Control device for thread cutting

Abstract

Control device (10) for a machine tool, which controls the synchronous operation of a main axis (12) and a feed axis (14), wherein the control device (10) is a numerical control unit (16) which generates a main axis command and a feed axis command based on a thread cutting machining program (P); a main axis control unit (18) that controls the rotation of the main axis (12) according to the main axis command; a rotation detection unit (20) that detects the rotation position of the main axis (12); and a feed axis control unit (22) that controls the feed operation of the feed axis (14) according to the feed axis command based on the rotation position, includes wherein the numerical control unit (16) incorporates a return-speed command value, which is independent of the highest rotational speed of the main axis (12) during machining and is faster than the highest rotational speed during machining, as a command for return operation from the target thread depth to the machining start position into the main axis command, wherein the control device (10) further comprises a storage unit (25) which stores a permissible maximum rotational speed at the time of no load on a drive source that drives the main axis (12), wherein the numerical control unit (16) incorporates the maximum permissible rotational speed stored in the memory unit (25) at the time of no load on the drive source as a return speed command value into the main axis command, wherein the numerical control unit (16) determines whether a maximum return rotational speed of the main axis (12) is specified by the thread cutting machining program (P) or not, and In the event that a maximum return rotational speed of the main axis (12) is specified by the threading program (P), and if the maximum return rotational speed specified by the threading program (P) is lower than the maximum permissible rotational speed at the time the drive source is unloaded, the maximum return rotational speed specified by the threading program (P) is included as the maximum return rotational speed value in the main axis command.

Description

General state of the art 1. Field of invention

[0001] The present invention relates to a control device for a machine tool which performs thread cutting operations by means of a synchronized operation of a main axis and a feed axis. 2. Description of the state of the art

[0002] For machine tools that perform thread cutting operations through the synchronized operation of a main axis and a feed axis, a reduction in cycle time while maintaining machining accuracy is required. For example, patent disclosure Hei-04-093114 describes how "thread cutting is performed, for example, at a main axis rotation speed of 2000 rpm up to a certain Z-axis depth. Then, after the internal thread has been cut, the main axis is rotated in the opposite direction at a speed for which this 2000 rpm has been multiplied by a tap return ratio, e.g., 200% at 4000 rpm."

[0003] DE 10 2015 013 283 A1 and DE 10 2016 006 525 A1 describe a device and a method for controlling a machine tool to control a synchronized operation of a spindle axis and feed axis.

[0004] From US patent 2004 / 0128018A1, a method and a device for controlling thread machining are known.

[0005] From DE 197 00 853 A1 a numerical control device and a method for controlling the acceleration / deceleration of a spindle motor of the numerical control device are known.

[0006] A numerical control system is known from DE 10 2015 001 509 A1. Brief description of the invention

[0007] In a machine tool performing thread cutting operations, the rotational speed of the main axis during thread cutting is generally set to a relatively low speed, taking into account the load on the threading tool and other factors. The goal is to reduce the overall cycle time for thread cutting even when the rotational speed of the main axis during thread cutting is set to a relatively low speed, again considering the load on the threading tool and other factors.

[0008] One form of the present disclosure is a control device for a machine tool that controls the synchronous operation of a main axis and a feed axis, wherein the control device comprises a numerical control unit that generates a main axis command and a feed axis command based on a thread-cutting machining program; a main axis control unit that controls the rotary operation of the main axis according to the main axis command; and a rotation detection unit that detects the rotational position of the main axis.and a feed axis control unit that controls the feed operation of the feed axis according to the feed axis command based on the rotational position, wherein the numerical control unit incorporates a return-speed command value, which is independent of the highest rotational speed of the main axis during machining and is faster than the highest rotational speed during machining, as a command for return operation from the target thread depth to the machining start position into the main axis command. Simple explanation of the drawings

[0009] The tasks, features, and advantages of the present invention will become even clearer through the following explanation of embodiments in conjunction with the accompanying drawings. In the drawings is Fig. 1 a functional block diagram showing the structure of a control device for a machine tool according to a first embodiment, is Fig. 2 a flowchart showing the thread cutting machining control operation according to the first embodiment, is Fig. 3 a diagram showing the operating pattern in the thread cutting machining control operation according to the first embodiment, is Fig. 4 a flowchart showing a thread cutting machining control operation designed to accommodate a user-defined maximum return rotational speed according to a thread cutting machining program, is Fig. 5 a flowchart showing the thread cutting machining control operation according to a second embodiment, is Fig. 6 a diagram showing a speed-acceleration characteristic curve of the main axle motor, is Fig. 7 a diagram showing the operating pattern in the thread cutting machining control operation according to the second embodiment, is Fig. 8 a functional block diagram showing the structure of a control device for a machine tool according to a third embodiment, is Fig. 9 a flowchart showing the thread cutting machining control operation according to the third embodiment, and is Fig. 10 a diagram showing the operating pattern in the thread cutting machining control operation according to the third embodiment. Detailed explanation

[0010] With reference to the drawings, embodiments of the present invention are explained below. Corresponding structural elements across the drawings are identified by common reference numerals. The scale of the drawings has been varied to facilitate understanding. The forms shown in the drawings represent an example of the embodiment of the present invention, but the present invention is not limited to the forms shown. First embodiment

