JPS6125754A - Tool breaking detector - Google Patents

Abstract

PURPOSE:To obtain a detector applicable on a super high speed spindle for such as static pressure air bearing by constituting such that the breaking is detected from the droppage of rotary speed detected in contactless under application of torque between the spindle of machine tool and the spindle body. CONSTITUTION:The rotary speed under machining of work is fed as a speed signal V from a position detector 5 through frequency/voltage converter 7 to a subtractor 8 to calculate the difference between the referential output V0 under no- load rotation thus to obtain the speed variation DELTAV due to load operaton. The speed variation DELTAV is compared with the threshold Vr in a comparator 9. Exceeding of the speed variation DELTAV over the threshold Vr is considered to be breaking thus to stop the machine. With such arrangement, highly accurate detection is realized even for the super high speed spindle such as static pressure air bearing.

Description

[Detailed Description of the Invention] The present invention relates to a tool breakage detection device, and more specifically, the present invention relates to a tool breakage detection device. The present invention relates to a tool breakage detection device that can be used for a spindle structure in which it is impossible to detect, for example, a spindle system supported in a non-contact manner by a hydrostatic air bearing.

Conventional methods for detecting breakage of tools attached to the spindle of countersunk machine tools include 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 tool breakage detection means, electrical conduction or ultrasonic signal propagation is mainly performed within the metal material, so ultra-high speed It becomes virtually impossible to detect tool breakage on the spindle. 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.

(The main purpose of the present invention is to provide a tool breakage detection device that can be attached to an ultra-high-speed spindle equipped with a hydrostatic air bearing, which has been widely used in recent years to improve the cutting speed and machining accuracy of workpieces.) It is about providing.

Another main object of the present invention is to completely overcome the practical limitations found in known tool breakage detection devices that utilize material failure signals or electrical continuity in the ultrasonic range.
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 negative torque during workpiece machining.

In view of the above object, the present invention provides a non-contact rotational speed detection mechanism (3) between the main spindle (1) and the main spindle body (2) of a machine tool.
, (4) and (5);
Subtractors (8) connected in series to the non-contact speed detector
) and 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 the main shaft body (2) via a hydrostatic air bearing (12).

1. EXAMPLE 1 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 the output signal appearing in the comparator circuit. In these drawings, inside the main shaft body (2) are first hydrostatic air bearing members (12a), (12b) made of porous metal material that function as radial bearings for the main shaft (1), and the main shaft. A hydrostatic air bearing (12) consisting of a second hydrostatic air bearing member (12G) and (12d) made of the same material as above, which functions as a thrust bearing for Conduction holes (13), (1) for supplying compressed air to
The main shaft (1), on which the main shaft (1) is disposed, is rotatably supported by the plurality of static pressure air bearing members, and at the same time is positioned while maintaining a non-contact state with respect to the main shaft body (2). ing. A turbine (I5) having a plurality of turbine pockets (14) is mounted on the side body of the main shaft (1).
), and the main shaft (1) is
Compressed air is ejected into the turbine (15) from a plurality of nozzles (16) bored on the circumference of the body (7) of the main shaft body (2) so as to face the turbine socket (1-04). By introducing it, it is driven to rotate at a high speed, for example, as high as 500 revolutions per minute. A cutting tool (18) is attached to the main shaft (1) via a collet (17) according to the usual method.
, for example, a drill is fixed, and this cutting tool (18
) The workpiece is processed by transmitting rotational driving force to the main shaft (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 main shaft (1). Correspondingly, the end wall portion of the spindle body (2) has position detection in digital output format so that it is located on the rotational movement locus of the hole (4)! S (5) is fixed. These rotational speed detection mechanisms (3), (4),
The speed detector (6) composed of (5) is connected to the main shaft (1).
The rotational speed of the main shaft (1) is detected while maintaining a non-contact state between the main shaft body (2) and the main shaft body (2). It is also possible to use a rotary encoder directly connected to (1) or a known tachometer generator or the like as a rotational speed detection device.

In the device of the present invention, when the main shaft (1) is rotating without load, the position detector (5) detects the rotational speed of the main shaft (1) and the hole ( A rectangular wave signal corresponding to the product of 4) and the number is output at a constant cycle. When the rotational speed of the spindle (1) decreases due to an increase in cutting resistance during machining of a workpiece, the output period of the square wave signal becomes longer (corresponding to the decrease in rotational speed). It is converted into an analog signal by the converter (7).If an analog output type sensor is used as the position detector (5), the installation of the frequency/voltage converter (7) can be omitted. .

