Numerical control device of a machine tool

Abstract

Numerical control device (20) of a machine tool (10) which controls the machine tool (10) which includes a spindle control section (11) for driving an induction motor as a spindle motor (12), wherein the numerical control device (20) comprises: a command sending device (21) that sends a speed command value and a magnetic flux command value to the spindle control section (11); a storage device (22) that stores corresponding magnetic flux quantities for tools (T) that can be used for the machine tool (10); a tool detection device (23) that detects a tool (T) selected for the machine tool (10); and a magnetic flux size setting device (24) which instructs the command sending device (21) to read a magnetic flux size corresponding to the tool (T) detected by the tool detection device (23) from the storage device (22) and to output the magnetic flux size to the spindle control section (11), wherein the magnetic flux size is increased in advance, before material removal with the selected tool (T), which can perform heavy material removal, by changing a magnetic flux command, corresponding to a diameter of the selected tool (T).

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The present invention relates to the numerical control device of a machine tool. Related technology

[0002] Traditionally, an induction motor can be used as the spindle motor of a machine tool. In this context, an induction motor refers to a motor in which an excitation current is passed through a stator coil in such a way that a rotating magnetic field is generated, thereby inducing a current in a rotor. The rotor is then rotated by this electromagnetic force, following the rotation of the magnetic field. A disadvantage of the induction motor is that the excitation current passes through the stator coil, generating heat. To avoid this disadvantage, a technology exists in which the magnetic flux of the rotating magnetic field or the excitation current is reduced when the induction motor's load is low, thus eliminating the need for high torque.

[0003] A conventional technology for the control device of an electric motor (an induction motor) is disclosed in patent specification 1. A conventional technology for a method for controlling the magnetic flux of an electric motor (a motor) is disclosed in patent specification 2. Furthermore, a conventional technology for a method for controlling an AC spindle motor is disclosed in patent specification 3. Patent specification 1: JP 2015 - 228 793 A Patent specification 2: JP S62 - 217 896 A Patent specification 3: JP S63 - 15 697 A

[0004] DE 10 2014 114 420 A1 describes a machine tool in which a spindle head is moved by a spindle head drive motor via a ball screw / nut mechanism, with tools of different weights being inserted into the spindle head beforehand. The load torque acting on the spindle head drive motor is recorded, and correlation data between the tool weight and the load torque is stored. When each tool is inserted into the spindle head, the tool's weight is estimated from the load torque with the spindle head stationary, as measured by a load torque detection unit, and from the correlation data between the tool weight and the load torque.

[0005] DE 10 2012 104 195 A1 describes a controller for a machine tool that cuts threads with a main shaft and a feed shaft, comprising a recognition unit that recognizes a size marking of the tap, a temperature detector unit that detects the temperature of a main shaft motor, an acceleration storage unit that stores the acceleration of the main shaft corresponding to the size marking of the tap, a rate storage unit that stores the rate of change of the acceleration of the main shaft depending on the temperature of the motor, and an acceleration calculation unit that calculates a new acceleration of the main shaft by multiplying an acceleration determined from the size marking of the tap and from the acceleration storage unit by a rate determined from the detected temperature and the rate storage unit.

[0006] DE 10 2010 054 401 A1 describes a machine tool with a tool holder having a coolant and / or lubricant line through which coolant and / or lubricant reaches the tool, wherein a valve arrangement is provided to which at least one line with coolant and / or lubricant is located at low operating pressure and another line with coolant and / or lubricant is located at high operating pressure, and a control system acts on the valve arrangement depending on the tool so that coolant and / or lubricant is located at low or high pressure, as well as a method for providing coolant and / or lubricant. SUMMARY OF THE INVENTION

[0007] However, in a case where these technologies are used, if an axis drive motor is used to start a heavy machining operation (a machining operation where the machining resistance is high) in a condition where the torque is reduced by reducing the magnetic flux of the induction motor serving as the spindle motor, and a large load is applied to the spindle motor, an abrupt load change at the start of the machining operation may cause a significant reduction in the spindle speed or a stalling of the spindle, thus making stability impossible during heavy machining.

[0008] In this respect, patent specification 1 discloses only a technology for storing an iron loss compensation current corresponding to the torque. Patent specification 2 also discloses only a technology for measuring and storing the relationship between a magnetic flux command and an excitation inductance at a load-free time. Furthermore, patent specification 3 discloses only a technology for controlling a spindle motor (for controlling it by inputting a speed command and an excitation current command) by a numerical control device.

