JP3164512B2 - Numerical control unit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a numerical controller for controlling a moving path of a moving body such as a tool or a table in accordance with a given command. In particular, in a machine tool, an interpolation error at the time of fraction processing is allowed. The present invention relates to a numerical control device that realizes highly efficient machining with an accuracy within an error.

[0002]

2. Description of the Related Art For example, in a machining center that performs three-dimensional machining, machining is performed by relatively moving a workpiece and a tool according to a shape specified by a machining program. In this case, a tool, a tool, a table, and the like are moving bodies, but these moving bodies differ depending on the actual machine configuration. However, according to the numerical control device, normally, when a command is output to a controller of a servomotor that drives the X-axis, the Y-axis, and the Z-axis, the moving body operates and machining is performed. FIG. 5 shows an example of the configuration of such a numerical control device.

The analysis means 1 reads the machining program PP, and reads from it a speed command F required for speed control, a target position G required for interpolation, an outer angle θ of a command shape between blocks (an angle difference between commands of each block), and the like. Is analyzed and stored in the block data buffer 2 as block data B for each block.

The block data supply means 3 comprises an interpolation means 10
From the completion notification E indicating that the interpolation has been completed,
The shape data Sn of the new n-th block is taken out from the block data buffer 2 and passed to the interpolation means 10. At the same time, it sends the speed command Fn to the interpolation unit amount calculation means 4.

[0005] The interpolation means 10 interpolates the shape represented by the shape data Sn in accordance with the interpolation unit amount Δf. This interpolation is performed at regular intervals. As shown in FIG. 7, when the current cycle is i, a point advanced by Δfi from the interpolation point Pi-1 of the previous cycle toward the target position Gn is defined as the interpolation point of the current cycle. It is output to the servo controller 11 as Pi. Further, the distance from the interpolation point Pi to the target position Gn is calculated, and is stored as the remaining distance ri + 1 for the calculation of the next cycle.

When the target position Gn is reached, the interpolation of the shape data Sn is completed, and the interpolation means 10 outputs a completion notification E to the block data supply means 3 to request the shape data Sn + 1 of the next block. At this time, if a point advanced by Δfi from the interpolation point Pi-1 exceeds the target position Gn, the shape data Sn + 1 is obtained, and then (Δfi
A point that has advanced to the target position Gn + 1 by −ri) is set as an interpolation point Pi in the current cycle (FIG. 3A). Interpolating across two blocks in this manner is hereinafter referred to as "fraction processing".

The interpolation unit amount calculating means 4 calculates an interpolation unit amount Δfi for each interpolation cycle and outputs the calculated interpolation unit amount Δfi to the interpolation means 10.
Basically, the speed command F from the block data supply means 3
n, but in order to be able to move at the maximum speed at which the acceleration is equal to or less than the allowable acceleration, from the block data of the n-th front and rear blocks of the block data buffer 2,
A speed pattern is calculated in consideration of the shape and the allowable acceleration Amax. FIG. 6A shows an example of the shape, and FIG. 6B shows an example of the velocity pattern. Then, from this speed pattern, the interpolation unit amount Δfi of the current cycle corresponding to the remaining distance ri from the interpolation means 10 is determined. The hatched area in FIG. 6C is the remaining distance ri,
The remaining distance ri from time t (Gn) corresponding to the target position Gn
The speed at the time corresponding to the previous time is obtained and set as the interpolation unit amount Δfi.

The servo controller 11 receives the interpolation points Pi instructed by the interpolation means 10 and drives the corresponding servo motors Mx, My and Mz according to the X, Y and Z components. As a result, the moving body moves and processing is performed.

According to such a numerical control device, when the operation is started or stopped, or even when the moving direction changes, acceleration / deceleration is performed at an allowable acceleration or less, so that an excessive load is applied to the motor. Also, it does not give a sudden shock to the mechanical system, and operates at the maximum speed that can be taken below the allowable acceleration, so that the processing efficiency is good. In particular, even in the vicinity of the target position G where the moving direction changes, a fractional process of interpolating the given interpolation unit amount over two blocks is performed, so that a rapid speed change does not occur.

