JP2001138178A - Thermal displacement correcting device for ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate deterioration of positioning precision caused by change in length of a ball screw by heat for improving machining precision. SOLUTION: A movable body 3 slidably supported by a base 26 and driven by a ball screw 12 is disposed on the base 26, a supporting device for rotatably and axially immovably supporting one end of the ball screw 12, and rotatably and axially movably supporting the other end of it is disposed on the base 26, a detector 24 to measure change in length of the ball screw 12 is installed, a lead and ball screw pitch error correcting value is operated based on a measured value, and this information subject to correction is registered in an NC device, whereby correct positioning is achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for correcting thermal deformation of a ball screw used for machine tools, industrial machines and the like.

[0002]

2. Description of the Related Art In a machine for positioning a movable body using a ball screw, for example, in a machine tool, heat generated between a ball screw and a nut or a supporting bearing is transmitted to the ball screw.
Further, the length of the ball screw changes due to a change in room temperature.
In particular, within a predetermined time, for example, about 90 minutes from the start of the machine, the change in the length of the ball screw is large, and the positioning accuracy of the movable body is deteriorated. There was a defect.

In order to solve the above-mentioned problem, in a first method, a machine tool is warmed up and machining is performed after a change in the length of a ball screw is reduced. In the second method, a cooling liquid whose temperature is controlled is passed through the inside of the ball screw to reduce a change in the length of the ball screw,
The decrease in positioning accuracy is reduced. Further, in the third method, even if the length of the ball screw changes, a decrease in the positioning accuracy is reduced by closed-loop control for positioning the movable body using the linear scale. In the fourth method, the touch sensor is mounted on the spindle,
A reference position provided on the table is measured, compared with a predetermined position, and a change in length is corrected to reduce a decrease in positioning accuracy.

[0004]

The first method has a drawback that productivity is deteriorated because machining cannot be performed during a warm-up operation. The second method has a drawback in that there is a time delay in cooling, and the change in the length of the ball screw cannot be prevented accurately. The third method is costly because a linear scale is used. Further, since the mounting position of the linear scale is offset from the position of the ball screw, a detection error occurs due to the inclination of the movable body when the movable body advances and retreats, and there is a disadvantage that the movable body cannot be correctly positioned. 4th
The method of (1) requires a time for mounting the touch sensor on the spindle and a time for measurement, thereby lowering productivity. Accordingly, it is an object of the present invention to eliminate a decrease in the positioning accuracy of a movable body caused by a change in the length of a ball screw due to heat without the disadvantages of the above-described conventional device.

[0005]

According to a first aspect of the present invention, there is provided a ball screw thermal displacement compensating apparatus, comprising: a movable body slidably supported by a base and driven by the ball screw; A detector for supporting the one end of a screw rotatably and immovable in the axial direction and supporting the other end rotatably and axially movably on a base, and measuring a change in the length of the ball screw. And calculates at least one of a lead and a ball screw pitch error correction value corresponding to a change in the length of the ball screw based on the output from the detector.
Register in the C device. Using the calculated information, a target value of the control axis is calculated by a known method. Thereby, the movable body is correctly positioned. In this case, the measurement of the change in the length of the ball screw is measured at the beginning of each operation cycle of the machine.
It can also be performed at the start of a predetermined number of operation cycles or at a predetermined time, and can be selected according to the purpose.
In addition, the calculated information is obtained at the start of one operation cycle of the machine,
It can be used at the start of a predetermined number of operation cycles or at a predetermined time, and can be selected as needed.

As the detector for measuring the length of the ball screw, an electromagnetic induction type detector can be used, but other types such as a laser type detector may be used. The means for calculating the ball screw lead information or the ball screw pitch error correction information based on the measured value may use the calculation function of the NC device, or may use calculation means provided separately from the NC device. good.

According to the first aspect, the method for correcting the thermal displacement of the ball screw using either the lead information or the ball screw pitch error correction information is described. This is a method of correcting the thermal displacement of the ball screw by using both of them as correction targets. By using the correction values of both information, the thermal displacement of the ball screw can be corrected with higher accuracy.

In a third aspect of the present invention, there is provided a ball screw thermal displacement compensating device further comprising means for registering in advance the threshold value corresponding to the compensation object in the NC device, The correction target is compared with the threshold, and only when the difference between the comparison results is larger than a predetermined value, the correction information newly calculated in place of the correction target information already registered in the NC device. Is registered in the NC device. Thus, the correction information used when the NC device calculates the target position of the movable body does not frequently change, and the positioning accuracy can be stabilized.

