JPH08137538A - Feed rate control method for numerical controller - Google Patents

Abstract

PURPOSE: To automatically set a deceleration distance to an optimum value corresponding to working conditions by deciding a deceleration start point immediately before the corner part of a command locus corresponding to the product of a deceleration command speed and the sum of the reciprocal of a position loop gain and an acceleration/deceleration time constant. CONSTITUTION: In the case of performing the deceleration processing of the corner part, in an NC language analysis part 2, the deceleration distance of the corner part and a deceleration speed are decided and transferred to an interpolation processing part 3. At the time, in the NC language analysis part 2, by using the value of an NC parameter 6 stored beforehand, the deceleration distance Ld is obtained from Ld=FdXΔtxn×60 where Δt=Tp+Ta. In this case, the deceleration speed Fd is set by an NC program or the NC parameter. Tp is the reciprocal of the position loop gain which is the NC parameter and Ta is the acceleration/deceleration constant of the NC parameter. A deceleration distance magnification (n) is set as a value for which the time required for a feed rate to decline from a command speed to the deceleration speed Fd can not be secured. Then, in the interpolation processing part 3, the interpolation processing of the corner part is performed by using the transferred deceleration distance and deceleration speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed speed control method for a numerical controller, and more particularly to a feed speed control method for setting a deceleration distance when the feed speed of a corner portion is decelerated.

[0002]

2. Description of the Related Art In a machine tool using a numerical control device,
When controlling each feed axis, generally, position loop control is performed for each feed axis, and in order to suppress the occurrence of shock due to changes in the position command, for example, acceleration / deceleration processing is performed for each axis using an acceleration / deceleration filter. It is carried out. If position loop control or acceleration / deceleration processing is performed for each axis, the actual speed during movement of the axis rises later than the command speed, and the actual position also lags the command position. FIG. 3 shows the delay due to the position loop processing, and T _p is a constant determined by the reciprocal of the position loop gain which is the NC parameter. Further, FIG. 4 shows a delay due to acceleration / deceleration processing using a general first-order delay filter, and T _a is _a constant determined by the acceleration / deceleration time constant of the NC parameter. The delay amount of the actual position with respect to the command position is proportional to the sum of the reciprocal of the position loop gain and the acceleration / deceleration time constant, and also proportional to the feed speed.
In FIGS. 3 and 4, a dotted line extending obliquely upward and rightward from the origin is a tangent line that is tangent to the actual velocity in the drawings at the origin. The time until this tangent line intersects the commanded speed corresponds to T _p and T _a , respectively. Because of this delay amount,
If the interpolation feed is performed with two or more axes, there is a problem that the machining accuracy is reduced in the command corner portion. FIG. 5 shows the trajectory error of the corner portion due to this delay amount, and the command trajectories P ₁ and P ₂
The machining locus deviates from the command locus from q ₁ in front of the corner part, and coincides with the command locus P ₂ at q ₂ after passing the corner part.
A processing error occurs between the processing loci q _{1 and} q ₂ . The reason why the processing loci q _{1 to} q ₂ occur will be described with reference to FIG.
In a program in which only the Y axis is moved and then only the X axis is moved, the waveforms of the command speed of the X axis and the Y axis and the actual speed are as shown in the figure. The trajectories q _{11 to} q ₂₂ in FIG. 5 will be described in the section of the embodiment. In this case, when the Y-axis command is output, the X-axis starts to move without the actual position of the Y-axis reaching the end point of the Y-axis movement amount due to the delay amount, so that at the corner portion. , XY both axes will move,
The robot moves along the locus represented by the broken line in FIG. 5, resulting in a decrease in processing accuracy. As a means for suppressing such a decrease in machining accuracy, a method of decelerating a certain section from a command speed is adopted in the command corner portion. As described above, since the delay amount is proportional to the feed speed, it is possible to suppress the deterioration of machining accuracy by decelerating only the corner portion.

[0003]

However, in the prior art, the decelerating constant section (hereinafter referred to as deceleration distance) is NC.
Since it is set by the value instructed by the program or NC parameter, it is often determined from the experience value of the operator. For this reason, if the set deceleration distance is long, the machining time becomes long, and conversely, if the set deceleration distance is short, it will pass through the corner without being sufficiently decelerated due to the delay amount. The deceleration effect cannot be obtained, and the machining accuracy is reduced. Therefore, in order to solve such a problem, an object of the present invention is to automatically set the deceleration distance to an optimum value according to the processing conditions.

[0004]

In order to solve the above problems, the present invention provides a feed rate control method for a numerical controller having a closed loop for position control, in which the reciprocal of the position loop gain and the sum of the acceleration / deceleration time constant and the deceleration. Depending on the product of command speed,
A feed speed control method for a numerical control device, characterized in that a deceleration start point immediately before a corner portion of a command locus is determined, and a feed speed is set to the deceleration command speed from the deceleration start point to the corner portion.

