ARRANGEMENT FOR DAMPING THE TRANSMISSION OF VIBRATIONS

Abstract: The invention relates to an arrangement for damping the transmission of vibrations between a vibration-producing first object, for example a vibrating machine, working equipment or tool, and a second object, for example a handle which is to be gripped by an operator, a frame, foundation or the like. The arrangement includes a resilient element (4,7, 11) of polymer material. In accordance with the invention the said element is restrained under a certain prestress between the said first (2, 3, 6) and second (1) object. Furthermore the prestressing force is preferably so chosen that the extension caused by the prestressing force is greater than the ampli­ tude of the vibrational oscillations.

Description: ARRANGEMENT FOR DAMPING THE TRANSMISSION OF VIBRATIONS TECHNICAL FIELD The invention relates to an arrangement for damping the transmission of vibrations between a vibration-producing initial object, for example a vibrating machine, working equipment or tool, and a second object, for example a handle which is to be gripped by an operator, a frame, foundation or the like. More particularly the invention relates to an arrangement which includes a resilient element of polymer material, e.g. rubber. BACKGROUND A major problem with machines, working equipment and tools producing vibrations is the damage to which the operator can be exposed and which is caused directly or indirectly by the vibrations. Even when no injury is caused to the person, the vibrations can give rise to major problems, for example they can cause disturbing noise, cause wear in various components, etc. Normally resilient rubber elements are employed within widely-disparate areas of technology so as to damp the transmission of vibrations. For example, rubber elements can be provided for damping the transmission of vibrations between the machine and the handle which is to be actuated by an operator. However, when in accordance with conventional technology the flexible properties of polymer materials, e.g. rubber, are employed within a certain area of movement, damping has the disadvantage that it can be employed only within certain frequency ranges, preferably low frequences, here up to 200 - 300Hz. Because of the fact that machine weights and the hardness of the rubber control the degree of damping, it is thus not possible to accurately combine good damping properties over the entire frequency range up to say 5 000he. One reason for rubber having a very limited damping capacity, in the case of conventionally designed dampers, is that rubber and other resilient polymer materials are only slightly compressible In connection with damping some degree of compression is taken as a basis and thus in the initial position the damper is made to function with a certain loading, i.e. so that the damping element is compressed. When the damper is subjected to vibrations, it thus operates mainly within the compressible range where the counter-forces because of the incompressibility of the material increase logarithmically with the depression. Although rubber and. certain other polymer materials are only neg-. ligibly compressible, they are however extremely extensible. This has been utilised in those dampers where one object is resiliently suspended in the other. Such an element presupposes however that one is working under specific conditions. For example such a construction cannot be employed if the arrangements are to adopt different positions in space. DESCRIPTION OF THE INVENTION One main object of the invention is to eliminate the limitations of the polymer, resilient material, a priori that of rubber, as regards compression and instead to utilise its great extensibility so that excellent possibilities are obtained for damping the transmission of vibrations, i.e. as regards vibrations to insulate a vibrations-producing object within the entire frequency range from about 8 Hz and above. One objective of the invention is preferentially also to provide an arrangement which can function in different positions in space. These and other objectives can be achieved when the resilient polymer element which is. arranged between or designed to be arranged between the said. first and second objects is pre-tensioned by a certain tensile prestress. More particularly, the prestressing force is at least so great that the extension which this causes is greater than the amplitude of the vibration oscillations caused by the said first object. The absolute value of the degree of prestress depends on a number of factors such as the dimensions of the element, the properties of the polymer material and on the loading. Normally however the prestress is so great that the elastic extension is between 15 and 250 Z. This means that the prestressing force must be so great that the resilient element will remain, under all the vibrational stresses normally encountered, loaded in tension, i.e. not subjected to compression, preferably regardless of the direction of the vibrational movement. A further characteristic of the prestressing conditions is that the resilient element is prestressed in tension in all positions which can be adopted by the first and the second object relative to each other within the working range envisaged for the resilient element and under all normally encountered loadings. In other words the tensile prestress of the resilient element is so great that the element is prestressed in tension in all parts of it even when the two objects have been displaced relative to each other so far as is maximal possible or as can maximal occur in normal handling of the two objects. In accordance with one embodiment the element is prestressed in tension even when it is not interconnected with one or both of the objects. This signifies that the prestressed element can have the form of a standard component ready for assembly and suitable in the prestressed state for mounting at the desired location, e.g. in a machine, in a machine handle or the