JP2006205350A - Tool damage abnormality detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and properly set a tolerable range of a comparison value between a current value and a late past average value concerning an index representing a load added to a tool. <P>SOLUTION: With a machining cycle count index i=O, machining is executed, while the load is detected at a prescribed periodic cycle, and the index H(i) (area S for the load value, maximum inclination absolute value G between two points when the load is lowered, etc.) are formed for n-cycles (S1-5). Comparison values between the respective index for n-cycles for the late past and the index value for the current cycle are formed. For the first-time comparison value, setting of the initial value for a threshold value can be used (S6-10). When any of the comparison values deviates from the tolerable range, the threshold value is updated to expand the tolerable range, and updated history is stored (S11-12). As a damage abnormality is visually checked, a threshold value update stopping command is inputted, and machining is stopped after completion of the cycle. An updated value for the newest threshold value is collected to be a set threshold value (S13-15). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  For example, when machining a workpiece of the same material with the same shape, or when machining a number of workpieces of the same specification using a machine tool, the tool breakage used in the machining is broken. More specifically, a technique for enabling the allowable range of an index used for detecting a tool damage abnormality to be appropriately and easily set in the apparatus. About. Typical tools for detecting damage anomalies include drills in machining centers and tapping tools in tapping.

  In general, in a tool used in a machine tool, the cutting edge is gradually worn with the passage of time used for machining, and the cutting resistance gradually increases. Further, over time, wear or breakage is added to the tool, causing the tool to be damaged or similar, and the predetermined machining accuracy required for the workpiece cannot be maintained. When such a situation occurs, it is of course inappropriate to continue the machining as it is, and it is necessary to take measures such as replacing the tool with a new one. In the present application, the above “damage or similar abnormality” is referred to as “damage abnormality”.

  Under such a background, a technique for automatically detecting a state corresponding to a tool damage abnormality has been already proposed in unmanned machining and long-time automatic machining that are frequently used recently. Many of the technologies that have been proposed in the past detect indices (the torque of the motor that drives the tool and the thrust load that acts on the tool) that represent the load applied to the tool for machining the workpiece over multiple machining cycles. For each machining cycle, the index in the current machining cycle is compared with the average value of the indices over a plurality of machining cycles preceding the current machining cycle. If it deviates, a method of determining that a tool damage abnormality has occurred is adopted (see Patent Documents 1 to 3 below).

Here, the setting of the allowable range of the index is performed by presetting threshold values (usually upper limit value and lower limit value) relating to the index, so how to determine the preset threshold value? It becomes important. If the preset threshold value is not appropriate, the detection of damage abnormality will be delayed and a defective product will be produced (if the allowable range is too wide upward or downward), conversely, the detection of damage abnormality will be premature. A tool having a sufficient remaining life is wasted (if it is narrowed too much above or below the allowable range).
However, it has been the actual situation that sufficient technical development has not been conducted on how to appropriately set the threshold value regarding the index representing the load applied to the tool.
For example, there is a method of determining a threshold value of an index (load average value) by multiplying a load average value by a cutting test or a load average value immediately before machining by a predetermined coefficient. The specific setting method is not specified. As an example, when the disclosure of the following Patent Document 1 (Rotary Tool Abnormality Detection Method and Apparatus) is taken into consideration, abnormalities are detected accurately and accurately in real time by setting a threshold value according to the rate of change of the load value. It is supposed to. Specifically, the threshold value is set by setting a constant k in the range of 0 to 1 determined from the rate of change ΔFn of the load value to the damage load level Lmax set constant according to the size of the drill or the like. The threshold is set by multiplication.
However, a specific determination method for Lmax and k used here is not always clearly shown. By the way, since damage load data generally differs depending on a processing machine, a tool, a work material, processing conditions, and the like, it is highly desirable to collect the data at an application site where processing is performed. In the case of drills and taps, even if an abnormality can be detected during machining, the countermeasure for the abnormality is made after the end of one machining cycle, and real-time detection is not necessarily required.

