Operational control method in a machine tool

Abstract

Operational control method in a machine tool (10) which includes a plurality of tool holders (A, B) with a cutting tool (31, 32), wherein the machine tool (10) moves the tool holders (A, B) relative to a workpiece (W) in order to machine the workpiece (W), and wherein the operational control method comprises: a first step in determining whether an abnormality has occurred on the cutting tool (31, 32) during machining or not; a second step of determining whether simultaneous machining, in which at least two or more of the tool holders (A, B) perform the machining operations on an identical workpiece (W), is carried out or not, and whether, if the abnormality is detected, the cutting tool (31, 32) that has the detected abnormality is the cutting tool (31, 32) that performs the simultaneous machining or not; and a third step of causing the tool holder (A, B) with the cutting tool (31, 32) which has the detected abnormality to perform an abnormality avoidance operation, and another of the tool holders (A, B), based on a determination result in the second step, to perform a reaction operation.

Description

[0001] The invention relates to an operational control method for an operation when, for example, an abnormality occurs in a cutting tool during simultaneous machining in which a plurality of tool holders are operated in a machine tool, such as an NC lathe.

[0002] Traditionally, there was a machining process that performed the machining of a workpiece by operating multiple tool holders, a process called simultaneous machining. Simultaneous machining includes, for example, a process that uses an NC lathe with multiple tool holders, applying the majority of the cutting tools to a workpiece simultaneously and performing different machining operations using the respective cutting tools at the same time (shown in Fig. 3) Such simultaneous machining can reduce the machining time for the workpiece. Furthermore, as described, for example, in the publication of the unexamined Japanese patent application JP H09-150348A, two cutting tools perform machining operations on a long workpiece during a turning process, with a workpiece positioned between them to minimize workpiece deformation and ensure precise machining.

[0003] On the other hand, a method has been developed which, if an abnormality is detected during machining, prevents damage to the workpiece and the machine tool by retracting the cutting tool from the workpiece. For example, in a method described in the publication of Japanese patent JP H07 25 006 B, a cutting load direction applied to a workpiece is observed, and if an abnormality is detected, a cutting tool is retracted in a direction opposite to the cutting load direction.

[0004] In the case where a cutting tool is withdrawn from a workpiece based on the detection of an abnormality during simultaneous machining in a machine tool that, as described above, contains multiple tool holders, a withdrawal operation must be performed that takes into account the condition of other tool holders. As an example, consider machining a workpiece W, which has an outer diameter of Ø 40 mm, down to Ø 30 mm. It is assumed that a Fig. 3. A cutting tool 31 (here a roughing tool insert) installed on tool holder A reduces the outer diameter to Ø 30.4 mm, and a cutting tool 32 (here a finishing tool insert) installed on tool holder B finishes the outer diameter to Ø 30 mm. Since tool holder B follows tool holder A, if an abnormality occurs with cutting tool 31 on tool holder A and tool holder A is then withdrawn, the cutting depth of cutting tool 32 on tool holder B increases from 0.2 mm to 5.0 mm. Consequently, the load applied to cutting tool 32 increases abruptly, leading to breakage of the cutting tool 32 and damage to the workpiece W.

[0005] It is assumed that while the two cutting tools are performing the machining operation with the workpiece positioned between them, an abnormality is detected in one of the cutting tools, and the retraction operation is then initiated. This results in degraded machining accuracy due to the lack of a deformation reduction effect on the workpiece, which is provided by the two cutting tools positioning the workpiece between them (for example, as in Fig. Figure 4 shows a situation that is first indicated by a two-point line, modified so that the workpiece W bends as indicated by a continuous line due to the retraction of the tool holder B).

[0006] Accordingly, if an abnormality was detected during simultaneous machining, the machining was stopped with all cutting tools and all cutting tools were withdrawn from the workpiece.

