Machine tools and their control devices

Abstract

The machine tool of the present invention comprises: a drive unit that drives a spindle that rotatably holds a workpiece; a servo motor that drives a tool to process the aforementioned workpiece held on the spindle; a power supply 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 the 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 when the current value detected by the current detection unit exceeds the upper limit current value immediately after the spindle starts, the control unit changes the acceleration / deceleration time constant from a first time constant to a second time constant with lower power consumption than the first time constant, and performs control of the servo motor.

Description

Technical Field

[0001] This disclosure relates to machine tools and control devices for machine tools. Prior Technology

[0002] Background Technology A known machine tool typically comprises a spindle that rotatably supports a workpiece and a tool for machining the workpiece. A servo motor is installed in the tool drive mechanism of the machine tool; by inputting a predetermined current to the servo motor, the tool of the machine tool can be moved.

[0003] However, if the power supply voltage of the machine tool drops, an excessive error alarm will occur. The aforementioned excessive error alarm is caused by the difference between the actual position of the servo motor and the commanded position value.

[0004] Patent No. 3252114 describes a method for achieving stable operation of an electric motor by increasing or decreasing the acceleration / deceleration time constant based on changes in the input voltage. The aforementioned acceleration / deceleration time constant adjusts the responsiveness of the electric motor's acceleration or deceleration. Patent No. 5149410 describes a method for calculating a motor output limit value that will not adversely affect the motor's drive based on the voltage of the AC power supply input to the motor, thereby determining the control parameters for the aforementioned acceleration / deceleration time constant or feed rate used to implement the limit. Summary of the Invention

[0005] Invention Summary Fluctuations in the power supply voltage of machine tools mostly originate from the drive unit that drives the spindle, which consumes the most power, especially during the startup of the spindle drive unit. However, the acceleration and deceleration time constants of the servo motors driving the tool cannot be controlled based on the control of the spindle drive unit.

[0006] The purpose of this disclosure is to provide a machine tool and a control device for the machine tool, which can easily avoid excessive error alarms by referring to the state of the drive unit of the drive spindle.

[0007] The machine tool of this embodiment includes: a drive unit that drives a spindle that rotatably holds a workpiece; a servo motor that drives the tool to process the workpiece held on the spindle; a power supply 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 the upper limit current value input to the servo motor; and a control unit that controls the servo motor to execute the drive control of the tool; and when the current value detected by the current detection unit exceeds the upper limit current value immediately after the spindle starts, the control unit changes the acceleration / deceleration time constant from a first time constant to a second time constant with lower power consumption than the first time constant, and executes the control of the servo motor.

[0008] In the machine tool of the embodiment disclosed herein, it is preferable to further include a voltage detection unit, which detects the power supply voltage value input from the power source; when the spindle is just started, if the current value detected by the current detection unit is below the upper limit current value and the power supply voltage value detected by the voltage detection unit is below the threshold voltage value, the control unit changes the acceleration / deceleration time constant from the first time constant to a third time constant with lower power consumption than the first time constant and higher power consumption than the second time constant, and controls the servo motor.

[0009] In the control device of the machine tool disclosed in this embodiment, the machine tool includes: a drive unit that drives a spindle that rotatably holds a workpiece; a servo motor that drives the tool to process the workpiece held on the spindle; and a power supply that supplies power to at least the drive unit and the servo motor; the control device of the machine tool includes: a current detection unit that detects the current value input to the servo motor; a memory unit that stores the 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 when the current value detected by the current detection unit exceeds the upper limit current value immediately after the spindle starts, the control unit changes the acceleration / deceleration time constant from a first time constant to a second time constant with lower power consumption than the first time constant, and performs control of the servo motor.

[0010] In the control device of the machine tool according to the disclosed embodiment, it is preferable to further include a voltage detection unit, which detects the power supply voltage value input from the power source; when the spindle is just started, if the current value detected by the current detection unit is below the upper limit current value and the power supply voltage value detected by the voltage detection unit is below the threshold voltage value, the control unit changes the acceleration / deceleration time constant from the first time constant to a third time constant with lower power consumption than the first time constant and higher power consumption than the second time constant, and controls the servo motor.