[0011] Fig. Figure 1 is a functional block diagram showing the structure of a control device 10 for a machine tool according to a first embodiment. In a machine tool (for example, a lathe, a drilling machine, a machining center, or the like) that performs thread cutting by means of synchronized operation of a main axis 12 and a feed axis 14, the control device 10 controls the synchronous operation such that the feed axis 14 follows the rotation of the main axis 12, taking into account the thread pitch determined by a thread cutting program P. Although not explicitly shown, the main axis 12 is a control axis that is mounted on a drive device, such as a servo motor, which rotates a holding section that holds a workpiece or tool at a speed required for the machining operation.Although no specific illustration was provided, the feed axis 14 is a control axis connected to a drive device, such as a servo motor, which drives a support section carrying the workpiece at a speed required for machining. For example, on a lathe, a tool can be advanced linearly by the feed axis 14 relative to a workpiece rotated by the main axis 12, or a workpiece rotated by the main axis 12 can be advanced linearly by the feed axis 14 relative to a tool. On a drilling machine, a tool rotated by the main axis 12 can be advanced linearly by the feed axis 14 relative to a workpiece, or a workpiece can be advanced linearly by the feed axis 14 relative to a tool rotated by the main axis 12.In all cases, by driving the feed axis 14 in this way—which has a comparatively large margin of error with respect to acceleration / deceleration torque during operation—it is possible to follow the main axis 12, which has a comparatively large margin of error with respect to acceleration / deceleration torque during operation, thus reducing synchronization errors and improving machining accuracy. In the present embodiment and the individual embodiments described later, there are no significant restrictions on the design of the machine tool.

[0012] The control device 10 comprises a numerical control unit 16, which generates a main axis command CS and a feed axis command CF based on a thread cutting machining program P, a main axis control unit 18, which controls the rotary operation of the main axis 12 according to the main axis command CS, a rotation detection unit 20, which detects the rotation position of the main axis 12, and a feed axis control unit 22, which controls the feed operation of the feed axis 14 according to the feed axis command CF based on the rotation position detected by the rotation detection unit 20.The numerical control unit 16 comprises a program interpretation unit 24, which interprets the thread-cutting machining program P; a main axis command output unit 26, which generates the main axis command CS according to the interpretation by the program interpretation unit 24 and sends the main axis command CS to the main axis control unit 18; and a feed axis command output unit 28, which generates the feed axis command CF according to the interpretation by the program interpretation unit 24 and sends the feed axis command CF to the feed axis control unit 22. The numerical control unit 16 can have the hardware structure of a generally known CNC device. The explanation relating to the basic structure of the control device 10 described above applies equally to the other embodiments described later.

[0013] As will be described in detail below, the control device 10 according to the first embodiment is designed such that it controls the main axis at the time of return during thread cutting operation in such a way that a permissible maximum rotational speed of the main axis motor at the time of non-load operation, which does not depend on the speed command for the main axis during machining as determined by the thread cutting operation program, is used as the target speed.

[0014] The numerical control unit 16 interprets the threading program P, determines the maximum machining rotational speed V0 of the main axis 12 from a machining start position (rotation position) to reaching a target thread depth (rotation position), and commands the main axis control unit 18 to use this maximum machining rotational speed V0 as the target speed during machining. Furthermore, at this time, the numerical control unit 16 determines the total rotational extent S0 of the main axis from the machining start position to reaching the target thread depth based on the threading conditions (thread pitch, thread depth, etc.) contained in the threading program P, and this total rotational extent S0 can be included in the main axis command CS to the main axis control unit 18.If the thread cutting machining program P contains, as an example, a command to machine an internal thread with a thread pitch of 1.25 mm and a thread depth of 30 mm at a maximum machining rotational speed V0 of the main axis 12 of 3000 rpm, the main axis command output unit V0 = 3000 (min. -1] ) and S0 = 24 (revolutions) in the main axis command CS, since the total revolution dimension S0 of the main axis 12 from the machining start position to reaching the target thread depth is 30 ÷ 1.25 = 24 (revolutions).

[0015] The main axis control unit 18 uses the rotation position (feedback value, hereinafter referred to as “rotation position FBS”) of the main axis 12 detected by the rotation detection unit 20 and controls the rotational operation of the main axis 12 by means of a general feedback control.

[0016] The feed axis control unit 22 uses, in addition to the feedback value of the feed position of the feed axis 14, the rotation position FBS of the main axis 12 and controls the feed operation of the feed axis 14 by means of a feedback control so that it follows the operation of the main axis 12. The rotation detection unit 20 can obtain the rotation position FBS from the output of a position detector (not shown), such as an encoder, which detects the drive position of the drive device of the main axis 12.

[0017] As in Fig. As shown in Figure 1, the numerical control unit 16 has a storage unit 25. The storage unit 25 contains a maximum return rotational speed Vr of the main axis, which is the maximum permissible rotational speed of the main axis motor when unloaded. The numerical control unit 16 commands the main axis control unit 18 to use this maximum return rotational speed Vr as the target speed of the main axis during the return operation, in order to retract the tool from the target thread depth. It is important to note that the commanded maximum return rotational speed Vr is the maximum permissible rotational speed of the main axis motor when unloaded, independent of the speed command of the main axis during machining (cutting operation).

[0018] Fig. Figure 2 is a flowchart showing the thread cutting control operation according to the first embodiment. The thread cutting control operation of Fig. 2 is executed under the control of the control device 10. When the thread cutting operation is started, the numerical control device 16 interprets the thread cutting program P, obtains the maximum machining speed V0 and the total rotational dimension S0, and commands these values ​​to the main axis control unit 18 (step S1). The main axis control unit 18, which has received the maximum machining speed V0 and the total rotational dimension S0, starts the machining operation with the maximum machining speed V0 as the target speed (step S2). In Fig. Figure 3 shows an example of the operating pattern (the change in the main axis rotation speed) when the main axis control unit 18 executes the main axis control according to V0 and S0. Fig. Figure 3 shows the vertical axis representing the rotational speed of the main axis and the horizontal axis representing time. During machining operation from t0 to t3, the main axis control unit 18 accelerates the main axis motor with a constant acceleration A0 to the highest machining rotational speed V0. Since the highest machining rotational speed V0 is set at a comparatively low value, taking into account the load on the tool during cutting operation, it is understood that an operating pattern occurs in which the main axis rotational speed is less than the highest machining rotational speed V0, as shown in Figure 3. Fig. Figure 3 shows that this is typically achieved within a relatively short time after the start of processing and the flat area (the area with constant rotational speed) is relatively long.

