JPH0266604A - Numerical control system - Google Patents

Abstract

PURPOSE:To ensure the stable working accuracy by correcting a command locus designated by a working program based on an allowable locus error inputted previously and at the same time correcting the feed speed based on the information obtained by detecting the corrected command locus and the position of a drive part. CONSTITUTION:A command locus Pc is corrected based on the position correction value Dc and a new command locus Pex is calculated. This new locus is sent to a function generating part 5 and also to a command form evaluating part 4'. The form data SD' is calculated based on the locus Pex. While a feed speed correcting part 9' calculates an allowable follow-up delay amount with which the locus error is kept within the value obtained by adding an allowable locus error Et and the value Dc together based on the data SD'. At the same time, the part 9' calculates an actual follow-up delay amount based on the shift value DELTAf set per unit time outputted from the part 5 and the detection value Pa given from a position detector 8. Furthermore the part 9 corrects the feed speed Ft so that the actual follow-up delay amount is kept within the allowed follow-up delay amount and calculates a new command feed speed Fex.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is designed to reduce the trajectory error between the commanded trajectory specified by a machining program and the actual tool trajectory to within an allowable trajectory error amount manually inputted in advance. Numerical control (hereinafter referred to as NC)
This paper relates to numerical control methods for controlling the drive parts of machine tools.

(Prior Art) In known NC machine tools, machining is performed by commanding the machining shape, feed rate, tools to be used, etc. using a machining program that is manually input. However, in actual machining, a deviation (trajectory error) occurs between the command trajectory commanded by the machining program and the actual tool trajectory due to delays in the servo system of the machine. This trajectory error becomes particularly noticeable in a curved portion where the machining shape changes when machining is performed at a high cutting feed rate, particularly in a corner portion where the rate of shape change is rapid.

For this reason, recently, the feed rate that makes the trajectory error less than the allowable trajectory error amount input in advance is calculated based on the commanded trajectory, and the drive section of the NC machine tool is controlled based on the calculated feed rate. A numerical control method has been proposed.

FIG. 7 is a block diagram showing an example of an NC device that implements this conventional numerical control method.

In the figure, the NC device that realizes the conventional numerical control method includes a machining program 1 stored on a paper tape, an external human power device 2 into which the allowable trajectory error amount Et is input, and a machining device that interprets the contents of the machining program l. A program interpretation section 3, a command shape evaluation section 4 that calculates machining shape data SD,
a function generating unit 5 that calculates a movement amount Δf per unit time;
A feed rate correction unit 9 that corrects the input feed rate FC, a servo motor (M) 7 that drives a tool, etc.
It is comprised of a servo control section 6 that controls the servo motor 7, and a position detector (D) 8 that detects the position of tools and the like.

A conventional numerical control method in the NC device having the above-mentioned configuration will be explained.

First, machining program 1 is sent to the NC via a tape reader, etc.
The data of each block of the machining program 1 is read into the machining program interpreter 3 manually.

The machining program interpreter 3 that has read the data for each block analyzes the data to create a command trajectory P. , and set the command feed rate F. This command trajectory PC is sent to the function generation section 5 and also to the command shape evaluation section 4, and the command shape evaluation section 4, which manually generated the command trajectory PC, calculates machining shape data SD based on it. This machining shape data SD is data indicating the shape of the commanded trajectory, and is used when calculating data such as feed rate due to the shape of the commanded trajectory. Examples include the radius of a virtual arc that passes through the command point of one arbitrary block and the command points of one block before and after that block, or the corner angle formed by one arbitrary block and the block next to that block. Alternatively, various forms can be considered, such as approximating a command point of one arbitrary block and command points of several blocks before and after that block to a curve, and using the slope of the curve at that time.

Then, this machining shape data SD is sent to the feed rate correction unit 9, and the feed rate correction unit 9 adjusts the allowable trajectory error so that the trajectory error is within the allowable trajectory error amount E5 specified by the operator via the external human power device 2. Calculate the tracking delay amount.

At this time, the allowable follow-up delay amount is calculated from the allowable trajectory error amount Et, machining shape data SD, constants of the servo system, and the like. Further, the allowable trajectory error amount Et can be specified not only from the external human power device 2 but also from the machining program 1.

