Patent Application
20120055688
The invention concerns an air-powered hand-held demolition tool of the type known as “hand scabbler” (or “scaling hammer”). The tool is used for small-scale demolition work of concrete, brick, ceramic tiles, floor tiles and other similar hard materials. The tool can be used also to remove rust, welding slag, paint and other types of surface deposits on steel.
The cylinder 2 comprises three pistons 7, which are arranged in a vertically directed bore in the cylinder 2. The tool is often named a “three-head hand scabbler” for this reason. Also hand-held demolition tools with one, two or more pistons 7 are available. The pistons 7 have at the bottom tool bits that can be exchanged and they have internal valve arrangements that produce upwards and downwards movement of the pistons in the bore of the cylinder 2 when the operator supplies the cylinder 2 with pressurised air. It may be the case that the pistons 7 are provided with fixed tool bits.
The rear handle 6 extends longitudinally along the extension of the tube 3 and it is connected to a valve housing 8, which has at its rear an arrangement for the connection of a pressurised air line. The valve housing 8 comprises at its bottom a valve release, with which the operator regulates the supply of pressurised air. The pressurised air supplied is led through the internal channels of the rear handle 6 and the valve housing 8 forwards and onwards in the tube 3, which is connected to the forward part of the valve housing 8. The second end of the tube 3 is connected to the cylinder 2 through the flexible coupling 4.
During operation, the operator presses the hammer-action tool bits of the tool against the surface by applying a light vertical pressure onto the forward handle 5. The hammer-action tool bits impact the surface layer of the surface in the manner intended, while at the same time causes undesired vibratory movements of a complex nature of the cylinder 2. The vibratory movements principally contain alternating vertical movement and alternating torsion movement. The latter movements are produced as a consequence of the upwards and downwards movements of the three pistons not being synchronised, and as a consequence of the tool bits receiving reaction forces that are asymmetrically directed when impacting the surface.
The forward handle 5 is arranged with a direction of longitudinal extension that is oblique relative to a vertical plane, coinciding with the direction of longitudinal extension of the rear handle 6. The forward handle 5 is arranged with a direction of longitudinal extension that is perpendicular to the vertical plane and that is located at a carefully chosen distance from the rear handle 6. The locations and orientations of the handles 5, 6 create an overall solution for grip ergonomics that is ideal for this type of machine, and that is used also for other types of machine such as, for example, hammer drills, motor saws, etc.
The forward handle 5 has a vibration-damped connection with the cylinder 2 in order to absorb the vibratory movements and in this way protect the hand of the operator from vibration-induced damage. The forward handle 5 is arranged at the bottom of a U-shaped handle yoke. The two legs of the U-shaped handle yoke are attached at their ends in a manner that allows them to pivot to opposite sides of the upper part of the cylinder 2.
The pivot action of the connection is damped and arranged to have a limit, through the legs being connected to elastic torsion elements between the two connections. Thus, the pivot action is arranged around a theoretical axis with an orientation that is perpendicular to the direction of longitudinal extension of the rear handle 6. The U-shaped handle yoke is arranged such that its legs form an angle with the direction of movement of the pistons 7, and the conditions required for the elastic torsion elements to absorb not only vertical but also horizontal vibratory movement of a moderate amplitude are in this way created.
The vibratory movements that are produced during the operation of the tool 1, however, cannot be regarded as moderate, having as they do amplitudes that result in the majority of them passing the damping to an unacceptable degree and leading to risks for the health of the operator. Furthermore, the arrangement has no possibilities at all of absorbing torsional movements, and these are transferred in essentially undamped magnitude to the forward handle 5.
The rear handle 6 is insulated from the vibratory movements through the flexible coupling 4 comprising a short piece of rubber tube. The rubber tube absorbs the vibratory movements by allowing small oblique displacements and torsional movements between the cylinder 2 and the tube 3. The torsional movements are, however, transferred in essentially undamped magnitude to the rear handle 6, since the short tube offers a rigidly damping response to this movement.
