JPH08243882A - Method and apparatus for monitoring cutting state of machine tool - Google Patents

Abstract

PURPOSE: To enable a device to supervise high accurately further surely a cutting condition of a machine tool, by deciding the cutting condition from cutting force in a prescribed axial direction, and outputting a decision signal to a control part of the machine tool. CONSTITUTION: A digital signal converted in an A/D converter 36, radius dimension, spindle axial line directional dimension and an interposition mounting angle of piezoelectric elements S1 to S6 are used to calculate cutting forces FX, FY in an arithmetic part 32. Next relating to X, Y, Z axial directions, the cutting forces FX, FY are decided for whether exceeding or not an upper limit preset value by a decision part 34. In the case that the cutting force in a prescribed axial direction exceeds the upper limit preset value, an overload is generated, consequently by adjusting a servomotor in this axial direction to decrease a feed speed, the cutting force is lowered down to time upper limit preset value or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting state monitoring method for a machine tool and its apparatus.

[0002]

2. Description of the Related Art Machining center (hereinafter referred to as MC)
In such a machine tool, when cutting a work (workpiece) with a tool, the cutting state is monitored to perform adaptive control or determine whether or not there is a cutting abnormality.

Conventionally, there has been known a cutting state monitoring device for monitoring various cutting states by detecting an input current to a motor for driving a main shaft or a servomotor for each feed axis. In the case of this monitoring device, it is not necessary to separately provide a sensor for monitoring on the machine tool of standard configuration. Since the current detection is relatively easy, there is less possibility that the reliability of the system will be deteriorated due to the failure or life of the detector, and the cost can be kept low.

[0004]

However, in the case of such a monitoring device that monitors the cutting state via the motor current, since the detection is indirect, the response is slow and it is affected by self-inertia. In particular, when detecting the input current of the servo motor for each feed axis, there are many power transmission mechanisms until the driving force of the servo motor is transmitted to the spindle, so errors are likely to occur and the pure cutting state Information is difficult to obtain. Therefore, for example, it is difficult to detect breakage of the small diameter drill.

Further, in Japanese Patent Laid-Open No. 2-116454, a detector such as a piezoelectric sensor is attached to a tool holder,
What detects the cutting load applied to a cutting tool is disclosed. However, in this case, the structure of the tool holder becomes complicated and special, and the cost also increases,
It is difficult to apply to MC etc. which uses many tools. In addition, the rigidity of the tool holder may decrease.

Further, Japanese Patent Application Laid-Open No. 1-222851 discloses a method of detecting the thrust force of the spindle by setting a sensor in a portion where the thrust force of the spindle is applied. However, in this case, only the force in the thrust direction is detected, and the cutting state when using various kinds of tools other than tools such as drills can be monitored with high accuracy and reliability. Was difficult.

The present invention has been made to solve the above problems, and provides a cutting state monitoring method and apparatus capable of monitoring the cutting state of a machine tool with high precision and reliability with a simple structure. The purpose is to do.

[0008]

In order to achieve the above-mentioned object, a method for monitoring the cutting state of a machine tool according to the present invention provides a plurality of forces at a position where a reaction force acting on the spindle in the direction of the spindle axis during cutting acts. The sensors are arranged apart from each other, the cutting force in the predetermined axis direction is calculated based on each force detected by the force sensor, and the cutting state is determined from the calculated cutting force in the predetermined axis direction, The judgment signal is output to the control unit of the machine tool.

Further, a cutting condition monitoring apparatus for realizing the above method includes a plurality of force sensors arranged at a position where a reaction force acting on the spindle in the axial direction of the spindle at the time of cutting acts so as to be separated from each other, and the force sensors. A calculation unit for calculating a cutting force in a predetermined axis direction based on each of the forces detected respectively, and a cutting state is judged based on the cutting force output from the calculation unit, and a judgment signal is sent to the control unit of the machine tool. And a determination unit that outputs

Preferably, the force sensor is at least 3
The piezoelectric element is a piezoelectric element, and a supporting member that rotatably supports the spindle is fastened to a spindle head main body of the machine tool with the piezoelectric element being circumferentially spaced from each other. The analog signal output from each of the piezoelectric elements,
The signal is amplified by the charge amplifier and converted into a digital signal by the A / D converter. Using this digital signal, the radial dimension from the center of the spindle to the piezoelectric element mounting position, the spindle axial direction dimension from the fastening portion to the tip position of the tool mounted on the spindle, and the mounting angle of the piezoelectric element. ,
The cutting force in the predetermined axis direction is calculated by the calculation unit.

