Actuator

A rotary driving source is connected to one end of a frame. The rotary driving force of the rotary driving source is transmitted to a slider by the aid of a driving pulley, a belt member, and a driven pulley. The slider is displaced in the axial direction of the frame while being guided by a guide mechanism. Each of the frame and the slider is formed of, for example, an aluminum alloy. First guide rails are installed in the frame and second guide rails are installed in side surfaces of the slider. The first guide rails and the second guide rails are formed of a metal material subjected to a hardening treatment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an actuator, which is capable of reciprocally moving a slider linearly along a frame under a driving action of a driving source.

2. Description of the Related Art

A transport mechanism such as an actuator has been hitherto used, for example, in order to transport a workpiece.

As shown inFIG. 12, the actuator comprises an inner block2, which is disposed inside an outer rail1, and which is displaceable in the axial direction. A ball screw3is screw-engaged with a substantially central portion of the inner block2in the axial direction.

The outer rail1comprises a pair of inner wall surfaces1a,1bformed so that the pair of inner wall surfaces1a,1bare opposed to the inner block2. A pair of ball-rolling grooves4a,4b, which extend in the axial direction, are formed on the inner wall surfaces1a,1b. Unillustrated ball grooves are formed on both side surfaces of the inner block2opposed to the ball-rolling grooves4a,4b. Return passages7, within which a plurality of balls6are circulated, are formed in the inner block2. The inner block2is guided to make displacement along the outer rail1by the balls6, which are allowed to circulate through the return passages7, the ball-rolling grooves4a,4b, and the ball grooves (not shown).

The ball screw3, which is integrally connected to a driving source such as an unillustrated electric motor, is rotated, and the inner block2, which is screw-engaged with the ball screw3, is displaced linearly in the axial direction of the outer rail1under rotary action of the ball screw3(see, for example, Japanese Laid-Open Patent Publication No. 2003-074551).

The actuator according to Japanese Laid-Open Patent Publication No. 2003-074551 includes a structure in which a plurality of balls6are circulated through the return passages7in the inner block2, the ball-rolling grooves4a,4b, and the unillustrated ball grooves, when the inner block2is displaced along the outer rail1under a driving action of the driving source. However, sliding resistance is generated when the balls6are circulated through the ball-rolling grooves4a,4band the ball grooves, and thus abrasion occurs on the inner block2and the inner wall surfaces1a,1bof the outer rail1.

Therefore, the outer rail1formed with the ball-rolling grooves4a,4band the inner block2formed with the ball grooves are each formed of a metal material (for example, stainless steel) capable of being subjected to a heat treatment (i.e., hardening treatment), and both the outer rail1and the inner block2are subjected to such a hardening treatment. Accordingly, abrasion that arises due to sliding action of the balls6is suppressed by increasing the hardness of the ball-rolling grooves4a,4band the ball grooves. However, when the hardening treatment is applied to the outer rail1and the inner block2, additional costs are incurred as a result of the heat treatment, and the number of production steps is increased.

On the other hand, in recent years, demands have grown for lightweight actuators and efforts have been made to further reduce the weight of actuators.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide an actuator, which makes it possible to reduce production costs and provide a lightweight actuator, while also suppressing abrasion at the sliding portions of a guide mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIGS. 1 to 4, reference numeral10indicates an actuator according to a first embodiment of the present invention.

The actuator10comprises a frame14(seeFIG. 2) which is formed with a plurality of attachment holes12(seeFIGS. 2 and 3) and which is integrally formed with a pair of side walls14b,14cmutually opposed to a flat plate-shaped bottom wall14a. A rotary driving source16is provided at one end of the frame14. The actuator10further comprises a driving force-transmitting mechanism18which converts the rotary driving force of the rotary driving source16into rectilinear motion that is transmitted to a slider20, which is displaceable in the axial direction of the frame14in accordance with the rectilinear motion transmitted from the driving force-transmitting mechanism18, and a guide mechanism22which guides the slider20in the axial direction of the frame14.

The frame14is integrally formed by applying, for example, an extrusion or drawing process to a light alloy material, a light metal material such as an aluminum alloy, or a lightweight high strength resin material such as carbon fiber reinforced plastics (CFRP) containing carbon fiber. A first housing24is integrally connected to one end of the frame14in the axial direction by the aid of bolt members28. A second housing26is integrally connected to the other end of the frame14in the axial direction by the aid of bolt members28.