[0011] According to the embodiments disclosed herein, a machine tool and a control device for the machine tool can be provided to easily avoid excessive error alarms by referring to the state of the drive unit of the drive spindle. Simple Explanation of the Diagram

[0012] Figure 1 is a partial perspective view of the machine tool of this embodiment. Figure 2 is a block diagram showing the internal structure of the machine tool shown in Figure 1. Figure 3 is a flowchart showing a series of workpiece machining processes performed in the machine tool of this embodiment. Figure 4 is a flowchart showing the process of determining the time constant of the servo motor in one of the series of workpiece machining processes shown in Figure 3. Figure 5 is a waveform diagram showing an example of the change in the rotational speed of a servo motor over time, which is controlled according to the current value shown in Figure 4. Implementation

[0013] Forms used to implement inventions The following description, with reference to the drawings, describes the machine tool of this embodiment. However, it should be noted that the scope of the technology disclosed herein is not limited to these embodiments, but covers the inventions described in the claims and their equivalents.

[0014] Figure 1 is a partial perspective view of the machine tool 1 of this embodiment. The machine tool 1 shown in Figure 1 is a device for processing a long bar in the shape of a round rod, i.e., a workpiece W. The machine tool 1 is composed of a spindle 2 that supports the workpiece W in a rotatable manner, a rotary tool drive device 13 including a B-axis rotary tool device 3, and a numerical control (NC) device 5 described later.

[0015] The spindle 2 is mounted on the support platform 6. The spindle 2 holds the workpiece W rotatably around the Z-axis, using the Z-axis as its axis. It also holds the workpiece W in a manner that allows it to move toward the front side of the support platform 6, using the power generated by the spindle motor (4th servo motor) MT4, which constitutes the drive unit DU. The support platform 6 is fixedly supported on the base 7.

[0016] A track 8 is provided on the front side of the support platform 6, extending along the X-axis direction (also known as the horizontal direction) orthogonal to the Z-axis direction. A base 10 is mounted on the track 8, sliding in the direction of arrow α1 using power generated by the first servo motor MT1. A track 11 is provided on the base 10, extending along the Y-axis direction (also known as the vertical direction) orthogonal to both the Z-axis and X-axis directions. A rotary tool drive device 13 is mounted on the track 11, sliding in the direction of arrow α2 using power generated by the second servo motor MT2.

[0017] The rotary tool drive 13 is a device for holding a tool used to process a workpiece W. The rotary tool drive 13 includes tools 131 and 132, and a B-axis rotary tool device 3 having a first tool 31 and a second tool 32. Tools 131 and 132 are arranged side-by-side along the X-axis with their front ends facing downwards. The first tool 31 and the second tool 32 are rotatably held in the B-axis rotary tool body 33 constituting the B-axis rotary tool device 3, and are arranged side-by-side along the X-axis with their front ends facing to the side. In this embodiment, the machine tool 1 can move the workpiece W in the Z-axis direction via the spindle 2, and move the rotary tool drive 13 in the direction of arrow α1 or arrow α2, thereby processing the workpiece W with a predetermined tool. The B-axis rotary tool body 33 is supported rotatably in the direction of arrow α3, centered on the rotation axis A of the rotary motor MT3, using power generated by the rotary motor (third servo motor) MT3.

[0018] Each servo motor MT1 to MT4 installed in the machine tool 1 is operated by power supplied by the power supply PS. The power supply PS converts the power supplied from a household or commercial power source into power that can be used in the machine tool 1 of this embodiment, and supplies the converted power to at least each servo motor MT1 to MT4.

[0019] Figure 2 is a block diagram showing the internal structure of the machine tool 1 shown in Figure 1. As shown in Figure 2, the B-axis rotary tool device 3 includes a B-axis rotary tool body 33, a horizontal movement mechanism M1, a first servo motor MT1, a vertical movement mechanism M2, a second servo motor MT2, a rotary mechanism M3, and a rotary motor MT3.

