JP7786286B2 - Temperature control system for ball screw devices - Google Patents

Description

This disclosure relates to a temperature management system for a ball screw device.

A ball screw device comprises a screw shaft, a nut, and multiple balls. When used in injection molding machines, presses, etc., ball screw devices convert rotational motion into linear motion. The nut also has a cylindrical nut body and an attachment portion provided at the end of the nut body. The nut body has an inner raceway surface on its inner circumferential surface. The attachment portion is the part that is fastened to a housing, etc., with a bolt, etc.

When a ball screw device is driven, the nut body generates heat. If an attachment portion is provided at one end of the nut body, heat is transferred from that end to the attachment portion, and then from the attachment portion to a housing or the like. In other words, the amount of thermal expansion at one end of the nut body is less than at the other end. As a result, load is concentrated on the balls rolling in the ball circuit on the one end side of the nut body, shortening the life of the ball screw device. To avoid this, the ball screw device in Patent Document 1 has a recess in the attachment portion. In other words, the contact area with components such as the housing is reduced, minimizing the amount of heat transferred to the housing or the like.

JP 2019-015318 A

When a ball screw device is driven, the screw shaft also generates heat. As the nut moves axially, the heat-generating areas are dispersed axially. As a result, the temperature of the nut body is generally higher than that of the screw shaft. However, as mentioned above, if heat is transferred to the mounting portion, the temperature of the screw shaft becomes higher than that of the nut body. As a result, the amount of thermal expansion of the screw shaft becomes greater than that of the nut body, and the gap between the screw shaft and the nut body becomes smaller. This causes the load to concentrate on the balls rolling in the ball circuit where the gap is narrowing, shortening the life of the ball screw device. Therefore, there is a need for the development of a temperature management system for ball screw devices that can reduce the temperature difference between the screw shaft and the nut and extend the life of the ball screw device.

The present disclosure has been made in light of the above, and aims to provide a temperature management system for a ball screw device that can extend the life of the ball screw device.

To achieve the above object, a temperature management system for a ball screw device according to one aspect of the present disclosure comprises a ball screw device having a screw shaft, a nut, and multiple balls; a heating device for heating the nut; a nut temperature measurement device for measuring the temperature of the nut; and a screw shaft temperature measurement device for measuring the temperature of the screw shaft. The nut has a nut body, an attachment portion, and multiple circulation parts for circulating the balls. The raceway between the screw shaft and the nut is divided into multiple ball circuits. The nut body has multiple cylindrical sections divided into ball circuits. The nut temperature measurement device is attached to the cylindrical section and has at least one or more cylindrical section measurement units that measure the temperature of the cylindrical section. The screw shaft temperature measurement device has at least one or more screw shaft measurement units that measure the temperature of a portion of the screw shaft located radially inward of the cylindrical section to which the cylindrical section measurement unit is attached. The heating device is attached to the outer peripheral surface of the cylindrical section to which the cylindrical section measurement unit is attached and has at least one or more cylindrical section heating units that heat the cylindrical section.

With this configuration, the cylindrical portion measurement unit and the screw shaft measurement unit can compare the temperatures of the cylindrical portion and a portion of the screw shaft, which are radially opposed to each other. In other words, it is possible to determine whether the temperature of the cylindrical portion is lower than that of the screw shaft. Furthermore, if the temperature of the cylindrical portion is low, the cylindrical portion can be heated by the cylindrical portion heating unit. This reduces the temperature difference between the cylindrical portion and a portion of the screw shaft, and increases the gap between the cylindrical portion and a portion of the screw shaft. This prevents load concentration on the ball circuit of the heated cylindrical portion, extending the life of the ball screw device. Furthermore, the inclusion of a screw shaft temperature measurement device (screw shaft measurement unit) makes it possible to determine the target temperature to which the cylindrical portion should be heated. In other words, without a screw shaft temperature measurement device, the cylindrical portion may be heated more than necessary, resulting in increased power consumption. Therefore, this increase in power consumption can be avoided according to the present disclosure.

In a preferred embodiment of the ball screw device according to one aspect of the present disclosure, the plurality of cylindrical portions includes a first cylindrical portion that is closest to the mounting portion. At least the first cylindrical portion is equipped with the cylindrical portion measuring portion, the screw shaft measuring portion, and the cylindrical portion heating portion.

