Workpiece detection device and machine tool

Abstract

To detect a workpiece (presence or absence of workpiece, length of workpiece) on a spindle without using a torque variation in a servo-equipped actuator, a workpiece detection device (30) comprises: an ejector rod (22) which is disposed inside a back spindle (20) that grips a workpiece (W) and which can be moved to press to eject the workpiece (W) to the outside; a servo motor (28) having a drive unit (28a) for moving the ejector rod (22) and an encoder (28b); and a control unit (60) that controls the drive unit (28a) on the basis of a detection result of the encoder (28b), wherein the control unit (60) moves the ejector rod (22) to a standby position, the encoder (28b) detects a movement when the workpiece (W) moves the ejector rod (22), and the control unit (60) calculates the presence or absence of the workpiece (W) on the basis of the movement.

Description

Workpiece detection device and machine tool

[0001] The present invention relates to a workpiece detection device and a machine tool.

[0002] There are cases where a workpiece held by the front spindle is transferred to the back spindle, and machining is performed on the workpiece held by the back spindle. In this case, it is necessary to check whether the workpiece has been properly transferred from the front spindle to the back spindle.

[0003] Therefore, a system has been proposed that includes a work supply means for supplying a workpiece to the spindle, and a recognition means for recognizing the insertion length of the workpiece into the spindle based on the position of the work supply means and the position of the spindle when the workpiece supply means supplies the workpiece to the spindle (see, for example, Patent Document 1).

[0004] JP 2009-166165 A

[0005] Specifically, the technology proposed in Patent Document 1 recognizes the insertion length of a workpiece by detecting torque fluctuations of an actuator with a servo using a recognition means.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a workpiece detection device and a machine tool equipped with a workpiece detection device that can detect the supply status of a workpiece to a spindle (presence or absence of a workpiece, length of the workpiece) with greater accuracy than when using torque fluctuations of a servo-equipped actuator.

[0007] A first aspect of the present invention is a workpiece detection device comprising: a movable body that is disposed inside a spindle that grips a workpiece, and that is movable in the axial direction of the spindle so as to press against the workpiece inserted inside the spindle and eject the workpiece outside the spindle; a drive mechanism having a drive unit that moves the movable body and a detection unit that detects the movement of the drive unit; and a control unit that feedback controls the drive unit based on the detection result of the detection unit, wherein the control unit moves the movable body to a specific position before the workpiece is inserted into the spindle, the detection unit detects the movement length of the movable body when the workpiece is inserted into the spindle and causes the movable body to move, and the control unit calculates the length of the workpiece based on the movement length.

[0008] A second aspect of the present invention is a machine tool comprising a spindle into which a workpiece is inserted and which grips the workpiece, a tool which processes the workpiece gripped by the spindle, a control device which controls the operation of the spindle and the tool, and a workpiece detection device according to the present invention, wherein a control unit of the workpiece detection device is the control device.

[0009] The workpiece detection device and machine tool according to the present invention can detect the supply status of the workpiece to the spindle (presence or absence of the workpiece, length of the workpiece) with greater accuracy than when using torque fluctuations of a servo actuator.

[0010] FIG. 1 is a plan view schematically showing the main configuration of an automatic lathe. FIG. 2 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, showing a state in which the front end face of the ejector rod has moved to a standby position coincident with the front end face of the back spindle. FIG. 3 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, showing a state in which the ejector rod has been pushed back by the workpiece (gripping position). FIG. 4 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, showing a state in which the front end face of the ejector rod has moved to a retracted position away from the insertion-side front end face of the workpiece. FIG. 5 is a block diagram showing the configurations of a workpiece discharge device and a workpiece detection device. FIG. 6 is a schematic diagram showing an example in which the ejector rod has set a known specific position as a standby position. FIG. 7 is a flowchart showing an example of the operation flow of an automatic lathe. FIG. 8 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, showing a state in which the front end face of the knockout jig has moved to a standby position where it protrudes from the front end face of the back spindle. FIG. 9 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, showing a state in which the knockout jig has been pushed back by the workpiece (gripping position). 10 is a cross-sectional view showing a cross section taken along a vertical plane including the axis of the back spindle, illustrating a state in which the front end surface of the ejector rod has moved to a retracted position away from the rear end surface of the tip receiving portion of the knockout jig. FIG.

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a workpiece detection device and a machine tool according to the present invention will be described below with reference to the drawings.

