NUMERICAL CONTROL

Abstract

A numerical controller (1) that machines a workpiece by controlling a machining device comprising a tool based on a machining program (200), and that performs an optimal advance of the tool in a cycle for cutting a screw thread, the numerical controller (1) comprising: an instruction analysis unit (130) that analyzes the machining program (200); a cycle motion start point determining unit (110) that calculates a cycle motion start point at which a cycle for cutting a screw thread toward an end side of the workpiece is to start; an acceleration or deceleration control unit (120) that moves the tool from the starting point of the cycle movement to the starting point for cutting a screw thread with overlapping movements of a plurality of axes; and a control unit (140) which controls the movements of the processing device based on control instructions received from the instruction analysis unit (130) and the unit (120) for controlling acceleration or deceleration, wherein the starting point of the cycle motion is a point from which acceleration or deceleration of a first axis parallel to a direction of cutting feed and a second axis orthogonal to the first axis begins to cause a speed of the first axis to reach a predetermined cutting feed rate and to cause a speed of the second axis to be substantially zero upon arrival at the starting point for cutting a screw thread.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a numerical controller, and more particularly to a numerical controller having an optimal lead function in a screw thread cutting cycle. General state of the art

[0002] Screw thread cutting refers to a technique for machining screw threads with a fixed pitch by a tool (feed axis) moving in a direction of a rotary axis while synchronously following a rotating workpiece (spindle). Fig. Figure 1 shows an example of a conventional screw thread cutting cycle for external threads. The dashed lines represent rapid traverse, and a solid line represents cutting feedrate. In process a, a tool moves from a screw thread cutting instruction start point to a screw thread cutting start point. In process b, the tool starts cutting feedrate from the screw thread cutting start point, reaches an end face of a workpiece, and machines the external thread on a surface of the workpiece. At the end of machining, the tool returns to the screw thread cutting instruction start point via processes c and d.

[0003] Under the condition that a distance between the starting point for cutting a screw thread and the end face of the workpiece in the process b is too small as shown in Fig. 2, machining begins even though the feed axis is still accelerating. Consequently, the screw threads may not be formed with a fixed pitch, resulting in an incomplete thread section. As shown in Fig. As shown in Figure 3, the starting point for cutting a screw thread was conventionally set relatively far from the end face, so that machining could begin after the feed axis speed stabilized. However, this method leads to the problem of increasing the cycle time. It is desirable to achieve an optimal feed motion that can solve this problem.

[0004] In this regard, JP H07-88743 A discloses that a path to the starting point for cutting a screw thread (cutting start point), an acceleration distance, and a feed rate are calculated, and that the tool feed rate in an acceleration region is a resultant speed of a speed in the Z-axis direction and a speed in the X-axis direction. JP 2011-183481 A points to the problem that the time of one cycle for cutting a screw thread may increase.

[0005] However, in a technique disclosed in JP H07-88743 A, further optimization is possible by setting the acceleration distance to a fixed value such as three or five pitches, setting a tool change position at the start point of a screw thread cutting instruction (the tool change position need not be set at the start point of a screw thread cutting instruction in a second cycle and thereafter), and the like. In JP 2011-183481 A, which adopts a technique for reducing the occurrence of the incomplete thread portion by synchronously controlling the rotation of a spindle and the rotation of a feed axis, there is no specific reference to the start point of a screw thread cutting instruction and the like.

[0006] DE 36 35 621 A1 describes a thread cutting control method in an NC device. SUMMARY OF THE INVENTION

[0007] The invention was conceived to solve these problems. One object of the invention is to provide a numerical control system that has an optimal pre-run function in a screw thread cutting cycle.

[0008] This object is achieved by a numerical control having the features of patent claim 1 and by a numerical control having the features of patent claim 5.

