JPH0415058B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly aims at accurately detecting the load applied to the rotating shaft or tool of a machine tool and the displacement of the rotating shaft.

Conventionally, methods have been proposed for detecting the load and displacement applied to a rotating shaft or tool during cutting.
The purpose of such a proposal is to transmit cutting conditions to a control device in the form of electrical signals, prevent damage to tools and machines due to overload, and optimize control of cutting conditions.

An example of a conventionally proposed cutting state detection device is shown in FIG. In FIG. 1, a cutting tool 1 is fixed to a rotating shaft 2 and rotates at the same time as the rotating shaft to machine a workpiece 3. 4 is a ball bearing, rotating shaft 2
While being rotatably supported, it is fixedly supported by the sleeve 5. Reference numeral 6 schematically represents a mechanical body that holds a workpiece and a rotating device 7 consisting of a rotating shaft 2, a ball bearing 4, and a sleeve 5. 8 is a sensor for detecting the load F _R during cutting, and in this example, a strain gauge attached to the sleeve 5 is used. 9 is a sensor for detecting the load F _A , and in this example, a non-contact displacement meter is used. 10 is a sensor amplifier that supplies an electric signal proportional to load or displacement to a detection control device 11 of the machine.

Next, the operation of this detection device will be explained.

Cutting loads F _R and F _A are generated by cutting. F _R is converted into an electrical signal proportional to the load (force) through the path of the tool 1 → rotary shaft 2 → ball bearing 4 → sleeve 5 → strain gauge 8 → sensor amplifier 10, and is supplied to the detection control device 11. Ru. In other words, the deflection of the sleeve 5 caused by F _R is detected by the strain gauge. F _A is ball bearing 4
By deforming the rotating shaft 2, the rotating shaft 2 is moved in the axial direction. Since the amount of movement is proportional to F _A , the rotation axis 2
If the amount of movement is measured by the non-contact displacement sensor 9, the output of the sensor amplifier 10 will be the cutting load
It is proportional to F _A and is supplied to the detection control device 11 in the same way as in the case of F _R. The voltage of the electrical signal from the strain gauge or non-contact displacement meter obtained in this way can be used to determine the cutting depth, and the vibration can be used to determine the cutting condition, such as the presence or absence of chatter, to prevent excessive loads from being applied to the tool. The detection control device can automatically set the optimum cutting conditions to avoid vibrations and chatter. In order to accurately control the cutting conditions with the detection device 11, it is important to increase the detection sensitivity of the cutting loads F _R and F _A . Therefore, in the case of a strain gauge, the wall thickness of the part of the sleeve 5 to which the strain gauge 8 is attached is made thinner to lower the rigidity, or the rigidity of the ball bearing 4 is lowered to reduce the cutting loads F _R and F _A of the sleeve or rotating shaft. We are trying to increase the detection sensitivity by increasing the amount of displacement.

Cutting condition detection devices such as those described above intentionally have low rigidity parts in order to increase the detection sensitivity of cutting loads, but lowering the rigidity tends to cause chatter vibrations and partially deform the machine. Because it is easy to use, it has the disadvantage of not being able to be processed with high precision, making it difficult to put it into practical use.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and provide a cutting state detection device that detects a cutting load without impairing high-precision workability.

FIG. 2 to FIG. 5 are specific examples of implementation of the present invention,
Figure 2 shows the cutting load F _A detection device, Figures 3 and 4.
The figure shows a detection device for _FR , and FIG. 5 shows a detection device for both _FR and _FA . In FIG. 2, 1-5 and 9, 10, 11 correspond to the numbers in FIG. 12
is an armature fixed to the rotating shaft 2 and receives an attractive force from the electromagnet 13. 14 is an electromagnet control device which controls the electromagnet current so that the gap 15 between the displacement sensor 9 and the rotating shaft 2 is always within a certain range.

Next, the operation will be explained.

When the cutting load F _A acts, the rotating shaft 2 is displaced in the same direction as F _A. This changes the air gap 15 between the rotation axis 2 and the displacement sensor. The amount of displacement of the rotating shaft is detected by the displacement sensor 9, and the sensor amplifier 10 supplies a signal voltage proportional to the displacement to the comparator 16 in the electromagnet control device 14. The comparator outputs the difference between the reference signal defining the initial value of the air gap 15 and the signal of the displacement sensor amplifier 10, which is supplied to the compensator 17. The compensator 17 includes a displacement sensor amplifier 10, a comparator 16, a compensator 17, and an electromagnet 1.
3. The closed loop servo system consisting of the armature 12 is stable, and the attraction force acting on the armature 12 of the electromagnet 13 is balanced with F _A (-)
It operates to perform gain compensation and phase compensation to generate F _A. The ratio of F _A to the change in the air gap 15,
The so-called rigidity can be expressed by the following formula.

