JPH09253975A - Device for reducing thermal deformation of threaded shaft and method for reducing thermal deformation of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict heat generated by friction between a threaded shaft and a nut member threadably engaged with the shaft to a specified value under a control of a supplying amount of compressed cooling air and its timing, reduce a thermal displacement at the threaded shaft and improve a position setting precision. SOLUTION: A ball nut 7 thredably engaged with a ball screw 9 is enclosed by a nut cover member formed with an air flowing-in passage. Compressed cooling air flowed from a compressor 21 is supplied to an air flowing-in passage of the nut cover member so as to cool a contacted location between the ball nut 7 and the ball screw 9 contacted with the ball nut 7. In turn, a difference in temperature between the nut cover member and a table 6 or the like is deleted by a thermocouple 26 or the like, and an ON/OFF control of the compressed cooling air is carried out in reference to whether or not the difference exceeds a reference value. With such an arrangement as above, a heat generated at the ball nut and the ball screw 9 is reduced and a position setting precision is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple device and method for reducing thermal deformation of a screw shaft, which is used in various machine tools or the like and reduces deformation of a feed screw shaft for thermal positioning of a moving part of the machine due to thermal expansion. .

[0002]

2. Description of the Related Art A feed screw shaft such as a ball screw is used in a portion such as a machine tool where a moving body needs to be moved and positioned at a predetermined position with high precision. In order to improve the positioning accuracy of the feed screw shaft, it is necessary to prevent this thermal deformation. As this means, various kinds of thermal deformation reducing means have been conventionally used. For example, one that avoids excessive preloading, one that selects a ball screw with a large lead to reduce the number of revolutions, one that anticipates the amount of thermal expansion due to temperature rise in advance, and one that is produced by subtracting the accumulated reference lead error by a predetermined amount. A pre-tension is applied to a screw shaft that is made slightly shorter in advance so as to generate an internal stress larger than the thermal stress, a proper lubricant is selected and used, a warm shaft is used after the temperature is stabilized, and a screw shaft is selected. A hollow type that allows a cooling medium to flow through it, a type that cools the screw shaft by allowing air or lubricating oil to flow on the outer peripheral surface of the screw shaft, and an air or oil mist that is provided through a hole in the spacer of the double nut preloaded ball screw. Various means have been devised and applied concretely, such as those that flow and cool and those that perform complementary control of thermal expansion amount by a closed loop control method.

[0003]

Although the above-described conventional heat generation reducing means for the screw shaft have their respective effects, the screw shaft having a special shape is required, and the control means thereof is complicated, and the cost is reduced. There is a problem with up. In addition, there is a problem that it is difficult to apply inexpensively and inexpensively. On the other hand, the main heat source that causes thermal deformation of the screw shaft is
Most of this is due to frictional heat during driving between the nut-shaped member of the ball screw and the screw shaft and the balls between them, and if the heat in this part can be forcibly and easily reduced, the screw shaft The thermal deformation of the can be significantly reduced. A compressor is always installed in a factory, and a cooler that cools the compressed air to a predetermined temperature is usually installed in many cases. If a vortex tube or the like is used, special provision is necessary. Therefore, it was clarified in the stage of preliminary experiments that the above-mentioned problems can be solved by directly cooling the nut-shaped member in contact with the screw shaft using this compressed cooling air. That is, a large amount of heat flows to the low temperature side by heat sinking between the members that engage with each other. Therefore, when the nut-shaped member is cooled, the temperature of the nut-shaped member becomes lower than that of the screw shaft, and heat flows to the nut-shaped member side. The heat conducted to the nut-shaped member is dissipated to the outside. From the above, it has been found that by controlling the temperature of the nut-shaped member, the heat conduction to the screw shaft side screwed to the nut-shaped member is reduced and the temperature is controlled.

