Servo control device

Abstract

A servo control device that controls a machine tool (10) that rotates a workpiece (W) by a cooperative operation of a plurality of axes, the servo control device comprising: a vibration command generating unit (23) that generates a vibration command to cause the workpiece (W) and the tool (11) to vibrate relatively; a deviation deduction unit (31, 241) that applies the vibration command based on a movement command to a positional deviation to cause the workpiece (W) and the tool (11) to move relatively, and deducts a residual positional deviation; and a learning control unit (27) that calculates a compensation amount from a positional deviation based on the movement command after subtracting the remaining positional deviation.

Description

Background of the inventionField of the invention

[0001] The present invention relates to a servo control device. Related technology

[0002] Conventionally, vibration machining is known that crushes chips by causing a tool and a workpiece to vibrate relatively in the machining direction (vibration operation) (see, for example, Japanese Patent No. 6416218 and Japanese Patent No. 5606658). Japanese Patent No. 6416218 discloses that "in the cutting tool 130, the machined portion in a forward movement and the machined portion in a backward movement partially overlap each other, and the cutting portion at the n+1st rotation of the peripheral surface of the workpiece W includes the portion already machined at the n tenRotation has been cut. In this section, a so-called idle operation takes place in which the cutting tool 130 does not cut the workpiece W and thus performs idle cutting while cutting is taking place. The chips generated from the workpiece W during machining are crushed by the idle operation. The machine tool 10 can smoothly perform machining of the outer shape of the workpiece W while the chips are crushed by the cutting tool 130 moving forward and backward along the cutting feed direction.

[0003] Furthermore, Japanese Patent No. 5606658 further discloses that "a configuration is made such that a command for performing vibration cutting, which defines the frequency of vibration and the amplitude to be applied during machining along the movement path, is provided in the machining program, a compensation path, which is a movement trajectory of a reference position of a tool 62 with respect to the machining target, is generated based on the compensation information from the program path based on a movement command in the machining program, thereby applying vibration along the compensation path to machining in this compensation path. With such a configuration, it is possible to cut portions other than the compensation path, or it is possible to prevent the machining target from being cut excessively."Furthermore, it is possible to finely crush the chips generated during cutting by means of vibration by setting the vibration along the compensation path so that it has an amplitude of several hundred micrometers or less and a frequency of a low-frequency vibration of several hundred Hz or less." Patent Document 1: Japanese Patent No. JP 6 416 218 B2. Patent Document 2: Japanese Patent No. JP 5 606 658 B1.

[0004] DE 10 2018 005 754 A1 discloses a control device for a machine tool for performing vibration cutting. The control device includes a command block timing detection unit for detecting any timing between adjacent command blocks based on a machining program of a machine tool including a plurality of command blocks. A feed axis control unit includes a learning controller and a determination unit that determines whether or not a current time is within the arbitrary timing between the adjacent command blocks and stops vibration of at least one feed axis based on the determination. Overview of the invention

[0005] It is desirable to prevent an unnecessary cut from being created during vibration machining.

[0006] An object of the present invention is to provide a servo control device that can prevent an unnecessary cut from being generated during vibration machining.

[0007] The problem is solved by a servo control device having the features of patent claim 1. (1) According to one aspect of the invention, a servo control device that controls a machine tool that rotates a workpiece by a cooperative operation of a plurality of axes includes: a vibration command generation unit that generates a vibration command to cause the workpiece and the tool to vibrate relatively; a deviation subtraction unit that applies the vibration command based on a movement command to a positional deviation to cause the workpiece and the tool to move relatively, and subtracts a residual positional deviation; and a learning control unit that calculates a compensation amount from a positional deviation based on the movement command after subtracting the residual positional deviation.

[0008] According to the present invention, it is possible to provide a servo control device that can prevent an unnecessary cut from being generated during vibration machining. Short description of the drawings Fig. 1 is a diagram illustrating the configuration of a machining system including a servo control device of a machine tool according to the present embodiment; Fig. 2 is a graph showing the relationship between a feed amount and a rotation angle in an oscillating operation; Fig. 3 is a graph illustrating an operation of a tool in a case where a residual error is not removed by a high-pass filter in the oscillating operation; and Fig. Figure 4 is a graph illustrating operation of a tool after a residual control error has been removed by the high-pass filter in oscillating operation. Detailed description of the invention

[0009] An example of an embodiment of the present invention will now be described with reference to the accompanying drawings. Note that identical or corresponding portions in the respective drawings are denoted by the same reference numerals.

