JPS646899B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a tool breakage detection device. Spindle structure, impossible to detect
The present invention relates to a tool breakage detection device that can be used, for example, in a spindle system supported in a non-contact manner by a hydrostatic air bearing.

Conventional technology As means for detecting breakage of a tool mounted on the spindle of a machine tool, there is a method that uses electrical continuity to detect the presence or absence of contact between a tool and a workpiece, and a method that uses ultrasonic waves (e.g. acoustic emission). A method of using a material failure signal as a breakage detection signal has been put into practical use.

However, in the above-mentioned means for detecting tool breakage, since electrical continuity or propagation of ultrasonic signals is mainly carried out within the metal material, it is supported by hydrostatic air bearings, which have recently become popular. Detection of tool breakage becomes virtually impossible with ultra-high speed spindles. In other words, in a spindle system that is rotatably supported via a hydrostatic air bearing, the spindle itself is supported in a non-contact manner with respect to the spindle head by the hydrostatic air bearing, so there is no electrical continuity or ultrasonic signal. propagation becomes almost impossible, and the tool breakage detection function is virtually lost.

Problems to be Solved by the Invention The main purpose of the present invention is to solve the problem of tool breakage that can be mounted on ultra-high-speed spindles equipped with hydrostatic air bearings, which have been widely used in recent years to improve the cutting speed and machining accuracy of workpieces. The object of the present invention is to provide a detection device.

Another main object of the present invention is to provide a method for processing workpieces that can completely overcome the practical limitations observed in known tool breakage detection devices that utilize material failure signals in the ultrasonic range or electrical continuity. An object of the present invention is to provide a tool breakage detection device that uses as a detection signal the presence or absence of a decrease in spindle rotational speed due to load torque.

Means for Solving the Problems In view of the above object, the present invention provides a main shaft 1 of a machine tool.
a speed detector 6 formed by forming non-contact rotational speed detection mechanisms 3, 4, and 5 between the spindle body 2 of the main shaft body 2; and a subtractor 8 connected in series to the non-contact speed detector.
and a speed signal comparison circuit 9 and the subtracter 8
No-load rotation speed signal setting device 10 connected to
and a threshold setting circuit 11 connected to the speed signal comparison circuit 9.

In a preferred embodiment of the present invention, the main shaft 1 of the machine tool is rotatably supported within a main shaft body 2 via a hydrostatic air bearing 12.

Embodiment FIG. 1 is a block diagram illustrating the overall structure of the apparatus of the present invention, and FIG. 2 is a rectangular coordinate diagram illustrating the waveform of an output signal appearing in a comparator circuit. In these drawings, inside the main shaft body 2, there are first hydrostatic air bearing members 12a, 12b made of porous metal material that function as radial bearings for the main shaft 1, and first hydrostatic air bearing members 12a and 12b that function as thrust bearings for the main shaft. A static air bearing 12 consisting of second static air bearing members 12c and 12d made of the same material, and through holes 13 and 14 for supplying compressed air to the respective air bearing members. is installed. The main shaft 1 is rotatably supported by the plurality of static pressure air bearing members, and at the same time the main shaft body 2
It is positioned while maintaining a non-contact state. A turbine 15 having a plurality of turbine pockets 14' is provided on the side body of the main shaft 1, with bearings aligned with the main shaft 1. The main shaft 1 has a main shaft main body 2 facing the turbine pockets 14'.
A plurality of nozzles 16 bored on the circumference of the side body of
By introducing compressed air ejected from the turbine 15 into the turbine 15, the turbine 15 is driven to rotate at a high speed, for example, up to 50,000 revolutions per minute. A cutting tool 18, for example a drill, is fixed to the main spindle 1 via a collet 17 in a conventional manner, and a workpiece is machined by transmitting rotational driving force to the cutting tool 18 via the main spindle 1.

In the present invention, a disk 3 having holes 4 for outputting rectangular wave signals formed at approximately equal intervals on a concentric circle is fixed to the base end of the spindle 1, and the spindle main body 2 is correspondingly fixed to the base end of the spindle 1.
A digital output type position detector 5 is fixed to the end wall portion of the hole 4 so as to be located on the rotational movement locus of the hole 4. These rotational speed detection mechanisms 3,
The speed detector 6 composed of the spindles 4 and 5 detects the rotational speed of the spindle 1 while maintaining a non-contact state between the spindle 1 and the spindle body 2, but as an alternative, a speed detector 6 having the same function as described above may be used. It is also possible to use other speed detecting means, such as a rotary encoder directly connected to the main shaft 1 or a known tachometer/generator as a rotational speed detecting device.

In the device of the present invention, when the main shaft 1 is rotating without load, the position detector 5 detects a signal corresponding to the product of the rotation speed of the main shaft 1 and the number of holes 4 drilled in the disk 3. A rectangular wave signal is output at regular intervals. When the rotational speed of the main spindle 1 decreases as cutting resistance increases during machining of a workpiece, the output cycle of the rectangular wave signal becomes longer corresponding to the decrease in rotational speed. This rectangular wave signal is converted into an analog signal by a frequency/voltage converter 7. Note that if an analog output type sensor is used as the position detector 5, the frequency/voltage converter 7 can be omitted.