The feed speed correction section 9 calculates the above-mentioned allowable follow-up delay amount, and also calculates the movement amount Δf per unit time from the function generation section 5.
The actual follow-up delay amount is calculated from the detected value P1 from the position detector 8 attached to the servo motor. Further, the difference between the calculated allowable follow-up delay amount and the actual follow-up delay amount is calculated, and the command feed speed FC is further corrected based on the difference, and the feed speed F ax is calculated. At this time, if the difference is positive, the feed rate Fa is increased to reduce the difference.
Set x<FC, and if the difference becomes equal to 1, the correction of the command feed rate is stopped and Fex=FC.

Finally, the function generator 5 generates the command trajectory PC and the feed rate Fa.
The moving amount Δf per unit time is calculated based on x, and the servo control unit 6 drives the servo motor 7 based on Δf.

As described above, conventionally, the actual follow-up delay amount is compared with the allowable follow-up delay amount obtained from the command trajectory of the machining program, the allowable trajectory error amount input in advance, etc., and the actual follow-up delay amount is By correcting the command feed rate so that it falls within the allowable trajectory error amount, it is possible to reduce the trajectory error to within the allowable trajectory error amount.

(Problems to be Solved by the Invention) In the conventional numerical control method as described above, even if the machining program commands a high cutting speed to complete the machining in a short time, the machining shape may change due to curved shapes. The situation was such that cutting was performed at a much slower speed than the feed rate commanded by the machining program, particularly in corner-shaped areas where the rate of shape change was rapid.

Therefore, there is a problem in that the overall machining time increases as a result. In addition, especially in mold machining where the machining time is long, this increase in machining time is a significant problem.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to keep the trajectory error within the allowable trajectory error amount,
Another object of the present invention is to provide a numerical control method that avoids an increase in machining time due to a decrease in feed speed and can guarantee stable machining accuracy, including errors caused by unpredictable factors.

(Means for Solving the Problems) The present invention relates to a numerical control method for controlling a drive section of a machine tool based on a command trajectory and a command feed rate commanded by a machining program, and the above object of the present invention is to , predicting a trajectory error between the actual trajectory of the drive unit and the commanded trajectory when the drive unit is controlled based on the commanded feed rate, and based on the predicted trajectory error and an allowable trajectory error amount manually inputted in advance. A position correction amount is calculated, the command trajectory is corrected based on the calculated position correction amount, and an allowable follow-up delay amount is calculated based on the corrected command trajectory and the allowable trajectory error amount, and the position of the drive unit is adjusted. The actual follow-up delay amount is calculated based on the information obtained by detecting the follow-up delay amount, and the command feed rate is corrected based on the calculated follow-up delay amount and the allowable follow-up delay amount, and the corrected command trajectory and correction are performed. This is achieved by controlling the drive unit based on the commanded feed rate.

(Function) The numerical control method of the present invention corrects the command trajectory commanded by the machining program based on the allowable trajectory error amount manually entered in advance, and also detects the corrected command trajectory and the position of the drive unit. By correcting the feed rate from the obtained information, it is possible to guarantee stable machining accuracy, including errors caused by unpredictable factors, without significantly reducing the feed rate.

(Embodiment) First embodiment; FIG. 1 is a block diagram showing a first embodiment of an NC device that realizes the numerical control method of the present invention, corresponding to FIG. will be added and the explanation will be omitted.

In the figure, this NC device calculates the feed rate F based on the command feed rate FC shape data SD and the allowable trajectory error amount E.
A feed rate calculation unit 11 that calculates t, predicts the trajectory error in the feed rate Ft caused by delays in the servo system, etc. based on the shape data SD, and calculates the predicted trajectory error and the allowable trajectory error 'L manually input in advance. A position correction amount calculation unit 10 that calculates the optimal position correction mDc according to each command trajectory PC based on Et, and shape data based on the command trajectory PeX as a result of correcting the command trajectory PC using the position correction amount DC. A commanded shape evaluation section 4'' for calculating SD' is newly provided.

FIG. 2 shows a flowchart of the operation of the numerical control method of the present invention. The operation of this embodiment will be explained based on FIG.

