Working machinery

Abstract

To provide a machine tool that is capable of restraining a workpiece from sliding in a workpiece holding part when it is determined that the workpiece is has not been cut off during cut-off processing and rotation of first and second main spindles is to be stopped.SOLUTION: A machine tool 1 includes: a control unit 300 that performs cut-off processing on a workpiece W with main spindles 11, 21 being rotated in synchronization. The control unit 300 includes a motor control section 301 and a cut-off processing section 302 that determines that cut-off processing is not being normally performed when rotations of the main spindles 11, 21 are synchronous upon elapse of a speed-reduction waiting time after an output torque of the motor 21m of the second main spindle 21 is reduced to zero subsequent to the cut-off processing. When it is determined that the cut-off processing is not being normally performed, the motor control section 301 increases the output torque of the motor 21m from zero and then sets a synchronous rotation speed of the main spindles 11, 21 to zero while the main spindles 11, 21 are keeping a synchronous rotation state.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a machine tool.

Background Art

[0002] The numerically controlled automatic lathe described in Patent Document 1 performs a parting process of separating a workpiece while rotating the workpiece with both ends grasped by a headstock and an opposed headstock, and then performs a parting process using a parting tool on the tool post. After that, it comprises a discrimination means for discriminating whether the parting process has been normally performed.

[0003] This discrimination means outputs a command to stop the headstock or rotate it at a predetermined rotational speed after performing the parting process on the workpiece. Then, when a certain period of time has elapsed, if the headstock stops or rotates at the predetermined rotational speed as commanded, it is determined that the parting process has been normally performed on the assumption that the headstock is not affected by the rotation of the opposed headstock via the workpiece. On the other hand, if the headstock does not stop or rotate at the predetermined rotational speed as commanded at this time, it is determined that the parting process has not been normally performed on the assumption that the headstock is affected by the rotational force of the opposed headstock via the workpiece, and the lathe is brought to an emergency stop.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the configuration described in Patent Document 1 above, if it is determined that the parting-off operation is not being performed correctly, an emergency stop is initiated. An emergency stop means that the rotational speed of both the headstock and the opposing headstock is reduced to zero, that is, decelerated, thereby stopping the rotation of both the headstock and the opposing headstock. During this deceleration in an emergency stop, the rotation of the headstock and the opposing headstock are not synchronized, so the time required for each to stop is different. The reasons for this include the difference in the length of the workpiece gripped by the headstock and the opposing headstock, and consequently, the difference in moment of inertia, as well as the difference in rotational force between the headstock and the opposing headstock due to their different structures. As a result, even during the above deceleration, the headstock and the opposing headstock rotate at different speeds, which may cause the workpiece to slip in the collet chuck of either the headstock or the opposing headstock, and consequently, there is a risk of damage to the collet chuck due to workpiece slippage. Furthermore, scratches inside the collet chuck may reduce the machining accuracy of the workpiece when it is machined next.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a machine tool that can suppress the slippage of the workpiece within the workpiece holding section when it is determined that the workpiece has not been separated during parting-off processing and the rotation of the first and second spindles is stopped. [Means for solving the problem]

[0007] To achieve the above objective, the machine tool according to the present invention includes: a first workpiece holder for holding a workpiece; a first spindle having a first motor that rotates together with the first workpiece holder by the rotation of the first motor; a second workpiece holder for holding a workpiece; a second spindle having a second motor that rotates together with the second workpiece holder by the rotation of the second motor and is positioned opposite the first spindle in the direction of the rotation axis of the first spindle; a spindle movement mechanism for moving the first spindle and the first workpiece holder relative to the second spindle and the second workpiece holder in the direction of the rotation axis of the first spindle; a tool movement mechanism for moving a parting tool in a direction intersecting the direction of the rotation axis of the first spindle; and while the first workpiece holder and the second workpiece holder, which have moved to opposing positions via the spindle movement mechanism, simultaneously hold different parts of the workpiece in the direction of the rotation axis of the first spindle, the cutting edge of the parting tool is moved from the outer surface of the workpiece toward the central axis of the workpiece via the tool movement mechanism while the first spindle and the second spindle rotate synchronously with the workpiece. The control unit includes a motor control unit that performs a parting operation to separate a workpiece between the first workpiece holding unit and the second workpiece holding unit, the control unit includes a motor control unit that controls the rotational speed of the first motor and the second motor, respectively, and a parting determination unit that, after the parting operation, when the motor control unit reduces the output torque of the first motor or the second motor to zero and a preset deceleration waiting time has elapsed, determines that the parting operation was performed normally if the rotation of the first spindle and the second spindle are not synchronized, and determines that the parting operation was not performed normally if the rotation of the first spindle and the second spindle are synchronized, the motor control unit, when the parting determination unit determines that the parting operation was not performed normally, increases the output torque of the first motor or the second motor, which has been reduced to zero, from zero, and performs a stop operation that sets the synchronous rotational speed of the first spindle and the second spindle to zero while maintaining the synchronized rotation of the first spindle and the second spindle. [Effects of the Invention]

