ROD FOR EXECUTING POSITIONING MEANS

Abstract: A rod for executing positioning means for a rectilinear reciprocating movement, especially a piston rod or similar, whereby the rod is composed of two in each other located parts (11, 12), an outer tubular shaped part (11) and a preferably likewise tubular shaped inner part (12). The outer tubular shaped part (11) of the rod is manufactured of a material or is provided with a coating whith high surface smoothness and the inner part (12) of a material with high tensile properties. The two parts (11, 12) are at the end parts fixedly connected with each other and/or via each of their connecting elements (26). The two parts (11, 12) are arranged to form a cooperating, integrated unit with each other and/or with at least one connecting element.

Description: ROD FOR EXECUTING POSITIONING MEANS The present invention concerns a rod for executing positioning means for a rectilinear reciprocating movement, especially a piston rod or similar, whereby the rod is composed of two in each other located parts, an outer tubular shaped part and a preferably likewise tubular shaped inner part. THE BACKGROUND OF THE INVENTION AND THE PROBLEM Piston rods have hitherto been manufactured homogeneously of a material, such as a high-tensile steel, and have been dimensioned with regards to the breaking risk, especially if it concerns very long piston rods.With regards to that the lead-through for the piston rod must fulfill high sealing demands, the surface of the piston rod must have very fine surface smoothness. A damage, for instance a score on the surface of the piston rod can lead to that the cylinder leaks along the piston rod. If it cannot be mended , then one must normally exchange the whole unit of piston and cylinder. In many cases one want nowdays to be able to control the exact position of the piston relatively the cylinder, which occurs with the aid of outer sensors for the piston position, which sensors can be exposed for severe impurities, agressive environments, but also mechanical wear or actuation. From US 4 717 874 and 4 804 913 are known sensors for the piston position, where in the piston rod magnetic sections alternating with non-magnetic sections or air gaps have been arranged and where a detector in the form of a number of coils detects the magnetic fields, which pass the detector during detection. The non-magnetic parts can consist of on the surface of the piston rod arranged screw line shaped or annular shaped elevations or recesses. US 5 367 944 proposes a sensor for measuring the amount of electrostatically charged colour in a container and where a piston rod is movable in the container for discharge of the colour. The sensor can be a magnet, which moves together with the piston rod and creates a magnetic field. A ferromagnetic device moves along the sensor in dependence of the movements of the magnetic fields, which are generated by the movable magnets. It is also known from EP-A-591 614 a unit of piston and cylinder with one outside the piston rod arranged scale which can be read optically or electrically outside the cylinder. Disregarding from the fact that these known devices are expensive as well as complicated they demand a continous maintenance and have a very limited area of use. THE PURPOSE WITH THE INVENTION AND THE SOLUTION OF THE PROBLEM The purpose with the invention is to achieve a rod for instance a piston rod, which - fulfills high demands on strength, - has a replaceable surface with very high surface finish, - is worth its price, - has a simple, exact and reliable sensor for the position of the piston along the whole rod, which is protected against occurring chemical attacks or physical actuations, - can be used in practically all occurring areas of use. These tasks have been solved by the features stated in the patent claims. DESCRIPTION OF THE DRAWING The invention will in the following be more closely described in connection with a few embodiments and with reference to the enclosed drawings. Figure 1 shows a longitudinal section through one end part of a combined piston rod and piston in accordance with the invention. Figure 2 shows a cross-section along the lines II-II in figure 1. Figure 3 shows in perspective the separate parts of a modified piston rod in accordance with the invention. Figure 4 shows a cross-section through the combined piston rod in accordance with figure 3. Figure 5 shows one with figure 1 analogous section through the end part of a piston rod with attachment for the piston rod. Figure 6 shows a longitudinal section through a variant of the piston rod in accordance with the invention. Figure 7 shows a cross-section through the piston rod in accordance with figure 6. DESCRIPTION OF EMBODIMENTS The rod shown