According to a fourth aspect of the present invention, there is provided a ball screw thermal displacement correcting apparatus according to the first or second aspect, wherein a threshold value corresponding to a change amount of the length of the ball screw obtained by the detector is set to the NC.
Means for pre-registering in the apparatus and comparing means for comparing the amount of change in the length of the ball screw with the corresponding threshold value, wherein the calculation is performed only when the difference between the comparison results is larger than a predetermined value. And the registration is performed. This makes it possible to stabilize the positioning accuracy by preventing the correction information used when the NC device calculates the target position of the movable body from changing frequently, and to achieve the above-mentioned object without performing unnecessary calculations. Can be achieved. According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the overall length of the ball screw is divided into a plurality of sections, and the calculation means calculates the correction target within the divided range. Therefore, it is possible to calculate a difference in deformation per unit length of the ball screw due to a difference in temperature depending on the position of the ball screw. Therefore, the thermal displacement of the ball screw can be corrected with higher accuracy.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a machine tool having a ball screw feeder according to an embodiment of the present invention. In FIG. 1, a bed 1 is provided with a jig 2 and a column 3 which moves in a (X) direction perpendicular to the paper surface.
The column 3 has a Y-axis slide 4 that moves up and down (Y).
, And the spindle head 5 that moves in the front-rear (Z) direction is guided by this. A tool 6 is detachable from the spindle head 5.

The ball screw feeder will be described with reference to the drawings. FIG. 2 shows an AA cross section of FIG. The column 3 fixes a nut 11. The nut 11 is a ball screw 12
Are engaged. One end of the ball screw 12 has a pair of bearings 13 inserted therein and is regulated by a ring nut 14 so as not to move in the axial direction. Also bearing 1
3 is fixed to the thrust support block 16 by a ring 15 which abuts on the outer ring, thereby the ball screw 12
Is rotatable and its movement in the axial direction is restricted. The ball screw 12 is connected to a servomotor 18 by a coupling 17.

The other end of the ball screw 12 is
Is inserted, and the ball screw 12 is
Is regulated in the axial direction. Also bearing 20
Are inserted into the support block 22. Bearing 2
0 is fitted in the inner hole of the support block 22 so as to be able to move in the axial direction. Therefore, when the length of the ball screw 12 changes due to heat, the ball screw 12 starts from the thrust support block 16 that restricts axial movement,
It extends toward a support block 22 that allows axial movement. A non-contact type detector 24 is attached to the ball screw support block 22 via a plate 23.

FIG. 3 is a control block diagram of the ball screw feeder described above. The CNC 40 is an arithmetic unit C
PU 41 and ROM 4 storing system programs and the like
2 and R storing the NC program and various parameters
AM 43, an input device 44 such as a keyboard, an output device 45 such as a CRT, and interfaces 46, 47, and 48.
Is the main component. Then, a movement command to the ball screw is output to the digital servo unit 49, and when the digital servo unit 49 drives the ball screw driving servo motor 18, the servo motor 18 changes the current position of the ball screw shaft 12 detected by the encoder 19. It is fed back and feedback controlled. The detector 24 is of a type that detects eddy current loss. That is, when the length of the ball screw 12 changes, an induction current flows through the end face 12 a of the ball screw due to electromagnetic induction generated by a high-frequency oscillation circuit (not shown) provided in the detector 24, whereby The inductance of the coil changes. This change amount is converted into a voltage value by the control unit 50, and is further converted into an analog-digital (A
-D) Converted to a digital value by the converter 51. This digital value is sent to CN via interface 48.
Input to C40.

Next, a measurement correction method in the above-described configuration will be described with reference to FIGS. 3 and 4 based on a flowchart shown in FIG. First, prior to the operation of the machine tool, the reference dimension A from the center 13a of the width of the pair of bearings 13 inserted into the thrust support block 16 to the end face 12a of the ball screw is stored in the RAM 43 of the CNC 40.
Register in. This reference dimension A (see FIG. 4) is obtained from design values. Further, for example, in a state where the temperature of the ball screw 12 matches the environmental temperature at the start of the operation of the machine tool (hereinafter referred to as a reference temperature), the detector 24 and the end face 12a of the ball screw 12 are used. And the distance B (hereinafter referred to as an initial value) from the
In the RAM 43.

When the operation of the machine is started and a signal indicating that the cycle has started is given, the routine of FIG. 5 is executed, for example, at predetermined time intervals. Step S1
At 00, the distance B 'between the detector 24 and the end surface 12a of the ball screw is measured by the detector 24. This is the control unit 50
Is converted to a voltage value, and further converted to a digital value by the analog-digital converter 51.