[0019] When the rotational speed reaches V0 at time t1, the main axis control unit 18, while maintaining V0, calculates the time t3 at which the main axis 12, with a deceleration of V0 by a deceleration factor of the same absolute value as the acceleration (-A0), reaches the total rotational degree S0. The area of ​​the trapezoidal region between t0 and t3 in the operating pattern of Fig. 3 corresponds to the total rotational extent S0. Consequently, the main axis control unit 18 can determine the time t2 of the start of the deceleration such that the area of ​​the trapezoidal region between t0 and t3 in the operating pattern of Fig. 3 becomes equal to the total degree of rotation. The main axis control unit 18 decelerates the main axis 12 from time t2 with a deceleration rate of the same absolute value as the acceleration (-A0), whereby the target thread depth (the total degree of rotation S0) is reached at time t3.

[0020] Regarding the acceleration A0 during machining, various methods can be used, such as the method in which it is determined based on the velocity-acceleration characteristic of the main axis motor, or the method in which a value is used that is entered into the numerical control unit 16 by the thread-cutting machining program or the like. In the first embodiment, any method for determining the acceleration A0 during machining can be used.

[0021] While the main axis control unit 18 controls the rotary operation of the main axis 12 from the machining start point to the target thread depth, the feed axis control unit 22 performs a feed operation in which it controls the feed axis 14 using the rotation position FBS of the main axis 12 so that it follows the operation of the main axis 12.

[0022] When the machining operation is completed in step S3, the numerical control unit 16 commands the main axis control unit 18 to use the highest return rotational speed Vr stored in the memory unit 25 (step S4). The main axis control unit 18, which has received the highest return rotational speed Vr from the numerical control unit 16, begins the return operation of the main axis 12 with the highest return rotational speed Vr as the target speed (step S5). The range of times t3 to t5 in Fig. Figure 3 shows the return operation. The main axis control unit 18 accelerates the main axis 12, for example, with the same acceleration (A0) as the acceleration during machining, rotating in the opposite direction to the highest return rotational speed Vr, and decelerates it at the time when the rotational extent of the main axis 12 has become half of the total rotational extent S0 (time t4), with a deceleration rate of the same absolute value as the acceleration (-A0). This causes the main axis to return to its position at the start of machining at time t5. When the main axis returns to the starting machining position, this machining control operation ends (step S6). In the return operation, which is described in Fig. As shown in Figure 3, the area of ​​the triangular operating pattern from t3 to t5 corresponds to the total rotational extent S0. Consequently, the main axis control unit 18 can determine the time t4 of the start of the deceleration such that the area of ​​the triangular region from t3 to t5 in the operating pattern of Fig. 3 equals the total rotational extent S0.

[0023] Since the return operation in Fig. 3. If a control is implemented where acceleration is achieved using the highest return rotational speed Vr as the target speed, this is typically done as in Fig. 3. Control via a triangular operating pattern is possible, which decelerates at a speed before the main axis rotation speed reaches the maximum return rotation speed Vr and completes the full rotation. By implementing control via such a triangular operating pattern, it is possible to avoid operation where the speed becomes constant (i.e., a trapezoidal operating pattern) and, in the case of constant acceleration, to return the main axis from the target thread depth position to the starting position as quickly as possible. This means that the return speed for retracting the tool along the machined thread path can be maximized, thus accelerating the cycle time for the entire threading operation.

[0024] While the main axis control unit 18 controls the rotational operation from the target thread depth of the main axis 12 to the machining start position, the feed axis control unit 22 performs a feed operation in which it controls the feed axis 14 using the rotational position FBS of the main axis 12 so that it follows the operation of the main axis 12.

[0025] There are also cases where the threading program P, taking into account the inertia or rigidity of the tool, specifies a comparatively low maximum return rotational speed of the main axis. In such a case, a version is possible that implements a control mechanism to accommodate the user-specified comparatively low maximum return rotational speed (hereinafter referred to as "maximum return rotational speed Vr'") according to the threading program P. Fig. Figure 4 is a flowchart that is a variation of the thread cutting machining control operation from Fig. 2 shows a control in which, if a low maximum return rotational speed Vr' is user-defined in the thread cutting machining program P, it is possible to take this user-defined maximum return rotational speed Vr' into account.

[0026] At the thread cutting machining control operation of Fig. 4. During machining, the same control is used as in steps S1 to S3 of the thread cutting machining control operation of the first embodiment ( Fig. 2) is carried out. When the main axis 12 reaches the target thread depth and the machining operation is complete (step S3), the numerical control unit 16 determines whether a maximum return rotational speed Vr' has been user-defined by the threading machining program P (step S11). If a maximum return rotational speed Vr' has been user-defined by the threading machining program P (S11: YES), the numerical control unit 16 determines whether the maximum return rotational speed Vr stored in the memory unit 25 is higher than the maximum return rotational speed Vr' defined by the threading machining program P (step S12).If no maximum return rotational speed Vr' is specified by the thread cutting machining program P (S11: NO), the numerical control unit 25 commands the main axis control unit 18 to set the maximum return rotational speed Vr.

[0027] If the highest return rotational speed Vr is higher than the highest return rotational speed Vr' specified by the machining program (S12: YES), the threading machining program P sets the target return speed to a lower speed than the maximum permissible return speed of the main axis motor at idle. In this case, the numerical control unit 16 commands the main axis control unit 18 to use the highest return rotational speed Vr' according to the control program P (step S13). When it receives the highest return rotational speed Vr' from the numerical control unit 16, the main axis control unit 18 controls the return operation with the highest return rotational speed Vr' as the target speed (step S14). The control of the return operation in step S14 corresponds to an operation in which the target speed Vr during the return operation in step S5 is set by Fig. 2 is replaced by Vr', and the basic control is the same.

