JP2886219B2 - Error correction device such as drive system in NC machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an error correction device such as a drive system in an NC processing machine useful for a machine tool which generates a processing error due to thermal influence. .

(Prior Art) As a drive system in a conventional NC processing machine, there are examples of a drive system using a semi-closed loop control system and a drive system using a full closed loop control system.

As is well known, in the former, a servomotor is provided with a position detector such as a rotary encoder or a resolver, and the moving body is driven via a power transmission mechanism using a ball screw or a rack and pinion. In the latter, the actual moving position of the moving body is detected by a highly accurate position detector such as a so-called optical scale.

However, in a control system using a semi-closed loop, there is a problem that thermal distortion of a power transmission machine including a ball screw or a rack and pinion and thermal distortion of a frame affect a speed reduction mechanism, thereby causing a processing error.

Comparing the ball screw and the rack and pinion, the thermal effect of the ball screw is larger, but it is difficult to say that the rack and pinion is originally superior because the positioning accuracy of the rack and pinion is lower.

Further, when the control of the full closed loop is used, the thermal distortion of the power transmission mechanism is removed, but the optical scale is very expensive, and physical breakage due to vibration at the time of processing is apt to occur. There is a problem such as tone generation. Further, since a feedback signal is always given to the servo system, there is a limit to the response speed, and the motor speed is limited. Further, there is a problem that the servo system becomes unstable due to the rigidity of the drive system and hunting occurs, which is advantageous and disadvantageous to the semi-closed loop. In particular, even with low-speed control, an error due to thermal distortion of a work or a frame cannot be removed.

(Problems to be Solved by the Invention) As described above, in the drive system of the conventional NC machine, both the semi-closed loop and the fully closed loop have problems.

Therefore, the present invention can correct the thermal distortion of the power transmission mechanism in both closed loops and semi-closed loops, and furthermore, in both closed loops, the heat transmission mechanism other than the power transmission mechanism generated in response to a change in environmental temperature such as expansion and contraction of a work It is an object of the present invention to provide a scale device used for error correction of a drive system or the like in an NC processing machine that can also correct target distortion.

[Configuration of the Invention] (Means for Solving the Problems) In view of the above-described conventional problems, the present invention has a moving body that is controlled in position by a closed loop control system,
In an error correction device such as a drive system in an NC processing machine that performs a predetermined processing while positioning a work or a tool attached to this moving body at a predetermined position, the thermal expansion coefficient is made of a material having a uniform thermal expansion rate, and the longitudinal direction thereof is Along with a master scale having a plurality of marks to be detected along the axis, one end of which is fixed in accordance with the origin position of the moving body, and the other end of which is expandable and contractable in accordance with a change in environmental temperature, A sensor for detecting each detected mark of the master scale, a command axis speed for moving the moving body, a known width of the detected mark, and a time when the sensor detects the detected mark. And a quality control unit for determining whether or not the current speed value of the moving object determined based on the predetermined speed is within an allowable value with respect to a predetermined speed.

(Example) Hereinafter, an example of the present invention will be described.

FIG. 1 is an explanatory view showing an example of a positioning device in which the present invention is applied to a punch press. The drive system is shown as an example of a semi-closed loop.

In the figure, a table 1 that is movable in the left-right direction (X direction) is fixed to a table bracket 2.
The table bracket 2 is movable in the X direction according to the rotation of the ball screw 4 by screwing a ball screw 4 extending in the X direction to a nut 3 embedded above the table bracket 2.

Both ends of the ball screw 4 are rotatably supported by bearings 5. One end of the ball screw 4 is connected to a servomotor 7 via a reduction gear 6.

The servomotor 7 is provided with a tachogenerator 8 and an incremental type rotary encoder 9.

A work clamp device 10 is provided on the table 1 so as to be movable in a Y direction orthogonal to the X direction (a method orthogonal to the paper surface in the figure), and the work clamp device 10 Above, it can be moved in the Y direction. Accordingly, the work W can be freely moved in the X, Y plane by driving the servo motor 7 in the X direction and driving the work clamp device 10 in the Y direction.

A fixed frame portion below the table 1 is provided with a master scale 12 for the X-axis which is supported at one point by a pin 11 at the origin position and is extendable and contractible in the X direction.