[0010] Fig. 1 is a diagram illustrating the configuration of a machining system 1 including a servo control device of a machine tool 10. The Fig. 1 includes a machine tool 10 and a servo control device for controlling the machine tool 10.

[0011] The machine tool 10 includes a tool 11. The tool 11 rotates a workpiece W, which has, for example, a cylindrical, columnar, conical, or truncated cone shape. In the example of Fig. 1, the tool 11 rotates the outer peripheral surface of the workpiece W. In the example of Fig. 1, the central axis line of the workpiece W, which serves as the rotation axis of the workpiece W, is represented as the z-axis, and the axis line perpendicular to the z-axis is represented as the x-axis.

[0012] The shape in the direction along the z-axis in which the machine tool 10 machines is not limited to a linear one, and the machine tool 10 is also capable of machining the workpiece W having an arc shape. Furthermore, the machine tool 10 is not limited to machining the outer peripheral surface of the workpiece W, and it is also possible to machine the inner peripheral surface of the workpiece W, such as a cylindrical shape. Furthermore, the machine tool 10 is not limited to turning, and it is also possible to perform machining such as cutting, lapping, grinding, or polishing.

[0013] The machine tool 10 includes a spindle M0 as the motor 12 and two feed axes M1 and M2 that interact with the spindle M0. The spindle M0 includes a spindle motor, and the feed spindles M1 and M2 include servo motors. The spindle M0 and the feed axes M1 and M2 are controlled by the servo control device.

[0014] The spindle M0 causes the workpiece W to rotate around the central axis line (the z-axis) of the workpiece W. The feed axis M1 is capable of both feeding the tool 11 in the z-axis direction (the first direction) and reciprocating (i.e., oscillating) the tool 11 in the z-axis direction. The feed axis M2 is capable of both feeding the tool 11 in the x-axis direction (the second direction) and reciprocating (i.e., oscillating) the tool 11 in the x-axis direction.

[0015] When a cylindrical or columnar workpiece W is rotated, the workpiece W is caused to rotate about the central axis line (the z-axis) of the workpiece W, and the tool 11 is fed only in the z-axis direction (in this case, the machining direction) along the generating line of the outer peripheral surface of the workpiece W.

[0016] In contrast, when the workpiece W having a different outer diameter in the z-axis direction, such as the workpiece W having a tapered shape or an arc shape, is rotated, the workpiece W is caused to rotate around the central axis line (the z-axis) around the workpiece W, and the tool 11 is fed in an oblique direction along the generating line of the outer peripheral surface of the workpiece W (the composite direction of the z-axis direction and the x-axis direction) (in this case, the machining direction). In this case, in order to feed the tool 11 in an oblique direction along the generating line of the outer peripheral surface of the workpiece W, at least two feed axes M1 and M2 are required. By controlling both the feed axis M1 and the feed axis M2, the tool 11 is fed in the oblique direction along the generating line of the outer peripheral surface of the workpiece W.

[0017] The servo control device is formed by a computer including a memory such as a ROM (read only memory) and a RAM (random access memory), a CPU (central processing unit), and a data transmission control unit, which are connected to each other by a bus. Furthermore, the servo control device includes a position command calculation unit 22, a vibration command generation unit 23 (including a vibration amplitude calculation part, a vibration frequency calculation part (not shown), and a vibration command calculation unit 231 described below). Fig. 2), a control unit (the adding devices 241 and 242, a subtracting device 251, a learning control unit 27 and a position-speed control unit 28 in Fig. 1, which will be described below), a high-pass filter 31 constituting a deviation extraction unit, and an unillustrated memory unit, and the function or operation of each component can be achieved with the cooperation between the CPU and the memory attached to the computer and the control program stored in the memory.

[0018] For example, machining conditions of the workpiece W are stored in the storage unit (not shown). The machining conditions of the workpiece W include, for example, the relative rotational speed of the workpiece W and the tool 11 around the center axis of the workpiece W, the relative feed rate of the tool 11 and the workpiece W, and the position command of the feed axes M1 and M2, etc.