Japanese Patent No. 3446518 JP 2003-326438 A JP 2004-130407 A

  Accordingly, an object of the present invention is to detect an index (such as a torque of a motor driving a tool or a thrust load acting on a tool) indicating a load applied to a tool for machining a workpiece over a plurality of machining cycles, For each machining cycle, the index in the current machining cycle is compared with the average value of the indices over a plurality of machining cycles preceding the current machining cycle. Is the ratio of the two; the same shall apply hereinafter), and if it deviates from the preset allowable range, the tool damage abnormality is detected by determining that the tool has failed. In the detection apparatus, the setting of the allowable range can be performed easily and appropriately.

The present invention provides a tool damage abnormality detection apparatus that detects a tool damage abnormality by the above-described method, and an allowable range of an index (an index representing a load applied to the tool; the same applies hereinafter) used as a criterion for detecting an actual damage abnormality. By providing setting threshold value determining means for determining a threshold value (hereinafter also referred to as “setting threshold value”), the above-mentioned problem is solved.
In the present invention, by this setting threshold value determining means, while setting an initial value of a threshold value related to the index, while performing monitoring of the occurrence of abnormal tool damage, machining is performed on a trial basis, and through a plurality of machining cycles. Using the index data obtained, when the threshold for the index is updated sequentially in the direction to extend the allowable range of the index, and the update is stopped upon receiving a command not to perform the update , Determining the set threshold value based on the latest updated threshold value at the same point or threshold data corresponding thereto (threshold history data obtained by near-last update) Thus, an allowable range setting (determining a set threshold value) reflecting an index value at the time of occurrence of a tool damage abnormality in the experimentally performed machining is performed.

  That is, the present invention detects an index representing a load applied to a tool for machining a workpiece over a plurality of machining cycles, and the index in the current machining cycle and a plurality of machining preceding the current machining cycle. When the comparison value representing the result of the comparison is compared with the average value of the index over a cycle and deviates from the allowable range represented by the set threshold value set for the comparison value, the tool is damaged abnormally. The present invention is applied to a tool damage abnormality detection apparatus that determines that the occurrence of the above has occurred.

And the tool damage abnormality detection device according to claim 1 that defines the basic requirements common to the present invention further comprises a setting threshold value determining means for determining the setting threshold value,
The setting threshold value determining means includes means for detecting the index over a plurality of machining cycles, and for each machining cycle, the index in the current machining cycle, and a plurality of machining cycles preceding the current machining cycle. A comparison means for comparing the average value of the index over the range to obtain a comparison value representing the comparison result, a first storage means for storing a threshold value for the comparison value, and the first Means for writing the initial value of the threshold value into the storage means, and an allowable range represented by the threshold value stored in the first storage means at the time when the comparison value obtained in a certain machining cycle is Means for updating the threshold value stored in the first storage means to a threshold value corresponding to the comparison value that has deviated from the permissible range when deviating, and a command for stopping the updating of the threshold value According to before Means for preventing the threshold from being updated, and the setting threshold based on the threshold stored in the first storage at the time when the threshold is no longer updated. It is characterized by including means for determining the value.

  Here, a second storage means for storing a threshold value history including at least a part of the threshold values stored in the first storage means by an update executed prior to the latest update. Further, when determining the set threshold value, the threshold value is updated instead of the threshold value stored in the first storage means when the threshold value is no longer updated. The set threshold value may be determined based on a threshold value history stored in the second storage means at the time when the threshold value is not performed (Claim 2). Based on both the threshold value stored in the first storage unit and the threshold value history stored in the second storage unit at the time when the update of is no longer performed, the set threshold value May be determined ( Motomeko 3).

  In any of these inventions, the previous index includes the difference between the maximum load value and the minimum load value in a certain machining cycle (M), the area (S) of the load value in a certain machining cycle, The average value (L) of the absolute value of the load, the difference (Ldiff) between the average value L of the absolute value of the load in a certain machining cycle and the average value L ′ of the absolute value of the load in the immediately preceding machining cycle, a certain machining cycle A value obtained by dividing the difference M between the maximum load value and the minimum load value in the case by the average value L of the absolute value of the load in the same machining cycle (M / L), the absolute maximum gradient between two points when the load increases in a certain machining cycle One or more of the value (G +) and the absolute gradient value between two points (G-) at the time of load reduction in a certain machining cycle can be included.

