JPH03166044A - Scale device used for correcting error of driving system etc. of nc machine - Google Patents

Abstract

PURPOSE:To correct all thermal deformations including those of a motive power transmitting mechanism, a work and a frame by providing a mark position detecting means for detecting the position of the mark to be detected of a master scale when a moving body is moved. CONSTITUTION:One end of a master scale 20 which is made from material uniform in coefficient of thermal expansion and which has a mark to be detected provided along its longitudinal direction is fixed to the position of the origin of a moving body 1 and the other end is supported in such a manner as freely expanding and contracting according to changes in environmental temperature. The position of the mark to be detected of a master scale 12 is detected by a mark position detecting means 13 when the moving body 1 is moved. The moving body 1 which is position controlled by a semi-closed loop is thus detected in a fixed position in such a manner that the condition of the moving body 1 can be converted into a fixed temperature; thereby a servo system is controlled so that the position of actual machining agrees with a set value at a fixed temperature.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention is useful for correcting errors in drive systems, etc. in NC processing machines, which are useful for machine tools that cause machining errors due to thermal effects. The present invention relates to a scale device used for.

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

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

However, a semi-closed loop control system has the problem of machining errors caused by thermal distortion of the power transmission machine including the speed reduction mechanism, ball screw or rack/binion, and thermal distortion of the frame.

Comparing a ball screw and a rack and pinion, the ball screw has a greater thermal effect, but since the rack and pinion inherently has lower positioning accuracy, it is difficult to say that the rack and pinion is superior.

Furthermore, although thermal distortion in the power transmission mechanism can be removed by using the full closed loop control described above, optical scales are extremely expensive, and are prone to physical damage due to vibration during processing, resulting in reduced scale signals. There are problems such as loss of synchronization.

Furthermore, since a feedback signal is always given to the servo system, there is a limit to the response speed, which limits the motor speed. Furthermore, there are other problems such as the servo system becoming unstable due to the rigidity of the drive system and hunting occurring, which has advantages and disadvantages compared to semi-closed loops. In particular, even with low-speed control, errors due to thermal distortion of the workpiece or frame cannot be removed.

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

Therefore, the present invention is capable of correcting the thermal distortion of the power transmission mechanism in both closed loops and in the semi-closed loop. It is an object of the present invention to provide a scale device used for error correction of a drive system, etc. in an NC processing machine, which can also compensate for thermal effects.

[Structure of the Invention] (Means for Solving the Problems) The present invention for solving the above problems has a moving body whose positioning is controlled by a closed loop control system, and a workpiece or two [tools] attached to the moving body. A scale device used to correct errors in the drive system, etc. of an NC processing machine that positions the machine at a predetermined position and performs a predetermined process is a scale device that is made of a material with a uniform coefficient of thermal expansion and has detection marks along its longitudinal direction. The master scale is fixed at one end in accordance with the origin position of the movable body, and the other end is supported in accordance with changes in environmental temperature. The present invention is characterized by comprising a mark position detection means for detecting the position of the mark to be detected.

Further, the master scale is created for each material of the workpiece and is detachable from the NC processing machine.

(Function) In the scale device used for error compensation in the drive system, etc. in the NC processing machine of the present invention, the moving body whose positioning is controlled by, for example, a semi-closed loop is kept at a constant temperature (for example, 20°C).
The servo system is controlled so that the actual gap increase position becomes the command value at a constant temperature. Therefore, all thermal distortions including those of the power transmission machine and the workpiece and frame can be corrected, and processing can be performed in accordance with the command values.

Furthermore, when using a cartridge-type master scale whose thermal expansion coefficient is the same as that of the workpiece, the workpiece and master scale expand and contract by the same amount in response to temperature changes, so the thermal expansion of the workpiece can be ignored. .

(Example) Examples of the present invention will be described below.

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

In the figure, a table 1 that is movable r1 in the left-right direction (X direction) is fixed to a table bracket 2.