The heat generation amount Q generated at the contact portion between the screw shaft and the nut-shaped member screwed to the screw shaft is generally obtained by the following equation. Q∝n · T (1) Here, n is the number of rotations of the screw shaft, and T is the torque value applied to the screwing portion. Further, the temperature increase Δθ of the screw shaft in this case is obtained by the following formula. Δθ = Q / β [1-exp (1-t · β / CM)] (2) where β is the heat radiation amount, CM is the heat capacity, and t is the elapsed time. Here, if the elapsed time t is increased, Δθ = Q / β and the saturation occurs. On the other hand, when the length of the screw shaft is L and the coefficient of thermal expansion is α, the thermal expansion amount ΔL of the screw shaft is as follows. ΔL = α · Δθ · L (3) FIG. 7 shows the relationship between the time t and the elongation of the screw shaft based on the above equations (1) to (3). The change in screw axis is shown.

From the above, the calorific value Q is forcibly reduced, the heat for Qj is removed from Q, and Q '= Q-Qj is set to ΔL.
By setting = α · Q ′ / β · L, the value of ΔL can be significantly reduced.

The present invention was devised in view of the above circumstances, and the permanent compressed cooling air by the compressor and the cooler is supplied to the nut-shaped member to forcibly cool the nut-shaped member and the temperature thereof is maintained. A method and apparatus for reducing thermal deformation of a screw shaft by a simple means and method for controlling the on / off control of the supply of compressed cooling air so as to keep the temperature within a predetermined reference value. The purpose is to provide.

[0007]

In order to achieve the above object, the present invention has a nut-shaped member held on the moving side of a machine and a nut-shaped member held on the stationary side of the machine and screwed onto the nut-shaped member. A thermal deformation reducing device for reducing heat generation during driving with a screw shaft that is rotationally driven by uniformly compressing compressed cooling air from a compressor and a cooler into an outer surface of the nut-shaped member. Nut-shaped member cooling means for cooling the nut-shaped member, detecting a temperature difference between the nut-shaped member side and the machine side, and turning on / off the supply of compressed cooling air of the nut-shaped member cooling means based on the detected value. The present invention constitutes a device for reducing thermal deformation of a screw shaft provided with a control unit for controlling. More specifically, the nut-shaped member cooling means is formed on a nut cover member that encloses the outer circumference of the nut-shaped member, and a contact portion between the nut cover member and the nut member, and is formed on the outer circumference of the nut-shaped member. And an air inflow passage formed uniformly along the air inflow passage, and a compressor and a cooler for letting compressed cooling air into and out of the air inflow passage, and the control unit is provided between the air inflow passage and the compressor. Control valve, and a control unit for performing on / off control of the control valve based on the difference between the temperature of the nut-shaped member and / or the nut cover member and the temperature of the machine side to which these are connected. It is characterized by a device for reducing thermal deformation of the screw shaft. Further, thermal deformation reduction for reducing heat generation during driving of a nut-shaped member held on the moving side of the machine and a screw shaft held on the stationary side of the machine and screwed into the nut-shaped member and driven to rotate. A method for detecting the temperature difference between the engaging portion of the screw shaft and the nut-shaped member and the machine side where these are held, and compressing and cooling supplied to the engaging portion based on the detected value. The present invention is characterized by a method of reducing thermal deformation of a screw shaft by controlling air on / off and maintaining the temperature difference within a reference value.

Compressed cooling air is evenly supplied to the outer periphery of the nut-shaped member by the nut-shaped member cooling means that engages with the nut-shaped member to uniformly cool the nut-shaped member. When the machine is driven, the temperature of the nut-shaped member is measured, and the supply of compressed cooling air is controlled to be turned on and off so that the temperature is maintained at a predetermined reference value. As described above, it is possible to reliably reduce the heat generated around the nut-shaped member and the screwed portion of the screw shaft screwed to the nut-shaped member by a very simple means and method.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a thermal deformation reducing device and method for a screw shaft according to the present invention will be described in detail below with reference to the drawings. First, the configuration of an embodiment of the thermal deformation reducing device of the present invention will be described with reference to FIG. The thermal deformation reduction device 1 is roughly divided into a nut-shaped member cooling means 2 and a compressed cooling air supply part 3.
And a control unit 4 for controlling the amount of compressed cooling air supplied.

