Control device for machine tool

Abstract

To provide a control device for a machine tool that suppresses an increase in power consumption.SOLUTION: A control device for a machine tool which performs a machining step by rotating a machining tool with an actuator according to an NC program, comprises: a control unit that feedback-controls a power value applied to the actuator so as to maintain the number of rotations of the machining tool constant; a determination unit that determines whether or not a lapsed time from when application of power to the actuator begins is before the lapse of a necessary time required for stabilization of the power value; and a correction unit that performs correction processing to correct the power value before the lapsed time exceeds the necessary time if the determination made by the determination unit is positive, wherein the correction unit performs correction processing in such a manner that the corrected power value before the lapsed time exceeds the necessary time is closer to the power value after the lapsed time has exceeded the necessary time than an uncorrected power value before the lapsed time exceeds the necessary time.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control device for a machine tool. [Background technology]

[0002] 2. Description of the Related Art There is known a machine tool that performs a machining process by rotating a machining tool with an actuator in accordance with an NC program (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2021-022014 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is conceivable to perform feedback control of the power value applied to the actuator so as to maintain a constant rotation speed of the machining tool. In this case, the power value may increase from when the power application to the actuator starts until the power value stabilizes. This may increase the power consumption of the machine tool.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a control device for a machine tool that suppresses an increase in power consumption. [Means for solving the problem]

[0006] The above object can be achieved by a control device for a machine tool that performs a machining process by rotating a machining tool with an actuator in accordance with an NC program, the control device comprising: a control unit that feedback controls a power value applied to the actuator so as to maintain a constant rotation speed of the machining tool; a judgment unit that judges whether the elapsed time since the application of power to the actuator began is before a required time required for the power value to stabilize has elapsed; and a correction unit that, if the judgment unit judges positive, executes a correction process to correct the power value before the elapsed time elapses the required time, wherein the correction unit executes the correction process so that the corrected power value before the elapsed time elapses the required time is closer to the power value after the elapsed time has elapsed the required time than the uncorrected power value before the elapsed time elapses the required time. Effect of the Invention

[0007] According to the present invention, it is possible to provide a control device for a machine tool that suppresses an increase in power consumption. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a machine tool. [Diagram 2] 4 is a time chart illustrating an example of power values ​​applied to a rotary actuator. [Diagram 3] 11 is a flowchart illustrating a correction process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] FIG. 1 is a schematic diagram of a machine tool 1. The machine tool 1 is, for example, a machining center. The machine tool 1 includes a spindle 10, a machining tool 12, an X-axis actuator 20, a Y-axis actuator 21, a Z-axis actuator 22, a rotary actuator 23, a sensor group 30, a controller 50, and a display 51. The machining tool 12 is attached to the tip of the spindle 10. The machining tool 12 extends along the Z-axis direction. The machining tool 12 is, for example, a cutting tool such as a milling cutter. Examples of the machining of the workpiece W by the machining tool 12 include cutting, grinding, finishing (polishing), drilling, and deburring.

[0010] The X-axis actuator 20, the Y-axis actuator 21, and the Z-axis actuator 22 move the machining tool 12 together with the spindle 10 in the X-axis, Y-axis, and Z-axis directions, respectively. The rotation actuator 23 rotates the machining tool 12 around a central axis extending along the Z-axis direction of the machining tool 12. The X-axis, Y-axis, and Z-axis directions are perpendicular to each other. The Z-axis direction is parallel to the vertical direction. The X-axis and Y-axis directions are both horizontal.

[0011] The sensor group 30 is composed of a plurality of sensors. Specifically, the sensor group 30 includes a sensor for detecting each torque of the X-axis actuator 20, the Y-axis actuator 21, the Z-axis actuator 22, and the rotation actuator 23, a sensor for detecting a power value applied to the rotation actuator 23, and a sensor for detecting a Z coordinate position of the machining tool 12. The torques of the X-axis actuator 20, the Y-axis actuator 21, the Z-axis actuator 22, and the rotation actuator 23 correspond to an X-axis torque, a Y-axis torque, a Z-axis torque, and a rotation torque that move the machining tool 12 in the X-axis direction, the Y-axis direction, the Z-axis direction, and the rotation direction, respectively.