[0020] The horizontal movement mechanism M1 enables the entire rotary tool drive unit 13, including the B-axis rotary tool body 33, to move in the direction of arrow α1. The first servo motor MT1 converts the input current into mechanical output (torque and rotational speed, etc.) and provides it to the horizontal movement mechanism M1. Thus, the horizontal movement mechanism M1 causes the B-axis rotary tool body 33 to move back and forth in the direction of arrow α1. The operation of the first servo motor MT1 is controlled by the motion controller C1.

[0021] Motion controller C1 receives power from power supply PS and inputs a predetermined current to the first servo motor MT1 according to the control signal transmitted from the NC device 5 (described later). The control signal transmitted to motion controller C1 includes at least the rotation amount (rad or steps) and revolutions (rpm) of the first servo motor MT1. A sensor Se1 is installed on the first servo motor MT1, which detects the actual rotation amount and actual revolutions of the first servo motor MT1 and transmits them to motion controller C1. Motion controller C1 compares the values ​​of the rotation amount and revolutions of the first servo motor MT1 contained in the control signal with the values ​​of the actual rotation amount and actual revolutions of the first servo motor MT1 detected by sensor Se1, and inputs the predetermined current to the first servo motor MT1 in a manner that eliminates the deviation of these values. Hereinafter, since the control methods of motion controllers C2 to C4 are the same as those of motion controller C1, detailed descriptions are omitted.

[0022] The vertical movement mechanism M2 enables the entire rotary tool drive unit 13, including the B-axis rotary tool body 33, to move up and down in the direction of arrow α2. The second servo motor MT2 generates power to operate the vertical movement mechanism M2. The operation of the second servo motor MT2 is controlled by the motion controller C2. Since the control method for the second servo motor MT2 using the motion controller C2 is the same as the control method for the first servo motor MT1 using the motion controller C1, detailed explanations are omitted.

[0023] The rotary mechanism M3 enables the B-axis rotating tool body 33 to rotate about the rotation axis A of the rotary motor MT3 in the direction of arrow α3. The rotary motor MT3 generates power to operate the rotary mechanism M3. The operation of the rotary motor MT3 is controlled by the motion controller C3. Since the control method of the rotary motor MT3 using the motion controller C3 is the same as the control method of the first servo motor MT1 using the motion controller C1, detailed explanation is omitted.

[0024] As shown in Figure 2, the spindle 2 comprises a spindle drive mechanism M4 constituting the drive unit DU, and a spindle motor MT4. The spindle drive mechanism M4 supports the workpiece W, which can rotate around the Z-axis, and uses the power generated by the spindle motor MT4 to support the workpiece W in a manner that allows it to move towards the front side of the support table 6. The spindle motor MT4 generates the power to operate the spindle drive mechanism M4. The operation of the spindle motor MT4 is controlled by a motion controller C4. Since the control method of the spindle motor MT4 using the motion controller C4 is the same as the control method of the first servo motor MT1 using the motion controller C1, detailed explanation is omitted. Furthermore, the spindle motor MT4 does not necessarily need to be a servo motor as long as it can achieve stable rotation.

[0025] The NC device 5 is used to control the movements of the spindle 2 and the B-axis rotary tooling 3. As shown in Figure 2, the NC device 5 comprises an interface 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 51, memory unit 52, input unit 53, output unit 54, current detection unit 55, voltage detection unit 56, and control unit 57 are interconnected via a bus 58. Various control signals from the control unit 57 are transmitted to motion controllers C1 to C5 via the interface 51. Multiple current values ​​output from motion controllers C1 to C4 to the corresponding servo motors MT1 to MT4 are transmitted to the current detection unit 55 via the interface 51.

[0026] The memory unit 52 may include, for example, a semiconductor memory device, which stores programs and data used in the processing of the control unit 57. The memory unit 52 stores at least the programs used to enable the control unit 57 to execute a series of workpiece machining processes performed by the spindle 2 and the B-axis rotary tooling 3. The programs may also be installed in the memory unit 52 using known setup programs or other computer-readable portable recording media such as CD-ROMs.