First, machining program 1 is sent to the NC via a tape reader, etc.
The data for each block of the machining program 1 is input to the machining program interpreter 3 (
Step 51). The machining program interpreter 3 that has read the data for each block calculates the command trajectory PC and command feed rate FC by analyzing the data (step S2).

Next, the feed rate calculation unit 11 sets the feed rate Ft, and the position correction amount calculation unit 1O predicts the trajectory error in the feed rate Ft caused by delays in the servo system based on the shape data SD. The optimum position correction amount Or corresponding to the commanded trajectory PC is calculated based on the trajectory error and the allowable trajectory error amount Et manually entered in advance. (Step S3)
. Further, the command trajectory PC is corrected based on the position correction unit Dc, and a new command trajectory P is obtained. X is calculated (step S4). The command trajectory Pex is sent to the function generating section 5 and also to the command shape evaluation section 4', and the command shape evaluation section 4' generates shape data SD based on the command trajectory Pax through the same process as the command shape evaluation section 4. ' Calculate.

On the other hand, the feed rate correction section 9° is within the magnitude of the trajectory error that occurs when the function generation section 5 generates the function based on the command trajectory PaX, or the sum of the allowable trajectory error amount Et and the position correction FX D c. The allowable follow-up delay amount is calculated based on the shape data SD' (step S5), and the amount of movement Δf per unit time output from the function generator 5 and the detected value from the position detector 8 are calculated. The actual follow-up delay amount is calculated based on P. Further, the feed rate Ft is corrected so that the actual follow-up delay amount is within the total allowable follow-up delay, and a new command feed rate Fax is calculated (step 56). Here, since the method of correcting the feed rate is the same as that of the prior art, the explanation will be omitted.

By the way, the function generator 5 generates a command trajectory P. The movement amount Δf per unit time is calculated by generating a function based on X and the commanded feed rate F ax. This movement amount Δf per unit time is determined by the feed rate correction section 9 as described above.
On the other hand, it is sent to the servo control section 6. The servo control unit 6 manually controls the movement amount Δf per unit time.
Based on this, the servo motor 7 is driven.

Figure 3 shows the command trajectory P. 8 is shown below.

In the figure, ε8 is a command trajectory P that is instructed to the machining program inside the position correction amount calculation unit IO. is the predicted trajectory error based on the shape of . As shown in the figure, this predicted trajectory error ε6 can be calculated by simulating the actual tool trajectory P5 that takes into account the delay of the servo system, or by using variables such as servo constants, feed rate, and shape data. Possible methods include calculating using a function. And this predicted trajectory error ε
8 and the allowable trajectory error amount Et, the position correction amount DC is calculated. At this time, the magnitude of this position correction ffi D c is the predicted trajectory error ε in a steady state where the rate of shape change of the machined shape is constant. to allowable trajectory error amount E
In a transient state where the shape change rate changes, the shape change rate or prediction of the machined shape is set so that it is approximately equal to the value obtained by subtracting t, and is larger than the value obtained by subtracting the allowable trajectory error amount Et from the predicted trajectory error ε8. It is calculated by taking into account the rate of change in the trajectory error. Then, a new command trajectory P is created by correcting the command trajectory PC based on this position correction amount DC. X is calculated.

Further, in the figure, d indicates the allowable follow-up delay amount calculated in the feed speed correction section 9'. Here, in the part where the shape change rate of the machined shape is constant, the feed rate Ft
The actual follow-up delay amount that occurs when executing the command trajectory P@x is approximately equal to the allowable follow-up delay 3iIdr, and the trajectory error is reduced to the allowable trajectory error amount Et by high-speed cutting feed without correcting the feed rate. In corner shapes where the shape of the machining shape changes rapidly, dynamic factors such as mechanical system delays that are difficult to predict occur, and the actual follow-up delay amount or the allowable follow-up delay amount d, Even if there is a case where the trajectory error exceeds the allowable trajectory error amount E,
By slightly correcting the feed rate using the feed rate correction section 9°, the trajectory error can always be kept within the allowable trajectory error amount Et.