First and second side covers30and32, each of which has a substantially L-shaped cross section, are detachably disposed on upper surfaces of the first housing24and the second housing26by the aid of screw members34, so that the first housing24and the second housing26are connected to one another. The first and second side covers30,32serve to cover the upper surfaces and parts of side surfaces of the first housing24and the second housing26, and also cover an upper portion of the frame14.

A pair of top covers36are detachably installed on upper surfaces of the first housing24and the second housing26between the first and second side covers30,32by the aid of screw members34respectively. That is, upper surfaces of the first and second housings24,26are covered entirely by the top covers36and the first and second side covers30,32.

Stopper members38, which mitigate shocks that may occur upon displacement and abutment of the slider20, are provided at respective ends of the first housing24and the second housing26opposed to the slider20(seeFIG. 3).

As shown inFIG. 6, a pair of first long grooves40a,40b, each of which is recessed and has a rectangular cross section, extend in the axial direction along portions of the frame14disposed in the vicinity of the bottom surface of the inner wall. Elongate guide rails42a,42b, having substantially the same cross-sectional shapes as the first long grooves40a,40b, are installed in the first long grooves40a,40b. The pair of first long grooves40a,40bare formed so that they are opposed to one another on opposite sides of the frame14.

As shown inFIG. 4, the rotary driving source16is connected to a bottom surface portion of the first housing24by the aid of unillustrated screw members. A drive shaft44of the rotary driving source16is connected via an opening50to a driving pulley48, which is arranged in a recess46of the first housing24. The driving pulley48is rotatably supported in the recess46.

The first housing24, in which the rotary driving source16and the driving pulley48are provided, functions as a single driving unit (first unit). That is, for example, when the frame14is exchanged in order to change the stroke amount of the actuator10, the operation for exchanging the frame14can be conveniently performed simply by assembling the driving unit to an end of another frame. Further, it is possible to use common parts, because the driving unit can be utilized as is.

On the other hand, a driven pulley54is rotatably supported in a recess52formed in the second housing26. A belt member56, which extends substantially in parallel to the frame14, runs annularly over the driving pulley48and the driven pulley54. That is, the driving pulley48, the driven pulley54, and the belt member56function as the driving force-transmitting mechanism18for transmitting rotary driving force of the rotary driving source16to the slider20, which is connected to the belt member56.

The second housing26, in which the driven pulley54is provided, functions as a single driven unit (second unit). That is, for example, when the frame14is exchanged in order to change the stroke amount of the actuator10, the operation for exchanging the frame14can be conveniently performed simply by assembling the driven unit to an end of another frame. Further, it is possible to use common parts, because the driven unit can be utilized as is.

A columnar pulley shaft58is inserted into a substantially central portion of the driven pulley54by the aid of a plurality of bearings. The pulley shaft58is fixed by threaded engagement with an adjusting plate60, which is installed in the recess52of the second housing26. As shown inFIG. 3, the adjusting plate60is fastened in the recess52of the second housing26in a direction substantially perpendicular to the axis by the aid of screw members62. Further, the adjusting plate60is disposed so as to be displaceable along a plurality of long holes64with which the screw members62are engaged, i.e., in the axial direction of the second housing26.

An adjusting screw68is screw-engaged with the adjusting plate60via a hole66that penetrates through the second housing26. The head of the adjusting screw68is accommodated in the hole66, and hence the head does not protrude from the end surface of the second housing26(seeFIG. 4).

When the adjusting screw68is turned, the adjusting plate60is displaced in the axial direction of the frame14. Therefore, the driven pulley54, which is fixed to the adjusting plate60, can be integrally displaced. Accordingly, it is possible to adjust the tension of the belt member56that runs over the driving pulley48and the driven pulley54. That is, for example, when the adjusting screw68is turned from the outside by the aid of, for example, a hexagon wrench, to adjust the degree of threaded engagement with respect to the adjusting plate60, the adjusting plate60is displaced by a minute distance in the recess52of the second housing26along the long holes64through which the screw members62engage with the adjusting plate60. Thus, it is possible to optimally adjust the tension of the belt member56.