[0007] If one considers a lathe, which, for example, includes a sub-spindle, as a machine tool that performs machining by operating multiple tool holders, then the main spindle and the sub-spindle may be machining different workpieces simultaneously. In such a situation, even if an abnormality is detected during machining on the main spindle, it is assumed that machining with all cutting tools is stopped and the cutting tools are withdrawn from the workpieces. Thus, even if the abnormality on the main spindle does not affect it, machining on the sub-spindle is halted, and the required expertise and time for recovery result in reduced machining efficiency. Furthermore, it is possible that the workpiece may become completely unmachinable.

[0008] The invention was made with regard to the problems described above, and it is an object of the invention to provide an operating control method in a machine tool which, if an abnormality is detected during machining, can perform a suitable reaction machining depending on a machining state.

[0009] The problem is solved by an operational control procedure according to the independent claims. An advantageous further development is the subject of the dependent claim.

[0010] To solve the problem described above, a control method for machining is provided in a machine tool, according to a first aspect of the invention. The machine tool contains a plurality of tool holders, each with a cutting tool, and moves the tool holders relative to a workpiece to machine the workpiece. The control method includes a first step of determining whether an abnormality has occurred in the cutting tool during machining. Furthermore, the machining control method includes a second step of determining, when the abnormality is determined, whether simultaneous machining, in which at least two or more of the tool holders perform machining operations on an identical workpiece, is being carried out, and whether the cutting tool exhibiting the detected abnormality is the cutting tool performing the simultaneous machining.Furthermore, the operational control procedure includes a third step of instigating that, based on a determination result in the second step, the tool holder with the cutting tool that has the detected abnormality performs an abnormality avoidance operation, and another of the tool holders performs a reaction operation.

[0011] To solve the problem described above, the invention, according to a second aspect of the invention, is an operating control method in a machine tool. The machine tool contains a plurality of tool holders with a cutting tool and moves the tool holders relative to a workpiece to machine the workpiece. The operating control method includes a first step of determining whether an abnormality has occurred in the cutting tool during machining. Furthermore, the operating control method includes a second step of determining, when the abnormality is detected, whether simultaneous machining, in which at least two or more of the tool holders perform the machining operations on an identical tool, is carried out, and whether the cutting tool exhibiting the detected abnormality is the cutting tool performing the simultaneous machining.Furthermore, the operational control procedure includes a third step of determining the extent of an effect on the machining process with another of the toolholders. In this case, the toolholder with the cutting tool exhibiting the detected abnormality is instructed to perform an abnormality avoidance operation. Additionally, the operational control procedure includes a fourth step of instructing, based on the determination results from the second and third steps, the toolholder with the cutting tool exhibiting the detected abnormality to perform the abnormality avoidance operation, while the other toolholder performs a reaction operation.

[0012] To solve the problem described above, the invention, according to a third aspect of the invention, is an operating control method in a machine tool. The machine tool contains a plurality of tool holders with a cutting tool and moves the plurality of tool holders relative to a workpiece in order to machine the workpiece simultaneously. The operating control method includes a first step of determining whether an abnormality has occurred in the cutting tool during machining or not. Furthermore, the operating control method includes a second step of determining the extent of an effect on the machining with another of the tool holders in the case where the tool holder with the cutting tool exhibiting the detected abnormality is caused to perform an abnormality avoidance operation when the abnormality is detected.Furthermore, the operational control procedure includes a third step of causing the tool holder with the cutting tool that has the detected abnormality to perform the abnormality avoidance operation, and the other tool holder to perform a reaction operation based on a determination result in the second step.

[0013] In the invention according to a fourth aspect corresponding to the second aspect or the third aspect, when determining the extent of the effect on the machining with the other tool holder, in the case where the tool holder with the cutting tool that has the detected abnormality is caused to perform the abnormality avoidance operation, the operating control method can perform at least one of a method of determining the magnitude of a change in the depth of cut on the workpiece based on a current position and direction of travel of each of the tool holders, and of a method of determining the magnitude of whether, based on the current position of each of the tool holders, each of the tool holders is in a preset affected area or not.