[0009] A numerical controller according to an embodiment of the invention is a numerical controller that machines a workpiece by controlling a machining device including a tool based on a machining program and that performs optimal advance of the tool in a cycle for cutting a screw thread.The numerical controller includes: an instruction analysis unit that analyzes the machining program; a cycle motion start point determination unit that calculates a cycle motion start point at which a screw thread cutting cycle (including an X-axis rapid traverse and a Z-axis cutting feedrate) toward an end side of the workpiece should start; an acceleration or deceleration control unit that moves the tool from the cycle motion start point to the screw thread cutting start point with overlapping movements of a plurality of axes; and a control unit that controls the movements of the machining device based on control instructions received from the instruction analysis unit and the acceleration or deceleration control unit.The numerical controller is characterized in that the starting point of the cycle movement is a point from which acceleration or deceleration of a first axis parallel to a direction of cutting feed and a second axis orthogonal to the first axis is started to cause a speed of the first axis to reach a predetermined cutting feed rate and to cause a speed of the second axis to be substantially zero upon arrival at the starting point for cutting a screw thread.

[0010] A numerical controller according to the embodiment of the invention is characterized in that the cycle motion start point determining unit calculates the coordinates of the cycle motion start point based on the coordinates of the screw thread cutting start point, a cutting feed rate, a rapid traverse rate, and time constants for the second axis (X-axis) and the first axis (Z-axis).

[0011] A numerical controller according to the embodiment of the invention is characterized in that the cycle motion start point determining unit calculates a displacement between the screw thread cutting start point and the cycle motion start point according to Expressions 1 to 4 to be described later.

[0012] A numerical controller according to the embodiment of the invention is characterized in that the acceleration or deceleration control unit controls the movement of the tool from the cycle movement start point calculated by the cycle movement start point determination unit to the screw thread cutting start point, from the screw thread cutting start point to a machining end point, and from the machining end point to the cycle movement start point, starts the acceleration or deceleration of the first axis parallel to the cutting feed direction and the second axis orthogonal to the first axis from the cycle movement start point, causes the speed of the first axis to reach the predetermined cutting feed speed, and causesthat the speed of the second axis is zero upon arrival at the starting point for cutting a screw thread, performs the cutting feed along the first axis from the starting point for cutting a screw thread, and performs the rapid traverse towards the starting point of the cycle movement from a point slightly shifted along the second axis from a point at which the cutting feed is terminated.

[0013] A numerical controller according to the embodiment of the invention is a numerical controller that machines a workpiece by controlling a machining device including a tool based on a machining program and that performs optimal advance in a machining cycle.The numerical controller includes: an instruction analysis unit that analyzes the machining program; a cycle motion start point determination unit that calculates a cycle motion start point at which a screw thread cutting cycle (including an X-axis rapid traverse and a Z-axis cutting feedrate) toward an end side of the workpiece should start; an acceleration or deceleration control unit that moves the tool from the cycle motion start point to the screw thread cutting start point with overlapping movements of a plurality of axes; and a control unit that controls the movements of the machining device based on control instructions received from the instruction analysis unit and the acceleration or deceleration control unit.The numerical controller is characterized in that the starting point of the cycle movement is a point from which acceleration or deceleration of a first axis parallel to a direction of cutting feed and a second axis orthogonal to the first axis starts to cause a speed of the first axis to reach a predetermined cutting feed rate and to cause a speed of the second axis to be substantially zero upon arrival at the starting point for cutting a screw thread.

[0014] According to the invention, a numerical controller having an optimal lead function in the screw thread cutting cycle can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above-mentioned and other objects and features of the invention will become apparent from the following description of the embodiment with reference to the accompanying drawings. Fig. 1 is a diagram illustrating an example of a conventional cycle for cutting a screw thread; Fig. 2 is a diagram illustrating an example of a conventional cycle for cutting a screw thread; Fig. 3 is a diagram illustrating an example of a conventional cycle for cutting a screw thread; Fig. 4 is a diagram illustrating a configuration of a numerical controller according to the invention; Fig. 5 is a diagram illustrating a movement caused by the numerical control; Fig. 6 is a diagram illustrating a movement caused by the numerical control; Fig. 7 is a diagram illustrating a movement caused by the numerical control; Fig. 8 is a diagram showing a movement caused by the numerical control; Fig. 9 is a diagram showing a movement caused by the numerical control; Fig. 10 is a diagram showing a movement caused by the numerical control; Fig. 11 is a diagram showing a movement caused by the numerical control; Fig. 12 is a diagram illustrating a movement caused by the numerical control; and Fig. 13 is a diagram illustrating a hardware configuration of the numerical controller according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] A numerical controller 1 according to an embodiment of the invention will be described using the drawings. Fig. 4 is a block diagram illustrating a functional configuration of the numerical controller 1. The numerical controller 1 includes a cycle motion start point determining unit 110, an acceleration or deceleration controlling unit 120, an instruction analysis unit 130, and a control unit 140 as functions for controlling the motions of a feed axis of a machining device to be controlled.

