JP3242190B2 - 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 control device for a numerically controlled machine tool.

[0002]

2. Description of the Related Art Generally, a numerical control device is controlled to drive a machine tool based on command shape data (position and function) commanded by a machining program and a feed speed command. This speed command is data indicating a moving speed between two points from a certain position of the command shape data to another certain position, and the speed between the two points is commanded as being constant.
Therefore, in the case of moving at a certain speed v from the stop state and stopping again, the speed command suddenly moves at the speed v from the state of speed 0 and then commands the speed 0 again. However, in an actual system, there is inertia of the system, and control for making the acceleration infinite as described above cannot be performed. Therefore, in an actual machine tool, the servo system is controlled so that a real system is realized at an acceleration that can actually be generated. This control is called acceleration / deceleration processing, in which a time (time constant) required for acceleration is determined, and acceleration from, for example, a speed 0 to v is performed within this time.

However, during the acceleration / deceleration processing, the vehicle is moving at a speed different from the actual speed command, and this difference appears as a control error called a tracking error.
This follow-up error appears as an error in the trajectory of the tool or the arm, and may be a cause of deteriorating the processing accuracy of the product. Particularly in recent numerical control devices for machine tools for high-speed and high-precision machining, the following error of the servo system is predicted by the command shape and the feed speed, and the speed command is set so as to fall within a predetermined trajectory error (tolerance amount). Control and
A method for controlling the servo system of a machine tool by correcting the position of a command shape has been realized.

FIG. 5 is a block diagram of control in a conventional apparatus. The program analysis unit 2 analyzes a machining program stored in the machining program storage unit 1 and calculates tolerance parameters (allowable machining error amount) required for high-speed machining and a tolerance parameter such as a cutting speed upper limit value, which are instructed by the machining program. While being stored in the tolerance parameter storage unit 3,
The shape determination unit 4 recognizes the shape from the shape command issued by the machining program. Using the shape recognized by the shape determination unit 4 and the tolerance parameter stored in the tolerance parameter storage unit 3, the speed calculation unit 5 calculates a machining speed that can guarantee a machining error amount obtained by multiplying the tolerance amount by a constant coefficient. Is done. The high-speed function generator 6 generates a function corresponding to the processing speed based on the command shape. Further, based on the function generation result, the acceleration / deceleration simulation unit 7
Simulates the following of the machine tool servo system. The position correction calculator 8 predicts a tracking error from a function generation result of the high-speed function generator 6 and a result of simulating the tracking of the servo system, and calculates a position correction amount for compensating the tracking error. In the function generator 11 after the position correction, the speed calculator 5 adds a position correction amount obtained by adding the position correction amount of the position correction calculator 8 to the function generation result of the high-speed function generator 6. A function is generated at the machining speed calculated in the step (1), and the axis drive control unit 12 drives and controls the servo system of the machine tool. When the machine is temporarily stopped, the pause signal is output from the function generator 11 after the position correction by the operation of the operator.
The operation of the function generator 11 after the position correction is temporarily stopped by the pause signal. For further detailed explanation, the explanation is supplemented by using the operation command trajectory of FIG.

[0005] P1 to P8 are trajectories indicated by the functions generated by the high-speed function generator 6. p7 to p14 are generated by the high-speed function generator 6 based on a processing speed capable of guaranteeing a processing error amount obtained by multiplying the tolerance amount by a constant coefficient;
The predicted trajectory based on the result of simulating the following of the servo system of the machine tool by the acceleration / deceleration simulation unit 7 based on the result is shown. Reference numerals 11 to 18 denote scalar quantities (P1-p) for which the tracking error of the servo system is predicted and the trajectory error is predicted from the result.
7,..., P8-p14). In order to correct the trajectory error predicted here, a trajectory error amount obtained by multiplying the scalar amount (trajectory error) by a predetermined coefficient (1/2 in this example) is subjected to position correction to the function generation trajectory. Command trajectories P1 'to P8' after position correction are created. If the servo system of the machine tool is drive-controlled based on the command trajectories P1 'to P8' after the position correction, the operation trajectory of the machine tool becomes p
7 ′ to p14 ′, indicating that the motion trajectory is controlled to be within the allowable machining error amount. Note that p8 → P
Reference numeral 8 denotes a tracking error amount due to the time constant of the servo system.

In such a numerical control device, when the suspension is performed, the machining speed is immediately set to 0 as shown in the time chart of FIG. FIG. 8 shows the trajectory motion at this time. The trajectory L0 is a command shape specified by the machining program, and the trajectory L1
Indicates a function generation locus after position correction, and a locus L2 indicates an actual operation locus of the machine tool. When the pause signal T is input, the speed command becomes 0, so that the function generation trajectory after the position correction is immediately stopped at the position Pa, but the operation trajectory of the machine tool is caused by the acceleration / deceleration of the servo system. When the temporary stop signal T is input because of the following error due to the constant, the position is at the position Pb and reaches the position Pa after the time constant elapses.

