Control device and control system of machine tool

Abstract

The present invention provides a control device and a control system for a machine tool. In a machine tool performing thread cutting machining, after the tool starts cutting feed, based on the timing when the relative feed speed between the tool and the workpiece reaches the thread cutting feed speed, a thread cutting startable region parallel to the X-axis of the machine tool is set. And, first, the tool is moved in the X-axis direction, and the rotational position of the spindle is monitored. When the thread cutting start angle of the spindle is detected, if the tool is traveling within the thread cutting startable region, the cutting feed of the tool in the Z-axis direction is started.

Description

Technical Field

[0001] The present invention relates to a control device and a control system for a machine tool that performs thread cutting. Background Art

[0002] When performing thread cutting with a machine tool, sometimes the thread cutting is not completed in one operation, but the thread cutting is repeated multiple times while gradually deepening the cut in the X-axis direction to machine one screw. In such thread cutting, during multiple thread cuttings, it is necessary to make adjustments so that the phase of the helical trajectory of the thread does not shift. In existing machine tools, the detection of the one revolution signal of the spindle is awaited, and when the one revolution signal is detected, thread cutting is started, thereby making the phases of the helical trajectories of the threads coincide.

[0003] Figure 11 It is a schematic diagram showing a driving method of an existing tool. The tool first stands by at the driving start position, and according to a control signal from the servo control unit, it moves along the X-axis to the thread cutting depth by rapid traverse. Next, the tool awaits the one revolution signal of the spindle, and at the timing when the one revolution signal is detected, thread cutting feed is started, and the tool is moved in the negative Z-axis direction to perform thread cutting. When the thread cutting is completed, the tool is moved in the positive X-axis direction by rapid traverse to move the tool away from the workpiece and then moved in the positive Z-axis direction to return the tool to the original driving start position. This series of operations is repeated to perform thread cutting.

[0004] The thread cutting device disclosed in Japanese Unexamined Patent Application Publication No. 2006-995 makes the spindle speed when machining an incomplete thread portion shallower than a specified thread groove lower than the spindle speed when machining an effective thread portion of the specified thread groove, and performs control by performing interpolation only on at least the first axis in the axial direction of the spindle and the second axis orthogonal to the first axis, thereby shortening the length of the incomplete thread portion and increasing the spindle speed to shorten the total machining time of the thread cutting.

[0005] In the case of machining one screw by repeating thread cutting multiple times, as Figure 11 shown, the tool repeatedly moves on the same track, but if the cycle time becomes shorter, the machining time of the thread cutting is shortened and the working efficiency is improved. Summary of the Invention

[0006] In view of this, a technique for improving the efficiency of thread cutting is sought.

[0007] A control device according to one aspect of the present invention controls a machine tool. The machine tool includes a first axis that moves a tool along the axial direction of a spindle and a second axis that moves the tool in a direction different from the axial direction of the first axis. The tool is driven by the first axis and the second axis to perform thread cutting on a workpiece mounted on the spindle. Then, the control device includes: a startable thread cutting area determination unit that, after the tool starts cutting feed in the direction of the first axis, determines a startable thread cutting area in the direction of the second axis of the tool based on the timing when the relative feed speed between the tool and the workpiece reaches the thread cutting feed speed; and a thread cutting start timing determination unit that starts the cutting feed of the tool when the position of the tool on the second axis is within the range of the startable thread cutting area.

[0008] The startable thread cutting area determination unit can determine the startable thread cutting area so that when the tool reaches the thread cutting feed speed, the tool reaches the thread cutting depth position.

[0009] The startable thread cutting area determination unit may also narrow the range of the startable thread cutting area so that the tool reaches the thread cutting depth position before reaching the thread cutting feed speed.

[0010] The startable thread cutting area determination unit may also expand the range of the startable thread cutting area when the tool reaches the thread cutting feed speed near the workpiece.

[0011] The control device may further include a rotational position detection unit that detects the rotational position of the spindle. The thread cutting start timing determination unit starts driving the tool when the rotational position detection unit detects a predetermined rotational position.