[0012] (Basic configuration of automatic lathe) Fig. 1 is a plan view showing a schematic diagram of the main configuration of an automatic lathe 100, and Figs. 2, 3, and 4 are cross-sectional views showing a cross section taken along a vertical plane including the axis C2 of the back spindle 20 of the automatic lathe 100. Fig. 2 shows a state in which the front end face 22a of the ejector rod 22 has moved to a standby position coinciding with the tip end face 20A of the back spindle 20, Fig. 3 shows a state in which the ejector rod 22 has been pushed back by the workpiece W (gripping position), and Fig. 4 shows a state in which the front end face 22a of the ejector rod 22 has moved to a retracted position away from the insertion side end face W1 of the workpiece W.

[0013] An automatic lathe 100 is one embodiment of a machine tool according to the present invention. As shown in Figure 1, the automatic lathe 100 includes a front spindle 10, a back spindle 20, a gang tool rest 40, a back tool rest 50, and a control unit 60 (control device).

[0014] The front spindle 10 grips a workpiece W, which is a bar material that is a long, rod-shaped member, and rotates the workpiece W around an axis C1. The front spindle 10 is fixed to a front headstock (not shown), and the front headstock moves along the z-axis parallel to the axis C1, thereby allowing the front spindle 10 to move in the z-axis direction. The movement of the front headstock in the z-axis direction is controlled by a control unit 60.

[0015] The back spindle 20 grips the workpiece W and rotates it about axis C2, and is disposed opposite the front spindle 10. Like axis C1, axis C2 is parallel to the z-axis direction. The back spindle 20 receives the workpiece W machined by the front spindle 10 from the front spindle 10, with axis C2 disposed coaxially with axis C1 of the front spindle 10. The back spindle 20 has the workpiece W inserted therein, grips the inserted workpiece W, and rotates the gripped workpiece W about axis C2.

[0016] The workpiece W handed over to the back spindle 20 is cut by a cut-off tool provided on the gang tool rest 40 at a position a predetermined protruding length L1 from the tip surface 20A of the back spindle 20 while also being held by the front spindle 10.

[0017] Then, the back spindle 20 processes the peripheral surface of the workpiece W cut to a predetermined length and the end face (discharge side end face) facing the front spindle 10 using tools provided on the comb tool rest 40 and the back tool rest 50.

[0018] The back spindle 20 is fixed to a back headstock (not shown), and can move in the z-axis direction by moving the back headstock along the z-axis parallel to axis C2, and can also move in the x-axis direction by moving the back headstock along the x-axis in a horizontal plane perpendicular to the z-axis. The movement of the back headstock in the z-axis and x-axis directions is controlled by a control unit 60.

[0019] The control unit 60 controls the operations of the front spindle 10, back spindle 20, gang tool rest 40, back tool rest 50, front headstock, and back headstock.

[0020] (Workpiece Discharge Device) Figure 5 is a block diagram showing the configurations of the workpiece discharge device 29 and the workpiece detection device 30. As shown in Figures 2 to 4, the back spindle 20 has a workpiece W inserted into it along axis C2 and supplied from the front spindle 10 arranged opposite the back spindle 20 as shown in Figures 3 and 4. Hereinafter, the end face of the workpiece W that becomes the leading end when inserted into the back spindle 20 will be referred to as the insertion side end face W1, and the end face that becomes the rear end when inserted into the back spindle 20 will be referred to as the discharge side end face W2. The discharge side end face W2 is the end face closer to the front spindle 10 than the insertion side end face W1.

[0021] A collet chuck 21 is provided at the tip of the back spindle 20 on the side closer to the front spindle 10. The collet chuck 21 has a sleeve 21a and a collet 21b, and by the control of the control unit 60, the sleeve 21a advances along the axis C2 toward the tip surface 20A of the back spindle 20, thereby reducing the inner diameter of the collet 21b and gripping the workpiece W inserted inside the collet 21b from the outer peripheral surface side.

[0022] The back spindle 20 is equipped with a workpiece discharge device 29 shown in Fig. 5. The workpiece discharge device 29 discharges the workpiece W held by the collet chuck 21 to the outside from the tip end surface 20A of the back spindle 20. As shown in Fig. 5, the workpiece discharge device 29 has a control unit 60, a servo motor 28 (drive mechanism), and an ejector rod 22 (moving body). The servo motor 28 and the ejector rod 22 are provided in the back spindle 20, and the control unit 60 is provided in the automatic lathe 100 separately from the back spindle 20.

[0023] 2 to 4, the ejector rod 22 is disposed inside the back spindle 20 along the axis C2. The ejector rod 22 is a rod-shaped member extending along the axis C2. The ejector rod 22 is provided so as to be linearly movable along the axis C2 between a retracted position shown in FIG. 4 where its front end surface 22a is spaced rearward from the insertion-side end surface W1 of the workpiece W gripped by the back spindle 20, and an ejection position shown in FIG. 2 where its front end surface coincides with the tip end surface 20A of the back spindle 20.

