Mounting tool for linear displacement measuring apparatus

There is provided a mounting tool, for a linear displacement measuring apparatus, which is capable of reducing thermal stress of a scale housing case and is detachable while having a simple structure.The mounting tool includes a cylindrical bush inserted into a through hole drilled in the scale housing case, an O-ring interposed between an inside wall of the through hole and the bush, a mounting screw inserted into a cylindrical hole of the bush and screwed into a mounting face, and a plate spring arranged between a head part of the mounting screw and an outside face of the scale housing case, and biasing the scale housing case toward the mounting face.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from Japanese patent application No. 2016-187085, filed on Sep. 26, 2016, the disclosure of which are incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mounting tool for a linear displacement measuring apparatus. More specifically, the present invention relates to a structure for mounting a linear displacement measuring apparatus to an object to be measured while escaping thermal stress.

2. Description of Related Art

There has been used a displacement measurement apparatus which is what is called an encoder to perform precise position control in various industrial machines. A linear displacement measuring apparatus is shown inFIG. 9. A linear displacement measuring apparatus10includes a scale part11and a detection head16. The scale part11includes an elongate main scale (not shown) and a scale housing case12housing the main scale.

In an example of a photoelectric apparatus, the main scale is mainly constituted by a glass substrate, and a diffraction grating is arranged on the glass substrate. The scale housing case12is hollow and long, and is mainly made of (light) metal, such as aluminum. A plurality of holes13to be mounted and fixed is drilled in the scale housing case12.

The detection head16is provided so as to be relatively movable in the longitudinal direction of the scale housing case12, and detects relative displacement or a relative position with respect to the main scale. A plurality of holes to be mounted and fixed is drilled in the detection head16.

The linear displacement measuring apparatus10is mounted on, for example, a moving stage90. It is assumed that the moving stage90is constituted by a base91and a stage92which is slidable relatively to the base91. In this case, the scale housing case12is screwed into a side end face93of the stage92, and the detection head16is screwed (20) into the base91. With this structure, it is possible to precisely measure the relative displacement of the stage92with respect to the base91.

Incidentally, the moving stage90is also made of metal, and is mainly made of, for example, steel to secure sufficient rigidity or to prevent deformation.

Here, while the linear expansion coefficient of steel is 11×10−6, the linear expansion coefficient of aluminum is 23×10−6. This means that the deformation amount (expansion/contraction amount) of aluminum when temperature changes is larger than that of steel.

When the scale housing case12is completely fixed to the side end face93of the stage92, expansion or contraction of the scale housing case12is restricted, and thermal stress is generated.

The thermal stress causes curves and distortion of the scale housing case12. Consequently, curves and distortion of the main scale inside the scale housing case12are caused, and measuring accuracy is deteriorated. Furthermore, when the thermal stress exceeds the fastening force between the scale housing case12and the stage92, a shift and looseness at the coupling part are generated. The deformation of the scale housing case12caused by the thermal stress leads to a problem which cannot possibly be ignored if the scale has a long length, such as 2 or 3 m. Thus, the coupling part between the scale housing case12and the stage92needs a mechanism for escaping thermal stress instead of being simply screwed.

If curves and distortion of the scale housing case12and the main scale can be avoided by escaping thermal stress, expansion or contraction in itself is not a fatal problem as long as linearity is kept. When expansion or contraction is only caused by temperature, the improvement of reproducibility of measurement accuracy can be (principally) performed.

The applicant has proposed some structures of a linear displacement measuring apparatus to reduce thermal stress (for example, JP 2004-301541 A). The elastic fixture for a length measurement apparatus disclosed in JP 2004-301541 A is shown inFIG. 10. The scale housing case12is mounted on the stage92with a permanent fixing block40and a plurality of elastic fixing blocks50. The permanent fixing block40is an inverted L-shaped bracket which has rigidity and will not deform. The permanent fixing block40is mounted (22) substantially at the center of the scale housing case12, and screwed into the side end face93of the stage92.

On the other hand, the elastic fixing block50is a similar inverted L-shaped bracket, and the mechanism of the parallel plate spring54by piercing a part of it so as to be a rectangle. One end (fixing part52) of the elastic fixing block50is screwed into the side end face93of the stage92, and the other end (connecting part56) is screwed (22) into the scale housing case12.

