Machine tool and machine tool control device

Abstract

To provide a machine tool and a control device for the machine tool that are able to easily avoid occurrence of an error excess alarm by referring to a state of a drive unit that drives a spindle.SOLUTION: A machine tool comprises: a drive unit configured to drive a spindle that rotatably holds a workpiece; a servo motor configured to drive a tool for machining the workpiece held by the spindle; a power supply configured to supply electric power to at least the drive unit and the servo motor; a current detection unit configured to detect a current value input to the servo motor; a storage unit configured to store an upper limit current value input to the servo motor; and a control unit configured to control the servo motor to execute drive control of the tool. When the current value detected by the current detection unit exceeds an upper limit current value immediately after start of the spindle, the control unit controls the servo motor by changing an acceleration / deceleration time constant from a first time constant to a second time constant lower in power consumption than the first time constant.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Generally, machine tools are known that include a spindle that rotatably supports a workpiece, a tool for machining the workpiece, etc. The tool drive mechanism of the machine tool is provided with a servo motor, and the tool of the machine tool can be operated by inputting a predetermined current to the servo motor.

[0003] However, when the power supply voltage of a machine tool drops, an excessive error alarm occurs, indicating that the actual position of the servo motor differs from the position command value.

[0004] In Patent Document 1, stable operation of an electric motor is achieved by executing control to increase or decrease the acceleration / deceleration time constant, which adjusts the responsiveness of the electric motor to acceleration or deceleration, in accordance with fluctuations in the input voltage.In Patent Document 2, a limit value for motor output that does not adversely affect motor drive is calculated based on the voltage of the AC power supply input to the motor, and the acceleration / deceleration time constant or feed override control parameter for implementing that limit is determined. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3252114 specification [Patent Document 2] Patent No. 5149410 specification Summary of the Invention [Problem to be solved by the invention]

[0006] Fluctuations in the power supply voltage of machine tools are often caused by the drive unit that drives the spindle, which has the largest power consumption, and are particularly likely to occur when the drive unit that drives the spindle is started. However, there is no attempt to control the acceleration / deceleration time constant of the servo motor that drives the tool in response to control of the drive unit that drives the spindle.

[0007] The present invention aims to provide a machine tool and a control device for the machine tool that can easily avoid the issuance of an excessive error alarm by referring to the state of the drive unit that drives the spindle. [Means for solving the problem]

[0008] A machine tool according to an embodiment of the present disclosure includes a drive unit that drives a spindle that rotatably holds a workpiece, a servo motor that drives a tool to machine the workpiece held by the spindle, a power source that supplies power to at least the drive unit and the servo motor, a current detection unit that detects the current value input to the servo motor, a memory unit that stores an upper limit current value input to the servo motor, and a control unit that controls the servo motor to drive and control the tool, and if the current value detected by the current detection unit exceeds the upper limit current value immediately after starting the spindle, the control unit changes the acceleration / deceleration time constant from a first time constant to a second time constant that consumes less power than the first time constant and controls the servo motor.

[0009] In a machine tool according to an embodiment of the present disclosure, it is preferable that the machine tool further includes a voltage detection unit that detects a power supply voltage value input from a power supply, and that if, immediately after starting the spindle, the current value detected by the current detection unit is equal to or less than an upper limit current value and the power supply voltage value detected by the voltage detection unit is equal to or less than a threshold voltage value, the control unit controls the servo motor by changing the acceleration / deceleration time constant from the first time constant to a third time constant that consumes less power than the first time constant and more power than the second time constant.

[0010] A control device for a machine tool according to an embodiment of the present disclosure is a control device for a machine tool including a drive unit that drives a spindle that rotatably holds a workpiece, a servo motor that drives a tool to machine the workpiece held by the spindle, and a power source that supplies power to at least the drive unit and the servo motor, and is equipped with a current detection unit that detects the current value input to the servo motor, a memory unit that stores an upper limit current value input to the servo motor, and a control unit that controls the servo motor to perform drive control of the tool, and if the current value detected by the current detection unit exceeds the upper limit current value immediately after starting the spindle, the control unit changes the acceleration / deceleration time constant from a first time constant to a second time constant that consumes less power than the first time constant and controls the servo motor.