As shown inFIG. 6, the slider20is composed of a light alloy material, a light metal material such as an aluminum alloy, or a lightweight high strength resin material such as carbon fiber reinforced plastics (CFRP) containing carbon fiber, in the same manner as the frame14. The slider20is disposed so as to be displaceable in the axial direction inside the frame14.

The slider20comprises a main body section70, disposed substantially centrally and which protrudes slightly upwardly between the first side cover30and the second side cover32, a pair of flange sections72a,72bthat are separated from each other by a predetermined spacing distance on both sides of the main body section70, and space sections74a,74bformed between the main body section70and the flange sections72a,72brespectively. A table or the like, on which a workpiece is placed by the aid of unillustrated screws or the like, is installed on an upper surface of the main body section70.

Flange sections72a,72bare formed with a smaller dimension in the height direction as compared with the main body section70. Second long grooves76a,76b, which have rectangular cross sections are recessed at a predetermined depth respectively, extending in the axial direction along both side surfaces of the slider20opposed to the frame14. The second long grooves76a,76bare formed at positions opposed to the first long grooves40a,40bformed in the frame14respectively.

Space sections74a,74bare formed between the main body section70and the flange sections72a,72band are recessed downwardly at a predetermined depth from upper surfaces of the flange sections72a,72b. As shown inFIGS. 3 and 6, a plate-shaped belt stopper80is installed by bolts78on one side surface of the main body section70in the axial direction. Both ends of the belt member56are interposed between one side surface of the main body section70and the belt stopper80(seeFIG. 3). Therefore, the belt member56is fixed to the slider20, and thus the slider20and the belt member56are displaced in an integrated manner.

In this arrangement, as shown inFIG. 3, a pair of depressions84, which have substantially semicircular cross sections, are formed at positions opposed to bolt holes82of the belt stopper80. Therefore, when the belt stopper80is fixed to the slider20, the heads of the bolts78are accommodated within the depressions84, and the heads do not protrude from a side surface of the slider20.

On the other hand, the belt member56, which runs over the driving pulley48and the driven pulley54, passes freely through the space section74abetween the flange section72aand the other side surface of the main body section70(seeFIG. 6).

As shown inFIG. 6, the guide mechanism22comprises the pair of first guide rails42a,42bwhich are installed along the first long grooves40a,40bof the frame14respectively, a pair of second guide rails86a,86bwhich are installed along the second long grooves76a,76bon side surfaces of the slider20, and a pair of ball-rolling holes88which are disposed proximately to the second guide rails86a,86band which penetrate through the inside of the slider20in the axial direction. The first guide rails42a,42band the second guide rails86a,86bare arranged at mutually opposed positions.

Each of the first guide rails42a,42band the second guide rails86a,86bcomprises a prism-shaped member composed of a metal material capable of being subjected to a hardening treatment (hereinafter referred to as “hardened steel”). First ball-rolling grooves90having substantially circular arc-shaped cross sections, in which balls89roll, extend in the axial direction on side surfaces of the first guide rails42a,42bopposed to the second guide rails86a,86b. On the other hand, second ball-rolling grooves92having substantially circular arc-shaped cross sections, in which balls89roll, extend in the axial direction on side surfaces of the second guide rails86a,86bopposed to the first guide rails42a,42b.

Any one of methods including, for example, adhesion, forcible insertion and fitting, and welding may be used for installing the first guide rails42a,42band the second guide rails86a,86binto the first and second long grooves40a,40b,76a,76brespectively.

As shown inFIG. 2, the guide mechanism22includes a pair of plates96and covers98integrally connected to lower portions of the slider20by the aid of screw members94, and return guides100installed to the side surfaces of the slider20. It is preferable that each of the plate96, the cover98, and the return guide100is formed of a resin material. The plate96, the cover98, and the return guide100, which are disposed on one side surface of the slider20, are constructed by the same constitutive parts as those disposed on the other side surface.

Covers98include therein ball-rolling grooves102, which are formed on end surfaces thereof and make abutment against the slider20. In this arrangement, annular endless circulating tracks, which allow the plurality of balls89to roll therein, are constructed by the first ball-rolling grooves90of the first guide rails42a,42b, the second ball-rolling grooves92of the second guide rails86a,86b, the ball-rolling holes88penetrating through the slider20, and the ball-rolling grooves102.