[0024] Then, as the front end surface 22a of the ejector rod 22 moves from the retracted position (FIG. 4) to the discharge position (FIG. 2), as shown in FIG. 3, the front end surface 22a comes into contact with the insertion side end surface W1 of the workpiece W after machining in the back spindle 20 has been completed and the workpiece W has been released from the collet chuck 21. In this contacting state, the ejector rod 22 pushes the workpiece W toward the tip surface 20A of the back spindle 20, and ejects the workpiece W out of the back spindle 20 before the ejector rod 22 reaches the discharge position shown in FIG.

[0025] The ejector rod 22 does not rotate around the axis C2 while moving linearly from the retracted position to the ejection position.

[0026] The servo motor 28 includes a drive unit 28a that rotates and an encoder 28b (detector). The encoder 28b detects the rotation of the drive unit 28a and the angle of rotation. The control unit 60 controls the rotation of the drive unit 28a based on the rotation angle (detection result) detected by the encoder 28b.

[0027] The drive unit 28a is connected to the ejector rod 22. The control unit 60 rotates the drive unit 28a to linearly move the ejector rod 22 along the axis C2. The control unit 60 also switches the rotation direction of the drive unit 28a between the forward direction and the reverse direction, thereby switching the ejector rod 22 between moving forward and backward along the axis C2. The control unit 60 also controls the rotation angle of the drive unit 28a to adjust the linear movement length of the ejector rod 22.

[0028] (Workpiece detection device) The back spindle 20 is equipped with a workpiece detection device 30 shown in Fig. 5. The workpiece detection device 30 is one embodiment of the workpiece detection device according to the present invention. The workpiece detection device 30 detects the presence or absence of a workpiece W supplied from the front spindle 10 to the back spindle 20 and the length of the workpiece. The workpiece detection device 30 is configured using a workpiece discharge device 29.

[0029] The work detection device 30 utilizes the servo motor 28 and the ejector rod 22 in the work discharge device 29, and by controlling these servo motor 28 and the ejector rod 22 with the control unit 60, it separately detects whether or not the work W is present and detects the length of the work W.

[0030] The workpiece detection device 30 includes the above-described control unit 60, servo motor 28, and ejector rod 22, as well as a notification unit 31 and a program change unit 32. The notification unit 31 and the program change unit 32 are controlled by the control unit 60.

[0031] The control unit 60, which is a component of the workpiece detection device 30, advances the ejector rod 22 along the axis C2 toward the tip surface 20A of the back spindle 20 before the back spindle 20 receives the workpiece W, and controls the driving of the servo motor 28 so that the ejector rod 22 is stopped at an ejection position (an example of a specific position) where the front end surface 22a coincides with the tip surface 20A of the back spindle 20, as shown in Figure 2.

[0032] With the front end surface 22a of the ejector rod 22 in the ejection position, the workpiece W is received from the front spindle 10. At this time, the collet chuck 21 of the back spindle 20 is released by the control of the control unit 60, and the workpiece W is allowed to be inserted inside the collet chuck 21.

[0033] The control unit 60 linearly moves at least one of the front headstock and the back headstock along the z-axis so that the front spindle 10 approaches the back spindle 20. As a result, the workpiece W held by the front spindle 10 approaches the back spindle 20, and then the workpiece W is inserted from the insertion side end face W1 into the inside of the collet chuck 21 of the back spindle 20 along the axis C2 arranged coaxially with the axis C1.

[0034] When the workpiece W reaches the tip end surface 20A of the back spindle 20, the insertion side end surface W1 of the workpiece W comes into contact with the front end surface 22a of the ejector rod 22. Then, as the workpiece W is inserted into the back spindle 20, with the insertion side end surface W1 of the workpiece W coming into contact with the front end surface 22a of the ejector rod 22, the workpiece W pushes the ejector rod 22 rearward along the axis C2, and the ejector rod 22 moves rearward.

[0035] Then, when the workpiece W is inserted to a predetermined position inside the back spindle 20 for processing by the back spindle 20, the transfer of the workpiece W from the front spindle 10 to the back spindle 20 is completed, and the workpiece W stops at the position shown in FIG. 3.

[0036] The control unit 60 controls the collet chuck 21 at the position where the workpiece W has stopped, and the collet chuck 21 grips the workpiece W. The position of the ejector rod 22 shown in FIG. 3 where the collet chuck 21 grips the workpiece W is hereinafter referred to as the gripping position.