By the way, the feed rate F, which is used when predicting the trajectory error in the position correction amount calculation unit 1O and which is corrected by the feed rate correction unit 9, is the same as that when the feed rate FC commanded by the machining program is used ( There are two possible cases: (1) and (2) where a trajectory error calculated in advance is n times the allowable trajectory error amount E (where ≧1) is used. Here, (1) is the command trajectory P in the feed rate calculation unit 11.
This is a method in which Ft-FC is always used regardless of the shape data SD of C, and (2) is a method in which the feed rate calculation unit 11 calculates the shape so that the trajectory error is within n times (n≧1) the allowable trajectory error amount Et. This is a method in which the feed rate calculated based on the data SD is Ft. At this time, n is an internal parameter held by the feed rate calculation unit ll.

The trajectory error predicted by the position correction amount calculation unit 10 increases in proportion to the feed rate Ft, and the position correction amount DC
is approximately equal to the magnitude of the predicted trajectory error in a steady state minus the allowable trajectory error 1Et (constant), so the magnitude of the position correction amount DC is also equal to the feed rate Ft
increases in proportion to the magnitude of Further, the trajectory error predicted by the position correction amount calculation unit 1O becomes larger at a corner shape portion where the shape change rate of the machining shape is rapid, so that the position correction amount also increases at the corner shape portion.

From the above explanation, in method (1), the higher the command feed rate FC commanded to the machining program, and the larger the shape change rate of the command trajectory PC commanded to the machining program, the more the position correction becomes. The amount DC increases.

On the other hand, in method (2), the magnitude of the predicted trajectory error is clamped to Etxn (n≧1) or less. Therefore, since the position correction II Dc is approximately equal to the size obtained by subtracting the allowable trajectory error amount Et from the predicted trajectory error size, if Etx (n-1) is the allowable position correction amount Ep, the position correction amount DC can be clamped to below the allowable position correction IEp regardless of the shape of the command trajectory Pc and the command feed rate FC commanded by the machining program.

A second embodiment of the system will be described below in which the allowable position correction amount Ep is manually inputted by the operator through an external input device, and the operator is allowed to set the upper limit value of the position correction amount.

Second Embodiment: FIG. 4 is a block diagram showing a second embodiment of the NC equipment for realizing the numerical control method of the present invention, corresponding to FIG. The explanation will be omitted.

In the figure, this NG device includes an external human power device 13 into which a coefficient m for clamping the magnitude of the trajectory error is input, and an allowable position correction I based on the allowable trajectory error amount Et and the coefficient m.
An allowable position correction amount calculation unit 12 that calculates fI E p is newly provided.

Therefore, the allowable position correction amount calculation unit 12 manually inputs the coefficient m corresponding to the coefficient (n-1) described in the first embodiment from the operator through the external human power device 13, and adds the coefficient to the allowable trajectory error amount Et. By multiplying by m, it becomes possible to calculate the allowable position correction ffi E p. Therefore, the value obtained by adding the allowable trajectory error amount Et to the calculated allowable position correction mE2 is defined as the feed speed calculation error amount Ev.

The feed rate calculation error ff1Ev corresponds to Etxn described in the first embodiment, and the internal parameter n is set from the outside by (m+1). Then, the feed rate calculation unit 11
calculates the feed rate Ft such that the trajectory error falls within the calculated feed rate calculation error amount Ev based on the shape data SD.

FIG. 5(A) shows how the position correction 'L D c changes based on the allowable position correction amount E set by the operator. Moreover, FIG. 5(B) shows the feed rate calculation error amount Ev
The feed rate F calculated by the feed rate calculation unit 11 based on
shows. In FIG. 5(A), the solid line indicates the command trajectory 200 instructed by the machining program, and the dotted line indicates the actual tool trajectory P8. - The dotted chain line is the command trajectory P after position correction. Indicates X.

Therefore, part (a) on the command trajectory is the allowable position correction amount Ep
is m times (m>1) the allowable trajectory error amount Et, (b)
The allowable position correction amount Ep is the allowable trajectory error amount E.

is equal to (m-1), and part (c) shows the case where the allowable position correction amount Ep is set by the operator so that it is (m"0). In this case, the feed rate that reaches part (a) is The calculated error amount Ev is (mal
), the feed speed calculation error amount Ev in the part (b) is equivalent to twice the allowable trajectory error amount E, and the feed speed calculation error E in the (C) part is equal to the allowable trajectory error amount Et. Become.