The frame14, the first housing24, and the second housing26of the actuator10shown inFIG. 4alternatively may be formed in an integrated manner, so that the driving pulley48, the driven pulley54, and the slider20are retained respectively within a single frame15, as shown inFIG. 5. In this arrangement, end plates104a,104bare installed on both ends of the frame15respectively, wherein the end plates104a,104bare substantially perpendicular to the axis of the frame15. A pair of retaining blocks106, each provided with stopper members38, are provided on the upper surface of the frame15. The stopper members38oppose end surfaces of the slider20.

Accordingly, it is possible to reduce the number of parts, by forming the frame15of the actuator10with an integrated shape. Therefore, the time required to produce the actuator10can be shortened, while also reducing production costs.

The actuator10according to the first embodiment of the present invention is basically constructed as described above. Next, its operations, functions and effects shall be explained.

When current is supplied from an unillustrated power source to the rotary driving source16, the drive shaft44is rotated under rotary action of the rotary driving source16, and a rotary driving force of the driving pulley48connected to the drive shaft44is transmitted to the belt member56that runs over the driving pulley48and the driven pulley54. The slider20, to which both ends of the belt member56are fixed, is displaced in the axial direction of the frame14in an integrated manner while being guided by the guide mechanism22. When the polarity of the current supplied to the rotary driving source16is reversed, under the control action of an unillustrated controller, the direction of displacement of the slider20can be reversed to move the slider20reciprocally in the axial direction of the frame14.

As the slider20moves reciprocally in the axial direction of the frame14, the plurality of balls89roll along the first ball-rolling grooves90and the second ball-rolling grooves92. Accordingly, the slider20is displaced smoothly along the frame14.

As described above, in the first embodiment, the first guide rails42a,42b, which have first ball-rolling grooves90formed therein for allowing the plurality of balls89to roll, and the second guide rails86a,86b, which have second ball-rolling grooves92formed therein, are each constructed separately from the frame14and the slider20. The first and second guide rails42a,42band86a,86b, in which the first ball-rolling grooves90and the second ball-rolling grooves92are formed, are produced from hardened steel that is capable of being subjected to a hardening treatment. Accordingly, the frame14and the slider20, which occupy the major portion of the volume of the actuator10, can be formed, for example, from aluminum alloys and carbon fiber reinforced plastics. Therefore, it is possible to greatly reduce the weight of the actuator10overall, thereby realizing a lightweight actuator.

Each of the first guide rails42a,42band the second guide rails86a,86bis formed of a metal material, which has been subjected to a heat treatment for hardening the metal material. Therefore, it is possible to suppress and minimize abrasion of the first guide rails42a,42band the second guide rails86a,86b, which would otherwise be caused by sliding movement when the balls89roll therein.

As a result, it is sufficient to increase the strength of the actuator by applying a hardening treatment only to the first guide rails42a,42band the second guide rails86a,86bin which the balls89roll, in contrast to the conventional technique, in which strength is improved by applying a heat treatment to the entirety of the frame14and slider20overall. Therefore, the costs required for performing the heat treatment can be reduced.

On the other hand, alternatively, when the frame14and the slider20each is formed of a metal material such as a general structural purpose carbon steel (SS material) that is used as a raw material without applying a heat treatment (e.g., a hardening treatment) thereto, in place of the aluminum alloy or the carbon fiber reinforced plastic discussed above, it is also possible to reduce costs, because it is unnecessary to perform a heat treatment such as hardening, as compared to the conventional case in which a hardened steel such as stainless steel is used.

The rigidity of the materials are substantially equivalent, whether a hardened steel, such as stainless steel capable of being hardened, is used, or a non-hardened steel, such as a general structural purpose carbon steel for which heat treatment is unnecessary, is used. Therefore, since heat treatment is unnecessary, when a non-hardened steel is used in place of hardened steel for the frame14in an actuator having a long stroke, i.e., in which the displacement amount of the slider20is large in the axial direction and wherein the length of the frame14in the axial direction is long, it is possible to reduce costs while maintaining rigidity and strength which are substantially equivalent to that of hardened steel.

