Machining method, evaluation method, control device, program, and evaluation workpiece

Abstract

This machining method for manufacturing an evaluation workpiece for evaluating thermal displacement of a machine tool is characterised by including: a thermal displacement load operation step (S101) for operating the machine tool on the basis of thermal displacement load information, which is information for reproducing thermal displacement caused by the machine tool performing actual machining; and an evaluation machining step (S102) for machining a workpiece by operating the machine tool on the basis of an evaluation machining path such that the amount of movement of the tool changes depending on a reference position of the tool in a first direction, which is an evaluation direction of thermal displacement, said tool moving in contact with the workpiece in a plane orthogonal to the first direction.

Description

Processing method, evaluation method, control device, program, and evaluation work piece

[0001] The present disclosure relates to a processing method, an evaluation method, a control device, a program, and an evaluation work piece for evaluating thermal displacement.

[0002] During the operation of a machine tool, heat is generated. For example, heat generated when converting electric power into motive power, heat associated with friction between a tool and a work piece which is the object to be processed, etc. are generated. When this heat is transmitted to the structure of the machine tool, the temperature of the structure of the machine tool rises and thermal expansion occurs, which may cause the structure to deform. When the structure deforms, it may change the relative position of the tool with respect to the work piece, and such displacement is called thermal displacement. Thermal displacement is known to cause a decrease in machining accuracy. It is important to accurately evaluate thermal displacement.

[0003] Patent Document 1 discloses a technique for evaluating the thermal displacement of a machine tool by performing machining on a work piece inclined with respect to the Y-axis direction which is the machining progress direction, without moving it in the Z-axis direction orthogonal to the progress direction, and measuring the length of the cutter marks obtained as a result of the machining. According to the technique disclosed in Patent Document 1, thermal displacement can be evaluated without installing a displacement sensor.

[0004] Japanese Patent Application Laid-Open No. 2012-86325

[0005] However, the above conventional technique has a problem that it may not be able to accurately evaluate the thermal displacement during actual machining. For example, the above conventional technique does not disclose what kind of operating motion is given to the machine tool during the evaluation of thermal displacement. Since thermal displacement varies depending on what kind of operating motion is performed, in the above conventional technique, the state of thermal displacement is different between the evaluation of thermal displacement and during actual machining, and it may be difficult to accurately evaluate the thermal displacement during actual machining.

[0006] The present disclosure has been made in view of the above, and an object thereof is to obtain a processing method capable of improving the evaluation accuracy of thermal displacement during actual machining when evaluating thermal displacement without installing a displacement sensor.

[0007] To solve the above-mentioned problems and achieve the objective, the processing method according to the present disclosure is a processing method for producing an evaluation workpiece for evaluating the thermal displacement of a machine tool, and is characterized by including: a thermal displacement load operation step of operating a machine tool based on thermal displacement load information, which is information for reproducing the thermal displacement caused by the machine tool performing actual processing; and an evaluation processing step of operating a machine tool based on an evaluation processing path in which the amount of movement of the tool that moves in contact with the workpiece in a plane perpendicular to the first direction changes depending on the reference position of the tool in the first direction, which is the evaluation direction of thermal displacement, and processing the workpiece.

[0008] The processing method described herein has the effect of improving the accuracy of thermal displacement evaluation during actual processing when evaluating thermal displacement without installing displacement sensors.

[0009] Figure 1 shows an example of the configuration of a machining system. Figure 2 shows an example of the configuration of a machine tool. Figure 3 shows an example of the functional configuration of the control device according to Embodiment 1. Figure 4 is an explanatory diagram of an example of thermal displacement load operation. Figure 5 is an explanatory diagram of an example of a machining path for evaluation. Figure 6 is an explanatory diagram of the correlation between thermal displacement and the length of the cutter mark. Figure 7 is a flowchart for explaining the operation of the control device shown in Figure 3. Figure 3 shows an example of the functional configuration of the control device according to Embodiment 2. Figure 8 is an explanatory diagram of the pitch distance of the ball screw of the feed axis of the machine tool. Figure 9 is an explanatory diagram of the motion error occurring in the feed axis of the machine tool shown in Figure 9. Figure 9 is an explanatory diagram of the effect of generating a pre-machined surface according to Embodiment 2. Figure 10 is an explanatory diagram of a pre-machined surface according to a comparative example. Figure 8 is a flowchart for explaining the operation of the control device shown in Figure 3. Figure 14 shows an example of the functional configuration of the control device according to Embodiment 3. Figure 14 is an explanatory diagram of an evaluation workpiece produced by the control device shown in Figure 14. Figure 14 is an explanatory diagram of an actual evaluation workpiece produced by the control device shown in Figure 14. Figure 14 is a flowchart for explaining the operation of the control device shown in Figure 14. Figure 14 shows an example of the hardware configuration of the control device according to Embodiments 1 to 3. Figure 14 is an explanatory diagram of dedicated hardware used to realize the functions of the control device according to Embodiments 1 to 3.

[0010] The processing method, evaluation method, control device, program, and evaluation workpiece according to the embodiments of this disclosure will be described in detail below with reference to the drawings.

[0011] Embodiment 1. Figure 1 shows an example of the configuration of a machining system 100. The machining system 100 includes a control device 1 and a machine tool 2. The control device 1 generates motor control commands for controlling the machine tool 2 based on a machining program and provides the generated motor control commands to the machine tool 2. The machine tool 2 processes a workpiece to produce an evaluation workpiece 3 for evaluating thermal displacement. A workpiece is an object processed by the machine tool 2 and is also called a workpiece. The machining program is an EIA (Electrical and Instrumentation Automation) program, including G-code, and is created in advance by the user.