[0028] If, on the other hand, the highest return rotational speed Vr is equal to or less than the highest return rotational speed Vr' (S12: NO), the numerical control unit 16 commands the master axis control unit 18 to achieve the highest return rotational speed Vr (step S4). Upon receiving the highest return rotational speed Vr, the master axis control unit 18 controls the return operation with the highest return rotational speed Vr as the target speed (step S5). In this case, the control of the controller during the return operation from step S5 in Fig. 2. When the main axis 12 returns to the machining start position, the current thread cutting machining control operation ends (step S6).

[0029] While the main axis control unit 18 controls the rotational operation of the main axis 12 during machining and return, the feed axis control unit 22 performs a feed operation in which it controls the feed axis 14 using the rotational position FBS of the main axis 12 so that it follows the operation of the main axis 12.

[0030] Through the thread cutting machining control operation of Fig. 4. The return operation can then be carried out if a comparatively low maximum return rotational speed Vr' is user-defined, taking this into account, and if no user-defined speed exists, the effect can be achieved through the thread cutting machining control operation described above. Fig. 2 will be received. Second embodiment

[0031] Fig. Figure 5 is a flowchart showing the thread cutting control operation according to a second embodiment. The thread cutting control operation of Fig. 5 is connected to the numerical control device 10 with the in Fig. The hardware setup shown in section 1 was executed. During the thread cutting machining control operation of Fig. The 5 steps are the same as in the thread cutting machining control operation of Fig. 2 are provided with the same reference numerals and their explanation is omitted.

[0032] At the thread cutting machining control operation of Fig. 5. The same control is used for operation during machining as in steps S1 to S3 in the thread cutting machining control operation of the first embodiment ( Fig. 2) is carried out. When the main axis 12 has reached the target thread depth and the cutting operation ends (step S3), the numerical control unit 16 calculates a velocity v.c and an acceleration a c upon return as explained below, and it commands the main axis control unit 18 to use these values ​​v c and a c as a speed command and as an acceleration command (step S4a). The speed V c The return speed is determined so that it is at most the highest return rotational speed Vr.

[0033] Fig. Figure 6 shows the speed-acceleration characteristic curve of the main axle motor. Fig. Figure 6 shows the horizontal and vertical axes, respectively, representing the velocity and acceleration of the main axis motor. The data, which form the velocity-acceleration characteristic of Fig. Figure 6 shows that values ​​can be stored in advance in the memory unit 25 of the numerical control unit 16 or entered by the user into the control device 10. In the case of return operation control with constant acceleration, as shown in Figure 6, the following applies: Fig. Figure 7 shows an operating pattern in which no constant speed range occurs (a triangular operating pattern), representing the fastest operating pattern. The highest rotational speed in the operating pattern of Fig. 7 is considered v c applied, and the acceleration is considered as a c The total rotation of the main axis 12 on the return stroke, determined from the target thread depth × thread pitch, is used as the thread-cutting operating condition S0. In this case, during the fastest operation of Fig. 7. The following relationship formula. In the following relationship formula, t is the time until the velocity v is reached. cfrom a state of velocity of 0 (the time until a return of v c to a speed of 0), and S0 is the total degree of rotation of the main axis. (1 / 2)act2=S0 / 2 act=vc

[0034] From the above formulas (1) and (2) the relationship of a c , v c and S0 as follows: vc2 / ac=S0

[0035] The numerical control unit 16 determines from the velocity-acceleration characteristic of Fig. 6 a speed v c and an acceleration a c , which satisfy the above formula (3). However, v c ≦ V r as a condition. For example, the point Pc on the velocity-acceleration curve of Fig. 6 as velocity v c and acceleration a c , which satisfy the above formula (3).

[0036] The control system described above allows for the fastest return operation to be performed in the case of constant acceleration with the highest return rotational speed Vr as the target speed (step S5a). This makes it possible to maximize the cycle time of the entire thread cutting operation.

[0037] While the main axis control unit 18 controls the rotational operation of the main axis 12 during machining and return, the feed axis control unit 22 performs a feed operation in which it controls the feed axis 14 using the rotational position FBS of the main axis 12 so that it follows the operation of the main axis 12. Third embodiment

[0038] Fig. Figure 8 is a block diagram showing the structure of a control device 10a according to a third embodiment. Fig. 8 are identical structural elements as in the control device according to the first embodiment of Fig. 1 are provided with the same reference symbols and their explanation is omitted.

[0039] In the present embodiment, a main axis command output unit 26a obtains, prior to the start of the thread cutting operation, from the command values ​​of the thread cutting operation program P interpreted by the program interpretation unit 24, the total rotational extent S0 of the main axis 12 from the machining start position (rotation position) to reaching the target thread depth (rotation position) and the highest rotational speed V0, and sends this total rotational extent S0 and this highest rotational speed V0 as a main axis command CS to a main axis control unit 18a.If, for example, the thread cutting machining program P contains, as in the first embodiment, a command to machine an internal thread with a thread pitch of 1.25 mm and a thread depth of 30 mm at a maximum machining rotational speed V0 of the main axis 12 of 3000 rpm, the main axis command output unit 26a reports to the main axis control unit 18a V0 = 3000 (min. -1] ) and S0 = 24 (revolutions).

[0040] The main axis control unit 18a controls the rotational operation of the main axis 12 by means of feedback control using the rotational position FBS of the main axis 12 detected by the rotation detection unit 20. The feed axis control unit 22 controls the feedal operation of the feed axis 14 by means of feedback control using the rotational position FBS of the main axis 12 so that it follows the operation of the main axis 12.