[0008] According to the present invention, when it is determined that the workpiece has not been separated during parting-off processing and the rotation of the first and second spindles is stopped, it is possible to suppress the workpiece from slipping within the workpiece holding section. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic front view of a machine tool according to one embodiment of the present invention. [Figure 2] This is a schematic plan view of a machine tool according to one embodiment of the present invention. [Figure 3] This is a schematic side view of a machine tool according to one embodiment of the present invention. [Figure 4] This is a schematic cross-sectional view of the first and second spindles when a parting operation according to one embodiment of the present invention is performed normally. [Figure 5] This is a schematic cross-sectional view of the first and second spindles when the parting-off process according to one embodiment of the present invention is abnormal. [Figure 6] This is a flowchart showing the procedure for a parting-off process according to one embodiment of the present invention. [Figure 7] This is a graph showing the change in rotational speed of the first and second spindles when a parting operation according to one embodiment of the present invention is performed normally, and a timing chart showing the synchronization completion signal and the output torque status. [Figure 8] This is a graph showing the change in rotational speed of the first and second spindles when a parting operation according to one embodiment of the present invention is abnormal, and a timing chart showing the synchronization completion signal and the output torque status. [Modes for carrying out the invention]

[0010] A machine tool according to one embodiment of the present invention will be described with reference to the drawings. As shown in Figures 1 and 2, machine tool 1 is an NC (Numerical Control) lathe for machining workpiece W. More specifically, machine tool 1 comprises a bed S which is a base that supports each component of machine tool 1, a first spindle unit 10, a first spindle movement mechanism 13, a second spindle unit 20, second spindle movement mechanisms 23, 24, a first tool unit 30, first tool movement mechanisms 32, 33, a second tool unit 40, a support base 65, and a control unit 300.

[0011] The first spindle unit 10 shown in Figure 4 grips a cylindrical workpiece W and rotates the gripped workpiece W around a rotation axis along the Z-axis. The first spindle unit 10 comprises a collet chuck 11a for gripping the workpiece W, a collet sleeve 11d, an air cylinder (not shown), a first spindle 11 that is rotatable together with the collet chuck 11a and the collet sleeve 11d, and a first headstock 15 that rotatably supports the first spindle 11.

[0012] The first spindle head 15 has a shape that surrounds the outer circumference of the first spindle 11. The first headstock 15 is equipped with a bearing 15a that rotatably supports the first spindle 11. As shown in Figure 1, the first spindle 11 is equipped with a motor 11m that generates the rotational force of the first spindle 11 as output torque. The motor 11m is built into the first headstock 15. When the output torque of the motor 11m is zero, the rotation of the first spindle 11 is not restricted, and the first spindle 11 is in a state where it can rotate freely. The first spindle movement mechanism 13 moves the first spindle unit 10 in the Z-axis direction under the control of the control unit 300.

[0013] As shown in Figure 4, the collet chuck 11a extends in the Z-axis direction, is formed to grip the periphery of the workpiece W, and has a substantially cylindrical shape divided into multiple parts in the circumferential direction. An inclined surface 11k is formed on the outer circumferential surface of the tip side (right side in Figure 4) of the collet chuck 11a. The inclined surface 11k is formed to be inclined radially outward of the collet chuck 11a as it moves toward the tip side of the collet chuck 11a.

[0014] The collet sleeve 11d is cylindrical and located on the outer circumference of the collet chuck 11a. The collet sleeve 11d can move back and forth in the Z-axis direction by the operation of an air cylinder. When the collet sleeve 11d moves toward the second spindle 21, the tip of the collet sleeve 11d pushes the inclined surface 11k radially inward, reducing the diameter of the collet chuck 11a. The collet chuck 11a grips the workpiece W by reducing its diameter. Conversely, when the collet sleeve 11d moves away from the second spindle 21, the collet chuck 11a opens and no longer grips the workpiece W.