The master scale 12 is formed in a band shape using a homogeneous material having a known coefficient of thermal expansion and has a plurality of optical sensor dog holes Pn (P1, P2) formed at a constant pitch (for example, 100 mm pitch) with respect to the pins 11. , P3,... PN) are provided. Since the pitch is used after being measured with a laser distance meter with high precision as described later, it is not always necessary to manufacture the pitch with high precision.

An optical proximity sensor 13 for detecting the dog hole Pn with the movement of the table 1 is provided on the lower surface of the table 1.
Is provided.

In this example, a crankshaft 13 is provided above the table 1, and a ram (not shown) attached to the crankshaft 13 is driven up and down to press a mold provided above and below the work W. It is designed to be punched. A dog 14 indicating a top dead center is provided at one position of the crankshaft 13,
By detecting this with the proximity sensor 15, it is possible to identify the top dead center, that is, the non-punched state.

The frame is provided with a temperature sensor TS for detecting the temperature as a representative value of the environmental temperature.

On the other hand, the control device for controlling the punch press having the above configuration is
The control device mainly includes an NC device and a programmable controller connected to the NC device.A counter circuit 16 is provided in, for example, the programmable controller of the control device. The counter circuit 16 includes a transmission / reception arithmetic processing device 17 and a servo parameter storage unit 18. Connected to a servo system 19 having The general servo system 19 has a position loop and a speed loop, and inputs a positioning target value output from the NC device, and controls the moving body, that is, the table 1 at the target speed at the target value. It is something.

The counter circuit 16 inputs a detection signal of the dog hole Pn of the master scale 12 at a predetermined timing, latches a position signal detected by the encoder 9 at that time, and transmits this value to the transmission / reception arithmetic unit 17. .

The transmission / reception arithmetic processing unit 17 has a buffer therein, inputs detection data of the dog hole Pn, sets servo parameters in the servo parameter storage unit 18, and rewrites them.

In the apparatus having the above configuration, the following description will be made in the order of the initial setting, the principle of correction, the process of changing servo parameters during machining, the material handling method, and the dog hole detection method.

At the time of assembly, a laser mirror is attached to a bracket or the like of the table 1, and a difference δ of an actual operation with respect to an NC command value is stored by a laser distance meter.

For example, assuming that the actual movement amount by laser detection is 100.05 mm with respect to a command value of 100 mm, a difference of 100.05−
100 = 0.05 is recorded, and the value is given to the arithmetic processing unit 17.

Therefore, after making the measurement value of the encoder accurate by the difference δ accurately measured by the laser distance meter, the pitch interval is measured, and this is converted to 20 ° C. to obtain the true pitch interval T (n, f4). And this is stored in the servo parameter storage unit 18.

Specifically, here, the machining accuracy of the dog hole (gauge) of the master scale 12 is not known in the micron order, the latch delay occurs due to the response speed of the optical sensor, and the measurement is performed by the axis speed setting value. Recognizing that the latch data is different, the initial value of the gauge must be determined.

First of all, it can be obtained by measuring the gauge alone with a measuring instrument, but it is not considered to calculate the reference value of the gauge using this means because it depends on the mounting position (the state with the sliding surface and the mounting reference hole position). .

Therefore, the master scale is attached as shown in the drawing. In addition, a mold is set and processing is prepared.

Set the axis speed to the override value F4, and input a command value C1mm (so as to be as large as possible with the measurable stroke of the measuring instrument) from the NC console for processing.

Next, input and process C2mm (near the origin of the work and around 10mm).

At this time, the work plate was laid all day and night under the control of 20 ° C, and measured with a measuring instrument, and the measured values at this time were M1mm and M2mm, respectively.
Suppose it was

Further, following the past, the measurement is performed at the axial speed F4 (under the same environment as the processing), and the counter latch coordinates Lnmm (x1, x2,..., XN) are stored at all the pitch points.

Similarly, the above measurement is repeated for each of the shaft velocities F3, F2, and F1, and latch coordinates are stored. From these, a latch coordinate table as shown in FIG. 2 is created.

Here, the average D of the delay at F3 compared to F4 (4-3)
Ask for.

D (4-3) = Σ (L (n, f3) −L (n, f4)) / N Similarly, compared with F4, the average of the delay at F2 and F1 D (4−3)
2) Find D (4-1).

D (4-2) = Σ (L (n, f2) −L (n, f4)) / N D (4-1) = Σ (L (n, f1) −L (n, f4)) / N The reason for calculating the average value is to keep the data to be managed as small as possible.
(N, f4) and D (4-3), D (4-2), D (4-1)
It is. FIG. 3 shows the relationship between the error and the speed f4.

