JP3294414B2 - Tool life detection method for machine tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tool life detecting method for a machine tool applied to an NC machine tool or the like.

[0002]

2. Description of the Related Art Conventionally, there have been the following two methods for detecting the life of a tool in a machine tool. In each case, it is inferred from the drive current of a spindle motor that rotates a spindle that drives a workpiece or a tool. The first is to set in advance a threshold value of what percentage increase in the rated current as a threshold value. Is determined as the end of the tool life. Secondly, the drive current of the spindle motor is continuously stored from the beginning to the end of machining, and tolerance data obtained by adding a certain percentage to the drive current is created, and there is a portion exceeding the tolerance data during the same machining. And that the tool life has come.

[0003]

However, in the first method, the driving current of the spindle motor is controlled by starting, stopping, and shifting the spindle motor, or by changing the machining conditions such as the material, shape, and presence of chips. It is difficult to respond accurately with a uniform threshold value. Also, the threshold value in the first method cannot be changed during processing. For this reason, there is a drawback that the threshold value must be set very high and accurate detection cannot be performed.

Also, the second method has a limitation that the actual processing must be performed under the same conditions as the test processing serving as the basis of the permissible data and cannot be changed from now. However, in actual machining, the feed rate,
It is often the case that machining conditions such as tool type and spindle speed are found to be better than those in test machining, and they have to be changed in terms of efficiency and precision. .

[0005] In any of the above methods, when the threshold value or the permissible data is exceeded, it is immediately determined that the tool life has expired, and this point is not practical.
Since the tool life depends on how much the allowable value has been exceeded and the accumulated time, accurate detection alone cannot be performed.

The present invention is intended to solve such a problem. In short, the present invention captures only the drive current of a spindle motor which is determined to be a load on a tool, and calculates the excess current and excess exceeding a predetermined value. The product of time is used as a tool life determining factor. And the operation that makes this possible is N
If it is a C machine tool, it can be changed by operating a program.

On the other hand, some machine tools feed a workpiece or a tool by an independent feed motor. In such a case, the tool life can be detected by monitoring the drive current of the feed motor. Therefore, the present invention is such that the tool life is detected even by the drive current of the feed motor in such a machine tool. In particular, since the output of the feed motor is consumed only for feeding the workpiece or the tool, the drive current directly corresponds to the load applied to the tool, and highly accurate detection is possible.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention relates to a method for detecting the life of a tool in a machine tool, comprising the steps of : When the change rate is within the predetermined change rate, the range is adopted, and the excess amount exceeding the preset threshold value is integrated with respect to the excess time, and when the integrated value exceeds the predetermined allowable value. Tool life detection method for machine tools characterized by issuing an alarm when the tool life has expired
It provides the law .

The present invention also relates to a method for detecting a tool life in a machine tool provided with a feed motor for feeding a workpiece or a tool, wherein the drive current of the feed motor is controlled by the feed rate change rate of the workpiece or the tool. When the change rate is within the predetermined change rate, the range is adopted, and the excess amount exceeding the preset threshold value is integrated with respect to the excess time, and the tool life is determined when the integrated value exceeds the predetermined allowable value. It also provides a tool life detecting method for a machine tool, which is characterized in that it has arrived and issues an alarm.

[0010]

By taking the above measures, the drive current of the spindle motor or the feed motor, which is determined to be the load on the tool, exceeds the excess amount exceeding the preset threshold value, which is determined to be the appropriate load of the tool, for an excess time. The tool life is determined when the integrated value exceeds a predetermined allowable value. Therefore, the determination is very accurate. .

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, the tool life is determined from the drive current of the spindle motor. FIG. 1 is a flowchart showing the operation procedure of the system when the present invention is applied to an NC machine tool. In the present invention, the drive current output from the spindle motor is read by the control device (normally detected as a digital value). At this time, a threshold value at which the drive current is determined to be an appropriate load for the tool is set in advance. The threshold value is sequentially set in the program as described later by indicating what percentage of the rated current of the spindle motor.

