shape of the grinding wheel 46 is transferred with each rotation cycle of the grinding wheel 46, i.e., with each rotation, and appears on the ground surface of the workpiece W. For example, if there are abrasive grains that protrude significantly on the surface of the grinding wheel 46, the portions of the ground surface of the workpiece W that come into contact with the abrasive grains are largely removed to form recesses. Alternatively, if there are recessed abrasive grains on the surface of the grinding wheel 46, the portions of the ground surface of the workpiece W that come into contact with the abrasive grains are left uncut to form protruding portions.

In this case, as shown in FIG. 7, for example, the convex portions, i.e., the remaining cut portions, formed on the workpiece W are formed at equal intervals in the rotational direction of the workpiece W each time the grinding wheel 46 rotates once, and the intervals between the convex portions in the circumferential direction of the workpiece W correspond to the rotation period (number of rotations) of the grinding wheel 46. Incidentally, the remaining cut portions (convex portions) generated in this manner during rough grinding are usually ground and removed through subsequent finishing processes (fine grinding, fine grinding, and spark-out processing).

However, in finishing processes (fine grinding, fine grinding, and spark-out processing), if the rotational speed ratio of the rotating grinding wheel 46 and the workpiece W is an integer multiple, the trajectory of the grinding wheel 46 on the grinding surface in the finishing process and the rough grinding process will be the same. As a result, in the finishing process, the remaining parts (protruding parts) on the grinding surface cannot be ground.

Therefore, when removing the uncut portion (convex portion) in the finishing process, the period change unit 55 shifts the phase of the uncut portion (convex portion) and the concave portion formed in the rough grinding process (i.e., the rotation period of the grinding wheel 46) by, for example, half a period (180 degrees). In this case, the period change unit 55 changes the rotation speed ratio of the grinding wheel 46 and the workpiece W so that it is not an integer multiple. As a result, as shown in FIG. 8, the grinding wheel 46 can contact the uncut portion (convex portion) in the finishing process and the uncut portion (convex portion) can be removed. As a result, it is possible to suppress the occurrence of sudden chatter in the finishing process (spark-out processing).

In the case of the grinding device 10, i.e., the cylindrical grinding machine 40, of this example, the rotational speed ratio of the grinding wheel 46 and the workpiece W is usually set so that it does not become an integer multiple, but there are cases where the rotational speed ratio of the grinding wheel 46 and the workpiece W accidentally becomes an integer multiple over time. Therefore, in such cases, the above-mentioned control is effective.

On the other hand, when the grinding device 10 is a cam grinding machine, the workpiece W has a complex shape. In this case, the rotational speed ratio of the grinding wheel T and the workpiece W may accidentally become an integer multiple due to a sudden acceleration or deceleration of the rotational speed of the workpiece W. Therefore, by changing the rotation period of at least one of the grinding wheel T and the workpiece W, preferably the workpiece W, and shifting the rotational speed ratio from an integer multiple, it is possible to remove the remaining cutting portions.

When the chatter determination unit 54 determines that the amplitude A is less than the determination value D, i.e., that chatter has occurred, the spark-out execution control unit 56 changes the content of the spark-out processing and executes it. In other words, since the situation in which chatter occurs is highly likely to be caused by unevenness of the remaining cutting material still remaining on the ground surface, it is necessary to perform spark-out processing with a changed content from the spark-out processing normally performed, remove the unevenness of the ground surface, and smooth out the surface properties.

Therefore, when the spark-out execution control unit 56 determines that chatter has occurred, i.e., that the surface quality of the ground surface is not good, it changes and executes the spark-out processing by extending the time for which the spark-out processing is performed or by increasing the number of times the spark-out processing is performed. Here, the spark-out execution control unit 56 outputs to the control device 12 a request command for performing normal spark-out processing and a change request command for performing modified spark-out processing.

The output unit 57 outputs the request command or change request command from the spark out execution control unit 56 to the control device 12, and also outputs the wear state of the grinding wheel 46 and the need for replacement to the display device 30 based on the amplitude A at the grinding wheel rotation frequency F in the rough grinding process, as described below. As a result, the control device 12 executes normal or changed spark out processing on the cylindrical grinding machine 40 by inputting the output request command or change request command. Meanwhile, the display device 30 notifies the operator that truing or dressing of the grinding wheel 46 of the cylindrical grinding machine 40 is required.

