Linear Actuator

Abstract: A linear actuator (10) has a cylinder body (12) having a slot (26a) defined therein, a slide table (14), a joint (24) connected substantially perpendicularly to a lower surface of the slide table (14), a pair of pistons (42a, 42b) slidably disposed in a through hole (32) defined in the cylinder body (12) and defining respective cylinder chambers in the through hole, for displacing the joint (24) in response to a fluid under pressure supplied to one of the cylinder chambers, a guide (56) projecting from a lower surface of the slide table (14), a pair of spaced guide blocks (18a, 18b) projecting from an upper surface of the cylinder body (12), and a plurality of balls (68) rollingly interposed between the guide (56) and the guide blocks (18a, 18b).

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a linear actuator according to the preamble of claim 1. Description of the Related Art: Linear actuators have heretofore been used as means for conveying workpieces or the like. Linear actuators are capable of linearly reciprocally moving a movable table along a cylinder body for thereby conveying a workpiece placed on the movable table. A linear actuator according to the preamble of claim 1 is known from US patent 4 991 494. Another known linear actuator is disclosed in Japanese laid-open utility model publication JP 5-42716 U, for example. FIGS. 6A and 6B of the accompanying drawings illustrate the disclosed linear actuator in the form of a fluid pressure cylinder assembly. As shown in FIGS. 6A and 6B, the fluid pressure cylinder assembly. generally designated by the reference numeral 1, comprises a cylinder body 2, a guide rail 3 projecting upwardly from and extending longitudinally on an upper surface of the cylinder body 2, and a slide table 4 mounted on the guide rail 3 for sliding displacement therealong in response to displacement of a piston disposed in a cylinder chamber which is defined in the cylinder body 2. The slide table 4 has a ball circulation hole (not shown) defined longitudinally therein and accommodating a plurality of balls for rolling movement therein. The slide table 4 also has a plurality of screw holes 5a ∼ 5d that are defined in an upper surface thereof for attachment of a workpiece to be conveyed by the fluid pressure cylinder assembly 1. The cylinder body 2 has a pair of attachment holes 6a, 6b defined in respective diagonally opposite corners thereof for installing the cylinder body 2 on another member (not shown). The cylinder body 2 has a transverse width L represented by L ≃ L 1 + (L 2 × 2) where L 1 is the width of the guide rail 3 and L 2 is the diameter of each of the attachment holes 6a, 6b. Therefore, the transverse width L is substantially equal to the sum of the width L 1 of the guide rail 3 and the diameters L 2 of the attachment holes 6a, 6b. The width L 1 of the guide rail 3 cannot be reduced because the rigidity of the slide table 4 would be lowered if width L 1 were reduced. As a result, the transverse width L is required to be substantially equal to the sum of the width L 1 of the guide rail 3 and the diameters L 2 of the attachment holes 6a, 6b so that the cylinder body 2 maintains a desired level of rigidity. Inasmuch as the transverse width L of the cylinder body 2 cannot be reduced because of the required width L 1 of the guide rail 3, the fluid pressure cylinder assembly 1 cannot be reduced in size and weight. A process of machining a slide table blank into the slide table 4 is complex because the ball circulation hole needs to be defined longitudinally in the slide table blank and the screw holes 5a - 5d need to be defined in the slide table in a direction different from the direction of the ball circuit hole. Document EP 0 536 799 A discloses a rodless cylinder having a conventional sealing member disposed centrally along the main body. The slide table comprises downwardly extending load transmitting means received in respective grooves on the upper face of the cylinder body and sliding along guide rails provided in these growes. The slide table and the pistons which reciprocally move along the cylinder body, are united with each other by way of a coupling part which projects through a slit formed in a longitudinal direction of the cylinder body. The grooves receiving the load transmitting means of the slide table are provided on both sides parallel to the slit. While preventing that upon the application of a lateral load the slit is narrowed and the piston is suddenly stopped, this is a rather complicated structure. SUMMARY OF THE INVENTION It is a general object of the present invention to provide a linear actuator which is reduced in size and weight through a reduction in the transverse width of a cylinder body without causing a reduction in the accuracy of linear