This table bracket 2 is made to move in the X direction according to the rotation of the ball screw 4 by screwing the ball screw 4 extending in the X direction into a nut 3 screwed in above the table bracket 2. Ru.

Both ends of the ball screw 40 are rotatably supported by a bearing 5. Further, one end of the ball screw 4 is connected to a servo motor 7 via a reduction gear 6.

The servo motor 7 is provided with a tacho generator 8 and an incremental rotary encoder 9.

A work clamping device 10 is provided on the table 1, and the workpiece clamping device 10 moves 11 times in the Y direction perpendicular to the X direction (perpendicular to the paper surface in the figure). 1 and is movable in the Y direction.

Therefore, by driving the servo motor 7 in the X direction and driving the work clamp device 10 in the Y direction, the workpiece W is moved in the X, Y direction.
It is movable within a plane.

An X-axis master scale 12 is attached to a fixed frame portion below the table 1, which is supported at one point by a pin 11 at the origin position and is extendable and retractable in the X direction.

The master scale 12 is formed into a band shape using a homogeneous material with a known coefficient of thermal expansion, and has a plurality of optical sensor dog holes Pn (PI. P2.P3,...,P
N) is provided. The pitch does not necessarily have to be manufactured with great precision, since it is measured with high accuracy using a laser range finder and then used, as will be described later.

Further, the dog hole Pnf! is formed on the lower surface of the table 1 as the table 1 moves. - An optical proximity sensor 13 for detection 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 molds provided above and below the workpiece W. It is designed to be punched. A dog 14 indicating the top dead center is provided at one position of the crankshaft 13, and by detecting this with a proximity sensor 15, the top dead center, that is, the non-punch state can be identified.

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 that controls the punch press with the above configuration is N
It is mainly composed of a C device and a programmable controller connected thereto, and a counter circuit 16 is provided in, for example, the programmable controller of this control device.
and one servo system including a servo parameter storage section 18. One general servo system has a position loop and a speed loop, and manually controls the positioning target value output by the NC device to control the moving body, that is, the table 1, at the commanded speed to this target value. It's something like this.

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

The transmitting/receiving arithmetic processing device 17 has a buffer therein, and manually inputs the detection data of the dog hole Pn, and sets and rewrites the servo parameters in the servo parameter storage section 18.

In the device with the above configuration, the initial settings, correction principle,
Changing servo parameters during machining, material handling methods,
The dog hole detection method will be explained in order.

During assembly, a laser mirror is attached to a bracket or the like of the table 1, and the difference δ between the actual operation and the NC command value is stored using the laser distance 21.

For example, if the actual movement amount due to laser protrusion is 100.05 mm with respect to the command value of 100 mm, record the difference 100.05-100-0.05 and send that value to the arithmetic processing unit 17! I can do it.

Therefore, after making the measured value of the encoder accurate using 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) This is written in the servo parameter storage section 18 as ↑0.

To be more specific, here is the hole of the master scale 12 (
Recognizing that the machining accuracy of the gauge (gauge) is not known in microns, that a latch delay occurs due to the response speed of the optical sensor, and that the measured latch data differs depending on the axis speed setting value, the initial value of the gauge was determined. There must be.

First, you can measure the gauge itself with a measuring device to find it, but since it depends on the mounting position (condition with the sliding surface and the position of the mounting reference hole), we do not consider using this method to find the reference value of the gauge. .

Therefore, the master scale will be installed according to the drawing. Also, set the mold and prepare for processing.

Set the shaft speed to the override value F4, and manually process the command value Clmm (1) so that it is as large as possible within the measurable stroke of the I-regulator) from the NC console.

Next, C2mm (around 10mm near the origin of the workpiece) is manually processed.

At this time, the processed plate was left overnight at 20°C and measured with a measuring device, and the measured values at this time were MlmmS and MlmmS.
Suppose it was M2mm.