[0015] As shown in Figures 1 and 2, the second spindle unit 20 is positioned opposite the first spindle unit 10 in the Z-axis direction, grips the workpiece W, and rotates the gripped workpiece W around a rotation axis along the Z-axis direction. As shown in Figure 4, the second spindle unit 20 includes a collet chuck 21a for gripping the workpiece W, a collet sleeve 21d, an air cylinder (not shown), a second spindle 21 that is rotatable together with the collet chuck 21a and the collet sleeve 21d, and a second headstock 25 that rotatably supports the second spindle 21. The second spindle 21, the second headstock 25, the collet chuck 21a, the collet sleeve 21d, and the air cylinder (not shown) are configured in the same way as the first spindle 11, the first headstock 15, the collet chuck 11a, the collet sleeve 11d, and the air cylinder (not shown), respectively. That is, the second spindle 21 is equipped with a motor 21m (see Figure 1) that generates the rotational force of the second spindle 21 as output torque. When the output torque of the motor 21m is zero, the rotation of the second spindle 21 is not restricted, and the second spindle 21 is in a state where it can rotate freely. The second headstock 25 is equipped with a bearing 25a that rotatably supports the second spindle 21. The collet chuck 21a has an inclined surface 21k similar to the inclined surface 11k. Similar to the collet chuck 11a described above, the collet chuck 21a grips the workpiece W by contracting its diameter through the operation of the collet sleeve 21d and the air cylinder, and does not grip the workpiece W by opening it.

[0016] As shown in FIG. 2, under the control of the control unit 300, the second main spindle moving mechanism 23 moves the second main spindle unit 20 in the Z-axis direction. The second main spindle moving mechanism 24 moves the second main spindle moving mechanism 23 and the second main spindle unit 20 in the X-axis direction under the control of the control unit 300.

[0017] As shown in FIG. 1, the support base 65 is located between the first main spindle unit 10 and the second main spindle unit 20 and is provided so as to be immovable with respect to the bed S. Either a rotary guide bush device 60 (see FIG. 1) or a guide bushless device 90 (see FIG. 4) is attached to the support base 65. The rotary guide bush device 60 is located on the tip side of the first main spindle 11 and rotates in synchronization with the first main spindle 11 while holding the work W held by the first main spindle 11. Note that the rotary guide bush device 60 is a direct drive guide bush device in the present embodiment, but is not limited to the present embodiment, and other types of guide bush devices, for example, a stationary guide bush device, a Kele type rotary guide bush device, a belt drive guide bush device, etc. may be used.

[0018] As shown in FIG. 4, the guide bushless device 90 includes a cylindrical portion 91 located on the outer peripheral side of the first main spindle 11. A through hole penetrating in the Z-axis direction is formed in the cylindrical portion 91. The tip side of the first main spindle 11 is configured to be able to pass through the through hole of the cylindrical portion 91.

[0019] As shown in FIG. 2, the second tool unit 40 is used when machining the work W grasped by the second main spindle unit 20. The second tool unit 40 includes a tool 41 and a tool holder 43 to which the tool 41 can be attached. The tool 41 includes a rotary tool, a fixed tool, and the like. The tool holder 43 is provided on the upper surface of the bed S and is configured to be movable in the Y-axis direction by a tool moving mechanism not shown.

[0020] As shown in Figure 3, the first tool unit 30 is used when machining a workpiece W held by the first or second spindle units 10, 20 (mainly the first spindle unit 10). The first tool unit 30 comprises a plurality of tools 31, 35, a tool base 34, a cross drill device 80, and a rear drive device 85.

[0021] As shown in Figure 1, the first tool moving mechanism 33 moves the tool base 34 in the Y-axis direction under the control of the control unit 300. As shown in Figure 2, the first tool moving mechanism 32 moves the tool base 34 in the X-axis direction under the control of the control unit 300.

[0022] As shown in Figure 3, the tool rest 34 consists of a frame that surrounds the outer circumference of the workpiece W held by the first spindle unit 10. A cross drill device 80 is fixed to one side of the tool rest 34 in the X-axis direction. A rear drive device 85 is fixed to the other side of the tool rest 34 in the X-axis direction. The cross drill device 80 and the rear drive device 85 are located on the upper part of the tool rest 34. Tools 35 are arranged in the cross drill device 80 and the rear drive device 85, respectively, so that the cutting edges face each other in the X-axis direction. Multiple tools 35, such as drills, are also rotatably mounted in the cross drill device 80 and the rear drive device 85.

[0023] Multiple tools 31, which are fixed tools such as cutting tools, are mounted on the lower part of the tool rest 34. Each tool 31 extends along the X-axis toward the workpiece W and is arranged in the Y-axis direction. One of the multiple tools 31 is a parting tool 31a. The parting tool 31a is located at the very bottom of the multiple tools 31 on the tool rest 34. Note that the mounting position of the parting tool 31a is not limited to this position and may be any position.