The output from the no-load rotation speed signal setter (10) for setting the reference output (■0) during no-load rotation, and the rotation speed signal (V) output from the frequency/voltage converter (7).
is subtracted by the subtractor (8), and the subtraction! 1
From (8), the speed fluctuation ΔV=V−Vo is output. Here, a DC/AC converter can be used instead of the frequency/voltage converter (7) as a means of calculating the speed fluctuation, but in any embodiment, the cutting resistance of the workpiece is zero. In other words, when the main shaft (1) is placed in a no-load state, the output of the wattage reducer (8) becomes zero.

The output of the subtracter (8) is compared in a comparison circuit (9) with a negative threshold voltage value (Vr) set in advance in a threshold setting circuit (11). The comparison circuit (9) is
It consists of an analog comparator circuit, and if the comparison result is ∆■ - Vr, the workpiece has been successfully cut without causing any breakage to the cutting tool (18), and the resulting cutting resistance has decreased. It is determined that the rotational speed of the main shaft (1) is decreasing due to the increase. On the other hand, if a decrease in the rotational speed of the spindle (1) is not detected, that is, if the comparison calculation result is Δ■>Vr, then the cutting tool (18
) is determined to have interrupted the machining of the broken workpiece, and an output signal indicating that the tool is broken is output.The output signal causes the machine tool to be stopped and the broken tool to be replaced.

Figure 2 shows the spindle rotation speed in the no-load state of 1824OR.
The speed waveform in the case of PM and the rotation speed waveform when machining a workpiece with a drill of diameter 0.5a + 11 are displayed on the same scale, and the rotation speed fluctuation (rotation speed) under no load is approximately 301? PM culm degree.

As can be understood from the example shown in FIG. 2, during cutting of a workpiece, a decrease in rotational speed of about 45 ORPM is observed. To be more specific, the cutting tool (18) comes into contact with the workpiece at point (A), and as the depth of cut into the workpiece increases, the rotational speed of the spindle (1) gradually decreases until it reaches the lowest point ( When the cutting tool (18) reaches the predetermined depth corresponding to the lowest point (B), cutting into the workpiece ends, so the cutting load is almost eliminated, and after this, the cutting tool (18) ) retreats, the rotation speed of the main shaft (1) gradually recovers, and the point (
Return to C).

In FIG. 2, by setting the threshold value Vr,
The detection device shown in FIG. 1 confirms whether the machining conditions of the workpiece are appropriate, that is, whether or not the tool is broken. 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 the breakage detection signal is is output. In addition, if the cutting tool (18) breaks during machining of the workpiece, the rotational speed waveform will be moved to the lowest point (B
), the curve returns to the initial rotational speed level, and a breakage detection signal is also output in this case.

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 the no-load rotational speed signal, threshold value, and control the output signal. Comparison or further comparison of the output signals to determine whether or not a tool is broken can all be performed automatically. In addition, 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 causes other than tool breakage, and such a threshold value (Ve) can be set. The second threshold value (Ve) also makes it possible to detect whether the cutting tool (18) is overloaded.

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 reduced by adjusting the no-load rotational speed (output of f5 and the threshold value). It is possible to reliably detect whether or not a cutting tool has broken by performing a comparison calculation with It is applicable to all types of machine tools.In other words, it has a main shaft structure that makes it virtually impossible to detect tool breakage using electrical conduction or material failure signals in the ultrasonic range. Even in the case of a spindle structure supported in a fixed state, the device of the present invention can significantly improve the accuracy of detecting tool breakage.Therefore, the device of the present invention can detect tool breakage of small diameters that cannot be detected by known detection devices. It is possible to exhibit an excellent breakage detection function even for cutting tools such as drills with a diameter of 1 ms+ or less.Furthermore, based on the above-mentioned improvement in detection accuracy, the device of the present invention can be used in fields other than tool breakage detection, such as It can also exhibit good detection functions in detecting the starting point of contact between a tool and a workpiece and in detecting tool wear.

[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 setting device, (11) L -□- Procedural amendment October 24, 1980 1, Incident display 1982 Patent Application No. 142049 2, Title of the invention: Tool breakage detection device 3, Relationship with the person making the amendment Patent applicant name: Osaka Kiko Co., Ltd. 4, Agent: Tatami 550 Address: 15 Edo W11-chome, Nishi-ku, Osaka City, Osaka Prefecture No. 26 No. 5, M positive subject Specification and Drawing 1, in the specification, page 5, line 8 and lines 1θ to 11 [Turbine pocket (14) J is referred to as "turbine pocket (14°)" to correct. ■Amend Figure 1 of the drawings to be shown in red on a separate sheet.

Claims (2)

[Claims] (1) Comparison of 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 subtractor connected in series to the non-contact speed detector, and a speed signal A tool breakage detection device comprising a circuit, a no-load rotation speed signal setter connected to the subtracter, and a threshold setting circuit connected to the speed signal comparison 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.