[0027] Furthermore, the memory unit 52 pre-memorizes the upper limit current values ​​input from motion controllers C1 to C4 to servo motors MT1 to MT4. The upper limit current values ​​are the current values ​​at which there is a risk of damage to the servo motors.

[0028] The input unit 53 can be any generally known device, as long as it can input data, to generate signals corresponding to the operations of the machine tool operator 1. The generated signals are supplied to the control unit 57 as instructions from the operator.

[0029] The output unit 54 can be any generally known device, as long as it can display images or pictures, and is used to display images corresponding to the image data supplied by the self-control unit 57, images corresponding to the image data, etc.

[0030] The current detection unit 55 detects the current values ​​input from the motion controllers C1 to C4 to the servo motors MT1 to MT4 and transmits the detection results to the control unit 57. The voltage detection unit 56 detects the power supply voltage values ​​input from the power supply PS to the spindle 2 and the B-axis rotary tool device 3 and transmits the detection results to the control unit 57.

[0031] The control unit 57 is the overall controller of all actions of the machine tool 1, such as a central processing unit (CPU). The control unit 57 executes a series of workpiece machining processes according to the program stored in the memory unit 52. The control unit 57 transmits the control signals used to execute the series of workpiece machining processes to the motion controllers C1-C4 via the interface 51, thereby controlling the servo motors MT1-MT4 to perform the drive control of the tool. The control signals include the rotation amount (rad or steps) and revolutions per second (rpm) of each servo motor.

[0032] Figure 3 is a flowchart showing a series of workpiece machining processes performed in the machine tool 1 of this embodiment.

[0033] If the workpiece machining instructions are input according to the predetermined program, the control unit 57 first executes the motion control of the spindle 2 according to the program stored in the memory unit 52 (step S10). Specifically, the control unit 57 transmits the predetermined control signal (rotation amount (rad or steps) and revolutions (rpm) of the spindle motor MT4) to the motion controller C4 via the interface 51. The motion controller C4 controls the spindle motor MT4 according to the control signal transmitted from the control unit 57, drives the spindle drive mechanism M4, thereby causing the workpiece W to rotate around the Z-axis and move the workpiece W on the front side of the support table 6.

[0034] Next, the control unit 57 executes the motion control of the tool (step S11). Specifically, the control unit 57 controls at least one of the servo motors MT1 and MT2 to move the B-axis rotating tool assembly 3, causing the B-axis rotating tool body 33 to move in the direction of arrow α1 or arrow α2. In this way, the machine tool 1 of this embodiment can press the tools 131, 132, and the first tool 31 and the second tool 32 against the rotating workpiece W to process the workpiece W.

[0035] Finally, the control unit 57 determines whether a series of workpiece processing steps have been completed (step S12). If the workpiece processing steps have not been completed (No in step S12), the process returns to step S10. If a series of workpiece processing steps have been completed (Yes in step S12), the series of workpiece processing steps ends.

[0036] Figure 4 is a flowchart illustrating the time constant determination process for the second servo motor MT2 in one of the series of workpiece machining processes shown in Figure 3. The process shown in Figure 4 is executed at fixed time intervals in one of the series of workpiece machining processes shown in Figure 3. Figure 4 uses the second servo motor MT2 as an example for illustration, but the same process can be performed for the other servo motors MT1 and MT3.

[0037] First, the control unit 57 determines whether the spindle 2 has just started (step S20). Furthermore, in this embodiment, "spindle 2 has just started" refers to the period from when the control signal to start the spindle 2's rotational motion is input to the motion controller C4 until the spindle 2 begins its rated motion. If the spindle 2 has not just started (No in step S20), the acceleration / deceleration time constant is set to the first time constant (step S23), ending the series of processes.

[0038] When spindle 2 is just started (Yes in step S20), control unit 57 determines whether the current value supplied to the second servo motor MT2 detected by current detection unit 55 exceeds the upper limit current value stored in memory unit 52 (step S21). When the current value of the second servo motor MT2 exceeds the upper limit current value (Yes in step S21), since there is a risk of damage to the second servo motor MT2, control unit 57 sets the acceleration / deceleration time constant to the second time constant (step S25), ending the series of processes.