[0009] In view of these circumstances, it is an object of the present invention to provide the numerical control device of a machine tool by which both a reduction in heat generation and stability during heavy machining can be achieved.

[0010] The claimed invention is defined by independent claim 1. Certain embodiments are described in the dependent claims.

[0011] (1) A numerical control device (for example, a numerical control device 20, which will be described later) of a machine tool according to the present invention, which controls the machine tool (for example, a machine tool 10, which will be described later) which includes a spindle control section (for example, a spindle control section 11, which will be described later) for driving a spindle motor (for example, a spindle motor 12, which will be described later), comprises: a command sending device (for example, a command sending section 21, which will be described later) which sends a speed command value and a magnetic flux command value to the spindle control section;a storage device (for example, a storage section 22, which will be described later) that stores magnetic flux quantities (for example, magnetic flux quantities Φ, which will be described later) corresponding to tools (for example, tools T, which will be described later) that can be used for the machine tool; a tool detection device (for example, a tool detection section 23, which will be described later) that detects a tool selected for the machine tool; and a magnetic flux quantity setting device (for example, a magnetic flux quantity setting section 24, which will be described later) that instructs the command sending device to read a magnetic flux quantity corresponding to the tool detected by the tool detection device from the storage device and to output the magnetic flux quantity to the spindle control section.

[0012] (2) In the case of the numerical control device of the machine tool according to (1), the tool selected for the machine tool may be a drilling tool.

[0013] According to the present invention, a magnetic flux command for a spindle motor is modified according to the requirements of a selected tool, and thereby it is possible to provide the numerical control device of a machine tool, through which both a reduction in heat generation and stability during heavy material removal can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a diagram showing the configuration of a numerical control system according to a first embodiment of the present invention; and Fig. Figure 2 is a flowchart showing the operation of the numerical control system according to the first embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] A first embodiment of the present invention is described below with reference to the drawings. [First embodiment]

[0015] Fig. Figure 1 is a diagram showing the configuration of a numerical control system according to a first embodiment of the present invention. Fig. Figure 2 is a flowchart showing the operation of the numerical control system according to the first embodiment of the present invention.

[0016] As in Fig. As shown in Figure 1, the numerical control system 1 according to the first embodiment is formed by a machine tool 10 and a numerical control device 20. The machine tool 10 comprises a spindle control section 11, such as an amplifier, a spindle motor 12, a torque transmission device 13, and a spindle 14. When a workpiece W is attached to the spindle 14, a drive current is output from the spindle control section 11 to the spindle motor 12. The torque of the spindle motor 12 is transmitted to the spindle 14 by the torque transmission device 13, thereby rotating the workpiece W. In this state, a tool T is brought into contact with the workpiece W, and the workpiece W can thus be machined by the tool T.

[0017] An induction motor is used as the spindle motor 12. In a case where, as described above, the induction motor is used as the spindle motor 12, there is a possibility that if the magnetic flux of the induction motor is reduced at a low load to reduce heat generation, stability during heavy machining will not be achieved.

[0018] Therefore, the numerical control device 20 includes a mechanism to prevent the occurrence of such an inconvenience as described in Fig. Figure 1 shows a command transmission section 21 serving as a command transmission device, a memory section 22 serving as a memory device, a tool detection section 23 serving as a tool detection device and a magnetic flux adjustment section 24 serving as a magnetic flux adjustment device.

[0019] The command sending section 21 sends a speed command value and a magnetic flux quantity command value to the spindle control section 11 of the machine tool 10.

[0020] The memory section 22 is integrated into the numerical control device 20 and stores corresponding magnetic flux quantities Φ for tools T that can be used for the machine tool 10.

[0021] The tool detection section 23 detects the tool T selected for the machine tool 10 from among the tools T that can be used for the machine tool 10. A specific procedure for this is described later.

[0022] The magnetic flux setting section 24 reads the magnetic flux quantity Φ corresponding to the tool T detected by the tool detection section 23 from the memory section 22 and instructs the command sending section 21 to output the magnetic flux quantity Φ to the spindle control section 11 of the machine tool 10.

[0023] Then, with reference to Fig. 2. The functionality of the numerical control system 1 is described. The workflow is executed, for example, immediately before the execution of a processing program.