The scale housing case12is fixedly screwed into the stage92by the one point of the permanent fixing block40, and the origin point is fixedly secured. On the other hand, the elastic fixing blocks50are interposed between the scale housing case12and the stage92at the other points, and the mechanism of the parallel plate spring54tolerates a lateral shift. Thus, relative expansion or contraction of the scale housing case12with respective to the stage92can be tolerated. Consequently, the thermal stress of the scale housing case12is escaped, and curves and distortion of the scale housing case12, that is, of the main scale can be prevented. Note that, since the scale housing case12is screwed (20), the linear displacement measuring apparatus10or the moving stage90can be replaced.

This structure exhibits excellent performance, but has a problem of a large number of parts. In other words, one permanent fixing block40, a plurality of elastic fixing blocks50, and a large number of screws are required. If the main scale has a long length such as 2 to 3 m, 20 or more elastic fixing blocks50are required.

Furthermore, the elastic fixing block50has a special shape, and the parallel plate spring54is to be crafted. Thus, the manufacturing cost of the elastic fixing block50is increased. The above structure has an advantage as long as a scale is relatively short.

However, it is difficult to use the above structure for a long scale because of installation man-hours, time, and cost.

Thus, the applicant adopts the following structure to reduce the number of parts.FIG. 11illustrates a plurality of mounting holes13drilled in the scale housing case12. Here, the diameter of a center hole (not illustrated) drilled substantially at the center of the longitudinal direction is substantially the same as the male screw diameter. The scale housing case12is fixedly screwed into the stage92by the center hole, and the origin point of the main scale is fixed. On the other hand, the diameters of the other holes13are a size larger than the diameter of a male screw14, and a gap is left between the shaft of the screw14and the hole13. This gap tolerates a lateral shift of the scale housing case12.

However, since vibrations and shocks are constantly generated in various industrial machines, the linear displacement measuring apparatus10needs to be prevented from rattling. Thus, a several O-rings15are interposed between the male screw14and the hole13, and an adhesive18is poured into the gap to fix the position of the O-rings15.FIG. 12illustrates the cross-sectional view. The O-ring15functions to tolerate a lateral shift by supporting the scale housing case12elastically, and to center the male screw14to be at the center of the hole13. The adhesive18is poured because the position of the O-ring15is not to be shifted.

This structure is simple, but excellent for stably installing a long linear displacement measuring apparatus10while tolerating a lateral shift.

SUMMARY OF THE INVENTION

Although the structure inFIGS. 11 and 12is excellent, the inventors have found it has the following problems.

One of the problems is that it is difficult to pour the adhesive18into the gap. The adhesive18has viscosity, and it takes time, effort, and skill to pour the adhesive18into the hole13. Furthermore, it is difficult to pour a right amount of the adhesive18into the hole. If the amount of the adhesive18is too small, the O-ring15is not sufficiently fixed. However, if the amount of the adhesive18is too large, the adhesive18is overflowed from the hole13, which deteriorates the appearance and takes time to clearly wipe off it.

A purpose of the present invention is to provide a mounting tool, for a linear displacement measuring apparatus, which is capable of reducing thermal stress of a scale housing case.

A mounting tool according to an embodiment of the present invention is a mounting tool which mounts a linear displacement measuring apparatus on a mounting face, the mounting tool includes:

a bush inserted into a through hole drilled in a scale housing case;

an elastic body provided between the through hole and the bush;

a mounting screw inserted into the bush and screwed into the mounting face; and

biasing means arranged between a head part of the mounting screw and the scale housing case, and biasing the scale housing case toward the mounting face.

In an embodiment of the present invention, it is preferable that the elastic body is rubber thermally welded to the bush.

In an embodiment of the present invention, it is preferable that

the bush has a flange part projecting in a direction perpendicular to a shaft, and

the biasing means is rubber thermally welded to a back face of the flange part.