movement of a slide table. According to the invention there is provided a linear actuator comprising the features of claim 1. Advantageous features of the invention are evident from the dependent claims. According to the present invention the linear actuator includes a slide table that can be machined with ease. The slide table further can be replaced with a variety of different slide tables. The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a linear actuator according to the present invention; FIG. 2 is an exploded perspective view of the linear actuator shown in FIG. 1; FIG. 3 is cross-sectional view taken along line III - III of FIG. 1; FIG. 4 is a cross-sectional view taken along line IV -IV of FIG. 3; FIG. 5 is a cross-sectional view taken along line V - V of FIG. 3; FIG. 6A is a plan view of a conventional fluid pressure cylinder assembly as a linear actuator; and FIG. 6B is a side elevational view of the conventional fluid pressure cylinder assembly shown in FIG. 6A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows in perspective a linear actuator 10 according to the present invention. The linear actuator 10 basically comprises a cylinder body 12, a slide table 14 mounted on the cylinder body 12 for linear reciprocating movement in longitudinal directions of the cylinder body 12, and a pair of slide mechanisms 16 (see FIG. 2) for reciprocally moving the slide table 14 smoothly in the longitudinal directions of the cylinder body 12. As shown in FIG. 2, the cylinder body 12 has a pair of integral guide blocks (second guide means) 18a, 18b disposed on an upper surface thereof in transversely spaced confronting relation to each other. The guide blocks 18a, 18b have respective ball circulation holes 20a, 20b and respective ball rolling grooves 22a, 22b defined therein in the longitudinal direction of the cylinder body 12 in spaced relation to the ball circulation holes 20a, 20b. The cylinder body 12 has a pair of substantially elliptical slots 26a, 26b (see FIG. 3) defined substantially centrally in respective upper and lower surfaces thereof for allowing a substantially cylindrical joint 24 (described later on) to be displaced freely therein. The cylinder body 12 also has a pair of attachment holes 30a, 30b defined in its upper surface at respective steps 28 in diagonally opposite corners thereof for installing the cylinder body 2 on another member (not shown) with bolts (not shown) inserted through the attachment holes 30a, 30b. The cylinder body 12 further has a through hole 32 (see FIGS. 2 and 3) defined longitudinally therein and communicating with the slots 26a, 26b. The opposite ends of the through hole 32 are closed by respective end caps 36a, 36b with respective seal rings 34 mounted thereon. The end caps 36a, 36b are hermetically retained in the opposite ends of the through hole 32 by respective retaining rings 38. The through hole 32 accommodates therein a pair of pistons 42a, 42b disposed for sliding displacement along an inner wall surface of the through hole 32. Seal rings 40 are mounted respectively on outer circumferential surfaces of the pistons 42a, 42b. The end caps 36a, 36b and the piston 42a, 42b jointly define respective cylinder chambers 44a, 44b in the through hole 32. The cylinder chambers 44a, 44b are held in communication with fluid outlet/inlet ports 48a, 48b (see FIGS. 1 and 5) defined in one side of the cylinder body 12, through respective fixed restrictions 46. The substantially cylindrical joint 24 which extends substantially vertically is positioned between the pistons 42a, 42b, and has an externally threaded upper end threaded in a threaded hole 50 (see FIGS. 2 and 3) defined substantially centrally in the slide table 14. The joint 24 includes a spigot portion 52 immediately below the externally threaded upper end. The spigot portion 52 is securely fitted in an annular step which is defined in the slide table 14 beneath the threaded hole 50, so that the joint 24 is firmly fixed to the slide table 14. When a fluid under pressure is introduced through one of the fluid outlet/inlet ports 48a, 48b into the corresponding one of the cylinder chambers 44a, 44b, the corresponding one of the pistons 42a, 42b is displaced into pressing engagement with the joint 24, which then displaces the slide table 14 in the longitudinal axial direction indicated by the arrow X, i.e., the arrow X 1 or X 2 (see FIGS. 1 and 3). As shown in FIGS. 1 and 2, the slide table 14 has a plurality of attachment holes 54a ∼ 54d defined therein at respective four corners thereof. The slide table 14 also has a guide (first guide means) 56 integrally projecting upwardly from and extending longitudinally on a lower surface of the slide table 14. The guide 56 has a pair of ball rolling grooves 58a, 58b (see also FIG. 5) defined in respective