[0012] The startable thread cutting area determination unit may also include: a feed speed calculation unit that calculates the relative feed speed between the tool and the workpiece from the start of the cutting feed until the thread cutting feed speed is reached; and a thread cutting feed speed reach time calculation unit that calculates the thread cutting feed speed reach time until the relative feed speed reaches the thread cutting feed speed based on the relative feed speed. The startable thread cutting area determination unit may also calculate the range of the startable thread cutting area based on the thread cutting feed speed reach time.

[0013] The thread cutting start timing determination unit may also pre-read a program that instructs operations to the machine tool. When there is an instruction for thread cutting in the program, it pre-monitors the position of the spindle and starts driving the tool when the spindle is in a predetermined position.

[0014] The control device may further include a throughput adjustment unit that accelerates the relative feed speed of the tool according to the throughput based on the throughput after the main shaft passes through a predetermined rotational position, so as to cancel out the throughput.

[0015] A system according to one aspect of the present invention controls a machine tool having a first axis for moving a tool along the axial direction of a main shaft and a second axis for moving the tool in a direction different from the axial direction of the first axis, and drives the tool through the first axis and the second axis to perform thread cutting on a workpiece mounted on the main shaft. The control system includes: a startable thread cutting area determination unit that determines a startable thread cutting area in the direction of the second axis of the tool based on the timing when the relative speed between the tool and the workpiece reaches the thread cutting feed speed after the tool starts cutting feed in the direction of the first axis; and a thread cutting start timing determination unit that starts the cutting feed of the tool when the position of the tool on the second axis is within the range of the startable thread cutting area.

[0016] Due to having the above structure, the present invention can shorten the time required for thread cutting. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic hardware structure diagram of a numerical control device in an embodiment of the present invention.

[0018] Figure 2 It is a functional block diagram of a numerical control device in an embodiment of the present invention.

[0019] Figure 3 It is a diagram for explaining the startable thread cutting area.

[0020] Figure 4A and Figure 4B It is a diagram for explaining the speed command of the thread cutting feed speed in the case of linear acceleration and deceleration.

[0021] Figure 5 It is a diagram showing the drive path of the tool.

[0022] Figure 6 It is a flowchart for explaining the operation of the numerical control device.

[0023] FIG. 7 is a diagram for explaining the difference in cycle time from an existing numerical control device.

[0024] Figure 8 It is a functional block diagram of a numerical control device including a throughput adjustment unit.

[0025] Figure 9It is a diagram illustrating the processing by the throughput adjustment unit.

[0026] Figure 10 It is a flowchart illustrating the operation of the throughput adjustment unit.

[0027] Figure 11 It is a diagram illustrating the movement path of the tool in the existing thread cutting process. Detailed implementation

[0028] Figure 1 It is a hardware structure diagram showing an overview of the main part of the numerical control device 1 equipped with the control device through one implementation.

[0029] The CPU 11 included in the numerical control device 1 of this implementation is a processor that overall controls the numerical control device 1. The CPU 11 reads the system program stored in the ROM 12 via the bus and controls the overall numerical control device 1 according to this system program. Temporary calculation data, display data, various data input by the operator via the input unit 22, etc. are temporarily stored in the RAM 13.

[0030] The non-volatile memory 14 is composed of, for example, a memory supported by a battery (not shown), an FD (Floppy Disk Drive), an HDD (Hard Disk Drive), an SSD (Solid State Drive), etc., and maintains the storage state even when the power of the numerical control device 1 is turned off. Programs read from an external device 80 via the interface 15, programs input via the input unit 22, and various data obtained from each part of the numerical control device 1 and the machine tool, etc. (for example, setting parameters obtained from the machine tool) are stored in the non-volatile memory 14. The programs and various data stored in the non-volatile memory 14 can also be loaded into the RAM 13 during execution / use. In addition, various system programs such as a known analysis program are pre-written in the ROM 12.

[0031] The interface 15 is an interface for connecting the numerical control device 1 and an external device 80 such as an adapter. Programs, various parameters, etc. are read from the external device 80 side. In addition, programs, various parameters, etc. edited in the numerical control device 1 can be stored in an external storage unit (not shown) via the external device 80. The programmable logic controller (PLC) 16 controls the input and output of signals between the numerical control device 1 and the peripheral devices of the machine tool, the robot, and devices such as sensors installed on the robot and the machine tool via the I / O unit 17 through a timing program built into the numerical control device 1.