(6. Sudden chatter detection program (grinding method))
Next, the grinding method of this embodiment will be described with reference to the flowcharts of Figures 9 and 10. For example, when grinding is continuously performed using a trued grinding wheel 46, if the number of workpieces W machined is small, the condition of the grinding wheel 46 is good and there is little uncut material, but as the number of workpieces W machined increases, the condition of the grinding wheel 46 tends to deteriorate and the amount of uncut material tends to increase. For this reason, the chatter detection device 20 (more specifically, the processor 21) starts executing the sudden chatter detection program in step S10.

In step S11, the chatter detection device 20 determines whether the value of the variable Q, which indicates the state of the grinding wheel 46, is "0." In other words, if the value of the variable Q is "1," which indicates that the state of the grinding wheel 46 is good, by executing the step process (grinding wheel state determination routine) in step S19 described below, the chatter detection device 20 determines "No" and ends the execution of the sudden chatter detection program in step S20 without detecting sudden chatter.

On the other hand, if the value of variable Q is "0" by executing the step process (grinding wheel condition determination routine) of step S19 described below, which indicates that the condition of the grinding wheel 46 has deteriorated, it is necessary to detect sudden chatter. Therefore, the chatter detection device 20 judges "Yes" and executes the step process of step S12. In this example, the value of variable Q is set to "0" as an initial value.

In step S12, the status data acquisition unit 51 of the chatter detection device 20 acquires drive current data, which is status data related to the grinding resistance detected by the detector 13, via the control device 12. Then, when the chatter detection device 20 acquires the drive current data, it executes the step processing of step S13.

In step S13, the grinding process determination unit 52 of the chatter detection device 20 determines whether the acquired drive current data is drive current data during finish processing in the finishing process based on the process information linked to the drive current data acquired in step S12. That is, the grinding process determination unit 52 determines "Yes" if the drive current data acquired by the status data acquisition unit 51 is detected during finish processing (fine grinding, fine grinding, and spark-out processing). Then, the chatter detection device 20 executes the step processing of step S14.

On the other hand, if the acquired drive current data is detected during a process other than the finish process, i.e., during rough grinding, the grinding process determination unit 52 determines "No." The chatter detection device 20 then executes a grindstone condition determination routine in step S19. The grindstone condition determination routine will be described in detail later.

In step S14, the feature extraction unit 53 of the chatter detection device 20 extracts the amplitude during the finishing process by frequency analyzing the drive current data during the finishing process. That is, the frequency analysis unit 53a performs frequency analysis (FFT) on the drive current data during the finishing process, i.e., during the finishing process, acquired from the grinding process judgment unit 52. As a result, the frequency analysis unit 53a extracts the amplitude for multiple frequency components contained in the drive current data (see FIG. 6).

Then, when the amplitudes of multiple frequency components are extracted by the frequency analysis unit 53a, the amplitude extraction unit 53b extracts the amplitude A2 during finish processing at the specific frequency, the grindstone rotation frequency F (see FIG. 6). In this way, when the amplitude A2 during finish processing at the grindstone rotation frequency F is extracted, the chatter detection device 20 executes the step processing of step S15.

In step S15, the chatter determination unit 54 of the chatter detection device 20 determines whether the magnitude of the amplitude A2 of the grindstone rotation frequency F during finish processing extracted in step S14 is equal to or greater than a preset determination value D2. Here, the determination value D2 is set based on a value obtained experimentally or empirically when removing the remaining cutting residue generated during rough grinding processing in finish processing, particularly fine grinding processing and spark-out processing. In this example, the chatter determination unit 54 illustrates a case in which the amplitude A2 of the grindstone rotation frequency F during fine grinding processing in finish processing is compared with the determination value D2.

As described above, the magnitude of the amplitude A2 is the amplitude at the grinding wheel rotation frequency F among the multiple frequency components contained in the drive current data, in other words, it represents the magnitude of the grinding resistance acting on the rotating grinding wheel 46. Therefore, when the magnitude of the amplitude A2 is equal to or greater than the judgment value D2, it corresponds to the fact that the residual cutting material from the rough grinding process has been removed by the fine grinding process. On the other hand, when the magnitude of the amplitude A2 is less than the judgment value D2, it corresponds to the fact that the residual cutting material from the rough grinding process has not been removed by the fine grinding process. And, if the residual cutting material from the rough grinding process cannot be removed before the fine grinding process, for example, there is a possibility that sudden chatter will occur due to the residual cutting material during spark-out processing.

Therefore, if the magnitude of the extracted amplitude A2 of the fine grinding is equal to or greater than the judgment value D2, the chatter judgment unit 54 judges "Yes" in step S15. That is, in this case, the residual cutting material from the rough grinding has been removed by the finishing process up to the fine grinding, and sudden chatter does not occur (is unlikely to occur), so the chatter detection device 20 executes the step process of step S16.

In step S16, the spark out execution control unit 56 of the chatter detection device 20 performs normal spark out processing (hereinafter referred to as "normal spark out processing") with preset contents on the ground surface of the workpiece W. That is, in this case, since the remaining cutting residue on the ground surface has already been removed, the spark out execution control unit 56 performs normal spark out processing for a preset processing time. Therefore, the spark out execution control unit 56 outputs a request command to the control device 12 via the output unit 57, requesting that normal spark out processing be performed.

After performing normal spark-out processing in step S16, the chatter detection device 20 ends execution of the chatter detection program in step S20. Then, when the next workpiece W is ground in the continuous processing, the chatter detection device 20 starts execution of the chatter detection program again in step S10.

On the other hand, if the amplitude A2 of the fine grinding process is less than the judgment value D2 in step S15, the chatter judgment unit 54 judges it as "No." In other words, in this case, there is a possibility that the residual cutting material from the rough grinding process has not been removed by the finishing process up to the fine grinding process, and sudden chatter occurs, so the chatter detection device 20 executes the step process of step S17.

In step S17, the period change unit 55 of the chatter detection device 20 changes the rotation period of the grinding wheel 46, for example, by half a period (180 degrees) so that the rotation speed ratio of the grinding wheel 46 and the workpiece W is not an integer multiple. This makes it easier for the grinding wheel 46 to remove the remaining material from the rough grinding process during spark-out processing. Then, when the chatter detection device 20 changes the rotation period of the grinding wheel 46 in step S17 so that the rotation speed ratio of the grinding wheel 46 and the workpiece W is not an integer multiple, it executes the step processing of step S18.

In step S18, the spark-out execution control unit 56 of the chatter detection device 20 performs modified spark-out processing on the ground surface of the workpiece W, which extends the processing time compared to the processing time in normal spark-out processing. That is, in this case, since there is still uncut material on the ground surface, the spark-out execution control unit 56 performs modified spark-out processing that extends the processing time with a rotation period that is half a period different from the rotation period of the grinding wheel 46 in rough grinding, fine grinding, and fine grinding. Therefore, the spark-out execution control unit 56 outputs a change request command to the control device 12 via the output unit 57, requesting that modified spark-out processing be performed. Note that, if the grinding device 10 is a cam grinding machine, modified spark-out processing that extends the processing time in spark-out processing or modified spark-out processing that increases the number of spark-out processing is performed.

After executing the modified spark-out machining in step S18, the chatter detection device 20 ends the execution of the chatter detection program in step S20. Then, when the next workpiece W is ground in the continuous machining, the chatter detection device 20 starts the execution of the chatter detection program again in step S10.

(6-1. Grindstone condition determination routine)
The chatter detection device 20 executes a grinding wheel condition determination routine (subroutine) shown in Fig. 10 in accordance with the "No" determination in step S13 of the sudden chatter detection program described above. When the grinding wheel condition determination routine is executed, the step processing in step S12 in the sudden chatter detection program is executed. As a result, the chatter detection device 20 acquires the grinding resistance of the rough grinding process in the rough grinding step, i.e., the drive current data which is the condition data detected in the rough grinding process.

The chatter detection device 20 starts executing the grinding wheel condition determination routine in step S19, and in step S31, the feature extraction unit 53 extracts the amplitude during the rough grinding process by frequency analyzing the drive current data detected during the rough grinding process. Here, the extraction of the amplitude by frequency analysis of the drive current data can be performed in the same manner as the step processing of step S14 of the sudden chatter detection program described above.