The coefficient of linear expansion, which indicates a temperature dependent rate of strain, is also substantially equivalent between hardened steel (for example, stainless steel) and non-hardened steel (for example, general structural purpose carbon steel). Therefore, the respective rates of strain are substantially identical, when the first and second guide rails42a,42band86a,86bformed from hardened steel, and the frame14and the slider20formed from non-hardened steel, are subjected to changes in temperature.

As a result, change in the clearance between the first guide rails42a,42band the second guide rails86a,86bof the guide mechanism22can be suppressed, and hence the clearance is maintained to be substantially constant. Therefore, it is possible to smoothly displace the slider20in the axial direction.

FIG. 7shows a modified embodiment of the actuator according to the first embodiment. In the following description, the same constitutive components as those of the actuator10according to the first embodiment described above are designated by the same reference numerals and detailed explanation thereof shall be omitted.

In the actuator150according to this modified embodiment, second ball-rolling grooves154a,154b, which have a substantially circular arc-shaped cross section for allowing the balls89to roll therein, are formed on both side surfaces of a slider152opposed to the first guide rails42a,42b, which are installed in the first long grooves40a,40bof the frame14. In other words, the second ball-rolling grooves154a,154b, which extend in the axial direction, are directly machined and formed in both side surfaces of the slider152.

The second ball-rolling grooves154a,154bare formed as a pair at positions opposed to the first ball-rolling grooves90of the first guide rails42a,42b. The balls89roll between the first ball-rolling grooves90and the second ball-rolling grooves154a,154b. In this arrangement, it is preferable for the slider152to be formed from a hardened steel (for example, stainless steel), which is subjected to a hardening treatment, whereas the frame14is formed from a lightweight material or a light alloy material such as aluminum alloys, a lightweight high strength resin such as carbon fiber reinforced plastics, or a non-hardened steel such as a general structural purpose carbon steel.

That is, when the pair of second ball-rolling grooves154a,154bare directly formed on both side surfaces of the slider152, it is possible to shorten time required for installing the second guide rails86a,86bto the slider20, as compared to the case when the slider20and the second guide rails86a,86bare formed as separate members, as in the actuator10according to the first embodiment.

Even when the frame14is formed from a non-hardened steel, such as a general purpose carbon steel, when the frame14and the slider152are deformed respectively due to temperature change, the rate of strain is substantially identical because the slider152is formed from a hardened steel having substantially the same coefficient of linear expansion as that of non-hardened steel.

As a result, when a temperature change arises in the environment of use of the actuator150, a substantially constant clearance is maintained without change between the first ball-rolling grooves90and the second ball-rolling grooves154a,154bof the slider152. Therefore, the slider152can be smoothly displaced in the axial direction.

Next, an actuator200according to a second embodiment is shown inFIGS. 8 to 11. In the following description, the same constitutive components of the actuator10according to the first embodiment described above are designated using the same reference numerals, and detailed explanation thereof shall be omitted.

The actuator200according to the second embodiment differs from the actuator10according to the first embodiment in that a driven unit202, including the driven pulley54, is provided with a tension-adjusting mechanism206. The tension-adjusting mechanism206is capable of automatically adjusting the tension of the belt member56, so that the tension thereof maintains a desired constant tension by the aid of a coil spring (spring member)204.

A single elongate frame15may be provided for the actuator200, in place of the first and second housings24,26, in the same manner as in the actuator10of the first embodiment shown inFIG. 5. Accordingly, it is unnecessary to provide the first and second housings24,26, and therefore, it is possible to reduce the cost and the number of parts that make up the actuator200.

The tension-adjusting mechanism206of the actuator200comprises a retaining bracket208, which is fixed to an inner wall surface207of the second housing26, a pulley holder210retained by the retaining bracket208and which rotatably supports the driven pulley54, and a coil spring204which is interposed between the retaining bracket208and the pulley holder210.

The retaining bracket208may be formed, for example, by pressing (press working) a thin plate member composed of a metal material. The retaining bracket208is fixed by bolts214and attachment flanges212which are formed along the inner wall surface207and the bottom surface of the second housing26. As shown inFIG. 9, the retaining bracket208is formed with a projection216protruding toward the driven pulley54having a substantially U-shaped cross section. A columnar spring guide218, which is fixed to the inner wall surface207of the second housing26, is arranged within the projection216. The end surface of the spring guide218abuts againsts the inner wall surface of the projection216.