[0011] In a control device for a machine tool according to an embodiment of the present disclosure, it is preferable that the control unit further includes a voltage detection unit that detects a power supply voltage value input from a power supply, and that if, immediately after starting the spindle, the current value detected by the current detection unit is equal to or less than an upper limit current value and the power supply voltage value detected by the voltage detection unit is equal to or less than a threshold voltage value, the control unit controls the servo motor by changing the acceleration / deceleration time constant from the first time constant to a third time constant that consumes less power than the first time constant and more power than the second time constant. [Effects of the Invention]

[0012] According to the machine tool of the embodiment of the present disclosure, it is possible to provide a machine tool and a control device for the machine tool that can easily avoid the generation of an excessive error alarm by referring to the state of the drive unit that drives the spindle. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a partial perspective view of a machine tool according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing the internal configuration of the machine tool shown in FIG. [Figure 3] 3 is a flowchart showing a series of workpiece machining steps executed in the machine tool according to the present embodiment. [Figure 4]4 is a flowchart showing a process for determining a time constant of a servo motor in a series of workpiece machining steps shown in FIG. 3. [Figure 5] 5 is a waveform diagram showing an example of a change over time in the rotation speed of a servo motor that is changed by controlling the current value shown in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a machine tool according to the present embodiment will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to the embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0015] Fig. 1 is a partial perspective view of a machine tool 1 according to this embodiment. The machine tool 1 shown in Fig. 1 is a device for machining a workpiece W, which is a long, round bar. The machine tool 1 includes a spindle 2 that rotatably supports the workpiece W, a rotary tool driving device 13 that includes a B-axis rotary tool device 3, and a numerically controlled (NC) device 5, which will be described later.

[0016] The spindle 2 is mounted on a support table 6. The spindle 2 holds the workpiece W rotatably around the Z axis, with the Z axis direction as its axis, and also holds the workpiece W movably to the front side of the support table 6 by power generated by a spindle motor (fourth servo motor) MT4 that constitutes the drive unit DU. The support table 6 is fixedly supported by a bed 7.

[0017] A rail 8 extending along the X-axis direction (also referred to as the horizontal direction) perpendicular to the Z-axis direction is installed on the front side of the support base 6. A base 10 is attached to the rail 8 and slides in the direction of arrow α1 by power generated by a first servo motor MT1. A rail 11 extending along the Y-axis direction (also referred to as the vertical direction) perpendicular to the Z-axis and X-axis directions is installed on the base 10. A rotary tool driving device 13 is attached to the rail 11 and slides in the direction of arrow α2 by power generated by a second servo motor MT2.

[0018] The rotary tool driving device 13 is a device that holds tools for machining a workpiece W. The rotary tool driving device 13 has a B-axis rotary tool device 3 that has tools 131 and 132, as well as a first tool 31 and a second tool 32. The tools 131 and 132 are arranged side by side along the X-axis direction with their tips facing downward. The first tool 31 and the second tool 32 are rotatably held by a B-axis rotary tool main body 33 that constitutes the B-axis rotary tool device 3, and are arranged side by side along the X-axis direction with their tips facing sideways. The machine tool 1 according to this embodiment can machine the workpiece W with a predetermined tool by moving the workpiece W in the Z-axis direction using the spindle 2 and moving the rotary tool driving device 13 in the direction of arrow α1 or arrow α2. The B-axis rotary tool main body 33 is supported so as to be rotatable in the direction of arrow α3 around the rotation axis A of the rotation motor MT3 by power generated by the rotation motor (third servo motor) MT3.

[0019] Each of the servo motors MT1 to MT4 provided in the machine tool 1 operates on power supplied from a power supply PS. This power supply PS converts power supplied from a household or commercial power source into power usable by the machine tool 1 according to this embodiment, and supplies the converted power to at least each of the servo motors MT1 to MT4.

[0020] Fig. 2 is a block diagram showing the internal configuration of the machine tool 1 shown in Fig. 1. As shown in Fig. 2, the B-axis rotary tool device 3 includes a B-axis rotary tool main body 33, a horizontal movement mechanism M1, a first servo motor MT1, a vertical movement mechanism M2, a second servo motor MT2, a turning mechanism M3, and a turning motor MT3.