[0017] The numerical controller 1 achieves an economical and optimal pre-travel motion through actions of the unit 110 for determining a starting point of a cycle motion and the unit 120 for controlling acceleration or deceleration. An example of a specific motion effected by the numerical controller 1 is shown using Fig. 5 and Fig. 6 shown. Fig. 5 and Fig. 6 depict a movement of a tool when cutting a screw thread according to a machining program which will be described later. Fig. 5 depicts a cycle motion for cutting a screw thread in the first cycle of a cycle for cutting a screw thread, and Fig. 6 represents a screw thread cutting cycle motion in the second cycle of a screw thread cutting cycle and thereafter. G92 denotes a screw thread cutting cycle instruction. O0001; G28 U0 W0; N001 M03 S50 P1; N002 X100.0 Z30.0; N003 G92 X80.0 Z-100.0 F20.0; M30;

[0018] The numerical controller 1 starts the X-axis movement from the start point of a screw thread cutting instruction (process E), starts the Z-axis movement from a cycle movement start point calculated by the cycle movement start point determining unit 110 (process A), and exercises control to achieve completion of the X-axis movement and a Z-axis speed equal to a cutting feed rate according to the instruction upon arrival at the screw thread cutting start point. That is, acceleration or deceleration control is exercised so that advance can be achieved with overlapping movements of the X-axis and the Z-axis, and so that the feed axis speed can be just stabilized, that is, made constant at the screw thread cutting start point.Thus, a distance between the start point of the cycle movement and the start point for cutting a screw thread can be optimized, so that the cycle time can be shortened. Then, the cutting of the screw thread is performed with a cutting feed at the constant speed (process B). After the end of machining, the movement from a machining end point (X = 80.0, Z = -100.0) toward the start point of the cycle movement is achieved in a shortest distance (process C), and the movement to a start point of the cycle movement in a subsequent cycle is achieved thereafter. In view of the machining quality, a slight deviation in a substantially positive direction along the X-axis from the machining end point can be made, and then the movement from a deviation point toward the start point of the cycle movement can be achieved in a shortest distance.The movement to the subsequent starting point of the cycle movement can be achieved after the end of the machining.

[0019] The above movements are performed using Fig. 7 to 12 are described in more detail.

[0020] Fig. 7 to 9 are diagrams illustrating a method by which the cycle motion start point determining unit 110 determines the start point of the cycle motion. In process A, the X-axis moves from the start point of a screw thread cutting instruction in the first screw thread cutting cycle. After the movement of the first screw thread cutting cycle is completed, the tool moves to the start point of the cycle motion, and therefore, the X-axis moves from the start point of the cycle motion in the second screw thread cutting cycle and thereafter. As shown in Fig. 7, the Z-axis starts moving from a position that is away from the starting point for cutting a screw thread by a distance required to reach the feed rate for the cutting feed (hereinafter referred to as the acceleration distance). In the first cycle for cutting a screw thread, as shown in Fig. 9, the X-axis accelerates from the starting point of a screw thread cutting instruction and then decelerates to a speed of zero before arriving at the end face of the workpiece. In the second screw thread cutting cycle and thereafter, as shown in Fig. As shown in Figure 8, the X-axis accelerates from the starting point of the cycle movement and then decelerates to zero speed. This prevents the occurrence of an incomplete thread section, allowing machining to start as quickly as possible.

[0021] The cycle motion start point determining unit 110 calculates the Z-axis acceleration distance δ satisfying the above-described conditions according to the following Expression 1. δ=VTC2

[0022] Where V is the feed rate for cutting the screw thread (cutting feed) and T C is the time constant for the Z axis.

