JPH0155941B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a cutting torque measuring device. The present invention relates to a cutting torque measuring device or a tool breakage detecting 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 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, electrical continuity or propagation of ultrasonic signals is mainly carried out within the metal material, so 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 measure cutting torque that can be installed 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. An object of the present invention is to provide a device or tool breakage 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. It is an object of the present invention to provide a cutting torque measuring device or a tool breakage detecting device that uses as a detection signal the presence or absence of a decrease in the spindle rotational speed due to the load torque.

Means for Solving the Problems In view of the above objects, the present invention provides a non-contact rotational speed detector formed between the main spindle and the main spindle body of a machine tool, a backward difference calculation circuit, and a cutting torque calculation circuit. are sequentially connected in series, and a clock pulse transmitting device is connected to the backward difference calculating circuit, and by interlocking with the clock pulse transmitting device of the backward difference calculating circuit, the rotation speed of the main shaft is sampled as a clock pulse and a trigger, and these Calculate the backward difference, and use the cutting torque calculation circuit to calculate the actual cutting time calculated as the product of the sampling time and the time count number when the value becomes negative, and the amount of decrease in the rotation speed of the spindle due to the increase in cutting torque. The gist of the present invention is a cutting torque measuring device that performs arithmetic processing to detect fluctuations in cutting torque and tool breakage.

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 an orthogonal coordinate diagram illustrating a state in which the main shaft rotational speed decreases due to an increase in cutting torque. Further, FIG. 3 is a rectangular coordinate diagram showing variations in cutting torque in correspondence with changes in spindle rotational speed, and FIG. 4 is an explanatory diagram of the operating status of the clock pulse generator and the backward difference calculation circuit. In these drawings, the main shaft body 2 includes first hydrostatic air bearing members 12a and 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 hydrostatic air bearing 12 consisting of second hydrostatic air bearing members 12c and 12d made of the same material as described above.
Through-holes 13 and 14 are provided for supplying compressed air to each of the above-mentioned air bearing members. The main shaft 1 is rotatably supported by the plurality of static pressure air bearing members described above, and is positioned at the same time while maintaining a non-contact state with respect to the main shaft body 2. An air turbine 15 having a plurality of turbine pockets 24 is mounted on the side body of the main shaft 1.
The main shaft 1 is provided with its axis aligned with that of the main shaft 1.
The air turbine 15 ejects compressed air from a plurality of nozzles 16 bored on the circumference of the side body of the main shaft body 2 so as to face the turbine pocket 24.
By introducing within a high speed, e.g. per minute
It is driven to rotate at a high speed of up to 50,000 revolutions. A cutting tool 18, such as 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. The length increases as the rotational speed of the spindle 1 decreases as cutting resistance increases during machining of a workpiece. 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.

The non-contact speed detector 6 is connected to the clock pulse transmitter 10 to measure the cutting time (τ).
and a backward difference calculation circuit 8 that calculates the amount of decrease in spindle rotation speed (ΔN) due to an increase in cutting torque and transmits the calculation result as an electrical signal, and an electrical signal transmitted from the backward difference calculation circuit 8. Cutting torque calculation circuits 9 are sequentially connected in series for calculating and processing and transmitting electrical signals corresponding to fluctuations in cutting torque (T _L ).

In such a cutting torque measuring device, the equation of motion of the main shaft 1 is given by the following equation ().

Jdω/dt=Td-T _B -T _L -() where J: moment of inertia of main shaft 1 ω: rotational angular velocity of main shaft 1 (ω=2π/60N, N: rotational speed of main shaft 1) Td: air turbine 15 Driving torque T _B : Braking torque due to air friction T _L : Cutting torque Figure 2 shows cutting during workpiece machining with the ultra-high speed spindle 1 supported by a static pressure air bearing 12 and driven by an air turbine 15. FIG. 2 is an orthogonal coordinate diagram illustrating a state in which the rotational speed (N) decreases due to an increase in torque (T _L ). As can be understood from Figure 2, the driving torque (Td) of the air turbine and the braking torque (T _B ) due to air friction are much smaller than the cutting torque (T _L ), so in the above equation (), The driving torque (Td) and the braking torque (T _B ) can be ignored as minute terms. Assume that under these conditions, a cutting torque (T _L ) is applied to the spindle 1 for an actual cutting time (τ) as shown in FIG. In this case, the amount of decrease (Δω) in the rotational angular velocity (ω) of the spindle 1 due to the impulse T _L・τ of the cutting torque
is obtained from the above equation () as shown in the following equation ().

Δω=ω ₁ −ω ₀ =−T _L /J・τ −() Therefore, ΔN/τ=−π/30・T _L /J −() In the above equation (), the moment of inertia of the main shaft 1 Since (J) takes a constant value, the cutting torque (T _L ) can be estimated from the rotational speed reduction amount of spindle 1 (ΔN) and the actual cutting time (τ) from the start of cutting to the start of retraction of the cutting tool. Can be done.

The clock pulse transmitting device 10 and the backward difference calculation circuit 8 are provided as transmitting devices for electrical signals corresponding to the actual cutting time (τ) and the rotational speed reduction amount (ΔN) of the spindle 1.
As shown in the figure, the rotation speed (Ni) of the main shaft 1 is sampled using the clock pulse (sampling time Δt) inside the controller as a trigger.
A backward difference (Ni-Ni _- 1) from the main shaft rotational speed Ni-1 at the time when the previous clock pulse was input is calculated, and whether it is positive or negative is determined. At this time (Ni−
If Ni _-1 )<0, time counting is performed assuming that the rotational speed (N) of the spindle 1 is decreasing due to the load of the cutting torque (T _L ). Based on this, the actual cutting time (τ) is calculated as the product of the sampling time (Δt) and the time count number (i).

Effects of the Invention As can be understood from the above explanation, by using the apparatus of the present invention, fluctuations in cutting torque during machining of a workpiece can be accurately measured. Therefore, it is possible to reliably detect whether or not cutting damage has occurred in the tool by utilizing the variation in cutting torque. The device of the present invention can detect fluctuations in cutting torque and tool breakage without installing a special sensor, so it can be applied 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 drawings]

FIG. 1 is a block diagram illustrating the overall structure of the apparatus of the present invention, and FIG. 2 is an orthogonal coordinate diagram illustrating a decrease in the spindle rotational speed due to an increase in cutting torque. Further, FIG. 3 is a rectangular coordinate diagram showing variations in cutting torque in correspondence with changes in spindle rotational speed, and FIG. 4 is an explanatory diagram of operating conditions of the clock pulse generator and backward difference calculation circuit. 1... Spindle, 2... Spindle body, 6... Speed detector, 7... Frequency/voltage converter, 8... Reverse difference calculation circuit, 9... Cutting torque calculation circuit, 10...
Clock pulse generator.

Claims (1)

[Scope of Claims] 1. A non-contact rotational speed detector formed between the main spindle and the main spindle body of a machine tool, a backward difference calculation circuit, and a cutting torque calculation circuit are connected in series, and the backward difference calculation circuit is connected in series. A clock pulse transmitter is connected to the circuit, and by interlocking with the clock pulse transmitter of the backward difference calculation circuit, the rotation speed of the main shaft is sampled using the clock pulse as a trigger, these backward differences are calculated, and the value is determined to be negative. The actual cutting time calculated as the product of the sampling time and the number of time counts when A cutting torque measuring device characterized by detecting tool breakage. 2. The cutting torque measuring device according to claim 1, wherein the main shaft of the machine tool is rotatably supported within a main shaft body via a hydrostatic air bearing.