[0041] The main axis control unit 18a includes an initial operation control unit 30, which sets the main axis 12 at the highest rotational speed V0 (min) sent by the main axis command output unit 26a. -1 ) as target value with maximum capacity, accelerating from the machining start position to the target thread depth, a maximum acceleration detection unit 32 which, during the accelerating rotation with maximum capacity based on the rotation position FBS, detects the highest acceleration A0 (min -1) detected, a residual rotation detection unit 34, which, based on the total rotation S0 (revolutions) sent by the main axis command output unit 26a and the rotation position FBS from the current position (rotation position), detects a residual rotation Sr (revolutions) of the main axis 12 until the target thread depth is reached, a current speed detection unit 36, which, based on the rotation position FBS, determines the current speed Vc (min -1) of the main axis 12 is detected, and a positioning control unit 38, which decelerates the main axis 12 after the accelerating rotation with maximum capacity based on the highest acceleration A0, the remaining rotational extent Sr, and the current velocity Vc, allows it to reach the target thread depth. In the present embodiment, the positioning control unit 38 can be configured to decelerate the main axis 12 with maximum capacity and allow it to stop at the target thread depth.

[0042] Fig. Figure 9 is a flowchart showing the thread cutting control operation according to the third embodiment. The thread cutting control operation of Fig. 9 is connected to the control device 10a by the in Fig. The hardware setup shown in section 8 was executed.

[0043] In step S101, the numerical control unit 16 commands the main axis control unit 18a to specify the total rotational extent S0 of the main axis 12 and the maximum machining rotational speed V0. In step S102, the main axis control unit 18a (comprising the initial operating control unit 30, the maximum acceleration detection unit 32, and the remaining rotational extent detection unit 34) accelerates the main axis 12 from its initial operating position, using the maximum permissible current of the drive source (the main axis motor), to the maximum operating rotational speed V0 as the target speed, and the thread cutting operation is performed. During this process, the main axis control unit 18a detects the maximum acceleration A0 and continuously detects the remaining rotational extent Sr from the current position (step S103). With each detection, the main axis control unit 18a reports the detected residual rotation Sr. to the numerical control unit 16a.

[0044] In step S104, the main axis control unit 18a performs position control up to the target thread depth using the maximum acceleration A0 and the remaining rotational extent Sr. A typical operating example for the position control is explained below. During the accelerating rotation, the main axis control unit 18a (the actual velocity detection unit 36) continuously detects the current velocity Vc at maximum capacity and determines with each detection whether the current velocity Vc has not reached the maximum rotational speed V0 or has. If Vc has not reached V0, the main axis control unit 18a determines whether the remaining rotational extent Sr has become at most half of the total rotational extent S0 or not.If Sr has become at most half of S0 before the current speed Vc reaches the highest rotational speed V0, the main axis control unit 18a rotates the main axis 12 at maximum capacity, using the maximum permissible current of the drive source, and the thread cutting operation continues.

[0045] Now, with reference to Fig. 10 as a typical operating example the operation of the main axis 12, when the remaining rotational extent Sr has become half of the total rotational extent S0 before the current velocity Vc reaches the maximum rotational speed V0, represented by a velocity-time diagram. In Fig. 10 is Vb as rotational speed (for example as the base speed of the servo motor) at which acceleration with a constant torque (i.e., a constant acceleration) is possible from start to speed Vb, is predefined for the main axis 12, and can be stored, for example, as one of the control parameters in the control unit 25 of the control device 10a.

[0046] The accelerating rotation of the main axis 12 with maximum capacity in step S102 occurs at times T1 and T2 in Fig. 10, and during the constant acceleration of time T1, the highest acceleration A0 is detected. If the rotational speed of the main axis 12 exceeds Vb, the acceleration of the main axis 12 gradually decreases from the highest acceleration A0 due to the characteristics of the servo motor (see Fig. 6) At time A, when the remaining rotational extent Sr has become half of the total rotational extent S0 (that is, when the rotational extent since the start of machining has become half of the total rotational extent S0), the operation of the main axis 12 is changed from accelerating rotation to decelerating rotation, and a decelerating rotation of the main axis 12 is performed at maximum capacity for a period of time T3. During this period, the main axis 12 is rotated decelerating from point A at a target speed Vb, but the deceleration of the main axis gradually increases, for example, due to the characteristics of the servo motor.Even during deceleration at maximum capacity, the main axis control unit 18a (the residual rotation detection unit 34, the actual speed detection unit 36) continuously detects the residual rotation Sr from the current position and the current speed Vc of the main axis 12.

[0047] The main axis control unit 18a (the positioning operating control unit 38) continuously monitors the continuously detected remaining rotation Sr (revolutions) and the continuously detected current velocity Vc (min -1 ) and determines the position of a time B using the formula below ( Fig. 10), to which it is predicted that Sr will decelerate with a maximum deceleration rate A0 (negative value), which corresponds to the maximum acceleration A0 (min -1 / s) corresponds to the current velocity Vc (min -1) 0 is (that is, the target thread depth is reached) as the absolute value of the remaining rotational dimension Sr considered from Sr = 0 (negative value).

[0048] From the general formula (Vc / 60) 2 = 2×|A0| / 60×|Sr| results in |Sr| = Vc 2 / |A0| / 120

[0049] In the present embodiment, it is assumed that the main axis 12ab is decelerated from point B with a constant maximum deceleration A0. Consequently, at time B, it can be assumed that the current velocity Vc of the main axis 12 has reached Vb. That is, the position |Sr| of point B can be considered |Sr|=Vb2 / |A0| / 120 to be determined.

[0050] Furthermore, in the present embodiment, the torque required for accelerating the main axis 12 (hereinafter referred to as the "acceleration torque") and the torque required for deceleration (hereinafter referred to as the "deceleration torque") are assumed to be equal. Since, in general, a load (resistance) arises on the machine structure during the rotation of the main axis 12, and the acceleration torque becomes greater than the deceleration torque, then, if the acceleration torque and the deceleration torque are equal, in the case of a comparison for the same change in speed, the acceleration time at maximum capacity will be longer than the deceleration time at maximum capacity. Consequently, the main axis 12 actually reaches the speed Vb after deceleration from point A in a shorter time than the time T2, and the position |Sr| at this time is... |Sr|>Vc2 / |A0| / 120 and then point B of |Sr|=Vb2 / |A0| / 120 by a rotation for an extremely short time at the constant velocity Vb ( Fig. 10).