[0012] Machine tool 2 is a machine that processes workpieces, and is, for example, a machining center as shown in Figure 2. Figure 2 is a diagram showing an example of the configuration of machine tool 2.

[0013] Machine tool 2 is a vertical orthogonal three-axis cutting machine. Machine tool 2 includes a spindle control unit 92 which includes a process control device for controlling one spindle 83, an X-axis drive unit 93 which includes a servo control device for driving the X-axis, a Y-axis drive unit 94 which includes a servo control device for driving the Y-axis, and a Z-axis drive unit 95 which includes a servo control device for driving the Z-axis. Machine tool 2 drives a tool 76 in the X-axis and Z-axis directions, drives a workpiece 78 placed on a worktable 77 in the Y-axis direction, and rotates the tool 76 using the spindle 83 to machine the workpiece 78. Machine tool 2 operates according to the control of control device 1 to machine the workpiece 78 into a desired shape.

[0014] The X-axis drive unit 93 includes a motor 71X, a guide mechanism 72X, and a lead screw 73X. The Y-axis drive unit 94 includes a motor 71Y, a guide mechanism 72Y, and a lead screw 73Y. The Z-axis drive unit 95 includes a motor 71Z, a guide mechanism 72Z, and a lead screw 73Z. A rotation angle detector 80X for detecting the rotation angle of motor 71X is attached to motor 71X. A rotation angle detector 80Y for detecting the rotation angle of motor 71Y is attached to motor 71Y. A rotation angle detector 80Z for detecting the rotation angle of motor 71Z is attached to motor 71Z. Hereinafter, when motors 71X, 71Y, and 71Z are not distinguished, they will simply be referred to as motor 71, using the common reference numeral 71. Motor 71X is the motor 71 provided in the X-axis drive unit 93. Similarly, when the guide mechanisms 72X, 72Y, and 72Z are not distinguished, they are simply referred to as the guide mechanism 72, and when the lead screws 73X, 73Y, and 73Z are not distinguished, they are simply referred to as the lead screws 73.

[0015] In machine tool 2, the rotational motion of the actuator motor 71 is converted into linear motion in the driving direction of each axis by the lead screw 73. At this time, the rotational motion is supported by the guide mechanism 72, so the axis has degrees of freedom only in the feed direction of the lead screw 73. As a result, in machine tool 2, the combined linear motion of each axis results in motion in three dimensions of XYZ space, i.e., three degrees of freedom, by the two degrees of freedom motion of the tool 76 in the XZ plane and the one degree of freedom motion of the workpiece 78 in the Y axis direction. Machine tool 2 processes the workpiece 78 by rotating the tool 76 using the spindle 83 and removing the material from the part of the workpiece 78 that interferes with the tool 76.

[0016] Figure 3 shows an example of the functional configuration of the control device 10 according to Embodiment 1. The control device 10 has a thermal displacement load operation unit 11, an evaluation workpiece manufacturing unit 12, and an evaluation unit 13. The control device 10 controls the machine tool 2 to process a workpiece 78 and manufacture an evaluation workpiece 3 for evaluating the thermal displacement of the machine tool 2.

[0017] Here, we will explain thermal displacement. When the machine tool 2 processes a workpiece 78, heat is generated within the machine tool 2. For example, the actuators, the motor 71 and servo amplifier (not shown), generate heat when converting electricity into power. In addition, during processes such as cutting and grinding, heat is generated due to material deformation, friction, etc. Furthermore, friction generated when the feed axis is operated also generates heat. When this heat is transferred to the structure of the machine tool 2, the temperature of the structure of the machine tool 2 rises and thermal expansion occurs. Since the temperature of the structure does not change uniformly, thermal expansion can cause different expansions depending on the position of the structure, and deformations other than simple expansion and contraction may occur, such as tilting, distortion, and twisting of the structure. Such deformations cause errors in the relative position between the tool 76 and the workpiece 78. Such errors, that is, the amount of change in the relative position between the tool 76 and the workpiece 78 caused by thermal deformation, are called thermal displacement. It is known that thermal displacement can reduce the positioning accuracy of the machine tool 2, and therefore the machining accuracy may decrease.

[0018] The control device 10 has the function of causing the machine tool 2 to perform an operation that generates thermal displacement, and then creating an evaluation workpiece 3 for evaluating the thermal displacement. The control device 10 may also have the function of evaluating the thermal displacement of the machine tool 2 using the evaluation workpiece 3. In Figure 3, the control device 10 is shown to have the function of an evaluation unit 13, but the evaluation of thermal displacement may be performed manually, in which case the function of the evaluation unit 13 is omitted.

[0019] The thermal displacement load operation unit 11 controls the machine tool 2 according to the machining program for the thermal displacement load step, and causes the machine tool 2 to perform a thermal displacement load operation in which it operates in an operating pattern that generates thermal displacement in the machine tool 2. In the thermal displacement load operation, the thermal displacement load operation unit 11 may operate only the spindle 83, only the feed axis, or both the spindle 83 and the feed axis. At this time, the thermal displacement load operation unit 11 causes the machine tool 2 to perform the thermal displacement load operation based on the thermal displacement load information. The thermal displacement load operation is, for example, an operation in which the spindle 83 is rotated at a predetermined speed for a predetermined time, an operation in which the feed axis is moved back and forth at a predetermined feed rate for a predetermined time, a combination of the above operations, or an operation in accordance with a machining program for evaluating the machine tool 2, for example, written in G code. In order to measure the amount of thermal displacement when there is no load, the thermal displacement load operation unit 11 may not move the spindle 83 and the feed axis. When the thermal displacement load operation unit 11 finishes the thermal displacement load operation, it outputs information to the evaluation workpiece manufacturing unit 12 indicating that the thermal displacement load operation has finished.