[0024] As shown in Figure 1, the control unit 300 controls the operation of each part of the machine tool 1. The control unit 300 consists of a CPU (Central Processing Unit), memory, etc. The control unit 300 includes a motor control unit 301 that controls the output torque of the motors 11m and 21m of each spindle 11 and 21, a parting determination unit 302 that determines whether or not parting work has been performed correctly, a rotation speed detection unit 303 that detects the rotation speed of each motor 11m and 21m (each spindle 11 and 21), and a synchronization detection unit 304 that detects whether or not the rotation of each spindle 11 and 21 is synchronized.

[0025] The rotational speed detection unit 303 receives a detection signal from a rotational speed detection sensor (not shown) and detects the rotational speed of each motor 11m and 21m, and outputs the detection result to the motor control unit 301 and the parting determination unit 302. The rotational speed detection unit 303 outputs a spindle speed zero signal S0 to the motor control unit 301 and the parting determination unit 302, indicating whether or not the rotational speed of motor 11m (first spindle 11) is zero. The spindle speed zero signal S0 is ON (1) when the rotational speed of motor 11m is zero, that is, when motor 11m has stopped rotating, and OFF (0) when the rotational speed of motor 11m is not zero, that is, when motor 11m is rotating. In addition, the spindle speed zero signal S0 may be off (0) when the motor 11m is stopped rotating and on (1) when the motor 11m is rotating.

[0026] The synchronization detection unit 304 outputs a synchronization completion signal S1 to the motor control unit 301 and the parting determination unit 302, indicating whether the rotations of the first spindles 11 and 21 are synchronized with each other. The synchronization completion signal S1 is ON (1) when the first spindle 11 and the second spindle 21 are synchronized, that is, rotating at a constant speed at a synchronous rotational speed, and OFF (0) when the first spindle 11 and the second spindle 21 are not rotating in sync. As shown in Figure 7, the synchronization detection unit 304 turns on the synchronization completion signal S1 when the speed difference ΔV, which is the difference between the first rotational speed of the first spindle 11 and the second rotational speed of the second spindle 21 (= first rotational speed - second rotational speed), is less than or equal to the threshold Th, and turns off the synchronization completion signal S1 when the speed difference ΔV exceeds the threshold Th. However, the synchronization completion signal S1 may also be off (0) when the first spindle 11 and the second spindle 21 are rotating synchronously, and on (1) when the first spindle 11 and the second spindle 21 are not rotating synchronously.

[0027] The motor control unit 301 monitors the rotational speed of each motor 11m and 21m based on the detection results of the rotational speed detection unit 303, and provides feedback control to the rotational speed of each motor 11m and 21m. When synchronously controlling the rotation of each motor 11m and 21m, the motor control unit 301 controls the rotational speed of each motor 11m and 21m to be constant at the synchronous rotational speed. The motor control unit 301 uses the first spindle 11 as the master shaft and the second spindle 21 as the slave shaft, and performs synchronous control to synchronize the rotation of the slave shaft with the rotation of the master shaft. Alternatively, the second spindle 21 may be used as the master axis and the first spindle 11 as the slave axis, contrary to this example.

[0028] Next, the workpiece machining process performed by the control unit 300 will be described. The control unit 300 performs this workpiece machining process according to a pre-set NC program. First, a workpiece W is supplied to the first spindle unit 10 from a workpiece supply device (not shown). The control unit 300 grasps the supplied workpiece W with the first spindle unit 10 (collet chuck 11a) and performs the first machining operation on the grasped workpiece W using the first tool unit 30.

[0029] Once this first machining is complete, the control unit 300, in a parting-off process described in detail later, separates the workpiece W, which was held by the first spindle unit 10 and the second spindle unit 20, between the first spindle 11 and the second spindle 21 using a parting-off tool 31a. As a result, as shown in the enlarged view at the bottom of Figure 4, if the parting-off process is performed correctly, the portion of the workpiece W that has undergone the first machining process, which was held by the first tool unit 30, is separated, and this separated workpiece Wa is held independently by the second spindle unit 20. Next, the control unit 300 performs a second machining operation on the workpiece Wa grasped by the second spindle unit 20 using the tool 41 of the second tool unit 40. Once this second machining operation is complete, the control unit 300 uses a workpiece discharge device (not shown) to discharge the machined workpiece Wa to the outside of the machine tool 1. This completes the workpiece machining process. This workpiece machining process is repeated each time a workpiece W is supplied.

[0030] Next, with reference to the flowchart in Figure 6, we will explain the parting-off process as a sub-flow of the above workpiece machining process. The motor control unit 301 rotates the first spindle 11 and the second spindle 21 in a synchronized manner while the first spindle unit 10 is gripping the workpiece W (step S101).

