JP2005327321A - Numerical control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a numerical control system for outputting a combination of main axis rotation number and feed rate for optimum cutting condition even in the case that a tool axis is not perpendicular to XY surface for processing free form surface. <P>SOLUTION: The numerical control system, comprising an analysis part (11) which reads a processing program, and outputs a tool axis vector and an amount of each axis motion, an axis motion vector calculation part (12) which obtains axis motion vector from the amount of each axis motion, a main axis rotation number control means (15) which outputs to a main axis driver the main axis rotation number calculated based on the inclination of the tool axis from the tool axis vector and axis motion vector and variation of contact position of the tool and work material following the direction of the axis motion indicated by the processing program, and a distribution part (16) which calculates the feed rate based on the output of the main axis rotation number control means and the amount of each axis motion from the analysis part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a numerical control apparatus suitable for processing a free-form surface at high speed and with high accuracy.

  In a numerically controlled (NC) machine tool that processes a free-form surface at high speed and with high accuracy, the movement path of the tool is commanded by a machining program, and the movement speed of the tool along this path is also entered in the machining program. Commanded by However, if the movement is performed at the speed commanded by the F code, the machining accuracy may not be maintained due to error factors such as a delay in the servo system.

  In recent NC systems for free-form high-speed and high-precision machining, as a function to prevent such problems, the shape of the commanded path is evaluated, and the maximum allowable speed for keeping the machining accuracy within the allowable error range. Some of them are determined according to the shape and automatically suppress the speed below the maximum allowable speed regardless of the speed specified by the F code.

  Further, the rotational speed of the main shaft is instructed by the S code in the program, but there are optimum combinations of the rotational speed of the main shaft and the feed speed of the shaft depending on the cutting conditions. However, if there is a function to automatically control the feed speed according to the shape described above, if these values are commanded by the F code and S code of the program, the speed value is limited and the rotation speed of the spindle is constant. However, there is a drawback that the speed may be far from the value commanded by the F code.

  In general, it is said that a good cutting condition is that the feed amount per blade is constant and the cutting speed, that is, the relative tangential speed of the contact point between the tool and the workpiece is constant.

  From this point of view, the inventors of the present invention maintain the optimum condition of the combination of the rotational speed of the main spindle and the feed rate determined by the cutting conditions in the processing of the free-form surface in Japanese Patent Application No. 7-175277 (JP 9-29584 A). In addition, we proposed a numerical control device that can reduce tool wear and enable high-speed and high-precision machining. This numerical control device controls a peripheral speed in accordance with a contact diameter of a tool that changes every moment depending on a curved surface shape, and synchronizes rotation and feed speed. Specifically, the spindle speed is changed by the spindle speed control means according to the feed speed obtained by the feed speed determining means based on the moving shape of the tool commanded by the machining program, and the axis moving direction The spindle rotation speed based on the change in the contact position between the tool and the workpiece is changed by the main rotation speed control means, and the axis movement direction information obtained by the feed speed determination means based on the moving shape of the tool The main shaft rotational speed is changed by the main rotational speed control means on the basis of the feed speed including.

  As a result, the actual cutting speed is stabilized, the tool life is extended, tool wear occurs, and a stable feed speed per blade is obtained, so that the quality of the machined surface is improved and the machining time is shortened by improving the feed speed. Can be expected.

  However, the invention previously proposed by the inventors is based on the premise that the tool axis is perpendicular to the XY plane of the machine tool.

  For this reason, when the tool axis is not perpendicular to the XY plane but perpendicular to the XY plane, such as when using an angle head, the rotational speed (S code) of the main shaft according to the moving direction according to the above-described invention. However, there is a problem that correct control is not performed between the tool and the shape even if the feed rate (F code) is controlled.

  The present invention has been made to solve such problems. In the machining of free-form surfaces, the optimum condition of the combination of the spindle speed and the feed rate determined by the cutting conditions even when the tool axis direction is not perpendicular to the XY plane. Provides a numerical control device that can prevent the actual machining conditions from being separated from each other, extend tool life by suppressing tool wear and breakage, enable high-speed and high-precision machining, and suppress increase in program capacity The purpose is to do.