[0037] When the ejector rod 22 moves rearward, the drive unit 28a of the servo motor 28 connected to the ejector rod 22 rotates in accordance with the movement of the ejector rod 22. In other words, the drive unit 28a rotates by an angle corresponding to the amount of rearward movement of the ejector rod 22. When the drive unit 28a rotates, the encoder 28b also rotates in synchronization with the rotation of the drive unit 28a. Therefore, the encoder 28b detects the angle of rotation corresponding to the amount of rearward movement of the ejector rod 22.

[0038] The control unit 60 stores in advance a correspondence between the rotation angle of the encoder and the amount of movement along the axis C2 of the ejector rod 22, and therefore receives input of the rotation angle detected by the encoder 28b and calculates the amount of rearward movement of the ejector rod 22 based on that rotation angle.

[0039] Then, the control unit 60 calculates the amount of movement of the ejector rod 22 from the standby position (FIG. 2) to the gripping position (FIG. 3). For example, if it is L2 as shown in FIG. 3, the insertion length of the workpiece W into the back spindle 20 is L2.

[0040] Here, when the workpiece W is transferred from the front spindle 10 to the back spindle 20, the workpiece W is still long and rod-shaped, and while the back spindle 20 is gripping the workpiece W (with the ejector rod 22 in a retracted position, which will be described later), the workpiece W is cut by a cut-off tool provided on the gang tool rest 40 at a position a predetermined length L1 (see FIG. 3) from the tip end surface 20A of the back spindle 20 under the control of the control unit 60. As a result, an end surface W2 of the workpiece W on the front spindle 10 side (the end surface opposite to the insertion side end surface W1; hereinafter referred to as the discharge side end surface W2) is formed.

[0041] The position of the discharge side end face W2 of the workpiece W is the position of the protrusion length L1 from the tip face 20A of the back spindle 20, and the control unit 60 acquires the protrusion length L1 at the machining stage where the discharge side end face W2 is formed. Therefore, the control unit 60 can calculate the length L of the workpiece W gripped by the back spindle 20.

[0042] Specifically, the control unit 60 can determine the length L (= L1 + L2) of the workpiece W as the sum (= L2 + L1) of the insertion length L2 into the back spindle 20 calculated from the rotation angle detected by the encoder 28b and the protrusion length L1 from the tip surface 20A of the back spindle 20 recognized during processing to form the discharge side end surface W2.

[0043] Note that the operation of supplying the workpiece W to the back spindle 20 causes the ejector rod 22 to move backward from the standby position, which means that the workpiece W has been inserted into the back spindle 20. Therefore, the encoder 28b detects the rotation angle, and the control unit 60 can detect the presence of the workpiece W (workpiece W present). On the other hand, if the encoder 28b does not detect the rotation angle even when the workpiece W is supplied to the back spindle 20, the control unit 60 does not detect the presence of the workpiece W (workpiece W absent). Therefore, the workpiece detection device 30 and the automatic lathe 100 can detect the presence or absence of the workpiece W.

[0044] As described above, the workpiece detection device 30 and the automatic lathe 100 of this embodiment detect the presence or absence of the workpiece W and the length of the workpiece W by the workpiece detection device 30 detecting the movement of the ejector rod 22 when the back spindle 20 receives and delivers the workpiece W. Therefore, the automatic lathe 100 of this embodiment can detect the supply status of the workpiece W to the back spindle 20 (presence or absence of the workpiece W, length L of the workpiece W) without detecting torque fluctuations of the servo motor 28.

[0045] Therefore, the workpiece detection device 30 and automatic lathe 100 of this embodiment can detect the supply status of the workpiece W to the back spindle 20 (presence or absence of the workpiece W, length of the workpiece W) with greater accuracy than when using the torque fluctuations of a servo-equipped actuator.

[0046] The workpiece detection device 30 and automatic lathe 100 of the above-described embodiment detect the presence or absence of the workpiece W and the length of the workpiece W as the supply status of the workpiece W to the back spindle 20, but the workpiece detection device and machine tool of the present invention may simply detect the presence or absence of the workpiece W as the supply status of the workpiece W.

[0047] When the automatic lathe 100 processes the workpiece W held by the back spindle 20 using tools provided on the gang tool post 40 or the back tool post 50, the back spindle 20 rotates the workpiece W around the axis C2, but the ejector rod 22 does not rotate around the axis C2. Therefore, as shown in FIG. 3, when the front end face 22a of the ejector rod 22 abuts against the insertion side end face W1 of the workpiece W, the rotation of the workpiece W may cause friction to wear out at least one of the insertion side end face W1 of the workpiece W and the front end face 22a of the ejector rod 22.