As shown inFIG. 10, the pulley holder210has a substantially U-shaped cross section formed, for example, by press working a thin plate member composed of a metal material. The spring guide218of the retaining bracket208is inserted into one end thereof via an insertion hole220. A pair of bearing holes222a,222bare formed at the other open end of the pulley holder210, in a direction substantially perpendicular to the axis of the spring guide218. Bearings224a,224bare installed into the bearing holes222a,222brespectively, and a columnar pulley shaft226is inserted into the bearings224a,224bso that the driven pulley54is retained by the pulley shaft226. Accordingly, the driven pulley54is supported on the other end side of the pulley holder210. In this arrangement, the driven pulley54is retained by the pulley holder210via the pair of bearings224a,224bthrough which the pulley shaft226is rotatably supported.

The coil spring204is interposed in a predetermined compressed state between the bottom-equipped one end of the pulley holder210and the inner wall surface of the projection216. The coil spring204is arranged while leaving a certain clearance between the inner wall surface of the projection216and the outer circumferential surface of the spring guide218. The coil spring204continuously urges the pulley holder210in a direction toward the inner wall surface207of the second housing26(in the direction of the arrow X1). A plate-shaped plate spring may be used, for example, in place of the coil spring204. That is, it is acceptable to use any other repulsive member, so long as it provides a sufficient repulsive force for urging the pulley holder210in the direction toward the inner wall surface207of the second housing26(in the direction of the arrow X1).

On the other hand, as shown inFIGS. 9 and 11, a wide-width section228, which extends in a widthwise direction substantially perpendicular to the axis of the frame14, is formed underneath the driven pulley54at the other end of the pulley holder210. Bent sections230, which are bent toward the center of the pulley holder210, are formed at both ends of the wide-width section228(seeFIG. 11). The pair of bent sections230, which have a curved shape, engage with the first ball-rolling grooves90of the first guide rails42a,42brespectively.

Specifically, the outer wall surface of the bent section230has a substantially circular arc-shaped cross section, wherein the outer wall surface of the bent section230corresponds to the cross-sectional shape of the first ball-rolling groove90, which comprises a circular arc-shaped recess. Therefore, the bent section230engages satisfactorily with the first ball-rolling groove90.

That is, the pulley holder210engages with the first guide rails42a,42binstalled in the frame14by the aid of the wide-width section228. Therefore, lateral displacement of the pulley holder210is prevented in a direction substantially perpendicular to the axis of the frame14. Accordingly, the pulley holder210is held in a state such that the pulley holder210is displaceable only in the axial direction (in the directions of the arrows X1, X2) of the frame14(i.e., along the first guide rails42a,42band the spring guide218) in accordance with the repulsive force of the coil spring204.

As described above, the pulley holder210, which rotatably retains the driven pulley54, is provided displaceably in only the axial direction (in the directions of the arrows X1, X2), thereby serving as the tension-adjusting mechanism206of the actuator200. Further, the driven pulley54is continuously urged in the direction away from the driving pulley48(in the direction of the arrow X1) due to the coil spring204interposed between the pulley holder210and the retaining bracket208fixed to the second housing26.

When the repulsive force (spring constant) of the coil spring204is set beforehand, so that the belt member56is placed under tension by aid of the coil spring204, the driven pulley54is slightly displaced in a direction away from the driving pulley48by the repulsive force. Thus, the tension of the belt member56is automatically adjusted to maintain a preset optimum value, even when the tension of the belt member56could be lowered by other factors, for example, due to elongation of the belt member56.

As a result, complicated maintenance operations, which hitherto have been performed by an operator for adjusting tension of the belt member56, such as visually observing the belt member56or measuring the tension of the belt member56depending on the situation of use of the belt member56, can be dispensed with.

Further, when the retaining bracket208and pulley holder210, which constitute the tension-adjusting mechanism206, are manufactured by pressing a thin plate member composed of, for example, a metal material, then the tension-adjusting mechanism206can be produced inexpensively, thereby reducing production costs.

While the invention has been particularly shown and described with reference to preferred embodiments, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.