Linear encoder

To provide a linear encoder including a scale unit and a slider that slides along the scale unit, wherein the slider includes a slider enclosure including a slider holding unit, a detection head holding unit mounted inside a scale enclosure of the scale unit, and a pillar extending between the outside and inside of the scale enclosure to connect these two holding units, and a part of the pillar closer to the detection head holding unit and a part of the detection head holding unit closer to the pillar are bored by a thickness larger than a thickness of the pillar.

PRIORITY INFORMATION

The present invention claims priority under 35 U.S.C. §119 to Japanese Application No. 2014-142006 filed on Jul. 10, 2014, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a linear encoder to be assembled into a machining tool, a semiconductor manufacturing device, or the like, for determining a position of a movable shaft.

BACKGROUND ART

FIG. 3shows a specific structure of a conventional linear encoder.FIG. 4is a cross sectional view along line B-B′ inFIG. 3. As shown in the cross section inFIG. 4, a scale unit1of the conventional linear encoder shown inFIG. 3includes a scale enclosure2that is open at and around a corner defined by the bottom surface thereof and the rear surface thereof, and has a main scale3secured inside the scale enclosure2. The main scale3is made of glass, and has a scale made of metallic thin film and carved in matrix on the surface thereof at a constant pitch in the longitudinal direction. A slider unit20of the linear encoder includes a slider enclosure21roughly including a slider holding unit22, a detection head holding unit23, and a pillar24that connects the two. The detection head holding unit23has a detection head secured thereon including a light-emitting unit7, a mirror8, and a light-receiving unit29. In the detection head, the light emitted from the light-emitting unit7is reflected on the mirror8at the right angle to be irradiated into the matrix portion of the main scale3, and the transmitted light is converted into an electric signal by the light-receiving unit29. The slider holding unit22is secured on a moving unit or the like of a machine, using a bolt. The slider holding unit22has a built-in circuit board27for converting the electric signal from the light-receiving unit29into a position data signal. A through hole26is formed in the pillar24and the detection head holding unit23so that an electric wire28passes through the through hole26from the detection head to the circuit board27. The position data signal outputted by the circuit board27is outputted to the outside via a waterproof connecter9mounted on the slider holding unit22. A cover4is securely attached to the slider holding unit22to protect the circuit board27from water, oil, or the like.

The scale unit1and the slider unit20are assembled to each other, as shown inFIG. 3, and the detection head, the detection head holding unit23, and a part of the pillar24are accommodated in the scale enclosure2. Seals5,6are fixedly attached near the opening of the scale enclosure2. The tip ends of the seals5,6are in contact with each other to thereby close the opening of the scale enclosure2to prevent intrusion of dust, water, oil, or the like from the outside. The pillar24is long in the longitudinal direction of the scale unit1, and thin in the width direction, and has a cross section having a ship-like shape. With this shape, the pillar24moves while breasting the two seals5,6in the advancing direction as the slider unit20moves. Further, with this shape, the tip ends of the seals5,6breasted are brought into contact with each other again on the opposite side of the advancing direction of the pillar24.

The slider enclosure21including the slider holding unit22, the detection head holding unit23, and the pillar24is integrally molded using metal, such as aluminum or the like, generally by means of lost wax casting, die casting, or the like. However, it is not possible to form the through hole26of the detection head holding unit23and the pillar24by means of integral molding, as the diameter of the hole is very small while the length thereof is as long as five times the hole diameter. Further, in the case where the through hole is formed in post processing, there are available only drill machining and discharge machining with high machining cost, and it is necessary to form a plurality of holes when there are many wires. Still further, as the pillar is very thin, machining defect may likely be caused at the time of drill machining by a drill by breaking through the surface of the pillar. Yet further, while a task of passing a plurality of electric wires through the through hole of the pillar, a task of soldering for connecting the electric wire passing through the through hole to the electric circuit, and a task of pressing the connecter terminal for attachment are necessary, the number of steps required for wiring also presents a problem. Note that as a method for improving a wiring task, there is available a method that uses an FCC (a flexible flat cable) instead of an electric wire. However, in order to pass an FCC through the through hole, it is necessary to form a long hole in the pillar, and formation of such a hole in post processing requires repetitive execution of discharge machining and drill machining. Further, there is available a method, as a method for forming a long hole in a pillar, that forms a part of the pillar of the slider enclosure, using two molded components having a shape divided by a long hole. This method, however, has a problem of reduced strength of the pillar that supports the detection head holding unit.

The present invention has been conceived in view of the above, and an object of the present invention is to implement a slider structure of a linear encoder in which a through hole of a detection head holding unit and a pillar of a slider enclosure is formed by means of integral molding or milling machining, to provide a linear encoder with a lower cost.