[0048] Therefore, after the automatic lathe 100 grips the workpiece W at the gripping position (FIG. 3), that is, after detecting the length L of the workpiece W, the control unit 60 controls the servo motor 28 to retract the front end surface 22a of the ejector rod 22 along the axis C2 to a position (see FIG. 4) away from the insertion side end surface W1 of the workpiece W. Note that the ejector rod 22 shown in FIG. 4 is in a position where the front end surface 22a is away from the insertion side end surface W1 of the workpiece W, and this position is referred to as the retracted position.

[0049] In this way, when the control unit 60 has retracted the ejector rod 22 to the retracted position, the front end surface 22a of the ejector rod 22 is not in contact with the insertion side end surface W1 of the workpiece W, so even if the automatic lathe 100 rotates the workpiece W around the axis C2, neither the insertion side end surface W1 of the workpiece W nor the front end surface 22a of the ejector rod 22 will be worn down due to friction.

[0050] In the automatic lathe 100 of this embodiment, the standby position where the ejector rod 22 waits before the workpiece W is transferred to the back spindle 20 is a position where the front end surface 22a is aligned with the tip end surface 20A of the back spindle 20. However, the standby position of the ejector rod 22 in the present invention is not limited to the position where the front end surface 22a is aligned with the tip end surface 20A of the back spindle 20.

[0051] In other words, the standby position of the ejector rod 22 in the present invention may be any known specific position that is set so that when the workpiece W to be handed over to the back spindle 20 is handed over to the back spindle, the insertion side end face W1 of the workpiece W abuts against the front end face 22a of the ejector rod 22, thereby moving the ejector rod 22 rearward from the standby position.

[0052] Fig. 6 is a schematic diagram showing an example in which the standby position of the ejector rod 22 is a known specific position other than the tip end surface 20A. When the ejector rod 22 is on standby at a position where its front end surface 22a protrudes a length La from the tip end surface 20A of the back spindle 20, as shown in the upper part of Fig. 6, for example, the workpiece W is transferred to the back spindle 20, causing the workpiece W to move the ejector rod 22, which is on standby at the specific position, rearward by a length Lc as shown in the lower part of Fig. 6, and the control unit 60 can detect the rearward movement of the ejector rod 22 from the standby position (specific position) and the length Lc of the movement.

[0053] The control unit 60 stores in advance the length La of the ejector rod 22 protruding from the tip surface 20A of the back spindle 20 at a specific position, and therefore the control unit 60 can calculate the length Lb of the part of the workpiece W inserted into the back spindle 20 by subtracting the length La of the part protruding from the tip surface 20A from the detected length Lc (Lb = Lc - La).

[0054] In addition, the known specific position may not be a position where the front end surface 22 a of the ejector rod 22 protrudes from the tip end surface 20A of the back main shaft 20, but may be a position where the front end surface 22 a of the ejector rod 22 retracts inward from the tip end surface 20A of the back main shaft 20.

[0055] The control unit 60 can then calculate the length L of the workpiece W held by the back spindle 20 as the sum of the length L1 protruding from the tip surface 20A of the back spindle 20 and the length Lb of the portion inserted into the back spindle 20 (L = L1 + Lb).

[0056] The automatic lathe 100 of this embodiment configured as described above operates, for example, as follows: Figure 7 is a flowchart showing an example of the flow of operation of the automatic lathe 100.

[0057] After the automatic lathe 100 has completed machining of the workpiece W held by the front spindle 10, it transfers the workpiece W to the back spindle (starts transferring the workpiece W to the back spindle 20) (S0 in FIG. 7).

[0058] The workpiece detection device 30 detects whether or not the workpiece W has been transferred to the back spindle 20 (S1). When the workpiece detection device 30 does not detect the workpiece W (no in S1), that is, when it does not detect that the ejector rod 22 has moved rearward from the standby position, the control unit 60 activates the alarm unit 31. That is, the alarm unit 31 displays an alarm (warning) indicating "no workpiece" (S5). Then, the control unit 60 skips the machining process in which the back spindle 20 grips the workpiece W, and stops the operation of the automatic lathe 100 after one cycle is completed (S5).

[0059] When the workpiece detection device 30 detects the workpiece W (present in S1), that is, when it detects that the ejector rod 22 has moved rearward from the standby position, the control unit 60 outputs the length L of the detected workpiece W, and the control unit 60 determines whether the length L of the detected workpiece W is appropriate (S2).

[0060] Here, the length of the workpiece W is deemed appropriate when the detected length L of the workpiece W matches the length of the workpiece W specified in the machining program loaded into the control unit 60 for machining the workpiece W by the automatic lathe 100. On the other hand, the length of the workpiece W is deemed inappropriate when the detected length L of the workpiece W does not match the length of the workpiece W specified in the machining program.