A major disadvantage, furthermore, is that the rubber tube permits also large oblique displacements between the cylinder 2 and the tube 3 when the operator applies working pressure to the forward handle 5. This undesired property of the flexible coupling 4 causes problems in particular when the rubber tube has become soft or has become worn, after a certain period of use of the tool 1. One extreme consequence of the undesired property is that the oblique displacement becomes so large that the tube bends in such a manner as to prevent the supply of air to the cylinder 2, whereby the operation is halted. It is obvious that the operator will experience such a tool as unstable and difficult to operate.
The purpose of the present invention is, as specified in the patent claims, to provide a hand-held demolition tool in which the above-mentioned disadvantages are avoided. The flexible coupling has such a design that the operator experiences the tool as stable and easy to operate. The flexible coupling of the tool is also arranged such that it filters out the majority of the vibratory movements that are produced in the cylinder.
According to one embodiment, the forward handle of the tool is damped to vibration according to known principles, but connected to the tool in such a manner that it is not exposed to the vibratory movements that are filtered out by the flexible coupling. The vibration damping has, in this way, the conditions required for, and reduces in practice the level of, vibration in the forward handle to acceptable levels.
The invention will be described in more detail with the aid of the attached drawings,
The hand-held demolition tool 1 in
The optimal arrangement is, as shown in
The cylinder 2, as has been previously described, is caused to undertake undesired vibratory movements during operation of the tool 1. That part of the vibratory movements that consists of alternating torsional movements is efficiently absorbed by the arrangement, since these movements result only in the cylinder 2 performing small pivoting movements forwards and backwards around the theoretical axis 9 relative to the forward handle 5. It is preferable that the torsional movements around the axis 9 take place nearly free of friction and without any elastic influence. The latter condition is to prevent the occurrence of problems with self-oscillation. The flexible coupling 4 is designed such that it satisfies these requirements and will be described in detail in association with
a-3b show a variant of the embodiment shown in
Those parts of the vibrations that contain alternating vertical vibratory movements pass through the flexible coupling 4 undamped. The vertical movements place the complete tool 1 into an oscillatory movement around a point that is located approximately in the centre of the longitudinal extension of the rear handle 6. The amplitude of the alternating vertical movements decreases as one approaches this point.
Since the longitudinal extension of the rear handle 6 is located in the immediate vicinity of this point, the handle and the hand of the operator are subject to extremely small vertical vibratory movements. The rear handle 6 is externally clad with a soft material that is easy to grip and that damps the remaining vibrations to an acceptable level. The forward handle 5 has a connection that is damped for vibration and that is connected to the tube 3 at a position that is located on the half of the longitudinal extension of the tube 3 that is located more closely to the rear handle 6.
The absence of torsional movement and the low amplitude of the vertical vibratory movements at this ideal position provide the conditions required by the vibration-damping connection at the forward handle 5 and they reduce in reality the amplitude of vibration in the handle 5 to a low and acceptable level. It is also possible to connect the forward handle 5 with the tube 3 at a position that is located on the second half of the longitudinal extension of the tube 3. A higher amplitude of vibration of the handle 5 is obtained in this case, but the level of vibration is still acceptable.
The forward handle 5 is arranged between the two upper legs of a Y-shaped handle yoke of aluminium. The handle 5 comprises a tubular rigid sheath that is externally clad with a soft material that is easy to grip. The lower leg of the Y-shaped handle yoke is designed as a clamp with an internal recess for a vibration-damping bushing. The bushing is externally clamped in the recess and internally connected to the tube 3 through a U-shaped fixture and a screw connection. The bottom of the U-shaped fixture has internally the same diameter as the tube 3 and it is joined by welding to the tube 3 at the ideal position described above. The lower leg of the Y-shaped handle yoke comprises also a stop lug, arranged to contact the tube 3 when the operator applies too large a vertical working pressure at the forward handle 5.
