JP2000317710A - Tool abnormality detection tethod and device for machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect tool breaking during working in real time under a machining condition changing in tool, machining condition, and work material quality. SOLUTION: A CPU of CNC device monitors during machining operation at an interval of an unit time Δt for instance 10 milliseconds. In case of drill machining, CPU computes a command rotational quantity of a main spindle per the unit time as a determination reference value B for detecting tool abnormality based on the rotating speed data of the main spindle and so on designated in NC program (a step 52), computes an actual rotational quantity ΔQ of the main spindle per the unit time (a step 55), and determines the occurrence of tool abnormality by comparing a difference between the command rotational quantity B and the actual rotational quantity ΔQ with a threshold value E (a step 57). In taping machining, the determination reference value B is computed as an increment of a rotational quantity of the tap (Pn-Pn-1) per the each unit time based on each rotational position of the tap determined in relation to each position of cutting depth per the unit time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for automatically detecting breakage or excessive wear of a cutting tool in cutting.

[0002]

2. Description of the Related Art Generally, drilling is performed by rotating a main spindle and a work relative to each other in the axial direction of the main spindle while rotating a main spindle having a tool attached to a tip thereof. Monitoring of tool breakage and excessive wear during drilling is an important function that an automated machine tool should have, and various tool breakage detection devices are conventionally known. As a conventional device that detects breakage of a tool in real time while the tool is cutting a workpiece, the torque value (current value) of a spindle motor that rotates and drives the tool spindle
, A type in which the reference load of each part of the machine tool sampled during model machining is compared with a load sampled in subsequent continuous machining, and an acoustic emission signal generated from a cutting point is monitored by an AE sensor. There have already been proposed ones of the type that detect the thrust force of a bearing supporting the tool spindle with a pressure transducer.

[0003]

However, in the above-described conventional apparatus, the torque value (current value) of the spindle motor tends to fluctuate under the influence of disturbance, and it is difficult to determine whether the tool is broken. Further, it is difficult to automatically create information serving as a criterion for this determination according to processing conditions and the like, and creation of this criterion information requires prior model processing as in the conventional apparatus. The conventional equipment premised on model machining is suitable for use in dedicated machine tools with fixed machining conditions.However, tools used to attach to the main spindle, such as machining centers, are frequently changed, and workpiece materials and machining conditions Is indefinite, it is practically difficult to apply. In addition, the above-mentioned type is susceptible to disturbance as in the case of the type described above, and the type requires the provision of a special device for the bearing mechanism of the tool spindle. Therefore, there is a problem that versatility is poor, such as requiring prior model processing.

Accordingly, a main object of the present invention is to solve the above-mentioned problems of the conventional apparatus and to provide a tool abnormality detecting method and apparatus capable of detecting tool breakage and excessive wear in real time during machining. . Another object of the present invention is to provide a versatile tool abnormality detection method and apparatus that can be used in a machining environment where tools, machining conditions, work materials, and the like are undefined. Another object of the present invention is to provide a tool abnormality detection method and apparatus capable of determining an appropriate tool abnormality in response to a change in machining operation per unit time during the machining operation. Still another object of the present invention is to provide
It is an object of the present invention to provide a tool abnormality detection method and apparatus that can create determination criterion information for determining an abnormality such as tool breakage or excessive wear without requiring model processing.

[0005]

According to a first aspect of the present invention, there is provided a tool abnormality detecting method and apparatus for machining a workpiece by a tool according to a machining program such as an NC program. A step or means for setting a commanded momentum to be generated between the tool and the workpiece for each unit time based on machining condition data specified in the machining program, and a unit time during the machining. A step or means for detecting an actual momentum actually generated between the tool and the workpiece, and a step or means for determining the presence or absence of a tool abnormality based on the commanded momentum and the actual momentum. I do.

According to the present invention, the difference between the relative command momentum between the tool and the workpiece per unit time during the machining operation and the actual momentum is grasped as a parameter of the tool abnormality. More specifically, when the tool is broken or excessively worn, the machining resistance between the tool and the work increases, so that the delay of the actual momentum with respect to the commanded momentum is a delay exceeding that when the tool is normal, Therefore, based on the commanded momentum and the actual momentum, for example, the presence / absence of a tool abnormality is determined by comparing the delay amount with a preset threshold for determining normality / abnormality. In this case, the commanded momentum per unit time can be calculated as the momentum between the tool and the work to be executed at that time according to the machining program, so that the commanded momentum can be used as the criterion information at that time, and, for example, The change can be made immediately in response to a change in the processing conditions when shifting from one processing to the next processing. As a result, it is not necessary to determine the criterion information in advance by performing model processing or the like. The commanded momentum may be calculated for each unit time, or the commanded momentum for each unit time may be collectively calculated prior to the machining operation.