[0032] The display unit 21 outputs and displays the data read into the memory and the data obtained as a result of executing the program, etc., via the interface 18. In addition, the input unit 22 composed of an MDI, an operation panel, a touch panel, etc. transmits the instructions and data based on the operator's operation to the CPU 11 via the interface 19.

[0033] The axis control circuit 40 for controlling each axis of the machine tool receives the tool movement command from the CPU 11, and outputs the tool movement command to the servo amplifier 41. The servo amplifier 41 receives the command and drives the servo motor 42 for moving the tool of the machine tool. The servo motor 42 has a built-in position / speed detector (not shown), and feeds back the position / speed feedback signal from the position / speed detector to the axis control circuit 40, thereby performing position / speed feedback control. Figure 1 In the hardware structure diagram, only one axis control circuit 40, servo amplifier 41, and servo motor 42 are shown, but in fact, the number of axes (in this embodiment, two axes, the X axis and the Z axis) possessed by the machine tool that is the control object is prepared.

[0034] The spindle control circuit 30 receives a spindle rotation command issued to the spindle of the machine tool, and outputs a spindle speed signal to the spindle amplifier 32. The spindle amplifier 32 receives the spindle speed signal and rotates the spindle motor 31 of the spindle at the commanded rotation speed. The spindle motor 31 is combined with a position encoder 33 (described later), and the position encoder 33 outputs a feedback pulse in synchronization with the rotation of the spindle, and the feedback pulse is read by the CPU 11.

[0035] Figure 2 This is a functional block diagram of a numerical control device in which the control device of the present invention is installed.

[0036] A numerical control device 1 controls a thread cutting operation of a machine tool (not shown). The machine tool includes, for example, a spindle S that rotates a workpiece and a tool rest on which a tool T is mounted to form a thread on the surface of a workpiece W mounted on the spindle. The tool rest on which the tool T is mounted can move relative to the workpiece via two axes, namely, a first axis that is an axial direction of the spindle and a second axis that is different from the axial direction of the spindle. In this embodiment, the first axis is referred to as the Z axis and the second axis is referred to as the X axis.

[0037] pass Figure 1The CPU 11 included in the numerically controlled device 1 shown executes a system program read from the ROM 12, mainly performs arithmetic processing using the RAM 13 and the non-volatile memory 14 based on the CPU 11, and thereby implements the program analysis unit 51. The program analysis unit 51 reads a program 52 stored in a predetermined storage area (not shown) provided in the non-volatile memory 14, analyzes the content of the program 52, and generates a movement instruction sent to the interpolation unit 53 and a spindle rotation instruction sent to the spindle control unit 56. The program analysis unit 51 includes a program pre-reading unit 54 that pre-reads the program 52. The program pre-reading unit 54 determines whether there is a thread cutting start instruction in the pre-read program 52, and when there is a thread cutting start instruction, outputs the rotation position information of the spindle S to a thread cutting start timing determination unit 70 (described later).

[0038] By Figure 1 The CPU 11 included in the numerically controlled device 1 shown executes a system program read from the ROM 12, mainly performs arithmetic processing using the RAM 13 and the non-volatile memory 14 based on the CPU 11, and thereby implements the interpolation unit 53. The interpolation unit 53 generates interpolation data obtained by interpolating the commanded path of the tool T at an interpolation cycle based on the movement instruction commanded from the program analysis unit 51, and outputs the generated interpolation data to the servo control unit 55.

[0039] By Figure 1 The CPU 11 included in the numerically controlled device 1 shown executes a system program read from the ROM 12, mainly performs arithmetic processing using the RAM 13 and the non-volatile memory 14 based on the CPU 11 and control processing of the servo motor 42 based on the axis control circuit 40 and the servo amplifier 41, and thereby implements the servo control unit 55. The servo control unit 55 controls the servo motor 42 based on the interpolation data generated by the interpolation unit 53, and thereby drives the tool T according to the commanded path.

[0040] By Figure 1 The CPU 11 included in the numerically controlled device 1 shown executes a system program read from the ROM 12, mainly performs arithmetic processing using the RAM 13 and the non-volatile memory 14 based on the CPU 11 and control processing of the spindle motor 31 based on the spindle control circuit 30 and the spindle amplifier 32, and thereby implements the spindle control unit 56. The spindle control unit 56 controls the rotation of the spindle motor 31 according to the spindle rotation instruction from the program analysis unit 51, and rotationally drives the workpiece W. The position encoder 33 detects the rotation position of the spindle S and transmits the detected rotation position to the spindle control unit 56. The spindle position management unit 71 always manages the position of the spindle S according to the signal from the spindle control unit 56.