[0011]

When the work is cut by the tool gripped by the spindle, a reaction force including a force (thrust force) in the thrust direction (for example, Z-axis direction) acts on the spindle. Since the plurality of force sensors are arranged apart from each other at the position where the thrust force acts, when a lateral force is applied to the tool, the measured value of each thrust force detected by each force sensor is different. Become. Therefore, based on the distribution of these thrust forces, for example, the cutting forces in the X-, Y-, and Z-axis directions are each calculated by a predetermined arithmetic expression, and the cutting force is compared with the upper limit and lower limit set values. Can be determined.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a diagram showing an embodiment of the present invention, a partial cross-sectional view of a spindle head of a machine tool, and FIG. 2 is a schematic configuration diagram of the embodiment. As shown in the figure, the present embodiment shows the case of a vertical machining center (MC) 1 as a machine tool, but other types of machine tools such as a horizontal MC may be used. Further, the present invention is preferably applied to a machine tool having a structure in which a spindle holds a tool and rotates like MC.
It can also be applied to a machine tool having a structure in which a spindle grips and rotates a work.

A column (not shown) is erected on the MC1 and a spindle head 2 is attached to the column so as to be movable in the Z-axis direction. The column moves on the bed 3 in the Y-axis direction, and the table 4 moves on the bed 3 in the X-axis direction. A spindle 5 is rotatably provided on the spindle head 2, and a tool 6 is detachably attached to the lower end of the spindle 5. The work 7 placed on the table 4 is cut by the tool 6. The axis of the main shaft 5 is defined as the Z-axis, and the directions orthogonal to the main axis 5 and forming the orthogonal coordinate system are defined as the X-axis and the Y-axis.

The spindle 5 has a built-in motor 12 in which a rotor 10 and a stator 11 are arranged between the spindle 5 and the spindle head 2.
Is driven to rotate. A support member (bearing support) 13 that rotatably supports the front side (lower side in FIG. 1) of the main spindle 5 is fastened to the main body 2a of the main spindle head 2, and the main spindle 5 is provided inside the support member 13. The bearings 14 and 15 are rotatably supported. Cylindrical support member 13
Has a flange 16 with a circular cross section,
Are fastened and fixed to the lower surface 18 of the spindle head body 2a by six bolts 17 which are evenly arranged in the circumferential direction.

A piezoelectric element (for example, a load washer manufactured by Kistler) S _{1 to} S ₆ as a force sensor is engaged with each bolt 17, and these piezoelectric elements include a spindle head lower surface 18 and a flange 16. It is sandwiched between and.
FIG. 2 showing a planar arrangement state shows a state in which six piezoelectric elements S _{1 to} S ₆ are evenly arranged apart from each other by an interposition angle of 60 degrees. Rear side of the spindle 5 (Fig. 1
The upper side) is rotatably supported by a lid member 20 mounted on the upper surface 19 of the spindle head body 2a via a rear bearing 21.

The cutting condition monitoring apparatus 30 of the present invention comprises a plurality of piezoelectric elements which are spaced apart from each other at a position (for example, a fastening portion 31 by the bolt 17) where a reaction force is applied to the spindle 5 in the spindle axis direction during cutting. Calculation for calculating the cutting force in the direction of a predetermined axis such as the X, Y, and Z axes based on the elements S _{1 to} S ₆ and the thrust forces as the forces respectively detected by the piezoelectric elements S _{1 to} S _6. Unit 32 and this operation unit 32
A determination unit 34 that determines the cutting state based on the cutting force output from the controller and outputs a determination signal to the control unit 33 of MC1.
It has and. An analog signal, which is a charge output from each piezoelectric element S _{1 to} S ₆ , is converted into a voltage and amplified by a charge amplifier (charge amplifier) 35, and an A / D
The digital signal is converted by the converter 36, and the digital signal is input to the arithmetic unit 32.

Next, the operation of this embodiment will be described with reference to FIGS. FIG. 3 is a flowchart showing the operation when performing adaptive control. With this control,
Whether or not the cutting force is within a predetermined set value is monitored, and each feed shaft servomotor is adjusted so that the cutting force is always within this range.

First, the start button is turned on and the built-in motor 12 is driven to rotate the spindle 5, and the servomotors in the X, Y, and Z-axis directions are driven, and the workpiece 6 is cut by the tool 6. (Step 10)
1). At the time of cutting, the tool 6 for processing the workpiece 7 receives a reaction force, and this reaction force can be divided into cutting forces F _X , F _Y and F _Z in the X, Y and Z axis directions. When the cutting forces F _X and F _{Y in} the X and Y axis directions act on the spindle 5 via the tool 6 in addition to the cutting forces F _Z in the Z axis direction, they are detected by the piezoelectric elements S _{1 to} S _6. The force in the Z-axis direction, that is, the thrust forces F _{1 to} F ₆ are biased. These thrust force F
_{1 to} F ₆ are detected by the respective piezoelectric elements S _{1 to} S ₆ (step 102).

