JP6741490B2 - Linear slide device using hydrostatic gas bearing mechanism - Google Patents

Description

The present invention relates to a linear slide device using a static pressure gas bearing mechanism.

Conventionally, a linear slide device using a static pressure gas bearing mechanism has been used in precision measuring equipment and ultra-precision processing machines, and a fixed guide shaft and a movable body that moves along the guide shaft using this guide shaft as a guide element. A static pressure gas layer is formed in the gap between the movable body and the guide shaft, and this static pressure gas layer serves as a fluid lubricating film, and the guide shaft receives the movable body in a non-contact manner. There is.

A linear slide device using such a static pressure gas bearing mechanism, for example, surrounds a guide shaft having a rectangular cross section and this guide shaft in order to eliminate displacement and blurring around the guide shaft when the movable body moves. There are known ones configured with a movable body (for example, Patent Document 1) and one configured to surround a guide shaft having a circular cross section in which two single movable bodies are arranged in parallel.

JP, 2004-60833, A (refer to claim 1 and Drawing 1 especially).

However, in the case of the static pressure gas bearing mechanism described in Patent Document 1, a guide shaft having a rectangular cross section is used, and such a guide shaft having a rectangular cross section has a perpendicularity between adjacent surfaces. Alternatively, it is necessary to process the parallelism between one surface and the opposite surface with high accuracy.
On the other hand, in the case of a static pressure gas bearing mechanism in which one movable body surrounds two guide shafts of circular cross section arranged side by side, it is easy to form the guide shaft itself of circular cross section with high roundness. , Two guide shafts must be arranged, and a slider corresponding to these two guide shafts must be provided.

Therefore, the former has a problem that high precision machining of the guide shaft and the movable body and highly precise fitting form of the movable body to the guide shaft are required, and the latter simply increases the number of parts of the guide shaft. Instead, there is a problem that a high-precision assembling burden on the two guide shafts is required, and the manufacturing cost increases.

Therefore, the present invention is to solve the above-mentioned problems of the prior art, that is, an object of the present invention is to make a slider in a non-contact state via a static pressure gas layer along the slide axial direction of a slide. (EN) Provided is a linear slide device that uses a hydrostatic gas bearing mechanism that is smoothly moved, and is easy to process and has a small number of parts.

The invention according to claim 1 is a linear slide device using a hydrostatic gas bearing mechanism including a slide shaft and a slider that moves in the slide shaft direction of the slide shaft through a hydrostatic gas layer,
The slide shaft includes a slide circumferential surface portion along the slide shaft direction and a slide flat surface portion along the slide shaft direction, and the slider faces the slide flat surface portion of the slide shaft to generate a static pressure gas. An air plate for jetting, and two air jets for static pressure gas facing the slide circumferential surface portion of the slide shaft in a both-supported state arranged so as to sandwich the air plate along the slide shaft direction of the slide shaft. By including the bush, the above-mentioned problems are solved.

The invention according to claim 2 further solves the above-mentioned problems by the linear slide device according to claim 1, wherein the slide flat surface portion is formed at a central portion in the slide axis direction. It is a thing.

The present invention according to claim 3 further solves the above-mentioned problems, in addition to the linear slide device according to claim 1, in which the slide plane portions are formed at both end portions in the slide axis direction. It is a thing.

In the invention according to claim 4, in addition to the linear slide device according to any one of claims 1 to 3, a plurality of the slide plane portions are formed along the slide axis direction. This further solves the above-mentioned problems.

In addition to the linear slide device according to any one of claims 1 to 4, the invention according to claim 5 provides static pressure generated in a gap between the air plate of the slider and the slide flat surface portion. By having the static pressure gas layer adjustment part which adjusts a gas layer, the above-mentioned subject is solved further.

According to a sixth aspect of the present invention, in addition to the linear slide device according to the fifth aspect, the static pressure gas layer adjusting portion is arranged near both ends in a width direction orthogonal to the slide axis direction. By having a push bolt, the above-mentioned problems are solved.

The invention according to claim 7 solves the above-mentioned problems by the static pressure gas being air in addition to the linear slide device according to any one of claims 1 to 6. It is a thing.

The invention according to claim 8 is the same as the linear slide device according to any one of claims 1 to 7, and the slide shaft is formed of a solid member. It solves the problem.

