RODLESS CYLINDER

Abstract: A rodless cylinder consisting of a cylinder (7), a piston (19) within the cylinder for reciprocal movement therein, a guide (1) along the outside of the cylinder, a drive block mechanism (49) constrained to move along the guide, a pulley (11) at each end of the cylinder and guide, a cable (29) extending from each end of the cylinder, around a respective pulley and secured to a respective end (47) of the drive block mechanism, a compressible resilient member (31) extending from each end of the piston, a sealing member (35) co-operable with a valve seat (37) located within a exit from each end of the cylinder such that when the piston approaches one end of the cylinder, the resilient member forces the sealing member into sealing contact with the valve seat so preventing egress of fluid from one end of the piston to the outside of the respective end of the cylinder. The pulleys, cables and cylinder are also completely enclosed so that only the top of the drive block is exposed to the outside environment.

Description: This invention relates to a fluid operated piston and cylinder arrangement which does not utilize a piston rod. These arrangements are known in the art as rodless cylinders. Rodless cylinders of the prior art comprise an elongated cylinder member containing a piston which is movable within the cylinder from one end to the other. This movement is responsive to the introduction of pressurized fluid into the cylindrical member. A flexible cable is secured to each end of the piston each cable passing through seals in the ends of the cylinders and around a pulley at each end of the cylinder with the outer ends of the cables being secured to opposite sides of a drive block. United States Patent No. 4,057,257 which issued on November 8, 1977 to Tol-O-Matic Inc. is representative of this type of prior art. Various types of guides are utilized for supporting the reciprocating drive block, these either resting upon the outer wall of the cylinder or being separate guides supported away from the cylinder. The cables which transfer the motion from the piston to the drive block must be kept under a slight tension so that during use the mechanism operates precisely with no slack occurring in either of the cables. The operation of a rodless cylinder is very rapid and there is little cushioning effect at the ends of the stroke with the result being that excessively large forces have to be contended with after the rapid acceleration of the cylinder from a stationary position. Large tension loads in the cables are therefore encountered which stretch the cables during use. The effects of such stretching cannot be tolerated and therefore an adjustment mechanism is required so that the cables can be periodically tensioned. Also, rodless cylinders are often located in a dirty environment which leads to premature wear of the guides which support the reciprocating drive block and also of the cables and pulleys. In DE-A-2404244, there is disclosed a cable cylinder comprising a cylinder, a piston, a guide, a drive block, a cable means, two pulleys, a damping chamber, a damping piston, a seal and a needle valve. In DE-B-2325882 there is disclosed a compressible resilient member and a sealing member co-operable with a valve seat surrounding an inlet/outlet means. In accordance with the present invention, there is provided in a rodless cylinder including a cylinder having first and second cylinder ends, a piston reciprocatably movable within the cylinder, a guide affixed to the cylinder, a drive block longitudinally movable along the guide, first and second pulleys each adjacent the respective first and second cylinder ends, a cable having a first portion secured to and extending from a first end of the piston, through a bore in the first cylinder end, around the first pulley and to the drive block, and having a second portion secured to and extending from a second end of the piston through a bore in the second cylinder end, around the second pulley, and to the drive block, means for inhibiting fluid flow from each end of the cylinder as the piston approaches an end thereof and a pressure sensitive relief valve at each end of the cylinder for automatically limiting the discharge of fluid from the cylinder to control fluid pressure within the cylinder at a preselected value to control deceleration of piston movement within the cylinder after fluid flow therefrom has been inhibited, characterised in that: the means for inhibiting fluid flow from each end of the cylinder comprises a valve seat adjacent the bore in the first and second cylinder ends, and sealing means carried by the cable and forced by a resilient member for sealing engagement with the valve seat when the piston approaches the respective first and second cylinder ends to prevent the fluid flow from the respective first and second ends of the piston, through the respective first and second bores in the respective first and second cylinder ends; and a cover passing around the rodless cylinder and having a top, a bottom, sides and ends, the top having a slot for permitting reciprocal movement of the drive block therein, an inwardly facing groove in the top of the cover and along each side of the slot, and a belt transversely extending into the grooves and longitudinally extending below a cover on the drive block, around the pulleys and below the cylinder to enclose the cylinder, the guide, the drive block, the pulleys, and the cable. The rodless cylinder may be one wherein an endwall portion of a bore within an end cap of the cylinder forms the valve seat. The valve seat may be formed at the intersection of concentric bore portions having differing dismeters. The rodless cylinder may be one wherein the resilient member extends from each end of the piston for a distance greater than the length of the piston, such that cushioned deceleration of the piston is obtained for a distance greater than the piston length. The rodless cylinder may be one wherein the guide is affixed to the cylinder and includes two spaced apart flanges having first and second parallel planar substantially horizontal surfaces and a third planar substantially vertical surface perpendicular to the first and the second planar surfaces, and wherein the drive block is longitudinally movable along the guide and has a plurality of first rollers for rolling engagement with the first surface, a plurality of second rollers for rolling engagement with the second surface and a plurality of third rollers for rolling engagement with the third surface, the first, second and third plurality of rollers cooperating with the first, second and third surfaces of the guide for limiting movement of the drive block in both a vertical direction and a direction transverse to the