[0041] ByFigure 1 The CPU 11 included in the numerical control device 1 shown executes the system program read from the ROM 12, mainly performs arithmetic processing using the RAM 13 and the non-volatile memory 14 based on the CPU 11, and thereby realizes the startable thread cutting area calculation unit 60. The startable thread cutting area calculation unit 60 calculates the startable thread cutting area.

[0042] In the present embodiment, the start of thread cutting means the start of cutting feed. The startable thread cutting area is an area on the X-axis calculated such that when cutting feed is started within this area, the position on the X-axis reaches the thread cutting depth at the end of the incomplete thread portion or before it. Within the startable thread cutting area, thread cutting can be performed at an appropriate thread cutting feed speed regardless of where thread cutting starts.

[0043] An example of the startable thread cutting area is Figure 3 shown.

[0044] As Figure 3 shown, the startable thread cutting area is the range between the position A where the position on the Z-axis is separated from the end C of the incomplete thread portion by the first distance and the position B where the position is separated from the position A by the second distance in the positive X-axis direction. Here, the first distance means the distance required for the relative feed speed of the tool T and the workpiece W in the Z-axis direction to reach the thread cutting feed speed after the cutting feed of the tool T starts on the Z-axis. In the stage before reaching the first distance, the tool T has not reached the thread cutting feed speed, so complete thread cutting cannot be performed. Within the first distance, the thread cutting becomes incomplete, so it is called an incomplete thread portion in the present embodiment.

[0045] In addition, in Figure 3 , the symbol S represents the main shaft, and the symbol i represents the rotation center axis of the workpiece W. The second distance means the distance that the tool T moves in the X-axis direction during the period until the relative feed speed of the tool T and the workpiece W in the Z-axis direction reaches the thread cutting feed speed, and corresponds to the range (width) of the startable thread cutting area.

[0046] The startable thread cutting area calculation unit 60 includes a feed speed calculation unit 61 and a thread cutting feed speed reach time calculation unit 62. The feed speed calculation unit 61 calculates the relative feed speed of the tool T and the workpiece W in the Z-axis direction from the start of the cutting feed of the tool T in the Z-axis direction until the thread cutting feed speed is reached.

[0047] The thread cutting feed speed arrival time calculation unit 62 calculates the thread cutting feed speed arrival time, which is the time until the relative feed speed between the tool T and the workpiece W reaches the thread cutting feed speed, based on the thread cutting feed speed calculated by the feed speed calculation unit 61. The startable thread cutting area calculation unit 60 calculates the second distance, which is the distance that the tool T moves in the X-axis direction at the thread cutting feed speed arrival time.

[0048] Here, refer to Figure 4A and Figure 4B which shows a calculation example of the startable thread cutting area in the case of linear acceleration and deceleration.

[0049] Figure 4A which shows the change of the thread cutting feed speed command during linear acceleration and deceleration, Figure 4B which shows the transfer function between the thread cutting feed speed command and the thread cutting feed speed. Under this condition, the thread cutting feed speed v Z (t) [m / sec] is expressed by the following equation (1). The feed speed calculation unit 61 solves the following equation (1) to calculate the thread cutting feed speed.

[0050] 0 ≤ t < T s When

[0051]

[0052] T s ≤ t When

[0053]

[0054] Here, V S is the thread cutting command speed [m / sec], T S is the acceleration and deceleration time constant [sec] after thread cutting interpolation, T Z is the time constant [sec] of the servo system of the Z-axis, α Z is the feedforward coefficient of the Z-axis. Such parameters are stored in the storage unit 50.

[0055] The second term (underlined part) inside the curly brackets of the equation (1) represents the ratio until the tool T reaches the thread cutting command speed. When this term falls within the allowable value, it is regarded that the relative feed speed between the tool T and the workpiece W has reached the thread cutting feed speed. If the lead of the screw is set to L [m] and the allowable error is set to ΔL [m], then the time t S [sec] at which it is regarded that the relative feed speed between the tool T and the workpiece W has reached the thread cutting feed speed can be calculated according to the following equation (2). The thread cutting feed speed arrival time calculation unit 62 solves the following equation (2) to calculate the thread cutting feed speed arrival time.