transverse opposite sides thereof and extending in the longitudinal direction thereof. As shown in FIG. 2, the slide mechanisms 16 are positioned respectively on longitudinal opposite ends of the guide blocks 18a, 18b. Each of the slide mechanisms 16, which are identical in structure to each other, comprises two pairs of covers 62a, 62b and two pairs of scrapers 64a, 64b which are mounted on respective longitudinally opposite ends of the guide blocks 18a, 18b by screws 60. The ball circulation holes 20a, 20b defined in the respective guide blocks 18a, 18b extend in the longitudinal direction thereof, and the ball rolling grooves 22a, 22b defined in the respective guide blocks 18a, 18b extend along confronting inner wall surfaces thereof in the longitudinal direction thereof. The slide mechanism 16 also has two pairs of return guides 66 mounted respectively on the longitudinally opposite ends of the guide blocks 18a, 18b and interconnecting the ball circulation holes 20a, 20b and the ball rolling grooves 22a, 22b, and two sets of balls (rolling elements) 68 placed in the ball circulation holes 20a, 20b and the ball rolling grooves 22a, 22b for rolling movement therealong. The covers 62a, 62b have respective recesses 70b, 70a defined therein which interconnect the ball circulation holes 20a, 20b and the ball rolling grooves 22a, 22b. The ball circulation holes 20a, 20b, the ball rolling grooves 22a, 22b, the return guides 66, and the recesses 70b, 70a jointly serve as endless circulatory tracks for the balls 68 to rolling move therealong. Operation and advantages of the linear actuator 10 will be described below. A fluid supplied under pressure from a fluid pressure supply (not shown) is introduced into the fluid outlet/inlet port 48b by a directional control valve (not shown). At this time, the other fluid outlet/inlet port 48a is vented to the atmosphere by the directional control valve. The introduced fluid is supplied through the fixed restriction 46 connected to the fluid outlet/inlet port 48b into the cylinder chamber 44b, displacing the piston 42b in the direction indicated by the arrow X 1 . The piston 42b is displaced until an end thereof abuts against the joint 24 as indicated by the broken lines in FIG. 3. Continued displacement of the piston 42b displaces the joint 24 along the slots 26a, 26b in the direction indicated by the arrow X 1 . Therefore, the slide table 14 coupled to the joint 24 is displaced in unison with the joint 24 in the direction indicated by the arrow X 1 . The slide table 14 reaches an end of its stroke when the joint 24 engages respective inner end surfaces of the slots 26a, 26b. For displacing the slide table 14 in the opposite direction indicated by the arrow X 2 , a fluid under pressure is introduced into the fluid outlet/inlet port 48a by the directional control valve. The introduced fluid is supplied through the fixed restriction 46 connected to the fluid outlet/inlet port 48a into the cylinder chamber 44a, displacing the piston 42a in the direction indicated by the arrow X 2 . The piston 42a pushes the joint 24 along the slots 26a, 26b in the direction indicated by the arrow X 2 , thereby displacing the slide table 14 also in the direction indicated by the arrow X 2 . The slide table 14 reaches an opposite end of its stroke when the joint 24 engages respective opposite inner end surfaces of the slots 26a, 26b. As described above, the guide 56 integrally projects upwardly from and extends longitudinally on the lower surface of the slide table 14, and the guide blocks 18a, 18b which guide the guide 56 through the balls 68 for sliding movement in the longitudinal direction of the cylinder body 12 are integrally formed with the cylinder body 12. The attachment holes 30a, 30b can be defined in the cylinder body 12 at desired positions thereon without being affected by the transverse width H 1 (see FIG. 5) of the cylinder body 12, which is not the case with the conventional linear actuator shown in FIGS. 6A and 6B. Consequently, the cylinder body 12 of the linear actuator 10 according to the present invention can reduce its transverse width H (see FIG. 5), with the result that the linear actuator 10 can be reduced in size and weight. The attachment holes 54a ∼ 54d are oriented in one direction with respect to the slide table 14. Since the slide table 14 does not have various holes defined in different directions, the slide table 14 can be machined relatively easily from a slide table blank. The guide 56 which is guided by the guide blocks 18a, 18b simply projects downwardly from the lower surface of the guide table 14. Therefore, the slide table 14 can be replaced with a variety of different slide tables insofar as they have guides identical to the guide 56. Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.