[0020] Here, we will explain thermal displacement load information. Thermal displacement load information is information for reproducing the thermal displacement caused by the machine tool 2 performing actual machining. For example, thermal displacement load information is information for operating the machine tool 2 based on the machining path of the actual machining. Note that "operating the machine tool 2 based on the machining path" means controlling at least one of the spindle 83 and the feed axis so that the tool 76 attached to the machine tool 2 moves relative to the workpiece according to the machining path. Alternatively, thermal displacement load information may be information for operating at least one of the spindle 83 and the feed axis of the machine tool 2 so that the average torque during thermal displacement load operation matches the average torque during actual machining. In actual machining, cutting force torque is applied to the spindle 83, but if actual cutting is performed every time thermal displacement is evaluated, the workpiece 78 will be consumed each time thermal displacement is evaluated, which is costly. Therefore, the average torque of the spindle 83 during the target actual machining is measured in advance, and in thermal displacement load operation, the spindle 83 is repeatedly accelerated and decelerated so that the average torque of the spindle 83 matches that of the actual machining.

[0021] Figure 4 is an explanatory diagram of an example of thermal displacement load operation. The upper part of Figure 4 shows the change in torque of the spindle 83 over time during actual machining. In thermal displacement load operation, the average torque of the spindle 83 during actual machining and the average torque T of the spindle 83 during thermal displacement load operation are shown. ave The machine tool 2 is operated in a driving pattern that matches the above. Since high torque is applied to the spindle 83 during acceleration and deceleration, a high average torque can be generated even when the workpiece 78 is not being cut by repeatedly accelerating and decelerating. This average torque T ave By making it match the average torque during actual machining, it becomes possible to simulate the load during actual machining and apply it to the machine tool 2, thereby reproducing the thermal displacement during actual machining.

[0022] Returning to the explanation of Figure 3, when the thermal displacement load operation unit 11 outputs information indicating that the thermal displacement load operation is complete, the evaluation workpiece manufacturing unit 12 controls the machine tool 2 based on the evaluation machining step machining program to operate the spindle 83 and feed axis of the machine tool 2 based on the evaluation machining path to machine the workpiece 78 and manufacture the evaluation workpiece 3. Here, the evaluation machining path is a machining path in which there is a correlation between the position of the tool 76 in a first direction, which is the thermal displacement evaluation direction, and the amount of movement of the tool 76 in a plane perpendicular to the first direction. The position of the tool 76 may be the tip of the tool 76, or it may be the point where the tool 76 and the workpiece 78 come into contact.

[0023] Figure 5 is an explanatory diagram of an example of a machining path 40 for evaluation. Here, the Z direction is defined as the first direction, which is the direction for evaluating thermal displacement, and the X direction is defined as the second direction, which is the direction of movement of the tool 76 and is perpendicular to the first direction. The tool 76 is a ball end mill. The machining path 40 has a correlation between the position of the tool 76 in the Z direction and the amount of movement of the tool 76 in the XY plane. Specifically, the machining path 40 has two components: a first amount of movement, which is the amount of movement of the tool 76 in the Z direction, and a second amount of movement, which is the amount of movement of the tool 76 in the Y direction. The second amount of movement is the amount of movement obtained by multiplying the first amount of movement by a predetermined multiplier. A groove is formed in a part of the workpiece 78 when the tool 76 and the workpiece 78 come into contact and the workpiece 78 is machined, and this groove is called a cutter mark 41. In the following explanation, depending on the state of the cutter marks 41, we may distinguish each cutter mark 41 by using a number following a hyphen, such as cutter mark 41-1, 41-2, etc.

[0024] For example, if the workpiece 78 is set up so that the relative distance between the tool 76 and the workpiece 78 approaches zero at the center coordinate in the Z direction of the machining path 40, and machining is performed using the machining path 40, the tool 76 will separate from the workpiece 78 midway through the machining process. As a result, cutter marks 41 are formed only on a portion of the workpiece 78. The length of the cutter marks 41 changes in proportion to the amount of thermal displacement generated in the Z axis. For example, a machining path is created with a first movement of 0.1 mm and a second movement of 100 mm. In this case, the second movement is 1000 times the first movement.

[0025] Figure 6 is an explanatory diagram illustrating the correlation between thermal displacement and the length of the cutter mark 41. Here, the tip position of the tool 76 is defined as the position of the tool 76. When no thermal displacement occurs, the tip position of the tool 76 is aligned with the coordinate of the center of the workpiece 78 in the Z direction, and this position is defined as the reference point A0. When thermal displacement occurs, even if the tip position of the tool 76 is intended to be aligned with the coordinate of the center of the workpiece 78 in the Z direction, a displacement will occur. The left side of Figure 6 shows the workpiece 78 when evaluation machining is performed from reference point A1, where a displacement in the negative Z direction has occurred due to thermal displacement. The right side of Figure 6 shows the workpiece 78 when evaluation machining is performed from reference point A2, where thermal displacement has occurred in the positive Z direction. When thermal displacement 42-1 occurs in the negative Z direction, the length of the cutter mark 41-1 formed on the workpiece 78 is defined as m1. As shown on the left side of Figure 6, when thermal displacement occurs in the negative Z direction, the length m1 of the cutter mark 41-1 is longer than the length m0 of the cutter mark 41 when there is no thermal displacement. Furthermore, let m2 be the length of the cutter mark 41-2 when a thermal displacement 42-2 occurs in the positive Z direction. As shown on the right of Figure 6, when a thermal displacement occurs in the positive Z direction, the length m2 of the cutter mark 41-2 is shorter than the length m0 of the cutter mark 41 when there is no thermal displacement.

