JP3300604B2 - Tool damage detection method and device - Google Patents

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 detecting breakage of a tool mounted on an NC machine tool, and more particularly to a method and an apparatus for detecting breakage of a small-diameter drill or tap by a load monitor. Things.

[0002]

2. Description of the Related Art An NC machine tool is provided with a load monitor. The load monitor detects a load on the motor based on a current value flowing through the motor and the like, and detects a processing reaction force of the workpiece. For example, in the case of a lathe, the processing reaction force of the work can be detected by detecting the loads of the spindle motor that drives the work to rotate and the feed motor that moves the tool.

[0003] When drilling with a lathe, a tool rotation unit is attached to a tool post, and the tool post is moved while rotating the tool. At this time, the load monitor monitors the processing load by detecting the load of the tool feed motor.

[0004] When a tool is damaged during machining, the damage can be detected by a load monitor. That is,
An abnormal load acts at the moment when the tool breaks, and this is reflected in the load of the motor. Therefore, the damage of the tool can be known from the detected value of the load monitor. Generally, when the load monitor detects an instantaneous load change exceeding a set value, it is determined that the tool is broken, and the machine is rapidly stopped. This is because if the machining is continued with the broken tool, the work or the machine is seriously damaged, especially in the case of drilling.

[0005]

However, when the tool is a thin drill or tap having a diameter of several mm or less, the load fluctuation caused when the tool is broken is very small, and is caused by acceleration / deceleration of the motor, entanglement of chips, and the like. It cannot be distinguished from load fluctuations, and cannot be accurately detected by the method described above.

FIG. 4 shows an example of an output signal of a load monitor when a tool breaks during machining by a drill having a diameter of 1 mm. The breakage (first time) of the tool occurs at a point indicated by A in FIG. Since the machining with the broken tool is continued, the broken portion of the tool comes into contact with the workpiece at the time point B, and the machining load fluctuates rapidly. As can be seen from the figure,
The load fluctuation detected when the tool breaks for the first time is very small.If such a small fluctuation is detected and the machine is stopped, the machine will be accelerated or decelerated due to disturbance without any problem. Stopping often occurs, which adversely affects the workpieces and tools.

According to the present invention, it is possible to reliably detect a minute load fluctuation when a small-diameter drill or the like breaks using a load monitor conventionally used for detecting a processing load of an NC machine tool. The task is to obtain technical means that can be used.

[0008]

According to the present invention, there is provided a method for detecting a tool breakage in an NC machine tool, comprising the steps of:
And a load monitor 16 for detecting the load value and comparing the detected value of the load monitor with a preset value.
In the method for detecting a tool breakage of a machine tool, a position deviation signal c which is a difference signal between a position command a and a position feedback signal b given to a servo control device 7 which controls the tool feed motor 5 is monitored and set in advance. When detecting a change corresponding to a change in the position deviation signal c generated at the time of tool breakage,
It is characterized in that a load signal e to be given to the load monitor 16 is amplified based on the detected fluctuation.

A tool breakage detecting device for an NC machine tool according to the present invention includes a load monitor 16 for detecting a load on a tool feed motor 5 of a machine tool, and a servo control device 7 for controlling the tool feed motor 5. An NC device 8 that outputs a tool position command a to the servo control device, a position detection unit 13 that detects a feed position of the tool and provides a position feedback signal b to the servo control device 7, A position deviation detector 17 for comparing a position deviation signal c, which is a difference signal between the position command and the position feedback signal, with a set value, and an amplifier for amplifying a load signal e provided to the load monitor 16 based on the output of the position deviation detector. 15 is provided.

[0010]

FIG. 1 is a block diagram showing an embodiment of the apparatus according to the present invention. A small-diameter drill 4 mounted on a turret 3 of a tool post 2 on a workpiece 10 held by a chuck 1
Drilling is performed. At this time, the tool post 2
Feeding in the drill axis direction is given by a feed screw 6 driven to rotate by a feed motor 5.

The servo control device 7 for controlling the feed motor 5 includes a position controller 11 and a speed controller 12, and is a command value of a current tool position from the NC device 8 to the servo control device 7. The position command a is given. Tool post 2
Is equipped with a position detector 13 such as a linear scale for detecting the position. A position feedback signal b detected by the position detector is fed back to the input side of the position controller 11, and a position command a The position controller 11 outputs a position deviation signal c which is a difference signal between the position feedback signal b and the position feedback signal b. A speed detector 14 such as a rotary encoder is mounted on the feed motor 5.
The detected speed feedback signal d is fed back to the input side of the speed controller 12 to control the speed of the feed motor 5 based on the difference signal between the position deviation (speed command) c and the speed feedback signal d. are doing.