That is, the frequency analysis unit 53a performs frequency analysis (FFT) on the drive current data during the rough grinding process, i.e., during rough grinding, acquired from the grinding process judgment unit 52. As a result, the frequency analysis unit 53a extracts the amplitudes of multiple frequency components contained in the drive current data (see FIG. 6). When the amplitudes of multiple frequency components are extracted by the frequency analysis unit 53a, the amplitude extraction unit 53b extracts the amplitude A1 during rough grinding at the grindstone rotation frequency F, which is a specific frequency, as a feature amount (see FIG. 6). When the amplitude A1 during rough grinding at the grindstone rotation frequency F is extracted, the chatter detection device 20 executes the step processing of step S32.

In step S32, the chatter detection device 20 determines whether the magnitude of the amplitude A1 during rough grinding at the grinding wheel rotation frequency F extracted in step S31 is equal to or greater than a preset judgment value D1. Here, the judgment value D1 is set based on a value obtained experimentally or empirically to determine the deterioration of the condition of the grinding wheel 46.

If the magnitude of the amplitude A1 during rough grinding is equal to or greater than the judgment value D1, the condition of the grinding wheel 46 has deteriorated to the point where it is causing sudden chatter, so the vibration detection device 20 judges "Yes" and executes the step processing of step S34. On the other hand, if the magnitude of the amplitude A1 during rough grinding is less than the judgment value D1, the condition of the grinding wheel 46 is good, so the device judges "No" and executes the step processing of step S33.

In step S33, the chatter detection device 20 changes the value of the variable Q, which is determined in step S11 of the sudden chatter detection program, from the initially set value of "0" to "1." Then, in step S36, the chatter detection device 20 ends the execution of the grinding wheel condition determination routine (subroutine), returns to the sudden chatter detection program, and executes the processing of each step from step S11 onward.

In this case, the value of variable Q is set to "1", and thus the sudden chatter detection program returns a "No" result in step S11. That is, when the value of variable Q is set to "1", the grinding wheel 46 is in good condition, and the sudden chatter detection program is not executed in accordance with the "No" result in step S11 of the sudden chatter detection program. Therefore, the cylindrical grinding machine 40 performs normal grinding.

In step S34, the chatter detection device 20 judges whether the magnitude of the amplitude A1 during rough grinding extracted in step S31 is less than a preset control value K. Here, the control value K is a value that is preset to manage the necessity of truing or dressing the grinding wheel 46, and is set to a value greater than the judgment value D1. If the magnitude of the extracted amplitude A1 is less than the control value K, the chatter detection device 20 judges "Yes" in step S34 because it is necessary to detect sudden chatter. Then, the chatter detection device 20 ends the execution of the grinding wheel state judgment routine (subroutine) in step S36, returns to the sudden chatter detection program, and executes each step process from step S11 onwards.

On the other hand, if the magnitude of the extracted amplitude A1 is equal to or greater than the control value K, the chatter detection device 20 judges it as "No" and executes the step processing of step S35. If the magnitude of the amplitude A1 is equal to or greater than the control value K, the drive current data in the rough grinding process is large, in other words, it corresponds to a state in which the grinding resistance is large. As a result, it is highly likely that the surface quality of the ground surface roughly ground by the grinding wheel 46 will deteriorate, and therefore it can be determined that truing or dressing of the grinding wheel 46 is necessary.

Therefore, in step S35, the chatter detection device 20 outputs information indicating that truing or dressing of the grinding wheel 46 is necessary to the display device 30 via the output unit 57. As a result, the display device 30 notifies, for example, the operator that truing or dressing of the grinding wheel 46 is necessary at an appropriate timing. Therefore, by having the operator perform truing or dressing in accordance with the notification, it is possible to prevent unnecessary truing or dressing from being performed. As a result, it is possible to reduce the cost required for maintenance of the grinding wheel 46, and ultimately the manufacturing cost of the workpiece W.

The chatter detection device 20 ends the execution of the grinding wheel condition determination routine (subroutine) in step S36. The chatter detection device 20 then returns to the sudden chatter detection program and executes each step process from step S11 onwards.