As will be described in detail in the embodiment, it has been confirmed by the inventor's experiments that the delay of the actual momentum with respect to the judgment reference information at the time of drill breakage is several tens times that of the normal case. The normal-abnormal threshold value can be set to a value that can be distinguished between a normal time and an abnormal time with a large margin, thereby realizing a tool abnormality determination that is hardly affected by disturbance. The command momentum and the unit time for specifying the actual momentum are preferably set as a time width of about several milliseconds to several tens of milliseconds. And it depends on the response characteristics of the servo system. In the case of a servo system having high response characteristics, the unit time can be set short to detect a tool abnormality with high sensitivity.However, in the case of a low response servo system, the delay of the actual momentum with respect to the command momentum is reduced when a tool abnormality occurs. Since the detection cannot be performed with high sensitivity, the unit time needs to be several tens of milliseconds or more.

It is desirable that both the commanded momentum and the actual momentum are momentums within the same unit time. However, even if the momentums are slightly deviated from each other as long as they do not hinder abnormality detection, there is no problem in practical use. Absent. This depends on the fact that the normal-abnormal threshold value can be set to a value that can be determined with a large margin between the normal state and the abnormal state, as described above.

According to the present invention, as set forth in claims 2 and 7, there is provided an abnormality detection method and apparatus suitable for use in thread cutting and drilling using a tap or a cutting tool. In this case, the commanded momentum and the actual momentum per unit time are set and detected as the rotation amount of the main shaft per unit time, respectively. By comparing the command rotation amount between the tool and the work with the actual rotation amount corresponding thereto, a tool abnormality can be detected by relatively simple processing. In other words, the present inventors have found that even within a relatively short unit time of, for example, about several tens of milliseconds, the difference between the commanded rotation amount and the actual rotation amount relative thereto is significantly different between a normal tool and an abnormal tool. Have been found through experiments, and based on this discovery, the idea of the present invention has been reached.

In the drilling, preferably, the command rotation amount per unit time, which is a judgment reference value, is determined by a rotation speed command of a tool spindle specified in a machining program. And calculating based on a sampling period set in advance to specify the unit time and a resolution of an encoder that detects a rotational angle position of the main shaft, and extracting an encoder output at the sampling period during an actual machining operation. Determine the actual rotation amount of the spindle per unit time, based on the command rotation amount and the actual rotation amount per unit time, for example, to determine whether the difference between these rotation amounts exceeds a preset threshold, Detects tool abnormalities. According to this configuration, the command rotation amount within a unit time of the spindle is set exclusively depending on the spindle rotation speed command in the machining program, so that the machining conditions are adapted to the drill attached to the spindle. A judgment reference value can be set, and a reliable tool abnormality judgment can be realized particularly in accordance with a drill to be used.

In the case of thread cutting using a tap or a cutting tool, preferably, a command cutting amount in which a tool and a work are to be moved per unit time in the spindle axis direction during the machining, as described in claims 4 and 9. In synchronization with the above, the command rotation amount that the main shaft should rotate every unit time is calculated as a determination reference value. For this calculation, based on the cutting speed data between the tool and the work specified in the machining program, the spindle rotation speed data, the screw pitch data to be machined, and the like, the spindle is set with respect to the tool cutting position set for each unit time. A known method is used in which the rotation position to be reached is interpolated under simultaneous two-axis control. By this calculation, the position where an arbitrary cutting point defined on the thread cutting tool reaches after the elapse of the unit time is defined as a group of a large number of interpolation points existing on the spiral locus. The command rotation amount per unit time can be obtained by obtaining an increment between two consecutive points in such an interpolation point group.

On the other hand, the actual rotation amount of the spindle per unit time is obtained by extracting the output of an encoder for detecting the rotation angle position of the spindle during an actual machining operation at a sampling period defining the unit time. The presence or absence of a tool abnormality is detected based on the command rotation amount and the actual rotation amount. According to this configuration, the command rotation amount that the spindle should rotate within the unit time is calculated as the determination reference value in synchronization with the tool cutting amount per unit time, so that the determination of the tool abnormality is simply performed by the spindle. It can be reliably executed by simple processing based on the command rotation amount and the actual rotation amount.

[0013] The detection of a tool abnormality in a threading operation using a tap or a threading tool can be more preferably realized by another method and apparatus defined in claims 5 and 10. In this case, the thread cutting start position, that is, the coordinates of the position where the synchronous control of the axial cutting and rotation of the spindle is started, is performed by reading the outputs of the encoder that detects the cutting motion and the encoder that detects the spindle rotation position. Is detected. Since the tap start position is specified in the machining program at the detection timing, the output can be read by reading the output of the spindle rotation detection encoder at the moment when the cutting axis reaches this position. The cutting-rotation ratio determined by the pitch of the screw to be processed is calculated based on the pitch of the screw to be processed, the amount of tool cut per unit time, and the amount of spindle rotation. The screw pitch is usually specified in the machining program, but the tool cutting amount and the spindle rotation amount are the tool-work cutting speed data, the spindle rotation speed data, the screw pitch data and the cutting depth specified in the processing program. It can be calculated based on data or the like. The cut-to-rotation ratio may be calculated for each unit time, or may be calculated in advance before executing the thread cutting.