[0019] A host computer (not shown) such as a CNC (Computer Numerical Controller), a PLC (Programmable Logic Controller), etc., is connected to the servo controller, and the above-mentioned rotational speed and feed rate can be input from the host computer into the storage unit (not shown). Furthermore, the storage unit (not shown) or the position command calculation unit 22 is not necessarily provided in the servo controller and can therefore be provided in the above-mentioned host computer.

[0020] Furthermore, the storage unit (not shown) stores a machining program to be executed by the machine tool 10, and a configuration may be made such that the CPU (not shown) in the servo controller reads the above-mentioned rotational speed and feed rate from the machining program as machining conditions and outputs them to the position command calculation unit 22 and the vibration command generation unit 23.

[0021] The position command calculation unit 22 generates a position command for causing the workpiece W and the tool 11 to move relatively. Specifically, the position command calculation unit 22 serves to generate the position command of the feed axes M1 and M2 based on the relative rotational speed of the workpiece W and the tool 11 around the center axis line of the workpiece W and the relative feed rate of the tool 11 and the workpiece W. This position command is a command for instructing a target position upon relative feed of the tool 11 and the workpiece W in a direction along the generating line of the outer peripheral surface of the workpiece W (the machining direction).

[0022] The vibration command generation unit 23 uses a position command from the position command calculation unit 22 to generate a vibration command for causing the workpiece W and the tool 11 to vibrate relatively. Specifically, the vibration command generation unit 23 generates a vibration command of the feed axis M1 so that, based on the above-mentioned rotational speed and the above-mentioned feed rate, a vibration frequency of a positive non-integer multiple with respect to the rotational speed is generated, and so that the tool 11 intermittently cuts the workpiece W. The vibration command is a periodic command generated to be asynchronous with respect to the above-described rotational speed about the central axis and includes the vibration frequency and vibration amplitude.That is, the operating state of oscillating operation is represented by the oscillation frequency or oscillation amplitude. The value expressed by the term S / 60×I in Equation (1) of the oscillation command described below corresponds to the oscillation frequency, and the value expressed by the term K×F / 2 in Equation (1) corresponds to the oscillation amplitude.

[0023] Herein, intermittent cutting indicates that the tool 11 rotates the workpiece W while the tool 11 periodically comes into contact with and separates from the workpiece W, and is also referred to as oscillation cutting or vibration cutting. In addition, although the workpiece W rotates and the tool 11 oscillates with respect to the workpiece W, Fig. 1 a design can be made such that the tool 11 rotates around the center axis line of the workpiece W and the workpiece W oscillates with respect to the tool 11. Furthermore, in Fig. 1, although both the feed operation and the oscillation operation of the workpiece W are carried out by a feed axis M1, M2, a design can be made such that the feed operation and the oscillation operation of the workpiece W are each carried out by different feed axes.

[0024] The following is a detailed description of the vibration command generating unit 23. Fig. Figure 2 is a graph showing the relationship between a feed amount and a rotation angle. The horizontal axis in Fig. 2 represents the rotation angle of the workpiece W, and the vertical axis represents the feed amount of the tool 11 in the machining direction (ie, the direction along the generating line of the outer peripheral surface of the workpiece W in Fig. 1). A plurality of straight, dashed lines C1, C2, C3... extending in the diagonal direction are drawn in Fig. 2. As can be seen from Fig. 2, the coordinate of the vertical axis of the intersection point between the dashed line C1 and the vertical axis corresponds to the coordinate of the vertical axis at the starting point of the next dashed line C2. Similarly, the coordinate of the vertical axis of the intersection point between the dashed line C2 and the vertical axis corresponds to the coordinate of the vertical axis at the starting point of the next dashed line C3. The plurality of straight dashed lines C1, C2, C3... represent the trajectory of movement of the tool 11 in the workpiece W in the case where there is no vibration command. In contrast, the Fig. 2 represent the trajectory of the tool 11 on the workpiece W in the case of the vibration command. That is, the dashed lines C1, C2, C3, etc., represent only the position command before the vibration command is added (the original command value), and the curves A1, A2, A3, etc., indicate the position command after the vibration command is added. Therefore, the curves A1, A2, and A3 represent a command obtained by adding a cosine vibration command to each position command represented by the dashed lines C1, C2, and C3.