 Next, T (n, f4) of the dimension to be obtained is obtained.

T (n, f3) = T (n, f4) + D (4-3) T (n, f2) = T (n, f4) + D (4-2) T (n, f1) = T (n, f4) ) + D (4-1) The value obtained as described above is stored in advance in a buffer in the transmission / reception arithmetic processing unit 17 as a 20 ° C. converted value, and the value of each pitch is determined according to the environmental temperature, and this is used as a servo parameter. , And a well-known pitch error correction.

<Correction principle> As described above, the position of each dowel hole Pn of the master scale 12 is
The position is managed after conversion to 20 ° C. In other words,
No matter how the environmental temperature changes, Master Scale 12
By detecting the position of the dog hole Pn, the actual machining deviation can be detected, and an appropriate correction value can be given according to the difference.

The basic operation is as follows: If a plate made of iron is placed in an environment of 25 ° C, the temperature is 11.7μm / 20mC per 1m.
℃ · mx (25-20) = 58.5 µm. When this plate was processed to have high rigidity and processed according to the theoretical value, and this plate was cooled to 20 ° C., it was conversely processed to be smaller by 58.5 μm.

So, in order not to do this, master scale 12
What is necessary is just to correct the positioning of the processing machine at the latch point of the dog hole Pn.

It should be noted that this correction value is obtained by detecting the actual machining position on an accurate scale with the temperature correction function, so it is affected not only by the mechanical distortion and temperature distortion of the power transmission machine, but also by the temperature of the work and frame. This means that the processing can be performed with the measurement accuracy of the master scale 12 and its measurement system.

A specific example will now be described.
Is slightly higher than the work temperature Fw, if the distortion of the ball screw is Δ1, the error due to the expansion of the work W is Δ2, and the distortion of the other frame is Δ3, these Δ1, Δ2, Δ
Whatever the case, it doesn't matter.

Therefore, if the servo parameters are appropriately corrected in accordance with a change in the condition, particularly, a change in the temperature, machining with little error can be permanently maintained.

In addition, comparing the effect of this semi-closed loop with that of a fully closed loop, from the practical point of view that high-speed machining is possible, there is no fear of step-out, and in addition, it can be designed at low cost, etc. The semi-closed loop is better. The error due to temperature is basically the same.

In this embodiment, the ball screw 4 is shown as an example, but this may be a rack and pinion. However, from the viewpoint of the original accuracy due to backlash and the like, the processing accuracy of the ball screw is better.

FIG. 4 shows a servo parameter setting method. At the start of machining, return to origin in step 401.
In 02, the start is prohibited to NC first.

Next, at step 403, a reset signal is sent to the current value counter, and at step 404, a signal for turning on the correction function is sent.

Next, in step 405, the data of the temperature sensor TS is transmitted. In step 406, the frame elongation at that temperature is calculated, and then in step 407, the NC is permitted to start.

In step 406, a servo parameter value corresponding to the temperature θ is set based on the value T (n · f4) converted into 20 ° C. In this example, it is assumed that the correction operation is performed by the servo system 19, but it is also possible to perform correction so as to change the original target value.

<Correction Parameter Change Processing> The change of the servo parameters is executed by the processing of FIGS. 5 and 6. FIG. 5 shows a change request procedure, and FIG. 6 shows a change procedure when a change request is made.

In FIG. 5, in the machining step 501, it is determined whether or not the punch is being performed by the proximity sensor 15 shown in FIG. 1. If the punch is not being performed, the process proceeds to the step 502, where the moving direction is set to the predetermined measurement direction. Is determined.

If it is a predetermined direction, proceed to step 503,
The latch coordinates of the dog hole Pn are sent out, and in step 504, the latch value for the dog hole Pn is loaded into the memory according to which dog hole Pn the latch coordinate is.

Therefore, in step 505, the value loaded in step 504 is compared with a reference value, that is, a value to be detected at a previously detected temperature based on a value converted at 20 ° C. If it is, the process proceeds to step 506 to turn on the parameter change request bit. In step 507, the frame temperature is received.

The parameter change request is issued mainly when the temperature of the ball screw 4 changes due to a temperature change, that is, a change in environmental temperature or a change in load.

Next, in FIG. 6, when the parameter change request is turned on in step 601, it waits in step 602 to return to the origin position, and in step 603, prohibits start to NC.