Further, during the machining operation, the output of the encoder for detecting the cutting position and the output of the encoder for detecting the rotational position of the spindle are extracted at the sampling cycle of the unit time, and the actual cutting amount within the unit time is obtained. Nominal total rotation amount that the spindle should have actually rotated was calculated based on the cutting amount and the cutting-rotation ratio, and based on the nominal total rotation amount and the actual rotation amount of the main shaft, whether or not the threading tool was abnormal. Is detected. According to this configuration, the nominal total rotation amount and the actual total rotation amount of the spindle that should be rotated by the spindle with respect to the cutting movement amount of the spindle when performing a threading process at a target pitch are calculated for each unit time. Since the presence / absence of the threading tool abnormality is determined based on these two rotation amounts, in addition to being able to detect the abnormality of the threading tool itself, it is possible to machine a screw whose lead error is guaranteed within a predetermined value.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1 showing an example of a machine tool embodying the present invention, a column 12 moves in a direction perpendicular to the plane of the drawing along an X-axis guideway 11 on a bed 10 (hereinafter, referred to as a column).
This is referred to as left-right movement. )it can. Column 12 that moves left and right
Is provided on the vertical side surface thereof, and guides the saddle 14 along the Y-axis guide way 13 so as to be vertically movable. Saddle 14
Guides the spindle head 16 along a Z-axis guideway 15 provided on its vertical side surface so as to be able to move back and forth (in the horizontal direction in the figure). The spindle head 16 supports the spindle 17 rotatably about a horizontal axis, and a drill, tap, end mill, milling machine,
Various tools T such as cutting tools can be selectively attached.

The X-axis feeder comprises a servomotor 21 fixed to the bed 10 and a feed screw (not shown) which is screwed to the column 12. The Y-axis feeder includes a servomotor 22 fixed to the upper surface of the column 12 and a feed screw 23 screwed to the saddle 14. Z-axis feeder is saddle 14
And a feed screw 25 screw-engaged with the spindle head 16. A servo motor 26 that rotationally drives the spindle 17 is fixed to the spindle head 16. The servomotors 21, 22, and 24 are of a type capable of controlling the rotational position and speed thereof, and the servomotor 26 for driving the spindle is of a type capable of controlling the speed.

A rotary indexing table 28 is provided in front of the column 12 on the bed 10 so as to be rotatable around a vertical axis by an indexing mechanism (not shown). A work W to be processed on the table 28 is not shown. It can be attached by the jig. Thereby, the work W can be drilled by a drill attached to the tip of the spindle 17 by an automatic tool changer (not shown), and a screw can be formed on the inner surface of the prepared hole w1 using a tap or a cutting tool. Further, a screw can be formed with a cutting tool on the outer periphery of the cylindrical projection w2 projecting from the front of the work W.

FIG. 2 shows a control system for controlling the machine tool. The CNC device 30 mainly includes a central processing unit (hereinafter, referred to as a CPU) 31 and a memory 32, and executes various arithmetic processes under the control of a system program STM stored in a ROM of the memory 32. The RAM of the memory 32 stores a numerical control program (hereinafter, NC)
Program) NCP storage area, ON / OFF of various signals
A flag area FLG for storing OFF, an area for storing various parameters, data BM, Qn, and the like, and a working area WORK for executing arithmetic processing are provided. C
The PU 31 is connected to the input device 33 via the interface 35.
And a programmable logic controller (hereinafter, referred to as a PLC) 34 for sequence control, and various kinds of information are transmitted or exchanged between them.
The input device 33 includes various command switches 331, a numeric keypad 332 for data input, a display device 333, and the like.

The CPU 31 has an interface 36
Is connected to the driving device 37 via the
Are the X-axis control unit DUX and the Y-axis control unit DU
Y and Z axis control unit DUZ and C axis control unit DU
C and the corresponding servomotors 21, 22, 2
4 and 26, and receives the outputs of encoders 211, 221, 241 and 261 for detecting the rotational positions of these motors. Referring to FIG. 3, which is an explanatory diagram of functions executed by the CPU 31, the CPU 31
3 for storing the NC program NCP and various parameters input from the memory 32, and conversely, displaying the various information calculated or stored in the CNC 30 on the display device 33, and the data between the processing and the PLC 34. And signal exchange processing, NC execution processing 41, and further movement command processing 4
2 is executed under the control of the system program STM.

Since these processing functions executed by the CPU 31 are known as general functions possessed by a CNC device for controlling this type of machine tool, the processing related to the present invention will be briefly described below. When the NC execution process 41 is instructed, the CPU 31 sequentially reads, decodes, and executes a plurality of data blocks constituting the NC program NCP from the memory 32 one by one. When a block to be executed instructs a feed control for a movable element such as a column 12, a saddle 14, and a spindle head 16 that constitute a machine tool, the CPU 31 moves the movable element at a target position specified by the instruction at a specified speed. Is executed to drive.