[0025] Furthermore, curve A1 is the trajectory of the tool 11 in the first rotation of the workpiece W, curve A2 is the trajectory of the workpiece 11 in the second rotation of the workpiece W, and curve A3 is the trajectory of the tool 11 in the third rotation of the workpiece W. For the sake of simplicity, the trajectory of the tool 11 after the fourth rotation of the workpiece W is not shown.

[0026] The vibration command generation unit 23 calculates the vibration command in the following manner. To calculate a command such as curves A1, A2, and A3 with each of the dashed lines C1, C2, and C3, which are the position commands of the feed axes M1 and M2 calculated by the position command calculation unit 22 as the reference axis line, the vibration command generation unit 23 determines the vibration frequency. S / 60×I in equation (1) described below becomes the vibration frequency.

[0027] When determining the above-mentioned oscillation frequency, as in Fig. As shown in Figure 2, the initial phase of the cosine curve A2 with a specific dashed line, for example, the dashed line C2, as the reference axis is preferably shifted by half a cycle with respect to the cosine curve A1 with a previous dashed line, for example, the dashed line C1, as the reference axis. The reason for this is that by shifting it by half a cycle, the vibration amplitude of the vibration command can be minimized, making it possible to crush the chips most efficiently.

[0028] To calculate a command such as curves A1, A2, and A3 with each of the dashed lines C1, C2, and C3 as the reference axis line, the vibration command generation unit 23 determines the vibration amplitude of the vibration command described above. The value corresponding to the term K×F / 2 in equation (1) described below becomes the vibration amplitude. The value in Fig. 2, curves A1 and A2 overlap at position B1, where the angle of rotation is approximately 0 degrees, and at position B2, where the angle of rotation is approximately 240 degrees. As can be seen from Fig. 2, at positions B1 and B2, the maximum value of curve A1 with respect to dotted line C1 is greater than the minimum value of curve A2 with respect to dotted line C2. In other words, it is desirable for the vibration command generation unit 23 to determine the vibration amplitude such that the previous curve A1 and the subsequent curve A2 partially overlap each other. Note that since the feed rate is constant in curves A1, A2, and A3, the vibration amplitudes of each vibration command are all the same.

[0029] At these overlapping positions B1 and B2, the workpiece W is not machined because the tool 11 is spaced apart from the workpiece W during machining on the movement path of the curve A2. In the present embodiment, it is possible to perform so-called intermittent cutting because such overlapping portions B1 and B2 are generated periodically. Fig. In the example shown in Figure 2, the chips are generated at positions B1 and B2, respectively, by the operation according to curve A2. In other words, two chips are generated at curve A2 in the second rotation. Since such intermittent cutting is performed periodically, it is possible to perform vibration cutting periodically.

[0030] Furthermore, curve A3 is designed so that the dashed line C3 has the same shape as curve A1. Curve A2 and curve A3 overlap each other at position B3, where the rotation angle is approximately 120 degrees, and at position B4, where the rotation angle is approximately 360 degrees. Chips are generated at positions B3 and B4, respectively, by the operation according to curve A3. In other words, two chips are generated in curve A3 in the third rotation. Subsequently, two chips are generated with each rotation of the workpiece. However, chips are not generated in the first rotation.

[0031] By defining the vibration frequency and vibration amplitude in this way, the vibration command generation unit 23 in the control unit 26 calculates the vibration command. For example, the vibration command is expressed as shown in Equation (1) below. [Math. 1] Oscillation command = K×F2cos(2π×S60×I×t)−K×F2

[0032] In equation (1), K is a vibration amplitude multiplication factor, F is the amount of movement of the tool 11 per rotation of the workpiece W, that is, the feed rate per rotation [mm / rev], S is the rotational speed around the center axis of the workpiece W [min-1] or [rpm], and I is a vibration frequency multiplication factor. Here, the aforementioned vibration frequency corresponds to the term S / 60×I in equation (1), and the aforementioned vibration amplitude corresponds to the term K×F / 2 in equation (1). However, the vibration amplitude multiplication factor K is a number 1 or greater, and the vibration frequency multiplication factor I is a non-integer greater than zero (for example, a positive non-integer such as 0.5, 0.8, 1.2, 1.5, 1.9, 2.3, or 2.5). The oscillation amplitude multiplication factor K and the oscillation frequency multiplication factor I are constants (in the example of Fig. 2, I is equal to 1.5). The reason why the vibration frequency multiplication factor I is not an integer is that in a case where the vibration frequency becomes exactly consistent with the rotational speed around the center axis of the workpiece W, it is not possible to generate the overlapping positions B1, B2, B3, B4, etc. described above, and therefore the chip crushing effect due to vibration cutting cannot be achieved.