The present invention according to claim 9 is, in addition to the linear slide device according to any one of claims 1 to 7, characterized in that the slide shaft is formed from a hollow member. Is the solution.

The linear slide device of the present invention uses the static pressure gas bearing mechanism including the slide shaft and the slider that moves in the slide shaft direction of the slide shaft through the static pressure gas layer. Not only can it be smoothly moved in a non-contact state via the static pressure gas layer along the slide axis direction, but also the following unique effects are exhibited.

According to the linear slide device of the invention according to claim 1, the slide shaft includes a slide circumferential surface portion along the slide axis direction and a slide flat surface portion along the slide axis direction, and the slider is An air plate facing the slide plane portion of the slide shaft and ejecting static pressure gas, and a slide circumference of the slide shaft in a double-sided state arranged so as to sandwich the air plate along the slide shaft direction of the slide shaft. By having two air bushes that face the surface part and eject static pressure gas, the slide circumferential surface part along the slide axis direction realizes movement with little deviation in position accuracy with high accuracy. Since the slide plane portion along the axial direction is supported by the air plate that ejects the static pressure gas, the rotation of the slide shaft can be prevented.

In the linear slide device of the invention according to claim 1, the slide circumferential surface portion refers to a portion including a substantially circular outer peripheral side surface. For example, even a portion where the slide flat surface portion is formed is a portion other than the slide flat surface portion. If the outer peripheral side surface is circular, it is referred to as a slide circumferential surface portion.

According to the linear slide device of the invention of claim 2, in addition to the effect of the invention of claim 1, the slide plane portion is formed at the central portion in the slide axis direction, so that the slider can be moved. Since the range is limited, not only the movement of the slider can be restricted to a preset range, but also a slider function is provided to prevent the slider from moving beyond the slider movement control range. It is possible to prevent an unexpected situation in measurement and processing due to movement.

According to the linear slide device of the invention of claim 3, in addition to the effect of the invention of claim 1, the slide flat surface portion is formed at both end portions in the slide axial direction, so that the slide flat surface portion is formed. Since it is possible to easily increase the length, it is possible to set a wide moving range of the slider.

According to the linear slide device of the invention of claim 4, in addition to the effect of the invention of any one of claims 1 to 3, a plurality of the slide plane portions are provided along the slide axis direction. By being formed, the slide shaft is set so as to face the air plate at the slide flat surface portion composed of two or more horizontal surfaces, so that it is necessary to accurately measure the perpendicularity between the guide surfaces as in the conventional case. Instead, it can be set according to the precision measuring equipment or ultra-precision processing machine on which the slider is installed.

According to the linear slide device of the invention of claim 5, in addition to the effect of the invention of any one of claims 1 to 4, the air plate of the slider is provided in a gap between the slider and the slide plane portion. By having a static pressure gas layer adjustment unit that adjusts the generated static pressure gas layer, the gap between the air plate of the slider and the slide flat surface section is set arbitrarily, so that optimum movement of the slider is realized. You can

According to the linear slide device of the invention of claim 6, in addition to the effect of the invention of claim 5, the static pressure gas layer adjuster is arranged near both ends in the width direction orthogonal to the slide axis direction. By having the pull bolt and the push bolt, it is possible to rotate the pull bolt and the push bolt to set and adjust the distance between the air plate of the slider and the flat surface of the slide shaft. Therefore, it is possible to achieve a highly accurate slider movement by balancing the support of the slider with the air bush and the support of the slider with the air plate.

According to the linear slide device of the invention of claim 7, in addition to the effect of the invention of any one of claims 1 to 6, the static pressure gas is air Moreover, since compressed air that can be supplied is used, general-purpose equipment can be used.

According to the linear slide device of the invention of claim 8, in addition to the effect of the invention of any one of claims 1 to 7, the slide shaft is formed of a solid member. With this, the slide shaft can be formed by processing the slide flat surface portion on the cylindrical shaft that can be processed with high circularity, so that the movement with less displacement of the position accuracy can be realized.

That is, according to the linear slide device of the invention of claim 8, the slide shaft having the cylindrical peripheral side surface with high circularity has higher accuracy than the conventional guide shaft having a rectangular cross section. Since it is easy to process, it is possible to inexpensively provide a slide shaft that is reliable as a guide mechanism for precision measuring equipment and ultra-precision processing machines.

