CONTROL DEVICE AND CONTROL SYSTEM FOR A MACHINE TOOL

Abstract

Control device (100) for controlling a machine tool which has a first axis which rotates a tool and a second axis which rotates a workpiece, and is configured to rotate the first axis and the second axis and to machine the workpiece into a polygon, wherein the control device (100) comprises: a machining data acquisition unit (16) that acquires machining data which changes according to the machining of the workpiece; and a position detection unit (18) which detects the position of a machining surface of the workpiece based on the change in the machining data.

Description

GENERAL STATE OF THE ART1. Field of the invention

[0001] The present invention relates to a control device and a control system for a machine tool. 2. General state of the art

[0002] Polygon machining is a technique for machining a workpiece by rotating a tool and the workpiece at a specific ratio to create a polygonal shape. In polygon machining, the workpiece can be machined into a polygonal shape, such as a square, a hexagon, or similar, by changing the rotation ratio of the workpiece and the tool, as well as the number of blades attached to the polygon machining tool.

[0003] In polygon machining, it sometimes happens that after a polygonal shape has been created on the workpiece surface, an additional machining operation such as drilling is performed. In this case, the center of the workpiece's machining area must be calculated, and the workpiece and tool must be precisely positioned.

[0004] To calculate the machining area after polygon machining, the position of the tool axis (the position of the blade tip) must first be determined before the polygon machining begins. If the position of the blade tip is unknown, a preparatory step, such as aligning the blade tip with the center of the machining area, is required before starting the polygon machining.

[0005] As a method for setting the position of the corners of a polygon, Japanese patent publication JP H04-164557A describes that “when machining a polygonal shape of a workpiece, machining is started from a setting position of the workpiece by moving the tool position from the machining start position of the workpiece by a difference of positional deviations obtained by dividing the command speeds for two main axes by respective position loop gains, starting operation of the two main axes, and starting machining after the two main axes have reached the command speed, thereby bringing the corners of the polygonal shape to the setting position of the circumferential surface of the workpiece.”

[0006] However, this technique is used to set the position of the corners of a polygon formed by polygon machining, and is not suitable for positioning a tool and a workpiece during additional machining after polygon machining.

[0007] From DE 602 01 556 T2, a method for determining the position of movement of at least one workpiece or tool in a machine tool is known. In this method, the contour of the desired workpiece shape is divided into a plurality of machining units after machining, arrival times for each turning point are calculated based on machining speed data, and the rotational angular position of the workpiece is determined as an accumulated count for each turning point, corresponding to the arrival time. BRIEF SUMMARY OF THE INVENTION

[0008] In the field of machine tools, a technique for detecting the position of a machining surface formed by polygon machining on a workpiece is desired. This problem is solved by a control device with the features of claim 1 and by a control system with the features of claim 11.

[0009] A control device according to one form of the present disclosure is a control device for controlling a machine tool, which has a first axis that rotates a tool and a second axis that rotates a workpiece, rotates the first axis and the second axis and machines the workpiece into a polygon, wherein the control device has a machining data acquisition unit that acquires machining data which changes in connection with the machining of the workpiece, and a position detection unit that detects the position of the machining surface of the workpiece based on the change in the machining data.

[0010] A control system according to one form of the present disclosure is a control system for controlling a machine tool which has a first axis that rotates a tool and a second axis that rotates a workpiece, rotates the first axis and the second axis and machines the workpiece into a polygon, wherein the control system has a machining data acquisition unit that acquires machining data which changes in connection with the machining of the workpiece, and a position detection unit that detects the position of the machining surface of the workpiece based on the change in the machining data. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a hardware layout diagram of a numerical control device in the present embodiment. Fig. Figure 2 is a block diagram of the numerical control device in the present embodiment. Fig. Figure 3 is a diagram showing an example of the change in load moment. Fig. Figure 4 is a block diagram of a numerical control device in the present embodiment. Fig. Figure 5 is a view showing a detection method of a machining surface center detection unit. Fig. Figure 6 is a block diagram of a numerical control device in the present embodiment. Fig. Figure 7 is a view showing a detection method of a machining surface center detection unit. Fig. Figure 8 is a block diagram of a numerical control device in the present embodiment. Fig. Figure 9 is a view showing multiple cutting of a machining surface and the change in the load moment. Fig. 10 is a view that shows program examples that use variables. Fig. Figure 11 is a block diagram of a numerical control device in the present embodiment. Fig. 12 is a view that shows an axis transformation process. Fig. Figure 13 is a block diagram of a numerical control device in the present embodiment. Fig. 14 is a view that shows processing to prevent false detection. Fig. Figure 15 is a flowchart showing the operation of a numerical control device. Fig. 16 is a view that shows the processing of a unit to calculate representative values. Fig. 17 is a program example of the present embodiment. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0011] An embodiment is shown below in which a control device according to the present disclosure is implemented in a numerical control device 100.