In step S 101, the measured value B ′ is registered in the RAM 43 via the interface 48. In step S102, the distance B ′ and RA
The initial value B registered in M43 is called to calculate the change in the length of the ball screw. The change ΔA in the length of the ball screw is calculated by ΔA = BB ′. In step S103,
Retrieve the ball screw lead L and the reference dimension A registered in the RAM 43 and change the length of the ball screw Δ
A is added to the value obtained by dividing A by A.
To calculate the correct lead L 'after the thermal change as a correction target. In step S104, the read L of the RAM 43 is rewritten to L '. In S105, the target position of the movable body is calculated using the corrected lead L ', and NC
Execute the program. Therefore, even if the ball screw is stretched by heat, the influence can be eliminated and the movable body can be positioned. Therefore, a decrease in positioning accuracy can be eliminated.

A second embodiment for correcting the thermal displacement of the ball screw will be described with reference to FIGS. 3, 4 and 6 based on a flowchart shown in FIG. This is characterized in that, in order to correct a change in the length of the ball screw, instead of calculating the lead, calculation is performed with a pitch error correction value as a correction target. FIG. 6 shows the relationship between the coordinates of the ball screw and the pitch error correction value. The horizontal axis indicates the distance from the center 13a of the width of the pair of bearings 13 to each coordinate of the ball screw with the starting point being 0. The ball screw end face 12
a corresponds to A on the vertical axis. The vertical axis indicates the pitch error correction value at that position. In this figure, a range J indicates a use stroke of the movable body, and a broken line U in the range J indicates a pitch error correction value before thermal deformation of the ball screw. This pitch error (P1, P2, P3,..., Pf) is measured in advance and registered in the RAM 43. The amount of elongation ΔA due to thermal displacement of the reference dimension A is shown on the vertical axis. Range J
When the elongation amount (proportional distribution amount) at each coordinate position and the pitch error of the corresponding coordinate position are added, the sum of the errors is indicated by a broken line V.

Steps S100 to S1 in FIG.
02 is the same as FIG. 5 and the description is omitted. Step S2
At 00, the counter value n = 1 is set. Step S201
Then, the first pitch error P1 registered in the RAM 43 is called. Usually, P1 is often 0 to be the origin of the stroke of the movable body. In step S202,
The reference dimension A registered in the RAM 43 is called out, and the value obtained by dividing the change ΔA in the length of the ball screw by A is multiplied by the coordinate D1 of the position corresponding to the pitch error P1. This is added to the pitch error P1 to calculate a correct pitch error correction value P1 'after the thermal change.

In step S203, the pitch error correction value P1 registered in the RAM 43 is rewritten to P1 '.
In step S204, 1 is added to the counter value n. In step S205, it is determined whether this counter value n has exceeded a preset number f. If the number f has not been exceeded, the process returns to step S201 to repeat the processing. As a result, the pitch error correction value L is corrected by the amount of elongation, and is replaced with a broken line V indicated by a dashed line. If the number f has been exceeded, the process proceeds to S105, and the NC program is executed based on this value. By using the corrected pitch error correction value in the calculation of the target position in the NC control, it is possible to prevent a decrease in the positioning accuracy of the movable body caused by a change in the length of the ball screw due to heat. Further, since the change in the length of the ball screw from the starting point 0 to the D1 can be added, the positioning can be performed with higher accuracy. FIG. 8 shows a third embodiment in which the thermal displacement of the ball screw is corrected using both the calculated lead information and the pitch error correction information. The details are not described because they are the combinations described above. In this embodiment, both the corrected lead information and the corrected pitch error correction value
Since it was used to calculate the target position in the control,
There is an advantage that the number of operations can be reduced by using the read information. In addition, by using the pitch error correction value, the change in the length of the ball screw from the starting point 0 to the D1 can be added, and accurate positioning can be performed.

FIG. 9 shows a flowchart in a fourth embodiment which is an alternative to the first embodiment in FIG. As a feature of this routine, in step S300, the absolute value of the difference between the calculated read L ′ and the read initial value L is compared with a preset threshold value K.
At 04, the read information of the RAM 43 is rewritten to the read information L 'after the calculation. If it is equal to or smaller than the threshold value K in step S300, the lead L registered before that is used. For this reason, the lead information used when the NC device calculates the target position of the movable body does not frequently change, and the positioning accuracy can be stabilized.