on the drawing is in first hand intended to be used as a piston rod, but can of course be used in many other similar connections , where a rectilinear movement shall be performed and where one wishes to keep track where the rod -piston- is located in relation to the cylinder. The piston rod in accordance with figure 1 comprises two parts, one outer tubular-shaped part 11, in the following called the cage, which with a little gap can be brought over an inner likewise tubular-shaped part 12, in the following called the tube. It consists of a material, which has been chosen for its very good strenght properties with regards to its application and which does not need to fulfill specific demands with regards to its surface finish, hardness or resistance against aggresive environments. It can thus be a tube of a high-tensile steel, for instance FC70CV, or another suitable material. The cage 11 can consist of a relatively thin tube of acidproof stainless steel, hard-chromed aluminium or a material which is specially adapted for the actual area of use. The cage 11 can be connected with the inner tube 12 in many different ways and the in figure 1 shown construction principle is only an example. The inner tube 12 is at some distance from one of its end provided with a peripheral groove 13 and ahead of it with threads 14 for one on the tube screwable piston 15. In the groove 13 the front end 16 of the cage 11 is pressed down , encasing a sealing ring 17 within the groove, so that a tight connection also at very high pressures is achieved. The piston 15 is provided with an inner step 18, which takes up the tube end 16, which is pressed down in the groove and which thus is protected by the piston 15. In a space between the outer tube 11 and the inner tube 12 or within one of these is provided a groove or a recess 20, in which is placed a measuring device 21, which in the embodiment shown in figure 1 and 4 is a magnetic strip, i.e. a plastic strip or a folie, which is covered with a ferrite layer, which in its turn is carrier of data, which can be in the form of a scale or similar, which is readable with a reading head (not shown) located outside the piston rod. In order to increase the strength of the rod, the tube 12 can be a tube of steel with longitudinal radial folds 22, which can be surrounded by one on the inside in a similar way formed outer tube 11 , which suitably is an extruded tube of aluminium. In the spaces between the radial folds 22 longitudinal recesses 20 are arranged in the AL-tube, which recesses can be used for placing said measuring device 21 and which recesses can be provided with inner threads for connection of a piston 15 in one end of the rod and an attachment 23 for the piston rod in the other end. The recess 20 for the measuring device can also be a longitudinal open groove, in which is placed a transparent bar of for instance toughened glass, which on the surface turned inwards is provided with a layer or a coating of a magnetic character, which layer or coating can be programmed for instance for controlling the movement of the piston, its velocity, positioning, but also to operate different units, for instance opening or closing of valves etc. The bar is preferably glued in the the groove. The manufacturing of the rod in accordance with the invention is preferably made by pushing the folded inner tube 12 into the with inner folds formed outer tube 11 of aluminium in connection with the extrusion of the outer tube so that a very good surface contact -fit-up- between the outer and inner tube is achieved. It is important that any hydraulic oil cannot enter the interspace between the outer and the inner tub. If any form of sealing between these is required, a sealing ring 17 can be applied as is shown in figure 1, but it is also possible that the parts are glued together for forming a tight connection. In certain cases, when it concerns very long rods and/or big axial loads it could be suitable to reinforce the piston rod axially. For this purpose longitudinal holes 24 for steel rods 25 or similar can be arranged in the outer rod 11, which steel rods can be fastened in a suitable way in the piston 15 and the attachment 23 for the piston. The embodiment in accordance with figures 6 and 7 differs from the above described by that connection elements 26 at the ends of the outer and inner tubes 11,12 are used to interconnect the tubes 11,12 with each other. The connection elements 26 are for this purpose tubular formed with an inner cavity 27, which essentially have the same form as the outer form of the inner tubes 12 so that these with forced fit can be applied into each other. The both ends of the inner tube are staked up or corbelled out for fit-up against a bevel 28. The inner cavity