[0024] In step S1, the tool detection section 23 identifies the tool T selected for machine tool 10 from among the tools T that can be used for machine tool 10. More precisely, the tool detection section 23 reads a tool number from the machining program executed by machine tool 10 with reference to that program and identifies the tool T corresponding to that tool number as the selected tool.

[0025] In step S2, the magnetic flux size setting section 24 reads the magnetic flux size Φ corresponding to the tool T detected by the tool detection section 23 from the memory section 22.

[0026] In step S3, the magnetic flux quantity setting section 24 instructs the command sending section 21 to output the magnetic flux quantity Φ to the spindle control section 11 of the machine tool 10. The command sending section 21 receives the command to output the magnetic flux quantity Φ to the spindle control section 11 of the machine tool 10.

[0027] Although the maximum material removal rate varies depending on the type, size, and other characteristics of the tool T, in the numerical control system 1, as described above, a magnetic flux command (excitation current command) is modified according to the selected tool T (if the tool T capable of heavy material removal is selected, the magnetic flux is increased beforehand), and thus it is possible with the numerical control device 20 of the machine tool to achieve both a reduction in heat generation and stability during heavy material removal.

[0028] In particular, compared to a case where the surface of the workpiece W is machined with a milling tool T used in milling or the like, a drilling tool T used in a drilling application has a large contact area at the beginning of contact with the workpiece W. Therefore, the load increases rapidly, and consequently, the speed of the spindle 14 is frequently reduced or stopped, thus necessitating a high increase in the magnetic flux magnitude Φ. Therefore, the present invention is advantageous for the drilling tool T described above.

[0029] In principle, when performing the same machining operation with the same type of tool T, the load increases with an increase in the diameter of the tool T, so that the magnetic flux quantity Φ is preferably increased. Therefore, the present invention is useful even in this case. [Other embodiments]

[0030] Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment described above. With regard to the results described in connection with the present embodiment, only the most desirable results obtained by the present invention have been listed, and the results of the present invention are not limited to those described in connection with the present embodiment.

[0031] According to the description of the first embodiment discussed above, the tool detection section 23 detects the tool T, for example, based on the tool number in the machining program, when the tool detection section 23 of the numerical control device 20 detects the tool T selected for the machine tool 10. However, there are no particular restrictions regarding the method for detecting the tool T. For example, a configuration can be used in which barcodes are attached to all tools T, with the barcodes being read by a barcode scanner (barcode reader) and the tools T thereby being detected. Alternatively, the tool T can be detected by reading the tool T itself using an image sensor.

[0032] Although the first embodiment discussed above describes a case in which the memory section 22 is integrated into the numerical control device 20, the memory section 22 does not necessarily have to be integrated into the numerical control device 20. A required magnetic flux quantity Φ can, for example, be retrieved from the memory section 22 located in a cloud via a network. EXPLANATION OF REFERENCE SYMBOLS 1 numerical control system 10 machine tool 11 Spindle control section 12 spindle motor 13 Torque transmission device 14 spindles 20 numerical control device 21 Command transmission section (command transmission device) 22 Storage section (storage device) 23 Tool detection section (tool detection device) 24 Magnetic flux size adjustment section (magnetic flux size adjustment device) T tool W workpiece

Claims

[1] Numerical control device (20) of a machine tool (10) which controls the machine tool (10) which includes a spindle control section (11) for driving an induction motor as a spindle motor (12), wherein the numerical control device (20) includes: a command sending device (21) that sends a speed command value and a magnetic flux command value to the spindle control section (11); a storage device (22) that stores corresponding magnetic flux quantities for tools (T) that can be used for the machine tool (10); a tool detection device (23) that detects a tool (T) selected for the machine tool (10); and a magnetic flux size setting device (24) which instructs the command sending device (21) to read a magnetic flux size corresponding to the tool (T) detected by the tool detection device (23) from the storage device (22) and to output the magnetic flux size to the spindle control section (11), wherein the magnetic flux size is increased in advance, before material removal with the selected tool (T), which can perform heavy material removal, by changing a magnetic flux command, corresponding to a diameter of the selected tool (T). [2] Numerical control device (20) of the machine tool (10) according to claim 1, wherein the tool (T) selected for the machine tool (10) is a drilling tool.

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