Further, since there is no difficulty in processing the slide flat surface portion formed on the slide shaft having a cylindrical peripheral side surface, for example, if a slide shaft forming only one slide flat surface portion is formed, it is a rectangular shape as in the conventional case. It is possible to easily form and process without being restricted by the perpendicularity or parallelism between the guide surfaces generated on the guide axis of the cross section.

According to the linear slide device of the invention of claim 9, in addition to the effect of the invention of any one of claims 1 to 7, the slide shaft is formed of a hollow member. Thus, the slide shaft can be configured by molding an annular steel pipe or the like, so that the slide shaft can be easily manufactured.

Further, according to the linear slide device of the invention according to claim 9, a slide shaft that does not require high precision can be provided at low cost, and the slide shaft can be formed by integral molding with resin or the like regardless of the metal material. it can.

The perspective view which shows the whole linear slide apparatus which is 1st Example of this invention. FIG. 2 is a cross-sectional perspective view in the slide axis direction of the linear slide device shown in FIG. 1. 1. The perspective view which shows the whole slide shaft shape in FIG. FIG. 3 is a sectional perspective view for explaining a moving state of the linear slide device shown in FIG. 2. FIG. 2 is a sectional perspective view in the slide axis direction illustrating the static pressure gas layer adjusting unit shown in FIG. 1. FIG. 2 is a cross-sectional perspective view of the static pressure gas layer adjusting unit shown in FIG. 1 in a direction orthogonal to a slide shaft. The sectional perspective view in the slide axis direction showing the linear slide device which is a 2nd example of the present invention.

The present invention relates to a linear slide device using a static pressure gas bearing mechanism, which comprises a slide shaft and a slider that moves in the slide shaft direction of the slide shaft through a static pressure gas layer. And a slide flat surface portion along the slide axis direction, wherein the slider faces the slide flat surface portion of the slide shaft and jets static pressure gas, and a slide shaft direction of the slide shaft. A slider is provided along the slide axis of the slide with two air bushes that eject static pressure gas facing the slide circumferential surface of the slide shaft in a two-sided state with the air plate sandwiched between them. Any specific embodiment may be used as long as it can be smoothly moved in a non-contact state via the static pressure gas layer, is easy to process, and has a small number of parts.
For example, the members described below may be metal or resin.
The static pressure gas may be a gas other than air.

Hereinafter, a linear slide device 100 that is a first embodiment of the present invention will be described with reference to FIGS. 1 to 6.
Here, FIG. 1 is a perspective view showing an entire linear slide device that is a first embodiment of the present invention, and FIG. 2 is a sectional perspective view in the slide axis direction of the linear slide device shown in FIG. 3 is a perspective view showing the overall shape of the slide shaft in FIG. 1, FIG. 4 is a cross-sectional perspective view explaining the moving state of the linear slide device shown in FIG. 2, and FIG. 5 is shown in FIG. FIG. 6 is a cross-sectional perspective view in the slide axis direction for explaining the static pressure gas layer adjusting unit, and FIG. 6 is a cross-sectional perspective view in the direction orthogonal to the slide shaft for explaining the static pressure gas layer adjusting unit shown in FIG. 1.

Referring to FIGS. 1 and 2, a linear slide device 100 according to a first embodiment of the present invention includes a rod-shaped slide shaft 110 having a circular outer peripheral side surface, and a slide shaft 110 and a slide via a static pressure gas layer. A static pressure gas bearing mechanism including a slider 120 that moves along the slide axis direction of the shaft 110 is used.

Referring also to FIG. 3, in the present embodiment, the slide shaft 110 is configured to be machined from a shaft having a cylindrical side surface.
However, other than the cylindrical shaft, the slide shaft 110 can be configured by, for example, an annular steel pipe or the like.
A slide flat surface portion 111 that is horizontal along the slide axis direction of the slide shaft 110 is formed on a part of the slide circumferential surface portion 112 formed of the cylindrical shaft.
In addition, except for the slide flat surface portion 111, the columnar shape of the slide circumferential surface portion 112 is a second slide circumferential surface portion 114 left on the outer peripheral side surface.

In the linear slide device 100 of the present invention, the slide circumferential surface portion refers to a portion including a substantially circular outer peripheral side surface, and is, for example, a portion where the slide flat surface portion is formed like the second slide circumferential surface portion 114. If the outer peripheral side surface other than the slide flat surface portion is circular, it is referred to as a slide circumferential surface portion.