  Then, the set threshold value is determined for each type of the index, and a tool damage abnormality can be detected based on at least one of the determined set threshold values. ). The load applied to the tool is typically a torque of a motor that drives the tool (Claim 5) or a thrust load acting on the tool (Claim 6).

  Furthermore, an initial value of the threshold value may be determined based on an initial comparison value obtained by the comparison means, and the determined initial value may be written in the first storage means (claim). Item 7). In each of the above inventions, a representative tool is a drill or a tap (claim 8).

  According to the present invention, in the tool damage abnormality detection apparatus that detects a tool damage abnormality by the above method, the allowable range of the index can be set easily and appropriately. Further, according to the present invention, it is easy to set the allowable range of the index at the site where the processing is performed.

  FIG. 1 is a block diagram of a control device (numerical control device) 100 for controlling a machine tool that also serves as a tool damage abnormality detection device according to the present invention. In the figure, a CPU 11 is a processor that controls the control device 100 as a whole. The CPU 11 reads a system program stored in the ROM 12 via the bus 20 and controls the entire control device according to the system program. The RAM 13 stores temporary calculation data, display data, and various data input by the operator via the display / MDI unit 80. The CMOS memory 14 is configured as a non-volatile memory that is backed up by a battery (not shown) and that retains the storage state even when the control device 100 is powered off.

  In the CMOS memory 14, a machining program read via the interface 15, a machining program input via the display / MDI unit 80, and the like are stored.

The ROM 12 is pre-stored with various system programs for executing processing in an editing mode and processing for automatic operation required for creating and editing a machining program. Furthermore, in the present embodiment, (a) a processing program for detecting a tool damage abnormality and (b) a processing program for determining a set threshold value are stored.
The former program (a) is a well-known program, and the above-described tool damage abnormality detection method, that is, an index representing a load applied to a tool for machining a workpiece is detected over a plurality of machining cycles. For each cycle, when the index in the current machining cycle is compared with the average value of the index over multiple machining cycles preceding the current machining cycle, and it deviates from the “preset index tolerance” This is a processing program for detecting a tool damage abnormality by a method of determining that a damage abnormality has occurred in the tool (hereinafter the same).

  On the other hand, the latter program (b) is unique to the present invention, and in the process (a), a threshold value that prescribes a “preset index allowable range”, that is, a “set threshold value” It is a processing program for determining. The processing contents of these programs, particularly the program (b) will be described in detail later.

  Returning to FIG. 1, the interface 15 enables connection between the control device 100 and an external device 82 such as an adapter. A machining program or the like is read from the external device 82 side. Further, the machining program edited in the control device 100 can be stored in the external storage means via the external device 82. The PMC (programmable machine controller) 16 outputs a signal to the auxiliary device of the machine tool (for example, an actuator such as a robot hand for tool change) via the I / O unit 17 by a sequence program built in the control device 100. Control.

  The display / MDI unit 80 is a manual data input device having a display, a keyboard and the like. The interface 18 receives commands and data from the keyboard of the display / MDI unit 80 and passes them to the CPU 11. The interface 19 is connected to an operation panel 81 provided in the machine tool body. The operation panel 81 is provided with an alarm device and an alarm lamp, and further provided with various switches for inputting various commands to the machine. ing.

  The axis control circuits 30 to 32 for each axis receive the movement command amount for each axis from the CPU 11 and output the command for each axis to the servo amplifiers 40 to 42. In response to this command, the servo amplifiers 40 to 42 drive the servo motors 50 to 52 for the X, Y, and Z axes. The servo motors 50 to 52 for each axis have a built-in position / speed detector. The position / speed feedback signal from the position / speed detector is fed back to the axis control circuits 30 to 32 to perform position / speed feedback control. .

  In addition, the drive current output from the servo amplifiers 40 to 42 to the servo motors 50 to 52 is also detected by the current detectors 60 to 62 in the same manner as in the prior art, and fed back to the axis control circuits 30 to 32 to control the current (torque). Is made. For each motor, the drive current flowing through the motor and the load torque applied to the motor or the thrust load of the feed shaft driven by the motor are substantially the same. In this embodiment, the Z-axis drive servomotor 52 used for tool feed is used in this embodiment. A means for detecting a thrust load applied to the tool is configured using a current detector 62 that detects a drive current flowing through the tool. Note that illustration of position and velocity feedback is omitted.