FIG. 10 shows a flowchart in a fifth embodiment which is an alternative to the embodiment in FIG. As a feature of this routine, in step S503, the absolute value of the change amount ΔA of the length of the ball screw is compared with a preset threshold value K. If the absolute value is larger than the threshold value K, the ball screw pitch error correction value of step S200 and subsequent steps is calculated. Perform the operation. This is the same as step S200 and subsequent steps in FIG. If it is smaller than the threshold value K in step S400, the pitch error information registered before that is used. Therefore, the ball screw pitch error correction information used when the NC device calculates the target position of the movable body does not change frequently, and the positioning accuracy can be stabilized.

FIG. 11 shows a sixth embodiment for calculating the object to be corrected. The horizontal axis indicates the distance from the center 13a of the width of the pair of bearings 13 to each coordinate of the ball screw with the starting point being 0. The ball screw end face 12a corresponds to the vertical axis A. The vertical axis indicates the correction value at that position. The amount of elongation ΔA due to thermal displacement of the reference dimension A is shown on the vertical axis. A straight line Q indicates a case where the variation ΔA of the length of the ball screw is proportional to the starting point 0 to the end face 12a. The position of the movable body at the coordinates D1, Dm, Df at the reference temperature is measured. Next, after driving for a predetermined time, the coordinates D1, Dm,
The position of the movable body at Df is measured. Since the difference between the measured values is a displacement, the difference is set as correction values M1, Mm, and Mf. From this, the correction value Mx between the coordinate D1 and the coordinate Dm is Mx = M1 + (Mm−M1) * (Dx−D
1) It is obtained by (Dm-D1). This is a straight line G1-
It is a point on Gm and is mathematically determined. Further, the correction value M1 ′ of the coordinates D1 after the start of the operation is M1 ′ = M1 * Δ
A ′ / ΔA is calculated. The correction value Mx between the coordinate Dm and the coordinate Df is Mx = Mm + (Mf−Mm) * (Dx−D
m) / (Df-Dm). These calculations are performed in step S202 of the flowcharts of FIGS. 7, 8, and 10.
Is executed in place of Pn ′. This is because the correction value is calculated by dividing the ball screw into a plurality of parts, so that even if the temperature differs depending on the position of the ball screw and the elongation of the ball screw changes, the correction can be accurately performed. Therefore, positioning can be performed with even higher precision.

FIGS. 12 and 13 show different measurement methods for the change in the length of the ball screw. FIG.
In the example, a hole 50a is formed at one end of the ball screw 50, and a ring-shaped magnet 52 is attached. A differential transformer 51 is attached to the ball screw support block 22 via a plate 53. This differential transformer 51 is arranged concentrically with the ring-shaped magnet 52 described above. The change in the length of the ball screw is measured by the differential transformer 51. The processing after the measurement is the same as the method described above. This method has the advantage that using a long detector does not lengthen the device. The example of FIG. 13 shows a method of measuring by providing the detector 60 in a direction perpendicular to the ball screw. The processing after the measurement is the same as the method described above. In this method, since the signal line 60a of the detector 60 is arranged in a direction perpendicular to the ball screw, there is an advantage that the apparatus can be shortened in the longitudinal direction of the ball screw. Although the reference temperature was set at the start of operation, the time when the temperature rise of the ball screw was saturated was taken as the reference temperature,
The detector 24 and the end face 12a of the ball screw 12 at that time
The distance B to the part is set as an initial value. This is advantageous in that the ratio of time from the start of operation to the saturation is small in the total operation time, so that the number of times of correction is small and the positioning accuracy can be stabilized.

[0024]

As described above, the thermal displacement compensating device for a ball screw according to the present invention comprises: a movable body slidably supported by a base and driven by the ball screw; A support device that supports immovably and supports the other end rotatably and axially movably is arranged on the base, and a detector for measuring the change in the length of the ball screw is attached. Based on this, a correction target consisting of at least one or both of the lead and pitch error correction values corresponding to the change in the length of the ball screw is calculated, and information on the correction target is registered in the NC device. Using the correction value information, a target value of the control axis is calculated by a known method, and the movable body is positioned. As a result, it is possible to eliminate a decrease in the positioning accuracy of the movable body due to a change in the length of the ball screw caused by heat, so that there is no need to perform a warm-up operation, and even if the machine is operated from the beginning of the morning, the machining can be accurately performed. it can. This is claimed in claims 1 to 5
This is a common effect.

According to a third aspect of the present invention, the calculated information of the correction target is compared with a pre-registered threshold value corresponding to the correction target, and only when the difference is larger than a predetermined threshold value, the NC device is notified. Since the correction target information after the calculation is used instead of the correction target information already registered, the lead information or the ball screw pitch error correction used when the NC device calculates the target position of the movable body is used. There is an advantage that the information cannot be frequently rewritten and the positioning accuracy can be stabilized.