The detected signal passes through the charge amplifier 35 and the A / D converter 36, and the arithmetic unit 3 including a CPU and the like.
Enter 2. The calculation unit 32 uses the following calculation formulas (1) to (3) to calculate X, Y based on the thrust force measurement values F _{1 to} F ₆ detected by the piezoelectric elements S _{1 to} S ₆ , respectively. , Z-axis direction cutting forces F _X , F _Y and F _Z are calculated (step 103).

[0021]

[Equation 1]

Here, F _{1 to} F ₆ : Outputs of the piezoelectric elements S _{1 to} S ₆ a: Radial dimension from the center of the spindle to the mounting position of the piezoelectric elements S _{1 to} S ₆ L: Lower surface 18 of the spindle head of the fastening portion To the tip of the tool 6 in the direction of the spindle axis.

Incidentally, the dimension L is the dimension M _z from the lower surface 18 of the spindle head to the gauge line of the spindle mounting portion, and each tool 6
Since it can be obtained by adding the tool length OF _zn of
Even if the tool 6 is replaced with another tool, this dimension L can be always obtained. The dimension M _z may be obtained in advance as a numerical value specific to each machine tool. Tool length of each tool OF _zn
Are stored in the tool compensation memory.

Thus, the cutting force F is calculated using the digital signal converted by the A / D converter 36, the radius dimension a, the dimension L of the spindle axis direction, and the angle of the piezoelectric element (for example, 60 degrees). After calculating _X , F _Y and F _Z in the calculation unit 32, the cutting forces F _X , F _Y and F _{Z in the} X, Y and Z axis directions are calculated.
The determination unit 34 determines whether or not exceeds the upper limit set value (step 104). If the cutting force in the specified axis direction exceeds the upper limit set value, it means that the overload has occurred, so adjust the servo motor in that axis direction to reduce the feed rate to reduce the cutting force to below the upper limit set value. Decrease (step 105). If the cutting force does not exceed the upper limit set value in step 104, it is not necessary to reduce the feed rate because normal cutting is performed.

Next, the judgment unit 34 judges whether or not the cutting force is smaller than the lower limit set value in the X, Y and Z axis directions (step 106). When the cutting force in the predetermined axis direction is smaller than the lower limit set value, there is a margin in cutting ability, so the servo motor in that axis direction is controlled to increase the feed speed to perform cutting with high efficiency (step 107). If it is not small, adaptive control is maintained, so there is no need to increase the feed rate. In addition, the upper limit setting value and the lower limit setting value of the cutting force are
It is stored in the storage unit by the operator previously inputting it from an input device such as a keyboard.

Then, it is judged whether or not the cutting is completed (step 108). If the cutting is completed, the monitoring operation of the cutting state is completed, and if the cutting is not completed, the step 10 is carried out.
Return to 2. Therefore, it is possible to detect a change in the state during cutting and perform adaptive control for always maintaining a predetermined state of cutting, so that the cutting ability of the MC1 can be maximized and high efficiency cutting can be performed.

As described above, in the cutting state monitoring method according to the present invention, the plurality of force sensors are separated from each other at the position (for example, the fastening portion 31) where the reaction force that the spindle 5 receives in the spindle axis direction at the time of cutting acts. The cutting force is arranged, the cutting force in the predetermined axis direction is calculated based on each thrust force as the force detected by the force sensor, and the cutting state is determined from the calculated cutting force in the predetermined axis direction. MC1 is controlled by inputting this determination result to the control unit 33.

FIG. 4 is a flow chart showing the operation when the presence or absence of cutting abnormality is monitored. In this case, first, the cutting is started in the same manner as described above (step 20).
1), each thrust force F ₁ by each piezoelectric element S _{1 to} S ₆
Through F ₆ are detected (step 202). The detection signal is input to the arithmetic unit 32 in the same manner as described above. The calculation unit 32
Similar to step 103, by using equations (1) to (3), the thrust forces F _{1 to} F _{6 are changed} to the cutting forces F _X ,
F _Y and F _Z are calculated (step 203).