  Next, the spindle control circuit 70 receives a spindle rotation command, performs speed control based on the command speed and a feedback signal from a position coder 73 that generates a feedback pulse in synchronization with the rotation of the spindle motor 72, and further controls the spindle. In response to a current feedback signal from a current detector 74 that detects a drive current flowing through the motor 72, current loop control is performed to control the rotation speed of the spindle motor 72. Since the load (torque) applied to the spindle motor is substantially proportional to the drive current, in this embodiment, the current detector 74 constitutes a means for detecting the load (torque) applied to the spindle motor.

  As a tool to be mounted on the spindle in this embodiment, a drill and a tapping tool are assumed. And setting for performing drilling or threading (tapping) sequentially on a large number of workpieces such as parts with the same specifications, and detecting damage abnormality of the drill or tapping tool by the above-mentioned method Determine the threshold. A tool (drill or tapping tool; hereinafter the same) is attached to a main shaft, and a work is attached to a table driven by X-axis and Y-axis servomotors 50 and 51 of a feed axis. The tool is moved relative to the workpiece by the Z-axis servomotor 52 of the feed shaft that moves the main shaft in the Z-axis direction orthogonal to the X-axis and Y-axis.

Next, in preparation for the program (a) (processing program for detecting tool damage abnormality), the program (b) (setting threshold determination processing program) for determining the “setting threshold” is prepared. The processing contents and items related to the “set threshold value” determined there (“comparison value”, “index”, etc.) will be described with reference to FIGS.
FIG. 2 is a flowchart showing an outline of the steps of the processing program for determining the threshold value in (b). FIGS. 3 and 4 show two types of tools (FIG. 3; drill drill / FIG. 4; tapping). It is the graph which showed the example of transition of the load (detection value) concerning the tool in the processing cycle which damage abnormality occurred about the tool), and the processing cycle just before / after that.

In the processing of the program of (b), the conditions (work type, type of machining, use of actual machining to which the program of (a) is applied (machining cycle repeated many times until a tool damage abnormality is detected) are used. The same conditions as the type of tool to be prepared) are prepared, and trial machining is performed.
The main points of each step will be described below. In addition, FIGS. 3 and 4 are referred to as appropriate for explanation of “index”, “comparison value” and the like related to the set threshold value.

Step S1: The count index i for counting the machining cycle is cleared and set to an initial value (i = 0).
Step S2: While executing the machining in the i-th cycle, a load applied to the tool (hereinafter also simply referred to as “load”) is detected at a predetermined period (for example, 8 msec; hereinafter the same), and an index H representing the load applied to the tool Create (i). The index calculated in the present embodiment is represented by the symbol H as appropriate. In addition, the index H obtained for the i-th cycle is expressed as H (i) or the like with the subscript (i).
Typical detected loads are the torque of the motor that rotates the tool and the thrust load of the Z-axis feed of the tool. As described above, for the former detection, the current detector 74 that detects the drive current flowing in the servo motor 72 that drives the spindle can be used. For the latter detection, a current detector 62 that detects a drive current flowing through the Z-axis drive servomotor 52 can be used.

  As is well known, the load applied to the tool exhibits a similar load transition pattern for each machining cycle. In general, when a damage abnormality occurs in the tool, a significant change appears in the load transition pattern immediately after that. 3 and 4 show examples thereof.

  FIG. 3 shows a case where a carbide drill having a diameter of 6.8 mm is used as a tool, and a workpiece of steel material S50C having a thickness of 27.2 mm is repeatedly drilled at a spindle rotation speed S7490 min-1 and a feed rate F3750 mm / min. The measured value of the thrust load on the feed shaft (Z-axis) is a graph plotting the machining cycle (jth cycle; for example, j = 2456) in which a damage abnormality has occurred (see arrow A) and the machining cycles immediately before and immediately after that. is there. Although illustration is omitted, a similar transition pattern can be obtained also when the torque (drive current) of the spindle motor that drives the tool (carbide drill) is detected.