[0061] When the control unit 60 determines that the detected length L of the workpiece W is not appropriate (NO in S2), the control unit 60 activates the notification unit 31. That is, the notification unit 31 displays an alarm (warning) indicating "incorrect workpiece length" (S6). Then, the control unit 60 immediately stops the machining process of the automatic lathe 100 (S6).

[0062] On the other hand, when the control unit 60 determines that the length L of the detected workpiece W is appropriate (YES in S2), the control unit 60 determines whether the workpiece W is part A or another part B having a different length from part A, depending on the detected length L of the workpiece W (S3).

[0063] When the control unit 60 determines that the detected workpiece W is part A (part A in S3), the control unit 60 instructs the program change unit 32 to change the machining program for the workpiece W held by the back spindle 20 to a machining program for part A, and processes the workpiece W on the automatic lathe 100 according to the machining program for part A (S4).

[0064] On the other hand, when the control unit 60 determines that the detected workpiece W is part B (part B in S3), the control unit 60 causes the program change unit 32 to change the machining program for the workpiece W held by the back spindle 20 to a machining program for part B, and the workpiece W is machined on the automatic lathe 100 in accordance with the machining program for part B (S7).

[0065] 7 shows how the machining program is changed (S3, S4, S7) in accordance with the length L of the workpiece W detected by the workpiece detection device 30, but the automatic lathe 100 of this embodiment is not limited to one that changes the machining program, and does not have to change the machining program in accordance with the detected length L of the workpiece W. In the automatic lathe 100 that does not change the machining program, when it is determined that the length L of the workpiece W detected in step 3 (S3) is appropriate (YES in S3), the control unit 60 only needs to control the machining of the workpiece W gripped by the back spindle 20 in accordance with the preset machining program.

[0066] In the automatic lathe 100 of this embodiment, in order to prevent the ejector rod 22 serving as the workpiece discharge device 29 from unintentionally moving, the control unit 60 controls the servo motor 28 to apply a predetermined excitation holding force to the servo motor 28. By holding the servo motor 28 in a stopped state with the predetermined excitation holding force, the ejector rod 22 is held in a predetermined position so as not to move, and unintentional movement can be prevented.

[0067] Unintentional movement does not mean that the ejector rod 22 is moved by driving the servo motor 28 with the purpose of moving the ejector rod 22, but rather that the ejector rod 22 moves even though there is no purpose to move the ejector rod 22, for example, due to vibrations caused by operating the automatic lathe 100.

[0068] As described above, if the servo motor 28 is held in a stopped state by the excitation holding force, there is a possibility that the ejector rod 22, which serves as the work detection device 30, may be hindered from retracting when it is pushed by the work W from the standby position to the gripping position.

[0069] Therefore, in the automatic lathe 100, after the ejector rod 22 has been moved to the standby position, while the workpiece W is being inserted into the rear spindle 20, it is preferable that the control unit 60 does not apply an excitation holding force to the servo motor 28, or reduces the excitation holding force applied to the servo motor to an extent that does not interfere with the action of the workpiece W pushing backward the ejector rod 22 stopped at the standby position.

[0070] In addition, a low excitation holding force that does not hinder the workpiece W from pushing backward the ejector rod 22 stopped at the standby position means an excitation holding force that is such that when the workpiece W pushes the ejector rod 22 backward, the workpiece W can move the ejector rod 22 backward, even when an excitation holding force is acting on the servo motor.

[0071] The workpiece detection device 30 of this embodiment has the ejector rod 22 and the servo motor 28 provided on the back spindle 20, but the workpiece detection device according to the present invention is not limited to one in which the ejector rod 22 and the servo motor 28 are provided on the back spindle 20.

[0072] That is, in the workpiece detection device 30 of this embodiment, the front spindle 10 of the automatic lathe 100 performs the function of supplying the workpiece W, so the explanation has been given in terms of the back spindle 20 as the side to which the workpiece W is supplied.

[0073] However, if the front spindle 10 is a machine tool that receives a workpiece W of a predetermined length that is not a rod-shaped member from the tip surface side, the workpiece detection device 30 may be one that is provided with an ejector rod 22 and a servo motor 28 on the front spindle 10. In this case, the machine tool that is provided with the workpiece detection device according to the present invention does not need to be provided with a back spindle.

[0074] The workpiece detection device 30 of this embodiment is provided with the notification unit 31 and the program change unit 32, but the workpiece detection device according to the present invention does not necessarily have to be provided with these notification unit 31 and program change unit 32.