[0021] The horizontal movement mechanism M1 enables the entire rotary tool driving device 13, including the B-axis rotary tool main body 33, to move in the direction of the arrow α1. The first servo motor MT1 converts input current into mechanical output (power such as torque and rotation speed) and supplies it to the horizontal movement mechanism M1. This causes the horizontal movement mechanism M1 to move the B-axis rotary tool main body 33 back and forth in the direction of the arrow α1. The operation of the first servo motor MT1 is controlled by a motion controller C1.

[0022] The motion controller C1 receives power from a power source PS and inputs a predetermined current to the first servo motor MT1 in response to a control signal transmitted from the NC device 5 (described later). The control signal transmitted to the motion controller C1 includes at least the rotation amount (rad or number of steps) and rotation speed (rpm) of the first servo motor MT1. The first servo motor MT1 is provided with a sensor Se1, which detects the actual rotation amount and rotation speed of the first servo motor MT1 and transmits them to the motion controller C1. The motion controller C1 compares the rotation amount and rotation speed values ​​of the first servo motor MT1 contained in the control signal with the actual rotation amount and rotation speed values ​​of the first servo motor MT1 detected by the sensor Se1, and inputs a predetermined current to the first servo motor MT1 so as to eliminate any deviation between these values. Hereinafter, the control methods of the motion controllers C2 to C4 are the same as those of the motion controller C1, and therefore detailed description thereof will be omitted.

[0023] The vertical movement mechanism M2 enables the entire rotary tool driving device 13, including the B-axis rotary tool main body 33, to move up and down in the direction of arrow α2. The second servo motor MT2 generates power for operating the vertical movement mechanism M2. The operation of the second servo motor MT2 is controlled by a motion controller C2. The method of controlling the second servo motor MT2 by the motion controller C2 is the same as the method of controlling the first servo motor MT1 by the motion controller C1, so a detailed description will be omitted.

[0024] The turning mechanism M3 can turn the B-axis rotary tool main body 33 in the direction of arrow α3 around the turning axis A of the turning motor MT3. The turning motor MT3 generates power for operating the turning mechanism M3. The operation of the turning motor MT3 is controlled by a motion controller C3. The method of controlling the turning motor MT3 by the motion controller C3 is the same as the method of controlling the first servo motor MT1 by the motion controller C1, so a detailed description will be omitted.

[0025] As shown in FIG. 2, the spindle 2 includes a spindle drive mechanism M4 and a spindle motor MT4 that constitute the drive unit DU. The spindle drive mechanism M4 supports the workpiece W rotatably around the Z axis, with the Z axis as its axis, and supports the workpiece W so that it can move toward the front side of the support table 6 using power generated by the spindle motor MT4. The spindle motor MT4 generates power for operating the spindle drive mechanism M4. The operation of the spindle motor MT4 is controlled by a motion controller C4. The method of controlling the spindle motor MT4 by the motion controller C4 is the same as the method of controlling the first servo motor MT1 by the motion controller C1, so a detailed description will be omitted. The spindle motor MT4 does not have to be a servo motor as long as stable rotation can be obtained.

[0026] The NC device 5 is a device for controlling the operation of each of the spindle 2 and the B-axis rotary tool device 3. As shown in FIG. 2, the NC device 5 is configured to include an interface unit 51, a memory unit 52, an input unit 53, an output unit 54, a current detection unit 55, a voltage detection unit 56, and a control unit 57. The interface unit 51, the memory unit 52, the input unit 53, the output unit 54, the current detection unit 55, the voltage detection unit 56, and the control unit 57 are connected to one another via a bus 58. Various control signals from the control unit 57 are transmitted to the motion controllers C1 to C5 via the interface unit 51. A plurality of current values ​​output from the motion controllers C1 to C4 to the corresponding servo motors MT1 to MT4 are transmitted to the current detection unit 55 via the interface unit 51.

