JPH1128637A - Protective device for feed mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device to protect a feed mechanism, by watching the temperature of a ball screw and the temperature of a ball screw nut, and limiting the feeding scope of a moving body at the time when the temperature difference is more than a set value. SOLUTION: The temperature of a ball screw nut 4 fixed to a moving body 3 is measured by a temperature detecting sensor N, while the temperature of a ball screw 5 is measured by a temperature detecting sensor A installed at the position on the moving body 3 opposing to the ball screw 5. The temperature difference tN-tA of both members is compared with a limit temperature difference tmax to be an excessive preload, and furthermore, it is compared with a temperature difference tHigh whose preload is increased, and giving a bad influence to a driving system. And when tN-tA>=tmax, the rotation motor 6 of the ball screw 5 is stopped by a controller 16, and when tHigh <=tN-tA<tmax, a warning is output to a worker, and when tN-tA<tHigh , the rotation of the motor 6 is continued, so as to protect the feed mechanism.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw feed mechanism for a machine tool or the like, and more particularly to a protection device against thermal expansion in a feed mechanism using a ball screw.

[0002]

2. Description of the Related Art When a moving body such as a table is slid and moved using a ball screw in a machine tool, the ball screw rotates at a high speed during rapid traverse. It is not preferable to give a large preload to However, when performing cutting feed, high rigidity is required, so that a large preload must be applied. When the moving body is reciprocated for a long time by performing the continuous operation under such conditions, the ball screw nut generates heat and becomes high in temperature, and the ball screw eventually rises in temperature and expands. At this time, since the ball always rolls with respect to the ball screw in the nut portion, the amount of heat generated is large and the temperature rise is large.

[0003] On the other hand, the ball screw is not always used over its entire length during continuous operation, and may be frequently used and rarely used. Also, frequently used parts are not always in contact with the ball screw nut. Therefore, the temperature rise is small and the amount of thermal displacement is small as compared with the ball screw nut. However, heat is accumulated in places frequently used, causing some thermal displacement. Therefore, at this point, the ball screw nut can move smoothly.

However, at a rarely used place such as the end of a ball screw, the temperature is transmitted only by heat conduction from a high temperature part, and since there is no heat generation at that place, the temperature rise is small and the heat which expands due to heat is small. The displacement is small. Therefore, when the ball screw nut with high thermal expansion at high temperature goes to such a place with small thermal expansion, the pitch between the ball screw and the ball screw nut does not match, and the state becomes the same as when the preload is excessive, and the ball screw nut part May cause damage to the device.

As described above, the difference in temperature of each part of the ball screw due to the frequency of use causes a difference in the amount of thermal displacement in the ball screw, resulting in a difference in the positioning error of the moving body. JP-A-54-12
No. 3,674 is known. This prior art focuses on the fact that the temperature rise due to heat generation in each part of the ball screw is different, and therefore the amount of thermal displacement is different, the ball screw is divided in the length direction, and the temperature distribution of each divided part is expressed by a relational expression. Approximate calculation or direct measurement is performed to determine the thermal displacement amount of each segmented portion, and correction feeding is performed at the time of positioning the moving body. However, no consideration has been given to the occurrence of a pitch difference between the ball screw nut and the ball screw due to thermal expansion.

[0006]

In the correction feeding technique described in the prior art, a ball screw is divided in a longitudinal direction and a positioning error of a moving body is corrected in accordance with a thermal displacement caused by a temperature of each part. is there. However, no consideration has been given to a defect caused by a pitch difference between a ball screw and a ball screw nut due to a difference in thermal expansion. Therefore, if the moving body moves randomly to the part where the temperature rise of the ball screw is low, the pitch difference between the ball screw and the ball screw nut will cause the ball screw and the ball screw nut to bite, resulting in the same condition as excessive preload. However, even if the motor is rotating, the rotation of the ball screw is stopped, and there is a problem that the machine may be damaged. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and has as its object to monitor the temperature of each part of a ball screw and the temperature of a ball screw nut to obtain a temperature difference of a set value or more. Sometimes we limit the range of the moving object,
It is an object to provide a device for protecting the feed mechanism.

[0007]

In order to achieve the above object, a protection device for a shaft feed mechanism according to the present invention is characterized in that a moving body having a ball screw nut fixed to a ball screw attached to a base is fixed to the ball screw. A feed mechanism that moves on the base by rotation; a first temperature detection sensor that detects a temperature of the ball screw nut; and a ball screw of the ball screw attached to a portion of the moving body facing the ball screw. A second temperature detection sensor for detecting a temperature and a difference between two temperatures detected by the first and second temperature detection sensors are compared with a set value, and the rotation drive of the ball screw is controlled based on the comparison result. And a control unit that performs the control. According to the above-described apparatus, the temperature difference is detected and compared with the set value, and the range of feeding is limited as necessary. Therefore, no excessive force acts on the feeding mechanism, and the machine is not damaged.