[0005]

By the above means, the deceleration distance at the corner portion is set to the optimum value in accordance with the deceleration speed, the position loop gain and the acceleration / deceleration time constant. Hereinafter, the principle of the present invention will be described with reference to FIG. In the figure, F is a command speed, Fd is a deceleration speed (mm / min) of a corner portion (hereinafter simply referred to as deceleration speed), Δt is a unit time determined by a position loop gain and an acceleration / deceleration time constant, and Ld is a deceleration distance. It corresponds to the shaded area in the figure. The straight line K in the figure is a tangent line that is in contact with the actual speed described in FIGS. 3 and 4, and the time until the straight line K intersects the deceleration speed Fd corresponds to Δt. The deceleration distance Ld in the present invention is calculated by the following equation. Ld = Fd × Δt × n × 60 (1) where Δt = Tp + Ta Tp: 1 / position loop gain (sec) Ta: acceleration / deceleration time constant (sec) n: deceleration distance multiplying formula (1), deceleration speed Fd Is NC program or NC
It is set by the parameter. Tp is the reciprocal of the position loop gain which is the NC parameter, and Ta is the acceleration / deceleration time constant of the NC parameter. The deceleration distance multiplying factor n is set to a value that can secure an intimidating time because the feed speed decreases from the command speed F to the deceleration speed Fd. This time is given as an NC parameter because it depends on the acceleration / deceleration method.
When exponential acceleration / deceleration by a general first-order lag filter is used, the value of n is preferably about 3-4. As described above, according to the present invention, the deceleration distance of the corner portion is
Since the optimum values are automatically set from the values of deceleration speed, position loop gain, and acceleration / deceleration time constant, the machining time is shortened.
It is also possible to suppress a decrease in the machining accuracy of the corner portion.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of a feed rate control method for a numerical controller according to the present invention. Reference numeral 1 is a program memory storing an NC program, 2 is an NC language analysis unit that analyzes the NC program and converts it into data of a format that can be interpolated, and 3 is based on data output from the NC language analysis unit. An interpolation processing unit that performs linear interpolation, circular interpolation, etc., and creates a movement command for each axis, 4 is an acceleration / deceleration processing unit that performs acceleration / deceleration of each axis,
Reference numeral 5 represents a servo control unit that performs position control of each axis and speed control current control. When performing deceleration processing for corners, NC
In the language analysis unit 2, the deceleration distance and deceleration speed of the corner portion are determined and transferred to the interpolation processing unit 3. At this time, the NC language analysis unit obtains the deceleration distance L _d from the equation (1) using the value of the NC parameter 6 stored in advance. The interpolation processing unit uses the deceleration distance and deceleration speed transferred from the NC language analysis unit to interpolate the corner portion. FIG. 2 is a diagram for explaining the principle of the present invention and the embodiment, and the deceleration distance magnification n =
4 is a velocity waveform of the example set to 4. By setting the deceleration distance Ld so that the actual speed represented by the broken line is sufficiently reduced, it is possible to obtain the deceleration distance in which the processing time is short and the deterioration of the processing accuracy can be suppressed. As a result, the accuracy of the machining locus of the corner portion is improved as compared with the related art. Processing trajectory q in FIG.
_{11 to} q ₂₂ are machining trajectories according to the present invention, which are conventional machining trajectories q
It shows that the processing accuracy is improved from _{1 to} q ₂ .

[0007]

As described above, according to the present invention, the deceleration distance of the corner portion in the feed speed control method for decelerating the command corner portion is automatically set to the optimum value. Conventionally, since the deceleration distance is set by the operator's judgment, if the set deceleration distance is too long, the machining time becomes long, and if the deceleration distance is too short, the machining accuracy deteriorates. Is automatically set to an optimum value, and as a result, such a problem in the related art is solved.

[Brief description of drawings]

FIG. 1 is a block diagram of a feed rate control method as an embodiment of the present invention.

FIG. 2 is a diagram that serves to explain the principle of the present invention and an embodiment.

FIG. 3 is a delay caused by position loop control.

FIG. 4 is a delay due to acceleration / deceleration processing.

FIG. 5 is a command and trajectory of a corner section.

FIG. 6 is a velocity waveform of X and Y axes.

[Explanation of symbols]

 1 Program Memory 2 NC Language Analysis Section 3 Interpolation Processing Section 4 Acceleration / Deceleration Processing Section 5 Servo Control Section 6 NC Parameters

Claims (1)

[Claims] 1. A feed rate control method for a numerical controller having a closed loop for position control, wherein a command immediately before a corner portion of a command locus is determined according to a product of a reciprocal of a position loop gain, a sum of acceleration / deceleration constants, and a deceleration command speed. A deceleration start point is determined, and a feed speed is set to the deceleration command speed from the deceleration start point to the corner portion.