[0056]

[0057] If the range of the thread cutting startable region is set to δ x [m], then based on the time t when the relative feed rate between the tool T and the workpiece W is considered to reach the thread cutting feed rate S , δ is calculated by the following formula (3) x . The thread cutting startable region calculation unit 60 solves the following formula (3) to calculate the range of the thread cutting startable region.

[0058] 0 ≤ t s <T r When

[0059]

[0060] T r ≤ t s When

[0061]

[0062] Here, V r is the rapid traverse command speed of the X-axis [m / sec], T r is the interpolation post-acceleration / deceleration time constant of the rapid traverse [sec], T X is the time constant of the servo system of the X-axis [sec], α X is the feedforward coefficient of the X-axis. Such parameters are stored in the storage unit 50. δ x is the distance that the tool T moves in the X-axis during the period from the start of thread cutting until the relative speed between the tool T and the workpiece W reaches the thread cutting feed rate. When starting thread cutting from the point A of the thread cutting depth, the cutting feed is performed parallel to the Z-axis direction in the same manner as in the prior art. When starting thread cutting from the point B farthest from the thread cutting depth, the timing at which the tool T reaches the end point C of the incomplete thread part is the same as the timing at which it reaches the thread cutting depth. That is, the thread cutting startable region is the region where the movement of the tool T towards the thread cutting depth is completed before the tool T passes through the end point C of the incomplete thread part.

[0063] It should be noted that when there is a surplus such that the thread cutting depth is reached at a position ahead of the end point of the incomplete thread portion, it is only necessary to make the range of the startable thread cutting region narrower than the range calculated by the above formula (3). Additionally, when the tool T reaches the cutting feed speed in front of the workpiece W (i.e., the workpiece W is installed separated in the negative Z-axis direction from the end point C of the incomplete thread portion), the range of the startable thread cutting region can also be made wider than the range calculated by the above formula (3). In this case, the position where the X-axis reaches the thread cutting depth becomes a position exceeding the end point of the incomplete thread portion. According to formula (3), before the tool T passes through the end point of the incomplete thread portion, the startable thread cutting region can be automatically calculated to complete the movement to the thread cutting depth. Furthermore, the calculated startable thread cutting region can also be adjusted according to the application.

[0064] By Figure 1 The CPU 11 of the numerical control device 1 shown executes the system program read from the ROM 12, mainly performing arithmetic processing using the RAM 13 and the non-volatile memory 14 based on the CPU 11, thereby implementing the thread cutting start timing determination unit 70. The thread cutting start timing determination unit 70 determines the timing to start thread cutting, which is the cutting feed in the Z-axis direction. The thread cutting start timing determination unit 70 determines whether the tool T exists in the startable thread cutting region, and when the tool T is included in the startable thread cutting region, it starts the determination process of the thread cutting start timing. When starting to determine the thread cutting start timing, the thread cutting start timing determination unit 70 inputs the position information of the spindle S from the spindle position management unit 71, and when the spindle S reaches a predetermined position (for example, the position where a 1-revolution signal is detected), it instructs the interpolation unit 53 to start thread cutting.

[0065] And, when the interpolation unit 53 receives the thread cutting start signal from the thread cutting start timing determination unit 70, it outputs interpolation data generated based on the thread cutting instruction to the servo control unit 55.

[0066] Figure 5 An example of the movement path of the tool is shown.

[0067] In Figure 5 the example, the tool T first stands by at the drive start position O. Then, in order to move the tool T to the thread cutting depth, the movement of the tool T in the negative X-axis direction is started ([1]). Additionally, the drive start position O of the tool T is calculated to be a sufficient distance away from the end point C of the incomplete thread portion in the Z-axis direction so that the relative feed speed between the tool T and the workpiece W reaches the thread cutting feed speed. The drive start position O of the tool T can either be included in the startable thread cutting region described later or be a position not included in the startable thread cutting region. In Figure 5In the example, the driving start position O is set at a position slightly separated from the startable thread cutting region.