[0031] Then, with the first spindle 11 and the second spindle 21 rotating synchronously, the control unit 300 grips the end of the workpiece W with the second spindle unit 20 (step S102). More specifically, in step S102, the control unit 300 moves the second spindle 21 to a position opposite the first spindle 11 via the second spindle moving mechanism 23, opens the collet chuck 21a, and inserts the end of the workpiece W held by the collet chuck 11a into the collet chuck 21a. Then, the control unit 300 closes the collet chuck 21a to grip the end of the workpiece W. As a result, the workpiece W rotates while being gripped by the collet chucks 11a and 21a. In the above example, the second spindle 21 was moved to face the first spindle 11, but this is not the only option; the first spindle 11 may be moved, or both the first spindle 11 and the second spindle 21 may be moved.

[0032] The control unit 300 then selects the parting tool 31a as the tool to be used for machining, and moves the tool rest 34 in the Y-axis direction via the first tool moving mechanism 33, as shown by arrow Ar1 in the enlarged view of the bottom of Figure 3, so that the cutting edge of the parting tool 31a is at the same height as the central axis of the workpiece W in the Y-axis direction (step S103).

[0033] Subsequently, the control unit 300 performs a parting operation to separate the workpiece W using the selected parting tool 31a (step S104). In step S104, the control unit 300 moves the tool rest 34 via the first tool moving mechanism 32 so that the cutting edge of the parting tool 31a reaches a position beyond the central axis of the workpiece W, which rotates with the first spindle 11 and the second spindle 21, as shown by arrow Ar2 in the enlarged view of the bottom of Figure 4.

[0034] Once the parting-off process is complete, the parting-off detection unit 302 performs a parting-off detection process according to steps S105 to S112. In steps S105 to S110, the rotational speed of the first spindle 11 is maintained at the rotational speed of the first spindle 11 during the parting-off process. The parting-off detection process will be described below.

[0035] First, the motor control unit 301 sets the output torque of the motor 21m of the second spindle 21 to zero from the value during parting (step S105). If the parting operation was performed correctly, as shown in Figure 7, from the moment the output torque of the motor 21m is set to zero (time t1), the second spindle 21 will continue to rotate freely due to inertia. However, due to friction of the bearing 25a and air resistance, the rotational speed of the second spindle 21 will decrease over time. At this time, since the motor 11m of the first spindle 11 continues to be driven, the rotational speed of the first spindle 11 is maintained at a constant speed.

[0036] Next, the parting-off determination unit 302 waits for the deceleration waiting time Ta to elapse using a timer (not shown) (step S106; NO). The deceleration waiting time Ta is set to the time (time t3) when the speed difference ΔV between the first spindle 11 and the second spindle 21 exceeds the threshold Th due to the decrease in the rotational speed of the second spindle 21. When the parting-off determination unit 302 determines that the deceleration waiting time Ta has elapsed (step S106; YES), it determines whether the synchronization completion signal S1 is off or not (step S107).

[0037] Here, we will explain the relationship between whether the parting-off process was performed successfully and the on / off state of the synchronization completion signal S1. If the parting-off process is performed correctly, the workpiece W is separated between the first spindle 11 and the second spindle 21, as shown in Figure 4. In this case, the second spindle 21 is not affected by the rotation of the first spindle 11. Therefore, as shown in Figure 7, the rotational speed of the second spindle 21 decreases over time, and the speed difference ΔV gradually increases until it exceeds the threshold Th (time t2), at which point the synchronization completion signal S1 switches from on to off. On the other hand, if the parting-off process is not performed properly due to reasons such as a missing parting tool 31a, i.e., if the parting-off process is abnormal, the workpiece W is not separated between the first spindle 11 and the second spindle 21, as shown in an enlarged view at the bottom of Figure 5, and the remaining portion Wb of the workpiece W is left behind. As a result, the workpiece W remains connected between the first spindle 11 and the second spindle 21. Therefore, even though the output torque of the motor 21m of the second spindle 21 is zero, as shown in Figure 8, the second spindle 21 rotates in conjunction with the rotation of the first spindle 11 via the workpiece W, the speed difference ΔV is maintained at zero, and the synchronization completion signal S1 remains ON. In this way, it is possible to determine whether or not the parting-off process was performed successfully based on whether or not the synchronization completion signal S1 is turned on or off when the deceleration waiting time Ta has elapsed.

[0038] Returning to the flowchart in Figure 6, when the parting-off determination unit 302 determines that the synchronization completion signal S1 is off (step S107; YES), it determines that the parting-off process has been performed successfully (step S108), terminates this parting-off process, and returns to the main flow, the workpiece machining process. Subsequently, in the workpiece machining process, with the second spindle unit 20 holding the workpiece Wa, the control unit 300 moves the second spindle 21 away from the first spindle 11 in the Z-axis direction via the second spindle movement mechanism 23, and performs the second machining on the workpiece Wa as described above.