This configuration makes it possible to manage the temperature of the first cylindrical section, which is most likely to become cold.

Furthermore, in a preferred embodiment of the ball screw device according to one aspect of the present disclosure, the cylindrical portion measuring unit, the screw shaft measuring unit, and the cylindrical portion heating unit are attached to all of the multiple cylindrical portions.

This configuration allows the temperature of all cylindrical sections to be controlled. In other words, the gap between all cylindrical sections and the screw shaft can be increased. This eliminates the ball circuit where loads are concentrated, extending the life of the ball screw device.

The temperature management system for the ball screw device disclosed herein extends the life of the ball screw device.

FIG. 1 is a diagram showing a temperature management system for a ball screw device according to an embodiment. FIG. 2 is an overall view of the temperature control system for the ball screw device as viewed in the direction of arrow II in FIG. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. FIG. 4 is a diagram showing an ideal load distribution in the ball circuit when the ball screw device is driven. FIG. 5 is a diagram showing an example of temperatures measured when the ball screw device is driven. FIG. 6 is a diagram showing an example of the load distribution of the ball circuit during temperature measurement (before heating).

The following describes in detail the mode for carrying out the invention, with reference to the drawings. The present disclosure is not limited to the content of the following description. Furthermore, the components described below include those that would be easily conceived by a person skilled in the art and those that are substantially identical. Furthermore, the components described below can be combined as appropriate.

Figure 1 is a diagram showing a temperature management system for a ball screw device according to an embodiment. Figure 2 is an overall view of the temperature management system for a ball screw device as viewed from the direction of arrow II in Figure 1. Figure 3 is a cross-sectional view taken along line III-III in Figure 3. Figure 4 is a diagram showing the ideal load distribution in the ball circuit when the ball screw device is in operation. Figure 5 is a diagram showing an example of temperatures measured when the ball screw device is in operation. Figure 6 is a diagram showing an example of the load distribution in the ball circuit when measuring temperatures (before heating).

First, a ball screw device 40 according to an embodiment will be described. As shown in FIG. 1, the ball screw device 40 comprises a screw shaft 1, a nut 2, and a plurality of balls 3. The screw shaft 1 is a rod-shaped component centered on an axis O. Hereinafter, the direction parallel to the axis O will be referred to as the axial direction. The screw shaft 1 comprises a screw shaft main body 10 and a first mounting portion 11. An outer peripheral raceway surface 12 is provided on the outer peripheral surface of the screw shaft main body 10. The groove shape of the outer peripheral raceway surface 12 is a Gothic arc. Note that in the present disclosure, the outer peripheral raceway surface 12 may also be a circular arc. The first mounting portion 11 extends in the axial direction from the end of the screw shaft main body 10. The first mounting portion 11 is supported on a fixed base (not shown) or the like so as to be rotatable but immovable in the axial direction.

The nut 2 comprises a nut body 20 and a second mounting portion 21. An inner circumferential raceway surface 22 is provided on the inner circumferential surface of the nut body 20. The groove shape of the inner circumferential raceway surface 22 is a Gothic arc. Note that in the present disclosure, the inner circumferential raceway surface 22 may also be a circular arc. A spiral raceway 4 is formed between the outer circumferential raceway surface 12 and the inner circumferential raceway surface 22.

The second mounting portion 21 is a flange that protrudes radially outward from the outer peripheral surface of the nut body 20. A moving object 41 to be moved in the axial direction is attached to the second mounting portion 21. The second mounting portion 21 is located at the axial end of the nut body 20. Hereinafter, within the axial direction, the direction in which the second mounting portion 21 is located when viewed from the axial center of the nut body 20 will be referred to as the first direction X1, and the direction opposite to the first direction X1 will be referred to as the second direction X2. Furthermore, the first mounting portion 11 of the screw shaft 1 is arranged in the second direction X2 relative to the screw shaft body 10.

The nut 2 includes multiple circulating parts 23. The circulating parts 23 are tubes. Note that in the present disclosure, the circulating parts may also be pieces. In this embodiment, 3.5 turns of the raceway 4 form one ball circuit 30. In other words, the raceway 4 has five ball circuits 30 divided into sections corresponding to the five circulating parts 23.