[0010]

However, in the prior art, an interpolation error ε occurs between the target position G specified by the machining program and the interpolated shape interpolated over two blocks in the fraction processing. (Fig. 3 (a)).
This interpolation error ε increases as the interpolation unit amount Δf increases, and increases as the outer angle θ of the two straddling shapes increases. Furthermore, it also depends on the distance from the interpolation point in the previous cycle to the target position. This means that accuracy cannot be guaranteed with the above-described conventional technology.

Although the target position G instructed by the machining program can always be output as an interpolation point without performing the fraction processing, a rapid change in speed occurs.
The interpolation unit amount calculating means can determine the interpolation unit amount so that the target position G is always output as the interpolation point. However, if the shape specified by the machining program is a minute linear shape, Therefore, the interpolation unit amount is suppressed by the length of the minute straight line, and the processing efficiency is reduced.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a numerical controller capable of guaranteeing accuracy and performing interpolation with good machining efficiency.

[0013]

According to the present invention, there is provided a numerical controller for controlling a moving body along a shape constituted by a plurality of linear movement commands given from a program. Interpolating means for interpolating according to the given interpolation unit amount and outputting the interpolation point and the remaining distance to the target position of the command being interpolated, and moving at a speed at which the acceleration is equal to or less than the allowable acceleration from the shape and the remaining distance An interpolation unit amount calculating means for calculating an interpolation unit amount for each cycle, an allowable error storage unit for storing an allowable error, an allowable error of the allowable error storage unit, an outer angle of a straight line during the interpolation and a next straight line, and A distance calculation unit that calculates a limit distance that is a distance from the target position of the interpolation point at which the interpolation error becomes the permissible error from the remaining distance to the target position, and calculates the limit distance and the remaining distance. An addition unit that sets a limit interpolation unit amount, and a minimum value selection unit that selects a smaller one of the limit interpolation unit amount and the interpolation unit amount from the interpolation unit amount calculation unit and sets the selected unit as the limit interpolation unit amount; The interpolation unit amount from the interpolation unit amount calculation unit is compared with the remaining distance from the interpolation unit. If the interpolation unit amount is larger than the remaining distance, the limited interpolation unit amount from the minimum value selection unit is interpolated. A switching unit that outputs the interpolated unit amount from the interpolated unit amount calculating unit to the interpolating unit if the interpolated unit amount is not output to the interpolating unit.

In the numerical controller according to the present invention, when fraction processing is performed, a limit distance at which the interpolation error is equal to or less than an allowable error is calculated from the outer angle of the shape and the remaining distance, and this limit distance and the remaining distance are calculated. The limit interpolation unit amount, which is the sum of the distances, is compared with the interpolation unit amount considering the allowable acceleration, and the smaller one is set as the interpolation unit amount to be actually interpolated. That is, the interpolation is performed with the maximum interpolation unit amount that does not exceed the allowable acceleration and that the interpolation error generated when performing the interpolation that crosses two straight lines is equal to or less than the allowable error.

[0015]

FIG. 1 is a structural example of an embodiment of a numerical controller according to the present invention. First, the present invention will be described with reference to FIG. Elements and signals having the same symbols as those in FIG.
The description is omitted because it is the same as that of the related art.

The switching unit is a fraction processing determination unit 5, and
It comprises three linked switches SW1, SW2 and SW3. The fraction processing determination unit 5 calculates the remaining distance ri and the interpolation unit amount Δ
When the remaining distance ri is smaller than the interpolation unit amount Δfi, fraction processing is executed by the interpolation means 10, so that the switches SW1, SW2,. SW3 is switched to a side. Conversely, if the remaining distance ri is greater than or equal to the interpolation unit amount Δfi, the fraction processing is not performed, and the switches SW1, SW2,
SW3 is switched to the b side. This state is the same as that of FIG. 5, that is, the configuration of the prior art, because the interpolation unit amount Δfi from the interpolation unit amount calculation unit 4 is directly input to the interpolation unit 10 via the switches SW2 and SW3. Hereinafter, the description with reference to FIG.
3 is limited to a side.

The permissible error storage unit 6 stores a permissible error .epsilon.
The operator sets the allowable error εt by setting means (not shown) such as a keyboard prior to machining.
Is specified according to the precision required for processing.

The distance calculator 7 calculates a limit distance d from the allowable error εt, the outer angle θn and the remaining distance ri.