[0039] On the other hand, if the parting-off detection unit 302 determines that the synchronization completion signal S1 is ON (step S107; NO), it determines that the parting-off process is abnormal (step S109). When it is determined that the parting-off process is abnormal (time t3 in Figure 8), the motor control unit 301 returns the output torque of the motor 21m of the second spindle 21 from zero to its original value during the parting-off process (step S110). Then, while maintaining the synchronized rotation of the first spindle 11 and the second spindle 21, it reduces the synchronous rotational speed of the first spindle 11 and the second spindle 21 to zero (step S111). As described above, when stopping the rotation of the first spindle 11 and the second spindle 21, the rotation of the first spindle 11 and the second spindle 21 is controlled to be synchronized. Therefore, the time it takes for the first spindle 11 and the second spindle 21 to stop rotating is the same. Also, because they are synchronized, the rotational force on the first spindle 11 and the second spindle 21 is equal, which suppresses twisting of the workpiece W and also suppresses slippage of the workpiece W within the collet chucks 11a and 21a.

[0040] Then, when the control unit 300 confirms that the synchronous rotational speed of the first spindle 11 and the second spindle 21 has become zero due to the spindle speed zero signal S0 switching from off to on, it stops the operation of each part of the machine tool 1 (alarm stop) (step S112), terminates this parting-off process, and interrupts the main flow, which is the workpiece machining process. Upon receiving this stop, the operator performs work to resolve any problems, such as replacing the parting-off tool 31a, and then releases the stop state and resumes the workpiece machining process.

[0041] The deceleration waiting time Ta is set to a different length for each machine tool model. The method for setting the deceleration waiting time Ta is described below. First, the control unit 300, in the same manner as in steps S101 to S105 described above, separates the workpiece W by parting off while synchronously rotating the first spindle 11 and the second spindle 21, and then sets the output torque of the motor 21m of the second spindle 21 to zero. Then, after setting the output torque to zero, the control unit 300 measures the deceleration time required for the speed difference ΔV between the first spindle 11 and the second spindle 21 to reach a threshold Th. The deceleration waiting time Ta is set by adding a buffer time to this deceleration time. The weight of the second spindle 21 and the coefficient of dynamic friction differ depending on the model of the machine tool 1, so the time required for the second spindle 21 to stop differs. However, by setting the deceleration waiting time Ta as described above, it is possible to set a deceleration waiting time Ta that is appropriate for the model of the machine tool 1. Therefore, the setting of an excessively long deceleration waiting time Ta is suppressed, and this suppresses the time required for the parting off process from becoming too long. The above buffer time is optional, and the measured deceleration time may be set as the deceleration waiting time Ta.

[0042] (effect) According to the embodiment described above, the following effects are achieved. (1) The machine tool 1 includes a collet chuck 11a, which is an example of a first workpiece holder for holding a workpiece W, and a first spindle 11 which has a first motor 11m and rotates together with the collet chuck 11a when the first motor 11m rotates, a collet chuck 21a, which is an example of a second workpiece holder for holding a workpiece W, and a second spindle 21 which has a second motor 21m and rotates together with the collet chuck 21a when the second motor 21m rotates, and is positioned opposite the first spindle 11 in the Z-axis direction, which is an example of the rotation axis direction of the first spindle 11, and a first spindle moving mechanism 13 or second spindle, which is an example of a spindle moving mechanism for moving the first spindle 11 and the collet chuck 11a relative to the second spindle 21 and the collet chuck 21a in the Z-axis direction The system includes a moving mechanism 23, first tool moving mechanisms 32 and 33 which are examples of tool moving mechanisms for moving the parting tool 31a in the X-axis or Y-axis direction intersecting the Z-axis direction, and a control unit 300 which performs a parting operation by moving the cutting edge of the parting tool 31a from the outer surface of the workpiece W toward the central axis of the workpiece W via the first tool moving mechanisms 32 and 33, while the collet chucks 11a and 21a, which have been moved to opposing positions via the first spindle moving mechanism 13 or the second spindle moving mechanism 23, simultaneously hold different parts of the workpiece W in the Z-axis direction, and the first spindle 11 and the second spindle 21 rotate synchronously with the workpiece W. The control unit 300 includes a motor control unit 301 that controls the output torque and rotational speed of motors 11m and 21m, respectively, and a parting determination unit 302 that, after parting, when the motor control unit 301 reduces the output torque of motor 21m to zero and a preset deceleration waiting time Ta has elapsed, determines that parting has been performed normally if the rotation of the first spindle 11 and the second spindle 21 are not synchronized, and determines that parting has not been performed normally if the rotation of the first spindle 11 and the second spindle 21 are synchronized. If the parting-off detection unit 302 determines that the parting-off process is not being performed correctly, the motor control unit 301 increases the output torque of the motor 21m, which has been set to zero, and then performs a stop process that sets the synchronous rotation speed of the first spindle 11 and the second spindle 21 to zero while maintaining the synchronized rotation of the first spindle 11 and the second spindle 21. With this configuration, when it is determined that the workpiece W is not detached during parting, and the rotation of the first spindle 11 and the second spindle 21 is stopped, output torque is output from both motors 11m and 21m, and the rotation of the first spindle 11 and the second spindle 21 is stopped by reducing the synchronous rotation speed of the first spindle 11 and the second spindle 21 from a state where their rotation is synchronized. As a result, it is possible to stop with no difference in rotation speed between the first spindle 11 and the second spindle 21, and it is possible to suppress the slippage of the workpiece W within the collet chucks 11a and 21a. This prevents the workpiece W from slipping within the collet chucks 11a and 21a and causing scratches inside the collet chucks 11a and 21a due to workpiece slippage. In addition, this also suppresses a decrease in the machining accuracy of the workpiece W when it is machined next.