SUMMARY OF THE INVENTION

A linear encoder according to the present invention is a linear encoder having a scale unit and a slider that slides along the scale unit, wherein the slider has a slider enclosure including a slider holding unit, a detection head holding unit mounted inside a scale enclosure of the scale unit, and a pillar extending between outside and inside of the scale enclosure to connect these two holding units, and a part of the pillar closer to the detection head holding unit and a part of the detection head holding unit closer to the pillar are bored by a thickness larger than a thickness of the pillar.

In this case, boring of the pillar may be applied to a part closer to the detection head holding unit than a position where a seal secured on the scale enclosure contacts the pillar when the pillar is assembled to the scale unit.

The slider enclosure may be formed so as to include a through hole integrally molded between the part bored of the pillar and the slider holding unit.

The slider enclosure may be given post processing for forming a through hole between the part bored of the pillar and the slider holding unit by means of milling machining.

According to the present invention, a part of the pillar closer to the detection head holding unit and a part of the detection head holding unit closer to the pillar are bored by a thickness larger than the thickness of the pillar. With the above, it is possible to reduce the length of the through hole. Thus, it is possible to integrally mold the slider enclosure including the through hole by means of lost wax casting, die casting, or the like. Further, even when integral molding is not possible, depending on the length of a through hole, it is possible to achieve a through hole shorter than that of a conventional slider enclosure, and to make the root portion of a milling tool as thick as the thickness of the pillar or even thicker, which facilitates milling machining for formation of a through hole. With the above, it is possible to readily form a long hole for an FCC by means of milling machining, and thus to reduce the number of wiring steps without increasing a machining cost. With the above, according to the present invention, it is possible to provide a slider unit of a linear encoder with lower cost.

Note that according to a conventional linear encoder, it has been considered senseless to form a bored portion in a pillar as in the present invention, as the formation deteriorates sealing performance of the linear encoder. However, an actual analysis of a relationship between a pillar and a seal proves that, at the middle portion of the pillar, the seal contacts the pillar only in a part closer to the slider holding unit and that a part of the pillar closer to the detection head holding unit does not contribute at all to sealing performance. This analysis can enable the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the present invention will be described with reference to the drawings.FIG. 1shows a specific structure of a linear encoder according to the present invention.FIG. 2is a cross sectional view along line A-A′ inFIG. 1. Note that for ready understanding, the seal6and the upper surface of the scale enclosure2(the right end surface inFIG. 2) are not shown inFIG. 1. InFIGS. 1 and 2, a member having the same function as that inFIGS. 3 and 4is given the same reference numeral, and is not described. The detection head holding unit13of the slider enclosure11and a part of the pillar14have a shape formed by boring a part up to a position immediately before a position where the pillar14contacts the seals5,6on the side of the detection head holding unit13by a thickness larger than the thickness of the pillar14.

That is, as is obvious from the drawing, the detection head holding unit13is fully accommodated in the hollow space formed inside the scale enclosure2. At the corner of the scale enclosure2, an opening is formed so as to provide communication between the outside and inside of the scale enclosure2, and the pillar14extends through the opening between the outside and inside of the scale enclosure2. That is, the detection head holding unit13is not exposed to the outside, while the pillar14is partly exposed to the outside. The seals5,6are secured on the scale enclosure2, and the respective tip ends of the seals5,6are in contact with the pillar14. A part of the pillar14closer to the detection head holding unit13than the position where the seals5,6contact the pillar14is not exposed to the outside.

In this embodiment, in a part of the pillar4closer to the detection head holding unit13than a position where the pillar14contacts the seals5,6; in other words, a part of the pillar14not exposed to the outside, and in a part of the detection head holding unit13closer to the pillar14, a bored portion15is formed. Note that it is desirable that the bored portion15is formed at substantially the middle of the pillar14in the scale longitudinal direction (the left-right direction inFIG. 1). However, so long as it is possible to ensure a seal for the opening of the scale enclosure2, the position of the bored portion15is not limited to the middle in the scale longitudinal direction, but may be at other positions.

Between the bored portion15of the pillar14and the slider holding unit12, a long through hole16is formed. In the slider enclosure11, the slider holding unit12, the detection head holding unit13, the pillar14, the bored portion15, and the through hole16are integrally molded by means of lost wax casting, die casting, or the like, using metal, such as aluminum or the like. An FCC18is connected to the light-receiving unit29, and also to an FPC connecter19mounted on the circuit board17while passing through the bored portion15and the long through hole16.

In the embodiment shown inFIGS. 1 and 2, an example is described in which the through hole16of the pillar14is integrally molded. However, in the case where integral molding of the through hole16is difficult to perform, the long through hole16may be formed in post processing by means of milling machining. Alternatively, the bored portion15may be formed not at the time of integral molding, but in post processing by means of milling machining. Although an optical linear encoder is described as an example in the above embodiment, the present invention can be applied to a magnetic or electromagnetic inductive linear encoder.