[0012] Fig. Figure 1 is a hardware layout diagram of the numerical control device 100 according to one embodiment.

[0013] A CPU 111, with which the numerical control device 100 is equipped according to the present embodiment, is a processor that controls the numerical control device 100 as a whole. The CPU 111 reads system programs stored in a ROM 112 via a bus 120 and controls the entire numerical control device 100 according to this system program. Temporary calculation data and display data, various data entered by an operator via an input unit (not shown), and the like are temporarily stored in a RAM 113.

[0014] A non-volatile memory 114 is formed, for example, by a storage device, a solid-state drive (SSD), or the like, which is supported by a battery (not shown). The non-volatile memory 114 retains its memory state even when the power supply to the numerical control device 100 is switched off. Programs read from an external device 72 via an interface 115, programs entered via an input unit 30, and various data obtained from different units of the numerical control device 100 or from a machine tool or the like (for example, setting parameters obtained from the machine tool, and the like) are stored in the non-volatile memory 114. The programs and the various data stored in the non-volatile memory 114 can be developed in RAM 113 during execution / use.Furthermore, various system programs, such as well-known analysis programs or the like, are pre-written in ROM 112.

[0015] Interface 115 is used to connect the numerical control device 100 and the external device 72. Programs, various parameters, and the like are read from the external device 72. Programs, parameters, and the like stored in the numerical control device 100 can be saved to an external storage medium via the external device 72. A PMC (programmable machine control) 116, using a sequence program stored in the numerical control device 100, uses an I / O unit 117 to input and output signals to a machine tool, a robot, or a device such as a sensor attached to the machine tool or robot, and controls these devices.

[0016] Various data read into the storage device, data obtained as a result of program execution, and the like, etc., are output to a display unit 70 via an interface 118. The input unit 30, which may be an MDI, an operator panel, a touch panel, or the like, transmits commands, data, and the like, based on operator input, to the CPU 111 via an interface 119.

[0017] Axis control circuits 130 for controlling the individual axes of the machine tool receive motion command values ​​from the CPU 111 and output the commands for the axes to servo amplifiers 140. The servo amplifiers 140 receive the commands and drive servo motors 150 to drive the axes with which the machine tool is equipped. Position / speed detectors are integrated into the servo motors 150 of the axes; and position / speed feedback signals from these position / speed detectors are fed back to the axis control circuit 130, thus enabling feedback control of the position / speed. In the hardware configuration diagram of Fig. Figure 1 shows only one axis control circuit 130, one servo amplifier 140, and one servo motor, but these are actually provided in a number corresponding to the number of axes with which the machine tool is equipped as a control object. The function block diagram described below ( Fig. 2) In the control device of the present embodiment, a tool axis driven by a servo motor is shown.

[0018] A spindle control circuit 160 receives a main axis rotation command to a main axis of the machine tool and outputs a spindle speed signal to a spindle amplifier 161. The spindle amplifier 161 receives this spindle speed signal and rotates a spindle motor 162 for the main axis at the commanded rotational speed, thereby driving the workpiece axis. A position encoder 163 is coupled to the spindle motor 162. The position encoder 163 outputs feedback pulses in synchronization with the rotations of the main axis, and these feedback pulses are read by the CPU 11.