  On the other hand, in FIG. 4, a high tap (tapping tool) having a diameter of 4 mm was used as a tool, and tapping (screw hole) machining was repeatedly performed on the same type of workpiece at a spindle rotation speed S717 min-1 and a feed rate F501.9 mm / min. The measured value of the thrust load of the feed axis (Z axis) at the time is determined based on the machining cycle (k-th cycle; for example, k = 1826) in which damage abnormality has occurred (see arrow B), the machining cycle immediately before and the machining cycle immediately after It is the graph which plotted about a part of. Although illustration is omitted, a similar transition pattern can be obtained when the torque (drive current) of the spindle motor that drives the tool (high tap) is detected.

  Based on the load data thus detected, various indices are calculated in sequence.

Various indicators H can be considered, and one or more of them are calculated. Here, the following indices M, S, L, Ldiff, M / L, G +, and G- are calculated. 3 and 4, the symbol T represents the processing time (not including the time for extracting the drill by drilling).
M: The difference between the maximum load value and the minimum load value in a certain machining cycle, and generally takes a positive value. The maximum and minimum load values may have opposite signs. For example, in FIG. 4 (tapping), in the latter half of the cycle, the tool rotates in the reverse direction and the thrust load is applied in the opposite direction, so the minimum load value becomes a negative value.
S: The area of the load value in a certain machining cycle. When the sign of the load is reversed in the first half of the cycle, as shown in FIG. 4, the area S + of the portion where the load> 0 and the area S− of the portion where the load <0 are added, and S = S ++ S- is calculated.

L: Average value S / T of the absolute value of the load in a certain machining cycle.
Ldiff: difference (absolute value) between the average value L of the absolute value of the load in a certain machining cycle and the average value L ′ of the absolute value of the load in the immediately preceding machining cycle.
M / L: A value obtained by dividing M in a certain machining cycle by L in the same machining cycle.
G-: The maximum absolute value of inclination between two points when the load is lowered in a certain machining cycle (see FIGS. 3 and 4).
G +: absolute value of the maximum inclination between two points when the load increases in a certain machining cycle (see FIGS. 3 and 4).

  The final deterministic values of these indices are determined after the end of the machining cycle. However, for indices that can be calculated using a method that updates intermediate values such as integrated values at predetermined intervals, calculation starts during machining. Is done. For example, the index S can be obtained by a procedure of integrating the detection value (absolute value) of the load for each detection cycle (final integrated value × detection cycle is S).

Step S3: The count index i is incremented by 1.
Step S4: The value of the counting index i is checked, and if it exceeds a predetermined n, the process proceeds to Step S5, and if not, the process returns to Step S2. Here, n is a positive integer of 2 or more, and a number corresponding to the number of preceding machining cycles taking an average value compared with the index in the current machining cycle is set in advance by the detection method described above. A suitable value for n is usually about 3-10. For example, when n = 5 is set, the judgment output of yes is obtained for the first time in the sixth step S4 from the start of the process, and during this time, the indicators H (1), H (2), H (3), H (4) and H (5) are accumulated.

Step S5: While performing machining in the i-th cycle, the load applied to the tool is detected at a predetermined period, and an index H (i) representing the load applied to the tool is created. The type of index H (i) to be created is as described in step S2.
Step S6: The comparison value R (1) is created / stored for each type of the created index H (i). When n = 5, the formula for calculating R (1) is
R (1) = 5 × H (6) / (H (1) + H (2) + H (3) + H (4) + H (5))
It becomes. For example, for index L,
R (1) L = 5 × L (6) / (L (1) + L (2) + L (3) + L (4) + L (5))
Calculated by

  Here, “ratio” is employed as the comparison value, but this is a typical example, and other similar amounts (quantities that quantitatively represent the magnitude relationship) may be employed. In addition, the number of preceding multiple cycles n used for calculating the comparison value may not necessarily be equal to the number of preceding multiple cycles (referred to as nreal) used when calculating the comparison value actually used in the tool damage inspection. Nreal ≦ n, but preferably nreal = n.