Next, in step 604, if the material of the work W is iron as before, the change value of the servo parameter is calculated in step 606, set in step 607, and start is permitted to NC in step 608. The calculation in step 606 is to calculate the servo parameters according to the current situation using the actually measured latch data. Step 605 will be described later. The measured latch data is corrected according to the speed at that time.

<Material handling method> There are two types of material handling methods as follows.

One is the expansion rate of each material, for example, iron… 11.7μm / m ・ ℃ copper… 16.7μm / m ・ ℃ aluminum… 23μm / m ・ ℃ In this method, correction is appropriately made.

In this case, for example, when the NC is returned to the origin, a material change is identified in step 604 of FIG. 6, a calculation for 20 ° C. is performed for each material in step 605, and the calculated value is stored. What should I do?

The other one is shown in FIGS. 7 (a) and 7 (b).
In this method, a cartridge type master scale 20 for each material as shown in FIG.

The bolt 22 attached to the guide 21 is for preventing displacement in a direction orthogonal to the moving direction. The tip of the bolt 22 is formed in a spherical shape, and lightly presses the cartridge scale 20 against the guide 21 so as to be slidable in the movement direction. Note that the support point of the pin 11 is also formed in a spherical shape so that the fixed point coincides with the origin. When the fixed point is shifted from the origin, it is necessary to perform a predetermined shift correction.

<Dog Hole Detection Method (Part 1)> This item is designed so that the quality of the detected data can be identified in the detection of the dog hole Pn.

 FIG. 8 shows a specific example of the detection circuit.

In the figure, the detection circuit of the dog hole Pn is a buffer (differential TTL) 23 for inputting the A and B2 phases output from the encoder 9.
And a counter latch control unit 24 for inputting a detection signal of the optical sensor 13. Both circuits 23 and 24 are provided with the counter circuit 1.
6 is entered. The internal clock signal CLK is input to the counter circuit 16.

The counter circuit 16 is connected to a sensor-on buffer 25 and a clock counter 26. The outputs of both circuits 25 and 26 are connected to a data pass / fail control unit 27. The control unit 27 is connected to a data bus 28. The clock counter 26 also has
The internal clock signal CLK is input.

In the above configuration, as shown in FIG.
13 moves in one direction, and obtains a signal 29 for one dog hole Pn. The signal 29 is a pulse-like signal that is turned on with a certain threshold and then turned off. The shaft speed command and b is ₀ mm / S. The width of dog hole Pn is known and a
mm.

 The signal processing method is shown in FIG.

In step 1001, the latch data when the sensor is on is temporarily stored in the buffer 25, and in step 1002, the clock counter
The time t until the sensor is turned on and then turned off is obtained by 26.

Therefore, in step 1003, the data quality control unit 27
Then, b ₀ t = a is determined, that is, it is determined whether or not the current speed value h is within an allowable value with respect to the planned speed b ₀ , and if it is within the allowable value, the latch data at the time of sensor ON is validated in step 1004. And flows this to the data bus 28. On the other hand, if the speed b is outside the allowable value, the latch data is invalidated in step 1005.

Therefore, in this example, the reliability of the latch data detected by the sensor 13 is improved, and the processing accuracy itself can be improved.

In this example, the detection of the dog hole Pn has been described. However, the mark of the master scale 12 is not limited to this.For example, a mark of a different color may be printed. It can be determined.

<Dog Hole Detection Method (Part 2)> This section shows an example in which latch data is corrected according to speed.

In FIG. 11, in the detection circuit of this example, a speed calculation unit 30 for detecting a waveform and a latch coordinate extraction unit 31 are connected to the counter circuit 16. The speed calculator 30 is connected to an average delay parameter value calculator 32.
32 and the latch coordinate extracting unit 31 are connected to a measurement result output unit 33.

The average delay parameter value calculator 32 has a correspondence table of the error ε generated by the speed and the signal delay as shown in FIG. 12, and the error ε is calculated according to the speed calculated from the waveform value by the speed calculator 30. Is calculated. Since the error varies, the average value is used.

The measurement result output unit 33 applies the error ε calculated by the calculation unit 32 to the latch coordinates extracted by the latch coordinate extraction unit 31,
It outputs a measured value close to the true value. The measurement value may be obtained by averaging a plurality of data for the same dog hole.