The movement command processing 42 is executed according to the control routine shown in FIG. 4. First, it is determined whether or not the command is a feed control command (step 80). Are executed (step 81). When the feed control command is issued, it is determined whether the process is a point-to-point (PTP) control process or a contour control process (step 82). PT
In the case of the P control process, the CPU 31 sequentially calculates a passing point to be reached by the movable element every unit time, for example, every 10 milliseconds, in order to position the designated movable element from the current position to the target position, (Step 83), and thereafter, passing point data is sequentially read from the distribution data area PDA in response to an interrupt given at intervals of the unit time and output to the corresponding control axis of the drive unit 37. (Step 84).

The distribution data area PDA includes control axes,
In other words, it is divided for each of the X, Y, Z and C axes, and each of these divisions can store the passing points to be reached at every unit time until the control axis reaches the target position. It has become. The passing point for each unit time is N
It is calculated based on the target position data and the speed command specified in the C data. That is, when the travel distance is calculated based on the target position data and the required travel time is calculated based on the speed command, the coordinates of the divided position obtained by dividing the required travel time by the unit time, that is, the passing point is determined. be able to.

If it is not PTP control (step 82),
It is determined whether the contour control is to control two or more control axes simultaneously or the threading is to be performed (step 85). In the case of the contour control, the CPU 31 should reach every target time on the path to the target position based on the respective target position data and speed command data of the control axes so as to simultaneously reach the respective target positions. The passing point is obtained by a known interpolation operation function and stored in the distribution data area PDA (step 8).
6) In response to the interruption per unit time, these passing point data are output to the control unit of the designated control axis (step 84). Each control unit DUX, DUX, Duz
Controls the control axis to be positioned at the passing point designated every unit time. In the case of threading control,
As described later, a threading control process is executed (step 87).

In order to implement the tool abnormality detecting function according to the present invention, the CPU 31 is configured to execute a monitoring process 43 which cooperates with the above-described movement command process 42. Hereinafter, a routine for executing the monitoring process 43 will be described with reference to FIG.
This will be described with reference to the flowchart of FIG. The CPU 31
When the monitoring processing routine shown in FIG. 5 is executed, an operation is performed to detect a tool abnormality during drilling and threading using a tap or a cutting tool.

(1) Tool abnormality detection in drilling:
When the movement command processing 42 is executed for the NC data block for drilling, steps 83 and 84 in FIG.
Is executed, and a passing point at which the spindle head 14 is to be positioned to a target position at which the drill tip should reach is output to the Z-axis control unit DUZ every unit time (10 milliseconds). At the same time, the spindle speed command specified in the NC data is C
It is output to the axis control unit DUC, and the main shaft 17 is rotated at a rotation speed according to the speed command. Thus, while the spindle 17 is rotated at the commanded rotation speed, the spindle head 16 is moved so as to sequentially track the passing points read from the distribution data area PDA per unit time, and the drill T
Is cut into the work W and a hole w1 is formed in the work W.

The monitoring processing routine shown in FIG. 5 is executed at a unit time interval of, for example, every 10 milliseconds when drilling or threading is started. When it is determined that the drilling is to be performed (step 51), a criterion value B for determining a tool abnormality suitable for the drilling condition is calculated by the following equation (1). B = S * N / 60/1000 * Δt (1) where Δt is a sampling period (unit: millisecond),
S indicates a rotation speed command of the main shaft expressed by the number of rotations per minute, and N indicates a resolution defined by the number of pulses per rotation of the encoder. This determination reference value B
When the spindle 17 is rotated at the command speed S, the spindle 17 is rotated during each interval of the sampling cycle as a unit time.
Amount of rotation that should be rotated (number of pulses corresponding to rotation angle)
The calculated reference value B is stored in the reference value storage area BM of the memory 32 (step 52).

Next, the actual rotation amount ΔQ, which is the actual movement amount of the spindle drive servomotor 26 within the unit time Δt, is obtained by taking in the feedback position Qn from the encoder 261 (step 53), and the feedback value Q
It is calculated by calculating the difference from n ₋₁ (step 55). The feedback position Qn is stored in the memory 32 to calculate the actual rotation amount ΔQ after the next unit time (step 56). The absolute value of the difference between the determination reference value B, which is the commanded momentum, and the actual momentum ΔQ is stored in the memory 32.
The breakage or excessive wear of the drill is detected based on whether or not the threshold value E stored in step (b) is exceeded (step 57). When a tool abnormality is detected, the display device 333 of the input device 33 is notified of the tool abnormality (step 58). In this embodiment, when the operator does not instruct the continuation of the operation from the input device 33 (step 59), the drilling operation is stopped (step 60). Then, when the operator inputs a command to retreat the spindle head 16 after checking the state of the tool abnormality (step 61), the spindle head 16 is retreated (step 62), but when the operator does not input the retraction command. After a predetermined time, this control routine ends.