  According to the present invention, in a numerical control device that controls a machine tool that processes a shape surface of a workpiece, an analysis unit that reads a machining program, outputs a tool axis direction vector, and outputs an amount of movement in each axis direction, An axis movement direction vector calculation means for obtaining an axis movement direction vector from each axial movement amount, a tool associated with the tool axis direction vector and the axis movement direction commanded by the machining program according to the inclination of the tool axis from the axis movement direction vector Calculates the spindle speed based on the change in the contact position of the work material, outputs the spindle speed to the spindle driver, outputs from the spindle speed control means, and moves in each axial direction from the analysis unit A distribution unit that calculates a feed rate based on the amount is provided.

A ball end mill having a radius R (mm) inclined by an angle θ with respect to the XY plane is used as a machining tool, and the optimum peripheral speed when the tool axis direction vector is Vt and the moving direction vector Vd, θ = π / 2. When V0 (mm / min) and the spindle speed at this time are S0 (rpm),
The spindle speed control means sets the spindle speed S to S = S0 | Vt || Vd | / Vt · Vd (rpm)
Calculated according to the formula
The distribution unit assumes that the feed speed for S0 is F0, and the feed speed F for S is F = F0 | Vt || Vd | / Vt · Vd (mm / min)
It is good to calculate according to the formula.

  It is preferable that the rotation speed control unit further includes a limiter that gives upper and lower limit values to the calculated spindle rotation speed to limit the calculated rotation speed.

  In the numerical control device according to the present invention, even when the tool axis is not perpendicular to the XY plane using an angle head or the like, the feed amount per blade is constant and the cutting speed, that is, the tool and the work piece are cut. The relative tangential speed of the contact point of the material becomes constant, so that tool wear and breakage can be suppressed, the tool life can be extended and the machining time can be shortened.

  As described above, in the numerical control device according to the present invention, the spindle speed and feed speed are controlled using the tool axis direction vector and the moving direction vector to maintain the optimum cutting speed. Even when the tool axis is not perpendicular to the XY plane, the feed rate per blade is constant, the cutting speed is constant, tool wear and breakage are suppressed, and tool life is extended. At the same time, the processing time can be shortened.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a numerical controller 10 according to an embodiment of the present invention. In this embodiment, the spindle rotational speed command value is not commanded in the machining program.

  The machining program 1 is sent to the analysis unit 11 where it is analyzed. The analysis unit 11 extracts a character string such as an X code, an S code, a G code, and an M code from the character string in the machining program, and the axis movement amount is obtained therefrom. For example, the movement amount along the X, Y, and Z axes can be obtained from the coordinates of the start point and end point of the machining. A tool axis direction vector is obtained from the coordinates and angle of the tool. These amounts are obtained for each block.

  The movement amount of each axis is converted into a movement command for each axis by the distribution unit 16 and sent to the servo system 20 for each axis.

  On the other hand, the movement amount of each axis is given to the axis movement direction vector calculation unit 12, and the axis movement direction vector is calculated and sent to the spindle rotation number calculation unit 15.

  Further, the spindle speed calculator 15 includes a desired cutting speed as a reference value stored in the desired cutting speed storage unit 13, a maximum spindle speed, a maximum spindle speed stored in the minimum spindle speed storage unit 14, The minimum spindle speed, the above-described tool axis direction vector, and the spindle override amount are input, and the spindle speed command value S is obtained based on these. The command value S is output to the spindle driver 30.

The method for calculating the spindle speed is, for example, as follows.
Since the present invention is based on the premise that the tool axis is not perpendicular to the workpiece plane, it is necessary to define the tool axis direction as a parameter or variable. Therefore, as shown in FIG. 2, a tool axis direction vector Vt and a moving direction vector Vd are defined.

2 shows a tool 40 and a workpiece 50 represented as an end mill, and the angles formed by the tool axis direction vector Vt and the movement direction vector Vd are ψ, π / 2−ψ = θ as shown in FIG. Then, the peripheral speed at the cutting point of the tool with the spindle speed S (rpm) and the radius R (mm) is V = 2πrS (mm / min)
r = Rsin (θ) (mm)
It becomes.

