LINEAR POWER UNIT

Abstract: In linear power units having a housing (1) and a slide (2) linearly movable relative to the housing, to relieve the slide of transverse forces, lateral forces etc., in order to reduce wear and eli­ minate jamming, is at least one guide rail (6) arranged parallel to the direction of action of the linear power unit, the housing (1) is fixedly connected to the guide rail (6), and the slide (2) is hingedly connected in a manner to transmit push and pull forces only, to a guide device (7) guided on the guide rail (6).

Description: The invention relates to a linear power unit according to the preamble of claim 1. The term "linear power unit" as used herein relates to power units for producing linear movements, such as piston-rodless hydraulic, pneumatic or electrically powered cylinders. These linear power units all have some type of a normally stationary housing or the like and some type of a normally movable runner or slide. Other movement patterns may also exist. One problem inherent in prior art linear power units is that the power-transmitting attachment of the slide is subjected not only to the forces of displacement of the power unit but also to other forces, e.g. lateral forces and other moments of load. The slide and its attachment as well as the means transmitting the linear propelling force should thus be dimensioned for a strength sufficient not only for the intended push and pull forces but also for said additional loads and stresses. This normally means an increased width and thickness of the material. However, since in linear power units of the type here concerned, the housing cannot normally be completely closed but must have a slot of at least the above-mentioned increased width of the material and a length corresponding to the stroke length or exceeding it, an increase of the slot width means reduced rigidity of the housing. It is previously known, e.g. through the company Mortonair, Fig. 1, in a linear power unit in the form of a piston-rodless pneumatic cylinder to provide the cylinder with external guide grooves on opposite sides thereof for guiding a guide which is mechanically and rigidly connected to the slide. Since the cylinder has a longitudinal slot, i.e. in principle U-shaped cross-section, high pressures in the cylinder may urge the U-legs slightly apart, whereby the guide will jam. Such jamming most often results both in reduced mobility and in increased wear of the guide grooves, with a consequential increase of the play and impaired accuracy. The risk of jamming and wear becomes still greater if lateral forces acting on the guide also occur. Moreover, restoring worn guide grooves involves high costs since the cylinder part must then normally be replaced in its entirety. A further drawback obviously is that the guide grooves are exposed to deposits of dust etc., which may also increase wear. Further, the guide can only be applied on the same side of the cylinder as the slot. EP-A-0157892 discloses a linear power unit of the type defined above and in the preamble of the main claim. Thus, the guide rail and the housing of this known linear power unit are formed as a monobloc, which means that the position of the guide rail relative to the slide is predetermined, this limiting the possibilies of mounting and using the linear power unit. An object of the present invention is to substantially reduce or eliminate the above-mentioned drawbacks of known linear power units and especially to allow different mounting positions of the guide rail relative to the slide. According to the invention, this object is achieved by a power unit having the features recited in the characterizing clause of claim 1. Further developments and special, preferred embodiments are stated in the sub-claims. The invention will now be described in more detail hereinbelow with reference to the accompanying drawings, in which: Fig 1 is a schematic view showing a known embodiment; Fig 2 is a part-sectional axial view of a guide arrangement according to the invention in a piston and cylinder assembly with no piston rod; and Fig. 3 shows a double guide arrangement similar to that of Fig. 2. Fig. 1 shows a known embodiment of a piston-rodless pressure-medium cylinder in the cylinder chamber of which a piston is linearly movable back and forth. Such linear piston-cylinder assemblies are available, e.g. under the trademarks Origa, Martonair and others. On its outside, the cylinder housing 1 has four grooves parallel to the longitudinal axis of the cylinder. The two upper grooves in Fig. 1 cooperate with a longitudinally displaceable guide device or slide 2 located above the cylinder. The slide 2 is rigidly connected to the piston (not shown) in the cylinder by means of a piston attachment extending through