According to a second aspect of the present invention, in the feed mechanism, a moving body having a ball screw nut screwed to a ball screw attached to the base is moved on the base by rotation of the ball screw. Two temperature detecting sensors attached to a portion of the moving body facing the ball screw so as to be spaced apart from each other in the axial direction of the ball screw, and the two moving distances of the moving body by a distance between the two temperature detecting sensors. A control unit for comparing the rate of change of the temperature difference at the same position of the ball screw detected by the two temperature detection sensors with a set value, and controlling the rotation drive of the ball screw based on the comparison result. It is. According to the above-described apparatus, the rate of change in temperature rise at one point of the ball screw is obtained and compared with a set value to limit the feed range as necessary, so that the temperature of the ball screw nut which becomes high temperature is measured. There is no need, and temperature measurement is easy.

According to a third aspect of the present invention, the ball screw nut is provided with a preload adjusting means, and the preload adjusting means is controlled instead of the rotation control of the ball screw. According to the above-described apparatus, the thickness of the spacer between the ball screw nuts is adjusted by the supply voltage to make the preload applied to the ball screw nuts variable, thereby acting to offset the amount of thermal displacement of the ball screw nuts. So
The moving body can be moved over the entire feed range without limiting the feed range.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. Sliding surface 2 of base 1 such as machine bed
A moving body 3 such as a table is mounted thereon, and a ball screw nut 4 is fixed to a lower surface of the moving body 3. Base 1
Has a ball screw 5 pivotally supported at both ends,
It is engaged with the ball screw nut 4. The ball screw 5 is rotated by a motor 6 attached to the base 1, and the moving body 3 is moved on the base 1 along the sliding surface 2 via the ball screw nut 4. It is assumed that the ball screw nut 4 is preloaded by a normal method such as interposing a spacer.

On the lower surface of the moving body 3 and just above the ball screw 5, a non-contact type temperature sensor such as an infrared sensor is provided along the axis of the ball screw 5 in front of and behind the ball screw nut 4 and away from the ball screw nut. The sensors A and B are attached, and detect the temperature at a predetermined position of the ball screw 5 immediately below the temperature detection sensors A and B. A contact-type temperature detection sensor N such as a thermocouple is also attached to the ball screw nut 4 to measure the temperature of the ball screw nut 4 itself.

In FIG. 1, when the moving body 3 slides in the direction of arrow A, the temperature t _A of the ball screw 5 detected by the temperature detection sensor A is stored in the register 11 and detected by the temperature detection sensor N. The temperature t _N of the ball screw nut 4 is stored in the register 12. The temperature difference t _N -t _A is calculated by the arithmetic circuit 13 from the outputs of the registers 11 and 12,
The output of the operation result is sent to the comparison circuit 14 first.

The comparison circuit 14 compares the value with tmax stored in the set value storage circuit 15 and sends an output to the control unit 16. Further, the output of the arithmetic circuit 13 is sent to the comparison circuit 17 separately, and t _High stored in the set value storage circuit 18 is used.
And the output is also sent to the control unit 16. Here, tmax indicates a limit temperature difference at which an excessive preload occurs.
t _High indicates a temperature difference that the preload increases to some extent and adversely affects the drive system, and both are values empirically obtained by a test or the like.

In the control section 16, the output of the comparison circuit 14 is t _N
When −t _A ≧ tmax, an alarm warning is issued and the motor 6 is stopped at the same time. The comparison circuit 14 and the comparison circuit 1
At the output of the 7, or displayed on the operation screen in the case of _{t High ≦ t N -t A <} tmax, the means to warn the like visually aurally operator sound or buzzer or blink the Patlite Take. The output of the comparison circuit 17 is t _N −t _A
When <t _High , the motor is instructed to continue rotation.

[0015]

FIG. 2 is an explanatory view showing another bearing of the present invention. Two temperature detection sensors A and C are mounted on the lower surface of the moving body 3 at a position just above the ball screw 5 and on the same side as the ball screw nut 4 along the axial direction of the ball screw 5 with a distance. A temperature detection sensor D is mounted on the opposite side of the ball screw nut 4 at a distance from the temperature detection sensor B. In FIG. 2, when the moving body 3 moves in the direction of arrow A, the temperature detection sensor A measures the temperature at a certain point on the ball screw 5 and the temperature t _{A at} that time is stored in the register 1.
1 is stored. Next, the moving body 3 moves and the temperature at the same location is measured by the temperature detection sensor C, and the temperature tc at that time is stored in the register 22.