If the optimum peripheral speed when θ = π / 2 is V0 (mm / min) and S at this time is S0 (rpm),
V0 = 2πRS0
Therefore, in order to always set the peripheral speed to V0 at an arbitrary θ,
2πRS0 = 2πRsin (θ) S
Because S = S0 / sin (θ)
Which is S = S0 / cos (ψ)
Can also be expressed.

Here, when considering the inner product of Vt and Vd, Vt · Vd = | Vt || Vd | cos (ψ)
Because
cos (ψ) = Vt · Vd / | Vt || Vd |
It becomes.

Using this relationship,
S = S0 | Vt || Vd | / Vt · Vd (rpm)
It becomes.

  The spindle rotation speed S is sent to the distribution unit 16, and the tool feed speed is also calculated.

That is, if the feed speed for S0 is F0, F for S is F = F0 | Vt || Vd | / Vt · Vd (mm / min)
It becomes. At this time, if the tool direction vector is a unit vector, | Vt | = 1.
F = F0 | Vd | / VtVd (mm / min)
Therefore, the F value may be set as the upper limit speed.
In the spindle speed calculator 15, the spindle speed determined in the above-described procedure can be corrected as necessary.
If Kx = actual feed speed / reference feed speed, Sx = command speed * Kx * spindle override. However, since this speed should be between a predetermined minimum speed and a maximum speed,
Sx may be determined so as to satisfy the condition of minimum rotational speed ≦ Sx ≦ maximum rotational speed.

  According to this embodiment, since the axis movement direction vector is obtained from the movement amount of each axis and the spindle rotation speed is obtained together with the tool axis direction vector specified by the machining program, the optimum rotation speed command for the spindle is obtained. Since there is no need to add a value (S command value) to the program, the machining program can be shorter than when the optimum S command value is added to the machining program, so there is less memory for storing the program, There is no need to increase the communication speed during buffer operation.

  Further, the optimum cutting conditions are maintained even when the tool axis is not perpendicular to the XY plane using an angle head or the like.

  In the above embodiment, the spindle speed is first optimized and the feed speed is followed. However, as shown in FIG. 1, the obtained optimum feed speed is again calculated as the spindle speed. It is also possible to input the signal to the unit and finally correct the spindle rotational speed.

It is a block diagram which shows embodiment of this invention. It is explanatory drawing which shows the principle in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Machining program 10 Numerical control apparatus 11 Analysis part 12 Axis movement direction vector calculation part 13 Desired cutting speed memory | storage part 14 Spindle maximum rotation speed and minimum rotation speed memory | storage part 15 Spindle speed calculation part 16 Distribution part 20 Servo mechanism 30 Spindle driver

Claims (3)

A numerical control device for controlling a machine tool for machining a shape surface of a workpiece,
An analysis unit that reads a machining program, outputs a tool axis direction vector, and outputs an amount of movement in each axis direction,
An axial movement direction vector calculating means for obtaining an axial movement direction vector from the respective axial movement amounts;
The spindle driver calculates the spindle speed based on the tool axis direction vector and the axis movement direction vector based on the inclination of the tool axis and the change in the contact position between the tool and the work material in accordance with the axis movement direction commanded by the machining program. Spindle speed control means for outputting to
A numerical control apparatus comprising: a distribution unit that calculates a feed rate based on an output of the spindle rotation speed control means and an amount of movement in each axial direction from the analysis unit. A ball end mill having a radius R (mm) inclined by an angle θ with respect to the XY plane is used as a machining tool, and the optimum peripheral speed when the tool axis direction vector is Vt and the moving direction vector Vd, θ = π / 2. When V0 (mm / min) and the spindle speed at this time are S0 (rpm),
The spindle speed control means sets the spindle speed S to S = S0 | Vt || Vd | / Vt · Vd (rpm)
Calculated according to the formula
The distribution unit assumes that the feed speed for S0 is F0, and the feed speed F for S is F = F0 | Vt || Vd | / Vt · Vd (mm / min)
The numerical control device according to claim 1, wherein the numerical control device is calculated according to the formula:   The numerical control device according to claim 1, wherein the rotation speed control unit further includes a limiter that applies upper and lower limits to the calculated spindle rotation speed to limit the calculated rotation speed.

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