[0026] For example, let's assume the length m0 of the cutter mark 41 is 50 mm. In this example, let's assume a displacement of 0.01 mm occurs in the positive Z direction, which is the evaluation direction for thermal displacement. As shown in the example on the right in Figure 6, let's assume the thermal displacement 42-2 is 0.01 mm. In this case, since the relative position of the workpiece 78 and the tool 76 moves away from each other throughout the entire machining path 40-2, the length m2 of the cutter mark 41-2 becomes 10 mm shorter than the length m0 of the cutter mark 41. In the example in Figure 6, length m0 - m2 = 10 mm. Thus, the displacement in the Z direction and the length of the cutter mark 41 are the same as the ratio of the second amount of movement to the first amount of movement, so by using the machining path 40, minute displacements occurring in the Z direction can be magnified and detected.

[0027] Returning to the explanation of Figure 3, the evaluation unit 13 performs thermal displacement evaluation using the evaluation workpiece 3 manufactured by the evaluation workpiece manufacturing unit 12. For example, the evaluation unit 13 may include a camera that photographs the surface of the evaluation workpiece 3 on which the cutter marks 41 are formed. By placing an object of known length, such as a jig or ruler, on the evaluation workpiece 3 and photographing the evaluation workpiece 3 with the camera, the length of the cutter marks 41 can be determined by comparing the object of known length in the captured image with the cutter marks 41.

[0028] In this example, the control device 10 performs the thermal displacement evaluation in the evaluation unit 13, but the user may manually measure the length of the cutter mark 41 using a measuring instrument such as a ruler to evaluate the thermal displacement.

[0029] Figure 7 is a flowchart illustrating the operation of the control device 10 shown in Figure 3. First, the thermal displacement load operation unit 11 executes the thermal displacement load operation step (step S101). The thermal displacement load operation step is a step in which the spindle 83 and feed axis of the machine tool 2 are operated based on thermal displacement load information, which is information for reproducing the thermal displacement caused by the machine tool 2 performing actual machining.

[0030] Following the thermal displacement loading operation step, the evaluation workpiece manufacturing unit 12 executes an evaluation machining step (step S102). The evaluation machining step is a step in which an evaluation workpiece 3 is manufactured by operating the machine tool 2 based on an evaluation machining path to machine the workpiece 78. The evaluation machining path is a machining path in which the amount of movement of the tool 76, which moves in contact with the workpiece 78 in a plane perpendicular to the first direction, changes depending on the reference position of the tool 76 in the first direction, which is the evaluation direction of thermal displacement, in the example above, the Z direction. In the example shown in Figure 5, the evaluation machining path 40 has two components: a first amount of movement in the Z direction and a second amount of movement in the X direction. The second amount of movement is the amount of movement obtained by multiplying the first amount of movement by a predetermined multiplier.

[0031] Following the evaluation machining step, the evaluation unit 13 performs an evaluation step (step S103) to evaluate the thermal displacement of the machine tool 2 using the evaluation workpiece 3. The evaluation step evaluates the thermal displacement of the machine tool 2 using the evaluation workpiece 3 produced in the evaluation machining step (step S102). The evaluation result is, for example, the amount of thermal displacement. As described above, the evaluation step may be performed manually by the user.

[0032] As described above, Embodiment 1 provides a machining method for producing an evaluation workpiece 3 for evaluating the thermal displacement of a machine tool 2, comprising: a thermal displacement load operation step in which the machine tool 2 is operated based on thermal displacement load information, which is information for reproducing the thermal displacement caused by the machine tool 2 performing actual machining; and an evaluation machining step in which the machine tool 2 is operated based on an evaluation machining path in which the amount of movement of the tool 76, which moves in contact with the workpiece 78 in a plane perpendicular to the first direction, changes depending on the reference position of the tool 76 in the first direction, which is the evaluation direction of thermal displacement, and the workpiece 78 is machined. In the above embodiment, the first direction corresponds to the Z direction. In this way, since thermal displacement load information is used in the thermal displacement load operation step, it becomes possible to reproduce thermal displacement that is closer to the thermal displacement that actually occurs in actual machining, and it becomes possible to improve the accuracy of evaluating thermal displacement when actual machining is performed without installing a displacement sensor. Furthermore, in the evaluation machining step, the machine tool 2 is operated based on an evaluation machining path such that the amount of movement of the tool 76, which moves in contact with the workpiece 78 in a plane perpendicular to the first direction, changes depending on the reference position of the tool 76 in the first direction, which is the evaluation direction of thermal displacement. As a result, it becomes possible to obtain an evaluation workpiece in which cutter marks, which are grooves of different lengths depending on the thermal displacement, are formed. Therefore, the user can evaluate the thermal displacement by, for example, measuring the length of the cutter marks machined on the evaluation workpiece, and it becomes possible to evaluate the thermal displacement without installing sensors. The length of the cutter marks may be measured manually, or the control device 10 may have a function to measure the length of the cutter marks. If the control device 10 has a function to measure the length of the cutter marks, for example, the control device 10 can measure the length of the cutter marks by analyzing an image taken of the machined surface of the manufactured evaluation workpiece.