Hereinafter, the five ball circuits 30 will be referred to as the first ball circuit 30A, the second ball circuit 30B, the third ball circuit 30C, the fourth ball circuit 30D, and the fifth ball circuit 30E, in order from the first direction X1. Furthermore, the portions of the nut body 20 divided axially corresponding to each ball circuit 30 will be referred to as cylindrical portions 24. In other words, the nut body 20 has five cylindrical portions 24. Hereinafter, the five cylindrical portions 24 will be referred to as the first cylindrical portion 24A, the second cylindrical portion 24B, the third cylindrical portion 24C, the fourth cylindrical portion 24D, and the fifth cylindrical portion 24E, in order from the first direction X1.

The balls 3 are steel balls. Each ball 3 is arranged in a respective ball circuit 30 of the track 4. Hereinafter, the ball 3 rolling in the first ball circuit 30A will be referred to as the first ball, the ball 3 rolling in the second ball circuit 30B as the second ball, the ball 3 rolling in the third ball circuit 30C as the third ball, the ball 3 rolling in the fourth ball circuit 30D as the fourth ball, and the ball 3 rolling in the fifth ball circuit 30E as the fifth ball 3E.

Next, the temperature management system 100 will be described. As shown in FIG. 2, the temperature management system 100 for the ball screw device 40 includes the ball screw device 40, a nut temperature measuring device 50, a screw shaft temperature measuring device 60, a heating device 70, and a control unit 80.

The nut temperature measuring device 50 is a device that measures the temperature of each cylindrical portion 24. The nut temperature measuring device 50 has five cylindrical portion measuring units 51, one for each cylindrical portion 24. The cylindrical portion measuring units 51 are, for example, thermocouples. As shown in FIG. 3, in order to attach the cylindrical portion measuring units 51 to the nut 2, a recess 25 recessed radially inward is provided on the outer peripheral surface of each cylindrical portion 24. The cylindrical portion measuring unit 51 measures the temperature of the cylindrical portion 24 within the recess 25 and transmits the temperature to the control unit 80. Note that the outer peripheral raceway surface 12 and inner peripheral raceway surface 22 have been omitted from FIG. 3 to avoid complicating the illustration.

The screw shaft temperature measuring device 60 is a device for measuring the temperature of the screw shaft 1. The screw shaft temperature measuring device 60 has five screw shaft measuring units 61, one for each cylindrical portion 24. The screw shaft measuring units 61 are, for example, thermographic cameras that can detect the surface temperature of an object without contact. As shown in Figure 3, to attach the screw shaft measuring units 61 to the nut 2, a through-hole 26 is provided radially through the outer surface of each cylindrical portion 24. Each ball circuit 30 has 3.5 turns. Therefore, the inner opening 26a of the through-hole 26 is positioned to overlap 0.5 turns of the raceway 4 where the balls 3 do not roll.

The screw shaft measuring unit 61 is fixed inside the through-hole 26. The screw shaft measuring unit 61 measures the temperature of a portion of the screw shaft 1 located radially inward of the inner opening 26a in the axial direction. The screw shaft measuring unit 61 then transmits the measured temperature to the control unit 80. The inner opening 26a of the through-hole 26 is sealed, for example with glass 27, to prevent grease from leaking out. A thermographic camera can pass through the glass 27 and measure the temperature of the screw shaft 1.

The heating device 70 heats the nut 2. As shown in Figures 1 and 2, the heating device 70 has five tube heating units 71, corresponding to the number of tube units 24. The tube heating units 71 are, for example, sheet-shaped electric heaters that convert electrical energy into thermal energy for heating. The tube heating units 71 are attached to the outer circumferential surface of each tube unit 24. This allows each tube unit 24 to be heated individually. The heating temperature of the tube heating units 71 is controlled by the control unit 80. The tube heating units 71 do not cover the entire circumferential surface of the tube unit 24. The circulating element 23 is exposed between one end and the other end of the tube heating unit 72 in the circumferential direction. This prevents the circulating element 23 from being directly heated by the tube heating units 71. Note that heating a resin circulating element 23 may cause the circulating element 23 to deform. Therefore, according to this embodiment, a resin circulating element 23 can be used, thereby avoiding a limited range of material options for the circulating element 23.