[0007]

According to the conventional control described above, if a temporary stop is performed, the stop is performed at the position after the position correction, so that the stop is performed at a position different from the command shape.
For this reason, a bite or a protruding shape is significantly generated in the processed shape. There has been a problem that repair work after processing is remarkably generated in order to correct the bite scratches and protrusions.

[0008] Therefore, it was necessary to consider the operation to minimize the pause during machining. However, there is a case where it is necessary to wind the chips during cutting or to stop the operation for safety. Cannot be completely eliminated. Therefore, it was necessary to solve the above-mentioned problem.

In view of the above problems, it is an object of the present invention to predict a tracking error of a servo system based on a command shape and a feed speed, control a speed command so as to fall within a predetermined trajectory error (tolerance amount), and provide a command. It is an object of the present invention to provide a numerical control device capable of stopping a stop position at a commanded shape even if a temporary stop is performed in a method of correcting a position of a shape and controlling a servo system of a machine tool.

[0010]

A numerical control device which operates in accordance with a command shape data of a machining program and a feed speed command, wherein a trajectory error caused by an acceleration / deceleration time constant of a drive control section for driving a feed shaft motor is controlled. Numerical control that predicts from the command shape data, the feed speed command, and the acceleration / deceleration time constant, calculates a correction amount such that the trajectory error is within a predetermined value, and performs position correction control for correcting the command position based on the correction amount. In the device, when a pause signal input means for inputting a pause signal from outside, and the pause signal is input,
Deceleration control means for gradually decelerating the speed of the speed command to decelerate so as to become 0 after a first predetermined time, and when the pause signal is input, gradually decreases the command position correction amount. A correction amount attenuating means for performing reduction control to be 0 after a first predetermined time, a restart signal input means for inputting a restart signal from outside, and, when the restart signal is input, reducing the speed of the speed command. A speed increasing means for gradually increasing the speed so as to become the initial speed command after a second predetermined time; and when the restart signal is inputted, the command position correction amount is gradually increased from 0 to the second speed command. A correction amount increasing unit for setting the correction amount to an initial correction amount after a predetermined time.

Further, the first and second predetermined times are calculated based on the acceleration / deceleration time constant.

[0012]

A speed reduction means for decelerating a speed command to a predetermined speed in response to a pause signal input from the outside and a position correction attenuation means for simultaneously reducing the position correction amount in a predetermined time after the predetermined time elapses. Since the calculation is stopped, there is no position correction amount at the time of stop, and the machine can be stopped on the command locus.

[0013]

An embodiment of the present invention will be described with reference to the drawings. FIG.
Is a block diagram showing one embodiment of the present invention, and the same components as those in the prior art are denoted by the same reference numerals and description thereof will be omitted. In FIG. 1, the machining speed calculated by the speed calculation unit 5 is subjected to speed acceleration / deceleration processing by a speed command acceleration / deceleration unit 9 based on a pause / restart signal, and the position correction amount calculated by the position correction calculation unit 8. Is temporarily stopped /
It is increased or decreased by a restart signal and sent to the function generator 11 after position correction. The position-corrected function generator 11 generates a function at the machining speed at which the speed acceleration / deceleration processing has been performed on the position-corrected command value obtained by adding the increased / decreased position correction amount, and performs axis drive control. The drive unit 12 controls the servo system of the machine tool.

The operation of the speed command acceleration / deceleration unit 9 and the position correction amount increasing / decreasing unit 10 added according to the present invention will be described with reference to the flowchart of FIG. The flag during the pause process is determined (step S1). If the flag is not during the pause process, it is determined whether a pause signal (pause button) has been input by an operator's operation (step S2), and the pause signal is input. If not, the process proceeds to step S20. When the temporary stop signal is input, the flag during the temporary stop processing is turned ON (step S3), the working counter W is counted up (step S6), and the working counter W is set to a predetermined number of times Tt / Ta (where Tt is a servo system). If Ta is a constant and Ta has reached the function generation control cycle, the working counter W is set to (Tt / Ta), the machining speed V and the position correction amount ε are set to zero, and the process is terminated (steps S8 and S9). If the working counter W has not reached the predetermined number of times Tt / Ta, the processing speed V obtained by performing the acceleration / deceleration processing on the processing speed Vc calculated by the speed calculation unit 5 is calculated by equation (1) (step S10). S11).

V = Vc × (Tt−W × Ta) / Tt (1) Further, the processing speed V subjected to the acceleration / deceleration processing is a predetermined coefficient calculated by the processing speed Vc calculated by the speed calculation unit 5. If the value is smaller than the value obtained by multiplying K, the processing speed V is clamped to a value obtained by multiplying the processing speed Vc by a predetermined coefficient K (steps S12 and S1).
3). The reason why the machining speed V is clamped to a value obtained by multiplying the machining speed Vc by a predetermined coefficient K is that when the machining speed is extremely reduced, the movement locus of the machine tool at the time of stoppage is disturbed due to a delay in the time constant of the servo system. In order to stop smoothly, it is actually measured, and in this embodiment, it is clamped at a speed of 1/2. Further, as for the position correction amount, a position correction amount ε obtained by increasing / decreasing the position correction amount εc calculated by the position correction calculation unit 8 is calculated by Expression (2) (Step S).
14).