[0068] When the tool T moves in the negative direction of the X axis and enters the range of the startable thread cutting region, the thread cutting start timing determination unit 70 receives the rotational position of the main shaft S from the main shaft position management unit 71. When the main shaft S reaches a predetermined thread cutting start angle (for example, the position where a one-revolution signal is detected), it instructs the interpolation unit 53 to start thread cutting. The interpolation unit 53 starts the cutting feed (thread cutting) of the tool according to the instruction. Before starting the cutting feed, the tool T is only driven in the X-axis direction, but if the cutting feed is started, it is accelerated in the Z-axis direction, so the movement path of the tool T becomes Figure 5 ([2]) the curve as shown. Near the end point C of the incomplete thread portion, the position of the tool T in the X-axis direction reaches the thread cutting depth, and at the end point of the incomplete thread portion, the speed of the tool T in the Z-axis direction reaches the thread cutting feed speed. When passing through the end point C of the incomplete thread portion, the tool T performs thread cutting on the surface of the workpiece W at a predetermined thread cutting feed speed ([3]).

[0069] As described above, if thread cutting starts when a one-revolution signal of the main shaft S is detected at any position within the startable thread cutting region, the time until reaching the end point C of the incomplete thread portion is the same. Therefore, when the tool T passes through the end point C of the incomplete thread portion, thread cutting can start from the same position on the surface of the workpiece W, so that the spiral trajectory of the thread is consistent.

[0070] Next, refer to Figure 6 to explain the operation of the numerical control device 1.

[0071] First, the program analysis unit 51 reads the program 52 from a predetermined storage area (step S1). The program analysis unit 51 analyzes the read program and outputs an instruction signal to the interpolation unit 53 and the main shaft control unit 56. At the same time, the program pre-reading unit 54 reads the program ahead of the program to be analyzed and determines whether a thread cutting instruction exists in the read program. If there is no thread cutting instruction in the preceding program (step S2); No), the interpolation unit 53 does not perform the thread cutting start process. If there is a thread cutting instruction in the pre-read program (step S2); Yes), the startable thread cutting region calculation unit 60 calculates the startable thread cutting region based on the time required to reach the thread cutting feed speed of the tool T (step S3).

[0072] Next, the thread cutting start timing determination unit 70 confirms the position of the tool T on the X-axis (step S4). Here, when the position of the tool T on the X-axis is included in the thread cutting startable region (step S5; YES), the thread cutting start timing determination unit 70 confirms the rotational position of the main shaft S (step S6). Further, when the position of the tool T on the X-axis is not included in the thread cutting startable region (step S5; NO), the process returns to step S3, and the monitoring of the position of the tool T is continued until the position of the tool T on the X-axis is included in the thread cutting startable region.

[0073] Further, in step S6, as a result of confirming the rotational position of the main shaft S, when the rotational position of the main shaft S reaches the thread cutting start angle (step S7; YES), the thread cutting start timing determination unit 70 outputs a thread cutting start instruction to the interpolation unit 53.

[0074] When the interpolation unit 53 is input with the thread cutting start instruction, the interpolation unit 53 outputs a control signal to the servo control unit 55 so as to start the thread cutting operation (cutting feed operation in the Z-axis direction) (step S8). Further, in step S7, when the rotational position of the main shaft S does not reach the thread cutting start angle (step S7; NO), the thread cutting start timing determination unit 70 returns to step S6 and continues to confirm the rotational position of the main shaft S.

[0075] As described above, the numerical control device 1 of the present embodiment first drives the tool T in the X-axis direction. Then, after the tool enters the thread cutting startable region, the rotation of the main shaft S is monitored, and when the main shaft S reaches the thread cutting start angle, the interpolation unit 53 is instructed to start thread cutting.

[0076] Referring to FIG. 7, the thread cutting process of the numerical control device of the present embodiment is compared with the thread cutting process of the conventional numerical control device.

[0077] In the conventional numerical control device, as shown in FIG. 7(a), after the tool T is moved in the negative X-axis direction to the thread cutting depth, it waits until the rotational position of the main shaft S reaches the output position for outputting a one-revolution signal, and then starts the thread cutting in the Z-axis direction from this point. However, as shown in FIG. 7(b), in the numerical control device 1 of the present embodiment, since the thread cutting in the Z-axis direction is started at the timing of outputting the one-revolution signal of the rotational position of the main shaft S while driving the tool T in the X-axis direction, the thread cutting in the Z-axis direction can be started in the middle of the rapid feed in the X-axis direction, and there is no need to wait for the one-revolution signal, so the cycle time is shortened.