[0023] The cycle motion start point determining unit 110 may calculate the motion start point according to Expressions 2 to 4 below. X1'={ V'(TC−TR2)(TC≥TR)aTC22(TC≤TR) X2'={V'(TC−TR)(TC≥2TR)aTC24(TC<2TR) Z'=δ

[0024] Where V' is a rapid traverse speed of the X-axis, T R is the time constant in the X-axis direction, and a is an acceleration in the X-axis direction. X1', X2', and Z' are the displacements in the X-axis direction and Z-axis direction from the screw thread cutting start point, respectively. In other words, X1' is a rapid traverse distance in the X-axis direction in the first screw thread cutting cycle, X2' is a rapid traverse distance in the X-axis direction in the second screw thread cutting cycle and thereafter, and Z' is the distance required to reach the feed rate for cutting the screw thread (cutting feed) in the Z-axis direction as instructed, that is, the acceleration distance.

[0025] In the first cycle for cutting a screw thread, a relationship T C ≥ T R a state in which the rapid traverse speed of the X-axis slows down after reaching a maximum speed (constant speed), as in Fig. 12. In contrast, a relationship T C < T R a state in which the Z-axis accelerates before the X-axis decelerates. In the second cycle for cutting a screw thread and thereafter, a relationship T C ≥ 2T R a state in which the rapid traverse speed of the X-axis slows down after reaching the maximum speed (constant speed), as in Fig. 11. In contrast, a relationship T C < 2T RA state in which the rapid traverse speed of the X-axis begins to slow down before reaching the constant speed. This embodiment assumes a feedforward coefficient of 100% and that there is no delay in a servo system.

[0026] In Fig. 10 to 12 are the relationships between T C , T R , δ, X', V and V' are shown as velocity waveforms.

[0027] The instruction analysis unit 130 sequentially reads and analyzes a machining program 200 stored in a storage unit 210 to be executed, analyzes information such as the cutting start point and a cutting end point of the cycle for cutting a screw thread according to instructions and a pitch of a screw, and outputs information generated based on a result of the analysis to the cycle motion start point determining unit 110 and the control unit 140.

[0028] The cycle motion start point determining unit 110 calculates the cycle motion start point based on the information such as the cutting start point and the cutting end point generated based on the result of analysis by the instruction analyzing unit 130, and the coordinates of the end side of the workpiece and the time constants for the X-axis and the Z-axis stored in the storage unit 210, and outputs a result to the acceleration or deceleration controlling unit 120.

[0029] In process A, the acceleration or deceleration control unit 120 controls the movement of the tool from the cycle motion start point calculated by the cycle motion start point determination unit 110 to the screw thread cutting start point. In the Z-axis direction, the acceleration or deceleration control unit 120 performs acceleration to the speed V according to the time constant T. C Regarding the X-axis, in the first cycle for cutting a screw thread, the acceleration to the speed V' is determined according to the time constant T R and then a deceleration to the speed of zero according to the time constant T Rat the time when a coordinate value of the X-axis reaches X1'. In the second cycle for cutting a screw thread and thereafter, the acceleration is carried out to the speed V' according to the time constant T R in the cycle for cutting a screw thread, and then the deceleration is reduced to zero speed according to the time constant T R at the time when the coordinate value of the X-axis reaches X2'.

[0030] In process B, the acceleration or deceleration control unit 120 performs the cutting feed at speed V, a deceleration, and a stop at the machining end point. In process C, the movement is performed along the shortest distance from the machining end point toward the start point of the cycle movement, ie, linearly and at rapid traverse, as shown in Fig. 5 and Fig. 6. Alternatively, a slight deviation in the substantially positive direction along the X-axis may be made from the machining end point, and then the movement may be performed from the deviation point toward the start point of the cycle movement over the shortest distance.

[0031] The control unit 140 controls the operations of a servo motor 50 and a spindle motor 62 included in the machining apparatus based on control instructions received from the instruction analysis unit 130 and the acceleration or deceleration control unit 120.

