JP3118996B2 - 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 (hereinafter, referred to as an NC device) provided with a device for detecting an absolute position of a machine tool.

[0002]

2. Description of the Related Art Conventionally, in an NC device having an absolute position detector on a feed shaft, when the power is turned off and then turned on again, the current position of the table can be detected by the absolute position detector. there were. However, since the absolute position detector is generally connected to the servomotor,
When the power is turned on, the position detected by the absolute position detector is the rotational position of the servomotor, and the position of the driven body driven by the servomotor is the position detected by the absolute position detector. It is necessary to make correction in consideration of the pitch error of the mechanism.

For this reason, for example, in Japanese Patent Application Laid-Open No. Hei 3-10742, a pitch error correction amount from the origin to the detected value is added to a value detected by an absolute position detector when the power is turned on, and the driven Was obtained, and this absolute position was set as the current position of the table when the power was turned on.

[0004]

However, if the power is cut off during machining due to a power failure or the like, the table moves even after the power is cut off due to inertia, and even if the power is turned on, the table remains at the value when the power was cut off. Unlike this, there is a problem that it is not possible to return the table to the position at the time of power-off and immediately continue the interrupted machining.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. Even if the power supply is cut off during processing, the driven body is accurately returned to the position at the time of power supply cut off, and the power supply is turned on even after the power supply is turned on. It is an object of the present invention to provide a numerical control device capable of continuously processing.

[0006]

In order to achieve this object, a numerical controller according to the present invention comprises an absolute position detecting means for detecting an absolute position of a driven body, and a current position of the driven body when power is cut off. When the power is turned on,
Calculating means for adding a pitch error correction value from the origin to the current position stored in the current position storage means, and the absolute value at the time of power-off is determined from the current position and the pitch error correction value added by the calculating means. Prediction means for predicting the value of the position detection means, reading means for reading the value of the absolute position detection means at power-on, difference calculation means for calculating the difference between the read value and the value predicted by the prediction means And the difference calculated by the difference calculation means is less than an allowable value.
Determination means for determining whether or not
When it is determined that less than capacity value, and a control means for driving only the driven body difference calculated by said difference calculating means.

[0007]

According to the numerical controller of the present invention having the above-mentioned structure, the current position of the driven body is stored in the current position storage means when the power is turned off, and the current position is stored in the current position storage means when the power is turned on. The pitch error correction values up to the above are added by the calculating means, and the absolute position of the driven body when the power is turned on is predicted by the predicting means from the added pitch error correction value and the current position. On the other hand, the absolute position of the driven body is read from the reading means, and the difference between the value predicted by the prediction means and the value read by the reading means is obtained by the difference calculation means,
The difference is determined by the determination means to be less than the allowable value.
In this case, by driving the driven body by the control means by the difference, the position of the driven body when the power is turned off matches the position of the driven body after the power is turned on, and the power is cut off during machining. Even after the power is turned on, processing can be continued without positioning.

[0008]

The present invention will now be described by way of an embodiment of the present invention.
An example applied to table positioning control of an NC machine tool will be described with reference to the drawings.

FIG. 1 is a block diagram for implementing the present invention. In FIG. 1, a ball screw 33 serving as a power transmission device connected to a servo motor 31 serving as a drive source is screwed with a table 30 serving as a driven body which is configured to be movable in the left and right directions in FIG. Have been.

The NC unit 10 has a processor (hereinafter referred to as a CPU).
), And the CPU 11 has a ROM 12, a RAM
13, a nonvolatile RAM 14, a program memory 15, a key input device 16, a display control circuit 19 for controlling a CRT display device 18, and a servo interface 20. A servo circuit 21 for driving a servo motor 31 is connected to the servo interface 20. The servo circuit 21 responds to a movement command output via the servo interface 20 by an incremental encoder 32.
The servomotor 31 is configured to perform position loop control and speed loop control in response to a feedback signal from the microcomputer.

The servo motor 31 is provided with an absolute position detector 34 for detecting the absolute position of the servo motor 31.

The ROM 12 stores a management control program to be processed by the CPU 11, and the program memory 15 stores an external storage device such as a tape reader or a floppy disk drive (not shown) or an operation program input from a key input device 16. Is stored. Also,
The RAM 13 is used for temporarily storing results of arithmetic processing performed by the CPU 11 and data. Further, the nonvolatile RAM 14 stores pitch error correction data of the ball screw 33 described later, the current position of the table 30 when the power is turned off, and an allowable value A for evaluating the moving width of the table 30 when the power is turned on again. Have been. The pitch error correction data is error data obtained by comparing the position detected by the incremental encoder 32 when the table 30 is at an arbitrary position within the movement range with the position actually measured by another high-precision measuring instrument. And so that it can be corrected to an accurate position of the table 30 corresponding to an arbitrary detection position during driving,
It is pre-installed as a conversion table.

The CPU 11 includes an NC device 10.
Is provided with a power supply voltage abnormality detection circuit 22 that outputs an abnormality signal when the power supply voltage falls below a predetermined level.
The abnormality signal output from the power supply voltage abnormality detection circuit 22 is C
It is input to the INT (interrupt terminal) of the PU 11.