[0051] With renewed reference to Fig. 10 determines the main axis control unit 18a (the positioning operating control unit 38) in step S104 whether the absolute value |Sr| of the remaining rotational extent at the current position of the main axis 12 |Sr| = Vb 2 / |A0| / 120 is satisfied or not (that is, whether the rotational position of the principal axis 12 has reached point B or not). If |Sr| = Vb 2If the condition / |A0| / 120 is met, the main axis control unit 18a (the positioning operating control unit 38) generates a command to rotate the main axis 12 at the highest deceleration A0 and to allow it to reach the point Sr = 0 (the thread target depth) (in one embodiment, a command to make it stop at the thread target depth), and this command results in position control of the main axis 12. If |Sr| = Vb 2If the condition / |A0| / 120 is not met, the determination is repeated until the equation is satisfied. Following the command from the main axis control unit 18a (the positioning operating control unit 38), the main axis 12 performs the thread cutting operation from point B to the target thread depth under decelerating rotation with the highest deceleration A0 and reaches the target thread depth at the time when Sr = 0 (in one embodiment, it stops at the target thread depth) (step S105). In this way, the main axis control unit 18a performs position control of the main axis 12 during the time T4 from point B until the target thread depth is reached.

[0052] While the main axis control unit 18a controls the rotation of the main axis 12 from the machining start position to the target thread depth, the feed axis control unit 22 performs a feed operation, controlling the feed axis 14 using the rotation position FBS of the main axis 12 so that it follows the operation of the main axis 12. During the control of the rotation from the machining start position to the target thread depth by the main axis control unit 18a, the numerical control unit 16a monitors the remaining rotation Sr reported by the main axis control unit 18a and can determine that the thread cutting operation has reached the target thread depth when the remaining rotation Sr reaches at most a first predetermined value (a very small value close to zero).

[0053] After the thread cutting operation has reached the target thread depth, the return operation is performed in steps S106 to S110. In step S106, the numerical control unit 16a obtains the total rotational extent S0' of the main axis 12 from the target thread depth to the return end position from the command values ​​of the thread cutting program P, which is interpreted by the program interpretation unit 24. The numerical control unit 16a then sends the total rotational extent S0' and the maximum return rotational speed Vr, stored in the memory unit 25, as a main axis command CS to the main axis control unit 18a. The return end position can be the same as the machining start position, or it can differ. If the return end position is the same as the machining start position, the total rotational extent S0' is equal to the total rotational extent S0 during cutting.

[0054] In step S107, the main axis control unit 18a (the initial operation control unit 30, the maximum acceleration detection unit 32, the remaining rotation extent detection unit 34) performs the following control operation. The initial operation control unit 30 executes the return operation, whereby the main axis 12 is accelerated in the opposite direction from the target thread depth to the return end position with the highest return rotational speed Vr as the target value, using maximum capacity and the maximum permissible current of the drive source. During the accelerating reverse rotation, the maximum acceleration detection unit 32 detects the highest acceleration A0' of the reverse rotation based on the rotational position FBS, using maximum capacity.The residual rotation detection unit 34 continuously detects the residual reverse rotation Sr' of the main axis 12 from the current position until the return end position is reached (step S108), based on the total reverse rotation S0' and the rotation position FBS. With each detection, the main axis control unit 18a reports the detected residual reverse rotation Sr' to the numerical control unit 16a.

[0055] In step S109, the main axis control unit 18a performs position control up to the machining start position using the maximum acceleration A0 and the remaining rotational extent Sr. Here, as a typical operating example, position control is performed as follows. During the accelerating reverse rotation, the main axis control unit 18a (the actual speed detection unit 36) continuously detects the current speed Vc' at maximum capacity based on the rotational position FBS and determines with each detection whether the current speed Vc' has reached the maximum return rotational speed Vr or not. If Vc' has not reached Vr, the main axis control unit 18a determines whether the remaining return rotational extent Sr' is at most half of the total return rotational extent S0' or not.If Sr' has become at most half of S0' before the current speed Vc' reaches the highest return rotation speed Vr, the main axis control unit 18a rotates the main axis 12 at maximum capacity, slowing down and using maximum of the permissible current of the drive source, and the return operation continues.

[0056] In step S109, the main axis control unit 18a (the positioning operating control unit 38) determines whether the absolute value |Sr'l of the remaining reverse rotation Sr' at the current position of the main axis 12 |Sr'| = Vb 2 / |A0'| / 120 is satisfied or not. If |Sr'| = Vb 2If the condition / |A0'| / 120 is met, the main axis control unit 18a (the positioning operating control unit 38) generates a command to rotate the main axis 12 in the opposite direction with the highest deceleration A0' and to stop at the point Sr' = 0 (i.e., the return end position), and this command results in position control of the main axis 12. If |Sr'| = Vb 2 If the equation / |A0'| / 120 is not satisfied, the determination is repeated until this equation is satisfied. Following the command from the main axis control unit 18a (the positioning operation control unit 38), the main axis 12 performs the return operation to the return end position under decelerating opposite rotation with the highest deceleration A0' and stops at the time when Sr' = 0 (step S110).

[0057] While the main axis control unit 18a controls the return operation of the main axis 12 from the target thread depth to the return end position, the feed axis control unit 22 performs a reverse feed operation, controlling the feed axis 14 using the rotation position FBS of the main axis 12 so that it follows the operation of the main axis 12. While the main axis control unit 18a controls the return operation of the main axis 12 from the target thread depth to the return end position, the numerical control unit 16a monitors the residual return rotation Sr' reported by the main axis control unit 18a and can determine that the return operation is complete and the tool has been withdrawn from the workpiece when the residual return rotation Sr' has reached at most a second specified value (close to zero).