Then, the excess amount and the excess time are detected in a range where the drive current exceeds the threshold value, and the product thereof is obtained as an integrated value. In the present embodiment, this processing is performed by digital processing using a pulse current. However, the excess amount is detected by the size of the pulse, and the excess amount is added for each pulse. At this time, an allowable value that is a limit of the tool life is predetermined as a pulse calculation value, and when the integrated value exceeds the allowable value, it is determined that the tool life is reached. This permissible value is easily determined by experience, and a method of inputting the value to the control device using a numeric key or the like is adopted.

Next, it is determined whether or not the drive current has exceeded a threshold value. As described above, the drive current abnormally increases when the spindle motor starts, stops, shifts, and the like. FIG.
Is a characteristic diagram showing the relationship between the drive current and time. As can be seen from this figure, the drive current greatly exceeds the rating when the spindle motor starts, stops, or shifts. Therefore,
If the drive current is taken in such a case, the tool life is erroneously determined, so the ranges a to d corresponding to these cases are excluded.

The determination as to whether or not to take in the drive current is made based on the rate of change in the number of revolutions. Since the rate of change in the number of revolutions in the case of normal machining is objectively and technically determined, it is determined appropriately, and only when the actual rate of change in the number of revolutions is within this range is adopted.
Otherwise, take a method that is not adopted as invalid. In this case, the rotation speed command change rate is determined by comparing the currently specified rotation speed command of the main shaft with the previous rotation speed command.

When the drive current exceeds the threshold value, the excess amount is added for each pulse. FIG. 3 is an explanatory diagram showing this, but if a sampling pulse of a constant frequency is supplied to the arithmetic circuit of the control device and this is connected to the drive current by an AND circuit, only the excess portion can be taken out. Then, if the threshold value of this part is subtracted from the drive current, the excess amount can be obtained as pulse operation values P _{1 to} P _n having a large value, and these are sequentially added for each pulse (P ₁ + P ₂ + ‥ + P _n ). Alternatively, a method of directly subtracting the threshold value from the drive current every minute time and adding only a positive value may be adopted.

If the integrated value obtained by adding the excess amount for each pulse exceeds an allowable value, an alarm is issued at that point. By the way, in this case, it is possible to appropriately select, with a switch or the like, whether to take in the integrated value, a cumulative type in which accumulation is performed until an allowable value is exceeded, or a non-cumulative type in which settlement is performed at an appropriate stage such as for each machining operation. It has become. When the accumulation type is selected, the numerical values are stored and accumulated sequentially even when the power of the control device is turned off. When the non-accumulation type is selected, the account is settled (reset) when the stage comes. .

When the alarm is issued, it means that the tool life has expired, so the operator performs appropriate post-life processing such as stopping the machine and replacing the tool. (Also reset the alarm). still,
The alarm may include turning on a warning lamp or sounding a buzzer. In some cases, the machine may be stopped by moving the tool away from the workpiece. Such an operation is effective when the tool is broken.

FIG. 4 is an explanatory view showing the relationship between a workpiece and a tool in an NC lathe. A case will be described in which the tool life detection system is incorporated into a program to carry out machining from 1) to 3). The program in this case is created as follows, for example. 1) Processing B060080 G1 Z-20. F0.4 2) Processing B060070 G1 X80. F0.3 3) Processing B060080 G1 Z-40. F0.4

In the above description, the B code is the setting of the threshold value. For example, 1) “B060080” of the processing is NO0
This means that the threshold value of the display counter of No. 6 was set to 80% of the rated current. As described above, the threshold value can be set in a plurality of frames (display counters), and the integrated value and the permissible value can be obtained for each frame. Therefore,
What is necessary is just to make the classification of a workpiece or a tool correspond to this frame. Further, the threshold value can be set to a different value for each processing block.