FIG. 4 shows the relationship between the pitch error correction value and the value of the absolute position detector 34. In FIG. 4, the pitch error correction data is "1" when the current position is "20", "2" when the current position is "40", and "-1" when the current position is "60". It is stored as Therefore, when the current position is “20”, the value of the absolute position detector 34 is a value “21” obtained by adding “1” of the pitch error correction data to “20”.

Next, the operation of the NC apparatus 10 will be described.

While the control of the table 30 is performed according to the data stored in the program memory 15,
When the power supply voltage falls below a predetermined level due to a power failure, an operation error, or the like, an abnormality signal is output from the power supply voltage abnormality detection circuit 22 to the CPU.
11 is output to the INT terminal. Then, the CPU 11 uses the abnormal signal as an interrupt signal and starts an interrupt program for performing necessary processing before power-off in a short time before the power supply voltage becomes completely zero.

The operation performed at this time will be described with reference to the flowcharts shown in FIGS. 2 and 3 based on the specific values shown in FIG.

In S100, the current position is stored in the nonvolatile RAM 14 as the current position X0 when the power is turned off. In the present embodiment, “60” is stored as X0.

When the power is turned on again, the determination program shown in FIG. 3 is started first.

In S200, the current position X0 at the time of power shutdown stored in S100 is read from the nonvolatile RAM 14. Then, in the next step S202, the amount corrected as the pitch error correction value while moving from the origin "0" to the current position X0 at the time of power shutdown is added, and the pitch error addition amount ε is calculated. In this embodiment, ε = 1 + 2 + (− 1) = 2. In S204, the pitch error addition amount ε is added to the current power-off current position X0 read in S200 (A0 = X0
+ Ε), the value of the absolute position detector 34 when the power is cut off is predicted. In the present embodiment, A0 = 60 + 2 = 62.

In step S206, the absolute position of the servo motor 31 is read from the absolute position detector 34. In the present embodiment, referring to FIG. And S2
In 08, the deviation ΔX between the absolute position of the servo motor 31 read in S206 and the absolute position A0 predicted and calculated in S204 is calculated.
A movement amount of 0 is obtained. In this embodiment, ΔX = 62−
65 = -3. In S210, the moving amount ΔX is compared with the allowable value A stored in the nonvolatile RAM 14, and when the moving amount ΔX is larger than the allowable value A (S
210: YES), the process proceeds to S212, an error signal is output to the display control circuit 19, and an error display is performed on the CRT display device 18.

At this time, the subroutine program shown in FIG. 3 ends and the program returns to the main program. The determination result of S210 is transmitted to the main program as return information. For this reason, in the main program, when the movement amount of the table 30 is larger than the allowable value A by the return information, the restart of the execution of the operation program is interrupted, and an operation such as indexing the origin of the table 30 is performed. Become.

On the other hand, if the moving amount ΔX is smaller than the allowable value A in S210 (S210: NO), no error signal is output, and the table 30 is moved by ΔX in S214, and the table 30 is moved to the position at the time of power-off. 30 is returned. In this embodiment, the value of the absolute position detector 34 is "62".
The table 30 moves to the position where. Therefore, the processing can be immediately performed without the operator having to manually return the table 30 to the position at the time of power-off in order to start the processing.

In this embodiment, an incremental encoder is used to perform position loop control. However, the present invention is not limited to this, and an absolute encoder that also serves as an absolute position detector is used. May be used. Note that the process of S210 is a determining means.
Function.

[0025]

As apparent from the above description, according to the numerical control machine of the present invention, the current position of the driven body at that time is stored when the power is turned off, and the current position is stored when the power is turned on. While adding the pitch error correction value from the origin to the current position to predict the absolute position of the driven body when power is turned on, the absolute position detection means detects the absolute position of the driven body, The difference between these values is taken , and the difference is judged by the judgment means to be less than the allowable value.
If it is the cross-sectional, by driving the difference only driven body, and the position of the driven member of the power-off, since it is intended to match the position of the driven member after power-on, the processing in the middle Even if the power supply is cut off, there is an excellent effect that processing can be performed without returning to the position at the time of power supply cutoff for starting processing after power-on.

[Brief description of the drawings]

FIG. 1 is a numerical controller (NC device) embodying the present invention.
FIG. 3 is a block diagram showing the configuration of FIG.

FIG. 2 is a flowchart showing an operation at the time of power interruption.

FIG. 3 is a flowchart showing an operation at the time of power-on.

FIG. 4 is a diagram showing a relationship between a pitch error correction value and a value of an absolute position detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 CPU 14 Non-volatile RAM 22 Power supply voltage abnormality detection device 30 Table 31 Servo motor 34 Absolute position detector

Claims (1)

(57) [Claims] 1. An absolute position detecting means for detecting an absolute position of a driven body, a current position storing means for storing a current position of the driven body when power is cut off, and a current position storing means from an origin when power is turned on. Calculating means for adding the pitch error correction value up to the current position stored in the memory, and predicting the value of the absolute position detecting means at the time of power shutdown from the current position and the pitch error correction value added by the calculating means. Reading means for reading the value of the absolute position detecting means at power-on, difference calculating means for calculating a difference between the read value and the value predicted by the predicting means, and the difference calculating means Whether the difference obtained is less than the tolerance
Determining means for determining whether or not the value is less than the allowable value by the determining means,
Control means for driving the driven body by the difference calculated by said difference calculation means.