[0033] Furthermore, according to equation (1), the vibration command is a command in which the term (K×F / 2) is subtracted as an offset value with respect to a cosine wave, and each of the dashed lines C1, C2, and C3 indicates the position command as the reference axis line. Therefore, it is possible to control the positional movement trajectory of the tool 11 based on the composite command value obtained by adding the vibration command to the position command, with the position corresponding to the position command in the machining direction of the tool 11 as the upper limit. Therefore, the curves A1, A2, A3, and the like in Fig. 2, the dashed lines C1, C2, C3 and the like in the + direction (ie, in the machining direction of the tool 11) are not. Furthermore, by defining the vibration command as shown by equation (1), as can be seen from the curve A1 in Fig. 2, a design such that a large vibration does not appear from the beginning in the feed direction of the tool 11 at the machining starting point (the position of 0 degrees of the horizontal axis). Note that the initial values ​​of the respective parameters (K and I in Equation (1)), which are adjusted when the vibration frequency and the vibration amplitude are determined, are stored in a storage unit (not shown) before the operation of the machine tool 10. The rotational speed (S) of the workpiece W is stored in advance as a machining condition in the storage unit (not shown). The feed amount per rotation F is calculated from the rotational speed (S) and the position command generated by the position command calculation unit 22.

[0034] For example, in a case where the machined workpiece has a cylindrical shape or a columnar shape, the vibration is performed along the machining direction, which is the direction of the feed axis M1 (z-axis) along the generating line of the outer peripheral surface of the workpiece W. On the other hand, in a case where the machined workpiece has a conical shape, a truncated cone shape (a tapered shape), or an arc shape, the vibration is performed along an oblique direction along the generating line of the outer peripheral surface of the workpiece W, that is, along the machining direction, which is a composite direction of the direction of the feed axis M1 (z-axis) and the direction of the feed axis M2 (x-axis).The vibration command calculation unit 231 of the vibration command generation unit 23 calculates the vibration command based on the vibration amplitude and the vibration frequency from the equation (1).

[0035] The control unit 26 has a function of calculating a torque command and controlling the feed axes M1 and M2 based on a composite command (for example, a position command value) obtained by adding the above-mentioned vibration command to the position deviation, which is the difference between the above-mentioned position command and the actual positions of the feed axes M1 and M2. The actual positions of the feed axes M1 and M2 correspond to the position feedback value obtained by a position detection unit such as a rotary encoder (not shown) mounted on the feed axes M1 and M2.

[0036] The control unit 26 includes the adders 241 and 242, the subtractor 251, the learning control unit 27, and the position-speed control unit 28. The subtractor 251 obtains the position deviation, which is the difference between a position command (movement command) calculated by the position command calculation unit 22 and a position feedback (a current position) from the rotary encoder in the feed axes M1 and M2. The adder 241 constitutes a deviation extraction unit and adds the position deviation outputted by the subtractor 251 and obtained by integration to the vibration command calculated by the vibration command generation unit 23, thereby calculating a composite command.The high-pass filter 31 constitutes the deviation extraction unit, allows the high-frequency component of the composite command to be passed immediately after it is output from the adder 241, thereby removing the low-frequency component to remove the residual control error included in the low-frequency component (residual position error), thereby generating the composite command.

[0037] The learning control unit 27 performs learning for one of the vibrations in the x-axis and z-axis directions during the vibration of the tool 11. The learning control unit 27 inputs the composite command output from the high-pass filter 31 and obtains the compensation amount of the composite command by performing learning control so as to reduce the compensation amount of the composite command. The adder 242 adds the compensation amount obtained by the learning control unit 27 to the composite command immediately before it is input to the position-speed control unit 28.