As shown in FIG. 13, the coordinate value when the sensor is turned on is obtained in step 1301, the speed value is calculated from the pulse width when the sensor is turned on in step 1302, the error ε is calculated in step 1303, and the corrected measurement is performed in step 1304. Output the value.

Therefore, the speed equivalent value is calculated from the waveform such as the scale,
By subtracting the corresponding delay parameter from the measurement data, the measurement accuracy and, consequently, the processing accuracy can be improved.

In this example, measurement can be performed at an arbitrary shaft speed. If the speed is constant, the accuracy can be further improved. In this example, the speed value is obtained by waveform detection, but the NC command value can be used on condition that the speed is stable.

As described above in detail, according to the present embodiment, the table 1 controlled by the semi-closed loop can be moved with the accuracy determined by the master scale 12.

At this time, since the master scale 12 is configured to be capable of temperature correction and configured to detect the actual processing position, it is possible to remove not only the distortion of the power transmission mechanism but also the thermal influence of the work and the frame. High precision of 0.01 mm or more, which was difficult in the past, can be easily cleared under all environmental conditions, and ultra-precision processing becomes possible. There is no need to worry about loss of synchronization or breakage as in a fully closed loop.

In the above embodiment, an example of a punch press was described, but other NCs such as a laser processing machine, a patch / laser combined processing machine, and a lathe
The same applies to machine tools.

Further, in the above-described embodiment, an example in which the workpiece is moved has been described, but the same applies to a machine tool that moves a tool.

Furthermore, in the above-described embodiment, the semi-closed loop is mainly used, but the present invention can be implemented even with a fully closed loop, thereby removing an error caused by thermal distortion of a work or a frame. is there.

The present invention is not limited to the above embodiments, but can be implemented in other appropriate modes by making appropriate design changes.

[Effects of the Invention] As can be understood from the above description of the embodiment, according to the present invention, one end of the master scale having a plurality of detected marks is fixed to the origin position of the moving body. The other end is provided so as to be able to expand and contract in response to a temperature change, so that it is easy to correct an error due to thermal distortion of a drive system or the like. When detecting the detected mark on the master scale, the speed of the moving body is calculated based on the command speed for moving the moving body, the known width of the detected mark, and the detection time of the sensor, and the current speed of the moving body is estimated. A data control unit for determining whether or not the speed is within an allowable value with respect to the speed of the data, so that the reliability of the data detected by the sensor can be improved and, consequently, the processing accuracy can be improved. It is.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a positioning device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of latch data for each speed, FIG. The figure shows a flowchart showing the servo parameter setting method,
FIG. 5 is a flowchart showing a parameter change request output method, FIG. 6 is a parameter change method flowchart, FIG. 7 (a) is a front view showing a cartridge type master scale created for each material, and FIG. b) is a right side view thereof, FIG. 8 is a block diagram showing an example of a latch data detecting circuit, FIG. 9 is an explanatory diagram showing the detecting operation, and FIG.
FIG. 11 is a flowchart showing a method of determining the quality of data, FIG. 11 is a block diagram showing another example of a latch data detection circuit, FIG. 12 is an explanatory diagram of data used by the circuit,
FIG. 13 is a flowchart showing a method of correcting a measured value of latch data. 1 Table 3 Nut 4 Ball screw 7 Servo motor 9 Encoder 11 Pin 12 Master scale 13 Optical sensor 16 Counter circuit 17 Transmission / reception calculation Processing unit 18 Servo parameter storage unit 19 Servo system Pn Dog hole TS TS Temperature sensor

Claims (1)

(57) [Claims] 1. A moving body whose position is controlled by a closed loop control system, and a predetermined processing is performed while a work or a tool attached to the moving body is positioned at a predetermined position.
In an error correction device such as a drive system in an NC processing machine, the coefficient of thermal expansion is made of a uniform material, has a plurality of detection marks along its longitudinal direction, and has one end aligned with the origin position of the moving body. A master scale that is fixed and the other end of which is expandable and contractable in response to a change in environmental temperature; a sensor that detects each detected mark of the master scale in accordance with the movement of the moving body; and a device that moves the moving body. The current speed value of the moving body, which is determined based on the command axis speed, the known width of the detected mark, and the time during which the sensor is detecting the detected mark, is within an allowable value with respect to the planned speed. An error correction device for a drive system or the like in an NC processing machine, comprising: a data quality control unit for determining whether or not the data is good or bad.