[0033] In the above embodiment, since the tool 76 moves in a straight line in the X direction, the amount of movement of the tool 76 in contact with the workpiece 78 in a plane perpendicular to the first direction is the amount of movement in the second direction. In the first embodiment, the tool 76 is moved in a straight line so that the cutter mark 41 is a straight line, but the cutter mark 41 is not limited to a straight line and may be a curve.

[0034] In this machining method, the thermal displacement load information can be information for operating the spindle 83 so that the average torque of the spindle 83 in the thermal displacement load operation step matches the average torque of the spindle 83 in actual machining. Alternatively, the thermal displacement load information may be information for operating the feed axis so that the average torque of the feed axis in the thermal displacement load operation step matches the average torque of the feed axis in actual machining. Specifically, the thermal displacement load information may be the average torque of the spindle 83 when the spindle 83 is operated in actual machining, or the average torque of the feed axis when the feed axis is operated in the machining path of actual machining. Here, average torque is the time-averaged value of the torque measured over a predetermined period of time. For example, if the thermal displacement load operation is an operation to move the spindle 83, the thermal displacement load information may include the average torque of the spindle 83 in actual machining. If the thermal displacement load operation is an operation to move the feed axis, the thermal displacement load information may include the average torque of the feed axis when the feed axis is operated in the machining path of actual machining.

[0035] In the thermal displacement load operation step, the machining torque actually generated may be simulated by machining the workpiece 78 with the tool 76. Alternatively, since high torque is generated when accelerating and decelerating the spindle 83, the machining torque can also be simulated by repeatedly accelerating and decelerating the spindle 83. In this method of repeatedly accelerating and decelerating, a high average torque can be generated even when the workpiece 78 is not being cut. Similarly, for the feed axis, the torque when machining the workpiece 78 with the tool 76 may be used to calculate the average torque, or the torque when accelerating and decelerating the feed axis may be used to calculate the average torque.

[0036] Furthermore, in the machining method according to Embodiment 1, the evaluation machining path has two components: a first amount of movement in the first direction and a second amount of movement in the second direction perpendicular to the first direction, where the second amount of movement is the amount of movement obtained by multiplying the first amount of movement by a predetermined multiplier. In the above embodiment, the first direction corresponds to the Z direction, and the second direction corresponds to the X direction.

[0037] Furthermore, according to Embodiment 1, an evaluation workpiece 3 can be provided, which is manufactured by performing the above processing method.

[0038] Furthermore, according to Embodiment 1, a control device 10 for executing the above-described machining method can be provided. The control device 10 is a device for controlling a machine tool 2 and is characterized by comprising: a thermal displacement load operation unit 11 that operates the machine tool 2 based on thermal displacement load information, which is information for reproducing the thermal displacement caused by the machine tool 2 performing actual machining; and an evaluation workpiece production unit 12 that produces an evaluation workpiece 3 for evaluating the thermal displacement of the machine tool 2 by operating the machine tool 2 based on an evaluation machining path such that the amount of movement of the tool 76, which moves in contact with the workpiece 78 in a plane perpendicular to the first direction, changes depending on the reference position of the tool 76 in the first direction, which is the evaluation direction of thermal displacement, and machining the workpiece 78.

[0039] Furthermore, according to Embodiment 1, a program is provided that causes the machine tool 2 to produce an evaluation workpiece 3 for evaluating thermal displacement by executing a thermal displacement load operation step which operates the machine tool 2 based on thermal displacement load information which is information for reproducing the thermal displacement caused by the machine tool 2 performing actual machining, and an evaluation machining step which operates the machine tool 2 to machine the workpiece 78 based on an evaluation machining path in which the amount of movement of the tool 76, which moves in contact with the workpiece 78 in a plane perpendicular to the first direction, changes depending on the reference position of the tool 76 in the first direction which is the evaluation direction of thermal displacement.

[0040] Embodiment 2. Figure 8 shows an example of the functional configuration of the control device 10A according to Embodiment 2. The control device 10A includes a thermal displacement load operation unit 11, an evaluation workpiece manufacturing unit 12, an evaluation unit 13, and a pre-processed surface generation unit 14. The control device 10A has the pre-processed surface generation unit 14 in addition to the configuration of the control device 10 according to Embodiment 1. Hereinafter, detailed explanations of parts that are the same as the control device 10 will be omitted, and the parts that differ from the control device 10 will be mainly explained.

[0041] The pre-machined surface generation unit 14 generates the pre-machined surface of the evaluation workpiece 3 by controlling the machine tool 2 based on the pre-machined surface generation step processing program, before the thermal displacement load operation unit 11 executes the thermal displacement load operation step. The pre-machined surface is the surface that will be machined when evaluation machining is performed in the evaluation machining step. In the second embodiment, a surface onto which the motion errors generated by the machine tool 2 are transferred is generated as the pre-machined surface, making it possible to evaluate thermal displacement and motion errors separately.

[0042] Motion errors occurring in the machine tool 2 include, for example, errors in the parallelism in the direction of the feed axis due to the assembly accuracy of a single feed axis, errors in the perpendicularity of two feed axes due to the assembly accuracy of the feed axes themselves, errors in parallelism due to the deflection of the feed axis under its own weight, and pitch errors that repeatedly occur due to the pitch period of the ball screw that drives the feed axis. These errors are strongly dependent on the position of the feed axis, and have the characteristic of being reproducible when the feed axis is positioned in the same position.