Then, the determining unit 34 determines the cutting force F _X ,
It is determined whether or not F _Y and F _Z have exceeded the upper limit set values (step 204). When the cutting force exceeds the upper limit set value, it is determined to be abnormal, an alarm is displayed on the display unit 37 such as the CRT of the control unit 33 to notify the operator of the abnormal state, and a signal is sent to the numerical control unit 38. The MC1 is brought to an emergency stop (step 205). If the cutting force does not exceed the upper limit set value in step 204, it is determined to be in a normal state. Next, it is judged whether or not the cutting is completed (step 206). When the cutting is completed, a series of cutting state monitoring operations is completed, but when the cutting is not completed, the process returns to step 202.

By the way, in the above embodiment, the six bolts 1
7 shows the case where the piezoelectric elements S _{1 to} S ₆ are arranged at all the fastening positions, respectively, but in the present invention, the support members 13 are circumferentially separated from each other in the fastening portions 31 that fasten the support member 13 to the spindle head body 2a. If at least three force sensors are provided, the cutting forces in the X-, Y-, and Z-axis directions can be detected. That is, in FIG. 2, for example, four piezoelectric elements S ₂ , S ₃ , S ₅ , and S ₆ are arranged at the illustrated positions,
A high-rigidity dummy collar having the same shape and dimensions as the piezoelectric element may be mounted at the positions where the remaining two piezoelectric elements S ₁ and S ₄ are to be arranged. By doing so, it is possible to reduce the total number of piezoelectric elements and realize cost reduction. In this case, the thrust force F _2, F ₃ are detected respectively from the piezoelectric elements _{S 2, S 3, S 5} , S 6, F 5, F
_The formulas for calculating the cutting forces F _X , F _Y , and F _Z using ₆ are the following formulas (4) to (6).

[0031]

[Equation 2]

As yet another modification, three piezoelectric elements S are used.
₁ , S ₃ and S ₅ are evenly arranged at intervals of 120 degrees from each other, and other piezoelectric elements S ₂ , S ₄ and S _{6 are used.}
In place of the piezoelectric element, a dummy collar similar to that described above may be attached at the position where is to be arranged. The formulas for calculating the cutting forces F _X , F _Y , and F _Z in this case are the following formulas (7) to (9).

[0033]

(Equation 3)

5 to 8 are views showing experiments conducted by the present inventor. FIG. 5 is an explanatory view showing an experimental state, in which (A) shows a plane and (B) shows FIG. 5 (A).
7 shows a cross section taken along line BB in FIG. In the experiment, an end mill 40 having a blade number of 1 and a diameter of 10 [mm] was used by using MC1.
The rectangular work 7 was cut by. As shown
The feed direction of the end mill 40 is the X-axis direction, the rotation speed of the spindle 5 is 3,000 [min ^-1 ], and the feed rate is 150 [mm.
/ min], the cutting width is 10 [mm], and the cutting depth is 1 [mm].

FIG. 6 is a graph showing experimental data. In the figure, the horizontal axis represents time [msec] and the vertical axis represents voltage [V], which represent output values f _{1 to} f ₆ from the piezoelectric elements S _{1 to} S ₆ , respectively.

FIG. 7 is a graph showing the calculation results when the calculation based on the equations (1) to (3) is performed, where the horizontal axis represents time [msec] and the vertical axis represents cutting force [N (Newton)]. Is shown. In the calculation unit 32, the thrust forces F _{1 to} F ₆ corresponding to the detection data f _{1 to} f ₆ are calculated, and the values of these thrust forces are substituted into the equations (1) to (3) to calculate, The cutting forces F _X , F _Y , and F _Z in the X, Y, and Z axis directions as shown are calculated. The determination unit 34, which has received the calculation result of the calculation unit 32, performs the determination process in the same manner as the operation shown in the above-described flowchart.

FIG. 8 shows measured values of the cutting force measured using a three-component power type (dynamometer for measuring three-component force 9257A: manufactured by Kistler) in order to confirm the accuracy of the calculation result according to the present invention. It is a graph showing, the horizontal axis is time [mse
c], the vertical axis represents the cutting force [N]. In this measurement work, a crystal piezoelectric three-component dynamometer was mounted between the table 4 of the MC 1 and the work 7, and the cutting forces F _XA and F _YA in the X and Y axis directions were measured. As a result, it was confirmed that the cutting force F _X and the actual measurement value F _XA obtained by the calculation according to the present invention and the cutting force F _Y and the actual measurement value F _YA substantially match each other. It is considered that the values of the calculation results F _X and F _Y are slightly different from the measured values F _XA and F _{YA because} of the difference in the measurement position. Is preferably multiplied by a required coefficient for correction.