[0038] The position-speed control unit 28 performs position control, speed control, and current control based on the composite command compensated by the learning control unit 27, and drives and controls the servo motor in the feed axes M1 and M2.

[0039] In the machining system 1 according to the above configuration, as described above, by removing the low-frequency component of the composite command immediately after it is output from the adder 241, the residual error included in the low-frequency component is removed by means of the high-pass filter 31. As shown in Fig. 4, the actual position (the graph of the bold line) therefore does not deviate significantly from the move command (the graph of the thin line) in the direction of the x-axis, which is the horizontal axis, and thus substantially agrees with the move command. Fig. Figure 4 is a graph illustrating the operation of the tool 11 after the residual control error has been removed by the high-pass filter 31 during oscillating operation.

[0040] In contrast, in a case where the residual control deviation is not subtracted by the high-pass filter 31, the learning control unit 27 even learns the residual control deviation. As shown in Fig. Therefore, as shown in Figure 3, the actual position (the bold line graph) deviates significantly from the motion command (the thin line graph) in the x-axis direction, which is the horizontal axis. Therefore, for example, in a case where the cross-sectional shape of the workpiece W is a tapered shape or an arc shape, an unnecessary cut is generated for the workpiece W. Fig. 3 is a graph illustrating the operation of the tool 11 in a case where the residual error is not removed by the high-pass filter 31 in the oscillating operation.

[0041] The present embodiment described above exerts the following effects. In the present embodiment, the high-pass filter 31 and the adder 241 are provided as the deviation subtraction unit that applies the vibration command based on the movement command to the positional deviation to cause the workpiece W and the tool 11 to move relatively, and subtracts the residual positional deviation, and the learning control unit 27 is provided as the learning control unit that calculates the compensation amount from the positional deviation based on the movement command after subtracting the residual positional deviation. With such a configuration, it is possible to prevent the actual position from significantly projecting with respect to the movement command by having the learning control unit 27 learn even the residual control deviation.Therefore, in particular, it is possible to prevent an unnecessary cut from being generated in the swing machining, and, for example, in a case where the cross-sectional shape of the workpiece W is a tapered shape or an arc shape, it is possible to prevent an unnecessary cut from being generated in the swing machining.

[0042] Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiments, and various modifications and variations are possible. For example, in the above-described embodiment, a configuration is exemplified in which the tool 11 oscillates along the generating line of the outer peripheral surface of the workpiece W as the workpiece W rotates; however, the present invention is not limited to this configuration. It may be configured such that the machine tool according to the present invention machines the workpiece W by controlling the spindle M0, which causes the workpiece W and the tool 11 to rotate relatively around the central axis line of the workpiece W, and at least two feed axes M1 and M2, etc., which relatively feed the workpiece W and the tool 11 in the machining direction along the central axis line.For example, a configuration may be adopted in which the tool 11 rotates around the central axis line of the workpiece W and the workpiece W swings with respect to the tool 11, or the workpiece W rotates and the workpiece W swings in the direction along the generating line of the outer peripheral surface of the workpiece W with respect to the tool 11. Furthermore, the present invention includes, as a type of machining, a machining method for cutting the workpiece W by causing the tool 11 to rotate around the central axis line. 1 processing system 10 Machine tool 11 Tools 23 Vibration command generation unit 27 Learning control unit (learning control unit) 31 high-pass filter (deviation subtraction unit) 241 Adding device (adding device, deviation deduction unit) 242 Adding device (adding device) 251 Subtraction device (subtraction device) M0 spindle M1, M2 feed axis W workpiece

Claims

[1] Servo control device that controls a machine tool (10) that rotates a workpiece (W) by means of a combined operation of a plurality of axes, wherein the servo control device comprises: a vibration command generation unit (23) that generates a vibration command to cause the workpiece (W) and the tool (11) to vibrate relative to each other; a deviation subtraction unit (31, 241) that applies the vibration command based on a motion command to a position deviation in order to cause the workpiece (W) and the tool (11) to move relative to each other, and subtracts a permanent position deviation; and a learning control unit (27) that calculates a compensation amount from a position deviation based on the movement command after subtracting the permanent position deviation. [2] Servo control device according to claim 1, wherein the deviation reduction unit (31, 241) comprises a high-pass filter (31).

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