[0014] This embodiment determines whether, when the abnormality is detected in the cutting tool performing the machining operation (the first and second aspects), simultaneous machining, in which at least two or more toolholders perform machining operations on the same workpiece, is carried out, and whether the cutting tool exhibiting the detected abnormality is the cutting tool performing the simultaneous machining operation. The invention also determines the magnitude of the effect on machining with the other toolholders in the case where the toolholder with the cutting tool exhibiting the detected abnormality is instructed to perform the abnormality avoidance operation (the second and third aspects).The toolholder with the cutting tool exhibiting the detected abnormality is then instructed to perform the abnormality avoidance operation, while the other toolholder is instructed to perform the reaction operation based on these findings. Accordingly, even if the abnormality occurs with only one toolholder, machining can continue, for example, if simultaneous machining is not performed and if the effect on machining with the other toolholder is minimal. This reduces the effort and time required for recovery, ensuring improved machining efficiency and a reduction in the number of workpieces with machining defects. Fig. Figure 1 is an explanatory view depicting an NC lathe. Fig. Figure 2 is a flowchart that represents operational control when an abnormality is detected during simultaneous processing. Fig. Figure 3 is an explanatory view that illustrates an example of simultaneous machining in the NC lathe. Fig. Figure 4 is an explanatory view that shows another example of simultaneous machining in the NC lathe. Fig. Figure 5 is a diagram that estimates the extent of deformation of a predetermined workpiece when the workpiece is machined with a predetermined cutting force.

[0015] The following describes an operating control method in an NC lathe 10 as an embodiment of the invention based on the drawings in detail.

[0016] Fig. Figure 1 is an explanatory view depicting the NC lathe 10.

[0017] First, the mechanical setup of the NC lathe 10 is described. The NC lathe 10 comprises a main spindle 1 and a sub-spindle 2, a tool holder A and a tool holder B, and a control unit 5. The main spindle 1 and the sub-spindle 2 are configured to rotate a clamped workpiece. The tool holder A and the tool holder B are each equipped with cutting tools 31 and 32, respectively. The control unit 5 controls operations of the main spindle 1 and the sub-spindle 2, and of the tool holder A and the tool holder B. The control unit 5 comprises an input unit 7, an operator 8, and an instruction unit 6. The input unit 7 is intended for an operator to, for example, enter a drive instruction for a motor. The operator 8 is intended for interpreting, for example, a configured machining program.Instruction unit 6, for example, is intended for issuing instructions to each of the motors based on the machining program. In the NC lathe 10, four motors—the main spindle 1, the sub-spindle 2, the tool holder A, and the tool holder B (two tool holders)—are configured to operate independently of one another under the control of the control unit 5.

[0018] Herein is a description of a main part of the invention, an operational control system, when an abnormality is detected during simultaneous machining in which a plurality of tool holders are operated. Fig. Figure 2 is a flowchart that represents the operational control when the abnormality is detected during simultaneous processing. Fig. 3 and Fig. Figure 4 are explanatory views that illustrate examples of simultaneous machining in the NC lathe 10.

[0019] First, we examine the overall control system. In the NC lathe 10, in conjunction with the start of machining, it is determined whether an abnormality occurs during machining or not (S1). If an abnormality occurs, it is determined whether simultaneous machining is performed or not (S2). Furthermore, if simultaneous machining is performed, the system determines the effect on the machining process in the event that a tool holder on the side where the abnormality occurred is withdrawn (S3). Based on the determination of the effect on the machining, operations of both tool holders A and B are controlled (S4).

[0020] Next, specific examples of the operations are described in detail, step by step. In S1, there is a procedure that detects a load on the motor driving toolholders A and B as a determination method. Based on the detected value exceeding a predetermined threshold, the procedure then determines that a loss or breakage has occurred in toolholders 31 and 32, i.e., that the machining abnormality has occurred. Another procedure can install accelerometers on toolholders A and B and detect the occurrence of the abnormality based on the output values. Furthermore, a procedure is considered that installs temperature sensors on toolholders A and B and detects the occurrence of the abnormality based on the output values ​​(detection of an abnormal temperature).