From the above, the position correction amount DC in the (a) part, (b) part, and (C) part is respectively DCl +DC2+D
c3, and the feed speeds Ft are Ft+, Ft2 .
When Ft3 is set, the following equation (1) holds true.

In this way, by freely clamping the position correction amount DC and keeping the trajectory ii + 8 error within the allowable trajectory error amount Et, the operator can adjust the position correction amount while observing the actual tool movement based on the machining status and machining contents. can be adjusted. Therefore, if you want to temporarily stop machining during machining, it is best to make the allowable position correction amount EP equal to the allowable trajectory error amount Et (m = 1), so that no matter when machining is temporarily stopped, the position The deviation from the command trajectory on the machining program due to correction always falls within the allowable trajectory error amount Et. In addition, in the part where manual cutting due to manual interruption intervenes, if the allowable position correction amount E is set to zero (m=0)
, smooth manual interrupts can be performed. On the other hand, if the machining does not involve intervention such as -time stop or manual interrupt, the maximum allowable position correction amount Ep can be set to the maximum value to perform the machining at the highest possible speed of cutting feed. Furthermore, if you want to avoid a situation where the actual trajectory error becomes larger than the predicted trajectory error due to unpredictable factors and the trajectory error exceeds the allowable trajectory error amount Et, the position correction amount is adjusted to a smaller value. This makes it possible to avoid this.

In this embodiment, the allowable position correction amount E.

Although a method is described in which the information for calculating is specified by the external human power device 13, an alternative method of commanding by the machining program 1 is also conceivable. Furthermore, although the coefficient m to be multiplied by the allowable trajectory error amount Et is specified as information for calculating the allowable position correction amount Ep at that time, a method of directly specifying the allowable position correction amount Ep is also conceivable.

According to the second embodiment described above, the magnitude of the position correction amount DC to be added to the command trajectory PC instructed to the machining program is
Although it is possible to freely change the position correction amount EP based on the allowable position correction amount EP set from the outside, another method is to change the position correction III D c according to the machining shape of the command trajectory. In other words, in a curved part where the rate of shape change of the machining state of the command trajectory PC changes, especially in a corner part where the rate of shape change is rapid, the acceleration of the drive unit changes, causing unpredictable delays in the servo system, etc. As a result, the trajectory error becomes difficult to predict, and the accuracy of the position correction amount DC calculated by the position correction amount calculation unit IO decreases. Therefore, if a method is adopted in which the position correction amount DC is changed according to the shape of the command trajectory Pe, the position correction amount DC may be made smaller in the part of the machining shape where the rate of shape change is rapid and the trajectory error is difficult to predict, or vice versa. In the part of the machined shape where the shape change rate is almost constant and the trajectory error is easy to predict, by maximizing the position correction amount, more accurate machining can be performed at high speed.

This method will be described below as a third embodiment.

Third example.

FIG. 6 is a block diagram showing a third embodiment of the NC device that implements the numerical control method of the present invention, corresponding to FIG. 4, and the same components are given the same reference numerals and the explanation will be omitted.

In the figure, this NC device is newly provided with an error prediction coefficient calculation unit 13 that calculates an error prediction coefficient based on the shape data SD output from the commanded shape evaluation unit 4.

Therefore, the error prediction coefficient calculation unit 13 analyzes the machining shape of the command trajectory PC instructed by the machining program based on the shape data SD output from the command shape evaluation unit 4, and calculates the error prediction coefficient. This error prediction coefficient satisfies the conditions O≦ and ≦1 depending on the shape data SD, and for example, in a corner shape part where the trajectory error is easily affected by factors that are difficult to predict, is a value close to zero. On the other hand, for machining shapes where the trajectory error is less susceptible to unpredictable factors,

takes a value close to l. Also. to this error prediction coefficient.

is sent to the allowable position correction amount calculation unit 14, and this allowable position correction amount calculation unit 14 further converts the coefficient m and error prediction coefficient input from the external input device 13 into an allowable trajectory error amount Et.
The allowable position correction amount Ep is calculated by multiplying by Ep.