[0078] Next, in Figure 8 Another embodiment of the numerical control device 1a including the throughput adjustment unit 72 is shown.

[0079] Figure 8 The thread cutting start timing determination unit 70 has a throughput adjustment unit 72. After the rotational position of the main shaft S has passed the position where a 1-revolution signal is output, during the period from the rotational position of the main shaft S where thread cutting originally starts to the current rotational position of the main shaft S, the throughput adjustment unit 72 outputs the pulses of the throughput of the Z-axis movement (hereinafter referred to as the "Z-axis delay amount") as command pulses to the Z-axis, thereby canceling the Z-axis delay amount and making the phase of the thread cutting consistent.

[0080] More specifically, when the thread cutting start timing determination unit 70 commands the interpolation unit 53 to start the thread cutting operation (start of the movement of the Z-axis), the throughput adjustment unit 72 commands an adjustment so that the pulse amount of the first control cycle output to the servo motor 42 for driving the Z-axis in the interpolation data for the thread cutting operation generated by the interpolation unit 53 becomes the pulse amount of the "Z-axis delay amount". By making such an adjustment, the acceleration at the start of the thread cutting in the Z-axis direction is larger than the acceleration at the start of the movement of the normal Z-axis. However, it is not necessary to wait for the start of the thread cutting before the rotational position of the main shaft S reaches the thread cutting start angle, so the cycle time of the thread cutting process can be shortened.

[0081] Refer to Figure 9 For explanation, if the throughput from the thread cutting start angle (for example, the position where the 1-revolution signal has passed) detected by the position encoder 33 is set as α, the throughput adjustment unit 72 calculates the command pulses (Z-axis delay amount) of the throughput of the Z-axis movement (the movement amount after the start of the movement of the Z-axis) during the time when the main shaft S moves through the throughput α, and instructs the interpolation unit 53 to adjust the pulse amount of the first control cycle of the interpolation data for the thread cutting operation generated by the interpolation unit 53 to the calculated command pulse amount. When the servo control unit 55 accelerates the servo motor 42 based on the adjusted interpolation data, the Z-axis delay amount is canceled, thereby eliminating the delay of the thread cutting feed speed from the 1-revolution signal. After eliminating the speed delay, the thread cutting feed speed is adjusted by normal control. In this way, it is also possible to accelerate the thread cutting feed speed by the amount of the acceleration delay without waiting for the 1-revolution signal, and make the spiral trajectory of the thread cutting consistent.

[0082] Refer to Figure 10 Describe the operation of the numerical control device 1a of the present embodiment.

[0083] First, the program analysis unit 51 reads out the program 52 from a predetermined storage area (step S11). The program analysis unit 51 analyzes the read program and outputs an instruction signal to the interpolation unit 53 and the spindle control unit 56. At the same time, the program look-ahead unit 54 reads out the program ahead of the program to be analyzed and determines whether there is a thread cutting instruction. When there is no thread cutting instruction in the ahead program (step S12; No), the interpolation unit 53 does not perform the thread cutting start process. When there is a thread cutting instruction in the look-ahead program (step S12; Yes), the thread cutting start area calculation unit 60 can calculate the thread cutting start area based on the time required to reach the thread cutting feed speed of the tool T (step S13).

[0084] Next, the thread cutting start timing determination unit 70 confirms the position of the tool T on the X-axis (step S14). Here, when the position of the tool T on the X-axis is included in the thread cutting start area (step S15; Yes), the thread cutting start timing determination unit 70 confirms the rotational position of the spindle S (step S16) and calculates the Z-axis delay amount based on the rotational position of the spindle S (step S17). In addition, when the position of the tool T on the X-axis is not included in the thread cutting start area (step S15; No), the process returns to step S14, and the monitoring of the position of the tool T is continued until the position of the tool T on the X-axis is included in the thread cutting start area.