Thus the vibration-damping bushing is protected from overload. The bushing is marketed by manufacturers of construction components and it has the same function and orientation as the elastic torsion elements that have been described in association with
b and 3b show how the flexibility of the flexible coupling 4 is arranged to allow a range of pivot between the cylinder 2 and the tube 3, around a rigid theoretical axis 9. The pivoting range of the cylinder 2 (shown with dashed lines) relative to the tube 3 is arranged to be limited to approximately ±10° from an initial position of the cylinder 2. (These are shown with a curved arrow and with fully drawn lines, respectively, in the drawings.) The limitation of the range of pivot of the cylinder 2 ensures that the tool bits of the pistons 7 are always correctly oriented relative to the surface that is to be demolished using the hand-held demolition tool 1. The design of the limitation to the range of pivot will be shown in
b shows also how the forward handle 5 is arranged with a direction of longitudinal extension that is oblique relative to a vertical plane, coinciding with the direction of longitudinal extension of the rear handle 6. The forward handle 5 is arranged with a direction of longitudinal extension that is perpendicular to the vertical plane. The forward handle 5 is, as has been described previously, arranged between the two upper legs of the Y-shaped handle yoke. The yoke has the ability to pivot in a vibration-damped manner around a theoretical axis that is oriented perpendicular to the above-mentioned vertical plane (shown with a dot-dash line in the drawing).
The flexible coupling 4 in
The axle spindle 10 has an internal thread at one of its ends for the connection to, for example, the tube 3. The swivel 11 is arranged with play between it and the axle spindle 10. The swivel 11 is integrally arranged in the cylinder 2, although it is possible also to design it as an individual component with a threaded connection to the cylinder 2. It is possible also, in a similar manner, to instead integrate an axle spindle into the cylinder and arrange a swivel with connection for a tube.
The flexible coupling 4 comprises also a race 12A with associated steel balls 12B. The race 12A is arranged in an outer circumference of the axle spindle 10 and inside the surrounding swivel 11. The race 12A and the balls 12B make it possible to achieve the ability to pivot that is approximately free of friction between the axle spindle 10 and the swivel 11, and it has in principle the same function as the corresponding components in a ball bearing. The balls 12B pass through a channel to the race 12A when the swivel 11 is mounted on the axle spindle 10 and provide in this manner an axial lock between the components. The balls 12B are retained in the race 12A by a cylindrical pin that is arranged to block the channel. It is possible also to arrange the coupling without a race and steel balls, arranging in this case a plain bearing. The locking can then be arranged with a Seeger ring or other component with a similar function.
The flexible coupling 4 comprises also a locking pin 13 and a locking groove 14. The locking pin 13 is driven into a suitable hole in the swivel 11 and passes, with a small play, in and along the locking groove 14, which is arranged in the axle spindle 10. The locking groove 14 has a U-shaped cross-section and extends in length along an arc of a circle around the axis 9. The length of the locking groove is adapted such that it makes possible and limits the range of pivot between the cylinder 2 and, for example, the tube 3, as has been previously described. The limited range of pivot is obtained when the locking pin 13 makes contact with the walls at the ends of the locking groove 14.
It would be possible also to arrange the flexible coupling 4 at another location between the cylinder 2 and the rear handle 6, for example, between the tube 3 and the valve housing 8, or between the valve housing 8 and the rear handle 6. The latter location is the least advantageous, since it does not damp in the same manner the vibrations to the forward handle 5.
The U-shaped fixture for the forward handle 5 is an integral part of the valve housing 8 on the hand-held demolition tool 1 shown in
The tube and its function have been integrated with the valve housing 8 in the fourth embodiment, shown in
The components that are parts of the hand-held demolition tool 1 can be manufactured from material that is used in prior art tools. The cylinder 2, the tube 3 and the flexible coupling 4, therefore, are manufactured from steel. The bearing surfaces of the flexible coupling 4 are case hardened. The valve housing 8 is manufactured from cast steel. It is fully possible to use other materials with similar properties, and other methods of optimising the bearing surfaces.
The invention is, naturally, not limited to the example described above: it can be modified within the scope of the attached patent claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0900868-1 | Jun 2009 | SE | national |
| 0900869-9 | Jun 2009 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2010/050601 | 6/1/2010 | WO | 00 | 10/17/2011 |