A specific description will be given with reference to FIG. Gn is n
It means the target position of the th block. The external angle formed by the line segment Gn-1Gn and the line segment GnGn + 1 is the external angle θn. The point Pi-1 is the interpolation point of the previous cycle, and the point Pi-1 to the point G
The distance to n is the remaining distance ri.

Now, as shown in FIG. 3A, if ri <Δfi, the fraction processing is executed, and the interpolation points Pi in the current cycle are executed.
Is taken on the line segment GnGn + 1. When the fraction processing is executed, the line segment Pi-1Pi becomes an interpolation shape, that is, a command shape to the servo controller 11. At this time, the line segment Pi-
1P i is separated from the target position Gn by the machining program by ε. This ε is called an interpolation error.

The interpolation error ε increases as the point Pi is farther from the point Gn. Therefore, when trying to make the interpolation error ε less than the allowable error εt, the point Pi must be within a certain distance from the point Gn. This distance is called a limit distance (FIG. 3B).
The distance calculation unit 7 calculates the limit distance d by the function fd () of Equation 1.
Is calculated.

[0022]

D = fd (εt, θn, ri) The function fd () will be described later. As long as the distance is equal to or less than the limit distance d, the interpolation error is within the allowable error εt regardless of the interpolation method.

The adder 8 adds the remaining distance ri and the limit distance d to obtain a limit interpolation unit amount u at which the interpolation error becomes an allowable error εt.
Ask for.

The minimum value selector 9 selects the smaller one of the limit interpolation unit amount u and the interpolation unit amount Δfi from the interpolation unit amount calculation means 4 to determine the limit interpolation unit amount v. This limited interpolation unit amount v is output to the interpolation means 10 via the switch SW3 as the interpolation unit amount Δfi. The limit interpolation unit amount u is the interpolation unit amount Δ from the interpolation unit amount calculation means 4.
If the value is smaller than fi, the value of the limit interpolation unit amount u is selected. Therefore, in the fraction processing of the interpolation means 10, a point where the interpolation error becomes the allowable error εt is interpolated. Conversely, if the interpolation unit amount Δfi from the interpolation unit amount calculation means 4 is smaller than the limit interpolation unit amount u, the value of the interpolation unit amount Δfi is selected. The error is equal to or smaller than the allowable error εt.

The above is an explanation of the present invention based on FIG.

Next, the function fd (εt, θ, r) will be described with reference to the flowchart of FIG.

When the process is started (step S0), first, in step S1, the outer angle θ is compared with 0 °, and if they are equal, the limit distance d is made infinite in step S2. This is because no interpolation error occurs if the two shapes are on the same straight line.

If the external angle θ is not 0 ° in step S1, the external angle θ is further compared with 90 ° in step S3, and if it is 90 ° or less, step S4 is executed. 9
If it is larger than 0 °, step S6 is executed.

In step S4, the remaining distance r is equal to ε.
If t / sin θ or less, the process jumps to step S2, where the limit distance d is set to infinity in step S2. In this case, no matter where the interpolation point is set, the interpolation error is equal to or smaller than the allowable error εt, so that there is virtually no limit. Otherwise, the process jumps to step S5, where the limit distance d is calculated by the function fd '() shown in equation (2).

[0030]

(Equation 2) If it is determined in step S3 that the outer angle θ is larger than 90 °, that is, if the outer angle θ is larger than 90 ° and equal to or smaller than 180 °, step S6 is executed. In step S6, the remaining distance r is compared with the allowable error εt. If the remaining distance r is equal to or smaller than the allowable error εt, the process jumps to step S2, and the limit distance d is set to infinity in step S2. Otherwise,
Jump to step S7.

In step S7, the remaining distance r is further reduced by -ε.
If it is determined that the difference is equal to or smaller than t / cos θ, the process jumps to step S5, and in step S5, the function fd ′ ()
To calculate the limit distance d. Otherwise, that is,
If the remaining distance r is larger than-? T / cos ?, the process jumps to step S8. In this case, the interpolation error is set to the allowable error εt.
In order to reduce the distance d, the critical distance d must be equal to or smaller than the allowable error εt.
Is equal to the allowable error εt.

In this way, the limit distance d is determined in any of steps S2, S5, and S8 based on the values of the external angle θ, the remaining distance r, and the allowable error εt. When these processes are completed, the process jumps to step S9 and ends.