According to a fourth aspect of the present invention, a threshold value corresponding to the change amount of the length of the ball screw is registered in the NC device in advance, and the registering means stores the change amount of the ball screw length and the corresponding threshold value. Compare. Then, only when the difference is larger than a predetermined value, the information on the correction target calculated by calculating the correction target is registered in the NC device.
Accordingly, there is an advantage that the correction target information used when the NC device calculates the target position of the movable body is not frequently rewritten, and the positioning accuracy can be stabilized. According to the fifth aspect, the total length of the ball screw is divided into a plurality of sections, and the correction target is calculated in each section. Therefore, it is possible to cope with a change in length depending on the area of the ball screw, and positioning can be performed with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic side view illustrating an example of a machine tool having a ball screw thermal displacement correction device according to the present invention.

FIG. 2 is a cross-sectional view of the ball screw drive device taken along line AA of FIG.

FIG. 3 is a block diagram of an NC device according to an embodiment of the present invention.

FIG. 4 is a partially enlarged cross-sectional view of the ball screw support of FIG. 2;

FIG. 5 is a flowchart of a control unit according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating a relationship between a ball screw coordinate and a ball screw pitch error correction value according to the second embodiment of the present invention.

FIG. 7 is a flowchart of a control unit according to the second embodiment of the present invention.

FIG. 8 is a flowchart of a control unit according to the third embodiment of the present invention.

FIG. 9 is a flowchart of a control unit according to the fourth embodiment of the present invention.

FIG. 10 is a flowchart of a control unit according to a fifth embodiment of the present invention.

FIG. 11 is a diagram illustrating a relationship between a ball screw coordinate and a ball screw pitch error correction value according to a sixth embodiment of the present invention.

FIG. 12 is an enlarged cross-sectional view of a ball screw support according to yet another embodiment corresponding to FIG. 4;

FIG. 13 is an enlarged cross-sectional view of a ball screw support according to yet another embodiment corresponding to FIG. 4;

[Explanation of symbols]

1 ... bed, 2 ... jig, 3 ... column,
4 ... Y-axis slide, 5 ... Spindle head, 6 ...
・ Tool, 11 ・ ・ ・ Nut, 12 ・ ・ ・ Ball screw, 16 ・ ・ ・ Thrust support block, 22 ・ ・ ・
Support block, 24 Detector, 18 Servo motor, 40 NC device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Michihiro Hanai 1-1-1 Asahi-cho, Kariya-shi, Aichi F-term in Toyota Koki Co., Ltd. (Reference) 3C001 KA01 KA05 KB10 TA01 TB01 TC05 5H269 BB03 EE05 JJ03 JJ19

Claims (5)

[Claims] 1. A base, a movable body slidably supported by the base, a nut fixed to the movable body, a ball screw engaged with the nut, and a shaft rotatable on one end of the ball screw. A means for supporting the other end so as to be immovable and the other end to be rotatable and axially movable; a servomotor connected to the ball screw; and an NC device for controlling the rotation of the servomotor by a numerical control program. In the ball screw feeder, a detector for measuring a change in the length of the ball screw, and at least one of a lead and a pitch error correction value corresponding to the change in the length of the ball screw based on the output of the detector. A calculating means for calculating a correction target; and a means for registering the information on the correction target calculated by the calculating means in the NC device. Thermal displacement correcting apparatus of the screw. 2. The ball screw thermal displacement correcting device according to claim 1, wherein said calculating means calculates both the lead and the pitch error value as the correction target. 3. The apparatus according to claim 1, further comprising means for registering in advance the threshold value corresponding to the correction target in the NC device, wherein the registration means compares the correction target with the threshold value corresponding thereto. Only when the difference is larger than a predetermined value, instead of the correction target information already registered in the NC device, the corrected correction target information is
A thermal displacement compensating device for a ball screw, which is registered in a C device. 4. The ball screw according to claim 1, wherein a threshold value corresponding to a change amount of the length of the ball screw obtained by the detector is registered in the NC device in advance. And a comparing means for comparing the threshold value corresponding to the correction value with the correction target. Only when the value calculated by the comparing means is larger than a predetermined value, the correction target calculated by the calculating means is calculated. A device for correcting thermal displacement of a ball screw, wherein information is registered in the NC device. 5. The ball screw according to claim 1, wherein the total length of the ball screw is divided into a plurality of lengths, and the calculating means calculates each of the correction targets within the divided range. Thermal displacement correction device.