[0019] Fig. Figure 2 is a block diagram of the main section of the numerical control device 100, which represents an embodiment of the present disclosure. The numerical control device 100 comprises a program 11, which describes a coordinate system and machining commands for the machine tool, an end command, and the like; a program analysis unit 12, which analyzes the program 11 and generates motion commands for an interpolation unit 13 and axis rotation commands for a spindle control unit 14; the interpolation unit 13, which generates interpolation data, for which an interpolation calculation of a command path for the tool was performed based on the motion commands from the program analysis unit 12, and outputs it to a servo control unit 15; the spindle control unit 14, which rotates the workpiece according to the axis rotation commands from the program analysis unit 12; and the servo control unit 15, which rotates the tool according to the interpolation data.The system comprises a machining data acquisition unit 16, which acquires machining data during polygon machining; a machining data storage unit 17, which stores the machining data acquired by the machining data acquisition unit 16; and a position detection unit 18, which detects the position of a machining surface of the workpiece based on the machining data stored in the machining data storage unit 17. In the present embodiment, the tool is driven by the servo motor 150 and the workpiece axis by the spindle motor 161; however, a configuration in which both axes are driven by servo motors is also possible.

[0020] The machining data acquisition unit 16 acquires machining data during polygon machining. This machining data can include the load torque, machining noise, vibrations, heat, and similar phenomena. When the tool comes into contact with the workpiece, phenomena such as an increase in the load torque, the generation of a specific noise, vibrations of the tool or workpiece, or heating of the contact point, etc., occur. The machining data acquisition unit 16 acquires such machining data, which changes during the execution of the polygon machining process.

[0021] The machining data acquisition unit 16 also acquires the position (angle) of the tool's axis of rotation (a first axis) and the workpiece's axis of rotation (a second axis). The machining data acquisition unit 16 obtains position information for the workpiece's axis of rotation from the position encoder 163 and position information for the tool's axis of rotation from the servo control unit 15. The machining data storage unit 17 stores the machining data acquired by the machining data acquisition unit 16 during polygon machining, along with the position information for the tool axis and the workpiece axis, in a related context.

[0022] With reference to Fig. Section 3 explains how the processing data changes during polygon editing. The following explanation uses the load moment as an example of processing data, but other processing data are also possible.

[0023] In polygon machining, the tool and the workpiece rotate simultaneously. The tool is not necessarily always in contact with the workpiece and performing a cutting action; there is a state in which the tool and workpiece are not in contact (referred to as the "non-cutting state"). Since the tool rotates freely in the non-cutting state, the load torque changes at a low value. When the tool begins cutting the workpiece, that is, when the tool and workpiece come into contact, the load torque increases. The load torque remains high while the tool is cutting the workpiece, and decreases when the tool and workpiece separate, that is, when the cutting process ends.

[0024] The position detection unit 18 detects the position of the workpiece's machining surface based on changes in the value of the machining data. The detection method differs depending on the machining data. If machining noise serves as the machining data, the position of the machining surface is detected based on the noise when the tool and workpiece come into contact, the noise when the tool cuts the workpiece, the noise when the tool is rotating freely, or similar. If vibrations are used as machining data, the position of the machining surface is detected based on the vibrations when the tool and workpiece come into contact, the vibrations when the tool cuts the workpiece, the vibrations when the tool is rotating freely, or similar.When heat is used as machining data, the position of the machining surface is detected based on the heat when the tool and the workpiece come into contact, the heat when the tool cuts the workpiece, or the like.

[0025] The position of the machining surface detected by the position detection unit 18 is stored as detected position 19. The position information of the machining surface stored as detected position 19 constitutes the analysis object of the program analysis unit 12. Since the position detection unit 18 automatically detects the position of the machining surface at the numerical control device 100 of the present embodiment, the numerical control device 100 can automatically acquire the position of the workpiece's machining surface, thus eliminating the need for preparation in which the tool position is set to the workpiece center before polygon machining or additional machining.

[0026] Next, with reference to Fig. 4 explains a numerical control device 100a, which is another form of the present disclosure. A position detection unit 18a of this numerical control device 100 has a cutting start detection unit 21, which detects the start of cutting the machining surface from the machining data, and a machining surface center detection unit 22, which determines the center of the machining surface of the workpiece based on the position of the workpiece axis at the time of detection of the cutting start.

[0027] The cutting start detection unit 21 detects the start of cutting the workpiece based on changes in the machining data. However, the method for detecting the start of cutting differs depending on the machining data described above (load torque, machining noise, vibrations, heat, and the like). Regarding the position of the cutting start, the position (angle) of the workpiece's axis of rotation at the moment of the start of cutting is defined as A.

[0028] Fig. Figure 5 is a view showing a method for calculating an angle α from a position A of the tool's axis of rotation to the start of cutting a workpiece and to the center of the machining surface. If the tool's outer shape (a tool compensation dimension) is defined as R, the workpiece's outer shape (the workpiece diameter before polygon machining) as D, and the tool's cutting dimension as X, a triangle connecting the center of the workpiece's axis of rotation, the center of the tool's axis of rotation, and the starting point of cutting forms a triangle with side lengths R, D, and R + D - X. Since the side connecting the center of the workpiece's axis of rotation and the center of the tool's axis of rotation passes through the center of the workpiece's machining surface, the angle α formed by this side and the side of length D is the difference from the starting point of cutting to the center of the machining surface.

[0029] This angle α can be calculated using the law of cosines as follows: R2=D2+(R+D−X)2−2D(R+D−X)cosα *Cosine law cosα=((R+D−X)2−R2+D2) / (2D(R+D−X)) α=arccos(((R+D−X)2−R2+D2) / (2D(R+D−X))) *Law of Cosines

[0030] The position detection unit 18a adds α to an angle A when detecting the start of the cutting process and determines the center of the machining surface (A + α).

[0031] Next, with reference to Fig. 6 describes a numerical control device 100b, which represents another embodiment of the present disclosure. A position detection unit 18b of this numerical control device 100b comprises the cutting start detection unit 21, which detects the contact of the tool and the workpiece, a cutting end detection unit 23, which detects the separation of the tool and the workpiece, and the machining surface center detection unit 22, which detects the center of the machining surface based on the cutting start position and the cutting end position.

[0032] Fig. Figure 7 shows the procedure by which the position detection unit 18b detects the center of the machining surface. Here, the load moment is used as machining data, and the machining surface of the workpiece is detected based on the workpiece's axis of rotation (hereinafter referred to as the workpiece axis). Since the load acting on the workpiece's axis of rotation is small in the non-cutting state, where the tool and workpiece are not in contact, the load moment changes at a low value. When the workpiece and tool come into contact, the load moment increases, with position A of the workpiece axis at this time being referred to as the cutting start position. When the workpiece and tool are rotated simultaneously and the workpiece is moved away from (released from) the tool, the load moment decreases. Position B of the tool axis at this time is referred to as the cutting end position.Since the machining surface center is located midway between the cutting start position and the cutting end position, the position detection unit 18b determines the center P of the machining surface using the formula below. P=A+(B−A) / 2

[0033] One in Fig. The numerical control device 100c shown in Figure 8 has a function for increasing the accuracy of the machining surface center P by determining representative values. A position detection unit 18c of this numerical control device 100c has a machining surface count detection unit 24, which detects the number of machining surfaces formed on a workpiece, and a representative value calculation unit 25, which calculates representative values ​​of the detected multiple machining surface centers. The numerical control device 100c determines the machining surface center several times and sets its average value as the representative value.

[0034] The cutting start detection unit 21, the cutting end detection unit 23, and the machining surface center detection unit 22 have the same functions as in the aforementioned numerical control device 100b. Therefore, they are designated with the same reference numerals, and their explanation is omitted.

[0035] Fig. Figure 9 shows a view of the state when a tool cuts multiple times. Fig. 9(a) the tool moves along a long axis (the Z-axis) of a workpiece while rotating and performs polygon machining. Fig. Figure 9(c) shows the change in the load moment during polygon machining. During polygon machining, the load moment increases and decreases with each machining surface. The number of faces of the polygon is equal to the number of increases (or decreases) of the load moment while the workpiece axis rotates 360 degrees (completes one revolution). If the load moment increases m times during one revolution of the workpiece axis, the number of faces of the polygon formed at the workpiece axis is m.

[0036] If the number of faces of the polygon is known, the machining data and the machining areas can be correlated. For example, if the number of faces of the polygon is m, the machining of the m faces is repeated starting from the first face. In the present embodiment, the starting cutting position is designated as A. ij , the cutting end position as B ijand the center of the processing area as P ij denoted by the index ij. The index ij denotes the number of revolutions and the number of areas. For example, A 11 the cutting starting position of the first surface during the first revolution, A 12 those of the second surface during the first revolution, ..., and A nm , those of the m-th surface during the n-th rotation. B 11 is the cutting end position of the first surface during the first revolution, B 12 those of the second surface during the first revolution, ..., and B nm those of the m-th surface during the n-th rotation.

[0037] P 11 shows the position of the machining surface center of the first surface during the first revolution, B 12 those of the second surface during the first revolution, ..., and P nm those of the m-th surface during the n-th rotation.

[0038] The representative value calculation unit 25 is determined using the values ​​P 11, ... , P nm The center points of the processing areas detected by the processing area center point detection unit yield representative values ​​(here, average values) of the individual processing area centers. The formula for determining the average values ​​is as follows: Center of machining area P1 (average of the first area) = (P11 + P21 + ... + Pn1) / n Center of machining area P2 (average of the second area) = (P12 + P22 + ... + Pn2) / n ... Center of machining area Pm (average of the m-th area) = (P1m + P2m + ... + Pnm) / n * n = number of revolutions

[0039] In this way, the average value is determined when the workpiece axis has rotated n times (or when machining data for n revolutions is used) by dividing the sum of the center positions of the respective machining surfaces by the number n of revolutions.

[0040] Besides the average value, a statistical measure such as the median or the most frequent value can also be used as a representative value. Since the accuracy increases with the depth of the cut, it is also possible to use data from after a certain number of times instead of the first detected edits. It is also possible to weight the edit data.

[0041] As in Fig. As shown in Figure 9(b), there is also a machining operation in which the cutting depth in the X-axis direction is cut several times while the Z-axis is fixed, and the cutting depth gradually increases. In such a machining operation, the machining surface center can also be detected several times, and a representative value of the detected machining surface center can be calculated.

[0042] The numerical control device 100c from Fig. Item 8 stores the values ​​of the machining surface centers as detection values. In this example, the positions of the machining surface centers P1 to P6 of the first to sixth faces of the hexagon formed on the workpiece surface are stored in variables #3301 to #3306. Storing this data in variables allows a program to reference the automatically detected positions of the machining surfaces and use them in additional processing after polygon machining.

[0043] Fig. Example 10 is an example of programs that use variables. In program example 1, the C-axis is moved to #3301 (the center of surface P1) using "G00 C#3301" and surface P1 is positioned accordingly; using "G00 C#3304", the C-axis is moved to #3304 (the center of surface P4) and surface P4 is positioned accordingly; and using "G00 C#3305 + 30,0)", the C-axis is moved to a position for which 30 degrees have been added to #3305 (the center of surface P5) and surface P5 is positioned accordingly.

[0044] Program example 2 of Fig. 10 generates positioning-specific commands P1, P2, ..., Pm. The commands P1, P2, ..., Pm correspond to the center positions P1, P2, ..., Pm of the machining surfaces. "G00 C00 P1" moves the C-axis to the center of surface P1 and positions it on surface P1; "G00 C00 P4" moves the C-axis to the center of surface P4 and positions it; and "G00 C00 P5 Q30,0" moves the C-axis to a position where 30 degrees have been added to the center of surface P5 and positions surface P5 + 30 degrees.

[0045] Then, with reference to Fig. 11 describes a numerical control device 100d according to another embodiment of the present disclosure. A position control unit 18d of this numerical control device 100d comprises an axis conversion unit 26 that converts the position of the tool axis into the position of the workpiece axis. In this example, the axis conversion unit 26 performs an axis conversion operation from a cutting surface center P' of the tool axis to a machining surface center P'' of the workpiece axis. The cutting surface center P' of the tool axis is the position (angle) of the midpoint between the position (angle) at which the tool started cutting and the position (angle) at which it finished cutting. A cutting surface center detection unit 27 detects the cutting start position and the cutting end position using the machining data.The detection method is the same as for the machining surface center detection unit 22 from . Fig. 6.

[0046] The formulas for determining the cutting edges P' are given below. 11 to P' 22 shown for two revolutions of the tool. Here, the cutting start position of the tool is defined by A'. 1k , the cutting end position through B' 1k and the cutting surface center through P'' 1k expressed. The index 1k The number of revolutions (1) and the machined cutting area (k) are specified. The cutting centers can also be determined in the same way for two or more revolutions. P11'=A11'+(B11'−A11') / 2P12'=A12'+(B12'−A12') / 2P13'=A13'+(B13'−A13') / 2 P21'=A21'+(B21'−A21') / 2P22'=A22'+(B22'−A22') / 2P23'=A23'+(B23'−A23') / 2

[0047] The axis conversion unit 26 performs (1) a conversion of the number of revolutions and the cutting area (the machining area) and (2) a conversion of the position (the angle).

[0048] (1) When converting the number of revolutions and the cutting area (machining surface), the number 1 of revolutions of the tool axis is converted into a number j of revolutions of the workpiece axis, and the cutting area k of the tool axis is converted into a machining area i of the workpiece axis. In polygon machining, the relationship between the tool axis and the workpiece axis is given by (number 1 of revolutions of the tool axis) × (number h of cuts per revolution) + (cutting area k of the tool axis) = (number m of machining surfaces) × (number j of revolutions of the workpiece axis) + (machining area i of the workpiece axis).Since the rotation ratio of the tool axis and the workpiece axis is constant, and the number h of cuts per revolution of the tool axis is equal to the number of cutting edges of the tool, then, if the number of revolutions of the tool axis and the cutting area k of the tool are determined, it is possible to convert them into the number j of revolutions of the workpiece axis and the cutting area i of the workpiece. (2) In the conversion of position (angle), the position of the workpiece axis relative to the position of the tool axis is calculated using the rotation ratio of the tool axis and the workpiece axis. For example, if the rotation ratio of the tool axis and the workpiece axis is R : S, the degree of rotation of the workpiece axis is determined by multiplying the position (angle) of the tool axis by S / R.If the initial phase difference θ between the tool axis and the workpiece axis is added to this value, a conversion from the position of the tool axis to the position of the workpiece axis is possible.

[0049] Since the rotation ratio of the tool axis and the workpiece axis in the example of Fig. If the ratio is 12 2 : 1, then S / R becomes 1 / 2 and the conversion formula is as follows. In this example, the machining data for two revolutions of the tool axis is converted into machining data for one revolution of the workpiece axis. In this example, the machining center position of the tool axis was converted into the machining center position of the workpiece axis, but the cutting start position A' and the cutting end position B' of the tool axis can also be converted into the cutting start position and the cutting end position of the workpiece axis. P11"=θ+P11' / 2P12"=θ+P12' / 2P13"=θ+P13' / 2P14"=θ+P21' / 2P15"=θ+P22' / 2P16"=θ+P23' / 2

[0050] In the formula of Fig. 12(c) The machining surface center Pi is determined after n rotations of the workpiece. The machining surface center Pi is the average of the machining surface centers P detected from the machining data of the workpiece axis. ij and the center of the machining area P'' ij , for which the cutting surface center P' ij The tool axis was converted into the workpiece axis. The formula for calculating the average is as follows (n is the number of revolutions of the workpiece axis). Center of machining area P1 (first surface) = (P11 + ... + Pn1 + P11" + ... + Pn1) / 2n Center of machining area P2 (second surface) = (P12 + ... + Pn2 + P12" + ... + Pn2) / 2n ...

[0051] Here, the average of the sum of the machining surface centers P detected from the machining data of the workpiece axis is calculated.ij and the center of the machining area P'' ij , for which the cutting surface center P' ij The tool axis was converted into the workpiece axis, but the average of one of them can also be calculated.

[0052] Next, with reference to Fig. 13 describes a numerical control device 100e, which is another embodiment of the present disclosure. A cutting start detection unit 21e and a cutting end detection unit 23e of this numerical control device 100e perform processing operations to prevent false detection.

[0053] Fig. Figure 14 shows the processing to prevent false detection when using the load torque as processing data. The numerical control device 100e defines two values: a non-contact state level (L1) and a contact state detection level (L2).

[0054] The non-contact state level (L1) is, for example, the average value of the load torque in the non-contact state (the average load torque from reaching a certain number of revolutions until the start of cutting).

[0055] The cutting state level (L2) is a load torque threshold used to determine whether the tool is in the cutting state or not. For example, the cutting state level (L2) is a value for which a specific value a has been added to the non-contact state level (L1), resulting in a load level of b% of the non-cutting state level (L1). The cutting state level (L2) can be an actual value determined from real-world machining data. The cutting state level (L2) can also be a suitable value to prevent false detection.