In an embodiment of the present invention, it is preferable that

the bush has a flange part projecting in a direction perpendicular to a shaft,

the biasing means is a plate spring, and has a hole for inserting the mounting screw into a stand part which is a center part, and a leg part formed by being bended at an end of the stand part, and

the leg part biases the scale housing case toward the mounting face while the stand part of the plate spring is being sandwiched between the flange part and the head part of the mounting screw.

In an embodiment of the present invention, it is preferable that a gap exists between the flange part and the scale housing case.

In an embodiment of the present invention, it is preferable that the flange part has a shape which is long in a length measurement direction and short in a direction perpendicular to the length measurement direction.

In an embodiment of the present invention, it is preferable that a stop ring fit onto the bush and preventing the bush from coming off from the through hole is included.

A linear displacement measuring apparatus according to an embodiment of the present invention is a linear displacement measuring apparatus capable of being mounted on a mounting face, the linear displacement measuring apparatus includes:

a scale housing case having a through hole;

a bush inserted into the through hole;

an elastic body between the through hole and the bush; and

a stop ring fit onto the bush and preventing the bush from coming off from the through hole.

A method for mounting a linear displacement measuring apparatus according to an embodiment of the present invention includes:

inserting a mounting screw into the bush; and

screwing the mounting screw into the mounting face.

DETAILED DESCRIPTION

Embodiments of the present invention are illustrated and described with reference to the reference signs attached to the elements in the drawings.

First Exemplary Embodiment

Before a mounting tool200is described, a stage92which is a mounting face93, and a linear displacement measuring apparatus100to be mounted are briefly described.

FIG. 1is a diagram illustrating the linear displacement measuring apparatus100mounted on a moving stage90with the mounting tool200according to the present exemplary embodiment.

A plurality of screw holes94are provided on a side end face93of the stage92at specified intervals to screw the linear displacement measuring apparatus100. (The screw hole94is illustrated in the cross-sectional view inFIG. 4.)

The position and size of the screw hole94is roughly determined according to the standard of the moving stage90.

The linear displacement measuring apparatus100is briefly described below. A scale housing case110of the linear displacement measuring apparatus100is mounted on the mounting face93with the mounting tool200.

The scale housing case110has a hexagonal shape in which one angle of a rectangle is drawn inside to be an obtuse angle when viewed from the side. Here, as the cross-sectional of the scale housing case110is illustrated inFIG. 3, the scale housing case110can be described as a shape in which a rectangular head130is on a hollow pentagon120housing a main scale101.

When the rectangular head130is mounted on the side end face93of the stage92with the mounting tool200, the hollow pentagon120appears to be hanged. Thus, the rectangular head130is referred to a hanging frame part130, and the hollow pentagon120is referred to as a hollow body120.

The back face of the scale housing case110is a substantially flat face so as to be in close contact with the side end face93of the stage92. The hanging frame part130has a front side face and a back-side face which are substantially parallel. By mounting the mounting tool200from the front side face, the hanging frame part130is pressed against the side end face93of the stage92with substantially no gap.

Taking the length of the screw into consideration, the width W1of the hanging frame part130should be thinner. However, as to be described later, an appropriate elastic force is required to be maintained between the screw and the scale housing case110to interpolate an elastic ring (the O-ring230). For this reason, the width W1sufficient for housing two or more O-rings230in parallel is needed. The height T1of the hanging frame part130is roughly determined according to the standard of the height of the stage92or the position of the screw hole94of the stage92. If the height T1of the hanging frame part130is desired to be a little longer, the height cannot be changed on the discretion of a measurement machine manufacturer (the manufacturer of a linear displacement measuring apparatus).

A plurality of through holes140is drilled in the hanging frame part130in the longitudinal direction at the same intervals as the screw holes94of the side end face93of the stage92. At the part where the through hole140is provided, a shallow recess150is provided on the back face of the hanging frame part130. An upper edge line161and a lower edge line162are projected in parallel sandwiching the through holes140on the front side of the hanging frame part130so as to form a shallow groove part160in the longitudinal direction.

The mounting tool200is described below.

FIGS. 2 and 3are exploded perspective views of the mounting tool200.FIG. 2is the exploded perspective view when viewed from the front side, andFIG. 3is the exploded perspective view when viewed from the back side.FIG. 4is a cross-sectional view taken along the line VI-VI inFIG. 1.