of the connecting element is furthermore at its inner end part provided with a peripher inner collar 29, which is arranged for taking up the both end parts of the outer tube 11. In this way is achieved an inexpensive and very strong construction, which can have an arbitrary length. The connecting elements can be a piston 15 and an attachment 23 for the piston rod. The invention is not limited to the above described embodiments, but a lot of variations are possible within the scope of the claims. The invention is especially suitable for very long piston rods, for instance up to length of 15 m, but can also be used on all types of piston rods. LIST OF REFERENCE NUMBERS 11 outer tube 12 inner tube 13 groove 14 threads 15 piston 16 tube end 17 sealing ring 18 inner step 19 gap 20 recess/groove 21 measuring device 22 radial folds 23 piston rod attachment 24 hole 5 steel rods 6 connecting element 7 inner cavity 8 bevel 9 collar

Claims: PATENT CLAIMS 1. A rod for executing positioning means for a rectilinear reciprocating movement, especially a piston rod or similar, whereby the rod is composed of two in each other located parts (11,12), an outer tubular shaped part and a preferably likewise tubular shaped inner part (12), characterized in that the outer tubular shaped part (11) is manufactured of a material or is provided with a coating with high surface smoothness and the inner part (12) of a material with high tensile properties, that the two parts (11,12) at the end parts are fixedly connected with each other and/or via each of their connecting element (26), and that the two parts (11,12) are arranged to form a cooperating, integrated unit with each other and/or with at least one connecting element. 2. A rod according to claim 1, characteized in that the connecting elements (26) are composed of the piston (15) of the positioning means and/or the attachment (23) for the piston rod. 3. A rod according to claim 1, characterized in that one or both end parts of the inner part (12) has a peripheral groove ( 13), in which the tube end (16) of the outer part (11) is pressed down, for forming a fixed connection between the parts. 4. A rod according to claim 1, characterized in that the outer part (11) is arranged concentrically in relation to the inner part (12), which with its outer side is arranged to fit-up against the inside of the outer part, and that one of the two parts is arranged to axially fix the other part via said connecting elements (26). 5. A rod according to claim 4, characterized in that the end parts of the inner part (12) with forced fit are led into each in respective connecting element (26) arranged inner cavity (27) with essentially the same cross-section form as the cross-section form of the inner part (12), that the end parts of the outer part (11) with forced fit are led into one in the connecting elements (26) arranged, with said recess coaxial collar with essentially the same cross-section form as the cross-section form of the outer part (11), that both ends of the inner part (12) are arranged to extend essentially through respective connection element and are fixedly connected with these, preferably through staking up or corbelling out of said ends. 6. A rod according to claim 1, characterized in that the inner part (12) is a tube, formed with longitudinal essentially radial folds (22) and that the outer tube (11) on the inside is provided with one with the form of the inner part complementary form. 7. A rod according to claim 6, characterized in that the outer tube is manufactured through extruding, for instance of aluminium, that the outer tube in connection with the extruding is arranged on the inner part and that the inner part (12) is formed in a roll forming machine of a cylindrical tube. 8. A rod according to claim 1, characterized in that in the longitudinal direction of the rod is arranged at least one oblong space (19 or 20) for placing of a programmed or programmable measuring device (21), for instance a magnetic strip (21), for detecting the relative position and/or contolling of the rod and/or outer units. 9. A rod according to claim 1, characterized in that the space (20) for the measuring device (21) is the gap between the outer tube (11) and the inner core (12) or is a recess (20,24) for instance an axial channel or an open longitudinal groove. 10. A rod according to claim 9, characterized in that in the open, longitudinal groove (24) is fixedly arranged a transparent bar, which on one side is provided with a layer or coating of a magnetic character.

Inventors: PETTERSSON THOMAS, PETTERSSON, THOMAS
Applicants: MULTIDOCK HYDRAULIC AB, PETTERSSON THOMAS, AB MULTIDOCK HYDRAULIC, PETTERSSON, THOMAS
Application year: 1998
Main classification: F15B15
IPC codes: F15B15