First, the feed mechanism portion 5 of a machine to which the thermal deformation reducing device 1 is applied will be described with reference to FIG. As shown in FIG. 2, a ball nut 7 is fixed to the table 6 on which an unillustrated workpiece or the like is mounted. On the other hand, the stationary bases 8 and 8 of the machine
Both ends of the ball screw 9 are pivotally supported therebetween, and a servo motor 10 is connected to one end of the ball screw 9. The servo motor 10 is connected to the NC device 12 via a servo amplifier 11. The NC device 12 controls the rotation speed of the servo motor 10. With the above-described structure, the ball screw 9 is rotated by rotating the servo motor 10, and the ball nut 7 and the table 6 screwed to the ball screw 9 are moved along the axis of the ball screw 9. In addition, the movement positioning of the table 6 is N
This is performed by controlling the rotation speed of the servo motor 10 by the C device 12. According to the above structure, when the ball screw 9 is thermally deformed as described above, the moving lengths of the ball nut 7 and the table 6 change even if the rotation speed of the servo motor 10 is the same, and the positioning cannot be performed at the correct position. Problems arise.

Next, an example of the nut-shaped member cooling means 2 will be described. As shown in FIG. 2, a ball nut 7 which is an example of the nut-shaped member in the present example includes a flange portion 7a and a shaft portion 7b, and a ball screw 9 which is an example of a screw shaft is screwed on an inner peripheral side thereof. The inner thread is formed and the shaft portion 7
On the outer circumference of b, a plurality of long grooves 13 equally divided in the circumferential direction are provided along the axial direction. On the other hand, the nut cover member 14 is a tubular body that mainly encloses the shaft portion 7b of the ball nut 7, and includes a flange portion 14a and a tubular body 14b fitted in the shaft portion 7b, and a cover 15 is attached.

3 and 4 show a state in which the nut cover member 14 is fitted in the ball nut 7. The nut cover member 14 is fitted into the ball nut 7 until the flange portion 14a contacts the flange portion 7a of the ball nut 7, and the tubular body 14b covers the shaft portion 7b of the ball nut 7. As shown in FIG. 2, the O-rings 16 and 17 are fitted on the ball nut 7 side to seal both ends of the ball nut 7 and the nut cover member 14. Also,
By fixing the cover 15 to the nut cover member 14 side, both ends of the long groove 13 of the ball nut 7 are sealed.

As shown in FIGS. 3 to 5, the flange portion 14a of the nut cover member 14 and the one end side of the shaft portion cylindrical body 14b are connected to the air inlet portion 18 and the air outlet portion 19 which communicate with the inside.
Is provided. By fitting the nut cover member 14 into the ball nut 7, an air inflow passage 20 is formed which connects the long groove 13 and both ends thereof to the air inlet portion 18 and the air outlet portion 19. With the above structure, when air is introduced into the air inlet 18, the air advances in the direction of the arrow as shown in FIG. 5, passes through the long groove 13, and is discharged from the air outlet 19.

Next, the compressed cooling air supply unit 3 will be described.
As shown in FIG. 1, the compressed cooling air supply unit 3 includes a compressor 21 and a cooler 2 for cooling the compressed air to a desired temperature.
2, an introduction passage 23 for introducing cooling air from the compressor 21 and the cooler 22 to the air inlet portion 18 of the nut cover member 14, and a solenoid valve which is an example of a control valve provided in the introduction passage 23. It consists of 24 mag. The compressor 21, the cooler 22, and the solenoid valve 24 are connected to and controlled by the NC device 12 side.

In this example, the control section 4 comprises a temperature measuring / cooling air control computer 25, a thermocouple 26 which is an example of a temperature detector, and the like, and is connected to the NC unit 12. A laser length measuring device 27 and an elongation measuring computer 28 are additionally provided, and the elongation measuring computer 28 is connected to the temperature measuring / cooling air controlling computer 25 side. Also,
In this example, the thermocouple 26 is connected to the nut cover member 14, the air inlet portion 18, the support base 8 that supports the table 6 and the ball screw 9, and detects the temperature at those portions. This detected value is input to the computer 25 for temperature measurement / cooling air control. On the other hand, the laser length measuring device 27 engages with the nut cover member 14 to measure the position of the nut cover member 14, and the measured value is input to the elongation measuring computer 28. It should be noted that the laser length measuring device 27 is not necessary in actual use, and the computer for temperature measurement / cooling air control can be changed to a small IC device.