The control unit 80 is a device that controls the heating temperature of each cylindrical portion heating unit 71 to adjust the temperature of each cylindrical portion 24. Specifically, the control unit 80 compares the measurement results of each cylindrical portion measuring unit 51 with those of each screw shaft measuring unit 61. Next, the control unit 80 identifies the cylindrical portion 24 that has a lower temperature than the screw shaft 1. Next, the control unit 80 operates the cylindrical portion heating unit 71 to heat the identified cylindrical portion 24 so that the temperature of the identified cylindrical portion 24 becomes the desired temperature. Here, the desired temperature means a temperature that is the same as or higher than the temperature of the portion of the screw shaft body 10 that faces the cylindrical portion 24.

Next, with reference to Figure 4, we will explain the ideal state of the load distribution on the balls 3 when the ball screw device 40 is in operation. Note that the ideal state is one in which the load is not concentrated on a specific ball circuit 30, and the life of the ball screw device 40 can be extended. The ideal state described below is just one example.

The plot shown in Figure 4 shows the relationship between the axial position of each ball 3 and the load acting on that ball 3. The plot shown in Figure 4 is divided into five sections along the horizontal axis of the graph. That is, from the first direction X1, it is divided into a plot for the first ball of the first ball circuit 30A, a plot for the second ball of the second ball circuit 30B, a plot for the third ball of the third ball circuit 30C, a plot for the fourth ball of the fourth ball circuit 30D, and a plot for the fifth ball of the fifth ball circuit 30E.

When plotted on a ball circuit 30-by-ball circuit basis, the load distribution for each ball circuit 30 appears as a line graph (wave-shaped). In other words, when the ball 3 is displaced in the axial direction, the load acting on the ball 3 periodically increases and decreases. This is because a radial load acts on the ball screw device 40, causing the ball screw device 40 to bend. As a result, the load acting on the ball 3 increases and decreases depending on the circumferential location of the ball 3. Furthermore, in the line graph, one cycle of the waveform represents one circumferential revolution of the ball 3. Since each ball circuit 30 has 3.5 turns, the cycle of increase and decrease in Figure 5 is also 3.5.

Furthermore, when comparing the load distribution of each ball circuit 30, the load on the third ball circuit 30C is the smallest, and the load gradually increases with axial displacement, with the load on the first ball circuit 30A and fifth ball circuit 30E being the largest. This is because an axial load acts on the ball screw device 40, causing it to expand and contract in the axial direction.

More specifically, when the ball screw device 40 is driven, a load is input to the first mounting portion 11, and axial stress acts on the screw shaft body 10. In particular, large stress acts on the portion of the screw shaft body 10 close to the first mounting portion 11. As a result, the outer peripheral raceway surface of the portion of the screw shaft body 10 facing the fifth cylindrical portion 24E is displaced in the axial direction. As a result, the load on the fifth ball circuit 30E increases. For the same reason, the load on the fourth ball circuit 30D also increases. However, the increase in load on the fourth ball circuit 30D is less than that on the fifth ball circuit 30E.

On the other hand, when the ball screw device 40 is driven, a load is also input to the second mounting portion 21, and axial stress acts on the nut body 20. In particular, large stress acts on the portion of the nut body 20 close to the second mounting portion 21. As a result, the inner circumferential raceway surface 22 of the first cylindrical portion 24A is displaced in the axial direction. As a result, the load on the first ball circuit 30A increases. For the same reason, the load on the second ball circuit 30B also increases. However, the increase in load on the second ball circuit 30B is less than that on the first ball circuit 30A.

From the above, the load distribution of the ball circuit 30 to extend the life of the ball screw device 40 is shown as a graph that is symmetrical with respect to the third ball circuit 30C, which is located in the center of the axial direction.

Next, we will explain an example of when the temperature management system 100 for the ball screw device 40 is operating. When the ball screw device 40 is driven, friction with the balls 3 and the temperature of the grease rise. As a result, the screw shaft body 10 and the nut body 20 generate heat. However, because the screw shaft 1 moves axially, the areas of the screw shaft body 10 that generate heat are dispersed axially. Therefore, the temperature of the screw shaft body 10 is lower than that of the nut body 20.