Claims: A linear actuator comprising: a cylinder body (12) having a through hole (32) defined in an axial direction thereof, a slot (26a) defined in an upper surface thereof in communication with said through hole (32), and fluid outlet/inlet ports (48a, 48b); a slide table (14) movably mounted on said cylinder body (12) for movement in the axial direction thereof; a joint (24) connected substantially perpendicularly to a lower surface of said slide table (14) through said slot (26a), for movement in unison with said slide table (14); a guide (56) being a unitary body disposed centrally on a lower surface of said slide table (14) along a center axis thereof and extending in the axial direction of said cylinder body (12); a pair of guide blocks (18a, 18b) disposed on an upper surface of said cylinder body (12) and confronting each other in a direction transverse to the axial direction of said cylinder body (12); and a pluralitiy of rolling elements (68) interposed between said guide (56) and said guide blocks (18a, 18b) characterized in, that a pair of pistons (42a, 42b) is slidably disposed in said through hole (32) and defines a pair of cylinder chambers (44a, 44b) in said through hole (32) in communication with said fluid outlet/inlet ports (48a, 48b), respectively, said pistons (42a, 42b) being slidable in said through hole (32) to move said joint (24) and said slide table (14) in the axial direction of said cylinder body (12) in response to a fluid under pressure which is introduced into one of said cylinder chambers (44a, 44b) through one of said fluid outlet/inlet ports (48a, 48b) which communicates with said one of the cylinder chambers (44a, 44b), that said plurality of rolling elements (68) is provided for rolling movement along an endless circulatory track; and that said slide table (14) has a threaded hole defined substantially centrally therein and an annular step defined therein adjacent to said threaded hole, said joint (24) having an end threaded in said threaded hole and a spigot portion (52) fitted in said annular step. A linear actuator according to claim 1, wherein each of said guide blocks (18a, 18b) has a ball circulation hole (20a, 20b) defined longitudinally therein, a ball rolling groove (22a, 22b) defined in an inner wall surface thereof in spaced relation to said ball circulation hole (20a, 20b), said endless circulatory track including said ball circulation holes (20a, 20b) and said ball rolling grooves (22a, 22b). A linear actuator according to claim 1, wherein said guide (56) projects from the lower surface of said slide table (14) toward said cylinder body (12), and has a pair of ball rolling grooves (22a, 22b) extending longitudinally therein. A linear actuator according to claim 1, wherein said joint (24) is connected to said slide table (14) perpendicularly to the axial direction of said slide table (14).

Inventors: HOSONO MASAYUKI, TOSHIMORI YOSHIHIRO, HOSONO, MASAYUKI, TOSHIMORI, YOSHIHIRO, HOSONO, MASAYUKI, C/O SMC K. K. TSUKUBA, Toshimori, Yoshihiro, c/o SMC K. K. Tsukuba
Applicants: SMC KK, SMC KABUSHIKI KAISHA
Application year: 1995
Main classification: B23Q1
IPC codes: B23Q1, F15B15, B23Q5