In addition, following the past measurement (under the same loading as machining), the counter latch coordinate Lnmm (x 1
, x2, -=, xN) are stored at all pitch points.

Similarly, the above measurements are repeated for each of the shaft speeds F3, F2, and F1, and the latch drift is memorized.

From these, a latch coordinate table as shown in FIG. 2 is created.

Here, the average delay D(4 −
Find 3).

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

D (4-2) - Σ(L (n, f 2) - L (n, f 4)) / ND
(4-1) ■Σ(L (n, f 1) - L (n, f4))/N The reason for calculating the average value is to keep the amount of data to be managed as small as possible, and it is not necessary to actually manage it on the software. is T(n
, f4) and D (4-3) , D (4-2) , D (
4-1). FIG. 3 shows the relationship between the error and the speed f4.

Next, find the dimension T(n, f4) to be found.

T (n, f 3) - T (n, f4) + D (.4 -
3) T (n.f2)=T (n, f4)+D (4-
2) T (n, f i) - T (n, f4) + D (4
-1) Store the values obtained above as 20°C equivalent values in the buffer in the transmitting/receiving arithmetic processing unit 17 in advance, determine the value of each pitch according to the environmental temperature, and use this as the servo parameter in the servo system. This allows the well-known pitch error correction to be performed.

Correction Principle> As described above, each dome hole Pn position of the master scale 12 is converted to 20° C. and the position is managed. In other words, no matter how the environmental temperature changes, the actual machining deviation can be detected by detecting the dog hole Pn position of the master scale 12, and an appropriate correction value can be given according to the difference. .

To show the basic operation, if a processed plate made of iron is placed in an environment of 25℃, then the
1.7μm/”C・mX (25-20)-58.5μ
m is growing. If this plate was made to have high rigidity and processed according to the theoretical value, and then cooled to 20°C, it would have been processed to be 58.5 μm smaller.

Therefore, in order to avoid this, master scale l2
The positioning of the processing machine may be corrected at the latch point of the dowel hole Pn.

It should be noted that this correction value is the actual position detected on an accurate scale using a temperature capture function, so it is not only the mechanical distortion and temperature distortion of the power transmission machine, but also the temperature of the workpiece and frame. It also cancels out the effects of
This means that processing can be performed with the measurement accuracy of the master scale 12 and its measurement system.

To give a concrete example, suppose that the ball screw 4, which is a power transmission function, is slightly higher than the workpiece temperature Fw, and the distortion of the ball screw is △1, the error due to the expansion of the workpiece W is Δ2, and other distortions of the frame, etc. are Δ3. , these values Δ1,
△2. It doesn't matter what Δ3 is.

Therefore, if the servo parameters are appropriately corrected in response to changes in conditions, especially changes in temperature, machining with almost no errors can be maintained permanently.

In addition, when comparing the effects of this semi-closed loop with that of a fully closed loop, from a practical point of view, semi-closed loop is preferable because it allows high-speed processing, there is no need to worry about tax regulations, and it can be designed at a lower cost. It can be said that closed loop is better. Errors due to temperature are basically the same.

Furthermore, although the ball screw 4 is shown as an example in this example, it may also be a rack/binion. However, in terms of the inherent accuracy due to pack lash, etc., the ball screw has better processing accuracy.

Figure 4 shows the servo parameter setting method.

At the start of machining, when the machine returns to the origin in step 401, in step 402, prohibition IL of starting to the NC is first performed.

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

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

In step 406, servo parameter values corresponding to the temperature θ are set based on the 20° C. equivalent value T(n−f4).

In this example, it is assumed that the correction work is performed by the servo system 19, but it is also possible to perform correction by changing the original gatepost value.

Correction Parameter Changing Process> The servo parameters are changed by the process shown in FIGS. 5 and 6. FIG. 5 shows the change request procedure, and FIG. 6 shows the change procedure when a change request is made.

In FIG. 5, in step 501 during processing, the proximity sensor 15 shown in FIG. Determine whether or not.