[0012] The controller 50 is electrically connected to the X-axis actuator 20, the Y-axis actuator 21, the Z-axis actuator 22, the rotary actuator 23, and the sensor group 30. The controller 50 is a computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an HDD (Hard Disk Drive). The controller 50 controls the X-axis actuator 20, the Y-axis actuator 21, the Z-axis actuator 22, and the rotary actuator 23 based on measurement data from the sensor group 30 and information previously stored in the ROM in accordance with an NC (Numerical Control) program previously stored in the HDD. In this way, the controller 50 controls the X-axis torque, the Y-axis torque, the Z-axis torque, and the rotary torque of the machining tool 12 and the position of the machining tool 12 to machine the workpiece W. The controller 50 executes measurement data collection control to collect measurement data from the sensor group 30 during the execution of the machining process. In addition, a display 51 capable of displaying the collected measurement data is connected to the controller 50. The controller 50 is an example of a control device for the machine tool 1. The CPU, ROM, and RAM of the controller 50 functionally realize a control unit, a determination unit, and a correction unit described below.

[0013] The controller 50 feedback controls the power value applied to the rotary actuator 23 so as to maintain the rotational speed of the machining tool 12 constant. In detail, the power value to the rotary actuator 23 is feedback controlled so as to reduce the deviation between the target rotational speed and the actual rotational speed of the rotary actuator 23. As a result, for example, when the actual rotational speed of the rotary actuator 23 is smaller than the target rotational speed, the power value is controlled to increase. When the actual rotational speed of the rotary actuator 23 is larger than the target rotational speed, the power value is controlled to decrease. This control is an example of control executed by the control unit. In addition, as will be described in detail later, the controller 50 executes the above feedback control while executing a correction process for correcting the power value applied to the rotary actuator 23 when a predetermined condition is satisfied.

[0014] Fig. 2 is a time chart illustrating the power value applied to the rotary actuator 23. Fig. 2 shows the transition of the power value after the machine tool 1 is started and the application of power to the rotary actuator 23 is started. Fig. 2 shows an uncorrected power value BW, which is the power value before the above-mentioned correction process is performed, a corrected power value AW, which is the power value after the correction process is performed, and a stable power value CW, which is the power value after stabilization. In Fig. 2, the uncorrected power value BW and the stable power value CW are shown by solid lines, and the corrected power value AW is shown by a dotted line.

[0015] First, the uncorrected power value BW and the stable power value CW will be described. As shown in FIG. 2, the uncorrected power value BW is maximum immediately after the application of power to the rotary actuator 23 starts from time t0. The uncorrected power value BW gradually decreases until time t1. After time t1, the stable power value CW is almost constant. In this way, a certain time is required from the start of the application of power to the rotary actuator 23 until the power value stabilizes. This time is called the required stabilization time. In this way, the uncorrected power value BW before time t1 is higher than the stable power value CW after time t1. This is considered to be due to the temperature of the rotary actuator 23. Immediately after the start of the application of power, the rotary actuator 23 is at a low temperature and the resistance to the rotation of the rotary actuator 23 is large. Therefore, a larger power value is required to maintain a predetermined rotation speed by the above-mentioned feedback control. Such an increase in the power value is a factor in increasing the power consumption of the machine tool 1.

[0016] 2 also shows a threshold value WT indicating that the power value applied to the rotary actuator 23 is abnormal. The controller 50 determines that some abnormality has occurred when the power value is equal to or greater than the power threshold value WT. For example, the controller 50 stops the machining process when an abnormality has occurred. As shown in FIG. 2, when the uncorrected power value BW is equal to or greater than the power threshold value WT, it may be erroneously determined that an abnormality has occurred when no abnormality has occurred, which may reduce the accuracy of the abnormality determination.

[0017] Therefore, the controller 50 executes a correction process to correct the power value applied to the rotary actuator 23. As shown in Fig. 2, the corrected power value AW becomes substantially the same as the stable power value CW. This makes it possible to suppress the power consumption of the machine tool 1. In addition, since the corrected power value AW becomes less than the power threshold value WT, erroneous determination of an abnormality can be avoided, and a decrease in the accuracy of the abnormality determination can be suppressed.