As can be understood from the above description, according to the chatter detection system 1 of this example, during grinding of the workpiece W, the detector 13 detects drive current data as status data related to the grinding resistance. The chatter detection device 20 can then determine the status of the grinding wheel 46 using the feature amount related to the grinding resistance extracted from the drive current data having the continuously detected frequency characteristics, i.e., the amplitude A1 during rough grinding of the grinding wheel rotation frequency F contained in the drive current data. The chatter detection device 20 can also determine the occurrence of chatter during finishing, particularly spark-out processing, using the amplitude A2 during finishing.

The characteristic quantities, amplitude A1 and amplitude A2, represent an increase or decrease in the grinding resistance, i.e., whether or not the grinding surface of the workpiece W is being ground by the grinding wheel 46. Therefore, the chatter detection device 20 can accurately determine whether or not the remaining material from the rough grinding process has been removed in the finish process, particularly based on the amplitude A2 in the finish process. This allows the chatter detection device 20 to accurately detect the occurrence of chatter (including chatter that occurs suddenly) caused by the remaining material during the grinding process, particularly during the finish process, and ultimately reduces the number of workpieces W that are subjected to machining defects.

(7. First Alternative Example)
In the above-described embodiment, the chatter detection device 20 executes the sudden chatter detection program shown in Fig. 9. Incidentally, for example, when grinding is continuously performed using a grinding wheel 46 that has been trued, there is a tendency that there is little uncut material when the number of machined workpieces W is small, and that the more the number of machined workpieces W, the more uncut material tends to be. In this case, for example, when the number of machined workpieces W is small, the grindstone state judgment may be omitted, and it is also possible to change the sudden chatter detection program as shown in Fig. 11.

As shown in FIG. 11, the sudden chatter detection program in the first modified example differs from the sudden chatter detection program of the present example shown in FIG. 9 in that step S21 is added between step S10 and step S11. That is, when the chatter detection device 20 starts execution of the sudden chatter detection program in step S10, it obtains a count value N representing the number of times the workpiece W has been machined from the control device 12 in step S21.

Then, in step S21, the chatter detection device 20 determines whether the acquired count value N is equal to or greater than a reference machining number N1 that represents a preset number of machining operations for the workpiece W. The reference machining number N1 is a machining number that is experimentally or empirically known to result in residual cutting during rough grinding, and is set to a value smaller than the machining number for machining the workpiece W during the interval (truing interval) at which truing of the grinding wheel 46 is performed.

If the count value N is equal to or greater than the reference machining number N1, the chatter detection device 20 judges "Yes" in step S21 because there is a high possibility that the ground surface will be left uncut, i.e., there is a high possibility that chatter will occur unexpectedly. Then, the chatter detection device 20 executes the step processing from step S11 onwards, as in the above-mentioned example.

On the other hand, if the count value N is less than the reference machining number N1, the chatter detection device 20 determines "No" in step S21 because the condition of the grinding wheel 46 has not deteriorated and there is little possibility of incomplete cutting on the grinding surface, i.e., there is little possibility of chatter occurring suddenly. Then, the chatter detection device 20 ends the execution of the sudden chatter detection program in step S20. In this case, normal grinding is performed.

(8. Other)
In the above-described present embodiment and the first modified embodiment, the spark-out execution control unit 56, which is the finishing processing content change unit, executes modified spark-out processing in which the processing time, which is the content of the spark-out processing, is changed to be extended. Alternatively, the spark-out execution control unit 56 can change the content of the spark-out processing, for example, by increasing the number of times that normal spark-out is executed.

In addition, in the above-mentioned present example and the first variant example, the finishing process content change unit is the spark-out execution control unit 56, and changes the content of the spark-out process among the finishing processes. However, the finishing process content change unit can also change the content of the fine grinding process or the fine grinding process, which are the finishing processes.

Furthermore, in the present embodiment and the first variant described above, the status data acquisition unit 51 of the chatter detection device 20 acquires drive current data as status data. Instead of this, as long as the data has a correlation with the grinding resistance, it is possible to acquire, for example, displacement data, torque data, or vibration data (acceleration data) as status data, without being limited to drive current data. Also, instead of data having a correlation with the grinding resistance, it is possible to acquire grinding resistance data that directly represents the grinding resistance. Each of these data also has frequency characteristics, and it is possible to extract the amplitude A1 of the grinding wheel rotation frequency F in the rough grinding process and the amplitude A2 in the finish grinding process as feature quantities. Therefore, in this case as well, the same effects as those of the present embodiment and the first variant described above can be obtained.