Step S7: Using the comparison value R (1) created for the index H (6), the set threshold values rmax0 and rmin0 are written in the threshold list as the initial set threshold values. There are various initial setting methods, for example, as follows.
rmax0 = (1 + α) R (1)
rmin0 = (1-α) R (1)
Here, rmax0 represents an initial setting value of the upper limit threshold value rmax of the comparison value R, and rmin0 represents an initial setting value of the lower limit threshold value rmin of the comparison value R. Α is a parameter for adjusting the “allowable range that is initially set for the comparison value of each index”, and is about 0 to 0.1. If α = 0, rmax0 = rmin0 = R (1), which means that the width of the allowable range of the comparison value at the initial setting is zero, but there is no problem because it is updated later. Conversely, care should be taken not to set α too large.

However, of the indicators M, S, L, Ldiff, M / L, G +, G−, the comparison value R calculated based on G + and G− (the value of the current cycle and the value of the past n cycles) As for the threshold value r, only rmax0 is initialized as described above, and rmin0 is initialized to rmin0 = 0. (There is no point in managing the lower limit of the absolute value of the slope, so a formal lower limit may be used. ).
Thus, in the case of this embodiment, the following 14 threshold values are initialized.
Upper limit of comparison value for M Lower limit of comparison value for M Upper limit of comparison value for S Lower limit of comparison value for S Upper limit of comparison value for L Lower limit of comparison value for L Upper limit of comparison value for Ldiff Ldiff Lower limit of comparison value for M / L Upper limit of comparison value for M / L Lower limit of comparison value for M / L Upper limit of comparison value for G- Lower limit of comparison value for G- Upper limit of comparison value for G + G + In addition, instead of this step S7, rmax0 and rmin0 may be separately initialized for the comparison value calculated from each index. Examples of setting values in this case are shown below.

(1) For each comparison value for the indicators G + and G-, rmax0 = 1 and rmin0 = 0.
(2) For each comparison value for the indices M, S, L, Ldiff, and M / L, rmax0 = 1.05 and rmin0 = 0.95.
Step S8: The value of the counting index i is incremented by 1.
Step S9: While performing machining in the i-th cycle, the load applied to the tool is detected at a predetermined period, and an index H (i) representing the load applied to the tool is created. The type of index H (i) to be created is as described in step S2.
Step S10: The comparison value R (in) is created / stored for each type of the created index H (i). When n = 5, the formula for calculating R (i-5) is
R (i-5) = 5 × H (i) / (H (i-1) + H (i-2) + H (i-3) + H (i-4) + H (i-5))
It becomes. For example, for index S,
R (i-5) S = 5 × S (i) / (S (i-1) + S (i-2) + S (i-3) + S (i-4) + S (i-5))
R (1) L = 5 × L (6) / (L (1) + L (2) + L (3) + L (4) + L (5))
Calculated by

Step S11: Check whether the comparison value R (in) deviates from the allowable range at that time (between the lower threshold value and the upper threshold value) for each index type. Return to step S8. Otherwise, the process proceeds to step S12.
Step S12: The latest threshold value in the threshold value list is updated according to the comparison value out of the allowable range. The previous data is stored as history data (threshold value update and history data addition). The history data includes a code for distinguishing between the value of the comparison value, the cycle number from which it was obtained, the upper limit, and the lower limit.

Step S13: It is checked whether or not a command for stopping the threshold update is input.
If not, the process returns to step S8. If so, the process proceeds to step S14. The threshold update stop command is input manually, for example, when the operator monitors the occurrence of a tool damage abnormality visually or by the output of a damage sensor provided separately, and recognizes the occurrence of the damage abnormality. It is also conceivable that the operator checks the state after processing (for example, the shape and dimensions of the hole) promptly and inputs it manually when it is determined that the accuracy has been lowered. Alternatively, a command for automatically stopping threshold value updating may be input by an output from a damage sensor or the like.