If it is the predetermined direction, proceed to step 503,
The latch coordinates of the dog hole Pn are sent, and in step 504,
Depending on which dog hole Pn the latch coordinates belong to, the latch value for that dog hole Pn is loaded into the memory.

Therefore, in step 505, the value loaded in step 504 is compared with the reference value, that is, the value that should be detected at the previously detected temperature based on the value converted to 20°C, and if it is not within the allowable value, For example, the process moves to step 506 and the parameter change request bit is turned on. Note that in step 507, the frame temperature is received.

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

Next, in FIG. 6, when a parameter change request is turned on in step 601, the controller waits for the return to the origin position in step 602, and outputs a start prohibition to the NC in step 603.

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

Material compatible method There are two types of material-compatible methods:

■ One is the expansion rate of each material, for example iron...11.
7 μm/m·°C Copper: 16.7 μm/m·°C Aluminum: 23 μm/m·°C This is a method of appropriately correcting the material of the master scale 12 currently used.

In this case, for example, when the NC is returned to the origin, the material change is identified in step 604 of FIG.
05, calculate the temperature at 20°C for each material, and store the calculated value.

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

A bolt 22 attached to the guide 21 is for preventing displacement in a direction perpendicular to the direction of movement. The tip of this bolt 22 is formed into a spherical shape, and the cartridge scale 20 is slidably moved in the direction of movement by the guide 21.
Press lightly against the Note that the support point of the pin 11 is also formed in a spherical shape in order to align the fixed point with the origin.

If 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 makes it possible to identify whether the detection data is good or bad when detecting 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) that manually inputs the ASB 2-phase output from the encoder 9.
23 and a counter latch control section 24 that manually inputs the detection signal of the optical sensor 13, and both circuits 23 and 24 are input to the counter circuit 16. The counter circuit 1
6, an internal clock signal CLK is input.

A sensor-on buffer 25 and a clock counter 26 are connected to the counter circuit 16, and the outputs of both channels 25 and 26 are connected to a data quality control section 27.
7 is connected to a data path 28. The clock counter 26 is also supplied with the internal clock signal CLK.

In the above configuration, as shown in FIG.
3 moves in one direction and signals 2 to one dog hole Pn.
Suppose you get 9. These two signals are pulse-like signals that turn on at a certain threshold and then turn off. Assume that the commanded shaft speed is bolIII/S. The width of the dog hole Pn is known and is assumed to be a+n+m.

The signal processing method is shown in FIG.

In step 1001, latch data when the sensor is on is temporarily stored in the buffer 25, and in step 1002, the clock counter 26 obtains the time t from sensor on until sensor off.

Therefore, in step 1003, the data quality control unit 27 performs b. ta is determined, that is, the current speed value h is the planned speed b. Determine whether or not it is within the allowable value for
If it is within the allowable value, the latch data when the sensor is turned on is validated in step 1004, and is sent 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 the tree example, the reliability of the latch data detected by the sensor 13 is improved, and the accuracy of the added XL itself can be improved.

In this example, the detection of the dog hole Pn has been described, but the mark on the master scale 12 is not limited to this, and may be printed with a different color, for example. In this case, the quality of the latch data can also be checked. 111 can be separated.

Dog Hole Detection Method (Part 2)> This section shows an example of iTE supplementing latch data according to speed.

In FIG. 11, in the detection circuit of this example, a speed calculation section 30 based on waveform detection and a latch coordinate extraction section 31 are connected to the counter circuit 16. Of which, speed calculation section 3
0 is connected to the average delay parameter value calculation unit 32,
The calculation section 32 and the latch coordinate extraction section 31 are connected to a measurement result output section 33.

The average delay parameter value calculation unit 32 has a correspondence table of errors ε caused by speed and signal delay as shown in FIG. Calculate ε. Since the errors vary, the average value is taken.

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, and outputs a measurement value close to the true value. The measured value may be used by averaging a plurality of data for the same dog hole.