[0039] Next, when 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 below the threshold voltage value (i.e., determines whether a voltage drop occurs in the power supply PS) (step S22). When the power supply voltage value of the power supply PS exceeds the threshold voltage value (No in step S22), since there is no risk of damage to the second servo motor MT2 and no voltage drop occurs in the power supply PS, the control unit 57 sets the acceleration / deceleration time constant to the first time constant (step S23), ending the series of processes.

[0040] Next, when the power supply voltage of the power supply PS is below the threshold voltage value (Yes in step S22), although there is no risk of damage to the second servo motor MT2, the control unit 57 sets the acceleration / deceleration time constant to the third time constant (step S24) because of the voltage drop in the power supply PS, thus ending a series of processes.

[0041] Here, the acceleration / deceleration time constant refers to the value corresponding to the time it takes for the servo motor's rotational speed to reach the set rotational speed. The first time constant corresponds to the time it takes for the second servo motor MT2 to reach the set rotational speed in the shortest possible time during normal operation. The second time constant is when the second servo motor MT2 reaches the set rotational speed slower than the first time constant, resulting in lower power consumption per unit time for the second servo motor MT2 compared to the first time constant. The third time constant is when the second servo motor MT2 reaches the set rotational speed slower than the first time constant but faster than the second time constant, resulting in lower power consumption per unit time for the second servo motor MT2 compared to the first time constant but higher power consumption per unit time compared to the second time constant.

[0042] According to the processing flow shown in Figure 4, for the second servo motor MT2, except when the spindle 2 has just started, the first time constant is set. After the spindle 2 has just started, any one of the first to third time constants is set according to the current value or power supply voltage value of the second servo motor MT2.

[0043] Figure 5 is a waveform diagram showing an example of the time-varying rotational speed of the second servo motor MT2, which varies according to the current value shown in Figure 4. In Figure 4, the horizontal axis represents time (time t1~t3) (ms), and the vertical axis represents the rotational speed of the servo motor (r / min).

[0044] During the series of workpiece machining processes shown in Figure 3, the control unit 57 generates a control signal based on the currently set time constant when controlling the second servo motor MT2, and transmits it to the motion controller C2. The motion controller C2 adjusts the current value input to the second servo motor MT2 according to the transmitted control signal. Therefore, the machine tool 1 of this embodiment can operate the second servo motor MT2 without worrying about changes in the input voltage and power supply voltage.

[0045] The solid line 61 in Figure 5 shows the change in the rotational speed of the second servo motor MT2 over time according to the first time constant. For example, when the first time constant is set before reaching the rotational speed P (r / min), it takes t1 = 70 ms from the start of the action. The dotted chain line 62 in Figure 5 shows the change in the rotational speed of the second servo motor MT2 over time according to the second time constant. For example, when the rotational speed P (r / min) is reached, it takes t2 = 100 ms from the start of the action. The dashed line 63 in Figure 5 shows the change in the rotational speed of the second servo motor MT2 over time according to the third time constant. For example, when the third time constant is set before reaching the rotational speed P (r / min), it takes t3 = 90 ms from the start of the action.

[0046] Compared to setting the time constant to the first time constant, setting it to the second time constant prevents the rotational speed of the second servo motor MT2 from increasing rapidly, thus ensuring that the supplied current does not exceed the upper limit. Consequently, compared to setting the time constant to the first time constant, setting it to the second time constant reduces the likelihood of damage to the second servo motor MT2 and the occurrence of an excessive error alarm. Similarly, compared to setting the time constant to the first time constant, setting it to the third time constant allows the rotational speed of the second servo motor MT2 to increase slowly, thus ensuring that the supplied current does not exceed the upper limit. Consequently, compared to setting the time constant to the first time constant, setting it to the third time constant further reduces the likelihood of damage to the second servo motor MT2 and the occurrence of an excessive error alarm.

[0047] In this embodiment of the machine tool 1, although a second servo motor MT2 is shown, the same applies to the other servo motors MT1 and MT3.