If no abnormality is determined in step 57,
Alternatively, this control routine is terminated when the operator gives an operation continuation command so as to ignore the abnormality as a minor abnormality. In this way, during drilling, the present control routine is executed at intervals of the unit time Δt, and the presence or absence of a drill abnormality is detected. FIG. 6 shows the relationship between the actual cutting speed calculated from the output of the encoder 241 of the Z-axis servo motor 24 sampled per unit time (10 milliseconds) in the drilling process and the encoder of the C-axis servo motor 26. 261 is a graph showing fluctuations in the spindle rotation speed calculated from the output of the main shaft 261. As understood from the enlarged portion of this graph, it was confirmed that during drilling, when there was no abnormality in the drill and the main shaft 17 was rotating normally, the speed fluctuation of the output of the encoder 261 was within about 4 pulses. . However, the rotation of the spindle 17 in the unit time immediately before the breakage of the drill is reduced by about 100 pulses from the normal rotation speed due to an increase in the load on the spindle 17, and at the moment when the drill breaks, the spindle 17 rotates. It was confirmed that the load on the motor rapidly decreased, and as a reaction, the rotational speed increased by about 100 pulses from the normal rotation speed.

That is, when the drill breaks, the spindle rotation speed per unit time fluctuates about 50 times that of a normal state, and by detecting this fluctuation, the breakage of the drill is detected. Similarly, although not shown in FIG. 6, when the drill is excessively worn, the cutting resistance to the spindle 17 increases, and the spindle rotation speed within a unit time is significantly reduced as compared with the normal rotation speed. In order to detect breakage and excessive wear of the drill, the unit time can be set within a range of several milliseconds to 100 milliseconds so as to reliably capture such fluctuations in the spindle rotation speed.

(2) Detection of Tool Abnormality in Thread Cutting: When tapping is instructed, the CNC 31 moves to FIG.
In step 87 of the movement command processing routine shown in
As shown in FIG. 7, a pass point Zn of the spindle head 16 along the Z axis is calculated every 10 milliseconds to a target position, and an arbitrary point on the outer periphery of the tap corresponds to the pass point Zn of the spindle head 16. The angle position Pn to be taken is calculated as an absolute angle from the starting point of the threading operation. This calculation is performed by a known simultaneous two-axis interpolation processing function. The passing point Zn of the spindle head 16 calculated in this way is output to the Z-axis control unit DUZ every 10 milliseconds. On the other hand, the output of the encoder 261 of the spindle drive servomotor 26 is taken in every 10 milliseconds and converted into an absolute angle from the starting point of the threading operation, and it is compared whether or not this absolute angle matches the commanded absolute angle. Based on the comparison result, the C-axis control unit DU is controlled so that the arbitrary point on the tap passes through the absolute angle position corresponding to each passing point (interpolation point) of the spindle head 16.
The speed command value output to C is controlled. As a result, many interpolation points along the Z-axis of the tap from the tap operation start point correspond to the absolute rotational positions of the tap, and a correct screw hole having the specified pitch in the workpiece W is formed.

While the tapping is performed as described above,
The control routine of FIG. 5 is executed every 10 milliseconds. Therefore, when it is determined that the tapping is being performed (step 50), steps 65 to 67 are performed, and the determination reference value B in the tapping is calculated in conformity with the processing condition in the tapping. In this case, the absolute rotation angle Pn calculated at that time is taken in (step 65), and the previous absolute rotation angle Pn stored in the memory 32 (FIG. 5).
In this case, it is shown as Pn _-1 for explanation. ) Is calculated (step 66), and the criterion storage area B of the memory 32 is determined.
M. Further, the absolute rotation angle Pn taken in step 65 is stored in the memory 32 (step 6).
7). Therefore, when steps 53 to 57 are subsequently performed in the same manner as in the case of drilling described above, the presence or absence of a tap abnormality is detected (step 57).

FIG. 8 shows a variation in the cutting speed based on the output of the encoder 241 of the Z-axis servomotor 24 sampled every unit time (10 milliseconds) and the main spindle based on the output of the encoder 261 of the C-axis servomotor 26 in tapping. 6 is a graph showing a change in rotation speed. As indicated by the broken line in the enlarged portion of this graph, the rotation speed of the spindle per unit time is slightly lower than the rotation speed indicated by the solid line at normal time due to an increase in the load on the spindle 17 immediately before breakage of the tap, At the moment when the drill breaks, the load on the main shaft 17 is sharply reduced, and as a reaction, the rotation speed is significantly increased from the normal rotation speed. The breakage of the tap is detected by detecting the fluctuation of the rotation speed of the spindle within this unit time.