The above is the description of the function fd (εt, θ, r). According to this function, the limit distance d at which the interpolation error becomes equal to or smaller than the allowable error εt can be calculated. For example, 0 ° <θ ≦ 9
At a certain outer angle θa of 0 °, the limit distance da as shown in FIG. 4A is determined. If the remaining distance is different (rb <ra) even at the same outer angle θa, the limit distance as shown in FIG. db is determined. Further, in the example of 90 ° <θ ≦ 180 °, even if the same ra as in FIG. 4A, the limit distance d as shown in FIG.
c is determined. In each of these examples, the interpolation error becomes the allowable error εt.

In the above numerical control device, the interpolation error becomes equal to or less than the allowable error according to the outer angle and the remaining distance (ie, the interpolation point of the previous cycle) each time the fractional processing is performed in addition to the allowable error. Determine the maximum limit interpolation unit quantity. Then, this limit interpolation unit amount is compared with the interpolation unit amount in which the allowable acceleration is considered for the stability of the machine operation, and the smaller one is set as the interpolation unit amount for actually interpolating, so that the allowable acceleration is not exceeded, and Interpolation can be performed with the maximum interpolation unit amount at which the interpolation error is equal to or less than the allowable error. When the fraction processing is not performed, the interpolation is performed according to the interpolation unit amount in consideration of the shape and the allowable acceleration from the interpolation unit amount calculation means, but no interpolation error occurs in any interpolation unit amount in the same linear shape.

[0035]

According to the numerical controller of the present invention described above, the interpolation error is always equal to or less than the allowable error, and the accuracy required for machining is guaranteed by specifying the allowable error. In addition, the interpolation unit amount in this case performs interpolation with the maximum interpolation unit amount permitted in both the machine operation and the interpolation error, so that unnecessary speed reduction is not caused and stable machining of the machine operation with high machining efficiency is performed. Can be done.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment of a numerical controller according to the present invention.

FIG. 2 is a flowchart showing processing of a function for calculating a limit distance d.

FIG. 3 is a diagram illustrating an interpolation error and a limit distance.

FIG. 4 is a diagram showing an example of a limit distance by the device of the present invention.

FIG. 5 is a block diagram illustrating a configuration of an example of a conventional numerical control device.

FIG. 6 is a diagram illustrating an interpolation unit amount calculation unit of the conventional device.

FIG. 7 is a diagram illustrating interpolation by an interpolation unit.

[Explanation of symbols]

4 Interpolation unit amount calculation means, 5 fraction processing determination unit, 6 allowable error storage unit, 7 distance calculation unit, 8 addition unit, 9 minimum value selection unit, 10 interpolation unit, SW3 interpolation unit amount switch, Δf interpolation unit amount, r Remaining distance, εt
Tolerance, θ outer angle, d limit distance, u limit interpolation unit amount, v limit interpolation unit amount.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G05B 19/4103 G05B 19/416

Claims (1)

(57) [Claims] 1. A numerical control device for controlling a moving body along a shape constituted by a plurality of linear movement commands given from a program, comprising: interpolating a commanded shape in accordance with an interpolation unit amount given at regular intervals. Interpolation means for outputting the interpolation point and the remaining distance to the target position of the command being interpolated, and the interpolation unit amount for each cycle so that the acceleration moves from the shape and the remaining distance at a speed not higher than the allowable acceleration. An interpolation unit amount calculating means for calculating; an allowable error storage unit for storing an allowable error; an allowable error of the allowable error storage unit; A distance calculation unit that calculates a limit distance that is a distance from the target position of the interpolation point at which the interpolation error becomes the permissible error, and a limit interpolation unit amount by adding the limit distance and the remaining distance. An adding unit, a minimum value selecting unit that selects a smaller one of the limit interpolation unit amount and the interpolation unit amount from the interpolation unit amount calculation unit and sets it as the limited interpolation unit amount, The interpolation unit amount is compared with the remaining distance from the interpolation means.If the interpolation unit amount is larger than the remaining distance, the limited interpolation unit amount from the minimum value selector is not output to the interpolation means. A switching unit that outputs an interpolation unit amount from the interpolation unit amount calculation unit to the interpolation unit, and performs interpolation with a maximum interpolation unit amount that causes an interpolation error to be equal to or less than an allowable error.