The mounting tool200includes a mounting screw210, a bush220, an O-ring230, a plate spring240, and a stop ring250.

Here, a mounting procedure is briefly described.

First, the O-ring230and the bush220are inserted into the through hole140of the hanging frame part130. The stop ring250is fit onto the bush220from the back face of the hanging frame part130. Then, the plate spring240is placed to cover the bush220from the front side, and the mounting screw210is screwed. In the background art, the mounting tool200corresponds to the elastic fixing block50. Thus, the hole (not illustrated) substantially at the center of the scale housing case110is used for fixedly screwing the hanging frame part130without the mounting tool200, the other holes (the through holes140) are used for the mounting tools200.

Each parts of the mounting tool200is described below.

The mounting screw210is what is called a male screw having a head part211and a screw shaft212. The head part211projects to some extent, and has a flat seat surface213. Here, it is obvious that the diameter of the head part211is a size larger than that of the through hole140, but the diameter of the screw shaft212is a size smaller than that of the through hole140. (The diameter of the through hole140is a size larger than that of the screw shaft212.) That is, when the mounting screw210is inserted into the through hole140, a gap is formed between the mounting screw210and the through hole140. The bush220and the O-ring230are arranged in the gap.

When the mounting screw210is inserted from the front side of the hanging frame part130, the shaft of the male screw212has a length sufficient for the tip side of the mounting screw210to be screwed into the screw hole94.

As to be described later, in order to sandwich a flange part225of the bush220between the seat surface213and the hanging frame part130, the shaft length of the male screw212is sufficiently longer than the width W1of the hanging frame part130.

The bush220has a cylindrical shape having both end openings, and is arranged in the gap between the screw shaft212and the through hole140. The O-ring230is arranged in the gap between the screw shaft212and the through hole140in addition to the bush220. For this reason, the bush220is designed so as to be thin. The inside diameter of the cylindrical hole of the bush220has a size into which the screw shaft212can be inserted, but it is preferable that the size is designed so that a slight clearance is secured between the cylindrical hole and the screw shaft212.

FIG. 5is a perspective view of the bush220.

The bush220has a cylindrical body part221and a flange part225projecting from one end (referred to as a base end) of the body part221.

On the outside face of the body part221, a plurality of annular projecting lines222is provided round the body part221. The projecting lines222are provided in the axial direction of the body part221at intervals. The projecting lines222are likened to bamboo nodes, and referred to as nodes222, and the part between the nodes222are referred to as an internode part223. The O-ring230is arranged at the internode part223, and the node222serves as a partition having the height which the O-ring230cannot cross over. The node222is only required to serve as a partition, and is not to be necessarily provided continuously round the body part221. The node222may be provided intermittently and be, for example, a projection projecting at intervals of predetermined angle (for example, 120°).

On the tip side of the body part221, an annular recessed line224is formed round the body part221. The stop ring250is fit onto the recessed line224.

The flange part225projects from the base end of the body part221in the direction perpendicular to the shaft. Here, the flange part225has a shape which is not a circle nor an oval, but a shape in which the top and bottom of a circle or oval are cut off and two semicircles are connected two lines when viewed from the axial direction. It has been stated that the height T1of the hanging frame part130is roughly determined according to the standard, and that the diameter of the through hole140is designed to be a size larger than that of the screw shaft212. Under such restrictions, in order to sufficiently secure the projecting width of the flange part225, the projections in the perpendicular direction are to be cut off, and the projections in the lateral direction (length measurement direction) are to be extended. A front side end face226of the flange part225is flat, and the plate spring240is sandwiched between the front side end face226of the flange part225and the seat surface213of the mounting screw210.

The length L1of the body part221of the bush220is slightly longer than the width W1of the hanging frame part130. The back face of the hanging frame part130is pressed against the side end face93of the stage92while the bush220is being inserted into the through hole140. Here, when the tip of the body part221hits the side end face93of the stage92, a gap G1is slightly left between the back face of the flange part225and the side face (groove part160) of the hanging frame part130(seeFIG. 4).

That is, the flange part225of the bush220does not directly press the hanging frame part130(the scale housing case110) against the side end face93of the stage92.