like. Furthermore one aspect of the invention involves the element being subjected to a tensile prestress which is not affected by the mass of the object. The resilient element is appropriately restrained or arranged to be symmetrically restrained between the two objects, but it is also possible to envisage asymmetrical restraint. In the first case the said initial object can be combined with the resilient element in a non- peripheral section, e.g. at its centre, from which the element extends outwards towards peripheral attachment pints, where it is joined with the second object. In this case the resilient element can include a prestressed membrane. It can also have the geometric form of for example spokes in a wheel As mentioned in the preamble the second object can have a number of differing shapes. One typical sphere of application for the invention is however handles on vibrating tools, working machines and the like In this case the second object can be described in such a way that it includes a tube or tubular channel. In accordance with a preferred embodiment of the invention two of the resilient elements are arranged in this tube or tubular channel at some distance from each other or beyond both ends of the tube or tubular channel. This signifies that the first object is connected to the handle via the two resilient elements inside the tube or in the area inside or outside both ends of the handle. Here it is appropriate to provide a limiting organ or buffer inside the tube or channel so as to restrict the movements of the second object, i.e. the handle, in the radial direction towards the first object. The need for such a restriction device or buffer can be particularly pressing if the handle is also to be used to raise a heavy machine or the like. This restricting device or buffer here at the same time provides the extreme limits for the "normal sphere of working" of the resilient element, which are referred to above. It should also be obvious that the application of the invention is not restricted merely to such membrane-shaped elements as illustrated in the example. Even elements which are prestressed in for example only two main directions can thus also be employed in certain applications. Further aims of and characteristics of the invention will be illustrated by the following description of preferred embodiments# and by the following patent claims. BRIEF DESCRIPTION OF DRAWINGS In the following description of preferred embodiments reference will be made to the appended drawings in which: Fig. 1 is a schematic force#xtension diagram of a rubber ele ment Fig. 2 is a diagram which illustrates schematically the tensile stresses in a resilient element in accordance with the invention as compared with a conventional element Fig. 3 is a side view, partially in section, of a handle provided with two resilient elements in accordance with a first embodiment of the invention Fig. 4 gives an axial section through a handle having resilient elements arranged at each end in accordance with a second embodiment of the invention Fig. 5 is a side view of a rivet dolly provided with a pair of res ilient elements in accordance with the invention and Fig. 6 gives an axial section through a prestressed element in accordance with one embodiment of the invention before the element is mounted in its position of use. BEST MODE OF CARRYING OUT THE INVENTION In accordance with the invention, as resilient element use is made of a polymer material, advisably rubber, which is prestressed-. More particularly the prestressing force should be so great that the extension caused by the prestressing is greater than the amplitude of the vibrational oscillations. This means that it is necessary to work in an area of the force-extension curve, Fig. 1, which is slightly up on the steep portion of the curve. The same case is also illustrated in the diagram in Fig. 2 where the lower curve illustrates conventional technique and the upper curve the conditions prevailing in accordance with the invention. The arrangement in Fig. 3 comprises a tubular handle 1 and a pair of rods 2 and 3 which are assumed to form part of a vibrating unit, e.g. a machine. The components 2 and 3 here comprise what has been designated in the preamble as the vibration-producing first object, whilst the handle 1 forms the said second object. The vibration rods 2 and 3 are each joined to their rubber membrane 4 and 5 respectively. In accordance with the embodiment the rods 2 and 3 are joined with the respective membranes 4 and 5 by vulcanising. The membranes 4 and 5 are considerably extended in the radial plane and their bent over edges 6 and 7 are threaded over a ring 8 and 9 respectively so that the portions of the membrane between the rods 2 and 3 and rings 8 and 9 respectively are greatly extended. The edge portions 6 and 7 are joined with the outsides of rings 8 and 9 by locking using an outer clamping ring which is not shown. To further improve adhesion the rings are provided with a groove 10 and 11 respectively. The resilient elements 13 and 14 respectively thus described are assembled in both ends of the tubular handle 1. For this purpose the rings 8 and 9 are provided with a snap flange 15 and 16 respectively which engages in corresponding grooves on the inside of the tube 1. The two rods 2 and 3 are also joined to each other by a tube 17 inside the handle tube 1. The rods 2 and 3 which are threaded at both ends are screwed into the tube 17 which for this purpose is provided with internal threads. By screwing the rods 2 and 3 in this manner into the tube 17 the membranes 4 and 5 are stretched further, and simultaneously as a result of this extension they adopt the shape of cones facing the interior of the handle. The total extension, i.e. the total initial (radial) elongation of membranes 4 and 5 and the elongation obtained by screwing the rods 2 and 3 into the tube 17 is by this means so great that it exceeds the amplitude of the vibrations, regardless of the direction of oscillation. Thus using the