[0032] According to the embodiment, the numerical controller 1 can achieve an optimal tool path in a screw thread cutting cycle. Specifically, the coordinates of the starting point of the cycle movement can be automatically identified based on the coordinates of the end face (starting point for cutting a screw thread) of the workpiece, the rapid traverse rate, a cutting feed rate, and the time constants for the X-axis and Z-axis. Thus, the cycle time for screw thread cutting can be shortened. Furthermore, the creation of the machining program is facilitated. Even for an existing program, a positioning point can be automatically converted by applying the embodiment, and thus, an improvement in the cycle time is expected.

[0033] Fig. Figure 13 is a schematic hardware configuration illustrating the main sections of the numerical controller 1 according to the embodiment of the invention and the machining device driven and controlled by the numerical controller 1. Each functional block of the numerical controller 1 shown in Fig. 4 is carried out by executing a system program for controlling the machining device and controlling the operations of the units of the numerical control 1 by a CPU 11 included in the numerical control 1, which is shown in Fig. 13 is shown.

[0034] The CPU 11 included in the numerical controller 1 according to the embodiment is a processor that generally controls the numerical controller 1. The CPU 11 reads the system program stored in a ROM 12 via a bus 20 and controls the entire numerical controller 1 according to the system program. Temporary calculation data and display data, various types of data input by the user via a display / MDI unit 70, and the like are stored in a RAM 13.

[0035] A non-volatile memory 14 is configured as a memory backed up by, for example, a battery (not shown), so that the memory status is maintained even when the numerical controller 1 is turned off. NC programs read via an interface 15, NC programs input via the display / MDI unit 70, which will be described later, data including machining states, and the like are stored in the non-volatile memory 14. The programs and the like stored in the non-volatile memory 14 can be decompressed into the RAM 13 when used. Various system programs for performing processing in a machining mode necessary for preparing and editing the NC programs and other necessary processing have been written in advance to the ROM 12.

[0036] The interface 15 is an interface for connecting the numerical controller 1 and an external device 72, such as an adapter. NC programs, various parameters, and the like are read from the external device 72. The NC programs processed in the numerical controller 1 can be stored in an external memory via the external device 72. A programmable machine controller (PMC) 16 outputs signals to and controls peripheral devices (actuators such as a robot hand for changing tools) for the machining device via an I / O unit 17 according to a sequence program stored in the numerical controller 1.In addition, the PMC 16 receives signals from various switches in an operation panel provided on the main unit of the machining device or the like, performs the necessary signal processing, and then transmits the signals to the CPU 11.

[0037] The display / MDI unit 70 is a manual data input device that includes a display, a keyboard, and the like. An interface 18 receives instructions, data, and the like from the keyboard of the display / MDI unit 70 and transmits the instructions, data, and the like to the CPU 11. An interface 19 is connected to the control panel 71, which includes a manual pulse generator for use in manually driving the axes or the like.

[0038] Axis control circuits 30 for controlling the axes provided in the machining device receive instructions from the CPU 11 regarding the travel path for the axes and output instructions for the axes to the servo amplifiers 40. The servo amplifiers 40 receive the instructions and drive the servo motors 50 that move the axes provided in the machining device. The servo motors 50 for the axes incorporate position / speed detectors, return position / speed feedback signals from the position / speed detectors to the axis control circuits 30, and perform position / speed control. Although the axis control circuits 30, the servo amplifiers 40, and the servo motors 50 are in a hardware configuration of Fig.13 to be provided only once each, the axis control circuits 30, the servo amplifiers 40 and the servo motors 50 are actually provided such that their number each corresponds to a number of feed axes provided in machining devices in systems to be controlled.

[0039] A spindle control circuit 60 receives a spindle rotation command for a manufacturing machine and outputs a spindle speed signal to a spindle amplifier 61. The spindle amplifier 61 receives the spindle speed signal, rotates the spindle motor 62 of the manufacturing machine at a speed according to the command, and thereby drives the tool. A position sensor 63 is coupled to the spindle motor 62 and outputs feedback pulses synchronously with the rotation of the spindle. The feedback pulses are read by the CPU 11.