[0043] (2) The control unit 300 processes the workpiece W held by the collet chuck 11a using tools 31 and 35, and then holds the end of the workpiece W with the collet chuck 21a and performs parting. The motor control unit 301 synchronizes the rotation of the first spindle 11 and the second spindle 21 by controlling the rotation speed of the second spindle 21 to match the rotation speed of the first spindle 11. After parting, the parting determination unit 302 sets the output torque of the motor 21m of the second spindle 21 to zero via the motor control unit 301 and waits for the deceleration waiting time Ta to elapse. In this configuration, the rotation of the second spindle 21 is synchronized with the rotation of the first spindle 11, but the rotation of the first spindle 11 is not synchronized with the rotation of the second spindle 21. Therefore, if the output torque of the motor 11m of the first spindle 11 is set to zero, the output torque of the motor 21m of the second spindle 21 will also become zero in synchronization with it, making it impossible to create a speed difference ΔV between the first spindle 11 and the second spindle 21. Thus, it becomes difficult to determine if the parting-off process is not being performed correctly. On the other hand, in this embodiment, the output torque of the motor 21m of the second spindle 21 is set to zero, and the rotational speed of the motor 11m of the first spindle 11 is maintained. Therefore, a speed difference ΔV can be created between the first spindle 11 and the second spindle 21, making it possible to determine if the parting-off process is not being performed correctly.

[0044] (3) When the motor control unit 301 performs the above-mentioned stopping process, it determines that the rotational speed of the first spindle 11 has become zero based on the spindle speed zero signal S0, which is an example of a spindle speed signal acquired, and determines that the synchronous rotational speed of the first spindle 11 and the second spindle 21 has become zero. With this configuration, it becomes possible to reliably determine when the synchronous rotational speed of the first spindle 11 and the second spindle 21 becomes zero.

[0045] (4) The motor control unit 301 maintains the rotational speed of the first spindle 11 at a constant speed from the time of parting off until the parting off discrimination unit 302 makes the discrimination, and reduces the output torque of the second motor 21m to zero when the parting off discrimination unit 302 makes the discrimination. With this configuration, there is no need to change the rotational speed of the first spindle 11 from parting off to parting off detection, allowing for a smooth transition from parting off to parting off detection. Furthermore, controlling the rotational speed of the first spindle 11 becomes simpler.

[0046] (modified version) However, the present invention is not limited to the embodiments and drawings described above. Modifications (including the deletion of components) can be made as appropriate without altering the essence of the invention. An example of a modification is described below.

[0047] In the above embodiment, either the cross drill device 80 or the rear drive device 85, or both the cross drill device 80 and the rear drive device 85, may be omitted.

[0048] In the above embodiment, there may be no rotary guide bushing device 60 or guide bushingless device 90 between the first spindle unit 10 and the second spindle unit 20. In the above embodiment, the parting detection process may be performed as a series of processes using M codes. This allows the parting detection process to be easily performed simply by issuing M codes in the NC program.

[0049] In the above embodiment, waiting times may be included between each step S101 to S112 of the parting-off process. The order of each step S101 to S112 can be changed as appropriate, and any multiple steps of each step S101 to S112 may be performed simultaneously. Furthermore, any step of each step S101 to S112 may be omitted, or new steps may be added.