(Second Embodiment) FIG. 9 shows another embodiment of a monitoring processing routine for executing a tool abnormality detecting function in tapping, for example, at unit time intervals such as 10 milliseconds. Be executed. When it is determined that tapping is being performed (step 70), tap operation start positions Pz ₀ and Pc ₀ of the spindle head 16 and the tool spindle 17 as first position data are fetched (step 71). Next, Z according to the pitch of the screw to be machined
Thread pitch information R indicating the ratio between the cut along the axis and the rotation of the main shaft 17 is fetched (step 72). The thread pitch information R is calculated by the following equation (2) prior to the start of the tap operation in the NC execution process 41 shown in FIG. 3, and is stored in the memory 32 before the start of tapping. R = PH * ΔC / ΔZ (2) Here, PH indicates the pitch (unit: mm) of the screw to be processed specified in the NC data, and ΔZ indicates the Z-axis feed screw 25. Represents the feed amount (unit: mm) of the spindle head 16 when the output is rotated by an angle corresponding to one output pulse of the encoder 241, and ΔC is the output 1 of the encoder 261.
The rotation angle of the main shaft 17 corresponding to a pulse is shown.

Next, cut position Qz _n and rotational position Qc _n taps of the second position data is obtained by reading the output of the encoder 241 and 261, respectively (step 73), against further movement in the Z-axis Spindle 1
The error G between the nominal total rotation amount (angle) that should be rotated in the normal state and the actual total rotation amount (angle) actually rotated is calculated using the following equation (3) (step 74). _{G = R * (Qz n -Pz} 0) - (Qc n -Pc 0) ····· (3) In this step 74, the cut position Qz at that time from the tap operation start position Pz ₀ along the Z axis The actual amount of movement up to _n is obtained, and this amount of movement is multiplied by the screw pitch information R to obtain a nominal total amount of rotation (angle) at which the spindle 17 should rotate corresponding to the actual amount of movement. The actual total rotation amount (angle) of the main shaft 17 actually rotated from the tap operation start position Pc ₀ to the current angular position Qcn is obtained, and the actual total rotation amount is subtracted from the nominal total rotation amount to obtain the main shaft 17. Is calculated.

FIG. 10 is a graph showing the relationship between the fluctuation of the rotation speed of the main shaft 17 and the fluctuation of the rotation error G in the second embodiment. The error G when the tap is normal is indicated by a broken line. As shown by the solid line, the error G when the tap is broken is 10 times the error G in the normal state.
Since the value is twice or more, by comparing the absolute value of the error G with the threshold value E, the presence or absence of a tap abnormality is reliably detected (step 75). Note that subsequent processing steps 581 to 621 in the routine of FIG. 9 correspond to steps 58 to 62 of the routine of FIG. 5, respectively, and thus detailed description will be omitted.

(Other Embodiments) In each of the above-described embodiments, as a preferred embodiment, fluctuations in the rotation angle of the main shaft 17 during drilling or tapping are detected for each unit time to perform drilling. According to the present invention, the feed position of the spindle head 16 in the Z-axis direction when the drill or the tap is abnormal is detected for each unit time, and the abnormality of these tools is detected. Can also be detected. From the viewpoint of detection sensitivity, the spindle head 1 including the spindle 17 has a larger mass than the spindle 17.
Since the mass of the system 6 is much larger, the above-described embodiment in which the fluctuation of the rotation angle of the spindle 17 is detected is more preferable than the detection of the fluctuation of the feed position of the spindle head 16.

The present invention is not limited to the detection of tool abnormalities during drilling and tapping, and these tools are mounted on the workpiece W with the end mill or milling machine mounted on the spindle 17 in the Z-axis direction and the X-axis direction. The present invention is also applicable to the case of sending in the direction or the Y-axis direction. In this case as well, a tool abnormality may be detected by detecting a change in the amount of rotation of the spindle 17 per unit time, or a change in the amount of movement per unit time in the Z-axis, X-axis, and Y-axis may be detected. It can also be implemented in a form that detects more than a tool. Further, in the above-described embodiment, the tool abnormality detection in the thread cutting using the tap has been described. However, the tool abnormality detection in the thread cutting in the present invention is performed in a state where the tool bit is attached to the main shaft 17 and rotated. The present invention is also applicable to the case where the outer periphery of the cylindrical projection w2 of the work W or the inner surface of the prepared hole having a relatively large diameter is threaded.

[0038]

As described above in detail, according to the first and sixth aspects of the present invention, the difference between the relative commanded momentum between the tool and the workpiece and the actual momentum during the cutting process is detected for each unit time. However, since the tool abnormality is detected based on this difference, it is not affected by disturbance, and the commanded momentum is calculated based on the machining program. That is, the data becomes the data for calculating the criterion information. Therefore, the criterion information can be automatically adapted in accordance with the change in the machining operation, and the effect of realizing the versatile tool abnormality detection can be obtained.

According to the second and seventh aspects of the present invention, the tool abnormality is determined by comparing the commanded rotation amount of the main spindle with the actual rotation amount for each unit time. This has the effect of reliably detecting breakage or excessive wear of a tool in drilling or threading, which is relatively small and for a short time. Preferably, as defined in claims 3 and 8, a command rotation amount per unit time of a spindle as a determination reference is specified by a spindle speed command specified in a machining program and the unit time. A unit is calculated based on a sampling period that is set in advance and a resolution that is set in advance for an encoder that detects the rotational angle position of the spindle, and extracts the encoder output at the sampling period during an actual machining operation. Since the actual rotation amount of the spindle per time is determined, a reliable tool abnormality detection is realized in the same manner as in the third and eighth aspects, and a special mechanism for detecting a tool abnormality is added. Instead, tool abnormality detection suitable for drilling and thread cutting is realized using a conventional hardware configuration such as a machining center.