[0040] Although the embodiment of the invention has been described above, the invention is not limited to the embodiment or the examples described above and can be embodied in various ways with appropriate modification. For example, although the above-described embodiment mainly adopted the example of machining external threads, the invention is not limited to the example and can be applied to machining internal threads, for example.

Claims

[1] Numerical control (1) which machines a workpiece by controlling a machining device comprising a tool based on a machining program (200), and which performs an optimal advance of the tool in a cycle for cutting a screw thread, the numerical control (1) comprising: an instruction analysis unit (130) that analyzes the machining program (200); a cycle motion start point determining unit (110) that calculates a cycle motion start point at which a cycle for cutting a screw thread toward an end side of the workpiece is to start; an acceleration or deceleration control unit (120) that moves the tool from the starting point of the cycle movement to the starting point for cutting a screw thread with overlapping movements of a plurality of axes; and a control unit (140) which controls the movements of the processing device based on control instructions received from the instruction analysis unit (130) and the unit (120) for controlling acceleration or deceleration, wherein the starting point of the cycle motion is a point from which acceleration or deceleration of a first axis parallel to a direction of cutting feed and a second axis orthogonal to the first axis begins to cause a speed of the first axis to reach a predetermined cutting feed rate and to cause a speed of the second axis to be substantially zero upon arrival at the starting point for cutting a screw thread. [2] The numerical controller (1) according to claim 1, wherein the cycle motion start point determining unit (110) calculates coordinates of the cycle motion start point based on coordinates of the screw thread cutting start point, a rapid traverse speed, a cutting feed speed, and time constants for the second axis and the first axis. [3] The numerical controller (1) according to claim 2, wherein the cycle motion start point determining unit (110) calculates a displacement between the screw thread cutting start point and the cycle motion start point according to the following expressions 1 to 4: δ=VTC2 X1'={ V'(TC−TR2)(TC≥TR)aTC22(TC≤TR) X2'={ V'(TC−TR)(TC≥2TR)aTC24(TC<2TR) Z'=δ, where Z' is the displacement of the first axis, X1' is the displacement of the second axis in a first cycle for cutting a screw thread, X2' is the displacement of the second axis in a second cycle for cutting a screw thread and thereafter, V is the speed of the cutting feed, T C the time constant for the first axis is T R is the time constant in the direction of the second axis, and a is an acceleration in the direction of the second axis. [4] Numerical controller (1) according to claim 1, wherein the acceleration or deceleration control unit (120) controls the movement of the tool from the cycle movement start point calculated by the cycle movement start point determination unit to the screw thread cutting start point, from the screw thread cutting start point to a machining end point, and from the machining end point to the cycle movement start point, starts the acceleration or deceleration of the first axis parallel to the cutting feed direction and the second axis orthogonal to the first axis from the cycle movement start point, causes the speed of the first axis to reach the predetermined cutting feed speed, and causes the speed of the second axis to be zero upon arrival at the screw thread cutting start point,performs the cutting feed along the first axis from the starting point for cutting a screw thread, and performs the rapid traverse towards the starting point of the cycle movement from a point slightly shifted along the second axis from a point at which the cutting feed is terminated. [5] Numerical control (1) which machines a workpiece by controlling a machining device comprising a tool based on a machining program (200) and which performs an optimal pre-run in a machining cycle, the numerical control (1) comprising: an instruction analysis unit (130) that analyzes the machining program (200); a cycle motion start point determining unit (110) that calculates a cycle motion start point at which a cycle for cutting a screw thread toward an end side of the workpiece is to start; an acceleration or deceleration control unit (120) that moves the tool from the starting point of the cycle movement to the starting point for cutting a screw thread with overlapping movements of a plurality of axes; and a control unit (140) which controls the movements of the processing device based on control instructions received from the instruction analysis unit (130) and the unit (120) for controlling acceleration or deceleration, wherein the starting point of the cycle motion is a point from which acceleration or deceleration of a first axis parallel to a direction of cutting feed and a second axis orthogonal to the first axis begins to cause a speed of the first axis to reach a predetermined cutting feed rate and to cause a speed of the second axis to be substantially zero upon arrival at the starting point for cutting a screw thread.

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