Next, the operation of the thermal deformation reducing device 1 of the present invention will be described. When the servomotor 10 is driven, the ball screw 9 is rotated, and the ball nut 7 moves along the ball screw 9, a frictional force is generated between the ball screw 9 and the ball nut 7, and the contact portion generates heat. The heat generation causes the temperature of the ball nut 7 to rise. Thermocouple 26 is ball nut 7
The degree of temperature rise is detected through the nut cover member 14, and the thermocouple 26 measures the temperature of the portion of the table 6 where the temperature change is relatively low. On the other hand, ball nut 7
The amount of positional deviation of the nut cover member 14 and the like due to a rise in ambient temperature is measured by the laser length measuring device 27 and input to the elongation measuring computer 28. On the other hand, the compressor 2
The compressed air from 1 is sent to the air inlet portion 18 of the nut cover member 14 via the cooler 22 and introduced into the air inflow passage 20. This compressed cooling air flows in the long groove 13 formed uniformly on the outer periphery of the shaft portion 7b of the ball nut 7, and absorbs the amount of heat generated at the contact portion between the ball nut 7 and the ball screw 9 during its circulation. In addition, since the long groove 13 is formed in the circumference of the shaft portion 7b at equal intervals, the ball nut 7 and the ball screw 9 are cooled uniformly. Ball nut 7
The compressed cooling air that has absorbed the frictional heat of the ball screw 9 is returned from the air outlet 19 to the compressor 21 side and is recirculated. The temperature of the nut cover member 14 can be controlled to a desired temperature by controlling the supply amount and timing of the compressed cooling air supplied from the compressor 21. For this reason, the amount of heat conducted to the ball screw is greatly reduced, and thermal deformation of the ball screw is suppressed to a minimum. In addition, the change in the positional deviation amount after control is determined by the laser length measuring device 27.
Is measured by

Next, an example of a method for reducing thermal deformation of the ball screw 9 and the like in the thermal deformation reducing apparatus 1 of the present invention will be described with reference to FIGS.
This will be described below. In FIG. 6, the vertical axis shows the elongation of the ball screw 9 [μ
m], the elapsed time [min] is plotted on the horizontal axis, the ball screw 9 is driven for 1 hour, and then an operation pattern is repeated in which driving is stopped for 30 minutes. In the figure, a curve C shows the case where the compressed cooling air is not supplied to the ball screw 9 side, and a curve D shows the case where the compressed cooling air is controlled and supplied according to the thermal deformation reduction method of the present invention. The curves show the cases where compressed cooling air is always supplied without control. As is clear from the diagram, the method for reducing thermal deformation of the present invention makes it possible to suppress elongation in an extremely small range.

FIG. 8 is a flow chart showing a specific example of the thermal deformation reducing method of the present invention. First, the machine is activated (step 100). Compressor 2 along with mechanical drive
1 is turned on, the solenoid valve 24 is opened, and compressed cooling air is supplied. That is, the air is turned on (step 101). Next, when the machine does not stop (in the case of no), the routine proceeds to step 103, where the temperature of the machine (for example, the temperature of the table 6) and the temperature of the ball screw 9 (specifically, the temperature of the nut cover member 14) are determined. Be compared. On the other hand, when the machine is stopped (in the case of yes), the operation of the compressor 21 is stopped, the electromagnetic valve 24 is closed, and the air is turned off (step 104). Next, the temperature of the machine side and that of the ball screw 9 are compared to determine the temperature difference, and it is determined whether or not the temperature difference is within a reference value (step 105). When it is within the reference value (in the case of yes), the process proceeds to step 104 to stop the air supply to prevent overcooling, and when it is more than the reference value (in the case of no), it is determined that the cooling is insufficient and the air is turned on. (Step 106). By repeating the above control, the temperature rise of the ball screw 9 is suppressed within a certain value.