[0021] In S2, a first method is considered, a determination method that makes a determination based on the current positions of the respective toolholders A and B. For example, if the current position of toolholder A is closer to the sub-spindle 2 than to the main spindle 1, it is determined that the cutting tool 31 of toolholder A is machining a workpiece clamped on the sub-spindle 2. If the current position of toolholder B is then closer to the sub-spindle 2 than to the main spindle 1, it is simply determined that simultaneous machining is performed. Otherwise, if the current position of toolholder B is close to the main spindle 1, it is simply determined that simultaneous machining is not performed. A second method is also considered, which makes a determination via an instruction coordinate system of the machining program configured for the NC lathe 10.This means that when different workpieces are machined on main spindle 1 and sub-spindle 2, program instructions are typically executed in different coordinate systems. Therefore, if the origins of the coordinate system referenced when machining with tool holder A and the coordinate system referenced when machining with tool holder B are identical, it is simply determined that simultaneous machining is performed. If the origins are different, it is simply determined that simultaneous machining is not performed.

[0022] Additionally, S2 considers a third method, which makes a determination based on the operating states of the main spindle 1 and the sub-spindle 2. For example, when machining a long workpiece, the machining is sometimes performed with one end of the workpiece clamped on the main spindle 1 and the other end clamped on the sub-spindle 2. At this point, the sub-spindle 2 is rotating synchronously with the main spindle 1, or, corresponding to a rotation of the main spindle 1, is rotating without a drive force. Therefore, if the operating state of the sub-spindle 2 is synchronous with the main spindle 1, or if it is rotating with it, it is simply determined that simultaneous machining is being performed; otherwise, it is simply determined that simultaneous machining is not being performed.

[0023] Furthermore, in S3, a first method is considered as a determination method which, during simultaneous machining, makes a determination from a relative position between toolholders A and B and a direction of travel of the toolholders A and B. For example, as in Fig. Figure 3 shows that simultaneous machining is performed in a -Z direction, with toolholder B following toolholder A. At this point, assuming that one X-coordinate of toolholder A is XA and one Z-coordinate of toolholder A is ZA, and one X-coordinate of toolholder B is XB and one Z-coordinate of toolholder B is ZB, then XA ≥ XB and ZA ≤ ZB. If this relationship holds, even if toolholder B is withdrawn, the effect on the machining is small. However, if toolholder B is withdrawn, the depth of cut in the Z-direction increases abruptly, and the effect on the machining is large. Thus, the procedure determines that a defect is very likely to occur.

[0024] As an alternative determination method, S3 considers a second method that defines an affected area in which machining accuracy deteriorates when simultaneous machining is stopped, and that determines whether each of the toolholders A and B is positioned within the affected area or not. For example, as in Fig. Figure 4 shows that, while simultaneous machining is being performed on the long workpiece, an abnormality has occurred on the cutting tool 32 of the tool holder B. Then, when the tool holder B is withdrawn, the following equation estimates a deformation of the workpiece due to a machining force. δ=P6l2EI[−(l−x)2(l+2x)]x3+3lx3(l−x)2 δ: Deflection [mm] x: Machining position [mm] I: Area moment of inertia [mm 4 ] P: Cutting force [N] I: Length between workpiece fixings [mm] E: Longitudinal modulus of elasticity [N / mm²] 2 ]

[0025] Here it presents Fig. Figure 5 presents a diagram that estimates the degree of workpiece deformation when machining a workpiece made of S45C steel with a cutting force of 15 N. The workpiece has a diameter of Ø 20 mm and a length of 1000 mm. If, for example, a required tolerance is 0.02 mm, and the current position of tool holder A is within a range of 0 to 250 mm or 750 to 1000 mm, then tool holder A is outside an affected area S. Thus, the required accuracy is achieved. Therefore, it is determined that even if tool holder B is retracted, the effect on the machining is small. However, if tool holder A is within a range of 250 to 750 mm, then it is highly likely that the required accuracy will not be achieved if tool holder B is retracted.Therefore, it is determined that the effect on the machining process is significant. Here, although the deformation of the workpiece is estimated, the target object can be a clamping device or a cutting tool, or a combination of the clamping device and the cutting tool.