[0027] The storage unit 52 includes, for example, a semiconductor storage device, and stores programs, data, and the like used for processing by the control unit 57. The storage unit 52 stores at least a program for causing the control unit 57 to execute a series of workpiece machining steps performed by the spindle 2 and the B-axis rotary tool device 3. The program may be installed into the storage unit 52 from a computer-readable portable recording medium such as a CD-ROM using a known setup program or the like.

[0028] Furthermore, the storage unit 52 stores in advance the upper limit current values ​​input from the motion controllers C1 to C4 to the servo motors MT1 to MT4. The upper limit current values ​​are current values ​​at which the servo motors may be damaged.

[0029] Input unit 53 may be any commonly known device that is capable of inputting data, and generates a signal corresponding to an operation by an operator of machine tool 1. The generated signal is supplied to control unit 57 as an instruction from the operator.

[0030] The output unit 54 may be any commonly known device capable of displaying video, images, etc., and displays video corresponding to video data supplied from the control unit 57, images corresponding to image data, etc.

[0031] The current detection unit 55 detects the current value input from the motion controllers C1 to C4 to the servo motors MT1 to MT4 and transmits the detection result to the control unit 57. The voltage detection unit 56 detects the power supply voltage value input from the power supply PS to the spindle 2 and the B-axis rotary tool device 3 and transmits the detection result to the control unit 57.

[0032] The control unit 57 comprehensively controls the overall operation of the machine tool 1 and is, for example, a CPU (Central Processing Unit). The control unit 57 executes a series of workpiece machining steps in accordance with a program stored in the memory unit 52. The control unit 57 controls the servo motors MT1 to MT4 and executes drive control of the tools by transmitting control signals for executing the series of workpiece machining steps to the motion controllers C1 to C4 via the interface unit 51. The control signals include the rotation amount (rad or number of steps) and rotation speed (rpm) of each servo motor.

[0033] FIG. 3 is a flowchart showing a series of workpiece machining steps executed by the machine tool 1 according to this embodiment.

[0034] When a command to process a workpiece is input according to a predetermined procedure, first, the control unit 57 executes operation control of the spindle 2 in accordance with a program stored in the memory unit 52 (step S10). Specifically, the control unit 57 transmits a predetermined control signal (the amount of rotation (rad or number of steps) and the rotation speed (rpm) of the spindle motor MT4) to the motion controller C4 via the interface unit 51. In response to the control signal transmitted from the control unit 57, the motion controller C4 controls the spindle motor MT4 to drive the spindle drive mechanism M4, thereby rotating the workpiece W about the Z axis and moving the workpiece W to the front side of the support table 6.

[0035] Next, the control unit 57 executes operation control of the tools (step S11). Specifically, the control unit 57 controls at least one of the servo motors MT1 and MT2 to move the B-axis rotary tool device 3 and move the B-axis rotary tool main body 33 in the direction of the arrow α1 or the arrow α2. This enables the machine tool 1 according to this embodiment to press the tools 131, 132, the first tool 31, and the second tool 32 against the rotating workpiece W to machine the workpiece W.

[0036] Finally, the control unit 57 determines whether the series of workpiece machining steps has been completed (step S12). If the series of workpiece machining steps has not been completed (No in step S12), the process returns to step S10. If the series of workpiece machining steps has been completed (Yes in step S12), the series of workpiece machining steps ends.

[0037] Fig. 4 is a flowchart showing the process of determining the time constant of the second servo motor MT2 in the series of workpiece machining steps shown in Fig. 3. The process shown in Fig. 4 is executed at regular time intervals in the series of workpiece machining steps shown in Fig. 3. In Fig. 4, the second thermomotor MT2 is described as an example, but similar processes may also be performed for the other servo motors MT1 and MT3.

[0038] First, the control unit 57 determines whether or not it is immediately after the spindle 2 has started (step S20). In this embodiment, "immediately after the spindle 2 has started" refers to the period from when a control signal for starting the rotation operation of the spindle 2 is input to the motion controller C4 until the spindle 2 starts operating at its rated speed. If it is not immediately after the spindle 2 has started (No in step S20), the acceleration / deceleration time constant is set to the first time constant (step S23), and the series of processes ends.