The outputs of the registers 11 and 22 are sent to an arithmetic circuit 23 to calculate the temperature difference tc-t _A , and the output of the operation result is sent to a division circuit 24. On the other hand, the time T during which the mobile unit 3 moves the distance between the temperature detection sensor A and the temperature detection sensor C from the control unit 16 is sent to the division circuit 24,
In the division circuit 24, the temperature change rate per unit time (tc−
t _A ) / T is determined. The output of the division circuit 24 is sent to the comparison circuit 25 and compared with the limit value of the temperature change rate stored in the setting circuit 26. The output of the comparison circuit 25 is sent to the control unit 16, and the control unit 16 instructs the motor 6 to continue rotating or stop rotating based on the comparison result with the limit value. The limit value of the temperature change rate stored in the setting circuit 26 is a value obtained in advance by an experiment. It is also possible to provide an alarm signal with two set values as in the embodiment of FIG.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Although the above-mentioned methods limit the operation depending on the temperature, it is also possible to change the preload of the ball screw nut. The ball screw nut is usually divided into two parts and a spacer is interposed in the middle, and the two divided parts are fixed to each other to be integrated. At this time, the magnitude of the preload applied to the ball screw nut is determined by adjusting the thickness of the spacer. When the temperature difference between the ball screw 5 and the ball screw nut 4 is large and a harmful preload is generated by using the piezoelectric element 30 as shown in FIG. Control the voltage applied to and adjust the preload. As a result, the thermal displacement of the ball screw nut 4 is offset. Since the preload adjustment is performed as described above, the ball screw nut 4 can be moved to any position of the ball screw 5, and the feed mechanism can be protected without limiting the feed range of the moving body 3. It is. In the above description, the case where the moving body 3 is moved in the direction of arrow A is described. However, even when the moving body 3 is moved in the direction opposite to the arrow, the temperature detection sensor B is used in the example of FIG. In the example of 2, the temperature detection sensor B,
Of course, by using D, the feeding mechanism can be similarly protected.

[0018]

As described above, the protective device for the feed mechanism according to the present invention measures the temperature of the ball screw nut fixed to the moving body, and also measures the temperature of the ball screw, based on the difference between the two temperatures. Since the ball screw rotation motor is controlled to limit the feed range of the moving body, no excessive force is applied to the feed mechanism, so that the feed mechanism is not damaged. In addition, the temperature of the moving body is measured using two temperature detection sensors provided on the moving body at the same point of the ball screw, and the ball screw rotating motor is controlled based on the temperature change rate of the difference between the two temperatures with respect to the moving time. In the case where the moving range of the moving body is limited, it is not necessary to measure the temperature of the ball screw nut, which becomes extremely high, and the temperature can be easily measured. In the case where the piezoelectric element is interposed between the ball screw nut and the spacer, the preload of the ball screw nut can be changed by controlling the magnitude of the voltage supplied to the piezoelectric element. The intended machining can be completely executed while protecting the feed mechanism without limitation.

[Brief description of the drawings]

FIG. 1 is a control explanatory diagram in a case where the temperatures of a ball screw and a ball screw nut are detected.

FIG. 2 is a control explanatory diagram in a case where the temperature of one location of a ball screw is detected twice.

FIG. 3 is an explanatory diagram when a piezoelectric element is used for a spacer between ball screw nuts.

[Explanation of symbols]

 Reference Signs List 1 base 3 moving body 4 ball screw nut 5 ball screw 16 control unit 30 piezoelectric element A, B, C, D, N temperature detection sensor

Claims (3)

[Claims] 1. A feed mechanism in which a moving body having a ball screw nut screwed onto a ball screw attached to a base moves on the base by rotation of a ball screw, detects a temperature of the ball screw nut. A first temperature detection sensor, a second temperature detection sensor attached to a portion of the moving body facing the ball screw and detecting a temperature of the ball screw; and a first temperature detection sensor. A protection unit for controlling the rotation of the ball screw based on the comparison result of a difference between the two temperatures detected by the control unit and a set value. 2. A feed mechanism in which a moving body to which a ball screw nut screwed to a ball screw attached to a base is fixedly moved on the base by rotation of the ball screw, wherein the ball screw of the moving body is Two temperature detection sensors attached to a portion facing each other in the axial direction of the ball screw, and the distance between the two temperature detection sensors is detected by the two temperature detection sensors with respect to the time the moving body moves. A protection device for a feed mechanism, comprising: a control unit configured to compare a change rate of a temperature difference at the same position of a ball screw with a set value and to control a rotation drive of the ball screw based on a comparison result. 3. The mechanism protection device according to claim 1, wherein a preload adjusting means is provided on the ball screw nut, and the preload adjusting means is controlled instead of the rotation control of the ball screw.