The output signal of the speed controller 12 changes the value of the current flowing through the feed motor 5, and the load signal e
Through the load monitor 16. An output c of the position controller 11, which is a difference signal between the position command a and the position feedback signal b, is given to a position deviation detector 17, and the output of the position deviation detector controls the amplification factor of the amplifier 15. ing. In the position deviation setting device 18 associated with the position deviation detector 17, a variation pattern of the position deviation generated when the tool is broken is set.

The load monitor 16 is provided with a comparator 21 and an upper limit load setting unit 22.
Is set with a load for emergency stop of the machine.

In a steady state, the position deviation signal c is
Only the position deviation detector 17 detects the position, and the position deviation detector 17 does not output a signal to the amplifier 15. If the small-diameter drill 4 breaks during machining and the position deviation signal c fluctuates due to the load fluctuation at that time, the position deviation detector 17 detects this by comparing with the set value of the position deviation setter 18. Then, a tool breakage signal f is output to the amplifier 15.
At this time, a slight change occurs in the load signal e of the feed motor 5 due to the change in the tool feed load. Tool breakage signal f
Increases the amplification factor of the amplifier 15, so that the load signal e
Is amplified and given to the load monitor 16.

Thus, the locally amplified load signal e is given to the load monitor 16, and the load fluctuation at the time of tool breakage appears as a large signal fluctuation.

FIG. 3 shows a change in the position deviation signal c when a drill having a diameter of 1 mm is broken, where A is a change when the tool breaks, and B is a contact between the broken tool and the workpiece. This is a change in position deviation caused by the above. A signal obtained by locally amplifying the load signal e by increasing the amplification factor of the amplifier 15 by the tool breakage signal shown in FIG.
Shown in

As is clear from the comparison between FIG. 2 and FIG.
In the conventional method, a signal which was detected only as a very small displacement when the tool was broken at first is changed to a large signal fluctuation of the portion A shown in FIG. 2 according to the method and apparatus of the present invention. By comparing this signal fluctuation with the set value of the upper limit load setting unit 22 of the load monitor 16, it is possible to reliably detect tool breakage and stop the machine in an emergency.

As apparent from a comparison between FIG. 3 and FIG. 4, it is possible to more reliably detect a tool breakage than the conventional load monitor only by detecting the position deviation. Therefore, it is possible to directly detect the tool breakage by using the detected value of the position deviation. However, in the present invention, by using the fluctuation of the position deviation as a signal for amplifying the signal of the load monitor, the load which has been conventionally performed is reduced. It is possible to follow the load detection by the monitor as it is, and there is an effect that the tool breakage can be detected more accurately without largely changing the device and the control system.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a detection signal of a load monitor according to the present invention;

FIG. 3 is a graph showing a change in position deviation when a tool is broken.

FIG. 4 is a graph showing a detection signal of a load monitor when a tool is broken according to a conventional method.

[Explanation of symbols]

 5 Feed motor 7 Servo controller 8 NC device 13 Position detector 15 Amplifier 16 Load monitor 17 Position deviation detector a Position command b Position feedback signal c Position deviation signal e Load signal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B23Q 17/00-23/00 G05B 19/18-19/46 B23B 47/24

Claims (2)

(57) [Claims] An NC machine tool comprising a load monitor (16) for detecting a load signal (e) of a tool feed motor (5), and comparing a detected value of the load monitor with a preset value. The position command given to the servo controller (7) controlling the tool feed motor (5)
(a) and a position deviation signal (c), which is a difference signal between the position feedback signal (b), is monitored, and when a fluctuation corresponding to the fluctuation of the position deviation signal (c) occurring at the time of tool breakage set in advance is detected, A method for detecting tool breakage in an NC machine tool, comprising amplifying a load signal (e) to be applied to a load monitor (16) based on the detected fluctuation. 2. A load monitor (16) for detecting a load on a tool feed motor (5) of a machine tool;
(5) Servo control device (7) and NC device that outputs tool position command (a) to this servo control device
(8) Servo control unit that detects the feed position of the tool (7)
And a position deviation detector (17) for comparing a position deviation signal (c), which is a difference signal between the position command and the position feedback signal, with a set value. ) And an amplifier (1) that amplifies the load signal (e) given to the load monitor (16) based on the output of the position deviation detector.
5) A tool damage detection device for an NC machine tool, comprising: