Numerical control device, and storage medium

Abstract

This numerical control device is for controlling a work machine having at least a first shaft and a second shaft. The numerical control device controls the synchronization of the first shaft and the second shaft of the work machine; acquires a cutting start position for a tool of the work machine; stores tool information being information relating to the tool; calculates a monitoring start position obtained by correcting the cutting start position on the basis of a tool shape included in the tool information; and begins monitoring a synchronization error between the first shaft and the second shaft when the tool of the work machine reaches or approaches the monitoring start position.

Description

Technical Field

[0001] The present invention relates to a numerical control device and a storage medium.

Background Art

[0002] Conventionally, there is a machining method for synchronizing a first axis and a second axis. For example, in tapping, a screw hole is formed while synchronizing so that the speed ratio between the main shaft and the feed shaft is constant.

[0003] Patent Document 1 describes that "since the deviation error amounts of the feed shaft deviation and the main shaft deviation are detected, and when the value becomes equal to or greater than a predetermined value, it is determined that there is an abnormality and the output of the compensation signal is stopped, it is possible to surely prevent tool breakage and thread collapse due to the deviation of synchronization between the main shaft and the feed shaft."

[0004] When forming a screw hole by the method shown in Patent Document 1, (1) first, a hole is drilled with a drill, (2) the drill is replaced with a tap, (3) the tap is moved to the R point at a rapid feed, (4) a screw is formed on the inner surface of the hole, and (5) the tap is withdrawn while rotating in the reverse direction. As described above, in forming a screw hole, it is necessary to synchronize the rotational speed of the main shaft and the feed speed in order to make the pitch of the thread constant. In conventional tapping, there are a method of temporarily stopping the movement of the main shaft at the R point to synchronize and a method of synchronizing without performing axis stop at the R point. When synchronizing after temporarily stopping, synchronization accuracy can be ensured, but it takes time for the main shaft to stop and restart. When starting synchronization control without performing axis stop at the R point, the cycle time can be shortened.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, if the axis stop is not performed at the R point, there is an error amount due to the operation immediately before reaching the R point. Therefore, when starting the monitoring of the synchronization error at the R point, the error amount due to the operation immediately before reaching the R point may be misrecognized as the synchronization error. If the allowable error is increased to cope with this, the error detection accuracy during the screw hole formation will decrease.

[0007] In the field of machining, a technique for shortening the cycle time while ensuring the accuracy of multi-axis control is desired.

Means for Solving the Problems

[0008] A numerical control device according to an aspect of the present disclosure is a numerical control device that controls a machine tool including at least a first axis and a second axis, and includes a synchronization control unit that controls the synchronization of the first axis and the second axis, a cutting start position acquisition unit that acquires a cutting start position by a tool of the machine tool, a tool information storage unit that stores tool information which is information about the tool of the machine tool, and a monitoring start position correction unit that calculates a monitoring start position obtained by correcting the cutting start position based on The length between the tip of the tool and the portion where thread cutting by the tool starts and a synchronization error monitoring unit that starts monitoring the synchronization error at or near the monitoring start position of the tool of the machine tool. A computer-readable storage medium according to an aspect of the present disclosure stores computer-readable instructions that, when executed by one or more processors, control the synchronization of the first axis and the second axis of a machine tool, acquire a cutting start position by a tool of the machine tool, store tool information which is information about the tool, calculate a monitoring start position obtained by correcting the cutting start position based on The length between the tip of the tool and the portion where thread cutting by the tool starts and start monitoring the synchronization error between the first axis and the second axis when the tool of the machine tool reaches or approaches the monitoring start position.

Advantages of the Invention

[0009] According to one aspect of the present invention, it is possible to shorten the cycle time while ensuring the accuracy of multi-axis control.

Brief Description of the Drawings

[0010]

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Mode for Carrying Out the Invention

[0011] Referring to FIG. 1, the hardware configuration of the numerical control device 100 that controls the machine tool 200 will be described. The CPU 111 included in the numerical control device 100 is a processor that controls the entire numerical control device 100. The CPU 111 reads out the system program processed in the ROM 112 via the bus, and controls the entire numerical control device 100 according to the system program. In the RAM 113, temporary calculation data, display data, various data input by the user via the input unit 71, etc. are temporarily stored.

[0012] The display unit 70 is a monitor or the like attached to the numerical control device 100. The display unit 70 displays the operation screen, setting screen, etc. of the numerical control device 100.

[0013] The input unit 71 is integrated with the display unit 70 or is a separate keyboard, touch panel, etc. from the display unit 70. The user operates the input unit 71 to input to the screen displayed on the display unit 70. Note that the display unit 70 and the input unit 71 may be a mobile terminal.

[0014] The non-volatile memory 114 is a memory that retains the storage state even when the power of the numerical control device 100 is turned off, for example, by being backed up by a battery (not shown). In the non-volatile memory 114, programs read from external devices via an interface (not shown), programs input via the input unit 71, and various data (for example, setting parameters obtained from the machine tool 200) obtained from each part of the numerical control device 100 and the machine tool 200 are stored. The programs and various data stored in the non-volatile memory 114 may be expanded to the RAM 113 during execution / use. Also, various system programs are pre-written in the ROM 112.

[0015] A controller 40 that controls a machine tool 200 converts a shaft movement command from a CPU 111 into a pulse signal and outputs it to a driver 41. The driver 41 converts the pulse signal into a current to drive a servo motor of the machine tool 200. The servo motor moves a tool according to the control of the numerical control device 100. In the present disclosure, the machine tool 200 has at least two axes of rotation and feed.

[0016] [First Disclosure] FIG. 2 is a block diagram of a numerical control device 100 according to the first disclosure. The numerical control device 100 performs synchronous control of a plurality of axes. In this machine tool 200, cutting is performed while maintaining the synchronization of the first axis and the second axis.

[0017] The numerical control device 100 includes a synchronous control unit 11 that performs synchronous control of axes, a synchronous error monitoring unit 12 that monitors the synchronous error of axes, a cutting start position acquisition unit 13 that acquires the cutting start position of a tool and a workpiece, a tool information storage unit 14 that stores tool information such as the tool shape, and a monitoring start position correction unit 15 that corrects the cutting start position based on the tool information.

[0018] The synchronous control unit 11 controls the synchronization of the axes of the machine tool 200 according to the synchronous conditions. The synchronous control unit 11 calculates the movement amount of the second axis by multiplying the movement amount of the first axis for each control cycle by a synchronous ratio defined by the synchronous conditions. Then, based on the movement amount of the first axis and the calculated movement amount of the second axis, the servo motors that drive the first axis and the second axis are controlled.

[0019] The synchronous error monitoring unit 12 stores a preset threshold value. The synchronous error monitoring unit 12 receives the position deviation of the first axis and the position deviation of the second axis. The position deviation is the difference between the actual position and the command. The synchronous error monitoring unit 12 calculates the synchronous error based on this position deviation. The synchronous error monitoring unit 12 compares the synchronous error with the threshold value, and if the synchronous error exceeds the threshold value, it determines that a synchronous error has occurred. In the present disclosure, the monitoring of the synchronous error is started at or near the monitoring start position described later.

[0020] The cutting start position acquisition unit 13 acquires the position of the tool when starting the cutting of the workpiece. The position includes the positional distance and the positional time. There are a method of detecting from the load torque and a method of estimating from drawings or the like as methods for acquiring the cutting start position. In the method of detecting the cutting start position from the load torque, the change in the load torque is monitored, and the position where the load torque rises is determined as the position where the cutting of the tool and the workpiece starts. When cutting the same surface multiple times, the rise of the load torque in front is determined as the cutting start position. In the method of estimating the cutting start position from drawings or the like, for example, the operator inputs the estimation result as a parameter to the numerical control device 100 or describes it in the machining program.

[0021] The monitoring start position correction unit 15 obtains the monitoring start position of the synchronization error based on the tool information and the cutting start position. The tool information includes the shape information of the tool. The monitoring start position correction unit 15 corrects the deviation of the cutting start position due to the tool shape. The position corrected based on the tool information is called the monitoring start position.

[0022] The synchronization control unit 11 starts synchronization control when the tool reaches the R point. The synchronization error monitoring unit 12 starts monitoring the synchronization error when the tool reaches the monitoring start position or its vicinity. By performing synchronization control from the R point to the monitoring start position, the synchronization error becomes sufficiently small. Since the monitoring of the synchronization error is started when the synchronization error becomes sufficiently small, the threshold value can be set small. By setting the threshold value small, the synchronization accuracy is improved.

[0023] The synchronization control of the first disclosure will be described with reference to the flowchart of FIG. 3. The numerical control device 100 acquires the cutting start position (step S1). The cutting start position can be acquired from information such as the load torque of the tool and the drawing. The numerical control device 100 calculates the monitoring start position obtained by correcting the deviation of the cutting start position due to the tool shape based on the cutting start position and the tool information (step S2).

[0024] The numerical control device 100 reads a machining program and moves the tool of the machine tool 200 to the position described in the machining program. The numerical control device 100 moves the tool at rapid feed to the R point (step S3), and moves it at cutting feed after passing the R point. When the tool passes the R point, the numerical control device 100 starts synchronous control of the first axis and the second axis (step S4).

[0025] When the tool reaches the monitoring start position or its vicinity (step S5), the numerical control device 100 starts monitoring the synchronization error (step S6). The numerical control device 100 performs cutting while monitoring the synchronization error (step S7).

[0026] As described above, the numerical control device 100 of the first disclosure is a numerical control device 100 that performs cutting while maintaining synchronization of at least two axes, the first axis and the second axis, calculates a monitoring start position obtained by correcting the cutting start position based on the tool shape, and starts monitoring the synchronization error from the monitoring start position.

[0027] The synchronization error is large at the R point where the feed changes from rapid feed to cutting feed, and gradually converges after passing the R point. Since the synchronization deviation from the R point until the start of cutting does not affect the cutting accuracy, monitoring is not necessary.

[0028] The numerical control device 100 of the present disclosure starts monitoring the synchronization error at the monitoring start position where cutting starts. Thereby, without detecting unnecessary synchronization deviation, the threshold value of the synchronization error can be set to an appropriate value, and necessary synchronous control can be ensured. Further, since the tool is shifted to cutting feed without stopping at the R point, the cycle time can be shortened.

[0029] [Second Disclosure] The numerical control device 100 of the second disclosure will be described using rigid tapping as an example. The rigid tapping will be described as a premise. In rigid tapping, a pilot hole is formed with a drill, and a thread is formed on the inner surface of the pilot hole. In the example of FIG. 4, the rigid tap moves from point I (starting point) to point R at rapid feed, and (2) switches to cutting feed at point R. During cutting feed, synchronous control is performed between the feed axis in the Z-axis direction and the rotation of the spindle. While maintaining synchronization, a thread is formed on the inner surface of the counterbore. When cutting is completed, (3) the rigid tap returns to point R while rotating in the reverse direction, and (4) moves at rapid feed after passing point R.

[0030] FIG. 5 is a block diagram of the numerical control device 100 of the second disclosure. The numerical control device 100 of the second disclosure includes a synchronization control unit 11 that performs axis synchronization control, a synchronization error monitoring unit 12 that monitors axis synchronization errors, a cutting start position acquisition unit 13 that acquires the cutting start positions of the tool and the workpiece, a tool information storage unit 14 that stores tool information such as tool shapes, a monitoring start position correction unit 15 that corrects the cutting start position based on the tool information, and a tool determination unit 16 that determines the tool to be used for cutting.

[0031] The synchronization control unit 11 controls the synchronization between the first axis and the second axis of the machine tool according to the machining program. In the second disclosure, the first axis and the second axis are the spindle and the Z-axis. FIG. 6 is an example of a machining program. "G84 Zxx Rxx;" is a command for tapping machining. "Zxx" is the distance from point R to the bottom of the hole, and "Rxx" is the distance from the initial level to point R. The synchronization control unit 11 starts synchronization control when it reaches point R.

[0032] The cutting start position acquisition unit 13 detects the position of the surface of the workpiece based on the load torque of the drill during counterbore formation. FIG. 7 shows the change in the load torque during counterbore formation. When the drill moves to the workpiece and the tip of the drill contacts the workpiece, the load torque rises. The cutting start position acquisition unit 13 monitors the load torque of the spindle and detects the cutting start position of the tool.

[0033] The tool information storage unit 14 stores the tool shapes of multiple types of tools. In FIG. 8, the shapes of two rigid taps are stored. The tool information describes, for example, the length of the biting part of the rigid tap. In the rigid taps of FIG. 8, the lengths of the biting parts are different.

[0034] The tool determination unit 16 analyzes the machining program and determines the tool to be used in machining. In the machining program of FIG. 6, the tool determination unit 16 determines which tool to use based on the code "T1" for tool selection. In the second disclosure, "T1" indicates the type of rigid tap.

[0035] Based on the determination result of the tool determination unit 16, the monitoring start position correction unit 15 reads tool information and corrects the deviation of the cutting start position due to the tool shape. The tool information describes the correction method for the cutting start position for each tool. The monitoring start position correction unit 15 calculates, according to the tool information, the position advanced by the length of the biting portion from the cutting start position as the monitoring start position.

[0036] FIG. 9 shows the relationship among the R point, the cutting start position, and the monitoring start position of the synchronization error. The cutting start position is the cutting start position during the formation of the pilot hole by the drill. A biting portion is formed at the tip of the rigid tap. The monitoring start position of the synchronization error is at the position advanced by the length of the biting portion of the rigid tap. The corrected cutting start position becomes the monitoring start position of the synchronization error.

[0037] With reference to FIGS. 10 and 11, the relationship between the change in the synchronization error and the threshold value in the conventional numerical control device will be described. FIG. 10 shows the change in the synchronization error in the conventional numerical control device. The synchronization error changes significantly negatively at the R point and converges to near zero before starting cutting. In the conventional numerical control device, since the synchronization error is monitored from the R point, the error detection threshold (allowable error) is set sufficiently large so that this large synchronization error is not determined as an error (see FIG. 11). However, when the threshold value is set large, there may be a case where an error affecting the accuracy during cutting cannot be detected.

[0038] FIG. 12 shows the change in the synchronization error in the numerical control device 100 of the present disclosure. Since the numerical control device 100 does not monitor the synchronization error from the R point to the monitoring start position, the synchronization error on the graph is zero. At the monitoring start position, the synchronization error is sufficiently converged. In the numerical control device 100 of the present disclosure, in order to start monitoring the synchronization error from the monitoring start position where the synchronization error has sufficiently converged (see FIG. 13), it is not necessary to set a large threshold value, and an appropriate threshold value can be set to improve the determination accuracy of the synchronization error.

[0039] In the numerical control device 100 of the present disclosure, by starting the monitoring of the synchronization error at the position where cutting starts or in the vicinity thereof, the threshold value for determining the synchronization error can be appropriately set. Further, since the tool is shifted to the cutting feed without stopping at the R point, the cycle time can be shortened.

[0040] The numerical control device 100 of the second disclosure includes a tool determination unit 16. The numerical control device 100 determines the tool to be used based on a machining program or the like and reads out tool information. The tool information describes a correction program for the monitoring start position for each tool. Even when there are a plurality of tools to be used, the numerical control device 100 can automatically determine the tool to be used for cutting and correct the monitoring start position according to the shape of the tool.

[0041] [Third Disclosure] The numerical control device 100 of the third disclosure will be described using a drill tap as an example. The drill tap machining will be described as a premise. A drill tap is a tool that can perform drilling and threading simultaneously. FIG. 14 shows an example of a drill tap. The tip of the drill tap is provided with a drilling portion, and a threading portion is provided following the drilling portion.

[0042] The length of the drilling portion of the drill tap of the third disclosure corresponds to the length of the biting portion of the rigid tap of the second disclosure. The drill tap starts synchronous control at the R point, and as shown in FIG. 15, cutting starts when the tip of the drilling portion contacts the workpiece. The numerical control device 100 can detect that the tip of the drilling portion has contacted the workpiece from the load torque. This position is set as the cutting start position. When the spindle is rotated and moved downward along the Z-axis, the drilling part forms a pilot hole. Then, the threading part forms a thread on the inner surface of the pilot hole. The tip position of the tool at the start of threading is the monitoring start position. When the thread is formed up to a predetermined position, the drill tap moves upward while rotating in the reverse direction.

[0043] The numerical control device 100 of the third disclosure has the same configuration as the numerical control device 100 of the second disclosure. Hereinafter, the differences from the numerical control device 100 of the second disclosure will be described.

[0044] The synchronization control unit 11 controls the synchronization of the first axis and the second axis of the machine tool 200. In the third disclosure, the first axis and the second axis are the spindle and the Z-axis. "G84 Zxx Rxx;" in FIG. 16 is a command for tapping. "Zxx" is the distance from the R point to the bottom of the hole, and "Rxx" is the distance from the initial level to the R point. The synchronization control unit 11 starts synchronization control when it reaches the R point.

[0045] The tool determination unit 16 analyzes the machining program and determines the type of tool used for machining. FIG. 16 is an example of a machining program. The tool determination unit 16 determines the type of tool based on the code "T1" for tool selection. In the third disclosure, "T1" indicates a drill tap.

[0046] The tool information storage unit 14 stores the method for obtaining the cutting start position for each tool, the method for calculating the monitoring start position, and the like.

[0047] The cutting start position acquisition unit 13 acquires the cutting start position according to the tool information by a method corresponding to the shape and type of the tool. In the case of a drill tap, the position where the tip contacts the workpiece is the cutting start position.

[0048] The monitoring start position correction unit 15 corrects the cutting start position based on the tool shape and uses it as the monitoring start position for the synchronization error. The monitoring start position is the position advanced by the length of the drilling part from the cutting start position. The monitoring start position correction unit 15 adds the length of the drilling part to the cutting start position to calculate the monitoring start position for the synchronization error.

[0049] The numerical control device 100 of the third disclosure reads the tool information of the drill tap and determines the monitoring start position of the synchronization error. According to the second disclosure and the third disclosure, it is possible to determine the tool used for machining and obtain the cutting start position and the monitoring start position according to the tool information.

Explanation of Signs

[0050] 100 Numerical control device 11 Synchronization control unit 12 Synchronization error monitoring unit 13 Cutting start position acquisition unit 14 Tool information storage unit 15 Monitoring start position correction unit 16 Tool determination unit 111 CPU 112 ROM 113 RAM 114 Non-volatile memory

Claims

1. A numerical control device for controlling a machine tool having at least a first axis and a second axis, a synchronization control unit for controlling the synchronization of the first axis and the second axis, a cutting start position acquisition unit for acquiring a cutting start position by a tool of the machine tool, a tool information storage unit for storing tool information which is information about the tool of the machine tool, a monitoring start position correction unit for calculating a monitoring start position obtained by correcting the cutting start position based on the length between the tip of the tool included in the tool information and the portion where thread cutting by the tool starts, a synchronization error monitoring unit for starting monitoring of a synchronization error at or near the monitoring start position of the tool of the machine tool, A numerical control device comprising.

2. Comprising a tool determination unit for determining a tool to be used for cutting, the tool information storage unit stores tool information of at least two tools, The numerical control device according to claim 1, wherein the monitoring start position correction unit reads out the tool information determined by the tool determination unit from the tool information storage unit and calculates the monitoring start position.

3. The tool information includes a method for acquiring a cutting start position, The numerical control device according to claim 1, wherein the cutting start position acquisition unit acquires a cutting start position according to the acquisition method.

4. The first axis is a main axis, and the second axis is a feed axis in the axial direction of the main axis, the synchronization control unit controls the synchronization between the rotation of the main axis and the speed of the feed axis, the tool is a tap, The numerical control device according to claim 1, wherein the monitoring start position correction unit calculates the monitoring start position obtained by correcting the cutting start position based on the length between the tip of the tap and the portion where the tap forms a thread.

5. By one or more processors executing, controlling the synchronization of the first axis and the second axis of a machine tool, acquiring a cutting start position by a tool of the machine tool, storing tool information which is information about the tool, calculating a monitoring start position obtained by correcting the cutting start position based on the length between the tip of the tool included in the tool information and the portion where thread cutting by the tool starts, starting monitoring of the synchronization error between the first axis and the second axis when the tool of the machine tool reaches or approaches the monitoring start position, A storage medium storing computer-readable instructions.

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