In addition, heat is transferred from the nut body 20 to the second mounting portion 21. As a result, as shown in FIG. 5, the temperatures of the first and second cylindrical portions 24A and 24B are lower than those of the portion of the screw shaft body 10 that is radially opposed to the first and second cylindrical portions 24A and 24B. With this temperature distribution, the load distribution of each ball circuit 30 is as shown in FIG. 6, with the first ball circuit 30A and the second ball circuit 30B increasing in load. Relatively, the loads of the third ball circuit 30C, the fourth ball circuit 30D, and the fifth ball circuit 30E decreasing. In other words, the load is concentrated on the first ball of the first ball circuit 30A and the second ball of the second ball circuit 30B, causing the first and second balls to wear out prematurely.

In this embodiment, the control unit 80 compares the measured temperatures of each cylindrical portion measurement unit 51 with the measured temperatures of each screw shaft measurement unit 61, and identifies the cylindrical portion 24 whose temperature is lower than that of the screw shaft main body 10. Therefore, in the temperature situation shown in Figure 5, the control unit 80 activates the cylindrical portion heating units 71 attached to the first cylindrical portion 24A and the second cylindrical portion 24B. As a result, the first cylindrical portion 24A and the second cylindrical portion 24B are heated by the cylindrical portion heating units 71, and their temperatures rise.

The control unit 80 also adjusts the temperature of the first cylindrical portion 24A and the second cylindrical portion 24B after heating so that they are the same as or higher than the temperature of the opposing portions of the screw shaft body 10. As a result, the temperatures of the first cylindrical portion 24A and the second cylindrical portion 24B are the same as or higher than the temperature of the opposing portions of the screw shaft body 10.

As a result, the amount of thermal expansion of the first and second cylindrical portions 24A and 24B is equal to or greater than the amount of thermal expansion of the opposing portions of the screw shaft body 10. This causes the gap between the first and second cylindrical portions 24A and 24B and the opposing portions of the screw shaft body 10 to expand. This reduces the load on the first and second ball circuits 30A and 30B, while increasing the load on the third, fourth, and fifth ball circuits 30C, 30D, and 30E, resulting in a symmetrical load distribution as shown in Figure 4. This prevents the load from concentrating on a specific ball circuit 30.

As described above, the temperature management system 100 for a ball screw device 40 according to an embodiment of the present invention includes a ball screw device 40 having a screw shaft 1, a nut 2, and multiple balls 3; a heating device 70 for heating the nut 2; a nut temperature measurement device 50 for measuring the temperature of the nut 2; and a screw shaft temperature measurement device 60 for measuring the temperature of the screw shaft 1. The nut 2 includes a nut body 20, an attachment portion (second attachment portion 21) provided at one end of the nut body 20, and multiple circulation parts 23 for circulating the balls 3. The raceway 4 between the screw shaft 1 and the nut 2 is divided into multiple ball circuits 30. The nut body 20 includes multiple cylindrical portions 24, each divided into a corresponding ball circuit 30. The nut temperature measurement device 50 is attached to each cylindrical portion 24 and includes at least one cylindrical portion measurement unit 51 for measuring the temperature of the cylindrical portion 24. The screw shaft temperature measurement device 60 includes at least one screw shaft measurement unit 61 for measuring the temperature of a portion of the screw shaft 1 located radially inward of the cylindrical portion 24 to which the cylindrical portion measurement unit 51 is attached. The heating device 70 is attached to the outer peripheral surface of the cylindrical portion 24 to which the cylindrical portion measuring portion 51 is attached, and has at least one cylindrical portion heating portion 71 that heats the cylindrical portion 24. In addition, the cylindrical portion measuring portion 51, the thread shaft measuring portion 61, and the cylindrical portion heating portion 71 are attached to all of the multiple cylindrical portions 24.

According to this embodiment, load concentration on some of the multiple ball circuits 30 is avoided. This extends the life of the ball screw device. Furthermore, the screw shaft measuring unit 61 can determine the target temperature to which the tubular portion 24 is heated. This prevents the tubular portion 24 from being heated more than necessary, thereby suppressing increases in power consumption.