a longitudinal slot in the top part of the cylinder wall 1. Arrangements of the type shown in Fig. 1 suffer from the drawback that the "cylinder legs" resulting from the slitting of the cylinder in its longitudinal direction tend, at high pressures in the interior of the cylinder, to move apart in the direction of the arrows P, with the consequences indicated above. Fig. 2 shows an embodiment according to the invention. A pressure-medium cylinder 1 has an internal piston (not shown) connected to a piston attachment (slide) generally designated 2, which is movable along the cylinder. The cylinder housing, having a generally square cross-section and rounded corners, is provided on three of its four sides with a respective pair of longitudinal grooves 3a, 3b, 3c. The central planes (in the longitudinal direction of the cylinder) of the grooves are at angles to each other suitably ranging between 20° and 160°. Two strips 4, 4′ each having a pair of profiled projections 5 are connected in a form-fitting and power-transmitting manner to the left-hand pair of grooves of the cylinder housing in Fig. 2, by insertion of the right-hand projections 5 of the strips 4, 4′ in a respective one of the grooves 3a, whereupon screws have been passed through bores (not shown in Fig. 2) provided in one of the strips parallel to the plane of the drawing, screwed in a respective threaded hole provided in the other strip 4 in the extension of said bore, and tightened. Since the cylinder, piston, slide, cylinder grooves, strips and profiled projections are prior art, these components will not be described in more detail here. However, before the above-mentioned tightening is effected, a guide rail 6, provided with a similar pair of grooves 3d as the cylinder housing 1, has been applied, in accordance with the inventive concept, to the left of the strips 4, 4′ to the left-hand projections 5 thereof. The dimensions of the guide rail 6 can be selected with regard both to the expected loads and stresses exerted by the linear power unit 1, 2 and to the loads to be displaced or supported/taken up the linear power unit. The guide rail 6 cooperates with a guide device 7 which, by lower and upper guide members 8a and 8b, respectively, is displaceable on the guide rail. The lower guide member or members 8a in Fig. 2 are each suitably provided with a position-adjusting device 9, here a set screw 9, for adjusting the play/clearance between the guide rail 6 and the guide members 8a, 8b of the guide device 7. The guide members are suitably exchangeable so that they can be replaced at a low cost when worn. At its upper right-hand portion, the guide device 7 is connected to the slide (piston attachment) 2 by means of a coupling 10. In connection with the present invention, the coupling 10 should have the property of only transmitting push and pull forces between the piston attachment and the guide device, whereas not lateral forces, transverse forces, torque or other similar possibly deforming stresses. Suitable such couplings are known in various designs and, within the scope of the present invention, are selected by the expert in view of the above-mentioned and other desirable properties on the basis of normal professional routines and knowledge. By means of such a coupling, the cylinder will be relieved of a substantial part of the loads or stresses otherwise applied to it or, in other words, the cylinder 1 is stiffened by the guide rail 6 and the guide device 7 in such a manner that the stresses are instead taken up by the guide rail mounted together with the guide device (slide) on the cylinder housing. This means that it is now possible, thanks to the invention, to choose a power unit, i.e. in this case the cylinder 1, only on the basis of the required push and pull forces whilst, when earlier choosing the power unit, it was necessary to pay regard also to other stresses, which has always resulted in the use of cylinders of increased diameters and, thus, higher costs and also higher consumption of pressure medium. A smaller cylinder stabilized by means of a guide rail according to the invention will however almost always be less expensive than an equally stable, larger cylinder. As appears from Fig. 3, a cylinder according to Fig. 2 can also be provided with two guide rails 6, 6′ or, in an analogous manner, though not shown in the drawing, even with three guide rails. The different guide rails may each have one guide device 7, 7′, as shown in Fig. 3, or all cooperate with a single guide device engaging one or more of the three guide rails. Further, the third guide rail may have no guide device and, for instance, then only serves as a rail for additionally stiffening the housing 1 of the power unit. Further, the guide device may in a known manner embrace