[0048] Furthermore, in the machine tool 1 of this embodiment, although three time constants are displayed as acceleration and deceleration time constants, two or more time constants can also be set according to parameters such as the current value of the servo motor and the power supply voltage value of the power supply PS.

[0049] Furthermore, in the machine tool 1 of this embodiment, the servo motors MT1 to MT4 that perform the operation of the spindle 2 and the B-axis rotating tool device 3 are mainly described, but the above control can also be applied to other servo motors such as the servo motor that drives the tool.

[0050] While the embodiments have been described above, all examples and conditions set forth herein are provided to aid in understanding the inventive concept applied to this invention and technology. In particular, the examples and conditions described are not intended to limit the scope of the invention, and the configuration of these examples in the specification does not represent any advantage or disadvantage 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.

[0051] 1: Machine Tool 2: Spindle 3: B-axis rotary tooling 31: The First Tool 32: The Second Tool 33: B-axis rotary tool body 5: Numerical Control (NC) Device 51: Interface 52: Memory Department 53: Input Section 54: Output Section 55: Current Detection Section 56: Voltage Detection Section 57: Control Department 58: Busbar 6: Support platform 7: Base 8: Track 10: Base 11: Track 13: Rotary tool drive device 131: Tools 132: Tools 61: Solid line 62: One-point chain 63: Dashed line A: Rotary shaft C1~C4: Motion controllers DU: Drive Unit M1: Horizontal movement mechanism M2: Vertical moving mechanism M3: Rotary mechanism M4: Spindle drive mechanism MT1: First servo motor MT2: Second servo motor MT3: Rotary Motor (3rd Servo Motor) MT4: Spindle motor (4th servo motor) PS: Power supply S10~S12, S20~S25: Steps Se1, Se2, Se3, Se4: Sensors t1, t2, t3: Time points W: Workpiece X, Y, Z: Direction α1~α3: Arrows

Claims

1. A machine tool comprising: a drive unit for driving a spindle that rotatably holds a workpiece; a servo motor for driving a tool to process the workpiece held on the spindle; a power supply for supplying power to at least the drive unit and the servo motor; a current detection unit for detecting a current value input to the servo motor; a memory unit for storing an upper limit current value input to the servo motor; and a control unit for controlling the servo motor to perform drive control of the tool; wherein, immediately after the spindle starts, the control unit, when the current value detected by the current detection unit exceeds the upper limit current value, changes the acceleration / deceleration time constant from a first time constant to a second time constant with lower power consumption than the first time constant, and performs control of the servo motor.

2. The machine tool according to claim 1 further includes a voltage detection unit that detects the power supply voltage value input from the power source; when the control unit detects that the current value detected by the current detection unit is below the upper limit current value and the power supply voltage value detected by the voltage detection unit is below the threshold voltage value immediately after the spindle is started, it changes the acceleration / deceleration time constant from the first time constant to a third time constant that has lower power consumption than the first time constant and higher power consumption than the second time constant, and controls the servo motor.

3. A control device for a machine tool, the machine tool comprising: a drive unit for driving a spindle that rotatably holds a workpiece; a servo motor for driving a tool to process the workpiece held on the spindle; and a power supply for supplying power to at least the drive unit and the servo motor; the control device for the machine tool further comprising: a current detection unit for detecting a current value input to the servo motor; a memory unit for storing an upper limit current value input to the servo motor; and a control unit for controlling the servo motor to perform drive control of the tool; wherein, immediately after the spindle is started, when the current value detected by the current detection unit exceeds the upper limit current value, the control unit changes the acceleration / deceleration time constant from a first time constant to a second time constant with lower power consumption than the first time constant, and performs control of the servo motor.

4. The control device of the machine tool as claimed in claim 3 further includes a voltage detection unit that detects the power supply voltage value input from the power source; when the control unit detects that the current value detected by the current detection unit is below the upper limit current value and the power supply voltage value detected by the voltage detection unit is below the threshold voltage value immediately after the spindle is started, it changes the acceleration / deceleration time constant from the first time constant to a third time constant that has lower power consumption than the first time constant and higher power consumption than the second time constant, and controls the servo motor.

Images