[0085] In addition, in step S17, the Z-axis delay amount based on the rotational position of the spindle S is calculated. As a result, when the acceleration in the case of accelerating the Z-axis according to the calculated Z-axis delay amount converges within the maximum acceleration set for the Z-axis (step S18; Yes), the thread cutting start timing determination unit 70 and the throughput adjustment unit 72 output a thread cutting start instruction with the initial speed adjusted by the Z-axis delay amount to the interpolation unit 53. In step S18, when the acceleration in the case of accelerating the Z-axis by the Z-axis delay amount exceeds the maximum acceleration set for the Z-axis (step S18; No), the process returns to step S16, and the monitoring of the spindle rotational position is continued.

[0086] The embodiments of the present invention have been described above. However, the present invention is not limited to the examples of the embodiments and can be implemented in various ways with appropriate modifications.

[0087] For example, in the above-described embodiment, an example in which the machined threaded portion is parallel to the Z-axis has been described. However, for example, when the threaded portion is inclined at a predetermined angle with respect to the Z-axis, the technology of the present invention can also be used. In such a case, the Z-axis is driven in the same manner as in the above-described embodiment, and the X-axis is moved in accordance with the angle of the threaded portion to perform thread cutting. By determining the timing of the start of the movement of the Z-axis in the thread cutting operation in the same manner as in the above-described embodiment, the spiral trajectory of the thread can be made consistent, and the cycle time can be shortened compared to the normal thread cutting method.

Claims

1. A control device controls a machine tool. The machine tool includes a first axis for moving a tool along the axial direction of a spindle and a second axis for moving the tool in a direction different from the axial direction of the first axis, and drives the tool using the first axis and the second axis to perform thread cutting on a workpiece mounted on the spindle. Characterized in that, The control device includes: A startable thread cutting area determination unit that, after the tool starts cutting feed in the direction of the first axis, determines a startable thread cutting area in the direction of the second axis of the tool based on the timing when the relative feed speed between the tool and the workpiece reaches the thread cutting feed speed; and A thread cutting start timing determination unit that starts the cutting feed of the tool when the position of the tool on the second axis is within the range of the startable thread cutting area. The startable thread cutting area determination unit determines the startable thread cutting area so that when the tool reaches the thread cutting feed speed, the tool reaches the thread cutting depth position.

2. The control device according to claim 1, Characterized in that, The control device further includes a rotational position detection unit for detecting the rotational position of the spindle. The thread cutting start timing determination unit starts driving the tool when the rotational position detection unit detects a predetermined rotational position.

3. The control device according to claim 1, Characterized in that, The startable thread cutting area determination unit includes: A feed speed calculation unit that calculates the relative feed speed between the tool and the workpiece from the start of the cutting feed until the thread cutting feed speed is reached; and A thread cutting feed speed reach time calculation unit that calculates the thread cutting feed speed reach time until the relative feed speed reaches the thread cutting feed speed based on the relative feed speed. The startable thread cutting area determination unit calculates the range of the startable thread cutting area based on the thread cutting feed speed reach time.

4. The control device according to claim 1, Characterized in that, The thread cutting start timing determination unit pre-reads a program for instructing operations to the machine tool. When there is an instruction for thread cutting in the program, it pre-monitors the position of the spindle and starts driving the tool when the spindle is at a predetermined position.

5. The control device according to claim 1, Characterized in that, The control device further includes a throughput adjustment unit. The throughput adjustment unit accelerates the relative feed speed of the tool according to the throughput after the spindle passes through a predetermined rotational position, so as to offset the throughput.

6. A control system controls a machine tool. The machine tool includes a first axis for moving a tool along the axial direction of a spindle and a second axis for moving the tool in a direction different from the axial direction of the first axis, and drives the tool using the first axis and the second axis to perform thread cutting on a workpiece mounted on the spindle. Characterized in that, The control system includes: A startable thread cutting region determination unit that, after the tool starts cutting feed in the direction of the first axis, determines a startable thread cutting region in the direction of the second axis of the tool based on the timing when the relative speed between the tool and the workpiece reaches the thread cutting feed speed; and A thread cutting start timing determination unit that starts the cutting feed of the tool when the position of the tool on the second axis is within the range of the startable thread cutting region, The startable thread cutting region determination unit determines the startable thread cutting region such that when the tool reaches the thread cutting feed speed, the tool reaches the thread cutting depth position.

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