[0026] In S4, as long as simultaneous machining with the other toolholder is not performed, only one toolholder is withdrawn and the other toolholder continues machining, even if the occurrence of an abnormality is detected on one of the toolholders. Even if simultaneous machining is performed, if it is determined that the effect on the machining is small, only one toolholder is withdrawn and the other toolholder continues machining. However, if it is determined that the effect on the machining is large, the other toolholder is withdrawn along with the first toolholder.

[0027] With the operating control procedure in the NC lathe 10 described above, even if the occurrence of an abnormality is detected in one tool holder, only that one tool holder is withdrawn and the other tool holder continues machining, as long as simultaneous machining with the other tool holder is not performed. Even if simultaneous machining is performed, if it is determined that the effect on the machining is small, only that one tool holder is withdrawn and the other tool holder continues machining.Accordingly, regardless of the situation, the effort and time required for recovery are lower compared to a conventional operational control procedure that causes all toolholders to perform a retraction operation, thus ensuring an improvement in machining efficiency and a reduction in the number of workpieces with machining defects.

[0028] The operating control method in the machine tool according to the invention is by no means limited to one aspect of the embodiment described above. It goes without saying that, if necessary, the overall configuration of the machine tool, as well as the operating control and the like, can be modified appropriately within a range that does not deviate from the spirit of the invention when an abnormality occurs.

[0029] For example, in the embodiment described above, since a chisel holder is the tool holder, the abnormality avoidance operation to be performed by that tool holder when the abnormality occurs in that tool holder is to withdraw it. However, if, for example, the tool holder is not a chisel holder but a tool holder containing a cutting tool on a rotating spindle, stopping the rotation can be performed as the abnormality avoidance operation.

[0030] In the embodiment described above, the other toolholder is withdrawn as a reaction operation to be performed by the other toolholder when the abnormality occurs on the first toolholder, and it is determined that if the first toolholder performs the abnormality avoidance operation, the effect on the machining is significant. However, if the machining is affected by a change in a process condition and a machining path (for example, in the one described in Fig. In the example shown (3), where a reduction in traverse speed, a reduction in cutting depth, and the like can be continued without stopping, it is possible to use a change in the process condition and the machining path as the reaction operation. This means, for example, that the other tool holder in the Fig.The example shown in point 3 illustrates how the reaction operation can be performed, such as reducing the feed rate and reducing the cutting depth.

[0031] Furthermore, in the embodiment described above, when simultaneous machining is performed, the extent of the effect on the machining at the other toolholder is determined in the case where the toolholder with the cutting tool exhibiting the detected abnormality performs the abnormality avoidance operation. However, a configuration without determining such an extent of effect is possible, so that the toolholder holding the cutting tool exhibiting the detected abnormality is withdrawn together with the other toolholder when simultaneous machining is performed, and conversely, when simultaneous machining is not performed, only the toolholder holding the cutting tool exhibiting the detected abnormality is withdrawn, while the other toolholder continues machining.

[0032] If the tool holder in tool A is the tool holder, and the other tool holder, without the abnormality, contains the cutting tool corresponding to that of the tool holder in which the abnormality occurred, a process of one tool holder can be reassigned to the other tool holder. For example, in a machining operation as described in the prior art, where the workpiece with an outside diameter of Ø 40 mm is finished to an outside diameter of Ø 30 mm, with the outside diameter being reduced to Ø 35 mm using cutting tool 31 of tool holder A and the outside diameter being finished to Ø 30 mm using cutting tool 32 of tool holder B, it is assumed that an abnormality occurs in tool holder B and tool holder B is withdrawn. At this point, the machining of tool holder B can be reassigned to tool holder A to continue the machining operation.This means that up to a synchronization point in a program, in order to perform a simultaneous operation, it is possible to complete the processing by alternately performing operations until the end.

[0033] Furthermore, if the machine tool is equipped with a tool changer, it is possible to resume machining after the cutting tool contained in the tool holder, which performed the abnormality avoidance operation due to the occurrence of the abnormality, has been replaced by a spare cutting tool.