F _A /X=K-Ku...K=K _S K _C K _F ... Here, for simplicity, we consider a steady state. K
is the loop gain, which is the proportional coefficient K _S of the output voltage proportional to the displacement by the displacement sensor 9, sensor amplifier 10, and comparator 16, and the proportional coefficient of the output current proportional to the input voltage of the compensator 17, which also includes the drive section of the electromagnet 13. It is the product of the coefficient K _C and the conversion coefficient K _F for current and attractive force, which indicates the performance of the electromagnet. Ku is armature 1
2 and the electromagnet 13, that is, the rotation axis 2
is the proportionality coefficient of the unstable force proportional to the displacement of .

As can be understood from the equation, by arbitrarily setting the loop gain K, the actual change X can also be arbitrarily set. On the other hand, the electromagnet current I for F _A can be expressed by the following equation.

F _A = K _I I ² ... Here, K _I is the armature 12 and electromagnet 1.
This is a constant determined by the shape-positional relationship of 3, the number of turns of the coil, etc.

As can be understood from the equation, the force F _A can be detected by measuring the current. "In other words, the current I (generally, to facilitate later signal handling, the current -
Use a voltage converter etc. to calculate the voltage e proportional to the current I.
To generate and observe the voltage e) is to observe the cutting load F ^A , and the cutting state can be known.

Note that it is also possible to monitor the cutting force by supplying a signal voltage e proportional to the current I to the detection control device 11, and to optimize cutting conditions such as preventing overload of the cutting tool.

As explained above, according to the present invention, unlike conventional cutting state detection devices, there is no need to partially lower the rigidity in order to increase detection sensitivity, and moreover, the attractive force by the electromagnet 13 is reduced by the compensator 17. Since it can be compensated electrically, chatter vibration is less likely to occur.
The electromagnet acts to counteract the cutting load, and the displacement of the rotating shaft can be set arbitrarily, which has the effect of enabling highly accurate machining. In addition, the cutting load is
By monitoring the electromagnet current, detection can be performed without a large time delay, which has the effect of providing excellent responsiveness and enabling highly reliable and stable cutting state detection.

The above is based on the axial cutting load F _A
Although the case of detecting the cutting load F _R in the radial direction has been described, the displacement sensor 9 and the electromagnet 13 may be arranged in the radial direction as shown in FIGS. 3 and 4. Furthermore, in order to detect the axial cutting load F _A with the displacement sensor 9 and electromagnet 13 arranged in the radial direction, the rotating shaft, the electromagnet, and the displacement sensor may be tapered as shown in FIG.

[Brief explanation of drawings]

FIG. 1 is a structural sectional view of a conventional cutting state detection device, FIGS. 2, 3, and 5 are structural sectional views of an embodiment of the present invention, and FIG. 4 is a line A-A in FIG. 3. FIG. DESCRIPTION OF SYMBOLS 1... Cutting tool, 2... Rotating shaft, 3... Workpiece, 4... Ball bearing, 5... Sleeve, 6... Machine body, 7... Rotating device, 8... Strain gauge, 9... ...Displacement sensor, 10...Sensor amplifier, 11...
Detection control device, 12... Armature, 13...
Electromagnet, 14... Electromagnet control device, 15... Air gap, 16... Comparator, 17... Compensator. In the figure, the shaded portion is a soft magnetic material.

Claims (1)

[Scope of Claims] 1. A rotating shaft that holds a workpiece or a tool, an armature fixed to the rotating shaft, an electromagnet that attracts the armature, a displacement sensor that detects displacement of the rotating shaft, and the displacement sensor. an electromagnet control device that controls a drive current of the electromagnet using an output to keep the position of the rotating shaft constant against cutting resistance, and detects a cutting state by monitoring the drive current and detects the detection result. The electromagnet control device includes a detection control device that optimally controls the cutting state based on the above, and the electromagnet control device outputs a difference between a reference signal that determines an initial value of the air gap between the armature and the electromagnet and an output signal of the displacement sensor. and a compensator to which the output of the comparator is input and performs gain compensation and phase compensation of the drive current so that the attractive force and cutting resistance acting on the armature by the electromagnet are balanced. Cutting condition detection device. 2 The armature is formed in a disk shape, and the electromagnet is configured to attract the armature in the axial direction, so that the detection control device detects the cutting load in the axial direction and optimizes the cutting state based on the detection result. The cutting state detecting device according to claim 1, wherein the cutting state detecting device controls the cutting state. 3 The armature is formed in a cylindrical shape, and the electromagnet is configured to attract the armature in the radial direction, so that the detection control device detects the cutting load in the radial direction and optimally controls the cutting state based on the detection result. The cutting state detection device according to claim 1. 4 The armature is formed in a conical shape, and the electromagnet is configured to attract the armature in the normal direction of its surface, so that the detection control device simultaneously detects the cutting load in the axial direction and the radial direction, and uses the detection result to The cutting state detection device according to claim 1, wherein the cutting state is optimally controlled based on the cutting state.