The slide plane portion 111 can be formed by cutting a cylindrical shaft, but in the case of an annular steel pipe, it can be formed by molding, and the slide circumferential surface portion 112 and the slide plane portion 111 (second The slide circumferential surface portion 114) may be arranged arbitrarily according to the usage of the linear slider device 100.

Here, as the slide shaft 110 described above, for example, a material obtained by subjecting a metal such as stainless steel to a heat treatment or an electroless nickel plating treatment can be used, but the material is not limited to the metal, and a wear-resistant synthetic resin or the like. Can also be used.

In the case of the metal slide shaft 110 according to the present embodiment, the slide circumferential surface portion 112 and the second slide circumferential surface portion 114 having the above-mentioned circular cross section are subjected to a cutting/polishing process in a cylindrical shape using a lathe or the like. As a result, it is possible to easily process the slider 120 to the required dimensional accuracy and finished surface roughness in order to eliminate axial deviation that may occur when the slider 120 moves.

Since the accuracy of the slide shaft 110 having a circular cross section is obtained by cutting the work that becomes the slide shaft 110, the accuracy of the perpendicularity and parallelism between the guide surfaces of the slide shaft having the rectangular cross section as in the conventional art is accurate. The demand can be easily satisfied as compared with the case of putting out.

In addition, the slide flat surface portion 111 formed of a horizontal plane of the slide shaft 110 described above is a slide formed at each shaft end portion of the slide shaft 110 so that the slide circumferential surface portion 112 having a circular cross section is left at both shaft end portions. A slide plane portion 111 is formed so as to be sandwiched between the circumferential surface portion 112 and the slide circumferential surface portion 112.

That is, the slide flat surface portion 111 is formed along the slide axis direction of the slide shaft 110 by processing the peripheral side surface of the slide circumferential surface portion 112 having a circular cross section with an end mill or the like while maintaining the horizontality of the slide shaft 110. It is formed as a horizontal surface.
Therefore, between the slide circumferential surface portion 112 and the slide flat surface portion 111, a wall portion 113 (so-called "D cut") having a cross-sectional shape of Roman "D" when viewed from the slide axis direction is formed. Will be done.

As a result, in the linear slide device 100 of the present embodiment, the stroke that provides the slide width that allows the slider 120 to move between the two wall portions 113, 113 formed along the slide axis direction of the slide shaft 110 is defined. To be done.
When such a slide flat surface portion 111 is provided on only one surface, it suffices to maintain the flatness of the slide flat surface portion 111, which facilitates setting when the slider 120 is inserted. Therefore, the assembling load of these is significantly reduced.

On the other hand, the above-mentioned slider 120 includes an air plate 121 that faces the slide flat surface portion 111 of the slide shaft 110 and ejects compressed air (static pressure gas), and the air plate 121 along the slide axis direction of the slide shaft 110. Two air bushes 122, 122 that are arranged so as to be sandwiched and face the slide circumferential surface portion 112 or the second slide circumferential surface portion 114 of the slide shaft 110 and eject the compressed air (static pressure gas) are provided.

Further, the air plate 121 described above is held on the bottom surface side of the air plate block 123, and the two air bushes 122, 122 are respectively held by air bush blocks 124 sandwiching the air plate block 123.
That is, the air bush block 124 is formed with a through hole 124a in the slide shaft direction into which the slide shaft 110 is inserted, and the air bush 122 is fitted in the opening of the through hole 124a. ..

Then, in the gap formed between the air bushes 122, 122 of the slider 120 and the slide circumferential surface portion 112 or the second slide circumferential surface portion 114 of the slide shaft 110, a static pressure gas layer serving as a fluid lubricating film is generated. Such a loose fitting state is appropriately set.
The compressed air supplied to the air bushes 122, 122 of the slider 120 is taken in from the two air inlets 125, 125, respectively.

The compressed air passes through the orifices in the air bushes 122, 122, the porous material, etc., and enters the gap between the air bushes 122, 122 of the slider 120 and the slide circumferential surface portion 112 or the second slide circumferential surface portion 114 of the slide shaft 110. The flow rate flowing in is appropriately adjusted to support the slider 120 while keeping them in a non-contact state.