More preferably, in order to machine a screw having a desired pitch, a tool and a workpiece are synchronized with a command cutting amount to be moved per unit time as defined in claims 4 and 9. Since the command rotation amount that the main spindle should rotate per unit time is used as a judgment reference value, and the judgment reference value is compared with the actual rotation amount of the main spindle extracted per unit time, a tool abnormality is detected. The tool abnormality can be judged when the actual rotation amount of the tool per unit time, which is constantly monitored, has a large difference from that in the normal state, so that it is possible to realize the reliable tool abnormality detection and the normal / abnormality of the machined screw itself. The effect that processing can be determined in parallel can be achieved.

More preferably, the screw pitch specified in the machining program for screw machining, the cut amount between the spindle and the work, and the rotation amount of the spindle are defined as defined in claims 5 and 10. Is calculated in advance or calculated per unit time, and the screw processing start position is extracted, and during the subsequent processing operation, the cutting position and rotation position of the main spindle are sampled at the sampling period of the unit time. Is extracted, and the spindle is adjusted to the unit based on the actual total cutting amount and the cutting-rotation ratio, at which the spindle is cut into the work from the screw machining start position by the unit time until the unit time elapses. Calculate the nominal total rotation amount that the spindle should have rotated before the time elapses, and start the screw machining by the time the nominal total rotation amount and the unit time elapse. The rotation error is calculated based on the actual total rotation amount of the main shaft actually rotated from the position, and a tool abnormality in screw machining is detected based on this error. In addition to being able to detect abnormalities in the thread cutting tool itself, it is possible to perform thread processing in which a lead error is guaranteed within a predetermined value.

[0042]

[Brief description of the drawings]

FIG. 1 is a side view showing an example of a machine tool that implements a tool abnormality detection method and device of the present invention.

FIG. 2 is a block diagram showing a control system of the machine tool.

FIG. 3 is a functional block diagram for explaining processing executed by a CPU shown in FIG. 2;

FIG. 4 is a flowchart showing an outline of a movement command processing routine executed by the CPU in the movement command processing shown in FIG. 3;

5 is a flowchart showing details of a monitoring processing routine executed by the CPU in the monitoring processing shown in FIG. 3 for detecting a tool abnormality.

FIG. 6 is a graph showing a change in the rotation speed of the spindle per unit time in relation to a change in the cutting speed per unit time in drilling.

FIG. 7 is a graph showing a relationship between a change in a cutting position to be generated between a tool and a work in a tapping process and a change in a rotational position to be taken by a main spindle in association with each unit time.

FIG. 8 is a graph showing a change in the rotational speed of the spindle per unit time in relation to a change in the cutting speed per unit time in tapping.

9 is a flowchart showing another embodiment of a part relating to a tool abnormality detection function at the time of thread cutting in the monitoring routine of FIG. 5;

FIG. 10 is a graph showing an error between the nominal total rotation amount and the actual total rotation amount of the spindle per unit time in tapping, in relation to a change in the rotation speed of the spindle.

[Explanation of symbols]

10: bed, 12: column, 14: saddle, 1
6: spindle head, 17: spindle, T: tool, W: work, 30: CNC device, 31: CPU, 32: memory, 37: drive device, 21, 22, 24, 26: X
Axis, Y axis, Z axis, C axis servo motor, 211, 22
1, 241, 261: X-axis, Y-axis, Z-axis, C-axis encoders.

Claims (10)