[0050] In the above embodiment, the motor control unit 301 maintained the rotational speed of the first spindle 11 at a constant speed from the time of parting off to the time of determination by the parting off determination unit 302. However, the motor control unit 301 is not limited to this, and may increase or decrease the rotational speed of the first spindle 11 when transitioning from parting off to determination. In the above embodiment, in step S110 of Figure 6, the motor control unit 301 returned the output torque of the motor 21m of the second spindle 21 from zero to its original value during the parting-off process. However, if it has increased from zero, it may be set to a value other than the original value. [Explanation of symbols]

[0051] 1...Machine tool, 10...First spindle unit, 11...First spindle, 11a,21a...Collet chuck, 11d,21d...Collet sleeve, 11k,21k...Inclined surface, 11m,21m...Motor, 13...First spindle moving mechanism, 15...First headstock, 15a,25a...Bearing, 20...Second spindle unit, 21...Second spindle, 23,24...Second spindle moving mechanism, 25...Second headstock, 30...First tool unit, 31,35,41...Tool, 31a...Parting tool, 32,33...First tool moving mechanism, 34 ...Tool base, 40...Second tool unit, 43...Cutting post, 60...Rotating guide bushing device, 65...Support base, 80...Cross drilling device, 85...Reverse drive device, 90...Guide bushingless device, 91...Cylindrical section, 300...Control unit, 301...Motor control unit, 302...Parting detection unit, 303...Rotation speed detection unit, 304...Synchronization detection unit, S...Bed, S0...Spindle speed zero signal, S1...Synchronization completion signal, ΔV...Speed ​​difference, W, Wa...Workpiece, Ta...Deceleration waiting time, Wb...Uncut portion, Th...Threshold

Claims

1. A first workpiece holding unit that holds the workpiece, A first spindle having a first motor, which rotates together with the first workpiece holding part by the rotation of the first motor, A second workpiece holding section that holds the workpiece, The second spindle has a second motor, which rotates together with the second workpiece holding part due to the rotation of the second motor, and is positioned so as to face the first spindle in the direction of the rotation axis of the first spindle, A spindle movement mechanism that moves the first spindle and the first workpiece holder relative to the second spindle and the second workpiece holder in the direction of the rotation axis of the first spindle, A tool moving mechanism that moves the parting tool in a direction intersecting the rotation axis direction of the first spindle, The control unit performs a parting operation in which the cutting edge of the parting tool is moved from the outer surface of the workpiece toward the central axis of the workpiece via the tool moving mechanism, while the first workpiece holder and the second workpiece holder, which have moved to opposing positions via the spindle moving mechanism, simultaneously hold different parts of the workpiece in the direction of the rotation axis of the first spindle, and the first spindle and the second spindle rotate synchronously with the workpiece, thereby separating the workpiece between the first workpiece holder and the second workpiece holder. The control unit is A motor control unit that controls the rotational speed of the first motor and the second motor, The system includes a parting determination unit that, after the parting operation, determines that the parting operation was performed correctly if the rotation of the first spindle and the second spindle are not synchronized when a preset deceleration waiting time has elapsed after the output torque of the first motor or the second motor has been reduced to zero by the motor control unit, and determines that the parting operation was not performed correctly when the rotation of the first spindle and the second spindle are synchronized. If the parting-off detection unit determines that the parting-off process is not being performed correctly, the motor control unit increases the output torque of the first motor or the second motor, whose output torque has been set to zero, from zero, and then performs a stop operation to set the synchronous rotational speed of the first spindle and the second spindle to zero while maintaining the state in which the rotation of the first spindle and the second spindle are synchronized. Machine tools.

2. The control unit processes the workpiece held by the first workpiece holding unit using a tool, then holds the end of the workpiece with the second workpiece holding unit and performs the parting-off process. The motor control unit synchronizes the rotation of the first and second spindles by controlling the rotation speed of the second spindle to match the rotation speed of the first spindle. The parting-off determination unit, after the parting-off process, sets the output torque of the second motor of the second spindle to zero via the motor control unit and then waits for the deceleration waiting time to elapse. The machine tool according to claim 1.

3. When the motor control unit performs the stop process, it determines, based on the spindle speed signal output from the rotation speed detection sensor that detects the rotation speed of the first spindle or the second spindle, that the rotation speed of the first spindle or the second spindle has become zero, and at the same time determines that the synchronous rotation speed of the first spindle and the second spindle has become zero. The machine tool according to claim 1 or 2.

4. The motor control unit reduces the output torque of the second motor to zero after the parting-off process, and the parting-off discrimination unit determines that the parting-off process is not performed correctly, and the output torque of the second motor increases from zero. The motor control unit maintains the rotational speed of the first spindle at a constant speed from the time of the parting-off process until the parting-off discrimination unit makes the determination, and reduces the output torque of the second motor to zero when the parting-off discrimination unit makes the determination. The machine tool according to claim 1 or 2.

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