On the other hand, the display counter has the following structure, for example.

In the above description, the allowable value of 150 in the display counter of NO06 means that the integrated value of the tool used in this display counter is allowable up to 150 (this numerical value can be appropriately changed. As described above, the display of the integrated value means that 100 pulses have been measured so far (regardless of whether the type is cumulative or non-cumulative). When this integrated value exceeds the allowable value, an alarm is issued. In this embodiment, the display counter is set to NO06-
That is, a total of 15 pieces are provided up to NO20.

Next, a case where the tool life is determined from the drive current of the feed motor will be described. Also in this case, when the drive current is greatly increased, such as when starting or changing the feed rate, the time is excluded from the adopted range. Therefore, only when the change rate of the feed amount command of the workpiece or the tool is within the predetermined change rate is set as the adoption range, and then, as in the case of the spindle motor, the integrated value exceeding the threshold value becomes the allowable value. It is determined that the time when it has reached is when the tool life has expired. In the case of feed speed,
Although there is a rapid traverse without using a tool, the rate of change of the feed amount at this time far exceeds the normal rate of change of the feed amount, and is naturally included in the exclusion range described above.

Although the embodiments of the present invention have been described above, the above description literally relates to the embodiments, and the present invention is not construed as being limited to only such specific examples. For example, the processing for obtaining the integrated value is not limited to the digital processing using the pulse current.
One that performs analog processing is also conceivable. FIG. 5 is an explanatory diagram in that case. The point is that it is only necessary to find the area (S _n ) of the range in which the drive current detected as an analog value exceeds the threshold value. One that processes with an integration circuit that integrates with time is also conceivable.

The present system is not applied only to NC machine tools. By assembling the minimum control device that performs the functions described above, it can be easily applied to general-purpose machine tools. In addition, although not enumerated one by one, it is natural that the present invention is carried out in various modified forms, and all such embodiments fall within the scope of the present invention unless departing from the gist of the present invention. It goes without saying that it is included in.

[0025]

As is clear from the above description, the present invention takes in only the drive current of the spindle motor or the feed motor which is determined to be a load on the tool, and determines that the excess current exceeds a predetermined value. Since it is determined that the tool life has expired based on the product of the excess time, the determination is very accurate. In addition, the operation to do this can be easily performed only by changing the program in the case of the NC machine tool.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating a relationship between a drive current of a motor and time.

FIG. 3 is an explanatory diagram for obtaining an integrated value.

FIG. 4 is an explanatory diagram showing a relationship between a workpiece and a tool in an NC lathe.

FIG. 5 is an explanatory diagram of another example for obtaining an integrated value.

[Explanation of symbols]

Claims (4)

(57) [Claims] 1. A method for detecting a tool life in a machine tool.
In law, the driving current of the spindle motor for driving the spindle,
When the rotation speed change rate of the main shaft is within the predetermined change rate, the adopted range is set, and the excess amount exceeding the preset threshold value is integrated with respect to the excess time, and the integrated value is set to the predetermined allowable value. A tool life detecting method for a machine tool, wherein an alarm is issued when it is determined that the tool life has expired. 2. A method for detecting tool life in a machine tool having a separate feed motor for feeding a workpiece or a tool, the drive current of the feed motor being controlled by a change in the feed amount of the workpiece or the tool. When the rate is within a predetermined rate of change, the range is adopted, and the excess amount exceeding the preset threshold value is added to the excess time, and the tool is set when the integrated value exceeds the predetermined allowable value. Tool life detection method for machine tools characterized by issuing an alarm when life is reached
Law . 3. The machine tool according to claim 1, wherein the excess amount is detected by a magnitude of a pulse transmitted at a constant frequency, and the detected value is added for each pulse to obtain an integrated value. Tool life detection method . 4. A threshold the tool life detection method in claim 1 or of the machine tool, characterized in that those that can be entered in the NC program.