As described above, according to the present invention, even when various kinds of tools are used, the cutting state can be monitored with high accuracy and reliability with a simple structure. That is, since the reaction force received by the main shaft is directly detected, a detection error is less likely to occur, and the response speed and accuracy of cutting force detection are improved. Etc. can also be detected. Also,
Since the tool holder does not need to have a special structure, the rigidity of the tool holder can be maintained high and the cutting can be performed well.

Further, the rigidity of the piezoelectric element itself and the dummy collar itself used in this embodiment is high, and the spindle support member 13 is provided at a plurality of places (for example, 6 places) through these members having high rigidity.
Is fixed to the spindle head 2, the piezoelectric element is not bent and the spindle 5 is not shaken. Therefore, it is possible to accurately detect the thrust force and perform highly accurate cutting. Furthermore, since no special tool holder or its attachment is required, cost reduction can be realized. The force detected by the force sensor is not limited to the thrust force in the Z-axis direction, and may be a force in a direction having an angle with respect to the Z-axis. In the drawings, the same reference numerals indicate the same or corresponding parts.

[0040]

Since the present invention is configured as described above, it is possible to monitor the cutting state of the machine tool with high accuracy and certainty with a simple configuration.

[Brief description of drawings]

1 to 8 are views for explaining one embodiment of the present invention, and FIG. 1 is a partial sectional view of a spindle head portion of a machine tool.

FIG. 2 is a schematic configuration diagram of the embodiment.

FIG. 3 is a flowchart showing an operation when performing adaptive control in this embodiment.

FIG. 4 is a flowchart showing an operation when monitoring the presence or absence of cutting abnormality in the present embodiment.

FIG. 5 is an explanatory diagram showing an experimental state.

FIG. 6 is a graph showing experimental data.

FIG. 7 is a graph showing a calculation result when a calculation based on the present invention is performed.

FIG. 8 is a graph showing data of cutting force actually measured using a three-component dynamometer.

[Explanation of symbols]

1 Vertical machining center (machine tool) 2 Spindle head 2a Spindle head main body 5 Spindle 13 Supporting member 30 Cutting state monitoring device 31 Fastening part (position where reaction force acts) 32 Calculation part 33 Control part 34 Judgment part 35 Charge amplifier 36 A / D converter a Radial dimension from the center of the spindle to the position where the piezoelectric element is inserted F _{1 to} F ₆ Thrust force (force) F _X X-axis cutting force F _Y Y-axis cutting force F _Z Z-axis cutting Force L Dimension in the direction of the spindle axis from the fastening part to the tool tip position S _{1 to} S ₆ Piezoelectric element (force sensor)

Claims (4)

[Claims] 1. A plurality of force sensors are arranged apart from each other at a position where a reaction force is applied to the spindle in the direction of the spindle axis during cutting, and a predetermined axial direction is obtained based on each force detected by the force sensor. Is calculated, the cutting state is judged from the calculated cutting force in the predetermined axis direction, and a judgment signal is output to the control unit of the machine tool. 2. The force sensor is at least three piezoelectric elements, and a support member for rotatably supporting the spindle is fastened to a spindle head main body of the machine tool at a fastening portion where the piezoelectric elements are circumferentially arranged. The analog signals output from the piezoelectric elements are amplified by a charge amplifier and converted into digital signals by an A / D converter, and the calculation of the cutting force in the predetermined axis direction is performed by Using the digital signal, the radial dimension from the center of the spindle to the piezoelectric element mounting position, the spindle axial direction dimension from the fastening portion to the tip position of the tool mounted on the spindle, and the mounting angle of the piezoelectric element. The cutting state monitoring method for a machine tool according to claim 1, wherein the cutting state monitoring method is performed. 3. A plurality of force sensors, which are arranged apart from each other at a position where a reaction force acting on the spindle in the axial direction of the spindle during cutting acts, and a predetermined axial direction based on each force detected by the force sensor. And a determining unit that determines a cutting state based on the cutting force output from the calculating unit and outputs a determination signal to the control unit of the machine tool. Machine tool cutting condition monitoring device. 4. The force sensor is at least three piezoelectric elements, and a support member that rotatably supports the spindle is fastened to a spindle head main body of the machine tool at a fastening portion. The analog signals output from the piezoelectric elements are amplified by the charge amplifier and converted into digital signals by the A / D converter. The cutting force in the predetermined axial direction is calculated using the radial dimension to the mounting position, the spindle axial direction dimension from the fastening portion to the tip position of the tool mounted on the spindle, and the mounting angle of the piezoelectric element. The cutting state monitoring device for a machine tool according to claim 3, wherein the cutting state monitoring device is calculated.