An output from the setting device 10 of a no-load rotation speed signal for setting a reference output Vo during no-load rotation;
The rotational speed signal V output from the frequency/voltage converter 7 is subtracted by a subtracter 8, and the subtracter 8 outputs a speed fluctuation ΔV=V−Vo. Here, a DC/AC converter can be used instead of the frequency/voltage converter 7 as a means for calculating the speed fluctuation, but in any embodiment, when the cutting resistance of the workpiece is zero, That is, when the main shaft 1 is placed in a no-load state, the output of the subtracter 8 becomes zero.

The output of the subtracter 8 is compared in a comparator circuit 9 with a negative threshold voltage value (Vr) set in advance in a threshold setting circuit 11. Comparison circuit 9
is composed of an analog comparator circuit, and if the comparison result is ΔV<Vr, the workpiece has been successfully cut without causing breakage to the cutting tool 18, and the cutting force increases accordingly. Therefore, it is determined that the rotational speed of the main shaft 1 is decreasing. On the other hand, if a decrease in the rotational speed of spindle 1 is not detected, that is, the comparison calculation result is ΔV>
If it is Vr, it is determined that the cutting tool 18 is broken and the machining of the workpiece is interrupted, and a broken tool output signal is output, which causes the machine tool to stop and the broken tool to be replaced. Ru.

Figure 2 shows the spindle rotation speed under no load condition.
Speed waveform when 18240RPM and diameter 0.5mm
The rotational speed waveform during workpiece machining with a drill is displayed on the same scale, and the rotational speed fluctuation (rotational unevenness) under no load is approximately 30 RPM.

As can be understood from the example shown in FIG. 2, during cutting of a workpiece, a decrease in rotational speed of approximately 450 RPM is observed. More specifically, the cutting tool 18 comes into contact with the workpiece at point A, and as the amount of cut into the workpiece increases, the rotational speed of the main spindle 1 gradually decreases until it reaches the lowest point B. When the cutting tool 18 reaches a predetermined depth corresponding to the lowest point B, the cutting into the workpiece ends and the cutting load is almost eliminated.After this, the rotation speed of the spindle 1 gradually decreases as the cutting tool 18 retreats. It recovers and returns to point C, where the rotation speed is the same as when no load was applied.

In FIG. 2, by setting the threshold value Vr, it is confirmed by the detection device shown in FIG. 1 whether the machining conditions of the workpiece are appropriate, that is, whether the tool is broken or not. On the other hand, if the cutting tool 18 that was broken in the preceding machining process is used as is without being replaced, the rotational speed waveform becomes a substantially horizontal straight line as shown by the dotted line in Figure 2, and a breakage detection signal is output. be done. In addition, if the cutting tool 18 breaks during machining of the workpiece, the rotational speed waveform will reach the initial rotational speed without reaching the preset lowest point B, as shown by the two-dot chain line in Fig. 2. The curve returns to the level, and a breakage detection signal is output in this case as well. In this case, it is necessary to incorporate an auxiliary gate circuit into the detection device to determine whether or not the rotational speed has decreased within the planned cutting section R.

In an automated numerically controlled machine tool such as a machining center, the device of the present invention uses the auxiliary signal (M function) of the numerical control device to set and output a no-load rotational speed signal and a threshold value. Comparison of signals or further comparison of the output signals to determine whether or not a tool is broken can all be automatically performed. As an application example of the present invention, it is also possible to set another threshold value Ve for detecting a decrease in rotational speed or stoppage of the spindle 1 due to a cause other than tool breakage, and such a second threshold value Ve can be set. It is also possible to detect whether the cutting tool 18 is overloaded by the threshold value Ve.

Effects of the Invention As can be understood from the above explanation, by employing the device of the present invention, the decrease in spindle rotational speed due to cutting load can be detected by outputting a preset no-load rotational speed signal and by adjusting the threshold value. By performing the comparison calculation, it is possible to reliably detect whether or not the cutting tool is broken. Since the device of the present invention can detect tool breakage without attaching a special sensor, it is applicable to almost all types of machine tools. That is, in a spindle structure in which it is virtually impossible to detect tool breakage using electrical continuity or material failure signals in the ultrasonic range, for example, in a spindle structure supported in a non-contact manner by a hydrostatic air bearing. However, the device of the present invention can significantly improve the accuracy of detecting tool breakage. Therefore, the device of the present invention:
It is possible to exhibit an excellent breakage detection function even for small-diameter cutting tools that cannot be detected by known detection devices, such as drills with a diameter of 1 mm or less. Furthermore, based on the above-mentioned improvement in detection accuracy, the device of the present invention exhibits good detection functions in application fields other than detecting tool breakage, such as detecting the starting point of contact between a tool and a workpiece and detecting tool wear. It's something you get.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating the overall structure of the device of the present invention, and FIG. 2 is a rectangular coordinate diagram illustrating the waveform of an output signal appearing in a comparator circuit. 1...Spindle, 2...Spindle body, 6...Speed detector, 7...Frequency/voltage converter, 8...Subtractor,
9...Speed signal comparison circuit, 10...No-load rotation speed signal setter, 11...Threshold value setting circuit.

Claims (1)

[Scope of Claims] 1. A speed detector formed by forming a non-contact rotational speed detection mechanism between the main spindle and the main spindle body of a machine tool;
A subtracter and a speed signal comparison circuit connected in series to the non-contact speed detector, a no-load rotation speed signal setter connected to the subtractor, and a speed signal comparison circuit connected to the non-contact speed detector. A tool breakage detection device consisting of a threshold setting circuit. 2. The tool breakage detection device according to claim 1, wherein the main shaft of the machine tool is rotatably supported within the main shaft body via a hydrostatic air bearing.