[0058] The return operation of main axis 12 described above can be represented by the same velocity-time diagram as the one in Fig. 10 are shown. As in Fig. Figure 10 shows that the current speed of the main axis 12 at the moment of reaching the target thread depth is zero, but the main axis 12 further follows a command from the main axis control unit 18 (the positioning operation control unit 38) by means of an accelerating opposite rotation, whereby while maintaining the highest deceleration degree A0 an acceleration A0 of an opposite rotation is generated and the current speed Vc (negative value) is gradually increased, during time T7 a return operation from the target thread depth to a point C.

[0059] The position of point C on the principal axis 12 can be arbitrarily defined. For example, as in Fig. Figure 10 shows the same position as that of point B, where the decelerating rotation with the highest deceleration A0 begins during the cutting operation, and is set as point C. In this case, point C becomes the position at which a reverse rotation by one revolution, |Sr'| = Vb, begins. 2 / |A0'| / 120 corresponds to the target thread depth. This design allows, as in Fig. Figure 10 shows the cutting operation of the main axis 12 (time T1 to T4) from the start of machining via point B until reaching the target thread depth, and the return operation of the main axis 12 (time T7 to T10) from the target thread depth via point C until reaching the return position. With the exception of a reversed sign of the velocity, these operations are effectively expressed by the same velocity-time diagram. That is, at time T7, the main axis 12 is rotated in the opposite direction, accelerating with the constant maximum acceleration A0, just as it is during the accelerating rotation at time T1 with the constant maximum acceleration A0.

[0060] Since the current speed of the opposite rotation of the principal axis 12 in the example that is in Fig. As shown in Figure 10, after reaching a specific rotation position (point C) Vb (negative value), the acceleration of the main axis during the accelerating reverse rotation with maximum capacity gradually decreases from A0 (time T8), for example, due to the characteristics of the servo motor. At a time D, when the remaining reverse rotation Sr' has become half of the total reverse rotation S0' (that is, when the rotation from the target thread depth has become half of the total rotation S0'), the operation of the main axis 12 is changed from accelerating reverse rotation to decelerating reverse rotation, and a decelerating reverse rotation of the main axis 12 with maximum capacity is performed during time T9.

[0061] Then the main axis control unit 12 (the positioning operating control unit 38) determines whether the absolute value |Sr'| of the residual reverse rotation Sr' at the current position of the main axis 12 |Sr'| = Vb 2 / |A0'| / 120 is fulfilled or not (that is, whether the rotational position of the main axis 12 is at point E ( Fig. 10) has reached or not). If |Sr'| = Vb 2If the condition / |A0'| / 120 is met, the main axis control unit 18a (the positioning operation control unit 38) generates a command to rotate the main axis 12 in the opposite direction with the highest deceleration A0' (the value corresponding to the acceleration of the opposite rotation at time T7) and to stop it at the point Sr' = 0 (i.e., at the return end position), and this command results in position control of the main axis 12. Following the command from the main axis control unit 18a (the positioning operation control unit 38), the main axis 12 executes the return operation to the return end position under deceleration in the opposite direction with the highest deceleration A0' and stops at the time when Sr' = 0.

[0062] The embodiment described above allows the main axis 12 to be controlled as the target speed during return operation at the highest return rotational speed Vr, which is the maximum permissible rotational speed of the main axis motor at idle. Consequently, it becomes possible to perform the return operation of the main axis using the fastest operating speed. This makes it possible to maximize the cycle time of the entire thread cutting operation.

[0063] In the foregoing, embodiments of the present invention have been described, but a person skilled in the art will understand that various improvements or modifications can be made without deviating from the disclosed scope of the following patent claims.

[0064] In the embodiments described above, the permissible maximum rotational speed of the main axis motor at the time of no load was used as the maximum return rotational speed Vr, but an acceleration of the return operation becomes possible if a high speed value is used for this maximum return rotational speed that is independent of the maximum rotational speed of the main axis at the time of machining and is faster than the maximum rotational speed at the time of machining.

[0065] To solve the problem described in this disclosure, various methods and their effects can be provided, as described below. The numbers in parentheses in the following explanation of the methods correspond to the reference symbols in the drawings of this disclosure.

[0066] For example, one form of the present disclosure is a control device (10) for a machine tool that controls the synchronous operation of a main axis (12) and a feed axis (14), wherein the control device (10) comprises a numerical control unit (16) that generates a main axis command and a feed axis command based on a thread-cutting machining program (P); a main axis control unit (18) that controls the rotary operation of the main axis (12) according to the main axis command; and a rotation detection unit (20) that detects the rotation position of the main axis (12).and a feed axis control unit (22) which controls the feed operation of the feed axis (14) according to the feed axis command based on the rotational position, wherein the numerical control unit (16) incorporates a return-speed command value, which is independent of the highest rotational speed of the main axis (12) during machining and is faster than the highest rotational speed during machining, as a command for return operation from the target thread depth to the machining start position into the main axis command.

[0067] The first form described above makes it possible to perform the return operation of the main axis at a high speed, independent of the highest machining rotational speed of the main axis.

[0068] A second form of the present disclosure is a control device (10) of the first form described above, which further comprises a storage unit (25) which stores a permissible maximum rotational speed at the time of no load on a drive source that drives the main axis, wherein the numerical control unit incorporates the permissible maximum rotational speed stored in the storage unit (25) at the time of no load on the drive source as a return speed command value in the main axis command.

[0069] A third form of the present disclosure is a control device (10) of the second form described above, wherein the numerical control unit (16) determines whether a maximum return rotational speed of the main axis (12) is specified by the threading program (P) or not, and in the case of a maximum return rotational speed of the main axis (12) being specified by the threading program (P), if the maximum return rotational speed specified by the threading program (P) is lower than the permissible maximum rotational speed at the time of no load on the drive source, the maximum return rotational speed specified by the threading program (P) is included as the maximum return rotational speed value in the main axis command.

[0070] A fourth form of the present disclosure is a control device (10) of the first form described above, wherein the numerical control unit (16) determines a return velocity and a return acceleration of the main axis from the thread cutting machining conditions and a velocity-acceleration characteristic of the drive source driving the main axis, at which the return operation becomes fastest in the case of constant acceleration, incorporates the return velocity as a return velocity command value into the main axis command, and incorporates the return acceleration into the main axis command.