[0019]

According to the present invention, the following remarkable effects are obtained. 1) Maintaining the shaft temperature at the original temperature by absorbing the heat generated when rough machining with a ball screw is assumed by forced cooling,
Thermal expansion of about 10 [μm] or less (measurement axis length 500 [mm]
In this case, the axial temperature was controlled within 2 [° C] because the linear expansion coefficient of structural carbon steel was 1.2 × 10 -6 [mm / ° C]. Was shown). In addition, by increasing the capacity of the cooler, it becomes possible to control the shaft temperature with higher accuracy even in rough machining. 2) The cooling capacity was higher than the heat generated when finishing was envisioned, and it was possible to suppress it to within ± 2 [μm] by performing ON / OFF control. 3) Since the temperature of the surface of the nut cover member is measured and turned on and off, the control is easy and the elongation of the shaft can be suppressed to a certain extent by setting a small on / off temperature range. 4) The present invention is a simple one that uses a permanent compressor or a nut-shaped cooling means having a simple structure, and can be implemented inexpensively and easily. 5) Forced cooling directly deprives the calorific value, and therefore does not leave heat as compared with other methods. 6) It can also be applied to existing machines.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an overall structure of a thermal deformation reducing device of the present invention.

FIG. 2 is a plan view showing the detailed structure of the nut-shaped member cooling means of the present invention.

FIG. 3 is an external view of nut-shaped member cooling means of the present invention.

FIG. 4 is a front view of arrow F in FIG.

FIG. 5 is a schematic view showing an air inflow path of the nut-like member cooling means of the present invention.

FIG. 6 is an extension time diagram showing the effects of the present invention and the prior art in comparison.

FIG. 7 is an extension time diagram showing the effects of the present invention and the prior art in comparison.

FIG. 8 is a flowchart for explaining the thermal deformation reduction method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal deformation reducing device 2 Nut-shaped member cooling means 3 Compressed cooling air supply part 4 Control part 5 Feed mechanism part 6 Table 7 Ball nut 7a Flange part 7b Shaft part 8 Support base 9 Ball screw 10 Servo motor 11 Servo amplifier 12 NC device 13 Long Groove 14 Nut Cover Member 14a Flange Part 14b Cylindrical Body 15 Cover 16 O-ring 17 O-ring 18 Air Inlet 19 Air Outlet 20 Air Inlet 21 Compressor 22 Cooler 23 Inlet 24 Solenoid Valve 25 Temperature Measurement / Cooling Air Control computer 26 Thermocouple 27 Laser length measuring instrument 28 Elongation measuring computer

Claims (3)

[Claims] 1. To reduce heat generation during driving of a nut-shaped member held on a moving side of a machine and a screw shaft held on a stationary side of the machine and screwed into the nut-shaped member to be rotationally driven. And a nut-shaped member cooling means for cooling the nut-shaped member by causing compressed cooling air from a compressor and a cooler to uniformly contact and engage the outer surface of the nut-shaped member. A thermal deformation of the screw shaft, comprising: a temperature difference between the member side and the machine side; and a control unit for controlling on / off of the supply of compressed cooling air of the nut-shaped member cooling means based on the detected value. Reduction device. 2. The nut-shaped member cooling means is formed at a nut cover member that encloses the outer periphery of the nut-shaped member and a contact portion between the nut cover member and the nut member, and the nut-shaped member is provided on the outer periphery of the nut-shaped member. And an air inflow passage formed uniformly along the air inflow passage, and a compressor and a cooler for letting compressed cooling air into and out of the air inflow passage, and the control unit is provided between the air inflow passage and the compressor. Control valve, and a control unit for performing on / off control of the control valve based on the difference between the temperature of the nut-shaped member and / or the nut cover member and the temperature of the machine side to which these are connected. The thermal deformation reduction device for a screw shaft according to claim 1, wherein 3. A nut-shaped member that is held on the moving side of a machine and a screw shaft that is held on the stationary side of the machine and screwed into the nut-shaped member to be driven to rotate are reduced in heat generation during driving. A thermal deformation reducing method, which detects a temperature difference between an engaging portion of the screw shaft and the nut-shaped member and a machine side where these are held, and supplies the temperature to the engaging portion based on the detected value. A method for reducing thermal deformation of a screw shaft, wherein the compressed cooling air is controlled to be turned on and off, and the temperature difference is maintained within a reference value.