Referring also to FIGS. 5 and 6, the air plate block 123 is provided near the center of the air bush block 124 in the slide shaft direction, and is formed so as to reach the through hole 124a and face the slide shaft 110. It is installed in the recess 124b of 124.

The air plate block 123 is made of a substantially rectangular parallelepiped block body, and both ends in the width direction orthogonal to the slide shaft 110 are also referred to in the direction of arrow A in FIG. And is mounted on the mounting surfaces 124c on both sides on the slide shaft 110 side, which is the bottom surface of the recess 124b of the air bush block 124.

An air plate 121 is installed on the bottom surface side of the air plate block 123 so as to face the slide plane portion 111 of the slide shaft 110.
Then, the compressed air supplied to the air plate 121 is taken in through the air inlet 128.
The flow rate of the compressed air passing through the orifice in the air plate 121, the porous material, etc., and flowing into the gap between the air plate 121 of the slider 120 and the slide flat surface portion 111 of the slide shaft 110 is appropriately adjusted so that both are Maintains non-contact state.

As the static pressure gas layer adjusting portion 120A for adjusting the gap between the air plate 121 of the slider 120 and the slide flat surface portion 111 of the slide shaft 110, a pull bolt 126 and a push bolt 127 are provided near both ends in the width direction orthogonal to the slide shaft 110. It is arranged.

In the vicinity of both ends in the width direction orthogonal to the slide axis of the air plate block 123, there are one drill hole 123a for the pull bolt 126 and a screw hole 123b for the push bolt 127 so as to sandwich the drill hole 123a in the axial direction. When the two ends are joined together, a total of 6 screw holes are drilled in the entire air plate block 123.

Further, screw holes 124d for fixing the air plate block 123 to the air bush block 124 are provided in the air bush block 124 so as to correspond to the drill holes 123a for the pull bolt 126.
The pull bolts 126 and the push bolts 127 are arranged such that two pull bolts 126 are provided on one end side in the width direction orthogonal to the slide axis of the air plate block 123, one push bolt 127 therebetween and two push bolts 127 on the other end side. One push bolt 127 and one pull bolt 126 may be arranged between them.

In this way, the air plate block 123 is fixed to the air bush block 124 by inserting the pulling bolt 126 into the drill hole 123a and screwing it into the screw hole 124d.
At this time, the push bolt 127 is appropriately turned so that the air plate 121 of the slider 120 maintains a predetermined gap with respect to the slide flat surface portion 111 of the slide shaft 110, and the surfaces can cope with each other without collapsing. By this, the extrusion length is adjusted.

That is, by adjusting the number of times the push bolt 127 is screwed into the screw hole 123b, the length of the tip of the push bolt 127 protruding from the lower surface of the air plate block 123 is adjusted, and the tip of the push bolt 127 protruding is adjusted. By contacting the mounting surface 124c of the recess 124b, the gap between the air plate block 123 and the mounting surface 124c of the air bush block 124 facing the air plate block 123 is kept constant.

The gap between the air plate block 123 formed by the cooperation of the pull bolt 126 and the push bolt 127 as described above and the mounting surface 124c of the air bush block 124 is the air plate 121 of the slider 120 and the slide shaft 110 sliding. It spreads to the gap with the flat surface portion 111 and stably forms the gap between them.
By adjusting the gap as described above, it is possible to balance the support of the slider 120 in the both-supported state by the air bush 122 and the support of the slider 120 by the air plate 121, and realize highly accurate movement of the slider 120.

In the linear slide device 100 of the present embodiment, the slide plane portion 111 is formed on the upper surface which is the upper side in the figure, but the position of the slide plane portion 111 is limited to the upper surface. is not.
That is, the position of the slide plane portion 111 is appropriately set in consideration of the balance of the load to be supported, gravity, etc., according to the mounting direction of the slide shaft 110, which is the moving direction of the slider 120.
For example, in the case where the slider 120 moves in the vertical direction (vertical direction with respect to the horizontal direction), in which direction is the load state when the slider 120 is provided as a guide mechanism of a precision measuring instrument or an ultra-precision machining machine. It is preferable to set by.

Next, the movement of the slider 120 in the linear slide device 100 of this embodiment will be described by comparing FIGS. 2 and 4.
First, as shown in FIG. 2, the slider 120 is arranged with respect to the slide shaft 110 so that the air plate 121 of the slider 120 faces the approximate center of the slide plane portion 111.