(The plate spring240directly presses the hanging frame part130(the scale housing case110) against the side end face93of the stage92.)

The O-ring230is what is called an O-ring on the market. The O-ring230is inserted into the through hole140while being arranged at the internode part223of the body part221.

The diameter of the O-ring230is selected so that the gap between the internode part223of the body part221and the inside wall of the through hole140is buried by the O-ring230. That is, the O-ring230having an inside diameter almost as large as the outside diameter of the internode part223, and an outside diameter larger than that of the projecting line222is used. Then, the O-ring230is fit onto the internode part223. When the bush220is inserted into the through hole140, the O-ring230is pressed by the inside wall of the through hole140, and expanded in the internode part223in the axial line direction of the bush220. Note that, the O-ring having the wire diameter of 1.5 mm and the inside diameter of 7.5 mm is used.

Since vibrations and shocks generated by various industrial machines need to be absorbed or buffered, it is preferable that a plurality of O-rings230is prepared.

The plate spring240is biasing means for pressing the scale housing case110against the side end face93of the stage92.

FIG. 6is a side view of the plate spring240.

The plate spring240has a shape in which a metal belt-shaped thin plate is bent to be an M-shape. When viewed from the side, the plate spring240has a stand part241the center of which is substantially flat, and the stand part241looks like having legs242at both sides. When viewed from the front, the plate spring240has a hole247, into which the screw shaft212of the mounting screw210can be inserted, at the center of the stand part241.

The leg part242is formed by bending the end of the stand part241. The shape of the leg part242is described with reference to the directions inFIG. 6. The upper part ofFIG. 6is referred as an upper side, and the lower part ofFIG. 6is referred to as a lower side. The leg part242begins by lightly bending the thin plate at the end of the stand part241. This part is referred to as a root part243of the leg part242. The leg part242is bent at the root part243and directed toward the direction upper than the stand part241at a shallow angle. Then, the leg part242is sharply bent at an angle of about 90° and directed downward. This sharp bending point244is referred to as a knee part244. The leg part242is directed downward from the knee part244, and bent at an angle of about 90° to form a heel part245. A toe part246which is the rest part from the heel part245is bent to the opposite side to the stand part241, that is, toward outside.

The width of the plate spring240is just the size fitting the groove part160provided on the front face of the hanging frame part130(for example, seeFIG. 1). While no force is being applied to the plate spring240, the height L2from the heel part245to the stand part241is required to some extent. Here.FIG. 7is a cross-sectional view of the scale housing case110being mounted on the stage92with the mounting tool200.

It has been stated that the gap G1is left between the flange part225of the bush220and the bottom face of the groove part160of the hanging frame part130while the tip of the bush220is hitting the side end face93of the stage92. Here, it is assumed that the plate spring240is arranged to cover the flange part225of the bush220. At this time, while the heel part245is in contact with the bottom face of the groove part160, the stand part241is required to be floated from the flange part225of the bush220(the gap G2inFIG. 7). Then, as the mounting screw210is tightened (arrow A1), the stand part241is pressed toward the flange part225by the seat surface213of the mounting screw210(arrow A2). The force of pressing the plate spring240by the seat surface213of the mounting screw210is propagated to the heel part245. The heel part245biases the scale housing case110toward the side end face93of the stage92with the force caused by the distortion gathered at the root part243. In this manner, the linear displacement measuring apparatus100(the scale housing case110) is in close contact with the side end face93of the stage92, and pressed by the plate spring240, and the linear displacement measuring apparatus100is prevented from rattling accordingly.

The stop ring250is what is called a C-shaped ring (C-shaped lock ring). The stop ring250is fit onto the recessed line224formed at the tip side of the bush220. The stop ring250is fit onto the bush220from the back side of the hanging frame part130so that the bush220is not to come off from the through hole140as illustrated inFIG. 4 or 7. Note that, the recess150is provided at the back side of the hanging frame part130so that the stop ring250does not project from the back face of the hanging frame part130.