[0075] In the workpiece detection device 30 of this embodiment, the encoder 28b of the servo motor 28 detects the rotation angle of the drive unit 28a, but the encoder 28b may also be a linear encoder that directly detects the linear movement length of the ejector rod 22 corresponding to the rotation angle of the drive unit 28a.

[0076] 8, 9, and 10 are cross-sectional views showing a cross section taken along a vertical plane including the axis C2 of the back spindle 20. FIG. 8 shows a state in which the front end surface 23 a of the knockout jig 27 has moved to a standby position protruding from the tip end surface 20A of the back spindle 20. FIG. 9 shows a state in which the knockout jig 27 has been pushed back by the workpiece W (gripping position). FIG. 10 shows a state in which the front end surface 22 a of the ejector rod 22 has moved to a retracted position away from the rear end surface 23 b of the tip receiving portion 23 of the knockout jig 27.

[0077] In the above-mentioned automatic lathe 100, an ejector rod 22 provided inside the back spindle 20 ejects the workpiece W to the outside of the back spindle 20. Therefore, in the automatic lathe 100 and the workpiece detection device 30, the control unit 60 controls the ejector rod 22 to detect the length L of the workpiece W.

[0078] 8, 9, and 10 has a workpiece detection device 30 with a knockout jig 27 added to the ejector rod 22. Because the ejector rod 22 is formed in a hollow cylindrical shape, when a hole that passes through in the direction of axis C2 is formed in the workpiece W held by the back spindle 20, there is a risk that chips generated during machining may enter the back spindle 20 through the through hole. The knockout jig 27 is used for the purpose of preventing chips from entering the interior even when machining is performed to form a through hole in the workpiece W. The knockout jig 27, together with the ejector rod 22, corresponds to a moving body in the workpiece detection device according to the present invention.

[0079] As shown in FIGS. 8 to 10, the knockout jig 27 includes a tip receiving portion 23, a cylindrical portion 24, a base portion 25, and a coil spring 26.

[0080] The tip receiving portion 23 is disposed forward of the ejector rod 22, with its rear end face 23b in contact with the front end face 22a of the ejector rod 22, and is pushed by the ejector rod 22 as the ejector rod 22 moves (advances) forward (toward the tip face 20A of the back spindle 20), thereby moving forward integrally with the ejector rod 22. The tip receiving portion 23 is formed with an outer diameter slightly smaller than the inner diameter of the collet chuck 21. The tip receiving portion 23 is not penetrated internally between the rear end face 23b and the front end face 23a, thereby preventing chips generated during machining of the workpiece W gripped by the back spindle 20 from entering the interior.

[0081] The cylindrical portion 24 is fixed to the rear portion of the tip receiving portion 23 and moves along the axis C2 integrally with the tip receiving portion 23. The cylindrical portion 24 is formed in a cylindrical shape that surrounds the tip portion of the ejector rod 22 from the outside in the radial direction centered on the axis C2.

[0082] The base 25 is fixed to the sleeve 21a of the back main shaft 20 and moves integrally with the sleeve 21a. The base 25 is also formed in a cylindrical shape that surrounds the ejector rod 22 from the outside in the radial direction centered on the axis C2. The base 25 is further formed so that the inner diameter of the cylinder is larger than the outer diameter of the cylinder portion 24, and is formed so that the cylinder portion 24 can pass through the inner space when the cylinder portion 24 moves back integrally with the tip receiving portion 23.

[0083] The coil spring 26 is disposed along the axis C2 between the base 25 and the cylindrical portion 24, and exerts an elastic force to move the cylindrical portion 24 away from the base 25. In other words, the coil spring 26 biases the cylindrical portion 24 and the tip receiving portion 23 toward the tip surface 20A of the back main shaft 20.

[0084] In this way, in the workpiece detection device 30 having the knockout jig 27 attached to the tip of the ejector rod 22, the control unit 60 advances and stops the ejector rod 22 at the standby position shown in Fig. 8 so that the front end surface 23a of the tip receiving portion 23 protrudes by a length L3 from the tip surface 20A of the back spindle 20. Therefore, the control unit 60 stores the length L3.

[0085] When the ejector rod 22 is in this standby position and a workpiece W is supplied from the front spindle 10, the insertion side end face W1 of the workpiece W comes into contact with the front end face 23a of the tip receiving portion 23, and the workpiece W pushes the tip receiving portion 23, the tubular portion 24, the coil spring 26, and the ejector rod 22 backward, and as shown in Figure 9, the workpiece W is inserted into the back spindle 20 up to a predetermined gripping position.