[0034] In addition, although the embodiment described above refers to an NC lathe with two tool holders, the invention can preferably be used, for example, in an NC lathe with a plurality of tool holders but only one spindle, and in a machining center with a plurality of work spindle heads on which cutting tools can be mounted.

[0035] It is explicitly stated that all features disclosed in the description and / or the claims are intended to be disclosed separately and independently of one another for the purpose of the original disclosure and for the purpose of limiting the claimed invention, irrespective of the combination of features in the embodiments and / or the claims. It is explicitly stated that all ranges of values ​​or specifications of groups of units disclose any possible intermediate value or intermediate unit for the purpose of the original disclosure and for the purpose of limiting the claimed invention, in particular as limits of ranges of values.

Claims

[1] Operational control method in a machine tool (10) comprising a plurality of tool holders (A, B) with a cutting tool (31, 32), wherein the machine tool (10) moves the tool holders (A, B) relative to a workpiece (W) in order to machine the workpiece (W), and wherein the operational control method comprises: a first step in determining whether an abnormality has occurred on the cutting tool (31, 32) during machining or not; a second step of determining whether simultaneous machining, in which at least two or more of the tool holders (A, B) perform the machining operations on an identical workpiece (W), is carried out or not, and whether, if the abnormality is detected, the cutting tool (31, 32) that has the detected abnormality is the cutting tool (31, 32) that performs the simultaneous machining or not; and a third step of causing the tool holder (A, B) with the cutting tool (31, 32) which has the detected abnormality to perform an abnormality avoidance operation, and another of the tool holders (A, B), based on a determination result in the second step, to perform a reaction operation. [2] Operational control method in a machine tool (10) comprising a plurality of tool holders (A, B) with a cutting tool (31, 32), wherein the machine tool (10) moves the tool holders (A, B) relative to a workpiece (W) in order to machine the workpiece (W), and wherein the operational control method comprises: a first step in determining whether an abnormality has occurred on the cutting tool (31, 32) during machining or not; a second step of determining whether simultaneous machining, in which at least two or more of the tool holders (A, B) perform the machining operations on an identical workpiece (W), is carried out or not, and whether, when the abnormality is detected, the cutting tool (31, 32) that has the detected abnormality is the cutting tool (31, 32) that performs the simultaneous machining or not; a third step of determining the magnitude of an effect on the machining with another of the tool holders (A, B) in a case where the tool holder (A, B) with the cutting tool (31, 32) that has the detected abnormality is caused to perform an abnormality avoidance operation; and a fourth step of causing the tool holder (A, B) with the cutting tool (31, 32) which has the detected abnormality to perform the abnormality avoidance operation, and of causing the tool holders (A, B), based on determination results in the second step and the third step, to perform a reaction operation. [3] Operational control method in a machine tool (10) which includes a plurality of tool holders (A, B) with a cutting tool (31, 32), wherein the machine tool (10) moves the plurality of tool holders (A, B) relative to a workpiece (W) in order to machine the workpiece (W) simultaneously, wherein the machining control method comprises: a first step in determining whether an abnormality has occurred on the cutting tool (31, 32) during machining or not; a second step of determining the magnitude of an effect on the machining with another of the toolholders (A, B) in a case in which, when the abnormality is detected, the toolholder (A, B) with the cutting tool (31, 32) that has the detected abnormality is caused to perform an abnormality avoidance operation; and a third step of causing the tool holder (A, B) with the cutting tool (31, 32) which has the detected abnormality to perform the abnormality avoidance operation and the other of the tool holders (A, B), based on a determination result in the second step, to perform a reaction operation. [4] Operational control method in the machine tool (10) according to claim 2 or 3, wherein, by determining the magnitude of the effect on the machining with the other of the tool holders (A, B) in the case in which the tool holder (A, B) with the cutting tool (31, 32) which has the detected abnormality is caused to perform the abnormality avoidance operation, the operational control method comprises at least one of: a method of determining the size from a change in a cutting depth in the workpiece (W) based on a current position and direction of travel of each of the tool holders (A, B); and a method of determining the size from whether, based on the current position of each of the tool holders (A, B), each of the tool holders (A, B) is positioned in a pre-selected affected area or not.

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