Then, when the slider 120 moves to the left in FIG. 2, it becomes as shown in FIG.
At this time, the end surface in the moving direction of the air plate block 123 (the left end surface in the drawing) contacts the wall portion 113 formed in the slide shaft 110 and having the shape of a roman letter “D” when viewed from the slide shaft direction of the slide shaft 110. Then, the further movement to the left is restricted.

Then, the above-described wall portion 113 can function as a stopper that prevents the slider 120 from moving beyond the movement control range of the slider 120, and an unexpected measurement or processing due to the movement of the slider 120 can occur. The situation can be prevented.

Next, a linear slide device 200 that is a second embodiment of the present invention will be described based on FIG.
The linear slide device 200 according to the second embodiment of the present invention is different from the above-described linear slide device 100 according to the first embodiment of the present invention only in the form of the slide flat surface portion formed on the slide shaft 110. Since the device configuration is the same, the same members are designated by the same reference numerals as those of the linear slide device 100 according to the first embodiment of the present invention, and detailed description thereof will be omitted.

That is, the linear slide device 200 of the second embodiment is formed so that the slide plane portion extends over the entire axial length of the slide shaft 110.
As a result, the linear slide device 200 according to the second embodiment of the present invention can move the slider 120 with a stroke wider than that of the linear slide device 100 according to the first embodiment described above.
If there is no strict limitation on the movement control range of the slider 120, it becomes a preferable form.

Further, although not shown, as a modification of the present embodiment, the slide shaft 110 having the slide plane portions formed of two or more horizontal planes can be set so that these slide plane portions face the air plate 121. ..

Regarding the specific installation form of these slide plane portions, if the slide plane portions are all formed of horizontal planes, the slider 120 can be installed without the need for precision in the perpendicularity between the guide surfaces as in the conventional case. It can be set according to the precision measuring equipment and ultra-precision processing machine to be installed.

Although the description of the present embodiment is finished above, the aspects of the present invention are not limited to the above-described embodiments, and modifications can be made without departing from the spirit of the present invention.

100, 200... Linear slide device 110... Slide shaft 111... Slide flat surface portion 112... Slide circumferential surface portion 113... Wall portion 114... Second slide circumferential surface portion 120... Slider 120A... Static pressure gas layer adjusting part 121... Air plate 122... Air bush 123... Air plate block 123a... Drill hole 123b... Screw hole 124... Air bush block 124a・・・Through hole 124b ・・・Concave part 124c ・・・Mounting surface 124d ・・・Screw hole 125 ・・・Injection port 126 ・・・Pulling bolt 127 ・・・Pushing bolt 128 ・・・Injection port

Claims (9)

In a linear slide device using a static pressure gas bearing mechanism composed of a slide shaft and a slider that moves in the slide shaft direction of the slide shaft through a static pressure gas layer,
The slide shaft includes a slide circumferential surface portion along the slide axis direction and a slide flat surface portion along the slide axis direction,
The slider is a both-sided state in which the slider is arranged so as to sandwich the air plate along the slide axis direction of the slide shaft, and an air plate facing the slide flat surface portion of the slide shaft to eject static pressure gas. A linear slide device, comprising: two air bushes that face a slide circumferential surface portion of a shaft and eject static pressure gas. The linear slide device according to claim 1, wherein the slide plane portion is formed at a central portion in the slide axis direction. The linear slide device according to claim 1, wherein the slide plane portions are formed at both end portions in the slide axis direction. The linear slide device according to any one of claims 1 to 3, wherein a plurality of the slide plane portions are formed along the slide axis direction. The air plate of the slider has a static pressure gas layer adjusting portion for adjusting a static pressure gas layer generated in a gap between the slider and the slide flat surface portion. The linear slide device according to the item. The linear slide device according to claim 5, wherein the static pressure gas layer adjusting portion has pull bolts and push bolts arranged near both ends in a width direction orthogonal to the slide axis direction. The linear slide device according to any one of claims 1 to 6, wherein the static pressure gas is air. The linear slide device according to any one of claims 1 to 7, wherein the slide shaft is formed of a solid member. The linear slide device according to any one of claims 1 to 7, wherein the slide shaft is formed of a hollow member.