  Step S14: The machining is stopped after the machining cycle that has been started is completed. Step S15: Based on the data written in the threshold list, “set threshold values” rmaxset and rminset for the comparison value are determined for each index type. The final decision can be made automatically based on a predetermined rule, for example. A typical rule is a method in which the latest threshold update values are collected for each comparison value of each index type and used as a set threshold value. Other rules include, for example, “collecting the latest update values of threshold values and performing minor adjustments such as applying a safety factor to each”.

  The above is the outline of the setting threshold value determination processing program. In the present embodiment, a comparison value for M, a comparison value for S, a comparison value for L, a comparison value for Ldiff, a comparison value for M / L, a comparison value for G−, and a comparison value for G + Are set threshold values (14 in total) that define an allowable range with an upper limit and a lower limit, respectively. However, this is merely an example, and only a part of the above may be determined. In addition, there are indexes other than the above-described examples indicating the load applied to the tool, and these may be adopted as the indexes.

All or a part of the set threshold value determined as described above is used for detecting a tool damage abnormality by the above method. Since this detection method is well known, an example will be briefly described.
First, after setting such as setting threshold values (for example, the above-mentioned 14 values) that are actually used in tool abnormality detection and mounting a new tool, n cycles are processed in the same manner as in steps S1 to S5. Index values are created, and from the (n + 1) th cycle, a comparison value is created for each index value type.
The method of creating the comparison value is the same as that in the above processing, and in particular, the “number of machining cycles preceding the current machining cycle” is the same as the number employed in step S6 or the like (for example, 5 cycles).

  Each time each comparison value is created, it is checked whether it deviates from the allowable range specified by the set threshold value. If even one comparison value deviates from the allowable range, the tool is damaged. It is determined that an abnormality has occurred, an alarm is output, and machining is stopped. The setting threshold used here is not determined based on the intuition and skill of the operator, but automatically reflects actual test results, as can be seen from the process of determining the setting threshold described above. It is. For this reason, variations in threshold setting due to a lot of experience are eliminated, and the reliability of detecting tool damage abnormality is improved.

It is a principal part block diagram of the control apparatus which comprises one Embodiment of this invention and controls a machine tool. It is the flowchart which described the outline of the steps of the processing program of the threshold value determination performed in embodiment. It is the graph which showed the example of transition of the load (detection value) concerning the tool in the processing cycle where damage abnormality occurred, and the processing cycle just before / after that about the case which used the carbide drill as a tool. It is the graph which showed the example of change of the load (detection value) concerning the tool in the processing cycle where damage abnormality occurred, and the processing cycle just before / after that about the case using a tapping tool (high tap) as a tool.

Explanation of symbols

T 1 Machining time of 1 machining cycle S Load waveform area during machining G- Maximum gradient absolute value between 2 points when load decreases G + Maximum absolute gradient value between 2 points when load increases

Claims (8)