[0043] Figure 9 is an explanatory diagram of the pitch distance P of the ball screw on the feed axis of machine tool 2. The pitch distance P of the ball screw feed screw 73Y is a value corresponding to the distance advanced in the feed direction in one rotation. In machine tool 2 (not shown in Figure 9) which has a feed screw 73X driven in the X-axis direction and a feed screw 73Y driven in the Y-axis direction, when the feed axis is driven by the ball screw feed screw 73Y, an error occurs in a direction different from the feed direction Y direction, in this case the Z direction, due to the effect of the runout of the feed screw 73Y. This error is called a motion error and occurs repeatedly with a period equal to the pitch distance P of the ball screw.

[0044] Fig. 10 is an explanatory diagram of the motion error occurring in the feed axis of the machine tool 2 including the configuration shown in Fig. 9. In the machine tool 2 having the configuration shown in Fig. 9, when the feed axis is driven by a feed screw 73Y which is a ball screw, as shown in Fig. 10, a motion error with a period of the pitch distance P repeatedly occurs in the Z direction. The motion errors related to parallelism and perpendicularity occur almost similarly even at positions differing by about several millimeters. In contrast, the pitch error is an error that periodically varies within one cycle of the ball screw, and if the positions where the error half-cycle, that is, more than half of the pitch distance P, differ, the amount of the pitch error generated also differs significantly and cannot be reproduced. Since the pitch of the ball screw is generally from several millimeters to several tens of millimeters, it is possible that the motion errors are significantly different even with a difference in position of about several millimeters.

[0045] Therefore, when generating a pre-machined surface by face milling, by using a tool 76 having a diameter sufficiently smaller than the pitch distance P of the ball screw, the pitch error is applied to the pre-machined surface. The tool 76 used for this machining is, for example, a square end mill, and it suffices if the diameter is at least half or less of the pitch distance P.

[0046] FIG. 11 is an explanatory diagram of the effect of generating a pre-machined surface according to Embodiment 2. As described above, in Embodiment 2, before the thermal displacement loading operation, a pre-machined surface is generated by face milling. Here, the feed direction is the Y direction, and a pre-machined surface on which the motion error in the Z direction is transferred is generated. At this time, the diameter Φ of the tool 76, for example, a square end mill, is smaller than half of the pitch distance P of the ball screw that drives the Y axis. As a result, the pitch error, which is the motion error in the Z direction, is reflected on the pre-machined surface. That is, although face milling is being performed on the pre-machined surface, a difference due to the motion error occurs in the position in the Z direction. The height of the workpiece 78 in the Z direction varies according to the motion error corresponding to the position in the Y direction after pre-machining. In the evaluation machining step, by using the workpiece 78 after pre-machining, as shown in the lower diagram of FIG. 11, when there is no thermal displacement, the distance between the tool 76 and the surface of the workpiece 78 becomes constant during evaluation machining. Thus, by producing the pre-machined surface of the evaluation workpiece 3 along substantially the same machining path as the evaluation machining step, the motion error when generating the pre-machined surface and the motion error during evaluation machining are made the same, and only the influence of thermal displacement appears as cutter marks 41 in the evaluation machining.

[0047] FIG. 12 is an explanatory diagram of a pre-machined surface according to a comparative example. FIG. 12 is a comparative example of the example shown in FIG. 11, and is an example in which a pre-machined surface is generated using a tool having a diameter Φ larger than half of the pitch distance P. In this case, the motion error in the Z direction during driving of the feed screw 73Y is not transferred to the surface of the workpiece 78, and the pre-machined surface is flat. In this case, as shown in the lower diagram of FIG. 12, during evaluation machining, the relative position between the tool 76 and the workpiece 78 changes depending on the position in the Y direction, and the cutter marks 41 formed on the workpiece 78 after evaluation machining reflect not only the influence of thermal displacement but also the influence of motion error.

[0048] Figure 13 is a flowchart illustrating the operation of the control device 10A shown in Figure 8. The pre-machined surface generation unit 14 of the control device 10A executes the pre-machined surface generation step (step S201). In the pre-machined surface generation step, the workpiece 78 is planarized using a tool 76 with a diameter Φ of less than half the pitch distance P of the ball screw that drives the feed axis. Steps S101 to S103 that follow are the same as in Embodiment 1, so a detailed explanation is omitted.

[0049] As described above, Embodiment 2 provides a machining method that further includes a pre-machining surface generation step, in which, prior to the thermal displacement load operation step, a tool with a diameter Φ of half or less of the pitch distance P of the ball screw of the feed axis is used to perform planar machining.

[0050] In the machining method according to Embodiment 2, the influence of motion errors of the machine tool 2 can be eliminated, and only the influence of thermal displacement can be extracted, making it possible to evaluate the thermal displacement that occurs during actual machining with even greater accuracy.

[0051] Embodiment 3. Figure 14 shows an example of the functional configuration of the control device 10B according to Embodiment 3. The control device 10B includes a thermal displacement load operation unit 11, an evaluation workpiece manufacturing unit 12B, an evaluation unit 13B, and a pre-machined surface generation unit 14. The thermal displacement load operation unit 11 is the same as in Embodiments 1 and 2, and the pre-machined surface generation unit 14 is the same as in Embodiment 2, so a detailed explanation is omitted.

[0052] Figure 15 is an explanatory diagram of the evaluation workpiece 3 produced by the control device 10B shown in Figure 14. The evaluation workpiece production unit 12B operates the spindle 83 and feed axis in an evaluation machining path to form one cutter mark 41, and then controls the tool 76 to move in the picking direction relative to the workpiece 78, thereby forming multiple cutter marks 41 on the workpiece 78.