The stop ring250is a stopper for the bush220, and may not be provided in consideration only of mounting the linear displacement measuring apparatus100(the scale housing case110). However, the stop ring250remarkably makes the mounting work of the linear displacement measuring apparatus100(the scale housing case110) efficient. That is, a measurement machine manufacturer attaches the bush220to the scale housing case110in advance at its factory. The O-ring230is arranged at the internode part223of the body part221, and the bush220is inserted into the through hole140and stopped by the stop ring250. When the linear displacement measuring apparatus100is mounted on an industrial machine at a client's factory, the plate spring240is placed on the bush220, and the mounting screw210is screwed.

The number of mounting points of a long linear displacement measuring apparatus100of 2 or 3 m can be 20 to 30. If a work needs such large number of bushes220or O-rings230at a client's factory, it is difficult and inefficient to manage the parts. Considering this point, the O-ring230and the bush220have been already mounted at the measurement machine manufacturer's factory, which is efficient to work at a client' factory.

The mounting tool200having such a structure according to the present exemplary embodiment has the following effects:

(1) In the mounting tool according to the present exemplary embodiment, the bush220is inserted into the through hole140of the scale housing case110, and the O-ring230is sandwiched between the bush220and the inside wall of the through hole140. Then, the internode part223is provided on the circumference of the bush220to stably arrange the O-ring230. Consequently, the O-ring230does not need to be fixed with an adhesive. This greatly contributes to the efficiency of the mounting work. Furthermore, since the O-ring230is not fixed with an adhesive, it is detachable.

(2) The bush220on which the O-ring230is arranged can be stopped in the through hole140by the stop ring250. Accordingly, the O-ring230and the bush220do not need to be separately considered in the mounting work, and using the bush220is substantially equivalent to just screwing. Thus, the mounting work becomes simple, and does not need a special skill.

Second Exemplary Embodiment

A second exemplary embodiment of the present invention is described below.

The basic structure in the second exemplary embodiment is the same as that in the first exemplary embodiment. However, in the second exemplary embodiment, an elastic body layer260is directly formed on a bush220instead of fitting an O-ring230onto the bush220.

As illustrated inFIG. 8, the elastic body layer260made of rubber (resin) is thermally welded to the bush220. Since the elastic body layer260is formed directly on the bush220, a projecting line222and an internode part223for fitting an O-ring are not required, and a body part221has a straight side face.

The elastic body layer260is formed on the side face of the body part221and the back face of a flange part225.

The thickness of the elastic body layer260is, for example, about 0.5 to 0.7 mm on the side face of the body part221, and about 0.2 mm on the back face of the flange part225.

InFIG. 8, there appears a gap between a through hole140of a hanging frame part130and the elastic body layer260, but the gap may be buried with, for example, a silicone adhesive. That is, before the bush220inserted into the through hole140, a silicone adhesive may be thinly applied to the outside of the elastic body layer260.

Alternatively, the through hole140and the elastic body layer260may be designed so as not to form a gap, and the bush220may be forcibly inserted into the through hole140.

In the second exemplary embodiment, the width of the hanging frame part130is to be substantially the same as the length of the body part221of the bush220, or to be slightly shorter than the length of the body part221of the bush220, that is, the width of the hanging frame part130.

Then, when the mounting screw210is inserted into the bush220and screwed into the hole94of the stage92, the seat surface213of the mounting screw210is to press the hanging frame part130via the flange part225of the bush220. At this time, the elastic body layer260formed on the back face of the flange part225is to be a cushion and biasing means for pressing the hanging frame part130with an appropriate force.

Although not illustrated inFIG. 8, a stop ring250may be attached to the bush220according to the second exemplary embodiment as a stopper.

Note that, the present invention is not limited to the above embodiments, and can be appropriately changed without deviating from the scope.

In the above embodiments, the plate spring240has been sandwiched between the flange part225of the bush220and the head part211of the mounting screw210.

Alternatively, by arranging an elastic member at the gap G1between the flange part225of the bush220and the hanging frame part130, an equivalent function can be obtained.

(When an elastic member is arranged at the gap G1, the head part of the mounting screw exists outside of the flange part, and thus the elastic member is certainly arranged between the head part of the mounting screw and the outside face of the scale housing case in this case.)

It has been described that the flange part of the bush has a shape which is long laterally (in the length measurement direction), but the flange part may have a circular shape according to the shape of the hanging frame part.