longitudinal movement of the drive block. The rodless cylinder may be one wherein the guide includes a channel-shaped support secured to the cylinder and defines the first, second and third planar surfaces. The rodless cylinder of the present invention may operate to provide smooth retardation of the piston. Where a relief valve is utilised at both ends of the cylinder, the degree of cushioning effect upon the piston can be limited. The shock forces in the cables are therefore substantially reduced so that, after the cables have been pretensioned, only occasional readjustment is required to keep the cables under acceptable working tension. The rodless cylinder is enclosed on both sides and the ends preferably by sheet or cast metal or plastic, and a wide groove is left along most of the length of the upper surface. Preferably, each side of this groove has a slotted guide and a flat belt is secured to the drive block and passes in both longitudinal directions through the slotted guide, around each pulley and below the cylinder. The unit may therefore be totally enclosed and can be used in a dirty environment. The rodless cylinder of this invention will now be described with reference to the attached drawings in which: FIGURE 1 is a side elevational view of an embodiment of the rodless cylinder of this invention showing part of the internal mechanism; FIGURE 2 is a top plan view of the rodless cylinder of Figure 1; FIGURE 3 is a side elevational view of the rodless cylinder of Figure 1; FIGURE 4 is a top plan view of the outside of the rodless cylinder of Figure 1; FIGURE 5 is a side elevational view of the outside of the rodless cylinder of Figure 1; FIGURE 6 is a side elevational view of the outside of the rodless cylinder of Figure 1; FIGURE 7 is an exploded view of the rodless cylinder of FIGURE 1, and FIGURE 8 is a perspective view, partly in section, of the rodless cylinder of Figure 1. Referring to the drawings, the rodless cylinder of this invention consists of a channel shaped guide support 1 having tracks or rails 3 secured to the upper ends of the flanges of the channel by countersunk tap bolts or other convenient means (not shown). The channel is bolted by bolts 5 to a cylinder 7 through cylinder ends 6. A pulley 11 is rotatably supported at an extension 9 from each end 6 by a shaft 13 held in conventional bearings 15 (not detailed). Set screw 17 or a roll pin or other securing means is used to attach each pulley to its respective shaft. A piston 19 is within cylinder 7 and includes conventional piston ring grooves and piston rings shown generally at 21. From each end of the piston 19 there are drilled concentric bores 23 and 25. Into bore 23, which is threaded, there is screwed an end connection 27 to which a cable 29 is firmly secured. The bore 25 includes a compressible resilient member such as a coil spring 3l, which acts between the shoulder 33 at the juncture of bores 23 and 25, and an annular disk sealing member 35 which can co-operate with a valve seat 31 in the end cap 6, or with a bore 8 in the end cap and then the valve seat 31, or solely with bore 39 in the end cap. The cable 29 passes through bore 39 and a seal 41 in the end cap 6. The cable 29 passes around pulley 11 and is secured to a drive block system which consists of two integral side end blocks 47 and a centre block 49. The centre block 49 can be dispensed with if required. A top plate 45 is bolted to the blocks. To each end block 47 are secured cam rollers 51, 53 and 55 which preferably utilize needle bearings, to support the drive block assembly for constrained reciprocal movement along the rails 3. Rollers 51 and 55 are preferably eccentrically mounted so that adjustments towards and away from the guides can be made. End blocks 47 have a passage therethrough to accept threaded ends 59 on cables 29 which have nuts 61 to provide tensioning adjustment for the cables. Belleville washers 60 are provided below the nuts 61 to accommodate minor changes due to cable stretching. A sheet metal or plastic cover 63 passes around the rodless cylinder ending at each side of the top in a strengthened outer top edge 65 which could conveniently, for example, be an extruded section. This part 65 has inwardly extending grooves 67 with plastic edge seals 68 therein and a flexible plastic or fabric belt 69 extends around both of the pulleys 11, below cylinder 7, and between seals 68, both ends joining and being secured below top plate 45 upon centre block 49. When a centre block is not utilized the belt can be joined below the cylinder by a known type of belt connector, securement of the belt still occurring with the top plate. End caps 71 which can conveniently be cast are secured to each end of the cover 63 by screws 73, and, after the addition of small upper end scraper plates 75 between the ends of grooves 67, the internal mechanism of the rodless cylinder will be completely enclosed. Support brackets 77 are secured by bolts 79 to extensions 9. During operation of the rodless cylinder, pressurized fluid enters through one of the ports 12, 14, a pipe 16 leading fluid from port 12 to the left hand end cap, passes through bore 39 and forces the piston 19 along the cylinder 7 so moving the drive block mechanism and the belt 69. When the piston has moved a set distance along the cylinder, annular disk seal 35 contacts at least seat 37 and prevents the exit of fluid from the opposite end of the piston. Note that when one port functions as an inlet the other functions as an exhaust. The resilient member 31 is preferably of a length such that fluid is prevented from leaving the cylinder at a location wherein the fluid cushion will be longer than the piston length. Pressure of trapped fluid then begins to build up on the opposite side of the piston and provides a cushion of fluid which smoothly decelerates the piston so preventing excessive shock which would occur upon rapid deceleration. The pressure of the cushion of fluid is permitted to rise to a predetermined level before it is allowed to escape via a pressure relief valve 81. The pressure relief valve 81 is preferably adjustable and also preferably has a leakdown which may be adjustable. It will thus be seen that a rodless cylinder has been disclosed which is constructed to lessen excessive shock loads upon the cables connecting the piston to the drive block mechanism so that stretching of the cables is minimized and adjustment is rarely required to tension the cables. The rodless clylinder also has a high strength guide channel which is equipped with rigid steel rails and needle bearing cam rollers which provides a degree of drive block load control which is not presently available in this art. The rodless cylinder is also completely enclosed so that it can be used in a dirty environment.