[0086] At this time, the ejector rod 22 retreats by a length L4 (= L3 + L2), which is the sum of the protruding length L3 (see Figure 8) of the tip receiving portion 23 of the knockout jig 27 at the standby position and the insertion length L2 of the workpiece W when it is inserted up to the gripping position, and this retreated length L4 is calculated by the control unit 60 of the workpiece detection device 30.

[0087] Here, the insertion length L2 of the workpiece W inserted into the back spindle 20 from the tip surface 20A is the detected length L4 minus the protruding length L3 of the tip receiving portion 23 (L2 = L4 - L3).

[0088] On the other hand, the position of the discharge side end face W2 of the workpiece W at the gripping position (the position at the length L1 from the tip face 20A) is known by the machining program as described above, and this protruding length L1 is the length of the workpiece W protruding outward from the back spindle 20. The length of the workpiece W is calculated as the sum (= L2 + L1) of the length L2 inserted into the back spindle 20 and the length L1 protruding from the back spindle 20. Therefore, the control unit 60 can calculate the length L of the workpiece W (= L4 - L3 + L1).

[0089] The knockout jig 27 on the back spindle 20 rotates around the axis C2 together with the workpiece W, but the ejector rod 22 does not rotate. Therefore, the ejector rod 22 is retracted by the servo motor 28 so that the front end surface 22a moves away from the rear end surface 23b of the tip receiving portion 23 of the knockout jig 27, as shown in FIG. 10.

[0090] At this time, when the tip receiver 23 retracts together with the ejector rod 22, the front end surface 23a of the tip receiver 23 moves away from the insertion side end surface W1 of the workpiece W, allowing chips to enter inside. However, in the automatic lathe 100 of this embodiment, the coil spring 26 biases the tip receiver 23 forward, so even if the ejector rod 22 retracts, the front end surface 23a of the tip receiver 23 does not move away from the insertion side end surface W1 of the workpiece W, preventing chips from entering inside the back spindle 20. CROSS-REFERENCE TO RELATED APPLICATIONS

[0091] This application claims priority based on Japanese Patent Application No. 2023-118899, filed with the Japan Patent Office on July 21, 2023, the entire disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A workpiece detection device comprising: a movable body that is disposed inside a spindle that grips a workpiece, and that is movable in the axial direction of the spindle so as to press the workpiece inserted inside the spindle and eject the workpiece outside the spindle; a drive mechanism having a drive unit that moves the movable body and a detection unit that detects the movement of the drive unit; and a control unit that controls the drive unit based on the detection result of the detection unit, wherein the control unit moves the movable body to a specific position in advance before the workpiece is inserted into the spindle, the detection unit detects the movement of the movable body when the workpiece is inserted into the spindle and causes the movable body to move, and the control unit detects the supply status of the workpiece to the spindle based on the movement.

2. The workpiece detection device of claim 1, wherein the detection unit detects the length of movement of the moving body when the workpiece is inserted into the spindle and causes the moving body to move, and the control unit detects the length of the workpiece supplied to the spindle as the supply status based on the length of movement.

3. The workpiece detection device of claim 2, wherein the control unit prestores an insertion length from the tip surface of the spindle to the specific position, acquires a protruding length of the workpiece protruding from the tip surface of the spindle, and calculates the length of the workpiece based on the insertion length and the protruding length.

4. The workpiece detection device according to claim 1, wherein the drive mechanism is a servo motor.

5. A workpiece detection device as set forth in claim 4, wherein said control unit reduces the excitation holding force of said servo motor while said workpiece is being inserted into said spindle.

6. A workpiece detection device as described in claim 2, wherein the control unit stops the operation of the spindle when the workpiece is not detected during the operation of inserting the workpiece into the spindle, or when it determines that the length of the workpiece is not appropriate.

7. A work detection device as described in claim 6, further comprising an alarm unit which notifies that the workpiece has not been detected or that the length of the workpiece is not appropriate, wherein the control unit controls the alarm unit to give an alarm when the workpiece has not been detected or when it is determined that the length of the workpiece is not appropriate during the operation of inserting the workpiece into the spindle.

8. A machine tool comprising: a spindle into which a workpiece is inserted and which grips the workpiece; a tool which machines the workpiece gripped by the spindle; a control device which controls the operation of the spindle and the tool; and a workpiece detection device according to any one of claims 1 to 7, wherein a control unit of the workpiece detection device is the control device.

9. The machine tool according to claim 8, wherein the control device changes the machining program that controls the operation of the spindle and the tool when the control device does not detect the workpiece during the operation of inserting the workpiece into the spindle or when the control device determines that the length of the workpiece is not appropriate.

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