[0039] If the spindle 2 has just started up (Yes in step S20), the control unit 57 determines (step S21) whether the current value supplied to the second servo motor MT2 detected by the current detection unit 55 exceeds the upper limit current value stored in the memory unit 52. If the current value of the second servo motor MT2 exceeds the upper limit current value (Yes in step S21), there is a risk of damage to the second servo motor MT2, so the control unit 57 sets the acceleration / deceleration time constant to the second time constant (step S25) and ends the series of processes.

[0040] Next, if the current value of the second servo motor MT2 does not exceed the upper limit current value (No in step S21), the control unit 57 determines whether the power supply voltage value of the power supply PS detected by the voltage detection unit 56 is equal to or less than the threshold voltage value (i.e., whether a voltage drop occurs in the power supply PS) (step S22). If the power supply voltage value of the power supply PS exceeds the threshold voltage value (No in step S22), there is no risk of damage to the second servo motor MT2 and no voltage drop occurs in the power supply PS, so the control unit 57 sets the acceleration / deceleration time constant to the first time constant (step S23) and ends the series of processes.

[0041] Next, if the power supply voltage value of the power supply PS is equal to or lower than the threshold voltage value (Yes in step S22), although there is no risk of damage to the second servo motor MT2, a voltage drop occurs in the power supply PS, so the control unit 57 sets the acceleration / deceleration time constant to the third time constant (step S24) and terminates the series of processes.

[0042] Here, the acceleration / deceleration time constant refers to a value corresponding to the time it takes for the rotational speed of the servo motor to reach a set rotational speed. The first time constant corresponds to the shortest time it takes for the rotational speed of the second servo motor MT2 to reach a set rotational speed during normal operation. The second time constant is slower than the first time constant in the time it takes for the rotational speed of the second servo motor MT2 to reach the set rotational speed, resulting in a lower power consumption per unit time of the second servo motor MT2 than with the first time constant. The third time constant is slower than the first time constant in the time it takes for the rotational speed of the second servo motor MT2 to reach the set rotational speed, but faster than the second time constant, resulting in a lower power consumption per unit time of the second servo motor MT2 than with the first time constant and higher than with the second time constant.

[0043] According to the processing flow shown in FIG. 4, the first time constant is set for the second servo motor MT2 except immediately after the spindle 2 is started, and immediately after the spindle 2 is started, one of the first to third time constants is set depending on the current value and power supply voltage value to the second servo motor MT2.

[0044] Fig. 5 is a waveform diagram showing an example of the change over time in the rotation speed of the second servo motor MT2 caused by the control of the current value shown in Fig. 4. In Fig. 4, the horizontal axis represents time (times t1 to t3) (ms), and the vertical axis represents the rotation speed (r / min) of the servo motor.

[0045] When controlling the second servo motor MT2 in the series of workpiece machining steps shown in Fig. 3, the control unit 57 generates a control signal based on the time constant set at that time and transmits it to the motion controller C2. The motion controller C2 adjusts the current value input to the second servo motor MT2 in accordance with the transmitted control signal. This allows the machine tool 1 according to this embodiment to operate the second servo motor MT2 without worrying about fluctuations in the input voltage value and power supply voltage value.

[0046] A solid line 61 in Fig. 5 shows the change over time in the rotation speed of the second servo motor MT2 according to the first time constant. For example, when the first time constant is set, it takes t1 = 70 ms from the start of operation to reach the rotation speed P (r / min). A dashed-dotted line 62 in Fig. 5 shows the change over time in the rotation speed of the second servo motor MT2 according to the second time constant. For example, when the third time constant is set, it takes t2 = 100 ms from the start of operation to reach the rotation speed P (r / min). A dashed line 63 in Fig. 5 shows the change over time in the rotation speed of the second servo motor MT2 according to the third time constant. For example, when the third time constant is set, it takes t3 = 90 ms from the start of operation to reach the rotation speed P (r / min).