An index representing a load applied to a tool for machining a workpiece is detected over a plurality of machining cycles,
For each machining cycle, the index in the current machining cycle is compared with the average value of the index over a plurality of machining cycles preceding the current machining cycle, and a comparison value representing the result of the comparison is In a tool damage abnormality detection apparatus that determines that a damage abnormality has occurred in the tool when it deviates from an allowable range represented by a set threshold value set for a comparison value,
A setting threshold value determining means for determining the setting threshold value;
The set threshold value determining means includes:
Means for detecting the indicator over a plurality of machining cycles;
Comparing means for comparing the index in the current machining cycle with the average value of the index over a plurality of machining cycles preceding the current machining cycle and obtaining a comparison value representing the comparison result for each machining cycle When,
First storage means for storing a threshold value for the comparison value;
Means for writing an initial value of the threshold value into the first storage means;
When the comparison value obtained in a certain machining cycle deviates from the allowable range represented by the threshold value stored in the first storage means at that time, it corresponds to the comparison value deviating from the allowable range. The threshold value is not updated in response to a threshold value stored in the first storage means and a command to stop the threshold value update. Means to
Characterized by comprising means for determining the set threshold value based on the threshold value stored in the first storage means when the threshold value is no longer updated. Tool damage abnormality detection device. An index representing a load applied to a tool for machining a workpiece is detected over a plurality of machining cycles,
For each machining cycle, the index in the current machining cycle is compared with the average value of the index over a plurality of machining cycles preceding the current machining cycle, and a comparison value representing the result of the comparison is In a tool damage abnormality detection apparatus that determines that a damage abnormality has occurred in the tool when it deviates from an allowable range represented by a set threshold value set for a comparison value,
A setting threshold value determining means for determining the setting threshold value;
The set threshold value determining means includes:
Means for detecting the indicator over a plurality of machining cycles;
Comparing means for comparing the index in the current machining cycle with the average value of the index over a plurality of machining cycles preceding the current machining cycle and obtaining a comparison value representing the comparison result for each machining cycle When,
First storage means for storing a threshold value for the comparison value;
Means for writing an initial value of the threshold value into the first storage means;
When the comparison value obtained in a certain machining cycle deviates from the allowable range represented by the threshold value stored in the first storage means at that time, it corresponds to the comparison value deviating from the allowable range. Means for updating a threshold value stored in the first storage means to a threshold value, and the threshold value stored in the first storage means by an update executed prior to the latest update. Second storage means for storing a threshold history including at least a part of
Means for preventing the threshold value from being updated in response to a command to stop the threshold value updating;
And means for determining the set threshold value based on the threshold value history stored in the second storage means when the threshold value is no longer updated. A tool damage abnormality detection device. An index representing a load applied to a tool for machining a workpiece is detected over a plurality of machining cycles,
For each machining cycle, the index in the current machining cycle is compared with the average value of the index over a plurality of machining cycles preceding the current machining cycle, and a comparison value representing the result of the comparison is In a tool damage abnormality detection apparatus that determines that a damage abnormality has occurred in the tool when it deviates from an allowable range represented by a set threshold value set for a comparison value,
A setting threshold value determining means for determining the setting threshold value;
The set threshold value determining means includes:
Means for detecting the indicator over a plurality of machining cycles;
Comparing means for comparing the index in the current machining cycle with the average value of the index over a plurality of machining cycles preceding the current machining cycle and obtaining a comparison value representing the comparison result for each machining cycle When,
First storage means for storing a threshold value for the comparison value;
Means for writing an initial value of the threshold value into the first storage means;
When the comparison value obtained in a certain machining cycle deviates from the allowable range represented by the threshold value stored in the first storage means at that time, it corresponds to the comparison value deviating from the allowable range. Means for updating a threshold value stored in the first storage means to a threshold value, and the threshold value stored in the first storage means by an update executed prior to the latest update. Second storage means for storing a threshold history including at least a part of
Means for preventing the threshold value from being updated in response to a command to stop the threshold value updating;
Based on the threshold value history stored in the second storage means and the threshold value stored in the first storage means when the threshold value is no longer updated, the setting is performed. A tool damage abnormality detecting device comprising means for determining a threshold value. The index includes a difference (M) between a maximum load value and a minimum load value in a certain machining cycle, an area (S) of a load value in a certain machining cycle, and an average value (L) of absolute values of loads in a certain machining cycle. The difference (Ldiff) between the average value L of the absolute value of the load in the machining cycle and the average value L ′ of the absolute value of the load in the immediately preceding machining cycle, and the difference M between the maximum load value and the minimum load value in a certain machining cycle Divided by the average value L of the absolute value of the load in the same machining cycle (M / L), the maximum gradient absolute value (G +) between two points when the load increases in a certain machining cycle, and in a certain machining cycle Including at least one of the absolute maximum gradient values (G-) between two points when the load is lowered,
The set threshold value is determined for each type of the indicator, and a tool damage abnormality is detected based on at least one of the determined set threshold values. The tool damage abnormality detection apparatus described in 1.   The tool damage abnormality detection device according to any one of claims 1 to 4, wherein the load applied to the tool is a torque of a motor that drives the tool.   The tool damage abnormality detection device according to any one of claims 1 to 5, wherein the load applied to the tool is a thrust load acting on the tool. Means for determining an initial value of the threshold based on an initial comparison value obtained by the comparison means;
The tool damage abnormality detection device according to any one of claims 1 to 6, further comprising means for writing the determined initial value into the first storage means. The tool damage abnormality detection device according to any one of claims 1 to 6, wherein the tool is a drill or a tap.

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