[0056] The cutting start detection unit 21e detects an angle Aa of the workpiece axis when the load moment reaches the cutting state level (L2), and an angle Ab of the workpiece axis when the load moment reaches the non-cutting state (L1) before Aa. The cutting start detection unit 21e classifies the displacement of the load moment between Aa and Ab into two patterns: pattern 1-1 and pattern 1-2. In pattern 1-1, the load moment increases and decreases between angles Aa and Ab. In this case, the angle at which the load moment changes from negative to positive is selected as the cutting start angle A. In pattern 1-2, the load moment increases monotonically between angles Aa and Ab. In this case, the angle Ab at which the load moment reaches the non-cutting level (L1) is selected as the cutting start angle A.

[0057] The cutting edge detection unit 23e observes the load moment and detects an angle Ba when the load moment has decreased to the cutting state level (L2), and an angle Bb when it has reached the non-cutting level (L1) after Ba. The cutting edge detection unit 23e classifies the displacement of the load moment between Ba and Bb into two patterns: pattern 2-1 and pattern 2-2. In pattern 2-1, the load moment increases and decreases between angles Ba and Bb. In this case, the angle at which the load moment changes from positive to negative is chosen as the cutting edge angle B. In pattern 2-2, the load moment decreases monotonically between angles Ba and Bb. In this case, the angle Bb at which the load moment reaches the non-cutting level (L1) is chosen as the cutting edge angle B.

[0058] The fluctuation that occurs when the tool and workpiece come into contact and separate can lead to false detection. Since the cutting start detection unit 21e and the cutting end detection unit 23e classify the patterns of change in machining data that can occur during contact and separation, and select the detected values ​​according to these patterns, false detection can be prevented.

[0059] Next, with reference to Fig. 15 explains the operation of the numerical control device 100c.

[0060] The numerical control device 100e performs polygon machining. The machining data acquisition unit 16 acquires the machining data (here, the load torque) of the machine tool representing the controlled object and the position of the workpiece axis (or the tool axis) at that time. The machining data storage unit 17 stores the machining data in a state in which it has been correlated with the position of the workpiece axis (step S1).

[0061] The cutting start detection unit 21 of the position detection unit 18c detects an angle At of the cutting start from the machining data stored in the machining data storage unit 17. The cutting end detection unit 23 detects an angle Bt of the cutting end (step S2) from the machining data stored in the machining data storage unit 17. Here, t is the number of detections of angle A or angle B.

[0062] The machining surface center detection unit 22 detects a center angle Dt of the machining surface based on the angle At of the cutting start and the angle Bt of the cutting end. The formula for detecting the machining surface center is Dt = At ​​+ (Bt - At) / 2 (step S3).

[0063] The machining surface count detection unit 24 calculates the number of machining surface centers detected within the range of a first revolution (0 to 360 degrees) of the workpiece axis. The number of machining surface centers Dt detected during one revolution corresponds to the area m of the machining surfaces (step S4).

[0064] The representative value calculation unit 25 converts the value of the machining area center Dt into Pij. The subscript i of Pij indicates the number of revolutions, and the subscript j indicates the machining area. Fig. 16(b) shows the state of the conversion of Dt to Pij.

[0065] Since D1 to Dm relate to the first revolution, they are converted to P11 to P1m; since Dm+1 to Dm+m relate to the second revolution, they are converted to P21 to P2m; and since D(n-1)*m to Dn*m relate to the nth revolution, they are converted to Pn1 to Pnm (step S5).

[0066] The representative value calculation unit 25 classifies the machining area centers Dt according to the number of revolutions and the machining areas and then calculates the average values ​​of the machining area centers. Fig. 16(c) is the formula for calculating the average values ​​of the cultivation area centers. The average values ​​Pj of the cultivation areas are determined by calculating the sum of P ij determined with the same index j and divided by the number n of revolutions.

[0067] The calculated values ​​P1, ..., Pm are stored as detection values ​​(step S6).

[0068] Fig. 17 shows a program example, whereby the execution program of Fig. The operation shown in Figure 15 is performed on a machine tool. In this program, after positioning the tool axis using "G00X100.0Z20.0S1000M03", the polygon machining process is initiated by "G51.2 P1 Q2". The X-axis is cut by "G01X80.0F10.0", a two-second pause is initiated by "G04X2.0", the X-axis is retracted by "G00S100.0", the polygon machining is terminated by "G50.2", and then the workpiece axis is stopped by "S0M05". This process corresponds to step S1 of the flowchart. Based on the machining data collected here, the numerical control device 100 detects the machining surface centers and stores the detection results in the variables (here, #3301 to #330m).