[0047] Compared to when the time constant is set to the first time constant, when the time constant is set to the second time constant, the rotation speed of the second servo motor MT2 does not need to be increased abruptly, so the supplied current value does not exceed the upper limit current value. As a result, compared to when the time constant is set to the first time constant, when the time constant is set to the second time constant, the possibility of the second servo motor MT2 being damaged and the occurrence of an excessive error alarm is reduced. Similarly, compared to when the time constant is set to the first time constant, when the time constant is set to the third time constant, the increase in the rotation speed of the second servo motor MT2 can be set more gradually, so the supplied current value does not exceed the upper limit current value. As a result, compared to when the time constant is set to the first time constant, when the time constant is set to the third time constant, the possibility of the second servo motor MT2 being damaged and the occurrence of an excessive error alarm is even further reduced.

[0048] Here, in the machine tool 1 according to this embodiment, the second servo motor MT2 is shown as an example, but the same applies to the other servo motors MT1 and MT3.

[0049] Furthermore, in the machine tool 1 according to this embodiment, three time constants are shown as acceleration / deceleration time constants, but two or four or more time constants may be set depending on parameters such as the current value of the servo motor and the power supply voltage value of the power supply PS.

[0050] Furthermore, in the machine tool 1 according to this embodiment, the servo motors MT1 to MT4 that mainly operate the spindle 2 and the B-axis rotary tool device 3 have been described, but the above control can also be applied to other servo motors, such as servo motors that drive tools.

[0051] Although the embodiments have been described above, all examples and conditions described herein are described for the purpose of helping to understand the concepts of the invention as applied to the invention and technology. The particularly described examples and conditions are not intended to limit the scope of the invention, and the construction of such examples in the specification does not indicate the advantages and disadvantages of the invention. Although the embodiments of the invention have been described in detail, it should be understood that various changes, substitutions, and modifications can be made without departing from the spirit and scope of the invention. [Explanation of symbols]

[0052] 1 Machine tools 2 spindle 3 B-axis rotary tool device 5. Numerical control device (NC device) 51 Interface section 52 Storage section 53 Input section 54 Output section 55 Current detection section 56 Voltage detection section 57 Control Unit MT1~MT4 1st servo motor~4th servo motor

Claims

1. a drive unit that drives a spindle that rotatably holds a workpiece; a servo motor that drives a tool to machine the workpiece held by the spindle; a power source that supplies power to at least the drive unit and the servo motor; a current detection unit that detects a current value input to the servo motor; a storage unit that stores an upper limit current value input to the servo motor; a control unit that controls the servo motor to perform drive control of the tool, when the current value detected by the current detection unit exceeds the upper limit current value immediately after starting the spindle, the control unit changes the acceleration / deceleration time constant from a first time constant to a second time constant having lower power consumption than the first time constant, and executes control of the servo motor. Machine tools.

2. a voltage detection unit that detects a power supply voltage value input from the power supply; when the current value detected by the current detection unit is equal to or less than the upper limit current value and the power supply voltage value detected by the voltage detection unit is equal to or less than a threshold voltage value immediately after starting the spindle, the control unit changes the acceleration / deceleration time constant from the first time constant to a third time constant that consumes less power than the first time constant and more power than the second time constant, and controls the servo motor. The machine tool according to claim 1.

3. A control device for a machine tool, comprising: a drive unit that drives a spindle that rotatably holds a workpiece; a servo motor that drives a tool to machine the workpiece held by the spindle; and a power source that supplies power to at least the drive unit and the servo motor, a current detection unit that detects a current value input to the servo motor; a storage unit that stores an upper limit current value input to the servo motor; a control unit that controls the servo motor to perform drive control of the tool, when the current value detected by the current detection unit exceeds the upper limit current value immediately after starting the spindle, the control unit changes the acceleration / deceleration time constant from a first time constant to a second time constant having lower power consumption than the first time constant, and executes control of the servo motor. Machine tool control device.

4. a voltage detection unit that detects a power supply voltage value input from the power supply; when the current value detected by the current detection unit is equal to or less than the upper limit current value and the power supply voltage value detected by the voltage detection unit is equal to or less than a threshold voltage value immediately after starting the spindle, the control unit changes the acceleration / deceleration time constant from the first time constant to a third time constant that consumes less power than the first time constant and more power than the second time constant, and controls the servo motor. The control device for a machine tool according to claim 3.

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