[0018] 3 is a flow chart illustrating the correction process. After the machine tool 1 is powered on, measurement of the elapsed time from when the application of power to the rotary actuator 23 begins is started (step S1). Next, the controller 50 judges whether the measured elapsed time is before the above-mentioned required stabilization time has elapsed (step S2). If the answer is No in step S2, that is, if the elapsed time has already elapsed after the required stabilization time, this control ends. Step S2 is an example of control executed by the judgment unit.

[0019] If the answer is Yes in step S2, the controller 50 executes the above-mentioned correction process (step S3). Step S3 is an example of control executed by the correction unit. In the correction process, the uncorrected power value BW is corrected so that the corrected power value AW is closer to the stable power value CW than the uncorrected power value BW. Specifically, the correction process is executed by the following calculation formula: Corrected power value AW = Uncorrected power value BW - Subtracted value ΔW Subtraction value ΔW = (temperature correction amount × weighting coefficient kt) + (average rotation speed correction amount × weighting coefficient kr)

[0020] The uncorrected power value BW is a power value at which the above-mentioned feedback control is performed. Since the controller 50 performs the feedback control, the uncorrected power value BW can be obtained. The temperature correction amount is a correction amount determined, for example, in consideration of the power value that decreases in accordance with the rise in temperature of the rotary actuator 23 from the start of application. For example, the temperature correction amount is a fluctuating value expressed as a function of the elapsed time from the start of application of power to the rotary actuator 23, which is a value obtained by subtracting the power value after stabilization from the power value before stabilization. Therefore, the subtraction value ΔW is expressed as a function of the elapsed time. The average rotation speed correction amount is a correction amount determined in consideration of the average rotation speed of the machining tool 12 when machining one workpiece W. The average rotation speed correction amount is, for example, a fixed value. The correction process is performed based on such an arithmetic expression. It should be noted that the subtraction value ΔW is not limited to the above content, and may not include, for example, the average rotation speed correction amount and the weighting coefficient kr.

[0021] The controller 50 collects the measurement data from the sensor group 30 during the execution of the machining process. For example, the controller 50 may collect the measurement data every time a predetermined number of machining processes are executed. When the measurement data is collected manually, the measurement data is collected until, for example, a collection end button displayed on the display 51 is operated. When the measurement data is collected automatically, the measurement data is collected from when the controller 50 detects a start trigger until it detects an end trigger or until a timeout occurs. The measurement data is stored in the RAM, for example, in a CSV (Comma Separated Value) format. The measurement data can be treated as continuous data and may be displayed, for example, as a graph on the display 51. Such measurement data can be used, for example, to analyze the cause of machining defects.

[0022] Furthermore, the controller 50 may collect measurement data for each type of workpiece W based on the O number and N number of the NC program. The O number is a program number for identifying the NC program. The N number is a sequence number for identifying the block number of the NC program, which is divided into blocks. For example, if the workpiece is an automobile part, measurement data may be collected and stored in the RAM for each type of car in which the part is used.

[0023] Furthermore, the controller 50 may collect only measurement data during a specific type of machining based on the O number and N number of the NC program. In this way, it is possible to collect measurement data limited to only necessary information.

[0024] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0025] 1 Machine tools 12 Processing tools 50 Controller (control device, control unit, judgment unit, correction unit)

Claims

[Claim 1] A control device for a machine tool that rotates a machining tool by an actuator in accordance with an NC program to perform a machining process, a control unit that feedback controls a power value applied to the actuator so as to maintain a constant rotation speed of the machining tool; a determination unit that determines whether or not a time that has elapsed since application of power to the actuator has started has elapsed before a required time that is necessary for the power value to stabilize has elapsed; a correction unit that executes a correction process to correct the power value before the elapsed time exceeds the required time when the determination unit makes a positive determination, A control device for a machine tool, wherein the correction unit performs the correction process so that the corrected power value before the elapsed time exceeds the required time is closer to the power value after the elapsed time has passed the required time than the uncorrected power value before the elapsed time has passed the required time.

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