[0069] This program then commands additional machining after the completion of the polygon machining. At "T2", the machine tool selects the tool (a drill) for the additional machining. "G00X50.0" positions the tool axis. The command "G83C#3301X-40.0F5.0" positions the C-axis (the workpiece axis) at '#3301', that is, at the center of the machining surface P1, and performs a drilling operation at the center of the machining surface from the X-axis. Similarly, "C#3302" performs a drilling operation at variable '#3302', that is, at the center of the machining surface P2. "C[#3305 + 30.0]" performs the drilling operation at variable '#3305', that is, in a surface inclined at 30 degrees from the center of the machining surface P5. At "G80M5", the defined cycle is stopped, and the main axis is stopped. Finally, the program terminates at "M30".If the position of the processing area center is stored in variables in this way, the processing of polygon editing and additional editing can be described in a single program.

[0070] Since the numerical control devices 100 to 100e in the present embodiment acquire the data during polygon machining in this way and detect the positions of the machining surfaces formed on the workpiece based on this data, positioning of the workpiece using the detected position information is possible. Therefore, a preparatory activity such as setting the position of the tool's blade tip to the workpiece center becomes unnecessary.

Claims

[1] Control device (100) for controlling a machine tool which has a first axis which rotates a tool and a second axis which rotates a workpiece, and is configured to rotate the first axis and the second axis and to machine the workpiece into a polygon, wherein the control device (100) comprises: a machining data acquisition unit (16) that acquires machining data which changes according to the machining of the workpiece; and a position detection unit (18) which detects the position of a machining surface of the workpiece based on the change in the machining data. [2] Control device (100) according to claim 1, wherein the position detection unit (18) detects a center of the machining surface of the workpiece. [3] Control device (100) according to claim 1, wherein the position detection unit (18) detects contact between the workpiece and the tool by changing the machining data and detects the position of the machining surface of the workpiece based on at least one of the position of the first axis and the position of the second axis at the time of detection of the contact. [4] Control device (100) according to claim 3, wherein the position detection unit (18) detects a separation of the workpiece and the tool from each other by a change in the machining data and detects the position of the machining surface of the workpiece on the basis of at least one of the position of the first axis and the position of the second axis at the time of contact of the workpiece and the workpiece and at least one of the position of the first axis and the position of the second axis at the time of separation of the workpiece and the workpiece. [5] Control device (100) according to claim 3, wherein the position detection unit (18) detects the midpoint between the position of the second axis at the time of contact of the workpiece and the tool and the position of the second axis at the time of separation of the workpiece and the tool as the midpoint of the machining surface. [6] Control device (100) according to claim 2, wherein the position detection unit (18) detects the center of the machining surface based on at least one of the position of the first axis and the position of the second axis at the time of detection of contact of the tool with the workpiece and a cutting dimension of the tool in relation to the workpiece. [7] Control device (100) according to claim 1, wherein the machining data acquisition unit (16) acquires data of multiple contacts of the workpiece and the tool and the position detection unit (18) detects the position of the workpiece using all or part of the positions of at least one of the positions of the first axis and the positions of the second axis at the times of the multiple contacts. [8] Control device (100) according to claim 1, wherein the machining data acquisition unit (16) detects data of the separation of the workpiece and the tool from each other several times and the position detection unit (18) detects the position of the workpiece using all positions or a part of the positions of at least one from the first axis and the second axis at the time of detection of the separation. [9] Control device (100) according to claim 1, comprising a machining surface number detection unit (24) which calculates the number of times the machining data changes during one revolution of the second axis and detects the number of machining surfaces formed on the workpiece. [10] Control device (100) according to claim 1, comprising an axis position conversion unit (26) which, based on a rotation ratio of the first axis and the second axis, converts a position of the first axis into a position of the second axis or converts a position of the second axis into a position of the first axis. [11] Control system for controlling a machine tool which has a first axis which rotates a tool and a second axis which rotates a workpiece, rotates the first axis and the second axis and machines the workpiece into a polygon, wherein the control system a machining data acquisition unit (16) that acquires machining data which changes in connection with the machining of the workpiece, and a position detection unit (18) which detects the position of a machining surface of the workpiece based on the change in the machining data, exhibits.

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