one or more guide rails and, optionally together with bellows or the like, protect the slide surfaces from deposits, contaminants, such as dust, splashing etc., thus increasing the life of the slide surfaces. Of course, the guide rails 6 can also be connected to the cylinder housing 1 other than by means of the above-mentioned strips 4, e.g. to the end walls of the cylinder. It is readily understood that the guide devices will not jam on the guide rails by the U-legs of the cylinders being slightly urged apart by the forces indicated by the arrows P in Fig. 1, since any such parting movement will be executed by both the guide rail and the guide device. As further appears from Fig. 2, the guide rail 6 may be provided with a pressure-medium channel 11. At one end, the channel 11 can be connected to one cylinder chamber located at said end, which means that the connection of both cylinder chambers to a pressure-medium source can be provided at one and the same cylinder end. Further, the guide rail 6 may be provided with additional channels 12, 12′ for connecting e.g. hydraulic or pneumatic position-sensing devices for selected positions of displacement. Such a position-sensing device may consist e.g. of a valve and a cam provided in said selected position of displacement. In this case, the valve is fixed to the guide device 7. When the guide device with the valve passes the cam, the valve is opened or closed, whereby the supply or discharge of pressure medium can be opened or closed, respectively, for connection, via said channels 12, 12′, to means operated by the position-sensing device. Of course, it is also possible in the channels 12, 12′ to insert insulating conductors and connect them to corresponding electric sensing means. When using more than one guide rail 6, 6′ (Fig. 3), only one guide rail 6 can be provided with said channels 11, 12, 12′. Of course, it is also possible to use the alternative of arranging the pressure-medium channel 11 in one guide rail 6 and the channels 12, 12′ in the other guide rail 6′.

Claims: 1. A linear power unit comprising a cylinder housing (1); a piston disposed in said housing an linearly movable relative to said housing for producing push and pull forces in the direction of relative movement; a slide (2) disposed externally of said housing and connected to said piston through a slot in said housing for movement with said piston relative to said housing; at least one linear guide rail (6) provided on said housing and extending in said direction of relative movement; a guide device (7, 7′) mounted on the guide rail and guided thereby in said direction of relative movement; and a coupling (10, 10′) transmitting push and pull forces between the slide (2) and the guide device (7, 7′) whereas no lateral forces, transverse forces, torque or other possibly deforming stresses, characterised in that the housing (1) and the guide rail (6) are provided with pairs of profiled grooves (3a, 3b, 3c, 3d), and that the housing (1) and the guide rail (6) are fixable to each other by means of two strips (4, 4′) having profiled projections (5) corresponding to said grooves (3a, 3b, 3c, 3d) and engaging in a respective groove (3a, 3b, 3c, 3d) . 2. A power unit as claimed in claim 1, characterised in that the profiled grooves (3a, 3b, 3c, 3d) are obliquely directed at an angle of 20-160° to each other, and that said strips (4, 4′) are tightenable in a direction towards each other. 3. A power unit as claimed in claim 1 or 2, characterised in that the guide rail (6) has a central longitudinal channel (11), e.g. for connecting pressure medium to one cylinder chamber of a hydraulic or pneumatic cylinder. 4. A power unit as claimed in claim 3, characterised in that the guide rail (6) has one or more additional channels (12, 12′), e.g. for connecting a hydraulic or pneumatic sensing device for selected positions of displacement. 5. A power unit as claimed in any one of the preceding claims, characterised in that the guide device (7, 7′) is provided with exchangeable guide bearings (8a, 8b) . 6. A power unit as claimed in claim 5, characterised in that the position of at least one guide bearing (8a) is adjustable for adjustment of clearance or play. 7. A power unit as claimed in any one of the preceding claims, characterised in that the housing (1) has a plurality of obliquely directed pairs of grooves (3a, 3b, 3c) or other attachments for fixing a plurality of guide rails (6) (Fig. 3). 8. A power unit as claimed in any one of the preceding claims, characterised in that the guide device (7, 7′) embraces one or more of the associated guide rails (6, 6′) .

Inventors: AMAN, MARTIN
Applicants: LINJAER TRANSPORTTEKNIK I STOCKHOLM AB
Application year: 1988
Main classification: F15B15
IPC codes: F15B15, B23Q1, F16C29