[0053] Figure 16 shows an actual evaluation workpiece 3 produced by the control device 10B shown in Figure 14. Multiple cutter marks 41 extending in the X direction are formed in the XY plane, aligned in the Y direction. Tool marks from the formation process remain on the pre-processed surface. In the example shown in Figure 16, the tool 76 is moved in the X direction while processing is performed to form the pre-processed surface. However, for example, the pre-processed surface may be formed by moving the tool 76 in the Y direction, and then the evaluation processing may be performed by moving the tool 76 in the X direction. In this case, the cutter marks 41 are formed as grooves extending in a direction perpendicular to the lines of the tool marks from the formation of the pre-processed surface.

[0054] The evaluation unit 13B uses an evaluation workpiece 3 on which multiple cutter marks 41 are formed, and evaluates the change in thermal displacement over time based on the lengths of the multiple cutter marks 41. The method for evaluating each thermal displacement is the same as that of the evaluation unit 13.

[0055] Figure 17 is a flowchart illustrating the operation of the control device 10B shown in Figure 14. Step S201, the pre-processed surface generation step, step S101, the thermal displacement load operation step, and step S102, the evaluation processing step, are the same as in Embodiment 2. After the evaluation processing step S102, the evaluation workpiece manufacturing unit 12B performs a pick-direction movement step in which it moves the tool 76 relative to the workpiece 78 by a predetermined amount in the pick direction (step S301). After the pick-direction movement step S301, the evaluation workpiece manufacturing unit 12B determines whether the process from step S101 to step S301 has been repeated a predetermined number of times (step S302).

[0056] If the predetermined number of steps has not been reached (Step S302: No), the evaluation workpiece manufacturing unit 12B notifies the thermal displacement load operation unit 11 to repeat the execution of the thermal displacement load operation step, and the process is repeated from step S101. If the predetermined number of steps has been reached (Step S302: Yes), the evaluation workpiece manufacturing unit 12B notifies the evaluation unit 13B that the production of the evaluation workpiece 3 is complete, and the evaluation unit 13B executes the evaluation step (Step S303). The evaluation step in Step S303 is a step in which the process of the evaluation step in Step S103 is performed for multiple cutter marks 41 to evaluate the change in thermal displacement over time. As a result, the control device 10B causes the machine tool 2 to repeat the thermal displacement load operation step and the evaluation machining step two or more times, and each time the evaluation machining step is completed, it causes the machine tool 2 to execute a pick direction movement step that moves the feed axis in the Y direction, which is a third direction orthogonal to both the Z direction and the X direction.

[0057] As described above, according to Embodiment 3, a machining method is provided which involves repeating the thermal displacement load operation step and the evaluation machining step two or more times, and each time the evaluation machining step is completed, the feed axis is moved in a third direction perpendicular to both the first direction and the second direction which is the direction of movement of the tool 76.

[0058] Furthermore, according to Embodiment 3, an evaluation method is provided that includes an evaluation step of evaluating the change over time of thermal displacement caused by the thermal displacement loading operation step based on the length of a plurality of cutter marks 41 formed on the workpiece 78 when the tool 76 and the workpiece 78 come into contact by the processing method described above.

[0059] Next, the hardware configuration of the control devices 10, 10A, and 10B according to Embodiments 1 to 3 will be described. The functions of each part of the control devices 10, 10A, and 10B are realized using processing circuits. The processing circuits may be realized by dedicated hardware or by using a CPU (Central Processing Unit). Figure 18 is a diagram showing an example of the hardware configuration of the control devices 10, 10A, and 10B according to Embodiments 1 to 3.

[0060] The functions of the control devices 10, 10A, and 10B are realized by a computer system as shown in Figure 18. The functions of the control devices 10, 10A, and 10B may be realized by one computer system or by multiple computer systems.

[0061] The computer system shown in Figure 18 comprises a control unit 101, an input unit 102, a storage unit 103, a display unit 104, a communication unit 105, and an output unit 106, which are connected via a system bus 107.

[0062] In Figure 18, the control unit 101 is, for example, a CPU. The control unit 101 executes a processing program that describes the processes to be performed by the control devices 10, 10A, and 10B of this embodiment. The input unit 102 is composed of, for example, a keyboard, mouse, etc., and is used by the user of the computer system to input various information. The storage unit 103 includes various types of memory such as RAM (Random Access Memory) and ROM (Read Only Memory), and storage devices such as a hard disk, and stores the program to be executed by the control unit 101, necessary data obtained in the process of processing, etc. The storage unit 103 is also used as a temporary storage area for the program. The display unit 104 is composed of an LCD (Liquid Crystal Display) etc., and displays various screens to the user of the computer system. The communication unit 105 is a communication circuit etc. that performs communication processing. The communication unit 105 may be composed of multiple communication circuits corresponding to multiple communication methods. The output unit 106 is an output interface that outputs data to external devices such as a printer or external storage device.

[0063] Note that Figure 18 is an example, and the configuration of the computer system is not limited to the example shown in Figure 18. For example, the computer system does not have to have an output unit 106. Also, if the functions of the control devices 10, 10A, and 10B are realized by multiple computer systems, not all of these computer systems have to be the computer system shown in Figure 18. For example, some computer systems do not have to have at least one of the display unit 104, output unit 106, and input unit 102 shown in Figure 18.

[0064] Furthermore, the functions of control devices 10, 10A, and 10B may be implemented using a cloud system. In a cloud system, the separation of computer system hardware and devices such as servers for each function can be arbitrarily configured. For example, one computer system may have the functions of multiple devices, or multiple computer systems may have the functions of a single device.