Therefore, in a corner shape part where it is difficult to completely predict the trajectory error, the allowable position correction amount E.

is a value close to ;, and position correction is not executed. Conversely, in a machining shape where a trajectory error is easy to predict, the allowable position correction amount E2 is approximately equal to the value entered manually by the operator, and position correction is executed.

In this embodiment, the error prediction coefficient is sent to the allowable position correction amount calculation section 12, but as another method, the error prediction coefficient is sent to the position correction amount calculation section 10, and the error prediction coefficient is sent to the position correction amount calculation section 12.
A method of changing the position correction ffi D C according to the machining shape of the command trajectory PC by multiplying the trajectory error predicted at 0 by the error prediction count and calculating the position correction ff1De based on the trajectory error. can also be considered.

(Effects of the Invention) As described above, according to the numerical control method of the present invention, it is possible to guarantee stable machining accuracy, including trajectory errors caused by unpredictable dynamic factors, and regardless of the machining shape. This enables high-speed, high-precision machining. Further, at this time, manual cutting can be easily performed by the operator.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a first embodiment of an NC device that implements the numerical control method of the present invention, Fig. 2 is a flowchart explaining an example of its operation, and Fig. 3 shows a method for calculating command trajectories P and x. 4 is a block diagram of a second embodiment of the NC device that implements the numerical control method of the present invention, FIG. 5 is an explanatory diagram showing changes in position correction amount Dc and feed rate Ft, and FIG. A block diagram of a third embodiment of an NC device that implements the numerical control method of the present invention, and FIG. 7 is a block diagram of an NC device that implements a conventional numerical control method. 1... Machining program, 2,2°... External human power device, 3... Machining program interpretation section, 4.4°... Commanded shape evaluation section, 5... Function generation section, 6... - Servo control unit, 7... Servo motor, 8... Position detector, 9.
9゛...Feed rate correction section, lO... Position correction amount calculation section, 11... Feed speed calculation section, 12... Allowable position correction amount calculation section, 13... Error prediction coefficient calculation section.

Claims (1)

[Claims] 1. In a numerical control method in which a drive unit of a numerically controlled machine tool is controlled based on a command trajectory and a command feed rate commanded by a machining program, the drive unit is controlled based on the command feed rate. A trajectory error between the actual trajectory of the drive unit and the commanded trajectory when controlled is predicted, a position correction amount is calculated based on the predicted trajectory error and an allowable trajectory error amount input in advance, and the calculated position is calculated. Based on information obtained by correcting the command trajectory based on the correction amount, calculating an allowable follow-up delay amount based on the corrected command trajectory and the allowable trajectory error amount, and detecting the position of the drive unit. calculate the actual amount of follow-up delay, correct the command feed rate based on the calculated amount of follow-up delay and the allowable follow-up delay amount, and correct the command feed rate based on the corrected command trajectory and the corrected command feed rate. A numerical control method characterized by controlling the drive unit. 2. Calculate a feed rate such that the trajectory error does not exceed a predetermined times the allowable trajectory error amount based on the command trajectory instructed by the machining program, and control the drive unit based on the calculated feed rate. 2. The numerical control method according to claim 1, wherein a trajectory error between the actual trajectory of the drive unit and the commanded trajectory is predicted in the case where the movement occurs, and the calculated feed rate is corrected. 3. Calculate a trajectory error prediction coefficient based on the command trajectory instructed by the machining program, correct the position correction amount based on the calculated trajectory error prediction coefficient, and correct the position correction amount based on the corrected position correction amount. 2. The numerical control method according to claim 1, wherein the command trajectory is corrected. 4. A feed rate is calculated such that the trajectory error does not exceed a value obtained by adding the allowable trajectory error amount to an allowable position correction amount set by an external device or the machining program. The numerical control method described in 2. 5. Calculate a trajectory error prediction coefficient based on the command trajectory instructed by the machining program, correct the allowable position correction amount based on the calculated trajectory error prediction coefficient, and adjust the allowable position with the corrected trajectory error. 5. The numerical control method according to claim 4, wherein the feed rate is calculated such that the feed rate does not exceed a value obtained by adding the allowable trajectory error amount to the correction amount.