arrangement shown in Fig. 3 extremely good vibration damping properties are achieved both in the radial and axial planes. The thickness of the membranes 4 and 5 in the space between rods 2 and 3 and the rings 8 and 9 is between 5 and 1 mm in accordance with the embodiment. The handle 1 illustrated in Fig. 3 is also to be capable of use for lifting relatively heavy machines, tools and the like To prevent the membranes 4 and 5 being overloaded during this or jamming, a restricting device or buffer 18 made of rubber is provided around the internal tube 17 so that the movements of the handle 1 in the radial direction are restricted. Fig. 4 shows a handle 1' which is a variation of the handle 1 shown in wig. 3. The two resilient elements 13' and 14' areFansalogously designed and have compcnents which corresj#c'nd to thqse in the embodiment shown in Fig. 3, so that the same notation has been##mployed for corresponding components with the supplement '. Hence for a description of the various components reference should be made to the above mentioned description of Fig. 3. The only fundamental difference in this case is that the two rods 2' and 3' have been screwed away from each other so that the membranes 4' and 5' instead extend outwards from the interior of the handle. Fig. 5 also illustrates an application of the same principle as in Fig. 4. The handle 1t' in this case comprises a handle to a rivet dolly which is provided with a flange 20 as thumb grip. The two prestressed membranes have been designated 4 " and 5 " . Of the left hand rod only the end 2 " can be seen. The other rod is screwed into the revet dolly 3 " . The arrangement shown in Fig. 5 has proved to have extremely good properties as a rivet dolly, which means that the resilient elements also have a very good capacity for damping vibrations in the axial direction. Examples of the spheres of application for a rivet dolly as shown in Fig. 5 are to be found in the aircraft industry where it is often necessary to work within very confined spaces. Fig. 6 illustrates a prestressed damping element 13a before this is mounted in its use position. The element consists of a threaded rod 2a on which the resilient element 13a is vulcanised by means of its wide central portion 21 in the same way as in the embodiments described previously. From this wide portion 21 a relatively thin membrane 4a extends outwards towards the edge portion 6a which has been turned over a ring iota. To ensure fixing of the edge portion 6a over the ring 10a there is an outer ring 22 which was also mentioned in conjunction with Fig. 3, so that the rubber edge portion 6a is clamped firmly between the inner ring 10a and the outer ring 22. The latter can also act as flange for snap-action in the same way as the components 15, 15' in the preceding embodiments. Hence the arrangement illustrated in Fig. 6 can comprise a ready-made element which can be employed for a number of different applications. The element should preferably be made in different sizes and with varying appearance so that it can fit in the majority of cases without needing to be modified. To increase the prestressing naturally this element can < .so be stretched further by axially extending it in the same way as shown in connection with Fig. 3, 4 and 5.

Claims: PATENT CLAIMS 1. Arrangement for damping the transmission of vibrations between a vibration-producing first object (2,3) e.g. a vibrating machine, working equipment or tool, and a second object (1) for example a handle which is to be gripped by an operator, a frame, foundation or the like, comprising a resilient element (4,7,11) of polymer material arranged between or designed to be arranged between the said first (2,3) and second (1) objects, c h a r a c t e r is e d in that the said element is prestressed by a certain tensile prestress. 2. Arrangement as in claim 1 c h a r a c t e r i s e d in that the prestressing force is at least so great that the extension which this causes is greater than the amplitude of the vibrational oscillations caused by the said first object. 3. Arrangement as in claim 1 or 2 c h a r a c t e r i s e d in that the resilient element is prestressed in tension in all positions which the first and second object can adopt relative to each other within a sphere of operation envisaged for the resilient element and under all normally prevailing loads. 4. Arrangement as in claims 1-3, c h a r a c t e r i s e d in that the resilient element is symmetrically restrained or arranged to be symmetrically restrained between the two objects. 5. Arrangement as in claims 1-3, c h a r a c t e r i s e d in that the resilient element is asymmetrically restrained or arranged to be asymmetrically restrained between the two objects. 6. Arrangement as in claim 4, c h a r a c t e r i s e d in that the said first object is joined with the said element in a non-peripheral portion from which the element extends outwards towards peripheral attachment points where it is joined with the said second object. 7. Arrangement in accordance with any of claims 1-6, c h a r a c t e r i s e d in that the resilient element includes a resilient, prestressed membrane (4, 7). 8. Arrangement in accordance with any of claims 1-7, c h a r a c t e r i s e-d in that the resilient element includes prestressed devices which have the geometric shape of spokes in a wheel. 9. Arrangement as in any of claims t-8, c h a r a c t e r i s e d in that the second object includes a tube or a tubular channel, that two of the said resilient elements are arranged in the said tube or tubular channel at a distance from each other or beyond both ends of the tube or the channel. 10. Arrangement as in claim 9, c h a r a c t e r i s e d in that the restricting device or buffer (18) is arranged inside the tube or channel which restricts the movements of the second object in the radial direction towards the said first object.

Inventors: HAGGMAN, HARDY, Häggman, Hardy
Applicants: SUNNEX AB
Application year: 1982
Main classification: F16F15
IPC codes: F16F1