[0065] When the functions of control devices 10, 10A, and 10B are implemented using dedicated hardware, these functions are implemented using the processing circuit 90 shown in Figure 19. Figure 19 is an explanatory diagram of the dedicated hardware used to implement the functions of control devices 10, 10A, and 10B according to Embodiments 1 to 3. The processing circuit 90 may be a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.

[0066] The configurations shown in the above embodiments are examples only, and it is possible to combine them with other known technologies, combine different embodiments, and omit or modify parts of the configuration without departing from the gist of the invention.

[0067] For example, in the above description, the bottom and top surfaces of the workpiece 78 are assumed to be parallel planes, and an evaluation machining path having components in the X and Z directions is used as shown in Figure 5, but the invention is not limited to such examples. For example, the above technique can also be applied to machining using a workpiece with a bottom surface that is a plane parallel to the XY plane and a surface that is inclined with respect to the XY plane, and using a machining path that moves in a straight line in the X or Y direction. In any case, the tool 76 can leave the workpiece 78 midway through the machining path, and cutter marks 41 of different lengths can be formed depending on the reference position in the Z direction.

[0068] 1, 10, 10A, 10B Control device, 2 Machine tool, 3 Workpiece for evaluation, 11 Thermal displacement load operation unit, 12, 12B Workpiece production unit for evaluation, 13, 13B Evaluation unit, 14 Pre-machined surface generation unit, 40, 40-2 Machining path, 41, 41-1, 41-2 Cutter mark, 42-1, 42-2 Thermal displacement, 71, 71X, 71Y, 71Z Motor, 72, 72X, 72Y, 72Z Guide mechanism, 73, 73X, 73Y, 73Z Lead screw, 76 Tool, 77 Work table, 78 Workpiece, 80X, 80Y, 80Z Rotation angle detector, 83 Spindle, 90 Processing circuit, 92 Spindle control unit, 93 X-axis drive unit, 94 Y-axis drive unit, 95 Z-axis drive unit, 100 Machining system, 101 Control unit, 102 Input unit, 103 Storage unit, 104 Display unit, 105 Communication unit, 106 Output unit, 107 System bus, A0, A1, A2 Reference points, m0, m1, m2 Length, P Pitch distance, T ave Average torque, Φ diameter.

Claims

1. A machining method for producing an evaluation workpiece for evaluating the thermal displacement of a machine tool, comprising: a thermal displacement load operation step of operating the machine tool based on thermal displacement load information, which is information for reproducing the thermal displacement caused by the machine tool performing actual machining; and an evaluation machining step of operating the machine tool based on an evaluation machining path in which the amount of movement of the tool, which moves in contact with the workpiece in a plane perpendicular to the first direction, changes depending on the reference position of the tool in a first direction which is the evaluation direction of thermal displacement, thereby machining the workpiece.

2. The machining method according to claim 1, characterized in that the thermal displacement load information is information for operating the machine tool so that the average torque in the thermal displacement load operation step matches the average torque in the actual machining.

3. The machining method according to claim 1, characterized in that the thermal displacement load information is information for operating the machine tool based on the machining path of the actual machining.

4. The machining method according to any one of claims 1 to 3, further comprising a pre-machining surface generation step, in which a tool with a diameter of less than or equal to half the pitch distance of the ball screw of the feed axis of the machine tool is used to perform planar machining before the thermal displacement load operation step.

5. The machining method according to any one of claims 1 to 4, characterized in that the machining path for evaluation has two components: a first amount of movement in the first direction and a second amount of movement in a second direction perpendicular to the first direction, and the second amount of movement is the amount of movement obtained by multiplying the first amount of movement by a predetermined multiplier.

6. The machining method according to any one of claims 1 to 5, further comprising: a pick direction movement step, in which the thermal displacement load operation step and the evaluation machining step are repeated two or more times, and each time the evaluation machining step is completed, the feed axis of the machine tool is moved in a third direction perpendicular to both the first direction and the second direction which is the direction of movement of the tool.

7. An evaluation method characterized by comprising an evaluation step of evaluating the thermal displacement generated by the thermal displacement loading operation step based on the length of a cutter mark formed on the workpiece by the tool coming into contact with the workpiece by performing the processing method described in any one of claims 1 to 6.

8. An evaluation method characterized by comprising an evaluation step of evaluating the change over time of the thermal displacement caused by the thermal displacement loading operation step, based on the lengths of a plurality of cutter marks formed on the workpiece when the tool and the workpiece come into contact by the processing method described in claim 6.

9. A control device for controlling a machine tool, comprising: a thermal displacement load operation unit that operates the machine tool based on thermal displacement load information, which is information for reproducing the thermal displacement caused by the machine tool performing actual machining; and an evaluation workpiece production unit that produces an evaluation workpiece for evaluating the thermal displacement of the machine tool by operating the machine tool based on an evaluation machining path such that the amount of movement of the tool, which moves in contact with the workpiece in a plane perpendicular to the first direction, changes depending on the reference position of the tool in a first direction which is the evaluation direction of the thermal displacement, and machining the workpiece.

10. A program characterized by causing the machine tool to produce an evaluation workpiece for evaluating the thermal displacement by executing: a thermal displacement load operation step which operates the machine tool based on thermal displacement load information which is information for reproducing the thermal displacement caused by the machine tool performing actual machining; and an evaluation machining step which operates the machine tool and performs machining on the workpiece based on an evaluation machining path such that the amount of movement of the tool, which moves in contact with the workpiece in a plane perpendicular to the first direction, changes depending on the reference position of the tool in the first direction which is the evaluation direction of the thermal displacement.

11. An evaluation workpiece characterized by being manufactured by performing the processing method described in any one of claims 1 to 6.

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