Claims: In a rodless cylinder including a cylinder(7) having first and second cylinder ends(6), a piston(19) reciprocatably movable within the cylinder(7), a guide(1) affixed to the cylinder(7), a drive block(47) longitudinally movable along the guide(1), first and second pulleys(11) each adjacent the respective first and second cylinder ends(6), a cable(29) having a first portion secured to and extending from a first end of the piston(19), through a bore(39) in the first cylinder end, around the first pulley(11) and to the drive block(47), and having a second portion secured to and extending from a second end(6) of the piston(19) through a bore(39) in the second cylinder end, around the second pulley(11), and to the drive block(47), means(31,35,37) for inhibiting fluid flow from each end of the cylinder(7) as the piston(19) approaches an end thereof and a pressure sensitive relief valve(81) at each end of the cylinder(7) for automatically limiting the discharge of fluid from the cylinder(7) to control fluid pressure within the cylinder(7) at a preselected value to control deceleration of piston(19) movement within the cylinder(7) after fluid flow therefrom has been inhibited, characterized in that: the means for inhibiting fluid flow from each end of the cylinder(9) comprises a valve seat(37) adjacent the bore(39) in the first and second cylinder ends(6), and sealing means(35) carried by the cable(29) and forced by a resilient member(31) for sealing engagement with the valve seat(37) when the piston(19) approaches the respective first and second cylinder ends(6) to prevent the fluid flow from the respective first and second ends of the piston(19), through the respective first and second bores(39) in the respective first and second cylinder ends(6); and a cover(63) passing around the rodless cylinder and having a top(65), a bottom, sides and ends, the top(65) having a slot for permitting reciprocal movement of the drive block(47) therein, an inwardly facing groove(67) in the top(65) of the cover(63) and along each side of the slot, and a belt(69) transversely extending into the grooves(67) and longitudinally extending below a cover(45) on the drive block(47), around the pulleys(11) and below the cylinder(7) to enclose the cylinder(7), the guide(1), the drive block(47), the pulleys(11), and the cable(29). The rodless cylinder as in claim 1 wherein an endwall portion of a bore(8) within an end cap(6) of the cylinder(7) forms the valve seat(37). The rodless cylinder as in claim 2, wherein the valve seat(37) is formed at the intersection of concentric bore portions (8,39) having differing diameters. The rodless cylinder as in claim 1, wherein the resilient member (31) extends from each end of the piston(19) for a distance greater than the length of the piston(19), such that cushioned deceleration of the piston(19) is obtained for a distance greater than the piston length. The rodless cylinder as in claim 1, wherein said guide(1) is affixed to the cylinder(7) and includes two spaced apart flanges having first and second parallel planar substantially horizontal surfaces and a third planar substantially vertical surface perpendicular to the first and second planar surfaces; and wherein the drive block (47) is longitudinally movable along the guide(1) and has a plurality of first rollers (53) for rolling engagement with the first surface, a plurality of second rollers(53) for rolling engagement with the second surface and a plurality of third rollers(53) for rolling engagement with the third surface, the first, second and third plurality of rollers(53) cooperating with the first, second and third surfaces of the guide(1) for limiting movement of the drive block(47) in both a vertical direction and a direction transverse to the longitudinal movement of the drive block(47). The rodless cylinder as defined in claim 5, wherein the guide(1) includes a channel-shaped support secured to the cylinder(7) and defines the first, second and third planar surfaces.

Inventors: DRY, ALAN GEORGE WILLIAM
Applicants: ASCOLECTRIC LIMITED
Application year: 1986
Main classification: F15B15
IPC codes: F15B15