[0071] A fifth embodiment of the present disclosure is a control device (10a) of the second embodiment described above, wherein the numerical control unit (16a) obtains the total rotational extent of the main axis (12) from the machining start position to reaching the target thread depth and the highest machining rotational speed from the thread-cutting machining program (P) and sends the total rotational extent and the highest machining rotational speed as a main axis command of the machining operation to the main axis control unit (18a), wherein the main axis control unit (18a) provides an initial operation control unit (30) that accelerates the main axis (12) at the highest machining rotational speed as the target speed with maximum capacity, using the maximum permissible current of the drive source, from the machining start position to the target thread depth; a maximum acceleration detection unit (32),the system comprises a unit that detects the highest acceleration during the accelerating rotation at maximum capacity based on the rotational position; a remaining rotation extent detection unit (34) that detects the remaining rotation extent of the main axis from the current position until the target thread depth is reached, based on the total rotation extent and the rotational position; an actual velocity detection unit (36) that detects the current velocity of the main axis (12) based on the rotational position; and a positioning operation control unit (38) that decelerates the main axis (12) after the accelerating rotation at maximum capacity based on the highest acceleration, the remaining rotation extent and the current velocity, and allows it to reach the target thread depth.In the return-to-start operation, the initial operation control unit (30) accelerates the main axis in the opposite direction from the target thread depth to the machining start position at the maximum permissible rotational speed of the drive source at the time of non-load operation, using the maximum permissible current of the drive source. The maximum acceleration detection unit (32) detects the highest acceleration during the accelerating opposite rotation at maximum capacity based on the rotational position. The remaining rotational extent detection unit (34) detects the remaining rotational extent of the main axis (12) from the current position until the machining start position is reached, based on the total rotational extent and the rotational position.and the positioning operating control unit (38) rotates the main axis (12) in the opposite direction after the accelerating opposite rotation with maximum capacity based on the highest acceleration and the remaining rotational extent and the current speed, decelerating it and allowing it to reach the machining start position.

Claims

[1] Control device (10) for a machine tool which controls the synchronous operation of a main axis (12) and a feed axis (14), wherein the control device (10) is a numerical control unit (16) which generates a main axis command and a feed axis command based on a thread cutting machining program (P); a main axis control unit (18) that controls the rotation of the main axis (12) according to the main axis command; a rotation detection unit (20) that detects the rotation position of the main axis (12); and a feed axis control unit (22) that controls the feed operation of the feed axis (14) according to the feed axis command based on the rotation position, includes wherein the numerical control unit (16) incorporates a return-speed command value, which is independent of the highest rotational speed of the main axis (12) during machining and is faster than the highest rotational speed during machining, as a command for return operation from the target thread depth to the machining start position into the main axis command, wherein the control device (10) further comprises a storage unit (25) which stores a permissible maximum rotational speed at the time of no load on a drive source that drives the main axis (12), wherein the numerical control unit (16) incorporates the maximum permissible rotational speed stored in the memory unit (25) at the time of no load on the drive source as a return speed command value into the main axis command, wherein the numerical control unit (16) determines whether a maximum return rotational speed of the main axis (12) is specified by the thread cutting machining program (P) or not, and In the event that a maximum return rotational speed of the main axis (12) is specified by the threading program (P), and if the maximum return rotational speed specified by the threading program (P) is lower than the maximum permissible rotational speed at the time the drive source is unloaded, the maximum return rotational speed specified by the threading program (P) is included as the maximum return rotational speed value in the main axis command. [2] Control device (10) according to claim 1, wherein the numerical control unit (16) determines a return speed and a return acceleration of the main axis from the thread cutting machining conditions and a velocity-acceleration characteristic of the drive source driving the main axis (12), at which the return operation is fastest in the case of constant acceleration, incorporates the return speed as a return speed command value into the main axis command, and incorporates the return acceleration into the main axis command. [3] Control device (10) according to claim 1, wherein the numerical control unit (16a) obtains the total rotational extent of the main axis (12) from the machining start position until the target thread depth is reached and the highest machining rotational speed from the thread cutting machining program (P) and sends the total rotational extent and the highest machining rotational speed as a main axis command of the machining operation to the main axis control unit (18a), wherein the main axis control unit (18a) is an initial operation control unit (30) which accelerates the main axis (12) from the machining start position to the target thread depth at the highest machining rotational speed as the target speed with maximum capacity, using the maximum permissible current of the drive source; a maximum acceleration detection unit (32) which detects the highest acceleration during the accelerating rotation with maximum capacity based on the rotational position; a residual rotation detection unit (34) which, based on the total rotation and rotation position, detects the residual rotation of the main axis from the current position until the target thread depth is reached; an actual velocity detection unit (36) which detects the current velocity of the main axis (12) based on the rotational position; and a positioning operation control unit (38) which, after the accelerating rotation, slows down the main axis (12) at maximum capacity based on the highest acceleration and the remaining rotational extent and the current velocity, allowing it to reach the target thread depth, includes where in the return operation the initial operating control unit (30) rotates the main axis at the maximum permissible rotational speed of the drive source at the time of non-load as the target speed with the maximum capacity under maximum use of the permissible current of the drive source in the opposite direction from the target thread depth to the machining start position, accelerating, the maximum acceleration detection unit (32) detects the highest acceleration during the accelerating opposite rotation with maximum capacity based on the rotational position, The residual rotation detection unit (34) detects the residual rotation of the main axis (12) from the current position until the machining start position is reached, based on the total rotation and the rotation position, and The positioning operating control unit (38) rotates the main axis (12) in a decelerating opposite direction after the accelerating opposite rotation with maximum capacity based on the highest acceleration and the remaining rotational extent and the current speed, and allows it to reach the machining start position.

Images