Ε = εc × (Tt−W × Ta) / Tt (2) On the other hand, if it is determined in step S1 that the suspension processing is being performed,
It is determined whether or not a restart signal (restart button) has been input by the operator (step S4). If the restart signal has been input, the restart flag is turned on (step S1).
5) Then, a restart process is performed in step S16 and later described later. Also, the flag during restart is determined (step S
5) If a restart is being performed, a restart process is performed in step S16 and later described later. If the restart is not being performed, the operation from step S6 described above is repeated to continue the temporary stop processing. Next, in steps S4 and S5, when it is determined that the restart signal is input or the restart is being performed and the restart processing is started, the working counter W is counted down (step S1).
6) Until the working counter W becomes zero or negative, the processing of accelerating the processing speed V and the processing of increasing the position correction amount ε are performed in steps S11 to S14 described above.
When the working counter W becomes zero or negative, the pause processing and the restart are turned off (steps S18 and S19), the working counter W is cleared (step S20), and the machining speed Vc calculated by the speed calculation unit 5 is calculated. And the position correction amount εc calculated by the position correction calculation unit 8 is output as it is as the processing speed V and the position correction amount ε (steps S21 and S22). The function generation unit 11 after the position correction is controlled to generate a function using the processing speed V and the position correction amount ε. The above operation is the operation described in the time chart of FIG. 2, and when the suspension is performed, the processing speed V is decelerated to a predetermined value, the position correction amount ε is reduced, and after the time of the servo system time constant T elapses. Stop. When restarting is performed, the machining speed V is started at a predetermined value and then accelerated, and the position correction amount ε
Is increasing. FIG. 4 shows the locus motion at this time.
The locus L0 is a command shape instructed by the machining program, the locus L1 is a function generation locus after position correction, and the locus L2 is an actual motion locus of the machine tool. When the pause signal T is input, the function generation trajectory after the position correction together with the reduction in the processing speed changes from the position Pa to the position Pat (a point on the command trajectory) because the position correction amount decreases, and stops. . When the restart is performed, the position correction amount increases with the increase in the processing speed, and when the restart processing is completed, the state returns to the normal processing state.

[0017]

According to the present invention, in a system for controlling the servo system of a machine tool by correcting the position of a commanded shape, the position correction amount is attenuated when the machine tool is temporarily stopped by a pause signal input from the outside. Since the stop position is stopped on the command shape, the bite or protrusion shape is reduced with respect to the machining shape, and the number of steps required for repair work after machining is significantly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a numerical control device according to the present invention.

FIG. 2 is a time chart of a temporary stop operation in the embodiment.

FIG. 3 is a flowchart of the present embodiment.

FIG. 4 is a diagram showing a trajectory of a temporary stop operation in the embodiment.

FIG. 5 is a block diagram of a conventional device.

FIG. 6 is a diagram illustrating a correction operation for correcting a position of a command shape.

FIG. 7 is a time chart of a temporary stop operation in the conventional device.

FIG. 8 is a diagram showing a trajectory of a temporary stop operation in the conventional device.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G05D 3/00-3/20 B23Q 15/00-15/28

Claims (2)

(57) [Claims] 1. A numerical control device which operates in accordance with a command shape data of a machining program and a feed speed command, wherein a trajectory error caused by an acceleration / deceleration time constant of a drive control unit for driving a feed shaft motor is determined by the command shape data. The numerical controller predicts from the feed speed command and the acceleration / deceleration time constant, calculates a correction amount such that the trajectory error is within a predetermined value, and performs a position correction control for correcting the command position based on the correction amount. A pause signal inputting means for inputting a pause signal from the controller; and a deceleration control for, when the pause signal is input, gradually reducing the speed of the speed command so as to become 0 after a first predetermined time. A correction amount attenuating unit that, when the pause signal is input, gradually reduces the command position correction amount and controls the command position correction amount to be 0 after the first predetermined time. Restart signal input means for inputting a restart signal from the control unit, and when the restart signal is input, gradually increase the speed of the speed command so that the speed command becomes the original speed command after a second predetermined time. A speed increasing unit; and a correction amount increasing unit that, when the restart signal is input, gradually increases the command position correction amount from 0 to become the initial correction amount after a second predetermined time. Numerical control device characterized by the above-mentioned. 2. The numerical control device according to claim 1, wherein
The numerical controller according to claim 1, wherein the first and second predetermined times are calculated based on the acceleration / deceleration time constant.