[Claims] 1. A machine tool for cutting a workpiece by the tool by rotating the spindle and a workpiece relative to each other in accordance with a set machining program while rotating a spindle attached to a tip of the tool. A setting step of setting a commanded momentum to be generated per unit time between the tool and the work during machining of the work based on machining condition data specified in the machining program; and A detection step of detecting an actual momentum actually generated between the tool and the workpiece within this unit time every time the unit time elapses, and a command momentum and an actual momentum related to each time the unit time elapses. A determination step of determining the presence or absence of a tool abnormality based on the tool abnormality detection method. 2. The tool abnormality detection method according to claim 1, wherein in the setting step, a command rotation amount at which the spindle is to be rotated per unit time is set as the command movement amount, and the actual rotation is set in the detection step. The amount of rotation that the main spindle has actually rotated within the unit time corresponding to the amount of momentum is detected, and in the determination step, the presence / absence of a tool abnormality is determined by comparing the command rotation amount with the actual rotation amount corresponding thereto. A tool abnormality detection method characterized in that: 3. The tool abnormality detection method according to claim 2, wherein the tool is a drill for drilling a workpiece, and in the setting step, the command rotation amount is set for the main spindle specified in the machining program. A rotation speed command, a sampling period set in advance to specify the unit time, and a resolution of an encoder that detects a rotation angle position of the main shaft, are calculated based on the rotation speed command. A tool abnormality detection method, wherein an output of the encoder is extracted at a sampling cycle to determine an actual rotation amount of the spindle per unit time. 4. The tool abnormality detecting method according to claim 2, wherein the tool is a threading tool for threading on the work, and in the setting step, the main shaft is in an axial direction relative to the work. Calculate a command rotation amount that the spindle should rotate per unit time in synchronization with a command cutting amount to be moved per unit time as a determination reference value, and in the detecting step, determine a rotation angle position of the spindle. A tool abnormality detection method, wherein an actual rotation amount of the main spindle is obtained by extracting at a sampling period related to a unit time. 5. A screw can be formed on the workpiece by synchronously controlling the rotation of the spindle with a threading tool attached to the tip thereof and the relative cutting of the spindle and the workpiece in the axial direction of the spindle according to a machining program. In the machine tool, the rotation position of the spindle and the cutting position in the direction of the spindle axis for starting threading performed in a state where the rotation of the spindle and the cutting feed are synchronously controlled are respectively referred to as first rotation position data and first rotation position data. (1) a starting position extracting step for extracting as cutting position data; a cutting-rotation ratio determining step for determining a cutting-rotation ratio which is a ratio between the rotation of the main shaft and the cutting feed required for forming the screw; The rotational position of the spindle and the cut position are extracted as second rotational position data and second cut position data, respectively, for each unit time. A current position extracting step, which is executed for each unit time, and calculates an actual cutting amount at that time based on the first and second cutting position data, based on the actual cutting amount and the cutting-rotation ratio. Calculating a nominal total rotation amount of the main shaft to be rotated from the first rotation position to the second rotation position;
And calculating the actual total rotation amount of the main shaft actually rotated from the first rotation position to the second rotation position based on the second rotation position data, and then calculating based on the actual total rotation amount and the nominal total rotation amount. Determining the presence or absence of an abnormality in the threading tool. 6. A machine tool for cutting a workpiece by the tool by rotating the spindle and a workpiece relative to each other in accordance with a preset machining program while rotating a spindle attached to a tip of the tool. Command momentum calculation means for calculating a command momentum to be executed between the tool and the workpiece for each unit time during the machining operation based on the information specified in the processing program; and Actual momentum detecting means for detecting the actual momentum executed between each unit time, and determining means for calculating an error between the commanded momentum and the actual momentum to determine the presence or absence of a tool abnormality. Tool abnormality detection device characterized by the above-mentioned. 7. The tool abnormality detecting device according to claim 6, wherein the command momentum calculating means calculates a command rotation amount that the main spindle should rotate per unit time as the command momentum. Sampling means for extracting the rotational position of the spindle in the unit time period, memory for storing the extracted rotational position, and rotational position previously extracted and stored in the memory; Means for calculating an actual rotation amount of the spindle within the unit time based on the determined rotation position. 8. The tool abnormality detection device according to claim 7, wherein a rotation speed command of the spindle specified in the machining program in drilling using a drill as the tool and the unit time are specified in advance. A tool, wherein the commanded momentum calculating means calculates the commanded rotation amount serving as a determination reference value based on a set sampling period and a resolution of an encoder for detecting a rotational position of the spindle. Anomaly detection device. 9. The tool notch detecting device according to claim 7, wherein a command cutting in which the threading tool as the tool and the work relatively move in the axial direction of the spindle every unit time during machining. A tool abnormality detecting device, wherein the command momentum calculating means is configured to calculate, as a determination reference value, a command rotation amount by which the spindle is to be rotated per unit time in synchronization with the amount. 10. A screw can be formed on the workpiece by synchronously controlling the rotation of the spindle with the threading tool attached to the tip thereof and the relative cutting of the spindle and the workpiece in the axial direction of the spindle according to a machining program. In the machine tool, the rotation position of the spindle and the cutting position in the direction of the spindle axis for starting threading performed in a state where the rotation of the spindle and the cutting feed are synchronously controlled are respectively referred to as first rotation position data and first rotation position data. (1) a starting position extracting means for extracting as cutting position data; a cutting-rotation ratio determining means for determining a cutting-rotation ratio which is a ratio of a rotation of the main shaft and a cutting feed required for forming the screw; Presently extracting the rotation position of the spindle and the cutting position for each unit time as second rotation position data and second cutting position data, respectively A position extracting means for calculating an actual cutting amount at that time based on the first and second cutting position data executed at each unit time, and calculating a first cutting amount based on the actual cutting amount and the cutting-rotation ratio; A nominal total amount of rotation of the main shaft rotated from a rotational position to the second rotational position is calculated, and the main shaft is rotated from the first rotational position to the second rotational position based on the first and second rotational position data. Determining the actual total rotation amount actually rotated, and determining whether or not the threading tool is abnormal based on the actual total rotation amount and the nominal total rotation amount. Tool error detection method.