As shown in FIG. 13, in step 1301, the coordinate value when the sensor is on is taken out, and in step 1302, the speed value is calculated from the pulse width when the sensor is on.
In step 3, the error ε is subtracted, and in step 1304, the corrected measurement value is output.

Therefore, calculate the j value for each speed from the waveform such as the scale,
By subtracting the corresponding delay parameter from the measurement data, the measurement accuracy and, by extension, the addition L accuracy can be improved.

In this example, measurements can be made at any shaft speed. Furthermore, if the speed is constant, accuracy can be further improved. Note that in this example, the speed value was obtained by waveform detection, but
An NC command value can also be used on the condition that the speed is stable.

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

In addition, since the master scale 12 is configured to be able to correct the temperature and to detect the actual machining position, it is possible to eliminate not only distortion of the power transmission mechanism but also thermal effects of the workpiece and frame. This makes it possible to easily achieve a high precision of 0.01 m+s or more, which was previously difficult, under all environmental conditions, making ultra-precision machining possible.

There is no need to worry about taxes or damage like with a fully closed loop.

In the above embodiments, the punch press was used as an example, or other NC machines such as laser processing machines, punch/laser combined processing machines, lathes, etc.
The same applies to machine tools.

Further, in the above embodiment, an example in which a workpiece is moved is shown, but the same applies to a machine tool in which a tool is moved.

Furthermore, although the above embodiment mainly shows a semi-closed loop, the present invention can also be practiced with a fully closed loop, and thereby it is possible to eliminate errors caused by thermal distortion of the workpiece or frame. It is something.

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

[Effects of the Invention] As described above, the present invention detects a moving object whose positioning is controlled in a closed loop with respect to a fixed position in a manner that can be converted to a constant temperature, and the actual machining position becomes a command value at a constant temperature. This is a scale device used for error correction in the drive system of an NC processing machine that controls the servo system, so it can compensate for all thermal distortions, including those of the power transmission mechanism and thermal distortions of the workpiece and frame. Can be supplemented. In addition, the master scale at the scale position can be made into a cartridge type so that it corresponds to the material of the workpiece.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the structure of a positioning device using scale position according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of latch data for each speed, and Fig. 3 is an explanatory diagram showing the error situation due to speed. 4 is a flowchart showing the servo parameter setting method, FIG. 5 is a flowchart showing the parameter change request output method, FIG. 6 is a flowchart of the parameter change method, and FIG. 7(a) is the flowchart for each material. Front view showing the cartridge-type master scale created in
Figure (b) is a diagram of the right side, Figure 8 is a block diagram showing an example of the latch data detection circuit, Figure 9 is an explanatory diagram showing the detection action, and Figure 10 is for determining whether the data is good or bad. FIG. 11 is a block diagram showing another example of the latch data detection circuit, FIG. 12 is an explanatory diagram of the data used by the circuit, and FIG. 13 is the latch data detection circuit.
1 is a flowchart showing the 1Pl constant value supplement i [method; 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 arithmetic processing unit 18... Servo parameter storage section 19... Servo system

Claims (2)

[Claims] (1) Error correction in the drive system, etc. of an NC processing machine that has a moving body whose positioning is controlled by a closed-loop control system, and performs prescribed machining while positioning a workpiece or tool attached to this moving body at a prescribed position. The scale device is made of a material with a uniform coefficient of thermal expansion, has a mark to be detected along its longitudinal direction, has one end fixed to the origin position of the moving body, and the other end to detect changes in environmental temperature. A drive in an NC processing machine characterized by comprising: a master scale that is supported in a flexible manner according to the moving body; and mark position detection means that detects the position of the mark to be detected on the master scale as the moving body moves. A scale device used to correct errors in systems, etc. (2) In claim 1, the master scale is created for each material of the workpiece and is removably attached to the NC processing machine, for correcting errors in drive systems, etc. in the NC processing machine. Scale device used.