1... Chatter detection system, 10... Grinding device, 11... Grinding machine, 12... Control device, 13... Detector, 14... Interface, 20... Chatter detection device, 21... Processor, 22... Storage device, 23... Interface, 30... Individual display device, 40... Cylindrical grinding machine, 41... Bed, 42... Headstock, 42a... Motor, 43... Tailstock, 44... Traverse base, 44a... Motor, 45... Grinding wheel head, 45a... Motor, 46... Grinding wheel, 46a... Motor, 47... Sizing device, 48... Grinding wheel correction device, 49...coolant device, 51...status data acquisition unit, 52...grinding process judgment unit, 53...feature extraction unit, 53a...frequency analysis unit, 53b...amplitude extraction unit, 54...chatter judgment unit, 55...period change unit, 56...spark out execution control unit (finishing processing content change unit), 57...output unit, A1, A2...amplitude (feature), F...grindstone rotation frequency (specific rotation frequency), D1, D2...judgment value, K...control value, Q...variable, N...count value (number of processing), N1...reference number of processing, T...grindstone, W...workpiece

Claims (11)

a grinding device in which a grinding wheel performs grinding processing on a workpiece through a plurality of grinding steps controlled by a control device;
a detector that detects status data relating to the grinding resistance of the grinding wheel that can be observed during the grinding process and outputs the detected status data;
a chatter detection device for detecting chatter occurring during the grinding process,
The chatter detection device is
a frequency analysis unit that performs frequency analysis on the state data having frequency characteristics acquired from the detector for each of a rough grinding process in a rough grinding step and a finishing process in a finishing step of the grinding process, and divides the state data into a plurality of frequency components;
an amplitude extraction unit that extracts, from among the plurality of frequency components divided by frequency analysis, an amplitude of a grindstone rotation frequency corresponding to a rotation speed of the grindstone of the grinding device for each of the rough grinding process and the finish grinding process;
a chatter determination unit which, when the magnitude of the amplitude of the grindstone rotation frequency of the extracted finish processing is less than a preset determination value , determines that the irregularities formed on the ground surface of the workpiece by the rough grinding processing have not been removed by the finish processing, and therefore the chatter will occur in the subsequent grinding processing ;
A chatter detection system comprising: The chatter detection system according to claim 1, wherein the state data is drive current data corresponding to the grinding resistance generated in the grinding wheel during each of the rough grinding process and the finish grinding process in the grinding device. The chatter detection system according to claim 1 or 2, further comprising a finishing process content change unit that changes the content of the finishing process in response to a determination by the chatter determination unit that chatter will occur. The finishing processing content change unit includes:
The chatter detection system according to claim 3 , further comprising: increasing the number of times the finish machining is performed; or extending a time period during which the finish machining is performed. The grinding device performs the grinding process while rotating the grindstone and the workpiece around their respective axes,
a period changing unit that changes the rotation period of at least one of the grindstone and the workpiece in response to a determination by the chatter determination unit that chatter will occur in the finish machining so that a rotation speed ratio between the grindstone and the workpiece is not an integer multiple;
The chatter detection system according to claim 3 or 4, wherein the finish processing content change unit changes the content of the finish processing in a state in which the rotation period of at least one of the grinding wheel and the workpiece is changed by the period change unit. The chatter detection device is
a grinding process determination unit that determines whether the process is the rough grinding process,
The chatter detection system according to claim 1 , further comprising a step of determining a state of the grinding wheel when the grinding process determination unit determines that the process is the rough grinding process. The chatter detection system according to claim 6, wherein the chatter detection device determines the condition of the grinding wheel using the amplitude extracted by the amplitude extraction unit during the rough grinding process. The chatter detection system according to any one of claims 1 to 7, wherein the chatter detection device detects the occurrence of chatter when the number of turns of the workpiece ground by the grinding wheel reaches or exceeds a preset reference number of turns. The chatter detection system according to any one of claims 1 to 8, wherein the chatter detection device is provided integrally with or separately from the grinding device. The chatter detection system according to any one of claims 3 to 5, wherein the finishing process includes at least fine grinding, fine grinding, and spark-out processing. The chatter detection system according to any one of claims 1 to 10, wherein, when the detector outputs the status data via the control device, the status data is supplemented by process information identifying the grinding process by the control device.

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