Although the above describes the embodiments, the present disclosure is not limited to the examples described in the embodiments. For example, in the embodiments, all five cylindrical sections 24 are provided with a cylindrical section measurement section 51, a thread shaft measurement section 61, and a cylindrical section heating section 71, but only one of the five cylindrical sections 24 may be provided with a cylindrical section measurement section 51, a thread shaft measurement section 61, and a cylindrical section heating section 71. Cylindrical section measurement sections 51, etc. may be provided every other cylindrical section 24 in the axial direction. Alternatively, cylindrical sections 24 that are likely to become cooler than the screw shaft 1 may be identified through experiments, etc., and cylindrical section measurement sections 51, etc. may be provided only on those cylindrical sections 24.

Furthermore, if there are multiple cylindrical sections 24 and only one of them is to be provided with a cylindrical section measuring section 51, it is desirable to provide the cylindrical section measuring section 51, etc. on the first cylindrical section 24A. As shown in Figure 5, the first cylindrical section 24A is close to the second mounting section 21 and is therefore more likely to be cooled by heat transfer (as load concentration is more likely to occur).

Furthermore, the present disclosure does not place any particular limitations on the arrangement of the cylindrical portion measuring unit 51, the thread shaft measuring unit 61, and the cylindrical portion heating unit 71. Furthermore, there are no particular limitations on the equipment and devices used in the cylindrical portion measuring unit 51, the thread shaft measuring unit 61, and the cylindrical portion heating unit 71.

In addition, although the second attachment portion 21 in the embodiment is located at the axial end of the nut body 20, it may also be located in the axial center of the nut body 20, and is not particularly limited. Furthermore, the present disclosure does not necessarily require the controller 80. In other words, the operator may recognize the measurement results of the cylindrical portion measuring portion 51 and the thread shaft measuring portion 61 and operate the cylindrical portion heating portion 71.

Note that when the ratio of the outer diameter D of the nut body 20 to the axial length L of the nut body satisfies L/D≧3.3, temperature differences are likely to occur between the ball circuits 30. Therefore, the temperature management system disclosed herein can be effectively applied to ball screw devices 40 that satisfy the L/D≧3.3 ratio.

REFERENCE SIGNS LIST 1 screw shaft 2 nut 3 ball 4 raceway 10 screw shaft body 11 first mounting portion 12 outer peripheral raceway surface 20 nut body 21 second mounting portion 22 inner peripheral raceway surface 23 circulating part 24 cylindrical portion 30 ball circuit 40 ball screw device 50 nut temperature measuring device 51 cylindrical portion measuring portion 60 screw shaft temperature measuring device 61 screw shaft measuring portion 70 heating device 71 cylindrical portion heating portion 80 control portion 100 temperature control system

Claims (3)

a ball screw device having a screw shaft, a nut, and a plurality of balls;
a heating device for heating the nuts;
a nut temperature measuring device for measuring the temperature of the nut;
a screw shaft temperature measuring device for measuring the temperature of the screw shaft;
Equipped with
The nut is
The nut body and
A mounting portion;
a plurality of circulation parts for circulating the balls;
and
The raceway between the screw shaft and the nut is divided into a plurality of ball circuits;
The nut body has a plurality of cylindrical portions divided into respective ball circuits,
The nut temperature measuring device has at least one or more cylinder portion measuring units attached to the cylinder portion and measuring the temperature of the cylinder portion,
The screw shaft temperature measuring device has at least one screw shaft measuring unit that measures the temperature of a part of the screw shaft arranged radially inside with respect to the cylindrical portion to which the cylindrical portion measuring unit is attached,
The cylindrical portion is formed with a through hole that penetrates in the radial direction,
a radially inner opening of the through hole is formed at a location on the raceway where the ball does not roll;
The screw shaft measuring unit is attached to the through hole,
The heating device has at least one or more cylindrical portion heating portions attached to the outer peripheral surface of the cylindrical portion to which the cylindrical portion measuring portion is attached, and heats the cylindrical portion. the plurality of cylindrical portions includes a first cylindrical portion that is closest to the attachment portion among the plurality of cylindrical portions,
The temperature management system for a ball screw device according to claim 1, wherein the cylindrical portion measuring unit, the screw shaft measuring unit, and the cylindrical portion heating unit are attached to at least the first cylindrical portion. The temperature management system for a ball screw device according to claim 1 , wherein the cylindrical portion measuring unit, the screw shaft measuring unit, and the cylindrical portion heating unit are attached to all of the plurality of cylindrical portions.